As a coating auxiliary silica matting agent is mainly synthetic silica, divided into fumed silica and precipitated silica 2 types, its microstructure is amorphous or in a glassy state. Precipitated synthetic silica is made from quartz sand as the main raw material, which is reacted with sodium hydroxide or sodium carbonate by high temperature fusion in a kiln and then post-processed.
Fumed silica is produced by hydrolysis of silicon tetrachloride vapor in a hydroxide flame. Compared with natural silica, silica has high silica purity, inertness and UV resistance. The refractive index of amorphous silica is 1.46, which is similar to the refractive index of many resins in the coating industry, and thus amorphous silica can be used as matting powder in coatings with good optical properties.
Use common emulsifiers
The standard formulation is based on 30molEO nonylphenol polyoxyethylene ether (such as Dispo nilNP 307) mixed with some anionic surfactants, such as nonylphenol ether sulfate (Dispo nilAES 72), as shown in Table 1-8. Two kinds of alkylphenol surfactants were successfully replaced: amide wax liquid replaced with newly developed nonionic surfactants; replaced with fatty alcohol ether sulfate anionic surfactants.
Before replacing nonylphenol ether sulfate, the surfactant system must be optimized by improving the efficiency of non-ionic surfactants. With the development of new high ethoxylated products, the technical defects in this area have been compensated, and the corresponding nonylphenol-containing and non-nonylphenol-containing emulsion indexes can be found in Table 1-9. Compared with nonylphenol surfactants, the new product improves storage stability and freeze-thaw stability to the same level. The water resistance in all tests is between 4% and 5%.
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