JP5650523B2 - Method for manufacturing glass substrate for magnetic recording medium - Google Patents

Description

  The present invention relates to a method for producing a glass substrate for use in a magnetic recording medium such as a hard disk.

  For example, a glass substrate for use in a magnetic recording medium such as a hard disk (HD) incorporated in a hard disk drive (HDD) is a glass melting process for melting a glass material, and by pressing the molten glass material with a mold. Press forming process for producing a disk-shaped glass substrate, coring process for forming a circular hole at the center of the obtained glass substrate, and grinding the main surface (recording surface) of the obtained annular glass substrate to obtain a glass substrate First lapping step for preliminarily adjusting the thickness, flatness, etc. of the glass, end surface grinding step for finely adjusting the outer diameter, roundness, etc. of the glass substrate by grinding the inner and outer peripheral end surfaces of the glass substrate, the glass substrate An end surface polishing step for polishing and smoothing the inner peripheral end surface and the outer peripheral end surface, and a second ladder for finely adjusting the thickness and flatness of the glass substrate by grinding again the main surface of the glass substrate. Ing step, polishing step of smoothing by polishing the major surface of the glass substrate, and it is manufactured through a cleaning process or the like for cleaning the glass substrate.

  In addition, a chemical strengthening process for strengthening the surface of the glass substrate, an inspection process for inspecting the thickness, flatness, etc. of the glass substrate may be performed. Further, in the end surface grinding process or the like, the inner peripheral end surface and the outer peripheral end surface of the glass substrate may be chamfered.

  Conventionally, in the end surface polishing step, a rotating brush is brought into contact with the inner peripheral end surface and / or the outer peripheral end surface of the glass substrate, thereby removing the processing scratches generated on the end surface in the previous processing operation and further smoothing the end surface. Is. In order to remove the processing flaws on the end face, the processing flaws are relatively rough. Therefore, it is preferable to increase the polishing rate (polishing rate) using a bristle brush having relatively high rigidity. Thereby, even if a grinding | polishing allowance is large, a processing flaw can be removed in a short time. However, if a bristle brush with relatively high rigidity is used, brush scratches remain, making it difficult to smooth the end face. On the other hand, in order to smooth the end face, it is preferable to use a bristle brush with relatively low rigidity so that no brush scratches remain. However, if a bristle brush having a relatively low rigidity is used, the polishing rate is lowered, and thus the productivity is lowered. That is, there is a problem that it is difficult to achieve both the removal of the processing scratches on the end face in a short time and the smoothing of the end face with high quality.

  In order to cope with this problem, Patent Document 1 discloses that an end surface polishing step for polishing an end surface of a glass substrate using a polishing brush is divided into a first polishing step and a second polishing step, and each has different polishing conditions. It describes that the end face of a glass substrate is polished. Specifically, it is described that a polishing brush having lower rigidity than that of the first polishing step is used in the second polishing step. According to this, in the first polishing step using the polishing brush having relatively high rigidity, it is possible to remove the processing scratches on the end face having a relatively large polishing allowance in a short time, and polishing with relatively low rigidity. In the second polishing step using a brush, the end face can be smoothed so that no brush scratches remain.

  Further, Patent Document 2 describes that after the slope portion (chamfered portion) of the inner peripheral end surface of the glass substrate is polished using a polishing brush, the side wall portion of the inner peripheral end surface is polished using a polishing pad. Yes. Specifically, it is described that a polishing brush is inserted into the circular hole of the glass substrate to polish the inner peripheral end face, and then a polishing pad is inserted into the circular hole of the glass substrate to polish the inner peripheral end face.

JP 2008-273777 A (paragraphs 0019 and 0041) JP 2007-1972235 A (paragraphs 0010 and 0041)

  However, in the technique described in Patent Document 1, in order to perform the first polishing step and the second polishing step, for example, a polishing brush having a relatively high rigidity for performing the first polishing step is provided. The glass substrate must be moved from the end face polishing apparatus provided to the end face polishing apparatus provided with a polishing brush having a relatively low rigidity for performing the second polishing step. Alternatively, in a single end surface polishing apparatus, the polishing brush for performing the first polishing step and the polishing brush for performing the second polishing step must be exchanged. Therefore, it takes time to move the glass substrate between the end surface polishing apparatuses and to replace the brush, and the productivity may be reduced. Further, the glass substrate may be damaged during the movement of the glass substrate between the end surface polishing apparatuses, the yield may be reduced, and the production cost may be increased.

  In the technique described in Patent Document 2, after polishing with a polishing brush, the polishing brush is removed from the circular hole, and instead the polishing pad is inserted into the circular hole. And productivity is reduced.

  The present invention provides a method for producing a glass substrate for a magnetic recording medium, which removes processing scratches on the end face in a short time without moving between the end face polishing apparatuses of the glass substrate or replacing the brush, and the end face has a high quality. An object of the present invention is to provide an end surface polishing step that can be smoothed.

  The present invention is a method for manufacturing a glass substrate for a magnetic recording medium including an end surface polishing step of polishing an inner peripheral end surface and / or an outer peripheral end surface of a glass substrate using a brush, the brush having a rotatable axis, A first brush portion having a relatively high rigidity, and a relatively short length from the shaft center to the tip of the brush portion; and a rigidity of the brush portion. At least a second brush portion having a relatively long length from the axial center to the tip of the brush portion, and the end surface polishing step includes a first polishing step, a second polishing step, In this order, in the first polishing stage, the first brush part and the second brush part are brought into contact with the end face of the glass substrate to rotate the brush around the axis, and in the second polishing stage, the glass The distance between the substrate end face and the brush axis is longer than in the first polishing stage. State, only the second brush portion, wherein the rotating brush is brought into contact with the end face of the glass substrate around the axis.

  According to this configuration, in the first polishing stage of the end surface polishing step, the inner peripheral end surface of the glass substrate and the first brush portion having relatively high rigidity and the second brush portion having relatively low rigidity Since the outer peripheral end face is polished, processing flaws on the end face having a relatively large polishing allowance can be removed in a short time. Next, in the second polishing stage of the end surface polishing step, the inner peripheral end surface and / or the outer peripheral end surface of the glass substrate are polished with only the second brush portion having relatively low rigidity, so that the end surface does not leave any brush scratches. Can be smoothed with high quality. In addition, since the switching from the first polishing stage to the second polishing stage increases the distance between the end surface of the glass substrate and the brush axis, the glass substrate remains set in a single end surface polishing apparatus. Well, it is not necessary to move the glass substrate between the end surface polishing apparatuses or replace the brush. As a result, a decrease in productivity and an increase in production cost can be suppressed.

  The state in which the distance between the end surface of the glass substrate and the brush axis is increased is, for example, that the distance between the end surface of the glass substrate and the brush axis is increased. Can be achieved without relative movement of the glass substrate and / or the brush. That is, as the end surface polishing in the first polishing stage in which the polishing by the first brush portion is dominant, the end surface of the glass substrate gradually recedes, and the distance between the end surface of the glass substrate and the brush axis is increased. This is because it becomes longer gradually. Then, when the contact amount between the end surface of the glass substrate and the first brush portion is reduced, the first brush portion is in an extended state, and polishing by the second brush portion becomes dominant, the first polishing stage. Therefore, the switch to the second polishing stage has occurred.

  In the present invention, in the end surface polishing step, it is preferable to polish a plurality of glass substrates stacked (bundled) in the thickness direction while aligning the centers. This is because the end surfaces of the plurality of glass substrates can be polished at once, so that the polishing efficiency is increased and the productivity is improved.

  In the present invention, in the end face polishing step, it is preferable to polish the glass substrate and the brush by immersing them in a bath of polishing liquid containing abrasive grains. This is because it is easy to always supply the polishing liquid to the contact portion (polishing portion) between the glass substrate and the brush.

  Moreover, in this invention, it is also preferable to grind | polish in an end surface grinding | polishing process, supplying the polishing liquid containing an abrasive grain to the contact part of a glass substrate and a brush. This is because abrasive grains having a constant diameter can always be supplied to the polishing section, and the quality of the glass substrate is stabilized even when the number of batches is increased.

  In that case, in the end face polishing step, it is preferable to change the diameter of the abrasive grains contained in the polishing liquid to a smaller one in accordance with the progress of the end face polishing. This is because the diameter of the abrasive grains is reduced in the second polishing stage, so that the end face can be smoothed with higher quality.

  According to the present invention, the end surface of the glass substrate is preferably chamfered. This is because corner chipping (chipping) between the main surface and the end surface of the glass substrate is suppressed. Further, when a plurality of glass substrates are bundled and polished, in the first polishing stage, the second brush having a relatively long length while performing end surface polishing predominantly with the first brush portion having relatively high rigidity. This is because the polishing scraps can be scraped from the chamfered portion (chamfer surface) at the portion.

  According to the present invention, in the end surface polishing step of the method for manufacturing a glass substrate for a magnetic recording medium, the processing scratches on the end surface are removed in a short time without moving between the end surface polishing apparatuses of the glass substrate or replacing the brush. In addition, the end face can be smoothed with high quality.

It is a manufacturing-process figure of the glass substrate for magnetic recording media which concerns on embodiment of this invention. It is a cross-sectional perspective view of the glass substrate for magnetic recording media which concerns on embodiment of this invention. It is a longitudinal cross-sectional view which shows schematic structure of the end surface grinding | polishing apparatus (immersion type) which can be used at the end surface grinding | polishing process which concerns on embodiment of this invention. It is a top view which shows the rotation direction of the glass substrate and brush in the end surface grinding | polishing apparatus shown in FIG. 4A is an enlarged view of a contact portion (polishing portion) between a glass substrate and a brush in a first polishing stage of an end surface polishing step according to an embodiment of the present invention, and FIG. . It is explanatory drawing of various dimensional relationships, such as the distance between the length of the 1st brush hair, the length of the 2nd brush hair, and the inner peripheral end surface of a glass substrate, and the axial center of a brush. BRIEF DESCRIPTION OF THE DRAWINGS It is explanatory drawing of the brush which can be used by embodiment of this invention, Comprising: (a) The side view of the spiral brush in which the bristle was helically planted by the axial center, (b) The bristle in parallel with the axial center It is a perspective view of the wing brush planted, (c) The top view of the dense brush in which the bristle was planted irregularly in the axial center. BRIEF DESCRIPTION OF THE DRAWINGS It is explanatory drawing of the bristle of the brush which can be used by embodiment of this invention, Comprising: (a)-(e) is an expanded view of the bristle provided with a 1st brush bristle and a 2nd brush bristle in a mutually different pattern. It is. It is explanatory drawing of the bristle of the brush which can be used in embodiment of this invention, Comprising: (a)-(f) is a development view of the bristle of a mutually different shape. It is a longitudinal cross-sectional view which shows schematic structure of the end surface grinding | polishing apparatus (shower type) which can be used at the end surface grinding | polishing process which concerns on embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a manufacturing process diagram of a glass substrate for a magnetic recording medium according to this embodiment, and FIG. 2 is a cross-sectional perspective view of the glass substrate for a magnetic recording medium according to this embodiment.

  In this embodiment, the glass substrate 10 for magnetic recording media includes a glass melting step (Step S1), a press forming step (Step S2), a coring step (Step S3), a first lapping step (Step S4), and an end surface grinding step. (Step S5), an end surface polishing step (Step S6), a second lapping step (Step S7), a polishing step (Step S8), and a cleaning step (Step S9).

In the glass melting step (S1), the glass material is melted. Glass material is composed of a glass composition whose main component is silicon dioxide (SiO _2). The glass composition may or may not contain magnesium, calcium and / or cerium. Exemplary glass compositions include, for _{example, SiO 2, Al 2 O 3} , B 2 O 3, Li 2 O, Na 2 O, K 2 O, MgO, CaO, BaO, SrO, and ZnO, and the like.

  In the press molding step (S2), a molten glass material is poured into a mold and press molded to produce a disk-shaped glass substrate. The dimensions of the glass substrate at this time are, for example, an outer diameter of 2.5 inches, 1.8 inches, 1.0 inches, 0.8 inches, and a thickness of 2 mm, 1 mm, 0.63 mm, and the like.

  In the coring step (S3), a circular hole is formed in the center of the obtained glass substrate using, for example, a diamond core drill. In the first lapping step (S4), the main surfaces (recording surfaces) 11 and 12 of the obtained annular glass substrate 10 are ground to preliminarily adjust the thickness, parallelism, flatness and the like of the glass substrate 10. For the grinding process in the first lapping step, for example, a double-sided grinding apparatus including a grinding plate on which diamond pellets are attached is used.

  In the end surface grinding step (S5), the inner peripheral end surface 13 and the outer peripheral end surface 14 of the glass substrate 10 are ground to finely adjust the outer diameter size, roundness, etc. of the glass substrate 10. In the end surface grinding step, the inner peripheral end surface 13 and the outer peripheral end surface 14 of the glass substrate 10 are chamfered using, for example, a diamond grindstone to form a chamfer surface 16. In the inner peripheral end surface 13 and the outer peripheral end surface 14, a portion sandwiched between the chamfer surfaces 16 and 16 is referred to as a side wall surface 15.

  In the end surface polishing step (S6), the inner peripheral end surface 13 and the outer peripheral end surface 14 of the glass substrate 10 are polished and smoothed. As will be described later, in the end surface polishing step, the end surface polishing apparatus 20 shown in FIG. 3 is used, and the first polishing step and the second polishing step are performed.

  In the second lapping step (S7), the main surfaces 11 and 12 of the glass substrate 10 are ground again to finely adjust the thickness, parallelism, flatness and the like of the glass substrate 10. For the grinding process in the second lapping step, for example, a double-sided grinding device including a grinding plate on which diamond pellets are attached is used. In the polishing step (S8), the main surfaces 11 and 12 of the glass substrate 10 are polished and smoothed. For polishing in the polishing process, for example, a double-side polishing apparatus including a pair of upper and lower surface plates to which a suede pad is attached as a polishing pad is used.

  In the cleaning step (S9), for example, filtered foreign water, ion-exchanged water, ultrapure water, acidic detergent, neutral detergent, alkaline detergent, organic solvent, and surfactant are removed from the foreign substances adhering to the glass substrate 10. Wash and remove using various cleaning agents.

  In addition, a chemical strengthening process for strengthening the surface of the glass substrate 10, an inspection process for inspecting the thickness, flatness, and the like of the glass substrate 10 may be performed. The glass substrate 10 manufactured through these steps is finally formed with a magnetic layer on the main surfaces 11 and 12 to form a magnetic recording medium such as a hard disk (HD).

  Hereinafter, the end surface polishing step (S6) which is a characteristic part of the present embodiment will be described in detail. FIG. 3 is a longitudinal sectional view showing a schematic configuration of an end surface polishing apparatus (immersion type) that can be used in the end surface polishing step according to the present embodiment, and FIG. 4 shows a rotation direction of the glass substrate and the brush in the end surface polishing apparatus. FIG. 5A is a plan view, FIG. 5A is an enlarged view of a contact portion (polishing portion) between the glass substrate and the brush in the first polishing step of the end surface polishing step according to the present embodiment, and FIG. It is an enlarged view of the grinding | polishing part in a grinding | polishing stage.

  As shown in FIG. 3, the immersion type end surface polishing apparatus 20 has a polishing liquid tank 21, and a polishing liquid 22 containing abrasive grains (free abrasive grains: not shown) is contained in the polishing liquid tank 21. It is accumulated. The glass substrate 10 is immersed in the polishing liquid 22. The glass substrate 10 is immersed as a bundle of glass substrates 10 in which a plurality of glass substrates 10... A bundle of glass substrates 10 is held by a jig 23 and set in the end surface polishing device 20 so as to be rotatable around a circular hole.

  A plurality (three in the illustrated example) of brushes 31, 32, and 33 are further immersed in the polishing liquid 22. Each brush 31, 32, 33 has rotatable shaft centers 31a, 32a, 33a and brush portions 31b, 32b, 33b arranged around the shaft centers. The brush 31 is disposed in a circular hole of the bundle of glass substrates 10, and the brushes 32 and 33 are disposed on the side of the outer peripheral end face 14 of the bundle of glass substrates 10. Each brush 31, 32, 33 is rotated by drive motors 31m, 32m, 33m.

  As shown in FIG. 4, the glass substrate 10 is rotated in the direction of arrow a, the brush 31 is rotated in the direction of arrow b, the brush 32 is rotated in the direction of arrow c, and the brush 33 is rotated in the direction of arrow d. As a result, when the glass substrate 10 and the brushes 31, 32, 33 are in contact, the rotation direction of the glass substrate 10 and the rotation direction of the brushes 31, 32, 33 are opposite to each other at the contact portion (polishing portion). become.

  In this embodiment, in order to increase the polishing efficiency at a low rotation, the rotation direction of the glass substrate 10 and the rotation direction of the brushes 31 to 33 are opposite to each other, but the tips of the brushes 31, 32, and 33 As long as a difference in speed sufficient for polishing occurs between the end faces 13 and 14 of the glass substrate 10, they may be in the same direction. For example, when the peripheral speed of the brushes 31, 32, 33 is large enough to perform the polishing compared to the peripheral speed of the glass substrate 10, or conversely, compared to the peripheral speed of the brushes 31, 32, 33 This corresponds to a case where the peripheral speed is large enough to allow sufficient polishing.

  In the present embodiment, the brushes 31, 32, and 33 are rotatable about the shaft centers 31a, 32a, and 33a, and in FIG. 3, the lateral direction (horizontal direction) and the vertical direction (vertical direction) are driven by a driving mechanism (not shown). Direction). When the brushes 31, 32, 33 are moved in the lateral direction and the brushes 31, 32, 33 are in contact with the glass substrate 10, the inner peripheral end surface 13 and the outer peripheral end surface 14 of the glass substrate 10 are brushed at the contact portion. It will be polished by 31, 32, 33.

  In this embodiment, the polishing liquid 22 is a slurry containing loose abrasive grains. The abrasive grains are not particularly limited, and those conventionally used generally in the field of glass polishing can be used. For example, cerium oxide, silicon carbide, silica, zirconia, alumina and the like can be preferably used. Among these, cerium oxide is more preferable from the viewpoints of cost, smoothness obtained, and the like. In terms of the obtained smoothness and the like, the abrasive grains preferably have an average particle diameter of about 1 to 3 μm, more preferably about 0.9 to 1.3 μm.

  In this embodiment, FIG. 5 (the illustrated example illustrates the brush 31 as a brush, but the same applies to the other brushes 32 and 33 / the illustrated example illustrates the inner peripheral end surface 13 as the end surface of the glass substrate 10, but the same applies to the outer peripheral end surface 14. ), The brush portion 31b of the brush 31 is composed of brush hairs. Although the material of the brush bristles 31b is not particularly limited, for example, nylon, polypropylene, polyethylene, polyester, polycarbonate, or the like can be preferably used. By producing the brush bristles 31b with such a synthetic resin, the same bristles as those used in the polishing liquid 22 can be contained in the bristles 31b.

  As shown in FIG. 5, the brush bristles 31 b include first brush bristles (first brush portions) 31 c that are relatively short from the axis 31 a of the brush 31 to the tip of the bristles, and the axis of the brush 31. A second brush hair (second brush portion) 31d having a relatively long length from 31a to the tip of the brush hair is provided. The first brush hair 31c has a relatively high rigidity, and the second brush hair 31d has a relatively low rigidity.

  In the end surface polishing step, the first polishing step and the second polishing step are performed in this order. In the first polishing stage, as shown in FIG. 5 (a), the first brush bristles 31c and the first brush bristles 31c and the first brush bristles 31 are relatively short with the distance between the end surface 13 of the glass substrate 10 and the axis 31a of the brush 31 being relatively short. The two brush hairs 31d are brought into contact with the end face 13 of the glass substrate 10 to rotate the brush 31 around the axis 31a. Thereby, the end surface 13 of the glass substrate 10 is polished by both the first brush hair 31c having a relatively high rigidity and the second brush hair 31d having a relatively low rigidity (according to the first brush hair 31c). Polishing is dominant), and processing flaws on the end face 13 having a relatively large polishing allowance can be removed in a short time.

  Next, in the second polishing stage, as shown in FIG. 5 (b), the second brush bristles with the distance between the end surface 13 of the glass substrate 10 and the axis 31a of the brush 31 relatively long. Only 31d is brought into contact with the end surface 13 of the glass substrate 10, and the brush 31 is rotated around the axis 31a. Thereby, since the end surface 13 of the glass substrate 10 is polished only by the second brush bristles 31d having relatively low rigidity, the end surface 13 can be smoothed with high quality so that no brush scratches remain.

  Note that when the distance between the end surface 13 of the glass substrate 10 and the axis 31a of the brush 31 is relatively short or long, the brush 31 and / or the glass substrate 10 is moved in the horizontal direction (horizontal direction). And it is achieved by adjusting the relative position of the brush 31 and the glass substrate 10 in the horizontal direction (horizontal direction). However, as the end face polishing in the first polishing stage where the polishing by the first brush bristles 31c is dominant, the end face 13 of the glass substrate 10 gradually recedes, and the end face 13 of the glass substrate 10 and the axis of the brush 31 are centered. Since the distance to 31a is gradually increased, switching from the first polishing stage to the second polishing stage is automatically performed without relatively moving the brush 31 and / or the glass substrate 10 in the horizontal direction (horizontal direction). Will be achieved. That is, the end surface polishing in the first polishing stage proceeds, the contact amount between the end surface 13 of the glass substrate 10 and the first brush bristles 31c is reduced, and the first brush bristles 31c are extended, and the second brush bristles are extended. When the polishing by 31d became dominant, the switching from the first polishing stage to the second polishing stage occurred.

  5 shows that the side wall surface 15 of the end surface 13 of the glass substrate 10 corresponds to the first brush hair 31c, and the chamfer surface 16 corresponds to the second brush hair 31d. For example, in FIG. 5A, the second brush bristles 31d may contact the side wall surface 15 and the first brush bristles 31c may also contact the chamfer surface 16, or in FIG. The second brush hair 31d may also contact the side wall surface 15.

  Reference is again made to FIG. For example, when the brush 32 moves to the left on the drawing, the brush 32 contacts the outer peripheral end surface 14 of the glass substrate 10. Since the glass substrate 10 is rotated in the a direction and the brush 32 is rotated in the c direction, the outer peripheral end surface 14 of the glass substrate 10 is all around even if the brush 32 and the glass substrate 10 are in contact at one point. It is polished over. The same applies to the other brushes 31 and 33. Further, with respect to the brush 31 disposed in the circular hole of the glass substrate 10, referring to FIG. 6, the diameter of the brush 31, that is, the first brush bristles 31 c that are relatively short and the lengths are relatively long. The outer diameter (R2) of the entire bristle 31b including the second long bristle 31d is preferably smaller than the inner diameter (r) of the glass substrate 10, that is, the diameter of the circular hole ("(i) in FIG. 6). R2 <r is preferred ”). Thus, in the end face polishing step, the brush 31 and the glass substrate 10 are 1 when the brush 31 is biased to either side from the center of the circular hole, whether in the first polishing stage or the second polishing stage. This is because contact is ensured only at points. However, referring also to FIG. 6, the outer diameter (R1) of the first brush hair 31c is smaller than the diameter (r) of the circular hole among the brush hairs 31b depending on the situation. The outer diameter (R2) may be equal to or larger than the diameter (r) of the circular hole (see “(ii) R1 <r, R2 ≧ r may be satisfied” in FIG. 6). According to this, even when the brush 31 is returned to the center of the circular hole in the end surface polishing step, the second brush bristles 31d of the brush 31 and the inner peripheral end surface 13 of the glass substrate 10 are in contact with each other over the entire circumference. A second polishing stage will be performed. Then, when the brush 31 is biased to either side from the center of the circular hole, the first brush bristles 31c come into contact with the inner peripheral end face 13 at one point, and the first polishing stage is performed.

  In FIG. 6, the length (length from the axial center 31a of the brush 31 to the tip of the first brush bristle 31c) H1 of the first brush bristles 31c is expressed as "(R1-R ) / 2 ". Similarly, the length of the second brush bristles 31d (the length from the axis 31a of the brush 31 to the tip of the second brush bristles 31d) H2 is expressed as "(R2-R) where R is the diameter of the axis 31a. / 2 ". In FIG. 6, the symbol x represents the distance between the inner peripheral end surface 13 of the glass substrate 10 and the axis 31 a of the brush 31, and the symbol y biased the brush 31 to either side in the circular hole. Represents the amount of overlap of the brush bristles 31b at the contact portion (polishing portion) at the time (the illustrated example shows the case where only the second brush bristles 31d overlap (second polishing stage), but the first polishing. In the stage, both the first brush bristles 31c and the second brush bristles 31d overlap.), Where “x + y = H2”.

  In the present embodiment, the switching from the first polishing stage to the second polishing stage is performed between the inner peripheral end face 13 and the outer peripheral end face 14 of the glass substrate 10 and the shaft centers 31a, 32a, 33a of the brushes 31, 32, 33. Since the distance becomes longer, the glass substrate 10 may remain set in the single end surface polishing apparatus 20, and there is no need to move the glass substrate 10 between the end surface polishing apparatuses or replace the brush. As a result, it is possible to suppress a decrease in productivity due to an increase in the number of operations and an increase in production cost due to a decrease in yield.

  In the present embodiment, in the end surface polishing step, the plurality of glass substrates 10... 10 are stacked (bundled) and polished in the thickness direction while being centered, so that the inner peripheral end surfaces 13. The outer peripheral end faces 14 ... 14 can be polished at a time, so that the polishing efficiency is increased and the productivity is improved.

  In the present embodiment, in the end face polishing step, the glass substrate 10 and the brushes 31, 32, 33 are immersed in a tank 21 of a polishing liquid 22 containing abrasive grains (free abrasive grains) using an immersion type end face polishing apparatus 20. Since the polishing is performed, it is easy to always supply the polishing liquid 22 to the contact portion (polishing portion) between the glass substrate 10 and the brushes 31, 32, 33.

  In the present embodiment, the inner peripheral end surface 13 and the outer peripheral end surface 14 of the glass substrate 10 are chamfered to form the chamfer surface 16, so that the gap between the main surfaces 11, 12 and the end surfaces 13, 14 of the glass substrate 10 is formed. The chipping (chipping) and the like of the corners are suppressed. Further, when the plurality of glass substrates 10... 10 are bundled and polished in the end surface polishing step, the length of the first polishing step is controlled while the end surface polishing is dominantly performed with the first brush bristles having relatively high rigidity. However, it is possible to scrape the polishing scraps from the chamfered portion (the chamfer surface 16) with the second brush bristles that are relatively long (see FIG. 5A).

  In addition, when the chamfer surface 16 is formed on the end surfaces 13 and 14 of the glass substrate 10, both the first brush bristles and the second bristles are the side wall surface 15 and the chamfer surface in the first polishing stage of the end surface polishing step. 16, the first brush bristle may contact only the side wall surface 15 while the second brush bristle may contact both the side wall surface 15 and the chamfer surface 16, and the first brush bristle and the first brush bristle Both of the two brush hairs may contact only the side wall surface 15. Further, in the second polishing stage of the end surface polishing step, the second brush bristles may contact both the side wall surface 15 and the chamfer surface 16, or the second brush bristles may contact only the side wall surface 15.

  In the end surface polishing step, when bundling and polishing a plurality of glass substrates 10... 10, the end surfaces 13 and 14 of each glass substrate 10 are rotated in contact with the end surfaces 13 and 14 from the viewpoint of uniform quality. It is preferable to reciprocate the brushes 31, 32, and 33 in the vertical direction (vertical direction).

  In the present embodiment, in the end surface polishing step, the inner peripheral end surface 13 and the outer peripheral end surface 14 of the glass substrate 10 are simultaneously polished using a plurality of brushes. 14 may be polished separately. Further, the number of brushes is not limited.

  In the present embodiment, the first polishing step and the second polishing step are performed in the end surface polishing step. However, the present invention is not limited to this, and after the second polishing step, the third polishing step, the fourth polishing step,... May be performed. That is, the polishing for removing the processing flaws on the end surfaces 13 and 14 and / or the polishing for smoothing the end surfaces 13 and 14 may be performed in a plurality of stages. For example, when the end surfaces 13 and 14 of the glass substrate 10 are polished using both the first brush bristles and the second brush bristles (polishing for removing processing flaws), the rotation speed of the brush, the end surfaces 13 and 14 By changing the distance between the brush and the center of the brush, the grain size of the abrasive grains of the polishing liquid 22, etc., polishing may be performed in stages under different polishing conditions. Similarly, only the second brush hair is used. When polishing the end surfaces 13 and 14 of the glass substrate 10 (polishing for smoothing the end surfaces), the rotational speed of the brush, the distance between the end surfaces 13 and 14 and the brush axis, and the polishing liquid 22 You may grind | polish in steps under different grinding | polishing conditions by changing the particle size of a grain. In accordance with this, the brush may further include third brush hair, fourth brush hair,... Different in length and rigidity from the first brush hair and the second brush hair.

  In the present embodiment, when the abrasive grains are included in the brush bristles, it is possible to further increase the quality of the end face by including the abrasive grains having a smaller particle diameter as the brush bristles have a relatively long length. It is preferable because it can be smoothed.

  In the present embodiment, the polishing allowance (total polishing amount through the first polishing stage and the second polishing stage) in the end face polishing process is, for example, about 30 to 60 μm.

  Next, specific modes of brushes that can be used in this embodiment will be described with reference to FIGS. 7 and 8 illustrate the brush 31 as a brush, but the same applies to the other brushes 32 and 33.

  As a brush that can be used in the present embodiment, as illustrated in FIG. 7A, a spiral brush in which the brush bristles 31b are spirally planted on the shaft center 31a may be used, or illustrated in FIG. 7B. As shown in FIG. 7C, the brush bristles 31b may be a blade brush in which the bristles 31b are planted in parallel with the shaft center 31a, or may be a dense brush in which the brush bristles 31b are planted in a disorderly manner on the shaft center 31a. Good. In addition, the method of fixing the brush hair 31b to the shaft center 31a is not limited to the flocking method, and other methods, for example, channel method, torsion method, or a combination thereof, for fixing the brush hair to the shaft center. Any of the methods generally used in the past can be employed without limitation.

  In the spiral brush illustrated in FIG. 7A, the bristles 31b have two spirals, but may be one or three or more. The pitch between the stripes is not particularly limited. However, when bundling and polishing a plurality of glass substrates 10... 10, continuous in the axial direction of the brush from the viewpoint of uniform quality of the end surfaces 13 and 14 of each glass substrate 10. And it is preferable that it is the same pitch.

  When the spiral of the brush bristles 31b is one, the first brush bristles and the second brush bristles must be mixed in the one. When the spiral of the brush bristles 31b is two or more, it can be divided into a strip including only the first brush bristles and a strip including only the second brush bristles. Of course, even when the spirals of the brush bristles 31b are two or more, a strip in which the first brush bristles and the second brush bristles are mixed can be used. Even in these cases, when bundling and polishing a plurality of glass substrates 10... 10, from the viewpoint of achieving uniform quality of the end surfaces 13 and 14 of each glass substrate 10, The ratio (the ratio itself is not a problem) is preferably the same ratio continuously in the axial direction of the brush. A specific example of the strip in which the first brush hair and the second brush hair are mixed will be described later with reference to FIG.

  In the blade brush illustrated in FIG. 7B, the number of rows of the brush bristles 31b is four, but is not limited thereto. Depending on the situation, one row may be used, but usually two or more rows are preferred. Moreover, although the row | line | column of the bristle 31b is allocated to the axial center 31a at equal intervals (equal angle) (symmetry), you may be allocated at mutually different intervals (angle) (asymmetric). In the case of symmetry, the manufacture of the brush becomes easy. In the case of the asymmetry, the resonance vibration generated due to the brush bristles 31b repeatedly contacting the end faces 13 and 14 of the glass substrate 10 at a constant period can be prevented. Moreover, in FIG.7 (b), the bristle 31b is planted by perpendicular | vertical (normal direction) to the axial center 31a, but the front-end | tip of the bristle 31b inclines in the downstream of the rotation direction of a brush, and planted May be. However, when the brush is rotated in both forward and reverse directions, the brush bristles 31b are preferably planted perpendicularly to the axis 31a.

  When the row of brush bristles 31b is one row, the first brush bristles and the second brush bristles must be mixed in the one row. When there are two or more rows of brush bristles 31b, it can be divided into a row containing only the first brush bristles and a row containing only the second brush bristles. Of course, even when there are two or more rows of brush bristles 31b, a row in which the first brush bristles and the second brush bristles are mixed can be used. Even in these cases, when bundling and polishing a plurality of glass substrates 10... 10, from the viewpoint of achieving uniform quality of the end surfaces 13 and 14 of each glass substrate 10, The ratio (the ratio itself is not a problem) is preferably the same ratio continuously in the axial direction of the brush. A specific example of the row in which the first brush hair and the second brush hair are mixed will be described later with reference to FIG.

  In the dense brush illustrated in FIG. 7C, the density of the bristles 31 b is not particularly limited, but the quality of the end faces 13 and 14 of each glass substrate 10 when the plurality of glass substrates 10. From the viewpoint of achieving uniformity, it is preferable that the density is continuously the same in the axial direction of the brush.

  FIGS. 8A to 8E are development views of brush bristles of a brush that can be used in the present embodiment. More specifically, it is a development view of brush hairs in which the first brush hairs and the second brush hairs are mixed in different patterns. For example, the spiral brush illustrated in FIG. 7A is obtained by spirally winding the brush bristles 31b shown in FIGS. 8A to 8E around the shaft 31a. Moreover, the blade brush illustrated in FIG.7 (b) is obtained by attaching each bristle 31b shown to Fig.8 (a)-(e) in parallel with the axial center 31a as a row | line | column.

  FIG. 8A shows an example in which the first brush hairs 31c and the second brush hairs 31d are alternately arranged at a ratio of 1: 1 every other hair. FIG. 8B is an example in which a plurality of first brush hairs 31c and second brush hairs 31d are alternately arranged at a ratio of 1: 1 every two (two in the illustrated example). FIG. 8C is an example in which the first brush bristles 31c and the second brush bristles 31d are regularly arranged at a ratio of 1: 2. FIG. 8D is an example in which the first brush hairs 31c and the second brush hairs 31d are irregularly arranged (the ratio of the first brush hairs to the second brush hairs is not limited). FIG. 8E shows an example in which one bristle is composed of first brush bristles 31c on the axis 31a side and second brush bristles 31d on the side opposite to the axis 31a. When manufacturing the spiral brush illustrated in FIG. 7A or the blade brush illustrated in FIG. 7B, one or more of these brush bristles 31b may be used in combination. Brush hair including only the first brush hair and / or brush hair including only the second brush hair may be used in combination.

  In the present embodiment, on the condition that the second brush hair 31d is longer than the first brush hair 31c, the length of the first brush hair 31c is, for example, about 3 to 7 mm, and the length of the second brush hair 31d is, for example, 5 About 9 mm. The ratio of the lengths of the first brush bristles 31c and the second brush bristles 31d is not particularly limited, but is preferably about 2: 3 (for example, the first brush bristles 31c are 4 mm: the second brush bristles 31d are 6 mm). In the case of FIG.8 (e), the length of a thick part is about 3-7 mm, for example, and the whole length is about 5-9 mm, for example.

  In the present embodiment, the first brush hair 31c is higher in rigidity than the second brush hair 31d. For that purpose, for example, the first brush hair 31c and the second brush hair 31d are made of the same material, and the first brush hair 31c has a diameter larger than that of the second brush hair 31d as shown in FIGS. Can be made thicker. For example, on the condition that the diameter of the first brush hair 31c is larger than that of the second brush hair 31d, the thickness (diameter) of the first brush hair 31c is, for example, about 0.3 to 0.7 mm, and the second brush hair 31d. The thickness (diameter) is, for example, about 0.1 to 0.5 mm. Alternatively, the first brush bristles 31c may be made of a material having higher rigidity than the second brush bristles 31d. For example, the first brush hair 31c may be made of a resin having higher rigidity than the second brush hair 31d, or the surface of the first brush hair 31c may be coated to increase the rigidity. A metal core material rich in elasticity may be embedded, or these may be combined.

  Further description will be given with reference to FIG. The brush bristles 31b shown in FIG. 5 and FIG. 8 have a flat shape at the tip of the brush bristles, whether the first bristles 31c or the second brush bristles 31d. As shown in FIG. 9 (a), it may have a square shape, or as shown in FIG. 9 (b), it may have an arc shape. Moreover, as shown in FIG.9 (c), the shape where the front-end | tip swelled rather than the main-body part may be sufficient (a base part and an intermediate part may be a bulge shape). Further, the brush bristles 31b shown in FIGS. 5 and 8 have the same thickness from the base to the tip, regardless of whether the first bristles 31c or the second brush bristles 31d are used. Instead, for example, the base may be thicker than the tip as shown in FIG. 9 (d), and the tip may be thicker than the base as shown in FIG. It may be thicker than the base). Furthermore, although the bristle 31b shown in FIGS. 5 and 8 is the first bristle 31c or the second brush bristle 31d, the shape of the bristle is a straight hair shape, but is not limited thereto. For example, as shown in FIG. 9F, other shapes generally used in the past such as a wave shape may be used. These various shapes may be used in various combinations depending on the situation.

  In the present embodiment, the immersion type end surface polishing apparatus 20 shown in FIG. 3 is used in the end surface polishing step, but a shower type end surface polishing apparatus 50 as shown in FIG. 10 may be used instead. . In this end face polishing apparatus 50, a polishing liquid containing abrasive grains (free abrasive grains) is supplied from a polishing liquid ejection nozzle 51 to a contact portion (polishing portion) between the glass substrate 10 and the brushes 31, 32, 33 (see arrows). ) The end faces 13 and 14 are polished. According to this, it is possible to always supply abrasive grains having a constant diameter to the polishing section, and there is an advantage that the quality of the glass substrate 10 is stabilized even if the number of batches is increased.

  When using the shower type end surface polishing apparatus 50, it is preferable to change the diameter of the abrasive grains contained in the polishing liquid to a smaller one according to the progress of the end surface polishing. This is because the diameter of the abrasive grains is reduced in the second polishing stage, so that the end face can be smoothed with higher quality.

  When the diameter of the abrasive grains contained in the polishing liquid is changed in the middle, the blade brush shown in FIG. 7B is preferable because the previously used polishing liquid does not easily remain in the brush and the polishing section. Further, the spiral brush shown in FIG. 7 (a) also removes the polishing liquid previously used in the manner of the screw feeder from the brush, so that the previously used polishing liquid hardly remains in the brush and the polishing part. It can be preferably used.

  Note that the used polishing liquid is collected and re-prepared and then recycled.

  Hereinafter, the present invention will be described in more detail through examples, but the present invention is not limited to these examples.

(Production of glass substrate)
In accordance with the manufacturing process shown in FIG. 1, a glass melting step (S1), a press molding step (S2), a coring step (S3), and a first lapping step (S4) using aluminosilicate glass materials generally used conventionally. ) And the end face grinding step (S5), an annular aluminosilicate glass substrate having an outer diameter of about 65 mm (2.5 inches) and an inner diameter (circular hole diameter) of about 20 mm was produced. The chamfa surface was not formed.

(Execution of end face polishing process)
Using the shower-type end surface polishing apparatus as shown in FIG. 10, the end surface of the obtained glass substrate was polished. That is, 100 glass substrates are bundled and set in an end surface polishing apparatus, a brush is placed in a circular hole of the glass substrate bundle, and a rotating brush is brought into contact with the inner peripheral end surface of the glass substrate to polish the inner peripheral end surface. Went. The polishing amount was 40 μm. During this end face polishing step, a polishing liquid containing cerium oxide was continuously supplied to the contact portion (polishing portion) between the glass substrate and the brush.

(Example)
In the example, a spiral brush as shown in FIG. 7A (however, one spiral) was used as the brush. Further, as the bristle, the bristle in which the first brush bristle and the second brush bristle are alternately arranged at a ratio of 1: 1 as shown in FIG. 8A was used. The brush bristles were made of nylon, and the first brush bristles had a length of 4 mm and a thickness (diameter) of 0.5 mm, and the second bristles had a length of 6 mm and a thickness (diameter) of 0.1 mm. Then, the first polishing step is performed by setting the distance between the inner peripheral end face of the glass substrate and the brush axis to 2 mm, and then the distance between the inner peripheral end face of the glass substrate and the brush axis is set to 5 mm. Two polishing steps were performed. As an evaluation, the polishing time required until the polishing amount reached 40 μm was measured. Further, the surface roughness (Ra) of the inner peripheral end surface after polishing was measured using a surface roughness measuring machine (measurement condition: a value obtained by arbitrarily measuring 10 points in the range of 1 μm with AFM and averaging them (arithmetic) The average roughness Ra) was defined as the surface roughness). As a result, the polishing time was 35 minutes (first polishing stage 25 minutes, second polishing stage 10 minutes), and the surface roughness (Ra) was 0.4 nm (average value measured by randomly extracting 10 out of 100 sheets) )Met. From this, it was found that the working surface of the end face was removed in a short time and the end face was smoothed with high quality without moving the glass substrate between end face polishing devices or replacing the brush. It was. In this example, aluminosilicate glass was used, but the same result is expected even when other conventionally used glass such as borosilicate glass is used.

(Comparative Example 1)
In Comparative Example 1 as well, a spiral brush as shown in FIG. 7A (however, one spiral) was used as the brush. However, only nylon brush hair having a length of 6 mm and a thickness (diameter) of 0.1 mm was used as the brush hair. And when the distance between the inner peripheral end face of the glass substrate and the axis of the brush was 5 mm, end face polishing was performed, and the same evaluation as in the example was performed. The polishing time was 130 minutes and the surface roughness (Ra) was It was 0.4 nm (average value measured by randomly extracting 10 out of 100 sheets). From this, it was found that in Comparative Example 1, the polishing rate was lowered and the productivity was lowered.

(Comparative Example 2)
In Comparative Example 2 as well, a spiral brush as shown in FIG. 7A (however, one spiral) was used as the brush. However, only nylon brush hair having a length of 4 mm and a thickness (diameter) of 0.5 mm was used as the brush hair. Then, the end surface was polished with the distance between the inner peripheral end surface of the glass substrate and the axis of the brush being 2 mm, and the same evaluation as in the example was performed. The polishing time was 25 minutes, and the surface roughness (Ra) was It was 1.8 nm (average value measured by randomly extracting 10 out of 100 sheets). From this, it was found that in Comparative Example 2, brush scratches remained on the end face and it was difficult to smooth the end face.

10 Glass substrates for magnetic recording media 11, 12 Main surface (recording surface)
DESCRIPTION OF SYMBOLS 13 Inner peripheral end surface 14 Outer peripheral end surface 15 Side wall surface 16 Chamfer surface 20 Immersion type end surface polishing apparatus 21 Polishing liquid tank 22 Polishing liquid 31, 32, 33 Brush 31a, 32a, 33a Axes 31b, 32b, 33b Brush part (brush hair)
31c 1st brush part (1st brush hair)
31d 2nd brush part (2nd brush hair)
50 Shower type end face polishing equipment

Claims (6)

A method for producing a glass substrate for a magnetic recording medium comprising an end face polishing step of polishing an inner peripheral end face and / or an outer peripheral end face of a glass substrate using a brush,
The brush has a rotatable shaft center and a brush portion arranged 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. A second brush part having a relatively long length,
The end surface polishing step includes a first polishing step and a second polishing step in this order,
In the first polishing stage, the first brush portion and the second brush portion are brought into contact with the end surface of the glass substrate, and the brush is rotated around the axis,
In 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 axis of the brush is longer than that in the first polishing stage. A method of manufacturing a glass substrate for a magnetic recording medium, wherein the brush is rotated about an axis.   The method for manufacturing a glass substrate for a magnetic recording medium according to claim 1, wherein in the end surface polishing step, the plurality of glass substrates are stacked and polished in the thickness direction while aligning the centers.   2. The method for producing a glass substrate for a magnetic recording medium according to claim 1, wherein, in the end face polishing step, the glass substrate and the brush are dipped in a bath of polishing liquid containing abrasive grains and polished.   The method for producing a glass substrate for a magnetic recording medium according to claim 1, wherein in the end surface polishing step, polishing is performed while supplying a polishing liquid containing abrasive grains to a contact portion between the glass substrate and the brush.   5. The method for manufacturing a glass substrate for a magnetic recording medium according to claim 4, wherein, in the end surface polishing step, the diameter of the abrasive grains contained in the polishing liquid is changed to a smaller one in accordance with the progress of the end surface polishing.   6. The method for producing a glass substrate for a magnetic recording medium according to claim 1, wherein an end surface of the glass substrate is chamfered.

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