Common Inhibitive Pigments

MIL-HDBK-1110

b) The chief function of the pigment is to provide

opacity (hiding) to obscure the substrate and protect the organic

resin from degradation by the sun's ultraviolet light. Organic

resins degrade to some extent in sunlight, some much more than

others. Titanium dioxide is the pigment most frequently used to

impart opacity to white paints and light tints, because it has

high opacity. If a coat of paint does not completely obscure a

surface, it is usually necessary to apply an additional coat.

c) Another important function of some pigments has

already been mentioned - corrosion control. Inhibitive pigments

can be very effective in reducing the corrosion that would

otherwise occur. Lead and chromate inhibitive pigments were

commonly used in paints in the past but are now restricted

because of adverse health effects. Examples of lead- and

chromate-containing pigments, and of those presently used,

environmentally acceptable corrosion-inhibitive pigments are

listed below:

Common Inhibitive Pigments

Relatively Hazardous

Relatively Nonhazardous

Red Lead

Zinc Oxide

White Lead

Zinc Phosphate

Zinc Chromate

Zinc Molybdate

Strontium Chromate

Calcium Borosilicate

Basic Lead-Silico-Chromate

Calcium Phosphosilicate

Zinc Phosphosilicate

Barium Metaborate

d) Pigments also may improve adhesion and decrease

moisture permeability. Leafing pigments such as aluminum tend to

align themselves as parallel plates in the film to effectively

increase film thickness by increasing the path that moisture must

take to reach the substrate.

e) Other things being equal, the greater the resin-to-

pigment ratio, the glossier will be the coating. The size of

pigment particles (fineness of dispersion or grind) of the

pigment in the vehicle also affects gloss. Other things being

equal, the finer the dispersion, the glossier the cured film.

Secondary or filler pigments (talc, silica, etc.) are used to

control viscosity, wet film build and leveling, and settling.

These cheaper pigments provide very little hiding. The pigment

to resin ratio, generally expressed as pigment volume

concentration (PVC), can vary widely. There can be no pigment,

or the pigment content can approach a value called the critical

pigment volume concentration (CPVC). As this point is

approached, there is insufficient binder to wet the individual

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