Pigment Manufacturing
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Generally, pigments and paints are not bound chemically to the covered surface, water-soluble dies react with fibers in a mordant bath. Apart from colored, decorative paints, white and black pigments have high importance. White titanium dioxide plays an important role in the painting industry, due to its stability, high covering effect, and UV-light absorbing property. Approximately 4.6 million tons of TiO2 pigment are produced annually worldwide, and its use continues to rise. On the other end of paints, carbon black is essential as a toner of the laser printer and filler in tires and other plastics, also due to its stability and UV-light absorbing capability.
Pigment manufacturing process
Natural sources of paint lost their importance. Lead oxide pigment dispersed in oil was widely used as primer paint, due to its excellent anticorrosive feature. Since heavy metal lead is poisonous, this red paint is nowadays forbidden. Indigo was extracted from plants cultivated in Asia, nowadays the blue die for denim cloth coloration is synthesized almost exclusively by the chemical industry. The coloring materials were solved in organic solvents, benzene, toluene, xilols, turpentine, and nitro thinner. All these solvents pollute the environment, and some of them are carcinogens. Nowadays water-based products are common; however most part of paints are not water-soluble. In order to avoid segregation, stable dispersion should be formed where the pigments do not sediment.
In order to eliminate solvents, powder coating is used for painting and decorating vehicles and other metal surfaces. Pigments are mixed with polymers, then extruded and milled. Classifier mills are preferable for a narrow particle size distribution
High sheer mixing for powder paints
Powder coatings are a solvent-free painting form where pigment is mixed with a polymer, a carrier material that melts in the painting oven so that the pigments adhere to metal objects. Pigments are micronized to have a smooth surface and become miscible with polymer beads. High shear mixing is necessary to break the force of cohesive powders and form polymer-pigment particles avoiding sedimentation in further processing. The video below shows a high-shear mixer for this purpose with a conical shape that provides a vertical upward movement along the wall.
How dispersion improves paint quality
In emulsion paint, the binding agent is dispersed in water. Dispersion as such an important process that has a big influence on the quality of the final product. Dispersing machines process immiscible materials in a high shear chamber, where sharp edge tools of high-speed rotor reduce the size of the paint particles and disperse them into the oily or water base matrix. A rotor can have paddles as well, to serve as a recirculation pump. The video below shows how at the top of the rotor a vacuum occurs, sucking in the ingredients, liquids, and powders.
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