Film-Forming Material

a substance capable of forming a film upon application to a solid surface; the main component of paints and varnishes.

The products most commonly used as film-forming materials include reactive (irreversible) oligomers such as alkyd, phenol-formaldehyde, epoxy, and polyester resins, as well as some non-reactive (reversible) polymers of relatively low molecular weight, among them chlorinated polyvinyl chloride resins, polyacrylates, and cellulose nitrates. Natural film-forming materials, particularly vegetable oils and rosin derivatives, still retain some importance in the paint and varnish industry.

Film-forming materials are most often used in the form of solutions in organic solvents (sometimes aqueous solutions or dispersions) and are applied by various methods. Nonreactive film-forming materials form films as a result of evaporation of the solvent; film formation by reactive materials is accompanied by chemical transformations.

The general properties of film-forming materials should include (1) good wetting of the surface to be protected and of the particles of the pigments and fillers dispersed in the material in the production of paints, primers, and spackling compounds; (2) firm binding of the particles in the film; (3) rapid drying in a thin layer (from a few minutes to 24 hr at 15°–200°C), with formation of strong moisture- and gas-resistant films that can withstand prolonged action of the external medium; and (4) good adhesion to the surface being protected. In many cases, these properties are obtained by combining two or more film-forming materials in the paint or varnish, as well as by the introduction of plasticizers.

The functions of film-forming materials may be performed by several macromolecular polymers (for example, polyethylene or fluoropolyethylene resins), which are applied in powder form by spraying.