JP2008226407A - Magnetic disk substrate manufacturing method, chemical strengthening apparatus, and magnetic disk manufacturing method - Google Patents

Abstract

A glass substrate for a magnetic disk and a magnetic disk excellent in surface smoothness and flatness are provided.
A method of manufacturing a glass substrate for a magnetic disk including a chemical strengthening step of chemically strengthening at least an end surface portion of the glass plate having a chamfered end surface, wherein the chemical strengthening step includes a plurality of chemical strengthening steps. A method for manufacturing a glass substrate for a magnetic disk, comprising: laminating the main surfaces of the doughnut-shaped glass plates together and subjecting the main surface to a pressurized state, and a donut with a chamfered end surface A glass substrate laminate for chemically strengthening a glass substrate for a magnetic disk that chemically strengthens at least an end surface portion of the glass plate of a glass plate, wherein the main surfaces of a plurality of donut glass plates are laminated together And a pressing means that pressurizes the magnetic dough through a pressing plate that is movable in the vertical axis direction of the main surface of the donut-shaped glass plate. Method of manufacturing a magnetic disk using chemical tempering apparatus and the glass substrate of the glass substrate for a click.
[Selection] Figure 3

Description

The present invention relates to a magnetic disk substrate manufacturing method, a magnetic disk substrate chemical strengthening apparatus, and a magnetic disk manufacturing method. This magnetic disk substrate is used for a magnetic recording medium mounted on various magnetic recording devices including an external storage device of a computer.
More specifically, the present invention relates to a manufacturing method and a chemical strengthening apparatus that can efficiently produce a glass substrate for a magnetic disk that has an end face portion that is reinforced and that is excellent in surface smoothness and flatness. The present invention relates to a magnetic disk manufacturing method using the obtained magnetic disk glass substrate.

  With the recent increase in recording density of magnetic disks, there is a demand not only for improving the performance of the magnetic layer for recording digital signals, but also for improving the performance of various components such as a magnetic head and a substrate for reading records. In consideration of such a demand, as a substrate, a glass substrate has been attracting attention in place of the conventionally used aluminum substrate.

  In other words, the glass substrate is easy to reduce the thickness of the substrate required for miniaturization and high density, easy to ensure the flatness of the substrate surface that enables low flying height of the magnetic head, glass Since the surface hardness of the substrate is high and the Young's modulus is large, it is suitable for mobile applications.

  Glass substrates are roughly classified into crystallized glass substrates and amorphous glass substrates. In the past, crystallized glass substrates have been used, but with the recent increase in magnetic recording density, amorphous glass substrates that can realize a smoother surface have become mainstream.

  By using a glass substrate on which high-density recording can be realized, a hard disk drive can store a sufficient amount of information even with a small magnetic disk. Such hard disk drives have come to be widely installed not only in those installed in stationary personal computers, but also in portable notebook personal computers.

  A small hard disk drive used for such portable applications has a risk of falling while being carried or used, and may be exposed to a strong impact force. The disk is required to have high impact resistance.

On the other hand, a disadvantage of the glass material is low fracture strength.
This is because micro-cracks are induced during the process of processing from a glass plate to a donut-shaped substrate, and stress applied in subsequent lapping / polishing, cleaning, film-forming processes, etc., and cracks extend and break down. It is to reach.

  There is an annular bending strength as an index of the breaking strength of a glass substrate for a hard disk. The breaking strength (circular bending strength) of the glass substrate for hard disks has been improved by the strengthening treatment to the glass substrate. As this strengthening treatment, chemical strengthening treatment is generally performed.

  A glass substrate for a magnetic disk is generally formed by directly forming a plate-like glass disk from molten glass by a pressing method, polishing the end face and main surface of the produced glass disk, and performing a strengthening process such as chemical strengthening. It is manufactured by doing.

  On the other hand, due to the recent trend toward high-density recording, magnetic heads equipped with magnetoresistive elements or large magnetoresistive elements are being used.

  A magnetic head equipped with a magnetoresistive element or a large magnetoresistive element has a sufficiently smooth surface and a clean surface compared to a magnetic disk on which information is reproduced by a conventional thin film element. Required.

  On the other hand, one of the factors that hinder the improvement of the smoothness and cleanliness of the main surface required for the magnetic disk glass substrate and the magnetic disk is the adhesion of foreign matter to the main surface of the glass disk in the chemical strengthening process.

  That is, in the chemical strengthening step, the treatment is performed at a high temperature exceeding 300 ° C. However, when processing at such a high temperature is performed, there is a problem that foreign matter tends to adhere to the main surface of the glass disk.

  In order to solve such a problem, Patent Document 1 proposes a glass substrate for a magnetic disk in which the main surface of the glass disk is polished after the chemical strengthening step. Patent Document 2 proposes a magnetic disk glass substrate in which a chemical strengthening agent is selectively applied only to an end surface of a glass disk to perform a chemical strengthening process.

Further, in Patent Document 3, after making a center hole in a columnar glass base material, the side surface of the obtained cylindrical glass base material is polished or mirror-finished, and then the side surface of the glass base material is processed. There has been proposed a glass substrate for a magnetic disk in which the chemical strengthening process is performed and then the cutting process is performed. Patent Document 4 proposes polishing inner and outer peripheral end faces in a state in which a plurality of doughnut-shaped glass substrates for a magnetic recording medium having chamfered end faces are laminated via a spacer.
JP-A-7-134823 JP-A-9-27150 JP 2006-277798 A JP 2001-162510 A

  However, in the proposal described in Patent Document 1, it is necessary to flatten the surface without impairing the strengthening effect of the chemical strengthening process. Therefore, it is necessary to precisely manage the polishing allowance (polishing amount), and the magnetic It is difficult to manufacture a glass substrate for a disk.

  In addition, in the glass substrate for magnetic disk described in Patent Document 2, since the location where the chemical strengthening solution is applied is subjected to the chemical strengthening treatment, it is difficult to accurately define the location where the chemical strengthening is performed, It becomes difficult to manufacture a glass substrate for a magnetic disk having a stable quality.

  In the glass substrate for magnetic disk described in Patent Document 3, it is difficult to accurately process the inner surface of a long cylinder, and it becomes difficult to manufacture a glass substrate for magnetic disk with stable quality.

  In addition, in the glass substrate for magnetic recording medium described in Patent Document 4, a method of polishing only the end face is proposed. What is the foreign matter adhesion to the main surface of the glass disk in the chemical strengthening process? No measures have been taken.

  In addition, for hard disk drives, there is a strong demand for cost reduction and mass production, and it is necessary to supply glass substrates for magnetic disks and magnetic disks in large quantities at low cost. For glass substrates for magnetic disks, it is difficult to accurately supply a large quantity of products while satisfying impact resistance, smoothness of the main surface, cleanliness and flatness, and a large quantity of magnetic materials without quality variations. It has become difficult to manufacture a disk stably.

  Therefore, the present invention is proposed in view of the above-mentioned circumstances, and the first object of the present invention is to reliably prevent the influence of foreign matter adhesion to the main surface in the chemical strengthening process, and to achieve surface smoothness. An object of the present invention is to provide a magnetic disk glass substrate and a magnetic disk excellent in surface smoothness and flatness particularly in the vicinity of the outer periphery, and to make such a glass disk and magnetic disk difficult to manufacture and cost. An object of the present invention is to provide a method of manufacturing a glass substrate for a magnetic disk that can be provided at low cost and in large quantities without causing an increase.

  That is, the method for manufacturing a glass substrate for a magnetic disk according to the present invention is a method for manufacturing a glass substrate for a magnetic disk including a chemical strengthening step of chemically strengthening at least an end surface portion of the glass plate of a doughnut-shaped glass plate having a chamfered end surface. In the chemical strengthening step, the main surfaces of a plurality of the doughnut-shaped glass plates are laminated together, and the main surface is subjected to a chemical strengthening process in a pressurized state.

  Further, the glass substrate chemical strengthening device of the present invention is a glass substrate chemical strengthening device for chemically strengthening at least an end surface portion of the glass plate of a doughnut-shaped glass plate whose end surface is chamfered. Pressurizing means for pressurizing the glass plate laminate formed by laminating the main surfaces of the doughnut-shaped glass plates through a pressing plate movable in the vertical axis direction of the main surface of the donut-shaped glass plates It is characterized by having.

  The magnetic disk manufacturing method of the present invention is characterized in that at least a magnetic layer is formed on the main surface of the magnetic disk glass substrate manufactured by the magnetic disk glass substrate manufacturing method.

  According to the method for producing a glass substrate for a magnetic disk of the present invention, by preventing chemical strengthening to the main surface, the influence on the main surface in the chemical strengthening treatment, and further the influence due to the adhesion of the remaining foreign matter can be prevented. It has a feature that it can provide a glass substrate for a magnetic disk and a magnetic disk excellent in surface smoothness, particularly surface smoothness and flatness in the vicinity of the outer peripheral portion. In addition, according to this manufacturing method, the magnetic disk glass substrate and the magnetic disk can be provided at low cost and in large quantities without causing difficulty in manufacturing or increasing the cost. A method can be provided.

The present invention will be described below with reference to the drawings.
FIG. 1 is a perspective view showing a configuration of a glass substrate for magnetic disk manufactured by the method for manufacturing a glass substrate for magnetic disk according to the present invention. As shown in FIG. 1, an inner hole 2 is provided at the center of a magnetic disk glass substrate 1.

  As the material of the glass substrate used in the present invention, any glass can be used as long as it can improve the breaking strength by chemical strengthening treatment, but it is preferable to use an aluminosilicate glass. The aluminosilicate glass can realize an excellent smooth mirror surface and can increase the breaking strength by performing chemical strengthening.

The aluminosilicate _{glass, SiO} 2: 62 to 75 _wt%, Al _{2 O} 3: 5 to 15 wt%, _Li 2 O: 4 to 10 wt%, _Na 2 O: 4 to 12 wt%, _ZrO 2: 5 0.5 to 15 wt% as a main component, the weight ratio of Na ₂ O to ZrO ₂ is 0.5 to 2.0, and the weight ratio of Al ₂ O ₃ to ZrO ₂ is 0.4 to 2 .5 is preferably used.

FIG. 2 is a cross-sectional view showing the shape of the end surface portion of the magnetic disk glass substrate 1.
The glass substrate for a magnetic disk produced according to the present invention has a chamfered ridge on both sides of the end face portion. That is, the outer peripheral side end surface portion of the magnetic disk glass substrate 1 and the inner peripheral side end surface portion of the inner hole 2 are chamfered from the inner peripheral end surface portion toward the main planes on both sides as shown in FIG. (C surface) 3 and 3 are formed, and also the outer peripheral side end surface portion of the magnetic disk glass substrate 1 has chamfered portions (C surface) from the outer peripheral side end surface portion toward the main planes on both sides. It is in a formed state.

  A portion between the chamfered portions 3 and 3 in the inner peripheral side end surface portion of the magnetic disk glass substrate 1 is a cylindrical side surface 4 formed of a vertical surface with respect to the main plane of the magnetic disk glass substrate 1. .

  Also, in the outer peripheral side end surface portion of the magnetic disk glass substrate 1, the portion between the chamfered portions is a cylindrical side surface that is a vertical surface with respect to the main plane of the magnetic disk glass substrate 1.

  The glass substrate for a magnetic disk has high crushing strength due to the chamfered edge portion of the end surface portion. In addition, the end surface part in this invention points out the part which match | combined the side surface and the chamfering surface.

The surface roughness Ra (center line surface roughness) of the main surface of the doughnut-shaped glass substrate is preferably 0.5 μm or less. If this surface roughness Ra is larger than 0.5 μm, the chemical strengthening treatment liquid tends to enter the main surface side during the chemical strengthening treatment, and the flatness may be deteriorated by the chemical strengthening treatment. The surface roughness Rmax (maximum height) is preferably 8 μm or less. If this surface roughness Rmax is larger than 8 μm, the chemical strengthening treatment liquid is likely to wrap around the main surface during the chemical strengthening process as in the case of Ra, and the flatness may be deteriorated by the chemical strengthening process.
Moreover, it is preferable that the flatness of the main surface of this donut-shaped glass substrate is 6 micrometers or less. Even when the flatness exceeds 6 μm, the chemical strengthening treatment liquid tends to enter the main surface side during the chemical strengthening treatment, and the flatness may be further deteriorated by the chemical strengthening treatment.

As an example, the glass substrate for magnetic disk can be manufactured by the following steps.
(1) First lapping step (2) Drilling step (3) Second lapping step (4) Chamfering step (5) Chemical strengthening step (6) First polishing step (7) Second polishing step (8) Cleaning step This In the process example, the chemical strengthening process is provided between the chamfering process and the first polishing process, but the chemical strengthening process may be provided after the chamfering process, and may be provided between the first polishing process and the second polishing process. Good.

(1) 1st lapping process Lapping is a sliding motion (grinding) with loose abrasive grains (abrasive) included, and polishing the work piece while finely cutting the work piece. It means loose abrasive processing that finishes flatly. Here, the main surface of the disk-shaped glass press material obtained by press molding molten glass is used to obtain a predetermined thickness using relatively coarse abrasive grains. Lapping is performed so that the parallelism and flatness of the glass disk are predetermined. The lapping process is performed using a double-sided lapping apparatus, alumina abrasive grains, silicon carbide abrasive grains, and the like.

(2) Drilling step In this step, a central hole having a predetermined size is formed along the central axis of the glass plate. This central hole is a central hole in the magnetic disk glass substrate, and forms a hole having an inner diameter slightly smaller than the inner diameter planned as the central hole of the magnetic disk glass substrate. This drilling step can be performed by, for example, a core drill using a diamond grindstone.

(3) Second lapping step This is a step of lapping the main surface of a holed doughnut-shaped glass plate and is processed using a double-sided lapping device, alumina abrasive grains, silicon carbide abrasive grains, etc. as in the first lapping process. I do. In the second lapping step, the abrasive is finer than the first lapping step and processed to a predetermined thickness to improve parallelism and flatness and reduce the surface roughness to a predetermined level.

(4) Chamfering step In this step, chamfering (C surface) processing of the inner periphery and outer periphery of the donut-shaped glass plate is performed. In the chamfering process, a grindstone having a shape obtained by transferring the chamfered shape is used, and the chamfering is performed by grinding, and the inner and outer diameter dimensions of a predetermined magnetic disk glass substrate to be manufactured are obtained.

In this step, the inner and outer peripheral side surfaces (circumferential surfaces) are further polished and mirror-finished. Polishing in this step is performed with a brush or the like using an abrasive. The abrasive grains contained in the abrasive used in this step can be used without particular limitation as long as they are abrasive grains that exhibit a polishing ability with respect to a glass plate. Examples thereof include cerium oxide (CeO ₂ ) abrasive grains, colloidal silica abrasive grains, alumina abrasive grains, and diamond abrasive grains, and cerium oxide abrasive grains are particularly preferable. The particle size of the abrasive grains can be selected as appropriate, but is preferably about 0.5 μm to 3 μm, for example. The abrasive is preferably used as a slurry abrasive by adding a liquid such as water (pure water) to an ordinary abrasive containing abrasive grains.

(5) Chemical strengthening process When a magnetic disk is set in the hard disk drive, the spindle motor hub is inserted into the inner hole 2 of the glass magnetic disk and fixed from above with a disk presser.
When an impact force is applied to the hard disk drive, the impact force concentrates on the end face portion of the inner diameter, so that a crack occurs in the end face portion and the glass magnetic disk is damaged. Therefore, if at least the end face portion is reinforced, the glass magnetic disk can be prevented from being damaged.

In the chemical strengthening treatment, the glass substrate is immersed in a heated chemical strengthening treatment solution, and ions on the surface of the glass substrate are ion-exchanged with ions in the chemical strengthening treatment solution to chemically strengthen the glass substrate.
In the manufacturing method of the glass substrate of this invention, chemical strengthening is given to the end surface part of a donut-shaped glass plate.

  Usually, ion exchange replaces alkali ions in the glass with alkali ions having a larger ion radius in a temperature range below the glass transition temperature (Tg), and increases the volume of the ion exchange part due to the substitution. The glass surface is strengthened by generating strong compressive stress.

Examples of the chemical strengthening treatment liquid include salts such as potassium nitrate (KNO ₃ ), sodium nitrate (NaNO ₃ ), potassium carbonate (K ₂ CO ₃ ), and mixtures of these salts (for example, KNO ₃ + NaNO ₃ , KNO ₃ + K ₂ CO ₃ or the like), or salts obtained by mixing salts of ions such as Cu, Ag, Rb, and Cs with these salts.

  Although heating temperature changes with the glass transition points of the glass to process, it is preferable that they are 250 to 650 degreeC, especially 350 to 500 degreeC, Furthermore, it is preferable that it is 350 to 450 degreeC.

The immersion time is preferably about 1 to 20 hours from the viewpoint of the bending strength and the compressive stress layer. The thickness of the compressive stress layer formed on the surface layer of the glass substrate is preferably about 60 to 300 μm from the viewpoint of improving impact resistance.
In addition, before immersing a glass substrate in a chemical strengthening process liquid, in order to prevent a glass substrate from a crack and a crack, it is preferable to preheat a glass substrate at 200-450 degreeC.

  In the method for producing a glass substrate of the present invention, this chemical strengthening treatment is performed in a state where the main surfaces of the plurality of doughnut-shaped glass plates are laminated together and pressure is applied to the main surfaces (pressurized state). . As a method of laminating the doughnut-shaped glass plates, it is preferable to employ a method of laminating a plurality of donut-shaped glass plates with the main surfaces alternately aligned with the donut-shaped spacers.

  The spacer is not particularly limited, but a spacer having good heat resistance and corrosion resistance is desirable. For example, a donut shape made of a material such as stainless steel and having a thickness of 0.1 to 0.5 mm is preferably used. When it is larger than 0.5 mm, the space efficiency is poor, and when it is smaller than 0.1 mm, the durability is lowered. The outer diameter of the spacer is preferably equal to or larger than the outer diameter of the doughnut-shaped glass plate, that is, the outer diameter of the spacer is equal to or larger than the outer diameter of the donut-shaped glass plate. By adopting such dimensions, the side surface of the glass plate can be exposed without exposing the main surface of the glass plate to the chemical strengthening treatment liquid during the chemical strengthening treatment in a pressurized state of the laminate of the donut glass plate and the spacer. Only chemical strengthening treatment can be performed.

  As a method of pressing the laminated body of the doughnut-shaped glass plate and the spacer, a pressing plate that can move in the vertical axis direction of the main surface of the laminated glass plate is used, and the pressing plate moves the laminated body to the vertical axis of the main surface. A method of pressing in the direction can be employed. The pressing of the pressing plate may be performed mechanically, or may be performed by gravity of a weight that is movable in the vertical axis direction of the main surface of the laminated glass plates.

  Thus, by immersing in the chemical strengthening solution, the lithium ions and sodium ions in the surface layer on the side surface of the glass base material are respectively replaced with sodium ions and potassium ions in the chemical strengthening solution, and the glass plate is strengthened.

  After chemical strengthening, it is preferable that the glass substrate is lifted from the chemical strengthening treatment solution and gradually cooled to a predetermined temperature so that the occurrence of thermal distortion can be suppressed. Such slow cooling can avoid damage due to thermal strain.

  The rate of slow cooling of the glass substrate is preferably 2 ° C / min to 100 ° C / min, particularly 5 ° C / min to 60 ° C / min, and more preferably 10 ° C / min to 50 ° C / min.

  For the slow cooling, for example, it is preferable to perform two-stage slow cooling in which the first and second slow cooling chambers are gradually cooled. First, the glass substrate is pulled up from the chemical strengthening treatment liquid and transferred to, for example, a first annealing chamber heated to 300 ° C., and held in this for about 10 minutes to slowly cool the glass substrate to 300 ° C. Next, the glass substrate is transferred from the first annealing chamber to, for example, the second annealing chamber heated to 200 ° C., and the glass substrate is gradually cooled from 300 ° C. to 200 ° C. Thus, by gradually cooling in two steps, the glass substrate can be released from damage due to thermal strain.

  A wash is then performed to remove the salt crystals. Cleaning is performed by immersing in water or warm water. The warm water may be normal water, but pure water is preferable in order to suppress adhesion of particles. Moreover, as warm water, what was heated at about 80 degreeC is used preferably. In addition, the crystalline substance of a salt is nitrate and chloride which are precipitation molten salts.

  In order to effectively remove the salt crystals, it may be washed not only by immersing in water or warm water but also by a method of propagating ultrasonic waves. Further, not only the salt crystals but also dirt such as other particles may be removed together. In this case, different foreign substances may be collectively cleaned by mixing a cleaning agent that removes dirt such as particles.

(6) 1st grinding | polishing process Next, a 1st grinding | polishing process is given as a main surface grinding | polishing process. The first polishing process is mainly intended to remove scratches and distortions remaining on the main surface in the lapping process described above. This process can be performed using a planetary gear mechanism using a double-side polishing apparatus and a hard resin polisher. As the abrasive, cerium oxide abrasive grains are preferably used.

(7) Second Polishing Step Next, a second polishing step is performed as a mirror polishing step for the main surface. The purpose of this second polishing step is to finish the main surface into a mirror surface. This step can be performed using a planetary gear mechanism using a double-side polishing apparatus and a soft foam resin polisher. As the abrasive, it is preferable to use finer colloidal silica abrasive grains than the cerium oxide abrasive grains used in the first polishing step.

(8) Cleaning step The glass substrate that has finished the second polishing step is immersed in each of the cleaning baths of neutral detergent, neutral detergent, pure water, pure water, IPA (isopropyl alcohol), and IPA (steam drying) in order. Wash. That is, two neutral detergent cleaning tanks, two pure water cleaning tanks are sequentially immersed and cleaned, and then the IPA cleaning tank is immersed and cleaned, and then placed in an IPA vapor drying tank to perform steam drying. In addition, it is preferable to apply an ultrasonic wave to each washing tank.

Next, the chemical strengthening apparatus of the present invention will be described.
FIG. 3 is a view showing the appearance of a chemical strengthening apparatus used in the method for manufacturing a glass substrate for a magnetic disk according to the present invention.
FIG. 3 a shows a state in which a plurality of donut-shaped glass plates 1 are stacked and installed in the chemical strengthening apparatus of the present invention. In this state, it is immersed in molten salt and subjected to chemical strengthening treatment. The donut-shaped glass plates 1 are preferably laminated via spacers (not shown).

  First, FIG. 3e shows a base plate 5 with two struts 6 and 6 upright. The base plate 5 on which the two columns 6 and 6 are erected is installed at an inclination, and a plurality of donut-shaped glasses are preferably laminated via spacers so as to be supported by the columns 6 and 6 and the base plate 5. The board 1 is installed. At this time, the column spacer is set so that the glass plate 1 does not directly contact the column but contacts via a column spacer (not shown). By doing in this way, as shown in FIG. 3d, the doughnut-shaped glass plate 1 laminated | stacked easily can be aligned. In addition, after fixing as shown in FIG. 3a, by removing the support side spacer, a gap can be provided between the glass plate 1 and the support 6, and uneven chemical strengthening due to contact with the support or the sliding It is possible to prevent damage and particle generation due to movement.

  Next, as shown in FIG. 3c, a third support column 6 is installed and the base plate 5 is placed downward. Next, as shown in FIG. 3b, a pressing plate 8 provided with a hole 12 larger than the diameter of the column is placed from above so that it can operate along the three columns 6, 6, 6 and shown in FIG. 3a. Thus, it fixes using the nut 10 in the state which pressurizes the main surface of a glass plate. By setting it as such a state, even if this is immersed in a chemical strengthening process liquid, it will be in the state which can be immersed in a chemical strengthening process liquid, without a chemical strengthening process liquid entering the main surface of a glass plate.

  When immersed in the chemical strengthening treatment liquid, holes 9 and 11 are provided in the center of the base plate 5 and the pressing plate 8 so as to be aligned with the inner hole 2 of the doughnut-shaped glass plate 1 to be installed. Since the base plate is provided with the projection 7 serving as a base, it can enter the inner hole portion of the glass plate laminated with the chemical strengthening treatment liquid, and the end surface portion of the inner diameter can be subjected to the chemical strengthening treatment.

  The pressure applied to the main surface of the glass plate can be adjusted by adjusting the thickness of the pressing plate 8. That is, in the case of FIG. 3, the pressing plate 8 also serves as a weight.

In order to increase the number of sheets processed at one time, it is possible to increase the number of processed sheets by simply increasing the length of the support column 6 and adding a weight on the pressing plate that can be operated and a hole for containing the chemical strengthening treatment liquid. I can do it.
That is, since only the thickness of the glass plate to be processed, the thickness of the base plate, the thickness of the pressing plate, and the thickness of the pressing plate are sufficient, for example, when processing by stacking 100 sheets, the thickness becomes 20 cm, and processing is performed with a conventional holder. Compared with about 70 cm of the case, it is 1/3 or less, and the space efficiency can be increased about 3 times.

Next, a method for manufacturing a magnetic disk according to the present invention will be described.
A magnetic disk is manufactured by the following process using the glass substrate for magnetic disk manufactured by the processes (1) to (8) described above.

(9) Magnetic Layer Formation Step In the magnetic layer formation step, at least a magnetic layer is formed on the main surface of the magnetic disk glass substrate. As the magnetic layer, a Co—Pt alloy magnetic layer is preferable. Further, an underlayer may be appropriately formed between the glass substrate for magnetic disk and the magnetic layer from the viewpoint of controlling the crystal orientation of the magnetic layer, grain, and miniaturization. As a method for forming these underlayer and magnetic layer, for example, a DC magnetron sputtering method can be used. As the underlayer, an underlayer made of a Cr alloy is preferable.
A protective layer forming step for providing a protective layer for protecting the magnetic layer on the magnetic layer formed in the magnetic layer forming step, and an impact from the magnetic head on the protective layer formed in the protective layer forming step. It is preferable to provide a lubricating layer forming step for forming a lubricating layer for relaxation.

(10) Protective layer forming step In the protective layer forming step, a protective layer for protecting the magnetic layer is provided on the magnetic layer formed in the magnetic layer forming step. Examples of the material for the protective layer include a carbon-based protective layer. As the carbon-based protective layer, hydrogenated carbon or nitrogenated carbon can be used. For the formation of this protective layer, plasma CVD or DC magnetron sputtering can be used.

(11) Lubricating layer forming step In the lubricating layer forming step, a lubricating layer for reducing the impact from the magnetic head is formed on the protective layer formed in the protective layer forming step. An example of the lubricating layer is a perfluoropolyether lubricating layer. In particular, an alcohol-modified perfluoropolyether lubricating layer having a hydroxyl group having excellent affinity with the protective layer is preferable. This lubricating layer can be formed using a dip method.

Hereinafter, the present invention will be described more specifically with reference to examples.
<Example 1>
As a material for manufacturing a glass substrate for a magnetic disk, a disc-shaped glass plate made of aluminosilicate glass formed by a melt press method and having a diameter of 66 mm and a thickness of 1.3 mm was used.
As the aluminosilicate glass, SiO ₂ is contained in 57% to 74%, Al ₂ O ₃ is ₃ to 15%, LiO ₂ is 7 to 16%, and Na ₂ O is 4 to 14% as a main component. Glass for chemical strengthening was used.

A first lapping process was performed on 1000 disc-shaped glass plates using a double-sided lapping apparatus and alumina abrasive grains (particle size: 45 μm) to obtain a glass plate having a thickness of 0.89 to 0.90 mm.
Next, a center hole of a predetermined size was formed along the central axis of the glass plate with a diamond drill core drill to obtain a donut-shaped glass plate.

  Then, the 2nd lapping process was performed with respect to the main surface of the donut-shaped glass plate which carried out the drilling process. In the second lapping process, a doughnut-shaped glass plate having a thickness of 0.66 to 0.68 mm was obtained by using a double-sided lapping apparatus and alumina abrasive grains (particle diameter: 6 μm). The flatness and surface roughness (Ra: 0.33 to 0.48 μm and Rmax: 4.1 to 7.7 μm) and flatness of the obtained glass plate were 0 to 10 μm. These substrates were classified into a glass substrate having a flatness of 0 to 4 μm, a glass substrate having a flatness of 4 to 6 μm, and a glass substrate having a flatness of greater than 6 μm. 100 glass substrates having a flatness of 0 to 10 μm were selected and chamfered.

  Next, the chemical strengthening process was performed to the end surface part of the doughnut-shaped glass plate which finished the above-mentioned chamfering process. 100 doughnut-shaped glass plates were laminated on the chemical strengthening apparatus shown in FIG. 3, preheated to 300 ° C., and then immersed in a chemical strengthening treatment solution. The thickness of the pressing plate 8 in FIG. 3 was adjusted, and the load applied to the glass plate was adjusted so that there was no gap between the glass plates. The chemical strengthening treatment was performed by immersing in a chemical strengthening treatment liquid in which potassium nitrate (60%) heated to 380 ° C. and sodium nitrate (40%) were mixed for 3 hours. The chemical strengthening treatment liquid did not enter between the laminated glass plates, and the main surface of the glass plate was not chemically strengthened.

After the chemical strengthening, the chemical strengthening apparatus pulls up the glass substrate from the chemical strengthening treatment liquid, transfers it to the first slow cooling chamber heated to 300 ° C., holds it therein for about 30 minutes, and slowly cools to 300 ° C. To do. Subsequently, the glass substrate was transferred from the first annealing chamber to the second annealing chamber heated to 200 ° C., and the glass substrate was gradually cooled from 300 ° C. to 200 ° C.
The chemical strengthening apparatus that had been slowly cooled was immersed in pure water heated to 80 ° C. for cleaning, and further immersed in pure water for cleaning. Note that ultrasonic waves were applied to each cleaning tank.

Next, the first polishing was performed using a double-side polishing apparatus and a hard resin polisher and using cerium oxide abrasive as an abrasive. Next, as the second polishing, a double-side polishing apparatus and a soft foamed resin polisher were used, a planetary gear mechanism was used, and colloidal silica abrasive grains were used as the polishing agent, and the surface was mirror-finished.
The glass substrate which finished the 2nd grinding | polishing process was immersed in each washing | cleaning tank of neutral detergent, neutral detergent, a pure water, a pure water, IPA (isopropyl alcohol), and IPA (steam drying) sequentially, and was wash | cleaned. Note that ultrasonic waves were applied to each cleaning tank.
In this way, a glass substrate for a magnetic disk was produced.

  The surface defect of the glass substrate for a magnetic disk was inspected with an optical surface defect inspection apparatus. Further, the flatness was measured by an optical flatness measuring device. Furthermore, the ring bending strength was measured. The results are shown in Table 1.

  A Cr underlayer, a CoPtCr magnetic layer, and a carbon protective layer are formed in this order on both sides of the obtained magnetic disk glass substrate by a magnetron sputtering method, and a perfluoropolyether-based lubricating layer is formed thereon using a dip method. As a result, a magnetic recording medium was produced and the electromagnetic conversion characteristics were evaluated.

<Example 2>
100 glass plates with a flatness of 4 to 6 μm classified in Example 1 were extracted, and chamfered, chemically strengthened, cleaned, first polished, second polished, and cleaned in the same manner as in Example 1 to produce magnetic disk glass. A substrate was manufactured. The obtained glass substrate for magnetic disk was measured for surface defects, flatness, and ring bending strength in the same manner as in Example 1. The results are shown in Table 1.
For the magnetic disk glass substrate obtained in Example 2, a magnetic recording medium was prepared in the same manner as in Example 1, and the electromagnetic conversion characteristics were evaluated.

<Example 3>
100 glass substrates having a flatness larger than 6 μm classified in Example 1 were extracted, and chamfered, chemically strengthened, washed, first polished, second polished, and washed in the same manner as in Example 1 to obtain a glass substrate for a magnetic disk. Manufactured. The obtained glass substrate for magnetic disk was measured for surface defects, flatness, and ring bending strength in the same manner as in Example 1. The results are shown in Table 1.

<Example 4>
In the second lapping process, a doughnut-shaped glass plate having a thickness of 0.66 to 0.68 mm was obtained in the same manner as in Example 1 except that it was processed using alumina abrasive grains (particle size: 10 μm). . The surface roughness (Ra 0.51 to 0.75 μm and Rmax 8.3 to 12.8 μm) and flatness of the obtained glass plate were 0 to 9 μm. 100 glass substrates having a flatness of 1 to 4 μm were selected from these substrates, and chamfered, chemically strengthened, cleaned, first polished, second polished, and cleaned in the same manner as in Example 1 to produce a magnetic disk glass substrate. . The obtained glass substrate for magnetic disk was measured for surface defects, flatness, and ring bending strength in the same manner as in Example 1. The results are shown in Table 1.

<Example 5>
100 glass plates with a flatness of 1 to 4 μm classified in Example 1 were extracted, and chamfered, chemically strengthened, washed, first polished, second polished, and washed in the same manner as in Example 1 to produce a magnetic disk glass. A substrate was manufactured.
However, in the strengthening process, 100 doughnut-shaped glass plates are stacked on the chemical strengthening apparatus shown in FIG. 3, the pressing plate 8 of FIG. 3 is placed, and the nut 10 is tightened so that there is no gap between the glass plates. Example 1 is the same as Example 1 except that the weight applied to is adjusted and fixed.
The obtained glass substrate for magnetic disk was measured for surface defects, flatness, and ring bending strength in the same manner as in Example 1. The results are shown in Table 1.

<Example 6>
100 glass substrates with a flatness of 1 to 4 μm classified in Example 1 were extracted, and SUS304 spacers and glass plates having an outer diameter and an inner diameter of the same dimensions as this glass plate were alternately used. The laminated body which laminated | stacked according to the surface was set to the chemical strengthening apparatus shown in FIG. 3 similarly to Example 1, and except having used this, a chemical strengthening process was performed like Example 1, and hereafter, Example 1 is referred to. A glass substrate for a magnetic disk was manufactured in the same manner as described above. The obtained glass substrate for magnetic disk was measured for surface defects, flatness, and ring bending strength in the same manner as in Example 1. The results are shown in Table 1.
For the magnetic disk glass substrate obtained in Example 6, a magnetic recording medium was prepared in the same manner as in Example 1, and the electromagnetic conversion characteristics were evaluated.

<Comparative Example 1>
100 glass substrates with a flatness of 1 to 4 μm classified in Example 1 were extracted and changed to chemical strengthening treatment conditions used conventionally. That is, after the chamfering process, after passing through the first polishing process, the second polishing process, and the cleaning process, the glass substrates were put one by one in the holder and subjected to chemical strengthening treatment, and the others were manufactured in the same manner. As the chemical strengthening treatment liquid, the same treatment liquid as used in Example 1 was used. In this case, the entire glass substrate is chemically strengthened. The obtained glass substrate for magnetic disk was measured for surface defects, flatness, and ring bending strength in the same manner as in Example 1. The results are shown in Table 1.
For the obtained magnetic disk glass substrate, a magnetic recording medium was produced in the same manner as in Example 1, and the electromagnetic conversion characteristics were evaluated.

  As is apparent from Table 1, the glass substrate for magnetic disk obtained in Comparative Example 1 had many surface defects due to the chemical strengthening treatment step although no deterioration in flatness due to chemical strengthening was observed. In comparison, all the glass substrates for magnetic disks obtained in Examples 1 to 6 have a small number of defects, and according to the method for producing a glass substrate of the present invention, the main surface of the glass substrate is caused by the chemical strengthening treatment liquid. It is presumed that there are no defects due to the occurrence.

  Further, from the comparison between Examples 1 and 2 and Example 3, in Example 1 with an average flatness of 3 μm and Example 2 with an average of 5 μm (both flatness is 6 μm or less), the flatness deteriorates due to chemical strengthening treatment. However, in Example 3 where the average flatness is 9 μm, the flatness is further lowered after the chemical strengthening treatment. Therefore, the flatness of the glass plate after the second lapping is preferably 6 μm or less.

  Further, from the comparison between Examples 1 and 2 and Example 4, in Examples 1 and 2 in which Ra is 0.5 μm or less and Rmax is 8 μm or less, deterioration in flatness due to chemical strengthening treatment is not observed, but Ra is 0 In Example 4 where the thickness is larger than 0.5 μm and Rmax is also larger than 8 μm, the flatness is lowered. Therefore, Ra of the glass plate after the second lapping is preferably 0.5 μm or less, and Rmax is preferably 8 μm or less. .

    Further, from the comparison between Examples 1 and 2 and Example 5, in Examples 1 and 2 pressed by a movable weight, flatness deterioration due to the chemical strengthening treatment is not seen, but the pressing plate 8 is In Example 5 which was tightened and pressurized with a nut, the flatness decreased after the chemical strengthening treatment. This is estimated that the support | pillar 6 thermally expanded by the heating in a chemical strengthening process, and the applied pressure fell. The pressurization by the movable weight as in Examples 1 and 2 is preferable because the applied pressure does not decrease even during heating.

  In the case of Example 6 manufactured using a spacer, the flatness was not lowered as in Examples 1 and 2. Further, when the roll-off value of 100 glass substrates was measured, in the case of Example 6, it was distributed in the range of 50 μm or less, whereas the roll-off value of Example 1 was distributed in the range of 100 μm or less. It was. In Example 6, the effect of preventing the chemical strengthening treatment liquid from entering the main surface is improved by the spacer, and the variation in the roll-off value is reduced. Here, the roll-off value refers to a deviation from the flat surface at the reference position of the outer diameter end when the flat surface of the main surface is used as a reference. If the roll-off value is large, the magnetic head cannot fly this portion, resulting in a decrease in the recording portion.

  As a result of evaluating the electromagnetic conversion characteristics of the magnetic recording media produced using the magnetic disk substrates of Examples 1, 2, 6 and Comparative Example 1, the magnetic recording media of this example were compared with the magnetic recording medium of Comparative Example 1 as a conventional substrate. The error rate of the magnetic recording media manufactured in Examples 1, 2 and 6 which are the glass substrates for magnetic disks of the invention was one or more digits lower, and the magnetic recording media showed excellent characteristics.

  According to the present invention, a glass substrate for a magnetic disk having high fracture strength, few surface defects, and excellent flatness can be obtained inexpensively and in large quantities, and magnetic recording obtained using this glass substrate for a magnetic disk The disc has a characteristic that the error rate is lower by one digit or more and exhibits excellent characteristics.

It is a perspective view which shows the structure of the glass substrate for magnetic discs manufactured with the manufacturing method of the glass substrate for magnetic discs of embodiment of this invention. It is sectional drawing which shows the shape of the end surface part of the glass substrate for magnetic discs of embodiment of this invention. It is a figure which shows the glass plate setting procedure to the chemical strengthening apparatus of embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glass substrate for magnetic discs 2 Inner hole 3 Chamfer part 4 Side surface 5 Base plate 6 Post 7 Protrusion 8 Pressing plate 9,11 Center hole 10 Nut 12 hole

Claims (8)

  A method for manufacturing a glass substrate for a magnetic disk, comprising a chemical strengthening step of chemically strengthening at least an end surface portion of the glass plate of a doughnut-shaped glass plate having a chamfered end surface, wherein the chemical strengthening step includes a plurality of the donut-shaped glasses. A method for producing a glass substrate for a magnetic disk, wherein the main surfaces of the plates are laminated together, and the main surface is subjected to a chemical strengthening treatment in a pressurized state.   2. The glass substrate for a magnetic disk according to claim 1, wherein the surface roughness Ra of the main surface of the doughnut-shaped glass plate before chemical strengthening is 0.5 [mu] m or less and Rmax is 8 [mu] m or less. Method.   The method for producing a glass substrate for a magnetic disk according to claim 1 or 2, wherein the flatness of the donut-shaped glass plate before chemical strengthening is 6 µm or less.   The lamination of the doughnut-shaped glass substrate is to laminate a plurality of donut-shaped glass plates with the main surfaces alternately aligned with donut-shaped spacers. The manufacturing method of the glass substrate for magnetic discs as described in any one of.   5. The method for manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the outer diameter of the spacer is equal to or larger than the outer diameter of the doughnut-shaped glass plate.   An apparatus for chemically strengthening a glass substrate for a magnetic disk that chemically strengthens at least an end surface portion of the glass plate having a chamfered end surface, the main surfaces of a plurality of the donut glass plates being laminated together A glass substrate chemical strengthening apparatus for a magnetic disk comprising pressurizing means for pressurizing a laminated glass plate through a pressing plate movable in a vertical axis direction of a main surface of the donut-shaped glass plate .   7. The chemical strengthening of a glass substrate for a magnetic disk according to claim 6, wherein the pressurizing means is means for pressurizing by gravity of a weight movable in the vertical axis direction of the main surface of the laminated glass plates. apparatus.   A magnetic disk comprising at least a magnetic layer formed on a main surface of a glass substrate for a magnetic disk manufactured by the method for manufacturing a glass substrate for a magnetic disk according to claim 1. Production method.

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