Method for manufacturing magnetic recording media

Abstract

The present invention provides a method for manufacturing a magnetic recording medium that efficiently removes foreign matter from the surface and improves the coverage rate by the lubricating layer. [Solution] A method for manufacturing a magnetic recording medium 1 in which a lubricating layer 12 is formed on a laminate 11 obtained by stacking a magnetic recording layer 112 and a protective layer 113 on a substrate 111 in this order includes the steps of applying a first and a second lubricant, burning the surface of the laminate to which the first and second lubricants have been applied with an abrasive, and removing the second lubricant from the laminate, wherein the step of applying the second lubricant is to use a dip method or a spin coating method, the solvent for the second lubricant is to have a higher dissolution rate for the second lubricant than for the dissolution rate for the first lubricant, the burning step includes pressing a tape containing an abrasive onto the surface of the laminate and rubbing it, and the step of removing the second lubricant includes irradiating the laminate to which the first and second lubricants have been applied with ultraviolet light or heat treating the laminate to which the first and second lubricants have been applied.

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a magnetic recording medium.

Background Art

[0002] Magnetic storage devices (also referred to as magnetic recording and reproducing devices) have been mounted in various products such as personal computers, video recorders, and data servers in recent years, and their importance has been increasing. A magnetic storage device is a device having a magnetic recording medium for storing electronic data by magnetic recording. For example, there is a hard disk drive (HDD: Hard Disk Drive).

[0003] A general magnetic recording medium has, for example, a multilayer film laminated structure in which an underlayer, an intermediate layer, a magnetic recording layer, and a protective layer are formed in this order on a non-magnetic substrate, and a lubricating layer is applied to the surface of the protective layer. The protective layer and the lubricating layer are provided to prevent the durability of the magnetic recording medium from deteriorating due to wear and damage caused by contact sliding with a magnetic head. As the protective layer, a hard carbon film is generally used, and the lubricating layer is formed by applying a liquid perfluoropolyether compound or the like to the surface.

[0004] For the purpose of increasing the bonding strength of the lubricating layer to the protective layer, it is known to perform various treatments on the lubricating layer. For example, Patent Document 1 discloses a method in which a heat treatment is performed on the applied lubricating layer, and further a light irradiation treatment using an ultraviolet lamp is performed.

[0005] Also, in order to remove foreign substances and protrusions on the surface of the protective layer, the surface of the magnetic recording medium is tape burnished with a polishing tape. At this time, it is known to perform tape burnishing after the formation of the lubricating layer in order to prevent scratches from occurring on the surface of the protective layer by tape burnishing.

[0006] Furthermore, Patent Document 2 discloses a method for manufacturing a magnetic recording medium, in which, after forming a protective layer, a first lubricant without end groups is applied to its surface, tape varnish is performed, the first lubricant is removed with a solvent, and a second lubricant having end groups is applied. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 11-25452 [Patent Document 2] Japanese Patent Publication No. 2002-222519 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] In the manufacturing of magnetic recording media, applying tape varnish after forming a lubricating layer can reduce the occurrence of scratches and other damage due to the lubricating properties of the layer. However, the lubricant used in the lubricating layer and the thickness of the lubricating layer may not be suitable for tape varnish in some cases.

[0009] As described in Patent Document 2 for the manufacturing method of magnetic recording media, it is conceivable to perform processing using a first lubricant suitable for tape varnish, then remove the first lubricant, and apply a second lubricating layer suitable for magnetic recording media. However, in this case, the following problems arise. Specifically, contaminants and lubricants dissolved in the solvent used to remove the lubricant re-adhere to the processed substrate, causing foreign matter on the surface of the magnetic recording media. Furthermore, it is difficult to completely remove lubricant bonded to the protective layer using a solvent, and any remaining lubricant causes foreign matter on the surface of the magnetic recording media, reducing the coverage rate of the magnetic recording media surface by the lubricating layer and complicating the manufacturing process of the magnetic recording media.

[0010] One aspect of this disclosure has been made in view of the above circumstances and aims to provide a method for manufacturing a magnetic recording medium that can efficiently remove foreign matter from the surface of the magnetic recording medium and improve the coverage rate by the lubricating layer. [Means for solving the problem]

[0011] This disclosure provides the configuration shown below. [1] A method for manufacturing a magnetic recording medium, wherein a lubricating layer is formed on a laminate obtained by stacking a magnetic recording layer and a protective layer on a substrate in this order, A step of applying a first lubricant and a second lubricant onto the laminate, A step of burning the surface of the laminate to which the first lubricant and the second lubricant have been applied with an abrasive, A step of removing the second lubricant from the laminate, Includes, The step of applying the second lubricant is performed using either a dip method or a spin-coat method. The solvent for the second lubricant used in the dip method or the spin-coating method has a higher dissolution rate for the second lubricant compared to the dissolution rate for the first lubricant. The burning step includes pressing a tape containing an abrasive material against the surface of the laminate and rubbing it, A method for manufacturing a magnetic recording medium, comprising the step of removing the second lubricant, which includes irradiating the laminate coated with the first lubricant and the second lubricant with ultraviolet light, or the step of heat-treating the laminate coated with the first lubricant and the second lubricant. [2] The method for manufacturing a magnetic recording medium according to [1], wherein the second lubricant has an average molecular weight of 300 to 1000 and contains two or fewer polar groups. [3] The method for manufacturing a magnetic recording medium according to [1] or [2], wherein the first lubricant has an average molecular weight of 900 to 3000 and contains 4 to 8 polar groups. [4] A method for manufacturing a magnetic recording medium according to any one of [1] to [3], wherein the film thickness of the first lubricant applied on the laminate is 5 to 10 Å, and the film thickness of the second lubricant is 5 to 20 Å. [5] The method for manufacturing a magnetic recording medium according to any one of [1] to [4], wherein the step of irradiating with ultraviolet light is performed in an inert gas atmosphere or in a vacuum. [6] The step of performing the heat treatment is the method for manufacturing a magnetic recording medium according to any one of [1] to [5], which is performed in an inert gas atmosphere.

Advantages of the Invention

[0012] According to one aspect of the present disclosure, foreign substances on the surface of the magnetic recording medium can be efficiently removed, and the coating rate by the lubricating layer can be improved.

Brief Description of the Drawings

[0013] [Figure 1] It is a 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 2] It is a diagram for explaining an example of an outline of the method for manufacturing a magnetic recording medium according to an embodiment of the present disclosure. [Figure 3] It is an enlarged cross-sectional view showing an example of a tape containing an abrasive used when burnishing. [Figure 4] It is a diagram showing an example of a burnishing processing apparatus used in the step of burnishing the surface of the laminate with an abrasive.

Modes for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. For ease of understanding the description, the same reference numerals are given to the same components in each drawing, and overlapping descriptions are omitted as appropriate. In addition, the scales of the respective members in the drawings may be different from the actual ones. In this specification, "~" indicating a numerical range means including the numerical values described before and after it as the lower limit value and the upper limit value, unless otherwise specified. Also, when only the unit of the upper limit value is described in the numerical range represented by "~", it means that the lower limit value is also in the same unit.

[0015] Hereinafter, when explaining the method for manufacturing a magnetic recording medium according to an embodiment of the present disclosure (hereinafter sometimes simply referred to as this embodiment), the configuration of the magnetic recording medium manufactured by the method for manufacturing a magnetic recording medium according to this embodiment will be explained.

[0016] [Magnetic Recording Medium] FIG. 1 is a cross-sectional view showing an example of a magnetic recording medium manufactured by the method for manufacturing a magnetic recording medium according to this embodiment. As shown in FIG. 1, the magnetic recording medium 1 has lubricating layers 12 on both surfaces of a laminate (also referred to as a laminated body) 11.

[0017] The laminate 11 includes a magnetic recording layer 112 and a protective layer 113 laminated in this order from the substrate 111 side on both surfaces of the substrate 111.

[0018] The substrate 111 is formed of a non-magnetic material. For the substrate 111, for example, a metal substrate formed of a metal material such as an aluminum alloy may be used, or for example, a non-metal substrate formed of a non-metal material such as glass may be used. Further, a NiP alloy layer may be formed on the surface of these metal substrates or non-metal substrates using, for example, a plating method or a sputtering method.

[0019] The magnetic recording layer 112 is a layer provided for recording and reproducing information. For example, it is provided to reverse the direction of magnetization by magnetic energy supplied from a magnetic head of an HDD and store data by maintaining the magnetization state.

[0020] The magnetic recording layer 112 uses, for example, an FePt-based alloy having an L10 structure, a CoPt-based alloy having an L10 structure, or a CoCrPt-based alloy having a hcp structure.

[0021] For forming the magnetic recording layer 112, known methods such as a sputtering method or an ion beam film formation method can be used.

[0022] The protective layer 113 is provided to suppress corrosion of the magnetic recording layer 112, prevent and protect the surface of the magnetic recording medium 1 from damage when the magnetic head comes into contact with the magnetic recording medium 1, and enhance the corrosion resistance of the magnetic recording medium 1.

[0023] The protective layer 113 can be formed from well-known materials, such as a hard carbon film or diamond-like carbon (DLC).

[0024] For forming the protective layer 113, known methods such as sputtering or ion beam deposition can be used.

[0025] The protective layer 113 may have its surface hydrogenated or nitrogenated. By hydrogenating or nitrogenizing the surface of the protective layer 113, the bonding force with the lubricating layer 12 formed on it can be increased. That is, since the first lubricant applied on the protective layer 113 has polarity, it forms a strong bond with the hydrogen atoms or nitrogen atoms on the surface of the protective layer 113. In particular, it is preferable that the surface of the protective layer 113 be nitrogenized.

[0026] The lubricating layer 12 is provided to suppress wear on the surface of the magnetic head and the magnetic recording medium 1 when the magnetic head comes into contact with the magnetic recording medium 1, thereby improving the corrosion resistance of the magnetic recording medium 1.

[0027] The thickness of the lubricating layer 12 is preferably 5 to 10 Å. By setting the thickness of the lubricating layer 12 to 5 to 10 Å, wear on the surface of the magnetic recording medium 1 is suppressed, the corrosion resistance of the magnetic recording medium 1 is improved, and the distance between the magnetic head and the magnetic recording medium 1 in the HDD can be shortened to achieve high recording density.

[0028] [Manufacturing method for magnetic recording media] Figure 2 shows an example of the outline of the manufacturing method for a magnetic recording medium according to this embodiment. As shown in Figure 2, the manufacturing method for a magnetic recording medium according to this embodiment includes the steps of: forming a laminate 11 by stacking a magnetic recording layer 112 and a protective layer 113 in that order on both sides of a substrate 111 (laminated body formation step); applying a first lubricant 121 and a second lubricant 122 onto the laminate 11 (application step); burning the surface of the laminate 11 to which the first lubricant 121 and the second lubricant 122 have been applied using an abrasive tape 20 containing an abrasive (burnishing step); and removing the second lubricant 122 from the laminate 11 (removal step).

[0029] Furthermore, the method for manufacturing a magnetic recording medium according to this embodiment may include other steps, such as forming an adhesion layer, a soft magnetic underlayer, a seed layer, or an orientation control layer between the substrate 111 and the magnetic recording layer 112. Also, if the method for manufacturing a magnetic recording medium according to this embodiment is provided by stacking multiple magnetic recording layers 112, it may include steps such as forming a non-magnetic layer between the magnetic recording layers 112.

[0030] In the manufacturing method of the magnetic recording medium according to this embodiment, a first lubricant 121 and a second lubricant 122 are applied to the surface of the laminate 11, and then the surface of the laminate 11 is burnished with an abrasive. Subsequently, the second lubricant 122 on the laminate 11 is removed by ultraviolet irradiation 31 or heat treatment 32. As a result, the first lubricant 121 remains on the surface of the protective layer 113 of the laminate 11, and the remaining first lubricant 121 becomes the lubricating layer 12 of the magnetic recording medium 1, thus forming the lubricating layer 12.

[0031] In this embodiment, ultraviolet irradiation 31 or heat treatment 32 is used to remove the second lubricant 122. As mentioned above, conventionally, the lubricant used in the burnishing process was removed by cleaning with a solvent. However, according to the inventors' investigation, the solvent used for cleaning contains not only the removed lubricant but also contaminants generated during burnishing, and when the solvent comes into contact with the surface of the protective layer 113, the contaminants reattach to the protective layer 113, causing foreign matter on the surface of the magnetic recording medium. Furthermore, it was found that it is difficult to completely remove the lubricant bonded to the protective layer 113 by solvent cleaning, and that the small amount of remaining lubricant is the cause of foreign matter on the surface of the magnetic recording medium 1.

[0032] In this embodiment, the second lubricant 122 on the laminate 11 is removed by ultraviolet irradiation 31 or heat treatment 32, i.e., a dry treatment. Therefore, the second lubricant 122 or contaminants dissolved in it quickly gasify and leave the surface of the laminate 11, so they do not cause foreign matter on the surface of the magnetic recording medium 1. Furthermore, by setting the conditions of ultraviolet irradiation 31 or heat treatment 32 to conditions that allow the second lubricant 122 to gasify, the second lubricant 122 on the laminate 11 can be completely removed. In addition, since the process of forming the lubricating layer 12 is simple, a highly productive method for manufacturing a magnetic recording medium can be provided.

[0033] [Laminate formation process] In the manufacturing method of the magnetic recording medium according to this embodiment, first, a laminate 11 is formed by stacking a magnetic recording layer 112 and a protective layer 113 in that order on both sides of a prepared substrate 111, as shown in Figure 1 (laminated body formation step).

[0034] The laminate 11 can be formed using a general method for depositing the magnetic recording layer 112 and the protective layer 113.

[0035] First, a magnetic recording layer 112 is formed on both sides of the substrate 111. A general film deposition method such as sputtering can be used to form the magnetic recording layer 112.

[0036] In the sputtering method, a target containing the material for forming the magnetic recording layer 112 can be used.

[0037] As a target containing the material for forming the magnetic recording layer 112, for example, an FePt-based alloy having an L10 structure, a CoPt-based alloy having an L10 structure, or a CoCrPt-based alloy having an hcp structure can be used.

[0038] As for sputtering methods, DC sputtering, DC magnetron sputtering, or RF sputtering can be used.

[0039] When forming the magnetic recording layer 112, RF (Radio Frequency) bias, DC bias, pulsed DC, or pulsed DC bias may be used as needed.

[0040] As the reactive gas, O2 gas, H2O gas, or N2 gas may be used.

[0041] The sputtering gas pressure is adjusted as needed to optimize the characteristics of each layer, but it is usually within the range of 0.1 to 30 Pa.

[0042] Next, a protective layer 113 is formed on the magnetic recording layer 112. The method for forming the protective layer 113 is not particularly limited, but general deposition methods such as the RF-CVD (Radio Frequency-Chemical Vapor Deposition) method, which decomposes a source gas consisting of hydrocarbons 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, can be used.

[0043] [Coating process] Next, as shown in Figure 2, the first lubricant 121 and the second lubricant 122 are applied to both sides of the laminate 11 (application step).

[0044] Note that "both sides of the laminate 11" refers to both main surfaces of the laminate 11 to which the first lubricant 121 and the second lubricant 122 are applied. The first lubricant 121 and the second lubricant 122 may be applied to one main surface of the laminate 11 and then to the other main surface of the laminate 11, or they may be applied to both main surfaces of the laminate 11 simultaneously.

[0045] When the first lubricant 121 is applied to the protective layer 113 of the laminate 11, it is ideally preferable that the entire surface of the protective layer 113 is covered with the first lubricant 121, but a portion of the surface of the protective layer 113 may remain uncoated. In that case, the second lubricant 122 may be applied to the portion not covered by the first lubricant 121.

[0046] Preferably, the average molecular weight of the first lubricant 121 is higher than that of the second lubricant 122, and the polarity of the first lubricant 121 is higher than that of the second lubricant 122. This makes it easy to select conditions for gasifying the second lubricant 122 without gasifying the first lubricant 121 when removing the second lubricant 122 by irradiating the laminate 11 coated with the first lubricant 121 and the second lubricant 122 on its surface with ultraviolet light or by heat-treating the laminate 11 in the removal process described later.

[0047] The organic compounds used as the first lubricant 121 and the second lubricant 122 can be exemplified by functional groups such as hydroxyl groups, amino groups, amide groups, carbonyl groups, carboxyl groups, cyano groups, phenyl groups, and methyl groups. Among these, the hydroxyl groups, amino groups, amide groups, carbonyl groups, carboxyl groups, and cyano groups are polar functional groups (polar groups).

[0048] The average molecular weight of the first lubricant 121 is preferably 900 to 3000, and the number of polar groups in the structural formula of the first lubricant 121 is preferably 4 to 8. This makes it easy to select conditions for gasifying the second lubricant 122 without gasifying the first lubricant 121 when removing the second lubricant 122 by irradiating the laminate 11 coated with the first lubricant 121 and the second lubricant 122 on its surface with ultraviolet light or by heat-treating the laminate 11 in the removal step described later.

[0049] The average molecular weight of the second lubricant 122 is preferably 300 to 1000, and the number of polar groups in the structural formula of the second lubricant 122 is preferably two or less, or none at all. This makes it easy to select conditions for gasifying the second lubricant 122 without gasifying the first lubricant 121 when removing the second lubricant 122 by irradiating the laminate 11 coated with the first lubricant 121 and the second lubricant 122 on its surface with ultraviolet light or by heat-treating the laminate 11 in the removal process described later.

[0050] The polar groups of the first lubricant 121 or the second lubricant 122 are preferably hydroxyl groups, amide groups, and cyano groups, with hydroxyl groups being particularly preferred among these. By having the above-mentioned preferred polar groups, the first lubricant 121 can be made suitable for the lubrication layer 12 of the magnetic recording medium 1, and the second lubricant 122 can be made suitable for varnishing the surface of the laminate 11. Furthermore, when performing the above-mentioned ultraviolet irradiation 31 or heat treatment 32, the effect of quickly removing the second lubricant 122 or contaminants dissolved therein is enhanced. In addition, by leaving the first lubricant 121 on the laminate 11 and increasing the bonding force between the protective layer 113 and the first lubricant 121, the coverage rate of the magnetic recording medium 1 by the lubrication layer 12 can be further improved.

[0051] For applying the first lubricant 121, known methods such as the dipping method, spin coating method, or vapor coating method can be used. The dipping method involves dissolving the lubricant in a solvent, immersing the laminate 11 in this solution, and then pulling up the laminate 11 at a constant speed to form a film of lubricant on the surface of the laminate 11. The spin coating method involves dissolving the lubricant in a solvent, applying this solution to the surface of the laminate 11, and then rotating the laminate 11 at high speed for a certain period of time to form a film of lubricant on the laminate 11. The vapor coating method involves placing the laminate 11 in a vacuum chamber and introducing a lubricant that has been gasified by heating into the vacuum chamber to form a film of lubricant on the laminate 11.

[0052] The second lubricant 122 is applied using either a dip method or a spin coating method. The solvent used for the second lubricant in the dip method and spin coating method is one in which the solubility of the second lubricant 122 is higher than that of the first lubricant 121. By using such a solvent, the first lubricant 121 and the second lubricant 122 are more likely to remain on the surface of the laminate 11 used in the burnishing process, and contaminants generated in the burnishing process are more likely to dissolve into the second lubricant 122. By removing the second lubricant 122 into which these contaminants have dissolved, foreign matter on the surface of the magnetic recording medium 1 can be efficiently removed, making it possible to provide a magnetic recording medium with a high coverage rate by the first lubricant 121.

[0053] The first lubricant 121 forms a lubricating layer 12 on the magnetic recording medium 1. Therefore, a film thickness of 5 to 10 Å for the first lubricant 121 is preferable, as it suppresses wear on the surface of the magnetic recording medium 1, improves the corrosion resistance of the magnetic recording medium 1, and shortens the distance between the magnetic head and the magnetic recording medium 1 in magnetic recording and playback devices such as HDDs to achieve high recording density.

[0054] The film thickness of the second lubricant 122 is preferably 5 to 20 Å. A film thickness of 5 to 20 Å for the second lubricant 122 makes it suitable for varnishing the surface of the laminate 11. Furthermore, the second lubricant 122 can be removed in a short time by ultraviolet irradiation 31 or heat treatment 32, thereby increasing the productivity of the magnetic recording medium 1.

[0055] [Burning process] Next, the surface of the laminate 11 is burnished with an abrasive (burnishing process).

[0056] The burning process includes a scraping step in which a tape containing an abrasive material (abrasive tape) 20 is pressed against the surface of the laminate 11 and scraped, as shown in Figure 2. In the burning process, a method can be used in which the abrasive tape 20 is pressed against the surface of the laminate 11 and scraped. The burning method and burning apparatus will be described in detail with reference to the figures.

[0057] Figure 3 is an enlarged cross-sectional view showing an example of a polishing tape 20 used when burning. As shown in Figure 3, the polishing tape 20 polishes the laminate 11 by sliding the polishing surface S against the surface of the laminate 11.

[0058] The polishing tape 20 has an abrasive layer 22 on a support 21. The abrasive layer 22 is composed of abrasive grains 221 and a binder 222, the binder 222 fixing the abrasive grains 221 to the support 21.

[0059] The material constituting the support 21 is not particularly limited, and various resins such as polyethylene terephthalate can be used.

[0060] The abrasive grains 221 can be used as an abrasive material contained in the polishing tape 20. Examples of abrasive grains 221 include particles having chromium oxide, α-alumina, silicon carbide, nonmagnetic iron oxide, diamond, γ-alumina, α,γ-alumina, fused alumina, corundum, or artificial diamond. The abrasive grains 221 may also be particles made from these materials. These may be used individually or in combination of two or more as appropriate.

[0061] The binder 222 is not particularly limited, and for example, thermosetting resins, thermoplastic resins, photosensitive resins, etc., can be used. The resin used as the binder 222 may be used alone or in combination of two or more types.

[0062] Furthermore, the polishing tape 20 may have a lubricating film 23 on the surface of the polishing surface S.

[0063] Figure 4 shows an example of a burnishing apparatus used in the process of burnishing the surface of a laminate 11 with an abrasive material. As shown in Figure 4, the burnishing apparatus 50 has a polishing tape 20 consisting of a pair of polishing tapes 20A and 20B that are positioned opposite each other so as to sandwich the laminate 11 from both sides, a rotating support means 51, and a tape moving means 52. In the burnishing apparatus 50, by positioning the polishing tapes 20A and 20B opposite each other so as to sandwich the laminate 11 from both sides, the abrasive grains 221 contained as abrasive material in the polishing tapes 20A and 20B can efficiently burnish both sides of the laminate 11 simultaneously.

[0064] The rotational support means 51 rotates the laminate 11 in the circumferential direction (direction of arrow r in Figure 4) while supporting the central opening of the laminate 11.

[0065] The tape moving means 52 presses the polishing tapes 20A and 20B against both surfaces of the rotated laminate 11 in the direction of arrow F, and moves the polishing tapes 20A and 20B relative to each other in the radial direction of the laminate 11.

[0066] Furthermore, the tape moving means 52 includes a pair of abrasive tape pressing means 521 and a pair of abrasive tape running systems 522, which are positioned opposite each other so as to sandwich the laminate 11 from both sides via the abrasive tapes 20A and 20B.

[0067] The pair of abrasive tape pressing means 521 comprises a first abrasive tape pressing means 521A and a second abrasive tape pressing means 521B. The pair of abrasive tape running systems 522 comprises a first abrasive tape running system 522A and a second abrasive tape running system 522B.

[0068] In other words, the tape moving means 52 includes a first polishing tape traveling system 522A and a first polishing tape pressing means 521A arranged on one side of the laminate 11, and a second polishing tape traveling system 522B and a second polishing tape pressing means 521B arranged on the other side.

[0069] The first abrasive tape transport system 522A includes a supply roll and a winding roll (not shown), and first guide rolls 523A-1 to 523A-4 arranged below the supply roll and winding roll, and transports the abrasive tape 40A in the direction of arrow Ra.

[0070] The second abrasive tape transport system 522B includes a supply roll and a winding roll (not shown), and second guide rolls 523B-1 to 523B-4 arranged below the supply roll and winding roll, and transports the abrasive tape 40B in the direction of arrow Rb.

[0071] [Removal process] Next, as shown in Figure 2, the second lubricant 122 on the laminate 11 is removed (removal step).

[0072] The removal step includes irradiating the laminate 11, which has the first lubricant 121 and the second lubricant 122 applied to its surface, with ultraviolet light (hereinafter also referred to as the ultraviolet irradiation step) or heating the laminate 11 (hereinafter also referred to as the heating step). It is preferable that the removal step uses either the step of irradiating the laminate 11 with ultraviolet light or the step of heating the laminate 11. By irradiating the laminate 11 with ultraviolet light or heating the laminate 11, the second lubricant 122 on the laminate 11 is removed. As a result, the first lubricant 121 remains on the surface of the protective layer 113 of the laminate 11, and the remaining first lubricant 121 becomes the lubricating layer 12 of the magnetic recording medium 1.

[0073] In the removal process, it is preferable that the second lubricant 122 is completely removed, but some of it may remain.

[0074] In the ultraviolet irradiation process, known irradiation sources can be used. Examples of known irradiation sources include ultraviolet lamps and LED lamps.

[0075] The emission wavelength of the light emitted from these irradiation sources, as well as the emission output and irradiation time of these irradiation sources, are preferably selected appropriately under processing conditions that allow for the removal of the second lubricant 122, and also taking into consideration processing conditions that enhance the bonding strength of the first lubricant 121 to the protective layer 113. For example, if the irradiation source is an ultraviolet lamp, the emission wavelength is preferably appropriately selected from three types with peak wavelengths of 100-280 nm, 280-315 nm, and 315-400 nm. If the irradiation source is an LED lamp, since the emission wavelength is easy to control, it is preferable to appropriately design the system so that LED light with a desired emission wavelength is emitted from the LED lamp, depending on the type of lubricant used.

[0076] From the viewpoint of productivity of the magnetic recording medium 1, the irradiation time is preferably within 1 minute.

[0077] It is preferable to adjust the light output so that the processing is completed within the set irradiation time.

[0078] The ultraviolet irradiation process is preferably carried out in an inert gas atmosphere or a vacuum. If the ultraviolet irradiation process is carried out in the atmosphere, ozone may be generated, and the generated ozone may adversely affect the manufacturing of the magnetic recording medium 1. By carrying out the ultraviolet irradiation process in an inert gas atmosphere or a vacuum, the generation of ozone can be suppressed, and adverse effects on the manufacturing of the magnetic recording medium 1 can be minimized.

[0079] The heat treatment process can use known heat sources. Examples of known heat sources include halogen lamp heaters, ceramic heaters, resistance heaters, and LED lamp heaters. The heating temperature and heating time using these heat sources should be appropriately selected under treatment conditions that allow for the removal of the second lubricant 122, and it is preferable to select treatment conditions that also enhance the bonding strength of the first lubricant 121 to the protective layer 113.

[0080] In the heat treatment process, the heating time is preferably within 15 minutes from the perspective of the productivity of the magnetic recording medium 1, so it is preferable to adjust the heating time so that the process is completed within that time.

[0081] The heating temperature is preferably 120°C or lower, from the standpoint of ease of designing the heating device.

[0082] The heat treatment process is preferably carried out in an inert gas atmosphere. Depending on the heat source, a large amount of degassing may be released from the heat source, and this degassing may be incorporated into the laminate 11, potentially adversely affecting the manufacturing of the magnetic recording medium 1. By carrying out the heat treatment process in an inert gas atmosphere, the effects of degassing can be suppressed, and adverse effects on the manufacturing of the magnetic recording medium 1 can be minimized.

[0083] As described above, the method for manufacturing a magnetic recording medium according to this embodiment includes a coating step, a burning step, and a removal step. In the coating step, the average molecular weight of the first lubricant coated on the laminate 11 is higher than the average molecular weight of the second lubricant coated on top of the first lubricant, and the polarity of the first lubricant is higher than that of the second lubricant. The burning step includes pressing an abrasive tape 40 against the surface of the laminate 11 and rubbing it. The removal step includes an ultraviolet step of irradiating the laminate 11 coated with the first lubricant 121 and the second lubricant 122 with ultraviolet light, or a heat treatment step of heat treating the laminate 11 coated with the first lubricant 121 and the second lubricant 122. In the removal step, the second lubricant 122 can be removed by ultraviolet irradiation 31 or heat treatment 32, and the first lubricant 121 can be formed as a lubricating layer 12, thereby improving the coverage of the lubricating layer 12 on the laminate 11 and reducing the amount of foreign matter generated on the surface of the lubricating layer 12. Therefore, according to the manufacturing method of the magnetic recording medium according to this embodiment, foreign matter can be efficiently removed from the surface of the magnetic recording medium 1, and a magnetic recording medium with improved coverage by the lubricating layer 12 can be manufactured.

[0084] As described above, the magnetic recording medium 1 manufactured using the manufacturing method for magnetic recording media according to this embodiment has fewer foreign matter on its surface and the coverage rate by the lubricating layer 12 can be improved, thereby suppressing wear damage due to contact sliding with the magnetic head and increasing durability. The magnetic recording medium 1 can maintain excellent electromagnetic conversion characteristics and have a stable high recording density, so it can be suitably used in a magnetic recording and playback device. The form of the magnetic recording and playback device is not particularly limited as long as it has a magnetic recording medium manufactured using the manufacturing method for magnetic recording media according to this embodiment, and may be a magnetic recording and playback device that records magnetic information on a magnetic recording medium using a heat-assisted recording method.

[0085] In this embodiment, the magnetic recording medium may include one or more of the following between the substrate 111 and the magnetic recording layer 112: an adhesion layer, a soft magnetic underlayer, a seed layer, and an orientation control layer. One or more of these layers may be laminated together.

[0086] In this embodiment, the magnetic recording medium may include a plurality of stacked magnetic recording layers. In this case, non-magnetic recording layers may be stacked between the magnetic recording layers.

[0087] As described above, embodiments have been explained, but these embodiments are presented as examples only, and the present disclosure is not limited by these embodiments. The above embodiments can be implemented in various other forms, and various combinations, omissions, substitutions, and 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. [Examples]

[0088] The embodiments will be described in detail below based on examples, but the embodiments are not limited to these examples.

[0089] <Example 1> [Manufacturing of magnetic recording media] A cleaned glass substrate (manufactured by HOYA, 2.5 inches in diameter) is placed in the deposition chamber of a DC magnetron sputtering system (Anelva C-3040), and the ultimate vacuum level is 1 × 10⁻¹⁰. -5 The deposition chamber was evacuated until the temperature dropped to Pa. Then, a 10 nm thick adhesion layer was formed on the glass substrate using a Cr target via sputtering.

[0090] Next, a soft magnetic underlayer was formed on the adhesion layer by sputtering. The soft magnetic underlayer consisted of a first soft magnetic underlayer, an intermediate layer, and a second soft magnetic underlayer, formed in sequence. First, a first soft magnetic underlayer with a thickness of 25 nm was deposited using a target of Co-20Fe-5Zr-5Ta (Fe content 20 atoms, Zr content 5 atoms, Ta content 5 atoms, remainder Co) at a substrate temperature of 100°C or less. Next, an intermediate layer made of Ru with a thickness of 0.7 nm was formed. After that, a second soft magnetic underlayer made of Co-20Fe-5Zr-5Ta with a thickness of 25 nm was deposited.

[0091] Next, a seed layer with a thickness of 5 nm was formed on the soft magnetic underlayer using a Ni-6W {W content of 6 atoms, remainder Ni} target by sputtering.

[0092] Subsequently, a Ru layer with a thickness of 10 nm was deposited on the seed layer as a first orientation control layer using sputtering, with a sputtering pressure of 0.8 Pa.

[0093] Next, a Ru layer with a thickness of 10 nm was formed on the first orientation control layer as a second orientation control layer by sputtering, using a sputtering pressure of 1.5 Pa.

[0094] Next, a first magnetic recording layer consisting of 91(Co15Cr16Pt)-6(SiO2)-3(TiO2){an alloy with 15 atomic% Cr content, 16 atomic% Pt content, and the remainder being Co, comprising 91 mol%, 6 mol% SiO2, and 3 mol% TiO2} was formed on the second orientation control layer by sputtering, with a layer thickness of 9 nm. The sputtering pressure used here was 2 Pa.

[0095] Next, a non-magnetic layer consisting of 88(Co30Cr)-12(TiO2){88 mol% of an alloy with 30 atomic% Cr content and the remainder being Co, and 12 mol% TiO2} was formed on the first magnetic recording layer by sputtering, with a layer thickness of 0.3 nm.

[0096] Subsequently, a second magnetic recording layer consisting of 92(Co11Cr18Pt)-5(SiO2)-3(TiO2){an alloy with 11 atomic% Cr content, 18 atomic% Pt content, and the remainder being Co (92 mol%), 5 mol% SiO2, and 3 mol% TiO2} was formed on the non-magnetic layer by sputtering to a thickness of 6 nm. The sputtering pressure used here was 2 Pa.

[0097] Subsequently, a non-magnetic layer made of Ru with a thickness of 0.3 nm was formed on the second magnetic recording layer using the sputtering method.

[0098] Next, a third magnetic recording layer with a thickness of 7 nm was formed on the non-magnetic layer by sputtering using a target made of Co-20Cr-14Pt-3B {Cr content 20 atoms%, Pt content 14 atoms%, B content 3 atoms%, remainder Co} at a sputtering pressure of 0.6 Pa.

[0099] A carbon hydride film was formed on the surface of the third magnetic recording layer using ion beam deposition with gasified toluene as the source gas. To deposit the carbon hydride film, the gas flow rate of the source gas supplied to the deposition chamber was set to 2.9 SCCM, and the reaction pressure to 0.2 Pa. Furthermore, the cathode power, which is the excitation source for the source gas, was set to 225 W (AC 22.5 V, 10 A). Then, the voltage between the cathode electrode and the anode electrode covering it was set to 75 V, the current to 1650 mA, the ion acceleration voltage to 200 V, the current to 180 mA, and the deposition time to 1.5 seconds, resulting in a carbon hydride film with a thickness of 3.5 nm. After the formation of the carbon hydride film, the supply of the source gas was stopped, and the deposition chamber was evacuated for 2 seconds.

[0100] Next, nitrogen gas was supplied to the deposition chamber at a gas flow rate of 2 SCCM and a reaction pressure of 5 Pa. Then, the cathode power was set to 128 W (AC 16V, 8A), the voltage between the cathode and anode electrodes was 75 V, the current was 1000 mA, the ion acceleration voltage was 200 V, the current was 90 mA, and the processing time was 1 second. Nitrogen ions formed from nitrogen gas were irradiated onto the surface of the carbon hydride film, exposing it to nitrogen plasma. This dehydrogenated and nitrogenized the surface of the carbon hydride film, forming a nitrogenized carbon film as a protective layer.

[0101] Next, D5OH(XS) (trade name, manufactured by MORESCO Corporation), having the following structural formula (i), was dissolved in Bartrell XF (trade name, manufactured by Mitsui DuPont Fluorochemicals Corporation), a solvent, to obtain the first lubricating layer forming solution. The concentration of the compound in the first lubricating layer forming solution was 0.3% by mass. The amount of the first lubricating agent (a) dissolved in Bartrell XF was 6.4 g / L.

[0102] [ka] (In structural formula (i), m is a positive integer.)

[0103] Next, the first lubrication layer forming solution was applied to the protective layer using the dip method. Specifically, the laminate, with each layer up to the protective layer formed, was immersed in the first lubrication layer forming solution placed in the immersion tank of the dip coating apparatus, and then the laminate was withdrawn from the immersion tank at a constant speed. In this way, the first lubrication layer forming solution was applied to the surface on the protective layer so that the thickness of the first lubrication layer was 7 Å. Subsequently, the first lubrication layer was formed on the surface of the laminate by drying the surface to which the first lubrication layer forming solution had been applied.

[0104] Next, the second lubricant (b) of the following structural formula (ii) was dissolved in the solvent HFE7200 (trade name, manufactured by 3M Corporation) to obtain a second lubricating layer forming solution. The concentration of the compound contained in the second lubricating layer forming solution was 0.3% by mass.

[0105] Note that the solubility of the second lubricant (b) in structural formula (ii) below in HFE7200 is greater than 10 g / L, while the solubility of the first lubricant (a) in structural formula (i) above in HFE7200 is 0.4 g / L. Here, the lubricant concentration in the solution when forming a lubricating layer on a laminate using the dip method or spin coating method is usually considerably lower than 1 mass%. Therefore, for solvents in which the lubricant solubility exceeds 10 g / L (the lubricant concentration is approximately 1 mass%), it is uniformly indicated as >10 (g / L) in Table 1. For solvents in which the lubricant solubility exceeds 10 g / L, the solubility of the lubricant can be considered to be substantially equal.

[0106] [ka] (In structural formula (ii), m is a positive integer.)

[0107] Next, the second lubricant (b) was applied to the surface of the laminate on which the first lubricating layer had been formed using the dip method. The thickness of the second lubricating layer was set to 7 Å. Subsequently, the second lubricating layer was formed on the surface of the laminate on which the first lubricating layer had been formed by drying the surface on which the second lubricating layer-forming solution had been applied.

[0108] Next, the surface of the laminate, on which the first and second lubrication layers were formed, was varnished using a polishing tape. The polishing tape used was Sumitomo 3M Co., Ltd.'s model DQ3, which uses Al2O3 with a particle size of 0.3 μm as the abrasive material. The varnishing conditions were a rotation speed of 1000 rpm for the laminate and a processing time of 3 seconds.

[0109] Next, the surface of the laminate on which the first and second lubricating layers were formed was irradiated with ultraviolet light. An ultraviolet lamp manufactured by Ushio Inc. was used for the irradiation, and the irradiation time was 10 seconds in a nitrogen gas atmosphere.

[0110] Next, the surface of the laminate on which the first and second lubricating layers were formed was heat-treated. The heat treatment was performed in a nitrogen gas atmosphere at 120°C for 1200 seconds. By heat-treating the surface of the laminate on which the first and second lubricating layers were formed, the second lubricating layer was removed from the surface of the first lubricating layer, and a new lubricating layer was formed from the first lubricating layer.

[0111] As a result, a magnetic recording medium was manufactured by laminating an adhesion layer, a soft magnetic underlayer, a seed layer, a first orientation control layer, a second orientation control layer, a first magnetic recording layer, a non-magnetic recording layer, a second magnetic recording layer, a non-magnetic recording layer, a third magnetic recording layer, a nitrogenized carbon film (protective layer), and a lubricating layer on both sides of a glass substrate in this order.

[0112] [Evaluation of the lubrication layer] The laminated material, after UV irradiation and heat treatment, was analyzed using ESCA and confirmed that the first lubricating layer with a thickness of 7 Å remained, while the second lubricating layer had been removed.

[0113] (Coverage of the lubricating layer) The coverage of the lubricating layer on the fabricated magnetic recording medium was measured. The coverage was determined by immersing the magnetic recording medium, after the lubricating layer had been formed, in a fluorocarbon solvent for 5 minutes, and measuring the difference between 1270 cm² and the same location on the same medium before and after immersion. -1 The absorbance in the vicinity was measured using ESCA, and the ratio was calculated as a percentage ((absorbance after immersion / absorbance before immersion) × 100 [%]). Bartrell XF (trade name, manufactured by Mitsui DuPont Fluorochemicals) was used as the fluorocarbon solvent. The coverage rate of the lubricating layer of the fabricated magnetic recording medium was 80%.

[0114] (TA (Thermal Asperity) Glide Evaluation) TA glide evaluation was performed on the fabricated magnetic recording media. An MR head (manufactured by TDK Corporation) was used as the inspection head for the TA glide evaluation. TA glide evaluation is a method that detects thermal asperities (TA), which are phenomena in which the signal waveform reproduced by the MR head fluctuates due to frictional heat generated when the MR head collides with protrusions on the surface of the magnetic recording media. The smoothness of the surface of the magnetic recording media is evaluated from the number of such signals (TA count). A smaller TA count indicates higher surface smoothness of the magnetic recording media. The average TA count for 100 fabricated magnetic recording media was 7 per surface.

[0115] Table 1 shows the conditions for preparing the first and second lubricating layers, and Table 2 shows the processing conditions for the first and second lubricating layers and the evaluation results of the lubricating layers.

[0116] <Examples 2-11, Comparative Examples 1 and 2> A magnetic recording medium was manufactured and evaluated in the same manner as in Example 1, except that the manufacturing conditions for the first and second lubricating layers and the processing conditions for the first and second lubricating layers were changed to the values ​​shown in Tables 1 and 2. The manufacturing conditions for the first and second lubricating layers are shown in Table 1, and the processing conditions for the first and second lubricating layers and the evaluation results of the lubricating layers are shown in Table 2.

[0117] Furthermore, the D4OH and D4OH(s) (both trade names, manufactured by MORESCO Corporation) used as the first lubricant (a) and second lubricant (b) in Examples 2 to 11 and Comparative Examples 1 and 2 have the following structural formula (iii) and structural formula (iv) is as shown below. The average molecular weight of D4OH was adjusted to be 2000, and the average molecular weight of D4OH(s) was adjusted to be 1600.

[0118] Structural formulas of D4OH and D4OH(s): CH2(OH)CH(OH)CH2OCH2CF2CF2(OCF2CF2CF2) m OCF2CF2CH2OCH2CH(OH)CH2OH ···(iii) (In structural formula (iii), m is a positive integer.)

[0119] Structural formula (iv): [ka]

[0120] In the AS300 (manufactured by AGC Inc.) used as the solvent for the second lubricant (b), the solubility of the first lubricant (a) and the second lubricant (b) in AS300 was greater than 10 g / L, and the solubility of the first lubricant (a) and the second lubricant (b) in AS300 was substantially equal. Similarly, in the AK225 (manufactured by Asahi Clean Co., Ltd.) used as the solvent for the second lubricant (b), the solubility of the first lubricant (a) and the second lubricant (b) in AK225 was greater than 10 g / L, and the solubility of the first lubricant (a) and the second lubricant (b) in AK225 was substantially equal. In Comparative Examples 1 and 2, the TA glide evaluation could not be performed because no lubrication layer remained after UV irradiation and heat treatment.

[0121] [Table 1]

[0122] [Table 2]

[0123] Tables 1 and 2 show that in each embodiment, the coverage rate of the lubricating layer was 74% or more, and the TA count was 15 or less. On the other hand, in each comparative example, the coverage rate of the lubricating layer was 0%, and the TA count could not be evaluated. Therefore, it can be said that by using the manufacturing method of the magnetic recording medium according to this embodiment, removing the second lubricant by irradiation with ultraviolet light or heat treatment, and forming a lubricating layer consisting of the first lubricant, a magnetic recording medium can be obtained that efficiently removes foreign matter from the surface of the magnetic recording medium and improves the coverage rate by the lubricating layer. [Explanation of Symbols]

[0124] 1 Magnetic recording medium 11 Laminated body (laminated body) 12 Lubricating layer 20, 20A, 20B abrasive tapes 21 Support 22 Abrasive layer 31. Ultraviolet irradiation 32 Heat treatment 111 circuit board 112 Magnetic recording layer 113 Protective layer 121 First Lubricant 122 Second lubricant 221 abrasive grains 222 Binder 50 Burnishing Machine 521 Pair of abrasive tape pressing means 522 A pair of abrasive tape transport systems 521A First polishing tape pressing means 521B Second polishing tape pressing means 522A First polishing tape transport system 522B Second polishing tape transport system S polished surface

Claims

1. A method for manufacturing a magnetic recording medium, comprising forming a lubricating layer on a laminate in which a magnetic recording layer and a protective layer are stacked on a substrate in that order, The process involves applying a first lubricant and a second lubricant onto the laminate, A step of burning the surface of the laminate to which the first lubricant and the second lubricant have been applied with an abrasive, A step of removing the second lubricant from the laminate, Includes, The step of applying the second lubricant is performed using either a dip method or a spin coat method. The solvent for the second lubricant used in the dip method or the spin coating method is configured such that the amount of the second lubricant dissolved is higher than the amount of the first lubricant dissolved. The burning step includes pressing a tape containing an abrasive material against the surface of the laminate and rubbing it, A method for manufacturing a magnetic recording medium, comprising the step of removing the second lubricant, which includes the step of irradiating the laminate coated with the first lubricant and the second lubricant with ultraviolet light, or the step of heat-treating the laminate coated with the first lubricant and the second lubricant.

2. The method for manufacturing a magnetic recording medium according to claim 1, wherein the second lubricant has an average molecular weight of 300 to 1000 and contains two or fewer polar groups, or does not contain any.

3. The method for manufacturing a magnetic recording medium according to claim 1 or 2, wherein the first lubricant has an average molecular weight of 900 to 3000 and contains 4 to 8 polar groups.

4. A method for manufacturing a magnetic recording medium according to claim 1 or 2, wherein the film thickness of the first lubricant applied to the laminate is 5 to 10 Å, and the film thickness of the second lubricant is 5 to 20 Å.

5. The method for manufacturing a magnetic recording medium according to claim 1 or 2, wherein the step of irradiating with ultraviolet light is performed in an inert gas atmosphere or in a vacuum.

6. The method for manufacturing a magnetic recording medium according to claim 1 or 2, wherein the heat treatment step is performed in an inert gas atmosphere.

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