WO2012133373A1

WO2012133373A1 - Method for producing magnetic-disk glass substrate

Info

Publication number: WO2012133373A1
Application number: PCT/JP2012/057870
Authority: WO
Inventors: 葉月中江
Original assignee: コニカミノルタアドバンストレイヤー株式会社
Priority date: 2011-03-30
Filing date: 2012-03-27
Publication date: 2012-10-04
Also published as: JPWO2012133373A1

Abstract

Provided is a method for producing a magnetic-disk glass substrate that can achieve a stable head levitation amount when integrated into a hard disk. This method for producing a magnetic-disk glass substrate involves a step of polishing the principal surface of a disk-shaped glass substrate precursor and is characterized in that: in the step of polishing the principal surface, at least two stages of polishing including a rough polishing step and a precise polishing step are performed; a cleaning step is performed between the rough polishing step and the precise polishing step; and the cleaning step is a step of removing the principal surface of the glass substrate precursor at a rate of 100 nm/min or less.

Description

Manufacturing method of glass substrate for magnetic disk

The present invention relates to a method for producing a glass substrate for a magnetic disk.

In recent years, in hard disk drives (HDD), the recording capacity of magnetic recording media has become higher. Along with this, the gap (head flying height) between the magnetic recording medium and the head for reading and writing the recording has decreased to a level of several nm. When the head flying height decreases, the head and the magnetic recording medium collide with each other to cause a phenomenon called head crash, which easily causes a read / write error of the hard disk.

There are several possible causes of the above error, and one of the causes is the influence of deposits adhering to the surface of the glass substrate. In other words, the adhering matter adheres to the surface of the glass substrate, so that the head flying height becomes non-uniform and head crushing tends to occur. In addition to cerium oxide and colloidal silica used as an abrasive in the polishing process, the above deposits may be iron, oxides thereof, carbon, and the like that are slightly present in the environment. Among these, in particular, cerium oxide tends to remain on the glass substrate. For this reason, various attempts have been made so far to remove cerium oxide adhering to the surface of the glass substrate.

For example, in Japanese Patent Application Laid-Open No. 2008-269767 (Patent Document 1), the surface of a glass substrate is polished with cerium oxide, and then the main surface of the glass substrate is etched to remove cerium oxide attached to the surface of the glass substrate. A method of removing is disclosed.

JP 2008-269767 A

However, when a magnetic disk manufactured using the glass substrate of Patent Document 1 is mounted on a hard disk and used, the flying height of the head becomes non-uniform and may collide with the head or cause a read / write error.

The present invention has been made under such circumstances, and an object of the present invention is to provide a method of manufacturing a glass substrate for a magnetic disk that can obtain a stable head flying height when taken into a hard disk. is there.

When the present inventors examined the cause of non-uniform head flying height of the glass substrate produced by the method of Patent Document 1, the cause is that the flatness and smoothness of the end surface portion of the glass substrate are inferior. I found. Furthermore, when the cause of inferior flatness and smoothness of the end face portion was examined, in the cleaning step of removing the main surface of the glass substrate, the sag of the etching solution occurs when the glass substrate is pulled up from the cleaning solution. It was found that the outer peripheral side was excessively etched when viewed from the center side of the glass substrate due to liquid sag.

Based on this knowledge, the inventors of the present invention have completed the present invention by earnestly examining the etching conditions performed in the glass substrate cleaning process after the polishing process. That is, the method for producing a glass substrate for a magnetic disk of the present invention includes a step of polishing the main surface of a disk-shaped glass substrate precursor, and the step of polishing the main surface includes at least a rough polishing step. This is a two-stage polishing with a precision polishing process, and includes a cleaning process between the rough polishing process and the precision polishing process, and the cleaning process is performed at a main surface of the glass substrate precursor at a rate of 100 nm / min or less. It is the process of removing.

The above washing step is preferably a step of removing the main surface of the glass substrate precursor using a solution having a surface tension of 30 to 50 mN / m. By removing the main surface of the glass substrate precursor with the etching solution having the surface tension as described above, the flatness and smoothness of the end face can be enhanced. If the surface tension is less than 30 mN / m, bubbles are likely to be generated, so that etching unevenness occurs on the entire surface of the glass substrate precursor. In addition, since bubbles tend to gather near the end face, the smoothness and flatness of the end of the glass substrate precursor are affected as a result. Moreover, when it exceeds 50 mN / m, the wettability to a glass substrate precursor will worsen, and the flatness and smoothness of an edge part vicinity will be affected. The cleaning step is preferably a step of removing a thickness of 30 to 100 nm from the main surface of the glass substrate precursor. If the removal amount is less than 30 nm, the cleaning effect may not be sufficiently obtained. Moreover, when it exceeds 100 nm, it will affect the shape of the edge part of a glass substrate precursor. The precision polishing step is preferably a step of removing a thickness of 0.3 μm or more and 5 μm or less from the main surface of the glass substrate precursor. When it is less than 0.3 μm, the surface roughness and waviness deteriorated in the step of removing the main surface of the glass substrate precursor cannot be corrected. If the thickness exceeding 5 μm is removed, so-called sagging occurs at the end face of the glass substrate precursor.

The method for producing a glass substrate for magnetic disk of the present invention has the above-described configuration, so that a glass substrate for magnetic disk capable of obtaining a stable head flying height when taken into a hard disk can be produced. Show the effect.

It is a perspective view which shows an example of the glass substrate for magnetic discs manufactured by the manufacturing method of this invention. It is a flowchart which shows an example of the order of the process of the manufacturing method of the glass substrate for magnetic discs of this invention.

Hereinafter, the glass substrate for magnetic disk of the present invention and the manufacturing method thereof will be described with reference to the drawings and flowcharts. Note that dimensional relationships such as length, width, thickness, and depth are changed as appropriate for clarity and simplification of the drawings, and do not represent actual dimensional relationships.

<Glass substrate for magnetic disk>
FIG. 1 is a perspective view showing an example of a glass substrate for a magnetic disk manufactured by the manufacturing method of the present invention. The glass substrate for a magnetic disk manufactured by the manufacturing method of the present invention is used as a substrate for an information recording medium in an information recording apparatus such as a hard disk drive apparatus. Such a glass substrate for a magnetic disk has a disk shape as shown in FIG. 1, and a hole 1H is formed at the center thereof. The surface of the glass substrate 1 for magnetic disks means the front main surface 1A, the back main surface 1B, the inner peripheral end surface 1C, and the outer peripheral end surface 1D.

The size and shape of the magnetic disk glass substrate 1 of the present invention are not particularly limited, and are, for example, 0.8 inch, 1.0 inch, 1.8 inch, 2.5 inch, or 3.5 inch. The thickness of the magnetic disk glass substrate 1 is preferably 0.30 to 2.2 mm, for example, from the viewpoint of preventing breakage. In addition, the thickness of the glass substrate 1 for magnetic disks is calculated by the average of the values measured at a plurality of arbitrary points to be pointed on the glass substrate. A typical example of the magnetic disk glass substrate 1 of the present invention is as follows. The magnetic disk glass substrate has an outer diameter of about 64 mm, an inner diameter of about 20 mm, and a thickness of about 0.8 mm. In general, a 2.5-inch hard disk uses a glass substrate for a magnetic disk having an outer diameter of 65 mm.

Aluminosilicate glass is preferably used as the material constituting the magnetic disk glass substrate of the present invention. The composition of such an aluminosilicate glass is 58% to 75% by weight of SiO ₂ , 5% to 23% by weight of Al ₂ O ₃ , 3% to 10% by weight of Li ₂ O, 4% to 13% by weight. % Na ₂ O as a main component. In addition, it is not limited only to such an aluminosilicate glass, The composition of various glass can be used.

<Method for manufacturing glass substrate for magnetic disk>
The method for producing a glass substrate for a magnetic disk according to the present invention includes a polishing step of polishing the main surface of a disk-shaped glass substrate precursor, and the polishing step includes at least a rough polishing step and a precision polishing step. This is a two-stage polishing, and includes a cleaning process between the rough polishing process and the precision polishing process, and the cleaning process is a process of removing the main surface of the glass substrate precursor at a rate of 100 nm / min or less. It is characterized by being.

By etching the main surface of the glass substrate precursor at a rate of 100 nm / min or less in the cleaning step as in the present invention, the glass substrate precursor is not excessively etched even if the etching solution causes dripping. Therefore, the flatness and smoothness of the glass substrate precursor can be improved. The glass substrate for a magnetic disk produced in this manner has excellent flatness and smoothness, and therefore has an excellent property that head crushing hardly occurs.

The method for producing a glass substrate for a magnetic disk of the present invention can include other steps as long as the cleaning step is performed between the rough polishing step and the precision polishing step. Here, as other processes, for example, a direct press process for processing a molten glass into a disk shape, a coring process for forming a hole in the center of the glass substrate precursor, and chamfering the inner peripheral end surface and the outer peripheral end surface of the glass substrate precursor. Examples thereof include an inside / outside processing step, a lapping step for grinding the main surface of the glass substrate precursor, and the like.

In the following, a case where a glass substrate precursor is produced by a direct press method will be described. However, the production method of the present invention is not limited to a method for producing a glass substrate precursor by a direct press method. A glass substrate precursor may be produced by cutting a sheet glass formed by a draw method or a float method with a grinding wheel.

Each process when producing the glass substrate for magnetic disk of the present invention according to the flowchart of FIG. 2 will be described. The method for manufacturing a glass substrate for a magnetic disk of the present invention includes a rough polishing step, a cleaning step, and a precision polishing step in this order, as long as the cleaning step removes the main surface of the glass substrate precursor at the above speed. Further, a cleaning step or a polishing step may be included between these steps, and the order of other steps may be appropriately changed.

(Direct press process: Step S10)
First, a molten glass is prepared by melting a glass material. The molten glass is poured into a lower mold and press-formed with an upper mold and a barrel mold to obtain a disk-shaped glass substrate precursor. The process of obtaining the glass substrate precursor from the molten glass in this way is called a direct press process. As described above, the production method of the present invention is not limited to the method for producing a glass substrate precursor by a direct pressing process, and a downdraw method or a float method may be used.

(Coring process: Step S20)
Next, a hole is made in the central portion of the glass substrate precursor in the coring process. In the drilling, a hole is drilled in the center by grinding with a core drill or the like equipped with a diamond grindstone or the like in the cutter part. The size of the hole can be appropriately changed depending on the outer diameter of the glass substrate precursor. For example, a hole having an inner diameter of 20 mm (the diameter of the hole 1H in the center) is formed at the center of the glass substrate precursor having an outer shape of 65 mm. Open.

(Rough wrapping process: Step S30)
A lapping process is performed on both the front and back surfaces of the glass substrate precursor. Here, the rough lapping is performed by, for example, a double-sided lapping apparatus. As a result, the overall shape, parallelism, flatness and thickness of the glass substrate precursor can be preliminarily adjusted.

(Internal / external machining process: Step S40)
Next, in the inside / outside processing step, chamfering of the outer peripheral end surface and the inner peripheral end surface of the glass substrate precursor is performed. Thereby, the flatness of the end surface of the glass substrate precursor can be increased.

(End face polishing process: Step S50)
Subsequently, in the end face polishing step, the outer peripheral end face and the inner peripheral end face of the glass substrate precursor are polished by a brush polishing method using a slurry (free abrasive grains) containing cerium oxide abrasive grains as polishing abrasive grains. In the brush polishing method, the outer peripheral end face and the inner peripheral end face are polished while rotating the glass substrate precursor. The inner peripheral end face of the glass substrate precursor is processed into a mirror surface state by further polishing the inner peripheral end face with a magnetic polishing method. Finally, the surface of the glass substrate precursor is washed with water.

(Fine wrapping process: Step S60)
Next, in the fine lapping process, the front and back surfaces of the glass substrate precursor are ground using a fixed abrasive polishing pad. Such a fine lapping process can be ground using a known grinding machine called a double-side grinding machine using a planetary gear mechanism. This double-sided grinding machine is equipped with a disk-shaped upper and lower surface plate arranged in parallel with each other in parallel, and the front and back surfaces of the glass substrate precursor are placed on the surfaces facing the upper surface plate and the lower surface plate, respectively. A plurality of diamond pellets for grinding are attached.

Between the upper surface plate and the lower surface plate, there are a plurality of carriers that rotate in combination with an internal gear provided in an annular shape on the outer periphery of the lower surface plate and a sun gear provided around the rotation axis of the lower surface plate. The carrier is provided with a plurality of holes, and the glass substrate precursor is fitted into the holes and arranged. The upper surface plate, the lower surface plate, the internal gear, and the sun gear can be operated by separate driving, and the upper surface plate and the lower surface plate rotate in opposite directions.

Then, the carrier sandwiched between the surface plates through the diamond pellets revolves in the same direction as the lower surface plate with respect to the rotation center of the surface plate while rotating while holding a plurality of glass substrate precursors. In the grinding machine operating in this way, the front and back surfaces of the glass substrate precursor can be ground by supplying a grinding liquid between the upper surface plate and the glass substrate precursor and between the lower surface plate and the glass substrate precursor. it can.

When using this double-side polishing machine, the weight of the surface plate applied to the glass substrate precursor and the number of rotations of the surface plate are adjusted as appropriate according to the desired grinding state. In the fine wrapping process, it is preferable to perform the wrapping in two steps of the first wrapping process and the second wrapping process. The weight in the first wrapping step and the second wrapping step is preferably 60 g / cm ² to 120 g / cm ² . Further, it is preferable that the rotation speed of the surface plate is about 10 rpm to 30 rpm, and the rotation speed of the upper surface plate is about 30% to 40% slower than the rotation speed of the lower surface plate. At the time when the second lapping process is completed, defects such as large undulation, chipping and cracking of the glass substrate precursor are removed.

Increasing the weight by the surface plate or increasing the rotation speed of the surface plate will increase the amount of grinding of the glass substrate precursor, but if the load is increased too much, the surface roughness of the glass substrate precursor will deteriorate. Therefore, it is not preferable. Further, when the rotation speed of the surface plate is too fast, the flatness is not good. Moreover, even if the load is too small or the rotation speed of the surface plate is too slow, the amount of grinding is reduced and the production efficiency is lowered.

As for the surface roughness of the main surface of the glass substrate precursor after the fine lapping step, Ra is preferably 0.05 to 0.4 μm, and the flatness of the main surface is 7 to 10 μm. It is preferable. By setting it as such a surface state, the polishing efficiency in the subsequent first polishing step can be enhanced.

(Main surface polishing step: Step S70)
The main surface polishing step performs at least two-step polishing, that is, a rough polishing step and a precision polishing step. The rough polishing process is performed to remove scratches and distortions remaining on the front and back surfaces of the glass substrate precursor in the fine lapping process, and the precise polishing process is performed to mirror-finish the front and back surfaces of the glass substrate precursor. It is. The method for producing a glass substrate for a magnetic disk of the present invention includes a cleaning step between the rough polishing step and the precision polishing step, and the cleaning step is performed at a main surface of the glass substrate precursor at a rate of 100 nm / min or less. It is the process of removing. In the following, the rough polishing process, the cleaning process, and the precision polishing process in the main surface polishing process will be described in this order.

(Rough polishing process: Step S71)
First, in the rough polishing step, a polishing pad whose polisher is a suede pad is set in the double-side polishing machine, and the front and back surfaces of the glass substrate precursor are polished. And deposits, such as an abrasive | polishing agent adhering to the main surface of the said glass substrate precursor, are removed by washing | cleaning. Thus, the thing with a big average particle diameter of the deposit | attachments adhering to the front and back of a glass substrate precursor is removed.

(Washing process: Step S72)
Next, in the cleaning step, the glass substrate precursor is immersed in an etching solution to remove deposits such as abrasives adhering to the main surface by cleaning. This cleaning step is characterized in that the main surface of the glass substrate precursor is removed at a rate of 100 nm / min or less. By washing the glass substrate precursor at such a low speed, even if liquid sag occurs when the glass substrate precursor is taken out from the cleaning liquid, the uniformity of the outer periphery of the glass substrate precursor is hardly impaired, and the flatness of the glass substrate for magnetic disks and Smoothness can be improved.

In order to make it difficult for the outer periphery of the glass substrate precursor to be etched even when dripping occurs as described above, it is preferably 10 to 80 nm / min, more preferably 30 to 60 nm / min. The removal rate of the glass substrate precursor by the above washing is preferably as slow as possible from the viewpoint of not impairing the uniformity of the outer periphery of the glass substrate precursor even when sag of the etching solution occurs. If it is less than 10 nm / min, the time required for the step of cleaning the glass substrate precursor becomes too long, which is not preferable for production. When the removal rate of the glass substrate precursor exceeds 100 nm / min, the outer peripheral side of the glass substrate precursor is excessively etched by the liquid dripping after cleaning, and the uniformity on the outer peripheral side is impaired, which is not preferable.

Further, the etching solution used in the cleaning process preferably has a surface tension of 30 to 50 mN / m, more preferably a surface tension of 40 to 48 mN / m. By using an etching solution having such a surface tension, the etching solution is easily wetted to the main surface of the glass substrate precursor, so that dripping is less likely to occur and the outer peripheral portion of the glass substrate precursor is excessively etched. This can be prevented.

Here, in the cleaning step, it is preferable to remove the thickness of 30 to 100 nm from the main surface of the glass substrate precursor, and more preferably to remove the thickness of 35 to 80 nm. If the thickness of the removal amount is less than 30 nm, the removal amount of the glass substrate precursor is insufficient, and there is a possibility that the deposit remains on the main surface of the glass substrate precursor. The surface may be etched too much.

As an etching solution used in the cleaning process, it is preferable to use an aqueous solution in which hydrogen fluoride, ammonium hydrogen fluoride, sodium fluoride, silicon fluoride acid or the like is dissolved in water. For example, when hydrogen fluoride is dissolved, It is more preferable to use an aqueous solution in which 0.1 to 1% by mass of hydrogen fluoride is mixed. The temperature of the etching solution varies depending on the material of the etching solution, but it is preferable to immerse the glass substrate precursor in a state adjusted to 20 to 50 ° C. Moreover, when immersing a glass substrate precursor in an etching liquid, it is preferable to irradiate an ultrasonic wave of about 80 kHz. Thereafter, ultrasonic cleaning at 120 kHz may be performed with a neutral detergent to further perform ultrasonic cleaning, or the main surface may be treated by rinsing with pure water.

(Precision polishing process: Step S73)
Subsequently, in the precision polishing step, the front and back surfaces of the glass substrate precursor are polished using a polishing pad that is a soft polisher (suede) with respect to the glass substrate precursor. Here, in the precision polishing step, it is preferable to remove a thickness of 0.3 μm or more from the main surface of the glass substrate precursor. If the thickness is less than 0.3 μm, an excessive etching area generated in the above-described cleaning process cannot be removed, and the smoothness of the magnetic disk glass substrate is lowered, which is not preferable. Moreover, as an abrasive | polishing agent used at a precision grinding | polishing process, it is preferable to use a silica abrasive grain finer than the cerium oxide used at the rough | crude grinding | polishing process.

(Final cleaning process: Step S80)
It is preferable to wash and dry the glass substrate precursor after the above polishing with a neutral detergent and pure water. By performing such cleaning, foreign substances adhering to the glass substrate precursor can be washed away, and the main surface of the magnetic disk glass substrate can be stabilized and excellent in long-term storage stability. . A glass substrate for a magnetic disk can be produced as described above. In addition, a magnetic disk can be obtained by performing a magnetic thin film formation process with respect to the glass substrate for magnetic disks produced in this way.

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

<Example 1>
In this example, a glass substrate for a magnetic disk was manufactured by performing the following steps in order.

(Direct press process: S10)
First, molten glass was prepared by melting a glass material. The molten glass was poured into a lower mold and directly pressed using an upper mold and a barrel mold to obtain a disk-shaped glass substrate precursor having a diameter of 66 mmφ and a thickness of 1.2 mm. Aluminosilicate glass was used as the glass material.

(Coring process: S20)
Next, a hole was made by grinding the central portion of the glass substrate precursor with a core drill having a diamond grindstone or the like in the cutter portion. In this way, a hole having an inner diameter of 20 mm (diameter of the hole 1H in the central part) was formed in the central part of the glass substrate precursor having an outer diameter of 65 mm.

(Coarse lapping process: S30)
Next, the glass substrate precursor is set in a double-sided wrapping apparatus, and alumina abrasive grains having a particle size of # 400 (particle size of about 40 to 60 μm) are used, and the load on the surface plate on alumina is set to about 100 kg. The front and back surfaces of the glass substrate precursor were polished. The glass substrate precursor thus housed in the carrier had a surface accuracy of both sides of 0 μm to 1 μm and a surface roughness Rmax of about 6 μm.

(Internal / external machining process: S40)
Next, chamfering of the outer peripheral end surface and the inner peripheral end surface of the glass substrate precursor was performed. As a result, the surface roughness of the end surface of the glass substrate precursor was about 2 μm in Rmax.

(End face polishing step: S50)
Subsequently, the outer peripheral end surface and the inner peripheral end surface of the glass substrate precursor were polished while rotating the glass substrate precursor by a brush polishing method using a slurry (free abrasive particles) containing cerium oxide abrasive grains as polishing abrasive grains. . Here, polishing was performed until the surface roughness of the outer peripheral end face and the inner peripheral end face of the glass substrate precursor was about 0.4 μm in Rmax and about 0.1 μm in Ra.

The inner peripheral side end face was further polished by a magnetic polishing method to be processed into a mirror surface state to prevent particles and the like from being generated. And after grind | polishing the inner peripheral end surface in this way, the main surface of the glass substrate precursor was wash | cleaned with water.

(Fine wrapping process: S60)
Next, in the fine lapping process, both the front and back surfaces of the glass substrate precursor were set in a double-side grinding machine using a planetary gear mechanism. Then, using a diamond sheet, the weight of the platen applied to the glass substrate precursor is changed from 60 g / cm ² to 120 g / cm ² , the rotation speed of the platen is changed from 10 rpm to 30 rpm, and the rotation speed of the upper platen is decreased. The front and back surfaces of the glass substrate precursor were polished at a rate slower by about 30% to 40% than the platen rotation speed. Thus, lapping was performed until the surface roughness Ra of the main surface of the glass substrate precursor was 0.1 μm or less and the flatness was 7 μm or less.

(Main surface polishing step: S70)
In the main surface polishing process, a cleaning process was performed between the rough polishing process and the precision polishing process as follows.

(Rough polishing step: S71)
First, the rough polishing process for removing the flaw and distortion which remained in the fine lapping process was performed using the double-side polish apparatus mentioned above. In this rough polishing step, the front and back surfaces of the glass substrate precursor were polished under the following conditions using a polishing pad whose polisher was a suede pad.

Polishing liquid: Cerium oxide (average particle size 1.3 μm) + water load: 80 to 100 g / cm ²
Polishing time: 30 to 50 minutes Removal method: 35 to 45 μm
(Washing process: S72)
Next, the abrasive | polishing agent adhering to the main surface of the said glass substrate precursor was removed by washing | cleaning. The cleaning was performed by using an aqueous solution containing 1% by mass of HF as an etchant, immersing the glass substrate precursor in this, and etching the glass substrate precursor at an etching rate of 10 nm / min. At this time, the temperature of the etching solution was adjusted to 30 ° C., and the surface tension of the etching solution was 48 mN / m. Thereafter, ultrasonic cleaning was performed by irradiating 120 kHz ultrasonic waves with a neutral detergent, and finally, rinsing with pure water was performed to dry IPA.

(Precision polishing process: S73)
Subsequently, in the precision polishing step, the front and back surfaces of the glass substrate precursor were polished using a polishing pad that was a soft polisher (suede) to remove a thickness of 1 μm from the main surface of the glass substrate precursor. In addition, as an abrasive | polishing agent used at a precision grinding | polishing process, the silica abrasive grain finer than the cerium oxide used at the rough | crude grinding | polishing process was used.

(Final cleaning process: S80)
The glass substrate precursor after the polishing treatment was washed with a neutral detergent and pure water and dried. As described above, the magnetic disk glass substrate of this example was produced.

<Examples 2 to 10, Comparative Example 1>
Table 1 shows the etching rate and removal amount of the glass substrate precursor in the cleaning process, the surface tension of the solution used in the cleaning process, and the stock removal of the glass substrate precursor in the precision polishing process for Example 1 above. The glass substrates for magnetic disks of Examples 2 to 10 and Comparative Example 1 were produced by the same method as in Example 1 except for the above.

<Comparative Example 2>
In Comparative Example 2, a glass substrate for a magnetic disk was produced by the same method as in Example 1 except that the cleaning process and the precision polishing process in the order of the processes in Example 1 were reversed. That is, the main surface of the glass substrate precursor was cleaned in the order of the rough polishing step, the precision polishing step, and the cleaning step, thereby producing a magnetic disk glass substrate of Comparative Example 2.

<Evaluation>
After a magnetic film was formed on the magnetic disk glass substrate prepared in each of the above examples and comparative examples, a medium was prepared, and then mounted on a GA tester, and the head floating stability (glide avalan value (GA value)) Was measured. The results are shown in the “GA value” column of Table 1. The GA value is measured by rotating the media at a rotational speed of 7200 rpm as if it were a drive, and the head gradually falls on it, and the height at which the head at the point r32 becomes unstable becomes the GA value. It was. Here, r32 is a point 32 mm from the center of the substrate. By measuring the GA value of r32, the influence of flatness in the vicinity of the outer end portion of the glass substrate precursor can be understood. The lower the GA value, the better the head floating stability, and the higher the flatness and smoothness of the magnetic disk glass substrate.

As is clear from Table 1, the glass substrates for magnetic disks of Examples 1 to 10 had low glide avalanche values, whereas the glass substrates for magnetic disks of Comparative Examples 1 and 2 had high glide avalanche values.

As a reason for the results of the GA values in Table 1 above, in Examples 1 to 10, the cleaning process is performed between the rough polishing process and the precision polishing process, and the removal rate of the glass substrate precursor in the cleaning process is high. Since it was 100 nm / min or less, the glass substrate for magnetic disk having high flatness and smoothness could be produced without excessive etching of the outer diameter of the glass substrate precursor even when liquid dripping occurred. Conceivable.

On the other hand, in Comparative Example 1, the removal rate of the glass substrate precursor in the cleaning process is 120 nm / min, so that part of the outer diameter of the glass substrate precursor is excessively removed when the etching solution is dripped. As a result, the flatness and smoothness of the glass substrate for magnetic disks were impaired. Moreover, in Comparative Example 2, since the cleaning process was performed after the precision polishing, the non-uniformity of the outer shape of the glass substrate precursor generated in the cleaning process could not be adjusted in the precision polishing process.

Therefore, it was shown that the glass substrate for magnetic disk manufactured according to the manufacturing method of the present invention has high flatness and smoothness. In particular, as shown in Example 6, when the cleaning process is performed using an etching solution having a high surface tension (surface tension 67 mN / m), the flatness and smoothness of the magnetic disk glass substrate are significantly reduced. there were. This is presumably because the etching liquid having a high surface tension was used to etch excessively even when liquid dripping occurred.

Further, as shown in Examples 7 to 8, when the machining allowance in the precision polishing step was set to 0.3 μm or less, the flatness and smoothness of the magnetic disk glass substrate were significantly improved. This is considered to be due to the fact that the end face of the glass substrate precursor that became non-uniform in the cleaning process could be uniformly prepared in the precision polishing process.

Also, as shown in Example 10, the GA value slightly increased when cleaning was performed using an etching solution having a surface tension of less than 30 mN / m. This is because the surface tension of the etching solution is small, and fine bubbles are generated in the etching solution, resulting in uneven etching and dripping, and the flatness of the end surface of the glass substrate precursor is deteriorated. it is conceivable that.

Although the embodiments and examples of the present invention have been described above, it is also planned from the beginning to appropriately combine the configurations of the above-described embodiments and examples.

It should be considered that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 Glass substrate precursor, 1A front main surface, 1B back main surface, 1C inner peripheral end surface, 1D outer peripheral end surface, 1H hole.

Claims

A method for producing a glass substrate for a magnetic disk comprising a step of polishing a main surface of a disk-shaped glass substrate precursor,
The step of polishing the main surface is at least two-step polishing of a rough polishing step and a precision polishing step,
Including a cleaning step between the rough polishing step and the precision polishing step;
The said washing | cleaning process is a manufacturing method of the glass substrate for magnetic discs which is a process of removing the main surface of the said glass substrate precursor at a speed | rate of 100 nm / min or less.
The method for producing a glass substrate for a magnetic disk according to claim 1, wherein the cleaning step is a step of removing the main surface of the glass substrate precursor using a solution having a surface tension of 30 to 50 mN / m.
3. The method for producing a glass substrate for a magnetic disk according to claim 1, wherein the cleaning step is a step of removing a thickness of 30 to 100 nm from the main surface of the glass substrate precursor.
4. The method for producing a glass substrate for a magnetic disk according to claim 1, wherein the precision polishing step is a step of removing a thickness of 0.3 μm or more from the main surface of the glass substrate precursor.