Coating compositions

Claim 1

An aqueous composition suitable for the production upon a substrate of a temporary protective coating which can subsequently be removed by treatment with an aqueous alkaline solution, the composition comprising a sterically stabilized dispersion in an aqueous medium of particles of a size in the range 0.1 to 10 microns of a polymer derived from a monomer mixture comprising (1) at least one acrylic monomer selected from the group consisting of alkyl esters, nitriles and amides of acrylic acid and methacrylic acid and from 5 to 40%, based on the, total weight of (1) and (2), of (2) an ethylenically unsaturated monocarboxylic acid, or a proportion equivalent thereto, in terms of carboxyl group content, of an ethylenically unsaturated polycarboxylic acid, the said dispersion being obtained by free radical-initiated polymerization of (1) and (2) in an aqueous medium which is a mixture comprising (a) at least 30% by weight of water and (b) not more than 70% by weight of a second constituent which is miscible with water, the nature and proportion of the second constituent being such that the aqueous medium as a whole is capable of dissolving (1) and (2) to the extent of at least 3% by weight but is a non-solvent for the polymer formed, the polymerization being carried out at a temperature which is at least 10° C. higher than the Tg (glass-rubber transition temperature) of the polymer, there being introduced into the reaction mixture, before the polymerization begins, a steric stabilizer precursor which is the acrylic or methacrylic ester of a polyethylene glycol, or a monoalkyl ether thereof, of molecular weight in the range 1500 to 4000, the concentration of free monomer in the polymerization mixture being maintained throughout at a level such that at no time does the free monomer form a separate phase.