JP5348304B2 - Method for manufacturing glass substrate for magnetic recording medium and method for manufacturing magnetic recording medium - Google Patents

Description

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

  Conventionally, an aluminum alloy substrate has been used as a substrate for a magnetic recording medium used in a magnetic recording apparatus or the like. However, with the demand for higher recording density, it is harder and more flat and smooth than an aluminum alloy substrate. Excellent glass substrates are becoming mainstream.

  In recent years, magnetic recording media have further increased in recording density and rotation speed, causing the magnetic head to lose sight of the servo information recording the radius / track position information of the magnetic recording medium, resulting in read / write errors. More and more phenomena occur than before.

  The occurrence of such errors has been considered to be caused by mechanical vibration due to the occurrence of disk fluttering accompanying the narrowing of track width and high-speed rotation accompanying high recording density.

  Therefore, in order to suppress such errors, for example, as a material for a glass substrate for a magnetic recording medium, specific elasticity (specific elasticity is an amount obtained by dividing Young's modulus by the density of glass, light and strong, light and deformed. It is an amount that serves as a guideline that expresses the characteristic of being difficult.Hereinafter, a material having a high specific Young's modulus) is used to suppress fluttering.

  Further, in Patent Document 1, by selecting a glass substrate for a magnetic recording medium whose symmetry in the thickness direction is within a predetermined range, errors in servo information recorded on the magnetic recording medium when a hard disk is formed can be reduced. A method for manufacturing a glass substrate for a magnetic disk is described.

JP 2010-277679 A

  As described above, methods for suppressing the occurrence of errors in the magnetic recording medium have been studied in the past, but the occurrence of errors has not been sufficiently suppressed, and problems still occur when the magnetic recording medium is used. was there.

  SUMMARY OF THE INVENTION In view of the above-described problems of the prior art, it is an object of the present invention to provide a method for manufacturing a glass substrate for a magnetic recording medium with a low error rate when the magnetic recording medium is used.

In order to solve the above problems, the present invention is a method for producing a glass substrate for a magnetic recording medium, comprising a main plane polishing step for polishing a main plane of a disk-shaped glass substrate,
In the glass substrate for a magnetic recording medium after the main surface polishing step,
The magnetic recording medium glass substrate is surrounded by a string and a circular arc provided at two opposing positions, and the maximum value of the distance between the string and the circular arc is 2.3 of the diameter of the magnetic recording medium glass substrate. The both ends in the diametrical direction having a length of% to 7.7% are supported from the lower surface side, and the width is 35 to 80% of the diameter of the glass substrate for a magnetic recording medium. A center line passes through the center of the magnetic recording medium glass substrate and is parallel to the chord, on the upper surface of the central region of the magnetic recording medium glass substrate (area of the main plane of the magnetic recording medium glass substrate) mm ² × After removing the load after adding the load calculated by 2.28 mN / mm ² for 48 hours, the flatness at the time of 5 hours after removing the load,
When the absolute value of the difference from the flatness before applying a load is the pseudoelastic deformation amount A,
Provided is a method for producing a glass substrate for a magnetic recording medium, wherein the pseudoelastic deformation amount A is set to 4.2 μm or less.

  The present invention provides a method of manufacturing a glass substrate for a magnetic recording medium that can return to its original shape within a predetermined time even when a load is applied to the magnetic recording medium and deformed. For this reason, even when the glass substrate for magnetic recording medium is deformed and packed in the cassette at the time of shipment, it is restored to its original shape at the time until servo information is written, and the servo information is placed at an appropriate position on the magnetic recording medium. It is possible to record, and it is possible to suppress the occurrence of subsequent errors (read / write errors).

Explanatory drawing of the measurement flow of the pseudo elastic deformation amount in the first embodiment according to the present invention. Explanatory drawing of the load addition method in the case of the pseudo elastic deformation amount measurement in 1st Embodiment based on this invention

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments, and the following embodiments are not departed from the scope of the present invention. Various modifications and substitutions can be made.

[First Embodiment]
In the present embodiment, a method for producing a glass substrate for a magnetic recording medium according to the present invention will be described.

  The inventors of the present invention have a specific elasticity as a material for a glass substrate for a magnetic recording medium (specific elasticity is an amount obtained by dividing the Young's modulus of glass by the density of glass and is light and strong, light and difficult to deform) (Hereinafter, also referred to as the specific Young's modulus.) Even if a material with a high specific Young's modulus is used, as a result of examining the cause of the read error in the magnetic recording medium, When the magnetic recording medium is deformed, it has been found that one of the causes is that the servo information is written before the deformation is sufficiently recovered, and the present invention has been completed.

  In general, a glass substrate for a magnetic recording medium is formed into a magnetic recording medium by forming a magnetic layer or the like on the surface thereof, and then placed in a cassette so that it does not come into contact with other magnetic recording media. And shipped to a hard disk drive manufacturing factory. When the magnetic recording medium is transported, the magnetic recording medium is contained in a cassette, but is further contained in a decompressed packaging container (packaging), so that a load may be applied and the magnetic recording medium may be deformed.

  Then, after being transported to the hard disk drive manufacturing factory, the magnetic recording medium is taken out from the cassette, assembled into the hard disk drive, written with servo information, and used for a read / write test.

  As described above, when a load is applied to the magnetic recording medium during deformation as described above, the load is removed by removing the magnetic recording medium from the cassette. Therefore, the magnetic recording medium gradually returns to the original shape during these steps. .

  Normally, servo information is written to the magnetic recording medium about 5 to 12 hours after the cassette is taken out. However, if the shape of the magnetic recording medium has not been sufficiently restored at this stage, the position will be displaced even after the servo information is written. For this reason, the writing position of the written servo information is shifted, causing an error.

  As a result of examining the cause of the read error in the magnetic recording medium, the magnetic recording medium has a magnetic layer formed on the surface of the glass substrate for the magnetic recording medium, so the shape of the magnetic recording medium is restored. It was found that the speed at which it is applied depends on the amount of pseudoelastic deformation of the glass substrate for magnetic recording media.

  The present invention relates to a magnetic recording medium in which a magnetic layer or the like is formed on the surface of a glass substrate for magnetic recording medium by setting the pseudoelastic deformation amount A of the glass substrate for magnetic recording medium after the main surface polishing step to 4.2 μm or less. It is intended to reliably suppress the occurrence of a read error.

  The pseudo-elastic deformation amount A here means that both opposing ends of the glass substrate for magnetic recording medium are supported from the lower surface side, and a load is applied to the upper surface of the central portion (central region including the center) of the glass substrate for magnetic recording medium. It is the absolute value of the difference between the flatness after 5 hours have passed after removing the load and the flatness when 5 hours have elapsed after applying the load and the flatness before applying the load.

  Here, when the amount of pseudoelastic deformation A is measured, the load is applied to the glass substrate for magnetic recording medium for 48 hours. After packing and shipping the magnetic recording medium, the packing is opened for assembling the hard disk drive. Until generally based on the time required. Furthermore, when the amount of pseudoelastic deformation is measured by the method of measuring the amount of pseudoelastic deformation A to C, which will be described later, the change in flatness has been saturated in about 16 hours even when any glass substrate is used. It was confirmed. For this reason, the change in flatness is saturated, and the time is set to 48 hours from the viewpoint of no change in flatness even when a load is applied for a longer time.

  Further, the reason for comparing the flatness after 5 hours after removing the load is that the time from writing the packing of the magnetic recording medium to writing servo information is usually about 5 to 12 hours. is there. In order to suppress the error, it is necessary that the glass substrate for magnetic recording medium is restored to the original shape to such an extent that subsequent displacement does not become a problem.

  The value of the pseudoelastic deformation amount A may be an allowable value even if the glass substrate for magnetic recording medium is displaced after servo information is recorded, and the value of the pseudoelastic deformation amount A is 4. 2 μm or less. The pseudoelastic deformation amount A is preferably 4.0 μm or less, more preferably 3.5 μm or less, and particularly preferably 3.0 μm or less. The lower limit value of the pseudoelastic deformation amount A is 0 μm. The same can be said for other pseudoelastic deformation amounts B and pseudoelastic deformation amounts C.

  Further, both ends of the magnetic recording medium glass substrate in the diameter direction are supported from the lower surface side, and the load is removed after applying the load to the upper surface of the central portion (central region including the center) of the magnetic recording glass substrate for 48 hours. The absolute value of the difference between the flatness after 5 hours from the removal of the flatness and the flatness after 48 hours after the removal of the load is defined as a pseudoelastic deformation amount B. In this case, it is preferable that the glass substrate for a magnetic recording medium has a pseudo elastic deformation amount B of 3.0 μm or less.

  The pseudo-elastic deformation amount B means a deformation amount from when 5 hours have elapsed since the load was removed to when 48 hours have elapsed. For this reason, the smaller the value, the smaller the displacement amount after the servo information is written when the load is removed and 5 hours have elapsed.

  Therefore, when the pseudoelastic deformation amount B satisfies the above-mentioned definition, the displacement amount after writing the servo information is small, and it becomes possible to further suppress the occurrence of errors when the magnetic recording medium is used.

  The value of the pseudoelastic deformation amount B may be a deformation amount that is allowed when data is read or written after servo information is written, but is preferably 3.0 μm or less as described above. . The pseudoelastic deformation amount B is more preferably 2.5 μm or less, and particularly preferably 2.0 μm or less.

  Further, both end portions of the glass substrate for magnetic recording medium are supported from the lower surface side, and the load is removed for 48 hours after applying the load to the upper surface of the central portion (central region including the center) of the glass substrate for magnetic recording medium. After removal, it is preferable that the pseudoelastic deformation amount C, which is the flatness after the lapse of 5 hours, is 5.5 μm or less.

  The pseudoelastic deformation amount C indicates that the smaller the value is, the smaller the flatness is after 5 hours have elapsed after the load is removed. The glass substrate for a magnetic recording medium satisfying such parameters has a small amount of deformation and / or has recovered its flatness within 5 hours after the load is removed even though the load is applied for 48 hours. Is shown. For this reason, even if the servo information is written when 5 hours have elapsed after the load is removed, the subsequent deformation amount of the glass substrate for magnetic recording medium is small, and the occurrence of errors can be suppressed.

  A method for measuring the pseudoelastic deformation amounts A to C described so far will be described with reference to FIGS.

  In the following description and FIG. 1, the flatness at each time is expressed as F (xh). In the equation, x represents the elapsed time since the load was removed, with the time when the load was removed as the reference (0h). Also, the time before the load is removed is represented by a minus value. For this reason, for example, F (−48 h) indicates the flatness of the glass substrate for a magnetic recording medium 48 hours before the load is removed, that is, before the load is applied.

  First, the pseudo-elastic deformation measurement flow will be described with reference to FIG.

  As shown in FIG. 1, first, before applying a load, the flatness F (−48 h) of the glass substrate for a magnetic recording medium is measured (point (1) in FIG. 1). Thereafter, a load is applied to the glass substrate for magnetic recording medium for 48 hours by the method described later. This is because it takes about 48 hours from packing and shipping the magnetic recording medium to opening it in a general hard disk drive assembly process. Further, as described above, it has been confirmed that the change in flatness is saturated in about 16 hours after the load is applied to any glass substrate (the glass substrate is completely deformed). For this reason, the change in flatness is saturated, and the time is 48 hours from the viewpoint of the time when the change in flatness does not occur even when a load is applied for a longer time.

  After 48 hours, the load was removed (point (2) in FIG. 1), and when 5 hours had elapsed after the load was removed, the flatness was measured again (point (3) in FIG. 1). 5h). This is because servo information is generally written after about 5 to 12 hours after unpacking in the hard disk assembly process.

  Further, after removing the load, the flatness when 48 hours passed was measured (point (4) in FIG. 1), and this was defined as F (48h). This is because a read / write test is performed when about 48 hours have elapsed after opening the package in a general hard disk drive assembly process.

Then, as described above, the pseudoelastic deformation amount A is calculated by the absolute value of the difference between the flatness F (−48 h) before the load is applied and the flatness when 5 hours have elapsed after the load is removed, It is represented by the following formula.
(Pseudoelastic deformation amount A) = | F (5h) −F (−48h) |
It shows that the smaller the value of the pseudoelastic deformation amount A, the more the shape (flatness) of the glass substrate for magnetic recording medium is restored from the deformation caused by applying a load.

The pseudoelastic deformation amount B is calculated by the absolute value of the difference between the flatness when 5 hours have elapsed after removing the load as described above and the flatness when 48 hours have elapsed, and is expressed by the following equation. .
(Pseudoelastic deformation amount B) = | F (5h) −F (48h) |
The pseudoelastic deformation amount C represents the flatness when 5 hours have elapsed after the load is removed. For this reason, it is represented by the following formula.
(Pseudoelastic deformation amount C) = F (5 h)
A means for measuring the flatness of the glass substrate for a magnetic recording medium is not particularly limited, and for example, measurement can be performed by a phase measurement interferometry (phase shift method).

  Next, a method for applying a load to the glass substrate for a magnetic recording medium when measuring the amount of pseudoelastic deformation will be described below.

  When applying a load to the glass substrate for magnetic recording medium, both opposite ends in the diametrical direction of the glass substrate for magnetic recording medium are supported from the lower surface side, and magnetic recording is performed on the central portion including the center of the glass substrate for magnetic recording medium. This is done by applying a load vertically downward from the upper surface of the medium glass substrate.

  A specific example will be described with reference to FIG.

  FIG. 2 shows a configuration example in which a load is applied to the glass substrate for magnetic recording medium in order to measure the amount of pseudoelastic deformation. FIG. 2 (a) is a lateral side view, and FIG. 2 (b) is a side view. The top views are respectively shown.

  As shown in FIG. 2, a V-shaped block 11 is used to support both ends of the glass substrate for magnetic recording medium, and a glass substrate 13 for magnetic recording medium and a load (weight) 15 are arranged on the V-shaped block 11. Apply load.

  The V-shaped block 11 has a V-shaped notch 12 at the center thereof. Then, by arranging the glass substrate 13 for magnetic recording medium so as to cover the V-shaped cut portion 12, only both end portions 14 of the glass substrate 13 for magnetic recording medium can be supported from the lower surface side. ing. The member that supports the glass substrate for magnetic recording medium is not limited to the V-shaped block, and any member that can support both end portions 14 of the glass substrate for magnetic recording medium may be used. For example, two rectangular columnar blocks may be arranged so as to support both end portions 14 of the glass substrate for a magnetic recording medium with a predetermined interval.

  In this case, both end portions (support portions) 14 provided at two diametrical ends that contact the V-shaped block and support the glass substrate for a magnetic recording medium are surrounded by strings 141 and 142 and arcs, respectively. . And the string 141 and the string 142 are the edge part of the notch part of a V-shaped block, and are parallel. The maximum value of the distance between the chord and the arc, that is, W1 in FIG. 2, is preferably set to a length of 2.3% to 7.7% of the diameter of the glass substrate for a magnetic recording medium, for example. More preferably, it is 3.0% to 4.6% of the diameter. This is because if the range of the supporting portion is too narrow, the glass substrate for the magnetic recording medium may fall off and be damaged when a load is applied. This is because the length becomes shorter, the change in flatness is less likely to occur, and the measurement resolution becomes lower.

  The load is not particularly limited as long as the load can be applied to the central portion including the center of the glass substrate for magnetic recording media, and the arrangement and the magnitude of the load are not particularly limited.

  For example, as shown in FIG. 2, it can be performed by placing a rectangular parallelepiped load (weight) at the center of the glass substrate for a magnetic recording medium. In this case, it is preferable that the load be arranged so as to be parallel to the strings 141 and 142 constituting both end portions supporting the glass substrate for magnetic recording medium. Further, as shown in FIG. 2B, the load is preferably disposed so as to cover all the glass substrate for magnetic recording medium having a certain width (range) from the center line parallel to the strings 141 and 142. For example, a rectangular parallelepiped whose width, that is, the length of W2 in FIG. 2 is 35% to 80% of the diameter of the glass substrate for a magnetic recording medium can be preferably used as the load (weight). A thing can be used more preferably.

  This is because, for example, if the load application range is too narrow, the glass substrate for the magnetic recording medium may be damaged due to the load being concentrated in a narrow range, the load becoming unstable and falling down, etc. This is because if the range is too wide, the distance between the supporting ends becomes narrow, the flatness hardly changes, and the measurement resolution becomes low.

  The longitudinal length of the load (heavy stone) is preferably the same length as the diameter of the glass substrate for the magnetic recording medium as described above, or a length longer than that.

  The weight of the load is not particularly limited as long as the deformation is sufficiently caused by pseudoelasticity and does not damage the glass substrate for the magnetic recording medium, and the area and strength of the glass substrate for the magnetic recording medium to be used. It can be selected according to the like.

For example, the load can be selected to be 0.233 gf (2.28 mN) per 1 mm ² of the main plane area of the glass substrate for magnetic recording medium. That is, a load calculated by (area of main plane of glass substrate for magnetic recording medium) mm ² × 0.233 gf / mm ² (2.28 mN / mm ² ) can be applied. For example, in the case of a magnetic recording medium glass substrate (2.5 inch magnetic recording medium glass substrate) having an outer diameter of 65 mm and an inner diameter (diameter of a circular hole in the center) of 20 mm, a load of 700 gf (6.86 N) Is added to the upper surface of the central portion of the glass substrate for a magnetic recording medium.

The glass substrate for magnetic recording media of the present invention can be produced by a production method including the following steps 1 to 4.
(Step 1) A shape imparting step of chamfering the inner peripheral end surface and the outer peripheral end surface after processing from a glass base substrate into a disk-shaped glass substrate having a circular hole in the center.
(Step 2) An end surface polishing step for polishing the end surfaces (the inner peripheral end surface and the outer peripheral end surface) of the glass substrate.
(Step 3) A main flat surface polishing step for polishing the main flat surface of the glass substrate.
(Step 4) A cleaning step of cleaning and drying the glass substrate.

  And the glass substrate for magnetic recording media obtained by the manufacturing method including the above steps can be used as a magnetic recording medium by further performing a step of forming a thin film such as a magnetic layer thereon.

Here, the shape imparting step of (Step 1) includes a glass substrate having a circular shape in the center, and a glass substrate formed by a float method, a fusion method, a press forming method, a down draw method or a redraw method. To be processed. The glass base substrate used is not particularly limited as long as the glass substrate for magnetic recording medium obtained by processing satisfies the pseudo-elastic deformation amount. For example, the glass may be amorphous glass, crystallized glass, or tempered glass having a compressive stress layer (strengthening layer) on the surface layer of the glass substrate. Glass substrate is preferably high specific modulus (specific modulus), for example, is preferably 29GPa · ^cm 3 / g or more, more preferably 30GPa · ^cm 3 / g or more.

  And the end surface grinding | polishing process of (process 2) end-polishes the end surface (a side part and a chamfer part) of a glass substrate.

  About the main plane polishing process of (Process 3), the upper and lower main planes of a glass substrate are grind | polished simultaneously using a double-side polish apparatus, supplying polishing liquid to the main plane of a glass substrate. The glass substrate of the present invention may be polished only by primary polishing, primary polishing and secondary polishing may be performed, or tertiary polishing may be performed after secondary polishing.

  Prior to the main plane polishing step (step 3), a main plane wrap (eg, loose abrasive wrap, fixed abrasive wrap, etc.) may be performed. In addition, glass substrate cleaning (inter-process cleaning) and glass substrate surface etching (inter-process etching) may be performed between the processes. The main plane lapping is polishing of the main plane in a broad sense.

Furthermore, you may implement the reinforcement | strengthening process (for example, chemical strengthening process) which forms a compression stress layer (strengthening layer) in the surface layer of a glass substrate before a grinding | polishing process, after a grinding | polishing process, or between grinding | polishing processes.
[Second Embodiment]
In the present embodiment, a method for manufacturing a magnetic recording medium using the glass substrate for magnetic recording medium obtained in the first embodiment will be described.

  The magnetic recording medium can be a magnetic recording medium (magnetic disk) by forming a magnetic layer or the like on the glass substrate for magnetic recording medium described in the first embodiment.

  The magnetic recording medium includes a horizontal magnetic recording method and a perpendicular magnetic recording method. Here, the procedure will be described below by taking the perpendicular magnetic recording method as an example.

  The magnetic recording medium includes at least a magnetic layer, a protective layer, and a lubricating film on the surface thereof. In the case of the perpendicular magnetic recording system, a soft magnetic underlayer made of a soft magnetic material that plays a role of circulating a recording magnetic field from a magnetic head is generally provided. For this reason, in order from the glass substrate surface, for example, a soft magnetic underlayer, a nonmagnetic intermediate layer, a perpendicular recording magnetic layer, a protective layer, and a lubricating film are laminated.

  Each layer will be described below.

  As the soft magnetic underlayer, for example, CoNiFe, FeCoB, CoCuFe, NiFe, FeAlSi, FeTaN, FeN, FeTaC, CoFeB, CoZrN, or the like can be used.

  The nonmagnetic intermediate layer is made of Ru, Ru alloy or the like. This nonmagnetic intermediate layer has a function for facilitating the epitaxial growth of the perpendicular recording magnetic layer and a function for breaking the magnetic exchange coupling between the soft magnetic underlayer and the recording magnetic layer.

The perpendicular recording magnetic layer is a magnetic film having an easy axis of magnetization oriented in a direction perpendicular to the substrate surface, and includes at least Co and Pt. In order to reduce intergranular exchange coupling that causes high intrinsic medium noise, a well-isolated fine particle structure (granular structure) is preferable. Specifically, an oxide (SiO ₂ , SiO, Cr ₂ O ₃ , CoO, Ta ₂ O ₃ , TiO _2, etc.), Cr, B, Cu, Ta, Zr or the like added to a CoPt alloy or the like Should be used.

  The soft magnetic underlayer, nonmagnetic intermediate layer, and perpendicular recording magnetic layer described so far can be continuously manufactured by an in-line sputtering method, a DC magnetron sputtering method, or the like.

Next, the protective layer is provided to prevent corrosion of the perpendicular recording magnetic layer and to prevent damage to the surface of the medium even when the magnetic head comes into contact with the medium, and is provided on the perpendicular recording magnetic layer. . As the protective layer, a material containing C, ZrO ₂ , SiO ₂ or the like can be used.

  As the formation method, for example, an in-line sputtering method, a CVD method, a spin coating method, or the like can be used.

  A lubricating layer is formed on the surface of the protective layer in order to reduce friction between the magnetic head and the recording medium (magnetic disk). For the lubricating layer, for example, perfluoropolyether, fluorinated alcohol, fluorinated carboxylic acid, or the like can be used. The lubricating layer can be formed by a dip method, a spray method, or the like.

  As described above, the magnetic recording medium obtained by forming a magnetic layer or the like on the glass substrate for magnetic recording medium described in the first embodiment has little displacement even after servo information is written. Therefore, it is possible to suppress the occurrence of errors.

  Specific examples will be described below, but the present invention is not limited to these examples.

First, a method for evaluating a glass substrate for a magnetic recording medium and a method for evaluating a magnetic recording medium in which a thin film such as a magnetic layer is formed on the glass substrate surface will be described in the following Examples and Comparative Examples.
(1) Pseudoelastic deformation amount As described in the first embodiment, the pseudoelastic deformation amounts A to C are first a flatness F (−48 h) before applying a load to the glass substrate for a magnetic recording medium, and After the load was applied for 48 hours, the flatness F (5 h) and F (48 h) after the lapse of 5 hours and 48 hours after removing the load were measured.

  The flatness at each time was measured by a phase measurement interferometry (phase shift method). Specifically, an interference type flatness measuring device (manufactured by Zygo, model: Zygo GI Flat (MESA)) was used, and measurement was performed at a measurement wavelength of 680 nm.

Thereafter, pseudoelastic deformation amounts A to C were calculated from the measured flatnesses by the following formula.
(Pseudoelastic deformation amount A) = | F (5h) −F (−48h) |
(Pseudoelastic deformation amount B) = | F (5h) −F (48h) |
(Pseudoelastic deformation amount C) = F (5 h)
Here, conditions for applying a load to the glass substrate for a magnetic recording medium will be described.

  First, as shown in FIG. 2, both end portions of the glass substrate for a magnetic recording medium were supported by V-shaped blocks.

  The support portion 14 is disposed at both ends in the diametrical direction, and the two end portions (support portions) are surrounded by the chords 141 and 142 and an arc (which is a shorter arc cut by the chord). Both ends have the same shape. The maximum value W1 of the distance between the chords 141 and 142 and the circular arc was arranged to be 3.8% of the diameter of the magnetic recording medium glass substrate.

  Next, the load 15 was arranged on the main plane of the glass substrate for magnetic recording medium so as to be parallel to the strings 141 and 142 constituting both end portions supported by the V-shaped block. In the present embodiment, as the size of the load, a load whose width, that is, W2 in FIG. 2 is 67% of the diameter of the glass substrate for magnetic recording medium was used. In this case, it arrange | positions so that the centerline of the width direction of a load may pass the center of the glass substrate for magnetic recording media.

Further, in the vertical direction, a material longer than the diameter of the glass substrate for magnetic recording medium was used so as to completely cover the glass substrate for magnetic recording medium over the entire range of the lateral width of the load.
(2) Read / Write Test A magnetic layer and the like were formed on the obtained glass substrate for a magnetic recording medium, and then a read / write test was performed according to the procedure described below.

  Specifically, a magnetic recording medium in which a magnetic layer or the like was formed on a glass substrate for a magnetic recording medium was incorporated into a hard disk drive (HDD), and servo information was written according to the following procedure. Thereafter, according to the procedure of the following embodiment, a magnetic signal is recorded under the condition of a track density of about 254 TPI (Track per inch) and a linear recording density of about 1500 BPI (Bit per inch), and whether or not an error occurs when the signal is read out is checked. confirmed.

  In this example, several types of glass substrates with high specific Young's modulus (Example 1 to Example 9 glass substrates for magnetic recording media shown in Table 1) were examined.

（磁気記録媒体用ガラス基板の製造）
各磁気記録媒体用ガラス基板は、表1の例１〜例９のガラス素基板を用いて、以下の手順により、直径６５ｍｍ、板厚０．６ｍｍ、中央部に２０ｍｍの円孔を有するドーナツ形状に加工した。

(Manufacture of glass substrates for magnetic recording media)
Each glass substrate for a magnetic recording medium is a donut shape having a diameter of 65 mm, a plate thickness of 0.6 mm, and a central hole of 20 mm using the glass base substrates of Examples 1 to 9 in Table 1 according to the following procedure. It was processed into.

  First, the glass base substrate is processed into a disk-shaped glass substrate having a circular hole in the center.

  The inner peripheral end face and the outer peripheral end face of the disk-shaped glass substrate are chamfered so as to obtain a glass substrate for a magnetic recording medium having a chamfering angle of 45 ° (inner peripheral chamfering process, outer peripheral chamfering process).

  After chamfering, the upper and lower principal planes of the glass substrate are lapped using alumina abrasive grains, and the abrasive grains are washed and removed.

  Next, the outer peripheral side surface portion and outer peripheral chamfered portion of the glass substrate for magnetic recording medium are polished with a polishing liquid containing a polishing brush and cerium oxide abrasive grains, and a work-affected layer (such as scratches) on the outer peripheral side surface and outer peripheral chamfered portion. ) And the outer peripheral end face is polished so as to be a mirror surface (outer peripheral end face polishing step).

  After the outer peripheral end surface is polished, the inner peripheral side surface portion and inner peripheral chamfered portion of the glass substrate for magnetic recording medium are polished with a polishing liquid containing a polishing brush and cerium oxide abrasive grains, and the inner peripheral side surface portion and inner peripheral chamfered portion are processed. The deteriorated layer (such as scratches) is removed, and the inner peripheral end face is polished so as to have a mirror surface (inner peripheral end face polishing step). The glass substrate subjected to the inner peripheral end surface polishing removes the abrasive grains.

  After processing the end face of the glass substrate, the upper and lower main planes of the glass substrate are lapped using a fixed grain tool containing diamond abrasive grains and a grinding liquid, and cleaned.

  Next, using a polishing liquid containing a hard urethane polishing pad and cerium oxide abrasive grains as a polishing tool, a 22B-type double-side polishing apparatus (product name: DSM22B-6PV-4MH manufactured by Speedfam Co., Ltd.) Was ground to remove cerium oxide.

  The glass substrate after the primary polishing is a 22B double-sided polishing using a polishing pad containing a soft urethane polishing pad as a polishing tool and a cerium oxide abrasive having an average particle size smaller than that of the cerium oxide abrasive. The upper and lower main planes were secondarily polished by an apparatus, and cerium oxide was removed by washing.

  The glass substrate after the secondary polishing is subjected to tertiary polishing (finish polishing). Using a polishing liquid containing a soft urethane polishing pad and colloidal silica as a polishing tool for tertiary polishing, the upper and lower main planes were polished by a double-side polishing apparatus.

  The glass substrate after final polishing (tertiary polishing) is subjected to scrub cleaning, ultrasonic cleaning immersed in a detergent solution, ultrasonic cleaning immersed in pure water (precision cleaning), and isopropyl alcohol vapor. Dried.

The obtained glass substrates for magnetic recording media were measured for pseudoelastic deformation amounts A to C. Table 2 shows the results.
(Manufacture of magnetic recording media)
Next, a magnetic recording medium was manufactured by sequentially providing an underlayer, a magnetic layer, a protective layer, and a lubricating layer on each of the 100 glass substrates for magnetic recording media of Examples 1 to 9.

The specific procedure will be described. On the surface of each of the glass substrates for magnetic recording media of Examples 1 to 9, using an in-line type sputtering apparatus, a NiFe layer as a soft magnetic underlayer, a Ru layer as a nonmagnetic intermediate layer, a perpendicular magnetic layer A granular structure layer of CoCrPtSiO ₂ was sequentially laminated as a recording layer. Next, a diamond-like carbon film was formed as a protective layer by a CVD method. Thereafter, a lubricating film having perfluoropolyether was formed by a dip method to obtain a magnetic recording medium.

  Each of these was stored in a shipping cassette (manufactured by Entegris), vacuum packaged in an Al laminate bag at a vacuum degree of 400 mmHg, and left for 48 hours.

  After 48 hours, the package was opened, the magnetic recording medium was taken out, assembled into an HDD device, and servo information was written under conditions corresponding to 254 kTPI. Servo information was written 5 hours after opening. An HDD read / write test was performed 43 hours after servo information writing (48 hours after opening).

  Table 2 shows the results of the read / write test.

これによると擬弾性変形緩和量Ａが本発明の規定を充足する実施例の例１〜例７においては、リード・ライトテストでのエラー発生率が最も大きいものでも３％程度であり、比較例である例８、例９と比較して半分程度に抑制できていることが確認できた。

According to this, in Examples 1 to 7 in which the pseudo-elastic deformation relaxation amount A satisfies the provisions of the present invention, even the highest error occurrence rate in the read / write test is about 3%. It was confirmed that it was suppressed to about half compared with Examples 8 and 9 which are.

  When the defects of the magnetic disks of Examples 8 and 9 where the error occurrence rate was high were analyzed, it was confirmed that errors were concentrated on the outer peripheral portion. The cause is considered as follows.

  The magnetic recording medium held in the shipping cassette is deformed by the pressure from the atmosphere by vacuum packaging, and after opening, gradually returns to its original shape according to the respective pseudoelastic characteristics. However, in Examples 8 and 9, which are inferior in pseudo-elasticity characteristics, the servo information has not yet returned to its original shape at the time of servo information writing, and then returns to the original shape. It is thought that it occurred.

  Since the change in shape is more conspicuous at the outer periphery, it is assumed that errors are concentrated on the outer periphery.

  Example 8 which is a comparative example has high specific elasticity even when compared with other glass substrates used in this case and the like, and fluttering is suppressed, so that the occurrence of errors should be suppressed in the evaluation of mounting of the magnetic recording medium. As mentioned above, the incidence of errors was high. This is considered to be caused by the large amount of pseudoelastic deformation of the glass substrate for magnetic recording medium of Example 8. From these results, in order to sufficiently suppress the occurrence of errors in the magnetic recording medium, it is not sufficient to use a glass substrate having a high specific elasticity as a glass substrate for a magnetic recording medium, as conventionally considered, It can be seen that it is necessary to use a glass substrate for a magnetic recording medium having a small amount of pseudoelastic deformation.

  Furthermore, with respect to the examples 1 to 6 that satisfy the provisions of the present invention for the pseudoelastic deformation amounts B and C, even when the error occurrence rate is particularly high, it is 1%, and the occurrence of errors can be particularly suppressed. It could be confirmed.

  From the results of the present embodiment, it is possible to obtain a magnetic recording medium in which errors (reading / writing errors) are suppressed by selecting a glass substrate for magnetic recording medium whose pseudoelastic deformation amount is in a predetermined range. I understand.

13 Glass substrate for magnetic recording medium 14 Both ends 15 Load

Claims (6)

A method for producing a glass substrate for a magnetic recording medium comprising a main plane polishing step for polishing a main plane of a disk-shaped glass substrate,
In the glass substrate for a magnetic recording medium after the main surface polishing step,
The magnetic recording medium glass substrate is surrounded by a string and a circular arc provided at two opposing positions, and the maximum value of the distance between the string and the circular arc is 2.3 of the diameter of the magnetic recording medium glass substrate. The both ends in the diametrical direction having a length of% to 7.7% are supported from the lower surface side, and the width is 35 to 80% of the diameter of the glass substrate for a magnetic recording medium. A center line passes through the center of the magnetic recording medium glass substrate and is parallel to the chord on the upper surface of the central region of the magnetic recording medium glass substrate (area of the main plane of the magnetic recording medium glass substrate) mm ² × After removing the load after adding the load calculated by 2.28 mN / mm ² for 48 hours, the flatness at the time of 5 hours after removing the load,
When the absolute value of the difference from the flatness before applying a load is the pseudoelastic deformation amount A,
A method for producing a glass substrate for a magnetic recording medium, wherein the pseudoelastic deformation amount A is 4.2 μm or less. In the glass substrate for a magnetic recording medium after the main surface polishing step,
The magnetic recording medium glass substrate is surrounded by a string and a circular arc provided at two opposing positions, and the maximum value of the distance between the string and the circular arc is 2.3 of the diameter of the magnetic recording medium glass substrate. The both ends in the diametrical direction having a length of% to 7.7% are supported from the lower surface side, and the width is 35 to 80% of the diameter of the glass substrate for a magnetic recording medium. A center line passes through the center of the magnetic recording medium glass substrate and is parallel to the chord, on the upper surface of the central region of the magnetic recording medium glass substrate (area of the main plane of the magnetic recording medium glass substrate) mm ² × After removing the load after adding the load calculated by 2.28 mN / mm ² for 48 hours, the flatness at the time of 5 hours after removing the load,
When the absolute value of the difference from the flatness after 48 hours after removing the load is the pseudoelastic deformation amount B,
The method for producing a glass substrate for a magnetic recording medium according to claim 1, wherein the pseudoelastic deformation amount B is 3.0 μm or less. In the glass substrate for a magnetic recording medium after the main surface polishing step,
The magnetic recording medium glass substrate is surrounded by a string and a circular arc provided at two opposing positions, and the maximum value of the distance between the string and the circular arc is 2.3 of the diameter of the magnetic recording medium glass substrate. The both ends in the diametrical direction having a length of% to 7.7% are supported from the lower surface side, and the width is 35 to 80% of the diameter of the glass substrate for a magnetic recording medium. A center line passes through the center of the magnetic recording medium glass substrate and is parallel to the chord, on the upper surface of the central region of the magnetic recording medium glass substrate (area of the main plane of the magnetic recording medium glass substrate) mm ² × 2. A load calculated by 2.28 mN / mm ² is applied for 48 hours, and then the load is removed. After removing the load, the amount of pseudoelastic deformation C, which is flatness after 5 hours, is set to 5.5 μm or less. The glass substrate for magnetic recording media according to 1 or 2 A manufacturing method of a board. In a glass substrate for a magnetic recording medium,
The magnetic recording medium glass substrate is surrounded by a string and a circular arc provided at two opposing positions, and the maximum value of the distance between the string and the circular arc is 2.3 of the diameter of the magnetic recording medium glass substrate. The both ends in the diametrical direction having a length of% to 7.7% are supported from the lower surface side, and the width is 35 to 80% of the diameter of the glass substrate for a magnetic recording medium. A center line passes through the center of the magnetic recording medium glass substrate and is parallel to the chord, on the upper surface of the central region of the magnetic recording medium glass substrate (area of the main plane of the magnetic recording medium glass substrate) mm ² × After removing the load after adding the load calculated by 2.28 mN / mm ² for 48 hours, the flatness at the time of 5 hours after removing the load,
When the absolute value of the difference from the flatness before applying a load is the pseudoelastic deformation amount A,
A magnetic recording medium manufacturing method using a glass substrate for a magnetic recording medium having a pseudoelastic deformation amount A of 4.2 μm or less. In a glass substrate for a magnetic recording medium,
The magnetic recording medium glass substrate is surrounded by a string and a circular arc provided at two opposing positions, and the maximum value of the distance between the string and the circular arc is 2.3 of the diameter of the magnetic recording medium glass substrate. The both ends in the diametrical direction having a length of% to 7.7% are supported from the lower surface side, and the width is 35 to 80% of the diameter of the glass substrate for a magnetic recording medium. A center line passes through the center of the magnetic recording medium glass substrate and is parallel to the chord, on the upper surface of the central region of the magnetic recording medium glass substrate (area of the main plane of the magnetic recording medium glass substrate) mm ² × After removing the load after adding the load calculated by 2.28 mN / mm ² for 48 hours, the flatness at the time of 5 hours after removing the load,
When the absolute value of the difference from the flatness after 48 hours after removing the load is the pseudoelastic deformation amount B,
The method for producing a magnetic recording medium according to claim 4, wherein a glass substrate for magnetic recording medium having a pseudo elastic deformation amount B of 3.0 μm or less is used. In a glass substrate for a magnetic recording medium,
The magnetic recording medium glass substrate is surrounded by a string and a circular arc provided at two opposing positions, and the maximum value of the distance between the string and the circular arc is 2.3 of the diameter of the magnetic recording medium glass substrate. The both ends in the diametrical direction having a length of% to 7.7% are supported from the lower surface side, and the width is 35 to 80% of the diameter of the glass substrate for a magnetic recording medium. A center line passes through the center of the magnetic recording medium glass substrate and is parallel to the chord, on the upper surface of the central region of the magnetic recording medium glass substrate (area of the main plane of the magnetic recording medium glass substrate) mm ² × 2. Magnetic recording in which the load calculated by 2.28 mN / mm ² is applied for 48 hours, then the load is removed, and after removing the load, the pseudoelastic deformation amount C, which is flatness after 5 hours, is 5.5 μm or less. A glass substrate for medium is used or claim 4 or 6. A method for producing a magnetic recording medium according to 5.

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