Abstract: A white polyester film containing voids, wherein a resin constituting the film has a layer (layer A) formed by using a polyester resin and a cyclic olefin copolymerized resin, and wherein a void ratio taken in a cross-section of the layer is more than 25% and 75% or less and the average particle size of the cyclic olefin copolymerized resin in the film is 0.1 ?m or more and 3 ?m or less.

Abstract: A white polyester film containing voids, wherein a resin constituting the film has a layer (layer A) formed by using a polyester resin and a cyclic olefin copolymerized resin, and wherein a void ratio taken in a cross-section of the layer is more than 25% and 75% or less and the average particle size of the cyclic olefin copolymerized resin in the film is 0.1 ?m or more and 3 ?m or less.

Abstract: This invention relates to a polyester film suited for use in optical recording medium. The polyester film of the present invention has a modulus of photoelasticity of not more than 0.9.times.10.sup.-3 mm.sup.2 /kgf, a maximum surface roughness Rt of not more than 100 nm and a mean interval Sm between adjacent surface projections of not less than 20 .mu.m, so that light scattering and interference are not caused, and optical strain is not generated even when a thermal stress or external force is exerted to the film. Thus, the polyester film of the present invention can be used as the supporting layer or cover layer of optical recording media such as optical cards, optical disks and optical recording tapes.

Abstract: A polyester film comprising a polyester whose dicarboxylic acid copolymerized component contains (i) an aromatic dicarboxylic acid having a metal sulfonate and/or a derivative thereof and (ii) a polyetherdicarboxylic acid represented by the following chemical formula (a) and having a mean molecular weight in the range of 600 to 20000 and/or a derivative thereof.R.sup.1 OOCCH.sub.2 --(O--R.sup.2).sub.n --OCH.sub.2 COOR.sup.3(a)Where, "R.sup.1 " and "R.sup.3 " are alkyl groups each having a carbon number of 1 to 8, "R.sup.2 " is alkylene group having a carbon number of 2 to 8 and "n" is a positive integer. The polyester film has excellent transparency, mechanical properties and dimensional stability such as those of a PET film and an excellent water absorption property such as that of a TAC film.

Abstract: A polyester film comprising a polyester whose dicarboxylic acid copolymerized component contains (i) an aromatic dicarboxylic acid having a metal sulfonate and/or a derivative thereof and (ii) a polyetherdicarboxylic acid represented by the following chemical formula (a) and having a mean molecular weight in the range of 600 to 20000 and/or a derivative thereof.R.sup.1 OOCCH.sub.2 --(O--R.sup.2).sub.n --OCH.sub.2 COOR.sup.3 (a)Where, "R.sup.1 " and "R.sup.3 " are H or alkyl groups each having a carbon number of 1 to 8, "R.sup.2 " is alkylene group having a carbon number of 2 to 8 and "n" is a positive integer. The polyester film has excellent transparency, mechanical properties and dimensional stability such as those of a PET film and an excellent water absorption property such as that of a TAC film.