JPWO2008111427A1 - Information recording apparatus, glass substrate for information recording medium used in the information recording apparatus, and magnetic recording medium - Google Patents

Abstract

The present invention provides an information recording apparatus in which the glass substrate for an information recording medium is not damaged even when a strong impact is applied to the information recording apparatus while the glass substrate is stably fixed to the hub of the SPM. To do. For this reason, the glass substrate for information recording medium has a position P1, a position P2, a position P3 on the contour line of one main surface in a cross section perpendicular to the main surface in the radial direction of the glass substrate for information recording medium. And the contour line descends in a direction away from the main surface from the position P2, passes through the position P3, reaches the inner peripheral end surface, and is based on a flat portion of the main surface. The distance Δh between the reference plane and the position P3 satisfies the conditional expression.

Description

  The present invention relates to an information recording apparatus, a glass substrate for an information recording medium used in the information recording apparatus, and a magnetic recording medium.

  Conventionally, as an information recording medium substrate in an information recording apparatus used in a computer or the like, an aluminum substrate has been generally used so far. However, in recent years, a glass substrate superior in hardness, strength and flatness compared to an aluminum substrate. The adoption of is increasing. In the case of a magnetic disk, the recording density has been increased along with the miniaturization and thinning of the magnetic disk, and the magnetic head mechanism has shifted from the CSS (Contact Start Stop) method to the LUL (Load Unload) method as the magnetic head is lowered. It's getting on. In the LUL method, since the magnetic head can be moved at a low flying height compared to the CSS method, higher density recording is possible and it is possible to cope with an increase in recording capacity. With the shift from the CSS system to the LUL system, the use of glass substrates is increasing.

  A magnetic disk having a magnetic layer on a glass substrate needs to be fixed to a hub that is a rotating shaft of a spindle motor (SPM) provided in the magnetic disk recording apparatus. As a method for fixing the magnetic disk to the hub, there are a method in which the magnetic disk is held between high-precision planes, and a method in which the magnetic disk is held between a high-precision plane and an annular protrusion. Specifically, the following cases can be considered. (1) The spacer is sandwiched between the end faces of a spacer having a high-precision plane. (2) It is sandwiched between an end face of a spacer having a highly accurate plane and a clamper having an annular projection. (3) It is sandwiched between a flange functioning as a magnetic disk receiving portion provided on the outer periphery of the lower end portion of the hub having the same projection as the clamper and an end surface of the spacer having a highly accurate plane.

  For example, consider a case where three magnetic disks are fixed to a hub. The magnetic disk, spacer, magnetic disk, spacer, and magnetic disk are inserted into the hub in order on the flange, and finally the clamper is fixed to the tip of the hub with a screw or the like. This clamper has a spring action. By applying this spring action and fixing the clamper to the tip of the hub, a pressing force is generated between the flange and the clamper, and the magnetic disk is fixed to the hub.

These conventional magnetic disk fixing methods are methods in which the flat portion of the disk is clamped from both sides and fixed. If there is a bulge etc. at the inner peripheral edge of the magnetic disk fixed to the hub, that is, the inner peripheral edge of the glass substrate that is the base of the magnetic disk, there is a problem that the magnetic disk is tilted or distorted and fixed. When the mechanical strength of the substrate is weak, there is a problem that cracks occur. For this reason, the glass substrate which makes the shape of an inner peripheral edge part the shape fits in the range of +/- 0.35 micrometer on the basis of the flat surface of a main surface is known (refer patent document 1).
JP 2001-167427 A

  However, according to experiments by the inventors, the glass substrate may be damaged even in the shape of the inner peripheral end described in Patent Document 1. It does not cause a problem when a magnetic disk recording device incorporating a glass substrate is normally used, but when a strong impact such as dropping is applied to the magnetic disk recording device, the glass substrate is fixed to the hub. There was a case where it was damaged in the part.

  The present invention has been made in view of the above-described problems. The object of the present invention is to provide a strong impact on a magnetic disk recording apparatus that is stably fixed to a hub of a SPM (spindle motor) and incorporates the SPM. It is an object to provide a glass substrate for information recording medium and a magnetic recording medium based on the glass substrate for information recording medium that are not damaged even when the above is added.

  Said subject is solved by the following structures.

1. A glass substrate for an information recording medium in a donut shape having a main surface with a flat portion, a concentric outer peripheral end surface and an inner peripheral end surface;
A spindle motor including a rotatable hub;
The surface facing the main surface is flat when fitted to the outer periphery of the hub and inserted into the hole formed by the inner peripheral end surface, and the outer periphery of the opposing surface has a radius Rs with the hole as a central axis. A first clamping member having a first shape which is a circular shape of
A second clamping member having a second shape having an annular protrusion at a radius Rp smaller than the radius Rs with the hole as a central axis on a surface facing the main surface;
An information recording apparatus that holds the glass substrate for information recording medium between the first holding member and the second holding member and is fixed to the hub,
The distance R1 from the central axis of the glass substrate for information recording medium on the contour line of one main surface of the cross section perpendicular to the main surface in the radial direction of the glass substrate for information recording medium is the radius of the hole. A position P1 for R0 + 5 mm and a position P3 for setting a distance R3 from the central axis of the glass substrate for information recording medium to a radius R0 + 0.35 mm of the hole are defined in the same cross section, and the contour line is the position P1. And a position P2 between the position P3 and a reference plane with the flat portion of the main surface as a reference in the thickness direction of the glass substrate for information recording medium, and the position from the central axis of the glass substrate for information recording medium An information recording apparatus satisfying the following conditional expression, wherein a distance to P2 is a distance R2 and a distance between the reference plane and the position P3 is Δh.

Value of distance R3 <Value of radius Rs <Value of distance R2 Value of distance R3 <Value of radius Rp <Value of distance R2 0.001 μm <Δh <5.0 μm.

  2. 2. The information recording apparatus according to 1, wherein a front surface and a back surface of the glass substrate for information recording medium are symmetrical.

  3. 2. The information recording apparatus according to 1, wherein a magnetic film is provided on a surface of the glass substrate for the information recording medium.

4). In a donut shape having a main surface with a flat part, a concentric outer peripheral end surface and an inner peripheral end surface,
In a state where a rotatable hub of a spindle motor constituting the information recording device is fitted and inserted into the hole formed by the inner peripheral end face,
A first clamping member having a first shape in which a surface facing the main surface is flat and an outer periphery of the facing surface is a circle having a radius Rs with the hole as a central axis;
A second clamping member having a second shape having an annular protrusion having a radius Rp smaller than the radius Rs with the hole as a central axis on a surface facing the main surface, and is fixed to the hub. In an information recording medium glass substrate,
On the outline of one main surface of the cross section perpendicular to the main surface in the radial direction of the glass substrate for information recording medium,
A position P1 where a distance R1 from the central axis of the glass substrate for information recording medium is a radius R0 + 5 mm of the hole;
A position P3 where the distance R3 from the central axis of the glass substrate for information recording medium is a radius R0 + 0.35 mm of the hole is determined in the same cross section,
The contour line is separated from a reference plane with the flat portion of the main surface as a reference at a position P2 between the position P1 and the position P3 in the thickness direction of the glass substrate for the information recording medium. A glass substrate for an information recording medium satisfying the following conditional expression, wherein a distance from the central axis of the glass substrate to the position P2 is a distance R2 and a distance between the reference plane and the position P3 is Δh.
Value of distance R3 <value of radius Rs <value of distance R2 value of distance R3 <value of radius Rp <value of distance R2 0.001 μm <Δh <5.0 μm
5). 5. A magnetic recording medium comprising a magnetic film on the surface of the glass substrate for information recording medium according to 4.

  According to the present invention, in the information recording apparatus in which the glass substrate for information recording medium is sandwiched between the first sandwiching member having the defined first shape and the second sandwiching member having the second shape, and is fixed to the hub. The shapes of the first and second clamping members and the shape of the inner peripheral end of the glass substrate have a predetermined relationship.

  By sandwiching the glass substrate in this defined relationship, the glass substrate is fixed to the spindle motor hub while having an appropriate contact area and gap with respect to the first and second clamping members. For this reason, the impact transmitted from the hub to the information recording medium glass substrate due to dropping or the like is sufficiently absorbed and alleviated when transmitted to the information recording medium glass substrate via the first and second clamping members.

  Therefore, the glass substrate for the information recording medium is not damaged even when a strong impact is applied to the information recording apparatus while the glass substrate is stably fixed to the hub of the SPM.

It is a figure which expands an inner peripheral edge peripheral part typically in the section cut through the plane perpendicular to the main surface through the center of the glass substrate for information recording media. It is a figure which shows the whole structure of the glass substrate for information recording media. It is a figure which shows an example of the magnetic recording medium provided with the magnetic film on the front main surface of the glass substrate for information recording media. It is a figure which shows typically a mode that three glass substrates for information recording media are mounted | worn with the magnetic disc recording device in a cross section. It is a figure which shows the example of the manufacturing process of the glass substrate for recording media with a flowchart. It is a figure explaining the jig for a drop test imitating a magnetic disc recording device for a drop test.

Explanation of symbols

1, 1A, 1B, 1C Information recording medium glass substrate (glass substrate)
2 Magnetic film 10a Front main surface 10b Back main surface 13 Hole 14 Outer peripheral end surface 15 Inner peripheral end surface 20 Screw 30 Hub 30a Flange 30b Motor bracket 40, 82 Base 50 Spindle motor 60A, 60B Spacer 70, 90 Clamp 70p, 30p Protrusion 80 Drop Test jig 84 Cover 92 Lamp D, 86, 88 Magnetic recording medium (magnetic disk)
P1, P2, P3, Pt Positions R1, R2, R3, Δh Distance Rs, Rp Radius BL Outline SH Reference plane C Central axis

  Although the present invention will be described based on the illustrated embodiment, the present invention is not limited to the embodiment.

  The inventors examined in detail the glass substrate that was damaged by the impact in the state of being incorporated in the magnetic disk recording device and the peripheral portion of the glass substrate of the magnetic disk recording device. As a result, the reason why the glass substrate subjected to the impact was damaged has been estimated as follows.

  The main surface of the glass substrate fixed to the hub, which is the rotation shaft of the spindle motor (SPM), is a mirror surface because it is a surface on which the recording layer is provided, and the glass surface of the spacer fixed with the glass substrate in between is in contact with it. The end face is usually ground with high precision. When a spacer with good flatness and flatness and a glass substrate are brought into contact with each other and fixed, they come into contact with each other over a wide area on the surfaces facing each other and have good adhesion. Therefore, it is firmly fixed to the hub. In this state, when an impact is applied to the magnetic disk recording apparatus incorporating the SPM from the outside, the portion sandwiched between the spacers of the glass substrate and fixed to the hub vibrates integrally with the hub. On the other hand, the portion that is sandwiched between the spacers of the glass substrate and not fixed to the hub is considered to be greatly bent in the direction perpendicular to the main surface of the glass substrate with the outer peripheral edge of the spacer fixed to the hub as a fulcrum. It is done. It is considered that the glass substrate is destroyed when the amount of deflection exceeds a certain limit. Therefore, the glass substrate does not have a problem such as breakage even if it is rotated at a high speed by SPM. However, the glass substrate is broken when an impact such as a drop is applied. From these points, the glass substrate is absorbed and relaxed so that the glass substrate does not cause problems even if the glass substrate is rotated at high speed, and so that the glass substrate does not bend so much that it is damaged when an impact is applied. It would be good if it could be loosely fixed to the hub. The present invention has been made paying attention to the above points.

  FIG. 2 shows the overall configuration of a glass substrate for information recording medium (hereinafter also referred to as a glass substrate) 1 according to the present invention. As shown in FIG. 2, the glass substrate 1 has a donut-like disk shape with a hole 13 formed in the center. Reference numeral 14 denotes an outer peripheral end face, 15 denotes an inner peripheral end face, 10a denotes a front main surface, and 10b denotes a back main surface.

  FIG. 3 shows an example of a magnetic recording medium D provided with the magnetic film 2 on the front main surface 10a of the glass substrate 1 shown in FIG. The magnetic film 2 can also be provided on the back main surface 10b. The thickness of the magnetic film 2 is sufficiently thin compared to the thickness of the glass substrate 1 and is almost constant. For this reason, the shape of the inner peripheral edge according to the present invention can be considered to be the same for both the glass substrate 1 and the magnetic recording medium D. Therefore, hereinafter, unless otherwise specified, even the magnetic recording medium D will be described as the glass substrate 1 constituting the substrate.

  FIG. 4 schematically shows in cross section how three glass substrates (magnetic recording media) 1A, 1B, and 1C are mounted on a magnetic disk recording apparatus. 40 is a base of the magnetic disk recording device, 50 is a spindle motor (SPM) for rotating the glass substrates 1A, 1B and 1C, 60A and 60B are spacers, 70 is a clamp, 20 is a clamp 70 at the tip of the hub 30 A screw for fixing is shown. The SPM 50 includes a rotating hub 30, a flange 30a functioning as a magnetic disk receiving portion provided on the outer periphery of the lower end of the hub, and a motor bracket 30b for fixing the SPM 50 to the base.

  The spacers 60A and 60B have a ring shape in which a hole for fitting into the hub 30 is provided at the center thereof, and both end faces of the ring shape are parallel and surface-ground with high accuracy. The spacers 60A and 60B maintain a constant distance between the glass substrates 1A, 1B, and 1C. The radius of the outer peripheral ends of the spacers 60A and 60B is a radius Rs. Therefore, the spacers 60A and 60B correspond to the first clamping member.

  The clamp 70 has a disk shape made of a material having a spring action. An annular projection 70p is provided on the outer peripheral end of one surface of the clamp 70, and the top portion of the projection 70p is in contact with the glass substrate 1A. The shape of the top portion is rounded. is doing. The position of the top of the projection 70p is at a radius Rp from the center of the clamp 70. This radius Rp is smaller than the radius Rs. Therefore, the clamp 70 corresponds to a second clamping member.

  The flange 30a is provided with an annular protrusion 30p at the outer peripheral end of the surface that receives the glass substrate 1C, and comes into contact with the magnetic recording medium 1C at the top of the protrusion 30p. Has roundness. The position of the top of the protrusion 30p is a radius Rp from the center of the flange 30a. Therefore, the flange 30a corresponds to a second clamping member.

  The magnetic recording medium 1C, the spacer 60B, the magnetic recording medium 1B, the spacer 60A, and the magnetic recording medium 1A are sequentially inserted into the hub 30 and stacked on the flange 30a. Finally, the clamp 70 is fixed to the tip of the hub 30 with the screw 20. To do. By doing so, a pressing force is generated between the clamp 70 and the flange 30a by the spring action of the clamp 70, and the glass substrate 1C, the spacer 60B, the glass substrate 1B, the spacer 60A, and the glass substrate 1A are fixed to the hub 30 by this force. can do.

  The shape of the inner peripheral end portion of the glass substrate fixed to the hub using the flange, spacer, and clamp described so far will be described.

  Consider a cross-section cut through a plane that passes through the center of the glass substrate 1 shown in FIG. 2 and is perpendicular to the front main surface 10a. In this cross section, the peripheral portion of the inner peripheral end of the glass substrate 1 is enlarged and schematically shown in FIG. The shape shown in FIG. 1 is symmetrical with the front main surface 10a even though there is an error in processing on the back main surface 10b. Therefore, the following description will be made with respect to the front main surface 10a side. Description is omitted.

  In FIG. 1, C is a rotation center axis of the glass substrate 1, BL is a contour line of the glass substrate 1 on the front main surface 10 a side, SH is a reference plane based on a flat portion of the main surface 10 a, and Pt is the glass substrate 1. The position of the inner peripheral end face 15 whose distance from the central axis C is R0, P3 is the position where the distance R3 from the central axis C is R0 + 0.35 mm, and P1 is the position where the distance R1 from the central axis C is R0 + 5 mm. . P2 is a position between the position P1 and the position P3, and the value of the distance R2 from the central axis C exceeds the value of the distance R3 and is less than the value of the distance R1. The contour line BL extends from the position P2 between the positions P1 and P3 toward the inner peripheral end surface 15 of the glass substrate in a direction away from the main surface.

  Taking a 2.5-inch glass substrate as an example, the position P1, the position P3, and the position Pt are as follows. If the center of the glass substrate 1 is 0 and the position Pt is 10 mm (= R0), the position P1 is 15 mm and the position P3 is 10.35 mm.

  The contour line BL from the front main surface 10a toward the inner peripheral end passes through the position P1, starts to descend from the position P2 to the substrate side, passes through the position P3, and reaches the inner peripheral end face 15 at the position Pt.

  Here, when a glass substrate is fixed to a hub and incorporated in a magnetic disk device and an impact is applied to the magnetic disk device, it is experimentally confirmed that the glass substrate is not damaged if the following conditions (1) to (3) are satisfied. Obtained.

The value of the distance R3 and the value of the distance R2 satisfy the following conditions with the value of the radius Rs of the outer peripheral ends of the spacers 60A and 60B.
Value of distance R3 <value of radius Rs <value of distance R2 (1)
Further, the value of the distance R3 and the value of the distance R2 satisfy the following conditions, and the value of the radius Rp that defines the positions of the annular protrusions 70p and 30p of the clamp 70 and the flange 30a, respectively.
Value of distance R3 <value of radius Rp <value of distance R2 (2)
Note that the value of the radius Rp is smaller than the value of the radius Rs.
The distance Δh between the reference plane SH and the position P3 with reference to the flat portion of the front main surface 10a satisfies the following conditional expression.
0.001 μm <Δh <5.0 μm (3)
The glass substrates 1A, 1B, and 1C on which the inner peripheral ends are formed are fixed to the hub 30 with clamps, flanges, and spacers so as to satisfy the conditional expressions (1) to (3). At this time, the fixed state of the glass substrates 1A, 1B, and 1C shown in FIG. 4 is as follows.

  In the case of the glass substrate 1A, it is as follows. The position where the glass substrate 1A and the spacer 60A are in contact is outside the position where the annular protrusion 70p of the clamp 70 is in contact with the glass substrate 1A. Further, the positions where the annular projections 70p of the spacer 60A and the clamp 70 are in contact with the glass substrate 1A are such that the main surface of the glass substrate 1A is lowered from the main surface reference SH and is on the outer peripheral side from the position P3. Therefore, the glass substrate 1A is in a state of being sandwiched by applying stress between the annular protrusion 70p of the clamp 70 and the outer edge portion of the spacer 60A. At this time, the distance from the spacer 60A at the position P3 of the glass substrate 1A is Δh that satisfies the conditional expression (3). Accordingly, the glass substrate 1A is fixed to the hub 30 with an appropriate contact area and gap with the end face of the spacer 60A.

  In the case of the glass substrate 1C, it can be considered that the case of the glass substrate 1A is upside down and is as follows. The position where the glass substrate 1C and the spacer 60B are in contact is outside the position where the annular projection 30p of the flange 30a is in contact with the glass substrate. Further, the positions where the annular projections 30p of the spacer 60B and the flange 30a come into contact with the glass substrate 1C are such that the main surface of the glass substrate 1C is lowered from the main surface reference SH and is on the outer peripheral side from the position P3. Therefore, the glass substrate 1C is in a state of being sandwiched by applying stress between the annular protrusion 30p of the flange 30a and the outer edge portion of the spacer 60B. At this time, the distance from the spacer 60B at the position P3 of the glass substrate is Δh that satisfies the conditional expression (3). Therefore, the glass substrate 1C is fixed to the hub 30 with an appropriate contact area and gap with the end face of the spacer 60B.

  When the distance Δh shown in the conditional expression (3) is 5.0 μm or more, when the contact area between the glass substrates 1A and 1C and the spacers 60A and 60B becomes too small and an impact is generated, the effect of sufficiently absorbing and relaxing the impact is obtained. It becomes difficult to obtain. When the distance Δh is 0.001 μm or less, there is no play (gap) between the glass substrates 1A and 1C and the spacers 60A and 60B, and the glass substrate that comes into contact with the outer peripheral ends of the spacers 60A and 60B when an impact occurs. Stress concentrates on the surfaces of 1A and 1C, and sufficient impact resistance cannot be obtained.

  In the present embodiment, the radius Rpf of the value that determines the position of the top of the protrusion 30p that the flange 30a has is set to the same value of the radius Rp as the value that determines the position of the top of the protrusion 70p of the clamp 70. In other words, the value of the radius Rpf should be smaller than the value of the radius Rs and satisfy the conditional expression (2).

  The glass substrate that satisfies the conditional expressions (1) to (3) is sandwiched between, for example, the clamp 70 and the spacer 60A even when both main surfaces are sandwiched between the spacers 60A and 60B as in the glass substrate 1B. Even if the impact of the same condition is applied, it does not break. Therefore, as in the case where both main surfaces are sandwiched between the spacers 60A and 60B, the flange 30a has no annular protrusion 30p and the surface in contact with the glass substrate 1C is the same as the end surface of the spacer 60B with high precision grinding. It may be in a finished state. In this case, if the radius to the outer peripheral end face of the flange is a radius Rsf, the radius Rsf is preferably the same as the radius Rs of the spacer.

  The glass substrate for an information recording medium of the present invention is not limited to a magnetic recording medium, and can be used for a magneto-optical disk or an optical disk.

(Manufacturing process of glass substrate for information recording medium)
The production of the glass substrate for information recording medium will be described. In FIG. 5, the example of the manufacturing process of the glass substrate for information recording media is shown with a flowchart. First, a glass material is melted (glass melting process), molten glass is poured into a lower mold, and press molding is performed with an upper mold to obtain a disk-shaped glass substrate precursor (press molding process). Note that the disk-shaped glass substrate precursor may be produced by cutting a sheet glass formed by, for example, a downdraw method or a float method with a grinding stone, without using press molding.

  In the press-molded glass substrate precursor, a hole is made in the center by a core drill or the like made of a diamond grindstone (coring step). Next, both surfaces of the glass substrate are polished while supplying a grinding liquid to a known double-side polishing machine using, for example, diamond pellets, and the entire shape of the glass substrate, that is, the parallelism, flatness and thickness of the glass substrate are preliminarily reserved. It is adjusted (first lapping step).

  Next, the outer peripheral end surface and inner peripheral end surface of the glass substrate are ground and chamfered to finely adjust the outer diameter and roundness of the glass substrate, the inner diameter of the hole, and the concentricity between the glass substrate and the hole ( Inner and outer diameter machining process). Thereafter, the inner peripheral end face of the glass substrate is polished to remove fine scratches (inner peripheral end face processing step).

  Next, both surfaces of the glass substrate are polished again using diamond pellets finer than those in the first lapping step, and the parallelism, flatness and thickness of the glass substrate are finely adjusted (second lapping step). Next, the outer peripheral end face of the glass substrate is polished to remove fine scratches (outer peripheral end face processing step).

  Next, after the glass substrate is washed, the chemical strengthening layer is formed on the glass substrate by immersing the glass substrate in a chemical strengthening solution for the purpose of improving impact resistance, vibration resistance, and the like (chemical strengthening step). The chemical strengthening method is not particularly limited as long as it is a conventionally known chemical strengthening method. For example, low temperature type chemical strengthening in which ion exchange is performed in a region not exceeding the transition temperature is preferable from the viewpoint of the glass transition point. Examples of the alkali molten salt used for chemical strengthening include potassium nitrate, sodium nitrate, and nitrates obtained by mixing them.

  After that, a polishing process is performed to finish precisely while supplying a polishing liquid using cerium oxide or the like as an abrasive to a known double-side polishing machine using urethane foam, suede or the like with the surface of the glass substrate as a pad (polishing process). The polishing process may be divided into a plurality of processes such as the first polishing process and the second polishing process by changing the pad and the abrasive according to the manufacturing efficiency and the required surface roughness. By adjusting the setting conditions of the pad, polishing liquid, and polishing machine to be used, the surface roughness can be set in the range of Rmax from 2 nm to 6 nm and Ra from 0.2 nm to 0.4 nm. The flatness can be 5 μm or less. And it passes through a washing process and an inspection process, and becomes a glass substrate for information recording media as a product.

  Here, Ra (center line average roughness) and Rmax (maximum height) are defined in JIS B0601. These can be measured by an atomic force microscope (AFM) or the like.

  In addition, in the manufacturing method of the glass substrate for information recording media, you may have various processes other than the above. For example, an annealing process for relaxing internal distortion of the glass substrate, a heat shock process for confirming the reliability of the strength of the glass substrate, and removing foreign substances such as abrasives and chemical strengthening treatment liquid remaining on the surface of the glass substrate. You may have a washing process, various inspection and evaluation processes, etc. Also, the polishing process reduces the chemically strengthened area of the surface of the glass substrate. There is no restriction on whether or not chemically strengthened regions remain on the surface of the glass substrate after the polishing process, or on the thickness of the remaining strengthened regions.

  Thus, the glass substrate for information recording media is manufactured. The glass substrate for information recording media having the shape of the inner peripheral edge of the present invention can be obtained by appropriately adjusting the conditions of the polishing process from the inner peripheral end face processing step.

(Material of glass substrate)
The material of the glass substrate is not particularly limited as long as it can be chemically strengthened by ion exchange. For example, soda lime glass mainly composed of SiO ₂ , Na ₂ O and CaO; aluminosilicate glass mainly composed of SiO ₂ , Al ₂ O ₃ and R ₂ O (R = K, Na, Li); borosilicate Glass; Li ₂ O—SiO ₂ glass; Li ₂ O—Al ₂ O ₃ —SiO ₂ glass; R′O—Al ₂ O ₃ —SiO ₂ glass (R ′ = Mg, Ca, Sr, Ba) Etc. can be used. Among these, aluminosilicate glass and borosilicate glass are particularly preferable because they are excellent in impact resistance and vibration resistance.

(Magnetic recording medium)
An information recording medium can be obtained by forming at least a recording layer on the glass substrate for information recording medium of the present invention. The recording layer is not particularly limited, and various recording layers utilizing properties such as magnetism, light, and magnetomagnetism can be used. Particularly, for the production of a magnetic recording medium (magnetic disk) using the magnetic layer as a recording layer. Is preferred.

  The magnetic material used for the magnetic layer is not particularly limited, and a known material can be appropriately selected and used. Examples thereof include CoPt, CoCr, CoNi, CoNiCr, CoCrTa, CoPtCr, CoNiPt, CoNiCrPt, CoNiCrTa, CoCrPtTa, and CoCrPtSiO containing Co as a main component. The magnetic layer may be divided by a nonmagnetic film (for example, Cr, CrMo, CrV, etc.) to have a multilayer structure in which noise is reduced.

As the magnetic layer, in addition to the above-mentioned Co-based material, ferrite or iron - and material of the rare earth-based, Fe, Co, CoFe, magnetic particles such CoNiPt are dispersed in a non-magnetic film made of SiO _2, BN A granular structure can also be used. The magnetic layer may be either an in-plane type or a vertical type.

  As a method for forming the magnetic film, a known method can be used. For example, a sputtering method, an electroless plating method, a spin coating method, and the like can be given.

The magnetic recording medium may be further provided with an underlayer, a protective layer, a lubricating layer, etc., if necessary. Any of these layers can be used by appropriately selecting a known material. Examples of the material for the underlayer include Cr, Mo, Ta, Ti, W, V, B, Al, and Ni. Examples of the material for the protective layer include Cr, Cr alloy, C, ZrO ₂ , and SiO ₂ . Moreover, as a lubrication layer, the thing etc. which apply | coated the liquid lubricant which consists of perfluoropolyether (PFPE) etc., and heat-processed as needed are mentioned, for example.

  As an information recording medium glass substrate, an aluminosilicate glass substrate having an outer diameter of 65 mm, an inner diameter of 20 mm, and a plate thickness of 0.635 mm was manufactured according to the manufacturing process of FIG.

Specifically, a glass material mainly composed of SiO ₂ , Al ₂ O ₃ , R ₂ O (R = K, Na, Li) is melted (glass melting step), and the molten glass is poured into the lower mold, A disk-shaped glass substrate precursor was obtained by press molding with a mold (press molding process).

  A hole was made in the center portion of the press-molded glass substrate precursor with a core drill composed of a diamond grindstone (coring step). Next, both surfaces of the glass substrate were polished with a known double-sided lapping machine equipped with diamond pellets of # 1000 mesh while supplying a grinding liquid, and the parallelism, flatness and thickness of the glass substrate were preliminarily adjusted ( First wrapping step).

  Next, the outer peripheral end surface and the inner peripheral end surface of the glass substrate are ground with a drum-shaped diamond grindstone and chamfered by about 0.1 mm to obtain the outer diameter and roundness of the glass substrate, the inner diameter of the hole, and the glass. The concentricity between the substrate and the hole was finely adjusted (inner / outer diameter machining process). Next, brushing was performed on the inner peripheral end surface of the glass substrate while supplying a polishing liquid to remove fine scratches (inner peripheral end surface processing step).

  Next, both surfaces of the glass substrate are polished again with a known double-sided lapping machine equipped with # 1500 mesh diamond pellets while supplying the grinding liquid, and the parallelism, flatness and thickness of the glass substrate are finely adjusted. (Second wrapping step). Then, brush polishing was performed on the outer peripheral end surface of the glass substrate while supplying a polishing liquid to remove fine scratches (outer peripheral end surface processing step).

Next, after washing the glass substrate, the glass substrate was immersed in a chemical strengthening solution to form a chemically strengthened layer on the glass substrate (chemical strengthening step). As the chemical strengthening solution, a chemical strengthening agent containing NaNO ₃ and KNO ₃ in a mass ratio of 5: 5 was added to the chemical strengthening tank and heated to 375 ° C.

  Then, the grinding | polishing process which finishes the surface of a glass substrate precisely was performed (polishing process). In the polishing process, both surfaces of the glass substrate were polished while supplying a polishing liquid with a known double-side polishing machine equipped with pads. By changing the conditions such as the type and particle size of the abrasive used for the polishing liquid supplied to the polishing machine, the number of rotations of the surface plate with pads contacting both surfaces of the glass substrate, and the pressure of the pad against the glass substrate, various Glass substrate No. having the inner peripheral end face shape 1 to No. 17 was obtained as a sample. The surface roughness of these glass substrates was in the range of Rmax from 2 nm to 6 nm and Ra from 0.2 nm to 0.4 nm.

  Thereafter, the glass substrate was washed, and then a magnetic film was provided on the glass substrate to obtain a magnetic recording medium. From the glass substrate side, the magnetic film consists of a Ni—Al base layer (thickness of about 100 nm), a Co—Cr—Pt recording layer (thickness 20 nm), and a protective film (DLN 5 nm) made of DLC (Diamond Like Carbon). Laminated sequentially. Thus, the thickness of the magnetic film is sufficiently thin compared to the thickness of the glass substrate.

  As shown in FIG. 4, the completed magnetic recording medium was inserted into an SPM hub equipped with a flange in the order of a glass substrate, a spacer, and a glass substrate, and two glass substrates were fixed using a clamp. This SPM was incorporated into a drop test jig 80 simulating a magnetic disk recording device shown in FIG. In the drop test jig 80, reference numeral 82 denotes an aluminum die-cast base to which the SPM is attached, 84 denotes a SUS cover, 86 and 88 denote glass substrates, and 90 denotes a clamp. Further, similarly to an actual magnetic disk recording apparatus, a ramp 92 is provided for waiting the magnetic head. Five drop test jigs 80 were prepared for each of the following samples.

  Thereafter, when the SPM of each drop test jig 80 was rotated at 7200 rpm, the sample No. Any of 1 to 17 operated without any problem. Next, a drop test was performed to examine whether the glass substrate was cracked. In the drop test, the above-described drop test jig 80 is fixed in a horizontal state (a glass substrate is in a horizontal state) on a separately prepared fixing jig by the same fixing method as that of an actual magnetic disk recording apparatus. The dropping test jig 80 is dropped together with the fixing jig while maintaining the level. The impact of the drop is received by the falling fixture under the acceleration jig provided at the fixture so that the acceleration of the attack that occurs at the beginning of the fall is 1000G and the duration of this acceleration is 1 ms. And the fall height was adjusted. The number of drops of the drop test jig 80 is as follows: a state in which the drop test jig 80 is attached to the fixed jig so that the hub of the SPM is on the lower side, and a state in which the drop test jig 80 is upside down. Dropped 3 times.

  The results are shown in Table 1. Table 2 shows the specifications of the flange, spacer, and clamp for fixing the magnetic recording medium used at this time to the SPM hub included in the drop test jig 80. In addition, since the radius of the hole of a glass substrate is 10 mm, the value of distance R1 is 15 mm and the value of distance R3 is 10.35 mm.

  From the above results, the magnetic recording medium having a shape satisfying the conditional expressions (1) to (3) is stably fixed to the hub of the SPM (spindle motor) and strong against the magnetic disk recording apparatus in which the SPM is incorporated. It was confirmed that it was not damaged when an impact was applied.

Claims (5)

A glass substrate for an information recording medium in a donut shape having a main surface with a flat portion, a concentric outer peripheral end surface and an inner peripheral end surface;
A spindle motor including a rotatable hub;
The surface facing the main surface is flat when fitted to the outer periphery of the hub and inserted into the hole formed by the inner peripheral end surface, and the outer periphery of the opposing surface has a radius Rs with the hole as a central axis. A first clamping member having a first shape which is a circular shape of
A second clamping member having a second shape having an annular protrusion at a radius Rp smaller than the radius Rs with the hole as a central axis on a surface facing the main surface;
An information recording apparatus that holds the glass substrate for information recording medium between the first holding member and the second holding member and is fixed to the hub,
The distance R1 from the central axis of the glass substrate for information recording medium on the contour line of one main surface of the cross section perpendicular to the main surface in the radial direction of the glass substrate for information recording medium is the radius of the hole. A position P1 for R0 + 5 mm and a position P3 for setting a distance R3 from the central axis of the glass substrate for information recording medium to a radius R0 + 0.35 mm of the hole are defined in the same cross section, and the contour line is the position P1. And a position P2 between the position P3 and a reference plane with the flat portion of the main surface as a reference in the thickness direction of the glass substrate for information recording medium, and the position from the central axis of the glass substrate for information recording medium An information recording apparatus satisfying the following conditional expression, wherein a distance to P2 is a distance R2 and a distance between the reference plane and the position P3 is Δh.
Value of distance R3 <Value of radius Rs <Value of distance R2 Value of distance R3 <Value of radius Rp <Value of distance R2 0.001 μm <Δh <5.0 μm.   2. The information recording apparatus according to claim 1, wherein the front surface and the back surface of the glass substrate for information recording medium have a symmetrical shape.   2. The information recording apparatus according to claim 1, further comprising a magnetic film on a surface of the glass substrate for the information recording medium. In a donut shape having a main surface with a flat part, a concentric outer peripheral end surface and an inner peripheral end surface,
In a state where a rotatable hub of a spindle motor constituting the information recording device is fitted and inserted into the hole formed by the inner peripheral end face,
A first clamping member having a first shape in which a surface facing the main surface is flat and an outer periphery of the facing surface is a circle having a radius Rs with the hole as a central axis;
A second clamping member having a second shape having an annular protrusion having a radius Rp smaller than the radius Rs with the hole as a central axis on a surface facing the main surface, and is fixed to the hub. In an information recording medium glass substrate,
On the outline of one main surface of the cross section perpendicular to the main surface in the radial direction of the glass substrate for information recording medium,
A position P1 where a distance R1 from the central axis of the glass substrate for information recording medium is a radius R0 + 5 mm of the hole;
A position P3 where the distance R3 from the central axis of the glass substrate for information recording medium is a radius R0 + 0.35 mm of the hole is determined in the same cross section,
The contour line is separated from a reference plane with the flat portion of the main surface as a reference at a position P2 between the position P1 and the position P3 in the thickness direction of the glass substrate for the information recording medium. A glass substrate for an information recording medium satisfying the following conditional expression, wherein a distance from the central axis of the glass substrate to the position P2 is a distance R2 and a distance between the reference plane and the position P3 is Δh.
Value of distance R3 <value of radius Rs <value of distance R2 value of distance R3 <value of radius Rp <value of distance R2 0.001 μm <Δh <5.0 μm A magnetic recording medium comprising a magnetic film on the surface of the glass substrate for information recording medium according to claim 4.