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Technical consultancy in Spinning NonwovensEnd breakage rateTesting of man made fibres and filamentsArticleYarn diameter specific volume and packing densityarticles on Nonwovens
Rando Opener
Rando Machine corporation was the first to introduce this system. This is found in many nonwoven plants. The fibres opened through a Blow room line are fed to a saw tooth Opening roller. Fibres picked almost in a single fibre status by the teeth of opening roller are taken round and deposited on a slow moving perforated lattice by means of an air stream blown above to form a batt (Fig 15 ).A powerful fan blows air through a narrow duct at the exit end of opening roller. A suction fan creates suction under the perforations of the conveyer lattice. Net result is randomisation of fibres deposited on lattice.
         Rando Opener
          Fig : 15 Rando Opener
Fibre orientation is nearly random in the horizontal and vertical plane and is fully isotropic. This greatly improves the insulation value and loftiness of the batt. This enhances the quality of such material for wadding, high lofts used in winter clothing and sound insulation material.
Random Card
Fehrer was the first to introduce this system. The random card used in this works on aerodynamic principles. The card consists of a series of small carding cylinders each fitted with a pair of worker and stripper rollers. Part of the fibres from the first card is delivered into a duct while the remaining part is taken forward to the next card. The delivered fibres from each card is transported via individual ducts to a common collecting perforated surface and is transported forward by a conveyor belt.(Fig :16)
         Random card
        Fig : 16 Random Card
As individual fibre layers from each of the ducts is laid one over the other on the conveyor, considerable doubling and randomisation is achieved. This contributes to uniformity of batt. The working width is 1 � 2.5 m. In the next generation batt forming line of Fehrer (Fig : 17), a pre web forming machine V21/R reduces the size of the tufts from the hopper feeder by means of an opening roller to form batt of 300-500 gsm. This is fed to a Random card K12 consisting of a cylinder and a pair of workers and strippers. The delivered fibres from the card is transported to a perforated conveyor supported by lamina air flow produced by a transversal blower. Suction at the high loft device at the delivery end increases the batt height and volume. This system is suitable for producing 'High Loft' material used in insulation. K12 card without "high loft" device is also offered. Production rates up to 50- 100 m/min are obtained with MD/CD ratio of 0.9 � 1.5 : 1 in the model K21 card.

      Fig : 17 Random Card K12
Spinnbau offers a Turbo-unit TU for aerodynamic web formation in a weight range 30 - 450 g/m and web speed of 60 m/min with applications in the medical, hygiene and cosmetic applications. They also offer Fiberlofter for the medium and higher gsm products.. In airlaying systems by Oerlikon Neumag and others, fibres and low melt powder material can be transported together to form blended batt or a multi layer product. Fluff pulp, bicomponent low melt fibre or superabsorbent fibre can be mixed with regular fibre to form batts which can be bonded to make products like table top and wipe material, hygienic products, health care, female incontinence. Schirp uses perforated drum linked to a special air system to form batt from the web fed by feed roller. The drum is fitted with steel pins or saw tooth wire. The system claims to make batts of 100 to 200 gsm with a maximum production rate of 14 m/min.Laroche has developed an airlay line for making batts from all types of fibres with weight range 200 � 5000 gsm and thickness up to 250 mm and width up to 4000 mm. They have also a compact resinfelt line for making resinated flts used as under lays of automobile carpets and for acoustic insultation.
Process Control
1. Wire points of the Opening roller and card wires of Random card should be checked for damages once in 3 months 2. Weight per unit area should be checked at 25 different places and CV % worked out every week and at the time of lot change. 3. MD/CD ratio should be checked once a week.
Crosslapping
Cross lappers are of two types The laying speeds are higher with the former and most of the modern cross lappers are therefore of horizontal type.
In crosslapping card web is laid by a laying/feed lattice on a delivery lattice which runs at 900 of it. Speed of laying lattice is many times that of Feed lattice and as a result, a number of layers of card web are laid one over the other in a zig zag manner as shown in Fig 18 .
Crosslapper
          Fig 18 Horizontal Crosslapper
Thus a batt of much higher thickness and weight is made from card web. The number of doublings depends upon the relative speed of laying and delivery lattice, web width and laying width. Let
 Laying lattice speed = F m/min
 Delivery lattice speed = D m/min
 Laying width = L m
 Web width = W m  Time taken to lay one layer = L/F
 Distance moved by delivery lattice during laying of one layer = (L/F)�D
 Number of doublings =W/[( L/F) � D].
Production rate of crosslapper therefore depends upon the number of doublings. Since the direction of web is changed by 900, the preferential orientation of fibres in the final batt is in cross direction. As a result, a higher strength is found in cross direction than in longitudinal direction. Laying speed depends upon the type of fibre, fineness and length, crimp, sticking tendency, web weight, spinfinish and humidity and temperature of department. With short and waste fibres lower laying speeds are used. Laying speed with modern cross lappers range between 150 - 270 m/min with card web input speed ranging from 120 to 200 m/min. Control systems are usually incorporated to control the card web as it enters the top carriage. This minimises web control problems encountered when top carriage approaches card and this facilitates higher laying speeds. A major problem in crosslapping is the disturbance caused by removal of air entrapped in the fibres of card leading to unevenness. To overcome this problem NSC has developed a system to remove entrapped air. In addition controls are used to prevent web accumulation at the reversal point. Dilo crosslapper prevents disturbance by air turbulence by guiding the web between two conveyor belts. Laying width in crosslappers can be varied from 1m to 10 m with step wise adjustment of 25 � 50 cm. For paper maker felts laying width go beyond 10 m.
Profiling systems
Profile technology is one of the major developments in cross lapper. Profile technology reduces the weight variations in the cross direction of finished fabric arising out of variable amount of distortions across the width during needling or web drafting. This results from differential shrinkage of material across the width during web bonding. Extent of shrinkage is more at the edges and progressively reduces towards the middle. Without profile technology, weight (gsm) will therefore be higher at the edges than at the centre, as shown in Fig, 19 because of differential shrinkage that takes place at the centre and edges of batt as it passes through bonding like needle loom or through web drafter.
         Profiling
            Fig : 19 GSM variation across the width with and without profiling
Profile systems have been developed by most manufacturers like NSC Nonwovens9 and Dilo10. With profile technology, drafting of web takes place exactly at those places which are laid as selvedge in crosslapping. The increase in thickness at selvedges which takes place in needle punching or other bonding systems compensates for the preformed thin selvedge. CV of GSM across the width is reduced as a result from 3-4% to around 1-1.5%. Scanning gauge based on Xray technology is used to scan thickness and the measurements are used to control laying speed to achieve uniform thickness in a closed loop system. A nonwoven manufacturer has to ensure a minimum target weight in his product. With a lower CV in gsm, target weight can be significantly reduced leading to savings in raw material costs. Apart from variation in gsm, MD/CD strength ratio also varies across the width because orientation of fibres takes place to a greater extent at the edges than at the centre. NSC nonwoven has developed ISO Prodyn profile which not only reduces gsm variations but also MD/CD strength ratio variations across the width of the fabric9. Weight is automatically adjusted by speed variations in card and croslapper as per the weight distribution in the final fabric. The extent of improvement in width wise variation of MD/CD strength ratio with such a profiling system is shown in Fig .20
       MD/CD with profiling
      Fig 20 : Variation of MD/CD ratio across the width with and without profiling
Web Drafting
Web drafting is used for reorienting the fibres from cross to machine direction thereby reducing the CD/MD strength ratio of the product and improve isotropy. Further as drafting reduces the weight, card web can be made heavier leading to a higher production. Common types of web drafters used are shown in Fig : 21.
Webdrafting
        Fig 21 : Web Drafter
Web drafter is used after preneedling. Sometimes it is used between crosslapping and needling. The drafting rollers are clothed with wire to reduce slippage. Draft in each zone is kept low around 1.2 to 1.3 to minimise uneven stretch and fibre breakages.
Spunbonding
In Spunbonding, Nonwoven batt is formed by extruding, drawing and laying the filaments on a moving perforated screen. The process is similar to synthetic filament spinning. The molten polymer is passed through a spinneret and the emerging filaments are drawn and laid on a moving conveyor. Raw materials are synthetic fibres like polypropylene, polyester, nylon, polyethylene and polyurethane. Polypropylene is most widely used because of higher coverage obtained, arising from low density. Further the fibre is available in dope dyed form in a wide range of colours and shades and in recycled form, apart from virgin fibre. The drawback of the fibre is its low UV stability, low creep resistance and lower melting point.
  • Polyester is the next widely used fibre. Higher strength, better abrasion and resistance to UV are its main merits. Low resistance to alkalis is its drawback.
  • Nylon 6 and 66 are also used for some applications. Energy costs are however higher with this material. It has a higher moisture regain than polyester and polypropylene which is an advantage in some applications.
  • Polyethylene has lower strength and low melting point and so cannot be used in applications involving higher temperature. Lower cost is its advantage
  • Polyurethane has merits in apparels and other products requiring higher stretch and recovery
  • Bicomponent fibres either of core/sheath or side by side can be used with advantage. By keeping low melt polymer on the surface and high melt fibre on the core thermal bonding can be achieved without adding a low melt fibre. Bycomponent fibre made of polylactic acid (PLA) fibre in the core and polypropylene on the surface enables eco-friendly fabrics to be made in hygiene sector. Two extruders are used to melt the different polymers and are combined at the spin pack to form bicomponent fibre.
    Batt manufacture
    The polymer chips laid in hopper are melted inside an extruder. The molten material is filtered and is pumped by a spinning pump through a spinneret to form a bunch of filaments. As the fabric is wide two or three spinnerets are laid side by side to increase the number of filaments. The emerging filaments are quenched by a stream of cold air (Fig 22) and are attenuated mechanically or pneumatically to orient the molecules so as o increase the strength. There are two methods of batt formation
    1.Partial orientation
    2.Full orientation
    The strength improvement by partial orientation is adequate for many products like coverstock for diapers and hygiene materials. With partial orientation higher production rates can be achieved. Partial orientation is achieved pneumatically by an air generation unit. However for products like geotextiles, carpet backing, roofings and industrial products, full orientation is achieved by drawing the filaments over heated godets, with draw ratio of 1 : 3 or 4 followed by pneumatic acceleration. The filaments are then passed through a pneumatic air gun where high velocity air is forced through a constricted area of low pressure. This helps to achieve high uniformity and cover. Electrostatic charge is applied to keep the filaments separate. Batt formation takes place by random and uniform deposition of filaments on a moving perforated conveyor. The batt is then taken forward for bonding. Lay down with preferential direction in cross or machine direction is also possible. Suction is provided under the conveyor to improve randomisation. Fig 22 outlines batt formation in spunbonding.
             Spunbonding
          Fig :22 Spunbonding
    Recofil system developed by Reifenhauser is the most widely used system of spunbonding. Latest Reicofil model 4 can produce light weight material for hygienic products at speeds of 800 meters/min. Energy consumption of 1 � 1.2 kwh/kg for melting and conveying the raw materials. Other systems are �Docan system� and �Lutrafil sysem�. Reiter spunbond system claims a production capacity of 5000 tons/year/beam and energy consumption less than 1kwh/kg Hills and Fre specialise in spunbonding equipment from bi and multi-component material and claim speeds over 5000 metres/min, In the latest developments, special emphasis is laid on energy conservation and reuse of waste made in production.Ratio between he components can be varied from 50 : 50 to 85 : 15. Spunbonding from bi component and multi-component fibres provides products with unique properties. The different components are melted in separate extruders and passed through separate spin assembly and afterwards combined to pass through special spinneret orifices to form bi or multi-component filaments Special spinneret orifices are available to form core/sheath or side by side and segmented pie profile bi-component structures.
    The relative merits of spun bonding and staple fibre bonding are given in Table 5 below.
    Table 5 : Relative merits of filament bonded and staple fibre bonded Nonwovens
    Spun BondingStaple fibre bonding
    Higher strengthLower Strength
    Lower ElongationHigher Elongation
    Higher Uniformity in thickness and gsmLower uniformity in thickness and gsm
    Lacking in textile character and feelHas good textile character and feel
    Higher tear strengthLower tear strength
    Products are normally of low to medium gsm (20 � 250)Wide range of products from low to medium to high gsm are available (20 � 1500)
    Less flexibility in regard to raw material. Generally line is suitable for either polypropylene or polyester or Nylon or bicomponent fibre. Some latest models however claim flexibility in regard to fibre All types of raw material can be processed in the same lineAll types of fibres, manmade and natural can be made in the same line
    High Plant capacity in terms of productionLow to medium capacity in terms of production
    High capital investmentLow to Medium capital investment
    Major Applications
    1.Coverstock for diapers and hygiene products
    2.Surgical materials
    3.Carpet backing
    4.Bedding and furniture
    5.Geotextiles
    6.Roof Materials and other construction material
    7.Filters
    8.Industrial products
    Meltblown Nonwoven
    Melblown nonwoven is batt formed of ultra fine filaments deposited on a screen. Polymer is extruded through a die consisting of several hundred holes.(Fig 23) Streams of hot air at temp of 220 to 3400C, passing from an outer channels of the die, rapidly attenuate the extruded polymer at 0.5 o 0.7 times the speed of sound, to form extremely fine micro filaments. The filaments are quenched by cool air flowing from the contours of the die and blown on to collector screen thus forming a self bonded nonwoven batt. The fibres are bonded together because of interlacing action of deposition and thermal bonding by the hot air. The meltblown material has low strength and is often used in combination with other nonwoven material. Because of the ultra fine size of the filaments and increase in specific surface area, meltblown material has a high filtration efficiency for gas and liquids and particles.
    Barrier material is formed by combining meltblown material with spunbonded. Absorbents are made by combining cellulose or wood pulp with meltblown material Meltblown material sandiwiched between two layers of spunbonded materials, known as sms nonwovens are widely used as hospital gowns, hygiene, and filtration products. SMMS are also sometimes made.
    Meltblown
            Fig 23 Meltblown Process
    Process Checkpoints
    1. Viscosity of polymer chips should be checked in viscosity meter.
    2.The spinnerets and other parts of the spinning system must be thoroughly cleaned of polymer build-up at periodic intervals and at the time pack change. When polymer build up contaminates the parts, production has to be brought down to maintain satisfactory processing. The quality of product also gets adversely affected by presence of defects like stripes, bars and doglegs. Traditional cleaning consists of 1 burning the hardened polymer by placing the spinneret in a furnace 2. Cleaning in an ultrasonic bath of caustic soda and 3. spray bath cleaning. This method is time consuming and there is risk of spinneret damage. The vacuum pyrolysis process of cleaning is much more rapid and ensures defect free thorough cleaning
    3. Spinnerets should be examined under magnification for wear and tear. Preferably, an automated spinneret examination system should be used to inspect the spinneret at the time of purchase and during use to ensure that the design specifications are maintained as this speeds up the process. If the holes of the spinneret show signs of wear they should be refurbished.
    References
    1. Nonwovens � Technoogy of manufacture and properties
    A.K. Rakshit, A.N. Desai and N. Balasubramanian, Proceedings of Symposium on Nonwovens, BTRA, 1987, Feb
    2. A comparison of woven and nonwoven geotextiles,
    J. Perfetti, Meliand Textilber (Eng. Edn.), 1985, March, p207
    3.Woven and Nonwoven medical/surgical materials
    D.V.Parikh, T.A.Calamari, A.P.S.Sawhney, N.D.Sachinwala, W.R.Goynes, J.M.Hemstreet, and T. Van Hoven, International Nonwovens J, 1999 Spring
    4. Development of a geocomposite canal liner � BTRA�S experience
    A.N.Desai and N.Balasubramanian, J. Textile Association, 1991 Jan, p187
    5. http://www.inda.org/wet-laid.html
    6. Relative merits of polypropylene and polyester
    N.Balasubramanian, Indian Textile J, 2004, 32, p32
    7. Influence of processing conditions on functional properties of high loft structures
    A.N.Desai and N.Balasubramanian, Indian J of Fibre and Textile Research, 1990, 15, p169
    8. Opening size and water permeability of nonwoven geotextile
    A.K.Rakshit and N.Balasubramanian, Indian Textile J., 1991 June, p 26
    9. Indian Textile J, 2009, July, p 71
    10. http://www.texdata.com/content/0082e.pdf
  • Nonwovens- Bonding by Needle punching

    N.Balasubramanian


    Retired Joint Director, BTRA & Consultant, 022 25280767
  • Relative merits of Nonwovens over wovens and various methods of batt formation have been discussed in an earlier article1. The batt has to be bonded to impart strength and dimensional stability. The following are the various methods of bonding widely prevalent in the industry.
    •Needle Punching
    • Hydroentanglement
    • Thermal Bonding
    • Chemical Bonding
    • Stitch Bonding
    • Ultrasonic Bonding
    In addition spun bonding and meltblown nonwovens are nonwovens made directly from filament extrusion. In this article, we will discuss various factors that affect quality and performance of needle-punched fabrics and various developments in the needles and the machine.
    Needle Punching
    Needle punching is by far the most versatile and commonly used method of bonding accounting for 20 -25 % of the nonwovens. Further, needle punched fabric forms the base in making many composites. Needle punching is carried out passing a number of needles with barbs, mounted in a board, through the batt at a high reciprocating speed.. The machine consists essentially of a needle board, stripper plate and stitching plate, Needles are arranged in a number of rows (up to 23-26) in a needle board with about 1500 to 5000 needles per 1 m working width. Board size ranges from 200 to 320m working width. Stripper and stitching plates are perforated so that needles pass through them during up and down movement of each stroke. The stroke varies from 30 to 60 mm. The needles are usually triangular in cross-section with barbs at the three edges. As the needle penetrates through the batt, the barbs carry fibres with them thereby causing mechanical entanglement of fibres as shown in Fig 1 below.
    Fig 1 This gives strength and dimensional stability to the batt. Upon needle punching, the batt becomes thinner, stiffer and stronger. The extent of bonding depends upon punch density, depth of needle penetration, needle type, shape and size, barb shape, size and angle and fibre characteristics. Depth of penetration of needle is the extent to which the needle has penetrated through the stitching plate as indicated in Fig 2. With increase in depth of penetration, more barbs go through the batt/felt and more fibres are transported in vertical direction.
    Fig 2 : Depth of Penetration
    Stitch density or punch density denotes the number of stitches or punches per square cm made by needles on the felt . Punch density is dependent upon the number of needles per board, number of boards, stroke frequency and delivery rate. Stroke frequency is indicated by the number of up and down strokes made by the needle board per min. This is usually 1000 in old machines and has gone up progressively upto 3000 in latest models.
    Net Advance
    Advance made by felt per stroke, mm = Needle punching machines also differ in regard to the direction of punching. In down stroke machines punching takes place from top to down while in up stroke machine punching takes place from bottom to top as shown in Fig 3
    Fig 3 : Up and Down Punching
    In addition, number of boards in a machine varies from 1 to 4. Number of needles per 1 metre width and production rate increase with number of boards. Latest model high production machines have 4 boards with up to a maximum of 20000 needles/m width. Width of needle punching machine ranges from 2 to 10 m.
    Process Factors
    The important process factors that affect quality of needle punched nonwovens are
    1. Type of batt preparation
    2. Punch density
    3. Depth of penetration
    4. Needle characteristics
    5. Feeding System
    6. Batt quality
    7. Fibre characteristics
    Batt Preparation
    The major methods of batt prepation and factors affecting batt quality have been discussed in an earlier article1.
    Punch density
    Punch density is determined by the number needles per metre width, production rate and stroke frequency.
    Punch Density = = Thus punch density can be increased by 1. increasing the needles per board 2. increasing stroke frequency at a given delivery rate and 3. reducing delivery rate at a given stroke frequency. Number of needles per metre width is determined by the make of the machine. Production rate can be increased by increasing net advance and or punching rate. There has been a substantial increase in needle density over the years contributing to marked increase in production rate. Number of needle boards per machine also varies with the model. With increase in number of boards, there will be more needles per metre width and consequently higher punch densities at a given production rate or higher production rate at a given punch density can be obtained.
    Needle punching is usually done in 2 stages viz; pre-needling and finish needling. This gives the best results in terms of uniformity as punching has been done in a gradual manner. However, later models have dispensed with pre needling machine. Gradual reduction of thickness of batt, optimum control by means of adjustable gap between conveyors and close feeding of material to needle are required to minimize uneven draft and irregularity in product. Comprssive batt feeder by Dilo and RDF/FFS and DFS of Oerlikon Neomag, and SFD and DCIN batt feeder of Asselin, are equipped with such features.
    Several authors have studied the effect of process parameters in needle punching on thickness, strength, elongation and other physical properties of Nonwovens,2,3,4,5,6,7,8,9. Apart from straightforward methods of varying process parameters, central composite rotatable experiment design and Taguchi methods have also been employed to study the effect of needling conditions on fabric properties9,12, Taguchi method with grey relational analysis is useful in getting multiple property optimization. Artificial neural network modeling has also been used to predict the effect of web gsm, punch density and depth of penetration on properties of nonwoven15 and the prediction shows good agreement with actual results.
    Fibre Properties
    For successful needle punching fibre length has to be beyond 40 mm to assist in entanglement. Strength and dimensional stability of nonwoven improves as length increases up to 80cm. Beyond that, strength improvements are marginal because of fibre breakages. With increase in fibre length, fibre entanglement during needle punching improves resulting in less slippage and higher strength (Fig 4). With reduction in fibre denier (tex), web becomes more compact and strength improves because of better entanglement due to increased specific surface area4,11,13. However, improvement is marginal beyond a point because very fine fibres are more susceptible to breakages. Further opening size, which is a critical property in geotextiles reduces11 with fineness because of compactness (Fig 5). So for filter and geotextile applications fibre denier has to be properly chosen to meet pore size requirements. Studies on mixture of fine and coarse fibre showed that compressibility, recovery and energy loss% increases with increase in fine fibre and later decreases16. Though not as important as in woven, fibre strength has also a significant influence on increasing strength of nonwovens. Contribution of fibre strength to nonwoven is, however, very low ranging between 5 – 15 %. With increase in ratio of kinetic to static fibre friction, nonwoven exhibits stick-slip tendency during load application. With increase in fibre friction, strength improves because of reduced fibre slippages and greater fibre carrying capacity of needles. Sometimes solutions are sprayed on the fibres to improve fibre friction With higher fibre crimp, consolidation improves resulting in better dimensional stability and strength of needle punched nonwovens. Rayon fibres consolidate more easily than courtelle or wool4. Fibre cross-section shape influences compression and recovery17. Initial thickness and thickness loss are highest with trilobal followed by round and hollow cross-section with polyester nonwovens. Hollow cross-section showed least % compression and minimum compression resilience. Nylon fibre has circular cross section while nomax has cocoon shape cross section. Nylon has therefore a greater packing factor when repeatedly pressed by hot press18 . Breaking strength and modulus increase with packing factor with nomax but decrease with nylon because of heat deterioration of latter upon subjecting it to repeated hot press action. Other properties like bending rigidity and antistatic properties have also some influence on properties of needle punched material. Jute has some inherent advantages as raw material because of its strength, rugged appearance, biodegradability and lower cost. However jute content should be kept within 30% in Jute/polypropylene blend, otherwise wear life and appearance of carpet will suffer19. By sandwiching jute nonwoven in between two layers of polypropylene nonwoven and needle punching, the loss in abrasion resistance and wear life can be minimized. This is because jute is hidden inside and does not come in contact with abrading material. In plain layered carpets made out of jute and polypropylene, needle punching in finish needling should be done from polypropylene side so that top surface is free from jute fibres.
    Resin bonded jute or waste cotton ‘Namda’ is commonly used as an underpad to needle-punched carpet in automobiles as floor covering to reduce vibration and noise. Needle- punched floor covering from kenaf, jute and cotton blended with polypropylene and polyester with an underpad of polyurethane foam or soft cotton nonwoven reduces noise significantly in automobiles20 Kevlar, carbon, steel, teflon and glass fibres can also be needle punched to produce composites used in bullet proof fabrics, insulation,filtration, reinforcement and fire resistant products.
    Fig 4 : Effect of denier on tensile strength
    Fig 5 : Effect of fibre denier on Opening size
    Thickness and gsm With increase in punch density, weight per unit area(gsm) and thickness of fabric show a progressive reduction2,3 and dimensional stability of fabric improves5. The extent of reduction is initially more marked and progressively reduces afterwards. In needle punching, barbs in the needle push the fibres from horizontal to vertical direction as shown in Fig 1 . The fibre displacement leads to drafting of the felt. As a result gsm and thickness of felt decreases. The effect of these factors increases with punch density. Beyond a certain level of punch density, the fabric resists further compression and so rate of thickness and gsm reduction becomes less. The thickness of felt is lower with finer fibre than coarser fibre because of better cosolidation1 but the effect is more pronounced at lower punch density. Density of the fibre also influences thickness. With lower density, thickness will be higher because of increased fibre diameter. Thickness will also be higher with crimped fibres and hollow fibres. Effect of punch density on weight/unit area and thickness are shown in Figs 6 and76
    . Fig 6 Effect of punch density on weight g/cm2
    Fig 7: Effect of punch density on thickness
    As strength of fabric is affected by variations in gsm, breaking tenacity is usually estimated. This is given by
    Tenacity
    Tenacity of the fabric is critically affected by punch density. In cross direction, tenacity initially increases with punch density, reaches a peak and thereafter falls2,21.. In machine direction tenacity increases continuously with punch density but the rate of increase is initially is steep and reduces progressively afterwards. The general nature of tenacity vs punch density relationship is shown in Fig 8
    Fig 8: Effect of punch density on breaking tenacity
    Tensile strength increases with punch density because of greater amount of interlocking of fibres. But the nature of the curve is slightly different between cross direction(CD) and machine(MD) direction. This is because in card – crosslapper preparation, fibres are preferentially oriented in cross direction. As a result CD strength is higher than MD at all punch densities. Higher interlocking of fibres, at higher punch density, helps to reduce fibre slippage and increase the contribution of fibre strength to the nonwoven strength. But beyond a point, increase of punch density does not increase interlocking much and at the same fibres get broken or damaged by the repeated passage of barbs5. This is the reason why there is an optimum punch density at which maximum strength is found in cross direction. But in machine direction, such an optimum is not found and strength continues to increase with punch density though the rate of increase diminishes. This is because majority of fibres slip rather than break during breakage of nonwoven in machine direction because of low orientation of fibres. With increase in punch density, extent of slippage gets reduced. Further CD/MD tenacity ratio decreases with punch density as shown in Fig 9
    Fig 9 : Effect of punch density on CD/MD ratio
    During needle punching drafting of batt takes place leading to orientation of fibres from cross to machine direction. With increase in punch density, draft increases and the reorientation of fibres increases. As a result CD/MD ratio reduces as shown in Fig 9
    Elongation
    Effect of punch density on elongation is shown in Fig 10 .Elongation is higher in machine direction than cross direction because fibre slippage during break is more in the former. Elongation reduces with punch density but the effect is more pronounced at low punch densities. With increase in punch density fibre entanglements become stronger, slippage of fibres is reduced and as a result elongation comes down. Beyond a certain level of punch density reduction of fibre slippage is reduced and so elongation is not much affected.
    Fig 10 : Effect of punch density on elongation
    Tear Strength
    Effect of punch density on tear strength follows the same pattern as tenacity2.
    Depth of penetration
    With increase in depth of penetration, tenacity increases initially but afterwards levels off2,3(Fig 11). With increase in depth of penetration more fibres pass through the batt and to a greater depth. As a result interlocking of fibres is increased, leading to higher strength. But beyond a point, increase of depth of penetration does not improve interlocking much and moreover causes damage to fibres as more barbs pass through the batt. As a result strength improvement levls off beyond a certain level of depth of penetration. Strength is higher in cross direction than machine direction at all depths of penetration because of preferential orientation of fibres in cross direction.
    Fig 11 : Effect of depth of penetration on tenacity
    Pore Size
    Pore size or opening size is an important parameter in nonwoven geotextiles. This determines separation function of the material of different size of gravels and its ability to to retain soil particles without clogging. Dry sieving using well graded spherical glass particles is one of the methods used for determining pore size.Percentage of particle retained after sieving for a known time is determined for different particle sizes. A plot of particle retained % against particle size is drawn from which the opening size at which 90% of particle is retained 090 is determined. The effect of punch density on poresize is shown in Fig 12 for fibres of different denier11.
    Fig 12 : Effect of punch density on opening size
    With increase in punch density, the fabric becomes more compact and as a result opening size reduces. The rate of reduction reduces with punch density. The fabric becomes more compact with finer fibre resulting in lower opening size.
    Compression and recovery
    With increase in punch density and depth of penetration, compressibility initially decreases sharply and afterwards reaches asymptotically a value. Recovery follows a reverse trend, increasing with punch density2. This is because the material becomes more compact and stiff with increase in punch density and depth of penetration. However in jute, compressional behavior decreases initially and later increases9. Recovery decreases with increase in punch density and depth of penetration9 because of greater compactness . Needle punched fabrics from staple fibre have a higher compressional energy loss than spun bonded22. This is because of the bulkiness of former. Needle punched nonwovens are more compressible with higher fatigue compression recovery than thermal bonded, wet laid and woven because of 3 dimensional fibre arrangement and higher bulkiness23. With hollow polyester fibres, cross laid batt has higher compressibility and lower recovery compared to parallel laid24. This means fibre orientation in the batt has influence on compressional behavior.
    Sound transmission loss decreases initially and later increases10 with punch density with jute.
    Air and water permeability
    Air and water permeability are broadly unaffected by punch density2, 11. Though pore size is reduced, fabric becomes more compact one compensating for other. Water flow rate through nonwovens could be predicted by finite element analysis25 with good agreement with actual measurements.
    Stiffness and Abrasion resistance
    With increase and punch density and depth of penetration fabric becomes thinner and more compact and as a result more stiff14. However at higher levels of punch density and depth of penetration stiffness reduces because of fibre breakages. Abrasion resistance improves with punch density and depth of penetration because of compactness and improved fibre integration into the product. Sandwiching hollow polyester between two layers of normal polyester improves abrasion resistance without increasing stiffness15.
    Bursting strength and puncture resistance
    Bursting strength and cone puncture resistance decrease with punch density2 because of reduction in thickness. Liquid absorption rate of cotton needle punched nonwoven increases with punch density and net advance26. Water absorbency and thickness of jute/polypropylene needle punched nonwovens increase with jute content27
    Thermal Conductivity
    Thermal conductivity increases with reduction in punch density as material is less compact and more air is entrapped28. On compressing the material by putting a weight over it, thermal conductivity is reduced. Thermal insulation is highest with 9 barbed needle and higher ceramic content in a multilayered needle punched nonwoven made up of ceramic and glass fibres29. On the other hand higher glass content increases radiative transmission of heat30. Radiation thermal conductivity increases with reduction in area density, gsm and thickness. Increase in pore size increases radiation thermal conductivity31
    Needle Design
    Needle design and shape have considerable influence on the property of nonwoven. Needle consists of 3 parts as shown in Fig 13. 1.Crank 2. Crank shaft and 3 Working blade. In double reduced needle, there is an intermediate blade between crank shaft and working blade (Fig:13). While the cross section of crank and crank shaft are circular, cross section of blade is triangular. The working blade has barbs on the the three apexes and the barbs are staggered. Essentially the barbs transport the fibres through the batt and carry out interlocking.
    The chief properties of the needle that influence nonwoven quality are
    • Gauge
    • Type of barb
    • Barb spacing
    • Barb angle
    • Kick up
    • Length of working blade
    • Cross section of working blade
    Fig 13 : Needle elements
    Gauge
    Gauge of the needle has to be chosen based on the denier(fineness)_ of the fibre. Finer barb has to be used with finer denier. Broad guidelines regard to the gauge of the barb to be used for different fineness is given in Table 1 below.
    Table 1 Gauge of needle in relation to denier of fibre Gauge Diameter,mm Above 30d 18 1.2 19 1.1 20 .95 21 .90 30d 23 0.85 25 0.80 28 0.75 18 – 20 d 30 0.70 32 o.65 12 – 18 d 34 0.60 3 – 12 d 36 0.55 38 0.50 1.5 D 40 0.45 42 0.40 Type of Barb
    Common type of barbs are conventional and diepressed types. Barbs are cut inside the blade with a chisel in conventional barb. As a result, the barb has a pronounced kick up and sharp edges. Fibres are therefore raked during needle punching causing disturbance and damage to fibres and sometimes fibre breakages. Further, the kick up wears away during use resulting in rapid change in needling efficiency and product quality.However, the products made from such needles are more bulky and lofty as a result of the kick up.Diepressed needle was developed to overcome these drawbacks (Fig 14). The barbs in the die pressed needle are formed on a die and so have rounded and smooth edges. Further a controlled amount of kick up can be had with these needles. As a result fibre breakages and damage are considerable reduced with die pressed needle. The products made are also more compact and have lower thickness. The strength is more and products are more smooth with these needles. Now a days, die pressed needles are invariably preferred for all products except for waddings and high lofts where conventional barb is used.
    Fig 14 : Conventional and diepressed needles
    Barb Spacing
    Needles of 4 barb spcings are commonly available, as discussed below and illustrated in Fig 15: Depth of penetration with different barb spacing is given in Table 2
    Regular Barb
    This is the most common type of needle and is available from 13 to 46 gauge. Spacing between barbs is highest, 6.3 mm. Uniform packing distribution of fibres and smooth surface are achieved from top to bottom with this needles because of large spacing between barbs. RB is invariably preferred in pre needling and for high lofts and waddings as it results in higher thickness
    Medium Barb (MB)
    Medium barb improves needling efficiency and results in more compact products and has a barb spacing of 4.8mm. This needle creates more distinct fibre tufts in the felt and as a reult results in slightly inferior surface appearance. This needle is therefore preferred in waste fibre felts used as underlays in carpets and shoddy. If regular barb is used for such material, the fibres will be pushed out of the felt and rapid fibre accumulations will be found on stitiching plate. MB allows more fibres to be carried per stroke with less penetration depth as a result of the reduced spacing between barbs. At times MB is also used in synthetic leather or shoe felts in intermediate needling.
    Close Barb
    This needle is invariably preferred in finish needling. Spacing between barbs is 3.3mm Its main merit is that it allows all the barbs to pass through the felt with a relatively low penetration depth.The resuction in depth prevents the first few barbs from pushing fibres too far below the stitching plate and thus cause a fuzzy surface. When fibres are pushed out of the main body, they will not be contributing to the strength. Further, draft during needle punching will be lower with closed barb. So close barb needle results in a more compact and stronger nonwoven than regular barb. Needle breakages is also lower with close barb as needles travel less distance. However, close barb should not be used in preneedling as it creates distinct fibre bundlesat the bottom and variations in density from top to bottom.
    High density Barb
    These needles have an extremely close barb spacing (1.3 mm). This combined with the short distance between first barb and needle tip enables all barbs to enter the felt with only 8.3mm penetration depth. This needle is preferred in finish needling with thin products. HDB barbs with extremely low kick up or no kpick up are commonly used to get very smooth surface combined with high punch density. These needles are preferred for manufacture of synthetic leather, automotive package tray, spun bonds, automotive trunk liner, shoe and hat felts. Because of of low depth of penetration, needle deflection and breakages are lower.
    Fig 15 : Needles of different barb spacing
    Table 2 Depth of penetration with different barb spacing Type of Needle Penetration depth
    RB 23.3 mm MB 19.1 mm CB 14.8 mm HDB 8.3 mm
    Barb Angle
    Fig 16 below shows the barb angle and kick up in a needle
    Fig 16 : Barb Angle
    Barbs with a lower barb angle facilitate needle penetration as fibres slip out of the barb and as a reult loftier and thicker products are formed. However, strength of the product is lower because of fibre slippage,
    Kickup
    Higher kickup rakes up the fibres without contributing to interlocking.Fibre damages are therefore more and further fabric surface is rough and strength is lower.However, thickness is more and hence higher kickup is preferred in high lofts and waddings.
    Working blade length
    Lower blade length reduces needle deflection and breakages and result in higher strength.Shorter blade lengths are therefore preferred in finish needling.
    Working blade length varies from 11 to 30mm length. Longer working blade lengths are preferred for thicker products but they are more prone to deflection and breakage
    Needle Crosssection
    Needle crosssection is usually triangular. However, newer designs have been developed for certain applications like geotextiles for getting higher strength.
    1. Pinch blade
    Pinch blade has 2 barbed edges with a diamond shaped crosssection (Fig 17).Needle apexes have an angle of 30 0 as against 600 in normal needle.Consequent to this narrow radius, fibres tend to wrap round the barb face firmly with reduced fibre slippage. Fibre carrying capacity of barb is increased and strength is therefore hogher. Moreover, each barb carries separate fibre fringes and the two barbs work independently. It is futher possible to orient the needle in such a way to reduce damage in machine direction or cross direction scrim cloth threads.Further damage to both warp and weft threads can be minimised by orienting the barb at 45 0. Pinch blade is eminently suitable for geotextiles and filters Pinch blades are preferred in geotextiles and filter fabrics. Pinch blade is however more aggressive than triangular and is therefore not preferred for smooth fabrics
    2. Star Blade
    Star blade has either 3 or 4 barbs.(Fig 17) The 3 edged star blade by Gros-Beckart has a slightly concave working area and a more acute edge angle which results in better grip of fibres and intensive bonding. The cross sectional area is lower by 8% compared to conventional needle. The blade is available primarily in 32 to 38 gauge. The additional barb in the 4 edged star blade in Gros-Beckart’s 4star and Foster, increases the fibre carrying capacity and interlocking by about 14% The angle between the outer edges of barb is 600 which increases carrying capacity of barb. Tensile strength and abrasion resistance of fabric is improved by 20 to 30% as a result with this barb. In addition, productivity is increased by 20%.Star blade is preferred with geottextiles particularly from spunbonds and automotive interiors and heavy duty materials.
    Fig 17 : Blade cross-sections of pinch and star blades
    Number of barbs
    Normal needle has 9 bars 3 on each apex. However, to have a smother fabric, needles with 3 or 6 barbs are preferred with each apex having 2 or 1 barb instead of 3. For extremely smooth fabrics 2 barb needle is recommended.
    Blade Style
    Flexing strength is an important characteristic that determines the needle's ability to withstand flexing forces.Flexing loads are high with waste and regenerated fibres and cotton and with rigid materials like aramid and at high punch densities. With normal needles of cylindrical crossection, needle breakages will be high and quality of product will be inferior under such conditions. Needle with conical shape has been developed to increase flexing strength. With conical shape, needle with a lower crosssection first enters the batt when resistance is low and the larger diameter enters afterwards when the resistance is higher Fig 18). So bending and breakage of needle is reduced. Gros-Beckert has developed an improved version of conical needles with a lower diameter, termed as Gebecon. It is claimed to have even higher flexing strength and breakage resistance. The working part of the needle is thinner, more flexible and has extended wear life
    Fig 18 : Needle cross-sections
    Quadro needle
    Quadro needle by Singer has a working blade in rhombic form. (Fig 19 ). The barbs are in two opposite edges that are most distant from one another. The barb arrangement with a coarse shank results in more intensive transportation of fibres with a smooth surface. It is possible to increase strength in machine or cross direction depending upon the orientation of fibres in the batt.Damage to scrim threads is also less.Quadro needles are preferred in geotextiles, filters, blankets and needle felts with support material.
    Fig 19 : Quadro Needle
    Needles for fine and micro fine fibres
    Gebecon needles by Grosbeckert have been developed for fine and micro fine fibres
    Orientation of Barbs
    By changing the orientation of barb in relation to orientation of fibres in felt needling efficiency, strength and surface appearance of product can be altered. We will first consider the case with a needle with one barb. This is often used to minimize damage to scrim cloth.
    Fig 20 : Arrangement of Barbs in relation to material Flow.
    The arrangement of barbs given in Fig 20 B is desirable when a smooth surface free from holes is desired. The fibres slip out of the barbs and so interlocking will be poor. But holes will not be prominent due to insertion of needle. This arrangement is preferred for syntheic leather, fibre fills, spunbonds and carpet backing. The arrangement in Fig 20 A will be preferred when higher strength is required. The fibres move into the barb and the carrying capacity of barb is increased with this arrangement.
    We will now consider the more common triangular needle which has barbs on all the three edges. Fig 21 shows two types of arrangement of needles in relation fibre flow.
    Fig 21 : Orientation of needles in relation to fibre flow With arrangement in Fig 21 B two barbs are favourably disposed to the fibre flow and will have high fibre carrying capacity and so this arrangement is normally preferred. But if needle marks are to be minimized arrangement in Fig 21 A may be used at the cost of slight reduction in strength.
    Scrim Cloth
    Scrim cloth is sandwiched between 2 layers of nonwoven and needle punched in making certain products like filter fabrics and blankets. Use of scrim improves dimensional stability, strength and life. Cotton, polyester, blends and HDPE woven tapes are used as scrim The cloth should be of sufficiently open construction, otherwise, threads will be pushed out of the fabric in the form loops and show as defects. Stringent specifications are prescribed in export for nonwoven filters. Calendering and heat setting of needle punched material have been found helpful in meeting export specifications with polyester filters32.
    Orientation of barb is even more important in products involving a scrim cloth. During needling such products, the needle barb cause damage to the warp and weft threads and lower the strength. Further, the barbs push the threads out of the felt and cause rolled up nep like defects. The most efficient way to minimize damage to threads is to have needle with barb only on one edge and orient it so that the barb is in most unfavourable position as shown in Fig 22A . Damage to scrim is minimum with such an arrangement but interlocking will be poor as there is only one barb. For improving interlocking without damage to scrim, barbs on 2 edges is used (Fig 22 B)
    Fig 22 : Orientation of barbs in triangular needle to avoid damage to scrim
    Alternately to increase interlocking arrangement, pinch needle with 2 barbs ( Fig 23) is used. The barbed edges are perpendicular to fibre flow and parallel to warp threads. Damage to warp threads are minimized while fibre carrying capacity of barbs are increased. By turning the barbs by 900 damage to weft threads can be minimized. The interlocking will be lower as the barbs are less favourably placed to incoming fibre. Pinch blade is more suitable for avoiding damage to scrim cloth as it has only 2 barb edges and at the same time a higher fibre carrying capacity. By arranging the barbs parallel to warp threads as shown in Fig 23 A, damage to warp threads is minimized and by arranging the barbs parallel to weft threads as shown in Fig 23 B, damage to weft threads is minimized. By keeping the barbs at 450 to warp and weft, damage to both is minimized.
    Fig 23 Orientation of barbs in pinch needle to avoid damage to scrim
    Teardrop shaped needle with a single barb is offered by Grosbeckert to minimize damage to scrim cloth (Fig 24).
    Fig 24: Teardrop Needle
    Needle Point
    Different type of needle points available are given in Fig 25 . Needle point is never totally sharp and there is slight rounding of the edges. Extent of rounding or its radius is based on the product. Nonwovens made from monofilaments get damages with needle with a sharp point. Rounded ballpoints are used with such products. Rounded points and polished points are preferred with papermakers felts, filters and blankets. Chisel point needle has been developed by Foster for needle punching into a support base/backing consisting of foam. Needle point has a chisel shape instead of conical. Buckling up foam is avoided by this needle.
    Fig 25 : Needle point
    Fibre damage
    Some amount of fibre damage and breakages takes place during needle punching. Damage can be minimized by using diepressed needles and needles with low kick up, fewer number of barbs and regular barb (RB). Fibre breakages and loss in strength with wool fibres increase with needle punch density, depth of penetration and kick up of the barb33
    Needle punching of cotton
    Needle punching of cotton is difficult because of lower fibre length and higher frictional and penetration resistance. Special needles have been developed by various manufacturers for needle punching of cotton (Fig 27).
    Fig 26 : Needle for cotton Essentially 3 changes have made in needle design 1. Working blade needle length is reduced from 30 mm to 22 mm
    2. Shape of the needle is conical as against cylindrical
    3. Needle point length is increased from 3 to 5 mm and further the point is polished
    Long point length and conical shape help in penetration while shorter working blade length contributes to stability and minimizes needle damage
    Results of typical study comparing the results of cotton products made by using conventional and cotton needle are shown in Table 3 below
    Table 3 : Improvements in Strength by using needle for cotton Type of needle Gsm Tenacity gms /tex Elongation % CD/MD MD CD MD CD Cotton 114 0.6 0.67 98 69 1.1 Conventional 100 0.36 0.36 96 75 1.0 Tenacity of product is improved substantially by using cotton needles in place of conventional
    Surface Coating
    Chromium and nickel plated needles have been developed for improving wear life particularly with hard fibres like aramid, glass, steel etc. Polished working blade is also available to facilitate easy penetration. Special surface treatment with titanium nitride and metallurgical treatment have been given in Gebedur needles by Gros-Beckert to improve wear life.
    Needle punching Force
    Needles experience maximum resistance and high punching force as the needles enter the batt34. Once the needles have entered the batt, needle punching force drops as needles penetrate further, because of passages created upon penetration. Punching force increases with area density, gsm, fibre length, finness and crimp34,35,36. Higher specific area with finer fibres increases resistance to penetration and punching force. Dynamic punching forces experienced by individual rows of needles showed that penetration force increases with needle location in the board33. Penetration force increases from feed side to delivery side up to a maximum and then decreases. Location of peak penetration force moves from feed to delivery side as punch density increases. While fabric breaking energy increases with needle energy, tearing strength reduces. Dynamic needle punching force in random velour machine (discussed later) is influenced by loom vibration, inertia of needle, rigidity of brush conveyor and the resistance offered by batt38.
    Transport of fibres during needle punching
    Fibre transport through layers during needle punching was examined by introducing coloured fibres and counting them39. Still and cine photos indicated that fibre extension takes place during reorientation caused by needle punching40. Fibre slippage then takes place leading to fibre transport. Fibre in the top layer of batt are preferentially picked by barb than those in inner layers41. Fibre transport increases with punch density and depth of penetration. Large barbs and cylindrical needles promote fibre transport.
    Needle punching of Woven fabrics
    Needle punching of woven fabrics is also sometimes carried out for 1. Roughening the surface to facilitate coating 2. To create special appearance and fuller texture. In such cases, round point needles are preferred to minimize damages Needle Replacement
    After a period of running, barbs wear out and a few needles break and the quality will deteriorate as a result. If needle replacement is done every 30 million cycles, a marked reduction in quality will be seen as shown by solid line in Fig 27 up to the point of next needle replacement, followed by a marked improvement in quality. To minimize this, rotation of needles is done by some nonwoven units. Phased replaced of needles in a needle board is a better method to achieve uniform quality over a long period as shown by dotted line in Fig 27.
    Fig 27 : Uniformity of quality with phased replacement of needle
    Section wise replacement of needles as shown in Fig 28 will maintain more uniform and stable quality. The needle board is divided widthwise into 3 sections identified as A, B, C. After 10 million strokes, all needles in section A (which has completed 30million cycles) are replaced. At the same time, broken needles in section B and C are replaced by good needles removed from A. After another 10 million strokes, all needles in section B are replaced and as before broken needles in section A and C are replaced by good needles removed from section B. The process is repeated every 10 million cycles. By following this practice, more consistent and uniform quality as shown by dotted line in Fig 27 is obtained.
    . Fig 28 : Phased replacement of Needle Modern Developments
    1. Elliptical movement of needle board
    In conventional needling machine, the material stops at the time of needle penetration. As soon as the needles leave the material, it is accelerated from zero to throughput speed. Uneven drafting and shrinkage are caused by this. To overcome this drawback elliptical movement of needle is employed in Hyperpunch needle machine. by Dilo and Muliti motion drive by Oerlikon neomag. Elliptical movement consists of a synchronised vertical and horizontal movement of needle beam. The horizontal movement reduces the speed difference between needles and material. To enable needle beam to follow the movement of material, stripper and stitching blades are slotted. To reduce speed difference between needle beam and material, horizontal stroke has to be adjusted as per the throughput speed. Such adjustment facility is available in Dilo loom HV. Elliptical movement reduces draft in MD and shrinkage in cross direction and improves regularity of product in pre-needling. In finish needling, it enables higher throughput speeds up to 150m/min at 3000 strokes/min with less needle breakage and improved fibre entanglement and higher strength. These looms are ideally suited for needling spunbonds and papermaker felts at high speeds.
    2 Hyperlace punching
    Hyperlace machine, developed as an alternative to spunlace technology, consists of several cyclo punching machines where a transalatory and circular moving path is provided for needle. As a result high density needling is achieved with small dimensional changes. 4 cyclo punching needle looms in tandem have about 20000 needles per meter width. Each needle has just one barb with .02 mm depth. Single fibre is transported by needle during each stroke thereby increasing the entanglement. Fine fibres of 1.5 to 3 denier can be processed. Production rate up to 2000 strokes per min and 100 metres per min delivery rate are claimed on light weight fabrics of 25 to 90 gsm.
    2. Hi Needle punching
    H1 needle punching technology by Fehrer claims superior nonwovens by oblique needle penetration. This is achieved through an asymmetrically curved needle zone with straight needle passage. Better fibre orientation, randomization and entanglement are achieved because of longer needle path in this loom. Surface and mechanical properties of 3 polyester/ cotton blends made on this loom have been reported42
    Needle board
    Needle removal and replacement have been automated by most of the manufacturers. Fraunhifer and Oerlikon Neomag have developed a software to simulate needle punch pattern which helps to optimize position of needles in needle board. Uniformity and freedom from streakiness are claimed with this. Needle positioning can be made as per customer requirements. Singer has a semi automated version. Pre-insertion and pre-positioning of needles is done by hand but pressing to ultimate position is done by machine. Removal of needle is done by pushing and extracting.
    Problems in Needle punching
    Some common problems faced in Needle punching and the solutions are given in Table 4 below
    Table 4 : Problems and Remedies in Needle punching Problems Solutions Accumulation of fibres, neps, clusters and plastic beads in Needles and Needle board 1. Increase the frequency of needle board cleaning 2. Use longer needles 3. Stripper plate should be set as close as possible to material while allowing free passage. Stripper plate should be inclined slightly forward to allow for a larger gap on the inlet side than outlet side 4. Check if scrim cloth is pushed through nonwoven in which case needles with lower number of barbs and with proper orientation should be used Horizontal lines across the fabric It occurs at certain net advances. Slowly vary the stroke frequency while keeping delivery speed constant till the horizontal lines disappear. Longitudinal lines along the fabric These are caused by broken or damaged needles. Rusted needles Special carbon steel needles and coated needles are less prone to corrosion. Spraying of needle boards with silicone based lubricants like WD40 will minimize corrosion Ensure compressed air used for cleaning is dry.
    Structure Needle Punching
    Structure needle punching was developed for making carpets with designs, fuller in appearance and thereby add value to the product. Common designs are ribs, velours, geometrical patterns and worm screw chenille. Designed carpets are preferred in wall coverings and floor carpets used in auditoriums, museums, theatres and other public places and in high priced automobiles. Nonwoven batt first pre needled and finish needled with a low punch density, is used as feed material for structuring. Fork needles are used to form a pile. The prongs at the tip of the needle push the loops from the base of the carpet into the openings between lamellae of stitching support. The stitching support consists of a grid of lamellae (Fig 29).The loops formed in a number of parallel row and are transported between stripper plate and lamellae as shown in Fig 30
    Fig 29 Lamelle grid in Structure needling.
    Fig 30 : Loop formation in Structure needling
    Needle design of fork needle is given in Fig 31. As in the case of normal needle , Fork needles are available as 1 Single reduced 2. Double reduced and 3 Cylindrical or Conical shape( Fig 31). Dimensions of the needle of different gauges are given in Table 5 below.
    Table 5 : Dimensions of different parts of needle for different gauges Gauge Cranked Shaft (mm) Intermediate Blade(mm) Working Blade(mm 15 1.83 16 1.62 1.50 17 1.35 1.35 18 1.20 19 1.10 20 0.95 22 0.90 25 0.85 30 0..75 36 0.55
    Fig 31 Design of Fork Needle
    Important parameters of fork needle which determine appearance of fabric, are fork depth and width shown in Fig 32. Fork width normally varies from 20 to 40 mm and depth from 20 to 50 mm. Fork depth should be selected based on the thickness of the carpet and depth of pile required. Fork width is determined based on width of pile required.
    Fig 32 : Parameters of Fork Needle
    Rib or velour
    By proper selection of needles it is possible to get rib or velour effect on the same machine. If the needle board has longitudinal and transverse grooves rib or cord effect can be obtained by the same needle by different positioning in the needle board as shown in Fig 33.
    Fig 33 : Different positioning of needles to get rib and velour effects
    Multiple geometrical designs can also be produced by inserting the needles in the board as per design and with computer program control of stripper and lamella plates. Structured carpets have a low strength and so have to be coated at the back with a binder. Machines to produce light weight carpets with random velours have also been developed like dilour of Dilo and Superlooper of Oerlikon Neomag and SDV 2A 50S of Assalin. These are preferred as floor carpets by some automobile units as they give an appearance similar to wovens. These looms use crown needles. These needles have 3 or 4 barbs at the same level (Fig 34). The needles are arranged in the board in a random pattern to produce velours with non linear appearance. Velours are formed by the penetration of crown needles into the batt transported by a brush conveyer( Fig 35). Penetration depth is high and as a result densely piled uniform velours are formed on the batt as it leaves the conveyor. Low area density carpets up to 100 gsm can be produced out of fine fibres Stroke frequency ranges from 1200 to 1600/min. Fine fork needles can also be used. Gros-Bekert has developed fine fork needles to cater production of structured nonwovens from ultra fine fibres in the range 1.1 to 3.3 dtex for producing random velour products.
    Fig 34 : Crown Needle
    Fig 35 : Random Velour Process
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    34. J.W.S. Hearle, M.A.I. Sultan, J Textile Institute, A study of needled fabric –Part VI The measurement of punching force during needling, 1968, 59, T237
    35. J. Lunenschloss, Meliand Textil International, 53, p144
    36. C. Goswamy, T. Beck and F.L. Scaridino, Influence of fibre geometry on the punching-force characteristics of webs during needle felting, Textile Research J, 1972, 42, p605
    37 A.M. Seyam, Application of on-line monitoring dynamic forces experienced by needles during formation of needled fabric, Int. Nonwoven J, 1999, 8, p 55
    38. H.Mashroteh and M.Zarrebini, Analysis of punching force during random-velour needling, Textile Research J, 2011, , 81, p471
    39. J.W.S.Hearle and T.N. Choudhari, J Textile Institute, 1969, 60, T478
    40. J.W.S. Hearle, A.T. Purdy and A.T. Jones, A Study of needle actionduring needle-punching, J Textile Institute, 1973, 64, T617
    41. M.Miao, An Experimental Study of the Needled Nonwoven Process Part II: Fiber Transport by Barbed Needles, Textile Reseearch J, 2004, 74, p394
    42. Surface and Mechanical Property Measurements of H Technology Needle-Punched Nonwovens, C. Roedel and S. S. Ramkumar,,Textile Research J, 2003,73, p381
  • .Nonwoven – Bonding by Thermalbonding
    N.Balasubramanian*
    Retd. Jt. Director, BTRA and Consultant
  • Thermal bonding represents one of the important methods of making nonwovens which possesses many advantages.
    1. It is an environmentally clean technology as no chemicals are used,
    2. Has high production rates and requires low space.
    3. No water pollution as in chemical bonding
    4. The products made from cellulosic are free from allergy to skin. In products close to skin like diapers, sanitary napkins and medical applications it is preferred.
    5. The products have a soft feel and are absorbent and permeable.
    6. There is no weight loss after washing as in chemical bonding
    7. Insulation products and composites can be made
    8. It is ideal for making waddings and paddings used in winter clothing
    However, this technology has not much headway in India. The reasons for this are there are no indigenous machine manufactures. Further, low melt fibres and powders have to be imported.
    In this paper, different methods of manufacturing various types of thermal bonded nonwovens are described. Influences of fibre properties of base and low melt fibre and process parameters on the properties of nonwovens are covered based on the research and development work carried out. Different types of bicomponent dibres and their merits over moncomponent low melt fibres are covered.
    I There are two major types of thermal bonding
    1. Hot calender bonding
    2. Through hot air bonding.
    The former makes stiffer, thinner and stronger products and the latter loftier thicker and low strength products. For both types of products, batt preparation is the same. A small percentage of low melt binder fibre or powder is added to the regular fibre at mixing stage and the material is passed through opening and carding and crosslapping or airlaying techniques to form a batt. Belt calendar bonding makes products with characteristic between the two.
    Calender Bonding
    The batt is passed through the nip of a pair of calendar rollers (Fig 1) with pressure applied on top roller. One or both calender rollers are heated to a temperature above the melting point of binder fibre. The low melt fibre softens or melts to form bonds between the fibres. Heating of calender rollers is usually by oil. Oil, heated in a separate unit by gas burner or electric heater, is force circulated through the calender rollers by a centrifugal pump. Temperature regulators are provided in heating unit to ensure uniform temperature. Afterwards, the bonded material is passed through cooling rollers, known as quenching, to form a cohesive bonded fabric. If the material is wound without cooling, there will be unrelieved stresses caused by tension. This may lead to shrinkage during subsequent use. Both calendar rollers may be plain or one of them may be engraved. The product obtained with engraved roller will be softer as bonding takes place only at the engraved points but it will have lower strength. One or both rollers may be Teflon quoted to minimize sticking of material to hot roller. Instead of direct passage through nip, S passage around the bottom roller to the nip is sometimes done (Fig 1) for increasing heating time especially for heavy material. Calender roller diameter ranges from 40 cm to 70 cm, length from 1.5 to 5m and pressure from 100 to500 KN. Normal pressure range is 30 to 150 kp/cm Material speed depends upon the type of fibre and gsm and usually ranges from 25 to 100 m/min
    . Fig 1 : Calender Bonding
    To improve the bonding, some manufactures offer 3 calender rollers with double nip bonding (Fig 2 ). After passing through the nip of top and middle roller, the batt passes around the middle roller and emerges from the nip of middle bottom roller after a second bonding action. Top and middle rollers are usually heated while bottom roller is not heated. This system is used for heavier products like geotextiles and for giving special effects. In 3 calender bonding engraved rollers with different engravings can used in the top and bottom roller to product with enhanced designs.
    Fig 2 : 3 Roller calendar Bonding
    Type of Loading
    Since pressure is applied at the sides of calender rollers, there will be a deflection of the roller leading to more pressure at the sides than at the centre. To obtain uniform pressure across the width, either of the following options are used
    1.Top and bottom rollers at kept at an angle
    Adjustable calendar pressure can be obtained by X crossing of calendar rollers to get uniform pressure across the width. CX calenders are used to get varying amounts of offsetting as per the pressure. The offsetting is adjusted electrically by an encoder.
    2. Top roller is made slightly convex.
    As pressure is applied at the edges, the roller straightens out giving uniform grip over the width. But this method has the drawback that the extent of concavity cannot be varied, which is required with varying pressure.
    3. Thermo hydrein calender by Ramisch Kleinwefers.
    Deflection of calendar rollers is compensated by the application of thin roller shelf with internal pressure in the vicinity of the nip of calendar rollers1. The internal pressure is generated by a system of double piston bearing elements and oil from a hydraulic unit. The cylinder pistons produce the required force. With constant internal pressure, nip pressure is likely to be constant.
    4 ‘S’ roll by Andritz Kusters
    In the ‘S’ roll, annular gap between rotating steel tube and fixed axle is separated by seals into two semi circular chambers. Hydraulic pressure by oil is applied in the chamber facing the nip in such a way that the pressure is in linear ratio to forces in cylinder. As a result deflection is automatically compensated and uniform and infinitely variable force is maintained across the full width. In the latest model direct drive is provided to this roll.
    4. Texcol Hycon by Andritz Kusters
    The deflection controlled calendar rollers have a flexiroll sleeve made of polyamide. The sleeve is supported by hydrostatic pistons. An oil film transfers infinitely adjustable forces to the sleeve to obtain uniform pressure across the width. In addition, pressing width can be easily adjusted by means of supporting elements.
    Preheating
    Preheating of web helps to achieve better bonding of inner layers. It also helps to keep calendar roller temperature lower thereby minimizing sticking tendency. Preheating is usually done by infra red heaters.
    Area Bonded Nonwovens
    Bonding with low melt fibre
    Area bonded nonwovens refer to those made with both calendar rollers smooth A small proportion of low melt binder fibre is mixed with normal fibre and passed though batt formation machinery in the usual manner. The batt is then bonded by passing through calender rollers. The effect of process parameters on such nonwovens are discussed below.
    Calender Roller Pressure
    Rakshit Patil and Balasubramanian2 carried out detailed investigations on effect of process parameters in thermal bonded viscose nonwovens made by mixing a small proportion of low melt fibre. With increase in calender roller pressure, thickness reduces initially at a faster rate, later slowly (Fig:3 ). Strength also increases initially up to critical pressure, beyond which improvements are marginal (Fig 4 ). Initial strength improvement is because of melting of binder fibres and bonding of the material. Beyond a critical pressure, fibres get flattened and damaged and strength improvements by bonding are offset by damage to fibres, Elongation reduces with pressure because of reduced fibre slippage due to bonding (Fig 5 ) Strength is higher and elongation lower in CD than MD with card – crosslapping because of preferential orientation fibres in cross direction. Bursting strength increases initially but later levels out because of stiffness by bonding.
    Fig 3 : Effect of Calender pressure on thickness
    Fig 4 : Effect of calender pressure on strength
    Fig 5 : Effect of calendar pressure on elongation
    Binder fibre concentration
    With increase in binder fibre %, thickness reduces, strength improves and elongation reduces steeply (Figs 6, 7 and 8). Extent of bonding improves with increase in binder fibre % which explains the above results. But as binder fibre tenacity is much lower than normal fibre, increase of binder fibre % beyond a limit does not improve strength.
    Fig 6 : Effect of binder fibre % on thickness
    Fig 7 : Effect of binder fibre % on strength
    Fig 8 : Effect of binder fibre % on elongation
    Temperature
    With increase in temperature of calender, strength improves initially, afterwards levels off and drops beyond a certain value. Initial increase is because of better bonding. Increase of temperature beyond the melting point of binder fibre does not improve the bonding. On the contrary, it damages the fibre leading to reduction in strength.
    Material Speed
    With increase in material speed strength decreases as the time of contact at the nip reduces with lower bonding action.
    Base Fibre properties
    Winchester and Whitewell3 found that crimp, linear density and staple length are the important properties of viscose fibre affecting rupture, elasticity and handle of nonwoven. Finer fibre denier increases strength and reduces air permeability. Staple length increases wet strength, tear strength and abrasion resistance. Crimp increases elongation and reduces air permeability. Binder fibre types, % of binder fibre and bonding conditions have significant influence on the properties of nonwoven. Polyester binder fibre results in loftier and less stiff nonwoven than vinyon binder fibre. The findings of this work have however the limitation that thermal bonding has been done by hot plate pressing under static conditions and not by calender bonding
    Type of binder fibre
    Binder fibre with higher birefringence and higher crystallinity and molecular orientation forms weak and brittle bonds and result in lower strength4. This is because of insufficient polymer flow and fibrillation. On the other hand binder fibre with lower birefringence and less developed morphology results in better bonding. Further high production rates can be obtained with such fibres because of shorter time taken by fibre to soften and melt. Though these studies were made with point bonded nonwovens made from polypropylene, they should also hold good with area bonded nonwovens made by adding binder fibre to normal fibre.
    Quench Rate
    Higher quench rate increases the strength and elongation of the material. This is because of recrystallisation and lower crystal size. However, at high quench rates stress concentration takes place leading to brittleness and reduced strength.
    Single nip and double nip
    Though double nip point (Fig 2) should increase strength because double boding action, this is not always realized. As the material is in contact with hot middle roller for 1800 rotation, the binding points get stretched, especially with stiffer fibres like cotton and broken leading to lower strength particularly with thinner material. Double nip bonding is generally preferred with heavier fabrics.
    Low melt monocomponent fibres
    Low melt fibres are based on polyolefin (polyethylene and Polypropylene), polyamides or polyester. Polyvinyl chloride , vinyl acetate copolymers and cellulose acetate are also sometimes used as binder fibre. Modifications with commonomers and additives help to lower the melting temperature of normal synthetic fibres for development of low melt fibres.. The fibres are copolymers with less developed morphology and lower crystallinity. As a result, the fibres have low strength. A good low melt fibre should have lower melt viscosity and good affinity/ adhesive property to base fibres. Further, it should solidify quickly upon emerging from heat treatment. The melting point ranges from 1100 to 1500C. Grilene KE 150 and 170 copolyester (Foss), vinyl chloride vinyl acetate copolymer (Wacker MP), Exelto polyolefin fibre (Exelto), low melt polyamide (Premiere), FSI 101 polyethylene, FSI 0200 polyvinyl alcohol, 0502 ethylene vinylacetate, 0800 polyester fibre (Fibre Science.inc), tergal 190 PETP (Tergal) are some common low melt fibres. Biodegradable binder fibres have the merit that they permit recycling of nonwovens. Some important biodegradable fibres are cellulose acetate from celanese, polyactic acid (from corn) by Dow –Cargill, Bio PET by Dupont, PTAT copolyester by Eastman Chemicals,
    Bicomponent fibres
    Bicomponent fibres produce more uniform bonding and improved strength. Bicomponent fibres consist of two polymers, one of normal type and another low melt type made from the same spinneret with both components in the same filament.
    Different types of bicomponent fibres are shown in Fig 9. Skin core, also known as sheath/core, types are shown at the left and right side of figure while side by side types are shown at the centre. In the skin core type, core is a normal and skin is made of low melt component. The two can be placed concentric as in left hand side or eccentric as in right hand side. In the side by side type, shown in centre, one half is normal and other half is low melt type. When the batt is heated to the melting point of low melt component, bonding takes place because of melting of this component. The main advantage of bicomponent fibre is uniform bonding throughout the material as the low melt component is part of the fibre. As a result, low variability in thickness, strength and elongation is obtained. Another advantage is a wider range of bonding temperature. Since the core is a normal material, strength of bonded material is higher. Further the product is softer compared to that made from mono component.
    Fig 9 : Common types of bicomponent fibres
    .With concentric skin core type, better strength is obtained while with eccentric skin core type higher bulkiness is obtained. Skin core type is also sometimes used for improving water absorbency, dyeability and soil resistance, these properties being provided by skin component. Side by side bicompomponent is used for making bulkier products because of the difference in shrinkage of the components. Trilobal type skin core type of bicomponent fibres are also available (Fig 10)
    Fig 10 : Bicomponent fibre with trilobal crossection
    Some of the common types of skin core fibres are
    1 1100 amorphous coPET/PET
    2.1800 amorphous coPET/PET
    3. 1500 melt crystalline coPET/PET
    4. PA/PET
    5. PE/PP or PET
    6. HDPE/PET
    6. Easter coPolyester/PP
    7. PETP/copolyester
    Islands in Sea bicomponent
    A number of pieces of one polymer (island) are placed in a sea of another polymer (Fig 11) . The island polymer has a higher strength and lower elongation than sea polymer. The sea has a lower melting point to ensure bonding without affecting the island. Polypropylene, nylon and polyester polymer usually form the island. Sea matrix are made of polyvinyl alcohol or water soluble polystyrene fibre.
    Fig 11 : Islands in sea bicomponent fibre
    Island/sea bicomponent fibre made from 75/25 N6 and PE resulted in stronger bonds than moncomponent N6 upon thermal bonding of spunbonds5. A strong interface occurs between sea and island polymers, the weaker PE holds the structure together and helps to transfer the stress to stronger islands.
    Segmented pie structure
    This is shown in Fig 12. There are 16 segments where alternate wedges are made of nylon and polyester. The fibres are carded and with the help of high pressure jet of air or water passed through the web fibres are split. The resulting entanglement results in a strong fabric. The reason for using polyester and nylon in the wedges is that they have a poor adhesion to each other and so under the action of jet of water, splitting easily occurs. Pie wedge fibres are used to make micro fibres. The main application for this is in synthetic suedes and leather and in technical wipes.
    Fig 12 : Hollow pie wedge fibre
    Thermal Bonded Cotton nonwovens
    Thermal bonding has several merits for application to cotton for making nonwovens. Because of its lower length, cotton is difficult to needle punch. Chemical bonding causes allergy and is not suitable for close to skin and medical products. Thermal bonding is therefore widely used for making cotton nonwovens. The factors affecting thermal bonding of cellulosic fibres has been reviewed earlier by Desai and Balasubramanian1.
    Area Bonded
    Since low melt fibres are imported and not available easily, studies were made to make cotton thermalbonded nonwovens by using locally available polypropylene (PP) fibre as a binder fibre6. Melting point of PP fibre is 1600 to 1700 and calendar rollers are heated to this point. As in the case normal low melt binder fibre, thickness reduces with increase in PP. Absorbency reduces with increase in PP content (Fig 13) but the rate of reduction is more with light weight nonwovens.. Absorbency is higher with heavier products except at high PP levels. Strike through time, which measures the time taken by distilled water to pass through nonwoven, increases with increase in PP (Fig 14). Strike through time is also more with heavier weight nonwovens Rewet property, which determines the ability of nonwoven to keep the skin of wearer dry, increases with PP with low weight and reduces with PP with heavier weight nonwoven (Fig 15).
    Fig 13 Effect of binder fibre%(PP) on absorbency
    Fig 14 : Effect of binder fibre% on strike through time, sec
    Fig 15 : Effect of Binder fibre % on rewet %
    Point bonded cotton nonwovens
    Point bonded nonwovens refer to those made with engraved rollers. They have much lower strength than area bonded as only part of the area is bonded but are softer. Use of ordinary cellulose acetate(OCA), plasticized cellulose acetate (PCA), easter/PP bicomponent and PE/PET bicomponent as binders in thermal spot bonding of cotton has been investigated byH.Rong7,8, High strength absorbent cotton thermal spot bonded can be produced using 50% Easter/PP bicomponent fibre as binder. Easter/PP bicomponent fibre enables bonding at lower calender temperature and gives higher strength than Easter unicomponent Shape of the bond point becomes smoother and well defined as bonding temperature increases. Cellulose acetate as binder fibre has the merit of biodegradability as against synthetic binder fibre. However cellulose acetate has high melting temperature and this poses difficulty when used as binder. This can be overcome by pretreating it with water. This lowers the softening temperature of cellulose acetate and improves significantly strength of cotton/cellulose acetate thermal bonded nonwovens9.Melting point of cellulose acetate can also brought down by treatment with solvent vapours 10,11. Higher strength and bonding at lower temperature can be obtained as a result. Cotton bonded with cellulose acetate has good biodegradability and could be easily degraded by microbial attack. Investigations are reported on thermal bonded nonwovens for short-wear-cycle applications. Thermal bonded composites made with cotton on one side or both sides with 41 – 75% content have excellent wicking rates, wetting, absorbency and retention properties with handle similar to hydroentangled or knitted products12. Thorough mixing of binder fibre with cotton is required to get optimum tensile properties13. Nonwoven mouldable automobile carpets can also be made by blending cotton, kenaf and flax with biodegradable binder polymers PTAT and PTAT/PP, Biopet and PE/PET, PLA and PCA bicomponent fibre. Such products have the advantage of being environmentally biodegradable14 and trimmings made during manufacture can be reused. Statistical prediction equation has been developed for determining optimum process conditions to achieve peak loads of cotton thermal bonded nonwovens15. Point Bonded Nonwovens from synthetics
    One of the calendar rollers is engraved to make point bonded nonwovens for making smoother products. Both calendar rollers can also be engraved to produce novonette pattern in the product. A helical pattern of lands and grooves on both rollers results in a diamond point. Point bonded nonwovens can be made from polypropylene fibres without addition of low melt fibre.
    Fibre Orientation
    Fibre orientation in the input material, known as orientation distribution function (ODF), has marked influence on tensile properties of such material. Random orientation of fibres in the input material results in maximum strength because of improved bonding arising from higher number of cross over points16. With preferentially oriented fibres, number of bonds will be less and strength will be lower. ODF also determines the nature of break of nonwoven. Fabrics tear across the preferred fibre direction when load is applied in machine or cross direction. ODF determines the structural changes and deformation that take place during loading of nonwoven. Bonding temperature has influence only on the point of failure16,17. ODF and anisotrophy of bond pattern determine the load elongation behavior of nonwovens. Orthotropic theory has been used for predicting the effect of mechanical conditions in nonwovens with preferred orientation distribution. Theory shows good agreement with experimental results18.
    Bond point Geometry
    Bond point geometry, area of the tip, concentration and % bond point area are some of the critical factors that influence properties of point bonded nonwovens. Generally bond point area should be 10 – 25 % of total area and bond point concentration should be 100 to 500 per square inch.
    Fig 16 : Bond point parameters
    Important bond point parameters are the length and width of the bond point tip, and side angle (Fig 16). Very low bond point concentration results in low strength and poor life of product. Smith19 et al; found that concentration beyond a point will result in stiff products. Lower bond point concentration increases elongation and decreases flexural rigidity of polyethylene point bonded nonwovens. Increase in angle of bond point increases tenacity. Measured bond area is found to be higher than engraved roll pattern possibly because of transmission of temperature at the periphery. Computer based study however shows that with increase in % bond area, tensile strength, energy to break and breaking elongation increase except with weak bond points20 Numerical method, based on finite element analysis, for prediction of nonwoven tensile behavior from bond point design and process parameters has been attempted by Mueller and Kochmann21. Rapid modeling of different point geometries and layouts is possible using this method and this will help manufacturers in developing design.
    Process Parameters
    Warner22 showed that unlike in area bonded, calender roller pressure does not have much effect on strength with point bonded material. Pressure however aids in compacting the web and facilitates plastic flow at melting temperature and reduces thickness. Melting temperature of polypropylene is increased by 150 with application of pressure due to clapeyron effect. Heat of deformation under pressure also increases the temperature substantially. Melting temperature at the centre of web is more important than that at the nip of calender rollers in order to get a good bond. However, heat transfer from calender nip to the centre of fabric is insufficient to increase temperature to melting point as conduction heating plays only a limited role in transferring heat from nip of rollers to the centre of fabric. Some diffusion also occurs but its contribution is much lower than flow. Because of these reasons, pressure does not have much effect on strength. The main function of pressure is to facilitate flow of polymer which mechanically locks the fibres upon solidification. Bond area, Bond size and bond temperature have got maximum effect on tensile properties23,24,, . Tensile modulus and shear increases with temperature and bond area23 . Fig. 17 shows the effect of temperature on strength of point bonded nonwovens
    Fig 17 : Effect of temperature on strength of point bonded nonwovens
    Shrinkage of fabric also increases with temperature25. Polypropylene melts over a range of temperatures and not at one specific value and this range decreases with increase in process speed. If bonding is done at low temperature, fibres can be teased out of the bonded portion. Breakage of nonwoven then occurs due to inter-fibrillar slippage. At high temperature beyond melting point, fibre damage occurs and the bonds are also brittle and weak at the periphery. With such material failure occurs at the periphery of bond spot by breakage of fibres.
    Mechanism of Breakage
    At high temperatures, a steep morphological gradient is found at the boundary of bonding area. Rapid loss in molecular orientation occurs from bridging fibres to bond edge, as a result of which most breakages occur in this region during breakage of nonwoven26. Fibres close to the bond periphery have a lower strength and elongation than in rest of unbonded area. Unequal strain distribution is therefore found in spot bonded nonwovens and as result only 10 – 15 % of fibre strength is realized. However, with polyethylene point bonded nonwovens fail due to disintegration of bond area rather than fibre breaking at perimeter19.Studies with polarised laser microspectroscopy showed that birefringence decreases to half its original value at the bonding point27,28 while it is unaltered in the non-bonded portion. Higher bonding temperature and longer bonding time result in larger differences in morphology at bonding region. While density at bond point is lower than that at bridge fibres, in polyester, opposite trend is found in polypropylene. Image acquisition equipment have been used by some workers to examine structural changes of thermal point bonded nonwovens during deformation29.This enables determination of orientation distribution, bond spot strain, unit bond repeat pattern strain as a function of macroscopic deformation.. Mode of application of deformation influences type of failure of material. Structural changes and microscopic deformation of bond spot are determined by initial orientation distribution function of the material17. Temperature of bonding has little influence on this. To get a clue to the low fibre strength utilization in thermal bonding, thermal bonding of a pair of fibres was carried out by passing them through a hot calendar roller30. This showed fibre strength reduces significantly upon bonding. The reduction is primarily because of heating and not because of pressure. This study confirmed that stronger bonds are formed with lower birefringence fibres even at lower temperatures.
    Morphology of Fibre
    Morphology of fibre has a marked influence on properties of thermal bonded material. Fibres with higher crystallinity and higher molecular orientation form weak and brittle bonds. This is the consequence of poor polymer flow compounded by fibrillation of fibres2,31 .Fibres with lower crystallinity and lower molecular orientation form stronger bonds and stronger fabrics. This is reinforced by a study where polypropylene fibres with varying molecular orientation were made on a pilot extrusion plant and made into point bonded nonwovens by Andrreassen et al;32Wei et al;25. Tensile strength of fabrics made from such fibres is found to be primarily influenced by molecular weight distribution and molecular orientation as determined by the conditions under which fibre is made primarily. Tensile strength of nonwoven increases with decreasing draw ratio and increase in extrusion temperature, though these conditions result in lower fibre strength. Fibres with low orientation or higher elongation also result in higher strength and flexural rigidity of nonwoven because of better load sharing33, . While increase of strength is desirable it should not lead to higher flexural rigidity as it makes the product stiff and board like. Changes in thickness due to bonding with poorly oriented fibre are lower25. T196 polypropylene fibre which has a sheath core structure with a lower refractive index at sheath, lower modulus and higher elongation than normal T101 performs better and result in higher strength in nonwoven. This is because T196 fibre produces stronger bonds at lower temperature, where strength degradation is minimum34.
    Computer simulation
    Computer model and simulation techniques have been used to predict stress strain relationship of point bonded polyester nonwovens. Bond layout, fabric density, orientation and curl of fibre and bond tensile properties were fed to the computer and a program used to determine stress strain curve during deformation35.Computer simulation program restricted to two dimensional nonwovens has been developed by Britton36 et al;. Mechanical properties of fibres laid in a web and held together by some means are first programmed. The changes in the fabric system, as it undergoes distortion, are computed. In another study an image simulation system is used to obtain an image of nonwoven using web density, fibre properties, unit cell size and bond properties and the effect of structural and process variables on the mechanical properties of nonwoven was examined37. Demirci38 et al; have developed a simulation technique to visualise a nonwoven composed of nonuniformly oriented fibres and bond points made from deformable fibres. Dynamic response of such a simulated material to process parameters bond points is determined using finite element software. Such studies have the merit that optimum process parameters can be obtained without extensive experimental investigations.
    Testing Conditions
    Effect of specimen length and width on strength of nonwovens in conventional tensile test and cyclic loading have been investigated by Hou et al;39. Longer specimen length generally result in higher modulus but sample width has insignificant effect. Cyclic loading reveals that the material is initially elastic but later on shows plastic behahiour.
    Applications
    Light to medium weight products in the range 30 – 100 gsm are made from calendar thermal bonded nonwovens. Main applications are
    1. Interlining
    2. Coverstock for diapers
    3. Filter material
    4. Sanitary napkins
    5. Wipes
    6. Tea bags
    7. Trims for automobile
    8. Geotextiles
    9. Surgical gowns and caps
    10. Face masks
    11. Automobile headliner
    12. Shoe composites
    13. Computer disc
    Belt Calendering
    In belt calendaring nonwoven batt is passed between a heated roller/drum and a heat resistant silicone coated blanket. Pressure is applied at the exit end by the guide roller on the hot roller. Nonwoven is in contact with the hot roller for longer time of 1- 10 sec and pressure is much lower, up to 9 N (9kp/cm), compared to hot calender bonding. The products are thicker, flexible, permeable and weaker than calender bonded material. By varying the speed, temperature and pressure special effects can be given. Patterned bonding can be obtained by using a patterned blanket. Heated drum from 0.5 to 2 m, width up to 6 m and speeds up to 100 m/min are available. Machines with 2 heated drums in tandem are available where fabric is bonded on one side in first drum and on other side in next.
    Embossed calender Bonding
    The web is passed though a pair of calendar rollers, one of which is male patterned metal roller and other matched female patterned felt roller. Many geometrical shapes including designs are used in embossed roller (Fig 18).
    Fig 18 : Embossed Calender Bonding
    Embossed calendar bonding is used for making baby wipes, coverstock, automobile products and special fabrics and clothings
    Through Hot Air Bonding
    Through hot air bonding is used to produce loftier products used as waddings in quilts, blankets and winter clothing and insulation material. The batt made out of normal and a small % of low melt fibre is passed over a slotted traversing lattice and is taken through a hot air chamber. The batt can also be guided between two belts through the chamber. Distance between the belts is adjustable as per the product specifications. Monocomponent low melt fibre or bicomponent fibres can also be used as binder fibre. Hot air at melting temperature of low melt fibre is drawn though the batt from the bottom as well as top as shown in Fig 19 through suction by a fan. Binder fibre melts and forms droplets on normal fibre and bonding takes place. Hot air chamber is in number of sections based on the capacity. Positive pressure from one side and negative pressure from opposite side is provided in each section to ensure even passage of hot air through the material. The direction of air supply is adjustable separately in each section. Air supply to the chamber is both from left and right to ensure uniform temperature. The same air after passage though batt is reheated and used for conserving energy. Temperature measuring units are placed in each chamber to facilitate monitoring and control. Temperature across the width is maintained with an accuracy of ± 1.5 % . Direct heating systems by gas or indirect heating by steam or thermal oil is used for heating air. The material then passes through a cooling chamber and a bulky product emerges. When products of lower width than the belt are made, systems are provided for lateral closing of air to minimize loss of air. Products made by this method are lofty, open, soft absorbent and porous. Width range is from 2 to 7m and material speed is up to 100 m/min.
    Fig 19: Through Hot air Bonding
    Fleissner uses a perforated drum, over which batt is taken round. Hot air is sucked from the end of drum through a radial fan through the perforations and passed through the batt to form a bonded material (Fig 20). Low melt fibre melts flows to the point of contact between fibres and forms the bond. After bonding the material becomes loftier and bulky. The material is soft, absorbent, resilient and has insulation value. Flow of air can be adjusted as per requirement. Working width up to 7m and fabric thickness up to 50 mm and speeds up to 1000 m/min are claimed.
    Fig 20 : Through Hot air bonding over perforated Drum
    Products made by through hot air bonding can be given cold calendering to make more compact products. Such products are softer, flexible and more extensible than hot calendered nonwovens.
    Struto Technology
    Struto technology consists of vertical lapper to make batt from card web. This is then taken through a hot air chamber for bonding. Vertical arrangement of fibres is achieved by this technology which improves loftiness. Thickness up to 40mm and production rates up to 100 m/min are possible.Jirsak40 et al ; found that compression properties of high lofts made from batts prepared from vertical lapper were significantly better than those made from conventional crosslapper. Further hollow polyester fibres bonded with newly developed binder fibres from Teijin using Struto technology have compression property close to polyurethane foam.
    Air laying
    Air laying method of batt preparation has also a 3 dimensional random arrangement of fibres. With through hot air bonding, these products will be loftier than card crosslapping batts.
    Fibre properties and process parameters
    Type of fibre, % of low melt fibre, temperature of hot air and duration of exposure are some of the important parameters that should be optimized to get most desirable high- loft. Desai and Balasubramanian41 investigated the influence of fibre crimp and type and process parameters on properties of high loft nonwovens from polyester fibres. Hollow and high crimp fibres result in thicker and bulkier product but loose their bulkiness most rapidly with cyclic loading compared to normal fibres. Hollow fibre high lofts are more compressible than normal fibre material and at the same time have higher insulation value. Increase of low melt fibre content and duration of bonding reduces specific compressibility and resilience (Fig 21 and 22). Thickness of the high loft is an important parameter that determines thermal resistance. Thermal insulation improves with thickness. The specific stress of such material increases with low melt fibre content, temperature and duration of exposure. The products are found to have good uniformity. If needle punching is done prior to through hot air bonding, a higher strength is obtained but the product becomes thinner and stiffer.
    Fig 21 Resilence vs low melt fibre%
    Fig 22 : Specific Compressibility vs low melt fibre %
    Hong42 et al found that PP through air bonded material has lower friction coefficient and withstands abrasion compared to polypropylene thermal bonded, tencel spunlace and cotton spunlace and therefore can be used as coverstock material for diapers. Its quick drying characteristic is another advantage. However consumers prefer cellulosic spunlace compared to surfactant treated polypropylene. Studies have been made to make nonwovens from kenaf by through hot air bonding43.Through hot air bonded kenaf has a soft feel and is lofty. If needle punching is done prior to hot air bonding, the product becomes stiffer. A statistical approach was employed to determine optimum bonding process parameters for getting minimum pore size of through hot air bonded nonwoven by Wang and Gong44. Lin45 et al; showed that bulk density of nonwoven has more influence on thermal conductivity and limiting oxygen index than thermal consolidation and processing methods. Nonwovens with good thermal insulation and low flammability can be made from FR polyester hollow fibre and low melt polyester fibre by thermal pressing of batt made out of them. Modelling thru air bonding process showed that the time needed to heat and melt the fibre decreases with increase in porosity of product and velocity of hot air46. Fibre orientation factor has maximum influence on bond formation. Bonding temperature and fibre diameter have a small influence on time required for bonding. Computational fluid dynamics modeling has been employed to examine the effect of fibre properties and process parameters on properties of bonded product47. Fibre orientation in the input material has a marked influence on the anisotropy of strength with through hot air bonded material48. These products have a good stability and elasticity. A model was developed to estimate initial tensile response of such products based on orientation averaging and Poisson’s ratio.
    Applications
    Medium weight products in the range 70 to 200 gsm are made by through hot air bonding. Common applications are
    1. Wadding or padding used in winter clothing
    2. Quilting
    3. Filters
    4. Seat cushions
    5. Sound proofing material
    6. Composites
    Thermal Bonding using powder
    Thermal bonding is also carried by using a low melt powder in place of fibre. Powders from polyethylene, low density polyamide, vinyl acetate/chloride copolymers are commonly used . The powder is added in the mixing stage in a controlled manner. It is also sprayed on the web or nonwoven fabric for making powder coated and mouldable products like automobile carpets (Fig 23). In airlaying fibre abd powder are dropped on the laying lattice.After application of powder the material passes through an infra red heating chamber and passes through a pair of calender rollers to form laminated products which can then be moulded to shape. Powder bonding can be made on one side (Fig 23) or both sides (Fig 24) Powder bonding has a wider range of temperature for bonding than low melt fibre.
    Fig 23 : Powder spray bonding
    Fig 24 : Double sided spray bonding
    An LDPE film or thermoplastic fabric can also be introduced over the material before calendaring. Powder bonder is suitable in open structures or mouldable materials and composites. The powder should withstand washing and chemical treatments and should not emit any fumes or odour during use.
    Applications
    1. Interlings for collar and outer wear
    2. Shoe inlays
    3. Automobile carpets
    4. Insulation material
    5. Building material
    6. Waddings and quilts
    Radiation Bonding
    Infra red lamps are used to provide the radiant energy to bond the Nonwovens with binder. While binder is melted there is no harmful effect on base fibre. Bonding takes place when material comes out of radiation chamber. This method has the advantage of low energy and capital costs.
    References
    1. A.N. Desai and N.Balasubramanian, Critical factors affecting properties of thermal-bonded Nonwovenswith special reference to cellulosic fibres, Indian J Fibre and Textile Research, 1994, 19, p209
    2. A.K. Rakshit, V.K.Patil and N.Balasubramanian, Studies on thermally bonded viscose Nonwovens, Resume of papers at 32nd Joint Technological conference, SITRA, 1991, June, p 215
    3. S.C. Winchester and J.C. Whitewell, Studies on nonwovens Part I – A multivariable approach, Textile Research J, 1970, 40, p 458
    4. S.Chand, G.S.Bhatt, J.E. Spruiell and S. Malkan, Role of fibre morphology in thermal bonding, International Nonwoven Journal, 2002 Fall, 11, p12
    5. N. Fedorova, S. Verenich, and , B.Pourdeyhimi, . ‘Strength optimization of thermally bonded Nonwovens, J of Engineered fibres and Fabrics, 2007, 2, issue 13.
    6, A.N.Desai, K.R.Bhatnagar and N.Balasubramanian, Influence of cotton content and area density on the properties of cotton thermal-bonded nonwovens, Indian J of fibre and Textile Research, 1994, 14, p 251
    7. H. Rong, Structure and properties of cotton based biodegradable/compostable nonwovens, Ph.D. Thesis, University of Tennessee, Knoxville, 2004, May.
    8. H.Rong and G.S.Bhatt, Preparation and properties of cotton-easter nonwovens, International Nonwovens J, 20003 Summer, 12, p53
    9. X. Gao, R.E. Duckett, G.Bhatt and H.Rong, Effects of water on processing and properties of thermally bonded cotton/cellulose acetate nonwovens, International Nonwovens J, 2001 summer, 10, p21
    10. H.Suh, K.E.Duckett and G.Bhatt, Biodegradable and tensile properties of cotton/cellulose acetate nonwovens, Textile Research J, 1996, 66, p230
    11. K.E.Duckett, H.Suh, and G.Bhatt Composite nonwovens from cotton/cellulose acetate blends, !995 Nonwovens Conference, p89
    12. L.C. Wadsworth and H.Suh, Cotton-Surfaced Nonwovens For Short-Wear-Cycle Apparel, International nonwovens J, 2000 Sept, 9, No2
    13. H.Rong and G.S. Bhatt, Binder fibre distribution and tensile properties of thermally point bonded nonwovens, J of applied polymer science, 2004, 91, issue 5 p3148
    14. M.G. Kamath, G.S. Bhatt, D.V.Parikh and H.Mueller, Cooton fibre nonwovens for automobile composites, International Nonwovens J, 2005 Spring, p34
    15. H.Rong, R.V.Leon and G.S. Bhatt, Statistical analysis of the effect of processing conditions on the strength of thermal point bonded cotton based nonwovens, Textile Research J, 2005, 75, p 35
    16. Michielsen, B. Pourdehimi and P.Desai, Review of thermally point bonded nonwovens, Materials, processes and properties, J of Applied polymer Science, 2006, 99, p 2489
    17. H.S.Kim, B.Pourdeyhemi, A.S. Abiraman and P. Desai, Effect of bonding temperature on load deformation structural changes in point-bonded nonwoven fabrics, Textile Research J, 2002, 72, p 645
    18. H.S.Kim, Orthotropic theory for the prediction of mechanical performance in thermally point-bonded nonwovens, Fibres and Polymers, 2004, 5, p139
    19. K. Smith, A.A.Ogale, R.Maugans, K.Walsh and R.M.Patel, Effect of bond roll pattern and temperature on microstructure and properties of polyethylene nonwovens, Textile Research J, 2003, 73, p 845
    20. T.F.Gilmore, X-Mi Zhang and S.K.Batrs, Effect of bond point design and bond strength on load-deformation of point bonded nonwovens- A computer based study, Tappi Nonwovens Conference, 1993, April
    21. D.H.Mueller, M. Kochmann, Numerical modeling for thermal bonded nonwovens, International Nonwovens J, 2004, spring, p56
    22. B.Warner, Thermal bonding of polypropylene fibre, Textile Research J, 1989, 59, p151
    23. K.S.Kim, B.Pourdeyhimi, P.Desai and A.S. Abhiraman, Anisotrophy in the mechanical properties of thermally spot bonded nonwovens – Experimental observations, Textile Research J, 2001, 71, p 965
    .24. P.K. Jangala, Effect of bonding variables in thermal bonding of polypropylene nonwovens, M.S. Thesis, University of Tennesee, Knoxwille, 2001, Aug
    25. K.Y.Wei, T.L.V.Vigo and B.C.Goswamy, Structure property relationships of bonded polypropylene nonwovens, J. applied polymer science, 1985, 30, No 4, p1523.
    26. S.Michielson and X. Wang, Rapid morphology changes at bond periphery in thermal point bonded nonwoven, International Nonwoven J, summer, 2002, p35
    27. X. Wang and S. Michielsan, Morphology gradients in thermal bonded polypropylene nonwoven, Textile Research J, 2001, 71, p475
    28. X. Wang and S. Michielsan, Morphology gradients in thermal bonded polyethylene terephalate nonwoven, Textile Research J, 2002, 72, p394
    29. H.S.Kim, A. Deshpande, B.Pourdeyhemi, A.S. Abiraman and P. Desai, Charaterising structural changes in point-bonded nonwoven fabrics during load deformation experiments, Textile Research J, 2001, 71, p157
    30. A. Chidambaram, H. Davis and S.K. Batra, Strength loss in thermally bonded nonwovens, International Nonwovens J, 2000 Fall, 9,
    .31 . S.Chand, G.S.Bhat, J.E.Spruiell and S. Malkan, Role of fibre morphology in thermal bonding, International Nonwoven J, 2002 Fall, p 12
    32. E. Andrreassen, O.J.Myhre, E.L. Hinrichsen, M.D. Brathen and K.Grostad, Relationships between properties of fibres and thermally bonded fabrics made of polypropylene, J of applied polymer science, 1995, 58, p1633
    33. K.Y. Wei, T.L. Vigo and B.C. Goswamy, Structure property relationships in thermally bonded nonwoven fabrics, J., of coated fabrics, 1984, 14, p100
    34. R.K. Dharmadhikary, H.Davis, T.F. Gilmore and S.K. Batra, Influence of fibre structure on properties of thermally point bonded polypropylene nonwovens, Textile Research J, 1999, 69, p 725
    35.T.H. Grindstaff and S.M. Hansen, Computer model for predicting point bonded nonwoven strength – Part I, Textile Research J, 1986, 56, p383
    36. F.N.Britton, A.J. Simpson, C.F.Elliott, H.W.Graben and W.E.Gettys, Computer simulation of the mechanical properties of nonwoven fabrics Part I- the method, Textile Research J, 1983, 53, p363
    37. H.S. Kim and B.Pourdeyhimi, Computational modeling of mechanical performance in thermally point bonded nonwovens, J of textile apparel, technology and management, 2001, Vol1, issue 4
    38. E.Domirci, M.Acar, B. Pourdeyhimi and V.V. Silberschmdt, Dynamic response of thermally bondedbicomponent nonwovens, J. of mechanics and materials, 2011, 10,p405
    39. X. Hou, M.Acar and V.A. Silberschmidt, Tensile behavior of low density thermally boned nonwovens, J of Engineered fibres and fabrics, 2009,4, issue 1, p 26
    40. I.Jirsak, T. Burian and P. Saskova, Improvements in compressional property of high lofts, Fibres and Textiles in Eastern Europe, 2003 July/Sept, 11, No3(42), p80
    41. A.N.. Desai and N.Balasubramnian, Influence of processing conditions on the functional properties of high loft structures, Indian J. Fibre and Textile Research, 1990, 15, p 169
    42. H.H.Hong, S.G.Kim, T.J.Kang and K.W.Oh, Effect of abrasion and absorbed water on the handle of nonwovens for disposable diapers,Textile Research J, 2005, 75, P 544.
    43. W.Tao, T. A. Calamari and L. Crook, Carding kenaf for nonwovens, Textile Research Journal 1998, 68, 402
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    48. . A.Rawal, S.Lomov, T. Ngo, I. Verpoest and J. Vakerrebrouck, Mechanical behavior of thr-air bonded nonwoven structures. Textile Research J., Textile Research J, 2007, 77, p 417
  • Nonwoven Moulded Automobile Carpets


    N.Balasubramanian
    Retd. Jt. Director (BTRA) & Consultant
    I, Rajeswari, 36, 17th Road, Chembur, Mumbai 400071 (Tel- 25280767)
  • Though Nonwovens possess several distinct advantages over woven in terms of labour, space, manufacturing costs besides possessing unique properties, nonwoven industry is in a nascent stage till recently in India. One of the major problems is developing suitable and stable market that gives adequate returns for investment. But the advent of several automobile manufacturing units during the last few years in the country has changed the scenario markedly. Moulded floor carpets, luggage trunk liners, seat covers, roof liners and furnishings used in automobile are invariably made of nonwoven because of their special properties and cost advantage. Nonwovens have better adhesion property than woven and so binder application is more uniform. They also possess higher thickness for a given weight per unit length and so are more voluminous and comfortable . In addition they have a more uniform, smooth and random surface. As a result nonwovens are preferred for moulded carpets used in modern cars. Several nonwoven manufacturers in India have therefore added additional facilities like lamination, moulding and trimming to their plant to produce moulded carpets. Since automobile manufactories are highly quality conscious and are committed to QS 9000 quality management systems, nonwoven manufacturers were also required to upgrade their quality monitoring systems and procedures to establish a reliable name in the market, achieve a higher market share and keep down rejections. An attempt is made in this article to outline the critical factors that affect quality of nonwoven moulded carpets, from raw material selection to process parameter selection at different stages of manufacture and the precautionary measures to overcome them. Improvements in checking and inspection and packing of finished product are suggested. Some of the common causes for rejection together with remedial measures are enumerated.
    Specifications
    Specifications and quality requirements vary from one automobile manufacturer to another. The specifications for moulded carpets for some of the major manufacturers are given in Table 1.
    Table 1 : Specifications for moulded nonwoven carpets
    Sr. NoPhysical PropertyMaruti ZenMaruti EsteemGMI Opel AstraTata IndicaHyundai SantroFiat India Uno Toyota PlainToyota Velour
    1Material Nonwoven feltBlend of 30%PES &70%PPBlend of PES & PP of different shadesBlend of 2 different shades of PP& 2 different shades of PESPES of single shadePES of single shadeBlend of PES of 2 different shadesBlend of 3 different shades of PPBlend of PP of 3 different shades
    2Binder back coatingAcrylicAcrylicThermo bondableAcrylicAcrylicAcrylicAcrylicAcrylic
    3LaminationLDPE Powder & FilmLDPE Powder & Film NilLDPE PowderLDPE PowderLDPE PowderLDPE PowderLDPE Powder
    4NamdaMixture of waste fibresMixture of waste fibres
    5GSM (gms/sq.m)
    NonWoven
    Binder
    LDPE
    Total
     
    330
    50
    260
    640
    Namda � 600
     
    650
    100
    225
    975
    Namda � 1200
     
    650
    150
    -
    800
     
     
    500
    100
    150
    750
     
     
    400
    100
    150
    650
     
     
    500
    100
    250
    850
     
     
     
    380
    40
    310
    730
     
     450
    50
    400
    900
     
    6Tolerance GSM+/_ 10%+/_ 10%Min � 800+/_ 10%+/_ 10%+/_ 10%+/_ 10%+/_ 10%
    7Surface of Non Woven PlainRibVelourVelourPlainPlainPlainVelour
    8Thickness, mm4 max55-73 min3.25 +/- 0.753.23.23.5
    9Tensile Strength (20 * 5 cm) kgf
    M/C Dir
    Cross Dir
     
     
    > 35
    >45
     
    &bsp;
    Min 25
    Min 25
    &bsp;
     
    40
    60
       
     
     
    >18
    > 35
     
     
    > 31
    > 41
    &bsp;
     
    > 40
    > 40
     
     
    > 40
    > 40
    10Abrasion Resistance10000 Cycles3000 cyclesWeight Loss after 1000 cycles � 20 g/sq mWeight Loss after 100 cycles - < 0.5%Weight Loss after 100 cycles - < 0.5%Weight Loss after 100 cycles � < 0.5%Weight Loss after 100 cycles - < 0.5%Weight Loss after 100 cycles � < 0.5%
    11Burning Rate ISO 3795Conform to FMVSS 302  Conform to FMVSS 302         
    12Colour Fastness
    - To Light
    - To Washing
    - To Rubbing
    &bsp; > 6
    4 �5
    > 3 � 4
     
    > 5
    >4
    > 4
     
    6
     
               
    13Temperature stability Dimensional stage
    M/c direction
    Cross direction
         
    +/- 1.5%
    +/- 1.5%
            
    The following important features emerge from Table I
    1. PP and PES are the fibres mainly used in making needle punched fleece which forms the top surface of the carpet. In Maruti Zen, Esteem and GMI Opel Astra, blend of PP and PES is used.
    2. While single shade of fibre is used in manufacturing non woven in Tata Indica and Hyundai Santro, a blend of 2 to 3 shades of fibres is used to get the shade requirements in Zen, Esteem, Opel Astra, Fiat Uno and Toyota. When a blend of fibres is used, more precautions are needed to ensure uniformity in blend proportion and colour of carpet.
    3. GSM of the non woven fleece as well as final moulded carpet vary widely from car to car. GSM is lowest in Zen at 640 and highest in Esteem at 975
    . 4. Plain, Rib and Velour surfaces are found. For velour type, Dilour machine of Dilo would give the best appearance because of random and uniform lay of the piles. As most of the nonwoven manufacturers in India are not equipped with this machine, Diloop type machine is used with a suitable arrangement of fork needles in the board to get velour surface.
    5. Though abrasion resistance is an important specification, different manufacturers prescribe different methods of estimating the same. For Zen and Esteem, the number of cycles to rupture or cause a hole in top surface is prescribed. For other manufacturers weight loss after 100 or 1000 cycles of abrasion are prescribed.
    6. For assessing flammability, burning rate on a horizontal flammability tester as per ISO 3795 is prescribed by all. All manufacturers require conformance to FMVSS 302 specifications, which is 4 in/min
    . Apart from those specified in Table I, specifications for temperature stability, static compressibility, peeling force, fogging resistance, dielectric weldability, and freedom from odour are prescribed by some manufacturers like GMI. Maruti prescribes specifications for static electricity generation and half decay time. Since nonwoven manufacturers do not have facilities for these tests, they are required to take the assistance of Research institutions like BTRA. Some of the test methods are peculiar to automobile industry and have to be developed and standardized even in Research institutes. Raw material for needle punched top surface Polyester and polypropylene are the commonly used fibres for manufacture of needle-punched fleece, which forms the top surface of carpet. Their relative merits are discussed below
    1. The two fibres are nearly comparable in tensile strength though polyester fibre is available in higher tenacity grades.
    2. Elongation is higher in polypropylene. This gives some advantages in terms of reduced tear during moulding.
    3. Density of polypropylene (0.91g/cc) is much lower than that of polyester
    (1.38 g/cc). As a result thicker, loftier and more comfortable carpets are made with the former for a given area density.
    4. Polypropylene is dope dyed and is available in an extensive range of colours and shades. It is therefore much easier to achieve colour and shade matching by mixing a minimum number of shades of fibres. Dope dyed polyester, on the other hand, is available only in a limited number of colours and shades. The required shade has often to be developed through R&D work or fibre has to be dyed.
    5. Melting point of polypropylene (165oC) is much lower than that of polyester (260oC). Heating time, temperature and pressing time are therefore more critical in moulding with polypropylene.
    6. Flame retardancy by burning rate is inferior with polypropylene than with polyester. A flame retardant compound has to be added to the binder to meet the flammability requirements in Exports with polypropylene. This adds to the costs.
    7. Resistance to UV light is inferior with polypropylene compared to polyester. UV stabiliser has to be added during manufacture of polypropylene to improve its resistance to UV light.
    8. Polypropylene tends to form beads during carding. The beads get deeply loaded on the cylinder wire and also on the needles. There has to be a regular programme for removing the beads from the wire and needle. Achievable production rates are therefore lower with polypropylene than polyester because of card loading. Card processing problems are more acute with lower deniers and recycled fibres with polypropylene.
    Manufacturing Process
    Moulded carpet manufacturing can be broadly divided into 4 sections 1. Needle punching 2. Back coating of needle-punched fleece with binder 3. Lamination, Blank cutting and Moulding 4. Trimming, checking and packing. A typical flow chart for manufacturing moulded carpets is given in Fig. 1.
    Needle punching Needle punching line is similar to that in a normal nonwoven plant. The following steps may be beneficial in getting good quality at lower manufacturing cost.
    Fig I: Flow Chart for Nonwoven Moulded Carpets
    The opening line consists of a Bale opener followed by 2 beating points. Use of high capacity mixing bin with automatic laying of material and simultaneous spraying of antistat such as found in Empto mix of Hergeth is helpful in ensuring intimacy of mixing and in minimising shade variations from place to place. Further performance in carding is improved because of uniform application of antistat. Feeding chute to card should have controls like photocells and vibrator or pressure switch to ensure uniform density of feed sheet. Incorporation of micro weighing system at the top of chute whereby small pre weighed tufts are dropped into the chute will improve batt weight uniformity further. Card � Cross lap sequence is preferred to air laying because of long length of fibres used for making the felt. Since the fibre denier ranges from 6 to 15 d, card should be mounted with appropriate wire of coarser gauge. The card room should have a good humidification system with some control over temperature. This will minimise loading of cylinder, doffer and stripping rollers especially with finer denier. Loading of rollers not only causes production loss but also is a major source of variations in lenier density (gsm). Needle punching machine of 2m width would be adequate, as the length and width of the carpets of automobiles is below 2m.The needle punching may be done in 2 stages i.e., Pre needling line and a Finish needling line with a break in between. This has the advantage that if the gsm of the material is lower than the requirements, correction is possible in finish needling by the addition of a thin felt of required gsm. A continuous line with preneedling followed by finish needling does not provide such correction facility.
    Pre needling
    With Die pressed needles with regular barb spacing should be preferred as it minimises fibre damage and achieves uniform fibre interlocking. Further 3.5 inch needle should be used, as it allows wider gauge between stripper and stitching plate which in turn minimises distortion of the voluminous batt as it enters the needle loom. 32-34 gauge with a punch density of 90 � 100 punches /sq cm and depth of penetration of 11 � 13 mm depending on thickness of felt is normally used.
    Finish needling
    3 inch needle with close barb spacing has the merit that it allows all the barbs to enter the fleece with a relatively low depth of penetration. This improves consolidation and minimises fuzzy surface at the bottom. The lower needle length is also less susceptible to breakage. RB needle however gives more smooth surface. The penetration depth is between 10 � 12 mm with punch density of 150 � 250 punches/sq cm in case of plain carpets. In the case of ribs and velours, a lower punch density of 90 � 100 punches/ sq cm is used to enable easy penetration of fork needles at structure needle machine
    Structure Needling
    In case carpets with rib or velour surface, a structure needle loom is used after finish needling. Diloop loom or its equivalent is used by majority of manufacturers though as pointed out earlier, Dilour machine by Dilo gives a more random and uniform pile surface. According to the position of fork in the needle board, rib or velour surface is obtained. For products with rib surface, penetration side of the fork needle will be reverse side of the finish-needled material, as it will give compact ribs. On the other hand, penetration side of fork needle will be the same side of finish needling in case of velour surface as this improves velour effect. Penetration depth is 7 � 8 mm in ribs and 8 � 10 mm in velours. The normally used fork needle is of 25 gauge.
    Back Coating
    Back coating with a binder in the form of foam, followed by curing in a stenter gives dimensional stability and strength to the carpet. An auto foaming unit will be helpful as it permits automatic adjustment of foam ratio so as to get uniform pick-up. Acrylic binder is normally used as it gives the required strength. The binder pick-up is kept low as the material is going to be subsequently laminated with LDPE. As seen from Table 1, binder pick-up varies from 10 � 20 % for carpet where subsequent lamination is done. Foam ratio is one of the important characteristics to be monitored and kept under control during the process to minimise variations in binder pick- up which ultimately leads to variations in linier density of carpet. Curing of binder is carried out in a stenter through heating by electrical heaters kept on both sides of the material. Temperature on the binder face is kept at 140oC and on the fibre side at 110oC. Material speed is adjusted as per the material and binder pick up and is usually between 2 � 3 m/min. To cut down processing time and costs, thermo bondable binder is sometimes used. With such binder there is no need for lamination with LDPE powder/film. Thermo bondable binder is special styrene/ butadiene latex. The latex not only binds the fibres but also provides mouldability to the material. The binder film is thermoplastic with little softening in the region of 35 � 90oC. On further heating the softening increases very rapidly in the region of 120oC enabling moulding. The ratio of styrene to butadiene in the binder determines the stiffness and thermo plasticity of the binder.
    Lamination
    Carpets back coated with normal binder (acrylic) require lamination with LDPE powder or film or with both to enable moulding. The properties of LDPE powder have considerable influence on moulding. The average micron size of powder is 70 microns. For satisfactory moulding, the size of the granules should not be uniform throughout but should be variable from 30 to 100 with a peak value of 70. A distribution consisting of coarse and finer particles on either side of the average improves mouldability. The powder is dusted on the moving carpet on the back-coated side by an applicator, which is automatically controlled to achieve the required powder application. The material is then preheated in steps by electrical heaters to softening temperature and calendared by a pair of high-pressure calendars. Lamination of the powder on the carpet takes place as a result of softening and pressure application. With some products a pre-heated film is also introduced into the nip of calendar rollers along with the carpet, which causes lamination of film on the carpet.
    Blank Cutting
    Laminated carpets are cut to required length on a blank cutting machine. The length requirements vary with the car and is standardised after initial trials. Lengths are marked on the Table of bank cutting machine with different colours ( for identification) for the different cars.
    Moulding
    The laminated and blank cut carpets are gripped on either side by grippers and moved to a pre-heating zone. The LDPE lamination is softened during pre heating. After preheating for a specified time the material is taken forward to a moulding press consisting of a male and female mould. The moulds are fabricated accurately as per the design of car body. Since car body is a patent of the car manufacturer, the moulds have to be prepared after a formal agreement with them to protect secrecy. Moulds are made either of aluminium or resin bonded fibreglass. The former though more expensive has a longer life and has a cooling arrangement, which reduces moulding time and increases productivity. Time for pre heating and pressing in moulding are critical factors affecting quality of moulding. They are determined by type of fibre, gsm of carpet, type of binder and lamination. Carpets made out of high proportion of polyester require in general more preheating than those with high proportion of polypropylene. Heavier carpets require more pressing time. Time for pre heating and pressing are standardised for each type of car after initial trials.
    With some cars like Maruti, Namda, which is a bulky material made out of waste fibres, is attached to the underside of the carpet either during moulding itself or subsequently by an adhesive. Namda improves insulation and helps to absorb vibrations.
    Trimming
    After moulding the carpets are trimmed to shape on a trimming unit. The extra material at the sides used for gripping the carpet during moulding is cut out and holes are punched at different place to accommodate car parts like seat legs, break, clutch and accelerator pedals. Trimming unit is made to match car body perfectly in minutes detail so that trimmed moulded carpets fit perfectly in the car.
    Inspection
    The moulded and trimmed carpets are checked for fitment on car body or a template provided by car manufacturer. Minor defects in the carpets are mended. Carpets with major defects and improper fitment are rejected. As majority of problems come from improper fitment, a great care has to be exercised in trimming and inspection. Too reduce labour costs, some manufacturers get trimming and inspection done on contractual basis by an outside party.
    Heel Pad Fixing
    In some cases, heel pad is welded to carpet on a high frequency plastic welder. The object of heel pad is to prevent wear of carpet due to foot pressure from driver of car. Heel pad is usually of PVC material and car manufacturer gives specification.
    Final Checking
    Final checking for fitment is done on car body. As this is time consuming, it will not be possible to have 100% checking. So random checking of 15 � 25% of production is usually done. It would be advantageous to carry out checking some carpets on car body with seats in position.
    Major Quality Problems
    Some major quality problems in moulded carpets which lead to rejection of the material and precautionary measures to overcome them are discussed below.
    Colour Mismatch
    Non matching of colour of the carpet with the master approved sample and variations in colour and shade from place to place and lot to lot form a major source of rejection.
    The following precautionary measures will help to overcome this problem.
    1. Raw material (fibre) should be matched in colour against master sample in a colour cabinet. It is advisable to have two master samples representing the extremes in tolerable colour variation.
    2. Intimacy of mixing of components can be improved by increasing the number of layers in the sandwich and by having one more toppling before processing.
    3. Dope dyed fibre should be preferred to dyed fibre as better consistency in colour and higher fastness to rubbing and light is obtained with the former.
    4. Scope for improvement in fibre opening in the line should be explored by addition of Kirschner beater.
    Contamination
    Contamination with foreign material and fibres from previous lot arises because of inadequate cleaning of card wires and needle board and stripper and stitching plate. Molten plastic beads and nep like clusters in needle board also result in contamination. Card wires should be washed with petrol once a shift and during lot change. Needle board should be removed and cleaned with compressed air. Fibre clusters firmly adhered to the barbs should be removed with a wire hook. Needle board cleaning should be done once every 4 hours and at the time of lot change.
    Weight variations
    High variations in weight (gsm) and thickness from place to place cause rejections. The variations in weight can be at needling stage or during back coating. Stoppages of card due to loading of material on cylinder, workers, strippers and transfer rollers is one of the causes of variations in gsm. This problem is more often encountered with fine deniers and with polypropylene. Optimisation of antistatic spray applied on the fibre and maintenance of proper humidity and temperature in card room will help minimise loading. The card wire should be washed with petrol and damages in wire rectified. Lower doffer speed with higher web density will also be helpful. Control of foam ratio in the binder during back coating will also minimise variations in binder pick-up.
    Lines in the Fabric
    Two types of defects are common.
    1. Longitudinal lines running along machine direction of needle punching line, arise from broken or worn out needles. A proper schedule for replacement of needle should be drawn up and adhered to. Life of needle depends on type of needles, barb size, type of product, punch density, gsm etc. and it would be difficult to give a schedule for needle replacement that will hold good at all times. Phased replacement of needles in the needle board as suggested by Foster Needle Co., will help minimise lines caused by needle wear and breakage. Needle board should be divided into 3 parts as shown in Fig. 2. All needles occupying one third of the width of the board (section A) is replaced at a time after about 10-15 million strokes. Broken needles in other 2 halves of board ( B & C) are replaced by good needles removed from the board at this time. After another 10-15 million strokes, all needles in section B are replaced and broken needles in section A & C replaced by good needles retrieved from B The same process is continued after another 10-15 million strokes in Section C.
    Fig 2: Needle Replacement procedure
    . A A A B B B C C C After 10-15 ms After 20- 30 ms After 30-45 ms 2. Horizontal lines in cross direction of fabric at regular intervals arise because needles are penetrating in the same hole as fabric advances. This arises because net advance of fabric during a stroke matches with the distance between two adjacent rows of needles. The defect can be overcome by altering the slowly the stroke frequency while keeping fabric delivery speed constant.
    Shape Retention
    Rejection due to deformation or non retention of the shape of moulded carpet is another source of rejection. Moulded carpets laminated with LDPE film in general retain he shape much better than those laminated with LDPE powder. But lamination with film alone is more difficult and wrinkles are encountered if the speed of film is not properly controlled or if the film is not properly rolled. So a good compromise is to laminate with both powder and film. Improper packing and transportation of carpets also leads to loss of shape. If a large number of carpets are stacked one over the other and transported, those at the bottom get deformed. Carpets should be laid on specially prepared rack with number of trays conforming to the shape of carpet. The carpets in different layers should be separated from another.
    Improper Fitment
    Improper fitment is one of the major complaints. This is mostly due to improper trimming arising from wrong methods or improper tools. Use of pre heated knife helps in getting sharp cuts. The tools used for cutting holes should be checked for wear and tear and sharpness. The car body used for checking carpets in moulding plant must match accurately in shape with the cars in automobile manufacturing unit.
    Holes in Carpet
    Excessive pre heating is one of the causes of holes particularly at corners. Excessive tensioning of material during moulding may also contribute to holes. Mould should be free from burrs or scratches or extraneous matter.
    Wrinkles in Carpet
    Wrinkles are caused because of inadequate or excessive pre heating or inadequate tensioning of material during moulding. Pre heating time has to optimised for different types of fibres and area density of carpet.
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