Abstract: A biaxially oriented laminated polyester film which is excellent in film winding properties and handling properties and provides excellent electromagnetic conversion characteristics when it is used as a base film for high-density magnetic recording media, particularly digital recording magnetic recording media. This film consists of a polyester A layer and a polyester B layer formed on one side of the polyester A layer and is characterized in that: (1) the polyester A layer contains three different types of fine particles which differ from one another in average particle diameter and has a surface roughness WRa of 5 to 20 nm and a WRz of 100 to 300 nm, (2) the polyester B layer has a surface roughness WRa of 2 to 10 nm and a WRz of 30 to 150 nm, and (3) the film has a friction coefficient of 0.5 or less.

Abstract: A biaxially oriented polyester film for a high-density magnetic recording medium, particularly a high-density magnetic recoding medium of linear recording system, which has high strength in longitudinal and transverse directions, excellent dimensional stability in a crosswise direction and is flat and excellent in output characteristics and a process for producing the same. The biaxially oriented film is made from polyethylene-2,6-naphthalate and has a Young's modulus in a longitudinal direction of 8 GPa or more, a Young's modulus in a transverse direction of 6 GPa or more, a temperature expansion coefficient in the transverse direction (&agr;t) of −5×10−6/° C. to +12×10−6/° C., a humidity expansion coefficient in the transverse direction (&agr;h) of 5×10−6/%RH to 12×10−6/%RH and a thermal shrinkage factor in the transverse direction at 105° C. of −0.5 to +1.

Abstract: A biaxially oriented laminate polyester film (1) has a first polyester layer having a thickness (tA) of 0.3 to 5 &mgr;m and a second polyester layer containing an inert fine particle lubricant and having a thickness (tB) of 1.5 to 9 &mgr;m, or (2) has a first polyester layer having a thickness (tA) of 2 to 8.5 &mgr;m and a second polyester layer containing an inert fine particle lubricant and having a thickness (tB) of 0.6 to 5 &mgr;m. The polyester of the second polyester layer may contain a recovered polyester having the same composition as a recovered laminate polyester film which is the biaxially oriented laminate polyester film or an unstretched film thereof.

Abstract: A biaxially oriented laminated polyester film comprising a first polyester layer which contains two different types of inert fine particles having different average particle diameters and has a surface roughness of 4 to 15 nm and a second polyester layer which may contain inert fine particles and has a surface roughness of 0.5 to 3.5 nm. The film has a friction coefficient between the first polyester layer and the second polyester layer of 0.5 or less and a good roll form. A cover layer may be further formed on the second polyester layer. The film can be used as a magnetic recording medium by forming a magnetic layer on the second polyester layer or the cover layer overlying the second polyester layer.

Abstract: A biaxially oriented laminate polyester film (1) has a first polyester layer having a thickness (tA) of 0.3 to 5 &mgr;m and a second polyester layer containing an inert fine particle lubricant and having a thickness (tB) of 1.5 to 9 &mgr;m, or (2) has a first polyester layer having a thickness (tA) of 2 to 8.5 &mgr;m and a second polyester layer containing an inert fine particle lubricant and having a thickness (tB) of 0.6 to 5 &mgr;m.

Abstract: A biaxially oriented laminate polyester film (1) has a first polyester layer having a thickness (tA) of 0.3 to 5 &mgr;m and a second polyester layer containing an inert fine particle lubricant and having a thickness (tB) of 1.5 to 9 &mgr;m, or (2) has a first polyester layer having a thickness (tA) of 2 to 8.5 &mgr;m and a second polyester layer containing an inert fine particle lubricant and having a thickness (tB) of 0.6 to 5 &mgr;m. The polyester of the second polyester layer may contain a recovered polyester having the same composition as a recovered laminate polyester film which is the biaxially oriented laminate polyester film or an unstretched film thereof.

Abstract: A biaxially oriented laminate polyester film in which each of the layers contains at least two different lubricant particles, and each of two members out of the lubricant particles of one layer and each of two members out of the lubricant particles of the other layer have the same substrates and the same average particle diameters, respectively, the biaxially oriented laminate polyester film enables the direct recycling of the recovered polymer for production of the film.

Abstract: A biaxially oriented laminate polyester film consisting of a polyester layer A containing lubricant particles I and II and a polyester layer B laminated on one side of the polyester A, wherein each of the lubricant particles I and II contains non-agglomerated particles in a proportion of 80 to 100%; the lubricant particles I are selected from the group consisting of silica, calcium carbonate and crosslinked polymer particles and have an average particle diameter of 0.3 to 1.0 .mu.m and are contained in an amount of 0.005% by weight or more but less than 0.1% by weight; the lubricant particles II are selected from the group consisting of silica and crosslinked polymer particles and have an average particle diameter which satisfies the following expression (1):1<d.sub.I /d.sub.II .ltoreq.10 (1)wherein d.sub.I is an average particle diameter of the lubricant particles I and d.sub.II is an average particle diameter of the lubricant particles II,and are contained in an amount of 0.

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 polyethylene-2,6-naphthalenedicarboxylate film, which can be used as a base film for a recording medium capable of high-density recording, characterized in that when h (unit: nm) stands for a height of a protrusion formed on the film surface, the numbers of protrusions in the range of 1.ltoreq.h<50, 50.ltoreq.h<100, and 100.ltoreq.h fall each within a specified range, that the film has a plane orientation coefficient (NS) and an average refractive index (n.sub.a) which satisfy the relationship NS.gtoreq.1.607n.sub.a -2.434, that the film has a surface roughness (Ra) of 2-10 nm and that the film has a heat shrinkage in the longitudinal direction of 0.08% or less when heat-treated under no load at 70.degree. C. for 1 hour.

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 polyester film, (A) which is formed from polyethylene-2,6-naphthalenedicarboxylate containing 0.01 to 1% by weight of inert solid fine particles having an average particle size of 0.05 to 3 .mu.m, (B) which has a refractive index, in a film thickness direction, of at least 1.498, and (C) which has a Young's modulus, at least in one direction, of at least 700 kg/mm.sup.2 ; and a process for the production thereof. This film is useful as a magnetic recording medium, particularly as a base film excellent in abrasion resistance and tear resistance.