PURPOSE:To avoid the deterioration of an enamel coating and to obtain the high insulation breakdown voltage by using a curing agent without a double bond in the molecules of 50mol% or more of an acid anhydride curing agent to be impregnated in resin when the electric parts including a polyestel enamel copper wire as a material for composing a coil is subjected to an electrical insulation treatment by use of an acid anhydride curing type epoxy resin composition. CONSTITUTION:When the electric parts including a polyestel enamel copper wire as a material for composing a coil is subjected to an electrical insulation treatment, an acid anhydride curing type epoxy resin composition is used for insulation. At this time, there is no particular restriction regarding the epoxy resin and diglycyzirether, deriviatives thereof and etc. are available. For an acid anhydride, hexahydrophthalic acid anhydride, methylhexahydrophthalic acid anhydride and denaturalized substances thereof are used. In addition, for the acid anhydride, the substance without a double bond in molecules is selected and even if the double bond is included, it is restrained at 50% of less.
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