GB621542A - Improvements in the manufacture of varnish resin interpolymers - Google Patents

Abstract

A varnish resin is prepared by heating a mixture of (1) from 30 to 90 per cent by weight of a drying oil, free acid of a drying oil, or synthetic ester of a drying oil acid, which has a degree of conjugation not substantially exceeding that of dehydrated castor oil, and (2) from 70 to 10 per cent of a mixture of a polymerizable monovinyl aromatic compound and a nuclear alpha-methylene-lower alkyl aromatic compound, the alpha-methylene-lower alkyl group containing 3 or 4 carbon atoms and the mixture containing 50-80 per cent by weight of the monovinyl compound, to effect interpolymerization. Suitable drying oils are dehydrated castor oil, linseed, soyabean, perilla and fish oils. A mixture of one of these oils with a smaller proportion of a highly conjugated oil, e.g. tung oil, may be used. The monovinyl aromatic compound is preferably styrene, but o- and p-methyl styrene, o- and p-ethyl styrene, o-p-dimethyl styrene, p-chlorostyrene, p-methoxy styrene and vinyl naphthalene may be employed. Suitable alphamethylene-lower alkyl aromatic compounds are a -methyl styrene, p-methyl a -methyl styrene, a -ethyl styrene and p-chloro-a -methyl styrene. Polymerization may be effected by heating the mixture below boiling, e.g. 120-160 DEG C., with or without a catalyst such as benzoyl peroxide, acetyl benzoyl peroxide, tertiary butyl perbenzoate and tert.-butyl hydroperoxide. Alternatively, the drying oil is first heated to the polymerization temperature and the mixture of styrene or derivative and a -methyl styrene or derivative and catalyst is then added slowly over a period of several hours. Polymerization may also be effected in aqueous emulsion or in solution in, for example, diethyl benzene. The viscosity and hardness of the resins may be increased by heating at a temperature above 250 DEG C., but below their decomposition temperature, e.g. 275-295 DEG C. The resins are soluble in aromatic and aliphatic solvents and are compatible with linseed oil, most phenolic resins, some modified alkyd resins, rosin - esters, paracoumarone - indene, urea and melamine resins. The examples describe varnishes comprising the resins dissolved in mineral spirits/xylene and mineral spirits/toluene mixtures, with cobalt and manganese naphthenate driers and in one case containing guaiacol to prevent skinning; and an enamel made by adding titanium dioxide.