Abstract: A method for producing a magnetic recording medium having low head abrasion loss and excellent mechanical strength characteristics, said medium having a magnetic layer mainly composed of a ferromagnetic powder and a binder on one surface of a non-magnetic support and a backcoat layer on the other surface of the support, wherein said ferromagnetic powder comprises chromium dioxide and cobalt-containing iron oxide within the weight ratio (wt %) range of 40:60 to 70:30, and said magnetic layer is formed of a paint prepared by a process comprising kneading cobalt-containing iron oxide and the binder at a solid concentration of 65% to 85% by weight, subsequently diluting the resulting product with the binder and a solvent, then, adding chromium dioxide thereto, followed by stirring to obtain a mixture, and subjecting the mixture to dispersion.

Abstract: Disclosed is a magnetic recording medium good in production efficiency, paint stability and electromagnetic characteristics, and improved in running properties and durability, which has a magnetic layer formed on a surface side of a non-magnetic support and a backcoat layer formed on a back side thereof, in which said backcoat layer is formed by kneading a compounded composition comprising 50 parts to 120 parts by weight of carbon black (P) per 100 parts by weight of a resin binder (B) (P/B=0.5/1 to 1.2/1), said carbon black (P) having an average particle size of 18 nm to 25 nm and a DBP oil absorption of 90 cc/100 g to 125 cc/100 g, 0.3 part to 2.

Abstract: Disclosed is a method for producing a magnetic recording medium comprising coating both sides of a non-magnetic support with paints for formation of coating films, followed by simultaneous drying of the respective coating films, in which the following four requirements are fulfilled, taking the amount of the paint coated on one side (a magnetic layer side) of the non-magnetic support as "W MAG" and the amount of the paint coated on the other side (a backcoat layer side) thereof as "W BC":2.0 g/m.sup.2 .ltoreq.W MAG.ltoreq.40.0 g/m.sup.2 (1)2.5 g/m.sup.2 .ltoreq.W BC.ltoreq.25.0 g/m.sup.2 (2)3 W MAG.gtoreq.-16 W BC+70 (3)9 W MAG.ltoreq.-10 W BC+385 (4)thereby being able to produce the magnetic recording medium excellent in electromagnetic characteristics, magnetic characteristics and running durability without deteriorating the appearance of a coated sheet roll.

Abstract: This invention produces a magnetic recording medium by applying a magnetic paint for the formation of the magnetic layer and a paint for the formation of the backcoat layer severally to the nonmagnetic support, drying the applied layers of the paints, optionally subjecting the layers to a calendering treatment, performing a curing treatment on the layers thereby adjusting the surface of the backcoat layer to a surface roughness (Ra).sub.B in the range of 10 nm to 30 nm, and thereafter subjecting the surface of the backcoat layer subsequent to the curing treatment to a polishing treatment by the use of a lapping tape the abrasive layer of which has a surface roughness (Ra).sub.L in the range of 150 nm to 550 nm. In a preferred embodiment of this invention, the Mohs hardness of the abrasive grains contained in the abrasive layer is set within a prescribed range and the conditions of the curing treatment are fixed within prescribed ranges.

Abstract: Disclosed is a magnetic recording medium comprising a nonmagnetic support and a paint film layer which is provided on the support and has a lamination structure consisting of two or more layers, wherein the top surface magneticlayer of the layers constituting the paint film layer contains abrasive particles having a Mohs hardness of not less than 6 in an amount of 3 to 16 parts by weight based on 100 parts by weight of a ferromagnetic powder and has a thickness of not more than 0.5 .mu.m, a ratio of a mean particle diameter of the abrasive particles to the thickness of the top surface magnetic layer is in the range of 1.0 to 1.8, and a content of the abrasive particles each having a size larger than the thickness of the top surface magnetic layer in the particle size distribution of the abrasive particles is in the range of 50 to 90% by weight.

Abstract: A magnetic recording medium has at least two coating layers on a non-magnetic substrate. The uppermost layer of the coating layers is a magnetic layer having a thickness of 0.2-0.5 .mu.m thick and comprising a ferromagnetic powder, inorganic material-containing alumina particles having a mean particle size of 0.1-0.3 .mu.m, and a binder. The medium ensures effective head cleaning and has improved durability and still life.

Abstract: A lapping tape has an abrasive coat which comprises an acicular iron oxide powder having a surface area of at least 30 m.sup.2 /g as determined by the BET method and a granular inorganic powder having a Moh's hardness of more than 7 and contained in an amount of from 2.0 to 30 percent by weight on the basis of the weight of the oxide powder. The coat has a centerline mean roughness between 0.015 and 0.03 .mu.m. Preferably the acicular iron oxide is magnetic, and the inorganic powder ranges in particle diameter from 0.05 to 0.4 .mu.m.

Abstract: In a magnetic recording medium consisting of a base coated with a magnetic coating material, or a dispersion of magnetic particles in a resinous binder, the binder comprises a copolymer composed of vinyl chloride, a vinyl alkylcarboxylate, another monomer copolymerizable with vinyl chloride, and a saponified vinyl alkylcarboxylate and having an OH/CH absorption ratio according to the infrared absorption spectrum of 0.2 to 0.7, a polyurethane resin having in its molecule a --SO.sub.3 M group wherein M represents an alkali metal atom, and a polyurethane resin or polyester resin or both containing no --SO.sub.3 M group wherein M represents an alkali metal atom, and a polyisocyanate.

Abstract: A magnetic recording medium having deposited on the surface of a non-magnetic substrate a magnetic layer formed by dispersing a powdered magnetic substance and a powdered abrasive in a binder, which magnetic recording medium is characterized by having abrasive particles activated on the surface thereof.