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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

Leafing Pigments

There are two categories of aluminum pigments -- leafing and nonleafing. Leafing aluminum pigments, as the name implies, have the ability to cover the surface of a suitable vehicle with layers of flakes, much as leaves cover a pond in autumn. This unique property is a function of the fatty acid lubricant used in milling the pigment and will manifest itself only in the presence of the proper vehicle and solvent system.

The lubricant generally used is a saturated fatty acid, such as stearic. The fatty acid that is adsorbed on the surface of the flakes exhibits both oleiphoic and hydrophobic characteristics. Therefore, the degree of leafing in any vehicle system will depend on the system's ability to wet the flakes. The greater the wetting, the more poor the leafing.

The solvents used also play a major role in developing the full leafing of the ink. As evaporation of the volatile takes place, convection currents are set up to permit the flakes to rise to the surface of the film, and interfacial tension holds them in this position. As further evaporation occurs, the ink film becomes more viscous and traps the flakes at or near the surface.

In leafing, the alignment of the aluminum flakes at or near the surface of the film is parallel to the substrate, and the film surface is in a multilayered interlocking position. This orientation provides a very bright appearance.

However, because of the unique leafing feature, the ability to color in this type of system is difficult. The opaque aluminum flakes will mask or hide any other color present in the system. Also, since the majority of the flakes are at or near the surface, the aluminum tends to crock or smudge, as there is very little resin holding the flakes to the surface of the film.