Magnetic disk substrate, magnetic disk, and method for manufacturing same

Abstract

The present invention relates to a magnetic disk substrate and a magnetic disk having a flatness of 40 μm or less, in which the mid-frequency Wq (root mean square waviness) is 7 μm or less and the mid-frequency TIR (difference between maximum and minimum) is 10 μm or less.

Description

Magnetic disk substrate, magnetic disk, and manufacturing method thereof

[0001] The present invention relates to a magnetic disk substrate having excellent flatness and smoothness, a magnetic disk, and a method for manufacturing the same.

[0002] Magnetic disks used in storage devices such as computers are manufactured using magnetic disk substrates that have good plating properties as well as excellent mechanical properties and processability (hereinafter, magnetic disk substrates may be simply referred to as "substrates"). These magnetic disk substrates are manufactured from aluminum alloy substrates based on aluminum alloys, glass substrates based on glass, etc. A known material for the aluminum alloy substrate is, for example, JIS 5086 aluminum alloy (containing 3.5 to 4.5 mass% Mg, 0.50 mass% or less Fe, 0.40 mass% or less Si, 0.20 to 0.70 mass% Mn, 0.05 to 0.25 mass% Cr, 0.10 mass% or less Cu, 0.15 mass% or less Ti, and 0.25 mass% or less Zn, with the balance being Al and unavoidable impurities).

[0003] In general, magnetic disks are manufactured by first preparing a circular magnetic disk substrate and then attaching a magnetic material to the surface of the magnetic disk substrate. For example, a magnetic disk using an aluminum alloy magnetic disk substrate made of the above-mentioned JIS 5086 aluminum alloy is manufactured by the following manufacturing process.

[0004] First, an aluminum alloy material having a predetermined chemical composition is cast, and the resulting ingot is hot-rolled and then cold-rolled to produce a rolled material having the thickness required for a magnetic disk. This rolled material may be annealed, if necessary, during the cold rolling. Next, this rolled material is punched into an annular shape to produce an annular aluminum alloy plate. Furthermore, in order to remove distortions and other problems caused by the manufacturing processes up to this point, the annular aluminum alloy plates are stacked and annealed while being pressed from both sides to flatten them, thereby producing an annular aluminum alloy disk blank.

[0005] The aluminum alloy disk blank thus produced is subjected to pre-treatments including cutting, grinding, degreasing, etching, and zincating (Zn substitution treatment), followed by electroless plating with Ni-P, a hard non-magnetic metal, as a base treatment, and polishing the plated surface to produce an aluminum alloy substrate for a magnetic disk.

[0006] Then, a magnetic material is sputtered onto the aluminum alloy substrate for the magnetic disk thus produced, thereby producing a magnetic disk made of an aluminum alloy. In addition to aluminum alloys, glass and the like are also used for magnetic disk substrates.

[0007] In recent years, due to the needs of multimedia and the like, there has been a growing demand for larger capacity and higher density for magnetic disk devices such as hard disk drives (hereinafter referred to as "HDDs"). Currently, perpendicular magnetic recording (PMR), shingled magnetic recording (SMR), and other magnetic recording methods are used as magnetic recording methods, but in order to achieve higher capacity, technologies such as thermally assisted magnetic recording (HAMR) and microwave assisted magnetic recording (MAMR) have been developed. To further increase capacity beyond the recording method, the number of magnetic disks installed in storage devices is on the rise, and accordingly, thinner magnetic disks are also required.

[0008] However, the reduction in rigidity associated with the thinning of the magnetic disk leads to a problem in that the flatness of the magnetic disk tends to deteriorate, which reduces the gap between the magnetic disk and other components, making the disk more susceptible to collision with other components when subjected to an impact, such as when the HDD is dropped, and this raises concerns about a reduction in impact resistance.

[0009] In addition to the deterioration of the flatness of the magnetic disk, there is also the problem that the smoothness of the magnetic disk tends to deteriorate due to the surface waviness and height difference in the circumferential direction of the magnetic disk, which makes it easier for the head to collide with the magnetic disk surface, resulting in an increase in read / write errors.

[0010] Therefore, in recent years, improvements in the impact resistance of magnetic disk devices and magnetic disk substrates have been studied. Since impact resistance may be related to the rigidity of the magnetic disk substrate, techniques for improving the rigidity of magnetic disk substrates are known. As an example, Patent Document 1 proposes a method of improving rigidity by incorporating a large amount of Si, which contributes to improving the rigidity of aluminum alloy substrates, into an aluminum alloy.

[0011] International Publication No. 2016 / 068293

[0012] Thus, the technique of increasing the Si content in the aluminum alloy disclosed in Patent Document 1 is effective in improving the rigidity of the aluminum alloy substrate. However, when addressing the issue of impact resistance itself, it is necessary to consider improving the flatness and smoothness associated with thinner magnetic disks. Patent Document 1 does not mention improving flatness and smoothness. Therefore, there is a need for the development of magnetic disks with improved flatness and smoothness.

[0013] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a magnetic disk substrate that exhibits excellent flatness and smoothness, a magnetic disk, and a method for manufacturing the same.

[0014] The present inventors have conducted extensive research into the relationship between the flatness and smoothness of magnetic disks and the manufacturing process, and have discovered that the preheating process performed before sputtering a magnetic material onto a magnetic disk substrate has a significant impact. In particular, the present inventors have focused on the temperature rise rate and temperature distribution in the preheating process, and have found that magnetic disk substrates that have been preheated to a specified degree can achieve excellent flatness and smoothness, leading to the completion of the present invention.

[0015] A magnetic disk substrate according to an embodiment of the present invention has a flatness of 40 μm or less, a root mean square waviness (Wq) of the middle periphery of 7 μm or less, and a TIR (height difference) of the middle periphery of 10 μm or less.

[0016] A method for manufacturing a magnetic disk substrate according to an embodiment of the present invention includes a preheating step of heating the magnetic disk substrate from room temperature to a predetermined temperature, and the temperature rise rate in the preheating step is 40° C. / second or less.

[0017] The magnetic disk according to the embodiment of the present invention has a flatness of 40 μm or less, a root mean square waviness (Wq) of 7 μm or less at the middle periphery, and a TIR (height difference) of 10 μm or less at the middle periphery.

[0018] A method for manufacturing a magnetic disk according to an embodiment of the present invention includes a preheating step of heating a magnetic disk substrate from room temperature to a predetermined temperature, and a sputtering step of depositing a magnetic material onto the surface of the preheated magnetic disk substrate by sputtering, wherein the temperature rise rate in the preheating step is 40°C / second or less.

[0019] According to the present invention, it is possible to provide a magnetic disk substrate that exhibits excellent flatness and smoothness, a magnetic disk, and a method for manufacturing the same.

[0020] FIG. 1 is a schematic diagram for explaining the area where the surface temperature of a magnetic disk substrate is measured in the preheating step.

[0021] The magnetic disk substrate, magnetic disk, and manufacturing method thereof according to this embodiment will be described in detail below.

[0022] [Magnetic Disk Substrate and Magnetic Disk] The magnetic disk substrate according to this embodiment and the magnetic disk produced using this magnetic disk substrate exhibit excellent flatness, since the flatness is 40 μm or less. Furthermore, the Wq (root mean square waviness) of the middle periphery is 7 μm or less, and the TIR (height difference) of the middle periphery is 10 μm or less, so they exhibit excellent smoothness. Magnetic disk substrates and magnetic disks having such flatness and smoothness properties can be produced from, for example, aluminum alloys, glass, etc.

[0023] <Flatness> The flatness of the magnetic disk substrate and the magnetic disk is 40 μm or less, preferably 30 μm or less, and more preferably 20 μm or less. If the flatness of the magnetic disk substrate and the magnetic disk exceeds 40 μm, the gap between the magnetic disk and other members when incorporated into an HDD will be small, and the magnetic disk will be more likely to collide with other members when subjected to impact, such as when the HDD is dropped, thereby reducing impact resistance.

[0024] Here, "flatness" refers to the difference between the maximum peak height and the maximum valley depth across the entire surface of the magnetic disk substrate and the magnetic disk. The maximum peak height is the highest value within the measurement range (the entire surface of the magnetic disk substrate and the magnetic disk), and the maximum valley depth is the lowest value within the measurement range (the entire surface of the magnetic disk substrate and the magnetic disk). Flatness measurements can be performed using a ZyGO non-contact flatness measuring instrument in accordance with the method specified in JIS B 0182-1993. JIS B 0182-1993 specifies "flatness," which can be evaluated as the same index of flatness as the above-mentioned flatness and has the same meaning as "flatness." Specifically, a jig for changing the angle with respect to the measurement surface of the flatness measuring instrument is fixed to the base installed on the flatness measuring instrument. For example, a jig equipped with three micrometers can be used, and the angle of the jig with respect to the measurement surface is adjusted with the micrometers in the θ direction (the direction tilted by an angle θ from the central angle 0°) and the ψ direction (diameter direction). Next, the substrate is set on the jig, and the angle is adjusted so that the substrate is parallel to the measurement surface of the flatness measuring instrument, thereby making it possible to measure the flatness.

[0025] <Wq (Root Mean Square Waviness) of the Middle Periphery> The Wq (Root Mean Square Waviness) of the middle periphery of the magnetic disk substrate and the magnetic disk is 7 μm or less, preferably 5 μm or less, more preferably 4 μm or less, and even more preferably 3 μm or less. Wq represents the root mean square of the reference length of the magnetic disk substrate and the magnetic disk. The reference length of the magnetic disk substrate and the magnetic disk is the circumferential length of the middle periphery of the substrate (the radial position of the value obtained by calculating 1 / 2 of the difference between 1 / 2 of the outer diameter and 1 / 2 of the inner diameter, and adding this value to 1 / 2 of the inner diameter), and refers to the middle periphery of the magnetic disk substrate and the magnetic disk, respectively. In other words, the Wq (Root Mean Square Waviness) of the middle periphery of the magnetic disk substrate and the magnetic disk corresponds to the root mean square height (Rq) of the reference length of the magnetic disk substrate and the magnetic disk, respectively. Here, the root mean square height (Rq) represents the root mean square of the reference length of the magnetic disk substrate and the magnetic disk, and means the standard deviation of the surface roughness.

[0026] By reducing Wq on the surface of a magnetic disk substrate and a magnetic disk, the effect of stabilizing the surface smoothness of the magnetic disk substrate and the magnetic disk is exhibited. If Wq exceeds 7 μm, the head is more likely to collide with the surface of the magnetic disk, which may increase read / write errors of the magnetic disk. Note that the smaller Wq is, the lower the risk of collision is, but if this value is too small, if the head adheres to the disk surface, it may be difficult to detach it, so the lower limit of Wq is preferably 0.5 μm or more. Here, Wq can be measured in accordance with JIS B0601:2013, for example, using a ZyGO non-contact flatness measuring instrument.

[0027] <TIR (height difference) of the middle circumference> The TIR of the magnetic disk substrate and the magnetic disk is 10 μm or less, preferably 8 μm or less, more preferably 5 μm or less, and even more preferably 3 μm or less. TIR represents the height difference in the reference length of the magnetic disk substrate and the magnetic disk. As described above, the reference length of the magnetic disk substrate and the magnetic disk is the circumferential length of the middle circumference of the disk (the radial position of the value obtained by calculating 1 / 2 of the difference between 1 / 2 of the outer diameter and 1 / 2 of the inner diameter, and adding this value to 1 / 2 of the inner diameter), and refers to the middle circumference of the magnetic disk substrate and the magnetic disk, respectively. In other words, the TIR (height difference) of the middle circumference of the magnetic disk substrate and the magnetic disk corresponds to the TIR in the reference length of the magnetic disk substrate, respectively. Here, TIR is an index that indicates the amount of waviness of a magnetic disk substrate and a magnetic disk, and means the sum of the distances from the highest point to the lowest point on the evaluation surface (substrate surface) to the least squares plane.

[0028] By reducing the TIR on the surface of the magnetic disk substrate and the magnetic disk, the effect of stabilizing the surface smoothness of the magnetic disk substrate and the magnetic disk is exhibited. If Wq exceeds 10 μm, the head is more likely to collide with the surface of the magnetic disk, which may increase read / write errors. Note that the smaller the TIR, the lower the risk of collision. However, if the head adheres to the disk surface, if this value is too small, it may be difficult to detach it. Therefore, the lower limit of TIR is preferably 0.5 μm or more. Here, TIR can be measured, for example, using a ZyGO non-contact flatness measuring instrument.

[0029] <Size of magnetic disk substrate and magnetic disk> The thickness (plate thickness) of the magnetic disk substrate and magnetic disk is preferably 0.50 mm or less, more preferably 0.49 mm or less, and even more preferably 0.42 mm or less. If the thickness of the magnetic disk substrate and magnetic disk exceeds 0.50 mm, the impact resistance of the magnetic disk is improved, but the number of magnetic disks that can be installed in the HDD is reduced, which is not suitable for promoting thinning of the magnetic disk. Furthermore, in order to prevent deformation or cracking of the magnetic disk when the magnetic disk is dropped during installation in the HDD, the lower limit of the thickness (plate thickness) of the magnetic disk substrate and magnetic disk is preferably 0.25 mm or more.

[0030] Furthermore, the outer diameter of the magnetic disk substrate and the magnetic disk is preferably 96 mm or more, and more preferably 97 mm or more. By having the outer diameter of the magnetic disk substrate and the magnetic disk be 96 mm or more, the recording capacity can be further increased.

[0031] <Materials of the magnetic disk substrate and the magnetic disk> The materials of the magnetic disk substrate and the magnetic disk are not particularly limited, but are preferably, for example, an aluminum alloy or glass. Magnetic disk substrates and magnetic disks made of such materials can be produced using, for example, an aluminum alloy substrate, a glass substrate, or the like.

[0032] <Aluminum Alloy Substrate for Magnetic Disk> The substrate for a magnetic disk may be, for example, an aluminum alloy substrate made of an aluminum alloy. The alloy composition of the aluminum alloy substrate for a magnetic disk will be described in detail below.

[0033] (Alloy composition of aluminum alloy) In order to further improve the fluttering resistance, impact resistance, and plating ability of the aluminum alloy substrate for magnetic disks, it is preferable that the aluminum alloy used for the aluminum alloy substrate contains at least one of Fe (iron): 0.001% by mass or more and 3.00% by mass or less and Mn (manganese): 0.001% by mass or more and 3.00% by mass or less as a first selective element (hereinafter, mass % will be simply referred to as "%").

[0034] The aluminum alloy may further contain, as a second selective element, one or more elements selected from the group consisting of Mg (magnesium): 0.100% or more and 6.000% or less, Ni (nickel): 0.100% or more and 5.000% or less, Cr (chromium): 0.001% or more and 5.000% or less, Zr (zirconium): 0.001% or more and 5.000% or less, Zn (zinc): 0.001% or more and 5.000% or less, Cu (copper): 0.001% or more and 5.000% or less, and Si (silicon): 0.01% or more and 0.40% or less.

[0035] Furthermore, the aluminum alloy may further contain, as a third selective element, one or more elements selected from the group consisting of Ti (titanium), B (boron), and V (vanadium) in a total content of 0.005% or more and 5.000% or less.

[0036] The balance of the aluminum alloy is composed of Al and unavoidable impurities, such as Ga (gallium), Sn (tin), Sr (strontium), P (phosphorus), and Na (sodium). The unavoidable impurities do not impair the properties of the aluminum alloy substrate, provided that each of the unavoidable impurities is less than 0.10% and the total amount of the unavoidable impurities is less than 0.20%.

[0037] <Magnetic Disk Glass Substrate> The magnetic disk substrate may be, for example, a glass substrate made of a glass material. Glass materials used for magnetic disk glass substrates will be described in detail below.

[0038] (Glass Material) As the glass material, glass ceramics such as amorphous glass and crystallized glass can be used, and amorphous glass is preferably used from the viewpoint of formability and processability. Examples of the glass material include aluminosilicate glass, soda-lime glass, soda-aluminosilicate glass, aluminoborosilicate glass, and borosilicate glass.

[0039] Specific glass components include SiO ２ : 55% or more and 75% or less as the main component, Al ２ O３ Preferably, the glass contains LiO: 0.3% or more and 25% or less and CaO: 0% or more and 20% or less. ２ O: 0.01% or more and 6% or less, Na ２ O: 0.7% or more and 12% or less, K ２ O: 0% or more and 8% or less, MgO: 0% or more and 7% or less, ZrO ２ : 0% or more and 10% or less and TiO ２ : Glass containing one or more of 0% to 1% is preferred.

[0040] SiO ２ When the content of SiO is 55% or more and 75% or less, the effect of increasing f (frequency) of the glass substrate is exhibited. ２ The content is more preferably 60% or more and 75% or less. ２ O ３ When the content of Al is 0.3% or more and 25% or less, the effect of increasing the p of the glass substrate is exerted. ２ O ３ The content of CaO is more preferably 1.0% or more and 25% or less. Furthermore, when the content of CaO is 0% or more and 20% or less, the effect of increasing f and ρ (density) of the glass substrate is exhibited. The content of CaO in the glass is more preferably 1% or more and 20% or less.

[0041] The above-mentioned glass contains B, which reduces viscosity and improves melting and clarification. ２ O ３ (Contained as an essential component in aluminoborosilicate glass and borosilicate glass), SrO and BaO reduce high-temperature viscosity, improve solubility, clarity and formability, and also have the effect of improving Young's modulus, ZnO improves ion exchange performance and reduces high-temperature viscosity without reducing low-temperature viscosity, and SnO improves clarity and ion exchange performance. ２ , Fe as a colorant ２ O ３ In addition to the above, As is used as a fining agent. ２ O ３ , Sb ２ O ３The glass may further contain oxides of La, P, Ce, Sb, Hf, Rb, Y, etc. as trace elements. The glass may contain 15% or less of these components in total.

[0042] <Magnetic Disk Substrate and Magnetic Disk Manufacturing Method> In order for the magnetic disk substrate according to this embodiment to achieve the above-mentioned standards for flatness, Wq, and TIR, it is necessary to optimize the heating conditions in the preheating step that is performed before the sputtering step in the process of manufacturing a magnetic disk using the magnetic disk substrate. A detailed explanation will be given later.

[0043] Below, each step and process condition of the manufacturing process for the magnetic disk substrate and magnetic disk according to this embodiment will be described in detail. First, the manufacturing methods for the aluminum alloy substrate and glass substrate will be described for each step up to the sputtering step. For the aluminum alloy substrate, the steps from adjusting the aluminum alloy components to cold rolling involve melting and casting a predetermined aluminum alloy to obtain an aluminum alloy material, which is then used to manufacture an aluminum alloy plate. Next, the aluminum alloy plate is pressed and flattened to manufacture an aluminum alloy disk blank. Furthermore, the manufactured disk blank is subjected to pretreatments such as cutting and grinding, zincating, and Ni—P plating, followed by surface polishing and heat treatment to manufacture an aluminum alloy substrate for a magnetic disk.

[0044] Next, an example of a method for manufacturing a glass substrate is described. First, a glass plate is manufactured as a raw material. Next, the manufactured glass plate is cored to form a doughnut-shaped glass substrate from the glass plate. Furthermore, chamfered surfaces are formed on the inner and outer peripheral edge surfaces of the formed glass substrate, and the inner and outer peripheral edge surfaces of the glass substrate with the chamfered surfaces are polished, followed by surface polishing. This polishing process consists of rough polishing and precision polishing, and a glass substrate for a magnetic disk is manufactured by this surface polishing.

[0045] The magnetic disk substrate, such as an aluminum alloy substrate for a magnetic disk or a glass substrate for a magnetic disk, manufactured as described above is subjected to a preheating step in which the substrate is heated under predetermined heating conditions. This allows a magnetic disk substrate exhibiting excellent flatness and smoothness to be obtained. The preheating step will be described in detail below.

[0046] Before attaching a magnetic material to the surface of a magnetic disk substrate made of aluminum alloy, glass, or the like, it is necessary to raise the temperature of the substrate. The preheating process is the process for achieving this. Because a large number of substrates must be processed in a short period of time, the substrate is rapidly heated to a predetermined temperature using infrared radiation or the like. Conventionally, the flatness and smoothness of the magnetic disk obtained in the preheating process were not impaired due to the thick substrate. However, it has been found that the flatness and smoothness deteriorate as the magnetic disk is thinned. This is thought to be due to the fact that, if the temperature rise rate in the preheating process is rapid, thermal stress occurs if there is a temperature distribution within the substrate surface, and the thinning of the magnetic disk reduces its rigidity, making the substrate more susceptible to deformation. By maintaining a temperature rise rate of 40°C / sec or less when heating from room temperature to a predetermined temperature, the deterioration of flatness and smoothness during the preheating process can be suppressed, resulting in a magnetic disk substrate exhibiting excellent flatness and smoothness. The temperature rise rate is preferably 30°C / sec or less, and more preferably 20°C / sec or less. Here, room temperature is in the range of 20°C ± 15°C, and the predetermined temperature is in the range of 150°C or higher and 750°C or lower, preferably in the range of 200°C or higher and 300°C or lower.

[0047] Furthermore, if the temperature rise rate is slowed, productivity of the magnetic disk decreases, so in the preheating step, it is preferable to heat not one substrate but multiple substrates simultaneously, preferably two or more substrates, and more preferably three or more substrates.

[0048] As described above, if there is a temperature distribution within the surface of the substrate during heating, the flatness of the substrate deteriorates. However, in the preheating process, if the maximum temperature difference between the surface temperature T1 of one region and the surface temperature T2 of the other region, which are positioned in a line-symmetrical relationship with respect to an axis passing through the center of the substrate and parallel to the surface of the substrate, is 20°C or more, the shape of the substrate changes to a concentric shape. Because the circumferential surface smoothness has a significant impact on the behavior of the head during HDD operation, a concentric substrate shape is preferable. A concentric substrate shape reduces circumferential waviness and elevation differences. Therefore, as described above, by creating a predetermined temperature difference between the surface temperature T1 of one region and the surface temperature T2 of the other region, which are positioned in a line-symmetrical relationship on the surface of the substrate, the smoothness of the surface of the magnetic disk substrate can be further improved. The temperature difference between the surface temperature T1 of one region and the surface temperature T2 of the other region, which are positioned in a line-symmetrical relationship on the surface of the substrate, is more preferably 25°C or more, and even more preferably 30°C or more. In addition, from the viewpoint of suppressing deterioration of flatness, the upper limit of the temperature difference is preferably 100° C. or less. Note that the above-mentioned one region and the other region are in a positional relationship of line symmetry with each other, have the same area and shape, and are the same distance from the center of the substrate, so long as they are all at the same distance from the center of the substrate, there are no particular limitations on the area, shape, or distance from the center of the substrate of each region. In addition, methods for obtaining the desired temperature difference include adjusting the position of the heat source.

[0049] A magnetic material is attached to the surface of a preheated magnetic disk substrate by sputtering. A magnetic disk is manufactured through this sputtering process, and a magnetic layer is formed on the surface of the magnetic disk substrate by sputtering.

[0050] The magnetic layer may be a single layer or may be formed from multiple layers having different compositions. After sputtering, if necessary, a protective layer made of a carbon-based material may be formed on the magnetic layer by CVD, or a lubricating layer may be formed by applying lubricating oil to the protective layer.

[0051] The above-mentioned preheating step and sputtering step can impart excellent flatness and smoothness to the obtained magnetic disk, and are particularly effective when the desired magnetic disk has a thin plate thickness, for example, when manufacturing a magnetic disk having a plate thickness of 0.49 mm or less and an outer diameter of 96 mm or more. Furthermore, such effects can also be applied to magnetic disks such as those used in thermally assisted magnetic recording (HAMR), which is a next-generation recording method, and therefore the magnetic disk substrate and magnetic disk according to this embodiment are effective for use as a magnetic disk substrate for a thermally assisted magnetic recording method and a magnetic disk substrate for a thermally assisted magnetic recording method, respectively.

[0052] Based on the above embodiments, the present invention relates to the following [1] to

[16] . [1] A magnetic disk substrate characterized by having a flatness of 40 μm or less, a Wq (root mean square waviness) of 7 μm or less at the middle periphery, and a TIR (height difference) of 10 μm or less at the middle periphery. [2] The magnetic disk substrate according to [1] above, having a thickness of 0.50 mm or less. [3] The magnetic disk substrate according to [2] above, having a thickness of 0.49 mm or less. [4] The magnetic disk substrate according to any one of [1] to [3] above, having an outer diameter of 96 mm or more. [5] The magnetic disk substrate according to any one of [1] to [4] above, which is a magnetic disk substrate for a thermally assisted magnetic recording system. [6] A method for manufacturing a magnetic disk substrate according to any one of [1] to [5] above, comprising a preheating step of heating the magnetic disk substrate from room temperature to a predetermined temperature, wherein the temperature rise rate in the preheating step is 40°C / second or less. [7] The manufacturing method according to [6] above, wherein a plurality of the substrates are heated simultaneously in the preheating step. [8] The manufacturing method according to [6] or [7] above, wherein in the preheating step, the maximum temperature difference between the surface temperature T1 of one region and the surface temperature T2 of the other region, which are positioned in a line-symmetrical relationship with respect to an axis passing through the center of the substrate and parallel to the surface of the substrate, is 20°C or more. [9] A magnetic disk characterized by having a flatness of 40 μm or less, a root-mean-square waviness (Wq) of the middle periphery of 7 μm or less, and a TIR (height difference) of the middle periphery of 10 μm or less.

[10] The magnetic disk according to [9] above, wherein the thickness is 0.50 mm or less.

[11] The magnetic disk according to the above item

[10] , having a thickness of 0.49 mm or less.

[12] The magnetic disk according to any one of the above items [9] to

[11] , having an outer diameter of 96 mm or more.

[13] The magnetic disk according to any one of the above items [9] to

[12] , which is a magnetic disk substrate for a thermally assisted magnetic recording system.

[14] The method for manufacturing a magnetic disk according to any one of [9] to

[13] above, comprising: a preheating step of heating a magnetic disk substrate from room temperature to a predetermined temperature; and a sputtering step of depositing a magnetic material on the surface of the preheated magnetic disk substrate by sputtering, wherein the temperature rise rate in the preheating step is 40°C / second or less.

[15] The manufacturing method according to

[14] above, wherein a plurality of the substrates are heated simultaneously in the preheating step.

[16] The manufacturing method according to

[14] or

[15] above, wherein the maximum temperature difference in the preheating step between the surface temperature T1 of one region and the surface temperature T2 of the other region that are positioned symmetrically with respect to an axis that passes through the center of the substrate and is parallel to the surface of the substrate is 20°C or more.

[0053] The above describes the magnetic disk substrate, magnetic disk, and manufacturing method thereof according to the present invention, but the present invention is not limited to the above-described embodiments, and various modifications and variations are possible based on the technical concept of the present invention.

[0054] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0055] In the following examples and comparative examples, a plurality of aluminum alloy substrates and glass substrates were manufactured as magnetic disk substrates, and their characteristics were evaluated.

[0056] A. Production of Aluminum Alloy Substrate for Magnetic Disk

[0033] A surface-polished aluminum alloy substrate was produced by a conventional method using an aluminum alloy consisting of 4.0% Mg, 0.02% Fe, 0.02% Si, 0.05% Cr, 0.02% Cu, 0.3% Zn, and the balance being Al and unavoidable impurities. The aluminum alloy substrate had an outer diameter of 97 mm, a circular hole with an inner diameter of 25 mm, and a plate thickness as shown in Table 1.

[0057] B. Manufacturing of Magnetic Disk Glass Substrates A glass substrate was prepared by a conventional method using a glass material made of aluminosilicate glass and had a polished surface. The glass substrate had an outer diameter of 97 mm, a circular hole with an inner diameter of 25 mm, and a plate thickness as shown in Table 1.

[0058] C. Evaluation of Magnetic Disk Substrate Characteristics Each substrate was preheated by the following method, and then the flatness, Wq of the central periphery, and TIR of the central periphery of the obtained substrate were measured and evaluated.

[0059] First, each substrate was preheated under the conditions shown in Table 1. An infrared heater lamp, a bulb-type radiant heat source that emits light by electrically heating a filament, was used as the heat source. After the substrate reached its maximum temperature, it was held for one minute or less, and then the heater was turned off and allowed to cool. During heating, the substrate was fixed at three points on its outermost periphery, as per standard practice. Furthermore, as shown in Figure 1 , surface temperatures were measured using an infrared radiation thermometer in one region R1 and the other region R2, which were positioned symmetrically with respect to an axis A passing through the center C of the substrate and parallel to the surface of the substrate. The temperature measurement interval was set to one second, and the temperature difference between regions R1 and R2 was calculated as the temperature difference over the same measurement period. The maximum measured temperature difference was taken as the temperature difference between the surface temperature T1 of region R1 and the surface temperature T2 of region R2. The temperature rise rate was calculated by calculating the difference between the temperature at a certain time and the temperature one second earlier, and using the time (t1) and surface temperature (T1) when the temperature difference in one second became 3°C or more at 50°C or less as the temperature rose from room temperature, and the time (t2) and surface temperature (T2) one second before the temperature difference in one second became less than 3°C at above 50°C, the temperature rise rate was calculated as (T2-T1) / (t2-t1).

[0060] After preheating, the flatness, Wq of the central periphery, and TIR of the central periphery were measured. The meanings of flatness, Wq, and TIR are as described above. The flatness, Wq, and TIR were measured using a ZyGO non-contact flatness measuring device.

[0061] Table 1 shows the evaluation results of the flatness, Wq and TIR of each substrate.

[0062]

[0063] As shown in Table 1, in all of Examples 1 to 5, the flatness was 40 μm or less, the Wq of the middle periphery was 7 μm or less, and the TIR of the middle periphery was 10 μm or less, so that magnetic disk substrates exhibiting excellent flatness and smoothness were obtained.

[0064] In contrast, in Comparative Example 1, the flatness was poor, being 81 μm or more, and stable flatness could not be obtained. In addition, Wq of the middle periphery was 18 μm or less, and smoothness was also poor.

[0065] D. Evaluation of Magnetic Disk Characteristics Each substrate was preheated in the same manner as described in C above, and then a 5 nm magnetic film was deposited by sputtering to obtain a magnetic disk. The flatness, Wq of the middle periphery, and TIR of the middle periphery were measured and evaluated.

[0066] Table 2 shows the evaluation results of the flatness, Wq, and TIR properties of each magnetic disk.

[0067]

[0068] As shown in Table 2, in all of Examples 6 to 8, the flatness was 40 μm or less, the Wq of the middle circumference was 7 μm or less, and the TIR of the middle circumference was 10 μm or less, so that magnetic disk substrates exhibiting excellent flatness and smoothness were obtained.

[0069] In contrast, in Comparative Example 2, the flatness was poor, being 81 μm or more, and stable flatness could not be obtained. In addition, Wq of the middle periphery was 18 μm or less, and smoothness was also poor.

[0070] The present invention can provide a magnetic disk substrate that exhibits excellent flatness and smoothness, a magnetic disk, and a method for manufacturing the same.

Claims

1. A magnetic disk substrate characterized in that the flatness is 40 μm or less, the Wq (root mean square waviness) in the middle circumference is 7 μm or less, and the TIR (height difference) in the middle circumference is 10 μm or less.

2. The magnetic disk substrate according to claim 1, wherein the plate thickness is 0.50 mm or less.

3. The magnetic disk substrate according to claim 2, wherein the plate thickness is 0.49 mm or less.

4. The magnetic disk substrate according to claim 1 or 2, wherein the outer diameter is 96 mm or more.

5. The magnetic disk substrate according to claim 1 or 2, which is a magnetic disk substrate for a heat-assisted magnetic recording system.

6. A method for manufacturing a magnetic disk substrate according to claim 1 or 2, including a preheating step of heating the magnetic disk substrate from room temperature to a predetermined temperature, wherein the heating rate in the preheating step is 40 ° C / second or less.

7. The manufacturing method according to claim 6, wherein in the preheating step, a plurality of the substrates are heated simultaneously.

8. The manufacturing method according to claim 6, wherein in the preheating step, the maximum temperature difference between the surface temperature T1 of one region and the surface temperature T2 of the other region, which are in a line-symmetric positional relationship with respect to an axis passing through the center of the substrate and parallel to the surface of the substrate, is 20 ° C or more.

9. A magnetic disk characterized in that the flatness is 40 μm or less, the Wq (root mean square waviness) in the middle circumference is 7 μm or less, and the TIR (height difference) in the middle circumference is 10 μm or less.

10. The magnetic disk according to claim 9, wherein the plate thickness is 0.50 mm or less.

11. The magnetic disk according to claim 10, wherein the plate thickness is 0.49 mm or less.

12. The magnetic disk according to claim 9 or 10, wherein the outer diameter is 96 mm or more.

13. The magnetic disk according to claim 9 or 10, which is a magnetic disk substrate for a heat-assisted magnetic recording system.

14. A method for manufacturing a magnetic disk according to claim 9 or 10, including a preheating step of heating the magnetic disk substrate from room temperature to a predetermined temperature, and a sputtering step of depositing a magnetic material on the surface of the preheated magnetic disk substrate by sputtering, wherein the heating rate in the preheating step is 40 ° C / second or less.

15. The manufacturing method according to claim 14, wherein in the preheating step, a plurality of the substrates are heated simultaneously.

16. The manufacturing method according to claim 14, wherein in the preheating step, the maximum temperature difference between the surface temperature T1 of one region and the surface temperature T2 of the other region, which are in a line-symmetric positional relationship with respect to an axis passing through the center of the substrate and parallel to the surface of the substrate, is 20°C or more.

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