Coated and Laminated Textiles Process and Application

Coated and Laminated Textiles Process and Application
Mr. Rushikesh Ashok Tarlekar
Department of Textile Technology
DKTE Society's Textile & Engineering Institute,
Ichalkaranji , Maharashtra, India.
Email: tarlekarr007@gmail.com


Abstract
Textiles are made impermeable to fluids by two processes, coating and laminating. Lamination consists of bonding pre-prepared polymer film or membrane with one or more textile substrates using adhesives, heat, or pressure. Coating is the process of applying a viscous liquid (fluid) or formulated compound on a textile substrate. In this paper we have gone through several methods of production used to manufacture a wide range of coated fabrics. Broadly, they are knife coating (Direct Coating), transfer coating, foam coating, hot melt coating, calender coating. The laminates are classified as Rigid laminate, Flexible laminate, Waterproof, Breathable laminate. A review is made on Coated and laminated textiles applications in Defense, Marine, medical, military, household, sports, and many other diverse end-product uses.

Introduction

Coating can be defined as "it is a composite textile material where the strength characteristics other components properties are improved by applying a suitable formulated composition" The selection of fibre or fabrics for coating depends upon type of coating and use performance required. The layers are bonded closely together by means of an added adhesive or by the adhesive properties. the performance of the coated and laminated fabric is checked by the properties like tensile and tearing strength, stiffness, dimensional stability, thermal stability, etc. To meet above requirements proper choice of fibres, fabrics and it's construction also polymeric coating compound are required.

Coated textile
Fig: Coated textile
Polymers Used for Coating

1. Polyurethane
Very variable compositions; properties range from inflexible, plastics to elastic, soft coatings. Some grades have good resistance to fuels and oils. Plasticizers not required. Excellent strength and resistance to tearing and abrasion . Moderate to high cost. Thermoplastic grades available.

Products/End Uses
2. PVC (Polyvinyl Chloride)
Naturally rigid material; requires careful formulating to produce durable, flexible coatings. Good chemical properties, although solvents tend to extract plasticizers and stiffen the polymer. High plasticizer content (up to 40% by weight) . Good weathering properties and flame resistance. Unless special plasticizers are used, poor low temperature performance. Thermoplastic and can therefore be seamed by hot air, ultrasonic welding techniques and radio-frequency. Low cost.

Products/End Uses

3. Rubber
Rubbers are soft and elastic at room temperature. Between the chains, there are physical entanglements acting ‘physical crosslinks’. Good resistance to heat aging, UV light, general chemical attack, oxidation, ozone. Low permeability to gases . Serviceable temperature range -50 to +125.C. Low to moderate cost.

Products/End Uses

  • Carpets
  • Packing material
  • Conveyer belt
4. PTFE (polytetrafluoroethylene)
Exceptional resistance to chemicals, micro-organisms, heat, solvents, oxidation and weatherin. Difficult to seam . Excellent electrical and non-stick properties. Serviceable temperature range -70 to +250.C.Very high cost.

Products/End Uses

  • Architectural purpose
  • Food and medical uses
  • Gaskets
5. Silicone
Silicone has good resistance to chemical and micro organisms. It is odourless . High tear resistance. Low toxicity, water repellent and some Breathability . It's temperature service ranges from 60°C to 200°C.

Products/End Uses

  • Lightweight covering
  • High profile tarpaulin
  • Woven curtains, Bags, etc
Compounding of Polymers (Resins)
Note that, the word ‘resin’ has become almost interchangeable with coating compounder polymer, within this context. Resins are supplied as emulsions or as solutions in water or solvent .The overall task of the compounder is to formulate a mixed compound which will process without problems. It should also be able to produce the coated fabric properties required by the customer – at the correct price. Material selection and formulation of recipe is where the compounder’s task starts. It also includes the physical mixing of all ingredients to produce uniform mix. This mix has to be stable during coating process as well as storage. Sometimes because of premature cross linking, poorly formulated compounds can develop lumps or go thick.

Coated Fabric Manufacturing Techniques
The original methods of coating were largely based on various impregnating techniques based on an impregnating trough followed by a pair of squeeze rollers to ensure a constant pick-up. Usually on a stenter, the material was then air dried at constant width and rolled. When the coating was required on one side of the fabric then total immersion of the fabric in the coating liquor was not possible and other techniques had to be developed.

1. Knife Coating
Knife coating is one of the oldest coating methods and is also known as spread coating. A dry, smooth fabric is fed over the bearer roll under a knife known as a knife or doctor blade. The coating material is poured in front of the knife by a ladle or by a pump over the entire width of the web. As the web is transported under the knife, the forward motion of the fabric and the fixed knife barrier give the viscous mass of the material a rotatory motion. This is known as the rolling bank that functions as a reservoir of coating compound in front of the knife. To prevent the fluid from spilling over the edges of the fabric, two adjustable guard plates known as dams are also provided. Proper tension is applied on the fabric as it is unwound, so the fabric is taut under the knife. Most machines can coat fabric widths up to 1.5 to 2.0 m, but specially designed machines can accommodate widths up to 4 m. Special care is taken that the material has adequate viscosity so that it does not strike through the fabric. The coated fabric then passes through the drying oven. The rate of evaporation of the solvent determines the rate of transport of the fabric and, thus, the coatingrate. The coating thickness is mainly controlled by the gap between the knife and web.

During application of the coating material, an important phenomenon occurs Wetting of the textile substrate. Wetting determines penetration and adhesion of the coating. When the coating material is poured, it spreads on the textile sub-strate and is wetted. The wetting property depends on the solvent. After a lapse of a few seconds, the solvent starts evaporating. The time lapse between application and evaporation is the period of equilibrium wetting. During spreading, the contact angle is zero, and as the solvent evaporates, there is an increase in viscosity, causing shrinkage and an increase in contact angle. The movement of the solvent front then ceases. This process allows for control of the coating process. 


Knife Coating mainly classified in four techniques:

    a. Knife over air. 

    b. Knife over roller
    c. Knife over slot. 

    d. Knife over blanket

a. Knife over air
The figure shows that knife over air or floating knife process of coating. Here the knife is fixed over the substrate and the doctors blade presses the upper surface of the substrate and forces the coating layer to penetrate into the substrate. The amount of coating applied is controlled by fabric tension and dimmention of the knife. The sharpness of the blade, alignment angle and degree of depression into the substrate influence the amount of coating applied.

Knife over air
Fig: Knife over air
b. Knife over roller
In this method of coating the knife blade is suspended above the roller. The roller is made up of steel or rubber coated. Here the knife is does not touch the substrate directly and there is a gap between substrate and knife which controls the thickness of the coating.

Knife over roller
Fig: Knife over roller
c. Knife over slot
In this method of fabric coating the slot is provided for the application of coating material on to the substrate. The figure shows that the roller over which the fabric is passed continuously with constant speed and tension. The coating material is present over the fabric guided by the slot and uniform application of coat on the fabric takes place. The thickness of coating is varied by varying the distance between slot and substrate.

Knife over slot
Fig: Knife over slot
d. Knife over blanket
In the knife over blanket arrangement, the web is supported by a short conveyor in the form of an endless rubber blanket stretched between two rollers. Because the tension applied on the blanket results in a uniform pressure between the knife and the substrate, the fabric is not subjected to stretching in this arrangement. It is possible to coat dimensionally unstable substrates with this technique.The amount of coating is dependent on the tension of the blanket, which is adjusted by the rollers. Care should be taken that there is no damage to the blanket and that no foreign matter is adhered on the inside of the belt, as this will result in irregularity in coating weight.

Knife over blanket
Fig: Knife over blanket
2. Transfer coating
Layout of transfer-coating process
Figure: Layout of transfer-coating process: (1) release paper, (2) first coating head, (3) first oven, (4) second coating head, (5) textile substrate, (6) laminating nip rolls, (7) second drying oven, (8) coated fabric take-off roll, and (9) release paper wind roll.
A layer of coating is applied on a release paper in the first coating head and then passed through the first oven, where it is dried and cured. This forms the top surface of the coated fabric. The release paper is usually embossed. The pattern of the paper is thus transferred on the coating. This is known as the top coat.

In the second coating head, an adhesive layer known as the tie coat is applied on the dry top coat, previously laid on the release paper. The release paper thus has two layers, the dry top coat and the tacky adhesive tie coat.

The textile substrate is then adhered to the release paper containing the top and the tie coats, while the tie coat is still tacky. The lamination is done by a of nip rolls. The composite layer is then passed through the second oven to dry and cure the tie coat.

The release paper is finally stripped off, leaving the coated textile.

3. Hot melt extrusion coating

Extrusion coating
Figure: Extrusion coating: (1) extruder, (2) die, (3) chill roll, (4) backup roll, and (5) pressure roll.
In extrusion coating, an extruder converts solid thermoplastic polymers into a melt at the appropriate temperature required for coating. This melt is extruded through a flat die vertically downwards into a nip of the coating rolls.

Two rolls at the nip are a chromium-plated chill roll and a soft, high-temper-ature-resistant elastomer coated backup roll. The chill roll is water cooled. The heat transfer should be adequate to cool the coated fabric so that it can be taken out of the roll smoothly. Means are provided to adjust the position of the die and the nip in three directions. The chill roll may be polished, matt finished, or embossed. Lamination can be done by introducing a second web over the chill roll. The molten resin acts as an adhesive. Extrusion coating is especially suitable for coating polyolefines on different substrates. Because polyolefines can be brought down to low viscosity without risk of decomposition, very high coating rates are achieved, and as such, the process is highly economical. For other polymeric coatings, including PVC, PU, and rubber, this process does not yield uniform coating across the width, particularly at thicknesses below 0.5 mm.In this method, the coating width can be adjusted by reducing the aperture of the die by insertion of shims. Thus, it is possible to coat different widths for a given die; however, the coating width cannot be changed while coating. Moreover, the process does not permit easy changeover of material. This restricts its use for coating industrial fabrics. A view of an extrusion coating plant is shown in above Figure

4. Calender coating

Calender coating
Figure: Calender coating
A calender is used for coating polymer directly onto the fabric or for making unsupported film that may be subsequently coated to a fabric.A calender is a series of hard pressure rollers used to finish or smooth a sheet of material such as paper, textiles, or plastics. Calender rolls are also used to form some types of plastic films and to apply coatings. Some calender rolls are heated or cooled as needed. The figure shows that 3 and 4 roll calendering action to apply the film on fabric. The arrow indicate place where material feed to coat the fabric. Calendering is a finishing process used on cloth and fabrics. A calender is employed, usually to smooth, coat, or thin a material.

With textiles, fabric is passed under rollers at high temperatures and pressures. Calendering is used on fabrics such as moire to produce its watered effect and also on cambric and some types of sateens.

5. Rotary screen coating

Rotary screen coating
Figure: Rotary screen coating: (1) web, (2) squeegee, (3) screen, (4) whisper blade, and (5) backup roll.
The rotary screen coating method is common for the coating and printing of textiles. The coating head is a screen that is a seamless nickel cylinder with perforations. This screen rests on the web. A squeegee is mounted in the screen, serving as the supply and distribution pipe of the coating paste. The squeegee blade, which is mounted to this pipe, pushes the paste out through the perforations of the screen in the form of dots that merge together to form a continuous coating. A whisper blade assists the coalescing of the dots to form a smooth, compact coating. A backup roll is provided for counter pressure. After coating, the coated material is sent to an oven for fusion of the polymers. The amount of coating applied is determined mainly by the mesh number of the screen, the squeege pressure (i.e., the angle between the blade and the screen), and the viscosity of the paste. Depending on the mesh size and design of the screen, continuous coating, coating of complex pattern, and dot coating can be done. In continuous coating, the coating can be up to 200 g/m2, by proper choice of the screen. Dot coating is useful for making fusible interlinings for both woven and nonwoven fabrics. In this process, the screen, the web, and the counter pressure roller all have the same speed. The coating is, therefore, done without tension and friction. Consequently, delicate and stretchable fabrics can be coated without difficulty. The coating is accurate, and the penetration can be controlled. A relatively new development by Stork (Stork Brabent, Holland) is the screen-to-screen technology (STS). Basically, the process consists of two screen-coating heads, back to back, each with its own coating feed system, squeegee roll, and whisper blade to smooth out the applied compound. The substrate travels between the screen either in a horizontal or a vertical position (depending on the model), and the compound is gelled/cured with infrared (IR) heaters. With STS technology, it is possible to coat (different colors) or print both sides of a substrate in one pass.

The Add on is controlled by:-

  • Resin viscosity.
  • Meshing of cylindrical screen.
  • Speed of machine.
  • Squeezing pressure.
6. Kiss Roll coating
A typical arrangement of kiss coating is shown in Figure. The pickup roll picks up coating material from the pan and is premetered by the applicator roll. The coating is applied on the web as it kisses the applicator roll. The pickup roll may be rubber covered, and the applicator roll may made of steel. The metering is done by nip pressure, and consequently, the amount of material coated on the web is dependent on nip pressure, speed of the operation, roll hardness, and its finish. The coating weight and splitting of the film as it leaves the roll are also dependent on web tension.

Kiss Roll coating
Figure: Kiss Roll coating:- (1) pickup roll (2) applicator roll.
7. Gravure Roll coating
Gravure Roll coating
Figure: Gravure Roll coating: (1) gravure roll, (2) backup roll, (3) doctor blade, and (4) smoothening rolls.
The use of a gravure roller in coating has been adopted from the printing industry to print designs. Engraved rollers are utilized in gravure coatings to meter a precise amount of coating on the substrate. The coating weight is usually controlled by the etched pattern and its fineness on the gravure roll. There are a few standard patterns, including the pyramid, quadrangular, and helical. For lighter coating weight, a pyramid pattern is used. In a direct, two-roll gravure coater (Figure ), the coating material is picked up by the gravure roll and is transferred to the web as it passes between the nip of the gravure and the backup roll. The pattern may be self-leveling, dependent on viscosity of coating material or the coated web is passed between smoothening rolls.

8. Reverse Roll coating

Reverse Roll Coating
Figure: Reverse Roll coating
Reverse roll coating is a roll-to-roll coating method for wet coatings. It is distinguished from other roll coating methods by having two reverse-running nips. The metering roll and the applicator roll contra-rotate, with an accurate gap between them. The surface of the applicator roll is loaded with an excess of coating prior to the metering nip, so its surface emerges from the metering nip with a precise thickness of coating equal to the gap. At the application nip, the applicator roll transfers all of this coating to the substrate, by running in the opposite direction to the movement of the substrate, wiping the coating onto the substrate.

Reverse roll coating machines demand high specifications in their construction, e.g. for the machining and bearings of the rollers and for highly uniform speed control. This makes them relatively expensive compared to other coating technologies. Unlike many other coating methods, they can however handle coatings with a very wide range of viscosities, from 1 to more than 50000 mPas, and are capable of producing extremely polished finishes on the coatings they apply. They have been produced in a variety of 3-roll and 4-roll configurations.

Products that have been manufactured on reverse roll coating machines include magnetic tapes; coated papers; and pressure sensitive tapes. The rise of slot-die coating has tended to eclipse reverse roll coaters as in most if not all cases, the same products can be made on cheaper machinery.

Applications of Coated Fabrics:

1. Agriculture:-

  • Bulk container. 
  • Making bags
  • Seed/Crop covers. 
  • Pond liners
2. Construction:-
  • Safety fencing. 
  • Wind covers
  • Conveyer belting. 
  • Safety vests
3. Clothing:-
  • Rainwear. 
  • Shoe upper and linings
  • Artificial leather. 
  • Water/Stain repellent fabric
4. Geotextiles:-
  • Settling pond liners. 
  • Irrigation liners
  • Erosion barriers. 
  • Landfill liners and covers
6. Home Furnishings:-
  • Upholstery. 
  • Drapery backing
  • Carpet backing. 
  • Bedding
7. Industrial:-
  • Filtration. 
  • Barrier material
  • Conveyer belts 
  • Field covers
8. Medical:-
  • Plaster. 
  • Gloves
  • Implants. 
  • Upholstery
9. Transportation:-
  • Aircrafts. 
  • Tyres
  • Airbags. 
  • Seating for automotive
10. Sport / Leisure:-
  • Athletic shoes. 
  • Rainwear
  • Artificial leather/bags/belts. 
  • Football
11. Protective:-
  • Aprons and Gloves. 
  • Chemical suits
  • Footwear space suit. 
  • Ballistic protection
12. Packaging:-
  • Gas holdings. 
  • Barrier packaging
  • Waterproof material 
  • Bulk containers
Fabric Lamination:
A illuminati fabric is a two (or more) layer construction with a polymer film bonded to a fabric. Laminated fabrics are used in rainwear, automotive, and other applications.

In the apparel industry handle and flexibility are of major importance. The durability to flexing and to washing is also important. Therefore, finding the best method and adhesive materials for a durable bond and applying them in a controlled manner to maintain the fabric flexibility and aesthetics during the lamination process is where the problem arises. For a bond of high strength, it is generally necessary for the adhesive to penetrate the material and to cover the widest possible surface area. The challenge is to select the best adhesive and application process which has the least effect on the substrate aesthetics. This factor is especially important when waterproof breathable fabrics are being prepared by lamination of a membrane to a fabric. Ideally, the least amount of a highly effective adhesive should be applied. It is usual to apply the adhesive – hot melt powder or moisture curing polyurethanes – in dot or discontinuous form. The waterproof breathable films are generally very thin and delicate materials and require considerable skill and care to handle without creasing.

The laminated fabrics are classified as follows:

  1. Rigid Laminate
  2. Flexible Laminate
  3. Waterproof Breathable Laminate
1. Rigid Laminate:-
Rigid laminates are composite product made of thin layer or sheets combined by adhesive usually they consists of several layers of fabric or other fibrous type of materials cemented or bonded together by resin to make a rigid plastic like material of any desired thickness both thermoplastic and thermosoftning resins are used.

Thermoplastic resins soften and melts under the application of heat and harden after cooling this action is reversible.

Resins used are:-

  • Polyesterene
  • Acrylics
  • Polyoliefin
  • Polyester, Etc
Thermosoftning Resins:-
Where subjected to heat curing hardence permanently usually via cross linking this action is irreversible. Subsequent heating may soften the material, but it is not possible to restore the resin. The resins used are

  • Epoxies
  • Formaldehyde
  • phenolic Aldehyde.
2. Flexible Laminate:-
Flexible laminating products are produced by laminating 1 fabric to another fabric by using thermoplastic resin aur aur or thermoplastic films flexible fabric laminates could also be laminate for fabric to films.

Film such as vinyl, polyurethene or polyester are bonded two fabric with heat and pressure. This method is used for flexible Laminates and allows large rollers to be produced on continuous operation.

3. Waterproof breathable Laminates:-
"GORETEX" is an outer wear breathable waterproof laminate fabric. This fabric is made up from microcorus, polymeric film of polytetrafluoroethylene (PTFF) having a thickness of 0.001 inch and more that 82% of the course having size 0.2 micrometer by laminating this type of fabric to cotton, rusti-c blander or nylon fabrics one can produce the fabric which are flexible, gives comfort to the wearer and this laminate is waterproof and durable to home washing.

Lamination by Adhesives:

General lamination method of with hot melt
Figure:- General lamination method of with hot melt: 1. adhesive coated fabric, 2. IR Heater, 3. laminating rolls, 4. second fabric, 5. laminate
The process of lamination involves the bonding of two webs. The webs may be fabrics, textile and foam, and textile and film. The bonding is usually done by adhesives. The adhesives used for the purpose may be solvent based, aqueous emulsion, or hot-melt. Solvent-based adhesives wet the surfaces easily and are easier to dry but are not eco-friendly. Water-based adhesives are safer but use a lot of energy in drying. Solvent- and water-based adhesives are usually applied by kiss coating or rotary screen printing. Hot-melt adhesives are preferred for lamination, as the process is cleaner. Lamination modifies the physical properties of the components and usually produces a stiffer product. This may be due to the nature of the adhesive and the extent of penetration. Selection of the hot-melt adhesive for a particular application is, therefore, important. Waterproof breathable films are invariably laminated between two fabrics (i.e., a shell fabric and a liner fabric). As previously discussed, adhesive nets or powders are used in these cases to retain breathability.

In lamination, the adhesive is generally applied on one of the webs, and the second web is bonded to it by heat and pressure. The common methods of application of hot-melt adhesives on a fabric. They are extrusion coating, dry powder coating, powder dot coating, and engraved roller coating. It was discussed that a laminate can be produced by passage of a second web between chill and backup roll in extrusion coating. In all other methods, the adhesive-coated web can be laminated to a second web by passage through the nip of two rollers shown in figure.

References:-

  1. Coated and Laminated Textiles by Walter Fung
  2. www.fibre2fashion.com
  3. www.slideshare.net
  4. www.wikipedia.org
  5. www.textileschool.com
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Mazharul Islam Kiron is a textile consultant and researcher on online business promotion. He is working with one European textile machinery company as a country agent. He is also a contributor of Wikipedia.


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