Patent GB-1082181-A (GB)
Title: Polyester-polyimide wire enamel
Inventor: MEYER JOHN FRAY
IPC: C08G73/16
Filed: 1966-01-04
Abstract: A polyester-polyimide comprises an alcohol component of which at least 20% by weight is tris(2-hydroxyethyl) isocyanurate and at least 50 wt. per cent of the acid component of the polyester is isophthalic or terephthalic acid or benzophenone dicarboxylic acid.  The polyimide constitutes 5-50 equivalent per cent of the polymer, and may be derived from e.g. (a) the anhydrides of trimellitic, pyromellitic, benzophenone - 2:4:21:31 - tetracarboxylic, 2:3:6:7-naphthalene tetracarboxylic and d diphenyl-3:31:4:41-tetracarboxylic acids and (b) methylene dianiline, 3:31-diaminodiphenyl, 1:4-diaminonaphthalene, m and p-phenylene diamines, nonamethylene diamine, 4:41-diaminodiphenyl ether, 4:4-dimethyl heptamethylene diamine - 1:7, diaminodiphenyl-ketone, bis - (4 - aminophenyl) - a ,a 1 - p-xylene, kylene diamines, ethylene diamine, hexamethylene diamine, 4:41-dicyclohexylmethane diamine and diaminodiphenyl sulphone.  These are generally used in a mol ratio of (a):(b) of 2:1, to provide the imide-acid.  The polyester-forming ingredients may be terephthalic, isophthalic and/or benzophenone dicarboxylic acids, and may include, besides the isocyanurate, ethylene glycol, glycerol, trimethylolethane, trimethylolpropane, pentaerythritol, sorbitol, mannitol, dipentaerythritol, trimethylene-, propylene-, tetramethylene- and pentamethylene glycols, neopentyl glycol, butene-2-diol-1:4, butyne-2-diol-1:4, 2:2:4:4-tetramethyl cyclobutane-diol-1:3, p-bis-(b -hydroxy-ethoxy)-benzene and 1:4-cyclohexane dimethanol. Acids suitable to provide up to 50 equivalent per cent of the acid component of the polyester are adipic, o-phthalic, hemimellitic, trimellitic, trimesic, succinic, sebasic, maleic, tetrachlorophthalic and chlorendic acids. When a cyclic-imide-forming dicarboxylic acid is used it should be added after formation of the imide component of the resin.  The polyester imide preferably is formed with an excess of hydroxy groups, equivalent to 1 to 1.6 times the carboxyl content. The polyesterimide is used in wire enamel compositions, and may be prepared in a solvent used in such enamels, e.g. N-methyl pyrrolidone, dimethylacetamide, dimethylformamide, dimethyl sulphoxide, dimethyl sulphone, N - methyl caprolactam, xylene, cresylic acid or a cresol or mixture thereof.  Aliphatic and aromatic hydrocarbon diluents may be added.  The enamel is usually modified by addition of 1-25 wt. per cent of a polyisocyanate and/or 0.01-10 wt. per cent of an alkyl titanate.  Suitable polyisocyanates are the tolylene, m-phenylene, hexamethylene diisocyanates, the trimers of 26 tolylene and diphenylmethane diisocyanates, benzene-1:3:5-triisocyanate, the phenol-blocked reaction product of tolylene diisocyanate and trimethylolpropane, and the m-cresol-blocked trimer of tolylene diisocyanates.  To the enamel may also be added 0.2-1 wt. per cent of metal driers, and 1-5 wt. per cent of a melamine- or phenol-formaldehyde resin.  In the examples a mixture of tris(2-hydroxyethyl) isocyanurate, ethylene glycol and dimethyl terephthalate or of tris(2-hydroxyethyl) isocyanurate and dimethyl benzophenone-dicarboxylate is mixed with trimellitic anhydride and oxydianiline (precondensed in Examples 1-8) in N-methyl pyrrolidone or cresylic acid. Enamels are formed by adding xylene and a chlorophenol/phenol/cresol mixture or cresylic acid, and isopropyl titanate, a phenol-formaldehyde resin, and a m-cresol-blocked trimer of tolylene diisocyanates.