JPH05282656A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To easily obtain a high orientation degree with stainless steel foil having >=1emu/g residual magnetization as a substrate. CONSTITUTION:Stainless steel contg. 20% Cr, 6% Ni, 9% Mn and 0.3% N in Fe is cold-rolled to produce foil having 1.0emu/g residual magnetization and satisfactory surface properties are ensured for the foil by polishing. The surface of the foil is then chemically treated and a middle layer of epoxy resin is formed on the foil. Silica having about 0.01-1.0mum particle diameter is incorporated into the middle layer so as to prevent blocking between the resulting substrates and to improve lubricity to a roll at the time of production. It will suffice that the thickness of the middle layer is 10-20mum. Magnetic barium ferrite particles are properly mixed with nitrocellulose, a lubricant, a reinforcing agent and an abrasive material to prepare a coating material and coating with this coating material is carried out by means of a known coater.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium capable of high density magnetic recording.

[0002]

2. Description of the Related Art With the widespread use of personal word processors or personal computers, many magnetic recording media represented by 3.5-inch size floppy disks have come into the market.

Magnetic recording media are roughly classified into those manufactured by using a vacuum technique and those manufactured by using a coating technique. In particular, a magnetic recording medium manufactured by using a coating technique is It is attracting attention because it can be mass-produced at low cost. Under such circumstances, in recent years, for magnetic recording media,
In particular, there is an increasing demand for larger capacity. Methods for increasing the capacity of the magnetic recording medium include a method for improving the track density and a method for improving the linear recording density.

As a method of improving the track density,
There is a method of ensuring accurate positioning between a magnetic head and a track by using a servo technique and realizing a narrow track interval.

However, in order to ensure accurate positioning between the magnetic head and the track, the dimensional stability of the magnetic recording medium against changes in the external environment becomes very important.

Generally, a conventional magnetic recording medium has a polyethylene terephthalate film (PE) as its support.
Since an organic polymer film such as T) is used, the dimensions of the magnetic recording medium change greatly with changes in the external environment, making accurate positioning between the magnetic head and the track difficult. ..

Therefore, in order to ensure the dimensional stability of the magnetic recording medium, for example, JP-A-60-163230 discloses that a laminate of an aluminum foil and a polyester film is used as a support. 57-20921 discloses the use of stainless steel foil as a support. By using such a metal foil, the dimensional stability of the magnetic recording medium with respect to changes in the external environment can be increased and the track spacing can be narrowed as compared with the conventional case.

As a method for improving the linear recording density, for example, magnetic powder having a high coercive force is used, fine magnetic powder is used at a high packing density, and the orientation ratio of the magnetic powder is improved. There are various methods, and it can be realized by properly combining these methods.

Among them, a perpendicular magnetic recording medium in which magnetic powder having a hexagonal plate shape and having an easy axis of magnetization in the direction perpendicular to the plate surface is oriented so that the easy axis of magnetization is perpendicular to the film surface is Since the demagnetizing field is small, it is suitable for high density recording, and research and development are underway.

[0010]

By the way, it is technically very difficult to increase the orientation ratio of the magnetic powder in the above-mentioned improvement of the linear recording density.

Usually, when orienting individual magnetic particles,
If the orientation magnetic field is applied for a long time until the magnetic particles are fixed, re-aggregation of the magnetic particles due to the orientation magnetic field and deterioration of the surface property are observed.Therefore, apply a magnetic paint on the support and apply the orientation magnetic field. However, a method is taken out of the orientation magnetic field in the undried state.

However, even if such a method is adopted, since the magnetic coating material is in an undried state when it is taken out of the orientation magnetic field, the orientation may collapse due to the repulsive force generated between the oriented individual magnetic particles. It was difficult to obtain a high orientation rate. SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and therefore an object of the present invention is to provide a magnetic recording medium capable of easily obtaining a high orientation rate and enabling high density recording.

[0013]

The magnetic recording medium of the present invention is a magnetic recording medium having a magnetic layer on at least one main surface of a support, and the support has a remanent magnetization of 1 (emu / g) or more. It is characterized by being a metal foil of.

[0014]

The magnetic recording medium of the present invention is characterized by using a stainless steel foil having a residual magnetization (σg) of 1 (emu / g) or more as a support as described above.

By allowing the support to have a remanent magnetization of 1 (emu / g) or more, the individual magnetic particles once oriented are influenced by a magnetic field in a fixed direction received from the support whose orientation direction is firmly fixed. This prevents the orientation directions from collapsing due to the repulsive forces between the magnetic particles. The present inventor repeated various experiments and found that the residual magnetization of the support was 1
It has been found that when it is smaller than (emu / g), the repulsive force between magnetic particles is poor, and it becomes difficult to secure a high orientation rate. In particular, the residual magnetization (σg) given to the support
Must be 1 (emu / g) or more. However, it is not preferable that the residual magnetization .sigma.g given to the support has a bad influence on recording / reproduction on the magnetic layer.

Further, when the material of the support is examined, a metal material which can obtain high dimensional stability against changes in the external environment is preferable, and stainless foil or nickel foil is particularly suitable for the magnetic recording medium of the present invention. preferable. Among them, stainless steel foil is particularly suitable for the present invention because plastic deformation is unlikely to occur during processing or use, and residual magnetization can be controlled by finely adjusting the composition or processing conditions.

An example of a method of giving the support of the magnetic recording medium of the present invention a remanent magnetization is as follows. For example, a ferromagnetic martensite phase is obtained by subjecting a chromium-nickel austenitic stainless steel to strong drawing at room temperature. Can be generated and magnetized. Further, in the magnetic recording medium, the surface property of the magnetic layer has a great influence on the electromagnetic conversion characteristics, and therefore the surface property of the metal foil is preferably good.

For example, in order to improve the surface property of the stainless steel foil, it is subjected to heat treatment after cold drawing, finish polishing with a fine belt, and further polishing using rotary buff polishing with fine particles of alumina or silicon carbide. By doing
Good surface properties can be secured.

Further, by providing an intermediate layer between the support and the magnetic layer, a better surface property of the magnetic layer can be ensured, and at the same time, good adhesion between the support and the magnetic layer. Can be secured.

Various materials such as acrylic resin, urethane resin, alkyd resin, and polyester resin can be used as the intermediate layer, but when the main component is an epoxy resin that can obtain particularly good adhesion to the metal foil. good. When the intermediate layer is provided after the surface of the metal foil is chemically treated, chromated, or polished, a better adhesive strength can be obtained.

Further, by mixing fine particles such as silica, titania, and carion having a particle size of about 0.01 to 1.0 micron in the intermediate layer, blocking between the supports is prevented and sliding with a roll during production is good. It can be anything. As the film thickness of the metal foil in the present invention, particularly 10
Sufficient stiffness can be secured at ~ 20 microns.

Examples of magnetic particles usable in the magnetic recording medium of the present invention include hexagonal magnetic particles such as Ba-ferrite magnetic particles, γ-ferrite magnetic particles, Co-adhered γ-ferrite magnetic particles, and oxides such as CrO. Magnetic particles, F
Examples include metal magnetic particles such as e-Al alloy, Fe-Ni-Co alloy, and Co-Ni alloy.

As the binder used for coating the magnetic particles, a fiber resin such as nitrocellulose, a urethane resin such as polyurethane, a vinyl chloride-vinyl acetate copolymer, a vinyl chloride-vinyl acetate alcohol copolymer, or vinyl chloride. Examples thereof include luacrylonitrile copolymer, epoxy resin, melamine resin, alkyd resin, and those having a polar group at their ends. Further, as the lubricant, the reinforcing agent, the abrasive, etc., conventionally known ones can be appropriately used. When applying the magnetic coating material, a conventionally known device such as a gravure coater, a reverse coater, or a spray coater can be used.

[0024]

The present invention will be described in detail below. (Specific Example 1) Co-Ti substituted Ba-ferrite magnetic particles 100 parts by weight Polyurethane 11 parts by weight Vinyl chloride-vinyl acetate copolymer 6 parts by weight Lecithin 3 parts by weight Carbon 1 part by weight Higher fatty acid ester 4 parts by weight Cyclohexanone 100 parts by weight Methyl ethyl ketone 100 parts by weight

After the above-mentioned coating material is stirred and sufficiently dispersed, it is coated on a support by using a gravure coater so that the film thickness after drying becomes 3 μm, and is applied in a direction perpendicular to the film surface for 2 seconds. An orientation magnetic field of 3000 (Oe) was applied and dried to obtain a magnetic recording medium.

In this example, stainless steel obtained by adding 20% chromium, 6% nickel, 9% manganese, and 0.3% nitrogen to iron was cold-rolled into a 25-micron foil, which was used as a support. The residual magnetization of the support at this time was measured and found to be 1.0 (emu / g). When the perpendicular orientation ratio of the magnetic recording medium thus obtained was measured, a very high orientation ratio of 88% could be obtained. still,
This orientation ratio was measured by using the ratio of the saturation magnetization at 10000 (Oe) and the residual magnetization corrected for the demagnetizing field. (Specific example 2)

A magnetic recording medium was obtained in the same manner as in Example 1 except that the annealing conditions at the time of processing the support in Example 1 were changed and a 21 micron foil was used as the support. The residual magnetization of the support at this time was measured and found to be 3.5 (emu / g
)Met. Further, when the perpendicular orientation ratio of the magnetic recording medium thus obtained was measured, a very high orientation ratio of 88% could be obtained as in Example 1. (Specific example 3)

40% stainless steel with 18% chromium added to iron
A magnetic recording medium was obtained in the same manner as in Example 1 except that the support was used as a thin film of micron thickness. The residual magnetization of the support at this time was measured and found to be 25.5 (emu / g).
The perpendicular orientation of the magnetic recording medium thus obtained was measured, and it was 90%, which was a very high orientation. (Specific Example 4)

A magnetic recording medium was obtained in the same manner as in Example 1 except that a 30 μm thick foil of nickel was used as the support. When the residual magnetization of the support at this time was measured, it was 33.5 (emu / g). Further, the perpendicular orientation ratio of the magnetic recording medium thus obtained was measured, and it was 91%, which was a very high orientation ratio. (Specific Example 5)

After washing the surface of the support in Example 1 with different annealing conditions at the time of processing the support with an organic solvent, an intermediate layer was applied by a gravure coater to a film thickness of 0.1 micron. This intermediate layer is an epoxy resin in which silica powder with an average particle size of 0.02 microns is dispersed by an organic solvent.
It is prepared by diluting to a concentration of 10% and adding a curing agent. The residual magnetization of the support at this time was measured and found to be 3.5 (emu / g).

Thereafter, a magnetic coating material having the same composition as in the above-mentioned specific example 1 was applied by using a gravure coater so that the film thickness after drying would be 3 μm, and was applied in a direction perpendicular to the film surface for 3000 seconds for 2 seconds. An orientation magnetic field of (Oe) was applied and dried to obtain a magnetic recording medium. When the orientation ratio in the vertical direction of the magnetic recording medium thus obtained was measured, a high orientation ratio of 87% could be obtained. Comparative Example 1 A magnetic recording medium was prepared in the same manner as in Example 1 except that a polyethylene terephthalate film having a thickness of 75 μm was used as a support for each of the above specific examples. When the perpendicular orientation ratio of the magnetic recording medium thus obtained was measured, it was 77%.

As is clear from the various experiments described above, according to this example, by using a metal foil having a remanent magnetization of 1 (emu / g) or more as a support for a magnetic recording medium, conventional polyethylene terephthalate was obtained. It was possible to easily obtain a very high orientation rate as compared with a magnetic recording medium using a film as a support. As a result, high density recording of the magnetic recording medium can be easily performed.

Further, the magnetic recording media of Example 5 and Comparative Example 1 were punched out into a 3.5-inch size disc, the surface of the magnetic layer was polished, and then the disc was rotatably housed in a hard jacket to form a disk cartridge. ..

Such a disk cartridge is stored at 25 ° C. 30
After being left in an environment of% RH for 24 hours, signals were recorded using a magnetic head having a track width of 25 μm. And 50
When the recorded signal was reproduced by leaving it in the environment of 80 ° C RH for 3 hours, the output of the disk cartridge according to the comparative example was reduced by 50%, but the output of the disk cartridge according to this specific example was decreased. Was hardly seen. This is because the magnetic recording medium of the present specific example can secure higher dimensional stability against changes in the external environment than the conventional magnetic recording medium.

As described in detail above, according to the magnetic recording medium of the present embodiment, it is possible to secure a high orientation rate and a high dimensional stability, thereby improving the linear recording density or the track density. Is possible.

Further, the high dimensional stability of the magnetic recording medium of the present embodiment described above does not correspond only to the change of the external environment but also high dimensional stability against heat generated by friction with the magnetic head. Can be secured. Therefore, even if the magnetic recording medium is used under high-speed rotation to reduce the access time, there is almost no dimensional change due to frictional heat as compared with the conventional magnetic recording medium. From the above, the present invention is particularly suitable for a large capacity magnetic recording medium.

[0037]

According to the magnetic recording medium of the present invention, it is possible to obtain a magnetic recording medium having a very high orientation rate of individual magnetic particles due to its unique constitution. Furthermore, extremely high dimensional stability is obtained even with changes in the external environment, which enables accurate positioning between the magnetic head and the regular track.

From the above, according to the magnetic recording medium of the present invention, it is possible to improve the linear recording density or the track density more than ever, and it is possible to easily achieve high density recording.

Claims (1)

[Claims] 1. A magnetic recording medium having a magnetic layer on at least one main surface of a support, wherein the support is a metal foil having a residual magnetization of 1 (emu / g) or more. ..