Coatings are widely used, and they are needed everywhere in home, building and industry. What’s more,they are usually made of resin, oil, or emulsion, with or without pigments, and with many additives, and organic solvents or water. Additives in coatings can improve the appearance and performance of coatings, such as color brightness, light transmittance, mildew resistance, uniform dispersion, adhesion and so on. Sodium hexametaphosphate is also an important coating additive.
Dispersion of sodium hexametaphosphate
Sodium hexametaphosphate is viscose after absorbing water, which closely relate to its own properties. The molecular formula of it is (NaPO3)6, which belongs to a kind of polyphosphate with indefinite composition, and its anions have high molecular weight, and generally the number of PO3-containing genes is as high as 30-90, forming a long chain.
Due to the addition of sodium silicate and some other basic substances, an alkaline environment with pH value of 10-10.5 was prepared, that is, the concentration of OH – ion in the coating was high, and the reaction proceeded to the right, which was conducive to the further decomposition of H3PO4 and the conversion of sodium hexametaphosphate to orthophosphate. And at this time, the phosphate will carry out the condensation of multiple phosphoric acid functional groups, especially at high temperature, the molecular groups of it will condense, and the condensed molecular groups combine with the three-dimensional network of bentonite molecular groups in the coating, which effectively plays the role of bonding.
With the increase of the content of sodium hexametaphosphate, the effect on the brushing property is more obvious. When the amount of sodium hexametaphosphate is 2%, the coating is thin and has good fluidity, but it is serious. There are obvious flow marks after the coating is applied, and the effect is poor. When the content of sodium hexametaphosphate in the coating rises to about 6%, it can satiate the coating, and the brushing is fast and smooth. Moreover, the coating material will automatically level after a period of time, leaving no trace, and the viscosity recovers. The dripping property of the coating with this content will be restored The coating with very low content can keep its inherent shape under the action of gravity, and reach the degree of balance with the dripping property.
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