WO2014104376A1

WO2014104376A1 - Method for producing glass substrate for magnetic disk and method for producing magnetic disk

Info

Publication number: WO2014104376A1
Application number: PCT/JP2013/085291
Authority: WO
Inventors: 太志長田; 智石井; 順平深田
Original assignee: Hoya株式会社
Priority date: 2012-12-31
Filing date: 2013-12-31
Publication date: 2014-07-03
Also published as: CN104823240B; JP5704777B2; MY169422A; CN104823240A; JPWO2014104376A1; SG11201505083VA

Abstract

The present invention provides a method for producing a glass substrate for a magnetic disk which is capable of producing a glass substrate for which flatness of the substrate after grinding processing by fixed abrasive grains is superior, and which is of high quality. This method for producing a glass substrate for a magnetic disk uses a lubricating fluid, and a pair of top and bottom platens for which fixed abrasive grains including diamond particles have been deployed on grinding surfaces thereof, and while supplying the lubricating fluid between the platens and the glass substrate, sandwiches both main surfaces of the glass substrate with the top and bottom platens so as to perform grinding at the same time. A sheet-like glass plate produced with a float glass process is used for the glass substrate, and on one of the main surface sides has a top portion of high tin content. The grinding step is set so that a difference in processing speed occurs between the top platen-side and the bottom platen-side, and the main surface side that has a top portion of higher tin content in the glass substrate is set on the platen side of slower processing speed and grinding is performed.

Description

Manufacturing method of glass substrate for magnetic disk and manufacturing method of magnetic disk

The present invention relates to a method for manufacturing a glass substrate for a magnetic disk mounted on a magnetic disk device such as a hard disk drive (HDD) and a method for manufacturing a magnetic disk.

There is a magnetic disk as one of information recording media mounted on a magnetic disk device such as a hard disk drive (HDD). A magnetic disk is configured by forming a thin film such as a magnetic layer on a substrate, and an aluminum substrate has been conventionally used as the substrate. However, recently, in response to the pursuit of higher recording density, the ratio of the glass substrate capable of narrowing the distance between the magnetic head and the magnetic disk as compared with the aluminum substrate is gradually increasing. Further, the surface of the glass substrate is polished with high accuracy so as to increase the recording density so that the flying height of the magnetic head can be reduced as much as possible. In recent years, there has been an increasing demand for HDDs with higher recording capacity and lower prices. In order to achieve this, it is necessary to further improve the quality and cost of glass substrates for magnetic disks. It is coming.

As described above, high smoothness on the surface of the magnetic disk is indispensable for reducing the flying height (flying height) necessary for increasing the recording density. In order to obtain a high smoothness on the surface of the magnetic disk, a substrate surface with a high smoothness is required in the end. Therefore, it is necessary to polish the glass substrate surface with high accuracy. In order to produce such a glass substrate, after adjusting the plate thickness and reducing the flatness (flatness) by grinding (lapping) processing, further polishing processing is performed to reduce surface roughness and microwaviness. High smoothness on the main surface has been realized.

By the way, conventionally, a grinding method using fixed abrasives using a diamond pad has been proposed in a grinding (lapping) process (for example, Patent Document 1) using loose abrasive grains (for example, Patent Document 2). A diamond pad is an agglomerate in which diamond particles or some diamond particles are hardened with a binder such as glass, ceramic, metal, or resin, and fixed using a support material such as resin (for example, acrylic resin). The obtained pellets are pasted on a sheet. In addition to this, a resin layer containing diamond may be formed on the sheet, and then a groove may be formed in the resin layer to form a protrusion. In addition, although the diamond pad said here is not necessarily a general name, it shall be called "diamond pad" for convenience in this specification.

In conventional loose abrasive grains, abrasive grains with a distorted shape are present between the surface plate and the glass and are non-uniform, so if the load on the abrasive grains is not constant and the load is concentrated, the surface of the surface plate Because of the low elasticity of cast iron, deep cracks enter the glass, the work-affected layer is deep, and the processing surface roughness of the glass also increases, so a large amount of removal was required in the subsequent mirror polishing process. It was difficult to reduce processing costs. In contrast, in grinding with a fixed abrasive using a diamond pad, the abrasive grains are uniformly present on the surface of the sheet, so that the load is not concentrated, and in addition, the abrasive is fixed to the sheet using resin. Therefore, even if a load is applied to the abrasive grains, the high elastic action of the resin fixing the abrasive grains makes the cracks (deformed layer) on the processed surface shallow, and the processed surface roughness can be reduced. The load on the machine (such as machining allowance) is reduced, and processing costs can be reduced.
After completion of this grinding (lapping) step, mirror polishing for obtaining a highly accurate plane is performed.

JP 2001-6161 A JP 2012-209010 A

As described above, according to the grinding method using the fixed abrasive using the diamond pad, the surface roughness of the processed surface can be reduced, the load on the subsequent mirror polishing process is reduced, and the processing cost of the glass substrate is reduced. Although reduction is possible, according to the study of the present inventors, it has been found that there are the following problems.
That is, both sides by fixed abrasive grains using a conventional diamond pad as disclosed in Patent Document 2 directly on a glass substrate obtained by cutting a sheet-like plate glass manufactured by the float process into a predetermined shape. When simultaneous grinding is performed, the flatness after processing deteriorates, and there are cases where sufficient smoothness cannot be achieved when a magnetic disk is obtained.

Note that mirror polishing is performed after the grinding, but the allowance for this mirror polishing is very small, and it is difficult to improve the deterioration of flatness caused by the grinding. Therefore, it is necessary to sufficiently reduce the flatness of the glass substrate by grinding.

The present invention has been made to solve such a conventional problem, and its purpose is to produce a high-quality glass substrate in which the flatness of the substrate after processing is good in grinding processing with fixed abrasive grains. It is to provide a method for producing a glass substrate for a magnetic disk, and a method for producing a magnetic disk using the glass substrate obtained thereby.

As a result of investigating the cause of deterioration in flatness after processing when performing double-sided simultaneous grinding with fixed abrasive using a conventional diamond pad, the present inventor has found that the tin content of the glass substrate is large after grinding. The surface roughness of the main surface side having the surface layer portion was larger than that of the main surface on the opposite side. That is, when a difference in surface roughness occurs between the two main surfaces of the glass substrate due to grinding, it is considered that the warpage of the substrate occurs due to a residual stress difference due to the Twiman effect.

In addition, the sheet-like plate glass manufactured by the float process has the surface layer part with much tin content on the one main surface side derived from the manufacturing method. In the present specification, hereinafter, the main surface having a surface layer portion with a high tin content of the glass substrate is simply referred to as a “tin surface” for the sake of convenience, and the main surface with a very low tin content on the opposite side is simply referred to as “non-surface”. It will be referred to as the “tin surface”.

As a result of further investigation, the present inventors have found that, in the case of a glass substrate using a plate glass manufactured by the float process, the processing speed of the tin surface is faster than that of the non-tin surface in the grinding with the fixed abrasive. . Further, using a pair of upper and lower surface plates in which fixed abrasive grains such as diamond particles are arranged on the grinding surface, while supplying a lubricating liquid between the surface plate and the glass substrate, In the double-side simultaneous grinding process in which the two main surfaces of the glass substrate are sandwiched, the surface roughness of the surface to be processed increases generally when the processing speed is high. In addition, when the tin surface side of a glass substrate with a high processing speed is processed with a surface plate with a high processing speed (for example, an upper surface plate), the surface roughness of both main surfaces of the glass substrate is increased due to the synergistic effect of increasing the processing speed. The difference becomes large, and as a result, it is presumed that the substrate warps.

The present invention has been made as a result of further intensive studies based on the above findings obtained by the study of the present inventors.
That is, in order to solve the above problems, the present invention has the following configuration.
(Configuration 1)
Using the lubricating liquid and a pair of upper and lower surface plates in which fixed abrasive grains containing diamond particles are disposed on the grinding surface, while supplying the lubricating liquid between the grinding surface and the glass substrate, A method of manufacturing a glass substrate for a magnetic disk including a grinding process for grinding with both upper and lower surface plates sandwiching both main surfaces of the glass substrate, wherein the glass substrate is a sheet-shaped plate glass manufactured by a float method. It is a glass substrate cut into a shape, and has a surface layer portion having a higher tin content than the other main surface side on one main surface side, and the grinding process is performed on the upper surface plate side and the lower surface plate The main surface having a surface layer portion with a high tin content of the glass substrate is ground and ground so that a difference in processing speed occurs between the side and the surface plate side of the slower processing speed. Manufacture of glass substrates for disks Law.

(Configuration 2)
2. The method for producing a glass substrate for a magnetic disk according to Configuration 1, wherein the substrate is ground so that the flatness of the substrate after grinding is within 2.5 [mu] m.
(Configuration 3)
The method for producing a glass substrate for a magnetic disk according to Configuration 1 or 2, wherein grinding is performed so that a difference in surface roughness between both main surfaces of the substrate after grinding is 0.01 μm or less in Ra.

(Configuration 4)
4. The method of manufacturing a glass substrate for a magnetic disk according to any one of configurations 1 to 3, wherein the surface roughness of both main surfaces of the substrate after grinding is 0.130 μm or less in Ra.
(Configuration 5)
Any one of configurations 1 to 4, wherein when a plurality of glass substrates are simultaneously ground, the main surfaces of the glass substrate having the surface layer portion having a large tin content are all set in the same direction. A method for producing a glass substrate for magnetic disk according to claim 1.

(Configuration 6)
6. The magnetism according to any one of configurations 1 to 5, wherein on the surface plate side having a relatively high processing speed, the protruding amount of the fixed abrasive is made larger than that on the surface plate side having a relatively low processing speed. A method for producing a glass substrate for a disk.
(Configuration 7)
The grinding process includes a first stage of roughening the surface of the glass substrate with a load higher than a load for grinding, and after the first stage, the glass with a load lower than the load of the first stage. A method for producing a glass substrate for a magnetic disk according to any one of Structures 1 to 6, further comprising a second step of grinding the surface of the substrate.

(Configuration 8)
8. The method for manufacturing a glass substrate for a magnetic disk according to any one of configurations 1 to 7, wherein a processing speed in the grinding processing is 3.0 μm / min to 9.0 μm / min.
(Configuration 9)
A magnetic disk manufacturing method comprising forming at least a magnetic recording layer on a magnetic disk glass substrate manufactured by the method for manufacturing a magnetic disk glass substrate according to any one of Structures 1 to 8.

ADVANTAGE OF THE INVENTION According to this invention, the deterioration of the flatness of the board | substrate in the grinding process using the conventional fixed abrasive can be improved. Thereby, it is possible to manufacture a high-quality glass substrate.
Furthermore, a highly reliable magnetic disk can be obtained by using the glass substrate obtained by the present invention.

It is a schematic sectional drawing which shows the structure of the diamond pad used for this invention. It is a schematic diagram for demonstrating the state at the time of a grinding process. It is a figure which shows an example of the sequence of the applied load in a grinding process.

Hereinafter, embodiments of the present invention will be described in detail.
The present invention uses a lubricating liquid and a pair of upper and lower surface plates in which fixed abrasive grains containing diamond particles are arranged on the grinding surface, as in configuration 1 above, and the lubricating liquid is mixed with the surface plate. A method of manufacturing a glass substrate for a magnetic disk including a grinding process of grinding between both main surfaces of the glass substrate with the pair of upper and lower surface plates while supplying between the glass substrates, A glass substrate obtained by cutting a sheet-like plate glass produced by a float method into a predetermined shape, and has a surface layer portion having a higher tin content than the other main surface side on one main surface side, and the grinding process The main surface having a surface layer portion with a large tin content of the glass substrate on the surface plate side on which the processing speed is lower so that a difference in processing speed occurs between the upper surface plate side and the lower surface plate side. It is characterized by setting and grinding A process for producing a glass substrate for a magnetic disk. Further, as in the above configuration 2, it is preferable to perform grinding so that the flatness of the substrate after grinding is within 2.5 μm.

A glass substrate for a magnetic disk is usually manufactured through a rough grinding process (rough lapping process), a shape processing process, a fine grinding process (fine lapping process), an end surface polishing process, a main surface polishing process, a chemical strengthening process, and the like. .
In the method for producing a glass substrate for a magnetic disk of the present invention, a glass substrate cut out to a predetermined size from a sheet-like glass produced by a float process is used. As explained before, the sheet-like plate glass produced by the float process has a surface layer portion with a large tin content on one main surface side due to the production method. The present invention solves a specific problem in the case of using a glass substrate obtained from a plate glass produced by this float process.

Next, this glass substrate is subjected to grinding (lapping) for improving dimensional accuracy and shape accuracy. This grinding process normally uses a double-sided lapping machine to grind the main surface of the glass substrate using hard abrasive grains such as diamond. By grinding the main surface of the glass substrate in this way, a predetermined plate thickness and flatness are processed, and a predetermined surface roughness is obtained.

The present invention relates to the improvement of this grinding process. The grinding process in the present invention is a grinding process using fixed abrasive grains containing diamond particles. For example, in a double-sided lapping device, the grinding process is held by a carrier between an upper surface plate and a lower surface plate each having a diamond pad attached thereto. The glass substrates are brought into close contact with each other, and both the main surfaces of the glass substrate are ground simultaneously by moving the glass substrate and the upper and lower surface plates relatively while holding the glass substrate with a predetermined pressure by the upper and lower surface plates. At this time, a lubricating liquid (coolant) is supplied to cool the working surface or to promote the processing.

The diamond pad 1 which is a grinding tool (fixed abrasive wheel) used in the present invention is schematically shown in FIG. 1, but some diamond particles 5 (see FIG. 2) are made of glass, ceramic, metal, Or the pellet 4 which fixed the aggregate 3 hardened with binders, such as resin, using support materials, such as resin (for example, acrylic resin etc.), is affixed on the sheet | seat 2. FIG. Of course, the configuration shown in FIG. 1 is merely an example, and the present invention is not limited to this. For example, a diamond pad in which a resin layer containing diamond is formed on a sheet and then a groove is formed in the resin layer to form a protrusion may be used. The size of each diamond particle contained in the aggregate is preferably 1 to 5 μm in average particle size.

It is possible to manufacture the aggregates having different particle diameters (average particle diameters) and abrasive density in the resin. In the present embodiment, the case where the diamond fixed abrasive is the aggregate will be described. Therefore, in the present invention, when it is referred to as diamond fixed abrasive grains, unless otherwise specified, it means the above-mentioned aggregate, and when it is referred to as the average particle diameter of diamond abrasive grains and the abrasive density. , And mean aggregate particle size and aggregate density in the pellets.
However, the present invention is not limited to the case where the diamond fixed abrasive is the aggregate. It is also possible to use a diamond pad in which the diamond fixed abrasive is not an aggregate but a single diamond particle.

As described above, in the grinding processing in the present invention, in the double-side simultaneous grinding processing, a difference in processing speed is caused between the upper surface plate side and the lower surface plate side, and the glass substrate is placed on the surface plate side with the lower processing speed. A tin surface having a surface layer portion with a high tin content is set and ground.
According to the present invention, for example, processing can be performed so that the flatness is improved as compared with the case where the tin surface of the glass substrate is set on the surface plate having the higher processing speed. Then, it is possible to perform grinding so that the flatness of the substrate after grinding is within 2.5 μm.

As explained before, in the case of a glass substrate using plate glass manufactured by the float process, in grinding with fixed abrasive grains, the tin surface has a higher processing speed than the non-tin surface, and the surface roughness after grinding has been reduced. Becomes bigger. Therefore, in the present invention, by setting the tin surface of the glass substrate on the side of the surface plate having the lower processing speed and grinding, the surface roughness of the substrate after the grinding processing becomes approximately the same on both main surfaces. Can be processed. As a result, it is possible to prevent the substrate from warping after grinding, and a glass substrate with good flatness can be obtained.

For example, when lowering the processing speed on the lower surface plate side of the upper and lower surface plates as compared with the processing speed on the upper surface plate side, it is preferable to set and grind the tin surface of the glass substrate on the lower surface plate side. On the other hand, when the processing speed on the upper surface plate side is slower than the processing speed on the lower surface plate side, it is preferable to set and grind the tin surface of the glass substrate on the upper surface plate side.

In the grinding processing in the present invention, it is necessary to set so that a difference in processing speed occurs between the upper surface plate side and the lower surface plate side in the double-side simultaneous grinding processing with fixed abrasive grains. If the processing speed is the same on the upper and lower surface plate sides, a difference in surface roughness due to the difference in processing speed between the tin surface and the non-tin surface of the glass substrate occurs on both main surfaces. For this reason, it is not possible to prevent the warpage of the substrate.

The difference in processing speed between the upper surface plate side and the lower surface plate side is preferably set so that the difference in processing speed between the tin surface and the non-tin surface of the glass substrate can be offset as much as possible. In the case of a glass substrate using plate glass manufactured by the float process, the processing speed of the tin surface and the non-tin surface is about 10 to 20% faster than that of the tin surface. It is preferable to set a difference in processing speed between the upper surface plate side and the lower surface plate side so that the difference in surface roughness between the two main surfaces of the generated substrate can be substantially offset. That is, it is preferable that the processing speed of the surface plate for processing the tin surface side is 10 to 20% slower than the opposite side.

The processing speed on the upper and lower surface plate side is determined by, for example, rotation of the work carrier, revolution of the work carrier determined by the rotation speed of the upper and lower surface plate, the rotation speed of the sun gear (sun gear) and the rotation speed of the internal gear (internal gear), etc. It is possible to adjust. Therefore, by adjusting these on the upper and lower surface plate sides, respectively, it is possible to set so that a desired processing speed difference occurs between the upper surface plate side and the lower surface plate side.

In the present invention, in order to obtain a glass substrate with good flatness, it is preferable to perform grinding so that the flatness of the substrate after grinding is within 2.5 μm. More preferably, it is ground so as to be within 2.0 μm. If the flatness of the substrate after grinding is greater than 2.5 μm, it is difficult to improve the flatness by subsequent polishing. The flatness of the substrate can be measured by the method described in the examples described later.

In the grinding process of the present invention, the tin surface of the glass substrate is set on the surface plate with the slower processing speed as described above, and the difference in surface roughness Ra between the two main surfaces of the substrate after grinding ( It is desirable to perform grinding so that ΔRa is within 0.01 μm. As a result, the flatness of the substrate after grinding can be made within 2.5 μm. More preferably, grinding is performed so that the difference (ΔRa) in the surface roughness Ra between the two main surfaces of the substrate after grinding is within 0.005 μm. As a result, the flatness of the substrate after the grinding can be further improved within 2.0 μm. The surface roughness of the substrate can be measured by the method described in the examples described later.

In the present invention, it is preferable that the surface roughness of both main surfaces of the glass substrate after the grinding process is 0.130 μm or less in terms of Ra. Thus, the processing load of the subsequent polishing process can be reduced by keeping the roughness of the finish by the grinding process low.

Usually, in manufacturing a glass substrate for a magnetic disk, a plurality of glass substrates (for example, about 100 in one batch) are ground simultaneously, but the tin surface of the plurality of glass substrates is placed on the surface plate side having a lower processing speed. It is preferable to perform processing by setting so that all are in the same direction. Thereby, the flatness of all the glass substrates after processing can be finished satisfactorily.

By the way, when performing grinding processing with a fixed abrasive using a diamond pad directly on a substrate having a mirror surface glass surface such as a plate glass manufactured by a float process, the substrate surface is a mirror surface. The diamond abrasive grains do not easily penetrate the surface of the substrate and slip, so that a time during which grinding cannot be performed tends to occur.

In the present invention, on the surface plate side where the processing speed is relatively high, it is preferable that the protruding amount of the fixed abrasive is relatively larger than that on the surface plate side where the processing speed is low. That is, on the surface plate side where the processing speed is relatively high, the protruding amount of the fixed abrasive is made relatively larger than the surface plate side where the processing speed is low, and the non-tin surface is processed on the surface plate side. It is preferable to do.
In the present invention, since the main surface of the input substrate is a mirror surface, sludge tends to accumulate on the surface of the fixed abrasive grindstone. In order to improve productivity, the present inventor has found that it is preferable to control the protruding amount of the fixed abrasive with an upper and lower surface plate when processing a large number of substrates using the same fixed abrasive wheel. .
In other words, the amount of protrusion of the fixed abrasive on the surface plate side with a relatively high processing speed is set to be relatively larger than that on the surface plate side with a low processing speed, so that a large number of substrates are processed between the substrates. The variation in flatness can be improved. This is considered to be due to the fact that the fixed abrasive grains bite into the non-tin surface at the same time by improving the biting characteristics of the fixed abrasive grains at the initial stage of grinding on the non-tin surface side that is difficult to be ground.

The protruding amount of the above-mentioned fixed abrasive can be measured as follows.
10%, 50%, 90% from the inner circumference when the distance from the inner circumference to the outer circumference is defined as 100% with respect to the grinding wheel of the upper and lower surface plates before grinding (usually formed in a disk shape). A total of 6 samples (pad pieces) each having a size of 2.5 mm × 2.5 mm are cut out from the% positions. For each of these six samples, for example, five arbitrary fixed abrasive grains are selected from an observation image obtained using, for example, a laser microscope, and the height difference between the abrasive grains and the resin portion around the abrasive grains is measured. The average value of the height difference of the abrasive grains is defined as the protruding amount of the fixed abrasive grains of the grinding wheel.

In order to adjust the protruding amount of the fixed abrasive, for example, dressing can be performed. Specifically, for example, a double-sided grinding device used for grinding is also applied to dressing processing, and a grinding wheel with an appropriate thickness variation is applied to the surface of a grinding wheel such as a diamond pad arranged on an upper and lower surface plate. The dressing process can be performed in a state where the upper and lower surface plates of the double-side grinding apparatus are rotated. The material of the grindstone used for the dressing process is not particularly limited, but for example, an alumina grindstone is suitable. In this case, the dressing process may be performed step by step using a plurality of grindstones having different thickness variations.
In order to obtain a stable effect, the difference in the protruding amount of the fixed abrasive grains on the upper and lower surface plates is preferably 0.1 μm or more. Further, if the difference in the protruding amount of the fixed abrasive is larger than 10 μm, there is a possibility that scratches may occur on the surface plate side where the protruding amount is large.

Further, in the grinding process in the present invention, the first stage of roughening the surface of the glass substrate with a load higher than the load for grinding, and after the first stage, lower than the load of the first stage. It is also preferable to perform the grinding process by the second stage of grinding the glass substrate surface with a load.
In order to directly grind the mirror glass surface with the diamond pad, first, it is necessary to apply a higher load to the glass surface than during normal grinding in order to cause the diamond abrasive grains to penetrate into the glass substrate surface. The higher the load, the deeper the cutting depth of the abrasive grains, the rougher the glass surface can be made (roughened). The first step is a step of roughening the surface of the mirror glass by causing the diamond abrasive grains to penetrate.

After the glass surface is roughened in the first stage during such processing, there is no need for a high load on the grinding process. Rather, the original condition is achieved by reducing the load and reducing the cutting depth of the abrasive grains. Grinding (main processing) is performed. The second stage is a stage where this main processing is performed. FIG. 2 is a diagram for explaining a state at the time of grinding, and shows a state in which the diamond abrasive grains 3 bite into the glass substrate 10 and are ground (image diagram).

By performing the grinding process having the first stage and the second stage as described above, it is possible to perform the grinding process without reducing the machining speed. Furthermore, by adjusting the detailed conditions of the grinding process, it is possible to keep the surface roughness of the finished processed surface low.
FIG. 3 is a diagram showing an example of a sequence of applied loads in this grinding process.
The horizontal axis in FIG. 3 is time, and the vertical axis is applied load. The load is gradually increased from the start, and the constant time (t1) is maintained at the time when the load reaches P1 (point A). This is the first stage, and the glass surface is roughened.
Note that the application of the load up to the point A may be performed in multiple steps. That is, the load may be increased stepwise (stepwise in the sequence).
Then, the load is gradually decreased from the point B, and a constant time (t2) is maintained at a point (point C) when the normal grinding load P2 is reached, and the grinding process is ended at the point D. This period is the second stage, which is the stage where the main machining is performed.

The load P1 in the first stage is preferably in the range of 130 to 200 g / cm ² . If the load P1 is smaller than 130 g / cm ^{2, the} time during which grinding cannot be performed cannot be sufficiently shortened, and the processing speed decreases. On the other hand, if the load P1 is larger than 200 g / cm ^{2, the} cutting time due to the abrasive grains becomes too deep and a lot of scratches are generated, so that it is necessary to increase the machining allowance for the main processing and the subsequent polishing step. Will become longer.
The load P2 in the second stage is preferably in the range of 50 to 120 g / cm ² . By adjusting the grinding conditions, the surface roughness of the processed surface can be kept low.
Moreover, it is preferable that P1 / P2 = 3.0 or less. This makes it possible to achieve low roughness after grinding in addition to improving the processing speed.

Further, the first stage load application speed (inclination k) from the start of processing to the point A (load P1) is preferably 0.5 to 15 g / (cm ² · sec). When the slope k is smaller than 0.5g / (cm ² · sec) (applying speed is slow), the abrasive grains do not slip and bite due to the low load, rather the abrasive grains wear and the grinding ability deteriorates. It is not preferable. On the other hand, when the inclination k is greater than 15 g / (cm ² · sec) (applying speed is fast), a sharp load is applied to the abrasive grains on the glass substrate, so that the abrasive grains are crushed and the grinding ability is reduced. Or the glass substrate breaks.

In addition, the time t1 for roughening with the load P1 in the first stage is preferably in the range of 10 to 600 seconds, for example. When t1 is shorter than 10 seconds, the abrasive grains are not sufficiently bited into the glass main surface, which may slow the processing speed. On the other hand, if t1 is longer than 600 seconds, deep scratches are likely to occur, and the finished main surface may become rough.
Further, it is preferable that the load is gradually decreased from point B (load P1) and the time from point B to point C reaching the normal grinding load P2 is, for example, in the range of 10 to 90 seconds. If the time between BCs is shorter than 10 seconds, the substrate flatness may be deteriorated due to a rapid load fluctuation. On the other hand, if the time between BCs is longer than 90 seconds, the glass is excessively ground during the transition from P1 (first stage) to P2 (second stage), making it difficult to control the plate thickness or deep scratches. May occur and the finished main surface roughness may increase.

Moreover, it is preferable that time t2 which grinds with the load P2 in the said 2nd stage shall be 30 second or more. If a certain amount is not processed with the load P2, the groove formed with the load P1 cannot be removed, which may remain as a scratch. The upper limit of t2 is appropriately determined in consideration of the finished quality in the grinding process.
Note that t1 <t2 is preferable because the roughness of the finish can be reduced.

In the present invention, the processing speed in the entire grinding processing is generally in the range of 3.0 to 9.0 μm / min, and it is possible to perform grinding without reducing the processing speed. The processing speed in the entire grinding processing means a value obtained by dividing the total grinding thickness by the total processing time (including the first stage and the second stage).

In the present invention, it is preferable that the diamond fixed abrasive has an average particle size of 20 to 40 μm. Further, the individual particle size of the diamond fixed abrasive is preferably 10 to 50 μm. When the average particle diameter or individual particle diameter of the diamond abrasive grains is below the above, the cut into the mirror-like glass substrate becomes shallow and the biting into the glass substrate does not proceed. On the other hand, if the average particle diameter or individual particle diameter of the diamond abrasive grains exceeds the above, the roughness of the finish becomes rough, so that the machining allowance load in the subsequent process increases.
In addition, as previously demonstrated, a diamond fixed abrasive means the said aggregate here.
The size of the individual diamond particles contained in the aggregate is preferably 1 to 5 μm in average particle size.

In the present invention, the average particle size is a point at which the cumulative curve is 50% when the cumulative curve is obtained with the total volume of the powder population in the particle size distribution measured by the laser diffraction method as 100%. (Hereinafter referred to as “cumulative average particle diameter (50% diameter)”). In the present invention, the cumulative average particle diameter (50% diameter) is specifically a value obtained by measurement using a particle diameter / particle size distribution measuring apparatus.

In the present invention, the surface roughness of the glass substrate used for the grinding treatment is usually 0.001 to 0.01 μm in Ra. In the present invention, the surface roughness of the glass substrate after completion of the first stage is generally in the range of 0.100 to 0.150 μm in Ra. By roughening the surface in this range, the subsequent second-stage grinding is favorably performed.
Further, the surface roughness of the glass substrate after completion of the second stage, that is, after completion of the polishing process is as described above.

As described above, the grinding process of the present invention includes the first stage of roughening the glass substrate surface with a high load and the second stage of grinding the glass substrate surface with a load lower than the load of the first stage. By performing the processing, it is possible to improve the decrease in productivity due to the occurrence of the time during which grinding cannot be performed, and the grinding processing having the first stage and the second stage is continuously performed using the same apparatus. Therefore, productivity can be increased. In addition, the surface roughness of the processed surface can be kept low without reducing the processing speed, and the processing load in the subsequent process can also be reduced.

In addition, when the grinding process in the present invention is performed in the first stage and the second stage as described above, conditions are set so that a difference in processing speed occurs between the upper surface plate side and the lower surface plate side, and glass It is necessary to process the tin surface side of the substrate with a surface plate having a slower processing speed.
Further, when grinding is performed in two stages, the tin surface of the glass substrate may be removed in the second stage (more preferably, the end of the second stage). In the present invention, since the processing speed is differentiated between the upper and lower surface plates, if all the tin surface of the glass substrate is completely removed at the initial stage of processing such as the first stage, only one of the main surfaces has a large machining allowance. This is because there are cases where the roughness after the grinding process differs between the two main surfaces.

In the present invention, the glass constituting the glass substrate is preferably an amorphous aluminosilicate glass. Such a glass substrate can be finished to a smooth mirror surface by mirror polishing the surface, and the strength after processing is good. As such an aluminosilicate glass, for example, a glass containing SiO ₂ as a main component and containing 20 wt% or less of Al ₂ O ₃ is preferable. Furthermore, it is more preferable to use glass containing SiO ₂ as a main component and containing 15% by weight or less of Al ₂ O ₃ . Specifically, SiO ₂ is 62 wt% to 75 wt%, Al ₂ O ₃ is 5 wt% to 15 wt%, Li ₂ O is 4 wt% to 10 wt%, and Na ₂ O is 4 wt%. % To 12% by weight, ZrO ₂ is contained in an amount of 5.5% to 15% by weight as a main component, and the weight ratio of Na ₂ O / ZrO ₂ is 0.5 to 2.0, Al ₂ O _An amorphous aluminosilicate glass containing no phosphorus oxide and having a ₃ / ZrO ₂ weight ratio of 0.4 to 2.5 can be used.

Further, as the heat resistant glass, for example, in terms of mol%, SiO ₂ is 50 to 75%, Al ₂ O ₃ is 0 to 5%, BaO is 0 to 2%, Li ₂ O is 0 to 3%, ZnO 0-5%, Na ₂ O and K ₂ O 3-15% in total, MgO, CaO, SrO and BaO 14-35% in total, ZrO ₂ , TiO ₂ , La ₂ O ₃ , Y ₂ O ₃ , Yb ₂ O ₃ , Ta ₂ O ₅ , Nb ₂ O ₅ and HfO ₂ are included in a total amount of 2 to 9%, and the molar ratio [(MgO + CaO) / (MgO + CaO + SrO + BaO)] is in the range of 0.85 to 1. And glass having a molar ratio [Al ₂ O ₃ / (MgO + CaO)] of 0 to 0.30 can be preferably used.
Further, a total of 6 to 15 mol of an alkali metal oxide selected from the group consisting of 56 to 75 mol% of SiO ₂ , 1 to 9 mol% of Al ₂ O ₃ , Li ₂ O, Na ₂ O and K ₂ O. %, A total of 10 to 30 mol% of an alkaline earth metal oxide selected from the group consisting of MgO, CaO and SrO, ZrO ₂ , TiO ₂ , Y ₂ O ₃ , La ₂ O ₃ , Gd ₂ O ₃ , Nb Glass containing oxides selected from the group consisting of ₂ O ₅ and Ta ₂ O ₅ in total exceeding 0% and not more than 10 mol% may be used.
In the present invention, the content of Al ₂ O ₃ in the glass composition is preferably 15% by weight or less. Furthermore, still preferably _Al 2 _{O 3} content is 5 mol% or less.

After completion of the grinding process in the present invention, mirror polishing for obtaining a highly accurate plane is performed. In the present invention, since the grinding process according to the present invention is applied in the grinding process, a substrate with good flatness can be obtained and the processed surface roughness can be reduced. The amount of removal in the machining process is small, the machining load is reduced, and the machining cost can be reduced.

As a mirror polishing method for a glass substrate, it is preferable to use a polishing pad of a polisher such as polyurethane while supplying a slurry (polishing liquid) containing a metal oxide abrasive such as cerium oxide or colloidal silica. is there. A glass substrate having high smoothness is obtained, for example, by polishing with a cerium oxide-based abrasive (first polishing process) and then with final polishing (mirror polishing) (second polishing process) using colloidal silica abrasive grains. It is possible.

In the present invention, the surface of the glass substrate after mirror polishing is preferably a mirror surface having an arithmetic average surface roughness Ra of 0.2 nm or less, more preferably 0.13 nm or less. In the present invention, Ra and Rmax are roughnesses calculated in accordance with Japanese Industrial Standard (JIS) B0601.
In the present invention, the surface roughness (for example, the maximum roughness Rmax, the arithmetic average roughness Ra) is practically preferable to be the surface roughness obtained by measuring with an atomic force microscope (AFM). . Note that the measurement area of the AFM is a range of 5 μm × 5 μm.

In the present invention, it is preferable to perform a chemical strengthening treatment after the first polishing process and before the second polishing process. As a method of the chemical strengthening treatment, for example, a low-temperature ion exchange method in which ion exchange is performed in a temperature range not exceeding the glass transition temperature is preferable. The chemical strengthening treatment is a process in which a molten chemical strengthening salt is brought into contact with a glass substrate, whereby an alkali metal element having a relatively large atomic radius in the chemical strengthening salt and a relatively small atomic radius in the glass substrate. This is a treatment in which an alkali metal element is ion-exchanged, an alkali metal element having a large ion radius is permeated into the surface layer of the glass substrate, and compressive stress is generated on the surface of the glass substrate. Since the chemically strengthened glass substrate is excellent in impact resistance, it is particularly preferable for mounting on a HDD for mobile use, for example. As the chemical strengthening salt, alkali metal nitrates such as potassium nitrate and sodium nitrate can be preferably used.
In addition, it is preferable that the surface layer part with much tin content by the side of the tin surface of a glass substrate is substantially removed at the time of putting into the said chemical strengthening process. This is because, if the surface layer portion with a high tin content remains before the chemical strengthening treatment, a problem arises in that the substrate is warped by the chemical strengthening treatment.

The present invention also provides a method for manufacturing a magnetic disk using the above glass substrate for a magnetic disk. In the present invention, the magnetic disk is manufactured by forming at least a magnetic layer on the magnetic disk glass substrate according to the present invention. As a material for the magnetic layer, a hexagonal CoCrPt-based or CoPt-based ferromagnetic alloy having a large anisotropic magnetic field can be used. As a method of forming the magnetic layer, it is preferable to use a method of forming a magnetic layer on a glass substrate by a sputtering method, for example, a DC magnetron sputtering method. Further, by interposing an underlayer between the glass substrate and the magnetic layer, the orientation direction of the magnetic grains of the magnetic layer and the size of the magnetic grains can be controlled. For example, by using a cubic base layer such as a Cr-based alloy, for example, the magnetization easy direction of the magnetic layer can be oriented along the magnetic disk surface. In this case, a magnetic disk of the in-plane magnetic recording system is manufactured. Further, for example, by using a hexagonal underlayer containing Ru or Ti, for example, the easy magnetization direction of the magnetic layer can be oriented along the normal of the magnetic disk surface. In this case, a perpendicular magnetic recording type magnetic disk is manufactured. The underlayer can be formed by sputtering as with the magnetic layer.

In addition, a protective layer and a lubricating layer may be formed in this order on the magnetic layer. As the protective layer, an amorphous hydrogenated carbon-based protective layer is suitable. For example, the protective layer can be formed by a plasma CVD method. Further, as the lubricating layer, a lubricant having a functional group at the end of the main chain of the perfluoropolyether compound can be used. In particular, it is preferable that the main component is a perfluoropolyether compound having a terminal hydroxyl group as a polar functional group. The lubricating layer can be applied and formed by a dip method.
By using the glass substrate obtained by the present invention, a highly reliable magnetic disk can be obtained.

Hereinafter, embodiments of the present invention will be specifically described with reference to examples. In addition, this invention is not limited to a following example.
(Example 1)
The following (1) substrate preparation step, (2) shape processing step, (3) end surface polishing step, (4) main surface grinding processing, (5) main surface polishing step (first polishing step), (6) chemistry A glass substrate for a magnetic disk of this example was manufactured through a strengthening step and (7) a main surface polishing step (second polishing step).

(1) Substrate preparation process A large plate glass made of aluminosilicate glass having a thickness of 1 mm manufactured by the float method was prepared, and was cut using a diamond cutter so as to form square pieces. Next, using a diamond cutter, it was processed into a disk shape having a circular hole with an outer diameter of 65 mm and an inner diameter of 20 mm at the center. This aluminosilicate glass is expressed in weight%
SiO ₂ 58 to 66%, Al ₂ O ₃ 13 to 19%, Li ₂ O 3 to 4.5%, Na ₂ O 6 to 13%, K ₂ O 0 to 5%, R ₂ O 10 to 18%, (However, R ₂ O = Li ₂ O + Na ₂ O + K ₂ O)
MgO 0 to 3.5%, CaO 1 to 7%, SrO 0 to 2%, BaO 0 to 2%, RO 2 to 10% (however, RO = MgO + CaO + SrO + BaO)
Composition of TiO ₂ 0-2%, CeO ₂ 0-2%, Fe ₂ O ₃ 0-2%, MnO 0-1% (provided that TiO ₂ + CeO ₂ + Fe ₂ O ₃ + MnO = 0.01-3%) The glass for chemical strengthening containing was used.

(2) Shape processing step Next, a diamond grindstone was used to make a hole in the central portion of the glass substrate, and a predetermined chamfering process was applied to the outer peripheral end surface and the inner peripheral end surface. In general, a 2.5-inch HDD (hard disk drive) uses a magnetic disk having an outer diameter of 65 mm.

(3) End surface polishing step Next, the surface of the end surface (inner periphery, outer periphery) of the glass substrate was polished by a known brush polishing method while rotating the glass substrate.

(4) Main surface grinding process This main surface grinding process was performed by using a double-sided grinder and setting a glass substrate held by a carrier between the upper and lower surface plates to which diamond pads were attached. As the diamond pad, a fixed abrasive grindstone was used in which agglomerates obtained by vitrifying and bonding a plurality of diamond particles with glass were fixed with a resin to obtain a fixed abrasive. Here, the average particle size of the aggregate was about 25 μm, and the average particle size (D50) of the individual diamond particles in the aggregate was 2.5 μm. Moreover, it carried out using the lubricating liquid. The main surface of the glass substrate before the grinding process was a mirror surface. Moreover, when the roughness of the main surface was measured with a stylus type roughness meter, the Ra was 5 nm.

Specifically, the number of rotations of the platen was appropriately selected in the range of 10 to 100 rpm, and the load on the glass substrate was applied according to the sequence shown in FIG. In this example, the first stage (roughening) load (P1) was set to 150 g / cm ² . Further, the load (P2) in the second stage (main processing) was set to 100 g / cm ² . The upper surface plate rotation speed was set to 20 rpm, and the lower surface plate rotation speed was set to 30 rpm. The rotation speed of the sun gear (sun gear) was set to 8 rpm, and the rotation speed of the internal gear (internal gear) was set to 3 rpm. Under this condition, the relative speed between the upper surface plate and the substrate is 10 to 20% faster than the relative speed between the lower surface plate and the substrate, and as a result, the processing speed is faster on the upper surface plate side than on the lower surface plate side. And the tin surface of the glass substrate was set toward the lower surface plate side where the processing speed was slow, and both surfaces of the glass substrate housed in the carrier were simultaneously ground.
The slope k in FIG. 3 was 10 g / (cm ² · sec), t1 was 60 seconds, the time between BCs was 15 seconds, and t2 was 200 seconds longer than t1.
The glass substrate that had been subjected to the grinding process was sequentially immersed in each washing bath (applied with ultrasonic waves) of neutral detergent and water to perform ultrasonic cleaning.

In this grinding process, a total of 100 batches were processed. About the glass substrate after a process, the flatness was measured using the oblique incidence interference method flatness tester. Moreover, the surface roughness (Ra) of both the main surfaces of the glass substrate after a process was measured using the stylus type surface roughness meter. Table 1 shows the measurement results of the flatness of the glass substrate after processing and the difference in surface roughness (ΔRa) between both main surfaces. In addition, the numerical value of Table 1 is an average value of 100 substrates. Moreover, the average value of the flatness of the glass substrate just before the grinding process was 2.5 μm.

(5) Main surface polishing step (first polishing step)
Next, the 1st grinding | polishing process for removing the damage | wound and distortion which remain | survived by the grinding process mentioned above was performed using the double-side polish apparatus. In a double-side polishing machine, a glass substrate held by a carrier is closely attached between an upper and lower polishing surface plate to which a polishing pad is attached, and this carrier is engaged with a sun gear (sun gear) and an internal gear (internal gear). The glass substrate is sandwiched between upper and lower surface plates. Thereafter, a polishing liquid is supplied and rotated between the polishing pad and the polishing surface of the glass substrate, whereby the glass substrate revolves while rotating on the surface plate to simultaneously polish both surfaces. Specifically, a hard polisher (hard foamed urethane) was used as the polisher, and the first polishing step was performed. The polishing liquid was water in which cerium oxide was dispersed as an abrasive, and the load was 100 g / cm ² . The glass substrate after the first polishing step was washed and dried.

(6) Chemical strengthening step Next, chemical strengthening was performed on the glass substrate after the cleaning. For chemical strengthening, a chemical strengthening solution prepared by mixing and melting potassium nitrate and sodium nitrate was prepared, and a glass substrate was immersed in the chemical strengthening solution to perform chemical strengthening treatment.

(7) Main surface polishing step (second polishing step)
Next, using the same double-side polishing apparatus as that used in the first polishing step, the second polishing step was performed by replacing the polisher with a polishing pad of soft polisher (suede). In this second polishing step, for example, the surface roughness of the glass substrate main surface is finished to a smooth mirror surface with a Ra of about 0.2 nm or less while maintaining the flat surface obtained in the first polishing step. Mirror polishing process. The polishing liquid was water in which colloidal silica was dispersed, and the load was 100 g / cm ² . The glass substrate after the second polishing step was washed and dried.

Further, when the surface roughness of the main surface of the glass substrate obtained through the above steps was measured with an atomic force microscope (AFM), it had an ultra-smooth surface with Rmax = 1.53 nm and Ra = 0.13 nm. A glass substrate was obtained. The measurement area of AFM is 5 μm × 5 μm. Moreover, when the surface of the glass substrate was analyzed with an atomic force microscope (AFM) and an electron microscope, it was specular and surface defects such as protrusions and scratches were not observed.
The obtained glass substrate had an outer diameter of 65 mm, an inner diameter of 20 mm, and a plate thickness of 0.635 mm.
Thus, a glass substrate for magnetic disk of this example was obtained.

(Comparative Example 1)
In the grinding process of Example 1, the tin surface of the glass substrate was set toward the upper surface plate with a high processing speed, and the grinding process was performed. And the glass substrate for magnetic discs was obtained like Example 1 except this grinding process.

(Comparative Example 2)
In the grinding processing of Example 1, the conditions were set so that the processing speeds of the upper and lower surface plates were substantially the same, and the tin surface of the glass substrate was set facing the upper surface plate side, and the grinding processing was performed. . And the glass substrate for magnetic discs was obtained like Example 1 except this grinding process.

(Examples 2 to 5)
In the grinding process of Example 1 above, the processing speed on the upper surface plate side is set to be slowed by 5, 10, 20, and 30%, respectively, and the tin surface of the glass substrate is set toward the upper surface plate side. The grinding process was carried out. And the glass substrate for magnetic discs was obtained like Example 1 except this grinding process.
Table 1 shows the measurement results of the flatness and the difference in surface roughness (ΔRa) between the main surfaces of the glass substrates after grinding in the above examples.

From the results in Table 1, the following can be understood.
1. In Example 1 in which the tin surface of the glass substrate was set on the lower surface plate side where the processing speed was slow and grinding was performed, the flatness of the processed substrate was good. Further, the difference in surface roughness between both main surfaces of the substrate is small, and the substrate roughness after grinding is processed so as to be substantially the same on both sides. Furthermore, from the comparison between Example 1 and Examples 2 to 5, the flatness of the substrate after processing becomes better when the processing speed of the upper surface plate is slowed and the tin surface is set on the upper surface plate side. I understand. This is thought to be related to the fact that a relatively large sludge is likely to be generated because the grinding process is performed with fixed abrasive grains, and the sludge tends to accumulate on the lower surface plate side. In other words, sludge tends to adhere to the surface of the surface of the lower surface plate, and the grinding rate tends to decrease.Therefore, increasing the processing speed on the surface of the lower surface stabilizes the processing, and improves the flatness and surface roughness. The difference seems to have improved. It can be seen that the best results are obtained when the difference in processing speed is 10 to 20%.
2. On the other hand, in Comparative Example 1 in which the tin surface of the glass substrate having a high processing speed was set on the upper surface plate side having a high processing speed and grinding was performed, the flatness of the substrate after processing deteriorated, The substrate warped. Moreover, the difference in surface roughness between both main surfaces of the substrate was large, which was a factor that deteriorated flatness.
Also in Comparative Example 2 in which the processing speed of the upper and lower surface plates was set to be substantially the same, the flatness of the substrate after processing deteriorated and the substrate warped. Further, the difference in surface roughness between both main surfaces of the substrate was larger than that in Example 1, which was a cause of deterioration in flatness. In Comparative Example 2, it is considered that the difference in processing speed between the tin surface and the non-tin surface of the glass substrate led to the difference in surface roughness between both main surfaces.

(Examples 6 to 9)
Next, a substrate was manufactured by making a difference between the upper and lower surface plates with respect to the protruding amount of diamond fixed abrasive grains (aggregates) in the diamond pad. The average protrusion amount on the upper surface plate side was fixed at 5 μm, and the average protrusion amount of the diamond fixed abrasive on the lower surface plate side was changed as shown in Table 2. The protrusion amount was changed by changing the number of dressing processes for the upper and lower surface plates.
Except for this point, grinding was performed in the same manner as in Example 4, the flatness of the 100 glass substrates obtained was measured, and the difference between the maximum value and the minimum value was obtained to determine the variation in flatness. About the magnitude | size of the variation in flatness of each Example, the value of Example 4 (The average protrusion amount of a fixed abrasive is equivalent with an upper and lower surface plate) was set to 1.00 (100%), and was shown by the relative value.

From Table 2, the variation in flatness can be improved by making the protruding amount of the fixed abrasive on the surface plate side (here, the lower surface plate side) relatively high in processing speed larger than that on the upper surface plate side. Recognize. This is considered to be due to the fact that the fixed abrasive grains bite into the non-tin surface on the non-tin surface side, which is hard to be ground, by improving the biting characteristics of the fixed abrasive grains at the initial stage of grinding. That is, it is considered that the substrate in which the timing of the biting of the fixed abrasive is delayed receives the pressure of the grinding pad slightly higher than the other substrates, and the processing speed is increased immediately after the biting occurs. It is considered that the variation in the grinding state during such processing also affects the flatness.
From the above results and considerations, on the surface plate side where the processing speed is relatively high, the protruding amount of the fixed abrasive is made relatively larger than the surface plate side where the processing speed is low, and the non-tin surface on the surface plate side. It can be seen that it is preferable to work.

(Example 10)
The following film formation process was performed on the magnetic disk glass substrate obtained in Example 1 to obtain a magnetic disk for perpendicular magnetic recording.
That is, an adhesion layer made of a Ti-based alloy thin film, a soft magnetic layer made of a CoTaZr alloy thin film, an underlayer made of a Ru thin film, a perpendicular magnetic recording layer made of a CoCrPt alloy, a carbon protective layer, and a lubricating layer are sequentially formed on the glass substrate. A film was formed. The protective layer is for preventing the magnetic recording layer from deteriorating due to contact with the magnetic head, and is made of hydrogenated carbon, and provides wear resistance. The lubricating layer was formed by dipping a liquid lubricant of alcohol-modified perfluoropolyether.
The obtained magnetic disk was installed in an HDD equipped with a DFH head, and a load / unload durability test was conducted for one month while operating the DFH function in a high temperature and high humidity environment of 80 ° C. and 80% RH. There were no particular obstacles and good results were obtained.

1 Diamond Pad 2 Sheet 3 Aggregate 4 Pellet 5 Diamond Particle 10 Glass Substrate

Claims

Using the lubricating liquid and a pair of upper and lower surface plates in which fixed abrasive grains containing diamond particles are disposed on the grinding surface, while supplying the lubricating liquid between the grinding surface and the glass substrate, A method for producing a glass substrate for a magnetic disk including a grinding process for grinding by sandwiching both main surfaces of the glass substrate with an upper and lower surface plate,
The glass substrate is a glass substrate obtained by cutting a sheet-like plate glass produced by a float method into a predetermined shape, and has a surface layer portion with a higher tin content than the other main surface side on one main surface side. And
The grinding process is performed so that a difference in processing speed occurs between the upper surface plate side and the lower surface plate side,
A method for producing a glass substrate for a magnetic disk, comprising setting and grinding a main surface having a surface layer portion having a high tin content of the glass substrate on a surface plate side having a lower processing speed.
2. The method for producing a glass substrate for a magnetic disk according to claim 1, wherein the substrate is ground so that the flatness of the substrate after grinding is within 2.5 [mu] m.
The method for producing a glass substrate for a magnetic disk according to claim 1 or 2, wherein grinding is performed so that a difference in surface roughness between both main surfaces of the substrate after grinding is 0.01 μm or less in Ra.
The method for producing a glass substrate for a magnetic disk according to any one of claims 1 to 3, wherein the surface roughness of both main surfaces of the substrate after grinding is 0.130 µm or less in Ra.
5. The method according to claim 1, wherein, when simultaneously grinding a plurality of glass substrates, the glass substrate is set so that the main surfaces having the surface layer portion having a large tin content are all in the same direction. The manufacturing method of the glass substrate for magnetic discs in any one.
6. The protrusion according to claim 1, wherein the protruding amount of the fixed abrasive is further increased on the surface plate side having a relatively high processing speed than on the surface plate side having a relatively low processing speed. Manufacturing method of glass substrate for magnetic disk.
The grinding process includes a first stage of roughening the surface of the glass substrate with a load higher than a load for grinding, and after the first stage, the glass with a load lower than the load of the first stage. The method for producing a glass substrate for a magnetic disk according to claim 1, further comprising a second step of grinding the surface of the substrate.
The method of manufacturing a glass substrate for a magnetic disk according to any one of claims 1 to 7, wherein a processing speed in the grinding processing is 3.0 μm / min to 9.0 μm / min.
A method for manufacturing a magnetic disk, comprising forming at least a magnetic recording layer on the glass substrate for a magnetic disk manufactured by the method for manufacturing a glass substrate for a magnetic disk according to claim 1.