JPH03703B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a magnetic recording medium suitable for high-density recording with low noise, and a method for manufacturing the same. Most conventional magnetic recording media are constructed by coating a paint made of magnetic powder and a resin binder on a support such as a polyester film. As the above-mentioned magnetic powder, acicular ferromagnetic powder using γ-Fe ₂ O ₃ type, Fe ₃ O ₄ type, cobalt adsorption type thereof, CrO ₂ type, etc. is mainly used. However, acicular ferromagnetic powder has a drawback in that it has already reached its limit in terms of recording density due to its small coercive force and cannot meet recent demands for high-density recording. Therefore, recently, in order to improve this drawback, it has been considered to reduce the particle length of the acicular ferromagnetic powder as much as possible, or to improve the coercive force (Hc) and maximum magnetic flux density (Ms). However, when the particle length of these acicular ferromagnetic powders is reduced,
This has the disadvantage that the electromagnetic conversion characteristics in the low range deteriorate due to the influence of the demagnetizing field, making it impossible to expect sufficient improvement in the characteristics. Therefore, attempts have been made to create a magnetic recording medium suitable for high-density recording by using ultrafine hexagonal ferrite magnetic powder of 0.1 μm or less in size instead of the acicular ferromagnetic powder that has such drawbacks. . This hexagonal ferrite magnetic powder usually has a regular hexagonal plate crystal structure, and when such hexagonal ferrite is used, a much higher recording density than conventional magnetic recording bodies can be obtained. For a recording medium using this ferrite, hexagonal ferrite powder with an average particle size of 0.1 μm or less is uniformly coated on the support surface together with a resin binder, and the axis of easy magnetization is set on the support surface using, for example, a magnetic field orientator. It was thought that the so-called perpendicular magnetic recording material, in which the coating film was dried after being oriented in a direction perpendicular to the magnetic field, was the best. However, the average particle size
It is difficult to obtain a high orientation rate for the ferrite particles of 0.1 μm or less in a vertical magnetic field, and as a result, not only the output characteristics do not increase as much in the high range as originally expected, but also the output characteristics in the low range do not increase as much as expected. It has come to be known that the properties of grains are also inferior to those of large-sized grains. The present inventors conducted various studies in order to eliminate these drawbacks of the conventional technology, and as a result, we found that the
It was discovered that when 5 to 40 parts by weight of hexagonal ferrite powder of M is added, the perpendicular orientation rate increases significantly, and not only the high-frequency output increases but also the low-frequency characteristics are improved. This led to the invention. That is, the present invention contains 80 to 95 parts by weight of hexagonal ferromagnetic powder with an average particle size of 0.01 to 0.1 μm;
The present invention relates to a magnetic recording medium characterized in that 5 to 20 parts by weight of hexagonal ferromagnetic powder of 0.2 to 0.4 μm is coated and oriented on a support together with a resin binder. Furthermore, the present invention has an average particle size of 0.01~
80 to 95 parts by weight of hexagonal ferromagnetic powder with a diameter of 0.1 μm and 5 to 95 parts by weight of a hexagonal ferromagnetic powder with an average particle size of 0.2 to 0.4 μm.
The present invention relates to a method for manufacturing a magnetic recording medium, which comprises applying 20 parts by weight of the magnetic powder on a support together with a resin binder, and then orienting the magnetic powder in a magnetic field perpendicular to the surface of the support. In the present invention, by using two types of hexagonal ferromagnetic powders with different average particle diameters, the perpendicular orientation rate is improved, thereby achieving high-density recording.
Furthermore, by adding powder with a particle size of 0.2 to 0.4 μm, the flow characteristics of the paint were significantly improved, a smooth coating surface was obtained, and the noise characteristics were also improved. These effects caused by adding 0.2 to 0.4 μm particle size powder are due to the fact that the surface of 0.2 to 0.4 μm particle size powder is covered or surrounded by 0.01 to 0.1 μm ultrafine powder, and when oriented in a magnetic field, large particle size powder promotes orientation, improving reproduction output, and in high-frequency recording and reproduction characteristics, the magnetization of the small particle size powder surrounding the large particle size powder works effectively to improve the frequency characteristics. It seems to be an improvement. The hexagonal ferromagnetic powder used in the present invention is Co,
Fine particles of metals that form hexagonal crystals by themselves such as Co-Cr, Co-Mn, Mn-Al, etc. may be fine particles, but hexagonal ferrite (which is expressed by the general formula Mo・n(Fe ₂ O ₃ )) M is one of Ba, Sr, Pb, Ca, n is 5 to 6, and part of Fe is Ti, Co,
(Optionally substituted with transition metals such as Zn, In, Mn, Cu, Ge, Nb, etc.) are particularly suitable. The fine particles of the hexagonal ferrite mentioned above are single crystals of regular hexagonal plates, and the particle size is usually expressed by the length of the diagonal line of the regular hexagonal plate, and the axis of easy magnetization is in the direction perpendicular to the plane of the plate. Such hexagonal ferromagnetic powders are disclosed in Japanese Patent Application Nos. 143859-1985 and 1983-143859 filed by the present applicant.
It can be produced by the glass crystallization method described in the specification of No. 34769. The particle size of these magnetic powders can be adjusted to any desired particle size by appropriately changing the reaction conditions during production.
The present invention can be easily carried out by employing magnetic powder that matches the particle size of the present invention. The resin binder used in the present invention is a flexible film-forming material, a support material,
Any material that has an affinity for magnetic powder can be used; examples of these include vinyl chloride.
Examples include vinyl acetate copolymer materials, NBR-polyvinyl acetate materials, urethane plasticized vinyl chloride-vinyl acetate copolymer materials, polyurethane materials, polyester resins, isocyanate materials, etc., which are known in the art. It is the material of In addition, polyester film is generally widely used as a support, but other materials can also be used as long as they have sufficient mechanical strength such as flexibility and tensile strength. . In the present invention, a magnetic coating is formed from hexagonal ferromagnetic powder having two types of average particle diameters, a resin binder, and a solvent, and this is coated on a support and oriented to form a magnetic recording medium. It is preferable that other known additives such as a dispersant, a lubricant, and an antistatic agent be blended into the magnetic paint. There are many known methods for applying this magnetic paint onto a support, using a reverse roll coater, a doctor blade coater, a gravure coater, etc., and any of these methods can be employed in the present invention. In addition, the orientation of the magnetic powder is determined by
Although the present invention can be carried out by the method and apparatus described in the specifications of Japanese Patent Application No. 132145-132145 and Japanese Patent Application No. 132138-1982, the present invention is not limited thereto. The present invention will be explained below with reference to Examples. (Example 1) With the same chemical composition as 10 parts by weight of substituted barium ferrite powder (Ms60cmu/g, iHc650) with an average particle size of _0.3μm and having the chemical composition BaO・6 (Fe0.86Co0.07Ti0.07) ₂ O 3 Conductive carbon black 2 is added to 90 parts by weight of substituted barium ferrite powder with an average particle size of 0.08 μm.
parts by weight, Aerosol OT (trade name, sodium octylsulfosuccinate) 1 part by weight, lecithin 4 parts by weight,
After thoroughly mixing with 50 parts by weight of methyl ethyl ketone and 50 parts by weight of toluene, vinyl chloride-vinyl acetate copolymer (molecular weight: about 20,000) was added, further mixed, and dispersed in a sand grinder for about 2 hours. After adjusting the viscosity of the obtained paint with a 1:1 mixed solvent of methyl ethyl ketone and toluene, it was passed through a SUS filter with a pore size of 1 μm, coated on a polyester film using a reverse roll coater, and then dried while being passed through a vertical magnetic field. Seshime, coating thickness 2μm
A magnetic recording layer was prepared and passed through a five-stage supercalender to obtain a magnetic recording medium with a magnetic layer surface roughness of 0.1 μm or less. In addition, as a comparative example, the above average particle size of 0.08 μm and
Each of 0.3μm substituted barium ferrite powder
100 parts by weight were made into paint in exactly the same manner as above.
A magnetic recording medium was obtained by coating and surface treatment. Regarding the three types of magnetic recording media obtained above, the surface roughness of the magnetic layer, the perpendicular orientation rate, and the recording wavelength of 0.5μ
Table 1 shows the results of comparing the recording/reproducing output S/N ratio and envelope disturbance at m, proving that the recording/reproducing characteristics of the mixed barium ferrite powder are significantly superior. In addition, the substituted barium ferrite powder in this example had an average particle diameter of 0.1 μm for both the magnetic powder whose iHc was increased by decreasing the amount of substitution, and the magnetic powder whose iHc was decreased by increasing the amount of substitution. Average particle size of 0.2μm or less of 20wt% or less for the following small particle size powders
A similar improvement in recording and reproducing characteristics was observed when a large particle size powder of 0.4 μm was mixed.

[Table]
As described above, the magnetic recording medium of the present invention has
It has excellent reproduction output and S/N ratio, and has a high vertical orientation rate, making it suitable for high-density recording and extremely excellent in practical use.

Claims (1)

[Scope of Claims] 1. 80 to 95 parts by weight of hexagonal ferromagnetic powder with an average particle size of 0.01 to 0.1 μm, and 5 to 20 parts by weight of hexagonal ferromagnetic powder with an average particle size of 0.2 to 0.4 μm. A magnetic recording medium characterized in that the magnetic recording medium is coated and oriented on a support together with a resin binder. 2 80 to 95 parts by weight of hexagonal ferromagnetic powder with an average particle size of 0.01 to 0.1 μm and 5 to 20 parts by weight of hexagonal ferromagnetic powder with an average particle size of 0.2 to 0.4 μm are supported together with a resin binder. 1. A method for manufacturing a magnetic recording medium, which comprises orienting the magnetic powder in a magnetic field perpendicular to the surface of the support after coating the magnetic powder on the support.