Polishing tape and method for manufacturing magnetic recording medium

Abstract

A polishing tape includes: a support; and abrasive grains of aluminum oxide provided on the support, the abrasive grains having an average primary particle diameter of 10 nm to 40 nm, inclusive, and an average secondary particle diameter of 50 nm to 200 nm, inclusive.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based upon and claims priority to Japanese Patent Application No. 2025-061030 filed on Apr. 2, 2025, the entire contents of which are incorporated herein by reference.BACKGROUND OF THE INVENTION1. Field of the Invention

[0002] The present disclosure relates to a polishing tape and a method for manufacturing a magnetic recording medium.2. Description of the Related Art

[0003] A magnetic recording device includes a magnetic recording medium for storing electronic data by magnetic recording. One example is a hard disk drive (HDD). In recent years, magnetic recording devices have been installed in various products such as personal computers, video recorders, and data servers, and have become increasingly important.

[0004] A magnetic recording medium included in a magnetic recording device has, for example, a structure in which an underlayer, an intermediate layer, a magnetic recording layer, a protective layer, and a lubricating layer are laminated in this order on a non-magnetic substrate. To manufacture such a magnetic recording medium, a burnishing process is performed to remove foreign matter and protrusions present on a surface of the protective layer or the lubricating layer.

[0005] Examples of the burnishing process include a tape burnishing process and a head burnishing process. In the tape burnishing process, a polishing tape containing an abrasive material such as abrasive grains is pressed against a surface of a laminate and rubbed against the surface. In the head burnishing process, a head slider formed of a sintered ceramic is caused to fly above the surface of the laminate to remove protrusions from the surface of the laminate.

[0006] For example, Japanese Examined Patent Application Publication No. H02-010486 discloses a method for smoothing a surface of a magnetic disk substrate, in which a lubricating protective film formed on the surface of the magnetic disk substrate is polished by tape polishing using a lapping film in a tape form. Moreover, Japanese Patent Application Laid-Open Publication No. H10-134347 discloses a burnishing apparatus using a head slider for burnishing a magnetic recording medium.SUMMARY OF THE INVENTION

[0007] It is an object of an aspect of the present disclosure to provide a polishing tape capable of improving overall productivity of magnetic recording media.

[0008] Aspects of the present disclosure are as follows.

[0009] <1> A polishing tape, including: a support; and abrasive grains of aluminum oxide provided on the support, the abrasive grains having an average primary particle diameter of 10 nm to 40 nm, inclusive, and an average secondary particle diameter of 50 nm to 200 nm, inclusive

[0010] <2> The polishing tape according to <1>, in which the polishing tape includes the abrasive grains on one surface of the support, and the polishing tape is wound in a roll.

[0011] <3> The polishing tape according to <2>, in which the aluminum oxide is α-aluminum oxide produced by a sol-gel method.

[0012] <4> A method for manufacturing a magnetic recording medium, including: burnishing a laminate by pressing a polishing tape against a surface of the laminate and rubbing the surface of the laminate with the polishing tape, the polishing tape including a support and abrasive grains of aluminum oxide that are provided on the support and have an average primary particle diameter of 10 nm to 40 nm, inclusive, and an average secondary particle diameter of 50 nm to 200 nm, inclusive, in which the laminate includes a substrate, a magnetic recording layer on the substrate, and a protective layer on the magnetic recording layer.

[0013] <5> The method for manufacturing the magnetic recording medium according to <4>, in which the laminate further includes a lubricating layer on the protective layer, and the burnishing is performed by pressing the polishing tape against the surface of the laminate including the lubricating layer and rubbing the surface of the laminate with the polishing tape.BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 is an example of head disk interface sensor (HDIs) inspection results for a surface of a magnetic recording medium subjected to a burnishing process using a polishing tape having abrasive grains with an average primary particle diameter of 200 nm;

[0015] FIG. 2A is an example of an atomic force microscope (AFM) image of protrusive defects on the surface of the magnetic recording medium of FIG. 1;

[0016] FIG. 2B is an example of a graph showing heights and widths of the protrusive defects in a cross section taken along line A-A of the AFM image of FIG. 2A;

[0017] FIG. 3 is an example of a schematic cross-sectional view of a polishing tape according to a present embodiment;

[0018] FIG. 4 is a schematic cross-sectional view illustrating an example of a structure of a laminate;

[0019] FIG. 5 is a schematic view illustrating an example of a polishing tape used in a burnishing step;

[0020] FIG. 6 is a schematic diagram illustrating an example of the burnishing step; and

[0021] FIG. 7 is a schematic diagram illustrating an example of a burnishing apparatus.DESCRIPTION OF THE EMBODIMENTS

[0022] In a manufacturing process of a magnetic recording medium, a protrusive defect may form on a surface of the magnetic recording medium. Since a magnetic recording medium having such a protrusive defect on the surface thereof is regarded as a defective product, overall productivity of magnetic recording media may decrease.

[0023] The inventors of the present disclosure have found that there is a correlation between a size of a protrusive defect formed on a surface of a magnetic recording medium and a size of abrasive grains of a polishing tape used in a tape burnishing process, which is one of the manufacturing processes of the magnetic recording medium. This will be described in detail with reference to FIGS. 1, 2A, and 2B.

[0024] FIG. 1 is an example of HDIs inspection results for a surface of a magnetic recording medium subjected to a burnishing process using a polishing tape having abrasive grains with an average primary particle diameter of 200 nm. In the HDIs inspection, an inspection head including a heat-sensitive resistance element is caused to fly above the surface of the magnetic recording medium, and presence or absence of protrusive defects and recessed defects on the surface of the magnetic recording medium is detected based on a signal output from the inspection head.

[0025] From the results of FIG. 1, it was found that, in many cases, widths of protrusive defects on the surface of the magnetic recording medium are substantially equal to the average primary particle diameter of the abrasive grains of a polishing tape. It was also found that heights of the protrusive defects are not correlated with the average primary particle diameter of the abrasive grains and are approximately 4 nm to 7 nm in many cases. It is considered that these protrusive defects are formed when abrasive grains that remain on the surface of the magnetic recording medium, for example, by piercing into the surface during the tape burnishing process are cut during a head burnishing process. That is, the inventors have found that heights of the protrusive defects are related to a flying height of a head slider in the head burnishing process.

[0026] FIG. 2A is an example of an AFM image of protrusive defects on the surface of the magnetic recording medium of FIG. 1. FIG. 2B is an example of a graph showing heights and widths of the protrusive defects in a cross section taken along line A-A of the AFM image of FIG. 2A.

[0027] From FIGS. 2A and 2B, it was found that the protrusive defects are formed by the abrasive grains that have pierced the surface of the magnetic recording medium and are cut into a flat shape.

[0028] Based on the above findings, the inventors of the present disclosure examined a polishing tape used in the tape burnishing process. The inventors have found that overall productivity of magnetic recording media can be improved by preventing shedding and fracture of the abrasive grains of the polishing tape used in the tape burnishing process. The inventors have also found that, even if shedding and fracture of the abrasive grains of the polishing tape occur, overall productivity of the magnetic recording media can be improved by preventing particles and fragments of the abrasive grains from remaining on the surface of the magnetic recording medium, for example, by piercing into the surface.

[0029] An embodiment of the present disclosure (hereinafter also referred to as the “present embodiment”) can provides a polishing tape capable of improving overall productivity of magnetic recording media by preventing shedding and fracture of abrasive grains.

[0030] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In order to facilitate understanding of the description, the same components are denoted by the same reference signs throughout the drawings, and repeated descriptions are omitted as appropriate. The scale of each member in the drawings may differ from the actual scale.(Polishing Tape)

[0031] A polishing tape according to the present embodiment includes: a support; and abrasive grains of aluminum oxide provided on the support and having an average primary particle diameter of 10 nm to 40 nm and an average secondary particle diameter of 50 nm to 200 nm. The polishing tape according to the present embodiment may include an additional member as necessary.

[0032] Hereinafter, the polishing tape will be described in detail with reference to FIG. 3. FIG. 3 is an example of a schematic cross-sectional view of the polishing tape according to the present embodiment.

[0033] As illustrated in FIG. 3, a polishing tape 200 has an abrasive layer 22 on a support 21. FIG. 3 illustrates a configuration in which the abrasive layer 22 is provided on one surface of the support 21. The polishing tape 200 preferably has the abrasive layer 22 on one surface of the support 21. In other words, the polishing tape 200 preferably has abrasive grains 221 on one surface of the support 21.<Support>

[0034] The material of the support 21 is not particularly limited and may be selected as appropriate depending on the intended purpose, but preferably includes at least one resin selected from the group consisting of a polyester resin, a polyolefin resin, an acrylic resin, and a polycarbonate resin. When these resins are contained in the support 21, mechanical properties of the polishing tape 200, that is, strength, durability, and flexibility can be improved.

[0035] Examples of the polyester resin include a polyethylene terephthalate resin, a polybutylene terephthalate resin, and a polyethylene naphthalate resin.

[0036] Examples of the polyolefin resin include a polyethylene resin and a polypropylene resin.

[0037] Examples of the acrylic resin include resins mainly composed of polystyrene, polyvinyl chloride, polyvinyl alcohol, or methacrylic alcohol.

[0038] The average thickness of the support 21 is not particularly limited and may be selected as appropriate depending on the intended purpose, but is preferably from 5 μm to 100 μm, and more preferably 10 μm to 75 μm, to ensure the mechanical properties of the polishing tape 200.(Abrasive Layer)

[0039] The abrasive layer 22 may be formed of the abrasive grains 221 and a binder 222 for fixing the abrasive grains 221 to the support 21.—Abrasive Grains—

[0040] The abrasive grains 221 are of aluminum oxide having an average primary particle diameter of 10 nm to 40 nm and an average secondary particle diameter of 50 nm to 200 nm. By having such abrasive grains 221, the polishing tape according to the present embodiment can prevent shedding and fracture of the abrasive grains 221 in the tape burnishing process, and overall productivity of magnetic recording media can be improved. In addition, even if shedding and fracture of the abrasive grains 221 occur, particles and fragments of the abrasive grains 221 are prevented from remaining on the surface of the magnetic recording medium, for example, by piercing into the surface, and overall productivity of the magnetic recording media can be improved. This will be described in detail below.

[0041] When the abrasive grains 221 are aluminum oxide having an average primary particle diameter of 10 nm to 40 nm, fracture resistance of the abrasive grains 221 themselves is increased. This prevents fracture of the abrasive grains 221 in the tape burnishing process. Moreover, even if fracture of the abrasive grains 221 occurs, the resulting fragments are small enough to be prevented from remaining on the surface of the magnetic recording medium. Even if the fragments remain on the surface of the magnetic recording medium, for example, by piercing into the surface, heights of protrusive defects are low. Thus, an influence on electromagnetic conversion characteristics of the magnetic recording medium is small.

[0042] When the abrasive grains 221 are aluminum oxide having an average secondary particle diameter of 50 nm to 200 nm, the binder 222 has an increased retaining force for the abrasive grains 221, thereby preventing shedding of the abrasive grains 221.

[0043] The average secondary particle diameter of the abrasive grains 221 is preferably about three times to five times the average primary particle diameter to increase the retaining force of the binder 222 for the abrasive grains 221.

[0044] A method for measuring the average primary particle diameter and the average secondary particle diameter of the abrasive grains 221 is not particularly limited and may be selected as appropriate depending on the intended purpose. Examples include laser diffraction, image analysis, and dynamic light scattering (DLS).

[0045] In laser diffraction, light scattered from the abrasive grains is measured using a laser beam. Since the scattering angle varies depending on the size of the grains, a particle size distribution can be obtained by analyzing the scattering angle. In image analysis, images of the abrasive grains are captured, and sizes and shapes of the grains are measured using image analysis software. In dynamic light scattering, sizes of the abrasive grains are estimated by measuring light scattered when the abrasive grains move in a liquid.

[0046] These methods are suitably used because of their high accuracy and reproducibility. In the present embodiment, the method for measuring the average primary particle diameter and the average secondary particle diameter of the abrasive grains 221 is preferably a method in which observation results obtained by scanning electron microscopy (SEM) are subjected to image analysis. A specific example will be described below.(1) Sample Preparation

[0047] Ultrasonic waves are applied to the abrasive grains to deagglomerate overlapping grains. The abrasive grains are fixed to an observation stage, and a conductive coating (e.g., gold or conductive carbon) is applied to the surfaces of the abrasive grains.(2) SEM Observation

[0048] An accelerating voltage and detector settings appropriate for the measurement apparatus are selected to acquire high-resolution images of the evaluation sample.(3) Calculation of Average Particle Diameter

[0049] Particle size distribution data of the powder particles in the SEM images are acquired using image analysis software, and an average primary particle diameter and an average secondary particle diameter are statistically calculated. The average particle diameter is defined as a particle diameter corresponding to a cumulative volume of 50% in the particle size distribution.

[0050] The aluminum oxide used for the abrasive grains 221 is not particularly limited and may be selected as appropriate depending on the intended purpose. Examples include α-aluminum oxide, γ-aluminum oxide, and α-γ aluminum oxide. These aluminum oxides may be used alone or in combination of two or more. The abrasive grains 221 may be particles made of these materials.

[0051] A method for manufacturing the aluminum oxide used for the abrasive grains 221 is not particularly limited and may be selected as appropriate depending on the intended purpose. Examples include electrofusion, combustion, a molten salt method, and a sol-gel method.

[0052] The aluminum oxide used for the abrasive grains 221 of the polishing tape according to the present embodiment is preferably α-aluminum oxide produced by the sol-gel method to improve fracture resistance. The sol-gel method is preferable because fine particles are readily obtained and the shapes of the primary particles tend to be close to spherical. In addition, since the sol-gel method allows the particle shapes to be easily controlled depending on manufacturing conditions, aluminum oxide having an average primary particle diameter of 10 nm to 40 nm and an average secondary particle diameter of 50 nm to 200 nm can be readily obtained.

[0053] When the method for producing α-aluminum oxide for the abrasive grains 221 employs a sol-gel method, the α-aluminum oxide can be produced, for example, by the following operations (1) to (5).(1) Preparation of Source Material

[0054] An aluminum alkoxide, an aluminum salt, or the like is prepared as an aluminum source. Examples of the aluminum alkoxide include aluminum isopropoxide. Examples of the aluminum salt include aluminum nitrate.

[0055] An alcohol such as ethanol or isopropanol is prepared as a solvent.(2) Formation of Sol

[0056] The aluminum source material is dissolved in the solvent, and water is added as necessary. Through this operation, a hydrolysis reaction is promoted, and a precursor of aluminum oxide is produced. As the hydrolysis reaction proceeds, a sol is formed, eventually resulting in a gel substance. When necessary, properties of the gel can be controlled by adjusting various conditions such as pH and temperature.(3) Drying of Gel

[0057] The resulting gel is air-dried or heated at a low temperature to evaporate the solvent and obtain a dried gel. Through this operation, the structure of the gel is stabilized.(4) Calcination

[0058] The dried gel is calcined at a high temperature (e.g., 1,000 °C or higher). Through this operation, moisture and organic components in the gel are removed, and crystals of α-aluminum oxide are formed. When necessary, properties of the α-aluminum oxide can be controlled by adjusting various conditions such as a calcination temperature and a calcination time.(5) Post-Treatment

[0059] After calcination, a particle size, a specific surface area, and a crystal structure of the α-aluminum oxide are evaluated, and post-treatment such as crushing is performed when necessary.—Binder—

[0060] The binder 222 is not particularly limited and may be selected as appropriate depending on the intended purpose. Examples include a thermosetting resin, a thermoplastic resin, and a photosensitive resin. These may be used alone or in combination of two or more.(Method for Manufacturing Magnetic Recording Medium, and Apparatus for Manufacturing Magnetic Recording Medium)

[0061] A method for manufacturing a magnetic recording medium according to the present embodiment includes a burnishing step, and may further include a laminate forming step and an additional step as necessary. The method for manufacturing a magnetic recording medium according to the present embodiment can be suitably implemented by an apparatus for manufacturing a magnetic recording medium.

[0062] An apparatus for manufacturing a magnetic recording medium according to the present embodiment includes a burnishing member, and may further include a laminate forming member and an additional member as necessary.<Laminate Forming Step and Laminate Forming Member>

[0063] The laminate forming step is a step of forming a laminate. The laminate forming step may include a lubricating layer forming step of forming a lubricating layer on a protective layer.

[0064] The laminate forming member is configured to form a laminate. The laminate forming member may include a lubricating layer forming member configured to form a lubricating layer on a protective layer.

[0065] The laminate forming step may be suitably performed by the laminate forming member, and the lubricating layer forming step may be suitably performed by the lubricating layer forming member.

[0066] Hereinafter, the laminate will be described in detail with reference to FIG. 4. FIG. 4 is a schematic cross-sectional view illustrating an example of a structure of the laminate.

[0067] As illustrated in FIG. 4, a laminate 100 includes a substrate 111, a magnetic recording layer 112 on the substrate 111, a protective layer 113 on the magnetic recording layer 112, and optionally a lubricating layer 12 on the protective layer 113. Although FIG. 4 illustrates a configuration in which each layer is provided on both surfaces of the substrate 111, each layer may be provided on only one surface of the substrate 111.—Substrate—

[0068] The material of the substrate 111 is not particularly limited and may be selected as appropriate depending on the intended purpose, but is preferably a nonmagnetic material. Specific examples of the substrate 111 include a metal substrate formed of a metal material such as an aluminum alloy, and a non-metal substrate formed of a non-metal material such as glass. A nickel-phosphorus (NiP) alloy layer may be formed on a surface of the metal substrate or the non-metal substrate by, for example, plating or sputtering.—Magnetic Recording Layer—

[0069] The magnetic recording layer 112 is a layer provided for recording and reproducing information. For example, data are recorded by reversing a direction of magnetization by magnetic energy supplied by a magnetic head of an HDD and maintaining a magnetization state.

[0070] The magnetic recording layer 112 may be formed of a FePt-based alloy having an L10 structure, a CoPt-based alloy having an L10 structure, or a CoCrPt-based alloy having an hcp structure.

[0071] A method for forming the magnetic recording layer 112 is not particularly limited and may be selected as appropriate depending on the intended purpose. For example, a general film-forming method such as sputtering or ion beam deposition may be used.

[0072] The sputtering is not particularly limited and may be selected as appropriate depending on the intended purpose. Examples include direct current (DC) sputtering, DC magnetron sputtering, and radio frequency (RF) sputtering.

[0073] When the method for forming the magnetic recording layer 112 employs sputtering, it is preferable to use a target containing a material for forming the magnetic recording layer 112. Examples of such a target include a FePt-based alloy, a CoPt-based alloy, and a CoCrPt-based alloy.

[0074] To form the magnetic recording layer 112, an RF bias, a DC bias, or a pulsed DC bias may be applied as necessary.

[0075] When the method for forming the magnetic recording layer 112 employs sputtering, a reactive gas for forming the magnetic recording layer 112 is not particularly limited and may be selected as appropriate depending on the intended purpose. Examples include O2 gas, H2O gas, and N2 gas.

[0076] When the method for forming the magnetic recording layer 112 employs sputtering, a sputtering gas pressure may be adjusted as appropriate depending on properties of each layer, and may be, for example, from 0.1 pascals (Pa) to 30 Pa, inclusive.

[0077] The laminate 100 may include a plurality of magnetic recording layers 112. In this case, a nonmagnetic layer may be formed between the plurality of magnetic recording layers 112.

[0078] If necessary, an adhesion layer, a soft magnetic underlayer, a seed layer, an orientation control layer, and the like may be formed between the substrate 111 and the magnetic recording layer 112.—Protective Layer—

[0079] The protective layer 113 suppresses corrosion of the magnetic recording layer 112 and protects the magnetic recording medium by suppressing damage to a surface of the magnetic recording medium during contact between a magnetic head and the magnetic recording medium.

[0080] The protective layer 113 may be formed of a material generally used for a protective layer of a magnetic recording medium. Examples include a hard carbon film and diamond-like carbon (DLC).

[0081] A method for forming the protective layer 113 is not particularly limited and may be selected as appropriate depending on the intended purpose. Examples include: radio frequency chemical vapor deposition (RF-CVD), in which a source gas composed of a hydrocarbon is decomposed by radio frequency plasma to form a film; ion beam deposition (IBD), in which a source gas is ionized by electrons emitted from a filament to form a film; and filtered cathodic vacuum arc (FCVA), in which a film is formed using a solid carbon target without using a source gas.

[0082] In order to improve bonding strength with the lubricating layer 12 to be formed later, a surface of the protective layer 113 may be hydrogenated or nitrogenated.—Lubricating Layer—

[0083] The lubricating layer 12 is provided in order to suppress wear of the magnetic head and a surface of the magnetic recording medium caused by contact between the magnetic head and the magnetic recording medium, and to improve corrosion resistance of the magnetic recording medium.

[0084] The lubricating layer 12 is formed using a lubricant. The lubricant is not particularly limited and may be selected as appropriate depending on the intended purpose. For example, a material generally used for a lubricating layer of a magnetic recording medium may be used.

[0085] An average thickness of the lubricating layer 12 is not particularly limited and may be selected as appropriate depending on the intended purpose, but is preferably from 5 Å to 10 Å. When the average thickness of the lubricating layer 12 is from 5 Å to 10 Å, wear of the surface of the magnetic recording medium is suppressed, corrosion resistance of the magnetic recording medium is enhanced, and a distance between the magnetic head and the magnetic recording medium in an HDD is shortened, thereby realizing high recording density.

[0086] A method for forming the lubricating layer 12 is not particularly limited and may be selected as appropriate depending on the intended purpose. For example, general film-forming methods such as dipping, spin coating, and a paper method may be used.

[0087] The shape of the laminate 100 is not particularly limited and may be selected as appropriate depending on the intended purpose, provided that the shape is applicable to a magnetic recording medium and a magnetic recording and reproducing device. Examples include a disk shape having a central opening.<Burnishing Step and Burnishing Member>

[0088] A burnishing step is a step of pressing a polishing tape against a surface of a laminate and rubbing the surface with the polishing tape. The burnishing step can be suitably performed by a burnishing member.

[0089] The burnishing member is configured to press a polishing tape against the surface of the laminate and rub the surface with the polishing tape. Note that the polishing tape is the same as the above-described polishing tape, and thus a repeated description thereof is omitted.

[0090] The burnishing step may be performed before or after the lubricating layer forming step. When the burnishing step is performed before the lubricating layer forming step, the surface to be rubbed is the protective layer 113. When the burnishing step is performed after the lubricating layer forming step, the surface to be rubbed is the lubricating layer 12.

[0091] Hereinafter, the burnishing step will be described in detail with reference to FIGS. 5 and 6. FIG. 5 is a schematic view illustrating an example of the polishing tape used in the burnishing step. FIG. 6 is a schematic diagram illustrating an example of the burnishing step.

[0092] The polishing tape 200 used in the burnishing step preferably includes the abrasive grains 221 on one surface of the support 21, and is a long polishing tape wound in a roll. More specifically, as illustrated in FIG. 5, the polishing tape 200 that is long is preferably wound in a roll around a core member 210. Note that the term “long” is not particularly limited. For example, the polishing tape 200 may have a width of several centimeters and a length of about 100 meters.

[0093] In the burnishing step, as illustrated in FIG. 6, the polishing tape 200 wound in a roll (hereinafter also referred to as a “polishing tape roll 200”) is set on a reel of a burnishing apparatus, and a polishing surface S of the polishing tape 200 supplied from the polishing tape roll 200 is pressed against the surface of the laminate 100 and rubbed against the surface of the laminate 100. Accordingly, the protective layer 113 of the laminate 100 is rubbed, thereby obtaining a burnished laminate.

[0094] Hereinafter, an example of a burnishing apparatus serving as a burnishing member will be described in detail with reference to FIG. 7.

[0095] As illustrated in FIG. 7, a burnishing apparatus 50 includes a pair of polishing tapes 200 (hereinafter also referred to as “a pair of polishing tapes 200A and 200B”), a rotation support member 51, and a tape moving member 52. The pair of polishing tapes 200 are arranged to face each other so as to sandwich the laminate 100, on which the protective layer 113 or the lubricating layer 12 is formed, from opposing sides.

[0096] The pair of polishing tapes 200A and 200B wound in rolls are respectively set on a first polishing tape supply reel 53A and a second polishing tape supply reel 53B to be supplied. The pair of polishing tapes 200A and 200B are respectively wound into rolls by a first polishing tape take-up reel 54A and a second polishing tape take-up reel 54B.

[0097] By arranging the pair of polishing tapes 200A and 200B to face each other so as to sandwich the laminate 100 from opposing sides, the burnishing apparatus 50 can perform burnishing on the laminate 100 simultaneously, thereby improving efficiency.

[0098] The rotation support member 51 supports a central opening of the laminate 100 on which the protective layer 113 or the lubricating layer 12 is formed, and rotates the laminate 100 in a circumferential direction (a direction indicated by arrow r in FIG. 7).

[0099] The tape moving member 52 presses the pair of polishing tapes 200A and 200B against the rotating laminate 100 in directions indicated by arrows F1 and F2, respectively, and relatively moves the pair of polishing tapes 200A and 200B in a radial direction of the laminate 100.

[0100] The tape moving member 52 includes a pair of polishing tape pressing members 521 and a pair of polishing tape running mechanisms 522. The pair of polishing tape pressing members 521 are arranged to face each other so as to sandwich the laminate 100, on which the protective layer 113 or the lubricating layer 12 is formed, from opposing sides with the pair of polishing tapes 200A and 200B interposed therebetween. The pair of polishing tape running mechanisms 522 are arranged likewise.

[0101] The pair of polishing tape pressing members 521 includes a first polishing tape pressing member 521A and a second polishing tape pressing member 521B. The pair of polishing tape running mechanisms 522 includes a first polishing tape running mechanism 522A and a second polishing tape running mechanism 522B. In other words, the tape moving member 52 includes the first polishing tape pressing member 521A and the first polishing tape running mechanism 522A disposed on one side relative to the laminate 100, and the second polishing tape pressing member 521B and the second polishing tape running mechanism 522B disposed on the opposite side relative to the laminate 100.

[0102] The first polishing tape pressing member 521A is a pressing member configured to press the polishing tape 200A supplied from the first polishing tape supply reel 53A toward the laminate 100 (in the F1 direction in FIG. 7).

[0103] The second polishing tape pressing member 521B is a pressing member configured to press the polishing tape 200B supplied from the second polishing tape supply reel 53B toward the laminate 100 (in the F2 direction in FIG. 7).

[0104] The first polishing tape running mechanism 522A includes first guide rollers 523A-1 to 523A-6 and causes the polishing tape 200A to run in the direction of arrow Ra.

[0105] The second polishing tape running mechanism 522B includes second guide rollers 523B-1 to 523B-6 and causes the polishing tape 200B to run in the direction of arrow Rb.

[0106] The magnetic recording medium manufactured by the method for manufacturing a magnetic recording medium according to the present embodiment has fewer protrusive defects on the surface of the magnetic recording medium, thereby improving quality reliability. In addition, the magnetic recording medium manufactured by the method for manufacturing a magnetic recording medium according to the present embodiment can suppress defects in writing and reading, and can maintain high reliability. Therefore, the magnetic recording medium can be suitably used in a magnetic recording and reproducing device.

[0107] The magnetic recording and reproducing device that includes the magnetic recording medium manufactured by the method for manufacturing a magnetic recording medium according to the present embodiment is not particularly limited, and may be, for example, a magnetic recording and reproducing device configured to record magnetic information on the magnetic recording medium using a heat-assisted recording method.EXAMPLES

[0108] Hereinafter, examples of the present embodiment will be described. However, the scope of the present disclosure is not limited to these examples.Example 1[Production of Polishing Tape]<Preparation of α-Aluminum Oxide>

[0109] α-Aluminum oxide was prepared by the following sol-gel method.

[0110] Aluminum isopropoxide was synthesized by reacting aluminum chloride with isopropyl alcohol. The aluminum isopropoxide was dissolved in ethanol, and water was added as necessary. Then, the resulting solution was air-dried and calcined at a high temperature (e.g., 1,000 °C), thereby obtaining α-aluminum oxide.

[0111] The average primary particle diameter and the average secondary particle diameter of the obtained α-aluminum oxide were measured. The average primary particle diameter was 30 nm, and the average secondary particle diameter was 120 nm. The average primary particle diameter and the average secondary particle diameter were measured by image analysis of SEM observation results, as described above. The average particle diameter was defined as a particle diameter corresponding to a cumulative volume of 50% (volume basis) in the particle size distribution.<Production of Polishing Tape>

[0112] A polishing tape was produced by bonding the α-aluminum oxide (abrasive grains) to one side of a polyethylene terephthalate (PET) substrate in a tape form (average thickness: 24 μm), using an epoxy resin.[Production of Laminate]

[0113] A cleaned aluminum substrate (available from RESONAC, outer diameter: 3.5 inches) was placed in a film-forming chamber of a DC magnetron sputtering apparatus (available from Anelva, C-3040), and the chamber was evacuated to 1×10−5 Pa. Thereafter, an adhesion layer having an average thickness of 10 nm was formed on the aluminum substrate using a Cr target by sputtering.

[0114] Next, a soft magnetic underlayer was formed on the adhesion layer by sputtering. The soft magnetic underlayer included a first soft magnetic recording layer, an intermediate layer, and a second soft magnetic recording layer, which were formed in this order.

[0115] The first soft magnetic recording layer was formed using a Co-20Fe-5Zr-5Ta target (Fe content: 20 atomic %, Zr content: 5 atomic %, Ta content: 5 atomic %, remainder: Co) at a substrate temperature of 100 °C or lower. The average thickness of the first soft magnetic recording layer was 25 nm. A Ru layer having an average thickness of 0.7 nm was formed as the intermediate layer. The second soft magnetic recording layer was formed using a Co-20Fe-5Zr-5Ta target (Fe content: 20 atomic %, Zr content: 5 atomic %, Ta content: 5 atomic %, remainder: Co). The average thickness of the second soft magnetic recording layer was 25 nm.

[0116] Next, a seed layer was formed on the soft magnetic underlayer by sputtering. The seed layer was formed using a Ni-6W target (W content: 6 atomic %, remainder: Ni) with an average thickness of 5 nm.

[0117] Next, a first orientation control layer and a second orientation control layer were sequentially formed on the seed layer by sputtering.

[0118] The first orientation control layer was formed at a sputtering pressure of 0.8 Pa as a Ru layer having an average thickness of 10 nm. The second orientation control layer was formed at a sputtering pressure of 1.5 Pa as a Ru layer having an average thickness of 10 nm.

[0119] Next, a first magnetic recording layer was formed on the second orientation control layer by sputtering. The first magnetic recording layer was formed at a sputtering pressure of 2 Pa as a layer having an average thickness of 9 nm and composed of 91 mol % of a Co-15Cr-16Pt alloy (Cr content: 15 atomic %, Pt content: 16 atomic %, remainder: Co), 6 mol % of SiO2, and 3 mol % of TiO2.

[0120] Next, a nonmagnetic layer was formed on the first magnetic recording layer by sputtering. The nonmagnetic layer was formed as a layer having an average thickness of 0.3 nm and composed of 88 mol % of a Co-30Cr alloy (Cr content: 30 atomic %, remainder: Co) and 12 mol % of TiO2.

[0121] Next, a second magnetic recording layer was formed on the nonmagnetic layer by sputtering. The second magnetic recording layer was formed at a sputtering pressure of 2 Pa as a layer having an average thickness of 6 nm, and composed of 92 mol % of a Co-11Cr-18Pt alloy (Cr content: 11 atomic %, Pt content: 18 atomic %, remainder: Co), 5 mol % of SiO2, and 3 mol % of TiO2.

[0122] Next, a nonmagnetic layer was formed on the second magnetic recording layer by sputtering. A Ru layer having an average thickness of 0.3 nm was formed as the nonmagnetic layer.

[0123] Next, a third magnetic recording layer was formed on the nonmagnetic layer by sputtering. The third magnetic recording layer was formed at a sputtering pressure of 0.6 Pa using a Co-20Cr-14Pt-3B target (Cr content: 20 atomic %, Pt content: 14 atomic %, B content: 3 atomic %, remainder: Co). The average thickness of the third magnetic recording layer was 7 nm.

[0124] A hydrogenated carbon film was formed as a protective layer on the surface of the third magnetic recording layer by ion beam deposition. Toluene gas was used as a source gas. The conditions for forming the hydrogenated carbon film were as follows. The flow rate of the source gas supplied to the deposition chamber was 2.9 standard cubic centimeters per minute (sccm), and the reaction pressure was 0.2 Pa. The cathode power, serving as an excitation source for the source gas, was 225 W (AC 22.5 V, 10 A). The voltage between the cathode electrode and the anode electrode covering the cathode electrode was 75 V, and the current was 1,650 mA. The ion acceleration voltage was 200 V, and the ion current was 180 mA. The deposition time was 1.5 seconds. The hydrogenated carbon film was formed to have an average thickness of 3.5 nm. After formation of the hydrogenated carbon film, the supply of the source gas was stopped, and the deposition chamber was evacuated for 2 seconds. Subsequently, nitrogen gas was supplied into the deposition chamber at a flow rate of 2 sccm and a reaction pressure of 5 Pa. At this time, the cathode power was 128 W (AC 16 V, 8 A). The voltage between the cathode electrode and the anode electrode was 75 V, and the current was 1,000 mA. The ion acceleration voltage was 200 V, the ion current was 90 mA, and the treatment time was 1 second. The surface of the hydrogenated carbon film was irradiated with nitrogen ions generated from the nitrogen gas and exposed to nitrogen plasma. As a result, the surface of the hydrogenated carbon film was dehydrogenated and nitrogenated.

[0125] Next, a lubricant (D5OH (XS), available from Matsumura Oil Research Institute) was applied onto the surface of the protective layer by dipping to form a lubricating layer having an average thickness of about 7 Å.[Manufacture and Evaluation of Magnetic Recording Media]

[0126] The surface of the laminate on which the lubricating layer was formed was burnished using the polishing tape to obtain a magnetic recording medium (burnishing step). The burnishing conditions included a rotational speed of the laminate of 2,000 rotations per minute (rpm) and a burnishing time of 7 seconds. The obtained magnetic recording medium was subjected to optical inspection, and magnetic recording media having large scratches or adhered grains were excluded. Subsequently, head burnishing with a burnishing head was performed to remove foreign matter adhered to the magnetic recording medium.

[0127] The obtained magnetic recording medium was subjected to glide inspection using a glide tester equipped with a head including a piezoelectric element. The glide height of the head was set to 10 nm, and magnetic recording media having large protrusions on the surface of the media were excluded. N ote that the glide height was defined as a distance between the head and the surface of the magnetic recording medium, assuming that the surface had no defects.

[0128] One hundred magnetic recording media that passed the glide inspection were prepared, and HDIs inspection was conducted on each magnetic recording medium using an inspection head having a thermoresistive element. Specifically, the glide height (a distance from the surface of the magnetic recording medium to the thermoresistive element) was set to 1.5 nm. A magnetic recording medium was judged to be acceptable when no defect location was detected at which a signal output from the thermoresistive element of the inspection head had an absolute value of 500 mV or more. During the inspection, the track pitch was set to 20 μm, and the magnetic recording medium was evaluated from an inner periphery to an outer periphery. This corresponds to evaluating 5% of the entire area of the magnetic recording medium. As a result, 97 magnetic recording media passed the inspection.Examples 2 and 3, and Comparative Examples 1 to 4

[0129] Magnetic recording media were manufactured and subjected to HDIs inspection in the same manner as in Example 1, except that the average primary particle diameter and the average secondary particle diameter of the α-aluminum oxide were changed as shown in Table 1 by adjusting the concentration of aluminum isopropoxide and the calcination conditions. The results are shown in Table 1.TABLE 1AVERAGEAVERAGEPRIMARYSECONDARYNUMBERPARTICLEPARTICLEOF MEDIADIAMETER OFDIAMETER OFPASSINGABRASIVEABRASIVEHDIsGRAINSGRAINSINSPECTIONEXAMPLE 130 nm120 nm97EXAMPLE 210 nm 50 nm98EXAMPLE 340 nm200 nm96COMPARATIVE 8 nm 40 nm83EXAMPLE 1COMPARATIVE50 nm250 nm80EXAMPLE 2COMPARATIVE50 nm200 nm80EXAMPLE 3COMPARATIVE40 nm210 nm90EXAMPLE 4

[0130] According to an aspect of the present disclosure, it is possible to provide a polishing tape capable of improving overall productivity of magnetic recording media.

[0131] As described above, the present disclosure has been described with reference to specific embodiments. However, these embodiments are provided by way of example only, and the present disclosure is not limited thereto. The above embodiments may be implemented in various other forms, and various combinations, omissions, substitutions, additions, and modifications may be made without departing from the scope and gist of the invention. Such embodiments and modifications thereof fall within the scope and gist of the invention and are intended to be included within the scope of the claims and their equivalents.

Claims

1. A polishing tape, comprising:a support; andabrasive grains of aluminum oxide provided on the support, the abrasive grains having an average primary particle diameter of 10 nm to 40 nm, inclusive, and an average secondary particle diameter of 50 nm to 200 nm, inclusive.

2. The polishing tape according to claim 1, whereinthe polishing tape includes the abrasive grains on one surface of the support, andthe polishing tape is wound in a roll.

3. The polishing tape according to claim 2, whereinthe aluminum oxide is α-aluminum oxide produced by a sol-gel method.

4. A method for manufacturing a magnetic recording medium, comprising:burnishing a laminate by pressing a polishing tape against a surface of the laminate and rubbing the surface of the laminate with the polishing tape, the polishing tape including a support and abrasive grains of aluminum oxide that are provided on the support and have an average primary particle diameter of 10 nm to 40 nm, inclusive, and an average secondary particle diameter of 50 nm to 200 nm, inclusive, whereinthe laminate includes a substrate, a magnetic recording layer on the substrate, and a protective layer on the magnetic recording layer.

5. The method for manufacturing the magnetic recording medium according to claim 4, whereinthe laminate further includes a lubricating layer on the protective layer, andthe burnishing is performed by pressing the polishing tape against the surface of the laminate including the lubricating layer and rubbing the surface of the laminate with the polishing tape.

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