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Binder or film former

The binder is the film-forming component of paint. It is the only component that is always present among all the various types of formulations. Many binders must be thick enough to be applied and thinned. The type of thinner, if present, varies with the binder.

The binder imparts properties such as gloss, durability, flexibility, and toughness.

Binders include synthetic or natural resins such as alkyds, acrylics, vinyl-acrylics, vinyl acetate/ethylene (VAE), polyurethanes, polyesters, melamine resins, epoxy, silanes or siloxanes or oils.

Binders can be categorized according to the mechanisms for film formation. Thermoplastic mechanisms include drying and coalescence. Drying refers to simply evaporating the solvent or thinner to leave a coherent film behind. Coalescence refers to a mechanism that involves drying followed by actual interpenetration and fusion of formerly discrete particles. Thermoplastic film-forming mechanisms are sometimes described as "thermoplastic cure," but that is a misnomer because no chemical curing reactions are required to knit the film. On the other hand, thermosetting mechanisms are true curing mechanisms involving chemical reaction(s) among the polymers that make up the binder.