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Coating

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.