WO2013001723A1

WO2013001723A1 - Method for producing hdd glass substrate

Info

Publication number: WO2013001723A1
Application number: PCT/JP2012/003664
Authority: WO
Inventors: 大士梶田
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: 2011-06-30
Filing date: 2012-06-05
Publication date: 2013-01-03
Also published as: JPWO2013001723A1

Abstract

This method for producing an HDD glass substrate is provided with a glass fusion step, a press-molding step, a heat treatment step, a coring step, a grinding step, a polishing step, and a cleaning step, and is characterized by the retardation (TIR) of one circuit in the peripheral direction at a position that is 0.75r₁ from the center of the glass blanks produced in the coring step before the grinding step, where r₁ is the radius of the glass blanks, being no greater than 1.0 nm. The present invention is able to provide a method for producing an HDD glass substrate that is superior in reducing read/write errors and head crashes and reducing the amount of head floatation when the glass substrate is loaded in a hard disk drive having a DFH mechanism.

Description

Manufacturing method of glass substrate for HDD

The present invention relates to a method for manufacturing a glass substrate for HDD.

A magnetic information recording device is a device that records information on an information recording medium by using magnetism, light, magneto-optical, or the like. A typical example is a hard disk drive (HDD) device. A hard disk drive device is a device that magnetically records information on a magnetic disk as an information recording medium having a recording layer formed on a substrate by a magnetic head. As a base material of such an information recording medium, a so-called substrate, a glass substrate is preferably used.

In addition, the hard disk drive device records information on the magnetic disk while rotating it at a high speed about several nanometers without rotating the magnetic head in contact with the magnetic disk. Furthermore, in recent years, the recording density of hard disks has been further improved, and accordingly, the difference between the magnetic head and the magnetic disk (hereinafter referred to as the head flying height) has been reduced. In particular, in a hard disk having a DFH (Dynamic Flying Height) mechanism, a head flying height of 3 nm or less has been developed. However, in the DFH mechanism, since the head flying height is extremely small, there is a frequent problem that the magnetic head and the magnetic disk collide with each other to cause a head crash.

On the other hand, as a method of producing a glass substrate, a glass intermediate formed body called glass blanks is made by a direct press method in which molten glass is pressed with a mold, and the glass blanks are subjected to grinding, polishing, etc. There is a method to finish the substrate. The glass substrate manufactured by this direct press method is known to be excellent in parallelism and flatness, but even if such a glass substrate is used, the problems such as the head crash described above have not been solved. .

In Patent Document 1, the direct press method is applied and the press finishes before the temperature distribution on the press molding surface becomes uniform, or the parallelism and flatness of the glass substrate using a method of setting the press time to 2 seconds or less. A technique is disclosed in which the degree is improved and brought close to the shape and dimensions of the glass substrate at the time of glass blanks. However, these molding methods only focus on the surface shape of the glass substrate and do not take into account the internal distortion of the glass substrate, so when mounted on a hard disk having a DFH mechanism, a head crash or read / write error occurs. Was supposed to occur.

JP 2004-161564 A

The present invention has been made in view of the above prior art, and is excellent in reducing head flying height, head crash, and read / write error when a glass substrate is mounted on a hard disk drive having a DFH mechanism. It aims at providing the manufacturing method of the glass substrate for HDD.

That is, a method for manufacturing a glass substrate for HDD according to one aspect of the present invention includes a method for manufacturing a glass substrate for HDD comprising a molten glass supply step, a press molding step, a heat treatment step, a coring step, a grinding step, a polishing step, and a cleaning step. a is, 1.0 nm in the coring step, when the radius of the glass blank before the grinding process was r _1, the circumferential direction one round of the retardation TIR at the position of 0.75 r ₁ from the center of the glass blank It is characterized by the following adjustment.

FIG. 1 is a schematic 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. FIG. 3 is a schematic diagram for explaining a molten glass supply step for supplying molten glass to a lower mold of a glass blank forming mold. FIG. 4 is a schematic view showing a pressurizing step of pressurizing the molten glass with a glass blanks molding die. FIG. 5 is a schematic view of glass blanks after the coring step. FIG. 6 is a schematic view showing an example of a glass substrate for HDD manufactured by the method for manufacturing a glass substrate for HDD of the present invention. FIG. 7 is a schematic cross-sectional view showing an example of a polishing apparatus used in a rough polishing step and a precision polishing step in the method for manufacturing a glass substrate for HDD according to the present embodiment. FIG. 8 is a partial cross-sectional perspective view showing a magnetic disk which is an example of a magnetic recording medium using the glass substrate for HDD manufactured by the method for manufacturing the glass substrate for HDD according to the present embodiment.

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

The inventors of the present invention focused on the circumferential strain of glass blanks produced by the direct press method (hereinafter referred to as “circumferential retardation TIR”) and conducted extensive studies.

As a result, by reducing the head flying height in HDD, head crash, and read / write error by intentionally making it by direct press method so that the retardation TIR in the circumferential direction of the glass blanks at the time of the intermediate molded body is minimized. It has been found that a glass substrate for HDD excellent in reducing the amount can be produced.

The manufacturing method of the glass substrate for HDD of this embodiment is a manufacturing method of the glass substrate for HDD provided with a molten glass supply process, a press molding process, a heat treatment process, a coring process, a grinding process, a polishing process, and a washing process, in the coring step, when the radius of the glass blank before the grinding process was r _1, to adjust the center of the glass blank in the circumferential direction one round of the retardation TIR at the position of 0.75 r ₁ below 1.0nm It is characterized by that.

Examples of the method for producing a glass substrate for HDD include a method including a molten glass supply process, a press molding process, a heat treatment process, a coring process, a grinding process, a polishing process, and a cleaning process. And it is preferable to employ | adopt a chemical strengthening process process once or several times besides the said process, and this chemical strengthening process process may be employ | adopted in any after a coring process, a grinding process, and a grinding | polishing process. . Also, the grinding process may be employed once or a plurality of times, or after the coring process.

Furthermore, a method including steps other than those described above may be used. For example, an end surface polishing step may be employed between the grinding step and the polishing step. In particular, the cleaning process may be employed after the rough polishing process, may be employed after the precision polishing process, or may be employed after the rough polishing process and the precision polishing process.

<Manufacture of glass blanks>
First, the manufacturing method of this invention manufactures the glass blanks which are the intermediate molded objects of the glass substrate for HDD 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 glass blank manufacturing method of the present invention, in addition to the above steps, if necessary, heat treatment is performed to correct the flatness of the glass blanks and remove internal distortion.

FIG. 1 is a schematic diagram of a mold and a press for producing the glass blanks of the present invention 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-molded by the press machine lower part 7 and the press machine upper part 2 arranged on the rotary table 9. 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).

Also, the lower mold 5 of the mold is installed on the lower part 7 of the press machine. At a predetermined position of the rotary table 9, the molten glass 23 is supplied to the lower mold 5 by the outflow nozzle 21. The lower mold 5 supplied with the molten glass 23 is transferred by the rotary table 9 together with the press machine lower part 7. The upper mold 3 installed in the upper part 2 of the press machine at another position is lowered to the position of the lower mold 5 and presses the molten glass 23.

A plurality of heaters (not shown) are installed inside the mold. 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 disposed in the press machine lower part 7 in the same manner as the press machine upper part 2. The heater is preferably arranged in the lower part 7 of the press depending on the pressurizing time to be pressed.

Therefore, the manufacturing process of the glass blanks in the present invention mainly includes a molten glass supply process 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.

(Molten glass supply process)
A molten glass supply process is a process of supplying molten glass to the 1st shaping | molding surface formed in the lower mold | type. FIG. 3 is a schematic diagram showing the lower mold 5 and the molten glass 23 in the molten glass supply process. First, the molten glass 23 flows out from the outflow nozzle 21 and is supplied to the lower mold 5 (FIG. 3A).

In the present invention, the viscosity η of the molten glass 23 immediately after being supplied satisfies the condition of log ₁₀ η> 2.6 dPa · s. When the viscosity η satisfies such a condition, if the rotation speed of the turntable 9 is within a specific range, the glass gob rotates without breaking its shape and can be press-molded. As a result, the glass blanks have a small internal strain. However, if the viscosity η satisfies the condition of log ₁₀ η ≦ 2.6 dPa · s, the glass gob may break the shape. As a result, there is a possibility that the distortion in the circumferential direction of the glass blanks after press molding may be decentered or uneven in the circumferential direction.

Thereafter, when the molten glass 23 reaches a predetermined amount, the blade 22 cuts the molten glass 23 and separates the molten glass 23 (FIG. 3B). The molten glass 23 supplied in the molten glass supply step comes into contact with the center portion of the first molding surface 6 (see FIG. 4), and cooling starts mainly by heat radiation from the center.

The lower mold 5 is temperature-controlled and heated to a predetermined temperature in advance. When the glass transition temperature of the molten glass 23 is Tg, the glass molding needs to be performed in a temperature range from Tg to Tg ± 100 (° C.). When the temperature is lower than Tg-100 (° C.), the flatness of the glass substrate deteriorates, wrinkles are generated on the transfer surface, and damage due to thermal shock occurs. Moreover, when the temperature is higher than Tg + 100 (° C.), it is not preferable because fusion with the glass occurs or the mold deteriorates remarkably. Therefore, the temperature of the lower mold 5 is controlled so that the molten glass 23 becomes Tg ± 100 (° C.).

In addition, when a heater is also installed in the upper part 2 of the press machine, the temperature of the upper mold 3 also needs to be controlled. The upper mold 3 is heated in the same range as the temperature of the lower mold 5 described above.

The heating means of the lower mold 5 and the upper mold 3 are heaters embedded in the press machine in contact with them. The set temperature of the heater can be adjusted to a predetermined temperature. Further, a cartridge heater and a burner are preferably used as the mold heating means. Among these, the cartridge heater is particularly preferable because it is not affected by the atmosphere and the temperature control of the mold is simpler.

The method of reducing the retardation TIR in the circumferential direction of the glass blanks is not limited to the method of arranging the plurality of heaters in the circumferential direction inside the press machine, and the glass blanks are directly changed by changing the mold material in the circumferential direction. A method for controlling the temperature, a method for managing the pressure applied to the press machine in the circumferential direction, and the like can be employed.

(Pressure process)
In the pressing step, the glass blanks are cooled by pressurizing the molten glass 23 supplied to the first molding surface 6 on the first molding surface 6 and the second molding surface 4 formed on the upper mold 3. 10 is a step of obtaining 10.

FIG. 4 is a schematic diagram showing the glass blanks molding die 1 and the glass blanks 10 in the pressurizing step. The lower mold 5 to which the molten glass 23 (see FIG. 3A) is supplied in the molten glass supply process rotates the rotary table to a position facing the upper mold 3 at a speed of 0.3 m / s or less. If the speed of the rotary table exceeds 0.3 m / s, the glass gob may lose its shape, and the distortion in the circumferential direction after press molding may be eccentric, or the circumferential direction may be uneven.

Thereafter, the molten glass is pressurized with the first molding surface 6 of the lower mold 5 and the second molding surface 4 of the upper mold 3. The molten glass 23 spreads by pressurization and contacts the peripheral portion of the first molding surface 3. The molten glass 23 is cooled and solidified by dissipating heat from the contact surface with the first molding surface 3 and the second molding surface 4, thereby forming the glass blanks 10.

The upper mold 3 is heated to a predetermined temperature in the same manner as the lower mold 5. The heating temperature and heating means are the same as in the case of the lower mold 5 described above. The heating temperature may be the same as or different from the lower mold 5.

As a pressurizing means for applying a load to the lower mold 5 and the upper mold 3 to pressurize the molten glass, a known pressurizing means can be appropriately selected and used. As the pressurizing means, for example, an air cylinder, a hydraulic cylinder, an electric cylinder using a servo motor, or the like can be used.

Next, the upper mold 3 is separated from the glass blanks 10, and the glass blanks 10 are taken out from the lower mold 5 with an adsorbing member or the like.

(Heat treatment process)
The heat treatment step is a step of performing heat treatment for the purpose of correcting flatness and removing internal strain. The heat treatment is performed by using a setter (alumina, zirconia, etc.), and alternately stacking with glass blanks and putting them in a heat treatment furnace. The heat treatment of the glass blank needs to be performed in a temperature range of Tg to Tg + 100 (° C.). When heat treatment is performed at a temperature lower than Tg, the flatness of the glass blanks cannot be corrected. On the other hand, when heat treatment is performed at a temperature higher than Tg + 100 (° C.), the shape of the glass blanks is deteriorated, and the possibility of fusion with the setter is increased. A particularly preferable temperature range for correcting the flatness and removing the internal strain is Tg to Tg + 70 ° C.

<Coring process>
The coring step is a step of forming a glass blank (perforated blanks material) by forming an inner hole (through hole) using a diamond core drill at the center of the surface of the blanks material obtained by the above-described step. It is. The center of the glass blanks is determined by this coring process. In this invention, a glass blank shall mean the glass molding before finishing a coring process and performing the grinding process of a main plane.

In FIG. 5, the top view which looked at the glass blanks 10 obtained by the said process from one surface is shown. In the present invention, the radius from the center of the glass blank 10 is r ₁ and the radius of the inner hole is r ₀ . Then, describing the position of 0.75 r ₁ measured in retardation TIR measurement method described later by the one-dot chain _line, denoted by a two-dot chain line the position of _{(2r 0 + r 1) /} 3.

<Retardation measurement>
In order that the glass substrate for HDD of the present invention obtained by the manufacturing method including the above-described steps and the steps described later is excellent in reducing head flying height, head crash, and read / write error, It is indispensable that the retardation TIR for one round in the circumferential direction at a position of 0.75r ₁ from the center of the doughnut-shaped glass molded product (glass blanks 10) obtained by the step is 1.0 nm or less.

The retardation TIR is an index representing the strain (internal strain) of the glass molded product (glass blank 10). As a measuring method of retardation TIR, PA-100 (manufactured by Photonics Lattice) was used for distortion at a point of 0.75r ₁ and (2r ₀ + r ₁ ) / 3 from the central hole of the glass blank. Thus, it is possible to adopt a method of allowing linearly polarized light to pass through the glass blank and observing the change in the polarization state after the passage. From this point, the variation in retardation amount (difference between the maximum value and the minimum value) when measuring one round concentrically is defined as the circumferential retardation TIR in the present invention.

When the circumferential retardation TIR is set to 1.0 nm or less, it becomes easy to cope with low head flying and high-speed rotation in an HDD incorporating the obtained glass substrate, and recording and reproduction can be performed stably. The circumferential retardation TIR is preferably 0.5 nm or less. Further, if the circumferential retardation TIR is larger than 1.0 nm, the shape of the obtained glass substrate becomes unstable, and it becomes difficult to stably control the distance between the head of the HDD and the recording medium. There is a risk that write errors will increase, and in some cases, recording / playback may become impossible due to contact between the head and the recording medium.

Further, in the HDD, the linear velocity of the head is different between the inside and the outside of the recording medium, and the lift force acts on the head due to the air flow generated by the high-speed rotation of the disk. For this reason, since the flying height of the head is reduced inside the disk, the inner portion of the glass molded product 10 is required to further reduce the circumferential direction TIR than the outer portion.

In other words, the head flying in the HDD using the glass substrate obtained when the retardation TIR for one circumference in the circumferential direction at the position (2r ₀ + r ₁ ) / 3 from the center of the glass molding is 0.5 nm or less can be reduced. It is preferable because it is easy to cope with high-speed rotation and recording / reproduction can be performed stably, and more preferably 0.3 nm or less. In addition, if the retardation TIR at the position is larger than 0.5 nm, it is difficult to stably control the distance between the head and the recording medium in the HDD using the obtained glass substrate, and read / write errors increase. In some cases, recording / reproduction may be impossible due to contact between the head and the recording medium.

In this way, by suppressing the retardation TIR to be small, not only can the above-mentioned problems caused by the shape of the recording medium be dealt with, but also in a clamp method that presses linearly in the circumferential direction as commonly used in ordinary HDDs, The distortion of the recording medium generated by the clamp can be reduced, and the risk of contact between the head and the substrate can be further avoided.

As described above, if the circumferential retardation TIR is created within a predetermined range when forming the glass blanks, the circumferential TIR of the glass substrate for HDD manufactured through the subsequent steps can be reduced.

In the past, in order to improve the circumferential direction TIR of the glass substrate, it was dealt with by correcting the shape in the grinding / polishing process, but when the shape was corrected in the grinding / polishing process, internal distortion and plate in the molding stage were corrected. Since the thickness is not uniform in the circumferential direction of the blanks, it may be difficult to achieve a desired circumferential direction TIR in part. When trying to reduce the circumferential direction TIR of the glass substrate, there has been a problem that the machining allowance increases, resulting in a reduction in thickness from a desired thickness or an increase in processing cost. Thus, it has become clear in the present invention that the circumferential direction TIR can be controlled by controlling the strain in the circumferential direction before the grinding / polishing step, that is, in the state of the glass blank.

Here, the circumferential direction TIR is an index representing the variation in flatness when the flatness of the glass substrate is measured once in the circumferential direction, unlike the above-described circumferential retardation TIR.

Note that the circumferential direction TIR is a method of measuring the surface shape using interference of white light (for example, a method of measuring using Phase Shift Technology Optiflat) or a laser beam obliquely with respect to the surface to be measured. Can be obtained with a higher reflectivity than the normal incidence method, and can be measured even on rough surfaces (for example, a measurement method using Flatmaster FM100XRA manufactured by TROPE). Good.

<Manufacture of glass substrates for HDD>
The glass substrate for HDD can be manufactured by adding the grinding process, the grinding | polishing process, the washing | cleaning process, the chemical strengthening process, etc. which are mentioned later to the glass blank manufactured by the above-mentioned process.

FIG. 6 is a diagram showing an example of a glass substrate for HDD manufactured by the method for manufacturing a glass substrate for HDD of the present invention. 6A is a perspective view, and FIG. 6B is a cross-sectional view. The glass substrate 30 for HDD is a disk-shaped glass substrate in which a center hole 33 is formed, and has a main surface 31, an outer peripheral end surface 34, and an inner peripheral end surface 35.

Chamfered portions

36 and 37 are formed on the outer peripheral end surface 34 and the inner peripheral end surface 35, respectively.

<Grinding process>
The grinding step is a step of processing the glass substrate into a predetermined plate thickness. Specifically, the process etc. which grind | polish (lapping) the both surfaces of the said glass blanks using an acidic grinding liquid are mentioned. By processing in this way, the parallelism, flatness and thickness of the glass substrate can be adjusted. Moreover, this grinding process may be performed once or twice or more. For example, when it is performed twice, the parallelism, flatness and thickness of the glass substrate are preliminarily adjusted in the first grinding step (first grinding step), and the glass substrate in the second grinding step (second grinding step). It is possible to finely adjust the parallelism, flatness and thickness of the film.

More specifically, examples of the first grinding step include a step of making the glass substrate have a substantially uniform flatness.

The second grinding step includes a step of grinding the roughened main surface of the glass substrate using a fixed abrasive polishing pad. In this second grinding step, for example, a roughened glass substrate is set in a grinding device, and a three-dimensional fixed abrasive with a surface pattern such as diamond tile is used, so that the glass substrate The surface can be ground.

When the second grinding step is performed, polishing performed in a rough polishing step described later can be efficiently performed. Further, the surface roughness Ra of the glass substrate used in the polishing process performed by the second grinding process is preferably 0.10 μm or less, and more preferably 0.05 μm or less.

The grinding step is usually performed after producing glass blanks, but may be performed after the coring step or may be performed a plurality of times.

<Rough polishing process>
The rough polishing step (primary polishing step) is a step of rough polishing the surface of the glass substrate that has been subjected to the grinding step. This rough polishing is intended to remove scratches and distortions remaining in the above-described grinding process, and is performed using the following polishing method.

The surface to be polished in the rough polishing step is a main surface and / or an end surface. The main end surface is a surface parallel to the surface direction of the glass substrate. The end surface is a surface composed of an inner peripheral end surface and an outer peripheral end surface. Moreover, an inner peripheral end surface is a surface which has an inclination with respect to the surface of an inner peripheral side perpendicular | vertical to the surface direction of a glass substrate, and the surface direction of a glass substrate. Further, the outer peripheral end surface is a surface that is inclined on the outer peripheral side, the surface perpendicular to the surface direction of the glass substrate and the surface direction of the glass substrate.

The polishing apparatus used in the rough polishing step is not particularly limited as long as it is a polishing apparatus used for manufacturing a glass substrate. Specifically, a polishing apparatus 11 as shown in FIG. FIG. 7 is a schematic cross-sectional view showing an example of the polishing apparatus 11 used in the rough polishing step and the precision polishing step in the method for manufacturing a glass substrate for HDD according to this embodiment.

7 is an apparatus capable of simultaneous grinding on both sides. The polishing apparatus 11 includes an apparatus main body 11a and a polishing liquid supply unit 11b that supplies a polishing liquid to the apparatus main body 11a.

The apparatus main body 11a includes a disk-shaped upper surface plate 12 and a disk-shaped lower surface plate 13, and they are arranged at intervals in the vertical direction so that they are parallel to each other. Then, the upper surface plate 12 and the lower surface plate 13 rotate in opposite directions.

A polishing pad 15 for polishing both the front and back surfaces of the glass blanks 10 is attached to each of the opposing surfaces of the upper surface plate 12 and the lower surface plate 13. The polishing pad 15 used in this rough polishing process is not particularly limited. Specifically, for example, a hard polishing pad made of polyurethane or the like can be used as the polishing pad 15.

Further, a plurality of rotatable carriers 14 are provided between the upper surface plate 12 and the lower surface plate 13. The carrier 14 is provided with a plurality of base plate holding holes 51, and the glass blanks 10 can be fitted and disposed in the base plate holding holes 51. For example, the carrier 14 may include 100 base plate holding holes 51 so that 100 glass blanks 10 can be fitted and arranged. If it does so, 100 glass blanks 10 can be processed by one process (1 batch).

The carrier 14 sandwiched between the upper surface plate 12 and the lower surface plate 13 via the polishing pad 15 holds the plurality of glass blanks 10 and rotates with respect to the rotation centers of the upper surface plate 12 and the lower surface plate 13. Revolve in the same direction as the lower surface plate 13. The disk-shaped upper surface plate 12 and the disk-shaped lower surface plate 13 can be operated by separate driving. In the polishing apparatus 11 operating in this way, the polishing slurry 16 is supplied between the upper surface plate 12 and the glass blanks 10 and between the lower surface plate 13 and the glass blanks 10, thereby the glass blanks 10. Rough polishing can be performed.

The polishing slurry supply unit 11b includes a liquid storage unit 110 and a liquid recovery unit 120. The liquid reservoir 110 includes a liquid reservoir main body 110a and a liquid supply pipe 110b having a discharge port 110e extending from the liquid reservoir main body 110a to the apparatus main body 11a. The liquid recovery unit 120 includes a liquid recovery unit main body 120a, a liquid recovery pipe 120b extended from the liquid recovery unit main body 120a to the apparatus main body 11a, and a liquid extended from the liquid recovery unit main body 120a to the liquid storage unit 110. And a return pipe 120c.

Then, the polishing slurry 16 put in the liquid storage unit main body 110a is supplied from the discharge port 110e of the liquid supply pipe 110b to the apparatus main body part 11a, and from the apparatus main body part 11a via the liquid recovery pipe 120b, the liquid recovery part main body 120a. To be recovered. The recovered polishing slurry 16 is returned to the liquid storage part 110 via the liquid return pipe 120c and can be supplied again to the apparatus main body part 11a.

Further, the polishing pad 15 used here is a foam of synthetic resin such as urethane or polyester containing a cerium oxide abrasive.

The polishing agent used in the polishing step performed before the chemical strengthening treatment step increases the polishing rate and sufficiently smoothes the polished glass substrate when the CeO ₂ content is high and the alkaline earth metal content is low. It is thought that it can be increased. Also for the polishing pad, as in the case of the above-mentioned abrasive, by using a material containing a large amount of CeO ₂ and a small amount of alkaline earth metal, the polishing rate is increased and the smoothness of the glass substrate after polishing is improved. It is thought that it can be sufficiently increased.

The use of an abrasive having a high CeO ₂ content is considered to be due to the following reasons that the polishing rate can be increased and the smoothness of the polished glass substrate can be sufficiently enhanced. First, when the glass substrate and CeO ₂ come into contact with each other with the pressure applied to the surface of the glass substrate during polishing, the Si—O bonds existing on the surface of the glass substrate are replaced with Ce—O bonds. Conceivable. This bond is easily decomposed, but it is considered that the bond with Si is difficult to form again. Therefore, it is considered that when an abrasive having a high CeO ₂ content is used, the polishing rate can be increased and the smoothness of the polished glass substrate can be sufficiently increased.

Further, by using an abrasive and a polishing pad having a high CeO ₂ content and a low alkaline earth metal content, not only the smoothness can be sufficiently improved, but also a glass substrate after polishing. It is considered that the adhesion of alkaline earth metal to is suppressed. It is considered that uniform chemical strengthening is achieved by applying a chemical strengthening treatment step to such a glass substrate in which adhesion of alkaline earth metal is suppressed.

When polishing with a polishing liquid in which the abrasive is dispersed in water, the alkaline earth metal is dissolved even when the alkaline earth metal is contained in the water. It is considered that the alkaline earth metal contained in the abrasive is less likely to adhere to the surface and is likely to adhere to the surface of the glass substrate. Therefore, it is considered that the adhesion of alkaline earth metal to the glass substrate after polishing can be sufficiently suppressed by using an abrasive with less alkaline earth metal.

The CeO ₂ content is preferably as high as possible. Namely, rare earth oxide contained in the abrasive, it is preferred that all are CeO _2. This is considered to be because CeO ₂ has the most influence on the polishing properties of the glass substrate. Further, the lower the alkaline earth metal content, the better. If the alkaline earth metal contained in the abrasive is small, it is considered that inhibition of the chemical strengthening treatment process by the alkaline earth metal is suppressed.

Further, the content of CeO ₂ is, to the abrasive total amount is preferably 90 mass% or more. By doing so, the glass substrate for HDD excellent in impact resistance can be manufactured, the polishing rate can be further increased, and the glass substrate for HDD having higher smoothness can be manufactured. This means that the content of alkaline earth metal that can hinder the chemical strengthening treatment process is small, and the content of CeO ₂ that improves the polishing property is simply large relative to the rare earth oxide contained in the abrasive. Rather, it is thought to be due to the fact that the amount is large relative to the total amount of abrasive.

Further, the polishing liquid is in a state where the acidic polishing agent is dispersed in a solvent such as water, and the content of CeO ₂ is 3 to 15% by mass with respect to the total amount of the polishing liquid. Is preferred. By doing so, the glass substrate for HDD excellent in impact resistance can be manufactured, the polishing rate can be further increased, and the glass substrate for HDD having higher smoothness can be manufactured. Further, in the case of the polishing liquid in which the abrasive is dispersed in water, as described above, since the alkaline earth metal is dissolved even if the alkaline earth metal is contained in the water, the glass substrate It is considered that the alkaline earth metal contained in the abrasive is likely to adhere to the surface of the glass substrate. Therefore, it is considered that the use of an abrasive having a small amount of alkaline earth metal can sufficiently suppress the adhesion of alkaline earth metal to the polished glass substrate.

The abrasive has a maximum particle size distribution measured by the laser diffraction scattering method of 3.5 μm or less, and a cumulative 50 volume% diameter D50 in the particle size distribution measured by the laser diffraction scattering method is 0.4 to 0.4. It is preferable that it is 1.6 μm.

If the particle size of the abrasive is too small, the polishing rate tends to decrease. When the particle size of the abrasive is too large, scratches that can be formed on the glass substrate by polishing tend to occur.

The maximum value in the particle size distribution measured by the laser diffraction scattering method is a cumulative curve obtained by setting the total volume of the powder population obtained by measurement with a laser diffraction particle size distribution measuring apparatus as 100%. It means the particle diameter of the point that is the maximum value of the curve. D50 means the particle diameter at which the cumulative curve is 50% when the total volume of the powder population obtained by measurement with a laser diffraction particle size distribution measuring device is 100%, and the cumulative curve is 50%. To do.

Further, the polishing liquid is preferably a polishing liquid having a fluorine content of 5% by mass or less in the rough polishing step.

The polishing pad 15 can contain zirconium silicate, zirconium oxide, manganese oxide, iron oxide, aluminum oxide, silicon carbide, or silicon dioxide in addition to cerium oxide. Among these, zirconium silicate is used. It is more preferable to make it contain.

The blending amount of cerium oxide in the polishing pad is preferably 10 to 30% by mass and more preferably 15 to 25% by mass with respect to the total amount of the polishing pad.

The polishing pad according to the present embodiment is manufactured by the following method, for example.

First, a resin solution and abrasive grains are mixed to produce an abrasive dispersion. Next, the abrasive dispersion is cured using a molding die to form a plate-like block in which the abrasive grains are fixed inside and on the surface. Subsequently, after the block is taken out of the mold, both sides of the block are ground and processed to a predetermined thickness.

More preferably, first, the resin solution and the abrasive grains are mixed, and this mixed liquid is depressurized and defoamed to produce a foam-free abrasive dispersion. Next, the foam-free abrasive dispersion is cured using a mold to form a plate-like block in which the abrasive grains are fixed inside and on the surface of the non-foamed body. Subsequently, after the block is taken out from the mold, both sides of the block are ground and processed to a predetermined thickness.

<Precision polishing process (secondary polishing process)>
The precision polishing process is a mirror polishing process that finishes a smooth mirror surface having a surface roughness (Rmax) of about 6 nm or less, for example, while maintaining the flat and smooth main surface obtained in the rough polishing process. . This precision polishing step is performed, for example, by using a polishing apparatus similar to that used in the rough polishing step and replacing the polishing pad from a hard polishing pad to a soft polishing pad. The surface to be polished in the precision polishing step is the main surface, similar to the surface to be polished in the rough polishing step.

Further, as the abrasive used in the precision polishing process, an abrasive that causes less scratching even if the polishing performance is lower than that used in the rough polishing process is used. Specifically, for example, an abrasive containing silica-based abrasive grains (colloidal silica) having a particle diameter lower than that of the abrasive used in the rough polishing step is used. The average particle diameter of the silica-based abrasive is preferably about 20 nm. And the polishing slurry liquid containing the said abrasive | polishing agent is supplied to a glass substrate, a polishing pad and a glass substrate are slid relatively, and the surface of a glass substrate is mirror-polished.

The surface roughness Ra of the HDD glass substrate after the precision polishing step is preferably 0.1 to 5 mm. If it is in such a range, while having the smoothness required as a glass substrate for a magnetic recording medium, the head is prevented from adsorbing on an excessively smooth magnetic disk, and the head is configured as a hard disk drive device. Can be stably levitated.

<Washing process>
The cleaning step is a step of cleaning the glass substrate that has been subjected to the rough polishing step or the precise polishing step.

The glass substrate after the rough polishing by the rough polishing step is preferably cleaned by a cleaning step. For example, the glass substrate is washed with an alkaline detergent having a pH of 13 or more, and the glass substrate is rinsed. Next, the glass substrate is washed with an acid detergent having a pH of 1 or less, and the glass substrate is rinsed. Finally, the glass substrate is cleaned using a hydrofluoric acid (HF) solution. For polishing using cerium oxide, it is most efficient to perform cleaning in the order of alkali cleaning, acid cleaning, and HF cleaning. This is because the abrasive is first dispersed and removed with an alkaline detergent, then the abrasive is dissolved and removed with an acid detergent, and finally the glass substrate is etched with HF to remove the abrasive that is deeply stuck in the glass substrate. It is.

The washing step is preferably performed in separate tanks for alkali washing, acid washing, and HF washing. When these washings are performed in a single tank, efficient washing may not be possible. In particular, when the acid detergent and HF are put in the same tank, the etching rate of HF decreases at a place where there is a lot of abrasive, so that there is a tendency that the inside of the substrate cannot be etched uniformly. Moreover, it is preferable to use a rinse tank after each washing. In some cases, a surfactant, a dispersing agent, a chelating agent, a reducing material, and the like may be added to these detergents. Moreover, it is preferable to apply an ultrasonic wave to each washing tank and to use deaerated water for each detergent.

As another method, first, the glass substrate is immersed in a cleaning solution containing 1% by mass of HF and 3% by mass of sulfuric acid. At that time, an ultrasonic vibration of 80 kHz is applied to the cleaning liquid. Thereafter, the glass substrate is taken out. And the taken-out glass substrate is immersed in a neutral detergent liquid. At that time, 120 kHz ultrasonic vibration is applied to the neutral detergent solution. Finally, the glass substrate is taken out, rinsed with pure water, and dried IPA.

The glass substrate after the cleaning step, the alkaline earth metal remaining on the surface thereof, is preferably 10 ng / cm ² or less, more preferably 5 ng / cm ² or less. By doing so, the glass substrate for hard disks excellent in impact resistance can be obtained. This is considered to be due to the small amount of alkaline earth metal adhering to the surface of the glass substrate subjected to the chemical strengthening treatment step, which can inhibit the chemical strengthening treatment step. Therefore, it is considered that chemical strengthening occurs uniformly on the entire surface of the glass substrate, and a glass substrate for hard disk that is superior in impact resistance can be obtained. That is, if there is too much alkaline earth metal remaining on the surface of the glass substrate after the cleaning step, the chemical strengthening treatment step is not suitably performed, and the impact resistance of the obtained glass substrate cannot be sufficiently increased. There is a case.

Further, the smaller the amount of alkaline earth metal remaining on the surface of the glass substrate after the cleaning step, the better. This is considered that the alkaline earth metal remaining on the surface of the glass substrate polished in the polishing step before the chemical strengthening treatment step inhibits the chemical strengthening treatment step and inhibits uniform chemical strengthening. Because. In the present embodiment, the smaller the amount of alkaline earth metal remaining on the surface of the glass substrate after the cleaning step, the better, and if the amount is 10 ng / cm ² or less, the hard disk is more excellent in impact resistance. Glass substrates can be manufactured.

The glass substrate after the rough polishing is washed so that the amount of cerium oxide on the surface of the glass substrate is 0.125 ng / cm ² or less. When the amount of cerium oxide on the surface of the glass substrate is too large, there is a tendency that the flatness of the glass substrate cannot be improved.

<Chemical strengthening process>
If the chemical strengthening process in the manufacturing method of this invention is a well-known method, it will not specifically limit. Specifically, the chemical strengthening treatment step includes, for example, a step of immersing a glass substrate in a chemical strengthening treatment solution. By doing so, a chemical strengthening layer can be formed in the surface of a glass substrate, for example, a 5 micrometer area | region from the glass substrate surface. And by forming a chemical strengthening layer, impact resistance, vibration resistance, heat resistance, etc. can be improved.

More specifically, in the chemical strengthening treatment step, by immersing the glass substrate in a heated chemical strengthening treatment liquid, alkali metal ions such as lithium ions and sodium ions contained in the glass substrate are potassium ions having a larger ion radius. It is carried out by an ion exchange method that substitutes alkali metal ions such as. Due to the strain caused by the difference in ion radius, compressive stress is generated in the ion-exchanged region, and the surface of the glass substrate is strengthened.

Further, the chemical strengthening treatment step in the present invention may be performed after the coring step, after the grinding step, after the rough polishing step, or after the precision polishing step, and may be performed a plurality of times depending on the composition of the glass. Good. Moreover, when performing a chemical strengthening process, since the influence on the dispersion | variation in the shape of the glass substrate finally obtained by the dispersion | variation in the plate | board thickness in glass blanks becomes remarkable, this invention is applied especially suitably.

In the present embodiment, it is considered that the reinforcing layer is suitably formed by this chemical strengthening treatment step by using a raw material having the following glass composition as the raw material of the glass substrate.
(Glass composition)
SiO ₂ : 55 to 75% by mass,
Al ₂ O ₃ : 5 to 18% by mass,
Li ₂ O: 1 to 10% by mass,
Na ₂ O: 3 to 15% by mass,
K ₂ O: 0.1 to 5% by mass,
However, the total amount of Li ₂ O + Na ₂ O + K ₂ O: 10 to 25% by mass,
MgO: 0.1 to 5% by mass,
CaO: 0.1 to 5% by mass,
ZrO ₂ : 0 to 8% by mass

Specifically, among the Li ₂ O, Na ₂ O, and K ₂ O, which are alkali components of the glass substrate, the content of Na ₂ O is large, and the sodium ions of this Na ₂ O are added to the chemical strengthening treatment liquid. It is thought that it is easily exchanged for contained potassium ions. Furthermore, since the polishing agent used in the polishing step before the chemical strengthening treatment step, here the rough polishing step, is an abrasive having the above composition, the alkaline earth metal adhering to the surface of the glass substrate is used. The amount is small and the chemical strengthening is considered to be uniform. Therefore, a glass substrate excellent in impact resistance can be produced by performing a precision polishing step on a glass substrate that has been subjected to suitable chemical strengthening as in this embodiment.

The chemical strengthening treatment liquid is not particularly limited as long as it is a chemical strengthening treatment liquid used in the chemical strengthening treatment step in the method of manufacturing a glass substrate for hard disk. Specifically, as the chemical strengthening treatment liquid, for example, a melt containing potassium ions, a melt containing potassium ions or sodium ions, or the like can be used.

Examples of these melts include melts obtained by melting potassium nitrate, sodium nitrate, potassium carbonate, sodium carbonate, and the like. Among these, it is preferable to use a combination of a melt obtained by melting potassium nitrate and a melt obtained by melting sodium nitrate from the viewpoint of low melting point and preventing deformation of the glass substrate. At that time, a mixed solution obtained by mixing approximately the same amount of a melt obtained by melting potassium nitrate and a melt obtained by melting sodium nitrate is preferable.

(Film formation process)
FIG. 8 is a partial cross-sectional perspective view showing a magnetic disk as an example of a magnetic recording medium using a glass substrate for HDD manufactured by the manufacturing method according to the present embodiment. The magnetic disk D includes a magnetic film 102 formed on the main surface of a circular HDD glass substrate 101. The magnetic film 102 can be formed by a known conventional means. The magnetic film 102 is formed by, for example, a forming method (spin coating method) in which a thermosetting resin in which magnetic particles are dispersed is spin-coated on the HDD glass substrate 101, or a HDD glass substrate 101. It can be formed by a formation method (sputtering method) for forming the magnetic film 102 by sputtering, a formation method (electroless plating method) for forming the magnetic film 102 by electroless plating on the glass substrate 101 for HDD, or the like. .

The thickness of the magnetic film 102 is about 0.3 to 1.2 μm when formed by spin coating, and about 0.04 to 0.08 μm when formed by sputtering. When formed by electrolytic plating, the thickness is about 0.05 to 0.1 μm. From the viewpoint of thinning and densification, it is preferably formed by sputtering or electroless plating.

The magnetic material used for the magnetic film 102 can be any known material and is not particularly limited. The magnetic material is preferably, for example, a Co-based alloy based on Co having high crystal anisotropy in order to obtain a high coercive force, and Ni or Cr added for the purpose of adjusting the residual magnetic flux density. More specifically, the magnetic material may be CoPt, CoCr, CoNi, CoNiCr, CoCrTa, CoPtCr, CoNiPt, CoNiCrPt, CoNiCrTa, CoCrPtTa, CoCrPtB, CoCrPtSiO, or the like whose main component is Co.

The magnetic film 102 has a multilayer structure (for example, CoPtCr / CrMo / CoPtCr, CoCrPtTa / CrMo / CoCrPtTa, etc.) divided by a nonmagnetic film (for example, Cr, CrMo, CrV, etc.) in order to reduce noise. May be. Magnetic material used for the magnetic layer 102, in addition to the magnetic material, ferrite or iron - may be a rare earth, also, Fe in a non-magnetic film made of _SiO 2, BN, etc., Co, FeCo, CoNiPt and the like A granular material having a structure in which the magnetic particles are dispersed may be used. In addition, for recording on the magnetic film 102, either an inner surface type or a vertical type recording format may be used.

Further, in order to improve the sliding of the magnetic head, the surface of the magnetic film 102 may be thinly coated with a lubricant. Examples of the lubricant include those obtained by diluting perfluoropolyether (PFPE), which is a liquid lubricant, with a freon-based solvent.

Further, if necessary, an underlayer or a protective layer may be provided for the magnetic film 102. The underlayer in the magnetic disk D is appropriately selected according to the magnetic film 102. Examples of the material for the underlayer include at least one material selected from nonmagnetic metals such as Cr, Mo, Ta, Ti, W, V, B, Al, and Ni. For example, in the case of the magnetic film 102 containing Co as a main component, the material of the underlayer is preferably Cr alone or a Cr alloy from the viewpoint of improving magnetic characteristics.

Further, the underlayer is not limited to a single layer, and may have a multi-layer structure in which the same or different layers are stacked. Examples of such an underlayer having a multilayer structure include multilayer underlayers such as Cr / Cr, Cr / CrMo, Cr / CrV, NiAl / Cr, NiAl / CrMo, and NiAl / CrV. Examples of the protective layer that prevents wear and corrosion of the magnetic film 102 include a Cr layer, a Cr alloy layer, a carbon layer, a hydrogenated carbon layer, a zirconia layer, and a silica layer. These protective layers can be continuously formed with the underlayer and the magnetic film 102 by an in-line sputtering apparatus. These protective layers may be a single layer, or may be a multi-layer structure composed of the same or different layers.

Note that another protective layer may be formed on the protective layer or instead of the protective layer. For example, instead of the protective layer, a SiO ₂ layer may be formed on the Cr layer. Such a SiO ₂ layer is formed by dispersing and applying colloidal silica fine particles in a tetraalkoxysilane diluted with an alcohol-based solvent on the Cr layer and further baking.

In such a magnetic recording medium based on the HDD glass substrate 101 in the present embodiment, the HDD glass substrate 101 is formed with the above-described composition, so that information can be recorded and reproduced with high reliability over a long period of time. Can do.

In the above description, the HDD glass substrate 101 in this embodiment is used as a magnetic recording medium. However, the present invention is not limited to this, and the HDD glass substrate 101 in this embodiment is a magneto-optical disk. It can also be used for optical discs and the like.

The technical characteristics of the above-described method for manufacturing a glass substrate for HDD are summarized below.

The manufacturing method of the glass substrate for HDD by one aspect of this invention is a manufacturing method of the glass substrate for HDD provided with a molten glass supply process, a press molding process, a heat treatment process, a coring process, a grinding process, a polishing process, and a washing process. Te, in the coring process, the radius of the glass blank before the grinding process when the r _1, the circumferential direction one round of the retardation TIR at the position of 0.75 r ₁ from the center of the glass blanks below 1.0nm It is characterized by adjusting.

According to the method for producing a glass substrate for HDD of the present invention, it is possible to provide a method for producing a glass substrate for HDD which is excellent in reducing the head flying height, reducing head crashes and read / write errors.

In the above production method, when the radius of the inner hole of the glass blank is r ₀ , the retardation TIR for one round in the circumferential direction at a position (2r ₀ + r ₁ ) / 3 from the center of the glass molded product is 0.5 nm or less. It is preferable to adjust to.

By adopting such a configuration, the present invention can easily cope with low head flying and high-speed rotation in an HDD using the obtained glass substrate, and can stably perform recording and reproduction. .

In the above manufacturing method, it is preferable to further include a chemical strengthening treatment step.

The present invention can further produce a glass substrate for hard disk having more excellent impact resistance by providing a chemical strengthening treatment step.

In the above manufacturing method, the viscosity of the molten glass immediately after supplying the molten glass in the molten glass supply step eta is, satisfies the condition of log ₁₀ η> 2.6dPa · s, the press machine is arranged in the press molding process It is preferable to adjust the rotation speed of the rotary table to 0.3 m / s or less.

In the present invention, by adopting such a configuration, the glass gob can be rotated and pressed without breaking the shape, and the internal distortion of the obtained glass blanks can be reduced.

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

Example 1
Glass having a glass composition as shown in Table 1 is melted and a molten glass having a viscosity η immediately after being supplied is log ₁₀ η = 2.8 dPa · s, and the speed of the rotary table is 0.25 m / s. Thus, the rotary table was rotated to perform press molding. Then, the retardation TIR measurement of the circumferential direction of the glass blanks which performed the heat processing process and the coring process was performed. The obtained glass blanks had a radius of 33.2 mm and a thickness of 1.05 mm.

For the retardation TIR measurement, distortion at a point of 0.75r ₁ and (2r ₀ + r ₁ ) / 3 from the center hole of the glass blank was measured using PA-100 (manufactured by Photonics Lattice). The measurement was performed by passing linearly polarized light through a glass blank and observing the change in the polarization state after the passage. From this point, the variation in retardation amount (difference between the maximum value and the minimum value) when measuring one round concentrically was defined as the circumferential retardation TIR.

The circumferential direction TIR of the glass substrate manufactured by subjecting the glass blanks after the retardation TIR measurement to a grinding process, a polishing process, and a cleaning process was measured.

In the grinding process, both main surfaces of the glass blanks were roughly polished using a double-side polishing machine (Hamai Sangyo Co., Ltd., 16B type). As the polishing pad, a polishing pad in which diamond abrasive grains having an average primary particle diameter of 9 μm were embedded in a resin pad was used, and water and coolant mixed at 9: 1 were used as polishing water. The weight was 200 g / cm ² . The amount of abrasive slurry added was 4.5 L / min. In addition, a circular center hole having a diameter of about 19.6 mm was formed in the center of the blank using a core drill equipped with a cylindrical diamond grindstone. 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.

Next, in the polishing step, 100 blanks were stacked, and in this state, the outer peripheral end surface and the inner peripheral end surface of the blanks were polished using an end surface polishing machine (manufactured by Hadano Machinery Co., Ltd., TKV-1). Nylon fiber having a diameter of 0.2 mm was used as the brush hair of the polishing machine. As the polishing liquid, a slurry containing cerium oxide having an average primary particle diameter of 3 μm as abrasive grains (polishing liquid component) was used.

As the rough polishing step, both main surfaces of the glass substrate were subjected to rough polishing using a double-side polishing machine (manufactured by Hamai Sangyo Co., Ltd., 16B type). The polishing pad was a urethane foam pad, the abrasive grains were cerium oxide abrasive grains having an average primary particle size of 1 μm, and the mixing ratio of water and cerium oxide was 80:20. Furthermore, pH was adjusted with the adjustment liquid containing a sulfuric acid. The load was 100 g / cm ² . The amount of abrasive slurry added was 8000 mL / min.

As the mirror polishing step, both main surfaces of the glass substrate were polished more precisely using a double-side polishing machine (Hamai Sangyo Co., Ltd., 16B type). As the abrasive slurry, colloidal silica having an average primary particle diameter of 20 nm was dispersed in water as abrasive grains to form a slurry, and the mixing ratio of water and colloidal silica was 80:20. Furthermore, pH was adjusted with the adjustment liquid containing a sulfuric acid. The load was 120 g / cm ² . The amount of abrasive slurry added was 500 mL / min. In this step, 100 batches of glass substrates were processed into 5 batches. Ra of the obtained glass substrate was 2 or less.

As a 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.

The circumferential TIR measurement was performed using an Optiflat manufactured by Phase Shift Technology, which measures the surface shape using white light interference. The measurement location in the circumferential direction TIR was set to a position of 0.75r _{1 and} a position of (r ₁ + 2r ₂ ) / 3, similarly to the position of the retardation TIR measurement.

(Example 2)
Using molten glass with a viscosity η immediately after the supply of log ₁₀ η = 2.4 dPa · s, measuring the retardation TIR before the heat treatment step, and preliminarily distorting the glass blanks with Tg using a heater Heat treatment was performed. Except these processes, it manufactured with the manufacturing method similar to Example 1, and measured the circumferential direction retardation TIR of glass blanks. Moreover, the circumferential direction TIR of the glass substrate which gave the processing process was measured.

(Example 3)
Glass blanks, which had been eccentric in advance, were manufactured by the same manufacturing method as in Example 2 except that an inner hole was formed at the center of the eccentricity in the coring process, and the circumferential retardation TIR of the glass blanks was measured. did. Moreover, the circumferential direction TIR of the glass substrate which gave the processing process was measured.

(Example 4)
A press molding process was performed by using a molten glass having a viscosity η immediately after the supply of log ₁₀ η = 2.8 dPa · s and rotating the speed of the rotary table to 0.25 m / s. The glass blanks, in which the strain was eccentric, were formed with an inner hole at the center of the eccentricity of the strain in the coring step, and further partially heat-treated with Tg using a heater. Except these processes, it manufactured with the manufacturing method similar to Example 1, and measured the circumferential direction retardation TIR of glass blanks. Moreover, the circumferential direction TIR of the glass substrate which gave the processing process was measured.

(Example 5)
It manufactured with the manufacturing method similar to Example 1 except having employ | adopted the chemical strengthening process between the rough polishing process and the mirror polishing process, and measured the circumferential retardation TIR of the glass blanks. Moreover, the circumferential direction TIR of the glass substrate which gave the processing process was measured. In the chemical strengthening treatment step, potassium nitrate was melted at 400 ° C., and the glass substrate was immersed for 1 hour.

(Comparative Example 1)
The press molding process was performed by using a molten glass having a viscosity η immediately after the supply of log ₁₀ η = 2.4 dPa · s and rotating the rotary table at a speed of 0.25 m / s. Then, the retardation TIR measurement of the circumferential direction of the glass blanks which performed the heat processing process and the coring process was performed. Moreover, the circumferential direction TIR of the glass substrate which gave the subsequent process process was measured.

(Comparative Example 2)
The press molding process was performed by using a molten glass having a viscosity η immediately after the supply of log ₁₀ η = 2.0 dPa · s and rotating the speed of the rotary table to 0.40 m / s. Then, the retardation TIR measurement of the circumferential direction of the glass blanks which performed the heat processing process and the coring process was performed. Moreover, the circumferential direction TIR of the glass substrate which gave the subsequent process process was measured.

(Evaluation methods)
A magnetic film was formed on the glass substrates of Examples 1 to 5 and Comparative Examples 1 and 2 and mounted on the HDD, and the read / write characteristics were evaluated. The magnetic film was made of a Co—Cr alloy by sputtering, and the film thickness was 15 nm. In the evaluation method, the number of errors was measured by rotating the number of revolutions of the HDD spindle at 15,000 rpm for 5 minutes. The number of tests is 25, and Table 2 shows the test evaluation of the average value of errors per sheet.

Test evaluation of circumferential retardation TIR, retardation TIR, and read / write error at each measurement position in Examples 1 to 5 and Comparative Examples 1 and 2 was performed. The results are shown in Table 3.

From the results of Table 3, the pressure step was performed so that the viscosity η of the molten glass was a condition of log ₁₀ η> 2.6 dPa · s and the rotation speed of the rotary table was 0.3 m / s or less. In the case of No. ₁ , the circumferential retardation TIR at the position of 0.75r ₁ and (2r ₀ + r ₁ ) / 3 at the time of glass blank production was 1.0 nm or less and 0.5 nm or less, respectively. This is because by making the viscosity of the molten glass higher and further lowering the rotation speed, the shape of the relatively soft molten glass supplied to the lower mold is not tilted by the centrifugal force of the rotation, and thus no distortion occurs. it is conceivable that.

Therefore, by the circumferential retardation TIR glass blanks and small, the position of 0.75 r ₁ also circumferentially TIR at the glass substrate production, and at the position of _{_{(2r 0 + r 1) /}} 3, respectively 1. It was as small as 0 nm or less and 0.5 nm or less. Therefore, since the circumferential direction TIR was small, the read / write evaluation when the magnetic film was formed on the glass substrate of Example 1 and mounted on the HDD was excellent.

In Example 2, which had a slightly lower viscosity than the molten glass of Example 1, the shape of the molten glass was tilted due to the speed of the rotary table after being transferred by the rotary table. The circumferential distortion caused by this could be eliminated by heat treatment using a heater. The glass blanks thus prepared had a circumferential retardation TIR at a position of 0.75r _{1 and} a position of (2r ₀ + r ₁ ) / 3 of 1.0 nm or less and 0.5 nm or less, respectively. The test was also excellent as in Example 1.

Further, Example 3 was a molten glass having the same viscosity as that of Example 2, and was transferred at the same rotational speed. However, in Example 3, the distortion was provided when the coring was formed, and the center of the inner hole was provided so as to be a position with no distortion in the circumferential direction of the glass substrate. By doing in this way, the circumferential retardation TIR at the position of 0.75r ₁ at the time of glass blank production was 1.0 nm or less, but the circumferential retardation TIR at the position of (2r ₀ + r ₁ ) / 3 was It exceeded 0.5 nm, and it was in a range where there was no problem as a product.

Further, in Example 4, the pressure step is performed so that the viscosity η of the molten glass is log ₁₀ η> 2.6 dPa · s, and the rotation speed of the rotary table is 0.3 m / s or less, and At the time of forming the coring, the center of the inner hole was provided so as to be a portion having no distortion with respect to the circumferential direction of the glass substrate, and the distortion in the circumferential direction was eliminated by heat treatment of the heater. By processing in this way, the circumferential retardation TIR at the position of 0.75r _{1 and} the position of (2r ₀ + r ₁ ) / 3 at the time of glass blanks production becomes extremely small, respectively. The direction TIR was also very small. Accordingly, since the circumferential direction TIR is extremely small compared to the first to third embodiments, the read / write evaluation when the magnetic film is formed on the glass substrate of the fourth embodiment and mounted on the HDD is very excellent. It was.

As for Example 5 employing the chemical strengthening treatment step, the position of 0.75 r ₁ during Similarly glass blank produced as in Example 1, and _{_{(2r 0 + r 1) /}} 3 in the circumferential direction of the retardation TIR at the position Were 1.0 nm or less and 0.5 nm or less, respectively. By making the circumferential retardation TIR of the glass blanks small, 1.0 nm or less at the position of 0.75r _{1 and} the position of (2r ₀ + r ₁ ) / 3 also in the circumferential direction TIR at the time of glass substrate production It was as small as 0.5 nm or less. Therefore, since the circumferential direction TIR is small, the read / write evaluation when the magnetic film was formed on the glass substrate of Example 5 and mounted on the HDD was excellent as in the case of Example 1.

On the other hand, Comparative Example 1 having a slightly lower viscosity than the molten glass of Example 1 and Comparative Example using a lower viscosity than the molten glass of Example 1 and further increasing the rotational speed In No. 1, since the glass blanks were not subjected to distortion elimination processing, the circumferential retardation TIR was 1.0 nm or less and exceeded 5 nm, respectively, and accordingly the circumferential TIR of the glass substrate also became a large value, and the read / write test. The result was very inferior.

DESCRIPTION OF SYMBOLS 1 Molding press machine 2 Upper part of press machine 3 Upper mold | type 4 2nd shaping | molding surface 5 Lower mold | type 6 1st shaping | molding surface 7 Lower press machine 8 Rotating shaft 9 Turning table 10 Glass blanks 11 Polishing apparatus 12 Upper surface plate 13 Lower surface plate 16 Polishing slurry 21 Outflow nozzle 22 Blade 23 Molten glass 101 Glass substrate for HDD

Claims

A manufacturing method of a glass substrate for HDD comprising a molten glass supply process, a press molding process, a heat treatment process, a coring process, a grinding process, a polishing process, and a cleaning process,
In the coring step, when the radius of the glass blank before the grinding process was r 1, to adjust the center of the glass blank in the circumferential direction one round of the retardation TIR at the position of 0.75 r 1 below 1.0nm The manufacturing method of the glass substrate for HDD.
When the radius of the inner hole of the glass blank is r 0 , the retardation TIR for one round in the circumferential direction at a position (2r 0 + r 1 ) / 3 from the center of the glass molded product is adjusted to 0.5 nm or less. Item 2. A method for producing a glass substrate for HDD according to Item 1.
The method for producing a glass substrate for HDD according to claim 1, further comprising a chemical strengthening treatment step.
In the molten glass supply step, the viscosity η of the molten glass immediately after supplying the molten glass satisfies a condition of log 10 η> 2.6 dPa · s,
The method for producing a glass substrate for an HDD according to any one of claims 1 to 3, wherein in the press molding step, a rotation speed of a rotary table on which a press machine is arranged is adjusted to 0.3 m / s or less.