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Contents:

1. The Milling Process
2. Leafing Pigments
3. Nonleafing Grades
4. Aesthetic Properties
5. Vehicle Selection
6. Uses
7. Metallics

Vehicle Selection

Vehicle selection is generally determined through a combination of cost analysis and end-use of the ink. Exterior versus interior usage, substrate coated, environmental restraints and speed of drying are only a few of the factors to be considered.

Generally, any vehicle that will be compatible with the carrier of the aluminum pigment and will not chemically interact to attack the aluminum flake should be suitable. Aluminum metal is amphoteric and as such acid number of vehicle systems should be held as low as possible.

If metallic dryers are necessary for the oxidation of the vehicle system, restrictions apply to leafing pigmented coatings. Only dryers that do not interfere with the stearic acid coating on the flakes should be used. Recommended dryers include cobalt, zirconium and manganese.

Solvent selection will largely depend on the vehicle system chosen for the formulation. Leafing aluminum pigments require nonpolar solvents only, preferably aliphatic or aromatic hydrocarbons with high surface tension. Polar solvents. including ketones and alcohols, remove the fatty acid lubricant on the flake and will deleaf the pigment.

Formulations with nonleafing pigments are far less restrictive in their solvent requirements. Nonleafing pigments can use a wide range of polar and nonpolar solvents. Water, a common contaminant in most solvents, should be kept to an absolute minimum in the ink system. Water reacts with both leafing and nonleafing aluminum pigments to yield hydrogen gas. Studies have shown that moisture levels in excess of 0.15% in the finished ink can generate sufficient gas to bulge or pop the end of the can.