| 摘要 |
PROBLEM TO BE SOLVED: To reduce irregurality of quality and stabilize strength of adhesive bonding, by eliminating insulating covering film having adhesive function and defining quantity of steel sheet surface oxide per a single surface of a steel sheet with oxygen METSUKE. SOLUTION: An electromagnetic steel sheet of 0.5 mm in thickness is thermally treated under a condition where degree of circumference oxidation and heating time are variously changed, and specimens different in quantity of oxide which is converted into quantity of oxygen per a single surface of the steel sheet are formed. Water emulsion coating liquid where weight ratio of compositions of acrylic resin, epoxy resin and phenolic resin is 19:4:3 and weight percentage of solid content is 20 wt.% is so spread on the specimens with a roll coater that the quantity of a covering film becomes 8 g/m2 per a single surface. Two test pieces are laminated, heated up to 200 deg.C in a pressing state of 10 kgf/cm2, and held for 60 seconds. Then strength of adhesive bonding is measured. In the condition that quantity of oxide is at least 0.005 g/m and at most 1.0 g/m2, irregurality of strength of adhesive bonding is decreased down to almost±10 kg/cm2, and mean value of strength of adhesive bonding is increased by about 10 kg/cm2 as compared with a case that thermal treatment is not performed before the covering film is spread.
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