Patent ID: 7471182

Claim:
A core having a superior end face insulation characterized in that end faces of the core are treated to give an insulation coating having an average film thickness of at least 0.5 μm, a breakdown voltage of at least 30V, and a heat resistance in air of at least 400° C. for 1 hour, comprised of at least 30 wt % of a silicon compound converted to SiO 2 , and said silicone compound is a dried film comprised of one or more types of a silicone resin, alkali silicate, colloidal silica, low melting point glass frit, a pure silicone polymer comprised of a compound produced by a hydrolysis reaction and dehydration condensation reaction of one or more types of substances expressed by (R 1 ) n Si(X 1 ) 4-n (where n is an integer of 0 to 3, R 1 is an alkyl group or phenyl group, the plurality of R 1 able to be different when n=2 or 3, X 1 being Cl (chlorine) or an alkoxy group expressed by O (R 2 ), where R 2 is an alkyl group, and the plurality of R 2 able to be different when n=0, 1, or 2), a modified silicone polymer comprised of a compound produced by a hydrolysis reaction and dehydration condensation reaction of one or more types of substances expressed by (R 3 ) n Si (X 2 ) 4-n (where n is an integer of 0 to 3, R 3 is an organic functional group other than an alkyl group or phenyl group, the plurality of R 3 able to be different when n=2 or 3, X 2 being Cl (chlorine) or an alkoxy group expressed by O (R 4 ), where R 4 is an alkyl group, and the plurality of R 4 able to be different when n=0, 1, or 2), and a mixed silicone polymer produced by a hydrolysis reaction and dehydration condensation reaction of one or more types of compounds expressed by (R 1 ) n Si (X 1 ) 4-n (where n is an integer of 0 to 3, R 1 is an alkyl group or phenyl group, the plurality of R 1 able to be different when n=2 or 3, X 1 being Cl (chlorine) or an alkoxy group expressed by O (R 2 ), where R 2 is an alkyl group, and the plurality of R 2 able to be different when n=0, 1, or 2) and one or more types of substances expressed by (R 3 ) n Si(X 2 ) 4-n (where n is an integer of 0 to 3, R 3 is an organic functional group other than an alkyl group or phenyl group, the plurality of R 3 able to be different when n=2 or 3, X 2 being Cl (chlorine) or an alkoxy group expressed by O (R 4 ), where R 4 is an alkyl group, and the plurality of R 4 able to be different when n=0, 1, or 2).