JP2010086631A - Method of manufacturing glass substrate for magnetic disk, and method of manufacturing magnetic disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a glass substrate for a magnetic disk, by which chamfering and grinding, and polishing can be simultaneously performed in outside diameter end surface working of a glass substrate. <P>SOLUTION: In the polishing of the outside diameter end surface of the glass substrate, a polishing liquid obtained by adding a polishing agent to a viscoelastic fluid is used. Thereby, the polishing of the outside diameter end surface of the glass substrate can be performed by using the same grinding stone 1 as a tool used for grinding finishing after the grinding finishing including chamfering working and the polishing and chamfering working of the outside diameter end surface of the glass substrate can be alternately and continuously performed without replacing the grinding stone 1 and the glass substrate. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a glass substrate for a magnetic disk used as a recording medium for a computer or the like, and a method for manufacturing a magnetic disk.

  In recent years, with the advancement of information technology, information recording technology, particularly magnetic recording technology, has made remarkable progress. An aluminum substrate has been widely used as a substrate for a magnetic recording medium such as an HDD (Hard Disk Drive) which is one of the magnetic recording media. However, with the miniaturization, thinning, and high recording density of magnetic disks, glass substrates that are superior in substrate surface flatness and substrate strength compared to aluminum substrates are gradually being replaced.

  In order to effectively use the main surface of the magnetic disk, an LUL (Load UnLoad) method has been used instead of the conventional CSS (Contact Start Stop) method. The CSS system is a system in which a magnetic head is brought into contact with a CSS zone provided on the main surface of the magnetic disk and retracted, and the LUL system is a system in which the magnetic head is retracted to a ramp (inclined portion) provided outside the magnetic disk. It is. The CSS zone cannot only be used as a recording area, but also has to have a certain surface roughness to prevent the magnetic head from being attracted. However, by adopting the LUL method, the entire surface of the magnetic disk can be used as a recording area, and it is not necessary to provide an uneven shape on the surface, and the surface of the magnetic disk can be extremely smoothed.

  Further, as the magnetic recording technology has been increased in density, the magnetic head has been changed from a thin film head to a magnetoresistive head (MR head) and a large magnetoresistive head (GMR head). However, the GMR head has high sensitivity and high recording density, and if the head and the substrate are separated from each other, information on adjacent recording bits is picked up. Therefore, it is necessary to keep the flying height of the magnetic head low. .

  Under these circumstances, the flying height of the magnetic head is required to be reduced, and the flying height of the magnetic head from the substrate is narrowed to about 8 nm.

  If the flying height of the magnetic head is reduced, a head crash failure or thermal asperity failure may occur. The head crash failure is a failure in which the magnetic head collides with the convex portion of the magnetic disk and is damaged. Thermal asperity failure means that the magnetoresistive element is heated by adiabatic compression or contact of air when the magnetic head passes over a minute convex or concave shape on the magnetic disk surface while flying. This is a failure that causes a read error. Therefore, for a magnetic head equipped with a magnetoresistive element, the magnetic disk surface is required to have extremely high smoothness and flatness, that is, low roughness.

  In particular, recently, as described in Patent Document 1, in order to further improve the recording density, the perpendicular magnetic recording method is becoming the main method. In the case of this perpendicular magnetic recording medium, since the recording density is higher than in the case of the in-plane magnetic recording method, the influence of the roughness of the glass substrate is more likely to appear. For this reason, the glass substrate is required to have even lower roughness.

  In the glass substrate used for such a magnetic disk, finishing of the outer diameter end face portion is also important. Conventionally, as the finishing method of the outer diameter end face part of the glass substrate, polishing finish is done with a “chamfering machine” dedicated to chamfering and an “outer diameter end polishing machine” dedicated to polishing the outer diameter end face. It was.

  First, the outer diameter end face portion of the chamfering machine is diamond-coated with an electrodeposition-bonded grindstone such as a circumscribed grindstone tool (for example, SD # 325, # 500) that transfers the end face shape by a single wafer method. After the chamfering process is performed by shape transfer using the electrodeposition grindstone, the glass substrate is removed, and then a finishing process is performed by a finish polishing method as a finish polishing process.

  This copying polishing method is a batch method or a single wafer method in which ceria slurry is used as an abrasive and polishing finish is performed with a nylon brush having a wire diameter of 0.2 mm to 0.3 mm as a tool, or a ceria slurry is applied to a urethane pad. Is used to finish the end face portion of the outer diameter by polishing.

  By these two roughly divided processes of chamfering grinding and profiling polishing, the outer diameter end surface portion of the glass substrate is finished to a high-quality mirror surface quality from which grinding damage is removed while having a predetermined shape.

JP 2005-44464 A

  By the way, in the above-described conventional manufacturing method, at least two processing processes of chamfering and outer diameter end face polishing are performed by individual dedicated apparatuses as the processing method of the outer diameter end face portion, and as a process configuration, Requires labor and personnel associated with transfer of process-specific equipment, auxiliary materials, and glass substrates, and requires management and operation costs.

  In addition, since replacement of glass substrates (replacement) is required between processes, an increase in machining allowance due to “center misalignment” is caused, resulting in deterioration of shape accuracy such as dimensional accuracy and concentricity. End up.

For these reasons, if there is a device that can complete from chamfering to polishing finish with one device, it is expected to have quality effects such as improvement of efficiency and processing, reduction of operation cost and maintenance and improvement of dimensional shape accuracy. Therefore, a first object of the present invention is to provide a method for manufacturing a glass substrate for a magnetic disk and a method for manufacturing a magnetic disk capable of simultaneously performing chamfering grinding and polishing in the outer diameter end face processing of the glass substrate. The second object is to provide a method of manufacturing a glass substrate for a magnetic disk and a method of manufacturing a magnetic disk that can reduce the outer end face processing cost of the glass substrate. The object is to provide a method for producing a glass substrate for a magnetic disk and a magnetic device capable of improving the shape quality without impairing the end face quality of the glass substrate. It is to provide a method for manufacturing a disk.

  In order to solve the above-described problems and achieve the above object, in the present invention, by using an inscribed outer diameter grinding wheel for outer diameter end surface grinding, it is possible to perform grinding that is chamfering of a glass substrate, Using the groove (chamfered shape) of the grindstone tool, a polishing liquid in which a polishing agent such as cerium oxide or silicon oxide is mixed into the groove portion with a viscoelasticity such as dilatancy characteristics is applied to the groove portion by a dispenser or the like. Injecting and forming a strong abrasive layer in the groove.

  After that, the glass substrate after chamfering by grinding is brought into contact with rotation, and the outer diameter end face is polished, so that it is possible to obtain high-quality end face quality after removing grinding marks and grinding damage. And

  That is, the present invention has any one of the following configurations.

[Configuration 1]
In the manufacturing method for manufacturing a glass substrate for a magnetic disk, a polishing liquid obtained by adding an abrasive to a viscoelastic fluid is used for polishing the outer diameter end surface portion of the glass substrate. In the method for manufacturing a glass substrate for a magnetic disk,
[Configuration 2]
In the method for manufacturing a glass substrate for a magnetic disk having Configuration 1, the viscoelastic fluid is a dilatancy fluid, and the abrasive is cerium oxide, silicon oxide, aluminum oxide, zirconium oxide, boron carbide, or diamond. It is characterized by.

[Configuration 3]
In the method for manufacturing a glass substrate for a magnetic disk having the configuration 1 or the configuration 2, the outer diameter end surface portion of the glass substrate is polished by a grinding tool including a chamfering process, and then the same tool as that used for the grinding process is used. It is characterized by being used.

[Configuration 4]
In the method for manufacturing a glass substrate for a magnetic disk having the configuration 3, an inscribed outer diameter grinding wheel is used for chamfering.

[Configuration 5]
In the method for manufacturing a glass substrate for a magnetic disk having Configuration 3 or Configuration 4, polishing and chamfering of the outer diameter end surface portion of the glass substrate are alternately and continuously performed without exchanging the tool and the glass substrate. It is characterized by.

[Configuration 6]
A method for manufacturing a magnetic disk, wherein at least a magnetic layer is formed on a surface of a glass substrate obtained by the method for manufacturing a glass substrate for a magnetic disk having any one of configurations 1 to 5. It is.

[Configuration 7]
In the method of manufacturing a magnetic disk having Configuration 6, the magnetic disk is a perpendicular magnetic recording type magnetic disk, the magnetic layer is composed of a plurality of layers, and at least one layer is a soft magnetic layer. To do.

  In the present invention, in the polishing of the outer diameter end surface portion of the glass substrate, the polishing of the outer diameter end surface portion of the glass substrate is performed by grinding using a chamfering process by using a polishing liquid obtained by adding an abrasive to a viscoelastic fluid. Later, the same tool as that used for this grinding finish can be used, and the outer diameter end face portion of the glass substrate is continuously polished and chamfered without changing the tool and the glass substrate. Can be done.

  That is, the present invention can provide a method for producing a glass substrate for a magnetic disk and a method for producing a magnetic disk capable of simultaneously performing chamfering grinding and polishing in the outer diameter end face processing of the glass substrate. It is possible to provide a method for manufacturing a glass substrate for a magnetic disk and a method for manufacturing a magnetic disk that can reduce the outer end face processing cost of the substrate, and further improve the shape quality without impairing the end surface quality of the glass substrate. The manufacturing method of the glass substrate for magnetic discs which can be manufactured, and the manufacturing method of a magnetic disc can be provided.

  The best mode for carrying out the present invention will be described below.

  In the present invention, a polishing liquid obtained by adding an abrasive to a viscoelastic fluid is used for polishing an outer diameter end surface portion of a glass substrate for a magnetic disk, and both grinding and polishing processes including chamfering are performed by one apparatus. I do. In the present invention, in order to give a grinding function to the grinding tool, a fluid having a viscoelastic characteristic such as a dilatancy fluid, cerium oxide, silicon oxide, aluminum oxide, zirconium oxide, boron carbide, diamond, etc. A polishing liquid mixed with an abrasive is used.

  Here, “dilatancy fluid” refers to a fluid that exhibits a phenomenon of changing from a liquid state to a solid when “shear stress (force applied to an object)” is generated in the liquid by applying pressure to the liquid from the outside. Call it.

  Further, by using an inscribed grinding tool capable of forming a uniform film thickness in a fluid by centrifugal force instead of a normal circumscribed grinding tool as a grindstone tool, a chamfering process which is a grinding process with one apparatus and a tool, and Then, it is possible to combine the subsequent polishing process, which is a subsequent process.

  The principle of this polishing process is that a polishing liquid having the characteristics of a dilatancy fluid is used to generate a polishing pressure by using a large shear stress generated between the fluid and the workpiece, as well as between the two who are in contact with each other. Thus, a practical polishing efficiency can be obtained by using a repulsive force acting when a new contact surface is generated at high speed, that is, a so-called dilatancy phenomenon as a polishing pressure.

  More specifically, first, outer diameter chamfering is performed one by one on a single-wafer method with an inscribed outer diameter grinding wheel tool on a glass substrate that has undergone pilot hole processing (calling). As shown in FIG. 1, the inscribed outer diameter grinding wheel is different from a conventional outer grinding wheel in that a chamfered shape 2 to be transferred, which is a groove shape, is formed inside the base material of the grindstone 1, and diamond This is an electrodeposition or metal bond grindstone tool using a grain size of abrasive grains SD # 325 to # 600.

  The glass substrate whose inner and outer diameters have been chamfered in this way waits until the next end surface polishing process is ready without removing the clamp that is the holding mechanism.

  Subsequently, the viscoelastic fluid containing the ceria abrasive is supplied to the groove portion of the grindstone by the quantitative dispenser while the inscribed outer diameter grinding grindstone is rotated. The supplied polishing liquid extends uniformly over the entire groove portion of the grindstone by centrifugal force and has a film thickness proportional to the supply amount. In this way, preparation for polishing is completed.

  When the glass substrate that has been waiting is pressed against the groove of the grindstone at a constant pressure, polishing pressure due to repulsive force and shear stress is generated between the viscoelastic fluid and the outer diameter end face part becomes more specular. As a result, the outer diameter end face quality equivalent to the conventional processing method can be obtained with the same apparatus (tool).

  Embodiments of a magnetic disk glass substrate and a magnetic disk manufacturing method to which the present invention is applied will be described below. This glass substrate for magnetic disk and magnetic disk are 0.8 inch type disk (inner diameter 6 mm, outer diameter 21.6 mm, plate thickness 0.381 mm), 1.0 inch type disk (inner diameter 7 mm, outer diameter 27.4 mm, It is manufactured as a magnetic disk having a predetermined shape such as a plate thickness of 0.381 mm) and a 1.8 inch type magnetic disk (inner diameter of 12 mm, outer diameter of 48 mm, plate thickness of 0.508 mm). Further, it may be manufactured as a 2.5 inch type disc or a 3.5 inch type disc. In this example, a 2.5-inch disk was produced.

(1) Shape processing step and first lapping step First, the melted aluminosilicate glass was molded into a disk shape by direct pressing using an upper die, a lower die, and a barrel die to obtain an amorphous plate glass. The aluminosilicate glass is a glass containing an alkali metal element having a network-like glass skeleton made of SiO and a structure containing aluminum as a modifying ion. In addition to direct pressing, a disk-shaped glass substrate for a magnetic disk may be obtained by cutting a sheet glass formed by a downdraw method or a float method with a grinding wheel. As the aluminosilicate _glass, SiO 2: 58 to 75 _{wt%, Al} 2 O 3: _{5~23 wt%,} Li 2 O: 3 to 10 _wt%, Na 2 O: 4 to 13 principal component weight% Chemically strengthened glass contained as

  Next, both main surfaces of the plate glass were lapped to form a disk-shaped glass base material. The lapping process is a grinding process in which a lapping platen is pressed against the main surface of the sheet glass and roughed.

(2) Cutting process (coring, forming)
Next, the inner hole was formed in the center part using the cylindrical diamond drill with respect to the glass substrate which passed the 1st lapping process (coring).

(3) End face grinding step and end face polishing step As shown in FIG. 1, normal chamfering is performed as an inscribed peripheral grinding process using a grinding wheel and a grinding fluid (coolant). The chamfering process was performed on the end face portion of the outer diameter using an inscribed outer diameter grinding wheel 1 having an outer diameter of φ100 and a thickness of 50 mm in the chamfering machine shown in FIG. The grindstone 1 is a grindstone in which diamond abrasive grains having a particle size of 40 to 50 μm and a grain size # 325 are hardened by electrodeposition bonding. The rotational speed of the grindstone is 5000 r. p. m. (Peripheral speed = 1500 m / min), and water-soluble coolant is discharged to both processing points. The glass substrate has a rotational speed of 120 r. p. m. In the form facing the grindstone by upcut, 0.0025 mm / rev. The grinding mechanism removes the outer diameter allowance of φ60 μm at a cutting speed of. The grinding time was 52 seconds. The surface roughness after chamfering grinding was Ry 1.5 μm and Ra 0.12 μm.

  Subsequently, as shown in FIG. 2, a fluid in which a ceria polishing liquid and a viscoelastic fluid are mixed is applied to the grooves of the grindstone tool. As a polishing liquid used for polishing, a fluid having high viscosity elastic characteristics using a dilatancy fluid was prepared. The basic composition was 200 g of starch powder, 200 g of ceria abrasive having an average particle size of 1.0 μm and 1 L of water, and kneaded well to obtain a polishing liquid having viscous dilatancy characteristics.

  The viscosity of the prepared polishing liquid is desirably 5000 to 10,000 psi. Below this viscosity, an efficient shear stress cannot be obtained, and when it exceeds this viscosity, a uniform polishing film cannot be formed. And this is stored in the tank 3 of a fixed quantity dispenser, stirring.

  Next, as shown in FIG. 3, the glass substrate was polished and finished with the polishing layer applied to the grindstone 1. While maintaining the rotational speed of the grindstone after chamfering grinding, the discharge port of the dispenser was tilted at an angle of 30 degrees or less in the rotational tangential direction of the groove and dropped 3 to 5 times at a discharge amount of 30 ml / time or less.

  As a result, a layer of polishing liquid (polishing layer) having the characteristics of a viscous viscoelastic fluid was formed in the grindstone groove 2 by the generation of centrifugal force by the rotation of the grindstone 1. The film thickness is desirably about 50 to 150 μm. This is because if the film is too thin, the film is broken and the required polishing pressure does not work, and if it is too thick, the shear stress acting between the workpiece and the viscoelastic fluid does not work.

  Subsequently, the glass substrate is pressed against the polishing film with a constant pressure load. The load pressure at this time is preferably 0.12 to 0.25 Mpa. By polishing this constant pressure load for 10 to 15 seconds, an outer diameter of φ8 μm was obtained, and a mirror surface quality of end surface roughness Ry 0.2 μm and Ra 0.015 μm was obtained. Further, since the viscoelastic fluid is polished while following the groove shape of the grindstone, an equal surface pressure is applied to the outer diameter end face of the substrate without breaking the shape of the outer diameter end face portion. In addition, there is no deterioration in concentricity because there is no replacement of the glass substrate. In addition, since the viscoelastic fluid also has the function of free abrasive grains, unlike a conventional brush or pad, a smooth glossy surface with an unobtrusive polish can be obtained.

  Then, as shown in FIG. 4, cleaning is performed in order to use the grindstone groove 2 after the polishing finish as the original grinding groove. After the polishing process is completed, 10 Mpa of high-pressure water and air are sprayed from the water gun nozzle into the groove 2 from the direction opposite to the circumferential rotation direction to remove the viscoelastic film. By removing the polishing film in this manner, the ground surface can be newly regenerated and the next chamfering grinding process can be performed.

  Therefore, by cycling these series of processes, without changing the glass substrate, the same equipment and tools can be used for grinding and polishing of outer diameter chamfering, which were conventionally separate processes. The end face machining process can be unified.

  FIG. 5 shows the adhesion between the ceria polishing liquid applied to the grindstone groove and the viscoelastic fluid. The polishing liquid nozzle that discharges the viscoelastic fluid and the high-pressure nozzle that removes the polishing liquid nozzle are installed separately.

(4) Second Lapping Step Next, a second lapping process was performed on both main surfaces of the obtained glass substrate in the same manner as in the first lapping step. By performing this second lapping process, it is possible to remove in advance the fine irregularities formed on the main surface in the previous cutting process and end face polishing process, and shorten the subsequent polishing process on the main surface. Will be able to be completed in time.

  In the second lapping step, # 1000 is selected as the grain size of the abrasive grains, the flatness of the main surface is 3 μm, the surface roughness Rmax is about 2 μm, and the arithmetic average roughness Ra is about 0.2 μm (Rmax and Ra are According to Japanese Industrial Standard (JIS) B0601). Rmax and Ra were measured with an atomic force microscope (AFM) (Digital Instruments Nanoscope). The flatness is measured by a flatness measuring device, and is the distance (height difference) between the highest part and the lowest part of the substrate surface in the vertical direction (direction perpendicular to the surface).

(5) 1st grinding | polishing process of a main surface First, the 1st grinding | polishing process was given as a grinding | polishing process of a main surface. The primary purpose of this first polishing step is to polish the main surface in advance prior to the second polishing step (mirror polishing step), which is the next step, and to remove scratches and distortions remaining on the main surface in the lapping step described above. To do.

  In the first polishing step, 100 to 200 glass substrates were polished at once by a double-side polishing apparatus capable of polishing. This double-side polishing apparatus performs polishing by sandwiching a large number of glass substrates with an upper surface plate and a lower surface plate through a polishing cloth and relatively moving them by a planetary gear mechanism. A hard resin polisher was used as the polishing cloth in the first polishing step. As the abrasive, cerium oxide abrasive grains were used, and those having a maximum particle size of 3.5 μm, an average value of 1.1 μm, and a D50 value of 1.1 μm were mixed in water.

  The glass substrate which finished this 1st grinding | polishing process was immersed in each washing tank of neutral detergent, a pure water, and IPA (isopropyl alcohol) one by one, and was wash | cleaned.

(6) Chemical strengthening process Next, the glass substrate which finished the above-mentioned lapping process and the 1st grinding | polishing process was chemically strengthened. For chemical strengthening, a chemical strengthening solution prepared by mixing potassium nitrate (60%) and sodium nitrate (40%) is prepared, and the chemically strengthened solution is heated to 375 ° C., and the cleaned glass substrate is preheated to 300 ° C. And was immersed in the chemical strengthening solution for about 3 hours. In this immersion, in order to chemically strengthen the entire surface of the glass substrate, it was performed in a state of being housed in a holder so that a plurality of glass substrates were held at the end surfaces.

  Thus, by immersing in a chemical strengthening solution, the lithium ion and sodium ion of the surface layer of a glass substrate are each substituted by the sodium ion and potassium ion in a chemical strengthening solution, and a glass substrate is strengthened. The thickness of the compressive stress layer formed on the surface layer of the glass substrate was about 100 μm to 200 μm.

  The glass substrate that had been subjected to the chemical strengthening treatment was immersed in a 20 ° C. water bath and rapidly cooled, and maintained for about 10 minutes. And the glass substrate which finished quenching was immersed in the concentrated sulfuric acid heated at about 40 degreeC, and was wash | cleaned. Further, the glass substrate after the sulfuric acid cleaning was cleaned by immersing in a cleaning bath of pure water and IPA (isopropyl alcohol) sequentially.

(7) Second polishing step for main surface Next, a second polishing step was performed as a polishing step for the main surface. The purpose of this second polishing step is to finish the main surface into a mirror surface. In the second polishing step, mirror polishing of the main surface was performed using a soft foam resin polisher, specifically, foamed polyurethane, as the polishing cloth, using the same double-side polishing apparatus as in the first polishing step.

  As an abrasive, colloidal silica abrasive grains having a particle size of 30 nm were prepared, and a polishing liquid was prepared using water and sulfuric acid as a totally dissociable inorganic acid.

  The content of silica in the polishing liquid is preferably 5 to 40% by weight. In this example, it was 10% by weight. The balance in the polishing liquid is ultrapure water.

(8) Cleaning step after mirror polishing The glass substrate after the second polishing step was immersed in a cleaning solution that is an aqueous NaOH solution having a concentration of 3 to 5 wt% to perform alkali cleaning.

  Cleaning was performed by applying ultrasonic waves. Furthermore, it wash | cleaned by immersing in each washing tank of neutral detergent, a pure water, a pure water, IPA, and IPA (steam drying) sequentially. Note that ultrasonic waves were applied to each cleaning tank.

(9) Inspection step of glass substrate for magnetic disk The glass substrate for magnetic disk manufactured as described above was inspected. The roughness of the glass substrate surface was measured with an AFM (atomic force microscope).

  In each example and comparative example, the surface of the glass substrate was in a clean mirror surface state. There were no foreign objects on the surface that could hinder the flying of the magnetic head or cause thermal asperity failure. That is, a flat and smooth high-rigidity glass substrate for a magnetic disk was obtained.

  In addition, by unifying the outer diameter end face process, the following effects could be confirmed as a result of actually adapting to the outer diameter end face machining of a 2.5 inch substrate. That is, the equipment introduction cost was reduced by 25%, the secondary material cost was reduced by 15%, and the fixed cost (personnel / management cost) was reduced by 60%. Further, the machining tact time was reduced from 64 seconds to 64 seconds.

  Further, the outer diameter dimensional accuracy has been improved from ± 20 μm, which is the conventional target value, to ± 12 μm. The concentricity after the outer diameter end face polishing was improved from the conventional Max ≦ 10 μm to Max ≦ 5 μm. Moreover, the outer diameter end face quality was good.

  That is, quality characteristics such as shape accuracy are greatly improved by the absence of glass substrate setup replacement, and the economic effects including fixed costs such as the introduction, management, and maintenance of the apparatus are enormous.

  Using the magnetic disk glass substrate manufactured as described above, a perpendicular magnetic recording type magnetic disk was manufactured.

(10) Magnetic disk manufacturing process On both surfaces of the glass substrate obtained through the above-described processes, an adhesion layer made of a Cr alloy, a soft magnetic layer made of a CoTaZr-based alloy, an underlayer made of Ru, and a CoCrPt group on the surface of the glass substrate A perpendicular magnetic recording disk was manufactured by sequentially forming a perpendicular magnetic recording layer made of an alloy, a protective layer made of hydrogenated carbon, and a lubricating layer made of perfluoropolyether. Although this configuration is an example of a configuration of a perpendicular magnetic disk, a magnetic layer or the like may be configured as an in-plane magnetic disk.

(11) Magnetic disk inspection process The magnetic disk manufactured as described above was inspected. When a head crash test was carried out by flying over a magnetic disk using an inspection head having a flying height of 10 nm, the magnetic disk made of any of the glass substrates of Examples 1 and 2 and Comparative Examples 1 and 2 was used. The magnetic head did not come into contact with foreign matter, and no crash failure occurred.

  Next, a head crash test using an inspection head with a flying height of 8 nm was performed. In the case of Examples 1 and 2, no crash failure occurred. On the other hand, in the case of Comparative Examples 1 and 2, a crash failure occurred. Although Ra (ave) of Comparative Examples 1 and 2 is similar to that of Examples 1 and 2, Ra (max) −Ra (min) is large, so Ra (max) is There is a large (coarse) part, and it is considered that a crash failure occurred at such a part. Therefore, it can be seen that Ra (max) −Ra (min) needs to be 0.02 or less, and the Asker C hardness of the polishing tape needs to be 88 or more.

  Next, with respect to the magnetic disk formed of the glass substrate of the example, the flying height is 8 nm, the reproducing element portion is a magnetoresistive element, the recording element portion is a single magnetic pole element, and recording is performed by the perpendicular recording method. When a reproduction test was performed, it was confirmed that information was recorded and reproduced normally. The thermal asperity signal was not detected in the reproduction signal. Recording and reproduction could be performed at 100 gigabits per square inch.

  Next, a glide height test was performed on the magnetic disk made of the glass substrate of the example. In this test, when the flying height of the inspection head is gradually lowered, the flying height is checked to determine the contact between the testing head and the magnetic disk. As a result, in the magnetic disk of this example, no contact occurred even when the flying height was 4 nm from the inner edge portion to the outer edge portion of the magnetic disk. At the outer edge portion of the magnetic disk, the glide height was 3.7 nm.

  As mentioned above, although the suitable Example of this invention was described, it cannot be overemphasized that this invention is not limited to the example which concerns. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

This is an example in which normal chamfering is performed as an inscribed peripheral grinding using a grinding wheel and a grinding fluid (coolant). This is an example in which a fluid in which a ceria polishing liquid and a viscoelastic fluid are mixed is applied to a groove of a grindstone tool. This is an example in which a glass substrate is polished with a polishing layer applied to a grindstone. This is an example of cleaning in order to make the grindstone groove after polishing finish the original grinding groove. It is an example which shows the adhesion state of the ceria polishing liquid apply | coated to the grindstone groove | channel, and a viscoelastic fluid.

Explanation of symbols

1 Whetstone 2 Groove 3 Tank

Claims (7)

In a manufacturing method for manufacturing a glass substrate for a magnetic disk,
A method for producing a glass substrate for a magnetic disk, wherein a polishing liquid obtained by adding an abrasive to a viscoelastic fluid is used for polishing the outer diameter end face portion of the glass substrate. The viscoelastic fluid is a dilatancy fluid;
The method of manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the abrasive is cerium oxide, silicon oxide, aluminum oxide, zirconium oxide, boron carbide, or diamond. The polishing of the outer-diameter end face portion of the glass substrate is performed using a tool that is the same as the tool used for the grinding finish after the grinding finish including chamfering. The manufacturing method of the glass substrate for magnetic disks of description. The method for producing a glass substrate for a magnetic disk according to claim 3, wherein an inscribed outer diameter grinding wheel is used for the chamfering process. 5. The magnetic disk according to claim 3, wherein the polishing of the outer diameter end surface portion of the glass substrate and the chamfering process are alternately and continuously performed without exchanging the tool and the glass substrate. Method for manufacturing glass substrate. A method for producing a magnetic disk, comprising forming at least a magnetic layer on a surface of a glass substrate obtained by the method for producing a glass substrate for a magnetic disk according to any one of claims 1 to 5. The magnetic disk is a magnetic disk for perpendicular magnetic recording system,
The method of manufacturing a magnetic disk according to claim 6, wherein the magnetic layer includes a plurality of layers, and at least one layer is a soft magnetic layer.

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