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 、 and hard disk drive Regarding. [Background technology]

[0002] With the recent rise of cloud computing, many hard disk drives (HDDs) are being used in cloud data centers to increase storage capacity. HDDs use magnetic disks, which are circular non-magnetic substrates with magnetic layers, as their storage media. To increase the storage capacity of HDDs, it is preferable to make the magnetic disks thinner and increase the number of magnetic disks installed.

[0003] 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 known edge shape of a magnetic disk substrate has a pair of chamfered surfaces connected to the main surfaces and a sidewall surface extending in the thickness direction between the chamfered surfaces. This edge shape can be obtained, for example, by edge grinding using a shaped grinding wheel having a grinding surface shaped to correspond to the target chamfered surface and sidewall surface (Patent Document 1). Also known is a glass substrate having an edge 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] Japanese Patent Application Laid-Open No. 2010-238302 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-40361 Summary of the Invention [Problem to be solved by the invention]

[0006] The annular plate (annular substrate) whose end faces have been machined to the target shape is then polished on its main surfaces using a double-side polishing machine. Polishing using a double-side polishing machine (double-side polishing) is performed by placing the annular substrate in a holding hole of a holding member (carrier) that holds the annular substrate and sandwiching the annular substrate between surface plates from above and below. The thickness of the carrier must be thinner than the thickness of the annular substrate. When performing such double-side polishing on an annular substrate with a curved end face, the annular substrate may slip out of the holding hole of the carrier and ride up on the carrier. In particular, if the thickness of the annular substrate to be polished is thin, the thickness of the carrier must be even thinner, making it more likely for the annular substrate to ride up on the carrier. If polishing continues while the annular substrate is riding up on the carrier, the main surfaces are more likely to be scratched. Furthermore, the strong force applied to the annular substrate sandwiched between the surface plate and the carrier may cause cracks or breaks in the annular substrate, resulting in damage. The above phenomenon may occur when both main surfaces of an annular substrate are ground using a holding member.

[0007] Therefore, an object of the present invention is to provide a circular substrate, a substrate for a magnetic disk, a magnetic disk, and a method for manufacturing a substrate for a magnetic disk, which makes it difficult for the circular substrate to come off the holding member that holds the circular substrate when double-sided grinding or double-sided polishing is performed on the circular 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 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 the thickness direction, the side wall surface has a radius of curvature of 1100 μm or more.

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

[0010] It is preferable that the length in the direction parallel to the main surface between the position where the chamfered surface is connected to the main surface and the position where the side wall surface is most convex outward is 100 μm or less.

[0011] The chamfered surface is curved so as to be convex outward, In a cross section of the magnetic disk substrate taken along the thickness direction, 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 of the magnetic disk substrate taken along the thickness direction, 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] In a cross section of the magnetic disk substrate along the thickness direction, it is preferable that the boundary portion between the chamfered surface and the side wall surface is rounded.

[0015] The plate thickness is preferably 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, In a cross section of the annular substrate along the thickness direction, the side wall surface has a radius of curvature of 1100 μm or more.

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

[0020] The magnetic disk substrate, magnetic disk, and annular substrate described above can prevent the annular substrate from coming off the holding member that holds the annular substrate when double-sided grinding or double-sided polishing is performed on the annular substrate. Furthermore, the magnetic disk substrate manufacturing method described above can provide such a magnetic disk substrate. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a diagram illustrating an external shape of a magnetic disk substrate according to an embodiment. [Figure 2] 1 is a diagram showing an example of a cross-sectional shape of an outer peripheral end face of a magnetic disk substrate. [Figure 3] 10A and 10B are diagrams showing a holding member holding an annular substrate in a holding hole. [Figure 4] 10A and 10B are diagrams showing the annular substrate coming off the holding hole and riding on the holding member. [Figure 5] FIG. 10 is a diagram illustrating end face grinding using a formed grindstone. [Figure 6] 10A and 10B are diagrams illustrating a method for determining the radius of curvature of the boundary portion between the chamfered surface and the side wall surface. [Figure 7] FIG. 10 is a diagram showing another example of the cross-sectional shape of the outer peripheral end face of a magnetic disk substrate. DETAILED DESCRIPTION OF THE INVENTION

[0022] 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 below. Note that, although the following description will be given using an example in which a glass substrate is used as the material for the magnetic disk substrate and the annular substrate, a metal substrate may also 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 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 with a nominal diameter of 2.5 inches or 3.5 inches. In the case of a glass substrate for magnetic disks with a nominal diameter of 2.5 inches, the outer diameter is 55 to 70 mm, for example, 65 mm, 67 mm, or 58 mm, the diameter of the inner hole is 20 mm, and the thickness is 0.3 to 1.3 mm. In the case of a glass substrate for magnetic disks with a nominal diameter of 3.5 inches, the outer diameter is 85 to 100 mm, for example, 95 mm, 97 mm, or 89 mm, the diameter of the inner hole is 25 mm, and the 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, since this allows for a thinner magnetic disk and therefore allows for a greater number of disks to be mounted in an HDD device. The thicknesses T are 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, in that order. The diameter and thickness values ​​listed above are nominal values, and may vary slightly due to variations in production. Furthermore, if a substrate with a nickel alloy plating film formed on the surface of an aluminum alloy substrate is used instead of a glass substrate, the above values ​​apply to the entire substrate, including the thickness of the nickel alloy plating film.

[0025] FIG. 2 shows an example of the cross-sectional shape of the outer peripheral end surface 5 of the glass substrate 1 along the 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 surfaces are not flat surfaces, such as curved surfaces, as will be described later, they are still called chamfered surfaces.

[0027] The side wall surface 1t is a surface that curves and extends between the chamfered surfaces 1c, 1c 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 (hereinafter referred to as a cross section along the thickness direction or simply a cross section) of the glass substrate 1 that passes through the center of the circular shape of the outer periphery of the glass substrate 1 and is taken along the thickness direction of the glass substrate 1. The glass substrate 1 having such a side wall surface 1t is less likely to disengage from the holding holes of the holding member (carrier) when a glass annular substrate (hereinafter also referred to as a glass plate) that serves as the raw material for the glass substrate 1 is double-sided ground or double-sided polished. Therefore, the glass plate is less likely to ride up on the carrier, and scratches, cracks, etc., on the main surfaces of the glass plate that would otherwise be caused by continuing double-sided grinding or double-sided polishing with the glass plate riding up on the carrier can be suppressed. The cross-sectional shape can be measured using a contour measuring instrument, such as a Contracer manufactured by Mitutoyo Corporation.

[0028] Double-sided grinding or polishing of a glass sheet is performed using a double-sided grinding machine or double-sided polishing machine equipped with a planetary gear mechanism. Double-sided grinding or polishing using a double-sided grinding machine or double-sided polishing is performed by placing a glass sheet G in a holding hole 18a of a carrier 18 and sandwiching the glass sheet G between surface plates 14 and 12 from above and below, as shown in FIG. 3 . The glass sheet G shown in FIG. 3 is sandwiched between surface plates 14 and 12 via a grinding member or polishing pad 20. In FIG. 3 , the chamfered surfaces and curved sidewall surfaces of the glass sheet G are omitted. The thickness of the carrier 18 is thinner than the thickness of the glass sheet G to ensure a sufficient removal allowance on both main surfaces of the glass sheet G. Furthermore, the thinner the thickness of the carrier 18, the better to ensure a high polishing rate. Therefore, if the radius of curvature of the sidewall surface of the glass sheet is too small, the glass sheet G' (see FIG. 4) will have a pointed shape at the center in the thickness direction. Therefore, during double-side grinding or double-side polishing, the edge of the carrier 18 that contacts the glass sheet G' will easily slide relative to the glass sheet G' in the thickness direction, making the glass sheet G more likely to come off the holding holes 18a. Therefore, as shown in FIG. 4, the glass sheet G' that has come off the holding holes 18a will easily ride up on the carrier 18. If grinding or polishing continues while the glass sheet G' is riding up on the carrier 18, the main surfaces of the glass sheet G' are likely to be scratched by contact with the carrier 18. The strong force applied to the glass sheet G' sandwiched between the surface plates 14, 12 and the carrier 18 may cause cracks or breaks in the glass sheet, resulting in damage. In particular, when double-side grinding or double-side polishing a thin glass sheet, an even thinner carrier 18 is used, making the glass sheet more likely to come off the holding holes 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 preventing the glass plate G from coming off the holding hole 18a when the glass plate G is thin. In this regard, the radius of curvature Rt of the side wall surface 1t is preferably 1200 μm or more.

[0029] As described below, the glass substrate 1 is made from a glass plate G that has been prepared by edge processing or edge polishing, and therefore the cross-sectional shapes of the sidewall surfaces and chamfered surfaces of the outer peripheral edge surface of the glass plate G are maintained in the glass substrate 1. Furthermore, when a magnetic film or the like is formed on the surface of the magnetic-disk glass substrate 1 to manufacture a magnetic disk, as described below, 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 surfaces and chamfered surfaces of the outer peripheral edge surface of the glass substrate 1 are maintained in the magnetic disk.

[0030] In this specification, "outside" means the side away from the center of the circular outer periphery of the glass substrate 1, and "outwardly convex" means 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 radius of curvature 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 Figure 2, for example, when a point on the side wall surface 1t that passes through the center of the glass substrate 1 in the plate thickness direction and intersects with a plane parallel to the main surface 1p is designated as T3, the radius of curvature Rt of the side wall surface 1t can be specified as the radius of an arc passing through three points: two intersections of a virtual circle of radius 100 μm drawn with the side wall surface 1t and the virtual circle centered at T3 and T3. Note that if the length of the side wall surface 1t is less than 200 μm and fitting of the arc of the virtual circle to the side wall surface 1t is poor, the radius of the virtual circle may be appropriately reduced.

[0032] The cross-sectional shape of the outer peripheral edge surface 5 of the glass substrate 1, including the sidewall surface 1t, can be obtained by producing a glass sheet G using, for example, a shaping grindstone 30 shown in FIG. 5. FIG. 5 shows the shaping grindstone 30 and a plate material (hereinafter referred to as a glass plate material) before edge grinding to be processed into a glass plate G. In FIG. 5, the area of ​​the glass plate material marked with a dashed line indicates the area to be removed by edge grinding. Also, in FIG. 5, the arrow pointing left indicates the relative movement direction of the shaping grindstone 30 with respect to the glass plate material when edge grinding is performed. The shaping grindstone 30 is, for example, formed in a cylindrical or columnar shape as a whole and has a groove 31 on its outer peripheral side surface. The groove 31 is configured so that the sidewall surface and chamfered surface of the glass plate G can be simultaneously formed by grinding. Specifically, the groove 31 has a grinding surface having a sidewall portion 31b and chamfered portions 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 edge surface of the glass sheet G or the glass substrate 1.

[0033] According to one embodiment, the radius of curvature Rt of the side wall surface 1t is preferably 2000 μm or less. A side wall surface 1t with a radius of curvature exceeding 2000 μm extends substantially linearly in the thickness direction, and therefore the corners between the side wall surface 1t and the chamfered surface 1c are prone to sharpening. When producing a glass sheet G using the shaping grindstone 30, the corners of the glass sheet are prone to receiving a load from the shaping grindstone 30, resulting in a concentration of load. This can lead to chipping. In particular, a glass sheet to be used as a thin glass substrate 1 is prone to bending under the load from the shaping grindstone 30 due to its thin thickness and reduced rigidity, and is therefore prone to load concentration at the corners. In this regard, the radius of curvature Rt of the side wall surface 1t is more preferably 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. Limiting the length Lc in this manner suppresses the overall outward sharpness of the cross-sectional shape of the outer peripheral edge surface 5, thereby contributing to improving the effect of suppressing the glass sheet G from being dislodged from the holding hole 18a. This is presumably because the smaller the degree of sharpness of the cross-sectional shape of the outer peripheral edge surface 5, the smaller the gap between the upper and lower surface plates. In this respect, the length Lc is more preferably 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. Furthermore, when the degree of sharpness is expressed as the value of Lc / T, it is preferable that Lc / T is 0.25 or less. If Lc / T exceeds 0.25, the sharpness may become too large, and the glass plate G may easily come off 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 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 edge surface 5 is likely to be reduced, contributing to an improved effect of suppressing the glass sheet G from being dislodged from the holding hole 18a. Furthermore, by providing the chamfered surface 1c in this form, the angle formed by the chamfered surface 1c and the side wall surface 1t is less likely to become small (i.e., the boundary portion 1b (described below) between the chamfered surface 1c and the side wall surface 1t is less likely to become sharp), which suppresses the concentration of load on the corner portion of the glass sheet material between the chamfered surface 1c and the side wall surface 1t when producing the glass sheet G using the shaping grindstone 30, thereby improving the effect of suppressing chipping. That is, by providing the chamfered surface 1c in the above-described form, it is possible to suppress the glass sheet G from coming off the holding hole 18a, and also to improve the effect of suppressing 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 that passes 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 that passes through three points: (1) the 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] Furthermore, 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 sidewall surface 1t is relatively smooth, thereby improving the effect of suppressing the glass sheet G from coming off the holding hole 18a and suppressing chipping when manufacturing the glass sheet G using the forming grindstone 30. The connection region 1ca is, for example, a region ranging from 5 to 20 μm in the thickness direction from the connection position Pc. The reason for excluding the immediate vicinity of the connection position Pc (the region less than 5 μm in the thickness direction from the main surface 1p) is that the connection position Pc appears to have no radius of curvature in the drawing, but in reality has a physically finite radius of curvature. This can be seen by enlarging the cross-sectional image. 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 from the connection position Pc in the plate thickness direction, is inclined with respect to the direction parallel to the main surface 1p.

[0038] According to one embodiment, the outer peripheral edge surface 5 of the glass substrate 1 preferably has a rounded 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. The boundary portion 1b is located between the chamfered surface 1c and the side wall surface 1t and connects the chamfered surface 1c and the side wall surface 1t. The presence of such a boundary portion 1b allows the chamfered surface 1c and the side wall surface 1t to be connected by a smooth curve, making it easier for the cross-sectional shape of the outer peripheral edge surface 5 to have a smooth curved shape overall. This cross-sectional shape of the outer peripheral edge surface 5 contributes to improving the effect of suppressing chipping when manufacturing the glass sheet G using the forming grindstone 30 while suppressing removal of the glass sheet G from the holding hole 18a.

[0039] From the above viewpoint, the boundary portion 1b preferably has a radius of curvature of 150 to 1500 μm, and more preferably 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 illustrating a method for determining the radius of curvature of the cross-sectional shape of boundary portion 1b. In FIG. 6, Rb is the radius of circle C2, which forms a curvature equivalent to that of boundary portion 1b in the cross-sectional shape, and is the radius of curvature of the shape of boundary portion 1b. First, P1 is defined as the intersection point between an imaginary line L1 extending a straight line portion of chamfered surface 1c or the above-mentioned arc and an imaginary arc L2 extending along the side wall surface 1t along the above-mentioned arc of side wall surface 1t. Next, an imaginary line L3 is defined that passes through intersection point P1 and extends perpendicular to imaginary line L1. Next, P2 is defined as the intersection point between boundary portion 1b and imaginary line L3. Next, in the cross-section of glass substrate 1, a circle C1 is defined that has a predetermined radius (e.g., 25 μm) and is centered at intersection point P2. Next, P3 and P4 are defined as the two intersection points between boundary portion 1b and the outer periphery of circle C1. Furthermore, a circle C2 is set that passes through each of the three intersection points P2, P3, and P4. The radius of curvature R of the cross-sectional shape of boundary portion 1b can be calculated by calculating the radius of circle C2. If the position of boundary portion 1b is difficult to clearly identify and the virtual line L1 and / or virtual arc L2 cannot be properly set, the value at which the radius of curvature Rb of circle C2 is smallest around the area believed to be boundary portion 1b can be used. The position of intersection point P2 is temporarily set on the end face, and circle C2 can be set while shifting it appropriately. Note that intersection points P3 and P4 must also be located on the end face.

[0040] 7 is a diagram showing another example of the cross-sectional shape of the outer peripheral edge surface 5 of the glass substrate 1. As shown in FIG. 7, the cross-sectional shape of the outer peripheral edge 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. Alternatively, the cross-sectional shape of the outer peripheral edge 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 thickness direction is not particularly limited, but is, for example, 0.02 to 0.15 mm. The length Lc1 (see FIG. 2) of the chamfered surface 1c in the 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] (Annular substrate) A glass plate G, which is an example of an annular substrate of one embodiment, has a pair of main surfaces, an outer peripheral edge surface, and an inner peripheral edge surface, and has an annular shape. The outer peripheral edge 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 a cross section of the glass plate G taken along the thickness direction of the glass plate, the side wall surface has a radius of curvature 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 position where the chamfered surface of the glass plate G is connected to 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, the chamfered surface of the glass plate G preferably 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 of the glass plate G taken along the thickness direction, the connection region of the chamfered surface located on the side of the connection position between the chamfered surface and 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 has the same structure 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 the cross section along the thickness direction of the glass plate 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 plate G is preferably less than 0.6 mm.

[0048] (Method of manufacturing a magnetic disk substrate) A method for manufacturing a magnetic disk substrate according to one embodiment includes polishing at least the main surface of a circular substrate. The circular substrate to be polished is the circular substrate of the above embodiment. Hereinafter, an example will be described in which the above-described glass plate is used as the circular substrate. The glass plate is not particularly limited, but may be made from a glass plate manufactured by, for example, a float process, a down-draw process, or a press process. For example, a plurality of circular glass plates having internal holes can be extracted from a wide sheet-like glass plate manufactured by the float process or the down-draw process. The method for extracting the circular glass plate from the wide sheet-like glass plate may be by forming a cut line and breaking it using a known scriber (cutter), or by irradiating the glass plate with a laser beam to form a circular defect and cut it out. The internal hole is a hole approximately concentric with the 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 450 to 850°C, for example.

[0050] A circular glass plate (glass substrate) undergoes edge processing to become a glass plate. Edge processing can be performed by edge grinding using a grinding wheel or edge melting, which melts the edge of the glass plate using laser light. This method avoids chipping caused by the grinding process and creates a single, smoothly curved, continuous curved surface shape across the entire edge. Creating such an edge also reduces chipping that occurs during subsequent processes such as grinding and polishing of the main surfaces and magnetic film deposition. After edge processing, edge polishing can be performed to polish the edge of the glass plate. Edge polishing can be performed using an abrasive brush while supplying free abrasive grains to the edge. When edge processing is performed by edge melting using laser light, 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 the forming grindstone or the conditions for edge polishing 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 a glass plate. Specifically, the glass plate is placed in a holding hole of a carrier of the double-sided grinding machine, and both main surfaces of the glass plate are ground while the outer peripheral edge of the glass plate is held. 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 the upper or lower surface plate, or both, are moved and the glass plate and each surface plate are moved relative to each other while supplying coolant, thereby grinding both main surfaces of the glass plate. For example, grinding can be performed by attaching a grinding member (diamond pad) made of a sheet-shaped fixed abrasive formed by fixing diamond with resin to the surface plate. Alternatively, instead of the combination of a 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 mentioned above, the thickness of the carrier must be smaller than the thickness of the glass plate to be held, and 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 placed in a holding hole of a carrier of a double-side polishing machine, and both main surfaces of the glass plate are polished while holding the outer peripheral edge 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, both main surfaces of a glass plate are polished using a double-side polishing machine with a configuration similar to that of a double-side grinding machine, while applying a polishing slurry containing free abrasive grains. The free abrasive grains used in the first polishing process include abrasive grains such as cerium oxide and zirconia. As with the double-side polishing machine, a glass plate is sandwiched between a pair of upper and lower platens. Polishing pads (e.g., resin polishers) are attached to the surfaces of the lower and upper platens. A suede-type polishing pad made of a resin such as polyurethane foam and with fine openings on the surface is preferred because it protects the glass plate from scratches and facilitates mirror polishing. Then, either the upper or lower platen, or both, are moved to move the glass plate relative to the platen, thereby polishing both main surfaces of the glass plate. The size of the 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 aims to mirror-polish the main surfaces. A double-sided polishing machine with the same configuration as the double-sided polishing machine used for the first polishing is also used for the second polishing. Specifically, the glass plate is placed in the holding hole of the carrier of the double-sided polishing machine, and both main surfaces of the glass plate are polished while the outer peripheral edge of the glass plate is held. The second polishing process differs from the first polishing process in the type and particle size of the free abrasive grains and the hardness of the resin polisher. The hardness of the resin polisher is preferably lower than that of 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 machine and the main surfaces of the glass plate to polish the main surfaces of the glass plate. The size of the abrasive grains used for the second polishing is preferably within the range of 5 to 50 nm in average particle size (d50). A suede-type polishing pad made of resin such as polyurethane foam and having fine openings on the surface is preferred because it is less likely to scratch the surface of the glass plate and makes it easier to achieve a mirror finish.

[0057] If chemical strengthening is performed, it is preferably performed before or after the second polishing. In the chemical strengthening treatment, a chemical strengthening liquid, such as a molten mixture of potassium nitrate and sodium nitrate, is used, and the glass sheet is immersed in the chemical strengthening liquid. This allows a compressive stress layer to be formed on the surface of the glass sheet G by ion exchange. Whether or not chemical strengthening treatment is required is determined and selected appropriately taking into account the glass composition and requirements.

[0058] In addition to the first polishing treatment and the second polishing treatment, another polishing treatment may be performed, or the first polishing treatment and the second polishing treatment may be performed in a single polishing treatment. 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 final polishing process or chemical strengthening process, whichever is later. In addition, another cleaning process may be added as appropriate between the grinding, polishing, chemical strengthening, etc. processes.

[0060] Here, a method for manufacturing a magnetic disk substrate when a metal substrate is used as the material for the annular substrate will be described. For example, an aluminum alloy having a nickel alloy film on its surface can also be used as the material for 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. Furthermore, titanium alloys or single-crystal silicon can be used instead of the aluminum alloy, and the nickel alloy film need not be used. Among these, an aluminum alloy substrate having a nickel alloy film on its surface is preferably used, as it is relatively lightweight, has high strength, and is easy to process.

[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 (aluminum alloy substrate) is cut from an aluminum alloy plate, heated at a predetermined temperature and time, and annealed. After that, the main surfaces are cut and the end faces are shaped. The end faces are ground or cut into a predetermined shape using a tool such as a forming tool or a single tool. Here, when processing the end faces of an aluminum alloy substrate, minute recesses may occur, similar to chipping in a glass plate. This is thought to be due to surface scraping or the detachment of crystallized deposits caused by the sliding of the substrate surface against the tool. These minute recesses remain on the surface even after the formation of a nickel alloy film or magnetic film, and are undesirable because they generate unstable airflows when a magnetic disk is rotated at high speed, which can worsen fluttering of the magnetic disk. The number of these minute recesses increases or decreases depending on the target shape of the end face. Annealing may be performed after processing the end faces or surface. A nickel alloy plating film, for example, with a thickness of 3 to 20 μm, may then be formed on the surface. 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 remains approximately the same even after the plating film is formed. The surface of the aluminum alloy substrate (annular-shaped substrate) with a nickel alloy plating film is then polished. From the viewpoint of achieving both improved surface quality and improved productivity, the polishing process preferably employs a two-stage or more polishing process, similar to the polishing of the glass plate described above. The specific polishing method can be similar to that used for the polishing of the glass plate described above, except that a polishing solution containing alumina abrasive grains is preferably used in the first polishing (rough polishing).

[0062] In this way, after manufacturing an annular substrate having an outer peripheral end face with the above-mentioned cross-sectional shape, at least the main surface of the annular substrate is polished, thereby manufacturing 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 a 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) To investigate the effectiveness of the present invention, edge grinding was performed using various grinding wheels with different grinding surface shapes. Annular glass plates (annular substrates) with a sidewall surface of the radius of curvature Rt shown in Table 1 below on the outer peripheral edge were prepared. After polishing the edge surface and grinding the main surface of each glass plate, the first polishing described above was performed using cerium oxide free abrasive grains and a suede-type polishing pad, and the frequency with which the glass plate came off the carrier's holding hole was investigated.

[0065] For the first polishing, a glass plate having the following specifications was used. Note that the specifications regarding the edge surface all relate to the outer peripheral edge surface. ·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 thickness direction. The curvature radius of the boundary between the side wall and the chamfer is less than 150 μm -Aluminosilicate glass ring-shaped glass plate The removal amount (polishing amount) of the main surfaces in the first polishing was 25 μm (12.5 μm on each side) based on the plate thickness, and the thickness of the carrier was 0.3 mm.

[0066] The first polishing was performed by placing a total of 25 glass plates G in five carriers, each with five holding holes (25 plates per batch). This first polishing was performed 20 times, and after each first polishing, the number of glass plates that had fallen out of the holding holes and landed on the carrier was counted. 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, and the test was considered to be acceptable. 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 decreases. 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 the holding hole is further reduced.

[0069] (Experimental Example 1-2) The first polishing was carried out 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 carried out 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 with a 10 μm NiP alloy plating film formed on the surface, 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 a 0.48 mm thick aluminum alloy substrate with a 10 μm NiP alloy plating film formed on the surface, 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) The specifications of the glass plate used in the first polishing were changed so that the radius of curvature of the boundary between the side wall surface and the chamfered surface was within the range of 150 to 400 μm. Except for this, the first polishing was carried out 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) The specifications of the glass plate used in the first polishing were changed such that the plate thickness was 0.43 mm and the radius of curvature of the boundary between the side wall surface and the chamfered surface was changed to within the range of 150 to 400 μm. Except for this, the first polishing was carried out 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 given an outer peripheral edge that appeared to be a single, smoothly curved, connected surface by edge melting with a laser beam and then grinding both main surfaces, and the frequency of detachment from the retaining hole was evaluated as A. The specifications of the outer peripheral edge were 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 connecting area with the main surface, and Lc of 100 μm The curvature radius of the boundary between the side wall and the chamfer is 100 to 500 μm

[0076] (Magnetic disk substrate and magnetic disk manufacturing) Of the annular substrates obtained in the above "Examples" after the first polishing, those that had fallen out of the retaining holes or had problems such as chipping or minute recesses were removed. The remaining annular substrates were then cleaned and subjected to the second polishing described above, with a removal allowance of 5 μm (2.5 μm per side) based on the substrate thickness. The total removal allowance from the first and second polishing was 30 μm based on the substrate thickness. For example, if the substrate thickness before the first polishing was 0.53 mm, the substrate thickness after the second polishing would be 0.50 mm. The second polishing used a polishing solution containing colloidal silica and a suede pad. After cleaning, magnetic disk glass substrates with an outer diameter of 97 mm, an inner diameter of 25 mm, and a thickness of 0.40 to 0.50 mm or aluminum alloy substrates with a nickel alloy plating film formed on their surfaces were obtained. Subsequently, an undercoat film, a magnetic film, a protective film, etc. were sequentially formed on the surface of each magnetic disk substrate to obtain magnetic disks. 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 chamfered surfaces, such as Lc, Lc1, and Lc2, had become slightly smaller due to the effects of polishing the main surface, but other parameters, such as the radius of curvature of the side wall surface, had largely maintained the shapes before the first polishing.

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

[0078] For the edge grinding, glass plates with the following specifications were used. Note that the specifications for the edge surfaces all relate to the outer peripheral edge surfaces. Outer diameter 98mm, inner diameter 24mm, plate thickness 0.59mm The end face extends approximately perpendicular to the main surface in cross section. Aluminosilicate glass circular plate The grinding allowance for the end faces was set to 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 being variable depending on Rt, and the radius of curvature of the boundary between the side wall surface and the chamfered surface being less than 150 μm. In the reference example, the side wall surface of the outer peripheral edge of the glass plate after edge grinding was shaped to extend linearly in the plate thickness direction.

[0079] In each experimental example, 500 glass plates were processed using a form grinding wheel with a grinding surface of 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 condenser lamp. The number of plates that had chipping (chipping) was counted and the frequency (occurrence rate) of chipping was calculated. If the total number of plates that had chipping was less than 2% of the total, it was evaluated as A, and if it was 2% or more, it was evaluated 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 sidewall 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-mentioned 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 forming grindstone was changed so that the radius of curvature of the boundary between the side wall surface and the chamfered surface would be within the range of 150 to 400 μm in the target shape of the chamfered surface of the glass plate after end face grinding (Examples 105 to 108).It was found that the frequency of chipping was reduced to 90% or less in all of 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, but the present invention is not limited to the above-mentioned embodiments and examples, and various improvements and modifications may be made within the 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 peripheral 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 Formed 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 protrudes most outward is 100 μm or less; A magnetic disk substrate characterized by:

2. A magnetic disk substrate as described in claim 1, wherein the magnetic disk substrate is made from a glass plate material 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 protrudes most outward is 100 μm or less; A magnetic disk substrate characterized by:

4. 4. The magnetic disk substrate according to claim 1, wherein the radius of curvature of the sidewall surface is 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 the 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 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 that of the side wall surface in a cross section along the 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 the 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 the magnetic disk substrate according to any one of claims 1 to 9, having at least a magnetic film on the surface thereof.

11. A hard disk drive comprising the magnetic disk described in claim 10 and a magnetic head.

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