JP6015259B2 - Manufacturing method of glass substrate for information recording medium and manufacturing method of magnetic disk - Google Patents

Description

  The present invention relates to a glass substrate for information recording media and a method for manufacturing a magnetic disk.

  In the recent trend of increasing the capacity of magnetic disks, technical challenges for glass substrates include improving surface smoothness and reducing deposits on the glass surface. The technical problems related to the reduction of deposits on the glass surface are as follows. In other words, it is known that cerium oxide abrasive grains suitably used for glass polishing remain as foreign matter as foreign matter remaining on the glass substrate because of a high polishing rate.

  Patent Document 1 discloses a method for producing a glass substrate for an information recording medium through a polishing process using a slurry containing cerium oxide abrasive grains for a glass disk made of aluminosilicate glass, followed by a glass circle following the cerium oxide polishing process. It is disclosed that a plate is washed at a liquid temperature of 50 ° C. or higher and 100 ° C. or lower using a cleaning liquid having a sulfuric acid concentration of 20% by mass to 80% by mass and a hydrogen peroxide concentration of 1% by mass to 10% by mass. .

  Also, as the final polishing step, polishing is typically performed using a slurry containing colloidal silica adjusted to acidity (hereinafter also referred to as colloidal silica slurry), and then an alkaline aqueous solution (or in order to reduce the colloidal silica residue) It is disclosed that glass is cleaned using an alkaline cleaning liquid).

  As a means for solving the technical problem relating to the improvement of the surface smoothness, colloidal silica having an average primary particle diameter of 5 to 50 nm and an acrylic acid / sulfonic acid copolymer having a weight average molecular weight of 1000 to 5000 are contained. Therefore, a polishing composition for glass substrates having a pH of 0.5 to 5 has been proposed (see Patent Document 2).

JP 2011-18398 A (Claims) JP 2007-191696 A (Claims)

  When the present inventors verified the smoothness improving effect by the colloidal silica slurry to which the acrylic acid / sulfonic acid copolymer was added, a slight improvement was observed. On the other hand, in the colloidal silica slurry to which the acrylic acid / sulfonic acid copolymer was added, it was also found that the polishing rate was lowered because the lubricity increased (described in the section of [Example 1] described later). From this, it is considered that the smoothness of the colloidal silica slurry to which the acrylic acid / sulfonic acid copolymer is added is improved by the reduction of the polishing rate.

  This invention is made | formed in view of the said problem, and reduces a polishing rate in the method of manufacturing the glass substrate for information recording media including the process of grind | polishing about the glass disc using the slurry containing colloidal silica. An object of the present invention is to provide a manufacturing method and a magnetic disk manufacturing method that can obtain a smoother glass substrate for an information recording medium without any problem.

The present inventor paid attention to the chelating ability of acid as a factor that determines the polishing rate and the polishing surface when aluminosilicate glass containing a large amount of Al ₂ O ₃ is polished with acidic colloidal silica slurry. As a result of examining the types of acids when adjusting to the above, it was found that the roughness of the polished surface differs depending on the types of acids.

  When the cause of the surface roughness was investigated, it was confirmed that the polished surface was hardly roughened by using a colloidal silica slurry containing a linear saturated dicarboxylic acid. Since linear saturated dicarboxylic acid has a carboxylic acid at the terminal and is linear, its chelating ability is smaller than that of branched or cyclic acid, so even if it is included in colloidal silica slurry, the polished surface is rough. It is considered difficult. From this, it has been found that the use of linear saturated dicarboxylic acid as an acid modifier for colloidal silica slurry improves the smoothness without lowering the polishing rate, thereby completing the present invention.

That is, the present invention is as follows.
1 . A process of polishing glass using a cerium-based abrasive, a cleaning process of cleaning glass using a cleaning liquid containing heated sulfuric acid and hydrogen peroxide, and a process of polishing a glass main surface using a slurry containing colloidal silica A method for producing a glass substrate for an information recording medium, characterized in that a linear saturated dicarboxylic acid is contained in the slurry.
2 . 2. The method for producing a glass substrate for an information recording medium according to 1 above, wherein the colloidal silica slurry has a pH of 3 or more and 5 or less.
3 . 3. The method for producing a glass substrate for an information recording medium according to item 1 or 2 , wherein the linear saturated dicarboxylic acid contained in the colloidal silica has 2 to 7 carbon atoms.
4 . 4. The glass for an information recording medium according to any one of items 1 to 3 , wherein the linear saturated dicarboxylic acid is one or more selected from the group consisting of succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, and azelaic acid. A method for manufacturing a substrate.
5 . 5. The information recording medium according to any one of 1 to 4 above, wherein the step of polishing the glass main surface using the slurry containing the colloidal silica is a finish polishing step, and then includes a cleaning step using an alkaline aqueous solution. A method for producing a glass substrate.
6 . 6. The method for producing a glass substrate for an information recording medium according to any one of items 1 to 5 , wherein the colloidal silica has an average particle size of 10 to 50 nm.
7 . 7. The method for producing a glass substrate for an information recording medium according to any one of items 1 to 6, wherein the information recording medium is a magnetic disk.
8 . 8. A method of manufacturing a magnetic disk , comprising forming a magnetic recording layer on a main surface of a glass substrate for information recording media obtained by the manufacturing method according to item 7 .

  When glass containing an alkali metal oxide (hereinafter sometimes simply referred to as alkali) is polished with a colloidal silica slurry adjusted to be acidic, there is a problem that the glass surface becomes rough. This phenomenon is considered to occur as follows. That is, as shown in FIGS. 1 (a) to 1 (c), when glass containing an alkali metal oxide [FIG. 1 (a)] is polished with colloidal silica slurry adjusted to an acidic state, hydronium ions are incorporated into the glass by leaching. The glass surface is roughened by polishing the leaching layer on the glass surface with colloidal silica [FIG. 1 (c)].

  As described above, it is considered that the factors that determine the smoothness of the polished surface when the glass containing alkali metal oxide is polished with an acidic colloidal silica slurry are the alkali amount of the glass and the size of the colloidal silica. . On the other hand, the factor that determines the polishing rate is considered to be the pH of the colloidal silica slurry in addition to the alkali amount of the glass and the size of the colloidal silica. This is because if an appropriate leaching phenomenon occurs, the glass surface is softened and the polishing rate is considered to be improved. The preferred pH from this viewpoint is 3-5.

Glass containing a large amount of Al ₂ O _3, factors that determine the smoothness of the polished surface even when typically include polishing with a colloidal silica slurry prepared glass Al ₂ O ₃ content is 4 mol% or more acidic It is considered to be the Al ₂ O ₃ amount of glass and the size of colloidal silica. In addition, when glass contains an alkali, the amount of alkali is also included in the same factor as described above.

As shown in FIGS. 2A to 2C, when the amount of Al ₂ O ₃ in the aluminosilicate glass increases, the acid resistance of the glass deteriorates, and the acid in the colloidal silica slurry has a large chelating action. Aluminum ions are chelated [FIG. 2 (b)]. The glass surface is roughened by polishing the leaching layer on the glass surface with colloidal silica [FIG. 2 (c)]. For this reason, when the final polishing of the aluminosilicate glass is performed using the colloidal silica slurry adjusted to be acidic, the surface may be roughened. This figure is for the case where the glass contains an alkali, but the same applies to the case where the glass contains no alkali or a very small amount, typically less than 4 mol%.

Al ₂ O factors determining the polishing rate of the _{glass 3} containing a large amount of the Al ₂ O ₃ of the glass, a pH of size and colloidal silica slurry of colloidal silica, may further contain alkali included in the factor even alkali amount It is thought that.

In addition to the factors described above, the chelating ability of the acid in the colloidal silica slurry is particularly important as a factor for determining the polishing surface when the aluminosilicate glass containing a large amount of Al ₂ O ₃ is polished with an acidic colloidal silica slurry. The present inventor found out that there was a present invention. That is, factors that determine the polishing surface include the alkali amount of glass or the amount of Al ₂ O ₃ and the size of colloidal silica. In addition to these, the chelating ability of acid is particularly important because of the chelating effect of aluminum. This is because it is considered that the glass network is broken by pulling, and the glass surface is reduced in hardness and roughened.

  Moreover, as shown in FIG. 3 of Experimental Example 1 to be described later, when glass is immersed in an acidic aqueous solution, the hardness of the glass surface is lowered. Therefore, the acidic aqueous solution is etchable with respect to the aluminosilicate glass, and the surface is further covered. It is thought that there is a risk of ruining.

  According to the present invention, a glass substrate for an information recording medium having high smoothness can be obtained without reducing the polishing rate. In addition, a glass substrate for a magnetic disk that can sufficiently cope with a high recording capacity required in the future can be obtained.

Fig.1 (a)-(c) shows the schematic diagram of the glass surface at the time of grind | polishing with the colloidal silica slurry which adjusted the glass containing a general purpose alkali to acidity. FIG. 2 is a schematic diagram of the glass surface when aluminosilicate glass containing a large amount of Al ₂ O ₃ is polished with an acidic colloidal silica slurry. FIG. 3 shows the results of investigating the correlation between surface displacement (nm) and hardness (GPa) by immersing a glass plate in a pH 2 HNO ₃ aqueous solution or a pH 11 NaOH aqueous solution. 4A to 4H show the results of measuring Ra of 1 μm × 1 μm using AFM after immersing a glass substrate in an acid-containing aqueous solution. FIGS. 5A to 5H show the results of immersing a glass substrate in an acid-containing aqueous solution and then in an alkali-containing aqueous solution and measuring 1 μm × 1 μm Ra using AFM. 6A to 6E show the results of measuring Ra after polishing a glass substrate with an acid-containing colloidal silica slurry and then scrubbing with an alkaline cleaning solution.

  The present invention relates to a method for producing a glass substrate including a step of polishing a glass main surface using a slurry containing colloidal silica, and relates to a method for producing a glass substrate in which a linear saturated dicarboxylic acid is contained in the slurry.

(Glass plate)
The manufacturing method of a glass plate is not specifically limited, Various methods can be applied. For example, the raw materials of each component normally used are prepared so as to have a target composition, and this is heated and melted in a glass melting kiln. Homogenize the glass by bubbling, stirring or adding a clarifying agent, etc., and forming it into a sheet glass of a predetermined thickness by a method such as the well-known float method, press method, fusion method or downdraw method, and after slow cooling, as necessary After processing such as grinding and polishing, a glass substrate having a predetermined size and shape is obtained. As the molding method, a float method suitable for mass production is particularly preferable. Further, continuous molding methods other than the float method, for example, a fusion method and a downdraw method are also preferable.

  The glass substrate for an information recording medium in the present invention is not particularly limited as long as it is used for an information recording medium, but is typically used for a magnetic disk. Hereinafter, a glass substrate for a magnetic disk will be described as an example, but the present invention is not limited to this example.

First, a glass disk is cut out from a glass plate made of glass. The glass is typically an aluminosilicate glass, and its Al ₂ O ₃ content is usually 4 mol% or more. Usually, Al ₂ O ₃ is an essential component of glass, and the reason is as follows. In other words, in order to improve the vibration characteristics and / or strength at high speed rotation of the magnetic disk, it is necessary to consider various characteristics such as Young's modulus, specific elastic modulus, specific gravity, thermal expansion coefficient, scratch resistance or fracture toughness. It is necessary to use a glass substrate having a glass composition. Al ₂ O ₃ is an effective component for achieving these mechanical properties.

The glass used for high temperature film formation is a low alkali aluminosilicate glass that does not contain alkali metal oxides or contains a total of less than 4 mol% of alkali metal oxides, and contains Al ₂ O ₃ A glass whose amount is 4 mol% or more is preferred.

As described above, when the content of Al ₂ O ₃ in the aluminosilicate glass is 4 mol% or more, the acid resistance of the glass is deteriorated, and hydronium ions are exchanged with alkali ions in the glass. Is chelated, and when polished with colloidal silica, the glass surface may be roughened. In the present invention, it allows the content of Al ₂ O ₃ in the glass is 10 mol% or more, which comprises a step of polishing the glass main surface with a colloidal silica slurry containing chelating ability is less straight-chain saturated dicarboxylic acid Even in this case, it is possible to prevent the polished surface from becoming rough.

Specific examples of the glass include the following glasses 1 to 3.
In (Glass 1) mol%, a SiO ₂ 55 to 75%, the _{Al 2 O 3 5~17%, Li} 2 O + Na 2 O + K 2 O and 0 to 27%, the MgO + CaO + SrO + BaO containing 0-20%, these Aluminosilicate glass with a total content of components of 90% or more.
(Glass 2)
In terms of mole percentage, SiO ₂ is 62 to 74%, Al ₂ O ₃ is 7 to 18%, B ₂ O ₃ is 2 to 15%, and any one or more of MgO, CaO, SrO, and BaO is 8 in total. 21% or more, the total content of the above 7 components is 95% or more, and any one or more of Li ₂ O, Na ₂ O and K ₂ O is contained less than 4% in total, or these 3 Low alkali aluminosilicate glass that does not contain any of the components.
(Glass 3)
In terms of mole percentage, SiO ₂ is 67 to 72%, Al ₂ O ₃ is 11 to 14%, B ₂ O ₃ is 0 to less than 2%, MgO is 4 to 9%, CaO is 4 to 6%, and SrO is 1 -6%, BaO 0-5%, MgO, CaO, SrO and BaO total content is 14-18%, total content of the seven components is 95% or more, Li ₂ O, Na ₂ A low alkali aluminosilicate glass containing less than 4% in total of any one or more components of O and K ₂ O, or containing none of these three components.

Each glass composition is demonstrated below. In the following, “mol%” is simply expressed as “%”.
(Glass 1)
SiO ₂ is a component that forms a glass skeleton and is essential. When SiO ₂ is less than 55%, the specific gravity increases, the glass is easily scratched, the devitrification temperature rises, the glass becomes unstable, or the acid resistance decreases. The content of SiO ₂ is preferably 60% or more, more preferably 61% or more, particularly preferably 62% or more, most preferably 63% or more, and typically 64% or more.

However, if SiO ₂ exceeds 75%, the Young's modulus decreases, the specific elastic modulus decreases, the thermal expansion coefficient decreases, or the viscosity becomes too high, making it difficult to melt the glass. The content of SiO ₂ is preferably 71% or less, more preferably 70% or less, and most preferably 68% or less. Acid resistance tends to decrease when SiO ₂ is less than 63 mol%.

Al ₂ O ₃ is a component that forms a glass skeleton and increases Young's modulus, specific elastic modulus, and fracture toughness, and is essential. If it is less than 5%, the Young's modulus becomes low, the specific elastic modulus becomes low, and the fracture toughness becomes low. The content of Al ₂ O ₃ is preferably 6% or more, more preferably 7% or more, and typically 8% or more. However, if Al ₂ O ₃ exceeds 17%, the thermal expansion coefficient becomes small, the viscosity becomes too high, and it becomes difficult to melt the glass, or the acid resistance is lowered. The content of Al ₂ O ₃ is preferably 15% or less, more preferably 14% or less. Acid resistance tends to decrease when Al ₂ O ₃ exceeds 12.5%.

As described above, the glass having less SiO _{2 and} more Al ₂ O ₃ has lower acid resistance. _{Therefore, (SiO 2 -Al 2 O 3} ) is reduced when the acid resistance of the glass decreases significantly. On the other hand, in order to improve mechanical properties such as Young's modulus, specific elastic modulus, or fracture toughness, it is effective that there is a large amount of Al ₂ O ₃ , and glass excellent in mechanical properties tends to have low acid resistance. _(SiO 2 _-Al 2 _{O 3)} is typically 48 to 62%.

  MgO, CaO, SrO and BaO are not essential, but are components that improve the solubility of the glass and increase the thermal expansion coefficient, and the total R′O content of these four components is in the range of up to 20%. You may contain. If it exceeds 20%, the specific gravity becomes large or the glass tends to be damaged. It is preferably 10% or less, more preferably 8% or less, most preferably 6% or less, and typically 4% or less.

In order to improve mechanical properties such as Young's modulus, specific elastic modulus, specific gravity, thermal expansion coefficient, scratch resistance or fracture toughness, SiO ₂ + Al ₂ O ₃ + R ₂ O + R′O needs to be 90% or more. . If it is less than 90%, this effect becomes small. Preferably it is 93% or more, More preferably, it is 95% or more, Most preferably, it is 97% or more.

  The glass 1 consists essentially of the above components, but may contain other components as long as the object of the present invention is not impaired.

For example, TiO ₂ , ZrO ₂ , Y ₂ O ₃ , Nb ₂ O ₅ , Ta ₂ O ₅ and La ₂ O ₃ have the effect of increasing Young's modulus, specific elastic modulus, or fracture toughness. When any one or more of these are contained, the total amount is preferably 7% or less. If the total amount exceeds 7%, the specific gravity may increase or the glass may be easily damaged, more preferably less than 5%, particularly preferably less than 4%, and most preferably less than 3%.

B ₂ O ₃ has the effects of improving the solubility of the glass, reducing the specific gravity, and making the glass difficult to damage. When it contains this, 3% or less is preferable. If B ₂ O ₃ exceeds 3%, the Young's modulus is lowered, the specific elastic modulus is lowered, or the glass quality may be lowered by volatilization. The content of B ₂ O ₃ is more preferably 2% or less, particularly preferably 1% or less, and most preferably 0.5% or less.

SO ₃ , Cl, As ₂ O ₃ , Sb ₂ O ₃ , SnO ₂ and CeO ₂ have the effect of clarifying the glass. When any of these is contained, the total content is preferably 2% or less.

(Glass 2)
SiO ₂ is an essential component. If SiO ₂ is less than 62%, the glass tends to be damaged, preferably 65% or more, and if it exceeds 74%, the solubility is lowered and glass production becomes difficult, preferably 69% or less.

Al ₂ O ₃ is an essential component. If Al ₂ O ₃ is less than 7%, the heat resistance is insufficient, the glass tends to phase-separate, and it may not be possible to maintain a smooth surface after processing / cleaning the substrate, or the glass may be easily damaged, preferably If it exceeds 9% and exceeds 18%, the solubility decreases and glass production becomes difficult, or the acid resistance such as sulfuric acid resistance decreases, preferably 12% or less.

Note that hardly put more scratch the glass is preferably that the total content of SiO ₂ and _Al 2 _{O 3} is 70% or more, more preferably 72% or more.

B ₂ O ₃ has an effect of improving the solubility of glass and is essential. If B ₂ O ₃ is less than 2%, the solubility of the glass is lowered, preferably 7% or more, and if it exceeds 15%, the glass tends to phase-separate and a smooth surface is maintained after processing and cleaning the substrate. It becomes impossible or acid resistance, such as sulfuric acid resistance, falls, Preferably it is 12% or less.

  MgO, CaO, SrO and BaO are components that improve the solubility of the glass, and must contain at least one component. If the total RO of the contents of these components is less than 8%, the glass solubility is lowered, making glass production difficult, and preferably 10% or more. On the other hand, if RO exceeds 21%, the glass tends to be damaged, preferably 16% or less.

  Of these four components, it is preferable to contain at least one of MgO and CaO. If the total MgO + CaO content of MgO and CaO is less than 3%, it may be difficult to dissolve the glass, or the glass may be easily damaged. If MgO + CaO exceeds 18%, the devitrification temperature becomes high and molding may be difficult.

  Moreover, when SrO or BaO is included among these four components, the total SrO + BaO of those contents is preferably 6% or less. If SrO + BaO exceeds 6%, when a cleaning solution containing sulfuric acid is used, SrO or BaO reacts with sulfuric acid to produce a hardly soluble sulfate, which may promote surface roughness.

  The glass 2 is essentially composed of the above seven components, but may contain other components as long as it is 5% or less in total within a range not impairing the object of the present invention. If the total content of components other than the above seven components exceeds 5%, the glass tends to be damaged. Hereinafter, components other than the above seven components will be exemplarily described.

  ZnO is a component that exhibits the same effect as MgO, CaO, SrO, and BaO, and may be contained in a range of 5% or less. In that case, the total content of ZnO and RO is preferably 8 to 21%, more preferably 10 to 16%.

Since Li ₂ O, Na ₂ O and K ₂ O reduce the heat resistance, the total R ₂ O content of these three components is 0% or less than 4%. From this viewpoint, R ₂ O is preferably 0%, but even when R ₂ O is not 0%, it is preferably less than 1%.

  Since an oxide having an atomic number larger than Ti such as V may easily damage the glass, when these oxides are contained, the total content thereof is preferably 3% or less, More preferably, it is 2% or less, particularly preferably 1% or less, and most preferably 0.3% or less.

SO ₃ , F, Cl, As ₂ O ₃ , Sb ₂ O ₃ , SnO _{2 and the} like are typical components as fining agents, and the total is typically less than 1%.

(Glass 3)
SiO ₂ is an essential component. If SiO ₂ is less than 67%, the glass tends to be damaged, and if it exceeds 72%, the solubility is lowered and glass production becomes difficult.

Al ₂ O ₃ is an essential component. If Al ₂ O ₃ is less than 11%, the glass tends to phase-separate and the smooth surface cannot be maintained after processing / cleaning the substrate, or the glass is likely to be damaged. Such as the acid resistance is reduced, or the solubility is lowered, making glass production difficult.

B ₂ O ₃ is not an essential component, but has an effect of improving the solubility of glass, and may be contained in a range of less than 2%. If B ₂ O ₃ is 2% or more, acid resistance such as sulfuric acid resistance or heat resistance may be lowered.

  MgO, CaO and SrO are components that improve the solubility of glass and are essential. If each content of MgO, CaO, and SrO is less than 4%, less than 4%, and less than 1%, solubility decreases. If each content of MgO, CaO, and SrO exceeds 9%, 6%, and 6%, the glass tends to be damaged.

  BaO is not an essential component, but has an effect of improving the solubility of glass, and may be contained in a range of 5% or less. If BaO exceeds 5%, the glass tends to be damaged.

  If RO is less than 14%, the solubility of the glass decreases and glass production becomes difficult. On the other hand, when RO exceeds 18%, the glass is easily damaged.

  Moreover, when it contains BaO, it is preferable that SrO + BaO is 6% or less. If SrO + BaO exceeds 6%, when a cleaning solution containing sulfuric acid is used, SrO, BaO and sulfuric acid react with each other to form a hardly soluble sulfate, which may promote surface roughness.

  The glass 3 is essentially composed of the above seven components, but may contain other components as long as it is 5% or less in total within a range not impairing the object of the present invention. If the total content of components other than the above seven components exceeds 5%, the glass tends to be damaged. Hereinafter, components other than the above seven components will be exemplarily described.

  ZnO is a component that exhibits the same effect as MgO, CaO, SrO, and BaO, and may be contained in a range of 5% or less. In that case, the total content of ZnO and RO is preferably 8 to 21%, more preferably 10 to 16%.

Since Li ₂ O, Na ₂ O and K ₂ O lower the annealing point, the total R ₂ O content of these three components is 0% or less than 4%. From this viewpoint, R ₂ O is preferably 0%, but even when R ₂ O is not 0%, it is preferably less than 1%.

  Since an oxide having an atomic number larger than Ti such as V may easily damage the glass, when these oxides are contained, the total content thereof is preferably 3% or less, More preferably, it is 2% or less, particularly preferably 1% or less, and most preferably 0.3% or less.

SO ₃ , F, Cl, As ₂ O ₃ , Sb ₂ O ₃ , SnO _{2 and the} like are typical components as fining agents, and the total is typically less than 1%.

  The specific gravity of the glass plate is preferably 2.60 or less. If it exceeds 2.60, a motor load is applied during rotation of the magnetic disk drive, which may increase power consumption or make the drive rotation unstable. Preferably it is 2.55 or less, More preferably, it is 2.53 or less, Most preferably, it is 2.52 or less.

Moreover, it is preferable that the thermal expansion coefficient (average linear expansion coefficient) in the range of −50 to + 70 ° C. of the glass plate is 60 × 10 ⁻⁷ / ° C. or more. If it is less than 60 × 10 ⁻⁷ / ° C., the difference from the coefficient of thermal expansion of other members such as a metal drive becomes large, and there is a risk that the substrate will be easily cracked due to the generation of stress during temperature fluctuations. Preferably it is 62 × 10 ⁻⁷ / ° C. or more, more preferably 65 × 10 ⁻⁷ / ° C. or more, and most preferably 70 × 10 ⁻⁷ / ° C. or more.

  Further, the Young's modulus of the glass plate is preferably 80 GPa or more, and the specific elastic modulus is preferably 32 MNm / kg or more. If the Young's modulus is less than 80 GPa or the specific elastic modulus is less than 32 MNm / kg, warping or deflection is likely to occur during drive rotation, and it may be difficult to obtain an information recording medium having a high recording density. More preferably, the Young's modulus is 81 GPa or more and the specific elastic modulus is 32.5 MNm / kg or more.

  The glass plate made of the glass of the above typical example tends to be excellent in various properties such as Young's modulus, specific elastic modulus, specific gravity, thermal expansion coefficient, resistance to scratching or fracture toughness.

  The method for producing a glass substrate for an information recording medium of the present invention typically comprises a lapping step for lapping a glass disk, a cerium oxide polishing step for polishing using cerium oxide abrasive grains, heated sulfuric acid and peroxide. It is preferable to include a cleaning step of cleaning the glass using a cleaning liquid containing hydrogen water, followed by a silica polishing step of polishing using a colloidal silica slurry.

(Lapping process)
The manufacturing method of the glass substrate for information recording media of this invention may also include a lapping process. In the lapping step, a circular hole is formed in the center of the glass disk, and chamfering, main surface lapping, and end mirror polishing are sequentially performed. The main surface lapping step may be divided into a rough lapping step and a fine lapping step, and a shape processing step (drilling at the center of the circular glass plate, chamfering, end polishing) may be provided between them.

  In addition, the mirror polishing of the end face may be performed by laminating glass disks and brushing the inner peripheral end face using cerium oxide abrasive grains, and performing etching treatment instead of brushing the inner peripheral end face. For example, a polysilazane compound-containing liquid may be applied to the treated inner peripheral end surface by a spray method or the like, and baked to form a coating (protective coating) on the inner peripheral end surface.

  The main surface lapping is usually performed using aluminum oxide abrasive grains having an average particle diameter of 6 to 8 μm or abrasive grains made of aluminum oxide. The lapped main surface is usually polished by 20 to 40 μm. The lapping may be performed by fixed abrasive grains using a pad in which diamond abrasive grains are embedded in a resin.

  In these processes, when a glass substrate having no circular hole in the center is manufactured, naturally, the drilling of the center of the glass disk and the mirror polishing of the inner peripheral end surface are unnecessary.

(Cerium oxide polishing process)
Then, the main surface of a glass disc is grind | polished using the slurry containing a cerium oxide abrasive grain. This main surface polishing step is performed using a urethane polishing pad or a suede pad. For example, the wavelength region is λ ≦ using a three-dimensional surface structure analyzer [for example, ADE Opti-flat (trade name)]. Polishing is performed so that the waviness (Wa) measured under the condition of 5 mm is 1 nm or less. Moreover, the reduction | decrease amount (polishing amount) of the plate | board thickness by grinding | polishing is typically 5-15 micrometers.

  The main surface polishing step may be performed by one polishing, or may be performed twice or more using cerium oxide abrasive grains having different sizes. The cerium oxide abrasive grains may be known ones, and usually contain a rare earth metal oxide such as lanthanum or fluorine in addition to cerium oxide.

  In addition, the cerium oxide polishing step in the present invention includes a cerium oxide main surface polishing step for removing scratches generated in the lapping step, but is not limited thereto, and if end surface mirror polishing with cerium oxide is performed after the lapping step, Including.

(Washing process)
Next, the glass disk is cleaned. In this cleaning process, an immersion process with pure water is performed, then a process of mixing sulfuric acid and hydrogen peroxide water and immersing in a heated cleaning liquid is performed, and finally a process of rinsing with pure water is performed. In addition, you may implement the pre-cleaning process using an acidic cleaning agent or an alkali cleaning agent before this cleaning process. Moreover, in the immersion process or rinse process with pure water, ultrasonic cleaning may be used in combination, or cleaning with running water or shower water may be performed.

  In the production method of the present invention, the glass is polished using a cerium-based abrasive, and the glass is cleaned using a cleaning solution containing heated sulfuric acid and hydrogen peroxide solution, thereby suppressing residual cerium-based abrasive. A glass substrate for an information recording medium with less surface roughness on the main surface can be obtained by polishing the glass main surface later with a slurry containing colloidal silica.

  The sulfuric acid concentration in the cleaning liquid is preferably 20% by mass or more and 80% by mass or less, and the hydrogen peroxide concentration is preferably 1% by mass or more and 10% by mass or less, more preferably the sulfuric acid concentration is 50% by mass or more and 80% by mass or less. Hydrogen concentration is 3 mass% or more and 10 mass% or less. By making the concentration of sulfuric acid and hydrogen peroxide equal to or higher than the lower limit, it is possible to prevent the cerium oxide abrasive grains from remaining without being dissolved. By making the concentration of sulfuric acid and hydrogen peroxide below the upper limit, the surface roughness due to leaching of the aluminosilicate glass is prevented from becoming significant, and the desired flatness can be easily obtained even by performing finish polishing described later. At the same time, it is preferable because a resin-made glass jig used for general purposes can be prevented from being oxidized and decomposed.

  For the same reason, the liquid temperature of the cleaning liquid is preferably 50 ° C. or higher and 100 ° C. or lower. Moreover, it is preferable that immersion time is 5 minutes or more and 30 minutes or less. Specifically, it is 25 minutes or more and 30 minutes or less in a cleaning solution of 50 ° C. or more and less than 60 ° C., 15 minutes or more and 30 minutes or less in a cleaning solution of 60 ° C. or more and less than 70 ° C. It is more preferable to immerse under the following conditions.

(Finishing polishing process)
In the above washing step, sulfuric acid is used, so that uneven leaching may occur, and the main surface of the glass disk is polished again to improve the flatness. Further, the cerium oxide abrasive grains remaining on the end face of the glass disk may be reattached to the main surface, but these reattachment abrasive grains are also removed.

  In the final polishing step, the final polishing is usually performed using a slurry containing colloidal silica abrasive grains. In the finish polishing step, polishing is usually performed using a slurry containing colloidal silica abrasive grains having an average particle size of 10 to 50 nm. Further, chemical strengthening may be performed before or after polishing with a slurry containing colloidal silica abrasive grains.

  In polishing with a slurry containing colloidal silica abrasive grains, colloidal silica using water glass as a raw material generally tends to undergo gelation in a neutral region. Therefore, the pH is preferably 1 to 6, more preferably 2 to 5. It is preferable to carry out with.

  As the pH adjuster for acidification, at least one kind of linear saturated dicarboxylic acid is used. Since the linear saturated dicarboxylic acid has a carboxylic acid at the terminal and is linear, the chelating ability is small as compared with a branched or cyclic acid. Since it is not easily roughened, a smoother glass substrate for information recording media can be obtained.

  The linear saturated dicarboxylic acid preferably has 7 or less linear carbon atoms, and more preferably 5 or less. It is preferable that the number of carbon atoms is 7 or less because it is easily dissolved in water. Examples of the linear saturated dicarboxylic acid include succinic acid (linear carbon number 2), glutaric acid (linear carbon number 3), adipic acid (linear carbon number 4), and pimelic acid (linear carbon). 5), suberic acid (straight carbon number 6), and azelaic acid (straight carbon number 7). These acids may be used alone or in combination. The pKa1 of these acids is 3.9 to 4.5, and when the pH is adjusted to 3 to 5, the slurry can have a buffering effect, which is preferable as the pH range.

  As the pH adjuster other than the linear saturated dicarboxylic acid, an inorganic acid is preferable if it is an acid. As the inorganic acid, hydrochloric acid, nitric acid or sulfuric acid is preferable. Nitric acid is particularly preferable. Sulfuric acid is not preferable because it combines with strontium or calcium used in the glass component to form a salt that is hardly soluble in water. In addition, hydrochloric acid is not preferable because it may hate chlorine in an electronic device.

  The pH adjustment is performed as follows. When the pH is 4 or more, the pH of the straight-chain saturated dicarboxylic acid having 4 or less carbon atoms can be adjusted only with the acid. For straight-chain saturated dicarboxylic acids having 5 or more carbon atoms, if the pH is 4 or more, the pH can be adjusted only with the acid, but if the pH is less than 4, the pH can be adjusted in combination with nitric acid. preferable. In that case, it is preferable to add 1% by weight or more of linear saturated dicarboxylic acid to the slurry. This is necessary to provide a function as a buffer.

The polishing tool is preferably a suede pad. This suede pad has a foamed resin layer, preferably has a Shore A hardness of 20 ° to 75 °, and a density of 0.2 to 0.9 g / cm ³ .

  After the finish polishing step, cleaning is performed to remove the colloidal silica abrasive grains. In this cleaning step, it is preferable to perform cleaning with an alkaline cleaning agent having a pH of 10 or more at least once. Thus, it is possible to reduce the colloidal silica residue by polishing using the colloidal silica slurry adjusted to acidity as the final polishing step and then washing the glass with an alkaline cleaning liquid.

  In other words, the colloidal silica surface in the colloidal silica slurry adjusted to acidity has almost no silanol groups separated and is in an inactive state, so it does not adhere firmly to the glass substrate during polishing. When washing is performed with an alkaline aqueous solution, it is considered that the ζ potential becomes negative for both the glass substrate and the colloidal silica, and the colloidal silica hardly remains on the glass substrate due to repulsion with respect to the potential.

  As a cleaning method, ultrasonic vibration may be applied by immersing a glass disk, or scrub cleaning may be used. Moreover, you may combine both. Furthermore, it is preferable to perform an immersion step or a rinsing step with pure water before and after cleaning.

  The glass disk is dried after the final rinsing step. As a drying method, a drying method using isopropyl alcohol vapor, spin drying, vacuum drying, or the like is used.

  Through the above series of steps, a highly flattened glass substrate is obtained. In such a magnetic disk having a magnetic recording layer formed on the main surface of the glass substrate, high-density recording is possible.

  Examples of the present invention will be specifically described below, but the present invention is not limited to these.

[Experiment 1]
Mol% composition _{schematic, SiO 2: 64.5%, Al} 2 O 3: 12%, ZrO 2: 1.8%, Li 2 O: 12.8%, Na 2 O: 5.5%, K _A glass plate of ₂ O: 3.4% was immersed in a pH 2 HNO ₃ aqueous solution or a pH 11 NaOH aqueous solution, and the correlation between surface displacement (nm) and hardness (GPa) was examined. The results measured under the following measurement conditions are shown in FIG.

Measuring instrument: MTS Nano Indenter G2000
Measurement indenter: Berkovich indenter measurement conditions (parameter: condition)
Drift value allowing test start: 0.600 nm / s
Maximum indentation depth: 200nm
Frequency used for continuous stiffness measurement: 75Hz
Amplitude value used for continuous stiffness measurement: 1 nm
Strain rate: 0.05 1 / s
Number of measurements: 6 points per sample

  As a result, as shown in FIG. 3, when the glass was immersed in the acidic aqueous solution, the glass hardness decreased compared to the case of the alkaline aqueous solution. This is considered to be because the alkali metal component on the glass surface was leached by the acid and the glass surface was softened. Moreover, it turns out that acidic aqueous solution has an etching property with respect to aluminosilicate glass, and also may roughen the surface.

[Experiment 2]
Mol% composition _{schematic, SiO 2: 64.5%, Al} 2 O 3: 12%, ZrO 2: 1.8%, Li 2 O: 12.8%, Na 2 O: 5.5%, K ₂ O: Cut out 50 donut-shaped glass discs with an outer diameter of 65 mm, an inner diameter of 20 mm, and a thickness of 0.635 mm from a glass plate of 3.4%, and grinding the inner and outer peripheral surfaces using a diamond grindstone And the 1st grinding process was implemented for the upper and lower main surfaces using the aluminum oxide abrasive grain.

  Next, chamfering was performed to provide a chamfered portion having a width of 0.15 mm and an angle of 45 ° on the inner and outer peripheral end faces. After the chamfering, the end surfaces on the inner and outer circumferences were mirror-finished by brush polishing using a slurry containing cerium oxide abrasive grains having a particle diameter of 1 to 1.5 μm as an abrasive and using a brush as a polishing tool. The removal amount in the radial direction was 30 μm.

  Next, the glass substrate ground in the first grinding step is obtained by using a second fixed abrasive tool and a grinding liquid with a double-sided grinding apparatus (manufactured by Hamai Sangyo Co., Ltd., product name: 16BF-4M5P). Was ground (second grinding step). A fixed abrasive tool (manufactured by 3M, product name: Trizact 4 μm AA1) in which diamond abrasive grains having an average particle diameter of 4 μm were bonded with a resin binder was used as the second fixed abrasive tool. The polishing amount at this time was 136 μm. The ground glass substrate was ultrasonically cleaned while immersed in an alkaline detergent solution.

  Next, the upper and lower main surfaces were polished by a double-side polishing apparatus using a slurry containing cerium oxide abrasive grains having an average particle size of 0.8 to 1 μmφ, using a suede pad as a polishing tool. The polishing amount was 25 μm in total in the thickness direction of the upper and lower main surfaces. As a preliminary cleaning after polishing the main surface of the glass disk, immersion cleaning with pure water, ultrasonic cleaning with an alkaline cleaning agent, and rinsing with pure water were performed in this order.

Next, washing was performed as follows. An aqueous solution of 71.4% sulfuric acid, aqueous hydrogen peroxide, and 7.7% was heated to 80 ° C., and glass was placed in it for cleaning. Then, after rinsing the glass with pure water, the upper and lower main planes of the glass substrate were polished by a double-side grinding apparatus (product name: 16BF-4M5P, manufactured by Hamai Sangyo Co., Ltd.) using a polishing slurry containing colloidal silica abrasive grains. As the polishing slurry, 62.5 g of citric acid was added to 12.5 L of pure water and stirred well, then 2.5 L of colloidal silica abrasive SI40 manufactured by Catalyst Kasei Co., Ltd. was added and stirred well. . The pH at this time was 4.0. As the polishing pad, a suede pad having a Shore A hardness of 60 ° and a density of 0.62 g / cm ³ was used.

  Then, after washing with pure water, ultrasonic cleaning with an alkaline cleaning liquid, scrub cleaning with an alkaline cleaning liquid, and ultrasonic cleaning with an alkaline cleaning liquid are performed, followed by rinsing with pure water, and drying using IPA drying. did. When Ra was measured in the range of 1 μm × 1 μm with AFM (SPA 400 manufactured by SII Nanotechnology), this substrate was 0.111 nm.

[Experiment 3]
A preliminary test was conducted as follows. The glass substrate obtained in Experimental Example 2 was immersed in the following aqueous solution with ultrasonic irradiation for 2 hours. Thereafter, Ra of 1 μm × 1 μm was measured using AFM. The results are shown in Table 1 and FIG.

  As shown in Table 1 and FIG. 4, in the succinic acid, adipic acid, pimelic acid and azelaic acid which are linear saturated dicarboxylic acids, it was confirmed that the roughness of the substrate surface was suppressed. This is considered to be because when the linear saturated dicarboxylic acid is contained in the colloidal silica slurry, the linear saturated dicarboxylic acid has an effect of making the glass surface less likely to be rough because the chelating action is small.

[Experimental Example 4]
The glass substrate obtained in Experimental Example 2 was immersed in the acidic aqueous solution shown in Table 2 while being irradiated with ultrasonic waves for 10 minutes. Then, it immersed in the alkaline aqueous solution shown in Table 2, performing ultrasonic irradiation for 10 minutes. Thereafter, Ra of 1 μm × 1 μm was measured using AFM. The results are shown in Table 2 and FIG.

  As shown in Table 2 and FIG. 5, if the acid immersion treatment using pimelic acid is performed among the linear saturated dicarboxylic acids, the surface roughness of the glass substrate is suppressed even if the immersion treatment is performed using a sodium hydroxide aqueous solution. As Ra, a small value of 0.111 nm was obtained. From this viewpoint, it can be seen that it is preferable to use pimelic acid as the linear saturated dicarboxylic acid. Although Ra in Example 11 is a relatively small value, triethanolamine is expensive and unsuitable for glass substrate cleaning.

[Example 1]
The following polishing test was conducted. The glass substrate obtained in Experimental Example 2 was polished with the following colloidal silica slurry and a suede pad. That is, the composition of the colloidal silica slurry is as shown in the column from acid type 1 to pH in Table 3, and as the colloidal silica, colloidal silica SI40 manufactured by Catalyst Kasei Co., Ltd. is used. Shown in the column.

  Then, after ultrasonic cleaning with an alkaline cleaning solution of pH 12, scrub cleaning was performed with an alkaline cleaning solution of pH 10, rinsed with pure water, dried, and Ra was measured under the same conditions as described above. Example 17 is a comparative example, and Examples 18 to 21 are examples. The results are shown in Table 3 and FIG. The polishing rate is also shown in Table 3.

  As shown in Table 3 and FIG. 6, when glass was grind | polished using the colloidal silica slurry containing a linear saturated dicarboxylic acid, it was confirmed that a grinding | polishing surface is not rough. For comparison, a polishing test using a slurry obtained by adding 0.1% of sodium salt of acrylic acid / sulfonic acid copolymer having an average molecular weight of 5000 to the slurry of Example 17 was performed in the same manner as in Examples 17-21. As a result, Ra was 0.082 nm, which was relatively small, but it was found that the polishing rate was 0.025 μm / min and decreased.

Claims (8)

  A process of polishing glass using a cerium-based abrasive, a cleaning process of cleaning glass using a cleaning liquid containing heated sulfuric acid and hydrogen peroxide, and a process of polishing a glass main surface using a slurry containing colloidal silica A method for producing a glass substrate for an information recording medium, characterized in that a linear saturated dicarboxylic acid is contained in the slurry.   The method for producing a glass substrate for an information recording medium according to claim 1, wherein the colloidal silica slurry has a pH of 3 or more and 5 or less.   The method for producing a glass substrate for an information recording medium according to claim 1 or 2, wherein the linear saturated dicarboxylic acid contained in the colloidal silica has 2 to 7 carbon atoms.   The information recording medium according to any one of claims 1 to 3, wherein the linear saturated dicarboxylic acid is one or more selected from the group consisting of succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid and azelaic acid. Method for manufacturing glass substrate.   The information recording according to any one of claims 1 to 4, wherein the step of polishing the glass main surface using the slurry containing colloidal silica is a finish polishing step, and then includes a cleaning step using an alkaline aqueous solution. A method for producing a glass substrate for a medium.   The method for producing a glass substrate for an information recording medium according to any one of claims 1 to 5, wherein the colloidal silica has an average particle diameter of 10 to 50 nm. Method of manufacturing a glass substrate for information recording medium according to claim 1 information recording medium is a magnetic disk. A method of manufacturing a magnetic disk , comprising forming a magnetic recording layer on a main surface of a glass substrate for information recording media obtained by the manufacturing method according to claim 7 .

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