Multilayered biaxially oriented polyester film, method of its preparation and its use

摘要

Biaxially-oriented polyester film with a base layer (B) of at least 80% thermoplastic polyester and two outer layers (A) and (C), in which (A) has a very smooth surface with essentially no external particles and (C) contains external particles, the number of bumps per unit area of film surface being correlated with the height of the bumps by a special equation. Biaxially-oriented polyester film with a base layer (B) comprising at least 80% thermoplastic polyester and two outer layers (A) and (C), in which (A) has a very smooth surface with essentially no external particles and (C) contains external particles, the number of bumps Nc per mm2 of film surface being correlated with the height of the bumps (h) by the equation Ah1 - Bh1 . log10 h/microns at most log10 (Nc/mm2) .. (1) where h = 0.01-1 micron, Ah1 = 0.05 and Bh1 = 3.3. An Independent claim is also included for a method for the production of this film which involves extrusion or coextrusion to form multilayer flat melt film, stretching the film biaxially and heat-fixing the stretched film.