Process for making polyester photographic film base and photographic element comprising said base

Abstract

A process for making polyester film base material comprising more than 65 mol % of 1,4-cyclohexanedimethanol (CHDM) of the total glycol component in the polyester material. The film base is prepared by sequentially carrying out the following steps: (a) casting a molten polyester resin in a machine direction onto a casting surface to form a continuous 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 70° C. to 130° C., (c) tentering the sheet in the transverse direction by stretching at a stretch ratio of from 2 to 4, and at a temperature ranging from 70° C. to 130° C. to obtain a biaxially oriented film, (d) heat-setting the oriented film at an actual temperature of from 160° C. to 200° C., and (e) cooling the heat-set film without substantial detentering to obtain a biaxially oriented, heat-set polyester-based film having a cutting index of 1 to 1.5 and a tensile toughness ranging from 15 to 55 MPa. The invention is also directed towards a silver halide light sensitive photographic element comprising the PET-based film base made by the present process. The photographic film base of the invention exhibits excellent dimensional stability, optical clarity and mechanical strength while also possessing a crystalline morphology that enables finishing by cutting, chopping or perforating techniques at reduced cutting index without requiring a detentering step after heat-setting.