Manufacturing method of disk-shaped substrate, and magnetic recording medium

Abstract

To provide a manufacturing method of a disk-shaped substrate having excellent flatness of a plating layer and uniformity of thickness of a chemically strengthened layer, and a magnetic recording medium.SOLUTION: A manufacturing method of a disk-shaped substrate includes: removing at least a part of macromolecular component of a grinding fluid on a surface of the disk-shaped substrate by subjecting the disk-shaped substrate ground with grinding fluid to at least one treatment selected from the group consisting of (1) heating, (2) washing with an organic solvent, and (3) ultraviolet irradiation treatment.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a disk-shaped substrate and a magnetic recording medium.

Background Art

[0002] A disk-shaped substrate is used for a magnetic recording medium used in a hard disk drive (HDD). As the disk-shaped substrate, generally, an aluminum substrate or an aluminum alloy substrate is used, and in recent years, the demand for a glass substrate is also increasing.

[0003] The disk-shaped substrate is processed into a donut shape having a circular through-hole at the center, and grinding is performed on the main surface and the end surface using a grinding fluid. The ground disk-shaped substrate is surface-treated in the next step using a plating solution (see, for example, Patent Document 1) for an aluminum substrate and an aluminum alloy substrate, and a chemical strengthening solution (see, for example, Patent Document 2) or the like for a glass substrate. After these treatments, a magnetic layer is formed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] The plating layer and the chemical strengthening layer obtained by the above surface treatment may have low thickness uniformity. When the thickness uniformity of the plating layer is low and the flatness is not excellent, the magnetic layer provided on the plating layer follows the surface shape of the plating layer and the flatness decreases, and the writing and reading properties by the magnetic head element deteriorate. In addition, if the uniformity of the thickness of the chemically strengthened layer is low and there are thin portions in the chemically strengthened layer, problems such as the glass substrate being prone to cracking from those portions will occur. Especially in recent years, thinning of magnetic recording media has been demanded, and the situation is such that the glass substrate is prone to cracking. Therefore, an object of the present disclosure is to provide a method for manufacturing a disk-shaped substrate excellent in the flatness of the plating layer and the uniformity of the thickness of the chemically strengthened layer, and a magnetic recording medium.

[0006] The present disclosure includes the following aspects. <1> A method for manufacturing a disk-shaped substrate, comprising performing at least one treatment selected from the group consisting of (1) heating, (2) cleaning with an organic solvent, and (3) ultraviolet irradiation treatment on a disk-shaped substrate ground with a grinding fluid, to remove at least a part of the polymer component of the grinding fluid on the surface of the disk-shaped substrate. <2> The method for manufacturing a disk-shaped substrate according to <1>, wherein the grinding fluid contains at least one selected from the group consisting of an oiling agent, an extreme pressure additive, a surfactant, a preservative, and an antifoaming agent. <3> The method for manufacturing a disk-shaped substrate according to <1> or <2>, wherein the disk-shaped substrate is an aluminum substrate, an aluminum alloy substrate, or a glass substrate. <4> The method for manufacturing a disk-shaped substrate according to any one of <1> to <3>, wherein the water contact angle of the surface of the disk-shaped substrate after performing the treatment is 45° or less. <5> A magnetic recording medium comprising a disk-shaped substrate obtained by the manufacturing method according to any one of <1> to <4>, a magnetic layer provided on the disk-shaped substrate, and.

Advantages of the Invention

[0007] According to the present disclosure, a method for manufacturing a disk-shaped substrate excellent in the flatness of the plating layer and the uniformity of the thickness of the chemically strengthened layer, and a magnetic recording medium are provided.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Mode for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present disclosure will be described in detail. However, the present disclosure is not limited to the following embodiments. In the following embodiments, the components (including element steps, etc.) are not essential unless otherwise specified. The same applies to numerical values and their ranges, which do not limit the present disclosure. In the numerical range indicated by "~" in the present disclosure, the numerical values described before and after "~" are included as the minimum value and the maximum value, respectively. In the numerical ranges described step by step in the present disclosure, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described in other step-by-step descriptions. Also, in the numerical ranges described in the present disclosure, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples. In the present disclosure, each component may contain a plurality of corresponding substances. When there are a plurality of substances corresponding to each component in the composition, the content rate or content of each component means the total content rate or content of the plurality of substances present in the composition, unless otherwise specified. In the present disclosure, the particles corresponding to each component may contain a plurality of types. When there are a plurality of types of particles corresponding to each component in the composition, the particle diameter of each component means a value for the mixture of the plurality of types of particles present in the composition, unless otherwise specified. In the present disclosure, the term "layer" includes not only the case where it is formed over the entire region where the layer exists but also the case where it is formed only in a part of the region when observing the region where the layer exists.

[0010] <Manufacturing Method of Disk-Shaped Substrate> The manufacturing method of the disk-shaped substrate of the present disclosure performs at least one treatment selected from the group consisting of (1) heating, (2) cleaning with an organic solvent, and (3) ultraviolet irradiation treatment on the disk-shaped substrate ground with a grinding fluid, to remove at least a part of the polymer component of the grinding fluid on the surface of the disk-shaped substrate. In the manufacturing method having the above configuration, the reason why the above problems are solved is considered as follows.

[0011] It has been found that a polymer component contained in the grinding fluid adheres to the surface of the disk-shaped substrate ground with the grinding fluid. Due to the presence of this polymer component, it is considered that the wettability of the plating solution and the chemical strengthening solution in the next process, or physical properties other than the wettability, are affected, and the flatness of the plating layer and the uniformity of the thickness of the chemical strengthening layer are reduced. Therefore, before applying the plating solution or the chemical strengthening solution, at least one treatment selected from the group consisting of (1) heating, (2) cleaning with an organic solvent, and (3) ultraviolet irradiation treatment is performed on the disk-shaped substrate after grinding. By heating the disk-shaped substrate, at least a part of the polymer component present on the surface is burned off. By cleaning the disk-shaped substrate with an organic solvent, at least a part of the polymer component present on the surface is washed away. By subjecting the disk-shaped substrate to ultraviolet irradiation treatment, at least a part of the molecular chains of the polymer component are cut and the molecular weight is reduced, and at least a part of the polymer component is removed. It is considered that the flatness of the plating layer formed in the next process or the uniformity of the thickness of the chemical strengthening layer of the disk-shaped substrate from which the polymer component has been removed from the surface by these treatments is improved.

[0012] The disk-shaped substrate may be an aluminum substrate, an aluminum alloy substrate, or a glass substrate. Hereinafter, the aluminum substrate, the aluminum alloy substrate, and the glass substrate are also collectively referred to as "substrate". Also, the aluminum substrate and the aluminum alloy substrate are also collectively referred to as "aluminum substrate".

[0013] As the aluminum substrate, those commonly used in the art can be applied, and from the viewpoints of strength, plating property, grindability, etc., an aluminum alloy of JIS-A5086 is preferable.

[0014] As the glass substrate, an amorphous, crystallized glass, etc. which are used as a glass substrate for a normal magnetic recording medium can be used. Specifically, for example, a glass substrate composed of a glass such as soda lime, aluminosilicate, lithium silicate, lithium aluminosilicate, aluminoborosilicate, etc. can be mentioned. Further, as the crystallized glass, for example, those obtained by reheating the glass under controlled conditions to precipitate and grow a large number of minute crystals can be mentioned. Further, as the crystallized glass, glasses such as Al2O3 - SiO2 - Li2O - based, B2O3 - Al2O3 - SiO2 - Li2O - based glasses can be mentioned. The thickness of the glass substrate for the magnetic recording medium is not particularly limited, and usually, those having a thickness of about 0.4 mm to 1 mm are used.

[0015] The substrate having a circular through - hole at the center is subjected to grinding using a grinding fluid on the main surface and the end surface. The grinding of the main surface and the grinding of the end surface may be performed collectively, continuously, or separately. The grinding of the end surface may be performed on the inner and outer peripheral end surfaces of the substrate, and chamfering may further be performed. The grinding and the end - surface processing may be performed, for example, in the order of the main - surface grinding process and the inner and outer peripheral end - surface grinding process.

[0016] In the main - surface grinding process, grinding is performed on both main surfaces of the substrate (the surfaces that will finally become the recording surfaces of the magnetic recording medium). In the grinding process, the substrate is sandwiched between a pair of platens that rotate in opposite directions to each other, a grinding fluid is supplied, and both main surfaces of the substrate are ground by a grinding pad provided on the platen. A plurality of substrates may be arranged between the pair of platens and ground collectively. In the grinding pad, abrasive grains such as diamond are fixed by a binder, and both main surfaces of the substrate are ground by these abrasive grains.

[0017] The grinding fluid is preferably an aqueous solution with water as the medium from the perspective of reducing environmental impact. From the perspectives of lubrication, cooling, and chip removal during grinding, it may contain at least one selected from the group consisting of an oiliness agent, an extreme pressure additive, a surfactant, a preservative, and an antifoaming agent. Some of these may remain on the surface of the disk-shaped substrate after grinding as a polymer component. In particular, oiliness agents, antifoaming agents, etc. tend to remain on the surface of the disk-shaped substrate after grinding as a polymer component.

[0018] The oiliness agent is not particularly limited as long as it is commonly used for abrasive applications, and examples include animal and vegetable oils and their hydrogenated products; fatty acids and their salts; fatty acid esters; sulfides of unsaturated carboxylic acids; polyoxyalkylene compounds, etc. The oiliness agent may be used alone or in combination of two or more.

[0019] The fatty acid is not particularly limited as long as it is commonly used for abrasive applications, and examples include fatty acids having 14 or more carbon atoms, preferably 16 to 24 carbon atoms. The fatty acid may be a saturated fatty acid or an unsaturated fatty acid. The fatty acid may be linear or branched. Specific examples of the fatty acid include oleic acid, linoleic acid, stearic acid, isostearic acid, palmitic acid, lauric acid, maleic acid, etc. The fatty acid may be used alone or in combination of two or more.

[0020] Examples of the salt of the fatty acid include alkali metal salts, alkaline earth metal salts, amine salts, etc. Examples of the alkali metal include sodium, potassium, etc., and examples of the alkaline earth metal include magnesium, calcium, barium, etc.

[0021] Examples of the fatty acid ester include esters of the aforementioned fatty acids and alcohols. Examples of the alcohol include methanol, ethanol, etc.

[0022] Examples of the sulfide of the unsaturated carboxylic acid include sulfides of oleic acid.

[0023] Examples of the polyoxyalkylene compound include compounds represented by the following general formula (1) or (2).

[0024] R 1 O-(R 2 O) i -R 3 (1)

[0025] In formula (1), R 1 and R 3 each independently represent a hydrogen atom or a hydrocarbon group having 1 to 30 carbon atoms, R 2 represents an alkylene group having 2 to 4 carbon atoms, and i represents an integer such that the number average molecular weight of the compound represented by general formula (1) is 100 to 3500.

[0026] E-[(R 4 O) j -R 5 k (2)

[0027] In formula (2), E represents a residue obtained by removing some or all of the hydrogen atoms of the hydroxyl groups of a polyhydric alcohol having 3 to 10 hydroxyl groups, R 4 represents an alkylene group having 2 to 4 carbon atoms, R 5 represents a hydrogen atom or a hydrocarbon group having 1 to 30 carbon atoms, j represents an integer such that the number average molecular weight of the compound represented by general formula (2) is 100 to 3500, and k represents the same number as the number of hydrogen atoms removed from the hydroxyl groups in E.

[0028] Examples of the extreme pressure additive include sulfur-based extreme pressure additives such as sulfurized fatty oils, chlorine-based extreme pressure additives such as chlorinated paraffins and chlorinated fatty acid esters, and phosphorus-based additives such as zinc dialkyldithiophosphate. The extreme pressure additive may be used alone or in combination of two or more.

[0029] ​Examples of surfactants include anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic surfactants, etc. The surfactant may be used alone or in combination of two or more. The surfactant preferably contains an anionic surfactant, and may be used in combination with an anionic surfactant and a nonionic surfactant.

[0030] The anionic surfactant is not particularly limited as long as it is commonly used in abrasive applications, and examples include higher alkyl sulfate salts (e.g., sodium lauryl sulfate and potassium lauryl sulfate), alkyl ether sulfate salts (e.g., POE-lauryl sulfate triethanolamine, and sodium POE-lauryl sulfate, where POE represents polyoxyethylene).

[0031] The nonionic surfactant is not particularly limited as long as it is commonly used in abrasive applications, and examples include sorbitan fatty acid esters (e.g., sorbitan monooleate), glycerin or polyglycerin fatty acids (e.g., glycerin monostearate), sucrose fatty acid esters, etc.

[0032] As the preservative, organic amines are preferred, and organic amines containing a hydroxyl group are more preferred. The organic amine is not particularly limited as long as it is commonly used in abrasive applications, and examples include trialkanolamines such as trimethanolamine, triethanolamine, tripropanolamine, and tributanolamine. The preservative may be used alone or in combination of two or more.

[0033] Examples of the defoaming agent include silicone-based defoaming agents, polyoxyalkylene-based defoaming agents, and mineral oil-based defoaming agents. Examples of the silicone-based defoaming agent include dimethylpolysiloxane and modified polysiloxane. Examples of the polyoxyalkylene-based defoaming agent include polyoxypropylene and polyoxybutylene. Examples of the mineral oil-based defoaming agent include naphthenic and paraffinic types. The defoaming agent may be used alone or in combination of two or more.

[0034] At least one treatment selected from the group consisting of (1) heating, (2) washing with an organic solvent, and (3) ultraviolet irradiation treatment is performed on the substrate ground with the grinding fluid.

[0035] The heating of the substrate is preferably at 250 °C or higher, more preferably at 270 °C or higher, and even more preferably at 290 °C or higher. The upper limit of the heating temperature is not particularly limited, but from the viewpoint of suppressing damage due to heating of the substrate, in the case of an aluminum substrate, it is preferably 360 °C or lower, more preferably 340 °C or lower, and even more preferably 310 °C or lower. In the case of a glass substrate, it is preferably 700 °C or lower, more preferably 600 °C or lower, and even more preferably 500 °C or lower.

[0036] The heating time is preferably 10 minutes or longer, more preferably 15 minutes or longer, and even more preferably 20 minutes or longer. Also, from the viewpoint of reducing the energy load, it is preferably 60 minutes or shorter, more preferably 45 minutes or shorter, and even more preferably 30 minutes or shorter.

[0037] The heating device is not particularly limited as long as it can heat to the target temperature, and a known heating device can be used. Specifically, as the heating device, an oven, an electric furnace, etc. can be used.

[0038] Since the grinding fluid in the previous step is an aqueous solution, the organic solvent used for washing is preferably a non-polar solvent. Examples of the non-polar solvent include isopropyl alcohol (IPA) and hydrofluoroether (HFE).

[0039] The cleaning method with an organic solvent is not particularly limited, and ordinary cleaning methods and cleaning apparatuses can be applied. For example, a method of spin-rinsing at room temperature using a spin-rinse apparatus can be mentioned.

[0040] The ultraviolet irradiation treatment can be performed using a light source such as an excimer laser, a high-pressure mercury lamp, or an arc lamp.

[0041] From the viewpoint of effectively cutting the molecular chains of the polymer components remaining on the surface of the disk-shaped substrate, the irradiation illuminance of the ultraviolet irradiation treatment is preferably 300 mW / m 2 or more, more preferably 600 mW / m 2 or more, and even more preferably 1200 mW / m 2 or more.

[0042] From the viewpoint of equalizing the irradiation range, the irradiation time of the ultraviolet irradiation treatment is preferably 2 seconds or more, may be 5 seconds or more, and may be 7 seconds or more.

[0043] From the viewpoint of enhancing the wettability of the plating solution or chemical strengthening solution in the next process, the water contact angle of the surface of the disk-shaped substrate after performing at least one treatment selected from the group consisting of (1) to (3) is preferably 45° or less, more preferably 30° or less, even more preferably 20° or less, and particularly preferably 15° or less.

[0044] The water contact angle is measured using a contact angle meter as the contact angle (after 0.2 seconds) of a water droplet (pure water, 2.0 μL) on the substrate surface at 25°C.

[0045] Based on the amount of the polymer component on the surface of the disk-shaped substrate before the treatments (1) to (3) being the reference (100% by mass), it is preferably reduced to 0.001% by mass or less after the treatments (1) to (3), and may be 0% by mass. The amount of the polymer component on the surface of the disk-shaped substrate can be measured by time-of-flight secondary ion mass spectrometry (TOF-SIMS).

[0046] After the processes (1) to (3), a plating layer is formed on the aluminum substrate by a plating solution, and a chemical strengthening layer is formed on the glass substrate by a chemical strengthening solution.

[0047] As the plating method, a known method can be used, and an electroless plating method is preferably used. Generally, a NiP-based nickel alloy plating layer is formed. Examples of the plating solution used to form the NiP alloy plating layer include a plating solution containing nickel sulfate as a nickel source and hypophosphite as a phosphorus source. An Mo salt or a W salt may be further added to the plating solution to form a NiMoP alloy plating layer or a NiWP alloy plating layer.

[0048] The chemical strengthening treatment is a treatment in which the glass substrate is immersed in a chemical strengthening solution to exchange ions in the chemical strengthening solution with ions in the glass. A known method performed on the glass substrate can be used for the chemical strengthening treatment. The chemical strengthening solution can be a high-temperature molten salt and preferably contains KNO3, NaNO3, etc.

[0049] The disk-shaped substrate obtained by the manufacturing method of the present disclosure can be suitably used as a magnetic recording medium used in a hard disk drive (HDD).

[0050] <Magnetic recording medium> The magnetic recording medium of the present disclosure has a disk-shaped substrate obtained by the manufacturing method of the present disclosure and a magnetic layer provided on the disk-shaped substrate. The disk-shaped substrate obtained by the manufacturing method of the present disclosure is excellent in the thickness uniformity of these layers when a plating layer or a chemical strengthening layer is formed.

[0051] When a magnetic layer is provided on a plating layer with excellent flatness, the magnetic layer has excellent flatness and excellent writeability and readability by a magnetic head element. The number of concave defects in the plating layer on the disk-shaped substrate can be 500 or less on one side, preferably 50 or less, more preferably 30 or less, and even more preferably 4 or less. The number of concave defects in the plating layer can be confirmed by observation with an optical inspection machine (for example, OSA7100 manufactured by KLA Tencor).

[0052] Moreover, according to the manufacturing method of the present disclosure, since the thickness uniformity of the chemically strengthened layer is excellent, a partial strength reduction of the glass substrate is suppressed, and the occurrence frequency of breakage defects is reduced.

[0053] The magnetic recording medium may further have a carbon protective layer, a lubricant layer, etc. on the magnetic layer. The magnetic recording medium may further have an adhesion layer, a soft magnetic underlayer, a seed layer, an orientation control layer, etc. between the substrate and the magnetic layer. These layers may be each one layer or two or more layers. As the materials for forming the magnetic layer, the carbon protective layer, the lubricant layer, the adhesion layer, the soft magnetic underlayer, the seed layer, the orientation control layer, etc., general materials used for magnetic recording media can be used.

[0054] FIG. 1 is a schematic cross-sectional view showing an example of an assist magnetic recording medium in which the disk-shaped substrate according to the present disclosure is applied as a substrate 1 for a magnetic recording medium. As shown in FIG. 1, the assist magnetic recording medium 40 includes a substrate 1 for a magnetic recording medium, a seed layer 41, a first underlayer 42, a second underlayer 43, a magnetic layer 44, a protective layer 45, and a lubricant layer 46 laminated in this order. The magnetic recording medium 40 can be used in a magnetic storage device.

[0055] FIG. 2 is a perspective view showing an example of a magnetic storage device using the magnetic recording medium according to the present disclosure. As shown in FIG. 2, the magnetic storage device 50 includes an assist magnetic recording medium 40, a magnetic recording medium driving unit 51 for rotating the assist magnetic recording medium 40, a magnetic head 52, a head moving unit 53 for moving the magnetic head 52, and a recording / reproducing signal processing unit 54. The magnetic head 52 has a recording head and a reproducing head (not shown). The recording head has a laser light generating unit for heating the assist magnetic recording medium and a waveguide for guiding the laser light generated from the laser light generating unit to a near-field light generating element. The magnetic storage device 50 attaches the central portion of the assist magnetic recording medium 40 to the rotation axis of the spindle motor, and while the magnetic head 52 floats and travels on the surface of the assist magnetic recording medium 40 that is rotationally driven by the spindle motor, information is written to or read from the assist magnetic recording medium 40. [Embodiment]

[0056] Hereinafter, the present disclosure will be specifically described with reference to embodiments, but the scope of the present disclosure is not limited to these embodiments.

[0057] [Comparative Example 1] [Manufacture of Aluminum Alloy Substrate] As a sheet material of an aluminum alloy, a product equivalent to A5086 (Mg: 4% by mass, Mn: 0.5% by mass, Fe: 0.3% by mass, Cr: 0.2% by mass, Si: 0.2% by mass, Zn: 0.2% by mass, the balance Al) was used. This sheet material was manufactured by obtaining an aluminum alloy ingot by a semi-continuous casting method and then rolling it.

[0058] Next, a sheet material with a thickness of 1.2 mm was punched into a donut disk shape to obtain an aluminum alloy substrate with a diameter of 97 mm having a central hole, and this was annealed at 380° C. for 1 hour. Then, both main surfaces and end surfaces of the aluminum alloy substrate were machined by a diamond bite to obtain an aluminum alloy substrate with a diameter of 95 mm and a thickness of 0.8 mm.

[0059] Next, with respect to this aluminum alloy substrate, using a grinding apparatus, while causing a plurality of aluminum alloy substrates held in the openings of each carrier plate to perform planetary motion, both main surfaces thereof were ground with grinding wheels provided on the upper surface plate and the lower surface plate.

[0060] A 4-way type double-sided grinding machine (Model 16B manufactured by Hamai Sangyo Co., Ltd.) was used as the grinding apparatus, the rotational speed of the surface plate was 30 rpm, and the processing pressure was 110 g / cm 2 and grinding was performed for 5 minutes. As the grinding fluid, a water-soluble grinding fluid containing 30% by mass of oleic acid was diluted with water to 1.0% by mass and used.

[0061] (Measurement of water contact angle) For the aluminum alloy substrate after grinding, using DM-501 manufactured by Kyowa Interface Chemical Co., Ltd., the contact angle (after 0.2 seconds) of water droplets (pure water, 2.0 μL) on the substrate surface at 25°C was measured.

[0062] (Formation of plating layer) The obtained aluminum alloy substrate was immersed in a NiP-based plating solution, and an 88Ni-12P (P content 12% by mass, the balance being Ni) layer was formed as a NiP-based plating layer on the surface of the aluminum alloy substrate using electroless plating.

[0063] The NiP-based plating solution contained nickel sulfate (nickel source) and sodium hypophosphite (phosphorus source), and a solution with the component amounts adjusted so as to obtain a NiP-based plating layer having the above composition was used. The NiP-based plating solution used to form the NiP-based plating layer had its liquid temperature adjusted to 90°C. The immersion time of the aluminum alloy substrate in the NiP-based plating solution was 2 hours.

[0064] Next, the aluminum alloy substrate on which the NiP-based plating layer was formed was heated at a required temperature and time to obtain an aluminum alloy substrate with a NiP-based plating layer. To remove the unevenness of the NiP plating layer, a polishing apparatus having polishing cloths made of foamed polyurethane on the upper and lower platens was used, and while discharging an abrasive containing alumina, zirconia, titania, colloidal silica, etc., the upper and lower platens were moved in a planetary motion to polish the substrate surface.

[0065] (Evaluation of concave defects in the plating layer) The entire surface of the aluminum alloy substrate was observed with an optical inspection machine (OSA7100 manufactured by KLA Tencor), and the number of concave defects on the entire substrate surface was counted. The evaluation criteria based on the number of concave defects on one side of the substrate are as follows. A and B are considered qualified.

[0066] A: The number of concave defects is 50 or less. B: The number of concave defects exceeds 50 and is 500 or less. C: The number of concave defects exceeds 500 and is 1000 or less. D: The number of concave defects exceeds 1000.

[0067] [Comparative Example 2] In Comparative Example 1, before forming the plating layer, the aluminum alloy substrate after grinding was scrubbed twice with a sponge made of polyvinyl alcohol (PVA) while discharging a detergent (nonionic surfactant) at room temperature, then spin-rinsed with a spin-rinse apparatus while discharging pure water, and then spin-dried.

[0068] For the aluminum alloy substrate after cleaning, the water contact angle was measured by the above method. Also, a plating layer was formed on the aluminum alloy substrate after cleaning by the same method as in Comparative Example 1.

[0069] [Example 1] In Comparative Example 2, the cleaning was performed by replacing the detergent with a nonpolar solvent of HFE. For the aluminum alloy substrate after cleaning, the water contact angle was measured by the above method. Also, a plating layer was formed on the aluminum alloy substrate after cleaning by the same method as in Comparative Example 1.

[0070] [Example 2] In Comparative Example 1, before forming the plating layer, the aluminum alloy substrate after grinding was heated at 300°C for 30 minutes. The heating was performed using a conveyor-type continuous atmosphere furnace device as an electric furnace. Regarding the aluminum alloy substrate after heating, the water contact angle was measured by the above method. Also, a plating layer was formed on the aluminum alloy substrate after heating by the same method as in Comparative Example 1.

[0071] [Example 3] In Example 2, heating was performed by changing the temperature to 200°C. Regarding the aluminum alloy substrate after heating, the water contact angle was measured by the above method. Also, a plating layer was formed on the aluminum alloy substrate after heating by the same method as in Comparative Example 1.

[0072] [Example 4] In Comparative Example 1, before forming the plating layer, ultraviolet irradiation treatment was performed at 1200 mW / m 2 for 2 seconds. For the ultraviolet irradiation treatment, Ballast for High power UV Lamp manufactured by SUN ENERGY was used. Regarding the aluminum alloy substrate after ultraviolet irradiation treatment, the water contact angle was measured by the above method. Also, a plating layer was formed on the aluminum alloy substrate after ultraviolet irradiation treatment by the same method as in Comparative Example 1.

[0073] [Table 1]

[0074] It can be seen that in Example 1 where cleaning was performed with an organic solvent before forming the plating layer, Example 2 and 3 where annealing was performed, and Example 4 where ultraviolet irradiation treatment was performed, the plating concave defects were significantly reduced compared to Comparative Example 1 where these treatments were not performed. In addition, in Comparative Example 2, although washing is performed with water before forming the plating layer, it can be seen that the number of plating concave defects is not significantly reduced.

Claims

1. A method for manufacturing a disk-shaped substrate, comprising performing at least one treatment selected from the group consisting of (1) heating, (2) cleaning with an organic solvent, and (3) ultraviolet irradiation treatment on the disk-shaped substrate ground with a grinding fluid, to remove at least a part of the polymer component of the grinding fluid on the surface of the disk-shaped substrate.

2. The method for manufacturing a disk-shaped substrate according to claim 1, wherein the grinding fluid contains at least one selected from the group consisting of an oiliness agent, an extreme pressure additive, a surfactant, a preservative, and an antifoaming agent.

3. The method for manufacturing a disk-shaped substrate according to claim 1 or claim 2, wherein the disk-shaped substrate is an aluminum substrate, an aluminum alloy substrate, or a glass substrate.

4. The method for manufacturing a disk-shaped substrate according to claim 1 or claim 2, wherein the water contact angle of the surface of the disk-shaped substrate after the treatment is 45° or less.

5. A magnetic recording medium, comprising: a disk-shaped substrate obtained by the manufacturing method according to claim 1 or claim 2; and a magnetic layer provided on the disk-shaped substrate. ​

Images