JP2005317181A - Glass substrate for magnetic disk and magnetic disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a glass substrate for a magnetic disk capable of manufacturing the magnetic disk which is so formed that a fly-stiction trouble can be prevented and floating characteristics of a magnetic head is made satisfactory even when the diameter of the magnetic disk is made small so as to be used for a small-sized hard disk drive which can be mounted on portable and in-vehicle devices such as a cell phone, a digital camera, a PDA (Personal Digital Assistant) and a car navigator. <P>SOLUTION: In the glass substrate for the magnetic disk, the surface roughness of the substrate in the circumferential direction is increased from the outer peripheral side to the inner peripheral side of a main surface by forming an anisotropic texture on the main surface thereof in the approximately circumferential direction. Also, the ratio (Ra-c/Ra-r) of the arithmetic average roughness (Ra-c) of the surface in the circumferential direction to the arithmetic average roughness (Ra-r) of the surface in the radial direction is increased from the outer peripheral side to the inner peripheral side of the main surface. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a magnetic disk glass substrate and a magnetic disk used in a hard disk drive (HDD) which is a magnetic disk device.

  Today, information recording technology, particularly magnetic recording technology, is required to undergo dramatic technological innovation with the development of the so-called IT industry. Unlike other magnetic recording media such as magnetic tapes and flexible disks, the magnetic disk mounted on a hard disk drive (HDD), which is a magnetic disk device used as a computer storage, is rapidly increasing in information recording density. Has been continued. The information capacity that can be stored in the personal computer device has been dramatically increased, supported by the increase in the information recording density described above.

  Such a magnetic disk is configured by forming a magnetic layer or the like on a substrate such as an aluminum alloy substrate. In a hard disk drive, a magnetic head flies over a magnetic disk rotated at high speed. This magnetic head records information signals as magnetic patterns on the magnetic layer and reproduces them.

  Therefore, a magnetic disk used in such a hard disk drive is required to have excellent magnetic characteristics in the flying direction of the magnetic head. Therefore, for example, as described in Patent Document 1, by performing concentric texture processing on the main surface of the magnetic disk substrate, the magnetic characteristics of the magnetic disk are given magnetic anisotropy in the circumferential direction, Techniques have been proposed for improving the magnetic characteristics of a magnetic recording medium and increasing the recording density.

  In recent years, there has been an increasing demand for mounting a hard disk drive on a portable device (so-called “notebook personal computer device” or the like) (so-called “mobile use”). Accordingly, a glass substrate that is a high-strength and high-rigidity material and has high impact resistance has been adopted as a substrate for a magnetic disk. Further, since the glass substrate can easily obtain a smooth surface, the flying height of the magnetic head that performs recording and reproduction while flying over the magnetic disk can be reduced. For this reason, if a glass substrate is used as a time disk substrate, a magnetic disk having a high information recording density can be obtained. That is, it can be said that the glass substrate is a substrate excellent in compatibility with the low flying height of the magnetic head.

  As such a glass substrate for a magnetic disk, for example, as described in Patent Document 2, the magnetic characteristics and recording / reproduction characteristics of the magnetic disk are improved by performing concentric texture processing on the main surface of the substrate. There have been proposals for improving and contributing to an increase in information recording density.

  On the other hand, in order to increase the information recording capacity of the magnetic disk, it is necessary to reduce the area of a useless area where information signals are not recorded on the magnetic disk. Therefore, instead of the conventionally used CSS method (“Contact Start Stop method”), the LUL method (“load unload”) that can increase the information recording capacity is used as a hard disk drive start / stop method. (Load Unload) method, also known as “ramp load method”) is being introduced.

  In the CSS system, it is necessary to provide a CSS zone on the magnetic disk on which the magnetic head is placed when the magnetic disk is not used (stopped).

  On the other hand, in the LUL system, when the magnetic disk is not used (stopped), the magnetic head moves to the outer peripheral side of the magnetic disk and is retracted from and supported by the magnetic disk. Therefore, unlike the CSS method, the magnetic head and the magnetic disk do not come into contact with each other, and it is not necessary to provide an uneven shape for preventing adsorption as in the CSS zone on the magnetic disk. For this reason, in the LUL method, the main surface of the magnetic disk can be extremely smoothed.

  Compared with the CSS magnetic disk, the magnetic head flying height can be further reduced in the LUL magnetic disk, and the S / N ratio (Signal Noise Ratio) of the recording signal can be improved. There is an advantage that the recording density can be increased.

  Due to such a decrease in the flying height of the magnetic head accompanying the introduction of the LUL system, it has been required that the magnetic head operate stably even at a very narrow flying height of 10 nm or less. However, when flying the magnetic head over the magnetic disk with a very narrow flying height, there has been a problem that fly stiction failure frequently occurs.

  The fly stiction failure is a failure in which the magnetic head flying and flying over the magnetic disk modulates the flying posture and the flying height, thereby causing irregular reproduction output fluctuations. Further, when this fly stiction failure occurs, a head crash failure may occur in which the flying magnetic head contacts the magnetic disk.

  In the conventional hard disk drive, in order to prevent such fly stiction failure, the relative linear velocity between the magnetic disk and the magnetic head is increased by increasing the rotational speed of the magnetic disk, Stabilization of flying performance has been achieved by the structure of the head.

JP 2002-30275 A JP 2002-32909 A

  As described above, in the recent magnetic disk, the spacing loss between the magnetic disk and the magnetic head is improved and the S / N ratio of the recording signal is improved. As a result, the information recording density is 40 per square inch. Over the gigabit, the ultra high recording density exceeding 100 gigabit per square inch is also being realized.

  The recent magnetic disks that have achieved such high information recording density have the feature that they can store a practically sufficient amount of information even with a much smaller disk area than conventional magnetic disks. doing. In addition, the magnetic disk has a feature that information recording speed and reproduction speed (response speed) are extremely fast compared with other information recording media, and information can be written and read at any time. .

  As a result of attention paid to various features of such magnetic disks, in recent years, so-called mobile phones, digital cameras, portable information devices (for example, PDA (personal digital assistant)), car navigation systems, etc. Thus, a small hard disk drive that is much smaller than a personal computer device and can be mounted on a device that requires a high response speed has been demanded. Specifically, for example, there is a demand for a small hard disk drive equipped with a magnetic disk manufactured using a substrate having an outer diameter of 50 mm or less and a plate thickness of 0.5 mm or less.

  In a magnetic disk having an outer diameter of 50 mm or less used in such a small hard disk drive, the relative linear velocity between the magnetic disk and the magnetic head is reduced in order to reduce both the outer diameter and the inner diameter. Decreases. Also, as the diameter of the magnetic disk is reduced, the spindle motor that rotates the magnetic disk is also downsized, and it is not easy to further increase the rotation speed of the magnetic disk. For this reason, there is a possibility that the influence on the flying posture and the flying height and the occurrence of the fly stiction failure as described above cannot be sufficiently prevented.

  Furthermore, since the magnetic head is reduced in size as the diameter of the magnetic disk is reduced, the flying stability of the magnetic head may be reduced.

  Therefore, the present invention has been made in view of the above-described circumstances, and a first object thereof is, for example, a portable information device such as a so-called mobile phone, digital camera, portable “MP3 player”, PDA, or the like. Or, even if the diameter is reduced so that it can be used for small hard disk drives that can be mounted on highly portable equipment such as in-vehicle equipment such as a “car navigation system”, fly stiction failure occurs. It is an object of the present invention to provide a magnetic disk capable of sufficiently preventing the occurrence of such a problem and to provide a glass substrate for a magnetic disk that makes it possible to manufacture such a magnetic disk.

  Further, as described above, in the case of a disk having a small diameter (such as 1 inch or 0.85 inch) due to a reduction in the diameter of the magnetic disk, the magnetic disk and the magnetic head on the inner circumference side (hereinafter referred to as ID side) are particularly important. Since the relative linear velocity between them becomes slow, the magnetic head tends to fall on the magnetic disk. In particular, the above phenomenon tends to occur during decompression. Therefore, touch down pressure (hereinafter referred to as TDO (Touch Down Pressure)) measurement and take-off pressure (hereinafter referred to as TOP (Take Off Pressure)) measurement are performed as evaluation of such floating improvement.

  In addition, portable devices (such as mobile phones, digital cameras, digital video cameras, portable music players, PDAs, etc.) incorporating a magnetic disk device as described above are used in environments where the atmospheric pressure changes due to portability, such as climbing and in airplanes. There is also a demand to use it. However, in such an environment where the change in atmospheric pressure is large, the atmospheric pressure inside the magnetic disk device is also affected by the change in atmospheric pressure in the usage environment, and the magnetic head tends to fall on the magnetic disk. For this reason, it is desired to improve the values of TDO (Touch Down Pressure) and TOP (Take Off Pressure) and the difference ΔP. In view of the above problems, a second object of the present invention is to provide a magnetic disk and a magnetic disk glass substrate capable of improving the flying characteristics by improving the TOP.

  As a result of conducting research to achieve the first object, the present inventor has found that the above problem can be solved by the following means. A texture (for example, a streak-like texture, hereinafter referred to as “anisotropic texture”) in which the uneven shape is anisotropically distributed with respect to the main surface of the magnetic disk glass substrate is the circumference of the magnetic disk glass substrate. When forming in a state of crossing each other with a directional component, the surface roughness in the circumferential direction of the glass substrate for magnetic disk on the main surface increases from the outer peripheral side to the inner peripheral side of the magnetic disk glass substrate. did. This anisotropic texture exhibited the effect of imparting magnetic anisotropy to the magnetic layer formed on the main surface, and at the same time, stabilized the flying characteristics of the magnetic head, particularly on the inner peripheral side.

  Further, when the angle (cross angle) at which the anisotropic textures intersect with the main surface of the glass substrate for magnetic disk is increased from the outer peripheral side to the inner peripheral side of the entire main surface, this anisotropy The texture exerts the effect of imparting magnetic anisotropy to the magnetic layer formed on the main surface, and at the same time, it can stabilize the flying characteristics of the magnetic head, particularly on the inner peripheral side, and solve the above problems. I found it.

  Further, as a result of researches to achieve the second object, the present inventor has found a solution to the surface roughness of the magnetic disk substrate in the same manner as the means for achieving the first object. That is, since the surface roughness of the magnetic disk is affected by the surface roughness of the magnetic disk substrate before forming the magnetic recording layer, the surface roughness of the magnetic disk can be controlled by controlling the surface roughness of the substrate. Controlled. It has been found that the TOP can be influenced by making the surface roughness of the magnetic disk surface different between the inner and outer peripheral sides.

  Specifically, in order to increase the surface roughness on the ID side of the magnetic disk, the surface roughness on the ID side of the magnetic disk substrate was increased to increase the surface roughness on the ID side of the magnetic disk. The surface roughness of the magnetic disk substrate is applied so as to increase continuously or stepwise from the outer peripheral side (hereinafter referred to as OD side) toward the ID side. As a result, even in a magnetic disk having a magnetic film formed on a substrate, the surface roughness increases continuously or stepwise from the OD side to the ID side.

  The anisotropic texture is formed in the circumferential direction on the main surface of the magnetic disk glass substrate, so that when the magnetic layer is formed on the magnetic disk glass substrate, the magnetic anisotropy of the magnetic layer is formed. It acts to induce the (magnetization easy axis) in the circumferential direction. Such an anisotropic texture can be formed by, for example, mechanical polishing (also called mechanical texture processing).

  The present invention has the following configuration.

[Configuration 1]
The glass substrate for a magnetic disk according to the present invention is a glass substrate for a magnetic disk mounted on a hard disk drive, and the surface roughness in the circumferential direction of the glass substrate for the magnetic disk on the main surface is the entire main surface. It increases from the outer peripheral side toward the inner peripheral side.

[Configuration 2]
The glass substrate for a magnetic disk according to the present invention is the glass substrate for a magnetic disk according to Configuration 1, wherein the surface roughness of the main surface in the circumferential direction of the glass substrate for the magnetic disk is from the outer peripheral side of the entire main surface. It is characterized by increasing continuously or stepwise toward the inner peripheral side.

[Configuration 3]
The glass substrate for a magnetic disk according to the present invention is the glass substrate for a magnetic disk according to Configuration 1 or Configuration 2, wherein the main surface has a radius of 6 mm from the center of the glass substrate for the magnetic disk. When the arithmetic average roughness (Ra-c) of the surface in the circumferential direction of the glass substrate is 0.25 nm or more and the radius of the main surface is 11 mm from the center of the glass substrate for magnetic disk, the glass for magnetic disk is used. The arithmetic average roughness (Ra-c) of the surface in the circumferential direction of the substrate is 0.24 nm or less.

[Configuration 4]
A glass substrate for a magnetic disk according to the present invention is the glass substrate for a magnetic disk according to any one of configurations 1 to 3, wherein the arithmetic average of the surface in the circumferential direction of the glass substrate for the magnetic disk on the main surface The ratio [Ra-c / Ra-r] to the arithmetic average roughness (Ra-r) of the surface of the glass substrate for magnetic disk in the radial direction on the main surface of the roughness (Ra-c) is the outer circumference of the entire main surface. It increases from the side toward the inner peripheral side.

[Configuration 5]
A glass substrate for a magnetic disk according to the present invention is the glass substrate for a magnetic disk according to any one of Structures 1 to 4, wherein the magnetic disk on the main surface is located on the main surface at a radius of 6 mm from the center of the glass substrate for the magnetic disk. Ratio of the arithmetic average roughness (Ra-c) of the surface of the glass substrate in the circumferential direction to the arithmetic average roughness (Ra-r) of the surface of the glass substrate for the magnetic disk in the radial direction at the main surface [Ra- c / Ra-r] is 0.61 or more and the surface of the main surface in the circumferential direction of the glass substrate for the magnetic disk at a location having a radius of 11 mm from the center of the glass substrate for the magnetic disk on the main surface. The ratio [Ra-c / Ra-r] of the average roughness (Ra-c) to the arithmetic average roughness (Ra-r) of the surface of the glass substrate for a magnetic disk in the radial direction on the main surface is 0.6. Is characterized in that the or less.

[Configuration 6]
The glass substrate for a magnetic disk according to the present invention is a glass substrate for a magnetic disk mounted on a hard disk drive, and the texture intersects with the circumferential component of the glass substrate for the magnetic disk on the main surface. The angle at which the textures intersect with each other is increased from the outer peripheral side to the inner peripheral side of the entire main surface of the glass substrate for magnetic disks.

[Configuration 7]
The glass substrate for a magnetic disk according to the present invention is the glass substrate for a magnetic disk according to Configuration 6, wherein the angle at which the textures intersect is from the outer peripheral side to the inner peripheral side of the entire main surface of the glass substrate for magnetic disk. It is characterized by increasing continuously.

[Configuration 8]
The glass substrate for a magnetic disk according to the present invention is the glass substrate for a magnetic disk according to Configuration 6, wherein an angle at which the textures intersect at a radius of 6 mm from the center of the glass substrate for the magnetic disk on the main surface is 5 The angle at which the texture intersects is 4.5 ° or less at a location of 0 ° or more and a radius of 11 mm from the center of the magnetic disk glass substrate on the main surface.

[Configuration 9]
A glass substrate for a magnetic disk according to the present invention is the glass substrate for a magnetic disk according to any one of configurations 1 to 8, and is formed into a magnetic disk by forming a magnetic layer on a main surface. It is a glass substrate for a magnetic disk, and is characterized in that a texture imparting magnetic anisotropy to the magnetic layer is formed on the main surface.

[Configuration 10]
A glass substrate for a magnetic disk according to the present invention is the glass substrate for a magnetic disk according to any one of Configurations 1 to 9, and is a 1-inch hard disk drive or a magnetic having a smaller diameter than the 1-inch hard disk drive. It is a glass substrate for a magnetic disk mounted on a hard disk drive using a disk.

[Configuration 11]
A magnetic disk glass substrate according to the present invention is the magnetic disk glass substrate according to any one of Structures 1 to 10, wherein the magnetic disk is mounted on a hard disk drive that performs a start / stop operation by a load / unload method. It is a glass substrate for disks.

[Configuration 12]
The glass substrate for a magnetic disk according to the present invention has a first region on the main surface and a second region that is rougher than the surface roughness of the first region, and the first region is the first on the circular plate-like glass substrate. It exists in the outer peripheral side rather than 2 area | regions.

[Configuration 13]
The glass substrate for a magnetic disk according to the present invention is the glass substrate for a magnetic disk according to Configuration 12, wherein the first region is a region where the magnetic head is introduced into the magnetic disk.

[Configuration 14]
A magnetic disk according to the present invention includes the glass substrate for a magnetic disk according to any one of Configurations 1 to 13, and at least a magnetic layer is formed on the glass substrate for a magnetic disk. To do.

[Configuration 15]
A magnetic disk according to the present invention is the magnetic disk according to Configuration 14, characterized in that the roughness of any region on the main surface of the magnetic disk is smaller than the surface roughness of the magnetic head used. To do.

  In addition, the arithmetic mean roughness (Ra-c) of the surface of the main surface of the glass substrate for magnetic disks in the circumferential direction is a measurement probe when measuring a 5 μm square area on the main surface with an atomic force microscope. Is the arithmetic average roughness of the surface measured when scanning in the circumferential direction of the glass substrate for magnetic disk.

  In addition, the arithmetic average roughness (Ra-r) of the surface of the main surface of the magnetic disk glass substrate in the radial direction is a measurement probe when measuring a 5 μm square castle on the main surface with an atomic force microscope. Is the arithmetic mean roughness of the surface measured when scanning in the radial direction of the glass substrate for magnetic disk.

  The arithmetic mean roughness (Ra) of the surface of the main surface of the glass substrate for magnetic disk means that when measuring a 5 μm square area on the main surface with an atomic force microscope, the measuring probe is attached to the glass substrate for magnetic disk. It shows the arithmetic mean roughness of the surface measured when scanned in the radial direction. The arithmetic average roughness is a value calculated in accordance with Japanese Industrial Standard (JIS) B0601.

  In the magnetic disk glass substrate according to the present invention, the surface roughness in the circumferential direction of the magnetic disk glass substrate on the main surface increases from the outer peripheral side of the entire main surface toward the inner peripheral side, The effect of imparting magnetic anisotropy to the magnetic layer formed on the main surface is obtained, and at the same time, the flying performance of the magnetic head is stabilized particularly on the inner peripheral side.

  Further, the arithmetic average roughness (Ra-c) of the surface in the circumferential direction of the glass substrate for magnetic disk is set to 0.25 nm or more at a location of 6 mm radius from the center of the glass substrate for magnetic disk on the main surface, and the main surface In this case, the arithmetic average roughness (Ra-c) of the surface in the circumferential direction of the glass substrate for magnetic disk is set to 0.24 nm or less at a location having a radius of 11 mm from the center of the glass substrate for magnetic disk. In particular, the flying performance of the magnetic head can be sufficiently stabilized on the inner peripheral side.

  Further, in the glass substrate for magnetic disk, the arithmetic average roughness (Ra-r) of the surface in the radial direction of the surface in the circumferential direction of the glass substrate for magnetic disk (Ra-c) on the main surface in the radial direction. ), That is, [Ra-c / Ra-r] increases from the outer peripheral side to the inner peripheral side of the main surface, so that the magnetic anisotropy is increased in the magnetic layer formed on the main surface. In addition, the flying performance of the magnetic head is stabilized especially on the inner peripheral side.

  In addition, the magnetic disk on the main surface has an arithmetic mean roughness (Ra-c) of the surface in the circumferential direction of the glass substrate for the magnetic disk on the main surface at a location of a radius of 6 mm from the center of the glass substrate for the magnetic disk on the main surface. The ratio [Ra-c / Ra-r] to the arithmetic average roughness (Ra-r) of the surface of the glass substrate in the radial direction is 0.61 or more, and a radius of 11 mm from the center of the glass substrate for the magnetic disk on the main surface The arithmetic average roughness of the surface in the radial direction of the glass substrate for the magnetic disk in the main surface (Ra-c) of the surface of the glass substrate for the magnetic disk on the main surface in the circumferential direction (Ra-c) By setting the ratio [Ra-c / Ra-r] to Ra-r) to 0.60 or less, the flying characteristics of the magnetic head can be sufficiently stabilized especially on the inner peripheral side of the main surface. That.

  In addition, the texture formed so as to intersect each other with the circumferential component of the magnetic disk glass substrate on the main surface has an angle (cross angle) at which the textures intersect the outer periphery of the entire main surface of the magnetic disk glass substrate. Since the magnetic layer is formed so as to increase from the side toward the inner peripheral side, an effect of imparting magnetic anisotropy to the magnetic layer formed on the main surface can be obtained. The flying property of the head is stabilized.

  The angle at which the textures in the magnetic disk glass substrate intersect is specified by Fourier transform of a measurement result obtained by measuring an area of 5 μm square on the main surface with an atomic force microscope. Can be identified accurately.

  Further, at a location having a radius of 6 mm from the center of the glass substrate for magnetic disk on the main surface, the angle at which the textures intersect is 5.0 ° or more, and at a location having a radius of 11 mm from the center of the glass substrate for magnetic disk on the main surface, By setting the angle at which the textures intersect to be 4.5 ° or less, the flying characteristics of the magnetic head can be sufficiently stabilized, particularly on the inner peripheral side of the main surface.

  Since the magnetic disk according to the present invention has at least a magnetic layer formed on the above-mentioned magnetic disk glass substrate, for example, even when the outer diameter is reduced to 50 mm or less. To provide a magnetic disk in which a magnetic layer formed on a main surface has magnetic anisotropy, stabilizes the flying performance of a magnetic head on the inner peripheral side, and has excellent load / unload durability. Can do. In other words, this magnetic disk can also be used favorably as a magnetic disk mounted on a hard disk drive that performs a start / stop operation by the LUL (load / unload) method.

  Furthermore, by making the surface roughness different on the ID side (inner circumference side) and OD side (outer circumference side) of the glass substrate for magnetic disk, compared with a magnetic disk having a constant surface roughness from the ID side to the OD side. Thus, the TOP on the ID side can be improved. Therefore, even if the atmospheric pressure in the hard disk drive drops to TDP and the magnetic head comes into contact with the magnetic disk, it rises immediately because the TOP is low, and the magnetic head moves away from the magnetic disk.

  Also for magnetic disks suitable for hard disk drives with good flying characteristics, which makes it difficult for magnetic heads to fall on magnetic disks and rise easily when dropped even in situations where there is a large change in atmospheric pressure, such as climbing or in airplanes. A substrate and a magnetic disk can be provided.

  Therefore, according to the present invention, for example, a so-called mobile phone, a digital camera, a portable “MP3 player”, a portable information device such as a PDA, or an in-vehicle device such as a “car navigation system” is very portable. It is possible to provide a magnetic disk capable of sufficiently preventing the occurrence of fly stiction failure even when the diameter is reduced so that it can also be used for a small hard disk drive that can be mounted on a high-end device. Thus, a glass substrate for a magnetic disk capable of manufacturing such a magnetic disk can be provided.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

  The glass substrate for a magnetic disk according to the present invention is obtained by grinding a main surface of a plate glass to obtain a glass base material, cutting the glass base material to cut out the glass disk, and polishing the main surface of the glass disk. It is manufactured through chemical strengthening and texturing.

  As plate glass used for the grinding treatment, plate glass having various shapes can be used. The plate-like glass may have a rectangular shape or a disk shape (disk shape). The disk-shaped plate-like glass can be ground using a grinding apparatus used in the manufacture of a conventional magnetic disk glass substrate, and a highly reliable process can be performed at low cost.

  The size of the plate glass needs to be larger than the glass substrate for magnetic disk to be manufactured. For example, when manufacturing a glass substrate for a magnetic disk used for a magnetic disk mounted on a “1-inch hard disk drive” or a small hard disk drive having a size smaller than that, the diameter of the glass substrate for the magnetic disk is Since the diameter is approximately 20 mm to 30 mm, the diameter of the disk-shaped plate glass is 30 mm or more, preferably 48 mm or more. In particular, if a disk-shaped plate glass having a diameter of 65 mm or more is used, a glass substrate for a magnetic disk used for a magnetic disk mounted on a plurality of “1-inch hard disk drives” is collected from a single sheet of glass. It is suitable for mass production. The upper limit of the size of the plate-like glass is not particularly limited, but in the case of a disk-like plate-like glass, it is preferable to use one having a diameter of 100 mm or less.

  This plate-like glass can be manufactured using a known manufacturing method such as a press method, a float method, or a fusion method, using, for example, molten glass as a material. Of these, plate glass can be produced at low cost by using the pressing method.

  Further, the material of the plate glass is not particularly limited as long as it is chemically strengthened glass, but aluminosilicate glass can be preferably mentioned. In particular, aluminosilicate glass containing lithium is preferable. Such an aluminosilicate glass can accurately obtain a compressive stress layer having a preferable compressive stress and a tensile stress layer having a tensile stress by an ion exchange type chemical strengthening treatment, in particular, a low temperature ion exchange type chemical strengthening treatment. Particularly preferred as a material for chemically strengthened glass substrates for magnetic disks.

The composition ratio of such aluminosilicate glass, a SiO _2, 58 to 75 wt%, the _Al 2 _{O 3,} 5 to 23 wt%, the Li ₂ O, 3 to 10 wt%, a Na ₂ O, It is preferable to contain 4 to 13% by weight as a main component.

Furthermore, the composition ratio of the aluminosilicate glass is as follows: SiO ₂ is 62 to 75 wt%, Al ₂ O ₃ is 5 to 15 wt%, Li ₂ O is 4 to 10 wt%, Na ₂ O is 4 wt%. to 12 wt%, the ZnO _2, 5.5 to 15 wt%, with containing as a main component, the weight ratio of Na ₂ O and _{ZnO 2 (Na 2 O / ZnO} 2) is 0.5 to 2.0 The weight ratio of Al ₂ O ₃ to ZnO ₂ (Al ₂ O ₃ / ZnO ₂ ) is preferably 0.4 to 2.5.

Further, in order to eliminate the protrusions on the surface of the glass disk caused by the undissolved material of ZnO ₂ , in terms of mol%, SiO ₂ is 57 to 74%, ZnO ₂ is 0 to 2.8%, Al the ₂ O _3, 3 to 15%, the LiO _2, 7 to 16%, a Na ₂ O, it is preferred to use chemical strengthening glass containing 4 to 14%.

  When such an aluminosilicate glass is subjected to a chemical strengthening treatment, the bending strength is increased and the Knoop hardness is excellent.

  The grinding process is a process aimed at improving the shape accuracy (for example, flatness) and dimensional accuracy (for example, plate thickness accuracy) of the main surface of the workpiece, that is, the sheet glass. In this grinding process, the main surface of the plate glass is ground by pressing a grindstone or a surface plate against the main surface of the plate glass and relatively moving the plate glass and the grindstone or the surface plate. Is done. Such a grinding process can be performed using a double-side grinding apparatus using a planetary gear mechanism.

  Moreover, in this grinding process, it is good to wash a sludge (grinding waste) from a grinding surface by supplying a grinding liquid to the main surface of sheet glass, and to cool a grinding surface. Furthermore, a slurry in which free abrasive grains are contained in this grinding liquid may be supplied to the main surface of the workpiece for grinding.

  As a grindstone used in the grinding process, a diamond grindstone can be used. Further, as the free abrasive grains, it is preferable to use hard abrasive grains such as alumina abrasive grains, zirconia abrasive grains, or silicon carbide abrasive grains.

  By this grinding treatment, the shape accuracy of the sheet glass is improved, the main surface is flattened, and the glass base material is reduced until the sheet thickness reaches a predetermined value.

  In the present invention, the main surface of the glass base material is flattened by a grinding process, and the plate thickness is reduced, so that the glass base material can be cut and a glass disk cut out from the glass base material. it can. That is, when a glass disk is cut out from the glass base material, it is possible to prevent the occurrence of defects such as chipping, cracking and cracking.

  The flatness of the glass base material is, for example, preferably 30 μm or less and more preferably 10 μm or less in 7088 mm 2 (the area of a circle having a diameter of 95 mm). The plate thickness of the glass base material is preferably 2 mm or less, and more preferably 0.8 mm or less. If the glass base material has a thickness of less than 0.2 mm, the glass base material itself may not be able to withstand the load in the process of cutting out the glass disk. Therefore, the thickness of the glass base material is 0.2 mm. The above is preferable. If the thickness of the glass base material exceeds 2 mm, the thickness may be too large to be precisely cut out, and defects such as chipping, cracking, and cracking may occur when the glass disk is cut out. .

  The glass base material needs to be larger than the magnetic disk glass substrate to be manufactured. For example, when manufacturing a glass substrate for a magnetic disk used for a magnetic disk mounted on a “1-inch hard disk drive” or a small hard disk drive having a size smaller than that, the diameter of the glass substrate for the magnetic disk is approximately Since it is about 20 mm to 30 mm, the diameter of the glass base material is preferably 30 mm or more, and preferably 48 mm or more. In particular, if a glass base material having a diameter of 65 mm or more is used, a plurality of glass disks to be used as a magnetic disk glass substrate used for a magnetic disk mounted on a “1-inch hard disk drive” are cut out from a single glass base material. It is suitable for mass production. The upper limit of the size of the glass base material need not be particularly limited, but in the case of a disk-shaped glass base material, the diameter is preferably 100 mm or less.

  The glass base material can be cut using a cutting blade or a grindstone containing a material harder than glass, such as a diamond cutter or a diamond drill. The glass base material may be cut using a laser cutter. However, it may be difficult to precisely cut out a small glass disk having a diameter of 30 mm or less using a laser cutter, and it is preferable to use a cutting blade or a grindstone because it can be easily cut out.

  Here, as a size of the glass disk cut out from the glass base material, a particularly preferable size is a diameter of 30 mm or less.

  Next, using a cylindrical grindstone, a circular hole having a predetermined diameter is formed in the central portion of the glass disk, and the outer peripheral end surface is ground to a predetermined diameter, and then the outer peripheral end surface and the inner peripheral end surface are formed. A predetermined chamfering process is performed.

  Then, at least a polishing process is performed on the glass disk cut out from the glass base material, and the main surface of the glass disk is mirror-finished.

  By performing this polishing treatment, cracks on the main surface of the glass disk are removed, and the surface roughness of the main surface is, for example, 7 nm or less for Rmax and 0.7 nm or less for Ra. If the main surface of the glass disk has such a mirror surface, even if the flying height of the magnetic head is 10 nm in a magnetic disk manufactured using this glass disk, for example, a so-called crash failure And thermal asperity failure can be prevented. Further, if the main surface of the glass disk is such a mirror surface, in the chemical strengthening process described later, the chemical strengthening process can be performed uniformly in the fine region of the glass disk, and delayed fracture due to micro cracks can be performed. Can be prevented.

  Rmax is the maximum height (also referred to as Ry), which is the height from the average line to the highest peak (maximum peak height: Rp) and the depth from the average line to the lowest valley bottom (maximum valley depth). The sum is represented by the sum of Rv) (Rp + Rv). The maximum height Rmax is a value calculated in accordance with Japanese Industrial Standard (JIS) B0601.

  This polishing treatment is performed, for example, by pressing a surface plate having a polishing pad (polishing cloth) attached to the main surface of the glass disk and supplying the polishing liquid to the main surface of the glass disk, Is relatively moved, and the main surface of the glass disk is polished. At this time, the polishing liquid may contain polishing abrasive grains. As the abrasive grains, cerium oxide abrasive grains, colloidal silica abrasive grains, or diamond abrasive grains can be used.

  In addition, it is preferable to grind | polish before grind | polishing a glass disk. The grinding process at this time can be performed by the same means as the grinding process for the plate-like glass described above. By performing the polishing process after the glass disk is ground, a mirror-finished main surface can be obtained in a shorter time.

  Moreover, it is preferable that the end surface of the glass disk is mirror-polished. Since the end surface of the glass disk has a cut shape, the generation of particles can be suppressed by polishing this end surface to a mirror surface. In a magnetic disk manufactured using this magnetic disk glass substrate, This is because the so-called thermal asperity failure can be satisfactorily prevented.

  Then, after the glass disk polishing step, chemical strengthening treatment is performed. By performing the chemical strengthening treatment, a high compressive stress can be generated on the surface of the glass substrate for magnetic disk, and the impact resistance can be improved. In particular, when aluminosilicate glass is used as the material of the glass disk, the chemical strengthening treatment can be suitably performed.

  The chemical strengthening treatment is not particularly limited as long as a known chemical strengthening treatment method is used. The chemical strengthening treatment of the glass disk is performed, for example, by bringing the glass disk into contact with a heated chemically strengthened salt, and ions on the surface layer of the glass disk are ion exchanged with ions of the chemically strengthened salt.

  Here, as the ion exchange method, a low temperature type ion exchange method, a high temperature type ion exchange method, a surface crystallization method, a dealkalization method on the glass surface, etc. are known. It is preferable to use a low temperature ion exchange method in which ion exchange is performed in a temperature range not exceeding.

  The low-temperature ion exchange method here refers to an increase in the volume of the ion exchange part by substituting alkali ions in the glass with alkali ions having a larger ion radius than the alkali ions in the temperature range below the annealing point of the glass. This refers to a method of generating a compressive stress on the glass surface layer and strengthening the glass surface layer.

  The heating temperature of the molten salt when performing the chemical strengthening treatment is preferably 280 ° C. to 660 ° C., particularly 300 ° C. to 400 ° C., from the viewpoint that ion exchange is performed satisfactorily. .

  The time for bringing the glass disk into contact with the molten salt is preferably several hours to several tens of hours.

  In addition, before making a glass disc contact with molten salt, it is preferable to heat a glass disc to 100 degreeC thru | or 300 degreeC as preheating. In addition, the glass disk after the chemical strengthening treatment is subjected to cooling, a cleaning process, and the like to be a product (a glass substrate for a magnetic disk).

  In addition, the material of the treatment rod for performing the chemical strengthening treatment is not particularly limited as long as it is excellent in corrosion resistance and has a low dust generation property. Chemically strengthened salt and chemically strengthened molten salt are oxidative and the processing temperature is high, so by selecting materials with excellent corrosion resistance, damage and dust generation are suppressed, resulting in thermal asperity failures and head crashes. It is necessary to suppress. From this point of view, a quartz material is particularly preferable as a material for the treatment rod, but a stainless material, or a martensitic or austenitic stainless material having particularly excellent corrosion resistance can also be used. In addition, although quartz material is excellent in corrosion resistance, since it is expensive, it can select suitably in consideration of profitability.

  The chemically strengthened salt material is preferably a chemically strengthened salt material containing sodium nitrate and / or potassium nitrate. This is because such a chemically strengthened salt can realize predetermined rigidity and impact resistance as a glass substrate for a magnetic disk when chemically strengthening glass, particularly aluminosilicate glass. Next, texture processing is performed on the main surface of the glass disk.

  FIG. 1 is a perspective view illustrating a configuration of a texture processing apparatus that performs texture processing in the present invention.

  In this texture processing, first, as shown in FIG. 1, the glass disk 1 is mounted on the tip side of the chucking shaft 101 of the texture processing device in the circular hole 2 in the center portion. The chucking shaft 101 has a cylindrical tip side divided into a plurality of portions in the axial direction, and the tip side can be expanded in diameter by applying a force from the inner side. By inserting the tip end side of the chucking shaft 101 into the circular hole 2 of the glass disk 1 and expanding the diameter, the glass disk is held by the chucking shaft 101.

  The chucking shaft 101 is rotated around the axis at a predetermined rotational speed as indicated by an arrow A in FIG. 1, and has a predetermined circumference in a direction perpendicular to the axis as indicated by an arrow B in FIG. And reciprocating with amplitude.

  In this texture processing apparatus, the pair of polishing tapes 102 and 103 are fed at a predetermined speed from the supply rolls 102a and 103a to the take-up rolls 102b and 103b as indicated by an arrow C in FIG. Has been wound up. These polishing tapes 102 and 103 are fed at an equal speed while being superposed on each other.

  The glass disk 1 held by the chucking shaft 101 is inserted between a pair of polishing tapes 102 and 103 to be fed at a portion that becomes the main surface. Then, these polishing tapes 102 and 103 are respectively pressed at predetermined pressures by the pair of pressure rollers 104 and 105 against the main surfaces on both sides of the glass disk 1 as indicated by arrows D and E in FIG. It is pressed at. That is, the glass disk 1 is sandwiched between the pair of polishing tapes 102 and 103 on both main surfaces.

  In this state, the chucking shaft 101 is rotated around the axis together with the glass disk 1, and the chucking shaft 101 is reciprocated with a predetermined circumference and amplitude in a direction orthogonal to the axis. At this time, the reciprocating direction of the chucking shaft 101 is a direction orthogonal to the feeding operation direction of the pair of polishing tapes 102 and 103. At this time, a liquid abrasive is supplied between the glass disk 1 and each of the polishing tapes 102 and 103.

  At this time, the glass disk 1 and the polishing tapes 102 and 103 are relatively slidably moved.

  FIG. 2 is a schematic diagram showing the relative sliding movement direction of the glass disk and the polishing tape in the texture processing according to the present invention.

  Since the speed of the feeding operation of each of the polishing tapes 102 and 103 is extremely slow, the relative sliding between the glass disk 1 and each of the polishing tapes 102 and 103 is determined by the rotational speed of the glass disk 1 and the period and amplitude of the reciprocating movement. The relative sliding of each of the polishing tapes 102 and 103 with respect to the glass disk 1 is based on the movement (F) in the circumferential direction (tangential direction) of the glass disk 1 as shown in FIG. The movement (G) swings in a sine curve with respect to the circumferential direction.

  On the main surface of the glass disk 1 on which the texture is formed in this way, the surface roughness in the circumferential direction is smaller than the surface roughness in the radial direction. That is, it can be said that the texture formed in this texture processing is basically an “anisotropic texture” formed along the circumferential direction of the glass disk 1.

  Further, on the main surface of the glass disk 1 with the texture formed in this way, the surface roughness in the circumferential direction of the glass disk 1 increases from the outer peripheral side of the entire main surface toward the inner peripheral side. Therefore, when a magnetic layer is formed on the main surface of the glass disk 1, the effect of imparting magnetic anisotropy to the magnetic layer is obtained, and in addition, the flying performance of the magnetic head is stable particularly on the inner peripheral side. It becomes.

  In the glass substrate for magnetic disk, the arithmetic average roughness (Ra-c) of the surface in the circumferential direction of the glass substrate for magnetic disk at the location of 6 mm radius from the center of the glass substrate for magnetic disk on the main surface. The arithmetic average roughness (Ra-r) of the surface in the circumferential direction of the glass substrate for magnetic disk is 0.24 nm or less at a location where the radius is 11 mm from the center of the glass substrate for magnetic disk on the main surface. It is preferable that In this case, the flying characteristics of the magnetic head can be sufficiently stabilized especially on the inner peripheral side of the main surface.

  Further, on the main surface of the glass disk 1 on which this texture is formed, the arithmetic average roughness (Ra-r) of the surface in the radial direction is calculated with respect to the arithmetic average roughness (Ra-c) of the surface in the circumferential direction. The ratio, that is, [Ra-c / Ra-r] increases from the outer peripheral side to the inner peripheral side of the main surface.

  In this glass substrate for magnetic disk, the arithmetic average roughness (Ra-c) of the surface in the circumferential direction of the glass substrate for magnetic disk on the main surface at a location having a radius of 6 mm from the center of the glass substrate for magnetic disk on the main surface. The ratio [Ra-c / Ra-r] to the arithmetic average roughness (Ra-r) of the surface in the radial direction of the glass substrate for magnetic disk on the main surface is 0.61 or more, and the glass for magnetic disk on the main surface Surface in the radial direction of the glass substrate for magnetic disk in the main surface of the arithmetic average roughness (Ra-c) of the surface in the circumferential direction of the glass substrate for magnetic disk on the main surface at a location of 11 mm radius from the center of the substrate The ratio [Ra-c / Ra-r] to the arithmetic average roughness (Ra-r) is preferably 0.60 or less. In this case, the flying characteristics of the magnetic head can be sufficiently stabilized especially on the inner peripheral side of the main surface.

  Further, the texture formed on the main surface of the glass disk 1 in this way is formed so as to intersect each other with a circumferential component of the glass disk 1 on the main surface, and an angle (cross) between the textures intersects each other. Are formed so as to increase from the outer peripheral side of the main surface of the glass disk 1 toward the inner peripheral side. This is because, on the main surface of the glass disk 1, the tangential speed on the inner peripheral side is slower than that on the outer peripheral side.

  Therefore, when a magnetic layer is formed on the main surface of the glass disk 1, the effect of imparting magnetic anisotropy to the magnetic layer is obtained, and at the same time, the flying performance of the magnetic head is stabilized particularly on the inner peripheral side. Is done.

  The cross angle of this texture can be easily and accurately specified by measuring an area of 5 μm square with an atomic force microscope on the main surface of the glass disk and Fourier transforming the measurement result. .

  In this magnetic disk glass substrate, the angle at which the textures intersect at a radius of 6 mm from the center of the magnetic disk glass substrate on the main surface is 5.0 ° or more, and from the center of the magnetic disk glass substrate on the main surface. It is desirable that the angle at which the textures intersect at a radius of 11 mm is 4.5 ° or less. In this case, the flying characteristics of the magnetic head can be sufficiently stabilized especially on the inner peripheral side of the main surface.

  After the texturing is completed, the glass disk 1 is washed to complete the magnetic disk glass substrate.

  The glass substrate for a magnetic disk according to the present invention manufactured as described above is a glass substrate for a magnetic disk to be mounted on a “1 inch type hard disk drive” or a hard disk drive smaller than the “1 inch type”. It is suitable as. In addition, the diameter of the glass substrate for magnetic disks for manufacturing the magnetic disk mounted in "1 inch type hard disk drive" is about 27.4 mm. Further, the diameter of the glass substrate for magnetic disk for manufacturing the magnetic disk to be mounted on the “0.85 inch type hard disk drive” is about 21.6 mm.

  In the magnetic disk according to the present invention, the magnetic layer formed on the magnetic disk glass substrate can be made of, for example, a cobalt (Co) ferromagnetic material. In particular, it is preferably formed as a magnetic layer made of a cobalt-platinum (Co—Pt) -based ferromagnetic material or a cobalt-chromium (Co—Cr) -based ferromagnetic material that provides a high coercive force. As a method for forming the magnetic layer, a DC magnetron sputtering method can be used.

  In addition, before the magnetic layer is formed, the magnetic characteristics can be improved by subjecting the glass disk to texture processing in the circumferential direction. Moreover, it is preferable to insert an underlayer or the like as appropriate between the glass substrate and the magnetic layer. As the material of these underlayers, an Al—Ru alloy, a Cr alloy, or the like can be used.

  In addition, a protective layer for protecting the magnetic disk from the impact of the magnetic head can be provided on the magnetic layer. As this protective layer, a hard hydrogenated carbon protective layer can be preferably used.

  Furthermore, by forming a lubricating layer made of a PFPE (perfluoropolyether) compound on this protective layer, interference between the magnetic head and the magnetic disk can be reduced. This lubricating layer can be formed, for example, by coating by a dip method.

  Hereinafter, the present invention will be specifically described by giving examples and comparative examples. In addition, this invention is not limited to the structure of these Examples.

[Example (1) (Example of glass substrate for magnetic disk)]
The glass substrate for magnetic disk in the present embodiment described below is produced by the following steps (1) to (8).

(1) Rough grinding step (2) Shape processing step (3) Fine grinding step (4) End mirror processing step (5) First polishing step (6) Second polishing step (7) Chemical strengthening step (8) Texture processing First, a disk-shaped glass base material made of amorphous aluminosilicate glass was prepared. This aluminosilicate glass contains lithium. The composition of this aluminosilicate glass is SiO ₂ 63.6% by weight, Al ₂ O ₃ 14.2% by weight, Na ₂ O 10.4% by weight, Li ₂ O 5.4% by weight. %, ZnO ₂ 6.0 wt%, and Sb ₂ O ₃ 0.4 wt%.

(1) Rough grinding process Using a sheet glass of 0.6 mm thickness formed from a molten aluminosilicate glass as a glass base material, from this sheet glass, a diameter of 28.7 mm and a thickness of 0.6 mm A disk-shaped glass disk was obtained.

As a method for forming the sheet glass, a downdraw method or a float method is generally used. However, in addition to this, a disk-shaped glass base material may be obtained by direct pressing. As the aluminosilicate glass which is the material of the sheet glass, SiO ₂ is 58 to 75 wt%, Al ₂ O ₃ is 5 to 23 wt%, Na ₂ O is 4 to 13 wt%, and Li ₂ O is used. What is necessary is just to contain 3 to 10% by weight.

  Next, a rough grinding process was performed on the glass disk in order to improve dimensional accuracy and shape accuracy. This rough grinding process was performed using abrasive grains of grain size # 400 using a double-side grinding apparatus.

  Specifically, first, using alumina abrasive grains of particle size # 400, setting the load to about 100 kg, and rotating the sun gear and the internal gear, both surfaces of the glass disk housed in the carrier are improved in surface accuracy. It was ground to 0 to 1 μm and surface roughness (Rmax) of about 6 μm.

(2) Shape processing step Next, while using a cylindrical grindstone, a circular hole having a diameter of 6.1 mm was formed in the central portion of the glass disk, and the outer peripheral end face was ground to a diameter of 27.43 mm. Then, predetermined chamfering was performed on the outer peripheral end surface and the inner peripheral end surface. The surface roughness of the end face of the glass disk at this time was about 4 μm in Rmax.

  In general, a “2.5 inch HDD (hard disk drive)” uses a magnetic disk having an outer diameter of 65 mm.

(3) Fine grinding step Next, the grain size of the abrasive grains is changed to # 1000, and the main surface of the glass disk is ground, so that the surface roughness of the main surface is about 2 μm for Rmax and about 0.2 μm for Ra. did.

  By performing this fine grinding step, it is possible to remove the fine uneven shape formed on the main surface in the rough grinding step and the shape processing step which are the previous steps.

  The glass disk after such a precision grinding process was sequentially immersed in each cleaning bath of neutral detergent and pure water to which ultrasonic waves were applied, and ultrasonic cleaning was performed.

(4) End mirror processing step Next, with respect to the end surface of the glass disk, the roughness of the surface of the end surface (the inner peripheral end surface and the outer peripheral end surface) of the glass disc is rotated while rotating the glass disc by brush polishing that has been conventionally used. , Rmax was polished to about 1 μm, and Ra was polished to about 0.3 μm.

  And the main surface of the glass disk which finished the end surface mirror surface process was washed with water.

  In this end mirror processing step, the end surfaces are polished by overlapping the glass disks. At this time, in order to avoid scratches or the like on the main surface of the glass disks, before the first polishing process described later. Alternatively, it is preferably performed before and after the second polishing step.

  By this end mirror processing step, the end surface of the glass disk was processed into a mirror surface state capable of preventing generation of particles and the like. It was 27.4 mm when the diameter of the glass disk was measured after the end surface mirror surface process.

(5) First Polishing Step Next, a first polishing step was performed using a double-side polishing apparatus in order to remove scratches and distortion remaining in the fine grinding step described above.

  In a double-side polishing apparatus, a glass disk held by a carrier is closely attached between an upper and lower surface plate to which a polishing pad is attached, and the carrier is meshed with a sun gear and an internal gear, and the glass disk is connected to an upper and lower surface plate. To pinch. Then, by rotating the sun gear while supplying the polishing liquid between the polishing pad and the polishing surface (main surface) of the glass disk, the glass disk revolves around the internal gear while rotating on the surface plate. Thus, both main surfaces are polished simultaneously.

The same apparatus is used as a double-side polishing apparatus used in the following examples. Specifically, the first polishing step was performed using a hard polisher (hard urethane foam) as the polisher. The polishing conditions were a polishing liquid composed of cerium oxide (average particle size 1.3 μm) and RO water, a load of 100 g / cm ² and a polishing time of 15 minutes. And the glass disk which finished this 1st grinding | polishing process is immersed in each washing | cleaning tank of a neutral detergent, a pure water (1), a pure water (2), IPA (isopropyl alcohol), and IPA (steam drying) one by one. , Ultrasonically cleaned and dried.

(6) Second polishing step Next, using a double-side polishing device similar to the double-side polishing device used in the first polishing step, the polisher is changed to a soft polisher (suede pad), and as a mirror polishing step of the main surface, A second polishing step was performed.

  In the second polishing step, the surface roughness Ra of the main surface is reduced to, for example, about 0.5 to 0.3 nm or less while maintaining the flat main surface obtained by the first polishing step. It is for the purpose.

The polishing conditions were a polishing liquid composed of colloidal silica (average particle size 80 nm) and RO water, a load of 100 g / cm ² and a polishing time of 5 minutes.

  And the glass disk which finished this 2nd grinding | polishing process is immersed in each washing | cleaning tank of neutral detergent, pure water (1), pure water (2), IPA (isopropyl alcohol), and IPA (steam drying) one by one. , Ultrasonically cleaned and dried.

(7) Chemical strengthening process Next, the chemical strengthening process was performed with respect to the glass disk which finished washing | cleaning. The chemical strengthening treatment was performed using a chemical strengthening solution in which potassium nitrate and sodium nitrate were mixed, and the lithium content eluted from the strengthened glass disk was measured using an ICP emission analyzer.

  This chemical strengthening solution was heated to 340 ° C. to 380 ° C., and the glass disk that had been washed and dried was immersed for about 2 hours to 4 hours to perform chemical strengthening treatment. In this immersion, in order to chemically strengthen the entire surface of the glass disk, it was carried out in a state of being accommodated in a holder so that a plurality of glass disks were held at the end surfaces.

  The glass disk that had been subjected to the chemical strengthening treatment was immersed in a water bath at 20 ° C. to be rapidly cooled and maintained for about 10 minutes.

  And the glass disk which finished quenching was immersed in the concentrated sulfuric acid heated at about 40 degreeC, and was wash | cleaned. In addition, the magnetic disk glass substrate that has been cleaned with sulfuric acid is immersed in each of the cleaning tanks of pure water (1), pure water (2), IPA (isopropyl alcohol), and IPA (steam drying) in order, and ultrasonic cleaning is performed. And dried.

  Next, a visual inspection was performed on the main surface and end surface of the glass disk that had been cleaned, and further a detailed inspection using light reflection, scattering, and transmission was performed. As a result, no defects such as protrusions or scratches due to deposits were found on the main surface and end surface of the glass disk.

  Further, the surface roughness of the main surface of the glass disk that has undergone the above-described steps was measured with an atomic force microscope (AFM). As a result, the Rmax was 2.5 nm and the Ra was 0.30 nm. It was confirmed that The numerical value of the surface roughness is calculated according to Japanese Industrial Standard (JIS) B0601 for the surface shape measured by AFM (Atomic Force Microscope).

  Further, the glass disk that has undergone the above-described steps has an inner diameter of 7 mm, an outer diameter of 27.4 mm, and a plate thickness of 0.381 mm. It was confirmed that the dimensions were predetermined.

  Further, the surface roughness of the inner peripheral side end face of the circular hole of this glass disk was 0.4 μm at the chamfered portion Rmax, 0.04 μm at Ra, 0.4 μm at the side wall portion Rmax, and 0.05 μm at Ra. The surface roughness Ra at the outer peripheral end face was 0.04 μm at the chamfered portion and 0.07 μm at the side wall portion. As described above, it was confirmed that the inner peripheral side end face was finished in a mirror surface like the outer peripheral side end face.

  In addition, no foreign matter or particles causing thermal asperity were found on the surface of the glass disk, and no foreign matter or cracks were found on the inner peripheral side end face of the circular hole.

(8) Texture processing Next, the texture processing was performed with respect to the glass disk which finished the chemical strengthening process. This texturing process was performed by using a texturing apparatus to relatively slide and move the glass disk and the polishing tape sandwiching both main surfaces of the glass disk in a predetermined state. The relative sliding between the glass disk and each polishing tape is based on the movement of the glass disk in the circumferential direction (tangential direction), and as a movement that swings in a sine curve with respect to the circumferential direction. went.

  At this time, a liquid abrasive containing diamond abrasive grains as abrasive grains was supplied between the glass disk and each abrasive tape.

  As shown in the following [Table 1], the conditions for this texturing are as follows. In this Example (1), a woven fabric tape is used as the polishing tape, and a polycrystalline diamond slurry is used as the abrasive (slurry). The rotation speed of the glass disk is 597 rotations per minute, the oscillation frequency of the glass disk is 7.8 Hz, the amplitude of the oscillation of the glass disk is 1 mm, and processing with a pressure roller The weight was set to 3.675 kg (1.5 pounds).

  After the texturing, the glass disk was washed to obtain a glass substrate for magnetic disk.

[Example (2) (Example of glass substrate for magnetic disk)]
As shown in [Table 1], Example (2) in which only the texture processing conditions were changed in Example (1) was created.

  In this example (2), the texture processing conditions were as follows: a woven fabric tape was used as the polishing tape, a polycrystalline diamond slurry was used as the abrasive (slurry), and the rotation speed of the glass disk was 883 rotations per minute. The oscillation frequency of the glass disk is 7.8 Hz, the oscillation amplitude of the glass disk is 1 mm, and the processing load by the pressure roller is 3.675 kg (1.5 pounds). did.

[Comparative Example (1)]
As shown in [Table 1], Comparative Example (1) in which only the texture processing conditions were changed in Example (1) was created.

  In this comparative example (1), the texture processing conditions were as follows: a woven fabric tape was used as the polishing tape, a polycrystalline diamond slurry was used as the abrasive (slurry), and the rotation speed of the glass disk was 1083 revolutions per minute. The oscillation frequency of the glass disk is 7.8 Hz, the oscillation amplitude of the glass disk is 1 mm, and the processing load by the pressure roller is 3.675 kg (1.5 pounds). did.

[Comparative Example (2)]
As shown in [Table 1], Comparative Example (2) in which the texture processing conditions were changed in Example (1) was created.

  This comparative example (2) is an example of a glass substrate for a magnetic disk having an outer diameter of 65 mm.

  In this comparative example (2), the texture processing conditions were as follows: a woven fabric tape was used as the polishing tape, a polycrystalline diamond slurry was used as the abrasive (slurry), and the rotation speed of the glass disk was 383 revolutions per minute. The frequency of oscillation (oscillation) of the glass disk was 5 Hz, the amplitude of oscillation (oscillation) of the glass disk was 1 mm, and the processing load by the pressure roller was 13.475 kg (5.5 pounds).

[Surface arithmetic average roughness (Ra-c) in the circumferential direction on the main surface of the glass substrate for magnetic disk, surface arithmetic average roughness (Ra-c) in the radial direction of the surface in the radial direction Ratio to arithmetic mean roughness (Ra-r) [Ra-c / Ra-r] and measurement of texture cross angle]
The arithmetic average of the surface in the circumferential direction on the main surface for Example (1), Example (2), Comparative Example (1) and Comparative Example (2) of the glass substrate for magnetic disk prepared as described above. The roughness (Ra-c) was measured.

  FIG. 3 is a graph showing the arithmetic average roughness (Ra-c) of the surface in the circumferential direction at each location on the main surface of the glass substrate for magnetic disks according to the present invention and the comparative example.

  Moreover, each location (from the center) of the main surface of the glass substrate for magnetic disks measured about Example (1), Example (2), Comparative example (1), and Comparative example (2) of the glass substrate for magnetic disks. Table 2 below shows the arithmetic average roughness (Ra-c) of the surface in the circumferential direction at a distance of 6.0 mm, 8.5 mm and 11.0 mm) (Comparative Example (2) Is shown about the places whose distance from the center is 14.5 mm, 22.0 mm, and 30.6 mm).

  The glass substrates for magnetic disks of [Comparative Example (1)] and [Comparative Example (2)] are the magnetic disk glasses of [Configuration 3], [Configuration 5] and [Configuration 8] described above in the present invention. This is a comparative example for the substrate.

  As shown in FIG. 3 and [Table 2], in the main surface in each example of the magnetic disk glass substrate according to the present invention, the surface roughness in the circumferential direction on the main surface is the outer peripheral side of the main surface. As can be seen from FIG.

  In the embodiment of the glass substrate for magnetic disk according to the present invention, the arithmetic average roughness of the surface in the circumferential direction of the glass substrate for magnetic disk at a location having a radius of 6 mm from the center of the glass substrate for magnetic disk on the main surface. (Ra-c) is 0.25 nm or more, and the arithmetic average roughness of the surface in the circumferential direction of the glass substrate for magnetic disk at a location of 11 mm radius from the center of the glass substrate for magnetic disk on the main surface ( Ra-c) is 0.24 nm or less.

  In addition, the arithmetic average roughness of the surface in the circumferential direction for Example (1), Example (2), Comparative Example (1), and Comparative Example (2) of the glass substrate for magnetic disks prepared as described above. The ratio [Ra-c / Ra-r] to the arithmetic average roughness (Ra-r) of the surface in the radial direction of the thickness (Ra-c) was measured.

  FIG. 4 shows the arithmetic average roughness of the surface in the radial direction of the surface arithmetic mean roughness (Ra-c) in the circumferential direction at each of the main surfaces of the glass substrate for the magnetic disk according to the present invention and the comparative example. It is a graph which shows ratio [Ra-c / Ra-r] with respect to (Ra-r).

  In addition, the circumference at each location on the main surface of the glass substrate for magnetic disk, measured for Example (1), Example (2), Comparative Example (1), and Comparative Example (2) of the glass substrate for magnetic disk. Table 2 shows the ratio [Ra-c / Ra-r] of the arithmetic average roughness (Ra-c) of the surface in the direction to the arithmetic average roughness (Ra-r) of the surface in the radial direction.

  As can be seen from FIG. 4 and [Table 2], in the main surface of the magnetic disk glass substrate according to the present invention, the surface roughness in the circumferential direction on the main surface is the surface in the radial direction on the main surface. It can be seen that it is smaller than the roughness.

  Further, the ratio of the surface arithmetic average roughness (Ra-c) in the circumferential direction to the surface arithmetic average roughness (Ra-r) in the radial direction, that is, [Ra-c / Ra-r] is It can be seen that the main surface continuously increases from the outer peripheral side toward the inner peripheral side.

  In the embodiment of the glass substrate for magnetic disk according to the present invention, the arithmetic average of the surface in the circumferential direction of the glass substrate for magnetic disk on the main surface at a location of 6 mm radius from the center of the glass substrate for magnetic disk on the main surface The ratio [Ra-c / Ra-r] to the surface arithmetic mean roughness (Ra-r) in the radial direction of the glass substrate for magnetic disk on the main surface of the roughness (Ra-c) was 0.61 or more. In the main surface, the magnetic disk on the main surface of the arithmetic average roughness (Ra-c) of the surface in the circumferential direction of the glass substrate for the magnetic disk on the main surface at a radius of 11 mm from the center of the glass substrate for the magnetic disk on the main surface. The ratio [Ra-c / Ra-r] to the arithmetic average roughness (Ra-r) of the surface of the glass substrate in the radial direction is 0.60 or less.

  Further, an area of 5 μm square was measured with an atomic force microscope on the main surface of the glass substrate for magnetic disk prepared as described above, and the measurement result was Fourier transformed by two-dimensional FFT.

  FIG. 5 is an image showing the result of Fourier transform of an atomic force microscope image measured for each location on the main surface of the magnetic disk glass substrate according to the present invention.

  Then, as shown in FIG. 5, the angle (cross angle) at which the textures formed so as to intersect each other with a circumferential component on the main surface of the magnetic disk glass substrate intersect was specified.

  FIG. 6 is a graph showing the cross angle of the texture at various points on the main surface of the magnetic disk glass substrate according to the present invention and the comparative example.

  Further, the texture of each part of the main surface of the glass substrate for magnetic disk, measured for Example (1), Example (2), Comparative Example (1) and Comparative Example (2) of the glass substrate for magnetic disk, was measured. The cross angles are shown in [Table 2].

  As a result, in this glass substrate for magnetic disk, as shown in FIG. 6, it was confirmed that the cross angle increased from the outer peripheral side to the inner peripheral side of the main surface. Assuming that the cross angle is θ, tan θ is inversely proportional to the distance r from the center of the magnetic disk glass substrate (that is, proportional to [1 / r]).

  In the example of the magnetic disk glass substrate according to the present invention, the angle at which the textures intersect (cross angle) is 5.0 ° or more at a location having a radius of 6 mm from the center of the magnetic disk glass substrate on the main surface. The angle (cross angle) at which the textures intersect is 4.5 ° or less at a location having a radius of 11 mm from the center of the magnetic disk glass substrate on the main surface.

[Example (3) (Example of magnetic disk)]
Next, the magnetic disk according to the present invention was manufactured through the following steps.

  On both main surfaces of the glass substrate for magnetic disk of Example (1) and Example (2) obtained by the above-described process, using a stationary facing DC magnetron sputtering apparatus, an Al—Ru alloy seed layer, Cr An underlayer of -W alloy, a magnetic layer of Co-Cr-Pt-Ta alloy, and a hydrogenated carbon protective layer were sequentially formed. The seed layer has the effect of miniaturizing the magnetic grains of the magnetic layer, and the underlayer has the effect of orienting the easy axis of magnetization of the magnetic layer in the in-plane direction.

  This magnetic disk is a non-magnetic substrate for a magnetic disk, a magnetic layer formed on the magnetic disk glass substrate, a protective layer formed on the magnetic layer, and formed on the protective layer. And at least a lubricated layer.

  A nonmagnetic metal layer (nonmagnetic underlayer) including a seed layer and an underlayer is formed between the magnetic disk glass substrate and the magnetic layer. In this magnetic disk, the layers other than the magnetic layer are all made of a nonmagnetic material. In this embodiment, the magnetic layer, the protective layer, the protective layer, and the lubricating layer are formed in contact with each other.

  That is, first, an Al—Ru (aluminum-ruthenium) alloy (Al: 50 at%, Ru: 50 at%) is used as a sputtering target, and is made of a 30 nm thick Al—Ru alloy on a magnetic disk glass substrate. A seed layer was formed by sputtering. Next, using a Cr—W (chromium-tungsten) alloy (Cr: 80 at%, W: 20 at%) as a sputtering target, an underlayer made of a 20 nm thick Cr—W alloy is formed on the seed layer 5. A film was formed by sputtering. Next, as a sputtering target, using a sputtering target made of a Co—Cr—Pt—Ta (cobalt-chromium-platinum-tantalum) alloy (Cr: 20 at%, Pt: 12 at%, Ta: 5 at%, balance Co), A magnetic layer made of a Co—Cr—Pt—Ta alloy having a film thickness of 15 nm was formed on the underlayer by sputtering.

  Next, a protective layer made of hydrogenated carbon was formed on the magnetic layer, and a lubricating layer made of PFPE (perfluoropolyether) was formed by a dip method. The protective layer functions to protect the magnetic layer from the impact of the magnetic head. In this way, a magnetic disk was obtained.

  Using the obtained magnetic disk, a glide inspection was performed with a glide head having a flying height of 10 nm. As a result, no colliding foreign matter was detected, and a stable flying state could be maintained. Further, when a recording / reproducing test was conducted at 700 kFCI using this magnetic disk, a sufficient signal intensity ratio (S / N ratio) could be obtained. Further, no signal error was confirmed.

  Furthermore, when mounted and driven in a “1-inch hard disk drive” that requires an information recording density of 60 gigabits or more per square inch, recording and reproduction could be performed without any particular problem. That is, no crash failure or thermal asperity failure occurred.

  In addition, magnetic disks were also prepared for the magnetic disk glass substrates of Comparative Example (1) and Comparative Example (2) obtained by the above-described steps, as in Example (3).

  And it produced using the magnetic disk produced using the glass substrate for magnetic disks of Example (1) and Example (2), and the glass substrate for magnetic disks of Comparative Example (1) and Comparative Example (2). The test was performed on the load / unload durability of the magnetic disk. The results of this load / unload durability test are shown in [Table 2].

  About the glass substrate for magnetic disks of the above-mentioned Example (1), the load / unload durability after constituting as a magnetic disk was 600,000 times or more, and it was confirmed that it was sufficient durability. .

  Also for the glass substrate for magnetic disk of Example (2) described above, the load / unload durability after forming as a magnetic disk was 500,000 times, and it was confirmed that the durability was sufficient.

  About the glass substrate for magnetic discs of the above-mentioned comparative example (1), the load / unload durability after constituting as a magnetic disc was 300,000 times or more, and it was confirmed that it did not have sufficient durability.

  Note that the glass substrate for magnetic disk of Comparative Example (2) described above has a sufficient load / unload durability of 600,000 times or more after being configured as a magnetic disk. Example (2) is an example of a magnetic disk having an outer diameter of 65 mm, and the measurement points such as the surface roughness are the distances from the center being 14.5 mm, 22.0 mm, and 30.6 mm. The comparison cannot be made for the case of 27.4 mm.

  Next, a second embodiment according to the present invention will be described.

  In the second embodiment, a magnetic disk substrate having a smaller diameter than that of the first embodiment is used. The production of the magnetic disk substrate, the texture processing for the magnetic disk substrate, and the production of the magnetic disk are substantially the same as in the first embodiment.

  [Table 3] shows the results obtained by measuring the arithmetic average roughness (Ra) of the magnetic disk substrate according to the present invention and the arithmetic average roughness (Ra) of the magnetic disk according to the present invention according to the measurement radius, The TOP at the measurement radius is shown. [Table 3] also shows TOP of Comparative Example (3) and Comparative Example (4) having different surface roughnesses for comparison. In addition, the value of 0.91 atm in TOP of [Table 3] is the normal pressure value at the measurement site.

  FIG. 7 is a graph showing the roughness in [Table 3]. The roughness of the magnetic disk substrate and the roughness of the magnetic disk in Example (3), Comparative Example (3), and Comparative Example (4). Is shown. The surface roughness here is measured with an atomic force microscope as described above. It can be seen that the roughness of the magnetic disk reflects the roughness of the magnetic disk substrate. That is, if the roughness of the magnetic disk substrate is increased, the roughness of the magnetic disk is also increased. Further, in Example (3), the roughness at a certain measurement radius (first region) is smaller than the roughness of the measurement radius (second region) on the inner circumference side than this measurement radius. Understand. The first area may be an area where the magnetic head may come into contact at the start of disk rotation or recording / reproduction, that is, an area where the magnetic head is introduced into the magnetic disk in the LUL method. As a result, the surface roughness on the inner peripheral side of this region becomes rough. Further, the surface roughness may be increased stepwise or continuously from the region toward the inner peripheral side.

  Here, TDO (Touch Down Pressure) and TOP (Take Off Pressure) will be described. In recent years, there is a concern that the contact frequency between the magnetic head and the magnetic disk may increase due to a decrease in the flying height of the magnetic head accompanying an increase in the recording density of the magnetic disk. Therefore, TDP measurement and TOP measurement are performed as evaluation of the flying characteristics.

  FIG. 8 is a conceptual diagram of the TOD / TOP test. TDO (Touch Down Pressure) refers to the value of atmospheric pressure when the magnetic head moves from a floating state to a sliding state when the atmospheric pressure in the hard disk drive is gradually lowered. TOP (Take Off Pressure) refers to the value of the atmospheric pressure when the magnetic head moves from the sliding state to the floating state when the atmospheric pressure in the hard disk drive is gradually increased contrary to TDO. The transition from the floating state to the sliding state, that is, the contact state between the magnetic disk and the magnetic head is confirmed by looking at the output of the AE (Acoustic Emission) sensor. The experiment was conducted in a container capable of controlling the atmospheric pressure.

  By measuring TDP, it is possible to see how hard the magnetic head is in contact with the magnetic disk. By TOP measurement, it is possible to see how easily the magnetic head in contact with the magnetic disk is separated from the magnetic disk. be able to. Therefore, both TOD and TOP are required to be small, and ΔP which is the difference between TOD and TOP is desired to be small. When this ΔP is small, it can be said that the head flying characteristics are good.

  FIG. 9 is a graph of TOP in [Table 3], in which TOP in Example (3), Comparative Example (3), and Comparative Example (4) is plotted according to the measurement radius. . Comparing Comparative Example (3), which has a small roughness compared to Example (3), and Example (3), it can be seen that the TOP is almost normal pressure because the roughness is small. In Comparative Example (4), the roughness is almost the same in the radial direction of the main surface, and therefore TOP has a larger TOP value compared to Example (3). In particular, since the roughness on the ID side is small, the TOP value is almost normal pressure.

  In any of the examples, the value of TOP on the ID side is high, particularly in the case of a small-diameter magnetic disk, because the relative destination speed of the magnetic disk and the magnetic head decreases toward the inner peripheral side. However, it is thought that it is because it cannot obtain sufficient lift and becomes unstable. Therefore, it is conceivable to further improve the TOP by increasing the roughness of the magnetic disk and the magnetic head. For example, it is conceivable to increase the roughness of the magnetic head. In this case, the surface roughness of the magnetic head is preferably rougher than any area of the magnetic disk.

  And a magnetic head having a drive unit for driving the magnetic disk in a recording direction, a reproducing unit and a recording unit, and means for moving the magnetic head relative to the magnetic disk. It is also preferable to use an NPAB slider. As a result, the magnetic head is less likely to contact and slide on the magnetic disk, and even if it contacts and slides, the magnetic head is likely to rise. Further, by combining these, the flying characteristics of the magnetic head become better.

  In the present invention, the diameter (size) of the glass substrate for magnetic disk is not particularly limited. However, the present invention exhibits excellent utility particularly when a small-diameter glass substrate for a magnetic disk is produced. The small diameter here is, for example, a glass substrate for a magnetic disk having a diameter of 30 mm or less.

It is a perspective view which shows the structure of the texture processing apparatus which performs a texture process in the manufacturing process of the glass substrate for magnetic discs which concerns on this invention. In the texture process in this invention, it is a schematic diagram which shows the relative sliding contact moving direction of a glass disk and an abrasive tape. It is a graph which shows the arithmetic mean roughness (Ra-c) of the surface about the circumferential direction in each location of the main surface of the glass substrate for magnetic discs which concerns on this invention, and a comparative example. Surface arithmetic average roughness (Ra-r) in the radial direction of the surface arithmetic average roughness (Ra-c) in the circumferential direction at each location on the main surface of the glass substrate for magnetic disk and the comparative example according to the present invention It is a graph which shows ratio [Ra-c / Ra-r] to. It is an image which shows the result of having carried out the Fourier-transform of the atomic force microscope image measured about each place of the main surface of the glass substrate for magnetic discs concerning this invention. It is a graph which shows the cross angle of the texture in each part of the main surface of the glass substrate for magnetic discs which concerns on this invention, and a comparative example. It is a graph which shows the arithmetic mean roughness (Ra) of the surface in each place of the main surface in the Example of the glass substrate for magnetic discs and magnetic disc which concerns on this invention, and a comparative example. It is a conceptual diagram of a TOD / TOP test. It is a graph which shows the TOP in each location of the main surface in the Example of the magnetic disc concerning this invention, and a comparative example.

Explanation of symbols

1 Glass disk 2 Circular hole 101 Chucking shaft 102,103 Abrasive tape

Claims (15)

A glass substrate for a magnetic disk mounted on a hard disk drive,
The glass substrate for a magnetic disk, wherein the surface roughness in the circumferential direction of the glass substrate for a magnetic disk on the main surface increases from the outer peripheral side to the inner peripheral side of the entire main surface. The glass substrate for a magnetic disk according to claim 1,
The surface roughness of the main surface in the circumferential direction of the glass substrate for magnetic disk is continuously increased from the outer peripheral side to the inner peripheral side of the entire main surface. substrate. A glass substrate for a magnetic disk according to claim 1 or claim 2,
In the main surface, at a location having a radius of 6 mm from the center of the magnetic disk glass substrate, the arithmetic average roughness of the surface in the circumferential direction of the magnetic disk glass substrate is 0.25 nm or more,
The arithmetic mean roughness of the surface in the circumferential direction of the glass substrate for magnetic disk is 0.24 nm or less at a location having a radius of 11 mm from the center of the glass substrate for magnetic disk on the main surface. Glass substrate for magnetic disk. A glass substrate for a magnetic disk according to any one of claims 1 to 3,
The ratio of the surface roughness in the circumferential direction of the glass substrate for magnetic disk on the main surface to the surface roughness in the radial direction of the glass substrate for magnetic disk on the main surface is less than the outer peripheral side of the entire main surface. A glass substrate for a magnetic disk, characterized by increasing toward the circumferential side. A glass substrate for a magnetic disk according to any one of claims 1 to 4,
The magnetic disk on the main surface has an arithmetic mean roughness of the surface in the circumferential direction of the glass substrate for the magnetic disk on the main surface at a location having a radius of 6 mm from the center of the glass substrate for the magnetic disk on the main surface. The ratio to the arithmetic mean roughness of the surface in the radial direction of the glass substrate for the glass is 0.61 or more,
The magnetic disk on the main surface has an arithmetic mean roughness of the surface in the circumferential direction of the glass substrate for the magnetic disk on the main surface at a location having a radius of 11 mm from the center of the glass substrate for the magnetic disk on the main surface. A glass substrate for a magnetic disk, wherein the ratio of the surface relative to the arithmetic mean roughness of the glass substrate in the radial direction is 0.60 or less. A glass substrate for a magnetic disk mounted on a hard disk drive,
On the main surface, the texture is formed so as to intersect each other with a circumferential component of the magnetic disk glass substrate,
The angle at which the textures intersect increases from the outer peripheral side to the inner peripheral side of the entire main surface of the magnetic disk glass substrate. The glass substrate for a magnetic disk according to claim 6,
The angle at which the textures intersect each other increases continuously from the outer peripheral side to the inner peripheral side of the entire main surface of the magnetic disk glass substrate. The glass substrate for a magnetic disk according to claim 6,
In the location where the radius is 6 mm from the center of the magnetic disk glass substrate on the main surface, the angle at which the textures intersect is 5.0 ° or more,
The glass substrate for a magnetic disk, wherein an angle at which the textures intersect is 4.5 ° or less at a location having a radius of 11 mm from the center of the glass substrate for the magnetic disk on the main surface. A glass substrate for a magnetic disk according to any one of claims 1 to 8,
A glass substrate for a magnetic disk that is a magnetic disk by forming a magnetic layer on the main surface;
The glass substrate for a magnetic disk, wherein a texture for imparting magnetic anisotropy to the magnetic layer is formed on the main surface. A glass substrate for a magnetic disk according to any one of claims 1 to 9,
A glass substrate for a magnetic disk, which is a glass substrate for a magnetic disk mounted on a 1-inch hard disk drive or a hard disk drive using a magnetic disk having a smaller diameter than the 1-inch hard disk drive. It is a glass substrate for magnetic discs as described in any one of Claims 1 thru | or 10, Comprising:
A glass substrate for a magnetic disk, which is a glass substrate for a magnetic disk to be mounted on a hard disk drive that performs a start / stop operation by a load / unload method. Having a first region on the main surface and a second region rougher than the surface roughness of the first region;
The glass substrate for a magnetic disk, wherein the first region is located on the outer peripheral side of the second region on a circular plate-like glass substrate. The glass substrate for a magnetic disk according to claim 12,
The glass substrate for a magnetic disk, wherein the first area is an area where the magnetic head is introduced into the magnetic disk. A glass substrate for a magnetic disk according to any one of claims 1 to 13, comprising:
A magnetic disk, wherein at least a magnetic layer is formed on the magnetic disk glass substrate. The magnetic disk according to claim 14, wherein
A magnetic disk characterized in that the roughness of any region on the main surface of the magnetic disk is smaller than the surface roughness of the magnetic head used.

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