SURFACE-TREATED CALCIUM CARBONATE, RESIN COMPOSITION FOR POROUS FILM, AND PRODUCTION OF POROUS FILM

摘要

PROBLEM TO BE SOLVED: To produce a porous film uniform in thickness and hardness. SOLUTION: This surface-treated calcium carbonate is obtained by treating the surface with a surface treating agent comprising an organic substance so as to make the ratio S2/S1 of the specific surface area S1 of the calcium carbonate prior to the surface treatment to the specific surface area S2 thereof after the surface treatment satisfy the formula: 0.55<S2/S1<0.95. The relationship between the grain size D (50% transmitted grain diameter) and the specific surface area S1 prior to the surface treatment of the calcium carbonate satisfies the formula: S1<3.73D0.63. The porous film is produced by forming a thermoplastic resin composition containing the surface treated calcium carbonate into a film and then orienting the formed film.