WO2013047288A1

WO2013047288A1 - Production method for glass substrate for information recording medium

Info

Publication number: WO2013047288A1
Application number: PCT/JP2012/073909
Authority: WO
Inventors: 葉月中江
Original assignee: コニカミノルタアドバンストレイヤー株式会社
Priority date: 2011-09-30
Filing date: 2012-09-19
Publication date: 2013-04-04

Abstract

A glass material having a main surface and including SiO₂ in the components thereof is prepared (S10). First free abrasive grains are supplied between the main surface of the glass material and a first polishing pad comprising a soft foamed resin pad, and the main surface of the glass material is mechanically polished using the first polishing pad (S15). The soft foamed resin pad has an Asker C hardness of 73-85. Then, second free abrasive grains differing from the first free abrasive grains are supplied between the main surface of the glass material and a second polishing pad, and the main surface of the glass material is chemically-mechanically polished using the second polishing pad (S16). Then, third free abrasive grains are supplied between the main surface of the glass material and a third polishing pad, and the main surface of the glass material is polished using the third polishing pad (S17).

Description

Manufacturing method of glass substrate for information recording medium

The present invention relates to a method for manufacturing a glass substrate for information recording media, and in particular, manufacturing a glass substrate for information recording media mounted as part of an information recording medium in an information recording device such as a hard disk drive (HDD). Regarding the method.

Information recording devices such as hard disk drives are built in various devices such as computers. Such an information recording apparatus is equipped with an information recording medium such as a magnetic disk formed in a disk shape. The information recording medium is manufactured by forming a magnetic recording layer for magnetic recording on the main surface of an aluminum or glass substrate. In recent years, since high strength and high hardness are required, glass substrates are widely used for manufacturing information recording media.

A glass substrate used for manufacturing an information recording medium is referred to as an information recording medium glass substrate (hereinafter also simply referred to as a glass substrate). A method for producing a glass substrate for an information recording medium is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2009-104776 (Patent Document 1) and Japanese Unexamined Patent Application Publication No. 2010-238272 (Patent Document 2).

The glass substrate is mounted in the information recording apparatus in a state where a magnetic recording layer is formed on the main surface as a part of a member constituting the information recording medium. In the information recording apparatus, information is recorded in the magnetic recording layer by magnetizing the magnetic recording layer formed on the glass substrate by the magnetic head. Information recorded in the magnetic recording layer is reproduced by being read by the magnetic head.

Demand for an increase in the amount of information (recording capacity) that can be recorded in an information recording apparatus is strong, and the density of information recorded in the magnetic recording layer tends to be higher. In order to increase the recording density, it is necessary to reduce the bit size and also reduce the gap (also called flying height) between the information recording medium and the magnetic head.

A magnetic head using a technology called DFH (Dynamic Flying Height) has been developed as a technology for further increasing the recording density. In the DFH technology, a special metal is used at a location where the magnetic head is mounted. Due to the special metal, the magnetic head protrudes at a fine distance.

∙ Various external factors (such as pressure fluctuation or temperature fluctuation) act on the hard disk drive. Variations that occur in the flying height due to the action of external factors can be corrected by the DFH technique. By adopting the DFH technique, the flying height can be kept constant, and in principle, the flying height can be set to several nm or less.

In the conventional glass substrate, even if irregularities of about several hundred nm were formed on the main surface, the flying height was relatively large, so it was not a problem. As described above, in recent years, the flying height may be set to several nm or less. When the flying height is set to several nanometers or less, the magnetic head and the information recording medium easily come into contact with each other (also referred to as a head crash) due to fine irregularities formed on the main surface of the glass substrate.

When a head crash occurs, a recording error or reading error occurs. In order to prevent the occurrence of a recording error or the like, higher smoothness and higher flatness than ever are required for the main surface of the glass substrate.

JP 2009-104776 A JP 2010-238272 A

When a glass substrate is manufactured, in order to obtain high smoothness and high flatness, the main surface of the glass substrate is generally polished using loose abrasive grains. In the conventional method for manufacturing a glass substrate containing SiO ₂ as a component, first, a hard urethane pad is used as a polishing pad on the main surface of the glass substrate, and rough polishing using cerium oxide, which is mainly chemical polishing. (Chemical mechanical polishing) is performed. Thereafter, a soft foam resin pad is used as a polishing pad on the main surface of the glass substrate, and precision polishing using colloidal silica or the like is performed.

Here, when a glass substrate is manufactured using a conventional manufacturing method and the glass substrate is mounted on an information recording apparatus as an information recording medium (magnetic disk), the flying height using DFH technology is extremely small (several nm). In the information recording apparatus, there has been a problem that mutual contact (head crash) between the information recording medium and the recording head frequently occurs.

As a result of the investigation of the cause by the present inventors, information caused by slight irregularities or scratches in the vicinity of the end of the glass substrate (the chamfer or the end surface of the inner and outer circumferences) that had not been a problem in the past. It was found that mutual contact between the recording medium and the recording head occurred.

As a result of further investigation of the cause by the present inventors, when chemical mechanical polishing is performed on a glass substrate containing SiO ₂ using cerium oxide or the like, although a high polishing processing rate can be obtained, it is intended by cerium oxide. It was found that a change in the edge shape was not caused. When the present inventors perform chemical mechanical polishing on the main surface of a glass substrate containing SiO ₂ using cerium oxide or the like, the chemical polishing action extends to the vicinity of the edge of the glass substrate. It has been found that the shape is disturbed due to excessive polishing near the end.

On the other hand, the present inventors have performed mechanical polishing using zirconium oxide as free abrasive grains on the main surface of the glass substrate in order to suppress the occurrence of shape disturbance near the edge of the glass substrate. After that, an attempt was made to perform precision polishing using colloidal silica as loose abrasive grains on the main surface of the glass substrate. Although the shape near the edge of the glass substrate is stable, mechanical polishing polishes the main surface of the glass substrate with rough cutting, so scratches formed by mechanical polishing are removed (or corrected) by precision polishing using colloidal silica. As a result, it has been found that it is difficult to effectively suppress the occurrence of head crashes by this method.

The present invention has been made in view of the above circumstances, and is for an information recording medium capable of suppressing mutual contact between an information recording medium such as a magnetic disk and a magnetic head for reading and writing data. It aims at obtaining the manufacturing method of a glass substrate.

Method of manufacturing a glass substrate for an information recording medium according to the present invention is a method for producing a glass substrate for an information recording medium which is built in the information recorder as part of the information recording medium, and has a main surface, SiO ₂ Preparing a glass material containing a component, and supplying the first free abrasive grains between the main surface of the glass material and the first polishing pad, and using the first polishing pad, the glass material. A first rough polishing step for mechanically polishing the main surface of the glass material, and the first loose abrasive grains between the main surface of the glass material polished in the first rough polishing step and a second polishing pad. Are polished in the second rough polishing step and the second rough polishing step in which the main surface of the glass material is chemically mechanically polished using the second polishing pad while supplying different second loose abrasive grains. Of the above glass material A precision polishing step of polishing the main surface of the glass material using the third polishing pad while supplying third loose abrasive grains between the main surface and the third polishing pad, The said 1st polishing pad used for 1 rough grinding | polishing process consists of a soft foamed resin pad, and the hardness of the said soft foamed resin pad is 73 to 85 degree | times in Asker C hardness.

Preferably, the first loose abrasive used in the first rough polishing step includes zirconium oxide, and the second free abrasive used in the second rough polishing step includes cerium oxide, and the precision polishing. The said 3rd free abrasive grain used for a process contains colloidal silica. Preferably, the glass material prepared in the preparation step includes 58% by mass or more and 68% by mass or less of SiO ₂ as a component.

Preferably, the glass material prepared in the preparation step is prepared by cutting out from a plate-like glass manufactured using a float process. Preferably, the abrasive grain size of zirconium oxide used as the first loose abrasive in the first rough polishing step is 0.7 μm or more and 1.4 μm or less.

Preferably, the average abrasive grain size of zirconium oxide used as the first free abrasive grains in the first coarse polishing step and the average abrasive grain size of cerium oxide used as the second free abrasive grains in the second coarse polishing step As for the ratio to the diameter, when the average abrasive grain size of zirconium oxide used as the first free abrasive grain is 1, the average abrasive grain diameter of cerium oxide used as the second free abrasive grain is 0.7 or more and 1. 0 or less. Preferably, a polishing processing rate by zirconium oxide used as the first free abrasive grains in the first rough polishing step, and a polishing processing rate by cerium oxide used as the second free abrasive particles in the second rough polishing step, The ratio of the polishing rate with cerium oxide used as the second loose abrasive is 1 and the polishing rate with zirconium oxide used as the first loose abrasive is 0.4 or more and 0.8 or less. .

Preferably, the allowance for the glass material by zirconium oxide used as the first loose abrasive grains in the first coarse polishing step, and the cerium oxide used as the second loose abrasive grains in the second coarse polishing step. The ratio of the machining allowance with respect to the glass material is 0.8 or more when the machining allowance with cerium oxide used as the second loose abrasive grain is 1, and the machining allowance with zirconium oxide used as the first loose abrasive grain is 1. 2 or less. Preferably, the ζ potential of zirconium oxide used as the first loose abrasive in the first rough polishing step is −50 mV to −30 mV.

According to the present invention, it is possible to suppress mutual contact between an information recording medium such as a magnetic disk and a magnetic head that reads and writes data by suppressing excessive polishing of the vicinity of the edge of the main surface of the glass substrate. The manufacturing method of the glass substrate for information recording media which can be performed can be obtained.

It is a perspective view which shows an information recording device provided with the glass substrate manufactured by using the manufacturing method of the glass substrate for information recording media in embodiment. It is a top view which shows the glass substrate manufactured by the manufacturing method of the glass substrate for information recording media in 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 provided with the glass substrate manufactured by the manufacturing method of the glass substrate for information recording media in embodiment as an information recording medium. FIG. 5 is a cross-sectional view taken along line VV in FIG. 4. It is a flowchart figure which shows each process of the manufacturing method of the glass substrate for information recording media in embodiment. It is a figure which shows each experimental condition in Example 1 and Comparative Examples 1 and 2. FIG. It is a figure which shows each experimental condition in the comparative example 3 and Examples 2-1 and 2-2. FIG. 5 is a flowchart showing steps of a method for manufacturing a glass substrate for information recording media in Examples 1, 2-1, 2-2 and Comparative Examples 2, 3. It is a flowchart figure which shows each process of the manufacturing method of the glass substrate for information recording media in the comparative example 1. It is a figure which shows the content rate of each component contained in the glass raw material used in Example 1, 2-1, 2-2, Comparative Examples 1-3. It is a figure which shows the experimental result in Example 1, 2-1, 2-2 and Comparative Examples 1-3. It is a figure which shows the experimental result in another Example.

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, the information recording medium 10 includes a chemical strengthening layer 12 (see FIGS. 4 and 5) and a magnetic recording layer 14 (see FIGS. 4 and 5) on the glass substrate 1. ) Is formed.

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 from the front surface side and the back surface side.

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 of 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) contains SiO ₂ as a component. The glass substrate 1 may contain 58% by mass or more and 68% by mass or less of SiO ₂ as a component.

The glass substrate 1 has a main surface 2, a main surface 3, an inner peripheral end surface 4, a hole 5, and an outer peripheral end surface 6, and is formed in a disk shape as a whole. 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.

(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.

As shown in FIGS. 4 and 5, the information recording medium 10 includes a glass substrate 1 and a chemically strengthened layer 12 formed so as to cover the

main surfaces

2 and 3, the inner peripheral end surface 4 and the outer peripheral end surface 6 of the glass substrate 1. And a magnetic recording layer 14 formed on the chemical strengthening layer 12. By forming the chemical strengthening 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 a housing 20 (not shown) using the holes 15.

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

Another protective layer may be formed on the protective layer or instead of the protective layer. For example, in place of the protective layer, tetraalkoxylane is diluted with an alcohol-based solvent on a Cr layer, and then colloidal silica fine particles are dispersed and applied, followed by baking to form a silicon oxide (SiO ₂ ) layer. It may be formed.

(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 glass material preparation step (S10), a cutout step (S11), an inside / outside processing step (S12), an etching step (S13), an inside / outside polishing step (S14), and a first roughening step. A polishing step (S15), a second rough polishing step (S16), a precision polishing step (S17), and a chemical strengthening step (S18) are provided.

A magnetic recording layer deposition step (S200) is performed on the glass substrate obtained through the chemical strengthening step (S18). The information recording medium 10 (see FIGS. 4 and 5) is obtained through the magnetic recording layer deposition step (S200). Hereinafter, the details of the steps S10 to S18 constituting the glass substrate manufacturing method S100 will be described in order. In the following description, simple cleaning appropriately performed between the steps S10 to S18 will be described in detail. There may not be.

(Glass material preparation process)
In the glass material preparation step (S10), a glass material constituting the glass substrate is prepared. The glass material includes SiO ₂ as a component, and is made of an amorphous glass material made of, for example, aluminosilicate glass.

The glass material in the present embodiment is prepared as a plate (or sheet) glass having a thickness of 1 mm, for example, by a float method. The glass material in the present embodiment contains 58% by mass or more and 68% by mass or less of SiO ₂ as a component.

The glass material is prepared by a so-called direct press method (DP method) in which a molten glass material is poured onto the lower mold and then the molten glass material is press-molded by the upper mold and the lower mold. May be. Also in this case, the glass material may contain 58% by mass or more and 68% by mass or less of SiO ₂ as a component.

(Cut out process)
In the cutting process (S11), a rectangular glass material including a region to be a disk-shaped glass substrate is cut out from the glass material using a diamond cutter (grinding grindstone) or the like. In the cutting-out process, a plurality of glass materials formed in a rectangular shape from one glass material may be cut out. The size of the glass material to be cut out is, for example, 50 mm × 50 mm to 100 mm × 100 mm.

(Internal / external machining process)
In the inside / outside processing step (S12), a cut line is formed on the bottom surface of the glass material cut into a rectangular shape using a glass cutter. The cut line is formed in a circular shape so as to draw each of a substantially peripheral edge on the outer peripheral side and a substantially peripheral edge on the inner peripheral side of the region to be the glass substrate. The diameter of the cut line formed on the substantially peripheral edge on the outer peripheral side is, for example, 67 mm, and the diameter of the cut line formed on the substantially peripheral edge on the inner peripheral side is, for example, 18 mm.

The outer peripheral incision and the inner peripheral incision formed in the inner and outer processing steps are formed so as to be inclined obliquely toward the outside with respect to the plate thickness direction. The inclination angle with respect to the normal direction of the glass material at each of the outer peripheral incision and the inner peripheral incision is, for example, 10 °.

(Etching process)
In the etching step (S13), minute cracks present on the main surface and the end face are removed with an aqueous solution containing hydrofluoric acid, ammonium fluoride, and the like. The thickness of the glass substrate to be removed is about 3 μm to 20 μm.

Next, the outer peripheral end face and the inner peripheral end face of the glass material are respectively ground so that the outer diameter becomes 65 mmφ and the inner diameter (the diameter of the circular hole in the center) becomes 20 mmφ. Further, a predetermined chamfering process is performed on the outer peripheral end surface and the inner peripheral end surface. The surface roughness of the end face of the glass material at this time is about 4 μm in Rmax. In general, a glass substrate having an outer diameter of 65 mm is used in a 2.5-inch hard disk drive.

(Internal and external polishing process)
In the inner and outer polishing step (S14), mirror polishing using a brush polishing method is performed on each of the outer peripheral end surface and the inner peripheral end surface of the glass material. As the abrasive grains, for example, a slurry containing cerium oxide abrasive grains (free abrasive grains) can be used. By the inner and outer polishing steps, a mirror surface state in which the occurrence of precipitation of sodium or potassium can be prevented at the end face of the glass material.

(First rough polishing process)
In the first rough polishing step (S15), both main surfaces of the glass material are mechanically polished using a double-side polishing apparatus having a planetary gear mechanism. In the first rough polishing step in which mechanical polishing is performed, almost no chemical action is used for polishing, and the mechanical (physical) action by the free abrasive grains (abrasive) is dominant. The main surface of the glass substrate is polished. Here, the amount of polishing with respect to the main surface of the glass substrate is predetermined depending on the physical properties (abrasive grain size or abrasive grain concentration) of free abrasive grains and the processing conditions (pressing force of the surface plate or the rotational speed of the surface plate). Determined by value.

A soft foamed resin pad (soft foamed resin polisher) is used as the polishing pad (first polishing pad) attached to the upper and lower surface plates of the double-sided polishing apparatus in the first rough polishing process. As this soft foamed resin pad, one having a hardness of 73 degrees to 85 degrees in Asker C hardness is used. As the polishing slurry (first free abrasive grains) in the first rough polishing step, zirconium oxide (zirconia), titanium oxide, diamond, or the like may be used. From the viewpoint of easy control of the particle size and cost, zirconium oxide (zirconia) is preferably used as the polishing slurry (first free abrasive grains).

When zirconium oxide (zirconia) is used as the polishing slurry (first free abrasive grains), the abrasive grain size of the zirconium oxide is preferably 0.7 μm or more and 1.4 μm or less. When zirconium oxide (zirconia) is used as the polishing slurry (first free abrasive grains), the ζ potential of zirconium oxide used as the first free abrasive grains in the first rough polishing step is −50 mV to −30 mV. Good.

In the first rough polishing step, the main surface of the glass material and the soft foam resin are in contact with each other of the main surfaces of the glass material and the soft foam resin pads disposed so as to sandwich the two main surfaces. A slurry such as zirconium oxide is supplied between the pad and the pad. By mechanically polishing the main surface of the glass material using the soft foamed resin pad and zirconium oxide, scratches formed on the main surface, distortion generated on the main surface, and the like are removed.

The glass material that has finished the first rough polishing step may be washed with a neutral detergent, pure water, IPA (isopropyl alcohol), UV (ultraviolet) ozone, or the like. Further, zirconia may be dissolved and removed by HF or the like.

(Second rough polishing step)
In the second rough polishing step (S16), both main surfaces of the glass material are chemically mechanically polished using a double-side polishing apparatus having a planetary gear mechanism. In the second rough polishing step in which chemical mechanical polishing is performed, chemical action is mainly used for polishing.

The chemical component in the polishing agent or polishing slurry mechanically polishes the main surface of the glass substrate while chemically changing the main surface of the glass substrate (substitution of Si—O and Ce—O). The main surface of the glass substrate is polished chemically and mechanically, so that the main surface of the glass substrate is polished at a faster polishing rate than when the main surface of the glass substrate is mechanically polished using an abrasive alone. Polished.

As the polishing pad (second polishing pad) attached to the upper and lower surface plates of the double-side polishing apparatus in the second rough polishing step, a soft foam resin pad (soft foam resin polisher) may be used. As the polishing slurry (second free abrasive grains) in the second rough polishing step, cerium oxide (ceria), manganese oxide, or the like may be used.

When cerium oxide (ceria) is used as the polishing slurry (second free abrasive grains) in the second rough polishing step, the average abrasive grain size of zirconium oxide (zirconia) used as the first free abrasive particles in the first rough polishing step And the average abrasive grain size of cerium oxide used as the second loose abrasive grains in the second rough polishing step, the ratio of the average abrasive grain diameter of zirconium oxide used as the first loose abrasive grains is 2, The average abrasive grain size of cerium oxide used as the free abrasive grains is 0.7 or more and 1.3 or less, preferably 0.7 or more and 1.0 or less.

In the second rough polishing step, the main surface of the glass material and the soft foam resin are in contact with each other of the main surfaces of the glass material and the soft foam resin pads disposed so as to sandwich the main surfaces. A slurry such as cerium oxide is supplied between the pad and the pad. The main surface of the glass material is polished chemically and mechanically using a soft foam resin pad and cerium oxide.

The ratio between the polishing rate by zirconium oxide used as the first loose abrasive in the first rough polishing step and the polishing rate by cerium oxide used as the second loose abrasive in the second rough polishing step is the second free rate. Assuming that the polishing rate with cerium oxide used as abrasive grains is 1, the polishing rate with zirconium oxide used as first loose abrasive grains is 0.4 or more and 0.8 or less, more preferably 0.5 or more and 0.00. It is good that it is 7 or less.

The allowance for the main surface of the glass material by zirconium oxide used as the first loose abrasive grains in the first rough polishing step, and the main surface of the glass material by cerium oxide used as the second loose abrasive particles in the second rough polishing step The ratio with the machining allowance is 1 when the machining allowance with cerium oxide used as the second loose abrasive grains is 1, and the machining allowance with zirconium oxide used as the first loose abrasive grains is 0.8 or more and 1.2 or less. Good. At this time, the machining allowance with respect to the main surface of the glass material by the colloidal silica used as the third loose abrasive grains in the precision polishing step to be described later is 3 if the machining allowance by the cerium oxide used as the second loose abrasive grains is 1. The allowance for colloidal silica used as the loose abrasive is preferably 0.1 or less.

By scratching the main surface of the glass material chemically and mechanically using the soft foam resin pad and cerium oxide, scratches remaining on the main surface of the glass substrate after the first rough polishing step are removed. .

The glass material that has finished the second rough polishing step may be washed with a neutral detergent, pure water, IPA (isopropyl alcohol), UV (ultraviolet) ozone, or the like. More preferably, for the glass material that has finished the second rough polishing step, it is preferable that the main surface is slightly dissolved with hydrofluoric acid or the like to completely remove the abrasive remaining on the main surface.

(Precision polishing process)
In the precision polishing step (S17), both main surfaces of the glass material are precisely mirror-polished using a double-side polishing apparatus having a planetary gear mechanism. As the polishing pad (third polishing pad) attached to the upper and lower surface plates in the precision polishing step, another soft foam resin pad (soft foam resin polisher) may be used. Colloidal silica or the like is preferably used as the polishing slurry (third free abrasive grains) in the precision polishing step.

The hardness of the other soft foam resin pad used as the polishing pad in the precision polishing process may be smaller than the hardness of the soft foam resin pad used as the polishing pad in the second rough polishing process. In other words, the hardness of the soft foam resin pad used as the polishing pad in the second rough polishing process is preferably larger than the hardness of another soft foam resin pad used as the polishing pad in the precision polishing process.

In the precision polishing step, the main surface of the glass material and the soft foam resin pad are placed in a state where the two main surfaces of the glass material and the soft foam resin pad arranged so as to sandwich the two main surfaces are in contact with each other. In the meantime, colloidal silica is supplied as a slurry. By precisely mirror-polishing the main surface of the glass material using the soft foam resin pad and colloidal silica, both main surfaces of the glass material are smoothed and finished in a mirror-like shape.

The glass material that has finished the third rough polishing step may be washed with neutral detergent, pure water, IPA (isopropyl alcohol), UV (ultraviolet) ozone, or the like. Through the above steps, the glass substrate 1 shown in FIGS. 2 and 3 is obtained.

(Chemical strengthening process)
In the chemical strengthening step (S18), a chemical strengthening process is performed on the glass substrate (glass material) obtained by the above steps. By the chemical strengthening treatment, a compressive stress layer (chemical strengthening layer) is formed on the main surface of the glass substrate. Examples of the chemical strengthening solution used for the chemical strengthening treatment include a mixed solution of potassium nitrate (content 60%) and sodium nitrate (content 40%), or potassium nitrate (content 70%) and sodium nitrate (content 30). %) And the like can be used.

In the chemical strengthening treatment, the chemical strengthening solution is heated to 300 ° C. to 400 ° C., and the cleaned glass substrate is preheated to 200 ° C. to 300 ° C. The glass substrate is immersed in the chemical strengthening solution for 3 to 4 hours. At the time of immersion, since both the entire surfaces of the glass substrate are chemically strengthened, the plurality of glass substrates are immersed in a holder or the like so that the plurality of glass substrates are held by the respective end faces. It is preferable.

The 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 than these ions (ion exchange method). Compressive stress is generated in the ion-exchanged region due to the strain caused by the difference in ion radius, and both main surfaces of the glass substrate are strengthened. The chemical strengthening process may be performed before the precision polishing process.

After each of the above steps is completed, the glass substrate is washed using a high frequency of 950 kHz or washed using an alkaline detergent so that the deposits remaining on the glass substrate are eliminated. Thereafter, the glass substrate is dried using IPA vapor.

An information recording medium such as a magnetic disk manufactured using the glass substrate 1 (see FIGS. 2 and 3) by removing the deposits remaining on the main surface of the glass substrate after the chemical strengthening step. 10 (see FIGS. 4 and 5) is reduced from occurrence of head crash. The manufacturing method of the glass substrate in the present embodiment is configured as described above.

(Magnetic thin film formation process)
Magnetic recording layers are formed on both main surfaces (or one of the main surfaces) of the glass substrate that has been subjected to the chemical strengthening treatment. 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.

(Action / Effect)
As described above, in the mechanical polishing, only the main surface of the glass substrate is mainly polished, and the main surface of the glass substrate is roughly polished. The main surface of the glass substrate is in a rough state. On the other hand, in the chemical mechanical polishing, the main surface of the glass substrate is further mechanically polished while being chemically changed (substitution of Si—O and Ce—O is performed).

Chemical mechanical polishing is characterized by a high polishing rate. However, in chemical mechanical polishing, the compatibility between the free abrasive grains (abrasive) and the glass substrate is good, so that the abrasive tends to remain on the surface of the glass substrate. Furthermore, in chemical mechanical polishing, the vicinity of the edge of the glass substrate is easily polished by the action of a chemical change, and a deteriorated portion called “sag” is formed at the edge of the glass substrate. There is also a feature.

In the manufacturing method of the glass substrate of the present embodiment, after the main surface of the glass substrate is mechanically polished using zirconium oxide or the like (after the first rough polishing step), the glass substrate is used using cerium oxide or the like. The main surface of is chemically and mechanically polished (second rough polishing step).

Of the main surface of the glass substrate, the portion roughened by the mechanical polishing in the first rough polishing step is preferentially polished by the chemical mechanical polishing in the second rough polishing step over the vicinity of the end of the glass substrate. The main surface of the glass substrate is mechanically polished by chemical mechanical polishing such as cerium oxide before the chemical polishing action reaches the end of the glass substrate and the vicinity of the end of the glass substrate is excessively polished. It is chemically polished so that most of the deep scratches caused by the surface become shallow.

The main surface of the glass substrate can be polished so as to obtain an appropriate polishing thickness by chemical mechanical polishing, and the scratches that become shallow by chemical mechanical polishing are colloidal in the precision polishing process that is the next process. It can be sufficiently removed by mirror polishing using silica or the like.

Therefore, according to the method for manufacturing a glass substrate (glass substrate for information recording medium) in the present embodiment, high smoothness on the main surface of the glass substrate is achieved by sequentially performing mechanical polishing, chemical mechanical polishing, and precision polishing. High flatness can be obtained, and a good state with no irregular shape and scratches can be obtained near the edge of the glass substrate. At the end of the glass substrate, a portion with a deteriorated shape called “sag” is not formed. Furthermore, by performing the chemical strengthening process on the glass substrate, the impact resistance and vibration resistance of the glass substrate are also improved, and a glass substrate that is resistant to impact and vibration is obtained.

As described at the beginning, in the conventional method of manufacturing a glass substrate, first, rough polishing (chemical mechanical polishing) using a hard urethane pad as a polishing pad is performed on the main surface of the glass substrate. Thereafter, precision polishing using a soft foam resin pad as a polishing pad is performed on the main surface of the glass substrate.

The reason why a hard urethane pad is used as a polishing pad during rough polishing (chemical mechanical polishing) is that when a soft urethane pad is used during rough polishing (chemical mechanical polishing), the processing efficiency decreases, and the glass substrate This is because many scratches and the like occur on the main surface. However, when a hard urethane pad is used as a polishing pad during rough polishing (chemical mechanical polishing), there is a problem that the shape near the edge of the glass substrate is deteriorated. This is because when a hard urethane pad is used, the polishing force is concentrated in the vicinity of the end of the glass substrate.

As described above, in the method for manufacturing a glass substrate of the present embodiment, the polishing pad (first polishing pad) used in the first rough polishing step is made of a soft foam resin pad in order to stabilize the processing efficiency. Thus, as this soft foamed resin pad, one having a hardness of 73 degrees to 85 degrees in Asker C hardness is used. By using such a soft foamed resin pad, the polishing force does not act concentrated on the vicinity of the end of the glass substrate, so the shape near the end of the glass substrate does not deteriorate.

Also, in the second rough polishing step, which is the next step of mechanical polishing, soft foamed resin urethane is also used for chemical mechanical polishing with cerium oxide. By finishing the polishing process before the scratches on the main surface or edge of the glass substrate increase, it is possible to further improve the edge shape (prevent deterioration of the edge shape) while suppressing the occurrence of scratches. It becomes.

Information recording medium 10 (see FIG. 4 and FIG. 5) provided with glass substrate 1 (see FIG. 2 and FIG. 3, etc.) obtained by the method of manufacturing a glass substrate (glass substrate for information recording medium) in the present embodiment. In the state incorporated as the information recording device 30, contact with the magnetic head is suppressed, and occurrence of data reading errors and the like can also be suppressed. Therefore, when the information recording medium provided with the glass substrate 1 is used as an information recording apparatus such as a hard disk, it has a high recording capacity and can ensure high operational stability.

In the production method of a glass substrate of this embodiment, the glass material is prepared in the glass material preparation step comprises 58 wt% or more 68 wt% or less of SiO ₂ to the ingredients. The content of SiO _{2 in} the glass material affects various physical properties of the glass material. In general, the higher the content of SiO ₂ contained in the glass material, the harder the glass material, and the lower the content of SiO ₂ contained in the glass material, the more chemically durable. Lower.

When the glass material prepared in the glass material preparation step has a SiO ₂ content of more than 68% by mass, the chemical durability of the glass material is increased to reduce the chemical polishing effect. Even with the polishing used, mechanical polishing is strongly performed, so that many scratches and the like are generated. On the other hand, when the glass material prepared in the glass material preparation step has a SiO ₂ content of less than 58% by mass, the chemical durability of the glass material is reduced, thereby reducing the polishing using cerium oxide. However, the shape of the edge of the glass substrate tends to deteriorate at the same time.

Therefore, the glass material prepared in the glass material preparation step contains 58% by mass or more and 68% by mass or less of SiO ₂ as a component, so that the glass substrate has high cleanliness, high smoothness, and high flatness with few scratches. Can be obtained.

In the glass substrate manufacturing method of the present embodiment, a glass material is prepared by using a float method. A glass substrate obtained from a glass material formed into a plate shape using the float process has few scratches and has a high flatness.

On the other hand, a glass substrate prepared by using the direct press method has more scratches and flatness than a glass substrate prepared by using the float method. The glass substrate prepared using the direct press method needs a grinding process using fixed abrasive grains. Moreover, since the glass substrate prepared using the direct press method has deep scratches, the scratches cannot be corrected by polishing with zirconium oxide, and thus the burden of chemical polishing using cerium oxide increases.

Therefore, by preparing the glass material using the float method in the glass material preparation step, it is possible to obtain a glass substrate with few scratches and high flatness.

In the method for manufacturing a glass substrate of the present embodiment, the abrasive particle diameter of zirconium oxide (zirconia) used as the polishing slurry (first free abrasive grains) is 0.7 μm or more and 1.4 μm or less. Depending on the abrasive grain size of zirconium oxide (zirconia), the shape and surface roughness of the main surface of the glass substrate to be polished change.

Zirconium oxide used as a polishing slurry (first free abrasive grains) in the first rough polishing step (mechanical polishing) needs to increase the processing efficiency. When it becomes larger than 4 μm, scratches and the like increase, which affects the quality of the finally obtained glass substrate. On the other hand, when the abrasive grain size is smaller than 0.7 μm, the processing efficiency is lowered.

Therefore, high processing efficiency is obtained when the abrasive grain size of zirconium oxide used as a polishing slurry (first loose abrasive grains) in the first rough polishing step (mechanical polishing) is 0.7 μm or more and 1.4 μm or less. At the same time, the quality of the finally obtained glass substrate can be improved.

In the manufacturing method of the glass substrate of the present embodiment, the average abrasive grain size of zirconium oxide (zirconia) used as the first free abrasive grains in the first coarse polishing step, and the second free abrasive grains in the second coarse polishing step. The ratio of the average abrasive grain size of cerium oxide used as the average abrasive grain size of zirconium oxide used as the first free abrasive grains is 1, and the average abrasive grain size of cerium oxide used as the second free abrasive grains Is 0.7 or more and 1.3 or less, preferably 0.7 or more and 1.0 or less.

When the average abrasive grain size of zirconium oxide used as the first free abrasive grains is 1, when the average abrasive grain size of cerium oxide used as the second free abrasive grains is larger than 1.0 or 1.3, oxidation occurs. The shape of the main surface of the glass substrate formed by the polishing of zirconium is deteriorated.

When the average abrasive grain size of zirconium oxide used as the first free abrasive grains is 1, when the average abrasive grain size of cerium oxide used as the second free abrasive grains is smaller than 0.7, it is polished by zirconium oxide. As a result, scratches caused by zirconium oxide in the first rough polishing step cannot be completely corrected by chemical mechanical polishing with cerium oxide in the second rough polishing step.

Therefore, when the average abrasive grain size of zirconium oxide used as the first free abrasive grains is 1, the average abrasive grain size of cerium oxide used as the second free abrasive grains is 0.7 or more and 1.3 or less, preferably 0. When the ratio is 0.7 or more and 1.0 or less, the shape of the end of the glass substrate is not deteriorated, and scratches generated on the main surface of the glass substrate by zirconium oxide are satisfactorily removed by cerium oxide. It becomes.

In the manufacturing method of the glass substrate of the present embodiment, the polishing processing rate by zirconium oxide used as the first free abrasive grains in the first rough polishing step and the oxidation used as the second free abrasive grains in the second rough polishing step. The ratio of the polishing process rate with cerium is 0.4 or more when the polishing process rate with cerium oxide used as the second free abrasive grains is 1, and the polishing process rate with zirconium oxide used as the first free abrasive grains is 0.4 or more. It is 8 or less, more preferably 0.5 or more and 0.7 or less.

Depending on the polishing rate with zirconium oxide and the polishing rate with cerium oxide, the shape and surface roughness of the main surface of the glass substrate to be polished change. When the polishing processing rate by cerium oxide used as the second free abrasive grains is 1, when the polishing processing rate by zirconium oxide used as the first free abrasive grains is greater than 0.8, the main surface of the glass substrate Will tend to form scratches.

On the other hand, when the polishing rate by cerium oxide used as the second free abrasive grains is 1, when the polishing rate by zirconium oxide used as the first free abrasive grains is smaller than 0.4 (relatively, oxidation When the polishing processing rate by cerium is increased), scratches generated by zirconium oxide in the first rough polishing step cannot be completely corrected by chemical mechanical polishing by cerium oxide in the second rough polishing step.

Therefore, if the polishing rate with cerium oxide used as the second free abrasive is 1, the polishing rate with zirconium oxide used as the first free abrasive is 0.4 or more and 0.8 or less, more preferably 0. The scratches generated on the main surface of the glass substrate by zirconium oxide can be satisfactorily removed by cerium oxide without deteriorating the shape of the edge of the glass substrate by being 0.5 or more and 0.7 or less. It becomes.

In the manufacturing method of the glass substrate of the present embodiment, the allowance for the main surface of the glass material by zirconium oxide used as the first loose abrasive grains in the first rough polishing step, and the second free abrasive in the second rough polishing step. The ratio of the cerium oxide used as grains to the machining allowance for the main surface of the glass material is 1 when the machining allowance by cerium oxide used as the second free abrasive grains is 1, and the removal by the zirconium oxide used as the first free abrasive grains. The cost is 0.8 or more and 1.2 or less.

The machining allowance for mechanical polishing using zirconium oxide and chemical mechanical polishing using cerium oxide is preferably substantially the same. The reason is that mechanical polishing with zirconium oxide adjusts the shape of the main surface of the glass substrate, but forms certain scratches. Chemical mechanical polishing with cerium oxide affects the shape of the edge of the glass substrate, but can repair the scratches generated by mechanical polishing with zirconium oxide. The best balance between mechanical polishing with zirconium oxide and chemical mechanical polishing with cerium oxide is when the machining allowances are approximately equal.

When the machining allowance by cerium oxide is 1, and the machining allowance by zirconium oxide used as the first loose abrasive is smaller than 0.8 (when the machining allowance by cerium oxide is large), the shape of the edge of the glass substrate is deteriorated. It becomes easy to do. When the removal allowance by cerium oxide is 1, and the allowance by zirconium oxide used as the first free abrasive grains is larger than 1.2 (when the allowance by cerium oxide is small), scratches caused by zirconium oxide are It cannot be corrected by chemical mechanical polishing with cerium oxide in the two rough polishing steps.

Therefore, if the removal allowance by cerium oxide used as the second free abrasive grains is 1, the allowance by zirconium oxide used as the first free abrasive grains is 0.8 or more and 1.2 or less, so that The scratches generated on the main surface of the glass substrate by zirconium oxide can be satisfactorily removed by cerium oxide without deterioration of the shape of the end portion.

In the manufacturing method of the glass substrate of the present embodiment, the allowance for the main surface of the glass material by the colloidal silica used as the third free abrasive grains in the precision polishing step is taken up by the cerium oxide used as the second free abrasive grains. If the allowance is 1, the allowance for colloidal silica used as the third loose abrasive is 0.1 or less. When the machining allowance with cerium oxide used as the second free abrasive grains is 1, when the machining allowance with colloidal silica becomes larger than 0.1, the shape of the end portion of the glass substrate tends to deteriorate.

Therefore, when the removal allowance by cerium oxide used as the second free abrasive grains is 1, the removal allowance by the colloidal silica used as the third free abrasive grains is 0.1 or less, so that the shape of the end portion of the glass substrate is reduced. It can be suppressed that the deterioration.

In the glass substrate manufacturing method of the present embodiment, the ζ potential of zirconium oxide used as the first free abrasive grains in the first rough polishing step is −50 mV to −30 mV. If the ζ potential due to zirconium oxide is lower than −50 mV, zirconium oxide tends to remain on the surface of the glass substrate, which causes a flaw during chemical mechanical polishing using cerium oxide. If the ζ potential due to zirconium oxide is higher than −30 mV, the repulsion between the glass substrate and zirconium oxide is too strong, and polishing cannot be performed smoothly, and the shape of the main surface of the glass substrate tends to deteriorate.

Therefore, the ζ potential of zirconium oxide used as the first free abrasive grains is −50 mV or more and −30 mV or less, so that the main surface of the glass substrate is less likely to be scratched and the shape of the main surface of the glass substrate is reduced. Deterioration can also be suppressed.

[Examples and Comparative Examples]
Hereinafter, with reference to FIGS. 7 to 12, Examples 1, 2-1, 2-2 performed based on the above-described embodiment and Comparative Examples 1 to 3 for these Examples will be described. FIG. 7 is a diagram showing experimental conditions in Example 1 and Comparative Examples 1 and 2. FIG. 8 is a diagram showing experimental conditions in Comparative Example 3 and Examples 2-1 and 2-2. FIG. 9 is a flowchart showing each step of the glass substrate manufacturing method in Examples 1, 2-1, 2-2 and Comparative Examples 2, 3. FIG. 10 is a flowchart showing each step of the glass substrate manufacturing method in Comparative Example 1.

FIG. 11 is a diagram showing the content ratio of each component contained in the glass material (glass material A) used in Examples 1, 2-1, 2-2 and Comparative Examples 1 to 3. About the glass raw material B and the glass raw material C which are described in FIG. 11, it is used in the other Example mentioned later. FIG. 12 is a diagram showing experimental results in Examples 1, 2-1, 2-2 and Comparative Examples 1 to 3.

In Examples 1, 2-1, 2-2 and Comparative Examples 1 to 3, as shown in FIG. 12, with respect to the glass substrate manufactured by using each manufacturing method, The degree of deterioration of the shape called “sag” was measured, and the number of deposits on the main surface of the glass substrate was calculated as an OSA (Optical Surface Analyzer) encounter number. In addition, a glide test was performed on the glass substrate manufactured by using each manufacturing method, and the number of occurrences of missing was calculated.

Example 1
As shown in FIGS. 7 and 9, the glass substrate manufacturing method S101 (see FIG. 9) of Example 1 is similar to the above-described embodiment in the glass material preparation step (S10), the cutting step (S11), Internal / external machining step (S12), etching step (S13), internal / external polishing step (S14), first rough polishing step (S15), second rough polishing step (S16), precision polishing step (S17), and chemical strengthening step ( S18).

In the glass material preparation step (S10), the glass material A was prepared using the float method. As shown in FIG. 11, the components constituting the glass material A are Li ₂ O 3.5 mass%, Na ₂ O 10.0 mass%, K ₂ O 0.5 mass%, and MgO 0 0.5% by mass, CaO 1.5% by mass, SrO 0.5% by mass, BaO 1.0% by mass, ZnO 0.5% by mass, B ₂ O ₃ 0.5% by mass, Al ₂ O ₃ is 11.5% by mass, SiO ₂ is 67.5% by mass, ZrO ₂ is 2.0% by mass, and CeO ₂ is 0.5% by mass.

Similarly to the above-described embodiment, the glass material A was sequentially subjected to a cutting process (S11), an internal / external processing process (S12), an etching process (S13), and an internal / external polishing process (S14) (see FIG. 9). .

As polishing conditions for mechanical polishing (see FIG. 7) in the first rough polishing step (S15), zirconium oxide (zirconia) having an average particle diameter of 0.6 μm is used as free abrasive grains (slurry), and the polishing processing rate Was 0.8 μm / min, and the machining allowance was 20 μm. As a polishing pad, a soft foamed resin pad having Asker C hardness of 80 degrees was used.

As polishing conditions (see FIG. 7) for chemical mechanical polishing in the second rough polishing step (S16), cerium oxide (ceria) having an average particle diameter of 1.0 μm is used as free abrasive grains (slurry), and polishing is performed. The processing rate was 1.0 μm / min, and the machining allowance was 20 μm. As the polishing pad, a soft foamed resin pad having Asker C hardness of 70 degrees was used.

As polishing conditions (see FIG. 7) for mirror polishing in the precision polishing step (S17), colloidal silica having an average particle diameter of 20 nm is used as free abrasive grains (slurry), and the polishing rate is 0.05 μm / min. The machining allowance was 1.5 μm. As the polishing pad, a soft foamed resin pad having Asker C hardness of 70 degrees was used.

The chemical strengthening step (S18) and the magnetic recording layer deposition step (S200) were sequentially performed on the glass substrate that had undergone the precision polishing step (S17) in the same manner as in the above-described embodiment.

(Evaluation of Example 1)
Referring to FIG. 12, the degree of “sag” at the edge of the glass substrate was measured for the glass substrate based on Example 1 obtained by the above steps. Specifically, using an optical surface analyzer “OSA6300” manufactured by KLA Tencol, the depth from the main surface (reference surface) of the glass substrate at a position of dimension R = 31.8 mm from the center of the glass substrate. When the dimension was measured, it was 24.3 nm. Moreover, when the number of scratches on the main surface of the glass substrate was measured as the number of scratches displayed on the screen of the measuring instrument as an OSA (Optical Surface Analyzer) encounter number, it was 19.

A glide test was also performed on the glass substrate based on Example 1. Specifically, the magnetic disk was manufactured from the glass substrate based on Example 1, and after the magnetic disk was incorporated into the hard disk drive, the glide (distance between the magnetic head and the surface of the magnetic disk) was set to 6 nm, Each of 4 nm, 3 nm, and 2 nm was set. It was observed whether or not the magnetic head and the surface of the magnetic disk collided (whether or not a head crash occurred) when the magnetic disk was rotated at a predetermined rotational speed.

When a head crush occurs when the glide is 6 nm, it is determined as an evaluation 1. However, as a glass substrate based on Example 1, a head crush does not occur when the glide is 6 nm (evaluation 2). Means it was obtained). Also, head crash did not occur even when the glide was 4 nm (meaning that the evaluation 3 was obtained), and head crash did not occur even when the glide was 3 nm (that the evaluation 4 was obtained). No head crush occurred even when the glide was 2 nm (meaning that the best evaluation 5 was obtained).

A missing test was also performed on the glass substrate based on Example 1. Specifically, the magnetic disk is manufactured from the glass substrate based on Example 1, and the magnetic disk is incorporated into the hard disk drive, and then the magnetic information is written and read, and the number of occurrences of read errors or write errors is determined. Counted as missing count.

For evaluation of the number of read / write errors (missing count number), a magnetic film was formed on the surface of the glass substrate for the divisional recording medium (magnetic disk) produced in Example 1 and then mounted on a hard disk drive having a DFH mechanism. Then, read / write errors on the entire surface of the magnetic disk were evaluated. The evaluation of the number of errors was performed by counting errors in which the read / write error area was 0.4 μm or more when reading / writing was performed on the entire surface of the magnetic disk. Although errors occur in units of bits, errors due to scratches occur in a certain number of bits, so an error region of 0.4 μm or larger was evaluated.

When the missing count number is 31 or more, it is determined as an evaluation C, when the missing count number is 21 or more and 30 or less, it is determined as an evaluation B, and when the missing count number is 11 or more and 20 or less, it is evaluated as A. When the missing count number is 0 or more and 10 or less, the evaluation S is determined. However, as the glass substrate based on Example 1, the missing count number is 8, and the evaluation S can be obtained. It was.

(Comparative Example 1)
As shown in FIGS. 7 and 10, the glass substrate manufacturing method S <b> 201 (see FIG. 10) of Comparative Example 1 is similar to Example 1 described above, in the glass material preparation step (S <b> 10), the cutting step (S <b> 11), It includes an internal / external processing step (S12), an etching step (S13), an internal / external polishing step (S14), and a precision polishing step (S17). Between the internal / external polishing step (S14) and the precision polishing step (S17), Only the rough polishing step (S16A) using mechanical polishing is performed.

In the glass material preparation step (S10), the glass material A was prepared using the float method as in Example 1 described above. For the glass material A, the cutting step (S11), the internal / external processing step (S12), the etching step (S13), and the internal / external polishing step (S14) were sequentially performed in the same manner as in Example 1 (see FIG. 10). .

As polishing conditions (see FIG. 8) for chemical mechanical polishing in the rough polishing step (S16A), cerium oxide (ceria) having an average particle diameter of 0.8 μm is used as free abrasive grains (slurry), and the polishing rate is The thickness was 1.0 μm / min and the machining allowance was 40 μm. As a polishing pad, a soft foamed resin pad having Asker C hardness of 80 degrees was used.

The polishing conditions (see FIG. 8) for mirror polishing in the precision polishing step (S17) are the same as those in Example 1 described above. Similarly to Example 1 described above, the chemical strengthening step (S18) and the magnetic recording layer deposition step (S200) were sequentially performed on the glass substrate that had undergone the precision polishing step (S17).

(Evaluation of Comparative Example 1)
Referring to FIG. 12, the degree of “sag” at the edge of the glass substrate was measured on the glass substrate based on Comparative Example 1 in the same manner as in Example 1 described above. The number of OSA encounters was 34. As a result of the glide test, a head crash occurred when the glide was 6 nm, and the evaluation was 1. Evaluation C was obtained as a result of the missing test.

(Comparative Example 2)
Referring to FIG. 7, Comparative Example 2 is different from Example 1 described above in that the hardness of the soft foam resin pad used in the first rough polishing step (S15) is 70 degrees in Asker C hardness. Different. The hardness of the soft foam resin pad used in the first rough polishing step (S15) of Example 1 described above is 80 degrees in Asker C hardness.

As shown in FIG. 12, the degree of “sag” at the edge of the glass substrate was measured on the glass substrate based on Comparative Example 2 in the same manner as in Example 1 above, and it was 25.2 nm. The number of OSA encounters was 43. As a result of the glide test, a head crash did not occur when the glide was 6 nm, and the evaluation was 4. Evaluation C was obtained as a result of the missing test.

(Comparative Example 3)
Referring to FIG. 7, Comparative Example 3 is different from Example 1 described above in that the hardness of the soft foam resin pad used in the first rough polishing step (S15) is 87 degrees in Asker C hardness. Different. The hardness of the soft foam resin pad used in the first rough polishing step (S15) of Example 1 described above is 80 degrees in Asker C hardness.

As shown in FIG. 12, the degree of “sag” at the edge of the glass substrate was measured on the glass substrate based on Comparative Example 3 in the same manner as in Example 1 above, and it was 32.5 nm. The number of OSA encounters was 48. As a result of the glide test, a head crash occurred when the glide was 6 nm, and the evaluation was 1. Evaluation C was obtained as a result of the missing test.

Example 2-1
Referring to FIG. 8, Example 2-1 is the same as Example 1 described above in that the hardness of the soft foam resin pad used in the first rough polishing step (S15) is 73 degrees in Asker C hardness. Is different. The hardness of the soft foam resin pad used in the first rough polishing step (S15) of Example 1 described above is 80 degrees in Asker C hardness.

As shown in FIG. 12, with respect to the glass substrate based on Example 2-1, the degree of “sag” at the edge of the glass substrate was measured in the same manner as in Example 1 above, and was found to be 24.0 nm. . The number of OSA encounters was 22. As a result of the glide test, head crush did not occur even when the glide was 3 nm, and the evaluation was 4. Evaluation A was obtained as a result of the missing test.

(Example 2-2)
Referring to FIG. 8, Example 2-2 is the same as Example 1 described above in that the hardness of the soft foam resin pad used in the first rough polishing step (S15) is 85 degrees in Asker C hardness. Is different. The hardness of the soft foam resin pad used in the first rough polishing step (S15) of Example 1 described above is 80 degrees in Asker C hardness.

As shown in FIG. 12, the degree of “sag” at the edge of the glass substrate measured for the glass substrate based on Example 2-2 in the same manner as in Example 1 was 25.0 nm. . The number of OSA encounters was 24. As a result of the glide test, head crush did not occur even when the glide was 3 nm, and the evaluation was 4. Evaluation A was obtained as a result of the missing test.

(Comparison of Examples 1, 2-1, 2-2 and Comparative Examples 1 to 3)
As shown in FIG. 12, when Examples 1, 2-1, 2-2 and Comparative Example 1 are compared, according to the glass substrate manufacturing method based on Examples 1, 2-1, 2-2, By performing the mechanical polishing in the rough polishing process, the chemical mechanical polishing in the second rough polishing process, and the mirror polishing in the precision polishing process in sequence, a portion with a deteriorated shape called “sag” is formed. This is suppressed, and furthermore, it is understood that generation (residue) of scratches on the main surface of the glass substrate is also suppressed.

Further, when Examples 1, 2-1, 2-2 and Comparative Examples 2, 3 are compared, according to the glass substrate manufacturing method based on Examples 1, 2-1, 2-2, the first rough polishing step In addition, when the hardness of the soft foam resin pad used as the polishing pad (first polishing pad) is 73 degrees or more and 85 degrees or less in Asker C hardness, a portion called “sag” is deteriorated. It can be seen that the generation of scratches (residue) on the main surface of the glass substrate is also suppressed.

[Other embodiments]
Example 3-1
Referring to FIG. 13, in Example 3-1, the glass material prepared in the glass material preparation step (S10) is glass material B (see FIG. 11), and the first rough polishing step (S15). ) Is used as free abrasive grains (slurry) in the second coarse polishing step (S16), and the average particle diameter of zirconium oxide (zirconia) used as free abrasive grains (slurry) in 1) is It differs from Example 1 described above in that the average particle diameter of cerium oxide (ceria) is 0.8 μm. The glass material prepared in the glass material preparation step (S10) of Example 1 described above is glass material A (see FIG. 11).

As shown in FIG. 11, the components constituting the glass material B are Li ₂ O 4.0 mass%, Na ₂ O 11.5 mass%, K ₂ O 0.5 mass%, and MgO 1 .0 wt%, CaO 2.5 wt%, _Al 2 _{O 3} is 15.0 wt%, and, SiO ₂ is 65.5 wt%.

As shown in FIG. 13, when the degree of “sag” at the edge of the glass substrate was measured on the glass substrate based on Example 3-1, as in Example 1 above, it was 13.5 nm. . The number of OSA encounters was 16. As a result of the glide test, head crush did not occur even when the glide was 3 nm, and the evaluation was 4. Evaluation S was obtained as a result of the missing test.

(Example 3-2)
Example 3-2 differs from Example 3-1 above in that the glass material prepared in the glass material preparation step (S10) is glass material C (see FIG. 11). The glass material prepared in the glass material preparation step (S10) of Example 3-1 is the glass material B (see FIG. 11).

As shown in FIG. 11, the components constituting the glass material C are Li ₂ O 10.5 mass%, Na ₂ O 3.0 mass%, K ₂ O 1.5 mass%, and CaO 7 0.5% by mass, BaO 2.5% by mass, Al ₂ O ₃ 11.0% by mass, SiO ₂ 57.0% by mass, ZrO ₂ 4.0% by mass, and Nb ₂ O ₅ 3 0.0% by mass.

As shown in FIG. 13, when the degree of “sag” at the edge of the glass substrate was measured on the glass substrate based on Example 3-2 in the same manner as in Example 3-1 described above, it was 18.1 nm. there were. The number of OSA encounters was 15. As a result of the glide test, head crush did not occur even when the glide was 4 nm, and the evaluation was 3. Evaluation S was obtained as a result of the missing test.

(Contrast of Example 3-1 and Example 3-2)
Comparing Example 3-1 and Example 3-2, when the glass material has a SiO ₂ content of less than 58% by mass (in the case of Example 3-2), the glass material is 58% by mass or more 68. It can be seen that the shape of the edge of the glass substrate tends to deteriorate compared to the case where the content of SiO ₂ is less than or equal to mass% (in the case of Example 3-1). Incidentally, if the content of SiO ₂ is a glass substrate below 58 wt%, it was sometimes processing does not work.

Example 4-1
In Example 4-1, the glass material prepared in the glass material preparation step (S10) is prepared by the direct press method, and used as free abrasive grains (slurry) in the first rough polishing step (S15). The average particle size of cerium oxide (ceria) used as free abrasive grains (slurry) in the second rough polishing step (S16) is that the average particle size of zirconium oxide (zirconia) is 1.0 μm It differs from Example 1 described above in that it is 0.8 μm. The glass material prepared in the glass material preparation step (S10) of Example 1 described above is prepared by the float method.

As shown in FIG. 13, with respect to the glass substrate based on Example 4-1, the degree of “sag” at the edge of the glass substrate was measured in the same manner as in Example 1 above, and it was 9.4 nm. . The number of OSA encounters was 35. As a result of the glide test, head crush did not occur even when the glide was 2 nm, and the evaluation was 5. Evaluation B was obtained as a result of the missing test.

(Contrast of Example 1 and Example 4-1)
In contrast to Example 1 and Example 4-1, when the glass material is prepared by using the float method, compared to when the glass material is prepared by using the direct press method, It turns out that generation | occurrence | production of the damage | wound on the main surface of the glass substrate finally obtained can be suppressed.

Example 5-1
In Example 5-1, the average particle diameter of zirconium oxide (zirconia) used as free abrasive grains (slurry) in the first rough polishing step (S15) is 0.7 μm, and the second rough polishing step The difference from Example 1 described above is that the average particle diameter of cerium oxide (ceria) used as free abrasive grains (slurry) in (S16) is 0.8 μm. The average particle diameter of zirconium oxide (zirconia) used as free abrasive grains (slurry) in the first rough polishing step (S15) of Example 1 is 0.6 μm, and the second rough polishing step (S16). The average particle diameter of cerium oxide (ceria) used as free abrasive grains (slurry) is 1.0 μm.

As shown in FIG. 13, the degree of “sag” at the edge of the glass substrate was measured for the glass substrate based on Example 5-1 in the same manner as in Example 1 described above, and was 10.15 nm. . The number of OSA encounters was 28. As a result of the glide test, head crush did not occur even when the glide was 2 nm, and the evaluation was 5. Evaluation B was obtained as a result of the missing test.

(Example 5-2)
In Example 5-2, the average particle diameter of zirconium oxide (zirconia) used as the loose abrasive grains (slurry) in the first rough polishing step (S15) is 1.4 μm. Different from -1. The average particle diameter of zirconium oxide (zirconia) used as loose abrasive grains (slurry) in the first rough polishing step (S15) of Example 5-1 is 0.7 μm.

As shown in FIG. 13, when the degree of “sag” at the edge of the glass substrate was measured on the glass substrate based on Example 5-2 in the same manner as in Example 5-1 described above, it was 9.1 nm. there were. The number of OSA encounters was 27. As a result of the glide test, head crush did not occur even when the glide was 2 nm, and the evaluation was 5. Evaluation B was obtained as a result of the missing test.

(Example 5-3)
In Example 5-3, the average particle diameter of zirconium oxide (zirconia) used as the free abrasive grains (slurry) in the first rough polishing step (S15) is 0.6 μm. Different from -1. The average particle diameter of zirconium oxide (zirconia) used as loose abrasive grains (slurry) in the first rough polishing step (S15) of Example 5-1 is 0.7 μm.

As shown in FIG. 13, with respect to the glass substrate based on Example 5-3, the degree of “sag” at the edge of the glass substrate was measured in the same manner as in Example 5-1 above. there were. The number of OSA encounters was 34. As a result of the glide test, head crush did not occur even when the glide was 2 nm, and the evaluation was 5. Evaluation B was obtained as a result of the missing test.

(Example 5-4)
In Example 5-4, the average particle diameter of zirconium oxide (zirconia) used as the free abrasive grains (slurry) in the first rough polishing step (S15) is 1.5 μm. Different from -1. The average particle diameter of zirconium oxide (zirconia) used as loose abrasive grains (slurry) in the first rough polishing step (S15) of Example 5-1 is 0.7 μm.

As shown in FIG. 13, when the degree of “sag” at the edge of the glass substrate was measured on the glass substrate based on Example 5-4 in the same manner as in Example 5-1 described above, it was 8.7 nm. there were. The number of OSA encounters was 42. As a result of the glide test, head crush did not occur even when the glide was 2 nm, and the evaluation was 5. Evaluation B was obtained as a result of the missing test.

(Contrast of Example 5-1 to Example 5-4)
Comparing Example 5-1 to Example 5-4, the abrasive grain size of zirconium oxide used as the loose abrasive grains (first loose abrasive grains) in the first rough polishing step is 0.7 μm or more and 1.4 μm or less. In some cases (in the case of Example 5-1 and Example 5-2), the abrasive grain size is smaller than 0.7 μm or larger than 1.4 μm (Example 5-3 and Example 5). 4), it can be seen that it is possible to suppress the occurrence of scratches on the main surface of the finally obtained glass substrate.

Example 6-1
In Example 6-1, the average particle diameter of zirconium oxide (zirconia) used as free abrasive grains (slurry) in the first rough polishing step (S15) is 0.7 μm. Is different. In Example 6-1, when the average particle diameters of zirconium oxide and cerium oxide are compared, when zirconium oxide is 1, cerium oxide is about 1.42.

The average particle diameter of zirconium oxide (zirconia) used as free abrasive grains (slurry) in the first rough polishing step (S15) of Example 1 described above is 0.6 μm, and the second rough polishing step (S16). The average particle size of cerium oxide (ceria) used as free abrasive grains (slurry) is 1.0 μm.

As shown in FIG. 13, with respect to the glass substrate based on Example 6-1, the degree of “sag” at the edge of the glass substrate was measured in the same manner as in Example 1 above, and was 9.45 nm. . The number of OSA encounters was 18. As a result of the glide test, head crush did not occur even when the glide was 2 nm, and the evaluation was 5. Evaluation S was obtained as a result of the missing test.

(Example 6-2)
In Example 6-2, the average particle diameter of zirconium oxide (zirconia) used as free abrasive grains (slurry) in the first rough polishing step (S15) is 1.1 μm, and the second rough polishing step ( The difference from Example 6-1 described above is that the average particle diameter of cerium oxide (ceria) used as loose abrasive grains (slurry) in S16) is 0.8 μm.

In Example 6-2, when the average particle diameters of zirconium oxide and cerium oxide are compared, when zirconium oxide is 1, the cerium oxide is about 0.73. In Example 6-1, when the average particle diameters of zirconium oxide and cerium oxide are compared, when zirconium oxide is 1, cerium oxide is about 1.42.

As shown in FIG. 13, when the degree of “sag” at the edge of the glass substrate was measured on the glass substrate based on Example 6-2 in the same manner as in Example 1 described above, it was 17.5 nm. . The number of OSA encounters was 16. As a result of the glide test, head crush did not occur even when the glide was 4 nm, and the evaluation was 3. Evaluation S was obtained as a result of the missing test.

(Example 6-3)
In Example 6-3, the average particle diameter of zirconium oxide (zirconia) used as loose abrasive grains (slurry) in the first rough polishing step (S15) is 0.7 μm, and the second rough polishing step ( The difference from Example 6-2 described above is that the average particle diameter of cerium oxide (ceria) used as loose abrasive grains (slurry) in S16) is 1.2 μm.

In Example 6-3, when the average particle diameters of zirconium oxide and cerium oxide are compared, when zirconium oxide is 1, the cerium oxide is about 1.71. In Example 6-2, when the average particle diameters of zirconium oxide and cerium oxide are compared, when zirconium oxide is 1, the cerium oxide is about 0.73.

As shown in FIG. 13, when the degree of “sag” at the edge of the glass substrate was measured on the glass substrate based on Example 6-3 in the same manner as in Example 1 above, it was 24.4 nm. . The number of OSA encounters was 18. As a result of the glide test, head crush did not occur even when the glide was 3 nm, and the evaluation was 4. Evaluation S was obtained as a result of the missing test.

(Contrast of Example 6-1 to Example 6-3)
Comparing Example 6-1 to Example 6-3, if the average abrasive grain size of zirconium oxide used as loose abrasive grains (first loose abrasive grains) in the first coarse polishing step is 1, the second coarse polish When the average abrasive grain size of cerium oxide used as free abrasive grains (second free abrasive grains) in the process is 0.7 or more and 1.3 or less (in the case of Example 6-2), cerium oxide Compared with the case where the average abrasive grain size is smaller than 0.7 or larger than 1.3 (in the case of Example 6-1 and Example 6-3), on the main surface of the finally obtained glass substrate It can be seen that it is possible to suppress the occurrence of flaws in.

Example 7-1
In Example 7-1, the polishing rate with zirconium oxide (zirconia) used as loose abrasive grains (slurry) in the first rough polishing step (S15) is 0.4 μm / min, and the first rough polishing step (S15). The average particle diameter of zirconium oxide (zirconia) used as loose abrasive grains (slurry) in the polishing step (S15) is 1.0 μm, and loose abrasive grains (slurry) in the second coarse polishing step (S16). Example 1 is different from Example 1 described above in that the average particle diameter of cerium oxide (ceria) used as the above is 0.8 μm. The polishing rate with zirconium oxide (zirconia) used as loose abrasive grains (slurry) in the first rough polishing step (S15) of Example 1 described above is 0.8 μm / min.

In Example 7-1, when the polishing processing rates of zirconium oxide and cerium oxide were compared, when the polishing processing rate by cerium oxide (1.0 μm / min) was 1, the polishing processing rate by zirconium oxide was 0. .4. In Example 1, when the polishing processing rates of zirconium oxide and cerium oxide are compared, when the polishing processing rate by cerium oxide (1.0 μm / min) is 1, the polishing processing rate by zirconium oxide is 0.8. It is.

As shown in FIG. 13, with respect to the glass substrate based on Example 7-1, the degree of “sag” at the edge of the glass substrate was measured in the same manner as in Example 1 above, and it was 8.7 nm. . The number of OSA encounters was 32. As a result of the glide test, head crush did not occur even when the glide was 2 nm, and the evaluation was 5. Evaluation B was obtained as a result of the missing test.

(Example 7-2)
In Example 7-2, the above-described implementation was performed in that the polishing rate with zirconium oxide (zirconia) used as loose abrasive grains (slurry) in the first rough polishing step (S15) was 0.5 μm / min. Different from Example 7-1. The polishing rate with zirconium oxide (zirconia) used as loose abrasive grains (slurry) in the first rough polishing step (S15) of Example 7-1 is 0.4 μm / min.

In Example 7-2, when the polishing processing rates of zirconium oxide and cerium oxide were compared, when the polishing processing rate by cerium oxide (1.0 μm / min) was 1, the polishing processing rate by zirconium oxide was 0. .5.

As shown in FIG. 13, with respect to the glass substrate based on Example 7-2, the degree of “sag” at the edge of the glass substrate was measured in the same manner as in Example 7-1. there were. The number of OSA encounters was 28. As a result of the glide test, head crush did not occur even when the glide was 2 nm, and the evaluation was 5. Evaluation B was obtained as a result of the missing test.

(Example 7-3)
In Example 7-3, the above-described implementation was performed in that the polishing rate with zirconium oxide (zirconia) used as loose abrasive grains (slurry) in the first rough polishing step (S15) was 0.7 μm / min. Different from Example 7-1. The polishing rate with zirconium oxide (zirconia) used as loose abrasive grains (slurry) in the first rough polishing step (S15) of Example 7-1 is 0.4 μm / min.

In Example 7-3, when the polishing processing rates of zirconium oxide and cerium oxide were compared, when the polishing processing rate by cerium oxide (1.0 μm / min) was 1, the polishing processing rate by zirconium oxide was 0. .7.

As shown in FIG. 13, when the degree of “sag” at the edge of the glass substrate was measured on the glass substrate based on Example 7-3 in the same manner as in Example 1 described above, it was 9.1 nm. . The number of OSA encounters was 21. As a result of the glide test, head crush did not occur even when the glide was 2 nm, and the evaluation was 5. Evaluation A was obtained as a result of the missing test.

(Contrast of Example 7-1 to Example 7-3)
Comparing Example 7-1 to Example 7-3, assuming that the polishing rate of cerium oxide used as the loose abrasive grains (second loose abrasive grains) in the second coarse polishing step is 1, the first coarse polishing step In the case where the polishing rate of zirconium oxide used as free abrasive grains (first free abrasive grains) is 0.5 or more and 0.7 or less (in the case of Example 7-2 and Example 7-3) As compared with the case where the polishing rate of zirconium oxide is less than 0.5 (in the case of Example 7-1), it is possible to suppress the occurrence of scratches on the main surface of the finally obtained glass substrate. I know that there is.

Example 8-1
In Example 8-1, the allowance for the main surface of the glass substrate by zirconium oxide (zirconia) used as loose abrasive grains (slurry) in the first rough polishing step (S15) is 14 μm, and the first The average particle diameter of zirconium oxide (zirconia) used as loose abrasive grains (slurry) in the coarse polishing step (S15) is 1.0 μm, and loose abrasive grains (slurry in the second coarse polishing step (S16)). ) Is different from the above-mentioned Example 1 in that the average particle diameter of cerium oxide (ceria) used as) is 0.8 μm. The allowance for the main surface of the glass substrate by zirconium oxide (zirconia) used as loose abrasive grains (slurry) in the first rough polishing step (S15) of Example 1 is 20 μm.

In Example 8-1, when the machining allowance between zirconium oxide and cerium oxide is compared, when the machining allowance with cerium oxide (20 μm) is 1, the machining allowance with zirconium oxide is 0.7.

As shown in FIG. 13, with respect to the glass substrate based on Example 8-1, the degree of “sag” at the edge of the glass substrate was measured in the same manner as in Example 1 above, and it was 25.7 nm. . The number of OSA encounters was 18. As a result of the glide test, head crush did not occur even when the glide was 6 nm, and the evaluation was 2. Evaluation S was obtained as a result of the missing test.

(Example 8-2)
In Example 8-2, the allowance for the main surface of the glass substrate by zirconium oxide (zirconia) used as loose abrasive grains (slurry) in the first rough polishing step (S15) is 16 μm. Different from Example 8-1. The allowance for the main surface of the glass substrate by zirconium oxide (zirconia) used as loose abrasive grains (slurry) in the first rough polishing step (S15) of Example 8-1 is 14 μm.

In Example 8-2, when the machining allowance between zirconium oxide and cerium oxide is compared, when the machining allowance with cerium oxide (20 μm) is 1, the machining allowance with zirconium oxide is 0.8.

As shown in FIG. 13, with respect to the glass substrate based on Example 8-2, the degree of “sag” at the edge of the glass substrate was measured in the same manner as in Example 8-1 described above. there were. The number of OSA encounters was 17. As a result of the glide test, head crush did not occur even when the glide was 4 nm, and the evaluation was 3. Evaluation S was obtained as a result of the missing test.

(Example 8-3)
In Example 8-3, the allowance for the main surface of the glass substrate by zirconium oxide (zirconia) used as loose abrasive grains (slurry) in the first rough polishing step (S15) is 18 μm, and the second rough polishing step (S15) It differs from the above-described Example 8-1 in that the allowance for the main surface of the glass substrate by cerium oxide (ceria) used as loose abrasive grains (slurry) in the polishing step (S16) is 15 μm.

The allowance for the main surface of the glass substrate by zirconium oxide (zirconia) used as loose abrasive grains (slurry) in the first rough polishing step (S15) of Example 8-1 is 14 μm, and the second The machining allowance for the main surface of the glass substrate by cerium oxide (ceria) used as loose abrasive grains (slurry) in the rough polishing step (S16) is 20 μm.

In Example 8-3, when the machining allowance between zirconium oxide and cerium oxide is compared, when the machining allowance with cerium oxide (15 μm) is 1, the machining allowance with zirconium oxide is 1.2.

As shown in FIG. 13, with respect to the glass substrate based on Example 8-3, the degree of “sag” at the edge of the glass substrate was measured in the same manner as in Example 8-1 described above. there were. The number of OSA encounters was 24. As a result of the glide test, head crush did not occur even when the glide was 2 nm, and the evaluation was 5. Evaluation A was obtained as a result of the missing test.

(Example 8-4)
In Example 8-4, the allowance for the main surface of the glass substrate by zirconium oxide (zirconia) used as loose abrasive grains (slurry) in the first rough polishing step (S15) is 20 μm, and the second rough polishing step (S15). It differs from the above-described Example 8-1 in that the allowance for the main surface of the glass substrate by cerium oxide (ceria) used as loose abrasive grains (slurry) in the polishing step (S16) is 15 μm.

In Example 8-4, when the machining allowance between zirconium oxide and cerium oxide is compared, when the machining allowance with cerium oxide (15 μm) is 1, the machining allowance with zirconium oxide is about 1.33.

As shown in FIG. 13, when the glass substrate based on Example 8-4 was measured for the degree of “sag” at the edge of the glass substrate in the same manner as in Example 8-1 described above, it was 8.7 nm. there were. The number of OSA encounters was 38. As a result of the glide test, head crush did not occur even when the glide was 2 nm, and the evaluation was 5. Evaluation B was obtained as a result of the missing test.

(Contrast of Example 8-1 to Example 8-4)
Comparing Example 8-1 to Example 8-4, if the removal allowance by cerium oxide used as the free abrasive grains (second free abrasive grains) in the second rough polishing step is 1, then in the first rough polishing step When the removal allowance by zirconium oxide used as the loose abrasive grains (first loose abrasive grains) is 0.8 or more and 1.2 or less (in the case of Example 8-2 and Example 8-3), the oxidation Compared to the case where the machining allowance by zirconium is smaller than 0.8 or larger than 1.2 (in the case of Example 8-1 and Example 8-4), the vicinity of the end of the glass substrate finally obtained It can be seen that the change in shape can be suppressed and the occurrence of scratches on the main surface of the glass substrate can be suppressed.

Example 9-1
In Example 9-1, the allowance for the main surface of the glass substrate by colloidal silica used as loose abrasive grains (slurry) in the precision polishing step (S17) is 3.0 μm. Different from -4. The allowance for the main surface of the glass substrate by colloidal silica used as loose abrasive grains (slurry) in the precision polishing step (S17) of Example 8-4 is 1.5 μm.

In Example 9-1, when the machining allowance between cerium oxide and colloidal silica is compared, when the machining allowance with cerium oxide (15 μm) is 1, the machining allowance with zirconium oxide is 0.2. In Example 8-4, when the removal allowance between cerium oxide and colloidal silica is compared, when the allowance with cerium oxide (15 μm) is 1, the allowance with zirconium oxide (1.5 μm) is 0.1 It is.

As shown in FIG. 13, with respect to the glass substrate based on Example 9-1, the degree of “sag” at the edge of the glass substrate was measured in the same manner as in Example 8-4 described above. there were. The number of OSA encounters was 18. As a result of the glide test, head crush did not occur even when the glide was 4 nm, and the evaluation was 3. Evaluation S was obtained as a result of the missing test.

(Contrast of Example 8-4 and Example 9-1)
Comparing Example 8-4 and Example 9-1, if the removal allowance by cerium oxide used as loose abrasive grains (second loose abrasive grains) in the second rough polishing step is 1, loose abrasives in the precision polishing step When the allowance by colloidal silica used as grains (third free abrasive grains) is 0.1 or less (in the case of Example 8-4), the allowance by colloidal silica is larger than 0.1 It can be seen that it is possible to suppress the occurrence of scratches on the main surface of the finally obtained glass substrate as compared with the case of Example 9-1.

(Example 10-1)
In Example 10-1, the ζ potential of zirconium oxide (zirconia) used as loose abrasive grains (slurry) in the first rough polishing step (S15) is −40 mV, so that Example 9-1 described above is used. Is different.

As shown in FIG. 13, when the degree of “sag” at the edge of the glass substrate was measured on the glass substrate based on Example 10-1 in the same manner as in Example 9-1 above, it was 8.7 nm. there were. The number of OSA encounters was 18. As a result of the glide test, head crush did not occur even when the glide was 2 nm, and the evaluation was 5. Evaluation S was obtained as a result of the missing test.

(Example 10-2)
Example 10-2 is the same as Example 10-1 described above in that the ζ potential of zirconium oxide (zirconia) used as free abrasive grains (slurry) in the first rough polishing step (S15) is −45 mV. Is different.

As shown in FIG. 13, when the degree of “sag” at the edge of the glass substrate was measured on the glass substrate based on Example 10-2 in the same manner as in Example 10-1 above, it was 13.25 nm. there were. The number of OSA encounters was 19. As a result of the glide test, head crush did not occur even when the glide was 3 nm, and the evaluation was 4. Evaluation S was obtained as a result of the missing test.

(Example 10-3)
In Example 10-3, the ζ potential of zirconium oxide (zirconia) used as free abrasive grains (slurry) in the first rough polishing step (S15) is −55 mV, and the above Example 10-1 Is different.

As shown in FIG. 13, with respect to the glass substrate based on Example 10-3, the degree of “sag” at the edge of the glass substrate was measured in the same manner as in Example 10-1 above, and it was 18 nm. . The number of OSA encounters was 18. As a result of the glide test, head crush did not occur even when the glide was 4 nm, and the evaluation was 3. Evaluation S was obtained as a result of the missing test.

(Example 10-4)
In Example 10-4, the ζ potential of zirconium oxide (zirconia) used as free abrasive grains (slurry) in the first rough polishing step (S15) is −35 mV, and the above Example 10-1 Is different.

As shown in FIG. 13, with respect to the glass substrate based on Example 10-4, the degree of “sag” at the edge of the glass substrate was measured in the same manner as in Example 10-1 above. there were. The number of OSA encounters was 27. As a result of the glide test, head crush did not occur even when the glide was 2 nm, and the evaluation was 5. Evaluation B was obtained as a result of the missing test.

(Example 10-5)
In Example 10-5, the ζ potential of zirconium oxide (zirconia) used as free abrasive grains (slurry) in the first rough polishing step (S15) is −25 mV, so that Example 10-1 described above is used. Is different.

As shown in FIG. 13, when the degree of “sag” at the edge of the glass substrate was measured on the glass substrate based on Example 10-5 in the same manner as in Example 10-1 described above, it was 9.1 nm. there were. The number of OSA encounters was 26. As a result of the glide test, head crush did not occur even when the glide was 2 nm, and the evaluation was 5. Evaluation A was obtained as a result of the missing test.

(Contrast of Example 10-1 to Example 10-5)
Comparing Example 10-1 to Example 10-4, when the ζ potential of zirconium oxide used as the first free abrasive grains in the first rough polishing step is −50 mV to −30 mV (Example 10-1) In the case of Example 10-2 and Example 10-4), the ζ potential of zirconium oxide is smaller than −50 mV or larger than −30 mV (Example 10-3 and Example 10-). 5), the main surface of the finally obtained glass substrate is less likely to be scratched and the shape of the main surface of the glass substrate can be prevented from deteriorating. .

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.

1 glass substrate (glass substrate for information recording medium), 2, 3 main surface, 4 inner peripheral end surface, 5 holes, 6 outer peripheral end surface, 7, 8 chamfer, 10 information recording medium, 12 chemical strengthening 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, S10 glass material preparation process, S11 cut out Step, S12 Internal / external processing step, S13 Etching step, S14 Internal / external polishing step, S15 First rough polishing step, S16A Rough polishing step, S16 Second rough polishing step, S17 Precision polishing step, S18 Chemical strengthening step, S100, S101, S201 Manufacturing method of glass substrate for information recording medium, S200 Magnetic recording layer forming step.

Claims

A method of manufacturing a glass substrate (1) for an information recording medium incorporated as a part of an information recording medium (10) in an information recording device (30),
A preparation step (S10) for preparing a glass material having a main surface (2, 3) and containing SiO 2 as a component;
A first rough polishing machine that mechanically polishes the main surface of the glass material using the first polishing pad while supplying first loose abrasive grains between the main surface of the glass material and the first polishing pad. Polishing step (S15);
The second polishing pad while supplying second free abrasive grains different from the first free abrasive grains between the main surface of the glass material polished in the first rough polishing step and the second polishing pad. A second rough polishing step (S16) for chemically and mechanically polishing the main surface of the glass material using
While supplying third loose abrasive grains between the main surface of the glass material polished in the second rough polishing step and a third polishing pad, the main material of the glass material is used with the third polishing pad. A precision polishing step (S17) for polishing the surface,
The first polishing pad used in the first rough polishing step (S15) is composed of a soft foam resin pad,
The soft foamed resin pad has a hardness of 73 degrees to 85 degrees in Asker C hardness.
A method for producing a glass substrate for an information recording medium.
The first loose abrasive used in the first rough polishing step (S15) includes zirconium oxide,
The second loose abrasive used in the second rough polishing step (S16) includes cerium oxide,
The third loose abrasive used in the precision polishing step (S17) includes colloidal silica.
The manufacturing method of the glass substrate for information recording media of Claim 1.
The glass material prepared in the preparation step (S10) includes 58% by mass or more and 68% by mass or less of SiO 2 as a component.
The manufacturing method of the glass substrate for information recording media of Claim 1 or 2.
The glass material prepared in the preparation step (S10) is prepared by cutting out from a sheet glass produced using a float method,
The manufacturing method of the glass substrate for information recording media in any one of Claim 1 to 3.
The abrasive grain size of zirconium oxide used as the first loose abrasive grains in the first rough polishing step (S15) is 0.7 μm or more and 1.4 μm or less.
The manufacturing method of the glass substrate for information recording media of Claim 2.
The average abrasive grain size of zirconium oxide used as the first loose abrasive grains in the first coarse polishing step (S15) and the cerium oxide used as the second loose abrasive grains in the second coarse polishing step (S16) The ratio to the average abrasive grain size is
When the average abrasive grain size of zirconium oxide used as the first free abrasive grains is 1, the average abrasive grain size of cerium oxide used as the second free abrasive grains is 0.7 or more and 1.0 or less.
The manufacturing method of the glass substrate for information recording media of Claim 2.
Polishing rate by zirconium oxide used as the first free abrasive grains in the first rough polishing step (S15) and polishing by cerium oxide used as the second free abrasive grains in the second rough polishing step (S16) The ratio to the processing rate is
When the polishing processing rate with cerium oxide used as the second free abrasive is 1, the polishing rate with zirconium oxide used as the first free abrasive is 0.4 or more and 0.8 or less.
The manufacturing method of the glass substrate for information recording media of Claim 2.
The allowance for the glass material by zirconium oxide used as the first loose abrasive in the first rough polishing step (S15), and the oxidation used as the second loose abrasive in the second rough polishing step (S16) The ratio of cerium to the stock allowance for the glass material is
If the removal allowance by cerium oxide used as the second free abrasive grains is 1, the allowance due to zirconium oxide used as the first free abrasive grains is 0.8 or more and 1.2 or less,
The manufacturing method of the glass substrate for information recording media of Claim 2.
Zirconium oxide used as the first loose abrasive in the first rough polishing step (S15) has a ζ potential of −50 mV to −30 mV.
The manufacturing method of the glass substrate for information recording media of Claim 2.