JPH09180183A - Production of substrate for magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lower the polishing resistance of the inner and outer peripheral end faces of a substrate body with a grinding wheel, to improve the service life and polishing speed of the grinding wheel and to lower the surface roughness of the inner and outer peripheral end faces by impressing an electric field on the substrate body and subjecting the substrate body to grinding. SOLUTION: An electric field is impressed on the substrate body 1A and the substrate body is subjected to grinding with the grinding wheels 22, 23 in a chamfering stage of the substrate body 1A. The + side of a DC power source 40 is connected to the substrate body 1A to impress the anode electric field thereon. The - side is connected to the electrode 41 near the grinding wheels 22, 23 to impress the cathode electric field. A soln. coolant contg. an electrolyte is supplied between the grinding wheels 22, 23 and the substrate body 1A. As a result, the surface layer of the substrate body 1A subjected to the electrolytic treatment is dissolved and the polishing resistance is lowered. In addition, the hydrophilic components generated by oxidation decomposition are exposed on the surface of the substrate body 1A, thereby, the lubricity is improved and the grinding resistance is lowered. The service life and grinding speed of the grinding wheels are thus improved.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for manufacturing a substrate for a magnetic recording medium.

[0002]

2. Description of the Related Art A substrate for a recording medium typified by a hard disk (HD) substrate is a lapping process for roughly polishing the surface of a substrate body, a chamfering process for chamfering the inner and outer peripheral end faces to be chamfered, and a final polishing for the surface. It is manufactured through a polishing process. Then, this substrate further has a texture step of forming a texture layer on the surface of the substrate body to appropriately roughen the surface, an underlayer forming step of forming an underlayer on the surface, and a magnetic layer formed on the surface. Magnetic layer forming step, a protective layer forming step of forming a protective layer on the magnetic layer,
A product is formed by forming a film on the surface of the substrate body in a lubricating layer forming step of forming a lubricating layer on the protective layer, and then performing a burnishing step of removing abnormal protrusions on the film surface.

However, the need for higher recording density in the hard disk substrate requires the surface of the substrate body and the inner and outer peripheral end faces to be mirror-finished.

[0004]

However, the conventional technique of grinding the inner and outer peripheral end faces of the substrate body by using a grindstone has the following problems. The grinding resistance of the grindstone is large. For this reason, the abrasion of the grindstone is severe and the life of the grindstone is shortened. Further, the grinding speed (material removal speed) of the grindstone cannot be increased, resulting in high production cost.

Since the grinding resistance of the grindstone is large, cracks and pits (unevenness flaws) resulting from the cracks are likely to occur in the substrate body, and it is difficult to achieve a mirror surface. If the inner and outer peripheral end faces of the substrate body are poorly mirror-finished and the surface roughness is too rough, the film adhesion durability after forming the recording layer is poor and film peeling occurs.

An object of the present invention is to reduce the grinding resistance of the inner and outer peripheral end faces of the substrate body due to the grindstone, to improve the life of the grindstone, improve the grinding speed of the grindstone, and reduce the surface roughness of the inner and outer peripheral end faces.

[0007]

According to a first aspect of the present invention, an electric field is applied to the substrate body in a method for manufacturing a substrate for a magnetic recording medium, in which the inner and outer peripheral end faces of the nonmagnetic substrate body are ground with a grindstone. In this state, the grindstone is used for grinding.

According to a second aspect of the present invention, in addition to the first aspect of the present invention, an electrolyte solution is used as a coolant supplied at the time of grinding by the grindstone.

According to a third aspect of the present invention, in addition to the first or second aspect of the present invention, the substrate body is made of carbon.

According to the present invention of claims 1 to 3,
Has the effect of When the substrate body is used as an anode and the coolant contains an electrolyte, (a) The substrate body is subjected to electrolytic treatment (anodic eluting oxidative decomposition, etching, polarization) and the surface layer of the substrate body is dissolved, resulting in low grinding resistance. Becomes The polarization phenomenon referred to here is a phenomenon in which the interatomic distance between constituent atoms (for example, C atoms) of the substrate body becomes large and the interatomic bond is easily broken (FIG. 3).

(B) The hydrophilic component generated by the oxidative decomposition of the substrate body appears on the surface of the substrate body, and the wettability (hydrophilicity) of the substrate body and thus the lubricity are increased, and the grinding resistance is reduced.

(C) Electrolysis of water at the anode or constituent atoms (for example, C atoms) of the substrate body are eluted or gasified by oxidative decomposition, and these gases remove chips on the surface of the substrate body to reduce grinding resistance. Becomes

When the substrate body is used as an anode and the coolant is not made to contain an electrolyte, (a) a polarization phenomenon occurs in the substrate body and the grinding resistance becomes small. (b) Same as (b) above. (c) Same as (c) above.

When the substrate body is used as a cathode, whether the coolant contains an electrolyte or not, (a) the cation component of the coolant invades the surface of the substrate body to wet the surface of the substrate body. (Hydrophilicity) As a result, lubricity is increased and grinding resistance is reduced.

(B) The gas generated by the electrolysis of the water that constitutes the coolant removes the chips on the surface of the substrate body and reduces the grinding resistance.

In a substrate made of a brittle material such as a carbon substrate, defects such as cracks and chips are likely to occur during processing of the substrate body. According to the present invention, even in a substrate made of such a brittle material, the grinding resistance is reduced by the above items to improve the life of the grindstone, improve the grinding speed of the grindstone, and reduce the surface roughness of the inner and outer peripheral end faces of the substrate body. Can be achieved.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic diagram showing a substrate grinding method according to the present invention, FIG. 2 is a principle diagram of electrolytic treatment of FIG. 1, FIG. 3 is a schematic diagram showing polarization phenomenon, and FIG. 4 is a resin synthesizing step. Schematic diagram showing the GC substrate manufacturing process from the core removal process to
5 is a schematic diagram showing the GC substrate manufacturing process from the lapping step before firing to the carbonizing step by firing, FIG. 6 is a schematic diagram showing the GC substrate manufacturing process from the lapping step after firing to the substrate completion, and FIG. FIG. 8 is a schematic diagram showing a film configuration of a hard disk according to an example, and FIG. 8 is a schematic diagram showing electrolytic current characteristics.

Glass-like carbon substrate for magnetic disk (G
The C substrate 1 is a product obtained by processing the substrate body 1A in the manufacturing process of (A) below and subjecting the processed substrate body 1A to the film formation of (B) below.

(A) GC Substrate Manufacturing Process FIGS. 4 to 6 show the GC substrate manufacturing process. (1) Resin synthesizing process, (2) Resin curing process, (3) Core removing process, (4) Before firing A lapping step, (5) firing carbonization step, (6) lapping step after firing, (7) chamfer processing step, and (8) polishing step are carried out in this order. However, depending on the degree of lapping in the pre-firing lapping step (4), the post-firing lapping step (6) can be omitted. Further, there is no particular problem even if the order of the post-firing lapping step (6) and the chamfering step (7) is interchanged. Furthermore, the lapping before firing in (4) may be omitted.

In the resin synthesizing step, the phenol-modified furan resin is synthesized in the reaction vessel 11. The liquid resin after resin synthesis is filtered by the filter 12.

In the resin curing step, the pair of glass plates 13,
A liquid resin containing a hardener added and mixed therein is injected between 13 and allowed to react by leaving it in a high temperature state to be cured. After that, it is taken out from the glass plates 13 and 13 to obtain a plate-shaped cured resin. obtain.

In the core removing step, for example, a laser cutter (or a router, a lathe, a press, etc.) is used to change a plate-shaped cured resin 14 from a disk-shaped cured resin (cured resin substrate) 15 having an outer diameter of 88 mm and an inner diameter of 25 mm. Cut out many.

In the lapping step before firing, the double side polishing machine 1
6, the surface of the cored cured resin substrate 2 is polished with free abrasive grains.

The abrasive grains used here have an average grain size of 1.0 to 1.0 provided that the lapping step after firing is omitted.
Abrasive grains in the range of 6.0μ. Then, the surface roughness after lapping is set to Ra = 0.4 μm or less. As for the thickness after lapping, the shrinkage rate after firing is about 75%, and the thickness obtained after firing is about 0.65 mm to 0.7 mm, 0.9 mm to 0.
Make it about 95 mm.

On the premise that the lapping step after firing is performed, if the only purpose is to make the thickness uniform in the lapping step before firing, an average abrasive grain in the range of 1.0 to 30.0 μ is used. Then, the surface roughness after lapping is set to Ra = 2.0 μ or less (range 0.02 to 2.0 μ).

In the firing carbonization step, a graphite plate (carbon plate) 1
A large number of cured resin substrates 15 are arranged on 7 and further a graphite plate 17 and a large number of cured resin substrates 15 are sequentially laminated thereon, and these are placed in a firing furnace, and in a inert gas atmosphere by a graphite heater, By firing at 1200 ° C., the cured resin is carbonized to obtain the fired GC substrate body 1A.

More specifically, along the firing temperature pattern, a temperature range is set between an inert gas atmosphere and a vacuum, such as an inert gas atmosphere in a certain temperature range and a vacuum in another temperature range. It is controlled according to. Specifically, nitrogen, argon, or the like is used as the inert gas.

At this time, the shrinkage is about 75%, and if the thickness before firing is about 0.9 mm to 0.95 mm, the thickness after firing is about 0.65 mm to 0.7 mm.

In the lapping step after firing, the double-side polishing machine 2
1, the surface of the baked GC substrate body 1A is polished with free abrasive grains.

The double-side polishing machine 21 used here may be the same as that used in the lapping step before firing.

The abrasive used has an average particle size of 1.0 to 1.0.
Abrasive grains in the range of 6.0μ. However, if the desired thickness and flatness / surface roughness are obtained after firing by using abrasive grains having an average particle size in the range of 1.0 to 6.0 μm in the pre-firing lapping step, the post-firing lapping step can be omitted. is there.

In the chamfering process, the GC substrate 1
The outer peripheral surface and the inner peripheral surface of A are ground with grinding stones 22 and 23 to make the diameter uniform and chamfer the corner.

In the final polishing step, the double side polishing machine 24 is used for final polishing. Through the above steps, the GC substrate body 1A is obtained.

(B) Film forming process on GC substrate (FIG. 7) An Al-10 wt% Si alloy texture layer having a thickness of 30 nm and an average surface roughness of 9.2 angstrom was provided by DC magnetron sputtering under Ar gas pressure of 2 mTorr.

Then, a first underlayer made of glassy carbon and having a thickness of 20 nm was provided by DC magnetron sputtering under the conditions of Ar gas pressure of 2 mTorr and substrate heating temperature of 250 ° C.

Further, the substrate heating temperature is set to 180 ° C. and Ar
Under a gas pressure of 10 mTorr, a second underlayer of Ti with a thickness of 50 nm, a third underlayer of Cr with a thickness of 40 nm, and a thickness of 30 on the third underlayer.
A Co-15 wt% Cr-10 wt% Pt layer (magnetic layer) having a thickness of nm was continuously formed.

Next, the substrate is placed in a chamber of an in-line type sputtering apparatus, the chamber is evacuated, and then Ar (partial pressure of 1.6 mTorr) and oxygen (partial pressure of 0.4 mTorr).
rr) was introduced, and sputtering was performed using graphite as a target to form a 15 nm protective layer on the magnetic layer.

Finally, after burnishing, a lubricant (Fomblin AM2001 manufactured by Aojimont Co., Ltd.) was dipped and applied on the protective layer to a thickness of 2 nm.

Therefore, in the present invention, the substrate body 1 described above is used.
As shown in FIGS. 1 and 2, the chamfering process of A is performed by the following (1) and (2) with the grindstones 22 and 23 in a state where an electric field is applied to the substrate body 1A.

(1) The chamfer processing device 30 includes a chuck stage 31, a clamp 32, a diamond grindstone 22,
It is configured to have 23.

The chuck stage 31 applies a vacuum pressure to the concentric convex portion 31A for supporting the substrate body 1A, a vacuum suction groove 31B for vacuum suctioning the substrate body 1A around the convex portion 31A, and a vacuum suction groove 31B. And a vacuum supply path 31C. As a result, the chuck stage 31 moves the substrate body 1
A can be vacuum-adsorbed.

The clamp 32 is a high-pressure water jet port 32A for applying high-pressure water to the substrate body 1A on the chuck stage 31.
And the substrate body 1A can be pressed and held on the chuck stage 31.

The diamond grindstone 22 makes it possible to grind the outer peripheral end face of the substrate body 1A to the outer diameter and chamfer, and the diamond grindstone 23 makes it possible to grind the inner peripheral end face of the substrate body 1A to the inner diameter and chamfer. At this time, the grindstone 22 (same for the grindstone 23) is a metal bond wheel (abrasive grains on the outer periphery of a straight wheel fixed with a metal binder).

(2) The positive side of the DC power source 40 is the substrate body 1
Connect to A and apply an anode electric field, and grindstone 22 on the negative side.
(23) A cathode electric field is applied by connecting to the electrode 41 in the vicinity. However, the wiring on the minus side may be directly connected to the grindstone 22 (23). Then, an aqueous solution coolant containing an electrolyte is supplied between the outer periphery of the grindstone 22 (23) and the substrate body 1A. As a result, the anode electric field is applied to the substrate body 1A, and the cathode electric field is applied to the grindstone 22 (23) through the coolant.

As described above, when electrolysis is performed in an electrolyte solution using a conductive substrate as an anode, phenomena such as electrolytic etching, electrolytic polishing, and anodic oxidation occur depending on the type of electrolyte and electrolysis conditions. That is, when a conductive substrate is subjected to anodic polarization in an electrolytic solution, it is generally classified into the following three regions as shown in FIG. 8 (Metal Electrochemistry, Takeo Oki, Kyoritsu Shuppan, 1969).
Year, p170).

Region (AC): When anodic polarization (V) is performed, the anodic current (I) increases parabolically according to Ohm's law.

Region (C-D): A region where the current does not increase even when the potential (electric field) is increased and the region is saturated.

Region (D-E): When the anodic polarization is further increased, the current again increases parabolically.

The phenomenon occurring in each region is as follows. : Electrolytic etching area. Initial anodic dissolution occurs, and metal ions are promoted by the anodic electric field and are directly eluted into the electrolytic solution. The metal surface is free to be melted away from the easily melted portion, so that an etching (corrosion) surface is formed on the metal surface.

Electrolytic polishing area. A region where metal dissolution / accumulation in the vicinity of the surface and formation of an anodic oxide film coexist, and the convex portion of the metal surface preferentially dissolves, resulting in a mirror finish.

Gas generation / discharge region: A region where oxygen gas is generated from the anode, the film is broken, or discharge occurs through the film.

When the substrate is carbon, it does not exhibit the same behavior as when it is a metal, but similar behaviors and phenomena occur.

The electrolyte solution may be an acid or alkali aqueous solution, and is 0.1 to 80 wt%, preferably 1 to 60 wt%.
The concentration of is used. Examples of the electrolyte component to be used include inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, hydrofluoric acid and perchloric acid, organic acids such as oxalic acid and formic acid, and alkanolamines. Alkali is Na
OH, KOH, etc. are mentioned. These may be used by blending two or more kinds. You may blend and use these electrolytes in a commercial coolant.

As the anode material, an ordinary electrode such as Pt,
Au, Pb and carbon electrodes can be used. The electrode waveforms used are, for example, direct current, alternating current such as single-phase alternating current and three-phase alternating current, pulse wave such as rectangular wave and triangular wave, single-phase half-wave, two-phase half-wave, and three-phase.
Special waveforms such as phase half wave, six phase half wave, single phase full wave, and three phase full wave are used. These waveforms may be used in combination. Considering productivity, three-phase alternating current is desirable.

Regarding the current density during electrolysis, considering the uniformity of electrolysis treatment, productivity, and equipment load, it is 1 to 200 mA / cm 2.
² is preferred. More preferably, it is 5 to 100 mA / cm ² .
That is, if the current density is too low, the productivity will decrease, and conversely 20
If it exceeds 0 A / cm ² and is too high, the uniformity of electrolytic treatment tends to deteriorate.

Therefore, according to this embodiment, the substrate body 1
Since A is the anode and the coolant contains the electrolyte, the following effects (a) to (c) are obtained. (a) Electrolytic treatment (oxidation decomposition, etching,
As a result of melting the surface layer of the substrate body 1A that has been polarized), the grinding resistance becomes small. The polarization phenomenon is caused by the substrate body 1
This is a phenomenon in which the interatomic distance between the constituent atoms of A (for example, C atom) becomes large and the interatomic bond is easily broken (FIG. 3).

(B) The hydrophilic component generated by the oxidative decomposition of the substrate body 1A appears on the surface of the substrate body 1A.
The wettability (hydrophilicity) and the lubricity are increased, and the grinding resistance is reduced.

(C) Constituent atoms (for example, C atoms) of the substrate body 1A are gasified by oxidative decomposition, and this gas removes chips on the surface of the substrate body to reduce grinding resistance.

That is, according to the above (a) to (c), the substrate body 1
It is possible to reduce the grinding resistance by the grindstones 22 and 23 on the inner and outer peripheral end faces of A, improve the life of the grindstones 22 and 23, improve the grinding speed of the grindstones 22 and 23, and reduce the surface roughness of the inner and outer peripheral end faces of the substrate body 1A. it can.

Incidentally, the present invention is a modified mode in which the substrate body 1A is used as an anode and the coolant does not contain an electrolyte as in the following (1), or the substrate body 1A is used as a cathode in the following (2). Can also be adopted, and each has the following effects.

(1) When the substrate body 1A is used as an anode and the coolant does not contain an electrolyte, (a) a polarization phenomenon occurs in the substrate body 1A, and the grinding resistance becomes small.

(B) The hydrophilic component generated by the oxidative decomposition of the substrate body 1A appears on the surface of the substrate body 1A.
The wettability (hydrophilicity) and the lubricity are increased, and the grinding resistance is reduced.

(C) Constituent atoms (for example, C atoms) of the substrate body 1A are gasified by oxidative decomposition, and this gas removes chips on the substrate body surface to reduce grinding resistance.

(2) When the substrate body 1A is used as a cathode, whether or not the coolant contains an electrolyte (a) the cation component of the coolant enters the surface of the substrate body 1A and The wettability (hydrophilicity) of the surface of 1A and thus the lubricity is increased, and the grinding resistance is reduced.

(B) The gas generated by the electrolysis of the water that constitutes the coolant removes the chips on the surface of the substrate body 1A, and the grinding resistance becomes small.

The present invention is preferably the substrate body 1A.
The maximum effect is achieved by adopting an electrolytic treatment method using as a positive electrode.

[0067]

EXAMPLES Examples of the present invention will be described together with comparative examples. However,
The present invention is not limited to the following examples. (Firing of Substrate Main Body) A furfuryl alcohol resin was molded by a known method and prebaked to produce a carbon substrate. More specifically, it was manufactured as follows. Furfuryl alcohol 500 parts by weight, 92% formaldehyde
400 parts by weight and 30 parts by weight of water were stirred and dissolved at 80 ° C.
Then, with stirring, a mixed solution of 520 parts by weight of phenol, 9.5 parts by weight of calcium hydroxide and 45 parts by weight of water was added dropwise at 80 ° C.
And reacted for 3 hours. Thereafter, 30 parts by weight of phenol and the above-mentioned phenol / calcium hydroxide / water mixture were further added dropwise, and reacted at 80 ° C. for 2 hours. After cooling to 30 ° C., the mixture was neutralized with a 30% aqueous solution of p-toluenesulfonic acid. The neutralized product was dehydrated under reduced pressure, 170 parts by weight of water was removed, 500 parts by weight of furfuryl alcohol was added and mixed, and the insoluble matter in the resin was filtered with a membrane filter. The amount of water that this resin can contain was measured and found to be 35% by weight.

To 100 parts by weight of this thermosetting resin, 70% by weight of paratoluenesulfonic acid, 20% by weight of water,
After adding 0.5 parts by weight of a 10% by weight mixed solution and sufficiently stirring, the mixture was poured into a disk-shaped mold having a thickness of 2 mm, and defoamed under reduced pressure. Then
The resin was cured by heating at 50 ° C for 3 hours and at 80 ° C for 2 days. This thermosetting product is processed into a predetermined donut shape, and then heated in an organic firing furnace to 700 ° C at a heating rate of 2 to 5 ° C / hour in a nitrogen atmosphere, and then to a temperature of 5 to 20 ° C / hour. It was heated and baked at a speed of 1200 ° C., held at this temperature for 2 hours, and then cooled to obtain a carbon substrate having a diameter of 1.8 inches. The carbon substrate thus obtained had a Ra350 angstrom, a density of 1.5 g / cm ² , a Vickers hardness of 650 and an amorphous structure.

(Processing of Substrate Main Body) A fired carbon substrate was subjected to GCB (green silicon carbide abrasive) # 800, which is one of pulverized silicon carbide abrasive grains, using a 9B 5L double-sided polishing machine manufactured by SPEED FAM. Was used for lapping with a free abrasive grain method with a concentration of 4% by weight. The platen used was a cast iron platen. The polishing margin was 200 μm per side. The Ra of the obtained carbon substrate was 2 μm. Thereafter, the inner and outer diameters were trimmed to predetermined dimensions and chamfering (45 °) (chamfering) was performed using a chamfering machine SG-T manufactured by Shiba Giken.

However, in the above chamfering process, as shown in Table 1, in Examples 1 to 5 which are examples of the present invention, a DC power source (manufactured by Takasago Seisakusho) was used to apply an anode electric field to the carbon substrate and Example 6 was used. In Comparative Examples 1 and 2, grinding processing was performed without applying an electric field to Comparative Example 1 and 2.

In Examples 1 to 7 and Comparative Examples 1 and 2, iron fiber bond grindstones SD400 N100 Fx3 to SD800 N100 Fx3 manufactured by Shinto Brator Co., Ltd. were used as the grindstones. The coolant is ELID No. 3 made by Yushiro Chemical.
5% 3% aqueous solution with 3% NaOH added was used. Table 1 shows the current density, the coolant temperature, and the grindstone feed rate in the electrolytic treatment.

According to the execution results (grinding stone life, average surface roughness) in Table 1, in the present invention examples (Examples 1 to 6), the life of the grinding stone is improved and the surface roughness of the inner and outer peripheral end faces of the substrate body are respectively determined. It is recognized that it can be improved significantly.

The surface roughness Ra after processing is a value obtained by measurement under the following conditions using a stylus type surface roughness meter (manufactured by Tencor Co., Ltd .: model P2).

Measurement conditions Stylus tip radius: 5 μm (needle curvature radius) Stylus pressing pressure: 7 mg Measurement length: 250 μm × 8 places Trace speed: 2.5 μm / sec Cutoff: 1.25 μm (low pass filter)

[0075]

[Table 1]

Although the embodiment of the present invention has been described in detail with reference to the drawings, the specific configuration of the present invention is not limited to this embodiment, and the design can be changed without departing from the gist of the present invention. Etc. are included in the present invention. For example, the material of the substrate body to which the present invention is applied is not limited to carbon,
It may be Al alloy, Ti, or the like.

[0077]

As described above, according to the present invention, the grinding resistance of the inner and outer peripheral end faces of the substrate body by the grindstone is reduced, the life of the grindstone is improved, the grinding speed of the grindstone is improved, and the surface roughness of the inner and outer peripheral end faces is reduced. Can be planned.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a method of grinding a substrate according to the present invention.

FIG. 2 is a diagram showing the electrolytic treatment principle of FIG.

FIG. 3 is a schematic diagram showing a polarization phenomenon.

FIG. 4 shows G from the resin synthesis process to the core removal process.
It is a schematic diagram which shows a C substrate manufacturing process.

FIG. 5 is a schematic diagram showing a GC substrate manufacturing process from a pre-firing lapping step to a firing carbonization step.

FIG. 6 is a schematic view showing a GC substrate manufacturing process from the lapping step after firing to the completion of the substrate.

FIG. 7 is a schematic diagram showing a film structure of a hard disk according to an embodiment of the present invention.

FIG. 8 is a schematic diagram showing electrolytic current characteristics.

[Explanation of symbols]

 1 substrate 1A substrate body 22, 23 grindstone

Claims (3)

[Claims] 1. A method of manufacturing a substrate for a magnetic recording medium, which grinds the inner and outer peripheral end faces of a non-magnetic substrate body with a grindstone, wherein the grinding work is performed with the grindstone while an electric field is applied to the substrate body. Manufacturing method of substrate for magnetic recording medium. 2. The method for manufacturing a substrate for a magnetic recording medium according to claim 1, wherein an electrolyte solution is used as a coolant supplied during the grinding process with the grindstone. 3. The method for manufacturing a substrate for a magnetic recording medium according to claim 1, wherein the substrate body is made of carbon.