JPH0463525B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a magnetic recording medium, and an object of the present invention is to provide a magnetic recording medium with excellent erasing characteristics and transfer characteristics. Magnetic recording media include magnetic tapes, magnetic sheets, magnetic cards, etc., and have been used for audio, video, and computers, and have made remarkable progress in recent years. These recording media are increasingly suited for high-density recording and high S/N, and as recording wavelengths become shorter, erasing characteristics and transfer characteristics have become increasingly important. Magnetic powders used in magnetic recording media include magnetic iron oxide, chromium dioxide, and alloy magnetic powder, but currently magnetic iron oxide accounts for most of them. Among these, magnetic iron oxides include magnetite (Fe ₃ O ₄ ) and gamma hematite (γ-Fe ₂ O ₃ ), and in order to use them for high-density recording media, each must contain cobalt Co ions to have a high coercive force. The converted version is used. However, in such magnetic iron oxides, magnetic recording media using Fe ₃ O ₄ generally have poor transfer characteristics, while those using γ-Fe ₂ O ₃ generally have poor erase characteristics, making it difficult to satisfy both characteristics simultaneously. It is difficult. Furthermore, if the above-mentioned Co ions are completely dissolved, a problem arises in that the transfer characteristics are further deteriorated. As a result of intensive studies on the above points, the present invention has been developed by using magnetic powder containing Co ions on the surface of acicular magnetic iron oxide with a lattice constant of 8.367 Å to 8.382 Å as magnetic powder. This is based on the discovery that a magnetic recording medium with excellent erasing characteristics and transfer characteristics can be obtained. That is, in the present invention, a magnetic coating solution is obtained by sufficiently mixing and dispersing a composition consisting of the Co-containing magnetic iron oxide powder, a binder, and various other additives and solvents added as necessary. After coating on a non-magnetic support, it is oriented and dried. By subjecting this dried magnetic film to a surface treatment using a calendar, a magnetic recording medium with extremely excellent erasing and transfer characteristics is provided. The magnetic iron oxide powder used in the present invention has a core material of
This is a high coercive force magnetic powder for high-density recording, which is spinel-shaped acicular magnetic iron oxide with a lattice constant of 8.367 to 8.382 Å and contains Co ions on its surface. The lattice constant is
If the lattice constant is smaller than 8.367 Å, satisfactory erasing properties cannot be obtained, while if the lattice constant is larger than 8.382 Å, satisfactory transfer properties cannot be obtained. Further, the above-mentioned magnetic iron oxide in which Co ions are dissolved as a solid solution is not preferable because the transfer characteristics and demagnetization characteristics become worse.
Since the lattice constant of pure Fe ₃ O ₄ is 8.400 Å and that of pure γ-Fe ₂ O ₃ is 8.340 Å, the lattice constant of the magnetic iron oxide is between these two values. Hereinafter, a method for manufacturing a magnetic recording medium according to the present invention will be explained using a magnetic tape as an example. A binder and, if necessary, a lubricant, a dispersant, a plasticizer, an antistatic agent, an abrasive, etc. are added to the magnetic powder of the present invention, and the mixture is sufficiently mixed and dispersed with a solvent to form a magnetic powder having a desired component ratio. Make paint. As the binder, conventionally known thermoplastic resins, thermosetting resins, reactive resins, and the like can be used alone or in combination.
Lubricants include higher fatty acids, higher fatty acid esters,
Silicone oil-based or fluorine oil-based lubricants are available. As a dispersant, the above-mentioned lubricants have this function, but lecithin, metal soap, etc. may also be used. In addition, as an antistatic agent,
Carbon black, graphite, surfactants, etc. As abrasives, Cr ₂ O ₃ , Al ₂ O ₃ , SiC,
There are high hardness fine powders such as TiO ₂ and α-Fe ₂ O ₃ . As the dispersing machine, a ball mill, a vibration mill, a sand mill, a dissolver, an attritor, a high-speed mixer, a kneader, etc. are used, and these may be used in combination. The magnetic paint thus obtained is applied onto a support such as a polyester film. The coating method may be any of a doctor blade method, a gravure method, a reverse roll method, and the like. Immediately after application, a smoother, wire smoother, film smoother, etc. can be used to further improve the smoothness of the coating film. After that, before drying the coating film, a magnetic field orientation device is used to align the magnetic powder in the coating film in one direction, and the coating film is passed through an appropriate magnetic field. The strength of the magnetic field applied at this time varies depending on the coercive force of the magnetic powder, but is preferably about 2 to 4 times the coercive force. Magnets include permanent magnets and electromagnets. After the orientation treatment is performed in this manner, it is dried to remove the solvent. In order to further smoothen the surface of the magnetic layer of the coated and dried wide magnetic film, surface treatment is performed using a super calender roll. The surface properties of the calender roll at this time have a great effect on the electromagnetic conversion characteristics of the magnetic tape, but the conditions at this time are as follows:
Temperature 50~100℃, pressure 50~400Kg/cm, speed 20~
200 m/min is preferred. Next, the wide magnetic film that has been surface-treated in this way is cut into a predetermined width.
At this time, it is desirable to achieve width accuracy without elongation on one side and to reduce width fluctuations. During the final product assembly process, make sure that the tape surface is free from dust and other substances that could cause dropouts. Hereinafter, the present invention will be specifically explained based on Examples. In addition, the component ratio part described in the example is
All parts are by weight. (Example) Co adsorption type magnetic iron oxide powder...100 parts Average particle size, length: 0.3 to 0.4 μm Axial ratio: 8/1 to 10/1 Coercive force: 630 to 650 Oe Lattice constant: Table below Shown below. Polyurethane resin (manufactured by Nippon Polyurethane Co., Ltd. N-
3113) ...15 parts vinyl chloride-vinyl acetate copolymer (manufactured by UCC)
VAGH) ... 5-part chromium oxide (Cr ₂ O ₃ ) average particle size = 0.2 μm
...3 parts carbon black ...4 parts lecithin ...1 part myristic acid ...1 part methyl ethyl ketone (MEK) ...100 parts methyl isobutyl ketone (MIBK) 100 parts toluene ...100 parts The above composition was heated in a ball mill for 48 hours After mixing and dispersing, 4 parts of hardener (Coronate L, manufactured by Nippon Polyurethane Co., Ltd.) was added, and the resulting kneaded product was passed through a filter having an average pore size of 3 μm to prepare a magnetic coating liquid. Next, this magnetic coating liquid was applied onto a polyester film having a thickness of 15 μm, and after drying, the surface of the magnetic layer was subjected to surface treatment using a super calendar roll, and the film was shredded to a predetermined width to produce a videotape. The video tapes obtained as described above were designated as Samples No. 1 to 6, and their erasing characteristics and transfer characteristics are summarized in the following table.

[Table] * Comparative example In the above table, (1) The lattice constant is determined by measuring the X-ray diffraction pattern of magnetic iron oxide powder using an X-ray diffraction device, and (hk) =
The interplanar spacing was determined from each peak of (731), (751), and (844), and the three lattice constants calculated from the following equation were averaged. 1/d ² = h ² + k ² + ² / a ² where d is the lattice spacing, a is the lattice constant, h, k,
indicates the surface index. (2) The coercive force of the tape is VSM− manufactured by Toei Kogyo Co., Ltd.
B with a maximum applied magnetic field of 2000 Oe using a mold
- It was determined from the measurement results of H characteristics. (3) For the erasure characteristics, a video tape recorder NV8200 manufactured by Matsushita Electric Industrial Co., Ltd. was used to record a signal 10 dB higher than the specified input level at a frequency of 1 kHz with a specified bias, and the recorded portion was erased with an erase current of 200 mA. and adjust the playback output level of the unerased portion.
The playback output level of the erased portion was determined as OdB. (4) To determine the transfer characteristics, a 1 kHz signal was recorded within one revolution of the cassette reel in the same manner as in (3) above, and then the unrecorded portion was removed for 10 revolutions and recorded several times in the same manner. This recorded portion is reproduced and the reproduction level of the original signal is set as a reference level. Then 30℃, 80%
The disc was left in an environment for 24 hours to return to room temperature, and 3 hours later, the playback output level of the unrecorded part adjacent to the recorded part was measured and compared with the reference level. As is clear from the above table, according to the present invention, it is possible to realize a magnetic tape with excellent erasing characteristics and transfer characteristics. It goes without saying that the gist of the present invention can be applied not only to magnetic tapes but also to magnetic recording media such as magnetic sheets and magnetic cards.

Claims (1)

[Claims] 1. Cobalt is deposited on the surface of an acicular magnetic iron oxide matrix with a crystal lattice constant of 8.367 Å to 8.382 Å, and a magnetic layer containing cobalt-coated magnetic powder is placed on a non-magnetic support. A magnetic recording medium provided.