The following sections will classify Pigments into these classes
- PRIME WHITE PIGMENTS
- COLORED PIGMENTS
- METALLIC PIGMENTS
- EXTENDER PIGMENTS
- FUNCTIONAL PIGMENTS
Prime White Pigments
Prime pigments are white, high refractive index materials used to opacify paint. The most widely used prime white pigment is titanium dioxide because of its high refractive index (2.71) and its resistance to chemicals and ultraviolet light. Prior to the 1950’s white lead pigments were the most widely used but titanium dioxide’s inertness, chemical and UV resistance, hiding power, high bulking value and low toxicity quickly took over the market.
Titanium Dioxide (TiO2) is now by far the most widely used white prime pigment in paint, as well as the most expensive. Titanium dioxide is manufactured for coatings in two distinct types: anatase and rutile. Rutile titanium dioxide is the most commonly used type and is highly resistant to ultra-violet light, chemicals, and discoloration. Anatase titanium dioxide releases from the film or “chalks” under exterior conditions and can be found in interior paints and in “self cleaning” exterior coatings.
Titanium dioxide pigment is non-reactive with most paint raw materials. The inertness of titanium dioxide makes it unaffected by water, organic and inorganic acids (other than hot concentrated sulfuric acid and hydrofluoric acid), dilute alkalis, and solvents. Its resistance to UV light and weathering is outstanding.
Lithopone is a mixture of 71% barium sulfate and 29% zinc sulfide. Once popular as a prime white pigment, lithopone has largely been replaced with the titanium pigments. Lithopone can still be found in interior paints in European and Latin American countries and is not recommended for exterior paints. In North America lithopone is sometimes used in industrial primers where it contributes to film hardness, hold-out, and sanding properties.
The oldest white pigment known, white lead was used extensively as a prime pigment for paints up until the late 1950’s. Concerns about the toxicity of lead and the development of titanium pigments have virtually eliminated its use. There are virtually no white lead-containing paints manufactured today.
Zinc is now used only infrequently as a fungicide in exterior paints.