WO2014115495A1

WO2014115495A1 - Method for manufacturing glass substrate for hard disk

Info

Publication number: WO2014115495A1
Application number: PCT/JP2014/000067
Authority: WO
Inventors: 塚田　和也
Original assignee: Hoya株式会社
Priority date: 2013-01-23
Filing date: 2014-01-10
Publication date: 2014-07-31

Abstract

One aspect of the present invention pertains to a method for manufacturing a glass substrate for a hard disk, the method being provided with a polishing step for polishing the glass substrate using a polishing slurry that contains abrasive particles, wherein the method is characterized in that a polishing slurry obtained by mixing a polishing slurry (A), which contains a group of abrasive particles (A) having a prescribed average particle diameter and a dispersant most suitable for the group of particles (A), and a polishing slurry (B), which contains a group of abrasive particles (B) having a larger average particle diameter than the group of particles (A) and a dispersant most suitable for the group of particles (B), is used to polish the glass substrate in the polishing step.

Description

Manufacturing method of glass substrate for hard disk

The present invention relates to a method for manufacturing a glass substrate for a hard disk (magnetic information recording medium) used as a magnetic disk mounted on a hard disk (HDD).

Glass substrates for magnetic information recording media such as HDDs are usually produced by performing a grinding process, a polishing process, a chemical strengthening process, etc. on a flat glass base plate obtained by a float method or a direct press method. The

In particular, in the processing of a glass substrate, after the grinding process for adjusting the flatness, a one-stage or two-stage polishing process for finishing the surface depending on the surface quality is usually added. Of the polishing steps, a cerium oxide abrasive having a high polishing rate is generally used for the so-called rough polishing step that is first performed.

High-hardness polyurethane pads have been used in polishing processes that use cerium oxide to achieve a high rate, but there are defects that leave scratches and deep damage, making it a high-quality finish that meets the demands of high-density substrates. It was a high issue. Therefore, a suede-shaped pad having a feature including a foam layer designed to have a lower hardness than before has been introduced, and scratches and damage can be improved (for example, Patent Document 1).

On the other hand, as a technique for improving the polishing slurry used in the polishing process, a method of using a slurry in which the secondary particle size distribution of the polishing material is adjusted and no aggregation occurs (Patent Document 2), and oxidation as a polishing material. A method of reducing the particle size and increasing the purity of cerium (Patent Document 3) has been reported.

By the way, in the polishing process, in order to shorten the manufacturing time, it is required to increase the polishing rate in order to obtain a desired polishing thickness (also referred to as polishing allowance) in a short period of time. It is required to adjust to the required surface roughness. However, it is difficult to adjust to the desired surface roughness when the particle size of the abrasive particles is increased in order to increase the polishing rate, and the trade-off relationship is that the polishing rate is decreased when the particle size of the abrasive particles is decreased. There was a need for improvement. In contrast, by using a mixture of relatively large abrasive particles and relatively small abrasive particles, the polishing rate is increased with large abrasive particles, and the finished surface roughness is achieved with small abrasive particles. The technology was examined. By using such an abrasive slurry, it became possible to adjust the desired polishing rate and the surface roughness after production to some extent. In addition, by combining such a technique with a polishing method using a suede pad in the rough polishing step using cerium oxide as described above, the polishing rate is increased and the total manufacturing time is shortened. It became possible to improve the quality. However, when the above-described technique is used, the polishing rate changes with running, and there arises a problem that variation in substrate polishing allowance occurs for each batch. It has been clarified that such a change in the polishing rate leads to a variation in the machining allowance, an increase in the variation in the finished thickness, and a serious problem in causing a poor quality of the polished surface.

Further, as a result of the study by the present inventors, the above-mentioned problems are caused by the change in the particle size distribution of the abrasive particles as the polishing proceeds when the abrasive particles having different particle sizes are used. However, when using abrasive particles having such a different particle size distribution, a technique for maintaining the particle size distribution of each abrasive particle is not yet known.

In order to solve such problems and increase the recording capacity in recent years and expand applications, there is a need for further improvement in productivity as well as further improvement in the quality of the recording surface of the glass substrate used as the base material. The current situation is.

JP 2011-104691 A JP 2010-165420 A JP 2001-72962 A

The present invention has been made in view of such circumstances, and an object of the present invention is to provide an efficient method of manufacturing a glass substrate for a hard disk capable of ensuring quality capable of meeting the demand for higher density.

As a result of intensive studies, the present inventor has found that the above problems can be solved by a manufacturing method having the following configuration, and has further completed the present invention based on such findings.

That is, the method for manufacturing a glass substrate for hard disk according to one aspect of the present invention includes a polishing step of polishing a glass substrate with a polishing slurry containing abrasive particles, and in the polishing step, An abrasive slurry A containing an abrasive particle group A having an average particle size and a dispersant optimal for the particle group A, an abrasive particle group B having an average particle size larger than the particle group A, and the particle group B Polishing is performed using a polishing slurry obtained by mixing polishing slurry B containing an optimal dispersant.

FIG. 1 is a view showing an example of a molding die for glass blanks and a press machine. FIG. 2 is a perspective view of a rotary table on which a glass blank forming press is disposed.

Hereinafter, embodiments according to the present invention will be described in detail, but the present invention is not limited thereto.

The method for manufacturing a glass substrate for hard disk according to the present embodiment includes a polishing step of polishing the glass substrate with a polishing slurry containing abrasive particles, and in the polishing step, the glass substrate has a predetermined average particle diameter. Abrasive slurry A containing an abrasive particle group A having and an optimal dispersant for the particle group A, an abrasive particle group B having an average particle size larger than the particle group A, and an optimal dispersant for the particle group B It grind | polishes using the polishing slurry obtained by mixing the polishing slurry B containing these.

The inventor diligently studied the cause of the rate reduction when using a suede pad or the like for polishing, and found that the change in the particle size distribution accompanying the running of the abrasive was influencing, and further researching the present invention. Was completed.

In the present embodiment, by the configuration described above, the abrasive particles having at least two different particle size distributions are maintained by selecting optimum different dispersants, and by using a polishing slurry in which they are mixed, It is thought that the rate can be improved while maintaining the quality.

According to the present invention, in the method of manufacturing a glass substrate for hard disk, it is possible to stably provide a high rate while maintaining the polished surface quality of the glass substrate by polishing. Thereby, a very high quality glass substrate can be produced efficiently. Therefore, the manufacturing method of the glass substrate for hard disks of this invention is very useful on industrial use.

As long as the manufacturing method of the glass substrate for hard disks according to the present embodiment includes at least the polishing step, the other steps are not particularly limited, and a step that can be used in a conventionally known manufacturing method is appropriately used. it can.

As a manufacturing method of the glass substrate for hard disks, for example, a melting process (glass blanks manufacturing process), a disk processing process, a rough grinding process (first grinding process), a fine grinding process (second grinding process), and a rough polishing process are usually performed. (Primary polishing step), cleaning step, chemical strengthening step, mirror polishing step (secondary polishing step), and a method including a final cleaning step. And each said process may be performed in this order, and the order of a chemical strengthening process and a mirror polishing process (secondary polishing process) may be replaced. Furthermore, a method including steps other than these may be used. For example, in addition to the above, a heat treatment step, a shape processing step, a coring step, an end surface polishing step, and an inspection step may be performed.

The polishing step of the present embodiment may be performed in a rough polishing step (primary polishing step) or may be performed in a mirror polishing step (secondary polishing step). Furthermore, it is desirable to perform both in the rough polishing process and the mirror polishing process in order to achieve more effects.

Hereinafter, an embodiment of the method for manufacturing the glass substrate for hard disk according to the present embodiment will be described.

In the drawings, each symbol indicates the following: 1 molding press, 2 upper press, 3 upper mold, 4 first molding surface, 5 lower mold, 6 second molding surface, 7 lower press machine, 8 rotary shaft, 9 rotary table, 21 outflow nozzle, 23 molten glass.

<Glass blanks manufacturing process>
First, as a glass material, for example, a general aluminosilicate glass is used. The aluminosilicate glass is composed of 58 mass% to 75 mass% SiO ₂ , 5 mass% to 23 mass% Al ₂ O ₃ , 3 mass% to 10 mass% Li ₂ O, and 4 mass% to 13 mass. % Na ₂ O as a main component. The glass material is not limited to aluminosilicate glass, and may be any material such as soda lime glass or borosilicate glass.

Next, glass blanks, which are intermediate molded bodies of glass substrates for hard disks, are produced by the direct press method. These glass blanks are generally manufactured by supplying molten glass and press-molding while cooling the molten glass. In the production of the glass blank of the present embodiment, in addition to the above steps, heat treatment may be applied to correct the flatness of the glass blank and remove internal strain. Further, a coring process may be provided in order to obtain a donut-shaped substrate.

FIG. 1 is a schematic view of a mold and a press for producing the glass blanks of the present embodiment by press molding. The press 1 for forming glass blanks is supplied with molten glass, and includes a lower mold 5 and a lower part 7 having a first molding surface 6 for pressurizing the supplied molten glass, and a lower mold 5. It has an upper die 3 and a press machine upper part 2 provided with a second molding surface 4 for pressurizing molten glass with one molding surface 6.

FIG. 2 is a perspective view showing a mechanism in which glass blanks are press-formed by the lower press 7 and the upper press 2 arranged on the rotary table. The press machine lower part 7 is embedded in the rotary table 9 side by side in the circumferential direction. The rotary table 9 is provided so as to be able to be driven to rotate around the rotary shaft 8 at a specific speed v (m / s).

Further, although the lower mold 5 of the mold is installed on the lower part 7 of the press machine, the molten glass 23 is supplied to the lower mold 5 by the outflow nozzle 21 at a predetermined position on the turntable. The lower mold 5 supplied with the molten glass 23 is transported by the rotary table together with the lower part 7 of the press machine, and the upper mold 3 installed on the upper part 2 of the press machine at another position is lowered to the position of the lower mold 5 to be melted. Pressurize the glass.

複数 Inside the mold, a plurality of heaters are installed. The heater is preferably arranged in one or more rounds and concentrically so as to be arranged at a uniform angle in the circumferential direction in terms of easy temperature control of the mold. Note that a plurality of heaters may or may not be arranged in the press machine lower part 7 in the same manner as the press machine upper part 2, but depending on the pressurizing time to be pressed, It is preferable that they are arranged.

Therefore, the manufacture of the glass blanks in the present embodiment is mainly performed by a molten glass supply step for supplying molten glass to the first molding surface 6 formed on the lower mold 5 and a second molding surface formed on the upper mold 3. 4 and a pressurizing step of obtaining glass blanks by cooling the molten glass supplied to the first molding surface 6 while pressurizing it.

A predetermined rough surface is formed on the molding surface 6 of the lower die 5 and the molding surface 4 of the upper die 3 for the purpose of improving the grinding rate in the next grinding step and suppressing grinding variation, and pressurizes the glass blank surface. The rough surface shape of the molding surface of each mold is transferred during the process.

<Heat treatment process>
The heat treatment step is a step aimed at correcting the flatness of glass blanks and removing internal strain. Although it does not specifically limit as a method of heat processing, For example, the method of using a setter (alumina, zirconia, etc.) and stacking alternately with glass blanks, putting into a heat processing furnace, and applying heat can be employ | adopted.

There are no particular restrictions on the heat treatment conditions. For example, the temperature during the heat treatment can be performed in a temperature range from Tg to Tg + 100 (° C.) of the glass blank. By performing the heat treatment within the temperature range, the flatness of the glass blanks can be sufficiently corrected, the deterioration of the shape of the glass blanks is reduced, and the adhesion marks caused by the fusion with the setter are further reduced. The possibility of occurring can be reduced.

<Coring process>
A coring process is a process of forming an inner hole (center hole) in the center part of the surface of the obtained glass blanks using a diamond core drill. The center of the glass blanks is determined by this coring process. In addition, in this embodiment, a glass blank means the glass molding before finishing the coring process and performing the grinding process (1st grinding process) of the main plane mentioned later.

<Shaping process>
Next, in the shape processing step, the glass blanks that have been subjected to the coring (inner peripheral cut) process are ground with a diamond grindstone on the inner peripheral end face and the outer peripheral end face that face the hole in the center portion. After being adjusted to dimensions, chamfering is also performed. For example, in the case of a 2.5 inch hard disk, a predetermined chamfering process is performed after setting the outer diameter to 65 mm and the inner diameter (diameter of the circular hole 1H in the center) to 20 mm. The surface roughness of the end face of the glass blanks at this time is about 2 μm in Rmax.

<Surface grinding (first grinding) process>
Next, in the first grinding step, a surface grinding process is performed on both main surfaces of the formed glass blanks for the purpose of improving dimensional accuracy and shape accuracy.

The grinding process is performed, for example, using a double-side grinding (lapping) device using a planetary gear mechanism. Specifically, the lapping platen is pressed from above and below on both main surfaces of the glass blanks obtained above, the grinding liquid is supplied onto both main surfaces, and the glass blanks and lapping platen are relatively moved. Thus, a grinding process is performed. By the grinding process, the approximate parallelism, flatness, thickness and the like of the glass substrate are preliminarily adjusted, and a glass substrate (glass base material) having a substantially flat main surface is obtained. As the grinding liquid, for example, a grinding liquid containing alumina abrasive grains having a particle size of # 400 (particle size of about 40 to 60 μm) is used. By setting the upper surface plate load to about 100 kg, both surfaces of the glass blanks are faced. It may be finished to an accuracy of 0 μm to 1 μm and a surface roughness Rmax of about 6 μm.

Preferably, grinding may be performed using a fixed abrasive type grinding pad in which diamond particles are supported on a resin, ceramic, or metal, which has the advantage of improving the balance between grinding speed and quality after grinding. . The particle diameter of diamond can be appropriately changed depending on the purpose, but the average particle diameter used in the first grinding is preferably 2 μm to 10 μm. If the diamond particle size is less than 2 μm for the first lapping, the processing speed is insufficient, and cracks generated on the main surface (upper and lower surfaces) of the glass substrate may not be removed. If the particle diameter of diamond exceeds 10 μm, there is a risk that cracks may occur on the

main surfaces

2 and 3 of the glass substrate 1 due to diamond.

<Second grinding (lapping) process>
Next, in the second grinding step, grinding processing is performed on both main surfaces of the glass substrate in the same manner as in the first grinding step. By performing this second grinding step, fine uneven shapes and processing damage such as fine scratches and protrusions formed on both main surfaces of the glass substrate in the first lapping or end face processing of the previous step are removed in advance. Therefore, it is possible to precisely control the polishing time of the main surface in the subsequent process, and to shorten it.

When using a grinding pad carrying diamond particles in the second grinding step, it is preferable to use a diamond pad having a particle size smaller than that of the diamond particles used in the first grinding, so that a surface suitable for polishing in the next step is used. Properties can be formed. Preferably, diamond particles having an average particle diameter of 1 μm to 5 μm are used. With the recent increase in density, the diamond particle diameter is becoming smaller, but a balance of workability is required, so 1.5 μm to 4 μm is more preferable.

In the first and second grinding steps, the glass substrate main surface (upper and lower surfaces) is ground to a thickness of about 50 μm to 250 μm.

<Inner circumference polishing process>
Next, in the inner peripheral polishing step, mirror polishing by brush polishing may be performed on the inner peripheral end surface of the glass substrate. Specifically, by supplying a polishing liquid containing an abrasive to the polishing brush, placing the polishing brush in contact with the inner peripheral end surface of the glass substrate, and then applying the polishing brush while rotating the glass substrate The inner peripheral end face of the glass substrate is polished. As the above abrasive, cerium oxide is usually selected and supplied as a polishing liquid at an appropriate concentration. As the polishing brush, a brush having an appropriate hardness and diameter is selected so that the polishing can be performed softly without damaging the end face.

<Outer periphery polishing process>
Next, an outer peripheral polishing step may be further performed. In this step, mirror polishing by brush polishing is performed on the outer peripheral end surface of the glass substrate. Specifically, by supplying a polishing liquid containing an abrasive to the polishing brush, placing the polishing brush in contact with the outer peripheral end surface of the glass substrate, and applying the polishing brush while rotating the glass substrate, The outer peripheral end surface of the glass substrate is polished. The abrasive and the polishing brush are selected in the same manner as the abrasive and the polishing brush used for polishing the inner peripheral end face of the glass substrate.

<Polishing process>
The polishing step is a step of polishing the glass substrate with a polishing slurry containing abrasive particles. In this embodiment, in the polishing step, the glass substrate is divided into the abrasive particle group A having a predetermined average particle diameter and the particles. A polishing slurry A containing the optimum dispersant for the group A, an abrasive particle group B having an average particle size larger than the particle group A, and a polishing slurry B containing the optimum dispersing agent for the particle group B are mixed. Polishing is performed using the resulting polishing slurry.

That is, in this embodiment, abrasive particle groups having different average particle diameters (particle size distribution) are prepared in advance, and the optimum dispersant (particle aggregation is controlled for each particle group to maintain the average particle diameter in the particle group. A plurality of polishing slurries are prepared by mixing a dispersing agent that can be used, and a polishing slurry obtained by mixing them is used.

The polishing step of this embodiment using a polishing slurry in which abrasive particles having different particle size distributions are mixed (that is, the particle size distribution has two or more peaks) is a rough polishing step (primary polishing). Step) or at least one of a mirror polishing step (secondary polishing step). Furthermore, it is desirable because a higher effect can be obtained by performing both in the rough polishing step and the mirror polishing step.

The abrasive particles contained in the polishing slurry are not particularly limited, but it is preferable to use particles having the same composition. That is, the polishing slurry preferably used in the present embodiment is a polishing slurry in which a plurality of abrasive particle groups having the same composition and different average particle sizes (particle size distribution) are mixed.

Further, a polishing slurry C containing an abrasive particle group C having an average particle diameter intermediate between the particle group A and the particle group B, and a dispersing agent optimum for the particle group C is obtained by using the polishing slurry A and the polishing slurry as described above. A polishing slurry mixed with B can also be used. By mixing polishing slurries having a plurality of different particle size distributions in this way, the particle distribution can have a shape suitable for stabilizing the polishing rate, and the optimum particle size distribution can be maintained with higher accuracy. Therefore, higher quality and higher rate can be provided.

Next, the polishing slurry used in the polishing process of this embodiment will be described more specifically.

The abrasive can be appropriately selected depending on whether it is used for rough polishing or mirror polishing. For example, cerium oxide, zirconium oxide, zirconium silicate and the like are preferable for rough polishing; colloidal silica and the like are preferable for mirror polishing. Can be used.

The average particle size in the slurry varies slightly depending on the type of abrasive used.

For example, in the case of cerium oxide, it is preferable to use about 0.5 to 2.5 μm. A slurry in which these are dispersed in a solvent is preferable. Although it does not specifically limit as a solvent, Neutral water and acidic / alkaline aqueous solution can be employ | adopted and neutral water is used preferably. Further, in the present embodiment, for these solvents, for example, cerium oxide, a dispersant that is compatible with the distribution of particle groups is added. The mixing ratio of the solvent and the total amount of cerium oxide is about cerium oxide: solvent = 0.5: 9.5 to 3: 7. When the average particle diameter is less than 0.5 μm, the polishing pad tends to be unable to polish both main surfaces well. On the other hand, when the average particle diameter exceeds 2.5 μm, the polishing pad may deteriorate the flatness of the end face or cause scratches.

On the other hand, for example, when colloidal silica is used, it is preferable to use a slurry obtained by dispersing colloidal silica having an average particle diameter of 10 to 80 nm in a solvent. Also in this case, it does not specifically limit as a solvent, Neutral water and acidic alkaline aqueous solution can be employ | adopted and neutral water is preferable. In the present embodiment, a suitable dispersant corresponding to the particle size distribution particle size is added to these solvents. The mixing ratio of the solvent and colloidal silica is preferably about silica: solvent = 1: 9 to 3: 7.

In this embodiment, a classifier is used to divide the particles into a group of particles having an average particle size (particle size distribution) on the large particle size side and a small particle size side, and according to the average particle size of each particle size distribution, a suitable dispersant and solvent are used. By adding each, a slurry (small average particle size (small particle size): slurry A, large average particle size (large particle size): slurry B) is adjusted. Each slurry thus prepared is mixed at a suitable mixing ratio (preferably 1: 1) and used for polishing. The ratio of the slurry A containing the particle group on the small particle size side and the slurry B containing the particle group on the large particle size side in this embodiment is preferably in the range of 0.8 to 1.2 in A / B, 0.9 To 1.1 are more preferable. Further, when the intermediate particle group C is included, the ratio thereof is A: B: C and is mixed in the range of about 0.1 to 0.4: 0.2 to 0.7: 0.1 to 0.4. It is preferable.

As described above, the average particle size of the particle group B is larger than the average particle size of the particle group A, but the deviation of the average particle size of each particle group varies depending on the abrasive type. For example, in the case of cerium oxide, it can be set with a deviation of 0.3 to 0.7 μm. When the intermediate particle group C is set, it is preferable to use intermediate particles separated from each of the particle groups A and B by at least 0.1 μm to 0.5 μm. When mixing the slurry, it is possible to supply it as a polishing liquid after making it uniform using a stirrer in a batch, or mix it in the supply hose while supplying each slurry using the in-line method. Then, it may be supplied to the polishing machine as a mixed slurry.

In addition, when colloidal silica is used, the group A and the group B are set with a difference of 20 to 60 nm. When the intermediate particle group C is set, it is preferable to use intermediate particles separated from each of the particle groups A and B by at least 10 nm to 30 nm.

Next, the dispersant used in this embodiment will be described. As the dispersant according to this embodiment, polymer compounds having various functional groups are used. As the functional group, carboxylic acid, carboxylate, sulfonic acid, sulfonate and the like are selected, and the counter cation forming the salt can be selected from alkali metal ions, ammonium and the like. The polymer may be a copolymer. The monomer type, the counter cation type, and the molecular weight of the polymer are appropriately selected so that the particle size distribution of each particle group described above can be maintained.

For example, the dispersant suitable for the abrasive particle group A having a predetermined average particle size is selected to have a smaller molecular weight than the dispersant suitable for the abrasive particle group B having an average particle size larger than that of the particle group A. The monomer structure preferably has a small number of functional groups (for example, one), and the functional group species may include a carboxylic acid or a salt thereof, but a sulfonic acid or a salt thereof is more preferable. On the other hand, a dispersant having a relatively high molecular weight is preferably selected as the dispersant suitable for the abrasive particle group B having a large particle size distribution, and the monomer structure has a larger number of functional groups (for example, 2 or more). Liked. Moreover, as a kind of functional group, carboxylic acid or its salt is preferable.

More specifically, for example, a sulfonic acid polymer having a molecular weight in the range of 500 to 2000 can be selected as the dispersant for the particle group A, and a dispersant having a molecular weight of 10,000 to 20000, for example, can be selected. A range of maleic acid polymers can be selected, but is not limited thereto. Furthermore, a dispersant suitable for the intermediate particle group C is a polymer having a molecular weight located between the particle groups A and B in terms of molecular weight, and the molecular structure is a monomer having one functional group and two monomers having a functional group. And a copolymer thereof can be preferably used.

(Rough polishing process)
The rough polishing step is a step of polishing both the main surfaces of the glass substrate with a polishing slurry so that the surface roughness finally required in the subsequent mirror polishing step can be efficiently obtained. It does not specifically limit as a grinding | polishing method employ | adopted at this process, It is possible to grind | polish using a double-side polisher.

As the polishing pad used, it is preferable to use a hard pad, for example, urethane foam is preferable because the shape change of the polishing surface increases when the hardness of the polishing pad decreases due to heat generated by polishing. A suede pad can also be used for further quality improvement.

As the polishing slurry, it is preferable to use the polishing slurry of the present embodiment as described above (especially, one using cerium oxide). However, when the polishing slurry of the present embodiment is used in the mirror polishing step described later, In this rough polishing step, a known polishing slurry used in normal rough polishing (cerium oxide having an average primary particle size of 0.5 to 2.5 μm, zirconium oxide, zirconium silicate is dispersed in a solvent. It is also possible to appropriately use a slurry).

Further, by using the polishing slurry of the present embodiment as described above as the polishing slurry, the polishing rate can be kept high even if a suede pad with low hardness is used.

The supply amount of the polishing slurry is not particularly limited and is, for example, 5 to 10 L / min.

The polishing amount of the glass substrate in the rough polishing step is preferably about 20 to 40 μm. When the polishing amount of the glass substrate is less than 20 μm, there is a tendency that scratches and defects are not sufficiently removed. On the other hand, when the polishing amount of the glass substrate exceeds 40 μm, the glass substrate is polished more than necessary, and the production efficiency tends to decrease.

The glass substrate after the rough polishing step is preferably washed with a neutral detergent, pure water, IPA or the like. A cleaning step may be provided, and the surface of the glass substrate 1 using a cleaning solution containing sulfuric acid and / or hydrofluoric acid for the purpose of removing any of the abrasive cerium oxide, zirconium oxide, or zirconium silicate in the previous step. Clean while etching. A polishing slurry such as cerium oxide, zirconium oxide, or zirconium silicate adhering to the surface of the glass substrate is appropriately removed by a strongly acidic cleaning liquid such as sulfuric acid and / or hydrofluoric acid. Thereafter, the glass substrate 1 is cleaned using an acidic cleaning solution.

The cleaning liquid used in the cleaning step varies depending on the chemical resistance of the glass substrate 1, but a concentration of about 1% by mass to 30% by mass is preferable for sulfuric acid, and 0.2% by mass for hydrofluoric acid. A concentration of about 5% by mass is preferred. Cleaning using these cleaning liquids may be performed while applying ultrasonic waves in a cleaning machine in which an aqueous solution is stored. The frequency of the ultrasonic wave used at this time is preferably 78 kHz or higher.

<Mirror polishing process>
The mirror polishing process is a process of polishing both main surfaces of the glass substrate more precisely. In the mirror polishing process, a double-side polishing machine similar to the double-side polishing machine used in the rough polishing process can be used.

The polishing pad is preferably a soft pad having a lower hardness than the polishing pad used in the rough polishing step, and for example, urethane foam or suede is preferably used.

As the polishing slurry, a slurry containing cerium oxide or the like similar to the rough polishing step can be used, but in order to make the surface of the glass substrate smoother, the polishing slurry has a finer grain size and less variation. Is preferably used. For example, it is preferable to use a slurry obtained by dispersing colloidal silica having an average primary particle size of 10 to 80 nm in a solvent to form a slurry. When the polishing slurry according to this embodiment as described above is used in the rough polishing step, a known polishing slurry (preferably, colloidal silica used for normal mirror polishing is used in the mirror polishing step. Can be used as appropriate.

Further, in the present embodiment, it is preferable to use the polishing slurry according to the present embodiment as described above (particularly, using colloidal silica) in the mirror polishing step in addition to the rough polishing step. . By applying this embodiment in both steps, it is possible to polish with high accuracy and provide high quality.

The supply amount of the polishing slurry is not particularly limited, and is, for example, 0.5 to 1 L / min.

The polishing amount in the mirror polishing step is preferably about 2 to 5 μm. By setting the polishing amount in such a range, the obtained glass substrate can remove fine defects such as minute roughness and waviness generated on the surface of the glass substrate, or minute scratches generated in the previous process. Is done. As a result, the glass substrate manufacturing method of the present embodiment can improve the flatness of the obtained glass substrate, and can manufacture a glass substrate on which the magnetic head can float more stably in the end region. . In this step, by appropriately adjusting the polishing conditions in the mirror polishing step, the flatness of both main surfaces of the glass substrate is reduced to 2 μm or less, and the surface roughness Ra of both main surfaces of the glass substrate is reduced to 0.1 nm. be able to.

<Chemical strengthening process>
The chemical strengthening step is a step of immersing the glass substrate in a strengthening treatment liquid to improve the impact resistance, vibration resistance, heat resistance, and the like of the glass substrate.

The chemical strengthening step is a step of chemically strengthening the glass substrate. Examples of the strengthening treatment liquid used for chemical strengthening include a mixed solution of potassium nitrate (60%) and sodium nitrate (40%). Chemical strengthening can be performed by heating the strengthening treatment liquid to 300 to 400 ° C., preheating the glass substrate to 200 to 300 ° C., and immersing in the strengthening treatment liquid for 3 to 4 hours. In this immersion, it is preferable that the immersion is performed in a state of being housed in a holder that holds the end faces of the plurality of glass substrates so that both main surfaces of the glass substrate are chemically strengthened.

In addition, after the chemical strengthening process, a standby process for waiting the glass substrate in the air and a water immersion process are adopted to remove the strengthening treatment liquid adhering to the surface of the glass substrate and to homogenize the surface of the glass substrate. It is preferable. By adopting such a process, the chemically strengthened layer is formed uniformly, the compressive strain is uniform, deformation is difficult to occur, the flatness is good, and the mechanical strength is also good. The waiting time and the water temperature in the water immersing step are not particularly limited. For example, it may be kept in the air for 1 to 60 seconds and immersed in water at about 35 to 100 ° C., and may be determined appropriately in consideration of production efficiency.

<Final cleaning process>
The final cleaning step is a step of cleaning and cleaning the glass substrate. It does not specifically limit as a washing | cleaning method, What is necessary is just the washing | cleaning method which can clean the surface of the glass substrate after a mirror polishing process. In this embodiment, scrub cleaning is employed.

As the scrub cleaning, for example, a cleaning liquid such as a detergent or pure water is used. The pH of the cleaning solution used for scrub cleaning is preferably 9.0 or more and 12.2 or less. Within this range, the ζ potential can be easily adjusted and scrub cleaning can be performed efficiently. As scrub cleaning, both scrub cleaning with a detergent and scrub cleaning with pure water may be performed. By using a detergent and pure water, the glass substrate 1 can be more appropriately cleaned. The glass substrate 1 may be further rinsed with pure water between scrub cleaning with a detergent and scrub cleaning with pure water.

After the scrub cleaning, the glass substrate may be further subjected to ultrasonic cleaning. After scrub cleaning with detergent and pure water, ultrasonic cleaning with chemical solution such as sulfuric acid aqueous solution, ultrasonic cleaning with pure water, ultrasonic cleaning with detergent, ultrasonic cleaning with IPA, and / or steam drying with IPA, etc. Further, it may be performed.

The cleaned glass substrate is subjected to ultrasonic cleaning and drying processes as necessary. The drying step is a step of drying the surface of the glass substrate after removing the cleaning liquid remaining on the surface of the glass substrate with isopropyl alcohol (IPA) or the like. For example, a water rinse cleaning process is performed on the glass substrate after scrub cleaning for 2 minutes to remove the cleaning liquid residue. Next, an IPA cleaning process is performed for 2 minutes, and water remaining on the surface of the glass substrate is removed by IPA. Finally, the IPA vapor drying step is performed for 2 minutes, and the liquid IPA adhering to the surface of the glass substrate is dried while being removed by the IPA vapor. The drying process of the glass substrate is not particularly limited, and for example, a known drying method such as spin drying or air knife drying can be employed.

<Inspection process>
The glass substrate that has undergone the final cleaning step may be further subjected to an inspection step before shipment. The inspection step is a step of inspecting the glass substrate that has undergone the above-described steps for the presence or absence of scratches, cracks, foreign matters, and the like. The inspection is performed visually or using an optical surface analyzer (for example, “OSA6100” manufactured by KLA-TENCOL). After the inspection, the glass substrate is stored in a dedicated storage cassette and vacuum-packed in a clean environment so that foreign matter or the like does not adhere to the surface, and then shipped.

This specification discloses various modes of technology as described above, and the main technologies are summarized below.

By using a polishing slurry obtained by mixing a polishing slurry containing an abrasive particle group having a different average particle size and a dispersant optimal for each particle size in the polishing step, each abrasive particle Agglomeration changes the particle size distribution of the abrasive particles derived from each polishing slurry. As a result, the particle size distribution in the mixed polishing slurry can be suppressed, and the quality of the polished surface is maintained. However, since the polishing rate can be stably maintained, it is possible to efficiently manufacture an excellent glass substrate.

Further, in the production method, the polishing slurry further includes an abrasive particle group C having an average particle diameter intermediate between the particle group A and the particle group B, and a dispersant optimal for the particle group C. It is more preferable to use a polishing slurry obtained by mixing the polishing slurry A and the polishing slurry B. With such a configuration, the particle distribution can have a shape more suitable for stabilizing the polishing rate, and the optimum particle size distribution can be maintained with higher accuracy, so that higher quality and higher rate can be provided.

Furthermore, it is preferable that the manufacturing method includes a rough polishing step and a mirror polishing step as the polishing step, and polishing is performed using the polishing slurry in at least one of the rough polishing step and the mirror polishing step.

In this way, the polishing process is performed in two stages, and at least one of them is used in the polishing slurry according to the present invention, leading to stabilization of the polishing rate of the applied process. When applied to the rough polishing process, rough polishing is performed. It is considered that high quality can be obtained because the variation in the subsequent substrate removal is small and a more uniform surface state can be obtained, so that high-precision polishing is possible in the subsequent precision polishing step. In addition, when applied to the precision polishing process, there is an advantage that high surface quality can be obtained because the fluctuation of processing at the time of precision polishing is reduced and more precise conditions can be taken.

Furthermore, in the manufacturing method, it is preferable to polish using the polishing slurry in both the rough polishing step and the mirror polishing step. With such a configuration, it is possible to provide a higher-quality glass substrate suitable for high-density hard disk drives and media.

In the manufacturing method, it is preferable to use cerium oxide as abrasive particles in the rough polishing step. Zirconium oxide, zircon, or the like may be used. However, by using cerium oxide, the effects of rate stabilization and reduction in machining allowance variation intended by the present invention can be exhibited more highly.

Furthermore, in the manufacturing method, it is preferable to use colloidal silica as abrasive particles in the mirror polishing step. Colloidal silica is suitable for obtaining higher surface quality.

In the manufacturing method, it is preferable that the concentration of the abrasive component is 0.2 to 20% by mass in each of the polishing slurries. Thereby, the effect of the present invention that a high rate can be provided while maintaining high quality can be obtained more reliably.

Furthermore, in the manufacturing method, it is preferable to use a suede pad as a polishing pad in the rough polishing step. By using a suede pad in rough polishing, the polishing quality is further improved, and by using the polishing slurry, the stability of the polishing rate can be obtained even if a suede pad is used.

Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the examples.

(Example 1)
[Glass melting process]
As the glass material, _SiO 2 of 61 wt%, 3 wt% of _Al 2 _O 3, 2.7 wt% of _Na 2 O, 6.9 wt% _K 2 O, 5.7 wt% of MgO, 11. In order to obtain an aluminosilicate glass containing 5% by mass of CaO and 9% by mass of ZrO ₂ , each raw material was prepared and melted at 1500 ° C. using a platinum crucible.

[Glass blanks manufacturing process]
The molten glass was allowed to flow out from a melting nozzle at 1300 ° C. The glass which flowed out was cut | disconnected every 10g with a pair of blade, and the glass blanks were obtained. A blade having a V shape in plan view was selected, and the inner angle of the V shape was set to 80 °. An arc shape was used as a planar view shape of the portion where the V-shaped crosses.

In press molding, a glass gob supplied to the center of the lower mold forming surface was used with an upper mold facing the lower mold, and a tungsten-based material was used for the upper mold and the lower mold. The pressing time was 1 second, and butt molding was performed so that the thickness of the blanks after molding was uniform. The plate thickness after molding was 1.1 mm on average.

[Heat treatment process]
The obtained glass blanks (Tg: 670 ° C.) were heat-treated at 670 ° C. for 3 hours in order to remove internal strain.

[Coring / Shaping process]
Using a core drill equipped with a cylindrical diamond grindstone, a circular center hole having a diameter of about 18.7 mm was formed in the center of the blank. Using a drum-shaped diamond grindstone, the outer peripheral end surface and the inner peripheral end surface of the blanks were processed to have an inner diameter and an outer diameter of 65 mm in outer diameter and 20 mm in inner diameter.

[Surface grinding (first grinding) process]
In the first grinding step, the main surface (upper and lower surfaces) of the glass substrate was processed by using diamond grains made of acrylic resin as abrasive grains. The diamond particle diameter was 4 μm.

[Second grinding process]
In the second grinding step, the main surface (upper and lower surfaces) of the glass substrate was processed using a diamond-shaped diamond resin sheet. A diamond particle diameter of 1.5 μm was used.

In the first and second grinding steps, the glass substrate 1 main surface (upper and lower surfaces) was ground to about 250 μm.

[Inner and outer periphery polishing process]
In the end face polishing step, the surface roughness of the outer peripheral end face and the inner peripheral end face of the glass substrate was polished by a brush polishing method so that the Rmax was 30 nm or less and the Ra was 10 nm or less. And the surface of the glass substrate which finished such end surface grinding | polishing was water-washed.

[Rough polishing process]
A cerium oxide abrasive having an average particle size of 1.2 μm and a wide particle size distribution is applied to a classifier, and the cerium oxide abrasive having an average particle size of 0.95 μm and an average particle size of 0.4 μm is obtained. Abrasive and obtained.

The ratio of cerium oxide used was 0.95 μm particles / 0.4 μm particles = 0.55 / 0.45.

For cerium oxide having an average particle size of 0.95 μm, a copolymer of maleic acid and acrylic acid (MW = 20,000) is added as a dispersant, and neutral water is used as a dispersion medium. A polishing slurry was prepared with an abrasive concentration of 10% by mass. This was designated polishing slurry A.

Next, an acrylic acid polymer (MW = 5000) is added as a dispersant to cerium oxide having a particle size distribution with an average particle size of 0.40 μm, neutral water is used as a dispersion medium, and an abrasive concentration of 9 A polishing slurry was prepared as a mass%. This was designated polishing slurry B.

The polishing slurry A and the slurry B were mixed one-on-one to obtain a polishing liquid used for rough polishing.

Next, both main surfaces of 100 glass substrates were subjected to rough polishing using a double-side polishing machine (manufactured by Hamai Sangyo Co., Ltd., 16B type) using the above polishing liquid. A suede urethane pad was used as the polishing pad. The load was 120 g / cm ² . The supply amount of the polishing slurry was 10 L / min.

The polishing liquid is supplied from the slurry tank to the polishing machine, and the liquid used in the processing is discharged from the polishing machine and returned to the slurry tank at the same time, and is circulated through the slurry tank and used for processing. The polishing time was set to 45 minutes.

Thus, polishing was performed continuously for 10 batches, with 100 glass substrates being polished per batch as one batch.

At that time, 10 out of 100 substrates are selected and the plate thickness before and after polishing is measured. The difference between the maximum thickness and the minimum thickness is Δt, and the average thickness difference of 10 sheets is the average machining allowance. The polishing rate is derived by dividing by the polishing time, and is shown in Table 1 below.

[Chemical strengthening process]
In the chemical strengthening step, chemical strengthening was performed on the glass substrate after the above steps. Specifically, first, a mixed melt obtained by melting a solid of potassium nitrate and sodium nitrate was prepared. In addition, this mixed melt is mixed so that the mixing ratio of potassium nitrate and sodium nitrate is 6: 4 by mass ratio. Then, this mixed melt was heated to 400 ° C., and the washed glass base plate was immersed in the heated mixed melt for 60 minutes.

[Mirror polishing process]
Subsequently, a mirror polishing process was performed using a polishing apparatus (made by Hamai Co., Ltd.). Also in this mirror polishing step, the main surface of the glass substrate was polished with a suede pad. In addition, as the abrasive, a liquid prepared to pH 2.0 with 20% colloidal silica was used. The polishing conditions, and a load 100 g / cm ^2, the rotational speed 5rpm of the upper stool were the rotational speed 15rpm of the lower stool. However, it was performed while changing as appropriate during these processes.

[Final cleaning process]
The glass substrate was scrubbed. As a cleaning liquid, a liquid obtained by diluting KOH and NaOH mixed at a mass ratio of 1: 1 with ultrapure water (DI water) and adding a nonionic surfactant to enhance the cleaning performance is obtained. Using. The cleaning liquid was supplied by spraying. After scrub cleaning, in order to remove the cleaning liquid remaining on the surface of the glass substrate, a water rinse cleaning process is performed in an ultrasonic bath for 2 minutes, an IPA cleaning process is performed in an ultrasonic bath for 2 minutes, and finally the glass substrate is cleaned with IPA vapor. The surface of was dried.

(Example 2)
A glass substrate was obtained in the same manner as in Example 1 except that the following polishing slurry was used in the rough polishing step.

A cerium oxide abrasive having an average particle size of 1.2 μm and a wide particle size distribution is applied to a classifier several times, and the cerium oxide abrasive having an average particle size of 0.98 μm and an oxidation of an average particle size of 0.67 μm. A cerium oxide abrasive having a particle size distribution with a cerium abrasive and an average particle size of 0.37 μm was obtained. The ratio of the cerium oxide used was an average particle size of 0.98 μm particles / 0.67 μm particles / 0.37 μm particles = 0.36 / 0.32 / 0.32.

For cerium oxide having a particle size distribution with an average particle size of 0.98 μm, a copolymer of maleic acid and acrylic acid (MW = 12,000) is added as a dispersant, and neutral water is used as a dispersion medium. A slurry was prepared with an abrasive concentration of 10% by mass. This is designated as slurry A '.

For cerium oxide having a particle size distribution with an average particle size of 0.67 μm, a copolymer of maleic acid and acrylic acid (MW = 5000) is added as a dispersant, and neutral water is used as a dispersion medium. A slurry was prepared with a concentration of 9% by mass. This is designated as slurry C. The copolymer used here was a copolymer having a maleic acid / acrylic acid ratio lower than that used for 0.95 μm.

For cerium oxide having a particle size distribution with an average particle size of 0.37 μm, an acrylic acid polymer (MW = 5000) is added as a dispersant, neutral water is used as a dispersion medium, and the abrasive concentration is 9% by mass. A slurry was prepared. This is designated as slurry B '.

Slurry A ', Slurry B', and Slurry C were mixed so as to have the above mixing ratio to obtain a polishing liquid used for rough polishing.

(Comparative Example 1)
A glass substrate was obtained in the same manner as in Example 1 except that the following polishing slurry D was used in the rough polishing step. A cerium oxide abrasive with an average particle size of 1.2 μm and a wide particle size distribution, a copolymer of maleic acid and acrylic acid (MW = 12000) is added as a dispersant and neutral water is used as a dispersion medium. A polishing slurry was prepared with a material concentration of 10% by mass. This was designated polishing slurry D.

(Comparative Example 2)
A glass substrate was obtained in the same manner as in Example 1 except that the following polishing slurry E was used in the rough polishing step. A slurry prepared by using an acrylic acid polymer (MW = 5000) as a dispersing agent to a polishing agent concentration of 10% by mass with respect to a cerium oxide abrasive having an average particle size of 1.2 μm and a wide particle size distribution. It was.

(Example 3)
In the mirror polishing step, a glass substrate was obtained in the same manner as in Comparative Example 1 except that the following polishing slurry was used. Colloidal silica having an average particle size of 11 nm and colloidal silica having an average particle size of 36 nm are prepared. To the former, a sulfone polymer (MW = 1000) is added as a dispersant to disperse neutral water. The slurry was used as a medium, the abrasive concentration was 20% by mass, and the pH was adjusted with a liquid further containing sulfuric acid to obtain a polishing slurry 1.

In the latter case, an acrylic acid polymer (MW = 3500) is added as a dispersant, neutral water is used as a dispersion medium, the abrasive concentration is 18% by mass, pH is further adjusted with a liquid containing sulfuric acid, and polishing slurry 2 It was.

Slurries 1 and 2 were mixed so as to have the following silica ratio to obtain a polishing liquid used for precision polishing. The ratio of the colloidal silica used was 11 nm particles / 35 nm particles = 0.55 / 0.45.

Next, both main surfaces of the glass substrate were polished more precisely using a double-side polishing machine (manufactured by Hamai Sangyo Co., Ltd., 16B type). The load was 120 g / cm ² and the supply amount of the polishing slurry was 10 L / min. In this step, 100 batches of glass substrates were processed as 10 batches.

The polishing liquid is supplied from the slurry tank to the polishing machine, and the liquid used in the processing is discharged from the polishing machine and returned to the slurry tank at the same time, and is circulated through the slurry tank and used for processing. The polishing time was set to 30 minutes.

10 out of 100 substrates are selected and the thickness before and after polishing is measured. The difference between the maximum thickness and the minimum thickness is Δt. The polishing rate was derived by dividing by 2 and is shown in Table 2 below.

Example 4
In the mirror polishing step, a glass substrate was obtained in the same manner as in Comparative Example 1 except that the following polishing slurry was used.

Colloidal silica having an average primary particle size of 9 nm, colloidal silica having an average primary particle size of 20 nm, and colloidal silica having an average primary particle size of 35 nm are prepared. A sulfone polymer (MW = 800) was added as a dispersant, neutral water was used as a dispersion medium, the abrasive concentration was 20% by mass, and the pH was further adjusted with a liquid containing sulfuric acid to obtain polishing slurry 1 '. To 20 nm silica, an acrylic acid polymer (MW = 1500) is added as a dispersant, neutral water is used as a dispersion medium, the abrasive concentration is 18% by mass, pH is further adjusted with a liquid containing sulfuric acid, and slurry 3 It was.

Acrylic acid polymer (MW = 3500) is added to 35 nm silica as a dispersant, neutral water is used as a dispersion medium, and the pH is adjusted with a liquid further containing sulfuric acid at an abrasive concentration of 18% by mass. 2 '.

Polishing slurries 1 ', 3, and 2' were mixed so as to have the following silica ratio to obtain a polishing liquid used for precision polishing. The ratio of the colloidal silica used was 9 nm particles / 20 nm / 35 nm particles = 0.32 / 0.32 / 0.36.

(Comparative Example 3)
In the mirror polishing step, a glass substrate was obtained in the same manner as in Comparative Example 1 except that the following polishing slurry 4 was used. In the same manner as in Example 3, an acrylic acid polymer (MW = 1500) is used as a dispersant in a colloidal silica liquid obtained by mixing colloidal silica having a particle size distribution with an average primary particle size of 11 nm and colloidal silica having a particle size distribution with an average primary particle size of 35 nm. ), Neutral water was used as a dispersion medium, the abrasive concentration was 20 mass%, and the pH was adjusted with a liquid further containing sulfuric acid to obtain a polishing slurry 4.

(Example 5)
In the mirror polishing process, a glass substrate was obtained in the same manner as in Example 1 except that the polishing slurry of Example 3 was used.

And the glass substrate obtained by each Example and the comparative example was evaluated by the following evaluation tests.

(Evaluation methods)
(Roughing polishing rate / maximum thickness difference Δt)
For the glass substrates obtained in Examples 1 and 2 and Comparative Examples 1 and 2, the polishing rate and the maximum thickness difference Δt after rough polishing were evaluated. Polishing was performed continuously for 10 batches, with 100 batches of glass substrate polishing per batch.

At that time, 10 out of 100 substrates are selected and the plate thickness before and after polishing is measured. The difference between the maximum thickness and the minimum thickness is Δt, and the average thickness difference of 10 sheets is the average machining allowance. The polishing rate was derived by dividing by the polishing time.

The thickness was measured using a Mitutoyo micrometer (measuring instrument).

(Polishing rate of mirror polishing and maximum thickness difference Δt)
For the glass substrates obtained in Examples 3 to 4 and Comparative Example 3, the polishing rate after mirror polishing and the maximum thickness difference Δt were evaluated. Polishing was performed continuously for 10 batches, with 100 batches of glass substrate polishing per batch.

The thickness was measured using a Mitutoyo micrometer (measuring instrument). The results are shown in Table 2.

(Roughing and mirror polishing polishing rate / maximum thickness difference Δt)
For the glass substrate obtained in Example 5, the polishing rate and the maximum thickness difference Δt were measured in each of rough polishing and mirror polishing. The results are shown in Table 3.

(Defect count)
OSA (defect count) defect inspection was performed. As the test apparatus, an optical defect inspection apparatus Candela-OSA6100 manufactured by KLA-Tencor was used.

In the defect inspection, a total of 100 glass substrates processed in each example and each comparative example are inspected, and a substrate determined to have a deposit of 10 or less and a scratch of 2 or less is determined to be a non-defective product. Evaluate as A (excellent) when there are more than 90 sheets, B (good) when 90 sheets or less less than 95 sheets, C (good) when less than 90 sheets and 85 sheets or more, and D (defect) when less than 85 sheets did. The results are shown in Tables 1 and 2.

(Surface roughness Ra)
Further, for the glass substrates obtained in Examples 3 to 4 and Comparative Example 3, the surface roughness Ra was evaluated by AFM (Atomic Force Microscope) manufactured by Veeco. The results are shown in Table 2.

As shown in Table 1, the glass substrate obtained by the production method according to the present invention is excellent in rate stability in the rough polishing step, as compared with the glass substrate of the comparative example obtained by the conventional method. The defect evaluation results also showed that there was very little variation in polishing allowance within one batch, and the final surface quality was excellent.

Furthermore, it was also found that the polishing rate was remarkably stabilized and the surface quality was excellent by using a slurry composed of three particle size distributions and each composed of a dispersing agent optimal for different distributions.

Moreover, as shown in Table 2, by using the polishing slurry according to the present invention in the mirror finishing step, the rate stability in the precision polishing step is excellent, and the variation in polishing removal within one batch is very large. The defect quality and Ra results also indicated that the final surface quality was excellent. Further, it was also found that the polishing rate was remarkably stabilized and the surface quality was excellent by using a slurry constituted by three particle size distributions and a dispersing agent optimal for different distributions.

Furthermore, as shown in Table 3, by using the polishing slurry according to the present invention in both the rough polishing step and the precise polishing step, the rate stability in the precision polishing step is further improved, and the polishing allowance is reduced. It can be seen that the variation is further suppressed. In the table, the degree of non-defective product by defect count is rank A, and there is no difference from the level where the present invention is applied to one process, but the non-defective product rate applied to both processes is 100-99%. It is found that the level is higher than the level (95 to 97%) of Examples 1 and 3 applied to No. 1, and the surface quality is also excellent.

This application is based on Japanese Patent Application No. 2013-10362 filed on January 23, 2013, the contents of which are included in the present application.

In order to express the present invention, the present invention has been described appropriately and sufficiently through the embodiments with reference to the drawings and the like. However, those skilled in the art can easily change and / or improve the above-described embodiments. It should be recognized that it can be done. Therefore, unless the modifications or improvements implemented by those skilled in the art are at a level that departs from the scope of the claims recited in the claims, the modifications or improvements are not limited to the scope of the claims. To be construed as inclusive.

The present invention has wide industrial applicability in the technical field of glass substrates for hard disks and their manufacturing methods.

Claims

In the method of manufacturing a glass substrate for hard disk comprising a polishing step of polishing a glass substrate with a polishing slurry containing abrasive particles,
In the polishing step, the glass substrate has a polishing slurry A containing an abrasive particle group A having a predetermined average particle diameter and a dispersant optimal for the particle group A, and an average particle diameter larger than that of the particle group A. A method for producing a glass substrate for a hard disk, wherein polishing is performed using a polishing slurry obtained by mixing an abrasive particle group B having a polishing slurry B containing a dispersing agent optimal for the particle group B.
As the polishing slurry, a polishing slurry C further comprising an abrasive particle group C having an average particle diameter intermediate between the particle group A and the particle group B, and a dispersing agent optimal for the particle group C, and the polishing slurry A and The method for producing a glass substrate for a hard disk according to claim 1, wherein a polishing slurry obtained by mixing the polishing slurry B is used.
The rough polishing step and the mirror polishing step are provided as the polishing step, and polishing is performed using the polishing slurry in at least one of the rough polishing step and the mirror polishing step. Method for manufacturing a glass substrate for hard disks.
The method for producing a glass substrate for a hard disk according to claim 3, wherein polishing is performed using the polishing slurry in both the rough polishing step and the mirror polishing step.
The method for producing a glass substrate for a hard disk according to any one of claims 1 to 4, wherein cerium oxide is used as the abrasive particles in the rough polishing step.
The method for producing a glass substrate for a hard disk according to any one of claims 1 to 5, wherein colloidal silica is used as the abrasive particles in the mirror polishing step.
The method for producing a glass substrate for a hard disk according to any one of claims 1 to 6, wherein in each of the polishing slurries, the concentration of the abrasive component is 0.2 to 20 mass%.
The method for producing a glass substrate for a hard disk according to any one of claims 1 to 7, wherein a suede pad is used as a polishing pad in the rough polishing step.