JP6642864B2 - Method of manufacturing glass substrate used for manufacturing glass substrate for magnetic disk, and method of manufacturing glass substrate for magnetic disk - 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.

A magnetic disk is one of information recording media mounted on a magnetic disk device such as a hard disk drive (HDD). A magnetic disk is formed 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, in recent years, in response to the pursuit of higher recording density, the ratio of a glass substrate capable of making the distance between a magnetic head and a magnetic disk narrower than that of an aluminum substrate has been gradually increasing. Further, the surface of the glass substrate is polished with high precision to achieve a high recording density so that the flying height of the magnetic head can be reduced as much as possible. In recent years, demands for higher recording capacity and lower price of HDDs are only increasing, and in order to realize this, glass substrates for magnetic disks also require higher quality and lower cost. Is coming.

As described above, high smoothness of the surface of the magnetic disk is indispensable for lowering the flying height (flying height) required for higher recording density. In order to obtain high smoothness on the surface of the magnetic disk, a substrate surface with high smoothness is ultimately required. Therefore, it is necessary to polish the glass substrate surface with high precision. In order to manufacture such a glass substrate, after adjusting the plate thickness and reducing flatness (flatness) by a grinding (lapping) process, a polishing process is further performed to reduce the surface roughness and minute waviness. And a very high smoothness on the main surface.

By the way, conventionally, in a grinding (lapping) step (for example, Patent Document 1 or the like) using free abrasive grains, a grinding method using fixed abrasive grains using a diamond pad has been proposed (for example, Patent Documents 2 and 3). etc). A diamond pad is a diamond pad or an aggregate of several diamond particles fixed with a binder such as glass, ceramic, metal, or resin using a support material such as a resin (eg, acrylic resin). The resulting pellets are attached to a sheet of resin or the like. Alternatively, a protrusion may be formed by forming a groove in the resin layer after forming a resin layer containing diamond on the sheet. The diamond pad mentioned here is not necessarily a general name, but is referred to as a “diamond pad” for convenience in the present specification.

With conventional loose abrasives, abrasive grains with a deformed shape intervene between the surface plate and the glass and exist unevenly, so when the load on the abrasive particles is not constant and the load is concentrated, the surface of the surface plate Because of the low elasticity of cast iron, the glass has deep cracks, the work-affected layer is deep, and the work surface roughness of the glass is also large, so a large amount of removal was required in the subsequent mirror polishing step, It was difficult to reduce the processing cost. In contrast, in grinding with fixed abrasive grains using a diamond pad, since the abrasive grains are uniformly present on the sheet surface, the load is not concentrated and the abrasive grains are fixed to the sheet using resin. Therefore, even if a load is applied to the abrasive grains, the cracks (work-affected layers) on the processed surface are shallow due to the high elasticity of the resin that fixes the abrasive particles, making it possible to reduce the processed surface roughness. Load (such as allowance) is reduced, and processing costs can be reduced.
After the completion of the grinding (lapping) step, mirror polishing is performed to obtain a highly accurate flat surface.

JP 2001-6161 A JP 2012-99173 A JP 2009-99249 A

As described above, according to the grinding method using fixed abrasive grains using a diamond pad, the surface roughness of the processed surface can be reduced, the load on the subsequent mirror polishing step is reduced, and the processing cost of the glass substrate is reduced. Although reductions are possible, the inventors have found that the following problems are encountered according to the study by the present inventors.
For example, a glass substrate obtained by cutting a sheet-like glass plate manufactured by a float method or the like into a predetermined shape is directly ground by a fixed abrasive using a conventional diamond pad as disclosed in Patent Document 2 described above. In the case of processing, since the surface of the glass substrate is a so-called mirror surface, there is a problem in that diamond abrasive grains are not easily sunk into the substrate surface and slip during the initial stage of processing, and there is a problem that time during which grinding cannot be performed occurs. This greatly reduces productivity.

It is to be noted that, in the above Patent Document 3, before the fixed abrasive grinding step of the specular glass, the surface of the specular glass is roughened mechanically or chemically to the extent that the fixed abrasives are polished (for example, liberation of alumina or the like). Although a technique of lapping using abrasive grains) is disclosed, another step is added, so that productivity is reduced. In addition, lapping with free abrasive grains enables stable processing of mirror-surface glass, but has a problem that the processing load in the subsequent process increases because the cuts (work-changed layers) enter deeply.

The present invention has been made to solve such a conventional problem, and an object thereof is to perform the grinding without reducing the processing speed by reducing the time during which grinding cannot be performed in the grinding with fixed abrasive grains. It is an object of the present invention to provide a method of manufacturing a glass substrate for a magnetic disk capable of manufacturing a high quality glass substrate at low cost, and a method of manufacturing a magnetic disk using the glass substrate obtained by the method.

In order to solve the above problems, the present invention has the following configurations.
(Configuration 1)
A method for manufacturing a glass substrate for a magnetic disk, comprising a grinding process of grinding a main surface of a glass substrate using a lubricating liquid and a surface plate provided with fixed abrasive grains including diamond particles on a grinding surface, The glass substrate is a glass substrate whose main surface is a mirror surface, and the grinding processing includes a first step of roughening the glass substrate surface with a load higher than a load for performing the grinding processing, and after the first step. Has a second stage of grinding the glass substrate surface with a lower load than the load of the first stage, the grinding process having the first stage and the second stage, the same processing A method for manufacturing a glass substrate for a magnetic disk, characterized by using

(Configuration 2)
When the load in the first stage is P1 (g / cm ² ) and the load in the second stage is P2 (g / cm ² ), P1 / P2 = 3.0 or less. 3. A method for manufacturing a glass substrate for a magnetic disk according to (1).
(Configuration 3)
3. A magnetic disk according to claim 2, wherein t1 <t2 when a time for maintaining the load P1 in the first stage is t1 and a time for maintaining the load P2 in the second stage is t2. A method for manufacturing a glass substrate.

(Configuration 4)
4. The method of manufacturing a glass substrate for a magnetic disk according to any one of Configurations 1 to 3, wherein the surface roughness of the glass substrate to be charged is 0.05 μm or less in Ra.

(Configuration 5)
5. The method of manufacturing a glass substrate for a magnetic disk according to any one of Configurations 1 to 4, wherein a processing speed in the grinding processing is 3.0 μm / min to 9.0 μm / min.
(Configuration 6)
6. The method of manufacturing a glass substrate for a magnetic disk according to any one of Configurations 1 to 5, wherein the surface roughness of the glass substrate after the second step is 0.080 μm to 0.130 μm in Ra.

(Configuration 7)
A method of manufacturing a magnetic disk, characterized by forming at least a magnetic recording layer on a glass substrate for a magnetic disk manufactured by the method of manufacturing a glass substrate for a magnetic disk according to any one of Configurations 1 to 6.

ADVANTAGE OF THE INVENTION According to this invention, the fall of productivity by generation | occurrence | production of the time which cannot grind in the grinding using the conventional fixed abrasive grain can be improved. Further, according to the present invention, it is possible to suppress the surface roughness of the processed surface without lowering the processing speed, and it is also possible to reduce the processing load in the subsequent steps. Thus, a high-quality glass substrate can be manufactured at low cost. Further, a highly reliable magnetic disk can be obtained using the glass substrate obtained thereby.

FIG. 2 is a schematic cross-sectional view illustrating a configuration of a diamond pad used in the present invention. It is a schematic diagram for explaining the state at the time of grinding. It is a figure showing an example of the sequence of the applied load in the grinding processing of the present invention. FIG. 2 is a schematic cross-sectional view illustrating a configuration of a diamond pad used in the present invention.

Hereinafter, embodiments of the present invention will be described in detail.
As described in the above configuration 1, the present invention provides a magnetic method including a grinding process for grinding a main surface of a glass substrate using a lubricating liquid and a surface plate provided with fixed abrasive grains including diamond particles on a grinding surface. A method for manufacturing a glass substrate for a disk, wherein the glass substrate is a glass substrate having a main surface having a mirror surface, and the grinding processing includes roughening the surface of the glass substrate with a load higher than a load for performing the grinding processing. A first step to perform, after the first step, a second step of performing a grinding process on the glass substrate surface with a lower load than the load of the first step, the first step and the second step Wherein the grinding process is performed using the same apparatus.

A glass substrate for a magnetic disk is usually manufactured through a rough grinding step (rough lapping step), a shape processing step, a fine grinding step (fine lapping step), an end face polishing step, a main surface polishing step, a chemical strengthening step, and the like. .
In the method of manufacturing a glass substrate for a magnetic disk according to the present invention, a glass substrate having a mirror-finished main surface is obtained by cutting a sheet glass manufactured by a float method or a downdraw method into a predetermined size. Alternatively, a glass substrate having a mirror-finished main surface manufactured by pressing from molten glass may be used.

Next, grinding (lapping) is performed on the glass substrate to improve dimensional accuracy and shape accuracy. In this grinding process, the main surface of the glass substrate is usually ground using a hard abrasive such as diamond using a double-sided lapping device. By grinding the main surface of the glass substrate in this manner, a predetermined thickness and flatness are obtained, and a predetermined surface roughness is obtained.

The present invention relates to the improvement of the grinding process. The grinding process in the present invention is a grinding process using fixed abrasive grains containing diamond particles. For example, in a double-sided lapping apparatus, an upper and lower platen on which a diamond pad as a grinding tool (fixed abrasive wheel) is attached. The glass substrate held by a carrier is brought into close contact with the glass substrate, and the glass substrate and the upper and lower platens are relatively moved while the glass substrate is pressed at a predetermined pressure by the upper and lower platens, so that the two substrates Grind the surface simultaneously. At this time, a lubricating liquid (coolant) is supplied to cool the working surface or to promote the working.

FIG. 4 schematically shows the configuration of a diamond pad 1 which is a grinding tool (fixed abrasive wheel) used in the present invention. Some diamond particles 5 (see FIG. 2) are made of glass, ceramic, metal, Alternatively, the aggregate 3 hardened with a binder such as a resin is fixed on a sheet using a support material 6 such as a resin (for example, an acrylic resin). FIG. 1 schematically shows another configuration. An aggregate 3 in which some diamond particles 5 (see FIG. 2) are fixed with a binder such as glass, ceramic, metal, or resin is formed into a resin (for example, acrylic). Pellets 4 fixed using a support material such as a base resin) are attached to the sheet 2. Needless to say, the configurations shown in FIGS. 1 and 4 are merely examples, and the present invention is not limited to this. For example, after a resin layer containing the above-mentioned aggregates 3 is formed on a sheet, a groove may be formed in the resin layer to form a protruding diamond pad.

It is possible to produce agglomerates 3 having different particle diameters (average particle diameters) and different abrasive grain densities in the resin.
In the present embodiment, the case where the diamond fixed abrasive grains are the above-mentioned aggregates will be described. Therefore, in the present invention, when referring to diamond fixed abrasive grains, unless otherwise specified, shall mean the above-mentioned aggregates, and also when the average grain size of the diamond fixed abrasive grains, and the abrasive grain density Means the average particle size of the aggregate and the density of the aggregate in the resin.
However, the present invention is not limited to the case where the diamond fixed abrasive is the above-mentioned aggregate. It is also possible to use a diamond pad in which the diamond fixed abrasive grains are not aggregates but one diamond particle.

  The grinding process in the present invention, as described above, the first step of roughening the glass substrate surface with a load higher than the load for performing the grinding process, after the first step, after the load of the first step And a second step of grinding the surface of the glass substrate with a low load. The grinding processing including the first step and the second step is performed using the same apparatus.

  In order to directly grind the mirror surface glass surface with a diamond pad, first, it is necessary to apply a higher load to the glass surface in order to cause the diamond abrasive grains to bite into the glass substrate surface than in the normal grinding process. The higher the load, the deeper the cutting depth of the abrasive grains, so that the glass surface can be roughened (roughened). The first step is a step of roughening the surface of the specular glass by intruding diamond abrasive grains into the surface.

  After the glass surface is roughened in the first stage during such processing, a high load is not required for the grinding, but rather the original condition under the condition that the load is reduced and the cutting depth of the abrasive grains is reduced. Perform grinding (main processing). The second step is a step for performing the main processing. FIG. 2 is a schematic diagram for explaining a state at the time of the grinding process, and shows a state where the aggregate 3 as the diamond fixed abrasive grains cut into the glass substrate 10 and is ground (expected view).

By performing the grinding process including the above first and second steps, the grinding process can be performed without reducing the processing speed. Further, by adjusting the detailed conditions of these grinding processes, the surface roughness of the finished processed surface can be suppressed to be low.
FIG. 3 is a diagram showing an example of a sequence of an applied load in the grinding processing of the present invention.
The horizontal axis in FIG. 3 is time, and the vertical axis is applied load. The load is gradually increased from the start, and when the load reaches P1 (point A), a predetermined time (t1) is maintained. This is the first stage, and the glass surface is roughened.
The application of the load to point A may be performed in multiple steps. That is, the load may be increased stepwise (in a stepwise manner in the sequence diagram).

Then, the load is gradually lowered from the point B, and when a normal grinding load P2 is reached (point C), the predetermined time (t2) is maintained, and the grinding is completed at the point D. This time is the second stage, which is the stage for performing the main processing.
Here, the “loads P1 and P2” indicate values that are maintained for a certain period of time, and do not include loads that are being raised.

The load P1 in the first stage is preferably in the range of 130 to 200 g / cm ² . When the load P1 is smaller than 130 g / cm ² , the surface roughening becomes insufficient, so that the time during which the grinding cannot be performed cannot be sufficiently reduced, and the processing speed may be reduced. That is, since the surface roughness after the first step does not become sufficiently large, the fixed abrasive grains may slip in the second step, and the grinding rate may be reduced. If the load P1 is smaller than 130 g / cm ² , the adhesion between the glass substrate and the surface plate may be insufficient. In this case, the difference between the load applied to the upper platen on the upper surface of the glass substrate and the load applied to the lower platen on the lower surface of the glass substrate increases, and a problem occurs in that the entire or part of the lower surface of the glass substrate is not ground. There are cases. This is presumably because the coolant easily accumulates on the lower surface plate due to the influence of gravity, and a coolant film is formed between the lower surface plate and the glass substrate. This problem can be solved by applying a load higher than 130 g / cm ² and firmly sandwiching the glass substrate between the upper and lower platens.
On the other hand, if the load P1 is larger than 200 g / cm ^{2, the} depth of cut by the abrasive grains becomes too deep, so that many scratches are generated, and it is necessary to increase the allowance for the main processing and the subsequent polishing step. May be longer. Further, the glass substrate may be broken or cracked.

The load P2 in the second stage is preferably in the range of 50 to 120 g / cm ² . By grinding the surface roughened with a load lower than the first stage and within the above range, the surface roughness of the processed surface can be suppressed to a low level.
Further, P1 / P2 is preferably 1.20 or more. By doing so, the processing speed can be further increased and the roughness can be reduced. More specifically, the surface roughness after the grinding process can be 0.12 μm or less.
Further, it is preferable that P1 / P2 = 3.0 or less. When P1 / P2 is larger than 3.0, the adhesion between the glass substrate and the surface plate is temporarily insufficient when shifting from the first stage to the second stage, and all or a part of the lower surface of the glass substrate May not be ground.

Further, it is preferable that the load application speed (gradient k) in the first stage from the start of processing to the point A (load P1) be 0.5 to 15 g / (cm ² · sec). If the slope k is less than 0.5 g / (cm ² · sec) (slow application speed), the abrasive grains will not slip and bite due to the low load, but rather the abrasive grains will be worn, and the coarseness in the first stage It is not preferable because the grinding ability is deteriorated, for example, the surface is insufficiently formed or the processing rate is reduced. On the other hand, if the inclination k is larger than 15 g / (cm ² · sec) (the application speed is high), a sharp load is applied to the abrasive grains on the glass substrate, so that the abrasive grains are crushed and the grinding ability is reduced. Or the glass substrate may be broken. Further, from the viewpoint of the number of times (life) that the grinding pad can be used, it is more preferable to set it to 4 g / (cm ² · sec) or more.

In addition, the time t1 for roughening the surface with the load P1 in the first stage is preferably, for example, in the range of 10 to 600 seconds. If t1 is shorter than 10 seconds, the penetration of abrasive grains into the glass main surface is insufficient, and the processing speed may be reduced. On the other hand, when t1 is longer than 600 seconds, deep scratches are likely to occur, and the finished main surface may be rough.

Further, it is preferable that the load is gradually reduced from the point B (load P1) to the point C at which the normal grinding load P2 is reached, for example, in a range of 10 to 90 seconds. If the time between BC is shorter than 10 seconds, the flatness of the substrate may be deteriorated due to a sudden load change. In such a case, by the same mechanism as when the above-mentioned load P1 is smaller than 130 g / cm ² , the upper platen acts on the load acting on the upper surface of the glass substrate and the lower platen acts on the load acting on the lower surface of the glass substrate. The difference is likely to temporarily increase. Therefore, it is presumed that the entire or a part of the glass substrate is not properly ground, so that a portion having poor flatness remains.
On the other hand, if the time between BCs is longer than 90 seconds, the glass is excessively ground during the transition from P1 (first stage) to P2 (second stage), so that it becomes difficult to control the thickness of the glass, May occur to increase the finished main surface roughness.

Further, it is preferable that the time t2 at which the grinding is performed with the load P2 in the second stage is 30 seconds or more. Unless a certain amount is processed by the load P2, the groove formed by the load P1 cannot be completely removed, and the groove may remain as a scratch. The upper limit of t2 is appropriately determined in consideration of the finish quality in the grinding process and the like.
It is preferable that t1 <t2 because the roughness of the finish can be reduced. If t1 ≧ t2, the surface roughness may not be reduced after processing. That is, the present invention is a technology that can achieve both a high grinding rate and low roughness after processing, but if the processing time of the second step due to low load is insufficient, the roughness increased by the first step is reduced by the second step. May be too low. Further, there is a possibility that scratches remain. These problems can be solved by increasing the allowance for the subsequent polishing step, but can contribute to an increase in manufacturing cost.
Further, it is preferable that P1 × t1 (area) <P2 × t2 (area). This makes it possible to sufficiently reduce the surface roughness after the grinding process.

Further, in the present invention, the processing speed in the entire grinding processing is preferably 2.0 μm / min or more, more preferably 3.0 μm / min or more. Within this range, it is possible to perform grinding without reducing the processing speed. The processing speed in the entire grinding processing is a value obtained by dividing the total grinding thickness by the total processing time (including the first step and the second step).

In the present invention, it is preferable that the diamond fixed abrasive has an average particle diameter of 20 to 40 μm. Further, the individual particle size of the diamond fixed abrasive is preferably 10 to 50 μm. If the average grain size or individual grain size of the diamond abrasive grains is less than the above, the cut into the mirror-like glass substrate becomes shallow, and the cut into the glass substrate does not progress. On the other hand, if the average particle size or the individual particle size of the diamond abrasive grains exceeds the above, the roughness of the finished product becomes coarse, so that the load for the allowance in the subsequent process increases.
Note that, as described above, the diamond fixed abrasive here means the aggregate. The size of each diamond particle contained in the aggregate is preferably 1 to 5 μm in average particle size.

In the present invention, the average particle diameter (D50) is defined as a cumulative curve when the total volume of the powder group in the particle size distribution measured by the laser diffraction method is 100% and the cumulative curve is 50%. (Hereinafter, referred to as “cumulative average particle diameter (50% diameter)”). In the present invention, the cumulative average particle diameter (50% diameter) is specifically a value obtained by measuring using a particle diameter / particle size distribution measuring device.

As described above, in the present invention, the grinding process uses the same fixed abrasive grindstone (diamond pad) and continuously performs “load higher than normal grinding + normal load” in one process. Then, in order to increase the productivity, the same process is repeated after replacing the substrate. At this time, it was ascertained that sludge tends to accumulate on the surface of the fixed abrasive whetstone because the main surface of the input substrate is a mirror surface. When processing a glass substrate after conventional lapping, the sludge accumulated on the grindstone surface due to the grinding process is removed by the new glass substrate surface that is thrown one after another because the surface roughness of the input substrate is large. However, the effect cannot be obtained when the mirror-finished glass substrate is directly ground as in the present invention.
In other words, it has been found that, when performing a large number of treatments using the same fixed abrasive grindstone in order to improve productivity, it is necessary to precisely control the protrusion amount of the abrasive grains.

  In the grinding process of the present invention, it is preferable to grind the main surface of the glass substrate using a grinding wheel having a suitably adjusted amount of protrusion of the grinding abrasive grains (that is, diamond fixed abrasive grains).

For example, when using a grinding wheel having a small protrusion amount of the above-mentioned grinding particles, sludge accumulates on the surface of the grinding wheel, which hinders the abrasive particles from contacting the glass surface and sufficiently acts on the glass surface. Since there are many abrasive grains that cannot be used (have a weak effect on the glass surface), the above-described partial grinding failure occurs, and as a result, the incidence of flatness failure after processing increases.

On the other hand, by using a grinding wheel in which the amount of protrusion of the grinding particles is suitably adjusted, even if sludge is accumulated on the surface of the grinding wheel, it is possible to suppress that the abrasive particles are prevented from being in contact with the glass surface. Therefore, the abrasive grains can stably act on the glass surface, and stable grinding without unevenness in grinding can be performed.

The protrusion amount of the abrasive grains of the grinding wheel can be measured as follows.
Assuming that the distance from the inner circumference to the outer circumference is 100% with respect to the grinding wheel (usually formed in a disk shape) of the upper and lower platens before the grinding process is performed, 10%, 50%, 90% from the inner circumference. From the% position, a total of six samples (pad pieces) each having a size of 2.5 mm × 2.5 mm are cut out. For each of the six samples, for example, five arbitrary abrasive grains were selected from an observation image obtained using, for example, a laser microscope, and the height difference between the abrasive grains and the resin portion around the abrasive grains was measured. The average value of the height difference of the abrasive grains is defined as the protrusion amount of the abrasive grains of the grinding wheel.

In order to adjust the protrusion amount of the abrasive grains, for example, it is possible to carry out a dressing process. Specifically, for example, a double-sided grinding device used for grinding is also applied to dress processing, and a grindstone controlled to have an appropriate thickness variation is formed on a grinding grindstone surface such as a diamond pad disposed on an upper and lower platen. The dressing process can be performed in a state where the upper and lower platens of the double-sided grinding machine are rotated while being brought into contact with each other. The material of the grindstone used for the dressing process is not particularly limited, but for example, an alumina grindstone is suitable. In this case, the dressing process may be performed stepwise using a plurality of grindstones having different thickness variations.

In the present invention, the main surface of the glass substrate to be put into the grinding process is a mirror surface, and the surface roughness is usually 0.05 μm or less in Ra, more preferably 0.001 to 0.01 μm. In the present invention, in particular, since the surface roughness Ra of the glass substrate to be put into the grinding process can be extremely low, that is, 0.001 to 0.01 μm, it is possible to minimize the post-process allowance, thereby reducing the cost. It is possible to manufacture a magnetic disk glass substrate.
In the present invention, the surface roughness of the glass substrate after the completion of the first step is generally in the range of 0.100 to 0.150 μm in Ra. By roughening the surface in this range, the subsequent second-stage grinding is favorably performed.
Further, in the present invention, the surface roughness of the glass substrate after the completion of the second step is finished in a range of 0.080 to 0.130 μm in Ra. As described above, the roughness of the finish can be suppressed to a low level, so that the processing load in the subsequent steps can be reduced.

As described above, in the grinding process of the present invention, it is possible to improve the decrease in productivity due to the occurrence of time during which grinding cannot be performed in the conventional grinding using fixed abrasive grains, Since the grinding processing including the second step can be performed continuously using the same apparatus, it is possible to increase productivity. Further, according to the grinding processing of the present invention, it is possible to suppress the surface roughness of the processed surface without lowering the processing speed, and it is also possible to reduce the processing load in the subsequent steps.

In the present invention, the glass constituting the glass substrate is preferably made of amorphous aluminosilicate glass. Such a glass substrate can be finished to a smooth mirror surface by mirror-polishing the surface, and has good strength after processing. As such aluminosilicate glass, for example, a glass containing SiO ₂ as a main component and containing Al ₂ O ₃ at 20% by weight or less is preferable. Further, it is more preferable to use glass containing SiO ₂ as a main component and Al ₂ O ₃ at 15% by weight or less. Specifically, SiO ₂ is 62% to 75% by weight, Al ₂ O ₃ is 5% to 15% by weight, Li ₂ O is 4% to 10% by weight, and Na ₂ O is 4% by weight. % To 12% by weight, 5.5% to 15% by weight of ZrO ₂ as a main component, and a weight ratio of Na ₂ O / ZrO ₂ of 0.5 to 2.0, Al ₂ O _An amorphous aluminosilicate glass containing no phosphorus oxide and having a weight ratio of ₃ / ZrO ₂ of 0.4 or more and 2.5 or less can be used.
Also, as this aluminosilicate glass, expressed in weight%,
_{SiO 2 58~66%, Al 2 O} 3 13~19%, Li 2 O 3~ 4.5%, Na 2 O 6~13%, K 2 O 0~ 5%, R 2 O 10~18%, (However, R ₂ O = Li ₂ O + Na ₂ O + K ₂ O)
MgO 0-3.5%, CaO 1-7%, SrO 0-2%, BaO 0-2%, RO 2-10%, where RO = MgO + CaO + SrO + BaO
TiO ₂ 0-2%, CeO ₂ 0-2%, Fe ₂ O ₃ 0-2%, MnO 0-1% (provided that TiO ₂ + CeO ₂ + Fe ₂ O ₃ + MnO = 0.01-3%) Chemical strengthening glass containing compositions can be used.

As the heat-resistant glass, for example, in mol%, the SiO ₂ 50 to 75%, the _{Al 2 O 3 0~5%, 0~2} % of BaO, 0 to 3% of Li ₂ O, the ZnO 0~5%, 3~15% in total of Na ₂ O and _{K 2 O, 14~35% MgO,} CaO, SrO and BaO in _{total, ZrO 2, TiO 2, La} 2 O 3, Y 2 O ₃ , Yb ₂ O ₃ , Ta ₂ O ₅ , Nb ₂ O ₅ and HfO ₂ are contained in a total amount of ₂ to 9%, and the molar ratio [(MgO + CaO) / (MgO + CaO + SrO + BaO)] is in the range of 0.85 to 1. A glass having a molar ratio [Al ₂ O ₃ / (MgO + CaO)] in the range of 0 to 0.30 can be preferably used.
Further, 56 to 75 mol% of SiO ₂ , 1 to 9 mol% of Al ₂ O ₃ , and a total of 6 to 15 mol of an alkali metal oxide selected from the group consisting of Li ₂ O, Na ₂ O and K ₂ O %, A total of 10 to 30 mol% of an alkaline earth metal oxide selected from the group consisting of MgO, CaO and SrO, ZrO ₂ , TiO ₂ , Y ₂ O ₃ , La ₂ O ₃ , Gd ₂ O ₃ , Nb _The glass may contain a total of more than 0% and 10 mol% or less of oxides selected from the group consisting of ₂ O ₅ and Ta ₂ O ₅ .
In the present invention, the content of Al ₂ O ₃ in the glass composition is preferably 15% by weight or less. More preferably, the content of Al ₂ O ₃ is 5 mol% or less.

Conventionally, the grinding process is generally performed through two stages of a rough grinding process (first grinding process) and a fine grinding process (second grinding process). By applying the treatment, it is possible to perform the treatment in one step.

After the completion of this grinding, mirror polishing is performed to obtain a highly accurate flat surface. In the present invention, in the grinding process, by applying the fixed abrasive method according to the present invention to the conventional loose abrasive method, it became possible to reduce the processing surface roughness, so in the subsequent mirror polishing process It is possible to reduce the amount of removal, reduce the processing load, and reduce the processing cost.

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 an abrasive of a metal oxide such as cerium oxide or colloidal silica. is there. A glass substrate having high smoothness is obtained by polishing using, for example, a cerium oxide-based abrasive (first polishing), and then performing final polishing (mirror polishing) (second polishing) using colloidal silica abrasive grains. It is possible.

In the present invention, the surface of the glass substrate after the mirror polishing is preferably a mirror surface having an arithmetic average surface roughness Ra of 0.2 nm or less, more preferably 0.13 nm or less. In the present invention, Ra and Rmax refer to the roughness calculated based on Japanese Industrial Standard (JIS) B0601.
In the present invention, the surface roughness (for example, the maximum roughness Rmax, the arithmetic average roughness Ra) is the surface roughness of the surface shape obtained when a 5 μm × 5 μm square area is measured with an atomic force microscope (AFM). It is practically preferable to set it to be. In addition, you may measure using a stylus type surface roughness meter.

In the present invention, it is preferable to perform a chemical strengthening process after the first polishing process and before the second polishing process. As a method of the chemical strengthening treatment, for example, a low-temperature ion exchange method in which ion exchange is performed in a temperature range not exceeding the glass transition temperature is preferable. Chemical strengthening treatment is a process of bringing a molten chemical strengthening salt into contact with a glass substrate to form a relatively large atomic radius alkali metal element in the chemical strengthening salt and a relatively small atomic radius in the glass substrate. This is a process in which an alkali metal element is ion-exchanged to cause the alkali metal element having a large ionic radius to penetrate into the surface layer of the glass substrate to generate a compressive stress on the surface of the glass substrate. The glass substrate that has been subjected to the chemical strengthening treatment is excellent in impact resistance, and therefore is particularly preferable to be mounted on, for example, a mobile HDD. As the chemical strengthening salt, an alkali metal nitrate such as potassium nitrate or sodium nitrate can be preferably used.

The present invention also provides a method for manufacturing a magnetic disk using the above-described glass substrate for a magnetic disk. In the present invention, the magnetic disk is manufactured by forming at least a magnetic layer on the glass substrate for a magnetic disk 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 for forming the magnetic layer, it is preferable to use a method for forming a magnetic layer on a glass substrate by a sputtering method, for example, a DC magnetron sputtering method. The orientation direction and the size of the magnetic grains of the magnetic layer can be controlled by interposing the underlayer between the glass substrate and the magnetic layer. For example, by using a cubic underlayer such as a Cr-based alloy, for example, the easy magnetization direction of the magnetic layer can be oriented along the surface of the magnetic disk. In this case, a magnetic disk of the longitudinal magnetic recording system is manufactured. Further, for example, by using a hexagonal underlayer containing Ru or Ti, for example, the easy magnetization direction of the magnetic layer can be oriented along the normal line of the magnetic disk surface. In this case, a perpendicular magnetic recording type magnetic disk is manufactured. The underlayer can be formed by a sputtering method similarly to the magnetic layer.

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

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

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

(2) Shape Processing Step Next, predetermined chamfering was performed on the outer peripheral end face and the inner peripheral end face. In general, a 2.5-inch HDD (hard disk drive) uses a magnetic disk having an outer diameter of 65 mm.

(3) End Face Polishing Step Next, the surface of the end face (inner circumference, outer circumference) of the glass substrate was polished by a known brush polishing method while rotating the glass substrate.

(4) Main Surface Grinding Processing This main surface grinding processing was performed using a double-sided lapping apparatus by setting a glass substrate held by a carrier between upper and lower platens to which diamond pads were attached. As a diamond pad, a fixed abrasive grindstone was used in which an agglomerate in which a plurality of diamond particles were vitrified by glass was fixed with a resin to obtain fixed abrasive grains. Here, the average particle size of the aggregate was about 25 μm, and the average particle size (D50) of the individual diamond particles in the aggregate was 2.5 μm. The test was performed while using a lubricating liquid. The main surface of the glass substrate before the grinding processing was a mirror surface. When the roughness of the main surface was measured with a stylus-type roughness meter, it was 5 nm in Ra.

Specifically, the rotation speed of the platen was appropriately selected within a range of 10 to 100 rpm, and the load on the glass substrate was applied in accordance with the sequence shown in FIG. In the present embodiment, the load (P1) of the first stage (roughening) is set to 150 g / cm ² , and the load (P2) of the second stage (main processing) is set to 100 g / cm ² , By rotating the sun gear and the internal gear, both surfaces of the glass substrate housed in the carrier were processed.
The slope k in FIG. 3 was 10 g / (cm ² · sec), t1 was 60 seconds, the time between BCs was 15 seconds, and t2 was 200 seconds longer than t1.
The glass substrate that had been subjected to the above-mentioned grinding processing was sequentially immersed in each of washing baths (application of ultrasonic waves) of a neutral detergent and water to perform ultrasonic cleaning.

In this grinding processing, 50 sheets were processed per processing (one batch). The surface roughness of the processed glass substrate was measured using a stylus type surface roughness meter. Tables 1 and 2 show the measurement results of the surface roughness (Ra) and the processing speed in the entire grinding processing. The processing speed in the entire grinding processing is a value obtained by dividing the total grinding thickness by the total processing time (including the first step and the second step). In addition, the evaluation of the scratch was performed by counting the number of glass substrates having scratches on the main surface using a condenser lamp in a dark room.

(5) Main surface polishing step (first polishing step)
Next, a first polishing step for removing scratches and distortion remaining in the above-described grinding was performed using a double-side polishing apparatus. In a double-side polishing apparatus, a glass substrate held by a carrier is brought into close contact between an upper and lower polishing platen to which a polishing pad is attached, and this carrier is meshed with a sun gear (sun gear) and an internal gear (internal gear). Then, the glass substrate is pressed between the upper and lower platens. Thereafter, by supplying a polishing liquid between the polishing pad and the polishing surface of the glass substrate and rotating the glass substrate, the glass substrate revolves while rotating on the surface plate, and both surfaces are simultaneously polished. Specifically, the first polishing step was performed using a hard polisher (hard urethane foam) as the polisher. As the polishing liquid, a liquid in which cerium oxide was dispersed in water as an abrasive was used.

(6) Chemical Strengthening Step Next, the glass substrate having been washed was chemically strengthened. The chemical strengthening treatment was performed by preparing a chemical strengthening solution in which potassium nitrate and sodium nitrate were mixed and melted, and immersing the glass substrate in the chemical strengthening solution.

(7) Main surface polishing step (second polishing step)
Next, the second polishing step was performed using the same double-side polishing apparatus as that used in the first polishing step, replacing the polisher with a polishing pad of a soft polisher (suede). This second polishing process is a mirror polishing process for maintaining the flat surface obtained in the above-described first polishing process and further reducing the surface roughness to finish the mirror surface into a smooth mirror surface. As the polishing liquid, a dispersion of colloidal silica in water was used. The glass substrate after the second polishing step was appropriately washed and dried.

When the surface roughness of the main surface of the glass substrate obtained through the above steps was measured by an atomic force microscope (AFM), the glass substrate had an ultra-smooth surface of Rmax = 1.53 nm and Ra = 0.13 nm. A glass substrate was obtained. When the surface of the glass substrate was analyzed with an atomic force microscope (AFM) and an electron microscope, it was mirror-like and no surface defects such as protrusions and scratches were observed.
The obtained glass substrate had an outer diameter of 65 mm, an inner diameter of 20 mm, and a thickness of 0.635 mm.
Thus, a glass substrate for a magnetic disk of this example was obtained.

(Example 2)
In the grinding processing of Example 1, the grinding processing was performed in the same manner as in Example 1 except that the load (P1) of the first stage (roughening) was set to 130 g / cm ² . Then, a glass substrate for a magnetic disk was obtained in the same manner as in Example 1 except for the grinding process.
Table 1 shows the measurement results of the scratch on the ground surface and the processing speed in the entire grinding process for the glass substrate after the grinding process.

(Example 3)
In the grinding processing of Example 1 described above, the grinding processing was performed in the same manner as in Example 1 except that the load (P1) of the first stage (roughening) was set to 200 g / cm ² . Then, a glass substrate for a magnetic disk was obtained in the same manner as in Example 1 except for the grinding process.
Table 1 shows the measurement results of the scratch on the ground surface and the processing speed in the entire grinding process for the glass substrate after the grinding process.

(Example 4)
In the grinding processing of Example 1, the grinding processing was performed in the same manner as in Example 1 except that the load (P2) of the second stage (main processing) was set to 50 g / cm ² . Then, a glass substrate for a magnetic disk was obtained in the same manner as in Example 1 except for the grinding process.
Table 2 shows the surface roughness (Ra) measured for the glass substrate after the grinding in the same manner as in Example 1 and the measurement results of the processing speed in the entire grinding.

(Example 5)
In the grinding processing of Example 1, the grinding processing was performed in the same manner as in Example 1 except that the load (P2) of the second stage (main processing) was set to 70 g / cm ² . Then, a glass substrate for a magnetic disk was obtained in the same manner as in Example 1 except for the grinding process.
Table 2 shows the surface roughness (Ra) measured for the glass substrate after the grinding in the same manner as in Example 1 and the measurement results of the processing speed in the entire grinding.

(Example 6)
In the grinding processing of Example 1 described above, the grinding processing was performed in the same manner as in Example 1 except that the load (P2) of the second stage (main processing) was set to 120 g / cm ² . Then, a glass substrate for a magnetic disk was obtained in the same manner as in Example 1 except for the grinding process.
Table 2 shows the surface roughness (Ra) measured for the glass substrate after the grinding in the same manner as in Example 1 and the measurement results of the processing speed in the entire grinding.

(Example 7)
In the grinding processing of Example 1, the grinding processing was performed in the same manner as in Example 1 except that the load (P1) of the first stage (roughening) was set to 120 g / cm ² . Then, a glass substrate for a magnetic disk was obtained in the same manner as in Example 1 except for the grinding process.
Table 1 shows the measurement results of the scratch on the ground surface and the processing speed in the entire grinding process for the glass substrate after the grinding process.

(Example 8)
In the grinding processing of Example 1, the grinding processing was performed in the same manner as in Example 1 except that the load (P1) of the first stage (roughening) was set to 210 g / cm ² . Then, a glass substrate for a magnetic disk was obtained in the same manner as in Example 1 except for the grinding process.
Table 1 shows the measurement results of the scratch on the ground surface and the processing speed in the entire grinding process for the glass substrate after the grinding process.

(Example 9)
In the grinding processing of Example 1 described above, the grinding processing was performed in the same manner as in Example 1 except that the load (P2) of the second stage (main processing) was set to 40 g / cm ² . Then, a glass substrate for a magnetic disk was obtained in the same manner as in Example 1 except for the grinding process.
Table 2 shows the surface roughness (Ra) measured for the glass substrate after the grinding in the same manner as in Example 1 and the measurement results of the processing speed in the entire grinding.

(Example 10)
In the grinding processing of Example 1 described above, the grinding processing was performed in the same manner as in Example 1 except that the load (P2) of the second stage (main processing) was set to 130 g / cm ² . Then, a glass substrate for a magnetic disk was obtained in the same manner as in Example 1 except for the grinding process.
Table 2 shows the surface roughness (Ra) measured for the glass substrate after the grinding in the same manner as in Example 1 and the measurement results of the processing speed in the entire grinding.

(Comparative example)
In the grinding processing of Example 1, the load (100 g / cm ²⁾ was set, and the grinding processing (main processing) was performed from the beginning. Then, a glass substrate for a magnetic disk was obtained in the same manner as in Example 1 except for the grinding process.
Table 1 shows the measurement results of the scratch on the ground surface and the processing speed in the entire grinding process for the glass substrate after the grinding process.

From the results in Tables 1 and 2, the following can be understood.
1. In the comparative example in which the load is set to the load of the grinding (main processing) without performing the first step and the grinding (main processing) is performed from the beginning, the time during which the grinding cannot be performed becomes longer, and the processing speed is reduced. Will drop.
2. On the other hand, according to the embodiment of the present invention, it is possible to reduce the time during which grinding cannot be performed in the conventional grinding using fixed abrasive grains, and to perform grinding without reducing the processing speed. Further, by adjusting the conditions of the grinding process, the surface roughness of the processed surface can be suppressed to be low. In particular, good results can be obtained by setting the load P1 in the first stage to a range of 130 to 200 g / cm ² and the load P2 in the second stage to a range of 50 to 120 g / cm ² .
If the load P1 in the first stage is smaller than 130 g / cm ² (Example 7), the time during which grinding cannot be performed cannot be sufficiently reduced, and the processing speed decreases. On the other hand, when the load P1 is larger than 200 g / cm ² (Example 8), the depth of cut by the abrasive grains becomes too deep, causing scratches, and it is necessary to increase the allowance for the main processing and the subsequent polishing step. Therefore, the overall processing time becomes longer. That is, P1 is preferably 130 g / cm ² or more from the viewpoint of processing speed, and preferably 200 g / cm ² or less from the viewpoint of scratching.
From the above results, the value of P1 / P2 is preferably 1.20 or more, or 3 or less.

Further, as another example (comparative example), P1 was set to 100 (g / cm ² ), and P2 was set to 130 (g / cm ² ). Ra was 0.132 μm, and it became necessary to increase the allowance for the subsequent polishing step, so that it was found that the manufacturing cost could not be reduced.

Further, continuous processing of 50 batches was continuously performed using a new glass substrate at all times using the respective conditions of the examples of Table 2, and a total of 2500 processed glass substrates were investigated. Only under the conditions of Example 9, one substrate in which a part of the main surface was not ground was found. Such an unground substrate can be found using the same method as the scratch inspection.
Further, similar continuous processing was performed by changing only P1 from the conditions of Example 4 to 160 (g / cm ² ) and 140 (g / cm ² ) (Examples 11 and 12 respectively). When P1 / P2 is 3.2, 2.8) or 140 (g / cm ² ), the above-mentioned unground substrate was not found, but was 160 (g / cm ² ). In that case one was found.
That is, from the results of Examples 4, 9, 11, and 12, it was found that when P1 / P2 was larger than 3, there was a possibility that an unground substrate would be generated during continuous processing.

In addition, the protrusion amount of the abrasive grains (aggregates) in the diamond pad used in Example 1 was changed between 0.3 μm and 8 μm.
Except for this point, the grinding treatment was continuously performed in the same manner as in Example 1, and the surface observation results of the obtained 2500 glass substrates are shown in Table 3 below.

  From the results in Table 3 above, it is preferable that the protrusion amount of the abrasive grains on the surface of the diamond pad used for the grinding treatment is particularly in the range of 0.5 μm to 7 μm.

(Manufacture of magnetic disks)
The magnetic disk glass substrate obtained in Example 1 was subjected to the following film forming process to obtain a magnetic disk for perpendicular magnetic recording.
That is, an adhesion layer made of a Ti-based alloy thin film, a soft magnetic layer made of a CoTaZr alloy thin film, an underlayer made of a Ru thin film, a perpendicular magnetic recording layer made of a CoCrPt alloy, a carbon protective layer, and a lubricating layer are sequentially formed on the glass substrate. A film was formed. The protective layer is for preventing the magnetic recording layer from deteriorating due to contact with the magnetic head, and is made of hydrogenated carbon and has abrasion resistance. The lubricating layer was formed by dipping a liquid lubricant of alcohol-modified perfluoropolyether.
The obtained magnetic disk was assembled in an HDD equipped with a DFH head and subjected to a one-month load / unload durability test while operating the DFH function under a high temperature and high humidity environment of 80 ° C. and 80% RH. Good results were obtained without any particular hindrance.

REFERENCE SIGNS LIST 1 diamond pad 2 sheet 3 aggregate 4 pellet 5 diamond particle 6 support material 10 glass substrate

Claims (8)

A lubricating liquid and a glass substrate used for manufacturing a magnetic disk glass substrate including a grinding process of grinding a main surface of the glass substrate using a surface plate provided with fixed abrasive grains including diamond particles on a grinding surface. A manufacturing method,
The glass substrate is a glass substrate whose main surface is a mirror surface,
The grinding process includes a first step of roughening the front Symbol glass substrate surface, after said first step, the second performing the grinding of the glass substrate surface under low load than the load of the first stage And
The grinding process having the first stage and the second stage, using the same fixed abrasive grindstone, and using the same device,
A method for manufacturing a glass substrate used for manufacturing a glass substrate for a magnetic disk, wherein the amount of protrusion of the fixed abrasive is 0.5 μm to 7 μm. A lubricating liquid and a glass substrate used for manufacturing a magnetic disk glass substrate including a grinding process of grinding a main surface of the glass substrate using a surface plate provided with fixed abrasive grains including diamond particles on a grinding surface. A manufacturing method,
The glass substrate is a glass substrate whose main surface is a mirror surface,
Glass the grinding process, a first stage of roughening the front Symbol glass substrate surface, after said first step, than the load of the first stage perform grinding of the glass substrate surface under low load Having a second stage of processing the substrate to a predetermined thickness and flatness,
The grinding process having the first stage and the second stage, using the same fixed abrasive grindstone, and used in the production of a glass substrate for a magnetic disk characterized by being performed using the same apparatus glass substrate manufacturing method being. A lubricating liquid and a glass substrate used for manufacturing a magnetic disk glass substrate including a grinding process of grinding a main surface of the glass substrate using a surface plate provided with fixed abrasive grains including diamond particles on a grinding surface. A manufacturing method,
The glass substrate is a glass substrate whose main surface is a mirror surface,
The grinding process includes a first step of roughening the front Symbol glass substrate surface, after said first step, the second performing the grinding of the glass substrate surface under low load than the load of the first stage And
The glass substrate for a magnetic disk, wherein the grinding processing including the first step and the second step is performed continuously using the same fixed abrasive grindstone and using the same apparatus. A method for producing a glass substrate used in the production of glass. The method for manufacturing a glass substrate for use in manufacturing a glass substrate for a magnetic disk according to claim 2, wherein an amount of protrusion of the fixed abrasive is 0.5 μm to 7 μm. The method for manufacturing a glass substrate used for manufacturing a glass substrate for a magnetic disk according to any one of claims 1 to 4, wherein the fixed abrasive has an average particle size of 20 to 40 µm. The average particle diameter of the manufacturing method of the glass substrates used in the manufacture of a glass substrate according to any one of claims 1 to 5, characterized in that a 1~5μm of the diamond particles. A method for manufacturing a glass substrate for a magnetic disk, comprising a method for manufacturing a glass substrate for use in manufacturing the glass substrate for a magnetic disk according to claim 1.   The method for manufacturing a glass substrate for a magnetic disk according to claim 7, further comprising a process of polishing a main surface of the glass substrate.

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