Manufacturing method for substrates for magnetic recording media

Abstract

To provide a method for manufacturing a magnetic recording medium substrate that can produce a magnetic recording medium substrate with excellent heat resistance, specific modulus of elasticity, and impact resistance at a low cost. [Solution] A method for manufacturing a substrate for a magnetic recording medium, comprising: a grinding step of grinding the surface of a steatite sintered body; an etching step of performing an etching treatment on the surface of the steatite sintered body after the grinding step; and a polishing step of polishing the surface of the steatite sintered body after the etching step.

Description

[Technical Field]

[0001] This disclosure relates to a method for manufacturing a substrate for a magnetic recording medium. [Background technology]

[0002] In recent years, with the development of the internet network and the expansion of big data utilization, the amount of data stored in data centers has continued to increase. From the perspective of securing space in data centers, there is a demand for hard disk drives with high storage capacity per unit.

[0003] Attempts to increase the storage capacity per standardized hard disk drive include, for example, increasing the storage capacity per magnetic recording medium and increasing the number of magnetic recording media that can be placed inside the drive case.

[0004] In attempts to increase the storage capacity per magnetic recording medium, assist recording media that use FePt alloys and CoPt alloys with L10 crystal structures in their magnetic layers are attracting attention. Assist recording media work by irradiating the magnetic recording medium with near-field light and microwaves to locally assist the surface of the magnetic recording medium, thereby reducing its coercivity and enabling writing. When manufacturing assist recording media containing FePt alloys and CoPt alloys in their magnetic layers, the substrate temperature must be raised to over 400°C, requiring high heat resistance from the substrate.

[0005] Attempts to increase the number of magnetic recording media that can be housed inside a drive case require thinning the circuit board. However, thinning the circuit board can sometimes cause fluttering of the magnetic recording media. Fluttering is the rattling of the magnetic recording media that occurs when it is rotated at high speed. If the fluttering of the magnetic recording media becomes large, stable reading and writing may become difficult in a hard disk drive.

[0006] To suppress fluttering of magnetic recording media, for example, Patent Document 1 describes using a material with a high specific modulus of elasticity (Young's modulus divided by glass density) as the material for the substrate of the magnetic recording media. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2015-026414 [Overview of the project] [Problems that the invention aims to solve]

[0008] One aspect of this disclosure aims to provide a method for manufacturing a magnetic recording medium substrate that can produce a magnetic recording medium substrate with excellent heat resistance, specific modulus of elasticity, and impact resistance at a low cost. [Means for solving the problem]

[0009] The means to solve the aforementioned problem are as follows: <1> A grinding process to grind the surface of the steatite sintered body, Following the grinding step, an etching step is performed on the surface of the steatite sintered body, A method for manufacturing a substrate for a magnetic recording medium, comprising a polishing step of polishing the surface of the steatite sintered body after the etching step. <2> The etching step involves performing the etching process using an etching solution containing at least one selected from the group consisting of sodium hydroxide, potassium hydroxide, and alkaline electrolyzed water. <1> This is a method for manufacturing a substrate for a magnetic recording medium as described above. <3> The steatite sintered body is disc-shaped. <1> or <2> This is a method for manufacturing a substrate for a magnetic recording medium as described above. [Effects of the Invention]

[0010] According to one aspect of the present disclosure, there can be provided a method for manufacturing a substrate for a magnetic recording medium, which can inexpensively manufacture a substrate for a magnetic recording medium excellent in heat resistance, specific modulus of elasticity, and impact resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] [Figure 1] It is a schematic perspective view showing an example of the structure of a grinding machine. [Figure 2] It is a schematic perspective view showing an example of the structure of an inner and outer circumferential grinding machine. [Figure 3] It is a schematic perspective view showing an example of the structure of an inner circumferential grinding machine. [Figure 4] It is a schematic perspective view showing an example of the structure of an outer circumferential grinding machine. [Figure 5] It is a schematic cross-sectional view showing an example of the surface of a steatite sintered body. [Figure 6] It is a schematic perspective view showing an example of the structure of a polishing machine. [Figure 7] It is a schematic cross-sectional view showing an example of a magnetic recording medium manufactured by the method for manufacturing a magnetic recording medium according to an embodiment of the present disclosure. [Figure 8] It is a schematic perspective view showing an example of the structure of a magnetic recording / reproducing apparatus. MODES FOR CARRYING OUT THE INVENTION

[0012] In recent years, the demand for increased storage capacity for hard disk drives has been unrelenting, and higher heat resistance and higher specific modulus of elasticity than ever before are required for substrates for magnetic recording media. In addition, in order to ensure interchangeability with conventional substrates for magnetic recording media, manufacturing costs equivalent to those of conventional substrates for magnetic recording media are required. As a substrate for a magnetic recording medium that satisfies such requirements, a substrate for a magnetic recording medium containing a steatite sintered body (MgO·SiO2) can be mentioned.

[0013] The steatite sintered body is mainly made of talc (Mg3Si4O 10This is a sintered body obtained by sintering powders such as (OH)2, kaolin (Al2Si2O5(OH)4), feldspar (KAlSi3O8), and magnesium oxide (MgO).

[0014] When steatite sintered bodies are used as substrates for magnetic recording media, the impact resistance of the substrate may be reduced due to minute pores that form on the surface of the sintered body. Furthermore, when steatite sintered bodies are used as substrates for magnetic recording media, scratches that form on the surface of the substrate during the lapping process may trigger a decrease in the impact resistance of the substrate.

[0015] The method for manufacturing a substrate for a magnetic recording medium according to the embodiment of this disclosure (hereinafter simply referred to as "this embodiment") can provide a substrate for a magnetic recording medium that is excellent in heat resistance, specific modulus of elasticity, and impact resistance at a low cost.

[0016] The details of this embodiment are described below.

[0017] (Method of manufacturing a substrate for magnetic recording media) The method for manufacturing a substrate for a magnetic recording medium according to this embodiment includes a grinding step of grinding the surface of a steatite sintered body, an etching step of performing an etching process on the surface of the steatite sintered body after the grinding step, and a polishing step of polishing the surface of the steatite sintered body after the etching step. The method for manufacturing a substrate for a magnetic recording medium according to this embodiment may include other steps as needed.

[0018] By applying the magnetic recording medium substrate obtained by the manufacturing method of the magnetic recording medium substrate according to this embodiment to a magnetic recording medium and a hard disk drive, it becomes possible to provide a high-capacity hard disk drive at a low cost that reduces fluttering, has excellent shock resistance, and enables stable reading and writing. Furthermore, since it is possible to provide a magnetic recording medium substrate that is compatible with assisted recording methods, it becomes possible to provide a high-capacity magnetic recording medium and a hard disk drive.

[0019] There are no particular restrictions on the shape of the substrate for the magnetic recording medium, and it can be appropriately selected according to the purpose, but from the viewpoint of application to magnetic recording media and hard disk drives, it is preferable to have a disc shape with an opening in the center. A magnetic recording medium can be manufactured by sequentially laminating a magnetic layer, a protective layer, and a lubricating film on a disc-shaped substrate for the magnetic recording medium. In a hard disk drive, the center of the obtained magnetic recording medium is attached to the rotation axis of a spindle motor and rotated, and information can be written to or read from the magnetic recording medium while a magnetic head is levitating and moving on the surface of the magnetic recording medium.

[0020] Magnetic recording medium substrates can be used to increase the number of magnetic recording media that can be housed in a standardized hard disk drive case. Therefore, it is preferable that they can be housed in a standardized hard disk drive case, i.e., a 2.5-inch hard disk drive case or a 3.5-inch hard disk drive case. For 2.5-inch hard disk drives, a disc-shaped magnetic recording medium substrate with a maximum diameter of approximately 67 mm and an inner diameter of approximately 20 mm is used. For 3.5-inch hard disk drives, a disc-shaped magnetic recording medium substrate with a maximum diameter of approximately 97 mm and an inner diameter of approximately 25 mm is used.

[0021] The thickness of the substrate for the magnetic recording medium is not particularly limited and can be appropriately selected according to the purpose, but it is preferably 1.27 mm or less, more preferably 0.8 mm or less, and even more preferably 0.5 mm or less.

[0022] <Grinding process> The grinding process is a process of grinding the surface of the steatite sintered body. The grinding process can be suitably carried out by a grinding means for grinding the surface of the steatite sintered body.

[0023] <<Steatite Sintered Body>> The magnetic recording medium substrate manufactured by the manufacturing method for magnetic recording medium substrates according to this embodiment contains a steatite sintered body (MgO·SiO2). The steatite sintered body mainly consists of talc (talc, Mg3Si4O 10 It is a ceramic material whose main component is (OH)2, and which also contains magnesium oxide (MgO) and silica (SiO2).

[0024] Steatite sintered bodies possess properties such as electrical insulation, heat resistance, and mechanical strength, and are therefore widely used in electrical components and insulators. As a result, thin sheets suitable for processing into substrates for magnetic recording media are readily available, enabling the inexpensive manufacture of such substrates.

[0025] There are no particular restrictions on the various physical properties of the steatite sintered body, and they can be appropriately selected according to the purpose. For example, if the density (ρ) is approximately 2.7 g / cm³ 3 The Young's modulus (E) is approximately 125 GPa, and the specific modulus of elasticity (E / ρ) is approximately 46 GPa·cm. 3 The density (ρ) can be set to approximately 1300°C. Conventionally, aluminum alloy substrates used as substrates for magnetic recording media have a density (ρ) of approximately 2.8 g / cm³. 3 The Young's modulus (E) is approximately 75 GPa, and the specific modulus of elasticity (E / ρ) is approximately 27 GPa·cm. 3 Its density (ρ) is approximately 2.5 g / cm³. 3 The Young's modulus (E) is approximately 80 GPa, and the specific modulus of elasticity (E / ρ) is approximately 32 GPa·cm. 3 The specific modulus (E / ρ) and melting point are approximately 550°C. Comparing the physical properties of the steatite sintered body of this embodiment with those of conventional aluminum alloy substrates and glass substrates, it can be seen that the steatite sintered body of this embodiment has superior specific modulus (E / ρ) and melting point. In other words, the magnetic recording medium substrate containing the steatite sintered body of this embodiment has superior heat resistance and specific modulus compared to conventional magnetic recording medium substrates.

[0026] The shape of the steatite sintered body is not particularly limited and may be appropriately selected depending on the purpose. From the viewpoint of application to magnetic recording media and hard disk drives, the steatite sintered body is preferably disk-shaped, similar to a substrate for a magnetic recording medium.

[0027] -Method for Producing Steatite Sintered Body- The method for producing the steatite sintered body is not particularly limited and may be appropriately selected depending on the purpose, and examples thereof include the following method.

[0028] As raw materials, powders of talc (Mg₃Si₄O 10 (OH)₂), kaolin (Al₂Si₂O₅(OH)₄), feldspar (KAlSi₃O₈), magnesium oxide (MgO) and the like are prepared. These powders are uniformly mixed at an appropriate ratio using a ball mill, a kneader or the like, and then molded. The obtained molded body is dried by air drying, a drying furnace or the like to remove moisture, and then fired at a high temperature. Then, talc is decomposed to form a steatite sintered body. The obtained steatite sintered body may be processed into a predetermined dimension by machining and surface finishing.

[0029] The powder molding method in the method for producing a steatite sintered body is not particularly limited and may be appropriately selected depending on the purpose. Examples thereof include compression molding in which powder is put into a mold and compressed at high pressure for molding, extrusion molding in which a mixed powder is extruded into a desired shape using an extruder, and cast molding in which a slurry-like mixture is poured into a mold and dried for molding.

[0030] The firing temperature of the molded body in the method for producing a steatite sintered body is not particularly limited and may be appropriately selected depending on the purpose, and may be, for example, 1200°C or higher and 1400°C or lower.

[0031] -HIP Treatment- It is preferable to perform HIP (Hot Isostatic Pressing) treatment on the steatite sintered body. HIP treatment is a process that uses argon gas or the like as a pressure medium and utilizes the synergistic effect of high temperature and high pressure to perform powder sintering, diffusion bonding, and removal of internal defects.

[0032] There are no particular restrictions on the various conditions for HIP treatment, and they can be appropriately selected according to the purpose, but it is preferable that the treatment temperature be between 1200°C and 1400°C, the pressure be between 100 MPa and 200 MPa, and the treatment time be between 1 hour and 4 hours.

[0033] When a steatite sintered body is subjected to HIP treatment, the fine voids and defects within the sintered body are compressed, thereby increasing the density of the steatite sintered body. This improves the mechanical strength and durability of the steatite sintered body.

[0034] Applying HIP treatment to a steatite sintered body improves its mechanical properties, such as toughness, hardness, compressive strength, and tensile strength.

[0035] When HIP treatment is applied to a steatite sintered body, defects and inhomogeneities within the steatite sintered body are corrected during the HIP process, improving the overall homogeneity of the steatite sintered body. This results in consistently higher product quality.

[0036] Applying HIP treatment to a steatite sintered body reduces defects within the sintered body, thereby improving its fatigue resistance and enabling long-term use.

[0037] When HIP treatment is applied to a steatite sintered body, the pores inside the steatite sintered body are closed, improving the airtightness of the steatite sintered body and reducing degassing during sputter deposition, as described later.

[0038] When a steatite sintered body is subjected to HIP treatment, it is treated in a high-temperature, high-pressure environment, which improves the chemical stability of the steatite sintered body and enhances its resistance to corrosion and oxidation.

[0039] -Film formation- The steatite sintered body preferably has a film on its surface containing SiO2, SiC, Si3N4, and Al2O3, etc.

[0040] Steatite sintered bodies, formed by sintering powder, are prone to developing fine voids within them. These voids can impair the smoothness of the magnetic recording medium substrate, or they can cause cracks, reducing the mechanical strength of the substrate. By having a film containing SiO2, SiC, Si3N4, and Al2O3 on the surface of the steatite sintered body, the surface voids are sealed, improving the smoothness of the magnetic recording medium substrate surface. Furthermore, crack formation is suppressed, improving the mechanical strength of the magnetic recording medium substrate.

[0041] Films containing SiO2, SiC, Si3N4, and Al2O3 have high heat resistance. Therefore, by having a film containing SiO2, SiC, Si3N4, and Al2O3 on the surface of a steatite sintered body, the heat resistance of the substrate for magnetic recording media is improved. The specific heat resistance temperatures of each material, although depending on the atmosphere, are approximately 1000°C for SiO2, 1500°C for SiC, 1000°C for Si3N4, and 1500°C for Al2O3.

[0042] The heat resistance temperature of the substrate for the magnetic recording medium is preferably higher than the heating temperature of the substrate during the manufacturing process of the magnetic recording medium. When an FePt alloy having an L10 crystal structure and a CoPt alloy having an L10 crystal structure are used for the magnetic layer of the magnetic recording medium, the heat resistance temperature of the substrate for the magnetic recording medium is preferably 400°C or higher, and more preferably 500°C or higher.

[0043] There are no particular limitations on the method for forming a film containing SiO2, SiC, Si3N4, and Al2O3 on the surface of a steatite sintered body, and a suitable method can be selected depending on the purpose. However, from the viewpoint of simplicity and low cost, a film formation method using a liquid is preferred. Specifically, examples include a spin coating method in which a liquid precursor is dropped onto the steatite sintered body and a uniform film is formed using a spin coater; a dip coating method in which a thin film is formed by immersing the steatite sintered body in a liquid precursor and then pulling it out; and a spray coating method in which a liquid precursor is sprayed onto the steatite sintered body using an airbrush or spray nozzle.

[0044] Examples of liquid precursors for forming SiO2 films include tetraethoxysilane (TEOS, chemical formula: Si(OC2H5)4) and methylsilisesquioxane (MSQ, chemical formula: (CH3SiO 3 / 2 Examples include )n). After coating with these liquid precursors, an SiO2 film can be formed on the surface of the steatite sintered body by firing at, for example, 800°C or below.

[0045] Examples of liquid precursors for forming SiC films include polysilazane-based precursors (e.g., polymethylsilazane) and silaniols. After coating with these liquid precursors, a SiC film can be formed on the surface of the steatite sintered body by firing at, for example, 800°C or higher.

[0046] Examples of liquid precursors for forming the Si3N4 film include polysilazane-based precursors (e.g., polydimethylsilazane) and aminosilanes. After coating with these liquid precursors, the Si3N4 film can be formed on the surface of the steatite sintered body by firing, for example, in an ammonia (NH3) or nitrogen (N2) atmosphere at 800°C or higher.

[0047] Examples of liquid precursors for forming the Al2O3 film include aluminum alkoxide (e.g., aluminum isopropoxide) and aluminum acetylacetonate. After coating with these liquid precursors, the Al2O3 film can be formed on the surface of the steatite sintered body by firing at, for example, 800°C or below.

[0048] The grinding process is a process of grinding the surface of the steatite sintered body obtained as described above. More specifically, the grinding process is a process of grinding (lapping) the surface of the steatite sintered body with a grinding means to make the surface of the steatite sintered body smooth. Here, the grinding process will be explained in detail with reference to Figure 1. In this specification, the objects of each process may be referred to as workpieces.

[0049] Figure 1 is a schematic perspective view showing an example of the structure of a grinding machine that performs a grinding process. The grinding machine 40 shown in Figure 1 is an example of a grinding means and includes a holder (carrier) 30 that holds multiple workpieces (steatite sintered bodies) in an opening, a lower platen 21a on which the workpieces are placed, and an upper platen 21b that applies the pressure necessary to press down on the workpieces from above and perform grinding.

[0050] The lower platen 21a has teeth 42 on its outer circumference, and a sun gear 44 is provided in the center of the lower platen 21a. The holder 30 has teeth 32 on its outer circumference, which mesh with both the teeth 42 of the lower platen 21a and the sun gear 44. Rotating shafts 46a and 46b are installed in the centers of the lower platen 21a and the upper platen 21b, respectively, for rotating them.

[0051] The lower platen 21a and the upper platen 21b are embedded with abrasive material for grinding the surface of the workpiece. There are no particular restrictions on the abrasive material, and it can be appropriately selected according to the purpose. Examples include alumina (aluminum oxide), diamond, silicon carbide, and cerium oxide. The particle size and particle size distribution of the abrasive material can be appropriately selected according to the surface shape of the workpiece before and after grinding.

[0052] When performing polishing, a coolant such as water may be supplied to the lower platen 21a and the upper platen 21b as appropriate.

[0053] There are no particular restrictions on the material of the holder 30, and it can be appropriately selected according to the purpose. For example, epoxy resin reinforced by mixing in aramid fibers and glass fibers can be used. The thickness of the holder 30 is preferably thinner than the finished thickness of the workpiece so that it does not come into contact with the upper platen 21b and hinder grinding when polishing the workpiece.

[0054] When operating the grinding machine 40, the upper rotating shaft 46b in Figure 1 is rotated in one direction, causing the upper platen 21b to rotate in the same direction. The lower rotating shaft 46a in Figure 1 is rotated in the opposite direction to the rotation of the rotating shaft 46b, causing the lower platen 21a to rotate in the same direction as the rotating shaft 46a. As a result, the teeth 42 of the lower platen 21a and the central sun gear 44 rotate in the same direction as the rotating shaft 46a. By rotating the upper platen 21b, the lower platen 21a, and the sun gear 44, the holder 30 that meshes with these gears and the workpiece fitted into the holder 30 perform what is known as planetary motion, a combination of rotation and revolution. In this way, the workpiece can be ground with greater precision and speed.

[0055] The manufacturing method for a substrate for a magnetic recording medium according to this embodiment may include, if necessary, an inner and outer circumference grinding step, an inner circumference polishing step, and an outer circumference polishing step.

[0056] <Internal and external grinding process> The inner and outer circumference grinding process is a process of grinding the inner and outer surfaces of the openings in a disc-shaped steatite sintered body. The inner and outer circumference grinding process can be suitably carried out by an inner and outer circumference grinding means that grinds the inner and outer surfaces of the openings in a disc-shaped steatite sintered body.

[0057] The inner and outer circumference grinding process is preferably performed after the grinding process and before the inner circumference polishing process and the outer circumference polishing process, which will be described later.

[0058] Figure 2 is a schematic perspective view showing an example of the structure of an internal and external grinding machine 45 that performs the internal and external grinding process. The internal and external grinding process is a process of rough grinding the inner and outer surfaces 13 of the opening 12 in a disc-shaped workpiece 10.

[0059] In the inner and outer circumferential grinding process, it is preferable to grind the inner surface of the opening 12 and the outer surface 13 simultaneously. Specifically, the inner surface of the opening 12 located in the center of the workpiece 10 is ground with the inner grinding wheel 22, and the outer surface 13 of the workpiece 10 is ground with the outer grinding wheel 23. At this time, the inner and outer surfaces of the workpiece 10 are sandwiched between the inner grinding wheel 22 and the outer grinding wheel 23 and processed simultaneously. This makes it easier to ensure the concentricity between the inner and outer diameters of the workpiece 10.

[0060] The inner grinding wheel 22 and the outer grinding wheel 23 have a wavy surface. Therefore, the inner and outer surfaces 13 of the opening 12 of the workpiece 10 can be ground. In addition, it is possible to chamfer the edges of the opening 12 and the outer surface 13 of the workpiece 10 at the same time.

[0061] <Inner circumference polishing process> The inner circumference polishing process is a process of polishing the inner circumference surface of the opening in the steatite sintered body obtained by the inner circumference grinding process to make it smoother. The inner circumference polishing process can preferably be carried out by an inner circumference polishing means that polishes the inner circumference surface of the opening in the steatite sintered body obtained by the inner circumference grinding process to make it smoother.

[0062] The inner circumference polishing process is preferably performed after the inner and outer circumference grinding process described above. However, the inner circumference polishing process may also be performed before or after the outer circumference polishing process, which will be described later.

[0063] Figure 3 is a schematic perspective view showing an example of the structure of an inner circumference polishing machine 46 that performs the inner circumference polishing process. First, the workpieces 10 are stacked and set in a holder (not shown), and a brush 24 is inserted into the center of the opening 12 of the workpiece 10. Then, while pouring polishing fluid into the opening 12 of the workpiece 10, the brush 24 is rotated at high speed to polish the inner circumference surface of the workpiece 10 to a smoother surface. In this way, the inner circumference surface of the workpiece 10 is polished to a smoother surface, and the chamfered edges of the opening 12 that were removed in the inner circumference grinding process are also polished in the same way.

[0064] There are no particular restrictions on the polishing fluid used in the inner circumference polishing process; it can be appropriately selected according to the purpose. For example, a slurry made by dispersing alumina abrasive particles in water can be used.

[0065] <Outer periphery polishing process> The outer perimeter polishing process is a process of polishing the outer surface of the steatite sintered body obtained by the inner and outer perimeter grinding process to make it smoother. The outer perimeter polishing process can be suitably carried out by an outer perimeter polishing means that polishes the outer surface of the steatite sintered body obtained by the inner and outer perimeter grinding process to make it smoother.

[0066] The outer circumference polishing process is preferably performed after the inner circumference grinding process. However, the outer circumference polishing process may also be performed before or after the inner circumference polishing process.

[0067] Figure 4 is a schematic perspective view showing an example of the structure of an outer perimeter polishing machine 47 that performs the outer perimeter polishing process. First, the workpieces 10 are stacked by passing them through the opening 12 of the workpiece 10 using a jig 25, and the workpieces 10 are set in the jig 25. Then, while pouring polishing fluid onto the outer perimeter surface 13 of the workpiece 10, the brush 26 is brought into contact with the stacked workpieces 10 and rotated at high speed. This makes it possible to polish the outer perimeter surface of the workpiece 10 to a smoother surface. In this way, the outer perimeter surface of the workpiece 10 is polished to a smoother surface, and the chamfered edges of the outer perimeter surface 13 that were removed in the inner and outer perimeter grinding process can also be polished in the same way.

[0068] There are no particular restrictions on the polishing fluid used in the outer surface polishing process, and it can be appropriately selected according to the purpose. For example, a slurry made by dispersing alumina abrasive particles in water can be used.

[0069] <Etching process> The etching process is a step performed after the grinding process to etch the surface of the steatite sintered body. The etching process can be suitably carried out by an etching means that performs etching on the surface of the steatite sintered body.

[0070] The etching process is not particularly limited as long as it is performed after the grinding process and before the polishing process described later, and can be appropriately selected according to the purpose. However, it is preferable to perform it after the inner and outer circumference grinding process, and more preferably after the inner and outer circumference grinding process, the inner circumference polishing process, and the outer circumference polishing process.

[0071] Here, the etching process will be explained in detail using Figure 5. Figure 5 is a schematic cross-sectional view showing an example of the surface of a steatite sintered body after each process has been carried out.

[0072] Tiny holes (pores) may occur on the surface of a steatite sintered body (workpiece 10) that has undergone a grinding process. There are various causes for the occurrence of pores, but the main causes include the shape of the raw material powder, non-uniformity of particle size, non-uniformity of pressure during molding, variation in molded body density, and the inclusion of impurities. For example, if a complex-shaped pore like that shown in Figure 5(a) occurs on the surface of workpiece 10, this pore may reduce the impact resistance of the magnetic recording medium substrate. Specifically, when the magnetic recording medium is rotated at high speed, or when the hard disk drive is subjected to impact, the magnetic recording medium may be damaged starting from that point. Although new pores may occur on the surface of the steatite sintered body after the polishing process described later, the amount of polishing during the polishing process is not very large, and the risk of new pores occurring is considered low. Therefore, it is considered that performing an etching process after the polishing process increases the risk of surface roughness.

[0073] Sharp scratches, as shown in Figure 5(b), may occur on the surface of the steatite sintered body (workpiece 10) after the grinding process. There are various causes for scratches, but the main causes include clogging of the grinding wheel, wear of the grinding wheel, and contamination of foreign matter. For example, if scratches like those shown in Figure 5(b) occur on the surface of workpiece 10, these scratches may reduce the shock resistance of the magnetic recording medium substrate. Specifically, when the magnetic recording medium is rotated at high speed, or when the hard disk drive is subjected to shock, the magnetic recording medium may be damaged starting from that point.

[0074] In the manufacturing method for a magnetic recording medium substrate according to this embodiment, by performing an etching process after the grinding process and before the polishing process described later, the pores in Figure 5(a) and the scratches in Figure 5(b) become the gently curved shapes shown in Figure 5(c). This reduces stress concentration and improves the impact resistance of the magnetic recording medium substrate.

[0075] There are no particular restrictions on the etching solution used in the etching process, and any known solution can be used as appropriate, such as hydrofluoric acid (HF), concentrated sulfuric acid (H2SO4), concentrated hydrochloric acid (HCl), and alkaline solutions. Among these, alkaline solutions are preferred because they have a slower etching rate compared to strong acids, efficiently dissolve only the pores and scratches on the surface of the workpiece 10, and avoid dissolving other areas. It is more preferable that the solution contains at least one selected from the group consisting of sodium hydroxide, potassium hydroxide, and alkaline electrolyzed water.

[0076] Alkaline electrolyzed water is an alkaline aqueous solution produced by electrolysis, specifically the aqueous solution produced at the cathode when water (H2O) is electrolyzed. There are no particular restrictions on the pH of alkaline electrolyzed water, and it can be appropriately selected depending on the purpose, but a pH of 10 or higher is preferred.

[0077] When sodium hydroxide and potassium hydroxide are used as etching solutions, various processing conditions such as concentration, processing time, and processing temperature can be appropriately selected according to the size and number of workpieces to be processed.

[0078] <Polishing process> The polishing process is a step of polishing the surface of the steatite sintered body after the etching process. The polishing process can be suitably carried out by a polishing means for polishing the surface of the steatite sintered body.

[0079] Here, the polishing process will be explained in detail using Figure 6.

[0080] Figure 6 is a schematic perspective view showing an example of the structure of a polishing machine used for the polishing process. In the polishing process, the surface of the workpiece 10 that has undergone the etching process is polished using a polishing machine (polishing device, polishing machine) 50 to further improve its smoothness. The polishing machine 50 has a configuration almost identical to that of the grinding machine 40 shown in Figure 1. Specifically, it comprises a lower platen 21a on which the workpiece 10 is placed, and an upper platen 21b for applying the necessary pressure to press down on the workpiece 10 from above for polishing. The workpiece 10 is placed on the lower platen 21a of the polishing machine 50 using a holder, and the workpiece 10 is polished by rotating the upper platen 21b, the lower platen 21a, and the sun gear. When polishing the workpiece 10 with the polishing machine 50, for example, a hard polishing cloth made of urethane can be used, and a polishing liquid can be used in which the abrasive material is dispersed in water to form a slurry.

[0081] There are no particular restrictions on the abrasive material used in the polishing process; it can be appropriately selected according to the purpose. Examples include granular alumina, diamond, silicon carbide, and cerium oxide. The particle size and particle size distribution of the abrasive material can be appropriately selected according to the surface shape of the workpiece before and after grinding.

[0082] The method for manufacturing a substrate for a magnetic recording medium according to this embodiment may include a secondary polishing step as needed.

[0083] <Secondary polishing process> The secondary polishing step is a step in which the surface of the magnetic recording medium substrate is further polished after the polishing step. The secondary polishing step can preferably be carried out by a polishing means that further polishes the surface of the magnetic recording medium substrate.

[0084] As a secondary polishing method, for example, the polishing machine 50 shown in Figure 6 can be used. When polishing the workpiece 10 with the polishing machine 50 in the secondary polishing process, for example, a suede-like soft polishing cloth can be used, and a polishing liquid can be used which is a slurry made by dispersing colloidal silica or the like in a dispersion medium such as water.

[0085] The manufacturing method for a magnetic recording medium substrate of this embodiment may include a cleaning step to remove contaminants such as abrasives. The cleaning step is not particularly limited and can be appropriately selected depending on the purpose. For example, chemical cleaning using chemicals combined with ultrasound is one example.

[0086] (Method of manufacturing magnetic recording media) The method for manufacturing a magnetic recording medium according to this embodiment may include a magnetic recording medium formation step, and may also include other steps as needed.

[0087] There are no particular restrictions on the magnetic recording media manufactured by the manufacturing method of the magnetic recording media, and they can be appropriately selected according to the purpose. Examples include conventional magnetic recording media, magnetic recording media used in the heat-assisted method, and magnetic recording media used in the microwave-assisted method.

[0088] In this embodiment, the method for manufacturing a magnetic recording medium is described below in detail with reference to Figure 7, using a magnetic recording medium used in the heat-assisted method as an example.

[0089] Figure 7 is a schematic cross-sectional view showing an example of a magnetic recording medium manufactured by the manufacturing method of the magnetic recording medium according to this embodiment.

[0090] The magnetic recording medium shown in Figure 7 has a base layer 2, a magnetic layer 3, a protective layer 4, and a liquid lubricant layer 5 sequentially laminated on both main surfaces of the magnetic recording medium substrate 1. A film 1a containing SiO2, SiC, Si3N4, and Al2O3 is provided on both sides of the magnetic recording medium substrate 1. Although Figure 7 shows the magnetic recording medium substrate 1 with each layer laminated on both sides, the magnetic recording medium may also have each layer laminated on only one side of the magnetic recording medium substrate 1.

[0091] The shape of the magnetic recording medium is not particularly limited as long as it can be applied to a magnetic recording and playback device, and can be appropriately selected according to the purpose. For example, a disc shape with a central hole can be used.

[0092] <Magnetic recording medium formation process> The magnetic recording medium formation process is a process of heating the substrate 1 for the magnetic recording medium to form a magnetic layer. The magnetic recording medium formation process may include a soft magnetic layer formation process, a base layer formation process, a magnetic layer formation process, a protective layer formation process, and a liquid lubricant layer formation process.

[0093] There are no particular limitations on the heating process in the magnetic recording medium formation process, and heating processes used in known film formation methods can be appropriately adopted. Examples include heating processes performed before and after the process of forming a thin film by sputtering (sputtering method), and heating processes for a laminate of thin films including a substrate for a magnetic recording medium. These heating processes are intended to improve and enhance the crystal structure of the thin film, repair defects, relieve stress, promote diffusion processes, accelerate chemical reactions, improve the adhesion of the thin film, promote surface diffusion, accelerate interfacial reactions, and form specific phases.

[0094] <<Soft magnetic layer formation process>> The soft magnetic layer formation process is a process of forming a soft magnetic layer on a substrate 1 for a magnetic recording medium.

[0095] There are no particular restrictions on the method for forming the soft magnetic layer, and it can be appropriately selected according to the purpose. For example, general film deposition methods such as sputtering can be used.

[0096] There are no particular restrictions on the sputtering method, and it can be appropriately selected depending on the purpose. Examples include DC (Direct Current) sputtering, DC magnetron sputtering, and RF (Radio Frequency) sputtering.

[0097] When using sputtering as a method for forming a soft magnetic layer, it is preferable to use a target containing the material for forming the soft magnetic layer. Examples of targets containing the material for forming the soft magnetic layer include soft magnetic alloys such as FeCo alloys, CoZrNb alloys, and CoTaZr alloys.

[0098] <<Underlayer formation process>> The underlayer formation process involves forming underlayer 2 on top of the soft magnetic layer. The sub-layer formation process may include a first sub-layer formation process in which a first sub-layer is formed on the soft magnetic layer, a second sub-layer formation process in which a second sub-layer is formed on the first sub-layer, and a third sub-layer formation process in which a third sub-layer is formed on the second sub-layer.

[0099] There are no particular restrictions on the method for forming the underlayer 2, and it can be appropriately selected according to the purpose. For example, general film deposition methods such as sputtering can be used.

[0100] When using the sputtering method as the method for forming the base layer 2, it is preferable to use a target that contains the material for forming the base layer.

[0101] In the first sublayer formation process, there are no particular restrictions on the material used to form the first sublayer, and it can be appropriately selected according to the purpose. For example, a Cr alloy in which a bcc alloy mainly composed of Cr is (100) oriented can be used.

[0102] In the second sublayer formation process, there are no particular restrictions on the material used to form the second sublayer, and it can be appropriately selected according to the purpose. For example, a W alloy in which a bcc alloy mainly composed of W is (100) oriented can be used.

[0103] In the third subsoil formation process, there are no particular restrictions on the material used to form the third subsoil; it can be appropriately selected according to the purpose. Examples include NaCl-type compounds. Examples of NaCl-type compounds include MgO.

[0104] <<Magnetic layer formation process>> The magnetic layer formation step is the step of forming a magnetic layer 3 on the underlying layer 2. Preferably, the magnetic layer 3 is a perpendicular magnetic layer.

[0105] There are no particular restrictions on the method for forming the magnetic layer 3, and it can be appropriately selected according to the purpose. For example, general film deposition methods such as sputtering can be used.

[0106] When using the sputtering method to form the magnetic layer 3, it is preferable to use a target containing the material for forming the perpendicular magnetic layer. There are no particular restrictions on the target containing the material for forming the magnetic layer 3, and it can be appropriately selected according to the purpose. For example, a target containing an alloy having an L10 structure can be used.

[0107] Examples of alloys having an L10 structure include alloys containing Fe or Co and Pt, etc. Specific examples of alloys having an L10 structure include FePt alloys and CoPt alloys.

[0108] From the viewpoint of improving the crystal orientation of the magnetic layer 3, the magnetic recording medium substrate 1, the soft magnetic layer, the underlayer 2, and the magnetic layer 3 are preferably heated in a laminated state during the magnetic layer formation process. As the heating means at this time, known methods such as halogen lamps, lasers, LEDs, high-frequency waves, and electromagnetic waves such as microwaves can be used.

[0109] When the magnetic layer 3 contains an FePt alloy having an L10 structure, it is preferable to heat it to a high temperature of 400°C or higher to order it. As a heating means, known methods such as halogen lamps, lasers, LEDs, high-frequency waves, and microwaves can be used. The magnetic recording medium substrate 1 of this embodiment has excellent heat resistance and can therefore be suitably used in the manufacture of magnetic recording media that include a high-temperature heating process.

[0110] <<Protective layer formation process>> The protective layer formation process is the process of forming a protective layer 4 on the magnetic layer 3.

[0111] There are no particular restrictions on the method for forming the protective layer 4, and general film deposition methods can be used. Examples include the RF-CVD (Radio Frequency-Chemical Vapor Deposition) method, which decomposes a hydrocarbon source gas with a high-frequency plasma to form a film; the IBD (Ion Beam Deposition) method, which ionizes the source gas with electrons emitted from a filament to form a film; and the FCVA (Filtered Cathodic Vacuum Arc) method, which uses a solid carbon target to form a film without using a source gas.

[0112] <<Liquid Lubricant Layer Formation Process>> The liquid lubricant layer formation step is the step of forming a liquid lubricant layer 5 on the protective layer 4.

[0113] The liquid lubricant layer 5 can be formed by applying a fluorine-based lubricant such as a perfluoropolyether using methods such as the dip method and the spin coating method.

[0114] (Magnetic recording and playback device) The magnetic recording and playback apparatus of this embodiment comprises a magnetic recording medium and a magnetic head for recording and playback of information on the magnetic recording medium, and may also include other components as needed. Note that the magnetic recording medium is the same as the magnetic recording medium obtained by the (Method for Manufacturing a Magnetic Recording Medium) described above, so redundant descriptions are omitted.

[0115] Figure 8 is a schematic perspective view showing an example of the structure of the magnetic recording and playback device of this embodiment. The hard disk drive 101, which is a magnetic recording and playback device shown in Figure 8, comprises a magnetic recording medium 111, a media drive unit 123 that drives the magnetic recording medium 111 in the recording direction, a magnetic head 124 consisting of a recording unit and a playback unit, a head movement unit 126 that moves the magnetic head 124 relative to the magnetic recording medium 111, and a recording and playback signal processing unit 128 that processes recording and playback signals from the magnetic head 124.

[0116] In typical hard disk drives, the magnetic recording medium is rotated at high speeds of 5000 rpm or more. If the mechanical properties of the magnetic recording medium are low, fluttering increases, making stable reading difficult in the hard disk drive. The magnetic recording medium of this embodiment includes a magnetic recording medium substrate with a high specific modulus of elasticity, thereby reducing fluttering in the hard disk drive and enabling stable reading. Furthermore, since the magnetic recording medium of this embodiment uses an inexpensive magnetic recording medium substrate, it is possible to reduce the cost of the hard disk drive. [Examples]

[0117] The following are examples of this embodiment, but the scope of this disclosure is not limited to these examples.

[0118] <Fabrication of substrates for magnetic recording media> A steatite plate (1 mm thick) manufactured by Nishimura Ceramics Co., Ltd. was processed into a donut-shaped disc (workpiece) with an outer diameter of 97 mm and an inner diameter of 25 mm. This steatite plate has a density of approximately 2.7 g / cm³. 3 The Young's modulus is approximately 125 GPa, and the specific modulus is approximately 46 GPa·cm. 3 Its melting point is approximately 1300°C. The workpiece underwent a HIP treatment. The HIP treatment was performed in an air atmosphere at a temperature of 1300°C, a pressure of 150 MPa, and a holding time of 2 hours, after which it was slowly cooled. Subsequently, a silica (SiO2) film was formed on the surface of the workpiece using tetraethoxysilane (TEOS) in a spin-on-glass (SOG) process. Specifically, the workpiece was washed with acetone, dried, and then a 10% TEOS solution diluted with ethanol was dropped onto the center of the workpiece. Using a spin coater, TEOS was spin-coated onto both sides of the workpiece at a rotation speed of 2000 rpm and a rotation time of 30 seconds. After drying the workpiece, it was fired at a firing temperature of 700°C, a heating rate of 5°C / min, a firing time of 30 minutes, and in an air environment. After firing, the workpiece was slowly cooled.

[0119] The obtained workpieces were subjected to grinding. Specifically, using the grinding machine 40 shown in Figure 1, multiple workpieces held in the opening of the carrier plate were subjected to planetary motion, and both main surfaces were ground using grinding pads provided on the upper and lower platens. At this time, diamond grinding wheels (product name: Trizact, manufactured by Sumitomo 3M) were used as grinding pads. These diamond grinding wheels have an outer dimension of 2.6 mm square for the protrusions, a height of 2 mm, a spacing of 1 mm between adjacent protrusions, an average particle size of diamond abrasive grains of 6 μm, and a diamond abrasive grain content of approximately 15 volume percent in the protrusions, with an acrylic resin used as a binder. In addition, a 4-way type double-sided grinding machine (16B model, manufactured by Hamai Sangyo Co., Ltd.) was used as the grinding apparatus, with a platen rotation speed of 30 rpm and a processing pressure of 110 g / cm². 2 Grinding was performed for 5 minutes. Water was used as the grinding fluid, and the amount of material removed from each side of the workpiece was approximately 100 μm.

[0120] Next, inner and outer circumference grinding was performed. Specifically, a lapping machine equipped with an inner circumference grinding wheel and an outer circumference grinding wheel, as shown in Figure 2, was used. Multiple workpieces were stacked with spacers in between, with their central holes aligned, and the stacked body was rotated around an axis. The inner circumference grinding wheel inserted into the central hole of the workpiece and the outer circumference grinding wheel positioned on the outer circumference gripped the workpiece radially. While these inner and outer circumference grinding wheels rotated in the opposite direction to the stacked body, the inner circumference grinding wheel ground the inner end surface of the workpiece, and the outer circumference grinding wheel ground the outer end surface of the workpiece. At this time, the inner circumference grinding wheel and outer circumference grinding wheel were used, containing 80 volume% of diamond abrasive grains with an average particle size of 10 μm, and using a nickel alloy as a binder. The inner circumference grinding wheel rotated at 1200 rpm and the outer circumference grinding wheel rotated at 600 rpm, and grinding was performed for 30 seconds.

[0121] Next, the inner circumference was polished. Specifically, a polishing machine equipped with an inner circumference polishing brush, as shown in Figure 3, was used. While dripping polishing fluid onto the inner circumference polishing brush, the laminate was rotated around its axis, and the inner circumference polishing brush inserted into the central hole of the workpiece was moved up and down while rotating in the opposite direction to the workpiece, thereby polishing the inner circumference end face of the workpiece. At this time, a nylon brush was used for the inner circumference polishing brush, and an alumina slurry was used as the polishing fluid. The inner circumference polishing brush was rotated at 300 rpm, and polishing was performed for 10 minutes.

[0122] Next, the outer perimeter was polished. Specifically, a polishing machine equipped with an outer perimeter polishing brush, as shown in Figure 4, was used. While applying polishing fluid to the outer perimeter polishing brush, the laminate was rotated around its axis, and the outer perimeter polishing brush was rotated in the opposite direction to the workpiece, thereby polishing the outer perimeter end face of the workpiece. At this time, a nylon brush was used for the outer perimeter polishing brush, and an alumina slurry was used as the polishing fluid. Then, the rotation speed of the inner perimeter polishing brush was set to 100 rpm, and polishing was performed for 10 minutes.

[0123] Next, the surface of the obtained workpiece was subjected to etching. A 30% by mass sodium hydroxide was used as the etching solution, and the treatment temperature was 80°C for a treatment time of 12 minutes.

[0124] Next, polishing was performed. Specifically, a two-stage, four-way double-sided polishing machine (System Seikou Co., Ltd., Model 11B) equipped with a pair of upper and lower polishing plates was used to polish the surface of the workpiece. A suede-type polishing pad (Filwel Co., Ltd.) was used. For the first stage of polishing, an aqueous solution was used, which was adjusted to the acidic range of pH 1.5 by adding alumina abrasive grains with a D50 of 0.5 μm, a chelating agent, and an oxidizing agent. For the second stage of polishing, an aqueous solution was used, which was adjusted to the acidic range of pH 1.5 by adding colloidal silica abrasive grains with a D50 of 30 nm, a chelating agent, and an oxidizing agent. The polishing time for each stage was 5 minutes. The processing pressure between the lower and upper polishing plates was 110 g / cm². 2 The rotation speed of the lower and upper polishing plates was set to 20 rpm, the amount of material removed in the first polishing stage was approximately 1.5 μm, and the amount of material removed in the second polishing stage was approximately 0.5 μm.

[0125] The shock resistance of the resulting magnetic recording medium substrate was evaluated using the following method.

[0126] [Method for evaluating impact resistance] A circuit board for magnetic recording media was chucked onto the spindle shaft of a hard disk drive, and the hard disk drive was dropped to the ground, applying an impact of 200G. -result- When the impact resistance of the substrate for magnetic recording media was evaluated, it was found to withstand impacts of 200G or more without damage and to be suitable for practical use.

[0127] <Fabrication of magnetic recording media> Next, an assist recording medium was manufactured using the obtained magnetic recording medium substrate. First, a Co-50at%Ti film with an average thickness of 50 nm was formed as the first underlayer on a magnetic recording medium substrate, and then heated to 200°C. Next, a MgO film with an average thickness of 5 nm was formed as the second underlayer, and then heated to 520°C. Then, a (Fe-45at%Pt-5at%Ag)-8mol%SiO2-4mol%Cr2O3 film with an average thickness of 12 nm was formed as the magnetic layer, and then a DLC (Diamond-Like Carbon) film with an average thickness of 3 nm was formed as the protective layer. After that, a perfluoropolyether with an average thickness of 12 Å was applied to the surface of the DLC film as a liquid lubricant layer using a dip method, and the magnetic recording medium was manufactured.

[0128] The resulting magnetic recording medium was suitable for practical use as a medium in assisted recording hard disk drives.

[0129] The shock resistance of the obtained magnetic recording media was evaluated using the following method.

[0130] [Method for evaluating impact resistance] A magnetic recording medium was chucked onto the spindle shaft of a hard disk drive, and the hard disk drive was dropped to the ground, applying a 200G impact. -result- When the shock resistance of the magnetic recording medium was evaluated, it was found to be able to withstand impacts of 200G or more without damage and is suitable for practical use.

[0131] As described above, this disclosure has been explained based on specific embodiments, but these embodiments are merely examples, and this disclosure is not limited to the above embodiments. The above embodiments can be implemented in various other forms, and various combinations, omissions, substitutions, additions, or modifications are possible without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of Symbols]

[0132] 1…Matrix substrate for magnetic recording media 2…base layer 3...Magnetic layer 4…Protective layer 5…Liquid lubricant layer 101... Hard disk drive 111…Magnetic recording media 123...Media drive unit 124... Magnetic head 126... Head movement unit 128... Recording and Playback Signal Processing Unit

Claims

1. A grinding process to grind the surface of the steatite sintered body, Following the grinding step, an etching step is performed on the surface of the steatite sintered body, A method for manufacturing a substrate for a magnetic recording medium, comprising a polishing step of polishing the surface of the steatite sintered body after the etching step.

2. The method for manufacturing a substrate for a magnetic recording medium according to claim 1, wherein the etching step is performed using an etching solution containing at least one selected from the group consisting of sodium hydroxide, potassium hydroxide, and alkaline electrolyzed water.

3. The method for manufacturing a substrate for a magnetic recording medium according to claim 1 or 2, wherein the steatite sintered body is disc-shaped.

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