Fuji Photo Film Company, Limited

Toshio Ono

Hiroshi Ogawa

Chiaki Mizuno

Shinji Saito

Yasuo Tamai

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.

Magnetic recording medium

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 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.

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.

An improvement of a process for producing a magnetic recording medium comprising coating a non-magnetic support with a magnetic paint comprising a magnetic layer forming component containing ferromagnetic powder and a resin component dispersed in an organic solvent and drying the coated layer. The improvement resides in the preparation of the magnetic paint. In the improvement, the magnetic paint is obtained by kneading said magnetic layer forming component and a first solvent having a solubility parameter of not lower than 9.5[cal..multidot.cm.sup.-3 ].sup.1/2 as measured by Small method and adding a second solvent to the resulting kneaded product so that the mixed organic solvent in the magnetic paint has a solubility parameter of lower than 9.5[cal.multidot.cm.sup.-3 ].sup.1/2 to thereby disperse the magnetic layer forming component in the organic solvent.

Process for producing magnetic recording medium

A magnetic recording medium having a heat shrinkage ratio of not higher than 1% and comprising a nonmagnetic support in the form of a tape which has a heat shrinkage ratio of not higher than 1.8%, a Young's modulus of 450 to 650 kg/mm.sup.2 in the longitudinal direction and a Young's modulus of 450 to 550 kg/mm.sup.2 in the width direction, and a magnetic recording layer provided on the support which comprises a binder and a ferromagnetic powder dispersed therein and has a squareness ratio of not less than 0.89. All the heat shrinkage ratios are values determined after being allowed to stand at 110.degree. C. for 4 hours.

Growing community of inventors

Kanagawa, Japan

Toshio Ono