JP2003272134A - Method for manufacturing magnetic recording medium and magnetic recording device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stabilize floating characteristics for a magnetic head by controlling the thickness of a protective film formed on a stamper surface and surface roughness. <P>SOLUTION: In a mold for injection molding, a magnetic disk substrate is injection-molded in a substrate cavity 22 by using stampers 25, 26 on which surfaces protective films are formed, and setting the surface roughness of the protective films in the range of 0.2 nm to 1.0 nm and very small waviness to 0.5 nm or lower. Thus, the surface of the manufactured magnetic disk substrate exhibits similar surface roughness and very small waviness, and the characteristics of magnetic head floating of 5 nm or lower are obtained. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a magnetic recording medium mounted on various magnetic recording devices such as an external storage device of a computer, and a magnetic recording device using the same.

[0002]

2. Description of the Related Art When a conventional non-magnetic metal substrate (aluminum or the like) is used as a magnetic disk substrate for a magnetic recording medium which requires a high degree of surface precision, a high degree of precision processing is required.

A conventional non-magnetic metal substrate is manufactured, for example, as follows. First, a metal material that has been heated and melted is rolled and heated and annealed, and then a blank material that has been processed into specified dimensions is produced, and then the inner and outer diameters are processed. Furthermore, after lapping is performed to improve the surface accuracy, a Ni—P plating layer is formed to 13 μm for the purpose of improving the surface hardness, and the surface is polished to have a surface roughness Ra = 1. It is polished to a size of not more than 0.0 nm (10Å), and a final lapping process (texturing) using a diamond slurry is performed. After that, in the CSS (contact start stop) zone,
For example, if the bump bite is 19.0 nm (190 Å) 30
A general magnetic disk substrate for a hard disk is obtained by performing laser zone texturing so as to have a density of one bump per μm square and performing precision cleaning.

On the magnetic disk substrate obtained as described above, Cr underlayer 50 nm (500 Å), CoCrTa magnetic layer (Co: Cr: Ta = 82: 14: 4) 30 nm
(300Å), and carbon protective layer 8.0 nm (80
Å) is sequentially formed by DC sputtering method, tape vanishing is performed on the surface after sputtering, and finally, a fluorine-based lubricating layer 2.0 nm (20 Å) is formed by dip coating or spin coating method for hard disk. A magnetic recording medium is obtained. However, the manufacturing method and configuration of the disk substrate and various recording media are not limited to the above.

The conventional methods for manufacturing the magnetic disk substrate and the magnetic recording medium as described above have become more and more complicated with the recent increase in recording density. On the other hand, there is a demand for a magnetic disk substrate and a magnetic recording medium that are cheaper than before while maintaining high performance. As a new magnetic disk substrate satisfying these contradictory requirements, a magnetic disk substrate and a magnetic recording medium using a thermoplastic resin (plastic) have been proposed.

[0006]

However, when a magnetic disk substrate, which is required to have a high degree of shape stability and surface accuracy, is manufactured by injection molding of plastic, it is different from the case of manufacturing it from a metal, glass or ceramic substrate. In comparison, since the mechanical strength is low, finish polishing (lapping, polishing, vanishing, etc.) cannot be performed. Therefore, it is necessary to adjust the surface accuracy (straightness, waviness, roughness, etc.) of a level required for the magnetic disk substrate at the end of injection molding. However, in resin molding, if the surface of the stamper is mirror-finished, the adhesion between the stamper and the substrate is improved, so that there is a problem that the substrate surface may be deformed abnormally at the time of release from the stamper.

Dozens of n on the substrate for the purpose of improving the recording density.
In a recording medium such as a hard disk in which a magnetic head levitates at a height of m, which requires a very high surface accuracy, when a substrate having a large flatness (poor surface accuracy) is used, the magnetic head and recording It is impossible to maintain a predetermined distance from the medium, and in the worst case, the magnetic head does not float, which causes a problem that actual reading and writing cannot be performed.

The present invention has been made in view of the conventional situation as described above, and controls the adhesiveness when the plastic substrate is released from the stamper to minimize abnormal deformation and has excellent head flying characteristics. Another object is to obtain a magnetic disk substrate and a magnetic recording medium.

[0009]

The inventors of the present invention have made earnest studies to achieve the above object, and as a result, when the surface of the magnetic disk is made to be a super-mirror surface (Ra 0.2 nm or less), the flying height of the magnetic head is lowered. It was confirmed that the floating stability deteriorated and abnormal crashes frequently occurred.

Therefore, by setting the surface roughness of the protective film on the surface of the stamper used in the mold to 0.2 nm to 1.0 nm, preferably 0.3 nm to 0.7 nm, abnormal fall of the magnetic head is suppressed. It was found that the minimum flying height of the magnetic head can be stably lowered to 5 nm or less. Further, by roughening the surface of the magnetic disk, the coefficient of friction when the magnetic disk and the magnetic head come into contact with each other is reduced even when the magnetic head crashes abnormally.
We have found that it is possible to suppress head crashes.

The present invention has been made on the basis of the above findings, and the surface roughness of the protective film on the stamper surface used in the mold at the time of injection molding of the substrate is in the range of 0.2 nm to 1.0 nm, preferably 0. It is characterized in that the thickness is 3 nm to 0.7 nm.

Further, according to the present invention, a DC sputtering method or an ion beam sputtering method can be used as a film forming apparatus for a stamper surface protective film.
Titanium (Ti), chromium (Cr), manganese (Mn),
Cobalt (Co), Nickel (Ni), Ruthenium (R
u), rhodium (Rh), palladium (Pd), tantalum (Ta), tungsten (W), rhenium (Re),
Osmium (0s), iridium (Ir), platinum (P
t) and at least one target of gold (Au) are used. Further, it is characterized in that the film is formed under high temperature and high vacuum using these protective film materials.

While forming the protective film on the stamper by using this method, the surface roughness can be controlled by the protective film thickness and the film forming conditions. The surface roughness at that time [R
a] is in the range of 0.2 nm to 1.0 nm, preferably 0.
It may be 3 nm to 0.7 nm. In addition to the above, the following methods can be applied as a method of controlling the surface roughness of the protective film. That is, the surface roughness of the metal surface after sputtering may be controlled by lapping using a tin platen, electron cyclotron etching, or the like.

Furthermore, the present invention is characterized in that the minute waviness (Wa) on the stamper surface is 0.5 nm or less.

Further, the present invention is characterized by including a step of forming a substrate using the above stamper and forming at least a magnetic recording layer on the substrate.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The magnetic disk substrate manufactured in the present invention can have a disk shape having a circular hole in the center. The central circular hole is used for mounting a spindle motor when a magnetic recording medium using the magnetic disk substrate is set in a magnetic recording device. The diameters of the central circular hole and the circular plate depend on the design of the magnetic recording device.

In injection molding used in the present invention, an injection molding apparatus known in the art can be used. It is preferable to use a screw type injection molding apparatus in order to improve the homogeneity of the resin. Although it is possible to use a screw to melt and measure the resin and a plunger to inject the resin, use an in-line screw injection molding machine that integrates the functions of melting, measuring, and injection. Is preferred.

A schematic sectional view of an in-line screw type injection molding apparatus which can be used in the present invention is shown in FIG.
This in-line screw type injection molding apparatus has a heating cylinder 13 having a heating means 14 and an injection port 16 for a mold, and a resin inside the heating cylinder 13 for melting a resin,
(Movable) screw 11 for metering and injection
And a supply means 1 for supplying resin to the screw 11.
5 (such as a hopper) and screw driving means 12 for driving the screw 11 for weighing and injection.
As a mold, a mold composed of two separable parts (a fixed part 17 and a movable part 18) is used, and a driving means 19 for applying a mold clamping pressure to the mold and driving the movable part 18 is used. However, it is not limited thereto. A stamper 25 having a mirror-finished or patterned protective film formed inside the mold,
26 is set.

A schematic sectional view of a mold that can be used in the present invention is shown in FIG. FIG. 2 shows a mold at the time of resin filling. The mold has a space corresponding to the shape of the substrate to be manufactured (hereinafter referred to as the substrate cavity 22) and a space connecting the substrate cavity 22 and the injection port 16 (hereinafter referred to as the sprue portion 21). The gate 23 is disposed between the substrate cavity 22 and the sprue portion 21, and the resin filled in the substrate cavity 22 and the sprue portion 21.
There is provided a punch (gate cutting means) 24 for separating (gate cutting) the resin.

When manufacturing the magnetic disk substrate of the present invention, the resin melted and measured by using the screw 11 is injected into the mold through the injection port 16 and the resin is injected into the sprue portion 21 and the substrate cavity 22. To fill. After that, the filled molten resin is cooled and hardened in the mold.
During cooling and hardening, the punch 24 is advanced to move the sprue portion 21
Then, the resin in the substrate cavity portion 22 is separated, and further cooled and cured to obtain a magnetic disk substrate.

The magnetic disk substrate of the present invention is ejected by using a die in which a stamper having a carbon protective film formed to have an appropriate film thickness and an appropriate surface roughness is set inside the die. It is molded.

In the present specification, "minimum flying height of magnetic head"
Is a magnetic head that floats on the surface of a substrate that has been rotated at a certain rotation speed or more, by gradually reducing the rotation speed of the substrate so that when the magnetic head (generally a piezo head) contacts the substrate. It is the height calculated from the substrate rotation speed (speed) when the electric signal reaches 1 V or more, and the lower the height, the better the substrate.

In injection molding, one of the factors that affect the floating property of the head on the substrate is that the degree of deformation varies depending on the ease of peeling when releasing the substrate by applying a physical force when peeling the substrate from the stamper. Things can be mentioned. When it is difficult to peel off, the substrate is more deformed, and when it is easy to peel off, a stable shape is obtained.

The present inventors have found that controlling the roughness of the surface of the protective film of the stamper improves the releasability of the substrate from the mold and stabilizes the substrate shape. By doing so, it is possible to reduce the release variation and suppress partial abnormal deformation of the substrate surface.

Further, when the stamper surface is a super-mirror surface, when the magnetic head is made to float lower on the magnetic disk,
Although abnormal crash frequently occurred, by performing the roughness control according to the present invention, the flying stability of the head on the magnetic disk is improved, and the flying height can be lowered more than ever before. Further, since the surface roughness of the magnetic disk is improved, the friction coefficient at the time of collision with the magnetic head is reduced, head crash is less likely to occur, and a disk with higher reliability can be provided.

The surface roughness [Ra] of the stamper used for producing the magnetic disk substrate of the present invention is 0.2 nm to 1.0 n.
In the range of m, the minute waviness [Wa] of the protective film is
It is 0.5 nm or less. When a stamper satisfying this condition is used for molding, it is possible to suppress abnormal deformation at the time of releasing the substrate, and it is possible to significantly improve the magnetic head flying property.

The magnetic disk substrate manufactured by using the stamper as described above has a surface roughness [Ra] of 0.2 n.
m-1.0 nm, and micro waviness [Wa] is 0.5 nm or less.

It is preferable that the magnetic disk substrate manufactured as described above is annealed to reduce the stress remaining in the substrate. The annealing treatment is performed at a temperature of (Tg-70) ° C. or higher of the material used (Tg-15 of the material used) or lower (Tg means the glass transition temperature of the resin) for 0.5 hour to 48 hours.
It is preferably done over time. The annealing temperature is preferably as high as possible provided that it does not cause deterioration of the resin and local shape change of the substrate. The annealing treatment can be performed in an air atmosphere or a low oxygen atmosphere. Further, in order to prevent bending of the substrate due to its own weight during the annealing process, it is preferable that the substrate is vertically placed and the annealing process is performed. It is possible to reduce the residual stress by performing sufficient annealing, minimize the shape change due to the release of the residual stress with time, and prevent the occurrence of local deformation.

The thermoplastic resin used in the present invention contains a polyolefin resin in addition to the polycarbonate resin and polymethylmethacrylate resin which are generally used for magneto-optical disk substrates. In particular, it is preferable to use a rigid structure polyolefin-based resin having high heat resistance and low hygroscopicity, for example, norbornene-based polycycloolefin resin. The Tg derived from the resin structure is in the range of 135 to 190 ° C., and the higher the Tg within this range, the more preferable.

When a magnetic recording medium is produced using the magnetic disk substrate produced as described above, at least a magnetic recording layer is laminated on the substrate. Further, a base layer, a protective layer, a lubricating layer and the like can be provided as needed. Depending on the application, the layers as described above may be provided on one side or both sides of the magnetic disk substrate to obtain single-sided and double-sided magnetic recording media, respectively.

When a magnetic recording medium of a horizontal recording system which has been generally used in a hard disk drive or the like is manufactured, it is preferable to provide an underlayer, a magnetic recording layer, a protective layer and a lubricating layer in this order. An intermediate layer may be provided between the underlayer and the magnetic recording layer for the purpose of improving the performance of the magnetic recording layer. Further, when manufacturing a perpendicular recording type magnetic recording medium, which has been attracting attention in recent years due to the possibility of improving the recording density, etc., an underlayer, a soft magnetic backing layer, a magnetic recording layer, a protective layer, and a lubricating layer are arranged in this order. It is preferable to provide. Also in this case, an intermediate layer may be provided between the underlayer and the soft magnetic backing layer and / or between the soft magnetic backing layer and the magnetic recording layer for the purpose of improving recording characteristics and the like.

Each of the above layers can be made from any material known in the art. For example, the underlayer can be made of a non-magnetic metal material of Cr or an alloy mainly containing Cr, and the magnetic recording layer can be made of Co and Cr.
Can be made of a magnetic material such as an alloy mainly containing, and the protective layer can be made of carbon (especially diamond-like carbon) or the like. Further, the lubricating layer can be made of a liquid lubricant such as fluorine-containing polyether, and the soft magnetic backing layer should be made of an amorphous Co alloy, a NiFe alloy, or a sendust (FeSiAl) alloy. You can A material such as Ti or TiCr alloy may be used as the intermediate layer.

Each of the above layers except the lubricating layer is formed by the sputtering method,
It can be laminated on the magnetic disk substrate by a conventionally known method such as a vapor deposition method or a CVD method. In particular, it is preferable to use the sputtering method. Moreover, the lubricating layer can be formed by a method such as dip coating, spin coating, or spraying.

As described above, the high heat resistant thermoplastic resin is used and injection molding is performed by satisfying the conditions of the present invention.
It is possible to manufacture a magnetic disk substrate with improved flying characteristics of the magnetic head. By using the magnetic disk substrate, it is possible to provide a magnetic recording medium having excellent low flying characteristics.

Embodiments to which the present invention is applied will be described below in detail with reference to the drawings. (Example 1) A mold having a mirror surface stamper with no servo information was fixed to an injection molding apparatus having a maximum injection molding pressure of 70 t which is commercially available. Chromium (Cr) is formed as a protective film on the surface of the stamper, the film thickness at this time is 5 μm, and the surface roughness [Ra] measured using an AFM (atomic force microscope) is 0.5 nm. Micro waviness when measured with a ZYGO (non-contact optical surface roughness measuring instrument) with a 10 × objective lens and a cutoff of 50 μm [W
a] was 0.2 nm. Norbornene-based polyolefin resin (Tg = 138 ° C)
Resin temperature 320 ° C, injection speed 120 mm /
s, mold clamping pressure 120 kg / cm2 (about 11.8MP
a), mold temperature (fixed side / movable side) 110 ° C / 110
℃, gate cut timing is 0.2 after resin filling
Injection molding was carried out under the condition of seconds, and within 1 hour, annealing was performed at 90 ° C. for 10 hours in a state where the substrate obtained by the molding was held vertically in the atmosphere, and a diameter of 25 mm was measured. A disk-shaped disk substrate having a central circular hole and having a diameter of 95 mm and a thickness of 1.27 mm was obtained.

(Example 2) Surface roughness of chromium protective film [R
A disk substrate was obtained in the same manner as in Example 1 except that a] was 0.2 nm.

(Example 3) Surface roughness of chromium protective film [R
A disk substrate was obtained in the same manner as in Example 1 except that a] was 0.3 nm.

(Example 4) Surface roughness of a chromium protective film [R
A disk substrate was obtained in the same manner as in Example 1 except that a] was 0.7 nm.

(Example 5) Surface roughness of chromium protective film [R
A disk substrate was obtained in the same manner as in Example 1 except that a] was 1.0 nm.

(Example 6) A disk substrate was obtained in the same manner as in Example 1 except that the fine waviness [Wa] of the chromium protective film was set to 0.1 nm.

Example 7 A disk substrate was obtained in the same manner as in Example 1 except that the fine waviness [Wa] of the chromium protective film was set to 0.5 nm.

(Comparative Example 1) Surface roughness of chromium protective film [R
A disk substrate was obtained in the same manner as in Example 1 except that a] was 1.2 nm.

(Comparative Example 2) Surface roughness of chromium protective film [R
A disk substrate was obtained in the same manner as in Example 1 except that a] was set to 1.5 nm.

Comparative Example 3 A disk substrate was obtained in the same manner as in Example 1 except that the fine waviness [Wa] of the chromium protective film was 0.8 nm.

Comparative Example 4 A disk substrate was obtained in the same manner as in Example 1 except that the fine waviness [Wa] of the chromium protective film was set to 1.0 nm.

(Evaluation method) Regarding surface roughness, AFM
Ra (center line average roughness) measured by (atomic force microscope)
Was derived. For the measurement, one substrate surface was measured at four 90 ° intervals, and the average value was used as the surface roughness of the substrate surface. The minute waviness was measured by ZYGO (non-contact optical surface roughness meter) to derive Wa (center line average waviness). As for surface roughness, 1
Measurements were made at four positions on each substrate surface at 90 ° intervals, and the average value was used as the microwaviness of the substrate surface.

(Evaluation Results) Surface roughness [Ra] of the stamper protective film and magnetic head flying property [Take off H
FIG. 3 shows the relationship between the height of the magnetic head and the micro waviness [Wa] of the stamper protective film, and the flying property of the magnetic head [Ta].
ke off Height] is shown in FIG.

As is clear from FIG. 3, when the surface roughness of the stamper protective film is in the range of 0.2 nm to 1.0 nm, the magnetic head flying property is good. Further, as is clear from FIG. 4, the lower the micro waviness of the stamper protective film, the better the magnetic head flying property.

Therefore, it is understood that the surface roughness and the minute waviness of the stamper protective film (substrate) are greatly related to the flying characteristics of the head, and according to the present invention, the magnetic disk substrate or the magnetic disk substrate excellent in the flying characteristics of the head can be obtained. It is obvious that a magnetic recording medium using the substrate can be manufactured.

As is clear from the above description, the disk substrate according to the present invention is manufactured by injection molding using a stamper having a protective film formed on its surface, and the surface roughness of the protective film is from 0.2 nm. By setting the range of 1.0 nm and the minute waviness to 0.5 nm or less, the produced magnetic disk surface also exhibits similar surface roughness and minute waviness, and the magnetic head flying characteristic can be 5 nm or less. Become.
Therefore, the magnetic disk substrate manufactured by the present invention and the magnetic recording medium using the substrate have excellent head flying characteristics. Similar results were also obtained for the stamper with a pattern in which servo information was entered on the surface of the stamper by controlling the mirror surface.

According to the present invention, a plastic magnetic disk substrate having excellent shape characteristics can be mass-produced at low cost, and a magnetic recording medium and a magnetic recording / reproducing apparatus using the plastic magnetic disk substrate can be mass-produced at low cost. To be able to manufacture. Therefore, the industrial value of the present invention is great.

[0052]

As described above, according to the present invention, by controlling the film thickness and surface roughness of the protective film formed on the stamper surface, the shape of the molded substrate and the shape of the substrate after annealing can be controlled. It is possible to stabilize the levitation property with respect to the magnetic head as well as the conventional aluminum substrate.

[Brief description of drawings]

FIG. 1 is a conceptual cross-sectional view showing an example of an injection molding apparatus that can be used for producing a magnetic disk substrate of the present invention.

FIG. 2 is a conceptual cross-sectional view showing an example of a mold that can be used for producing the magnetic disk substrate of the present invention.

FIG. 3 is a graph showing the relationship between the levitation characteristics and the surface roughness of the carbon protective film of the magnetic disk substrates manufactured according to each example and comparative example.

FIG. 4 is a graph showing the relationship between the levitation characteristics of the magnetic disk substrates manufactured according to each of the examples and comparative examples and the microwaviness of the carbon protective film.

[Explanation of symbols]

11 screw 12 Screw drive means 13 Heating cylinder 14 Heating means 15 Supplying means 16 Exit 17 Mold fixing part 18 Movable part of mold

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Katsunori Suzuki             1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa             Within Fuji Electric Co., Ltd. (72) Inventor Isao Sekiguchi             1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa             Within Fuji Electric Co., Ltd. F-term (reference) 4F202 AF01 AG05 AG19 AH38 AJ02                       AJ09 AR13 CA11 CB01 CD23                       CK43                 5D006 CB01 DA03 FA00                 5D112 AA02 AA24 BA01 BA10

Claims (4)

[Claims] 1. A substrate for information recording medium is prepared by injection molding or injection compression molding of a thermoplastic resin material using a molding stamper, and a magnetic recording medium is manufactured using the substrate for information recording medium. A method for manufacturing a magnetic recording medium, wherein a protective film is formed on the surface of the molding stamper, and the surface of the protective film has a surface roughness (Ra) of 0.2 n.
A method of manufacturing a magnetic recording medium, wherein the magnetic recording medium has a thickness of m to 1.0 nm. 2. The microwaviness (W) on the surface of the protective film of the molding stamper according to claim 1.
a) is 0.5 nm or less, a method for producing a magnetic recording medium. 3. The stamper protective film material according to claim 1, wherein the protective film material of the stamper is titanium, chromium, manganese, cobalt, nickel, ruthenium, rhodium, palladium, tantalum, tungsten, rhenium, osmium, iridium, platinum, or gold. At least one of
A method of manufacturing a magnetic recording medium, characterized in that it is made of different types. 4. A magnetic recording device comprising a magnetic recording medium manufactured by the manufacturing method according to claim 1.