Fabricating polyester film e.g. biaxially oriented polyethylene terephthalate film used for manufacturing photovoltaic cell, comprises drying material constituted of discrete elements and then extruding through die to form multilayer

The process comprises providing a first material constituted of discrete elements such as granules of polyester having an average molecular weight of 18000-40000 and an intrinsic viscosity of 0.6-1.2 dl/g, drying the first material, optionally mixing the raw materials to promote homogenization, extruding the first material through a die for forming a monolayer or a multilayer and the rapidly cooling, optionally coating a side of the film to impart specific properties to the film, biaxially stretching the film according to a draw ratio and a draw temperature to obtain a crystalline phase. The process comprises providing a first material constituted of discrete elements such as granules of polyester having an average molecular weight of 18000-40000 and an intrinsic viscosity of 0.6-1.2 dL/g, drying the first material, optionally mixing the raw materials to promote homogenization, extruding the first material through a die for forming a monolayer or a multilayer and the rapidly cooling, optionally coating a side of the film to impart specific properties to the film, biaxially stretching the film according to a draw ratio and a draw temperature to obtain a crystalline phase, thermosetting the film at a temperature of 180-250[deg] C, performing transverse relaxation of the film, winding the film and then performing cutting, coating, vacuum coating, annealing and/or UV, plasma or corona treatment, controlling the hydrolysis resistance and/or performance of the film, and increasing the thickness of crystallites to increase adhesion of film. The parameters of the steps are selected to control a thickness of the film or to increase a thickness of the film. The longitudinal stretching is performed at a draw ratio of 2-6, 2.5-5 or 2.8-4.5 and a draw temperature of 70-150[deg] C, 85-140[deg] C or 90-135[deg] C. The transverse stretching is performed at a draw ratio of 2-6, 3.5-5 and 3.5-4.5 and at a draw temperature of 95-150[deg] C, 105-145[deg] C and 110-140[deg] C. During the thermosetting process of the film, the rise in temperature is 4-14[deg] C/second. An independent claim is included for a biaxially oriented polyester film. L'invention concerne un procédé de fabrication d'un film polyester, de préférence un film polyéthylène téréphtalate PET, biétiré et comprenant des cristallites; caractérisé en ce qu'il comprend les étapes suivantes (a) Mise en oeuvre de granulés, à base de polyester (15000 et 50000D), et de viscosité intrinsèque comprise entre 0,4 et 1,3 dL