Tdk Corporation

Kiyoto Fukushima

Kiyonori Hinoki

Shigeo Kurose

Shigeharu Watase

Yoshisuke Yamakawa

Hiroyuki Miyabara

Sadafumi Iijima

Yoshio Kawakami

Shigeru Takamatsu

Shinji Abe

Hiroshi Ohta

Shuji Iida

Eiji Kitaura

Koji Matsuno

Motoyuki Tsunoda

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 2.5 parts by weight of large-sized carbon black or carbon graphite having an average particle size of 150 nm to 500 nm per 100 parts by weight of said carbon black, and a vinyl chloride copolymer as the resin binder, said copolymer containing at least amine-modified vinyl units and acidic functional group-containing vinyl units at the same time, so as to satisfy that the concentration of nonvolatile components is 45 to 60%, and that the P/B is 1.5/1 to 3.5/1, and then, dispersing the kneaded compound by dilution.

Magnetic recording medium

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.

Method for producing magnetic recording medium

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':

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. The magnetic recording medium produced by this invention, therefore, never suffers the surface of the backcoat layer to sustain a scratch, provides thorough protection against the occurrence of instantaneous clogging and DO, and exhibits a veritably excellent running property (evinced particularly by the realization of low torque against the POM guide).

Method for production of magnetic recording medium

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. The magnetic recording medium having such constitution is excellent in running endurance and running properties and shows high electromagnetic conversion characteristics.

Magnetic recording medium having a magnetic layer containing abrasive

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.

Magnetic recording medium having at least two layers wherein the

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.

Lapping tape

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.

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.

Growing community of inventors

Nagano, Japan

Kiyoto Fukushima