Improvements in or relating to the manufacture of coating compositions for electrical conductors

Polyurethane wire enamels prepared by reacting hydroxyl group-containing polyesters with polyisocyanates are characterized in that the polyester is the product of reaction of (1) 9 molar proportions of terephthalic acid or isophthalic acid or mixtures thereof (2) from 4 to 8 molar proportions of ethylene glycol and (3) from 5 to 9 molar proportions of at least one saturated aliphatic polyhydric alcohol having at least three hydroxyl groups, and that the proportion of polyisocyanate used is from 70 to 120% and preferably from 80 to 105% by weight of that equivalent to the hydroxyl content of the polyester. The polyisocyanate may be 2, 4- or 2, 6tolylene diisocyanate, diphenyl methane diisocyanate, 4; 41: 411-triphenylmethane triisocyanate, 3 : 31-dimethylphenylene- 4: 41diisocyanate, or the isocyanate derivatives described in Specifications 809,809 and 842,154. In examples an enamel is made by dissolving (1) an isophtalic acid/trimethylolethane/glycol polyester; (2) a terephthalic acid/glycol/trimethylol propane polyester; and (in a comparison experiment) a phthalic acid/glycol/triemthylolpropane polyester in a cresol/butyl acetate/heavy naphtha mixture and adding a polyisocyanate adduct (from 2:4-tolylene diisocyanate, diethylene glycol, glycerol and phenol). The mixture is used to coat a wire and curing is effect at 420 DEG C. Specifications 775,081 and 775,082 also are referred to.