Disks for information recording media, and disk intermediates

Abstract

A disk for an information recording medium according to an embodiment has a plate thickness of 0.51 mm or less, and comprises a substrate and a coating layer. The substrate has one main surface and another main surface, and also has sidewall surfaces which connect the two main surfaces. The coating layer covers both main surfaces and the sidewall surfaces of the substrate. The disk has a specific modulus of elasticity E / d [×106m2 / s2], which is calculated from the Young's modulus E[GPa] and density d[g / cm3] thereof, of 40 or more. When the disc is subjected to an impact of 30 [G] at 2 [m / sec.] in the normal direction of the main surfaces of the disk substrate while the inner peripheral end section of the disk is fixed, the maximum amplitude of the outer peripheral end section of the disk substrate caused by vibrations in the plate thickness direction is 0.25 mm or less.

Description

Information recording medium disc, disc intermediate, and information recording medium substrate

[0001] The present invention relates to a disk for an information recording medium in which a substrate is covered with a covering layer, a disk intermediate, and a substrate for an information recording medium.

[0002] With the recent rise of cloud computing, many hard disk drives (HDDs) (magnetic recording devices) are being used in cloud data centers to increase storage capacity. HDDs use information recording medium disks, each having a magnetic layer on a circular substrate, as their storage medium. In order to increase the storage capacity of HDDs, it is preferable to increase the recording density of the magnetic layer of the information recording medium disk, as well as to thin the information recording medium disk and increase the number of information recording medium disks that can be installed.

[0003] Magnetic disks, which are used as information recording media in HDD devices, are required to minimize fluttering (surface wobble) when rotated at high speeds in order to ensure stable reading of information recorded on the magnetic layer. However, reducing the thickness of information recording media disks to increase the number of disks that can be mounted results in insufficient strength of the information recording media disks, resulting in increased fluttering. Therefore, for the manufacture of thin information recording media disks, it is preferable to use substrates made of hard materials with a high Young's modulus. However, hard materials are difficult to cut, and long polishing and grinding processes are required to reduce the surface roughness of the substrate, resulting in the problem of inefficient production of substrates.

[0004] A known substrate used in conventional information recording medium discs is a laminated substrate in which a glass coating film is provided on the surface of a ceramic substrate (Patent Document 1). Because the glass coating film is softer and easier to cut than ceramic materials, the surface roughness of the laminated substrate can be reduced in a short time, allowing for the efficient production of information recording medium discs with good surface properties.

[0005] Japanese Unexamined Patent Publication No. 61-48123

[0006] However, if the thickness of the conventional laminated substrate is reduced to increase the number of information recording medium discs that can be mounted, the ceramic substrate will become thinner, resulting in insufficient strength and increased fluttering of the information recording medium disc. Here, it has been found that even if the rigidity of the information recording medium disc is increased to suppress fluttering, it is not possible to effectively suppress fluttering as an information recording medium disc.

[0007] Therefore, an object of the present invention is to provide an information recording medium disc, a disc intermediate, and an information recording medium substrate that can suppress fluttering of the information recording medium disc while improving the problems of the information recording medium disc caused by its thin plate thickness.

[0008] The present disclosure includes the following aspects: Aspect 1: A disk for an information recording medium having a thickness of 0.51 mm or less, comprising: a substrate having one main surface and another main surface and further having a side wall surface connecting both main surfaces; and a coating layer covering both main surfaces and the side wall surface of the substrate, wherein the disk has a Young's modulus E [GPa] and a density d [g / cm 3 ], the specific elastic modulus E / d [× 10 6 m 2 / s 2 ] is 40 or more, and when an impact of 30 [G] is applied to the disk for 2 [ms] in the normal direction of the main surface of the disk with the inner peripheral edge of the disk fixed, the maximum amplitude due to vibration in the thickness direction of the outer peripheral edge of the disk is 0.25 mm or less.

[0009] Aspect 2: A disk for an information recording medium having a thickness of 0.51 mm or less, comprising: a substrate having one main surface and the other main surface, and further having side wall surfaces connecting both main surfaces; and a coating layer covering both main surfaces and the side wall surfaces of said substrate, wherein the product F·D of the fluttering characteristic F [nm] represented by the sum of the flutter vibration amounts of said disk at 1000 to 4000 Hz and the disk thickness D [mm] is 47.0 or less, and wherein when an impact of 30 [G] is applied to said disk for 2 [ms] in the direction normal to the main surfaces of said disk with the inner peripheral edge of said disk fixed, the maximum amplitude of vibration in the thickness direction of said outer peripheral edge of said disk is 0.25 mm or less.

[0010] Aspect 3 is a disk for information recording media having a thickness of 0.51 mm or less, comprising: a substrate having one main surface and the other main surface and further having sidewall surfaces connecting both main surfaces; and a cover layer covering both main surfaces and the sidewall surfaces of the substrate, wherein the disk has a fluttering characteristic F [nm] expressed as the sum of the flutter vibration amounts of the disk at 1000 to 4000 Hz and a disk thickness D [mm], where F·D is 47.0 or less, and with respect to the thickness in the thickness direction, a ratio T / t of a thickness T [mm] of each of the cover layers covering both main surfaces to a thickness t [mm] of the substrate is 0.01 to 0.4, the thickness t of the substrate is 0.43 mm or less, and the thickness T of the cover layer is 0.1 mm or less, and the disk has a Young's modulus E [GPa] and a density d [g / cm 3 ], the specific elastic modulus E / d [× 10 6 m 2 / s 2 ] is 40 or more.

[0011] Aspect 4: An information recording medium disc having a thickness of 0.51 mm or less, comprising: a substrate having one main surface and another main surface and further having side wall surfaces connecting both main surfaces; and a cover layer covering both main surfaces and the side wall surfaces of said substrate, wherein, with respect to the thickness in the thickness direction, a ratio T / t of a thickness T [mm] of each of said cover layers covering both main surfaces to a thickness t [mm] of said substrate is 0.01 to 0.4, the thickness t of said substrate is 0.43 mm or less, and the thickness T of said cover layer is 0.1 mm or less, and the product F·D of a fluttering characteristic F [nm] represented by the sum of the flutter vibration amounts of said disc at 1000 to 4000 Hz and a thickness D [mm] of said disc is 47.0 or less.

[0012] Aspect 5: The disk for an information recording medium according to any one of Aspects 1 to 4, wherein the substrate is made of one of ceramic, aluminum alloy, and glass, and the covering layer is made of glass or a nickel alloy.

[0013] Aspect 6: The disk for an information recording medium according to any one of Aspects 1 to 4, wherein the product F·D of the fluttering characteristic F [nm], which is expressed as the sum of the flutter vibration amounts of the disk at 1000 to 4000 Hz, and the thickness D [mm] of the disk is 45.0 or less.

[0014] Aspect 7: The thickness D [mm] and specific elastic modulus E / d [×10 6 m 2 / s 2 and Qa, which is a Q value of the disc at 3000 Hz measured at 25°C, satisfy the following formula 1: 65.0<(Qa×E / d) / 1000×D<270.0.

[0015] Aspect 8: The thickness D [mm] and specific elastic modulus E / d [×10 6 m 2 / s 2and Qa, which is a Q value of the disc at 3000 Hz measured at 25°C, satisfy the following formula 2: 150<(Qa×E / d) / 1000×D<700.

[0016] Aspect 9: The disc for an information recording medium according to any one of Aspects 1 to 4, wherein the disc has a thickness of 0.45 mm or less.

[0017] Aspect 10: The information recording medium disk according to any one of Aspects 1 to 5, wherein the covering layer is made of glass and contains a crystalline phase in an interface layer region located in a depth region that is at least 5% of the thickness T of the covering layer in the plate thickness direction from the interface with the substrate.

[0018] Aspect 11: The information recording medium disk according to Aspect 10, wherein, in a cross section of the interface layer region in the thickness direction, the crystalline phase is present in a region of 50% or more of a length per unit length in an extending direction of the cover layer perpendicular to the thickness direction.

[0019] Aspect 12: The information recording medium disk according to any one of Aspects 1 to 7, wherein the covering layer is made of glass and does not contain a crystalline phase in a surface region located at a depth of at least 5% of the thickness T of the covering layer in the plate thickness direction from the surface of the covering layer on the opposite side to the interface with the substrate.

[0020] Aspect 13: The disc for an information recording medium according to any one of Aspects 1 to 8, wherein the arithmetic mean roughness Ra of the main surface of the substrate is 0.01 to 0.75 μm.

[0021] Aspect 14. The disk for an information recording medium according to any one of Aspects 1 to 9, wherein the difference between the maximum and minimum values ​​of the distance from the surface of the cover layer on the opposite side of the interface between the cover layer and the substrate in the plate thickness direction to the substrate is 7.5 to 12.5 μm.

[0022] Aspect 15: The disk for an information recording medium according to any one of Aspects 1 to 10, wherein the main surface of the substrate has a portion in which concaves and convexes appear alternately in a waviness curve obtained from a cross-sectional curve that passes through the center of the main surface and shows a cross-sectional shape of the substrate in a plate thickness direction, and the length of the repeating unit of the concaves and convexes in the extending direction of the coating layer, which is perpendicular to the plate thickness direction, is 100 to 150 μm.

[0023] Aspect 16: The disc for an information recording medium according to any one of Aspects 1 to 11, wherein the thickness of the covering layer on the sidewall surface is greater than the thickness T of the covering layer on the main surface of the substrate.

[0024] Aspect 17: The disc for an information recording medium according to any one of Aspects 1 to 12, wherein the disc has a diameter of 95 mm or more.

[0025] Aspect 18: A disk for an information recording medium according to any one of Aspects 1 to 13, wherein when an impact of 50 G is applied to the disk for 2 ms in the direction normal to the main surface of the disk with the inner peripheral edge of the disk fixed, the maximum amplitude of vibration in the thickness direction of the outer peripheral edge of the disk is 0.30 mm or less.

[0026] Aspect 19: The disk for an information recording medium according to any one of Aspects 1 to 14, wherein the disk has a diameter of 95 mm or more, and a fluttering characteristic F expressed as the sum of flutter vibration amounts of the disk at 1000 to 4000 Hz is 80 nm or less.

[0027] Aspect 20: The disk for an information recording medium according to any one of Aspects 1 to 15, wherein the main surface of the substrate that forms the interface with the cover layer has a maximum height Rz of surface roughness of 0.1 to 50 μm.

[0028] Aspect 21 A disk intermediate having a thickness of 0.59 mm or less, which serves as a base plate for a disk for an information recording medium, comprising: a substrate having one main surface and the other main surface and further having side wall surfaces connecting both main surfaces; and a covering layer covering both main surfaces and the side wall surfaces of said substrate, wherein, in the thickness direction, a ratio T / t of a thickness T [mm] of each of said covering layers to a thickness t [mm] of said substrate is 0.1 to 0.75, said thickness t of said substrate is 0.43 mm or less, and said thickness T of said covering layer is 0.15 mm or less, and said disk intermediate has a Young's modulus E [GPa] and a density d [g / cm 3 ], the specific elastic modulus E / d [× 10 6 m 2 / s 2 ] is 40 or more.

[0029] It is a diagram showing the external shape of an information recording medium disc according to one embodiment.It is a diagram showing the layer structure of an information recording medium disc.It is a backscattered electron image showing the cross section of a coating layer.It is a microscope photograph showing the cross section of a laminated substrate.

[0030] The information recording medium disc, the disc intermediate, and the information recording medium substrate according to the embodiment will be described in detail below.

[0031] The information recording medium disk (hereinafter simply referred to as magnetic disk) of this embodiment includes four types of magnetic disks described below.

[0032] (First embodiment) Fig. 1 is a diagram showing the external shape of a magnetic disk 1 according to a first embodiment. Fig. 2 is a diagram showing the layer structure of the magnetic disk 1. The magnetic disk 1 has a thickness of 0.51 mm or less, and as shown in Fig. 2, includes a substrate 3, a coating layer 5, and a metal film (not shown, described below).

[0033] By making the thickness of the magnetic disk 1 0.51 mm or less, it is possible to increase the number of magnetic disks 1 that can be mounted in an HDD device, thereby increasing the storage capacity of the HDD device. The thickness of the magnetic disk 1 is preferably 0.50 mm or less, 0.48 mm or less, 0.46 mm or less, 0.45 mm or less, 0.43 mm or less, 0.42 mm or less, 0.40 mm or less, 0.38 mm or less, 0.35 mm or less, 0.32 mm or less, 0.30 mm or less, 0.28 mm or less, 0.25 mm or less, 0.22 mm or less, 0.20 mm or less, or 0.18 mm or less. The lower limit of the thickness of the magnetic disk 1 is not particularly limited, but is, for example, 0.15 mm.

[0034] The substrate 3 is a circular plate material with an inner hole. The substrate 3 has one main surface 3a and the other main surface 3b, and further has a sidewall surface (not shown) connecting the two main surfaces 3a and 3b. The main surfaces 3a and 3b are a pair of surfaces parallel to each other. The sidewall surfaces are located at the outer peripheral edge and the inner peripheral edge of the substrate 3, respectively.

[0035] The covering layer 5 is a layer that covers both main surfaces 3 a and 3 b and the side wall surfaces of the substrate 3 .

[0036] The magnetic disk 1 has a Young's modulus E [GPa] and a density d [g / cm 3 ], the specific elastic modulus E / d [10 ６ ・m ２ / s ２ ] is preferably 40 or more. It is known that the larger the specific elastic modulus E / d, the less fluttering (flutter vibration) occurs. When the specific elastic modulus E / d of the magnetic disk 1 is 40 or more, fluttering of the magnetic disk 1 when rotated at high speed is significantly suppressed.

[0037] The Young's modulus E of the magnetic disk 1 can be measured based on Japanese Industrial Standard JIS R1602-1995. A test specimen can be cut from the magnetic disk 1 as a rectangular parallelepiped having a length of 50 mm, a width of 10 mm, and a thickness equal to the thickness of the magnetic disk 1, and can be measured at room temperature. The density d of the magnetic disk 1 is calculated as d = {(d1 x t) + (d2 x 2T)} / (t + 2T), where d1 is the density of the substrate 3, t is the thickness of the substrate 3, d2 is the density of the coating layer 5, and T is the thickness of the coating layer 5. The magnetic disk 1 includes a metal film including a magnetic layer (magnetic recording layer). However, since the film thickness of the metal film is approximately 100 nm or less, the metal film can be ignored in the thickness of the magnetic disk 1 and can be ignored in the characteristics of the magnetic disk 1, such as the specific elastic modulus E / d, the maximum amplitude, and the product F·D, which will be described later.

[0038] The specific elastic modulus of the magnetic disk E / d [×10 6 m 2 / s 2 ] is preferably 25.0 or more, 27.0 or more, 28.0 or more, 37.5 or more, 38.2 or more, 38.5 or more, 39.0 or more, more preferably 40.0 or more, 41.0 or more, 45.0 or more, 65.0 or more. Furthermore, the lower limit of the specific elastic modulus E / d is not particularly limited, but is, for example, 20.0. From the viewpoint of increasing the specific elastic modulus E / d, the Young's modulus E of the magnetic disk 1 is preferably 75.0 GPa or more, more preferably 78.0 GPa or more, 80 GPa or more, 86 GPa or more, 96.0 GPa or more, 101.0 GPa or more, 106.0 GPa or more, 110.0 GPa or more, 115.0 GPa or more, 120.0 GPa or more. On the other hand, even if the Young's modulus is high, if the density is high, the weight of the magnetic disk 1 itself may cause large vibrations. Therefore, the density d of the magnetic disk 1 is 4.5 g / cm when the substrate 3 is made of ceramic. 3 Below, 4.0g / cm 3 Further, 4.2 g / cm 3 Below, 4.0g / cm 3 When the substrate 3 is made of an aluminum alloy, the density is preferably 2.90 g / cm 3 Below 2.65g / cm 3 Further, 2.86 g / cm3 Below 2.80g / cm 3 When the substrate 3 is made of glass, the density is preferably 2.65 g / cm 3 Below, 2.45g / cm 3 Further, 2.60 g / cm 3 Below, 2.50g / cm 3 It is preferable that this is equal to or greater than this.

[0039] In the first embodiment, when a 30 G impact is applied to the magnetic disk 1 in the direction normal to the main surface of the magnetic disk 1 while the inner peripheral edge of the magnetic disk 1 is fixed, the maximum amplitude of vibration in the thickness direction of the outer peripheral edge of the magnetic disk 1 is 0.25 mm or less. Unlike steady-state flutter vibrations that occur in a steady rotation state due to the rotating magnetic disk and the air flow around it, vibrations caused by external impacts decay over time. It has been known that particle generation in HDDs can be suppressed by reducing the maximum amplitude when a large impact is applied to the magnetic disk. Particles are generated when the magnetic disk comes into contact with a ramp in the HDD, adjacent magnetic disks, or even the ceiling surface of a magnetic disk container due to vibrations that displace the magnetic disk in the out-of-plane direction of the main surface, resulting in chipping of the magnetic disk at the contacted portion. However, it has been found that magnetic disks with thicknesses of 0.51 mm or less experience large amplitudes even when subjected to small impacts, resulting in contact with other components, such as the ramp inside the HDD, making it impossible to suppress particle generation. Therefore, in the magnetic disk 1 of the first embodiment, the maximum amplitude when subjected to a 30 G impact is limited to 0.25 mm or less. A magnetic disk 1 of the first embodiment having a specific elastic modulus E / d of 40 or more and a maximum amplitude of 0.25 mm or less can be obtained, for example, by adjusting the materials and thicknesses of the substrate 3 and the coating layer 5. The maximum amplitude is preferably 0.30 mm or less when a 50 G impact is applied to the magnetic disk 1 for 2 ms in the normal direction of the main surface of the magnetic disk 1 with the inner peripheral edge of the magnetic disk 1 fixed. The small amplitude when subjected to small impacts, as well as the small amplitude when subjected to larger impacts, effectively suppresses particle generation from various external impacts.

[0040] The impact test can be performed, for example, using an AVEX-SM-110-MP testing machine manufactured by Air Brown Co., Ltd. The maximum amplitude is preferably measured using a magnetic disk 1 having a diameter of 95 mm or 97 mm. The inner peripheral edge portion of the magnetic disk 1 that is fixed during the impact test preferably corresponds to the area inside a circle having a diameter of 25 mm (a region with a radius of 12.5 mm from the center of the magnetic disk 1). This inner peripheral edge portion is approximately the same size as the inner peripheral edge portion that is fixed when a magnetic disk 1 having a diameter of 95 mm or 97 mm is installed in a HDD device.

[0041] According to the first embodiment of the magnetic disk 1, the specific elastic modulus E / d is 40 or more, and the maximum amplitude when an impact test is conducted at 30 [G] is 0.25 mm or less, thereby suppressing fluttering and suppressing the generation of particles within the HDD.

[0042] (Second Form) The magnetic disk 1 of the second form is a magnetic disk in which, instead of the specific elastic modulus E / d being within the above range, the product F·D described below is within a predetermined range, and except for this point, is configured in the same way as the magnetic disk 1 of the first form.

[0043] In the magnetic disk 1 of the second embodiment, the product F·D of the fluttering characteristic F [nm], which is expressed as the sum of the flutter vibration amounts of the magnetic disk 1 at 1000 to 4000 Hz (Root of Sum of Squares) RSS, and the thickness D [mm] of the magnetic disk 1, is 47.0 or less. Specifically, the fluttering characteristic F is the sum of the vibration amounts when the frequency is changed within the range of 1000 Hz to 4000 Hz, and is the square root of the integrated value of the square of the amplitude of the flutter vibration. The RSS in the range of 1000 Hz to 4000 Hz can be calculated, for example, by dividing ρ by the density [g / cm] of the magnetic disk 1 at room temperature. ３ ], Q is the Q value of the magnetic disk 1 at room temperature at 3000 Hz, E is the Young's modulus [GPa] of the magnetic disk 1 at room temperature, and ν is the Poisson's ratio of the magnetic disk 1 at room temperature, and 2 ρ(1-ν) of the magnetic disk 1 ２ ・Q / E is 25 [g / cm ３ / GPa], the amplitude at the outer peripheral edge of the magnetic disk 1 can be reduced (for example, to less than 80 nm) (see JP2020 / 032146A). ２ The amplitude is proportional to / E / ξ (ξ is the damping ratio of the magnetic disk 1), and the damping ratio ξ is expressed as 1 / (2·Q) (Q is the Q value), so the amplitude is 2·ρ·(1−ν) ２ ・Proportional to Q / E.

[0044] The Q value (Quality Factor) is the vibration energy stored in the vibrating magnetic disk 1 during one cycle divided by the energy dissipated from the vibrating magnetic disk 1; the smaller this value, the greater the vibration damping. For example, the Q value at 3000 Hz can be obtained as follows. First, a laser Doppler vibrometer (LDV) is used to generate vibrations in the magnetic disk 1 rotated by a spin stand, and a laser is applied to the approximate outer periphery of the magnetic disk 1 to measure the vibration. The obtained data is then appropriately Fourier transformed to obtain a frequency response function (horizontal axis: frequency (unit: Hz), vertical axis: NRRO (Non Repeatable Runout) Amplitude (unit: nm)). Next, for each peak observed in the frequency response function, the Q value (= f0 / (f2-f1)) is calculated using the half-width method (a calculation method using frequencies f1 and f2 (> f1) corresponding to a value 3 dB lower than the NRRO peak value and the frequency f0 (resonance frequency) corresponding to that peak value). The obtained measurement results are plotted on an XY plane with the horizontal axis being frequency and the vertical axis being Q value, and a linear approximation is performed using the least squares method to obtain an approximate straight line. The Q value at 3000 Hz can be obtained on the obtained approximate straight line, or by extrapolating the approximate straight line as necessary. The magnetic disk 1 used for evaluation using the laser Doppler vibrometer has an outer diameter of 95 to 97 mm, an inner diameter of 25 mm, and a thickness of 0.51 mm or less. The magnetic disk rotation speed is 6900 rpm, and the measurement position is a radial position of 46.5 to 47.5 mm from the center of the magnetic disk (1 mm inside from the outer edge), and the measurement is performed at room temperature.

[0045] The impact of flutter vibrations in the frequency band below 1000 Hz has been reduced due to recent advances in head servo technology, while flutter vibrations in the band above 4000 Hz are still small to begin with. Therefore, it has become important to reduce flutter vibrations in the 1000 to 4000 Hz band.

[0046] When the magnetic disk is thick, the magnitude of vibration is significantly affected by the thickness, and vibration due to fluttering is suppressed. However, when the magnetic disk is thin, vibration due to fluttering increases. However, even when the magnetic disk is thin, by controlling the product F·D [nm·mm] of the fluttering characteristic F [nm] and the thickness D [mm] to 47.0 or less, it is possible to prevent scratches or particles due to contact between the magnetic disk and other components, as well as read / write errors on the magnetic disk. According to the inventor's research, the magnitude of fluttering during rotation of a thin magnetic disk can be evaluated using the product F·D [nm·mm] of the fluttering characteristic F [nm] and the thickness D [mm], where D is the thickness of the magnetic disk. It was found that when the product F·D is 47.0 or less, fluttering of the magnetic disk 1 during high-speed rotation can be significantly suppressed. Therefore, in the magnetic disk 1 of the second embodiment, the product F·D is limited to 47.0 or less. That is, by having the product F·D be 47.0 or less, fluttering of the magnetic disk 1 during high-speed rotation can be significantly suppressed. The fluttering characteristic F is a characteristic that depends on the material and thickness of the substrate 3 and the covering layer 5. Therefore, a magnetic disk 1 having a product F·D of 47.0 or less can be obtained by adjusting the material and thickness of the substrate 3 and the covering layer 5, respectively. When the diameter of the magnetic disk 1 is 95 mm, the fluttering characteristic F of the magnetic disk 1 is preferably 80 nm or less. Since magnetic disks 1 having a diameter of 95 mm or more tend to exhibit significant fluttering, such a small fluttering characteristic F is effective in suppressing fluttering. From the viewpoint of further improving the effect of suppressing fluttering of a magnetic disk 1 having a thickness of 0.51.0 mm or less, the product F·D is preferably 45.0 or less, 43.0 or less, 40.0 or less, further 35.0 or less, 32.0 or less, further 30.0 or less, 24.0 or less, or 20.0 or less.

[0047] According to the second form of magnetic disk 1, the product F·D is 47.0 or less, and the maximum amplitude when an impact test is conducted at 30 [G] is 0.25 mm or less, thereby suppressing fluttering and suppressing the generation of particles within the HDD.

[0048] (Third Form) The magnetic disk 1 of the third form is a magnetic disk in which, instead of the magnetic disk 1 of the first form having the maximum amplitude in the impact test within the above range, the product F·D is 47.0 or less, and the thickness T of the coating layer 5, the thickness t of the substrate 3, and the thickness ratio T / t are within predetermined ranges, and is otherwise configured in the same manner as the magnetic disk 1 of the first form.

[0049] In the magnetic disk 1 of the third embodiment, the ratio T / t of the thickness T [mm] of each of the coating layers 5 on both sides of the substrate 3 to the thickness t [mm] of the substrate 3 in the thickness direction is 0.01 to 0.4, the thickness t of the substrate 3 is 0.49 mm or less, and the thickness T of the coating layer 5 is 0.15 mm or less. By having the ratio T / t of 0.4 or less, even if the thickness of the magnetic disk 1 is limited, the thickness T of the coating layer 5 does not become excessively thick, and the thickness t of the substrate 3 is ensured. This ensures the rigidity of the magnetic disk 1 and contributes to suppressing fluttering. On the other hand, by having the ratio T / t of 0.01 or more, the thickness T of the coating layer 5 does not become excessively thin, thereby suppressing deterioration of the flatness of the magnetic disk 1. According to the inventor's investigations, when manufacturing the magnetic disk 1, if the thickness T of the coating layer 5 is excessively thin, the coating layer 5 may locally peel off from the substrate 3 during heat treatment of the metal film provided on the surface of the coating layer 5, resulting in a deterioration in the flatness of the magnetic disk 1. By setting the thickness t of the substrate 3 to 0.49 mm or less, it becomes easier to ensure the thickness T of the coating layer 5 while keeping the thickness of the magnetic disk 1 to 0.51 mm or less. If the thickness T of the coating layer 5 is too thin, the flatness of the magnetic disk 1 may deteriorate, as described above. Furthermore, by setting the thickness T of the coating layer 5 to 0.15 mm or less, it becomes easier to ensure the thickness t of the substrate 3 while keeping the thickness of the magnetic disk 1 to 0.51 mm or less. If the thickness t of the substrate 3 is too thin, it becomes difficult to ensure the rigidity of the magnetic disk 1, as described above, and to suppress fluttering. That is, by having the ratio T / t, thickness t, and thickness T of the magnetic disk 1 within the above ranges, it is possible to suppress fluttering of the magnetic disk 1 while suppressing deterioration of the surface properties of the magnetic disk 1. From the viewpoint of effectively exerting the above effects, it is preferable that the Young's modulus of the substrate 3 is higher than the Young's modulus of the coating layer 5.

[0050] The ratio T / t is preferably 0.01 to 0.4, 0.01 to 0.3, and more preferably 0.085 to 0.3. The thickness t of the substrate 3 is preferably 0.49 mm or less, more preferably 0.43 mm or less, and even more preferably 0.38 mm or less. The thickness T of the coating layer 5 is preferably 0.025 mm or less, more preferably 0.01 mm or less, and even more preferably 0.006 mm or less.

[0051] The flatness of the magnetic disk 1 (flatness as defined in JIS B0621-1984) is 15 μm or less, preferably 10 μm or less. A magnetic disk 1 having such flatness has the effect of further reducing fluttering when rotated at high speed. The flatness can be measured, for example, using an interferometric flatness measuring device and a phase measurement interferometry (phase shift method) at a predetermined measurement wavelength (for example, 680 nm). The thickness deviation of the magnetic disk 1 (the difference between the maximum thickness and the minimum thickness) is 15 μm or less, preferably 10 μm or less.

[0052] According to the third form of magnetic disk 1, the ratio T / t is 0.01 to 0.4, the thickness t is 0.43 mm or less, the thickness T is 0.1 mm or less, the product F·D is 47.0 or less, and the specific elastic modulus E / d is 40 or more, thereby suppressing fluttering while achieving both suppression of fluttering of the magnetic disk 1 and good surface properties.

[0053] (Fourth embodiment) The magnetic disk 1 of the fourth embodiment does not require the specific elastic modulus E / d to be within the above range, and is otherwise configured in the same manner as the magnetic disk 1 of the third embodiment.

[0054] According to the fourth form of magnetic disk 1, the ratio T / t is 0.01 to 0.4, the thickness t is 0.43 mm or less, the thickness T is 0.1 mm or less, and the product F·D is 47.0 or less, thereby suppressing fluttering while achieving both suppression of fluttering of the magnetic disk 1 and good surface properties.

[0055] Each of the magnetic disks 1 of the first to fourth embodiments preferably has the following additional configuration. The magnetic disks 1 of the first and second embodiments preferably have the ratio T / t, the thickness t of the substrate 3, and the thickness T of the coating layer 5 configured similarly to the magnetic disks 1 of the third and fourth embodiments. This provides the effect of suppressing fluttering of the magnetic disk 1 while maintaining good surface properties. The magnetic disk 1 of the first embodiment preferably has the product F·D similar to the magnetic disks 1 of the second, third, and fourth embodiments. This enhances the effect of suppressing fluttering. The magnetic disks 1 of the second and fourth embodiments preferably have the specific elastic modulus E / d similar to the magnetic disks 1 of the first and third embodiments. This enhances the effect of suppressing fluttering. The magnetic disks 1 of the third and fourth embodiments preferably have the maximum amplitude when an impact is applied similarly to the magnetic disks 1 of the first and second embodiments. This provides the effect of suppressing particle generation in the HDD.

[0056] As described above, the magnetic disk 1 includes a metal film. The metal film includes, for example, at least an adhesive layer, an underlayer, a magnetic layer (magnetic recording layer), a protective layer, and a lubricating layer, which are stacked on the main surface of the covering layer 5 in this order from the side closest to the main surface. Of these, the adhesive layer, underlayer, and magnetic layer are sequentially deposited on the main surface of the covering layer 5 by DC (Direct Current) magnetron sputtering in an Ar atmosphere, for example, by introducing a laminated substrate having the main surface of the covering layer 5 as its main surface into a vacuum-drawn film-forming apparatus. For example, CrTi can be used as the adhesive layer, and a material containing Ru or MgO can be used as the underlayer. A soft magnetic layer or a heat sink layer may be added as appropriate. After the above-described film formation, a protective layer is formed using C2H4 by, for example, CVD (Chemical Vapor Deposition), and then a nitriding process is performed in the same chamber to introduce nitrogen into the surface. After that, for example, PFPE (polyfluoropolyether) is applied to the protective layer by dip coating to form a lubricating layer. In this manner, the magnetic disk 1 can be manufactured.

[0057] To achieve even higher recording densities on the magnetic disk 1, the magnetic recording layer preferably contains a magnetic material with high magnetic anisotropy energy. From this perspective, preferred magnetic materials include Fe—Pt-based magnetic materials or Co—Pt-based magnetic materials. Here, "based" means "contained." That is, the magnetic disk 1 preferably has a magnetic recording layer containing Fe and Pt, or Co and Pt, as the magnetic recording layer. For magnetic recording layers containing such magnetic materials and methods for forming such layers, see paragraph 0074 of WO 2011 / 019010 A1 and the Examples therein. Furthermore, a magnetic disk 1 having such a magnetic recording layer is preferably applied to a magnetic recording device using a recording method known as energy-assisted magnetic recording (EAMR). Among energy-assisted recording methods, a recording method that assisted magnetization reversal by irradiation with near-field light or the like is called thermally-assisted magnetic recording (HAMR), and a recording method that assisted magnetization reversal by microwaves is called microwave-assisted magnetic recording (MAMR). For details thereof, see paragraph 0075 of WO2011 / 019010A1. Note that a conventional CoPtCr-based material may be used as the magnetic material for forming the magnetic recording layer.

[0058] The substrate 3 and covering layer 5 of the magnetic disk 1 of the first embodiment are preferably made of a material that provides a specific elastic modulus E / d of 40 or more and a maximum amplitude of 0.25 mm or less when an impact test is performed at 30 G. The substrate 3 and covering layer 5 of the magnetic disk 1 of the second embodiment are preferably made of a material that provides a product F·D of 47.0 or less and a maximum amplitude of 0.25 mm or less when an impact test is performed at 30 G. The substrate 3 and covering layer 5 of the magnetic disk 1 of the third embodiment are preferably made of a material that provides a specific elastic modulus E / d of 40 or more and a product F·D of 47.0 or less. The substrate 3 and covering layer 5 of the magnetic disk 1 of the fourth embodiment are preferably made of a material that provides a product F·D of 47.0 or less.

[0059] The material of the substrate 3 is preferably any one of ceramic, aluminum alloy, and glass, because it is easy to make the specific elastic modulus E / d of the magnetic disk 1 40 or more. The ceramic material is silicon carbide (SiC), sapphire (Al ２ O ３ ), alumina (Al ２ O ３ ), aluminum nitride (AlN), silicon nitride (Si ３ N ４ ), titanium carbide (TiC), or titanium nitride (TiN) is preferred, and among these, silicon carbide (SiC), sapphire (Al ２ O ３ ), alumina (Al ２ O ３ The aluminum alloy material is preferably an aluminum alloy containing Si in the range of 3.0 to 40.0 mass % or an aluminum alloy containing Fe in the range of 0.1 to 5.0 mass % and having high rigidity with a Young's modulus E [GPa] of 75 or more. The glass material is preferably silica (SiO ２ silica-based glass containing aluminum oxide component (Al) at high purity (for example, 90 mass % or more); ２ O ３ Preferably, the glass has high rigidity with a Young's modulus E [GPa] of 80 or more, such as aluminosilicate glass or crystallized glass containing 20 mass % or more of hydroxybenzoate.

[0060] The coating layer 5 is preferably made of glass or a nickel alloy. Glass materials are preferred because the surface properties can be easily adjusted by grinding or polishing. Examples of glass materials include aluminosilicate glass, soda-lime glass, soda-aluminosilicate glass, aluminoborosilicate glass, borosilicate glass, and polysilazane SiO ２and the like are preferably used. From the viewpoint of ensuring heat resistance when the magnetic layer is subjected to heat treatment, the glass material preferably has a glass transition point (Tg) of 750°C or higher, more preferably 770°C or higher. Nickel alloys are preferred materials because they can compensate for the rigidity of the substrate 3 and increase the rigidity of the magnetic disk 1. Nickel phosphorus (NiP) alloys are preferably used as the nickel alloy, and furthermore, in order to prevent magnetization due to heating during magnetic disk manufacturing, a NiWP-based plating coating layer containing tungsten (W) in the range of 10 to 30 mass % or a NiPMo-based plating coating layer containing molybdenum (Mo) in the range of 0.1 to 10 mass % is preferably used.

[0061] Preferred combinations of materials for the substrate 3 and the coating layer 5 include, for example, a ceramic such as alumina (substrate) and glass or a nickel alloy (coating layer), a high-rigidity aluminum alloy (substrate) and glass or a nickel alloy (coating layer), and a high-rigidity glass (substrate) and glass or a nickel alloy (coating layer). Here, the high-rigidity aluminum alloy and high-rigidity glass refer to aluminum alloys or glass that provide a magnetic disk 1 with a specific elastic modulus E / d of 40 or more, or a magnetic disk 1 with a thickness of 0.51 mm or less, in which an impact test is performed at 30 G and the maximum amplitude of the magnetic disk 1 is 0.25 mm or less, preferably 0.30 mm or less, in which an impact test is performed at 50 G. As described above, the high-rigidity aluminum alloy material is preferably an aluminum alloy containing 3.0 to 40.0 mass % of Si or 0.1 to 5.0 mass % of Fe, which has high rigidity and a Young's modulus E [GPa] of 75 or more. The highly rigid glass material is silica (SiO ２ silica-based glass containing aluminum oxide component (Al) at high purity (for example, 90 mass % or more); ２ O ３ Preferably, the glass has a Young's modulus E [GPa] of 80 or more and high rigidity, such as aluminosilicate glass, crystallized glass, or single crystal glass containing 20 mass % or more of the above-mentioned crystalline glass.

[0062] On the other hand, if an aluminum alloy other than a high-rigidity aluminum alloy or a glass other than a high-rigidity glass is used as the substrate material, even when combined with a coating layer, the desired impact resistance and fluttering characteristics cannot be obtained if the thickness of the magnetic disk 1 is 0.51 mm or less.

[0063] Each of the magnetic disks 1 of the first to fourth embodiments preferably further comprises the following configuration.

[0064] The thickness D [mm] and the specific elastic modulus E / d [×10 6 m 2 / s 2 ] and Qa, which is the Q value of the magnetic disk 1 at 3000 Hz measured at 25°C, preferably satisfy the following formula 1: 65.0<(Qa×E / d) / 1000×D<270.0 (Formula 1) According to the study by the present inventors, it has been found that when the magnetic disk 1 has a small specific elastic modulus E / d, if formula 1 is satisfied, the product F·D is likely to become small. For example, when the specific elastic modulus E / d is 75[×10 6 m 2 / s 2 ], satisfying formula 1 is preferable because the product F·D is likely to be 40.0 or less. A magnetic disk 1 with a small product F·D is preferable because it further improves the effect of suppressing fluttering in a magnetic disk 1 with a thickness of 0.51 mm or less. By satisfying formula 1, a thin magnetic disk 1 with suppressed fluttering can be obtained, even for a magnetic disk 1 with relatively low rigidity and a large maximum amplitude.

[0065] On the other hand, the thickness D [mm] and the specific elastic modulus E / d [×10 6 m 2 / s 2 ] and Qa, which is the Q value of the magnetic disk 1 at 3000 Hz measured at 25°C, preferably satisfy the following formula 2: 150<(Qa×E / d) / 1000×D<700 (Formula 2) According to the study by the present inventors, it has been found that when the magnetic disk 1 has a large specific elastic modulus E / d, if formula 2 is satisfied, the product F·D tends to become small. For example, when the specific elastic modulus E / d is 75[×106 m 2 / s 2 ] or more, satisfying Expression 2 makes it easier for the product F·D to be 40.0 or less, which is preferable. A magnetic disk 1 with a small product F·D is preferable in that it further improves the effect of suppressing fluttering in a magnetic disk 1 with a plate thickness of 0.51 mm or less.

[0066] FIG. 3 is a backscattered electron (BSE) image showing a cross section of the coating layer 5. As shown in FIG. 3, the coating layer 5 is preferably made of glass and further contains a crystalline phase 5c in an interface layer region Ta located at a depth of at least 5% of the thickness T of the coating layer 5 in the thickness direction (vertical direction in FIG. 3 ) from the interface 5a with the substrate 3 (the surface in contact with the main surface 3a of the substrate 3). The crystalline phase 5c is the whitish portion of the coating layer 5 near the interface 5a of the coating layer 5 in FIG. 3 (see the area surrounded by a rectangle in FIG. 3 ). The inventors' studies have found that the inclusion of the crystalline phase 5c in the interface layer region Ta firmly bonds the coating layer 5 to the substrate 3 and makes it less likely to peel off from the substrate 3. By including such a coating layer 5 in the magnetic disk 1, local peeling of the coating layer 5 during heat treatment of the magnetic layer can be suppressed, thereby suppressing deterioration of the flatness of the magnetic disk 1.

[0067] In this case, as shown in FIG. 3 , in the cross section of the interface layer region Ta in the sheet thickness direction, the crystalline phase 5c is preferably present in a region of a total length of 50% or more per unit length in the extension direction of the coating layer 5 (the left-right direction in FIG. 3 ), which is perpendicular to the sheet thickness direction. The high density of the crystalline phase 5c near the interface 5a enhances the effect of suppressing peeling of the coating layer 5 from the substrate 3. The total region where the crystalline phase 5c is present is preferably 70% or more, more preferably 90% or more, per unit length. To obtain the interface layer region Ta containing such a high density of crystalline phase, for example, it is preferable to apply the glass that will become the coating layer 5 to the surface of the substrate 3 and then hold it at a predetermined temperature (e.g., 700 to 1200°C) for a predetermined time (e.g., 30 to 120 minutes).

[0068] The coating layer 5 is preferably made of glass, and further, the surface region Tb, located at a depth of at least 5% of the thickness T of the coating layer 5 in the thickness direction (vertical direction in FIG. 3 ) from the surface 5b (main surface of the coating layer 5) opposite the interface 5a with the substrate 3, is preferably free of crystalline phase 5c. Glass having crystalline phase 5c is harder and more difficult to grind than glass having an amorphous phase (the dark portion of the coating layer 5 surrounding the crystalline phase 5c in FIG. 3 ). Therefore, grinding or polishing the coating layer 5 formed on the main surface of the substrate 3 may result in an uneven surface texture, potentially worsening the surface texture of the magnetic disk 1. To obtain such a surface region Tb that does not contain or has little crystalline phase, it is preferable, for example, to apply the glass that will become the coating layer 5 to the surface of the substrate 3, hold it at a predetermined temperature for a predetermined time, and then rapidly cool it (e.g., 10 to 30°C / min). The term "small amount of crystalline phase" means that the area where the crystalline phase exists is, for example, a total area of ​​10% or less per unit length in the extending direction of the coating layer 5.

[0069] The arithmetic mean roughness Ra (JIS B0601:2001) of the main surfaces 3a, 3b of the substrate 3 is preferably 0.01 to 0.75 μm, and more preferably 0.05 to 0.5 μm. The main surfaces 3a, 3b of the substrate 3 having such an arithmetic mean roughness Ra have relatively large irregularities, and the portions of the coating layer 5 in contact with the substrate 3 penetrate into the recesses, thereby providing an anchor effect that firmly bonds the coating layer 5 to the substrate 3. This improves the effect of preventing the coating layer 5 from peeling off from the substrate 3. The present inventors have confirmed that, in particular, in the interface layer region Ta of the coating layer 5 made of glass, crystal growth is likely to occur starting from the portions in contact with the irregularities of the main surfaces 3a, 3b of the substrate 3. Therefore, when the arithmetic mean roughness Ra of the main surfaces 3a, 3b of the substrate 3 is within the above range, a large amount of crystalline phase 5c can be formed in the interface layer region Ta of the coating layer 5, and the coating layer 5 can be more firmly bonded to the substrate 3.

[0070] Although the surface of the substrate 3 is covered with the coating layer 5, a cross-sectional image of the main surfaces 3a and 3b of the substrate 3 can be obtained, and the arithmetic mean roughness Ra can be determined. Specifically, the main surfaces of the magnetic disk 1 are first cut using an ion polishing method along a plane passing through the center of the magnetic disk 1 and perpendicular to the main surfaces, to create a sample in which the main surfaces 3a and 3b of the substrate 3 are exposed. A cross-sectional image of this cross section is obtained at a magnification of, for example, 5000 times using a scanning electron microscope (SEM). From this image, the concave-convex curves of the main surfaces 3a and 3b of the substrate 3 that form the interface of the substrate 3 with the coating layer 5 are obtained, for example, by binarizing the cross-sectional image or visually tracing it, and a 20 μm-wide region at any location on the concave-convex curve is extracted to determine the arithmetic mean roughness Ra.

[0071] The difference between the maximum and minimum values ​​of the distance in the plate thickness direction from the surface 5b (main surface of the coating layer 5) opposite the interface 5a with the substrate 3 of the coating layer 5 to the substrate 3 is preferably 7.5 to 12.5 μm, and more preferably 8.5 to 11.5 μm. Such a magnetic disk 1 has large irregularities on the main surfaces 3a, 3b of the substrate 3, which enhances the anchoring effect of the coating layer 5 to the substrate 3 and enhances the effect of suppressing peeling of the coating layer 5 from the substrate 3. The distance between the main surfaces of the coating layer 5 and the substrate 3 can be determined by obtaining the irregularity curves of the main surfaces of the substrate 3 and the coating layer 5 according to the above-described method for determining the arithmetic mean roughness Ra of the main surfaces 3a, 3b of the substrate 3, and then extracting, for example, a 20 μm-wide region at any location on the irregularity curve.

[0072] FIG. 4 shows a cross section of the laminated substrate. As shown in FIG. 4 , in a cross-sectional image of the laminated substrate photographed using a scanning electron microscope (SEM) at a magnification of, for example, 200 to 500 times, the main surfaces 3a and 3b of the substrate 3 preferably have portions in which concaves and convexes alternately appear in a waviness curve obtained from a cross-sectional curve showing the cross-sectional shape of the substrate 3 in the thickness direction (vertical direction in FIG. 4 ) passing through the center of the main surfaces 3a and 3b. In this case, the length P of the repeating unit of the concaves and convexes in the extending direction of the coating layer 5 (horizontal direction in FIG. 4 ), which is perpendicular to the thickness direction, is preferably 100 to 150 μm (in FIG. 4 , the length of the corresponding main surface 3a of the substrate 3 is indicated by P). According to the inventor's studies, it has been confirmed that a length P of the repeating unit of the concaves and convexes of 100 to 150 μm enhances the effect of firmly bonding the coating layer 5 to the substrate 3. The scale bar added to the bottom of the micrograph in FIG. 4 indicates a length of 100 μm. The waviness curve can be calculated from the profile curve obtained by measuring the surface texture of the main surfaces 3a and 3b of the substrate 3. Specifically, the profile curve is obtained by measuring using a stylus-type measuring device (JIS B0651:2001). Then, in accordance with JIS B0632:2001, predetermined cutoff values ​​(λc and λf) are set, and a phase compensation filter (band-pass filter) that passes only wavelength components between λc and λf is applied to the profile curve to calculate a waviness curve consisting of wavelength components between λc and λf. The length of the repeating unit of the irregularities is, for example, the average length P of the irregularities that appear within the range of the measurement length (the wavelength of the waviness curve).

[0073] The thickness T2 of the coating layer 5 on the sidewall surface of the substrate 3 is preferably thicker than the thickness T1 of the coating layer 5 on the main surfaces 3a and 3b of the substrate 3. By making the thickness T2 of the coating layer 5 on the sidewall surface of the substrate 3 thick, the substrate 3 can be reliably covered by the coating layer 5 on the sidewall surface of the magnetic disk 1, preventing the substrate 3 from being exposed. When a chamfered surface is formed on the outer peripheral edge of the magnetic disk 1, the maximum amplitude when an impact test is performed at 30 G is 0.25 mm or less, thereby improving the effect of suppressing particle generation within the HDD. The chamfered surface is a surface formed on both ends of the sidewall surface of the magnetic disk 1, which connects to both main surfaces of the magnetic disk 1, and extends in a direction inclined relative to the plate thickness direction. Note that the thickness T2 of the coating layer 5 on the sidewall surface of the substrate 3 refers to the maximum thickness when there is a thickness distribution in the plate thickness direction. The ratio T2 / T1 of the thickness T2 to the thickness T1 of the coating layer 5 is preferably 1.01 to 1.5, and more preferably 1.05 to 1.15, from the viewpoint of ensuring a chamfered surface while also ensuring the length of the substrate 3 in the main surface direction and maintaining good rigidity of the magnetic disk 1.

[0074] The diameter of the magnetic disk 1 is preferably 95 mm or more (nominal 3.5-inch standard or more). While a magnetic disk 1 with such a large diameter allows a magnetic layer to be provided over a wide area, it contributes to increasing the storage capacity of the HDD device, but it is prone to increased fluttering and read / write problems. Furthermore, the amplitude of vibration of the magnetic disk 1 caused by external impact increases as the outer diameter of the magnetic disk 1 increases, and is less likely to be attenuated. As described above, the magnetic disk 1 of this embodiment suppresses fluttering, thereby increasing storage capacity while suppressing read / write problems in the HDD device. Furthermore, if the maximum amplitude of the magnetic disk 1 when subjected to an impact test at 30 G is 0.25 mm or less, particle generation within the HDD is suppressed, as described above, even if the diameter of the magnetic disk 1 is large. The upper limit of the diameter of the magnetic disk 1 is not particularly limited, but is, for example, 98 mm.

[0075] The diameter of the inner hole of the magnetic disk 1 is, for example, 25 mm or 20 mm, and when the diameter of the magnetic disk 1 is 95 mm or more, the diameter of the inner hole is preferably 25 mm.

[0076] The maximum height Rz (JIS B 0601:2001) of the surface roughness of the main surfaces 3a, 3b of the substrate 3 is preferably 0.1 to 50 μm, and more preferably 5 to 50 μm. The main surfaces 3a, 3b of the substrate 3 having the maximum height Rz in the above range have large localized irregularities, and the portions of the coating layer 5 in contact with the substrate 3 penetrate deeply into the recesses, enhancing the anchor effect that firmly bonds the coating layer 5 to the substrate 3. Furthermore, in the interface layer region Ta of the glass coating layer 5, crystal growth can easily occur starting from the portions in contact with the large irregularities of the substrate 3. The maximum height Rz of the surface roughness of the main surfaces 3 a, 3 b of the substrate 3 can be determined by obtaining a cross-sectional image at a magnification of 5000 times using a scanning electron microscope (SEM) according to the above-mentioned method for determining the arithmetic mean roughness Ra of the main surfaces 3 a, 3 b of the substrate 3, and specifically, drawing an average line at the interface between the substrate 3 and the coating layer 5 from the image, and determining the maximum height Rz as the distance between a line parallel to the average line passing through the highest point at the interface within a range of 20 μm in the longitudinal direction of the interface and a line parallel to the average line passing through the lowest point at the interface.

[0077] (Disk intermediate) Next, a disk intermediate of one embodiment will be described. The disk intermediate of this embodiment is a plate material with a thickness of 0.59 mm or less, which serves as a base plate for forming the magnetic disk 1 with a thickness of 0.51 mm or less as described above. The magnetic disk 1 is produced, for example, by polishing the main surfaces of the disk intermediate and then forming a metal film including a magnetic layer. The disk intermediate includes a substrate and a covering layer. The substrate is a plate having one main surface and the other main surface, and further having sidewall surfaces connecting the two main surfaces. The substrate is configured in the same manner as the substrate 3 of the magnetic disk 1. The covering layer is a layer that covers both main surfaces and the sidewall surfaces of the substrate. The covering layer is configured in the same manner as the covering layer 5 of the magnetic disk 1, except for its thickness and surface properties. With respect to the thickness in the thickness direction of the disk intermediate, the ratio T / t of the thickness T [mm] of each coating layer to the thickness t [mm] of the substrate is 0.1 to 0.75, the thickness t of the substrate is 0.43 mm or less, and the thickness T of the coating layer is 0.15 mm or less. By having the ratio T / t, thickness t, and thickness T of the disk intermediate within the above ranges, it is possible to suppress fluttering of the magnetic disk 1 produced from the disk intermediate, while suppressing deterioration of the surface properties of the magnetic disk 1. The disk intermediate has a Young's modulus E [GPa] and a density d [g / cm 3 ], the specific elastic modulus E / d [× 10 6 m 2 / s 2 ] is 40 or more. When the specific elastic modulus E / d is 40 or more, fluttering during high speed rotation is significantly suppressed in the magnetic disk 1 produced from the disk intermediate.

[0078] (Substrate for Information Recording Medium) Next, an embodiment of a substrate for an information recording medium will be described. The substrate for an information recording medium of this embodiment (hereinafter referred to as a magnetic disk substrate or substrate) is the substrate 3 described above used for the magnetic disk 1 described above, and is a substrate made of one of ceramic, aluminum alloy, and glass. The ceramic, aluminum alloy, and glass are the same as the ceramic, aluminum alloy, and glass described above. A magnetic disk 1 produced using such a substrate 3 can achieve the effects of the magnetic disk 1 described above.

[0079] (Method of Manufacturing Magnetic Disk, Disk Intermediate, and Substrate) The magnetic disk 1, disk intermediate, and substrate 3 described above can be manufactured, for example, by performing the following processes. First, a base material for the substrate 3, which will serve as the base plate for the substrate 3, is manufactured. Then, the base material for the substrate 3 is shaped. Next, a coating layer 5 is formed on the surface of the base material for the substrate 3, and a laminated substrate is obtained by laminating the coating layer 5 on the substrate 3. Then, the laminated substrate is subjected to polishing of the edge surfaces, grinding of the main surfaces, first polishing of the main surfaces, and second polishing of the main surfaces. The disk intermediate described above is a state after the coating layer has been formed (a laminated substrate), and may be one in which polishing of the edge surfaces and grinding or polishing of the main surfaces have been performed. Note that the above processes do not always need to be performed, and the order of the above processes may be changed as appropriate, or may be omitted as appropriate. For example, among the above, the edge surface polishing and the second polishing of the main surfaces may not be performed. After the last process performed, a metal film including a magnetic layer is formed on the main surface of the laminated substrate. Each process will be described below.

[0080] (a) Preparation of Substrate Base Material The substrate base material 3 is preferably prepared by slicing a workpiece, which is a cylindrical block of ceramic, aluminum alloy, or glass. Slicing a block of substrate material allows efficient production of multiple thin substrate base materials 3. Furthermore, by adjusting the cutting blade used to slice the workpiece and the cutting time, the main surfaces of the sliced ​​substrate base material 3 can be adjusted to the desired surface texture, thereby obtaining the ranges of arithmetic mean roughness Ra and maximum height Rz described above for the substrate 3 of the magnetic disk 1. Furthermore, the waviness curve obtained for the substrate 3 allows the range of the length of the repeating unit of the irregularities described above to be obtained. In the magnetic disk 1, the surface of the substrate 3 is coated with a coating layer 5, and the surface texture of the magnetic disk 1 can be adjusted by grinding or polishing the coating layer 5. This eliminates the need to grind or polish the main surfaces of the substrate base material 3, thereby improving the productivity of the magnetic disk 1. The substrate base material 3 may be prepared by other methods, such as press molding, instead of the slicing method.

[0081] (b) Shape Processing Next, shape processing is performed. In the shape processing, first, a base material for the substrate 3 is prepared, and then a circular hole and an outer periphery are formed using a known processing method to obtain a disk-shaped substrate 3 with a circular hole. Then, the edge surfaces of the substrate 3 are chamfered. As a result, a side wall surface including a chamfered surface that is connected to the main surfaces 3a and 3b and inclined in the thickness direction is formed on the edge surface of the substrate 3. In the chamfering process, the side wall surface including the chamfered surface may be formed by grinding the edge surface of the substrate 3 using a forming grindstone. Note that shape processing may also be performed on a block of substrate material before slicing. In other words, the base material for the substrate 3 may be prepared using a block of shaped substrate material. In this case, shape processing after preparing the base material for the substrate 3 is omitted.

[0082] (c) Formation of Coating Layer Next, the coating layer 5 is formed. The glass coating layer 5 is formed, for example, by spraying a glass paste onto the surface of the substrate 3 and firing it. Specifically, the glass paste is sprayed onto the surface of the substrate 3 from a nozzle opening while the nozzle is moved relative to the substrate 3, thereby coating the substrate 3 with the glass paste to a thickness in the range of 10 to 300 μm. After application, the glass paste is heated to a temperature above the glass transition temperature depending on the material used in the glass paste, and then cooled at a predetermined rate, thereby forming the coating layer 5 without residual distortion in the glass. Specifically, the cooling time is set to be longer than the heating time. In this way, the coating layer 5 is formed, and a laminated substrate is produced. The thickness of the applied glass is determined taking into account the allowance for grinding or polishing, and is, for example, 10 to 300 μm, preferably 40 to 150 μm.

[0083] (d) Edge Polishing Next, the edge polishing of the laminated substrate is performed. Edge polishing is a process in which, for example, a polishing liquid containing free abrasive grains is supplied between the polishing brush and the outer and inner edge faces of the laminated substrate, and the polishing brush and the laminated substrate are moved relative to each other. In edge polishing, the inner and outer edge faces of the laminated substrate are polished to a mirror finish.

[0084] (e) Grinding (Rough Grinding, Fine Grinding) In rough grinding, both main surfaces of the laminated substrate are ground. For example, loose abrasive grains are used as the abrasive. In rough grinding, the laminated substrate is ground so as to approximate the target thickness dimension and flatness of the main surfaces. Note that rough grinding is performed depending on the dimensional accuracy or surface roughness of the formed laminated substrate, and may not be performed in some cases. Next, fine grinding is performed on the main surfaces of the laminated substrate. For example, the main surfaces of the laminated substrate are ground using a double-sided grinding device with a planetary gear mechanism. In this case, for example, fixed abrasive grains are provided on a surface plate for grinding. Alternatively, grinding using loose abrasive grains may also be performed. Note that fine grinding may not be performed in some cases.

[0085] (f) First Polishing (Rough Polishing) Next, the main surfaces of the laminate substrate are subjected to the first polishing. The first polishing uses a polishing pad attached to a surface plate with loose abrasive grains. The first polishing removes cracks and distortions remaining on the main surfaces after fine grinding with fixed abrasive grains, for example. The first polishing can reduce the surface roughness of the main surfaces, such as the arithmetic mean roughness Ra, while preventing excessive depression or protrusion of the edge shape of the main surfaces. The loose abrasive grains used in the first polishing are not particularly limited, but examples include cerium oxide abrasive grains or zirconia abrasive grains. Note that the first polishing may not be performed in some cases.

[0086] (g) Second Polishing (Mirror Polishing) Next, the laminated substrate is subjected to second polishing. The second polishing is intended to mirror-polish the main surfaces. The second polishing is performed using a polishing device with the same configuration as the first polishing. In the second polishing, the type and particle size of the free abrasive grains are changed from those in the first polishing, and a softer resin polisher is used as the polishing pad to perform mirror polishing. This reduces the roughness of the main surfaces while preventing excessive depression or protrusion of the edge shape of the main surfaces. The roughness of the main surfaces is preferably 0.2 nm or less in terms of arithmetic mean roughness Ra (JIS B 0601 2001). The laminated substrate is then cleaned.

[0087] Thereafter, an adhesive layer, an underlayer, a magnetic layer (magnetic recording layer), a protective layer, and a lubricating layer are laminated in this order on the main surface of the laminated substrate, and a metal film is formed to manufacture the magnetic disk 1. Then, an HDD including the magnetic disk 1 and a magnetic head is manufactured.

[0088] Here, we will explain a method for manufacturing the magnetic disk 1 when the above-mentioned high-rigidity aluminum alloy material is used as the material for the substrate 3. The high-rigidity aluminum alloy can be, for example, an aluminum alloy containing 3.0 to 40.0 mass% Si or an aluminum alloy containing 0.1 to 5.0 mass% Fe. The nickel alloy film can be, for example, a plating film of a Ni-P (nickel-phosphorus) alloy containing at least phosphorus.

[0089] First, a disk-shaped base material is cut from a high-rigidity aluminum alloy plate, heated for a predetermined temperature and time, and annealed. Subsequently, the main surfaces are machined and the end faces are shaped. In the end face shaping, the end faces are ground or machined to a predetermined shape using a tool such as a forming tool or a single tool. Annealing may be performed after the end face or surface processing. A nickel alloy plating film is then formed on the surface to a thickness of, for example, 3 to 70 μm, to produce a laminated substrate. Here, since the thickness of the plating film is sufficiently small compared to the overall thickness of the laminated substrate, the shape of the end faces formed by grinding or machining remains approximately the same even after the plating film is formed. The surface of the laminated substrate is then polished. From the perspective of achieving both improved surface quality and improved productivity, the polishing process preferably employs two or more polishing steps, similar to the polishing of the laminated substrate described above. The specific polishing method can be substantially the same as the polishing of the laminated substrate described above, except that a polishing solution containing alumina abrasive grains is preferably used in the first polishing (rough polishing).

[0090] (Experiment 1) In order to examine the effect of the magnetic disk 1 of the first embodiment, various magnetic disks with different specifications were fabricated.

[0091] (Magnetic Disk Fabrication) A cylindrical block of substrate material measuring 100 mm in diameter and 30 mm in length was sliced ​​using a cutting blade to prepare a substrate base material. A circular hole with a diameter of 25 mm and an outer periphery with a diameter of 95 mm were formed in the substrate base material to prepare a substrate (Examples 11 to 14, 17, 18, Comparative Examples 11, 12, 15). Of these, except for Example 17, a glass paste was sprayed onto the surface of the substrate and fired to form a coating layer, resulting in a laminated substrate. In Example 17, a NiP film was formed by electroless plating to cover the entire surface of the substrate. Separately, a disk-shaped base material cut from an aluminum alloy plate was annealed, its main surfaces were machined, and its end faces were shaped as described above to prepare a substrate, and a NiP film was formed by electroless plating to cover the entire surface of the substrate (Example 16, Comparative Examples 13 and 14). The laminate substrates of each example and comparative example were subjected to edge polishing, grinding, first polishing, and second polishing. A metal film (thickness 30 nm or less) including a magnetic layer was further formed on the main surface of the obtained laminate substrates of each example and comparative example to produce magnetic disks.

[0092] The compositions or types of materials of the substrate and coating layer shown in the table are as follows: (Substrate) "High-rigidity aluminum alloy 1": Aluminum alloy containing 3.0 to 40.0 mass % of Si "High-rigidity glass 1": SiO ２ Silica-based glass containing 90% by mass or more of the above "High-rigidity glass 2": Crystallized glass "Glass": Aluminosilicate glass "Aluminum alloy": Aluminum alloy containing 3.5% by mass or more of Mg (coating layer) "Glass": Perhydropolysilazane "NiP": Nickel alloy containing at least 3 to 10% by mass of P, the remainder being Ni

[0093] (Specific Elastic Modulus E / d) The specific elastic modulus E / d of the magnetic disk was determined as described above, and if the specific elastic modulus E / d was 40 or more, it was evaluated as having sufficient rigidity and being able to suppress fluttering, and if it was less than 40, it was evaluated as having little effect in suppressing fluttering.

[0094] (Maximum Amplitude) The magnetic disk was attached to an evaluation device equipped with a high-speed camera to determine the maximum amplitude. This evaluation device can apply an external impact (acceleration) of any magnitude and capture the resulting movement (vibration) of the outer edge of the magnetic disk as a video. Then, by analyzing the video, the displacement of the outer edge in the normal direction of the main surface can be measured. Using this evaluation device, an impact test was performed in which a 30 G impact was applied to the magnetic disk for 2 ms in the normal direction of the main surface of the magnetic disk, and the vibration of the outer edge in the normal direction of the main surface was measured. From the waveform data resulting from the measurement, the maximum displacement of the outer edge of the magnetic disk in either direction normal to the center, where the displacement amount was 0, was determined as the maximum amplitude. In the same manner, an impact test was performed with an impact magnitude of 50 G to determine the maximum amplitude.

[0095] Actual HDDs incorporate ramps for the magnetic head ramp load mechanism, which provide a 0.25 mm gap from both main surfaces when each magnetic disk is installed. In other words, the gap between the ramps for the magnetic disk to fit is the thickness of the magnetic disk plus 0.5 mm. Actual HDDs are designed to maintain this gap constant even when the thickness of the magnetic disk changes. On the other hand, the evaluation device does not include such ramps. Therefore, determining whether the vibration of the magnetic disk will cause contact with other components such as the ramp (adjacent magnetic disks, ramps, or HDD containers) in an actual HDD is determined by the maximum amplitude of the magnetic disk's vibration. If the maximum amplitude is 0.25 mm or less, it can be determined that contact with the ramp will not occur. If the maximum amplitude exceeds 0.25 mm, there is a very high possibility of contact with other components. The maximum amplitude was measured for three magnetic disks, and the average of the maximum amplitudes was used. In this evaluation, the magnetic disks were not rotating but were stationary.

[0096] (Quality Evaluation) To evaluate the quality of the manufactured magnetic disks, a commercially available HDD was disassembled. The magnetic disks and spacers of each example and comparative example were attached to a spindle, and a simulated ramp member made of engineering plastic was attached so that it protruded from the surface of the magnetic disk. A gap of 0.25 mm was maintained between the ramp member and the magnetic disk. Then, with the magnetic disk still attached, an impact test was conducted in which a 30 G impact was applied for 2 ms in the normal direction to the main surface of the magnetic disk 1. This test is an accelerated test in which the outer edge of the magnetic disk 1 is deliberately collided with the ramp member several times or more. The particle distribution around the area where the ramp member contacted the magnetic disk surface was then observed. Due to the difficulty of quantifying the results, a relative evaluation was used. Rank 1: Almost no particles; Rank 2: Medium number of particles; Rank 3: Large number of particles. The evaluation results are shown in Table 1 below. The lower the rank value, the better the quality evaluation, with Rank 1 representing the highest evaluation.

[0097]

[0098]

[0099] As can be seen from a comparison of Examples 11 to 14, 16 to 18, and Comparative Examples 11 to 15, even for magnetic disks with a thin plate thickness (here, 0.43 mm or less) to accommodate a large number of magnetic disks in an HDD, the specific elastic modulus E / d is 40 or more, and the maximum amplitude when an impact test is performed at 30 G is 0.25 mm or less, thereby suppressing fluttering and reducing the number of particles. Comparative Example 14 has a plate thickness exceeding 0.51 mm, making it difficult to increase the number of disks mounted in an HDD device and increase storage capacity. Comparative Example 15 has a maximum amplitude exceeding 0.25 mm, so the effect of reducing the number of particles is small. Furthermore, when the impact magnitude was changed from 30 G to 50 G and the above impact test was performed and quality evaluation was performed, Examples 11 to 13 and 16 to 18 were ranked 1, while Example 14 was ranked 2, and Comparative Example 15 was ranked 3.

[0100] (Experiment 2) In order to examine the effect of the magnetic disk 1 of the second embodiment, various magnetic disks with different specifications were fabricated.

[0101] (Magnetic Disk Fabrication) A cylindrical block of substrate material measuring 100 mm in diameter and 30 mm in length was sliced ​​using a cutting blade to prepare a substrate base material. A circular hole with a diameter of 25 mm and an outer periphery with a diameter of 95 mm were formed in the substrate base material to prepare a substrate (Examples 21-24, 27-30, Comparative Example 25). Of these, except for Examples 25 and 27, a glass paste was sprayed onto the surface of the substrate and baked to form a coating layer, resulting in a laminated substrate. In Examples 25 and 27, a NiP film was formed by electroless plating to cover the entire surface of the substrate. The laminated substrates of each Example and Comparative Example were subjected to edge polishing, and grinding, first polishing, and second polishing on the main surfaces. Separately, disk-shaped base materials cut from aluminum alloy plate were annealed, the main surfaces were machined, and the edge surfaces were shaped to prepare substrates (Examples 20, 25, 26, Comparative Example 23) in the same manner as above. Of these, in Example 25 and Comparative Example 23, a NiP film was formed by electroless plating so as to cover the entire surface of the substrate, and in Examples 20 and 26, a coating layer was formed on the surface of the substrate by spraying a glass paste onto the surface of the substrate and baking it, thereby obtaining a laminated substrate. The laminated substrates of each Example and Comparative Example were subjected to edge polishing, and grinding, first polishing, and second polishing on the main surfaces. A metal film (thickness 30 nm or less) including a magnetic layer was further formed on the main surfaces of the laminated substrates of each Example and Comparative Example obtained as described above, to produce magnetic disks.

[0102] The compositions or types of the substrate and coating layer materials shown in the tables are the same as those shown in Tables 1 and 2. Of the substrate materials shown in Tables 3 and 4, "high-rigidity aluminum alloy 2" refers to an aluminum alloy containing at least one of Fe, Mn, and Ni, with the total content of Fe, Mn, and Ni falling within the range of 3.5 to 8.0 mass%.

[0103] (Calculation of Fluttering Characteristics F) Using a laser Doppler vibrometer, the Q value at 0 to 4000 Hz was determined in the manner described above, and the Q value at 3000 Hz was designated as Qa. The sum total of the flutter vibration amounts RSS was calculated using the obtained Q value, as well as the density, Young's modulus, and Poisson's ratio of the magnetic disk 1, which had been calculated in advance, to designate the fluttering characteristics F [nm]. In the evaluation using the laser Doppler vibrometer, the rotation speed of the magnetic disk 1 was 6900 rpm, and the measurement position was a radial position of 46.5 mm from the center of the magnetic disk 1 (1 mm inside from the outer periphery), and the measurement was performed at room temperature (25°C).

[0104] In order to evaluate magnetic disks of different thicknesses, the product F*D was calculated from the obtained fluttering characteristic F and the thickness D of the magnetic disk 1, and if the product F*D was 47.0 or less, it was evaluated as being able to suppress fluttering, and if it exceeded 47.0, it was evaluated as having little effect in suppressing fluttering.

[0105]

[0106]

[0107] As can be seen from a comparison of Examples 20 to 30 with Comparative Examples 23 and 25, even for magnetic disks with a thin plate thickness (here, 0.51 mm or less) to accommodate a large number of magnetic disks in an HDD, the product F·D is 47.0 or less, and the maximum amplitude when an impact test is conducted at 30 G is 0.25 mm or less, thereby suppressing fluttering and reducing the number of particles. Comparative Example 23 has a product F·D greater than 47.0, so the effect of suppressing fluttering is small. Note that if the plate thickness exceeds 0.51 mm, it becomes difficult to increase the number of disks mounted in an HDD device and increase storage capacity. Comparative Example 25 has a maximum amplitude greater than 0.25 mm, so the effect of reducing the number of particles is small. Note that the impact magnitude was changed from 30 G to 50 G, and the above impact test was conducted and quality evaluation was performed. Example 24 and Comparative Example 23 were ranked 2, and Comparative Example 25 was ranked 3.

[0108] The specific elastic modulus E / d of Examples 21 to 24 and Comparative Example 25 was calculated to be 75 [×10 6 m2 / s 2 ] or more. Comparing Examples 21 to 24 with Comparative Example 25, it was found that when the specific elastic modulus E / d of the magnetic disk was large and (Qa·E / d) / (1000D) was 150 to 700, the product F·D was small, 40.0 or less. Furthermore, when the specific elastic modulus E / d of Examples 20, 25 to 30, and Comparative Example 23 was calculated, it was found that all of them were 75 [×10 6 m 2 / s 2 Comparing Examples 20, 25 to 28 with Examples 29, 30, and Comparative Example 23, it was found that when the specific elastic modulus E / d of the magnetic disk was small and (Qa·E / d) / (1000D) was 65.0 to 270.0, the product F·D was small, being 40.0 or less.

[0109] (Experiment 3) In order to examine the effects of the magnetic disks 1 of the third and fourth embodiments, various magnetic disks with different specifications were fabricated.

[0110] (Magnetic Disk Fabrication) A cylindrical block of substrate material measuring 100 mm in diameter and 30 mm in length was sliced ​​using a cutting blade to prepare a substrate base material. A circular hole with a diameter of 25 mm and an outer periphery with a diameter of 95 mm were formed in the substrate base material. A glass paste was sprayed onto the surface of the substrate and fired to form a coating layer, resulting in a laminated substrate (Examples 31, 33, 34, 38, 40, Comparative Examples 32, 37-39). Separately, a disk-shaped base material was cut from an aluminum alloy plate material in the same manner as above, followed by annealing, cutting the main surfaces, and shaping the edge surfaces to prepare a substrate. A NiP film was then formed by electroless plating to cover the entire surface of the substrate (Examples 35, 36, Comparative Examples 33, 34). The laminated substrate or glass substrate in each Example and Comparative Example was subjected to edge polishing, grinding, first polishing, and second polishing. A metal film (thickness of 30 nm or less) including a magnetic layer was further formed on the main surface of the laminate substrate or glass substrate of each of the examples and comparative examples obtained as described above, to prepare a magnetic disk.

[0111] The compositions or types of the substrate and coating layer materials shown in the table are the same as those shown in Tables 1 to 4.

[0112] (Thickness of Coating Layer and Substrate) The thickness T of the coating layer and the thickness t of the substrate were determined as the average thicknesses measured at multiple points within the region of the measurement length using an SEM photograph showing the cross section.

[0113] (Evaluation of Flatness and Product F·D) The flatness of the manufactured magnetic disk was measured using a flatness measuring device. As a result, when the flatness was 15 μm or less, it was evaluated as A, when it was more than 15 μm and 20 μm or less, it was evaluated as B, and when it was more than 20 μm, it was evaluated as C.

[0114] Furthermore, the product F·D of the magnetic disk obtained in the above manner was evaluated as A if it was 40.0 or less, as B if it was over 40.0 and 45.0 or less, and as C if it was over 45.0.

[0115] The above evaluation is performed depending on the magnitude of the specific elastic modulus E / d. Therefore, when the specific elastic modulus E / d is large (75 [×10 6 m 2 / s 2 ] or more), for the magnetic disks shown in Table 5, when the product F·D was rated A or B and the flatness was rated A, it was evaluated that good flatness was obtained while suppressing fluttering. 6 m 2 / s 2 ]), for the magnetic disks shown in Table 6, when the product F·D and the flatness were both rated A, it was evaluated that good flatness was obtained while suppressing fluttering.

[0116]

[0117]

[0118] As can be seen from the comparison between Examples 31, 33, 34, and 40 and Comparative Examples 37 to 39, even if the magnetic disk is thin (here, 0.43 mm or less) in order to store many magnetic disks in an HDD, for magnetic disks with a large specific elastic modulus E / d, if the product F-D is 47.0 or less, the ratio T / t is 0.01 to 0.4, the substrate thickness t is 0.43 mm or less, and the coating layer thickness T is 0.1 mm or less, the product F-D evaluation is A or B, the flatness evaluation is A, and it can be seen that good surface properties can be obtained while suppressing fluttering. On the other hand, Comparative Examples 37 to 39 did not meet the requirements of the product F-D being 47.0 or less, the ratio T / t being 0.01 to 0.4, the substrate thickness t being 0.43 mm or less, and the coating layer thickness T being 0.1 mm or less, and did not achieve the product F-D evaluation of A or B, and the flatness evaluation of A. Therefore, in Comparative Examples 37 to 39, it is not possible to obtain good surface properties while suppressing fluttering. In particular, in Comparative Example 39, the ratio T / t is less than 0.01 and the flatness evaluation is B, so the effect of improving the flatness of the magnetic disk is small. In addition, in Comparative Example 38, the thickness T of the coating layer exceeds 0.1 mm and the product F·D evaluation is C, so the effect of suppressing fluttering is small.

[0119] As can be seen from the comparison between Examples 35, 36, and 38 and Comparative Examples 32 to 34, even if the magnetic disk is thin (here, 0.43 mm or less) in order to store many magnetic disks in an HDD, for magnetic disks with a small specific elastic modulus E / d, when the product F-D is 47.0 or less, the ratio T / t is 0.01 to 0.4, the substrate thickness t is 0.43 mm or less, and the coating layer thickness T is 0.1 mm or less, the product F-D and flatness evaluation are both A, and it can be seen that good surface properties can be obtained while suppressing fluttering. On the other hand, Comparative Examples 32 to 34 did not meet the requirements of the product F-D being 47.0 or less, the ratio T / t being 0.01 to 0.4, the substrate thickness t being 0.43 mm or less, and the coating layer thickness T being 0.1 mm or less, and therefore the product F-D and flatness evaluation were not both A. Therefore, in Comparative Examples 32 to 34, it is not possible to suppress fluttering while obtaining good surface properties. In particular, in Comparative Example 33, the product F·D exceeds 47.0, so the effect of suppressing fluttering is small. In Comparative Example 34, the plate thickness exceeds 0.51 mm, so it is difficult to increase the number of disks mounted on an HDD device and increase storage capacity. In Comparative Example 34, the ratio T / t is less than 0.01 and the flatness rating is B, so the effect of improving the flatness of the magnetic disk is small.

[0120] In addition, a comparison of Examples 35, 36, and 38 with Comparative Examples 32 to 34 reveals that the specific elastic modulus E / d of the magnetic disk is small (75 [×10 6 m 2 / s 2 ]), and when (Qa·E / d) / (1000D) was 65.0 to 270.0, the product F·D was small, being 40.0 or less.

[0121] The above has described in detail the information recording medium disc, disc intermediate, and information recording medium substrate of the present invention, but the present invention is not limited to the above-mentioned embodiments and examples, and various improvements and modifications may be made within the scope of the present invention.

[0122] REFERENCE SIGNS LIST 1 Information recording medium disc 3 Information recording medium substrate 5 Covering layer 5a Main surface of covering layer 5b Interface between covering layer and substrate 5c Crystalline phase

Claims

1. A disk for information recording media with a plate thickness of 0.51 mm or less, A substrate having one main surface and the other main surface, and further having a side wall surface connecting the two main surfaces, The substrate comprises a coating layer that covers both main surfaces and side wall surfaces, The disk has a Young's modulus E [GPa] and a density d [g / cm³]. 3 The specific modulus of elasticity E / d calculated from ] is 40 [×10 6 I understand 2 / s 2 That's all, The thickness D [mm] and specific modulus E / d [×10⁶ m² / s²] of the disk, and the Q value Qa of the disk at 3000 Hz measured at 25°C are given by the following equation 1 65.0<(Qa×E / d) / (1000×D)<270.0 Or the following formula 2 150<(Qa×E / d) / (1000×D)<700 A disk for an information recording medium characterized by satisfying the following conditions.

2. A disk for information recording media with a plate thickness of 0.51 mm or less, A substrate having one main surface and the other main surface, and further having a side wall surface connecting the two main surfaces, The substrate comprises a coating layer that covers both main surfaces and side wall surfaces, When the disk is subjected to an impact of 30 G over 2 m seconds in the direction normal to the main surface of the disk while the inner circumference of the disk is fixed, the maximum amplitude due to vibration in the thickness direction of the outer circumference of the disk is 0.25 mm or less. The specific modulus E / d [×10⁶ m² / s²] calculated from the disk thickness D [mm], Young's modulus E [GPa], and density d [g / cm³], and the Q value Qa of the disk at 3000 Hz measured at 25°C are given by the following equation 1 65.0<(Qa×E / d) / (1000×D)<270.0 Or the following formula 2 150<(Qa×E / d) / (1000×D)<700 A disk for an information recording medium characterized by satisfying the following conditions.

3. A disk for information recording media with a plate thickness of 0.51 mm or less, A substrate having one main surface and the other main surface, and further having a side wall surface connecting the two main surfaces, The substrate comprises a coating layer that covers both main surfaces and side wall surfaces, The disk has a fluttering characteristic F [nm], which is the sum of the flutter vibrations of the disk in the range of 1000 to 4000 Hz, and a product F・D of the disk thickness D [mm] of 47.0 or less. The specific modulus E / d [×10⁶ m² / s²] calculated from the disk thickness D [mm], Young's modulus E [GPa], and density d [g / cm³], and the Q value Qa of the disk at 3000 Hz measured at 25°C are given by the following equation 1 65.0<(Qa×E / d) / (1000×D)<270.0 Or the following formula 2 150<(Qa×E / d) / (1000×D)<700 A disk for an information recording medium characterized by satisfying the following conditions.

4. A disk for information recording media with a plate thickness of 0.51 mm or less, A substrate having one main surface and the other main surface, and further having a side wall surface connecting the two main surfaces, The substrate comprises a coating layer that covers both main surfaces and side wall surfaces, The disk has a Young's modulus E [GPa] and a density d [g / cm³]. 3 The specific modulus of elasticity E / d calculated from ] is 40 [×10 6 I understand 2 / s 2 That's all, A disk for an information recording medium, characterized in that the coating layer is made of glass.

5. A disk for information recording media with a plate thickness of 0.51 mm or less, A substrate having one main surface and the other main surface, and further having a side wall surface connecting the two main surfaces, The substrate comprises a coating layer that covers both main surfaces and side wall surfaces, When the disk is subjected to an impact of 30 G over 2 m seconds in the direction normal to the main surface of the disk while the inner circumference of the disk is fixed, the maximum amplitude due to vibration in the thickness direction of the outer circumference of the disk is 0.25 mm or less. A disk for an information recording medium, characterized in that the coating layer is made of glass.

6. A disk for information recording media with a plate thickness of 0.51 mm or less, A substrate having one main surface and the other main surface, and further having a side wall surface connecting the two main surfaces, The substrate comprises a coating layer that covers both main surfaces and side wall surfaces, The disk has a fluttering characteristic F [nm], which is the sum of the flutter vibrations of the disk in the range of 1000 to 4000 Hz, and a product F・D of the disk thickness D [mm] of 47.0 or less. A disk for an information recording medium, characterized in that the coating layer is made of glass.

7. The disk for information recording medium according to any one of claims 1 to 6, wherein the substrate is made of one of the materials: ceramic, aluminum alloy, and glass.

8. The disk for information recording medium according to any one of claims 1 to 6, wherein the thickness of the disk is 0.45 mm or less.

9. The disk for an information recording medium according to any one of claims 1 to 6, wherein the coating layer includes a crystalline phase in an interface layer region located at a depth of at least 5% of the thickness T of the coating layer in the thickness direction from the interface with the substrate.

10. The information recording medium disk according to any one of claims 1 to 6, wherein the diameter of the information recording medium disk is 95 mm or more.

11. A disk for an information recording medium according to any one of claims 1 to 6, wherein when an impact of 50 [G] is applied to the disk in the direction normal to the main surface of the disk in 2 [msec] while the inner peripheral end of the disk is fixed, the maximum amplitude due to vibration in the thickness direction of the outer peripheral end of the disk is 0.30 mm or less.

12. The disk for information recording medium according to any one of claims 1 to 6, wherein the disk has a diameter of 95 mm or more, and the fluttering characteristic F, which is expressed as the sum of the flutter vibrations of the disk in the range of 1000 to 4000 Hz, is 80 nm or less.

13. The disk for an information recording medium according to any one of claims 1 to 6, wherein the maximum height Rz of the surface roughness of the main surface forming the interface with the coating layer of the substrate is 0.1 to 50 μm.

14. A disk intermediate having a thickness of 0.59 mm or less, which serves as the base plate for a disk used as an information recording medium. A substrate having one main surface and the other main surface, and further having a side wall surface connecting the two main surfaces, The substrate comprises a coating layer that covers both main surfaces and side wall surfaces, With respect to the thickness in the thickness direction of the plate, the ratio T / t of the thickness T [mm] of each coating layer to the thickness t [mm] of the substrate is 0.1 to 0.

75. The disk intermediate has a specific elastic modulus E / d calculated from the Young's modulus E [GPa] and the density d [g / cm 3 of 40 [×10 6 m 2 / s 2 or more, The thickness D [mm] and specific modulus E / d [×10⁶ m² / s²] of the disk, and the Q value Qa of the disk at 3000 Hz measured at 25°C are given by the following equation 1 65.0<(Qa×E / d) / (1000×D)<270.0 Or the following formula 2 150<(Qa×E / d) / (1000×D)<700 A disk intermediate characterized by satisfying the following conditions.

15. A disk intermediate having a thickness of 0.59 mm or less, which serves as the base plate for a disk used as an information recording medium. A substrate having one main surface and the other main surface, and further having a side wall surface connecting the two main surfaces, The substrate comprises a coating layer that covers both main surfaces and side wall surfaces, With respect to the thickness in the thickness direction of the plate, the ratio T / t of the thickness T [mm] of each coating layer to the thickness t [mm] of the substrate is 0.1 to 0.

75. The aforementioned disk intermediate has a Young's modulus E [GPa] and density d [g / cm³]. 3 The specific modulus of elasticity E / d calculated from ] is 40 [×10 6 I understand 2 / s 2 That's all, The disk intermediate is characterized in that the coating layer is made of glass.

16. The disk intermediate according to claim 14 or 15, wherein the coating layer includes a crystalline phase in an interface layer region located at a depth of at least 5% of the thickness T of the coating layer in the thickness direction from the interface with the substrate.