| 摘要 |
PROBLEM TO BE SOLVED: To reduce the variation of the adhesive strength of a magnetic steel sheet for laminated bonded core by adjusting the pencil hardness of the coating films of the steel sheet to a specific value. SOLUTION: A water emulsion type coating solution containing acrylic, epoxy, phenol resins at a mixing ratio of about 20:60:20 wt.% among them and at a solid content of about 20 wt.% is applied to a magnetic steel sheet at a rate of about 8 g/m2 on one surface by using a roll coater. Then the hardness of the films formed by drying the solution is adjusted by adjusting the drying temperature and drying time. The hardness of the coating films is determined by the so-called pencil hardness method by which whether or not the coating films are scratched with a pencil is judged. When the pencil hardness falls within the range of 2H to 5H, the average value of the bonding strength is as high as about >=170 kg/cm2 and the variation of the strength is reduced and stabilized. In addition, the coating films are not damaged so much.
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