Copolymer latex and its production

A process for preparing a copolymer latex by polymerization of at least one aliphatic conjugated diene monomer, at least one ethylenically unsaturated carboxylic acid monomer and at least one monoolefinic monomer copolymerizable with them in a weight proportion of 19.5-80:0.5-10:10-80, which consists essentially of the following sequential steps (a) subjecting to emulsion polymerization a mixture of starting monomers comprising the whole amount of the aliphatic conjugated diene monomer, the whole amount of the ethylenically unsaturated carboxylic acid monomer and a portion of the monoolefinic monomer, the combined amount of them being from 45 to 99% by weight on the basis of the total amount of the starting monomers, and (b) after conversion of said starting monomers reaches 70% or more the remainder of the monoolefinic monomer in an amount of from 1 to 55% by weight of the basis of the total amount of the starting monomers is added to the reaction mixture, whereupon further emulsion polymerization is carried out;

• and wherein in each step said monoolefinic monomer is selected from the group consisting of styrene and mixtures of styrene with another monoolefinic monomer.