WO2015046543A1

WO2015046543A1 - Method for manufacturing glass substrate for magnetic disk and method for manufacturing magnetic disk

Info

Publication number: WO2015046543A1
Application number: PCT/JP2014/075966
Authority: WO
Inventors: 博則吉川
Original assignee: Hoya株式会社
Priority date: 2013-09-28
Filing date: 2014-09-29
Publication date: 2015-04-02
Also published as: JPWO2015046543A1; CN105579198B; JP6313314B2; JP6490842B2; MY176672A; JP2018092697A; CN108447507B; SG10202006113YA; CN105579198A; WO2015046543A8; SG11201602379QA; CN108447507A

Abstract

The present invention provides a method whereby not only the machining speed can be improved during a grinding process utilizing a stationary grinding wheel, but stable grinding can also be enabled. In the present invention, during a grinding process for grinding a main surface of a glass substrate, the main surface of the glass substrate is ground by using a grinding tool that has grinding abrasive grains, a binding material for binding the grinding abrasive grains together, and dispersed grains that are harder than the binding material yet softer than the grinding abrasive grains, wherein the grinding abrasive grains and the dispersed grains are bound together in a dispersed state in the binding material.

Description

Manufacturing method of glass substrate for magnetic disk, manufacturing method of magnetic disk, and grinding tool

The present invention relates to a grinding tool applied to manufacture of a magnetic disk glass substrate mounted on a magnetic disk device such as a hard disk drive (HDD), a method of manufacturing a glass substrate for magnetic disk using the grinding tool, and a magnetic disk It relates to a manufacturing method.

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, further polishing is performed to reduce the surface roughness and microwaviness, thereby reducing the main surface. Has achieved extremely high smoothness.

By the way, in the grinding process (for example, patent document 1 etc.) which conventionally used the loose abrasive grain, the grinding method by the fixed abrasive using a diamond pad is proposed (for example, patent document 2 etc.). A diamond pad is a combination of diamond particles or agglomerates (concentrated abrasive grains) in which several diamond particles are hardened with a fixing material such as glass, using a binding material such as a resin (for example, an acrylic resin). It is fixed. 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. The diamond pad referred to here is not necessarily a general name, but is referred to as a “diamond pad” for convenience of explanation 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.
Patent Document 2 discloses a tool for grinding using fixed abrasive particles in which a polishing complex (aggregate) in which diamond abrasive particles are bonded with a binder is dispersed in an organic resin at a constant ratio.

JP 2001-6161 A Special Table 2003-534137

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.

When grinding a glass substrate using a grinding tool with a fixed abrasive as disclosed in Patent Document 2 above, select an agglomerate density that matches the workpiece and adjust the processing pressure. It is always necessary to control the pressure applied to the tip portion (blade edge) of the diamond abrasive grains. It is advantageous to select a grinding tool having a low agglomerate density, particularly when processing is desired to be performed quickly. In this case, since the interval between the aggregates is large, the processing speed increases, but the wear of the tool also increases. Further, when the aggregate density is low, the distance between the dispersed aggregates tends to be non-uniform, and uneven wear tends to occur. When mass production of a glass substrate using such a conventional grinding tool is performed, the processing speed is fast in the initial stage, but grinding abrasive grains fall off, uneven wear, clogging, etc. are repeated, and the tool surface undulates. Components are formed, and at a relatively early stage (several batches have elapsed since the start of processing), the processing speed decreases and the quality after processing decreases. In particular, the quality deterioration of flatness becomes remarkable. Although it is possible to recover the machining speed reduced by the correction work for removing the waviness component generated on the tool surface, it is necessary to frequently perform such a correction work, so that the production load is large.
In short, in the prior art, it is difficult to achieve both the processing speed and the processing quality (particularly the flatness of the substrate), and good processing quality cannot be stably obtained for a long time at a stable processing speed.

The present invention has been made to solve such a conventional problem, and its purpose is to achieve both processing speed and processing quality (particularly flatness of the substrate) in grinding processing using fixed abrasive grains. We provide a grinding tool that can be applied to the grinding process of glass substrates that can stably obtain good processing quality for a long period of time at a stable processing speed. It is an object to provide a method for producing a glass substrate for a magnetic disk that can be produced, and a method for producing a magnetic disk using the glass substrate obtained thereby.

As a result of searching for a solution that can increase the processing speed and perform stable grinding, the present inventor has completed the present invention.
That is, in order to solve the above problems, the present invention has the following configuration.
(Configuration 1)
A method of manufacturing a glass substrate for a magnetic disk including a grinding process for grinding a main surface of a glass substrate, wherein the grinding process includes grinding abrasive grains, a binder for bonding the abrasive grains, and a binder. A glass substrate main surface using a grinding tool which is hard and includes dispersed particles softer than the abrasive grains, and is bonded in a state where the abrasive grains and the dispersed particles are dispersed in the binder. A method for producing a glass substrate for a magnetic disk, characterized in that:

(Configuration 2)
2. The method for manufacturing a glass substrate for a magnetic disk according to Configuration 1, wherein the binding material is a resin material.
(Configuration 3)
3. The method for manufacturing a glass substrate for a magnetic disk according to Configuration 1 or 2, wherein the grinding abrasive grains are concentrated abrasive grains in which a plurality of abrasive grains are bonded with a fixing material.

(Configuration 4)
4. The method for manufacturing a glass substrate for a magnetic disk according to any one of configurations 1 to 3, wherein the grinding abrasive grains include diamond abrasive grains.
(Configuration 5)
5. The method for manufacturing a glass substrate for a magnetic disk according to any one of configurations 1 to 4, wherein the dispersed particles are made of alumina or zirconia.

(Configuration 6)
5. The method for manufacturing a glass substrate for a magnetic disk according to any one of configurations 1 to 4, wherein the dispersed particles are made of glass softer than glass to be ground.
(Configuration 7)
5. The method of manufacturing a glass substrate for a magnetic disk according to any one of configurations 1 to 4, wherein the dispersed particles are aggregates in which a plurality of dispersed particles are bonded with glass softer than glass to be ground.

(Configuration 8)
8. A method of manufacturing a glass substrate for a magnetic disk according to any one of configurations 1 to 7, wherein a ratio of the dispersed grains to the abrasive grains in the binder is in a range of 0.1 to 5 times. .
(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.

(Configuration 10)
A grinding tool for grinding a glass substrate surface for an electronic device, comprising: grinding abrasive grains; a binder for binding the abrasive grains; and a dispersed grain that is harder than the binder and softer than the abrasive grains. A grinding tool, wherein the grinding abrasive grains and the dispersed grains are bonded in a state of being dispersed in the binder.

According to the present invention, the above-described configuration can solve the conventional problems, and in the grinding process using the fixed abrasive grains, the processing speed and the processing quality (particularly the flatness of the substrate) are balanced, and the processing quality is stable at a stable processing speed. Thus, it is possible to provide a grinding tool applied to a grinding treatment of a glass substrate that can be stably obtained for a long period of time. In addition, it is possible to manufacture a high-quality glass substrate at a low cost including a grinding process using this grinding tool. Furthermore, a highly reliable magnetic disk can be obtained using the glass substrate obtained thereby.

It is a schematic sectional drawing which shows the structure of the conventional diamond pad. It is a schematic diagram for demonstrating the state at the time of a grinding process.

Hereinafter, embodiments of the present invention will be described in detail.
A glass substrate for a magnetic disk is usually manufactured through shape processing, main surface grinding, end surface polishing, main surface polishing, chemical strengthening, and the like.
In the method for producing a glass substrate for a magnetic disk according to the present invention, a glass substrate is obtained by cutting into a predetermined size from a sheet-like glass produced by a float method or a downdraw method. In addition to this, a sheet-like plate glass produced by pressing from molten glass may be used. The present invention is suitable when a glass substrate having a mirror-like main surface is used at the start of grinding.

Next, the glass substrate is subjected to a grinding process for improving dimensional accuracy and shape accuracy.
In this grinding process, a main surface of the glass substrate is generally ground using a double-side grinding apparatus and 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, for example, grinding abrasive grains (fixed abrasive grains) containing diamond particles, and in a double-side grinding apparatus, for example, between upper and lower surface plates on which diamond pads are attached as grinding tools. By closely moving the glass substrate and the upper and lower platen while the glass substrate held by the carrier is in close contact, and sandwiching the glass substrate at a predetermined pressure by the upper and lower platen, both main surfaces of the glass substrate are simultaneously Grind. At this time, a lubricating liquid (coolant) is supplied to cool the working surface or to promote the processing.

The grinding tool (fixed abrasive grindstone) used for the grinding process is, for example, a diamond pad, and its configuration is schematically shown in FIG. A diamond pad 1 shown in FIG. 1 uses a binding material such as a resin (for example, an acrylic resin), which is a collection of abrasive grains 3 in which several diamond particles 5 (see FIG. 2) are hardened with a fixing material such as glass. The pellet 4 fixed in this manner is affixed to the sheet 2. 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 that has a resin layer containing diamond particles formed on a sheet and then has grooves formed in the resin layer to form protrusions may be used.

In the present embodiment, when it is referred to as fixed abrasive grains or simply abrasive grains, unless otherwise specified, it means a grinding abrasive grain such as the above diamond grain, and the average grain of the abrasive grains. When it says a diameter, it shall mean the average particle diameter of the said abrasive grain.

As described above, the present inventor is difficult to achieve both the processing speed and the processing quality (particularly the flatness of the substrate) with the above-described conventional technology, and the stable processing speed and the good processing quality are stable for a long period of time. I found out that I could not get it.
Therefore, as a result of searching for a solution that can increase the processing speed and perform stable grinding, the present inventor used a combination of abrasive grains and dispersed grains softer than the abrasive grains. The present inventors have found that the above-described problems can be solved by applying a grinding tool in which these abrasive grains and dispersed grains are dispersed in a binder.

In the grinding tool of the present invention, when the glass substrate is sandwiched between the upper and lower surface plates, the force applied to each of the abrasive grains from the surface plate is dispersed by the presence of the dispersed particles. In other words, it is possible to increase the processing speed by reducing the grinding grain density, increasing the grinding grain spacing, and even if the grinding grain spacing is large, there are dispersed grains between them. Sometimes, the force applied from the surface plate can be dispersed, and the wear of the tool can be suppressed. Also, if the grinding abrasive density is low, the distance between the dispersed abrasive grains tends to be non-uniform, but in the present invention, as described above, the dispersed grains are dispersed in addition to the abrasive grains, As a result, the abrasive grains are dispersed at a uniform distance, and uneven wear hardly occurs.

Therefore, even if mass production of a glass substrate is performed using such a grinding tool of the present invention, it is possible to suppress the formation of a swell component on the tool surface if processing is continued as in the prior art. As a result, it is possible to achieve both processing speed and processing quality (particularly the flatness of the substrate), and good processing quality can be stably obtained for a long period of time at a stable processing speed.

That is, the grinding tool applied to the grinding process in the present invention is a grinding tool for grinding the glass substrate surface, and is harder than the grinding abrasive grains, the binder for bonding the abrasive grains, and the binder. In addition, dispersed abrasive particles softer than the abrasive grains are provided, and the abrasive grains and the dispersed grains are bonded in a state of being dispersed in the binder.
Further, the present invention is characterized in that in the grinding process for grinding a glass substrate, the glass substrate main surface is ground using the grinding tool.

The abrasive grains may be abrasive grains themselves, but are preferably concentrated abrasive grains in which a plurality of abrasive grains are bonded with a fixing material. Since the single abrasive grains have a small surface area, the gripping resin strength is low and they easily fall off.
In the present invention, the abrasive grains are preferably diamond grains. In this case, it is preferable that the average particle diameter of the diamond abrasive grains is in the range of about 1.5 to 10 μm.
When the average particle diameter of the diamond abrasive grains is less than the above range, the cut into the mirror-like glass substrate becomes shallow and the biting into the glass substrate is difficult to proceed. On the other hand, when the average particle diameter of the diamond abrasive grains exceeds the above range, the roughness of the finish becomes rough, so that there is a possibility that the machining allowance load in the subsequent process becomes large.
Further, in the case of diamond abrasive grains, it is preferable that the accumulated abrasive grains have a cumulative average particle diameter of about 30 to 50 μm.
Moreover, as a fixing material which fixes abrasive grains, a glass material is suitable, for example.

In the present invention, the average particle diameter is a point where the cumulative curve is 50% when the cumulative curve is obtained with the total volume of the powder group in the particle size distribution measured by the laser diffraction method as 100%. (Referred to as “cumulative average particle diameter (50% diameter)”). The cumulative average particle diameter (50% diameter) is a value that can be measured using a particle diameter / particle size distribution measuring device.

Examples of the binder for bonding the abrasive grains include metals, glass, resin materials, etc., but resin materials are particularly preferable from the viewpoint of having an appropriate cushioning property and not causing excessive damage to the glass. It is. Examples of the resin material include acrylate, epoxy, polycarbonate, and polyester.

In the present invention, the dispersed particles dispersed together with the abrasive grains in the binder are grains that are harder than the binder and softer than the abrasive grains. When a glass substrate is sandwiched between upper and lower surface plates during processing, the force applied to each of the abrasive grains from the surface plate can be dispersed by the presence of the dispersed particles. Although the hardness of the dispersed grains depends on the material of the binder and the abrasive grains, the hardness is generally Mohs and the abrasive grains are about 6.5 to 9.5, so long as the hardness is softer than that. Moreover, it is preferable that the glass used for the grains has a lower Mohs hardness than the abrasive grains.

The material of the dispersed particles is not particularly limited as long as it satisfies the above-mentioned requirements with respect to hardness, but is preferably made of glass, alumina, or zirconia in terms of Mohs hardness. Moreover, the mixture of the grain from which a material differs may be sufficient. Since these materials are moderately softer than diamond, they wear out before the diamond abrasive grains. Therefore, diamond processing is not hindered. The range of the average particle diameter of the alumina or zirconia particles is preferably the same as the average particle diameter of the diamond abrasive grains.

The dispersed particles may be the particles themselves, but may also be aggregates in which a plurality of dispersed particles are bonded with a glass fixing material such as vitrified bonding. In this case, the plurality of dispersed grains may be the same or different from each other. Moreover, it is preferable that the glass in this case is softer than the glass substrate to be ground.
The size of the dispersed particles is preferably the same as that of the aggregate in the case of the particles themselves. By doing so, it becomes easy to disperse both uniformly.
Further, it is preferable that the ratio of the size of the abrasive grains (the size in the case of concentrated abrasive grains) and the size of the dispersed grains is substantially equal, and in particular, both are the same size. Is desirable. The ratio of the size of the abrasive grains to the dispersed grains is the ratio of the average grain diameter of the dispersed grains to the average grain diameter of the abrasive grains ((average grain diameter of dispersed grains) / (average grain diameter of abrasive grains)). In the range of 0.8 to 1.2. By doing so, it becomes easy to disperse both uniformly.
Moreover, when the fixing material of a grinding grain and the fixing agent of a dispersion grain are used, it is preferable that both binder is the same material. By doing so, it becomes easy to disperse both uniformly.

The dispersed grains may be grains composed only of glass that is preferably softer than the glass to be ground.
In the case of the dispersed particles made of only glass, the size of the dispersed particles and the ratio of the size to the abrasive grains are the same as in the case of the dispersed particles such as alumina.

The grinding tool of the present invention is bonded in the state where the abrasive grains and the dispersed grains are dispersed in the binder, and specifically, for example, diamond abrasive grains and non-diamond such as alumina. Use in combination with dispersed grains, combined use of diamond abrasive grains and dispersed grains made of glass, or combined use of diamond abrasive grains, non-diamond dispersed grains such as alumina, and dispersed grains made of glass, etc. As mentioned.
In the present invention, an embodiment in which diamond grinding abrasive grains and dispersed grains made of glass are used in combination is particularly suitable. According to this embodiment, the dispersion effect that prevents the generation of the swell component is the highest.

In the present invention, the ratio of the abrasive grains to the dispersed grains in the binder is not particularly limited, but the following dispersion ratio is preferable from the viewpoint of sufficiently achieving the effects of the present invention.
When the diamond abrasive grains are used in combination with non-diamond dispersed grains such as alumina, the range of the dispersed grains is 0.1 to 3 times that of the abrasive grains 1.
Further, when the diamond abrasive grains are used in combination with the dispersed grains made of glass, the range of 0.1 to 5 times the dispersed grains with respect to the abrasive grains 1 is preferable.
In the case of using a combination of diamond grinding grains, non-diamond dispersion grains such as alumina, and dispersion grains made of glass, the total amount of the dispersion grains is 0.1 to 5 times that of the grinding grains 1. Is preferred.
Further, the density of the fixed abrasive grains dispersed in a binder such as a resin (counted as one in the case of aggregated abrasive grains or aggregates) on the grinding surface is 10 to 40 (pieces / mm ² ). It is preferable that it is the range of these. Further, the content of the fixed abrasive grains in the grinding tool is preferably 5 to 80% by volume. If the content of the fixed abrasive deviates from the above range (both excess and deficiency), both may increase the processing time and increase the cost.
In the present invention, the abrasive grains of a material softer than the diamond abrasive grains and the aggregates thereof are dispersed together with the diamond aggregate abrasive grains, whereby the distance between the abrasive grains of the diamond aggregate abrasive grains can be uniformly extended. In addition, excessive pressure concentration on the diamond collecting abrasive grains can be prevented. Thereby, processing can be stabilized even at a high processing speed, and good flatness can be maintained.

In the grinding treatment in the present invention, the load during processing is preferably 15 to 200 g / cm ^{2 in} terms of surface pressure.
When grinding a mirror-like glass substrate surface with, for example, a diamond pad, first, in order to cause the diamond abrasive grains to bite into the glass substrate surface, a higher load load may be applied to the glass surface than during normal grinding. Is preferred. The higher the load, the deeper the cutting depth of the abrasive grains, the rougher the glass surface can be made (roughened).
After the glass surface has been roughened in such an initial stage of processing, there is no need for a high load on the grinding process. Rather, the grinding should be performed under conditions where the cutting depth of the abrasive grains is reduced by reducing the load. Is desirable. FIG. 2 is a schematic diagram for explaining a state at the time of grinding, and shows a state in which the diamond abrasive grains 3 are biting into the glass substrate 10 and are ground (expected view).

In the present invention, the surface roughness of the glass substrate after completion of the grinding treatment is preferably finished in the range of 0.02 to 3.0 μm in Ra. Thus, the processing load of a subsequent process can be reduced by keeping the roughness of the finish low.

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 SiO2 as a main component and containing 20 wt% or less of Al2O3 is preferable. Further, it is more preferable to use glass containing SiO2 as a main component and containing Al2O3 or less by 15% by weight or less. Specifically, SiO2 is 62% by weight to 75% by weight, Al2O3 is 5% by weight to 15% by weight, Li2 重量 O is 4% by weight to 10% by weight, Na2O is 4% by weight to 12% by weight, ZrO2 is contained in an amount of 5.5% to 15% by weight as a main component, the weight ratio of Na2O / ZrO2 is 0.5 to 2.0, and the weight ratio of Al2O3 / ZrO2 is 0.4 to 2.5. Amorphous aluminosilicate glass that does not contain the following phosphorous oxide can be used.

The heat-resistant glass used for the next generation heat-assisted magnetic recording magnetic disk is, for example, 50 to 75% of SiO2, 0 to 5% of Al2O3, and 0 to 2% of BaO in terms of mol%. , Li2O 0-3%, ZnO 0-5%, Na2O and K2O 3-15% in total, MgO, CaO, SrO and BaO 14-35% in total, ZrO2, TiO2, La2O3, Y2O3, Yb2O3 , Ta2O5, Nb2O5 and HfO2 in total 2 to 9%, the molar ratio [(MgO + CaO) / (MgO + CaO + SrO + BaO)] is in the range of 0.85 to 1, and the molar ratio [Al2O3 / (MgO + CaO)] is 0. Glass having a range of ˜0.30 can be preferably used.
Further, SiO2 is 56 to 75 mol%, Al2O3 is 1 to 9 mol%, a total of 6 to 15 mol% of alkali metal oxides selected from the group consisting of Li2O, Na2O and K2O, and a group consisting of MgO, CaO and SrO 10 to 30 mol% in total of alkaline earth metal oxides selected from the group consisting of oxides selected from the group consisting of ZrO2, TiO2, Y2O3, La2O3, Gd2O3, Nb2O5 and Ta2O5 in total exceeding 0% and not more than 10 mol% Including glass.
In the present invention, the content of Al2O3 in the glass composition is preferably 15% by weight or less. Furthermore, it is more preferable that the content of Al2O3 is 5 mol% or less.

After the above-described grinding process is finished, mirror polishing is performed to obtain a highly accurate plane. In the present invention, since stable processing can be performed in the grinding process using the fixed abrasive grains, the amount of removal in the subsequent mirror polishing process can be reduced, the processing load can be reduced, and the processing 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 0.1 nm or less. In the present invention, the arithmetic average roughness Ra is a roughness calculated in accordance with Japanese Industrial Standard (JIS) B0601.
In the present invention, the surface roughness (the arithmetic average roughness Ra) is preferably practically the surface roughness obtained when measured with an atomic force microscope (AFM).

In the present invention, chemical strengthening treatment can be performed. 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.

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 produced by forming at least a magnetic recording layer (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, a protective layer and a lubricating layer may be formed on the magnetic recording layer. As the protective layer, an amorphous carbon-based protective layer is suitable. 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.
By using the glass substrate for magnetic disk 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
(1) Substrate preparation, (2) Shape processing, (3) End surface polishing, (4) Main surface grinding, (5) Main surface polishing (first polishing), (6) Chemical strengthening, (7) Main A glass substrate for a magnetic disk of this example was manufactured through surface polishing (second polishing).

(1) Substrate preparation A large glass plate made of aluminosilicate glass having a thickness of 1 mm produced by the float method was prepared, and cut into a 70 mm × 70 mm square piece using a diamond cutter. Subsequently, it processed into the disk shape of outer diameter 65mm and internal diameter 20mm using the diamond cutter. This aluminosilicate glass contains SiO2: 62-75 wt%, ZrO2: 5.5-15 wt%, Al2O3: 5-15 wt%, Li2O: 4-10 wt%, Na2O: 4-12 wt% Glass that can be chemically strengthened was used.
The surface of the obtained substrate was a mirror surface with a surface roughness Ra of 5 nm or less.

(2) Shape processing Next, a diamond grindstone was used to make a hole in the central portion of the glass substrate, and a predetermined chamfering was applied to the outer peripheral end surface and the inner peripheral end surface.

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

(4) Main surface grinding This main surface grinding was performed by using a double-sided grinding machine and setting a glass substrate held by a carrier between the upper and lower surface plates to which diamond pads were attached. In this example, as a diamond pad, a plurality of diamond abrasive grains consolidated with glass, an aggregate in which a plurality of alumina particles are fixed with glass, and a plurality of the aggregate abrasive grains and aggregates are combined. The average particle size of the diamond abrasive grains is 4.0 μm, the average particle size of the diamond collecting abrasive grains is 40 μm, the average particle size of the alumina particles is 4.0 μm, and the average particle size of the alumina aggregate is 40 μm. A diamond pad dispersed in a resin was used so that the maximum particle size was 45 μm and the ratio of diamond aggregated abrasive grains to alumina aggregate was 1: 0.5. The glass in which the abrasive grains were hardened had a lower hardness than the glass to be processed. The density of the fixed abrasive grains on the total ground surface was 20 (pieces / mm ² ). Moreover, it carried out using the lubricating liquid. Moreover, the rotation speed of the surface plate and the load on the glass substrate were adjusted as appropriate.

(5) Main surface polishing (first polishing)
Next, the 1st grinding | polishing for removing the flaw 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, the first polishing was performed using a hard polisher (hard foamed urethane) as the polisher. The polishing liquid was pure water in which cerium oxide was dispersed as an abrasive, and the load and polishing time were appropriately set. The glass substrate after the first polishing step was sequentially immersed in cleaning baths of neutral detergent, pure water, IPA (isopropyl alcohol), and IPA (steam drying), ultrasonically cleaned, and dried.

(6) Chemical strengthening Next, chemical strengthening was performed on the glass substrate after the cleaning. For chemical strengthening, a chemical strengthening solution in which potassium nitrate and sodium nitrate were mixed was prepared, the chemical strengthening solution was heated to 380 ° C., and the cleaned and dried glass substrate was immersed for about 4 hours to perform chemical strengthening treatment.

(7) Main surface polishing (second polishing)
Next, using the same double-side polishing apparatus as that used in the first polishing, the polishing was changed to a polishing pad (made of polyurethane foam) of a soft polisher (suede), and the second polishing was performed. This second polishing is, for example, mirror polishing for finishing the surface roughness of the glass substrate main surface to a smooth mirror surface with a Ra of about 0.2 nm or less while maintaining the flat surface obtained by the first polishing described above. It is processing. The polishing liquid was pure water in which colloidal silica was dispersed, and the load and polishing time were appropriately set. The glass substrate after the second polishing step was sequentially immersed in each cleaning bath of neutral detergent, pure water, IPA, and IPA (steam drying), ultrasonically cleaned, and dried.

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), a glass substrate having an ultra-smooth surface with Rmax = 1.53 nm and Ra = 0.13 nm. Got.

(Example 2)
In the main surface grinding process of the first embodiment, a collecting abrasive grain obtained by hardening a plurality of diamond abrasive grains with glass, a plurality of dispersed grains made of glass, and a resin that binds the plurality of the concentrated abrasive grains and the dispersed grains. The average particle size of the diamond abrasive grains is about 4.0 μm, the average particle size of the diamond concentrating abrasive grains is 40 μm, the average particle size of the glass dispersed particles is 4.0 μm, and the maximum particle size of the glass aggregate is 45 μm, The magnetic disk was ground in the same manner as in Example 1 except that a diamond pad dispersed in the resin was used so that the ratio of diamond aggregated abrasive grains to glass aggregate was 1: 0.5. A glass substrate was prepared.

Example 3
In the main surface grinding process of Example 1, aggregated abrasive grains obtained by solidifying a plurality of diamond abrasive grains with glass, aggregates in which a plurality of alumina particles are fixed with glass, a plurality of dispersed grain aggregates made of glass, A plurality of aggregated abrasive grains, a resin that binds the alumina particle aggregates and the glass dispersed grain aggregates, and the average particle diameter of the diamond abrasive grains is about 4.0 μm, and the average particle diameter of the alumina particles is about 1 to 4.0 μm, the average particle size of the glass particles is about 1 to 4.0 μm, the maximum particle size of the alumina aggregate and the glass aggregate is 45 μm, and the ratio of these diamond agglomerated abrasive grains to the alumina aggregate and the glass aggregate is 1: Grinding was performed in the same manner as in Example 1 except that a diamond pad dispersed in the resin so as to be 0.5: 0.5 was used, and a glass substrate for a magnetic disk was produced.

(Comparative Example 1)
In the main surface grinding process of Example 1, a conventional diamond pad is used in which concentrated abrasive grains obtained by hardening a plurality of diamond abrasive grains with glass (the average grain diameter of the diamond abrasive grains is about 4.0 μm) are dispersed in the resin. Except for this, grinding was performed in the same manner as in Example 1 to produce a magnetic disk glass substrate.
(Comparative Example 2)
Grinding was carried out in the same manner as in Comparative Example 1 except that a diamond pad with a fixed grinding grain density of 30 (pieces / mm ² ) was used for the total fixed abrasive grains (in this example, only diamond abrasive grains). A glass substrate for a magnetic disk was produced.

In each of the above Examples and Comparative Examples, the main surface grinding was performed continuously for 100 batches, 100 batches in total.
In the above examples and comparative examples, the flatness of the glass substrate after grinding is measured using a flat nesting tester, and a predetermined standard (3 μm or less) is determined as a non-defective product. The rate (flatness defect rate) was calculated, and the results are shown in Table 1. Table 1 also shows the processing speed during grinding (processing speed ratio with respect to Comparative Example 1).

From the results in Table 1, the following can be understood.
1. In Comparative Example 1 using a conventional grinding tool (diamond pad) containing only diamond concentrating abrasive grains, when 100 batches are continuously processed, the processing speed and processing quality are lowered, and stable grinding cannot be performed.
On the other hand, in Examples 1 to 3 using the grinding tool in which the alumina particle aggregate or the glass dispersed particle, or both the alumina particle aggregate and the glass dispersed particle are dispersed together with the diamond concentrating abrasive grains, the processing speed and the processing are performed. Good quality (particularly the flatness of the substrate) can be achieved, and good processing quality can be stably obtained over a long period of time at a stable processing speed. In particular, in Example 2 in which diamond concentration abrasive grains and glass dispersion grains were used in combination, the flatness failure rate was zero%.
Further, it can be seen from the comparison between Comparative Examples 1 and 2 that when the grinding surface density of the fixed abrasive grains is decreased in the conventional diamond pad, the flatness defect rate is deteriorated although the processing speed is improved. This shows that stable processing cannot be achieved simply by lowering the fixed abrasive density.

(Manufacture of magnetic disk)
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 protective layer, and a lubricating layer are sequentially formed on the glass substrate. Filmed. As the protective layer, a hydrogenated carbon layer was formed. 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 Concentrated Abrasive Grain 4 Pellet 5 Diamond Particle 10 Glass Substrate

Claims

A method of manufacturing a glass substrate for a magnetic disk including a grinding process for grinding a main surface of a glass substrate,
The grinding process includes grinding abrasive grains, a binder that bonds the abrasive grains, and dispersed grains that are harder than the binder and softer than the abrasive grains. A method for producing a glass substrate for a magnetic disk, comprising grinding a main surface of a glass substrate using a grinding tool in which grains and the dispersed grains are bonded in a dispersed state.
2. The method for manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the binder is a resin material.
3. The method for producing a glass substrate for a magnetic disk according to claim 1, wherein the abrasive grains are concentrated abrasive grains in which a plurality of abrasive grains are bonded with a fixing material.
4. The method for producing a glass substrate for a magnetic disk according to claim 1, wherein the grinding abrasive grains include diamond abrasive grains.
5. The method for producing a glass substrate for a magnetic disk according to claim 1, wherein the dispersed particles are made of alumina or zirconia.
5. The method for manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the dispersed particles are made of glass softer than glass to be ground.
5. The method of manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the dispersed particles are aggregates in which a plurality of dispersed particles are bonded with glass softer than glass to be ground. .
The production of a glass substrate for a magnetic disk according to any one of claims 1 to 7, wherein a ratio of the dispersed grains to the abrasive grains in the binder is in a range of 0.1 to 5 times. Method.
A method for producing a magnetic disk, comprising forming at least a magnetic recording layer on the glass substrate for a magnetic disk produced by the method for producing a glass substrate for a magnetic disk according to any one of claims 1 to 8.
A grinding tool for grinding a glass substrate surface for an electronic device,
Grinding abrasive grains, a binder for bonding the abrasive grains, and dispersed grains that are harder than the binder and softer than the abrasive grains, and the abrasive grains and the dispersed grains in the binder And a grinding tool characterized by being combined in a dispersed state.