Interaction between Latex and Starch in Coatings during Drying

Abstract

Binder migration that occurs in a drying process for coated paper was studied in the light of interaction between latex and starch. It is well known as binder migration that latex particles and starch concentrate near the top surface of a coating layer as a result of intensive drying. The results showed followings. Latex migration was induced by starch formulated as a co-binder. This inducement increased as amount of formulated starch increased.Dextrin of a degree of polymerization (DP) of about 33induced latex migration to a greater extent than starch phosphate of a DP of a few hundred, but glucose had a much less effect. Starch migration per se had the same tendency regarding DP. Electric charge of starch did not affect latex migration. There was no difference in latex and starch migrations between anionic starch phosphate and nonionic hydroxyl ethyl starch. The peculiarity of starch to inducement of latex migration seems to be related to ease with which starch tends to gel at high temperatures, approaching to high solids. In rapid drying, if the concentrations of latex and starch near the top surface increase and the starch gels.a sudden increase in color viscosity lowered the diffusion velocity of the latex particles and the starch into the bulk. Thus, the whole coatingsolidifies. maintaining their concentrations at the top surface higher than the rest of it. This mechanismwas predicted for latex migration occurring in the presence of starch.