JP2000311332A - Magnetic recording medium and production of magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the decomposition of a lubricant due to the lower floating associated with high-density recording and the wear of a protective layer and to stabilize lubricating characteristics over a long period of time by adding a cyclic triphosphazene- base lubricant into a lubricating layer formed on an underlying layer, a magnetic layer and protective layer on a nonmagnetic substrate. SOLUTION: This magnetic recording medium contains the cyclic triphosphazene-base lubricant expressed by formula (n is an integer from 0 to 6) in the lubricating layer. Further. the lubricating layer contains the perfluoropolyether-base lubricant having one polar terminal group and its weight average molecular weight is preferably 1500 to 5500. The magnetic recording medium is obtained by a stage of laminating the ground surface layer, the magnetic layer and the protective layer in this order on the nonmagnetic substrate and laminating the lubricating layer on the protective layer. The lubricating layer is formed by using the cyclic triphosphazene-base lubricant of the formula. The triphosphazene-base lubricant and the perfluorpolyether-base lubricant may be applied separately or in combination. The lubricating characteristic and CSS durability to the magnetic head of a low floating type are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetic recording medium mounted on an external recording device of a computer and a method for manufacturing the magnetic recording medium. In particular, the present invention relates to a lubricant applied on the surface of a magnetic recording medium and having improved lubrication properties (CSS durability).

[0002]

2. Description of the Related Art Generally, in a recording apparatus using a solid magnetic recording medium, a magnetic head floats when the magnetic recording medium rotates, and a contact head in which the magnetic head comes into contact with the surface of the magnetic recording medium when the rotary drive motor stops. A start / stop (CSS) method is employed. In a conventional magnetic recording medium, a material in which a small amount of N, Si, or the like is further added to diamond-like carbon (DLC) as a surface protective layer is used. In general, a perfluoropolyether-based lubricant is applied on the surface protective layer in order to improve the lubricating properties of the surface protective layer. Using such a lubricant to cover the surface of the protective layer prevents a harmful gas or organic contaminant from adsorbing to the surface, further improves the lubricating characteristics, and provides a stable magnetic recording medium having excellent CSS durability. It is one way to gain.

[0003] The surface of the DLC carbon is covered with a thin oxide film having a functional group such as a reactive carbonyl group, carboxyl group or hydroxyl group, and contaminants are actively adsorbed and bonded to the thin oxide film. The adsorption of such contaminants can be suppressed by using a perfluoropolyether having a polar end group. However, if the molecular weight of the perfluoropolyether is too low, the lubricating properties decrease, and conversely, the molecular weight decreases. Is too high, the tendency of adsorption between the head and the lubricating layer increases. In addition, when a perfluoropolyether having a relatively large molecular weight is used, a gap is generally formed between molecules when several tens of degrees are applied on the protective layer, and it is difficult to completely cover the surface of the protective layer. It is. Therefore, in order to completely cover the surface of the protective layer using such a perfluoropolyether having a relatively large molecular weight, the thickness of the lubricant must be applied to a thickness of 50 ° or more, and the thickness of the lubricant is reduced to about 50 °. If the thickness is too large, it is difficult to avoid adsorption between the magnetic recording medium and the magnetic head.

In recent years, the flying height of a magnetic head has been reduced along with high-density recording, and the structure of the magnetic head has been changed from a conventional TRC head to a low flying type head such as a tri-mega head or an MR head. Was. with this,
When the head material is catalyzed or generates frictional heat, the decomposition proceeds in the main chain portion (ether portion) of the perfluoropolyether-based lubricant. Further, corrosive components such as these decomposed products and gas adsorbed on the disk surface are transferred to the surface of the magnetic head, disturbing the flying characteristics of the magnetic head, and lowering the reproduction output. Also,
The decomposed perfluoropolyether-based lubricant deteriorates the lubricating properties and causes wear of the protective layer, and in the worst case, causes a head crash.

On the other hand, it has been known that a cyclic triphosphazene-based lubricant is effective in improving lubricating characteristics and suppressing decomposition of a perfluoropolyether-based lubricant.
For example, Japanese Patent Application Laid-Open No. 9-305961 discloses a lubricating property in a magnetic recording medium by using a cyclic triphosphazene-based lubricant represented by the following structural formula (II) in combination with a perfluoropolyether-based lubricant. Is improved.

[0006]

Embedded image

However, the perfluoropolyether-based lubricant and the cyclic triphosphazene-based lubricant are very difficult to mix with each other, and are further applied as a lubricating layer and aggregate when left in a certain environment. There is a problem to be solved. As a result, in the conventional technology,
In some cases, the characteristics of a recording device using a fixed magnetic recording medium may be significantly reduced. In addition, various attempts have been made to use various perfluoropolyether-based lubricants in order to solve the above-mentioned problems, but a technique capable of satisfying all required performances has not yet been established. It is.

Accordingly, an object of the present invention is to prevent the decomposition of the lubricant and the wear of the protective layer due to the low flying height of the magnetic head accompanying the high density recording, and to stabilize the lubrication characteristics for a long time (C
It is an object of the present invention to provide a magnetic recording medium that realizes (SS durability improvement) and a method for manufacturing the magnetic recording medium.

[0008]

Means for Solving the Problems In order to achieve the above object, the present inventors have intensively studied a lubricant used for a lubricating layer. As a result, the present inventors have found that a novel lubricant having a small molecular weight, high stability and excellent heat resistance is obtained. It has been found that the above object can be achieved by using the above-mentioned cyclic phosphazene-based lubricant, and the present invention has been completed. That is, the magnetic recording medium of the present invention has an underlayer, a magnetic layer, a protective layer, and a lubricating layer on a nonmagnetic substrate, and the lubricating layer has at least the following structural formula (I):

[0009]

Embedded image And a cyclic triphosphazene-based lubricant represented by the formula: The lubricating layer described above may further include a perfluoropolyether-based lubricant having at least one polar end group, and the weight average molecular weight of the perfluoropolyether-based lubricant is from 1,500 to 5,50.
It is preferably 0.

According to the method of manufacturing a magnetic recording medium of the present invention, a step of laminating an underlayer on a nonmagnetic substrate, a step of laminating a magnetic layer on the underlayer, and a step of laminating a protective layer on the magnetic layer And a step of laminating a lubricating layer on the protective layer, wherein the lubricating layer has at least the following structural formula (I):

[0011]

Embedded image And formed using a cyclic triphosphazene-based lubricant represented by The above-described lubricating layer may be further formed using a perfluoropolyether-based lubricant.

In the method of manufacturing a magnetic recording medium according to the present invention, the step of laminating a lubricating layer may be performed by separately applying the above-mentioned cyclic triphosphazene-based lubricant and the perfluoropolyether-based lubricant, or A triphosphazene-based lubricant and a perfluoropolyether-based lubricant may be mixed and applied. The coating is preferably performed by a dip coating method or a spin coating method.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A magnetic recording medium according to the present invention
In order to improve the lubrication characteristics of the surface of the magnetic recording medium, a novel cyclic triphosphazene-based lubricant represented by the following structural formula (I) is used for the lubrication layer.

[0014]

Embedded image The cyclic triphosphazene-based lubricant can be used alone or in combination with a perfluoropolyether-based lubricant having at least one polar end group. When a cyclic triphosphazene-based lubricant is used in combination with a perfluoropolyether-based lubricant, each lubricant is separately applied to form a two-layer structure, or each lubricant is first mixed and applied. can do. The lubricants mix well and do not cause the coagulation that has traditionally been a problem. Further, each lubricant may be diluted with an arbitrary solvent as needed.

The cyclic triphosphazene-based lubricant represented by the structural formula (I) is not limited.
Cyclic triphosphazene compound and reaction formula (1) shown below
And by mixing the compound obtained in (2).

That is, according to a conventional method, in the presence of a solvent, 1,2,3,4,
5,6-Fluoroheptanol [F (CF ₂ ) ₆ CH ₂ O
H] and metallic sodium at a low temperature to form sodium alkoxide.

[0017]

Embedded image Further, according to a conventional method, m-trifluoromethyl-phenol and sodium metal are reacted at a low temperature in the presence of a solvent as shown in the reaction formula (2) to obtain sodium phenoxide.

[0018]

Embedded image By reacting the compound obtained by the above reaction formulas (1) and (2) with a cyclic triphosphazene compound,
A cyclic triphosphazene-based lubricant represented by the structural formula (I) is obtained.

Further, the perfluoropolyether-based lubricant which may be used in combination with the above-mentioned cyclic triphosphazene-based lubricant is preferably from 1,500 to 5,500,
More preferably, it has a weight average molecular weight of 2,500 to 4,000. If the molecular weight is too low, the lubricating properties deteriorate, and if the molecular weight is too high, the tendency of the head to adsorb to the lubricating layer increases. By combining a perfluoroether having at least one polar end group, it is possible to more effectively prevent adhesion of contaminants to a magnetic recording medium. One example of such a perfluoropolyether lubricant is Montecatini Co., Ltd.
Fomblin Z-dol 4000 (trade name).

The application of each lubricant is preferably performed by a method known to those skilled in the art, preferably, a dip coating method or a spin coating method. At the time of application, each lubricant may be diluted with an appropriate solvent as needed, and a concentration of 0.05 wt% is appropriate. By completely covering the surface of the protective layer of the magnetic recording medium with the cyclic triphosphazene-based lubricant of the present invention as described above, or the cyclic triphosphazene-based lubricant combined with the perfluoropolyether-based lubricant, contaminants are removed. Improves adsorption suppression and lubrication properties of C
A magnetic recording medium having excellent SS durability can be obtained.

One embodiment of the magnetic recording medium according to the present invention is shown in FIG. 1 and outlined below with reference to FIG. 1, but is not limited thereto.

In one embodiment of the magnetic recording medium according to the present invention, the non-magnetic substrate 11 (for example, Al-Mg) and the non-magnetic metal layer 12 (for example, Ni-P electrolessly plated on an alloy substrate) are used. A non-magnetic substrate 1, a non-magnetic metal underlayer 2 laminated on the substrate 1, and a magnetic layer 3 of a ferromagnetic alloy laminated on the metal underlayer 2 on a thin film (for example,
Co-Cr-Ta, Co-Cr-Pt, etc.) and a protective layer 4 (for example, a carbon layer) laminated on the magnetic layer 3
And And, as described above, the lubrication layer 5 is further provided after being sequentially laminated up to the protection layer 4.

Hereinafter, the method of manufacturing a magnetic recording medium according to the present invention will be described with reference to examples. However, the present invention is not limited to the examples described below, and various modifications can be made without departing from the gist of the present invention. Needless to say, there is.

1. Production of Magnetic Recording Medium (Example 1) First, the preparation of the cyclic triphosphazene-based lubricant represented by the structural formula (I) used for the lubricating layer of the magnetic recording medium according to the present invention will be exemplified.

(A) Sodium alkoxide formation 30 ml of HFE7200 well dehydrated by distillation or the like
1.0 g of 1,2,3,4,5,6-fluoroheptanol [F (CF ₂ ) ₆ CH ₂ OH] and 1.0 g of metallic sodium (trade name, manufactured by 3M Company) 0.1 g of pyridine was added to a solution of 100 ml of HFE7200 and then cooled to 0 ° C. The temperature of this solution is 0 ° C
Stir for 10 hours, keeping below. NM
After confirming the end point of the reaction by R measurement, the reaction solution was filtered to remove solid matter, washed with pure water, and further washed with HFE7.
1,2,3,4,5,6-
7.3 g of fluoroheptanol alkoxide were obtained.

(B) Sodium phenoxide formation A mixture of 30 ml of diethyl ether, which has been sufficiently dehydrated by distillation or the like, and 1.0 g of sodium metal added thereto, is added to 10 g of m.
-Added to a solution of trifluoromethylphenol and 0.1 g of pyridine in 80 ml of diethyl ether and cooled to 0 ° C. The solution was stirred for 5 hours while maintaining the temperature at 0 ° C or lower. After confirming the end point of the reaction by NMR measurement, the reaction solution was filtered to remove solids, washed with pure water, and diethyl ether was removed to remove the target sodium m-trifluoromethyl-.
8.5 g of phenoxide were obtained.

(C) Preparation of cyclic triphosphazene-based lubricant In an autoclave, the 1,2,3,
4,5,6-Fluoroheptanol alkoxide was added to 2.0
g, 6.0 g of sodium m-trifluoromethyl-phenoxide obtained in (b), 3.0 g of hexachlorophosphazene N ₃ P ₃ Cl ₆ , and HFE720
After adding 70 ml of N.0 and replacing the inside of the autoclave with N ₂ , the reaction was carried out at 80 ° C. for 250 hours. NM
After confirming the end point of the reaction by R measurement, it is washed with water and ethanol, and 2.4 g of 1,2,3,4,5,6-fluoroheptanol having a desired cyclic triphosphazene at the terminal of the chain molecule. Obtained. The obtained lubricant is diluted with an appropriate solvent as necessary.

Next, the production of a magnetic recording medium using the cyclic triphosphazene-based lubricant obtained as described above will be described.

A non-magnetic metal layer having a Ni-P plating of 13 μm is formed on an Al—Mg alloy substrate by electroless plating, and the surface thereof is polished to a surface roughness Ra of 10 μm.
After polishing, concentric grooves were textured using diamond slurry so that the surface roughness Ra was 40 °. After the obtained substrate was washed, a nonmagnetic metal underlayer made of Cr having a thickness of 500 、 was formed by DC sputtering, and then a Co-
Magnetic layer made of Cr-Ta, and DL having a thickness of 150 °
A protective layer made of C was produced.

As described above, the protective layer is sequentially laminated (hereinafter, referred to as the protective layer), and then the previously prepared cyclic triphosphazene-based lubricant (the compound represented by the structural formula (I), n is 1 to 6) to form a lubricating layer.
At this time, the cyclic triphosphazene-based lubricant is diluted with n-hexane as a solvent, and the concentration thereof is 0.05 w
It was prepared in advance to be t%. The obtained lubricant solution was applied by a dip coating method to produce a magnetic recording medium having a lubricating layer of 20 °.

Comparative Example 1 Instead of the compound represented by the structural formula (I), the following structural formula (II):

[0032]

Embedded image A corresponding magnetic recording medium was produced by performing the same operation as in Example 1 except that a conventional cyclic triphosphazene-based lubricant represented by the following formula was used on the protective layer.

Example 2 On the protective layer described in Example 1, a cyclic triphosphazene-based lubricant represented by the structural formula (I) wherein n is 1 to 6 was formed. At this time, the cyclic triphosphazene-based lubricant was diluted with n-hexane as a solvent, prepared in advance to a concentration of 0.05 wt%, applied by dip coating, and coated with
Was formed.

Next, Fomblin Z-Montecatini Co., Ltd.
The weight average molecular weight of dol 4000 (trade name) etc. is 4,000
And a perfluoropolyether having a hydroxyl group at a terminal group is diluted with a fluorocarbon such as FC-77 (trade name) manufactured by 3M as a solvent, and the concentration thereof is 0.0
It was adjusted to be 5 wt%. The obtained lubricant solution is applied by spin coating (at 1,800 rpm),
A perfluoropolyether-based lubricating layer having a thickness of 20 ° was formed. Then, a magnetic recording medium having each lubricating layer was produced.

(Comparative Example 2) A conventional cyclic triphosphazene-based lubricant represented by the structural formula (II) was used on the protective layer instead of the compound represented by the structural formula (I). The corresponding magnetic recording medium was manufactured by performing the same operation as in Example 2.

Comparative Example 3 A corresponding magnetic recording medium was produced by performing the same operation as in Example 2 except that the cyclic triphosphazene-based lubricant was not formed on the protective layer. did.

[0037] 2. Evaluation of Magnetic Recording Medium With respect to the lubricating layer on the surface of the magnetic recording medium produced in Examples 1 and 2 and Comparative Examples 1 to 3 described above, decomposition evaluations as shown in Evaluations 1 and 2 were performed. Evaluation 1 One drop of a mixed solution of Al ₂ O ₃ —TiC powder and ultrapure water was dropped on the surface of each of the magnetic recording media prepared in Examples 1 and 2 and Comparative Examples 1 to 3 described above, and then a desiccator. And left for 24 hours under the conditions of 80 ° C./80% relative humidity.
Next, the presence or absence of decomposition of the lubricant on the surface of the magnetic recording medium was confirmed using a Fourier transform infrared spectrophotometer (FT-IR). The results are shown in Table 1 below.

Evaluation 2 For each of the magnetic recording media produced in Examples 1 and 2 and Comparative Examples 1 to 3 described above, a magnetic recording medium having one drop of ultrapure water dropped on the surface thereof and 10 cc of 1% H 2. _Two
Put the Petri dish containing SO ₄ in the desiccator,
After leaving for 24 hours under the condition of ° C / 80% relative humidity, the presence or absence of decomposition of the medium surface lubricant was confirmed by a Fourier transform infrared spectrophotometer (FT-IR). The results are shown in Table 1 below.

[0039]

[Table 1] As is clear from Table 1, in both Evaluation 1 and Evaluation 2, it was found that no lubricant was decomposed on the magnetic recording medium coated with at least the cyclic triphosphazene-based lubricant of the present invention. Was.

Next, the lubricating properties of the magnetic recording media prepared in Examples 1 and 2 and Comparative Examples 1 to 3 were evaluated as shown in Evaluations 3 and 4 below.

Evaluation 3 A head load of 10 was applied on the surface of each of the magnetic recording media manufactured in Examples 1 and 2 and Comparative Examples 1 to 3 described above.
gf magnetic pole head at a radial position of 21.5 mm and a rotation speed of 1
is slid in rpm, was measured dynamic friction coefficient mu _I at this time. Then, after sliding at 100 rpm for 1 hour, the coefficient of dynamic friction μ when sliding at 100 rpm was performed.
_L was measured. The results are shown in Table 2 below.

Evaluation 4 Each of the magnetic recording media produced in Examples 1 and 2 and Comparative Examples 1 to 3 was incorporated into an actual magnetic disk drive using the same head as in Evaluation 3, and the initial friction coefficient μ _I Was measured. Then, at room temperature / humidity (25 ° C / 5
0%) and 60 ° C./80% relative humidity.
After repeating 00 times of CSS, to measure the friction coefficient μ _L. Under the condition of 60 ° C./80% relative humidity, CSS
Was repeated 20,000 times, and the presence or absence of dirt on the head was observed with an optical microscope. The results are shown in Table 2 below.

[0043]

[Table 2] As is clear from Table 2, regarding the evaluations 3 and 4, the magnetic recording media (Examples 1 and 2) in which the protective layer was coated with at least the cyclic triphosphazene-based lubricant of the present invention exhibited an initial friction under any environment. small coefficient μ _I, 2
The increase in the coefficient of friction at 000 CSSs is also small. On the other hand, when only the perfluoropolyether-based lubricant was used (Comparative Example 3), the coefficient of friction was increased, and the protective layer was further worn. From this, it was found that the use of the lubricant according to the present invention can improve the sliding characteristics and CSS durability characteristics of the magnetic recording medium.

In the magnetic recording media prepared in Examples 1 and 2 and having the lubricant according to the present invention applied to the surface, no contamination of the head could be confirmed.

Lastly, the lubrication layer on the surface of the magnetic recording medium produced in Examples 1 and 2 and Comparative Examples 1 to 3 was evaluated for aggregation as shown in Evaluation 5 below.

Evaluation 5 Each of the magnetic recording media prepared in Examples 1 and 2 and Comparative Examples 1 to 3 was left in a thermo-hygrostat at 80 ° C./80% for 5 days. The presence or absence of aggregation was observed with an optical microscope. The results are shown in Table 3 below.

[0047]

[Table 3] As is clear from Table 3, in Example 1 in which the cyclic triphosphazene-based lubricant according to the present invention was used, no aggregation phenomenon was observed. Similarly, in Example 2 in which the cyclic triphosphazene-based lubricant according to the present invention was combined with perfluoropolyether, no aggregation phenomenon was observed, and it can be seen that the respective lubricants were well mixed.

On the other hand, in Comparative Examples 1 and 2 using the conventional cyclic triphosphazene-based lubricant represented by the structural formula (II), an aggregation phenomenon was confirmed.

[0049]

As is apparent from the above description, the use of the cyclic triphosphazene-based lubricant according to the present invention alone or in combination with the perfluoropolyether-based lubricant makes it possible to provide a low-flying type magnetic head. On the other hand, it improves lubrication characteristics and CSS durability. As a result, it is possible to provide a magnetic recording medium that has excellent characteristics stability during long-term use as compared with conventional magnetic recording media.

[Brief description of the drawings]

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Base 2 Metal underlayer 3 Magnetic layer 4 Protective layer 5 Lubrication layer 11 Nonmagnetic substrate 12 Nonmagnetic metal layer (plating layer)

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C10N 40:18 (72) Inventor Shinji Shirai 1-1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd. In-house F term (reference) 4H104 BH14A CD04A EA03A LA20 PA16 5D006 AA01 AA06 DA03 FA02 FA06 5D112 AA07 AA11 AA24 BC02 BC10 CC01 CC05

Claims (9)

[Claims] In a magnetic recording medium having a base layer, a magnetic layer, a protective layer, and a lubricating layer on a nonmagnetic substrate, the lubricating layer has at least the following structural formula (I): A magnetic recording medium comprising a cyclic triphosphazene-based lubricant represented by the formula: 2. The magnetic recording medium according to claim 1, wherein the lubricating layer further contains a perfluoropolyether-based lubricant having at least one polar end group. 3. The magnetic recording medium according to claim 2, wherein the perfluoropolyether-based lubricant has a weight average molecular weight of 1,500 to 5,500. 4. A step of laminating an underlayer on a nonmagnetic substrate, a step of laminating a magnetic layer on the underlayer, a step of laminating a protective layer on the magnetic layer, and a step of lubricating on the protective layer. Laminating layers, the method of manufacturing a magnetic recording medium comprising:
The lubricating layer has at least the following structural formula (I): A method for producing a magnetic recording medium, wherein the method is formed by using a cyclic triphosphazene-based lubricant represented by the formula: 5. The method according to claim 4, wherein the lubricating layer is further formed using a perfluoropolyether-based lubricant. 6. The method according to claim 1, wherein the step of laminating the lubricating layer includes a step of applying the cyclic triphosphazene-based lubricant and a step of applying the perfluoropolyether-based lubricant. 6. The method for manufacturing a magnetic recording medium according to item 5. 7. The method according to claim 5, wherein the step of laminating the lubricating layer comprises a step of mixing and applying the cyclic triphosphazene-based lubricant and the perfluoropolyether-based lubricant. The manufacturing method of the magnetic recording medium according to the above. 8. The method according to claim 6, wherein the applying step is a dip coating method or a spin coating method.
Or a method for manufacturing a magnetic recording medium according to item 7. 9. A recording apparatus comprising the magnetic recording medium according to claim 1 mounted thereon.