Showa Denko K.k.

Tomiharu Yamada

Eiji Kanbara

Yukihiko Takahashi

One embodiment of the invention provides the corundum for filling in resin comprising three components having different secondary particle sizes and specific surface areas as follows: component X of 35 to 80 &#x3bc;m and 1 to 0.01 m/g; component Y of 1 to 5 &#x3bc;m and 3 to 0.5 m/g; and component Z of 0.3 to 1.5 &#x3bc;m and 15 to 3 m/g, with a composition ratio by mass (X:Y:Z) being in the range surrounded by four points of (60:40:0), (95:0:5), (95:5:0) and (60:0:40) not including the borderlines in the ternary compositional diagram, and a composition obtained by filling a specific amount of the corundum into silicone oil has a viscosity of less than 2,000 poise and a linseed oil absorption of 10 ml/100 g or less.

Corundum for filling in resin and resin composition

A process for producing roundish alumina particles includes heating at 1,000 to 1,600&#xb0; C. a composition containing at least one of electrofused alumina and sintered alumina having a mean particle size greater than 35 &#x3bc;m, and at least one species selected from the group consisting of a halogen compound, a boron compound and an alumina hydrate; and crushing the composition.

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Kanagawa, Japan

Tomiharu Yamada