Aluminum Paste, also called is a mixture of solvent or water and aluminum pigments with particle shapes and sizes that have been manipulated through a milling process to create aesthetic properties. Both chemical solvents and water can be used as a liquid when producing aluminum paste.
Aluminum paste is a packaged metallic pigment or dust. Aluminum pigments are used to create the metallic aesthetics found in a wide range of paints, coatings and inks. Manipulating the particle shape and size within the coating, ink or masterbatch (ink for Graphic Arts and masterbatch for plastics) creates different effects. It is not enough to simply add pigments to a paint or ink. The aluminum pigments are combined with a dispersant comprised of solvent or water to create a paste. Often, the Paste is referred to a slurry or a pigment slurry.
The reason for not using dry pigments is that dry pigments are not typically used is for safety and easy handling. Aluminum flake and dust are referred to as fines. These airborne fines can quickly spread heat when ignited. If exposed to electricity, phenomena known as arch flash will occur. The very dust used intentionally to aid rocket boosters and pyro techniques, presents severe hazards as a machining and thermal spray byproduct. Additionally, manufactures of coatings, inks or masterbatched containing aluminum metallic pigments do not want to create this hazardous dust during their production.
A variety of solvents can be used to create paste. While the solvent used will depend on the end use, mineral spirit is common. Even water can be used should the paste be needed for water based coatings. Water based aluminum paste is also used in lightweight concrete. A water and alkaline solution, mixed with aluminum, will give off gasses that result in small air pockets within the concrete. The result is a lighter concrete known as "aerated concrete." Generally, Aluminum flake pigments can react with water. When the two are combined, they create hydrogen. Hydrogen is a flammable and dangerous gas if not properly handled.
In many cases the properties of metallic effect pigments can be deduced directly from the production process. The gold bronze pigments are dry milled in ball mills (Hametag process), but for safety reasons aluminum pigments are produced almost exclusively in a wet milling process adding white spirit (Hall process).The raw material - atomized, spattered aluminum with a minimum purity of 99.5% according to EN 576 – is milled respectively shaped to flake-like particles in ball mills, filled with grinding aids (lubricant).
The milling parameters and the lubricant are determined by the application for which the aluminum paste pigment is intended. The pigment slurry is screened, pressed on filter presses and adjusted in mixers to a ratio of 65% solids and 35% solvent. The final product can be tailor-made for its later application by the addition of particular solvents or additives to the filter cake.