Aluminum powder pigments are currently the most widely used type of flake-effect pigment in industrial applications. They are divided into two main categories: floating and non-floating. Non-floating aluminum powder accounts for the vast majority of the market share, exceeding 80%.
Non-floating aluminum powder includes varieties with larger particle sizes and a crystalline luster, and varieties with finer particle sizes and a satin luster. Due to the organic color film on the surface, it has good pigment wetting properties and is evenly distributed in the powder coating.
Floating lead powder mostly arranges itself on the coating surface, presenting a bright, even chrome-plated, coating appearance with excellent hiding power. The characteristics of metallic aluminum powder on powder coatings or coating surfaces are as follows:
Hiding and Shielding Effects
Aluminum powder is flaky, with a substrate diameter/thickness ratio of approximately (40:1) to (100:1). The particles are arranged in multiple parallel layers within the coating, forming continuous multi-layered aluminum powder that shields the substrate and reflects incident light. The interlacing pores between the aluminum powder layers cut off the capillary pores of the coating and the pathways for external moisture, making it very difficult for water vapor to enter the coating and reach the substrate.
Optical Characteristics
Aluminum powder is made from high-gloss, light-colored, and high-purity metallic aluminum. Through specific processing, the surface of the aluminum particles is smooth and flat, achieving a reflectivity of 60% to 90% for visible light, infrared light, and ultraviolet light with wavelengths of 280-400 nm, resulting in a bright, silvery-white appearance.
"Angle-dependent color variation" effect
Aluminum powder possesses a metallic luster and the characteristic of being aligned parallel to the surface of the object being coated. In transparent or poorly opaque coating systems, the gloss and color depth of aluminum particles change with the angle of incidence and the angle of observation, producing light and color variations commonly referred to as the "two-color effect" or "interference effect." Of course, the good parallel orientation of the aluminum powder is a prerequisite for this optical effect.
Floating property
During the production process, the surface of the flake-like aluminum powder is coated with high-grade fatty acids. The fatty acids on the surface of the aluminum powder have two adsorption layers. The lipophilic groups of the outer layer of fatty acid are connected to the lipophilic groups of the inner layer of fatty acid, causing the carboxyl groups to face outwards. Therefore, after the fatty acid coating, the aluminum powder becomes an oleophobic powder. When molten and flowing, the aluminum particles migrate towards the coating surface under the action of "Bénard eddies," causing the aluminum powder to float on the coating surface.