JP2012142044A - Method for manufacturing glass substrate for information recording medium and information recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a glass substrate for an information recording medium, in which end surfaces of the glass substrate are smoothly finished in a high level surface condition and costs can be suppressed.SOLUTION: A method for manufacturing a glass substrate for an information recording medium, in which a magnetic recording layer is formed on a surface of a circular disk-shaped glass substrate 1, comprises steps of forming the glass substrate 1, and supplying polishing liquid 50 containing loose abrasive grains to end surfaces of the glass substrate 1 and polishing the end surfaces by contacting a rotating rotary brush 4, having a surface densely arranged with no gap, with the end surfaces.

Description

  The present invention relates to a method for manufacturing a glass substrate for information recording medium and an information recording medium, and in particular, includes a method for manufacturing a glass substrate for information recording medium used for manufacturing an information recording medium, and the glass substrate for information recording medium. The present invention relates to an information recording medium.

  An information recording medium such as a magnetic disk is mounted as a hard disk in a computer or the like. An information recording medium is manufactured by forming a magnetic thin film layer including a recording layer using properties such as magnetism, light, or magnetomagnetism on the surface of a substrate. As the recording layer is magnetized by the magnetic head, predetermined information is recorded on the information recording medium.

  Conventionally, an aluminum substrate has been used as a substrate for an information recording medium. However, as the recording density is improved, it is gradually being replaced by a glass substrate that is superior in smoothness and strength of the substrate surface as compared with an aluminum substrate. In general, in order to improve the strength, a glass substrate that has been chemically strengthened or a crystallized glass substrate that has been increased in strength by crystallization is used as the glass substrate.

  In the hard disk drive device, when there is a projection defect such as a foreign substance on the surface of the substrate, there is a problem that a defect called a head crash occurs in which the projection defect contacts the head and the head or the substrate is destroyed. Therefore, foreign matter on the substrate surface is often a problem even if it is very small. In recent years, the distance (flying height, about 10 nm) between the magnetic head and the magnetic disk has been reduced, and accordingly, the allowable size of foreign matter on the substrate surface when formed as a magnetic disk has also been reduced. It is coming.

  The surface state of the end surface of the glass substrate is not smooth, which is considered to be a cause of the presence of foreign matter on the substrate surface. That is, when the end surface is not smooth, the end surface is rubbed against the wall surface of the resin case for transporting the substrate, thereby generating resin or glass particles. The generated particles or other fine particles are trapped on the end surface of the substrate which is not smooth and adhere to the surface when the substrate is rotated, which is a major cause of foreign matter on the substrate surface. Therefore, conventionally, various techniques relating to polishing for smoothing the end face of the substrate have been proposed (see, for example, Patent Documents 1 and 2).

JP 2000-185927 A JP 2004-342307 A

  In recent years, a new mechanism called DFH (Dynamic Flying Height) has been introduced as a mechanism of a magnetic head. DFH is a technique in which a special metal is used at a position where the head is mounted, and the head is thermally expanded to protrude at a fine distance. By using this technique, the distance between the disk and the head can be kept constant regardless of external factors such as pressure or temperature fluctuations. Therefore, DFH has been widely adopted for high-density recording systems.

  When DFH is employed, the flying height is reduced to less than 2 nm, and in this case, the foreign matter on the smaller substrate surface causes the head crash. As the problem of deposits on the substrate surface has become prominent in this way, it has become more important to smooth the end face of the substrate. The end face processing that can cause dust generation is required to be finished with a smoothness that is higher than ever, which raises the cost of processing and results in an increase in the cost of the glass substrate. .

  The present invention has been made in view of the above problems, and its main purpose is to finish the surface state of the end surface of the glass substrate used for the information recording medium smoothly at a high level, and to suppress the cost. It is to provide a method for producing a glass substrate for an information recording medium.

  The method for producing a glass substrate for information recording medium according to the present invention is a method for producing a glass substrate for information recording medium in which a magnetic recording layer is formed on the surface of a circular disk-shaped glass substrate, the step of forming the glass substrate And a step of polishing the end face by supplying a polishing liquid containing loose abrasive grains to the end face of the glass substrate and bringing the polishing brush whose surface is closely packed without any gaps while rotating.

  In the above method, the end surface may be an outer peripheral end surface of the glass substrate. Alternatively, a circular hole may be formed in the center of the glass substrate, and the end surface may be an inner peripheral end surface of the glass substrate.

  In the above method, in the polishing step, end surfaces of a plurality of stacked glass substrates may be polished.

  In the above method, the polishing liquid may be supplied to the end surface from above the glass substrate. The polishing liquid supplied from above may flow downward through the gap. Alternatively, the glass substrate may be immersed in the polishing liquid.

  In the above method, the free abrasive grains may have an average particle size of 0.5 μm or more and 2.0 μm or less.

  In the above method, the polishing brush may reciprocate in the axial direction of the rotation shaft.

  An information recording medium according to the present invention includes a glass substrate obtained by the method for manufacturing a glass substrate for information recording medium according to any one of the above aspects, and a magnetic recording layer formed on the surface of the glass substrate.

  According to the method for producing a glass substrate for an information recording medium of the present invention, the surface state of the end surface of the glass substrate can be finished smoothly at a high level, and the cost can be suppressed.

It is a perspective view which shows the glass substrate obtained by the manufacturing method of the glass substrate in embodiment. It is a perspective view which shows the magnetic disc provided with the glass substrate obtained by the manufacturing method of the glass substrate in embodiment. It is a flowchart which shows the manufacturing method of the glass substrate in embodiment. It is sectional drawing which shows the grinding | polishing apparatus which concerns on this Embodiment. It is a top view which shows the structure of a rotating brush. FIG. 6 is a side view of the rotating brush shown in FIG. 5. It is a schematic diagram which shows the outline of the structure which grind | polishes the outer peripheral end surface of a glass substrate. FIG. 6 is a cross-sectional view showing a polishing apparatus according to a second embodiment. It is a top view which shows the structure of the conventional rotating brush. FIG. 10 is a side view of the conventional rotating brush shown in FIG. 9.

  Embodiments based on the present invention will be described below with reference to the drawings. In the description of the embodiments, when referring to the number, amount, and the like, the scope of the present invention is not necessarily limited to the number, amount, or the like unless otherwise specified. In the description of the embodiments, the same parts and corresponding parts are denoted by the same reference numerals, and redundant description may not be repeated.

(Embodiment 1)
[Glass substrate 1 and magnetic disk 10]
With reference to FIG. 1 and FIG. 2, the glass substrate 1 obtained by the manufacturing method of the glass substrate for information recording media based on this Embodiment and the magnetic disc 10 provided with the glass substrate 1 are demonstrated first. FIG. 1 is a perspective view showing a glass substrate 1 used for a magnetic disk 10 (see FIG. 2). FIG. 2 is a perspective view showing a magnetic disk 10 provided with a glass substrate 1 as an information recording medium.

  As shown in FIG. 1, a glass substrate 1 (glass substrate for information recording medium) used for a magnetic disk 10 has an annular disk shape with a circular hole 1H formed at the center. The circular disk-shaped glass substrate 1 has a front main surface 1A, a back main surface 1B, an inner peripheral end surface 1C, and an outer peripheral end surface 1D.

  The size of the glass substrate 1 is not particularly limited, and is, for example, 0.8 inch, 1.0 inch, 1.8 inch, 2.5 inch, or 3.5 inch outer diameter. The thickness of the glass substrate 1 is, for example, 0.30 to 2.2 mm from the viewpoint of preventing breakage. The glass substrate 1 in the present embodiment has an outer diameter of about 64 mm, an inner diameter of about 20 mm, and a thickness of about 0.8 mm. The thickness of the glass substrate 1 is a value calculated by averaging the values measured at a plurality of arbitrary points that are point targets on the glass substrate 1.

  As shown in FIG. 2, the magnetic disk 10 is configured by forming a magnetic film on the front main surface 1A of the glass substrate 1 and forming a magnetic thin film layer 2 including a magnetic recording layer. The In FIG. 2, the magnetic thin film layer 2 is formed only on the front main surface 1A, but the magnetic thin film layer 2 may also be formed on the back main surface 1B.

  The magnetic thin film layer 2 is formed by spin-coating a thermosetting resin in which magnetic particles are dispersed on the front main surface 1A of the glass substrate 1 (spin coating method). The magnetic thin film layer 2 may be formed on the front main surface 1A of the glass substrate 1 by a sputtering method or an electroless plating method.

  The film thickness of the magnetic thin film layer 2 formed on the front main surface 1A of the glass substrate 1 is about 0.3 μm to 1.2 μm in the case of the spin coating method, about 0.04 μm to 0.08 μm in the case of the sputtering method, In the case of the electroless plating method, the thickness is about 0.05 μm to 0.1 μm. From the viewpoint of thinning and high density, the magnetic thin film layer 2 is preferably formed by sputtering or electroless plating.

  The magnetic material used for the magnetic thin film layer 2 is not particularly limited, and a conventionally known material can be used. However, in order to obtain a high coercive force, Co having high crystal anisotropy is basically used for the purpose of adjusting the residual magnetic flux density. A Co-based alloy to which Ni or Cr is added is suitable. Further, as a magnetic layer material suitable for heat-assisted recording, an FePt-based material may be used.

  In addition, a lubricant may be thinly coated on the surface of the magnetic thin film layer 2 in order to improve the sliding of the magnetic recording head. Examples of the lubricant include those obtained by diluting perfluoropolyether (PFPE), which is a liquid lubricant, with a solvent such as Freon.

  Furthermore, you may provide a base layer and a protective layer as needed. The underlayer in the magnetic disk 10 is selected according to the magnetic film. Examples of the material for the underlayer include at least one material selected from nonmagnetic metals such as Cr, Mo, Ta, Ti, W, V, B, Al, and Ni.

  Further, the underlayer is not limited to a single layer, and may have a multi-layer structure in which the same or different layers are stacked. For example, a multilayer underlayer such as Cr / Cr, Cr / CrMo, Cr / CrV, NiAl / Cr, NiAl / CrMo, or NiAl / CrV may be used.

  Examples of the protective layer that prevents wear and corrosion of the magnetic thin film layer 2 include a Cr layer, a Cr alloy layer, a carbon layer, a hydrogenated carbon layer, a zirconia layer, and a silica layer. These protective layers can be continuously formed together with an underlayer, a magnetic film and the like by an in-line type sputtering apparatus. In addition, these protective layers may be a single layer, or may have a multilayer structure including the same or different layers.

Another protective layer may be formed on the protective layer or instead of the protective layer. For example, instead of the protective layer, a tetraalkoxysilane is diluted with an alcohol-based solvent on a Cr layer, and then colloidal silica fine particles are dispersed and applied, followed by baking to form a silicon oxide (SiO ₂ ) layer. It may be formed.

[Glass substrate manufacturing method]
Next, the manufacturing method of the glass substrate (glass substrate for information recording media) in this Embodiment is demonstrated using the flowchart figure shown in FIG. FIG. 3 is a flowchart showing a method for manufacturing a glass substrate in the embodiment.

  The glass substrate manufacturing method in the present embodiment includes a forming step (step S10), a first lapping step (step S20), a shape processing step (step S30), an inner peripheral polishing step (step S40), and a second lapping step ( Glass obtained through step S50), outer periphery polishing step (step S60), first main surface polishing step (step S70), second main surface polishing step (step S80), and chemical strengthening step (step S90). A magnetic film forming step (step S100) may be performed on the substrate (corresponding to the glass substrate 1 in FIG. 1). The magnetic disk 10 is obtained by the magnetic film forming step (step S100).

  Hereinafter, each of these steps S10 to S100 will be described in order. In the following, simple cleaning that is appropriately performed between steps S10 to S100 is not described.

(Molding process)
In the forming step (step S10), the glass material constituting the glass substrate is melted. For example, general aluminosilicate glass is used as the glass material. Aluminosilicate glass, and SiO ₂ of 58 wt% to 75 wt%, and _Al 2 _{O 3} of 5 wt% to 23 wt%, and Li ₂ O 3 wt% to 10 wt%, 4 wt% to 13 wt % Na ₂ O as a main component. After the molten glass material is poured onto the lower mold, it is press-molded by the upper mold and the lower mold. A disk-shaped glass blank (glass base material) is formed by press molding.

  The glass blank material may be formed by cutting out a sheet glass (sheet glass) formed by a downdraw method or a float method with a grinding wheel. Further, the glass material is not limited to aluminosilicate glass, and may be any material.

(First wrapping process)
Next, in the first lapping step (step S20), a lapping process is performed on both main surfaces of the press-molded glass blank material for the purpose of improving dimensional accuracy and shape accuracy. Both main surfaces of a glass blank material are the main surfaces used as the front main surface 1A and the main surface used as the back main surface 1B in FIG. 1 through each process mentioned later (henceforth, both main surfaces) Also called).

  The lapping process is performed using a double-sided lapping device using a planetary gear mechanism. Specifically, the lapping platen is pressed from above and below on both main surfaces of the glass blank material, the grinding liquid is supplied onto both main surfaces, and the glass blank material and lapping platen are moved relative to each other for lapping. Processing is performed. By the lapping treatment, the approximate parallelism, flatness, thickness, etc. of the glass substrate are preliminarily adjusted, and a glass base material having an approximately flat main surface is obtained. For example, by using a grinding fluid containing alumina abrasive grains having a particle size of # 400 (particle size of about 40 to 60 μm) and setting the load on the upper surface plate to about 100 kg, both surfaces of the glass substrate have surface accuracy of 0 μm to 1 μm, You may finish to about 6 micrometers in surface roughness Rmax.

(Shaping process)
Next, in the shape processing step (step S30), a coring (inner peripheral cut) process is performed on the center portion of the glass blank material using a cylindrical diamond drill. By the coring process, an annular glass substrate having a hole in the center is obtained. Thereafter, the inner peripheral end face and the outer peripheral end face opposed to the hole in the central part are ground with a diamond grindstone so that the outer diameter is 65 mm and the inner diameter (the diameter of the circular hole 1H in the central part) is 20 mm. Processing is performed. The surface roughness of the end surface of the glass substrate at this time is about 2 μm in Rmax. In general, a glass substrate having an outer diameter of 65 mm is used for a 2.5-inch hard disk.

(Inner grinding process)
Next, in the inner peripheral polishing step (step S40), mirror polishing is performed on the inner peripheral end surface 1C of the glass substrate 1 by brush polishing. FIG. 4 is a cross-sectional view showing the polishing apparatus according to the present embodiment.

  The polishing apparatus shown in FIG. 4 includes a substrate case 20 that stores a large number of glass substrates 1 to be polished, a rotation holding base 3 that rotatably holds and holds the substrate case 20, and a plurality of stacked glass substrates 1. The rotating brush 4 inserted in the circular hole part (inner peripheral hole part) and the polishing liquid supply part 5 for supplying the polishing liquid are provided.

  The substrate case 20 is affected by the rotation of the substrate case 20 and the rotating brush 4 due to the friction coefficient between the main surfaces of each glass substrate 1 by tightening the tightening cover 22 from the upper part in the axial direction via the collar 21. And a mechanism for holding the glass substrate 1.

  The rotation holding table 3 is coupled to a rotation shaft 32 of the rotation shaft portion 31 and can be rotated in both forward and reverse directions by a rotation drive device 34 that rotationally drives the rotation shaft 32. In addition, this rotation drive device 34 can change the rotation speed, and can select now an appropriate rotation speed according to the grinding | polishing objective. Further, by supplying air through an air supply path 36 from an air supply port 35 provided in the rotary shaft cover 33 in the rotary shaft portion 31, an air seal portion 37, an air curtain, or the like is formed, and the polishing liquid is supplied to the rotary shaft. 32 is prevented from flowing.

  The rotating brush 4 is connected to the rotating shaft 42 of the rotation driving device 41 and is configured to be rotatable in both forward and reverse directions. The rotation brush 4 is set so that the position of the rotation center of the rotation brush 4 coincides with the rotation center of the substrate case 20 in the initial state. Further, the rotating brush 4 is pressed against the inner peripheral end surface of the glass substrate 1 by a mechanism (not shown) using an air cylinder or the like, that is, the brush, in order to adjust the contact length of the brush hair to the glass substrate 1. The amount of pressing in the direction perpendicular to the direction of the rotation axis can be adjusted. The rotating brush 4 is fixed, and the pressing amount can be adjusted by moving the substrate case 20. The rotating brush 4 is configured to be able to swing by a cam mechanism (not shown) while reciprocating along the rotation axis direction of the brush simultaneously with being pressed against the inner peripheral end surface.

  As shown in FIG. 4, the rotating brush 4 is provided with a bearing 46 for fixing the rotating shaft to at least the rotating shaft 45 on the side opposite to the rotating shaft 44 on the rotation driving device side, and the rotating shaft is inserted into this bearing. This is preferable because polishing can be performed without shifting the rotation axis even when polishing the end face, and high-precision polishing without variations in surface roughness and size can be performed. As the bearing, a known bearing such as a bearing, a ball bearing, a roller bearing, or a sliding bearing can be used. The bearing also serves as a guide member when inserting the rotating brush. In this case, the inner diameter of the inlet of the bearing can be widened, which is preferable because the rotating shaft of the rotating brush can be easily inserted into the bearing. Further, a plurality of bearings can be provided, and can also be provided on the rotary shaft on the rotary drive device side.

  Hereinafter, the details of the rotating brush 4 will be described. FIG. 5 is a plan view showing the configuration of the rotating brush 4. FIG. 6 is a side view of the rotating brush 4 shown in FIG. As shown in FIGS. 5 and 6, the rotating brush 4 as the polishing brush has a rotating shaft 40 and a wing portion 43 attached to the outer surface of the rotating shaft 40. The rotating shaft 40 is formed in a cylindrical shape, and the wings 43 extend radially from the outer surface of the rotating shaft 40 which is the outer peripheral surface of the cylinder. The wing portion 43 extends along the radial direction of the rotating shaft 40. Further, the wing portion 43 extends in the axial direction of the rotating shaft 40. The wing portion 43 is formed by densely gathering bristles planted in a direction perpendicular to the rotation shaft 40.

  Each wing portion 43 is bundled in the circumferential direction in the root portion in the vicinity of the rotation shaft 40, and a gap 47 is formed between the wing portions 43 adjacent in the circumferential direction of the rotation shaft 40 in the vicinity of the root portion. Yes. A gap 47 having a certain width in the circumferential direction exists at a portion of the wing portion 43 close to the rotation shaft 40. The wing portion 43 spreads in the circumferential direction from the root portion toward the radially outer side of the rotation shaft 40. In the tip portion 48 at the outermost radial direction, the wing portion 43 adjacent in the circumferential direction is substantially in contact with the circumferential direction. At the tip 48, which is the outermost surface far from the rotation shaft 40, the wing 43 spreads in an appropriate range in the circumferential direction, so that there is almost no gap at the tip 48, resulting in a dense brush. The tip portions 48 of the plurality of wing portions 43 are arranged in a substantially circumferential shape and are in a dense state. The wing parts 43 are arranged densely in the circumferential direction of the rotating shaft 40. The wing parts 43 are continuously provided in the rotation direction.

  A plurality of wing portions 43 are provided in the circumferential direction of the rotating shaft 40. As shown in FIG. 5, the plurality of wing parts 43 are arranged point-symmetrically with respect to the center of the rotation shaft 40. Since the plurality of wing portions 43 are arranged point-symmetrically, the occurrence of eccentricity is suppressed when the rotating brush 4 rotates as described later. That is, it is possible to suppress the center of the rotational motion from being shifted during the rotational motion of the rotary brush 4.

  The wings 43 are densely gathered continuously perpendicularly to the outer peripheral surface of the rotating shaft 40 and along the axial direction of the rotating shaft 40, and the bristles are planted on the outer peripheral surface of the rotating shaft 40. ,It is formed. The brush bristles are attached to the outer peripheral surface of the rotating shaft 40 so as to extend along the radial direction of the rotating shaft 40. Each of the bristle has a shape curled in a meandering shape so that the wing portion 43 spreads from the root portion toward the tip portion 48. The brush bristles 49 may be formed to have a constant thickness from the root to the tip, but are not limited to this, and the tip is tapered, the tip is tapered, or the tip or the root is arbitrarily deformed. , It may be formed in any shape. The fiber that is curled and tapered at the tip is excellent in contact with a dent or the like, and for example, the chamfered portion of the circular hole 1H of the glass substrate 1 shown in FIG. 4 can be more efficiently polished. The shape of the rotating brush 4 is not limited to the wing shape described above, and may be any shape as long as the brush surface is densely spaced. For example, the rotating brush 4 in which the brush hairs 49 are densely arranged in a spiral shape on the rotating shaft 40 may be used.

  For example, nylon fiber, vinyl chloride fiber, pig hair, piano wire, stainless steel fiber, or the like may be used as the material for forming the brush hair. If fibers having low hardness or fibers having high flexibility are used, it is possible to prevent excessive rubbing force due to elastic deformation of the brush bristles, and to better prevent the occurrence of scratches such as scratches. In addition, if the abrasive | polishing agent is mixed in resin, and this is shape | molded as a bristle, and what contains the abrasive | polishing agent in the bristle is used, a grinding | polishing rate can be raised further.

  The dimension of the bristle may be 0.1 to 0.4 mm in diameter and 4 to 7 mm in length.

  Returning to FIG. 4, the polishing liquid supply unit 5 supplies the polishing liquid 50 containing free abrasive grains from above the glass substrate 1 to the circular holes 1 </ b> H of the glass substrate 1. As the free abrasive grains, cerium oxide is used, but other abrasives such as iron oxide, magnesium oxide, zirconium oxide, and manganese oxide can also be used. Preferably, free abrasive grains having a hardness close to that of the material to be polished (glass substrate 1) are desirable. In the case of a glass substrate, cerium oxide is desirable. If the loose abrasive grains are too hard, the glass substrate end face is damaged, which is not preferable. Further, if the loose abrasive grains are too soft, the glass substrate end face cannot be made into a mirror surface, which is not preferable.

  The average grain size of the free abrasive grains is preferably 0.5 μm or more and 2.0 μm or less, more preferably 0.5 μm or more and 1.0 μm or less in order to finish the mirror surface. When the particle size is less than 0.5 μm, the free abrasive grains have a weak force to grind the glass substrate and are often polished with the tip of the rotating brush in direct contact with the end surface of the glass substrate. It is difficult to control the shape, and the portion between the end surface (side wall surface) and the chamfered portion is not preferable because it is bent. On the other hand, when the particle size exceeds 2.0 μm, the particle size of the free abrasive grains is large, and the surface roughness of the glass substrate is increased.

  A mode of supplying the polishing liquid 50 by the polishing liquid supply unit 5 is not particularly limited, and examples thereof include a mode in which spraying, spraying, water discharge, and application are performed by one water flow, shower, water droplets, and the like. Further, the polishing apparatus of the present invention is formed with a polishing liquid circulation port 23 through which the polishing liquid 50 supplied from the polishing liquid supply unit 5 is distributed to the outside of the apparatus. The polishing liquid 50 that has flowed out of the apparatus via the polishing liquid circulation port 23 is recovered by a polishing liquid recovery unit (not shown). The polishing liquid 50 recovered by the polishing liquid recovery part is circulated to the polishing liquid supply part 5 again after being cleaned by a circulation mechanism (not shown).

  Next, an example of a polishing method using the polishing apparatus will be described. First, the rotating brush 4 is retracted from the substrate case 20 by an appropriate amount, a large number of glass substrates 1 are stacked on the substrate case 20, and the collar 21 is arranged vertically and clamped by tightening the tightening cover 22. . At this time, the misalignment of the inner peripheral hole portion of the glass substrate 1 is determined by the clearance due to the dimensional difference between the inner peripheral portion of the substrate case 20 and the outer peripheral portion of the glass substrate 1. This clearance needs to be adjusted depending on workability and the roundness of the inner periphery of the substrate case. However, the range from the clearance fit to the intermediate fit in JIS B 0401 (1986) is appropriate.

  A substrate case 20 in which a large number of the glass substrates 1 are set is set on the rotation holding table 3. Here, the glass substrate 1 to be set has already been chamfered on the inner and outer peripheries.

  Next, the rotating brush 4 that is on the same line as the rotation center of the substrate case 20 is inserted into the inner peripheral portion of the glass substrate 1 as shown in FIG. The stop position of the rotating brush 4 is a position where the range from the lowermost part to the uppermost part of the set glass substrate 1 is within the flocking range of the brush hair of the rotating brush 4.

  Subsequently, a polishing liquid 50 having a flow rate of 500 ml / min to 3000 ml / min is supplied from the polishing liquid supply unit 5 toward the inner peripheral end surface 1C of the glass substrate 1. The polishing liquid 50 supplied to the rotating brush 4 from above flows downward through the gap 47 between the blades 43 and reaches the bottom of the rotating brush 4, that is, the lower side of the stacked glass substrates. The glass substrate is quickly reached.

  Next, the pressing amount of the rotating brush 4 is adjusted so that the brush bristles of the rotating brush 4 come into contact with the inner peripheral end surface of the glass substrate 1. In the case of the nylon fiber with curled bristles, this adjustment is performed at a position where the tip of the bristles is pressed against the surface to be polished of the glass substrate 1 by about 1 to 5 mm. In addition, it is preferable to adjust the contact pressure of the brush by pressing on the inner peripheral end surface of the glass substrate 1 by a mechanism using an air cylinder or the like. Specifically, for example, the air pressure of the air cylinder is preferably in the range of 0.05 to 0.1 MPa for strong brush hairs, and the air cylinder air pressure is in the range of 0.05 to 1 MPa for weak brush hairs. Is preferred.

  Next, polishing is performed in a state where the rotation holding table 3 and the rotation brush 4 are rotated in opposite directions. In this case, the preferable rotation speed of the rotating brush 4 is 100 to 15000 rpm during idling. After rotating the rotating brush 4 for a certain time, the rotation direction of the rotation holding table 3 and the rotating brush 4 may be switched and reversely rotated. By switching the rotation direction, the inclination of the blade 43 with respect to the radial direction of the rotating shaft 40 The condition of the rotating brush 4 such as the state is adjusted. The rotating brush 4 reciprocates in the axial direction of the rotating shaft 40 in addition to the rotating motion of the rotating shaft 40 in the circumferential direction. The inner peripheral end face 1 </ b> C is polished by contacting the inner peripheral end face 1 </ b> C of the glass substrate 1 while rotating the rotating brush 4.

  When the predetermined amount of polishing is completed, the apparatus is stopped and the substrate case 20 is taken out. When removing the substrate case 20, it is necessary to move the rotating brush 4 to a position that does not interfere with the attachment / detachment of the substrate case 20. Finally, the glass substrate 1 is taken out from the taken-out substrate case 20 in the reverse order.

(Second wrapping process)
Returning to FIG. 3, next, in the second lapping step (step S50), the lapping process is performed on both main surfaces of the glass substrate in the same manner as in the first lapping step (step S20). By performing this second lapping step, it is possible to remove in advance the fine irregularities such as fine scratches and protrusions formed on both main surfaces of the glass substrate in the coring or end face processing in the previous step. It is possible to shorten the polishing time of the main surface in the subsequent process.

(Outer periphery polishing process)
Next, in the outer peripheral polishing step (step S60), the outer peripheral end surface of the glass substrate is subjected to mirror polishing by brush polishing. FIG. 7 is a schematic diagram showing an outline of a structure for polishing the outer peripheral end face of the glass substrate 1.

  For polishing the outer peripheral end face 1D of the glass substrate 1, the rotating brush 4 described with reference to FIGS. The size of the brush bristles for polishing the outer peripheral end surface may be 0.2 mm to 0.6 mm in diameter and 10 mm to 25 mm in length.

  Two sets of glass substrates 1 stacked in a plural number are sandwiched between a pair of rotating brushes 4, and in this state, the polishing liquid 50 containing the above-mentioned free abrasive grains is supplied to the outer peripheral end face 1D of the glass substrate. Cerium oxide is used as the loose abrasive. The average grain size of the free abrasive grains is preferably 0.5 μm or more and 2 μm or less, more preferably 0.5 μm or more and 1 μm or less in order to finish the mirror surface. Subsequently, the contact pressure of the rotating brush 4 by pressing against the outer peripheral end surface of the rotating brush 4 is adjusted by a mechanism using an air cylinder or the like so that the bristles of the rotating brush 4 abut on the outer peripheral end surface of the glass substrate 1. . Subsequently, the glass substrate 1 and the rotating brush 4 are rotated in the arrow direction shown in FIG. 7, and the outer peripheral end surface 1 </ b> D is polished by contacting the outer peripheral end surface 1 </ b> D of the glass substrate 1 while rotating the rotating brush 4.

(First main surface polishing process)
Returning to FIG. 3, the first main surface polishing step (step S <b> 70) is then performed as a rough polishing step that is the first step of the main surface polishing step of the glass substrate. The main purpose of the first main surface polishing step is to correct warpage of the glass substrate while removing scratches remaining on the main surface of the glass substrate in the lapping step described above. In the first main surface polishing step, the main surface is polished by a double-side polishing apparatus having a planetary gear mechanism. For example, polishing is performed using a polishing pad such as hard velor, urethane foam, or pitch-impregnated suede. As the abrasive, general cerium oxide abrasive grains are used.

(Second main surface polishing step)
Next, a second main surface polishing step (step S80) is performed as a precision polishing step which is the second step of the main surface polishing step of the glass substrate. In the second main surface polishing step, when coating the main surface of the glass substrate, or when separating the glass substrate, etc., the fine defects generated on the main surface of the glass substrate are eliminated to finish it in a mirror shape, And it aims at eliminating the curvature of a glass substrate and finishing to desired flatness. In the second main surface polishing step, the main surface is polished by a double-side polishing apparatus having a planetary gear mechanism. For example, polishing is performed using a polishing pad which is a soft polisher made of suede or velor. As the abrasive, general colloidal silica finer than the cerium oxide used in the first main surface polishing step is used.

(Chemical strengthening process)
Next, in the chemical strengthening step (step S90), the glass substrate that has finished the main surface polishing step described above is chemically strengthened. After the glass substrate is washed, the glass substrate is immersed in a chemical strengthening treatment solution such as a solution for mixing potassium nitrate (70%) and sodium nitrate (30%) heated to 300 ° C. for 30 minutes, Perform chemical strengthening.

  As a result of this treatment, alkali metal ions (for example, lithium ions and sodium ions in the case of using aluminosilicate glass) existing in the inner peripheral end face and outer peripheral end face of the glass substrate are included in the chemical strengthening treatment liquid. Are replaced with sodium ions and potassium ions having a larger ionic radius (ion exchange method). Due to the strain caused by the difference in ion radius, compressive stress is generated in the ion-exchanged region, and both main surfaces of the glass substrate are strengthened. For example, on both main surfaces of the glass substrate, a chemically strengthened layer may be formed in a range from the glass substrate surface to about 5 μm to improve the rigidity of the glass substrate. In this way, a glass substrate corresponding to the glass substrate 1 shown in FIG. 1 is obtained.

(Magnetic film forming process)
Finally, in the magnetic film forming step (step S100), after cleaning the glass substrate on which the chemical strengthening process has been completed, both main surfaces (or one of the main surfaces) of the glass substrate corresponding to the glass substrate 1 shown in FIG. The magnetic thin film layer 2 is formed by forming a magnetic film on the surface. The magnetic thin film layer 2 is made of an adhesion layer made of a Cr alloy, a soft magnetic layer made of a CoFeZr alloy, an orientation control underlayer made of Ru, a perpendicular magnetic recording layer made of a CoCrPt alloy, a protective layer made of a C system, and an F system. The lubricating layer is formed by sequentially forming a film. By forming the magnetic thin film layer, a perpendicular magnetic recording disk corresponding to the magnetic disk 10 shown in FIG. 2 can be obtained.

  The magnetic disk in the present embodiment is an example of a perpendicular magnetic disk composed of a magnetic thin film layer. The magnetic disk may be composed of a magnetic layer or the like as a so-called in-plane magnetic disk.

[Action / Effect]
A predetermined chamfering process is performed on the end surface of the glass substrate 1 that is an object to be polished, after being ground and trimmed. The rotating brush 4 reciprocates in the axial direction of the rotating shaft 40 along with the rotating motion. Since the outermost surface of the rotating brush 4 is closely packed without any gap, the polishing action on the end surface of the glass substrate 1 by the rotating brush 4 acts continuously in both the rotating direction and the axial direction. The influence of disturbance can be reduced.

  Therefore, the end surface of the glass substrate 1 can be polished with high quality, and the surface state of the inner peripheral end surface 1C and the outer peripheral end surface 1D of the glass substrate 1 for information recording media such as a magnetic disk is smoothly finished at a high level. And cost can be reduced. As a result, it is possible to obtain an information recording medium that can suppress the occurrence of a head crash failure due to the adhesion of foreign matter on the surface when the information recording medium is formed, and that can reduce costs.

(Embodiment 2)
FIG. 8 is a cross-sectional view showing the polishing apparatus of the second embodiment. Unlike the polishing apparatus of the first embodiment shown in FIG. 4, the polishing apparatus of the second embodiment is a polishing liquid supply unit 5 in which a cylindrical side wall 52 is hermetically attached to the outer periphery of a disc-shaped bottom plate 51. Is provided. A polishing liquid 50 is accommodated in the internal space of the tank-shaped polishing liquid supply unit 5. The glass substrate 1 and the rotating brush 4 are immersed in the polishing liquid 50.

  Instead of the configuration in which the polishing liquid 50 containing the loose abrasive grains described in the first embodiment is supplied from above, the glass substrate 1 is polished on the rotating brush 4 while being immersed in the polishing liquid 50 as shown in FIG. It is also possible to polish the end face of the glass substrate 1 by circulatingly supplying the liquid 50. In this case, since sufficient polishing liquid 50 can always be supplied to the end face, it is possible to eliminate the problem of poor polishing due to running out of liquid.

  Examples of the present invention will be described below. First, the spiral rotating brush 104 used as a comparative example and having a gap (about 1.5 mm) on the surface will be described. FIG. 9 is a plan view showing a configuration of a conventional rotating brush 104. FIG. 10 is a side view of the conventional rotating brush 104 shown in FIG. As shown in FIGS. 9 and 10, a conventional rotating brush 104 used as a comparative example includes a rotating shaft 140 and a wing portion 143 configured by brush hairs spirally planted on the outer peripheral surface of the rotating shaft 140. ,including. The wing portion 143 is inclined at an angle of 2 ° to 30 ° with respect to the radial direction of the rotating shaft 140.

  When used as an inner diameter brush for polishing the inner peripheral end face of the glass substrate, the rotating brush 104 has a diameter of 0.1 to 0.3 mm and a length of 5 to 10 mm. When used as an outer diameter brush for polishing the outer peripheral end face of the glass substrate, the rotating brush 104 has a diameter equivalent to the inner diameter brush and a length of 10 to 30 mm.

  Table 1 shows a comparison between the rotating brush 4 of the embodiment of the present invention and the rotating brush 104 of the comparative example described above. In addition, the outer diameter of the rotating shaft 40 of the rotating brush 4 of the embodiment used for polishing the inner peripheral end surface 1C of the glass substrate is 6 mm, the brush bristle diameter is 0.10 mm, the length is 4.5 mm, and the inner circumference When polishing the end face 1C, the rotation speed of the rotary holding base 3 is 15 rpm, the rotation speed of the rotary brush 4 is 3500 rpm, the polishing time is about 20 minutes, the vertical swing speed of the rotary brush 4 is 400 mm / s, The amount of movement was 20 mm. Further, the outer diameter of the rotating shaft 40 of the rotating brush 4 of the embodiment used for polishing the outer peripheral end face 1D of the glass substrate is 6 mm, the brush bristle diameter is 0.2 mm, the length is 15 mm, and the outer peripheral end face 1D is polished. The rotational speed of the rotating brush at this time was 700 to 1000 rpm, the rotational speed of the glass substrate was 60 rpm, and the polishing time was about 20 minutes.

  As shown in Table 1, Ra (arithmetic mean roughness) between the glass substrate polished using the spiral brush of the comparative example and the glass substrate polished using the wing brush of the example was measured by AFM (Atomic Force). 10 points were arbitrarily measured in a 1 μm range using a Microscope), averaged, calculated, and compared. As a result, the surface roughness Ra of the end face was 1.2 nm and 1.0 nm, respectively.

  Further, a magnetic disk was prepared using the glass substrate polished using the prepared spiral brush of the comparative example and the glass substrate polished using the feather brush of the example. The manufactured magnetic disk was mounted on a load / unload type hard disk drive device, and a durability test of the magnetic disk was performed. In the durability test, a magnetic head using a DFH mechanism was used, the flying height of the magnetic head was about 2 nm, and load / unload operations were repeated. As a result, both were good without failure even after 3 million load / unload operations.

  Next, the processing rate of the end polishing of the glass substrate using a spiral brush having a gap on the surface of the comparative example and the end polishing of the glass substrate using a dense wing brush without a gap on the surface of the example is set. Compared. As shown in Table 1, the processing rate of the example was 0.8 μm / min, whereas the processing rate of the comparative example was 0.4 μm / min, and a double difference was confirmed in the processing rate. . Since the processing rate is twice, the glass substrate manufactured by the manufacturing method according to the present embodiment can be processed faster, so that the cost can be reduced. As a factor causing such a processing rate difference, it is conceivable that a dense brush acts on the polished portion of the glass substrate in a larger amount.

  Although the embodiments of the present invention have been described above, the configurations of the embodiments may be appropriately combined. In addition, it should be considered that the embodiments and examples disclosed this time are examples in all respects and are not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  1 glass substrate, 1A front main surface, 1B back main surface, 1C inner peripheral end surface, 1D outer peripheral end surface, 1H circular hole, 2 magnetic thin film layer, 4 rotating brush, 5 polishing liquid supply unit, 10 magnetic disk, 40 rotating shaft, 43 wings, 47 gaps, 48 tips, 50 polishing liquid.

Claims (10)

A method of manufacturing a glass substrate for an information recording medium in which a magnetic recording layer is formed on the surface of a circular disk-shaped glass substrate,
Forming the glass substrate;
And supplying a polishing liquid containing loose abrasive grains to the end face of the glass substrate and polishing the end face by rotating and bringing a polishing brush whose surface is densely packed without any gaps between them. Method for manufacturing glass substrate.   The method for manufacturing a glass substrate for an information recording medium according to claim 1, wherein the end surface is an outer peripheral end surface of the glass substrate. A circular hole is formed in the center of the glass substrate,
The method for manufacturing a glass substrate for an information recording medium according to claim 1, wherein the end surface is an inner peripheral end surface of the glass substrate.   The manufacturing method of the glass substrate for information recording media in any one of Claims 1-3 which grind | polishes the said end surface of the said glass substrate laminated | stacked two or more in the said process to grind | polish.   The method for producing a glass substrate for an information recording medium according to any one of claims 1 to 4, wherein the polishing liquid is supplied to the end face from above the glass substrate.   The method for producing a glass substrate for an information recording medium according to claim 5, wherein the polishing liquid flows downward through the gap.   The method for manufacturing a glass substrate for an information recording medium according to any one of claims 1 to 4, wherein the glass substrate is immersed in the polishing liquid.   The method for producing a glass substrate for an information recording medium according to any one of claims 1 to 7, wherein the loose abrasive grains have an average particle diameter of 0.5 µm or more and 2.0 µm or less.   The method for manufacturing a glass substrate for an information recording medium according to any one of claims 1 to 8, wherein the polishing brush reciprocates in an axial direction of the rotation shaft. A glass substrate obtained by the method for producing a glass substrate for information recording medium according to any one of claims 1 to 9,
An information recording medium comprising: a magnetic recording layer formed on a surface of the glass substrate.

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