Abstract: A biaxially oriented polyester film having excellent scratch resistance and chipping resistance by the inclusion of particles (A) having an average primary particle diameter of 5-300 nm, an average degree of aggregation of 5-100 and a Mohs' hardness of 6-10 by the content of 0.01-5 wt. %. The scratch resistance and chipping resistance of the film can be further increased by the inclusion of particles (B) having an average particle diameter of 0.3-3 .mu.m, a Mohs' hardness smaller than that of particles (A) and/or non-incorporated particles.

Abstract: A biaxially oriented polyester film wherein the ratio (=I.sub.MD /I.sub.ND) of the peak intensity (I.sub.MD) in the longitudinal direction to the peak intensity (I.sub.ND) in the thickness direction determined at 1615 cm.sup.-1 by laser Raman scattering method is 6 or more; and a process for production of a biaxially oriented polyester film which comprises the steps of controlling the ratio (A/B) of the maximum thickness (A) of the edge portion of a cast film to the thickness (B) of the central portion in the transverse direction thereof in the range of 2 to 6, biaxially stretching the cast film, and controlling the peak intensity ratio of the biaxially oriented film determined by the laser Raman scattering method in the above-described range. The biaxially oriented polyester film thus produced has a specific orientation in the longitudinal direction, and therefore has great strength in the longitudinal direction and small irregularity in properties such as thickness or birefringence.

Abstract: A biaxially oriented polyester film having excellent scratch resistance and chipping resistance by the inclusion of particles (A) having an average primary particle diameter of 5-300 nm, an average degree of aggregation of 5-100 and a Mohs' hardness of 6-10 by the content of 0.01-5 wt. %. The scratch resistance and chipping resistance of the film can be further increased by the inclusion of particles (B) having an average particle diameter of 0.3-3 .mu.m, a Mohs' hardness smaller than that of particles (A) and/or non-incorporated particles.

Abstract: Disclosed is a biaxially oriented film and a laminated film containing specified organic particles at a content of 0.001 to 20% by weight. The strength when deformed by 10% (S.sub.10) of the organic particles is in the range of 3 to 30 kgf/mm.sup.2, the thermal decomposition temperature for causing 10% loss in weight thereof is not lower than 350.degree. C. The weight average diameter thereof is in the range of 0.005 to 5 .mu.m. Since the organic particles have a good affinity with the matrix resin of the film and a good thermal resistance and the hardness of the particles is appropriate, desired protrusions hardly chipped and having an appropriate hardness for hardly scratching a magnetic surface can be formed on a film surface easily and uniformly. Therefore, a film excellent in abrasion resistance and scratch resistance at a high running speed and excellent in running durability can be obtained, which is useful particularly as a base film of a magnetic tape.

Abstract: Disclosed is a biaxially oriented laminated film having at least three layers which has excellent abrasion resistance and electromagnetic conversion property when the film is used as the base film of a magnetic recording media. The biaxially oriented laminated film comprises at least one outermost layer containing particles A, the particle density ratio at surface layer of the particles A is not less than 0.01, and the mean primary particle size D of the particles A and the thickness T of the outermost layer containing the particles A satisfies the equation; D.ltoreq.T.ltoreq.200D.

Abstract: A biaxially oriented polyester film having excellent scratch resistance and chipping resistance by the inclusion of particles (A) having an average primary particle diameter of 5-300 nm, an average degree of aggregation of 5-100 and a Mohs' hardness of 6-10 by the content of 0.01-5 wt. %. The scratch resistance and chipping resistance of the film can be further increased by the inclusion of particles (B) having an average particle diameter of 0.3-3 .mu.m, a Mohs' hardness smaller than that of particles (A) and/or non-incorporated particles.

Abstract: A biaxially oriented polyester film suited as a substrate for magnetic recording media. The film comprises a polyester and inert particles and has at least one surface with protrusions formed by the existence of the inert particles. The surface has a parameter of surface topography .sqroot.(.beta./.sigma.) of 0.1 to 0.7. The average distance between adjacent protrusions is not more than 20 um and the coefficient of friction of the surface and the parameter of surface topography satisfies the following equations (1) and (2): ##EQU1## wherein y is the coefficient of friction, .beta. is mean flatness of protrusions and .sigma. is standard deviation of height distribution of protrusions.