JP2012077145A - Method for producing glass substrate for hard disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a glass substrate for hard disks excellent in impact resistance.SOLUTION: The method for producing a glass substrate for hard disks includes: a polishing step of polishing a surface of a glass blank using an abrasive and a polishing pad; and a chemical strengthening step of strengthening the polished surface of the glass blank using a chemical strengthening treatment liquid after the polishing step, wherein a glass blank containing 0.02-1.0 mass% of cerium oxide is used as the glass blank, an abrasive having a cerium oxide content of 99 wt.% or more relative to the total rare earth oxides (TREO) and an alkaline earth metal content of 10 ppm or less is used as the abrasive, and a polishing pad having a cerium oxide content of 99 wt.% or more relative to the total rare earth oxides (TREO) and an alkaline earth metal content of 10 ppm or less is used as the polishing pad.

Description

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

  A magnetic information recording apparatus records information on an information recording medium by using magnetism, light, magneto-optical, and the like. A typical example is a hard disk drive 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 by only a few nanometers without contacting the magnetic head with the magnetic disk. Due to such a mechanism, if there are protrusions such as scratches or deposits on the disk, a problem with the hard disk drive device will occur if the magnetic head collides with these. Since the protrusions on the disk are often caused by the glass substrate itself of the magnetic disk, the surface of the glass substrate for hard disk is required to have high smoothness and high cleanliness.

  Moreover, the manufacturing method of the said glass substrate for hard disks has the grinding | polishing process which consists of a rough grinding | polishing method and a precision grinding | polishing method in a manufacturing process. In particular, a technique for polishing using a polishing agent or a polishing pad mainly composed of cerium oxide is disclosed for a rough polishing method.

For example, Patent Document 1 describes a cerium oxide abrasive containing cerium oxide particles having a specific particle diameter. Patent Document 2 describes a cerium oxide-based abrasive having CeO ₂ / TREO of 95% by mass or more. It is described that when the above-described abrasive is used, it is possible to obtain an abrasive having a high polishing speed and few friction scratches. However, even if the polishing agent is polished on an object to be polished, the scratches have not been sufficiently reduced.

  Patent Document 3 describes a method for producing a glass substrate for an information recording medium that is polished by using abrasive grains containing cerium oxide, and the amount of fluorine contained in the abrasive grains is 5% or less. It is described that there is. However, even if such abrasive grains are used, polishing scratches remain on the glass substrate, and a satisfactory polishing effect cannot be obtained.

  On the other hand, Patent Document 4 describes a method of polishing with a polishing pad containing solid cerium oxide in urethane or the like. However, when the polishing pad is used, sagging occurs in the end surface portion of the glass container substrate, and if it is used as it is, there arises a problem that the life is shortened.

JP 2010-30041 A JP 2008-88325 A JP 2002-109727 A JP 2007-250166 A

The inventions described in Patent Documents 1 and 2 are abrasives simply having an increased CeO ₂ content in order to increase the polishing rate and suppress the occurrence of polishing flaws, and elements other than TREO in the abrasive used Not paying attention to. In addition, the invention described in Patent Document 3 discloses the use of an abrasive having a low content of fluorine, which is a causative substance that generates a component that erodes a glass substrate, in a strong acid treatment for removing the polishing residue after the polishing treatment. This technique does not focus on elements other than TREO and TREO in the abrasive used. That is, these abrasives are not composed so as to reduce the content of alkaline earth metal. Therefore, it is considered that depending on the abrasive used, even if the chemical strengthening method is applied to the polished glass substrate, the impact resistance of the glass substrate may not be sufficiently improved.

  The present invention has been made in view of the above prior art, and an object to be solved is to provide a method for producing a glass substrate for hard disk having excellent impact resistance.

  In order to solve the above-mentioned problems, the present inventors have conducted intensive studies focusing on the composition of the glass base plate, the abrasive used in the polishing process for polishing the glass base plate, and the components contained in the polishing pad. As a result, the glass base plate is made to contain cerium oxide, and further, the glass base plate is polished by using a polishing agent and a polishing pad containing a specific amount of cerium oxide and having a small amount of alkaline earth metal. It has been found that a glass substrate with excellent impact resistance can be produced by reducing scratches, cracks, pits, etc. on the surface of the base plate and reducing impurities adhering to the glass substrate that may hinder chemical strengthening. The present invention has been completed.

  The method for producing a glass substrate for hard disk according to the present invention comprises a polishing step of polishing the surface of a glass base plate using an abrasive and a polishing pad, and a surface of the glass base plate polished after the polishing step, A chemical strengthening step for strengthening using a chemical strengthening treatment liquid, and the glass base plate containing 0.02 to 1.0% by mass of cerium oxide, and the abrasive containing cerium oxide The amount of the cerium oxide is 99% by weight or more based on the total rare earth oxide (TREO) and the alkaline earth metal content is 10 ppm or less. It is characterized by using 99% by weight or more with respect to the oxide (TREO) and having an alkaline earth metal content of 10 ppm or less.

  According to such a structure, the manufacturing method of the glass substrate for information recording media excellent in impact resistance can be provided.

  This is considered to be due to the following.

  First, by using a glass composition containing cerium oxide as described above as a glass base plate that is a raw material for the glass substrate, the reinforcing layer is more suitably formed in the chemical strengthening step.

  That is, in the rough polishing step with this cerium oxide-containing abrasive, when the glass base plate and cerium oxide come into contact with each other with pressure applied to the surface of the glass base plate, Si, which is the main composition, on the surface of the glass base plate. The —O bond replaces the Ce—O bond. And this Ce-O bond is easily decomposed, but the bond with Si is difficult to be formed again. Therefore, it is considered that by using a polishing agent containing cerium oxide, the polishing rate can be increased and the smoothness of the polished glass base plate can be sufficiently increased.

  Further, when cerium oxide is present in the composition of the glass base plate to be polished, polishing can be performed more smoothly. This is because the presence of cerium oxide in the glass composition facilitates the replacement of the Si—O bond in the glass base plate with the Ce—O bond and the breakage of the Ce—O bond. And since these substitution and cutting | disconnections are performed smoothly, the deposit | attachment of the impurity with respect to a glass base plate can also be reduced, and it is thought that it can give easily also in the washing | cleaning process of a glass substrate.

  The content of cerium oxide in the glass base plate is preferably 0.02 to 1.0% by mass, more preferably 0.5 to 0.8% by mass, and 0.1 to 0.6% by mass. % Is more preferable. When the content is less than 0.02% by mass, the smoothness of the glass base plate may not be sufficiently improved. Further, when the content is more than 1.0% by mass, the effect is not particularly improved even if the content is more than this.

Next, the polishing agent used in the polishing step performed before the chemical strengthening step uses a material containing a large amount of CeO ₂ and a small amount of alkaline earth metal, thereby increasing the polishing rate and increasing the glass element after polishing. It is considered that the smoothness of the plate can be sufficiently enhanced.

It is considered that the reason why the polishing agent having a high CeO ₂ content can increase the polishing rate and sufficiently increase the smoothness of the polished glass base plate is as follows. First, when the glass base plate and CeO ₂ come into contact with each other in the state where pressure is applied to the surface of the glass base plate during polishing, Si—O bonds, which are the main composition on the surface of the glass base plate, are Ce— It is thought to replace the bond of O. 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 glass base plate after polishing can be sufficiently increased.

And by using such an abrasive having a high CeO ₂ content and having a low alkaline earth metal, not only can the smoothness be sufficiently increased, but also the alkali with respect to the polished glass base plate. It is thought that adhesion of earth metal is suppressed. It is considered that uniform chemical strengthening is achieved by applying a chemical strengthening step to such a glass base plate in which adhesion of alkaline earth metal is suppressed.

  Note that when polishing with a polishing liquid in which the abrasive is dispersed in water, the alkaline earth metal is dissolved even if the alkaline earth metal is contained in the water. It is considered that the alkaline earth metal contained in the abrasive is likely to adhere to the surface of the glass base plate. Therefore, it is considered that adhesion of alkaline earth metal to the glass base plate after polishing can be sufficiently suppressed by using a polishing agent with little alkaline earth metal.

  From these things, it is thought that the glass substrate for information recording media excellent in impact resistance can be manufactured. Furthermore, according to this manufacturing method, it is considered that a glass substrate for an information recording medium having a sufficiently high polishing rate and a sufficiently high smoothness can be manufactured.

  In the method for producing a glass substrate for an information recording medium, the content of the cerium oxide as the abrasive is 99% by weight or more based on the total rare earth oxide (TREO), and an alkaline earth metal is used. It is preferable to use one having a content of 5 ppm or less.

According to such a structure, the manufacturing method of the glass substrate for information recording media excellent in impact resistance can be provided. Furthermore, it is considered that the polishing rate can be further increased and a glass substrate for an information recording medium having higher smoothness can be produced. This is considered to be due to the fact that the content of CeO ₂ that enhances the polishing property is large and the content of alkaline earth metal that can inhibit the chemical strengthening process is small.

  Moreover, in the manufacturing method of the glass substrate for information recording media, it is preferable to use a cerium oxide content of 90% by mass or more based on the abrasive.

According to such a configuration, it is possible to manufacture a glass substrate for information recording media excellent in impact resistance, and further to increase the polishing rate, and to manufacture a glass substrate for information recording media with higher smoothness. Can do. This means that the content of the alkaline earth metal that can hinder the chemical strengthening process is small, and the content of CeO ₂ that enhances the polishing property is merely large relative to the rare earth oxide contained in the abrasive. It is thought that this is also due to the large amount of the abrasive.

Further, in the method for manufacturing a glass substrate for hard disk, the glass base plate after the cleaning step is further provided with a cleaning step for cleaning the glass base plate polished in the polishing step before the chemical strengthening step. The alkaline earth metal remaining on the surface is preferably 10 ng / cm ² or less.

  According to such a structure, the manufacturing method of the glass substrate for information recording media excellent in impact resistance can be provided. This is considered to be due to the small amount of alkaline earth metal adhering to the surface of the glass base plate subjected to the chemical strengthening step, which can inhibit the chemical strengthening step.

  In the method for manufacturing a glass substrate for information recording medium, the abrasive has a maximum particle size distribution measured by a laser diffraction scattering method of 3.5 μm or less, and a particle size distribution measured by a laser diffraction scattering method. It is preferable that cumulative 50 volume% diameter D50 in is 0.4 to 1.6 μm.

  According to such a configuration, it is possible to manufacture a glass substrate for information recording media excellent in impact resistance, and further to increase the polishing rate, and to manufacture a glass substrate for information recording media with higher smoothness. Can do. This is considered to be because the abrasive having the particle size as described above can suppress the generation of scratches by polishing while ensuring a high polishing rate.

Further, in the method for producing a glass substrate for information recording medium, the polishing step is used in a state of a polishing liquid in which the abrasive is dispersed in water, and the CeO ₂ content is based on the total amount of the polishing liquid. It is preferable that it is 3-15 mass%.

  According to such a configuration, it is possible to manufacture a glass substrate for information recording media excellent in impact resistance, and further to increase the polishing rate, and to manufacture a glass substrate for information recording media with higher smoothness. Can do.

First of all, since the CeO ₂ content is high as a polishing liquid, it is considered that the polishing rate can be further increased and a glass substrate with higher smoothness can be obtained.

  Further, in the case of a 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, It is difficult to adhere to the surface of the plate, and it is considered that the alkaline earth metal contained in the abrasive is likely to adhere to the surface of the glass base plate. 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 base plate.

  ADVANTAGE OF THE INVENTION According to this invention, it can provide the manufacturing method of the glass substrate for hard disks which has the outstanding surface smoothness and surface cleanliness, and was excellent in impact resistance.

It is a top view which shows the glass substrate for hard disks manufactured by the manufacturing method of the glass substrate for hard disks which concerns on this embodiment. It is a schematic sectional drawing which shows an example of the grinding | polishing apparatus used at the rough grinding | polishing process and the precision grinding | polishing process in the manufacturing method of the glass substrate for hard disks which concerns on this embodiment. It is a partial cross section perspective view which shows the magnetic disk which is an example of the magnetic recording medium using the glass substrate for hard disks manufactured by the manufacturing method of the glass substrate for hard disks which concerns on this embodiment.

  Hereinafter, although the embodiment concerning the present invention is described, the present invention is not limited to these.

  The manufacturing method of the glass substrate for hard disks according to the present embodiment includes a polishing step of polishing the surface of the glass base plate using an abrasive and a polishing pad, and a surface of the polished glass base plate after the polishing step. And a chemical strengthening step for strengthening using a chemical strengthening treatment liquid, and using the glass base plate containing 0.1 to 2% cerium oxide, and the abrasive having a cerium oxide content. 99% by weight or more with respect to the total rare earth oxide (TREO) and an alkaline earth metal content of 10 ppm or less, and the polishing pad has a cerium oxide content of the total rare earth oxide. 99% by weight or more with respect to (TREO) and an alkaline earth metal content of 10 ppm or less are used.

First, the composition of the glass base plate used in the production method of the present invention will be described in detail.
<Glass base plate composition>
In this embodiment, the glass material used as the material of the glass substrate for information recording medium is an aluminosilicate glass material usually used as the material of the glass substrate for information recording medium, and 0.1 to 2% by mass of cerium oxide. If it contains, it will not specifically limit. The aluminosilicate glass is advantageous in that it can be chemically strengthened and can provide a magnetic disk substrate having excellent main surface flatness and substrate strength.

  Next, the skeleton component of the glass base plate will be described.

As the skeleton component of the glass workpiece to be used in the present embodiment, as described above, SiO ₂ is 58 to 70 wt%, _Al 2 _{O 3} is 12 to 18 _wt%, B 2 _{O 3} is 0-3 wt% (However, 0 is included), and the total thereof, that is, the total of SiO ₂ , Al ₂ O _3, and B ₂ O ₃ is 72 to 85 mass%.

SiO ₂ is a component that forms a glass skeleton (matrix). If the content of SiO ₂ is too small, the glass structure becomes unstable and the chemical durability is deteriorated, and the viscosity characteristics at the time of melting are deteriorated, which may impair the moldability. If the content of SiO ₂ is too large, with the productivity becomes poor meltability decreases, sufficient rigidity may become impossible to obtain. Therefore, the content of SiO ₂ is preferably 58 to 70% by mass.

Al ₂ O _{3 is} also a component that forms a skeleton of glass, and contributes to improvement of durability and strength and surface hardness of glass. If the content of Al ₂ O ₃ is too small, the durability and strength of the glass substrate for hard disk may not be sufficient. Further, when the content of Al ₂ O ₃ is too large, intensified devitrification tendency of the glass, it may stable glass formation is difficult. Therefore, the content of Al ₂ O ₃ is preferably 12 to 18% by mass.

B ₂ O ₃ has the effect of improving the chemical durability by improving the meltability and improving the productivity and stabilizing the glass structure by entering the glass skeleton. However, B ₂ O ₃ tends to volatilize when melted, and the glass component ratio tends to become unstable. Further, since the strength is lowered, the hardness is lowered, the glass substrate is easily damaged, the fracture toughness value is reduced, and the substrate tends to be damaged. For these reasons, the content of B ₂ O ₃ is preferably 3% by mass or less. _Further, it is possible to a composition that does not contain B 2 _{O 3.} In the _above, the 0 wt% in the content of 0-3 wt% B 2 _{O 3,} which means that may include aspects that do not contain B 2 _{O 3.} In addition, the notation of “0 mass%” in the glass composition of the present application document is in agreement with this, and means that it may include an embodiment not containing the component (hereinafter, the same notation is agreed).

Then, the total amount of SiO ₂ and _Al 2 _{O 3} and _B 2 _{O 3} w (FMO) is preferably 70 to 85 wt%. This is to stabilize the glass structure. If the total amount is too small, the glass structure tends to become unstable. Moreover, when there is too much this total amount, the viscosity characteristic at the time of a fusion | melting will deteriorate, and there exists a tendency for productivity to fall.

  Next, the alkali component of the glass base plate will be described.

As an alkaline component of the glass base plate used in the present embodiment, as described above, Li ₂ O is 1 to 8% by mass, Na ₂ O is ₂ to 13% by mass, and K ₂ O is 0.2 to ₂ % by mass. And the sum thereof, that is, the sum of Li ₂ O, Na ₂ O and K ₂ O is 3.2 to 23% by mass.

Li ₂ O has a unique property among alkali metal elements, and has a function of improving the solubility of the glass, while greatly improving the Young's modulus by improving the ion filling rate in the glass structure. Has an effect. Li 2 _O content is too small, there is a tendency that it is impossible to exhibit sufficient effect on improvement of the improvement and the Young's modulus of solubility. Further, the content of Li 2 _O, is too large, as described above, there are cases where the surface of the recording layer of the information recording medium serving as a trigger of a very small and thin reaction precipitates. Therefore, the content of Li ₂ O, is preferably 1 to 8 wt%.

Na 2 _O has an effect of lowering the melting temperature of the glass, the effect of increasing the coefficient of linear expansion. Further, it is considered to be a component that greatly affects the effect of chemical strengthening in the chemical strengthening process. That is, when the content of Na ₂ O is too small, not only does the melting temperature tend not to be sufficiently lowered, but the strength cannot be sufficiently increased by the chemical strengthening step. On the other hand, if the content of Na ₂ O is too large, the amount of elution increases and the recording layer may be adversely affected. Therefore, the content of Na ₂ O is preferably _{2 to} 13% by mass. In addition, this content is more than the content in a general glass substrate.

K 2 _O is, have the effect of lowering the melting temperature of the glass, the effect of increasing the coefficient of linear expansion. When the content of K ₂ O is too small, there is a tendency that the melting temperature cannot be lowered sufficiently. On the other hand, when the content of K ₂ O is too large, not only does the amount of elution increase and the recording layer may be adversely affected, but there is a tendency that the strength cannot be sufficiently increased by the chemical strengthening step. This is thought to be due to the fact that the chemical strengthening process replaces potassium ions instead of sodium ions of Na ₂ O to form a strengthened layer and inhibits this exchange. Therefore, the content of K ₂ O is preferably 0.2 to 2% by mass.

Then, Li ₂ O, Na ₂ O and _{K 2} O to the total amount w of (R2 O) is preferably a 11.2 to 17.5% by weight. If the total amount is too small, there is a tendency that the melting temperature cannot be lowered sufficiently. If the total amount is small, the content of Na ₂ O is also small, and chemical strengthening is sufficiently exerted. It tends to be difficult. On the other hand, if the total amount is too large, the amount of elution increases and the recording layer may be adversely affected.

  In addition, MgO, CaO, BaO, SrO, and ZnO, which are alkaline earth components of the glass base plate, have the effect of improving the meltability as well as increasing the thermal expansion coefficient and rigidity. The total amount w (MgO + CaO + BaO + SrO + ZnO) of MgO, CaO, BaO, SrO and ZnO is preferably 1 to 10%. If the total amount is too small, the effect of improving rigidity and improving meltability tends to be insufficient. Moreover, when there is too much this total amount, there exists a tendency for a chemical structure to fall while glass structure becomes unstable and melt productivity falls.

Moreover, as a glass base plate, you may contain components other than the above. Specifically, for example, ZrO ₂ or cerium oxide may be contained. Then, the content of ZrO _2, is preferably from 0 to 5 wt%. Moreover, as content of a cerium oxide, 0-2 mass% is preferable. In addition, cerium oxide has an effect which suppresses generation | occurrence | production of a fine unevenness | corrugation when grind | polishing a glass base plate using the abrasive | polishing agent containing a cerium oxide.

  Moreover, the manufacturing method of the glass substrate for information recording media which concerns on this embodiment will not be specifically limited if the said grinding | polishing process and the said chemical strengthening process are provided. Specifically, the polishing agent used in the polishing step performed before the chemical strengthening step, and the glass base plate that is a raw material of the glass substrate for information recording medium is not particularly limited, except for using the above-described materials, Any conventional production method may be used.

  As a method for manufacturing a glass substrate for hard disk, for example, a disk processing step, a lapping step, a rough polishing step (primary polishing step), a cleaning step, a chemical strengthening step, a precision polishing step (secondary polishing step), and a final cleaning step And the like. The steps may be performed in this order, or the order of the chemical strengthening step and the precision polishing step (secondary polishing step) may be switched. Furthermore, a method including steps other than these may be used. For example, an end surface polishing step may be performed between the lapping step and the rough polishing step (primary polishing step).

Here, the rough polishing process (primary polishing process) in the production method of the present invention will be described in detail.
<Rough polishing process>
The rough polishing step (primary polishing step) is a step of rough polishing the surface of the glass base plate that has been subjected to the lapping step. This rough polishing is intended to remove scratches and distortions remaining in the lapping step described above, 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 base plate. 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 base plate, and the surface direction of a glass base plate. Moreover, an outer peripheral end surface is a surface which has an inclination with respect to the surface direction of the outer peripheral side perpendicular | vertical to the surface direction of a glass base plate, and the surface direction of a glass base plate.

  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, there is a polishing apparatus 1 as shown in FIG. FIG. 2 is a schematic cross-sectional view showing an example of the polishing apparatus 1 used in the rough polishing process and the precision polishing process in the method for manufacturing the glass substrate for hard disk according to the present embodiment.

  A polishing apparatus 1 as shown in FIG. 2 is an apparatus capable of simultaneous grinding on both sides. Further, the polishing apparatus 1 includes an apparatus main body 1a and a polishing liquid supply unit 1b that supplies a polishing liquid to the apparatus main body 1a.

  The apparatus main body 1a includes a disk-shaped upper surface plate 2 and a disk-shaped lower surface plate 3, and they are arranged at intervals in the vertical direction so that they are parallel to each other. Then, the disk-shaped upper surface plate 2 and the disk-shaped lower surface plate 3 rotate in directions opposite to each other.

  A polishing pad 6 for polishing both the front and back surfaces of the glass base plate 10 is attached to each of the opposing surfaces of the disk-shaped upper surface plate 2 and the disk-shaped lower surface plate 3. The polishing pad 6 used in the rough polishing step is not particularly limited as long as it is a polishing pad used in the rough polishing step. Specifically, for example, a hard polishing pad made of polyurethane or the like can be used.

  In addition, a plurality of rotatable carriers 5 are provided between the disk-shaped upper surface plate 2 and the disk-shaped lower surface plate 3. The carrier 5 is provided with a plurality of base plate holding holes 51, and the glass base plate 10 can be disposed in the base plate holding holes 51. For example, the carrier 5 may have 100 base plate holding holes 51 so that 100 glass base plates 10 can be fitted and arranged. Then, 100 glass base plates 10 can be processed by one processing (1 batch).

  The carrier 5 sandwiched between the surface plates 2 and 3 via the polishing pad is the same as the lower surface plate 3 with respect to the rotation center of the surface plates 2 and 3 while rotating while holding the plurality of glass base plates 10. Revolve in the direction. The disk-shaped upper surface plate 2 and the disk-shaped lower surface plate 3 can be operated separately. In the polishing apparatus 1 operating as described above, the polishing slurry 7 is supplied between the upper surface plate 2 and the glass base plate 10 and between the lower surface plate 3 and the glass base plate 10, so that the glass base material is supplied. Rough polishing of the plate 10 can be performed.

  The polishing slurry supply unit 1 b includes a liquid storage unit 11 and a liquid recovery unit 12. The liquid reservoir 11 includes a liquid reservoir main body 11a and a liquid supply pipe 11b having a discharge port 11e extending from the liquid reservoir main body 11a to the apparatus main body 1a. The liquid recovery part 12 was extended to the liquid recovery part main body 12a, the liquid recovery pipe 12b extended from the liquid recovery part main body 12a to the apparatus main body part 1a, and the polishing slurry supply part 1b from the liquid recovery part main body 12a. And a liquid return pipe 12c.

  Then, the polishing slurry 7 put in the liquid storage unit main body 11a is supplied from the discharge port 11e of the liquid supply pipe 11b to the apparatus main body part 1a, and the liquid recovery part main body 12a from the apparatus main body part 1a through the liquid recovery pipe 12b. To be recovered. The recovered polishing slurry 7 is returned to the liquid storage part 11 via the liquid return pipe 12c and can be supplied again to the apparatus main body part 1a.

The polishing liquid 7 used here is a liquid in which an abrasive is dispersed in water, that is, a slurry liquid. Then, as the polishing agent, as described above, it comprises a rare earth oxide, and the content of CeO ₂ is more than 99 mass% relative to the content of the rare earth oxide, the content of alkaline earth metal What is 10 ppm or less with respect to the said abrasive | polishing agent whole quantity is used.

  If such an abrasive | polishing agent is used, the glass substrate for information recording media excellent in impact resistance can be manufactured.

Further, the polishing pad 6 used here is a foam of synthetic resin such as urethane or polyester containing a cerium oxide abrasive. As described above, the polishing pad contains a rare earth oxide, the content of CeO ₂ is 99% by mass or more with respect to the content of the rare earth oxide, and the content of alkaline earth metal is The amount of the abrasive is 10 ppm or less with respect to the total amount of the abrasive.

  This is considered to be due to the following.

First, it is thought that a strengthening layer is suitably formed by the chemical strengthening process mentioned later by using the thing of the above glass compositions as a glass base plate which is a raw material of a glass substrate. Specifically, among Li ₂ O, Na ₂ O, and K ₂ O, which are alkali components of the glass base plate, the content of Na ₂ O is large, and the sodium ions of Na ₂ O are chemically strengthened. This is thought to be because it is easily exchanged for potassium ions contained in.

Next, the polishing agent used in the polishing step performed before the chemical strengthening step uses a high CeO ₂ content and a low alkaline earth metal content, thereby increasing the polishing rate and It is considered that the smoothness of the glass base plate can be sufficiently enhanced. As for the polishing pad, as in the case of the above-described polishing agent, the polishing rate is increased by using a material containing a large amount of CeO ₂ and a small amount of alkaline earth metal, and the smoothness of the glass base plate after polishing. Is considered to be sufficiently increased.

It is considered that the reason why the polishing agent having a high CeO ₂ content can increase the polishing rate and sufficiently increase the smoothness of the polished glass base plate is as follows. First, when the glass base plate and CeO ₂ come into contact with each other in the state where pressure is applied to the surface of the glass base plate during polishing, Si—O bonds, which are the main composition on the surface of the glass base plate, are Ce— It is thought to replace the bond of O. 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 glass base plate after polishing 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 the glass substrate after polishing is used. It is thought that adhesion of alkaline earth metal to the plate is suppressed. It is considered that uniform chemical strengthening is achieved by applying a chemical strengthening step to such a glass base plate in which adhesion of alkaline earth metal is suppressed.

  Note that when polishing with a polishing liquid in which the abrasive is dispersed in water, the alkaline earth metal is dissolved even if the alkaline earth metal is contained in the water. It is considered that the alkaline earth metal contained in the abrasive is likely to adhere to the surface of the glass base plate. Therefore, it is considered that adhesion of alkaline earth metal to the glass base plate after polishing can be sufficiently suppressed by using a polishing agent with little alkaline earth metal.

  From these things, it is thought that the glass substrate for information recording media excellent in impact resistance can be manufactured. Furthermore, according to this manufacturing method, it is considered that a glass substrate for an information recording medium having a sufficiently high polishing rate and a sufficiently high smoothness can be manufactured.

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 base plate. 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 the inhibition of the chemical strengthening process by the alkaline earth metal is suppressed. In the present embodiment, the content of the alkaline earth metal is preferably as low as possible. When the content of the alkaline earth metal is 10 ppm or less with respect to the total amount of the abrasive, a glass substrate for an information recording medium excellent in impact resistance is obtained. It has been found that it can be manufactured.

Further, the abrasive has a CeO ₂ content of 99.99% by mass or more based on the rare earth oxide content, and an alkaline earth metal content of 5 ppm based on the total amount of the abrasive. The following is preferable. By doing so, the manufacturing method of the glass substrate for information recording media excellent in impact resistance can be provided. Furthermore, it is considered that the polishing rate can be further increased and a glass substrate for an information recording medium having higher smoothness can be produced. This is considered to be due to the fact that the content of CeO ₂ that enhances the polishing property is large and the content of alkaline earth metal that can inhibit the chemical strengthening process is small.

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 information recording media excellent in impact resistance can be manufactured, the polishing rate can be further increased, and the glass substrate for information recording media having higher smoothness can be manufactured. This means that the content of the alkaline earth metal that can hinder the chemical strengthening process is small, and the content of CeO ₂ that enhances the polishing property is merely large relative to the rare earth oxide contained in the abrasive. It is thought that this is also due to the large amount of the abrasive.

The abrasive contains a rare earth oxide, the CeO ₂ content is 99% by mass or more with respect to the rare earth oxide content, and the alkaline earth metal content is the total amount of the abrasive. The content of CeO ₂ is preferably 90% by mass or more based on the total amount of the abrasive. Therefore, it is preferable that the abrasive is mostly CeO ₂ as the rare earth oxide, and the content of CeO ₂ is 90% by mass or more based on the total amount of the abrasive. The alkaline earth metal content is very low. In addition, components other than rare earth oxides such as CeO ₂ and alkaline earth metals in the abrasive include those contained in general abrasives used in the production of glass substrates for information recording media. May be. That is, as described above, the abrasive is the same as the general abrasive used in the production of a glass substrate for information recording media except that the content of CeO ₂ is large and the content of alkaline earth metal is small. Can be used.

The polishing liquid 7 is in a state where the abrasive is dispersed in water, and the content of CeO ₂ is preferably 3 to 15% by mass with respect to the total amount of the polishing liquid. By doing so, the glass substrate for information recording media excellent in impact resistance can be manufactured, the polishing rate can be further increased, and the glass substrate for information recording media having higher smoothness can be manufactured. Further, in the case of a 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, It is difficult to adhere to the surface of the plate, and it is considered that the alkaline earth metal contained in the abrasive is likely to adhere to the surface of the glass base plate. 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 base plate.

  The abrasive has a maximum particle size distribution of 3.5 μm or less measured by the laser diffraction scattering method, 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.

  When the particle size of the abrasive is too small, the polishing rate tends to decrease. Moreover, when the particle size of the abrasive is too large, scratches that can be formed on the glass base plate due to polishing tend to occur. Therefore, it is considered that by using an abrasive having the above particle diameter as the abrasive, it is possible to suppress the generation of scratches due to polishing while ensuring a high polishing rate. As a result, a glass substrate for information recording media excellent in impact resistance can be produced, and the polishing rate can be further increased, and a glass substrate for information recording media having higher smoothness can be produced.

  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.

  The polishing liquid 7 preferably has a fluorine content of 5% by mass or less in the rough polishing step.

  The polishing pad 6 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 can be contained. 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, for example, by the following method.

  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 the mixed liquid is depressurized and defoamed to produce a foam-free abrasive dispersion. Next, the foam-free abrasive dispersion is cured using a mold, and a plate-like block in which the abrasive grains are fixed inside and on the surface of the non-foamed body is formed. Subsequently, after the block is taken out from the mold, both sides of the block are ground and processed to a predetermined thickness.
<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, for example, a step of immersing a glass base plate in a chemical strengthening treatment liquid and the like can be mentioned. By doing so, a chemical strengthening layer can be formed in the surface of a glass base plate, for example, a 5 micrometer area | region from the glass base plate surface. And by forming a chemical strengthening layer, impact resistance, vibration resistance, heat resistance, etc. can be improved.

  More specifically, in the chemical strengthening step, by immersing the glass base plate in a heated chemical strengthening treatment liquid, alkali metal ions such as lithium ions and sodium ions contained in the glass base plate are potassium having a larger ion radius. It is carried out by an ion exchange method for substituting alkali metal ions such as ions. 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 base plate is strengthened.

In this embodiment, it is thought that a strengthening layer is suitably formed by this chemical strengthening process by using the glass composition as described above as a glass base plate that is a raw material of the glass substrate. Specifically, among Li ₂ O, Na ₂ O, and K ₂ O, which are alkali components of the glass base plate, the content of Na ₂ O is large, and the sodium ions of Na ₂ O are chemically strengthened. This is thought to be because it is easily exchanged for potassium ions contained in. Further, since the polishing agent used in the polishing step before the chemical strengthening step, here the rough polishing step, is an abrasive having the above composition, the alkaline earth metal adhering to the surface of the glass base plate 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 base plate 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 step in the method for producing a glass substrate for hard disk. Specifically, for example, a melt containing potassium ions, a melt containing potassium ions and sodium ions, and the like can be given.

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 base plate. At that time, a melt obtained by melting potassium nitrate and a melt obtained by melting sodium nitrate are preferably mixed in approximately the same amount.
<Disk processing process>
In the disk processing step, a through-hole 10a is formed in the center portion of a glass base plate formed from a glass material having a predetermined composition so that the inner periphery and the outer periphery are concentric circles as shown in FIG. This is a process of processing into a disk-shaped glass base plate 10. Specifically, for example, processing is performed as follows. First, a glass base plate that is formed into a plate shape and has a glass composition that will be described later and has a thickness of 0.95 mm is cut into a square having a predetermined size.

  Then, a circular cut line is formed on one surface of the cut glass base plate so as to form the inner circumference and the outer circumference described above with a glass cutter. And the glass base plate in which this cut line was formed is heated from the surface of the side in which the cut line was formed. By doing so, the said cut line becomes deep toward the other surface of a glass base plate. And it processes into the disk shaped glass base plate 10 in which the through-hole 10a was formed in the center part so that an inner periphery and an outer periphery may become a concentric circle.

  In this disk processing step, for example, the outer diameter r1 is 2.5 inches (about 64 mm), 1.8 inches (about 46 mm), 1 inch (about 25 mm), 0.8 inches (about 20 mm), etc., and the thickness is It is processed into a disk-shaped glass base plate of 2 mm, 1 mm, 0.63 mm or the like. Further, when the outer diameter r1 is 2.5 inches (about 64 mm), the inner diameter r2 is processed to 0.8 inches (about 20 mm) or the like. FIG. 1 is a top view showing a glass substrate for hard disk manufactured by the method for manufacturing a glass substrate for hard disk according to the present embodiment.

Moreover, the manufacturing method of the glass base plate shape | molded in plate shape is not specifically limited, For example, what was manufactured by the float glass process etc. is mentioned. The float method is, for example, a method in which a molten liquid obtained by melting a glass material is poured onto molten tin and solidified as it is. Since the obtained glass base plate is a free surface of glass and the other surface is an interface between glass and tin, the smoothness is high, for example, the arithmetic average roughness Ra is 0.001 μm. The following mirror surface is provided. And as the thickness, a 0.95 mm thing is mentioned, for example. In addition, the surface roughness, for example Ra, of a glass base plate or a glass substrate can be measured using a general surface roughness measuring machine.
<Wrapping process>
The lapping step is a step of processing the glass base plate to a predetermined plate thickness. Specifically, the process etc. which grind | polish (lapping) the both surfaces of a glass base plate are mentioned. By processing in this way, the parallelism, flatness and thickness of the glass base plate can be adjusted. Further, this lapping step may be performed once or twice or more. For example, when it is performed twice, the parallelism, flatness and thickness of the glass base plate are preliminarily adjusted in the first lapping process (first lapping process), and glass is used in the second lapping process (second lapping process). It becomes possible to finely adjust the parallelism, flatness and thickness of the base plate.

  More specifically, examples of the first lapping step include a step of making the entire surface of the glass base plate have a substantially uniform surface roughness. At that time, for example, when the arithmetic average roughness Ra of the glass base plate is measured at a plurality of locations, the difference between the minimum value and the maximum value of Ra obtained is preferably about 0.01 to 0.4 μm.

  The second lapping step may include a process of grinding the main surface of the roughened glass substrate using a fixed abrasive polishing pad. In this second wrapping step, for example, a roughened glass substrate is set in a wrapping apparatus, and a three-dimensional fixed abrasive with a surface pattern such as diamond tile is used. The surface can be wrapped.

When the second lapping step is performed, polishing performed in a rough polishing step described later can be performed efficiently. Moreover, it is preferable that surface roughness Ra of the glass base plate used for the grinding | polishing process performed by the 2nd lapping process is 0.10 micrometer or less. The surface roughness Ra is preferably 0.01 μm or more. If it is smaller than 0.01 μm, the surface becomes too smooth, and processing in the lapping process may be difficult.
<Washing process>
The cleaning step is a step of cleaning the glass base plate that has been subjected to the rough polishing step.

  The glass base plate after the rough polishing by the rough polishing step is preferably cleaned by a cleaning step. The washing process is not particularly limited. Specifically, for example, the following washing steps are mentioned.

  First, the glass base plate is washed with an alkaline detergent having a pH of 13 or more, and the glass base plate is rinsed. Next, the glass base plate is washed with an acid detergent having a pH of 1 or less, and the glass base plate is rinsed. Finally, the glass base plate is cleaned using a hydrofluoric acid (HF) solution. Regarding cerium oxide, it is most efficient to perform cleaning in the order of alkali cleaning, acid cleaning, and HF cleaning. This is done by first dispersing and removing the abrasive with an alkaline detergent, then dissolving and removing the abrasive with an acid detergent, and finally etching the glass substrate with HF to remove the abrasive that is deeply stuck in the glass substrate. To do.

  The cleaning step is preferably performed in separate tanks for alkali cleaning, acid cleaning, and HF cleaning. This is because 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 large amount of abrasive, and therefore there is a tendency that the inside of the substrate cannot be uniformly etched. 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 base plate 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 base plate is taken out. And the taken-out glass base plate is immersed in a neutral detergent liquid. At that time, 120 kHz ultrasonic vibration is applied to the neutral detergent solution. Finally, the glass base plate is taken out, rinsed with pure water, and IPA dried.

Further, the glass workpiece after the washing 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 base plate subjected to the chemical strengthening step, which can inhibit the chemical strengthening step. Therefore, it is considered that chemical strengthening occurs uniformly on the entire surface of the glass base plate, 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 base plate after the cleaning step, the chemical strengthening 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 base plate after the washing step, the more preferable. This is because the alkaline earth metal remaining on the surface of the glass base plate polished in the polishing step before the chemical strengthening step inhibits the chemical strengthening step and inhibits uniform chemical strengthening. It is. In the present embodiment, the smaller the amount of alkaline earth metal remaining on the surface of the glass base plate after the cleaning step, the better. The amount is 10 ng / cm ² or less, and the impact resistance is excellent. It has been found that a glass substrate for a hard disk can be produced.

The glass substrate after the rough polishing is cleaned so that the amount of cerium oxide on the surface of the glass substrate is 0.125 ng / cm ² or less. If the amount of cerium oxide on the surface of the glass base plate is too large, the flatness of the glass base plate after precision polishing by the precision polishing step described later tends to be not good.
<Precision polishing process (secondary polishing process)>
The precision polishing step is, for example, a mirror polishing process that finishes a smooth mirror surface having a surface roughness (Rmax) of about 6 nm or less while maintaining the flat and smooth main surface obtained in the rough polishing step. 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 step, an abrasive that causes fewer scratches even if the abrasiveness is lower than the abrasive used in the rough polishing step is used. Specifically, for example, a polishing agent containing silica-based abrasive grains (colloidal silica) having a particle diameter lower than that of the polishing agent used in the rough polishing step. 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 base plate, a polishing pad and a glass base plate are slid relatively, and the surface of a glass base plate is mirror-polished.
<Final cleaning process>
The final cleaning step is a step of cleaning so as to remove the abrasive from the surface of the polished glass base plate. Specifically, the process etc. which are performed as follows with respect to the glass base plate which finished the precision grinding | polishing process are mentioned, for example.

  First, the glass base plate that has been subjected to the precision polishing step is stored in water without being dried (including natural drying), and is transported to the next cleaning step in a wet state. This is because if the glass base plate is dried with the polishing residue remaining, it may be difficult to remove the abrasive (colloidal silica) by the cleaning treatment. The cleaning here is required to remove the abrasive without exposing the surface of the mirror-finished glass base plate.

  And the magnetic recording medium using the glass substrate for hard disks manufactured by the manufacturing method of the glass substrate for hard disks which concerns on the said embodiment is demonstrated.

  FIG. 3 is a partial cross-sectional perspective view showing a magnetic disk as an example of a magnetic recording medium using the glass substrate for hard disk manufactured by the method for manufacturing a glass substrate for hard disk according to the present embodiment. The magnetic disk D includes a magnetic film 102 formed on the main surface of a circular hard disk glass substrate 101. For the formation of the magnetic film 102, a known method is used. For example, a formation method (spin coating method) in which a magnetic film 102 is formed by spin-coating a thermosetting resin in which magnetic particles are dispersed on a glass substrate 101 for hard disk, or magnetism by sputtering on the glass substrate 101 for hard disk. Examples include a forming method for forming the film 102 (sputtering method) and a forming method for forming the magnetic film 102 on the glass substrate 101 for hard disk by electroless plating (electroless plating method).

  The thickness of the magnetic film 102 is about 0.3 to 1.2 μm when the spin coating method is used, and is about 0.04 to 0.08 μm when the sputtering method is used. In some cases, the thickness is about 0.05 to 0.1 μm. From the viewpoint of thinning and densification, film formation by sputtering is preferable, and film formation by electroless plating is preferable.

  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, CoPt, CoCr, CoNi, CoNiCr, CoCrTa, CoPtCr, CoNiPt, CoNiCrPt, CoNiCrTa, CoCrPtTa, CoCrPtB, CoCrPtSiO, and the like whose main component is Co can be given.

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.

  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.

  Furthermore, an underlayer or a protective layer may be provided on the magnetic film 102 as necessary. 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 multilayer 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 glass substrate 101 for hard disk in this embodiment, the glass substrate 101 for hard disk 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 case where the hard disk glass substrate 101 in this embodiment is used as a magnetic recording medium has been described. However, the present invention is not limited to this, and the hard disk glass substrate 101 in this embodiment is a magneto-optical disk. It can also be used for optical discs and the like.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

First, two types of glass base plates having the glass composition (% by mass) shown in Table 1, 7 types of abrasives shown in Table 2, and 6 types of polishing pads shown in Table 3 were prepared. The composition of the polishing agent and the polishing pad is such that components other than rare earth oxides such as CeO ₂ and alkaline earth metals are included in general polishing agents and polishing pads used in the production of glass substrates for information recording media. Is included. That is, except that instead of the content of the rare earth oxide or an alkaline earth metal such as CeO _2, is similar to that of a typical abrasive and a polishing pad used in the manufacture of a glass substrate for information recording medium.

  Moreover, in Table 1, "-" shows that it is not contained except the thing inevitably mixed. In Table 2, “-” means that the abrasive is first dissolved with sulfuric acid, and the solution is detected by ICP-AES (inductively coupled plasma emission spectrometer) for the elements contained in the abrasive. , Indicating no detection.

Example 1
Using the glass base plate 1 shown in Table 1, a disk processing step and a lapping step were performed by a known method. And the rough polishing process similar to the well-known method was given except having used the abrasive | polishing agent 1 and the polishing pad 1 which are shown in Table 2. Thereafter, a cleaning process was performed by a known method.

  Specifically, first, the glass base plate was immersed in a cleaning solution containing 1% by mass of HF and 3% by mass of sulfuric acid for 6 minutes. At that time, an ultrasonic vibration of 80 kHz was applied to the cleaning liquid. Thereafter, the glass base plate was taken out. And the taken-out glass base plate was immersed in neutral detergent liquid for 6 minutes. At that time, 120 kHz ultrasonic vibration was applied to the neutral detergent solution. Finally, the glass base plate was taken out, rinsed with pure water, and IPA dried.

In addition, as shown in Table 4, the alkaline earth metal (ion contamination) remaining on the surface of the glass base plate after washing in the washing step was 9 ng / cm ² or less.

  This ion contamination was measured as follows.

  First, the glass base plate after being washed in the washing step was immersed in 20 ml of ultrapure water (20 ° C.) of 18 MΩ · cm or more, and allowed to stand for 10 minutes. At this time, stirring or the like was not performed, and during the standing, the lid of the container was closed and the work was further performed in a class 100 room. After standing for 10 minutes, only the glass base plate was taken out, and the ultrapure water in which the glass base plate was immersed was contained using an ion black graph (ICS-2100 manufactured by Dionex Corporation). The amount of earth metal was measured. Then, the amount of alkaline earth metal (ion contamination) remaining on the surface of the glass base plate after being washed in the washing step was calculated from the measured amount of alkaline earth metal.

  Thereafter, a chemical strengthening step, a precision polishing step (secondary polishing step), and a final cleaning step were performed by a known method.

  In addition, as a chemical strengthening process, specifically, first, a mixed melt obtained by melting potassium nitrate and sodium nitrate was prepared. In addition, this mixed melt is mixed so that the mixing ratio of potassium nitrate and sodium nitrate is 1: 1 by mass ratio. Then, this mixed melt was heated to 400 ° C., and the washed glass base plate was immersed in the heated mixed melt for 60 minutes.

(Example 2)
In the rough polishing step, the same as Example 1 except that the abrasive 2 shown in Table 2 was used.

In addition, as shown in Table 4, the alkaline earth metal (ion contamination) remaining on the surface of the glass base plate after washing in the washing step was 3 ng / cm ² or less.

(Example 3)
In the rough polishing step, it is the same as Example 1 except that the abrasive 3 shown in Table 2 was used.

In addition, as shown in Table 4, the alkaline earth metal (ion contamination) remaining on the surface of the glass base plate after the washing in the washing step was 8 ng / cm ² or less.

Example 4
In the rough polishing step, the same as Example 1 except that the abrasive 4 shown in Table 2 was used.

In addition, as shown in Table 4, the alkaline earth metal (ion contamination) remaining on the surface of the glass base plate after washing in the washing step was ² ng / cm ² or less.

(Example 5)
The rough polishing process is the same as that of Example 4 except that the polishing pad 2 shown in Table 3 was used.

In addition, as shown in Table 4, the alkaline earth metal (ion contamination) remaining on the surface of the glass base plate after washing in the washing step was 5 ng / cm ² or less.

(Example 6)
The rough polishing process is the same as that of Example 4 except that the polishing pad 3 shown in Table 3 was used.

In addition, as shown in Table 4, the alkaline earth metal (ion contamination) remaining on the surface of the glass base plate after washing in the washing step was 3 ng / cm ² or less.

(Comparative Example 1)
The rough polishing process is the same as that of Example 1 except that the polishing pad 4 shown in Table 3 was used.

In addition, as shown in Table 4, the alkaline earth metal (ion contamination) remaining on the surface of the glass base plate after the washing in the washing step was 8 ng / cm ² or less.

(Comparative Example 2)
In the rough polishing step, it is the same as Comparative Example 1 except that the abrasive 5 shown in Table 2 was used.

In addition, as shown in Table 4, the alkaline earth metal (ion contamination) remaining on the surface of the glass base plate after washing in the washing step was 7 ng / cm ² or less.

(Comparative Example 3)
In the rough polishing step, it is the same as Comparative Example 1 except that the abrasive 6 shown in Table 2 was used.

In addition, as shown in Table 4, the alkaline earth metal (ion contamination) remaining on the surface of the glass base plate after washing in the washing step was 19 ng / cm ² or less.

(Comparative Example 4)
The rough polishing process is the same as Comparative Example 3 except that the polishing pad 6 shown in Table 3 was used.

In addition, as shown in Table 4, the alkaline earth metal (ion contamination) remaining on the surface of the glass base plate after washing in the washing step was 25 ng / cm ² or less.

(Comparative Example 5)
In the rough polishing step, it is the same as Comparative Example 1 except that the abrasive 7 shown in Table 2 and the polishing pad 5 shown in Table 3 were used.

In addition, as shown in Table 4, the alkaline earth metal (ion contamination) remaining on the surface of the glass base plate after washing in the washing step was 53 ng / cm ² or less.

(Comparative Example 6)
In the rough polishing step, the same as Example 1 except that the abrasive 5 shown in Table 2 was used.

In addition, as shown in Table 4, the alkaline earth metal (ion contamination) remaining on the surface of the glass base plate after washing in the washing step was 11 ng / cm ² or less.

(Comparative Example 7)
The rough polishing process is the same as that of Example 1 except that the glass base plate 2 shown in Table 1 was used.

In addition, as shown in Table 4, the alkaline earth metal (ion contamination) remaining on the surface of the glass base plate after washing in the washing step was 15 ng / cm ² or less.

(Cracking test)
First, a magnetic disk was manufactured by forming a magnetic film on the surface of the obtained glass substrate for information recording media by a known method. And the hard disk drive device (HDD) provided with the magnetic disk was manufactured.

Then, 10 HDDs were dropped at each level so that an impact of 1000 G was applied to the obtained HDD. At that time, “◎” if the number of the magnetic disk provided in the HDD is broken is “0”, “◯” if it is 1 or 2 times, “△” if it is 3-5 times or more, 6 If more, it was evaluated as “×”. 1G is about 9.80665 m / s ² .

  The results are shown in Table 4 together with the amount of the glass base plate, abrasive and ion contamination used.

  As is apparent from the results in Table 4, a glass base plate containing 0.1 to 2% cerium oxide was used, and the cerium oxide content was 99% by weight or more based on the total rare earth oxide (TREO). In addition, an abrasive having an alkaline earth metal content of 10 ppm or less is used, and the cerium oxide content is 99% by weight or more based on the total rare earth oxide (TREO). In Examples 1 to 7 using a polishing pad having a content of 10 ppm or less, the occurrence of cracks in the crack test was suppressed.

On the other hand, when the abrasive does not satisfy the above range (Comparative Example 6), when the polishing pad does not satisfy the above range (Comparative Example 1), or the abrasive that does not satisfy the above range. When the polishing pad was combined (Comparative Examples 2 to 5), the amount of ion contamination was more than 5 ng / cm ² , and the impact resistance was inferior. Further, when cerium oxide was not included in the composition of the glass base plate (Comparative Example 7), the amount of ion contamination was increased, and the impact resistance was also inferior to that of the above example.

DESCRIPTION OF SYMBOLS 1 Polishing apparatus 6 Polishing pad 10 Glass base plate 101 Glass substrate for hard disk 102 Magnetic film

Claims (6)

A polishing step of polishing the surface of the glass base plate using an abrasive and a polishing pad;
A chemical strengthening step of strengthening the surface of the polished glass base plate using a chemical strengthening treatment liquid after the polishing step;
As the glass base plate, one containing 0.02 to 1.0% by mass of cerium oxide,
As the abrasive, a cerium oxide content of 99 wt% or more with respect to the total rare earth oxide (TREO) and an alkaline earth metal content of 10 ppm or less,
For the hard disk, the polishing pad having a cerium oxide content of 99 wt% or more with respect to the total rare earth oxide (TREO) and an alkaline earth metal content of 10 ppm or less is used. A method for producing a glass substrate.   The abrasive is characterized in that the cerium oxide content is 99% by weight or more with respect to the total rare earth oxide (TREO) and the alkaline earth metal content is 5 ppm or less. The manufacturing method of the glass substrate for hard disks of Claim 1.   The method for producing a glass substrate for a hard disk according to claim 1 or 2, wherein the cerium oxide content is 90% by mass or more based on the abrasive. In the manufacturing method of the glass substrate for hard disk,
Before the chemical strengthening step, further comprising a cleaning step of cleaning the glass base plate polished in the polishing step,
The method for producing a glass substrate for a hard disk according to any one of claims 1 to 3, wherein the alkaline earth metal remaining on the surface of the glass base plate after washing in the washing step is 10 ng / cm ² or less.   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 1. It is 6 micrometers, The manufacturing method of the glass substrate for hard disks of any one of Claims 1-4. The polishing step is used in a state of a polishing liquid in which the abrasive is dispersed in water,
The method for producing a glass substrate for a hard disk according to any one of claims 1 to 5, wherein a content of the cerium oxide is 3 to 15% by mass with respect to the total amount of the polishing liquid.