Abstract: A biaxially oriented polyethylene-2,6-naphthalate film suitable for producing magnetic recording media wherein the film has a Young's modulus of at least 550 kg/mm.sup.2 in the longitudinal direction and a Young's modulus of at least 800 kg/mm.sup.2 in the transverse direction with the Young's modulus in the transverse direction being greater than the Young's modulus in the longitudinal direction by more than 200 kg/mm.sup.2 ; a surface roughness Ra of 1-12 nm; and low heat shrinkage. The film also contains 0.005-2% by weight inorganic or organic fine particles.

Abstract: A biaxially oriented polyester film which has excellent resistances to dry heat deterioration and wet heat deterioration, which can withstand the use in an atmosphere of relatively high moisture content, and which is useful, for example, as an electrical insulating film, a film for transparent electrode, a film for absorption of electromagnetic wave (e.g. a film used as an inspection window of microwave oven) and a reflection film. This polyester contains ?ethylene-2,6-naphthalenedicarboxylate as the main recurring unit.! 99.5 to 95 mole % of ethylene-2,6-naphthalenedicarboxylate and 0.5 to 5 mole % of ethylene-2,7-naphthalenedicarboxylate and has a density of 1.355 to 1.370 g/cm.sup.3 and an intrinsic viscosity of 0.62 to 0.90. The polyester film has an amount of terminal carboxyl in the polyester of 40 eg/10.sup.6 g or less and an amount of oligomers of 2.0 mg/m.sup.2 film or less.

Abstract: A magnetic recording tape or disk formed from a biaxially oriented laminated polyester base film which comprises a layer (A) of a polyester consisting essentially of 2,6-naphthalenedicarboxylic acid and ethylene glycol components and a layer (B) of a copolyester consisting essentially of 2,6-naphthalenedicarboxylic acid, ethylene glycol, and diethylene glycol components, wherein the copolyester contains 1-5% by weight of the diethylene glycol component, based on the weight of the layer (B) copolyester, layer (B) being present on one or both surfaces of layer (A).

Abstract: A biaxially oriented polyethylene-2,6-naphthalate film suitable for producing magnetic recording media wherein the film has a Young's modulus of at least 550 kg/mm.sup.2 in the longitudinal direction and a Young's modulus of at least 800 kg/mm.sup.2 in the transverse direction with the Young's modulus in the transverse direction being greater than the Young's modulus in the longitudinal direction by more than 230 kg/mm.sub.2, a surface roughness Ra of 1-12 nm; and low heat shrinkage. The film also contains 0.005-2% by weight inorganic or organic fine particles.

Abstract: A biaxially oriented laminated polyester film comprises a polyester substrate layer (A) and a polyester surface layer (B) containing inert particles wherein the polyester surface layer (B) has a thickness of 0.2 to 3 .mu.m with the thickness of the polyester surface layer (B) varying along the film width direction so that the surface layer (B) is thicker at the edges of the film and thinner at the center of the film. The thickness of the surface layer (B) also satisfies specified relationships based on surface layer thickness, birefringence, and orientation angle values at two different points along the film width direction in order to obtain a film whose surface layer (B) has a uniform surface roughness in the film width direction wherein the polyester surface layer (B) has a surface roughness Ra of 3 to 40 nm and a surface roughness Ra fluctuation ratio of 5% or less when measured along a distance of 500 mm in the film width direction. The laminated film can be slit and easily wound into pancake rolls.

Abstract: A biaxially oriented laminated polyester film comprising:(A) a first thin polyester layer formed from an aromatic polyester containing two kinds of inert fine particles having different size and(B) a second polyester layer formed from an aromatic polyester, on at least one surface of which the above first thin polyester layer is present. This biaxially oriented laminated polyester film is is excellent in lubricity, abrasion resistance and scratch resistance and is particularly useful as a base film for a magnetic recording medium.

Abstract: A biaxially oriented laminated polyester film comprising a first thin polyester layer containing large-diameter inert particles and small-diameter inert particles; a second polyester layer containing large-diameter inert particles; and a third thin polyester layer containing large-diameter inert particles and small-diameter inert particles, the biaxially oriented laminated polyester film satisfying the following expression (1), ##EQU1## wherein: W.sub.1 is the content (wt. %) of the large-diameter inert particles in the first thin polyester layer, W.sub.2 is the content (wt. %) of the large-diameter inert particles in the second polyester layer, D.sub.13 is a total of the thickness (.mu.m) of the first thin polyester layer and the thickness (.mu.m) of the third thin polyester layer, and D.sub.2 is the thickness (.mu.m) of the second polyester layer. This film is useful as a base film for a magnetic medium.

Abstract: Provided are a biaxially oriented base film formed from polyethylene-2,6-naphthalenedicarboxylate as a raw material and a high-density magnetic recording floppy disk using the same. The base film and the floppy disk are characteristic in that they inhibit vibration in the film surface and have excellent viscoelasticity thereby to accomplish a contact with a magnetic head under given conditions even when rotated at high speed.

Abstract: A biaxially oriented laminated polyester film comprising a first polyester surface layer having (a1) a central line average roughness R.sub.aA of 1 to 7.9 nm, (b1) a 10-points average roughness R.sub.ZA of 15 to 400 nm and (c1) an R.sub.ZA /R.sub.aA ratio of 11-51, and a second polyester surface layer having (a2) a central line average roughness R.sub.aB which is greater than R.sub.aA and is 5 to 40 nm, (b2) a 10-points average roughness R.sub.ZB of 75 to 600 nm and (c2) an R.sub.ZB /R.sub.aB ratio of 20 or less, and satisfying the relationship between the first polyester surface layer and the second polyester surface layer, which is represented by the following expressions,R.sub.aA .times.R.sub.aB <50 (1)R.sub.ZA .times.R.sub.ZB =130 to 3,000 (2).This biaxially oriented laminated polyester film is excellent in lubricity, high-speed take-up properties, processability and electromagnetic characteristics when used for a magnetic film, and is particularly useful as a base film for a magnetic recording medium.

Abstract: A biaxially oriented laminated polyester film comprising:(A) a first thin polyester layer formed from an aromatic polyester containing two kinds of inert fine particles having different size and(B) a second polyester layer formed from an aromatic polyester, on at least one surface of which the above first thin polyester layer is present. This biaxially oriented laminated polyester film is is excellent in lubricity, abrasion resistance and scratch resistance and is particularly useful as a base film for a magnetic recording medium. The two kinds of inert fine particles include inorganic fine particles having an average particle diameter, d.sub.a of 0.02 to 0.3 .mu.m and organic fine particles having an average particle diameter, d.sub.b of 0.2 to 1.5 .mu.m, and d.sub.b >d.sub.a.

Abstract: A laminated polyester film for use in a magnetic recording medium, which comprises (A) a first layer of a first polyester which contains at least 95 mol %, based on the total content of its dicarboxylic acid components, of a 2,6-naphthalenedicarboxylic acid component and whose main recurring unit is composed of ethylene-2,6-naphthalenedicarboxylate, and (B) a second layer of a second polyester containing 93 to 99 mol %, based on the total content of its recurring units, of an ethylene-2,6-naphthalenedicarboxylate recurring unit. The second layer is laminated on at least one surface of two surfaces of the above first layer.

Abstract: A magnetic recording tape, in particular a VTR tape, comprising;(A) a substrate composed of a biaxially oriented polyethylene-2,6-naphthalate film of which(a) the Young' modulus in the longitudinal direction is at least 650 kg/mm.sup.2, the Young' modulus in a transverse direction is the same as, or greater than, the Young's modulus in the longitudinal direction,(b) the heat shrinkage in the transverse direction is in the range of 1.0 to 3.0% when treated at 100.degree. C. for 30 minutes,(c) the surface roughness, Ra, is not more than 0.005 .mu.m, and(d) the amount of bled-out oligomer is not more than 0.01 area % when treated in air at 160.degree. C. for 5 minutes,(B) a thin magnetic metal layer having a thickness of 100 to 1,500 nm and formed on one surface of the substrate, and(C) a lubricant-containing thin organic polymer layer having a thickness of not more than 1 .mu.

Abstract: A biaxially oriented, unidirectionally long polyethylene-2,6-naphthalate film,(A) which contains(a) 0.05 to 0.4% by weight of first inert solid particles having an average particle diameter of 0.05 to 0.3 .mu.m, and(b) 0.005 to 0.05% by weight of second inert solid particles having an average particle diameter of 0.3 to 1.0 .mu.m, this average particle diameter being greater than the average particle diameter of the first inert solid particles by at least 0.2 .mu.m, wherein:(B) the Young's modulus in the length direction is at least 650 kg/mm.sup.2, the Young's modulus in the width direction is at least 600 kg/mm.sup.2, the Young's modulus in the length direction is greater than the Young's modulus in the width direction,(C) the heat shrinkage factor in the length direction in heat treatment at 70.degree. C. for 1 hour under no load is not more than 0.08%, and(D) the surface roughness, Ra, is 3 to 10 nm; and a magnetic tape obtained therefrom.

Abstract: A biaxially oriented polyester film for magnetic recording media, which comprises:(A) 0.05 to 1.0% by weight of .theta.-aluminum oxide or mixed (.alpha.+.gamma.) aluminum oxide having an average particle diameter in the range of from 0.02 to 0.3 .mu.m and a specific surface area in the range of from 50 to 120 m.sup.2 /g, and(B) 0.01 to 1.5 % by weight of inert organic particles having an average particle diameter which is in the range of from 0.1 to 1.5 .mu.m and greater than the average particle diameter of the aluminum oxide.

Abstract: A magnetic tape for audio cassettes wherein a magnetic layer is provided on base film characterized in that the a base film, is biaxially oriented polyethylene-2,6-naphthalate film having a Young's modulus in the longitudinal direction of 850 Kg/mm.sup.2 or more, a Young's modulus in the transverse direction of 550 Kg/mm.sup.2 or more a surface roughness Ra in the range of 0.015 to 0.040 .mu.m, and a thermal shrinkage rate in the longitudinal direction of 0.3% or less in a case where it was held at a temperature of 100.degree. C. for 1 hour.A magnetic tape for audio cassettes is provided which is capable of long-time recording and wherein deterioration of magnetic characteristics does not easily occur in use, storage and the like at a high temperature, for example in the open during summer or in cars, compared to conventional ones.

Abstract: A biaxially oriented polyester film for magnetic recording media, which comprises:(A) 0.05 to 1.0% by weight of .theta.-aluminum oxide or mixed (.alpha.+.gamma.) aluminum oxide having an average particle diameter in the range of from 0.02 to 0.3 .mu.m and a specific surface area in the range of from 50 to 120 m.sup.2 /g, and(B) 0.01 to 1.5% by weight of inert particles having an average particle diameter which is in the range of from 0.1 to 1.5 .mu.m and greater than the average particle diameter of the aluminum oxide.

Abstract: A process for producing a film of reduced thickness unevenness which comprises extruding a thermoplastic resin from an extrusion die into a film form, exposing the extrudate to an electric field induced by an electrostaticity applying electrode, and then pinning it to the surface of a cooling drum, wherein a shielding object is disposed between the extrusion surface of the die and the electrostaticity applying electrode thereby to maintain the applied voltage constant in the widthwise direction of the extrudate and to enable the extrudate to adhere intimately to the surface of the cooling drum, and an apparatus for producing a film of reduced thickness unevenness comprising an extrusion die equipped with means for adjusting the thickness unevenness of the film by temperature control, an electrode for applying electrostaticity, a cooling drum and a shielding object, said shielding object being a conductive object, a non-conductive object or a combination of these, and being disposed between the extrusion surfa