Patent ID: 7977410

Claim:
A fine pore formation agent for porous resin films containing inorganic particles, wherein the inorganic particles satisfy the following formulas (a) to (d) and (f): 0.1≦ D 50≦1.5(μm); (a) Da≦ 20(μm); (b) 3≦ Sw≦ 60(m 2 /g; and (c) Ir≧ 1.0×10 5 (Ω·cm) (d) H x≦ 500(ppm) (f) wherein D50: average particle diameter (μm) of particles in 50% cumulative total by weight from the larger particle side in particle size distribution by laser diffraction spectrometry (micro-track FRA); Da: maximum particle diameter (μm) in the particle size distribution by laser diffraction spectrometry (micro-track FRA); Sw: BET specific surface area (m 2 /g) measured by nitrogen adsorption method; and Ir: volume resistivity (Ω·cm) of hydrochloric acid-insoluble matter; and H X : hydrochloric acid-insoluble matter contained in 500 g of the fine pore formation agent.