Compositions for producing on a substrate a temporary protective coating subsequently removable with aqueous alkali

Claim 2

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 stabilised 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 at least one acrylic monomer and from 5% to 40%, based on the total weight of the monomer mixture, of an ethylenically unsaturated monocarboxylic acid, or a proportion equivalent thereto, in terms of carboxyl group content, of an ethylenically unsaturated polycarboxylic acid.

Claim 3

A composition as claimed in claim 1, which contains from 10% to 20% by weight of an ethylenically unsaturated monocarboxylic acid, or a corresponding proportion of an unsaturated polycarboxylic acid.

Claim 4

A composition as claimed in claim 1 or claim 2 which is obtained by free radical-initiated polymerisation of the monomer mixture 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 the monomer mixture to the extent, of at least 3% by weight but is a non-solvent for the polymer formed, the polymerisation being carried out at a temperature which is at least 10°C higher than the Tg (glass-rubber transition temperature) of the polymer, in the presence in the aqueous medium as steric stabiliser of a block or graft copolymer which contains in the molecule a polymeric component of one type which is solvatable by the aqueous medium and a polymeric component of another type which is not solvatable by the aqueous medium and is capable of becoming associated with the polymer particles formed, the concentration of free monomer in the polymerisation mixture being maintained throughout at a level such ,that at no time does the free monomer form a separate phase, the total amount of monomer mixture polymerised being such that the resulting dispersion contains at least.20% by weight of the polymer.

Claim 5

A composition as claimed in claim 3, wherein the second, water-miscible constituent of the aqueous medium is ethanol.

Claim 6

A composition as claimed in claim 3 or claim 4, wherein the temperature of polymerisation of the monomer mixture is at least 30°C higher than the Tg of the polymer which is formed.

Claim 7

A composition as claimed in any one of claims 3 to 5, wherein the steric stabiliser is formed in situ during the polymerisation by introducing into the reaction mixture, before polymerisation begins, a precursor which is the acrylic or methacrylic ester of a polyethylene glycol, or a monoalkyl ether thereof, of molecular weight in the range 1500-4000.

Claim 8

A composition as claimed in claim 6, wherein the proportion of stabiliser precursor is from 0.5% to 20% by weight of the polymer content of the dispersion.

Claim 9

A composition as claimed in any one of claims 1 to 7, having a polymer solids content of 25% by weight.

Claim 10

A composition as claimed in any one of claims 1 to 8, wherein the carboxylic acid groups in the polymer of the dispersion are neutralised wholly or in-part by addition of a water-soluble amine.

Claim 11

A process for the production upon a substrate of a temporary protective coating which can subsequently be removed by treatment with an aqueous alkaline solution, which comprises applying to the substrate a composition as claimed in any one of claims 1 to 9 and allowing the composition to dry.