Mechanism of action of dispersants for emulsion paints

The mechanism of the action is electrostatic repulsion stabilization through hydrogen bonding and chemical adsorption. The advantage is that the dosage is low, about 0.1%, and the dispersion effect is good for inorganic pigments and fillers.

But there are shortcomings: First, with the rise in pH and temperature, polyphosphate is easy to hydrolyze, resulting in poor long-term storage stability; second, polyphosphate in ethylene glycol, propylene glycol and other diol solvents are not completely dissolved, will affect the gloss of light emulsion paint.

The Russian scholar 1121 dispersed China Blue in perchlorovinyl resin. After 120 hours of grinding, the pigment fineness was still higher than 130gm. Add octadecylamine with 3%~4% of China Blue in the same dispersion system. After 24 hours of grinding and dispersion, the fineness does not exceed 10pm, and about 85% of the particle size is 5gm. If the amount of additives is increased by 2 times, the dispersion effect will not continue to improve. If the chemical adsorption capacity of Hualan is exceeded, the dispersion effect will deteriorate.

This example shows that in a non-polar resin solution that does not contain reactive groups, it is impossible to disperse pigments without adding wetting and dispersing agents.

Hualan has two active centers on its surface. Both anionic and cationic surfactants can form a chemical adsorption layer on its surface. However, the adsorption capacity of amine is higher than the adsorption capacity of acid, because there are a large number of [Fe(CN)]-centers that can adsorb amines on the surface of Hualan, and octadecylamine and stearic acid are on the surface of Hualan. There is no physical adsorption, shield wax with ptfe and stearyl alcohol has only physical adsorption on the surface of China Blue, not chemical adsorption.

This example also tells us that in the non-polar resin base, the choice of pigment dispersant is very important. It is necessary to consider the interaction between pigments and additives, and at the same time pay attention to the compatibility of additives with resin polymers.