JPH10143838A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve sliding durability by forming a protective layer from carbon-based or oxide ceramic materials and forming a lubricant layer of a mixture of first and second fluorine-contg. compds. expressed by specified formulae on the protective film layer. SOLUTION: A Ni-P plating film is formed on an aluminum alloy substrate, and then successively a base film, magnetic recording layer and protective film layer are deposited thereon. A fluorine-contg. compd. expressed by formula I having 500 to 5000 number average mol.wt. and a second fluorine-contg. compd. expressed by formula II having 500 to 5000 number average mol.wt. are mixed by 25 to 400wt.% proportion to obtain a lubricant and to prepare a coating compsn. In formulae I, II, (p) and (q) are integers. The obtd. compsn. is applied to 20Å film thickness by dipping method on the surface of the protective film layer. Thereby, the obtd. medium shows excellent lubricating property and wear resistance, chemical stability even at high temp. for a long time, and improved reliability.

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 used in a magnetic disk drive, and more particularly to a magnetic recording medium having a lubricating layer having excellent long-term stability and sliding durability.

[0002]

2. Description of the Related Art A thin film type magnetic recording medium is manufactured by depositing a ferromagnetic metal or an alloy thereof on a non-magnetic substrate by sputtering, vapor deposition, electroless plating or the like. In actual use, the magnetic head and the magnetic recording medium often contact and slide at a high speed, so that the magnetic head is damaged by wear and the magnetic characteristics are deteriorated. Therefore, by providing a protective film or a lubricating layer on the magnetic layer, static / dynamic friction at the time of contact sliding is reduced as much as possible, and wear resistance is improved. As such a protective film layer, a carbonaceous film, an oxide film of SiO ₂ or ZrO ₂ , a nitride film, a boride film, and the like are generally used.
Generally, perfluoropolyether
rs) The compound is applied to the disk surface. As the perfluoropolyether compound,

Embedded image Product name "Fomblin Zet Doll (FOMB
LIN ZDOL) "(manufactured by AUSIMONT).

As described above, the magnetic head and the magnetic recording medium often slide at high speed during use. That is, when the magnetic recording medium is started, the head floats as the disk medium is rapidly rotated and accelerated from the stopped state, but when the power is cut off and the motor that rotates the disk medium stops, The disk medium and the head slide while contacting at high speed. On the other hand, for the purpose of increasing the areal recording density, it is required to lower the flying height of the head and to increase the speed of disk rotation. Although providing a lubricating layer to reduce the dynamic friction coefficient is extremely effective for the purpose of suppressing wear damage and deterioration of magnetic characteristics caused by the contact sliding, the film thickness of the lubricating layer is particularly large. In the case or when the medium substrate is smooth, the sticking phenomenon easily occurs between the head and the disk, so that the coefficient of static friction increases,
The head becomes stuck on the disk and becomes inoperable. Moreover, such an adsorption phenomenon is more likely to occur as the medium substrate is made smoother. Conversely, when the thickness of the lubricating layer is small, the occurrence of the adsorption phenomenon can be suppressed, but sufficient durability is not obtained, and wear damage and deterioration of magnetic properties due to high-speed contact sliding are likely to occur. Becomes Therefore, various attempts have been made to solve the above-mentioned problem by carefully selecting the lubricant used for the lubricating layer. For example, the “Fomblin Zetdall” has CH ₂ O at both ends of the molecule.
Since it has an H group, the bond with the surface of the protective film layer is strong, and excellent sliding resistance is provided.

[0004]

However, "Fomblin Zett Doll" is described in the literature ("Degradation of
perfluoropolyethers catalyzed by aluminum oxid
e ”, Paul H. Kasai, Wing T. Tang and Patrick Wheeler,
As shown in Applied Surface Science, 51 (1991) 201 to 211), since a molecule has a bond of an O—CF ₂ —O unit, aluminum oxide (α) which is a constituent component of a magnetic head is used. -Al ₂ O ₃ ) easily decomposes at a temperature of about 200 ° C. In addition, at the time of CSS (contact start / stop), the local instantaneous temperature becomes 90 to 4 due to contact between the magnetic recording medium and the magnetic head.
The temperature will be as high as 50 ° C or more. Therefore, aluminum oxide, which is a component of the slider portion of the magnetic head, acts as a catalyst, and "fomblin zett doll" is decomposed. When the decomposition of the lubricant occurs, the decomposed components volatilize and the thickness of the lubricating layer decreases,
The coefficient of kinetic friction increased, and as a result, there was a problem that abrasion damage and deterioration of magnetic properties due to high-speed contact sliding were likely to occur. Furthermore, when a part of the decomposed components adheres to the magnetic head, the flying height of the head increases, causing a decrease in the reproduction output, and the head is attracted to the recording medium surface.

However, as described above, “Fomblin Zetdall” has excellent binding properties between the polar functional groups at both ends of the molecule and a carbon-based or oxide ceramic-based protective film layer, and is excellent. Since it has the advantage of imparting sliding characteristics, there has been a need for a method of suppressing contact decomposition by a magnetic head while maintaining such an advantage.

Also, the chemical formula

Embedded image[Compound name “Fomblin Zet Tet”
Laor ”(Audimont)
O-CF in the molecule _Two -O
Multidentate coordination of polar functional groups despite the unit structure
Due to the structure, aluminum oxide in the slider part of the head
Is moderated and chemically stable.
In addition, the polar functional groups at both ends are carbon-based or oxide-based.
Shows high affinity with Lamix-based protective film,
Excellent stability because it contributes to the improvement of turn-off properties.

However, since the affinity between the polar functional groups at both ends and the carbon-based or oxide ceramic-based protective film is too high, a freely movable lubricant on the upper side of the lubricating layer contributing to the improvement of durability. Almost no components. For this reason, the sliding durability is inferior when combined with the pseudo contact type head.

[0008]

SUMMARY OF THE INVENTION The present invention has been proposed in view of the above, and provides a high-density magnetic recording medium that can withstand years of use by selecting a lubricating layer composition having excellent durability. In a magnetic recording medium provided with at least a ferromagnetic thin film layer and a protective film layer on a non-magnetic substrate, the protective film layer is selected from carbon-based or ceramic oxide-based And a chemical formula on the surface of the protective film layer.

Embedded image And a fluorine-containing compound represented by the following formula (hereinafter referred to as a first fluorine-containing compound)

Embedded image (Hereinafter, referred to as a second fluorine-containing compound).

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The first fluorine-containing compound used in the lubricating layer in the present invention is the product name "FOMBLIN ZDO Doll" described in the above-mentioned prior art.
L) "(manufactured by AUSIMONT) can be used as it is, and as described above, the polar functional groups at both ends of the molecule have a high binding property with the carbon-based or oxide ceramic-based protective film layer. And has the advantage that excellent sliding characteristics are imparted. On the other hand, aluminum oxide, which is a component of the slider portion of the magnetic head, acts as a catalyst and is easily decomposed, and the decomposed component is volatilized to reduce the thickness of the lubricating layer, thereby increasing the coefficient of kinetic friction. There is a drawback that abrasion damage and deterioration of magnetic properties due to high-speed contact sliding are likely to occur. As the second fluorine-containing compound, the above-mentioned trade name “Fomblin Zet Tetraol” (manufactured by Ausimont) can be used as it is, and as described above, the head slider is formed by the polydentate structure of the polar functional group. The contact reaction (decomposition) with the aluminum oxide in the part is relaxed and chemically stable, and the polar functional groups at both ends show high affinity with the carbon-based or oxide ceramic-based protective film. It has the advantage of being excellent in stability because it contributes to improvement in spin-off properties. On the other hand, the affinity between the polar functional groups at both ends and the carbon-based or oxide ceramic-based protective film is too high, and the freely movable lubricant component on the upper side of the lubricating layer contributing to the improvement of the durability is generated. There is almost no drawback that the sliding durability is inferior in combination with a pseudo contact type head. The mixed lubricating layer of the first fluorinated compound and the second fluorinated compound, by mixing both in an appropriate ratio, eliminates the catalytic decomposition which is a disadvantage of the first fluorinated compound, and The sliding property, which is a disadvantage of the two fluorine-containing compounds, can be overcome. For this reason,
Excellent long-term stability and sliding durability. Moreover, it has been found that not only the characteristics of the two kinds of fluorine-containing compounds are simply combined, but also that the specific low dynamic friction coefficient and low static friction coefficient can be obtained. As a result, the reliability of the magnetic recording medium is dramatically improved.

In order to further improve the durability of the magnetic recording medium, the mixing ratio of the second fluorinated compound to the first fluorinated compound is desirably 25 to 400 wt%. If the mixing ratio of the second fluorine-containing compound to the first fluorine-containing compound is less than 25 wt%, the long-term stability is not sufficient, and if it exceeds 400 wt%, the sliding durability is not sufficient. The method of forming the lubricating layer, that is, the method of applying the lubricant, may be performed by any known method such as a dipping method, a spin method, and a spray method.

When a carbon-based film is used as the protective film layer in the present invention, a hydrogenated, nitrogenated or fluorinated carbon film may be used. When an oxide ceramic film is used, it is preferable to use SiO ₂ or ZrO ₂ .

[0012]

EXAMPLES <Production of Test Magnetic Disk> [Example 1] FIG. 1 shows a sectional view of a hard disk according to the present invention. An aluminum alloy substrate 1 is coated with a Ni-P plating film 2 having a thickness of 13 μm as a hard underlayer.
{Co-Cr-Ta alloy 400 for the magnetic recording layer (magnetic film) 4} and carbon 20 for the protective film layer 5
0 ° laminated. Next, the chemical formula as a lubricant

Embedded image A first fluorinated compound having a number average molecular weight of 2,000 represented by

Embedded image The second fluorine-containing compound having a number average molecular weight of 2,000 represented by the following formula is mixed at a ratio (weight ratio) of 4: 1 to a fluorocarbon solvent [trade name "AK225" manufactured by Asahi Glass Co., Ltd.] to a concentration of 0.02.
The composition for coating was prepared by dissolving to 6 wt%. Then, the coating composition prepared as described above was coated on the upper surface of the protective film layer 5 by a dipping method to a thickness of 20 ° (E).
(Measured using SCA) to form a lubricating layer 6 to obtain the magnetic disk of Example 1.

Example 2 The magnetic recording of Example 2 was performed in the same manner as in Example 1 except that the mixing ratio (weight ratio) of the first fluorine-containing compound and the second fluorine-containing compound was 2: 1. I got the medium.

Example 3 The magnetic recording of Example 3 was performed in the same manner as in Example 1 except that the mixing ratio (weight ratio) of the first fluorine-containing compound and the second fluorine-containing compound was 3: 2. I got the medium.

Example 4 The magnetic recording of Example 4 was performed in the same manner as in Example 1 except that the mixing ratio (weight ratio) of the first fluorine-containing compound and the second fluorine-containing compound was 1: 1. I got the medium.

Example 5 The magnetic recording of Example 5 was performed in the same manner as in Example 1 except that the mixing ratio (weight ratio) of the first fluorine-containing compound and the second fluorine-containing compound was 1: 2. I got the medium.

Example 6 The magnetic recording of Example 6 was performed in the same manner as in Example 1 except that the mixing ratio (weight ratio) of the first fluorine-containing compound and the second fluorine-containing compound was 1: 4. I got the medium.

Comparative Example 1 Chemical formula as a lubricant

Embedded image The magnetic recording medium of Comparative Example 1 was obtained in the same manner as in Example 1 except that the first fluorine-containing compound having a number average molecular weight of 2,000 represented by was used alone.

Comparative Example 2 Chemical Formula as Lubricant

Embedded image A magnetic recording medium of Comparative Example 2 was obtained in the same manner as in Example 1 except that the second fluorine-containing compound having a number average molecular weight of 2000 represented by the following formula was used alone.

<Test 1: Long-term stability test> Al ₂ O ₃ was added as a catalyst to each of the fluorine-containing compounds used in Examples 1 to 6 and Comparative Examples 1 and 2, and heated to 250 ° C. Table 1 shows the weight loss 4 hours after the first heating.

[Table 1] As is evident from Table 1 above, while weight loss was hardly observed for each of the fluorine compounds used in Examples 1 to 6 and Comparative Example 2, the fluorine-containing compound used in Comparative Example 1 was almost unresolved. Decomposed and evaporated.

<Test 2: Measurement of Bonding Ratio / Measurement of Adhesion with Protective Film> The magnetic disks of Examples 1 to 6 and Comparative Examples 1 and 2 were measured for film thickness at a radius of 20 mm by ESCA. Thereafter, the disk was immersed in a fluorine-based solvent (trade name “PF5052”, manufactured by Minnesota Mining and Manufacturing Co., Ltd.) for 15 minutes, taken out, and the film thickness at a radius of 20 mm was measured again by ESCA. The film thickness ratio (bonded ratio) before and after immersion in the fluorine-based solvent “5052” was determined, and this value is shown in Table 1. As is clear from Table 1, the bonded ratio of the magnetic disk of Comparative Example 1 is very small, and only about 20% of the lubricant is firmly bonded to the protective film. Each of the magnetic disks of Examples 1 to 6 and Comparative Example 2 had a bonded ratio of 55% or more, indicating that many components strongly bonded to the protective film in the lubricant.

<Test 3: CSS Durability Test—Measurement of Dynamic Friction Coefficient> The magnetic disks of Examples 1 to 6 and Comparative Examples 1 and 2 were subjected to a CSS (Contact-Start-Stop) test.
A commercially available CSS tester (manufactured by Matsubo) was used for the CSS tester, and 10,000 times of CSS was performed using an Al ₂ O ₃ —TiC slider head for the magnetic head. 100
Table 1 shows the values of the coefficient of kinetic friction after 00 times. As is evident from Table 1, the dynamic friction coefficient of each of the magnetic disks of Examples 1 to 6 was about 0.5 even after 10,000 times of CSS.
3, but the magnetic disks of Comparative Examples 1 and 2 exhibited a high dynamic friction coefficient of 0.6 to 1.2.

<Test 4: CSS Durability Test—Measurement of Static Friction Coefficient> The magnetic disks of Examples 1 to 6 and Comparative Examples 1 and 2 were subjected to a CSS (Contact-Start-Stop) test.
A commercially available CSS tester (Matsubo Co., Ltd.) was used for the CSS tester, and an Al ₂ O ₃ —TiC slider head was used for the magnetic head.
Times CSS was performed. Table 1 shows the value of the coefficient of static friction after allowing the disk and the head to stand for 24 hours. As is clear from Table 1, the magnetic disks of Examples 1 to 6 have a low static friction coefficient of 0.7 to 1.0, but the magnetic disks of Comparative Examples have high static friction coefficients of 2 to 4. Was showing.

The protective film layer is made of SiO ₂ , ZrO ₂
In the same manner as above, a test magnetic disk was prepared in the same manner, and the tests 3 and 4 were performed. The same results as above were obtained.

Although the present invention has been described based on the embodiments, the present invention is not limited to the above-described embodiments, and can be implemented in any manner unless the configuration described in the claims is changed. it can.

[0026]

As described above, the magnetic recording medium of the present invention has excellent lubricity and abrasion resistance and has been carefully selected from a lubricating layer which is chemically stable over a long period of time even at a high temperature. In particular, even when a smooth substrate corresponding to the low flying height of the head is used, good sliding durability and sufficient stability for a long period are obtained. Therefore, the magnetic recording medium of the present invention can increase the data recording density and has high reliability for a long time.

[Brief description of the drawings]

FIG. 1 is a sectional view schematically showing an example of a hard disk according to the present invention.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Sachiyo Takanashi 5-1 Yawata Kaigandori, Ichihara-shi, Chiba Prefecture Showa Denko Corporation HD Plant

Claims (2)

[Claims] 1. A magnetic recording medium having at least a ferromagnetic thin film layer and a protective film layer provided on a non-magnetic substrate, wherein the protective film layer is selected from carbon-based or ceramic oxide-based. Chemical formula on the surface of the film layer And a fluorine-containing compound represented by the formula: A magnetic recording medium comprising a lubricating layer mixed with a fluorine-containing compound represented by the formula: 2. The lubricating layer comprises: 25 to 400% by weight based on the fluorine-containing compound represented by
Of 2. The magnetic recording medium according to claim 1, comprising a fluorine-containing compound represented by the following formula.