Water-dilutable film-forming binders

Abstract

A low-solvent aqueous binder includes: a water-insoluble synthetic resin component A; and an emulsifier resin B in a mass ratio of A to B of from 70:30 to 30:70. The emulsifier resin B is a reaction product of a water-insoluble synthetic resin B1 that includes hydroxyl groups as functional groups, a synthetic resin B2 that includes carboxyl groups as functional groups, and a neutralizing agent for the carboxyl groups of B. The amount of the neutralizing agent is such that the neutralizing agent is able to neutralize from 5 to 200% of the carboxyl groups of B. A process for preparing a low-solvent aqueous binder includes: mixing the water-insoluble synthetic resin component B1 comprising hydroxyl functional groups and the synthetic resin B2 in bulk or dissolved in an organic solvent to form a mixture; removing the solvent by applying subatmospheric pressure and heating until the content of the mixture is at least 85% by mass; maintaining the mixture at a temperature from 90° to 150° C. until the reaction product of the mixture is homogeneously emulsifiable in a mass ratio of 3 parts of resin to 7 parts of water; neutralizing the reaction product by adding a neutralizing agent in an amount sufficient to neutralize from 5 to 200% of carboxyl groups that have remained following the reaction; adding the water-insoluble synthetic resin A in a mass ratio of A to B of from 70:30 to 30:70, and emulsifying the mixture in water.