WO2014103982A1

WO2014103982A1 - Method for manufacturing glass substrate for information recording medium

Info

Publication number: WO2014103982A1
Application number: PCT/JP2013/084416
Authority: WO
Inventors: 葉月中江
Original assignee: Hoya株式会社
Priority date: 2012-12-27
Filing date: 2013-12-24
Publication date: 2014-07-03

Abstract

This method for manufacturing a glass substrate for an information recording medium is provided with a step of preparing a glass substrate having a glass transition temperature of 650°C or higher, and a chemical strengthening step of chemically strengthening the principal face of the glass substrate. The chemical strengthening step includes a step of forming an ion- exchange layer of less than 3 μm in depth from the principal face while maintaining an ion-exchange rate of 0.05 μm/min to 0.25 μm/min, ion exchange in the ion-exchange layer being such that, when a sum total of a mass of Na replaced by K and a mass of Li repl aced by Na is assumed to be 100%, the percentage of a mass of Na replaced by K is 80 mass% (wt%) to 100 mass% (wt%).

Description

Manufacturing method of glass substrate for information recording medium

The present invention relates to a method for producing a glass substrate for an information recording medium.

Today, information recording devices (hard disk drives (HDD) and the like) have been built into various devices. The performance required for information recording devices is also diversifying. In particular, demands for further improvements in recording density and impact resistance have become more severe than ever.

The reason why the information recording apparatus is required to have impact resistance is that it is necessary to mount the information recording apparatus on a portable device such as a laptop (laptop) personal computer.

Further improvement in quality is demanded for a glass substrate (hereinafter simply referred to as a glass substrate) mounted on an information recording apparatus. Specifically, a high-hardness glass substrate is required to improve high smoothness and improve impact resistance in order to improve recording density.

Smoothness affects the flying stability of a magnetic head that reads and writes data. The high hardness is to prevent the glass substrate from being deformed or damaged even when an impact is applied.

In order to increase the recording capacity of the information recording apparatus, it is necessary to increase the recording capacity per 1 bit (recording capacity per unit). In that case, the flying height of the magnetic head is reduced because reading and writing of the recording is performed stably. The flying of the magnetic head is performed by utilizing the air resistance when rotating at high speed.

When the smoothness of the glass substrate is poor, this air resistance varies. As a result, the flying height of the magnetic head becomes unstable. If the smoothness of the glass substrate is extremely bad, the glass substrate and the magnetic head may collide.

Also, the glass substrate needs to have high hardness, and a glass substrate that is difficult to break is demanded. This is because, for example, when used as a hard disk drive of a notebook (laptop) personal computer, the glass substrate is not damaged even when an external impact is applied.

Glass substrates are generally excellent in impact properties. However, in order to make the glass substrate more difficult to break, a so-called chemical strengthening step of providing a compressive stress layer on the surface layer of the glass substrate by exchanging ions on the surface layer of the glass substrate with large ions in the manufacturing process of the glass substrate It has come to be adopted (see JP 2008-108413 A (Patent Document 1)).

JP 2008-108413 A

In recent years, in addition to the above, a glass substrate having heat resistance is used for an information recording apparatus. This is because it is necessary to read and write the record stably in order to cope with the higher density. Specifically, it is necessary to stabilize the magnetic material.

When forming a magnetic material on a glass substrate, it is essential to process at a higher temperature than before. When the glass substrate is deformed by high-temperature processing, the problem of smoothness occurs as described above. Therefore, it is necessary to use a glass substrate that can withstand high-temperature processing, that is, a glass substrate having heat resistance. Generally, a glass substrate having heat resistance is a glass substrate having a high glass transition temperature (Tg), specifically, a glass transition temperature (Tg) of 650 ° C. or more.

Here, a glass substrate for an information recording medium is manufactured using the above manufacturing method (see Patent Document 1) using a glass substrate having a high glass transition temperature (Tg) corresponding to further densification. When a glass substrate for a recording medium is mounted on an information recording apparatus, reading and writing of the recording may become unstable.

Investigating the cause revealed that the flatness of some glass substrates for information recording media deteriorated. Furthermore, as a result of diligent consideration by the inventor, in the process of chemically strengthening a glass substrate having a high glass transition temperature (Tg), rapid ion exchange is performed, whereby a compressive stress layer formed on the glass substrate. It turned out that the glass substrate with which the flatness deteriorated was manufactured by varying the depth and strength.

An object of the present invention is to solve the above-mentioned problems, and in the manufacturing process of a glass substrate for information recording medium using a glass substrate having a high glass transition temperature (Tg), it is possible to suppress deterioration of the flatness of the glass substrate. It is providing the manufacturing process of the glass substrate for information recording media provided with a various manufacturing process.

The method for producing a glass substrate for information recording medium according to the present invention is a method for producing a glass substrate for information recording medium, the step of preparing a glass substrate having a glass transition temperature of 650 ° C. or higher, A chemical strengthening step for chemically strengthening the surface, wherein the chemical strengthening step maintains an ion exchange rate of 0.05 μm / min to 0.25 μm / min and has an ion exchange depth of less than 3 μm from the main surface. In the ion exchange of the ion exchange layer, Na is replaced by K when the total of the mass in which Na is replaced by K and the mass in which Li is replaced by Na is 100%. The ratio of the applied mass is 80 mass% (wt%) to 100 mass% (wt%).

In one embodiment, the chemical strengthening step raises the temperature of the glass substrate under conditions of 0.5 ° C./min to 2 ° C./min.

In one embodiment, the chemical strengthening step performs ion exchange of the ion exchange layer in 5 min to 30 min.

In one embodiment, after the chemical strengthening step, at least 0.05 μm or more from the main surface of the ion exchange layer formed on the glass substrate or a polishing step for removing all of the ion exchange layer. Further prepare.

According to the present invention, in a manufacturing process of a glass substrate for an information recording medium using a glass substrate having a high glass transition temperature (Tg), the information includes a manufacturing process capable of suppressing deterioration in flatness of the glass substrate. It is possible to provide a manufacturing process of a glass substrate for a recording medium.

2 is a perspective view showing an information recording device 30. FIG. It is a top view which shows the glass substrate 1 manufactured by the manufacturing method of the glass substrate for information recording media based on this Embodiment. FIG. 3 is a cross-sectional view taken along line III-III in FIG. 2. It is a top view which shows the information recording medium 10 provided with the glass substrate 1 as an information recording medium. FIG. 5 is a cross-sectional view taken along line VV in FIG. 4. It is a flowchart which shows the manufacturing method of a glass substrate. It is a figure which shows the evaluation result of the flatness of Examples 1 to 5 and Comparative Examples 1 and 2. It is a figure which shows the evaluation result of the flatness of Example A to D.

Embodiments and examples based on the present invention will be described below with reference to the drawings. In the description of the embodiments and the examples, when the number, amount, and the like are referred to, the scope of the present invention is not necessarily limited to the number, amount, and the like unless otherwise specified. In the description of the embodiment and each example, the same parts and corresponding parts are denoted by the same reference numerals, and redundant description may not be repeated.

[Embodiment]
(Information recording device 30)
First, the information recording device 30 will be described with reference to FIG. FIG. 1 is a perspective view showing the information recording apparatus 30. The information recording apparatus 30 includes the glass substrate 1 manufactured by the method for manufacturing a glass substrate for information recording medium (hereinafter also simply referred to as a glass substrate) in the embodiment as the information recording medium 10.

Specifically, the information recording device 30 includes an information recording medium 10, a housing 20, a head slider 21, a suspension 22, an arm 23, a vertical shaft 24, a voice coil 25, a voice coil motor 26, a clamp member 27, and a fixing screw. 28. A spindle motor (not shown) is installed on the upper surface of the housing 20.

An information recording medium 10 such as a magnetic disk is rotatably fixed to the spindle motor by a clamp member 27 and a fixing screw 28. The information recording medium 10 is rotationally driven by this spindle motor at, for example, several thousand rpm. Although details will be described later with reference to FIGS. 4 and 5, in the information recording medium 10, a compression stress layer 12 (see FIG. 5) and a magnetic recording layer 14 (see FIGS. 4 and 5) are formed on the glass substrate 1. To be manufactured.

The arm 23 is attached so as to be swingable around the vertical axis 24. A suspension 22 formed in a leaf spring (cantilever) shape is attached to the tip of the arm 23. A head slider 21 is attached to the tip of the suspension 22 so as to sandwich the information recording medium 10.

A voice coil 25 is attached to the opposite side of the arm 23 from the head slider 21. The voice coil 25 is clamped by a magnet (not shown) provided on the housing 20. A voice coil motor 26 is constituted by the voice coil 25 and the magnet.

A predetermined current is supplied to the voice coil 25. The arm 23 swings around the vertical axis 24 by the action of electromagnetic force generated by the current flowing through the voice coil 25 and the magnetic field of the magnet. As the arm 23 swings, the suspension 22 and the head slider 21 also swing in the direction of the arrow AR1. The head slider 21 reciprocates on the front and back surfaces of the information recording medium 10 in the radial direction of the information recording medium 10. A magnetic head (not shown) provided on the head slider 21 performs a seek operation.

While the seek operation is performed, the head slider 21 receives a levitation force due to the air flow generated as the information recording medium 10 rotates. Due to the balance between the levitation force and the elastic force (pressing force) of the suspension 22, the head slider 21 travels with a constant flying height with respect to the surface of the information recording medium 10. By the traveling, the magnetic head provided on the head slider 21 can record and reproduce information (data) on a predetermined track in the information recording medium 10. The information recording apparatus 30 on which the glass substrate 1 is mounted as a part of the members constituting the information recording medium 10 is configured as described above.

(Glass substrate 1)
FIG. 2 is a plan view showing glass substrate 1 manufactured by the method for manufacturing a glass substrate for information recording medium according to the present embodiment. 3 is a cross-sectional view taken along the line III-III in FIG.

As shown in FIGS. 2 and 3, the glass substrate 1 (glass substrate for information recording medium) used as a part of the information recording medium 10 (see FIGS. 4 and 5) has a main surface 2, a main surface 3, It has the inner peripheral end surface 4, the hole 5, and the outer peripheral end surface 6, and is formed in a disk shape as a whole. The hole 5 is provided so as to penetrate from one main surface 2 toward the other main surface 3. A chamfer 7 is formed between the main surface 2 and the inner peripheral end surface 4 and between the main surface 3 and the inner peripheral end surface 4. Between the main surface 2 and the outer peripheral end surface 6 and between the main surface 3 and the outer peripheral end surface 6, a chamfered portion 8 (chamfer portion) is formed.

The size of the glass substrate 1 is, for example, 0.8 inch, 1.0 inch, 1.8 inch, 2.5 inch, or 3.5 inch. The thickness of the glass substrate is, for example, 0.30 mm to 2.2 mm from the viewpoint of preventing breakage. In the present embodiment, the glass substrate has an outer diameter of about 64 mm, an inner diameter of about 20 mm, and a thickness of about 0.8 mm. The thickness of the glass substrate is a value calculated by averaging the values measured at a plurality of arbitrary points to be pointed on the glass substrate. From the viewpoint of increasing the hardness of the glass substrate, the Vickers hardness of the glass substrate 1 is preferably 610 kg / mm ² or more.

The glass substrate may have any composition as long as the glass transition temperature (Tg) is 650 ° C. or higher, but in the chemical strengthening step (S70) described later, the aluminosilicate glass is subjected to stress due to ion exchange. It is preferable from the viewpoint of easily forming the layer. More preferably, when a glass having the following composition is used, a better stress layer can be easily formed.

The preferred glass substrate composition is, for example, SiO ₂ is 50 mass (wt)% to 60 mass (wt)%, Al ₂ O ₃ is 12 mass (wt)% to 20 mass (wt)%, B ₂ O ₃ is 2 mass (wt)% to 7 mass (wt)%, P ₂ O ₅ is 0.1 mass (wt)% to 3 mass (wt)%, Na ₂ O is 2 mass (wt)% ~ 6 mass (wt)%, MgO is 6 mass (wt)% to 12 mass (wt)%, CaO is 0.1 mass (wt)% to 3 mass (wt)%, ZnO is 3 mass ( wt)% to 8 mass (wt)%, TiO ₂ is 3 mass (wt)% to 8 mass (wt)%, Li ₂ O is 0 mass (wt)% to 4 mass (wt)%, Na ₂ O is 2 mass (wt)% to 6 mass (wt)%, and K ₂ O is 0 mass (wt)% to 3 mass (wt)%.

(Information recording medium 10)
FIG. 4 is a plan view showing an information recording medium 10 provided with a glass substrate 1 as an information recording medium. FIG. 5 is a cross-sectional view taken along the line VV in FIG.

4 and 5, the information recording medium 10 includes a glass substrate 1, a compressive stress layer 12, and a magnetic recording layer 14. The compressive stress layer 12 is formed so as to cover the

main surfaces

2 and 3, the inner peripheral end face 4, and the outer peripheral end face 6 of the glass substrate 1. The magnetic recording layer 14 is formed so as to cover a predetermined region on the

main surfaces

2 and 3 of the compressive stress layer 12. By forming the compressive stress layer 12 on the inner peripheral end face 4 of the glass substrate 1, a hole 15 is formed inside the inner peripheral end face 4. The information recording medium 10 is fixed to a spindle motor provided on the housing 20 (see FIG. 1) using the holes 15.

In the information recording medium 10 shown in FIG. 5, the magnetic recording layer 14 is formed on both the compressive stress layer 12 formed on the main surface 2 and the compressive stress layer 12 formed on the main surface 3 (both sides). Is formed. The magnetic recording layer 14 may be provided only on the compression stress layer 12 (one side) formed on the main surface 2, or on the compression stress layer 12 (one side) formed on the main surface 3. It may be provided.

The magnetic recording layer 14 is formed by spin-coating a thermosetting resin in which magnetic particles are dispersed on the compressive stress layer 12 on the

main surfaces

2 and 3 of the glass substrate 1 (spin coating method). The magnetic recording layer 14 may be formed by a sputtering method or an electroless plating method performed on the compressive stress layer 12 on the

main surfaces

2 and 3 of the glass substrate 1.

The thickness of the magnetic recording layer 14 is about 0.3 μm to 1.2 μm for the spin coating method, about 0.04 μm to 0.08 μm for the sputtering method, and about 0.05 μm to about the electroless plating method. 0.1 μm. From the viewpoint of thinning and high density, the magnetic recording layer 14 is preferably formed by sputtering or electroless plating.

As a magnetic material used for the magnetic recording layer 14, a Co-based alloy or the like containing Ni or Cr as a main component is added for the purpose of adjusting the residual magnetic flux density. Is preferably used.

In order to improve the sliding of the magnetic head, the surface of the magnetic recording layer 14 may be thinly coated with a lubricant. Examples of the lubricant include those obtained by diluting perfluoropolyether (PFPE), which is a liquid lubricant, with a solvent such as Freon.

The magnetic recording layer 14 may be provided with a base layer or a protective layer as necessary. The underlayer in the information recording medium 10 is selected according to the type of magnetic film. Examples of the material for the underlayer include at least one material selected from nonmagnetic metals such as Cr, Mo, Ta, Ti, W, V, B, Al, and Ni.

The underlayer provided on the magnetic recording layer 14 is not limited to a single layer, and may have a multilayer structure in which the same or different layers are stacked. For example, a multilayer underlayer such as Cr / Cr, Cr / CrMo, Cr / CrV, NiAl / Cr, NiAl / CrMo, or NiAl / CrV may be used.

Examples of the protective layer for preventing wear and corrosion of the magnetic recording layer 14 include a Cr layer, a Cr alloy layer, a carbon layer, a hydrogenated carbon layer, a zirconia layer, and a silica layer. These protective layers can be formed continuously with an in-line type sputtering apparatus together with the underlayer and the magnetic film. These protective layers may be a single layer, or may have a multilayer structure composed of the same or different layers.

Other protective layers may be formed on the protective layer or instead of the protective layer. For example, instead of the protective layer, colloidal silica fine particles are dispersed and coated on a Cr layer with tetraalkoxylane diluted with an alcohol solvent, and then fired to form a silicon oxide (SiO2) layer. May be.

(Glass substrate manufacturing method)
Next, the manufacturing method S100 of the glass substrate (glass substrate for information recording media) in this Embodiment is demonstrated using the flowchart figure shown in FIG. The glass substrate manufacturing method S100 in the present embodiment includes a plate-like glass forming step S10, a crystallization step S15, a cut-out forming step S20, a blasting step S30, a lapping step S40, an end surface polishing step S50, a rough polishing step S60, and a cleaning step. S65, chemical strengthening process S70, precision polishing process S80, and scrub cleaning process S90 are provided.

The magnetic thin film forming step S200 is performed on the glass substrate obtained through the scrub cleaning step S90. Through the magnetic thin film forming step S200, the information recording medium 10 (see FIGS. 4 and 5) is obtained. Hereinafter, the details of the steps S10 to S90 constituting the glass substrate manufacturing method S100 will be described in order.

(Plate-shaped glass forming step S10)
First, in the glass sheet forming step S10, a glass sheet is manufactured using a known glass forming method such as a direct press method, a float method, a down draw method, a redraw method, or a fusion method using a molten glass as a material. Among these, the direct press method can be directly molded from a melted glass into a target glass molded product, and thus is suitable for producing a large amount of plate-like glass having the same shape. In the direct press method, molten glass is supplied to a press mold and pressed with a press mold while the glass is in a softened state to form a sheet glass.

The Vickers hardness of the glass substrate 1 is 610 kg / mm 2 or more. The glass transition temperature (Tg) is 650 ° C. or higher. As a material of the glass substrate, for example, amorphous glass or crystallized glass can be used. When amorphous glass is used, chemical strengthening can be appropriately performed, and a glass substrate for an information recording medium excellent in flatness of the main surface and substrate strength can be provided.

(Crystallization step S15)
In the crystallization step S15, crystals are generated by heat-treating the glass substrate after the sheet glass forming step S10. This heat treatment is preferably performed in two stages. A nucleation step is performed at a first temperature, and then a crystal growth step is performed at a second temperature.

The first temperature in the nucleation step is preferably 600 ° C. to 750 ° C., and the treatment time is preferably 1 hour to 24 hours. The second temperature in the crystal growth step is preferably 650 ° C. to 850 ° C., and the treatment time is preferably 1 hour to 24 hours.

Further, the heat treatment at the first temperature and the second temperature can be performed without deteriorating the flatness of the glass substrate by alternately laminating ceramic setters and glass substrates.

(Cut-out molding step S20)
In the cut-out forming step S20, an inner hole is formed in the center of the glass substrate using a cylindrical diamond drill, and an annular glass substrate is formed (coring process). Thereafter, the inner peripheral end face and the outer peripheral end face are ground with a diamond grindstone and subjected to predetermined chamfering (forming, chamfering).

(Blasting process S30)
In the blasting step S30, a plurality of particles (abrasive grains) 200 are sprayed on the

main surfaces

2 and 3 of the glass substrate 1 formed by the plate-like glass forming step S10, whereby the main of the glass substrate (glass substrate precursor) 1

Surfaces

2 and 3 are ground (first grinding).

(Lapping step S40)
In the lapping step (second grinding step) S40, lapping (second grinding) is performed on the main surface of the glass substrate 1, for example, using a double-side polishing apparatus.

(End face polishing step S50)
In the end surface polishing step S50, the inner peripheral end surface and the outer peripheral end surface of the glass substrate 1 are polished using a polishing brush having a spiral brush bristle material. While supplying the polishing slurry between the polishing brush and each end surface of the glass substrate 1, the polishing brush is rotated in contact with each end surface. With the glass substrate 1 immersed in the polishing liquid, the polishing brush may be rotated in contact with each end face.

(Rough polishing step S60)
The glass substrate 1 whose inner peripheral end face and outer peripheral end face are polished has its

main surfaces

2 and 3 polished roughly in a plurality of times. For example, the

main surfaces

2 and 3 are polished in two steps of the first and second rough polishing steps. By gradually increasing the finishing accuracy of the glass substrate 1, the glass substrate 1 having a highly smooth and flat surface can be obtained. When performing rough polishing in two steps, the first rough polishing step is mainly intended to remove scratches and distortions remaining on the

main surfaces

2 and 3 in the lapping step, and the second rough polishing step The purpose is to finish the

main surfaces

2 and 3 in a mirror shape.

(Washing step S65)
After the rough polishing step S60, the glass substrate 1 is subjected to a cleaning process using an acidic cleaning liquid. The purpose of this cleaning treatment is to remove from the surface of the glass substrate 1 any of cerium oxide, zirconium oxide, or zirconium silicate used as a polishing slurry in the rough polishing step S60, which is the previous step.

(Chemical strengthening step S70)
After the cleaning step S65, the glass substrate 1 is chemically strengthened. The chemical strengthening solution used in the chemical strengthening step will be described in the examples described later.

Here, the ions that are chemically strengthened will be described below. Chemical strengthening is obtained by forming a compressive stress by replacing ions contained in the glass composition with larger ions. Generally, the ions to be substituted are mainly alkali metal ions.

This is because ion exchange is performed up to a relatively deep portion because alkali metals have a higher diffusion rate in glass than other ions. For example, in the case of an alkaline earth metal, even if it is attempted to carry out the ion exchange, since the ion exchange is not performed at a depth of 1 μm or more, a desired compressive stress layer cannot be obtained.

Among the alkali metal ions, generally used are substitution of Li with Na and substitution of Na with K. In this case, the substitution of Li for Na tends to go deeper, and the compressive stress layer is formed relatively deeply. However, the compressive stress value is relatively weak. On the other hand, the replacement of Na with K is difficult to enter deeply and the compressive stress is shallow, but the compressive stress value is high. Generally, the deeper the compression layer is, the higher the compressive stress value is, and the flatness of the glass substrate is likely to deteriorate.

The ion exchange layer means a layer in which ion exchange has been performed, and the compressive stress layer means a layer in which compressive stress is generated due to the formation of the ion exchange layer. Therefore, the compressive stress layer includes an ion exchange layer, and the depth of the compressive stress layer from the glass substrate surface is deeper than the depth of the ion exchange layer from the glass substrate surface. Further, the ion exchange layer means a layer in which 10% or more of ions are exchanged for larger ions from the original composition of the glass substrate.

The ion exchange layer is increased in volume by ion exchange, so that compressive stress is generated and impact resistance is improved. The impact resistance is affected by two points: “compressive stress strength” and “compressive stress depth”. When the ion exchange layer is formed rapidly (the ion exchange rate is increased), a very strong compressive stress is generated on the surface of the glass substrate. However, the formed compressive stress layer has a large variation in “compressive stress strength” and “compressive stress depth”.

Conversely, if the ion exchange layer is formed more slowly (the ion exchange rate is reduced), the “compression stress depth” is stably formed, but the “compression stress intensity” near the surface of the glass substrate is reduced. Since it is inferior, it will be inferior to impact resistance (it will be easy to generate a crack by an impact). Further, it becomes difficult to form the “compression stress depth” deeply.

Therefore, in the embodiment, in this chemical strengthening step S70, ion exchange with a depth from the main surface of the glass substrate of less than 3 μm while maintaining an ion exchange rate of 0.05 μm / min to 0.25 μm / min. 80% to 100% of ions to be ion-exchanged in this ion-exchange layer are Na.

As a result, even when a glass substrate having a glass transition temperature (Tg) of 650 ° C. or higher is used, heat resistance is achieved by satisfying both “compression stress strength” and “compression stress depth”. This makes it possible to realize a stable glass substrate with excellent impact resistance and flatness.

In the chemical strengthening step, the temperature of the glass substrate is preferably raised under the condition of 0.5 ° C./min to 2 ° C./min. In addition, the chemical strengthening step may be performed in the ion exchange layer for 5 min to 30 min. Details will be described in Examples described later.

The immersion of the glass substrate 1 in the chemical strengthening solution is performed on the holder so that the plurality of glass substrates 1 are held at their respective end surfaces so that the entire

main surfaces

2 and 3 of the glass substrate 1 are chemically strengthened. It is preferable to carry out the storage.

By immersing the glass substrate 1 in the chemical strengthening solution, alkali metal ions (lithium ions and sodium ions) on the surface layer of the glass substrate 1 are chemically strengthened salts (sodium ions) having a relatively large ion radius in the chemical strengthening solution. And potassium ions). As a result, a compressive stress layer having a depth of, for example, 50 μm to 200 μm including the ion exchange layer is formed on the surface layer of the glass substrate 1.

The surface of the glass substrate 1 is strengthened by the formation of the compressive stress layer, and the glass substrate 1 has good impact resistance.

(Precision polishing step S80)
After the chemical strengthening step S70, a precision polishing process is performed on the glass substrate 1. The precision polishing step S80 is intended to finish the main surface of the glass substrate 1 in a mirror shape. In the precision polishing step S80, similarly to the rough polishing step S60 described above, the glass substrate 1 is precisely polished using a double-side polishing machine (see FIG. 11).

In the fine polishing step S80 and the rough polishing step S60, the composition of the polishing abrasive grains contained in the polishing liquid (slurry) used and the polishing pad used are different. In the precision polishing step S80, the grain size of the abrasive grains in the polishing liquid supplied to the

main surfaces

2 and 3 of the glass substrate 1 on which the compressive stress layer is formed is made smaller than in the rough polishing step S60. Soften the hardness.

The polishing pad used in the precision polishing step S80 is, for example, a soft foam resin polisher. The precision polishing step S80 uses loose abrasive grains, and includes a first polishing step with abrasive grains mainly composed of Ce and a second polishing step of polishing with abrasive grains mainly composed of Si.

The ion exchange layer formed on the glass substrate 1 may be at least 0.05 μm or more from the main surface, or all of the ion exchange layer may be removed.

(Scrub cleaning step S90)
After the precision polishing step S80, a scrub cleaning process is performed on the glass substrate 1. Specifically, the glass substrate 1 after the precision polishing is removed from the polishing pad used in the precision polishing step S80, and then the cleaning liquid is supplied to the surface of the glass substrate 1 while the compression stress layer is formed. Scrub cleaning is performed on the surface using a scrub cleaning device.

The glass substrate 1 may be temporarily stored in water after being removed from the polishing pad of the double-side polishing machine. By storing in water, it is possible to reduce the amount of foreign matter such as polishing wrinkles or loose abrasive grains adhering to the glass substrate 1 after precision polishing while preventing the surface of the glass substrate 1 from drying after precision polishing. After the glass substrate 1 is stored in water for a predetermined time, the glass substrate 1 is set in a scrub cleaning device and scrub cleaning is performed on the glass substrate 1.

As the scrub cleaning, for example, a cleaning liquid such as a detergent or pure water is used. The pH of the cleaning solution used for scrub cleaning is preferably 9.0 or more and 12.2 or less. Within this range, the ζ potential can be easily adjusted and scrub cleaning can be performed efficiently. As scrub cleaning, both scrub cleaning with a detergent and scrub cleaning with pure water may be performed. By using a detergent and pure water, the glass substrate 1 can be more appropriately cleaned. The glass substrate 1 may be further rinsed with pure water between scrub cleaning with a detergent and scrub cleaning with pure water.

After the scrub cleaning, the glass substrate 1 may be further subjected to ultrasonic cleaning. After scrub cleaning with detergent and pure water, ultrasonic cleaning with chemical solution such as sulfuric acid aqueous solution, ultrasonic cleaning with pure water, ultrasonic cleaning with detergent, ultrasonic cleaning with IPA, and / or steam drying with IPA, etc. Further, it may be performed.

The manufacturing method S100 of the glass substrate 1 in the present embodiment is configured as described above. By using manufacturing method S100 of glass substrate 1, glass substrate 1 of this embodiment shown in Drawing 2 and Drawing 3 can be obtained.

(Magnetic thin film forming step S200)
A magnetic recording layer is formed on the main surfaces 2 and 3 (or one of the main surfaces 2 and 3) of the glass substrate 1 after the scrub cleaning process is completed. The magnetic recording layer includes, for example, an adhesion layer made of a Cr alloy, a soft magnetic layer made of a CoFeZr alloy, an orientation control underlayer made of Ru, a perpendicular magnetic recording layer made of a CoCrPt alloy, a protective layer made of a C system, and an F system. Are formed by sequentially forming the lubricating layer. By forming the magnetic recording layer, the information recording medium 10 shown in FIGS. 4 and 5 can be obtained.

In each of the following examples and comparative examples, except for the chemical strengthening step S70 shown in FIG. 6, a sheet glass forming step S10, a crystallization step S15, a cut forming step S20, a blasting step S30, a lapping step S40, an end face The same process is adopted for polishing process S50, rough polishing process S60, cleaning process S65, precision polishing process S80, scrub cleaning process S90, and magnetic thin film forming process S200h.

The glass substrate 1 having the above composition was used as the glass substrate 1. The glass transition temperature (Tg) is 650 ° C. and the crystallinity is 8%.

(Example 1)
In the chemical strengthening method in Example 1, a potassium nitrate solution was used as a chemical strengthening solution, and the glass substrate 1 was immersed in the potassium nitrate solution to chemically strengthen the glass substrate 1. The temperature of the chemical strengthening solution immediately after immersion of the glass substrate 1 was set to 450 ° C., then the temperature was increased at 1 ° C./min, and the treatment was performed at the maximum temperature of 470 ° C. The treatment time was 20 minutes.

As for the ion exchange rate, one glass substrate 1 being processed is extracted every minute, and EDX ((Energy Dispersive X-ray Spectroscopy) using SEM (Scanning Electron Microscope) is used. ): Energy dispersive X-ray spectroscopy))) and derived from the alkali metal signal intensity in the cross section of the glass substrate 1.

In the table shown in FIG. 7, the ion exchange rate every 5 minutes is averaged. The average ion exchange rate from 0 to 5 minutes (μm / min) is 0.15 μm / min, the average ion exchange rate from 5 to 10 minutes (μm / min) is 0.15 μm / min, The average ion exchange rate (μm / min) between 10 minutes and 15 minutes is 0.1 μm / min, and the average ion exchange rate between 15 minutes and 20 minutes (μm / min) is 0.1 μm / min. is there. In the ion exchange in the ion exchange layer, Na was 100% by mass (wt%) (Na was 100% by mass (wt%) and was exchanged with K).

Here, ion exchange in the ion exchange layer is performed when the total of “mass in which Na is replaced with K (A1)” and “mass in which Li is replaced with Na (A2)” is 100%. It means the ratio of “mass in which Na is replaced by K (A2)” ([A2 / (A1 + A2)] × 100%). Therefore, when Na is 100 mass% (wt%), ion exchange in the ion exchange layer means only when Na is replaced by K. The same applies hereinafter.

As shown in FIG. 7, the ion exchange depth from the surface of the glass substrate 1 in Example 1 was 2.5 μm. The evaluation of the drop impact test was “A”. The evaluation of the flatness was “A”.

Evaluation of the flatness was performed by using NIDEC FT-17 manufactured by Mitutoyo Corporation for the information recording medium 10 obtained through the steps shown in FIG. A flatness of less than 3 μm was evaluated as “A”, a flatness of 3 μm or more and less than 5 μm was evaluated as “B”, and a flatness of 5 μm or more was evaluated as “C”.

Here, the impact resistance test was evaluated by performing a drop impact test on the information recording apparatus 30 after mounting the information recording medium 10 obtained in the process shown in FIG. . The drop test was performed on 100 information recording devices 30. As a drop test, when the information recording device 30 is dropped and an impact of 1200 G is applied to the information recording device 30 and the information recording medium 10 is taken out from the information recording device 30, the glass substrate 1 is not cracked or broken. It was judged.

The case where the glass substrate 1 has no cracks or defects is regarded as acceptable, the case where the acceptance ratio is 80% or more is “A”, the case where the acceptance ratio is 70% or more and less than 80% is “B”, and the acceptance ratio is less than 70%. Evaluated as “C”.

Hereinafter, the evaluation of the drop impact test and the evaluation of the flatness in each example and each comparative example are the same.

(Example 2)
In Example 2, the temperature of the chemical strengthening solution immediately after immersion of the glass substrate 1 was set to 430 ° C., then the temperature was increased at 1 ° C./min, and the treatment was performed at the maximum temperature of 460 ° C. Other conditions are the same as those in the first embodiment. The treatment time was 30 minutes.

In the table shown in FIG. 7, the ion exchange rate every 5 minutes is averaged. The average (μm / min) ion exchange rate between 0 and 5 minutes is 0.07 μm / min, the average ion exchange rate (μm / min) between 5 and 10 minutes is 0.06 μm / min, The average ion exchange rate (μm / min) between 10 minutes and 15 minutes is 0.06 μm / min, and the average ion exchange rate between 15 minutes and 20 minutes (μm / min) is 0.05 μm / min. The average ion exchange rate (μm / min) between 20 and 25 minutes is 0.05 μm / min, and the average ion exchange rate between 25 and 30 minutes (μm / min) is 0.05 μm / min. is there. In the ion exchange in the ion exchange layer, Na was 100% by mass (wt%) (Na was 100% by mass (wt%) and was exchanged with K).

As shown in FIG. 7, the ion exchange depth from the surface of the glass substrate 1 in Example 2 was 1.7 μm. The evaluation of the drop impact test was “B”. The evaluation of the flatness was “A”.

(Example 3)
In Example 3, the temperature of the chemical strengthening solution immediately after immersion of the glass substrate 1 was set to 460 ° C., then the temperature was increased at 2 ° C./min, and the treatment was performed at the maximum temperature of 480 ° C. Other conditions are the same as those in the first embodiment. The treatment time was 10 minutes.

In the table shown in FIG. 7, the ion exchange rate every 5 minutes is averaged. The average ion exchange rate from 0 to 5 minutes (μm / min) is 0.2 μm / min, and the average ion exchange rate from 5 to 10 minutes (μm / min) is 0.2 μm / min. is there. In the ion exchange in the ion exchange layer, Na was 100% by mass (wt%) (Na was 100% by mass (wt%) and was exchanged with K).

As shown in FIG. 7, the ion exchange depth from the surface of the glass substrate 1 in Example 3 was 2 μm. The evaluation of the drop impact test was “A”. The evaluation of the flatness was “A”.

Example 4
The chemical strengthening method in Example 4 uses a strong acid salt (mass ratio 9: 1) of potassium nitrate and sodium nitrate as the chemical strengthening solution, and the glass substrate 1 is immersed in the chemical strengthening solution. Chemical strengthening was performed. The temperature of the chemical strengthening solution immediately after immersion of the glass substrate 1 was set to 430 ° C., and the temperature was maintained until the end of strengthening. The measurement result by EDX using SEM was K: Na = 8: 2. The treatment time was 10 minutes.

In the table shown in FIG. 7, the ion exchange rate every 5 minutes is averaged. The average ion exchange rate from 0 to 5 minutes (μm / min) is 0.12 μm / min, the average ion exchange rate from 5 to 10 minutes (μm / min) is 0.12 μm / min, The average ion exchange rate (μm / min) between 10 minutes and 15 minutes is 0.08 μm / min, and the average ion exchange rate between 15 minutes and 20 minutes (μm / min) is 0.08 μm / min. is there. In the ion exchange in the ion exchange layer, Na was 80.3% by mass (wt%). That is, 80.3% by mass (wt%) of Na was replaced with K, and 19.7% by mass (wt%) of Li was replaced with Na.

As shown in FIG. 7, the ion exchange depth from the surface of the glass substrate 1 in Example 4 was 2 μm. The evaluation of the drop impact test was “A”. The evaluation of the flatness was “A”.

(Example 5)
In Example 5, the temperature of the chemical strengthening liquid immediately after immersion of the glass substrate 1 was set to 470 ° C., then the temperature was increased at 2 ° C./min, and the treatment was performed at the maximum temperature of 480 ° C. Other conditions are the same as those in the first embodiment. The treatment time was 5 minutes.

In the table shown in FIG. 7, the ion exchange rate every 5 minutes is averaged. The average (μm / min) ion exchange rate between 0 and 5 minutes is 0.25 μm / min. The ion exchange in the ion exchange layer was 100% Na (100% Na was exchanged for K).

As shown in FIG. 7, the ion exchange depth from the surface of the glass substrate 1 was 1.25 μm. The evaluation of the drop impact test was “A”. The evaluation of the flatness was “B”.

(Comparative Example 1)
In Comparative Example 1, the temperature of the chemical strengthening solution immediately after immersion of the glass substrate 1 was 480 ° C., and the temperature was maintained until the end of strengthening. Other conditions are the same as those in the first embodiment. The treatment time was 10 minutes.

In the table shown in FIG. 7, the ion exchange rate every 5 minutes is averaged. The average ion exchange rate from 0 to 5 minutes (μm / min) is 0.35 μm / min, and the average ion exchange rate from 5 to 10 minutes (μm / min) is 0.25 μm / min. is there. The ion exchange in the ion exchange layer was 100% Na (100% Na was exchanged for K).

As shown in FIG. 7, the ion exchange depth from the surface of the glass substrate 1 was 3 μm. The evaluation of the drop impact test was “A”. The evaluation of the flatness was “C”.

(Comparative Example 2)
In Comparative Example 2, the temperature of the chemical strengthening solution immediately after immersion of the glass substrate 1 was 420 ° C., and the temperature was maintained until the end of strengthening. Other conditions are the same as those in the first embodiment. The treatment time was 30 minutes.

In the table shown in FIG. 7, the ion exchange rate every 5 minutes is averaged. The average (μm / min) ion exchange rate between 0 and 5 minutes is 0.05 μm / min, the average ion exchange rate between 5 and 10 minutes (μm / min) is 0.02 μm / min, The average ion exchange rate (μm / min) between 10 minutes and 15 minutes is 0.02 μm / min, the average ion exchange rate between 15 minutes and 20 minutes (μm / min) is 0.01 μm / min, The average ion exchange rate (μm / min) between 20 minutes and 25 minutes is 0.01 μm / min, and the average ion exchange rate between 25 minutes and 30 minutes (μm / min) is 0.01 μm / min. is there. The ion exchange in the ion exchange layer was 100% Na (100% Na was exchanged for K).

As shown in FIG. 7, the ion exchange depth from the surface of the glass substrate 1 was 0.6 μm. The evaluation of the drop impact test was “C”. The evaluation of the flatness was “A”.

(Example A)
In the chemical strengthening method in Example A, the glass substrate 1 was immersed in a strong acid salt (mass ratio 0.01: 0.99) of calcium nitrate and potassium nitrate to chemically strengthen the glass substrate 1. The temperature of the chemical strengthening solution immediately after immersion of the glass substrate 1 was 470 ° C., and the temperature was maintained until the end of strengthening. Other conditions are the same as those in the first embodiment. The treatment time was 20 minutes.

In the table shown in FIG. 8, the ion exchange rate every 5 minutes is averaged. The average ion exchange rate (μm / min) between 0 and 5 minutes is 0.1 μm / min, and the average ion exchange rate (μm / min) between 5 and 10 minutes is 0.1 μm / min, The average ion exchange rate (μm / min) between 10 minutes and 15 minutes is 0.06 μm / min, and the average ion exchange rate between 15 minutes and 20 minutes (μm / min) is 0.06 μm / min. is there. The ion exchange in the ion exchange layer was 100% Na (100% by weight), and the ion exchange in the ion exchange layer was 100% by weight (wt%). )

As shown in FIG. 8, the ion exchange depth from the surface of the glass substrate 1 was 1.6 μm. The evaluation of the drop impact test was “B”. The evaluation of the flatness was “A”.

(Example B)
In the chemical strengthening method in Example B, the same chemical strengthening process as in Example 1 was performed, but this chemical strengthening process was performed after the precision polishing process S80.

As shown in FIG. 8, the ion exchange depth from the surface of the glass substrate 1 was 2.5 μm. The evaluation of the drop impact test was “B”. The evaluation of the flatness was “B”.

(Example C)
In Example C, the glass substrate 1 was chemically strengthened by immersing the glass substrate 1 in the potassium nitrate solution using the potassium nitrate solution as the chemical strengthening solution as in the case of Example 1. The temperature of the chemical strengthening solution immediately after immersion of the glass substrate 1 was set to 460 ° C., and the temperature was maintained until the end of strengthening. Other conditions are the same as those in the first embodiment. The treatment time was 4 minutes.

In the table shown in FIG. 8, the ion exchange rate over 4 minutes is shown as an average. The average (μm / min) ion exchange rate between 0 and 4 minutes is 0.2 μm / min. In the ion exchange in the ion exchange layer, Na was 100% by mass (wt%) (Na was 100%). Mass% (wt%), replaced with K).

As shown in FIG. 8, the ion exchange depth from the surface of the glass substrate 1 was 0.8 μm. The evaluation of the drop impact test was “B”. The evaluation of the flatness was “B”.

(Example D)
In Example D, the glass substrate 1 was chemically strengthened by immersing the glass substrate 1 in the potassium nitrate solution and using the potassium nitrate solution as the chemical strengthening solution in the same manner as in Example 1. The temperature immediately after the immersion of the glass substrate 1 was set to 430 ° C., then the temperature was increased at 1.0 ° C./min, and the treatment was performed at the maximum temperature of 470 ° C. Other conditions are the same as those in the first embodiment. The treatment time was 40 minutes.

In the table shown in FIG. 8, the ion exchange rate every 5 minutes is averaged. The average (μm / min) ion exchange rate between 0 and 5 minutes is 0.08 μm / min, the average ion exchange rate between 5 and 10 minutes (μm / min) is 0.07 μm / min, The average (μm / min) ion exchange rate between 10 minutes and 15 minutes is 0.06 μm / min, the average ion exchange rate between 15 minutes and 20 minutes (μm / min) is 0.06 μm / min, The average ion exchange rate (μm / min) between 20 minutes and 25 minutes is 0.06 μm / min, and the average ion exchange rate between 25 minutes and 30 minutes (μm / min) is 0.05 μm / min. The average ion exchange rate (μm / min) between 30 and 35 minutes is 0.05 μm / min, and the average ion exchange rate between 35 and 40 minutes (μm / min) is 0.05 μm / min. is there. In the ion exchange in the ion exchange layer, Na was 100% by mass (wt%) (Na was 100% by mass (wt%) and was exchanged with K).

As shown in FIG. 8, the ion exchange depth from the surface of the glass substrate 1 was 2.4 μm. The evaluation of the drop impact test was “B”. The evaluation of the flatness was “B”.

As described above, a glass substrate having a high glass transition temperature (Tg) is not subjected to ion exchange unless the treatment temperature is increased as compared with a glass substrate having a low glass transition temperature (Tg). Therefore, when the processing temperature is increased, the ion exchange rate (particularly near the surface of the glass substrate) is increased, and ion exchange is rapidly performed. As a result, the ion exchange layer was strongly formed on the main surface, thereby causing variations in the depth and strength of the compressive stress layer, thereby deteriorating the flatness of the glass substrate.

However, in the above-described embodiment based on the present invention, in order to suppress rapid ion exchange, by limiting the ions that perform ion exchange, and further by making the ion exchange rate slower and more uniform than before, It is possible to obtain a glass substrate with good flatness while suppressing variations in depth and strength of the compressive stress layer and maintaining impact resistance.

Specifically, the chemical strengthening step includes a step of forming an ion exchange layer having a depth of less than 3 μm from the main surface while maintaining an ion exchange rate of 0.05 μm / min to 0.25 μm / min, The ion exchange of the ion exchange layer is performed by using “mass where Na is replaced with K” when the sum of “mass where Na is replaced with K” and “mass where Li is replaced with Na” is 100%. The ratio of is 80 mass% (wt%) to 100 mass% (wt%).

Thereby, in the manufacturing process of the glass substrate for information recording medium using the glass substrate having a high glass transition temperature (Tg), it is possible to suppress the deterioration of the flatness of the glass substrate.

In the chemical strengthening step, the temperature of the glass substrate is preferably raised under the condition of 0.5 ° C./min to 2 ° C./min.

In addition, the chemical strengthening step may be performed in the ion exchange layer for 5 to 30 minutes. The chemical strengthening process consists of a balance between the application and relaxation of the stress strengthening layer. This is because when the time of the chemical strengthening step is long, relaxation is likely to occur, and thus the stress strengthening layer is hardly formed.

Further, after the chemical strengthening step, it is preferable that the ion exchange layer formed on the glass substrate is further provided with a polishing step for removing at least 0.05 μm or more from the main surface or all of the ion exchange layer. Thereby, the main surface is polished and the flatness can be improved.

In the present embodiment, the glass substrate may be crystallized glass. In particular, the present embodiment can be applied to crystallized glass having a crystallinity of 20% or less.

As mentioned above, although embodiment and each Example based on this invention were described, embodiment and each Example disclosed this time are illustrations in all points, and are not restrictive. The technical scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

2, 3 main surface, 4 inner peripheral end surface, 5,15 hole, 6, outer peripheral end surface, 7,8 chamfered portion, 10 information recording medium, 12 compressive stress layer, 14 magnetic recording layer, 20 housing 21 head slider, 22 Suspension, 23 arm, 24 vertical axis, 25 voice coil, 26 voice coil motor, 27 clamp member, 28 fixing screw, 30 information recording device.

Claims

A method for producing a glass substrate for an information recording medium, comprising:
Preparing a glass substrate having a glass transition temperature of 650 ° C. or higher;
A chemical strengthening step for chemically strengthening the main surface of the glass substrate;
With
The chemical strengthening step includes
Forming an ion exchange layer having a depth of less than 3 μm from the main surface while maintaining an ion exchange rate of 0.05 μm / min to 0.25 μm / min,
In the ion exchange of the ion exchange layer, the ratio of the mass in which Na is substituted with K when the sum of the mass in which Na is substituted with K and the mass in which Li is substituted with Na is 100% is 80%. Mass% (wt%) to 100 mass% (wt%),
A method for producing a glass substrate for an information recording medium.
The chemical strengthening step includes
The method for producing a glass substrate for an information recording medium according to claim 1, wherein the temperature of the glass substrate is increased under the condition of 0.5 ° C / min to 2 ° C / min.
3. The method for producing a glass substrate for an information recording medium according to claim 1, wherein the chemical strengthening step performs ion exchange of the ion exchange layer in 5 min to 30 min.
2. The method further comprises a polishing step of removing at least 0.05 μm or more of the ion exchange layer from the main surface of the ion exchange layer formed on the glass substrate after the chemical strengthening step. 4. A method for producing a glass substrate for an information recording medium according to any one of items 1 to 3.