JP5029952B2 - GLASS SUBSTRATE, ITS MANUFACTURING METHOD, AND MAGNETIC DISC USING THE GLASS SUBSTRATE - Google Patents

Description

  The present invention relates to a glass substrate. More specifically, the glass substrate of the present invention relates to a glass substrate that realizes excellent strength when used for a magnetic disk or the like of a fixed magnetic disk recording apparatus. The present invention relates to a method for producing such a glass substrate. The present invention relates to a magnetic disk using such a glass substrate.

  An aluminum material or a glass material is used as a substrate material for a magnetic disk incorporated in a recording medium such as a computer. In particular, a glass material exhibiting high rigidity is used as a substrate material used for a portable mobile such as a notebook personal computer that is required to be both compact, thin and impact resistant.

  Such glass materials are roughly classified into two types: crystallized glass and amorphous glass. In recent years, with the increase in recording density of magnetic disks, substrate materials are required to have high flatness. For this reason, as the substrate material, amorphous glass having high flatness due to the absence of crystal grain boundaries is used as compared with crystallized glass having low flatness due to the presence of crystal grain boundaries.

  However, amorphous glass is inferior in mechanical strength to crystallized glass. In view of such a situation, the following techniques are disclosed.

  Patent Document 1 discloses a technique related to an optical disk using a chemically strengthened glass obtained by reinforcing the bending strength of amorphous glass by chemical treatment as a substrate. This technology applies a compressive stress to the glass surface by a chemical strengthening method to suppress the generation of cracks, and suppresses the generation of microcracks that are the starting point of fracture by chemical etching.

  Here, the chemical strengthening method in Patent Document 1 is to replace ions existing on the glass surface with larger ions at a temperature below the glass transition point, and form a compressive stress layer with a steep distribution on the glass surface. This is a method for strengthening the glass surface. Ion substitution is performed by immersing glass in a molten salt of potassium nitrate or sodium nitrate heated to about 350 to 450 ° C.

  However, since this method requires a long time of 2 to 6 hours, the product may remain in the step of performing the method, and the productivity may decrease. Further, the ion substitution causes a deformation called ski jump in which the end of the glass material slightly rises. For this reason, it is necessary to secure a surface sag amount forming process for offsetting the deformation amount due to ski jump separately from the polishing process. Therefore, not only does the production of the substrate become complicated due to the increase in the number of steps, but the glass substrate is processed in more steps, so that the yield rate of the glass substrate may be reduced.

  On the other hand, when the etching disclosed in Patent Document 1 is performed on a glass material by 5 to 50 μm or more, microcracks existing on the glass surface are removed, and the strength is improved about 5 to 10 times. However, in the main surface polishing process after etching, the cleaning process, the film forming process, and the transfer between these processes, and in the process of incorporating the completed glass substrate into the magnetic disk device, a new microcrack is generated, and the glass substrate May deteriorate. In view of such a situation, the following techniques are disclosed.

  Patent Document 2 discloses a donut-shaped glass plate whose inner peripheral surface end face is etched, and the inner peripheral face end face subjected to the etching has a hardness with a pencil scratch value of 5H or more. A glass substrate for a magnetic disk coated with a film is disclosed. This technology is related to a glass substrate with a hard coating, but if the silica film obtained by reactive curing of polysilazane, which is a preferred coating material, is made thick, cracks are generated in the film due to external force. It becomes easy to do. For this reason, it is necessary to make the film thickness 4 μm or less practically. However, such a thin film lacks strength. In the disk manufacturing process and hard disk device assembly process, hard dust may be caught between the hand or spindle and the substrate. In such a case, when the hard dust is locally pressed, the coating may be broken without sufficiently withstanding the load due to the above insufficient strength, and cracks may enter the glass substrate. is there. It is almost impossible to identify and eliminate such a defective substrate in the process, and there is a high possibility that it will flow out to the market as a product. Therefore, when the substrate is used for a magnetic disk, the reliability may be significantly impaired.

  In Patent Document 3, a magnetic recording medium substrate compatible with a magnetoresistive head (MR head) or a large magnetoresistive head (GMR head) is used, and at least one surface of a chamfered portion and a side wall portion is a mirror surface. An aluminosilicate glass substrate for a magnetic recording medium is disclosed. This technique discloses that the chamfered portion and the side surface portion of the glass substrate for magnetic recording medium have an arithmetic surface roughness Ra of less than 1 μm and Rmax of 0.01 to 4 μm.

  In Patent Document 4, a circular hole is provided at the center, and the inner peripheral end surface is an etching surface formed by a number of adjacent pits having different curvature radii, and the curvature radius r of the pits on the etching surface is 0.5 μm or less. A glass substrate for a magnetic disk having a pit presence rate of 5% or less is disclosed. This technique discloses that the inner peripheral end surface of the glass substrate is finish-polished so that the arithmetic surface roughness Ra is 1.0 μm or less, and then the finish-polished surface is etched by 2.5 to 25 μm.

  In Patent Document 5, the mirror finishing process of the end face part is performed by polishing the surface of the end face part by bringing a polishing means into contact with the end face part and moving the polishing means and the glass disk relatively, and thereafter A method of manufacturing a glass substrate for a magnetic disk is disclosed in which the end surface portion is chemically treated and the crack existing in the surface layer portion is removed while maintaining the mirror surface state of the surface.

Japanese Patent Laid-Open No. 62-143243 Japanese Patent Laid-Open No. 11-328665 JP 2003-228814 A JP 2006-196144 A JP 2005-285276 A

  As described above, technologies related to various glass substrates have been disclosed, but there is a demand for a glass substrate that realizes excellent strength when used in a magnetic disk or the like.

  Accordingly, an object of the present invention is to provide a glass substrate capable of realizing excellent strength when used in a magnetic disk. Moreover, the objective of this invention is providing the manufacturing method of the said glass substrate, and the magnetic disc using the said glass substrate.

  The present invention comprises a main surface, an inner peripheral surface extending to the inside of the main surface, and an outer peripheral surface extending to the outside of the main surface, and the arithmetic of the chamfered portion and the side portion of the inner peripheral surface The present invention relates to a glass substrate having an average roughness Ra of 0.05 to 1 μm, a maximum height Ry of 0.5 to 15 μm, and a developed length ratio Lr of 1.006 or more. The glass substrate of the present invention is used as a constituent member of a magnetic disk incorporated in a recording medium such as a computer. The glass substrate of the present invention has an arithmetic average roughness Ra of the chamfered portion and side surface portion of the outer peripheral surface of 0.05 to 1 μm, a maximum height Ry of 0.5 to 15 μm, and It is desirable that the developed length ratio Lr is 1.006 or more. Moreover, it is more desirable that the arithmetic average roughness Ra of the main surface is 0.5 nm or less.

  The present invention is a method for producing the doughnut-shaped glass substrate, wherein the glass material comprises a main surface, an inner peripheral surface extending inside the main surface, and an outer periphery extending outside the main surface. Including a step of forming a donut shape having a surface, a step of polishing the inner peripheral surface to form a chamfered portion and a side portion, and a step of etching the chamfered portion and the side portion. The present invention relates to a method for manufacturing a glass substrate. In such a method of manufacturing a glass substrate, it is desirable to perform the etching process with a thickness of 5 to 50 μm.

  The method for producing a glass substrate of the present invention includes a step of polishing the outer peripheral surface to form a chamfered portion and a side portion, and a step of etching the chamfered portion and the side portion. It is desirable. In such a method of manufacturing a glass substrate, it is more desirable to perform the etching process with a thickness of 5 to 50 μm.

  Further, the polishing treatment can be at least one of a grinding stone treatment and a sand blasting treatment. The treatment with the grindstone can be performed using loose abrasive grains and a soft brush. The loose abrasive grains can be at least one of cerium oxide and colloidal silica, and the soft brush can be made of nylon.

  In addition, in the method for producing a glass substrate of the present invention, in the etching process, the solution in which the glass material is immersed can be a mixed solution containing hydrofluoric acid, an aqueous ammonium fluoride solution, and an organic acid. Moreover, in the said method, the said mixed solution can be made into the mixed solution containing a mixed solution of hydrofluoric acid and hydrogen ammonium diphosphate instead. Furthermore, in the said method, the said mixed solution can be made into the mixed solution which contains ammonium fluoride and alcohols further alternatively.

  The present invention includes a magnetic disk using the glass substrate.

  In the glass substrate of the present invention, the arithmetic average roughness Ra, the maximum height Ry, and the developed length ratio Lr are set to values within a predetermined range for at least the chamfered portion and the side surface portion of the inner peripheral surface of the donut shape. By doing, the outstanding intensity | strength of a glass substrate is realizable.

  The preferred embodiments of the present invention will be described below with reference to the drawings. The examples shown below are merely examples, and the design can be changed as appropriate within the scope of ordinary creation ability of those skilled in the art.

<Glass substrate>
FIG. 1 is a perspective view showing a donut-shaped glass substrate 10 of the present invention. As a material of the glass substrate 10, aluminosilicate glass, soda lime glass, soda aluminum silicate glass, aluminoborosilicate glass, borosilicate glass, quartz glass, chain silicate glass, and crystallized glass can be used. In particular, an amorphous glass is preferably used for a glass substrate applied to a perpendicular magnetic disk capable of high storage density recording from the viewpoint of high surface flatness.

  Glass substrate 10 includes a main surface 12 and an inner peripheral surface 14 and an outer peripheral surface 16 extending inward and outward of main surface 12, respectively. The shape of the glass substrate is, for example, an outer diameter of 65 mm, an inner diameter of 20 mm, and a plate thickness of 0.635 mm (2.5 inch type), or an outer diameter of 48 mm, an inner diameter of 12 mm, and a plate thickness of 0.508 mm (1.8 inch type). It can be.

  A magnetic disk including such a glass substrate 10 is fixed by inserting a flange of a motor shaft of a fixed magnetic disk device into a cavity defined by an inner peripheral surface 14 thereof. For this reason, the load at the time of motor rotation concentrates on the inner peripheral surface end of the magnetic disk including the glass substrate 10. This local load may be a starting point for destroying the glass substrate 10, and the most important reinforcement target portion of the glass substrate 10 is an end portion of the inner peripheral surface.

  FIG. 2 is a cross-sectional view showing a chamfered portion 22 and a side surface portion 24 of the inner peripheral surface of the glass substrate, and a part of the main surface 26, showing the circled portion A of FIG. As shown in the figure, the chamfered portion 22 extends at an angle θ of 40 to 50 ° with respect to an extension line of the main surface 26. The angle of the chamfered portion 22 has no meaning in the function of the hard disk device. However, the angle serves to prevent the glass substrate from being damaged by point contact by matching with the angle of the receiving part of the jig or hand used in the substrate manufacturing process or the hard disk device assembly process. On the other hand, the side surface portion 24 extends substantially perpendicular to the main surface 26. As a result, it is possible to accurately position the magnetic disk on the flange of the spindle motor of the hard disk device so that there is no eccentricity that becomes an obstacle when the magnetic disk is rotated at high speed.

  Under such a setting condition of the angle θ, the arithmetic average roughness Ra of the chamfered portion 22 and the side surface portion 24 is set to 0.05 to 1 μm on the inner peripheral surface as the reinforcement target portion. Moreover, those maximum heights Ry shall be 0.5-15 micrometers. Further, the developed length ratio Lr is set to 1.006 or more.

  The arithmetic average roughness Ra and the maximum height Ry are both indices defined in JIS B0601. The reason why the destruction of the glass substrate can be effectively suppressed by the suitable setting of the arithmetic average roughness Ra and the maximum height Ry is as follows. That is, when the contact surface of the glass substrate with the flange of the motor shaft is a mirror surface, even if only one minute hard particle is interposed, the entire load is concentrated at the position where the hard particle is interposed. , There is a risk of starting cracks. However, when the contact surface is not a mirror surface and is finished to an appropriate roughness, the hard particles are mixed into the uneven portions present on the contact surface, particularly into the concave portions, and the hard particles become a starting point for receiving a load. The possibility is significantly reduced. In such a case, even if a crack is generated, only a part of the convex portion is missing from the unevenness, and the risk that the crack further develops is extremely low.

  About arithmetic mean roughness Ra, the effect of suppression of board | substrate damage is acquired by setting it as 0.05 micrometer or more. On the other hand, in order to ensure the accuracy of incorporation into the hard disk device, it is necessary that the inner diameter intersection is within ± 10 μm. However, by setting Ra to 1 μm or less, the inner diameter intersection is within the predetermined range, and excessively The effect that the formation of unevenness can be prevented.

  About the maximum height Ry, the effect of suppressing substrate breakage can be obtained by setting it to 0.5 μm or more. On the other hand, when the thickness is 15 μm or less, the effect of advantageously ensuring the accuracy of incorporation into the hard disk device described above can be obtained.

  Even when the arithmetic average roughness Ra is set to more than 1 μm and the maximum height Ry is set to more than 15 μm, the above-described effect of suppressing the breakage of the glass substrate can be obtained. However, the maximum height Ry is preferably 15 μm or less in order to achieve the mounting accuracy required by the hard disk device. Considering that Ry is about 10 times Ra, Ra should be 1.5 μm or less in order to make Ry 15 μm or less, but considering the safety factor, arithmetic average roughness Ra should be 1 μm or less. It is necessary to.

The developed length ratio Lr is the ratio (L ₀ / l) between the developed length L ₀ of the cross-sectional curve obtained by the arithmetic average roughness measurement and the reference length l (L ₀ / l). It is an index showing. Here, the reference length l refers to the distance between both ends of the cross-sectional curve for calculating the surface roughness parameter. The developed length ratio Lr is a value calculated by measurement using a stylus type surface roughness meter using a stylus having a tip angle of 60 ° and a tip radius of 2 μm. For example, in the case of a general transparent glass such as soda lime glass, a surface having an Lr of less than 1.004 has a gloss of 10 to 12% when a light having a wavelength of 380 to 780 nm is vertically incident. Surface. On the other hand, a surface having an Lr of 1.006 or more is a matte surface having the reflectance of 14% or more.

  Combined with the effects of the arithmetic average roughness Ra, the maximum height Ry, and the development length ratio Lr described above, excellent strength of the glass substrate is realized as a result.

  Next, in the magnetic disk including the glass substrate 10 shown in FIG. 1, the outer periphery of the medium in the magnetic disk device is a free end, and there is no possibility of cracks occurring in the device. And / or during the assembly process of the magnetic disk device, the outer periphery is held or supported. For this reason, there is a possibility that cracks may also occur at the end of the outer peripheral surface of the magnetic disk including the glass substrate 10. The cracks generated in this way may be a starting point for destroying the glass substrate 10, and an outer peripheral surface can be cited as an important reinforcement target site in order to use the glass substrate 10 more stably.

  FIG. 3 is a cross-sectional view showing the chamfered portion 32 and the side surface portion 34 of the outer peripheral surface of the glass substrate, and a part of the main surface 36, showing the circled portion B of FIG. As shown in the figure, the chamfered portion 32 extends at an angle θ of 40 to 50 ° with respect to an extension line of the main surface 36. The angle of the chamfered portion 32 has no meaning in the function of the hard disk device. However, the angle serves to prevent the glass substrate from being damaged by point contact by matching with the angle of the receiving part of the jig or hand used in the substrate manufacturing process or the hard disk device assembly process.

  Under such a setting condition of the angle θ, the arithmetic average roughness Ra of the chamfered portion 32 and the side surface portion 34 is 0.05 to 1 μm on the outer peripheral surface as the reinforcement target portion, and the maximum It is preferable that the height Ry is 0.5 to 15 μm, and the development length ratio Lr of the chamfered portion 32 and the side surface portion 34 is 1.006 or more. Thereby, reinforcement | strengthening of an outer peripheral surface is implement | achieved and by extension, destruction of a glass substrate can be suppressed more effectively.

  Furthermore, the main surface 12 of the glass substrate 10 shown in FIG. 1 usually has innumerable microcracks serving as crack starting points. The strength of the region where microcracks exist is the theoretical strength of 10 GPa when there are no cracks ("How is the strength of glass determined?" MRS-J NEWS Vol7, No4, November 2005 Jun Matsuoka: Professor, Department of Materials, Faculty of Engineering, Shiga Prefectural University ) Of about 1/100 to 1/1000. However, as described above, by appropriately setting the arithmetic average roughness Ra, the maximum height Ry, and the development length ratio Lr of the chamfered portion and the side surface portion of the inner peripheral surface and the outer peripheral surface, It is possible to suppress the progress of cracks generated on the outer peripheral surface and / or to advantageously suppress the crack transfer to the main surface.

  In the magnetic disk including the glass substrate 10 shown in FIG. 1, in order to ensure a flying height of 5 nm suitable for the magnetic head to read and write magnetic information on the disk with a good signal intensity, high flatness and smooth surface are required. is required. Further, in the case of the perpendicular magnetic recording system, it is preferable to realize a smooth surface because noise during reading of magnetic information is generated when the variation in crystal axis orientation of the magnetic layer is large. Therefore, in the case of a 2.5-inch magnetic disk, it is preferable that the flatness is PV = 4 μm or less and the arithmetic average roughness Ra of the main surface is 0.5 nm or less. As a result, the magnetic head can be stably floated without causing a gap or undulation that prevents the magnetic head from flying.

<Glass substrate manufacturing method>
(Formation of glass material)
Manufactures doughnut-shaped glass materials. First, a glass material having a predetermined shape is obtained by a press molding method or a cutting method from a sheet glass.

  Any known means may be used as the press molding method.

  Any known means may be used as a cutting method from the sheet glass.

  Next, lapping is performed on the surface of the glass material obtained by these methods to obtain flatness required by the magnetic disk (for example, PV ≦ 4 μm for a 2.5-inch substrate). For example, in the case of a 2.5-inch substrate having a product plate thickness of 0.635 mm ± 0.015 mm, it is processed to about 0.64 ± 0.010 mm to 0.68 ± 0.010 mm by lapping. This plate thickness is determined by the subsequent polishing process allowance, and is an amount necessary for completely removing the processing marks (grains) by the lapping process to make a mirror surface, preferably 0.05 to 0.1 mm on both sides. .

  As the lapping, for example, a lapping machine with a cast iron surface plate can be used, and silicon carbide (SiC) abrasive grains can be used as the machining fluid.

  Thereafter, washing is carried out in an ultrasonic dip bath to which a detergent is added, rinsing is carried out in a water washing bath, and hot air drying is performed to remove the slurry and the abrasive powder, thereby obtaining a clean surface.

  After polishing, glass powder, abrasive grains and cast iron powder adhering to the substrate are removed by ultrasonic immersion cleaning. The ultrasonic wave can select a frequency of several tens of kHz to several MHz depending on the contamination to be removed, that is, the size of the foreign matter. In addition, an aqueous solution of acid detergent, neutral detergent, alkaline detergent or the like is effective as the immersion liquid at that time. Also, ultrasonic cleaning under different conditions can be combined. Further, it can be scrubbed by scrub cleaning. After washing with detergent, rinsing with tap water or industrial water that has been filtered through a filter of about 0.2 to 1.0 μm is performed as necessary. Then, if necessary, it is dried by a known method such as air blowing, hot air, hot water pulling, solvent replacement or the like.

  Next, it is preferable to perform inner and outer diameter processing using a grinding machine and a grooved diamond grindstone (# 400) capable of simultaneously processing the inner surface end and the outer surface end of the glass material. A suitable dimension for the inner / outer diameter processing can be calculated by adding a polishing process or etching process allowance performed in a subsequent process to the inner / outer diameter dimension of the product.

(Chamfering of glass material)
Next, a chamfering process is performed on at least the inner peripheral surface of the inner peripheral surface and the outer peripheral surface of the glass material to obtain a chamfered portion and a non-chamfered portion (side surface portion). Chamfering is performed by using a twin-shaft grinder that simultaneously processes the inner and outer diameters, which is equipped with a diamond electroplating grindstone that matches the cross-sectional shape of each of the inner and outer diameters. The relative speed can be 5 to 100 m / sec.

  In particular, in a method in which rough surface processing is not performed in the subsequent etching step, the arithmetic average roughness Ra is 0.05 to 1 μm and the maximum height Ry is 0.5 to 15 μm in this step. Furthermore, it is necessary to create a surface shape having a developed length ratio Lr of 1.006 or more. Here, it is preferable that the diamond abrasive mesh is # 600 to 2000 and the relative speed is 10 to 20 m / sec. In the subsequent process, the arithmetic average roughness Ra is 0.05 to 1 μm and the maximum height Ry is 0.5 to 15 μm by polishing method, sandblasting method, etching method, etc. When creating a surface shape having a length ratio Lr of 1.006 or more, larger abrasive grains (diamond abrasive grain meshes # 350 to # 600) may be used. In performing the chamfering process, the angle formed by the glass material surface and the chamfered portion is generally 40 to 50 °. By matching with the shape of the receiving part of the jig or hand used in the magnetic disk manufacturing process or the hard disk device assembly process, the glass substrate can be prevented from being damaged due to point contact.

(Polishing of chamfered part and side part)
Subsequently, at least the chamfered surface of the inner peripheral surface and the outer peripheral surface of the glass material that has undergone the chamfering process is polished as necessary. Hereinafter, a polishing process for the inner peripheral surface will be described, but this process can also be applied to the outer peripheral surface.

In a method in which the roughening etching process is not performed in the subsequent process, and in the chamfering process of the previous process, the arithmetic average roughness Ra is 0.05 to 1 μm and the maximum height Ry is 0.5 to 15 μm. In addition, the arithmetic average roughness Ra is 0.05 to 1 μm by, for example, grinding with a grindstone or sandblasting without forming the surface shape with a developed length ratio Lr of 1.006 or more. Thus, the maximum height Ry is 0.5 to 15 μm, and the developed length ratio Lr is 1.006 or more.
Further, in the method of performing the roughening etching process in the subsequent process, as a pretreatment, the mirror surface is polished to Ra ≦ 0.01 μm or less by a polishing process.

By grindstone processing using loose abrasive grains and a soft brush, the arithmetic average roughness Ra is 0.05 to 1 μm, their maximum height Ry is 0.5 to 15 μm, and further, their developed length A surface shape having a ratio Lr of 1.006 or more can be formed. Here, free abrasive grains refer to a polishing slurry in which abrasive grains are dispersed in water. As abrasive grains, silicon carbide powder of # 1000 to # 8000, aluminum oxide powder, silica powder, zircon sand, etc. can be used. Moreover, as a soft brush, it is preferable to use the brush made from nylon from a viewpoint of moderate softness | flexibility and a familiarity with polishing slurry. Furthermore, as a processing condition of the grindstone, a relative speed of 0.1 m / sec to 10 m / sec is appropriate.
The surface can be mirror-finished to Ra ≦ 0.01 μm or less by a grinding wheel treatment using a loose grinding wheel and a soft brush. In that case, it is preferable to use cerium oxide or colloidal silica for the abrasive grains, and nylon for the soft brush, and a relative speed of 0.1 m / sec to 10 m / sec is appropriate as a processing condition.

  On the other hand, the processing by sandblasting can be performed using # 160 to # 1200 silicon carbide, alumina, zirconia, garnet or the like. As processing conditions for sandblasting, the injection pressure can be 0.1 to 0.5 MPa, and 0.1 to 0.3 MPa is preferable from the viewpoint of stability of the injection state and prevention of breakage of the workpiece.

  As described above, the polishing treatment can be performed by the above-described grindstone or sandblasting, but the treatment mode is not limited to the above example, and the treatment can be performed by any different method. By such a polishing process, in a process in which roughening etching is not performed in the subsequent process, the arithmetic average roughness Ra of the chamfered portion and the side surface portion of the predetermined portion is set to 0.05 to 1 μm and the maximum height thereof is set. Ry can be set to 0.5 to 15 μm. Further, in the step of performing roughening etching in a subsequent step, a mirror surface with Ra ≦ 0.1 μm or less can be obtained.

  In the polishing process, the sign θ in FIG. 2 (inner peripheral surface) and / or FIG. 3 (outer peripheral surface) is suitably controlled, so it is important that the polishing amount be 30 μm or less, and the influence of chamfering is excluded. Therefore, since processing of 5 μm or more is effective, the thickness is preferably 5 to 30 μm.

(Etching treatment of glass material)
Finally, an etching process is performed on the chamfered portion and the side surface portion of at least the inner peripheral surface of the inner peripheral surface and the outer peripheral surface of the glass material that has been subjected to the polishing process. Hereinafter, an etching process for the inner peripheral surface will be described, but this process can also be applied to the outer peripheral surface.

  The chamfered portion that has been mirror-finished by polishing processing has an arithmetic average roughness Ra of 0.05 to 1 μm, a maximum height Ry of 0.5 to 15 μm, and a developed length ratio Lr thereof. The etching process on the inner peripheral surface having a surface shape of 1.006 or more can be performed by immersing a glass material in a mixed solution containing hydrofluoric acid, an aqueous ammonium fluoride solution, and an organic acid. At this time, as etching conditions, the etching solution is an aqueous solution of 10 to 50 wt% hydrofluoric acid, 6 to 30 wt% ammonium fluoride, and 30 to 60 wt% organic acid composed of at least one of formic acid, acetic acid, and propionic acid. 15 ° C. to 35 ° C., and time 5 minutes to 120 minutes. It is preferable from the viewpoint of obtaining the desired surface shape that the etching solution is 10 to 20 wt% hydrofluoric acid, 15 to 30 wt% ammonium fluoride, and residual water, and the time is 10 to 60 minutes.

  Further, as an alternative treatment to the above-described embodiment, a glass material is immersed in a mixed solution containing a mixed solution of hydrofluoric acid and 2 ammonium hydrogen phosphate. At this time, as etching conditions, the etching solution is an aqueous solution of 10 to 35 wt% hydrofluoric acid and 20 to 70 wt% diammonium hydrogen phosphate, and the temperature is set to 35 to 65 ° C. for 1 to 90 minutes. it can. From the viewpoint of obtaining the desired surface shape, the etching solution is an aqueous solution of 10 to 20 wt% hydrofluoric acid and 20 to 60 wt% diammonium hydrogen phosphate, and the temperature is set to 35 to 65 ° C. for 1 minute to 10 minutes. preferable.

  Further, a further alternative treatment for these embodiments includes immersing the glass material in a mixed solution containing ammonium fluoride and alcohols. At this time, as an etching condition, an etching solution is a solution of ammonium fluoride 10 to 30 wt%, hydrofluoric acid 0 to 15 wt%, sulfuric acid 5 to 10 wt%, and ethanol 0 to 30 wt%, 15 to 35 ° C., The time can be 10 to 120 minutes. From the viewpoint of obtaining a desired surface shape by using an etching solution of 10 to 20 wt% ammonium fluoride, 5 to 10 wt% hydrogen fluoride, and 15 to 30 wt% ethanol for 15 to 25 ° C. for 10 to 30 minutes. To preferred.

  Thus, the etching process can be performed using the mixed solution or the frost solution, but the processing mode is not limited to the above example. That is, these solutions can be sprayed or applied to a predetermined portion of the glass material, or can be processed by any different method. By such an etching process, the development length ratio Lr between the chamfered part and the side part of the predetermined part can be set to 1.006 or more, and the desired arithmetic average roughness Ra and the maximum due to the above-described polishing process being performed. In combination with the height Ry, a desired matte state, i.e. a pear ground state, can be realized.

  The etching amount is preferably 5 to 50 μm. By setting the thickness to 5 μm or more, the excellent strength of the glass substrate can be realized. On the other hand, when the thickness is 50 μm or less, etching unevenness can be suppressed, and an inner diameter accuracy of ± 10 μm, which is required as accuracy for incorporation into a magnetic disk device, can be realized at a high level on a glass substrate used for a magnetic disk. it can.

(Main surface treatment)
Finally, the main surface is optionally treated. For example, using a double-side polishing machine with a pad containing a predetermined material, a slurry in which a predetermined abrasive is suspended in water is dropped to perform mirror polishing of the main surface of the glass material.

  The predetermined material is preferably a cerium oxide-containing urethane pad from the viewpoint of good flat workability and high processing speed, and the abrasive is oxidized from the viewpoint of high processing speed and difficulty of scratching. Cerium abrasive is preferred.

  The machining allowance in the mirror polishing process is preferably 0.05 to 0.10 mm from the viewpoint of completely removing the lapping process marks (grains). By polishing with cerium oxide, a glass surface having an arithmetic average roughness Ra of 0.5 to 2.0 nm is obtained.

  Next, weak alkali cleaning combined with ultrasonic waves and pure water rinsing are sequentially performed to sufficiently clean the surface and side surface abrasives and chips.

  Further, for example, the main surface is finally polished using a double-sided polishing machine with a foamed urethane pad and a colloidal silica polishing liquid.

  The processing allowance in the final polishing process is preferably 0.0001 to 0.001 mm from the viewpoint of changing the surface roughness of the cerium polishing surface to the surface roughness of the colloidal silica polishing surface. A glass surface with an arithmetic average roughness Ra of 0.5 nm or less is obtained by polishing colloidal silica.

  Next, weak alkali cleaning combined with ultrasonic waves and pure water rinsing are sequentially performed, and further, precision cleaning and drying including each step of room temperature IPA immersion and IPA vapor drying is performed to obtain a clean glass substrate for a magnetic disk. .

  The arithmetic average roughness of the main surface can be measured using an atomic force microscope (AFM), the arithmetic average roughness Ra is 0.05 to 0.5 nm, and the maximum height Ry is 0.5 to 5 nm. It is preferable that The arithmetic average roughness Ra is desirably as small as possible, but it is difficult to process it to less than 0.05 nm due to the presence of unevenness at the atomic level. Moreover, if it is 0.5 nm or less, the effect that the influence of the fluctuation of the crystal axis with respect to the noise at the time of reading of magnetic information does not appear is obtained. On the other hand, the maximum height Ry is desirably as small as possible, but it is difficult to process it to less than 0.5 nm for the same reason as Ra. On the other hand, when the thickness is 5 nm or less, the effect of not disturbing the stable flying of the perpendicular magnetic recording head can be obtained. Thereby, it can have sufficient surface smoothness to serve as a glass substrate for a high-density perpendicular magnetic disk.

<Magnetic disk>
A magnetic disk using the glass substrate will be described. The magnetic disk body shown below is a perpendicular magnetic recording medium, but the disk of the present invention is not limited to such an example, and any type of disk can be used as long as the glass substrate can be used.
FIG. 4 is a schematic cross-sectional view showing an example of the structure of a magnetic disk using the glass substrate. According to the figure, the magnetic disk 40 includes a glass substrate 42, a soft magnetic backing layer 44 formed on the glass substrate 42, a nonmagnetic crystal orientation control layer 46 formed on the soft magnetic backing layer 44, The underlayer 48 formed on the nonmagnetic crystal orientation control layer 46, the magnetic layer 50 formed on the underlayer 48, the protective layer 52 formed on the magnetic layer 50, and the protective layer 52 are formed. And a lubricating layer 54.

  Any type of glass substrate 42 may be used as long as it is obtained as described above. The film thickness of the glass substrate 42 is adjusted according to the size of the substrate, and is preferably in the range of 0.3 to 1.3 mm.

  The soft magnetic underlayer 44 is an optionally used layer that plays a role of suppressing the spread of magnetic flux generated from the head during recording of information and ensuring a sufficient vertical magnetic field. As a material of the soft magnetic backing layer 44, Ni alloy, Fe alloy, Co alloy, Ta alloy, and Zr alloy can be used. For example, by using an amorphous Co—Zr alloy such as CoZrNb, CoTaZr and CoTaZrNb, or an amorphous Fe—Co alloy such as CoFeNb, CoFeZrNb and CoFeTaZrNb, good electromagnetic conversion characteristics can be obtained. In addition to these, various soft magnetic materials such as Fe-B alloys and Fe alloys with a ferrite structure can be used.

  The film thickness of the soft magnetic underlayer 44 is preferably in the range of 10 nm to 100 nm in consideration of the structure of the magnetic head used for recording and productivity. By setting the film thickness to 10 nm or more, an effect of suppressing the spread of magnetic flux can be obtained. Moreover, the outstanding productivity is realizable by the said film thickness being 100 nm or less.

  The nonmagnetic crystal orientation control layer 46 is an optionally used layer that plays a role of controlling the orientation and grain size of the underlayer 48 formed as an upper layer, and thus the magnetic layer 50. For example, Au, Ag, and It is preferable to use a material containing a noble metal element such as Pt. In addition, when a material that is easily oxidized is used for the nonmagnetic crystal orientation control layer 46, a high vacuum state is maintained before formation of the underlayer 48 to prevent adhesion of oxygen to the surface. A non-oxidized surface state of 46 can be obtained.

  The film thickness of the nonmagnetic crystal orientation control layer 46 is appropriately adjusted so that the magnetic characteristics and electromagnetic conversion characteristics of the magnetic layer 50 finally become desired values, and is preferably in the range of 2 nm to 20 nm. By setting the film thickness to 2 nm or more, deterioration of the orientation of the underlayer 48 and hence the magnetic layer 50 is suppressed. Further, by setting the film thickness to 20 nm or less, the particle size of the nonmagnetic crystal orientation control layer 46 is not excessively increased, and thereby the particle size of the magnetic layer 50 is reduced through the underlayer 48. And deterioration of electromagnetic conversion characteristics can be suppressed.

  The underlayer 48 can improve the orientation of the magnetic layer 50 formed as an upper layer and refine the grain size by improving the orientation of the base layer 48 and reducing the grain size, and is undesirable in terms of magnetic properties. This is a nonmagnetic layer that suppresses the generation of an initial layer of the magnetic layer 50. The underlayer 48 can be formed from Cr or the like.

  Furthermore, in order to suppress the formation of the initial layer of the magnetic layer 50, it is important to obtain good crystallinity of the underlayer 48, and it is preferable that the thickness of the underlayer 48 be in the range of 1 nm or more. As a result, the deterioration of orientation due to the good crystallinity of the underlayer 48 can be suppressed, and accordingly, the excellent orientation of the magnetic layer 50 and the separation of crystal grains can be achieved, and the initial growth of the magnetic layer 50 can be achieved. Layer formation is suppressed. Further, by setting the thickness of the underlayer to 20 nm or less, the particle size of the underlayer 48 does not increase, and accordingly, the increase in the particle size of the magnetic layer 50 can be suppressed. Such control of the film thickness of the underlayer 48 can further reduce noise.

  The magnetic layer 50 is a layer for recording and reproducing information. In order to use the magnetic layer 50 as a part of the perpendicular magnetic recording medium, it is necessary to orient the easy axis of magnetization in the direction perpendicular to the substrate surface. The magnetic layer 50 is made of a material containing an alloy containing Co. As the alloy containing Co, a Co—Pt alloy and a Co—Cr alloy can be used.

  The thickness of the magnetic layer 50 is preferably in the range of 8 nm to 20 nm. By setting the thickness to 8 nm or more, deterioration of thermal stability can be suppressed. Further, by setting the thickness to 20 nm or less, the head magnetic field can reach the entire magnetic film, and good write characteristics can be obtained.

The protective layer 52 is a layer formed for the purpose of preventing corrosion of the magnetic layer 50 and preventing damage to the magnetic layer 50 when the magnetic head contacts the medium. The protective layer 52 may be a layer mainly composed of any of commonly used materials such as C, SiO ₂ , and ZrO ₂ . The thickness of the protective layer 52 is preferably in the range of the film thickness used in a normal magnetic recording medium, for example, in the range of 2 nm to 5 nm.

  The lubrication layer 54 is a layer formed for the purpose of ensuring lubrication characteristics between the magnetic head and the medium. The lubricating layer 54 may be made of a commonly used material such as a perfluoropolyether, a fluorinated alcohol, and a fluorinated carboxylic acid lubricant. The thickness of the lubricating layer 54 can be in the range of the film thickness normally used in magnetic recording media, for example, in the range of 0.5 nm to 2 nm.

<Magnetic disk manufacturing method>
Next, an example of a method for manufacturing the magnetic disk of the present invention shown in FIG. 4 will be described. The example shown below is an example including a soft magnetic backing layer and a nonmagnetic crystal orientation control layer, which are optional elements in the present invention.

(Cleaning of glass substrate 42)
The glass substrate 42 is cleaned. As the cleaning, dry cleaning using various plasmas or ions can be used in addition to solution cleaning with a predetermined chemical, for example, acid or alkali, which is highly effective as a method of removing the natural oxide film. In particular, it is preferable to use the above-described dry cleaning from the viewpoint of increasing the precision of the design dimensions, treating the waste liquid generated from the chemicals used, and automating the cleaning.

(Formation of soft magnetic underlayer 44)
The cleaned glass substrate 42 is introduced into the sputtering apparatus. The soft magnetic backing layer 44 is formed by various sputtering methods using a predetermined target. For example, a DC magnetron sputtering method can be used. Here, the atmosphere in the sputtering apparatus is an argon atmosphere, the pressure in the apparatus is 0.7 to 1.5 Pa, the temperature in the apparatus is not heated, the film formation rate is 2 to 10 nm / second, and the target and the substrate The distance is preferably 5 to 15 nm.

(Formation of Nonmagnetic Crystal Orientation Control Layer 46)
A nonmagnetic crystal orientation control layer 46 is formed on the soft magnetic backing layer 44 by various sputtering methods using a predetermined target. For example, a DC magnetron sputtering method can be used. Here, the atmosphere in the sputtering apparatus is an argon atmosphere, the pressure in the apparatus is 0.7 to 2 Pa, the temperature in the apparatus is not heated, the film formation rate is 2 to 10 nm / second, and the distance between the target and the substrate is It is preferable to set it as 5-15 nm.

(Formation of underlayer 48)
An underlayer 48 is formed on the nonmagnetic crystal orientation control layer 46. At this time, as the formation method of the underlayer 48, when an aromatic compound is used for the underlayer 48, it is preferable to use a vapor deposition method that does not destroy the molecular structure.

  As a vapor deposition method, an underlayer 48 is formed on the nonmagnetic crystal orientation control layer 46 by various sputtering methods using a predetermined target. For example, a DC magnetron sputtering method can be used. Here, when the sputtering method is used, the atmosphere in the sputtering apparatus is an argon atmosphere, the pressure in the apparatus is 2.5 to 12 Pa, the temperature in the apparatus is not heated, and the film formation rate is 2 to 10 nm / second. The distance between the target and the substrate is preferably 5 to 15 nm.

(Formation of the magnetic layer 50)
On the underlayer 48, the magnetic layer 50 is formed by various sputtering methods using a predetermined target. For example, a DC magnetron sputtering method can be used. Here, the atmosphere in the sputtering apparatus is an argon atmosphere, the pressure in the apparatus is 0.7 to 4 Pa, the temperature in the apparatus is not heated, the film formation rate is 2 to 10 nm / second, and the distance between the target and the substrate is It is preferable to set it as 5-15 nm.

(Formation of protective layer 52)
The laminated body in which the soft magnetic backing layer 44, the nonmagnetic crystal orientation control layer 46, the underlayer 48, and the magnetic layer 50 are formed in this order on the glass substrate 42 is transferred from the sputtering apparatus to the vacuum apparatus, and is protected on the magnetic layer 50. The layer 52 can be formed by a CVD method. In addition, as another formation method of the protective layer 52, the sputtering method using a carbon target, an ion beam method, etc. are mentioned, These methods can employ | adopt a well-known aspect. In particular, when the CVD method or the ion beam method is used, the protective layer 52 can be made thin.

(Formation of the lubricating layer 54)
Finally, the laminated body on which the protective layer 52 is formed is taken out from the vacuum apparatus, and the lubricating layer 54 is formed on the protective layer 52 by the dipping method to obtain the perpendicular magnetic recording medium of the present invention.

Hereinafter, the present invention will be described in detail with reference to examples, and the effects of the present invention will be demonstrated.
<Formation of glass substrate>
Example 1
Thickness 1.5 mm, a width of 1000 mm, and a length of _{1000mm, SiO 2: 65mol%,} Al 2 O 3: 12mol%, Li: 7mol%, Na 2 O: 10mol%, ZnO 2: 2mol%, and The remaining aluminosilicate sheet glass was prepared. From this sheet glass, 250 pieces of donut-shaped glass material having an outer diameter of 66 mm and an inner diameter of 19 mm were obtained by cutting using a grinding wheel. These glass materials are mounted on a double-sided lapping machine equipped with a cast iron surface plate, a slurry in which an abrasive (WA # 1200) is suspended in water is dropped, and double-sided simultaneous lapping is performed. It was formed to 68 mm.

  Next, using a grinding machine and a grooved diamond grindstone (# 400) capable of simultaneously processing the inner peripheral surface end and the outer peripheral surface end of the glass material, the inner diameter is 20.01 ± 0.003 mm, the outer diameter is 65 ± 0. The inner and outer diameters were processed to be 01 mm and concentricity ≦ 3 μm.

  Further, as shown in FIG. 5, the inner peripheral surface end and the outer peripheral end were chamfered so that the length in the plate thickness direction of the side surface portion was 0.3 mm. The angle formed by the glass material surface and the chamfered portion was 45 ± 5 °.

  At this time, the entire surface including the inner peripheral surface and the outer peripheral surface of the glass substrate was matte (like a satin background). In order to confirm this, the arithmetic average roughness Ra and the maximum height Ry of the chamfered portion and the side portion of the inner peripheral surface were measured based on JIS B0601, and as a result, Ra = 0.56 μm and Ry = 6.3 μm. It was. Further, the developed length ratio Lr between the chamfered portion and the side surface portion of the inner peripheral surface is a stylus type surface roughness meter (Mitutoyo Foam Tracer with a tip angle of 60 ° and a tip radius of 2 μm). As a result of measurement using CS-3100), Lr = 1.006. Furthermore, when the reflectance was measured using a reflectance measuring machine (Olympus USPM-RUIII), it was 20.8%. This reflectivity is a value when light having a wavelength of 380 to 780 nm is vertically incident according to JIS R3106, and is an index indicating the glossiness of the glass surface.

  Next, using a double-sided polishing machine with a cerium-containing pad, a slurry in which a cerium oxide abrasive is suspended in water is dropped to perform mirror polishing of the main surface of the glass substrate, and the thickness is 0.637 mm. It was processed into. Thereafter, weak alkali cleaning combined with ultrasonic waves and pure water rinsing were sequentially performed to sufficiently clean the surface and side surface abrasives and chips.

  Furthermore, the main surface was finally polished using a double-sided polishing machine with a foamed urethane pad and a colloidal silica polishing liquid (trade name: Compol 80 (Fujimi Incorporated)), and the plate thickness was processed to 0.635 mm. Thereafter, precision cleaning and drying including the steps of weak alkali cleaning using ultrasonic waves, pure water rinsing, room temperature IPA immersion, and IPA vapor drying were performed to obtain a clean glass substrate for a magnetic disk.

Arithmetic average roughness and the like of the main surface were measured using AFM, and were found to be Ra = 0, 28 nm and Ry = 3.2 nm. As a result, it was found that the surface had sufficient surface smoothness to serve as a glass substrate for a high-density perpendicular magnetic disk.
The glass substrate of Example 1 was obtained as described above.

(Example 2)
In the same manner as in Example 1, a glass substrate subjected to cutting, lapping, inner / outer diameter processing, and chamfering was prepared. The properties of the chamfered portion and the side surface portion of the inner peripheral surface were Ra = 0.50 μm, Ry = 7.1 μm, and Ir = 1.007.

  Next, mirror polishing was applied to the glass substrate in the same manner as in Example 1, and 10 vol at room temperature (25 ° C.) diluted by adding deionized water 4 to 50 vol% hydrofluoric acid 1 of electronic industry grade. The substrate was immersed in a 10% hydrofluoric acid etching solution for 10 minutes and quickly taken out. In addition, the etchant was thoroughly rinsed with deionized water. The surface including the inner peripheral surface and outer periphery of the glass substrate became translucent by etching, but the pear ground shape was maintained, and the chamfered portion and the side surface portion of the inner peripheral surface had an arithmetic average roughness Ra. The maximum height Ry was 0.61 μm, the developed length ratio Lr between the chamfered portion and the side portion was 1.008 or more.

  Moreover, the etching amount defined by the difference between the radius before etching and the radius after etching was 12 μm from the difference between the values measured by the micrometer before and after the etching. Furthermore, when the reflectance was measured by a reflectance meter (Olympus USPM-RUIII), it was 16.1%.

Subsequently, the main surface was subjected to final polishing and precision cleaning and drying by the same process as in Example 1 to produce a magnetic disk glass substrate. The lapping marks on the main surface disappeared completely, but the chamfered portion and the side surface portion of the inner peripheral surface remained pear-shaped (matte). When arithmetic mean roughness and the like of the main surface were measured using AFM, they were Ra = 0.30 nm and Ry = 4.2 nm.
As described above, a glass substrate of Example 2 was obtained.

(Example 3)
In the same manner as in Example 1, a glass substrate subjected to cutting, lapping, inner / outer diameter processing, and chamfering was prepared. With respect to this glass substrate, the glass substrate surface was grind | polished using the cerium oxide abrasive | polishing agent and the nylon brush, and it was set as the mirror surface. The arithmetic average roughness of the chamfered portion and the side portion of the inner peripheral surface was Ra = 0.003 μm, Ry = 0.04 μm, and Ir = 1.002.

  Next, an electronic industrial grade 50 vol% hydrofluoric acid 30 wt%, a reagent special grade ammonium fluoride 10 wt%, a reagent special grade glacial acetic acid 30 wt%, and the balance being deionized water were prepared. The substrate subjected to the above mirror polishing at room temperature (25 ° C.) was immersed in this frost solution for 20 minutes and quickly taken out. In addition, the etchant was thoroughly rinsed with deionized water. The surface including the inner peripheral surface and the outer peripheral surface of the glass substrate became translucent by etching, but the pear ground shape was maintained, and the chamfered portion and the side surface portion of the inner peripheral surface had an arithmetic average roughness Ra. The maximum height Ry was 1.00 μm, and the development length ratio Lr between the chamfered portion and the side surface portion was 1.007.

  The etching amount measured by the same method as in Example 2 was 17 μm. Furthermore, when the reflectance was measured by a reflectance meter (Olympus USPM-RUIII), it was 16.9%.

Subsequently, the main surface was subjected to final polishing and precision cleaning and drying by the same process as in Example 1 to produce a magnetic disk glass substrate. When arithmetic mean roughness and the like were measured by AFM, Ra = 0.27 nm and Ry = 4.0 nm.
The glass substrate of Example 3 was obtained as described above.

(Comparative Example 1)
In the same manner as in Example 1, a glass substrate subjected to cutting, lapping, inner / outer diameter processing, and chamfering was prepared. The chamfered portion and the side surface portion of the inner peripheral surface and the outer peripheral surface were polished with a cerium oxide abrasive and a nylon brush while rotating the glass substrate to obtain mirror surfaces. The arithmetic average roughness of the chamfered portion and the side surface portion of the inner peripheral surface was Ra = 0.003 μm, Ry = 0.038 μm, and Ir = 1.002. Moreover, it was 10.7% when the reflectance was measured with the reflectance measuring device (Olympus USPM-RUIII).

  Subsequently, the main surface was subjected to final polishing and precision cleaning and drying by the same process as in Example 1 to produce a magnetic disk glass substrate. When arithmetic mean roughness and the like of the main surface were measured using AFM, Ra = 0.31 nm and Ry = 3.5 nm.

Further, the glass substrate was chemically strengthened by immersing it for 4 hours in a chemical strengthening tank made of SUS316 stainless steel in which a mixed salt of reagent special grade sodium nitrate 40 wt% and reagent special grade potassium nitrate 60 wt% was maintained at 360 ° C.
As described above, a glass substrate of Comparative Example 1 was obtained.

(Comparative Example 2)
In the same manner as in Example 1, a glass substrate subjected to cutting, lapping, inner / outer diameter processing, and chamfering was prepared. The chamfered portion and the side surface portion of the inner peripheral surface and the outer peripheral surface were polished with a cerium oxide abrasive and a nylon brush while rotating the glass substrate to obtain mirror surfaces. The arithmetic average roughness of the chamfered portion and the side surface portion of the inner peripheral surface was Ra = 0.003 μm, Ry = 0.015 μm, and Ir = 1.002. Moreover, it was 11.0% when the reflectance was measured with the reflectance measuring device (Olympus USPM-RUIII).

Subsequently, the main surface was subjected to final polishing and precision cleaning and drying by the same process as in Example 1 to produce a magnetic disk glass substrate. When measured using AFM on the main surface, Ra = 0.29 nm and Ry = 3.1 nm.
As described above, a glass substrate of Comparative Example 2 was obtained.

(Comparative Example 3)
In the same manner as in Example 1, a glass substrate subjected to cutting, lapping, inner / outer diameter processing, and chamfering was prepared. With respect to this glass substrate, the glass substrate surface was grind | polished using the cerium oxide abrasive | polishing agent and the nylon brush, and it was set as the mirror surface. The arithmetic average roughness of the chamfered portion and the side surface portion of the inner peripheral surface was Ra = 0.003 μm, Ry = 0.42 μm, and Ir = 1.003.

  Next, in the same manner as in Example 2, a 10 vol% hydrofluoric acid etching solution at room temperature (25 ° C.) diluted by adding deionized water 4 to 50 vol% hydrofluoric acid 1 of an electronic industry grade was used. The substrate was dipped for 10 minutes and quickly taken out. In addition, the etchant was thoroughly rinsed with deionized water. The surface including the inner peripheral surface and the outer peripheral surface of the glass substrate remains a mirror surface, and the chamfered portion and the side surface portion of the inner peripheral surface have an arithmetic average roughness Ra of 0.003 μm and a maximum height Ry of 0. The developed length ratio Lr between the chamfered portion and the side surface portion was 1.002.

  Moreover, the etching amount defined by the difference between the radius before etching and the radius after etching was 10 μm from the difference between the values measured by the micrometer before and after the etching. Further, the reflectivity was measured by a reflectometer (Olympus USPM-RUIII) and found to be 11.3%.

Subsequently, the main surface was subjected to final polishing and precision cleaning and drying by the same process as in Example 1 to produce a magnetic disk glass substrate. When measured using AFM on the main surface, Ra = 0.27 nm and Ry = 2.9 nm.
As described above, a glass substrate of Comparative Example 3 was obtained.

<Measurement of ring bending strength against glass substrate>
100 pieces of each of the glass substrates of Examples 1 to 3 and Comparative Examples 1 to 3 manufactured as described above were used with a material strength tester (Shimadzu Corporation: AG-1S), an outer diameter of 40 mm, and a tip. An annular jig 42 having a radius of 2 mm, a hemispherical jig 44 having R = 14.1 mm, and a glass substrate 46 are set at predetermined positions, and a bending strength is applied from above the hemispherical jig 44 at a test speed of 0.5 mm / sec. The ring bending strength was performed by gradually loading. FIG. 6 is a schematic view of the instrument used for the actual measurement of the bending strength of the ring. According to the figure, the annular jig 62 and the hemispherical jig 64 and the glass substrate 66 are set, and the hemispherical jig 64 is in contact with the load device 68 disposed above. A load F is applied. FIG. 7 is a partially enlarged cross-sectional view of the encircled portion C of FIG. 6, that is, the hemispherical jig 64, and the chamfered portion 66a and the side surface portion 66b of the glass substrate. According to the figure, the hemispherical jig 64 is in contact with the side surface portion 66b of the glass substrate 66, and the load F is substantially applied to the side surface portion 66b.
The results (minimum value, maximum value, and average value for each 100 sheets) relating to the measurement of the ring bending strength of the glass substrate are shown below.

  According to Table 1, for Examples 1 to 3 included in the scope of the present invention, the arithmetic average roughness Ra, the maximum height Ry of the chamfered portion and the side surface portion of the inner peripheral surface, and the chamfered portion and the side surface portion. Since the unfolded length ratio Lr is set to a predetermined value, even if chemical strengthening as in Comparative Example 1 is not performed, a bending strength equal to or greater than that in Comparative Example 1 is obtained for the glass substrate. I know that.

  For this reason, it was demonstrated that each glass substrate of Examples 1 to 3 can achieve excellent strength.

  In addition, when Examples 1-3 are compared, when etching is performed after grinding stone processing (Example 2), when mirror polishing is performed by frost etching and microcracks are removed (Example 3), Example 1 is used. It can be seen that the bending strength can be further improved.

<Formation of magnetic disk>
In addition to the glass substrates of Examples 1 to 3 and Comparative Examples 1 to 3 used for the measurement of the above-mentioned ring bending strength, 100 glass substrates were similarly prepared in each example. These glass substrates were introduced into a sputtering apparatus, and a CoZrNb amorphous soft magnetic layer 100 nm, a Ti seed layer 10 nm, a magnetic recording layer 30 nm made of a CoCrPt alloy, and a carbon protective layer 8 nm were sequentially formed and then taken out from the vacuum apparatus. . All of these sputtering films were formed by DC magnetron sputtering under an Ar gas pressure of 5 mTorr. Thereafter, a liquid lubricant layer 2 nm made of perfluoropolyether was formed by the dipping method, and the perpendicular magnetic disks of Examples 1 to 3 and Comparative Examples 1 to 3 were obtained.

<Measurement of ring bending strength for magnetic disk>
For each example of these perpendicular magnetic disks, the annular bending strength was measured with a material strength test apparatus in the same manner as in the case of the glass substrate described above. The results (minimum value, maximum value, and average value for each 100 sheets) relating to the measurement of the ring bending strength of the magnetic disk are shown below.

  According to Table 2, for the magnetic disk using the glass substrates of Examples 1 to 3 included in the scope of the present invention, the arithmetic average roughness Ra, the maximum height Ry of the chamfered portion and the side portion of the inner peripheral surface Since the development length ratio Lr between the chamfered portion and the side surface portion is set to a predetermined value, even if chemical strengthening as in Comparative Example 1 is not performed, the magnetic disk is equal to or more than in Comparative Example 1 It can be seen that the bending strength is obtained.

  For this reason, it was proved that excellent strength could be realized for each of the magnetic disks of Examples 1 to 3.

  In addition, when Examples 1 to 3 are compared, when etching is performed after grinding wheel processing (Example 2), when mirror polishing is performed by frost etching to remove microcracks (Example 3), the case of a glass substrate It can be seen that the bending strength can be further improved as compared with Example 1.

  Further, when the chamfered portion and the side surface portion of the inner peripheral surface are mirror-finished by a polishing method (Comparative Example 2), and when microcracks are further removed by etching (Comparative Example 3), when chemical strengthening is performed ( It was also found that, unlike Comparative Example 1), the bending strength after forming a magnetic layer and a protective layer and forming a magnetic disk was greatly reduced compared to the bending strength immediately after etching. This is because a new microcrack was generated in the chamfered portion and / or the side portion of the inner peripheral surface due to a load during processing or handling in a later process than the polishing step and the etching step of the chamfered portion and the side portion. It is thought that.

  According to the present invention, the arithmetic average roughness Ra, the maximum height Ry of the chamfered portion and the side surface portion of the inner peripheral surface of the doughnut-shaped glass substrate, and the developed length ratio Lr of the chamfered portion and the side surface portion. By suitably setting, the excellent strength of the glass substrate can be realized. Therefore, the present invention is promising in that it can stably manufacture a magnetic disk incorporated in a computer or the like that is required to have higher strength in the future.

It is a perspective view which shows the doughnut-shaped glass substrate 10 of this invention. FIG. 2 is a cross-sectional view showing a chamfered portion 22 and a side surface portion 24 of an inner peripheral surface of a glass substrate, and a part of a main surface 26, showing a circled portion A of FIG. FIG. 2 is a cross-sectional view showing a chamfered portion 32 and a side surface portion 34 of the outer peripheral surface of the glass substrate, and a part of a main surface 36, showing a circled portion B of FIG. It is a cross-sectional schematic diagram which shows an example of the structure of the magnetic disc using the glass substrate of this invention. It is side sectional drawing of the glass substrate of this invention. FIG. 6 is a cross-sectional view showing a set state of the annular jig 62, the hemispherical jig 64, and the glass substrate 66. It is an expanded sectional view of the circled part C of FIG.

Explanation of symbols

10, 42, 66 Glass substrate 12, 26, 36 Main surface 14 Inner peripheral surface 16 Outer peripheral surface 22, 32, 66a Chamfered portion 24, 34, 66b Side surface portion 40 Magnetic disk 44 Soft magnetic backing layer 46 Nonmagnetic crystal orientation control Layer 48 Underlayer 50 Magnetic layer 52 Protective layer 54 Lubricating layer 62 Ring jig 64 Hemispherical jig 68 Loading device

Claims (15)

In a donut-shaped glass substrate comprising a main surface, an inner peripheral surface extending inside the main surface, and an outer peripheral surface extending outside the main surface, a chamfered portion and a side surface of the inner peripheral surface a arithmetic average roughness Ra 0.05~1μm parts is their maximum height Ry of 0.5 to 15 m, further, their deployment length ratio Lr is Ri der least 1.006, the inner peripheral surface, a glass substrate reflectance when light having a wavelength 380~780nm was normal incidence to said matte side der Rukoto over 14%.   The arithmetic average roughness Ra of the chamfered portion and the side surface portion of the outer peripheral surface is 0.05 to 1 μm, the maximum height Ry thereof is 0.5 to 15 μm, and the developed length ratio Lr The glass substrate according to claim 1, wherein the glass substrate is 1.006 or more.   3. The glass substrate according to claim 1, wherein an arithmetic average roughness Ra of the main surface is 0.5 nm or less. A method for producing a donut-shaped glass substrate,
Forming a glass material into a donut shape comprising a main surface, an inner peripheral surface extending inside the main surface, and an outer peripheral surface extending outside the main surface;
Subjected to abrasive treatment to the inner circumferential surface, it viewed including the step of forming a chamfered portion and side portions, and a step of performing an etching process to said chamfered portion and side portions,
The method of manufacturing a glass substrate, wherein the etching process is a process of forming a matte surface having a reflectance of 14% or more when light having a wavelength of 380 nm to 780 nm is vertically incident on the inner peripheral surface .   The method for manufacturing a glass substrate according to claim 4, wherein the etching process is performed at a thickness of 5 to 50 μm.   6. The method according to claim 4, comprising a step of polishing the outer peripheral surface to form a chamfered portion and a side surface portion, and a step of etching the chamfered portion and the side surface portion. Glass substrate manufacturing method.   The method for manufacturing a glass substrate according to claim 6, wherein the etching process is performed at a thickness of 5 to 50 μm.   The method for producing a glass substrate according to any one of claims 4 to 7, wherein the polishing treatment is at least one of a grinding stone treatment and a sand blasting treatment.   The method for producing a glass substrate according to claim 8, wherein the treatment with the grindstone is a treatment performed using loose abrasive grains and a soft brush.   The method for producing a glass substrate according to claim 9, wherein the loose abrasive is at least one of cerium oxide and colloidal silica.   The method for manufacturing a glass substrate according to claim 9 or 10, wherein the soft brush is made of nylon.   The glass substrate according to any one of claims 4 to 11, wherein the etching treatment is a treatment of immersing a glass material in a mixed solution containing hydrofluoric acid, an aqueous ammonium fluoride solution, and an organic acid. Production method.   The method for producing a glass substrate according to any one of claims 4 to 11, wherein the etching treatment is a treatment of immersing the glass material in a mixed solution containing hydrofluoric acid and diammonic hydrogen phosphate.   The method for producing a glass substrate according to any one of claims 4 to 11, wherein the etching process is performed by immersing a glass material in a mixed solution containing ammonium fluoride and alcohols.   A magnetic disk using the glass substrate according to claim 1.

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