PH12012000178A1 - Glass base plate for magnetic recording medium, and process for producing glass substrate for magnetic recording medium - Google Patents
Glass base plate for magnetic recording medium, and process for producing glass substrate for magnetic recording medium Download PDFInfo
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- PH12012000178A1 PH12012000178A1 PH12012000178A PH12012000178A PH12012000178A1 PH 12012000178 A1 PH12012000178 A1 PH 12012000178A1 PH 12012000178 A PH12012000178 A PH 12012000178A PH 12012000178 A PH12012000178 A PH 12012000178A PH 12012000178 A1 PH12012000178 A1 PH 12012000178A1
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- Prior art keywords
- recording medium
- magnetic recording
- protective film
- base plate
- glass substrate
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Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P40/00—Technologies relating to the processing of minerals
- Y02P40/50—Glass production, e.g. reusing waste heat during processing or shaping
- Y02P40/57—Improving the yield, e-g- reduction of reject rates
Landscapes
- Manufacturing Of Magnetic Record Carriers (AREA)
Abstract
To obtain a glass substrate for a magnetic recording medium excellent in smoothness of principal planar surfaces in good yield with high productivity, while preventing defects such as scratches which are likely to be formed before a principal planar surface-polishing step. A glass base plate for a magnetic recording medium, which has principal planar surfaces and a side surface, to form a disk-shaped glass substrate for a magnetic recording medium having a circular hole in the center, characterized in that it has a protective film comprising a resin, on at least one of the principal planar surfaces. A process for producing a glass substrate for a magnetic recording medium, comprises a step of preparing a glass base plate for a magnetic recording medium, having principal planar surfaces and a side surface, a shaping step of processing the glass base plate for a magnetic recording medium into a dish-shaped glass substrate having a circular hole in the center, a principal planar surface-polishing step of polishing the principal planar surfaces of the glass substrate, and a cleaning step of cleaning the glass substrate, wherein the step of preparing a glass base plate for a magnetic recording medium includes a protective film-forming step of forming a protective film comprising a resin, on at least one of the principal planar surfaces of the glass base plate, to form the glass base plate for a magnetic recording medium.
Description
) v
GLASS BASE PLATE FOR MAGNETIC RECORDING MEDIUM, AND PROCESS FOR
PRODUCING GLASS SUBSTRATE FOR MAGNETIC RECORDING MEDIUM
The present invention relates to a glass base plate for a magnetic recording medium, and a process for producing a glass substrate for a magnetic recording medium by using the glass base plate.
In recent years, densification for high recording density has ‘been rapidly in progress in the field of magnetic recording media, particularly in the field of magnetic disk devices. In magnetic disk devices, random access has been realized by letting a magnetic head scan over a recording medium (disk) rotating at a high speed with a minimum flying height. In order to attain a high recording density and high speed access simultaneously, it is required to reduce the spacing (head flying height) between a magnetic head and a magnetic disk and to increase the rotation speed of the magnetic disk. The base material for a magnetic disk used to be mainly an aluminum (Al) alloy substrate on which nickel-phosphorus (Ni-P) plating is applied, but it has become common to use a glass substrate which is hard as compared with an aluminum alloy substrate, excellent in impact resistance of the substrate surface against a magnetic head and excellent in planarization and smoothness.
In order to reduce the flying height of a magnetic head, the principal planar surface of the magnetic disk must be flat and smooth, and otherwise, the magnetic head is likely to contact the principal planar surface, thus leading to a trouble. Further, if the surface roughness of the principal planar surface of a magnetic disk is large so that the distance from the magnetic head changes, there will be a problem that read/write reliability deteriorates. Therefore, a glass substrate for a magnetic recording medium having a principal planar surface free from defects such as scratches is required.
Usually, a glass substrate for a magnetic recording medium is produced via a step :
st 5 : of cutting a glass base plate into a shape readily processable in the next step, a step of processing the cut plate into a disk-shaped glass substrate having a circular hole in the center, a chamfering step of grinding the inner peripheral edge and outer peripheral edge of the disk-shaped substrate, an edge-polishing step of polishing the chamfered inner peripheral edge and/or outer peripheral edge, a principal planar surface-polishing step of polishing principal planar surfaces of the glass substrate after the edge-polishing, and a cleaning step of cleaning the glass substrate to increase cleanness. In between the above respective steps, a step of cleaning the glass substrate or a step of etching the glass substrate may be provided, as the case requires.
In such a production of a glass substrate for a magnetic recording medium, in a processing step prior to the principal planar surface-polishing step, it is common to stack a plurality of glass substrates so that their principal planar surfaces are in contact with one another or to directly hold the principal planar surfaces, and at the time of such overlaying or holding, glass cullets or foreign maters were likely to be included. ]
Therefore, there was a problem that defects such as scratches were likely to be formed on the principal planar surfaces of the glass substrates.
Usually, defects such as scratches formed on the principal planar surfaces of glass substrates will be removed by polishing the principal planar surfaces in the principal planar surface-polishing step. However, the depths of scratches formed by e.g. inclusion of foreign matters are not constant, and deep scratches may not be removed by the principal planar surface-polishing step. Thus, defects such as scratches were likely to remain in a product, thus leading to deterioration of the yield of the product. Further, in order to remove defects such as deep scratches formed by e.g. inclusion of foreign matters, it is required to increase the polishing depth (removal amount) in the principal planar surface-polishing step, and in order to increase the polishing depth (removal amount), it is required to increase the thickness of the glass base plate in order to secure a prescribed thickness as a product. Therefore, there was a problem such that a loss of material was substantial, and it takes time for the operation of e.g. polishing.
Further, therefore, in order to prevent formation of defects such as scratches in the production or delivery of plate glass, transportation or processing steps, a method has been proposed to form a covering film made of an inorganic salt such as a sulfate on the surface of a glass plate by treating the glass plate with e.g. sulfurous acid gas (e.g.
Patent Document 1). However, even if it is attempted to use the method disclosed in
Patent Document 1 for the prevention of the above-mentioned defects such as scratches to be formed in the process for producing a glass substrate for a magnetic recording medium, since the thickness of the protective covering film is very thin, itis not possible to sufficiently prevent the defects such as scratches due to e.g. inclusion of foreign matters at the principal planar surfaces of the glass substrate.
PRIOR ART DOCUMENT
PATENT DOCUMENT
Patent Document 1: WQ02002/051767
The present invention has been made to solve the above-described problem and it is an object of the present invention to provide a glass base plate for a magnetic recording medium and a process for producing a glass substrate for a magnetic recording medium, in order to obtain a glass substrate for a magnetic recording medium excellent in smoothness of principal planar surfaces in good yield, while preventing defects such as scratches which are likely to be formed before a principal planar surface-polishing step, particularly defects such as scratches which are likely to be formed due to e.g. inclusion of foreign matters.
The glass base plate for a magnetic recording medium of the present invention is a glass base plate which has principal planar surfaces and a side surface, to form a disk-shaped glass substrate for a magnetic recording medium having a circular hole in the center, characterized in that it has a protective film comprising a resin, on at least one of the principal planar surfaces.
In the glass base plate for a magnetic recording medium of the present invention, the protective film preferably has an annular planar shape with a circular opening in the center. Further, the protective film preferably has a film thickness of from 0.01 mm to
EE : 0.5 mm.
The process for producing a glass substrate for a magnetic recording medium of the present invention is a process for producing a glass substrate for a magnetic recording medium, which comprises a step of preparing a glass base plate for a magnetic recording medium, having principal planar surfaces and a side surface, a shaping step of processing the glass base plate for a magnetic recording medium into a disk-shaped glass substrate having a circular hole in the center, a principal planar surface-polishing step of polishing the principal planar surfaces of the glass substrate, and a cleaning step of cleaning the glass substrate, wherein the step of preparing a glass base plate for a magnetic recording medium includes a protective film-forming step of forming a protective film comprising a resin, on at least one of the principal planar surfaces of the glass base plate, to form the glass base plate for a magnetic recording medium.
In the process for producing a glass substrate for a magnetic recording medium of the present invention, the protective film-forming step may include a step of printing or applying a composition comprising a liquid curable resin, on at least one of principal planar surfaces of the glass base plate to form a printed or applied layer, and a step of curing the printed or applied layer. Further, the protective film-forming step may include a step of bonding a protective film comprising a resin, to at least one of principal planar surfaces of the glass base plate. Further, the protective film formed in the protective film-forming step preferably has an annular planar shape with a circular opening in the center. Further, the protective film formed in the protective film-forming step preferably has a film thickness of from 0.01 mm to 0.5 mm. Still further, the process of the present invention preferably includes a protective film-removing step of removing the protective film between the shaping step and the principal planar surface- polishing step.
In this specification, a glass plate prior to formation of a protective film is referred to as a “glass base plate”. And, a structure having a protective film formed on a principal planar surface of this “glass base plate” is referred to as a “glass base plate for a magnetic recording medium”, and thus, the “glass base plate” and the “glass base plate for a magnetic recording medium” are distinguished. 1
According to the glass base plate for a magnetic recording medium and the process for producing a glass substrate for a magnetic recording medium of the present invention, it is possible to obtain a glass substrate for a magnetic recording medium excellent in smoothness of principal planar surfaces and free from concave defects in good yield, while preventing defects such as scratches which are likely to be formed before the principal planar surface-polishing step. Further, it is possible to reduce the thickness of the glass base plate or the glass base plate for a magnetic recording medium to be used for the production of a glass substrate for a magnetic recording medium and to reduce the removal amount, whereby it is possible to reduce a loss of material and to improve the productivity.
Fig 1 is a cross-sectional perspective view of a glass substrate for a magnetic ] recording medium which is produced by the present invention.
Fig. 2 is a plan view illustrating an embodiment of the glass base plate for a magnetic recording medium of the present invention.
Fig. 3 is a view illustrating an example of a method of printing a resin material for forming a protective film in an embodiment of the present invention.
Fig. 4 is a view illustrating an example of a method for curing a resin composition formed by e.g. printing, in an embodiment of the present invention.
Fig. 5 is a flowchart showing the process for producing a glass substrate for a magnetic recording medium in Examples 1 to 3 as Working Examples of the present invention.
Fig. 6 is a flowchart showing the process for producing a glass substrate for a magnetic recording medium in Examples 4 to 6 as Working Examples of the present invention.
Fig. 7 is a flowchart showing the process for producing a glass substrate for a magnetic recording medium in Examples 7 to 9 as Working Examples of the present invention. 1
Fig. 8 is a flowchart showing the process for producing a glass substrate for a magnetic recording medium in Example 10 as a Working Example of the present invention and in Example 11 as a Comparative Example.
Now, the present invention will be described with reference to embodiments, but it should be understood that the present invention is by no means limited to such embodiments. <Glass base plate for magnetic recording medium>
The glass base plate for a magnetic recording medium of the present invention is a glass base plate for producing a disk-shaped glass substrate for a magnetic recording medium having a circular hole in the center.
Firstly, an example of the glass substrate for a magnetic recording medium to be produced by using the glass base plate for a magnetic recording medium of the present invention, is shown in Fig. 1. The glass substrate 10 for a magnetic recording medium shown in Fig. 1 has a disk shape having a circular hole 11 as a circular through-hole in the center and has a disk shape comprising an inner peripheral side surface 101 as an inner wall surface of the circular hole 11, an outer peripheral side surface 102 and a pair of upper and lower principal planar surfaces 103. And, chamfers 104 (inner peripheral chamfers and outer peripheral chamfers) are formed, respectively, at intersections of the inner peripheral side surface 101 and outer peripheral side surface 102 with the upper and lower principal planar surfaces 103. :
An example of the glass base plate for a magnetic recording medium of the present invention is shown in Fig. 2. The glass base plate 20 for a magnetic recording medium shown in Fig. 2 has a pair of upper and lower principal planar surfaces and a side surface, and it has a protective film 22 comprising a resin, on at least one principal planar surface 21. The resin to constitute the protective film 22 may, for example, be a liquid curable resin capable of forming a cured film after the application, e.g. a reaction curable resin such as a thermosetting resin or a photocurable resin. From the viewpoint of safety in the curing operation, the working environment, the handling efficiency, etc., a photocurable resin is preferred, and a visible light-curable resin is i more preferred. Further, a resin, of which a cured product has a good adhesion to glass and yet can readily be peeled, is preferred, and rather than a resin of a type which is peeled by an organic solvent, a resin which can be peeled by water or warm water is preferred. Further, the protective film 22 comprising a resin may be formed by bonding a resin film.
A preferred resin material to form the protective film 22 and a method for forming the protective film 22 will be described in a section for the process for producing a glass substrate for a magnetic recording medium, given hereinafter.
As shown in Fig. 2, the planar shape of a protective film 22 is preferably a disk shape having a circular opening in the center i.e. a doughnut shape. And, the outer diameter of such a doughnut-shaped protective film 22 and the inner diameter of the circular opening are, respectively, preferably the same as the outer diameter of the principal planar surfaces and the inner diameter of the circular hole of the glass substrate after the after-described circular processing step, more preferably the same as the respective diameters after the chamfering. Further, the outer diameter of the protective film 22 and the inner diameter of the circular opening are particularly preferably the same as the respective diameters of the glass substrate for a magnetic recording medium as the final product, for such a reason that the protective film will not be scraped off in processing steps before the principal planar surface-polishing, the processing operation efficiency will thereby be good, and a loss of the protective film material will be less.
Here, the protective film 22 may not be limited to a so-called solid film type completely covering the planar region of e.g. the doughnut shape without an open space and may be one which covers this planar region with small size patterns of e.g. lattice-form or dot-form. Such a protective film 22 having the doughnut shape formed with lattice-form or dot-form patterns may be inferior to the above solid-film type protective film from the viewpoint of protection of the principal planar surface, but has such a merit that not only peeling is easy but also it is possible to reduce the amount of the protective film material such as a resin to be used.
The thickness of the protective film 22 is preferably made to be from 0.01 mm to 0.5 mm. If the thickness of the protective film 22 is less than 0.01 mm, it may not be possible to sufficiently prevent defects such as scratches of the principal planar surface due to e.g. inclusion of glass cullets or foreign matters. On the other hand, if the film thickness exceeds 0.5 mm, there may be such a trouble that it takes time for the removal of the protective film 22 or it takes time for curing of the resin material to form the protective film 22. Further, the productivity may be deteriorated in other processing steps (e.g. an edge surface-polishing step) to be carried out in between formation of the protective film 22 and the principal planar surface-polishing. The thickness of the protective film 22 is preferably from 0.05 mm to 0.5 mm, further preferably from 0.05 mm to 0.4 mm, particularly preferably from 0.06 mm to 0.2 mm.
By producing a glass substrate for a magnetic recording medium by the following process by using such a glass base plate for a magnetic recording medium having a protective film comprising a resin, on at least one principal planar surface of the glass base plate, it is possible to obtain a glass substrate for a magnetic recording medium having the principal planar surface excellent in smoothness in good yield, while preventing defects such as scratches which are likely to be formed before the principal planar surface-polishing step. Further, it is possible to reduce the thickness of the glass base plate and to reduce the removal amount, whereby it is possible to reduce a loss of e.g. glass material and to improve the productivity by e.g. shortening of the polishing time. <Process for producing glass substrate for magnetic recording medium>
The process for producing a glass substrate for a magnetic recording medium according to an embodiment of the present invention comprises: (1) a step of preparing a glass base plate for a magnetic recording medium, (2) a shaping step, (3) an edge surface-polishing step, (4) a protective film-removing step, (5) a principal planar surface-polishing step, and (6) acleaning step. And, (1) the step of preparing a glass base plate for a magnetic recording medium is characterized in that it includes a protective film-forming step (1a) of forming a protective film comprising a resin, on at least one principal planar surface of the glass base plate.
In the process for producing a glass substrate for a magnetic recording medium of such an embodiment, between the respective steps, cleaning of the glass substrate (cleaning between steps) or etching of the glass substrate surface (a part or entire ] surface of the glass substrate (e.g. at least a part of the principal planar surfaces, inner peripheral edge surface and outer peripheral edge surface)) (etching between steps)
may be carried out. Further, in a case where high mechanical strength is required for the glass substrate for a magnetic recording medium, a strengthening step (e.g. a chemical strengthening step) of forming a strengthened layer as a surface layer of the glass substrate may be carried out before the principal planar surface-polishing step or after the principal planar surface-polishing step, or during the principal planar surface- polishing step (between the primary polishing and the secondary polishing, or between the secondary polishing and the tertiary polishing).
Now, each step will be described. (1) Step of preparing glass base plate for magnetic recording medium (1) The step of preparing a glass base plate for a magnetic recording medium is a step to prepare a glass base plate for a magnetic recording medium i.e. a glass base plate having principal planar surfaces and a side surface and having a protective film comprising a resin, on at least one of the principal planar surfaces, and comprises a protective film-forming step (1a) of forming a protective film on the surface of the glass base plate, and a cutting step (1b) of cutting the glass base plate having the protective film formed on its surface into a prescribed size.
The glass to constitute the glass base plate may be amorphous glass or - crystallized glass, or strengthened glass (e.g. chemically strengthened glass) having a strengthened layer as its surface layer. Further, the glass base plate may be one formed by a float process or one formed by a fusion method, a downdraw method, a redraw method, a roll out method or a press molding method. (1a) Protective film-forming step
In the protective film-forming step, a protective film comprising a resin is formed on at least one principal planar surface of a glass base plate. Formation of a protective film may be carried out on one principal planar surface of the glass base material, but it is preferred to form a protective film on both principal planar surfaces.
The resin to constitute the protective film may be a curable resin such as a thermosetting resin or a photocurable resin. Among such curable resins, the photocurable resin may, for example, be a visible light curable resin or an ultraviolet curable resin. As the visible light curable resin, an acrylic resin or a polythiol-modified acrylic resin may specifically be exemplified, and as the ultraviolet curable resin, an epoxy resin, an acrylic resin, a methacrylate resin, a polyimide resin, a silicone resin, an epoxy acrylate resin, an urethane acrylate resin, an oxetane resin, a vinyl ether resin or a benzoxazine resin may, for example, be exemplified. Further, as the thermosetting resin, an epoxy resin, a melamine resin, a phenol resin or vinyl acetate resin may, for example, be exemplified.
In a case where the protective film comprising a resin is formed by bonding a resin film to at least one principal planar surface of a glass base plate, the resin film may, for example, be a polyethylene terephthalate film, a silicone resin film, a polyvinyl chloride resin film, a polyethylene film, a polyolefin film, a polyester film, a fluororesin film, a polycarbonate film, a polypropylene film, a polyphenylene sulfide film, a para-aramid film, a polylactic acid film, a polyimide film or a nylon film.
As mentioned above, from the viewpoint of safety in curing operations, the working environment, the handling efficiency, etc., a photocurable resin is preferred, and a visible light curable resin is more preferred. Further, a resin, of which a cured product has good adhesion to glass and yet can easily be peeled, is preferred, and rather than a resin of a type to be peeled with an organic solvent, a resin which can be peeled with water or warm water, is preferred.
The above-mentioned curable resin is a resin curable by heat or light, and the protective film in the present invention is practically constituted by a cured product of such a curable resin. In this specification, a resin constituting the protective film i.e. one after curing (a cured product of resin) is referred also as a “cured resin”, and a resin material to form such a “cured resin” (a composition containing a curable resin) is referred to also as a “curable resin composition”.
In a protective film made of such a curable resin, microbeads or microcapsules (average particle size: 0.005 to 0.05 mm) composed mainly of a resin or silica particles (average particle size: 0.005 to 0.1 mm) may be contained. The content is preferably at most 88 mass% to the resin constituting the protective film. Here, in this specification, the average particle size represents d50 which is a particle diameter at a cumulated 50% point in the particle size distribution. The particle size is a value measured by using a particle size distribution meter of e.g. a laser diffraction system or a laser scattering system, or a scanning electron microscope (SEM).
The following may be mentioned as useful microbeads or microcapsules. ‘Polymer hollow microsphere composite hybrid hollow microspheres
....Matsumoto Microsphere MFL series (manufactured by Matsumoto Yushi-
Seiyaku Co., Ltd.) -Polymer hollow microsphere composite (outer shell; thermoplastic resin + inner; aliphatic hydrocarbon blowing agent) 5 ....Kureha Microspheres (manufactured by KUREHA CORPORATION)
Thermally expandable microcapsules (outer shell; thermoplastic polymer + inner core; low boiling point hydrocarbon) ....Matsumoto Microsphere F, FN series (manufactured by Matsumoto Yushi-
Seiyaku Co., Ltd.)
Thermally expandable microcapsules (a foaming agent (liquid hydrocarbon) is encapsulated in an outer shell resin) ....EXPANCEL (manufactured by Japan Fillite Co., Ltd.) -Microbeads (microparticles made of polymethyl methacrylate) ....Matsumoto Microsphere M series (manufactured by Matsumoto Yushi-
Seiyaku Co., Ltd.) -Microbeads (microparticles having rubber plasticity, made of crosslinked polyalkyl acrylate) ....Matsumoto Microsphere S series (manufactured by Matsumoto Yushi-
Seiyaku Co., Ltd.)
Hydrophilic microbeads (microparticles of acrylic polymer) ‘Fine resin beads (acry! beads, polyethylene beads, polypropylene beads, polyvinylchloride beads, or polystyrene beads)
By incorporating such microparticles (microbeads or microcapsules) to the protective film, there may be such merits that the amount of the curable resin to constitute the protective film can be reduced, control of the film thickness will be easy, the protective film can be easily peeled with warm water, adhesion of glass substrates to one another can be prevented, and it becomes easy to separate glass substrates from a stack of glass substrates after the edge surface-polishing.
As a preferred resin material (curable resin composition) to form a protective film made of a cured resin, for example, Clearpresto CP3722 (tradename: manufactured by
Adell Corporation) may be mentioned. This resin material is a liquid material composed mainly of a high boiling point methacrylate and a high boiling point dimethacrylate containing thermo-foaming microcapsules and can be cured by irradiation with visible light to form a protective film composed mainly of an acrylic resin and having a good adhesive property. Further, the protective film thus formed can easily be peeled by dipping in warm water.
In order to form a protective film made of the cured resin, a liquid curable resin composition as a resin material to form the cured resin is printed or applied to at least one principal planar surface of a glass base plate to form a printed or applied layer, and then, the printed or applied layer is cured. The following methods may be mentioned as the printing method and the coating method. (1) Printing methods
A liquid curable resin composition is printed in a prescribed shape by means of a printing block system of e.g. relief printing (typographical printing), intaglio printing (gravure printing), planographical printing (offset printing) or perforated block printing (screen printing), or an ink jet system.
As the relief printing, (typographical printing), printing may be carried out by an infiltration system as shown in Fig. 3. In Fig. 3, reference numeral 30 represents an infiltration system stamper, and reference numeral 31 represents a glass base plate.
Further, reference numeral 32 represents a printed layer. This stamper 30 is made of e.g. a porous rubber and has a printing portion 301 having a prescribed pattern shape : (e.g. a doughnut shape) to be printed and a storage portion 302 provided above the printing portion 301 and containing a liquid curable resin composition in fine interconnected cells. And, by pressing the printing portion 301 onto the glass base plate 31, the liquid curable resin composition infiltrated to the printing portion 301 from the storage portion 302 is transferred to the principal planar surface of the glass base plate 31 to form a printed layer 32 of the same shape as the printing portion 301. l (2) Coating methods
A coating layer of a prescribed planar shape (such as a doughnut shape) is formed on the principal planar surface of a glass base plate by e.g. brush coating, roller coating, spray coating (spraying or air spraying) or roll coating.
The printed layer or coating layer (hereinafter referred to also as a printed layer or the like) thus formed on the principal planar surface of the glass base plate may be cured by applying a curing means corresponding to the type of the resin i.e. a curing means such as irradiation with visible light or ultraviolet rays, or heating.
For example, curing of a liquid resin composition composed mainly of a photocurable resin, may be carried out as shown in Fig. 4. That is, it is possible to employ a system of curing the printed layer or the like 41 by irradiating it with light from a visible light source 44 while continuously moving the glass base plate 42 having the printed layer or the like 41 formed thereon, by a conveyor belt 43.
In the formation of a protective film made of such a curable resin, a method is employed wherein a liquid curable resin composition to form a cured resin by curing, is printed or applied, and the printed layer or the like is cured. However, the protective film may be formed by bonding an adhesive-attached resin film or a self-adhesion type resin film preliminarily formed into a prescribed shape such as a doughnut shape, on the principal planar surface of a glass base plate. Such a resin film for forming a protective film may, for example, be a polyvinyl chloride resin film, a polyethylene film, a polyolefin film, a polyester film, a fluororesin film, a polycarbonate film, a polypropylene film, a polyphenylene sulfide film, a para-aramid film, a polylactic acid film, a polyimide film, a polyethylene terephthalate film, a silicone resin film or a nylon film. (1b) Cutting step (1b) In the cutting step, the glass base plate having a protective film of a prescribed shape (e.g. a doughnut shape) formed on the principal planar surface is cut into a prescribed shape and size to surround the outer periphery of the protective film to obtain a small plate having a prescribed planar shape (e.g. a rectangular planar shape such as a square shape, or a disk-shape). This cutting step (1b) may be carried out before the protective film-forming step (1a). That is, a large size glass base plate may be cut into small plates each having a size corresponding to a glass substrate for a magnetic recording medium, and then, on every small plate, a protective film having a : planar shape such as the doughnut shape may be formed. Otherwise, on every glass base plate formed into a disk shape or doughnut shape by press forming, a protective film having a planar shape such as the doughnut shape may be formed. Thus, itis possible to obtain a glass base plate for a magnetic recording medium having a prescribed shape and size and having a protective film on at least one principal planar surface. (1c) First principal planar surface-grinding step
(1c) In the first principal planar surface-grinding step, both upper and lower principal planar surfaces of a glass base plate, or principal planar surfaces of a glass base plate cut into a prescribed size and shape in a cutting step (1b) provided before the protective film-forming step (1a), are subjected to grinding.
In this principal planar surface-grinding, by means of a both sides grinding device or a one side grinding device, loose abrasive grinding employing loose abrasive or fixed abrasive grinding employing a fixed abrasive tool is carried out.
As such loose abrasive or fixed abrasive, it is possible to use diamond particles, alumina particles, silicon carbide particles, etc. having an average particle size larger than the average particle size of abrasive grains which are used in the after-described second principal planar surface-grinding step. (2) Shaping step (2) The shaping step is a step of processing the glass base plate for a magnetic recording medium having a planar shape of a prescribed size and having a protective film on at least one principal planar surface, into a disk-shaped glass substrate having a circular hole in the center, and comprises (2a) a circular processing step and (2b) a chamfering step.
Further, in a flow wherein the cutting step (1b) is carried out after the protective film-forming step (1a), the cutting step (1b) may be included in (2) the shaping step. (2a) Circular processing step (2a) In the circular processing step, not only the glass base plate for a magnetic recording medium is cut out in a circular shape, but also a circular hole (a circular through hole) is formed in the center. (2b) Chamfering step (2b) In the chamfering step, intersecting portions of the inner peripheral side surface with both upper and lower principal planar surfaces, and intersecting portions of the outer peripheral side surface with both upper and lower principal planar surfaces, of the circularly processed glass substrate, are, respectively, chamfered to form inner peripheral chamfers and outer peripheral chamfers. (3) Edge surface-polishing step (3) The edge surface-polishing step, in order to remove scratches, etc. formed at the time of the circular processing and chamfering of the glass substrate and at the same time, to planarize a roughened ground surface formed at the edge surface by chamfering, thereby to reduce the roughness of the edge surface, polishing of the inner peripheral edge surface (the inner peripheral side surface and the inner peripheral chamfers) and the outer peripheral edge surface (the outer peripheral side surface and the outer peripheral chamfers) is carried out. After the edge surface-polishing, etching of the inner peripheral edge surface may be carried out. (3) Inthe edge surface-polishing step, for example, a plurality of glass substrates may be stacked to form a stack of glass substrates, whereupon the inner peripheral edge surfaces and the outer peripheral edge surfaces may be polished by using a polishing brush and a polishing slurry containing abrasive grains. Polishing of the inner peripheral edge surfaces and polishing of the outer peripheral edge surfaces may be carried out simultaneously or separately. Or, only either polishing of the inner peripheral edge surfaces or polishing of the outer peripheral edge surfaces may be carried out. In a case where polishing of the inner peripheral edge surfaces and polishing of the outer peripheral edge surfaces are carried out separately, the operation order is not particularly limited, and either polishing may be carried out first. For example, it is possible to employ a method wherein polishing of the outer peripheral edge surfaces is carried out against a stack of glass substrates, then polishing of the inner peripheral edge surfaces is carried out in the form of the stack of glass substrates, and then, the stacked glass substrates are separated into one by one and individually accommodated in cassettes, etc. to be sent to the next step.
As the abrasive grains, cerium oxide particles, silica particles, alumina particles, zirconia particles, zircon particles, silicon carbide particles, boron carbide particles, : diamond particles, etc. may be used. From the viewpoint of the polishing rate, it is g preferred to use cerium oxide particles. The average particle size of abrasive grains is preferably selected to be from 0.1 to 5 um from the viewpoint of e.g. the edge surface- polishing efficiency (polishing rate) and smoothness of the edge surface obtainable by 1 the polishing. Here, as mentioned above, in this specification, the average particle size represents d50 being a particle diameter at an accumulated 50% point in the particle size distribution. The particle size is a value measured by means of a particle size distribution meter of e.g. laser diffraction system or laser scattering system. (4) Protective film-removing step
In the protective fim-removing step, the protective film on the principal planar oo 16 surface of the glass substrate is removed before the after-described (5) principal planar surface-polishing step. Removal of the protective film is carried out by a method of directly peeling the protective film off or a method of dipping in e.g. water, warm water or an organic solvent to dissolve or peel the protective film. Otherwise, before (5) principal planar surface-polishing step, a step of grinding the principal planar surface (the second principal planar surface-grinding step) may be provided so that in this step, the protective film is removed by grinding. Further, after peeling the protective film by e.g. water, warm water or an organic solvent, the above-mentioned second principal surface-grinding step may further be carried out. Further, such (4) protective film- removing step may be omitted. That is, although the polishing rate in (5) principal planar surface-polishing step may decrease, it is possible to carry out the principal planar surface-polishing against the glass substrate while the protective film is still attached thereto. (4a) Protective film-peeling step
In (4a) protective film-peeling step, the glass substrate is dipped in water, warm water or a peeling or dissolving solvent such as an organic solvent to soften, swell or dissolve the resin which constitutes the protective film, thereby to peel the protective film from the glass substrate or to dissolve and remove the protective film. The peeling solvent may be selected depending upon the type of the resin which constitutes the ; protective film. Further, when the glass substrate is dipped in water, warm water or a peeling or dissolving solvent such as an organic solvent, ultrasonic waves may be applied. (4b) Second principal planar surface-grinding step
In (4b) second principal planar surface-grinding step, the planarity and thickness of the glass substrate are adjusted. Further, by grinding the principal planar surface of the glass substrate, the protective film formed on the principal planar surface may be scraped off. In the second principal planar surface-grinding, by means of a both side grinding device or a one side grinding device, loose abrasive grinding employing loose abrasive or fixed abrasive grinding employing a fixed abrasive tool is carried out. As the loose abrasive and the fixed abrasive, it is possible to use, for example, diamond particles, alumina particles, silicon carbide particles, etc. having an average particle size j of from 0.5 to 10 um.
(5) Principal planar surface-polishing step
In the production of the glass substrate for a magnetic recording medium, polishing of the principal planar surface is carried out for the purpose of removing e.g. scratches formed during the circular processing, the chamfering, the grinding of the principal planar surfaces, etc. and smoothing irregularities to form a mirror surface. In (5) principal planar surface-polishing step, it is preferred to carry out polishing both upper and lower principal planar surfaces by means of a both sides polishing device by using a polishing slurry containing abrasive grains and a polishing pad made of an foam resin (hard polishing pad or soft polishing pad).
As the abrasive grains, silica particles, alumina particles, zirconia particles, zircon particles, cerium oxide particles, etc. may be used. Only primary polishing may be carried out, but after carrying out primary polishing, secondary polishing may be carried out by using abrasive grains having a smaller average particle size. Further, after the secondary polishing, tertiary polishing (finish polishing) may further be carried out by using abrasive grains having a further smaller particle size. (6) Cleaning step
In (6) cleaning step, the glass substrate having the principal planar surfaces polished is subjected to, for example, scrub-cleaning by using a detergent, and then, ultrasonic wave-cleaning in a state of being dipped in a detergent solution and ultrasonic wave-cleaning in a state of being dipped in pure water are sequentially carried out. After the cleaning, drying is carried out. The drying method may, for example, be vapor drying by an isopropyl! alcohol vapor, warm water-warm air drying by warm air, a spin drying or the like. On the glass substrate for a magnetic recording medium thus obtained, thin film layers such as base layers, a magnetic layer, a protective layer and a lubricant layer are formed to obtain a magnetic disk.
By the process for producing a glass substrate for a magnetic recording medium according to an embodiment of the present invention, it is possible to prevent defects such as scratches which are likely to be formed before the principal planar surface- polishing step and to obtain a glass substrate for a magnetic recording medium excellent in smoothness of the principal planar surfaces in good yield. Further, it is possible to reduce the thickness of a glass base plate to be provided for the production of a glass substrate for a magnetic recording medium, thereby to reduce the removal amount, whereby it is possible to reduce a loss of material and to improve the productivity.
Now, Examples of the present invention will be described in detail, but it should be understood that the present invention is by no means limited to such Examples.
Among the following Examples 1 to 11, Examples 1 to 10 are Working Examples of the present invention, and Example 11 is a Comparative Example.
EXAMPLE 1
A glass base plate formed by a float process, containing SiO; as the main component and having a thickness of 0.7 mm, was processed in accordance with the flowchart of Example 1 shown in Fig. 5 to produce a glass substrate for a magnetic recording medium. Details of each step in the flowchart of Example 1 will be described as follows. [First fixed abrasive grinding step of principal planar surfaces] (S101)
By means of a both sides grinding device, grinding of both principal planar surfaces of the glass base plate was carried out by using a fixed abrasive tool including diamond abrasive grains having an average particle size of 20 um. The grinding depth (removal amount) was 25 pm (0.025 mm) in total of both surfaces. [Protective film-forming step] (S102)
By means of an infiltration stamp type printing device shown in Fig. 3, on both principal planar surfaces of the glass base plate, a visible light-curable resin (tradename: Clearpresto CP3722, manufactured by Adell Corporation) was printed in a disk shape (doughnut shape) having a circular opening in the center. Then, visible light was applied for about 10 minutes to cure the printed layer thereby to form a protective film having a thickness of 100 um (0.1 mm). [Dicing (cut into small size) step] (S103)
The glass base plate for a magnetic recording medium, having doughnut-shaped protective films formed on both principal planar surfaces, was cut to surround the outer peripheries of the protective films with four sides to obtain a square plate having a square planar shape of 75 mm x 75 mm. Thus, a glass base plate for a magnetic recording medium, having protective films on both principal planar surfaces, was obtained. [Circular processing step] (S104)
The above square plate was cut out along a circular outer periphery, and at the same time, a circular hole was formed in the center so as to finally obtain a glass substrate for a magnetic recording medium having an outer diameter of 65 mm and an inner diameter of 20 mm. [Chamfering step] (S105)
The inner peripheral side surface and the outer peripheral side surface of the glass substrate processed into the disk shape having a circular hole in the center, were chamfered so as to finally obtain a glass substrate for a magnetic recording medium having a chamfer width of 0.15 mm and a chamfer angle of 45°. [Edge surface-polishing step] (S106)
The outer peripheral edge surface (outer peripheral side surface and outer peripheral chamfers) and the inner peripheral edge surface (inner peripheral side surface and inner peripheral chamfers) of the chamfered glass substrate were polished by using a polishing slurry containing cerium oxide abrasive grains having an average particle size of 1.3 um and a pair of polishing brushes. The polishing was carried out in the order of polishing of the outer peripheral edge surface, followed by polishing of the inner peripheral edge surface. The polishing depth (removal amount) was 12 um (0.012 mm) at each of the outer peripheral edge surface and the inner peripheral edge surface. [Etching step] (S107)
After the edge surface polishing, the inner peripheral surface of the glass substrate was subjected to etching with a hydrofluoric acid/nitric acid mixed acid aqueous solution to blunt the sharpness of the bottoms and the edges of scratch marks on the inner peripheral edge surface. [Protective film-peeling step] (S108)
The glass substrate was dipped in warm water of 60°C, and the protective films ) were peeled. [Second fixed abrasive grinding step of principal planar surfaces] (S109)
By means of a both sides grinding device, the principal planar surfaces of the glass substrate after peeling the protective films, were subjected to grinding by using a fixed abrasive tool including diamond abrasive grains having an average particle size of 3 um. The grinding depth (removal amount) was 20 pm (0.02 mm) in total of both surfaces. [Principal planar surface-polishing step] (S110)
By means of a both sides polishing device, the principal planar surfaces of the glass substrate were polished. The polishing was carried out in two stages of primary polishing and finish polishing. In the primary polishing, a polishing slurry containing cerium oxide abrasive grains having an average particle size of 0.8 um, and a suede type of polyurethane pad were used, and in the finish polishing, a polishing slurry containing silica abrasive grains having an average particle size of 20 nm and a suede type of polyurethane pad were used. The polishing depth (removal amount) (depth) was 20 um (0.02 mm) in total of both surfaces, as the polishing depth (removal amount) of the primary polishing and the finish polishing were totalled. ; [Precision cleaning step] (S111)
After the principal planar surface-polishing, the glass substrate was subjected to scrub cleaning and ultrasonic wave-cleaning sequentially and then vapor-dried by isopropyl alcohol. Thus, a glass substrate for a magnetic recording medium having an outer diameter of 65 mm, an inner diameter of 20 mm and a thickness of 0.635 mm, was obtained. :
EXAMPLES 2to0 10
A glass base plate formed by a float process, containing SiO, as the main component and having a thickness of 0.7 mm was processed in accordance with each flowchart shown in each of Figs. 5 to 8, to obtain a glass substrate for a magnetic recording medium having an outer diameter of 65 mm, an inner diameter of 20 mm and a thickness of 0.635 mm. In each flowchart in each of Examples 2 to 10, only the sequence of steps was changed from the flow in Example 1, and each step was carried out under the same conditions as in Example 1. Further, the fixed abrasive grinding step of principal planar surfaces in each of Examples 3, 4, 8 and 9, was carried out in the same manner as the second fixed abrasive grinding step of principal planar surfaces in Example 1. 4
EXAMPLE 11 : A glass base plate formed by a float process, containing SiO, as the main component and having a thickness of 1.27 mm was processed in accordance with the flowchart of Example 11 shown in Fig. 8 to obtain a glass substrate for a magnetic recording medium having an outer diameter of 65 mm, an inner diameter of 20 mm and a thickness of 0.635 mm. Here, in Example 11, the grinding depth (removal amount) in the first fixed abrasive grinding step of principal planar surfaces (S101) was 365 um (0.365 mm) in total of both surfaces, and the grinding depth (removal amount) in the second fixed abrasive grinding step of principal planar surfaces (S109) was 250 um (0.25 mm) in total of both surfaces, and the polishing depth (removal amount) in the principal planar surface-polishing step (S110) was 20 um (0.02 mm) in total of both surfaces, and other steps were carried out under the same conditions as in Example 1.
Then, with respect to the glass substrates for magnetic recording media thus obtained in Example 1 to 11 (500 substrates in each Example), scratch defects on the principal planar surfaces were visually inspected by applying light with 300,000 lux in a dark room. And, the number of glass substrates on which scratch defects were detected, was counted, and with respect to each Example, the scratch defect percentage was obtained by the following formula, and the relative scratch defect percentage to the scratch defect percentage in Example 11 as the Comparative
Example, was calculated. Values of the relative scratch defect percentage by visual : observation thus calculated are shown in Table 1.
Scratch defect percentage by visual observation =(number of glass substrates on which scratches were visually observed/ ] number of substrates visually inspected)x 100
Relative scratch defect percentage (%) by visual observation =(scratch defect percentage by visual observation in each Example/ scratch defect percentage by visual observation in the Comparative
Example)x100
Further, with respect to glass substrates on which no scratch defects were detected by visual inspection among the glass substrates for magnetic recording media obtained in Examples 1 to 11, inspection by AOI (automatic optical inspection apparatus) was carried out to detect scratch defects. And, the scratch defect percentage was calculated by the following formula, and further, the relative scratch defect percentage to the scratch defect percentage in the Comparative Example was
. 22 calculated. - Scratch defect percentage by AOI =(number of glass substrates on which scratches were observed by AOI/ number of substrates inspected by AOl)x 100
Relative scratch defect percentage (%) by AOI =(scratch defect percentage by AOI in each Example/ scratch defect percentage by AOI in the Comparative Example)x100
Values of the relative scratch defect percentage by AOI thus calculated are shown in Table 1.
TABLE 1 ’ cp
Relative scratch defect percentage by visual 3.1 3.2 1.3 1.5 1.0 3.7 4.0 2.4 2.1 1.8 100.0 observation (%
Relative scratch defect | ~~ 01 | 041 18 | 23 | 15 | 14 | 13 | 1000 bercentage by AOI (%
BEE
' 24
As is evident from Table 1, in Example 1 to 10 wherein the circular processing step (S104) and subsequent respective processing steps were carried out by using glass base plates for magnetic recording media having protective films formed on the principal planar surfaces, the proportion of glass substrates wherein scratch defects were detected on the principal planar surfaces by visual inspection is remarkably small as compared with Example 11 wherein a glass base plate having no protective film was used. Further, among glass substrates wherein no scratch defects were detected on the principal planar surfaces by visual inspection, the proportion of the glass substrates having scratch defects newly detected by AOI inspection, is also remarkably small as compared with Example 11.
According to the present invention, it is possible to prevent defects such as scratches which are likely to be formed before the principal planar surface-polishing step of a glass substrate and to obtain a glass substrate for a magnetic recording medium excellent in smoothness of the principal planar surfaces in good yield.
REFERENCE SYMBOLS
10: glass substrate for magnetic recording medium, 11: circular hole, 103: principal planar surface, 20: glass base plate for magnetic recording medium, 22: : protective film, 30: infiltration type stamper, 31, 42: glass base plate, 32, 41: printed layer, 301: printing portion, 302: storage portion, 44: visible light source
Claims (9)
1. A glass base plate for a magnetic recording medium, which has principal planar surfaces and a side surface, to form a disk-shaped glass substrate for a magnetic recording medium having a circular hole in the center, wherein it has a protective film comprising a resin, on at least one of the principal planar surfaces.
2. The glass base plate for a magnetic recording medium according to Claim 1, wherein the protective film has an annular planar shape with a circular opening in the center.
3. The glass base plate for a magnetic recording medium according to Claim 1 or 2, wherein the protective film has a film thickness of from 0.01 mm to 0.5 mm.
4. Aprocess for producing a glass substrate for a magnetic recording medium, which comprises: a step of preparing a glass base plate for a magnetic recording medium, having principal planar surfaces and a side surface, a shaping step of processing the glass base plate for a magnetic recording medium into a disk-shaped glass substrate having a circular hole in the center, a principal planar surface-polishing step of polishing the principal planar surfaces of the glass substrate, and a cleaning step of cleaning the glass substrate, wherein the step of preparing a glass base plate for a magnetic recording medium includes a protective film-forming step of forming a protective film comprising a resin, on at least one of the principal planar surfaces of the glass base plate, to form the glass base plate for a magnetic recording medium. ]
5. The process for producing a glass substrate for a magnetic recording medium according to Claim 4, wherein the protective film-forming step includes a step of printing or applying a composition comprising a liquid of curable resin, on at least one of principal planar surfaces of the glass base plate to form a printed or applied layer, and a step of curing the printed or applied layer.
6. The process for producing a glass substrate for a magnetic recording medium according to Claim 4, wherein the protective film-forming step includes a step of bonding a protective film comprising a resin, to at least one of principal planar surfaces of the glass base plate.
7. The process for producing a glass substrate for a magnetic recording medium according to any one of Claims 4 to 6, wherein the protective film formed in the protective film-forming step has an annular planar shape with a circular opening in the center.
8. The process for producing a glass substrate for a magnetic recording medium according to any one of Claims 4 to 7, wherein the protective film formed in the protective film-forming step has a film thickness of from 0.01 mm to 0.5 mm.
9. The process for producing a glass substrate for a magnetic recording medium according to any one of Claims 4 to 8, which includes a protective film-removing step of removing the protective film between the shaping step and the principal planar surface-polishing step.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2011156621A JP5953664B2 (en) | 2011-07-15 | 2011-07-15 | Glass base plate for magnetic recording medium and method for manufacturing glass substrate for magnetic recording medium |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| PH12012000178A1 true PH12012000178A1 (en) | 2014-12-22 |
Family
ID=47482593
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| PH12012000178A PH12012000178A1 (en) | 2011-07-15 | 2012-06-22 | Glass base plate for magnetic recording medium, and process for producing glass substrate for magnetic recording medium |
Country Status (3)
| Country | Link |
|---|---|
| JP (1) | JP5953664B2 (en) |
| CN (1) | CN102881295A (en) |
| PH (1) | PH12012000178A1 (en) |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6718612B2 (en) * | 1999-08-04 | 2004-04-13 | Asahi Glass Company, Ltd. | Method for manufacturing a magnetic disk comprising a glass substrate using a protective layer over a glass workpiece |
| JP2003030822A (en) * | 2001-07-13 | 2003-01-31 | Fuji Electric Co Ltd | Method for processing magnetic disk substrate |
| JP2010003365A (en) * | 2008-06-20 | 2010-01-07 | Furukawa Electric Co Ltd:The | Manufacturing method of glass substrate |
| JP2010086632A (en) * | 2008-10-02 | 2010-04-15 | Konica Minolta Opto Inc | Method for manufacturing glass substrate for magnetic recording medium |
-
2011
- 2011-07-15 JP JP2011156621A patent/JP5953664B2/en not_active Expired - Fee Related
-
2012
- 2012-06-22 PH PH12012000178A patent/PH12012000178A1/en unknown
- 2012-07-11 CN CN2012102397223A patent/CN102881295A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| CN102881295A (en) | 2013-01-16 |
| JP2013025829A (en) | 2013-02-04 |
| JP5953664B2 (en) | 2016-07-20 |
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