The pigment is one of the main and important constituent of the paint. These are granular solids integrated into the paint to contribute color, toughness, texture or simply to reduce the cost of the paint. Alternatively, some paints contain dyes instead of or in combination with pigments. In general, pigments should be opaque to ensure good covering power and chemically inert to secure stability, hence long life. Pigments should be nontoxic, or at least of very low toxicity, to both the painter and the inhabitants. Finally, pigments must be wet by the film-forming constituents and be of low cost.
Hiding pigments protect the substrate from the harmful effects of ultraviolet light. Hiding pigments include titanium dioxide, phthalo blue, red iron oxide, and many others.
Pigments can be classified as either natural or synthetic types. Natural pigments include various clays, calcium carbonate, mica, silicas, and talcs. Synthetics include engineered molecules, calcined clays, blanc fixe, precipitated calcium carbonate, and synthetic pyrogenic silicas.
These are special type of pigments that thicken the film of the paint, support its structure and simply increase the volume of the paint. Fillers are usually made of cheap and inert materials, such as diatomaceous earth, talc, lime, barytes, clay, etc. Some paints contain very large proportions of pigment/filler and binder.
The binder, commonly referred to as the vehicle, is the actual film forming component of paint. It is the only component that must be present; other components listed below are included optionally, depending on the desired properties of the cured film.
The binder imparts adhesion, binds the pigments together, and strongly influences such properties as gloss potential, exterior 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, or oils. Binders can be categorized according to drying, or curing the mechanism. The four most common are:
1. simple solvent evaporation,
2. oxidative cross-linking,
3. catalyzed/cross linked polymerization,
The main purpose of the solvent is to adjust the curing property and viscosity of the paint. It is volatile and does not become part of the paint film. Its main function is as the carrier for the non volatile components. It also controls flow and application properties, and affects the stability of the paint while in liquid state. In order to spread heavier oils as in oil-based interior house-paint, a thinner oil is required.
These volatile substances impart their properties temporarily—once the solvent has evaporated or disintegrated, the remaining paint is fixed to the surface. This component is optional: some paints have no diluents. Water is the main diluent for water-borne paints, even the co-solvent types.
Besides above three ingredients, paint can have a long range of various additives, which are usually added in very small amounts and give a very significant effect on the product. Some examples include additives to modify surface tension, improve flow properties, improve the finished appearance, increase wet edge, improve pigment stability, impart antifreeze properties, control foaming, control skinning, etc. Other types of additives include catalysts, thickeners, stabilizers, emulsifiers, texturizers, adhesion promoters, UV stabilizers, flatteners (de-glossing agents), biocides to fight bacterial growth, and the like.
Additives normally do not significantly alter the percentages of individual components in a formulation.
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