What are the differences between silica and alumina in powder coatings? Almost all of them are rheological additives and anti - caking groups.
There are many methods for matting agents. They can be divided into two kinds according to their manufacturing process. One is made by hydrothermal method, and the produced silica is relatively loose. Products made from silica gel are tough in texture. The treated two types of products can be made into standard silica matting agents. Processing refers to the use of organic (Paraffin) or inorganic materials to modify the surface of silicon dioxide to a certain extent.Compared with silica matting agent, the treated silica has different particle size, particle size distribution and pore volume. Hydrothermal matting agents are also different in particle size and distribution. Untreated and treated products are also different. At present, there is only one kind of matting agent suitable for special occasions. The matting agent is prepared by pyrolysis and has strong extinction efficiency, and is especially suitable for water base coating system. The extinction effect of silica is relatively strong, which may lead to higher viscosity when the concentration is high. The tendency to precipitate during storage, especially untreated silica. To avoid accumulation, we can use paraffin or pyrolytic silica. The matting agent can adjust the extinction degree of 45 DEG, 60 DEG and 85 deg. Coatings with silica matting agents can be painted. All of these are "stir-in" products. The synthetic aluminum silicate can partly substitute titanium dioxide as a high quality increment agent and can be applied to emulsion primers. The product can exhibit a balanced extinction effect in the dried emulsion film. It can be used as matting agent in long oil alkyd resin system, but it must be dispersed with pigment and filler. In addition to the powder coating system, the silica matting agent can be applied to all coatings.
The gas phase is alumina using A1Cl3 sublimation in combustion gas of oxyhydrogen flame, by high temperature hydrolysis generated a fluffy white powder, the primary particle size in the range of 7 ~ 40nm, the presence of particles is not isolated, but "agglomerate", these agglomerates the maximum particle size should be 5 ~ 6um, usually in 4 ~ 5um. Gas phase alumina has the characteristics of fine particle, high purity, good dispersion and positive surface. It is widely used in fluorescent energy-saving lamps, high gloss paper and powder coatings.
Currently sold in the market for powder coating fumed alumina is mainly Degussa AEROXIDEAluC and SpectrAI100 produced by Cabot Corporation, Guangzhou jibishisheng tech. Industrial Company also built a gas phase of alumina production line, and is used for the gas phase oxidation of aluminum powder coating products have been pushed to the market.
The positive charge of vapor phase alumina makes it an effective additive for the formulation of friction powder coatings. Whether it is an epoxy polyester mixture, polyester -TGIC or other resin systems, gas phase alumina provides excellent combination of fluidity and charge in friction coating applications.
