JPH09330516A - Manufacture of substrate for magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a substrate whose low surface roughness can be achieved without generating a microcrack and whose mirror working speed is enhanced by a method wherein the surface of the substrate is irradiated with a laser beam, uneven parts are formed and the surface is then mirror-worked. SOLUTION: A mirror working apparatus 1 is constituted of a substrate holding part 10 which holds and turns a substrate, of a grinding part 20 in which the substrate is ground by a whetstone 25 and of a laser-beam irradiation part 30 in when uneven parts are formed on the surface of the substrate while the surface is irradiated with a laser beam. As a process, an in-line system is adopted in such a way that the uneven parts are formed on the substrate by the laser-beam irradiation part 30 and that, in succession, the uneven parts are ground by the grinding part 20 so as to perform a mirror working operation. In the laser-beam irradiation part 30, a pulsed laser 31 which is generated by a laser light source 32 is passed through a mask material 33 so as to form a multiple beam, the multiple beam is condensed by a lens 34, the substrate is irradiated with the beam, and the uneven parts are formed on the substrate. The mirror working operation is performed so as to be regulated by the feed depth of a straight wheel 21 at the grinding part 21.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a substrate for a magnetic recording medium, and more specifically, it can achieve a low surface roughness without generating microcracks and has a mirror surface processing speed of the substrate. The present invention relates to a method for manufacturing an improved magnetic recording medium substrate.

[0002]

2. Description of the Related Art In recent years,
As a magnetic disk substrate used in a fixed disk device, a substrate made of a brittle material such as a carbon substrate or a glass substrate, which has a smaller specific gravity than that of an aluminum alloy substrate which has been conventionally used and has excellent mechanical properties, has been attracting attention. There is. With the increase in recording density of magnetic disks due to the increase in the recording capacity of fixed disk devices, demands for improving the smoothness of these magnetic disk substrates are becoming stricter year by year, and magnetic disk substrates with even smaller surface roughness are being demanded. It has been demanded. Along with this, there is an increasing demand for the development of super-mirror surface processing technology for magnetic disk substrates.

As a mirror-finishing technique for the above-mentioned magnetic disk substrate, a polishing process using free abrasive grains is generally used. For example, as a method of polishing a carbon substrate for a magnetic disk,
Japanese Unexamined Patent Publication No. 6-339853 describes a polishing method using a polishing liquid composed of water, alumina abrasive grains, and a polishing aid such as aluminum nitrate.

However, when free abrasive grains are used to polish a substrate made of a brittle material such as a carbon substrate or a glass substrate, microcracks may occur on the substrate surface during polishing due to the brittleness. When a magnetic disk is manufactured using a substrate in which microcracks are generated, it is a major cause of recording / reproducing errors.

On the other hand, various methods of mirror-finishing a substrate without using free abrasive grains have been studied. As one of them, a grinding method using fixed abrasive grains such as a diamond wheel in which diamond abrasive grains are fixed with a metal binder or a resin binder has been proposed. According to this grinding method, a good crack-free mirror surface can be obtained, but when the quality of the substrate to be ground is poor, it is necessary to take a large grinding allowance, resulting in a long processing time and a decrease in productivity. It will be. Also, since the wheel load increases, the life of the wheel also decreases.

Therefore, an object of the present invention is to provide a method for manufacturing a substrate for a magnetic recording medium which can achieve a low surface roughness without generating microcracks and which has an improved mirror surface processing speed of the substrate. .

[0007]

As a result of intensive investigations by the present inventors, prior to the mirror-finishing of a substrate, the surface of the substrate is irradiated with a laser beam to form an uneven shape for a magnetic recording medium. It has been found that a method of manufacturing a substrate can achieve the above object.

The present invention has been made based on the above findings, and a method for producing a substrate for a magnetic recording medium, which comprises irradiating a laser beam on the substrate surface to form an uneven shape, and then mirror-finishing the surface. The above object is achieved by providing a method.

Further, the present invention is an apparatus preferably used in the above method, wherein a substrate holding portion for holding and rotating the substrate, a grinding portion for grinding the substrate with a grindstone made of fixed abrasive grains, and a laser beam for irradiation are used. It is composed of a laser light irradiation unit for forming an uneven shape on the substrate surface, the laser light irradiation unit irradiates the substrate surface with laser light to form an uneven shape, and subsequently, the formed uneven shape portion is formed. The present invention provides a mirror surface processing apparatus for a magnetic recording medium substrate, characterized by being ground by the grinding section for mirror surface processing.

[0010]

In the present invention, prior to the mirror finishing of the substrate,
Irradiate a laser beam on the surface of the substrate to form an uneven shape,
By roughening the surface in advance, the burden of material removal during mirror surface processing is reduced, and the mirror surface processing speed is improved. In particular, when mirror-finishing is performed by grinding using fixed abrasive grains such as a diamond wheel, the wheel load during grinding can be reduced, and the wheel life is improved.

In the present specification, "mirror surface processing" refers to general smoothing processing of a substrate including grinding and polishing.
In addition, "grinding" refers to a smoothing process using fixed abrasives, and "polishing" refers to a smoothing process using free abrasives.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a method for manufacturing a substrate for a magnetic recording medium of the present invention will be described with reference to the drawings based on a preferred embodiment taking a carbon substrate as an example. Here, FIG.
3 is a schematic view of a mirror surface processing apparatus preferably used in the method for manufacturing a magnetic recording medium substrate of the present invention, FIG. 2 is a plan view showing a work table on which the substrate is mounted, and FIG.
(A)-(c) is a principal part top view showing the shape of the slit in a mask material.

A mirror surface processing apparatus 1 shown in FIG. 1 is a rotary flat surface processing machine for performing traverse grinding using the outer periphery of a straight wheel and is provided with a laser beam irradiation device. More specifically, the mirror finishing device 1 is
A substrate holding unit 10 for holding and rotating the substrate, a grinding unit 20 for grinding the substrate with a grindstone made of fixed abrasive grains, and a laser beam irradiation unit 30 for forming an uneven shape on the substrate surface by laser beam irradiation. The laser beam irradiator 30 irradiates the substrate surface with a laser beam to form an uneven shape, and subsequently, the formed uneven part is ground by the grinding section 20 to be mirror-finished. ing.

The substrate holder 10 has a work table 11 for holding and fixing a carbon substrate to be ground, a chuck 12 for holding and fixing the work table 11,
And a first spindle 13 for rotating the work table 11 in the direction of arrow A in the figure (that is, the in-plane direction of the carbon substrate). The first spindle 13 is held and fixed on a first slide base (not shown). The first slide base is movable in the direction of the arrow X in the figure, which enables the work table 11 to be traversed.

The work table 11 will be described in detail with reference to FIG. 2. The work table 11 is provided with a predetermined number of mounting portions for mounting the substrate 100 to be ground (in FIG. 8 places). A vacuum suction hole (not shown) is provided in the mounting portion, and the vacuum suction hole is connected to a vacuum pump (not shown). By operating the vacuum pump to reduce the pressure of the mounting portion,
The substrate 100 is held and fixed to the mounting portion by a vacuum chuck method. The work table 11 is configured to rotate in the direction of arrow A in the figure as described above.

As shown in FIG. 1, the grinding section 20 includes a straight wheel 21 and a second spindle 22 for rotating the straight wheel 21 in the direction of arrow B in the drawing.
It is composed of Further, a coolant for suppressing heat generation during grinding is supplied to the grinding section 20 through a coolant supply pipe 23. An opening / closing valve 24 is attached to the coolant supply pipe 23, and the supply amount of the coolant is controlled by the opening / closing operation of the opening / closing valve 24. The second spindle 22 is held and fixed on a second slide base (not shown). The second slide base is movable in the direction of the arrow Z in the figure, whereby the straight wheel 21 can be cut and fed.

The straight wheel 21 has a layer (grinding stone) 25 of fixed abrasive grains formed by dispersing and fixing abrasive grains by a bonding agent on the outer peripheral surface thereof. There is no particular limitation on the material, shape and particle size of the abrasive grains and the material of the bonding agent, and the material of the substrate to be mirror-finished,
It can be appropriately selected depending on the degree of roughening of the uneven shape formed by the irradiation of the laser beam, the machining allowance (the cutting depth of the straight wheel 21), and the like. For example, the substrate is a carbon substrate, the center line average roughness of the uneven shape is about 100 nm, and the machining allowance is 20 μm.
In the case of m / one side, the average grain size of the abrasive grains is preferably 1 to 5 μm (count # 2000 to # 300).
0), more preferably 1 to 2.5 μm (count # 2000
0 to # 6000) industrial diamond abrasive grains are used, and a metal bonding agent is used as the bonding agent.

The laser light irradiating section 30 comprises a laser light source 32 for generating a pulse laser 31, a mask material 33 for making the pulse laser 31 a multiple beam, and a lens 34 for condensing the multiple beam. The multiple beams are arranged to illuminate the substrate at right angles. Examples of the light source in the laser light source 32 include an excimer laser, an Nd: YAG laser, a CO ₂ laser, and a semiconductor laser, which can be appropriately selected according to the material of the substrate. Further, as the mask material 33,
For example, a mesh mask as shown in FIG. 3A can be used, but the mask is not limited to this, and a mask having cross-shaped slits as shown in FIG.
It is also possible to use a slit or the like, as shown in (c), which is formed by three straight lines that are 120 degrees apart from each other, have the same length, and have one end located on the same point.

In the mirror surface processing apparatus 1 shown in FIG. 1, the substrate mounted on the work table 11 is first formed with an uneven shape on the surface thereof by the laser light irradiation section 30. The formed concavo-convex shape is subsequently ground by the grinding section 20 and mirror-finished. As described above, in the mirror surface processing apparatus 1, the step of irradiating the substrate surface with the laser beam to form the uneven shape and the step of grinding the formed uneven shape to perform the mirror surface processing are performed by an in-line method. Therefore, the production efficiency of the substrate is significantly improved. Particularly, since the substrate and the grinding surface (grinding surface) of the straight wheel are in line contact with each other, the grinding progresses,
By grinding after the formation of the uneven shape, the damage to the substrate and the straight wheel is significantly reduced, and the occurrence of microcracks in the substrate is further suppressed,
The life of the straight wheel is improved.

Next, a method for manufacturing the carbon substrate of this embodiment, including a mirror surface processing step using the mirror surface processing apparatus shown in FIG. 1, will be described. First, a curing agent is added to and mixed with a liquid raw material resin, and the mixture is sandwiched between a pair of glass plates and cured. Next, the cured resin having a predetermined thickness taken out from between the glass plates is cored into a disc shape to obtain a large number of disc-shaped cured resins. The disk-shaped cured resin is fired to carbonize it to obtain a glass-like carbon disk substrate. Then, the carbon substrate is roughly ground using a diamond grindstone or the like (generally, the center line average roughness Ra is 0.
The thickness is set to be 0.5 to 2 μm), and defects, undulations, warps, etc. on the substrate surface are removed and reduced. After that, the inner diameter and outer diameter of the disk are set to predetermined dimensions, and the inner and outer circumferences of the disk are chamfered to chamfer a predetermined amount. After the chamfering process, the mirror surface processing apparatus shown in FIG. 1 is used to irradiate the surface of the carbon substrate with a laser beam to form an uneven shape, and the formed uneven shape portion is ground to perform mirror surface processing. The final substrate is obtained with a predetermined low surface roughness.

The mirror surface processing step using the mirror surface processing apparatus shown in FIG. 1 will be described in more detail. First, the pulse laser 31 generated by the laser light source 32 in the laser light irradiation section 30 must pass through the mask material 33. Results in multiple beams. The multiple-beam pulse laser is focused by the lens 34 to have a predetermined beam diameter, and then is irradiated onto the carbon substrate. At the portion irradiated with the pulsed laser, material removal occurs due to the energy of the pulsed laser, and an uneven shape is formed. That is, a photochemical reaction occurs at the site irradiated with the pulsed laser, and the bonds between the atoms and molecules at the site are cut off.
The uneven shape is formed by instantly dispersing and scattering molecules. As shown in FIG. 4, the concavo-convex shape formed by the individual beams of the pulsed laser is a so-called crater shape, that is, the contour is a substantially circular shape in plan view, and the contoured portion 101 is convex, and the contour is formed. It is composed of a pit 102 which is surrounded by a portion 101 and which is depressed in a concave shape. In this embodiment, since the pulse laser is irradiated as a multiple beam, the crater-like shape formed by the individual beams of the pulse laser is formed. The uneven shapes 103 are in a state of overlapping each other. The degree of this overlap can be adjusted by changing the shape of the slit in the mask material.

In the mirror surface processing apparatus 1 shown in FIG. 1, the pulse laser irradiation is performed from the left along the arrow X direction in the drawing while the work table 11 rotates in the arrow A direction in the drawing. It is performed while moving to the right. As a result, the uneven shape is formed on the entire surface of the substrate.

Irradiation conditions of the pulse laser, for example, pulse period of the pulse laser, output, irradiation number and irradiation area,
In addition, the number of rotations of the work table and the like can be appropriately selected according to the type of the substrate and the degree of the uneven shape (the degree of roughening). For example, when an uneven shape is formed on the surface of a carbon substrate using an excimer laser, the pulse period is preferably 50 to 200 kHz, the output is preferably 0.01 to 1000 mJ, and the irradiation number is It is preferably 1000 to 1000 × 10 ⁶ times. The irradiation area is preferably ¹ to 80 mm ² . Further, it is preferable that the rotation speed of the work table is the same as the rotation speed of the work table in the grinding step described later.

Subsequent to the formation of the concavo-convex shape by the irradiation of the pulse laser, the grinding section 20 in the mirror-finishing apparatus 1 shown in FIG. 1 grinds the portion where the concavo-convex shape is formed. The grinding by the grinding unit 20 is performed by rotating the work table 11 in the direction of arrow A in the drawing and moving the substrate holding unit 10 from left to right along the direction of arrow X in the drawing while In a state where the straight wheel 21 and the substrate are in contact with each other so as to approach the work table 11 along the direction of the middle arrow Z and the cutting depth of the straight wheel 21 in the grinding portion 20 becomes a predetermined value. Done.

In the above grinding, there are grinding modes such as ductile mode grinding and brittle mode grinding depending on the grinding conditions. In the present invention, the grinding mode is not particularly limited,
From the viewpoint of suppressing the generation of microcracks, it is preferable to perform the ductile mode grinding. In the present specification, "ductile mode grinding" means a plastic-fluid removal process that does not cause cracks even in a brittle material, that is, a grinding process characterized by no damage to the material rather than brittle fracture (crushing). . Ductile mode grinding is achieved by keeping the depth of cut of each abrasive grain into the substrate always below the ductility-brittleness transition point (hereinafter also referred to as "dc"). The means for achieving the ductile mode grinding is not particularly limited, and a known method can be used. For example, most brittle materials such as carbon and glass have a ductility-brittleness transition point of 2 to 100 nm, and therefore, the set cutting depth of the abrasive grains in the ductile mode grinding is preferably 0.05 to 20.
μm, more preferably 0.1 to 10 μm, and further preferably 0.1 to 5 μm. The certified depth of cut is defined as 0 when the straight wheel 21 is brought close to the work table 11 along the arrow Z direction in FIG. 1 and comes into contact with the outermost surface of the substrate to be processed attached to the work table 11. From that point, the straight wheel 2
The amount by which 1 is pushed further.

If R (curvature) is added to the shoulder portion of the outer circumference of the straight wheel (grinding stone) according to the set cutting depth of the abrasive grains, the microcracks are further generated even if the set cutting depth of the abrasive grains is large. It is more preferable because a suppressed ductile mode ground surface can be obtained. Regarding the shape of R and the like, it is preferable to set the cutting depth d _g of each abrasive grain to be smaller than the dc of the substrate (that is, d _g <dc). Here, the cutting depth d _g of each abrasive grain is calculated from the following formula.

[0027]

[Equation 1]

Incidentally, the grinding load of the straight wheel (grinding stone) in the ductile mode grinding is, for example, 1 to 10 when a wheel having a wheel width of 1 to 20 mm is used.
It is preferably 60 kgf, more preferably 1 to 30 kgf. The peripheral speed of the straight wheel (grinding stone) is preferably 300 to 5000 m / min, more preferably 600 to 2000 m / min. Further, the feed rate along the X direction of the work table (corresponding to the feed rate of the straight wheel) is preferably 10 to 120 mm / min,
More preferably, it is 30 to 60 mm / min. Furthermore,
The rotation speed of the work table is 50 to 1000 rpm
Is preferable, and 100-500 rpm is more preferable.

Using the mirror finishing device shown in FIG.
Processing marks (grinding marks) on the substrate surface ground by ground grinding
Has a fan shape as schematically shown in FIG. Such fan
In the shape of the processing marks, the processing marks did not intersect with each other.
Therefore, the occurrence of microcracks is further suppressed, so
preferable. In the present specification, "fan-shaped processing marks"
Is a substantially concentric circle, as shown schematically in FIG.
It is a processing mark that forms an arc. The center of the concentric circle is on the substrate
It may be or may be outside the substrate. In particular, the substrate
Radius r₁And the radius r of the processing mark ₂Between r₂≧ r₁Become
Preferably related, especially to worktables
Of substrate mounting workability and processing accuracy of mirror surface processing equipment
100r from the point₁≧ r ₂≧ 2r₁To have a relationship
preferable. It should be noted that grinding is performed so that fan-shaped processing marks are formed.
To shave, mount the substrate on the work table
At this time, as shown in FIG.
Eccentric mounting so that the center of rotation of the table 11 is not included
Then, as shown in FIG. 1, the work table 11 is rotated.
And contact the straight wheel 21 with the substrate
While making the straight wheel 21 work,
You can traverse along the cable 11.

In the carbon substrate mirror-finished by the above-mentioned method, the generation of microcracks is extremely suppressed, and the center line average roughness (Ra) is preferably 200 Å or less, more preferably 2 to 50 Å. , And more preferably 2 to 10Å. Also, the maximum protrusion height (Rp) is preferably 1000 Å or less,
More preferably 5 to 200 Å, and even more preferably 5
It will be ~ 50Å. The methods for measuring the center line average roughness (Ra) and the maximum protrusion height (Rp) will be described in detail in Examples below.

Next, the second and third embodiments of the method of manufacturing a magnetic recording medium substrate of the present invention will be described with reference to FIGS. Here, FIG. 6 is a schematic view showing a grinding device used for electrolytic in-process dressing, and FIG.
FIG. 8 is a schematic view showing a cup wheel, and FIG. 8 is a plan view schematically showing multiple iris-shaped processing marks. In addition,
In the second and third embodiments, only the points different from the first embodiment will be described, and as for points not particularly detailed, the detailed description of the first embodiment will be applied as appropriate. 6 to 8, the same members as those in FIGS. 1 to 5 are designated by the same reference numerals.

In the second embodiment, the grinding is performed by ductile mode grinding using electrolytic in-process dressing (hereinafter referred to as "ELID"). This makes it possible to perform grinding with higher accuracy and higher efficiency.
In the ELID, as shown in FIG. 6, a straight wheel 21 having a layer (grinding stone) 25 of fixed abrasive grains formed by dispersing and fixing abrasive grains with a metal bond agent on the outer peripheral surface thereof.
And a grinding device including an electrode 27 is used.
The electrode 27 is held and fixed by an insulator 26 and is arranged so as to cover a part of the outer circumference of the grindstone 25. The distance between the electrode 27 and the grindstone 25 is
It is kept at a predetermined value by the gap adjusting screw 28. Further, a coolant supply pipe 29 is formed so as to penetrate the insulator 26 and the electrode 27. Examples of the metal bonding agent include Fe (cast iron etc.), C
A simple metal such as u or Ni or an alloy containing one or more of these can be used.

A method of performing ELID using the grinding device shown in FIG. 6 will be explained.
Aqueous solution containing electrolyte from the grindstone 25
And the substrate (not shown), the above-mentioned grindstone 25
And a negative electric field is applied to the electrode 27. In this state, the straight wheel 21 and the substrate are rotated as in the case of the first embodiment. As a result, the metal bonding agent on the surface of the grindstone 25 in the straight wheel is dissolved in the anode, and the grinding progresses with the abrasive grains exposed on the surface by a predetermined amount. Since the dissolution of the metal bonding agent in the anode is stopped by the formation of an oxide film due to the oxidation of the metal bonding agent during grinding, the abrasive grains are not exposed more than necessary. When grinding progresses further and the abrasive grains wear, the oxide film also wears accordingly, and as a result, the surface of the new (that is, non-oxidized) metal bonding agent is exposed. The surface of the new metal bonding agent is anodic-dissolved as described above. Hereinafter, the above mechanism, that is, the formation of the oxide film in the metal bond agent, the abrasion thereof, and the dissolution of the anode are repeated, whereby the abrasive grains are always exposed on the surface of the grindstone 25, and a constant grinding efficiency is maintained. It As a result, more accurate and more efficient grinding is performed. In addition,
Examples of the electrolyte-containing aqueous solution used for ELID include CEM and AFG-M manufactured by Noritake Company Limited, and ELI manufactured by Yushiro Kagaku Co., Ltd.
D No. 32, No. 35, Similon CG-6 manufactured by Daido Chemical Industry Co., Ltd., and the like.

In the third embodiment, a cup wheel is used instead of the straight wheel used in the grinding section in the first embodiment. That is, as shown in FIG. 7, the cup wheel 21 ′ has a layer (grinding stone) 25 of fixed abrasive grains formed by dispersing and fixing abrasive grains by a bonding agent on the lateral cutting surface of a cylindrical wheel. Is to have. The cup wheel 21 '
In the grinding using, while rotating the work table 11 and the cup wheel 21 ', the cup wheel 21' is fed at a predetermined speed in the direction of the arrow shown in FIG. 7 (wheel feed speed), and grinding is performed for a predetermined time. To do. in this case,
The rotation direction of the cup wheel 21 ′ and the rotation direction of the work table 11 may be opposite to each other as shown in FIG. 7, or may be the same. When one substrate 100 is set at the center of the work table 11, the ground substrate 100 has multiple iris-shaped processing marks as shown in FIG.

The method for manufacturing a magnetic recording medium substrate of the present invention has been described above based on its preferred embodiment, but the present invention is not limited to the above embodiment, and various modifications are possible. For example, the method of the present invention may be applied directly to a glassy carbon substrate obtained by carbonization (that is, without rough grinding), or to a glassy carbon substrate after rough grinding and intermediate grinding. The method of the present invention may be applied as finish grinding. In addition to the carbon substrate, a brittle material such as a glass substrate such as tempered glass or crystalline glass, or an aluminum alloy substrate can be used as the substrate. Among these substrates, the carbon substrate has excellent grinding stability and low surface roughness, and therefore the method of the present invention has a particularly excellent effect when applied to the carbon substrate. Further, in the grinding, the straight wheel may move only one pass along the arrow X direction in FIG. 1, or may move two or more passes.
Further, when moving in two or more passes, the count of the abrasive grains may be gradually increased each time the passes are overlapped. Further, the step of irradiating the surface of the substrate with a laser beam to form an uneven shape and the step of mirror-finishing the surface may be performed using separate devices. Further, the irradiation of the laser light may be irradiation as a single beam without using the mask material,
Alternatively, multiple beam irradiation using a plurality of laser light sources may be used. In addition, after the laser light irradiation, mirror surface processing by polishing using free abrasive grains may be performed instead of mirror surface processing by grinding. Such mirror finishing by polishing can be carried out, for example, according to the method described in JP-A-6-339853, column 5, lines 17 to 22 and column 7, table 1. In addition, after the above-mentioned mirror surface processing, a super-mirror surface processing step may be performed if necessary.

[0036]

[Embodiment 1] Next, the effectiveness of the method for producing a magnetic recording medium substrate of the present invention will be illustrated by means of an embodiment. However, the scope of the present invention is not limited to the above embodiments.

Example 1 A glassy carbon substrate obtained by curing a phenol resin and then carbonizing the same was subjected to rough polishing and chamfering, and the center line average roughness Ra was about 1000Å. A glassy carbon substrate of 0.8 inch was obtained. The mirror surface processing device is an ultra-precision horizontal surface grinding device (HPG-2A) manufactured by Nisshin Kikai Seisakusho Ltd.
Using the above, 9 glassy carbon substrates were mounted on a work table, and the surface thereof was irradiated with laser light and ground under the conditions shown in Table 1. In addition, the flat portion and the shoulder portion of the straight wheel are # 200 diamond wheel [SD20 manufactured by Oriental Diamond Tool Laboratory Co., Ltd.]
0 Q75M] for precision truing to adjust the generatrix shape as shown in FIG. 9, and the cutting depth of each abrasive grain during grinding is about the ductile-brittle transition point (dc) of the carbon substrate. It was set to be 50 nm or less.
Further, the glassy carbon substrate was fixed by a vacuum chuck method by means of vacuum suction holes provided in large numbers in the mounting portion of the work table. The surface state of the obtained glassy carbon substrate was observed by an optical microscope and an atomic force microscope (AFM), and the center line average roughness Ra was measured.
The maximum protrusion height Rp and the grinding speed were measured by the following methods. Table 1 shows the results.

<Centerline average roughness Ra and maximum protrusion height R
Measuring method of p> Stylus surface roughness meter [Tencor Corporation
Manufactured by Model P2] and measured under the following conditions.・ Stylus tip radius: 0.6μm ・ Stylus pressing pressure: 7mg ・ Measuring length: 250μm × 8 places ・ Trace speed: 2.5μm / sec ・ Cutoff: 1.25μm (low pass filter) <Measuring method of grinding speed > In the case of a straight wheel; 9 glassy carbon substrates were set on a work table, and 9 substrates were simultaneously ground. The plate thickness of the glassy carbon substrate before and after grinding
The measurement was carried out at each of 9 locations with a precision micrometer manufactured by Mitutoyo, and the difference between the average values was used as the grinding amount, which was divided by the required processing time to obtain the grinding speed as the grinding amount per unit time. In the case of cup wheel; one glassy carbon substrate was set at the center of the work table and ground. The grinding amount and the grinding speed were obtained in the same manner as in the case of the straight wheel.

[Examples 2 to 6] Under the conditions shown in Table 1, glassy carbon substrates were obtained by the same operations as in Example 1 except that the laser beam was irradiated and the grinding was performed. In addition, for the cup wheel grinding in Example 6, an ultra-precision rotary surface grinding machine (HSG-10A2) manufactured by Fujikoshi Co., Ltd. was used, and one glassy carbon substrate was set and ground.
The grinding conditions for the cup wheel are: wheel speed: 250
The rotation speed was 0 rpm, the work table rotation speed was 300 rpm, and the wheel feed speed was 4 μm / min. The obtained glassy carbon substrate was observed and measured in the same manner as in Example 1. Table 1 shows the results. The plane portion of the cup wheel was subjected to precision truing in the same manner as in Example 1, and the shoulder portion was provided with an arc of about R900 mm. The ELID conditions in Examples 2 to 6 are as follows.・ Power supply: Shinto Blator Co., Ltd., pulse power supply EDP-1
0A ・ Initial dressing: 3A × 15 minutes ・ ELID voltage: 60V ・ Pulse (square wave) cycle: 4 microseconds

Comparative Example 1 A glassy carbon substrate was obtained by the same operation as in Example 6 except that the laser beam was not irradiated and the grinding was performed under the conditions shown in Table 1. The obtained glassy carbon substrate was observed and measured in the same manner as in Example 1. Table 1 shows the results. The ELID conditions are the same as in Examples 2-6.

Comparative Example 2 A glassy carbon substrate was obtained by the same operation as in Comparative Example 1 except that the grinding conditions were as follows. The obtained glassy carbon substrate was observed and measured in the same manner as in Example 1. Table 1 shows the results. Wheel rotation speed: 1000 rpm Work table rotation speed: 300 rpm Wheel feed speed: 1 μm / min

[0042]

[Table 1]

As is clear from the results shown in Table 1, according to the method of the present invention, the glass surface was obtained by irradiating the substrate surface with a laser beam to form an uneven shape and then grinding the surface ( In Examples 1 to 6), as compared with the glassy carbon substrate of Comparative Example 1 obtained by grinding without irradiating laser light, microcracks were not generated and low surface roughness was achieved. At the same time, the grinding load is reduced and the grinding speed is improved.

[0044]

According to the present invention, there is provided a method of manufacturing a substrate for a magnetic recording medium which can achieve a low surface roughness without generating microcracks and which has an improved mirror surface processing speed. Particularly, by performing the mirror surface processing by the ductile mode grinding, and particularly by performing the mirror surface processing by the ductile mode grinding in which the processing marks are fan-shaped, the generation of the microcracks is further suppressed. Further, according to the method of the present invention, when the above-mentioned mirror finishing is performed by grinding using fixed abrasive grains such as a diamond wheel, the wheel load at the time of grinding can be reduced and the wheel life is improved. In particular, by using a grindstone for a straight wheel, the generation of microcracks is further suppressed and the wheel life is further improved. The method of the present invention is particularly effective for mirror-finishing a substrate made of a brittle material such as carbon or glass.

[Brief description of drawings]

FIG. 1 is a schematic view of a mirror surface processing apparatus used in a method for manufacturing a magnetic recording medium substrate of the present invention.

FIG. 2 is a plan view showing a work table on which a substrate is mounted.

FIG. 3A to FIG. 3C are plan views of relevant parts showing the shapes of the slits in the mask material.

FIG. 4 is a cross-sectional view schematically showing an uneven shape formed on a substrate.

FIG. 5 is a plan view schematically showing a fan-shaped processing mark.

FIG. 6 is a schematic diagram showing a grinding device used for electrolytic in-process dressing.

FIG. 7 is a schematic view showing a cup wheel.

FIG. 8 is a plan view schematically showing multiple iris-shaped processing marks.

FIG. 9 is an enlarged view showing a main part of a straight cup used in an example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mirror finishing device 10 Substrate holding unit 11 Work table 12 Chuck 13 First spindle 20 Grinding unit 21 Straight wheel 21 'Cup wheel 22 Second spindle 23 Coolant supply pipe 24 Opening / closing valve 30 Laser light irradiation unit 31 Pulse laser 32 Laser light source 33 Mask material 34 Lens 100 Carbon substrate

Claims (9)

[Claims] 1. A method of manufacturing a substrate for a magnetic recording medium, which comprises irradiating a laser beam on a surface of a substrate to form an uneven shape, and then mirror-finishing the surface. 2. The method for manufacturing a substrate for a magnetic recording medium according to claim 1, wherein the uneven shape is formed by removing a material. 3. The method for manufacturing a substrate for a magnetic recording medium according to claim 1, wherein the mirror finishing is grinding or polishing. 4. The method for manufacturing a substrate for a magnetic recording medium according to claim 3, wherein the grinding is performed by ductile mode grinding. 5. The method for manufacturing a substrate for a magnetic recording medium according to claim 4, wherein the processing marks formed by the ductile mode grinding are fan-shaped. 6. The method for manufacturing a substrate for a magnetic recording medium according to claim 4, wherein the grinding is performed by ductile mode grinding using electrolytic in-process dressing. 7. The magnetic recording medium according to claim 1, wherein the center line average roughness (Ra) is 200 Å or less and the maximum projection height (Rp) is 1000 Å or less. Substrate manufacturing method. 8. The substrate according to claim 1, which is a carbon substrate.
8. The method for manufacturing a substrate for a magnetic recording medium according to any one of 7. 9. A substrate holding unit for holding and rotating a substrate, a grinding unit for grinding the substrate with a grindstone made of fixed abrasive grains, and a laser beam irradiation unit for forming an uneven shape on the substrate surface by laser beam irradiation. The laser light irradiation unit irradiates the substrate surface with laser light to form an uneven shape, and subsequently, the formed uneven shape portion is ground by the grinding unit to be mirror-finished. A mirror surface processing apparatus for a substrate for a magnetic recording medium, characterized in that