Spherical alumina powder, resin composition, and heat dissipation material

A resin composition comprising a resin and a spherical alumina powder, the spherical alumina powder having, in a particle size distribution measured with a laser diffraction scattering particle size distribution analyzer,

• a maximum particle diameter showing a maximum peak in the range of 35 to 70 μm, the maximum particle diameter showing a frequency of 5 to 15%, and
• an accumulated value of frequencies respectively at 20 particle diameter points, obtained by dividing a particle diameter range of 1 to 20 μm equally into 19 sections, of 3 to 17% by volume,
• the spherical alumina powder providing
• a ratio (VY/VX) of a viscosity VY of a resin composition Y to a viscosity VX of a resin composition X of 0.85 or more, the resin composition X containing the spherical alumina powder and a vinyl group-containing polymethylsiloxane, the spherical alumina powder being contained in an amount of 88.1% by mass, the resin composition Y being the same as the resin composition X except for containing the same spherical alumina powder as in the resin composition X in an amount of 79.3% by mass and containing an alumina powder for testing in an amount of 8.8% by mass, the vinyl group-containing polymethylsiloxane and the spherical alumina powder for testing satisfying the following conditions:
• the vinyl group-containing polymethylsiloxane
• has a viscosity (23° C., JIS K 6209) of 1.1 to 1.3 Pa·s;
• the alumina powder for testing
• (1) has an average particle diameter (D50) of 6.8 μm, and
• (2) has a specific surface area of 0.4 m2/g,
• wherein the resin is a silicone resin, a fluororesin, a polyamide, a polyimide, a polyamideimide, a polyether imide or a polysulfone.