JP6193388B2 - Method of manufacturing glass substrate for magnetic disk, method of manufacturing glass substrate, method of manufacturing magnetic disk, and fixed abrasive wheel - Google Patents

Description

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

By the way, conventionally, a grinding method using fixed abrasive grains using a diamond pad has been proposed in a grinding process using loose abrasive grains (for example, Patent Document 1). A diamond pad is a sheet of diamond particles or agglomerates in which some diamond particles are hardened with a binder such as glass, ceramic, metal, or resin, using a support material such as resin (for example, acrylic resin). It is fixed on the top. 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.
After the grinding process is finished, mirror polishing is performed to obtain a highly accurate plane.

JP 2001-6161 A JP 2012-43492 A JP 2009-99249 A JP 2003-534137 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.
Conventionally, in the grinding process using fixed abrasive grains, when trying to increase the grinding speed, the density of the fixed abrasive grains has been increased (see Patent Document 2). However, according to the study by the present inventor, it has been found that the processing speed may not be increased only by increasing the density of the fixed abrasive grains. Further, it has been found that the processing speed varies even when diamond pads having the same abrasive density are used.

  The present inventor examined this cause, and when changing the fixed abrasive density, the dispersion state of the fixed abrasive in the pellet may be deteriorated, and the load applied to each fixed abrasive at this time is not uniform. In particular, it has been found that machining does not proceed at the initial stage of machining, and the machining speed decreases. In particular, when grinding directly with a fixed abrasive using a diamond pad on a glass plate manufactured by a float method or the like, since the glass substrate surface is a so-called mirror surface at the start of processing, diamond Since the abrasive grains do not readily penetrate the surface of the substrate and slip, and a time during which grinding cannot be performed (dead time) occurs, the above-described problem is remarkably generated. Moreover, even if the abrasive grain density is the same, the dispersion state of the fixed abrasive grains may be different, which may affect the processing speed.

The present invention has been made to solve such a conventional problem. The purpose of the present invention is to perform stable grinding by increasing the processing speed in grinding using fixed abrasive grains. It is providing the manufacturing method of the glass substrate for magnetic discs which can manufacture this glass substrate, and the manufacturing method of a magnetic disc using the glass substrate obtained by it.

As a result of earnest studies to solve the above problems, the present inventor found that the average inter-abrasive distance between the fixed abrasive wheels and the processing speed when the glass substrate was ground using the fixed abrasive wheels. We found that there is a correlation. Therefore, such a correlation is obtained in advance, a fixed abrasive wheel having an average inter-abrasive distance that provides a desired processing speed is selected based on the obtained correlation, and the selected fixed abrasive wheel is selected. It has been found that by using it, it is possible to increase the processing speed and perform stable grinding. It was also found that the main surface is particularly suitable for grinding a glass substrate having a mirror surface.
That is, in order to solve the above problems, the present invention has the following configuration.

(Configuration 1)
A method for producing a glass substrate for a magnetic disk, comprising a grinding process for grinding a main surface of a glass substrate using a lubricating liquid and a surface plate on which a fixed abrasive wheel is disposed on a grinding surface, the fixed abrasive The grindstone includes fixed abrasive grains contained in a support material, and grinds the glass substrate using the average abrasive distance between the fixed abrasive grains on the grinding surface of the fixed abrasive grindstone and the fixed abrasive grindstone. A correlation with the processing speed in the case of processing is obtained in advance, a fixed abrasive wheel having an average inter-abrasive distance that provides a desired processing speed is selected based on the obtained correlation, and the selected fixed abrasive A method for producing a glass substrate for a magnetic disk, wherein the grinding process is performed using a grain grindstone.

(Configuration 2)
A method for producing a glass substrate for a magnetic disk, comprising a grinding process for grinding a main surface of a glass substrate using a lubricating liquid and a surface plate on which a fixed abrasive wheel is disposed on a grinding surface, the fixed abrasive The grindstone includes fixed abrasive grains contained in a support material, and the average inter-abrasive distance of the fixed abrasive grains on the grinding surface of the fixed abrasive grindstone is 80 μm to 200 μm. A method for manufacturing a substrate.

(Configuration 3)
2. The method of manufacturing a glass substrate for a magnetic disk according to Configuration 1, wherein the average inter-abrasive distance is 80 μm to 200 μm.
(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 fixed abrasive has an average particle diameter of 15 to 50 [mu] m.

(Configuration 5)
The method for manufacturing a glass substrate for a magnetic disk according to any one of Structures 1 to 4, wherein the fixed abrasive grains include diamond abrasive grains.
(Configuration 6)
The method for producing a glass substrate for a magnetic disk according to any one of Structures 1 to 5, wherein the fixed abrasive is an abrasive grain or an abrasive aggregate in which a plurality of abrasive grains are hardened with a binder.

(Configuration 7)
7. The method of manufacturing a glass substrate for a magnetic disk according to any one of Structures 1 to 6, wherein the glass substrate is a glass substrate having a mirror-like main surface at the start of grinding.
(Configuration 8)
Machining load, method of manufacturing a glass substrate for a magnetic disk according to Structure 1, wherein a is ^{50g / cm 2 ~200g / cm 2} .

(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.

According to the present invention, it is possible to solve the conventional problems with the above-described configuration, and to perform stable grinding by increasing the processing speed in the grinding by the fixed abrasive. Thereby, it is possible to manufacture a high-quality glass substrate at low cost. Furthermore, a highly reliable magnetic disk can be obtained using the glass substrate obtained thereby.

It is a schematic sectional drawing which shows an example of a structure of a fixed abrasive grindstone (diamond pad). 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 measurement location of the distance between average abrasive grains on a fixed abrasive grindstone. It is a figure which shows the relationship between the distance between average abrasive grains, and a grinding rate.

Hereinafter, embodiments of the present invention will be described in detail.
A glass substrate for a magnetic disk is usually manufactured through a shape processing step, a grinding step, an end surface polishing step, a main surface polishing step, a chemical strengthening step, and the like.
In the method for producing a glass substrate for a magnetic disk of 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, this glass substrate is ground to improve 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, fixed abrasive grains containing diamond particles. In a double-side grinding apparatus, for example, a carrier is placed between upper and lower surface plates on which diamond pads are bonded as fixed abrasive grains. Both the main surfaces of the glass substrate are ground at the same time by closely moving the glass substrate and the upper and lower surface plates while closely holding the held glass substrate and sandwiching the glass substrate with the upper and lower surface plates with a predetermined pressure. . At this time, a lubricating liquid (coolant) is supplied to cool the working surface or to promote the processing.

As the fixed abrasive grindstone used in the present invention, for example, a diamond pad can be used, and an outline of the configuration is shown in FIG. The diamond pad 1 shown in FIG. 1 is an abrasive aggregate (collected abrasive grains or aggregated abrasive grains) in which a plurality of diamond particles 4 (see FIG. 2) are hardened with a binder such as glass, ceramic, metal, or resin. 2) is fixed using a support material 3 such as a resin (for example, acrylic resin). 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 grooves are formed in a resin layer after a resin layer containing diamond abrasive aggregates is formed on a sheet may be used. Further, instead of the above-mentioned abrasive aggregates, for example, single diamond particles may be dispersed as they are on a support material.

It is possible to produce the aggregates having different particle diameters (average particle diameter) and abrasive density. In the present embodiment, when it is referred to as fixed abrasive grains or simply abrasive grains, unless otherwise specified, it means the above-mentioned aggregate, and the average particle diameter of fixed abrasive grains, and abrasive grains When it says a density, it shall mean the average particle diameter of the said aggregate, and an abrasive grain density.

  The grinding process in the present invention is a grinding process in which the main surface of the glass substrate is ground using a lubricating liquid and a surface plate in which a fixed abrasive grindstone is provided on the grinding surface, as in the configuration 1 described above. The fixed abrasive whetstone includes fixed abrasive contained in a support material, and an average inter-abrasive distance of the fixed abrasive on the grinding surface of the fixed abrasive whetstone and the fixed abrasive whetstone Preliminarily obtained a correlation with the processing speed when grinding the glass substrate, and select a fixed abrasive grindstone having an average inter-abrasive distance to obtain a desired processing speed based on the obtained correlation, The grinding process is performed using the selected fixed abrasive grindstone.

  As previously explained, even if a fixed abrasive grindstone with the same abrasive grain density and grain size is used, the processing speed varies depending on the dispersion state of the abrasive grains, and stable grinding performance is achieved. It was not obtained. In short, the current performance is that the grinding performance of a fixed-abrasive grindstone such as a diamond pad cannot be understood unless it is actually used. The reason for this is, for example, that the physical properties of the abrasive grains and the resin differ greatly depending on the material, so that it is relatively difficult to uniformly disperse them in the manufacturing process.

As a result of intensive studies to solve the problems of the prior art, the inventor of the present invention grinds an average inter-abrasive distance between fixed abrasive grains on a grinding surface of a fixed abrasive grindstone and grinds a glass substrate using the fixed abrasive grindstone. It has been found that there is a correlation between the machining speed and the processing speed. Therefore, such a correlation is obtained in advance, and a fixed abrasive wheel having an average inter-abrasive distance that provides a desired processing speed is selected based on the obtained correlation. And, by selecting and using a fixed abrasive wheel having this predetermined average inter-abrasive distance, a high processing speed and stable grinding performance can be obtained, so that the processing speed is increased and stable grinding is performed. Is possible.
In short, it is possible to stably and increase the processing speed in grinding by using a fixed abrasive wheel in which the distance between the fixed abrasives is appropriately controlled on the surface of the fixed abrasive wheel (grinding surface). is there. The present invention is particularly suitable for grinding a glass substrate having a mirror-like main surface.

In the present invention, the average inter-abrasive distance of the fixed abrasive wheel is a value determined as follows.
(1) The surface (grinding surface) of a fixed abrasive wheel such as a diamond pad is observed using a scanning electron microscope (SEM).
(2) In the present invention, a rectangular area of 1.25 mm × 0.825 mm (= 1.03 mm ² ) is set as the measurement range.

In addition, the said measurement range is an example, Comprising: When determining a measurement range, it determines so that 15 or more fixed abrasives may be contained in one measurement range. Although details will be described later, the average inter-abrasive distance is obtained by calculating and averaging a plurality of values, so that the average inter-abrasive distance can be stably calculated.
If the set measurement range does not include 15 or more fixed abrasive grains, another measurement range is set. In addition, the fixed abrasive grains counted at this time are larger than the average particle diameter (D50) of the fixed abrasive grains when the diameter is obtained by approximating the circle among the fixed abrasive grains observed within the measurement range. Count the number of things only. The average particle diameter of the fixed abrasive may be obtained in advance. The reason for counting by focusing on fixed abrasive grains having an average particle diameter or larger is that other abrasive grains contribute very little to the grinding process. That is, when the fixed abrasive grains are mostly buried in the grindstone and the amount of protrusion from the grinding surface is small, or the abrasive grains having a small size themselves contribute very little to the processing. If these are also counted, there is a possibility that the correlation with the processing rate cannot be obtained.

In the present invention, the average particle diameter (D50) is 50% when the cumulative curve is determined with the total volume of the powder population in the particle size distribution measured by the laser diffraction method as 100%. The particle size (hereinafter referred to as “cumulative average particle size (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.

Moreover, in order to improve the reliability of the measurement result, it is desirable to provide a plurality of measurement locations. In the present invention, as shown in FIG. 3, two measurement regions are provided for each of the inner circumferential portion, the middle circumferential portion, and the outer circumferential portion on the grinding surface of one annular shaped fixed abrasive grindstone. The two locations are preferably provided so as to be point-contrast with respect to the center of the fixed abrasive wheel. And the said measurement location is provided about each of the upper and lower surface plates. As a result, a total of 12 measurement ranges are provided for one grinding apparatus.

(3) Of the plurality of abrasive grains present in each measurement range, pay attention to an arbitrary abrasive grain, select the abrasive grain closest to the abrasive grain, and determine the distance between the centers of the abrasive grains. measure. And the same measurement is performed about all the abrasive grains which exist in a measurement range, and the value which averaged the measured value of the obtained several distance between abrasive grains is made into the distance between abrasive grains of the measurement range. Similarly, the value measured and averaged at all 12 locations is taken as the “average distance between abrasive grains” of the fixed abrasive wheel.

In the present invention, the fixed abrasive is preferably a diamond abrasive aggregate. In this case, it is preferable that the average particle diameter (D50) of one diamond abrasive grain is about 1 to 10 μm. The average particle diameter (D50) of the diamond abrasive agglomerates is preferably about 15 μm to 50 μm. If the average particle diameter of the diamond abrasive grains is less than the above, the cutting with respect to the mirror-like glass substrate becomes shallow, and there is a possibility that the grinding of the glass substrate is difficult to proceed. On the other hand, if the average particle diameter of the diamond abrasive grains exceeds the above, the roughness of the finish becomes rough, so there is a possibility that the machining allowance load in the subsequent process becomes large.

In the present invention, as described above, based on the correlation between the average inter-abrasive distance obtained in advance and the processing speed when the glass substrate is ground using the fixed abrasive wheel, a desired processing speed is obtained. Is selected, and the average inter-abrasive distance is preferably in the range of 80 μm to 200 μm, for example. If the average inter-abrasive distance is too small, not only does the correlation with the processing speed disappear, but the average inter-abrasive distance is too close, and the processing speed may be reduced, resulting in a significant deterioration in productivity. On the other hand, even if the average inter-abrasive distance is too far, there is no correlation with the processing speed, and the processing speed decreases.

The density in the grinding surface of the fixed abrasive grains contained in the support material is preferably in the range of about 10 to 40 pieces / mm ^2.
Moreover, it is preferable that content of the fixed abrasive in a fixed abrasive grindstone is 5-80 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 grinding process according to the present invention, the load during processing, it is preferable to ^{50g / cm 2 ~200g / cm 2} . If it is smaller than this range, the processing speed becomes too low, and the productivity may be deteriorated. If it is larger than this range, scratches may occur.
In addition, when grinding a mirror-like glass substrate surface with a fixed abrasive wheel, first, for example, a diamond load is applied to the glass substrate surface so that a higher load is 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 aggregate 2 of diamond abrasive grains 4 bites into the glass substrate 10 and is ground (expected view).

The load at the start of processing or at the initial stage of processing is preferably in the range of 130 to 200 g / cm ² , for example. If the load is less than 130 g / cm ^{2, the} time during which grinding cannot be performed (dead time) cannot be sufficiently shortened, and the processing speed is reduced. On the other hand, if the load is larger than 200 g / cm ^{2, the} depth of cut by the abrasive grains becomes too deep and a lot of scratches are generated, so that it is necessary to increase the allowance for subsequent processing and subsequent polishing steps. The time will be longer.
Moreover, it is preferable that the load in the stage after the glass surface is roughened shall be the range of 50-120 g / cm < ² >, for example. By adjusting the grinding conditions, the surface roughness of the processed surface can be kept low.

In the present invention, it is preferable that the processing speed in the grinding processing is approximately in the range of 50 to 160 μm / min. Therefore, it is desirable to select a fixed abrasive grindstone having an average inter-abrasive distance at which such a processing speed can be obtained from the above correlation.

In the present invention, the surface of the glass substrate to be put into the grinding process is in a mirror state, and the surface roughness is, for example, Ra, 0.001 to 0.01 μm.
Moreover, in this invention, it is preferable that the surface roughness of the glass substrate after completion | finish of a grinding process finishes in the range of 0.080-0.130 micrometer by Ra. Thus, the processing load of a subsequent process can be reduced by keeping the roughness of the finish low.

According to the present invention, the plate thickness of the original material before being put into the grinding process is changed due to the design change of the process, the target plate thickness after the processing is changed, or the original material varies. Thus, even when the machining allowance has to be changed, the machining speed can be controlled, so that the grinding time can be made constant. As a result, when mass production is performed using a large number of grinding machines, the movement of the glass substrate can be systematically performed without waste such as time loss in the process chain of pretreatment, grinding treatment, and posttreatment, so that production efficiency Can be dramatically improved. This is extremely effective when mass production such as the manufacture of a glass substrate for a magnetic disk is assumed.

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. Examples of such aluminosilicate glass include SiO2 58 to 66%, Al2O3 13 to 19%, Li2O 3 to 4.5%, Na2O 6 to 13%, K2O 0 to 5%, and MgO. An amorphous aluminosilicate glass having a composition of 0 to 3.5% and CaO of 0 to 7% can be used.
Further, a glass containing SiO2 as a main component and containing 20% by weight or less of Al2O3 is preferable. Furthermore, it is more preferable to use glass containing SiO2 as a main component and containing Al2O3 by 15% by weight or less. Specifically, SiO2 is 62 wt% to 75 wt%, Al2 O3 is 5 wt% to 15 wt%, Li2 O is 4 wt% to 10 wt%, Na2 O is 4 wt% to 12 wt%, ZrO2 5.5% to 15% by weight as a main component, the weight ratio of Na 2 O / ZrO 2 is 0.5 to 2.0 and the weight ratio of Al 2 O 3 / ZrO 2 is 0.4 to 2.5 It is possible to use amorphous aluminosilicate glass that does not contain phosphorous oxide.

Further, as a heat-resistant glass used for the next-generation heat-assisted magnetic recording magnetic disk, for example, in terms of mol%, SiO2 is 50 to 75%, Al2O3 is 0 to 5%, and BaO is 0 to 2%. , 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 a total amount of 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, a group consisting of 56 to 75 mol% of SiO2, 1 to 9 mol% of Al2O3, 6 to 15 mol% in total of alkali metal oxides selected from the group consisting of Li2O, Na2O and K2O, 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 completion of the grinding process described above, mirror polishing is performed to obtain a highly accurate plane.
In the present invention, by applying the fixed abrasive method to the conventional free abrasive method in the grinding process, the processing surface roughness can be reduced, so the amount removed in the subsequent mirror polishing process Therefore, the processing load is 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 0.13 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 may 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. 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)
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 process was prepared, and cut into 70 mm x 70 mm square pieces using a diamond cutter. Subsequently, it processed into the disk shape of outer diameter 65mm and internal diameter 20mm using the diamond cutter. As the aluminosilicate _{glass, SiO 2 58~66%, Al 2} O 3 13~19%, Li 2 O3~ 4.5%, Na 2 O 6 ~13%, K 2 O 0~ 5%, MgO 0 Glass for chemical strengthening containing ~ 3.5%, CaO 0-7% 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.
(3) End surface polishing step 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 processing This main surface grinding processing is performed by using a double-sided grinding machine and setting a glass substrate held by a carrier between upper and lower surface plates on which diamond pads are attached as fixed abrasive wheels. It was. In the double-sided grinding device, the glass substrate held by the carrier is brought into close contact between the upper and lower surface plates to which the diamond pad is attached, and this carrier is engaged with the sun gear (sun gear) and the internal gear (internal gear), The glass substrate is sandwiched between upper and lower surface plates. After that, by supplying and rotating a grinding liquid between the diamond pad and the grinding surface of the glass substrate, the glass substrate revolves while rotating on the surface plate to simultaneously grind both surfaces.
The diamond pad includes fixed abrasive grains composed of aggregates of diamond abrasive grains. The average particle diameter of the aggregates is about 25 μm, and the average grain diameter (D50) of the diamond abrasive grains is about 2.5 μm. A plurality of diamond pads were prepared. 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.

In this grinding process, the average inter-abrasive distance of the fixed abrasive grains in each diamond pad was determined by the above-described method, and 10,000 diamonds were processed using each diamond pad.
Then, a correlation between the inter-abrasive distance (average inter-abrasive distance) of each diamond pad and the processing speed (grinding rate) when the glass substrate was ground using the diamond pad was determined. The results are shown in Tables 1 and 2 below. In Table 1, the value of the abrasive density is also shown. 4 is a graph showing the relationship between the inter-abrasive distance (average inter-abrasive distance) and the processing speed (grinding rate) based on Tables 1 and 2.
The grinding speed is a value obtained by dividing the total grinding thickness by the total machining time.

(5) Main surface polishing step (first polishing step)
Next, a first polishing process for removing scratches and distortions remaining in the above-described grinding process was performed using a double-side polishing apparatus having the same configuration as the grinding process. Specifically, a hard polisher (hard foamed urethane) was used as the polisher, and the first polishing step was performed. 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 subjected to ultrasonic cleaning 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 in which potassium nitrate and sodium nitrate were mixed was prepared, and the cleaned and dried glass substrate was immersed in a solution obtained by heating and melting the chemical strengthening solution to perform chemical strengthening treatment. .

(7) Main surface polishing step (second polishing step)
Next, the same double-side polishing apparatus as used in the first polishing step was used, and the second polishing step was carried out by replacing the polisher with a polishing pad (made of polyurethane foam) of a 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 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 ultrasonically cleaned 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. Further, the main surface of the glass substrate was mirror-like, and when examined using a laser-type surface defect analyzer, surface defects such as abnormal 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.

From the results of Tables 1 and 2, the following can be understood.
The relationship between the processing speed (grinding rate) and the abrasive density is low, and the correlation with the inter-abrasive distance (average inter-abrasive distance) is high. In particular, a good correlation with the grinding rate is observed when the distance between abrasive grains (average distance between abrasive grains) is in the range of 80 μm to 200 μm (see FIG. 4).
Accordingly, by selecting and using a fixed abrasive grindstone having an inter-abrasive distance that provides a desired processing speed based on the obtained correlation, a high processing speed and stable grinding performance can be obtained. This makes it possible to perform stable grinding processing.
In addition, when the average particle diameter (D50) of the diamond abrasive grains is 1.5 μm and the average particle diameter (D50) of the aggregates is 15 μm, the average particle diameter (D50) of the diamond abrasive grains is 9 μm and the average particles of the aggregates When the diameter (D50) was 50 μm, the same investigation was performed, and a good correlation with the grinding rate was observed when the average distance between the abrasive grains was in the range of 80 μm to 200 μm.

(Manufacture of magnetic disk)
The following film forming steps were performed on the magnetic disk glass substrate obtained in the above example 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 Abrasive aggregate (concentrated abrasive grains)
3 Support material 4 Diamond particle 10 Glass substrate

Claims (19)

A method for producing a glass substrate for a magnetic disk including a grinding process for grinding a main surface of a glass substrate using a lubricating liquid and a surface plate on which a fixed abrasive grindstone is arranged on a grinding surface,
Grinding the main surface of the glass substrate while sandwiching the glass substrate with an upper and lower surface plate,
The fixed abrasive grindstone includes a fixed abrasive contained in a support material,
The correlation between the average inter-abrasive distance of the fixed abrasive grains on the grinding surface of the fixed abrasive grindstone and the processing speed when the glass substrate is ground using the fixed abrasive grindstone is determined in advance,
Based on the obtained correlation, a fixed abrasive wheel having an average inter-abrasive distance that provides a desired processing speed is selected, and the grinding process is performed using the selected fixed abrasive wheel. Manufacturing method of glass substrate for magnetic disk. A method for producing a glass substrate for a magnetic disk including a grinding process for grinding a main surface of a glass substrate using a lubricating liquid and a surface plate on which a fixed abrasive grindstone is arranged on a grinding surface,
Grinding the main surface of the glass substrate while sandwiching the glass substrate with an upper and lower surface plate,
The fixed abrasive grindstone includes a fixed abrasive contained in a support material,
The method for producing a glass substrate for a magnetic disk, wherein an average inter-abrasive distance of the fixed abrasive grains on the grinding surface of the fixed abrasive grindstone is 80 μm to 200 μm.   The method for producing a glass substrate for a magnetic disk according to claim 1, wherein the average inter-abrasive distance is 80 μm to 200 μm.   4. The method for producing a glass substrate for a magnetic disk according to claim 1, wherein the fixed abrasive has an average particle diameter of 15 μm to 50 μm. The fixed abrasive process for producing a glass substrate for a magnetic disk according to any one of claims 1 to 4, characterized in that it comprises a diamond abrasive particles. The fixed abrasive, abrasive particles or, more abrasive particles of glass substrate according to any one of claims 1 to 5, characterized in that a abrasive grain agglomerates which are hardened by the binder Production method. The glass substrate, method of manufacturing a glass substrate for a magnetic disk according to any one of claims 1 to 6, characterized in that the main surface during grinding start is a glass substrate of a mirror surface. Machining ^{load, 50g / cm 2 ~200g / cm} 2 A method of manufacturing a glass substrate according to any one of claims 1 to 7, characterized in that. A method for producing a glass substrate including a grinding process for grinding a main surface of a glass substrate using a lubricating liquid and a surface plate provided with a fixed abrasive grindstone on a grinding surface,
The glass substrate is a glass substrate that is a source of a glass substrate for a magnetic disk,
Grinding the main surface of the glass substrate while sandwiching the glass substrate with an upper and lower surface plate,
The fixed abrasive grindstone includes a fixed abrasive contained in a support material,
The correlation between the average inter-abrasive distance of the fixed abrasive grains on the grinding surface of the fixed abrasive grindstone and the processing speed when the glass substrate is ground using the fixed abrasive grindstone is determined in advance,
Based on the obtained correlation, a fixed abrasive wheel having an average inter-abrasive distance that provides a desired processing speed is selected, and the grinding process is performed using the selected fixed abrasive wheel. A method for producing a glass substrate. A method for producing a glass substrate including a grinding process for grinding a main surface of a glass substrate using a lubricating liquid and a surface plate provided with a fixed abrasive grindstone on a grinding surface,
The glass substrate is a glass substrate that is a source of a glass substrate for a magnetic disk,
Grinding the main surface of the glass substrate while sandwiching the glass substrate with an upper and lower surface plate,
The fixed abrasive grindstone includes a fixed abrasive contained in a support material,
The method for producing a glass substrate, wherein an average inter-abrasive distance of the fixed abrasive grains on the grinding surface of the fixed abrasive grindstone is 80 μm to 200 μm. The method for producing a glass substrate according to claim 9, wherein the average inter-abrasive distance is 80 μm to 200 μm. The method for producing a glass substrate according to claim 9, wherein the fixed abrasive has an average particle diameter of 15 μm to 50 μm. The method for manufacturing a glass substrate according to claim 9, wherein the fixed abrasive grains include diamond abrasive grains. The method for manufacturing a glass substrate according to any one of claims 9 to 13, wherein the fixed abrasive is an abrasive grain or an abrasive aggregate in which a plurality of abrasive grains are hardened with a binder. A method for producing a glass substrate for a magnetic disk, comprising performing at least polishing treatment on a main surface of the glass substrate produced by the method for producing a glass substrate according to claim 9. A magnetic disk comprising at least a magnetic recording layer formed 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 . Manufacturing method. A fixed abrasive grindstone used for grinding processing to grind the main surface of the glass substrate while sandwiching the glass substrate with an upper and lower surface plate provided on the grinding surface.
The fixed abrasive grindstone includes a fixed abrasive contained in a support material,
The fixed abrasive includes diamond abrasive particles,
The fixed abrasive grindstone, wherein an average inter-abrasive distance between the fixed abrasive grains on a grinding surface of the fixed abrasive grindstone is 80 μm to 200 μm. The fixed abrasive grain according to claim 17, wherein the fixed abrasive grains are abrasive grains or an abrasive aggregate in which a plurality of abrasive grains are hardened with a binder. The fixed abrasive grindstone according to claim 17 or 18, wherein an average particle diameter of the fixed abrasive is 15 µm to 50 µm.

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