JP2008282539A - Glass substrate for magnetic recording medium, and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a glass substrate for a magnetic recording medium capable of preventing breakage of a magnetic disk and to provide its manufacturing method. <P>SOLUTION: The glass substrate 100 for the magnetic recording medium of a doughnut shape has a chamfered surface 104a for connecting a main surface 101a and an outer peripheral surface 102. The chamfered surface 104a consists of an annular curved surface part 104a' and a conical surface part 104a" connected to each other. The percentage ratio of the length d1 of the external form line of the annular curved surface part 104a' to the length L of the external form line 200 of the chamfered surface 104a at the section of the glass substrate 100 inclusive of a central line 106 of the glass substrate 100 is ≥20%. The radius R of curvature of the annular curved surface part 104a' is 0.10 to 0.50 mm. The angle θ formed by the main surface 101a and the conical surface part 104a" is 136 to 165°. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a glass substrate for a magnetic recording medium and a method for manufacturing the same.

  As a substrate for a magnetic recording medium such as a magnetic disk, an aluminum substrate has been widely used. However, with the spread of notebook-type and mobile-type PCs (personal computers), the magnetic disk is made thinner and has a higher recording surface. In addition to increasing density, demands for durability against changes in the usage environment have increased. In order to cope with this requirement, in recent years, low impact of the head, which has high impact resistance, rigidity and hardness, and high chemical durability against changes in the use environment, is indispensable for increasing the recording surface density. A glass substrate having flatness that realizes floating is widely used.

  Generally, in mechanical processing such as grinding processing for adjusting the dimensions of the inner peripheral end surface and outer peripheral end surface of the doughnut-shaped glass substrate to predetermined dimensions and chamfering processing for processing the chamfered surface into a predetermined shape, the glass substrate is attached to the grinding wheel. A predetermined size and shape are realized by scraping off the glass with the abrasive grains.

  The mechanism by which the abrasive grains scrape the glass is such that the abrasive grains attached to the rotating grinding wheel generate a crack on the surface of the glass substrate by impact force, and the crack grows, so that a small amount of glass is generated from the surface of the glass substrate. Is peeled off.

  However, when a minute amount of glass has been peeled off, microcracks remain on the surface of the glass substrate. This microcrack is a mechanical shock that occurs when a magnetic disk using a glass substrate is incorporated into an HDD (Hard Disk Drive) on a glass substrate processed by a grinding wheel, or when a magnetic disk using the glass substrate is incorporated into an HDD (Hard Disk Drive). When the stress due to mechanical shock or thermal shock generated by impact or changes in the usage environment of a notebook or mobile type PC incorporating a magnetic disk is generated and dispersed throughout, the above machine When stress due to mechanical shock or thermal shock is concentrated at one place and the place where the stress is concentrated coincides with the existence of a microcrack, it grows at a considerably high speed. The crack becomes a so-called crack, and the crack damages the magnetic disk using the glass substrate.

  As the residual factors of the microcracks, there are a shape defect and a large particle size of the diamond abrasive grains attached to the grinding wheel, a large grinding speed of mechanical processing, and the like.

  In addition, stress based on mechanical shock or thermal shock is likely to be concentrated on the boundary portion between one of the inner peripheral end surface and the outer peripheral end surface and the chamfered surface, and since this boundary portion is processed with a grinding wheel from both sides, Cracks are likely to remain.

  Furthermore, at the boundary between the main surface and the chamfered surface, small chipping called chipping due to glass peeling tends to occur on the main surface side during mechanical grinding, and the cause of this glass peeling is the chamfered surface and the main surface. Is an obtuse angle of 135 ° or less.

  An object of the present invention is to provide a glass substrate for a magnetic recording medium that can prevent damage to the magnetic recording medium and a method for manufacturing the same.

  To achieve the above object, a glass substrate for a magnetic recording medium according to claim 1 has a main surface, an outer peripheral end surface and an inner peripheral end surface, and connects the main surface and one of the outer peripheral end surface and the inner peripheral end surface. In the doughnut-shaped glass substrate for a magnetic recording medium having a chamfered surface, the chamfered surface includes a conical surface portion and an annular curved surface portion that are connected to each other, and the chamfered surface in a cross section of the glass substrate including a central axis of the glass substrate. The percentage ratio of the length of the outer shape line of the annular curved surface portion to the length of the outer shape line is 30% or more, and the angle formed by the chamfered surface and the main surface is 136 to 165 °.

  The glass substrate according to claim 2 is the glass substrate according to claim 1, wherein the percentage ratio is 50% or more.

  The glass substrate according to claim 3 is characterized in that, in the glass substrate according to claim 1 or 2, the radius of curvature of the outline of the annular curved surface portion is 0.10 to 0.35 mm.

  The glass substrate according to claim 4 is the glass substrate according to claim 3, wherein the radius of curvature is 0.20 to 0.35 mm.

  The glass substrate according to claim 5 is the glass substrate according to any one of claims 1 to 4, wherein an angle formed between the chamfered surface and the main surface is 140 to 155 °.

  The glass substrate according to claim 6 is the glass substrate according to any one of claims 1 to 5, wherein the Weibull constant calculated based on the fracture stress is 20.0 or more.

  The glass substrate according to claim 7 is subjected to a chemical strengthening treatment in which the alkali component in the surface layer of the glass substrate is replaced with one having a larger ionic radius in the glass substrate according to any one of claims 1 to 6. It is characterized by.

  In order to achieve the above object, a method for producing a glass substrate for a magnetic recording medium according to claim 8 is a donut-shaped glass substrate for a magnetic recording medium having a main surface, an outer peripheral end surface, and an inner peripheral end surface. 7. A chamfering process for forming a glass substrate for a magnetic recording medium according to any one of claims 1 to 6 by chamfering a corner between one of the outer peripheral end surface and the inner peripheral end surface. It is characterized by.

  The manufacturing method according to claim 9 is the manufacturing method according to claim 8, wherein after the chamfering step, a main surface polishing step of polishing the main surface by 5 μm or more, and polishing the outer peripheral end surface and the inner peripheral end surface by 5 μm or more. And an end face polishing step.

The manufacturing method according to claim 10 is the manufacturing method according to claim 9, wherein the glass substrate is made of a silicate glass in which the mother glass contains Li ₂ O or Na ₂ O as an alkali oxide component, The manufacturing method includes a chemical strengthening treatment step of replacing the alkali component of the surface layer on the main surface with an alkali component having an ionic radius larger than that of the alkali oxide component after the main surface polishing step.

  According to the glass substrate of claim 1, the percentage ratio of the length of the outline of the annular curved surface portion to the length of the outline of the chamfered surface in the cross section of the glass substrate including the central axis of the glass substrate is 30% or more. Since the angle formed between the chamfered surface and the main surface is 136 to 165 °, the stress generated at the boundary between the outer peripheral end surface and the inner peripheral end surface and the chamfered surface due to mechanical shock or thermal shock may be dispersed. Thus, damage to the magnetic recording medium can be prevented. In addition, the chamfered surface of the chamfered surface is prevented by preventing the wobbling of the glass substrate during chamfered surface processing with a grinding wheel, preventing the narrowing of the width of the chamfered surface and dispersing the stress generated on the chamfered surface. In addition, micro cracks can be removed from the surface, and in addition, the occurrence of chipping at the boundary between the main surface and the chamfered surface can be prevented, and the amount of polishing in the polishing process for chipping removal can be reduced. Can be reduced.

  According to the glass substrate of claim 2, the percentage ratio of the length of the outline of the annular curved surface portion to the length of the outline of the chamfered surface in the cross section of the glass substrate including the central axis of the glass substrate is 50% or more. Therefore, the effect by the glass substrate of Claim 1 can be show | played more reliably.

  According to the glass substrate of claim 3, since the curvature radius of the contour line of the annular curved surface portion is 0.10 to 0.35 mm, the grinding wheel is increased by increasing the lower limit of the radius of curvature of the grinding wheel for processing the annular curved surface portion. In addition to the fact that the surface abrasive grains can be uniformly adhered, and the exchange life of the grinding wheel can be increased by strengthening the adhesive force of the abrasive grains, the conical surface portion and the annular shape can be reduced by reducing the upper limit of the radius of curvature. The boundary between the curved surface and the curved surface can be prevented from becoming discontinuous, and the stress generated at the boundary between the conical surface and the annular curved surface can be dispersed, preventing damage to the magnetic disk more reliably. can do.

  According to the glass substrate of Claim 4, the effect by the glass substrate of Claim 3 can be show | played more reliably.

  According to the glass substrate of Claim 5, since the angle which a chamfering surface and a main surface comprise is 140-155 degrees, there exists reliably the effect by the glass substrate of any one of Claims 1 thru | or 4. be able to.

  According to the glass substrate of the sixth aspect, since the Weibull constant calculated based on the fracture stress is 20.0 or more, the magnetic disk can be reliably prevented from being damaged.

  According to the glass substrate of Claim 7, since the chemical strengthening process which replaces the alkali component in the surface layer of a glass substrate with a thing with a larger ionic radius is performed, the intensity | strength of a glass substrate can be improved.

  According to the method for manufacturing a glass substrate for a magnetic recording medium according to claim 8, chamfering is performed on a corner portion between the main surface and one of the outer peripheral end face and the inner peripheral end face. Since the glass substrate for a magnetic recording medium described in any one of the above items is formed, the stress generated at the boundary between the outer peripheral end surface and one of the inner peripheral end surfaces and the chamfered surface due to mechanical shock or thermal shock can be dispersed. Thus, damage to the magnetic recording medium can be prevented.

  According to the manufacturing method of claim 9, after chamfering the glass substrate, the main surface is polished by 5 μm or more, and the outer peripheral end surface and the inner peripheral end surface are polished by 5 μm or more, so that microcracks can be reliably removed. Therefore, it is possible to reliably prevent the magnetic disk from being damaged.

According to the manufacturing method of claim 10, the alkali component of the surface layer on the main surface of the glass substrate made of silicate glass in which the mother glass contains either Li ₂ O or Na ₂ O as an alkali oxide component is alkalinized. Since the alkali component having an ionic radius larger than that of the oxide component is substituted, the strength of the glass substrate can be improved.

  As a result of intensive studies to achieve the above object, the present inventor has a main surface, an outer peripheral end surface and an inner peripheral end surface, and a chamfered surface connecting the main surface and one of the outer peripheral end surface and the inner peripheral end surface. In the doughnut-shaped glass substrate for magnetic recording medium, the chamfered surface is composed of a conical surface portion and an annular curved surface portion that are connected to each other, and is circular with respect to the length of the outline of the chamfered surface in the cross section of the glass substrate including the central axis of the glass substrate. When the percentage ratio of the length of the contour line of the curved surface portion is 20% or more, preferably 50% or more, it occurs at the boundary portion between one of the outer peripheral end surface and the inner peripheral end surface and the chamfered surface due to mechanical shock or thermal shock. It has been found that the stress to be distributed can be dispersed, and thus damage to the magnetic recording medium can be prevented.

  The inventor has a main surface, an outer peripheral end surface and an inner peripheral end surface, and a doughnut-shaped glass substrate for a magnetic recording medium having a chamfered surface connecting the main surface and one of the outer peripheral end surface and the inner peripheral end surface. When the angle formed between the chamfered surface and the main surface is 136 to 165 °, preferably 140 to 155 °, the glass substrate for magnetic recording medium is prevented from shaking during chamfering processing with a grinding wheel, and the width of the chamfered surface is reduced. This prevents the generation of unground parts and removes microcracks from the chamfered surface, in addition to chamfering one of the outer peripheral end surface and the inner peripheral end surface. It has been found that chipping at the boundary with the surface can be prevented, the amount of polishing in the polishing process for chipping removal can be reduced, and thus the manufacturing cost can be reduced.

  Further, the present inventor has chamfered a corner portion between the main surface and one of the outer peripheral end surface and the inner peripheral end surface in a donut-shaped glass substrate for a magnetic recording medium having a main surface, an outer peripheral end surface, and an inner peripheral end surface. 7. A chamfering process for forming the glass substrate for a magnetic recording medium according to claim 1, wherein the outer peripheral end surface and the inner peripheral end surface are subjected to mechanical shock or thermal shock. It has been found that the stress generated at the boundary with the chamfered surface can be dispersed, thereby preventing damage to the magnetic recording medium.

  Hereinafter, a glass substrate for a magnetic recording medium according to an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a cross-sectional view of a glass substrate for a magnetic recording medium according to an embodiment of the present invention.

  In FIG. 1, a glass substrate 100 for a doughnut-shaped magnetic recording medium includes two main surfaces 101a and 101b, an outer peripheral end surface 102, an inner peripheral end surface 103, and a chamfered surface 104a connecting the main surface 101a and the outer peripheral end surface 102. The chamfered surface 104b connecting the main surface 101b and the outer peripheral end surface 102, the chamfered surface 105a connecting the main surface 101a and the inner peripheral end surface 103, and the chamfered surface 105b connecting the main surface 101b and the inner peripheral end surface 103.

  FIG. 2 is an enlarged cross-sectional view of the glass substrate 100 of FIG.

  The chamfered surface 104a includes an annular curved surface portion 104a 'and a conical surface portion 104a' 'that are connected to each other.

  The percentage ratio (d1 / L) of the length d1 of the outline of the circular curved surface portion 104a ′ to the length L of the outline 200 of the chamfered surface 104a in the cross section of the glass substrate 100 including the central axis 106 of the glass substrate 100 is 20%. Above, preferably 50% or more. As a result, the stress generated at the boundary between the outer peripheral end face 102 and the chamfered surface 104a due to mechanical shock or thermal shock can be dispersed, and damage to the magnetic recording medium can be prevented.

  The curvature radius R of the annular curved surface portion 104a 'is 0.10 to 0.50 mm, preferably 0.20 to 0.35 mm. As a result, it is possible to uniformly attach the abrasive grains on the grinding wheel surface by increasing the lower limit of the radius of curvature of the grinding wheel that processes the annular curved surface portion 104a ′, and thus the replacement life of the grinding wheel by strengthening the adhesion of the abrasive grains. In addition, it is possible to prevent the boundary portion between the conical surface portion 104a ″ and the annular curved surface portion 104a ′ from becoming discontinuous by reducing the upper limit of the radius of curvature, and thus the conical surface portion 104a. ”And the annular curved surface portion 104a ′ can be dispersed, and the magnetic disk can be more reliably prevented from being damaged.

  The angle θ formed between the main surface 101a and the conical surface portion 104a is 136 to 165 °, preferably 140 to 155 °. This prevents the glass substrate 100 from shaking during chamfering with a grinding wheel, prevents the chamfered surface 104a from narrowing, disperses the stress generated on the chamfered surface 104a, and prevents the occurrence of unground parts. By removing the microcracks from the chamfered surface 104a, the magnetic disk can be prevented from being damaged. In addition, the chipping removal at the boundary between the main surface 101a and the chamfered surface 104a is prevented. Therefore, the amount of polishing in the polishing process can be reduced, thereby reducing the manufacturing cost.

  When the angle θ is 135 ° or less, chipping is likely to occur at the boundary between the main surface 101a and the chamfered surface 104a. On the other hand, when the angle θ is 165 ° or more, the positioning deviation between the grinding wheel and the glass substrate 100 is increased. As a result, the glass substrate 100 is shaken and generally the length L of the outer circumferential intersection line 200 and the inner circumferential intersection line is increased. Therefore, the chamfered surface 104a is removed when the microcracks are removed by polishing the chamfered surface 104a. As a result, fine cracks are likely to remain in the unpolished portion.

  The same can be said for the chamfered surfaces 104b, 105a, 105b.

  Further, the glass substrate 100 is made of a silicate glass having chemical durability and rigidity against alkali or the like, or crystallized glass obtained by crystallizing silicate glass by heat treatment.

  Examples of the silicate glass include soda lime silicate glass, aluminosilicate glass, borosilicate silicate glass, and chemically tempered glass used for architectural window glass. Easily tempered glass is made by bringing glass into contact with potassium nitrate molten salt to exchange lithium or sodium components in the glass with potassium ions having a larger ionic radius, or bringing glass into contact with molten sodium nitrate to bring the glass into contact with the glass. By replacing lithium ions with sodium ions having a larger ion radius, compressive stress is formed on the surface layer (about 50 to 200 μm). As such glass, SiO2: 60 to 65%, Al2O3: 10 to 20%, MgO: 0 to 5%, CaO: 0 to 5%, Li2O: 2 to 10%, Na2O: What contains 5 to 15% can be illustrated. The crystallized glass can be exemplified by those having as a main component a component selected from SiO2, Al2O3, Li2O, MgO, P2O3, ZrO, CeO2, TiO2, Na2O, and K2O.

  The composition of the crystallized glass is not particularly limited. For example, in terms of mass%, SiO2: 70 to 80%, Al2O3: 2 to 8%, K2O: 1 to 7%, Li2O: 5 to 15%, P2O5: What contains 1 to 5% can be illustrated.

  The glass substrate 100 may be formed into a donut shape by a polishing grindstone from a plate-like glass material molded by a float glass manufacturing method, a downdraw manufacturing method, or a redraw manufacturing method, and an upper mold and a lower mold are formed from molten glass. It may be formed directly in a donut shape by a direct press using. When forming a donut shape with a polishing grindstone, the outer diameter of the plate-shaped glass material is formed in a circle using a polishing grindstone, and then the center of the glass material formed in a circular outer diameter using a cylindrical grindstone You may form by hollowing out a part.

  Next, the manufacturing method of the glass substrate for magnetic recording media which concerns on embodiment of this invention is demonstrated with reference to drawings.

  FIG. 3 is a flowchart of the manufacturing procedure of the glass substrate for magnetic recording media according to the embodiment of the present invention.

  This procedure manufactures the glass substrate for magnetic recording media according to the embodiment of the present invention described above.

  In FIG. 3, first, a glass base plate having a glass composition of aluminosilicate glass formed into a plate shape on a molten metal by a float glass manufacturing method is prepared, and a cemented carbide cutter is used from the prepared glass base plate. The doughnut-shaped glass substrate 100 having an outer diameter of 96 mmφ, an inner diameter of 24 mmφ and a thickness of 1.15 mm is formed by simultaneously processing the outer periphery and the inner periphery (step S300).

  Next, the size of the outer peripheral end face 102 of the glass substrate 100 is adjusted to 95 mmφ and the dimension of the inner peripheral end face 103 is adjusted to 25 mmφ by grinding using the grinding wheel of FIG. A chamfered surface 104 a connecting the end surface 102, a chamfered surface 104 b connecting the main surface 101 b and the outer peripheral end surface 102, a chamfered surface 105 a connecting the main surface 101 a and the inner peripheral end surface 103, a main surface 101 b and the inner peripheral end surface 103. The connecting chamfered surfaces 105b are formed. At this time, the curvature radius R of the annular curved surface portion 104a ′ existing at the intersection of each of the chamfered surfaces 104a, 104b, 105a, and 105b and any one of the outer peripheral end surface 102 and the inner peripheral end surface 103 is adjusted to 0.2 mm. Then, the angle θ is adjusted to 155 ° (step S301).

  FIG. 4 is a diagram showing the grinding wheel used in step S301 of FIG.

  In FIG. 4, the grinding wheel is constituted by an outer peripheral end face grinding grindstone 400 that adjusts the dimension of the outer peripheral end face 102 and an inner peripheral end face grinding grindstone 401 that adjusts the dimension of the inner peripheral end face 103.

  The outer peripheral end surface grinding wheel 400 includes a rotating shaft 402 and a grindstone group 404. The grindstone group 404 is formed by laminating a predetermined number of annular grindstones 403 having processing grooves in a shape in which the shapes of the outer peripheral end surface 102 and the chamfered surfaces 104a and 104b are complemented on the outer diameter portion thereof. The outer peripheral end surface grinding wheel 400 rotates around the rotation shaft 402, adjusts the dimension of the outer peripheral end surface 102 of the glass substrate 100 by contacting the outer peripheral end surface 102 through the processing groove, and chamfered surfaces 104a and 104b. Are formed into a predetermined shape.

  Further, the inner peripheral end face grinding grindstone 401 is also composed of a rotating shaft 405 and a grindstone group 407. The grindstone group 407 is formed by laminating a predetermined number of grindstones 406 each having a processing groove having a shape in which the shapes of the inner peripheral end surface 103 and the chamfered surfaces 105a and 105b are complemented on the outer diameter portion thereof. The inner peripheral end surface grinding wheel 401 rotates about the rotation shaft 405 and adjusts the dimension of the inner peripheral end surface 103 of the glass substrate 100 by contacting the inner peripheral end surface 103 via the machining groove, and also chamfered. 105a and 105b are formed in a predetermined shape. Further, diamond abrasive grains are attached to the surface of the processing groove of the grindstones 403 and 406.

  Returning to FIG. 3, a plurality of glass substrates 100 are stacked and rotated so that a main surface 101 a of any glass substrate 100 and a main surface 101 b of another glass substrate 100 are in contact with each other, and the stacked glass substrates 100 are rotated. A slurry in which an abrasive is dissolved in water is applied, and the outer peripheral end surface 102, the inner peripheral end surface 103, and the chamfered surfaces 104a, 104b, 105a, and 105b of the laminated glass substrate 100 are polished with a polishing brush of 5 μm or more (step S302).

  In subsequent step S303, the upper and lower main surfaces 101a and 101b of the glass substrate 100 are lapped to the glass substrate 100 using an abrasive having a particle size # 1000. At this time, the polishing material remaining on both the main surfaces 101a and 101b of the glass substrate 100 is damaged in the first polishing step (main surface polishing step) of step S304 described below, such as scratches on both the main surfaces 101a and 101b. Since it becomes a factor, after lapping is completed, all surfaces of the glass substrate 100 are washed with an acidic or alkaline aqueous solution.

  Next, using a fine abrasive such as a suspension of cerium oxide, in the first polishing step of step S304, scratches on both the main surfaces 101a and 101b generated by the lapping of step S303 are removed, and the subsequent first step of step S305 is performed. In the 2 polishing step (main surface polishing step), the thickness of the glass substrate 100 is adjusted to 1.0 mm by precision polishing, and both the main surfaces 101a and 101b are made smooth. The total thickness to be polished in step S304 and step S305 is 5 μm or more, and then both main surfaces 101a and 101b are washed with an acidic or alkaline aqueous solution.

  The glass substrate 100 from which both the main surfaces 101a and 101b have been cleaned is further strengthened by a chemical strengthening process so as to ensure the strength at the time of high-speed rotation of the magnetic disk, and cleaned with warm water, alkaline cleaning water or pure water. Then, this process is terminated (step S306).

  This chemical strengthening treatment replaces the alkali component in the surface layer of the glass substrate 100 with one having a larger ionic radius. Specifically, by immersing the glass substrate 100 in a molten salt of potassium nitrate (KNO 3) and sodium nitrate (NaNo 3) at 400 to 450 ° C. for 2 to 5 hours, sodium ions in the surface layer of the glass substrate 100 are converted into potassium ions. In addition, lithium ions are replaced with sodium ions to improve the strength of the glass substrate 100.

  According to the procedure of FIG. 3, the stress generated at the boundary between one of the outer peripheral end surface 102 and the inner peripheral end surface 103 and one of the chamfered surfaces 104a, 104b, 105a, 105b can be dispersed by mechanical shock or thermal shock. Thus, damage to the magnetic recording medium can be prevented.

  Next, examples of the present invention will be specifically described.

  First, the procedure of FIG. 3 was executed up to step S302, and test pieces of 10 types of glass substrates for magnetic recording media shown in Table 1 were produced (Examples 1 to 9, Comparative Example 1).

  Thereafter, for each of these 10 types of test pieces, the fracture stress was measured using a strength tester (trade name: AUTOGRAPH) (FIG. 5) manufactured by Shimadzu Corporation, and the Weibull constant was determined based on the measured fracture stress. Was calculated.

  FIG. 5 is a side view showing a schematic configuration of the strength tester used in the example of the present invention.

  In FIG. 5, the test piece 500 was set on a steel table 501, and a steel ring 502 was set on the set test piece 500. Thereafter, the relative displacement speed between the cradle 501 and the ring 502 is adjusted to 0.5 mm / min, the test piece 500 is pressurized via the cradle 501 and the ring 502, and the load when the test piece 500 breaks is loaded into the load cell. 503 detected.

  The detection of the above breaking load was performed 100 times for each test piece 500, the detected breaking load was converted to the breaking stress data, and the Weibull constant was calculated based on the breaking stress data for 100 times.

  In addition, 10,000 films each having a surface recording density of 7 gigabits / in 2 on the magnetic disk are formed for each of the test pieces 500, and the damaged number of the 10,000 test pieces 500 is formed. Calculated as damage rate.

  Further, the probability of occurrence of chipping occurring at the boundary between one of the main surfaces 101a and 101b and one of the chamfered surfaces 104a, 104b, 105a, and 105b was calculated as a chipping failure rate.

  Table 1 also shows the Weibull constant, the damage rate during film formation, and the chipping failure rate.

  As apparent from Table 1 above, in Comparative Example 1, the percentage ratio of the length d1 of the annular curved surface portion 104a ′ to the length L of the outline 200 is as small as 17%, that is, the outer peripheral end surface 102 and the chamfered surface 104a, Since the stress tends to concentrate on the boundary with 104b, the Weibull constant indicating that the strength reliability is lower as the constant value is smaller is 15.2, and the damage rate during film formation is as high as 5/10000. On the other hand, in Example 9, the percentage of the annular curved surface portion 104a ′ is as large as 30%, that is, the stress is difficult to concentrate on the boundary portion between the outer peripheral end surface 102 and the chamfered surfaces 104a and 104b. In addition, the damage rate during film formation was 2/10000, which was a value satisfying strength reliability. Furthermore, in Example 5, the percentage of the annular curved surface portion 104a ′ is as large as 56%, that is, the stress is less likely to concentrate at the boundary between the outer peripheral end surface 102 and the chamfered surfaces 104a and 104b. It was 0, and the damage rate during film formation was 1/10000, which was a value satisfying the strength reliability. Thus, it was confirmed that damage to the magnetic disk can be reliably prevented if the percentage of the annular curved surface portion 104a 'is 30% or more, preferably 50% or more.

  Further, as apparent from Table 1 above, in Comparative Example 1, the radius of curvature R of the annular curved surface portion 104a ′ is as small as 0.05 mm, that is, stress tends to concentrate on the annular curved surface portion 104a ′, so the Weibull constant is 15 2 and the damage rate during film formation was as high as 5/10000, while in Example 4, the radius of curvature R of the annular curved surface portion 104a ′ was as large as 0.10 mm, that is, the annular curved surface portion 104a ′. Since the stress is difficult to concentrate, the Weibull constant is 20.0, and the damage rate during film formation is 2/10000, which satisfies the strength reliability. Further, in Example 7, the radius of curvature R of the annular curved surface portion 104a ′ is larger than 0.20 mm, that is, the stress is less likely to concentrate on the annular curved surface portion 104a ′, and the Weibull constant is 21.8. The film breakage rate was 1/10000, a value more satisfying strength reliability. Thereby, if the radius of curvature R of the annular curved surface portion 104a ′ is 0.10 mm or more, the magnetic disk can be prevented from being damaged. Preferably, if it is 0.20 mm or more, the magnetic disk can be reliably prevented from being damaged. It could be confirmed.

  Further, as apparent from Table 1 above, in Example 2, the radius of curvature R of the annular curved surface portion 104a ′ is as small as 0.35 mm, that is, the stress is less likely to concentrate on the annular curved surface portion 104a ′. It was 21.5, and the failure rate during film formation was 1/10000, which was a value satisfying the strength reliability. As a result, it was confirmed that the magnetic disk could be reliably prevented from being damaged if the radius of curvature R of the annular curved surface portion 104a 'was 0.50 mm or less, preferably 0.35 mm or less.

  Further, as apparent from Table 1 above, in Example 6, the angle θ is as small as 165 °, that is, a portion where the width of the chamfered surface is narrowed based on the shake of the glass substrate 100 (hereinafter referred to as “narrow portion”). Therefore, the Weibull constant was 20.0, and the damage rate during film formation was 2/10000, which was a value satisfying strength reliability. Further, in Example 3, the angle θ is smaller than 155 °, that is, the narrow portion is less likely to occur. Therefore, the Weibull constant is 20.8, the damage rate during film formation is 1/10000, and the strength is more reliable. A value satisfying the property was shown. As a result, it was confirmed that damage to the magnetic disk could be reliably prevented if the angle θ was 165 ° or less, preferably 155 ° or less.

  Further, as apparent from Table 1 above, since Comparative Example 1 has a small angle θ of 135 °, the chipping failure rate showed a high value of 3.0%, while Example 5 had an angle θ of 136 °. Therefore, the chipping failure rate was 1.0%. Further, in Example 7, since the angle θ was 140 °, the chipping defect rate was 0.8%. Thus, it was confirmed that the manufacturing cost can be reduced when the angle θ is 136 ° or more, and that the manufacturing cost can be further reduced when the angle θ is preferably 140 ° or more.

It is sectional drawing of the glass substrate for magnetic recording media which concerns on embodiment of this invention. It is an expanded sectional view of the glass substrate 100 for magnetic recording media of FIG. It is a flowchart of the manufacture procedure of the glass substrate for magnetic recording media which concerns on embodiment of this invention. It is a figure which shows the grinding wheel used in step S301 of FIG. FIG. 5 is a side view showing a schematic configuration of the strength tester used in the example of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Glass substrate 101 for magnetic recording media Main surface 102 Outer peripheral end surface 103 Inner peripheral end surface 104a, 104b, 105a, 105b Chamfered surface 104a 'Annular curved surface part 104a "Conical surface part 200 Outline line 400 Outer peripheral end face grinding wheel 401 For inner peripheral end face grinding Grinding stone 402,405 Rotating shaft 403,406 Grinding stone 404,407 Grinding wheel group

Claims (10)

In a doughnut-shaped glass substrate for a magnetic recording medium having a main surface, an outer peripheral end surface and an inner peripheral end surface, and having a chamfered surface connecting the main surface and one of the outer peripheral end surface and the inner peripheral end surface;
The chamfered surface is composed of a conical surface portion and an annular curved surface portion connected to each other, and the length of the contour line of the annular curved surface portion with respect to the length of the contour line of the chamfered surface in the cross section of the glass substrate including the central axis of the glass substrate. The percentage ratio is 30% or more,
The glass substrate for a magnetic recording medium, wherein an angle formed by the chamfered surface and the main surface is 136 to 165 °.   The glass substrate for a magnetic recording medium according to claim 1, wherein the percentage ratio is 50% or more.   3. The glass substrate for a magnetic recording medium according to claim 1, wherein a radius of curvature of an outer shape line of the annular curved surface portion is 0.10 to 0.35 mm.   The glass substrate for a magnetic recording medium according to claim 3, wherein the radius of curvature is 0.20 to 0.35 mm.   5. The glass substrate for a magnetic recording medium according to claim 1, wherein an angle formed by the chamfered surface and the main surface is 140 to 155 °.   6. The glass substrate for a magnetic recording medium according to claim 1, wherein the Weibull constant calculated based on the breaking stress is 20.0 or more.   7. The glass substrate for a magnetic recording medium according to claim 1, wherein a chemical strengthening treatment is performed to replace an alkali component in a surface layer of the glass substrate with a material having a larger ionic radius. . In the method for manufacturing a glass substrate for a donut-shaped magnetic recording medium having a main surface, an outer peripheral end surface and an inner peripheral end surface,
A chamfering process for forming a glass substrate for a magnetic recording medium according to any one of claims 1 to 6, wherein a chamfering process is performed on a corner portion between the main surface and one of the outer peripheral end surface and the inner peripheral end surface. A method for producing a glass substrate for a magnetic recording medium, comprising a step.   9. The magnetism according to claim 8, further comprising a main surface polishing step for polishing the main surface by 5 μm or more after the chamfering step, and an end surface polishing step for polishing the outer peripheral end surface and the inner peripheral end surface by 5 μm or more. A method for producing a glass substrate for a recording medium. The glass substrate is made of silicate glass in which a mother glass contains either Li ₂ O or Na ₂ O as an alkali oxide component, and the manufacturing method includes a surface layer of the main surface after the main surface polishing step. The method for producing a glass substrate for a magnetic recording medium according to claim 9, further comprising a chemical strengthening treatment step of substituting the alkali component of the component with an alkali component having an ionic radius larger than that of the alkali oxide component.

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