Method for forming an electric insulating film having excellent punching property and heat resistance on an electrical steel sheet

摘要

A method for forming on an electrical steel sheet an electric insulating film having excellent punching property and heat resistance comprising coating on the steel sheet a treating solution comprising a composition composed of one or more of chromic anhydride, chromate, bichromate and 1 - 35 parts (as solid) of styrene resin containing not less than 50% stylene and/or vinyl acetate resin emulsion per 10 parts of chromium ion in the composition and heating the coating at a temperature between 150 DEG and 500 DEG C.