JP3807607B2 - Manufacturing method and manufacturing apparatus for magnetic recording medium substrate - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic recording medium mounted on various magnetic recording devices including an external storage device of a computer, a manufacturing method thereof, and a magnetic recording device using the same.
[0002]
[Prior art]
When a conventional non-magnetic metal substrate (aluminum, etc.) is used as a magnetic disk substrate for a magnetic recording medium that requires a high degree of surface accuracy, high precision processing is required. For example, it is manufactured as follows.
[0003]
After the metal material first heated and melted is rolled and heat-annealed, a blank material processed to a specified size is produced, and then the inner and outer diameters are processed. Further, after lapping is performed to improve the surface accuracy, a Ni—P plating layer is formed to have a thickness of 13 μm for the purpose of improving the surface hardness, and the surface is polished to have a surface roughness of Ra = 1. Polish to a thickness of 0.0 nm (10 mm) or less, and perform final lapping (texturing) using diamond slurry. After that, in the CSS (contact start / stop) zone, for example, the bump bite is 19.0 nm (190 mm), laser zone texture processing is performed so that the density of one bump is 30 μm square, and then precision cleaning is performed. Thus, a general magnetic disk substrate for hard disk can be obtained.
[0004]
On the magnetic disk substrate obtained as described above, a Cr underlayer 50 nm (500 mm, CoCrTa magnetic layer (Co: Cr: Ta = 82: 14: 4) 30 nm (300 mm), and a carbon protective layer 8.0 nm (80 mm). ) Are sequentially formed by DC sputtering, and tape varnishing is performed on the surface after sputtering, and finally, a fluorine-based lubricating layer 2.0 nm (20 mm) is formed by dip coating or spin coating, and magnetic recording for a hard disk is performed. However, the manufacturing method and configuration of the disk substrate and various recording media are not limited to those described above.
[0005]
Conventional magnetic disk substrates and methods for producing magnetic recording media as described above are becoming more and more complicated with the recent increase in recording density. On the other hand, there is a need for a magnetic disk substrate and a magnetic recording medium that are cheaper than before while maintaining high performance. Magnetic disk substrates and magnetic recording media using thermoplastic resins (plastics) have been proposed as new magnetic disk substrates that satisfy these conflicting requirements.
[0006]
[Problems to be solved by the invention]
However, when a magnetic disk substrate that requires a high degree of shape stability and surface accuracy is manufactured by plastic injection molding, the mechanical strength is lower than when it is manufactured from a metal, glass, or ceramic substrate. Therefore, finish polishing (lapping, polishing, varnishing, etc.) cannot be performed. Therefore, at the end of injection molding, it is necessary to adjust the surface accuracy (straightness, swell, roughness, etc.) required for the magnetic disk substrate. However, in the resin molding, if the surface of the stamper is mirror-finished, the adhesion between the stamper and the substrate becomes high, so there is a problem that the substrate itself may be deformed when released from the stamper and the flatness is lowered. there were.
[0007]
Low flatness (poor surface accuracy) for recording media that require very high surface accuracy, such as a hard disk with a magnetic head flying up several tens of nanometers above the substrate to improve recording density When a substrate having a magnetic head is used, a predetermined distance between the magnetic head and the recording medium cannot be maintained, and in the worst case, the magnetic head does not float and actual reading / writing cannot be performed. cause.
[0008]
The present invention has been made in view of the above-described conventional situation, and realizes high flatness by controlling adhesion when a plastic substrate is released from a stamper, and has excellent head flying characteristics. An object is to provide a medium substrate and a magnetic recording medium.
[0009]
[Means for Solving the Problems]
As a result of intensive studies to achieve the above-mentioned problems, the inventors have determined that the center line average surface roughness Ra of the protective film on the stamper surface used in the mold is in the range of 0.2 nm to 2.0 nm. Thus, it has been found that the releasability from the stamper during injection molding is improved, the substrate shape is greatly improved, and the minimum flying height of the magnetic head can be stably reduced to 5 nm or less.
[0010]
In addition, the thickness of the protective film is preferably in the range of 0.01 μm to 9 μm, and the thickness of the protective film is further in the range of 0.01 μm to 5 μm in consideration of the manufacturing cost. Is preferred.
[0011]
The method for manufacturing a substrate for magnetic recording medium of the present invention is a method for manufacturing a substrate for magnetic recording medium in which a thermoplastic resin is injected into a molding die and molded, and an area corresponding to at least the substrate recording area in the molding die. The molding surface is coated with a carbon coating, the thickness of the carbon coating layer is in the range of 0.01 μm to 9 μm, and the center line average surface roughness Ra of the layer is in the range of 0.2 nm to 2.0 nm. Inside, injection molding is performed using the molding die.
[0012]
The method for manufacturing a magnetic recording medium substrate according to the present invention is further characterized in that the thickness of the layer coated with the carbon coating is in the range of 0.01 μm to 5 μm.
[0013]
The apparatus for manufacturing a magnetic recording medium substrate according to the present invention is an apparatus for manufacturing a magnetic recording medium substrate in which a thermoplastic resin is injected into a molding die and molded, and an area corresponding to at least the substrate recording area in the molding die. A carbon coating is applied to the molding surface, the thickness of the carbon coating layer is in the range of 0.01 μm to 9 μm, and the center line average surface roughness Ra of the layer is 0.2 nm to 2.0 nm. It is within the range.
[0014]
In the magnetic recording medium substrate manufacturing apparatus of the present invention, the carbon coating layer has a thickness in the range of 0.01 μm to 5 μm.
[0015]
Furthermore, the magnetic recording medium substrate manufacturing apparatus of the present invention is characterized in that the molding surface is formed on a stamper.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
As a film forming apparatus for the stamper surface protective film of the present invention, a DC sputtering apparatus or a plasma CVD processing apparatus can be used, and while forming a carbon protective film on the stamper using this apparatus, the protective film thickness is increased. The surface roughness can be controlled by the film forming conditions, and the centerline average surface roughness [Ra] at that time is in the range of 0.2 nm to 2.0 nm, preferably 0.2 nm to 1.0 nm. it can. Further, as a method for controlling the surface roughness of the protective film, in addition to the above, for example, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, etc. can be used as an adhesion layer under the protective film. By forming a film by sputtering, it becomes possible to more easily control the required surface roughness.
[0017]
In this specification, “flatness” is the maximum amount of displacement in the direction perpendicular to the substrate surface over the entire disk substrate.
[0018]
The "magnetic head minimum flying height" refers to a magnetic head (generally used by a piezo head) by gradually decelerating the rotation speed of a magnetic head floating on a substrate surface rotated at a certain rotation speed or higher. Is the height calculated from the number of rotations (speed) of the substrate when the electrical signal when contacting the substrate reaches 1V or more, and the lower the height, the better the substrate. means.
[0019]
The magnetic disk substrate manufactured using the stamper of the present invention has a flatness of 10 μm or less and a minimum flying height of the magnetic head of 5 nm or less.
[0020]
The magnetic disk substrate produced 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 installed in a magnetic recording apparatus. Here, the diameters of the central circular hole and the disc depend on the design of the magnetic recording apparatus.
[0021]
For the injection molding used in the present invention, an injection molding apparatus known in the art can be used. In order to improve the uniformity of the resin, it is preferable to use a screw type injection molding apparatus. It is possible to melt and meter the resin using a screw and to inject the resin using a plunger, but use an inline screw type injection molding device that integrates the functions of melting, metering and injection. Is preferred.
[0022]
FIG. 1 shows a schematic cross-sectional view of an in-line screw type injection molding apparatus that can be used in the present invention. This in-line screw type injection molding apparatus includes a heating cylinder 13 having a heating means 14 and an injection port 16 for a mold, and a (movable) screw in the heating cylinder 13 for melting, measuring and injecting resin. 11, a supply means 15 (such as a hopper) for supplying resin to the screw 11, and a screw drive means 12 for measuring and injecting the screw 11. As the mold, a mold composed of two separable parts (fixed part 17 and movable part 18) is used, and a driving means 19 for driving the movable part 18 by applying mold clamping pressure to the mold is further provided. However, it is not limited to this. Stampers 24 and 25 having a mirror-finished or patterned protective film are set inside the mold.
[0023]
The stamper may be provided on either the fixed side or the movable side depending on the usage of the molded substrate. Further, a protective film having a pattern directly on the mold surface corresponding to the recording area molding surface may be provided.
[0024]
FIG. 2 shows a schematic cross-sectional view of a mold that can be used in the present invention. FIG. 2 shows a mold at the time of resin filling. The mold is composed of a movable mold 18 and a fixed mold 17 that face each other, and a movable stamper 25 and a fixed stamper are respectively provided on surfaces of the movable mold 18 and the fixed mold 17 on which resin molding is performed. 26.
[0025]
The mold has a space (hereinafter referred to as a substrate cavity 22) corresponding to the shape of the substrate to be manufactured, and a space (hereinafter referred to as a sprue portion 21) that connects the substrate cavity and the injection port 16. Further, a gate 23 is disposed between the substrate cavity 22 and the sprue portion 21, and gate cutting means 24 is provided for separating the resin filled in the substrate cavity 22 from the resin of the sprue portion 21 (gate cutting). It has been.
[0026]
When the magnetic disk substrate of the present invention is manufactured, the resin melted and measured using the injection device having the screw 11 is injected into the mold through the injection port 16, and the sprue portion 21 and the substrate cavity 22 are injected. Fill with resin. Thereafter, the filled molten resin is cooled and cured in a mold. During the cooling and curing, the punch 24 as the gate cutting means is advanced to separate the resin of the sprue portion 21 and the substrate cavity portion 22 and further cooled and cured to obtain the magnetic disk substrate.
[0027]
The magnetic disk substrate of the present invention was injection-molded using a mold in which a stamper in which a carbon protective film controlled to an appropriate film thickness and an appropriate surface roughness was formed was set inside the mold. Is.
[0028]
One of the reasons why the flatness is not improved in injection molding is that the degree of deformation differs depending on the ease of peeling when a physical force is applied to release the substrate from the stamper. When it is difficult to peel off, the substrate is more deformed, and when it is easily peeled off, a stable shape is obtained. The present inventors need to improve the releasability and stabilize the shape of the protective film on the stamper surface by using carbon having higher lubricity, and the protective film roughness on the stamper surface is also necessary. It has also been found that the releasability is further improved when the mirror surface is not used. By doing so, it is possible to improve the releasability and further reduce the variation in the releasability, thereby suppressing the deformation of the entire substrate.
[0029]
The protective film thickness of the stamper surface when producing the magnetic disk substrate of the present invention is in the range of 0.01 μm to 5 μm, and the center line average surface roughness Ra of the protective film is 0.2 nm to 2.0 nm. To do. When molding is performed using a stamper that satisfies this condition, the deformation at the time of releasing the substrate can be suppressed, and the flatness of the substrate can be greatly improved.
[0030]
The magnetic disk substrate manufactured using the stamper as described above has a flatness of 10 μm or less, more preferably 5 μm or less. The surface roughness has a centerline average surface roughness Ra of 0.2 to 2.0 nm.
[0031]
Furthermore, it is preferable to relieve the stress remaining in the substrate by annealing the magnetic disk substrate manufactured as described above. The annealing treatment is performed at a temperature of (Tg-70 of the material used) ° C. or higher (Tg-15 of the material used) ° C. or lower (Tg means the glass transition temperature of the resin) for 0.5 hour to 48 hours. It is preferable to carry out over. It is preferable that the annealing temperature be as high as possible on condition that the resin does not deteriorate and the local shape change of the substrate does not occur. The annealing treatment can be performed in an air atmosphere or a low oxygen atmosphere. Further, in order to prevent the bending due to the weight of the substrate during the annealing process, it is preferable to perform the annealing process by placing the substrate vertically. By performing sufficient annealing, the residual stress can be reduced, the change in shape due to the release of the residual stress over time can be minimized, and the occurrence of local deformation can be prevented.
[0032]
The thermoplastic resin used in the present invention contains a polyolefin resin in addition to a polycarbonate resin and a polymethyl methacrylate resin generally used for a magneto-optical disk substrate. In particular, it is preferable to use a rigid-structure polyolefin-based resin, such as a norbornene-based polycycloolefin resin, which has high heat resistance and low hygroscopicity. The Tg derived from the resin structure is in the range of 135 ° C. to 190 ° C., and the higher the Tg within this range, the better.
[0033]
When a magnetic recording medium is manufactured using the magnetic disk substrate manufactured as described above, at least a magnetic recording layer is laminated on the substrate. Moreover, a base layer, a protective layer, a lubricating layer, etc. can be provided as needed. Furthermore, depending on the application, the above-described layers can be provided on one side or both sides of the magnetic disk substrate to obtain single-sided and double-sided magnetic recording media, respectively.
[0034]
In the case of producing a horizontal recording type magnetic recording medium that is conventionally used in a hard disk device or the like, it is preferable to provide an underlayer, a magnetic recording layer, a protective layer, and a lubricating layer in this order. For the purpose of improving the performance of the magnetic recording layer, an intermediate layer may be provided between the underlayer and the magnetic recording layer. In addition, when producing a perpendicular recording type magnetic recording medium that has been attracting attention in recent years due to the possibility of an increase in recording density, the underlayer, the soft magnetic backing layer, the magnetic recording layer, the protective layer, and the lubricating layer are arranged in this order. It is preferable to provide it. In this case, a medium layer may be provided between the underlayer and the soft magnetic underlayer and / or between the soft magnetic underlayer and the magnetic recording layer for the purpose of improving the recording characteristics.
[0035]
Each of the above layers can be made from any material known in the art. For example, the underlayer can be made of Cr or a non-magnetic metal material of an alloy mainly containing Cr, and the magnetic recording layer can be made of a magnetic material such as an alloy mainly containing Co and Cr, and can be protected. The layer can be made of carbon (particularly diamond-like carbon) or the like. Further, the lubricating layer can be made from a liquid lubricant such as a fluorine-containing polyether, and the soft magnetic backing layer can be made using a non-quality Co alloy, NiFe alloy, Sendust (FeSiAl) alloy, or the like. it can. A material such as Ti or TiCr alloy may be used as the intermediate layer.
[0036]
Each of the above layers excluding the lubricating layer can be laminated on the magnetic disk substrate by a conventionally known method such as sputtering, vapor deposition, or CVD. In particular, it is preferable to use a sputtering method. The lubricating layer can be formed by a method such as dip coating, spin coating or spraying.
[0037]
By using a high heat-resistant thermoplastic resin and satisfying the conditions of the present invention and injection molding, the flatness of the substrate can be greatly improved, and thereby a magnetic disk substrate with improved magnetic head flying characteristics can be produced. . Further, by using the magnetic disk substrate, it is possible to provide a magnetic recording medium having excellent head flying characteristics.
[0038]
[Example]
Embodiments to which the present invention is applied will be described in detail below with reference to the drawings.
[0039]
Example 1
A mold having a stamper fixed thereto was attached to a commercially available injection molding apparatus with a maximum injection molding pressure of 70 t. On the stamper surface, DLC (Diamond Like Carbon) is formed as a protective film. The film thickness at this time is 0.5 μm and the center line average surface roughness measured using an AFM (Atomic Force Microscope). A material having a [Ra] of 0.5 nm was used. However, in this case, in order to make the surface roughness constant, a Cr layer of 3 μm was provided on the base of the carbon protective film. As the resin, norbornene-based polyolefin resin (Tg = 138 ° C.) is used, the resin temperature is 320 ° C., the injection speed is 120 mm / s, the clamping pressure is 120 kg / cm ² (about 11.8 MPa), the mold temperature (fixed side / movable) Side) Injection molding was performed under the conditions of 110 ° C./110° C. and a gate cut timing of 0.2 seconds after completion of resin filling. Within 1 hour, annealing was performed at 90 ° C. for 10 hours with the substrate held vertically in an air atmosphere, having a central circular hole with a diameter of 25 mm, a diameter of 95 mm, and a thickness of 1.27 mm. A disk-shaped disk substrate having the following dimensions was obtained.
[0040]
(Example 2)
A disk substrate was obtained in the same manner as in Example 1 except that the thickness of the carbon protective film was 0.01 μm.
[0041]
Example 3
A disk substrate was obtained in the same manner as in Example 1 except that the thickness of the carbon protective film was 0.05 μm.
[0042]
Example 4
A disk substrate was obtained in the same manner as in Example 1 except that the thickness of the carbon protective film was 0.1 μm.
[0043]
(Example 5)
A disk substrate was obtained in the same manner as in Example 1 except that the thickness of the carbon protective film was 1 μm.
[0044]
(Example 6)
A disk substrate was obtained in the same manner as in Example 1 except that the thickness of the carbon protective film was 3 μm.
[0045]
(Example 7)
A disk substrate was obtained in the same manner as in Example 1 except that the thickness of the carbon protective film was 5 μm.
[0046]
(Example 8)
A disk substrate was obtained in the same manner as in Example 1 except that the thickness of the carbon protective film was 7 μm.
[0047]
Example 9
A disk substrate was obtained in the same manner as in Example 1 except that the thickness of the carbon protective film was 9 μm.
[0048]
(Comparative Example 1)
A disk substrate was obtained in the same manner as in Example 1 except that the thickness of the carbon protective film was 0.001 μm.
[0049]
(Comparative Example 2)
A disk substrate was obtained in the same manner as in Example 1 except that the thickness of the carbon protective film was 0.003 μm.
[0050]
(Comparative Example 3)
A disk substrate was obtained in the same manner as in Example 1 except that the thickness of the carbon protective film was 0.005 μm.
[0051]
(Example 10)
A mold having a stamper fixed thereto was attached to a commercially available injection molding apparatus with a maximum injection molding pressure of 70 t. On the stamper surface, DLC (Diamond Like Carbon) is formed as a protective film. The film thickness at this time is 5 μm, and the centerline average surface roughness measured using an AFM (Atomic Force Microscope) [ Ra] was used in a state of 0.5 nm. As the resin, norbornene-based polyolefin resin (Tg = 138 ° C.) is used, the resin temperature is 320 ° C., the injection speed is 120 mm / s, the clamping pressure is 120 kg / cm ² (about 11.8 MPa), the mold temperature (fixed side / movable) Side) Injection molding was performed under the conditions of 110 ° C./110° C. and a gate cut timing of 0.2 seconds after completion of resin filling. Within 1 hour, annealing was performed at 90 ° C. for 10 hours with the substrate held vertically in an air atmosphere, having a central circular hole with a diameter of 25 mm, a diameter of 95 mm, and a thickness of 1.27 mm. A disk-shaped disk substrate having the following dimensions was obtained.
[0052]
(Example 11)
A disk substrate was obtained in the same manner as in Example 10 except that the center line average surface roughness Ra (hereinafter simply referred to as surface roughness) of the carbon protective film was 0.2 nm.
[0053]
(Example 12)
A disk substrate was obtained in the same manner as in Example 10 except that the surface roughness of the carbon protective film was 0.8 nm.
[0054]
(Example 13)
A disk substrate was obtained in the same manner as in Example 10 except that the surface roughness of the carbon protective film was 1 nm.
[0055]
(Example 14)
A disk substrate was obtained in the same manner as in Example 10 except that the surface roughness of the carbon protective film was 1.5 nm.
[0056]
(Example 15)
A disk substrate was obtained in the same manner as in Example 10 except that the surface roughness of the carbon protective film was 2 nm.
[0057]
(Comparative Example 4)
A disk substrate was obtained in the same manner as in Example 10 except that the surface roughness of the carbon protective film was set to 0.1 nm.
[0058]
(Comparative Example 5)
A disk substrate was obtained in the same manner as in Example 10 except that the surface roughness of the carbon protective film was 3 nm.
[0059]
(Comparative Example 6)
A disk substrate was obtained in the same manner as in Example 10 except that the surface roughness of the carbon protective film was changed to 5 nm.
[0060]
(Evaluation methods)
The flatness [Flatness] of the substrate surface was measured with a Flatness Tester FT-12 made by Nidek, and the amount of displacement was derived. Five sheets were measured for one condition, and the average value was defined as the flatness at that time.
The surface roughness [Ra] was measured with an atomic force microscope [AMF], and Ra (center line average roughness) was derived. With respect to the surface roughness, measurements were made at four locations every 90 degrees on one substrate surface, and the average value was defined as the roughness of the substrate surface.
[0061]
(Evaluation results)
The relationship between the stamper protective film thickness, the magnetic head flying height (Take off Height), and the flatness is shown in FIG. 3, and the relationship between the stamper protective film surface roughness, the magnetic head flying height (Take off Height), and the flatness is illustrated in FIG. As shown in FIG.
[0062]
As is apparent from FIG. 3, the higher the stamper protective film thickness, the better the magnetic head flying characteristics and the higher the flatness.
[0063]
As is clear from FIG. 4, the magnetic head flying characteristics and the flatness were good when the stamper protective film surface roughness was in the range of 0.2 nm to 2 nm.
[0064]
It is well known that the flatness and surface roughness of the substrate are largely related to the flying characteristics of the head. According to the present invention, the magnetic disk substrate having excellent flying characteristics of the head or magnetic recording using the substrate is used. The medium can be manufactured.
[0065]
【The invention's effect】
As is clear from the above description, the disk substrate according to the present invention is manufactured by injection molding using a stamper on which a carbon protective film is formed, the carbon protective film thickness is 0.01 μm or more, and the center line average By setting the surface roughness Ra in the range of 0.2 nm to 2.0 nm, the flatness of the substrate can be made 10 μm or less, and the magnetic head flying characteristics can be made 5 nm or less. Therefore, according to the present invention, it is possible to manufacture a magnetic disk substrate having excellent head flying characteristics and a magnetic recording medium using the substrate.
[0066]
In addition, the method of the present invention makes it possible to produce a large amount and a low cost of a plastic magnetic disk substrate having excellent shape characteristics. As a result, a large number of magnetic recording media and magnetic recording / reproducing apparatuses using the plastic magnetic disk substrate can be obtained. It can be manufactured at low cost.
[0067]
As described above, according to the present invention, the post-molding substrate and the annealed substrate shape can be controlled by forming a carbon film on the stamper surface and controlling the film thickness and surface roughness. Can be stabilized like a conventional aluminum substrate.
[Brief description of the drawings]
FIG. 1 is a conceptual cross-sectional view showing an example of an injection molding apparatus that can be used to manufacture 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 to manufacture the magnetic disk substrate of the present invention.
FIG. 3 is a graph showing the relationship between the flying characteristics and the carbon protective film thickness and the relationship between the flatness and the carbon protective film thickness of the magnetic disk substrates produced in each example and comparative example.
FIG. 4 is a graph showing the relationship between the flying characteristics and the carbon protective film surface roughness and the relationship between the flatness and the carbon protective film surface roughness of the magnetic disk substrate produced by each example and comparative example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 Screw 12 Screw drive means 13 Heating cylinder 14 Heating means 15 Supply means 16 Injection port 17 Mold fixed part 18 Mold movable part 19 Movable part drive means 21 Sprue part 22 Substrate cavity 23 Gate 24 Punch 25 Movable part stamper 26 Fixed part stamper

Claims (10)

In the method of manufacturing a magnetic recording medium substrate in which a thermoplastic resin is injected into a molding die and molded,
Carbon molding is applied to the molding surface of at least the area corresponding to the substrate recording area in the molding die, and the thickness of the carbon coating layer is in the range of 0.01 μm to 9 μm, and the center line average surface of the layer The roughness Ra is in the range of 0.2 nm to 2.0 nm,
A method for manufacturing a substrate for a magnetic recording medium, wherein injection molding is performed using the molding die.   2. The method of manufacturing a substrate for a magnetic recording medium according to claim 1, wherein a thickness of the layer coated with the carbon coating is in a range of 0.01 [mu] m to 5 [mu] m. Method of manufacturing a substrate for a magnetic recording medium according or claim 1 to claim 2, characterized in that formed on the stamper to the molding surface. Is shaped by the method claimed in any of claims 3, 0 is the center line average surface roughness Ra. 2nm~2., Characterized in that be in the range of 0nm with the following flatness 10μm A magnetic recording medium substrate.   A magnetic recording medium comprising the substrate according to claim 4. In an apparatus for manufacturing a magnetic recording medium substrate in which a thermoplastic resin is injected into a molding die and molded,
Carbon molding is applied to the molding surface of at least the area corresponding to the substrate recording area in the molding die, and the thickness of the carbon coating layer is in the range of 0.01 μm to 9 μm, and the center line average of the layer An apparatus for producing a substrate for a magnetic recording medium, wherein the surface roughness Ra is in the range of 0.2 nm to 2.0 nm.   7. The apparatus for manufacturing a substrate for a magnetic recording medium according to claim 6, wherein the thickness of the carbon coating layer is in the range of 0.01 [mu] m to 5 [mu] m. The or claim 6, characterized in that the molding surface formed on the stamper magnetic recording medium substrate manufacturing apparatus according to claim 7. Molded by An apparatus according claim 6 to claim 8, 0 is the center line average surface roughness Ra. 2nm~2., Characterized in that be in the range of 0nm having the following flatness 10μm A magnetic recording medium substrate.   A magnetic recording medium comprising the substrate according to claim 9.

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