JP2014071930A - Method for manufacturing glass substrate for magnetic disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a glass substrate for a magnetic disk, in manufacture of a glass substrate for a magnetic disk having a pair of main surfaces, an inner periphery end surface, and an outer periphery end surface, which is capable of: suppressing occurrence of damage on an outer periphery end surface of a glass substrate when processing (grinding or polishing) the main surfaces of the glass substrate; preventing mechanical strength of the glass substrate from lowering; and hardly forming foreign materials such as fine particles on the main surfaces of the glass substrate for a magnetic disk.SOLUTION: A method for manufacturing a glass substrate for a magnetic disk comprises: a main surface processing step of grinding or polishing a pair of main surfaces of a glass substrate of a magnetic disk while holding an outer periphery end surface of the glass substrate for a magnetic disk in a holding hole provided on a holding member, in a state where a protective layer is provided on the outer periphery end surface of the glass substrate for a magnetic disk; and, after the main surface processing step, a removal step of removing the protective layer from the glass substrate for a magnetic disk.

Description

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

  Today, a personal computer, a notebook personal computer, a DVD (Digital Versatile Disc) recording device, or the like has a built-in hard disk device for data recording. In particular, in a hard disk device used for portable equipment such as a notebook personal computer, a magnetic disk having a magnetic layer provided on a magnetic disk glass substrate is used. On the surface of the magnetic disk, magnetic recording information is recorded on or read from the magnetic layer of the magnetic disk by a magnetic head (DFH (Dynamic Flying Height) head) slightly lifted from this surface. As the substrate of this magnetic disk, a glass substrate is preferably used because it has a property that it is less likely to undergo plastic deformation than a metal substrate or the like.

Today, in response to a request for an increase in storage capacity in a hard disk device, the density of magnetic recording is being increased. Along with this, the magnetic recording information area is miniaturized by extremely shortening the flying distance from the magnetic recording surface of the magnetic head. In such a glass substrate for a magnetic disk, the surface unevenness of the substrate is made as small as possible.
In a magnetic head used in a hard disk device, if there are minute irregularities on the surface of the magnetic disk, a known thermal asperity failure may occur, causing a malfunction in reproduction or making reproduction impossible. The cause of this thermal asperity failure is that the convex portion formed on the surface of the magnetic disk by the foreign matter on the glass substrate causes adiabatic compression and adiabatic expansion of the air in the vicinity of the head due to high-speed rotation of the magnetic disk, thereby causing the magnetic head Is caused by heat generation.

  Therefore, in order to prevent this thermal asperity failure, the surface of the magnetic disk needs to be finished to a highly smooth surface free from foreign matter. When manufacturing a glass substrate for a magnetic disk, magnetically prevent the particles that cause unevenness on the main surface of the glass substrate for the magnetic disk from adhering to the end surface of the glass substrate being processed, or prevent the particles from generating dust. The end surface of the glass substrate for magnetic disk, which is a material being processed to become the glass substrate for disk, needs to be polished extremely smoothly like the main surface of the glass substrate. Also, in order not to lower the mechanical strength of the glass substrate for magnetic disk, it is polished so that not only the main surface of the glass substrate but also the scratch that becomes the starting point of the progress of cracks that cause fracture is present on the end surface. It is necessary to be.

  By the way, when manufacturing a glass substrate for a magnetic disk, the end surface and the main surface of the glass substrate are ground and polished. Even if the end surface is ground and polished, the main surface is polished to be mirrored. In some cases, the end surface of the glass substrate may be damaged. Further, when the abrasive grains being polished on the main surface adhere to the end face as fine particles, the adhered fine particles may become a generation source of fine particles on the main surface in a subsequent process.

  Regarding the occurrence of scratches on the end face of the glass substrate described above, the contact between the side wall of the inner peripheral portion of the holding hole of the carrier for grinding or polishing and the end face on the outer peripheral side of the glass substrate to be polished can be cited as a factor. Generally, the polishing carrier is formed of a fiber reinforced resin in order to obtain high rigidity. However, when a glass substrate is polished using such a polishing carrier, the outer peripheral side end surface of the glass substrate contacts the side wall of the inner peripheral portion of the holding hole provided in the polishing carrier, and the end surface is scratched. Will occur. The holding hole is provided for holding the glass substrate at a predetermined position in the polishing carrier.

On the other hand, for fine particles generated on the main surface of the magnetic disk glass substrate, scratches existing on the end surface of the glass substrate during the production of the magnetic disk glass substrate or abrasive abrasive particles adhering to the end surface generate particles. This is considered to be one of the factors. The presence of scratches on the end surface of the glass substrate causes fine particles to be generated when the inside of the storage container and the outer periphery of the glass substrate come into contact with each other and rub against each other when the glass substrate is put in and out. The generated fine particles adhere to the main surface of the glass substrate, thereby causing a head crash and a thermal asphery failure.
Similarly, the abrasive grains used in the main surface polishing step adhere to the end surface of the glass substrate, so that when the end surface of the glass substrate comes into contact with the glass substrate storage container, the abrasive particles peel off from the end surface of the glass substrate. Adhering to the surface causes the magnetic disk to become defective and deteriorate in quality. In addition, the abrasive grains adhering to the end face during the magnetic disk manufacturing process or during use of the magnetic disk peel off from the end face and fall onto the main surface, increasing the surface irregularities, resulting in defective magnetic disks and reduced quality. Invite.

  On the other hand, one of the factors governing the decrease in the mechanical strength of the magnetic disk glass substrate is scratches present on the inner peripheral end surface and the outer peripheral end surface of the glass substrate. As a method of reducing scratches existing on these end faces and suppressing a decrease in mechanical strength of the glass substrate for magnetic disks, there is a multi-step process of polishing the end faces using abrasive grains having finer grades. . However, in this multi-stage processing, there is a fatal problem that the productivity and cost are greatly deteriorated.

  Under such circumstances, from the viewpoint of preventing scratches on the inner peripheral side end surface of the glass substrate and preventing adhesion of abrasive grains to the inner peripheral side end surface, a resin such as silicone resin or polyimide is used on the inner peripheral side of the glass substrate. A technique for covering the end face is known (Patent Document 1). Also, a technique is known in which a protective layer is provided on the side wall of the inner peripheral portion of the holding hole of the holding member of the polishing carrier from the viewpoint of preventing scratches on the outer peripheral end surface of the glass substrate and preventing adhesion of abrasive grains. (Patent Document 2).

JP 2005-203080 A JP 2006-88314 A

However, the technique disclosed in Patent Document 1 does not mention removal of the coated resin, and further, how to remove the resin when removing the resin. Therefore, when the resin is not removed, when a magnetic disk is manufactured using a glass substrate for a magnetic disk in which the inner peripheral side end surface is coated with resin, a part of the resin is peeled off and a part of the resin is on the main surface. It may become a foreign object. Moreover, in order to improve mechanical strength with respect to the glass substrate which coat | covered resin to the inner peripheral side end surface, the chemical strengthening performed at 400-500 degreeC cannot be employ | adopted. When the glass substrate coated with the resin is chemically strengthened, the resin is melted in the chemical strengthening solution, and may cause generation of fine particles at high temperature.
Moreover, in the technique disclosed in Patent Document 2, since the side wall of the inner peripheral portion of the holding hole of the polishing carrier is coated with resin, it is possible to prevent scratches on the outer peripheral side end surface of the glass substrate during grinding or polishing. . However, during grinding or polishing, the resin used for coating the side wall of the inner periphery of the holding hole is peeled off during processing, and a part of the resin is sandwiched between a pair of surface plates on the main surface of the glass substrate to be processed. Or it may enter on the surface of the carrier. As a result, a gap is generated between the polishing pad or the grinding sheet of the surface plate and the carrier, the glass substrate is detached from the carrier being ground or polished, and the glass substrate is likely to be damaged during the grinding or polishing. . Once the glass substrate is damaged during grinding or polishing, the other glass substrates for magnetic disks that have been polished or ground simultaneously with the damaged glass substrate cannot be ensured in surface quality, so they should be finished products. Production efficiency is greatly reduced.

  Therefore, in the present invention, when manufacturing a glass substrate for a magnetic disk, when the main surface of the glass substrate that is a material of the glass substrate for a magnetic disk is processed (grinding or polishing), scratches on the outer peripheral side surface of the glass substrate are generated. A method for producing a glass substrate for a magnetic disk that can suppress the reduction of the mechanical strength of the glass substrate and that is difficult to form foreign matter such as fine particles on the main surface of the glass substrate for a magnetic disk. The purpose is to provide.

One aspect of the present invention is a method of manufacturing a glass substrate for a magnetic disk having a pair of main surfaces, an inner peripheral side end surface, and an outer peripheral side end surface. The method is
The magnetic disk glass substrate while holding the outer peripheral side end surface of the magnetic disk glass substrate in a holding hole provided in a holding member in a state where a protective layer is provided on the outer peripheral side end surface of the magnetic disk glass substrate A main surface processing step of grinding or polishing the pair of main surfaces of
And a removal step of removing the protective layer from the magnetic disk glass substrate after the main surface processing step.

  As a preferred embodiment of the above method, the outer peripheral side end surface is provided between the pair of interposed surfaces and the pair of interposed surfaces inclined with respect to the main surface and connected to the main surface, and the main surface And a side wall surface extending so as to be orthogonal to. At this time, a part on the main surface side of each of the interposition surfaces is a region where the protective layer is not formed.

  As another preferable mode of the above method, a target processing amount of the main surface in the main surface processing step is determined in advance, and between the end portions on both sides of the protective layer in the thickness direction of the glass substrate for magnetic disk This distance is smaller than the thickness obtained by subtracting the target processing amount from the thickness of the magnetic disk glass substrate.

  As another preferred embodiment of the above method, an outer surface polishing step for polishing the outer peripheral side end surface of the glass substrate for magnetic disks, and the outer peripheral side after the end surface polishing step and before the main surface processing step And a protective layer forming step of providing the protective layer on the end face.

  As another preferred embodiment of the above method, the protective layer forming step is performed on a laminate obtained by laminating at least one glass substrate for magnetic disk in addition to the glass substrate for magnetic disk. Thus, the protective layer is provided on each of the outer peripheral side end surfaces of the plurality of magnetic disk glass substrates of the laminate.

  As another preferred embodiment of the above method, in the protective layer forming step, a protective agent film to be the protective layer is formed on the surface of the transfer substrate, and the outer peripheral side of the magnetic disk glass substrate from the transfer substrate. The film is transferred to an end face, and the protective layer is provided on the outer peripheral end face.

  As another preferable mode of the above method, the method further includes a chemical strengthening step of chemically strengthening the glass substrate for magnetic disk after the main surface processing step. At this time, the removal step is performed before the chemical strengthening step.

  As another preferred embodiment of the above method, the protective layer is a layer made of a resin material that can be removed from the end face on the outer peripheral side by applying heat, light, or electromagnetic waves.

  According to the above-described method for manufacturing a magnetic disk glass substrate, it is possible to suppress the occurrence of scratches on the outer peripheral side end surface of the glass substrate that occurs during processing (grinding or polishing) of the main surface of the magnetic disk glass substrate. Further, it is possible to prevent the mechanical strength of the magnetic disk glass substrate from being lowered. Furthermore, according to the method for manufacturing a glass substrate for a magnetic disk described above, it is difficult for foreign matters such as fine particles to be formed on the main surface of the glass substrate for a magnetic disk.

(A) is a schematic block diagram which shows an example of the magnetic disc produced using the glass substrate for magnetic discs, (b) is sectional drawing of an example of a magnetic disc. It is a figure which shows the flow of one Embodiment of the manufacturing method of the glass substrate for magnetic discs. (A)-(c) is a figure explaining an example of formation of the protective film of this embodiment. It is a figure explaining the modification 1 of formation of the protective film of this embodiment. It is a figure explaining arrangement | positioning of the protective layer formed in the glass substrate for magnetic discs of this embodiment. It is a figure explaining the apparatus which performs a main surface process on a glass substrate.

  Hereinafter, the manufacturing method of the glass substrate for magnetic disks of this invention is demonstrated in detail.

(Magnetic disk and glass substrate for magnetic disk)
First, a magnetic disk manufactured using a magnetic disk glass substrate will be described with reference to FIG. FIG. 1A is a schematic configuration diagram showing an example of a magnetic disk manufactured using a magnetic disk glass substrate. FIG. 1B is a schematic cross-sectional view of a magnetic disk.

As shown in FIG. 1A, the magnetic disk 1 has a ring shape in which a central portion of a disk shape is hollowed out concentrically, and rotates around the center of the ring as a rotation axis. As shown in FIG. 1B, the magnetic disk 1 includes a glass substrate 2 and at least magnetic layers 3A and 3B.
In addition to the magnetic layers 3A and 3B, for example, an adhesion layer, a soft magnetic layer, a nonmagnetic underlayer, a perpendicular magnetic recording layer, a protective layer, a lubricating layer, and the like (not shown) are formed. For the adhesion layer, for example, a Cr alloy or the like is used. The adhesion layer functions as an adhesive layer with the glass substrate 2. For the soft magnetic layer, for example, a CoTaZr alloy or the like is used. As the nonmagnetic underlayer, for example, a granular nonmagnetic layer is used. For example, a granular magnetic layer is used for the perpendicular magnetic recording layer. A material made of hydrogen carbon is used for the protective layer. For the lubricating layer, for example, a fluorine-based resin or the like is used.

The magnetic disk 1 will be described using a more specific example. In this embodiment, CrTi adhesion layer, CoTaZr / Ru / CoTaZr soft magnetic layer, CoCrSiO ₂ non-magnetic granular underlayer, CoCrPt—SiO _{2 are} formed on both main surfaces of the glass substrate 2 using an in-line sputtering apparatus. A TiO ₂ granular magnetic layer and a hydrogenated carbon protective film are sequentially formed. Further, a perfluoropolyether lubricating layer is formed on the formed uppermost layer by dipping.

  Aluminosilicate glass, soda lime glass, borosilicate glass, or the like can be used as the material for the magnetic disk glass substrate in the present embodiment. In particular, aluminosilicate glass can be suitably used in that it can be chemically strengthened and a glass substrate for a magnetic disk excellent in the flatness of the main surface and the strength of the substrate can be produced.

Although it does not limit the composition of the glass substrate for magnetic disks of this embodiment, when converted into an oxide standard as an aluminosilicate glass, SiO ₂ is 50 to 75% and Al ₂ O ₃ in terms of mol%. 1 to 15%, at least one component selected from Li ₂ O, Na ₂ O and K ₂ O in total 12 to 35%, at least one selected from MgO, CaO, SrO, BaO and ZnO 0-20% the ingredients in total, and _at least one component selected from _{ZrO 2, TiO 2, La 2} O 3, Y 2 O 3, Ta 2 O 5, Nb 2 O 5 and HfO ₂ It is preferable to use an aluminosilicate glass having a composition of 0 to 10% in total.

(Method for producing glass substrate for magnetic disk)
Next, with reference to FIG. 2, the flow of the manufacturing method of the glass substrate for magnetic discs is demonstrated. FIGS. 3A to 3C and FIGS. 4 and 5 are diagrams for explaining an example of forming the protective film of the present embodiment.
As shown in FIG. 2, first, a glass blank as a material for a plate-shaped magnetic disk glass substrate having a pair of main surfaces is formed (step S10). Next, the molded glass blank is scribed to produce a ring-shaped (annular) glass substrate with a hole in the center (step S20). Next, shape processing (chambering processing) is performed on the scribed glass substrate (step S30). Thereby, a glass substrate is produced | generated. Next, the end surface of the glass substrate is polished (step S40). Next, a protective layer is formed on the outer peripheral side end face of the glass substrate subjected to end face polishing (step S50). Next, the glass substrate is ground with fixed abrasive grains (step S60). Next, 1st grinding | polishing is performed to the main surface of a glass substrate (step S60). Next, the protective layer formed on the outer peripheral side end surface in step 40 is removed from the glass substrate subjected to the first polishing (step S80). Next, chemical strengthening is performed on the glass substrate from which the protective layer has been removed (step S90). Next, the second polishing is applied to the chemically strengthened glass substrate (step S100). Through the above steps, a magnetic disk glass substrate is obtained. Hereinafter, each step will be described in detail.

(A) Glass blank forming step (step S10)
In forming a glass blank, for example, a float method is used. In the glass blank forming step, first, molten glass is poured continuously into a bath filled with a molten metal such as tin to obtain, for example, plate-like glass having the above-described composition. The molten glass flows along the traveling direction in a bathtub that has been subjected to a strict temperature operation, and finally a plate-like glass adjusted to a desired thickness and width is formed. From this plate glass, a plate-shaped glass blank having a predetermined shape (for example, a quadrangular shape in plan view) that is a base of the magnetic disk glass substrate is cut out. Since the surface of the molten tin in the bath is horizontal, the flat glass surface obtained by the float process has a sufficiently high flatness.
In addition to the float method, for example, a press molding method can be used for forming the plate-shaped glass blank. In the molding of a plate-shaped glass blank by press molding, a glass gob (glass lump) made of molten glass is supplied onto a lower mold that is a receiving gob forming mold, and an upper mold that is a lower gob and an opposing gob forming mold is used. The glass gob is press-molded. Thereby, the disk-shaped glass blank used as the origin of the glass substrate for magnetic discs is produced.
In addition, a plate-shaped glass blank can be manufactured not only using the method mentioned above but well-known manufacturing methods, such as a downdraw method, a redraw method, and a fusion method. A disk-shaped glass blank that is the basis of a glass substrate for magnetic disks is cut out from a sheet glass made by a known manufacturing method such as a float method, a downdraw method, a redraw method, a fusion method, etc. It is.

(B) Scribe process (step S20)
Next, the scribe process will be described. After the glass blank forming step, in the scribe step, scribing is performed on the formed glass blank.
Here, scribe refers to two concentric circles (inner circumference side) by a scriber made of super steel alloy or diamond particles on the surface of the glass blank in order to use the formed glass blank as a ring-shaped glass substrate of a predetermined size. Concentric circles and outer peripheral concentric circles) are provided with cutting lines (linear scratches). The glass blank scribed in the shape of two concentric circles is partially heated, and due to the difference in thermal expansion of the glass blank, the outer portion of the outer concentric circle and the inner portion of the inner concentric circle are removed. Thereby, a ring-shaped glass substrate with circular holes is obtained. In addition, the disk-shaped glass substrate with the circular hole can also be obtained by forming a circular hole using a core drill etc. with respect to a glass blank.

(C) Shape processing step (step S30)
Next, the shape processing step will be described. The shape processing step includes chamfering processing (chamfering of the outer peripheral side end surface and the inner peripheral side end surface) for the end portion of the glass substrate after the scribe step. A chamfering process is a shape process which chamfers with a diamond grindstone in the outer peripheral side end surface and inner peripheral side end surface of the glass substrate after a scribe process. A glass substrate having a predetermined shape is generated by this shape processing. The chamfering inclination angle is preferably, for example, 20 to 80 degrees with respect to the main surface.

(D) End face polishing step (step S40)
Next, the end face polishing step will be described. In the end surface polishing, mirror finishing is performed by brush polishing on the inner peripheral side end surface and the outer peripheral side end surface of the glass substrate. At this time, an abrasive slurry containing fine particles such as cerium oxide as free abrasive grains is used. By polishing the end surface, removing contamination such as contamination and scratches on the end surface of the glass substrate will prevent the occurrence of thermal asperity failure and cause corrosion such as sodium and potassium. The occurrence of ion precipitation can be prevented.

(E) Protective layer forming step (Step S50)
Next, the protective layer forming step will be described. In the protective layer forming step, a protective layer is provided on the outer peripheral side end face of the polished glass substrate. A protective layer is a layer which consists of a resin material which can be removed from the outer peripheral side end surface of a glass substrate, for example by applying a heat | fever, light, or electromagnetic waves. For example, the protective layer may be a thermosetting resin adhesive mixed with a material having a heat melting property or a heat decomposability, for example, a disassembling adhesive in which a thermoplastic adhesive is added to a known epoxy resin adhesive The layer which consists of is mentioned. As the protective layer, an acrylic resin that can be cured by ultraviolet rays and can be removed by heating may be used. In this case, in order to remove the protective layer described later, the protective layer can be removed by heating the protective layer to weaken the adhesive force. In addition, by mixing thermally expandable microcapsules in thermoplastic resin adhesives or thermosetting resin adhesives, the protective layer peels off from the outer peripheral end surface due to expansion of the microcapsules during heating. It can also be made easier. A thermoplastic resin adhesive can also be used as the protective layer.
In addition, as an example in which the protective layer can be peeled off, the protective layer may be removable from the outer peripheral end surface of the glass substrate by applying light or electromagnetic waves. As an example of removing the protective layer by adding light, a method using excimer light (for example, Japanese Patent Application Laid-Open No. 2012-1601) can be given. As an example of removing the protective layer by applying an electromagnetic wave (high-frequency electromagnetic wave), a method by induction heating (JP 2007-314711 A) or the like can be given.

  The thickness of the protective layer is, for example, 1 to 200 μm, for example, 50 to 80 μm. In addition, the thickness of a protective layer here is an average value of the thickness of four protective layers measured every 90 degree | times on the circumference on the periphery of the outer peripheral side end surface of a glass substrate. In addition to the glass substrate, the outer peripheral side of each of the plurality of glass substrates of the laminate by performing a protective layer forming process on the laminate obtained by laminating at least one other glass substrate A protective layer can also be provided on the end face. This method is preferable from the viewpoint of efficiently producing a glass substrate for a magnetic disk. For example, as shown in FIG. 3A, the protective layer is formed by laminating a plurality of glass substrates and holding the laminate 10 with a laminate holder (not shown) to form a liquid that becomes a protective layer from the plurality of spray devices 12. Spray the protective agent.

  Or a protective layer can also be provided in each glass substrate of the laminated body 10 with a form as shown in FIG.3 (b). Specifically, a film 24 having a uniform and constant thickness of the protective agent 22 is formed on the conveyor belt 18 provided on the rollers 14 and 16 by using a doctor blade 20. By rotating the laminated body 10 while keeping the laminated body 10 in contact with the film 24 in a state where the laminated body is spaced apart from the film 24, the laminated body is fixed on the circumference of the outer peripheral side end surface of each glass substrate of the laminated body. A protective layer having a thickness can be provided. In addition, in order to provide a protective layer in the predetermined range of the outer peripheral side end surface of a glass substrate, the separation distance of the laminated body 10 with respect to the film | membrane 24 formed on the conveyance belt 18 is adjusted correctly. The reason why the protective layer is provided in a predetermined range on the outer peripheral side end surface of the glass substrate is to prevent the protective layer from being shaved during grinding, first polishing, and the like described later.

  Furthermore, a protective layer can be provided on each glass substrate of the laminate 10 in a form as shown in FIG. Specifically, a film 24 having a uniform and constant thickness of the protective agent 22 is formed on the conveyor belt 18 using the doctor blade 20 on the conveyor belt 18 provided on the rollers 14 and 16. From this film 24, a film 25 transferred onto the roll coater 26 is formed by using a roll coater 26, and the laminate 10 is contacted with the film 25 while rotating the laminate 10 at a predetermined distance from the film 25. By doing so, a protective layer having a certain thickness can be provided on the periphery of the outer peripheral side end surface of the glass substrate. That is, when forming a protective layer, a film 25 of a protective agent serving as a protective layer is formed on the surface of a roll coater 26 that is a transfer substrate, and the laminated body 10 in which the glass substrates for magnetic disks are bundled from the transfer substrate. The film 25 is transferred to the outer peripheral end face, and a protective layer is provided on the outer peripheral end face.

  Moreover, a protective layer can also be provided on each glass substrate of the laminate 10 in the form shown in FIG. Specifically, a film 24 having a uniform and constant thickness of the protective agent 22 is formed on the roller 28 using the doctor blade 20, and the film 24 is laminated on the film 24 in a state of being spaced apart by a certain distance. By contacting the body 10 while rotating, a protective layer having a certain thickness can be provided on the periphery of the outer peripheral side end surface of the glass substrate. In the example shown in FIG. 4, for example, when the protective agent 22 includes an ultraviolet curable resin or the like, the protective agent 22 can be easily removed by irradiating the protective layer with the ultraviolet rays 32 using the light source 30 immediately after the protective layer is provided. It can be cured and a protective layer having a uniform thickness can be efficiently formed.

In addition, the outer peripheral side end surface of the glass substrate is chamfered in the shape processing step (step S30). FIG. 5 is a view for explaining the arrangement of the protective layer formed on the glass substrate of the present embodiment.
As shown in FIG. 5, a protective layer 54 made of the protective agent 22 is provided on the outer peripheral side end face 52 of the glass substrate 50. Since the glass substrate 50 is chamfered on the outer peripheral side end surface in the end surface polishing step (step S <b> 40), the outer peripheral side end surface 52 has interposition surfaces 58 and 60 and a side wall surface 62. The interposed surfaces 58 and 60 are inclined with respect to the main surface 56 at an inclination angle of greater than 0 degree and less than 90 degrees, preferably at an inclination angle in the range of 20 to 80 degrees and connected to the main surface. It is a chamfered surface. The side wall surface 62 is a surface provided between the pair of interposition surfaces 58 and 60 and extending so as to be orthogonal to the main surface 56.
In such an outer peripheral side end face 52, the protective layer 54 covers the entire side wall face 62 and covers a part of the interposition faces 58 and 60 on the side wall face 62 side. A part of each of the interposition surfaces 58 and 60 on the main surface 56 side is a region where the protective layer 54 is not formed. That is, in the non-formation region, the surfaces of the interposition surfaces 58 and 60 are exposed.

As described above, the protective layer 54 has a non-formation region in which the protective layer 54 is not formed in a part of the interposed surfaces 58 and 60 on the main surface 56 side. This is to prevent the protective layer 54 from being scraped during grinding and polishing in step S60) and the first polishing step (step S70). When the protective layer 54 is ground or polished, since the protective layer 54 is formed of a material such as a resin, the resin that has become viscous due to a high temperature during grinding and polishing adheres to the main surface to be ground and polished. In addition to hindering grinding and polishing, the scraped resin adheres to the glass substrate, and the polishing progresses while the resin is sandwiched between the glass substrate and the polishing pad, thereby causing a defect such as polishing scratches. .
Therefore, the distance W ₁ between the end portions on both sides of the protective layer 54 in the thickness direction of the glass substrate 50 is made smaller than the thickness obtained by subtracting the target processing amount D from the thickness W ₀ of the glass substrate 50. In addition, a protective layer 54 is formed. The target processing amount D is a target processing amount of the main surface 56 in the main surface processing step including the grinding step using the fixed abrasive and the first polishing step, and is determined in advance. The target processing amount D is determined by grinding the glass substrate in consideration of variations such as the thickness of the glass substrate when it is produced by molding a glass blank, unevenness of the main surface, or deviation in the thickness of one glass substrate. By polishing, it is possible to efficiently determine the target main surface irregularities, plate thickness, plate thickness deviation or the like based on past knowledge. Therefore, the protective layer 54 is not ground or polished in the main surface processing step.
Thus, the protective layer 54 is provided on the outer peripheral side end face 52 of the glass substrate 50.

(F) Grinding process with fixed abrasive (step S60)
In the grinding process using the fixed abrasive grains, the main surface of the glass substrate is ground using a double-side grinding apparatus having a planetary gear mechanism. Specifically, with the protective layer 54 provided on the outer peripheral side end surface 52 of the glass substrate 50, the outer peripheral side end surface 52 of the glass substrate 50 is held in the holding hole provided in the holding member of the double-side grinding apparatus. However, the main surfaces on both sides of the glass substrate 50 are ground. Grinding with fixed abrasive grains is one of the main surface processing steps. The machining allowance by grinding is, for example, about several μm to 100 μm. The particle size of the fixed abrasive is, for example, about 10 μm. The double-sided grinding apparatus has a pair of upper and lower surface plates (upper surface plate and lower surface plate), and a glass substrate is sandwiched between the upper surface plate and the lower surface plate. And, by moving either the upper surface plate or the lower surface plate, or both, the glass substrate and each surface plate are moved relatively to grind both main surfaces of the glass substrate. Can do. FIG. 6 is a diagram showing an example of a double-side grinding apparatus.

  A double-side grinding apparatus 100 shown in FIG. 6 includes a lower surface plate 102, an upper surface plate 104, an internal gear 106, a carrier (holding member) 108, and a sun gear 112. The double-side grinding apparatus 100 sandwiches the internal gear 106 between the lower surface plate 102 and the upper surface plate 104 from the up and down direction. A plurality of carriers 108 are held in the internal gear 106 during grinding. In FIG. 6, four carriers 108 are held. A surface of a diamond sheet (not shown) bonded to the lower surface plate 102 and the upper surface plate 104 in a plane is a ground surface. That is, the glass substrate 50 is ground with fixed abrasive grains using a diamond sheet.

A plurality of glass substrates 50 to be ground are arranged and held in circular holding holes provided in each carrier 108 as shown in FIG. The outer diameter (diameter) of the glass substrate 50 is about 500 μm smaller than the inner diameter (diameter) of the holding hole of each carrier 108. For this reason, even if the protective layer 54 is provided on the outer peripheral side end face 52 of the glass substrate, a gap of about several hundred μm still remains between the glass substrate 50 held in the holding hole and the holding hole. Such a gap is a gap necessary for grinding the glass substrate 50. Without this gap, the glass substrate does not have a degree of freedom of rotation in the holding hole, so that desired grinding cannot be performed.
However, because of this gap, the outer peripheral side end surface 52 of the glass substrate 50 contacts the inner peripheral side wall of the holding hole during grinding. By this contact, when the protective layer 54 is not provided on the outer peripheral side end face 52, it is easy to make a scratch that becomes the starting position of the progress of cracks on the outer peripheral side end face. Further, the abrasive grains for grinding adhere to the outer peripheral side end surface, and are liable to cause fine particles (particles). For this reason, the protective layer 54 is provided on the outer peripheral side end face 52 as described above. In addition, since the protective layer 54 is only provided on the side wall surface 62 and part of the interposition surfaces 58 and 60, the protective layer 54 is not polished.

Further, since the protective layer 54 is not in contact with the diamond sheet during grinding and is not ground, a part of the protective layer 54 is not broken during grinding. Accordingly, the debris of the protective layer 54 does not enter between the diamond sheet and the main surface of the glass substrate 50, and the glass substrate 50 is not detached from the carrier 108 during grinding, and the grinding process can be performed stably. Can do. That is, the glass substrate can be prevented from being damaged due to the separation of the protective layer 54 from the carrier 108 of the glass substrate 50 during grinding.
The glass substrate 50 thus ground is polished so that the surface unevenness becomes smaller. In the example shown in FIG. 6, each of the carriers 108 has a configuration in which only one glass substrate 50 is held. However, each of the carriers 108 has a plurality of carriers so that a plurality of glass substrates 50 can be held. A holding hole may be provided.

(G) First polishing step (step S70)
Next, the first polishing is performed on the main surface of the ground glass substrate 50. The first polishing is one of the main surface processing steps. Specifically, with the protective layer 54 provided on the outer peripheral side end surface 52 of the glass substrate 50, the outer peripheral side end surface 52 of the glass substrate 50 is held in a holding hole provided in the holding member of the double-side polishing apparatus. However, the main surfaces on both sides of the glass substrate 50 are polished. The machining allowance by the first polishing is, for example, about several μm to 50 μm. The purpose of the first polishing is, for example, to remove scratches or distortions remaining on the main surface when grinding with fixed abrasive grains, or to adjust minute surface irregularities (microwaveness, roughness). The machining allowance by the first polishing is, for example, about several μm to 50 μm.

  In the first polishing step, the glass substrate 50 is polished while applying a polishing slurry using a double-side polishing apparatus having the same configuration as the double-side grinding apparatus 100 used for grinding with fixed abrasive grains (step S60). In the first polishing step, a polishing slurry containing loose abrasive grains is used instead of fixed abrasive grains, unlike the grinding with fixed abrasive grains. As the free abrasive grains used in the first polishing, for example, cerium oxide abrasive grains or zirconia abrasive grains (particle size: diameter of about 1 to 2 μm) is used. Similarly to the double-side grinding apparatus 100, the double-side polishing apparatus also holds the glass substrate 50 between a pair of upper and lower surface plates. An annular flat polishing pad (for example, a resin polisher) is attached to the upper surface of the lower surface plate and the bottom surface of the upper surface plate as a whole. Then, the main surfaces of the glass substrate 50 are polished by relatively moving the glass substrate 50 and the respective surface plates by moving either or both of the upper surface plate and the lower surface plate. . Also in the double-side polishing apparatus, there is a gap of about several hundred μm between the glass substrate 50 held in the holding hole and the holding hole. Due to this gap, the outer peripheral side end surface 52 of the glass substrate 50 contacts the side wall of the inner peripheral portion of the holding hole during the first polishing. However, since the protective layer 54 is provided on the outer peripheral side end face 52 of the glass substrate 50, the scratch that becomes the starting position of the progress of the crack hardly occurs. Further, the loose abrasive grains are prevented from adhering to the outer peripheral side end face 52 and causing particles. In particular, when zirconia abrasive grains having a high rigidity and sharp shape are used as the loose abrasive grains, the zirconia abrasive grains are likely to pierce the outer peripheral side end face 52 without the protective layer 54. In this respect, when using zirconia abrasive grains, the effect of providing the protective layer 54 on the outer peripheral side end face 52 is great.

(H) Protective layer removal step (step S80)
Next, the protective layer 54 is removed from the glass substrate 50 after the first polishing. The method for removing the protective layer 54 varies depending on the type of the protective layer 54 used. For example, when the protective layer 54 is a material in which a thermosetting resin adhesive is mixed with a thermosetting resin adhesive, the protective layer 54 and the outer peripheral side end face 52 are heated by heating the protective layer 54. The protective layer 54 can be removed by weakening the adhesive force between the two. The heating method is performed, for example, by immersing in water at a constant temperature. Alternatively, the protective layer 54 can be removed from the outer peripheral end surface 52 by weakening the adhesive force by blowing hot air. Further, when the protective layer 54 is a material in which a thermally expandable microcapsule is mixed in a thermoplastic resin adhesive, a thermosetting resin adhesive, or the like, by heating the protective layer 54, The protective layer 54 can be easily removed from the outer peripheral side end face 52 by expanding the microcapsule. Further, depending on the material used for the protective layer 54, the protective layer 54 can be removed from the outer peripheral end face 52 by applying light or electromagnetic waves.

(I) Chemical strengthening process (step S90)
Next, the glass substrate 50 from which the protective layer 54 has been removed is chemically strengthened. As the chemical strengthening solution, for example, a mixed solution of potassium nitrate (60% by weight) and sodium sulfate (40% by weight) can be used. In the chemical strengthening step, the chemical strengthening solution is heated to, for example, 300 ° C. to 400 ° C., and after the cleaned glass substrate 50 is preheated to, for example, 200 ° C. to 300 ° C., the glass substrate 50 is placed in the chemical strengthening solution, for example, 3 hours to Immerse for 4 hours.
By immersing the glass substrate 50 in the chemical strengthening solution, lithium ions and sodium ions in the glass composition on the surface layer of the glass substrate 50 are converted into sodium ions and potassium ions having a relatively large ion radius in the chemical strengthening solution, respectively. By the replacement, a compressive stress layer is formed on the surface layer portion, and the glass substrate 50 is strengthened.
Note that the chemically strengthened glass substrate 50 is cleaned. For example, after washing with sulfuric acid, it is washed with pure water or the like.

(J) Second polishing (final polishing) step (step S100)
Next, 2nd grinding | polishing is given to the glass substrate 50 after a chemical strengthening process. The second polishing step aims at mirror polishing of the main surface. Also in the second polishing, a double-side polishing apparatus having the same configuration as the double-side polishing apparatus used for the first polishing is used. The machining allowance by the second polishing is, for example, about 1 μm. The second polishing step is different from the first polishing step in that the type and particle size of the free abrasive grains are different and the hardness of the resin polisher is different.

As the free abrasive grains used in the second polishing step, for example, fine particles (particle size: diameter of about 10 to 50 nm) such as colloidal silica made turbid in slurry are used. The polished glass substrate 50 is washed with a neutral detergent, pure water, IPA, or the like, whereby the magnetic disk glass substrate 50 is obtained.
The second polishing step is not necessarily an essential step, but it is preferable that the second polishing step is performed in that the level of surface irregularities on the main surface of the glass substrate 50 can be further improved. By performing the second polishing step, the roughness (Ra) of the main surface can be set to 0.1 nm or less and the micro waveness (MW-Rq) of the main surface can be set to 0.1 nm or less. In the second polishing, since the protective layer 54 is not provided on the outer peripheral side end face 52, the outer peripheral side end face 52 is easily damaged during the polishing, or the abrasive grains are likely to be attached as deposits. Therefore, in order to suppress scratches on the outer peripheral end face 52 and adhesion of abrasive grains to the outer peripheral end face 52, it is preferable to perform the second polishing before removing the protective layer. However, in the second polishing, abrasive grains having a very small particle size are used. Therefore, the degree of scratches formed on the outer peripheral side end surface 52 by the second polishing and the amount of deposits adhering to the outer peripheral side end surface 52 are determined in steps. It is smaller than the grinding in S60 or the first polishing in Step S70. For this reason, the influence which it has on the suppression of the fall of the mechanical strength of the glass substrate for magnetic discs and the formation of the foreign material on the main surface of the glass substrate for magnetic discs is small.

  In this way, the second polished glass substrate 50 is washed with water to become a magnetic disk glass substrate.

In the present embodiment, the main surface processing (grinding and first polishing) is performed on the main surfaces on both sides of the glass substrate 50 in a state where the protective layer 54 is provided on the outer peripheral side end face 52 of the glass substrate 50, and then the glass substrate 50. Since the protective layer 54 is removed from the main surface of the glass substrate, abrasive grains for polishing or grinding are not attached to the outer peripheral end surface 52, and foreign matter is hardly formed on the main surface of the magnetic disk glass substrate. In the present embodiment, since the protective layer 54 is provided on the outer peripheral side end surface 52, it is possible to suppress the occurrence of scratches that cause cracks on the outer peripheral side end surface 52 of the glass substrate 50, and the magnetic disk glass. A decrease in the mechanical strength of the substrate can be prevented. Further, in the present embodiment, since the protective layer 54 is provided on the outer peripheral side end face 52, foreign matters such as fine particles are hardly formed on the main surface of the magnetic disk glass substrate.
Further, due to the chamfering of the outer peripheral side end face 52 of the glass substrate 50, a part of each of the interposed surfaces 58 and 60 on the main surface side is a region where the protective layer 54 is not formed. For this reason, the protective layer 54 is not ground and polished in the main surface processing such as the grinding step (step S60) and the first polishing step (step S70). Since the protective layer 54 is not ground and polished, the processing accuracy of the grinding and polishing of the glass substrate 50 can be maintained. Further, the target processing amount D of the main surface in the main surface processing step is determined in advance. The distance between both ends of the protective layer 54 in the thickness direction of the glass substrate 50 is smaller than the thickness obtained by subtracting the target processing amount D from the thickness of the glass substrate 50. For this reason, the protective layer 54 is not reliably ground and polished.

  Further, since the protective layer 54 is provided on the outer peripheral side end surface 52 after polishing the outer peripheral side end surface 52 of the glass substrate 50 and before main surface processing, the protective layer 54 is formed in a state where the surface irregularities of the outer peripheral side end surface 52 are small. Provided. For this reason, the high-quality outer peripheral end face 52 can be maintained even after the main surface processing. As a general technique, it is expected that a high-quality end face can be obtained by performing end face polishing after main surface processing. However, such a method is not preferable because scratches are generated on the main surface when a laminated body is formed by laminating glass substrates for end face polishing.

  In addition, by providing the protective layer 54 on the outer periphery of the laminate obtained by laminating a plurality of glass substrates, the protective layer 54 is provided on the outer peripheral side end face 52 of each of the plurality of glass substrates of the laminate at a time. Can be.

  In the formation of the protective layer 54, the protective layer 54 is provided on the outer peripheral side end surface 52 using a roll coater. Therefore, the protective layer 54 having a uniform thickness can be provided on the periphery of the outer peripheral side end surface 52. When grinding or polishing by holding the glass substrate 50 in the holding hole of the carrier in the double-side grinding apparatus and double-side polishing apparatus, the protective layer 54 is held by providing the protective layer 54 with a uniform thickness on the outer peripheral side end face 52. It is possible to translate and rotate by evenly contacting the inner peripheral side wall of the hole without being biased. For this reason, the quality unevenness | corrugation of the surface unevenness | corrugation in a glass substrate surface can be suppressed, and the grinding | polishing and grinding | polishing of a main surface can be performed with high precision.

  Since removal of the protective layer 54 is performed before chemical strengthening, efficient chemical strengthening can be performed on the outer peripheral side end face 52.

  The protective layer 54 is a layer made of a resin material that can be removed from the outer peripheral side end face 52 by applying, for example, heat, light, or electromagnetic waves. For this reason, the protective layer 54 can be easily removed from the glass substrate 50.

  As mentioned above, although the manufacturing method of the glass substrate for magnetic discs of this invention was demonstrated in detail, this invention is not limited to the said embodiment and Example, In the range which does not deviate from the main point of this invention, various improvement and a change are carried out. Of course.

DESCRIPTION OF SYMBOLS 1 Magnetic disk 2 Glass substrate 3A, 3B Magnetic layer 10 Laminate body 12 Spray apparatus 14, 16, 28 Roller 18 Conveyor belt 20 Doctor blade 22 Protective agent 24 Film 26 Roll coater 30 Light source 32 Ultraviolet ray 50 Glass substrate 52 Outer peripheral side end face 54 Protection Layer 56 Main surface 58, 60 Intervening surface 62 Side wall surface 100 Double-side grinding device 102 Lower surface plate 104 Upper surface plate 106 Internal gear 108 Carrier 112 Sun gear

Claims (8)

A method of manufacturing a glass substrate for a magnetic disk having a pair of main surfaces, an inner peripheral side end surface, and an outer peripheral side end surface,
The magnetic disk glass substrate while holding the outer peripheral side end surface of the magnetic disk glass substrate in a holding hole provided in a holding member in a state where a protective layer is provided on the outer peripheral side end surface of the magnetic disk glass substrate A main surface processing step of grinding or polishing the pair of main surfaces of
After the main surface processing step, a removal step of removing the protective layer from the magnetic disk glass substrate,
The manufacturing method of the glass substrate for magnetic discs characterized by the above-mentioned. The outer peripheral side end surface is provided between the pair of interposed surfaces inclined with respect to the main surface and connected to the main surface, and extends so as to be orthogonal to the main surface. An existing side wall surface,
2. The method of manufacturing a glass substrate for a magnetic disk according to claim 1, wherein a part of each of the interposed surfaces on the main surface side is a non-formation region of the protective layer. The target processing amount of the main surface in the main surface processing step is predetermined,
The distance between both ends of the protective layer in the thickness direction of the magnetic disk glass substrate is smaller than a thickness obtained by subtracting the target processing amount from the thickness of the magnetic disk glass substrate. 2. A method for producing a glass substrate for a magnetic disk according to 2. Further, an end surface polishing step for polishing the outer peripheral side end surface of the magnetic disk glass substrate,
4. The magnetic disk according to claim 1, further comprising: a protective layer forming step of providing the protective layer on the outer peripheral side end surface after the end surface polishing step and before the main surface processing step. A method for producing a glass substrate.   In addition to the magnetic disk glass substrate, by performing the protective layer forming process on a laminated body obtained by laminating at least one magnetic disk glass substrate, a plurality of magnetic disks of the laminated body The manufacturing method of the glass substrate for magnetic discs of Claim 4 with which the said protective layer is provided in the said outer peripheral side end surface of each glass substrate.   In the protective layer forming step, a film of a protective agent serving as the protective layer is formed on the surface of the transfer substrate, and the film is transferred from the transfer substrate to the outer peripheral side end surface of the magnetic disk glass substrate. The manufacturing method of the glass substrate for magnetic discs of Claim 4 or 5 with which the said protective layer is provided in a side end surface. Furthermore, after the main surface processing step, including a chemical strengthening step of chemically strengthening the magnetic disk glass substrate,
The said removal process is a manufacturing method of the glass substrate for magnetic discs of any one of Claims 1-6 performed before the said chemical strengthening process.   8. The glass substrate for a magnetic disk according to claim 1, wherein the protective layer is a layer made of a resin material that can be removed from the end face on the outer peripheral side by applying heat, light, or electromagnetic waves. Manufacturing method.

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