| 摘要 |
<p>A transparent biaxially oriented polyester film comprises: (1) a base layer B comprising at least 80 wt.% thermoplastic polyester; (2) at least one intermediate layer Z; and (3) at least one top layer A containing a copolymer or a mixture of homo- and copolymer, which contains specific units. A transparent biaxially oriented polyester film comprises: (1) a base layer B comprising at least 80 wt.% thermoplastic polyester; (2) at least one intermediate layer Z; and (3) at least one top layer A containing a copolymer or a mixture of homo- and copolymer, which contains 85 wt.% ethylene-2,6-naphthalate units and up to 15 wt.% ethylene terephthalate units and/or units from cycloaliphatic or aromatic diols and/or dicarboxylic acids. The intermediate layer Z, from a polymer or a mixture of polymers/copolymers, or copolymers comprises at least 3 wt.% of ethylene-2,6-naphthalate units and/or up to 97 wt.% ethylene terephthalate units from cycloaliphatic or aromatic diols and/or dicarboxylic acids, where the T2 value of the film is higher than that of the polyester of the basic layer B but lower than that of polyester of top layer A. An Independent claim is also included for a preparation of the film from base layer B, intermediate layer Z, and a top layer or layers involving coextrusion of the layers, stretching of the film, and heat fixing of the stretched film. The film is stretched in the longitudinal direction at a 80-130 degrees C and in the transverse direction at 90-150 degrees C, at a longitudinal stretching ratio of 2.5:1 to 6:1, preferably 3:1 to 5.5:1, and a transverse stretching ratio of 3:1 to 5.5:1, preferably 3.5:1 to 4.5:1.</p> |
