By: Carme Salgado
TECNITEX INGENIEROS S.L.
Textile coating can be defined as the process of depositing a resin over a textile substrate, on one or two sides. Different to the chemical finishing, which consists of the impregnation of the fibres, not only are the yarns coated, but also the spaces in between them. The different characteristics between the substrate and the coating product are combined to produce a new structure that acquires the best properties of each component: fabric and resin.
There are different procedures for the coating of textiles and not all are suitable for all products or substrates.
One of the procedures most used is direct coating, which is based on the application of one or various layers of polyurethane, PVC, acrylic resins, etc. paste, over the textile substrate, using a scraper, knife, cylinder, etc.
Foam coating consists of submerging the textile material in a bath which contains the foam compound using a solution or a watery dispersion and afterwards draining off the excess liquid. A similar process is the coating that is done by foam flattening, which is used for fabrics with an open structure, that cannot be coated by the direct system. The difference between this and the former method is that the solid content in the foam compound is greater, reducing the penetration into the fabric and, in this way, allowing fabrics that are smoother and of a better drape to be made.
To get articles known as "artificial leather", the transfer coating method is used, which consists of the application of one or various layers of a polyurethane paste onto non-stick paper or separator, which is later transferred to the textile substrate.
In calendar coating five or more cylinders are placed in various positions, that with there rotation break and smoothen the coating to obtain a layer with a uniform thickness.
The process of coating via polyurethane coagulation implies a solution of polyurethane and its later extraction under controlled conditions for its precipitation or coagulation. The material obtained is smooth and has a porous structure.
Finally, there is the Hot Melt coating, using the extrusion method for polyolefins, or the dry powder coating method (dot coating and scatter coating) for polyethylene, polyamide, polyester and EVA.
The possible uses of coated fabrics are many, with applications in agriculture: containers, fencing, coverings for crop protection, bags, shading materials, etc. In the civil engineering field they are used as geotextiles for soil waterproofing in landfills.
In construction, their application can be found in waterproofing materials for covers or in textile architecture.
The use of coated fabrics is common in industry, in transmission belts, conveyor belts or barrier materials.
Equally, in the field of health, coated fabrics are used as barrier materials, implants, incontinence products, hospital equipment and hygiene products.
Textile coatings are common in gloves, cut resistant materials, clothing for clean rooms, fire, bad weather or NBC protection clothing, high visibility clothing, etc.
They also have their applications in the sports (shoes, anoraks, etc.) and leisure sectors (haversacks, camping tents, sleeping bags, etc.)
The possible uses of coated textiles are constantly growing, especially the breathable and waterproofing textiles. With this increase, there is a notable variation in the materials employed. From two years ago a progressive decrease in PVC coating (except for truck canvas) and an increase of polyurethane coatings are noticed. On the other hand, an increase is foreseen in coated textiles being used in textile architecture (PES/PVC or glass/PTFE), airbags, reflectors or posters and publicity flags amongst others.
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