JPH10320764A - Magnetic recording medium substrate and method of manufacturing the same - Google Patents

Abstract

Abstract: [PROBLEMS] To provide a substrate for a magnetic recording medium in which the occurrence of microcracks is suppressed, texture can be easily applied, and the attraction force between the magnetic recording medium and the magnetic head is reduced, and a method for manufacturing the same. To do. A magnetic recording medium substrate obtained by grinding a substrate by ductile mode processing using a grindstone and having fan-shaped processing marks on both surfaces, wherein the processing marks are formed on one surface and the other surface of the substrate. A magnetic recording medium substrate characterized by forming a cross angle of 10 ° to 90 ° with the magnetic recording medium, wherein the surface of the substrate is ground by ductile mode processing to form fan-shaped processing marks on both surfaces of the substrate. A method for manufacturing a substrate for a recording medium, wherein the processing mark is formed on one side and the other side of the substrate by 10 to 9 days.
A method of manufacturing a substrate for a magnetic recording medium, wherein the substrate has a cross angle of 0 °.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a substrate for a magnetic recording medium using a brittle material and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, there has been a demand for a precision processing technique for a substrate made of a brittle material typified by ceramics and carbon, particularly an ultra-smooth processing technique. For example, substrates such as glass substrates, carbon substrates, and ceramic substrates have applications as substrates for magnetic recording media. Further, a silicon wafer or the like is used as a semiconductor material. Since ultra-smoothness is required for the above-mentioned substrate for a magnetic recording medium and a silicon wafer, these substrates are generally smoothed using free abrasive grains.

When a brittle material such as a glass substrate, a carbon substrate, a ceramics substrate, or a silicon wafer is polished using free abrasive grains in particular, microcracks may occur during polishing due to the brittleness of the substrate. Such cracks may cause a recording / reproducing error when the substrate is made into a magnetic recording medium, or induce corrosion of the substrate due to contaminants entering during polishing or the like or water condensing in a capillary during standing. Danger exists. For this reason, conventionally,
Generally, the polishing process is divided into multiple stages at the expense of productivity to reduce the occurrence of microcracks. In addition, polishing with loose abrasive grains has many artistic technical elements, and requires high skill to stabilize quality.

[0004] As another problem, there is a problem that a part of the abrasive grains remains in the polished substrate. This residue is difficult to completely remove even by washing. If a sputtered film is formed on the substrate with the abrasive particles remaining, a film defect due to the remaining abrasive particles will occur, and as a result, the magnetic head will be damaged. In addition, when the above substrate is polished by using free abrasive grains, polishing unevenness due to inhomogeneity of the material, that is, recesses (shallow pits) due to deep polishing of portions that are easily polished occurs. There is.

In order to solve such a problem, various methods for smoothing without using free abrasive grains have been studied. One of the methods is to perform smoothing by grinding in ductile mode processing using fixed abrasive grains. A method has been proposed (Hara et al., Proceedings of the 1992 Japan Society for Precision Engineering Autumn Meeting, pages 19 and 20). Grinding a brittle material such as a carbon substrate or a ceramic substrate by ductile mode processing is expected to be more preferable because the following effects can be expected. That is, in this method, 1) since the amount of individual abrasive grains biting into the substrate can be set to be equal to or less than the transition point between the ductility and brittleness of the substrate, the processing mode of the substrate can be controlled from brittle fracture to ductile (plastic) deformation center. The generation of microcracks is suppressed. 2) Since there is no need to use free abrasive grains, there is no danger of abrasive grains remaining on the substrate. 3)
Excellent flatness and low surface drooling at the edge 4) Fixed abrasives are minimally consumed, which greatly reduces the cost of consumable tools compared to disposable loose abrasives 5) Art There are advantages that there are few technical elements, process control and full automation are easy, and 6) a uniform ground surface can be obtained regardless of the presence or absence of material non-uniformity.

However, the above-mentioned Hara et al.
Since the grinding is performed with the cup wheel mounted on the PE ultra-precision grinding machine, the grinding marks have a multiple iris shape as shown in FIG. In such grinding marks, the grinding marks may intersect with each other in some places, and microcracks may occur at the overlapping points, or the density difference of the grinding marks appears in the radial direction. Unevenness occurs in the distribution of the residual internal stress or the work-affected layer. For this reason, the physical and chemical properties of the surface become non-uniform, which may cause a difference in the etching properties and adhesion of the surface, and may cause warpage. Also, in the case of grinding using a double-sided polishing machine with fixed abrasive grains, the grinding marks have a random cross shape, and the grinding marks have many intersections, which may cause microcracks. Furthermore, in the case of surface grinding using a cup wheel, the workpiece and the wheel working surface are in surface contact. Therefore, the cutting feed direction is at right angles to the contact surface, and the substrate to be processed and the wheel are easily damaged due to excessive grinding resistance in the direction of cutting, which is likely to cause grain breakage and cause deep scratches and microcracks on the substrate to be processed.

In the final step of manufacturing a conventional substrate for a magnetic recording medium, the substrate has a surface roughness Ra = 5 to 25 °.
A degree of smoothing (mirror finishing) is applied, and then the substrate is given a so-called texture. Since a substrate made of a brittle material such as carbon is liable to crack when mechanically textured, usually, a method of imparting texture using a tape or a slurry of abrasive grains to which abrasive grains are attached, or by sputtering. A method of providing a film having irregularities on the surface has been performed. However, such a method is troublesome because it cannot rely entirely on machines,
Alternatively, the load on the film forming apparatus increases, which is a hindrance to improving productivity. In addition, there is a problem regarding the application of the texture, how to suppress the attraction force between the magnetic recording medium and the magnetic head when the magnetic head is at rest.

[0008]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems, by suppressing the occurrence of microcracks, by easily giving a texture, and by reducing the attraction force between a magnetic recording medium and a magnetic head. An object of the present invention is to provide a magnetic recording medium substrate and a method for manufacturing the same, which are reduced.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, 1) When grinding the substrate surface, the cutting depth of each abrasive grain in the grindstone was reduced. The occurrence of microcracks is suppressed by performing grinding so that grinding marks are formed in a fan shape using a surface grinding machine while keeping the ductility of the substrate-brittle transition point or less,
2) If surface grinding is performed using the outer circumference of the straight wheel during grinding, the substrate to be processed and the wheel working surface make line contact, so that damage to the substrate to be processed and the wheel during processing is significantly improved. 3) Since the processing marks essentially exhibit the same function as the texture of the tape or the like, the processing marks can be used as the texture as they are, and 4) the cross-angle between the front side and the back side of the substrate. The present inventors have found that when a substrate having various processing marks is used as a medium, the total attraction force of the front surface and the back surface between the medium and the magnetic head is reduced, and the present invention has been completed.

That is, the gist of the present invention is that [1] a substrate obtained by grinding a substrate by ductile mode processing using a grindstone.
A magnetic recording medium substrate having fan-shaped processing marks on both surfaces, wherein the processing marks are 10 to 9 on one surface and the other surface of the substrate.
A magnetic recording medium substrate having a cross angle of 0 °, [2] the substrate according to [1], which is obtained by performing ductile mode processing in combination with electrolytic in-process dressing, [3]. Ra (surface roughness) is 2
The substrate according to the above [1] or [2], wherein the substrate has an Rp (projection height) of 4 to 300 [deg.], And the density of the processing marks in the orthogonal direction is 300 to 100000 / cm. The substrate according to any one of 1) to [3], [5]
The above [1] to [r], in which the relationship between the radius of the substrate (r ₁ ) and the radius of the processing mark (r ₂ ) is 100r ₁ ≧ r ₂ ≧ 2r _1.
[4] The substrate according to any one of [6], and the flatness is 10 μm.
m, the substrate according to any one of [1] to [5],
[7] The above [1] to wherein the material of the substrate is a brittle material
[6] The substrate according to any one of the above,

[8] The substrate according to the above [7], wherein the brittle material is carbon,

[9] A method for manufacturing a substrate for a magnetic recording medium, in which a surface of a substrate is ground by ductile mode processing to form fan-shaped processing marks on both surfaces of the substrate, wherein the processing marks are formed on one surface of the substrate and the other surface. A method for manufacturing a substrate for a magnetic recording medium, wherein the cutting angle is set to 0.05 to 20 μm.

[9] The production method according to the above,
[11] Grinding by ductile mode processing using electrolytic in-process dressing

[9] or the production method according to [10], [12] a loop rigidity of 150 N / μm
The above grinding using the above grinding device

[9]-[1
1] The method according to any one of the above.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION

1. The magnetic recording medium substrate of the present invention is a magnetic recording medium substrate obtained by grinding a substrate by ductile mode processing using a grindstone and having fan-shaped processing marks on both surfaces. The processing marks form a cross angle of 10 to 90 ° between one surface and the other surface of the substrate. The substrate to be ground in the present invention may be immediately after molding or immediately after firing, and has a Ra (surface roughness) of 0.05 to 20 μm, preferably 0.01 to 0.5 μm, so-called coarse grinding. Or may have finished intermediate grinding. The rough grinding and intermediate grinding of the substrate are not particularly limited, and may be performed by a commonly known method. That is, the substrate for a magnetic recording medium of the present invention is (1) a substrate obtained immediately after molding or immediately after firing and processed by the method of the present invention, and (2) a substrate immediately after molding or immediately after firing is roughly obtained by a conventional method. Grinding,
Any of those obtained by intermediate grinding and finish grinding by the method of the present invention, and those obtained by the method of the present invention by performing (3) intermediate grinding by a conventional method and finish grinding by the method of the present invention may be used. In the present specification, Ra and Rp are determined by using a stylus type surface roughness meter (manufactured by Tencor Co., Ltd .: model P2) under the following conditions in the direction perpendicular to the shape of the processing mark (the roughness or the like becomes maximum). Direction), and the value obtained by measuring by scanning the stylus in the direction.

Measurement conditions Stylus tip radius: 0.6 μm (radius of needle curvature) Stylus pressing pressure: 7 mg Measurement length: 250 μm × 8 places Trace speed: 2.5 μm / sec Cutoff: 1.25 μm (Low bass filter)

The substrate material to be ground is not particularly limited and may be a commonly used known material. However, in the present invention, the brittle material can be sufficiently exerted particularly when grinding a brittle material. Is preferred. Specific examples thereof include carbon, glass, ceramics, and silicon. Above all, carbon is excellent in grinding stability and low Ra can be obtained, so that the production method of the present invention can obtain particularly excellent effects when applied to a carbon substrate.

In the present specification, "ductile mode processing" refers to plastic fluid removal processing that does not involve generation of cracks even in a brittle material, that is, grinding processing characterized by no damage to the material instead of brittle fracture (crushing). Means Such processing technology always makes the cutting depth of individual abrasive grains into the material ductile-
This is achieved by keeping the temperature below the brittle transition point. The means for achieving this is not particularly limited,
Usually, a known method can be used. For example, many of the materials generally used for substrates for magnetic recording media, silicon wafers, and the like, including the brittle materials such as carbon, glass, ceramics, and silicon, have a ductile-brittle transition point (dc) of 2 to 2. Since it is 100 nm, the set cutting depth of the grindstone is preferably 0.05 to 20 μm, more preferably 0.1 to 10 μm, and particularly preferably 0.1 to 5 μm.
μm may be used. Here, the set depth of cut of the grindstone is preferably 0.05 μm or more from the viewpoint of device positioning accuracy, and is preferably 20 μm or less from the viewpoint of suppressing the grinding load and the occurrence of microcracks.

[0016] Furthermore, by forming an R (roundness) on the shoulder on the outer periphery of the wheel (fixed abrasive) in accordance with the set cutting depth of the grindstone, the ductility processing without micro cracks can be performed even if the set cutting depth of the grindstone is large. This is more preferable because a surface can be obtained. The shape of R and the like may be set so that the cutting depth of each abrasive grain is smaller than dc of the material to be ground. For example, in the formula shown below,

[0017]

(Equation 1)

(Where d _N is the depth of cut per rotation of the substrate to be processed, and is expressed by the following equation.

[0019]

(Equation 2)

Further, f is the amount of lateral feed of the wheel per one rotation of the substrate to be processed, Δ is the set cutting depth, R is the radius of curvature of the shoulder on the outer periphery of the wheel, d _g is the cutting depth of each abrasive grain,
a abrasive grains interval, V _w the workpiece substrate peripheral velocity, V _s is the wheel peripheral velocity, and D is the wheel diameter. It is sufficient to set d _g <dc.

By grinding as described above, a magnetic recording medium substrate in which the occurrence of microcracks is suppressed can be obtained. In addition, since fan-shaped processing marks are given, smoothing by grinding and texture processing of the substrate are simultaneously achieved,
Economically advantageous.

[0022] In the present specification, "fan-shaped" of a fan-shaped machining mark
Is a substantially concentric shape as schematically shown in FIG. The center of the concentric circle may be on the substrate or may be outside the substrate. Preferably, the radius r of the substrate
The relationship between ₁ and the radius r _{2 of the} processing mark satisfies r ₂ ≧ r ₁ , and is more preferably ₁₀₀ r from the viewpoint of workability of mounting a substrate to be processed (work) and processing accuracy of the apparatus.
_It satisfies the relationship of ₁ ≧ r ₂ ≧ 2r ₁ .

Further, by performing the grinding by ductile mode processing using electrolytic in-process dressing (hereinafter referred to as ELID), it is possible to perform more accurate and efficient grinding. Specifically, in the grinding device, the fixed abrasive is a metal bond wheel (the abrasive is fixed on the outer periphery of a straight wheel with a metal binder), and the electrode is installed so as to cover a part of the outer periphery of the wheel, An ELID type ductile working can be achieved by supplying an aqueous solution coolant containing an electrolyte between the outer peripheral surface of the wheel and the substrate to be processed, applying a positive electric field to the wheel side, and grinding while rotating both the substrate and the wheel.

As described above, the substrate for a magnetic recording medium of the present invention is obtained. Here, Ra of the obtained substrate is preferably 2 to 60 °, more preferably 4 to 40 °, and particularly preferably 8 to 30 °. The angle is preferably 2 ° or more from the viewpoint of grinding productivity, and is preferably 60 ° or less from the viewpoint of the flying characteristics of the head. The Rp of the obtained substrate is preferably 4 to 300 °, more preferably 12 to 300 °.
The angle is 250 °, particularly preferably 25 to 200 °. Here, in order to avoid the magnetic head from being attracted, the angle is preferably 4 ° or more.
Å The following is preferred. Further, the substrate for a magnetic recording medium of the present invention preferably has a flatness of 10 μm or less from the viewpoint of the floating running stability of the magnetic head. A more preferred value is 6 μm or less.

The density of the processing traces on the substrate obtained in the orthogonal direction is preferably 300 to 100000 / cm.
More preferably, the number is from 0.00 to 3000 / cm, and from 400 to 20
00 / cm is particularly preferred. It is preferably at least 300 / cm from the viewpoint of CSS (sliding) durability, and is preferably at most 100,000 / cm in order to avoid the magnetic head from being attracted. In this specification, the orthogonal direction of the processing trace is a direction of a straight line connecting the center P when the substrate is a circle and the center Q of a concentric circle forming a sector-like processing trace, as shown in FIG. .

Also, the magnetic recording medium substrate of the present invention has fan-shaped processing marks on both sides, and the processing marks form a cross angle of 10 to 90 ° between one surface and the other surface of the substrate. It is characterized by doing. Here, the cross angle is more preferably 30 to 90 °, particularly preferably 45 to 90 °, and the effect is the highest when it is 90 °. In addition,
The angle is preferably 10 ° or more from the viewpoint of avoiding head suction or positioning accuracy of the substrate during grinding. In this specification, the “cross angle” is an angle θ formed by tangent lines m and n of the processing traces at the intersection of the processing traces formed on the front surface and the back surface of the substrate, as shown in FIG.

Here, the relationship between the cross angle and the attraction force between the medium and the magnetic head will be described. Since a hard disk has recording layers on both sides, in a hard disk drive, magnetic heads are arranged on both sides of the disk. Generally, when the drive is stopped, the head comes into contact with the disk surface and stays still. At the time of startup, the disk rotates, and the head floats by air flowing between the head and the disk to perform recording and reproduction. If the suction force and the static friction coefficient at the interface between the head and the disk are high, the disk cannot rotate, causing a trouble. In recent years, due to the trend of miniaturization, thinning, and low power consumption, motor power has become smaller, and the above-mentioned troubles have increased. As a countermeasure, it is essential to reduce the attraction force and the static friction coefficient at the head / disk interface as much as possible. In the present invention, the load on the drive motor is reduced by preventing the sum of the contact areas of the head and the disk on the front surface, the back surface, and both surfaces when the head is stationary (at the time of landing). By shifting the arrangement of the fan-shaped processing marks that perform the texture function,
Care has been taken to avoid the generation of the largest contact area.

2. Regarding the manufacturing method of the present invention, the method of manufacturing a substrate for a magnetic recording medium of the present invention includes a substrate for a magnetic recording medium in which the surface of the substrate is ground by the above-described ductile mode processing to form fan-shaped processing marks on both surfaces of the substrate. Wherein the processing marks form a cross angle of 10 to 90 ° between one surface and the other surface of the substrate. In addition, it is preferable that the set depth of cut of the grindstone at the time of ductile mode processing is 0.05 to 20 μm from the viewpoint of the device positioning accuracy and the viewpoint of suppressing the grinding load and the occurrence of microcracks.

The set cutting depth of the grindstone is 0.05 to 20.
In order to achieve ductile mode processing at μm, the grinding device, abrasive grains, and the like must satisfy the following conditions. 1) Design and manufacture of a grinding wheel spindle with extremely high dynamic rigidity.
Radial and axial movement errors are 100 nm or less. 2) Design and manufacture of extremely high dynamic rigidity work support and motion system. Based on empirical rules, the loop stiffness between the processing machine tool and the workpiece is 150 N / μm (static stiffness) or more. 3) Dressing of abrasive binder to ensure high precision truing and moderate porosity of the wheel. Furthermore, it is desirable that the cutting edge height distribution of the individual abrasive grains on the wheel is not more than dc.

Therefore, the grinding device used in the present invention is not particularly limited as long as it satisfies the above conditions. Specifically, for example, an ultra-precision surface grinding device (HPG-2A) manufactured by Nissin Machinery Co., Ltd. is exemplified. Ultra-precision surface grinding machine (HPG-2A)
It has been developed for the purpose of ductile mode processing of brittle materials and has the following characteristics. 1) Radial and axial movement accuracy is 100 nm or less 2) Loop rigidity between the machine tool and the workpiece is 170 N / μ
m (static rigidity) 3) Truing accuracy is 100 nm Therefore, this ultra-precision surface grinding device (HPG-2A)
Satisfies all of the above device conditions.

In order to form a fan-shaped machining mark, for example, a substrate to be processed (work) is placed on a work mounting face plate (work table) of a work spindle so as not to include the rotation center of the work spindle, that is, r. _It may be mounted eccentrically so as to satisfy the relationship of ₂ ≧ r ₁ , and the face plate is rotated to give a minute cut to the straight wheel, and then the wheel may be traversed along the face plate. Eccentricity is 0,
That is, even if the work is attached to the center of the work table,
Non-intersecting processing marks can be given,
Since only one sheet can be attached, productivity is low, which is not preferable. According to the method of the present invention, since a plurality of works can be attached, it is advantageous in terms of productivity and reduction of grinding cost.

Further, in order to perform grinding so that a processing mark forms a cross angle of 10 to 90 ° between one surface and the other surface of the substrate, the setting position (angle) of the substrate at the time of front / back processing is shifted. Is achieved by Since the grinding is usually performed by single-sided processing, the above-mentioned measures can be easily taken.

Further, by performing the grinding in the ductile mode working together with the electrolytic in-process dressing (hereinafter referred to as ELID), it is possible to perform the grinding with higher precision and efficiency.

The grinding step in the present invention will be described with reference to FIG. Here, FIG. 5 is a schematic configuration diagram of an ultra-precision surface grinding device (HPG-2A). This apparatus is a rotary plane processing machine that performs traverse grinding using the outer circumference of a straight wheel. The NC controls two axes. That is, positioning of the X axis (traverse feed of the work table) and the Z axis (set depth of cut of the wheel).

The design features of this machine are: T-shaped X-axis and Z-axis planar arrangement, closed-loop positioning system without screws, 10 nm laser scale, VV sliding guide surface, low thermal expansion cast iron, standard straightness Straightness in-process correction by gauge. The performance is characterized by contour processing at a command resolution of 10 nm. The position of the correction wheel is X
By controlling with Z, it is possible to obtain a desired accurate shape. Further, in order to grind the grinding marks into a fan shape using the present apparatus, for example, as shown in FIG. 6, the substrate to be processed may be mounted on a work table.

In order to grind a brittle material without cracks (ductile mode grinding), it is necessary to keep the cutting depth of each abrasive grain below the ductile-brittle transition point (dc value). For that purpose, a high-rigidity and high-precision processing machine is required. This device has a grinding wheel shaft of 1300N / μm by itself
As described above, the worktable shaft alone satisfies the above-mentioned conditions at a 1000 N / μm or more and a loop rigidity of 150 N / μm or more. The run-out in the thrust direction of the work table, the radial run-out of the grinding wheel shaft, and the peripheral run-out of the grinding wheel after truing are all 100 nm or less. The positioning of the X axis and the Z axis is controlled by a laser scale having a resolution of 10 nm, and the set cutting depth can be suppressed to 100 nm or less.

The fixed abrasive grains (wheels) used for grinding are not particularly limited, and commonly used known abrasive grains are used.
The type of abrasive grains and the shape, grain size, bonding agent, and wheel shape differ depending on the processing margin (set depth of cut of the grindstone), so it cannot be said unconditionally. For example, the above grinding device (HP
G-2A), when the substrate is a carbon substrate, the degree of intermediate grinding is Ra 100 nm, and the processing margin is 20 μm / one side,
Industrial diamond abrasive grains are used as the abrasive grains (the average grain size of the abrasive grains is 1 to 5 μm, more preferably 1 to 2.5 μm), and a metal or the like is used as the bonding agent. When the ELID method is used, it is preferable to use a simple substance such as Fe (eg, cast iron), Cu, or Ni, or an alloy containing one or more of these, as the bonding agent. Further, other conditions in this case, such as the grinding wheel peripheral speed, the feed speed, the work table rotation speed, and the like are not particularly limited, and may be a commonly used known degree.

[0038]

EXAMPLES The present invention will be described below in more detail with reference to Production Examples, Examples and Comparative Examples, but the present invention is not limited to these Examples and the like. Production Example 1 A carbon substrate was produced by molding and pre-baking a furfuryl alcohol resin in a known manner. More specifically, it was manufactured as follows. 500 parts by weight of furfuryl alcohol, 400 parts by weight of 92% formaldehyde and 30 parts by weight of water were dissolved by stirring at 80 ° C. Then, a mixture 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 with stirring.
The reaction was performed at 80 ° C. for 3 hours. Thereafter, 80 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 to remove 170 parts by weight of water, 500 parts by weight of furfuryl alcohol was added and mixed, and the mixture was filtered with a membrane filter to remove insoluble components in the resin. The amount of water that the resin could contain was 35% by weight.

To 100 parts by weight of the thermosetting resin, 0.5 part by weight of a mixed solution of 70% by weight of paratoluenesulfonic acid, 20% by weight of water and 10% by weight of cellosolve was added. And the mixture was degassed under reduced pressure. Then, it was heated and cured at 50 ° C. for 3 hours and at 80 ° C. for 2 days. This thermosetting material is processed into a predetermined donut shape, and then heated to 700 ° C. in a nitrogen atmosphere in an organic baking furnace at a rate of 2 to 5 ° C./hour, and then heated to 5 to 20 ° C./hour. The resultant was heated and fired at a speed of 1200 ° C., kept at this temperature for 2 hours, and then cooled to obtain a carbon substrate having a diameter of 1.8 inches. The carbon substrate obtained in this manner has R
a 10 μm, density 1.5 g / cm ³ , Vickers hardness 6
50, the structure was amorphous.

Production Example 2 The carbon substrate obtained in Production Example 1 was polished using a 9B5L type double-side polishing machine (manufactured by Speed Farm), using GC (green silicon carbide abrasive) # 600 as pulverized silicon carbide abrasive grains, at a concentration of 4%. A lapping process was performed by a weight-% loose abrasive method. The platen used was a cast iron platen. The polishing margin was 300 μm per side. Ra of the obtained carbon substrate is 2
μm. After this, Shiba Giken chamfering machine S
According to GT, the inner and outer diameters were trimmed to predetermined dimensions, and chamfering (45 °) (hereinafter referred to as chamfering) was performed.

Production Example 3 The carbon substrate obtained in Production Example 2 was further lapped and polished under the following conditions. Using the same device as in Production Example 2, GC #
Polishing was carried out by a loose abrasive method with a concentration of 20% by weight using 4000 abrasive grains. Use a cast iron surface plate for the surface plate,
It was 50 μm per side. R of the obtained carbon substrate
a was 0.1 μm. Thereafter, chamfering was performed in the same manner as in Production Example 2.

Examples 1 to 4 The carbon substrate obtained in Production Example 3 was subjected to finish grinding by ductile mode processing to obtain a substrate for a magnetic recording medium. The main processing conditions are as follows. Grinding device: Ultra-precision horizontal surface grinding device (HPG-2A manufactured by Nisshin Kikai Seisakusho Co., Ltd.) Diameter of work table: 200 mm Number of rotations of work table: 530 rpm Wheel peripheral speed: 1260 m / min Wheel feed speed: 60 mm / min

Abrasive grain type / count: # 12000 diamond (average particle size: about 1.2 μm) (Shinto Breta Co., Ltd. iron fiber bond whetstone: SD
12000N100FX3) Coolant: ELIDNO. 2% of 35
Aqueous solution ELID power supply: Shinto Breta Co., Ltd., pulse power supply ED
P-10A Initial truing: # 200 diamond (average particle size of about 75 μm) (manufactured by Oriental Diamond Tool Laboratory: SD200)
Q75M) Initial dressing: 3A x 15 minutes Pulse (square wave) cycle: 4 microseconds

As shown in FIG. 7, the shoulder of the grinding wheel is adjusted to a generatrix shape by precision truing, and the cutting depth of each abrasive grain is adjusted to the ductile-brittle transition point (about 50) of the carbon substrate.
nm). The substrate was fixed by a vacuum chuck method using a plurality of vacuum suction holes provided on a work table. The surface was ground using a # 12000 wheel with 2 passes and a 1 μm pass with the set cutting depth of the grindstone being 3 μm. Next, the substrate was turned over and set so as to form a cross angle (θ) shown in Table 1, and the same grinding was performed. At this time, the work table and the end face of the substrate were marked so that the rotation angle could be understood. FIG. 6 shows a state in which the substrate to be processed is set on the work table, and FIG. 8 shows a mounting configuration of the ELID electrodes.

Examples 5 to 7 Both surfaces of the carbon substrate obtained in Production Example 3 were ground by ductile mode processing under the same conditions as in Examples 1 to 4 except for the following to obtain a substrate for a magnetic recording medium. Abrasive grain type / counter: # 8000 diamond (average particle size of about 1.2 μm) (Fuji Die Co., Ltd. iron-based bond whetstone, SD # 8000
N100M) Grinding was performed using a # 8000 wheel for 2 passes with a set depth of cut of the grindstone of 3 μm and 1 pass with 1 μm. Next, the substrate was turned over and set so as to form a cross angle (θ) shown in Table 1, and the same grinding was performed. At this time, the work table and the end face of the substrate were marked so that the rotation angle could be understood. The grinding wheel shoulder is precision truing, and the # 8000 wheel is trimmed into a generatrix shape as shown in FIG. 7, and the cutting depth of each abrasive grain is set at the ductile-brittle transition point (about 50
nm).

Comparative Example 1 A polishing tape of WA # 6000 manufactured by Nippon Micro Coating Co., Ltd. was used for the carbon substrate obtained in Production Example 3, a processing pressure of 1.5 kg / cm ² , a tape vibration of 300 reciprocations / minute, and a work rotation speed. Tape texture was performed at 50 rpm for a processing time of 15 seconds to obtain a substrate for a magnetic recording medium.

Comparative Example 2 Finish grinding was performed in the same manner as in Example 1 to obtain a substrate for a magnetic recording medium. However, the cross angle (θ) was 3 °.

The surface roughnesses Ra and Rp of the magnetic recording medium substrates obtained in the above Examples and Comparative Examples were measured for the front and back surfaces, respectively. Table 1 shows the results.

Further, the coefficient of static friction of the magnetic recording medium manufactured using the magnetic recording medium substrates obtained in the above Examples and Comparative Examples was measured to evaluate the error characteristics. Table 1 shows the results. The magnetic recording medium was obtained as follows. A Ti layer 32 having a thickness of 100 nm was provided on the magnetic recording medium substrate 31 by DC magnetron sputtering under the condition that the Ar gas pressure was 3 mTorr and the substrate temperature was kept at 180 ° C. On the Ti layer 32, a Cr layer 33 having a thickness of 40 nm was provided, and then a CoCrPtB-based alloy magnetic layer 34 having a thickness of 40 nm was provided. When forming the layers 32 to 34, a bias voltage of -200 V was applied to the substrate. Further, a protective layer (glassy carbon layer) 35 is formed on the CoCrPtB-based alloy magnetic layer 34 by DC magnetron sputtering.
A thickness of 5 nm was provided. Thereafter, a Fomblin Z03 solution was applied by dip coating to provide a lubricating layer 38 having a thickness of 15 ° to obtain a magnetic recording medium as shown in FIG.

Static friction coefficient: The static friction coefficient is a coefficient of static friction (μ _S ) between the magnetic recording medium and the head at the end of 20,000 cycles repeated ON / OFF of the vibration of the magnetic recording medium under the following conditions. Is measured and evaluated using this value. ON / OFF time: 5 seconds / 5 seconds Head: 50% Altics slider Head load: 3.5 g Rotation speed: 4500 rpm Measurement radius: 12 mm Head flying height: 2.8 μ inch

Error characteristic: The error characteristic is PROQUIP
The evaluation was performed using a MG-1507 apparatus manufactured by the Company, a 70% slider head, and a recording density of 51 KFC2. The slice level was 70%, and the number of missing errors of less than 15 bits was counted. A pass of less than 15 per medium was indicated as a pass rate (percentage) out of 36 sheets. S: 80% or more A: 60% or more and less than 80% B: 30% or more and less than 60% C: less than 30%

[0052]

[Table 1]

From the above results, a magnetic recording medium substrate having fan-shaped processing marks on both surfaces obtained by grinding the substrate by ductile mode processing using a grindstone, wherein the processing marks are on one surface of the substrate The magnetic recording medium obtained using the magnetic recording medium substrate having a cross angle of 10 to 90 ° with the other surface has a small static friction coefficient and good error characteristics (Example 1). -Example 7). On the other hand, in the example in which the substrate was not ground by the ductile mode processing and the texture was given using a polishing tape (Comparative Example 1), and the example in which the cross angle was out of the range of 10 to 90 ° (Comparative Example 2), the static friction was observed. The coefficient was large. Further, in Comparative Example 1, the error characteristics were inferior. Further, according to the production method of the present invention,
A good substrate with small Ra and Rp could be obtained.

[0054]

The substrate for a magnetic recording medium according to the present invention has a low coefficient of static friction when formed into a medium, and the attraction force between the medium and the head is reduced. Further, the production method of the present invention suppresses the occurrence of microcracks and can easily impart texture.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a processing mark of a multiple iris shape.

FIG. 2 is a schematic diagram showing a fan shape.

FIG. 3 is a diagram showing a direction perpendicular to a processing trace of a substrate in the present invention.

FIG. 4 is a diagram showing a “cross angle” in the present invention. Solid lines indicate processing marks on the front surface of the substrate, and broken lines indicate processing marks on the back surface of the substrate.

FIG. 5 is a schematic configuration diagram of an apparatus for carrying out an example of the production method of the present invention.

FIG. 6 is a schematic diagram showing a setting state of a substrate to be processed set on a work table in the grinding apparatus of FIG. 5;

FIG. 7 is a schematic diagram showing a generatrix shape of a shoulder portion of a grinding wheel.

FIG. 8 is a schematic diagram showing an attachment configuration of an ELID electrode.

FIG. 9 is a sectional view of a main part of a magnetic recording medium obtained by using the substrate for a magnetic recording medium of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Work table 2 Grinding wheel 3 Correction wheel 4 Chuck 5 Slide base 6 Spindle / hydrostatic bearing 7 Low expansion material 8 Coolant supply unit 9 Workpiece (substrate to be processed) 11 Gap adjusting screw 12 Insulator 13 Electrode 14 Grindstone 21 Abrasive grain Coating layer NC Numerical controller PI Proportional / integral controller a Pressure control servo valve b Pressure oil source c Hydraulic actuator d Laser scale (resolution 10 nm) 31 Magnetic recording medium substrate 32 Ti layer 33 Cr layer 34 CoCrPtB-based alloy magnetic layer 35 Protective layer 38 Lubricating layer

Claims (12)

[Claims] 1. A magnetic recording medium substrate obtained by grinding a substrate by ductile mode processing using a grindstone and having fan-shaped processing marks on both surfaces, wherein the processing marks are formed on one surface of the substrate and the other surface. A substrate for a magnetic recording medium, wherein the substrate has a cross angle of 10 to 90 ° with the surface. 2. The substrate according to claim 1, which is obtained by performing ductile mode processing in combination with electrolytic in-process dressing. 3. The substrate according to claim 1, wherein Ra (surface roughness) is 2 to 60 ° and Rp (projection height) is 4 to 300 °. 4. The processing mark has a density of 300 to 10 in the orthogonal direction.
The substrate according to any one of claims 1 to 3, wherein the number is 0000 lines / cm. 5. The radius of the substrate (r ₁ ) and the radius of the processing mark (r)
The substrate according to any one of claims 1 to 4, wherein the relationship with ₂ ) is 100r ₁ ≧ r ₂ ≧ 2r ₁ . 6. The method according to claim 1, wherein the flatness is 10 μm or less.
5. The substrate according to any one of 5. 7. The substrate according to claim 1, wherein the material of the substrate is a brittle material.
6. The substrate according to any one of 6. 8. The substrate according to claim 7, wherein the brittle material is carbon. 9. A method of manufacturing a substrate for a magnetic recording medium, wherein a surface of a substrate is ground by ductile mode processing to form fan-shaped processing marks on both surfaces of the substrate, wherein the processing marks are formed on one surface of the substrate. And forming a cross angle of 10 to 90 ° with the other surface. 10. The set depth of cut of the grinding wheel is 0.05 to 0.05.
The method according to claim 9, wherein the thickness is 20 μm. 11. The manufacturing method according to claim 9, wherein the grinding is performed by ductile mode processing using electrolytic in-process dressing. 12. The method according to claim 9, wherein the grinding is performed using a grinding device having a loop rigidity of 150 N / μm or more.