JP2012216255A - 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 using a new processing method without using a grinding stone for the processing of the end part of the glass substrate.SOLUTION: The method for manufacturing a glass substrate for a magnetic disk includes a processing step for processing an outer peripheral end of an annular glass substrate in which the glass substrate is processed while rotating around the center axis so as to remove a part of the outer peripheral end of the glass substrate by injecting a blast material against the outer peripheral end from the outside of the glass substrate.

Description

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

  2. Description of the Related Art Today, a personal computer, a DVD (Digital Versatile Disc) recording device, or the like has a built-in hard disk device (HDD: Hard Disk Drive) for data recording. In particular, in a hard disk device used in a portable computer such as a notebook personal computer, a magnetic disk in which a magnetic layer is provided on a glass substrate is used, and the magnetic head slightly floats above the surface of the magnetic disk. Magnetic recording information is recorded on or read from the magnetic layer by a (DFH (Dynamic Flying Height) head). As a substrate for this magnetic disk, a glass substrate is preferably used because it has a property that it is less likely to be plastically deformed than a metal substrate (aluminum substrate) or the like.

  The magnetic head includes a magnetoresistive element, for example, and may cause a thermal asperity failure as a failure inherent in such a magnetic head. Thermal asperity failure means that when a magnetic head passes over the main surface of a minute uneven surface of a magnetic disk while flying, the magnetoresistive element is heated by adiabatic compression or contact of air, causing a read error. It is an obstacle. For this reason, in order to avoid thermal asperity failure, the substrate surface roughness of the magnetic disk and the micro-waveness (hereinafter collectively referred to as “surface irregularities” as appropriate) are prepared at a favorable level.

  In addition to the level of surface irregularities on the main surface of the magnetic disk, strict accuracy control is required for the inner diameter dimensional error in the circular hole provided in the center of the magnetic disk. This is because the dimensional error of the inner peripheral end surface of the magnetic disk directly affects the installation accuracy when the magnetic disk is fitted to the HDD spindle motor. If the inner diameter error of the magnetic disk is large, when the magnetic disk is mounted on the HDD and operated, the magnetic disk will run out of rotation, making it difficult to position the HDD head at an appropriate position on the magnetic disk. As a result, data recording / reproduction may not be possible.

  Also, when manufacturing a glass substrate for magnetic disk, chamfering (chambering) is performed on the outer peripheral end (outer peripheral end), so that it is interposed between the main surface and the side wall perpendicular to the main surface. A chamfered portion is formed. The chamfering is performed because not only is it dangerous when the outer peripheral end portion is in an edged state (that is, a state where the corners are sharp), but also a crack or the like is likely to occur, and the mechanical strength is lowered. After chamfering, both the side wall portion and the chamfered portion are mirror-polished at the outer peripheral end portion. If scratches (cracks, chips, etc.) remain on the side wall or chamfered part without sufficient polishing, particles are trapped in the scratches, and the trapped particles are deposited on the main surface of the glass substrate during a later process. This is because they may adhere and cause thermal asperity failure.

  The chamfering method for the outer peripheral edge of the glass substrate for magnetic disk is disclosed in, for example, Patent Documents 1 and 2 below. According to these patent documents, conventionally, the chamfering uses an outer diameter processing grindstone such as a diamond grindstone provided with a predetermined pattern of processing grooves, and relatively rotates the outer diameter processing grindstone and the glass substrate. Process the outer edge. At this time, the processing is performed while supplying a grinding liquid obtained by adding a rust inhibitor or the like to water to the processing portion of the glass substrate. Patent Document 1 discloses chamfering performed by a single wafer method using an outer diameter processing grindstone, that is, chamfering of each glass substrate. In Patent Document 2, a plurality of glass substrates are adhered and laminated with an adhesive, and chamfering is performed on the plurality of glass substrates in the laminated state using an outer diameter processing grindstone. It is disclosed to peel a plurality of glass substrates into individual glass substrates.

Japanese Patent Laid-Open No. 11-198012 JP 2000-52212 A

However, in the conventional chamfering of the outer peripheral end portion with respect to the glass substrate, relatively expensive equipment including a drive motor for rotating the outer diameter processing grindstone at a high speed (4000 to 20000 rpm in Patent Document 1) is required. At the same time, regular management of the grindstone by truing and dressing is necessary.
Moreover, in the conventional processing method using a grindstone, in order to obtain the target chamfer angle, it is difficult to adjust the grindstone groove shape, the groove pitch, and the positioning of the glass substrate and the grindstone. Further, the surface roughness (Rmax) of the outer peripheral end (side wall portion and chamfered portion) is relatively large, about 20 μm, and cracks generated on the surface of the outer peripheral end by processing become as deep as the surface roughness. Therefore, in the conventional processing method using a grindstone, not only the surface roughness is not good, but the machining allowance in the subsequent polishing step is large, and the productivity is poor.

In addition, as a result of the extremely low flying height due to the DFH head, the head flying failure has been caused by extremely fine foreign matter present on the main surface of the glass substrate. As a result of investigating this foreign matter, it was found that it was abrasive grains (such as colloidal silica) containing silicon dioxide used in the final polishing step. As a result of the investigation, these abrasive grains are those in which the abrasive grains used in the final polishing process are captured by scratches (cracks, chips, etc.) on the outer peripheral edge and adhere to the main surface in the subsequent process. I understood.
This is because a substance containing silicon dioxide, such as colloidal silica, has the property of being easily attached because the composition is similar to that of a glass substrate, and the grain size of the abrasive grains used in the final polishing step is as extremely small as 30 nm or less. As a result, even a slight scratch is captured. The reason why 30 nm or less abrasive grains have been used is that the surface roughness required for the main surface of the glass substrate has become smaller than before.

  Therefore, an object of this invention is to provide the manufacturing method of the glass substrate for magnetic discs using the new processing method which does not use a grindstone about the process of the edge part of a glass substrate.

  As a result of searching for a new processing method that does not use an outer diameter processing grindstone in view of the above-described problems, the inventors have a chamfered portion that is flat along the outer periphery at the outer peripheral end of the glass substrate for magnetic disk. Focusing on the fact that it is not always necessary, the inventors have devised processing the outer peripheral end by blasting by projecting a blast material onto the outer peripheral end. According to this blasting process, the edge of the glass substrate is rounded as a whole, and no chamfered portion is formed at the outer peripheral end portion. Since the strength does not decrease, there is no problem as a glass substrate for a magnetic disk.

  As described above, the present invention is a method for manufacturing a glass substrate for a magnetic disk having two opposing main surfaces and an end interposed between the main surfaces, and is a method for manufacturing at least one of the two main surfaces. A part of the edge part adjacent to the peripheral part of the surface is blasted to be processed into a desired edge shape.

  Further, the present invention is a method for manufacturing a glass substrate for a magnetic disk having an outer periphery processing step for processing an outer peripheral end portion of an annular glass substrate, and in the outer periphery processing step, the outer periphery of the glass substrate is formed from the outside of the glass substrate. The outer peripheral end of the glass substrate is processed into a desired shape by projecting a blast material toward the end.

  In the method for manufacturing a glass substrate for a magnetic disk, at least a part of an end portion of the glass substrate is processed into a round shape by blasting.

  In the method for manufacturing a glass substrate for a magnetic disk, a chamfered portion is formed in a part of the end portion by blasting.

  In the method for manufacturing a glass substrate for a magnetic disk, in the outer periphery processing step, the processing is performed by projecting a blast material onto a laminated body in which a plurality of glass substrates are stacked.

  According to the method for manufacturing a glass substrate for a magnetic disk of the present invention, since a grindstone is not used during processing of the outer peripheral end portion of the glass substrate, facilities for processing can be simplified. Further, the surface roughness of the outer peripheral end portion is lower than that in the case of using a grindstone, and cracks generated on the surface of the outer peripheral end portion are also shallower. Therefore, the machining allowance in the subsequent polishing step is reduced, and the productivity is improved.

The figure which shows the shape of the glass substrate for magnetic discs of embodiment. The figure which shows the structure of the laminated body of the glass substrate loaded into the outer periphery processing apparatus of embodiment. The side view which shows the structural example of the outer periphery processing apparatus of embodiment.

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

[Magnetic disk glass substrate]
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 the composition of the glass substrate for a magnetic disk of this embodiment is not limited, the glass substrate of this embodiment is preferably converted to an oxide standard and expressed in mol%, SiO ₂ is 50 to 75%, Al ₂ O ₃ 1 to 15%, at least one component selected from LiO ₂ , Na ₂ O and K ₂ O in total 5 to 35%, at least selected from MgO, CaO, SrO, BaO and ZnO 1 to 20% in total of one component, 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 Is an aluminosilicate glass having a composition having 0 to 10% in total.

  The glass substrate for a magnetic disk in the present embodiment is an annular thin glass substrate. Although the size of the glass substrate for magnetic disks is not ask | required, for example, it is suitable as a glass substrate for magnetic disks with a nominal diameter of 2.5 inches.

  FIG. 1 is a diagram showing the shape of a magnetic disk glass substrate according to the present embodiment, wherein (a) is a perspective view of the magnetic disk glass substrate, and (b) is a magnetic disk glass substrate near the outer peripheral edge. Cross sections are shown respectively. As shown in FIG. 1A, an inner hole 15 is provided in the magnetic disk glass substrate. In the case of a glass substrate for a magnetic disk having a diameter of 2.5 inches, the diameter of the inner hole 15 is, for example, 18 to 21 mm. In the glass substrate for a magnetic disk of the present embodiment, the main surface 10, the inner peripheral end portion, and the outer peripheral end portion are mirror-polished. As shown in FIG. 1B, the outer peripheral end 20 has a rounded shape extending from the front-side main surface 10 to the back-side main surface 10. The plate thickness T of the magnetic disk glass substrate is 1 mm or less, for example, about 0.2 to 0.8 mm.

[Method of manufacturing glass substrate for magnetic disk]
Hereinafter, the manufacturing method of the glass substrate for magnetic disks of this embodiment is demonstrated for every process. However, the order of each step may be changed as appropriate.

(1) Forming and lapping process of sheet glass For example, in the process of forming sheet glass by the float method, first, for example, molten glass having the above-described composition is continuously poured into a bath filled with molten metal such as tin. To obtain plate glass. 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, plate glass (glass substrate) having a predetermined shape, which 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 glass substrate obtained by the float process has a sufficiently high surface flatness.
For example, in the step of forming a sheet glass by a press molding method, a glass gob 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 mold and an opposing gob forming mold is used. Glass gob is press molded. More specifically, after a glass gob made of molten glass is supplied onto the lower mold, the lower surface of the upper mold cylinder and the upper surface of the lower mold cylinder are brought into contact with each other, and the upper mold and the upper mold mold are slid. A thin plate-like glass molding space is formed outside the moving surface and the sliding surface between the lower die and the lower die, and the upper die is lowered and press-molded. To rise. Thereby, the glass substrate used as the origin of the glass substrate for magnetic discs is shape | molded.
In addition, a glass substrate can be manufactured not only using the method mentioned above but well-known manufacturing methods, such as a downdraw method.

  Next, lapping using an alumina-based loose abrasive is performed on both main surfaces of the glass substrate cut into a predetermined shape, if necessary. Specifically, the lapping platen is pressed on both sides of the glass substrate from above and below, a grinding liquid (slurry) containing loose abrasive grains is supplied onto the main surface of the glass substrate, and these are moved relative to each other for lapping. I do. In addition, when the glass substrate is formed by the float process, the lapping process may be omitted because the accuracy of the roughness of the main surface after forming is high.

(2) Coring step Using a cylindrical diamond drill, an inner hole is formed in the center of the glass substrate to obtain an annular glass substrate.

(3) Chamfering process of inner peripheral end part After the coring process, a chamfering process of forming a chamfered part at the inner peripheral end part is performed. In the chamfering step, the inner peripheral end of the glass substrate is chamfered by, for example, a metal bond grindstone using diamond abrasive grains provided with a predetermined pattern of processing grooves. In this chamfering, a grinding stone is applied to the inner peripheral edge of the glass substrate, and processing is performed while supplying a coolant aqueous solution to a processing portion of the glass substrate. Note that the inner peripheral end portion may be processed by blasting in the same manner as the outer peripheral processing step described later.

(4) Peripheral processing step The outer peripheral processing step is a step of processing the outer peripheral end of the glass substrate to be rounded as shown in FIG. 1B by blasting the outer peripheral end of the glass substrate. It is. This outer peripheral processing step may be performed by a single-wafer method in which glass substrates are processed one by one, but in the following, a lamination method in which a plurality of glass substrates are laminated and a plurality of glass substrates in the laminated state are simultaneously processed. explain. This lamination method is effective in that the processing tact time can be shortened.

  First, as shown in FIG. 2, a laminated body in which a plurality of glass substrates are laminated is formed. FIG. 2 shows a cross section of a laminate of glass substrates. FIG. 2 shows a laminate L produced by applying or sticking the adhesive 100 between the glass substrates G. Here, the adhesive 100 may be anything as long as the glass substrates can be bonded or peeled off. For example, since the ultraviolet curable resin is easily solidified by irradiation with ultraviolet rays having a predetermined wavelength, the bonding operation is easy. Moreover, what can peel easily the glass substrate adhere | attached with warm water or the organic solvent as an ultraviolet curable resin is preferable. As the adhesive, in addition to the UV curable resin, wax, photo curable resin, visible light curable resin, or the like can be used. Since the wax is softened at a predetermined temperature to become a liquid and becomes a solid at normal temperature, the bonding / peeling operation is easy. A spacer may be attached instead of the adhesive. When a spacer is attached between the glass substrates G instead of the adhesive, a thin spacer made of a resin material, a fiber material, a rubber material, a metal material, or a ceramic material can be used. The thickness of the adhesive or the spacer is, for example, about 50 to 70 μm.

  As shown in FIG. 2, the glass substrate before the outer periphery processing step has an outer peripheral end portion of a side wall portion 210 perpendicular to the main surface 10 and an edge interposed between the main surface 10 and the side wall portion 210 on the front and back sides. Part 220. In this outer periphery processing step, the side wall part 210 and the edge part 220 are blasted, but the adhesive (or spacer) 100 is used as an edge part so as not to block the projection of the blast material onto the edge part 220. It is arranged on the inner peripheral side with respect to 220.

Next, a peripheral processing apparatus that performs blasting on the laminate L shown in FIG. 2 will be described with reference to FIG. FIG. 3 is a diagram showing an outline of the outer periphery processing apparatus of the present embodiment.
The outer peripheral machining apparatus shown in FIG. 3 includes an injection nozzle 70 and a rotation drive device 80.

  The rotation drive device 80 is a device that rotates the laminated body L of glass substrates at a predetermined number of rotations, and includes a mounting table 81, a rotation shaft 82, and a holder 83. The rotating shaft 82 is a cylindrical member having a diameter set according to the size of the inner hole of the glass substrate. When the stacked body L is loaded into the rotation driving device 80, the stacked body L is placed on the mounting table 81 while the inner hole of the stacked body L is inserted into the rotating shaft 82. The rotation drive device 80 rotates the rotary shaft 82 with a drive mechanism (not shown) in a state where the stacked body L is loaded, so that the stacked body L is held by the holder 83 around the central axis of the rotary shaft 82. It is rotated at a predetermined rotational speed. The rotation speed of the laminated body L is, for example, 20 to 300 rpm.

The jet nozzle 70 projects a blast material (projection material) having a predetermined jet pressure from the jet port 70 a toward the stack L while the stack L is rotating. At this time, the injection nozzle 70 is arranged so that the injection port 70a faces the outer peripheral end of each glass substrate constituting the laminate L from the outside of the laminate L. The distance from the injection port 70a of the injection nozzle 70 to the outer peripheral end of the laminate L is, for example, 50 to 200 mm, and the injection pressure of the blast material by the injection nozzle 70 is, for example, 0.3 to 0.8 MPa. The particle size of the blast material is preferably 40 to 10 μm, and the material of the blast material may be, for example, silicon carbide, alumina, zirconia, or garnet. The jetting time of the blast material is preferably 60 to 300 seconds.
In addition, in each glass substrate constituting the laminated body L, the processing force by the blast material decreases as the vertical position moves away from the injection port 70a (that is, the machining allowance by the blast material decreases), A drive mechanism for moving the injection nozzle 70 up and down in the stacking direction of the stacked body L may be provided so that the allowance is uniform for each glass substrate regardless of the position in the stacked body of the glass substrate.

  When the laminated body L is processed by the outer periphery processing apparatus shown in FIG. 2, the side wall portion 210 and the edge portion 220 constituting the outer peripheral end portion of each glass substrate constituting the laminated body L are blasted with substantially uniform pressure as a whole. Processed by the material. As a result, as shown in FIG.1 (b), the edge of the outer peripheral end part of the glass substrate after a process becomes round, and an outer peripheral end part becomes a rounded shape as a whole.

In this outer periphery processing step, a grindstone is not used when processing the outer peripheral end portion of the glass substrate, and therefore an apparatus for rotating the grindstone is unnecessary, and therefore, equipment for processing is simple. Further, since no grinding fluid is used in this outer periphery processing step, there is an advantage that it is not necessary to clean and dry the glass substrate before the next end face polishing step. In addition, the outer peripheral edge of the glass substrate after processing has a rounded shape (round edge shape) without a sharp portion like a conventional chamfer, and is damaged (cracked) in combination with the subsequent end surface polishing process. , Chips, etc.) are less likely to remain, so that the risk of the edge portion being chipped or the glass substrate being broken in the subsequent glass substrate processing step and film forming step can be reduced as compared with the conventional case. If the conventional processing method using a grindstone is used, it is difficult to adjust the groove shape of the grindstone, the pitch of the grindstone, the positioning of the glass substrate and the grindstone, and the outer peripheral end is rounded (set as a round edge). Is extremely difficult.
Further, in the conventional processing method using a grindstone, the surface roughness (Rmax) of the outer peripheral end portion (side wall portion and chamfered portion) is about 20 μm, whereas it is obtained by blast processing used in this outer peripheral processing step. The surface roughness (Rmax) of the outer peripheral edge is 10 μm or less, and the surface roughness can be reduced to half or less. Similarly to the surface roughness, the depth of cracks generated on the surface of the outer peripheral edge by processing is less than half of the conventional processing method in the blast processing used in the outer peripheral processing step. Therefore, according to the blasting process used in the outer peripheral processing step, the risk of the outer peripheral end portion being chipped or the glass substrate being broken can be reduced as compared with the conventional method, and the machining allowance in the subsequent end surface polishing step is conventional. It is also possible to increase productivity by lowering than that.

In addition, although the method of rounding the outer peripheral end by round blasting in the outer peripheral processing step (making it a round edge) has been described, the inner peripheral end or outer peripheral end of the glass substrate is processed into a desired end shape by blasting. You may make it do. In order to process into a desired end shape, the injection direction of the blast material viewed from the end of the glass substrate may be appropriately adjusted.
Moreover, in order to process into a desired end shape, a part of the side wall portion perpendicular to the main surface of the end portion of the glass substrate before processing is made of a member having mechanical strength that can withstand the projection of the blast material. By masking, the region projected by the blast material in the end portion of the glass substrate may be limited. In this case, since a part of the edge part adjacent to the peripheral part of at least one of the two main surfaces on the front side and the back side of the glass substrate is subjected to blasting, the edge part of the glass substrate after processing is Rather than being rounded as a whole over both main surfaces, an R-shaped chamfered portion is formed in which only a part of its end is rounded.

(5) End surface polishing step Next, the end surface of the glass substrate is polished in the laminated state.
In the end surface polishing, the inner peripheral end surface and the outer peripheral end surface of the glass substrate are mirror-finished by brush polishing. At this time, a slurry containing fine particles such as cerium oxide as free abrasive grains is used. By polishing the end face, removal of contamination such as dust, damage or scratches attached to the end face of the glass substrate can prevent the occurrence of thermal asperity and cause corrosion such as sodium and potassium. The occurrence of ion precipitation can be prevented.
The outer peripheral edge of the glass substrate is processed into a rounded shape as a whole by the outer peripheral processing step in the previous process, but in this process the tip of the polishing brush follows the rounded surface of the outer peripheral edge. Then, the rounded surface is mirror-polished by polishing. When the end surface polishing step is completed, the glass substrate laminate is separated into individual glass substrates.

(6) Grinding process with fixed abrasive grains In the grinding process with fixed abrasive grains, the main surface of the glass substrate is ground using a double-sided grinding device equipped with a planetary gear mechanism. The machining allowance by grinding is, for example, about several μm to 100 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.

(7) 1st grinding | polishing (main surface grinding | polishing) process Next, 1st grinding | polishing is given to the main surface of the ground glass substrate. The machining allowance by the first polishing is, for example, about several μm to 50 μm. The purpose of the first polishing is to remove scratches and distortions remaining on the main surface by grinding with fixed abrasive grains, and to adjust surface irregularities (microwaveness, roughness). In the first polishing step, polishing is performed using a double-side polishing apparatus having a structure similar to that in the grinding step while supplying a polishing liquid. The polishing agent contained in the polishing liquid is, for example, cerium oxide abrasive grains or zirconia abrasive grains.

In the first polishing step, the surface roughness of the main surface of the glass substrate is polished so that the roughness (Ra) is 0.5 nm or less and the micro waveness (MW-Rq) is 0.5 nm or less. Do. Here, the micro waveness can be expressed by an RMS (Rq) value calculated as a roughness of a wavelength band of 100 to 500 μm in an area of a radius of 14.0 to 31.5 mm on the entire main surface. It can measure using Model 4224 made from.
The roughness of the main surface is represented by the arithmetic average roughness Ra defined by JIS B0601: 2001. When the roughness is 0.006 μm or more and 200 μm or less, for example, the roughness is measured with a Mitutoyo Corporation roughness measuring machine SV-3100, It can be calculated by a method defined in JIS B0633: 2001. As a result, when the roughness is 0.03 μm or less, for example, it is measured with a scanning probe microscope (atomic force microscope; AFM) nanoscope manufactured by Japan Veeco, and calculated by the method defined in JIS R1683: 2007. it can. In the present application, the arithmetic average roughness Ra when measured at a resolution of 512 × 512 pixels in a 1 μm × 1 μm square measurement area can be used.

(8) Chemical Strengthening Step Next, the annular glass substrate after the first polishing 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 the cleaned glass substrate is preheated to, for example, 200 ° C. to 300 ° C., and then immersed in the chemical strengthening solution for, for example, 3 hours to 4 hours. To do.
By immersing the glass substrate in the chemical strengthening solution, the lithium ions and sodium ions on the surface layer of the glass substrate are respectively replaced with sodium ions and potassium ions having a relatively large ionic radius in the chemical strengthening solution. A compressive stress layer is formed on the glass substrate and the glass substrate is strengthened. Note that the chemically strengthened glass substrate is cleaned. For example, after washing with sulfuric acid, it is washed with pure water or the like.

(9) Second Polishing (Final Polishing) Step Next, second polishing is performed on the glass substrate that has been chemically strengthened and sufficiently cleaned. The machining allowance by the second polishing is, for example, about 1 μm. The second polishing is intended for mirror polishing of the main surface. In the second polishing, for example, the polishing apparatus used in the first polishing is used. At this time, the difference from the first polishing is 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, for example, fine particles (particle size: diameter of about 10 to 50 nm) such as colloidal silica made turbid in the slurry are used.
The polished glass substrate is washed with a neutral detergent, pure water, IPA or the like to obtain a glass substrate for a magnetic disk.
Although it is not always essential to carry out the second polishing step, it is preferred that the second polishing step is carried out in that the level of surface irregularities on the main surface of the glass substrate 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.

[Magnetic disk]
Through the above steps, a magnetic disk glass substrate is produced. Using this glass substrate for magnetic disk, a magnetic disk is obtained as follows.
A magnetic disk has a configuration in which, for example, at least an adhesion layer, an underlayer, a magnetic layer (magnetic recording layer), a protective layer, and a lubricating layer are laminated on the main surface of a glass substrate in order from the side closer to the main surface. .
For example, the substrate is introduced into a film forming apparatus that has been evacuated, and a film is sequentially formed from an adhesion layer to a magnetic layer on the main surface of the substrate in an Ar atmosphere by a DC magnetron sputtering method. For example, CrTi can be used as the adhesion layer, and CrRu can be used as the underlayer. As the magnetic layer, for example, a CoPt alloy can be used. It is also possible to form a CoPt-based alloy and FePt based alloy L ₁₀ regular structure and magnetic layer for heat-assisted magnetic recording. After the above film formation, a magnetic recording medium can be formed by forming a protective layer using, for example, C ₂ H ₄ by a CVD method and subsequently performing nitriding treatment for introducing nitrogen into the surface. Thereafter, for example, PFPE (perfluoropolyether) is applied on the protective layer by a dip coating method, whereby a lubricating layer can be formed.

  In the following, the present invention is further illustrated by examples. However, this invention is not limited to the aspect shown in the Example.

(1) Production of molten glass The raw materials were weighed and mixed to obtain a compounded raw material so that a glass having the following composition was obtained. This raw material was put into a melting vessel, heated and melted, clarified and stirred to produce a homogeneous molten glass free from bubbles and unmelted materials. In the obtained glass, bubbles, undissolved material, crystal precipitation, refractory constituting the melting vessel and platinum contamination were not recognized.
[Glass composition]
In terms of mol%, converted into oxide standards, SiO ₂ is 50 to 75%, Al ₂ O ₃ is 1 to 15%, at least one component selected from LiO ₂ , Na ₂ O and K ₂ O. 5 to 35% in total, 0 to 20% in total of at least one component selected from MgO, CaO, SrO, BaO and ZnO, and ZrO ₂ , TiO ₂ , La ₂ O ₃ , Y ₂ O ₃ , Aluminosilicate glass comprising a composition having a total of 0 to 10% of at least one component selected from Ta ₂ O ₅ , Nb ₂ O ₅ and HfO ₂

(2) Production of glass substrate Melted glass that flows out from the pipe at a constant flow rate and is received by a lower mold for press molding so that a predetermined amount of molten glass lump is obtained on the lower mold. The glass was cut with a cutting blade. Then, the lower mold on which the molten glass block was placed was immediately carried out from below the pipe, and was press-formed into a thin disk shape using the upper mold and the barrel mold opposed to the lower mold. After the press-formed product is cooled to a temperature at which it does not deform, it is removed from the mold and annealed. Then, the lapping process was performed with respect to the glass substrate obtained by press molding. In the lapping process, alumina abrasive grains (# 1000 grain size) were used as free abrasive grains. In this way, a glass disk having an outer diameter of 65.5 mm was obtained.

(3) Coring and chamfering (only on the inner circumference side)
Using a cylindrical diamond drill, an inner hole was formed in the center of the disk-shaped glass material to form an annular glass substrate (coring). The inner peripheral end face was ground with a # 500 diamond grindstone and subjected to predetermined chamfering (chambering).

(4) Peripheral processing process Next, the blast material was projected with respect to the outer peripheral edge part of the glass substrate, and the peripheral process was given. In this step, an acrylic photo-curable resin having a thickness of 50 μm was applied as a spacer between the glass substrates to interpose between the glass substrates, thereby producing a laminate of 25 glass substrates. Note that the outer diameter of the spacer portion is the same as the outer diameter of the glass substrate.
Thereafter, the resin was cured by applying light to the laminate. This laminate was loaded into the peripheral processing apparatus shown in FIG. 3 to perform peripheral processing. At this time, the processing conditions were as follows.
・ Rotational speed of laminate: 120 rpm
・ Blast material: Molten alumina of WA # 1000 ・ Injection pressure: 0.5 MPa
・ Injection time: 120 seconds ・ Distance between the injection port and the outer peripheral edge of the laminate: 100 mm
In addition, the nozzle which projects a blast material was moved to the lamination direction of a laminated body, and the allowance was uniform in each glass substrate irrespective of the position in the laminated body of a glass substrate.

(5) End surface polishing process Next, the laminated body of the glass substrate was loaded into the end surface polishing apparatus, and the end surface was polished with a polishing brush (roll brush using nylon fiber bristles). First, the laminate was fixed and held in the end surface polishing apparatus, and the polishing brush set on the inner periphery of the laminate was rotated at 1000 rpm for 60 minutes. The slurry used at this time was produced by mixing 10% by weight of cerium oxide (CeO ₂ ) abrasive grains having an average particle diameter of 1 μm with pure water filtered water (RO water) or pure water and stirring sufficiently. Next, the polishing brush set on the outer periphery of the laminate was rotated at 3500 rpm for 30 minutes. For the outer periphery, the same slurry as that used when the inner periphery was polished was used.

The glass substrate of the Example was obtained by the above steps.
On the other hand, the glass substrate of the prior art example was obtained by performing chamfering of the outer peripheral side instead of the said outer periphery processing process. In this outer chamfering, the outer peripheral end was ground with a # 500 diamond grindstone and subjected to a predetermined chamfering process. The end surface polishing step is the same between the example and the conventional example.

The peripheral edge portions of the glass substrates of the conventional example and the example were magnified 200 times and magnified with a video scope, and the edge-shaped profile was observed. In the conventional example, it was confirmed that a chamfered portion (chamfer) was formed at an angle of 40 to 50 degrees between the main surface and the side wall portion. Further, in the example, a rounded profile was confirmed as a whole over the main surfaces on the front side and the back side. Furthermore, when the surface of the outer peripheral end portion was observed for scratches (cracks, cracks, etc.), no scratches (cracks, cracks, etc.) were found in both the conventional examples and the examples.
Moreover, about the Example before an end surface grinding | polishing process and a prior art example, the chamfered part of the outer peripheral edge part of a prior art example and the outer peripheral edge part of an Example are expanded 20 times using the Keyence Corporation laser microscope (VK9700), and a 150 micrometer square. When the surface roughness was measured for this area, the distance between the highest point and the lowest point in the measurement area was 20 μm in the conventional example and 9 μm in the example. The crack depth is considered to be equal to or proportional to this distance. Therefore, in the embodiment, the crack depth and the polishing allowance can be reduced to half or less of the conventional example.
Even if a round edge can be formed at the outer peripheral edge of the glass substrate using a grindstone, the surface roughness is expected to be equivalent to that of the conventional example.

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

(Magnetic disk glass substrate)
DESCRIPTION OF SYMBOLS 10 ... Main surface 15 ... Inner hole 20 ... Outer peripheral edge part (peripheral processing apparatus)
DESCRIPTION OF SYMBOLS 70 ... Injection nozzle 70a ... Injection port 80 ... Rotation drive device 81 ... Mounting stand 82 ... Rotating shaft 83 ... Holder

Claims (5)

A method of manufacturing a glass substrate for a magnetic disk having two opposing main surfaces and an end interposed between the main surfaces,
A glass substrate for a magnetic disk, which is processed into a desired end shape by blasting a part of the end portion adjacent to a peripheral portion of at least one of the two main surfaces. Manufacturing method. A method of manufacturing a glass substrate for a magnetic disk having an outer peripheral processing step of processing an outer peripheral end portion of an annular glass substrate,
In the outer periphery processing step, the outer peripheral end of the glass substrate is processed into a desired shape by projecting a blast material from the outer side of the glass substrate toward the outer peripheral end of the glass substrate. A method for manufacturing a substrate. It is a manufacturing method of the glass substrate for magnetic discs of Claim 1 or 2, Comprising:
A method of manufacturing a glass substrate for a magnetic disk, wherein at least a part of the end portion is processed into a round shape by blasting. It is a manufacturing method of the glass substrate for magnetic discs of Claim 1 or 2, Comprising:
A method for producing a glass substrate for a magnetic disk, wherein a chamfered portion is formed on a part of the end portion by blasting. It is a manufacturing method of the glass substrate for magnetic discs described in any one of Claims 1-4,
The method of manufacturing a glass substrate for a magnetic disk, characterized in that, in the outer peripheral processing step, the blast material is projected onto a laminated body in which a plurality of glass substrates are laminated.

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