Coating compositions

#This invention relates to coating compositions which cure by means of a condensation polymerisation reaction, more particularly to such compositions which have a high content of film-forming material and in which a substantial proportion of that material consists of polymer microparticles.

#In the coatings art, there has in recent years been a marked interest in increasing as much as possible the proportion present in coating compositions of actual film-forming material, and hence of reducing the proportion of inert liquid diluents which are required to evaporate during the process of forming a film and causing it to dry or cure. One factor which has promoted this interest is the realisation that such use of inert diluents is inherently wasteful, but perhaps the most significant factor is the need to reduce atmospheric pollution caused by their evaporation. The achievement of higher contents of film-forming material is, however, subject to difficulties, of which the most immediate is the penalty of high viscosity which is incurred when attempts are made to dissolve a high proportion of film-forming polymer in a small proportion of liquid diluent. This penalty may be avoided or minimised by using film-forming materials of lower molecular weight which are capable of undergoing further polymerisation after application to the substrate, but other difficulties then arise due to the fact that these materials are required to have a high functionality in order to achive an acceptable rate of cure of the film. This in turn gives rise to problems in achieving balanced film properties, and any compromise made to overcome the latter results in inferior mechanical properties or durability. Additionally, application difficulties are found in systems comprising solely low molecular weight resins.

#Coating compositions have already been proposed in which part of the film-forming polymer is present as insoluble polymer microparticles; films or coatings prepared from such compositions are of a composite character, having a polymer matrix or continuous phase derived from polymer which was originally in solution, and a disperse phase derived from the microparticles. These proposals have had as their principal objective the useful modification of the mechanical properties, e.g. of impact strength, of the matrix polymer by the presence of the microparticles.

#The invention is illustrated but not limited by the following Examples, in which parts and percentages are by weight.

#To a 10-liter reaction vessel fitted with stirrer, nitrogen inlet and a Dean & Stark separator there was charged:

#______________________________________ 12-Hydroxystearic acid 5400 g Dimethylolpropionic acid 402 g Aliphatic hydrocarbon (boiling range 190.degree.-210.degree. C.) 580 g Methane sulphonic acid 12 g ______________________________________