PURPOSE: To obtain the titled film improved in abrasion resistance and running stability, by using a composition obtained by adding specified non-incorporated particles depositing in a reaction system and a surface-roughening agent to a polymer based on a polyester.
CONSTITUTION: A composition is obtained by adding non-incorporated particles depositing in a reaction system (A), average particle diameter of 0.3W3μ, containing at least 1 part of at least one element selected from among 0.005W0.025wt% Li, 0.01W0.04wt% Ca, 0.02W0.05wt% P and 0.02W0.04wt% Sb and 0.005W0.2wt% inorganic inert incorporated particles (B) (e.g., TiO2) of an average particle diameter of 0.1W3μ as a surface-roughening agent to a polyester based on an aromatic dibasic acid ester containing at least 80mol%, based on the main repeating units, ethylene terephthalate units. This composition is formed into a sheet, and this sheet is biaxially oriented to obtain a biaxially oriented polyester film for magnetic tapes on at least either surface of which fine protrusions of a parameter of distribution (PD value) ≥0.5 are formed.
MOGI MASAHIKO
KIDA KATSUMI
