コーティングカラーの流動特性に関する研究 第２報 電顕写真の観察から見たコーティングカラーの静電的相互作用

Abstract

For the purpose of visualizing the interaction between latex and pigment particles by electron microscopy, a new fixation technique was introduced that can preserve the shape of latex particles during the drying process. The method consists of mounting a drop of highly diluted coating color on a Formvar-coated copper grid for transmission electron microscopy (TEM) and treating the solution on the grid with osmium tetroxide vapor in a dessicator. Metal coating of this grid provided a specimen suited for scanning electron microscopy (SEM).When the pH of sample suspension was adjusted by using phosphate buffer, the SEM observation revealed a striking difference in behavior between a conventional anionic latex and an amphoteric latex in aggregating tendencies with clay particles. While the anionic latex particles were dispersed nearly uniformly on the substrate at both acidic and alkaline conditions, the amphoteric latex particles were strongly adsorbed onto clay particles in acidic and nearly neutral conditions. These results suggest the effectiveness of using amphoteric latexes as a means to control the latex-pigment interaction in coating colors for improving flow properties and preventing binder migration.The pH dependences of viscosity and the sediment volume ratio of undiluted coating colors were consistent with the latex-clay interaction as indicated by SEM observation.