JP5719785B2 - GLASS SUBSTRATE FOR INFORMATION RECORDING MEDIUM, INFORMATION RECORDING MEDIUM, AND INFORMATION RECORDING DEVICE - Google Patents

Description

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

  2. Description of the Related Art A substrate using a glass substrate is known as a substrate of a small information recording apparatus used for a notebook type personal computer or a card type recording medium. In such a portable information recording apparatus, the magnetic head and the recording layer of the information recording medium are protected from external impacts while the apparatus is at a position where it overlaps the end of the information recording medium. There is known a ramp load type in which a magnetic head is retracted to an arranged lamp and recording is performed by sliding the magnetic head out of the lamp when the apparatus is started.

  Although the ramp load type information recording apparatus uses an information recording medium that does not cause a particular problem even if it is dropped or given an impact when incorporated in a non-ramp load type apparatus. However, it has been found that the glass substrate is damaged by a sudden impact such as a drop or a collision. In particular, this problem was significant when a glass substrate that was not subjected to a tempering treatment was used.

  The cause of this problem is that the information recording medium is sandwiched between the crow mouth part at the tip of the lamp with a slight gap between them, so when the recording medium is bent, it collides with the lamp and the glass substrate is broken. This is probably because of this.

  In order to solve such problems, a glass substrate for an information recording medium has been proposed in which the main surface is inclined so that the thickness of the substrate decreases from the central portion toward the outer surface to prevent the substrate from cracking due to a lamp collision. (For example, refer to Patent Document 1).

JP 2006-318583 A

  In general, in an information recording apparatus, an information recording medium is inserted into a rotating shaft of a spindle motor, and the information recording medium is sandwiched between a cylindrical ring jig and a clamp jig provided with an annular protrusion, and the rotating shaft is inserted into the rotating shaft. Fix it. At this time, the information recording medium is tightened in the thickness direction by the clamp jig and the ring jig so that the torque generated by the rotational drive of the spindle motor can be sufficiently transmitted to the information recording medium.

  In recent years, with the improvement in performance required for information recording apparatuses, the spindle motor has been rotated at a higher speed. For this reason, the amount of tightening force required to reliably transmit the torque generated by the rotational drive of the spindle motor to the information recording medium is increased, and the information recording medium is warped by being strongly tightened.

  When such a warp occurs, the outermost periphery of the information recording medium is located closer to the lamp side than the middle position of the crow mouth portion of the lamp, and the information recording medium and the lamp come close to each other, so even a slight external impact can cause the lamp. I found out that it would collide.

  However, the conventional information recording apparatus does not consider such warpage. Therefore, even if the glass substrate for information recording media described in Patent Document 1 is used, the glass substrate may be cracked due to lamp collision.

  However, in order to improve the existing information recording medium fixing mechanism of the information recording apparatus and prevent the warp when the information recording medium is fixed to the rotating shaft, a large amount of investment is necessary and it is difficult to do so immediately. It is.

  The present invention has been made in view of the above problems, and prevents the occurrence of warping when fixing an information recording medium to a rotating shaft using a conventional information recording medium fixing mechanism. It is an object of the present invention to provide a glass substrate for an information recording medium, an information recording medium, and an information recording apparatus using the information recording medium capable of preventing the substrate from cracking.

  In order to solve the above problems, the present invention has the following characteristics.

1. A disc-shaped glass substrate for an information recording medium comprising a through-hole into which a rotation shaft is inserted at a central portion, sandwiching a peripheral portion of the through-hole on the main surface from both sides and fixed to the rotation shaft,
A convex or concave warpage is provided in advance from the through hole so that the main surface is corrected and flattened by a force that sandwiches the peripheral edge from both sides when fixed to the rotating shaft. A glass substrate for an information recording medium.

2. The contours of the main surface on both sides are
2. The glass substrate for an information recording medium as described in 1 above, wherein both are concentric circles and the intervals are equal.

3. The thickness of the information recording medium glass substrate is:
3. The glass substrate for information recording media according to 1 or 2, wherein the glass substrate is thinner from the center toward the outer surface.

4). The thickness of the information recording medium glass substrate is:
3. The glass substrate for information recording media as described in 1 or 2 above, which is 0.78 to 2.2 mm.

  5. 5. The glass substrate for information recording media according to any one of 1 to 4, wherein a circumferential direction TIR of the main surface in the vicinity of the through hole is 0.7 μm or less.

  6). 6. An information recording medium comprising a recording layer provided on the main surface of the glass substrate for information recording medium according to any one of 1 to 5 above.

7). An information recording apparatus having a cylindrical ring jig, a clamp jig provided with an annular protrusion, and a drive mechanism for rotating a rotating shaft,
The information recording medium described in 6 above,
A head for reading and writing the information recording medium;
A lamp arranged such that the position of the tip overlaps the end of the information recording medium;
A head driving mechanism for loading the head retracted on the ramp onto the information recording medium and unloading the head onto the ramp;
Have
The information is obtained by penetrating the rotating shaft in the order of the ring jig and the information recording medium and pressing an annular protrusion of the clamp jig against the surface of the information recording medium and sandwiching the information between the ring jig and the information recording medium. An information recording apparatus, wherein the information recording medium is fixed to the rotating shaft by correcting warping of the recording medium.

  The glass substrate for an information recording medium of the present invention is provided with a convex or concave warp from the through hole toward the outside so that the main surface is flattened when fixed to the rotating shaft. Therefore, the warp provided in advance by the force of tightening when the peripheral portion of the through hole on the main surface is sandwiched from both sides and fixed to the rotating shaft is corrected, and the substrate can be flattened.

  Therefore, when the information recording medium is fixed to the rotating shaft by using the conventional information recording medium fixing mechanism, it is possible to prevent the substrate from cracking due to the collision of the lamp so as not to warp. A glass substrate, an information recording medium, and an information recording apparatus using the information recording medium can be provided.

It is sectional drawing which shows one Embodiment of the glass substrate for information recording media which concerns on this invention. It is an example of the interference fringe generated on the glass substrate using the interferometer. It is sectional drawing of the magnetic disc 5 which is an example of the information recording medium based on this invention. FIG. 3 is a top view of a ramp load type hard disk device 200, which is an example of an information recording apparatus according to the present invention, on which a magnetic disk 5 is mounted. FIG. 10 is a perspective view of relevant parts showing an operation example of the hard disk device 200. 3 is a schematic cross-sectional view showing a state in which a magnetic disk 5 is fixed to a rotary shaft 6. FIG. 6 is a cross-sectional view for explaining a cause of warping of a flat magnetic disk 59 when it is fixed to a rotary shaft 6. FIG. It is sectional drawing which shows 2nd Embodiment of the glass substrate for information recording media concerning this invention. FIG. 9 is a schematic cross-sectional view showing a state in which a magnetic disk 5 manufactured from the glass substrate 1 shown in FIG. 8 is fixed to a rotating shaft 6. It is a manufacturing-process figure of an example of the manufacturing method of the glass substrate which concerns on this invention. It is explanatory drawing which shows the state which mounted the glass substrate 1 in the lower polishing tray 13 of an Oscar polisher. It is a cross-sectional view of an Oscar polisher. It is a top view of the Oscar grinder for demonstrating the upper grinding | polishing dish 14 rock | fluctuated right and left. It is explanatory drawing explaining the process of making the thickness of a glass substrate thin from an inner periphery to an outer periphery. 2 is a plan view of a magnetic disk 5. FIG.

  FIG. 1 is a cross-sectional view showing an embodiment of a glass substrate for an information recording medium according to the present invention.

  The glass substrate 1 for information recording medium has a donut-shaped disk shape with a through hole 20 formed in the center. The through-hole 20 is used for fixing the glass substrate 1 to the rotation shaft 6 (not shown in FIG. 1) and rotating the glass substrate 1 around the center. The glass substrate 1 is fixed to the rotary shaft 6 by sandwiching the peripheral portions of the through holes 20 of the main surface 10a and the main surface 10b from both sides. The main surface 10a and the main surface 10b of the glass substrate 1 are smooth surfaces.

  As shown in FIG. 1, the cross section of the glass substrate 1 is formed in a shape in which the vicinity of the through hole 20 of the main surface 10 a and the main surface 10 b is convexly convex from the through hole 20 toward the outer surface 40.

  Since the main surface 10b of the glass substrate 1 can be used with the main surface 10a on the upper side of the drawing and the main surface 10a on the lower side of the drawing, the cross section of the glass substrate 1 is warped in the vicinity of the through hole 20 in that case. Will be.

  Since the glass substrate 1 is warped from the time of manufacture in this way, the reverse is achieved by clamping the peripheral portions of the through holes 20 of the main surface 10a and the main surface 10b from both sides and fixing them to the rotating shaft 6 in the subsequent process. The glass substrate 1 can be flattened by generating a warp in the direction. The glass substrate 1 is attached to the rotating shaft 6 so that the warping direction of the substrate is opposite to the warping that occurs when the substrate is fixed to the rotating shaft 6.

  FIG. 2A is an example of interference fringes generated by irradiating the main surface 10a with laser light using an interferometer. FIG. 2B is a cross section of the glass substrate 1, and W indicates warpage.

  In FIG. 2A, e1, e2, and e3 are darkened portions of the interference fringes and correspond to contour lines of the main surface 10a. In the example shown in FIG. 2A, the contour lines e1, e2, e3 are all concentric circles, and the intervals are equal. Further, even if the main surface 10b is irradiated with laser light to generate interference fringes, three contour lines are similarly generated. The contour lines are all concentric circles, and the intervals are equal.

  In this way, when the main surface 10a and the main surface 10b are shaped so that the contour lines are concentric and the intervals are equal, the peripheral portions of the through holes 20 of the main surface 10a and the main surface 10b are sandwiched from both sides. The glass substrate 1 can be made flatter by fixing to the rotating shaft 6.

  FIG. 3 is a cross-sectional view of a magnetic disk 5 which is an example of an information recording medium according to the present invention. In the magnetic disk 5, the magnetic film 11a is directly formed on the main surface 10a of the circular glass substrate 1, and the magnetic film 11b is directly formed on the main surface 10b. In this embodiment, an example in which the magnetic film 11 is formed on both surfaces of the magnetic disk 5 will be described. However, the magnetic film 11 may be provided only on either the main surface 10a or the main surface 10b.

  The glass substrate 1 of the present invention can also be used as a glass substrate for a magneto-optical disk.

  FIG. 4 is a top view of a ramp load type hard disk device 200, which is an example of an information recording apparatus according to the present invention, in which the magnetic disk 5 is mounted. FIG. 5 is a perspective view of a main part showing an operation example of the hard disk device 200, showing a state in which the suspension 54 that supports the recording / reproducing head 53 is retracted on the sliding surface 51 a of the ramp 51.

  As shown in FIGS. 4 and 5, the hard disk device 200 of this embodiment includes a suspension 54 that supports a recording / reproducing head 53 and an arm 37 that fixes the suspension 54. The arm 37 is rotatably attached to the housing 501 with the pivot 38 as an axis, and is driven to rotate by a voice coil motor (not shown) provided on the opposite side of the suspension 54 with the pivot 38 interposed therebetween.

  The lift tab 52 is a protrusion provided at the tip of the suspension 54 and is located on the tip side of the recording / reproducing head 53. The ramp 51 has a sliding surface 51 a with which the lift tab 52 comes into contact. While the lift tab 52 is in contact with the sliding surface 51 a of the ramp 51, the interval between the two suspensions 54 is regulated, and the recording / reproducing head 53. Contact between each other and contact between the recording / reproducing head 53 and the magnetic disk 5 are prevented.

  The recording / reproducing head 53 floats from the surface of the magnetic disk 5 by an air flow generated by the rotation of the magnetic disk 5. For this reason, when loading the recording / reproducing head 53 onto the surface of the magnetic disk 5, it is necessary to support the lift tab 52 with the ramp 51 until the recording / reproducing head 53 reaches the surface of the magnetic disk 5. Further, when the recording / reproducing head 53 is unloaded to the outside of the magnetic disk 5, it is necessary to support the lift tab 52 by the ramp 51 before the recording / reproducing head 53 comes out of the magnetic disk 5.

  That is, as shown in FIG. 5, it is necessary to support the lift tab 52 with the ramp 51 in a state where the recording / reproducing head 53 is positioned on the surface near the outer periphery of the magnetic disk 5. Here, when the recording / reproducing head 53 is positioned on the surface of the magnetic disk 5, the lift tab 52 is also positioned on the surface of the magnetic disk 5, so that the contact point between the lift tab 52 and the ramp 51 is on the surface of the magnetic disk 5. Therefore, it is necessary to dispose the tip of the ramp 51 at a position covering the surface of the magnetic disk 5. Usually, since two recording / reproducing heads 53 are provided for both sides of one magnetic disk 5, the tip portions 51 b and 51 c of the lamp 51 are arranged so as to sandwich the magnetic disk 5 as shown in FIG. It is formed in a shape. Such a lamp can be manufactured by molding a resin material.

  The clamp jig 2 provided with an annular protrusion on the side facing the magnetic disk 5 is fixed to a rotating shaft 6 of a magnetic disk drive motor (not shown) by a screw 3 as shown in FIG. A magnetic disk 5 is sandwiched between a ring-shaped jig 7 (not shown) and fixed to the rotary shaft 6.

  Next, a change in warpage caused by fixing the magnetic disk 5 to the rotating shaft 6 will be described with reference to FIGS.

  FIG. 6 is a schematic cross-sectional view showing a state in which the magnetic disk 5 is fixed to the rotary shaft 6, and FIG. 7 explains the cause of warping of the flat magnetic disk 59 when the magnetic disk 5 is fixed to the rotary shaft 6. FIG.

  First, a phenomenon in which a warp occurs when a conventional flat magnetic disk 59 is fixed to the rotating shaft 6 of the hard disk device 200 will be described with reference to FIG.

  FIG. 7A shows a state in which the ring-shaped jig 7 and the flat magnetic disk 59 are inserted into the rotating shaft 6 in this order, and the clamp jig 2 is tightened with screws 3 from now on. A screw hole that is screwed into the screw 3 is provided at the center of the rotary shaft 6. In the figure, a point indicated by an arrow A is a point where the annular protrusion 2 a of the clamp jig 2 abuts the magnetic disk 59, and a point indicated by an arrow B is the magnetic disk 59 at the outermost periphery of the ring-shaped jig 7. The point of contact, the point indicated by arrow C, is the center of the thickness of the outermost periphery of the magnetic disk 59. Lc is the diameter to point C. In the example of FIG. 7A, the diameter La of the annular protrusion 2 a of the clamping jig 2 is smaller than the outer diameter Lb of the ring-shaped jig 7.

  FIG. 7B shows a state in which the screw 3 is tightened and the magnetic disk 59 is sandwiched between the ring-shaped jig 7 and the clamp jig 2 with a predetermined pressure. When the screw 3 is tightened, pressure is applied to the magnetic disk 59 from the projection 2a of the clamp jig 2 and the contact part of the magnetic disk 59 indicated by A in the figure. Due to this pressure, the tip of the magnetic disk 59 is warped toward the clamping jig 2 as shown in FIG. FIG. 7B shows a state in which the magnetic disk 59 is warped toward the clamp jig 2 from the center line S of the thickness of the flat magnetic disk 59 in FIG. The warpage amount α is defined as a positive direction for warping in the direction of the clamping jig 2 (upward on the paper surface) and a negative direction for warping in the direction of the ring jig 7 (downward on the paper surface).

  Next, an example in which the diameter La of the annular protrusion 2a of the clamp jig 2 is larger than the outer diameter Lb of the ring-shaped jig 7 will be described.

  FIG. 7C shows a state in which the ring-shaped jig 7 and the flat magnetic disk 59 are inserted into the rotating shaft 6 in this order, and the clamp jig 2 is tightened on the screw provided at the center of the rotating shaft 6 from now on. Is shown. In the example of FIG. 7C, the diameter La of the annular protrusion 2 a of the clamp jig 2 is larger than the outer diameter Lb of the ring-shaped jig 7.

  FIG. 7D shows a state in which the screw 3 is tightened and the magnetic disk 59 is sandwiched between the ring-shaped jig 7 and the clamp jig 2 with a predetermined pressure. When the screw 3 is tightened, pressure is applied to the magnetic disk 59 from the projection 2a of the clamp jig 2 and the contact part of the magnetic disk 59 indicated by A in the figure. Unlike the case of FIG. 7B, the clamp jig 2 and the ring-shaped jig 7 in FIG. 7D are La> Lb. 7 is bent in the direction of the ring-shaped jig 7 so as to be bent from the tip portion. FIG. 7D shows a state in which the magnetic disk 59 is warped in the direction of the ring-shaped jig 7 from the center line S of the thickness of the flat magnetic disk 59 in FIG. ing.

  Next, FIG. 6 will be described. FIG. 6 is an example in which the diameter La of the annular protrusion 2a of the clamp jig 2 is smaller than the outer diameter Lb of the ring-shaped jig 7 as shown in FIGS. 7 (a) and 7 (b). The distance between the tip portions 51b and 51c of the lamp 51 is D.

  6A and 6B show an embodiment of the present invention, and FIG. 6A shows a state in which the magnetic disk 5 shown in FIG. 3 is inserted into the rotary shaft 6 so that the cross section is convex. 6 (b) shows a state in which the magnetic disk 5 is sandwiched between the ring-shaped jig 7 and the clamp jig 2 with a predetermined pressure by tightening the screws 3.

  6 (c) and 6 (d) show a conventional example, FIG. 6 (c) shows a state in which a flat magnetic disk 59 is inserted into the rotary shaft 6, and FIG. 6 (d) shows a ring shape by tightening the screw 3. The magnetic disk 59 is sandwiched between the jig 7 and the clamp jig 2 with a predetermined pressure.

  6 (e) and 6 (f) are comparative examples, and FIG. 6 (e) shows a state in which the magnetic disk 5 shown in FIG. 3 is inserted into the rotating shaft 6 so that the cross section is concave, and FIG. Is a state in which the magnetic disk 5 is sandwiched between the ring-shaped jig 7 and the clamp jig 2 with a predetermined pressure by tightening the screws 3.

  When the magnetic disk 5 of the present invention is inserted into the rotating shaft 6 with the cross-section curved as shown in FIG. 6A, and the screw 3 is tightened to a pressure corresponding to the thickness of the glass substrate 1, FIG. As shown in b), the warp of the magnetic disk 5 is corrected and can be made flat. As a result, the outer peripheral portion of the magnetic disk 5 is equidistant from the tip portions 51b and 51c of the ramp 51, and the probability that the magnetic disk 5 collides with the ramp 51 and is damaged can be reduced.

  In addition, it is preferable to make the thickness of the glass substrate 1 into the range of 0.78 mm-2.2 mm. When the thickness of the glass substrate 1 exceeds 2.2 mm, the glass substrate 1 hardly warps even when sandwiched at a predetermined pressure. However, if the thickness of the substrate is thick, the distance between the glass substrate 1 and the tip portions 51b and 51c of the lamp 51 is narrowed, and the probability of damage due to collision with the lamp 51 increases. Therefore, the thickness should be 2.2 mm or less. desirable.

  Further, when the thickness of the glass substrate 1 is less than 0.78 mm, the glass substrate 1 is greatly warped when sandwiched at a predetermined pressure. Therefore, it is necessary to prepare the glass substrate 1 having a large warp amount in advance. However, since the glass substrate 1 having a thin substrate and a large amount of warpage has a low yield rate, the thickness is preferably 0.78 mm or more.

  Further, the circumferential direction TIR (Total Induced Runout) of the main surface 10 in the vicinity of the through hole 20 is preferably 0.7 μm or less.

  TIR is an index representing the flatness (waviness) of the glass substrate 1, and the distance from the least square plane to the highest point of the evaluation surface (main surfaces 10a, 10b) and the distance from the least square plane to the lowest point. And the total. In the present embodiment, the circumferential direction TIR refers to a TIR for one round in the circumferential direction at a position in the vicinity of the through hole 20 with which the annular protrusion 2a of the lamp jig 2 contacts.

  Since the annular protrusion 2a of the clamp jig 2 abuts in the vicinity of the through hole 20, in the magnetic disk 5 using the glass substrate 1 having a circumferential direction TIR larger than 0.7 μm, the protrusion 2a of the clamp jig 2 Contact on the surface of the magnetic disk 5 is not uniform, resulting in discontinuous line contact. As a result, the shape of the surface of the magnetic disk 5 after clamping becomes different depending on the cross-sectional direction.

  In the case of the magnetic disk 5 using the glass substrate 1 having a circumferential direction TIR of 0.7 μm or less, the contact between the protrusion 2a of the clamp jig 2 and the surface of the magnetic disk 5 is a substantially uniform circumferential shape. The shape of the surface of the subsequent magnetic disk 5 is almost the same in any cross section. Therefore, it is possible to reduce the probability that the magnetic disk 59 collides with the lamp 51 and is damaged.

  Such a TIR in the circumferential direction can be obtained by measuring the surface shape using interference of white light (for example, Optiflat manufactured by Phase Shift Technology) or by injecting laser light obliquely with respect to the surface to be measured. What is necessary is just to measure by the system (for example, FlatMaster FM100XRA by TROPEL) etc. which can obtain a high reflectance compared with a normal incidence system, and can also measure in a rough surface shape.

  Furthermore, when the absolute value α1 of the warp amount of the recording medium before the screw 3 is tightened and α2 is the absolute value of the correction amount of the warp when the screw 3 is fastened and fixed to the rotary shaft 6, α1 ≧ α2 is satisfied. It is desirable.

  In the case of α1 <α2, the internal distortion of the glass substrate 1 in the vicinity of the protrusion 2a increases, and the glass substrate 1 is likely to break due to the vibration transmitted from the drive rotation shaft at the time of a drop impact.

  When the Young's modulus E is less than 84 GPa, there is a tendency that α1 <α2 when the magnetic disk 5 is sandwiched at a predetermined pressure to fix the magnetic disk 5 to the rotating shaft 6. Therefore, the Young's modulus of the glass substrate 1 for information recording media E (GPa) is preferably 84 or more.

  On the other hand, in the case of FIG. 6D using the conventional flat magnetic disk 59, the diameter La of the annular protrusion 2 a of the clamp jig 2 is smaller than the outer diameter Lb of the ring-shaped jig 7. When 3 is tightened, the magnetic disk 59 is warped in the upward direction on the paper surface as in FIG. Therefore, the outer periphery of the magnetic disk 59 approaches the tip 51b of the lamp 51, and the probability that the magnetic disk 59 collides with the lamp 51 and is damaged increases.

  Further, when the magnetic disk 5 is inserted into the rotating shaft 6 with the cross-section warped in a concave shape as shown in FIG. 6E and the screw 3 is tightened, the warp of the magnetic disk 5 is further increased as shown in FIG. It gets bigger. Thus, if the insertion direction of the magnetic disk 5 is wrong, the outer peripheral part of the magnetic disk 5 comes closer to the tip 51b of the ramp 51, and the probability that the magnetic disk 59 collides with the ramp 51 and is damaged becomes very high.

  When the diameter La of the annular protrusion 2a of the clamp jig 2 is larger than the outer diameter Lb of the ring-shaped jig 7, the magnetic disk 5 is inserted into the rotary shaft 6 so that the cross section is warped concavely, When the screw 3 is tightened, the warp can be corrected.

  Next, the glass substrate for information recording media of 2nd Embodiment is demonstrated.

  FIG. 8 is a sectional view showing a second embodiment of the glass substrate for information recording medium according to the present invention. FIG. 9 is a schematic cross-sectional view showing a state in which the magnetic disk 5 produced from the glass substrate 1 shown in FIG. The diameter La of the annular protrusion 2a of the clamp jig 2 shown in FIG. 9 is smaller than the outer diameter Lb of the ring-shaped jig 7 as shown in FIGS. 7 (a) and 7 (b).

  The entire structure of the glass substrate 1 for information recording medium is a disk-shaped thing, and the through-hole 20 is opened in the center part. Similar to the embodiment of FIG. 1, the through hole 20 is used to fix the glass substrate 1 to the rotation shaft 6 and rotate the glass substrate 1 around the center. The main surface 10a and the main surface 10b of the glass substrate 1 are smooth surfaces.

  As shown in FIG. 8, the cross section of the glass substrate 1 warps in a convex shape from the through hole 20 toward the outer surface 40, and the thickness decreases from the through hole 20 toward the outer surface 40 as a whole. In addition, the main surfaces 10a and 10b are slightly inclined.

  FIG. 9A shows a state in which the magnetic disk 5 manufactured from such a glass substrate 1 is inserted into the rotating shaft 6, and FIG. 9B shows a ring-shaped jig 7 and a clamp jig 2 by tightening the screws 3. Is a state in which the magnetic disk 5 is sandwiched at a predetermined pressure.

  When the magnetic disk 5 of the second embodiment is inserted into the rotating shaft 6 with the convex shape as shown in FIG. 9A, and the screw 3 is tightened with a pressure corresponding to the thickness of the glass substrate 1, FIG. As shown in (b), the warp of the magnetic disk 5 is corrected and can be made flat.

In the second embodiment, the main surfaces 10a and 10b are tapered from the central portion toward the outer surface 40 in an overall tapered manner, so that the magnetic surfaces are more magnetic than those in the first embodiment shown in FIG. The distances x ₁ and x ₂ between the outer peripheral portion of the disk 5 and the front end portions 51b and 51c of the lamp 51 can be evenly widened. Further, since the connection from the main surface 10a to the outer surface 40 can be made more gentle, stress concentration is less likely to occur. As a result, the probability of the magnetic disk 59 colliding with the lamp 51 and being damaged can be further reduced.

<Manufacturing process of glass substrate>
Next, the manufacturing process of the glass substrate 1 will be described.

  There is no particular limitation on the size of the glass substrate 1. For example, there are glass substrates 1 having various sizes such as 2.5 inches, 1.8 inches, 1 inch, and 0.8 inches in outer diameter. The thickness of the glass substrate 1 is preferably in the range of 0.78 mm to 2.2 mm.

  FIG. 10 is a production process diagram of an example of a method for producing a glass substrate according to the present invention. The manufacturing process of the glass substrate of the embodiment will be described in detail with reference to FIG.

(Glass melting process)
First, the glass material is melted.

There is no restriction | limiting in particular as a material of a glass substrate. For example, soda lime glass mainly composed of SiO ₂ , Na ₂ O, CaO; aluminosilicate glass mainly composed of SiO ₂ , Al ₂ O ₃ , 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.

(Press molding process)
Molten glass is poured into the lower mold and press-molded with the upper mold to obtain a disk-shaped glass substrate precursor. The disc-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.

(Coring process)
The press-molded glass substrate precursor is drilled at the center with a core drill or the like having a diamond grindstone or the like at the cutter.

(First lapping process)
Next, both surfaces of the glass substrate are lapped to preliminarily adjust the overall shape of the glass substrate, that is, the shape and thickness of the glass substrate shown in FIG.

(Inner / outer diameter machining process)
Next, the inner and outer diameters are processed by grinding the outer peripheral end surface and the inner peripheral end surface of the glass substrate with a grinding wheel such as a drum-like diamond. By this inner / outer diameter processing, the outer diameter and roundness of the glass substrate, the inner diameter of the through hole, and the concentricity between the glass substrate and the through hole are finely adjusted. For example, chamfering of 45 ° from about 0.1 mm to 0.2 mm is performed.

(Inner peripheral end face machining process)
Thereafter, the corners of the chamfered portion are curved by brush polishing using a polishing liquid on the inner peripheral end surface of the glass substrate, and fine scratches and the like are removed.

(Second wrapping process)
Next, the both surfaces of the glass substrate are lapped again to finely adjust the parallelism, flatness and thickness of the glass substrate.

(Outer peripheral end face machining process)
And the corner | angular part of a chamfering part is made into a curved surface by brush grinding | polishing which uses polishing liquid for the outer peripheral end surface of a glass substrate, and a fine crack etc. are removed.

  In addition, the order from the 1st lapping process after a coring process to an outer periphery end surface process is not limited to what was shown in FIG. 10, It can change suitably according to a condition. For example, the lapping process may be performed first, and then the inner / outer diameter machining process, the inner circumference, and the outer circumference end face machining process may be performed. Further, after the first lapping step and the inner / outer diameter machining step, a second lapping step, an inner circumference and an outer circumference end face machining step may be performed.

  A polishing machine for lapping a glass substrate in the first and second lapping steps will be described. As the polishing machine, for example, a known polishing machine called an Oscar polishing machine can be used.

  FIG. 11 is an explanatory view showing a state in which the glass substrate 1 is placed on the lower polishing tray 13 of the Oscar polishing machine, FIG. 12 is a cross-sectional view of the Oscar polishing machine, and FIG. FIG. 14 is a top view of an Oscar polishing machine for explaining 14.

  The Oscar polishing machine rotates the lower polishing dish 13 as indicated by an arrow U with the glass substrate 1 as an object to be polished placed on the jig 12 between the upper polishing dish 14 and the lower polishing dish 13. The polishing dish 14 is swung left and right as shown in FIG. 13A shows a state where the upper polishing plate 14 has moved to the left side of the lower polishing plate 13, FIG. 13B shows a state where the upper polishing plate 14 has moved to a position where it overlaps the lower polishing plate 13, FIG. c) is a state in which the upper polishing plate 14 has moved to the right side of the lower polishing plate 13.

  By such an operation of the Oscar polishing machine, polishing can be performed so that the shapes of the upper polishing dish 14 and the lower polishing dish 13 are transferred to the glass substrate 1 that is the object to be polished. Further, depending on the conditions, rotation of the accompanying polishing object can be promoted. By rotating the glass substrate 1, the point-symmetrical glass substrate 1 as shown in FIG. 1 can be manufactured.

  In such a working polishing machine, the glass substrate 1 can be lapped by supplying the grinding liquid between the upper polishing dish 14 and the glass substrate 1 and between the lower polishing dish 13 and the glass substrate 1. .

(1st polishing process)
Next, the polishing process will be described. In the polishing step, the surface of the glass substrate is precisely finished and the shape of the outer peripheral end of the main surface is polished to a desired shape.

  First, in the first polish polishing step, the surface roughness is improved and the desired shape is finally made efficient so that the surface roughness finally required in the second polish polishing step can be efficiently obtained. Polishing can be obtained well.

  The polishing method uses a polishing machine having the same configuration as the polishing machine used in the first and second lapping processes except that the polishing liquid is used instead of the grinding liquid used in the lapping process.

(First cleaning process)
The glass substrate is cleaned using a known ultrasonic cleaner, and the abrasive and the like adhering in the first polishing polishing step are removed. Pure water or the like can be used as the cleaning liquid.

(Preheating process)
The glass substrate is heated to a predetermined temperature in a preheating tank before being immersed in the chemical strengthening treatment liquid heated to 300 ° C. to 400 ° C. in the next chemical strengthening step. The preheating temperature is, for example, 200 ° C. or higher.

  By heating in the preheating step, it is possible to prevent the glass substrate from being cracked or microcracked due to thermal shock when immersed in the heated chemical strengthening treatment liquid. In addition, this process can also be abbreviate | omitted when there is no possibility that the glass substrate may be cracked or fine cracks may occur in the chemical strengthening process.

(Chemical strengthening process)
Prior to the second polishing step, the glass substrate is immersed in a chemical strengthening solution to form a chemically strengthened layer on the glass substrate. By forming the chemical strengthening layer, the surface state of the glass substrate can be improved, and impact resistance, vibration resistance, heat resistance, and the like can be improved.

  In the chemical strengthening step, by immersing the glass substrate in a heated chemical strengthening solution, alkali metal ions such as lithium ions and sodium ions contained in the glass substrate are converted into alkali ions such as potassium ions having a larger ion radius. This is performed by the ion exchange method for substitution. Compressive stress is generated in the ion-exchanged region due to the distortion caused by the difference in ion radius, and the surface of the glass substrate is strengthened.

  There is no restriction | limiting in particular in a chemical strengthening process liquid, A well-known chemical strengthening process liquid can be used. Usually, it is common to use a molten salt containing potassium ions or a molten salt containing potassium ions and sodium ions. Examples of the molten salt containing potassium ions and sodium ions include potassium and sodium nitrates, carbonates, sulfates, and mixed molten salts thereof. Among these, from the viewpoint that the melting point is low and deformation of the glass substrate can be prevented, it is preferable to use nitrate.

  The chemical strengthening treatment liquid is heated to a temperature higher than the temperature at which the above components melt. On the other hand, when the heating temperature of the chemical strengthening treatment liquid is too high, the temperature of the glass substrate is excessively increased, and the glass substrate may be deformed. For this reason, the heating temperature of the chemical strengthening treatment liquid is preferably lower than the glass transition point (Tg) of the glass substrate, more preferably lower than the glass transition point −50 ° C.

  The thickness of the chemically strengthened layer is preferably in the range of about 5 μm to 15 μm from the viewpoint of improving the strength of the glass substrate and shortening the polishing process time. When the thickness of the reinforcing layer is within this range, a glass substrate having good impact resistance, which is flatness and mechanical strength, can be obtained.

  The shape of the outer peripheral end portion of the main surface 10a after the chemical strengthening step is almost the same as that before the chemical strengthening step, and the above-mentioned chemical strengthening layer of about 5 μm to 15 μm is almost uniformly placed on the entire surface of the glass substrate. Become.

(Second polishing step)
The second polish polishing step is a step of further precisely polishing the surface of the glass substrate after the first polish polishing step. The pad used in the second polishing step is preferably a soft pad softer than the pad used in the first polishing step, such as urethane foam or suede. As the polishing agent, the same cerium oxide, colloidal silica, zirconium oxide, titanium oxide, manganese oxide, etc. as in the first polishing step can be used, but in order to make the surface of the glass substrate smoother, the particle size is larger. It is preferable to use an abrasive that is fine and has little variation.

(Second cleaning process)
(Inspection process)
After completion of the second polishing step, the glass substrate is cleaned and inspected to complete the glass substrate.

  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 strain of the glass substrate, a heat shock process for confirming the reliability of the strength of the glass substrate, various inspection / evaluation processes, and the like may be included.

  In the second polishing process, the polishing machine used in the first polishing process is not used as it is, but polishing is performed using another polishing machine that has the same configuration but is prepared for each process. Is preferred. This is because, if the polishing machine used in the first polishing process is used as it is, the polishing accuracy in the second polishing process decreases due to the abrasive remaining in the first polishing process, the polishing conditions are reset, etc. This is because this complicated operation is required and the production efficiency is lowered.

(The process of reducing the thickness of the glass substrate from the inner periphery to the outer periphery)
In the second embodiment, this step is performed to reduce the thickness of the glass substrate from the inner periphery to the outer periphery as shown in FIG.

  FIG. 14 is an explanatory diagram illustrating a process of reducing the thickness of the glass substrate from the inner periphery to the outer periphery. FIG. 14A is a cross-sectional view illustrating an example of a processing method, and FIG. 14B is a cross-sectional view illustrating a shape after processing.

  In this step, as shown in FIG. 14A, the vicinity of the inner diameter of the glass substrate 1 is sandwiched and fixed by the fixing members 20 and 21, and the upper and lower main surfaces of the glass substrate 1 are sandwiched by the elastic suede material 22. .

  Next, the glass substrate 1 is rotated together with the fixing members 20 and 21 by a motor (not shown), and polishing is performed while supplying colloidal silica as an abrasive.

  When the polishing is performed for a predetermined time, a glass substrate 1 having a reduced thickness from the inner periphery to the outer periphery as shown in FIG. 14B is obtained.

(Magnetic film forming process)
Next, the magnetic film 11 provided on the glass substrate will be described. Hereinafter, the magnetic disk 5 provided with the magnetic film 11 will be described with reference to FIG.

  As a method for forming the magnetic film 11, a conventionally known method can be used. For example, a method in which a thermosetting resin in which magnetic particles are dispersed is spin-coated on a substrate, a method in which sputtering or electroless plating is used. The method of doing is mentioned. The film thickness by spin coating is about 0.3 μm to 1.2 μm, the film thickness by sputtering is about 0.04 μm to 0.08 μm, and the film thickness by electroless plating is 0.05 μm to 0.1 μm. From the viewpoint of thinning and densification, film formation by sputtering and electroless plating is preferable.

The magnetic material used for the magnetic film is not particularly limited, and a conventionally known material can be used. However, in order to obtain a high coercive force, Ni having a high crystal anisotropy is basically used, and Ni or A Co-based alloy to which Cr is added is suitable. Specific examples include CoPt, CoCr, CoNi, CoNiCr, CoCrTa, CoPtCr, and CoNiPt containing Co as a main component, CoNiCrPt, CoNiCrTa, CoCrPtTa, CoCrPtB, and CoCrPtSiO. The magnetic film may have a multilayer structure (for example, CoPtCr / CrMo / CoPtCr, CoCrPtTa / CrMo / CoCrPtTa) that is divided by a nonmagnetic film (for example, Cr, CrMo, CrV, etc.) to reduce noise. In addition to the above magnetic materials, granular materials such as ferrite, iron-rare earth, and non-magnetic films made of SiO ₂ , BN, etc. in which magnetic particles such as Fe, Co, FeCo, CoNiPt are dispersed, etc. Also good. Further, the magnetic film may be either an inner surface type or a vertical type recording format.

  In addition, a lubricant may be thinly coated on the surface of the magnetic film in order to improve the sliding of the magnetic head. Examples of the lubricant include those obtained by diluting perfluoropolyether (PFPE), which is a liquid lubricant, with a freon-based solvent.

  Furthermore, you may provide a base layer and a protective layer as needed. The underlayer in the magnetic disk is selected according to the magnetic film. Examples of the material for the underlayer include at least one material selected from nonmagnetic metals such as Cr, Mo, Ta, Ti, W, V, B, Al, and Ni. In the case of a magnetic film containing Co as a main component, Cr alone or a Cr alloy is preferable from the viewpoint of improving magnetic characteristics. Further, the underlayer is not limited to a single layer, and may have a multi-layer structure in which the same or different layers are stacked. For example, a multilayer underlayer such as Cr / Cr, Cr / CrMo, Cr / CrV, NiAl / Cr, NiAl / CrMo, or NiAl / CrV may be used.

Examples of the protective layer that prevents wear and corrosion of the magnetic film include a Cr layer, a Cr alloy layer, a carbon layer, a hydrogenated carbon layer, a zirconia layer, and a silica layer. These protective layers can be formed continuously with an in-line type sputtering apparatus, such as an underlayer and a magnetic film. In addition, these protective layers may be a single layer, or may have a multilayer structure including the same or different layers. Note that another protective layer may be formed on the protective layer or instead of the protective layer. For example, in place of the protective layer, tetraalkoxysilane is diluted with an alcohol-based solvent on the Cr layer, and then colloidal silica fine particles are dispersed and applied, and then baked to form a silicon dioxide (SiO ₂ ) layer. It may be formed.

<Examples 1-4>
The glass substrate used for the magnetic disk 5 of Examples 1-4 was produced as follows.

(Production of glass substrate)
According to the manufacturing process diagram of the first embodiment described in FIG. 10, 1000 glass substrates 1 of Examples 1 to 3 were produced. Moreover, in Example 4, after the same process as Example 2, (the process of thinning the thickness of a glass substrate from an inner periphery to an outer periphery) was performed, and 1000 glass substrates 1 of 2nd Embodiment were produced.

  Aluminosilicate glass (Tg: 500 ° C.) was used as a glass material, and a molten glass was press-molded to produce a blank material. A glass substrate having an outer diameter of 63.5 mm, an inner diameter (diameter of the through hole 20) of 20 mm, and a substrate thickness of 0.8 mm was obtained through the inner and outer peripheral processing steps and the lapping step. In addition, the board | substrate thickness here is an average value of the value measured in arbitrary several points on a board | substrate. The target value of the warp amount α of Example 1 is −4 μm, the target value of the warp amount α of Example 2 is −5 μm, the target value of the warp amount α of Example 3 is −6 μm, and the warp amount α of Example 4 is The target value was −5 μm.

(1st polishing process)
The diameters of the upper polishing dish 14 and the lower polishing dish 13 of the Oscar polishing machine were 1000 mm, and an elastic suede was attached to the opposing surfaces of the upper polishing dish 14 and the lower polishing dish 13. One hundred sets of the fitting jig 12 having an inner diameter of 65 mm, an outer diameter of 67 mm, and a thickness of 0.5 mm fitted with the glass substrate 1 after the lapping process are placed on the lower polishing dish 13 as shown in FIG.

  As an abrasive, cerium oxide was used, and the particle size of the abrasive was 0.6 (μm).

  In Example 1, the lower polishing dish 13 was rotated at a rotation speed of 50 (rpm), and the upper polishing dish 14 was swung in a range of 500 mm on the left and right from the center of the lower polishing dish 13 by 25 reciprocations per minute. The glass substrate rotates along with the relative movement of the upper and lower polishing dishes. The polishing time is 40 minutes.

  In Examples 2 and 4, the lower polishing plate 13 was rotated at a rotation speed of 60 (rpm), and the upper polishing plate 14 was swung 30 reciprocations in the range of 500 mm from the center of the lower polishing plate 13 to the left and right. The rotation speed of the glass substrate is faster than that in Example 1. The polishing time is 30 minutes.

  In Example 3, the lower polishing dish 13 was rotated at a rotation speed of 70 (rpm), and the upper polishing dish 14 was swung 35 reciprocations in the range of 500 mm from the center of the lower polishing dish 13 to the left and right. The rotation speed of the glass substrate is faster than that of Example 2. The polishing time is 20 minutes.

(First cleaning process)
Washing was performed for 10 minutes with an ultrasonic washer.

(Preheating process)
The glass substrate was heated for 30 minutes in the preheating tank heated to the preheating temperature T0 (° C.).

(Chemical strengthening process)
The glass substrate was immersed in the chemical strengthening treatment liquid heated to the strengthening temperature T1 (° C.). Potassium nitrate was used for the chemical strengthening treatment solution.

(Second polishing step)
An Oscar polishing machine in which suede was attached to the upper polishing plate 14 and the lower polishing plate 13 was used, and cerium oxide and colloidal silica were used as the polishing agent, and the particle size of the polishing agent was set to 30 (nm). The upper polishing dish 14 and the lower polishing dish 13 were operated under the same conditions as in the first polishing process.

(Second cleaning process)
As the third cleaning step, brush cleaning was performed with a roll scrub machine and a cup scrub machine, and then cleaning was performed with an ultrasonic cleaner.

(The process of reducing the thickness of the glass substrate from the inner periphery to the outer periphery)
In Example 4, by the processing method described with reference to FIG. 14, the thickness near the inner periphery was 0.8 mm and the outermost periphery was polished to 0.7 mm so as to become thinner toward the outer periphery.

(Magnetic film forming process)
An adhesion layer made of a Cr alloy, a soft magnetic layer made of a CoFeZr alloy, an orientation control underlayer made of Ru, a perpendicular magnetic recording layer made of a CoCrPt alloy, a C-type protective layer, an F-type on both surfaces of the cleaned glass substrate 1 A lubricating layer made of is sequentially formed on both surfaces of the substrate by a sputtering apparatus. The total film thickness is about 100 nm.

  In the present embodiment, the magnetic disk 5 on which the magnetic film for perpendicular magnetic recording is formed as described above is manufactured. However, the present invention is not particularly limited, and a magnetic layer or the like may be configured as an in-plane magnetic disk.

<Examples 5-9>
The thickness of the glass substrate 1 was changed, and 1000 magnetic disks 5 of Examples 5 to 7 were produced. The thickness of the glass substrate 1 is 0.635 mm in Example 5, 0.77 mm in Example 6, 0.78 mm in Example 7, 1.5 mm in Example 8, and 2.2 mm in Example 9. The proper tightening torque varies depending on the thickness of the glass substrate 1, and the amount of warpage generated by the clamping force at the time of fixing also varies. The target value of the warpage amount α was determined according to the amount of warpage generated by the clamping force at the time of fixing.

  The target value of the warp amount α of Example 5 is −15 μm, the target value of the warp amount α of Example 6 is −10 μm, the target value of the warp amount α of Example 7 is −8 μm, and the warp amount α of Example 8 is The target value was −4 μm, and the target value of the warpage amount α in Example 9 was −2 μm. Magnetic disks 5 of Examples 5 to 7 were manufactured by setting the number of rotations of the lower polishing dish 13 and the polishing time so that the target warpage amount α was obtained. Other conditions are the same as those in the second embodiment.

<Examples 10 to 13>
Using the glass substrate 1 having a different circumferential direction TIR at a position of φ22 mm in the vicinity of the through hole 20, 1000 magnetic disks 5 of Examples 10 to 13 were manufactured in the same thickness and in the same process as in Example 3. The circumferential direction TIR of Example 10 is 0.4 μm, the circumferential direction TIR of Example 11 is 0.7 μm, the circumferential direction TIR of Example 12 is 0.8 μm, and the circumferential direction TIR of Example 13 is 1.0 μm.

  The measurement of the circumferential direction TIR was performed using Optiflat manufactured by Phase Shift Technology.

[Comparative example]
<Comparative Example 1>
In Comparative Example 1, a glass substrate having a target warpage amount α of 0 μm was produced by changing the conditions in the same process as in the example.

  In Comparative Example 1, the lower polishing dish 13 was rotated at 0.5 rpm in each polishing step, and the upper polishing dish 14 was reciprocated twice in a range of 300 mm from the center of the lower polishing dish 13 in one minute. The polishing time is 150 minutes. Under this condition, the glass substrate hardly rotates due to the relative movement of the upper and lower polishing dishes, so that the shape of the upper and lower polishing dishes can be transferred as it is. Other manufacturing conditions are the same as in Example 1.

  In Comparative Example 1, 1000 magnetic disks 59 were produced.

<Comparative Examples 2 and 3>
The thickness of the glass substrate of Comparative Example 2 is 2.3 mm, and the thickness of the glass substrate of Comparative Example 3 is 2.5 mm. Since the thickness is thick, no warp is generated by the clamping force at the time of fixing. Therefore, a glass substrate having a target warpage amount α of 0 μm was produced by changing the thickness of the glass substrate under the same conditions as in Comparative Example 1.

[Evaluation method]
A method of evaluating the warpage that occurs when the information recording medium is fixed to the rotating shaft of the glass substrate and the cracking of the substrate due to the collision of the lamp will be described.

  The evaluation of the magnetic disk 5 was conducted by attaching the magnetic disks of Examples and Comparative Examples to the hard disk device 200 shown in FIG.

  The outer diameter of the ring-shaped jig 7 of the hard disk device 200 used for the evaluation experiment is 24 mm (Lb = 12 mm), the inner diameter is 20 mm, and the thickness is 1.8 mm. The diameter of the protrusion 2a of the clamp jig 2 is 22 mm (La = 11 mm). Therefore, the diameter La of the protrusion 2a is smaller than the diameter Lb of the ring-shaped jig 7.

  Moreover, the space | interval D of the front-end | tip part 51b of the lamp | ramp 51 used for the evaluation experiment of Examples 1-4 and the comparative example 1 and the front-end | tip part 51c is 1.5 mm. In the evaluation experiments of Examples 1 to 4, Examples 10 to 13, and Comparative Example 1, the screw 3 of the clamp jig 2 was fastened with a torque of 20 N · m to fix the magnetic disk 5 or the magnetic disk 59 to the rotating shaft 6.

  In the evaluation experiments of Examples 5 to 9 and Comparative Examples 2 and 3, a lamp 51 having a gap D of 2.6 mm between the tip portions 51b and 51c was used.

  The amount of warpage is measured using a multi-function disk interferometer (manufactured by Optiflat Phase Shift Technology. Inc.) and the entire surface of the glass substrate is measured. The measurement principle is a method of measuring the shape of the surface by irradiating the surface of the glass substrate with white light and measuring the change in the intensity of interference between the reference light and the measurement light having different phases.

  The evaluation of the crack of the substrate due to the collision of the lamp was performed by dropping the hard disk device 200 to which the magnetic disk of the example or the comparative example was attached from a certain height using a commercially available drop impact tester. In the experiment, after the hard disk device 200 was dropped from a height of 1 mm, the hard disk device 200 was disassembled and the presence or absence of cracking of the magnetic disk was visually confirmed.

[Evaluation results]
Table 1 shows the evaluation results of the hard disk device 200 for each of the 1000 magnetic disks produced in Examples 1 to 4 and Comparative Example 1. In the determination of the crack occurrence rate after the drop test, “◎” indicates that the generated crack is 1 or less, “◯” indicates 2-5, and “x” indicates 6 or more cracks.

  As shown in Table 1, the average value of the warping amount α after fixing in Example 1 is 1 μm, the average value of the warping amount α after fixing in Example 2 is 0 μm, and the warping amount α after fixing in Example 3 is The average value was −1 μm, and the average value of the warping amount α after fixing Example 4 was 0 μm. In addition, the number of cracks is 1 in Example 2, 0 in Example 4, and 3 in Examples 1 and 3. The crack occurrence rate is determined in Examples 2 and 4, and Examples 1 and 3 are used. Was ○.

In the first to fourth embodiments, the magnetic disk 5 was positioned substantially at the center with respect to the gap of 1.5 mm between the tip portions 51b and 51c of the lamp 51. In Example 1, the interval _{x 1} of the distal end portion 51b and the magnetic disk 5 0.349Mm interval _{x 2} of the distal end portion 51c and the magnetic disk 5 was 0.351Mm. In Example 2, _{x 1} is 0.350 mm, _{x 2} is 0.350 mm, in Example 3, _{x 1} is 0.351mm, _{x 2} is 0.349Mm, in Example 4, _{x 1} is 0. 4mm, _{x 2} was 0.4mm.

On the other hand, in Comparative Example 1, as shown in Table 1, the average value of the warping amount α after fixing was 5 μm. In addition, eight cracks occurred, and the determination of the crack occurrence rate was x. In Comparative Example 1, _{x 1} is 0.345mm, _{x 2} is 0.355 mm, spacing of the tip portion 51b of the magnetic disk 59 and lamp 51 were narrowed.

  As described above, in the first to fourth embodiments, the amount of warping α becomes substantially zero when fixed to the fixed shaft 6 of the hard disk device 200, and the magnetic disk 5 is positioned substantially at the center of the gap between the tips 51 b and 51 c of the ramp 51. As a result, there was little cracking after the drop test. In particular, in Example 4, since the space | interval of the front-end | tip parts 51b and 51c of the lamp | ramp 51 and the magnetic disc 5 can be widened, generation | occurrence | production of crack after a drop test was able to be made zero.

  On the other hand, in Comparative Example 1, since the average value of the warping amount α after fixing was as large as 5 μm, cracks occurred frequently after the drop test.

  Table 2 shows the evaluation results of the hard disk device 200 of 1000 magnetic disks produced in Examples 5 to 9 and Comparative Examples 2 and 3. In this experiment, it was determined that the glass substrate non-defective rate was 95% or more at the time of prototyping, ◯ when the non-defective rate was less than 95%, and x when the non-defective rate was 60% or less.

  As shown in Table 2, the average value of the warping amount α after fixing in Example 5 is 3 μm, the average value of the warping amount α after fixing in Example 6 is 2 μm, and the warping amount after fixing in Examples 7 to 9 The average value of α was 0 μm. In addition, the number of cracks of Example 5 is 5, the number of cracks of Example 6 is 3, and the determination of crack occurrence rate is ○, the number of cracks of Examples 7 to 9 is 0, and the determination of crack occurrence rate is Both were ◎. The substrate non-defective rate is almost 100% in Examples 7 to 9 and the determination is ◎, but in Examples 5 and 6, the substrate non-defective rate decreases because the thickness is thin and the target warpage amount is large. ○.

On the other hand, the average value of the warping amount α after fixing in Comparative Examples 2 and 3 is 0 μm, but the thickness of the substrate is thick and the distances x ₁ and x _{2 from} the tip portions 51b and 51c of the lamp 51 are narrow. 7 was cracked in 2 and 6 cracks were generated in Comparative Example 3, and the determination of the crack occurrence rate was x.

  Next, Table 3 shows the evaluation results of the hard disk device 200 for each of 1000 magnetic disks produced in Examples 10-13.

  The evaluation of the amount of warpage was performed at two points of a section CC shown in FIG. 15 and a section DD orthogonal to the section CC. FIG. 15 is a plan view of the magnetic disk 5.

  As shown in Table 3, the average values of the warpage amounts α of the sections C-C and D-D after fixing Examples 10 and 11 were both −1 μm. Moreover, the number of cracks was one in each of Examples 10 and 11, and the crack occurrence rate was judged as ◎.

  The average values of the warpage amounts α of the cross section CC and the cross section DD after fixing in Example 12 are −2 μm and −1 μm, respectively, and the warpage amounts of the cross section CC and the cross section DD after fixing in Example 13 are as follows. The average values of α were −4 μm and +2 μm, respectively. In addition, the number of cracks was 3 and 5 in Examples 12 and 13, respectively, and the determination of crack occurrence rate was “good”.

  As described above, in Examples 10 and 11 in which the circumferential direction TIR is 0.7 μm or less, the warpage amount α of the cross-section CC and the cross-section DD after fixing is the same, and the determination of the crack occurrence rate is also ◎. It was. This is because the contact between the main surface 10 of the magnetic disk 5 and the protrusion 2a of the clamp jig 2 is substantially uniform over the entire circumference.

  On the other hand, in Examples 12 and 13 in which the circumferential direction TIR exceeds 0.7 μm, the warpage amount α between the cross-section CC and the cross-section DD after fixing is different, and the determination of the crack occurrence rate is “good”. This is presumably because the contact between the main surface 10 of the magnetic disk 5 and the protruding portion 2a of the clamp jig 2 is not uniform, resulting in discontinuous line contact.

  As described above, according to the present invention, when the information recording medium is fixed to the rotating shaft using the conventional information recording medium fixing mechanism, the substrate is prevented from cracking due to the collision of the lamp so as not to warp. An information recording medium glass substrate, an information recording medium, and an information recording apparatus using the information recording medium can be provided.

DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Clamp jig 3 Screw 5 Magnetic disk 6 Rotating shaft 10 Main surface 11 Magnetic film 12 Inserting jig 13 Lower polishing dish 14 Upper polishing dish 20 Through hole 37 Arm 38 Pivot 40 Outer surface 51 Lamp 51a Sliding surface 51b , 51c Tip 52 Lift tab 53 Recording / reproducing head 54 Suspension 59 Magnetic disk 200 Hard disk device 501 Housing

Claims (6)

A disc-shaped glass substrate for an information recording medium comprising a through-hole into which a rotation shaft is inserted at a central portion, sandwiching a peripheral portion of the through-hole on the main surface from both sides and fixed to the rotation shaft,
A convex or concave warpage is provided in advance from the through hole so that the main surface is corrected and flattened by a force sandwiching the peripheral edge from both sides when fixed to the rotating shaft ;
The thickness of the glass substrate for information recording medium is 0.78 to 2.2 mm, and
The glass substrate for an information recording medium , wherein the warpage is 2 to 8 μm in terms of an absolute value of warpage . The contours of the main surface on both sides are
The glass substrate for an information recording medium according to claim 1, wherein all of them are concentric circles and their intervals are equal. The thickness of the information recording medium glass substrate is:
The glass substrate for an information recording medium according to claim 1 or 2, wherein the glass substrate is thinner from the central portion toward the outer surface. Circumferential TIR, a glass substrate for an information recording medium according to any one of claims 1 to 3, characterized in that at 0.7μm or less of the main surface in the vicinity of the through hole. An information recording medium comprising a recording layer provided on the main surface of the glass substrate for an information recording medium according to any one of claims 1 to 4 . An information recording apparatus having a cylindrical ring jig, a clamp jig provided with an annular protrusion, and a drive mechanism for rotating a rotating shaft,
An information recording medium according to claim 5 ;
A head for reading and writing the information recording medium;
A lamp arranged such that the position of the tip overlaps the end of the information recording medium;
A head driving mechanism for loading the head retracted on the ramp onto the information recording medium and unloading the head onto the ramp;
Have
The information is obtained by penetrating the rotating shaft in the order of the ring jig and the information recording medium and pressing an annular protrusion of the clamp jig against the surface of the information recording medium and sandwiching the information between the ring jig and the information recording medium. An information recording apparatus, wherein the information recording medium is fixed to the rotating shaft by correcting warping of the recording medium.