JPWO2011096310A1 - Glass substrate for information recording medium, method for producing glass substrate for information recording medium, and information recording medium - Google Patents

Abstract

In order to provide a glass substrate for an information recording medium having a chemically strengthened layer by chemical strengthening and having a sufficiently small TIR in the circumferential direction, a portion having a chemically strengthened layer on the surface forming the recording layer and excluding the chemically strengthened layer Is SiO2: 55-75 mass%, Al2O3: 5-18 mass%, Li2O: 1-10 mass%, Na2O: 3-15 mass%, K2O: 0.1-5 mass%, provided that the total amount of Li2O + Na2O + K2O: 10 to 25 mass%, MgO: 0.1 to 5 mass%, CaO: 0.1 to 5 mass%, ZrO2: 0 to 8 mass%, and the mass ratio of (MgO + CaO) to (Li2O + Na2O + K2O) is 0.00. 10 ≦ (MgO + CaO) / (Li 2 O + Na 2 O + K 2 O) ≦ 0.80, a disk-shaped glass substrate having an outer periphery radius of r1, Circumferentially one round of the TIR after the polishing by step, a glass substrate for an information recording medium is 1μm or less in the position of 0.75r1 from the center of the surface.

Description

  The present invention relates to a glass substrate for an information recording medium used for an information recording medium having a recording layer for recording information using properties such as magnetism, light, and magnetomagnetism, a method for producing the glass substrate for information recording medium, and information recording It relates to the medium.

  Among information recording media having a recording layer for recording information using properties such as magnetism, light, and magnetomagnetism, there is a magnetic disk as a representative one. Conventionally, aluminum substrates have been widely used as magnetic disk substrates. However, in recent years, with the demand for a reduction in the flying height of the magnetic head for improving the recording density, the surface smoothness is superior to that of an aluminum substrate and the surface defects are few, so that the flying height of the magnetic head can be reduced. The proportion of using glass substrates as magnetic disk substrates is increasing.

Such a glass substrate for an information recording medium such as a magnetic disk is required to have high impact resistance and vibration resistance. Therefore, there has been proposed a glass substrate that has improved impact resistance and vibration resistance by strengthening the surface by chemically strengthening aluminosilicate glass containing SiO ₂ , Al ₂ O ₃ , Li ₂ O and the like. (See Patent Document 1).

JP 2004-63062 A

  Chemical strengthening treatment compresses the surface of the glass substrate by exchanging alkali metal ions such as lithium ions and sodium ions contained in the glass substrate with alkali metal ions such as potassium ions having a larger ion radius than these ions. This is a method of strengthening a glass substrate by forming a stress layer (chemical strengthening layer). Usually, it is carried out by immersing the glass substrate in a heated chemical strengthening treatment solution.

  According to the description of Patent Document 1, a glass substrate having a surface that is strengthened and has a small surface roughness is obtained by performing such chemical strengthening treatment and polishing treatment on an aluminosilicate glass by a predetermined method. It is supposed to be possible.

  On the other hand, in order to further reduce the flying height of the magnetic head, it is not sufficient to reduce the surface roughness of the glass substrate, and TIR (Total Indicated Runout) in the circumferential direction, which is an index indicating the flatness of the glass substrate. It was found that it is important to reduce the size.

  However, in the method described in Patent Document 1, since the uniformity of ion exchange during the chemical strengthening treatment is not sufficient, the balance of compressive stress acting on the surface is lost, flatness is deteriorated, and the TIR in the circumferential direction is sufficiently increased. There is a problem that it is difficult to reduce the size. Furthermore, there is a problem that the TIR in the circumferential direction may be deteriorated due to thermal deformation of the glass substrate during the chemical strengthening treatment.

  The present invention has been made in view of the technical problems as described above, and an object of the present invention is to provide a glass substrate for an information recording medium that includes a chemical strengthening layer formed by a chemical strengthening treatment and has a sufficiently small circumferential TIR. It is another object of the present invention to provide a method for producing a glass substrate for an information recording medium and an information recording medium.

  In order to solve the above problems, the present invention has the following features.

1. A disk-shaped glass substrate having a chemical strengthening layer on the surface for forming a recording layer,
The portion excluding the chemical strengthening layer is
SiO _2: 55~75% by weight,
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 wt%,
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,
The mass ratio of (MgO + CaO) to (Li ₂ O + Na ₂ O + K ₂ O) is
The glass composition is in the range of 0.10 ≦ (MgO + CaO) / (Li ₂ O + Na ₂ O + K ₂ O) ≦ 0.80,
Wherein when the radius of the outer circumference of the glass substrate was set to r _1, a glass substrate for information recording medium, wherein the TIR from the center in the circumferential direction one turn at the position of 0.75 r ₁ of said surface is 1μm or less.

2. The glass substrate has an inner hole in the center of the surface,
When the radius of the outer periphery of the glass substrate is r ₁ and the radius of the inner hole is r ₀ , the TIR for one round in the circumferential direction at a position of (2r ₀ + r ₁ ) / 3 from the center of the surface is 0.5 μm. 2. The glass substrate for information recording media as described in 1 above, which is as follows.

  3. 3. The glass substrate for information recording media according to 1 or 2, wherein the glass composition contains neither As (arsenic) nor Sb (antimony).

  4). The glass composition includes V (vanadium), Mn (manganese), Ni (nickel), P (phosphorus), Nb (niobium), Mo (molybdenum), Sn (tin), Ce (cerium), and Ta (tantalum). And the glass substrate for an information recording medium according to any one of 1 to 3 above, which contains at least one polyvalent element selected from Bi (bismuth).

  5. 5. The information recording medium as described in 4 above, wherein the glass composition contains at least one polyvalent element selected from P (phosphorus), Sn (tin) and Ce (cerium). Glass substrate.

  6). The glass substrate for an information recording medium according to any one of 1 to 5, wherein the thickness is 0.635 mm to 2 mm.

7). SiO _2: 55~75% by weight,
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 wt%,
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,
The mass ratio of (MgO + CaO) to (Li ₂ O + Na ₂ O + K ₂ O) is
A grinding step of grinding a glass substrate made of a glass composition in a range of 0.10 ≦ (MgO + CaO) / (Li ₂ O + Na ₂ O + K ₂ O) ≦ 0.80 to a predetermined thickness;
A polishing step of reducing the surface roughness by polishing the surface of the glass substrate for forming the recording layer;
A chemical strengthening treatment step of strengthening the glass substrate by ion exchange, and a manufacturing method of a disk-shaped glass substrate for an information recording medium,
When the radius of the outer circumference of the glass substrate was set to r _1, TIR circumferential one rotation after the polishing by the polishing process, and characterized in that a 1μm or less at the position of 0.75 r ₁ from the center of said surface A method for manufacturing a glass substrate for an information recording medium.

  8). 8. The method for producing a glass substrate for an information recording medium according to 7, wherein the chemical strengthening treatment step is performed after the grinding step.

  9. 9. The glass for an information recording medium according to 7 or 8, wherein the polishing step is performed after the chemical strengthening treatment step to reduce the surface roughness of the surface of the glass substrate strengthened by ion exchange. A method for manufacturing a substrate.

  10. 10. The method for producing a glass substrate for an information recording medium according to 9, wherein a polishing amount in the polishing step is 0.5 μm to 10 μm.

  11. 9. The glass for an information recording medium according to 7 or 8, wherein the chemical strengthening treatment step is performed after the polishing step to perform ion exchange on the surface of the glass substrate whose surface roughness has been reduced by polishing. A method for manufacturing a substrate.

  12 12. The method for producing a glass substrate for information recording medium as described in 11 above, wherein the polishing amount in the polishing step is 30 μm or more.

  13. The said 11 or 12 characterized by further reducing the surface roughness of the surface of the said glass substrate strengthened by ion exchange by performing a 2nd grinding | polishing process further after the said chemical strengthening process process. The manufacturing method of the glass substrate for information recording media of.

  14 14. The method for producing a glass substrate for an information recording medium as described in 13 above, wherein the polishing amount in the second polishing step is 0.5 μm to 10 μm.

  15. 15. The information recording medium according to any one of 7 to 14, wherein the polishing step includes a rough polishing step having a high polishing rate and a fine polishing step having a polishing rate lower than that of the rough polishing step. Method for manufacturing glass substrate.

  16. 16. The method for manufacturing a glass substrate for an information recording medium according to any one of 7 to 15, wherein an oscar type polishing machine is used in the polishing step.

  17. 17. The method for producing a glass substrate for information recording media according to any one of 7 to 16, wherein a grinding amount in the grinding step is 100 μm or more.

18. The glass substrate for information recording media according to any one of 1 to 6,
An information recording medium comprising: a recording layer for recording information provided on the surface of the glass substrate for information recording medium.

  19. 19. The information recording medium as described in 18 above, wherein the recording layer is a magnetic layer for recording information by magnetism.

According to the present invention, for the aluminosilicate glass having the above components, the mass ratio of the alkaline earth metal component (MgO + CaO) to the alkali metal component (Li ₂ O + Na ₂ O + K ₂ O) is in the above range. Therefore, the uniformity of ion exchange during the chemical strengthening treatment is high, and the compressive stress can be applied uniformly to the surface of the glass substrate. Moreover, it has moderate heat resistance and suppresses thermal deformation of the glass substrate during the chemical strengthening treatment. As a result, it is possible to provide a glass substrate for an information recording medium, a method for producing the glass substrate for an information recording medium, and an information recording medium having a chemical strengthening layer by chemical strengthening treatment and having a sufficiently small TIR in the circumferential direction. Become.

It is a schematic diagram of the glass substrate for information recording media of this embodiment. It is a flowchart which shows the order of a grinding process, a grinding | polishing process, and a chemical strengthening process. It is sectional drawing which shows the structure of an Oscar double-side polisher. It is a figure which shows typically the motion of the upper and lower polishing dishes and a glass substrate in an Oscar double-side polisher. It is a schematic diagram of the information recording medium of this embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. 1 to 5, but the present invention is not limited to the embodiments.

(Glass composition)
In the glass substrate for information recording medium of the present embodiment, the portion excluding the chemical strengthening layer on the surface is
SiO _2: 55~75% by weight,
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 wt%,
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,
The mass ratio of (MgO + CaO) to (Li ₂ O + Na ₂ O + K ₂ O) is
Consisting 0.10 ≦ (MgO ₊ CaO) / glass composition is in the range of _{(Li 2 O + Na 2 O} + K 2 O) ≦ 0.80.

  The reason why each component is limited to the above range is as follows.

SiO ₂ is an important component for forming a glass network structure, and greatly contributes to chemical durability. If the content of SiO ₂ is less than 55% by mass, chemical durability may be deteriorated. Conversely, if it exceeds 75 mass%, the melting temperature becomes too high. Therefore the content of SiO ₂ is required to be in the range of 55 to 75 wt%. Among these, Preferably it is the range of 60-70 mass%.

Al ₂ O ₃ is an important component that forms a network structure together with SiO ₂ , and has a function of improving ion exchange performance as well as improving chemical durability. When the content of Al ₂ O ₃ is less than 5% by mass, chemical durability and ion exchange performance may be deteriorated. Conversely, when it exceeds 18 mass%, devitrification resistance will deteriorate. For this reason, the content of Al ₂ O ₃ needs to be in the range of 5 to 18% by mass. Among these, Preferably it is the range of 7-16 mass%.

Li ₂ O is a component necessary for performing chemical strengthening treatment by ion exchange. In the chemical strengthening treatment, the glass substrate is strengthened by ion exchange of Li ⁺ ions in the glass with Na ⁺ ions and K ⁺ ions in the chemical strengthening treatment liquid. When the content of Li ₂ O is less than 1% by mass, this ion exchange performance is lowered, and the effect of improving the meltability cannot be obtained. Conversely, when it exceeds 10 mass%, devitrification resistance and chemical durability will deteriorate. Therefore, the content of Li ₂ O needs to be in the range of 1 to 10% by mass. Among these, Preferably it is the range of 3-6 mass%.

Na ₂ O is a component necessary for performing chemical strengthening treatment by ion exchange. In the chemical strengthening treatment, the glass substrate is strengthened by ion exchange of Na ⁺ ions in the glass with K ⁺ ions in the chemical strengthening treatment liquid. When the content of Na ₂ O is less than 3% by mass, the ion exchange performance is lowered and the meltability and devitrification resistance are deteriorated. Conversely, when it exceeds 15 mass%, chemical durability will fall. Therefore, the content of Na ₂ O needs to be in the range of 3 to 15% by mass. Among these, Preferably it is the range of 6-10 mass%.

K ₂ O has an effect of improving the meltability. If the content of K ₂ O is less than 0.1% by mass, the effect of improving the meltability cannot be obtained. Conversely, if it exceeds 5% by mass, the chemical durability is lowered. Therefore, the content of K ₂ O is set in the range of 0.1 to 5% by mass. Among these, Preferably it is the range of 0.1-3 mass%.

_Then, the total amount of _{Li 2 O + Na 2 O +} K 2 O in the range of 10 to 25 wt%. If the total amount is less than 10% by mass, a sufficient improvement effect of melting property cannot be obtained, and an alkali mixing effect cannot be obtained, so that chemical durability is also lowered. On the contrary, when the total amount exceeds 25% by mass, the chemical durability is lowered. More preferably, it is the range of 12-23 mass%.

  MgO has the effect of increasing the rigidity and improving the meltability. If the content of MgO is less than 0.1% by mass, the effect of increasing the rigidity and the effect of improving the meltability cannot be obtained. Conversely, if the content exceeds 5% by mass, the glass structure becomes unstable and the devitrification resistance Sexuality will deteriorate. Therefore, the content of MgO is set in the range of 0.1 to 5% by mass. Among these, Preferably it is the range of 0.3-3.5 mass%.

  CaO has the effect of increasing the linear thermal expansion coefficient and rigidity and improving the meltability. If the CaO content is less than 0.1% by mass, the effect of increasing the linear thermal expansion coefficient and the rigidity cannot be sufficiently obtained. Conversely, if the content exceeds 5% by mass, the glass structure becomes unstable and the devitrification resistance Will get worse. Therefore, the content of CaO is set in the range of 0.1 to 5% by mass. Among these, Preferably it is the range of 0.5-4.0 mass%.

ZrO ₂ has the effect of improving the chemical durability and increasing the rigidity, and may be contained as necessary. However, when the content of ZrO ₂ exceeds 8% by mass, the devitrification resistance is deteriorated. Therefore, the content of ZrO ₂ is set in the range of 0 to 8% by mass. Among these, Preferably it is the range of 0-7 mass%.

_Further, the mass ratio of (MgO + CaO) for _{(Li 2 O + Na 2 O} + K 2 O), was _{0.10 ≦ (MgO + CaO) /} (Li 2 O + Na 2 O + K 2 O) ≦ 0.80. By setting the mass ratio of the alkaline earth metal component (MgO + CaO) to the alkali metal component (Li ₂ O + Na ₂ O + K ₂ O) within the above range, the glass material has appropriate heat resistance and is thermally deformed during the strengthening treatment. Can be prevented. In addition, since the ion exchange is highly uniform and a uniform compressive stress can be applied to the glass substrate surface, the flatness (circumferential direction TIR) of the substrate can be suppressed.

If the mass ratio is less than 0.10, the heat resistance of the glass material is too low, so that thermal deformation during the tempering treatment cannot be avoided, and the chemical durability of the glass material is deteriorated. When the mass ratio exceeds 0.80, it is difficult to perform ion exchange so that the compressive stress works uniformly on the substrate surface. In some cases, the heat resistance of the glass material is too high, and thus the ion exchange itself is performed. It becomes difficult. _Therefore, the mass ratio of for _{(Li 2 O + Na 2 O} + K 2 O) (MgO + CaO) , it is important to _{0.10 ≦ (MgO + CaO) /} (Li 2 O + Na 2 O + K 2 O) ≦ 0.80.

  Moreover, it is preferable that neither As (arsenic) nor Sb (antimony) contain from an environmental and health viewpoint. Here, the term “not contained” means that the glass raw material is intentionally excluded, and is contained in a trace amount that is inevitably contained by being contained as an impurity in the raw materials of other components. If allowed.

  Also, V (vanadium), Mn (manganese), Ni (nickel), P (phosphorus), Nb (niobium), Mo (molybdenum), Sn (tin), Ce (cerium), Ta (tantalum) and Bi (bismuth) It is preferable to contain at least one polyvalent element selected from These polyvalent elements function as fining agents and can effectively remove bubbles in the molten glass. Only one kind of polyvalent element may be contained alone, or two or more kinds of polyvalent elements may be contained. Among these, P (phosphorus), Sn (tin), and Ce (cerium) are particularly preferable because they can remove bubbles effectively.

(Glass substrate for information recording media)
In FIG. 1, the schematic diagram of the glass substrate for information recording media of this embodiment is shown. 1A is a top view seen from one surface, and FIG. 1B is a cross-sectional view.

  A glass substrate 10 for an information recording medium according to the present embodiment is a disk-shaped glass substrate having chemical strengthening layers 12a and 12b on surfaces 11a and 11b for forming a recording layer, respectively, and has an inner hole at the center. 13.

The glass substrate 10 contains the above components except for the chemical strengthening layers 12a and 12b whose composition ratio has been changed by ion exchange, and an alkaline earth metal component (for Li ₂ O + Na ₂ O + K ₂ O) ( It consists of a glass composition whose mass ratio of MgO + CaO is in the above range. Therefore, the uniformity of ion exchange during the chemical strengthening treatment is high, and the compressive stress can be applied uniformly to the surface of the glass substrate. Moreover, it has moderate heat resistance and suppresses thermal deformation of the glass substrate during the chemical strengthening treatment. Therefore, the TIR in the circumferential direction can be made sufficiently small.

  In the present embodiment, TIR (Total Indicated Runout) is an index representing the flatness (waviness) of the glass substrate 10, and the distance from the least square plane of the evaluation surface (surfaces 11a and 11b) to the highest point; This is the sum of the distance from the least square plane to the lowest point.

In order to further reduce the head flying height and increase the rotational speed of the recording medium, it is essential to suppress the TIR in the circumferential direction of the glass substrate 10. When the radius of the outer periphery of the glass substrate 10 is r ₁ , the TIR (hereinafter referred to as “outer periphery TIR”) for one circumference in the circumferential direction at the radius r _out = 0.75r ₁ of the surfaces 11a and 11b is 1.0 μm. The following makes it easy to cope with low head flying and high-speed rotation, and stable recording and reproduction can be performed. If the outer periphery TIR is larger than 1.0 μm, there is a possibility that a recording / reproducing error due to contact between the head and the recording medium may occur. Therefore, the outer periphery TIR is preferably 1.0 μm or less. Among these, 0.5 μm or less is preferable.

Further, in the HDD, the linear velocity of the head is different between the inner peripheral side and the outer peripheral side of the recording medium, and the inner peripheral side portions of the surfaces 11a and 11b are required to have higher flatness than the outer peripheral side portion. Is done. Therefore, assuming that the radius of the outer periphery of the glass substrate 10 is r ₁ and the radius of the inner hole 13 is r ₀ , one round in the circumferential direction at the position of the radius r _in = (2r ₀ + r ₁ ) / 3 of the surfaces 11a and 11b. If the TIR (hereinafter referred to as “inner circumference TIR”) is 0.5 μm or less, it becomes easy to cope with low head flying and high-speed rotation, and recording / reproduction can be performed stably. If the inner circumference TIR is larger than 0.5 μm, a recording / reproducing error due to contact between the head and the recording medium may occur in some cases. Therefore, the inner circumference TIR is preferably 0.5 μm or less. Among these, it is preferably 0.3 μm or less. Not only can the above-mentioned problems caused by the shape of the recording medium be suppressed by keeping the inner circumference TIR small, but it is also generated by clamping in the clamping method that presses linearly in the circumferential direction as commonly used in ordinary HDDs The distortion of the recording medium to be performed can be reduced, and the risk of contact between the head and the substrate can be further avoided.

  Such a TIR in the circumferential direction can be obtained by measuring the surface shape using interference of white light (for example, Optiflat manufactured by Phase Shift Technology) or by injecting laser light obliquely with respect to the surface to be measured. It can be measured by a method (for example, FlatMaster FM100XRA manufactured by TROPEL) that can obtain a higher reflectance than a normal incidence method and can measure even a rough surface shape.

  The thickness of the glass substrate 10 is generally 0.635 mm. Since the glass substrate 10 of this embodiment can form a uniform compressive stress layer (chemical strengthening layers 12a and 12b), the TIR in the circumferential direction can be sufficiently reduced. Moreover, in order to ensure mechanical strength and suppress fluttering amount, a glass substrate 10 thicker than 0.635 mm may be required. In the case where the thickness of the glass substrate 10 is thicker than 0.635 mm, there is a method of increasing the strength of the substrate by further extending the tempering treatment time and forming a compressive stress layer deeper. If so, since the composition is suitable for chemical strengthening treatment, the effect becomes more remarkable as the strengthening time is lengthened and the compressive stress layer is deepened. In particular, it is effective when the thickness is 0.635 mm to 2 mm.

(Method for producing glass substrate for information recording medium)
The glass substrate 10 for an information recording medium of the present embodiment contains the above components, and the mass ratio of the alkaline earth metal component (MgO + CaO) to the alkali metal component (Li ₂ O + Na ₂ O + K ₂ O) is in the above range. It consists of a glass composition. For this reason, a glass substrate having a small circumferential direction TIR can be manufactured by a known general manufacturing method without requiring a complicated process or a special apparatus for manufacturing.

  In general, after a blank material to be the basis of the glass substrate 10 for an information recording medium is manufactured, it is generally manufactured through processes such as inner and outer peripheral processing, grinding / polishing processing, chemical strengthening processing, and cleaning. As for the production of the blank material, a method of producing by pressing a molten glass or a method of producing by cutting a sheet-like glass are known. The inner and outer peripheral processing is a step of performing drilling of the inner hole 13, grinding processing for ensuring the shape and dimensional accuracy of the inner and outer periphery, polishing processing of the inner and outer periphery, and the like. Grinding / polishing is a process of grinding a glass substrate to a predetermined thickness, or polishing to reduce the surface roughness by polishing the surfaces 11a and 11b for forming the recording layer. . Usually, it is often performed in several stages such as rough grinding, fine grinding, rough polishing, and fine polishing. The chemical strengthening treatment is a step of immersing the glass substrate in a chemical strengthening treatment solution and strengthening the glass substrate 10 by ion exchange. The cleaning is a step of removing foreign matters such as abrasives and chemical strengthening treatment liquid remaining on the surfaces 11a and 11b of the glass substrate 10.

  Since the glass substrate 10 for an information recording medium of the present embodiment is made of an aluminosilicate glass containing the above glass component, high impact resistance and vibration resistance can be ensured by performing chemical strengthening treatment. . In the chemical strengthening treatment, by immersing the glass substrate 10 in a heated chemical strengthening treatment solution, lithium ions and sodium ions that are components of the glass substrate 10 are replaced with sodium ions, potassium ions, and the like having a larger ion radius than these ions. It is performed by the ion exchange method. Compressive stress is generated in the ion-exchanged region due to the distortion caused by the difference in ion radius, and the surfaces 11a and 11b of the glass substrate 10 are strengthened.

As the chemical strengthening treatment liquid, a molten salt containing sodium ions or potassium ions is generally used. For example, sodium and potassium nitrates, carbonates, sulfates, and mixed molten salts thereof can be used. Among them, it is preferable to use a mixed molten salt of sodium nitrate (NaNO ₃ ) and potassium nitrate (KNO ₃ ) from the viewpoint that the melting point is low and deformation of the glass substrate can be prevented.

  Among the above steps, a grinding step of grinding the glass substrate 10 made of the glass composition to a predetermined thickness, and polishing the surfaces 11a and 11b for forming the recording layer to reduce the surface roughness. FIGS. 2A to 2E show preferable examples of the polishing process to be performed and the processing sequence of the chemical strengthening treatment process for strengthening the glass substrate 10 by ion exchange. Even if it manufactures by any process shown in FIG. 2, the glass substrate 10 with high flatness (small circumferential direction TIR) can be manufactured. In addition, in FIG. 2, preparation of the above-mentioned blank material, inner and outer periphery processing, etc. are a pre-process, and washing | cleaning etc. are post processes.

  When grinding is performed after the chemical strengthening process, it is difficult to leave the chemically strengthened layers 12a and 12b formed on the upper and lower surfaces 11a and 11b of the glass substrate 10 uniformly, and the flatness and mechanical strength of the substrate are ensured. May be difficult to do. Therefore, it is desirable to perform the chemical strengthening treatment process after the grinding process.

  When the grinding step is performed before the chemical strengthening treatment step, if the grinding amount is less than 100 μm, the effect of flattening the surface may not be sufficiently obtained. Therefore, the grinding amount in the grinding process in this case is desirably 100 μm or more. Among these, Preferably it is 150 micrometers or more.

  The polishing step may be performed after the chemical strengthening treatment step as shown in FIGS. 2 (a) and 2 (b), or before the chemical strengthening treatment step as shown in FIGS. 2 (c) and (e). Also good. Moreover, it is also preferable to perform a chemical strengthening process after a grinding | polishing process like FIG.2 (d), and to perform a 2nd grinding | polishing process further after that. Further, as shown in FIGS. 2B and 2E, the polishing process is divided into two stages: a rough polishing process with a high polishing rate and a fine polishing process with a lower polishing rate than the rough polishing step. It is also preferable.

  Surfaces 11a and 11b of glass substrate 10 reinforced by ion exchange by performing a polishing step (or a second polishing step) after the chemical strengthening treatment step as shown in FIGS. 2 (a), (b), and (d). In the case of the method of reducing the surface roughness, there is an advantage that the surface roughness of the surfaces 11a and 11b can be further reduced. In this case, by setting the polishing amount to 10 μm or less, it becomes easy to ensure the balance of stress between the upper and lower chemical strengthening layers 12a and 12b, and high flatness can be obtained. On the other hand, when the polishing amount is 0.5 μm or more, the effect of smoothing the surfaces 11a and 11b can be sufficiently ensured. Therefore, the polishing amount in the polishing step performed after the chemical strengthening treatment step is desirably in the range of 0.5 μm to 10 μm, and preferably in the range of 0.7 μm to 8 μm. As shown in FIG. 2B, when the polishing step after the chemical strengthening treatment step is divided into a rough polishing step and a fine polishing step, the total polishing amount in both steps is in the range of 0.5 μm to 10 μm. Among these, it is preferable that the thickness is in the range of 0.7 μm to 8 μm.

  In the method of performing ion exchange on the surfaces 11a and 11b of the glass substrate 10 whose surface roughness has been reduced by polishing by performing a chemical strengthening treatment step after the polishing step as shown in FIGS. There is an advantage that the uniformity of exchange can be further improved. In this case, the effect of planarizing the surface can be sufficiently ensured by setting the polishing amount to 30 μm or more. Therefore, the polishing amount in the polishing step performed before the chemical strengthening treatment step is desirably 30 μm or more. Among these, Preferably it is 35 micrometers or more. As shown in FIG. 2 (e), when the polishing step before the chemical strengthening treatment step is divided into a rough polishing step and a fine polishing step, the total polishing amount in both steps is preferably 30 μm or more. Of these, the thickness is preferably 35 μm or more.

  In order to further improve the smoothness of the glass substrate 10 and make the outer periphery TIR 1.0 μm or less or the inner periphery TIR 0.5 μm or less, it is preferable to use an Oscar double-side polisher in the polishing step. FIG. 3 is a cross-sectional view showing the configuration of the Oscar double-side polishing machine 20. FIG. 4 is a diagram schematically showing the movement of the upper and lower polishing dishes and the glass substrate. The solid line portion shows the lower polishing plate 22 and the glass substrate 10, and the broken line portion shows the upper polishing plate 21.

  As shown in FIGS. 3 and 4, the Oscar double-side polishing machine 20 includes an upper polishing dish 21 and a lower polishing dish 22, and the surfaces 11 a and 11 b of the glass substrate 10 placed in the recesses of the lower polishing dish 22 ( 1B) is an apparatus for polishing with various abrasives. The lower polishing dish 22 is rotated about the rotation shaft 23 at a predetermined rotation speed ω, but the upper polishing dish 21 is not rotated, but is only swung left and right (in the direction of arrow A in the figure). Therefore, since the glass substrate 10 is polished while naturally rotating (spinning) by the rotation of the lower polishing plate 22, the flatness in the circumferential direction can be particularly improved, and the outer circumferential TIR and inner circumferential TIR in the circumferential direction can be increased. It can be made smaller.

  There is no restriction | limiting in particular in the abrasive | polishing agent and polishing pad to be used. For example, cerium oxide, diamond, alumina and the like are suitable as the abrasive, and nonwoven fabric, urethane foam, suede and the like are suitable as the polishing pad.

  Since the glass substrate of the present embodiment is composed of a glass composition having the above composition ratio, it is suitable for chemical strengthening treatment, and although the ion exchange uniformity during chemical strengthening treatment is high, both surfaces of the glass substrate. Unless a completely uniform compressive stress layer (chemical strengthening layers 12a and 12b (see FIG. 1B)) is formed, at least some of the warp is generated outside the glass substrate. However, by polishing while rotating the glass substrate 10 naturally using the above-described Oscar double-side polishing machine 20, it is possible to remarkably reduce the warpage of the outside of the glass substrate, and to realize a smaller outer peripheral TIR. Can do. In some cases, the outer circumference is longer in the circumferential direction than the inner circumference of the glass substrate. Basically, the circumferential direction TIR often satisfies the relationship of inner circumference TIR <outer circumference TIR.

(Information recording medium)
FIG. 5 schematically shows the information recording medium of the present embodiment. 5A is a top view seen from the surface 11a side, and FIG. 5B is a cross-sectional view. The information recording medium 30 includes a recording layer 31 for recording information on the surfaces 11a and 11b of the glass substrate 10 for information recording medium described above.

  The recording layer 31 may be provided on at least one of the two surfaces 11a and 11b of the glass substrate 10. The type of the recording layer 31 is not particularly limited, and various recording layers 31 utilizing properties such as magnetism, light, and magnetomagnetism can be used. In particular, the information recording medium 30 (using the magnetic layer as the recording layer 31 ( It is suitable for a magnetic disk.

  There are no particular restrictions on the magnetic material used for the magnetic layer, and any known material can be selected and used as appropriate. Is preferred. Specific examples include CoPt, CoCr, CoNi, CoNiCr, CoCrTa, CoPtCr, CoNiPt, CoNiCrPt, CoNiCrTa, CoCrPtTa, CoCrPtSiO, and the like. Further, a multilayer structure (for example, CoPtCr / CrMo / CoPtCr, CoCrPtTa / CrMo / CoCrPtTa, etc.) in which the magnetic layer is divided by a nonmagnetic material (for example, Cr, CrMo, CrV, etc.) to reduce noise may be used.

As the magnetic layer, in addition to the above-mentioned Co-based material, ferrite or iron - and material of the rare earth-based, Fe, Co, CoFe, magnetic particles such CoNiPt are dispersed in a non-magnetic film made of _SiO 2, BN A granular structure can also be used. The magnetic layer may be either in-plane type or perpendicular type recording format.

  A known method can be used as a method for forming the magnetic layer. For example, a method of spin-coating a thermosetting resin in which magnetic particles are dispersed on the glass substrate 10 for information recording medium, a method by sputtering, and a method by electroless plating can be mentioned. From the viewpoint of thinning and increasing the density of the magnetic layer, a sputtering method and a method by electroless plating are preferable.

  The magnetic disk may further be provided with a base layer as necessary. Examples of the material for the underlayer include nonmagnetic metals such as Cr, Mo, Ta, Ti, W, V, B, Al, and Ni. When the magnetic layer contains Co as a main component, the material for 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 layers made of the same or different materials are stacked. For example, Cr / Cr, Cr / CrMo, Cr / CrV, NiAl / Cr, NiAl / CrMo, NiAl / CrV, etc. are mentioned.

Moreover, you may provide the protective layer for preventing the abrasion and corrosion of a magnetic layer on the surface of a magnetic layer. Examples of the protective layer include a Cr layer, a Cr alloy layer, a carbon layer, a hydrogenated carbon layer, a ZrO ₂ layer, and a SiO ₂ layer. The protective layer may be a single layer or may be a multilayer structure composed of the same or different layers. These protective layers can be continuously formed with an in-line type sputtering apparatus together with an underlayer, a magnetic layer, and the like. Further, when forming a protective film in which a SiO ₂ layer is laminated on a Cr layer, a solution in which tetraalkoxysilane is diluted with an alcohol-based solvent to disperse colloidal silica fine particles is applied on the Cr layer, it may be further formed an SiO ₂ layer by firing.

  Further, a lubricating layer for improving the sliding of the magnetic head may be provided on the surface of the magnetic layer or the protective layer. As the lubricating layer, for example, a liquid lubricant composed of perfluoropolyether (PFPE) or the like is applied, and heat treatment is performed as necessary.

  Hereinafter, although the Example performed in order to confirm the effect of this invention is described, this invention is not limited to these.

  A predetermined amount of raw material powder was weighed and placed in a platinum crucible, mixed, and then melted at 1500 ° C. in an electric furnace. After the raw materials were sufficiently dissolved, a stirring blade was inserted into the glass melt and stirred for about 1 hour. Thereafter, the stirring blade was taken out and allowed to stand for 30 minutes, and then the melt was poured into a jig to obtain a glass block. Thereafter, the glass block was reheated to the vicinity of the glass transition point of each glass and slowly cooled to remove strain.

  The obtained glass block was sliced into a disc shape of about 1 mm in thickness and 2.5 inches, and cut out using a cutter so that the inner circumference and outer circumference were concentric circles. And according to each process shown to Fig.2 (a)-(e), a grinding process, a rough polishing process, a fine polishing process, and a chemical strengthening process are performed, and the glass substrate of outer diameter 65mm, inner diameter 20mm, and thickness 0.635mm Was made.

  Grinding and polishing processes are performed on a polishing carrier having a gear portion that meshes with a sun gear and an internal gear of the polishing machine (polishing method A) using the Oscar double-side polishing machine shown in FIGS. The substrate was placed and the upper polishing plate and the lower polishing plate were rotated in opposite directions, and the polishing was performed by two methods (polishing method B). In either case, diamond pellets were used in the grinding process, and cerium oxide was used as the abrasive in the polishing process. For rough polishing, a polyurethane polishing pad was used, and for fine polishing, a suede polishing pad was used.

  In addition, the Example and comparative example of Table 2-Table 5 processed by the grinding | polishing method A using an Oscar double-side polisher.

The chemical strengthening treatment is performed by immersing in a nitrate mixed solution in which sodium nitrate (NaNO ₃ ) and potassium nitrate (KNO ₃ ) heated to 350 ° C. are mixed at a molar ratio of 1: 1 for a predetermined time (30 minutes or 60 minutes). And finally, the abrasive and nitrate mixed solution were removed by washing, and samples of Examples and Comparative Examples were obtained. The time of chemical strengthening treatment (immersion time) when there is no description in the table is 30 minutes.

  Evaluation of the outer peripheral TIR and inner peripheral TIR (Table 1) and evaluation of the number of remaining bubbles (Table 2) were performed on the glass substrate prepared in the step of FIG.

  Moreover, evaluation of the outer periphery TIR (Table 3) and evaluation of the outer periphery TIR when the amount of grinding / polishing was changed (Table 4) were performed for each process shown in FIGS.

  Further, glass substrates having various thicknesses were prepared in the step of FIG. 2 (e), and each was subjected to chemical strengthening treatment for two types of time, and the outer periphery TIR was evaluated (Table 5).

The outer circumference TIR and the inner circumference TIR were measured by using Optiflat manufactured by Phase Shift Technology, which measures the surface shape using interference of white light. Regarding the measurement location in the circumferential direction TIR, the outer periphery TIR was positioned at a radius r _out = 24.38 mm from the center of the substrate, and the inner periphery TIR was positioned at a radius r _in = 17.50 mm. Evaluation of the number of remaining bubbles was carried out by measuring the number of bubbles per glass substrate using a 50 × optical microscope for the entire surface of the glass substrate.

  These evaluation results are shown in Tables 1 to 5 below.

  Table 1 shows the measurement results of the outer periphery TIR and the inner periphery TIR for the glass substrates manufactured under the same processing conditions (two kinds of polishing methods) by the step of FIG.

From the results of Table 1, when compared with the same polishing method, the glass substrates of Examples 2 to 9 in the range of 0.10 ≦ (MgO + CaO) / (Li ₂ O + Na ₂ O + K ₂ O) ≦ 0.80 It was confirmed that the outer periphery TIR and the inner periphery TIR were smaller than the glass substrates of Comparative Examples 1 and 10 outside the range.

  Further, it was confirmed that higher flatness can be obtained by processing by the polishing method A using an Oscar double-side polishing machine than by processing by the polishing method B. In the case of the polishing method A, all the glass substrates of Examples 2 to 9 had an outer periphery TIR of 1 μm or less and an inner periphery TIR of 0.5 μm or less, and were able to obtain very high flatness.

  Table 2 shows the measurement results of the number of remaining bubbles for the glass substrate manufactured under the same processing conditions by the process of FIG.

  From the results of Table 2, V (vanadium), Mn (manganese), Ni (nickel), P (phosphorus), Nb (niobium), Mo (molybdenum), Sn (tin), Ce with respect to the above glass composition (Cerium), Ta (tantalum), and Bi (bismuth), it is confirmed that the number of bubbles remaining in the glass is significantly reduced by containing at least one polyvalent element selected from the group consisting of It was done. Among these, Sn, Ce, and P were confirmed to have a particularly high clarification effect.

  Table 3 shows the results of measuring the outer periphery TIR of the glass substrate produced in various process orders.

  Examples 23 to 28 used the glass composition of Example 2 in Table 1, and Comparative Examples 29 to 34 used the glass composition of Comparative Example 1 in Table 1. In addition, Examples 23 to 27 and Comparative Examples 29 to 33 are prepared in the order of processes shown in FIGS. 2A to 2E, respectively. In Example 28 and Comparative Example 34, the chemical strengthening process is performed before the grinding process. It was produced in the order of steps performed.

  From the measurement results of the outer periphery TIR shown in Table 3, when the same steps are compared, the example (the glass composition of Example 2 in Table 1) rather than the comparative example (the glass composition of Comparative Example 1 in Table 1). It was confirmed that a glass substrate having a small outer peripheral TIR was obtained. Further, as shown in FIGS. 2A to 2E, the outer peripheral TIR is set to a very small value of 1 μm or less for the glass substrates of Examples 23 to 27 in which the chemical strengthening treatment process is performed after the grinding process. I was able to.

  Table 4 shows the measurement results of the outer circumference TIR when the grinding / polishing amount is changed for each process in the case of the glass composition of Example 2 in Table 1.

  As in the results of Table 4, it was confirmed that a glass substrate having a small outer peripheral TIR was obtained in any case.

  Further, from the comparison between Examples 35 and 36, it is assumed that the outer peripheral TIR can be reduced to 1 μm or less when the grinding amount is set to 100 μm or more, preferably 150 μm or more in the grinding process performed before the chemical treatment process.

  From the comparison of Examples 37 and 38 and the comparison of Examples 41 and 42, the total polishing amount in the polishing step performed after the chemical strengthening treatment step is in the range of 0.5 μm to 10 μm, preferably in the range of 0.7 μm to 8 μm. Then, it is assumed that the outer periphery TIR can be 1 μm or less.

  Further, from comparison between Examples 39 and 40, it is assumed that the outer peripheral TIR can be reduced to 1 μm or less if the polishing amount in the polishing step performed before the chemical strengthening treatment step is set to 30 μm or more, preferably 35 μm or more.

  Further, from the comparison of Examples 43 and 44, when the polishing step before the chemical strengthening treatment step is divided into a rough polishing step and a fine polishing step, the total polishing amount in both steps is preferably 30 μm or more, preferably If it is 35 μm or more, it is assumed that the outer periphery TIR can be 1 μm or less.

  Table 5 shows the results of measuring the outer periphery TIR according to the thickness of the glass substrate produced in the step of FIG.

  The thickness of the glass substrate is 0.635 mm, 0.8 mm, 1 mm, 1.2 mm, 1.5 mm, and 2 mm, and Examples 45 to 56 are manufactured using the glass composition of Example 2 in Table 1. Comparative Examples 57 to 68 were produced using the glass composition of Comparative Example 1 in Table 1.

  From the results of Table 5, in the case of substrates having a thickness of 0.635 mm to 2 mm, it was confirmed that when the same thickness was compared, a glass substrate having a smaller outer peripheral TIR was obtained in the example than in the comparative example. . Further, in the comparative example, when the chemical strengthening treatment time is lengthened, the outer peripheral TIR is greatly deteriorated, whereas in the example, even if the chemical strengthening treatment time is lengthened, the outer peripheral TIR hardly changes. In particular, the results are particularly advantageous.

DESCRIPTION OF SYMBOLS 10 Glass substrate 11a, 11b Surface 12a, 12b Chemical strengthening layer 13 Inner hole 20 Oscar double-side polisher 21 Upper polishing dish 22 Lower polishing dish 23 Rotating shaft 30 Information recording medium 31 Recording layer

Claims (19)

A disk-shaped glass substrate for information recording medium having a chemically strengthened layer on the surface for forming a recording layer,
The portion excluding the chemical strengthening layer is
SiO _2: 55~75% by weight,
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 wt%,
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,
The mass ratio of (MgO + CaO) to (Li ₂ O + Na ₂ O + K ₂ O) is
0.10 ≦ (MgO + CaO) / (Li ₂ O + Na ₂ O + K ₂ O)
≦ 0.80
Consisting of a glass composition in the range of
Wherein when the radius of the outer circumference of the glass substrate was set to r _1, a glass substrate for information recording medium, wherein the TIR from the center in the circumferential direction one turn at the position of 0.75 r ₁ of said surface is 1μm or less. The glass substrate has an inner hole in the center of the surface,
When the radius of the outer periphery of the glass substrate is r ₁ and the radius of the inner hole is r ₀ , the TIR for one round in the circumferential direction at a position of (2r ₀ + r ₁ ) / 3 from the center of the surface is 0.5 μm. The glass substrate for an information recording medium according to claim 1, wherein:   The glass substrate for an information recording medium according to claim 1 or 2, wherein the glass composition contains neither As (arsenic) nor Sb (antimony).   The glass composition includes V (vanadium), Mn (manganese), Ni (nickel), P (phosphorus), Nb (niobium), Mo (molybdenum), Sn (tin), Ce (cerium), and Ta (tantalum). 4. The glass substrate for an information recording medium according to claim 1, wherein the glass substrate contains at least one polyvalent element selected from Bi and bismuth. 5.   5. The information recording according to claim 4, wherein the glass composition contains at least one polyvalent element selected from P (phosphorus), Sn (tin) and Ce (cerium). Glass substrate for media.   The glass substrate for an information recording medium according to any one of claims 1 to 5, wherein the thickness is 0.635 mm to 2 mm. SiO _2: 55~75% by weight,
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 wt%,
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,
The mass ratio of (MgO + CaO) to (Li ₂ O + Na ₂ O + K ₂ O) is
0.10 ≦ (MgO + CaO) / (Li ₂ O + Na ₂ O + K ₂ O)
≦ 0.80
A grinding step of grinding a glass substrate made of a glass composition in a range to a predetermined thickness;
A polishing step of reducing the surface roughness by polishing the surface of the glass substrate for forming the recording layer;
A chemical strengthening treatment step of strengthening the glass substrate by ion exchange, and a manufacturing method of a disk-shaped glass substrate for an information recording medium,
When the radius of the outer circumference of the glass substrate was set to r _1, TIR circumferential one rotation after the polishing by the polishing process, and characterized in that a 1μm or less at the position of 0.75 r ₁ from the center of said surface A method for manufacturing a glass substrate for an information recording medium.   The method for producing a glass substrate for an information recording medium according to claim 7, wherein the chemical strengthening treatment step is performed after the grinding step.   9. The information recording medium according to claim 7, wherein the polishing step is performed after the chemical strengthening treatment step to reduce the surface roughness of the surface of the glass substrate strengthened by ion exchange. A method for producing a glass substrate.   The method for producing a glass substrate for an information recording medium according to claim 9, wherein the polishing amount in the polishing step is 0.5 μm to 10 μm.   9. The information recording medium according to claim 7, wherein ion exchange is performed on the surface of the glass substrate whose surface roughness has been reduced by polishing by performing the chemical strengthening treatment step after the polishing step. A method for producing a glass substrate.   The method for producing a glass substrate for an information recording medium according to claim 11, wherein a polishing amount in the polishing step is 30 μm or more.   The surface roughness of the surface of the glass substrate strengthened by ion exchange is further reduced by further performing a second polishing step after the chemical strengthening treatment step. The manufacturing method of the glass substrate for information recording media of description.   The method for producing a glass substrate for an information recording medium according to claim 13, wherein the polishing amount in the second polishing step is 0.5 μm to 10 μm.   The information recording according to any one of claims 7 to 14, wherein the polishing step includes a rough polishing step with a high polishing rate and a fine polishing step with a polishing rate lower than that of the rough polishing step. A method for producing a glass substrate for a medium.   The method for manufacturing a glass substrate for an information recording medium according to any one of claims 7 to 15, wherein an oscar type polishing machine is used in the polishing step.   The method for producing a glass substrate for an information recording medium according to any one of claims 7 to 16, wherein a grinding amount in the grinding step is 100 µm or more. A glass substrate for an information recording medium according to any one of claims 1 to 6,
An information recording medium comprising: a recording layer for recording information provided on the surface of the glass substrate for information recording medium.   The information recording medium according to claim 18, wherein the recording layer is a magnetic layer that records information by magnetism.