The electrostatic interaction between coating color components affecting the viscoelastic properties and the interfacial electrokinetic behavior of coating color system was studied by using two types of latexes with the same styrene-butadiene ratio but with different surface charges ; one containing usual anionic groups (anionic latex) and the other containing both anionic and cationic groups (amphoteric latex).
The coating color containing amphoteric latex was found to have the following characteristics as compared with anionic latex :
1) The absolute value of zeta potential was remarkably decreased by lowering pH from around pH 7 and reversed to positive values below pH 4.
2) Viscosity was significantly increased below about pH 7.
3) Thermal treatment of the color resulted in irreversible gelation in nearly neutral conditions.
These phenomena indicate that the dissociation of amino groups on the surface of amphoteric latex is dependent on the pH of the medium, thus affecting the properties of coating color through the electrostatic interaction between clay and latex or between latex particles. The important finding is that the coating color containing amphoteric latex has as similar stability and viscoelastic properties as those of anionic color in alkaline conditions, suggesting the applicability to conventional operations in color handling and color application. When applied onto base paper, however, the characteristics of the amphoteric system come into play through possible changes in pH, thus resulting in favorable features of coated paper.