JP2003288715A - Magnetic disk medium and magnetic disk device - Google Patents

Abstract

(57) [Problem] To provide a magnetic disk having a thin protective film and improved sliding resistance. A lubricant is disposed on a magnetic disk medium,
As the lubricant, a lubricant represented by the following formulas 1 and 2 is used.
A magnetic disk wherein a portion of not less than 00 and 4500 is 70% by weight or more, and a portion having a molecular weight of less than 1500 is 20% by weight or less, and a portion having a molecular weight of more than 4500 is 10% by weight or less. Embedded image (Where a and b are each 1 or 2)

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic disk medium in which at least a magnetic film and a protective film are formed on a non-magnetic substrate, and a liquid lubricant is arranged thereon, and a magnetic disk device having such a magnetic disk medium. Regarding

[0002]

2. Description of the Related Art The recording density in a magnetic disk device has been increasing remarkably, and recently, the recording density is 1
More than 00 gigabits have been announced. In order to achieve such a high recording density, it is necessary to make the distance between the magnetic head and the magnetic recording layer of the magnetic disk, that is, the loss distance as close as possible, and at present, 20 nm.
You are in a situation where you must:

Most of this loss interval is occupied by the thickness of the protective film provided on the magnetic recording layer of the magnetic disk and the flying height of the magnetic head. Therefore, the magnetic disk is required to have a protective film as thin as possible and have high sliding resistance against contact with the magnetic head. As expected from the loss interval, it is preferable to achieve a protective film thickness of 5 nm or less in the future.

Further, in recent magnetic disk devices, it is necessary to minimize the surface roughness of the magnetic disk in order to make the distance between the magnetic head and the magnetic disk as close as possible. Therefore, conventionally, a contact start / stop method, that is, a method in which the magnetic disk and the magnetic head are in contact with each other when the rotation of the magnetic disk is stopped and the magnetic head levitates due to the air flow when the magnetic disk starts to rotate, has been used. , Recently, when the rotation of the magnetic disk is stopped, the magnetic head retracts (unloads) away from the magnetic disk, and when the magnetic disk starts to rotate, the magnetic head is loaded on the magnetic disk. The method is being adopted. In this case, the requirement for the sliding resistance is slightly relaxed, but it is necessary to withstand the impact at the time of load-on and the contact due to the abnormal posture of the magnetic head that occurs suddenly even during the normal operation.

As the protective film, US Pat. No. Re32464 is used.
Carbon-based materials such as those disclosed in Japanese Laid-Open Patent Publication No. 59-154 have been conventionally used.
Addition of hydrogen as described in Japanese Patent No.
As described in Japanese Patent No. 106629, many proposals have been made to increase the hardness of a carbon-based protective film to reduce its thickness by adding nitrogen gas during film formation by a sputtering method.

Particularly, a diamond-like carbon film having a high hardness among the hydrogenated carbon protective films has been attracting attention for a long time, and the discharge is carried out by using the carbon-hydrogen gas as described in JP-A-59-154641. A chemical vapor deposition method (hereinafter referred to as a CVD method) in which a generated gas is decomposed and deposited on a substrate, or a thermoelectron generated by using a heated filament is irradiated to a hydrocarbon gas for ionization, Various manufacturing methods such as an ion beam deposition method (hereinafter referred to as an IBD method) in which an ion beam is accelerated by a bias voltage applied to the substrate and collided with the substrate to deposit the ion beam have been proposed.

The method of forming the protective film by the CVD method or the IBD method is more expensive than the conventionally used sputtering method in terms of initial investment of equipment and running cost for magnetic disk production equipment. is there. It would be preferable in terms of cost if a thin protective film could be achieved by combining a protective film by a conventional sputtering method in which hydrogen or nitrogen is added with an appropriate lubricant.

On the other hand, as described in Japanese Patent Application Laid-Open No. 61-126827, the sliding resistance cannot be improved only by increasing the hardness of the carbon-based protective film, and it is used in combination with a fluorine-based lubricant having a perfluoropolyether structure. It has been clarified that this must be done, and proper combination with a lubricant is also an important factor in designing a magnetic disk.

As a lubricant, AUSIMO of Italy
A derivative of NT company's FOMBLIN Z (trade name) is used, and FOMBLIN Z DEAL, Z DIA
C, Z DISOC, Z DOL, Z DOL TX,
Z TETRAOL AM2001, AM3001 are mentioned. The molecular weights of these commercially available lubricants are widely distributed and vary with the batch produced. Therefore, as described in JP-A-2000-315314 and US Pat. No. 6,099,937, it has been proposed to extract and use only a component having an appropriate molecular weight distribution over a wide range.

In order to improve the performance of the lubricant,
As described in U.S. Pat. No. 5,908,817, an additive having a phosphazene ring is mixed, or as described in JP-A-6-220077, a perfluoropolyether having a phosphazene ring at the terminal is added. Lubricants have also been proposed. Furthermore, JP-A-6-22
Japanese Patent No. 0077 describes that the material of the base film of the magnetic recording layer also affects the sliding resistance of the magnetic disk.

[0011]

In the above-mentioned prior art, the sliding resistance of a magnetic disk having a thin protective film, for example, about 5 nm or less was not sufficiently considered.

A first object of the present invention is to provide a magnetic disk having a thin protective film and improved sliding resistance. A second object of the present invention is to provide a magnetic disk device having high reliability and excellent durability.

[0013]

In order to achieve the first object, the magnetic disk medium of the present invention has at least a magnetic recording layer and a protective film formed on a non-magnetic substrate and a lubricant on the surface. The lubricant represented by the formula 1 and the formula 2 below is contained as the lubricant, and the lubricant represented by the formula 1 is added in an amount of 70% by weight or more in a portion having a molecular weight of 1500 or more and 4500 or less. Further, a portion having a molecular weight of less than 1500 is 20% by weight or less, and a portion having a molecular weight of more than 4500 is 10% by weight or less.

[0014]

[Chemical 3] (However, a and b are 1 or 2 respectively)

[0015]

[Chemical 4] The portion of the lubricant represented by Formula 1 having a molecular weight of less than 1500 and the portion having a molecular weight of more than 4500 may each be 0% by weight. That is, the molecular weight is 1500 or more and 4500
The following portion may be 100% by weight. But,
Most of those industrially used have a sharp molecular weight distribution, and most of them have a wide molecular weight in at least one of the parts having a molecular weight of less than 1500 or more than 4500.

When there is a portion having a molecular weight of less than 1500, it is preferable that the portion having a molecular weight of less than 1500 and 500 or more is the majority, for example, 99 to 100% by weight thereof. Also, when there is a portion exceeding 4500,
It is preferable that the portion exceeding 4500 and 13000 or less is the majority, for example, 99 to 100% by weight of the portion.

The composition of the lubricant is preferably in the range of 10 to 50% by weight of the lubricant represented by the formula 2, as will be described in Examples below.

The protective film is preferably a thin film. For example, a film having a thickness of 2.5 mm to 5 mm is preferable. The material is preferably a carbon-based material, and may be simply carbon, but hydrogenated carbon and nitrogen-added carbon are particularly preferable. Hydrogen-added carbon and nitrogen-added carbon are produced by allowing hydrogen gas or nitrogen gas to be present when the protective film is formed, but hydrogen or nitrogen may be present in the protective film itself in the form of gas. Also, all or part of them may be included in some state other than gas.

In order to achieve the second object,
A magnetic disk device of the present invention includes any one of the above magnetic disk mediums, a magnetic head provided corresponding to each surface of the magnetic disk medium and having a recording head and a reproducing head, a magnetic disk medium and a magnetic head. A drive unit for changing the relative position, a magnetic head drive unit for positioning the magnetic head at a desired position, and a recording / reproduction signal processing for inputting a signal to the magnetic head and reproducing an output signal from the magnetic head. It is configured to consist of a system.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a glass substrate which is commercially available for a magnetic disk is preferably used as the non-magnetic magnetic disk substrate. Since the surface roughness of the magnetic disk medium surface reflects the surface roughness of the substrate surface, the roughness of the substrate surface is Ra 0.35 to 0.8 nm, Rp 4.0 to 7.
One having a thickness of 0 nm was prepared. Here, Ra and Rp are
The arithmetic mean roughness of JIS B0601-1994, respectively
It is the distance between the summit line and the average line. A Co alloy film is generally used as the magnetic film. A base film made of a Cr alloy and a seed layer made of a Co alloy, a Ni alloy or the like are formed under the magnetic film.

A protective film containing carbon as a main component is formed on the magnetic film. As the protective film, a nitrogen-added carbon protective film formed by a sputtering method was used.

As the lubricant, a perfluoropolyether derivative is used, and an appropriate amount is dissolved in a dilutable solvent, and the magnetic disk is dipped in and taken out to form a lubricating film.

Hereinafter, the present invention will be described in more detail with reference to examples.

In both the example and the comparative example, a glass substrate having a diameter of 84 mm was purchased and used. Ra0.7 as substrate type
nm, Rp 5.6 nm was used. Substrate roughness AF
M (scanning probe microscope; Nanoscope III)
Scan size 10 × 1 in tapping mode by (trademark) (Digital Instruments)
0 μm, scan rate 1 Hz, sample number 512, Z
-Limit 440V, filtered Flatte
n, Lowpass, made of cantilever single crystal silicon,
The measurement was performed under the measurement condition that the tip curvature radius was 5 to 20 nm. The measurement was performed several times, and the average value was used as the measurement result. The dispersion of the measured values was about 0.1 nm in arithmetic mean roughness Ra and about 1.5 nm in maximum projection height Rp.

After cleaning the substrate, a film was formed by a sputtering apparatus MDP-250 (trademark) (manufactured by Intevac). First, heat the substrate to 290 ° C,
After that, a NiTa alloy was deposited to a thickness of 30 nm. This layer is a crystal control layer of a base film called a seed layer. Furthermore, a CrTiB alloy having a thickness of 10 nm as a base film, a CoCrPt alloy having a thickness of 4 nm, and Ru having a thickness of 0.5 n are further formed thereon.
m, a CoCrPtB alloy having a thickness of 17 nm was formed.

The protective film is a nitrogen-added carbon film formed by a sputtering method, and a film forming apparatus manufactured by Intevac Co. was used. The film forming conditions for the sputtering method are a film forming rate of 0.4.
To 0.8 nm / s, and nitrogen was added as a sputtering gas at a concentration of 18% with respect to argon. The standard thickness of the protective film was 4.0 nm. The X-ray reflection method is used to measure the protective film thickness, and C is placed on the protective film to improve the accuracy of the film thickness measurement.
A 5 nm film of r was formed and quantified. The film thickness was quantified by the X-ray reflection method using SLX2000 (trademark) manufactured by Rigaku Denki Kogyo Co., Ltd. using X-rays of Cu K _α1 . Regarding the measurement principle, Journal of Applied Physics 6
6 (4), 15, August 1989 p1861 (J. App.
l. Phy. 66 (4), 15 (1989) p186
It is described in 1).

Table 1 shows a list of the lubricants used here. The average molecular weight in the table is obtained from NMR measurement.

[0028]

[Table 1] A commercially available lubricant having the structure of formula (1) was extracted by supercritical carbonic acid to prepare fractions for each molecular weight range. The lubricant of formula (1) is AUSIM Italy
It is sold as FOMBLIN Z DOL TX by ONT. Here, the lubricant prepared for each molecular weight range is referred to as lubricant 1, lubricant 2, and lubricant 3. Figure 1
The results of measuring the molecular weight distribution of lubricants 1, 2, and 3 are shown in FIG. These lubricants were one lubricant at the time of purchase, but three types of liquid lubricants having different average molecular weights and molecular weight distributions were obtained.

Further, FOMBLI represented by the equation (1)
Depending on the lot, some NZ DOL TX were difficult to dissolve in HFE-7100, HFE-7200 (manufactured by Sumitomo 3M Limited) and Vertrel XF (manufactured by Mitsui DuPont Fluorochemicals Ltd.) which were dilution solvents. When compared at a lubricant concentration of 15%, there was a clear cloudiness at the visual level. When the molecular weight was divided into a certain range, it was found that when a large amount of those having a molecular weight of less than 1500 was contained, it was difficult to dissolve in such a solvent. Therefore, by excluding the molecular weight range in which it is difficult to dissolve in a solvent, it became possible to uniformly dissolve it in the solvent used to apply the lubricant to the magnetic disk.

The lubricant represented by the formula (2) is represented by the formula (3)
The compound (average molecular weight 2000) represented by the formula (1) was synthesized using the raw material of Mw / Mn = 1.1 from the measurement of the molecular weight distribution.

[0031]

[Chemical 5] From the NMR (nuclear magnetic resonance) measurement, the terminal synthetic substitution ratio 53
%, In thermal analysis (TGA), the synthetic substitution rate was 91%, which was defined from the residual rate at the raw material disappearance temperature when the temperature was raised at 5 ° C./min. For thermal analysis, DuPont T
GA2000 type was used.

From these analysis results, in the lubricant represented by the formula 2, a component having a phosphazene ring in both R1 and R2 is 20% in molar composition ratio, and one of R1 and R2 is a phosphazene ring and either one is -OH. 66 with
%, It can be inferred that the original raw material is a mixture containing 14%. X in the formula (2) is considered to be in the range of X = 1 to 5 structurally, but from the ³¹ P-NMR spectrum, the integral intensity ratio of the main spectrum is about 1: 2, so X
It is estimated to be theoretically close to = 5. The lubricant of the formula (2) prepared here is referred to as a lubricant 4.

Two kinds of lubricants having different average molecular weights of the compound represented by the formula (3) are referred to as a lubricant 5 and a lubricant 6.

The average molecular weight was determined by ¹⁹ F-NMR (nuclear magnetic resonance) analysis to be --CF just inside both ends of PFPE.
₂ CH ₂ - and -OCF ₂ - was determined from the integrated intensity ratio of peaks assigned to (in the chemical formula n, q, corresponds to s) - (wherein m, p, r considerably) and _-OC 2 _{F 4} . The terminal synthetic substitution rate of the lubricant 3 is -CF due to the raw materials and the synthetic products.
_It was calculated from the integrated intensity ratio of ₂ CH ₂ -signal.

For the measurement of the molecular weight distribution, GPC columns KF604 and KF602.5 manufactured by Showa Denko KK were used by substituting the solvent Vertrel XF (manufactured by Mitsui DuPont Fluorochemicals Co., Ltd.) with a Hitachi HPLC pump. (L6010), Showa Denko differential refractive index detector (RI-
74). The measurement condition is a sample concentration of about 15
%, Injection volume 5 μl, flow rate 0.5 cm ³ /
min, pressure is about 95 kgf / cm ² . To calibrate the molecular weight value, the chemical formula (1) obtained by extraction with supercritical carbonic acid was used, and each average molecular weight value obtained by NMR measurement and the elution time at which the peak of the chromatograph obtained from each sample was obtained. Then, it was calibrated using the cubic formula. Since the calibration standard could not be obtained when the molecular weight was 1,000 or less,
It contains a lot of error.

A lubricant solution was prepared by adjusting the concentration of each of the lubricants shown in Table 1 using HFE-7100 manufactured by Sumitomo 3M Co., Ltd. as a solvent, and a magnetic disk medium was dipped into the lubricant solution to form a lubricant film. . Then, the magnetic disk medium was heat-treated. The temperature is 80 ℃
And the time is 30 minutes. The lubricating film thickness is measured by FTIR (Fourier transform type infrared spectrophotometer), and FOMBL
The film thickness of IN Z DOL was set to 1.8 nm.

The preparation of the mixed lubricating film of the lubricant 2 and the lubricant 4 was carried out by using the lubricant 4 in an amount of 10, 20 with respect to the weight ratio of the total lubricant.
A lubricating film was formed by mixing 30% with a solution in advance, dipping the magnetic disk in the solution and pulling it up in the same manner as described above. Then, heat treatment was performed at 80 ° C. for 30 minutes. The lubricating film thickness was similarly set to 1.8 nm. Lubricants 5, 6
The lubricating film was prepared in the same manner as described above, and the film thickness was set to 1.8 nm.

The reliability and wear resistance of these samples were evaluated by the following methods. In order to evaluate the wear resistance in extremely low levitation, the motor is rotated in the reverse direction to keep the head in contact with the magnetic disk medium at all times, seek between the radius of 29 to 31 mm of the magnetic recording medium, and crash. The time was measured. The environmental temperature is room temperature (about 23 ° C.), and the rotation speed is 10,000 min ⁻¹ .

Next, the effectiveness of the present patent will be explained by the test results of each sample. First, lubricants 1, 2,
The wear resistance of the magnetic disk coated with No. 3 and lubricants 5 and 6 was evaluated. The result is shown in FIG. As is clear from the figure, the lubricants 1, 2, 3 represented by the formula (1) include
It can be seen that there is an appropriate molecular weight range that improves wear resistance. Further, in the lubricants 5 and 6 represented by the formula (3), the wear resistance was not improved even if the molecular weight range was changed.

Here, among the lubricants represented by the formula (1),
When using lubricant 1 having a low molecular weight and increasing the film thickness,
Droplet-like granular masses were observed by an optical microscope on the disc surface. Lubricant 1 was observed at 2.5 nm or more, but lubricants 2 and 3 were not observed up to 3 nm. When such a lump is generated on the disk, the flying property of the head is deteriorated and the reliability of the entire magnetic disk device is deteriorated.

For observation with an optical microscope, a mercury lamp was used as a light source, and the observation was carried out in a dark field with an objective of 20 times and an intermediate magnification of 2 times. The image was captured by a phosphorescent CCD camera for 1 second.

Spin-off tests of lubricants 1, 2, 3, 5, 6 were also conducted. Test environment is 12000m at 60 ℃
The magnetic disk was rotated at in ⁻¹ and the residual film thickness of the lubricant after 400 hours was compared with the initial film thickness and expressed as a residual rate. The results are shown in Table 2. As a result, it was found that the lubricant represented by the formula (1) was superior in spin-off characteristics to the lubricant represented by the formula (3).

Next, an abrasion resistance test was conducted on a sample prepared by mixing the lubricant 2 with the lubricant 4 represented by the formula (2). The lubricant 4 was prepared by changing the mixing ratio with respect to the total weight of the lubricant in the solution state.

FIG. 3 shows the wear resistance evaluation results when the mixing ratio of the lubricant 4 was changed. From the figure, it was found that the time to the crash was extended by about twice or more as compared with the case where the lubricant 2 was used alone together with the mixture of the lubricant 4. It was also clarified that there is an optimum mixing ratio of the lubricant 4 to the lubricant 2 that improves wear resistance. The solvent used when applying the lubricant is HEE-
In the case of 7100, the mixing ratio of the lubricant 4 is preferably in the range of 10 to 50% by weight.

Further, the mixing ratio of the lubricant 2 and the lubricant 4 is 2
A wear resistance test was conducted by changing the film thickness of the protective film at 5% and the lubricating film thickness of 1.8 nm. The result is shown in FIG.
When a conventional lubricant was used, a crash occurred in less than 1 hour with a protective film thickness of 4 nm, but it became possible to keep the time up to 10 times that with a protective film thickness of 3 nm.

From these results, it was found that the conventional magnetic recording medium, which could not achieve high reliability because it crashed immediately with an ultrathin film of several nm, was equivalent to a conventional magnetic recording medium with a protective film thickness of 5 nm or more. It has become possible to provide the above reliability.

From the above examples, the lubricant used is
A lubricant 2 having a structure represented by the formula (1) having a molecular weight of less than 1500 is 20% by weight or less and a portion having a molecular weight of more than 4500 is 10% by weight or less, and a structure represented by the formula (2). Despite the fact that the magnetic disk medium containing the following components and the protective film are extremely thin films, they are considered to have wear resistance equal to or higher than that of the conventional magnetic disk medium.

Further, in the magnetic disk device of the present invention, the magnetic head having the recording head and the reproducing head, which are provided corresponding to the respective surfaces of the magnetic disk medium, and the relative positions of the magnetic disk medium and the magnetic head are arranged. A drive unit for changing, a magnetic head drive unit for positioning the magnetic head at a desired position, and a recording / reproducing signal processing system for performing signal input to the magnetic head and reproduction of an output signal from the magnetic head, When any one of the above magnetic disk media was used as the above magnetic disk medium, all had excellent durability and high reliability.

[0049]

According to the present invention, it is possible to provide a magnetic disk medium having high reliability and excellent wear resistance even if the protective film is an extremely thin film. Further, it was possible to provide a magnetic disk device having high reliability and excellent durability.

[Brief description of drawings]

FIG. 1 is a diagram showing a molecular weight distribution of a lubricant.

FIG. 2 is a diagram showing wear resistance of a lubricant.

FIG. 3 is a diagram showing a relationship between a mixing ratio of a lubricant and wear resistance.

FIG. 4 is a diagram showing a relationship between a film thickness of a protective film and wear resistance.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Mitsuhiro Masada             2880 Kozu, Odawara City, Kanagawa Stock Association             Company Hitachi Ltd. Storage Division (72) Inventor Koji Sonoda             2880 Kozu, Odawara City, Kanagawa Stock Association             Company Hitachi Ltd. Storage Division (72) Inventor Takayuki Nakagawa             7-1-1, Omika-cho, Hitachi-shi, Ibaraki Prefecture             Inside the Hitachi Research Laboratory, Hitachi Ltd. (72) Inventor Hiroshi Ishikawa             2880 Kozu, Odawara City, Kanagawa Stock Association             Company Hitachi Ltd. Storage Division (72) Inventor Minori Ozaki             2880 Kozu, Odawara City, Kanagawa Stock Association             Company Hitachi Ltd. Storage Division F-term (reference) 4H104 CD04A PA16                 5D006 AA01 AA05 AA06 DA03 FA02                       FA06

Claims (3)

[Claims] 1. A magnetic disk medium having at least a magnetic recording layer and a protective film formed on a non-magnetic substrate and a lubricant disposed on the surface thereof, wherein the lubricant is represented by the following formula 1 and formula 2.
The lubricant represented by the formula 1 contains a lubricant having a molecular weight of 1,500 or more and 4,500 or less.
20% by weight or less for the portion having a molecular weight of 1500 or more and less than 1500 and 1 for the portion having a molecular weight of more than 4500.
A magnetic disk medium characterized by being 0% by weight or less. [Chemical 1] (However, a and b are 1 or 2 respectively) 2. The protective film has a thickness of 2.5 nm to 5 n.
The magnetic disk medium according to claim 1, wherein the magnetic disk medium is in the range of m. 3. A magnetic disk medium according to claim 1, a magnetic head provided corresponding to each surface of the magnetic disk medium and having a recording head and a reproducing head, the magnetic disk medium and the magnetic head. Drive unit for changing the relative position of the magnetic head, a magnetic head drive unit for positioning the magnetic head at a desired position, and recording for performing signal input to the magnetic head and reproduction of an output signal from the magnetic head. A magnetic disk device comprising a reproduction signal processing system.