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

Abstract

The purposes of the present invention are to provide a magnetic disk substrate and a magnetic disk capable of maintaining long-term reliability of a hard disk while dealing with an increase in capacity of the hard disk and to provide a manufacturing method by which a magnetic disk (substrate therefor) having the above-mentioned characteristic can be manufactured.　The present invention pertains to: a magnetic disk (substrate therefor) having a pair of main surfaces, wherein a 0.4 to 5.0 mm cutoff wavelength of at least one of the main surfaces of the magnetic disk (substrate therefor) at 25 ˚C after a predetermined thermal shock test has long wavelength waviness Wa of 2.0 nm or less, especially 0.5 to 2.0 nm, and a 0.08 to 0.45 mm cutoff wavelength thereof has short wavelength waviness µWa of 0.15 nm or less, especially 0.05 to 0.15 nm; and a manufacturing method thereof.

Description

[Technical Field]

[0001] This invention relates to a substrate for a magnetic disk, a method for manufacturing the same, and a magnetic disk. [Background technology]

[0002] In recent years, the rapid spread of cloud computing has led to a demand for higher capacity hard disks (including hard disk drives and other hard disk devices) used in data centers. Specifically, this increased capacity can be achieved by thinning the magnetic disk substrate to increase the number of disks that can be stored, or by increasing the diameter of the magnetic disk substrate. However, the size of hard disk enclosures is standardized, making it difficult to increase the diameter of the magnetic disk substrate housed within them. Therefore, there is a strong demand for thinner magnetic disk substrates.

[0003] Magnetic disks mounted (equipped) in hard disks are generally formed by providing a magnetic layer or the like on the main surface of a disc-shaped magnetic disk substrate. Various types of such magnetic disk substrates have been proposed. For example, Patent Document 1 discloses a glass substrate for magnetic disks for constructing a magnetic disk with a thickness of 0.8 mm, in which the amount of change in flatness and surface waviness in the disk blank state before precision polishing are set to a specific range. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Patent No. 6259022 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] To date, several technologies have been disclosed to reduce malfunctions such as head crashes and thermal asperity failures in hard disk drives. For example, studies have been conducted on the waviness and roughness of magnetic disk substrates (e.g., Patent Document 1) with the aim of suppressing thermal asperity defects. However, conventional studies on the waviness and roughness of magnetic disk substrates have focused on the waviness and / or roughness at stages before use as a magnetic disk, such as before and after precision polishing. No studies have focused on the long-wavelength waviness Wa and short-wavelength waviness μWa after thermal shock tests, which are accelerated tests that simulate actual usage environments.

[0006] On the other hand, as mentioned above, with the increase in hard disk capacity, the number of magnetic disks that can be stacked has increased, meaning that the magnetic disk substrates that make up the magnetic disks have been made thinner. In particular, magnetic disk substrates with a thickness of less than 0.5 mm may develop greater warping of the substrate when incorporated into a hard disk, compared to magnetic disk substrates with a thickness of 0.5 mm or more, which can cause a decrease in the tracking performance of the magnetic head after long-term use (operation) of the hard disk, such as 1 million to 1.5 million hours. When the warping of the magnetic disk substrate increases, it reduces the tracking performance of the magnetic heads, which are arranged at predetermined intervals (e.g., 10 nm) on the main surface of the magnetic disk, relative to the main surface of the magnetic disk substrate. This, in turn, can prevent desired reading and writing during long-term operation of the hard disk, reducing reliability (long-term reliability).

[0007] The present invention aims to provide a magnetic disk substrate and magnetic disk that can accommodate increased hard disk capacity (increased number of disks) while maintaining the long-term reliability of the hard disk. The present invention also aims to provide a manufacturing method that can produce a magnetic disk substrate having the above characteristics. [Means for solving the problem]

[0008] The inventors of this invention have diligently studied the long-term reliability of high-capacity hard disks and have found that, for example, surface waviness occurring on the main surface of a magnetic disk substrate (or magnetic disk) thinned to less than 0.5 mm, after a specific thermal shock test simulating actual usage conditions, is one of the factors that reduces the long-term reliability of the hard disk.

[0009] Based on this finding, further investigation revealed that when a magnetic disk substrate as a component is heated at 120°C for 30 minutes and then cooled at -40°C for 30 minutes, this cycle is repeated 200 times (continuously) in a thermal shock test. After this test, the long-wavelength undulation Wa with a cutoff wavelength of 0.4 to 5.0 mm measured at 25°C on one main surface of the magnetic disk substrate is set to 2.0 nm or less, for example, 0.5 to 2.0 nm, and the short-wavelength undulation μWa with a cutoff wavelength of 0.08 to 0.45 mm is set to 0.15 nm or less, for example, 0.05 to 0.15 nm. This shows that even a magnetic disk substrate thinned to less than 0.5 mm can achieve long-term reliability equivalent to or better than that of a magnetic disk substrate with a thickness of 0.5 mm or more. This invention was completed after further investigation based on these findings.

[0010] In other words, the objectives of the present invention were achieved by the following means. [1] A substrate for a magnetic disk having a pair of main surfaces, A magnetic disk substrate wherein, at least one of the main surfaces, after the thermal shock test described below, has a long-wavelength swell Wa of 0.4 to 5.0 mm at 25°C that is 2.0 nm or less, and a short-wavelength swell μWa of 0.08 to 0.45 mm at 0.15 nm or less. <Thermal shock test> The thermal shock test is performed by heating the magnetic disk substrate at 120°C for 30 minutes, followed by cooling at -40°C for 30 minutes, with each cycle being repeated 200 times. [2] A substrate for a magnetic disk, wherein the long-wavelength undulation Wa is 0.5 nm or more, and the short-wavelength undulation μWa is 0.05 nm or more. [3] A substrate for magnetic disks as described in [1] or [2], having a thickness of less than 0.50 mm. [4] A magnetic disk substrate as described in any one of items [1] to [3], which is a disc with an outer diameter of 95 mm or more. [5] A magnetic disk substrate for HAMR (heat-assisted magnetic recording) or MAMR (microwave-assisted magnetic recording), as described in any one of items [1] to [4]. [6] A magnetic disk having a pair of main surfaces, A magnetic disk having, after the thermal shock test described below, at least one of the main surfaces, a long-wavelength swell Wa with a cutoff wavelength of 0.4 to 5.0 mm at 25°C is 2.0 nm or less, and a short-wavelength swell μWa with a cutoff wavelength of 0.08 to 0.45 mm is 0.15 nm or less. <Thermal shock test> The thermal shock test is performed by heating the magnetic disk at 120°C for 30 minutes, followed by cooling at -40°C for 30 minutes, with each cycle being repeated 200 times. [7] A method for manufacturing a magnetic disk substrate as described in any one of items [1] to [5], When obtaining a circuit board for magnetic disks from a disk blank, The process includes a rough polishing step of simultaneously rough polishing both main surfaces of the disc blank, and a precision polishing step of precisely polishing both main surfaces of the roughly polished disc blank. A method for manufacturing a substrate for a magnetic disk, comprising inverting the front and back surfaces of the disk blank during the rough polishing process. [8] As a pre-process of the rough grinding process, a dummy substrate manufactured under the same conditions as the disk blank is polished using two polishing pads used in the rough grinding process under the same conditions as the rough grinding process until the long wavelength undulation Wa with a cut-off wavelength of 0.4 to 5.0 mm on one side becomes less than 2.5 nm to obtain a polishing pad with the surface state adjusted, including a dummy polishing process. In the rough grinding process, the disk blank is roughly ground using the polishing pad with the surface state adjusted. The method for manufacturing a substrate for a magnetic disk according to [7].

[0011] In this specification, the numerical range represented by using "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value, respectively.

Advantages of the Invention

[0012] When the substrate for a magnetic disk of the present invention is provided with a magnetic layer on the main surface and mounted on a hard disk as a magnetic disk, it is possible to realize a high capacity of the hard disk while maintaining the long-term reliability of the hard disk. The magnetic disk of the present invention also exhibits the same effect. According to the method for manufacturing a substrate for a magnetic disk of the present invention, a substrate for a magnetic disk and a magnetic disk having the above characteristics can be manufactured.

Brief Description of the Drawings

[0013] [Figure 1] FIG. 1 is a flow chart for explaining an example of an aluminum alloy substrate for a magnetic disk and a method for manufacturing a magnetic disk using the same. [Figure 2] FIG. 2 is a flow chart for explaining an example of a glass substrate for a magnetic disk and a method for manufacturing a magnetic disk using the same. [Figure 3] FIG. 3 is a schematic diagram showing the measurement locations of short wavelength undulations in the examples.

Embodiments for Carrying Out the Invention

[0014] {Substrate for Magnetic Disk} A magnetic disk substrate is a substrate used in the manufacture of magnetic disks. Its material and shape are not particularly limited; it may be in the form of a plate, or it may be a disc-shaped or annular shape obtained from a plate, such as a disc body. The magnetic disk substrate has a pair of opposing main surfaces.

[0015] The magnetic disk substrate of the present invention has, after the thermal shock test described below, at least one of its main surfaces has a long-wavelength swell Wa with a cutoff wavelength of 0.4 to 5.0 mm at 25°C that is 2.0 nm or less, for example, 0.5 to 2.0 nm, and a short-wavelength swell μWa with a cutoff wavelength of 0.08 to 0.45 mm that is 0.15 nm or less, for example, 0.05 to 0.15 nm. That is, the magnetic disk substrate of the present invention includes an embodiment in which one of the main surfaces (usually the main surface on which the magnetic heads are arranged facing each other) satisfies the long-wavelength swell Wa and short-wavelength swell μWa after the thermal shock test, and an embodiment in which both of the main surfaces satisfy the long-wavelength swell Wa and short-wavelength swell μWa after the thermal shock test. <Thermal shock test> The thermal shock test is performed by heating the magnetic disk substrate at 120°C for 30 minutes, followed by cooling at -40°C for 30 minutes, with each cycle being repeated 200 times.

[0016] The above thermal shock test can be carried out specifically by the method described in the examples. This thermal shock test is performed using a magnetic disk substrate without a magnetic layer, but since the magnetic layer is generally formed as a thin film thinner than the magnetic disk, variations in its thickness do not substantially affect the long-wavelength and short-wavelength swells.

[0017] The thermal shock test described above simulates thermal shock in an environment more severe than the actual operating environment of a hard disk. By evaluating the surface waviness after this test, it is possible to assess the durability of the magnetic disk substrate (and magnetic disk) against sudden changes in actual ambient temperature when incorporated into a hard disk. If, after this test, the long-wavelength waviness Wa with a cutoff wavelength of 0.4 to 5.0 mm is 2.0 nm or less, for example, 0.5 to 2.0 nm, and the short-wavelength waviness μWa with a cutoff wavelength of 0.08 to 0.45 mm is 0.15 nm or less, for example, in the range of 0.05 to 0.15 nm, then it is considered that even after being incorporated into a hard disk and used for 1 million to 1.5 million hours under normal operating conditions, the tracking ability of the magnetic head to the main surface of the magnetic disk substrate will not deteriorate significantly. In other words, even with long-term use, scanning is possible without interference between the main surface and the magnetic head, and data reading is possible. In this way, the long-term reliability of the hard disk can be improved.

[0018] The above-mentioned "long-wavelength swell Wa with a cutoff wavelength of 0.4 to 5.0 mm" (hereinafter sometimes simply referred to as "Wa") refers to the arithmetic mean swell measured on the main surface of a magnetic disk substrate in the cutoff wavelength range of 0.4 to 5.0 mm. The above-mentioned "short-wavelength swell μWa with cutoff wavelengths of 0.08 to 0.45 mm" (hereinafter sometimes simply referred to as "μWa") refers to the arithmetic mean swell measured on the main surface of a magnetic disk substrate in the cutoff wavelength range of 0.08 to 0.45 mm. The "cutoff wavelength" is a wavelength set to exclude components that do not fall within this cutoff wavelength range from the measured cross-sectional curve when determining long-wavelength or short-wavelength swells. In this invention, the Wa and μWa of the main surface of the magnetic disk substrate are measured after the thermal shock test described above. Wa and μWa after the thermal shock test can be measured by the method described in the examples.

[0019] If the Wa after thermal shock testing exceeds 2.0 nm, or if the μWa after thermal shock testing exceeds 0.15 nm, the magnetic head may not be able to follow the surface of the magnetic disk when the magnetic disk is rotated at high speed. In other words, when a magnetic disk substrate is used as a magnetic disk and mounted on a hard disk, and used for a long period of time such as 1 million to 1.5 million years, surface warping may occur, and the magnetic head may not be able to follow the surface of the magnetic disk. While it is desirable to set the Wa after thermal shock testing to less than 0.5 nm and the μWa after thermal shock testing to less than 0.05 nm in terms of improving the reliability of the hard disk, this may result in a significant increase in processing time. Therefore, considering the cost, it is preferable to set the Wa to 0.5 to 2.0 nm and the μWa to 0.05 to 0.15 nm. By keeping both Wa and μWa within the above ranges, surface warping can be suppressed even after long-term use, and the reliability of the hard disk can be improved.

[0020] The Wa value after the thermal shock test is preferably 0.5 to 1.8 nm, and more preferably 0.5 to 1.6 nm. The μWa after the thermal shock test is preferably 0.05 to 0.13 nm, and more preferably 0.05 to 0.11 nm. The Wa and μWa values ​​after the thermal shock test can be set to the above range in the case of aluminum alloy substrates described later by performing DC casting, setting pressure annealing conditions, setting polishing conditions, etc. In the case of glass substrates described later, the above range can be set by setting polishing conditions.

[0021] The thickness of the magnetic disk substrate can be the same as that of a normal magnetic disk substrate, and it can also be made thinner. Preferably, the thickness of the magnetic disk substrate is less than 0.50 mm, which enables the creation of high-capacity hard disks. There is no particular lower limit to the thickness of the magnetic disk substrate, but 0.30 mm or more is practical.

[0022] The outer diameter of the magnetic disk substrate can be the same as that of a standard magnetic disk substrate. When the magnetic disk substrate is used for a 3.5-inch hard disk, the outer diameter of the magnetic disk substrate of the present invention is preferably 95 mm or more. The upper limit is limited by the internal dimensions of the case, and 97 mm or less is practical.

[0023] The inner diameter of the magnetic disk substrate can be the same as that of a standard magnetic disk substrate. When used for a 3.5-inch hard disk, the inner diameter of the magnetic disk substrate of the present invention is preferably 26 mm or less. The lower limit is restricted by the outer diameter of the rotating shaft, and 25 mm or more is practical.

[0024] The magnetic disk substrate of the present invention can be used as a magnetic disk by forming a magnetic layer on at least one of its main surfaces. It is preferable to form magnetic layers on both main surfaces. The magnetic layer can be provided in the same way as a normal magnetic disk.

[0025] The resulting magnetic disk can be used, for example, for a nominal 3.5-inch hard disk. Common thicknesses for enclosures used with major 3.5-inch hard drives include 20mm and 26mm. If the thickness of the magnetic disk is 0.5 mm, the number of magnetic disks that can be mounted in a standard 26 mm thick enclosure for 3.5-inch hard drives is 9 or less. However, by reducing the thickness of the magnetic disk to less than 0.5 mm, it becomes possible to mount 10 or more magnetic disks in a hard drive without significantly increasing the enclosure thickness beyond 26 mm.

[0026] Generally, materials that provide good mechanical properties, workability, and resistance to defects are used as materials for magnetic disk substrates. Specifically, aluminum alloys and glass can be used. Hereinafter, magnetic disk substrates manufactured using aluminum alloys may be referred to as aluminum alloy substrates, and magnetic disk substrates manufactured using glass may be referred to as glass substrates.

[0027] The magnetic disk substrate of the present invention can be used as a magnetic disk substrate for any recording method, but it is preferably used as a magnetic disk substrate for HAMR (heat-assisted magnetic recording) and MAMR (microwave-assisted magnetic recording). When used as a substrate for magnetic disks in HAMR, it is preferable to use a glass substrate with excellent heat resistance. For use as a substrate for magnetic disks in MAMR, either a glass substrate or an aluminum substrate can be used.

[0028] <Aluminum alloy substrate> First, let me explain about aluminum alloy substrates. The aluminum alloy used in the aluminum alloy substrate preferably contains elements such as Mg, Cu, Zn, and Cr, which have been used conventionally. It may also contain elements such as Fe, Mn, and Ni, which can improve rigidity.

[0029] As aluminum alloys, Al-Mg alloys, Al-Fe-Mn-Ni alloys, and Al-Fe-Mn-Mg-Ni alloys can be used. As an Al-Mg alloy, for example, A5086 (containing Mg: 3.5-4.5 mass%, Fe: 0.50 mass% or less, Si: 0.40 mass% or less, Mn: 0.20-0.7 mass%, Cr: 0.05-0.25 mass%, Cu: 0.10 mass% or less, Ti: 0.15 mass% or less, and Zn: 0.25 mass% or less, with the remainder being Al and unavoidable impurities) can be used.

[0030] A preferred embodiment of the aluminum alloy is an aluminum alloy containing Mg: 1.0 to 6.5 mass%, further containing one or more of Cu: 0.070 mass% or less, Zn: 0.60 mass% or less, Fe: 0.50 mass% or less, Si: 0.50 mass% or less, Cr: 0.20 mass% or less, Mn: 0.50 mass% or less, Zr: 0.20 mass% or less, and Be: 0.0020 mass% or less, with the remainder being aluminum and unavoidable impurities.

[0031] Another preferred embodiment of the aluminum alloy is an aluminum alloy containing, as a stiffening agent, Fe, an essential element, and one or two of the optional elements Mn and Ni, with the total content of Fe, Mn, and Ni being between 1.00 and 7.00 mass%, and further containing one or more of the following elements: Si: 14.0 mass% or less, Zn: 0.7 mass% or less, Cu: 1.0 mass% or less, Mg: 3.5 mass% or less, Cr: 0.30 mass% or less, Zr: 0.20 mass% or less, Be: 0.0015 mass% or less, Sr: 0.1 mass% or less, Na: 0.1 mass% or less, and P: 0.1 mass% or less, with the remainder being aluminum and unavoidable impurities. Such aluminum alloys are referred to as Al-Fe-Mn-Ni alloys or Al-Fe-Mn-Mg-Ni alloys, depending on the components they contain.

[0032] Each of the above aluminum alloys may contain elements other than those mentioned above. The content of these other elements may be, for example, 0.1% by mass or less for each element and 0.3% by mass or less in total.

[0033] <Glass substrate> Let's explain glass substrates. As the material for the glass substrate, glass ceramics such as amorphous glass or crystallized glass can be used. However, from the viewpoint of moldability, processability, and surface roughness of the product, amorphous glass is preferred, and for example, aluminosilicate glass, soda-lime glass, soda-aluminosilicate glass, aluminoborosilicate glass, and borosilicate glass are preferred.

[0034] Preferred forms of glass used for magnetic disk substrates are glass mainly composed of SiO2: 55-75%, with Al2O3: 0.7-25%, Li2O: 0.01-6%, Na2O: 0.7-12%, K2O: 0-8%, MgO: 0-7%, CaO: 0-10%, ZrO2: 0-10%, and TiO2: 0-1% added; particularly glass containing SiO2: 60-70%, Al2O3: 10-25%, Li2O: 1-6%, Na2O: 0.7-3%, MgO: 0-3%, CaO: 1-7%, ZrO2: 0-3%, and TiO2: 0-1%; or glass to which B2O3: 1-7% and P2O5: 0.1-3% are further added. In the compositions above and below, "%" all mean "mass%".

[0035] SiO2 is the main component that forms the framework of glass. If the SiO2 content is below 55%, the chemical durability will decrease, and if it exceeds 75%, the melting temperature will become too high, making it unsuitable.

[0036] Al2O3 is an ingredient that improves ion exchange and chemical durability. Concentrations below 0.7% may result in insufficient effects, while concentrations above 25% may be unsuitable due to decreased solubility and devitrification resistance.

[0037] Li2O is a component that chemically strengthens glass by exchanging with Na ions, improving meltability, moldability, and Young's modulus. If the concentration is less than 0.01%, the ion exchange rate decreases, and if it exceeds 6%, the devitrification resistance and chemical durability decrease, making it unsuitable in some cases.

[0038] Na2O is a component that chemically strengthens glass by exchanging with K ions, while also reducing high-temperature viscosity, improving meltability and moldability, and enhancing devitrification resistance. Below 0.7%, devitrification resistance decreases, and above 12%, chemical durability and Knoop hardness decrease, making it unsuitable.

[0039] K2O reduces high-temperature viscosity, improving meltability, moldability, and devitrification resistance. However, concentrations exceeding 8% can lead to decreased low-temperature viscosity and increased thermal expansion, resulting in reduced impact resistance, making it unsuitable in some cases.

[0040] MgO and CaO (essential components in soda-lime glass) reduce high-temperature viscosity, improve solubility, clarity, and moldability, and also have the effect of improving Young's modulus. However, if the MgO content exceeds 7% and the CaO content exceeds 10%, it may become unsuitable because it reduces ion exchange performance and devitrification resistance.

[0041] ZrO2 increases Knoop hardness and improves chemical durability and heat resistance. However, concentrations exceeding 10% may decrease meltable properties and devitrification resistance, making it unsuitable.

[0042] While TiO2 has the effect of lowering high-temperature viscosity, improving meltability, stabilizing the structure, and enhancing durability, concentrations exceeding 1% may be unsuitable because they reduce ion exchange performance and decrease resistance to devitrification.

[0043] The above glass may also contain B2O3 (an essential component in aluminoborosilicate glass and borosilicate glass) to reduce viscosity and improve solubility and clarity, SrO and BaO which reduce high-temperature viscosity, improve solubility, clarity and moldability, and have an effect of improving Young's modulus, ZnO which improves ion exchange performance and reduces high-temperature viscosity without reducing low-temperature viscosity, SnO2 which improves clarity and ion exchange performance, Fe2O3 as a coloring agent, as well as As2O3 and Sb2O3 as clarifying agents, and P2O5. Furthermore, trace elements such as oxides of La, P, Ce, Sb, Hf, Rb, and Y may also be included. The above glass may also have a composition containing SiO2: 60-70%, Al2O3: 10-25%, Li2O: 1-6%, Na2O: 0.7-3%, MgO: 0-3%, CaO: 1-7%, ZrO2: 0-3%, TiO2: 0-1%, B2O3: 0.1-7%, and P2O5: 0.1-3%.

[0044] {Manufacturing method for magnetic disk substrates} The method for manufacturing a magnetic disk substrate is not particularly limited, as long as it is a method capable of manufacturing a magnetic disk substrate in which the long-wavelength swell Wa and short-wavelength swell μWa after the thermal shock test are within the above range. From the viewpoint of setting the long-wavelength swell Wa and short-wavelength swell μWa within the above range, the method for manufacturing a magnetic disk substrate of the present invention is preferably a manufacturing method that, in obtaining a magnetic disk substrate from a disk blank (disk-shaped blank substrate), includes a rough polishing step of simultaneously rough polishing both main surfaces of the disk blank, and a precision polishing step of precision polishing both main surfaces of the roughly polished disk blank, wherein the front and back surfaces of the disk blank are reversed during the rough polishing step.

[0045] A manufacturing method for a magnetic disk substrate comprises a rough polishing step in which both main surfaces are roughly polished simultaneously using a polishing solution containing abrasive grains with an average particle size of 0.1 to 1.0 μm and a hard or soft polishing pad, and a precision polishing step in which the above two main surfaces (roughly polished main surfaces) are precisely polished using a polishing solution containing abrasive grains with an average particle size of 0.01 to 0.1 μm and a soft polishing pad, and it is more preferable that the front and back surfaces of the disk blank are reversed during the rough polishing step. The abrasive grains used in the precision polishing step shall have a smaller average particle size than the abrasive grains used in the rough polishing step. Here, "hard" refers to a hardness (Asker C) of 85 or higher as measured by the measurement method specified in the Japan Rubber Association Standard (compliant standard: SRIS0101), and "soft" refers to a hardness of 60 to 80. The average particle size (d50) is the so-called median diameter, and it is the particle size at which the cumulative distribution reaches 50% when the total volume of the particles is set to 100% in the cumulative distribution, measured by laser diffraction and scattering methods.

[0046] The details of the conditions for the rough polishing and precision polishing processes can be set according to the raw materials of the magnetic disk substrate to be manufactured. Details of these polishing processes will be explained later in the sections on the manufacturing method of an aluminum alloy substrate for magnetic disks and a magnetic disk using the same, and the manufacturing method of a glass substrate for magnetic disks and a magnetic disk using the same. In the manufacturing method of an aluminum alloy substrate for magnetic disks described later, the polishing process in step S111 corresponds to the rough polishing and precision polishing processes described above. Also, in the manufacturing method of a glass substrate for magnetic disks described later, the rough polishing process in step S204 and the precision polishing process in step S205 correspond to the rough polishing and precision polishing processes described above.

[0047] The rough polishing process can be carried out using a commercially available batch-type double-sided simultaneous polishing machine. This double-sided simultaneous polishing machine comprises an upper and lower platen made of cast iron, a carrier that holds multiple disc blanks between the upper and lower plates, and hard or soft polishing pads (i.e., the number of polishing pads is twice the number of disc blanks) attached to the contact surfaces of the upper and lower plates with the disc blanks. The double-sided simultaneous polishing machine holds multiple disc blanks between the upper and lower plates using the carrier, and clamps each disc blank with a predetermined processing pressure between the upper and lower plates. As a result, each disc blank is clamped simultaneously from above and below (parallel to the direction of gravity) by the polishing pads. Next, while supplying polishing fluid at a predetermined rate between the polishing pads and each disc blank, the upper and lower plates are rotated in opposite directions. At this time, the carrier also rotates on its own axis by the sun gear, causing the disc blanks to undergo planetary motion. This causes the disc blanks to slide against the surface of the polishing pads, and both surfaces are polished simultaneously. Furthermore, since the polishing pad is porous (having bag-like holes with open surfaces), polishing fluid is supplied between the polishing pad and the disc blank via the polishing pad.

[0048] The precision polishing process can be carried out using the double-sided simultaneous polishing machine described above.

[0049] To reduce Wa and μWa after thermal shock testing, it is preferable to uniformly introduce strain into the disc blank, mainly during the rough polishing stage of the polishing process. Here, "uniformly introducing strain" means making the waviness distribution uniform across the entire main surface of the disc blank. Wa and μWa tend to decrease as the amount of polishing increases. By making the amount of polishing on the front and back surfaces as similar as possible during the rough polishing stage, the above-mentioned waviness distribution can be made uniform across the entire main surface. From the viewpoint of uniformly introducing strain, it is preferable to reverse the front and back surfaces of the disc blank during the rough polishing stage. By reversing the front and back surfaces of the disc blank, the polishing pads that polish each main surface (polished surface) of the disc blank are swapped, and the way gravity acts is reversed, which is thought to make the amount of polishing on the front and back surfaces closer together.

[0050] Furthermore, from the viewpoint of uniformly introducing distortion, it is preferable to control the surface condition of the polishing pad used in the rough polishing process. Controlling (adjusting) the surface condition of the polishing pad can be done when it is difficult to make the long-wavelength waviness Wa in the cutoff wavelength range of 0.4 to 5.0 mm less than 2.5 nm in the rough polishing process. Adjusting the surface condition of the polishing pad can be done by conventional methods, such as dummy polishing, if the surface condition of the polishing pad can be adjusted so that the long-wavelength waviness Wa in the cutoff wavelength range of 0.4 to 5.0 mm of the disc blank before rough polishing is less than 2.5 nm. For example, this can be done by dummy polishing. For example, if the polishing pad used in the rough polishing process is brushed, it is preferable to perform dummy polishing before rough polishing.

[0051] Dummy polishing is a polishing process used to adjust the surface condition of the polishing pad used in the rough polishing process described above. In this specification, polishing performed to adjust the surface condition of the polishing pad is referred to as "dummy polishing," and polishing performed using the polishing pad after dummy polishing, to which the long-wavelength waviness Wa with a cutoff wavelength of 0.4 to 5.0 mm is less than 2.0 nm, is referred to as "rough polishing." Dummy polishing can be performed as follows.

[0052] In dummy polishing, it is preferable to use a disk blank in its pre-rough polishing state as the dummy substrate. For example, if the object to be rough polished is an aluminum alloy substrate, a disk blank that has undergone electroless Ni-P plating treatment (described later) but is pre-rough polishing can be used as the dummy substrate. If the object to be rough polished is a glass substrate, a disk blank obtained in step S202 or S203 (described later) can be used as the dummy substrate. Dummy polishing is performed using the above-mentioned dummy substrate until the long-wavelength waviness Wa of the main surface with a cutoff wavelength of 0.4 to 5.0 mm is less than 2.5 nm. Dummy polishing can be performed under the same conditions as the rough polishing process. The number of polishing cycles (number of dummy polishing cycles) is not particularly limited and can be continued until the above-mentioned Wa is achieved.

[0053] By using a polishing pad that has been surface-conditioned after performing dummy polishing on a dummy substrate until the long-wavelength undulation Wa (cutoff wavelength 0.4-5.0 mm) is less than 2.5 nm in the rough polishing process, it is possible to adjust the polishing pad so that the difference in polishing amount between the front and back surfaces does not become large. Reducing the difference in polishing amount makes it easier to achieve the above-mentioned Wa and μWa.

[0054] From the above viewpoint, one embodiment of the manufacturing method for a magnetic disk substrate of the present invention may be a manufacturing method that includes a dummy polishing step as a step prior to the rough polishing step, in which the surface condition (condition of the polished surface) of the polishing pad used in the rough polishing step is adjusted. Preferably, this dummy polishing step is a step in which a dummy substrate manufactured under the same conditions as the disk blank is polished using two polishing pads used in the rough polishing step under the same conditions as the rough polishing step (size of polishing grains, hardness of polishing pad, polishing time, rotation speed of the polishing platen, rotation speed of the sun gear, polishing fluid supply speed, processing pressure, amount of polishing), until the long-wavelength undulation Wa on one side with a cutoff wavelength of 0.4 to 5.0 mm is less than 2.5 nm, thereby obtaining a polishing pad with an adjusted surface condition. When the dummy polishing step is performed, in the rough polishing step after the dummy polishing, a disk blank other than the dummy substrate is roughly polished using the polishing pad with the adjusted surface condition.

[0055] The manufacturing methods for the magnetic disk substrate and magnetic disk of the present invention will be described below, divided into a method for manufacturing an aluminum alloy substrate for magnetic disks and a method for manufacturing a glass substrate for magnetic disks.

[0056] <Manufacturing method for aluminum alloy substrates> The following describes in detail each step and process condition in the manufacturing process of an aluminum alloy substrate for magnetic disks and magnetic disks using the same. In the manufacturing of the aluminum alloy substrate for magnetic disks of the present invention, it is preferable to use an aluminum alloy material cast by a semi-continuous casting (DC casting) method. In continuous casting (CC casting) methods, the distribution of intermetallic compounds in the aluminum alloy becomes uneven, which can result in uneven strain remaining in the manufactured substrate and increasing the waviness.

[0057] Figure 1 is a flowchart illustrating an example of a method for manufacturing an aluminum alloy substrate and a magnetic disk using the same. In Figure 1, the aluminum alloy preparation process (step S101) to cold rolling (step S105) is a process in which an aluminum alloy material is manufactured by melting and casting, and this is made into an aluminum alloy sheet. Next, an aluminum alloy disk blank is manufactured by pressure planarization treatment (step S106). Then, the manufactured disk blank is subjected to cutting and grinding processes (step S107), degreasing and etching processes (step S108), zincate treatment (step S109), electroless Ni-P plating (step S110), and polishing processes (step S111) to manufacture an aluminum alloy substrate. The manufactured aluminum alloy substrate becomes a magnetic disk by a magnetic material attachment process (step S112). The details of each step will be explained below, referring to Figure 1.

[0058] First, a molten aluminum alloy material having the above-mentioned component composition is prepared by heating and melting it according to a conventional method (step S101).

[0059] Next, the prepared molten aluminum alloy material is cast, for example, by a semi-continuous casting (DC casting) method (step S102). Compared to continuous casting (CC casting), DC casting allows for a more uniform distribution of intermetallic compounds, so that Wa and μWa after the thermal shock test can be within the above range. The manufacturing conditions for the aluminum alloy material in DC casting and CC casting are not particularly limited and can be carried out by conventional methods. DC casting may be vertical semi-continuous casting or horizontal semi-continuous casting.

[0060] In DC casting, molten metal poured through a spout loses heat to the bottom block, the water-cooled mold walls, and the cooling water directly discharged around the outer circumference of the ingot, causing it to solidify and be drawn downwards as an aluminum alloy ingot. The ingot obtained in this process is sometimes called a slab.

[0061] On the other hand, in the CC casting method, molten metal is supplied through a casting nozzle between a pair of rolls (or belt casters, block casters), and thin sheets of aluminum alloy are directly cast by heat dissipation from the rolls.

[0062] The main difference between DC casting and CC casting lies in the cooling rate during casting. CC casting, with its higher cooling rate, is characterized by smaller second-phase particle size compared to DC casting.

[0063] Next, the aluminum ingot obtained by DC casting is hot-rolled into a sheet material (step S104). Prior to this hot rolling, a homogenization treatment (step S103) can be performed as needed. In CC casting, it is also possible to skip these steps and proceed directly from step S102 to step S105.

[0064] In step S103, when homogenization treatment is performed, it is preferable to perform heat treatment at 280 to 620°C for 0.5 to 30 hours, and more preferably at 300 to 620°C for 1 to 24 hours. Within the above temperature range, homogenization is sufficient, and the variation in the loss coefficient for each aluminum alloy substrate can be reduced. Furthermore, the occurrence of melting of the aluminum alloy ingot can be suppressed. If the heating time during the homogenization treatment exceeds 30 hours, the effect saturates, and no further significant improvement can be obtained.

[0065] In step S104 applied to the DC casting method, an aluminum alloy ingot that has undergone or has not undergone homogenization treatment is hot-rolled to form a sheet material. The conditions for hot rolling are not particularly limited, but the starting temperature for hot rolling is preferably 250 to 600°C, and the ending temperature for hot rolling is preferably 230 to 450°C.

[0066] Next, the hot-rolled sheet or the cast sheet cast by the CC casting method is cold-rolled to produce an aluminum alloy sheet with a thickness of approximately 0.30 to 0.6 mm (step S105). The cold-rolling conditions are not particularly limited and should be determined according to the required product sheet strength and thickness, with a rolling ratio of 10 to 95% being preferred. Before or during cold-rolling, annealing treatment may be performed to ensure cold-rollability. If annealing treatment is performed, for example, if batch heating is used, it is preferable to perform it at 300 to 450°C for 0.1 to 10 hours, and if continuous heating is used, it is preferable to perform it at 400 to 500°C for 0 to 60 seconds. Here, a holding time of 0 seconds means that cooling is performed immediately after reaching the desired holding temperature.

[0067] Then, the aluminum alloy sheet obtained by cold rolling is formed into an annular shape to form a disc-shaped aluminum alloy sheet. The disc-shaped aluminum alloy sheet is then subjected to a pressure flattening treatment (step S106) to become a disc blank. The disc shape can be formed by punching with a press. In the pressure flattening treatment, the disc-shaped aluminum alloy sheet is subjected to pressure in the air at, for example, 30-60 kgf / cm². 2 Under pressure, a load is applied and pressure annealing is performed at 250-450°C for 0.5-10 hours to produce a flattened disc blank.

[0068] If the pressure annealing temperature is too low, for example around 200°C, distortion will remain in the material (making it impossible to make the distortion in the material uniform), and consequently, it may not be possible to bring the Wa and μWa after the thermal shock test within the above range. For this reason, when manufacturing the magnetic disk substrate of the present invention, it is preferable to perform pressure annealing at a temperature of 250 to 450°C, particularly around 300 to 400°C.

[0069] Before zincate treatment and other processes, the disc blank undergoes cutting and grinding (step S107) and, if necessary, heat treatment. In the cutting and grinding process, the inner and outer circumferences of the disc blank are cut to shape it, and the main surface is ground. Before this process, the recording surface of the disc blank may be cut as a preliminary treatment for grinding. In this process, chamfering may also be performed on the inner and outer end faces.

[0070] Grinding can be performed using SiC grinding wheels of grits 800 to 4000 and a standard batch-type double-sided simultaneous grinding machine. This double-sided simultaneous grinding machine comprises an upper and lower platen made of cast iron, a carrier that holds multiple aluminum substrates between the upper and lower platens, and SiC grinding wheels attached to the contact surfaces of the upper and lower platens with the aluminum substrates. Since Wa changes depending on the finished state of the grinding, it is preferable to finish with a 4000 grit grinding wheel. In the grinding process, the upper and lower platens are rotated in opposite directions while the disc blank is held by the carrier. The rotation speed of the upper and lower platens can be 10 to 30 rpm. Since the carrier rotates with a sun gear, the disc blank is ground while undergoing planetary motion on the grinding wheel.

[0071] Furthermore, when heat treatment is performed, the disc blank is heated at 200-350°C for 5-60 minutes. Heat treatment removes distortions introduced during cutting and grinding, resulting in uniform distortion.

[0072] Furthermore, the disk blank is subjected to degreasing and etching (step S108). Degreasing can be carried out by conventional methods, preferably using a commercially available degreasing solution at a temperature of 40-70°C for a processing time of 3-10 minutes. The etching process can be carried out using conventional methods, and it is preferable to use commercially available etching solutions, for example, at a temperature of 50-75°C and a processing time of 0.5-5 minutes.

[0073] Next, the disk blank surface is subjected to zincate treatment (Zn substitution treatment) (step S109). In zincate treatment, a zincate film is formed on the surface of the disk blank. Zincate treatment can be performed using a commercially available zincate treatment solution, preferably under conditions of a temperature of 10-35°C, a treatment time of 0.1-5 minutes, and a concentration of 100-500 mL / L. Zincate treatment is performed at least once, and may be performed two or more times. By performing zincate treatment multiple times, fine Zn can be deposited, forming a uniform zincate film. When performing zincate treatment two or more times, it is preferable to perform a Zn stripping treatment in between. The Zn stripping treatment is preferably performed using a nitric acid (HNO3) solution, under conditions of a temperature of 15-40°C, a treatment time of 10-120 seconds, and a concentration of 10-60%. Furthermore, it is preferable to perform the second and subsequent zincate treatments under the same conditions as the first zincate treatment.

[0074] Furthermore, electroless Ni-P plating (step S110) is performed on the zincate-treated disk blank surface as a pre-treatment for magnetic material adhesion. The electroless Ni-P plating process is preferably carried out using a commercially available plating solution, under conditions of a temperature of 80-95°C, a processing time of 30-180 minutes, and a Ni concentration of 3-10 g / L.

[0075] After electroless Ni-P plating, the plated surface is polished (step S111). In this polishing process, it is preferable to perform polishing in multiple stages by adjusting the diameter of the abrasive grains used. This polishing process includes at least two stages of polishing: rough polishing and precision polishing. For example, rough polishing can be performed by roughly polishing the main surface using a polishing solution containing alumina with an average particle size of 0.1 to 1.0 μm and a hard or soft polishing pad, followed by precision polishing of the main surface using a polishing solution containing colloidal silica with an average particle size of about 0.01 to 0.1 μm and a soft polishing pad.

[0076] Other polishing conditions during the rough polishing described above are difficult to determine uniquely because they are influenced by the aluminum alloy used, the processing conditions from steps S101 to S110, etc. However, for example, a polishing time of 2 to 5 minutes, a polishing plate rotation speed of 10 to 35 rpm, a sun gear rotation speed of 5 to 15 rpm, a polishing fluid supply rate of 500 to 5000 mL / min, especially 800 to 1500 mL / min, and a processing pressure of 20 to 120 g / cm². 2 The polishing amount can be set to 2.5 to 3.5 μm per side. In the manufacturing method of the present invention, the disc blank is inverted during the rough polishing process. There are no particular restrictions on when the disc blank is inverted, but it is preferable to ensure that both sides of the disc blank are polished evenly, and it is more preferable to invert it when half of the total polishing time of the rough polishing process has elapsed. It is preferable that the polishing conditions are the same before and after inversion.

[0077] Other polishing conditions during the precision polishing described above are difficult to determine definitively as they are influenced by the aluminum alloy used, the processing conditions from step S101 to rough polishing, etc. However, for example, a polishing time of 2-5 minutes, a polishing plate rotation speed of 10-35 rpm, a sun gear rotation speed of 5-15 rpm, a polishing fluid supply rate of 500-5000 mL / min, especially 800-1500 mL / min, and a processing pressure of 20-100 g / cm². 2 The polishing amount can be set to 1.0 to 1.5 μm per side. The disc blank may be reversed during the precision polishing process. When reversing the disc blank, there are no particular restrictions on when to reverse it, but it is preferable to ensure that both sides of the disc blank are polished evenly, and it is more preferable to reverse it when half of the total polishing time of the precision polishing process has elapsed.

[0078] As described above, a dummy polishing step may be performed prior to the rough polishing step described above. The conditions for the dummy polishing step are as described above.

[0079] As described above, an aluminum alloy substrate for magnetic disks is manufactured through the processes up to the polishing process (surface polishing) after the electroless Ni-P plating treatment.

[0080] The magnetic material attachment process (step 112) can be carried out by a conventional method. It is preferable to form the magnetic material layer without excessive heat treatment so that the Wa and μWa values ​​of the magnetic disk substrate (magnetic disk) after the thermal shock test are the same as those of the magnetic disk substrate after the thermal shock test.

[0081] <Method for manufacturing glass substrates> Next, an example of a glass substrate for magnetic disks and a method for manufacturing magnetic disks using the same will be described. Figure 2 is a flowchart illustrating an example of a method for manufacturing a glass substrate and a magnetic disk using the same. As shown in Figure 2, the manufacturing method for this glass substrate begins by preparing a glass plate of a predetermined thickness (step S201). Next, the prepared glass plate is cored, and the inner and outer edges are polished to form a disc-shaped disk blank (step S202). If necessary, the disc-shaped disk blank is then lapped (step S203). Next, the formed disk blanks are pressed together from above and below with polishing pads, and a rough polishing step (step S204) is performed in which multiple disk blanks are simultaneously polished with, for example, cerium oxide abrasive grains. Subsequently, a precision polishing step (step S205) is performed in which each disk blank polished in step S204 is further polished simultaneously with, for example, colloidal silica abrasive grains to manufacture the glass substrate. The manufactured glass substrate becomes a magnetic disk through a magnetic material attachment step (step S206). The following explains each step in detail, referring to Figure 2.

[0082] First, the preparation of the glass plate in step S201 can be carried out using known manufacturing methods such as the float method, downdraw method, or direct press method, for example, using molten glass as the raw material. Furthermore, it is preferable to use the redraw method, in which a base glass plate manufactured using the float method or the like is heated and softened, and then stretched to the desired thickness, as this allows for the relatively easy production of glass plates with small variations in thickness.

[0083] Next, in step S202, the formation of the disc-shaped disk blank is carried out from the glass plate prepared in step S201 by a coring process and an inner and outer edge polishing process. The formed disk blank is a disc-shaped disk blank having two main surfaces and a circular hole formed in the center.

[0084] If necessary, the lapping process in step S203 can be performed to adjust the thickness of the disc blank formed in step S202 by lapping the disc-shaped disc blank. This lapping process is preferably performed when there is a large variation in the thickness of the glass plate, such as when the redraw method was not adopted in step S201. The lapping process can be performed so that the variation in the thickness of the glass plate is approximately ±3 μm. The lapping process can be performed using a conventional method, for example, by using a batch-type double-sided polishing machine with diamond pellets.

[0085] Next, the main surface of the disc blank obtained in step S202 or S203 is polished. In this polishing process, it is preferable to perform polishing in multiple stages with adjusted diameters of abrasive grains. This polishing process includes at least two stages of polishing: rough polishing (S204) and precision polishing (S205).

[0086] In step S204, the rough polishing process, the main surface of the disc blank is roughly polished. The conditions for rough grinding are not particularly limited, but generally include using a hard grinding pad with a hardness of 86-88, a grinding plate rotation speed of 10-35 rpm, a sun gear rotation speed of 5-15 rpm, a grinding fluid supply rate of 1000-5000 mL / min, especially between 1000 mL / min and 2000 mL / min, and a processing pressure of 20-120 g / cm². 2It is preferable to polish for 2 to 10 minutes and polish 40 to 60 μm per side. It is preferable to use a polishing pad made of hard polyurethane or the like as the polishing pad. It is preferable to use a polishing liquid that contains abrasive particles made of cerium oxide with an average particle size of 0.1 to 1.0 μm as the polishing liquid.

[0087] In the manufacturing method of the present invention, the disc blank is inverted during the rough polishing process. The timing of inverting the disc blank is not particularly limited, but it is preferable to ensure that both sides of the disc blank are polished evenly, and it is more preferable to invert it when half of the total polishing time of the rough polishing process has elapsed. It is preferable that the polishing conditions before and after inversion are the same. Note that inversion (flipping) of the disc blank only needs to be performed once during the polishing process, but it may be performed two or more times. For example, if flipping is performed multiple times, the total time that each side is facing upwards should be equal to the total time that each side is facing downwards during polishing.

[0088] As described above, a dummy polishing step may be performed prior to the rough polishing step S204 described above. The conditions for the dummy polishing step are as described above.

[0089] Next, in the precision polishing step S205, the roughly polished main surface is precision polished. Precision polishing can be performed by replacing the polishing pad of the double-sided simultaneous polishing machine with a softer precision polishing pad made of, for example, foamed urethane, and polishing the glass substrate using the polishing pad while supplying a polishing solution containing abrasive particles made of colloidal silica with an average particle size of 0.01 to 0.10 μm. As a result, the main surface of the disk blank is polished to a mirror finish, and a glass substrate for a magnetic disk is manufactured.

[0090] The conditions for precision polishing are not particularly limited, but generally, a soft polishing pad with a hardness of 75-77 is used, the rotation speed of the polishing platen is 10-35 rpm, the rotation speed of the sun gear is 5-15 rpm, the polishing fluid supply rate is 1000-5000 mL / min, especially between 1000 mL / min and 2000 mL / min, and the processing pressure is 20-100 g / cm². 2Preferably, the polishing time is 2 to 12 minutes, and the amount of polishing is 5 to 15 μm per side.

[0091] The disc blank may be inverted during the precision polishing process. When inverting the disc blank, there are no particular restrictions on when to do so, but it is preferable to ensure that both sides of the disc blank are polished evenly, and it is more preferable to invert it when half of the total polishing time of the precision polishing process has elapsed.

[0092] Furthermore, chemical strengthening treatment with sodium nitrate solution or potassium nitrate solution may be performed during the polishing process.

[0093] The magnetic material attachment process (step S206) can be carried out by a conventional method. It is preferable to form the magnetic material layer on the magnetic disk substrate (magnetic disk) after the magnetic material layer is formed without excessive heat treatment, so that the Wa and μWa values ​​after the thermal shock test are the same as those of the magnetic disk substrate after the thermal shock test.

[0094] {magnetic disk} The present invention also relates to a magnetic disk having a pair of main surfaces, This also includes magnetic disks in which, after the thermal shock test described below, at least one of the main surfaces has a long-wavelength swell Wa of 0.4 to 5.0 mm at 25°C of 2.0 nm or less, and a short-wavelength swell μWa of 0.08 to 0.45 mm at 0.15 nm or less. <Thermal shock test> The thermal shock test is performed by heating the magnetic disk at 120°C for 30 minutes, followed by cooling at -40°C for 30 minutes, with each cycle being repeated 200 times.

[0095] The magnetic disk of the present invention may be formed from any known substrate, and there are no particular restrictions on its size or material. However, in order to obtain a magnetic disk with higher flatness, it is preferable that the magnetic disk be based on an aluminum alloy substrate or a glass alloy substrate. Furthermore, in order to particularly highlight the effects of the present invention, it is preferable that the substrate be based on a substrate with a thickness of less than 0.5 mm or an outer diameter of 95 mm or more. More preferably, it is formed from the magnetic disk substrate of the present invention, and particularly preferably from a magnetic disk substrate of the material obtained by the above manufacturing method.

[0096] In the magnetic disk substrate of the present invention, even if a magnetic layer and optionally a protective film layer or lubricating film layer are provided on its surface, the thickness of the magnetic layer, etc., is very thin compared to the substrate. Therefore, it does not substantially affect long-wavelength swells or short-wavelength swells after thermal shock tests, maintaining high long-term reliability and achieving the objectives of the present invention. [Examples]

[0097] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0098] (Example 1) A5086 alloy (aluminum alloy A) was melted according to a standard method (step S101), and a slab was obtained by DC casting (vertical semi-continuous casting) to a width of 1310 mm and a thickness of 500 mm (step S102). Each of the four sides of this slab (at least the main surface) was machined by 10 mm, and after homogenization treatment at 540°C for 6 hours (step S103), it was hot-rolled at a starting temperature of 540°C and an ending temperature of 350°C to obtain a hot-rolled sheet with a thickness of 3.0 mm (step S104). This hot-rolled sheet was then cold-rolled to obtain a cold-rolled sheet with a thickness of 0.48 mm (step S105).

[0099] This cold-rolled sheet is punched out into a disc shape with an inner diameter of 24 mm and an outer diameter of 98 mm using a press, and then annealed in air using a continuous annealing furnace at 30 kgf / cm². 2The material was subjected to pressure annealing at 320°C for 3 hours while applying a load and pressure to perform pressure flattening treatment (Step S106). In this way, a disc blank was obtained. Furthermore, the inner and outer circumferences of the disc blank were machined to create a disc-shaped disc blank with an inner diameter of 25 mm and an outer diameter of 97 mm. At the same time, chamfering was performed on the inner and outer end faces.

[0100] The processed disc blank was surface-ground using a 4000-grit SiC grinding wheel and a batch-type double-sided simultaneous grinding machine (product name: 9B double-sided grinding machine, manufactured by SPEEDFAM) to a plate thickness of 0.46 mm (step S107). The rotation speed of the upper and lower grinding plates was set to 30 rpm. Both sides of this disk blank were subjected to the following treatments: degreasing, etching (step S108), first zincate treatment, Zn stripping treatment, and second zincate treatment (step S109).

[0101] Degreasing was performed using degreasing solution AD-68F (product name, manufactured by Uemura Kogyo Co., Ltd.) under the following conditions: temperature 45°C, processing time 3 minutes, and concentration 500 mL / L. The etching process was performed using AD-107F (product name, manufactured by Uemura Kogyo Co., Ltd.) etching solution at a temperature of 60°C, a processing time of 2 minutes, and a concentration of 50 mL / L. The first zincate treatment was performed using zincate treatment solution AD-301F-3X (product name, manufactured by Uemura Kogyo Co., Ltd.) under the conditions of a temperature of 20°C, a treatment time of 1 minute, and a concentration of 200 mL / L. The Zn stripping treatment was performed using a commercially available nitric acid reagent under the following conditions: temperature 25°C, treatment time 60 seconds, and nitric acid concentration 30%. The second zincate treatment was carried out under the same conditions as the first zincate treatment. Furthermore, pure water washing was performed between each treatment step, from the degreasing treatment to the second zincate treatment.

[0102] Subsequently, electroless Ni-P plating was performed on both sides of the disk blank obtained in step S109 using Nimden HDX (product name, manufactured by Uemura Kogyo Co., Ltd.) plating solution at a temperature of 88°C, a processing time of 130 minutes, and a Ni concentration of 6 g / L (step S110).

[0103] Furthermore, the Ni-P plated disc blank was placed in a double-sided simultaneous polishing machine (product name: 9B double-sided grinding machine, manufactured by SPEEDFAM), and a dummy polishing process, a rough polishing process, and a precision polishing process (step S111) were performed to manufacture an aluminum alloy substrate. Details are described below.

[0104] First, prior to the rough polishing process, dummy polishing was performed. For dummy polishing, one of several electroless Ni-P plated substrates (before rough polishing) was used as the dummy substrate, and a hard urethane polishing pad with a hardness of 87 (product name: FF-5, manufactured by Fujibo Ehime Co., Ltd.) was used as the polishing pad. After performing dummy polishing multiple times under the conditions of the rough polishing process described later, the long-wavelength waviness Wa of the dummy substrate after polishing, measured at a cutoff wavelength of 0.4~5.0 mm, was less than 2.5 nm (2.19 nm), so the dummy polishing was terminated.

[0105] In addition, in the rough polishing of Examples 2-3 and Comparative Examples 1-2 described later, dummy polishing was not performed before rough polishing because the polishing pad used in Example 1 had its surface condition adjusted by dummy polishing.

[0106] The Ni-P plated main surface of the Ni-P plated disc blank was roughly polished using a hard urethane polishing pad with a hardness of 87 obtained from the dummy polishing process described above, and a polishing solution containing alumina abrasive grains with an average particle size of 0.4 μm. The disc blank was inverted during the rough polishing process (when half the polishing time had elapsed). Other polishing conditions in the rough polishing process were: polishing time 5 minutes, polishing plate rotation speed 30 rpm, sun gear rotation speed 10 rpm, polishing solution supply rate 1000 mL / min, and processing pressure 100 g / cm². 2 The polishing amount was set to 3.0 μm per side.

[0107] After rough polishing, the Ni-P plated disk blank was washed with pure water, and then precision polished with a soft urethane polishing pad with a hardness of 76 (product name: FK1-N, manufactured by Fujibo Ehime Co., Ltd.) and a polishing solution containing colloidal silica abrasive grains with an average particle size of 0.08 μm to create an aluminum alloy substrate with a thickness of 0.48 mm for use as a magnetic disk substrate. Other polishing conditions in the precision polishing process included a polishing time of 5 minutes, a polishing plate rotation speed of 30 rpm, a sun gear rotation speed of 10 rpm, a polishing solution supply rate of 1000 mL / min, and a processing pressure of 60 g / cm². 2 The polishing amount was set to 1.3 μm per side.

[0108] (Example 2) Al-Fe-Mn-Ni alloy (aluminum alloy B) was melted according to a standard method and a slab was obtained by DC casting (vertical semi-continuous casting) to a width of 1310 mm and a thickness of 500 mm. Each side of this slab was machined by 10 mm, and after homogenization treatment at 520°C for 6 hours, it was hot-rolled at a starting temperature of 520°C and an ending temperature of 330°C to obtain a hot-rolled sheet with a thickness of 3.0 mm. This hot-rolled sheet was cold-rolled to obtain a cold-rolled sheet with a thickness of 0.48 mm. Except for using this cold-rolled sheet in place of the cold-rolled sheet in Example 1, an aluminum alloy substrate with a thickness of 0.48 mm was prepared in the same manner as shown in Example 1. The composition of aluminum alloy B consisted of Fe: 0.7 mass%, Mn: 0.9 mass%, Ni: 1.7 mass%, with the remainder being aluminum and unavoidable impurities.

[0109] (Example 3) Al-Fe-Mn-Mg-Ni alloy (aluminum alloy C) was melted according to a standard method and a slab was obtained by DC casting (vertical semi-continuous casting) to a width of 1310 mm and a thickness of 500 mm. Each of the four sides of this slab was machined by 10 mm, and after homogenization treatment at 520°C for 6 hours, it was hot-rolled at a starting temperature of 520°C and an ending temperature of 330°C to obtain a hot-rolled sheet with a thickness of 3.0 mm. This hot-rolled sheet was cold-rolled to obtain a cold-rolled sheet with a thickness of 0.48 mm. Except for using this cold-rolled sheet in place of the cold-rolled sheet in Example 1, an aluminum alloy substrate with a thickness of 0.48 mm was prepared in the same manner as shown in Example 1. The composition of aluminum alloy C included Fe: 0.7% by mass, Mn0.3: 0.3% by mass, Mg: 1.4% by mass, Ni: 1.8% by mass, with the balance being aluminum and inevitable impurities.

[0110] (Example 4) Using the drawdown method, a glass plate made of aluminosilicate glass (containing SiO2: 65% by mass, Al2O3: 18% by mass, B2O3: 4% by mass, Li2O: 4% by mass, Na2O: 1% by mass, CaO: 4% by mass, P2O5: 1% by mass, and other trace components) with a width of 100 mm and a length of 10 m was manufactured, and a glass plate with a thickness of 0.60 mm was selected (step S201). For the selected glass plate, core drilling and end face polishing of the inner and outer circumferences were performed to obtain a disc-shaped blank with an outer diameter of 97 mm and an inner diameter of the circular hole of 25 mm (step S202). Further, the formed disc-shaped blank was set on a double-sided simultaneous polishing machine, and a rough polishing process (step S204) and a precision polishing process (step S205) were performed to manufacture a glass substrate. Since the polishing pad was adjusted to a suitable state, dummy polishing was not performed.

[0111] In the rough polishing process, a hard urethane polishing pad with a hardness of 87 (product name: FF-5, manufactured by Fujibo Ehime Co., Ltd.) and a polishing liquid prepared by adding pure water to cerium oxide polishing grains with an average particle size of 0.19 μm to form free abrasive grains were used. Five minutes after starting the rough polishing, the disc blank was inverted to reverse the front and back surfaces, and rough polishing was continued for another five minutes. Other polishing conditions in the rough polishing process were as follows: the rotation speed of the polishing platen was 25 rpm, the rotation speed of the sun gear was 10 rpm, the polishing liquid supply rate was 1500 mL / min, and the processing pressure was 120 g / cm 2 , and the polishing amount was 50 μm per side. In this way, a glass substrate with a plate thickness of 0.50 mm was obtained.

[0112] On the other hand, in the precision polishing process, a soft urethane polishing pad with a hardness of 76 (product name: FK1-N, manufactured by Fujibo Ehime Co., Ltd.) and a polishing solution made by adding pure water to colloidal silica with an average particle size of 0.08 μm to create free abrasive particles were used. Other polishing conditions in the precision polishing process included a polishing plate rotation speed of 25 rpm, a sun gear rotation speed of 10 rpm, a polishing solution supply rate of 1500 mL / min, a polishing time of 8.5 minutes, and a processing pressure of 50-120 g / cm². 2 The polishing amount was set to 10 μm per side. In this way, a glass substrate with a plate thickness of 0.48 mm was prepared.

[0113] (Comparative Example 1) The pressure annealing conditions were 30 kgf / cm² in air. 2 An aluminum alloy substrate was obtained in the same manner as in Example 1, except that the load was applied and pressurized while the temperature was changed at 200°C for 3 hours, and the disc blank was not inverted during the rough polishing process.

[0114] (Comparative Example 2) An Al-Fe-Mn-Ni alloy (aluminum alloy B) was melted according to a standard method and cast into a 1420 mm wide x 6.0 mm thick coil using CC casting (continuous casting). This continuously cast coil was cold-rolled to a thickness of 0.48 mm. This cold-rolled sheet was used in place of the cold-rolled sheet in Example 1, and the disc blank was not reversed during the rough polishing process, but otherwise, an aluminum alloy substrate with a thickness of 0.48 mm was obtained in the same manner as shown in Example 1.

[0115] (Comparative Example 3) A glass substrate was prepared in the same manner as in Example 4, except that in the rough polishing process, a hard urethane polishing pad with a hardness of 87 and a polishing solution made by adding pure water to cerium oxide abrasive grains with an average particle size of 1.50 μm to create free abrasive grains were used, and the disc blank was not reversed during the rough polishing process.

[0116] The aluminum alloy substrates of Examples 1-3 and Comparative Examples 1 and 2, as well as the glass substrates of Example 4 and Comparative Example 3, obtained as described above, were subjected to thermal shock tests, and the long-wavelength waviness Wa and short-wavelength waviness μWa of these substrates were measured. Details are described below.

[0117] (Thermal shock test) Using a small environmental tester SH-261 (product name, manufactured by ESPEC), the aluminum alloy substrate and glass substrate were subjected to a process of heating at 120°C for 30 minutes, followed by cooling at -40°C for 30 minutes. This cycle was repeated 200 times.

[0118] (Measurement of long-wavelength swell) Long-wavelength swell with cutoff wavelength 0.4~5.0mm Wa: Using an Optiflat surface profile analyzer (product name, manufactured by Phase Shift Technology), the long-wavelength waviness Wa of the main surface of aluminum alloy substrates or glass substrates after the thermal shock test was measured, with a cutoff wavelength of 0.4 to 5.0 μm. The measurement range was the entire main surface (one side) of the aluminum alloy substrate or glass substrate after the thermal shock test, and the measurement temperature was 25°C. Measurements were performed on three aluminum alloy substrates and three glass substrates after the thermal shock test (n=3). The average of the three measured values ​​was defined as the long-wavelength waviness Wa.

[0119] (Measurement of short-wavelength swell) Short-wavelength swell μWa with cutoff wavelength 0.08~0.45 mm: Using a microZAM-1200 particle size analyzer (product name, manufactured by Phase Shift Technology), the short-wavelength waviness μWa with a cutoff wavelength of 0.08 to 0.45 mm was measured in a 9.9 mm × 3.5 mm rectangular area located in the radial center of the main surface (one side) of an aluminum alloy substrate or glass substrate after the thermal shock test (positioned so that the virtual center line in the long side direction of 9.9 mm is parallel to the radial direction). The measurement temperature was 25°C. Measurements were taken using three aluminum alloy substrates and three glass substrates after the thermal shock test, at three locations each in the radial center, located at 0°, 90°, and 180° in the circumferential direction, as shown in Figure 3. The average of the nine measurements obtained in this way was defined as the short-wavelength waviness μWa.

[0120] The results obtained are shown in Table 1. In the "Evaluation" column of Table 1, "○" is indicated when the long-wavelength swell Wa is 2.0 nm or less and the short-wavelength swell μWa is 0.15 nm or less, and "×" is indicated when at least one of the long-wavelength swell Wa and the short-wavelength swell μWa is outside these ranges. Note that, due to their measurement principles, neither Optiflat nor microZAM-1200 can measure long-wavelength and short-wavelength undulations in transparent glass. Therefore, after thermal shock testing, aluminum was deposited onto the measurement surface of the glass substrate to make it optically opaque before measurement. The deposited layer is very thin and smooth, so it does not affect the measurement of the long-wavelength and short-wavelength undulations mentioned above.

[0121] Table 1 shows the evaluation results. The magnetic disk substrates of Examples 1 to 4 showed a long-wavelength swell Wa of 2.0 nm or less with a cutoff wavelength of 0.4 to 5.0 mm, and a short-wavelength swell μWa of 0.15 nm or less with a cutoff wavelength of 0.08 to 0.45 mm, as measured at 25°C after the thermal shock test. On the other hand, none of the magnetic disk substrates in Comparative Examples 1 to 3 satisfied the above-mentioned Wa and μWa requirements. In Comparative Examples 1 to 3, the disk blanks were not inverted during the rough polishing process (and in Comparative Example 3, the average particle size of the abrasive grains during the rough polishing process was large), resulting in uneven distortion remaining in the material. Therefore, it is thought that Wa and μWa could not be adjusted even with the manufacturing method of the present invention.

[0122] [Table 1] [Explanation of Symbols]

[0123] Preparation of S101 aluminum alloy Casting of S102 aluminum alloy S103 Homogenization treatment S104 Hot Rolling S105 Cold Rolling S106 Heat Planarization Treatment S107 Cutting and Grinding Process S108 Degreasing and Etching Treatment S109 Zincate treatment S110 Ni-P plating treatment S111 Polishing process S112 Magnetic material deposition process S201 Preparation of glass plate S202 Formation of disc-shaped disblank S203 Wrapping S204 Rough polishing S205 Precision polishing S206 Magnetic material deposition process

Claims

1. A substrate for a magnetic disk having a pair of main surfaces, A magnetic disk substrate, wherein at least one of the main surfaces, after the thermal shock test described below, has a long-wavelength swell Wa with a cutoff wavelength of 0.4 to 5.0 mm at 25°C of 2.0 nm or less, and a short-wavelength swell μWa with a cutoff wavelength of 0.08 to 0.45 mm of 0.15 nm or less. <Thermal shock test> The thermal shock test is performed by heating the magnetic disk substrate at 120°C for 30 minutes, followed by cooling at -40°C for 30 minutes, with each cycle being repeated 200 times.

2. The magnetic disk substrate according to claim 1, wherein the long-wavelength undulation Wa is 0.5 nm or more, and the short-wavelength undulation μWa is 0.05 nm or more.

3. The plate thickness is less than 0.50 mm. A substrate for a magnetic disk according to claim 1 or 2.

4. A magnetic disk substrate according to claim 1 or 2, wherein the outer diameter of the disk is 95 mm or more.

5. A magnetic disk substrate according to claim 1 or 2, for use with HAMR (heat-assisted magnetic recording) or MAMR (microwave-assisted magnetic recording).

6. A magnetic disk having a pair of main surfaces, A magnetic disk wherein, after the thermal shock test described below, at least one of the main surfaces has a long-wavelength swell Wa of 0.4 to 5.0 mm at 25°C that is 2.0 nm or less, and a short-wavelength swell μWa of 0.08 to 0.45 mm at 0.15 nm or less. <Thermal shock test> The thermal shock test is performed by heating the magnetic disk at 120°C for 30 minutes, followed by cooling at -40°C for 30 minutes, with each cycle being repeated 200 times.

7. A method for manufacturing a magnetic disk substrate according to claim 1 or 2, When obtaining a circuit board for magnetic disks from a disk blank, The process includes a rough polishing step of simultaneously rough polishing both main surfaces of the disc blank, and a precision polishing step of precisely polishing both main surfaces of the roughly polished disc blank. A method for manufacturing a substrate for a magnetic disk, comprising inverting the front and back surfaces of the disk blank during the rough polishing process.

8. As a step prior to the rough polishing step, a dummy substrate manufactured under the same conditions as the disk blank is polished using two polishing pads used in the rough polishing step, under the same conditions as the rough polishing step, until the long-wavelength undulation Wa on one side with a cutoff wavelength of 0.4 to 5.0 mm is less than 2.5 nm, thereby obtaining a polishing pad with an adjusted surface condition. The method for manufacturing a substrate for a magnetic disk according to claim 7, wherein in the rough polishing step, the disk blank is roughly polished using a polishing pad whose surface condition has been adjusted.

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