GB1049030A - Improvements in or relating to stoving varnishes - Google Patents

Abstract

A stoving varnish comprises the reaction product of a high molecular weight insoluble glycol polyester of terephthalic acid and/or isophthalic acid and a polyhydric alcohol, dissolved in a volatile organic solvent. In a modification the varnish comprises the reaction product of a primary polyamine with the transesterification product of the high molecular weight polyester with a polyhydric alcohol and a di-, tri- or tetra-carboxylic acid capable of forming an anhydride, or an ester-forming derivative thereof, dissolved in the organic solvent. The polyester may be, e.g., scrap polyethylene terephthalate from the manufacture of fibres and foils. Suitable polyols are ethylene, propylene, trimethylene, 1,3-butylene, and neopentyl glycols, p, p1-dihydroxycyclohexylpropane, glycerol, trimethylolethane, trimethylolpropane, pentaerythritol, sorbitol, the adduct of 2 mols of ethylene oxide and p,p1-dihydroxydiphenylpropane, and 1,4-dimethylolcyclohexane. The proportion of trihydric alcohol in the polyol is preferably at least 10 mol per cent, and the proportion of higher polyols is preferably not more than 20 mol per cent. Suitable polyamines are ethylene diamine, diethylene triamine, propylene diamine, pentaor hexa - methylene diamine, phenylene diamine, diaminodiphenylmethane, diaminodiphenylethane, diaminodiphenyl ether or a transesterification product of p, p1-diphenylol-propane with ethylene imine. Suitable polycarboxylic acids are maleic, itaconic, citraconic, succinic, phthalic, pyromellitic, trimellitic, mellophanic acids, a benzene polycarboxylic acid from the nitric acid oxidation of coal, an adduct of maleic anhydride with abietic acid, styrene or a terpene, or a fatty acid with conjugated olefinic bonds. The simple transesterification may be carried out above 180 DEG C., and the reaction with the polyamine at 170-250 DEG C. In the simple transesterification 30-120 equivalent per cent of polyol may be used referred to the carboxylic groups in the polyester. In the modified varnish 3-45 equivalent per cent of polyamine may be used related to the total of OH, NH2 and COOH groups (free and combined) in the reaction mixture. The polyhydric alcohol and the polycarboxylic acid may each amount to 10-50 equivalent per cent of all like groups (i.e. OH + NH2 or COOH) (free or combined), and preferably together provide 10-43% of all such groups. Preferably before addition of the polyamine the mixture contains at least a 5% excess of OH groups. The HMW polyester may be treated with the polyol and polyacid in one stage as such or as a low M.W. polyester or with each in turn before the polyamine is added. Preferably there is added the polyol, then the polyacid, then the polyamine. In Examples 1-6 polyethylene terephthalate scrap is treated with glycol and/or glycerol, then with trimellitic anhydride and methylene dianiline. In Examples 7 and 8 the scrap is treated with trimellitic or maleic anhydride, then with a glycol/glycerol mixture, then with methylene dianiline. In Examples 9-13 the scrap is treated only with glycerol which may contain some pentaerythritol, or with a pentaerythritol/butane-1:3-diol mixture. The product resins melt above 70 DEG C., and may be dissolved in phenol, cresol, cresol/xylene, DMF, xylenol or DMSO.