Magnetic disk substrate, magnetic disk, and hard disk drive

Abstract

To provide a substrate for a magnetic disk, a magnetic disk, an annular-shaped substrate, and a manufacturing method for a substrate for a magnetic disk, to make it difficult for the annular-shaped substrate from a holding member that holds the annular-shaped substrate when double-sided grinding or polishing is performed on the annular-shaped substrate.SOLUTION: A glass substrate for a magnetic disk (magnetic disk substrate) 1 includes a pair of main surface 1p and outer peripheral end surface 5, the outer peripheral end surface has a pair of chamfered surfaces 1c, each of which is connected to the main surface, and a side wall surface 1t extending between the pair of chamfered surfaces and curved outwardly so as to be convex, and the side wall surface 1t has a radius of curvature Rt of 1100 μm or more in a cross-section along the plate thickness T direction of the magnetic disk substrate. To prevent the generation of fine particles, it is preferable that the outer peripheral end surface of the magnetic disk substrate is smoothed. In addition, it is preferable to align the outer peripheral end surface to a target shape.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a magnetic disk substrate having a pair of main surfaces and an outer peripheral end surface, a magnetic disk, an annular substrate, and a method for manufacturing a magnetic disk substrate. [Background technology]

[0002] With the recent rise of cloud computing, many hard disk drives (HDD) are being used in cloud data centers to increase storage capacity. HDD devices use magnetic disks, which are circular non-magnetic magnetic disk substrates with a magnetic layer, as storage media. In order to increase the storage capacity of HDD devices, it is preferable to make the magnetic disks thinner and increase the number of magnetic disks that can be installed.

[0003] Incidentally, when manufacturing a magnetic disk substrate, it is preferable to smooth the end face of the magnetic disk substrate, which is the final product, from the viewpoint of preventing the generation of fine particles. Also, it is preferable to align the end face to a target shape from the viewpoint of accurately incorporating the magnetic disk into an HDD device.

[0004] Conventionally, a shape having a pair of chamfered surfaces connected to the main surfaces and a side wall surface extending in the plate thickness direction between the chamfered surfaces is known as an end face shape of a magnetic disk substrate. Such an end face shape can be obtained, for example, by performing end face grinding using a formed grindstone having a grinding surface shaped to correspond to the shapes of the target chamfered surface and side wall surface (Patent Document 1). Also, conventionally, a glass substrate is known that has an end face shape in which the region between the main surface and the outer surface has a continuous convex curved surface (Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2010-238302 A [Patent Document 2] JP 2006-40361 A Summary of the Invention [Problem to be solved by the invention]

[0006] The main surface of the annular plate (annular substrate) whose end surface has been processed to a target shape is further polished using a double-sided polishing machine. Polishing using a double-sided polishing machine (double-sided polishing) is performed in a state where the annular substrate is accommodated in a holding hole of a holding member (carrier) that holds the annular substrate, and the annular substrate is sandwiched between a surface plate from above and below. At this time, the thickness of the carrier needs to be thinner than the thickness of the annular substrate. When such double-sided polishing is performed on an annular substrate having a curved end surface, the annular substrate may come off the holding hole of the carrier and ride up on the carrier. In particular, when the thickness of the annular substrate to be polished is thin, the thickness of the carrier needs to be even thinner than that, so that the annular substrate is likely to ride up on the carrier. If polishing is continued in a state where the annular substrate rides up on the carrier, the main surface is likely to be scratched. Furthermore, when a strong force is applied to the annular substrate sandwiched between the surface plate and the carrier, the annular substrate may crack or break, resulting in damage. The above phenomenon may also occur when a holding member is used to grind both main surfaces of an annular substrate.

[0007] Therefore, an object of the present invention is to provide a circular-shaped substrate, a substrate for a magnetic disk, a magnetic disk, and a method for manufacturing a substrate for a magnetic disk, in which the circular-shaped substrate is less likely to come off from the holding member that holds the circular-shaped substrate when double-sided grinding or double-sided polishing is performed on the circular-shaped substrate. [Means for solving the problem]

[0008] One aspect of the present invention is a magnetic disk substrate having a pair of main surfaces and an outer peripheral end surface. The magnetic disk substrate comprises: the outer peripheral end surface has a pair of chamfered surfaces connected to the main surfaces, respectively, and a side wall surface extending between the pair of chamfered surfaces and curved outwardly so as to be convex, The side wall surface has a radius of curvature of 1100 μm or more in a cross section along a thickness direction of the magnetic disk substrate.

[0009] The side wall surface preferably has a radius of curvature of 2000 μm or less.

[0010] It is preferable that the length in a direction parallel to the main surface between the connection position of the chamfered surface with the main surface and the outermost protruding position of the side wall surface is 100 μm or less.

[0011] The chamfered surface is curved so as to be convex outward, In a cross section along the thickness direction of the magnetic disk substrate, the chamfered surface preferably has a radius of curvature smaller than the radius of curvature of the side wall surface.

[0012] The radius of curvature of the chamfered surface is preferably 100 to 500 μm.

[0013] In a cross section along a thickness direction of the magnetic disk substrate, it is preferable that a connection region of the chamfered surface located on the side of a connection position between the chamfered surface and the main surface is inclined at an angle of 30 to 70 degrees with respect to a direction parallel to the main surface.

[0014] It is preferable that, in a cross section along the thickness direction of the magnetic disk substrate, a boundary portion between the chamfered surface and the side wall surface is rounded.

[0015] It is preferable that the plate thickness is less than 0.6 mm.

[0016] The magnetic disk substrate is preferably a glass substrate.

[0017] Another aspect of the present invention is a magnetic disk. The magnetic disk comprises: The magnetic disk substrate has at least a magnetic film on its surface.

[0018] Another aspect of the present invention is an annular substrate having a pair of main surfaces, an outer peripheral end face, and an inner peripheral end face. the outer peripheral end surface has a pair of chamfered surfaces connected to the main surfaces, respectively, and a side wall surface extending between the pair of chamfered surfaces and curved outwardly so as to be convex, The side wall surface has a radius of curvature of 1100 μm or more in a cross section along a plate thickness direction of the annular substrate.

[0019] Another aspect of the present invention is a method for producing a magnetic disk substrate, comprising a process for polishing at least a main surface of the annular substrate. Effect of the Invention

[0020] According to the above-mentioned magnetic disk substrate, magnetic disk, and annular substrate, when the annular substrate is subjected to double-sided grinding or double-sided polishing, the annular substrate is less likely to come off the holding member that holds the annular substrate. Also, according to the above-mentioned manufacturing method for the magnetic disk substrate, such a magnetic disk substrate can be obtained. [Brief description of the drawings]

[0021] [Figure 1] 1 is a diagram illustrating an external shape of a magnetic disk substrate according to an embodiment. [Diagram 2] 1 is a diagram showing an example of a cross-sectional shape of an outer peripheral end face of a magnetic disk substrate. [Diagram 3] 13 is a diagram showing a holding member holding an annular substrate in a holding hole. FIG. [Figure 4] 13A and 13B are diagrams showing the annular substrate coming out of the holding hole and riding on the holding member. [Diagram 5] FIG. 1 is a diagram illustrating end face grinding using a formed grindstone. [Figure 6] 11A and 11B are diagrams illustrating a method for determining the radius of curvature of the boundary portion between a chamfered surface and a side wall surface. [Figure 7] 11 is a diagram showing another example of the cross-sectional shape of the outer peripheral end face of a magnetic disk substrate. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, a magnetic disk substrate, a magnetic disk, an annular substrate, and a method for manufacturing a magnetic disk substrate according to an embodiment will be described in detail. In the following description, a glass substrate is used as the material for the magnetic disk substrate and the annular substrate, but a metal substrate may be used as the material instead of the glass substrate.

[0023] Fig. 1 is a diagram showing the external shape of a glass substrate, which is an example of a magnetic disk substrate according to one embodiment. The outer periphery of the glass substrate 1 is circular. The glass substrate 1 of the example shown in Fig. 1 is an annular substrate having an inner periphery with an inner hole 3 concentric with the above-mentioned circular circle. That is, the glass substrate 1 of the example shown in Fig. 1 has a pair of main surfaces 1p, 1p (see Fig. 2), an outer peripheral end face 5, and an inner peripheral end face 7. Note that in Fig. 1, chamfered surfaces and side wall surfaces of the glass substrate 1, which will be described later, are omitted from illustration.

[0024] The glass substrate 1 is a glass substrate for magnetic disks. The size of the glass substrate 1 is not limited, but may be, for example, the size of a glass substrate for magnetic disks having a nominal diameter of 2.5 inches or 3.5 inches. In the case of a glass substrate for magnetic disks having a nominal diameter of 2.5 inches, the outer diameter is 55 to 70 mm, for example, the outer diameter is 65 mm, 67 mm, or 58 mm, the inner hole diameter is 20 mm, and the plate thickness is 0.3 to 1.3 mm. In the case of a glass substrate for magnetic disks having a nominal diameter of 3.5 inches, the outer diameter is 85 to 100 mm, for example, the outer diameter is 95 mm, 97 mm, or 89 mm, the inner hole diameter is 25 mm, and the plate thickness is 0.3 to 1.3 mm. The thickness T (see FIG. 2) of the glass substrate 1 is preferably as thin as possible, in order to make the magnetic disk thinner and increase the number of disks that can be mounted on an HDD device, and is preferably less than 0.6 mm, 0.56 mm or less, 0.51 mm or less, 0.46 mm or less, and 0.41 mm or less. The above diameter and thickness values ​​are nominal values, and may include values ​​that deviate slightly due to variations in production, etc. In addition, when a substrate having a nickel alloy plating film formed on the surface of an aluminum alloy substrate is used instead of a glass substrate, the above values ​​correspond to the entire substrate, including the thickness of the nickel alloy plating film.

[0025] FIG. 2 shows an example of a cross-sectional shape of an outer peripheral end surface 5 of glass substrate 1 taken along the plate thickness direction. The outer peripheral end surface 5 has a pair of chamfered surfaces 1c, 1c and a side wall surface it.

[0026] The pair of chamfered surfaces 1c, 1c are surfaces connected to the main surfaces 1p, 1p, respectively. In the present invention, even if the chamfered surface is not a flat surface, such as a curved surface, as described later, it is still called a chamfered surface.

[0027] The side wall surface 1t is a surface that extends between the chamfered surfaces 1c, 1c in a curved manner so as to be convex outward. The side wall surface 1t has a radius of curvature Rt of 1100 μm or more in a cross section along the thickness direction of the glass substrate 1 (hereinafter, referred to as a cross section along the thickness direction or simply as a cross section) that passes through the center of the circular shape of the outer periphery of the glass substrate 1. The glass substrate 1 having such a side wall surface 1t is unlikely to come off the holding hole of the holding member (carrier) when a glass annular substrate (hereinafter, also referred to as a glass plate) that is the raw plate of the glass substrate 1 is ground or polished on both sides. Therefore, the glass plate is unlikely to ride up onto the carrier, and it is possible to suppress the occurrence of scratches, cracks, cracks, etc. on the main surface of the glass plate by continuing double-sided grinding or double-sided polishing in a state where the glass plate rides up onto the carrier. The above cross-sectional shape can be measured using a contour shape measuring device such as a Contracer manufactured by Mitutoyo Corporation.

[0028] The double-sided grinding or polishing of the glass plate is performed using a double-sided grinding machine or a double-sided polishing machine equipped with a planetary gear mechanism. In double-sided grinding using a double-sided grinding machine or double-sided polishing using a double-sided polishing machine, as shown in FIG. 3, the glass plate G is accommodated in a holding hole 18a of a carrier 18, and the glass plate G is sandwiched between the platens 14 and 12 from both the top and bottom. The glass plate G shown in FIG. 3 is sandwiched between the platens 14 and 12 via a grinding member or polishing pad 20. In FIG. 3, the chamfered surface and curved side wall surface of the glass plate G are omitted. The thickness of the carrier 18 is thinner than the thickness of the glass plate G in order to ensure the machining allowance of both main surfaces of the glass plate G. In addition, in order to ensure a high polishing rate, the thinner the thickness of the carrier 18, the better. For this reason, if the radius of curvature of the side wall surface of the glass sheet is too small, the glass sheet G' (see FIG. 4) will have a shape that is pointed outward at the center in the thickness direction, so that during double-sided grinding or double-sided polishing, the edge of the carrier 18 that comes into contact with the glass sheet G' will easily slide in the thickness direction relative to the glass sheet G', and the glass sheet G will easily come off the holding hole 18a. For this reason, as shown in FIG. 4, the glass sheet G' that has come off the holding hole 18a will easily ride up on the carrier 18. If grinding or polishing is continued while the glass sheet G' is riding up on the carrier 18, the main surface of the glass sheet G' will easily be scratched due to contact with the carrier 18, and a strong force will be applied to the glass sheet G' sandwiched between the platen 14, 12 and the carrier 18, which may cause cracks or breaks in the glass sheet and damage it. In particular, for double-sided grinding or double-sided polishing of a thin glass sheet, an even thinner carrier 18 is used, so that the glass sheet will be more likely to come off the holding hole 18a. In the glass substrate 1 of this embodiment, the radius of curvature Rt of the side wall surface 1t is limited to 1100 μm or more, thereby suppressing dislocation from the holding hole 18a when the glass plate G is thin. In this respect, the radius of curvature Rt of the side wall surface 1t is preferably 1200 μm or more.

[0029] Since the glass substrate 1 is made from a glass plate G produced by edge processing or edge polishing as described later, the cross-sectional shapes of the sidewall surface and chamfered surface of the outer peripheral edge surface of the glass plate G are maintained in the glass substrate 1. In addition, when a magnetic film or the like is formed on the surface of the glass substrate 1 for magnetic disks to produce a magnetic disk as described later, the total film thickness of the magnetic film or the like is, for example, 100 nm or less, which is sufficiently thin compared to the plate thickness. Therefore, the cross-sectional shapes of the sidewall surface and chamfered surface of the outer peripheral edge surface of the glass substrate 1 are maintained in the magnetic disk.

[0030] In this specification, the term "outside" refers to the side away from the center of the circular outer periphery of the glass substrate 1, and the term "convex outward" refers to protruding outward from a straight line connecting both ends of the side wall surface 1t or the chamfered surface 1c in the plate thickness direction.

[0031] The curvature radius Rt of the side wall surface 1t is specified as the radius of an arc passing through three specific points on the side wall surface 1t that are different in the plate thickness direction. In the example shown in FIG. 2, the curvature radius Rt of the side wall surface 1t can be specified as the radius of an arc passing through three points, namely, two intersection points between a virtual circle of radius 100 μm and the side wall surface 1t when the point on the side wall surface 1t that passes through the center of the plate thickness direction of the glass substrate 1 and intersects with a plane parallel to the main surface 1p is T3. If the length of the side wall surface 1t is less than 200 μm and the fitting between the arc of the virtual circle and the side wall surface 1t is not good, the radius of the virtual circle may be appropriately reduced.

[0032] The cross-sectional shape of the outer peripheral end surface 5 of the glass substrate 1 including the side wall surface 1t is obtained by preparing a glass sheet G using, for example, a forming grindstone 30 shown in FIG. 5. FIG. 5 shows the forming grindstone 30 and a plate material (hereinafter referred to as a glass plate material) before end surface grinding to be processed into a glass sheet G. In FIG. 5, the area of ​​the glass plate material with a dashed line indicates the area to be removed by end surface grinding. Also, in FIG. 5, an arrow pointing to the left indicates the relative movement direction of the forming grindstone 30 with respect to the glass plate material when performing end surface grinding. The forming grindstone 30 is formed, for example, in a cylindrical or cylindrical shape as a whole, and has a groove 31 on the outer peripheral side surface. The groove 31 is configured so that the side wall surface and the chamfered surface of the glass sheet G can be formed simultaneously by grinding. Specifically, the groove 31 has a grinding surface having a side wall portion 31b and a chamfered portion 31a located on both sides thereof. The side wall portion 31b and the chamfered portion 31a of the groove 31 are formed to a predetermined size and shape, taking into consideration the target shape of the finished outer peripheral end surface of the glass sheet G or the glass substrate 1.

[0033] According to one embodiment, the curvature radius Rt of the side wall surface 1t is preferably 2000 μm or less. The side wall surface 1t with a curvature radius exceeding 2000 μm extends substantially linearly in the plate thickness direction, so that the corner between the side wall surface 1t and the chamfered surface 1c is likely to be sharp. When the glass plate G is produced using the shaping grindstone 30, the portion of the glass plate material that becomes such a corner is likely to be subjected to a load from the shaping grindstone 30 and thus to be concentrated. For this reason, chipping may occur. In particular, the glass plate material that becomes the thin glass substrate 1 has a thin plate thickness and is likely to have a low rigidity, so that it is likely to bend under the load from the shaping grindstone 30, and the load is likely to be concentrated on the portion that becomes the corner. In this respect, it is more preferable that the curvature radius Rt of the side wall surface 1t is 1800 μm or less.

[0034] According to one embodiment, the length Lc (see FIG. 2) in the direction parallel to the main surface 1p between the connection position Pc of the chamfered surface 1c with the main surface 1p and the outermost convex position of the side wall surface 1t is preferably 100 μm or less. By limiting the length Lc in this way, the overall outward sharpness of the cross-sectional shape of the outer peripheral end surface 5 is suppressed, contributing to improving the effect of suppressing the glass sheet G from being removed from the holding hole 18a. This is presumably because the smaller the degree of sharpness of the cross-sectional shape of the outer peripheral end surface 5, the smaller the gap between the upper and lower surface plates becomes. In this respect, it is more preferable that the length Lc is 80 μm or less. The upper limit of the length Lc is, for example, 150 μm. On the other hand, the length Lc is preferably 20 μm or more to prevent chipping during handling of the glass sheet G. In addition, when the degree of sharpness is expressed by the value of Lc / T, it is preferable that Lc / T is 0.25 or less. If Lc / T exceeds 0.25, the sharpness becomes too large, and the glass sheet G may easily come off from the holding hole. On the other hand, Lc / T is preferably 0.1 or more. If the Lc / T value is less than 0.1, chipping may easily occur. From these viewpoints, the Lc / T value is more preferably within the range of 0.1 to 0.25.

[0035] According to one embodiment, the chamfered surface 1c is preferably curved so as to be convex outward. In this case, the chamfered surface 1c preferably has a radius of curvature Rc smaller than the radius of curvature Rt of the side wall surface 1t in a cross section along the plate thickness direction of the glass substrate 1. By providing the chamfered surface 1c in this form, the overall outward sharpness of the cross-sectional shape of the outer peripheral end surface 5 is likely to be mitigated, which contributes to improving the effect of suppressing the glass sheet G from being removed from the holding hole 18a. In addition, by providing the chamfered surface 1c in the above form, the angle between the chamfered surface 1c and the side wall surface 1t is unlikely to become small (i.e., the boundary portion 1b (described later) between the chamfered surface 1c and the side wall surface 1t is unlikely to be sharp), which suppresses the concentration of load on the portion of the glass sheet material that is the corner between the chamfered surface 1c and the side wall surface 1t when the glass sheet G is produced using the shaped grindstone 30, thereby improving the effect of suppressing the occurrence of chipping. That is, by providing the chamfered surface 1c in the above-described form, it is possible to improve the effect of suppressing the glass sheet G from coming off from the holding hole 18a, while suppressing the occurrence of chipping when the glass sheet G is produced using the forming grindstone 30. In this regard, it is preferable that the radius of curvature Rc of the chamfered surface 1c is 100 to 1000 μm.

[0036] When the chamfered surface 1c is curved, the radius of curvature Rc is specified as the radius of an arc passing through three specific points on the chamfered surface 1c that are different in the sheet thickness direction. That is, the radius of curvature Rc of the chamfered surface 1c can be specified as the radius of an arc passing through three points: (1) a connection position Pc on one of the main surfaces, (2) a position on the chamfered surface 1c that is 30 μm away from the connection position Pc in the sheet thickness direction, and (3) a position on the chamfered surface that is 60 μm away from the connection position Pc in the sheet thickness direction.

[0037] In addition, in a cross section along the thickness direction of the glass substrate 1, the connection region 1ca of the chamfered surface 1c located on the side of the connection position Pc of the chamfered surface 1c with the main surface 1p is preferably inclined at an inclination angle θ of 30 to 70 degrees with respect to a direction parallel to the main surface 1p. By making the chamfered surface 1c inclined in this manner, the connection with the curved side wall surface 1t becomes relatively smooth, and the above effect of suppressing chipping when the glass sheet G is produced using the forming grindstone 30 while suppressing the glass sheet G from coming off the holding hole 18a is improved. The connection region 1ca is, for example, a region in the range of 5 to 20 μm in the thickness direction from the connection position Pc. Here, the reason for excluding the immediate vicinity of the connection position Pc (a region less than 5 μm in the thickness direction from the main surface 1p) is that the connection position Pc does not appear to have a radius of curvature on the drawing, but in reality has a physically finite radius of curvature. This can be understood by enlarging the image of the cross section. When the connection position Pc is rounded or the chamfered surface 1c is a curved surface, the inclination angle θ of the connection region may be the angle at which the tangent at the position of the connection region 1ca, which is 10 μm away from the connection position Pc in the plate thickness direction, is inclined with respect to a direction parallel to the main surface 1p.

[0038] According to one embodiment, the outer peripheral end surface 5 of the glass substrate 1 preferably has a boundary portion 1b (see FIG. 6) between the chamfered surface 1c and the side wall surface 1t in a cross section along the thickness direction of the glass substrate 1 that is rounded. The boundary portion 1b is a portion that is interposed between the chamfered surface 1c and the side wall surface 1t and is connected to the chamfered surface 1c and the side wall surface 1t. By providing such a boundary portion 1b, the chamfered surface 1c and the side wall surface 1t are connected by a smooth curve, and the cross-sectional shape of the outer peripheral end surface 5 tends to be a smooth curved shape as a whole. Such a cross-sectional shape of the outer peripheral end surface 5 contributes to improving the above-mentioned effect of suppressing chipping when the glass sheet G is produced using the forming grindstone 30 while suppressing the glass sheet G from coming off the holding hole 18a.

[0039] From the above viewpoints, the boundary portion 1b preferably has a radius of curvature of 150 to 1500 μm, and more preferably has a radius of curvature of 150 to 400 μm, in a cross section along the thickness direction of the glass substrate 1. The radius of curvature of the boundary portion 1b is smaller than the radius of curvature of the side wall surface 1t. The radius of curvature R of the boundary portion is calculated as follows. FIG. 6 is a diagram for explaining a method of calculating the radius of curvature of the cross-sectional shape of the boundary portion 1b. In FIG. 6, Rb is the radius of a circle C2 that forms a curvature equivalent to the curvature of the boundary portion 1b in the cross-sectional shape, and is the radius of curvature of the shape of the boundary portion 1b. First, the intersection point between the virtual line L1 obtained by extending the straight line portion of the chamfered surface 1c or the above-mentioned arc and the virtual arc L2 obtained by extending the side wall surface 1t along the above-mentioned arc of the side wall surface 1t is set as P1. Next, a virtual line L3 is set that passes through the intersection point P1 and extends perpendicularly to the virtual line L1. Next, the intersection point between the boundary portion 1b and the virtual line L3 is set as P2. Next, in the cross section of the glass substrate 1, a circle C1 having a predetermined radius (for example, 25 μm) is set with the intersection point P2 as the center. Next, the two intersection points between the boundary portion 1b and the outer periphery of the circle C1 are set as P3 and P4, respectively. Furthermore, a circle C2 is set that passes through each of the three intersection points P2, P3, and P4. In this way, the radius of the circle C2 is obtained, and the radius of curvature R of the cross-sectional shape of the boundary portion 1b is obtained. If the position of the boundary portion 1b is difficult to clearly recognize and the virtual line L1 and / or virtual arc L2 cannot be set properly, the value when the radius of curvature Rb of the circle C2 is smallest around the portion that is thought to be the boundary portion 1b may be set. At this time, the position of the intersection point P2 is temporarily set on the end face, and the circle C2 may be set while being appropriately shifted. At this time, the intersection points P3 and P4 also need to be located on the end face.

[0040] Fig. 7 is a diagram showing another example of the cross-sectional shape of the outer peripheral end surface 5 of the glass substrate 1. As shown in Fig. 7, the cross-sectional shape of the outer peripheral end surface 5 of the glass substrate 1 may be a single curved surface shape in which the chamfered surface 1c, the connection position Pc, and the boundary portion 1b (T1, T2 in Fig. 2) are all curved (or rounded) as a whole. In addition, the cross-sectional shape of the outer peripheral end surface 5 of the glass substrate 1 may be a shape in which at least one of the chamfered surface 1c, the connection position Pc, and the boundary portion 1b (T1, T2 in Fig. 2) is curved (or rounded).

[0041] The length Lt (see FIG. 2) of the side wall surface 1t in the plate thickness direction is not particularly limited, but is, for example, 0.2 to 0.5 mm. The length Lc2 (see FIG. 2) of the chamfered surface 1c in the sheet thickness direction is not particularly limited, but is, for example, 0.02 to 0.15 mm. A length Lc1 (see FIG. 2) of the chamfered surface 1c in a direction parallel to the main surface 1p is not particularly limited, but is, for example, 0.02 to 0.15 mm.

[0042] The cross-sectional shape of the inner peripheral end surface 7 of the glass substrate 1 may be the same as or different from the cross-sectional shape of the outer peripheral end surface 5 .

[0043] (Ring-shaped substrate) A glass plate G, which is an example of an annular substrate of an embodiment, has a pair of main surfaces, an outer peripheral end surface, and an inner peripheral end surface, and has an annular shape. The outer peripheral end surface of the glass plate G has a pair of chamfered surfaces connected to the main surfaces, respectively, and a side wall surface that curves and extends between the chamfered surfaces so as to be convex outward. In the cross section of the glass plate G along the thickness direction of the glass plate, the side wall surface has a curvature radius of 1100 μm or more. The glass plate G is used as a base plate for the glass substrate 1 of the above embodiment.

[0044] The radius of curvature of the side wall surface of the glass plate G is preferably 2000 μm or less. The length in the direction parallel to the main surface between the connection position of the chamfered surface of the glass plate G with the main surface and the outermost convex position of the side wall surface of the glass plate G is preferably 200 μm or less. The chamfered surface of the glass plate G is curved so as to be convex outward, and in a cross section along the thickness direction of the glass plate G, it is preferable that the chamfered surface of the glass plate G has a radius of curvature smaller than the radius of curvature of the side wall surface of the glass plate G. The radius of curvature of the chamfered surface of the glass plate G is preferably 100 to 500 μm.

[0045] In a cross section taken along the thickness direction of the glass sheet G, a connection region of the chamfered surface located on the side of the connection position of the chamfered surface with the main surface is preferably inclined at an angle of 10 to 70 degrees with respect to a direction parallel to the main surface. The connection region is configured in the same manner as the connection region 1ca of the glass substrate 1.

[0046] It is preferable that the boundary portion between the chamfered surface and the side wall surface is rounded in a cross section along the thickness direction of the glass sheet G. The boundary portion has a structure similar to that of the boundary portion 1b of the glass substrate 1.

[0047] The thickness T of the glass sheet G is preferably less than 0.6 mm.

[0048] (Method of manufacturing magnetic disk substrate) The manufacturing method of the magnetic disk substrate of one embodiment includes at least a process of polishing the main surface of the annular substrate. The annular substrate to be polished is the annular substrate of the above embodiment. Hereinafter, an example will be described in which the above glass plate is used as the annular substrate. The glass plate is not particularly limited, but is made from a glass plate manufactured by, for example, a float method, a down-draw method, or a press method. For example, a plurality of annular glass plates having inner holes can be taken out from a wide sheet-like glass plate manufactured by a float method or a down-draw method. The method of taking out the annular glass plate from the wide sheet-like glass plate may be performed by forming a cut line and breaking it using a well-known scriber (cutter), or may be performed by irradiating the glass plate with a laser beam to form a circular defect and cut out the glass plate. The inner hole is a hole that is approximately concentric with the above circular circle.

[0049] The glass material of the glass plate can be amorphous glass such as aluminosilicate glass, soda-lime glass, borosilicate glass, etc. The glass plate has a glass transition temperature Tg of, for example, 450 to 850°C.

[0050] The circular glass plate (glass substrate) is processed into a glass plate by edge processing. Edge processing can be performed by edge grinding using a grinding wheel or edge melting by irradiating a laser beam to melt the edge of the glass plate. By using this method, the entire edge can be smoothly curved and connected into one curved surface shape while avoiding chipping due to grinding. In addition, by making such an edge, chipping that occurs during subsequent processes such as grinding and polishing of the main surface and magnetic film formation can be reduced. After edge processing, edge polishing can be performed to polish the edge of the glass plate. Edge polishing can be performed using a polishing brush while supplying free abrasive grains to the edge. When edge processing is performed by edge melting using laser beam, edge polishing after edge processing may or may not be performed.

[0051] The outer peripheral edge surface of the glass plate can be made into the above-mentioned cross-sectional shape by, for example, adjusting the shape of the grinding surface of a formed grindstone or the conditions for polishing the edge surface using an abrasive brush.

[0052] In the manufacturing method of this embodiment, various treatments such as grinding, first polishing, second polishing, chemical strengthening, and cleaning can be carried out as described below.

[0053] In the grinding process, a double-sided grinding machine is used to grind the main surfaces of the glass plate. Specifically, the glass plate is accommodated in a holding hole of a carrier of the double-sided grinding machine, and both main surfaces of the glass plate are ground while holding the outer peripheral end surface of the glass plate. The double-sided grinding machine has a pair of upper and lower surface plates (upper and lower surface plates), and the glass plate is sandwiched between the upper and lower surface plates. Then, either one of the upper and lower surface plates, or both, is moved, and the glass plate and each surface plate are moved relatively while supplying coolant, thereby grinding both main surfaces of the glass plate. For example, a grinding member (diamond pad) formed of fixed abrasive grains fixed with diamond by resin and formed into a sheet shape can be attached to the surface plate for grinding. Also, instead of the combination of diamond pad and coolant, a combination of a cast iron surface plate and a slurry containing alumina abrasive grains or the like may be used. As described above, the thickness of the carrier must be smaller than the thickness of the glass plate to be held, and more specifically, it is preferably 0.05 mm or more smaller than the thickness of the glass plate, more preferably 0.1 mm or more smaller, and even more preferably 0.15 mm or more smaller. The diameter of the holding hole must be larger than the diameter of the glass plate to be held, and may be, for example, 0.1 to 3.0 mm larger than the diameter of the glass plate.

[0054] The first polishing is performed on the main surfaces of the glass plate after grinding. Specifically, the glass plate is accommodated in a holding hole of a carrier of a double-sided polishing device, and both main surfaces of the glass plate are polished while holding the outer peripheral edge surface of the glass plate. The purpose of the first polishing is to remove scratches and distortions remaining on the main surfaces after grinding, or to adjust minute surface irregularities (microwaviness, roughness). The first polishing is preferably mirror polishing.

[0055] In the first polishing process, a double-sided polishing machine having the same configuration as the double-sided grinding machine is used to polish both main surfaces of the glass plate while providing a polishing slurry containing free abrasive grains. As the free abrasive grains used in the first polishing, for example, abrasive grains such as cerium oxide and zirconia are used. In the double-sided polishing machine, like the double-sided grinding machine, a glass plate is sandwiched between a pair of upper and lower platens. A polishing pad (for example, a resin polisher) is attached to the surface of the lower platen and the upper platen. The polishing pad is preferably a suede type made of resin such as polyurethane foam and having fine openings on the surface, since it is difficult to scratch the surface of the glass plate and it is easy to make it mirror-finished. Then, by moving either one or both of the upper platen and the lower platen, the glass plate and each platen are moved relatively to each other, and both main surfaces of the glass plate are polished. The size of the polishing abrasive grains is preferably within the range of 0.5 to 3 μm in average particle size (D50).

[0056] The second polishing is performed on the glass plate after the first polishing. The second polishing process is aimed at mirror-polishing the main surface. In the second polishing, a double-sided polishing apparatus having the same configuration as the double-sided polishing apparatus used in the first polishing is used. Specifically, the glass plate is accommodated in a holding hole of a carrier of the double-sided polishing apparatus, and both main surfaces of the glass plate are polished while holding the outer peripheral end surface of the glass plate. In the second polishing process, the type and particle size of the free abrasive grains are different from those in the first polishing process, and the hardness of the resin polisher is different. It is preferable that the hardness of the resin polisher is smaller than that in the first polishing process. For example, a polishing liquid containing colloidal silica as free abrasive grains is supplied between the polishing pad of the double-sided polishing apparatus and the main surface of the glass plate, and the main surface of the glass plate is polished. The size of the polishing abrasive grains used in the second polishing is preferably within the range of 5 to 50 nm in average particle size (d50). It is preferable to use a suede-type polishing pad made of resin such as foamed polyurethane and having fine openings on the surface, because it is difficult to scratch the surface of the glass plate and it is easy to make it mirror-finished.

[0057] When chemical strengthening is performed, it is preferable to perform it before or after the second polishing. In the chemical strengthening process, a mixed molten liquid of potassium nitrate and sodium nitrate is used as a chemical strengthening liquid, and the glass plate is immersed in the chemical strengthening liquid. This allows a compressive stress layer to be formed on the surface of the glass plate G by ion exchange. The necessity of chemical strengthening is determined and appropriately selected in consideration of the glass composition and necessity.

[0058] In addition to the first polishing treatment and the second polishing treatment, another polishing treatment may be added, or the first polishing treatment and the second polishing treatment may be combined into one polishing treatment. Also, the order of the above treatments may be changed as appropriate.

[0059] The cleaning is performed using a cleaning liquid (e.g., water) after the last polishing process or the chemical strengthening process. In addition, another cleaning process may be appropriately added between the above steps of grinding, polishing, chemical strengthening, etc.

[0060] Here, a method for manufacturing a magnetic disk substrate when a metal substrate is used as the material of the annular substrate will be described. For example, an aluminum alloy having a nickel alloy film on its surface can be used as the material of the metal substrate. For example, an Al-Mg (aluminum-magnesium) alloy containing at least magnesium can be used as the aluminum alloy. For example, a Ni-P (nickel-phosphorus) alloy plating film containing at least phosphorus can be used as the nickel alloy film. In addition, a titanium alloy or single crystal silicon can be used instead of the aluminum alloy, and the nickel alloy film may not be used. Among these, an aluminum alloy substrate having a nickel alloy film on its surface, which is relatively light, has high strength, and is easy to process, can be preferably used.

[0061] When manufacturing an aluminum alloy substrate having a nickel alloy film on its surface instead of a glass substrate, for example, a disk-shaped plate material (aluminum alloy substrate) is cut out from an aluminum alloy plate material, heated at a predetermined temperature and time, and annealed, and then the main surface is cut and the end face is shaped. In the shaping of the end face, the end face is ground or cut into a predetermined shape using a tool such as a formed bit or a single bit. Here, in the end face processing of the aluminum alloy substrate, minute recesses may be generated corresponding to chipping in the glass plate. This is considered to be due to the surface being torn off or crystallized substances falling off due to the sliding between the substrate surface and the tool. These minute recesses remain on the surface even after the nickel alloy film or magnetic film is formed, and when the magnetic disk is rotated at high speed, an unstable air flow is generated, which causes the fluttering of the magnetic disk to worsen, which is not preferable. These minute recesses increase or decrease depending on the target shape of the end face. Annealing may be performed after processing the end face or surface. Then, a nickel alloy plating film may be formed on the surface to a thickness of, for example, 3 to 20 μm. Here, since the thickness of the plating film is sufficiently small compared to the thickness of the entire substrate, the shape of the end face formed by grinding or cutting is maintained almost the same even after the plating film is formed. Thereafter, the surface of the aluminum alloy substrate (annular substrate) with the nickel alloy plating film is polished. From the viewpoint of achieving both improved surface quality and improved productivity, the polishing process preferably employs a polishing process of two or more stages, similar to the polishing of the glass plate described above. The specific polishing method can be almost the same as that of the polishing of the glass plate described above, except that it is preferable to use a polishing solution containing alumina abrasive grains in the first polishing (rough polishing).

[0062] In this manner, after producing a ring-shaped substrate having an outer peripheral end surface with the cross-sectional shape described above, at least the main surface of the ring-shaped substrate is polished to produce a magnetic disk substrate that satisfies the conditions required for a magnetic disk substrate. Thereafter, at least a magnetic film is formed on the main surface of the magnetic disk substrate to manufacture a magnetic disk, and then an HDD including the magnetic disk and a magnetic head is manufactured.

[0063] (Magnetic Disk) The magnetic disk of one embodiment has at least a magnetic film on the surface of the magnetic disk substrate. The magnetic film is preferably formed at least on the main surface of the magnetic disk substrate, but is generally also formed on the end surface of the magnetic disk substrate. The magnetic disk preferably has films such as an undercoat film, a magnetic film, and a protective film, in this order from the surface side of the magnetic disk substrate.

[0064] (Experimental Example 1-1) In order to investigate the effect of the present invention, end face grinding was carried out using formed grindstones with various different shapes of grinding surface. Annular glass plates (annular substrates) with a side wall surface of the radius of curvature Rt shown in Table 1 below on the outer peripheral end face were produced, and the end face of each glass plate was polished and the main surface was ground, and then the above-mentioned first polishing was carried out using free abrasive grains of cerium oxide and a suede-type polishing pad, and the frequency with which the glass plate came off the holding hole of the carrier was investigated.

[0065] For the first polishing, a glass plate having the following specifications was used. Note that the specifications for the end faces all relate to the outer peripheral end faces. ·Outer diameter 97mm, inner diameter 25mm, plate thickness 0.53mm The radius of curvature Rt is as shown in Table 1. The chamfered surface is approximately linear in cross section, with a 45° inclination angle in the connection area and a length of 85 μm in the plate thickness direction. The radius of curvature at the boundary between the side wall and the chamfer is less than 150 μm. -Aluminosilicate glass ring-shaped pane The removal amount (polishing amount) of the main surface in the first polishing was 25 μm based on the plate thickness (12.5 μm on each side), and the thickness of the carrier was 0.3 mm.

[0066] The first polishing was performed by storing a total of 25 glass plates G in five carriers each having five holding holes (25 plates per batch). This first polishing was performed 20 times, and the number of glass plates that had fallen out of the holding holes and landed on the carriers was counted each time the first polishing was completed. If the total number was less than 2% of the total number of glass plates used in the first polishing, it was evaluated as A, if it was 2% or more but less than 4%, it was evaluated as B, and if it was 4% or more, it was evaluated as C. If the evaluation was A or B, the frequency (occurrence rate) of glass plates falling out of the holding holes was low, so it was a pass. The results are shown in Table 1.

[0067] [Table 1]

[0068] A comparison between the examples and the comparative examples shows that when the radius of curvature Rt of the side wall surface of the glass plate is 1100 μm or more, the frequency of the glass plate coming off the holding hole is reduced. A comparison between Example 1 and Examples 2 to 4 shows that when the radius of curvature Rt of the side wall surface of the glass plate is 1200 μm or more, the frequency of the glass plate coming off from the holding hole is further reduced.

[0069] (Experimental Example 1-2) The first polishing was performed under the same conditions as in Experimental Example 1-1 and Table 1, except that the thickness of the glass plate used in the first polishing was changed to 0.48 mm (Comparative Examples 3 and 4, Examples 5 to 8), and results equivalent to those in Table 1 were obtained.

[0070] (Experimental Example 1-3) The first polishing was performed under the same conditions as in Experimental Example 1-1 and Table 1, except that the thickness of the glass plate used in the first polishing was changed to 0.43 mm (Comparative Examples 5 and 6, Examples 9 to 12), and results equivalent to those in Table 1 were obtained.

[0071] (Experimental Example 1-4) The annular substrate used in the first polishing was changed from a glass plate to an aluminum alloy substrate having a 10 μm NiP alloy plating film formed on the surface thereof, and the free abrasive grains were changed to alumina abrasive grains. Except for this, the first polishing was carried out under the same conditions as in Experimental Example 1-1 and Table 1 (Comparative Examples 7 and 8, Examples 13 to 16), and results equivalent to those in Table 1 were obtained.

[0072] (Experimental Example 1-5) The annular substrate used in the first polishing was changed from a glass plate to an aluminum alloy substrate having a thickness of 0.48 mm and a 10 μm NiP alloy plating film formed on the surface thereof, and the free abrasive grains were changed to alumina abrasive grains. Except for this, the first polishing was carried out under the same conditions as in Experimental Example 1-1 and Table 1 (Comparative Examples 9 and 10, Examples 17 to 20), and results equivalent to those in Table 1 were obtained.

[0073] (Experimental Example 1-6) In the specifications of the glass plate used in the first polishing, the radius of curvature of the boundary between the side wall surface and the chamfered surface was changed to be within the range of 150 to 400 μm, but the first polishing was performed under the same conditions as in Experimental Example 1-1 and Table 1 (Comparative Examples 11 and 12, Examples 21 to 24), and results equivalent to those in Table 1 were obtained.

[0074] (Experimental Example 1-7) In the specifications of the glass plate used in the first polishing, the plate thickness was changed to 0.43 mm, and the radius of curvature of the boundary between the side wall surface and the chamfered surface was changed to be within the range of 150 to 400 μm. Except for this, the first polishing was performed under the same conditions as in Experimental Example 1-1 and Table 1 (Comparative Examples 13 and 14, Examples 25 to 28), and results equivalent to those in Table 1 were obtained.

[0075] (Experimental Example 1-8) The first polishing was carried out under the same conditions as in Example 3 of Experimental Example 1-1, except that the glass plate used in the first polishing was made into an outer peripheral edge surface that looked like a single smoothly curved, connected surface by edge melting with a laser beam and then grinding both main surfaces, and the frequency of coming off from the retaining hole was evaluated as A (Example 29). The specifications of the outer peripheral edge surface are as follows: - Radius of curvature Rt is 1500μm The chamfered surface has a curved shape with a curvature radius of 200 to 500 μm in cross section, an inclination angle of 40° in the connection area with the main surface, and Lc of 100 μm. The radius of curvature at the boundary between the side wall surface and the chamfered surface is 100 to 500 μm.

[0076] (Manufacture of magnetic disk substrates and magnetic disks) Among the annular substrates obtained in the above "Example" after the first polishing, those that fell out of the holding hole, those that had problems such as chipping and minute recesses were removed, and the remaining annular substrates were washed, and then the above second polishing was performed with a removal allowance of 5 μm (2.5 μm on each side) based on the plate thickness. The total removal allowance of the first and second polishing is 30 μm based on the plate thickness, so for example, if the plate thickness before the first polishing is 0.53 mm, the plate thickness after the second polishing is 0.50 mm. In the second polishing, a polishing liquid containing colloidal silica and a suede pad were used. After that, washing was performed to obtain a magnetic disk glass substrate or an aluminum alloy substrate having an outer diameter of 97 mm, an inner diameter of 25 mm, and a plate thickness of 0.40 to 0.50 mm, on whose surface a nickel alloy plating film was formed. Then, an undercoat film, a magnetic film, a protective film, etc. were sequentially formed on the surface of each magnetic disk substrate to obtain a magnetic disk. When the shapes of the outer peripheral end faces of each magnetic disk substrate and magnetic disk were checked, it was found that the lengths of the chamfers Lc, Lc1, and Lc2 had become slightly smaller due to the influence of the main surface polishing, but other parameters such as the radius of curvature of the side wall surface had almost maintained the shapes before the first polishing.

[0077] (Experimental Example 2-1) As in Experimental Example 1, end face grinding was carried out using various formed grindstones, and the frequency of chipping on the glass plate after end face grinding was investigated.

[0078] For the edge grinding, a glass plate material with the following specifications was used. Note that the specifications for the edge are all for the outer peripheral edge. Outer diameter 98mm, inner diameter 24mm, plate thickness 0.59mm The end face extends at a right angle to the main surface in cross section. -Aluminosilicate glass ring-shaped plate The machining allowance for the end face grinding was 1 mm on the diameter basis for both the outer and inner diameters. In addition, the target shape of the chamfered surface of the glass plate after edge grinding was a straight line in cross section, with an inclination angle of the connection area of ​​45°, a length in the plate thickness direction of 115 μm, Lt = 360 μm, Lc variable depending on Rt, and a radius of curvature of the boundary between the side wall surface and the chamfered surface of less than 150 μm. In the reference example, the side wall surface of the outer peripheral end surface of the glass sheet after the end surface grinding was shaped to extend linearly in the sheet thickness direction.

[0079] In each experimental example, 500 glass plates were processed using a form grinding wheel having a grinding surface with a shape corresponding to the target shape and the radius of curvature Rt shown in Table 2 below, and the outer peripheral edge faces of the glass plates after edge grinding were inspected in a darkroom using a condensing lamp to count the number of plates with chipping (chipping) and calculate the chipping occurrence frequency (occurrence rate). When the total number of plates with chipping was less than 2% of the total, it was rated as A, and when it was 2% or more, it was rated as B.

[0080] [Table 2]

[0081] A comparison between the working examples and the reference examples shows that the frequency of chipping is reduced by producing a glass plate having a side wall surface with a curvature radius Rt of 2000 μm or less. If chipping occurs on the edge surface of the glass plate, for example, it may be necessary to increase the machining allowance in the subsequent edge polishing, or the number of defective products may increase, which is undesirable from the viewpoint of production efficiency.

[0082] (Experimental Example 2-2) The above end face grinding was carried out under the same conditions as in Experimental Example 2-1 and Examples 101 to 104 in Table 2, except that the shape of the formed grindstone was changed so that the radius of curvature of the boundary between the side wall surface and the chamfered surface in the target shape of the chamfered surface of the glass plate after end face grinding was within the range of 150 to 400 μm (Examples 105 to 108).It was found that the frequency of chipping was reduced to 90% or less compared to the corresponding Examples.

[0083] The magnetic disk substrate, magnetic disk, annular substrate, and method for manufacturing a magnetic disk substrate of the present invention have been described in detail above. However, the present invention is not limited to the above-described embodiments and examples, and various improvements and modifications may be made without departing from the spirit and scope of the present invention. [Explanation of symbols]

[0084] 1. Magnetic disk glass substrate (magnetic disk substrate) 1b Boundary part 1c Chamfered surface 1ca Connection Area 1t side wall 1p main surface 3. Inner hole 5 Outer edge 7 Inner periphery end face 10 Double-sided grinding device 11 Double-sided polishing machine 12 Lower surface plate 14 Upper surface plate 18 Holding member (carrier) 18a Retaining hole 20 Abrasive material or polishing pad 30 Fully molded whetstone 31 Groove 31a Chamfered part 31b Side wall part G Glass plate (ring-shaped substrate)

Claims

1. A magnetic disk substrate having a pair of main surfaces and an outer peripheral end surface, the outer peripheral end surface has a pair of chamfered surfaces connected to the main surfaces, respectively, and a side wall surface extending between the pair of chamfered surfaces and curved outwardly so as to be convex, In a cross section of the magnetic disk substrate along a thickness direction, the side wall surface has a radius of curvature of 1100 μm or more; the magnetic disk substrate is a glass substrate, The thickness of the magnetic disk substrate is 0.46 mm or less, a length in a direction parallel to the main surface between a connection position of the chamfered surface with the main surface and a position of the side wall surface that is most outwardly convex is 100 μm or less; A magnetic disk substrate comprising:

2. The magnetic disk substrate as described in claim 1, wherein the magnetic disk substrate is made from a glass plate manufactured by a downdraw method.

3. A magnetic disk substrate having a pair of main surfaces and an outer peripheral end surface, the outer peripheral end surface has a pair of chamfered surfaces connected to the main surfaces, respectively, and a side wall surface extending between the pair of chamfered surfaces and curved outwardly so as to be convex, In a cross section of the magnetic disk substrate along a thickness direction, the side wall surface has a radius of curvature of 1100 μm or more; the magnetic disk substrate is an aluminum alloy substrate having a nickel alloy film on its surface, The thickness of the magnetic disk substrate is 0.46 mm or less, a length in a direction parallel to the main surface between a connection position of the chamfered surface with the main surface and a position of the side wall surface that is most outwardly convex is 100 μm or less; A magnetic disk substrate comprising:

4. 4. The magnetic disk substrate according to claim 1, wherein the side wall surface has a radius of curvature of 2000 [mu]m or less.

5. 5. The magnetic disk substrate according to claim 1, wherein a boundary portion between the chamfered surface and the side wall surface is rounded in a cross section along a thickness direction of the magnetic disk substrate.

6. The magnetic disk substrate according to claim 5, wherein the radius of curvature of the rounded boundary portion between the chamfered surface and the side wall surface is 150 to 1500 μm.

7. The chamfered surface is curved so as to be convex outward, 7. The magnetic disk substrate according to claim 1, wherein the chamfered surface has a radius of curvature smaller than a radius of curvature of the side wall surface in a cross section along a thickness direction of the magnetic disk substrate.

8. The chamfered surface is curved so as to be convex outward, 8. The magnetic disk substrate according to claim 1, wherein the radius of curvature of the chamfered surface is 100 to 1000 μm in a cross section along a plate thickness direction of the magnetic disk substrate.

9. A magnetic disk substrate described in any one of claims 1 to 8, wherein the length in a direction parallel to the main surface between the connection position of the chamfered surface with the main surface and the outermost convex position of the side wall surface is 80 μm or less.

10. A magnetic disk comprising at least a magnetic film on a surface of the magnetic disk substrate according to any one of claims 1 to 9.

11. A hard disk drive comprising the magnetic disk according to claim 10 and a magnetic head.

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