JP5821188B2 - Manufacturing method of glass substrate for information recording medium - Google Patents

Description

  The present invention relates to a method for producing a glass substrate used for an information recording medium such as a magnetic disk and an optical disk.

  A glass substrate is used as a substrate of a magnetic disk used in a magnetic disk storage device or the like. This glass substrate is usually in the shape of a disc having a circular hole in the center, and both the main surface and the end surface are desired to eliminate the presence of foreign matter defects in order to eliminate read / write errors by the head. .

  Also, in magnetic disk storage devices, etc., aiming to improve recording density, the distance between the outermost surface of the magnetic film coated on the glass substrate for information recording media and the head tends to be closer, and there is a foreign object defect on the glass substrate surface. If the head is present, the head collides with a foreign object defect at the time of reading and writing, causing a head crash.

  A glass substrate used for an information recording medium is usually cut into a glass plate, rounded, chamfered, ground, peripheral and inner peripheral polishing, etching, primary and secondary polishing, final polishing, scrub and final cleaning. It is manufactured by. Conventionally, a treatment liquid containing sulfuric acid has been used as a treatment liquid used for etching and cleaning in a glass substrate manufacturing process (for example, Patent Document 1).

JP 7-296380 A

  However, the present inventors, in particular, in the process of producing a glass substrate from a glass plate containing an alkaline earth metal oxide, when using a treatment liquid containing sulfuric acid for etching and cleaning, the alkaline earth metal oxide and sulfuric acid As a result, a slightly soluble salt that is a reaction product is generated, and the reaction product remains as a defective foreign substance on the glass surface, and etching proceeds as a mask, thereby improving the flatness and smoothness of the glass substrate surface. It confirmed that it fell remarkably.

  Accordingly, the present invention provides a method for producing a glass substrate for magnetic disk information recording medium that does not cause a foreign matter defect on the glass substrate surface when producing a glass substrate for information recording medium from a glass plate containing an alkaline earth metal oxide. The purpose is to provide.

  As a result of intensive studies in view of the above problems, when etching and cleaning a glass plate containing an alkaline earth metal oxide, nitric acid, acetic acid, hydrochloric acid, perchloric acid, propionic acid, butyric acid, without containing sulfuric acid as an acid, A treatment solution containing at least one selected from tartaric acid, malonic acid, malic acid, succinic acid, fumaric acid, maleic acid, citric acid, ascorbic acid, hydrobromic acid, hydroiodic acid, alkylsulfonic acid and alkylphosphonic acid As a result, it was found that the reaction product was not generated on the surface of the glass substrate and the flatness and smoothness were improved, and the present invention was completed.

  That is, the gist of the present invention is as follows.

A disk processing step of processing a glass plate containing one or more of CaO, SrO and BaO into a glass disc, a wrapping step of wrapping the main surface of the glass disc, and a main surface of the glass disc wrapping A method for producing a glass substrate for an information recording medium comprising a main surface polishing step to be polished and a step of surface-treating a glass disk in or after these steps,
Treatment liquid used for surface treatment is nitric acid, acetic acid, hydrochloric acid, perchloric acid, propionic acid, butyric acid, tartaric acid, malonic acid, malic acid, succinic acid, fumaric acid, maleic acid, citric acid, ascorbic acid, hydrobromic acid And a method for producing a glass substrate for an information recording medium, comprising at least one selected from hydroiodic acid, alkylsulfonic acid, and alkylphosphonic acid.

A disk processing process for processing a glass plate into a glass disk, a lapping process for lapping the main surface of the glass disk, a main surface polishing process for polishing the lapped main surface of the glass disk, and between these processes. Or a method for producing a glass substrate for an information recording medium comprising a step of surface-treating a glass disc after these steps,
The glass plate contains mole percentages of SiO ₂ 62-74%, Al ₂ O ₃ 7-18%, B ₂ O ₃ 2-15%, MgO 0-10%, CaO, SrO and 1 to 21% in total of any one component of BaO is contained, the total content of MgO, CaO, SrO and BaO is 8 to 21%, and the total content of the seven components is 95% or more,
Treatment liquid used for surface treatment is nitric acid, acetic acid, hydrochloric acid, perchloric acid, propionic acid, butyric acid, tartaric acid, malonic acid, malic acid, succinic acid, fumaric acid, maleic acid, citric acid, ascorbic acid, hydrobromic acid And a method for producing a glass substrate for an information recording medium, comprising at least one selected from hydroiodic acid, alkylsulfonic acid, and alkylphosphonic acid.

A disk processing process for processing a glass plate into a glass disk, a lapping process for lapping the main surface of the glass disk, a main surface polishing process for polishing the lapped main surface of the glass disk, and between these processes. Or a method for producing a glass substrate for an information recording medium having a step of surface-treating a glass disc after these steps,
A glass plate mole percentage display, a SiO ₂ 67 to 72% _Al 2 _{O 3 11-14%} contain B less than 2 _{O 3} 0-2% the MgO 4 to 9% of CaO 4 ~ 6%, SrO 1-6%, BaO 0-5%, MgO, CaO, SrO and BaO total content is 14-18%, total content of the above 7 components is 95% or more ,
Treatment liquid used for surface treatment is nitric acid, acetic acid, hydrochloric acid, perchloric acid, propionic acid, butyric acid, tartaric acid, malonic acid, malic acid, succinic acid, fumaric acid, maleic acid, citric acid, ascorbic acid, hydrobromic acid And a method for producing a glass substrate for an information recording medium, comprising at least one selected from hydroiodic acid, alkylsulfonic acid, and alkylphosphonic acid.

  The method for producing a glass substrate for an information recording medium, wherein the total content of CaO, SrO and BaO in the glass plate is 7% or more in terms of mole percentage.

  The manufacturing method of the glass substrate for information recording media whose annealing point of a glass plate is 650 degreeC or more.

  The method for producing a glass substrate for an information recording medium, wherein the surface treatment is etching.

  The method for producing a glass substrate for an information recording medium, wherein the treatment liquid used for etching further contains hydrofluoric acid.

  A method for producing a glass substrate for information recording medium, comprising the step of forming a hole in the center of a glass disk, wherein the inner surface of the hole of the glass substrate for information recording medium is the etched surface or polished A method for producing a glass substrate for an information recording medium, which is a processed surface.

  The method for producing a glass substrate for an information recording medium, wherein the surface treatment is cleaning.

  The manufacturing method of the said glass substrate for information recording media which manufactures a glass plate using a float glass process or a down draw method.

  The method for producing a glass substrate for an information recording medium, wherein the information recording medium is a magnetic disk.

  According to the production method of the present invention, it is possible to effectively suppress the occurrence of foreign matter defects on the surface of a glass substrate containing an alkaline earth metal oxide. As a result, the flatness and smoothness of the surface of the glass substrate for information recording media can be suppressed. The degree can be improved.

  The manufacturing method of the present invention includes a disk processing step for processing a glass plate into a glass disc, a wrapping step for wrapping the main surface of the glass disc, a main surface polishing step for polishing the lapped main surface of the glass disc, and It is a manufacturing method of the glass substrate for information recording media which has the process of surface-treating a glass disk between these processes, in these processes, or after these processes.

The glass plate (hereinafter sometimes referred to as substrate glass) contains at least one component of CaO, SrO, and BaO as an alkaline earth metal oxide. The total content of CaO, SrO and BaO in the substrate glass is preferably 7% or more, more preferably 7.5% or more, and still more preferably 8% or more, in terms of a molar percentage composition. . Further, it is usually preferably 21% or less, more preferably 18% or less, and further preferably 14% or less.

  When the total content of CaO, SrO and BaO in the substrate glass is 7% or more, the treatment liquid used for the etching and cleaning steps is nitric acid, acetic acid, hydrochloric acid, perchloric acid, propionic acid, butyric acid, tartaric acid, malonic acid. By treating with at least one selected from malic acid, succinic acid, fumaric acid, maleic acid, citric acid, ascorbic acid, hydrobromic acid, hydroiodic acid, alkylsulfonic acid and alkylphosphonic acid, Generation | occurrence | production of a foreign material defect can be suppressed more effectively.

  When surface treatment is performed on a substrate glass having a total content of CaO, SrO and BaO of 7% or more using a treatment solution containing sulfuric acid, CaO, SrO, BaO and sulfuric acid react with each other to form a hardly soluble sulfate. Is generated and becomes a foreign matter defect. Therefore, by using an acid other than sulfuric acid as the acid used in the treatment liquid, the occurrence of the foreign matter defect is suppressed.

  Moreover, by making the total content 21% or less, it is possible to prevent the glass from becoming too high in the devitrification temperature, and to produce by a process suitable for mass production such as a float method, a fusion method, and a downdraw method. .

  As substrate glass used for this invention, the substrate glass 1 and the substrate glass 2 of the following compositions are preferable. Hereinafter, mol% is simply expressed as%.

(Substrate glass 1)
The substrate glass 1 contains SiO ₂ 62 to 74%, Al ₂ O _{3 7} to 18%, B ₂ O ₃ 2 to 15% in terms of mole percentage, MgO 0 to 10%, CaO, A substrate containing 1 to 21% in total of any one or more of SrO and BaO, a total content of MgO, CaO, SrO and BaO of 8 to 21%, and a total content of the seven components of 95% or more It is glass.

SiO ₂ is an essential component. The content of SiO ₂ in the substrate glass 1 is 62% or more, and preferably 65% or more. Moreover, it is 74% or less, and it is more preferable that it is 69% or less. If it is less than 62%, the glass tends to be damaged, and the acid resistance of the glass becomes low. On the other hand, if it exceeds 74%, the solubility is lowered and glass production becomes difficult.

Al ₂ O ₃ is an essential component. The content of Al ₂ O ₃ in the substrate glass 1 is 7% or more, and more preferably 9% or more. Moreover, it is 18% or less, and it is more preferable that it is 12% or less. If it is less than 7%, the glass tends to undergo phase separation, and there is a possibility that a smooth surface cannot be maintained after the substrate is processed and washed. Or glass may be easily damaged. On the other hand, if it exceeds 18%, the solubility is lowered and glass production becomes difficult. Moreover, the acid resistance of glass becomes low.

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. The content of B ₂ O ₃ in the substrate glass 1 is 2% or more, and preferably 7% or more. Moreover, it is 15% or less, and it is preferable that it is 12% or less. If it is less than 2%, the solubility of the glass decreases. On the other hand, if it exceeds 15%, the glass tends to undergo phase separation, and a smooth surface cannot be maintained after processing and cleaning the substrate. Moreover, the acid resistance of glass becomes low.

  Although MgO is not essential, the solubility of glass can be improved by containing MgO. Moreover, there exists an effect which reduces the thermal expansion coefficient of glass. The content of MgO in the substrate glass 1 is 10% or less, and preferably 0 to 7%. If it exceeds 10%, phase separation tends to occur. Moreover, the devitrification temperature of glass becomes high.

  CaO, SrO, and BaO are components that improve the solubility of the glass, and must contain at least one component. The total content of CaO, SrO and BaO in the substrate glass 1 is 1 to 21%, and preferably 7 to 14%. When the total content is less than 1%, the solubility is lowered and glass production becomes difficult. On the other hand, if it exceeds 21%, the devitrification temperature of the glass becomes high. In addition, the glass may be easily damaged.

  Further, the total content (RO) of MgO, CaO, SrO and BaO in the substrate glass 1 is 8% or more, and preferably 10% or more. Moreover, it is 21% or less, and it is preferable that it is 16% or less. If the total content is less than 8%, the solubility of the glass is lowered and glass production becomes difficult. On the other hand, when RO exceeds 21%, the devitrification temperature of the glass increases. Moreover, it becomes easy to damage glass.

  The substrate glass 1 is essentially composed of the above seven components, but may contain other components as long as the total content is less than 5% within a range not impairing the object of the present invention. If the total content of components other than the above seven components is 5% or more, the glass is easily 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. In the substrate glass 1, it may be contained in a range of less than 5%. Further, the total content of ZnO and RO is preferably 8 to 21%, and more preferably 10 to 16%.

Since Li ₂ O, Na ₂ O and _{K 2} O decreases the annealing point _{T A,} it is preferable that the total content of these three components in the substrate glass 1 to be less than is either 1% 0%.

  An oxide having an atomic number larger than Ti, such as V, may easily damage the glass. When these oxides are contained in the substrate glass 1, the total content is preferably 3% or less, more preferably 2% or less, still more 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.

(Substrate glass 2)
Substrate glass 2 in molar percentage display, a SiO ₂ 67 to 72% _Al 2 _{O 3 11-14%} contain B less than 2 _{O 3} 0-2% 4-9% The MgO, CaO 4-6%, SrO 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 It is substrate glass which is.

Substrate glass 2 is a suitable substrate glass when it is desired to increase the annealing point T _A or acid resistance.

SiO ₂ is an essential component. The content of SiO ₂ in the substrate glass 2 is 67% or more, more preferably at least 68%. Moreover, it is 72% or less, and 71% or less is more preferable. If it is less than 67%, the glass tends to be damaged. Moreover, the acid resistance of glass becomes low. On the other hand, if it exceeds 72%, the solubility is lowered and glass production becomes difficult.

Al ₂ O ₃ is an essential component. The content of Al ₂ O ₃ in the substrate glass 2 is 11% or more, and more preferably 12% or more. Moreover, it is 14% or less, and it is more preferable that it is 13.5% or less. If it is less than 11%, the glass tends to phase-separate, and it may become impossible to maintain a smooth surface after the substrate is processed and washed, or the glass may be easily damaged. On the other hand, if it exceeds 14%, the solubility is lowered and glass production becomes difficult.

B ₂ O ₃ is not an essential component, but has an effect of improving the solubility of glass. The content of B ₂ O ₃ in the substrate glass 2 is preferably less than 2%. Is 2% or more may decrease acid resistance or T _A.

  MgO, CaO and SrO are components that improve the solubility of glass and are essential. The content of MgO in the substrate glass 2 is 4% or more, and preferably 4.5% or more. Moreover, it is 9% or less, and it is preferable that it is 8.5% or less. If the MgO content is less than 4%, the solubility is lowered. If it exceeds 9%, the glass tends to be damaged. Moreover, the devitrification temperature of glass becomes high.

  The content of CaO in the substrate glass 2 is 4% or more, and preferably 4.5% or more. Moreover, it is 6% or less, and it is preferable that it is 5.5% or less. If the CaO content is less than 4%, the solubility is lowered. If it exceeds 6%, the glass tends to be damaged. Moreover, the devitrification temperature of glass becomes high.

  The SrO content in the substrate glass 2 is 1% or more, preferably 1.5% or more. Moreover, it is 6% or less, and it is preferable that it is 5% or less. If the SrO content is less than 1%, the solubility is lowered. If it exceeds 6%, the glass tends to be damaged. Moreover, the devitrification temperature of glass becomes high.

  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 it exceeds 5%, the glass tends to be damaged. Moreover, the devitrification temperature of glass becomes high.

  Further, the total content (RO) of MgO, CaO, SrO and BaO in the substrate glass 2 is 14% or more, and preferably 15% or more. Moreover, it is 18% or less, and it is more preferable that it is 17.5% or less. If RO is less than 14%, the solubility of the glass decreases, making glass production difficult. On the other hand, when RO exceeds 18%, the glass is easily damaged. Moreover, the devitrification temperature of glass becomes high.

  Substrate glass 2 consists essentially of the above seven components, but may contain other components as long as the total content is less than 5% within the 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 effects as MgO, CaO, SrO, and BaO. The ZnO content in the substrate glass 2 is preferably less than 5%. Further, the total content of ZnO and RO is preferably 14 to 18%, and more preferably 15 to 17.5%.

Since Li ₂ O, Na ₂ O and _{K 2} O decreases the _{T A,} it is preferable that the total content of these three components in the substrate glass 2 to be less than is either 1% 0%.

  Since oxides having an atomic number larger than Ti such as V may easily damage the glass, when these oxides are contained in the substrate glass 2, the total content is preferably 3% or less. % Or less is more preferable, 1% or less is more preferable, and 0.3% or less is most preferable.

SO ₃ , F, Cl, As ₂ O ₃ , Sb ₂ O _3, SnO _{2 and the} like are typical components as fining agents.

It is preferred that the annealing point T _A of the substrate glass is 650 ° C. or higher, more preferably 680 ° C. or higher, further preferably 700 ° C. or higher. Moreover, it is preferable that it is 750 degrees C or less normally. By setting the temperature to 650 ° C. or higher, the glass is less likely to warp when the magnetic recording layer is formed, and reading / writing troubles are less likely to occur.

  The crack occurrence rate p (unit:%) of the substrate glass is preferably 50% or less, more preferably 30% or less, and particularly preferably 10% or less. By setting it to 50% or less, the glass is hardly scratched and stress concentration hardly occurs. As a result, brittle fracture is less likely to occur even under weak stress.

  p is measured as follows. After polishing the glass with a cerium oxide abrasive having an average particle diameter of 2 mm, the glass is polished with a colloidal silica abrasive having an average particle diameter of 20 nm, the thickness is 1 to 2 mm, the size is 4 cm × 4 cm, and the surface roughness Ra is 15 nm or less. A glass plate is prepared, and the glass plate is held at a slow cooling point or a glass transition point for 30 minutes, and then cooled to room temperature at a rate of 1 ° C./min or less. A Vickers indenter is driven at a load of 1000 g in a room controlled at 23 ° C. and a relative humidity of 70% on the surface of the glass plate, and the number of cracks generated from the four apexes is measured. This measurement is repeated 10 times, and 100 × (total number of cracks) ÷ 40 is defined as p.

The acid resistance of the substrate glass is preferably 0.1 mg / cm ² or less. By setting it to 0.1 mg / cm ² or less, it is possible to suppress surface roughness in a polishing or cleaning process using an acid. The acid resistance is determined by measuring the amount of weight loss after immersing the substrate glass in 0.1N hydrochloric acid at 90 ° C. for 20 hours and dividing by the sample surface area.

  The specific gravity of the substrate glass is preferably 2.65 or less, more preferably 2.60 or less, still more preferably 2.55 or less, and most preferably 2.52 or less. By setting it to 2.65 or less, it is possible to prevent a motor load from being applied during rotation of the magnetic disk drive, to reduce power consumption and to stabilize drive rotation.

  In the production method of the present invention, a glass substrate for an information recording medium is usually produced through the following steps. That is, the glass plate is made into a glass disc (disc processing step), a circular hole is formed in the center of the glass disc, and end surface polishing, chamfering, main surface lapping (lapping step), and outer peripheral end surface mirror polishing are sequentially performed. Then, a disk-shaped glass plate is laminated | stacked, an inner peripheral end surface is etched, and it polishes as needed. Next, the main surface of the disk-shaped glass plate is polished (main surface polishing step) to obtain a flat and smooth surface, which is a glass substrate for an information recording medium.

  The manufacturing method of this invention includes the process of surface-treating a glass disk between each process of a disk processing process, a lapping process, and a main surface grinding | polishing process, or after these processes. In the present invention, “surface treatment” refers to etching treatment or cleaning treatment.

(Manufacture of glass plates)
The manufacturing method of the glass plate used for the manufacturing method of this invention is not specifically limited, Various methods are applicable.

  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, adding a clarifying agent, etc., and forming it into a sheet glass of a predetermined thickness by methods such as the well-known float method, press method, fusion method or down draw 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 suitable. Further, continuous molding methods other than the float method, that is, the fusion method and the downdraw method are also suitable.

  In addition, it is preferable that the thickness of a glass plate is about 0.38-1.2mm normally.

(Disc processing process)
The disk processing step is a step of cutting a glass plate into a donut-shaped glass disk by cutting out an inner diameter and an outer diameter.

(Grinding of inner and outer peripheral end faces)
After processing into a donut-shaped glass disk, the inner peripheral end face and the outer peripheral end face are ground using a diamond grindstone. The diamond grindstone is preferably a # 800 mesh under product.

(Lapping process)
The lapping step is a step of grinding (lapping) the main surface of the glass disk. The main surface lapping is usually preferably performed using aluminum oxide abrasive grains having an average particle diameter of 6 to 8 μm or aluminum oxide abrasive grains. The lapped main surface is usually preferably polished by 30 to 40 μm.

  After lapping the main surface, end face mirror polishing is 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 the end surface mirror polishing, brush polishing is performed using a cerium oxide slurry as an abrasive and a brush as a polishing tool, and the outer peripheral end surface is mirror-finished. The cerium oxide as the abrasive is preferably a # 200 to # 1000 mesh product. In addition, the polishing amount at this time is suitably about 30 μm in terms of the removal amount in the radial direction. By this mirror finishing, the surface roughness (Ra) is preferably 1.0 μm or less, and more preferably 0.7 μm or less.

  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 face are unnecessary.

(Etching process)
After end mirror polishing, the inner periphery or the entire surface is etched. Moreover, you may etch the inner surface of the hole of the glass disc center. In the end surface mirror polishing, a glass disk may be laminated, and the inner peripheral end surface may be subjected to brush polishing using cerium oxide abrasive grains and subjected to an etching process.

  Further, instead of brushing the inner peripheral end face, for example, a polysilazane compound-containing liquid may be applied to the etched inner peripheral end face by a spray method or the like and baked to form a coating (protective coating) on the inner peripheral end face. Good.

  The etching process is generally performed by immersing a disk-shaped glass plate in an etching solution, but can be performed by a spray method or other methods. In addition, it is preferable that this etching process is a thing which does not form a high protrusion in an inner peripheral end surface, and when this etching process is a surface treatment in this invention, it is made to contact with etching liquid.

  The etching depth, which is the etching amount of the inner peripheral end face, that is, the removal thickness of the inner peripheral end face glass by the etching process, is preferably 2 to 25 μm. By setting the thickness to 2 μm or more, it is possible to sufficiently remove deep scratches existing on the inner peripheral end face and improve the mechanical strength. Preferably it is 5 micrometers or more. Moreover, by setting it as 25 micrometers or less, it can prevent that a high protrusion is formed in an inner peripheral end surface. Preferably it is 20 micrometers or less.

  When the etching treatment is a surface treatment in the present invention, the treatment liquid used for the treatment is nitric acid, acetic acid, hydrochloric acid, perchloric acid, propionic acid, butyric acid, tartaric acid, malonic acid, malic acid, succinic acid, fumaric acid, maleic acid, It contains at least one selected from citric acid, ascorbic acid, hydrobromic acid, hydroiodic acid, alkylsulfonic acid and alkylphosphonic acid, and more preferably further contains hydrofluoric acid. The treatment solution does not contain sulfuric acid.

  Among these acids, nitric acid and hydrochloric acid are particularly preferable from the viewpoint of workability on site. Moreover, these acids may be used independently and may be used in combination of multiple types. As a combination of plural kinds, a combination of hydrofluoric acid and nitric acid, or a combination of hydrofluoric acid and hydrochloric acid is particularly preferable from the viewpoint of workability on site.

  When hydrofluoric acid and nitric acid are used in combination, the mixing ratio (mass) of concentrated hydrofluoric acid, concentrated nitric acid and water is preferably 2: 1: 7 to 1: 3: 6, and 1: 1: 8 to 1. : 2: 7 is more preferable. By setting it as the said range, an etching rate becomes appropriate and it becomes easy to perform an etching process.

When a glass substrate is produced using a substrate glass containing at least one component of CaO, SrO and BaO as an alkaline earth metal oxide by using a treatment solution containing the acid as a treatment solution used for the etching treatment. The occurrence of foreign matter defects on the glass substrate surface can be effectively suppressed, and the flatness and smoothness can be remarkably improved.

  The content of the acid in the treatment liquid used for the etching treatment is preferably 1 to 20% by mass, and more preferably 4 to 18% by mass. By setting it to 1% by mass or more, a minimum necessary etching rate can be easily obtained. By setting it to 20% by mass or less, the etching rate becomes appropriate and the etching process is facilitated.

(Polishing the inner peripheral surface)
After the above steps, it is preferable to polish the inner peripheral end surface. As a polishing method, brush polishing, sponge polishing, viscous fluid polishing, magnetic fluid polishing, and sponge grindstone polishing are preferable. These polishing methods may be used alone or in appropriate combination. Further, the glass substrates may be polished one by one, or a plurality of stacked substrates may be polished at once.

  In addition, it is preferable to perform brush grinding | polishing using the slurry and resin brush containing the cerium oxide whose average particle diameter is 0.5-1.8 micrometers. The sponge polishing is preferably performed using a slurry containing cerium oxide having an average particle diameter of 0.5 to 1.8 μm and a sponge made of urethane.

  Viscous fluid polishing includes cerium oxide having an average particle size of 0.5 to 1.8 μm, polyacrylic acid, ethylene glycol, glycerin, polyvinyl alcohol, sodium carboxymethylcellulose, galactomannan, methylated polygalacturonic acid, etc. It is preferable to use a slurry containing a thickener and having a viscosity of 0.01 Pa · s or more.

  The magnetic fluid polishing is preferably performed using a mixed slurry of cerium oxide and magnetic powder having an average particle size of 0.5 to 1.8 μm.

  The sponge grindstone polishing is preferably performed using a foamed urethane sponge grindstone in which any one of cerium oxide, aluminum oxide, magnesium oxide, and calcium carbonate having an average particle diameter of 0.5 to 1.8 μm is mixed.

  By such a polishing process, the ridgeline formed by the etching process is worn away, and the generation of glass fine powder when it comes into sliding contact with the spindle shaft can be suppressed.

  Furthermore, the etching process can be performed again after the above polishing process. By this etching process, the edge of the ridge line caused by abrasion disappears, and the generation of glass fine powder can be further suppressed.

(Main surface polishing process)
Next, the main surface is polished. This polishing is preferably performed using a slurry containing cerium oxide having an average particle size of 0.9 to 1.8 μm and a urethane polishing pad. The reduction amount (polishing amount) of the plate thickness at this time is suitably 30 to 40 μm, for example. Thereafter, the polishing is further performed using cerium oxide having an average particle diameter smaller than that of the above cerium oxide as the abrasive, for example, an average particle diameter of 0.15 to 0.25 μm, and using a urethane pad as the polishing tool. The polishing amount at this time is suitably about 1.6 μm, for example.

  Some magnetic disk recording devices hold the outer peripheral end face of the magnetic disk. For the glass substrate for a magnetic disk used in such a magnetic disk recording apparatus, the above etching process and polishing process are similarly performed on the outer peripheral end surface of the glass plate.

(Washing process)
The cleaning step is a step of cleaning the glass disk by immersing the glass disk in pure water, then immersing it in a cleaning liquid heated by mixing sulfuric acid and hydrogen peroxide, and finally rinsing with pure water. It is.

  In addition, you may implement the pre-cleaning process using an acidic cleaning agent and an alkaline cleaning agent before a 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.

  When the cleaning is a surface treatment in the present invention, the treatment liquid used for the treatment is nitric acid, acetic acid, hydrochloric acid, perchloric acid, propionic acid, butyric acid, tartaric acid, malonic acid, malic acid, succinic acid, fumaric acid, maleic acid, citric acid. It contains at least one selected from acids, ascorbic acid, hydrobromic acid, hydroiodic acid, alkylsulfonic acid and alkylphosphonic acid, and does not contain sulfuric acid.

  Among these acids, nitric acid, hydrochloric acid, citric acid, and ascorbic acid are particularly preferable from the viewpoints of on-site workability and cleaning effect. These acids may be used alone or in combination of two or more, but are usually used alone.

When a glass substrate is produced using a substrate glass containing at least one component of CaO, SrO and BaO as an alkaline earth metal oxide by using a treatment solution containing the acid as a treatment solution used for cleaning, Generation | occurrence | production of the foreign material defect on the surface of a glass substrate can be suppressed effectively, and flatness and smoothness can be improved significantly.

The acid content in the treatment solution used for washing is preferably 10 ⁻⁶ to 10 ⁻² mol / L, and more preferably 10 ⁻⁴ to 10 ⁻⁵ mol / L. By setting it to 10 ⁻² mol / L or less, excessive leaching hardly occurs. By setting it to 10 ⁻⁶ mol / L or more, it becomes easy to obtain a cleaning effect.

  The pH of the treatment liquid used for washing is preferably 2 to 6, and more preferably 4 to 5. When the pH is set to 2 or more, surface changes due to excessive leaching of alkali metal components or alkaline earth metal components in the glass are less likely to occur. Further, when the pH is set to 6 or less, the etching rate becomes appropriate and the cleaning effect is easily obtained.

  The liquid temperature of the cleaning liquid may be appropriately selected according to the etching rate.

(Finishing polishing process)
In the final polishing step, final polishing is performed using the slurry. In the case of a glass having poor acid resistance, it is preferable to perform polishing using a slurry and a suede pad before the final polishing step (repolishing step). The suede pad preferably has a foamed resin layer having a Shore A hardness of 60 ° or less attached to PET or a nonwoven fabric. Moreover, it is preferable that the said Shore A hardness is 20 degrees or more.

  By setting the Shore A hardness to 60 ° or less, it is difficult to reduce the porosity and it is easy to maintain hydrophilicity. Further, by setting the Shore A hardness to 20 ° or more, it is possible to prevent the polishing rate from becoming slow.

  The foamed resin layer may be a single layer or may be a laminate of two or more foam layers having different foam forms. In the latter case, the Shore A hardness of the first foamed resin layer in contact with the glass is 20 ° or more and 50 ° or less, the lower second foamed resin layer is 40 ° or more and 60 ° or less, and the first foam layer is It is preferable that the hardness is lower than that of the second foam layer.

Such a foamed resin layer is typically polyurethane. In particular, the suede pad is typically made of a urethane foam resin having a Shore A hardness of 30 to 60, a compressibility of 0.5 to 10%, and a density of 0.2 to 0.9 g / cm ^3. .

  The Shore A hardness is measured by a method for measuring the durometer A hardness of plastic specified in JIS K7215.

The compression rate (unit:%) is measured as follows. That is, for a measurement sample cut out to an appropriate size from the polishing pad, a material thickness t ₀ when a stress of 10 kPa is applied for 30 seconds from a no-load state using a shopper type thickness measuring device is obtained, Next, the material thickness t ₁ when a stress load of 110 kPa is immediately applied for 5 minutes from the state where the thickness is t ₀ is obtained, and from the values of t ₀ and t ₁ , (t ₀ −t ₁ ) × 100 / to calculate the t _0, and this is the compression ratio.

(Final cleaning process)
It is preferable to perform final cleaning after the finish polishing step. In the final cleaning step, it is preferable to perform cleaning with an alkaline cleaner having a pH of 10 or more at least once. 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 rinse step with pure water before and after cleaning.

  When the cleaning in the final cleaning step is a surface treatment in the present invention, the treatment liquid is nitric acid, acetic acid, hydrochloric acid, perchloric acid, propionic acid, butyric acid, tartaric acid, malonic acid, malic acid, succinic acid, fumaric acid, maleic acid And at least one selected from citric acid, ascorbic acid, hydrobromic acid, hydroiodic acid, alkylsulfonic acid and alkylphosphonic acid, and does not contain sulfuric acid.

  Among these acids, nitric acid and hydrochloric acid are particularly preferable from the viewpoint of workability on site and cleaning effect. These acids may be used alone or in combination of two or more, but are usually used alone.

When a glass substrate is produced using a substrate glass containing at least one component of CaO, SrO and BaO as an alkaline earth metal oxide by using a treatment liquid containing the acid as a treatment liquid used for final cleaning. The occurrence of foreign matter defects on the glass substrate surface can be effectively suppressed, and the flatness and smoothness can be remarkably improved.

The acid content in the treatment liquid used for final cleaning is preferably 10 ⁻⁶ to 10 ⁻² mol / L, and more preferably 10 ⁻⁵ to 10 ⁻³ mol / L. By setting it to 10 ⁻² mol / L or less, excessive leaching hardly occurs. By setting it to 10 ⁻⁶ mol / L or more, it becomes easy to obtain a cleaning effect.

  The pH of the treatment liquid used for the final cleaning is preferably 2 to 6, and more preferably 3 to 5. When the pH is set to 2 or more, surface changes due to excessive leaching of alkali metal components or alkaline earth metal components in the glass are less likely to occur. Further, when the pH is set to 6 or less, the etching rate becomes appropriate and the cleaning effect is easily obtained.

  The liquid temperature of the final cleaning treatment liquid is preferably adjusted as appropriate according to the cleanliness of the final substrate surface.

  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.

  The glass substrate for information recording medium obtained by the production method of the present invention does not contain sulfuric acid even when the total content of CaO, SrO and BaO is expressed in mole percentages, for example, 7% or more. By performing surface treatment (etching or cleaning) with the treatment liquid, generation of a reaction product between the treatment liquid and the glass component can be suppressed. This reaction product is measured by an optical microscope, an electron microscope, an atomic force microscope, an optical inspection device, or the like.

  The present invention will be further described below with reference to examples.

(Substrate glass)
Substrate glasses 1 and 2 having the following composition and physical properties formed by the float process were used.

[Substrate glass 1]
Mol% composition: SiO ₂ 66.2%, Al ₂ O ₃ 11.3%, B ₂ O ₃ 7.6%, MgO 5.3%, CaO 4.7%, SrO 4.9%
Specific gravity: 2.50
Acid resistance: 0.1 mg / cm ²
Annealing point: 725 ° C
Crack occurrence rate p: 0%

[Substrate glass 2]
Mol% _{composition: SiO 2 64.5%, Al 2} O 3 12.0%, ZrO 2 1.8%, Li 2 O 12.8%, Na 2 O 5.5%, K 2 O 3.4 %.
Specific gravity: 2.47
Acid resistance: 0.1 mg / cm ²
Annealing point: 520 ° C
Crack generation rate p: 10%

The physical properties of the substrate glass were evaluated by the following methods.
(1) Acid resistance (mg / cm ² )
The acid resistance of the glass was determined by measuring the weight loss after immersing the substrate glass in 0.1N hydrochloric acid at 90 ° C. for 20 hours and dividing by the sample surface area.

(2) Slow cooling point (° C)
The annealing point of the substrate glass was measured based on the method of ASTM C336.

(3) Crack generation rate p (%)
The crack occurrence rate p of the substrate glass was measured as follows. After polishing the glass with a cerium oxide abrasive having an average particle diameter of 2 mm, the glass is polished with a colloidal silica abrasive having an average particle diameter of 20 nm, the thickness is 1 to 2 mm, the size is 4 cm × 4 cm, and the surface roughness Ra is 15 nm or less. A glass plate was produced.

  The glass plate was held at a slow cooling point or a glass transition point for 30 minutes, and then cooled to room temperature at a rate of 1 ° C./min or less. On the surface of the glass plate, a Vickers indenter was driven at a load of 1000 g in a room controlled at 23 ° C. and a relative humidity of 70%, and the number of cracks generated from the four apexes was measured. This measurement was repeated 10 times, and 100 × (total number of cracks) ÷ 40 was defined as p.

(Evaluation method)
The substrate glass 1 and 2 were subjected to an inner circumference etching test under the following conditions. The presence or absence of foreign matter defects in the substrate glass was examined using an optical microscope. The component of the foreign substance defect of the substrate glass was examined by a scanning electron microscope. Although the components were found with a scanning electron microscope, the compounds were not identified. Therefore, the compound identification of the foreign substance defect of the substrate glass was examined by a micro Raman spectroscope.

[Inner etching test]
Concentrated hydrofluoric acid: concentrated nitric acid: water = 1: 2: 7 (liquid A) and concentrated hydrofluoric acid: concentrated sulfuric acid: water = 1: 1: 8 (liquid B) were prepared, and liquid A and liquid B at 25 ° C. were prepared. The substrate glasses 1 and 2 were etched for 2 minutes each and then observed with an optical microscope (MX50 manufactured by Olympus Corporation). As a result, the presence of foreign matter was confirmed.

As a result, no foreign matter was observed in either of the substrate glasses 1 and 2 when etched with the liquid A, but no foreign matter was found in the substrate glass 2 when etched with the liquid B. In glass 1 , the presence of foreign matter was observed.

Moreover, as a result of analyzing the foreign material of the substrate glass 1 with a scanning electron microscope (S4700, manufactured by Hitachi High-Tech), a large amount of sulfur and alkaline earth metals such as Ca and Sr were detected in addition to the glass component. Further the identification of foreign matter Raman spectrometer (Thermo Fisher Scientific Inc. Nicolet Almega), was confirmed to be the calcium sulfate or strontium sulfate or mixed salts thereof.

  The present invention can be used for manufacturing a magnetic disk and a glass substrate for an information recording medium.

Claims (3)

A molar percentage display, the SiO ₂ 62-74% of _{Al 2 O 3 7~18%, B} 2 O 3 and containing 2-15%, the MgO 0% CaO, or SrO and BaO It contains 1 to 21% in total of one or more components, the total content of MgO, CaO, SrO and BaO is 8 to 21%, the total content of the seven components is 95% or more, Li ₂ O, Na ₂ A disk processing step of processing a glass plate having a total content of O and K ₂ O of less than 1% into a glass disc, a wrapping step of wrapping the main surface of the glass disc, and a main surface of the glass disc that has been wrapped A method for producing a glass substrate for an information recording medium, comprising a main surface polishing step for polishing the surface and a step of surface-treating the glass disk during or after these steps,
The surface treatment is cleaning, and the processing solution used for the cleaning is nitric acid, acetic acid, hydrochloric acid, perchloric acid, propionic acid, butyric acid, tartaric acid, malonic acid, malic acid, succinic acid, fumaric acid, maleic acid, citric acid , ascorbic acid, hydrobromic acid, hydroiodic acid, see contains at least one selected from alkyl sulfonic acids and alkyl phosphonic acid, acid content is ¹⁰ -6 ~10 ^-4 mol / ^L information recording medium Method for manufacturing glass substrate. Float process, a pressing method, a fusion method or process for producing a glass substrate for information recording medium according to claim 1 for producing a glass plate using a down-draw method. The method for producing a glass substrate for an information recording medium according to claim 1 or 2 , wherein the information recording medium is a magnetic disk.