JPH06259740A - Magnetic recording medium - Google Patents

Abstract

(57) [Summary] (Correction) [Purpose] To provide a metal thin film type magnetic recording medium having a good head touch and excellent running stability and durability. [Structure] A magnetic recording layer of a metal thin film is provided on at least one surface of a substrate, and the stiffness of the entire magnetic recording medium is 1 / k.
0 [Unit: kgfmm] is n: number of layers constituting the magnetic recording medium E _k : Young's modulus of the kth layer [unit: kgf / mm ² ] I _k : moment of inertia of the kth layer [unit: mm ³ ]) and the shape is A magnetic recording medium having a disk shape.

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 having a magnetic recording layer formed of a metal thin film.

[0002]

2. Description of the Related Art In recent years, with the development of information processing technology and image processing technology, demands for larger capacity and higher image quality of magnetic recording media have been increasing. In order to meet this demand, research and development of magnetic recording media capable of high-density recording have been actively conducted. In particular, Co and C are used as the magnetic recording layer for coating type magnetic recording media which are generally used at present.
A metal thin film magnetic recording medium in which a ferromagnetic metal thin film such as o-Ni, Co-Cr, or Co-O is directly formed on a substrate by a vacuum deposition method or a sputtering method is regarded as a promising medium for high density recording. ing.

On the other hand, the 3.5 "floppy disk (hereinafter abbreviated as FD), which is the most popular as the primary medium for personal computers, word processors, etc., has recently achieved high recording due to the demand for a large capacity of 20 MB or more. Research and development of a new magnetic head for density, a magnetic recording medium, a tracking servo technology, a signal processing technology, etc. is under way.For a large capacity FD of 20 MB or more, the recording wavelength is 0.8 μm or less.
In order to perform recording / reproduction in such a short wavelength region, the uniformity of the contact state (head touch) between the magnetic recording medium and the head is particularly important. If the contact state (head touch) becomes non-uniform, a spacing loss occurs during recording and reproduction, which causes fluctuations in output and reduction in output.

[0004]

In order to realize the above-mentioned short wavelength recording, a conventional coating type medium (for example, Cr
O _2, in the case where the γ-Fe ₂ O ₃ or the like with use one) in the magnetic layer, as the recording signal becomes shorter, the demagnetizing field in the magnetic layer becomes strong, the attenuation and rotation of residual magnetization Therefore, there is a problem that the reproduction output is significantly reduced.

Therefore, it is strongly desired to use a metal thin film magnetic recording medium capable of high density recording as the FD. However, a metal thin film type magnetic recording medium which realizes a good head touch with a magnetic head has not yet been obtained. That is, when a metal thin film magnetic recording medium is used as an FD, abrasion powder or sliding marks are generated on the surface of the medium or the head within a few seconds to a few hours, the output is reduced, and practical durability reliability is obtained. There was no problem.

[0006]

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a metal thin film type magnetic recording medium having a good head touch and excellent running stability and durability. And

The magnetic recording medium of the present invention has a magnetic recording layer of a metal thin film on at least one surface of a substrate, and the stiffness of the entire magnetic recording medium is 1 / k ₀ [unit: kgfmm].
But,

[0008]

[Equation 3] And has a disk shape.

In the magnetic recording medium of the present invention, as shown in FIG. 1, a magnetic recording layer 2 of a metal thin film, a protective layer 3 and a back coat layer 4 are formed on a substrate 1.

The substrate 1 is preferably a polymer film, and polyethylene terephthalate, polyimide, aramid, etc. are particularly preferably used. Fine protrusions may be formed on the front side or the back side of the substrate 1 in order to improve the slip property of the film, the running property of the medium, and the durability. Examples of the method for forming the fine protrusions include a method of internally filling the polymer film with inorganic fine particles and a method of coating a polymer film solution containing the inorganic fine particles. Carbon, CaCo ₃ , BaSO ₄ , SiO ₂ , TiO ₂ or the like is used as the inorganic fine particles, and the particle size thereof is preferably 0.005 to 0.2 μm. However, it is preferable that the surface roughness of the recording surface side of the substrate 1 has a maximum height of 0.05 μm or less in consideration of a reduction in output due to spacing loss and dropout.

Further, in order to improve the magnetic characteristics of the magnetic recording medium, heat may be applied to the substrate 1 when forming the metal thin film. For example, when forming the Co—Cr magnetic layer, the substrate 1 is heated to near 150 ° C. Therefore, it is preferable to select a polymer material having a high glass transition point for the substrate 1. For example, Upilex S type and R type manufactured by Ube Industries, Ltd. are excellent for the following reasons.

The glass transition temperature is 500 ° C. or higher.

It is possible to make the surface of the substrate less rough and defective and to make the surface roughness ultra-smooth up to R _max (maximum height) <0.005 μm.

The coefficient of thermal expansion is 1 × 10 ^{-6 to} 3 × 10 ^-5
Since it can be controlled between cm / cm / ° C., it can be matched with the thermal expansion coefficient of the metal thin film layer used as the magnetic recording layer. Therefore, the occurrence of curl is suppressed.

Young's modulus is 800 to 1200 kg / cm
Since it is as high as ² , the thickness of the substrate can be reduced.

The magnetic recording layer 2 is made of Fe, Ni or Co.
As a main component, for example, Co-Ni, Co-C
It is a metal thin film such as a ferromagnetic alloy such as r, Co—O, or Co—Pt—B, a ferromagnetic oxide, or a ferromagnetic nitride.

The magnetic recording layer 2 is formed by a physical vapor deposition method such as a vacuum vapor deposition method or a sputtering method, or a plating method. Among them, 8 to 23 wt% of Cr formed by vacuum deposition or sputtering method, and the balance of C mainly consisting of Co
The o-Cr perpendicular magnetic film is very excellent for high density recording as compared with the conventional in-plane magnetic film.

On the magnetic recording layer 2, wear resistance, lubricity,
The protective layer 3 is generally formed for the purpose of improving the corrosion resistance. The protective layer 3 includes a metal oxide film obtained by directly oxidizing the surface of the magnetic recording layer 2, an inorganic protective layer 3a such as SiO ₂ , Al ₂ O ₃ , Co ₃ O ₄ , amorphous carbon, or diamond-like carbon, and an inorganic protective layer 3a. The lubricant layer 3b is formed on the upper surface of the lubricant layer 3b such as a fluorine resin or an ester oligomer, but either one may be used alone.
The inorganic protective layer 3a and the lubricating layer 3b are formed by a physical vapor deposition method such as vacuum vapor deposition, sputtering or ion plating, or a coating liquid application method such as spin coating or wire bar.

The back coat layer 4 may be any of those conventionally used as a back coat for magnetic recording media. For example, a binder such as polyester resin or polyurethane resin in which inorganic fine particles such as carbon black, graphite or CoCO ₃ are dispersed can be used. The back coat layer 4 is formed by, for example, a coating liquid coating method.

The magnetic recording medium shown in FIG. 2 has magnetic recording layers 2 and 2 ', inorganic protective layers 3a and 3a', and lubricating layers 3b and 3b 'on both sides of the substrate 1, which are symmetrical with respect to the substrate 1 in this order. It was formed in. Both sides of the magnetic recording medium can be used as recording surfaces. Further, since the layer structure is symmetrical with respect to the substrate 1, it is effective in preventing curling.

The magnetic recording medium shown in FIG. 3 is the same magnetic recording medium as that of the embodiment shown in FIG. 2 except that the underlying layers 5 and 5'are formed on both surfaces of the substrate 1.

The underlayer 5 is made of Al, G for the purpose of improving adhesion, crystal orientation, or magnetic properties.
It is a thin film of e, Cr, Ti, SiO ₂ or the like, or a thin film of a Fe—Ni alloy or a Co—Ni alloy as a base of the perpendicular magnetic recording layer. The underlayer 5 is formed by a vacuum vapor deposition method, a sputtering method, an ion plating method, a plating method, or the like.

In the metal thin film magnetic recording medium of the present invention, the stiffness of the entire medium is 1 / k ₀ [unit: k
gfmm] is in the following range.

[0024]

[Equation 4] The above 1 / k _{0 and} further 1.2 × 10 ⁻¹¹ ≦ 1 / k ₀ ≦
The range of 2.7 × 10 ^-11 is preferable. The above k-th layer is
It means all layers constituting the magnetic recording medium, including the substrate 1.

The inventors of the present invention can keep the contact state between the magnetic recording medium and the magnetic head stable during traveling of the magnetic recording medium by setting the stiffness of the entire magnetic recording medium within the above range, and the running durability is improved. The present invention has been found to be achieved.

The stiffness referred to in the present invention will be described below.

As shown in FIG. 4, when a force of F is applied to a thin plate 11 of a two-layer structure having a width w and a thickness (t ₁ + t ₂ ) fixed at one end at a distance of l from the fixed end, The displacement δ at the position is within a relatively small range of δ,

[0028]

[Equation 5] Can be expressed as In the above equation (1), the entire factor applied before F is bending compliance, of which l ³ /
w is related to the geometrical arrangement,

[0029]

[Equation 6] The part of has a value that reflects the structure of the layer and the physical properties of the material constituting the layer. Therefore, 1 / k ₀ is defined as the stiffness of the present invention.

[0030]

[Equation 7] The above formula (2) can be expanded even when the thin plate has an n-layer structure.

[0031]

[Equation 8] That is, in the present invention, the stiffness includes all layers constituting the magnetic recording medium such as the substrate, the magnetic recording layer, the protective layer and the back coat layer, and when the magnetic recording medium is composed of n layers,

[0032]

[Equation 9] It is defined as

In the present invention, Young's modulus E was calculated by conducting a tensile test. The tensile test was performed using a tensile tester manufactured by Toyo Baldwin. Sample shape is width 8mm, length 50mm, pulling speed 4mm / mi
n (8% / min). Young's modulus of the substrate is 0.2
It was calculated by subtracting the contribution of the substrate from the load at the time of% elongation.

Next, an example of stiffness calculation will be described using the magnetic recording medium shown in FIG. 2 as an example.

In the magnetic recording medium of FIG. 2, a polyimide film is used as the substrate 1 and a Co—Cr alloy thin film (Young's modulus: 16,0) having a thickness of 0.3 μm is used as the magnetic recording layer 2.
00 kg / mm ² ) and the thickness of the magnetic recording layer 2 ′ is 0.1.
5 μm Co-Cr alloy thin film (Young's modulus: 16,000
kg / mm ² ) is used. Inorganic protective layer 3a, 3
The thicknesses of the a'and the lubricating layers 3b and 3b 'are extremely smaller than the thickness of the base body 1, and can be ignored in the calculation.

When the Young's modulus of the polyimide film is 1,100 kg / mm ² , the stiffness is calculated by using the equation (3), and the stiffness when the thickness of the polyimide film is changed as shown in FIG. Is calculated.

In the case of this example, the thickness of the polyimide film is preferably 28 to 52 μm, more preferably 30 to 40 μm.

The thickness of each layer of the magnetic recording medium of the present invention varies depending on the material used, but considering the stiffness, magnetic characteristics, spacing loss, etc. of the magnetic recording medium, the following is preferable. That is, the thickness of the substrate 1 is 50 μm or less, more preferably 40 μm or less, and further preferably 3
The thickness of the magnetic recording layers 2 and 2 ′ is in the range of 0 to 35 μm.
It is preferably at least 01 μm, more preferably at least 0.1 μm. The upper limit of the thickness of the magnetic recording layers 2 and 2'is 1 .mu.m or less, more preferably 0.
It is preferably 5 μm or less. The inorganic protective layers 3a and 3a 'have a thickness of 50 to 500Å, further 50 to 200Å, and the lubricating layers 3b and 3b' have a thickness of 5 to 200Å, further 10 to 5
The range of 0Å, the thickness of the underlayer 5, 5'is several hundred Å ~ 5000
The range of Å is preferable.

The magnetic recording medium of the present invention has a diameter of 5
This is effective when used as a 0 mm or larger floppy disk.

[0040]

EXAMPLES The present invention will be specifically described below with reference to examples. The evaluation of the examples was carried out using a floppy tool deck (rotation speed, magnetic head, floppy disk surface height, etc., variable). Further, the magnetic recording medium is a floppy disk having a diameter of 3.5 ″, and the following (i),
The evaluation of (ii) was performed. The used track was the 40th track of the 80 tracks, and the rotation speed was 600 rpm.

(I) Head touch ... Head touch is qualitatively determined from the shape of the reproduction envelope at 1 MHz.
It was divided into stages (⊚, ○, Δ, ×).

FIG. 6 shows the envelope shape as an evaluation standard.

Those of ⊚ and ○ are practically usable.

(Ii) Durability: Reproduction output (1MH
The evaluation was performed by the pass rotation until z) decreased by 3 dB from the initial value. It is preferable that the durability of 10 million passes or more be obtained, but if it is 3 million passes or more, there is no practical problem. Example 1 This medium has the configuration shown in FIG.

A 30 μm-thick polyimide film (Upilex S type, manufactured by Ube Industries, Ltd.) was used as the substrate. The thermal expansion coefficient of this substrate is 0.8 × 10 ⁻⁵ cm / c
m / ° C., Young's modulus 1,100 kg / mm ² , surface roughness Ra 27Å, R _max 222Å, protrusion density 6 × 10 ^6.
The number of pieces / mm ² . Before forming the magnetic recording layer on this substrate, heat treatment in vacuum (200 ° C., 10 minutes) was performed.

A perpendicular magnetized film containing 80% by weight of Co and 20% by weight of Cr was formed on both sides of the substrate by an RF magnetron sputtering apparatus to have a thickness of 0.3 μm on the A side (front surface) side and a thickness of 0.15 μm on the B side (rear surface) side. Formed. The curl of the medium was controlled by the film thickness on the B side (back side). The temperature of the substrate during film formation was 200 ° C.

Further, S is formed as an inorganic protective layer on the Co--Cr film.
An iO ₂ thin film was formed on each side by an RF magnetron sputtering device to a thickness of 200 Å.

Further, a silane coupling agent was formed as a lubricating layer on the SiO ₂ protective layer to form 20 Å on each side.

This medium was punched and mounted in a 3.5 ″ disk shape.

Also calculated by calculating the stiffness of this medium
By the way, 1 / k₀ = 1.23 x 10 ^-11 [Kgfmm]
Met.

A side (front surface) of this phyloppy disk
Table 1 shows the results of various evaluations with the recording surface as a recording medium. It was confirmed that this floppy disk was flat with almost no curl and had excellent head touch and durability. Example 2 The same as Example 1 except that the thickness of the substrate was 35 μm. When the stiffness of this floppy disk was calculated, it was 1 / k ₀ = 1.84 × 10 ^-11 [kgfmm].

Table 1 shows the results of various evaluations with the side A of the floppy disk as the recording surface. It was confirmed that this floppy disk was flat with almost no curl and had excellent head touch and durability. Example 3 The same as Example 1 except that the thickness of the substrate was 40 μm. When the stiffness of this floppy disk was calculated, it was 1 / k ₀ = 2.62 × 10 ^-11 [kgfmm].

Table 1 shows the evaluation results when the surface A of this floppy disk was used as the recording surface. This floppy disk is flat with almost no curl, head touch,
It was confirmed that both durability was excellent. Example 4 The same as Example 1 except that the thickness of the substrate was 50 μm. When the stiffness of this floppy disk was calculated, it was 1 / k ₀ = 4.78 × 10 ^-11 [kgfmm].

Table 1 shows the evaluation results when the side A of this floppy disk was used as the recording surface. The floppy disk was flat with almost no curl, the head touch was a little bad, and the durability was close to the target spec. Comparative Example 1 The same as Example 1 except that the thickness of the substrate was 25 μm. When the stiffness of this floppy disk was calculated, it was 1 / k ₀ = 0.77 × 10 ^-11 .

Table 1 shows the evaluation results when the surface A of this floppy disk was used as the recording surface. This floppy disk was flat with almost no curl, but had poor head touch and durability.

[0056]

[Table 1]

[0057]

As described above, the magnetic recording medium of the present invention has a stiffness of 1 / k ₀ [unit: kgfmm] within a specific range, so that a good head touch is obtained and the running is stabilized. Therefore, the magnetic recording medium of the present invention exhibits excellent durability.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of a magnetic recording medium of the present invention.

FIG. 2 is a sectional view showing another example of the magnetic recording medium of the present invention.

FIG. 3 is a sectional view showing another example of the magnetic recording medium of the present invention.

FIG. 4 is a diagram for explaining the stiffness referred to in the present invention.
The perspective view which showed the state which bent the thin plate of a layered structure.

FIG. 5 is a graph showing the relationship between substrate thickness and stiffness.

FIG. 6 is a diagram showing a reproduction envelope (judging the quality of head touch).

[Explanation of symbols]

 1 Substrate 2, 2'Magnetic Recording Layer 3a, 3a 'Inorganic Protective Layer 3b, 3b' Lubricating Layer 5, 5'Underlayer

Claims (13)

[Claims] 1. A stiffness 1 of the entire magnetic recording medium having a magnetic recording layer of a metal thin film on at least one surface of a substrate.
/ K ₀ [unit: kgfmm] is And a disk-shaped magnetic recording medium. 2. The stiffness 1 / k ₀ [unit: kg
The magnetic recording medium according to claim 1, wherein fmm] is 1.2 × 10 ⁻¹¹ ≦ 1 / k ₀ ≦ 2.7 × 10 ⁻¹¹ . 3. The magnetic recording medium according to claim 1, wherein the substrate is polyimide. 4. A fine protrusion is formed on the surface of the polyimide substrate on the magnetic recording layer side, and the protrusion height is R _max ≦ 0.1 μm.
The magnetic recording medium according to claim 3, wherein m and the protrusion density are 10 ⁴ pieces / mm ² or more. 5. The magnetic recording medium according to claim 1, wherein the magnetic recording layer is provided on one surface of the substrate. 6. The magnetic recording medium according to claim 1, 2 or 3 or 4, wherein the magnetic recording layer is provided on both surfaces of the substrate. 7. The magnetic recording medium according to claim 5, wherein the magnetic recording layer is a perpendicular magnetization film containing Co as a main component. 8. The magnetic recording layer comprises 8 to 23% by weight of Cr.
9. A magnetic recording medium according to claim 7, which is a Co—Cr perpendicular magnetization film made of Co and Cr of 92 to 77% by weight. 9. The magnetic recording medium according to claim 1, which has a diameter of 50 mm or more and 200 mm or less. 10. The substrate according to claim 1, wherein the substrate is 25 to 50 μm thick polyimide, and the magnetic recording layer is a perpendicular magnetization film containing Co as a main component. Magnetic recording medium. 11. The magnetic recording medium according to claim 10, wherein the substrate has a thickness of 30 to 40 μm. 12. A magnetic recording layer of a Co—Cr perpendicularly magnetized film, a protective layer of SiO ₂ and a lubricating layer are provided on both surfaces of the substrate in order from the substrate side. 11. The magnetic recording medium according to item 11. 13. A metal thin-film magnetic layer having a thickness of 0.1 μm or more on both sides of a disk-shaped substrate made of a heat-resistant polymer material having a glass transition point of 180 ° C. or more and having a diameter of 50 mm or more and a thickness of 50 μm or less. And a magnetic recording medium.