WO2013099148A1

WO2013099148A1 - Hdd glass substrate manufacturing method

Info

Publication number: WO2013099148A1
Application number: PCT/JP2012/008057
Authority: WO
Inventors: 葉月中江
Original assignee: コニカミノルタ株式会社
Priority date: 2011-12-28
Filing date: 2012-12-17
Publication date: 2013-07-04
Also published as: JPWO2013099148A1

Abstract

This HDD glass substrate manufacturing method is characterized by involving: a rough polishing step, in which a glass substrate is polished using an abrasive slurry containing an abrasive agent, wherein said abrasive agent contains an abrasive material with cerium oxide as a main component, a dispersant containing anionic polymers having a carboxyl group inside the molecule, and first group element or second group element positive ions having an 80-160pm ionic radius in six-coordinate conversion; a chemical strengthening step performed after the rough polishing step; and a precision polishing step in which the rough-polished glass substrate undergoes precision polishing, wherein the content of the positive ions is 0.05-5 mmol/kg relative to the content of the cerium oxide.

Description

Manufacturing method of glass substrate for HDD

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

In recent years, a magnetic disk device (for example, a hard disk drive: HDD) equipped with a magnetic recording medium has been used for various purposes, and the required quality has become more sophisticated. Specifically, demands for higher density and improved impact resistance of magnetic disks have been advanced. Along with this, the quality required for the glass substrate for HDD is becoming more sophisticated, and high smoothness and excellent impact resistance are required.

Here, as a method of improving the impact resistance of the glass substrate for HDD, there is a method of performing chemical strengthening treatment in which alkali ions existing in the glass substrate for HDD are ion-exchanged to alkali ions having a larger ion radius. Specifically, for example, the surface of the HDD glass substrate is chemically strengthened by being immersed in a chemical strengthening treatment solution containing nitrate (KNO ₃ or NaNO ₃ ) or the like at about 360 ° C., from the ion exchange layer and the compressive stress layer. A method for forming a reinforcing layer is known.

By providing a compressive stress layer on the surface of the HDD glass substrate by the above method, even if the surface of the HDD glass substrate is scratched, the tensile stress generated from the scratch can be countered. As a result, scratches do not extend and damage to the glass substrate for HDD can be prevented.

For example, Patent Document 1 discloses a method in which precision polishing is performed after a chemical strengthening step in order to keep a compressive stress layer on the surface of a glass substrate for HDD and maintain the smoothness of the substrate surface.

JP 2009-104703 A

An object of the present invention is to provide a method for producing a glass substrate for HDD having excellent impact resistance even in a high temperature and high humidity environment.

One aspect of the present invention is a polishing material containing cerium oxide as a main component, a dispersant containing an anionic polymer having a carboxyl group in the molecule, and an ionic radius of 80 to 160 pm in terms of hexacoordination. A rough polishing step of polishing a glass substrate using a polishing slurry containing a cation of a group 1 element or a group 2 element; a chemical strengthening step performed after the rough polishing step; and the rough polished glass substrate. A method of manufacturing a glass substrate for HDD, wherein the content of the cation is 0.05 to 5 mmol / kg with respect to the content of cerium oxide. It is.

The objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description and the accompanying drawings.

FIG. 1 is a manufacturing process diagram illustrating a process in a method for manufacturing a glass substrate for HDD. FIG. 2 is a diagram illustrating the overall configuration of the glass substrate.

According to the study of the present inventor, the glass substrate for HDD obtained by performing the chemical strengthening process such as the manufacturing method described in Patent Document 1 deteriorates in impact resistance when placed in a high temperature and high humidity environment. There was a case.

When investigating the cause, in a glass substrate having deteriorated impact resistance, there are places where ion exchange is insufficient in the chemical strengthening process of the glass substrate, and there are places where the compressive stress layer is thin in a part of the substrate. I understood. Furthermore, as a result of further investigation, in a glass substrate having deteriorated impact resistance, ions are eluted from a part of the glass substrate in the rough polishing step performed before the chemical strengthening step, so that ions are generated in the subsequent chemical strengthening step. It has been found that there are places where the exchange is insufficient, and as a result, there are places where the compressive stress layer is thin in a part of the substrate, resulting in inferior drop impact properties.

The present invention has been made in view of such circumstances, and stably performs the chemical strengthening step by preventing ion elution of the glass substrate in the rough polishing step, and is excellent in impact resistance even in a high temperature and high humidity environment. It aims at providing the manufacturing method of the glass substrate for HDD.

In order to solve the above-mentioned problems, the present inventors have intensively studied and found that a glass substrate for HDD having high impact resistance can be obtained by the manufacturing method having the following constitution, and have completed the present invention.

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

<Method for producing glass substrate for HDD>
The manufacturing method of the glass substrate for HDD according to this embodiment includes an abrasive mainly composed of cerium oxide, a dispersant containing an anionic polymer having a carboxyl group in the molecule, and an ionic radius in terms of hexacoordinate. A rough polishing step of polishing a glass substrate using a polishing slurry containing a cation of a Group 1 element or a Group 2 element having a valence of 80 to 160 pm, a chemical strengthening step performed after the rough polishing step, A precision polishing step of precisely polishing the roughly polished glass substrate, wherein the cation content is 0.05 to 5 mmol / kg with respect to the cerium oxide content.

The process for manufacturing the glass substrate for HDD according to the present embodiment may employ a chemical strengthening process after the rough polishing process. Moreover, the manufacturing method of the glass substrate for HDD which concerns on this embodiment, for example, as FIG. 1 shows, the washing | cleaning process which removes the abrasives adhering by the grinding | polishing process, and the outer peripheral end surface and inner peripheral end surface of a glass substrate. It may have a chamfering inner / outer diameter precision processing, a grinding process for removing large waviness, chipping, cracks and the like of the glass substrate.

As shown in FIG. 1, the polishing process is divided into two processes in terms of smoothness and the like, and is divided into a rough polishing process for performing rough polishing and a precision polishing process for performing precise polishing. In recent years, from the viewpoint of smoothness and processing efficiency, it is common to use cerium oxide in the rough polishing step and colloidal silica in the fine polishing step. Further, since two steps in the grinding step are preferable in terms of surface roughness and the like, the manufacturing method shown in FIG. 1 is divided into a first grinding step and a second grinding step. In the present invention, the polishing slurry refers to an abrasive (also referred to as abrasive grains) that has a polishing action on a substrate that is an object to be polished, and a solvent that is a dispersion medium (also referred to as a polishing liquid). In some cases, the polishing slurry is referred to as an abrasive.

Moreover, if the chemical strengthening process is performed after performing the rough polishing process using the polishing slurry according to the present embodiment, the order of the processes is not particularly limited. For example, in the manufacturing process in FIG. You may have an internal diameter grinding | polishing process immediately after a process.

A magnetic recording medium is obtained by forming a magnetic film on the glass substrate for HDD obtained by the above manufacturing method, and is mounted on the HDD.

Conventionally, the chemical strengthening process is generally performed after the precision polishing process, but the smoothness deteriorates when the chemical strengthening process is performed. Therefore, in recent years, in a glass substrate for hard disk having a density of 500 GB / P or higher, higher smoothness is required. Therefore, by performing a polishing process after the chemical strengthening process, The compatibility with high smoothness is achieved while leaving the compressive stress layer.

However, it has been confirmed that when a glass substrate manufactured by such a manufacturing method is used in a high-temperature and high-humidity environment, impact resistance such as drop impact resistance may deteriorate in the glass substrate. The present inventor considered this cause and found out that the glass substrate with a deteriorated impact resistance has a cause that a part of the substrate is not sufficiently ion-exchanged in the chemical strengthening process. It was.

Furthermore, when the rough polishing step is performed using a polishing slurry to which a dispersant is added, the abrasive particle size of the abrasive contained in the polishing slurry used is relatively large at 0.5 to 1.5 μm in D50 value. Cause ions to elute from a part of the glass substrate. Therefore, it turned out that the location where ion exchange is inadequate with respect to a glass substrate was produced in the chemical strengthening process performed later.

As described above, when the ion-eluting substrate is chemically strengthened, portions where the chemical strengthening is insufficient are generated, and as a result, the strength of the compressive stress varies. When such a glass substrate is placed in a high-temperature and high-humidity environment, stress relaxation occurs mainly in a portion where the compressive stress is weak. In other words, if there is unevenness in the strength of the compressive stress in the glass substrate, stress relaxation due to unevenness in the strength of the compressive stress increases at high temperatures and high humidity. When this occurs, cracks occur from the weak portions of the compressive stress layer when subjected to an impact. That is, the impact resistance is deteriorated.

In order to avoid the above problems, in a method for producing a glass substrate, in which a chemical strengthening step is performed after a rough polishing step using a polishing slurry containing a polishing agent containing a cerium oxide as a main component, to which a dispersant is added, A polishing slurry containing cations that can suppress ion elution is used in the polishing step. In general, an ionic component (particularly alkali metal) in a glass composition is gradually dissolved in an aqueous solution, but the dissolution rate is slow, and the amount of elution during polishing is not so large.

However, when a dispersant is added to the polishing slurry, the component eluted from the glass is trapped by the dispersant, so that the speed of ion elution is greatly increased. By preliminarily containing cations in the polishing slurry, the dispersant preferentially captures cations and does not trap ions eluted from the glass substrate so much, thereby suppressing the ion elution rate from the glass substrate. be able to. As a result, ion elution from the glass substrate during polishing can be prevented, and excellent impact resistance can be imparted to the glass substrate.

Further, since the abrasive particle size of the abrasive in the polishing slurry used in the rough polishing process is relatively large, a dispersant is required to maintain the dispersibility of the abrasive.

The dispersing agent generally serves to attach a polymer around the abrasive grains and impart a dispersing action by utilizing the repulsive force (for example, electrostatic force) between the polymers. If a nonionic dispersant (for example, polyoxyalkylene glycol or the like) is used in a polishing slurry containing an abrasive mainly composed of cerium oxide as described above, it is difficult to stably disperse cerium oxide. This is because repulsion is difficult because the isoelectric point of cerium oxide is near neutrality. Therefore, in order to impart dispersibility, it is preferable to use an anionic dispersant.

First, the rough polishing process and the chemical strengthening process according to the embodiment of the present invention will be described.

<Rough polishing process>
The rough polishing step in the present embodiment is a step of reducing the surface roughness while eliminating scratches generated on the glass substrate in the grinding step described later. In the rough polishing process, the main surface of the glass substrate from which large waviness and the like have been removed by the grinding process can be made into a mirror surface.

Hereinafter, the polishing slurry used in the rough polishing step according to the present embodiment will be described in detail.

(Polishing slurry)
The polishing slurry used in the present embodiment has an abrasive mainly composed of cerium oxide, a dispersant containing an anionic polymer, and an ionic radius (hexacoordinate ionic radius) of 80 to 80 in terms of six coordination. It contains a cation of a Group 1 element or a Group 2 element that is 160 pm.

Further, the cation of the group 1 element or the group 2 element having an ionic radius of 80 to 160 pm in terms of hexacoordinate refers to an alkali metal ion, magnesium ion having an ionic radius of 80 to 160 pm in terms of hexacoordination, Alkaline earth metal ions. Specifically, lithium ions (6-coordinate ion radius: 90 pm), sodium ions (6-coordinate ion radius: 116 pm), potassium ions (6-coordinate ion radius: 152 pm), magnesium ions (6-coordinate) Ionic radius: 86 pm), calcium ions (6-coordinate ion radius: 114 pm), strontium ions (6-coordinate ion radius: 132 pm), and barium ions (6-coordinate ion radius: 149 pm).

-Cerium oxide The polishing slurry used in the present embodiment contains cerium oxide used as an abrasive such as optical glass and various glass substrates. The cerium oxide is not particularly limited as long as it is usually used as an abrasive for a glass substrate.

The content of cerium oxide is preferably 1 to 10% by mass, more preferably 3 to 5% by mass, based on the total amount of the polishing slurry. If the content of cerium oxide is too small, the polishing rate tends to decrease, and the shape of the polished substrate tends to deteriorate. Moreover, when there is too much content of cerium oxide, there exists a tendency for productivity to worsen.

Further, cerium oxide is a main component of the abrasive. Specifically, the abrasive may be made of cerium oxide, and even if it contains other components, the content of cerium oxide is 80% by mass with respect to the abrasive. The above is preferable. That is, the content of cerium oxide is preferably 80 to 100% by mass in the abrasive.

The average particle diameter (D ₅₀ ) of the cerium oxide is preferably 0.5 to 1.5 μm, and more preferably 0.7 to 1.2 μm. When the average particle diameter (D ₅₀ ) of cerium oxide is too small, the polishing rate tends to decrease. Moreover, when the average particle diameter (D ₅₀ ) of cerium oxide is too large, scratches on the glass substrate tend to increase.

Here, the average particle diameter (D ₅₀ ) is 50% (D ₅₀ ) based on JIS R 1629-1997 “Method for measuring particle size distribution of fine ceramic raw material by laser diffraction / scattering method”. ₅₀ ) means a particle diameter corresponding to ₅₀ ), and is generally used as an average particle diameter of ultrafine metal powder.

-Dispersant Moreover, the polishing slurry used by this embodiment contains the anionic polymer which has a carboxyl group in a molecule | numerator as a dispersing agent. When the polishing slurry contains the anionic polymer as a dispersant, it is possible to appropriately capture the eluted ions of the glass substrate and improve the dispersibility of the abrasive.

Further, the dispersant contains the anionic polymer, and preferably contains the anionic polymer as a main component. Specifically, it is preferable to contain 80 to 100% by mass of the anionic polymer in the dispersant. By containing the anionic polymer in such a range, the effect of the present invention can be further enhanced.

In addition to the anionic polymer, examples of what can be included in the dispersant include a pH adjuster and a reducing agent.

Specific examples of the anionic polymer having a carboxyl group in the molecule include acrylic acid / maleic acid copolymer, polyacrylic acid, polymethacrylic acid, polystyrene carboxylic acid, and copolymers thereof. Carboxylic acid is mentioned. Examples of the polycarboxylic acid include those obtained by polymerizing a polymerizable carboxylic acid such as polyacrylic acid or polymethacrylic acid. The polycarboxylic acid is not only such a polymer, but also a polymerizable carboxylic acid such as a copolymer of acrylic acid / methyl acrylate, and other single quantities copolymerizable with the carboxylic acid. Also includes copolymers with the body. In this case, the copolymerization ratio of carboxylic acid is preferably 50% by weight or more.

The dispersant is most preferably an acrylic acid / maleic acid copolymer. This is because the carboxylic acid in the acrylic acid / maleic acid copolymer can most efficiently disperse the abrasive.

If an anionic polymer that does not have a carboxyl group in the molecule, such as a polystyrene sulfonate polymer, is used as the dispersant, it will trap too much ions eluted from the glass substrate or dispersibility of the abrasive. May be damaged.

The content of the dispersant is preferably 0.01 to 2% by mass and more preferably 0.1 to 1% by mass with respect to the content of the cerium oxide. When there is too little content of the said dispersing agent, there exists a tendency for the dispersibility of an abrasives to deteriorate. Moreover, when there is too much content of the said dispersing agent, there exists a tendency for the viscosity etc. of polishing slurry to change and to have a bad influence on grinding | polishing.

The weight average molecular weight (Mw) of the acrylic acid / maleic acid copolymer is preferably 100 to 10,000, and more preferably 1,000 to 5,000. If the molecular weight (Mw) is too low, the dispersibility of the abrasive tends to deteriorate and the polishing processability tends to deteriorate. On the other hand, when the molecular weight (Mw) is too high, the viscosity of the polishing slurry increases and the polishing characteristics tend to deteriorate.

-Cation The ionic radius of the cation in terms of six coordination is 80 to 160 pm, preferably 80 to 120 pm. When the ion radius is less than 80 pm, ion elution of the glass substrate cannot be sufficiently suppressed, and when the ion radius exceeds 160 pm, the cation does not sufficiently contribute to suppression of ion elution. Therefore, when the polishing slurry containing a cation of a Group 1 element or a Group 2 element having an ionic radius of 80 to 160 pm in terms of hexacoordination is used, ion elution of the glass substrate is suitably suppressed. be able to. Therefore, elution of ions during rough polishing is suppressed, and a glass substrate for HDD having excellent impact resistance even at high temperature and high humidity can be obtained.

Further, the cation is preferably at least one cation selected from the group consisting of magnesium ion, calcium ion, sodium ion, and potassium ion. When these cations are used, ion elution from the glass substrate during the polishing process can be further suppressed, and a highly dispersible polishing slurry can be obtained.

In addition, as the anion as the counter ion of the cation, chloride ion or carbonate ion can be used. And the salt which consists of the said cation and an anion is used suitably as a component of the grinding | polishing slurry which can suppress the ion elution from the glass substrate at the time of a grinding | polishing process.

Among the salts, magnesium chloride, magnesium sulfate, calcium sulfate, calcium carbonate, potassium iodide, sodium carbonate, and the like are preferable because the pH change of the solution is small and the paired ions do not affect the polishing.

Furthermore, the content of the cation is 0.05 to 5 mmol / kg, preferably 0.2 to 1 mmol / kg, relative to the content of cerium oxide. That is, when adding the salt to the polishing slurry, it is preferable to add the cation so that the cation content is in the range of 0.05 to 5 mmol / kg with respect to the cerium oxide content. If the cation concentration is less than 0.05 mmol / kg, the ion elution cannot be suppressed because the contribution to the dispersant is small, and if it exceeds 5 mmol / kg, the dispersibility of the abrasive is adversely affected. Aggregation of abrasives occurs.

-Solvent As a solvent used with the polishing slurry used in the present embodiment, for example, water can be used. Examples of the water include distilled water, ion exchange water, pure water, and ultrapure water. The content of the solvent in the polishing slurry used in the present embodiment is preferably 55% by mass or more, and more preferably 75% by mass or more because the handling of the polishing slurry becomes easier.

The polishing slurry used in this embodiment may further contain an acid, an oxidizing agent, a bactericidal agent, an antibacterial agent, a thickener, a dispersant, a rust preventive agent, a basic substance, a pH adjuster, and the like.

The polishing slurry used in this embodiment can be used in any polishing process in the substrate manufacturing method, and among these, is suitable for use in the rough polishing process in the substrate manufacturing method.

Next, the polishing process in the rough polishing process will be described.

(Polishing process)
In the rough polishing step, the shape of the glass substrate after the grinding step described later is adjusted, and the surface roughness is removed more precisely. And it grind | polishes so that the surface roughness finally required at a precision grinding | polishing process can be obtained efficiently.

As a machine for polishing the front and back surfaces of the glass substrate in the rough polishing step, a known polishing machine called a double-side polishing machine can be used. The double-side polishing machine includes a disk-shaped upper surface plate and a lower surface plate that are arranged vertically so as to be parallel to each other, and rotate in opposite directions. A plurality of diamond pellets for grinding the main surface of the glass substrate are attached to the opposing surfaces of the upper and lower surface plates.

Between the upper and lower surface plates, there are a plurality of carriers that rotate in combination with an internal gear provided in an annular shape on the outer periphery of the lower surface plate and a sun gear provided around the rotation axis of the lower surface plate. The carrier is provided with a plurality of holes, and a glass substrate is fitted into the holes. The upper and lower surface plates, the internal gear and the sun gear can be operated by separate driving.

The operation of the double-side polishing machine is such that the upper and lower surface plates rotate in opposite directions, and the carrier sandwiched between the surface plates via the diamond pellets rotates while maintaining a plurality of glass substrates. Revolves in the same direction as the lower surface plate with respect to the center of rotation. In such a working polishing machine, polishing of glass polishing can be performed by supplying the above-described polishing slurry between the upper surface plate and the glass substrate, and the lower surface plate and the glass substrate.

The supply rate of the polishing slurry is preferably 1 to 10 L / min. By supplying the polishing slurry in this range, a stable polishing process can be performed on the glass substrate.

The polishing pad is a hard pad having a hardness A of about 80 to 90, and for example, urethane foam is preferably used. When the pad hardness becomes soft due to heat generated by polishing, the shape change of the polished surface increases, so it is preferable to use a hard pad.

The machining allowance in the rough polishing step is preferably 10 to 30 μm. If it is less than 10 μm, scratches and defects cannot be sufficiently removed, and the remaining ion exchange layer cannot be removed. If it exceeds 30 μm, the surface roughness can be in the range of 2 to 60 nm for Rmax and 0.2 to 0.4 nm for Ra, but the polishing is performed more than necessary and the production efficiency is lowered. .

The weight applied to the glass substrate by the surface plate is preferably 90 to 110 g / cm ² . The load applied to the glass substrate by the surface plate greatly affects the shape of the outer peripheral edge. As the weight is increased, the inner side of the outer peripheral end portion tends to decrease and increase toward the outer side. Further, when the weight is reduced, the outer peripheral end portion tends to be close to a plane and the surface sagging increases. The weight can be determined while observing these trends.

In order to improve the surface roughness, it is preferable that the rotation speed of the surface plate is 25 to 50 rpm, and the rotation speed of the upper surface plate is 30 to 40% slower than the rotation speed of the lower surface plate.

<Chemical strengthening process>
Specific examples of the chemical strengthening step according to the present embodiment include a method of immersing a glass substrate in a chemical strengthening treatment solution. By this method, a compressive stress layer can be formed on the surface of the glass substrate, for example, in a region of 5 μm from the glass substrate surface. Further, the ion exchange layer can be formed on the outer side of the compressive stress layer. And by forming a compressive stress layer, impact resistance, vibration resistance, heat resistance, etc. can be improved.

In other words, by immersing the glass substrate in the heated chemical strengthening solution, alkali metal ions such as lithium ions and sodium ions contained in the glass substrate are replaced with alkali metal ions such as potassium ions having a larger ion radius. Performed by ion exchange. Due to the strain caused by the difference in ion radius, compressive stress is generated in the ion-exchanged region, and the surface of the glass substrate is strengthened.

As the salt used for the treatment liquid in the chemical strengthening step, known salts can be used. Examples of the salt include nitrate, carbonate, sulfate and the like. Examples of ions to be ion exchanged include sodium and potassium. Of these, potassium nitrate is the best. Since potassium nitrate has a low melting point, it is easy to handle, and ion exchange can be performed without variation by exchange of potassium ions.

In the chemical strengthening step, by immersing the glass substrate in a heated chemical strengthening solution, alkali metal ions such as lithium ions and sodium ions contained in the glass substrate are converted into alkali ions such as potassium ions having a larger ion radius. This is performed by the ion exchange method for substitution. Compressive stress is generated in the ion-exchanged region due to the distortion caused by the difference in ion radius, and the surface of the glass substrate is strengthened.

The chemical strengthening treatment liquid is heated to a temperature higher than the temperature at which the above components melt. On the other hand, when the heating temperature of the chemical strengthening treatment liquid is too high, the temperature of the glass substrate is excessively increased, and the glass substrate may be deformed. For this reason, the heating temperature of the chemical strengthening treatment liquid is preferably lower than the glass transition point (Tg) of the glass substrate, more preferably lower than the glass transition point −50 ° C.

<Precision polishing process>
The precision polishing step is a step of further precisely polishing the surface of the glass substrate after the rough polishing step.

As the machine for polishing the glass substrate in the precision polishing process, a polishing machine similar to the double-side polishing machine used in the rough polishing process can be used.

As the polishing slurry used in the precision polishing step, it is preferable to use a slurry containing an abrasive having a finer particle size and less variation in order to make the surface of the glass substrate smoother. For example, it is preferable to use a polishing slurry containing colloidal silica having an average particle size of 20 to 40 nm.

The machining allowance in this precision polishing step is preferably 0.3 to 3 μm. When the polishing amount is within this range, minute defects such as minute roughness and undulation generated on the surface and minute scratches generated in the process so far can be efficiently removed. However, if the machining allowance in the precision polishing step is smaller than 0.3 μm, scratches in the rough polishing step remain, and if it is larger than 3 μm, the end face shape is destroyed.

The pad used in the precision polishing step is a soft pad having a hardness of about 65 to 80 (Asker-C), which is softer than the pad used in the rough polishing step. For example, urethane foam or suede is preferably used.

In the precision polishing step, the weight applied to the glass substrate by the surface plate is preferably 90 to 110 g / cm ² . Although the weight applied to the glass substrate by the surface plate greatly affects the shape of the outer peripheral edge as in the rough polishing step, the shape cannot be changed as efficiently as the rough polishing step because the polishing speed is slow. The change in the shape of the outer peripheral end due to the increase / decrease of the weight is the same as in the rough polishing step, and when the weight is increased, the inner periphery of the outer peripheral end tends to decrease and increase toward the outer side. Further, when the weight is reduced, the outer peripheral end portion tends to be close to a plane and the surface sagging increases. In order to obtain the shape of the outer peripheral edge, the weight can be determined while observing such a tendency. The rotation speed of the surface plate is preferably 15 to 35 rpm, and the rotation speed of the upper surface plate is preferably 30 to 40% slower than the rotation speed of the lower surface plate.

As described above, the surface roughness of the main surface of the glass substrate after performing the precision polishing step can be set such that Rmax is 2 to 6 nm and Ra is 0.2 to 0.4 nm.

Subsequently, manufacturing processes other than the above-described rough polishing process, chemical strengthening process, and precision polishing process will be described in detail. However, if the present embodiment includes the polishing process and the chemical strengthening process, the other processes will be described. Is not limited to the following.

<Disk processing process>
In the disk processing step, a through-hole 5 is formed in the central portion so that the inner periphery and the outer periphery are concentric as shown in FIG. Is a step of processing into a disk-shaped glass substrate 1 on which is formed.

(Glass melting process)
First, a glass material is melted as a glass melting step. The material for the glass substrate is not particularly limited. For example, a glass material that can be generally used can be used as the material of the glass substrate for HDD. More specifically, a glass material having a composition shown in Table 1 below can be used.

(Pressing process)
Next, as a pressing step, molten glass is poured into a lower mold and press-molded with an upper mold to obtain a disk-shaped glass substrate precursor. The disk-shaped glass substrate precursor may be produced by cutting a sheet glass formed by, for example, a downdraw method or a float method with a grinding stone, without using press molding.

There is no limitation on the size of the glass substrate. For example, there are glass substrates of various sizes such as an outer diameter of 2.5 inches, 1.8 inches, 1 inch, and 0.8 inches. Further, the thickness of the glass substrate is not limited, and there are glass substrates having various thicknesses such as 2 mm, 1 mm, and 0.63 mm.

(Coring process)
The press-molded glass substrate precursor is pierced at the center in the coring process. In the drilling, a hole is drilled in the center by grinding with a core drill or the like equipped with a diamond grindstone or the like in the cutter part.

<Inner and outer diameter precision machining process>
Next, as the inner / outer diameter precision machining step, the outer peripheral end surface and the inner peripheral end surface of the glass substrate precursor are ground with an abrasive wheel such as a drum-shaped diamond to process the inner / outer diameter, thereby producing a glass substrate. .

<Inner diameter polishing process>
A plurality of glass substrates that have been subjected to the inner / outer diameter precision processing step are stacked and stacked, and in this state, the inner peripheral surface is polished using an end surface polishing machine.

<Grinding process>
The grinding process can remove large undulations, chips, cracks, and the like on the surface of the glass substrate. The grinding step preferably has two steps, a first grinding step and a second grinding step, from the viewpoint that the parallelism and flatness of the glass substrate can be precisely adjusted.

<Outside diameter polishing process>
In the outer diameter polishing step, a plurality of glass substrates are stacked and laminated, and in this state, the outer peripheral end surface is polished using an end surface polishing machine or a polishing brush. A known apparatus can be used for the end face polishing machine.

(First grinding process)
As the first grinding step, both surfaces of the glass substrate are ground, and the overall shape of the glass substrate, that is, the parallelism, flatness and thickness of the glass substrate are preliminarily adjusted. In the first grinding step, it is preferable to use fixed abrasive grains.

(Second grinding process)
As the second grinding step, after the first grinding step, both surfaces of the glass substrate are ground again to finely adjust the parallelism, flatness and thickness of the glass substrate.

As a machine for grinding the front and back surfaces of the glass substrate in the first and second grinding steps, a polishing machine similar to the double-side polishing machine used in the polishing process can be used.

Upon completion of the second grinding process, defects such as large waviness, chipping and cracks are removed, and the surface roughness of the main surface of the glass substrate is about 2 to 4 μm for Rmax and about 0.2 to 0.4 μm for Ra. Is preferable.

In the first grinding process, roughly large undulations, chips and cracks are efficiently removed so that the second grinding process can be performed efficiently. For this reason, it is preferable to use diamond pellets of about # 800 mesh to # 1200 mesh coarser than # 1300 mesh to # 1700 mesh used in the second grinding step. The surface roughness at the time when the first grinding step is completed is preferably set such that Rmax is about 4 to 8 μm and Ra is about 0.4 to 0.8 μm.

It should be noted that the polishing machines used in the first grinding process and the second grinding process have the same configuration, but it is preferable to perform grinding using different polishing machines prepared for each process. This is because the dedicated diamond pellets are pasted, so that the replacement is a large-scale operation, and complicated operations such as resetting the polishing conditions are required, resulting in a reduction in manufacturing efficiency.

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

The glass substrate after the grinding step and the glass substrate after the polishing step are preferably washed by a washing step each time. The washing process is not particularly limited. Specifically, for example, the following washing steps are mentioned.

First, the glass substrate is washed with an alkaline detergent having a pH of 13 or more, and the glass substrate is rinsed. Next, the glass substrate is washed with an acid detergent having a pH of 1 or less, and the glass substrate is rinsed. Moreover, it is preferable to use a rinse tank after each washing. In some cases, a surfactant, a dispersing agent, a chelating agent, a reducing material, and the like may be added to these detergents. Moreover, it is preferable to apply an ultrasonic wave to each washing tank and to use deaerated water for each detergent. Finally, the glass substrate is taken out, rinsed with pure water, and dried IPA.

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

This specification discloses various modes of technology as described above, and the main technologies are summarized below.

According to such a configuration, the elution of ions during rough polishing can be suppressed, and a glass substrate for HDD having excellent impact resistance even at high temperature and high humidity can be obtained.

In the method for manufacturing a glass substrate for HDD, the cation preferably has an ionic radius of 80 to 120 pm in terms of six coordination.

According to such a configuration, ion elution from the glass substrate can be further suppressed.

In the method for producing a glass substrate for HDD, the cation is preferably at least one cation selected from the group consisting of magnesium ion, calcium ion, sodium ion, and potassium ion.

According to such a configuration, since ions can stably exist in the aqueous solution, the action on the dispersant can be stably supplied, and as a result, ion elution can be effectively suppressed. .

In the method for manufacturing a glass substrate for HDD, it is preferable that the dispersant is an acrylic acid / maleic acid copolymer having a weight average molecular weight (Mw) of 100 to 10,000.

According to such a configuration, the effect of improving the dispersibility of the abrasive by the dispersant can be further exhibited, and the aggregation of the abrasive can be further prevented.

In the method for manufacturing a glass substrate for HDD, the content of the dispersant is preferably 0.01 to 2% by mass with respect to the content of cerium oxide.

According to such a configuration, the effect of enhancing the dispersibility of the abrasive by the dispersant can be more exerted, so that cerium oxide, which is the main component of the abrasive, exists more stably in the polishing slurry. Can do. Therefore, aggregation of the abrasive can be further prevented.

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

<Example 1>
A glass substrate before the polishing step produced by the following steps was prepared.

(Disc machining process)
As the glass material, a glass material (see Table 1 for the composition) was used, and the molten glass material was press-molded to produce disc-shaped blanks having an outer diameter of about 66 mm. The thickness of the blanks was 1.05 mm.

(Inner / outer diameter machining process)
Using a core drill equipped with a cylindrical diamond grindstone, a circular hole (center hole) having a diameter of 20.5 mm was formed in the center of the blank. Next, using a drum-shaped diamond grindstone, inner and outer diameter processing was performed so that the outer peripheral end surface and the inner peripheral end surface of the blanks had an outer diameter of 65 mm and an inner diameter of 20 mm. Subsequently, the outer peripheral end surface and the inner peripheral end surface of the glass substrate after the disk processing step were ground by an inner and outer peripheral processing machine (TKV-1, manufactured by Hadano Machinery Co., Ltd.).

(Grinding process)
The main surface of the glass substrate after the inner and outer diameter processing step was ground with a 35 μm allowance so that the flatness of the main surface was 10 μm using a double-side grinding machine. Next, both surfaces of the glass substrate were ground again, and the main surface was ground with a machining allowance of 50 μm so that the flatness of the glass substrate was 3 μm.

(Rough polishing process)
10% by mass of cerium oxide as an abrasive, 0.1% by mass of an acrylic acid / maleic acid copolymer having a weight average molecular weight (Mw) of 1000, 0.0017% by mass of magnesium carbonate, and 89.9% of water as a solvent. The polishing slurry 1 was prepared by stirring the mass% using a three-one motor. In addition, the magnesium ion in the said magnesium carbonate was 0.2 mmol / kg with respect to content of the said cerium oxide.

(Chemical strengthening process)
The polished glass substrate was melted at 480 ° C. with a strengthening salt in which 54% sodium nitrate and 46% potassium nitrate were mixed, and the glass substrate was immersed for 4 hours.

(Precision polishing process)
Using a polishing machine of the same type as the double-side polishing machine used in the rough polishing process, polishing is performed using a polishing slurry containing colloidal silica having an average particle diameter of 20 nm as polishing abrasive grains, and the surface of the glass substrate is reduced to 2 mm. Finished. The machining allowance was 1 μm.

(Washing process)
The glass substrate subjected to the precision polishing step was scrubbed. As a cleaning liquid, a liquid obtained by diluting KOH and NaOH mixed at a mass ratio of 1: 1 with ultrapure water (DI water) and adding a nonionic surfactant to enhance the cleaning performance is obtained. Using. The cleaning liquid was supplied by spraying. After scrub cleaning, in order to remove the cleaning liquid remaining on the surface of the glass substrate, a water rinse cleaning process is performed in an ultrasonic bath for 2 minutes, an IPA cleaning process is performed in an ultrasonic bath for 2 minutes, and finally the glass substrate is cleaned with IPA vapor. The surface of was dried.

[Evaluation of impact resistance]
The glass substrate obtained by the above process was formed into a film, then incorporated into a hard disk drive, and allowed to stand at 250 ° C. and RT 80% for 96 hours, and then subjected to an impact resistance test. In this impact resistance test, each glass substrate after being left to stand is incorporated into a drive and dropped to perform a test while changing the load, and the maximum value of the load at which the substrate did not break was measured. It was evaluated as follows.

A: The maximum value is 1200 G or more.
○: The maximum value is 1100G or more and less than 1200G.
X: The maximum value is less than 1100G.

<Examples 2 to 13>
In Examples 2 to 4, as shown in Table 2 below, the polishing slurry was prepared such that the magnesium ions were 0.05 mmol / kg, 5 mmol / kg, and 1 mmol / kg with respect to cerium oxide, respectively. Polishing slurries 2 to 4 were prepared in the same manner as in Example 1.

In Examples 5 to 6, polishing was performed in the same manner as in Example 1 except that a polishing slurry was prepared using calcium carbonate having calcium ions having an ionic radius of 80 to 160 pm and potassium chloride having potassium ions. Slurries 5-6 were obtained.

In Examples 7 to 9, the molecular weight of the acrylic acid / maleic acid copolymer as a dispersant was set to 700, 5000, and 10,000, respectively, and magnesium ions were added to 1 mmol / kg, 2 mmol / kg of cerium oxide, respectively. Polishing slurries 7 to 9 were made in the same manner as in Example 1 except that the polishing slurry was prepared to 3 kg / kg.

Further, Example 10 was the same as Example 4 except that a polishing slurry was prepared using a styrene / maleic acid copolymer having a weight average molecular weight (Mw) of 1000 as a dispersant. Was prepared.

In Examples 11 to 13, the blending amount of the acrylic acid / maleic acid copolymer as the dispersant is 0.01% by mass, 2% by mass, and 0.005% by mass with respect to cerium oxide, respectively. Polishing slurries 11 to 13 were prepared in the same manner as in Example 1 except that the polishing slurry was prepared.

Subsequently, in Comparative Examples 1 and 2, a polishing slurry was prepared using an aqueous solution having iron (III) ions (iron (III) phosphate dissolved and neutralized in hydrochloric acid) and cesium chloride having cesium ions. Abrasive slurries 14 to 15 were prepared in the same manner as in Example 4 except that the slurry was prepared.

In Comparative Example 3, a polishing slurry 16 was prepared in the same manner as in Example 4 except that a polishing slurry was prepared using a polystyrene sulfonic acid polymer as a dispersant.

In Comparative Examples 4 to 5, polishing slurries 17 to 18 were prepared in the same manner as in Example 1 except that the polishing slurry was prepared so that the magnesium ions were 0.04 mmol / kg and 6 mmol / kg with respect to cerium oxide, respectively. Prepared.

Then, an impact resistance test was performed in the same manner as in Example 1 except that the polishing slurries 2 to 18 according to Examples 2 to 13 and Comparative Examples 1 to 5 were used as described above, and the above evaluation was performed. went.

The results obtained in Examples 1 to 13 and Comparative Examples 1 to 5 are shown in Table 2 below.

As shown in Table 2 above, a dispersant containing an anionic polymer having a carboxyl group in the molecule, and a positive ion of a Group 1 or Group 2 element having an ionic radius of 80 to 160 in terms of hexacoordination. When polishing is performed using a polishing slurry (polishing slurry 1 to 13) containing 0.05 to 5 mmol / kg of ions with respect to cerium oxide (Examples 1 to 13), a glass substrate having excellent impact resistance is used. I was able to get it. It is considered that this is because the cation suppresses ion elution and the dispersing agent can maintain the dispersing effect.

In particular, when a polishing slurry containing 0.2 to 1 mmol / kg of a cation of a Group 1 element or Group 2 element having an ionic radius of 80 to 160 pm in terms of hexacoordination is used (Example 1, Example) In 4 to 6), a glass substrate having further excellent impact resistance could be obtained.

Further, when the molecular weight of the acrylic acid / maleic acid copolymer contained as a dispersant is 5000 (Example 8), or 0.01% by mass of acrylic acid / maleic acid copolymer as a dispersant. Even in the case of containing in mass% (Examples 11 and 12), it was possible to obtain a glass substrate further excellent in impact resistance.

On the other hand, when a polishing slurry (polishing slurry 14) containing ions other than the Group 1 element or Group 2 element was used (Comparative Example 1), a glass substrate inferior in impact resistance was obtained. This is presumably because the dispersant was strongly captured by ions in the glass substrate and ion elution occurred.

Further, when a polishing slurry (polishing slurry 15) containing cesium ions whose ionic radius in hexacoordinate conversion is not in the range of 80 to 160 pm (Comparative Example 2) is used, the same reason as in Comparative Example 1 is obtained. The obtained glass substrate was inferior in impact resistance.

Next, when a polishing slurry (polishing slurry 16) containing a polystyrenesulfonic acid copolymer having no carboxyl group in the molecule is used as a dispersant (Comparative Example 3), the obtained glass substrate is The result was inferior in impact resistance. This is because the polystyrene sulfonic acid copolymer cannot sufficiently disperse cerium oxide, so that the glass substrate is fully scratched during processing, and even after chemical strengthening, cracks originated from the scratch. It is thought that.

Further, when a polishing slurry (polishing slurry 17) containing 0.04 mmol / kg of magnesium ions was used (Comparative Example 4), the obtained glass substrate was inferior in impact resistance. This is considered to be because the ion elution preventing effect by the cation and the dispersing agent is low and ions are eluted from the glass substrate.

Furthermore, when a polishing slurry (polishing slurry 18) containing 6 mmol / kg of magnesium ions was used (Comparative Example 5), the obtained glass substrate was inferior in impact resistance. This is considered to be caused by the following. First, the dispersibility of the abrasive decreased, and the glass substrate was damaged by processing. Therefore, it is considered that the cause is that the cracks originated from scratches even after chemical strengthening.

According to the present invention, there is provided a method for producing a glass substrate for HDD having excellent impact resistance even in a high temperature and high humidity environment.

Claims

An abrasive mainly composed of cerium oxide, a dispersant containing an anionic polymer having a carboxyl group in the molecule, and a group 1 element or group 2 having an ionic radius of 80 to 160 pm in terms of hexacoordination A rough polishing step of polishing a glass substrate using a polishing slurry containing an element cation;
A chemical strengthening step performed after the rough polishing step;
A precision polishing step of precisely polishing the roughly polished glass substrate,
The method for producing a glass substrate for HDD, wherein the cation content is 0.05 to 5 mmol / kg with respect to the cerium oxide content.
2. The method for producing a glass substrate for HDD according to claim 1, wherein the cation has an ionic radius in terms of six coordination of 80 to 120 pm.
3. The glass substrate for HDD according to claim 1, wherein the cation is at least one cation selected from the group consisting of magnesium ion, calcium ion, sodium ion, and potassium ion. Method.
The method for producing a glass substrate for HDD according to any one of claims 1 to 3, wherein the dispersant is an acrylic acid / maleic acid copolymer having a weight average molecular weight of 100 to 10,000.
The production of a glass substrate for HDD according to any one of claims 1 to 4, wherein the content of the dispersant is 0.01 to 2% by mass with respect to the content of cerium oxide. Method.