JP4860580B2 - Magnetic disk substrate and magnetic disk - Google Patents

Description

  The present invention relates to a substrate for a magnetic disk mounted on a hard disk drive device.

  There is a magnetic disk as a magnetic recording medium mounted on a hard disk drive device (HDD device). The magnetic disk is manufactured by depositing a NiP film on a metal substrate made of an aluminum-magnesium alloy or the like, or laminating a magnetic layer or a protective layer on a glass substrate or a ceramic substrate. Conventionally, an aluminum alloy substrate has been widely used as a substrate for a magnetic disk. However, with recent downsizing, thinning, and high-density recording of magnetic disks, surface flatness and A glass substrate having excellent strength with a thin plate has been used.

In a magnetic disk substrate, particularly a glass substrate, a chamfered surface is provided between a main surface and an end surface in order to prevent the substrate from being damaged. For this chamfered surface, for example, a surface having a curvature between the main surface and the chamfered surface (R) to reduce the roughness of the chamfered surface to prevent corrosion or to prevent generation of particles (R And the like have been proposed (Patent Document 1).
JP 2006-92722 A

  In recent years, in HDD devices, in addition to the CSS (Contact Start Stop) method in which the magnetic head is brought into contact with the substrate surface when the disk is stopped, a load / unload method in which the magnetic head is retracted to the outside of the substrate when the disk is stopped has been adopted. ing. In the HDD device, the magnetic disk has been rotated at a rotational speed of 7200 rpm or higher, and it is expected that the rotational speed will be 10,000 rpm or higher in the future.

  As described above, when considering the method and the rotational speed of the HDD device, the size and roughness of the main surface, chamfered surface, and end surface from the viewpoint of preventing head crashes and accurately recording and reproducing information. The parameters are determined. The required accuracy is also determined for the parameter of the position of the boundary point between the main surface and the chamfered surface. However, even if a substrate that satisfies various required parameters is used, head crashes occur at a certain rate, and head crashes cannot be completely prevented.

  The present invention has been made in view of this point, and an object of the present invention is to provide a magnetic disk substrate and a magnetic disk that can prevent the occurrence of a head crash in an HDD device with a very high probability.

A magnetic disk substrate of the present invention is a magnetic disk substrate for a magnetic disk device of a type in which a magnetic head loads / unloads with respect to a main surface of the magnetic disk via an outer edge of the magnetic disk, substrate for a magnetic disk, a flat main surface, with an end face, and a chamfer surface between the main surface and the end face, have a circular shape, from the center of the substrate for the magnetic disk to the end face A first imaginary line connecting a position on the main surface that is 50% from the center at the first distance and a position on the main surface that is 80% from the center, and 0.15% from the end face at the first distance When the intersection of the second imaginary line connecting the position on the chamfered surface and the position on the chamfered surface of 0.30% from the end surface is a cross point, the main surface is viewed in plan At the cross point The circularity of a formed circle is 0.5 mm or less, and the magnetic disk has a second distance from the cross point to a projection position on the chamfered surface of the cross point when the main surface is viewed in plan The variation over the entire circumference of the substrate is 5 μm or less .

  According to this configuration, by forming the chamfered surface so that the position of the cross point on the main surface is in the above-described range, the variation in the position of the boundary point between the main surface and the chamfered surface is kept below a certain level. As a result, a glass substrate that can prevent head crashes at a very high rate can be realized.

  According to this configuration, by forming the chamfered surface so that the position of the cross point on the main surface is in the above-described range, the variation in the position of the boundary point between the main surface and the chamfered surface is kept below a certain level. As a result, a glass substrate that can prevent head crashes at a very high rate can be realized.

In the magnetic disk substrate of the present invention, it is preferable that a second distance from the cross point to a projection position on the chamfered surface of the cross point when the main surface is viewed in plan is 15 μm or less. Moreover, it is preferable that the roundness of the circle formed by the cross point is 0.340 mm or less.

In the magnetic disk substrate of the present invention, it is preferable that the variation of the second distance over the entire circumference of the magnetic disk substrate is 4 μm or less.

  In the magnetic disk substrate of the present invention, the distance between the center of the circle formed at the cross point when the main surface is viewed in plan and the center of the magnetic disk substrate is 1200 μm or less. preferable.

  In the magnetic disk substrate of the present invention, the magnetic disk substrate is preferably made of glass.

  The magnetic disk of the present invention comprises the above-described magnetic disk substrate and a magnetic layer formed on the magnetic disk substrate.

  In the magnetic disk of the present invention, it is preferable that the magnetic head is mounted on a magnetic disk apparatus of a type that loads / unloads to / from the main surface of the magnetic disk via an outer edge of the magnetic disk. The magnetic disk of the present invention may be mounted on a CSS type (Contact Start and Stop) type magnetic disk device.

  The magnetic disk of the present invention is preferably mounted on a magnetic disk device that rotates the magnetic disk at a rotational speed of at least 7200 rpm.

  In the magnetic disk of the present invention, the touchdown height is preferably 4 nm or less.

In the magnetic disk of the present invention, the recording density is preferably 200 Gbit / inch ² or more.

  The hard disk drive device of the present invention comprises the above magnetic disk and a magnetic head for recording and / or reproducing information on the magnetic disk.

  According to the magnetic disk substrate of the present invention, the magnetic disk substrate has a substantially flat main surface, an end surface, and a chamfered surface between the main surface and the end surface, has a substantially circular shape, and extends along the main surface. Since the cross point where the direction and the direction along the chamfered surface intersect is located at substantially the same distance from the center of the magnetic disk substrate over the entire circumference of the magnetic disk substrate when the main surface is viewed in plan. The occurrence of a head crash in the HDD device can be prevented with a very high probability.

  The present inventors conducted an operation test on the position of the boundary point between the main surface and the chamfered surface using a substrate that satisfies the required control value, and a head crash occurs depending on the sample. Focused on that. Therefore, the present inventors conducted an operation test in a similar manner with the management value of this parameter being made stricter (managed under conditions stricter than the required value). Although it decreased, a head crash occurred. Therefore, the present inventors focused on the variation in the position of the boundary point between the main surface and the chamfered surface for the cause of this head crash, and by adjusting the variation in the position of this boundary point to a certain level or less, It has been found that head crashes can be prevented at a very high rate, and the present invention has been achieved.

  That is, the essence of the present invention comprises a substantially flat main surface, an end surface, and a chamfered surface between the main surface and the end surface, has a substantially circular shape, and the direction along the main surface and the A cross point intersecting with a direction along the chamfered surface is located at substantially the same distance from the center of the magnetic disk substrate over the entire circumference of the magnetic disk substrate when the main surface is viewed in plan. Thus, the occurrence of a head crash in the HDD device is prevented with a very high probability.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
In the present embodiment, the case where the magnetic disk substrate is made of glass will be described. However, the present invention is not limited to this, and the magnetic disk substrate may be made of metal or ceramics.

FIG. 1 is a view showing a part of a glass substrate which is a magnetic disk substrate according to an embodiment of the present invention. The glass substrate 1 shown in FIG. 1 has a substantially circular shape, and has a hole 11 for mounting on the spindle motor of the HDD device at the center thereof. The glass substrate 1 has a pair of main surfaces 12 facing each other and an end surface (side wall surface) 13 on the outer peripheral edge. Further, the glass substrate 1 has a chamfered surface 14 between the main surface 12 and the end surface 13 over the entire circumference. The glass substrate 1 has a D ₂ (distance from the substrate center C to the end face 13) outside diameter, the hole portion 11 has an inner diameter D _1. Moreover, the main surface of the glass substrate 1 is processed substantially flat.

  The glass substrate 1 may be manufactured by molding a molten aluminosilicate glass into a disk shape by direct pressing, and is cut out from a sheet glass formed by a downdraw method or a float method with a grinding wheel to form a disk-shaped glass substrate. It may be produced. Aluminosilicate glass is preferable because chemical strengthening treatment is easy. As the aluminosilicate glass, a glass for chemical strengthening can be used. Note that other multi-component glass or crystallized glass may be used instead of aluminosilicate glass. The other component glass is preferable because the impact resistance can be improved by the chemical strengthening treatment.

2 (a) is a diagram showing a part of the glass substrate shown in FIG. 1, FIG. 2 (b) is an enlarged view of part X in FIG. 2 (a), and FIG. 1 is a plan view of a glass substrate 1. FIG. As shown in FIG. 2B, the boundary region between the main surface 12 and the chamfered surface 14 is not actually the boundary between the main surface 12 and the chamfered surface 14 but appears on the main surface. There is a gradual transition from 12 to the chamfered surface 14. In the present invention, the position (cross point CP) of the boundary point between the main surface 12 and the chamfered surface 14 is a position where the direction A along the main surface 12 and the direction B along the chamfered surface 14 intersect. Further, the cross point CP is a position on the main surface 12 that is 50% from the center C and a position on the main surface 12 that is 80% from the center C in the distance (D ₂ ) from the center C to the end face 13 of the glass substrate 1. And a virtual line connecting a position on the chamfered surface 14 of 0.15% from the end face 13 and a position on the chamfered face 14 of 0.30% from the end face 13 at the distance (D ₂ ). It can be represented by the intersection of (B). In addition, the position which forms a virtual line is an example, and if it is a position which can pinpoint the position of the boundary point between the main surface 12 and the chamfering surface 14, it will not be limited to the said position in an outer diameter.

  About the cross point CP specified as described above, as shown in FIG. 2C, when the main surface 12 is viewed in plan, it is substantially the same distance from the center C of the glass substrate 1 over the entire circumference of the glass substrate 1. Located in. That is, in FIG. 2C, the distance E from the center C of the glass substrate 1 to the cross point CP is substantially the same over the entire circumference of the glass substrate 1. This “substantially the same” can be defined by the roundness of the circle of the cross point CP in a plan view or the relationship between the center of the circle formed by the cross point CP and the center C of the glass substrate 1. That is, it is preferable that the roundness of a circle (circle CP in FIG. 2C) formed by the cross point CP when the main surface 12 is viewed in plan is 0.5 mm or less. Alternatively, even when the center of the circle formed by the cross point CP (circle CP in FIG. 2C) and the center C of the glass substrate 1 are shifted when the main surface 12 is viewed in plan, The distance is preferably 1200 μm or less.

  Moreover, it is preferable that the projection position CP ′ on the chamfered surface 14 of the cross point CP when the main surface 12 is viewed in plan is substantially the same position in the thickness direction of the glass substrate 1 over the entire circumference of the glass substrate 1. That is, in FIG. 2B, the distance t from the cross point CP to the projection position on the chamfered surface 14 of the cross point CP when the main surface 12 is viewed in plan is substantially the same over the entire circumference of the glass substrate 1. That is, it is preferable that the variation of the distance t over the entire circumference of the glass substrate 1 is 5 μm or less (variation of 5 μm or less). In this case, the distance t is preferably 15 μm or less.

  In this way, by forming the chamfered surface 14 so that the cross point CP and the distance t are in the ranges as described above, the variation in the position of the boundary point between the main surface 12 and the chamfered surface 14 is kept below a certain level. As a result, a glass substrate that can prevent head crashes at a very high rate can be realized.

  The present applicant pays attention to a so-called ski jump (bump shape) or roll-off (sink shape) at the outer edge of the magnetic disk substrate, and controls the shape so as to satisfy a certain condition, thereby causing a head crash. Has been proposed (Japanese Patent Application No. 2007-38926). That is, in this proposal, the height and interval of the ski jump pole 21 as shown in FIG. 3A and the roll-off pole 21 as shown in FIG. By prescribing, head crash is prevented. All this content is included here. Therefore, by specifying the cross point CP and the distance t as described above and controlling the shape of the ski jump and roll-off so as to satisfy a certain condition, it is possible to further effectively prevent the head crash. It becomes. Further, the head crash can be more effectively prevented by controlling the distance F between the ski jump and roll-off pole portion 21 shown in FIG. 3 and the cross point CP within a predetermined range.

  In the present embodiment, it is described that the above condition is satisfied for the chamfered surface 14 of the outer edge of the glass substrate 1. However, in the present invention, the same applies to the chamfered surface provided in the hole 11 of the glass substrate 1. It is possible to apply to. By satisfying the above condition for the chamfered surface of the hole 11, a load can be applied evenly when the magnetic disk is assembled and clamped in the HDD device. Furthermore, it is preferable to satisfy the above conditions for the chamfered surface 14 of the outer edge of the glass substrate 1 and the chamfered surface of the hole 11.

Next, the manufacturing method of the said glass substrate is demonstrated.
In the production of a glass substrate, (1) shape processing step and first lapping step, (2) end shape step (coring step for forming a hole, chamfering at the end (outer peripheral end and inner peripheral end) Chamfering step for forming a surface (chamfered surface forming step)), (3) end surface polishing step (outer peripheral end and inner peripheral end), (4) second lapping step, (5) main surface polishing step (first And a second polishing step), (6) a chemical strengthening step, and (7) a texture treatment step. Note that the end polishing step and the second lapping step may be mixed. Further, the texture processing step is not required for a magnetic disk substrate used in a perpendicular magnetic recording type HDD apparatus.

  In order to satisfy the above condition for the chamfered surface 14 of the outer edge of the glass substrate 1, it can be performed by chamfering the outer edge of the glass substrate 1 using an apparatus as shown in FIG. That is, as shown in FIG. 4, one side of the glass substrate 1 is attached to a polishing body 31 that is supported by a rotating shaft 32 that can rotate in the direction of an arrow, has a spherical concave surface, and a polishing cloth is attached to the concave surface. The polishing body 31 and the glass substrate 1 are moved relative to each other while the chamfered portions of the glass substrate 1 are simultaneously brought into contact with each other and the chamfered portion on one side of the glass substrate 1 is simultaneously pressed against the polishing cloth over the entire circumference. To do. The present applicant has proposed such a polishing technique (Japanese Patent Application Nos. 2006-237515 and 2006-237879). All this content is included here.

  Alternatively, the rotation axis of the laminated body of glass substrates and the rotation axis of the polishing member (polishing brush, polishing pad) can always be maintained parallel and equidistant during the end face polishing step. At this time, the rotation axis of the laminated body of glass substrates and the central axis of the glass substrate constituting the laminated body coincide. Furthermore, in the chamfering process, the gripping accuracy of the apparatus for gripping the glass substrate 1 (reducing the tilt of the substrate surface with respect to the horizontal direction), the type and grain size of abrasive grains used for grinding, the load, the platen rotation speed, polishing It can also be performed by controlling grinding conditions such as the liquid flow rate.

  The cross-point condition for the magnetic disk substrate according to the present invention is suitable for a substrate size of 3.5 inches or less (particularly 2.5 inches or 1.8 inches). In the case of a glass substrate, the above conditions are the most important because processing is difficult and it is difficult to keep the shape constant compared to an aluminum alloy substrate.

  Next, a magnetic disk manufactured using the magnetic disk substrate according to the present invention will be described. The magnetic disk according to the present invention is configured by forming at least a magnetic layer on the glass substrate described above.

  A magnetic disk is usually manufactured by sequentially laminating an underlayer, a magnetic layer, a protective layer, and a lubricating layer on a glass substrate 1 that has been subjected to chemical strengthening treatment on the surface as necessary. The underlayer in the magnetic disk is appropriately selected according to the magnetic layer.

  Examples of the material constituting the underlayer include at least one selected from nonmagnetic metals such as Cr, Mo, Ta, Ti, W, V, B, and Al. In the case of a magnetic layer 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, CrV / CrV, Al / Cr / CrMo, Al / Cr / Cr, Al / Cr / CrV, Al / CrV / CrV, etc. .

  Examples of the material constituting the magnetic layer include CoPt, CoCr, CoNi, CoNiCr, CoCrTa, CoPtCr, CoNiPt containing Co as a main component, CoNiCrPt, CoNiCrTa, CoCrTaPt, and CoCrPtSiO. The magnetic layer may be a multilayer structure (for example, CoPtCr / CrMo / CoPtCr, CoCrTaPt / CrMo / CoCrTaPt) in which the magnetic film is divided by a non-magnetic film (for example, Cr, CrMo, CrV) to reduce noise. Good.

The material of the magnetic layer corresponding to the magnetoresistive head (MR head) or the large magnetoresistive head (GMR head) is selected from Co-based alloys from Y, Si, rare earth elements, Hf, Ge, Sn, and Zn. An impurity element to be formed or an oxide of these impurity elements may be included. As the magnetic layer, in addition to the above, ferritic, iron - rare-earth and, SiO _2, BN Fe nonmagnetic film, which is constituted by a, Co, FeCo, magnetic particles such as CoNiPt dispersed structure Alternatively, a granular film or the like may be used.

Examples of the material constituting the protective layer include Cr, Cr alloy, carbon, zirconia, and silica. These protective films can be continuously formed by an in-line type sputtering apparatus together with an underlayer, a magnetic layer, and the like. These protective films may be a single layer, or may be a multilayer structure of the same or different films. Further, another protective layer may be formed on the protective layer or instead of the protective layer. For example, instead of the protective layer, a silicon oxide (SiO ₂ ) film obtained by dispersing and applying colloidal silica fine particles in a tetraalkoxylane diluted with an alcohol-based solvent on a Cr film, and further baking it. May be used.

  For example, the lubricating layer may be obtained by diluting perfluoropolyether (PFPE), which is a liquid lubricant, with a solvent such as Freon, and applying it to the surface of the medium by dipping, spin coating, or spraying. Go and form.

  FIG. 5 is an exploded view showing an outline of the HDD device (load / unload method) on which the above-described magnetic disk is mounted. This HDD device includes at least one magnetic disk and a magnetic head for recording and / or reproducing information on the magnetic disk. That is, as shown in FIG. 5, in the HDD device, the hole of the magnetic disk 44 is mounted on the spindle motor 43 of the base 42 having the circuit board 41 and the spindle motor 43, and further, the bottom yoke 45, the magnet 47, and A bottom coil motor composed of a head assembly 46 sandwiched between top yokes 48 is attached. In this HDD device, the head advances into the recording area (main surface) of the magnetic disk 44 when recording and reproducing information, and the head retracts from the recording area (main surface) via the outer edge of the magnetic disk 44 when stopped. (Load / Unload method).

Satisfying the above condition of the position of the cross point is very effective for a magnetic disk substrate mounted on an HDD device in which the flying height of the head is reduced. For example, a magnetic disk substrate for an HDD apparatus in which a magnetic head is loaded / unloaded with respect to the main surface of the magnetic disk via the outer edge of the magnetic disk, and an HDD apparatus that rotates the magnetic disk at a rotational speed of at least 7200 rpm The present invention is very effective for magnetic disk substrates, magnetic disk substrates having a touchdown height of 4 nm or less, and magnetic disk substrates having a recording density of 200 Gbit / inch ² or more.

Next, examples performed for clarifying the effects of the present invention will be described.
(Examples 1-3)
(1) Shape processing step and first lapping step First, the melted aluminosilicate glass was molded into a disk shape by direct pressing using an upper die, a lower die, and a barrel die to obtain an amorphous plate glass. In addition, the glass for chemical strengthening was used as aluminosilicate glass. The obtained disk-shaped plate glass had a diameter of 68 mm and a plate thickness of 1 mm.

  Next, both main surfaces of the plate glass were lapped to form a disk-shaped glass base material. This lapping process was performed using alumina free abrasive grains with a double-sided lapping apparatus using a planetary gear mechanism. Specifically, the lapping platen is pressed on both sides of the plate glass from above and below, the grinding liquid containing free abrasive grains is supplied onto the main surface of the plate glass, and these are moved relative to each other for lapping. went. By this lapping process, a glass base material having a flat main surface was obtained. Moreover, the plate | board thickness of the glass base material was reduced rather than plate glass by this lapping process, and became 0.7 mm.

(2) End shape process (coring, chamfering)
Next, the glass base material was cut using a diamond cutter, and a glass substrate was cut out from the glass base material. Next, using a cylindrical core drill, a hole was formed in the center of the glass substrate to obtain an annular glass substrate (coring). At this time, holes were formed from both surfaces of the glass substrate using two core drills. And about the outer peripheral edge part, it grind | pulverized with the diamond grindstone using the apparatus shown in FIG. 4, and performed the predetermined chamfering (chambering).

(3) Mirror polishing process Next, the end surface of the glass substrate was mirror-polished by a brush polishing method. At this time, as the abrasive grains, a slurry (free abrasive grains) containing cerium oxide abrasive grains was used. Further, the inner peripheral end portion was mirror polished by a magnetic polishing method. And the glass substrate which finished the mirror polishing process was washed with water. By this mirror polishing process, the end portion of the glass substrate was processed into a mirror surface state capable of preventing generation of particles and the like. As a result, the diameter of the glass substrate was 65 mm, and the substrate used for the 2.5-inch magnetic disk could be obtained.

(4) Second Lapping Step Next, a second lapping process was performed on both main surfaces of the obtained glass substrate in the same manner as in the first lapping step. By performing this second lapping process, the fine uneven shape formed on the main surface in the end shape process and the mirror polishing process, which are the previous processes, can be removed in advance, and the subsequent polishing process on the main surface Could be completed in a short time.

(5) Main surface polishing step As the main surface polishing step, first, a first polishing step was performed. The first polishing step is mainly intended to remove scratches and distortions remaining on the main surface in the lapping step described above. In the first polishing step, the main surface was polished using a hard polishing pad by a double-side polishing apparatus having a planetary gear mechanism. As the abrasive, cerium oxide abrasive grains were used. And the glass substrate which finished this 1st grinding | polishing process is immersed in each washing tank of neutral detergent, pure water (1), pure water (2), IPA (isopropyl alcohol), and IPA (steam drying) sequentially. , Washed.

  Next, a second polishing step was performed as the main surface polishing step. The purpose of this second polishing step is to finish the main surface into a mirror surface. In the second polishing step, mirror polishing of the main surface was performed using a soft polishing pad by a double-side polishing apparatus having a planetary gear mechanism. As the abrasive, cerium oxide abrasive grains finer than the cerium oxide abrasive grains used in the first polishing step were used. And the glass substrate which finished this 2nd grinding | polishing process is made into neutral detergent (1), neutral detergent (2), pure water (1), pure water (2), IPA (isopropyl alcohol), IPA (vapor drying) ) Were sequentially immersed in each washing tank and washed. Note that ultrasonic waves were applied to each cleaning tank.

(6) Chemical strengthening process Next, the glass substrate which finished the lapping process and the polishing process described above was chemically strengthened. For chemical strengthening, a chemical strengthening solution in which potassium nitrate (60%) and sodium nitrate (40%) are mixed is prepared, this chemical strengthening solution is heated to 380 ° C., and the cleaned glass substrate is placed therein for about 4 hours. This was done by dipping. In this immersion, in order to chemically strengthen the entire surface of the glass substrate, it was carried out in a state of being accommodated in a holder so that a plurality of glass substrates were held at the end surfaces.

  Thus, by immersing in a chemical strengthening solution, the lithium ion and sodium ion of the surface layer of a glass substrate are each substituted by the sodium ion and potassium ion in a chemical strengthening solution, and a glass substrate is strengthened. The thickness of the compressive stress layer formed on the surface layer of the glass substrate was about 100 μm.

  The glass substrate that had been subjected to the chemical strengthening treatment was immersed in a water bath at 20 ° C. for rapid cooling and maintained for about 10 minutes. And the glass substrate which finished quenching was immersed in the concentrated sulfuric acid heated at about 40 degreeC, and was wash | cleaned. Further, the glass substrate after the sulfuric acid cleaning was cleaned by immersing in a cleaning tank of pure water (1), pure water (2), IPA (isopropyl alcohol), and IPA (steam drying). In addition, ultrasonic waves were applied to each cleaning tank.

  Thus, by applying the first lapping process, the edge shape process, the mirror polishing process, the second lapping process, the main surface polishing process (first and second polishing processes), the precision cleaning, and the chemical strengthening process, In addition, a smooth and highly rigid glass substrate for a magnetic recording medium was obtained.

  For the glass substrates (Examples 1 to 3) thus obtained, the position of the cross point CP on the main surface of the glass substrate 1 when the main surface is viewed in plan using a stylus type surface shape measuring instrument. Examined. The result is shown in FIG. Further, regarding the distance t (cross point spacing) to the projection position on the chamfered surface 14 of the cross point CP, the position on the main surface of the glass substrate 1 when the main surface was viewed in plan was examined. The result is shown in FIG.

  As can be seen from FIG. 6, the glass substrates of Examples 1 to 3 had extremely small variations in the position of cross points on the main surface of 0.192 mm, 0.275 mm, and 0.340 mm, respectively. That is, the roundness of the circle formed at the cross point was 0.5 mm or less. Further, as can be seen from FIG. 7, the glass substrates of Examples 1 to 3 had extremely small variations in cross point spacing positions on the main surface of 0.003 mm, 0.004 mm, and 0.002 mm, respectively. That is, the variation of the cross point spacing was 5 μm (0.005 mm) or less.

(Comparative Examples 1 and 2)
In the chamfering step, a glass substrate for a magnetic recording medium was obtained in the same manner as in Examples 1 to 3 except that the outer peripheral end and the inner peripheral end were ground with a diamond grindstone and chamfered. For the glass substrates thus obtained (Comparative Examples 1 and 2), in the same manner as in Examples 1 to 3, the position and cross of the cross point CP on the main surface of the glass substrate 1 when the main surface was viewed in plan view. The position of the point spacing was examined. The results are shown in FIGS. 6 and 7 respectively.

  As can be seen from FIG. 6, the glass substrates of Comparative Examples 1 and 2 had large variations in the position of cross points on the main surface, which were 0.608 mm and 0.694 mm, respectively. That is, the roundness of the circle formed at the cross point exceeded 0.5 mm. Further, as can be seen from FIG. 7, the glass substrates of Comparative Examples 1 and 2 each had a large variation in the position of the cross point spacing on the main surface of 0.006 mm. That is, the variation in cross point spacing exceeded 5 μm (0.005 mm).

  Next, the relationship between the variation in the position of the cross point and the head crash was examined. In this case, after the texture treatment and precision cleaning are performed on the glass substrate obtained as described above, an underlayer, a magnetic layer, a protective layer, and a lubricating layer are sequentially laminated to produce a magnetic disk. Was loaded into a load / unload type HDD device, and the incidence of head crashes was examined. Here, the head crash refers to a disc in which 1000 drive testers are used and a scratch is found by looking at the outer edge every 100 times in repeated seek head tests (hole → outer edge → hole movement). This is the number of sheets divided by the parameter. Here, the head flying height was examined as 7 nm, 10 nm, 12 nm, and 15 nm, respectively. The result is shown in FIG.

  As can be seen from FIG. 8, if the variation in the position of the cross point is 0.5 mm or less, the head crash hardly occurs regardless of the head flying height. For this reason, it turns out that a head crash can be prevented in a very high ratio by using the glass substrate of the said Examples 1-3. On the other hand, when the variation in the position of the cross point exceeds 0.5 mm, the head crash rate increases. In particular, as the head flying height decreases, the head crash rate increases significantly. For this reason, it can be seen that the glass substrates of Comparative Examples 1 and 2 cannot sufficiently prevent head crashes.

  The present invention is not limited to the above embodiment, and can be implemented with appropriate modifications. For example, the number, size, processing procedure, and the like of the members in the above embodiment are merely examples, and various changes can be made within the range where the effects of the present invention are exhibited. In addition, various modifications can be made without departing from the scope of the object of the present invention.

It is a figure showing a part of glass substrate which is a substrate for magnetic discs concerning an embodiment of the invention. (A) is a figure which shows a part of glass substrate shown in FIG. 1, (b) is an enlarged view of the X section of (a), (c) is a top view of the glass substrate 1. FIG. . (A), (b) is a figure for demonstrating the state of the edge part vicinity of a glass substrate. It is the schematic which shows the grinding | polishing apparatus used when producing the glass substrate which is a board | substrate for magnetic discs concerning embodiment of this invention. It is an exploded view which shows schematic structure of a HDD apparatus. It is a figure which shows the dispersion | variation in the position of the cross point in a main surface. It is a figure which shows the dispersion | variation in the position of the cross point spacing in a main surface. FIG. 6 is a characteristic diagram showing a relationship between variation in cross point position on the main surface and head crash.

Explanation of symbols

1 Glass substrate 11 Hole 12 Main surface 13 End surface 14 Chamfered surface CP Cross point C Center of substrate

Claims (11)

A magnetic disk substrate for a magnetic disk apparatus of a type in which a magnetic head is loaded / unloaded to the main surface of the magnetic disk via an outer edge of the magnetic disk,
The substrate for a magnetic disk, includes a flat main surface, an end face, and a chamfer surface between the main surface and the end face, it has a circular shape,
A first imaginary line connecting a position on the main surface of 50% from the center and a position on the main surface of 80% from the center at a first distance from the center of the magnetic disk substrate to the end surface; The intersection of the second imaginary line connecting the position on the chamfered surface of 0.15% from the end surface and the position on the chamfered surface of 0.30% from the end surface at the first distance is defined as a cross point. Occasionally, the roundness of the circle formed by the cross points Ri der less 0.5 mm, from said cross-point, said cross point when viewed from above the said main surface when viewed in plan the main surface The magnetic disk substrate is characterized in that the variation of the second distance to the projection position on the chamfered surface is 5 μm or less over the entire circumference of the magnetic disk substrate. Before Stories second distance, a magnetic disk substrate according to claim 1, wherein a is 15μm or less. 2. The magnetic disk substrate according to claim 1, wherein the roundness of a circle formed at the cross point is 0.340 mm or less. Magnetic disk substrate according to claim 1, wherein the variation of the second distance over the entire circumference of the substrate for the magnetic disk is 4 [mu] m or less. The center of the circle formed by the cross points in a plan view of the main surface, claims 1 to 4, the distance between the center of the substrate for the magnetic disk is equal to or less than 1200μm The magnetic disk substrate according to any one of the above. Substrate according to any one of claims 1 to 5 in which the substrate for the magnetic disk is characterized by being composed of glass. A magnetic disk comprising: the magnetic disk substrate according to any one of claims 1 to 6 ; and a magnetic layer formed on the magnetic disk substrate. Magnetic disk 請 Motomeko 7, wherein you, characterized in that it is mounted on at least a magnetic disk device for rotating the magnetic disk at a rotational speed of 7200 rpm. 9. The magnetic disk according to claim 7 , wherein the touchdown height is 4 nm or less. 10. The magnetic disk according to claim 7 , wherein the recording density is 200 Gbit / inch ² or more. 11. A hard disk drive device comprising: the magnetic disk according to claim 7; and a magnetic head for recording and / or reproducing information with respect to the magnetic disk.

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