JP2014182844A - Manufacturing method for glass substrate for magnetic disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To polish an end face of a glass plate without leaving an unpolished part of an interposing face, when manufacturing a glass substrate for a magnetic disk.SOLUTION: The end face of the glass substrate includes a side wall face perpendicular to a main face of the glass substrate, and the interposed face which is interposed between the main face and the side wall face. In the manufacturing method of the glass substrate for the magnetic disk, an end face polishing process is performed by relatively moving a polishing brush and the glass substrate while supplying a polishing liquid containing free abrasive grains between the polishing brush and the end face of the glass substrate. The end face polishing process includes a first process for polishing the side wall face, and a second process for at least performing polishing of the interposed face after the first process while maintaining the surface roughness of the side wall face.

Description

  The present invention relates to a method for manufacturing a glass substrate for a magnetic disk including an end surface polishing process in which a polishing brush is pressed against an end surface of a disk-shaped glass substrate having a circular hole in the center.

  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 general, the inner peripheral side of the circular hole provided at the center of the glass substrate for magnetic disk and the end surface on the outer peripheral side of the disk shape of the glass substrate are a side wall surface orthogonal to the main surface of the glass substrate, and the main surface And an intervening surface interposed between the side wall surfaces. The interposed surface is, for example, an inclined surface that is chamfered with an inclination angle with respect to the main surface. It is preferable that the side wall surface and the interposition surface have a small surface roughness and have a shape as designed. For this purpose, when a glass substrate for a magnetic disk is manufactured, the glass substrate, which is a base plate, is shaped and then subjected to end face polishing.

  In general, in order to produce a glass substrate for a magnetic disk, the intervening surface and the side wall surface of the glass substrate, which is a base plate, are brush-polished using, for example, a slurry containing cerium oxide abrasive grains (free abrasive grains) as abrasive grains. It is polished by. Such a polishing example is described in paragraph 0034 of Patent Document 1 below, for example.

JP2012-203922A

  In the conventional end surface polishing as described in Patent Document 1, the side wall surface and the intervening surface are simultaneously polished, but the intervening surface is farther from the polishing brush than the side wall surface, and the intervening surface is an inclined surface. Therefore, when the side wall surface and the intervening surface are polished at the same time, there may be a polishing residue on the intervening surface.

  Accordingly, an object of the present invention is to provide a method for producing a glass substrate for a magnetic disk capable of polishing an end face of a glass plate so that there is no residual polishing of the intervening surface when producing a glass substrate for a magnetic disk. To do.

  The inventor of the present application has found that there is a polishing residue on the interposition surface in the conventional end surface polishing method in which the interposition surface and the sidewall surface are simultaneously polished. Therefore, as a result of intensive studies to suppress this polishing residue, the present invention having the following contents has been achieved.

  One aspect of the present invention is a method for manufacturing a glass substrate for a magnetic disk, including an end surface polishing process in which a polishing brush is pressed against an end surface of a disk-shaped glass substrate having a circular hole in the center, the surface being polished. The end surface of the substrate has a side wall surface and an intervening surface interposed between the main surface and the side wall surface, and the end surface polishing treatment is performed between the polishing brush and the end surface of the glass substrate. A polishing process is performed by supplying a polishing liquid containing grains and relatively moving the polishing brush and the glass substrate, and the end surface polishing process is a first process for polishing the side wall surface; A method for manufacturing a glass substrate for a magnetic disk, comprising: a second process for simultaneously polishing the side wall surface and the interposition surface after the first process.

  At this time, the first treatment is polished so that the surface roughness Rz of the side wall surface is 0.15 μm or less, and the second treatment is that the surface roughness Rz of the interposition surface is 0.15 μm or less. It is preferable to polish as described above.

  Moreover, it is preferable that the length of the bristle of the said polishing brush used by the said 1st process and the said 2nd process is the same.

  In the first process and the second process, it is preferable that the polishing brush is moved in the thickness direction of the glass substrate during polishing.

  In the second process, it is preferable to perform polishing by moving the position of the polishing brush to a position closer to the intervening surface than the position of the polishing brush in the first process.

  In the method for manufacturing a glass substrate for a magnetic disk described above, the end face of the glass plate can be polished so that there is no residual polishing of the intervening surface.

(A), (b) is a figure which shows the state which grind | polishes each of the inner peripheral end surface and outer peripheral end surface of a disk-shaped glass substrate using a polishing brush. It is a figure which expands and demonstrates grinding | polishing of a glass substrate. It is a figure which shows an example of the time change of the distance L from the center axis | shaft of a grinding | polishing brush to a side wall surface in the end surface grinding | polishing process performed with the manufacturing method of the glass substrate for magnetic discs in this embodiment. (A) is a figure which shows the comparative example of the time change of the distance L from the central axis of a grinding | polishing brush to a side wall surface in the end surface grinding | polishing process performed with the manufacturing method of the glass substrate for magnetic discs, (b) It is a figure which shows an example of the cross-sectional shape of the glass substrate obtained by the method shown to (a).

  Hereinafter, the manufacturing method of the glass substrate for magnetic disks of this invention is demonstrated in detail. In addition, in this invention, the glass substrate for magnetic discs means what performed the end surface grinding | polishing process concerning this invention. Specifically, for example, the glass substrate for a magnetic disk according to the present invention may be one immediately after the end surface polishing treatment is performed, or after performing the end surface polishing treatment, It may be in a state before post-processing such as chemical strengthening processing and before the magnetic film or the like is formed.

(Outline of polishing used in this embodiment)
In the method for manufacturing a magnetic disk glass substrate according to this embodiment, a disk-shaped glass substrate having a circular hole in the center is manufactured. The end surface of the glass substrate has a side wall surface and an interposed surface (chamfered surface) interposed between the main surface and the side wall surface. The method for manufacturing a glass substrate for a magnetic disk according to the present embodiment is characterized by a processing method of an end surface polishing process in which a polishing brush is pressed against the end surface of the glass substrate for polishing.
Further, in the method for manufacturing a magnetic disk glass substrate according to this embodiment, the magnetic disk glass substrate includes an end surface polishing process in which a polishing brush is pressed against the end surface of a disk-shaped glass substrate having a circular hole in the center. It is a manufacturing method, Comprising: The end surface of the said glass substrate has a side wall surface and the interposition surface interposed between the said main surface and the said side wall surface, The said end surface grinding | polishing process is the said polishing brush and the said glass A polishing liquid containing loose abrasive grains is supplied between the end face of the substrate and the polishing brush and the glass substrate are moved relative to each other to polish the end face polishing process. And a second process of simultaneously polishing the side wall surface and the interposition surface after the first process.
Here, in the end face polishing treatment, polishing is performed by supplying a polishing liquid (slurry) containing free abrasive grains between the polishing brush and the end face of the glass substrate and relatively moving the polishing brush and the glass substrate. . At this time, the end face polishing process includes a first process for polishing the side wall surface and a second process for simultaneously polishing the interposition surface and the side wall surface after the first process.
In the present embodiment, the end surface may be the outer peripheral side end surface of the glass substrate or the inner peripheral side end surface. In the following description, a glass substrate having a circular hole formed in the center is inserted into the circular hole portion of the laminated body laminated via a spacer, and at least one of the polishing brush and the laminated body is rotated. The inner peripheral side end surface polishing for polishing the inner peripheral side end surface of the glass substrate will be described.

After the side wall surface is polished by the polishing process according to this embodiment, the intervening surface is polished. Therefore, compared to the conventional case where the intervening surface and the side wall surface are polished simultaneously, the intervening surface located far from the side wall surface when viewed from the polishing brush can be polished so that there is no residual polishing. . In this embodiment, when the interposed surface is polished, the connecting portion between the interposed surface and the side wall surface is also partially polished, the curvature of the connecting portion is reduced, and the connecting portion has a gentle curved surface shape. For this reason, it can prevent that the said connection part collides with a jig | tool and makes a chip | tip in the 1st grinding | polishing process after a grinding | polishing process, a chemical strengthening process, and a 2nd grinding | polishing process.
Further, by performing the end surface polishing treatment according to the present embodiment, the difference in surface roughness (maximum height: Rz) between the intervening surface and the side wall surface is reduced, specifically, within 0.05 μm. be able to. Further, by performing the end surface polishing treatment according to the present embodiment, the surface roughness (maximum height: Rz) of the intervening surface and the side wall surface can be set to 0.15 μm or less, respectively. Furthermore, by performing the end surface polishing treatment according to the present embodiment, the arithmetic average roughness (Ra) of the intervening surface and the side wall surface can be 0.015 μm or less, more preferably 0.010 μm or less. The roughness is measured using a stylus meter (measurement distance: 0.25 mm in the plate thickness direction).

For example, end polishing is performed using one polishing brush. At this time, the portion that can be efficiently polished with the polishing brush is the tip of the brush hair of the polishing brush. The abdominal part, which is an intermediate part between the hair tip part and the hair base part, cannot be polished efficiently. Therefore, the side wall surface is polished (first treatment) by fixing the polishing brush at a position where the bristle portion that efficiently polishes contacts the side wall surface and slightly bends. Thereafter, the position of the polishing brush is moved to a position where the bristle portion is in contact with the intervening surface and slightly bent, and the interpolated surface is polished (second processing). That is, in the second treatment, the interposition surface and the side wall surface are polished simultaneously.
When this second treatment is performed, the polishing brush contacts the side wall surface, so that the side wall surface is also polished. However, since the side wall surface has already been polished by the first treatment, it is more preferable that the second treatment is polished while maintaining the surface roughness of the side wall surface. In the second treatment, the side wall surface may be polished so that the surface roughness is further improved. Since the polishing brush is brought close to the glass substrate so as to polish the interposed surface, the interposed surface The polishing residue can be prevented.
Hereinafter, the manufacturing method of the glass substrate for magnetic disks of this embodiment is demonstrated in detail.

An example of a method for producing the magnetic disk glass substrate of the present embodiment will be described below.
First, a glass blank as a material for a plate-like glass substrate for a magnetic disk having a pair of main surfaces is formed. Next, the glass blank is appropriately processed to produce a disk-shaped glass substrate in which a circular hole is formed in the center portion and the end face (at least one of the inner peripheral end face and the outer peripheral end face) is chamfered. Thereafter, end face polishing and main surface polishing are performed. The end surface polishing process and the main surface polishing process may be performed in a plurality of processes as necessary. Moreover, you may perform the grinding process of the main surface and end surface of a glass substrate before a main surface polishing process. At this time, the order of each process may be determined as appropriate.
Hereinafter, each process will be described.

(A) Glass blank forming treatment In forming the glass blank, for example, a press forming method can be used in addition to the float 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 blank serving as a base of the magnetic disk glass substrate is cut out by appropriately performing shape processing on the plate-shaped glass produced by these known manufacturing methods.

(B) Shape processing processing Next, shape processing processing is performed. In the shape processing, a disk-shaped glass substrate having a circular hole is obtained by forming a circular hole using a known processing method after the glass blank forming process. Thereafter, further chamfering is performed. Thereby, the side wall surface orthogonal to the main surface and the interposition surface (chamfering surface) connecting the side wall surface and the main surface are formed on the end surface of the glass substrate.

(C) End surface polishing treatment Next, an end surface polishing treatment of the glass substrate is performed. The end surface polishing process 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 relatively moving the polishing brush and the glass substrate. In the end surface polishing, the inner peripheral side end surface and the outer peripheral side end surface of the glass substrate are in a mirror state. At this time, a slurry containing fine particles such as cerium oxide as free abrasive grains is used. By performing the end surface polishing, it is possible to remove contamination such as dust, foreign matter particles such as dust on the end surface of the glass substrate, damage, or scratches. Thereby, even if it is a case where a magnetic disc is manufactured using this glass substrate, generation | occurrence | production of thermal asperity can be prevented. Further, from the viewpoint of preventing the occurrence of ion precipitation that causes corrosion such as sodium and / or potassium, at least the surface roughness (maximum height: Rz) of the side wall surface and the interposed surface is 0.15 μm or less. It is preferable to polish so as to become 0.10, more preferably 0.10 μm or less. Moreover, in the said viewpoint, it is preferable that the surface roughness (Ra) of at least a side wall surface is 0.015 micrometer or less, and it is more preferable that it is 0.010 micrometer or less. The roughness is measured using a stylus meter (measurement distance: 0.25 mm in the plate thickness direction). The end face polishing process will be described later.

(D) First polishing treatment Next, a first polishing treatment is performed on the main surface of the glass substrate. Specifically, the main surfaces on both sides of the glass substrate are polished while holding the glass substrate in a holding hole provided in a holding member (carrier) attached to the double-side polishing apparatus. In addition, in order to further reduce the surface roughness or perform more precise adjustment, the first polishing process may be divided into a plurality of polishing processes.

(E) Chemical strengthening treatment 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 the chemical strengthening treatment can be determined as appropriate. However, if the polishing treatment is performed after the chemical strengthening treatment, the foreign matter fixed to the surface of the glass substrate by the chemical strengthening treatment can be removed together with the smoothing of the surface. This is particularly preferable because it can be performed.

(F) Second Polishing (Final Polishing) Process Next, a second polishing process is performed on the glass substrate after the chemical strengthening process. Also in the second polishing, a double-side polishing apparatus having the same configuration as the double-side polishing apparatus used for the first polishing is used. After the second polishing, the glass substrate is washed to produce a magnetic disk glass substrate.

(End face polishing treatment)
Here, the end surface polishing treatment according to the present invention will be described in more detail. The end surface polishing process includes a first process for polishing the side wall surface and a second process for polishing the intervening surface in a state where the surface roughness of the side wall surface is maintained after the first process. In the first process and the second process, a polishing liquid containing loose abrasive grains is supplied between the end surface of the glass substrate laminated in large numbers and the polishing brush. Examples of the means for supplying the polishing liquid include spraying with a shower or a mode in which the polishing liquid is ejected from a plurality of polishing liquid supply nozzles. Further, the laminated body of the glass substrate and the polishing brush may be immersed in the polishing liquid, and end face polishing may be performed in the polishing liquid.
Abrasives such as cerium oxide, iron oxide, magnesium oxide, zirconium oxide, and manganese oxide can be used as the free abrasive grains. In particular, cerium oxide is preferably used from the viewpoint of high processing speed. The temperature of the polishing liquid is preferably about 25 ° C. to 40 ° C., for example. In addition, when the polishing liquid is supplied by spraying onto the glass substrate laminate, the polishing is performed after the temperature at the time of supply and the end surface supplied between the glass substrate laminate and the polishing brush are polished. The difference between the temperature of the liquid and, in other words, the difference between the temperature of the polishing liquid when supplied to the polishing apparatus and the temperature of the polishing liquid discharged from the polishing apparatus is preferably 5 degrees or less, preferably 3 degrees or less. More preferred is 1 degree or less. By performing end face polishing under the above conditions, variations in end face quality (surface roughness) between individual glass substrates constituting the laminate can be reduced.

  FIG. 1A is a diagram showing a state in which the inner peripheral end surface of the disk-shaped glass substrate 10 is polished using a polishing brush 12. FIG. 2 is an enlarged view for explaining the polishing of the glass substrate. In FIG. 2, the code | symbol 10a has shown the interposition surface, and the code | symbol 10b has shown the side wall surface. When the end surface polishing treatment is performed, a plurality of glass substrates are stacked with the intervening member 14 (spacer) interposed therebetween, and the stacked body of the glass substrates obtained by stacking is polished together with the polishing brush 12. The polishing brush 12 may include a central shaft 12a and brush hairs 12b that are closely planted and extend linearly outward from the central shaft 12a. 12b may be spirally wound.

The laminated body of the glass substrate 10 is hold | maintained with the holder so that the relative position of each glass substrate 10 may not change. And the holder is connected to the rotating shaft of the drive motor which is not illustrated. Therefore, the laminated body of the glass substrate 10 rotates according to rotation of a drive motor. Further, the central shaft 12a of the polishing brush 12 is connected to a rotation shaft of a drive motor different from the drive motor that rotates a laminate (not shown). Therefore, the polishing brush 12a rotates according to the rotation of the drive motor. In this way, the end surface of the glass substrate 10 is polished by the relative movement between the glass substrate 10 and the polishing brush 12. The rotation direction of the laminated body of the glass substrate 10 and the rotation direction of the polishing brush 12 may be the same or different.
Here, the first treatment polishes the side wall surface. In the first treatment, polishing is preferably performed so that the arithmetic mean roughness Ra (JIS B 0601: 2001) of the surface roughness of the side wall surface is 0.015 μm or less, and 0.010 μm or less. More preferred. In the first treatment, polishing is preferably performed so that the surface roughness (maximum height: Rz) of the side wall surface is 0.15 μm or less, and more preferably 0.10 μm or less.
The second treatment is preferably polished so that the arithmetic mean roughness Ra of the surface roughness of the interposition surface is 0.015 μm or less while maintaining the surface roughness of the side wall surface after the first treatment, for example, Ra. More preferably, the thickness is 0.010 μm or less. In the second treatment, the surface roughness (maximum height: Rz) of the intervening surface is polished to 0.15 μm or less while maintaining the surface roughness of the side wall surface after the first treatment, for example, Rz. Preferably, polishing is performed so that the thickness is 0.10 μm or less.
The surface roughness of the side wall surface was measured using a stylus meter (measurement distance: 0.25 mm in the plate thickness direction). On the other hand, the surface roughness of the intervening surface was also measured using the stylus meter (measurement distance: 0.25 mm in the circumferential direction).
In the first treatment, polishing is performed by positioning so that the tip of the polishing brush 12 contacts the side wall surface. Note that the polishing brush 12 may be positioned at a position where the bristles are slightly bent.

  In the second process, polishing is performed by moving the position of the polishing brush 12 to a position closer to the intervening surface as compared with the position of the polishing brush 12 in the first process. At this time, the polishing is performed by positioning so that the tip of the polishing brush 12 contacts the intervening surface. Note that the polishing brush 12 may be positioned at a position where the bristles are slightly bent.

FIG. 3 is a diagram illustrating an example of a temporal change in the distance L from the central axis 12a of the polishing brush 12 to the side wall surface in the end surface polishing process.
First, in the end surface polishing treatment, the distance L of the polishing brush 12 is fixed to the distance L ₁ and polishing is performed from time 0 to time T ₁ . This distance L ₁ is a distance at which the tip of the polishing brush 12 contacts the side wall surface. Therefore, the first process is a process in which the distance L is fixed to the distance L ₁ and the polishing is performed until the time T ₁ . Next, the distance L of the polishing brush 12 is moved from the distance L ₁ to the distance L ₂ and fixed, and polishing is performed from time T ₁ to time T ₂ . This distance L ₂ is, bristle tips of the polishing brush 12 is the distance in contact with the intervening surface. Accordingly, the second process is a process in which the distance L is fixed to the distance L ₂ (distance L ₁ > distance L ₂ ) and the polishing is performed until the time T ₂ . The polishing time T ₁ and the polishing time (T ₂ -T ₁ ) at this time are such that the surface roughness (Rz) between the interposed surface and the side wall surface of the glass substrate 10 is 0.15 μm or less, and the interposed surface and side What is necessary is just to set suitably so that the difference of the surface roughness (Rz) with a wall surface may become small, specifically, the said difference will be less than 0.05 micrometer.
In the above description, the structure in which the distance L ₂ and the distance L ₁ are fixed and polished is described, but the surface roughness (maximum height: Rz) between the interposition surface and the side wall surface of the glass substrate 10 is described. each becomes 0.15μm or less, and, as the difference in surface roughness between the intervening surface and the side wall surface (Rz) is within 0.05 .mu.m, continuously over time between the distance L ₂ to a distance L ₁ Or it is good also as a structure which moves by grinding | polishing intermittently.
Thereby, when this glass substrate 10 is used as a magnetic disk, dust generation from the intervening surface and the side wall surface can be suppressed.

  Thus, since the same brush is used for the polishing brush 12 used in the first process and the second process, the length of the bristle is the same regardless of the position. Therefore, unlike the case of using a polishing brush having long brush hairs and short brush hairs, long brush hairs do not wear quickly, so that the polishing brush can be used stably for a long period of time. Further, it is preferable to move the polishing brush 12 in the thickness direction of the glass substrate 10 in order to polish the intervening surface and the side wall surface uniformly and efficiently regardless of the location. By such movement of the polishing brush 12, uniform and efficient polishing is possible by using the polishing brush 12 having the same bristle length. When a polishing brush having long bristles and short bristles is used, it cannot be uniformly and efficiently polished due to the length of the bristles. When long brush bristles contact the end surface of the glass substrate, short brush hairs do not contact the end surface. When the end surfaces of the short brush hairs are brought into contact with each other, the abdominal portion that is an intermediate portion of the long brush hairs comes into contact with each other, so that a linear scratch is easily formed on the side wall surface. In this regard, it is preferable to use a polishing brush having the same bristle length at any position.

  Moreover, the interposition surface is closer to the side wall surface than the deep interposition surface (first surface), which is the interposition surface located in the most recessed portion connected to the main surface of the glass substrate 10, and the side wall surface. The second process includes a third process for mainly polishing the shallow intervening surface, and a third process after the third process. The fourth process of moving the position of the polishing brush 12 to a position closer to the intervening surface as compared with the position of the polishing brush 12 in the third process to mainly polish the deep intervening surface may be included. That is, by polishing the shallow intervening surface after polishing the shallow intervening surface, it is possible to more reliably suppress the polishing residue of the intervening surface.

In the above description, the configuration for polishing the inner peripheral side end surface of the glass substrate 10 has been described. However, as shown in FIG. 1B, the configuration for polishing the outer peripheral side end surface using a polishing brush is also disclosed. Can be applied.
In the above description, the configuration in which the relative distance between the polishing brush and the laminate of the glass substrate 10 is changed to polish both the side wall surface and the interposed surface of the glass substrate 10 has been described. A method other than the above may be used as a method for polishing so as to improve the roughness and not leave any polishing residue on the intervening surface.
For example, in the polishing of the outer peripheral side end face, the abrasive grain size of the polishing abrasive grains may be changed between a first process in which the side wall surface is mainly polished and a second process in which the intervening surface is mainly polished. Specifically, when polishing the side wall surface, using a slurry having a larger abrasive particle size than the second treatment, supplying this slurry to the side wall surface for polishing, and polishing the intervening surface, A slurry having a smaller abrasive particle size than that in the first treatment may be used, and this slurry may be supplied to the intervening surface for polishing.
Moreover, in addition to the structure which changes the relative distance of the laminated body of a grinding | polishing brush and the glass substrate 10, you may change the relative speed (rotation speed) of a glass substrate and a grinding | polishing brush by a 1st process and a 2nd process. For example, the side wall surface and the interposed surface may be polished by rotating the second process at a higher speed than the first process and rotating the first process at a lower speed than the second process.

[Experimental example]
In order to confirm the effect of this embodiment, the end surface of the glass substrate was polished by three different polishing methods (Example, Conventional example, Comparative example).
A disk-shaped glass substrate having an outer diameter of 65 mm and a thickness of 0.8 mm was used as the glass substrate to be polished. One batch of glass substrates was laminated by laminating 100 sheets to make a laminated body, and edge polishing was performed for 10 batches without changing the polishing brush. In the examples, conventional examples, and comparative examples described later, polishing brushes composed of brush hairs having the same length from the rotating shaft were used. Cerium oxide was used as the loose abrasive. The laminated body of the glass substrate was immersed in the slurry liquid containing free abrasive grains. End face polishing was performed by rotating the polishing brush so that the rotation speed direction and the rotation direction of the glass substrate were opposite to each other.

In the example, as shown in FIG. 3, end face polishing was performed so that the distance between the rotating shaft of the polishing brush having the same length of bristles and the glass substrate was changed. On the other hand, in the conventional example, using the polishing brush having the same length of bristle, the interposition surface and the side wall surface were simultaneously polished while keeping the distance between the rotating shaft of the polishing brush and the glass substrate constant. In addition, about the Example and the prior art example, the end surface grinding | polishing was performed so that it might become the same time, respectively.
Then, the side wall surface of the glass substrate that has been subjected to end surface polishing for 10 batches of 100 batches obtained by polishing of Examples and Conventional Examples is examined by microscopic observation to determine whether there is any residual polishing of the intervening surface. It was. Presence or absence of polishing residue was determined based on whether or not there was a region in which the surface irregularities of the intervening surface partly abruptly increased in the microscopic observation.
As a result, in the glass substrate obtained by the polishing of the example, there was no polishing residue out of 100 sheets. That is, the polishing residue was less than 1%. On the other hand, in the glass substrate obtained by the conventional polishing, 5 of the 100 unpolished residues were found. That is, the polishing residue was 5%.

Further, the surface roughness (Ra, Rz) between the interposition surface and the side wall surface of the glass substrate obtained by the polishing of the example and the conventional example is obtained, and the surface roughness between the interposition surface and the side wall surface in one glass substrate is obtained. The difference in thickness (Rz) and the variation in surface quality between 10 batches were evaluated.
In the case of the glass substrate of the example, the difference in surface roughness (Rz) between the intervening surface and the side wall surface was determined to be within 0.05 μm, but in the case of the glass substrate of the conventional example, 0.05 μm Something beyond was found. Furthermore, when the variation between batches was examined, in the conventional example, the variation in the surface roughness of the interposition surface and the side wall surface was large.

Further, as a comparative example, as shown in FIG. 4A, end face polishing was performed so that the distance L between the rotating shaft of the polishing brush and the glass substrate was changed. That is, after interpolating the surface first, the side wall surface was mainly polished. In the comparative example, the grinding conditions were the same as in the example except that the order of polishing the intervening surface and the side wall surface was changed.
The curvature radius of the connection portion between the intervening surface and the side wall surface of the 10 glass substrates obtained by polishing of the example and the comparative example was imaged from the cross section of the connection portion, and the curvature radius of the connection portion was examined.
As a result, the radius of curvature of the connecting portion of the glass substrate obtained by polishing of the example was larger than the radius of curvature of the connecting portion of the glass substrate obtained by polishing of the comparative example. As a result, the glass substrate obtained by the polishing of the comparative example has the end face of the glass substrate colliding with an external jig during the first polishing process, the chemical strengthening process, and the second polishing process, and FIG. As shown, there is a high risk of becoming a glass substrate 100 in which the connection portion between the interposition surface and the side wall surface is partially lost. On the other hand, in the glass substrate obtained by the polishing of the example, since the radius of curvature of the connecting portion between the interposition surface and the side wall surface is large, the connecting portion is hardly lost.
From this, the effect of this embodiment is clear.

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

DESCRIPTION OF SYMBOLS 10, 100 Glass substrate 10a Interposition surface 10b Side wall surface 12 Polishing brush 12a Central axis 12b Brush hair 14 Interposition member

Claims (5)

A method of manufacturing a glass substrate for a magnetic disk, including an end surface polishing process in which a polishing brush is pressed against an end surface of a disk-shaped glass substrate having a circular hole at the center,
The end surface of the glass substrate has a side wall surface, and an interposition surface interposed between the main surface and the side wall surface,
In the end surface polishing process, a polishing liquid containing loose abrasive grains is supplied between the polishing brush and the end surface of the glass substrate, and polishing is performed by relatively moving the polishing brush and the glass substrate. And
The end surface polishing process includes a first process for polishing the side wall surface;
A method of manufacturing a glass substrate for a magnetic disk, comprising: a second process for simultaneously polishing the side wall surface and the interposition surface after the first process. The first treatment is performed so that the surface roughness Rz of the side wall surface is 0.15 μm or less,
2. The glass substrate for a magnetic disk according to claim 1, wherein the second treatment is performed such that the surface roughness Rz of the interposition surface is 0.15 μm or less while maintaining the surface roughness of the side wall surface. Production method.   The method for manufacturing a glass substrate for a magnetic disk according to claim 1 or 2, wherein the length of the bristles of the polishing brush used in the first process and the second process is the same.   4. The method for manufacturing a glass substrate for a magnetic disk according to claim 1, wherein, in the first treatment and the second treatment, the polishing brush is moved in a thickness direction of the glass substrate during polishing. 5. . 5. The polishing according to claim 1, wherein the polishing is performed by moving the position of the polishing brush closer to the interposed surface than the position of the polishing brush in the first process. The manufacturing method of the glass substrate for magnetic discs as described in a term.

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