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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

Uses

Leafing and nonleafing aluminum pigments are used in the ink industry to provide attractive silver, gold and polychromatic finishes. To discuss aluminum products for ink, it is necessary to categorize them by ink systems. The requirements for paste inks (offset) are different from fluid inks. Paste ink requires a very fine particle size that is highly reflective. This limits the selection of products to fine leafing grades.

The physical form of aluminum pigments is either dry powder mineral spirits paste, or ink oil paste. The two paste forms are preferrable, as the dry powder is messy and can be hazardous. Nonleafing grades have severe limitations. These grades contain insufficient numbers of fine particles, thus coverage is extremely poor. Metallic colors can be obtained by using leafing grades, and they will yield a satin-like appearance.

Fluid inks can produce brilliant silvers and clean metallic colors. The maximum pigment particle size is limited by the printing ink process which generally has a partial limit of 25 to 30 microns. Types of aluminum pigments available for fluid inks are dry pigments, IPA and other common ink solvent pastes, plasticizer-wet damp powders and resin-based granules. Which form to use depends on personal preference, as well as on the ink formulation.

Both leafing and nonleafing pigments can be used in fluid inks. Leafing pigments produce a bright silver appearance, which is highly reflective and has good coverage. On the other hand, they have several deficiencies. Since most fluid inks use polar solvents, the leafing pigments might deleaf, thus resulting in poor aging characteristics. Also because the flakes are at the surface of the film, they have poor rub resistance and might give rise to intercoat adhesion problems.

These deficiencies can be overcome by using nonleafing pigments in fluid inks. In general, nonleafing aluminum pigments have excellent rub resistance and intercoat adhesion characteristics. This is because the flakes are distributed throughout the ink film, rather than being only at the surface.

The nonleafing pigments have a tightly controlled particle distribution and, as a result, will produce bright metallic colors. They also produce a bright silver, but, the appearance will be somewhat different from that obtained by the leafing pigments. Because of the controlled particle distribution, higher concentrations are generally used to maximize coverage.