Process for preparing a surface sizing agent

摘要

The preparation of the surface sizing agent for paper and board is effected by modifying 1.0 mol parts of an alternating alpha-methylstyrene-maleic anhydride copolymer which contains anhydride groups with from 0.7 to 1.0 mol parts of an aliphatic amine and from 0.9 to 1.2 mol parts of ammonia. According to the invention, a stirred vessel is charged with from 11 to 33 mol parts of water. At 10 to 80@C a 20 to 60% strength acetonic solution of alpha-methylstyrene copolymer as obtained by the free radical polymerisation of molar amounts of alpha-methylstyrene with maleic anhydride in acetone is stirred in. The acetone is then distilled off. Thereafter the aliphatic amine and ammonia are added as a mixture. After the dissolving of the polymer, the acetone still enclosed in the polymer is driven off. Thereafter the size is adjusted in a conventional manner with water to the desired size concentration. The advantage of the process is the avoidance of not only apparatus- but also labour-intensive powder technology.