JP2015069674A - Manufacturing method of magnetic disk glass substrate, and polishing treatment carrier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polishing treatment carrier and a manufacturing method of a magnetic disk glass substrate which are capable of suppressing the occurrence of a scratch on an end surface of a glass substrate and suppressing the formation of defects due to the attachment of fine particles or the like onto a principal face of the glass substrate.SOLUTION: A glass substrate includes: a side wall surface provided on an end surface of the glass substrate orthogonal to a glass principal face; and a chamfered face provided on a part of the end surface, the part being between the side wall surface and both the glass principal faces. The glass substrate is held between an upper surface plate and a lower surface plate while being held in a holding hole of a carrier, and the principal face of the glass substrate is polished. In this case, a thickness of the carrier is smaller than the total lengths of the side wall surface and of one chamfered face in a plate thickness direction of the glass substrate. A part in contact with the upper surface plate, of a boundary part between an internal surface of the holding hole of the carrier and a carrier surface is composed of a softer material than the material composing the inside of the carrier.

Description

  The present invention relates to a method for producing a glass substrate for a magnetic disk, and a polishing carrier used for polishing the glass substrate.

  Conventionally, a glass substrate has been suitably used for a magnetic disk used as one of information recording media. Today, in response to a request for an increase in storage capacity in a hard disk drive device, the density of magnetic recording has been increased. Along with this, the magnetic recording information area is miniaturized by extremely shortening the flying distance from the magnetic recording surface of the magnetic head. It is preferable that the size and shape of the glass substrate used for such a magnetic disk be manufactured with high accuracy as intended.

In order to manufacture the glass substrate with high accuracy in size and shape, the surface of the glass substrate is ground and polished. In grinding and polishing of a glass substrate, a plate-like grinding or polishing carrier for holding a glass substrate to be ground or polished by being sandwiched between two surface plates during grinding or polishing is used. The carrier is provided with a holding hole for holding the glass substrate.
Conventionally, a fiber reinforced resin obtained by reinforcing a resin with glass fiber has been widely used as the carrier from the viewpoint of mechanical strength and cost. In particular, a carrier having a configuration in which a plurality of layers in which an epoxy resin is reinforced with glass fibers is laminated is preferably used. However, in this carrier, when the glass substrate is ground or polished, a defect, for example, a concave scratch may occur on the end surface (outer peripheral end surface) of the glass substrate. The depth of the scratch is deeper and longer than other scratches formed on the end face. In some cases, the abrasive grains in the slurry adhere to the concave portions of the scratches, and the glass chips generated by the scratches adhere to the end surface to become a dust generation source. In particular, the abrasive grains in the slurry used in the final polishing are sandwiched between the end face and the carrier, adhere to the concave wound as fine particles, and further adhere. The fine particles attached in this way may be detached from the end face of the glass substrate during sputtering performed when forming the magnetic layer on the glass substrate and get on the main surface to create a defect in the magnetic layer.

  Under such circumstances, a technique for mounting or applying a resin to a holding hole of a carrier is known (Patent Document 1, Patent Document 2, and Patent Document 3). All of these techniques are performed in order to prevent the outer peripheral end face of the substrate from being damaged.

JP 2006-088314 A JP 2006-068895 A JP 2000-288922 A

  However, when a resin is applied to the side surface of the holding hole of the carrier, the applied resin is partially peeled, and the peeled resin creates a gap between the carrier and the surface plate. When the glass substrate being polished or ground is sandwiched between the gaps, the glass substrate is easily damaged. Furthermore, a part of the peeled resin becomes fine particles and is mixed in the slurry and remains on the main surface of the ground or polished glass substrate to form convex defects, or the fine particles are rubbed on the main surface of the glass substrate. To make scratches on the main surface. Such a problem also occurs when a resin is attached to the holding hole of the carrier.

  Therefore, the present invention suppresses the occurrence of scratches on the end face of the glass substrate, and further suppresses the formation of defects due to adhesion of fine particles or the like to the main surface of the glass substrate. It aims at providing the manufacturing method of a glass substrate.

In order to solve the above-described conventional problems, the present inventor has intensively studied the carrier and the glass substrate, and the edge portion, which is the boundary between the inner wall surface of the carrier holding hole and the surface of the carrier, is ground or polished. In the middle, it was found that the outer peripheral end face of the glass substrate was damaged by contacting the side wall surface of the outer peripheral end face of the glass substrate. That is, it has been found that the edge portion of the carrier holding hole comes into contact with the side wall surface of the glass substrate during grinding or polishing of the glass substrate, and the edge portion is damaged by applying a force concentrated on the side wall surface. In particular, when the carrier is composed of a glass fiber reinforced resin, the surface of the carrier is also rubbed during grinding or polishing of the glass substrate, although the thickness of the carrier is thinner than that of the glass substrate, compared to the resin on the surface. Hard glass fiber is easily exposed. Further, since the holding hole of the carrier comes into contact with the glass substrate during grinding or polishing, the glass fiber is more likely to be exposed at the edge of the holding hole on the surface of the carrier. As described above, the edge portion comes into contact with the side wall surface of the glass substrate, so that the side wall surface of the outer peripheral end surface of the glass substrate is easily damaged.
Based on the above findings, the present inventors have found the following invention.

That is, one aspect of the present invention is a method for producing a glass substrate for a magnetic disk. The manufacturing method includes a side wall surface provided on an end surface of a glass substrate orthogonal to the glass main surface, and a chamfer provided in each portion of the end surface between the side wall surface and both glass main surfaces. The glass substrate is sandwiched between an upper surface plate and a lower surface plate in a state where the glass substrate having a surface is held in a holding hole provided in the carrier, the main surface on both sides of the glass substrate, the upper surface plate, and the lower surface plate It includes a polishing process for polishing the main surface of the glass substrate by relatively moving the disc.
The thickness of the carrier is smaller than the sum of the length of the side wall surface and one chamfered surface in the thickness direction of the glass substrate.
Of the boundary portion between the inner wall surface of the holding hole of the carrier and the carrier surface, the portion facing the upper surface plate is made of a softer material than the material inside the carrier.

  At that time, the carrier has a laminated structure in which a plurality of sheet-like materials are laminated, and the sheet-like material constituting the carrier surface arranged on the upper surface plate side during the polishing treatment is the soft material. It is preferable that it is comprised.

  Further, the carrier has a laminated structure in which a plurality of sheet-like materials are laminated, and the sheet-like material constituting the carrier surface is made of a resin that does not contain fibers and constitutes the inside of the carrier. It is also preferable that the sheet-like material currently comprised is comprised with the fiber reinforced resin.

  Another embodiment of the present invention is a holding hole for holding the glass substrate when the glass main surface of the glass substrate is polished by sandwiching the disk-shaped glass substrate between the upper surface plate and the lower surface plate. A carrier for polishing treatment having The polishing carrier has a laminated structure in which a plurality of sheet-like materials are laminated, and the sheet-like material constituting the inside of the polishing carrier is made of a fiber reinforced resin containing fibers, The sheet-like material constituting at least one surface layer of the carrier for polishing treatment is made of a resin not containing fibers.

  According to the above-described method for manufacturing a glass substrate for magnetic disk and the carrier for polishing treatment, it is possible to suppress the generation of scratches on the end face of the glass substrate and to further suppress the formation of defects on the main surface of the glass substrate.

It is a disassembled perspective view of an example of the grinding device (double-side polish apparatus) using the carrier of this embodiment. It is sectional drawing of an example of the grinding apparatus shown in FIG. It is sectional drawing of an example of the carrier of this embodiment. It is a figure explaining the contact state of the end surface of the glass substrate in grinding | polishing, and the side wall surface of the holding hole of the carrier of this embodiment.

  Hereinafter, the manufacturing method of the polishing carrier and the magnetic disk glass substrate of the present invention will be described in detail. In the present specification, the polishing treatment includes grinding of the glass substrate and polishing of the glass substrate to reduce the roughness of the glass main surface of the glass substrate after grinding. Therefore, the polishing carrier is a carrier that can be used for grinding and polishing a glass substrate.

[Polishing equipment]
A glass substrate polishing apparatus using the polishing carrier of this embodiment will be described with reference to FIGS. FIG. 1 is an exploded perspective view of a polishing apparatus (double-side polishing apparatus). FIG. 2 is a sectional view of the polishing apparatus. Since the grinding apparatus has the same configuration as the polishing apparatus, description of the grinding apparatus is omitted.

  As shown in FIG. 1, the polishing apparatus has a pair of upper and lower surface plates, that is, an upper surface plate 40 and a lower surface plate 60. An annular glass substrate G is held between the upper surface plate 40 and the lower surface plate 60, and either one or both of the upper surface plate 40 and the lower surface plate 60 are moved to operate the glass substrate G and each By moving the surface plate relative to each other, both main surfaces of the glass substrate G can be polished. A polishing slurry containing abrasive grains is supplied between the glass substrate and the surface plate. Hereinafter, when the upper surface plate 40 and the lower surface plate 60 are collectively described, they are simply referred to as a surface plate.

The configuration of the polishing apparatus will be described more specifically with reference to FIGS.
In the polishing apparatus, the polishing pad 10 is attached to the upper surface of the lower surface plate 60 and the lower surface of the upper surface plate 40. In FIG. 1, the polishing pad 10 is shown in a sheet form. For the polishing pad 10, for example, foamed urethane resin or the like can be used.
The carrier 30 has a holding hole for holding the glass substrate G when the disk-shaped glass substrate G is sandwiched between the upper surface plate 40 and the lower surface plate 60 and the main surface of the glass substrate G is polished. Specifically, the carrier 30 includes a tooth portion 31 provided on the outer peripheral portion and meshing with the sun gear 61 and the internal gear 62, and one or a plurality of holding holes 32 for receiving and holding the glass substrate G. . The sun gear 61, the internal gear 62 provided on the outer edge, and the disk-shaped carrier 30 constitute a planetary gear mechanism centered on the central axis CTR as a whole. The disc-shaped carrier 30 meshes with the sun gear 61 on the inner peripheral side and meshes with the internal gear 62 on the outer peripheral side, and accommodates and holds one or more glass substrates G. On the lower surface plate 60, the carrier 30 revolves while rotating as a planetary gear, and the glass substrate G and the lower surface plate 60 are relatively moved. For example, if the sun gear 61 rotates in the counterclockwise direction, the carrier 30 rotates in the clockwise direction, and the internal gear 62 rotates in the counterclockwise direction. As a result, a relative motion occurs between the lower surface plate 60 and the glass substrate G. Similarly, the glass substrate G and the upper surface plate 40 may be moved relatively.

  During the operation of the relative movement, the upper surface plate 40 is pressed against the glass substrate G held by the carrier 30 (that is, in the vertical direction) with a predetermined pressure, and thereby the polishing pad is pressed against the glass substrate G. 10 is pressed. In addition, as shown in FIG. 2, the polishing slurry is supplied between the glass substrate G and the polishing pad 10 from a supply tank 71 via one or a plurality of pipes 72 by a pump (not shown).

FIG. 3 is a cross-sectional view of an example of the carrier 30. The carrier 30 has a laminated structure in which five sheet-like materials are laminated. The surface layer on one side of the carrier 30 is a resin layer 30a. On the other hand, the inner three layers sandwiched between the surface layers on both sides of the carrier 30 and the surface layer on the surface opposite to the resin layer 30a are fiber reinforced resin layers 30b having a configuration different from that of the resin layer 30a. The sheet-like material constituting the resin layer 30a on the carrier surface is not a resin reinforced with fibers but a sheet-like resin material containing no fibers. The sheet-like material constituting the surface layer on the other side of the carrier 30 and the internal fiber reinforced resin layer 30b is made of a fiber reinforced resin obtained by reinforcing the same resin as the resin constituting the resin layer 30a with glass fibers. . The fiber reinforced resin layer 30b is laminated inside the carrier 30 because the carrier 30 causes bending deformation and shear deformation due to the force received from the sun gear 61 and the internal gear 62 during polishing, and as a result, the glass substrate G is damaged. This is to ensure bending rigidity, shear rigidity, and mechanical strength so as not to occur.
The resin layer 30a is softer than the glass fiber used for the fiber reinforced resin layer 30b. Soft means that it is soft in terms of hardness. Here, the hardness is Rockwell hardness and is defined in JIS 2245: 2011. For example, when a fiber of glass having a Rockwell hardness HRC of 55.2 to 57.8 (Mohs hardness of about 6.5 and Vickers hardness of 600 to 640 HV) is used for the fiber reinforced resin layer 30b, 55.2. A material having a lower Rockwell hardness may be used for the resin layer 30a. As an index of hardness, Mohs hardness or Vickers hardness can be used in addition to Rockwell hardness.
This embodiment has a five-layer laminated structure in which three layers are provided inside and two layers are provided on the surface layer, but is not limited to a five-layer laminated structure, and may be three layers, four layers, six layers, seven layers, or the like. .

  The carrier 30 has a five-layer laminated structure in which one resin layer 30a and four fiber-reinforced resin layers 30b are laminated. Since the five-layer laminated structure is formed over the entire carrier 30, the holding hole Also on the side wall surface of 32, it has a laminated structure of five layers. Therefore, in the resin layer 30a that is the outermost layer of the carrier 30, the boundary portion between the inner wall surface of the holding hole 32 that contacts the end surface of the glass substrate G and the surface of the carrier 30 (on the side facing the upper surface plate 40). All materials constituting the outermost layer including the edge portion which is the boundary portion), that is, the resin is at least one material constituting the inner layer region surrounding the holding hole 32 in the inner layer of the carrier 30, ie, glass in the resin. Softer than fiber. The inner layer of the carrier 30 refers to a layer at the innermost portion of the outermost layer on both sides of the carrier 30.

The reason why the resin layer 30a and the fiber reinforced resin layer 30b are laminated as described above and the resin layer 30a is used as the outermost layer on one side of the carrier 30 is as follows. FIG. 4 is a diagram for explaining a contact state between the end surface of the glass substrate G being polished and the inner wall surface of the holding hole 32 of the carrier 30.
As shown in FIG. 4, the carrier 30 is set so that the side on which the resin layer 30 a is provided on the surfaces on both sides of the carrier 30 is positioned on the upper surface plate 40 side. The end surface of the glass substrate G to be polished includes a side wall surface T orthogonal to the glass main surface, and a chamfered surface C provided at each portion of the end surface between the side wall surface T and the glass main surfaces on both sides. The shape is processed to have. The lengths of the chamfered surfaces C in the thickness direction are the same. At this time, the thickness of the carrier 30 is smaller than the sum of the lengths of the side wall surface T and one chamfered surface C in the thickness direction of the glass substrate G. In this case, the edge portion E ₁ located above the holding hole 32 of the carrier 30 in the drawing contacts the side wall surface T of the glass substrate G. Since the edge portion E ₂ located below the carrier 30 in the drawing is at the same height as the inclined surface C that is the chamfered surface of the glass substrate G, the edge portion E ₂ corresponds to the end surface of the glass substrate G. Do not touch. The edge portion E ₁ is in contact with the end surface of the glass substrate G, but since the edge portion E ₁ is a portion included in the resin layer 30a, the resin that forms the edge portion E ₁ is the glass fiber that forms the reinforced resin layer 30b. Softer than that. Therefore, the side wall surface T receives the force of the glass substrate G from the edge portion E ₁ is alleviated. In the case of the conventional carrier, since the glass fiber is exposed at the edge portion E ₁ , the side wall surface of the glass substrate G is caused by the concentrated force received from the edge portion E ₁ and further by the glass fiber exposed from the edge portion E _1. Is easy to cause scratches. On the other hand, in the carrier 30 of the present embodiment, the edge portion E ₁ is made of a resin having a lower hardness than glass fibers, and is made of a resin layer without glass fibers. that side wall surface of being damaged from the edge portion E _1, can be suppressed as compared with the conventional carrier.

Thus, the carrier 30 of the present embodiment has a laminated structure in which a plurality of sheet-like materials are laminated, and the sheet-like material constituting the carrier surface arranged on the upper surface plate 40 side during the polishing process. Is preferably made of a softer material than the material inside the carrier 30.
Further, the carrier 30 of the present embodiment has a laminated structure in which a plurality of sheet-like materials are laminated, and the sheet-like material constituting the carrier surface is made of a resin that does not contain fibers. It is preferable that the sheet-like material which comprises the inside of a carrier is comprised with the fiber reinforced resin.

Moreover, the carrier 30 can also be comprised with the resin layer which does not contain a fiber at all instead of the fiber reinforced resin layer 30b other than the laminated structure comprised with the resin layer 30a and the fiber reinforced resin layer 30b. Even in this case, the resin used for the resin layer 30a, which is the outermost layer of the carrier 30, is made of a soft material as compared with the resin used for the resin layer not containing any fibers. That is, of the outermost layer of the carrier 30, the resin that forms the outermost layer including the edge portion E ₁ of the holding hole 32 that contacts the end surface of the glass substrate G is the inner layer that surrounds the holding hole 32 among the inner layers of the carrier 30. Softer than the resin that composes the region (low hardness). For this reason, also in this case, the edge portion E ₁ can suppress the damage to the side wall surface of the glass substrate G due to the edge portion E ₁ compared to the conventional carrier. The type of sheet material used for the fiber reinforced resin layer 30b is not particularly limited, and examples thereof include glass fiber cloth, glass fiber nonwoven cloth, aramid fiber woven cloth, and polyester fiber woven cloth. The fiber reinforced resin layer 30b is obtained by impregnating a resin such as a woven fabric or a non-woven fabric with a resin. In addition, the fiber reinforced resin layer 30b includes micro or nano-sized fibers as a filler to improve mechanical strength and rigidity. It may be. The type of resin used for the resin layer 30a is not particularly limited, and examples thereof include epoxy resins, phenol resins, unsaturated polyester resins, and polyimide resins, and also examples include polyacetal resins (POM) and polyphenylene sulfide resins (PPS). .

3, the resin layer 30a is provided only on one side of the outermost layers on both sides of the carrier 30, but the resin layer 30a may be provided on the outermost layer on both sides of the carrier 30. This is preferable in that it is not necessary to set the side of the carrier 30 on which the resin layer 30a is provided so as to face the upper surface plate 40 before polishing. In other words, the carrier 30 has a laminated structure in which a plurality of sheet-like materials are laminated, and the sheet-like material constituting the carrier surface arranged on the upper surface plate 40 side during the polishing process is inside the carrier 30. It is preferable that it is made of a soft material as compared with the material.
As described above, the carrier 30 has a laminated structure in which a plurality of sheet-like materials are laminated, and the sheet-like material constituting the carrier surface is made of a resin that does not contain fibers. It is preferable that the sheet-like material which comprises the inside is comprised with the fiber reinforced resin.

Further, the uppermost in the present embodiment includes a stacked structure of the resin layer 30a and the fiber-reinforced resin layer 30b, but using a configuration in which the entire carrier 30, the edge portion E ₁ of the holding hole 32 which is in contact with the end face of the glass substrate G You may use the structure which provides the resin layer 30a only on a surface layer. In this case, a portion other than the outermost layer may be provided with a fiber reinforced resin layer reinforced with glass fibers as in the conventional case. However, providing the laminated structure of the resin layer 30a and the fiber reinforced resin layer 30b on the entire carrier 30 is preferable in that it does not leave the outermost layer surrounding the holding hole 32 of the resin layer 30a.

  Moreover, in this embodiment, it is preferable that the same resin material is used for the resin layer 30a and the fiber reinforced resin layer 30b from the viewpoint of ensuring the mechanical strength of the laminated structure. When different resin materials are used, peeling or the like is likely to occur at the layer boundary. For example, epoxy resin, polyacetal resin (POM), polyphenylene sulfide resin (PPS), or the like is used as the type of resin.

Further, the ratio of the thickness of the inner layer not including the outermost layer to the plate thickness of the carrier 30 is preferably 30% or more from the viewpoint of securing the bending rigidity, shear rigidity, and mechanical strength of the carrier 30. . More preferably, it is 50% or more. In this case, the upper limit of the ratio is preferably 95% from the viewpoint of securing the thickness of the resin layer 30a and suppressing the end surface of the glass substrate G from being damaged.
Further, the ratio of the thickness of the resin layer 30a which is the surface layer to the thickness of the carrier 30 is 2.5% or more and 35% or less, so that the thickness of the resin layer 30a is secured and the glass substrate G It is preferable at the point which suppresses damaging the end surface. A more preferable lower limit of the thickness of the resin layer 30a is 5%.

1 and 2, the polishing pad is attached to the upper surface plate 40 or the lower surface plate 60. The upper surface plate 40 or the lower surface plate 60 is provided with fixed abrasive grains, and the glass substrate G and A coolant may be supplied between the upper surface plate 40 or the lower surface plate 60. The carrier 30 can also be used in a grinding device for grinding the glass substrate G in addition to the polishing device.
A polishing apparatus using such a carrier 30 and further a grinding apparatus having substantially the same configuration as the polishing apparatus can be used suitably for manufacturing a glass substrate for a magnetic disk as shown below. In grinding using a glass substrate grinding apparatus, the roughness Ra of the main surface of the glass substrate after grinding is larger than in grinding. In such grinding, the main surface of the glass substrate may be ground by supplying a grinding liquid between each of the upper surface plate and the lower surface plate and the glass substrate. Alternatively, fixed abrasive grains may be provided on each of the upper surface plate and the lower surface plate, and a lubricating liquid may be supplied between the fixed abrasive particles and the glass substrate to grind the main surface of the glass substrate.

(Description of manufacturing method of glass substrate for magnetic disk)
In the manufacturing method of the present embodiment, first, a glass blank that is a material for a plate-shaped magnetic disk glass substrate having a pair of main surfaces is formed. Next, rough grinding of this glass blank is performed. Thereafter, shape processing and end face polishing are performed on the glass blank. Thereafter, fine grinding using fixed abrasive grains is performed on the glass substrate obtained from the glass blank. Thereafter, first polishing, chemical strengthening, and second polishing are performed on the glass substrate. In the present embodiment, the above process is performed. However, the above process is not necessarily performed, and these processes may not be appropriately performed. Hereinafter, each process will be described.

(A) Molding of glass blank In the molding of a glass blank, for example, a press molding method can be used. A circular glass blank can be obtained by the press molding method. Furthermore, it can manufacture using well-known manufacturing methods, such as a downdraw method, a redraw method, and a fusion method. A disk-shaped glass substrate serving as a base of the magnetic disk glass substrate can be obtained by appropriately performing shape processing on the plate-shaped glass blanks produced by these known production methods.

(B) Rough grinding In rough grinding, specifically, a glass blank was provided on a holding member (carrier) to be mounted on a well-known double-side grinding apparatus of a planetary gear mechanism similar to the apparatus shown in FIGS. The main surfaces on both sides of the glass blank are ground while being held in the holding holes. At this time, the carrier 30 described above can be used. For example, loose abrasive grains are used as the abrasive. In rough grinding, the glass blank is ground so as to approximate the target plate thickness and the flatness of the main surface. In addition, rough grinding is performed according to the dimensional accuracy or surface roughness of the formed glass blank, and may not be performed depending on the case.

(C) Shape processing Next, shape processing is performed. In the shape processing, after forming the glass blank, a circular hole is formed using a known processing method to obtain a disk-shaped glass substrate having a circular hole. Thereafter, the end surface of the glass substrate is chamfered. Thereby, the end face of the glass substrate is chamfered (intervening surface) inclined with respect to the glass main surface between the side wall surface T orthogonal to the main surface and the side wall surface and the glass main surfaces on both sides. C is formed.

(D) End surface polishing Next, end surface polishing of the glass substrate is performed. The end surface polishing is a process for performing polishing by supplying a polishing liquid containing loose abrasive grains between the polishing brush and the end surface of the glass substrate and moving the polishing brush and the glass substrate relatively, for example. In the end surface polishing, the inner peripheral side end surface and the outer peripheral side end surface of the glass substrate are to be polished, and the inner peripheral side end surface and the outer peripheral side end surface are in a mirror state.

(E) Fine grinding Next, fine grinding is performed on the main surface of the glass substrate. Specifically, grinding is performed on the main surface of the glass substrate using a double-side grinding device having a planetary gear mechanism similar to the polishing device shown in FIGS. Do. In this case, fixed abrasive grains are provided on the surface plate instead of the polishing pad. Specifically, grinding of the main surfaces on both sides of the glass substrate is performed with fixed abrasive grains while holding the glass substrate in the holding holes provided in the carrier 30 described above, which is a holding member of the double-side grinding apparatus. The machining allowance by grinding is, for example, about 10 μm to 200 μm.
In the grinding of this embodiment, the grinding surface containing fixed abrasive grains and the main surface of the glass substrate are brought into contact with each other to grind the main surface of the glass substrate. However, grinding using loose abrasive grains may be performed.

(F) 1st grinding | polishing Next, 1st grinding | polishing is given to the main surface of a glass substrate. Specifically, the main surface on both sides of the glass substrate G is polished while holding the outer peripheral side end face of the glass substrate in the holding hole 32 provided in the carrier 30 of the polishing apparatus shown in FIGS. . The first polishing uses a polishing pad attached to a surface plate using loose abrasive grains. The first polishing removes cracks and distortions remaining on the main surface when, for example, grinding with fixed abrasive grains is performed. In the first polishing, it is possible to reduce the surface roughness of the main surface, for example, the arithmetic average roughness Ra, while preventing the shape of the end portion of the main surface from excessively dropping or protruding.
The free abrasive grains used for the first polishing are not particularly limited. For example, cerium oxide abrasive grains or zirconia abrasive grains are used.
Although the kind in particular of a polishing pad is not restrict | limited, For example, a hard foaming urethane resin polisher is used.

(G) Chemical strengthening The glass substrate can be appropriately chemically strengthened. As the chemical strengthening liquid, for example, a molten liquid obtained by heating potassium nitrate, sodium nitrate, or a mixture thereof can be used. Then, by immersing the glass substrate in the chemical strengthening solution, lithium ions and sodium ions in the glass composition on the surface of the glass substrate are converted into sodium ions and potassium ions having relatively large ion radii in the chemical strengthening solution, respectively. By replacing each, a compressive stress layer is formed in the surface layer portion, and the glass substrate is strengthened.
The timing of performing chemical strengthening can be determined as appropriate, but it is particularly preferable to perform polishing after chemical strengthening because foreign matters fixed on the surface of the glass substrate by chemical strengthening can be removed along with smoothing of the surface. . Moreover, chemical strengthening should just be performed as needed and does not need to be performed.

(H) Second polishing (mirror polishing)
Next, 2nd grinding | polishing is given to the glass substrate after chemical strengthening. The second polishing is intended for mirror polishing of the main surface. Also in the second polishing, a double-side polishing apparatus of a planetary gear mechanism having the same configuration as the double-side polishing apparatus used for the first polishing is used. Specifically, the main surface on both sides of the glass substrate G is polished while holding the outer peripheral side end face of the glass substrate in the holding hole 32 provided in the carrier 30 of the polishing apparatus shown in FIGS. . By doing so, it is possible to reduce the roughness of the main surface while preventing the shape of the end portion of the main surface from excessively dropping or protruding. The second polishing differs from the first polishing in that the type of loose abrasive grains is different and the particle size is reduced, and the hardness of the resin polisher of the polishing pad is softened.

As the free abrasive grains used for the second polishing, for example, fine particles such as colloidal silica are used. By cleaning the polished glass substrate, a glass substrate for a magnetic disk can be obtained.
Although 2nd grinding | polishing is not necessarily essential, it is preferable to implement by the point which can make the level of the surface unevenness | corrugation of the main surface of a glass substrate still better. Thus, the glass substrate subjected to the second polishing becomes a glass substrate for a magnetic disk.

In at least one polishing process of rough grinding, fine grinding, first polishing, and second polishing performed by a grinding device or a polishing device, an upper surface plate and a lower surface plate that sandwich the glass substrate G from the vertical direction are used. The outermost layer on which the resin layer 30 a is provided is provided on one main surface of the carrier 30. In this case, in at least one of rough grinding, fine grinding, first polishing, and second polishing, the outermost layer provided with the resin layer 30a is positioned on the upper surface plate side, that is, faces the upper surface plate. Further, it is preferable that the carrier 30 is disposed between the upper surface plate and the lower surface plate in order to make it difficult to damage the side wall surface of the glass substrate G by the edge portion E ₁ .
Moreover, as shown in FIG. 4, the end surface of the glass substrate G has two side walls T extending in the direction perpendicular to the main glass surface, and two side walls T connecting the main glass surfaces on both sides. And an inclined surface C. In this case, the thickness of the carrier 30 is thinner than the sum of the lengths of the side wall surface T and one chamfered surface C in the thickness direction of the glass substrate G. Therefore, the edge portion E ₁ of the holding hole 32 on the upper surface plate 40 side of the carrier 30 contacts the side wall surface T during the grinding or polishing process. Even in such a case, the side wall surface T of the glass substrate G can be hardly damaged by using the carrier 30 of the present embodiment.

  The carrier 30 of the present embodiment is used in polishing performed using a slurry containing loose abrasive grains, and makes it difficult to damage the end surface of the glass substrate G by capturing fine particles that cause defects on the glass main surface. This is preferable. In particular, since the processing of the main surface of the glass is final in the second polishing, it is preferable to use the carrier 30 of the present embodiment for the second polishing from the viewpoint of making it difficult to damage the end surface of the glass substrate G.

As described above, the thickness of the carrier 30 in the present embodiment is smaller than the sum of the lengths of the side wall surface T and one chamfered surface C in the thickness direction of the glass substrate G, and the carrier 30 is retained. Of the boundary portion between the inner wall surface of the hole 32 and the carrier surface, the boundary portion facing the upper surface plate 40 is made of a softer material than the material inside the carrier 30. That is, all the materials constituting the outermost layer including the edge portion E ₁ of the holding hole 32 in contact with the end face of the glass substrate G among the outermost layer of the carrier 30 surround the holding hole 32 in the inner layer of the carrier 30. A soft material is used as compared with at least one material constituting the inner layer. For this reason, the generation | occurrence | production of the damage | wound to the end surface of a glass substrate can be suppressed during grinding or grinding | polishing of the glass main surface. For this reason, since the microparticles | fine-particles and glass chip which are captured by a damage | wound lessen, it can suppress that a defect is formed in the main surface of the glass substrate G.

[Examples, conventional examples, comparative examples]
In order to confirm the effect of the present embodiment, various carriers were produced, the glass substrate using this carrier was polished, and scratches (end surface defects) on the end surface of the glass substrate were examined. The glass substrate for magnetic disk to be processed was a glass substrate having a size of 2.5 inches and a thickness of 0.8 mm.
After performing the manufacturing method of the glass substrate mentioned above to (e) fine grinding, (f) 1st grinding | polishing and (h) 2nd grinding | polishing of the glass main surface were carried out on condition of the following using the carrier shown in following Table 1. went.
Each carrier has a five-layer structure in which sheet-like materials are stacked, and the outermost layer (one layer) of the carrier located on the upper surface plate 40 side, its inner layer (three layers), and the lower surface plate 60 side. As shown in Table 1 below, the materials used for the outermost layer (one layer) of the carrier located in FIG. The thickness of the outermost layer of the carrier is shown as a ratio to the thickness of the carrier. The ratio of the thickness of the inner layer is a value obtained by subtracting the total ratio of the thicknesses of the outermost layers on both sides from 100%.
After polishing using the carrier, the state of the outer peripheral end face of the glass substrate G was observed with a video scope over the entire circumference, and the presence or absence of scratches by the edge portion E ₁ was examined. Table 1 below also shows the results of a survey for the presence or absence of scratches.

Both the polyacetal resin and the polyphenylene sulfide resin are softer than the glass fiber. Therefore, the outermost layer of Examples 3 and 4 is made of a softer material than the inner layer. Thus, when grinding | polishing using the carrier 30 of Examples 1-4, since there is no damage | wound in the outer peripheral end surface of the glass substrate G and there is a damage | wound in a prior art example and Comparative Examples 1 and 2, this embodiment The effect of is obvious. In addition, in the case of the glass substrate which carried out the grinding | polishing process using the carrier 30 of Example 1, although the clear damage | wound was not observed on the outer peripheral end surface, the thin linear recessed part was observed. In the case of the glass substrate polished using the carrier 30 of Examples 2 to 4, no slight recess was observed on the outer peripheral end face.
Thus, the thickness of the outermost layer is preferably 5% or more of the thickness of the carrier 30.

Further, the same epoxy resin and glass fiber + epoxy resin as in Examples 1 and 2 were used, and the thickness of the outermost layer on both sides (the thicknesses of the difference surface layers on both sides were the same as each other) while keeping the plate thickness of the carrier 30 constant. When various changes were made, the presence or absence of damage to the glass substrate G due to polishing was examined. Furthermore, the state of the outer peripheral end surface of the polished glass substrate G was observed over the entire circumference with a video scope, and the presence or absence of scratches due to the edge portion E _{1 on} the outer peripheral end surface of the glass substrate was examined. Table 2 below shows the specifications of the carrier 30, the presence / absence of damage to the glass substrate G, and the results of investigations for the presence / absence of scratches.

  None of the glass plates polished using the carrier 30 of Examples 5 to 8 had any scratches on the outer peripheral end face. Further, if the thickness of the inner layer is 30% or more of the thickness of the carrier, the glass substrate G can be polished without being damaged, and the bending rigidity, shear rigidity, and mechanical strength of the carrier 30 are ensured. I knew it was possible.

  As mentioned above, although the manufacturing method of the glass substrate for magnetic discs of this invention and the carrier for grinding | polishing processing were demonstrated in detail, this invention is not limited to the said embodiment and Example, In the range which does not deviate from the main point of this invention, it is various. Of course, improvements and changes may be made.

DESCRIPTION OF SYMBOLS 10 Polishing pad 30 Carrier 31 Tooth part 32 Holding hole 40 Upper surface plate 60 Lower surface plate 61 Sun gear 62 Internal gear 71 Supply tank 72 Piping

Claims (4)

A side wall surface provided on the end surface of the glass substrate orthogonal to the glass main surface, and a chamfered surface provided in each portion of the end surface between the side wall surface and the glass main surfaces on both sides. The glass substrate is sandwiched between an upper surface plate and a lower surface plate while the glass substrate is held in a holding hole provided in a carrier, and the main glass surface, the upper surface plate, and the lower surface plate are relatively moved. Thus, a method for producing a glass substrate for a magnetic disk including a polishing treatment for polishing the main surface of the glass substrate,
The thickness of the carrier is a thickness that is thinner than the sum of the length of the side wall surface and one chamfered surface in the thickness direction of the glass substrate,
Of the boundary portion between the inner wall surface of the holding hole of the carrier and the carrier surface, the portion facing the upper surface plate is made of a softer material than the material inside the carrier. A method for producing a glass substrate for a magnetic disk.   The carrier has a laminated structure in which a plurality of sheet-like materials are laminated, and the sheet-like material constituting the carrier surface arranged on the upper surface plate side during the polishing process is constituted by the soft material. The method for producing a glass substrate for a magnetic disk according to claim 1.   The carrier has a laminated structure in which a plurality of sheet-like materials are laminated, and the sheet-like material constituting the carrier surface is made of a resin not containing fibers, and constitutes the inside of the carrier. The manufacturing method of the glass substrate for magnetic discs of Claim 1 or 2 with which the sheet-like material which is comprised with the fiber reinforced resin. A polishing carrier having a holding hole for holding the glass substrate when the glass main surface of the glass substrate is polished by sandwiching a disk-shaped glass substrate between an upper surface plate and a lower surface plate,
The polishing carrier has a laminated structure in which a plurality of sheet-like materials are laminated, and the sheet-like material constituting the inside of the polishing carrier is made of a fiber reinforced resin containing fibers, A carrier for polishing treatment, wherein the sheet-like material constituting at least one surface layer of the carrier for polishing treatment is made of a resin not containing fibers.

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