SG189605A1

SG189605A1 - Glass substrate for magnetic recording medium and magnetic recording medium using the glass substrate for magnetic recording medium

Info

Publication number: SG189605A1
Application number: SG2012045670A
Authority: SG
Inventors: Tamada Minoru
Original assignee: Asahi Glass Co Ltd
Priority date: 2011-10-14
Filing date: 2012-06-19
Publication date: 2013-05-31
Also published as: JP2013089264A; JP4977795B1; CN102855888A; MY156113A; CN102855888B

Abstract

GLASS SUBSTRATE FOR MAGNETIC RECORDING MEDIUM AND MAGNETIC RECORDING MEDIUM USING THE GLASS SUBSTRATE FOR MAGNETIC RECORDING MEDIUM[Designation of Document] Abstract [Abstract]The present invention has an object to provide a glass substrate for a magnetic recording medium in which, regarding the entire surface of a recording/reproducing5 area, variation of microwaviness falls within a given range, and to provide a magnetic recording medium using the glass substrate for a magnetic recording medium. The present invention provides a glass substrate for a magnetic recording medium, having a pair of main surfaces, an outer peripheral surface and an inner peripheral surface, in which at least one main surface is that: when microwaviness (nWq) is measured in each10 lattice-shaped evaluation area set to entire surface of the main surface including entire surface of an area to be a recording/reproducing area when a magnetic disk has been formed, an absolute value of variation of microwaviness (AnWq) between one evaluation area and the adjacent evaluation area is that a ratio (rate of change) to microwaviness of the one evaluation area is 10% or less; and a mean value of the15 microwaviness (nWq) measured in the each lattice-shaped evaluation area is 0.080 nm or less, and provides a magnetic recording medium using the glass substrate for a magnetic recording medium. Fig. 1

Description

[Designation of Document] Specification [Title of the Invention]

GLASS SUBSTRATE FOR MAGNETIC RECORDING MEDIUM AND MAGNETIC

RECORDING MEDIUM USING THE GLASS SUBSTRATE FOR MAGNETIC

RECORDING MEDIUM

[Technical Field]

[0001]

The present invention relates to a glass substrate for a magnetic recording medium and a magnetic recording medium using the glass substrate for a magnetic recording medium. [Background Art]

[0002]

An aluminum alloy substrate has conventionally been used as a substrate for a magnetic recording medium, used in a magnetic disk recording apparatus and the like.

However, recently, with a requirement of an increase in recording density, a glass substrate that is hard as compared with the aluminum alloy substrate and has excellent flatness and smoothness is becoming mainstream.

[0003]

Furthermore, with a recent increase in recording density of a magnetic disk (hereinafter referred to as a “magnetic recording medium”), magnetic signals are getting to be finely recorded on the magnetic disk, and because of this, signal is becoming weak. For reading and recording such a weak signal, there is a demand of shortening a distance between a magnetic disk and a magnetic head as possible.

[0004]

In order to decrease a distance between a magnetic disk that rotates high speed and a magnetic head, that is, a flying height of a magnetic head, a surface of a glass substrate for a magnetic recording medium, that is a substrate of a magnetic disk must be a flat surface having small microwaviness such that the magnetic disk does not contact the magnetic head.

[0005]

Regarding a surface of a glass substrate for a magnetic recording medium, microwaviness has heretofore been evaluated on some areas arbitrarily selected, by a laser Doppler vibrometer or the like as described in, for example, Patent Document 1. [Background-Art Documents] [Patent Documents]

[0006]

Patent Document 1: W02009/084534 [Summary of the Invention] [Problems that the Invention is to Solve]

[0007]

However, in a glass substrate for a magnetic recording medium obtained by the conventional evaluation method, certain flatness is secured in areas which have been measured, but there was a case that other areas locally have a part having large microwaviness and roughness.

[0008]

For example, in the case where a part having locally large microwaviness is present, when such a glass substrate is used as a magnetic disk, a distance between a magnetic head and a magnetic disk greatly fluctuates depending on a place, and magnetic noise is increased. As a result, there was a problem that read/write precision of recording and recording density were decreased. Furthermore, there was a problem that because there was a possibility of contact between a magnetic disk and a magnetic head, it was difficult to shorten a distance between the magnetic disk and the magnetic head.

[0009]

In view of the above problems of the prior art, the present invention has an object to provide a glass substrate for a magnetic recording medium, in which regarding the entire surface of a recording/reproducing area, variation of microwaviness falls within a given range. [Means for Solving the Problems]

[0010]

In order to solve the above-mentioned problem, the present invention provides a glass substrate for a magnetic recording medium, having a pair of main surfaces, an outer peripheral surface and an inner peripheral surface, wherein at least one main surface is that: when microwaviness (nWq) is measured in each lattice-shaped evaluation area set to entire surface of the main surface including entire surface of an area to be a recording/reproducing area when a magnetic disk has been formed, an absolute value of variation of microwaviness (AnWq) between one evaluation area and the adjacent evaluation area is that a ratio (rate of change) to microwaviness of the one evaluation area is 10% or less; and a mean value of the microwaviness (nWq) measured in the each lattice-shaped evaluation area is 0.080 nm or less. [Advantages of the Invention]

[0011]

According to the glass substrate for a magnetic recording medium of the present invention, the variation of microwaviness (root-mean-square waviness) falls within a given range in the entire surface of at least one main surface, Therefore, when a magnetic disk is formed using the glass substrate, a distance between a magnetic disk and a magnetic head can be decreased. Furthermore, since the distance between a magnetic disk and a magnetic head stabilizes, read/write precision of recording and recording density can be increased as compared with the conventional those. [Brief description of the drawings]

[0012]

Fig. 1 is an explanatory view of a glass substrate for a magnetic recording medium according to a first embodiment of the present invention, and its evaluation area. [Modes for Carrying Out the Invention)

[0013]

The mode for carrying out the present invention is described below by reference to the drawing, but the invention is not limited to the following embodiments, and various changes and substitutions can be added to the following embodiments without departing the scope of the invention.

[0014]

First Embodiment

The glass substrate for a magnetic recording medium of the present invention is described in the present embodiment.

[0015]

The glass substrate for a magnetic recording medium of the present invention has a pair of main surfaces, an outer peripheral surface and an inner peripheral surface.

At least one main surface of the glass substrate for a magnetic recording medium is that the entire surface including the entire surface of an area to be a recording/reproducing area when a magnetic disk has been formed is that when microwaviness (nWq) of each evaluation area set into a lattice shape is measured, an absolute value of variation of microwaviness (AnWq) between one evaluation area and the adjacent evaluation area is that the ratio to microwaviness of the one evaluation area (hereinafter referred to as “rate of change of microwaviness™) is 10% or less.

[0016]

It is considered that variation of flying height of a magnetic head occurs by rapid change of local microwaviness on a surface of a magnetic disk, that is, a main surface of a glass substrate for a magnetic recording medium.

[0017]

As described above, the evaluation has conventionally been made by a value of waviness measured in, for example, arbitrary areas of two places on a main surface.

However, the conventional method could not evaluate local rapid change of microwaviness on a main surface.

[0018]

The reason for this is as follows. For example, even in the case that there is a great difference in measurement values between areas of two places, in the case that waviness mildly changes on the entire surface of a magnetic disk, rapid variation in flying height of a magnetic disk does not occur. Furthermore, even in the case that the difference of the measurement values in the areas of two places is small, in the case that there is a part that microwaviness locally greatly changes in areas other than the areas, rapid change of flying height of a magnetic head occurs.

[0019]

Thus, the conventional evaluation method did not correctly evaluate the influence giving variation of flying height of a magnetic head, and was insufficient to achieve high recording density of a magnetic disk.

[0020]

On the other hand, the present invention is that microwaviness (nWq) is measured in each lattice-shaped evaluation area set on the entire surface of a main surface, and the difference between adjacent evaluation areas makes to fall within a given range. As a result, the present invention can provide a glass substrate for a magnetic recording medium, free of local rapid change of microwaviness which may affect variation of flying height of a magnetic head.

[0021]

Specific evaluation method is described by reference to Fig. 1.

[0022]

The glass substrate for a magnetic recording medium has a disk shape having a circular hole at the center thereof as shown in Fig. 1{A). In the present invention, the entire surface of at least one main surface of the glass substrate for a magnetic recording medium is a main surface including the entire surface of an area to be a recording/reproducing area when a magnetic disk has been formed. In the present invention, microwaviness (nWq) is measured in every evaluation area set in a lattice shape on a main surface including the entire surface of an area to be a recording/reproducing area when a magnetic disk has been formed, on at least one main surface of a glass substrate for a magnetic recording medium.

[0023]

Measurement means of microwaviness is not limited so long as microwaviness in every evaluation area set in a lattice shape can be measured. For example, the microwaviness can be measured by, for example, a scanning interference microscope.

[0024]

A size of the evaluation area set in a lattice shape is not particularly limited.

For example, a size of one evaluation area can be set to desired size and shape, such as 100 pm square, 50 pum square, 40 pm square, 30 um square or 20 pm square.

[0025]

The size of the evaluation area set in a lattice shape is preferably smaller than a size of a magnetic head. The size of the evaluation area is preferably from 100 pum square to 20 um square, further preferably from 100 pm square to 30 um square, and particularly preferably from 80 pm square to 30 pm square.

[0026]

The evaluation area is described below. Each evaluation area is schematically shown in Figs. 1(A) and 1(B). Lines are shown in the drawing. This is to show lattices for explaining evaluation areas, and lines are not actually drawn on a glass substrate.

[0027]

Fig. 1(B) is that a part of Fig. 1(A) is enlarged in order to explain the evaluation area. Each square lattice shown in Fig. 1(B) indicates an evaluation area, and, for example, A to F each is set to 30 pm.

[0028]

Each lattice indicated as (a) to (e) means an evaluation area. For example, regarding evaluation area (a), adjacent evaluation areas mean evaluation areas (b) to (¢) sharing sides with the evaluation area (a).

[0029]

The glass substrate for a magnetic recording medium of the present invention is that rate of change of an absolute value of variation of microwaviness between the respective adjacent evaluation areas is 10% or less.

[0030]

This is explained as follows by reference to the evaluation area (a) in Fig. 1.

Microwaviness of the evaluation area (a) is used as a standard, and the respective microwaviness of the evaluation areas (b) to (e) adjacent thereto is that the rate of change is 10% or less. The same is applied to all of evaluation areas on at least one main surface of the glass substrate for a magnetic recording medium.

[0031]

The rate of change of microwaviness can be calculated by, for example, 100xjnWq(a)mWq(b)[/nWq(a) when microwaviness of the evaluation area (a) is nWq(a) and microwaviness of the evaluation area (b) adjacent thereto is nWq(b).

[0032]

The glass substrate for a magnetic recording medium has upper and lower main surfaces. There is a case that the surface to be a recording/reproducing area when a magnetic disk has been formed is any one of two surfaces. Therefore, at least any one of main surfaces must satisfy the above requirement, but it is more preferred that both main surfaces satisfy the requirement. This is the same regarding a mean value and a standard deviation of microwaviness (nWq) described hereinafter.

[0033]

By satisfying the above element, the glass substrate for a magnetic recording medium of the present invention can be made that microwaviness falls within a given range, that is, the entire surface of the main surface does not have a part having locally high waviness. For this reason, when a magnetic layer and the like have been formed on the glass substrate for a magnetic recording medium of the present invention to obtain a magnetic disk, a distance between a magnetic head and a magnetic recording medium stabilizes, and generation of magnetic noise can be suppressed. Furthermore, read/write precision and recording density can be improved.

[0034]

The rate of change of microwaviness is preferably 7% or less, further preferably 5% or less, and particularly preferably 3% or less.

[0035]

A mean value of microwaviness (nWq) measured in each lattice-shaped evaluation area set on the entire surface of at least one main surface of a glass substrate for a magnetic recording medium is 0.080 nm or less. The mean value in the present invention means an arithmetic mean value.

[0036]

Such a mean value is preferred for the reason. By that the mean value of microwaviness of the main surface of a glass substrate for a magnetic recording medium satisfies the above range, when a magnetic layer and the like have been formed on the glass substrate of the present invention to obtain a magnetic disk, a distance between a magnetic head and a magnetic disk can be decreased. Furthermore, a distance between a magnetic head and a magnetic disk stabilizes. As a result, generation of magnetic noise can be suppressed, making it possible to improve read/write precision of recording and recording density.

[0037]

A mean value of microwaviness (nW¢q) measured in each lattice-shaped evaluation area set on the entire surface of at least one main surface of a glass substrate for a magnetic recording medium is 0.080 nm or less, more preferably 0.055 nm or less, and particularly preferably 0.045 nm or less.

[0038]

Standard deviation of microwaviness (nWq) measured in each lattice-shaped evaluation area set on the entire surface of at least one main surface of a glass substrate for a magnetic recording medium is preferably 0.0060 nm or less.

[0039]

The reason for this is that variation of microwaviness on the entire surface of the main surface of a glass substrate is decreased by that the standard variation of microwaviness in each evaluation area measured on the entire surface of at least one main surface, that is, the entire surface of at least recording/reproducing area, of a glass substrate for a magnetic recording medium satisfies the above range. That is, an area having locally high microwaviness value is not present. As a result, when a magnetic layer and the like have been formed on the glass substrate of the present invention to obtain a magnetic disk, a distance between a magnetic head and a magnetic disk can be decreased, which is preferred. Furthermore, a distance between a magnetic head and a magnetic disk stabilizes. As a result, generation of magnetic noise can be suppressed, making it possible to improve read/write precision of recording and recording density.

[0040]

A method for manufacturing a glass substrate for a magnetic recording medium is described below.

[0041]

The glass substrate for a magnetic recording medium can be manufactured by a manufacturing method comprising the following steps 1 to 4.

Step 1: a shape-forming step of processing a glass sheet into a disk-shaped substrate having a circular hole at the center thereof and chamfering an inner peripheral surface and an outer peripheral surface.

Step 2: a peripheral surface-polishing step of polishing peripheral surfaces (inner peripheral surface and outer peripheral surface) of the glass substrate.

Step 3: a main surface-polishing step of polishing main surfaces of the glass substrate.

Step 4: a cleaning step of precision-cleaning the glass substrate, followed by drying.

[0042]

The glass substrate for a magnetic recording medium obtained by the manufacturing method comprising the above each step is further subjected to a step of forming a thin film such as a magnetic layer on the glass substrate, whereby a magnetic recording medium can be formed.

[0043]

The shape-forming step of Step 1 processes a glass sheet molded by a float process, a fusion process, a press molding process, a down draw process or a redraw process into a disk-shaped glass substrate having a circular hole at a center thereof.

The glass sheet used may be amorphous glass, crystallized glass and a strengthened glass having a strengthening layer on a surface layer of a glass substrate.

[0044]

The peripheral surface-polishing step of Step 2 polishes peripheral surfaces (side surface part and chamfered part) of a glass substrate.

[0045]

The main surface-polishing step of Step 3 simultaneously polishes upper and lower main surfaces of a glass substrate while supplying a polishing slurry to the main surfaces of the glass substrate using a double side polishing machine. The polishing step may perform only a primary polishing, may perform a primary polishing and a secondary polishing, and may perform a tertiary polishing after a secondary polishing.

[0046]

A polishing pad used in a finish polishing is preferably a soft urethane polishing pad having a mean value of an open pore size of pores appeared on a polishing surface of less than 12 pm and a standard deviation of less than 3 pm.

[0047]

Use of the polishing pad enables variation of microwaviness on the surface of a glass substrate to suppress.

[0048]

The finish polishing means a final polishing step in the main surface-polishing step. Specifically, when the main surface-polishing step is conducted up to a tertiary polishing, the tertiary polishing is the final polishing, and when only a primary polishing is conducted, the primary polishing is the final polishing.

[0049]

A main surface lapping (for example, loose abrasive lapping or fixed abrasive lapping) may be carried out before the main surface-polishing step of Step 3.

Furthermore, cleaning of a glass substrate (in-process cleaning) and etching of a glass substrate surface (in-process etching) may be carried out between the respective steps.

The main surface lapping is polishing of a main surface in a broad sense.

[0050]

In the case that high mechanical strength is required in a glass substrate for a magnetic recording medium, a strengthening step (for example, chemical strengthening step) of forming a strengthening layer on a surface layer of a glass substrate may be carried out before the polishing step, after the polishing step or during the polishing step.

Second Embodiment

A magnetic recording medium (magnetic disk) using the glass substrate for a magnetic recording medium described in the first embodiment is described in the present embodiment.

[0051]

The constitution of the magnetic recording medium of the present invention is not limited so long as the glass substrate for a magnetic recording medium described in the first embodiment is used. For example, a magnetic recording medium having a magnetic layer, a protective layer and a lubricating layer on the surface thereof may be mentioned.

[0052]

The magnetic recording medium includes a horizontal magnetic recording system and a vertical magnetic recording system. Here, a specific manufacturing method is described below by reference to the vertical magnetic recording system.

[0053]

The magnetic recording medium has at least a magnetic layer, a protective layer and a lubricating layer on the surface thereof. In the case of the vertical magnetic recording medium, a soft magnetic underlayer comprising a soft magnetic material which plays a role of refluxing recording magnetic field from a magnetic head is generally provided. For this reason, for example, a soft magnetic underlayer, a non- magnetic intermediate layer, a vertical recording magnetic layer, a protective layer and a lubricating layer are laminated in this order from the surface of the glass substrate.

[0054]

Each layer is described below.

[0055]

CoNiFe, FeCoB, CoCuFe, Nile, FeAlSi, FeTaN, FeN, FeTaC, CoFeB, CoZrN and the like can be used as the soft magnetic underlayer.

[0056]

The non-magnetic intermediate layer is constituted of Ru, Ru alloy or the like.

The non-magnetic layer has a function for facilitating epitaxial growth of a vertical recording magnetic layer, and a function of breaking magnetic exchange bond between the soft magnetic underlayer and the recording magnetic layer,

[0057]

The vertical recording magnetic layer is a magnetic layer that a magnetization faces a vertical direction to a substrate surface, and contains at least Co and Pt. The vertical recording magnetic layer preferably has a fine particle structure (granular structure) well isolated in order to reduce intergranular exchange bond causing high inherent medium noise. Specifically, a material comprising a CoPt alloy having added thereto oxides (S10, SiO, Cr,03, CoO, Tay0s, TiO; and the like), Cr, B, Cu, Ta, Zr and the like is preferably used.

[0058]

The soft magnetic underlayer, non-magnetic intermediate layer and vertical recording magnetic layer described above can continuously be produced by an inline sputtering method, a DC magnetron sputtering method or the like.

[0059]

The protective layer is provided to prevent corrosion of the vertical recording magnetic layer and to prevent breakage of a surface of a medium even in the case that a magnetic head contacts the medium, and is provided on the vertical recording magnetic layer. A material containing C, ZrO, SiO; and the like can be used as the protective layer.

[0060]

The formation method can use an inline sputtering method, a CVD method, a spin coat method and the like.

[0061]

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).

The lubricating layer can use perfluoropolyether, fluorinated alcohol, fluorinated carboxylic acid and the like. The lubricating layer can be formed by a dip method, a spray method or the like.

[0062]

The magnetic recording medium prepared is evaluated by a glide height test and a certification test (MP evaluation).

[0063]

The glide height test is a test for evaluating abnormal protrusions on the main surface of a magnetic recording medium.

[0064]

An apparatus for conducting the glide height test (glide height avalanche test) is described below. The apparatus comprises a spindle rotating a magnetic disk, and a glide slider locating on the magnetic disk and flying by rotation of the magnetic disk.

Furthermore, the test is conducted using an apparatus constituted of an AE sensor detecting elastic wave generated when the glide slider has contacted fine protrusions on the magnetic disk, and a contact detection part detecting as to whether or not output through a filter of the AE sensor is a certain value or more,

[0065]

The magnetic disk is rotated to float the glide slider. The glide slider moves to the entire surface of a recording area on the magnetic disk, and elastic wave generated when the glide slider has contacted fine protrusions on the magnetic disk is detected by the AE sensor.

[0066]

After rotating the magnetic disk in a certain rotation speed, the rotation speed is gradually decreased to gradually decrease flying height of the glide slider. Flying height of the glide slider when the output through the filter of the AE sensor becomes a certain value or more (for example, when fine protrusions having a flying height of the glide slider are present on a magnetic disk and the glide slide collides against the fine protrusions) is used as a glide height.

[0067]

The flying height of the glide slider is calculated from rotation speed of the magnetic disk.

[0068]

The certification test is a test for evaluating defects (signal quality) of a magnetic recording film and the like of a magnetic disk. The relationship between a magnetic head of a magnetic disk apparatus and a magnetic disk is reproduced using a test head comprising a head slider having provided thereon a magnetic head for the certification test, and writing, reproducing, erosion, re-reproducing and the like of signal are conducted every track of a magnetic disk to evaluate. Specifically, evaluation on the presence or absence of MP {Missing Pulse) error is conducted.

[0069]

The MP error is that reproducing signal of less than a certain slice level to an average reproducing voltage of a test head is generated in a part of track when, for example, flying height and flying pose of a head become unstable for the reasons of foreign matters in the inside of a magnetic recording medium, breakage of a recording film, microwaviness (size and in-plane uniformity) of a main surface, and the like.

The MP error disables a proper signal treatment of a magnetic disk.

[0070]

In the Examples of the present invention described hereinafter, a magnetic recording medium free of generation of MP error was judged as “A” (accepted product), a ratio of judgment A (examination pass ratio) when 100 magnetic recording media were evaluated was obtained, and evaluation was made.

[0071]

The magnetic recording medium of the present invention is that glide height measured by a glide height test is preferably 2.5 nm or less, more preferably 2.0 nm or less, and particularly preferably 1.8 nm or less.

[0072]

The ratio of judgment A in MP evaluation by a certification test is preferably 50% or more, and more preferably 55% or more.

[0073]

A magnetic recording medium (magnetic disk) manufactured using the glass substrate for a magnetic recording medium of the present invention by the procedures described above is that microwaviness on the entire surface of a main surface of a glass substrate falls within a given range. As a result, a distance between a magnetic disk and a magnetic head can be decreased as compared with the conventional distance.

Furthermore, a distance between a magnetic disk and a magnetic heat stabilizes. This makes it possible to suppress generation of magnetic noise and to increase read/write precision of recording and recording density as compared with the conventional those. [Examples]

[0074]

The present invention is described below by reference to specific Examples, but the invention is not construed as being limited thereto.

[0075]

Evaluation method of a glass substrate for a magnetic recording medium, and evaluation method of a magnetic recording medium comprising the glass substrate having formed on the surface thereof a thin film such as a magnetic layer, in the following Examples and Comparative Examples are described below.

[0076] (1) Microwaviness (nWq)

The microwaviness (root-mean-square waviness) was measured using a scanning interference microscope (manufactured by Zygo, ZeMapper). Measurement area of the microwaviness was the entire surface of a main surface so as to include a recording/reproducing area of a glass substrate for a magnetic recording medium. The measurement was individually conducted on each evaluation area obtained by dividing one main surface of a glass substrate for a magnetic recording medium into 30 pm square lattice shape. Wavelength components other than wavelength component of 0.2 um to 1.8 pm were filtered out from waviness information obtained by the measurement, and microwaviness having a period (wavelength) of from 0.2 pm to 1.8 pum was obtained.

[0077]

In the present Examples, it is considered that waviness component having a period smaller than that of microwaviness of a main surface affects generation of MP error with decreasing a size of a magnetic head, and microwaviness having a period of from 0.2 pm to 1.8 pm was evaluated as above.

[0078]

The rate of change of microwaviness in the adjacent evaluation areas was calculated by the following calculation equation when, for example, microwaviness of the evaluation area (a) in Fig. 1 is nWq(a) and microwaviness of the adjacent evaluation area (b) therein is nWq(b).

Rate of change of microwaviness= 100x|nWq(a)-nWq(b)|/nWq(a)

[0079] (2) Glide height test

A magnetic recording medium is set to a glide height test apparatus, and the magnetic recording medium is rotated at a certain rotation speed. The rotation speed of the magnetic recording medium is gradually decreased to decrease a flying height of a glide slider. Glide slider height when output of AE sensor reached a certain value or more was used as a glide height.

[0080] (3) Certification test

In the present Examples, evaluation of MP (Missing Pulse) was performed to 100 magnetic recording media. A magnetic recording medium in which the number of generation of MP error was 0 was judged as A. The number of magnetic recording media having the judgment A was counted to obtain the ratio of judgment A.

[0081]

A glass substrate for a magnetic recording medium and a method for manufacturing a magnetic recording medium, in Examples and Comparative Examples are described below.

[0082]

The glass substrate for a magnetic recording medium was produced by the following procedures.

[0083]

A glass substrate comprising SiO, as a main component, molded by a float process was processed into a disk-shaped glass substrate having a circular hole at a center thereof so as to obtain a glass substrate for a magnetic recording medium, having an outer diameter of 65 mm, an inner diameter of 20 mm and a thickness of 0.635 mm.

[0084]

An inner peripheral surface and an outer peripheral surface of the disk-shaped glass substrate was chamfered so as to obtain a glass substrate for a magnetic recording medium having a chamfering width of 0.15 mm and a chmmfring angel of 45° (inner peripheral chamfering step and outer peripheral chamfering step).

[0085]

After chamfering, upper and lower main surfaces of the glass substrate were lapped using alumina abrasives, and the abrasives were then removed by cleaning.

[0086]

The outer peripheral side part and the outer peripheral chamfered part of the glass substrate for a magnetic recording medium were polished using a polishing brush and a polishing slurry containing cerium oxide abrasives to remove a damaged layer (scratches and the like) on the outer peripheral side part and the outer peripheral chamfered part, and the outer peripheral surface was polished so as to obtain a mirror surface (outer peripheral surface polishing step).

[0087]

After polishing the outer peripheral side, the inner peripheral side part and the inner peripheral chamfered part of the glass substrate for a magnetic recording medium were polished using a polishing brush and a polishing slurry containing cerium oxide abrasives to remove a damaged layer (scratches and the like) of the inner peripheral side part and the inner peripheral chamfered part, and the inner peripheral surface was polished so as to obtain a mirror surface (inner peripheral surface polishing step). The glass substrate in which the inner peripheral surface had been polished was cleaned to remove abrasives.

[0088]

After processing the peripheral surface of the glass substrate, the upper and lower main surfaces of the glass substrate were lapped using a fixed abrasive tool containing diamond abrasives and a lapping liquid, followed by cleaning.

[0089]

The glass substrate was subjected to primary polishing with a 22B double side polishing machine (manufactured by SpeedFam, product name: DSM22B-6PV-4MH) using a hard urethane polishing pad as a polishing tool and a polishing slurry containing cerium oxide abrasives (polishing slurry composition containing cerium oxide having an average particle diameter (hereinafter referred as an average particle size) of about

1.3 um) such that a removal volume is 20 pum, and cerium oxide was removed by cleaning. 216 pieces of glass substrates were simultaneously polished in one lot.

[0090]

The upper and lower main surfaces of the glass substrate after the primary polishing were subjected to secondary polishing with the 22B double side polishing machine using a soft urethane polishing pad as a polishing tool and a polishing slurry containing cerium oxide abrasives having an average particle size smaller than that of the above cerium oxide abrasives (polishing slurry composition containing cerium oxide having an average particle size of about 0.5 pm as a main component) such that the removal volume is 5 um, and cerium oxide was removed by cleaning.

[0091]

The glass substrate after the secondary polishing is subjected to tertiary polishing. The tertiary polishing was conducted such that the upper and lower main surfaces were polished with a 22B double side polishing machine using a soft urethane polishing pad as a polishing tool and a polishing slurry containing colloidal silica (polishing slurry composition containing colloidal silica as a main component) such that the removal volume is 1 pum.

[0092]

Polishing pressure in conducting the tertiary polishing, a mean value of an open pore size of pores (open pores) appeared on a polishing surface of the polishing pad, and a standard deviation were described in Examples 1 to 10 described hereinafter.

[0093]

A mean value of open pore size of the polishing surface was calculated as follows. Photographs of an area of 5 cm and an area of 10 cm, from an outer peripheral edge of a polishing pad mounted on a polishing platen, a central area part of the polishing pad, and an area of 10 cm and an area of 5 cm, from an inner peripheral edge of the polishing pad, total 5 places, were taken using a microscope (Keyence,

Digital Microscope VHX-900), and average value and a variance (standard deviation) were calculated from open pore sizes of all of openings present in a visual field of observation.

[0094]

The glass substrate after the tertiary polishing was successively subjected to scrub cleaning, ultrasonic cleaning in a state of being dipped in a detergent solution, and ultrasonic cleaning in a state of being dipped in pure water (precision cleaning), and then dried with vapor of isopropyl alcohol.

[0095]

Regarding the main surface of the glass substrate for a magnetic recording medium obtained by the above procedures, microwaviness was evaluated by the method described above.

[0096]

Furthermore, a multilayer film having a magnetic layer was formed on the surface of the glass substrate for a magnetic recording medium obtained by the above procedures to obtain a magnetic recording medium, and a glide height fest and a certification test (MP evaluation) were conducted.

[0097]

Formation of the multilayer film having a magnetic layer on the surface of the glass substrate for a magnetic recording medium was carried out by the following procedures.

[0098]

NiFe layer as a soft magnetic underlayer, Ru layer as a non-magnetic intermediate layer and a granular structure layer of CoCrPtSiO; as a vertical magnetic recording layer were successively laminated on the surface of the glass substrate for a magnetic recording medium having been subjected to cleaning before film formation, using an in-line sputtering apparatus. A diamond-like carbon film was then formed as a protective layer with a CVD method. Thereafter, a lubricating film having perfluoropolyether was formed with a dipping method.

[0099]

Processing conditions of finish polishing (tertiary polishing) of the main surface are described in the following Examples 1 to 10. Examples 1 to 6 are

Invention Examples, and Examples 7 to 10 are Comparative Examples.

[0100]

Maximum value (3) of the rate of change of microwaviness to the adjacent evaluation area, average value (nm) of microwaviness (nWq) and standard deviation (nm), in the entire surface of the main surface of the glass substrates for a magnetic recording medium processed under the processing conditions of Examples 1 to 10 are shown in Table 1. Glide height (nm) of a magnetic recording medium and the ratio (%) of judgment A in MP evaluation are also shown in Table 1. (Example 1)

The glass substrate for a magnetic recording medium, the main surfaces of which having been subjected up to the secondary polishing by the above procedures, was polished in finish polishing (tertiary polishing step) of the main surfaces using a soft urethane polishing pad having a mean value of an open pore size of openings on a polishing surface of 5 um and a standard deviation of 2 um under a main polishing pressure of 8 kPa.

The glass substrate after polishing the main surfaces was subjected to precision cleaning as described above to obtain a glass substrate for a magnetic recording medium.

Multilayer film having a magnetic layer was formed on the surface of the glass substrate for a magnetic recording medium to obtain a magnetic recording medium, and a glide height test and MP evaluation were performed. (Example 2)

A glass substrate for a magnetic recording medium and a magnetic recording medium (magnetic disk) were produced in the same manner as in Example 1, except that in the finish polishing (tertiary polishing step) of the main surface polishing, the polishing pressure was changed to 10 kPa. The glass substrate for a magnetic recording medium and magnetic recording medium obtained were evaluated. The results are shown in Table 1. {Example 3)

A glass substrate for a magnetic recording medium and a magnetic recording medium (magnetic disk) were produced in the same manner as in Example 1, except that in the finish polishing (tertiary polishing step) of the main surface polishing, the polishing pressure was changed to 12 kPa. The glass substrate for a magnetic recording medium and magnetic recording medium obtained were evaluated. The results are shown in Table 1. (Example 4)

A glass substrate for a magnetic recording medium and a magnetic recording medium (magnetic disk) were produced in the same manner as in Example 1, except that in the finish polishing (tertiary polishing step) of the main surface polishing, a soft urethane polishing pad having a mean value of an open pore size of 8 um and a standard deviation of 2 um was used, and the polishing pressure was changed to 8 kPa. The glass substrate for a magnetic recording medium and magnetic recording medium obtained were evaluated. The results are shown in Table 1. (Example 5)

A glass substrate for a magnetic recording medium and a magnetic recording medium (magnetic disk) were produced in the same manner as in Example 1, except that in the finish polishing (tertiary polishing step) of the main surface polishing, a soft urethane polishing pad having a mean value of an open pore size of 8 um and a standard deviation of 2 um was used, and the polishing pressure was changed to 10 kPa. The glass substrate for a magnetic recording medium and magnetic recording medium obtained were evaluated. The results are shown in Table 1. (Example 6)

A glass substrate for a magnetic recording medium and a magnetic recording medium (magnetic disk) were produced in the same manner as in Example 1, except that in the finish polishing (tertiary polishing step) of the main surface polishing, a soft urethane polishing pad having a mean value of an open pore size of 8 pm and a standard deviation of 2 um was used, and the polishing pressure was changed to 12 kPa. The glass substrate for a magnetic recording medium and magnetic recording medium obtained were evaluated. The results are shown in Table 1. (Example 7)

A glass substrate for a magnetic recording medium and a magnetic recording medium (magnetic disk) were produced in the same manner as in Example 1, except that in the finish polishing (tertiary polishing step) of the main surface polishing, a soft urethane polishing pad having a mean value of an open pore size of 12 um and a standard deviation of 3 um was used, and the polishing pressure was changed to 10 kPa.

The glass substrate for a magnetic recording medium and magnetic recording medium obtained were evaluated. The results are shown in Table 1. (Example 8)

A glass substrate for a magnetic recording medium and a magnetic recording medium (magnetic disk) were produced in the same manner as in Example 1, except that in the finish polishing (tertiary polishing step) of the main surface polishing, a soft urethane polishing pad having a mean value of an open pore size of 20 pm and a standard deviation of 5 um was used, and the polishing pressure was changed to 10 kPa.

The glass substrate for a magnetic recording medium and magnetic recording medium obtained were evaluated. The results are shown in Table 1. (Example 9)

A glass substrate for a magnetic recording medium and a magnetic recording medium (magnetic disk) were produced in the same manner as in Example 1, except that in the finish polishing (tertiary polishing step) of the main surface polishing, a soft urethane polishing pad having a mean value of an open pore size of 20 pm and a standard deviation of 8 jum was used, and the polishing pressure was changed to 10 kPa.

The glass substrate for a magnetic recording medium and magnetic recording medium obtained were evaluated. The results are shown in Table 1. (Example 10)

A glass substrate for a magnetic recording medium and a magnetic recording medium (magnetic disk) were produced in the same manner as in Example 1, except that in the finish polishing (tertiary polishing step) of the main surface polishing, a soft urethane polishing pad having a mean value of an open pore size of 40 um and a standard deviation of 10 pm was used, and the polishing pressure was changed to 10 kPa. The glass substrate for a magnetic recording medium and magnetic recording medium obtained were evaluated. The results are shown in Table 1.

[0101]

It is seen from the results of Table 1 that the magnetic recording media manufactured using the glass substrates for a magnetic recording medium of Examples 1 to 6 satisfying the requirements of the present invention each are that the glide height is small as 2.0 nm or less, and a distance between a magnetic head and a magnetic recording medium can be decreased.

[0102]

Furthermore, the ratio of judgment A in MP evaluation is about 60% or more, and it is seen that the ratio is considerably high value as compared with that of the magnetic recording media of Examples 7 to 10 that do not satisfy the requirements of the present invention.

[0103]

The reason for this is considered as follows. In the magnetic recording media using the glass substrates for a magnetic recording medium of Examples 1 to 6, because a distance between a magnetic disk and a magnetic head stabilizes, generation of magnetic noise was suppressed, and as a result, read/write precision of recording could be improved and recording density could be increased.

[0104]

Q

—= fan) c. = 0

Q, < + ) oO oo ~~

L

3 =, < — < N=

Eo ~ S g |~| &

A > o .

Q

= tn a, 0 — on —| =~

Em ow =| 8 |= ® i |e 2 —~

Eo a = EB 8

ES cgQ8>e EE = od Oo Ql = = =| < 88 s= 283 EE na =a SBE TE gE pr > =e e =| 5 an yl = 28 3 =| 5 wm oo ol SE wl

Ea] =. 2 3&5

Ea cu 8 = 2S >=s5ssEN35 (UES

Se 2 8G a = £238 =9¢g

OO mm 52 2&3

So bg = a — o bh Q Bh i x2 SEE [EEE

SE Leg = 95 3 1 9 5 g 7° .2 oO .5 = 9 L gE HET

Am 0 5 g 9 8 Sg E = 2 EQ = 2

[0105]

The present application is based on Japanese Patent Application No. 2011- 226946 filed on October 14, 2011, and the contents are incorporated herein by reference.

Claims

[Designation of Document] Claims

[Claim 1] A glass substrate for a magnetic recording medium, having a pair of main surfaces, an outer peripheral surface and an inner peripheral surface, wherein at least one main surface is that: when microwaviness (nWq) is measured in each lattice-shaped evaluation area set to entire surface of the main surface including entire surface of an area to be a recording/reproducing area when a magnetic disk has been formed, an absolute value of variation of microwaviness (AnWq) between one evaluation area and the adjacent evaluation arca is that a ratio (rate of change) to microwaviness of the one evaluation area is 10% or less; and a mean value of the microwaviness (nWq) measured in the each lattice-shaped evaluation area is 0.080 nm or less.
[Claim 2] The glass substrate for a magnetic recording medium according to claim I, wherein the mean value of the microwaviness (n'W¢q) measured in the each lattice- shaped evaluation area is 0.060 nm or less.
[Claim 3] The glass substrate for a magnetic recording medium according to claim 1 or 2, wherein a standard deviation of the microwaviness (nWq) measured in the each lattice- shaped evaluation area is 0.0060 nm or less.
[Claim 4] A magnetic recording medium using the glass substrate for a magnetic recording medium according to any one claims 1 to 3.