CN102881295A - Glass substrate used in magnetic recording media and method for manufacturing the same - Google Patents

Abstract

[Problem] Obtain a glass substrate for magnetic recording media with high yield and excellent smoothness of the main plane while preventing defects such as scratches generated before the main plane polishing step. [Solution] A glass plain plate for magnetic recording media, which is a glass plain plate for forming a disc-shaped glass substrate for magnetic recording media having a circular hole in the center, and has resin-containing glass on at least one main plane. protective film. A method for manufacturing a glass substrate for a magnetic recording medium, the method comprising: a step of preparing a glass plain plate for a magnetic recording medium; a step of forming the glass plain plate into a disk-shaped glass substrate having a hole in the center; and grinding The main plane grinding process of the main plane of the glass substrate; and the cleaning process of the glass substrate, the preparation process of the glass plain plate for magnetic recording media includes: forming a protective film containing resin on at least one main plane of the glass plate. film, and a protective film forming process to make a glass plate for magnetic recording media.

Description

Glass plain plate for magnetic recording medium and method for producing glass substrate for magnetic recording medium

technical field

The present invention relates to a glass substrate for magnetic recording media and a method for producing a glass substrate for magnetic recording media using the same.

Background technique

In recent years, magnetic recording media, particularly magnetic disk memories, have rapidly increased recording density. Disk storage achieves random access by exposing the magnetic head slightly to the high-speed rotating recording medium (disk) for scanning. In order to achieve both high recording density and high-speed access, it is desirable to reduce the distance between the magnetic disk and the magnetic head (the exposure of the magnetic head) and Increase the rotation speed of the disk. At present, the mainstream disk substrate is a substrate plated with nickel phosphorus (Ni-P) on aluminum (Al). However, the development trend is to use a glass substrate. The glass substrate is harder than the aluminum alloy substrate, and the impact resistance of the magnetic head to the substrate surface Excellent, excellent flatness and smoothness.

When reducing the lift-off amount of the magnetic head, if the main plane of the magnetic head is not a smooth surface, there is a possibility that the magnetic head may be hindered from contacting the main plane. In addition, when the surface roughness of the main plane of the magnetic disk is large and the distance from the magnetic head varies, there is a problem that the reliability of reading and writing decreases. Furthermore, if there are defects such as scratches on the main plane, there is a possibility that the reading and writing volume may decrease. Therefore, a glass substrate for a magnetic recording medium without defects such as scratches on the main plane is required.

Generally, glass substrates for magnetic recording media are manufactured through the following steps: a step of cutting a glass plain plate into a shape that is easy to process; a disc shape processing step of processing it into a disc shape with a hole in the center; grinding The process of chamfering the inner peripheral end and the outer peripheral end of the disc-shaped substrate; the process of grinding the inner peripheral end and/or the outer peripheral end after grinding the chamfer; grinding the main plane of the glass substrate after grinding the end surface The main plane grinding process; and the cleaning process for cleaning the glass substrate and improving the cleanliness, etc. If necessary, a step of cleaning the glass substrate and a step of etching the glass substrate may be provided between the above steps.

In the manufacture of such glass substrates for magnetic recording media, in the processing process before the main plane grinding process, the main planes of the plurality of glass substrates are overlapped or directly held. Inclusion of glass shards or foreign matter. Therefore, there is a problem that defects such as scratches are likely to occur on the main plane of the glass substrate.

Generally, defects such as scratches generated on the main plane of the glass substrate can be removed by grinding the main plane in the main plane grinding process. The surface grinding process cannot be completely removed, and there is a concern that defects such as scratches may remain in the product, reducing the yield of the product. In addition, in order to remove defects such as deep scratches caused by inclusions of foreign matter, it is necessary to increase the amount of grinding in the main plane grinding process. of plate thickness. Therefore, there is a problem that the loss of material is large, and operations such as a polishing process take time.

For a long time, in order to prevent defects such as scratches in the manufacturing, conveying, conveying, and processing steps of plate glass, it has been proposed to treat the glass plate with sulfurous acid gas, etc., and form a coating film composed of inorganic salts such as sulfate on the surface (such as , refer to Patent Document 1). However, even if the method described in Patent Document 1 is intended to prevent defects such as the above-mentioned scratches in the manufacturing process of the glass substrate for magnetic recording media, since the thick film of the film is very thin, it cannot sufficiently prevent foreign matter caused by the main plane of the glass substrate. Defects such as scratches caused by inclusions, etc.

prior art literature

patent documents

Patent Document 1: International Publication No. WO2002/051767

Contents of the invention

The technical problem to be solved by the invention

The present invention was conceived to solve the above-mentioned problems, and its object is to provide a main plane capable of preventing defects such as scratches generated before the grinding process of the main plane, especially preventing defects such as scratches caused by inclusion of foreign matter, etc., with good yield. A method for producing a glass substrate for a magnetic recording medium, a glass substrate for a magnetic recording medium having excellent smoothness, and a glass substrate for a magnetic recording medium.

Technical solutions adopted to solve technical problems

The glass plain plate for magnetic recording media of the present invention is a glass plain plate having a main plane and side surfaces for forming a disk-shaped glass substrate for magnetic recording media having a circular hole in the center, and is characterized in that at least On one main plane, there is a protective film containing resin.

In the glass plain plate for magnetic recording media of the present invention, it is preferable that the protective film has a circular planar shape having a circular hole in the center. In addition, the protective film preferably has a film thickness of 0.01 mm to 0.5 mm.

The manufacturing method of the glass substrate for magnetic recording media of the present invention comprises: preparing a glass frit plate for magnetic recording medium having a main plane and a side surface of a frit sheet for magnetic recording medium; A step of shaping the glass substrate into a disk-shaped glass substrate with a hole in the center; a main plane grinding step of grinding the main plane of the glass substrate; and a cleaning step of the glass substrate, wherein the magnetic recording medium The step of preparing a glass plain plate includes a protective film forming step of forming a protective film containing a resin on at least one main plane of the glass plain plate to obtain a glass plain plate for magnetic recording media.

In the method for producing a glass substrate for magnetic recording media according to the present invention, the protective film forming step includes: printing or applying a composition containing a liquid curable resin on at least one main plane of the vitrified glass plate; and A step of curing the printed layer or coated layer. In addition, the protective film forming step may include a step of bonding a protective film containing a resin to at least one main plane of the vitrified glass plate. The protective film formed in the protective film forming step preferably has a circular planar shape with a circular hole in the center. In addition, the protective film formed in the protective film forming step preferably has a film thickness of 0.01 mm to 0.5 mm. Furthermore, it is preferable to include a protective film removal step for removing the protective film between the shaping step and the main surface polishing step.

In this specification, the glass plate before formation of a protective film is described as a "vitreous plain plate". In addition, the structure in which the protective film is formed on the main plane of the "vitreous plain plate" is described as "vitreous plain plate for magnetic recording media", and "vitreous plain plate" and "vitreous plain plate for magnetic recording medium" are described separately. .

The effect of the invention

According to the manufacturing method of the vitrified glass plate for magnetic recording media and the glass substrate for magnetic recording media of the present invention, it is possible to obtain defects such as preventing defects such as scratches generated before the grinding process of the main plane, excellent smoothness of the main plane, and no defects in the main plane with good yield. A glass substrate for a magnetic recording medium with concave defects. In addition, it is possible to reduce the thickness of the vitrified glass plate for magnetic recording media and the vitrified glass plate supplied to manufacture the glass substrate for magnetic recording media, reduce the amount of grinding, reduce material loss and improve productivity.

Description of drawings

[ Fig. 1 ] A cross-sectional perspective view of a glass substrate for magnetic recording media produced by the present invention.

[ Fig. 2] Fig. 2 is a plan view showing an embodiment of the glass plate for magnetic recording media of the present invention.

[ Fig. 3] Fig. 3 is a diagram showing an example of a method of printing a resin material for forming a protective film in an embodiment of the present invention.

[ Fig. 4] Fig. 4 is a diagram showing an example of a curing method of a resin composition formed by printing or the like in an embodiment of the present invention.

[ Fig. 5 ] is a flow chart showing a method of manufacturing a glass substrate for a magnetic recording medium according to Examples 1 to 3 of the present invention.

[ Fig. 6] Fig. 6 is a flow chart showing a method for manufacturing a glass substrate for a magnetic recording medium according to Examples 4 to 6 of the present invention.

[ Fig. 7] Fig. 7 is a flowchart showing a method of manufacturing a glass substrate for a magnetic recording medium according to Examples 7 to 9 of the present invention.

[ Fig. 8 ] A flow chart showing a method for manufacturing a glass substrate for a magnetic recording medium according to Example 10 of the present invention and Comparative Example 11.

Detailed ways

Hereinafter, modes for implementing the present invention will be described, but the present invention is not limited to the embodiments described below.

<Glass plain plate for magnetic recording media>

The glass plain plate for magnetic recording media of this invention is a glass plain plate for manufacturing the disk-shaped glass substrate for magnetic recording media which has a circular hole in the center part.

First, an example of the glass substrate for magnetic recording media manufactured using the glass frit plate for magnetic recording media of this invention is shown in FIG. 1. The glass substrate 10 for magnetic recording media shown in FIG. 1 has a disc shape with a circular through hole, namely a circular hole 11, at the central portion, and has an inner peripheral side 101 and an outer peripheral side 102 formed by the inner wall surface of the circular hole 11, and the upper and lower sides. A disc shape formed by a pair of main planes 103 . Furthermore, the intersections of the inner peripheral side 101 and the upper and lower main planes 103 and the intersections of the outer peripheral side 102 and the upper and lower main planes 103 form chamfers 104 (inner peripheral chamfers and outer peripheral chamfers), respectively.

An example of the vitrified glass plate for magnetic recording media of the present invention is shown in FIG. 2 . The glass plain plate 20 for magnetic recording media shown in FIG. 2 has a pair of upper and lower main planes and side surfaces, and has a resin-containing protective film 22 on at least one of the main planes 21 . The resin constituting the protective film 22 may, for example, be a liquid curable resin that forms a cured film after coating, for example, a reaction curable resin such as a thermosetting resin or a photocurable resin. From the viewpoints of safety in curing work, working environment, ease of handling, etc., photocurable resins are preferred, and visible light curable resins are more preferred. In addition, a cured product is preferably a resin that has good adhesion (adhesion) to glass and is easy to peel, and a resin that can be peeled in water or warm water is more preferable than a type that peels in an organic solvent. In addition, the resin-containing protective film 22 can be formed by bonding a resin film.

The preferable resin material for forming the protective film 22 and the formation method of the protective film 22 are demonstrated under the manufacturing method of the glass substrate for magnetic recording media mentioned later.

The planar shape of the protective film 22 is, as shown in FIG. 2 , preferably a donut shape having a circular hole in the center. In addition, the outer diameter of the donut-shaped protective film 22 and the inner diameter of the circular hole are preferably the same as the outer diameter and inner diameter of the main plane of the glass substrate after the circular processing step described later. It is preferably the same as the above-mentioned dimension after chamfering. Furthermore, the outer diameter of the protective film 22 and the inner diameter of the circular hole are particularly preferable because the protective film does not need to be chipped off in the processing step before the main plane grinding, the processing workability is good, and the loss component of the protective film material is small. The size is the same as the above-mentioned size of the glass substrate for a magnetic recording medium as a final product.

The protective film 22 is not limited to the so-called β-standard film-shaped film that covers the flat area such as the donut shape without gaps, and may be a film that covers the flat area in a small-sized pattern such as a grid shape or a dot shape. . The donut-shaped protective film 22 formed in a grid-like or dot-like pattern is inferior to the β-standard film-shaped protective film in terms of the protection of the main plane, but it has the advantages of being easy to peel and can reduce resin and other protective films. The amount of material used has these advantages.

The film thickness of the protective film 22 is preferably 0.01 mm to 0.5 mm. When the film thickness of the protective film 22 is less than 0.01 mm, defects such as scratches on the main plane caused by glass shards or inclusion of foreign matter may not be sufficiently prevented. In addition, when the film thickness exceeds 0.5 mm, it may take time to remove the protective film 22 and it may take time to cure the resin material forming the protective film 22 . In addition, there is also a possibility that the yield may be lowered in other processing steps (for example, an end surface grinding step, etc.) performed between the formation of the protective film 22 and the grinding of the main plane. The film thickness of the protective film 22 is preferably 0.05 mm to 0.5 mm, more preferably 0.05 mm to 0.4 mm, particularly preferably 0.06 mm to 0.2 mm.

In this way, by using a glass substrate for magnetic recording media having a protective film containing resin on at least one main plane of the glass substrate, and manufacturing a glass substrate for magnetic recording media according to the following method, it is possible to obtain a good yield to prevent A glass substrate for magnetic recording media having a main plane excellent in smoothness due to defects such as scratches that occurred before the main plane polishing process. In addition, the thickness of the glass plate can be reduced, the amount of grinding can be reduced, the loss of glass materials, etc. can be reduced, and the productivity can be improved by shortening the grinding time.

<Manufacturing method of glass substrate for magnetic recording medium>

The manufacturing method of the glass substrate for magnetic recording media which concerns on embodiment of this invention has:

(1) Preparation process of glass plain plate for magnetic recording medium,

(2) Forming process,

(3) End face grinding process,

(4) Protective film removal process,

(5) Main plane grinding process, and

(6) Cleaning process. (1) The step of preparing a glass fibrous plate for a magnetic recording medium includes a protective film forming step (1a) of forming a protective film containing a resin on at least one main plane of the glass fibrous plate.

In the method for manufacturing a glass substrate for a magnetic recording medium according to the embodiment, cleaning of the glass substrate (cleaning between processes) and the surface of the glass substrate (partial or entire surfaces of the glass substrate (for example, main plane, inner periphery, etc.) may be performed between each process. end face and at least a part of the peripheral end face)) (inter-process etching). In addition, when the glass substrate for magnetic recording media is required to have high mechanical strength, it can be ground before the main plane grinding process or after the main plane grinding process, or between the main plane grinding process (between the first grinding and the second grinding or between the second grinding and the third grinding). Between grinding) a strengthening step (for example, a chemical strengthening step) is performed to form a strengthening layer on the surface layer of the glass substrate.

Each step will be described below.

(1) Preparation process of glass plain plate for magnetic recording medium

(1) The process of preparing a glass plain plate for magnetic recording media is a process of preparing a glass plain plate for magnetic recording media that has a main plane and side surfaces, and a protective film containing resin on at least one of the main planes. A protective film forming step (1a) of forming a protective film on the surface of a plain plate, and a cutting process (1b) of cutting the glass plain plate on which the protective film is formed on the surface into a predetermined size.

The glass constituting the vitreous plate may be amorphous glass or crystal glass, or tempered glass (for example, chemically strengthened glass) with a strengthening layer on the surface. In addition, the glass plain plate can be formed by float method or formed by melting method, down draw method, redraw method, rolling method or pressure forming method. .

(1a) Protective film formation process

In the protective film forming step, a protective film containing a resin is formed on at least one main plane of the glass plain plate. The protective film may be formed on one main plane of the plain glass plate, preferably on two main planes.

The resin constituting the protective film may, for example, be curable resins such as thermosetting resins and photocurable resins. Among these curable resins, examples of photocurable resins include visible light curable resins and ultraviolet curable resins. Specific examples of visible light-curable resins include acrylic resins and polythiol-modified acrylic resins, and examples of ultraviolet-curable resins include epoxy resins, acrylic resins, methacrylic resins, and polyimide resins. , silicone resin, epoxy acrylate resin, acrylate urethane resin, oxetane resin, vinyl ether resin, benzoxazine resin, etc. In addition, examples of thermosetting resins include epoxy resins, melamine resins, phenol resins, vinyl acetate resins, and the like.

When bonding a resin film on at least one main plane of a glass plain plate to form a resin-containing protective film, the resin film may, for example, be a polyethylene terephthalate film, a polysiloxane resin film, a polyvinyl chloride film, or a polyvinyl chloride film. Resin film, polyethylene film, polyolefin film, polyester film, fluororesin film, polycarbonate film, polypropylene film, polyphenylene sulfide film, para-aramid film, Polylactic acid film, polyimide film, nylon film, etc.

As described above, from the viewpoints of safety in curing work, working environment, ease of handling, etc., photocurable resins are preferred, and visible light curable resins are more preferred. In addition, a cured product is preferably a resin that has good adhesion (adhesion) to glass and is easy to peel, and a resin that can be peeled in water or warm water is more preferable than a type that peels in an organic solvent.

The curable resin is a resin that can be cured by heat and light. The protective film of the present invention is actually composed of a cured product of the curable resin. In this specification, the cured product (resin cured) material) is also referred to as "cured resin", and the resin material (composition containing curable resin) used to form the "cured resin" is also referred to as "curable resin composition".

The protective film made of such a curable resin may contain resin-based beads or microcapsules (average particle diameter: 0.005 to 0.5 mm), or silica particles (average particle diameter: 0.005 to 0.1 mm). The content ratio is preferably 88% by mass or less with respect to the resin constituting the protective film. In the present specification, the average particle diameter means d50 which is the particle diameter at the cumulative 50% point of the particle size distribution. The particle size is a value measured using a particle size distribution meter such as a laser diffraction type or a laser scattering type, or a scanning electron microscope (SEM).

Examples of microbeads or microcapsules that can be used are as follows.

· Polymer hollow microsphere composite mixed hollow microspheres

……… MatsumotoMaikrosfea-MFL series (manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd.)

· Polymer hollow microsphere composite (shell thermoplastic resin + internal aliphatic hydrocarbon foaming agent)

………Krehamai Crossfea One (manufactured by Kureha Co., Ltd.)

Heat-expandable microcapsules (thermoplastic polymer shell + low-boiling hydrocarbon core)

………… Matsumotomaicross Feria-F, FN series (manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd.)

・Heat-expandable microcapsules (encapsulation of a blowing agent (liquid hydrocarbon) in a resin shell)

………… EXPANCEL (manufactured by Japan Phillight Co., Ltd.

・Microbeads (fine particles made of polymethyl methacrylate)

………… Matsumotomaicrossfea-M series (manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd.)

・Microbeads (rubber-like elastic particles composed of cross-linked polyalkylacrylate)

………… Matsumotomaicrossfea-S series (manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd.)

・Hydrophilic microbeads (acrylic polymer particles)

· Micro resin beads (acrylic beads, polyethylene beads, polypropylene beads, polyvinyl chloride beads, polystyrene beads)

By including such fine particles (beads or microcapsules) in the protective film, the amount of curable resin constituting the protective film can be reduced, the control of the film thickness is easy, it is easy to peel off in warm water, and it is difficult to adhere to the glass substrates , It is easy to separate the glass substrate from the glass substrate laminate after end surface grinding.

A preferable resin material (curable resin composition) for forming a protective film made of a cured resin may, for example, be Clear Presto CP3722 (trade name: manufactured by Andrew Co., Ltd.). This resin material is a liquid material mainly composed of high-boiling-point methacrylic acid and high-boiling-point dimethacrylic acid containing heat-expandable microcapsules. It is cured by irradiating visible light to form a protective film with good adhesion mainly composed of acrylic resin. . In addition, the protective film thus formed was easily peeled off by immersion in warm water.

In order to form the protective film composed of the cured resin, the resin material for forming the cured resin, that is, the liquid curable resin composition is printed or coated on at least one main plane of the glass plate to form a printed layer or a coated layer Afterwards, the printed layer or coated layer is cured. As the printing method and coating method, the following methods can be exemplified.

(1) Printing method

Print the liquid curable resin composition into a prescribed form using letterpress printing, gravure printing, offset printing, screen printing, or inkjet. shape.

As shown in Figure 3, letterpress printing (type printing) can be printed by dipping. In Fig. 3, reference numeral 30 denotes a immersion stamper, and reference numeral 31 denotes a glass plain plate. In addition, reference numeral 32 denotes a printing layer. This stamper 30 is made of porous rubber or the like, has a printing part 301 of a predetermined pattern shape (for example, a donut shape) to be printed, and a liquid curable resin that is provided on the printing part 301 and absorbed in fine open cells. The absorption part 302 of the composition. In addition, by pressing the printing part 301 on the glass plain plate 31, the liquid curable resin composition permeated into the printing part 301 from the receiving part 302 is transferred to the main plane of the glass plain plate 31 to form a printed part. 301 is the same shape as the printing layer 32.

(2) Coating method

By brushing, roller coating, blow coating (spray coating, airless spray coating), roll coating, etc., a coating layer with a predetermined planar shape (eg, donut shape) is formed on the main plane of the glass plate.

The printed layer or coated layer (hereinafter also referred to as printed layer, etc.) formed on the main plane of the vitrified plate can be cured by applying a curing method corresponding to the type of resin, that is, visible light or ultraviolet radiation, heating, and other curing methods.

For example, curing of a liquid resin composition containing a photocurable resin as a main component can be performed as shown in FIG. 4 . That is, a method may be adopted in which the printed layer 41 is irradiated with light from the visible light source 44 to cure the printed layer 41 while continuously moving the glass plate 42 on which the printed layer 41 is formed by the conveyor belt 43 .

When forming a protective film made of such a curable resin, a method of printing or applying a liquid curable resin composition that forms the curable resin by curing to cure the printed layer, etc. A resin film with an adhesive or a self-adhesive resin film having a predetermined shape such as a donut shape is bonded to the main plane of the plain glass plate to form a protective film. Such protective film-forming resin films include polyvinyl chloride resin films, polyethylene films, polyolefin films, polyester films, fluororesin films, polycarbonate films, polypropylene films, polystyrene films, and polystyrene films. Sulfide film, para-aramid film, polylactic acid film, polyimide film, polyethylene terephthalate film, polysiloxane resin film, nylon film, etc.

(1b) Cutting process

(1b) In the cutting process, the glass plate with a protective film of a predetermined shape (for example, a donut shape) is cut into a predetermined shape and size on the main plane so that it surrounds the outer periphery of the protective film, and a glass plate with a predetermined shape is formed. Small plates of planar shapes (such as rectangular planar shapes such as squares or disc shapes). This cutting step (1b) may be performed before the protective film forming step (1a). That is, after cutting a large-sized glass plain plate into small plates corresponding to the size of one glass substrate for magnetic recording media, a protective film having a planar shape such as the donut shape described above is formed on each small plate. Alternatively, a protective film having a planar shape such as the donut shape is formed for each plain glass plate formed into a disc shape or a donut shape by press molding. In this way, a vitrified glass plate for magnetic recording media having a predetermined shape and size and having a protective film on at least one main plane was obtained.

(1c) The first main surface grinding process

In (1c) the first main plane grinding step, the upper and lower main planes of the glass plain plate are ground or cut into predetermined dimensions and The principal plane of the plain glass plate of the shape. In this main surface grinding, free abrasive grinding using free abrasives or fixed abrasive grinding using a fixed abrasive tool is performed by a double-side grinding device or a single-side grinding device. As the free abrasive grains and the fixed abrasive grains, diamond grains, alumina grains, silicon carbide grains, etc. having an average grain diameter larger than that of the abrasive grains used in the second main surface grinding step described later can be used.

(2) Shaping process

(2) The shaping step is a step of processing a glass substrate for magnetic recording media having a planar shape of a predetermined size and having a protective film on at least one main plane into a disc-shaped glass substrate with a round hole in the center, which has ( 2a) Circular machining process and (2b) chamfering process. In the flow of performing the cutting step (1b) after the protective film forming step (1a), the cutting step (1b) may be inserted into the (2) shaping step.

(2a) Circular machining process

(2a) In the circular processing step, a circular hole (circular through-hole) is formed in the center while cutting the above-mentioned glass plain plate for magnetic recording media into a circular shape.

(2b) Chamfering process

(2b) In the chamfering process, chamfering is performed on the inner peripheral side of the circularly processed glass substrate and the intersection of the upper and lower main planes, and the intersection of the outer peripheral side and the upper and lower main planes, respectively, to form The chamfered part of the inner peripheral surface and the chamfered part of the outer peripheral surface.

(3) End face grinding process

(3) In the end surface grinding process, in order to remove scratches and the like generated during rounding and chamfering of the glass substrate, and at the same time to smooth the concave-convex grinding surface that forms the end surface during the chamfering process, and reduce the roughness of the end surface, Grinding of the inner peripheral end face (inner peripheral side and inner peripheral chamfer) and outer peripheral end (outer peripheral side and outer peripheral chamfer) is performed. Etching of the inner peripheral end face may also be performed after end face grinding.

(3) In the end surface polishing step, for example, a plurality of glass substrates are stacked to form a plurality of glass substrate laminates, and the inner peripheral end surface and the outer peripheral end surface are polished using a polishing liquid containing abrasive grains and a polishing brush. The grinding of the inner peripheral end surface and the grinding of the outer peripheral end surface may be performed simultaneously or separately. In addition, only one of the grinding of the inner peripheral end surface and the grinding of the outer peripheral end surface may be performed. When the grinding of the inner peripheral end surface and the grinding of the outer peripheral end surface are performed separately, the order of performing is not particularly limited, and either grinding may be performed first. For example, it is also possible to adopt a method of grinding the outer peripheral end face of the glass substrate laminated body of the laminated glass substrate, then directly polishing the inner peripheral end face in the state of the glass substrate laminated body, and then laminating the glass substrates. The body is separated, and the glass substrates are stored one by one in a box or the like, and sent to the next process.

As abrasive grains, ceria particles, silica ions, alumina particles, zirconia particles, zircon particles, silicon carbide particles, boron carbide particles, diamond particles and the like can be used. From the point of view of the polishing rate, it is preferable to use ceria particles. The average particle size of the abrasive grains is preferably 0.1 to 5 μm from the viewpoint of the efficiency of end surface grinding (polishing speed) and the smoothness of the end surface obtained by grinding. As mentioned above, in this specification, an average particle diameter means the particle diameter of the cumulative 50% point of a particle size distribution, ie d50. The particle size is a value measured using a particle size distribution meter such as a laser diffraction type or a laser scattering type.

(4) Protective film removal process

In the protective film removal process, the protective film of the main plane of a glass substrate is removed before the (5) main plane grinding process mentioned later. Removal of the protective film can be performed by a method of directly peeling off the protective film, or by immersing in water, warm water, or an organic solvent to peel or dissolve the protective film. In addition, a step of grinding the main plane (second main plane grinding step) may be provided before the (5) main plane grinding step, and the protective film may be removed by grinding in this step. The second main surface grinding step may be performed after passing through a glass protective film such as water, warm water, or an organic solvent. Such (4) protective film removal process can also be omitted. That is, although the polishing rate in the (5) main surface polishing step decreases, the main surface polishing step can be directly performed on the glass substrate in a state with a protective film.

(4a) Protective film peeling process

(4a) In the protective film peeling process, the glass substrate is immersed in a peelable or soluble solvent such as water, warm water, or an organic solvent to soften, swell or dissolve the resin constituting the protective film, thereby removing the protective film from the glass substrate. Peel off, or dissolve and remove. The peeling solvent can be selected according to the type of resin constituting the protective film. In addition, ultrasonic waves may be irradiated when the glass substrate is immersed in a releasable or soluble solvent such as water, warm water, or an organic solvent.

(4b) The second main surface grinding process

(4b) Adjust the flatness and plate thickness of the glass substrate in the second main surface grinding step. In addition, the protective film formed on the main plane can be chipped off by grinding the main plane of the glass substrate. In the second main surface grinding, free abrasive grinding using free abrasives or fixed abrasive grinding using a fixed abrasive tool is performed by a double-side grinding device or a single-side grinding device. As the free abrasive grains and the fixed abrasive grains, for example, diamond grains, alumina grains, silicon carbide grains and the like having an average grain diameter of 0.5 to 10 μm can be used.

(5) Main plane grinding process

In the manufacture of glass substrates for magnetic recording media, the grinding of the main plane is performed for the purpose of removing flaws, etc. generated during circular processing, chamfering, grinding of the main plane, etc., and smoothing the unevenness to make a mirror surface . (5) In the main plane polishing process, it is preferable to use a polishing liquid containing abrasive grains and a foamed resin polishing pad (hard polishing pad or soft polishing pad), and use a double-sided polishing device to polish the upper and lower main planes.

As abrasive grains, silica particles, alumina particles, zirconia particles, zircon particles, ceria particles and the like can be used. Grinding may be performed only once, or secondary grinding may be performed using abrasive grains with a smaller average particle size after the primary grinding. In addition, it is also possible to further perform third grinding (final grinding) using abrasive grains having a small particle size after the second grinding.

(6) Cleaning process

(6) In the cleaning process, after the glass substrate whose main plane has been polished is scrubbed with detergent, for example, ultrasonic cleaning in a state of immersion in a detergent solution, and immersion in pure water are sequentially performed. ultrasonic cleaning. After washing, carry out drying. Drying methods include, for example, steam drying using isopropanol vapor, warm water and warm air drying using warm air, and spin drying. Thin films such as a magnetic layer are formed on the glass substrate for magnetic recording media manufactured in this way to manufacture a magnetic disk.

According to the method for producing a glass substrate for magnetic recording media according to an embodiment of the present invention, glass for magnetic recording media that prevents defects such as scratches generated before the main plane grinding step and has excellent smoothness of the main plane can be obtained with good yield. substrate. In addition, it is possible to reduce the thickness of the vitrified plate supplied to manufacture the glass substrate for magnetic recording media, reduce the amount of grinding, reduce material loss and improve productivity.

Example

The present invention will be specifically described below through examples, but the present invention is not limited by these examples. Among the following Examples 1 to 11, Examples 1 to 10 are examples of the present invention, and Example 11 is a comparative example.

example 1

A vitreous plate with a thickness of 0.7 mm and mainly composed of SiO ₂ formed by the float process was processed according to the flow chart of Example 1 shown in FIG. 5 to manufacture a glass substrate for magnetic recording media. The details of each process in the flowchart of Example 1 are as follows.

[The first main plane fixed abrasive grinding process] (S101)

Grinding of both main planes of the vitrified plate was performed by a double-sided grinding apparatus using a fixed abrasive tool containing diamond abrasive grains with an average particle diameter of 20 μm. The amount of grinding (depth) was 25 μm (0.025 mm) on both surfaces.

[Protective film forming process] (S102)

On the two main planes of the plain glass plate, using the osmotic pressure pattern printing device shown in Fig. 3, a visible light-curable resin (Adel Co., Ltd., product CLIA PRESTO CP3722) was printed so that the central part had The ring shape (doughnut shape) of the circular hole. Then, the printed layer was cured by irradiating with visible light for about 10 minutes to form a protective film with a film thickness of 100 μm (0.1 mm).

[Cut corner (chopping) process] (S103)

A vitrified glass plate for magnetic recording media having a donut-shaped protective film formed on two main planes was cut so that the outer periphery of the protective film was surrounded by four sides, and a square plate having a square planar shape with a length and width of 75 mm was produced. Thus, a vitrified glass plate for magnetic recording media having protective films on both main planes was obtained.

[Circular machining process] (S104)

The above-mentioned square plate was cut along the circular outer periphery, and a circular hole was formed in the central part, and finally a glass substrate for magnetic recording media with an outer diameter of 65 mm and an inner diameter of 20 mm was formed.

[Chamfering process] (S105)

A glass substrate for magnetic recording media with a final chamfer width of 0.15 mm and a chamfer angle of 45° was obtained by chamfering the inner and outer side surfaces of a disc-shaped glass substrate having a circular hole in the center.

[End surface grinding process] (S106)

The outer peripheral end surface (outer peripheral side and outer peripheral chamfer) and inner peripheral end surface (inner peripheral side and inner week chamfer). The grinding of the inner peripheral end surface is performed sequentially after the grinding of the outer peripheral end surface. The amount of grinding (depth) was 12 μm (0.012 mm) on both the outer peripheral end surface and the inner peripheral end surface.

[Etching process] (S107)

The inner peripheral surface of the end-polished glass substrate was etched with a hydrofluoric acid-nitric acid mixed acid aqueous solution. Then, the front part of the processing flaw on the inner peripheral end surface was blunted.

[Protective film peeling process] (S108)

The glass substrate was immersed in warm water at 60° C., and the protective film was peeled off.

[Second main plane fixed abrasive grinding process] (S109)

The main plane of the glass substrate from which the protective film was peeled was ground using a fixed abrasive tool containing diamond abrasive grains having an average particle diameter of 3 μm with a double-side grinding apparatus. The grinding amount (depth) was 20 μm (0.02 mm) on both surfaces.

[Main surface grinding process] (S110)

Grind the main planes of the glass substrate using a double-sided grinding device. Grinding is divided into two stages of primary grinding and final grinding. In the primary grinding, a slurry containing ceria abrasive grains with an average particle size of 0.8 μm and a suede pad are used. In the final grinding, a slurry containing The grinding liquid and the suede pad of the silica abrasive grains with an average particle size of 20nm were carried out separately. The amount of grinding (depth) is 20 μm (0.02 mm) on both sides, which is the sum of the grinding amount of the primary grinding and the final grinding.

[Precise cleaning process] (S111)

The glass substrate after the grinding of the main surface was scrubbed and cleaned in sequence, ultrasonically cleaned, and vapor-dried with isopropanol. In this way, a glass substrate for a magnetic recording medium having an outer diameter of 65 mm, an inner diameter of 20 mm, and a plate thickness of 0.635 mm was obtained.

Example 2~Example 10

According to the flow charts shown in Figures 5 to 8, a glass plain plate with a thickness of 0.7 mm and a main component of _SiO2 formed by the float process was processed to obtain a magnetic recording medium with an outer diameter of 65 mm, an inner diameter of 20 mm, and a thickness of 0.635 mm. Use a glass substrate. Each process flow of Examples 2 to 10 only changes the process flow and process sequence in Example 1, and each process is carried out under the same conditions as Example 1. The principal plane fixed abrasive grinding process in Examples 3 and 4 and Examples 8 and 9 were carried out in the same manner as the second principal plane fixed abrasive grinding process in Example 1.

Example 11

According to the flow chart of example 11 shown in Fig. 8, process the glass element plate with _SiO2 as the main component plate thickness 1.27mm by float forming, obtain the magnetic recording medium with outer diameter 65mm, inner diameter 20mm, plate thickness 0.635mm Glass base board. In Example 11, the amount of grinding (depth) in the first main plane fixed abrasive grinding process (S101) is 365 μm (0.365 mm) on both surfaces, and the second main plane fixed abrasive grinding process (S109 ) is 250 μm (0.25 mm) on both surfaces, the grinding amount (depth) in the main plane grinding process (S110) is 20 μm (0.02 mm) on both surfaces, and other processes Carried out under the same conditions as in Example 1.

Next, the glass substrates for magnetic recording media obtained in Examples 1 to 11 in this way (500 sheets for each example) were irradiated with light of 300,000 lux in a dark room, and visually inspected for flaws on the main plane. Then, the number of glass substrates in which flaw defects were detected was investigated, and the flaw defect rate of each example was obtained according to the following formula, and the relative flaw defect rate with respect to the flaw defect rate of Comparative Example 11 was calculated. Table 1 shows the values of the relative flaw defect rate calculated by visual observation in this way.

Defect rate of scars by visual inspection

= (Number of glass substrates (pieces) with flaws found by visual inspection/Number of substrates (pieces) that were visually inspected) × 100

Relative scar defect rate by visual inspection (%)

=(Visual flaw defect rate of each example/Visual flaw defect rate of Comparative Example)×100

Furthermore, among the glass substrates for magnetic recording media obtained in Examples 1 to 11, inspection by AOI (automatic optical inspection apparatus) was performed on glass substrates in which flaws were not detected by visual inspection, and flaws were detected. Then, the flaw defect rate was calculated by the following formula, and the relative flaw defect rate with respect to the flaw defect rate of the comparative example was calculated further.

Scar defect rate using AOI

= (Number of glass substrates (pieces) with flaws found by AOI/Number of substrates (pieces) inspected by AOI) × 100

Relative scar defect rate using AOI (%)

=(Scar defect rate using AOI in each example/Scar defect rate using AOI in Comparative Example)×100

Table 1 shows the values of the relative flaw defect rate using AOI thus calculated.

[Table 1]

As can be seen from Table 1, in Examples 1 to 10, each processing step after the circular processing step (S104) was performed using a glass plain plate for magnetic recording media on which a protective film was formed on the main plane, so visual inspection was performed on the main plane. The ratio of the glass substrates in which flaw defects were detected was significantly smaller than that of Example 11 using a glass plate without a protective film. In addition, the proportion of glass substrates in which flaw defects were not detected on the main plane by visual inspection and re-inspection by AOI was significantly lower than in Example 11.

Possibility of industrial use

According to the present invention, it is possible to obtain a glass substrate for a magnetic recording medium having excellent smoothness of the main plane while preventing defects such as scratches generated before the main plane grinding step of the glass substrate with good yield.

Explanation of symbols

10...Glass substrate for magnetic recording medium, 11...Circular hole, 103...Principal plane, 20...Glass plain plate for magnetic recording medium, 22...Protective film, 30...Immersion type stamper, 31, 42...Glass plain plate, 32 , 41... printing layer, 301... printing part, 302... absorbing part, 44... visible light source.

Claims (9)

1. A glass plain plate for magnetic recording media, which is used to form a glass substrate for magnetic recording media having a disc shape with a circular hole in the center, a glass plain plate with a main plane and side surfaces, characterized in that, At least one main plane has a resin-containing protective film. 2. The glass plate for magnetic recording media according to claim 1, wherein the protective film has a circular planar shape with a circular hole in the center. 3. The glass plain plate for magnetic recording media according to claim 1 or 2, wherein the protective film has a film thickness of 0.01 mm to 0.5 mm. 4. A method for manufacturing a glass substrate for a magnetic recording medium, the method having: A process of preparing a glass plain plate for magnetic recording media having a main plane and side surfaces; A forming step of processing the glass plain plate for magnetic recording media into a disk-shaped glass substrate having a circular hole in the center; a main plane grinding process of grinding the main plane of the glass substrate; and The cleaning process of the glass substrate is characterized in that the preparation process of the glass plain plate for magnetic recording medium includes: forming a protective film containing resin on at least one main plane of the glass plain plate, and forming a glass plain plate for magnetic recording medium. Plate protective film forming process. 5. The manufacturing method of a glass substrate for magnetic recording media according to claim 4, wherein said protective film forming step comprises: printing or coating a composition containing a liquid curable resin on at least one main plane of said glass plain plate. and the process of curing the printed layer or coating layer. 6 . The method for manufacturing a glass substrate for magnetic recording media according to claim 4 , wherein the protective film forming step includes a step of attaching a resin-containing protective film to at least one main plane of the vitrified glass plate. 7 . 7. The manufacturing method of a glass substrate for magnetic recording media according to any one of claims 4 to 6, wherein the protective film formed in the protective film forming step has a circular ring with a circular hole in the center Shaped plane shape. The said protective film formed in the said protective film formation process has a film thickness of 0.01 mm - 0.5 mm, The manufacturing method of the glass substrate for magnetic recording media in any one of Claims 4-7. 9. The manufacturing method of a glass substrate for magnetic recording media according to any one of claims 4 to 8, wherein there is a protective film for removing the protective film between the shaping step and the main plane grinding step. Remove process.

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