JP6199047B2 - Manufacturing method of glass substrate for magnetic disk - Google Patents

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. In such a magnetic disk, thermal asperity may occur and cause problems.

  This defect of the magnetic disk is caused by fine foreign particles adhering to the main surface of the magnetic disk glass substrate and forming a surface roughness on the magnetic layer thereon. The foreign particles may be particles that adhere to fine linear scratches formed on the end surface of the glass substrate and are detached from the end surface of the glass substrate and adhere to the main surface during the manufacture of the magnetic disk. Many. For this reason, the end surface of the glass substrate is polished in a mirror state so that no flaw is formed.

The end surface of the glass substrate for magnetic disk is generally orthogonal to the main surface of the glass substrate on both the inner periphery side of the circular hole provided in the disk-shaped glass substrate and the outer periphery side of the disk shape of the glass substrate. A sidewall surface, and an intervening surface interposed between the main surface and the sidewall surface. The interposed surface is, for example, an inclined surface that is chamfered with an inclination angle with respect to the main surface.
It is well known that the interposition surfaces and the side wall surfaces, which are the end surfaces of such a magnetic disk glass substrate, are polished by brush polishing using, for example, slurry (free abrasive grains) containing, for example, cerium oxide abrasive grains as abrasive grains. It is. Examples of such polishing are described in paragraph 0034 of Patent Document 1 below and Claim 1 of Patent Document 2 below.

JP2012-203922A JP 2012-142051 A

In the conventional end surface polishing as described in Patent Document 1, when the side wall surface and the intervening surface are simultaneously polished, the side wall surface becomes a mirror surface state earlier than the intervening surface and the polishing is completed. However, polishing for a longer time is performed so that the intervening surface is also polished to a mirror state. In addition, in polishing the intervening surface, the tip of the polishing brush is the most efficient so that there is no residue left on the intervening surface far from the central axis of the polishing brush and the polishing quality of the intervening surface is good. The position of the polishing brush is set so that it often abuts the intervening surface.
When polishing the interposition surface in this way, the contact of the polishing brush with the side wall surface becomes too strong, and the side wall surface is polished by the abdomen of the brush hair of the polishing brush (intermediate portion between the tip of the hair and the base of the hair). It will be. For this reason, the side wall surface may be rubbed by the abdomen of the brush hair to generate a linear scratch. As described above, foreign particles may adhere to the scratches, and the foreign particles may be detached from the end face and adhere to the main surface in a later process of manufacturing the magnetic disk. Further, when polishing is performed so as not to cause scratches on the side wall surface, the interposed surface may be insufficiently polished.

  On the other hand, in the method for manufacturing a glass substrate for a magnetic recording medium described in Patent Document 2, a polishing brush used for polishing has a rotatable shaft center and a brush portion disposed around the shaft center. The brush portion has a relatively high rigidity, a first brush portion having a relatively short length from the shaft center to the tip of the brush portion, and a relatively low rigidity, from the shaft center to the tip of the brush portion. And a second brush portion having a relatively long length. In the end surface polishing, as the first polishing step, the first brush portion and the second brush portion are brought into contact with the interposition surface and the side wall surface which are the end surfaces of the glass substrate, and the brush is rotated around the axis. Further, as the second polishing stage, only the second brush portion is brought into contact with the end face of the glass substrate in a state where the distance between the end face of the glass substrate and the brush axis is longer than that of the first polishing stage. And rotate the brush around the axis. However, in the first polishing stage, the interposition surface and the side wall surface are polished simultaneously. For this reason, since the 2nd brush part with long hair wears first, it cannot use a polishing brush stably for a long period of time. Further, even in this case, since the intervening surface and the side wall surface are polished simultaneously, a linear flaw may remain on the side wall surface after the end surface polishing. Further, in the case of the polishing brush described in Patent Document 2, when the polishing brush is swung in the stacking direction of the laminated glass substrate during the end face polishing, the second brush portion having long hair Will also polish the side wall surface. For this reason, the second brush portion may cause scratches on the side wall surface. In addition, since the second brush portion is more concentrated than the first brush portion, there is a problem in that the end face quality varies greatly when end face polishing is performed continuously for a plurality of batches. .

  Therefore, the present invention provides a glass substrate for a magnetic disk that has no linear scratch on the side wall surface and can maintain the surface quality of both the intervening surface and the side wall surface even when a plurality of batch end faces are polished. It aims at providing the manufacturing method of.

  The inventor of the present application shows that in the conventional end surface polishing method in which the intervening surface and the side wall surface are simultaneously polished, linear flaws are likely to occur on the side wall surface of the glass substrate due to an increase in pressing against the side wall surface of the polishing brush. When the heading or pressing is weakened, the side wall surface is not scratched, but the surface quality of the intervening surface is found to be insufficient, and the present invention 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 glass substrate has a side wall surface orthogonal to the main surface of the glass substrate, and an intervening surface interposed between the main surface and the side wall surface, and the end surface polishing treatment includes the polishing brush and A polishing liquid containing free abrasive grains is supplied between the end surface of the glass substrate and the polishing brush and the glass substrate are relatively moved to perform polishing, and the end surface polishing processing is performed as described above. A first treatment for polishing at least the interposition surface by bringing the bristles of the polishing brush into contact with the interposition surface; and after the first treatment, in a state where the surface roughness of the interposition surface is maintained, and a second process for polishing, only contains The bristle length of the polishing brushes used in the first process and the second process is the same, a method of manufacturing a glass substrate for a magnetic disk.

  At this time, the first treatment is performed such that the surface roughness Rz of the interposition surface is 0.15 μm or less, and the second treatment is performed while maintaining the surface roughness of the interposition surface while the side wall surface is maintained. It is preferable to perform polishing so that the surface roughness Rz is 0.15 μm or less.

  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 that polishing is performed by moving the position of the polishing brush away from the side wall surface as compared with the position of the polishing brush in the first process.

  When the intermediate surface is divided into a first surface that is connected to the main surface and a second surface that is closer to the side wall surface than the first surface and is connected to the side wall surface, the first treatment is: A third process for mainly polishing the first surface of the interposition surface, and a fourth process for mainly polishing the second surface of the interposition surface after the third process. In the fourth process, It is preferable to perform polishing by moving the position to a position away from the side wall surface as compared with the position of the polishing brush in the third treatment.

  In the above-described method for manufacturing a glass substrate for magnetic disk, there is no linear scratch on the side wall surface, and the surface quality of the side wall surface and the intervening surface can be improved.

(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. It is a figure which shows the other 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.

  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 orthogonal to the main surface of the glass substrate and an intervening 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.
Here, in the end surface polishing treatment, polishing is performed by supplying a polishing liquid containing free abrasive grains between the polishing brush and the end surface of the glass substrate and relatively moving the polishing brush and the glass substrate. At this time, the end surface polishing process includes a first process for polishing at least the intervening surface, and a second process for polishing the side wall surface while maintaining the surface roughness of the intervening 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.

  By the polishing treatment according to the present embodiment, compared to the conventional case where the intervening surface and the side wall surface are polished simultaneously, the intervening surface located farther from the side wall surface as viewed from the polishing brush is left unpolished. It can be polished so that there is no. At this time, the side wall surface is also polished at the same time as in the conventional end surface polishing process. For this reason, as described above, the above-described linear scratch may occur on the side wall surface. However, since the side wall surface polishing is performed after the first treatment while maintaining the surface roughness of the intervening surface, the linear scratches generated on the side wall surface disappear and become a mirror surface state. For this reason, there is no linear flaw on the side wall surface of the polished glass substrate, and the surface roughness of the side wall surface and the interposition surface can be reduced. Specifically, by performing the polishing process according to the present embodiment, the difference in surface roughness (maximum height: Rz) between the interposition surface and the side wall surface is reduced, specifically, within 0.05 μm. It can be. In addition, by performing the 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. Furthermore, by performing the polishing treatment according to the present embodiment, the arithmetic average roughness (Ra) of the intervening surface and the side wall surface can be made 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. For this reason, the polishing surface is polished (first treatment) by fixing the polishing brush at a position where the bristle portion that efficiently polishes is in contact with the interposed surface and slightly bent. At this time, the abdomen of the brush bristles of the polishing brush comes into contact with the side wall surface, so that the side wall surface is rubbed by foreign particles such as abrasive grains and dust between the abdomen portion and the side wall surface. May occur. However, after that, the position of the polishing brush is moved to a position where the bristle portion comes into contact with the side wall surface and is slightly bent and fixed, and the side wall surface is polished (second processing). At this time, since the polishing brush does not substantially contact the intervening surface, it is not polished. Thus, since the side wall surface is polished after the interposed surface is polished, even if a linear scratch occurs in the first process, it disappears by the polishing in the second process. That is, the polishing method of the present embodiment has a mirror surface state in which the side wall surface after polishing is free from linear scratches and has a small surface roughness.
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, this glass blank is appropriately processed to produce a disk-shaped glass substrate having a chamfered edge with a circular hole in the center. 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 G 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 that polishes at least the interposed surface, and a second process that polishes the side wall surface while maintaining the surface roughness of the interposed surface 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 at least the intervening surface. At this time, the side wall surface may be polished in addition to the intervening surface. In the first treatment, polishing is preferably performed so that the arithmetic average roughness Ra (JIS B 0601: 2001) of the surface roughness of the intervening 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 intervening 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 sidewall surface is 0.015 μm or less while maintaining the surface roughness of the sidewall 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 side wall surface is polished to be 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 the bristle tip of the polishing brush 12 so as to contact the most depressed position of the interposition surface so that there is no polishing residue on the interposition surface. Note that the polishing brush 12 may be positioned at a position where the bristles are slightly bent. At this time, as shown in FIG. 2, the belly portion of the polishing brush 12 abuts on the side wall surface. For this reason, the side wall surface may be rubbed by loose abrasive grains or foreign particles pressed at the belly portion, and a linear scratch may occur on the side wall surface.

  In the second process, polishing is performed by moving the position of the polishing brush 12 to a position farther from the side wall than the position of the polishing brush 12 in the first process. At this time, 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.

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 most depressed position of the intervening 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 side wall surface. Therefore, the process of polishing until time T ₂ while fixing the distance L to the distance L ₂ (distance L ₂ > distance L ₁ ) is the second process. 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 be made 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 lengths of the brush hairs are the same. Therefore, unlike conventional ones, long brush hairs do not wear quickly, so that the 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 as in the prior art, polishing cannot be performed uniformly and efficiently 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 long brush hairs are brought into contact with the abdomen, so that it is easy to form a linear scratch 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 first process includes a third process of mainly polishing the deep interposition surface, and a third process after the third process. And a fourth process in which the position of the polishing brush 12 is moved to a position farther from the side wall surface than the position of the polishing brush 12 in the third process to mainly polish the shallow intervening surface. That is, by polishing the shallow intervening surface after polishing the deep interposing surface, it is possible to more reliably suppress the polishing residue of the intervening surface. FIG. 4 is a diagram illustrating another 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.

In the end surface polishing process, 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 (third process). This distance L ₁ is a distance such that the bristles of the polishing brush 12 are in contact with the deep interposition surface and the bristles are slightly bent. Next, the distance L of the polishing brush 12 is moved from the distance L ₁ to the distance L ₃ and fixed, and polishing is performed from time T ₁ to time T ₃ (fourth process). This distance L ₃ is a distance such that the bristles of the polishing brush 12 are in contact with the shallow intervening surface and the bristles are slightly bent.
Thus the distance L ₃ is greater than the distance L _1. Next, move the distance L Ken 0 polishing brush 12 from the distance L ₃ to a distance L ₂ is polished from a fixed to time T ₃ to time T ₂ (second processing). This distance L ₂ is, bristle tips of the polishing brush 12 is distance enough to flex slightly abuts and hair on the side wall surface. Therefore, the distance L ₂ is larger than the distance L ₃ .
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. Methods other than those described above may be used as a method for improving the roughness and preventing scratches that may be formed on the side wall surface.
For example, in the polishing of the end face on the outer peripheral side, the abrasive grain size of the polishing abrasive grains may be changed between a first process that mainly polishes the intervening surface and a second process that mainly polishes the side wall surface. Specifically, when polishing the intervening surface, using a slurry having a smaller abrasive particle size compared to the second treatment, supplying and polishing this slurry to the intervening surface, when polishing the side wall surface, A slurry having a larger abrasive particle size than that in the first treatment may be used, and this slurry may be supplied to the side wall 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 first process at a higher speed than the second process and rotating the second process at a lower speed than the first 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 1 and Conventional Example 2).
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 described below and Conventional Example 1, a polishing brush composed of brush bristles having the same length from the rotating shaft was used. In Conventional Example 2, a polishing brush in which short brush hairs and long brush hairs from the rotation axis are alternately arranged is used as the polishing brush. Cerium oxide was used as the loose abrasive. The laminated body of glass substrates was immersed in a 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 and the glass substrate was changed between the first process and the second process. On the other hand, in Conventional Example 1, using a polishing brush having the same length of bristles, 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. Further, in the conventional example 2, as disclosed in Patent Document 2, the rigidity is relatively high, the first brush part having a relatively short length from the shaft center to the tip of the brush part, and the rigidity is A polishing brush including at least a second brush portion that is relatively low and has a relatively long length from the axial center to the tip of the brush portion was used. In the end surface polishing, the first brush portion and the second brush portion were brought into contact with the interposed surface and the side wall surface of the glass substrate, and the polishing brush was rotated to perform end surface polishing. In addition, about the Example, the comparative example 1, and the comparative example 2, the end surface grinding | polishing was performed so that it might become respectively the same time.
Then, whether or not there is a linear scratch on the side wall surface by microscopic observation of the side wall surface of the glass substrate subjected to end surface polishing for 10 batches of 100 batches obtained in Examples and Conventional Examples 1 and 2 I investigated. Further, the surface roughness (Ra, Rz) between the intervening surface and the side wall surface is obtained for each, and the difference in surface roughness (Rz) between the interposing surface and the side wall surface in one glass substrate and between 10 batches The surface quality variation was evaluated.

As a result of microscopic observation, none of the glass substrates obtained by the method of the Examples had a linear scratch on the side wall surface. On the other hand, some glass substrates obtained by the method of Conventional Example 1 were found to have a linear scratch on the side wall surface. Further, the glass substrate obtained by the method of Conventional Example 2 also had a linear scratch on the side wall surface. Moreover, the wear of long brush hairs was fast.
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 found to be within 0.05 μm. Found to exceed .05μm.
Furthermore, when the variation between batches was examined, in the conventional example 2, the variation in the surface roughness of the interposition surface and the side wall surface was large.
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 Glass substrate 10a Interposition surface 10b Side wall surface 12 Polishing brush 12a Central axis 12b Brush hair 14 Interposition member

Claims (4)

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 orthogonal to the main surface of the glass substrate, and an intervening 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 at least the interposition surface by bringing a hair tip portion of the polishing brush into contact with the interposition surface ;
After the first treatment, while maintaining the surface roughness of the intervening surface, seen including a second process for polishing the side wall,
The method of manufacturing a glass substrate for a magnetic disk, wherein the lengths of the bristles of the polishing brush used in the first process and the second process are the same . The first treatment is performed so that the surface roughness Rz of the intervening 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 side wall surface is 0.15 μm or less while maintaining the surface roughness of the interposed surface. Production method. Wherein the first process and the second process, during polishing, moving the abrasive brush in the thickness direction of the glass substrate, according to claim 1 or 2 method for producing a glass substrate according to. Wherein in the second process, the position of the polishing brush, compared to the position of the polishing brush in the first process, is polished by moving to a position away from the side wall, claim 1-3 2. A method for producing a glass substrate for a magnetic disk according to item 1.

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