JP2014071931A - 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 that is capable of enhancing stability in grinding or polishing processing while preventing mechanical strength of a glass substrate from lowering due to damage on an outer periphery end surface of the glass substrate for a magnetic disk, when manufacturing the glass substrate for a magnetic disk.SOLUTION: The method for manufacturing a glass substrate for a magnetic disk is a method for manufacturing a glass substrate for a magnetic disk having a pair of main surfaces, an inner periphery end surface, and an outer periphery end surface that includes a side wall surface and a pair of intermediate surfaces each of which is disposed between the pair of main surfaces and the side wall surface and is tilted with respect to the pair of main surfaces. The method comprises: a protective layer forming step of forming a protective layer by applying a protective agent to the outer periphery end surface so that a portion of a side of the main surface in each of the pair of intermediate surfaces is made to be a non-forming region in the protective layer; and a main surface processing step of grinding or polishing the pair of main surfaces.

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.
A glass substrate used for a magnetic disk is preferably used because the material itself has a higher hardness, flatness and smoothness than an aluminum substrate, and can meet the demand for higher density magnetic recording. Yes. However, since the glass substrate is made of a brittle material, damage during manufacture and use is one of the problems.

One of the factors governing the decrease in the mechanical strength of the magnetic disk glass substrate is scratches present on the inner peripheral side end surface and the outer peripheral side end surface of the glass substrate. These end faces of the glass substrate are generally polished to such an extent that scratches are removed, and a high-accuracy processed surface, unlike the fact that the main surface is required to have a very high level of flatness and smoothness. The polishing process is not performed so that The reason for this is that the end surface of the glass substrate is a rough surface because it is a cut surface cut out from the glass plate, is a surface that is not directly related to magnetic recording, and is also highly accurate because it is a curved surface. If the polishing process is performed, the cost is extremely high.
As a method for reducing scratches on the end face of a glass substrate and finishing it to a high-quality processed surface, multistage processing is known in which the end surface is polished stepwise using finely-grained abrasive grains. However, such multi-stage processing has a fatal problem that it causes a significant deterioration in productivity and cost of the glass substrate.

  Under such circumstances, as a method for preventing a decrease in mechanical strength due to scratches existing on the end face of the glass substrate, it is known to form a protective layer by applying a protective agent to the inner peripheral side end face of the glass substrate. (Patent Document 1).

JP 2005-203080 A

  The technique disclosed in Patent Document 1 is to efficiently coat the inner peripheral side end surface of the glass substrate in a state where the glass substrate is laminated, using a protective agent, but the resin is applied to the outer peripheral side end surface of the glass substrate. It does not mention efficient application. When resin is applied to the outer peripheral side end face of the glass substrate by the coating method disclosed in Patent Document 1, the entire outer peripheral side end face in the thickness direction of the glass substrate is applied. For this reason, if surface polishing is performed later, the resin on both ends of the outer peripheral side end surface in the thickness direction of the glass substrate is scraped off, and the scraped resin causes scratches and contamination on the main surface of the glass substrate. Can cause

  In addition to this, during grinding or polishing, the resin scraped from the outer end face is peeled off during processing, and a part of the resin is sandwiched between a pair of surface plates and processed on the main surface of the glass substrate or on the carrier. There is a risk of entering the surface. As a result, a gap is generated between the polishing pad or 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 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.

On the other hand, when the outer peripheral side end surface of the glass substrate is not sufficiently protected in the manufacturing process of the glass substrate, the following inconvenience occurs. The outer peripheral side end surface of the glass substrate has a higher frequency of scratches in the glass substrate manufacturing process than the inner peripheral side end surface, and adheres to substances that cause contamination of the main surface, such as abrasives used during surface polishing. It's easy to do.
Furthermore, the outer peripheral side end surface of the glass substrate is likely to be damaged when the inside of the storage container and the outer peripheral portion of the glass substrate come into contact with each other when the storage container for the glass substrate is put in and out at the time of manufacture. Further, it is known that scratches present on the outer peripheral side end face of the glass substrate become a generation source of particles (fine particles). If particles generated from the outer peripheral side end surface adhere to the main surface of the glass substrate and a convex portion is formed on the surface of the magnetic disk, a thermal asperity failure may occur. The thermal asperity failure is a failure caused by a convex portion formed on the surface of the magnetic disk causing adiabatic compression and adiabatic expansion of air in the vicinity of the head due to high-speed rotation of the magnetic disk, thereby causing the magnetic head to generate heat. .
Furthermore, even if there is no scratch on the outer peripheral side end surface of the glass substrate, if the abrasive adheres to the outer peripheral side end surface of the glass substrate in the surface polishing step, the abrasive is peeled off from the outer peripheral side end surface in the subsequent step, and the glass substrate Adhering to the main surface of the magnetic disk leads to defective and low quality magnetic disks.

  Therefore, the present invention provides a grinding or polishing process while avoiding a decrease in mechanical strength of the glass substrate due to scratches present on the outer peripheral side end surface of the magnetic disk glass substrate when manufacturing the magnetic disk glass substrate. An object of the present invention is to provide a method for producing a glass substrate for a magnetic disk capable of improving the stability of the magnetic disk.

One aspect of the present invention is a method of manufacturing a glass substrate for a magnetic disk. The method is
A pair of main surfaces, an inner peripheral side end surface, and an outer peripheral side end surface, the outer peripheral side end surface extending side by side perpendicular to the pair of main surfaces; and the pair of main surfaces and the A method of manufacturing a glass substrate for a magnetic disk, comprising a pair of interposed surfaces that are respectively disposed between side wall surfaces and are inclined with respect to the pair of main surfaces,
A protective layer forming step of providing a protective layer by applying a protective agent so that a part of the main surface side of each of the pair of interposed surfaces becomes a non-formation region of the protective layer with respect to the outer peripheral side end surfaces;
A main surface processing step of grinding or polishing the pair of main surfaces of the magnetic disk glass substrate while holding the magnetic disk glass substrate provided with the protective layer in a holding hole provided in a holding member. And including.

As a preferred embodiment of the above method, the target processing amount of the main surface in the main surface processing step is predetermined,
The distance between the opposite ends of the protective layer in the thickness direction of the magnetic disk glass substrate is smaller than the thickness obtained by subtracting the target processing amount from the thickness of the magnetic disk glass substrate.

  As a preferred embodiment of the above method, in the protective layer forming step, before applying the protective agent to the outer peripheral side end surface, coating is performed so that the thickness of the protective agent applied to the outer peripheral side end surface is uniform. The thickness of the protective agent in the previous state is adjusted in advance.

  As a preferred embodiment of the above method, by performing the protective layer forming step on a laminate obtained by laminating at least one magnetic disk glass substrate in addition to the magnetic disk glass substrate, The said protective layer is provided in the said outer peripheral side end surface of each of the some glass substrate for magnetic discs.

  As a preferred embodiment of the above method, 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 base, and from the transfer base to the outer peripheral side end face of the magnetic disk glass substrate. The film of the protective agent is transferred, and the protective agent is applied to the outer peripheral side end face.

  As a preferred embodiment of the above method, the protective layer has a thickness of 10 to 200 μm.

As a preferred embodiment of the above method, further, a removal step of removing the protective layer from the magnetic disk glass substrate after the main surface processing step;
And a chemical strengthening step of chemically strengthening the magnetic disk glass substrate after the removing step.

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

  According to the above-described method for manufacturing a glass substrate for a magnetic disk, when the glass substrate for a magnetic disk is manufactured, the mechanical strength of the glass substrate is prevented from being reduced by scratches present on the outer peripheral end surface of the glass substrate for the magnetic disk. However, the stability of grinding or polishing can be improved.

(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. It is a figure explaining arrangement | positioning of the protective layer formed in the glass substrate for magnetic discs of this embodiment. (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 the main surface processing given to the glass substrate for magnetic discs of this embodiment.

  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. 3, 4A to 4C, and FIG. 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 S40 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. The glass substrate for magnetic disks has a pair of main surfaces, an inner peripheral side end surface, and an outer peripheral side end surface. The outer peripheral side end surfaces are disposed between the pair of main surfaces and the pair of main surfaces and the pair of main surfaces and the side wall surfaces, respectively, and are inclined with respect to the pair of main surfaces. And an intervening surface. 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-like glass, a plate-shaped glass blank having a predetermined shape that is the basis of the glass substrate for magnetic disk 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, the scribe means two concentric circles (inner concentric circles and inner concentric circles) by a scriber made of super steel alloy or diamond particles on the surface of the glass blank in order to make the molded glass blank into a ring-shaped glass substrate of a predetermined size. It means that an outer concentric circle-like cutting line (linear flaw) is provided. 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, JP 2012-1601 A) can be mentioned. As an example of removing the protective layer by applying electromagnetic waves (high frequency electromagnetic waves), a method by induction heating (Japanese Patent Laid-Open No. 2007-314711) can be given.

The outer peripheral side end surface of the glass substrate is chamfered in the shape processing step (step S30). FIG. 3 is a diagram for explaining the arrangement of protective layers formed on the glass substrate of the present embodiment.
As shown in FIG. 3, a protective layer 54 formed by applying the protective agent 22 is provided on the outer peripheral side end face 52 of the glass substrate 50. The glass substrate 50 is chamfered on the outer peripheral side end surface 52 in the end surface polishing step (step S <b> 40), and the outer peripheral side end surface 52 has interposition surfaces 58 and 60 and side wall surfaces 62. The intervening surfaces 58 and 60 are inclined with respect to the main surface 56 at an inclination angle greater than 0 degree and less than 90 degrees, for example, at an inclination angle of 20 to 80 degrees, and a pair of chamfered surfaces connected to the main surface. It is. 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, the scraped resin adheres to the main surface of the glass substrate. In this state, the ground or polished surface may cause scratches or remain on the main surface of the glass substrate. This causes problems such as contamination of the glass substrate. When the resin adheres to the main surface of the glass substrate and is held by a holding member of a double-sided grinding device, which will be described later, in the subsequent grinding step or first polishing step, the glass substrate rises from the holding hole of the holding member and crashes. There is a risk of it happening.
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.

  The thickness of the protective layer is preferably 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. When the thickness of the protective layer is 1 μm or more, the outer peripheral side end face can be sufficiently protected, and the glass substrate has a lower mechanical strength and particle generation due to scratches present on the outer peripheral side end face. It can be surely suppressed. Moreover, when the thickness of the protective layer is 200 μm or less, when grinding the main surface of the glass substrate using the double-side grinding device in step S60, the inside of the holding hole provided in the holding member of the double-side grinding device; A sufficient gap with the glass substrate held in the holding hole can be secured.

  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. In this case, for example, as shown in FIG. 4A, the protective layer is formed by laminating a plurality of glass substrates and holding the laminated body 10 with a laminated body holder (not shown) from the plurality of spray devices 12. It is carried out by spray application of a liquid protective agent.

  Alternatively, in the form as shown in FIG. 4B, that is, before applying the protective agent to the outer peripheral end surface, the thickness of the protective agent applied to the outer peripheral end surface is uniform. A protective layer can be provided on each glass substrate of the laminate 10 by adjusting the thickness of the protective agent in advance. Specifically, a film 24 having a uniform and constant thickness of the liquid protective agent 22 is formed using the doctor blade 20 on the transport belt 18 transported by the rotation of the rollers 14 and 16 by the doctor blade method. . The laminated body 10 is rotated with a certain distance from the conveyor belt 18 and is brought into contact with the film 24, whereby the laminated body 10 has a constant thickness on the periphery of the outer peripheral side end surface of each glass substrate. The protective layer can be provided continuously. In this way, by adjusting the thickness of the protective agent to be applied in advance by the doctor blade method, a portion that is not applied appears on the outer peripheral side end surface of the glass substrate, or it is excessively applied and a non-forming region is not secured. Can be avoided. 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, after the thickness of the protective agent applied to the outer peripheral side end surface is adjusted to be uniform using the doctor blade method as described above, that is, the doctor blade method described above, the protective layer becomes a protective layer. It is also possible to provide a protective layer on each glass substrate of the laminate 10 by forming a film of the agent on the surface of the transfer substrate and transferring the film of the protective agent from the transfer substrate to the outer peripheral side end surface of the glass substrate. . Specifically, a film 24 having a uniform and constant thickness of the liquid protective agent 22 is formed on the transport belt 18 transported by the rotation of the rollers 14 and 16 by using a doctor blade 20. From this film 24, a film 25 transferred onto the roll coater 26 is formed using a roll coater (transfer base material) 26, and the laminate 10 is rotated with a certain distance from the roll coater 26. While contacting the film 25, a protective layer having a certain thickness can be continuously provided on the periphery of the outer peripheral side end surface of the glass substrate. Thus, by adjusting the thickness of the protective agent in advance by the doctor blade method and providing the protective layer using the film 25 transferred to the roll coater 26, a more uniform thickness is provided on the outer peripheral side end surface of the glass substrate. A protective layer can be provided.

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 is laminated on the film 24 with a certain distance from the roller 28. 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. 5, 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. Also here, by adjusting the thickness of the protective agent in advance by the doctor blade method and using the roller 28 in combination, uneven application to the outer peripheral side end surface can be suppressed.
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) that is planarly bonded to the upper surface of the lower surface plate 102 and the bottom surface of the upper surface plate 104 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 end surface 52 of the glass substrate 50 contacts the side wall of the inner peripheral portion 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. Therefore, the debris of the protective layer 54 does not enter between the diamond sheet and the main surface of the glass substrate, and the glass substrate 50 is not detached from the carrier 108 being ground, and the grinding process can be performed stably. it can. That is, it is possible to avoid breakage of the glass substrate due to separation of the glass substrate 50 from the carrier 108 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 carrier 108 holds only one glass substrate 50, but each carrier 108 is provided with a plurality of holding holes so that a plurality of glass substrates 50 can be held. May be.

(G) First polishing step (step S70)
Next, 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 an essential step, but it is preferable to carry out the second polishing step 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 protective agent 22 is applied so that a part of the main surface side of each of the interposition surfaces 58 and 60 becomes a non-formation region of the protective layer 54 by chamfering the outer peripheral side end face 52 of the glass substrate 50. . Therefore, in the main surface processing such as the grinding process (step S60) and the first polishing process (step S70), the protective layer 54 is ground and polished, and the resin constituting the protective layer 54 is not scraped off. The resin does not cause scratches or contamination on the main surface of the glass substrate. Further, since the resin of the protective layer 54 removed during grinding or polishing is not peeled off, it does not enter on the main surface of the glass substrate processed between the pair of surface plates or on the surface of the carrier. , Stable grinding or polishing can be performed.
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 generation of scratches that cause cracks on the outer peripheral side end surface 52 of the glass substrate 50, and the magnetic disk The mechanical strength of the glass substrate can be prevented from decreasing. Moreover, since the protective layer 54 is provided on the outer peripheral side end face 52 of the glass substrate 50 in this way, even if the main surface processing (grinding and first polishing) is performed on the main surfaces on both sides of the glass substrate 50, the glass substrate During the processing of the main surface, abrasive grains for polishing or grinding are not attached to the outer peripheral side end face 52, and it is difficult for foreign matter to be formed on the main surface of the magnetic disk glass substrate. In particular, the outer peripheral side end surface of the glass substrate is more frequently damaged than the inner peripheral side end surface during the production of the glass substrate, and a substance that becomes a source of contamination of the main surface is likely to adhere to the protective layer. It is effective that the outer peripheral side end face is protected by 24.

  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.

  Furthermore, in the protective layer forming step, before applying the protective agent to the outer peripheral side end surface of the glass substrate, the thickness of the protective agent applied to the outer peripheral side end surface is adjusted by the doctor blade method so as to be uniform. It is possible to avoid such a disadvantage that a portion that is not applied appears on the end face or that a non-formed region is not sufficiently secured due to excessive application.

  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, quality variation within the glass substrate surface can be suppressed, and the main surface can be ground and polished with high accuracy.

  After performing the main surface processing (grinding and first polishing) on the main surfaces on both sides of the glass substrate 50, the protective layer 54 is removed from the glass substrate 50 before the chemical strengthening. In addition, since the protective layer dissolves in the chemical strengthening liquid, it is possible to avoid such disadvantages that the ion exchange of the chemical strengthening liquid does not proceed and the life of the chemical strengthening liquid is shortened.

  The protective layer 54 is a layer made of a resin material that can be removed from the outer peripheral 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 pair of main surfaces, an inner peripheral side end surface, and an outer peripheral side end surface, the outer peripheral side end surface extending side by side perpendicular to the pair of main surfaces; and the pair of main surfaces and the A method of manufacturing a glass substrate for a magnetic disk, comprising a pair of interposed surfaces that are respectively disposed between side wall surfaces and are inclined with respect to the pair of main surfaces,
A protective layer forming step of providing a protective layer by applying a protective agent so that a part of the main surface side of each of the pair of interposed surfaces becomes a non-formation region of the protective layer with respect to the outer peripheral side end surfaces;
A main surface processing step of grinding or polishing the pair of main surfaces of the magnetic disk glass substrate while holding the magnetic disk glass substrate provided with the protective layer in a holding hole provided in a holding member. And a method for producing a glass substrate for a magnetic disk. 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 1.   In the protective layer forming step, before applying the protective agent to the outer peripheral side end surface, the protective agent in a state before application is applied so that the thickness of the protective agent applied to the outer peripheral side end surface is uniform. The manufacturing method of the glass substrate for magnetic discs of Claim 1 or 2 which adjusts thickness beforehand.   In addition to the magnetic disk glass substrate, by performing the protective layer forming step on a laminate obtained by laminating at least one magnetic disk glass substrate, a plurality of magnetic disk glass substrates are obtained. The manufacturing method of the glass substrate for magnetic discs of any one of Claims 1-3 with which the said protective layer is provided in each said outer peripheral side end surface.   In the protective layer forming step, a protective agent film serving as the protective layer is formed on the surface of the transfer substrate, and the protective agent film is transferred from the transfer substrate to the outer peripheral end surface of the magnetic disk glass substrate. The manufacturing method of the glass substrate for magnetic discs of any one of Claims 1-4 which apply | coats the said protective agent to the said outer peripheral side end surface.   The method of manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the protective layer has a thickness of 1 to 200 μm. Further, 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 of any one of Claims 1-6 including the chemical strengthening process of chemically strengthening the said glass substrate for magnetic discs after the said removal 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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