JPH0845050A - Magnetic recording media - Google Patents

Abstract

(57) [Summary] [Construction] A magnetic recording medium comprising a non-magnetic support 1 and a metal magnetic thin film 4 formed thereon.
Surface roughness SRa in the range of 2 μm × 2 μm, for example, by providing the mat layer 3 on the non-magnetic support,
Adjust to m or less. [Effect] It is possible to obtain a magnetic recording medium that exhibits a high output in a high-density recording region because the coercive force of the metal magnetic thin film is significantly increased. Therefore, it can be said that the present invention greatly contributes to the improvement of the recording density in the magnetic recording field.

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 metal magnetic thin film type magnetic recording medium.

[0002]

2. Description of the Related Art Conventionally, as a magnetic recording medium, a powder magnetic material such as an oxide magnetic powder or an alloy magnetic powder is coated on a non-magnetic support with a vinyl chloride-vinyl acetate copolymer, polyester resin, urethane resin, A so-called coating type magnetic recording medium in which a magnetic layer is formed by coating and drying a magnetic coating material dispersed in an organic binder such as polyurethane resin is widely used.

On the other hand, with the increasing demand for high density recording, Co--Ni alloys, Co--Cr alloys, Co--Ni--
A magnetic metal material such as O or Co-O is directly coated on a non-magnetic support such as a polyester film, polyamide, or polyimide film by plating or a vacuum thin film forming means (vacuum deposition method, sputtering method, ion plating method, etc.). A magnetic recording medium of a so-called metal magnetic thin film type in which a magnetic layer is formed by attaching the magnetic recording medium has been proposed and attracts attention.

This metal magnetic thin film type magnetic recording medium is excellent not only in coercive force and squareness ratio but also in electromagnetic conversion characteristics at a short wavelength, and because the magnetic layer can be made extremely thin, recording demagnetization and The thickness loss during reproduction is extremely small,
Since it is not necessary to mix a binder, which is a non-magnetic material, in the magnetic layer, there are various advantages such that the packing density of the magnetic material can be increased.

Particularly, an oblique vapor deposition type magnetic recording medium in which a metal magnetic material is vapor-deposited in an oblique direction has already been put to practical use because it has excellent electromagnetic conversion characteristics and a large reproduction output can be obtained.

[0006]

In such a metal magnetic thin film type magnetic recording medium, the crystal growth direction and surface shape of the metal magnetic thin film are affected by the surface property of the non-magnetic support.

For example, if the surface of the non-magnetic support is rough, the crystal directions of the metal magnetic thin film are not uniformly aligned, and the coercive force of the medium cannot be sufficiently increased.

Further, the surface shape of the non-magnetic support is directly reflected on the surface shape of the metal magnetic thin film formed thereon by the layered action. Therefore, if the surface of the non-magnetic support is rough and has projections or the like, a spacing loss occurs between the metal magnetic thin film and the magnetic head due to the shape of the projections. On the contrary, when the surface of the non-magnetic support is too smooth, the surface of the metal magnetic thin film is also smoothed by reflecting it. In this case, it is advantageous in suppressing the spacing loss and aligning the crystal direction of the metal magnetic thin film, but at the time of recording / reproducing, the contact area of the metal magnetic thin film with the sliding member such as the magnetic head or the guide pin becomes large. From that,
These, the sliding member, and the metal magnetic thin film will adhere to each other, which deteriorates the running performance.

As described above, various characteristics of the metal magnetic thin film are greatly influenced by the surface property of the non-magnetic support. However, regarding the surface property of the non-magnetic support, measures have been taken so far in order to improve the runnability, for example, by adding a filler to the non-magnetic support to impart surface roughness. However, little consideration has been given to the coercive force of the metal magnetic thin film. Therefore, the metal magnetic thin film type magnetic recording media proposed so far still have room for improvement in coercive force, and cannot be said to be sufficiently satisfactory as a medium for high density recording.

Therefore, the present invention has been proposed in view of such a conventional situation, and provides a magnetic recording medium having a high coercive force and exhibiting a high output in a short wavelength region, which is suitable for high density recording. The purpose is to do.

[0011]

In order to achieve the above object, the magnetic recording medium of the present invention is a magnetic recording medium comprising a nonmagnetic support and a metal magnetic thin film formed on the nonmagnetic support. Surface roughness S in the range of 2 μm × 2 μm of body
Ra is 4 nm or less.

Further, an undercoat layer is provided on the surface on which the metal magnetic thin film is formed. After the undercoat layer is formed,
It is characterized in that it is stretched in the width direction and heat-treated.

Further, the metal magnetic thin film is characterized by being mainly composed of Co.

Further, the invention is characterized in that a lubricant layer is formed on the metal magnetic thin film.

The magnetic recording medium to which the present invention is applied is a so-called metal magnetic thin film type in which a magnetic layer is formed by directly depositing a metal magnetic material on a non-magnetic support by a vacuum thin film forming technique. It is a magnetic recording medium.

In such a metal magnetic thin film type magnetic recording medium, the crystal growth direction of the metal magnetic thin film is influenced by the surface property of the non-magnetic support, and the crystal growth direction of the metal magnetic thin film is aligned to enhance the coercive force. In addition, the surface of the non-magnetic support must be smooth to some extent.

Therefore, in the present invention, the surface roughness SRa of the surface of the non-magnetic support on the side where the metal magnetic thin film is formed, particularly in the range of 2 μm × 2 μm, is restricted to 4 nm or less.

Surface roughness S in the range of 2 μm × 2 μm
Ra is an atomic force microscope (AFM: Atomic Force Microscope) adapted to detect the displacement of the probe, which changes due to the repulsive force acting between the atom of the sample to be measured and the atom at the tip of the probe.
Force Microscope). The measurement conditions are shown below.

AFM measurement conditions Scan size: 2 μm Zrange: 0.1 μm Number of samplings: 400 point Scan rate: 4.34 Hz Non-magnetic having a surface roughness SRa of 4 nm or less in the thus measured 2 μm × 2 μm range. On the support, the metal magnetic material grows in a uniform crystallographic direction to obtain a metal magnetic thin film having a high coercive force.

The range for setting the surface roughness SRa is 2
The reason for setting μm × 2 μm is as follows.

That is, it is the protrusions densely present on the non-magnetic support that adversely affect the crystal growth of the metallic magnetic material. Even if there are protrusions on the non-magnetic support, 2
This is because when SRa satisfies the above-mentioned value when the measurement is performed in the range of μm × 2 μm, the surface property is not affected by the protrusions, and the metal magnetic material can grow crystals in a uniform crystal direction.

The non-magnetic support having the surface roughness SRa satisfying the above condition can be obtained by controlling the conditions for forming the raw material of the non-magnetic support into a film. Considering the limits,
It is realistic to provide an undercoat layer for controlling the surface property on the surface of the non-magnetic support obtained under normal conditions on the side where the metal magnetic thin film is formed.

This undercoat layer is a layer formed by applying an aqueous solution of a thermoplastic polyester onto a non-magnetic support and drying it. By providing such a subbing layer on the non-magnetic support, stretching the film in the width direction, and then performing heat treatment, the thickness of the subbing layer and the heat treatment temperature after the stretching are controlled to control the surface of the non-magnetic support. The sex can be as desired. It is appropriate that the thickness of the undercoat layer is 10 to 20 nm and the heat treatment temperature is around 200 ° C.

As the non-magnetic support on which the above-mentioned undercoat layer is formed, a polyester film, a polyimide film, a polyamide film or the like, which is a plastic film used as a non-magnetic support in this type of magnetic recording medium, is used. Can also be used.

A filler may be added (or coated) to the non-magnetic support in order to improve the running property.

That is, FIG. 1 shows the structure of the non-magnetic support 1 to which the filler 2 is added and the undercoat layer 3 is formed on the surface thereof, and the state of the metal magnetic thin film 4 formed thereon.

The above-mentioned non-magnetic support is formed by adding and dispersing filler 2 in a non-magnetic support raw material and forming a film thereof, and the surface thereof has a height substantially reflecting the particle diameter of the filler 2. The surface protrusion of is protruding.

As the filler 2, microgel particles made of a crosslinkable polymer, Ti, Si, Ca, Mg, A
Oxides such as 1, Zn, Ba, etc., carbonates, phosphates, and sulfates can be used alone or as complex salts, and these may be mixed and used. For example, CaCO ₃ , SiO
Inert inorganic particles such as ₂ , Al ₂ O ₃ , natural clay, kaolinite, carbon, Ca, Si, Mn, Mg, S
Polymer insoluble compositions containing catalyst residues such as b, Ge, P, Li, K and Na can also be used, and these may be used alone or in combination of both.

The height of the surface protrusions is 40 to 120 n.
m, the density is 0.5 to 25,000 pieces / mm ² , and more preferably 15,000 pieces / mm ² .

In this case, the undercoat layer 3 is formed by coating the surface projections of the non-magnetic support with an aqueous solution of a thermoplastic polyester and drying it. After stretching, heat treatment,
At that time, the surface property of the non-magnetic support can be made desired by controlling the thickness of the undercoat layer and the heat treatment temperature after stretching.

When a metallic magnetic material is deposited on such a non-magnetic support 1 by a vacuum thin film forming technique, the surface protrusions are separated from the order in which the proper density and height influence the crystal growth of the metallic magnetic material. Since it has no effect on the crystal growth, the surface 5 made flat by the undercoat layer 5
Thus, the metallic magnetic material grows in a uniform crystal direction.

In the formed metal magnetic thin film 4, the shape of the surface protrusions on the non-magnetic support is raised by the layered action, and the surface shape reflects the surface shape of the non-magnetic support. Therefore, the contact area with the sliding member is small at the time of recording / reproducing, and good running performance can be obtained.

The surface protrusions can also be formed by applying a filler colloidal solution in which a filler is dispersed in a water-soluble polymer on a non-magnetic support and drying, and the same effect can be obtained in this case.

As the metal magnetic thin film formed on the non-magnetic support as described above, any of those usually used in magnetic recording media of metal magnetic thin film type can be used, for example, oblique vapor deposition method or vertical vapor deposition method. A metal thin film mainly composed of iron, cobalt, nickel, or the like, or a metal thin film mainly composed of an alloy thereof is suitable. Further, in order to improve the corrosion resistance and the wear resistance, the metal magnetic thin film may be made to contain oxygen by introducing oxygen into the vapor deposition atmosphere. The thickness of the metal magnetic thin film is preferably 40 nm or more from the viewpoint of ensuring durability.

In the magnetic recording medium of the present invention, when a lubricant layer is formed on the surface of the metal magnetic thin film, the running property is further improved. In particular, when a surface protrusion is provided on the non-magnetic support, if a lubricant layer is further provided, excellent runnability can be obtained by the synergistic effect of the surface shape and the lubricating performance. As the lubricant, for example, fatty acid, fatty acid ester, fatty acid amide, metal soap, fatty acid alcohol, paraffin, silicone, fluorine-based surfactant, inorganic activator and the like can be used. The lubricant layer is formed by applying these lubricants to the surface of the metal magnetic thin film by a coating method or a transfer method.

Further, in the above-mentioned magnetic recording medium, a back coat layer is provided on the surface of the non-magnetic support opposite to the side on which the metal magnetic thin film is formed, in the same manner as a normal magnetic recording medium, so that the running property is improved. Oxygen-containing metal thin film such as Ti, Cr, Ni, etc., or Al between the non-magnetic support and the metal magnetic thin film.
Forming oxide thin films of ₂ O ₃ , SiO ₂ etc., and rust preventives, antistatic agents, mold proofing agents, etc. The various additives may be retained. Various conditions such as the material of the back coat layer and the kinds of additives may be based on the conditions usually used.

[0037]

Function: Surface roughness SRa in the range of 2 μm × 2 μm is 4
When a metallic magnetic material is deposited on a non-magnetic support having a thickness of not more than 10 nm, the metallic magnetic material grows in a uniform crystal direction on the non-magnetic support to form a metallic magnetic thin film with high coercive force. Be filmed. The magnetic recording medium in which the metal magnetic thin film having a high coercive force is formed as the magnetic layer as described above exhibits high output in a short wavelength region and is suitable as a medium for high density recording.

[0038]

EXAMPLES Examples to which the present invention is applied will be described below based on experimental results.

First, various non-magnetic supports having different surface roughness were prepared as follows.

A PET (polyethylene terephthalate) polymer chip, which is a raw material for the non-magnetic support, was melted, extruded from a die slit, and rapidly cooled to form a film.

This PET film was sequentially stretched in one direction by a biaxial stretching method, and then a thermoplastic polyester aqueous solution was applied to the surface on which the metal magnetic thin film was to be formed and dried to form an undercoat layer. And PE with an undercoat layer formed
The T film was stretched in the width direction and heat-treated. At this time, the thickness of the undercoat layer and the heat treatment temperature were changed as shown in Table 1.

2 μm × of various non-magnetic supports produced
The surface roughness SRa in the range of 2 μm is shown in Table 1 together with the film thickness of the undercoat layer and the heat treatment temperature. The surface roughness S
Ra is AFM (Digital Instrument)
s company).

[0043]

[Table 1]

As can be seen from Table 1, the surface roughness SRa of the non-magnetic support changes depending on the thickness of the undercoat layer and the heat treatment temperature. That is, the thicker the undercoat layer and the higher the heat treatment temperature, the smaller the surface roughness and the higher the smoothness.

Then, the produced non-magnetic supports are connected to each other to form one roll, and the surface of the undercoat layer is
Co was formed by continuous vacuum oblique deposition in an atmosphere containing a small amount of oxygen.
A Ni magnetic metal thin film was formed. The vapor deposition conditions are shown below. The Co—Ni metal magnetic thin film has a composition of 80 wt% Co and 20 wt% Ni and has a thickness of 180 nm.
Is.

Deposition conditions Vacuum degree: 10 ^-2 to 10 ^-3 Pa Oxygen flow rate: 2 liter / min Film feed rate: 55 m / sec Co-Ni minimum incident angle: 50 ° Finally, the deposited Co-Ni metal A magnetic tape was prepared by applying stearic acid as a lubricant to the surface of the magnetic thin film in an amount of 10 mg / mm ² and slitting it into a predetermined width.

Then, the coercive force of each of the magnetic tapes prepared as described above was measured at the portion corresponding to each non-magnetic support. The results are shown in Table 2. Also,
Fig. 2 shows the relationship between the surface roughness SRa of the non-magnetic support and the coercive force of the tape. For further reference, the coercive force of the tape and 7 MHz
FIG. 3 shows the relationship of the output at.

[0048]

[Table 2]

First, as can be seen from FIG.
The output at MHz changes greatly due to the coercive force. Then, in order to obtain an output of a practical level or higher, the coercive force must be at least 70 kA / m or higher.

Next, referring to FIG. 2, the coercive force of the tape is
It can be seen that there is a correlation with the surface roughness SRa of the non-magnetic support, and the coercive force of the tape increases as the surface roughness SRa of the non-magnetic support decreases. It is when the surface roughness SRa of the non-magnetic support is 4 nm or less that a coercive force of 70 kA / m or more, which leads to an output of a practical level or more, is obtained.

From the above results, in order to enhance the coercive force of the metal magnetic thin film and obtain a medium exhibiting a high output in the short wavelength region, the surface roughness of the nonmagnetic support in the range of 2 μm × 2 μm is 4 nm. I found it necessary to:

[0052]

As is apparent from the above description, according to the present invention, in the magnetic recording medium in which the metal magnetic thin film is formed on the non-magnetic support, 2 μm of the non-magnetic support is used.
Since the surface roughness SRa in the range of × 2 μm is regulated to 4 nm or less, the coercive force of the metal magnetic thin film is significantly increased,
It is possible to obtain a magnetic recording medium that exhibits high output in the high density recording area. Therefore, it can be said that the present invention greatly contributes to the improvement of the recording density in the magnetic recording field.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an essential part showing a structural example of a magnetic recording medium to which the present invention is applied.

FIG. 2 is a non-magnetic support 2 μm × 2 μ of a magnetic recording medium.
It is a characteristic view which shows the relationship between surface roughness SRa and coercive force in the range of m.

FIG. 3 is a characteristic diagram showing a relationship between a coercive force and an output at 7 MHz of a magnetic recording medium.

[Explanation of symbols]

 1 non-magnetic support 2 filler 3 undercoat layer 4 metal magnetic thin film

Claims (4)

[Claims] 1. A magnetic recording medium comprising a non-magnetic support and a metal magnetic thin film formed thereon, wherein the non-magnetic support has a surface roughness SRa in the range of 2 μm × 2 μm of 4 nm or less. Characteristic magnetic recording medium. 2. The non-magnetic support has an undercoat layer on the surface on which the metal magnetic thin film is formed. After the undercoat layer is formed, it is stretched in the width direction and heat-treated. The magnetic recording medium according to claim 1, wherein: 3. The magnetic recording medium according to claim 1, wherein the metal magnetic thin film is mainly composed of Co. 4. The magnetic recording medium according to claim 1, wherein a lubricant layer is formed on the metal magnetic thin film.