コーティングカラーの流動特性に関する研究 （第１報） バインダーラテックスの界面および粘弾性特性

Abstract

The viscoelastic properties of binder latices for paper coating were investigated, together with dynamic viscoelastic properties of latex films and electron micrographs of latices, under various conditions. The amphoteric latex, binder-pigment latex and anionic latex were used in this work. The amphoteric latex has both anionic and cationic functional groups on its surface. The binder-pigment latex with a core-shell structure has dual functions : plastic pigment and binder.The low-shear and high-shear viscoelasticity of binder latices and clay slurry were measured with Brookfield viscometer and Hercules high-shear viscometer, respectively.At low-shear rates, the viscosity decreased with increasing particle size of latex. However, at high-shear rates, the different results were observed.On the amphoteric latex surface, the carboxyl groups are assumed to be fully dissociated over the region of pH 9-12, but the density of negative groups seems to increase because of the gradual decrease in the degree of dissociation of amino groups. Since the apparent particle size of latex increases with surface charge, the electroviscous effect, i. e. increase in viscosity by surface charge, can be observed. On the anionic latex surface, the charge density is assumed to be nearly constant above pH 8. However, below pH 8 the coagulation of particles could be observed probably because of the decrease in charge density.The time-dependent phenomena could not be observed at low-shear rate. However at high-shear rate, thixotropic properties of flow, and the internal structural breakdown of flow could be observed from time-dependent phenomena.