Multilayer, biaxially oriented polyester film, method for its production and its use

摘要

A specific cover layer protrusion distribution is used to give the films improved aesthetic and oxygen barrier properties. A biaxially oriented, coextruded polyester film containing at least three layers includes at least one basis layer (B) comprising at least 80 wt.% thermoplastic polyester and cover layers (A, C) on either side of the basis layer, which contain internal (sic) and/or inert particles. The number (N) of protrusions present in (A) and (C) per mm<2> is defined by the following equations (1) and (2) : h = protrusion height ; d = protrusion diameter ; Ad1 = 1.700 ; Ad2 = 4.700 ; Ah1 = -1.000 ; Ah2 = 2.477 ; Bd1 = 3.86 ; Bd2 = 3.7 ; Bh1 = 3.7 ; and Bd2 = 2.22. An Independent claim is also included for the preparation of the films by extrusion a polyester melt corresponding to the material used in (A)-(C) onto a cooling roll, biaxially stretching and heat-setting.