JP2638228B2 - Manufacturing method of magnetic recording medium - Google Patents

Description

The present invention relates to a magnetic recording medium mounted on a fixed magnetic disk device used as an external memory of a computer or the like,
In particular, the present invention relates to a method for manufacturing a magnetic recording medium having excellent lubrication performance.

[Conventional technology]

In recent years, as information processing has increased, the capacity of memories such as computers has increased, and the storage elements of magnetic disk drives have been replaced by continuous magnetic magnetic layers made of ferromagnetic metals, which enable higher-density recording. A so-called thin-film magnetic disk using a thin film as a recording layer has become mainstream.

The fixed magnetic disk device generally adopts the CSS method. The magnetic disk is incorporated in the apparatus in combination with the magnetic head, and the magnetic head comes into contact with the surface of the magnetic disk that is stopped while the apparatus is stopped, and stops. When the apparatus is driven (when information is recorded / reproduced), The device travels while slightly floating on the surface of the magnetic disk rotating at high speed, and slides in contact with the surface of the magnetic disk when the apparatus starts and stops driving. Therefore, the magnetic disk has excellent magnetic characteristics that can cope with high-density recording, and has a surface that can be slidably contacted with the magnetic head, and has a suitable level so that the magnetic head does not stick when stopped. It is required that the magnetic head has excellent lubrication characteristics on a rough surface and that there are no minute protrusions that disturb the low flying running of the magnetic head for enabling high-density recording.

For this purpose, thin-film magnetic disks are usually placed on a non-magnetic substrate in which a Ni-P non-magnetic base layer is formed on an Al alloy substrate by electroless plating, or on a non-magnetic substrate made of glass, if necessary. A non-magnetic metal underlayer to improve magnetic properties, for example, a Cr underlayer, and a continuous magnetic layer made of a ferromagnetic metal, for example, a Co alloy by sputtering or vapor deposition, also a thin hard protective layer Are sequentially deposited and laminated. The hard protective layer is provided to protect the magnetic layer, and includes carbon, oxides such as silicon dioxide,
Alternatively, it is made of a stable and hard material such as another ceramic material. The surface of the hard protective layer has good lubricating properties and stable low-flying running of the magnetic head (flying amount of 0.1 μm to 0.3 μm).
m), the center line average roughness Ra is 20Å to 10
The surface is finely roughened to 0 °, and the fine projections on the surface are removed. Thus, a lubricating layer coated with a liquid lubricant is formed on the surface of the protective layer to further improve the lubricating characteristics.

As the liquid lubricant, a fluorocarbon liquid lubricant such as Fomblin (trade name; manufactured by Montezison), Krytox (trade name; manufactured by DuPont), Demnum (trade name; manufactured by Daikin Industries, Ltd.) is effective. It is known that As a method of applying a liquid lubricant, a spin coating method, a spray method, a buff method, an immersion method, and the like are known, and an immersion method with high productivity is frequently used.

[Problems to be solved by the invention]

The thickness of the lubrication layer formed on the surface of the magnetic disk is 10 mm.
It is required to be a thin layer of about 20 mm. If the thickness is less than about 10 mm, it is difficult to form a uniform and stable layer, and good lubrication properties cannot be obtained. When the thickness is about 20 mm or more, the magnetic head is likely to be attracted. It is very difficult to apply a liquid lubricant in such a thin and uniform manner.

Further, it is necessary that the liquid lubricant once formed with a lubricating layer is firmly adhered to the disk surface and stably exists without causing migration or detachment during use. However, since the surface of the protective layer under the lubricating layer is an extremely fine and rough surface, the mechanical adhesion to the liquid lubricant is weak, and the material of the protective layer is inert. However, there is a problem that a strong bonding force is weak, and it is difficult to obtain strong adhesion.

Further, the liquid lubricant, which is a polymer material, has a molecular weight distribution, and low molecular weight components are easily vaporized. For this reason, there is also a problem that the low molecular weight component of the liquid lubricant applied to the surface of the magnetic disk volatilizes during use, and the lubricating properties of the lubricating layer change.

In order to solve these problems, many proposals have been made on a protective layer material, a lubricant material, a method for forming a lubricating layer, and the like, but the situation has not yet been sufficiently satisfactory.

When a liquid lubricant is applied to the surface of the protective layer, especially the protective layer made of a carbon sputtered film, it is desirable that the surface is clean and the amount of adsorbed water is small. However, in practice, the film thickness of the adsorbed layer composed of adsorbed water after carbon sputtering increases with time as shown in FIG. 2 showing the measurement results by an ellipsometer, and this adsorbed layer has an effect on the lubricating layer. Stable lubrication characteristics cannot be obtained.

The amount of this adsorbed water can be measured by other means,
FIG. 3 shows the measurement results. FIG. 3 shows the work function of the surface of the carbon protective layer after the magnetic recording medium was left under the various conditions for one hour, measured with a low energy electron spectrometer. In the figure, 1 is a high humidity condition of 33 ° C. and 80% RH, 2 is a normal temperature and normal humidity condition of 23 ° C. and 50% RH, 3 is a heating condition of 150 ° C., and 4 is a heating condition of 200 ° C. 1 at room temperature and normal humidity of 50% RH
It is the result measured after leaving for a while. This figure shows that the water is adsorbed on the surface of the carbon protective layer, so that the carbon surface is positively charged, indicating that the amount of adsorption can be measured.

In view of the above, the present invention removes the adsorbed water adsorbed on the carbon protective layer so that a stable lubricating property can be obtained without being affected by the state of the adsorbed water adsorbed during the standing period. It is an object of the present invention to provide a method for manufacturing a magnetic recording medium.

According to the present invention, there is provided a method of manufacturing a magnetic recording medium, comprising: forming a carbon protective layer on a magnetic layer by sputtering, and applying a liquid lubricant on the carbon protective layer to form a lubricating layer. Wherein the method further comprises a step of heating to 100 ° C. or more in the atmosphere after forming the carbon protective layer and before applying the liquid lubricant.

It is preferable that the method further comprises a step of heating the liquid lubricant to 100 ° C. or more after the liquid lubricant is applied.

[Action]

In the present invention, since a step of heating to 100 ° C. or more in the atmosphere before applying the liquid lubricant is provided, the step removes the adsorbed water adsorbed on the surface of the carbon protective layer during the standing period. In addition to reducing the effect of adsorbed water,
The adhesion of the carbon protective layer to the lubricating layer is improved.

In addition, by further heating to 100 ° C or higher after applying the liquid lubricant, even if the liquid lubricant contains a low molecular weight component, it is volatilized and removed, and a stable lubrication over time is obtained. It can be a layer. Depending on the composition of the liquid lubricant, heating at 200 ° C. or lower for 1 hour or more can remove unstable low-molecular-weight components to such an extent that there is no practical problem.

〔Example〕

Example 1 Disc-shaped Al-Mg having an outer diameter of 95 mm, an inner diameter of 25 mm, and a thickness of 2.7 mm
After forming a Ni-P alloy layer on the surface of the alloy substrate by electroless plating and polishing the surface to make it smooth, the surface is further textured with a polishing tape in the circumferential direction. A magnetic disk substrate of about 35 mm in Ra was used. A 1500 mm thick Cr underlayer, a 450 mm thick Co-Ni-Cr alloy magnetic layer, and a 370 mm thick carbon protective layer were sequentially formed on this substrate by sputtering.

FIG. 4 shows the change in the carbon film thickness before and after the heat treatment measured by an ellipsometer, which is a film thickness measuring device by measuring the polarization angle of reflected light with respect to incident light. According to this figure, a change in the carbon film thickness indicates the presence of some surface contaminant layer, which indicates that it is removed by the heat treatment. However, even if it is removed by the heat treatment, it is easy to guess that a contaminated layer will be formed by leaving it after that, so it is preferable to apply the liquid lubricant immediately after the heat treatment. In addition, the fifth
In the figure, a water drop is dropped on the substrate surface formed up to the carbon protective layer, and the contact angle is measured. This contact angle can be used as a measure of the surface adhesion performance, and it can be said that the larger the contact angle, the poorer the adhesion. As is clear from this figure, the contact angle increases with the passage of time, and the contact angle decreases by performing the heat treatment. In other words, it can be seen that the presence of the contaminant layer on the surface of the carbon protective layer affects the adhesion of the lubricant. By performing the heat treatment after the formation of the protective layer in this manner, the substrate surface is cleaned, the liquid lubricant is stably fixed, and the friction characteristics can be improved. The lower limit of the heat treatment is 100 ° C. for evaporating the water adsorbed on the carbon protective layer, and the upper limit is 270 ° C. for preventing the magnetization of the Ni—P base layer. More preferably, the temperature is 120 ° C. to 220 ° C. on condition that the temperature difference from room temperature is as small as possible and the temperature gradient is small. In this embodiment, 14
Heat treatment was performed at 0 ° C. for 2 hours.

Next, a fluorocarbon-based liquid lubricant (Fomblin AM2001: Montezison) Was immersed in a solution diluted to 0.2% with Freon 113 (CFC113) and pulled up at a rate of 60 mm / min to apply a liquid lubricant. Subsequently, post-heating treatment was performed at 140 ° C. for 2 hours in a clean oven. Subsequently, tape burnishing was performed. CSS (contact start / stop) was performed on these magnetic disks to measure the friction coefficient. The measurement results are shown in the diagram of FIG. As is apparent from FIG. 1, the heat-treated embodiment has better CSS characteristics than those of the comparative examples in which it is left for several hours immediately after the formation of the protective layer and is subjected to tape burnishing. The burnishing process before forming the lubricating layer is intended to softly cut the outermost surface of the carbon protective layer.
It is preferable that the number of rotations is 3000 to # 6000, and the number of rotations is 100 rpm to 2,000 rpm, and the number of rotations is 3 or less.

Reference Example The same as Example 1 up to the formation of the carbon protective layer.
After forming the carbon protective layer, the substrate is immersed in a solution prepared by diluting a fluorocarbon liquid lubricant (Fomblin AM2001: manufactured by Montezison) to 0.2% with Freon 113 (CFC113),
The lifting liquid lubricant was applied at a speed of 60 mm / min. Subsequently, post-heating treatment was performed at 140 ° C. for 2 hours in a clean oven. FIG. 6 is a graph showing the change with time of the thickness of the lubricating layer on the surface of the magnetic recording medium and the change in the thickness of the lubricating layer after the coating. Also,
FIG. 7 is a diagram showing the measurement results of the sliding contact test when the post-heating is performed and when the lubrication performance is not performed. From these results, it is understood that a good lubricating layer is formed by heating after applying the liquid lubricant. The heating conditions after the formation of the lubricating layer are considered to be in the range of 100 ° C to 270 ° C, which is the same as the heating conditions before the formation of the lubricating layer. So 1
A range from 00C to 160C is preferred.

Example 2 Example 1 is the same as Example 1 up to the formation of the carbon protective layer.
After forming the carbon protective layer, heating is performed at 140 ° C. for 2 hours. Within one hour after heating, the same liquid lubricant as in Example 1 and Reference Example was applied by a dip coater. Subsequently, after heating at 140 ° C. for 2 hours in a clean oven, tape burnishing is performed. The purpose of the tape burnisher after applying lubricant is to wipe the applied lubricant to make it a uniform thickness, and use a tape with a fine count of # 10000 or more, 50 rpm
Processing at a low speed of ~ 300 rpm is desirable. In this embodiment, the number of reciprocations is # 20000 and 100 rpm2. The measurement results by CSS for the case where heating and burnishing were performed and for the case where lubrication performance was not performed are shown in the diagram of FIG. It can be seen that after 10,000 CSS operations, the coefficient of friction improved from 0.5 when not performed to 0.3 when performed. Fig. 9 and Fig. 9 show the measurement results of the adsorption force after leaving for 24 hours in an environment of 33 ° C and 80% RH.
Figure 10 shows. Fig. 9 shows the measurement results of a medium that has not been subjected to heat treatment and burnishing, and Fig. 10 shows the measurement results of a medium that has been subjected to heat treatment and burnishing. You can see that it has improved.

Example 3 Example 1 is the same as Example 1 up to the formation of the carbon protective layer.
After forming the carbon protective layer, tape burnishing is performed using a polishing tape made of # 4000 white alumina at a work rotation speed of 500 rpm. Next, in the atmosphere at 200 ° C1
Perform heat treatment for a time. Thereafter, a fluorocarbon-based liquid lubricant (Fomblin AM2001: manufactured by Montezison) was immersed in a solution diluted to 0.8 wt% with Freon 113 (CFC113), and the liquid lubricant was applied at a rate of 60 mm / min. . Subsequently, a heat treatment was performed at a temperature of 120 ° C. for one hour, and a buffing was performed using a wiping cloth under the conditions of a rotation speed of 100 rpm, a pressing pressure of 2.5 kg / cm ² , and eight times.
FIG. 11 shows the measurement results by CSS as the lubricating performance of the magnetic recording medium thus prepared, together with a comparative example in which heating was not performed before forming the lubricating layer. CSS from Fig. 11
The dynamic friction coefficient after 10,000 cycles is 0.6 in the comparative example, and 0.2 in the present example, which is a stable value. Since the heating before forming the lubricant is performed in the atmosphere, a vacuum chamber is unnecessary, so that there is no need for a process such as evacuation and atmospheric pressure leakage, so that the heat treatment can be easily performed and a good lubricating layer can be formed. It is formed.

〔The invention's effect〕

According to the present invention as described above, after the carbon protective layer is formed and before the liquid lubricant is applied, by heating to 100 ° C. or more in the air, the water adsorbed on the surface of the carbon protective layer is removed. As a result, the influence of the adsorbed water is reduced, and the adhesion of the carbon protective layer to the lubricating layer is improved, so that magnetic recording media having excellent lubricating properties can be stably mass-produced.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the number of CSS times of the magnetic disk and the friction coefficient, FIG. 2 is a diagram showing the change over time of the thickness of the adsorption layer, and FIG. 3 is a work function of the surface of the carbon protective layer. Diagram, FIG. 4 is a diagram showing the change over time of the carbon film thickness, FIG. 5 is a diagram showing the change over time of the contact angle, and FIG. 6 is a diagram showing the change over time of the lubricant film thickness. , FIG. 7 is a diagram showing the relationship between the sliding time and the coefficient of friction, FIG. 8 is a diagram showing the relationship between the number of CSSs and the coefficient of friction, FIGS. 9 and 10 are diagrams showing the attraction force, FIG. 11 is a diagram showing the relationship between the number of CSS times and the coefficient of friction.

Continuation of the front page (56) References JP-A-1-277319 (JP, A) JP-A-62-282858 (JP, A) JP-A-1-184624 (JP, A) JP-A 64-70921 (JP) , A) JP-A-61-261820 (JP, A)

Claims (2)

(57) [Claims] In a method for manufacturing a magnetic recording medium, a carbon protective layer is formed on a magnetic layer by sputtering, and a liquid lubricant is applied on the carbon protective layer to form a lubricating layer. A method for manufacturing a magnetic recording medium, comprising a step of heating to 100 ° C. or more in the atmosphere after forming and before applying the liquid lubricant. 2. The method according to claim 1, further comprising:
The method for manufacturing a magnetic recording medium according to claim 1, further comprising a step of heating the magnetic recording medium to a temperature of not less than ° C.