Coatings for building and construction textiles

A large variety of desirable properties for membranes may be provided by the fibres themselves or by their finishing and post-treatment before the production of the fabric. If these do not provide the required properties such as watertightness, dirt and oil repellence, UV protection, flame retar-dance or abrasion resistance, the fabric must be coated or laminated. Additionally an unweldable textile (e.g. PTFE) may have a weldable coating applied. 

When adding a coating to breathable membranes, the coating must also be breathable, i.e. water repellent while permitting water vapour to penetrate both membrane and coating. This property is produced by microporosity or by water vapour diffusion and results in improved climate conditions within the enclosed space. 

Coatings may consist of one to three layers, depending on cost and quality. High quality coatings have a base or tie coat, an intermediate or filler coat, and finally a top coat. The base coat ensures adequate adhesion to the textile material. The intermediate coat is responsible for the system volume and the mechanical properties. The top coat determines the appearance and surface properties and also seals the surface. 

The basic chemicals for coatings are polymers which form a film or crosslink on the fibre or fabric, together with additives and auxiliaries. Additives may be pigments for colour or for the reflection of UV or IR radiation. In the future, it will become possible to apply the filler as nanoparticles, thus creating a new class of properties. 

In the first step of a lamination process, a foil or film is produced. This is then laminated onto the fabric, either by heat and pressure or by means of an adhesive. The laminated foil places considerable constraints on the flexibility of the fabric but offers better protection than a coating and is self-cleaning. 

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