Patent ID: 8778247
Filing Date: 2014-07-15
Classification: B29C,B29K,C08G,C08J,C08L,H05K

Abstract:
1. A process for the production of a dimensionally stable polymer film, comprising steps of: (i) melt-processing a polymer moulding composition at a temperature above a melting temperature (Tm) to form a polymer melt thereof, wherein the moulding composition comprises at least 80 wt. % relative to the total weight of the polymer composition of a semi-crystalline semi-aromatic polyamide having a melting temperature (Tm) of at least 290° C. as measured according to ASTM D3418-03 by DSC with a heating rate of 10° C. and a glass transition temperature (Tg) measured according to ASTM E 1356-91 by DSC with a heating rate of 10° C., wherein the semi-crystalline semi-aromatic polyamide comprises repeat units derived from dicarboxylic acids and diamines, the dicarboxylic acids consisting of 70-100 mole % terephthalic acid, and other repeat units in a total amount in the range of 0-5 mole %, relative to the total molar amount of repeat units derived from dicarboxylic acids and diamines; (ii) extruding the polymer melt obtained in step (i) into a film and thereafter immediately casting and cooling the film to a temperature below the glass transition temperature (Tg) to form a cast film; (iii) biaxially stretching the cast film obtained in step (ii) at a temperature in a range of Tg-5° C up to and including Tg+10° C.; and (iv) heat-setting the biaxially stretched film obtained in step (iii) at a temperature between the glass transition temperature and the melting temperature to obtain a dimensionally stable polymer film having an average thermal expansion coefficient (TEC) in a temperature range of 20° C.-Tg, measured in a plane according to ASTM D696-08, of at most 40 ppm/K.