JPS62298920A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having excellent durability and magnetic characteristics by controlling the average grain size of a polishing agent to be incorporated and dispersed into a magnetic coated film to >=0.7mum and the thickness of the magnetic coated film to >=6mum. CONSTITUTION:The polishing powder having >=0.7mum average grain size is incorporated and dispersed into the magnetic coated film of the magnetic recording medium constituted by forming the magnetic coated film contg. ferromagnetic metallic powder and binder on a nonmagnetic substrate and the thickness of the magnetic coated film is >=6mum. More specifically, the polishing powder having a large grain size and reinforcing effect is usable by specifying the thickness of the magnetic layer to >=6mum. The decrease in SN is obviated even if the polishing powder is incorporated slightly more to surely improve the durability.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention [Field of Application] The present invention relates to magnetic recording media such as disk-shaped or tape-shaped magnetic recording media, particularly high-density GC! The present invention relates to a magnetic recording medium suitable for recording.

[Conventional technology]

Conventionally, in order to achieve high-density recording, materials made of, for example, acicular metal iron and having a coercive force of 1000 Oe or more and B
Ferromagnetic metal powder with an ET specific surface area of 25 to 70n (/g),
A magnetic recording medium has been proposed in which a magnetic coating film is formed on a non-magnetic substrate with a binder made of an organic compound (Japanese Patent Laid-Open No. 122623/1983).

[Problem 3 to be solved by the invention: Ferromagnetic metal powder is more easily worn than materials made of other metal oxides, so hard abrasive powder is used to improve the durability of the magnetic coating. need to be mixed. Although the above-mentioned proposal also mixes a small amount of abrasive powder, the particle size of the abrasive powder used and the magnetic coating film are not considered, and therefore sufficient durability and magnetic properties cannot be obtained.

In addition, it is generally recommended to use ferromagnetic metal powder to obtain magnetic recording media with excellent high-density recording, but when attempting to increase the density, the thickness loss changes due to changes in the thickness of the magnetic layer. Therefore, studies have been conducted to make the magnetic layer as thin as possible (Tohoku University Dentsu Colloquium Record Vol. 31, No. 5, No. 3, pp. 95-104, published September 1960).

However, when the thickness of the magnetic layer is, for example, less than 0.5 μm, the particle size and particle size distribution of the polished H2'A mixed and dispersed in the magnetic layer to maintain the flatness of the surface of the magnetic layer are limited. There is a problem in terms of productivity, and the ultrafine abrasive powder tends to aggregate, causing the surface of the magnetic layer to lose its flatness, resulting in deterioration of magnetic properties and abnormal wear of the magnetic head.

The purpose of the present invention is to eliminate such drawbacks of the prior art,
An object of the present invention is to provide a magnetic recording medium with excellent durability and magnetic properties.

[Means for solving problems]

In order to achieve the above-mentioned purpose, the average particle size of the abrasive, such as α-F-tos, mixed and dispersed in the magnetic coating film is set to 0.
The thickness of the magnetic coating is regulated to 7 μm or more, preferably 0.7 to 3 μm, and the thickness of the magnetic coating is 6 μm or more, preferably 6 to 1 μm.
It is characterized by being regulated to a range of 0 μm.

[Effect]

As a result of the inventors' various studies regarding the thickness of the magnetic layer,
If the coercive force of the magnetic layer is, for example, 1200 or more, D. It was discovered that the characteristics were not dependent on film thickness, and that it was actually better to increase the film thickness. That is, by making the thickness of the magnetic layer 6 μm or more as in the present invention, it is possible to use abrasive powder with a large particle size and a reinforcing effect. It has the feature that the S/N ratio does not decrease even if a small amount is added.

〔Example〕

The nonmagnetic substrate used in the present invention may be made of, for example, polyethylene terephthalate, polyester, polyimide, aluminum, or the like.

The magnetic coating film formed thereon is made of a combination of, for example, ferromagnetic metal powder, a binder such as vinyl chloride-vinyl acetate-vinyl alcohol copolymer, or polyurethane, and an organic material such as ketones, toluene, or alcohol. It is obtained by applying a paint containing a solvent on the non-4fi substrate and subjecting it to a calendaring process.

Examples of the polishing powder used in the present invention include α-F, 2
0i −cr2o3 , A j! ! ○*+S+C+
S, ○.

etc. are preferably used.

When the magnetic recording medium according to the present invention is used as a 6n disk, the magnetic particles need to be oriented irregularly in the plane or along the circumferential direction of the disk.

Next, a specific example will be explained.

(Composition of magnetic paint) ・I7! ! Magnetic metal iron powder 450 weight ratio 5
・Vinyl chloride-vinyl acetate-vinyl alcohol copolymer 50 parts by weight ・Polyurethane resin 30 parts by weight ・Trifunctional low molecular weight isocyanate compound 20 parts by weight ・Carbon black 36 parts by weight ・α-F
-zch powder 18 parts by weight 2 ethylhexyl oleate 14 parts by weight cyclohexanone
650 parts by weight/toluene
650 parts by weight of a magnetic paint having this composition was applied onto a non-magnetic substrate made of polyethylene terephthalate with a thickness of 75 μm,
Each sample magnetic recording medium was prepared by calendering (50° C., 30 kg/c+d) to a film thickness of 1 to 15 μm, and this was punched into a disk with a diameter of 1301 m. The output and modulation of each sample at a recording density of 40kBP■ were measured, and the results are shown in the table below.
Note that the average particle size of the polishing powder α-F1tOz used in this test was 2 μm.

Table As is clear from this table, if the thickness of the magnetic coating film is 54 m or less, the output at a recording density of 40 kBP+ is 0.48 m.
The output waveform is low, less than V, and the modulation is high, more than 5.0%, making the output waveform unstable.

On the other hand, if the film thickness is 11 μm or more, uneven coating tends to occur, and output fluctuations become large (modulation: 6.2 to 7.8%), which poses problems in terms of reliability. If the film thickness is regulated within the range of 6 to 10 μm, the recording density is 4.
It is possible to obtain a highly reliable magnetic recording medium in which the output of 0 kBP I is secured to Q, 5 mV or more, the modulation is suppressed to less than 5%, and there is no output fluctuation.

By regulating the film thickness to a range of 6 to 10 μm in this way, it not only has the magnetic properties of high reproduction output and small output fluctuations, but also has great advantages in terms of durability. It is.

Next, this point will be explained. Using the coating composition described above, a magnetic coating film with a thickness of 8 μm was formed using abrasive powders having different average particle diameters, and a disk-shaped magnetic recording medium with a diameter of 130 + n was manufactured. The SN ratio and durability of each sample are shown in the figure. Durability was measured by attaching a disk-shaped magnetic recording medium to a recording/reproducing device, and observing a decrease in the reproduction output level due to wear of the magnetic coating while sliding the magnetic recording medium against a magnetic head. The running time until the temperature decreased was measured.

As is clear from this figure, if the average particle size of the abrasive powder mixed and dispersed in the magnetic coating film is finer than 0.7 μm, the reinforcing effect of the abrasive powder will not be sufficiently exerted, and as a result, the wear of the magnetic coating film will be significant. However, there are problems with durability. This is also related to the film thickness of the magnetic coating film, and if the film thickness of the magnetic coating film is set to 6 μm or more as in the present invention, it is difficult to use polishing powder with an average particle size of less than 0.7 μm as described above. However, its effect has hardly been achieved. Furthermore, the use of abrasive powder with an average particle diameter of less than 0.7 μm not only requires a long grinding time but also requires strict control of the particle size distribution, which is not preferable from a production standpoint.

On the other hand, magnetic recording media using abrasive powder with an average particle size of 0.7 μm or more have excellent durability due to less wear on the magnetic coating, and have less reduction in playback output. By using abrasive powder with a relatively large abrasive powder, its reinforcing effect can be sufficiently exhibited. By making the film thickness of 6 μm or more,
As mentioned above, even relatively large abrasive powder having an average particle diameter of 0.7 μm or more can be dispersed and maintained uniformly with sufficient margin, and the magnetic coating film can be reinforced as a whole. In addition, by making the magnetic coating thicker, the abrasive powder that protrudes on the magnetic coating during the calendaring process during the manufacture of magnetic recording media is pushed into the magnetic coating and buried.

can be retained. Furthermore, by increasing the thickness of the magnetic coating film, the amount of ferromagnetic metal powder filled can be increased, so as is clear from the figure, there is almost no decrease in the S/N ratio due to the contamination of the polished powder. Furthermore, since the average particle size of the polishing powder is relatively large, the grinding time is short and the particle size distribution can be controlled relatively roughly, which is advantageous from the viewpoint of productivity.

However, if the average particle size of the polishing powder exceeds 3 μm, fine irregularities may remain on the surface of the magnetic coating even after calendering, and there is a concern that the lack of surface flatness will adversely affect the playback output. be. Therefore, the average particle size of the polishing powder is 0.
It is better to limit the thickness to a range of 7 to 3 μm.

As a result of various studies on the mixing ratio of polishing powder to ferromagnetic metal powder, it was found that 1 to 20% by weight is appropriate. If the mixing ratio of the polishing powder is less than 1% by weight, even if the average particle size is large as described above, the reinforcing effect of magnetism = e will not be sufficiently exhibited.On the other hand, if the mixing ratio of the polishing powder is 20%
If it exceeds this weight percentage, the magnetic coating film will have an abrasive effect, and the magnetic head will wear out, causing problems with its durability. Therefore, in order to fully demonstrate the reinforcing effect of the magnetic coating film and to suppress the wear of the magnetic head as much as possible, the mixing ratio of polishing powder to ferromagnetic metal powder must be controlled within the range of 1 to 20% by weight as described above. It's better to do so.

〔Effect of the invention〕

Since the present invention has the above-described configuration, it is possible to provide a magnetic recording medium with excellent magnetic properties and durability.

[Brief explanation of drawings]

The figure is a characteristic diagram showing the relationship between the average particle size of polishing powder, durability, and S/N ratio. Layer (2<)

Claims (5)

[Claims] (1) In a magnetic recording medium in which a magnetic coating film containing ferromagnetic metal powder and a binder is formed on a non-magnetic substrate, abrasive powder with an average particle size of 0.7 μm or more is mixed into the magnetic coating film. 1. A magnetic recording medium characterized in that the magnetic coating film is dispersed and has a thickness of 6 μm or more. (2) A magnetic recording medium according to claim (1), characterized in that the average particle diameter of the abrasive powder is regulated to 3 μm or less. (3) A magnetic recording medium according to claim (1), wherein a mixing ratio of the abrasive powder to the ferromagnetic metal powder is 1% by weight or more. (4) A magnetic recording medium according to claim (3), characterized in that the mixing ratio of the abrasive powder is regulated to 20% by weight or less. (5) In claim (1), the thickness of the magnetic coating film is regulated to 10 μm or less (6
) Claim (1) describes that the abrasive powder is α-Fe_2O_3, C_r_2O_3, Al_2O
A magnetic recording medium comprising at least one inorganic compound selected from the group consisting of SiC and SiO_2.