Teijin Limited

Minoru Tamura

Shigenobu Sobajima

Yoichi Azuma

Kiyoshi Takekata

An electrically insulating powdery material with a volume resistivity of at least 1 .times. 10.sup.10 ohms-cm, which consists of a calcined product of a mixture of magnesium oxide with boron oxide and if desired, at least one of titanium, iron and chromium oxides and has a special novel structure wherein a core of magnesium oxide particles is surrounded by a sheath of a double oxide of the magnesium oxide and the boron oxide and if desired, the other metal oxide. This insulating powdery material is produced by calcining the above mixture under specified calcining conditions determined by a special temperature-time relation. A thermally conducting and electrically insulating resin composition especially having superior electrical properties under high temperature-high humidity conditions can be prepared using the above powdery material as a filler.

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Hachioji, Japan

Minoru Tamura