Method for manufacturing disk-shaped substrate, disk-shaped substrate, and magnetic recording medium

Abstract

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

Description

Method for manufacturing disk-shaped substrate, disk-shaped substrate, and magnetic recording medium

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

[0002] 2. Description of the Related Art Magnetic recording media used in hard disk drives (HDDs) employ disk-shaped substrates, which are generally aluminum or aluminum alloy substrates, although demand for glass substrates has been increasing in recent years.

[0003] The disk-shaped substrate is machined into a doughnut shape with a circular through-hole in the center, and the main surface and end surfaces are ground using a grinding fluid. In the next step, the ground disk-shaped substrate is surface-treated using a plating solution (see, for example, Patent Document 1) for aluminum substrates and aluminum alloy substrates, or a chemical strengthening solution (see, for example, Patent Document 2) for glass substrates. After these treatments, a magnetic layer is formed.

[0004] JP 2020-107382 A International Publication No. 2015 / 041301

[0005] The plated layer and chemically strengthened layer obtained by the above-mentioned surface treatment may have low thickness uniformity. If the plated layer has low thickness uniformity and poor flatness, the magnetic layer formed on the plated layer will follow the surface shape of the plated layer, resulting in reduced flatness and impaired writability and readability by the magnetic head element. Furthermore, if the thickness uniformity of the chemically strengthened layer is low and thin portions of the chemically strengthened layer exist, problems such as the glass substrate being prone to cracking at those portions occur. In particular, in recent years, there has been a demand for thinner magnetic recording media, making glass substrates more prone to cracking. Therefore, the present disclosure aims to provide a method for manufacturing a disc-shaped substrate, a disc-shaped substrate, and a magnetic recording medium that have excellent flatness of the plated layer and uniformity of the thickness of the chemically strengthened layer.

[0006] The present disclosure includes the following aspects. <1> A method for manufacturing a disk-shaped substrate, comprising: subjecting a disk-shaped substrate ground with a 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, to remove at least a portion of the polymer component of the grinding fluid from the surface of the disk-shaped substrate. <2> A 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 oiliness agent, an extreme-pressure additive, a surfactant, an antiseptic, and an antifoaming agent. <3> A 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> A method for manufacturing a disk-shaped substrate according to any one of <1> to <3>, wherein the surface of the disk-shaped substrate after the treatment has a water contact angle of 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>; and a magnetic layer provided on the disk-shaped substrate. <6> A disk-shaped substrate having a ground main surface, the main surface having a water contact angle of 45° or less. <7> A magnetic recording medium comprising: the disk-shaped substrate according to <6>; and a magnetic layer provided on the disk-shaped substrate.

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

[0008] 1 is a schematic cross-sectional view showing an example of an assisted magnetic recording medium in which a disk-shaped substrate according to the present disclosure is used as a substrate for a magnetic recording medium;

[0009] Embodiments of the present disclosure are described in detail below. However, the present disclosure is not limited to the following embodiments. In the following embodiments, components (including elementary steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and do not limit the present disclosure. In the present disclosure, numerical ranges indicated using "to" include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in the present disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in the present disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples. In the present disclosure, each component may contain multiple corresponding substances. When multiple substances corresponding to each component are present in the composition, the content or amount of each component means the total content or amount of the multiple substances present in the composition, unless otherwise specified. In the present disclosure, each component may contain multiple types of particles. When a composition contains multiple types of particles corresponding to each component, the particle size of each component refers to the value for a mixture of the multiple types of particles present in the composition, unless otherwise specified. In the present disclosure, the term "layer" includes cases where the layer is formed over the entire area when the area where the layer exists is observed, as well as cases where the layer is formed only in a part of the area.

[0010] <Method for manufacturing a disk-shaped substrate> In the method for manufacturing a disk-shaped substrate of the present disclosure, a disk-shaped substrate that has been ground with a grinding fluid is subjected to at least one treatment selected from the group consisting of (1) heating, (2) washing with an organic solvent, and (3) ultraviolet light irradiation treatment, thereby removing at least a portion of the polymer component of the grinding fluid from the surface of the disk-shaped substrate. The reason why the manufacturing method having the above configuration solves the above problem is thought to be as follows.

[0011] It has been found that polymeric components contained in the grinding fluid adhere to the surface of a disk-shaped substrate ground with a grinding fluid. The presence of these polymeric components is believed to affect the wettability of the plating solution and chemical strengthening solution in the subsequent process, or other physical properties, thereby reducing the flatness of the plating layer and the uniformity of the thickness of the chemically strengthened layer. Therefore, before applying the plating solution or chemical strengthening solution, the ground disk-shaped substrate is subjected to at least one treatment selected from the group consisting of (1) heating, (2) washing with an organic solvent, and (3) ultraviolet irradiation treatment. Heating the disk-shaped substrate burns off at least a portion of the polymeric components present on the surface. Washing the disk-shaped substrate with an organic solvent washes off at least a portion of the polymeric components present on the surface. UV irradiation of the disk-shaped substrate breaks the molecular chains of at least a portion of the polymeric components, resulting in low molecular weight and removing at least a portion of the polymeric components. It is believed that disk-shaped substrates from which the polymeric components have been removed by these treatments will improve the flatness of the plating layer formed in the subsequent process or the uniformity of the thickness of the chemically strengthened layer.

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

[0013] The aluminum substrate may be one that is commonly used in this field, and from the viewpoints of strength, plating ability, grindability, etc., an aluminum alloy of JIS-A5086 is preferred.

[0014] The glass substrate can be made of amorphous glass, crystallized glass, or the like, which is commonly used as a glass substrate for magnetic recording media. Specific examples include glass substrates made of soda lime, aluminosilicate, lithium silicate, lithium aluminosilicate, and aluminoborosilicate. Crystallized glass can be obtained by reheating glass under controlled conditions to precipitate and grow a large number of minute crystals. Crystallized glass can also be made of Al２ Examples include O3-SiO2-Li2O-based glasses, B2O3-Al2O3-SiO2-Li2O-based glasses, etc. The thickness of the glass substrate for the magnetic recording medium is not particularly limited, and typically, a thickness of about 0.4 mm to 1 mm is used.

[0015] A substrate having a circular through-hole in the center is ground on its main surface and edge surfaces using a grinding fluid. The grinding of the main surface and the edge surfaces may be performed simultaneously, in a series, or separately. The edge surface grinding may be performed on the inner and outer peripheral edge surfaces of the substrate, and may further include chamfering. The grinding and edge surface processing may be performed, for example, in the order of a main surface grinding step and an inner and outer peripheral edge surface grinding step.

[0016] In the main surface grinding process, grinding is performed on both main surfaces of the substrate (the surfaces that will ultimately become the recording surfaces of the magnetic recording medium). In the grinding process, the substrate is sandwiched between a pair of surface plates that rotate in opposite directions, a grinding fluid is supplied, and both main surfaces of the substrate are ground using grinding pads provided on the surface plates. Multiple substrates may be placed between the pair of surface plates and ground together. Abrasive grains such as diamond are fixed to the grinding pads with a binder, and these abrasive grains are used to grind both main surfaces of the substrate.

[0017] From the viewpoint of reducing the environmental load, the grinding fluid is preferably an aqueous solution using water as a medium, and from the viewpoint of lubrication, cooling, removal of chips, etc. during grinding, it may contain at least one selected from the group consisting of oiliness agents, extreme pressure additives, surfactants, preservatives, and antifoaming agents. At least a portion of these may remain as polymer components on the surface of the disk-shaped substrate after grinding. In particular, oiliness agents, antifoaming agents, etc. tend to remain as polymer components on the surface of the disk-shaped substrate after grinding.

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

[0019] The fatty acid is not particularly limited as long as it is one that is commonly used in abrasive applications, and examples thereof 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 fatty acids include oleic acid, linoleic acid, stearic acid, isostearic acid, palmitic acid, lauric acid, and maleic acid. The fatty acids may be used alone or in combination of two or more.

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

[0021] Examples of fatty acid esters include esters of the above-mentioned fatty acids with alcohols, such as methanol and ethanol.

[0022] An example of the sulfide of an unsaturated carboxylic acid is a sulfide 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 represents 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 3,500.

[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, and R ４ represents an alkylene group having 2 to 4 carbon atoms, and 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 extreme pressure additives 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. One type of extreme pressure additive may be used alone, or two or more types may be used in combination.

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

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

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

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

[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 naphthene-based and paraffin-based defoaming agents. One type of defoaming agent may be used alone, or two or more types may be used in combination.

[0034] The substrate that has been ground with the grinding fluid is subjected to at least one treatment selected from the group consisting of (1) heating, (2) cleaning with an organic solvent, and (3) ultraviolet irradiation treatment.

[0035] The substrate is preferably heated to 250° C. or higher, more preferably 270° C. or higher, and even more preferably 290° C. or higher. There is no particular upper limit to the heating temperature, but from the viewpoint of suppressing damage to the substrate due to heating, in the case of an aluminum substrate, the temperature is preferably 360° C. or lower, more preferably 340° C. or lower, and even more preferably 310° C. or lower, and in the case of a glass substrate, the temperature 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 more, more preferably 15 minutes or more, and even more preferably 20 minutes or more, and from the viewpoint of reducing the energy load, is preferably 60 minutes or less, more preferably 45 minutes or less, and even more preferably 30 minutes or less.

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

[0038] Since the grinding fluid used in the previous step is an aqueous solution, the organic solvent used for cleaning is preferably a non-polar solvent, such as isopropyl alcohol (IPA) or hydrofluoroether (HFE).

[0039] The method for cleaning with an organic solvent is not particularly limited, and a conventional cleaning method and cleaning device can be used, for example, a method of spin rinsing at room temperature using a spin rinse device.

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

[0041] The irradiation intensity of the ultraviolet irradiation treatment is set to 300 mW / m from the viewpoint of effectively cutting the molecular chains of the polymer components remaining on the surface of the disk-shaped substrate. ２ More than 600 mW / m ２ More preferably, 1200 mW / m or more ２ The above is even more preferable.

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

[0043] From the viewpoint of enhancing the wettability of the plating solution or chemical strengthening solution in the next step, the water contact angle of the surface of the disc-shaped substrate after 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] The amount of polymer components on the surface of the disk-shaped substrate is preferably reduced to 0.001% by mass or less, or may be 0% by mass, after the treatments (1) to (3), with the amount before the treatments (1) to (3) being taken as the reference (100% by mass). The amount of polymer components 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 using a plating solution, and a chemically strengthened layer is formed on the glass substrate using a chemically strengthened solution.

[0047] As the plating method, a known method can be used, and electroless plating is preferably used. Generally, a NiP-based nickel alloy plating layer is formed. Examples of plating solutions used to form the NiP alloy plating layer include those containing nickel sulfate as a nickel source and hypophosphite as a phosphorus source. A 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 a glass substrate is immersed in a chemical strengthening solution to exchange ions in the chemical strengthening solution with ions in the glass. The chemical strengthening treatment can be performed by a known method performed on glass substrates. The chemical strengthening solution can be a high-temperature molten salt, such as KNO ３ , NaNO ３ It is preferable to include the following.

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

[0050] <Disc-shaped substrate> One aspect of the disc-shaped substrate of the present disclosure has a ground main surface, and the water contact angle of the surface of the main surface is 45° or less. The water contact angle of the ground main surface is preferably within the range of water contact angles described in the above-mentioned method for manufacturing a disc-shaped substrate. For other requirements, refer to those described in the above-mentioned method for manufacturing a disc-shaped substrate.

[0051] <Magnetic Recording Medium> The magnetic recording medium of the present disclosure includes 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 has excellent thickness uniformity when a plating layer or a chemically strengthened layer is formed on the disk-shaped substrate. Furthermore, one aspect of the magnetic recording medium of the present disclosure includes a disk-shaped substrate having a water contact angle of 45° or less on the main surface of the ground surface, and a magnetic layer provided on the disk-shaped substrate.

[0052] When a magnetic layer is provided on a plating layer with excellent flatness, the magnetic layer has excellent flatness and excellent writability and readability by a magnetic head element. The number of concave defects in the plating layer on the disk-shaped substrate can be limited to 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 using an optical inspection machine (e.g., OSA7100 manufactured by KLA Tencor Corporation).

[0053] Furthermore, according to the manufacturing method of the present disclosure, the chemically strengthened layer has excellent thickness uniformity, which prevents a partial decrease in strength of the glass substrate and reduces the frequency of breakage defects.

[0054] The magnetic recording medium may further include a carbon protective layer, a lubricant layer, etc. on the magnetic layer. The magnetic recording medium may further include an adhesion layer, a soft magnetic underlayer, a seed layer, an orientation control layer, etc. between the substrate and the magnetic layer. Each of these layers may consist of one layer or two or more layers. Materials that form the magnetic layer, carbon protective layer, lubricant layer, adhesion layer, soft magnetic underlayer, seed layer, orientation control layer, etc. may be general materials used in magnetic recording media.

[0055] Fig. 1 is a cross-sectional schematic diagram showing an example of an assisted magnetic recording medium that uses a disk-shaped substrate according to the present disclosure as a magnetic recording medium substrate 1. As shown in Fig. 1, the assisted magnetic recording medium 40 includes a magnetic recording medium substrate 1, 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 stacked in this order. The magnetic recording medium 40 can be used in a magnetic storage device.

[0056] 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 drive unit 51 for rotating the assist magnetic recording medium 40, a magnetic head 52, a head movement 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), and the recording head has a laser light generator for heating the assist magnetic recording medium and a waveguide for guiding the laser light generated from the laser light generator to a near-field light generating element. In the magnetic storage device 50, the center of the assist magnetic recording medium 40 is attached to the rotation shaft of a spindle motor, and the magnetic head 52 writes or reads information to or from the assist magnetic recording medium 40 while floating and traveling above the surface of the assist magnetic recording medium 40, which is rotated and driven by the spindle motor.

[0057] The present disclosure will be specifically described below using examples, but the scope of the present disclosure is not limited to these examples.

[0058] Comparative Example 1 (Production of Aluminum Alloy Substrate) An aluminum alloy plate equivalent to A5086 (Mg: 4 mass%, Mn: 0.5 mass%, Fe: 0.3 mass%, Cr: 0.2 mass%, Si: 0.2 mass%, Zn: 0.2 mass%, balance Al) was used. This plate was produced by rolling an aluminum alloy ingot obtained by semi-continuous casting.

[0059] Next, the 1.2 mm thick plate material was punched into a doughnut-shaped disk to obtain an aluminum alloy substrate having a diameter of 97 mm and a center hole, which was then annealed for 1 hour at 380° C. Thereafter, both main surfaces and end surfaces of the aluminum alloy substrate were machined with a diamond turning tool to obtain an aluminum alloy substrate having a diameter of 95 mm and a thickness of 0.8 mm.

[0060] Next, a grinding machine was used to grind both main surfaces of the aluminum alloy substrates with grindstones provided on upper and lower surface plates while performing planetary motion on the aluminum alloy substrates held in the openings of each carrier plate.

[0061] The grinding device used was a 4-way type double-sided grinder (16B type manufactured by Hamai Sangyo Co., Ltd.), with the rotation speed of the surface plate set at 30 rpm and the processing pressure set at 110 g / cm. ２ The grinding fluid used was a water-soluble grinding fluid containing 30% by mass of oleic acid diluted with water to 1.0% by mass.

[0062] (Measurement of Water Contact Angle) The contact angle (after 0.2 seconds) of a water droplet (pure water, 2.0 μL) on the surface of the ground aluminum alloy substrate at 25° C. was measured using DM-501 manufactured by Kyowa Interface Science Co., Ltd.

[0063] (Formation of plating layer) The obtained aluminum alloy substrate was immersed in a NiP-based plating solution, and an 88Ni-12P (P content 12 mass%, balance Ni) layer was formed as a NiP-based plating layer on the surface of the aluminum alloy substrate using an electroless plating method.

[0064] The NiP-based plating solution contained nickel sulfate (nickel source) and sodium hypophosphite (phosphorus source), and the amounts of the components were adjusted so as to obtain a NiP-based plating layer of the above composition. The temperature of the NiP-based plating solution used to form the NiP-based plating layer was adjusted to 90°C. The aluminum alloy substrate was immersed in the NiP-based plating solution for 2 hours.

[0065] Next, the aluminum alloy substrate with the NiP-based plating layer formed thereon was heated at a required temperature for a required time to obtain an aluminum alloy substrate with a NiP-based plating layer. To remove the irregularities in the NiP-based plating layer, a polishing machine having polyurethane foam polishing cloths on the upper and lower platens was used, and the upper and lower platens were moved in planetary motion while an abrasive containing alumina, zirconia, titania, colloidal silica, etc. was discharged.

[0066] (Evaluation of concave defects in plating layer) The entire surface of the aluminum alloy substrate was observed using an optical inspection machine (OSA7100 manufactured by KLA Tencor Corporation), and the number of concave defects on the entire surface of the substrate 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 to be pass.

[0067] A: The number of pit defects is 50 or less. B: The number of pit defects is more than 50 and 500 or less. C: The number of pit defects is more than 500 and 1000 or less. D: The number of pit defects exceeds 1000.

[0068] [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) at room temperature while discharging a detergent (nonionic surfactant), and then spin-rinsed in a spin-rinsing device while discharging pure water, and then spin-dried.

[0069] The water contact angle of the washed aluminum alloy substrate was measured by the method described above. A plating layer was formed on the washed aluminum alloy substrate by the same method as in Comparative Example 1.

[0070] [Example 1] In Comparative Example 2, cleaning was performed using a non-polar solvent of HFE instead of detergent. After cleaning, the aluminum alloy substrate was measured for water contact angle using the method described above. Furthermore, a plating layer was formed on the aluminum alloy substrate after cleaning using the same method as in Comparative Example 1.

[0071] [Example 2] In Comparative Example 1, the ground aluminum alloy substrate was heated at 300°C for 30 minutes before forming a plating layer. The heating was performed using a conveyor-type continuous atmospheric furnace as an electric furnace. The water contact angle of the heated aluminum alloy substrate was measured by the method described above. Furthermore, a plating layer was formed on the heated aluminum alloy substrate by the same method as in Comparative Example 1.

[0072] [Example 3] In Example 2, heating was performed at a temperature of 200°C. The water contact angle of the heated aluminum alloy substrate was measured by the method described above. In addition, a plating layer was formed on the heated aluminum alloy substrate by the same method as in Comparative Example 1.

[0073] [Example 4] In Comparative Example 1, before forming the plating layer, ２The aluminum alloy substrate was subjected to ultraviolet irradiation treatment for 2 seconds at 1000 kJ / min for 2 seconds. For the ultraviolet irradiation treatment, a Ballast for High power UV Lamp manufactured by SUN ENERGY Corporation was used. The water contact angle of the aluminum alloy substrate after the ultraviolet irradiation treatment was measured by the above-mentioned method. Furthermore, a plating layer was formed on the aluminum alloy substrate after the ultraviolet irradiation treatment by the same method as in Comparative Example 1.

[0074]

[0075] It can be seen that Example 1, in which cleaning with an organic solvent was performed before forming the plating layer, Examples 2 and 3, in which annealing was performed, and Example 4, in which ultraviolet irradiation treatment was performed, had significantly reduced plating concave defects compared to Comparative Example 1, in which these treatments were not performed. Furthermore, it can be seen that Comparative Example 2, in which cleaning with water was performed before forming the plating layer, did not reduce the number of plating concave defects very much.

[0076] The disclosure of Japanese Patent Application No. 2023-216244 is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards in this disclosure are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. A method for manufacturing a disk-shaped substrate, comprising the steps of: (1) heating a disk-shaped substrate that has been ground with a grinding fluid; (2) washing with an organic solvent; and (3) subjecting the disk-shaped substrate to at least one treatment selected from the group consisting of ultraviolet light irradiation treatment to remove at least a portion of the polymeric component of the grinding fluid on the surface of the disk-shaped substrate.

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

4. The method for producing a disk-shaped substrate according to claim 1 or 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 2; and a magnetic layer provided on the disk-shaped substrate.

6. A disk-shaped substrate having a main surface which is a ground surface, the main surface having a water contact angle of 45° or less.

7. A magnetic recording medium comprising: the disk-shaped substrate according to claim 6; and a magnetic layer provided on the disk-shaped substrate.

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