Biaxially oriented polyester film

摘要

A biaxially oriented polyester film formed from an aromatic polyester composition containing: (A) 100 parts by weight of an aromatic polyester, and (B) 0.005 to 5 parts by weight of calcium carbonate particles defined by: (a) a length/width ratio (2a/2b) in the range of from 1.25 to 3, (b) an average particle diameter (D), as a diameter of a circle converted from an area, in the range of from 0.05 to 5 mu m, and (c) an ellipse coefficient, represented by the following equation (1), in the range of from 0.7 to 1.2, $wherein\; R\; is\; an\; ellipse\; coefficient,\; S1\; is\; an\; observed\; area\; of\; a\; projected\; plane\; of\; a\; particle,\; and\; S2\; is\; an\; elliptical\; area\; determined\; on\; the\; basis\; of\; observed\; values\; of\; the\; length\; (2a)\; and\; width\; (2b);\; and\; a\; magnetic\; recording\; medium\; formed\; of\; the\; above\; biaxially\; oriented\; polyester\; film\; and\; a\; magnetic\; layer\; formed\; thereon.$