GB1057727A - Improvements in or relating to electrically insulating varnishes and to electrically insulating materials produced therefrom - Google Patents

Abstract

A process for the preparation of an electrically insulating varnish comprises reacting (a) at least one tetracarboxylic acid dianhydride and/or at least one tetracarboxylic acid monoester monoanhydride in which the carboxyl group and the ester group are attached to adjacent carbon atoms, and/or at least one tetracarboxylic acid diester in which a carboxyl group and an ester group are attached to adjacent carbon atoms, with (b) at least one diprimary diamine containing at least 2 carbon atoms, at a temperature below 100 DEG C. in the presence of a solvent consisting of or including at least one phenol and at least 75 mol. per cent (based on the total amount of tetracarboxylic acid derivatives) of at least one volatile tertiary amine. The products may be converted by thermal or chemical treatment to polyimides. Specified diamines are benzidine, 4:41 - diaminophenylmethane, 4:41 - diaminophenylpropane, 4:41 - diaminophenylether, 4:41 - diaminophenylsulphone, 2:11 - diaminododecane, 4:41 - diaminophenyl sulphide, 1:2 - bis - (3 - aminopropoxy) ethane, 2:17 - diaminoeicosadecane, 1:4 - diaminocyclohexane, 1:10 - diamino - 1:10 - dimethyldecane, 1:12 - diamino octadecane, the bis-p-amino ethers of 4:41-dihydroxyldiphenyl, diphenylol propane, diphenylol methane, diphenylol ether, diphenylol sulphone and hydroquinone and m- and p-phenylene, 2:4 - toluylone, hexamethylene, octamethylene, nonamethylene, decamethylene, tetramethylene, 3 - methylheptamethylene, 4:4 - dimethylheptamethylene, - 2:2 - dimethylpropylene, 3 - methoxyhexamethylene, 2:5 - dimethylhexamethylene, 2:5 - dimethyl heptamethylene, 3 - methyl heptamethylene and 5 - methylnonamethylene diamine. Specified acid derivatives are those of pyromellitic, 2:3:6:7 - naphthalene tetracarboxylic, 3:31:4:41 - diphenyl tetracarboxylic, 1:2:5:6 - naphthalene tetracarboxylic, 2:21:3:31 - diphenyl tetracarboxylic, perylene - 3:4:9:10 - tetracarboxylic and ethylene tetracarboxylic acid, and bis - (3:4 - dicarboxyyphenyl) sulphone and bis - (3:4 - dicarboxyphenyl) ether. Specified solvents are phenol, cresol, xylenol and mixtures thereof, optionally admixed with benzene hydrocarbons or esters. Specified amines are N:N-dimethyl aniline, N:N-diethylaniline, pyridine, prioline, lutidine, collidine and quinoline.ALSO:A process for producing an electrically insulating coating comprises depositing a layer of a varnish made by reacting a tetracarboxylic acid dianhydride and/or a tetracarbocylic acid monoester monoanhydride and/or a tetracarboxylic acid diester with a primary diamine in the presence of a phenol and a volatile tertiary amine (see Division C3) on a base, removing the solvent therefrom and converting the residual product to a polyimide by thermal or chemical treatment. Examples 1 to 5 describe the coating of copper wire with polyimides derived from pyromellitic dianhydride and:- (1) and (4) 4:4\sv-diaminodiphenyl ether; (2) and (3) m-phenylene diamine and 4:4\sv-diaminophenyl ether, and (5) 4:4\sv-diphenylolpropone- 2:2- di (-p-aminophenyl) ether.