| abstract |
(57) [Abstract] [Problem] It has excellent uniform light diffusivity and heat-resistant dimensional stability. Provided is a polyester film which is excellent in luminance and is suitable as a substrate of a light diffusion plate of a liquid crystal display device. SOLUTION: (1) The main repeating unit is ethylene- It is composed of an aromatic polyester which is 2,6-naphthalenedicarboxylate, and (2) orthogonally crosses in the film plane. In the direction, the heat shrinkage when heat-treated at 105 ° C. for 30 minutes under no load is 0.3% or less. (3) From 30 ° C. to 1 under a load of 0.37 MPa based on the cross-sectional area of the film. A dimensional change rate in a temperature range of 50 ° C. is 1.0% or less in two orthogonal directions in a film plane; (4) a density of 1.350 g / cm 3 or more; The total light transmittance is 87% or more, (6) the haze value is less than 1.5%, and (7) the thickness is 50 to 130 μm. m, a biaxially oriented polyester film for a light diffusion plate. |