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Coating and Laminating

Coating and lamination techniques are used to impart properties to fabrics which are not necessarily those naturally assumed by textile fabrics. Having widespread application across a range of technical textiles sectors, they increase functionality and durability as well as value. They can include; waterproofness, increased abrasion, stain, flame and UV resistance, retro-Reflectionhttp://missionscience.nasa.gov/ems/03_behaviors.html or Fluorescence?, anti microbial or Phase Change Materials.

These functions can be imparted using a range of application methods, dictated by the materials being processed and the required outcome, whether they are applied as a coating or laminate is also determined by this criteria. The definition between the two is a technicality relating to the application method, generally coatings are applied to a fabric in their preparatory state, often in liquid form. Lamination requires the pre-preparation of a laminate membrane that is then applied to the textile.

The application for coated and laminated textiles is widespread across a variety of technical textile sectors, these include; 

Sector

Application/Role

Automotive and Aerospace

Vehicle interiors- textiles often laminated onto interior components such as door panels.

 

Medical and Hygiene

Anti Bacterial Coatings

Waterproof breathable Hydrophilic? membranes

 

Construction and Engineering

Tarpaulins

Bulk bags

 

Interiors

Upholstery- Stain resistance

UV resistance

 

Technical Apparel and PPE?

Waterproof Breathable Membranes

Phase Change Materials

Fluorescence?

 

Apparel

Fashion, luggage and accessories- textured looks such as high shine or ‘wet’ look

PVC/Faux leather

 

Sports and leisure

Sail cloth

Bouncy castles

 

Coatings and laminates will interact differently with the fabric; this is due to the way in which they affix to the textile surface. Figure A demonstrates how a coating covers the surface of the fabric, as applied in liquid form, it is able to penetrate the fabric structure, filling the air pockets and bridging the interstices. Figure B depicts how a laminate sits on the fabric surface, the fabric retains its air pockets and the laminate has fewer points of contact. 

Fig A

Figure A. Schematic of a coated textile

Fig B

Figure B. Schematic of a laminated textile. 

As with both lamination and coating the bonding mechanism is of importance. The bonding can occur through the thermoplastic qualities of the coating or laminate, whereas it is heat set, although this is not appropriate for all materials, so solvent or water-based adhesives are used. The use of adhesives is a highly technical area, as gaining a strong yet flexible bond can be a challenge.

Fabric pre-treatment prior to coating is important, particularly its stabilisation, as some coatings bridge the interstices within the textile, and for the coating to remain functional this must remain the case. Therefore ensuring a fabric is stabilised prior to coating limits the risk of movement within the fabric structure which may impact on the coating or laminate applied. 

The end product is sometimes referred to as a composite, as it is a composition of a textile and non-textile component. Many of the mechanical properties are determined by the fabric, such as tear strength, the coating largely determines the chemical properties, and the handle is often determined by both.

It is not just technical applications which utilise coating and lamination technology, the fast paced fashion market is constantly giving the technology new challenges with the need to create innovative and visually interesting looks such as a high shine, futuristic finish, or imitation animal skin. 

 

The Textile Institutes defines a coated textile as;

“A material composed of two or more layers, at least one of which is a textile fabric and at least one of which is a substantially continuous polymeric layer.”

This Polymeric layer is applied in liquid form in a solvent or water base, which evaporates off to leave the polymer behind, applied to one or both surfaces. Dependant upon the application method the liquid may require thickening so it does not soak through the fabric, or an anti-foaming agent to aid processing. The thickness of the coating, or amount of product applied is controlled. Bonding occurs either through the drying process (evaporation) or through a curing process, required to provoke crosslinking.

The term coating can apply to the adherence of a textile membrane to the fabric surface, or to a coating of micro or nano particles that adhere to the fibre surface forming a ‘substantial’, but not necessarily ‘continuous layer’. Figure 1 depicts what is traditionally viewed as a coated fabric; the fabric is coated on one side, and would be visible to the naked eye and detectable by fabric handle. Figure 2 displays a fabric coated with microencapsulated Phase Change Materials (PCM’s), unlike a traditional coated fabric this would not be visible on the fabric surface as the adherence is between micro sized particles and the fibre, not the fabric structure. This coating technique is used to add agents such as microencapsulated ingredients containing; fragrances, cosmetics, FR agents, Anti microbial agents, or materials such as; cyclodextrines, abrasion or stain resistant materials, and UV blockers. As they are often at the micro or nano scale, they are not visible by the naked eye, though adhesive agents or surfactants used in their application may display a residue, but this is not ideal. Dependant upon the end requirements, coatings such as those displayed in figure 2 they should have little if any impact on fabric handle.

Fig 1

Figure 1. Image from; http://www.walkandramble.co.uk/Glossary/GlossaryT.html Low Alpines, Triplepoint fabric

Fig 2

Figure 2. Image shows PCM’s in a textile. From; International Journal of Clothing Science and Technology http://www.emeraldinsight.com/journals.htm?articleid=1501621&show=html

The chemical formation of the coating is dictated by the end use. This formation may contain a range of functional additives to improve the mechanical properties, increasing durability, fire retardant or UV resistant properties. Table 1 outlines a range of properties imparted using different coating chemicals.  

Table 1

Table 1. From; A review on coating and Lamination in Textiles; Processes and Applications http://article.sapub.org/10.5923.j.ajps.20120203.04.html

In coatings, the melted, liquid version of the polymeric substance is sometimes used, for example in calendering. If this is the case then the melt temperature (Tm) of the applied coating must be outside of that which will be experienced during use. If this is not possible, it is more appropriate to create a pre-prepared membrane, applied through a lamination technique. 

 

Knife Coating (floating knife) or Direct Coating

In Knife Coating, as seen in Figure 3, the liquid coating is applied to the fabric while being run at tension under a floating knife blade, the distance between the fabric and the knife blade determines the thickness of the coating. The blade can be angled and have different profiles to affect the coverage. For this process to be effective the liquid coating must be quite viscous in order to prevent it soaking through the fabric, the coating is then dried or cured. 

This technique is best used for Filament? yarns as the staple fibres in spun yarns can protrude on the surface creating an un-even finish, but this is dependant upon the thickness of the applied coating. For this type of coating to be most successful the weave structure has to be quite tight and the fabric capable of being held taught. 

Fig 3

Figure 3. Fung, W, 2002, Coated and Laminated Textiles, UK;Woodhead Publishing; http://books.google.co.uk/books/about/Coated_and_Laminated_Textiles.html?id=U0Rh-TrvMz4C

Direct Roll Coating

In this process coating liquid is rolled onto the fabric by a roller suspended in the coating solution, often a blade is positioned close to the roller to ensure not too much coating solution is applied. 

Fig 4

Figure 4. Direct Roll Coating from;Sen, A K, 2008, Coated Textiles; Principles and Applications, 2nd Edition, USA;Taylor and Francis.

http://books.google.co.uk/books?id=4K7-VM6T2A4C&printsec=frontcover#v=onepage&q&f=false

Pad-Dry-Cure

Also referred to as Padding?, this technique, widely regarded as a textile finishing technique, can in fact be used to add a variety of coatings, but this usually refers to a fibre coating for the application of micro or nano materials or chemical compositions.

As shown in figure 5, the fabric is submerged in the coating solution then the excess squeezed out in the rollers, which dictates the pick-up percentage, the fabric is then dried and cured. 

Fig 5

Figure 5. Image adapted from; http://www.kenencoregroup.com/aloevera-finish.html

Calender coating

Calender finishing involves the fabric passing through a set of heated rollers to singe off any surface fibres and add lustre and smoothness. Calender coating is the same principle in which the fabric passes through heated rollers, but through this process a coating is applied as demonstrated in figure 6. This image demonstrates the simultaneous coating of both sides of the fabric with the thickness of the coating determined by the width of the nip in-between the rollers, more rollers used can provide a thinner coating. 

Fig 6

Figure 6. Depicts calender coating. Image from; TPO coated PP fabrics and their applications  http://www.fibre2fashion.com/industry-article/pdffiles/16/1526.pdf

Hot melt extrusion coating

Hot melt extrusion coating is applied in the same process as calendering with the coating being melted from granules fed to heated rollers which then nip the coating to the fabric. It is used to produce un-supported films and these freshly produced films are added direct to fabric. Its uses are mainly for Thermoplastic polymers such as Polyurethane, Polyolefin’s and PVC.

Foam Finishing

Foam finishing was developed as a more environmentally friendly version of the pad-dry-cure system, as the chemical applied requires less product in weight, but equates to a high surface area. Foam also ensures less wetting takes place, which requires less drying; furthermore waste is reduced in terms of residual liquor. This technique is useful in coating heavy fabrics such as carpets and can be used to effectively coat only one side. 

Laminated textiles consist of one or more layers of textile and component. The Textile Institute defines a laminated or combined fabric as;

‘a material composed of two or more layers, at least one of which is a textile fabric, bonded closely together by means of an added adhesive, or by the adhesive properties of one or more of the component layers’

This adhesive is required to bond the fabric and component layers together. Creating a strong bond, which will not deteriorate through conditions experienced in use such as movement and laundering, is not the biggest challenged faced. Adhesives are often associated with making the fabric too rigid and thus affecting the handle, which is often a negative characteristic, particularly for applications in performance clothing where comfort is a requirement. Environmental consideration has led towards more interest in hot melt adhesives, rather than solvent based adhesive, or the use of flame adhesion. (ref to  http://article.sapub.org/10.5923.j.ajps.20120203.04.html  )

Laminated fabrics are widely used in high performance apparel where fabrics are required to be waterproof yet breathable. In this case a laminate membrane Laminates often consist of a non-textile membrane sandwiched between 2 textiles, for example in the case of the micropourous membrane Gore Tex.

Fig 8

Figure 8. Gore Tex laminated fabric depicts the functions for the different layers. Image from; Gore-tex?.co.uk/">www.Gore-tex?.co.uk

Usually the reverse or technical back of the fabric surface is laminated, so as to not affect the look of the fabric, and in the case of the Hydrophilic? membranes, these are more effective worn close to the body. As in the gore tex example, the membrane or laminate is often sandwiched between two fabric layers. However this is not the case for fashion fabrics where the look is the priority over function. Lamination is carried out on the fabric surface to produce some visually interesting designs such as foil holograms or textures. 

Lamination is widely used in garment manufacture where woven or non-woven fabrics are pre-prepared with thermoset adhesive. These are then cut and applied to the fabric as part of the manufacturing process to provide reinforcement, for example of a button hole, or to give shape and stability, for example in a collar. These ‘fusible’s’ are applied under heat and pressure for a specified time, to set the thermo adhesive.  

 

Flame Lamination

This technique is mainly used to attach foam to a textile fabric, which is widely used in automotives. As displayed in figure 9 the foam is presented to the flame, which encourages melting; as it then dries it bonds the textiles. This technique has associated health and safety risks due to the release of gases when melting takes place.  

Fig 9Figure 9. Flame lamination. Image from; www.textileworld.com http://www.textileworld.com/Articles/2003/January/Nonwovens_Technical/Combining_Nonwovens_By_Lamination_And_Other_Methods.html

Hot melt lamination

There are two processes involved in hot melt lamination, the application of a thermo-set adhesive, and the fusing of the fabric and the non-textile component through heat and pressure. Adhesive is applied either to the whole surface, or discreet, where the adhesive is applied as a thermo-set, which just attaches in patterns, such as glue dots. Discreet provides greater flexibility due to the reduced contact areas.  

Fig 10

Figure 10. Hot Melt Gravure Lamination, image from; www.beckmannconverting.com http://beckmannconverting.com/optional_section3/full.cfm?ID=152