Patent ID: 6737226
Filing Date: 2004-05-18
Classification: B29C,B29K,C08J,G03C,Y10T

Abstract:
A process for making a biaxially stretched polyester photographic film base comprising the steps of:(a) casting a molten form of a PET-based polyester material comprising more than 65 mol % of 1,4-cyclohexanedimethanol, based on the total glycol component in the material, onto a casting surface in a machine direction to form a continuous solid sheet, (b) drafting the sheet by stretching in the machine direction at a stretch ratio of from 2 to 4, and at a temperature ranging from 80Â° C. to 130Â° C., (c) tentering the sheet in a transverse direction by stretching at a stretch ratio of from 2 to 4, and at a temperature ranging from 80Â° C. to 130Â° C., (d) heat-setting the tentered sheet at an actual heat-set temperature in the range of from 160Â° C. to 191Â° C., wherein the actual heat-set temperature is determined from a differential scanning calorimetry thermogram of the biaxially-stretched sheet and is represented by the secondary low-temperature melting peak recorded on the thermogram, and, (e) cooling the heat-set sheet to obtain a stretched, heat-set PET-based polyester film having a cutting index of 1 to 1.5 and tensile toughness of 15 to 55 MPa.