コーティングカラーの流動特性に関する研究 （第５報） コーティングカラーの成分粒子間の相互作用に対するｐＨの影響

Abstract

The interaction affecting the surface charge of constituent particles in coating color was studied through electrophoresis measurement and scanning electron microscopy (SEM) with the technique of osmium tetroxide fixation of latex.The pH dependence of aggregation state of amphoteric latex, which has both anionic and cationic groups, was visualized by SEM. Charge reversal of amphoteric latex and satin white by pH control affects significantly the dispersion state and electrokinetic properties of coating color. The transition pH for the dispersion state of amphoteric latex was ca. 7.1, showing some inconsistency with the electrophoretic behavior, which seemed to result from the relative strengths of electrostatic repulsion and Van der Waals attraction between latex particles. In the three-component system consisting of amphoteric latex/anionic latex/clay, the amphoteric latex mediates the binding between anionic latex and clay. This phenomenon might be useful in preventing the binder migration in actual coating procedures.The pH of charge reversal of satin white was ca. 7.5 as determined by electrophoresis. The coagulation behavior of latex particles onto satin white, as observed by SEM, clearly showed the role of this charge reversal : both types of latices were more uniformly distributed under alkaline conditions than under acidic conditions. In the latter condition, however, the difference between the two latices was not remarkable as expected.