JPS586526A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium excellent in recording density, by coating a resin composition including specific magnetic substance powder on a base and forming a magnetic recording layer. CONSTITUTION:To 100pts.wt. uniaxial anisotropic magnetic substance particles having easy magnetization axis for the vertical direction to a flat plate surface of <=0.2mu thick, >=2 of the ratio of plate diameter/plate thickness (e.g., barrium ferrite CoTi permutated substance), 10-40pts.wt. binder resin (e.g., polyurethane resin), 0.5-20pts.wt. dispersion agent (e.g., lecithin), and about 200pts.wt. solvent (e.g., methyl ethyl ketone) are incorporated, and kneaded to obtain a paint resin composition. A curing agent is added to the composition and coated on a support base. After the magnetic substance powder particles are magnetically oriented to the magnetic head running direction of the magnetic recording medium, the base is dried.

Description

[Detailed description of the invention] The present invention relates to a high-density magnetic recording medium for reproduction.

As is well known, in magnetic recording media used for video recording, computer data recording, etc.

In order to achieve larger recording capacity and smaller size, there is a strong demand for higher recording density. Conventionally, as a medium for magnetic recording, a medium in which acicular magnetic powder such as r-Few Os acarch is coated and oriented on a carrier has been widely used. In order to obtain a recording medium suitable for high-density recording using such acicular magnetic powder, it is necessary to make the maximum dimension of the acicular magnetic powder sufficiently smaller than the recording wavelength or recording bit length. Currently, acicular magnetic powder with a size of about α3 μm is already in practical use, and a shortest recording wavelength of about 1 μm has been obtained. In order to obtain a medium capable of higher density recording in the future, it will be necessary to further reduce the size of the acicular magnetic powder. However, such small acicular magnetic powders are extremely thin, with a thickness of less than 100A, and the particle volume is extremely small, less than 10-IF-, so phenomena that cannot be avoided as ultrafine particles occur. do. That is, the magnetic properties deteriorate due to thermal disturbance and surface effects, and even if a magnetic field is applied to the magnetic coating to orient the particles, sufficient orientation cannot be obtained. This fact is a major obstacle in increasing the recording density of magnetic recording media.

The present inventors focused on the above-mentioned problems, and as a result of various studies on high-density recording magnetic materials, we used plate-shaped magnetic particles having -axis anisotropy as magnetic powder, and obtained a plate of magnetic particles. It has been found that an excellent recording medium suitable for high-density recording can be obtained by aligning the surfaces in the running direction of the magnetic spatula r.

Based on this knowledge, an object of the present invention is to provide a high-density magnetic recording medium with stable characteristics that significantly exceeds conventional recording densities.

That is, one aspect of the present invention provides a magnetic recording medium comprising a substrate and a magnetic recording layer formed by coating the substrate with a resin composition containing magnetic powder, in which the particles of the magnetic powder are
Flat plate shape with easy magnetization axis perpendicular to the plate surface, plate thickness α
The magnetic recording medium is characterized in that it has a diameter of 2 μm or less, preferably αl-αO of 1 μm, a plate diameter/thickness ratio of 2 or more, and is magnetically oriented in the in-plane longitudinal direction of the magnetic recording medium.

In recording media using conventional acicular magnetic powder, the particle size that determines the shortest recording wavelength is the length of the needle, whereas in the recording medium according to the present invention, the plate thickness of the plate-shaped magnetic particles determines the shortest recording wavelength. The wavelength will be determined. In the case of the former acicular magnetic powder, the needle length is limited to 0.3 .mu.m at most, and acicular crystals shorter than this lead to deterioration in characteristics as described above. However, in the case of the latter plate-shaped crystal grains, even if the plate thickness is 02 μm or less, the plate diameter is more than twice the plate thickness, so it is not an ultrafine particle.
Thermal disturbance 1 Phenomena peculiar to ultrafine particles such as surface effects do not occur, so even higher density recording can be achieved without deteriorating the characteristics of the recording medium 0 Thickness of plate-shaped particles used in the present invention is αo5~0. It can be used without difficulty even with a wavelength of about 1 μm, and the recordable wavelength is 0.2
It can be shortened to about #m.

The plate-shaped magnetic powder used in the present invention includes, for example, hexagonal heptagonal 7-elite powder, i.e., substituted products of barium ferrite, strontium ferrite, lead ferrite, calcium ferrite, manganese bismuth, hexagonal cobalt alloys, etc., and is particularly preferable. Examples include barium ferrite and strontium ferrite F substituted with Co.

The substrate of the recording medium of the present invention may be made of diesters such as polyethylene terephthalate, diolefins, cellulose conductors, vinyl resins, other plastics, or aluminum, copper, tin, zinc, or any of these materials. Alloys containing these can be used in the form of tapes and sheets.

Examples include discs, car Ys, drums, etc.

The magnetic recording medium of the present invention can be easily manufactured as follows. That is, a resin as a binder, such as vinyl chloride-acetic acid, is added to 100 parts by weight of CoTi substituted fine particles of barium ferrite, for example, uniaxially anisotropic magnetic particles having a plate thickness of 0.2 μm or less and a plate diameter/4 [thickness ratio of 2 or more]. 10 to 40 parts by weight of vinyl copolymer, polyurethane resin, etc., 0.5 to 20 parts by weight of lecithin as a dispersant, and about 200:m parts of a solvent such as methyl ethyl ketone, methyl isobutyl ketone, 7 clohexano/toluene, etc. The mixture is thoroughly cross-dispersed using, for example, a sand grinder, a gall mill, a three-roll mill, etc., to prepare a paint-like V& property composition. A curing agent such as incyanate is appropriately added to this composition, and it is coated on a supporting substrate such as a polyethylene terephthalate film using a reverse coater, a gravure caulk, a spin coater, etc.
A desired magnetic recording medium can be obtained by performing an orientation process using an electromagnetic coil or the like to align the particles, and then drying the particles.

Embodiments of the present invention will be described with reference to the arrows.

Example average plate diameter 0.1 μm, average plate thickness 0.02 μm /4
per 80 parts by weight of CoTi substituted fine particle powder, 10 parts by weight of vinyl chloride-vinyl acetate copolymer as a binder, 4 parts by weight of lecithin as a dispersant, 80 parts by weight of methyl isobutyl ketone as a solvent, and 8 parts by weight of toluene.
01 wrinkles, cyclohexafluoride (80% by weight) was added and dispersed using a sand mill. In this way 1
ijIJ & Incyanate 10'Ms for violating the Shita Boat Law
f: A strained polyethylene Tele 7 film was coated on the surface of the film, and then an orientation magnetic field of 20,000° was passed therethrough. After orientation, a drying calender treatment was performed to obtain a magnetic recording medium.

Magnetic adhesive determination was performed on the magnetic recording medium manufactured in G4 as described above, and Brm1500Ganmg He-9000 was obtained.
e squareness ratio α90t-obtained 9. Further, on this magnetic recording medium, recording was performed using a ferrite core magnetic head, and the reproduction output was measured. From the results, the recording density reproduction output characteristics of the recording medium of this example were determined. show.

For comparison, the drawing also shows the recording density fm% of the reproduction output of a conventional magnetic recording tape using acicular magnetic powder yJ. It can be seen that the reproduction output of the medium is significantly improved in the high density area. That is, it can be seen that the recording density of the magnetic recording medium according to the present invention is significantly the same as above.

By the way, one of the reasons why the magnetic recording medium of the present invention is capable of recording at a high height is that the plate-like particles can have a larger volume in the same orientation direction than the needle-like particles.
This is thought to be due to the fact that when the particles are oriented, the thickness of the plate determines the shortest recording wavelength, so this value can be easily reduced.

[Brief explanation of the drawing]

The drawing is a diagram showing the frequency characteristics of the reproduction output of magnetic recording media according to an example (solid line) of the present invention and a comparative example (broken line). Part record release rate (Bu Weio Trap / cm, xlo') Continued from page 1 0 Inventor Mitsuo Shigegashi 1 Komukai Toshiba-cho, Saiwai-ku, Kawasaki City, Tokyo Shibaura Electric Co., Ltd. Research Center

Claims (1)

[Claims] (1) In a magnetic recording medium comprising a substrate and a magnetic recording layer formed by coating the substrate with a resin composition containing magnetic powder, the particles of the magnetic powder are plate-shaped and arranged on the plate surface. A magnetic material characterized in that the perpendicular direction is the magnetization crystal axis, the plate thickness is 01 m or less, the plate diameter/plate thickness ratio is 2 or more, and the magnetic recording medium is magnetically oriented in the running direction of the magnetic head. Record - medium. 3) A magnetically arranged medium according to claim 1, wherein the magnetic material is hexagonal ferrite.