PURPOSE: To obtain an insulating membrane of an excellent heat-resisting prop erty by using a varnish mainly of a polyester resin including an imido-ring in the molecular structure, and containing acidic phosphor compound in about 0.05 to 3 equivalent % of the excessive alcoholic hydroxide base of the polyester resin.
CONSTITUTION: To a polybasic acid such as terephthalic acid, imido-acid (dicarboxylic acid) is added in 60 equivalent % or less to the polybasic compo nent. Furthermore, an alcohol of trihydric or more such as glycerin of 20 to 75 equivalent % or more to the polyhydric alcohol component is added to a dihydric alcohol such as etylene glycol, heated at 100 to 250°C, and the water and the alcohol generated are removed to compose a polyester resin containing imido-sings. By including an acidic phosphor compound such as orthophosphoric acid about 0.05 to 3 wt% to the excessive alcoholic hydroxide base of the polyes ter resin when the resin is composed, it acts as a catalyst for ester reaction. By dissolving the resin in cresol or the like, and spreading and baking on a wire or the like, an insulating membrane of an excellent heat-resisting property and a good adhesive property by the acidic phosphor compound can be obtained.
MAZAKI SHIRO
SHIBATA HIROSHI
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