Substrate for magnetic disk and magnetic disk using the same

Abstract

Provided are a magnetic disk substrate having a pair of front and back main surfaces, wherein each of the front and back main surfaces has a fixing site which is brought into contact with a fixing jig when the magnetic disk substrate made into a magnetic disk is incorporated into a hard disk drive, and the fixing sites on the front and back main surfaces have a root mean square deviation Rq of surface roughness of 0.01-0.44 μm, and a magnetic disk using the magnetic disk substrate.

Description

Technical Field

[0001] The present invention relates to a substrate for a magnetic disk having high strength and good impact resistance characteristics, and a magnetic disk using the same.

Background Art

[0002] In recent years, memory devices (including hard disk devices such as hard disk drives) have been required to have increased capacity and higher density in response to the expanding needs for multimediaization and the like, which handle multiple types of information (text, video, music, etc.) together. The increase in the capacity of a hard disk device can be achieved by increasing the number of magnetic disks mounted in the hard disk device. For example, there is a hard disk device in which a plurality of magnetic disks are stacked and mounted. In such a hard disk device, if the number of magnetic disks simply increases, it is necessary to increase the size of the hard disk device. However, the size of the housing for the hard disk device may be standardized, and it is difficult to significantly change the size. For this reason, there is also a demand for thinning the substrate for a magnetic disk, which occupies most of the thickness of the magnetic disk. A magnetic disk mounted (equipped) in a hard disk device is generally created by providing a magnetic layer or the like on the main surface of a disk-shaped substrate for a magnetic disk. Various substrates for magnetic disks have been proposed. For example, Patent Document 1 discloses a substrate for a magnetic disk that includes a substrate body having two main surfaces and a film of a metal material having a specific loss coefficient, the thickness including the film is 0.7 mm or less, the film covers the entire surface of the substrate, and at the end face of the substrate for a magnetic disk, the thickness of the film is made thicker than the film thickness of the film on the main surface.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a hard disk drive, generally, information recorded on a magnetic disk is read by a magnetic head. In a hard disk drive, this magnetic head retracts from the storage area of the magnetic disk in order to prevent contact between the magnetic head and the storage area of the magnetic disk when the hard disk drive stops. As one of the retraction methods, there is a method of retracting the magnetic head onto a ramp (ramp load method). In this method, the ramp is arranged so as to project onto the main surface of the magnetic disk. As described above, due to the thinning of the magnetic disk, thinning of the substrate for the magnetic disk is desired. However, when the substrate for the magnetic disk is thinned and incorporated into a hard disk drive as a magnetic disk, the magnetic disk may vibrate greatly due to an impact from outside the hard disk drive. If the amplitude of this vibration is large, the magnetic disk, more specifically, the substrate for the magnetic disk itself or a magnetic layer formed on the substrate for the magnetic disk, etc., may collide with surrounding members (external members) such as a ramp arranged so as to project onto the main surface of the magnetic disk, or with an adjacent magnetic disk. When such a collision occurs, it is likely to lead to problems such as the member in contact with the magnetic disk being worn away to generate particles, and defects such as scratches on the surface of the magnetic disk. Therefore, there is a demand for a substrate for a magnetic disk that can form a magnetic disk with suppressed vibration and excellent impact resistance. On the other hand, in order to increase the number of magnetic disks loaded in a hard disk drive, it has been considered to further narrow the gap between the main surface of the magnetic disk and the ramp. The substrate for a magnetic disk described in Patent Document 1 was developed assuming that the gap between the main surface of the magnetic disk and the ramp is 0.2 mm (200 μm). Patent Document 1 mentions 2 msec, 120G (1177 m / s 2When an impact is applied to , it is described that the number of times the displacement amount in the plate thickness direction at the outer peripheral end of the substrate for magnetic disk becomes 0.2 mm or more can be suppressed to 4 times or less. However, the substrate for magnetic disk described in Patent Document 1 cannot necessarily be said to be applicable to a form in which the gap between the main surface of the magnetic disk and the head is further narrowed from 200 μm (for example, a form in which the gap is 165 μm) while thinning the substrate for magnetic disk to, for example, 0.5 mm or less in plate thickness in order to cope with the increase in the storage capacity of the hard disk drive. An object of the present invention is to provide a substrate for magnetic disk that can cope with an increase in the storage capacity (increase in the number of loaded disks) of a hard disk drive and can improve the shock resistance characteristics of the hard disk drive, and a magnetic disk using the same.

Means for Solving the Problems

[0005] As a result of earnestly studying the shock resistance characteristics of a thinned magnetic disk by focusing on the substrate for magnetic disk that occupies most of the thickness of the magnetic disk, the inventors of the present invention have found that controlling the surface roughness of the portion (fixed portion) that contacts the fixing jig when assembled into the hard disk drive is effective in suppressing the displacement amount due to an external shock in a substrate for magnetic disk having a pair of front and back main surfaces. Based on this finding, further studies were conducted, and as a result, among the physical properties characterizing the surface roughness of the fixed portion of the substrate for magnetic disk having the pair of main surfaces, by setting the root mean square deviation Rq of the surface roughness to 0.01 to 0.44 μm respectively, it was found that even in a substrate for magnetic disk thinned to 0.5 mm or less in plate thickness, shock resistance characteristics equivalent to or better than those when using a substrate for magnetic disk having a plate thickness exceeding 0.5 mm can be realized. The present invention has been completed through further studies based on these findings.

[0006] That is, the problems of the present invention have been achieved by the following means. 〔1〕 A substrate for magnetic disk having a pair of front and back main surfaces, On each of the front and back main surfaces, there is a fixing portion that comes into contact with a fixing jig when the substrate for magnetic disk is assembled into a hard disk drive with the substrate for magnetic disk used as a magnetic disk. A substrate for magnetic disk, wherein the root mean square roughness Rq of the surface of each fixing portion on the front and back main surfaces is 0.01 to 0.44 μm. 〔2〕 The substrate for magnetic disk according to 〔1〕, wherein the absolute value of the difference ΔRq in Rq of the fixing portions on the front and back main surfaces is 0.01 to 0.11 μm. 〔3〕 When the substrate for magnetic disk is vibrated by the following impact test, the maximum value H of the displacement amount in the plate thickness direction at the outer peripheral end of the substrate for magnetic disk is 165 μm or less, and the attenuation rate E of the displacement amount is 17.7 μm / msec or more. The substrate for magnetic disk according to 〔1〕 or 〔2〕. <Impact Test> With the substrate for magnetic disk held vertically from above and below by a fixing jig at the fixing portion and fixed horizontally to a bearing, an impact of 2.8 msec and 490 m / s 2 is applied from below in the normal direction of the main surface of the substrate for magnetic disk. 〔4〕 A disk-shaped substrate for magnetic disk having an outer diameter of 97 mm or more, an inner diameter of 26 mm or less, and a plate thickness of 0.5 mm or less, according to any one of 〔1〕 to 〔3〕. 〔5〕 A magnetic disk using the substrate for magnetic disk according to any one of 〔1〕 to 〔4〕.

[0007] In this specification, the numerical range represented by using "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value.

Advantages of the Invention

[0008] By using the above-described substrate for magnetic disk in the production of a magnetic disk, when incorporated into a hard disk drive, contact between the magnetic disk and external members such as a lamp caused by an impact received from the outside is reduced, and generation of particles, scratches, and defects on the surface of the magnetic disk is less likely to occur. Therefore, even if the plate thickness of the substrate for magnetic disk is made thinner, the impact resistance characteristics can be improved in a hard disk drive in which the distance from the external member is reduced. The magnetic disk of the present invention can improve the impact resistance when incorporated into a hard disk drive.

Brief Description of the Drawings

[0009]

Figure 1

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Figure 3

Figure 4

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Figure 9

Embodiments for Carrying Out the Invention

[0010] Hereinafter, an embodiment of a substrate for a magnetic disk and a magnetic disk according to the present invention will be described with reference to FIGS. 1 to 3. The substrate 1 for a magnetic disk is a substrate used for manufacturing the magnetic disk 2, and its shape is generally disk-shaped or annular. FIG. 1 is a plan view of an example of a substrate for a magnetic disk viewed in a plan view from the normal direction of one main surface. The substrate 1 for a magnetic disk shown in FIG. 1 has a disk shape and has a circular hole 12 at the center. The substrate 1 for a magnetic disk can also be disk-shaped without the circular hole 12, but it is preferably disk-shaped with the circular hole 12 at the center. The substrate 1 for a magnetic disk has a pair of front and back main surfaces 14.

[0011] The substrate 1 for a magnetic disk has two fixing portions 11, that is, on the front and back main surfaces 14 respectively. The fixing portion 11 refers to a portion that contacts the fixing jig 3 when the substrate 1 for a magnetic disk is incorporated into a hard disk device with the substrate 1 for a magnetic disk as the magnetic disk 2. The fixed portion 11 is an (concentric) annular portion defined by an inner edge disposed at the inner peripheral end 15 of the magnetic disk substrate 1 and an outer edge (virtual line 13) disposed in a (concentric) circular shape at a distance of 32 mm or less, preferably 30 mm or less, from the center of the magnetic disk substrate 1. When used for a 2.5-inch hard disk drive, the fixed portion 11 is an annular portion defined by an inner edge disposed at the inner peripheral end 15 of the magnetic disk substrate 1 and an outer edge (virtual line 13) disposed in a circular shape at a distance of 29 mm or less, preferably 27 mm or less, from the center of the magnetic disk substrate 1. In FIG. 1, the inner diameter of the fixed portion 11 coincides with the inner diameter of the magnetic disk substrate 1, but the inner diameter of the fixed portion 11 can also be set to a diameter slightly larger than the inner diameter of the magnetic disk substrate 1. The outer diameter of the fixed portion 11 can be set according to the outer diameter of the fixing jig 3 used when fixing the magnetic disk 2, and can be the same as, slightly larger than, or slightly smaller than the outer diameter of the fixing jig 3. When the magnetic disk substrate 1 is used as the magnetic disk 2, a magnetic layer is formed on the outside in the direction from the center to the outer periphery (radial direction) of the fixed portion 11. On the other hand, no magnetic layer is formed on the fixed portion 11 of the magnetic disk substrate 1. In this sense, when the magnetic disk substrate 1 is used as the magnetic disk 2, the fixed portion 11 of the magnetic disk substrate 1 and the fixed portion 21 of the magnetic disk 2 can be regarded as the same.

[0012] In the present invention, as illustrated in FIG. 3, the fixing jig 3 refers to a member that is disposed in contact with the fixed portion 11 (fixed portion 21 of the magnetic disk 2) of the magnetic disk substrate 1 when the magnetic disk substrate 1 used as the magnetic disk 2 is incorporated into the hard disk drive. The fixing jig 3 usually has a disk-like or annular shape in plan view. The fixing jig 3 may be any member that is usually used when incorporating the magnetic disk 2 into the hard disk drive, such as a disk clamper 31, a large-diameter portion 33a provided on the bearing (also referred to as the large-diameter portion of the bearing), a spacer 34, etc. The fixing jig 3 can be made of an aluminum alloy. An example of the arrangement of the fixing jig 3 with respect to the fixing portion 11 on one main surface is shown in FIG. 2. In FIG. 2, the fixing portion 11 and the fixing jig 3 (34) have the same shape in plan view. Although they are separated in FIG. 2, the fixing jig 3 (34) is arranged in contact with the fixing portion 11. The form of the arrangement of the fixing portion 11 and the fixing jig 3 when incorporated into the hard disk drive is not particularly limited as long as the position where the fixing jig 3 is arranged is inside the fixing portion 11 in plan view. The fixing jig 3 may be in contact with the entire fixing portion 11 in plan view or may be in contact with a part of the fixing portion 11 in plan view. The magnetic disk substrate 1 is incorporated into a hard disk drive or the like in a state where it is fixed at the fixing portion 21 after being made into the magnetic disk 2. More specifically, at the fixing portion 21, it is sandwiched from above and below in the thickness direction by the fixing jig 3 and fixed to the bearing of the hard disk drive. FIG. 3 shows an exploded perspective view schematically showing an example of the form of incorporating the magnetic disk 2 into the hard disk drive. Specifically, FIG. 3 shows an example of the form of arranging the magnetic disks 2 when incorporating three magnetic disks 2. In FIG. 3, the three magnetic disks 2 are arranged in the order shown in FIG. 3 together with the fixing jig 3 (disk clamper 31, large diameter portion 33a of the bearing, spacer 34). By screwing six mounting screws 4 into the bearing 33 from the side of the disk clamper 31, the three magnetic disks 2 are supported by the large diameter portion 33a of the bearing 33 and fixed to the bearing 33 via two spacers 34. The core 33b of the bearing is inserted into the circular hole of the magnetic disk 2 and the circular hole of the spacer 34. The outer diameter of the fixing portion 21 on the magnetic disk 2, the diameter of the large diameter portion 33a of the bearing, the outer diameter of the spacer 34, and the diameter of the disk clamper 31 are the same. The inner diameter of the magnetic disk 2 and the inner diameter of the spacer 34 are the same. The diameter of the core 33b of the bearing is such that there is no gap when the magnetic disk 2 and the spacer 34 are inserted. After the mounting screws 4 are screwed in, the three magnetic disks 2 are incorporated in a form in which they are in contact with the large diameter portion 33a of the bearing, two spacers 34, the disk clamper 31, and the fixing portion 21. From the viewpoint of clearly showing the form of incorporation, the magnetic layer of the magnetic disk 2, as well as external members such as magnetic heads and lamps, and the housing are not shown in FIG. 3. The incorporated form is not limited to the above form and can be a normal incorporated form including the above. For example, a spacer 34 may be further disposed between the large-diameter portion 33a of the bearing and the magnetic disk 2.

[0013] For the substrate 1 for magnetic disk of the present invention, the root mean square deviation Rq of the surface roughness of the two main surfaces 14, 14 at the two fixing portions 11, 11 is 0.01 to 0.44 μm respectively. When the root mean square deviation Rq of the surface roughness is within the above range, when the substrate 1 for magnetic disk is used as the magnetic disk 2 and incorporated into the hard disk device, the vibration of the magnetic disk 2 is suppressed and the impact resistance characteristics can be enhanced. By controlling and adjusting the Rq of the surface roughness of the fixing portion 11 within the above range, the fulcrum distribution of the deformation (also referred to as the difference in displacement amount) of the substrate 1 for magnetic disk during impact becomes more uniform, and it is considered that the deformation of the outermost peripheral portion of the substrate 1 for magnetic disk due to impact is reduced. The root mean square deviation Rq of the surface roughness of the fixing portion 11 is preferably 0.10 to 0.44 μm, and more preferably 0.15 to 0.40 μm. The root mean square deviation Rq of the surface roughness of the fixing portion 11 can also be 0.17 to 0.40 μm. The root mean square deviation Rq of the surface roughness of the above fixing portion 11 can be measured by the method described in the examples according to JIS B 0601-2001. Even when the substrate 1 for magnetic disk is used as the magnetic disk 2, the root mean square roughness Rq of the surface roughness at the fixing portion 21 of the magnetic disk 2 can be measured to measure the root mean square roughness Rq of the surface roughness at the fixing portion 11 of the substrate 1 for magnetic disk. This is because the fixing portion 21 of the magnetic disk 2 and the fixing portion 11 of the substrate 1 for magnetic disk are usually the same. The method for adjusting the root mean square roughness Rq of the surface is not particularly limited. For example, in the polishing process, polishing is performed while supplying a polishing liquid at a rate of 10 ml / min or more per disk blank described later, diluting the polishing liquid with water having an electrical resistivity of 1 MΩ·cm or more, continuously stirring during the supply of the polishing liquid, and when supplying the polishing liquid to the polishing pad via a pipe, cleaning the pipe to such an extent that when water having an electrical resistivity of 10 MΩ·cm or more is supplied from the inlet of the pipe, the electrical resistivity of the water at the outlet of the pipe becomes 1 MΩ·cm or more. By these means, it can be set within the above range. Whichever preparation method is adopted, Rq tends to decrease. From the viewpoint of reducing the above electrical resistivity, pure water is preferably used as the water for diluting the polishing liquid, and deionized water and distilled water are more preferably used.

[0014] The absolute value of the difference ΔRq in Rq between the two fixing portions 11 of the substrate 1 for magnetic disks (that is, the absolute value of Rq of the fixing portion 11 on the surface side - Rq of the fixing portion 11 on the back surface side) is preferably 0.01 to 0.11 μm. By setting the absolute value of ΔRq within the above range, the damping rate of vibration of the substrate 1 for magnetic disks can be increased. It is considered that by making the surface roughness of the front and back of the fixing portion 11 uniform, the difference in the displacement amount above and below the substrate becomes smaller and the vibration decays faster. From the viewpoint of further increasing the damping rate, the absolute value of ΔRq is preferably 0.01 to 0.08 μm, more preferably 0.01 to 0.05 μm, and even more preferably 0.01 to 0.05 μm. The method for adjusting the absolute value of ΔRq is not particularly limited. For example, in the polishing process, the polishing liquid can be supplied from the upper platen side, the disk blank can be inverted up and down and polished for the same period of time, and the disk blank can be inverted up and down in the plate thickness direction one or more times to set it within the above range.

[0015] The thickness of the substrate 1 for magnetic disk can be the same as that of a normal substrate for magnetic disk, and can also be further thinned. The thickness of the substrate 1 for magnetic disk is preferably 0.50 mm or less. The lower limit of the thickness of the substrate 1 for magnetic disk is not particularly limited, but 0.30 mm or more is practical. The outer diameter of the substrate 1 for magnetic disk can be the same as that of a normal substrate for magnetic disk. When the substrate 1 for magnetic disk is used for a 2.5-inch hard disk drive, the outer diameter of the substrate 1 for magnetic disk is preferably 65 mm or more. The upper limit is limited by the inner dimension of the housing of the hard disk drive, and 70 mm or less is practical. When the substrate 1 for magnetic disk is used for a 3.5-inch hard disk drive, the outer diameter of the substrate 1 for magnetic disk of the present invention is preferably 95 mm or more, more preferably 97 mm or more. The upper limit is limited by the inner dimension of the case, and 101 mm or less is practical. The inner diameter of the substrate 1 for magnetic disk can be the same as that of a normal substrate for magnetic disk. When used for a 2.5-inch hard disk drive, the inner diameter of the substrate 1 for magnetic disk of the present invention is preferably 22 mm or less. The lower limit is limited by the diameter of the rotating shaft, and 18 mm or more is practical. When used for a 3.5-inch hard disk, the inner diameter of the substrate 1 for magnetic disk of the present invention is preferably 26 mm or less. It can also be 25 mm or less. The lower limit is limited by the diameter of the rotating shaft, and 24 mm or more is practical. A preferred form of the substrate 1 for magnetic disk is a form with an outer diameter of 97 mm or more, an inner diameter of 26 mm or less, and a thickness of 0.5 mm or less. The substrate 1 for magnetic disk of the present invention has the following form, and when used in a hard disk drive with the following specifications, particularly preferable effects are achieved. Size of the substrate 1 for magnetic disk: outer diameter 97 mm or less, inner diameter 25 mm or less, thickness 0.5 mm or less Material: Al-Mg alloy or aluminosilicate glass Mode of use: magnetic recording disk Specifications of the hard disk drive: 3.5-inch hard disk or 2.5-inch hard disk (both are ramp load type) Gap between the magnetic disk and the lamp: for example, less than 171 μm, more preferably 165 μm or less

[0016] Since the substrate 1 for magnetic disk satisfies the above root mean square deviation Rq, when an impact is applied by the following impact test, the maximum value H of the displacement amount in the plate thickness direction of the outer peripheral end portion of the substrate 1 for magnetic disk and its attenuation rate E can be suppressed within the following ranges respectively. Thereby, when the substrate 1 is incorporated into the hard disk device as the magnetic disk 2, even if vibration occurs, generation of particles, scratches on the magnetic disk surface, and generation of defects can be effectively suppressed. <Impact test> With one substrate 1 for magnetic disk held horizontally by the fixing jig 3 (disk clamper 31 and spacer 34) from above and below at the fixing portion 11 and fixed to the bearing 33, an impact of 2.8 msec, 490 m / s 2 is applied from below in the normal direction (plate thickness direction) of the main surface 14 of the substrate 1 for magnetic disk (from the bearing 33 side toward the disk clamper 31 side). In the impact test, the vertical direction refers to the plate thickness direction (clamping direction) of the substrate for magnetic disk, and "upper (side)" refers to the disk clamper 31 side, and "lower (side)" refers to the bearing 33 side. The maximum value H of the displacement amount is the absolute value (μm) of the displacement that first drops significantly downward when the substrate 1 for magnetic disk is vibrated by the impact in this impact test and the displacement amount in the plate thickness direction of the outer peripheral end portion due to this impact is plotted against time to obtain a displacement - time graph as shown in FIG. 8. Further, the attenuation rate E of the displacement amount refers to the slope (μm / msec) when the peaks of the displacements that drop significantly for the first and second times are connected in this graph. Specifically, the above impact test can be performed by the method described in the examples. This impact test is performed using the substrate 1 for magnetic disk on which the magnetic layer is not formed. Since the magnetic layer is generally a thin film, its rigidity does not substantially affect the maximum value H of the displacement amount and the attenuation rate E. When the substrate 1 for magnetic disk is vibrated by the above impact test, it is preferable that the maximum value H of the displacement amount in the plate thickness direction at the outer peripheral end of the substrate 1 for magnetic disk is 165 μm or less. More preferably, the maximum displacement amount H is 164 μm or less, still more preferably 150 μm or less, and even more preferably 130 μm or less. The lower limit of the maximum displacement amount H is not particularly limited, but it is practical that it is 100 μm or more. When the substrate 1 for magnetic disk is vibrated by the above impact test, it is preferable that the attenuation rate E of the displacement amount in the plate thickness direction at the outer peripheral end of the substrate 1 for magnetic disk is 17.7 μm / msec or more. The upper limit of the attenuation rate E is not particularly limited, but it is practical that it is 30 μm / msec or less. A more preferable form is that the substrate 1 for magnetic disk has the maximum value H of the displacement amount of 165 μm or less and the attenuation rate E of the displacement amount of 17.7 μm / msec or more. Even when the substrate 1 for magnetic disk is the magnetic disk 2, the displacement amount H and the attenuation rate E measured by the same method except using the magnetic disk 2 can be regarded as the displacement amount H and the attenuation rate E of the substrate 1 for magnetic disk. This is because the magnetic layer does not affect these measured values as described above.

[0017] The conditions of the above impact test are the conditions that reproduce the impact (such as the impact when inserting the hard disk drive terminal into the terminal of the blade and pushing the blade to the deepest part while sliding the blade along the side guide of the blade server) when fixing the hard disk drive to the HDD mount track, computer, etc. during actual use. In order to reproduce this impact, in the present invention, the action time is set to 2.8 msec and the maximum acceleration (applied acceleration) is set to 490 m / s 2 In Patent Document 1, an impact test is also performed. However, in the test of applying an impact with an action time of 2 msec and a maximum acceleration of 120 G (1177 m / s 2 ), the action time is too short to reproduce the impact when fixing the target hard disk drive to the HDD mount track, computer, etc. Fig. 9 shows an explanatory diagram of an impact pulse used in an impact test. The vertical axis represents acceleration and the horizontal axis represents time. The impact pulse is composed of an applied acceleration G (corresponding to the maximum acceleration) and an action time.

[0018] The magnetic disk 2 of the present invention is a magnetic disk using the magnetic disk substrate 1 described above. The magnetic disk substrate 1 of the present invention can be used as the magnetic disk 2 by forming a magnetic layer on at least one of the main surfaces 14. It is preferable to form magnetic layers on both of the main surfaces 14. The structure of the magnetic disk 2 can be the same as that of a normal magnetic disk except having the above-mentioned fixing portion 21. The description of the fixing portion 11 can be applied to the fixing portion 21, and it can have the same root mean square deviation Rq of surface roughness, inner diameter, and outer diameter as those of the fixing portion 11, and the preferable embodiments are also the same as those of the fixing portion 11. The magnetic layer can have the same structure as that of a normal magnetic disk. The thickness of the magnetic layer is not particularly limited, but is preferably 1 to 100 nm.

[0019] Since the substrate 1 has the above characteristics, the magnetic disk 2 obtained by using the magnetic disk substrate 1 of the present invention can be used not only for a normal 3.5-inch hard disk but also for a nominal 2.5-inch or 3.5-inch hard disk that requires more severe shock resistance. As the thickness of a main 2.5-inch hard disk housing, 7 mm, 9.5 mm, 12.5 mm are known, and as the thickness of a main 3.5-inch hard disk housing, 20 mm, 26 mm, etc. are known. When the plate thickness of the magnetic disk 2 is 0.5 mm, the number of magnetic disks 2 that can be mounted in a housing with a thickness of 26 mm for a normal 3.5-inch hard disk is 9 or less. However, by making the plate thickness of the magnetic disk 2 less than 0.5 mm, it becomes possible to mount 10 or more magnetic disks on the hard disk without making the thickness of the housing much larger than 26 mm. In a normal hard disk drive, the gap between the main surface of the magnetic disk and an external member such as a lamp on the same side as the main surface may be set to about 200 μm. By using the magnetic disk substrate 1 of the present invention, the gap between the magnetic disk 2 and the external member can be further reduced. In this way, it becomes possible to mount more magnetic disks in the hard disk device. According to the present invention, it is possible to make the above gap a narrower gap such as 170 μm, and further 165 μm.

[0020] As the material of the magnetic disk substrate 1, generally, materials excellent in mechanical properties and workability are used. Specifically, aluminum alloys and glass can be preferably used. In particular, in the substrate of the present invention in which the root mean square deviation Rq of the substrate 1 is set within the above range, the conventional aluminum alloys and glass used as the material of the substrate can be used without particular limitation. Hereinafter, the magnetic disk substrate manufactured using an aluminum alloy may be referred to as an aluminum alloy substrate, and the magnetic disk substrate manufactured using glass may be referred to as a glass substrate.

[0021] <Aluminum alloy substrate> First, the aluminum alloy substrate will be described. As the aluminum alloy of the substrate material, Al-Mg based alloys, Al-Fe-Mn-Ni based alloys, and Al-Fe-Mn-Mg-Ni based alloys can be preferably used, but are not limited thereto. As the Al-Mg based alloy, for example, JIS5086 (A5086) (containing 3.5 to 4.5 mass% of Mg, 0.50 mass% or less of Fe, 0.40 mass% or less of Si, 0.20 to 0.70 mass% of Mn, 0.05 to 0.25 mass% of Cr, 0.10 mass% or less of Cu, 0.15 mass% or less of Ti, and 0.25 mass% or less of Zn, and the balance being Al and inevitable impurities) can be used.

[0022] Hereinafter, an example of the manufacturing method of the magnetic disk aluminum alloy substrate and the magnetic disk using the same will be described. The manufacturing method of the aluminum alloy substrate for magnetic disks is not particularly limited as long as it can manufacture a substrate for magnetic disks with the root mean square roughness Rq of the surface within the above range. From the viewpoint of making the root mean square roughness Rq of the surface within the above range, the manufacturing method of the aluminum alloy substrate for magnetic disks uses an abrasive liquid containing abrasive grains with a particle size of 0.03 μm or more and 1.0 μm or less (the particle size can also be 0.1 μm or more and 1.0 μm or less) and an average particle size of 0.2 μm or more and 0.85 μm or less, and a hard or soft polishing pad to roughly polish the main surface, and then uses an abrasive liquid containing abrasive grains with a particle size of 0.01 μm or more and less than 0.1 μm and an average particle size of 0.02 μm or more and 0.08 μm or less, and a soft polishing pad to precisely polish the main surface, and preferably has at least these two steps. The rough polishing step corresponds to step S111 described later, and the fine polishing step corresponds to step S112 described later. For details of the rough polishing step and the fine polishing step, refer to the descriptions of steps S111 and S112. It is preferable that at least one of the following preferable steps is performed in the above rough polishing step and / or fine polishing step. It is preferable that the above rough polishing step and / or fine polishing step is a step of polishing while supplying the abrasive liquid from the upper surface plate side to the polishing pad. It is preferable that the above rough polishing step and / or fine polishing step is a step of polishing while supplying an abrasive liquid of 10 ml / min or more per disk blank described later. It is preferable that the above rough polishing step and / or fine polishing step uses an abrasive liquid diluted with water having an electrical resistivity of 1 MΩ·cm or more. In the above rough polishing step and / or fine polishing step, it is preferable to supply the abrasive liquid under stirring to the polishing pad. In the above rough polishing step and / or fine polishing step, it is preferable to invert the disk blank one or more times in the vertical direction of the plate thickness during the polishing process. Prior to the above rough polishing step and / or fine polishing step, it is preferable to clean the pipe through which the abrasive liquid is supplied so that when water with an electrical resistivity of 10 MΩ·cm or more is supplied from the inlet, it becomes 1 MΩ·cm or more at the outlet of the pipe.

[0023] Figure 4 is a flowchart for explaining an example of an aluminum alloy substrate and a method for manufacturing a magnetic disk using the same. In Figure 4, the steps from the preparation process (step S101) to the cold rolling (step S105) of the aluminum alloy are steps for manufacturing an aluminum alloy material by melting and casting and forming it into an aluminum alloy plate. Next, an aluminum alloy disk blank is manufactured by a pressure flattening process (step S106). Then, pretreatment such as a cutting and grinding process (step S107) and a degreasing and etching process (step S108) is performed on the manufactured disk blank, and a zincate process (step S109), a Ni-P plating process (step S110), a rough polishing process (step S111), and a precision polishing process (step S112) are carried out to manufacture an aluminum alloy substrate for a magnetic disk. The manufactured aluminum alloy substrate for a magnetic disk becomes a magnetic disk by a magnetic material adhesion process (step S113). Hereinafter, the details of each process will be described in detail with reference to this Figure 4.

[0024] First, a molten metal of an aluminum alloy material having the above-described component composition is prepared by heating and melting it according to a conventional method (step S101).

[0025] Next, the molten metal of the prepared aluminum alloy material is cast by a semi-continuous casting (DC casting) method, a continuous casting (CC casting) method, or the like to cast the aluminum alloy material (step S102). DC casting may be vertical semi-continuous casting or horizontal semi-continuous casting. The manufacturing conditions of the aluminum alloy material in the DC casting method and the CC casting method are as follows. In the DC casting method, the molten metal poured through a spout is deprived of heat by the bottom block, the wall of the water-cooled mold, and the cooling water directly discharged to the outer peripheral portion of the ingot (cast block), solidifies, and is drawn downward as an aluminum alloy cast block. The ingot obtained in this process is sometimes referred to as a slab. On the one hand, in the CC casting method, molten metal is supplied through a casting nozzle between a pair of rolls (or a belt caster, a block caster), and a thin plate of aluminum alloy is directly cast by heat extraction from the rolls. A major difference between the DC casting method and the CC casting method lies in the cooling rate during casting. In the CC casting method with a high cooling rate, the size of the second-phase particles is smaller compared to that in DC casting, which is a characteristic feature.

[0026] Next, for the aluminum ingot obtained by DC casting, hot rolling is performed to obtain a plate material (step S104). Prior to this hot rolling, for the aluminum alloy ingot cast by DC casting, a homogenization treatment can be carried out as required (step S103). In CC casting, these steps are not performed, and step S105 is carried out following step S102. As step S103, when performing the homogenization treatment, it is preferably carried out by heat treatment at 280 to 620 °C for 0.5 to 30 hours, and more preferably at 300 to 620 °C for 1 to 24 hours. If the heating temperature during the homogenization treatment is less than 280 °C or the heating time is less than 0.5 hours, the homogenization treatment may be insufficient, and there is a risk that the variation in the loss coefficient for each aluminum alloy substrate will increase. If the heating temperature during the homogenization treatment exceeds 620 °C, there is a risk of melting occurring in the aluminum alloy ingot. Even if the heating time during the homogenization treatment exceeds 30 hours, the effect will saturate, and no further significant improvement effect can be obtained.

[0027] In step S104, the aluminum alloy ingot (DC casting) that has been subjected to the homogenization treatment or has not been subjected to the homogenization treatment is hot rolled to obtain a plate material (step S104). When performing hot rolling, the conditions are not particularly limited, but the hot rolling start temperature is preferably 250 to 600 °C, and the hot rolling end temperature is preferably 230 to 450 °C.

[0028] Next, the hot-rolled rolled plate or the cast plate cast by the CC casting method is cold-rolled to obtain an aluminum alloy plate with a thickness of about 0.3 to 0.6 mm (step S105). The conditions for cold rolling are not particularly limited and may be determined according to the required product plate strength and thickness. The rolling ratio is preferably 10 to 95%. Before cold rolling or during cold rolling, annealing treatment may be performed to ensure cold rolling workability. When performing the annealing treatment, for example, in the case of batch heating, it is preferably performed under the conditions of 300 to 450 °C for 0.1 to 10 hours, and in the case of continuous heating, it is preferably performed under the conditions of holding at 400 to 500 °C for 0 to 60 seconds. Here, a holding time of 0 seconds means cooling immediately after reaching the desired holding temperature.

[0029] Then, the aluminum alloy plate obtained by cold rolling is punched into a disk shape to obtain a disk-shaped aluminum alloy plate. The disk-shaped aluminum alloy plate becomes a disk blank by pressure flattening treatment (step S106). In the pressure flattening treatment, a pressure annealing is performed on the disk-shaped aluminum alloy plate in the atmosphere at a temperature of, for example, 200 to 450 °C for 0.5 to 10 hours while applying a load of 30 to 100 MPa to flatten the disk blank.

[0030] Before the disk blank is subjected to a zincate treatment or the like, cutting and grinding (step S107) and heat treatment are performed as necessary. In the cutting and grinding process, the inner and outer circumferences of the disk blank are cut to adjust the shape, and the main surface is ground. Before performing this process, the recording surface of the disk blank may be cut as a pretreatment for grinding. In this process, chamfering may be further performed on the inner and outer circumferential end faces. Grinding can be carried out using SiC grindstones numbered 800 to 4000 and a commercially available batch-type double-sided simultaneous polishing machine. This double-sided simultaneous polishing machine includes a cast iron upper platen and a lower platen, a carrier for holding a plurality of aluminum substrates between the upper platen and the lower platen, and SiC grindstones attached to the contact surfaces of the upper platen and the lower platen with the aluminum substrates. In the grinding process, while holding the disk blank with the carrier, the upper and lower platens are rotated in opposite directions. The rotational speed of the upper and lower platens can be set to 10 to 30 rpm. Since the carrier rotates by a sun gear, the disk blank is ground while performing a planetary motion on the grindstone. When heat treatment is performed, the disk blank is heat-treated under the condition of being held at 200 to 350 °C for 5 to 60 minutes. By performing the heat treatment, the strain introduced by cutting and grinding can be removed.

[0031] Next, the surface of the disk blank is degreased and etched (step S108). The degreasing treatment can be carried out by a normal method. For example, it is preferably carried out using a commercially available degreasing solution under the conditions of a temperature of 40 to 70 °C, a treatment time of 3 to 10 minutes, and a concentration of 10 to 500 ml / L. The etching treatment can be carried out by a normal method. For example, it is preferably carried out using a commercially available etching solution under the conditions of a temperature of 50 to 75 °C, a treatment time of 0.5 to 5 minutes, and a concentration of 1 to 50 mL / L.

[0032] Next, a zincate treatment (Zn replacement treatment) is performed on the surface of the disk blank (step S109). In the zincate treatment, a zincate film is formed on the surface of the disk blank. For the zincate treatment, a commercially available zincate treatment solution can be used, and it is preferably carried out under the conditions of a temperature of 10 to 35°C, a treatment time of 0.1 to 5 minutes, and a concentration of 100 to 500 mL / L. The zincate treatment is carried out at least once and may be carried out two or more times. By carrying out the zincate treatment a plurality of times, fine Zn can be deposited to form a uniform zincate film. When the zincate treatment is carried out two or more times, Zn stripping treatment can be carried out in between. The Zn stripping treatment is preferably carried out using an HNO3 solution under the conditions of a temperature of 15 to 40°C, a treatment time of 10 to 120 seconds, and a nitric acid concentration of 10 to 60%. Also, the second and subsequent zincate treatments are preferably carried out under the same conditions as the first zincate treatment.

[0033] Furthermore, electroless Ni-P plating treatment (step S110) is performed as a pretreatment for magnetic body adhesion on the surface of the zincate-treated disk blank. For the electroless Ni-P plating treatment step, it is preferable to carry out the plating treatment using a commercially available plating solution or the like under the conditions of a temperature of 80 to 95°C, a treatment time of 30 to 180 minutes, and a Ni concentration of 3 to 10 g / L. Pure water washing may be carried out between each treatment from degreasing treatment to zincate treatment.

[0034] A rough polishing step and a fine polishing step are performed as polishing processes for smoothing on the plated surface after electroless Ni-P plating (Steps S111 and S112). In this polishing process, if the root mean square roughness Rq of the surface roughness can be obtained, the details are not particularly limited, but it is preferable to perform polishing in multiple steps with the diameter of the polishing abrasive grains adjusted. The polishing process preferably performs at least two steps of polishing with different particle sizes of the polishing abrasive grains used. For example, using a polishing liquid containing large-diameter polishing abrasive grains with a particle size of 0.03 μm or more and 1.0 μm or less and an average particle size of 0.2 μm or more and 0.85 μm or less, and a hard or soft polishing pad, the main surface is roughly polished. Next, using a polishing liquid containing small-diameter polishing abrasive grains with a particle size of 0.01 μm or more and less than 0.1 μm and an average particle size of 0.02 μm or more and 0.08 μm or less, and a soft polishing pad, the main surface is finely polished. As the small-diameter polishing abrasive grains in the fine polishing step, those with a smaller diameter than the large-diameter polishing abrasive grains used in the rough polishing step are used. Here, "hard" refers to those with a hardness (Asker C) of 85 or more measured by the measurement method defined in the Japan Rubber Association Standard Specification (Standard: SRIS0101), and "soft" refers to those with the same hardness of 60 to 80. The average particle size (d50) is the so-called median diameter, which means the particle size when the particle size distribution is measured by the laser diffraction / scattering method and the cumulative distribution reaches 50% when the total volume of the particles is 100%. In addition, other polishing conditions in the rough polishing step are difficult to uniquely determine because they are affected by the aluminum alloy used, the processing conditions from Steps S101 to S110, etc. However, for example, the rotation speed of the polishing platen is 5 to 35 rpm, the polishing liquid supply rate is 10 to 500 ml / min (more preferably 50 to 500 ml / min), the polishing time is 1 to 10 minutes, and the processing pressure is 10 to 100 g / cm 2 , and the polishing amount can be 0.1 to 10 μm. During the rough polishing step, it is preferable to invert the upper and lower directions in the plate thickness direction of the disk blank. The inversion can be done once or multiple times. The timing of inverting the disk blank is not particularly limited, but it is preferable to ensure that both sides of the disk blank are evenly polished, and it is more preferable to invert it when half of the total polishing time of the rough polishing step has elapsed. Other polishing conditions in the above precision polishing process are difficult to uniquely determine because they are affected by the aluminum alloy used, the processing conditions up to rough polishing in steps S101, etc. For example, the rotational speed of the polishing surface plate is 5 to 35 rpm, the polishing liquid supply rate is 10 to 500 ml / min (more preferably 50 to 500 mL / min), the polishing time is 1 to 10 minutes, and the processing pressure is 10 to 100 g / cm 2 and the polishing amount can be 0.01 to 1 μm. During the precision polishing process, it is preferable to invert the upper and lower parts of the disk blank in the plate thickness direction. The inversion can be done once or multiple times. The timing of inverting the disk blank is not particularly limited, but it is preferable to ensure that both sides of the disk blank are polished evenly, and it is more preferable to invert it when half of the total polishing time of the precision polishing process has elapsed.

[0035] The rough polishing process and the fine polishing process can be carried out using a commercially available batch-type double-sided simultaneous polishing machine. This double-sided simultaneous polishing machine includes a cast iron upper surface plate and a lower surface plate, a carrier for holding a plurality of disk blanks between the upper surface plate and the lower surface plate, and polishing pads (that is, the number of polishing pads is twice the number of disk blanks) attached to the contact surfaces of the upper surface plate and the lower surface plate with the disk blanks. Then, this double-sided simultaneous polishing machine holds a plurality of disk blanks between the upper surface plate and the lower surface plate by the carrier, and clamps each disk blank with a predetermined processing pressure by the upper surface plate and the lower surface plate. Then, each disk blank is clamped by the polishing pads from above and below (parallel to the gravitational direction) all at once. Next, while supplying a polishing liquid at a predetermined supply amount between the polishing pads and each disk blank, the upper surface plate and the lower surface plate are rotated in different directions from each other. At this time, since the carrier also rotates by the sun gear, the disk blank performs a planetary motion. As a result, the disk blank slides on the surface of the polishing pad and polishes both surfaces simultaneously. Since the polishing pad is porous (having bag-shaped holes with open surfaces), the polishing liquid is supplied between the polishing pad and the disk blank through the polishing pad. The supply of the polishing liquid to the polishing pad can be carried out by a normal method. For example, the polishing liquid can be supplied from a tank storing the polishing liquid to the polishing pad via a pipe. The tank storing the polishing liquid preferably includes a stirring means. The polishing liquid is preferably supplied to the polishing pad from the upper surface plate side. Specifically, supplying from the upper surface plate side to the polishing pad means making holes in the upper surface plate and the polishing pad and dropping and pouring the grinding liquid from above into the holes. For the polishing pads used in the rough polishing step and the precision polishing step, porous polishing pads are used.

[0036] By the polishing process (surface polishing) after the electroless Ni-P plating process described above, the aluminum alloy substrate for magnetic disk according to the present invention is manufactured.

[0037] The step of attaching the magnetic material (step 113) can be carried out by a normal method. The formation of the magnetic layer is performed by attaching a magnetic material to the surface of the aluminum alloy substrate in the case of a general aluminum alloy substrate.

[0038] <Glass substrate> The glass substrate will be described. As the material of the glass plate, glass ceramics such as amorphous glass and crystallized glass can be used. From the viewpoints of formability, processability, and surface roughness of the product, it is preferable to use amorphous glass. For example, aluminosilicate glass, soda-lime glass, soda-aluminosilicate glass, aluminoborosilicate glass, borosilicate glass, etc. are preferably used.

[0039] A preferred embodiment of the glass used for the magnetic disk substrate is glass containing SiO2: 55 to 75% as the main component, and adding Al2O3: 0.7 to 25%, Li2O: 0.01 to 6%, Na2O: 0.7 to 12%, K2O: 0 to 8%, MgO: 0 to 7%, CaO: 0 to 10%, ZrO2: 0 to 10%, TiO2: 0 to 1%.

[0040] An example of a glass substrate for a magnetic disk and a method for manufacturing a magnetic disk using the same will be described below. The method for manufacturing a glass substrate for a magnetic disk is not particularly limited as long as it can manufacture a substrate for a magnetic disk in which the root mean square roughness Rq of the surface roughness is within the above range. From the viewpoint of setting the root mean square roughness Rq of the surface roughness within the above range, the method for manufacturing a glass substrate for a magnetic disk includes a step of roughly polishing the main surface using a polishing liquid containing polishing abrasive grains having a particle size of 0.1 μm or more and 1.0 μm or less and an average particle size of 0.2 μm or more and 0.85 μm or less and a hard polishing pad, and then, using a polishing liquid containing polishing abrasive grains having a particle size of 0.01 μm or more and less than 0.1 μm and an average particle size of 0.02 μm or more and 0.08 μm or less and a soft polishing pad, it is preferable to have at least a step of precisely polishing the main surface. The conditions in the rough polishing step and the precision polishing step can also be applied to the conditions for manufacturing an aluminum alloy substrate. For example, in the rough polishing step, abrasive grains having a particle size of 0.03 μm or more and 1.0 μm or less can also be used. The rough polishing step corresponds to step S204 described later, and the precision polishing step corresponds to step S205 described later. For details of the rough polishing step and the precision polishing step, the descriptions of steps S204 and S205 can be referred to. It is preferable that the above rough polishing step and / or precision polishing step perform at least one of the following preferable steps. It is preferable that the above rough polishing step and / or precision polishing step is a step of polishing while supplying a polishing liquid from the upper surface plate side to the polishing pad. It is preferable that the above rough polishing step and / or precision polishing step is a step of polishing while supplying a polishing liquid of 10 ml / minute or more per disk blank described later. It is preferable that the above rough polishing step and / or precision polishing step is a step of using a polishing liquid diluted with water having an electrical resistivity of 1 MΩ·cm or more. In the above rough polishing step and / or precision polishing step, it is preferable to supply the polishing liquid under stirring to the polishing pad. In the above rough polishing step and / or precision polishing step, it is preferable to invert the disk blank up and down in the plate thickness direction one or more times during the polishing process. Prior to the above-mentioned rough polishing step and / or precision polishing step, it is preferable to clean the pipe through which the polishing liquid is supplied so that when water with an electrical resistivity of 10 MΩ·cm or more is supplied from the inlet, the resistivity at the outlet of the pipe becomes 1 MΩ·cm or more.

[0041] FIG. 5 is a flowchart for explaining an example of a method for manufacturing a glass substrate and a magnetic disk using the same. In the manufacture of this glass substrate, as shown in FIG. 5, first, a glass plate with a predetermined thickness is prepared (step S201). Next, the prepared glass plate is cored and the inner and outer peripheral end faces are polished to form a disk blank in a disk shape (step S202). Further, if necessary, a step of lapping the disk blank in a disk shape is performed (step S203). Next, the formed or lapped disk blank is clamped from above and below with a polishing pad all at once, and a rough polishing step (step S204) is performed in which a plurality of disk blanks are polished simultaneously with cerium oxide abrasive grains. Subsequently, a precision polishing step is performed in which each disk blank polished in step S204 is further polished simultaneously with colloidal silica abrasive grains (step S205) to manufacture a glass substrate. The manufactured glass substrate becomes a magnetic disk by an adhesion step of a magnetic material (step S206). Hereinafter, each step will be specifically described with reference to FIG. 5.

[0042] First, the preparation of the glass plate in step S201 can be carried out using a known manufacturing method such as the float method, the down-draw method, or the direct press method using molten glass as a raw material. Further, if the redraw method of heating and softening the base glass plate manufactured by the float method or the like and stretching it to a desired thickness is used, a glass plate with a small thickness variation can be manufactured relatively easily, which is preferable.

[0043] Next, in the formation of the disk-shaped disk blank in step S202, a disk-shaped disk blank is formed from the glass plate prepared in step S201 through a core ring process and an end face polishing process for the inner and outer circumferences. The formed disk blank is a disk-shaped disk blank having two main surfaces and a circular hole formed in the central portion.

[0044] If necessary, the lapping process in step S203 is performed, and lapping is carried out on the disk-shaped disk blank formed in step S202, whereby the thickness of the disk blank can be adjusted. This lapping process is preferably performed when there is a large variation in the thickness of the glass plate, such as when the re-draw method is not adopted in step S201. The lapping process can be performed so that the variation in the thickness of the glass plate is about ±3 μm. The lapping process can be performed by a normal method, for example, it can be carried out using a batch-type double-sided polishing machine using diamond pellets.

[0045] Next, polishing is performed on the main surface of the disk blank obtained in step S202 or S203. In this polishing process, it is preferable to perform polishing in a plurality of stages with the diameter of the polishing abrasive grains adjusted. This polishing process includes at least two stages of polishing: rough polishing (S204) and fine polishing (S205).

[0046] In the rough polishing process of step S204, the main surface of the disk blank is rough polished. Rough polishing can be carried out using a polishing liquid containing polishing abrasive grains with a particle size of 0.1 μm or more and 1.0 μm or less and an average particle size of 0.2 μm or more and 0.85 μm or less, and a hard polishing pad. Other polishing conditions for rough polishing are as follows: using a hard polishing pad with a hardness of 86 - 88, the rotation speed of the polishing surface plate is 5 - 35 rpm, the rotation speed of the sun gear is 5 - 35 rpm, the polishing liquid supply speed is 10 - 500 ml / min (more preferably 50 - 500 mL / min), and the processing pressure is 10 - 120 g / cm 2It is preferable that the polishing time is 1 to 10 minutes and the polishing amount is 0.1 to 1.2 μm per side. As the polishing pad, it is preferable to use a polishing pad made of hard polyurethane or the like. As the polishing liquid, it is preferable to use one containing polishing abrasive grains made of cerium oxide with a particle size of 0.1 μm or more and 1.0 μm or less and an average particle size of 0.2 μm or more and 0.85 μm or less. During the rough polishing process, it is preferable to invert the upper and lower sides in the plate thickness direction of the disk blank. The inversion may be performed once or multiple times. The timing of inverting the disk blank is not particularly limited, but it is preferable to ensure that both sides of the disk blank are polished evenly, and it is more preferable to invert when half of the total polishing time of the rough polishing process has elapsed. The rough polishing process and the fine polishing process can be carried out using a commercially available batch-type double-sided simultaneous polishing machine. In the method for manufacturing a glass substrate, the double-sided simultaneous polishing machine described in the method for manufacturing an aluminum substrate can also be used.

[0047] Next, in the fine polishing process of step S205, the main surface that has been roughly polished is finely polished. Fine polishing can be carried out by replacing the polishing pad of the double-sided simultaneous polishing machine with a softer polishing pad for fine polishing made of, for example, foamed urethane, and supplying a polishing liquid containing polishing abrasive grains made of colloidal silica with a particle size of 0.01 μm or more and less than 0.1 μm and an average particle size of 0.02 μm or more and 0.08 μm or less, and polishing the glass substrate using the above polishing pad. As a result, the main surface of the disk blank is polished to a mirror surface, and a glass substrate for a magnetic disk is manufactured. Other polishing conditions for fine polishing are to use a soft polishing pad with a hardness of 75 to 77, the rotation speed of the polishing table is 5 to 35 rpm, the rotation speed of the sun gear is 5 to 35 rpm, the polishing liquid supply rate is 10 to 500 ml / min (more preferably 50 to 500 mL / min), and the processing pressure is 10 to 120 g / cm 2It is preferable that the polishing time is 1 to 10 minutes and the polishing amount is 5 to 15 μm per side. Also, the polishing amount can be 0.01 to 1 μm. During the precision polishing process, it is preferable to invert the upper and lower sides in the plate thickness direction of the disk blank. The inversion may be performed once or may be performed multiple times. The timing of inverting the disk blank is not particularly limited, but it is preferable to make the polishing of both sides of the disk blank uniform, and it is more preferable to invert it when half of the total polishing time of the precision polishing process has elapsed.

[0048] Note that during the polishing process, chemical strengthening treatment with a sodium nitrate solution or a potassium nitrate solution can be performed.

[0049] The step of attaching the magnetic material (step S205) can be performed by a normal method.

Examples

[0050] Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited thereto.

[0051] In Examples 1 to 3 and Comparative Examples 1 to 2, substrates for magnetic disks with an outer diameter of 97 mm, an inner diameter of 25 mm, and a thickness of 0.50 mm were produced. The details of each example are described below.

[0052] (Example 1) Alloy A5086 (aluminum alloy A) was melted according to a standard method and DC cast (vertical semi-continuous casting) into a slab with a width of 1310 and a plate thickness of 500 mm. The four sides of this slab were each face-milled by 10 mm, and after homogenization treatment at 540 °C for 6 hours, hot rolling was performed at a hot rolling start temperature of 540 °C and a hot rolling end temperature of 340 °C to obtain a hot-rolled plate with a plate thickness of 3.0 mm. This hot-rolled plate was cold-rolled to obtain a cold-rolled plate with a plate thickness of 0.48 mm. This cold-rolled sheet was punched into an annular shape with an inner diameter of 24 mm and an outer diameter of 98 mm by pressing, and in the atmosphere, using a continuous annealing furnace, while applying a load of 30 MPa and pressurizing, pressure annealing was carried out at 320 °C for 3 hours for pressure flattening treatment. In this way, a disk blank was obtained. Further, by machining the inner and outer circumferences of the disk blank, an annular disk blank with an inner diameter of 25 mm and an outer diameter of 97 mm was obtained. At this time, chamfering was simultaneously performed on the inner and outer circumferential end faces. The surface of this processed disk blank was ground with a 4000 grit SiC grinding wheel to a plate thickness of 0.46 mm. Both sides of this disk blank were subjected to degreasing treatment, etching treatment, first zincate treatment, Zn stripping treatment, and second zincate treatment as follows. The degreasing treatment was carried out using degreasing liquid AD-68F (trade name, manufactured by Uemura Kogyo), at a temperature of 45 °C, a treatment time of 3 minutes, and a concentration of 500 mL / L. The etching treatment was carried out using AD-107F (trade name, manufactured by Uemura Kogyo) etching liquid, at a temperature of 60 °C, a treatment time of 2 minutes, and a concentration of 50 mL / L. The first zincate treatment was carried out using zincate treatment liquid AD-301F-3X (trade name, manufactured by Uemura Kogyo), at a temperature of 20 °C, a treatment time of 1 minute, and a concentration of 200 mL / L. The Zn stripping treatment was carried out using a commercially available nitric acid reagent, at a temperature of 25 °C, a treatment time of 60 seconds, and a nitric acid concentration of 30%. The second zincate treatment was carried out under the same conditions as the first zincate treatment. Also, pure water washing was carried out between each treatment from degreasing treatment to second zincate treatment. Thereafter, electroless Ni-P plating treatment was carried out on both sides of the disk blank, using a Nimmden HDX (trade name, manufactured by Uemura Kogyo) plating solution, at a temperature of 88 °C, a treatment time of 130 minutes, and a Ni concentration of 6 g / L. Furthermore, the Ni-P plated disk blank was set in a double-sided polishing machine (trade name: 9B double-sided grinding machine, manufactured by SPEEDFAM), and a rough polishing process and a precision polishing process were carried out to manufacture an aluminum alloy substrate. Details are described below. In the rough grinding process, the grinding conditions were as follows: a urethane foam grinding pad with a hardness of 66, and a grinding fluid prepared by adding pure water to aluminum oxide with a particle size of 0.03 μm or more and 1.0 μm or less and an average particle size of 0.85 μm to form free abrasive grains. In addition, as other grinding conditions in the rough grinding process, the grinding fluid was supplied from the upper platen side, the rotation speed of the grinding platen was 35 rpm, the grinding fluid supply rate was 100 ml / min, the grinding time was 2 minutes, and the processing pressure was 80 g / cm 2 , and the grinding amount was 1 μm. Further, the disk blank was installed with its thickness direction reversed up and down and ground under the same conditions. Next, a fine grinding process was performed. In the fine grinding process, a urethane foam grinding pad with a hardness of 76, and a grinding fluid prepared by adding pure water to colloidal silica with a particle size of 0.01 μm or more and less than 0.1 μm and an average particle size of 0.08 μm to form free abrasive grains were used. In addition, as other grinding conditions in the fine grinding process, the grinding fluid was supplied from the upper platen side, the rotation speed of the grinding platen was 35 rpm, the grinding fluid supply rate was 150 ml / min, the grinding time was 2 minutes, and the processing pressure was 80 g / cm 2 , and the grinding amount was 0.2 μm. Further, the disk blank was installed with its thickness direction reversed up and down and ground under the same conditions. As described above, in the rough grinding process and the fine grinding process, grinding was performed while supplying the grinding fluid at a supply rate of 10 ml / min or more per disk blank. When preparing the grinding fluid used for rough grinding and fine grinding, in both cases, the abrasive grains were diluted using water with an electrical resistivity of 1 MΩ·cm or more. In both rough grinding and fine grinding, the grinding fluid was continuously stirred during supply. When performing rough grinding and fine grinding, the pipe through which the grinding fluid was supplied was cleaned to such an extent that the electrical resistivity at the outlet of the pipe was 1 MΩ·cm or more when water with an electrical resistivity of 10 MΩ·cm or more was supplied from the inlet. In this way, the substrate for a magnetic disk of Example 1 was obtained.

[0053] (Example 2) The Al-Fe-Mn-Ni alloy (alloy B) was melted according to a conventional method and DC cast (vertical semi-continuous casting) into a slab with a width of 1310 and a thickness of 500 mm. This slab was surface-machined by 10 mm on each side, homogenized at 520 °C for 6 hours, and then hot-rolled at a hot-rolling start temperature of 520 °C and a hot-rolling end temperature of 340 °C to obtain a hot-rolled sheet with a thickness of 3.0 mm. This hot-rolled sheet was cold-rolled to obtain a cold-rolled sheet with a thickness of 0.48 mm. The composition of alloy B included Fe: 0.7 mass%, Mn: 0.9 mass%, and Ni: 1.7 mass%, with the balance being aluminum and inevitable impurities. This cold-rolled sheet was punched into an annular shape with an inner diameter of 24 mm and an outer diameter of 98 mm by pressing, and in the atmosphere, using a continuous annealing furnace, while applying a load of 30 MPa and pressurizing, pressure annealing was performed at 320 °C for 3 hours for pressure flattening treatment. In this way, a disk blank was obtained. Further, by machining the inner and outer circumferences of the disk blank, an annular disk blank with an inner diameter of 25 mm and an outer diameter of 97 mm was obtained. At this time, chamfering was simultaneously performed on the inner and outer circumferential end faces. After this processing, the disk blank was surface-ground with a #4000 SiC grinding wheel to a thickness of 0.46 mm. Both sides of this disk blank were subjected to degreasing treatment, etching treatment, first zincate treatment, Zn stripping treatment, and second zincate treatment as follows. The degreasing treatment was performed using degreasing liquid AD-68F (trade name, manufactured by Uemura Industries) at a temperature of 45 °C, a treatment time of 3 minutes, and a concentration of 500 mL / L. The etching treatment was performed using AD-107F (trade name, manufactured by Uemura Industries) etching solution at a temperature of 60 °C, a treatment time of 2 minutes, and a concentration of 50 mL / L. The first zincate treatment was performed using zincate treatment liquid AD-301F-3X (trade name, manufactured by Uemura Industries) at a temperature of 20 °C, a treatment time of 1 minute, and a concentration of 200 mL / L. The Zn stripping treatment was performed using a commercially available nitric acid reagent at a temperature of 25 °C, a treatment time of 60 seconds, and a nitric acid concentration of 30%. The second zincate treatment was performed under the same conditions as the first zincate treatment. Also, pure water washing was performed between each treatment from degreasing treatment to second zincate treatment. Thereafter, electroless Ni-P plating treatment was performed on both sides of the disk blank using a Nimmden HDX (trade name, manufactured by Kamimura Kogyo Co., Ltd.) plating solution under the conditions of a temperature of 88°C, a treatment time of 130 minutes, and a Ni concentration of 6 g / L. Furthermore, the Ni-P plated disk blank was set in a double-sided polishing machine (trade name: 9B double-sided grinding machine, manufactured by SPEEDFAM), and a rough polishing process and a precision polishing process were performed to manufacture an aluminum alloy substrate. Details are described below. As the polishing conditions in the rough polishing process, a urethane foam polishing pad with a hardness of 66 and a polishing liquid obtained by adding pure water to aluminum oxide with a particle size of 0.03 μm or more and 1.0 μm or less and an average particle size of 0.85 μm were used as free abrasive grains. In addition, as other polishing conditions in the rough polishing process, the polishing liquid was supplied from the upper platen side, the rotation speed of the polishing platen was 35 rpm, the polishing liquid supply rate was 100 ml / min, the polishing time was 2 minutes, and the processing pressure was 80 g / cm 2 , and the polishing amount was 1 μm. Further, the disk blank was installed with its thickness direction reversed up and down and polished under the same conditions. Next, a precision polishing process was performed. In the precision polishing process, a urethane foam polishing pad with a hardness of 76 and a polishing liquid obtained by adding pure water to colloidal silica with a particle size of 0.01 μm or more and less than 0.1 μm and an average particle size of 0.08 μm were used as free abrasive grains. In addition, as other polishing conditions in the precision polishing process, the polishing liquid was supplied from the upper platen side, the rotation speed of the polishing platen was 35 rpm, the polishing liquid supply rate was 150 ml / min, the polishing time was 3 minutes, and the processing pressure was 80 g / cm 2 , and the polishing amount was 0.2 μm. Further, the disk blank was installed with its thickness direction reversed up and down and polished under the same conditions. As described above, in the rough polishing process and the precision polishing process, polishing was performed while supplying the polishing liquid at a supply rate of 10 ml / min or more per disk blank. When preparing the polishing liquid used for rough polishing and precision polishing, in both cases, the abrasive grains were diluted using water with an electrical resistivity of 1 MΩ·cm or more. In both rough polishing and precision polishing, the polishing liquid was continuously stirred during supply. When performing rough polishing and precision polishing, the piping through which the polishing liquid was supplied was cleaned to such an extent that the electrical resistivity at the outlet of the piping was 1 MΩ·cm or more when water with an electrical resistivity of 10 MΩ·cm or more was supplied from the inlet. In this way, the substrate for magnetic disk of Example 2 was obtained.

[0054] (Example 3) Using the drawdown method, a glass plate made of aluminosilicate glass with a width of 100 mm and a length of 10 m or more was manufactured, and a glass plate with a thickness of 0.6 mm was selected. For the selected glass plate, core ring and end face polishing of the inner and outer circumferences were performed to form a disc blank in a disc shape. Further, the formed disc blank was set in a double-sided simultaneous polishing machine, and a rough polishing process and a precision polishing process were performed to manufacture a glass substrate. As the polishing conditions in the rough polishing process, a urethane polishing pad with a hardness of 87 (manufactured by Hamai Sangyo Co., Ltd.: HPC-90D) and a polishing liquid obtained by adding pure water to cerium oxide polishing abrasive grains with a particle size of 0.1 μm or more and 0.4 μm or less and an average particle size of 0.2 μm were used as free abrasive grains. Further, as other polishing conditions in the rough polishing process, the polishing liquid was supplied from the upper platen side, the rotation speed of the polishing platen was 25 rpm, the rotation speed of the sun gear was 10 rpm, the polishing liquid supply rate was 150 ml / min, the polishing time was 2 minutes, the polishing amount was 1 μm per side, and the processing pressure was 120 g / cm 2 was set. Further, the disc blank was installed with its thickness direction reversed up and down and polished under the same conditions. In this process, the total polishing amount for both sides was 2 μm. Next, in the precision polishing process, a foamed urethane polishing pad with a hardness of 76 (manufactured by Fujibo Ehime Co., Ltd.) and a polishing liquid obtained by adding pure water to colloidal silica with a particle size of 0.01 μm or more and less than 0.1 μm and an average particle size of 0.08 μm were used as free abrasive grains. In addition, as other polishing conditions in the precision polishing process, the polishing liquid was supplied from the upper platen side, the rotation speed of the polishing platen was 25 rpm, the rotation speed of the sun gear was 10 rpm, the polishing liquid supply rate was 150 ml / min, the polishing time was 5 minutes, the polishing amount was 0.2 μm per side, and the processing pressure was 50 g / cm 2 was set. Further, the disc blank was installed with its thickness direction reversed up and down and polished under the same conditions. In this process, the total polishing amount for both sides was 0.4 μm. As described above, in the rough polishing process and the fine polishing process, polishing was performed while supplying the polishing liquid at a supply rate of 10 ml / min or more per disk blank. When preparing the polishing liquid used for rough polishing and fine polishing, in each case, abrasive grains were diluted with water having an electrical resistivity of 1 MΩ·cm or more. In both the rough polishing and the fine polishing, the polishing liquid was continuously stirred while being supplied. When performing rough polishing and fine polishing, the pipe through which the polishing liquid is supplied was cleaned to such an extent that the electrical resistivity at the outlet of the pipe was 1 MΩ·cm or more when water having an electrical resistivity of 10 MΩ·cm or more was supplied from the inlet. In this way, the substrate for magnetic disk of Example 3 was obtained.

[0055] (Comparative Example 1) A substrate for magnetic disk was obtained in the same manner as in Example 1, except that the polishing process was performed under the following conditions. As the rough polishing conditions of Comparative Example 1, a urethane foam polishing pad with a hardness of 66 and a polishing liquid obtained by adding pure water to aluminum oxide having a particle size of 0.03 μm or more and 1.0 μm or less and an average particle size of 0.85 μm were used as free abrasive grains. In addition, as other polishing conditions in the rough polishing process, the polishing liquid was supplied from the upper platen side, the rotation speed of the polishing platen was 35 rpm, the polishing liquid supply rate was 80 ml / min, the polishing time was 4 minutes, and the processing pressure was 100 g / cm 2 , and the polishing amount was 1 μm. The disk blank was not reversed. Next, a fine polishing process was performed. In the fine polishing process, a urethane foam polishing pad with a hardness of 76 and a polishing liquid obtained by adding pure water to colloidal silica having a particle size of 0.01 μm or more and less than 0.1 μm and an average particle size of 0.08 μm were used as free abrasive grains. In addition, as other polishing conditions in the fine polishing process, the polishing liquid was supplied from the upper platen, the rotation speed of the polishing platen was 35 rpm, the polishing liquid supply rate was 150 ml / min, the polishing time was 4 minutes, and the processing pressure was 100 g / cm 2 , and the polishing amount was 0.2 μm. The disk blank was not reversed. In addition, when performing rough polishing and fine polishing, the pipe through which the polishing liquid is supplied was not cleaned to such an extent that the electrical resistivity at the outlet of the pipe was 1 MΩ·cm or more when water having an electrical resistivity of 10 MΩ·cm or more was supplied from the inlet. In this way, the substrate for magnetic disk of Comparative Example 1 was obtained.

[0056] (Comparative Example 2) A substrate for magnetic disk was obtained in the same manner as in Example 2, except that the polishing process was carried out under the following conditions. As the rough polishing conditions of Comparative Example 2, a urethane foam polishing pad with a hardness of 66 and a polishing liquid obtained by adding pure water to aluminum oxide with a particle size of 0.03 μm or more and 1.0 μm or less and an average particle size of 0.85 μm were used as free abrasive grains. In addition, as other polishing conditions in the rough polishing process, the polishing liquid was supplied from the upper platen side, the rotation speed of the polishing platen was 35 rpm, the polishing liquid supply rate was 80 ml / min, the polishing time was 2 minutes, and the processing pressure was 100 g / cm 2 , and the polishing amount was 1 μm. The disk blank was not reversed. Next, a fine polishing process was carried out. In the fine polishing process, a urethane foam polishing pad with a hardness of 76 and a polishing liquid obtained by adding pure water to colloidal silica with a particle size of 0.01 μm or more and less than 0.1 μm and an average particle size of 0.08 μm were used as free abrasive grains. In addition, as other polishing conditions in the fine polishing process, the polishing liquid was supplied from the upper platen side, the rotation speed of the polishing platen was 35 rpm, the polishing liquid supply rate was 150 ml / min, the polishing time was 6 minutes, and the processing pressure was 100 g / cm 2 , and the polishing amount was 0.2 μm. The disk blank was not reversed. In addition, when performing rough polishing and fine polishing, the pipe through which the polishing liquid is supplied was not cleaned to such an extent that the electrical resistivity at the outlet of the pipe was 1 MΩ·cm or more when water with an electrical resistivity of 10 MΩ·cm or more was supplied from the inlet. In this way, the substrate for magnetic disk of Comparative Example 2 was obtained.

[0057] (Measurement of Rq of the front and back surfaces) For each of the prepared substrates for magnetic disk, the root mean square deviation Rq of the surface roughness at the fixed site was measured. In this measurement, the root mean square deviation Rq of the surface roughness of a part of the fixed portion was measured to represent the root mean square deviation Rq of the surface roughness of the fixed portion. The position on the substrate for magnetic disks where this Rq was measured is on the circumference with a radius of 30 mm from the center of the substrate for magnetic disks produced for each type of magnetic disk. (That is, it is the location indicated by the virtual line 6 located within the fixed portion 11 on the substrate for magnetic disks 1 shown in FIG. 6.) The measurement was performed using an optical measuring instrument (Zygo Corporation, Mesa Horizontal Laser Interferometer (trade name)). The mode during measurement was set to the mode of measuring the surface roughness on the above-mentioned circumference. The obtained data was used with the MetroPro8.3.3 software attached to the above-mentioned optical measuring instrument to determine the root mean square deviation Rq (μm) of the surface roughness. The measurement was performed for both main surfaces of the substrate for magnetic disks. The root mean square deviation Rq of the surface roughness of one main surface was described in the "Surface Rq" column of Table 1, and the root mean square deviation Rq of the surface roughness of the other main surface was described in the "Back Surface Rq" column of Table 1. Furthermore, the absolute value of the difference ΔRq between the surface Rq and the back surface Rq was described in the "Difference between Front and Back Surfaces ΔRq" column.

[0058] (Measurement of the maximum displacement H, measurement of the damping ratio E) For each of the produced substrates for magnetic disks, the maximum value H of the displacement amount in the thickness direction of the outer peripheral end portion (measurement position of the following sensor) of the substrate for magnetic disks when the substrate for magnetic disks was vibrated by an impact test, and the damping ratio E of this displacement amount were determined as follows. This measurement was performed at room temperature (25°C). <Impact Test> With the substrate for magnetic disks fixed from above and below by a fixing jig at the fixed portion and horizontally fixed to the bearing, an impact of 2.8 msec and 490 m / s 2 was applied from below in the normal direction (thickness direction) of the main surface of the substrate for magnetic disks. For the measurement, an impact testing machine (manufactured by Air Brown, SM-110-MP (product name)) was used. This impact testing machine is equipped with one test bench, and by dropping this test bench, an external impact of any size can be applied to the specimen. Also, a displacement measuring device (manufactured by Unipulse, UMA-500 (product name)) was used. This displacement measuring device is equipped with a capacitance-type sensor, and by measuring the capacitance between the sensor and the object to be measured, the distance between the sensor and the object to be measured can be calculated. The substrate for magnetic disk was attached to the test bench of the above impact testing machine using the same jig as that of a commercially available hard disk drive so that the main surface of the substrate for magnetic disk was parallel to the test bench. The attachment was specifically carried out as follows. First, the above hard disk drive (12TB HDD [HUH721212ALE600], manufactured by Western Digital, equipped with 8 substrates for magnetic disk) was disassembled to take out the fixing jigs (disk clamp, spacer) made of aluminum alloy and 6 screws with a nominal diameter of M2. Separately, a bearing having the same shape except that the bearing and the core of the above hard disk drive were shorter (for one substrate for magnetic disk) was prepared and fixed to the test bench. One substrate for magnetic disk was clamped with the fixing jigs (disk clamp, spacer) taken out from the above hard disk drive, and the 6 screws were screwed from above the disk clamp with a torque of 50 cN·m and assembled to the bearing. After the assembly, the substrate for magnetic disk was in contact with the fixing jig at the fixing part 11 provided at its inner peripheral part (the part surrounded by the inner peripheral end and the circumference with a radius of 14.5 mm from the center of the substrate for magnetic disk). The outer diameter of the disk clamp was 30 mm and the thickness was 5.6 mm. The spacer was annular, with an inner diameter of 25 mm, an outer diameter of 32 mm, and a thickness of 1.7 mm. As shown in Fig. 7, in order to measure the displacement amount of the outer peripheral end portion of the substrate for magnetic disk generated with the addition of an external impact, sensors of the displacement measuring device were attached on the test bench as the inner peripheral end sensor 7 and the outer peripheral end sensor 8. The inner peripheral end sensor 7 was positioned 20 mm in the outer peripheral direction from the center of the substrate for magnetic disk before applying vibration, which was the object to be measured, on the test bench, and the outer peripheral end sensor 8 was positioned 44.18 mm in the outer peripheral direction from the center of the substrate for magnetic disk. They were respectively attached so as to be able to measure the distance between the substrate for magnetic disk 1 and the sensor along the normal direction of the main surface of the stationary substrate for magnetic disk 1. Fig. 7 shows an end view of the arrangement of the inner peripheral end sensor 7, the outer peripheral end sensor 8, and the substrate for magnetic disk 1 with respect to the substrate for magnetic disk 1 as seen from the horizontal direction (perpendicular to the thickness direction of the substrate for magnetic disk). In Fig. 7(a), the substrate for magnetic disk 1 is in a stationary state (the state before impact application), and the inner peripheral end sensor 7 and the outer peripheral end sensor 8 are arranged perpendicular to the main surface of the substrate for magnetic disk 1. In Fig. 7(a), the substrate for magnetic disk 1 is clamped at a fixing portion (not shown) by the disk clamper 31 and the spacer 34 and fixed to a bearing (not shown). Although the outer diameters of the disk clamper 31 and the spacer 34 are different, in Fig. 7(a), they are shown with the same diameter for simplification. Let the distance between the inner peripheral end sensor 7 and the main surface of the substrate for magnetic disk 1 (the closer one to the inner peripheral end sensor 7: the opposing main surface) be h2, and the distance between the outer peripheral end sensor 8 and the main surface of the substrate for magnetic disk 1 (the closer one to the outer peripheral end sensor 8: the opposing main surface) be h1. Fig. 7(b) shows an end view of the arrangement of the inner peripheral end sensor 7 and the outer peripheral end sensor 8 with respect to the substrate for magnetic disk 1 that is deformed and deflected downward due to the vibration caused by the impact application. In Fig. 7(b), due to the above-mentioned deflection, both h1 and h2 are larger than h1 and h2 in Fig. 7(a). Although not shown, the substrate for magnetic disk 1 vibrates in the plate thickness direction (up and down direction) due to the vibration caused by the impact, and the vibration decays over time. With the above-mentioned impact testing machine, the test bench was dropped vertically at 490 m / s with respect to the bearing 2, An impact of 2.8 msec was applied from below in the normal direction of the main surface of the substrate for magnetic disk. At this time, the distance (h1) between the outer peripheral end sensor 8 and the substrate 1 for magnetic disk, and the distance (h2) between the inner peripheral end sensor 7 and the substrate 1 for magnetic disk were measured, and the displacement amount of the distance between the outer peripheral end sensor and the outer peripheral end from the stationary state to the vibrating state, and the displacement amount of the distance between the inner peripheral end sensor and the inner peripheral end from the stationary state to the vibrating state were obtained (both in units of μm). The difference (h1 - h2) of these displacement amounts at the same time was calculated, and this difference was taken as the displacement amount of the outer peripheral end of the substrate for magnetic disk. In this way, by obtaining the displacement amount of the outer peripheral end as the difference between the displacement amounts h1 and h2 at two points, the inner peripheral end and the outer peripheral end on the substrate for magnetic disk, the influence of the displacement of the bearing can be eliminated. When the obtained displacement amount of the outer peripheral end was shown in a displacement amount - time graph (vertical axis: displacement amount (μm), horizontal axis: time (msec)) with the displacement in the upward normal direction of the main surface of the substrate for magnetic disk being positive as shown in Fig. 8, the absolute value of the displacement that first greatly drops downward was taken as the maximum displacement amount H (μm), and the slope when connecting the peaks of the displacements that greatly drop for the first and second times was taken as the attenuation rate E (μm / msec) of the displacement amount due to vibration. In this test, the substrate for magnetic disk was not rotated by the motor.

[0059] The evaluation results are shown in Table 1. For the substrates for magnetic disk of Comparative Examples 1 and 2, the surface Rq and the back surface Rq were too large, and the displacement amount H could not be reduced. Moreover, the attenuation rate E was also small. For the substrates for magnetic disk of Examples 1 to 3, both the surface Rq and the back surface Rq were in the range of 0.01 to 0.44 μm, and the displacement amount H was reduced. Also, the attenuation rate E was improved. It can be seen that the magnetic disk using the substrate for magnetic disk of the present invention can reduce the displacement amount H and improve the attenuation rate E, and therefore, the impact resistance of the hard disk drive can be improved by using this magnetic disk. 490 m / s 2If the maximum displacement H when receiving an impact of 2.8 msec is less than 171 μm, even when the substrate for magnetic disk is incorporated as a magnetic disk into a hard disk drive with a gap of 165 μm between the magnetic disk and an external member such as a ramp, it is possible to obtain a hard disk drive in which the magnetic head is less likely to contact an external member such as a ramp and particles are less likely to be generated due to abrasion of the ramp member, and in some cases, scratches and defects are less likely to occur on the surface of the magnetic disk. Also, 490 m / s 2 If the attenuation rate E when receiving an impact of 2.8 msec is 17.7 μm / msec or more, when the substrate for magnetic disk is incorporated as a magnetic disk into a hard disk drive, even if large vibrations occur in the magnetic disk, the vibrations can be attenuated in a short time, and the number of contacts with an external member is reduced. Also, in a situation where the magnetic disk is not rotating, repeated contacts at the same position on the magnetic disk are reduced. As a result, it is possible to obtain a hard disk drive in which the generation of particles, as well as scratches and defects on the surface of the magnetic disk, are even less likely to occur.

[0060] [Table 1]

[0061] Although the present invention has been described with its embodiments, we do not intend to limit our invention in any detail of the description unless otherwise specified, and we believe that it should be broadly interpreted without departing from the spirit and scope of the invention shown in the appended claims.

[0062] This application claims priority based on Japanese Patent Application No. 2022-002122 filed in Japan on January 11, 2022, the content of which is incorporated herein by reference as part of the description of this specification. [Explanation of Reference Numerals]

[0063] 1 Substrate for magnetic disk 11 Fixed portion 12 Circular hole 13 Virtual line 14 Main surface 15 Inner peripheral end 2 Magnetic disk 21 Fixed part 3 Fixing jig 31 Disk clamper 33 Bearing 33a Large diameter part of bearing 33b Core of bearing 34 Spacer 4 Screw 6 Virtual line 7 Inner peripheral end sensor 8 Outer peripheral end sensor S101 Adjustment of aluminum alloy composition S102 Casting of aluminum alloy S103 Homogenization treatment S104 Hot rolling S105 Cold rolling S106 Heating flattening treatment S107 Cutting and grinding S108 Degreasing and etching treatment S109 Zincate treatment S110 Ni-P plating treatment S111 Rough grinding S112 Precision grinding S113 Attachment of magnetic material S201 Preparation of glass plate S202 Formation of disk-shaped blank S203 Lapping process S204 Rough grinding S205 Precision grinding S206 Attachment of magnetic material

Claims

1. A substrate for a magnetic disk having a pair of front and back main surfaces, each of the front and back main surfaces has a fixing portion that contacts a fixing jig when the magnetic disk substrate is assembled into a hard disk drive with the magnetic disk substrate as a magnetic disk, the root mean square roughness Rq of the surface of each fixing portion of the front and back main surfaces is 0.01 to 0.44 μm, a substrate for a magnetic disk in which, when the magnetic disk substrate is vibrated by the following impact test, the maximum value H of the displacement amount in the plate thickness direction of the outer peripheral end portion of the magnetic disk substrate is 165 μm or less, and the attenuation rate E of the displacement amount is 17.7 μm / msec or more. <Impact Test> The magnetic disk substrate is sandwiched from above and below by a fixing jig at the fixing portion and fixed horizontally to a bearing, and an impact of 2.8 msec and 490 m / s2 is applied from below in the normal direction of the main surface of the magnetic disk substrate to the bearing.

2. The magnetic disk substrate according to claim 1, wherein the absolute value of the difference ΔRq of Rq of the fixing portions of the front and back main surfaces is 0.01 to 0.11 μm.

3. A disk-shaped magnetic disk substrate according to claim 1, having an outer diameter of 97 mm or more, an inner diameter of 26 mm or less, and a plate thickness of 0.5 mm or less.

4. A magnetic disk using the magnetic disk substrate according to any one of claims 1 to 3.

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