| abstract |
A white-colored porous polymer film having elongated spherical pores, which is characterized in that said pores exposed on a surface created by cutting the film along longitudinal direction satisfy the following formulae, possesses a low density, good surface and mechanical property and good processability: <IMAGE> wherein, PL,90 is an average length of longer axes of 90% or more of the exposed pores; PD,90 is an average length of shorter axes of 90% or more of the exposed pores; PL/D,50 is an average of the longer axis to the shorter axis length ratios of the exposed pores; PN is the number of exposed pores per 1000 mu m2 of the exposed surface; and PA is the ratio of the exposed pore area to the exposed surface area. The polymer film of the present invention comprises a polyester and polyolefin resin mixture, inorganic particles, a metal sulfonate and a hindered phenol. |