Fuji Photo Film Company, Limited

Other

Chiaki Mizuno

Hiroshi Ogawa

Yasuo Tamai

Shinji Saito

Toshio Ono

Kiyomi Ejiri

Noburo Hibino

Hiroaki Araki

Shinichi Funabashi

Masatoshi Kiyama

Takao Komi

Masaaki Fujiyama

Masatoshi Takahashi

Goro Akashi

Nobuo Tsuji

Naoyoshi Chino

Akira Kasuga

Kouichi Masaki

Masaaki Suzuki

Tsutomu Sugisaki

Minoru Kanazawa

Masaya Kojima

Koozi Kamiyama

In a magnetic recording medium comprising a nonmagnetic substrate, a first magnetic layer, and a second magnetic layer mounted in this order, the first magnetic layer has a greater coercive force and a lower residual flux density than the second magnetic layer. When the second magnetic layer is directly mounted on the first magnetic layer, the second magnetic layer has a thickness within the range of 0.05-0.5 .mu.m and a coercive force within the range of 1200-2000 Oe while the first magnetic layer has a coercive force greater than that of the second magnetic layer by 800-2500 Oe and a residual flux density in the range of 30-70% of that of the second magnetic layer. When a nonmagnetic layer is held between the first and second magnetic layers, the first magnetic layer has a coercive force not smaller than 2000 Oe and a residual flux density not greater than 70% of that of the second magnetic layer while the second magnetic layer has a coercive force not smaller than 1200 Oe, a residual flux density not lower than 1600 G, and a thickness not greater than 0.5 .mu.m.

Magnetic recording medium

A method of preparing a magnetic coating composition comprises a first process for kneading ferromagnetic grains, a binder and a binder solution Y1 by use of a two-shaft continuous kneading and mixing machine to obtain a kneaded mixture K1 having a solid content within the range of 65 wt % to 95 wt %, a second process for kneading a binder solution Y2 and the kneaded mixture K1 by use of the two-shaft continuous kneading and mixing machine to obtain a primary diluted mixture K2 having a solid content within the range of 50 wt % to 70 wt %, a third process for diluting and dispersing the primary diluted mixture K2 in an organic solvent to obtain a secondary diluted mixture K3 having a solid content within the range of 25 wt % to 50 wt %, and a fourth process for finely dispersing the secondary diluted mixture K3 to obtain a dispersion mixture K4 having a solid content within the range of 25 wt % to 45 wt %.

Method of preparing magnetic coating composition

A magnetic recording medium is described, comprising a nonmagnetic support having thereon a first magnetic layer and having on the first magnetic layer a second magnetic layer, in that order, said second magnetic layer comprising a magnetic particle, a binder, abrasive particles and carbon black having an average primary particle diameter of 80 m.mu. or more, said first magnetic layer comprising a magnetic particle, a binder and carbon black having an average primary particle diameter of 40 m.mu. or less without substantially containing abrasive particles in the first magnetic layer, and the thickness ratio of the first layer to the second layer, first layer thickness/second layer thickness is 1.8 or more.

A single two-shaft continuous kneading and mixing machine, which is provided with a pair of shafts having blade members secured thereto, and a barrel accommodating the shafts such that they can be rotated, carries out kneading of a mixture of magnetic grains and a solution, which contains a binder in an organic solvent, in a normal kneading region and thereafter carries out dilution kneading of the mixture, which resulted after kneading in the normal kneading region was carried out, and an organic solvent in a dilution kneading region. The solids concentration in the mixture subjected to kneading in the normal kneading region is adjusted so that it falls within the range of 65 to 95 wt %. The solids concentration in the mixture subjected to dilution kneading is adjusted so that it falls within the range of 30 to 60 wt %. The width of a gap between blade members, which are secured to different shafts and which face each other, and the width of a gap between each blade member and the inner surface of the barrel in the dilution kneading region are made smaller than the widths of corresponding gaps in the normal kneading region.

Method for preparing magnetic coating compositions

A magnetic recording medium is described, comprising a non-magnetic support having thereon a first magnetic layer comprising at least about 1.0 part by weight of carbon black having an average primary particle diameter of from about 20 to 80 m.mu., per 100 parts by weight of magnetic particles contained in the first magnetic layer; and on the first magnetic layer, a second magnetic layer containing from about 0.1 to less than 1.0 part by weight of carbon black having an average primary particle diameter of from about 20 to 150 m.mu., per 100 parts by weight of magnetic particles contained in the second magnetic layer. The medium has excellent electromagnetic characteristics, running durability and heat resistance.

A method of preparing a kneaded mixture for a magnetic coating material comprises a kneading start process and a continuous kneading process. In the kneading start process, a low-viscosity composition, which is composed of magnetic layer forming materials containing ferromagnetic grains and a binder, and a solvent, is introduced into a kneading vessel of a two-shaft continuous kneading and mixing machine, and kneading is started. In the continuous kneading process, after the start of the kneading, a high-viscosity composition, in which a solvent amount is smaller by at least 7 wt % than the solvent amount in the low-viscosity composition used in the kneading start process, is continously introduced into the kneading vessel, and the kneading is continued while high shearing force is being given to the high-viscosity composition.

Method of preparing kneaded mixture for magnetic coating material

A magnetic recording medium comprises a nonmagnetic support, a first magnetic recording layer and a second magnetic recording layer, superposed in order, wherein each of binders contained in said first and second magnetic recording layers comprises a polymer, and the polymer contained in the second magnetic recording layer has a polymerization degree of not less than 250, said polymerization degree being more than that of the polymer contained in the first magnetic recording layer by at least as much as 20.

An improvement of a magnetic recording medium comprising a nonmagnetic support and a magnetic recording layer provided on the support which comprises a binder and a ferromagnetic powder dispersed therein is disclosed. The binder contains a resin component having a metal sulfonate group and the ferromagnetic powder contains water in an amount corresponding to moles of 20-80 times as much as the number of moles of the metal sulfonate group contained in the binder.

An improvement of a magnetic recording medium comprising a nonmagnetic support and a magnetic recording layer provided on the support which comprises a binder and a ferromagnetic powder dispersed therein is disclosed. The binder contains a resin component having an epoxy group and the ferromagnetic powder contains water in an amount corresponding to moles of 1-5 times as much as the number of moles of the epoxy group contained in the binder.

A magnetic tape having a leader tape excellent in cleaning effect and free from change of the apppearance and decrease of the cleaning effect even after storage at high temperatures is provided. This magnetic tape has a leader tape at at least one end of the tape, the leader tape comprising a coating layer provided on the one or both sides of a support, and is characterized in that the coating layers contains an inorganic pigment powder with a grain size of 0.01 to 10 .mu.m or a mixture of an inorganic pigment powder with a grain size of 0.01 to 5 .mu.m and a resin powder with a grain size of 0.1 to 10 .mu.m, and a binder, the support has a haze of 20 to 80% and the leader tape has a percent photo-transmission of at least 20%.

Magnetic tape having a leader tape

A magnetic recording medium comprising a nonmagnetic support, a first magnetic recording layer and a second magnetic recording layer, superposed in order, wherein:

Magnetic recording medium and process for the preparation of the same

A magnetic recording medium such as an audio-tape or a video-tape comprising a flexible support and a magnetic recording layer provided on a surface of said support, which is characterized in that the ratio of Young's modulus of said magnetic recording layer in the longitudinal direction (Em) to Young's modulus of said support in the longitudinal direction (Eb), namely Em/Eb, is in the range of 1.20-3.20.

A magnetic recording medium comprising a flexible support having coated thereon a magnetic layer is disclosed. The support has a surface roughness of from 0.01 to 0.1 .mu.m, the magnetic recording medium has a percent heat shrinkage of 1% or less in the direction of maximum shrinkage thereof after standing at 110.degree. C. for 4 hours, and the magnetic layer contains a metal or alloy fine powder as a ferromagnetic powder. The magnetic recording medium has a excellent running property after repeated use and a small percent heat shrinkage.

A magnetic recording medium such as an audio cassette tape or a video cassette tape comprising a flexible nonmagnetic support and a magnetic recording layer which contains a ferromagnetic cobalt-containing iron oxide, in which the nonmagnetic support has a surface of a center line average height in the range of 0.01 to 0.1 .mu.m on both sides and the magnetic recording medium has a heat shrinkage ratio of not higher than 1%, the heat shrinkage ratio being determined after allowing to stand at 110.degree. C. for 4 hours.

A magnetic recording medium such as an audio-tape or a video-tape comprising a flexible support and a magnetic recording layer provided on one surface of said support, which is characterized in that the total of the thickness of said magnetic recording layer (dM) and the thickness of said support (dB), namely dM plus dB, is not larger than 14 .mu.m; the ratio of the thickness of said magnetic recording layer (dM) to the thickness of said support (dB), namely dM/dB, is in the range of 0.6-1.0; and said magnetic recording medium has F-3 tensile strength in the range of 6.0-8.5 kg/mm.sup.2.

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Kanagawa, Japan

Chiaki Mizuno