Magnetic disk and substrate for magnetic disk

Abstract

The present invention provides a magnetic disk that is thin and flat and is less likely to have physical errors. The present invention is a magnetic disk having a hole in a center portion and a thickness dimension of 0.60 mm or less, wherein, when the radius of the disk is set as R (mm), the radial distance measured from the center of the disk is set as r (mm), TIR at the outer peripheral side region of the disk where r / R is 0.70 or more and 0.99 or less is set as TIR1 (μm) and TIR2 (μm) when measured on the circumferences at different radial distances r1 (mm) and r2 (mm), and the radial variation amount ΔTIR of TIR represented by the absolute value of the ratio of the difference (TIR1-TIR2) between TIR1 and TIR2 to the difference (r1-r2) between the radial distance r1 and the radial distance r2 of the disk |(TIR1-TIR2) / (r1-r2)| is 0.50 μm / mm or less.

Description

TECHNICAL FIELD

[0001] The present application relates to a magnetic disk and a substrate for a magnetic disk. In detail, the present application relates to a magnetic disk which is thin-walled, has a small amount of variation in TIR in the radial direction, is flat, and has a reduced occurrence of physical errors, and particularly relates to a magnetic disk such as a hard disk mounted in a data center or a computer, and a substrate for a magnetic disk such as an aluminum alloy substrate and a glass substrate. BACKGROUND

[0002] As a storage device of a data center or a computer, a hard disk drive (hereinafter, sometimes referred to as "HDD") device is used. In recent years, due to the spread of smartphones and smart home appliances, the advancement of the Internet of Things (IoT), and the rapid spread of cloud computing, the amount of data to be recorded has rapidly increased. These large amounts of data are read and written to HDD devices in a data center via the Internet. In order to record large amounts of data, HDD devices need to be increased in capacity.

[0003] For HDD devices, a magnetic disk for recording data is used. As a technique for achieving an increase in capacity of HDD devices, one approach is to thin the thickness of the magnetic disk and increase the number of disks mounted in the HDD device. As another technical trend, a technique is also being explored in which the diameter of the magnetic disk is increased so that the data area on the disk surface is as close as possible to the outer diameter end portion, thereby expanding the data area of each disk.

[0004] If the thickness of the magnetic disk is simply thinned, the rigidity will decrease, and thus there is a tendency for the deformation of the magnetic disk to increase when vibrations (chatter) and impacts are applied when the magnetic disk is rotating. Therefore, for example, in an HDD device in which a plurality of thin-walled magnetic disks using an aluminum alloy substrate and a glass substrate are mounted, the spacing between the disks or even the spacing between the disks and components such as a magnetic head becomes narrow, and contact between the disks or between the disks and the magnetic head is likely to occur. As a result, errors are likely to occur during reading and writing. In order to reduce physical errors in such an HDD device, several approaches related to the flattening of the magnetic disk have been explored.

[0005] For example, in Patent Literature 1, a technique is disclosed in which the amount of variation in height at the outer peripheral end portion of a substrate for a magnetic disk and the TIR are regulated in order to suppress a head crash of an HDD. Here, the TIR is an index indicating the degree of flatness of the surface. The TIR at the outer peripheral end portion refers to the difference (PV value) between the highest point (P) located above and the lowest point (V) located below when the height of the outer peripheral end portion of the substrate is measured in the circumferential direction, with a plane that best fits the main surface of the outer peripheral end portion of the substrate being found by the least squares method. In Patent Literature 2, a technique is disclosed in which a glass substrate of a specific composition is precisely polished in such a way that the TIR at the radii of two specified points becomes a predetermined value or less.

[0006] [Prior Art Documents]

[0007] (Patent Documents)

[0008] Patent Document 1: Japanese Patent Application Publication No. 2013-16214

[0009] Patent Document 2: Japanese Patent Application Publication No. 2011-225436 SUMMARY

[0010] [Problems to be Solved by the Invention]

[0011] Conventionally, flatness of a magnetic disk is defined in terms of flatness, undulation, TIR value on a circumference at an arbitrary position, etc. of the entire surface of a substrate. For example, in Patent Documents 1 and 2, flatness is evaluated by TIR when measured in the circumferential direction. However, with recent thinning and enlargement of magnetic disks, unprecedented new problems have emerged. When the thickness is simply reduced, for example, to 0.60 mm or less, the deformation of the magnetic disk becomes large when vibration (chatter) or impact is applied during rotation of the magnetic disk, and thus the frequency of occurrence of physical errors of the magnetic disk becomes high. In addition, when evaluating the magnetic disk, it is sometimes difficult to determine whether or not read / write errors are within an allowable range. The size of the substrate that is the object of investigation in Patent Documents 1 and 2 is relatively small, for example, 2.5 inches (about 65 mm) or less in outer diameter, and more than 0.635 mm in thickness. Therefore, it is possible to avoid physical errors by defining only TIR, etc. of the outer circumferential end portion, but in a thin-walled large magnetic disk, this alone is not sufficient as a countermeasure to avoid errors.

[0012] In addition, in recent HDD devices, the distance between the magnetic disk and the magnetic head during operation of the HDD is becoming shorter. For example, in the case of a thin magnetic disk having a thickness of about 0.60 mm or less, the magnetic head that reads and writes while floating on the main surface can become unstable due to variations in the shape of the main surface, resulting in operation errors such as read / write errors. Therefore, in an HDD substrate in which the distance between the substrate and the magnetic head is short, it is also necessary to consider the shape of the main surface, not just the outer circumferential end portion. In particular, if the area from the vicinity of the radial center on the main surface to the outermost circumferential portion is not flat, errors are likely to occur during operation of the HDD.

[0013] An object of the present application is to provide a magnetic disk and a substrate for a magnetic disk that are thin-walled and flat, are less likely to have physical errors, and can cope with high capacity of hard disks.

[0014] [Technical Means for Solving the Problems]

[0015] The present inventors have made intensive studies, and as a result, have found that by measuring respective TIRs on a plurality of concentric circles in a specific area of a magnetic disk and setting the radial variation amount of the TIRs to be equal to or less than a predetermined value, even a thin magnetic disk having a thickness dimension of 0.60 mm or less is less likely to suffer from physical errors and can cope with high capacity of the hard disk; thus the present invention has been completed.

[0016] In order to achieve the above object, the gist of the present invention is configured as described below.

[0017] (1) A magnetic disk having a hole in a center portion, and

[0018] a thickness dimension of 0.60 mm or less,

[0019] a radius of the aforementioned magnetic disk is set to R (mm),

[0020] a radial distance of the aforementioned magnetic disk measured from the center of the aforementioned magnetic disk is set to r (mm),

[0021] an outer peripheral side area of the aforementioned magnetic disk where r / R is 0.70 or more and 0.99 or less,

[0022] when TIRs measured on circumferences of different radial distances r1 (mm) and r2 (mm) of the aforementioned magnetic disk are set to TIR1 (pm) and TIR2 (pm),

[0023] a radial variation amount ATIR of the TIR represented by the absolute value of the ratio of the difference between the aforementioned TIR1 and the aforementioned TIR2 (TIR1-TIR2) to the difference between the aforementioned radial distance r1 of the aforementioned magnetic disk and the aforementioned radial distance r2 of the aforementioned magnetic disk (r1-r2) | (TIR1-TIR2) / (r1-r2) | is 0.50 pm / mm or less.

[0024] (2) The magnetic disk according to the aforementioned (1), wherein the flatness PV is 20.0 pm or less.

[0025] (3) The magnetic disk according to the aforementioned (1) or (2), wherein an outer diameter dimension is 95 mm or more.

[0026] (4) A substrate for the magnetic disk according to any one of the aforementioned (1) to (3).

[0027] (5) A manufacturing method of a magnetic disk according to any one of the aforementioned (1) to (3), characterized in that,

[0028] the aforementioned magnetic disk is manufactured from an aluminum alloy substrate,

[0029] the manufacturing method of the aforementioned magnetic disk has a grinding process of grinding the aforementioned aluminum alloy substrate,

[0030] The aforementioned lapping process is performed under conditions that the pressurizing pressure is 50 g / cm 2 or more and 120 g / cm 2 The aforementioned lapping process is performed under conditions that the platform rotation speed is 10 rpm or more and 35 rpm or less, and the coolant flow rate is 1 L / min or more and 10 L / min or less.

[0031] (6) A method of manufacturing a magnetic disk according to any one of the above (1) to (3), characterized in that,

[0032] The aforementioned magnetic disk is manufactured from a glass substrate,

[0033] The aforementioned method of manufacturing a magnetic disk has a lapping process of lapping the aforementioned glass substrate,

[0034] The aforementioned lapping process is performed under conditions that the pressurizing pressure is 100 g / cm 2 or more and 200 g / cm 2 The aforementioned lapping process is performed under conditions that the platform rotation speed is 10 rpm or more and 35 rpm or less, and the coolant flow rate is 1 L / min or more and 10 L / min or less.

[0035] (7) A method of manufacturing a magnetic disk according to the above (5) or (6), wherein, in the aforementioned lapping process, the lapping amount is 2.5 μm or more and 25 μm or less.

[0036] (8) A method of manufacturing a magnetic disk according to any one of the above (5) to (7), wherein, in the aforementioned lapping process, at least once the front and back surfaces of the aforementioned aluminum alloy substrate or the aforementioned glass substrate are reversed and lapping is continued.

[0037] (9) A method of manufacturing a magnetic disk according to any one of the above (5) to (8), wherein, after the aforementioned lapping process, a polishing process of polishing the aforementioned aluminum alloy substrate or the aforementioned glass substrate is further performed, and, in the aforementioned polishing process, at least once the front and back surfaces of the aforementioned aluminum alloy substrate or the aforementioned glass substrate are reversed and polishing is continued.

[0038] (EFFECTS OF THE INVENTION)

[0039] According to the present application, a magnetic disk can be provided which is thin-walled with a thickness dimension of 0.60 mm or less, and is extremely flat with a ΔTIR of 0.50 μm / mm or less, and thus is less likely to collide with an adjacent disk. Therefore, the magnetic disk of the present application can be mounted in an HDD device in multiple numbers, and thus can cope with the high capacity of a hard disk. In addition, the magnetic disk of the present application can be large-sized, for example, can have an outer diameter dimension of 95 mm or more. Furthermore, up to the limit of the outer peripheral end portion of the disk, it can be used as a data area, and in this respect, can also contribute to the high capacity of a hard disk. Furthermore, the magnetic disk of the present application is less likely to cause a head collision even if mounted in an HDD device in which the distance between the disk and the head is short, and is less likely to cause an error in the operation of the HDD device. Therefore, the magnetic disk of the present application is particularly suitable as a magnetic disk for a hard disk mounted in a data center or a computer or the like. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 is a conceptual view for explaining a measurement site and an outer peripheral side area of a radial variation amount of TIR in the magnetic disk of the present application.

[0041] Figure 2 is a conceptual view illustrating an example of a graph in which a height measured in the circumferential direction on the concentric circle Ca or Cb in Figure 1 is plotted against the angle at the measurement site.

[0042] Figure 3 is a flowchart illustrating an example of a manufacturing process of the aluminum alloy substrate for a magnetic disk of the present application.

[0043] Figure 4 is a flowchart illustrating an example of a manufacturing process of the glass substrate for a magnetic disk of the present application. DETAILED DESCRIPTION

[0044] Hereinafter, the magnetic disk of the present application will be described in detail.

[0045] Magnetic Disk

[0046] The disk of the present application has a hole in the center portion, and has a thickness dimension of 0.60 mm or less. When the radius of the disk is set as R (mm), the radial distance of the aforementioned disk measured from the center of the disk is set as r (mm), TIR measured at the outer peripheral side region of the disk where r / R is 0.70 or more and 0.99 or less, at the circumferences of different radial distances r1 (mm) and r2 (mm) of the disk, is set as TIR1 (μm) and TIR2 (μm), respectively, and the difference (TIR1 - TIR2) between TIR1 and TIR2 with respect to the ratio of the absolute value of the difference between the radial distance r1 of the disk and the radial distance r2 of the disk (r1 - r2) to the radial variation amount ΔTIR of TIR represented by |(TIR1 - TIR2) / (r1 - r2)| is 0.50 μm / mm or less.

[0047] As described above, in the disk of the present application, it is an important condition that the radial variation amount ΔTIR of TIR in the outer peripheral side region is 0.50 μm / mm or less. In the case where the thickness of the disk is thin, particularly 0.60 mm or less, if ΔTIR in the outer peripheral side region is greater than 0.50 μm / mm, a physical error is likely to occur. On the other hand, in the disk of the present application where ΔTIR is 0.50 μm / mm or less, a physical error is unlikely to occur even though the thickness dimension is 0.60 mm or less.

[0048] Here, the "outer peripheral side region" means, as described above, a region where the ratio r / R of the radial distance r measured from the center of the disk to the radius R of the disk is 0.70 or more and 0.99 or less. Figure 1 is a conceptual view for explaining the measurement position of the radial variation amount of TIR and the outer peripheral side region in the disk of the present application. In the disk 1 shown in Figure 1 For example, in the disk 1 shown in, the region divided by the two concentric circles shown by the broken lines, i.e., the outer peripheral circle Ca at the position where the aforementioned ratio r / R is 0.99 and the inner peripheral circle Cb at the position where the aforementioned ratio r / R is 0.70, is the outer peripheral side region.

[0049] Radial Variation Amount of TIR

[0050] The radial variation amount of TIR is an amount representing how much TIR varies due to the difference in radial distance when TIR is measured at the circumferences of two concentric circles having different radial distances of the disk surface. In Figure 1The TIR is measured on the circumferences of the concentric circles C1 and C2 at the radial distances r1 (mm) and r2 (mm) in the outer peripheral region of the main surface of the disk 1, and TIR1 (pm) and TIR2 (pm) are obtained. Next, the difference between TIR1 and TIR2 is divided by the difference between r1 and r2, and the absolute value is taken as the radial variation amount ΔTIR of the TIR, as shown in the following (Formula 1).

[0051] ΔTIR = | (TIR1 - TIR2) / (r1 - r2) | ··· (Formula 1)

[0052] (TIR)

[0053] TIR is an abbreviation of Total Indicated Reading, and is an index indicating the flatness of a surface. In the case of the disk 1, the radial variation amount ΔTIR of the TIR is calculated as follows. Figure 1 First, a plane that best fits the main surface of the disk is obtained by the least squares method. Next, the height (unevenness) of the main surface of the disk in the concentric circle Ca or Cb portion is measured in the circumferential direction. Figure 2 is a conceptual diagram illustrating an example of a graph in which the height measured in the circumferential direction is plotted against the angle at the measurement site. Here, the difference (PV value) between the highest point (P) above the aforementioned plane and the lowest point (V) below the plane is the TIR on the circumference. As for the TIR, the measurement can also be performed on the circumferences of the same radius on both main surfaces, and the higher value is taken as the TIR on the circumference.

[0054] (ΔTIR)

[0055] The TIR measurement on the circumference described above is performed on a plurality of concentric circles having different radial distances, and the value calculated according to the above (Formula 1) is the radial variation amount ΔTIR of the TIR for each radial distance. Therefore, ΔTIR is a value that includes not only the variation in the height on a specific circumference (e.g., the outer circumference) of the disk, but also the variation in the height in the radial direction. That is, ΔTIR is an index indicating the variation (thickness, undulation, unevenness, etc.) in the height in both the circumferential and radial directions of the disk. It can be said that the closer ΔTIR is to 0, i.e., the smaller the absolute value of ΔTIR, the flatter the disk, and the less likely the disk is to cause physical errors due to collisions, etc.

[0056] In the magnetic disk of the present application, as the radial variation ΔTIR, the value in the outer peripheral side region of the disk, i.e., the region where r / R is 0.70 or more and 0.99 or less, is used as described above. According to the present inventor's finding, the disk surface has a tendency to be particularly uneven in this region. In the manufacture of the disk, polishing / grinding of the substrate of glass or metal is performed, and in the polishing / grinding process, the outer peripheral side region is a portion where the roughness is particularly likely to vary. Therefore, if the disk is one in which the radial variation ΔTIR in the outer peripheral side region is small, it can be evaluated as a more planar disk that is excellent in polishing / grinding precision or the like.

[0057] The magnetic disk of the present application, since the above ΔTIR is extremely small, 0.50 μm / mm or less, in the outer peripheral side region, has the effect of being thin-walled with a thickness dimension of 0.60 mm or less, and not easily causing a collision with an adjacent disk or head in the HDD device, and not easily causing a physical error. From the viewpoint of further reducing the physical error, the ΔTIR in the magnetic disk of the present application is preferably 0.40 μm / mm or less, further 0.30 μm / mm or less, and particularly 0.20 μm / mm or less.

[0058] (Method for evaluating the shape of a disk)

[0059] The surface shape of the above-described TIR or the like of a disk can be evaluated, for example, with a general optical inspection device. The evaluation method and the inspection device are not particularly limited, and for example, FT-17 (trade name) manufactured by Nidec Corporation, mesa (trade name) manufactured by Zygo Corporation, FM-200 manufactured by Tropel Corporation, or the like can be appropriately used.

[0060] In order to make the magnetic disk of the present application less likely to cause a physical error, it is preferable to evaluate by a plurality of ΔTIR. For example, in a disk having an outer diameter of 95 mm (radius R of 47.5 mm), three kinds of radial variations ΔTIR are calculated from the TIR on concentric circles at a distance r of 40 mm (r / R = 84%), 45 mm (r / R = 95%), 46 mm (r / R = 97%), and 47 mm (r / R = 99%) from the center. If the absolute values of these three ΔTIR are all 0.50 μm / mm or less, it is possible to provide an HDD device that further reduces the operational error and is more reliable.

[0061] <Flatness of a disk>

[0062] In addition, the disk of the present application preferably has a small value of flatness PV. If PV is small, particularly if the disk is 20.0 μm or less, the risk of collision is low even if a plurality of disks are mounted in an HDD device, and physical errors are unlikely to occur. In addition, from the viewpoint of shape evaluation, it is also preferable that PV be as small as possible. If the flatness PV is large, in the case where the surface shape of the disk is measured with an optical inspection device, in the optical system in which the measurement light emitted from the inspection device is reflected on the surface of the disk and returned to the sensor of the inspection device, sometimes a portion of the reflected measurement light cannot be returned to the sensor of the inspection device, and the surface shape of the desired area cannot be evaluated. On the other hand, if PV is small, for example, 20.0 μm or less, the surface shape can be evaluated without problems with an optical inspection device.

[0063] Here, the flatness PV is a value obtained by first, as with the above-described TIR on the circumference, finding a plane that best fits the main surface of the disk by the least squares method, and then finding the difference between the highest point (P) and the lowest point (V) in the height (roughness) measurement of the main surface of the disk over the entire surface. The flatness PV indicates the flatness of the entire surface of the disk including not only the surface roughness of the disk but also the undulations and irregularities of the main body of the disk. If ΔTIR is 0.50 μm / mm or less and the flatness PV is small, for example, 20.0 μm or less, the risk of collision is low even if a plurality of disks are mounted in an HDD device, and operational errors are unlikely to occur. From the viewpoint of reducing physical errors, the flatness PV of the disk of the present application is further preferably 15.0 μm or less, particularly 10.0 μm or less. Here, the flatness can also be set to the flatness of the substrate for which the higher value is measured in the measurement of both main surfaces.

[0064] <Size of Disk>

[0065] As described above, since the disk of the present application has a very flat surface, the effect that collision is unlikely even if a plurality of disks are mounted in an HDD device is exhibited. The effect of the present application is particularly significant in a thin-walled disk having a thickness dimension of 0.60 mm or less, particularly 0.50 mm or less, 0.48 mm or less, and further 0.38 mm or less. This is because, in such a thin-walled substrate, since the rigidity is low compared to a disk having a greater thickness, the flatness greatly affects the reliability of the hard disk. For the same reason, the effect of the present application is significant in a disk having an outer diameter dimension (diameter) of, for example, 65 mm or more, particularly 95 mm or more.

[0066] The disk of the present application is not only flat in the circumferential direction but also flat in the radial direction, and therefore, the risk of the fluctuation or unevenness of the outer circumferential side region increasing with the large-scale of the disk (expansion of the radius) and causing a collision is also reduced. Therefore, the disk of the present application is suitable as a large-scale hard disk of 95 mm or more in diameter, further 96 mm or more, and particularly 97 mm or more. In addition, the present application also includes a disk of 95 mm or more in outer diameter size. The outer circumferential side of the disk is particularly greatly contributed to the expansion of the data area, and therefore, the large-scale and flat disk of the present application is useful for the realization of large capacity. In addition, the disk of the present application exhibits a flatness of ΔTIR of 0.50 μm / mm or less in the region of 0.99 times or less of the outer circumferential radius, and therefore, up to the limit of the outer circumferential end of the disk, it can be used as a data area. In this respect, the disk of the present application is also particularly useful for the realization of large capacity of the HDD device.

[0067] In addition, the disk of the present application can be used as a disk for any recording method. For example, as a large-capacity disk for a data center, a disk of a perpendicular magnetic recording method (PMR) or a shingled magnetic recording method (SMR) can be suitably used. In order to realize further large capacity, energy-assisted magnetic recording technologies such as a heat-assisted magnetic recording method (HAMR) and a microwave-assisted magnetic recording method (MAMR) have also been developed, and researches using a bit pattern medium for further improving the recording density of the surface are also being conducted. The disk of the present application is suitable for such use.

[0068] The disk of the present application can be any kind of disk as long as the thickness size is 0.60 mm or less and the ΔTIR is 0.50 μm / mm or less as described above, and the material is not particularly limited. In general, a disk is manufactured by forming a magnetic film on a substrate of metal or glass, resin, or the like. In the disk of the present application, the material and the film formation method of the magnetic film are not particularly limited.

[0069] Substrate

[0070] Further, the present application also includes a substrate for the above-described magnetic disk (substrate for magnetic disk). The material of the substrate is not particularly limited, and can be any material as described above. The substrate is generally polished before film formation, and the substrate of the present application can be polished in any method / condition. However, in terms of making the magnetic disk of the present application have the degree of flatness as described above, it is preferable to use a substrate composed of a metal substrate, particularly an aluminum alloy or glass (in the present specification, sometimes referred to simply as "aluminum alloy substrate" and "glass substrate"). The aluminum alloy substrate and the glass substrate are less likely to generate defects, and have good mechanical properties and workability, and thus are suitable as the substrate for magnetic disk of the present application. In particular, as the substrate for magnetic disk for HAMR described above, a glass substrate having excellent heat resistance is preferable. As the substrate for magnetic disk for MAMR, either of a glass substrate and an aluminum alloy substrate can be used.

[0071] Further, in terms of planarizing the substrate for magnetic disk, it is preferable to polish in a method / condition corresponding to the material of the substrate. Hereinafter, with respect to the aluminum alloy substrate and the glass substrate, the particularly preferable material is exemplified, and with respect to these substrates, the preferable polishing method and condition are described. Note that the material and the manufacturing method of the substrate are not limited to the following description.

[0072] <Aluminum Alloy Substrate>

[0073] The material of the aluminum alloy substrate is not particularly limited, and various known materials can be used. For example, an alloy containing elements such as magnesium (Mg), copper (Cu), zinc (Zn), or chromium (Cr) that has been used in the past can be exemplified, but is not limited to these. From the viewpoint of improving rigidity, an alloy containing elements such as iron (Fe), manganese (Mn), or nickel (Ni) is preferable. More preferably, an alloy of the A5000 series or the A8000 series, particularly A5086 is used. If such an alloy is used, defects are less likely to occur in the substrate, and in addition, sufficient mechanical properties can be imparted.

[0074] If examples of the specific composition of the above-mentioned aluminum alloy are listed, for example, in A5086, Mg: 3.5 to 4.5%, Fe: 0.50% or less, Si: 0.40% or less, Mn: 0.20 to 0.7%, Cr: 0.05 to 0.25%, Cu: 0.10% or less, Ti: 0.15% or less, and Zn: 0.25% or less are contained, and the remainder is composed of Al and inevitable impurities. In addition, as examples of the specific other composition of the aluminum alloy, a case where Mg: 1.0 to 6.5%, Cu: 0 to 0.070%, Zn: 0 to 0.60%, Fe: 0 to 0.50%, Si: 0 to 0.50%, Cr: 0 to 0.20%, Mn: 0 to 0.50%, Zr: 0 to 0.20%, Be: 0 to 0.0020% are contained, and the remainder is composed of aluminum and inevitable impurities can be listed. In addition, with respect to the components other than the above, for example, each element can be contained at 0.1% or less, and the total amount of the contained elements can be 0.3% or less. Furthermore, in the above-mentioned composition, "%" means "mass %".

[0075] As the substrate for a magnetic disk of the present application, a substrate of an aluminum-iron alloy can also be used. In general, the aluminum-iron alloy is an alloy containing Fe as an essential element, and one or both of Mn and Ni as optional elements. Further preferably, the total amount of these Fe, Mn, and Ni is 1.00 to 7.00 mass%, and particularly preferably, one or two or more of 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, and Zr: 0.20 mass% or less is further contained, and the remainder is composed of an aluminum alloy of aluminum and inevitable impurities and other trace elements. These aluminum-iron alloys have high rigidity and are less likely to be deformed, and thus are particularly useful as the substrate for a magnetic disk of the present application.

[0076] <GLASS SUBSTRATE>

[0077] The glass substrate has characteristics that defects are less likely to occur, mechanical properties and processability are also good, and also has the advantage that plastic deformation is less likely to occur, and is therefore suitable as a substrate for a magnetic disk. The material of the glass substrate is not particularly limited, and a glass ceramic such as amorphous glass or crystalline glass can be used. In addition, from the viewpoint of flatness and formability, processability of the substrate, it is preferable to use amorphous glass. The material is not particularly limited, and as examples, aluminosilicate glass (alumina-silica glass), soda-lime glass, aluminosilicate soda glass, boro-aluminosilicate glass, borosilicate glass (boron-silica glass), and physically strengthened glass or chemically strengthened glass subjected to air cooling or liquid cooling treatment, or the like can be given, but are not limited thereto. Among these, aluminosilicate glass, and particularly amorphous aluminosilicate glass is preferable. The substrate of such a material is excellent in flatness and strength, and long-term reliability can also be made good.

[0078] As the aluminosilicate glass, for example, a substance in which SiO2: 55 to 75% is a main component, and Al2O3: 0.7 to 25%, Li2O: 0.01 to 12%, Na2O: 0.7 to 12%, K2O: 0 to 8%, MgO: 0 to 7%, CaO: 0 to 10%, ZrO2: 0 to 10%, TiO2: 0 to 1% are contained is known, and a substrate of such a material can also be used in the present application. In addition, in the above and below compositions, "%" means "mass%".

[0079] In the above glass composition, SiO2is a main component that forms the skeleton of the glass. If the content rate thereof is 55% or more, high chemical durability is easily exhibited, and if it is 75% or less, there is a tendency that the melting temperature does not become excessively high, and forming becomes easy.

[0080] Al2O3is a component that has the effect of improving ion exchange property and chemical durability, and in order to exert the effect, it is preferable to set the content rate of Al2O3to 0.7% or more. In addition, if the content rate of Al2O3is 25% or less, the solubility and devitrification resistance do not decrease. Therefore, it is preferable to set the content rate of Al2O3to 0.7 to 25%.

[0081] Li2O is a component that has the effect of chemically strengthening the glass by ion exchange with Na ions, and improving the melting property, formability, and Young's modulus. In order to exert the effect, it is preferable to set the content rate of Li2O to 0.01% or more. In addition, if the content rate of Li2O is 12% or less, and particularly 6% or less, the devitrification resistance and chemical durability do not decrease. Therefore, it is preferable to set the content rate of Li2O to 0.01 to 6%.

[0082] Na2O is a component having an effect of chemical strengthening of the glass by ion exchange with K ions, and reducing high-temperature viscosity, improving meltability, formability, and improving resistance to devitrification. In order to exert the effect, the content of Na2O is preferably 0.7% or more. If the content of Na2O is 12% or less, chemical durability and Knoop hardness do not decrease, and thus is preferable.

[0083] Further, K2O, MgO, CaO, ZrO2, and TiO2 are arbitrary additive components that can be contained as needed. K2O is a component having an effect of reducing high-temperature viscosity, and having an effect of improving meltability, improving formability, and improving resistance to devitrification, but if the content of K2O exceeds 8%, there is a tendency that low-temperature viscosity decreases, and thermal expansion rate increases, and impact resistance decreases. Thus, the content of K2O is preferably 0% to 8%.

[0084] MgO and CaO are components having an effect of reducing high-temperature viscosity, and improving melting and fineness, formability, and improving Young's modulus, and in particular, CaO is contained as a necessary component in soda-lime glass. Here, MgO and CaO, while reducing high-temperature viscosity, improving melting and fineness, formability, and improving Young's modulus, can also be expected to have an effect of improving Young's modulus, but if the content of MgO exceeds 7% and / or the content of CaO exceeds 10%, there is a tendency that ion exchange performance and resistance to devitrification decrease. Thus, the content of MgO is preferably 7% or less, and the content of CaO is preferably 10% or less.

[0085] ZrO2 is a component having an effect of increasing Knoop hardness, and improving chemical durability and heat resistance, but if the content of ZrO2 exceeds 10%, there is a tendency that meltability and resistance to devitrification decrease. Thus, the content of ZrO2 is preferably 0% to 10%.

[0086] TiO2 is a component having an effect of reducing high-temperature viscosity, improving meltability, and improving structural stabilization and durability, but if the content of TiO2 exceeds 1%, there is a tendency that ion exchange performance and resistance to devitrification decrease. Thus, the content of TiO2 is preferably 0% to 1%.

[0087] In addition, the glass having the above composition can further contain As2O3, Sb2O3 as a fining agent, in addition to B2O3 which has the effect of lowering viscosity, improving melting property and fining property; SrO or BaO which has the effect of lowering high-temperature viscosity, improving melting property and fining property, improving Young's modulus; ZnO which lowers high-temperature viscosity while improving ion exchange property without lowering low-temperature viscosity; SnO2 which has the effect of improving fining property and ion exchange property; Fe2O3 or the like which functions as a colorant. In addition, as a trace element, oxides of lanthanum (La), phosphorus (P), cerium (Ce), antimony (Sb), hafnium (Hf), rubidium (Rb), yttrium (Y) or the like can be contained. Furthermore, B2O3 is contained as an essential component in aluminoborosilicate glass or borosilicate glass. In addition, the above glass can have a composition containing SiO2: 45 to 60%, Al2O3: 7 to 20%, B2O3: 1 to 8%, P2O5: 0.5 to 7%, CaO: 0 to 3%, TiO2: 1 to 15%, BaO: 0 to 4%, and other oxides such as MgO: 5 to 35%.

[0088] If the aluminum alloy substrate or the glass substrate having the above composition is used, high flatness can be exhibited, and thermal deformation is unlikely to occur, so that a magnetic disk having a thickness of 0.60 mm or less and a ΔTIR of 0.50 μm / mm or less can be manufactured. Hereinafter, first, a method of manufacturing such a flat aluminum alloy substrate from an aluminum alloy as described above will be described with reference to a representative example.

[0089] <Method of manufacturing an aluminum alloy substrate>

[0090] Figure 3 is a flowchart illustrating an example of a manufacturing process of an aluminum alloy substrate for a magnetic disk according to the present application. In the manufacturing process of the aluminum alloy substrate for a magnetic disk according to the present application, first, an aluminum alloy substrate is prepared (step S1). The aluminum alloy substrate is manufactured by a method described below. Figure 3In the present embodiment, the aluminum alloy component preparation step (step S101), the aluminum alloy casting step (step S102), the homogenization treatment step (step S103), the hot rolling step (step S104), and the cold rolling step (step S105) are steps for manufacturing an aluminum alloy raw material by melting and casting, and for manufacturing an aluminum alloy sheet from the aluminum alloy raw material. Next, a desired inner diameter and outer diameter of a disk (hereinafter, sometimes referred to as "blank") composed of an aluminum alloy is manufactured by a press working step (step S106) using a press machine or the like (blanking), and is preferably delivered to a pressurized flattening treatment step (step S107). Then, the manufactured blank is subjected to a pretreatment such as a cutting working / abrasive working step (steps S108-S109), and a circular ring-shaped aluminum alloy sheet (hereinafter, also referred to as "base plate" or simply "base") having a size or the like adjusted is manufactured. The base plate is subjected to a zincate treatment step (step S110) and a non-electrolytic Ni-P plating treatment step (step S111), and an aluminum alloy substrate for a magnetic disk is manufactured. The manufactured aluminum alloy substrate for a magnetic disk is delivered to a rough polishing step (step S112) and a precision polishing step (step S113), and becomes a magnetic disk by a magnetic body attaching step (step S114). Hereinafter, the contents of each step will be described in detail in accordance with the flow of the present embodiment. Figure 3

[0091] First, a molten metal of an aluminum alloy raw material having the above-described component composition is prepared by heating / melting in accordance with a normal method (step S101). Next, the prepared molten metal of the aluminum alloy raw material is cast by a semi-continuous casting (DC (direct chill casting) casting) method or a continuous casting (CC (continuous casting) casting) method or the like, and the aluminum alloy raw material is cast (step S102). A vertical semi-continuous casting is particularly preferable. The manufacturing conditions of the aluminum alloy raw material in the DC casting method and the CC casting method or the like are as described below.

[0092] In the DC casting method, the molten metal injected through a spout absorbs heat from a lower pad, a wall of a water-cooled mold, and cooling water directly sprayed to the outer peripheral portion of an ingot (block), and solidifies, and is drawn downward as an aluminum alloy block.

[0093] On the other hand, in the CC casting method, the molten metal is supplied between a pair of rolls (or a belt caster, a block caster) through a casting nozzle, and a thin sheet of an aluminum alloy is directly cast using heat dissipation from the rolls.

[0094] The large difference between the DC casting method and the CC casting method is the cooling speed at the time of casting. In the CC casting method in which the cooling speed is large, the size of the second phase particles is characterized as being smaller than that in the DC casting.​

[0095] For the aluminum alloy ingot cast by DC casting, homogenization treatment is performed as necessary (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 preferable to perform heat treatment at 300 to 620°C for 1 to 24 hours. When the heat treatment temperature is less than 280°C or the heat treatment time is less than 0.5 hour, it is possible that the unevenness of the loss coefficient of each aluminum alloy sheet becomes large due to insufficient homogenization treatment. If the heat treatment temperature exceeds 620°C during homogenization treatment, it is possible that melting occurs in the aluminum alloy ingot. Even if the heat treatment time exceeds 30 hours during homogenization treatment, the effect is saturated and no additional significant improvement effect can be obtained.

[0096] Next, the aluminum alloy ingot on which homogenization treatment has been performed as necessary or on which homogenization treatment has not been performed (DC casting) is subjected to hot rolling to produce a sheet (step S104). The conditions for hot rolling are not particularly limited, and the hot rolling start temperature is preferably set to 250 to 600°C and the hot rolling end temperature is preferably set to 230 to 450°C.

[0097] Next, the calendered sheet on which hot rolling has been performed or a cast sheet cast by the CC casting method is subjected to cold rolling to produce an aluminum alloy sheet of, for example, about 0.30 to 0.60 mm (step S105). The conditions for cold rolling are not particularly limited and can be set as appropriate in accordance with the strength or thickness of the desired product sheet, and the reduction rate is preferably set to 10 to 95%.

[0098] Further, it is preferable to perform a soaker treatment to ensure cold rolling workability before or during cold rolling. The temperature during the soaker treatment is preferably set to 250 to 500°C, and particularly 300 to 450°C. By performing the soaker treatment under such conditions, deformation is less likely to occur during long-term use, and good flatness can be maintained. As more specific soaker conditions, for example, if batch heating is performed, it can be performed under conditions of 300 to 450°C for 0.1 to 10 hours, and if continuous heating is performed, it can be performed under conditions of 400 to 500°C for 0 to 60 seconds. Here, the case where the holding time is 0 seconds means that cooling is performed immediately after the desired holding temperature is reached.

[0099] Then, the aluminum alloy sheet obtained by cold rolling is punched into a circular ring shape by a press or the like to produce a circular ring-shaped aluminum alloy sheet (blank) (step S106). The circular ring-shaped aluminum alloy sheet is preferably subjected to blanking / press flattening treatment (step S107) to produce a disc blank. The blanking / press flattening treatment (also referred to as "press soaker") is preferably performed at a temperature of 30 to 60 kg / cm 2The pressure is applied, for example, by stacking the blanks on top of each other and pressing them in the atmosphere at a temperature of 250 to 500°C, particularly 300 to 400°C, for 0.5 to 10 hours, particularly 1 to 5 hours, thereby producing a flattened blank.

[0100] Next, the blank is subjected to cutting processing to produce a disc having a desired inner diameter, an outer diameter, and a chamfered portion (hereinafter, referred to as "T base") (step S108). Here, the two surfaces of the blank can also be subjected to cutting processing to produce a T base having a thickness adjusted. Further, the T base can also be subjected to heat treatment, for example, at a temperature of 150 to 350°C for 0.1 to 10.0 hours, for the purpose of removing processing strain generated in the material due to the cutting processing.

[0101] The obtained T base is delivered to a grinding processing (Grind processing) process in which both side main surfaces are ground using a grinding machine or the like, to produce a disc having a desired thickness (hereinafter, referred to as "G base") (step S109). After this process, the G base can also be subjected to heat treatment, for example, at a temperature of 150 to 350°C for 0.1 to 10.0 hours, for the purpose of removing processing strain generated in the material due to the cutting processing. Here, the problem of the ΔTIR in the disc diameter, which is a problem of the present application, is mainly caused by the grinding processing. Therefore, the grinding processing will be described below together with the lapping processing.

[0102] Next, a disc in which a plating layer having a desired thickness is formed on all surfaces including the surface, the side surface, and the chamfered surface of the G base (hereinafter, referred to as "M base") is produced. Prior to this, the G base is subjected to pretreatment for the purpose of improving the adhesion of the plating layer.

[0103] The pretreatment method for the G substrate is not particularly limited. For example, the surface of the G substrate is subjected to degreasing, etching, and zincate treatment (Zn displacement treatment) (step S110). The degreasing can be performed using, for example, a commercially available AD-68F (manufactured by Kamachi Sangyo Co., Ltd.) degreasing solution, at a concentration of 200 to 800 mL / L, at a temperature of 40 to 70°C, and for a treatment time of 3 to 10 minutes. The etching can also be performed by performing acid etching using, for example, a commercially available AD-107F (manufactured by Kamachi Sangyo Co., Ltd.) etching solution, at a concentration of 20 to 100 mL / L, at a temperature of 50 to 75°C, and for a treatment time of 0.5 to 5 minutes. In the zincate treatment, a zincate film is formed on the surface of the substrate. The zincate treatment can be performed using a commercially available zincate treatment solution, and is preferably performed at a concentration of 100 to 500 mL / L, at a temperature of 10 to 35°C, and for a treatment time of 0.1 to 5 minutes. The zincate treatment is performed at least once, and can be performed two or more times. By performing the zincate treatment multiple times, fine Zn is precipitated and a uniform zincate film is formed. In the case where the zincate treatment is performed twice, Zn stripping treatment can be performed therebetween. The Zn stripping treatment is preferably performed using an HNO3 solution, at a concentration of 10 to 60%, at a temperature of 15 to 45°C, and for a treatment time of 10 to 120 seconds (hence, also referred to as "nitric acid stripping treatment"). In addition, the zincate treatment after the second time is preferably performed under the same conditions as the initial zincate treatment.

[0104] Further, plating treatment is performed on the surface of the substrate subjected to the zincate treatment as a base treatment for the attachment of the magnetic body, and an M substrate is produced (step S111). As the plating treatment, non-electrolytic Ni-P plating treatment is preferable. The non-electrolytic Ni-P plating treatment process is preferably performed using a commercially available plating solution, such as NIMUDEN (registered trademark) HDX manufactured by Kamachi Sangyo Co., Ltd., at a Ni concentration of 3 to 10 g / L, at a temperature of 80 to 95°C, and for a treatment time of 30 to 180 minutes. In order to remove internal stress at the time of plating, heating treatment can be performed on the M substrate, for example, at a temperature of 280 to 295°C for 15 to 60 minutes, or the like. Since crystallization occurs when the temperature exceeds 300°C, imparting magnetism, the heating temperature must be less than 300°C.

[0105] Both main surfaces of the M substrate thus obtained are subjected to polishing treatment as described later (steps S112 to S113), and a substrate for a magnetic disk is produced. A magnetic body is attached to the substrate (step S114), and is stacked as necessary, whereby a magnetic disk such as a hard disk can be produced. The method and conditions of the polishing treatment will be described in detail below together with the lapping process (grinding process).

[0106] <Method for manufacturing a glass substrate>

[0107] Figure 4 is a flowchart illustrating an example of a manufacturing process of a glass substrate for a magnetic disk according to the present application. First, a glass plate of a predetermined thickness is prepared (steps S201 to S202). Next, the prepared glass plate is subjected to coring and inner and outer peripheral end surface polishing processing, thereby forming / machining a glass substrate in a circular ring shape (steps S203 to S205). Next, desirably, the formed glass substrate is delivered to a lapping process using diamond particles or the like (step S206). Then, or according to the state of the glass substrate, after step S205, a rough polishing process in which a plurality of glass substrates are simultaneously polished by, for example, ceria abrasive grains by sandwiching the glass substrates from above and below with a polishing pad (step S207) is performed, and chemical strengthening treatment is performed as necessary (step S208), after which, for example, a precision polishing process based on colloidal silica abrasive grains is performed (step S209). Next, a magnetic disk is manufactured by a magnetic body attachment process (step S210). Hereinafter, the contents of each process will be described in detail in accordance with the flow of Figure 4

[0108] First, a molten glass raw material having the above-described composition is prepared by heating / melting in accordance with a normal method (step S201). Next, the prepared molten glass raw material is formed into a glass plate by a known manufacturing method such as a float method, a down-draw method, a direct press method, a redraw method, a fusion method, or the like (step S202). Here, if the redraw method is used, that is, a mother glass plate manufactured using a float method or the like is heated and softened and drawn to a desired thickness, a glass plate having a small thickness unevenness can be relatively easily manufactured, and thus the redraw method is preferred. However, the method of forming the glass plate is not limited to the redraw method, and for example, the glass plate can be formed by a direct press method in which a molten block is pressed and formed from both sides to produce a glass plate having a desired thickness.

[0109] Next, a glass substrate in a circular ring shape is formed from the glass plate obtained in step S202 by a coring process (step S203). The inner and outer peripheral end surfaces can be polished by cutting / end surface grinding processing (steps S204 to S205). The formed glass substrate (glass blank) has two main surfaces and a circular hole formed in the central portion, and is in a circular ring shape.

[0110] ​The glass blank thus obtained can also be subjected to a lehr treatment (annealing treatment). The lehr treatment can be performed, for example, by holding the glass blank at a temperature near the strain point for 15 minutes or more and slowly cooling for 3 to 12 hours or so. The temperature during the lehr treatment also depends on the glass material, and is preferably set to 250 to 750°C, particularly 500 to 700°C. By performing the lehr treatment under such conditions, deformation is less likely to occur during long-term use, and good flatness can be maintained. As more specific lehr conditions, for example, if batch heating is performed, the conditions can be set to 0.1 to 10 hours at 500 to 650°C, and if continuous heating is performed, the conditions can be set to 0 to 60 seconds at 500 to 750°C. Here, the case where the holding time is 0 seconds means that the glass is immediately cooled after reaching the desired holding temperature. In addition, the glass substrate of the present application can also be manufactured by forming a commercially available glass substrate having the above composition into a circular ring shape and performing a lehr treatment.

[0111] Next, in step S206, the circular ring-shaped plate thus formed is subjected to a lapping process (polishing) in which both main surfaces are lapped using a lapping machine or the like, and the plate thickness is adjusted. In addition, based on the plate thickness of the glass substrate obtained in the processes up to step S205, the lapping process S206 can also be omitted, and the process can be shifted to the polishing process described below. For example, a glass plate manufactured by the redraw method generally has small thickness unevenness, and thus the lapping process S206 can sometimes be omitted, but in order to planarize the substrate, it is desirable to perform lapping. In addition, in the case of manufacturing a glass plate by the float method or the direct press method, it is highly necessary to perform the lapping process S206. The lapping process can be performed, for example, using a batch-type double-sided polisher using diamond particles. Here, the problem of the large ΔTIR in the disc radial direction, which is a problem of the present application, is mainly caused by the lapping process in the glass substrate. Therefore, the lapping process will be described in detail separately below.

[0112] The surface of the glass substrate (blank substrate) thus obtained is subjected to a polishing treatment as described below (steps S207 to S209), and a substrate for a magnetic disc is manufactured. A magnetic body is attached to the substrate (step S210), and the substrate can be stacked as needed, and thus a magnetic disc such as a hard disc can be manufactured.

[0113] The above polishing process is roughly divided into a rough polishing process (step S207) and a precision polishing process (step S209) as described later. It is preferable to perform a chemical strengthening process (step S208) on the glass substrate between the rough polishing process and the precision polishing process. By the chemical strengthening, lithium ions and sodium ions in the surface layer of the glass substrate are replaced with sodium ions and potassium ions having a larger ionic radius than the lithium ions and the sodium ions in the chemical strengthening solution, respectively, and as a result, a compressive stress layer is formed in the surface layer portion, so that the glass substrate can be strengthened. The chemical strengthening process is not particularly limited, and for example, it can be performed by immersing the glass substrate in a chemical strengthening solution heated to 300 to 400°C for about 3 to 4 hours. Here, the chemical strengthening solution is not particularly limited, and for example, a potassium nitrate solution or a sodium sulfate solution, a mixed solution thereof, particularly a mixed solution of 60% by weight of potassium nitrate and 40% by weight of sodium sulfate, or the like can be used. Further, it is preferable to clean the glass substrate before the chemical strengthening process and to preheat the glass substrate to about 200 to 300°C. In addition, it is preferable to subject the glass substrate subjected to the chemical strengthening process to a cleaning process. For example, it is sufficient to further clean the glass substrate with pure water or the like after cleaning with an acid such as sulfuric acid.

[0114] <Grinding / polishing process>

[0115] In the process of manufacturing the base plate, as described above in the manufacture of the aluminum alloy substrate, grinding processing (abrasive processing) is generally performed, and in the manufacture of the glass substrate, polishing is desirably performed. In addition, the substrate for a magnetic disk is generally subjected to polishing processing for planarization before a magnetic substance is attached, regardless of the material of the substrate. In this polishing process, it is preferable to perform polishing in a plurality of stages in which the diameter of the polishing abrasive has been adjusted. These grinding processing (abrasive processing, polishing), rough polishing, and precision polishing are generally preferably performed using a double-sided polishing machine. The substrate for a magnetic disk of the present application can also be ground or polished using a commercially available batch-type double-sided polishing machine. Further, it is preferable to perform dummy polishing before the grinding / polishing processing, particularly rough polishing, to manage the surface of the polishing pad.

[0116] (Double-sided polishing machine)

[0117] A double-sided polishing machine generally has an upper platen and a lower platen made of cast iron, a carrier that holds a plurality of substrates between the upper platen and the lower platen, and a polishing pad or a grindstone installed on the substrate contact surfaces of the upper platen and the lower platen. In the polishing process, the plurality of substrates are held between the upper platen and the lower platen by the carrier, and each substrate is clamped by the upper platen and the lower platen with a predetermined processing pressure. Then, each substrate is clamped from above and below by the polishing pad or the grindstone. Next, a polishing liquid or a cooling liquid is supplied between the polishing pad and each substrate at a predetermined supply amount, and the upper platen and the lower platen are rotated in different directions. At this time, since the carrier also rotates by the sun gear, the substrates perform planetary motion. As a result, the substrates slide on the surface of the polishing pad or the grindstone, and both surfaces are polished at the same time.

[0118] (Carrier)

[0119] The material and size of the carrier used in double-sided polishing are not particularly limited, and a general carrier can be used. From the viewpoint of the strength of the carrier, a resin carrier made of an aromatic polyamide resin or an epoxy resin, etc. can be appropriately used. A fibrous reinforcing material such as carbon fiber or glass fiber can also be contained for the purpose of improving the strength. The thickness of the carrier can be arbitrarily selected depending on the thickness of the disc as the workpiece. Among them, if the carrier is too thin, it can be damaged during the lapping process. Therefore, the thickness of the carrier is preferably 0.3 mm or more, and more preferably 0.4 mm or more.

[0120] [Grinding process of an aluminum alloy substrate (milling process)]

[0121] In the grinding process of the aluminum alloy substrate (milling process, step S109), a double-sided polishing machine as described above is used to press a fixed abrasive grain called a grindstone against the substrate held on the carrier from the upper and lower surfaces, thereby performing grinding processing on the main surfaces on both sides of the substrate.

[0122] [Grinding process of a glass substrate (polishing)]

[0123] In the grinding process of the glass substrate (polishing process, step S206), a double-sided polishing machine as described above is also used to press a grindstone against the substrate held on the carrier from the upper and lower surfaces, thereby performing grinding on the main surfaces on both sides of the substrate.

[0124] [Grinding process conditions]

[0125] (Rotation speed of the polishing platen, etc.)

[0126] In the grinding process, in the lapping process, the coolant is supplied to the substrate, the carrier, and the grinding stone in the lapping process. The rotation speed of the lapping platform (grinding stone) is set in the range of 10 to 35 rpm, and particularly preferably in the range of 15 to 30 rpm, in order to obtain a smooth substrate. If the rotation speed is too high, the grinding stone becomes unstable, and the shape deteriorates. In addition, if the rotation speed is too high, the amount of coolant differs between the inner and outer circumferential portions of the substrate or the platform. In detail, the coolant is discharged by the centrifugal force generated by the rotation of the platform, but the coolant on the outer circumferential side is discharged to assist the lapping, and thus the desired TIR cannot be achieved, and as a result, the ΔTIR deteriorates. In addition, the productivity deteriorates if the rotation speed is low, and thus it is not preferable.

[0127] The rotation speed of the sun gear is not particularly limited, and for example, can be set to 5 to 15 rpm. In addition, the lapping process is preferably performed for about 1 to 10 minutes, and particularly preferably for about 2 to 5 minutes, and the lapping amount is set to about 2.5 to 25 μm, and for example, about 5 to 20 μm. In addition, face cutting can be performed before the lapping process.

[0128] (Grinding Stone)

[0129] The grinding stone is composed of abrasive grains and a binder that bonds the abrasive grains. In the grinding process of an aluminum alloy substrate, the abrasive grains can be appropriately used Si-C particles, and the binder can be appropriately used a porous sponge-like elastomer such as poly vinyl alcohol (PVA). As the grinding stone used in the lapping of a glass substrate, for example, a grinding stone in which abrasive grains such as diamond particles are bonded with a binder can be listed. In the grinding process, in the lapping, a cutting groove can be dug in the grinding stone in order to improve the discharge property of the lapping chips generated in the lapping process.

[0130] As described above, the non-planarization, that is, the deterioration of the shape of the substrate, is mainly caused by the lapping process (grinding process, lapping process). According to the findings of the present inventor, the main cause of the deterioration of the shape of the substrate is the uneven clogging of the grinding stone. This occurs because the lapping chips generated at the time of lapping are accumulated on the surface of the grinding stone. In the case where the uneven clogging of the grinding stone occurs, the lapping of the surface of the substrate becomes uneven, and the surface shape deteriorates. At the time of lapping, the lapping liquid is discharged from the outer circumferential portion on the main surface, but the area of the outer circumferential side region is relatively large, and thus is greatly affected by the unevenness of the lapping. Thus, by suppressing the clogging of the grinding stone, the deterioration of the shape can be suppressed, and the operation error of the HDD device in which the magnetic disk is mounted can be reduced. As a method of preventing the clogging of the grinding stone, it is effective to add the cutting groove described above, and a method of periodically trimming (dressing) the surface of the grinding stone before the clogging of the grinding stone, and the like.

[0131] (Pressure Application to Grinding Stone)

[0132] Other methods to prevent grinding stone clogging, such as applying appropriate external pressure to the substrate of the double-sided grinding device (grinding device, polishing device) platform to improve the removal of grinding chips, are effective. However, excessive pressure not only applies processing strain, deteriorating the substrate shape, but also presses the grinding stone surface against the substrate surface, thus restricting the flow of coolant. In particular, when the coolant flow rate is low, the removal of grinding chips is hindered, resulting in grinding with grinding chips remaining on both the grinding stone and substrate surfaces.

[0133] Regarding the applied pressure (external pressure), in the case of an aluminum alloy substrate, a pressure of 50–120 g / cm³ is preferred. 2 If the applied pressure exceeds 120 g / cm 2 If the grinding stone undergoes partial elastic deformation, the parallel fracture between the substrate and the grinding stone may occur. This results in a difference in pressure applied to the inner and outer peripheries of the aluminum alloy substrate, leading to a deterioration of the TIR and potentially an increase in ΔTIR. Furthermore, if the applied pressure exceeds 120 g / cm², further damage may occur. 2 As mentioned above, the restricted flow path of the coolant leads to an increased coefficient of friction between the aluminum alloy substrate and the grinding stone. This causes the substrate to become stuck during rotation, making uniform grinding difficult and resulting in a flatness exceeding 20 μm. Therefore, the applied pressure is preferably set to 70–110 g / cm³. 2 Especially 75-100g / cm 2 .

[0134] In the case of a glass substrate, the applied pressure (external pressure) is preferably 100 to 200 g / cm³. 2 Glass substrates generally have a higher Vickers hardness than aluminum alloy substrates, thus allowing for higher applied pressure settings. However, if the applied pressure exceeds 200 g / cm², the pressure may be insufficient. 2 Sometimes, the drawback of increased ΔTIR, as seen in the aluminum alloy substrate mentioned above, will occur. Furthermore, if the applied pressure in a glass substrate exceeds 200 g / cm³,... 2 If this occurs, abrasive particles may bite into the substrate, creating cuts and scratches. This necessitates increasing the removal allowance in the S206 polishing process and the subsequent grinding process. Therefore, the upper limit is preferably set to 200 g / cm³. 2 The applied pressure in the glass substrate is more preferably 130–200 g / cm. 2 .

[0135] (coolant)

[0136] In terms of suppressing clogging of the grindstone, it is also effective to supply the coolant at an appropriate flow rate. The coolant is used for purposes other than cooling of heat generated by the grinding process, such as improvement of lubricity, improvement of discharge of grinding chips, and the like. The flow rate of the coolant is preferably about 1 to 10 L / min, and further preferably about 3 to 5 L / min. If the flow rate of the coolant is insufficient, there is a case where the grinding chips cannot be sufficiently discharged, and the shape of the substrate deteriorates. In more detail, if the flow rate of the coolant is small, there are cases where a portion where fresh coolant is in contact with the substrate and can be well removed, and a portion where deteriorated coolant is in contact with the substrate and the amount of cutting is reduced, appear on the substrate. In particular, at the outer circumferential portion where the coolant is discharged, the coolant is insufficient, the amount of grinding becomes uneven, and thus the TIR deteriorates, and ΔTIR easily becomes large. In addition, since the ability to cut the entire substrate uniformly is impaired, there are cases where the flatness deteriorates.

[0137] In addition, the coolant is discharged to the outside of the table by centrifugal force generated by rotation of the table, but in the case where the flow rate of the coolant is large, there is a case where the amount of coolant that is not useful for grinding increases, and productivity deteriorates, and thus the upper limit is preferably set to 10 L / min.

[0138] The material of the coolant is not particularly limited, and a general product such as mechano aquacut ECO #408 (trade name) manufactured by Ouchi Shokai Co., Ltd. can be used. Here, by adding a surfactant or a lubricant or the like to the coolant, a substrate having more excellent flatness can be produced.

[0139] Regarding the rotation speed of the aforementioned table and the flow rate of the coolant, by increasing to a certain value, the amount of cutting per unit time (this will be referred to as cutting ability) can be increased, but above this, there are cases where the cutting ability decreases in terms of the rotation speed of the table, and the cutting ability reaches a limit in terms of the flow rate of the coolant. Furthermore, these two parameters are determined so as to be the desired values with the pressurizing pressure as the center. In the manufacturing method of the present application, it was found that, for an aluminum alloy substrate, the pressurizing pressure is 100 g / cm 2 and 200 g / cm 2 Hereinafter, the rotation speed of the table is 10 rpm or more and 35 rpm or less, and the flow rate of the coolant is 1 L / min or more and 10 L / min or less; for a glass substrate, the pressurizing pressure is 50 g / cm 2 and 120 g / cm 2 Hereinafter, the rotation speed of the table is 10 rpm or more and 35 rpm or less, and the flow rate of the coolant is 1 L / min or more and 10 L / min or less.

[0140] That is, the present application includes a manufacturing method of a magnetic disk, which is the manufacturing method of the magnetic disk described above, characterized in that the magnetic disk is manufactured from an aluminum alloy substrate, and the manufacturing method of the magnetic disk has a lapping process of lapping the aluminum alloy substrate, the lapping process being performed at a pressurizing pressure of 50 g / cm 2 or more and 120 g / cm 2 or less.

[0141] Further, the present application includes a manufacturing method of a magnetic disk, which is the manufacturing method of the magnetic disk described above, characterized in that the magnetic disk is manufactured from a glass substrate, and the manufacturing method of the magnetic disk has a lapping process of lapping the glass substrate, the lapping process being performed at a pressurizing pressure of 100 g / cm 2 or more and 200 g / cm 2 or less.

[0142] [Coarse lapping]

[0143] The method of the coarse lapping is not particularly limited, and can be performed under any conditions corresponding to the material of the substrate. For example, the coarse lapping of the aluminum alloy substrate can be performed using a lapping liquid containing alumina having a particle diameter of 0.1 to 1.0 μm, and a lapping pad composed of hard or soft polyurethane or the like. Further, the coarse lapping of the glass substrate can be performed using a lapping liquid containing ceria having a particle diameter of 0.1 to 1.0 μm, and a lapping pad composed of hard polyurethane or the like. Instead of alumina and ceria, abrasive grains of silica, zirconia, SiC, diamond or the like having a desired particle diameter can also be used. Further, the hard substance means a substance having a hardness (ASKER C) of 85 or more as measured by a measuring method prescribed in the Japan Rubber Association Standard Specification (Reference Specification: SRIS0101), and the soft substance means a substance having a hardness of 60 to 80.

[0144] The specific conditions of the coarse lapping are also affected by the material of the substrate used and the processes (for example, steps S101 to S111 in the manufacturing of the aluminum alloy substrate, and steps S201 to S206 in the manufacturing of the glass substrate) up to the coarse lapping, and it is difficult to determine them fundamentally. Further, they are not limited to specific conditions. For example, the conditions of the coarse lapping of the aluminum alloy substrate can be set to a lapping time of 2 to 5 minutes, a rotation speed of the lapping platform: 10 to 35 rpm, a rotation speed of the sun gear: 5 to 15 rpm, a lapping liquid supply speed: 1 to 5 L / minute, and a processing pressure: 20 to 250 g / cm 2 , preferably 30 to 120 g / cm 2Grinding amount (removal amount): 2.5 to 3.5 μm

[0145] The conditions for the rough grinding of the glass substrate are not particularly limited either. For example, it is preferable to use a hard grinding pad having a hardness of 86 to 88, and to set the rotation speed of the grinding table to 10 to 35 rpm, particularly 15 to 30 rpm; the rotation speed of the sun gear to 5 to 15 rpm; the grinding liquid supply speed to 1 to 5 L / min, particularly 2 to 4 L / min; the processing pressure to 20 to 250 g / cm 2 , particularly 30 to 120 g / cm 2 ; and the grinding time to 2 to 10 minutes. The grinding amount (removal amount) is not particularly limited either, but it is preferable to set it to about 2 to 50 μm, for example, about 5 to 25 μm.

[0146] (Simulation grinding)

[0147] The surface of the grinding pad can be managed by simulation grinding prior to the rough grinding as described above at the time of the grinding process. In general, the simulation grinding process is performed using a simulation substrate, and like the rough grinding process, it is preferable to perform it under the same conditions. The simulation substrate used is not particularly limited, and for example, an aluminum alloy substrate can be used for simulation grinding prior to the rough grinding of the glass substrate, but it is preferable to use a blank substrate of the same kind as the product blank substrate, particularly a blank substrate manufactured under the same conditions as the product blank substrate. The simulation grinding process, for example, is preferably performed to grind the simulation substrate to a state where ΔTIR in at least one surface of the simulation substrate becomes 0.50 μm / mm or less or the flatness PV becomes 20.0 μm or less.

[0148] By the simulation grinding as described above, the surface of the grinding pad used in the rough grinding process described above can be adjusted to an appropriate state. In addition, the simulation grinding is an arbitrary process, and it can be omitted as long as the surface of the grinding pad is adjusted / managed. For example, the simulation grinding can be performed before the start of the rough grinding batch, and the rough grinding of the product blank substrate can be repeatedly performed in multiple batches using the adjusted grinding pad.

[0149] [Fine grinding]

[0150] The method of precision polishing is not particularly limited, and various known methods can be used. For example, the precision polishing of an aluminum alloy substrate can be performed using a polishing liquid containing colloidal silica having a particle diameter of about 0.01 to 0.10 μm and a soft polishing pad. In addition, the precision polishing of a glass substrate can be performed using a polishing liquid containing colloidal silica having a particle diameter of about 0.01 to 0.10 μm, particularly about 10 to 50 nm, and a softer polishing pad composed of foamed urethane or the like. Of course, the conditions for precision polishing are not limited to these. Abrasive grains of cerium oxide, zirconium oxide, SiC, diamond, or the like having a desired particle diameter can be used. In addition, the main surface of the substrate is polished to a mirror surface by this treatment, thereby producing a substrate for a magnetic disk. The substrate for a magnetic disk of the present application that has undergone the above polishing process is also excellent in flatness after a thermal shock test, and exhibits a predetermined PV value. Furthermore, the polished substrate is preferably cleaned using a neutral detergent, pure water, isopropyl alcohol (IPA), or the like.

[0151] The specific conditions for precision polishing are also influenced by the material of the substrate used and the process up to rough polishing, and thus it is difficult to determine them fundamentally, and they are not limited to specific conditions. For example, in the precision polishing of an aluminum alloy substrate, the polishing time can be set to 2 to 5 minutes, the rotation speed of the polishing table: 10 to 35 rpm, the rotation speed of the sun gear: 5 to 15 rpm, the polishing liquid supply speed: 1000 to 5000 mL / minute, the processing pressure: for example, 10 to 200 g / cm 2 , particularly 20 to 100 g / cm 2 , and the polishing amount: 1.0 to 1.5 μm.

[0152] The conditions for precision polishing of a glass substrate are not particularly limited. For example, a soft polishing pad having a hardness of 75 to 77 is preferably used, and the rotation speed of the polishing table: 10 to 35 rpm, the rotation speed of the sun gear: 5 to 15 rpm, the polishing liquid supply speed: 1000 to 5000 mL / minute, the processing pressure: for example, 10 to 200 g / cm 2 , particularly 20 to 100 g / cm 2 , and the polishing time: 2 to 12 minutes are set. The polishing amount can be set to about 2 to 50 μm, particularly about 5 to 25 μm, for example.

[0153] (Flip)

[0154] Here, in the manufacture of the substrate for a magnetic disk according to the present application, the front and back surfaces of the substrate can be reversed (turned over) halfway through the lapping process (grinding process or polishing process) and / or the polishing process. That is, in the lapping process, the front and back surfaces of the aluminum alloy substrate or the glass substrate are reversed at least once and lapping is continued. Alternatively, after the lapping process, a polishing process is performed on the aluminum alloy substrate or the glass substrate, and in the polishing process, the front and back surfaces of the aluminum alloy substrate or the glass substrate are reversed at least once and polishing is continued. Thus, the substrate after lapping / polishing can be easily processed into a more planar substrate. It is preferable that the turning over be performed halfway through the rough polishing process, particularly, halfway through the lapping process and the rough polishing process.

[0155] In double-sided polishing, the thickness of the layer removed by polishing can easily differ on the upper land side and the lower land side of the substrate. This tendency is particularly high in rough polishing. If a magnetic disk is manufactured using a substrate polished in this manner, there is a case where the planarity deteriorates. By turning over halfway through the lapping / polishing process, particularly, the rough polishing process, the risk of deformation of the magnetic disk can be reduced. Furthermore, the turning over can be performed once in the lapping or polishing process, but can be performed two or more times. In addition, it is preferable that the turning over be performed in such a manner that the two surfaces of the substrate are each brought into contact with each of the polishing pads on the upper land side and the lower land side under the same conditions. For example, in the case where the turning over is performed once, the lapping / polishing speed and the polishing time are made the same before and after the turning over, and in the case where the turning over is performed a plurality of times, the polishing is performed in such a manner that the total time for which each surface is on the upper side and the total time for which each surface is on the lower side are consistent.

[0156] <Method for evaluating a magnetic disk and a substrate>

[0157] By performing the lapping / polishing process, particularly, the lapping process (grinding process or polishing process) as described above, a substrate for a magnetic disk having a thickness of 0.60 mm or less and a ΔTIR of 0.50 μm / mm or less can be manufactured. The magnetic disk according to the present application is thin-walled and planar, and thus, in an HDD device, collision is less likely to occur, and the operation error can be reduced. Furthermore, the magnetic disk can be evaluated, for example, by a method in which a magnetic head is floated on a rotating magnetic disk, and the signal from the magnetic disk is detected by the magnetic head. A magnetic disk that passes the evaluation test is used in the next HDD process, but when the thickness of the magnetic disk is 0.60 mm or less, the yield rate generally decreases. According to the present inventors' findings, the result of such an evaluation test is related to the rate of change ΔTIR of the TIR in the radial direction. The magnetic disk according to the present application has a ΔTIR of 0.50 μm / mm or less, and thus, has a planar and good surface shape, and thus, even when the thickness is 0.60 mm or less, the magnetic disk can pass the evaluation test as described above.

[0158] Further, according to the present inventors' findings, the surface shape of the substrate and the magnetic disk hardly changes before and after the magnetic film is formed. Therefore, it is preferable to measure ΔTIR for the polished aluminum alloy substrate and the glass substrate and the like before the magnetic film is formed. That is, the evaluation of ΔTIR and PV as described above is preferably performed as a checking process of the substrate after the substrate is manufactured. In addition, as described above, regarding the surface shape of the magnetic disk, in the case of the aluminum alloy substrate, the surface shape is mainly caused by the grinding process, and in the case of the glass substrate, the surface shape is mainly caused by the polishing process, and in either substrate, the surface shape is affected by a plurality of factors such as the distribution of the thickness of the substrate, internal stress generated at the time of processing, and the like. Therefore, if the evaluation of the substrate is performed after the lathing (grinding) process or the polishing process is completed, the quality of the substrate of each processing lot can be immediately confirmed, and it is more preferable.

[0159] The above describes the embodiments of the present application, but the present application is not limited to the above-described embodiments, but includes all aspects of the present application and the claims, and various changes can be made within the scope of the present application.

[0160] Examples

[0161] The present application is described in more detail below based on examples, but the present application is not limited to these.

[0162] [Example 1]

[0163] An aluminum alloy substrate for a magnetic disk having a thickness of 0.50 mm and an outer diameter of 97 mm was manufactured. In Example 1, an Al-Mg alloy was used.

[0164] First, a slab was manufactured by a semi-continuous casting method, and the slab was subjected to hot rolling and cold rolling processes to manufacture a plate having a thickness of 0.52 mm. The plate was subjected to press working using a press machine to manufacture a blank having an inner diameter of 24 mm and an outer diameter of 98 mm. Next, the blanks were stacked on each other, and the blanks were subjected to pressure braising at 320°C for 3 hours under a pressure of 30 kg / cm 2 Next, the inner and outer diameter portions of the blank were subjected to cutting and chamfering processes using a lathe machine to manufacture a T-bottom having an inner diameter of 25 mm and an outer diameter of 97 mm, and the T-bottom was subjected to heating at 300°C for 30 minutes. Next, the surfaces of both sides of the T-bottom were subjected to lathing (grinding) to manufacture a G-bottom having a thickness of 0.48 mm. After the G-bottom was subjected to pretreatment, a non-electrolytic Ni-P plating process was performed to apply a Ni-P plating layer having a thickness of 10 μm to each of the single sides to manufacture an M-bottom. Next, after the M-bottom was subjected to heating at 250°C for 30 minutes, the surfaces of both sides of the M-bottom were subjected to polishing using a polishing machine to manufacture an aluminum alloy substrate for a magnetic disk.

[0165] Further, the above-mentioned pretreatment of G bottom and non-electrolytic Ni-P plating treatment were performed as follows.

[0166] (Pretreatment)

[0167] • Degreasing treatment of G bottom: AD-68F manufactured by Uemura Industrial Co., Ltd. was used as a degreasing solution, and the treatment was performed under the conditions of concentration: 500 mL / L, temperature: 45°C, and treatment time: 3 minutes.

[0168] • Acid etching treatment: AD-107F manufactured by Uemura Industrial Co., Ltd. was used as an etching solution, and the treatment was performed under the conditions of concentration: 50 mL / L, temperature: 60°C, and treatment time: 2 minutes.

[0169] • Zincate treatment: The zincate treatment was performed twice with nitric acid peeling treatment in between, and specifically, the treatment was performed in the order of first zincate treatment, pure water washing, nitric acid peeling treatment, pure water washing, and second zincate treatment.

[0170] The first zincate treatment was performed using AD-301F-3X manufactured by Uemura Industrial Co., Ltd. as a zincate treatment solution under the conditions of concentration: 200 mL / L, temperature: 20°C, and treatment time: 1 minute. The nitric acid peeling treatment was performed under the conditions of nitric acid concentration: 30 vol%, temperature: 25°C, and treatment time: 1 minute. The second zincate treatment was performed under the same conditions as the first zincate treatment.

[0171] (Non-electrolytic Ni-P plating treatment)

[0172] NIMUDEN (registered trademark) HDX manufactured by Uemura Industrial Co., Ltd. was used as a non-electrolytic plating solution, and the treatment was performed under the conditions of Ni concentration: 6 g / L, temperature: 88°C, and treatment time: 130 minutes.

[0173] In addition, the above-mentioned lapping was performed under the following conditions.

[0174] (Lapping)

[0175] • Lapping plate: #4000 silicon carbide (SiC) lapping plate

[0176] • Lapping pressure: 100 g / cm 2

[0177] • Rotational speed of lapping plate: 30 rpm

[0178] • Cooling liquid flow rate: 3.5 L / minute

[0179] • Lapping time: 5 minutes

[0180] The above-mentioned lapping was performed by double-sided lapping under the following conditions.

[0181] (coarse polishing)

[0182] • abrasive grains: alumina abrasive grains having a particle diameter of 0.4 μm

[0183] • polishing pad: hard urethane polishing pad having a hardness of 87

[0184] • processing pressure: 100 g / cm 2

[0185] • rotation speed of polishing stage: 30 rpm

[0186] • rotation speed of sun gear: 10 rpm

[0187] • polishing liquid supply speed: 3.5 L / min

[0188] • lapping time: 5 minutes

[0189] (fine polishing)

[0190] • abrasive grains: colloidal silica abrasive grains having a particle diameter of 0.08 μm

[0191] • polishing pad: foamed urethane polishing pad having a hardness of 76

[0192] • processing pressure: 100 g / cm 2

[0193] • rotation speed of polishing stage: 30 rpm

[0194] • rotation speed of sun gear: 10 rpm

[0195] • polishing liquid supply speed: 3.5 L / min

[0196] • lapping time: 3 minutes

[0197] For the substrate for a magnetic disk, the TIR at the circumferences of the radial distances r = 40 mm, 45 mm, 46 mm, and 47 mm from the center were measured using an optical inspection device Mesa manufactured by Zygo, Inc., and ΔTIR was calculated in accordance with the above (Formula 1) for the adjacent radial distances. In the case where all of the three ΔTIRs calculated were within 0.5 μm, the comprehensive evaluation was regarded as O, and in the case where one of the three ΔTIRs calculated exceeded 0.5 μm, the comprehensive evaluation was regarded as X. In addition, the flatness PV was measured using the same optical inspection device Mesa manufactured by Zygo, Inc. These results are shown together with the lapping processing conditions in Table 1 described later.

[0198] [Examples 2 to 4, Comparative Examples 1 to 3]

[0199] An aluminum alloy substrate for a magnetic disk described below was produced in the same manner as in Example 1.

[0200] • Examples 2, 4, Comparative Examples 1 to 3: Al-Fe alloy

[0201] • Example 3: Al-Mg alloy.

[0202] The same operation as in Example 1 was performed except that the flow rate of the coolant during the lapping process was increased to 10.0 L / min (Example 2). In addition, the same operation as in Example 1 was performed except that the thickness of the aluminum alloy substrate was set to 0.60 mm (Example 3), or the processing pressure was set to 70 g / cm 2 (Example 4). Further, the same operation as in Example 1 was performed except that the processing pressure variation during the lapping process was set to 150 g / cm 2 (Comparative Example 1), the rotation speed of the lapping platform was varied to 40 rpm (Comparative Example 2), or the flow rate of the coolant was varied to 0.1 L / min (Comparative Example 3). The evaluation results for each of the obtained substrates for magnetic disks are shown in Table 1 described later together with the material of the substrate and the lapping process conditions.

[0203] [Example 5]

[0204] An aluminum silicate glass substrate for a magnetic disk having a thickness of 0.60 mm and an outer diameter of 97 mm was produced as follows.

[0205] The glass raw material described above was heated at 1600 to 1700°C to produce a molten liquid, and a drawing method was used to form an aluminum silicate glass plate having a thickness of 100 mm and a length of 10 m. Thereafter, a glass plate having a thickness close to 0.6 mm was selected and subjected to core removal and end face grinding of the inner and outer peripheries (cutting of the inner and outer diameters of the glass disk, size adjustment, chamfering, and lapping of the chamfered portions), to produce a glass plate in the form of a circular ring having an outer diameter of 97 mm and an inner diameter of a circular hole of 25 mm. The glass substrate was produced by lapping (polishing), rough lapping, and precision lapping of the glass plate using a double-sided lapping machine.

[0206] The polishing described above was performed under the following conditions.

[0207] (Polishing)

[0208] • Abrasive stone: diamond particles

[0209] • Processing pressure: 150 g / cm 2

[0210] • Rotation speed of the lapping platform: 30 rpm

[0211] • Flow rate of the coolant: 3.5 L / min

[0212] • Polishing time: 5 minutes

[0213] The rough polishing and the precision polishing described above were each performed by double-side polishing under the following conditions.

[0214] (Rough Polishing)

[0215] • Abrasive grains: cerium oxide abrasive grains having a particle size of 0.1 to 0.4 μm and an average particle size of 0.19 μm

[0216] • Polishing pad: hard urethane polishing pad having a hardness of 87

[0217] • Processing pressure: 160 g / cm 2

[0218] • Rotational speed of polishing stage: 15 rpm

[0219] • Rotational speed of sun gear: 10 rpm

[0220] • Polishing liquid supply speed: 2.0 L / min

[0221] • Polishing time: 5 minutes

[0222] (Precision Polishing)

[0223] • Abrasive grains: colloidal silica abrasive grains having a particle size of 10 to 100 nm and an average particle size of 80 nm

[0224] • Polishing pad: foamed urethane polishing pad having a hardness of 76

[0225] • Processing pressure: 100 g / cm 2

[0226] • Rotational speed of polishing stage: 30 rpm

[0227] • Rotational speed of sun gear: 10 rpm

[0228] • Polishing liquid supply speed: 3.5 L / min

[0229] • Polishing time: 5 minutes

[0230] The ΔTIR and the flatness PV were evaluated for the obtained substrate for an aluminum silicate glass magnetic disk in the same manner as in Example 1. The evaluation results are shown in Table 1 together with the polishing (lapping) conditions.

[0231] [Table 1]

[0232] [Material / Polishing Conditions and Evaluation Results of Each Sample in Table 1]

[0233]

[0234] 1) mm 2) g / cm 2 3) rpm 4) L / min 5) μm

[0235] 6) Radial change rate of TIR (μm / mm) on each circumference of the radial distance rl and r2 shown in the line directly below

[0236] 6a) ΔTIR in the case of rl = 40 mm, r2 = 45 mm (rl / R = 0.82, r2 / R = 0.93)

[0237] 6b) ΔTIR in the case of rl = 45 mm, r2 = 46 mm (rl / R = 0.93, r2 / R = 0.95)

[0238] 6c) ΔTIR in the case of rl = 46 mm, r2 = 47 mm (rl / R = 0.95, r2 / R = 0.97)

[0239] According to the present application, a substrate for a magnetic disk is provided, which is thin-walled with a thickness dimension of 0.60 mm or less and is extremely flat with ΔTIR of 0.50 μm / mm or less. These substrates can be mounted in HDD devices in a plurality due to the flatness, and also, since the outer diameter is 97 mm, which is large, the data area of the surface can also be enlarged. In addition, the flatness PV of the substrates for a magnetic disk of Examples 1 to 3 is also 20.0 μm or less, and a good surface shape is exhibited. Therefore, it is understood that the magnetic disk based on these substrates can reduce physical errors even when assembled into HDD devices, and can cope with the high capacity of hard disks.

[0240] On the other hand, in Comparative Example 1, since the pressing pressure of the aluminum alloy substrate is high, a difference is generated in the externally applied pressure depending on the position within the aluminum alloy substrate, the TIR deteriorates, and as a result, ΔTIR deteriorates.

[0241] In Comparative Example 2, since the rotation speed of the platform is too fast, the grindstone is unstable, and in addition, the coolant assisting the grinding at the outer peripheral side is discharged, as a result, the TIR is uneven depending on the measurement site, and ΔTIR deteriorates.

[0242] In Comparative Example 3, since the coolant flow is small, the grinding chips are not sufficiently discharged, and overall, the TIR deteriorates, and ΔTIR deteriorates.

[0243] Example 5 is a glass substrate, and therefore, even if the pressing pressure is 150 g / cm 2 , the TIR is good, and as a result, a substrate for a magnetic disk is provided, which is extremely flat with ΔTIR of 0.50 μm / mm or less.

[0244] Reference Signs

[0245] 1 magnetic disk

[0246] 2 center of the disk 1

[0247] C1 circle for TIR1 measurement at a radial distance of r1 from the center 2 of the disk 1

[0248] C2 circle for TIR2 measurement at a radial distance of r2 from the center 2 of the disk 1

[0249] Ca represents an outer periphery circle of an outer periphery side region in the disk 1

[0250] Cb represents an inner periphery circle of an outer periphery side region in the disk 1

Claims

1. A magnetic disk having a hole in a center portion, and the thickness dimension is 0.60 mm or less, the radius of the aforementioned magnetic disk is set as R (mm), the radial distance of the aforementioned magnetic disk measured from the center of the aforementioned magnetic disk is set as r (mm), the outer peripheral side region of the aforementioned magnetic disk where r / R is 0.70 or more and 0.99 or less, when TIR at the circumferences of different radial distances r1 (mm) and r2 (mm) of the aforementioned magnetic disk are measured respectively, TIR1 (μm) and TIR2 (μm) are set, the radial variation amount ΔTIR of TIR represented by the absolute value of the ratio of (TIR1 - TIR2) to (r1 - r2) is 0.50 μm / mm or less.

2. The magnetic disc of claim 1 wherein, the flatness PV is 20.0 μm or less.

3. The magnetic disc according to claim 1 or 2, wherein, the outer diameter dimension is 95 mm or more.

4. A substrate for use in the magnetic disk according to any one of claims 1 to 3.

5. A manufacturing method of a magnetic disk according to any one of claims 1 to 3, characterized in that, the aforementioned magnetic disk is manufactured from an aluminum alloy substrate, the manufacturing method of the aforementioned magnetic disk has a lapping process step of lapping the aforementioned aluminum alloy substrate, The aforementioned grinding process is performed at a pressurized pressure of 50 g / cm 2 The aforementioned grinding process is performed at a pressurized pressure of 120 g / cm 2 The aforementioned grinding process is performed at a pressurized pressure of 120 g / cm 6. A manufacturing method of a magnetic disk according to any one of claims 1 to 3, characterized in that, the aforementioned magnetic disk is manufactured from a glass substrate, the manufacturing method of the aforementioned magnetic disk has a lapping process step of lapping the aforementioned glass substrate, The aforementioned grinding process is performed at a pressurized pressure of 100 g / cm 2 The above and 200 g / cm 2 The following, the platform rotation speed is 10 rpm or more and 35 rpm or less, the cooling liquid flow is 1 L / min or more and 10 L / min or less under the condition.

7. The method of manufacturing a magnetic disk according to claim 5 or 6, wherein in the aforementioned lapping process step, the lapping amount is 2.5 μm or more and 25 μm or less.

8. The method for manufacturing a magnetic disk according to claim 5 or 6, wherein in the aforementioned lapping process step, at least once the front and back surfaces of the aforementioned aluminum alloy substrate or the aforementioned glass substrate are reversed and lapping is continued.

9. The method for manufacturing a magnetic disk according to claim 5 or 6, wherein after the aforementioned lapping process step, a polishing process step of polishing the aforementioned aluminum alloy substrate or the aforementioned glass substrate is further performed, and in the aforementioned polishing process step, at least once the front and back surfaces of the aforementioned aluminum alloy substrate or the aforementioned glass substrate are reversed and polishing is continued.

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