Manufacturing method of magnetic recording medium

Abstract

To provide a manufacturing method for a magnetic recording medium that can efficiently remove extraneous matter from the surface of the magnetic recording medium and has a high coverage rate of a lubricant layer.SOLUTION: A manufacturing method for a magnetic recording medium according to the present invention is a manufacturing method for a magnetic recording medium forming a lubricant layer on a laminate body, including: a step of applying a first lubricant and a second lubricant to the laminate body; a step of burnishing the surface of the laminate body to which the first lubricant and the second lubricant are applied with an abrasive; and a step of removing the second lubricant on the laminate body, in which the average molecular weight of the first lubricant is higher than that of the second lubricant, the polarity of the first lubricant is higher than that of the second lubricant, the step of burnishing includes a step of pressing a tape including the abrasive against the surface of the laminate and rubbing it, and the step of removing the second lubricant includes a step of irradiating the laminate body coated with the first lubricant and the second lubricant with ultraviolet light or a step of heat-treating the laminate body coated with the first lubricant and the second lubricant.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] In recent years, magnetic storage devices have been installed in various products such as personal computers, video recorders, and data servers, 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).

[0003] A general magnetic recording medium has, for example, a multilayer film stack 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 a light irradiation treatment using an ultraviolet lamp is further performed.

[0005] In addition, 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] Further, Patent Document 2 discloses a method for manufacturing a magnetic recording medium in which, after forming a protective layer, a first lubricant having no terminal group is applied to the surface thereof, tape burnishing is performed, the first lubricant is then removed with a solvent, and a second lubricant having a terminal group is applied.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] In the manufacture of a magnetic recording medium, by performing tape burnishing after forming a lubricating layer, the lubricity of the lubricating layer can reduce the occurrence of scratch marks and the like. However, depending on the lubricant and film thickness used for the lubricating layer, it may not be suitable for tape burnishing.

[0009] It is also conceivable to perform processing using a first lubricant suitable for tape burnishing as in the method for manufacturing a magnetic recording medium of Patent Document 2, and then remove this, and apply a second lubricating layer suitable for the magnetic recording medium. However, in this case, there are the following problems. That is, contaminants and lubricants dissolved in the solvent used for removing the lubricant reattach to the processing substrate, causing foreign matter on the surface of the magnetic recording medium. Also, it is difficult to completely remove the lubricant bonded to the protective layer using a solvent, and the remaining solvent causes foreign matter on the surface of the magnetic recording medium, and also reduces the coverage rate of the surface of the magnetic recording medium by the lubricating layer, and complicates the manufacturing process of the magnetic recording medium.

[0010] The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for manufacturing a magnetic recording medium capable of efficiently removing foreign matter on the surface of the magnetic recording medium and having a high coverage rate by a lubricating layer.

Means for Solving the Problems

[0011] The present invention has the following configuration. [1] A method for manufacturing a magnetic recording medium in which a lubricating layer is formed on a laminate in which a magnetic recording layer and a protective layer are laminated in this order on a substrate, a step of applying a first lubricant and a second lubricant on the laminate; a step of burnishing the surface of the laminate coated with the first lubricant and the second lubricant with an abrasive; a step of removing the second lubricant on the laminate; including, the average molecular weight of the first lubricant is higher than the average molecular weight of the second lubricant, the polarity of the first lubricant is higher than the polarity of the second lubricant, the burnishing step includes a step of pressing and rubbing a tape containing an abrasive against the surface of the laminate; the step of removing the second lubricant includes a step of irradiating the laminate coated with the first lubricant and the second lubricant with ultraviolet rays, or a step of heat-treating the laminate coated with the first lubricant and the second lubricant. A method for manufacturing a magnetic recording medium. [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 has two or less polar groups, or does not contain any 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 has 4 to 8 polar groups. [4] The 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 Å to 10 Å, and the film thickness of the second lubricant is 5 Å 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 ultraviolet rays is performed in an inert gas atmosphere or in a vacuum. [6] The step of performing the heat treatment is carried out in an inert gas atmosphere, and is the method for manufacturing a magnetic recording medium according to any one of [1] to [5]. [Advantages of the Invention]

[0012] According to one aspect of the present invention, foreign substances on the surface of the magnetic recording medium can be efficiently removed, and the coverage rate by the lubricating layer can be increased. [Brief Description of the Drawings]

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

[0014] Hereinafter, embodiments of the present invention 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 duplicate descriptions are omitted as appropriate. Also, 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.

[0015] Hereinafter, a method for manufacturing a magnetic recording medium according to an embodiment of the present invention will be described. A magnetic recording medium manufactured by the method for manufacturing a magnetic recording medium according to this embodiment will be described.

[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 the present 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 layer to be laminated).

[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, a metal substrate formed of a metal material such as an aluminum alloy may be used, or 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 surfaces of these metal substrates and 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] For the magnetic recording layer 112, an FePt-based alloy having an L10 structure, a CoPt-based alloy having an L10 structure, a CoCrPt-based alloy, etc. are used.

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

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

[0023] The protective layer 113 can be formed of a well-known material. For example, a hard carbon film or diamond-like carbon (DLC) is used.

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

[0025] The surface of the protective layer 113 may be hydrogenated or nitrided. By hydrogenating or nitriding the surface of the protective layer 113, the bonding force with the lubricating layer 12 formed thereon can be enhanced. 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 to nitride the surface of the protective layer 113.

[0026] The lubricating layer 12 is provided to suppress wear on the surfaces of the magnetic head and the magnetic recording medium 1 when the magnetic head contacts the magnetic recording medium 1 and to enhance the corrosion resistance of the magnetic recording medium 1.

[0027] The thickness of the lubricating layer 12 is preferably 5 Å to 10 Å. By setting the thickness of the lubricating layer 12 to 5 Å to 10 Å, wear on the surface of the magnetic recording medium 1 can be suppressed, the corrosion resistance of the magnetic recording medium 1 can be enhanced, 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 of magnetic recording medium] The manufacturing method of the magnetic recording medium according to this embodiment includes a step of forming a laminate 11 in which a magnetic recording layer 112 and a protective layer 113 are laminated in this order on both surfaces of a substrate 111 (laminate forming step), a step of applying a first lubricant 121 and a second lubricant 122 on the laminate 11 (coating step), a step of burnishing the surface of the laminate 11 coated with the first lubricant 121 and the second lubricant 122 with an abrasive (burnishing step), and a step of removing the second lubricant 122 on the laminate 11 (removing step). The manufacturing method of the magnetic recording medium according to this embodiment may include other steps such as a step of 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. Further, when the magnetic recording medium according to this embodiment includes a plurality of laminated magnetic recording layers 112, the manufacturing method may include a step of forming a non-magnetic recording layer between the magnetic recording layers 112 and the like.

[0029] In the manufacturing method of the magnetic recording medium according to this embodiment, first, a laminate 11 in which a magnetic recording layer 112 and a protective layer 113 are laminated in this order on both surfaces of a prepared substrate 111 is formed (laminate forming step).

[0030] The laminate 11 can be formed using a general film forming method for the magnetic recording layer 112 and the protective layer 113.

[0031] First, the magnetic recording layer 112 is formed on both surfaces of the substrate 111. As a method for forming the magnetic recording layer 112, a general film forming method such as a sputtering method (sputter method) can be used.

[0032] In the sputtering method, a target containing a material for forming the magnetic recording layer 112 can be used.

[0033] As a target containing a 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, a CoCrPt-based alloy, etc. can be used.

[0034] As the sputtering method, a DC sputtering method, a DC magnetron sputtering method, an RF sputtering method, etc. can be used.

[0035] When forming the magnetic recording layer 112, if necessary, an RF (Radio Frequency) bias, a DC bias, a pulsed DC, a pulsed DC bias, etc. may be used.

[0036] As the reactive gas, an O2 gas, an H2O gas, an N2 gas, etc. may be used.

[0037] The sputtering gas pressure is appropriately adjusted so that the characteristics of each layer are optimized, but it is usually in the range of about 0.1 Pa to 30 Pa.

[0038] 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. For example, an RF-CVD (Radio Frequency-Chemical Vapor Deposition) method in which a source gas composed of a hydrocarbon is decomposed by high-frequency plasma for film formation, an IBD (Ion Beam Deposition) method in which a source gas is ionized by electrons emitted from a filament for film formation, a general film formation method such as an FCVA (Filtered Cathodic Vacuum Arc) method in which a solid carbon target is used for film formation without using a source gas can be used.

[0039] Next, a first lubricant 121 and a second lubricant 122 are applied onto the laminate 11 (coating step). An example of the method for forming the lubricating layer 12 will be described with reference to FIG. 2.

[0040] After applying the first lubricant 121 and the second lubricant 122 onto the laminate 11 in which the magnetic recording layer 112 and the protective layer 113 are laminated in this order on both surfaces of the substrate 111, the surface of the laminate 11 is burnished with an abrasive 21. Then, the second lubricant 122 on the laminate 11 is removed by ultraviolet irradiation 31 or heat treatment 32. Thereby, the first lubricant 121 forms the lubricating layer 12 of the magnetic recording medium 1.

[0041] That is, after applying the first lubricant 121 and the second lubricant 122 to the surface of the laminate 11, in the step of performing ultraviolet irradiation 31 or heat treatment 32, since the second lubricant 122 is removed, the first lubricant 121 remains on the surface of the protective layer 113. When the first lubricant 121 is applied onto the protective layer 113, ideally, it is preferable that the entire surface of the protective layer 113 is covered by the first lubricant 121, but a part of the surface of the protective layer 113 may remain uncoated. In that location, the second lubricant 122 may be applied.

[0042] Also, in the step of performing ultraviolet irradiation 31 or heat treatment 32, it is preferable that the second lubricant 122 is completely removed, but a part of it may remain.

[0043] In the present embodiment, ultraviolet irradiation 31 or heat treatment 32 is used to remove the second lubricant 122. As described above, the removal of the lubricant used in the burnishing process has conventionally been performed by washing with a solvent. However, according to the study by the present inventors, in the solvent used for washing, in addition to the lubricant to be removed, contaminants generated during burnishing are also dissolved, and since the solvent remains on the surface to be washed for a while, it has been clarified that the contaminants and the lubricant reattach to the substrate to be processed, which causes foreign matter on the surface of the magnetic recording medium. Also, it has been clarified that it is difficult to completely remove the lubricant bonded to the protective layer by solvent washing, and the slightly remaining lubricant causes the generation of foreign matter on the surface of the magnetic recording medium.

[0044] In this embodiment, since the removal of the second lubricant 122 on the laminate 11 is performed by ultraviolet irradiation 31 or heat treatment 32, that is, a dry process, the second lubricant 122 or the contaminants dissolved therein are quickly gasified and separated from the surface of the laminate 11, so they do not cause foreign matter on the surface of the magnetic recording medium. Further, by setting the conditions of the ultraviolet irradiation 31 or the heat treatment 32 to conditions that can gasify the second lubricant 122, the second lubricant 122 on the laminate 11 can be completely removed. In addition, since the formation process of the lubricating layer 12 is simple, a manufacturing method of a highly productive magnetic recording medium can be provided.

[0045] 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.

[0046] The organic compound used as the lubricant contains, as functional groups, a hydroxyl group, an amino group, an amide group, a carbonyl group, a carboxyl group, a cyano group, a phenyl group, a methyl group, etc. Among these, the functional groups having polarity (polar groups) are a hydroxyl group, an amino group, an amide group, a carbonyl group, a carboxyl group, and a cyano group.

[0047] The average molecular weight of the first lubricant 121 is preferably 900 to 3000, and the number of polar groups contained in the structural formula of the first lubricant 121 is preferably 4 to 8.

[0048] The average molecular weight of the second lubricant 122 is preferably 300 to 1000, and the number of polar groups contained in the structural formula of the second lubricant 122 is preferably 2 or less, or not contained.

[0049] As the polar groups of the first lubricant 121 and the second lubricant 122, a hydroxyl group, an amide group, and a cyano group are preferable, and among these, a hydroxyl group is particularly preferable. By having the above-mentioned preferable polar groups, the first lubricant 121 can be made suitable for the lubricating layer 12 of the magnetic recording medium 1, and the second lubricant 122 can be made suitable for the burnishing of the surface of the laminate 11. When performing the above-mentioned ultraviolet irradiation 31 or heat treatment 32, the effect of quickly removing the second lubricant 122 or the contaminants dissolved therein is enhanced. In addition, since the first lubricant 121 can be left on the laminate 11 to increase the bonding strength between the protective layer 113 and the first lubricant 121, foreign matters on the surface can be further reduced, and the coverage rate of the magnetic recording medium 1 by the lubricating layer 12 can be further increased.

[0050] For the application of the first lubricant 121 and the second lubricant 122, known methods such as a dip method, a spin coating method, and a vapor method can be used. The dip method is a method of forming a lubricant film on the surface of the laminate 11 by immersing the laminate 11 in a liquid in which the lubricant is dissolved and then pulling up the laminate 11 at a constant speed. The spin coating method is a method of forming a lubricant film on the laminate 11 by applying a liquid in which the lubricant is dissolved to the surface of the laminate 11 and then rotating the laminate 11 at a high speed for a certain period of time. The vapor method is a method of forming a lubricant film on the laminate 11 by placing the laminate 11 in a vacuum container and introducing a lubricant gasified by heating into the vacuum container.

[0051] When using the dip method or the spin coating method for the application of the second lubricant 122, the solvent for dissolving the second lubricant needs to be selected from a solvent that does not dissolve the first lubricant 121, a solvent that is difficult to dissolve, or a solvent that leaves a certain film thickness even when dissolved.

[0052] The first lubricant 121 will form the lubricating layer 12 of the magnetic recording medium 1. Therefore, the film thickness of the first lubricant 121 is preferably 5 Å to 10 Å from the viewpoints of suppressing wear on the surface of the magnetic recording medium 1, improving the corrosion resistance of the magnetic recording medium 1, and shortening the distance between the magnetic head and the magnetic recording medium 1 in the HDD to achieve a high recording density.

[0053] The film thickness of the second lubricant 122 is preferably 5 Å to 20 Å. If the film thickness of the second lubricant 122 is 5 Å to 20 Å, it can be made suitable for burnishing the surface of the laminate 11. In addition, since the second lubricant 122 can be removed in a short time by ultraviolet irradiation 31 or heat treatment 32, the productivity of the magnetic recording medium 1 can be increased.

[0054] In the step of burnishing the laminate 11 with the abrasive 21, a method of pressing and rubbing a tape (abrasive tape) containing the abrasive 21 against the surface of the laminate 11 can be used. The burnishing method and the burnishing apparatus will be described in detail with reference to the drawings.

[0055] FIG. 3 is an enlarged cross-sectional view showing an example of the abrasive tape 40 used for burnishing. As shown in FIG. 3, the abrasive tape 40 polishes the laminate 11 by sliding the polishing surface S against the surface of the laminate 11.

[0056] The abrasive tape 40 has an abrasive layer 42 on a support 41. The abrasive layer 42 has abrasive grains 421 and a binder 422 that binds the abrasive grains 421 to each other and binds the abrasive grains 421 to the support 41 to fix the abrasive grains 421 to the abrasive layer 42.

[0057] The material constituting the support 41 is not particularly limited, and various resins such as polyethylene terephthalate are used.

[0058] The abrasive grains 421 can be used as the abrasive 21 contained in the polishing tape 40. Examples of the abrasive grains 421 include particles having chromium oxide, α-alumina, silicon carbide, non-magnetic iron oxide, diamond, γ-alumina, α,γ-alumina, fused alumina, corundum, synthetic diamond, and the like. The abrasive grains 421 may be particles made of these materials. These may be appropriately combined singly or in two or more kinds.

[0059] The binder 422 is not particularly limited, and for example, a thermosetting resin, a thermoplastic resin, a photosensitive resin, etc. can be used. The resin used as the binder 422 may be used singly or in combination of two or more kinds.

[0060] Also, a lubricating film 43 may be provided on the surface of the polishing surface S.

[0061] FIG. 4 is a diagram showing an example of a burnishing apparatus used in the step of burnishing the surface of the laminate 11 with the abrasive 21. As shown in FIG. 4, the burnishing apparatus 50 includes a pair of polishing tapes 40 (polishing tapes 40A and 40B) arranged to face each other so as to sandwich the laminate 11 from both sides, a rotation support means 51, and a tape movement means 52. In the burnishing apparatus 50, the polishing tapes 40A and 40B are arranged to face each other so as to sandwich the laminate 11 from both sides, and efficient burnishing can be performed on both surfaces of the laminate 11 simultaneously.

[0062] The rotation support means 51 rotates the laminate 11 in the circumferential direction (arrow r direction) while supporting the central opening of the laminate 11.

[0063] The tape movement means 52 relatively moves the polishing tapes 40A and 40B in the radial direction of the laminate 11 while pressing the polishing tapes 40A and 40B against both surfaces of the rotated laminate 11 in the direction of arrow F.

[0064] Further, the tape moving means 52 includes a pair of polishing tape pressing means 521 and a pair of polishing tape running systems 522 that are arranged to face each other so as to sandwich the laminate 11 from both sides via the polishing tapes 40A and 40B.

[0065] The pair of polishing tape pressing means 521 includes a first polishing tape pressing means 521A and a second polishing tape pressing means 521B. The pair of polishing tape running systems 522 includes a first polishing tape running system 522A and a second polishing tape running system 522B.

[0066] That is, the tape moving means 52 includes a first polishing tape running system 522A and a first polishing tape pressing means 521A disposed on one side with the laminate 11 interposed therebetween, and a second polishing tape running system 522B and a second polishing tape pressing means 521B disposed on the other side.

[0067] The first polishing tape running system 522A includes a supply roll and a take-up roll (not shown), and first guide rolls 523A-1 to 523A-4 disposed below the supply roll and the take-up roll, and runs the polishing tape 40A in the direction of arrow Ra.

[0068] The second polishing tape running system 522B includes a supply roll and a take-up roll (not shown), and second guide rolls 523B-1 to 523B-4 disposed below the supply roll and the take-up roll, and runs the polishing tape 40B in the direction of arrow Rb.

[0069] In the present invention, the step of removing the second lubricant 122 from the laminate 11 uses a step of irradiating the laminate 11 with ultraviolet rays or a step of heat-treating the laminate 11.

[0070] For the step of irradiating the laminate 11 with ultraviolet rays, a known irradiation source can be used. Examples of the known irradiation source include an ultraviolet lamp or an LED lamp. The emission wavelength, emission output, and irradiation time used for these lamps are appropriately selected under the processing conditions that can remove the second lubricant 122. Furthermore, it is preferable to consider the processing conditions that enhance the bonding strength of the first lubricant 121 to the protective layer 113. Specifically, for the ultraviolet lamp, it is preferable to appropriately select from three types with peak wavelengths of 100 nm to 280 nm, 280 nm to 315 nm, and 315 nm to 400 nm. Also, for the LED lamp, since the control of the emission wavelength is easy, the LED lamp can be designed according to the type of lubricant used, which is preferable.

[0071] The irradiation time is preferably within 1 minute from the viewpoint of the productivity of the magnetic recording medium. Therefore, it is preferable to adjust the emission output so that the treatment is completed within that time.

[0072] Also, if the step of irradiating with ultraviolet rays is performed in the air, ozone is generated, which may have an adverse effect on the production of the magnetic recording medium. Therefore, in order to suppress the generation of ozone, the step of irradiating with ultraviolet rays is preferably performed in an inert gas atmosphere or in a vacuum.

[0073] For the step of heat-treating the laminate 11, a known heat source can be used. Examples of the known heat source include a halogen lamp heater, a ceramics heater, a resistance heating heater, and an LED lamp heater. The heating temperature and heating time by these heat sources are appropriately selected under the processing conditions that can remove the second lubricant 122. Furthermore, it is preferable to consider the processing conditions that enhance the bonding strength of the first lubricant 121 to the protective layer 113.

[0074] The heating time is preferably within 15 minutes in view of the productivity of the magnetic recording medium, and thus it is preferable to adjust the heating time so that the treatment is completed within that time. From the viewpoint of ease of design of the heating device, the heating temperature is preferably 120°C or lower. Also, depending on the heat source, there may be a large amount of degassing released from the heat source, and the degassing may be incorporated into the laminate 11, which may have an adverse effect on the production of the magnetic recording medium. In order to suppress the influence of degassing, the heat treatment step is preferably performed in an inert gas atmosphere.

[0075] Thus, the method for manufacturing a magnetic recording medium according to this embodiment includes a coating step, a burnishing step, and a removal step. In the coating step, the average molecular weight of the first lubricant applied onto the laminate 11 is higher than the average molecular weight of the second lubricant applied onto the first lubricant, and the polarity of the first lubricant is higher than the polarity of the second lubricant. The burnishing step includes a step of pressing and rubbing the polishing tape 40 against the surface of the laminate 11. The removal step includes an ultraviolet ray step of irradiating ultraviolet rays onto the laminate 11 coated with the first lubricant 121 and the second lubricant 122 or a heat treatment step of heat-treating the laminate 11 coated with the first lubricant 121 and the second lubricant 122. Since the removal step can remove the second lubricant 122 by ultraviolet irradiation 31 or heat treatment 32 and form the first lubricant 121 as the lubricating layer 12, it is possible to increase the coverage rate of the lubricating layer 12 on the laminate 11 and reduce the amount of foreign matter generated on the surface of the lubricating layer 12. Therefore, according to the method for manufacturing a magnetic recording medium according to this embodiment, foreign matter on the surface of the magnetic recording medium 1 can be efficiently removed, and a magnetic recording medium with a high coverage rate by the lubricating layer 12 can be manufactured.

[0076] The magnetic recording medium 1 manufactured using the method for manufacturing a magnetic recording medium according to this embodiment has, as described above, few foreign substances on the surface of the magnetic recording medium 1 and a high coverage rate by the lubricating layer 12. Therefore, wear damage due to contact sliding with the magnetic head is suppressed, and the durability can be enhanced. The magnetic recording medium 1 can maintain excellent electromagnetic conversion characteristics and can stably have a high recording density, and thus can be suitably used in a magnetic recording and reproducing apparatus. The form of the magnetic recording and reproducing apparatus is not particularly limited as long as it has a magnetic recording medium manufactured using the method for manufacturing a magnetic recording medium according to this embodiment, and it may be a magnetic recording and reproducing apparatus that records magnetic information on the magnetic recording medium using a heat assist recording method or the like.

[0077] Note that in this embodiment, the magnetic recording medium may include one or more of an adhesion layer, a soft magnetic underlayer, a seed layer, and an orientation control layer between the substrate 111 and the magnetic recording layer 112. Any of these layers may be laminated one or more times.

[0078] In this embodiment, the magnetic recording medium may include a plurality of magnetic recording layers laminated. At this time, a non-magnetic recording layer may be laminated between the magnetic recording layers.

[0079] As described above, the embodiments have been described, but the above embodiments are presented as examples, and the present invention is not limited by the above embodiments. The above embodiments can be implemented in various other forms, and various combinations, omissions, replacements, changes, etc. can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalent scope thereof.

Example

[0080] Hereinafter, this embodiment will be specifically described based on examples, but this embodiment is not limited by these examples.

[0081] <Example 1> [Manufacture of Magnetic Recording Medium] A cleaned glass substrate (manufactured by HOYA, with an outer dimension of 2.5 inches) was placed in the film deposition chamber of a DC magnetron sputtering apparatus (C-3040 manufactured by Anelva), and the film deposition chamber was evacuated until the ultimate vacuum reached 1×10 -5 Pa. Then, a 10-nm thick adhesion layer was formed on the glass substrate using a Cr target by sputtering method.

[0082] Next, a soft magnetic underlayer was formed on the adhesion layer by sputtering method. As the soft magnetic underlayer, a first soft magnetic recording layer, an intermediate layer, and a second soft magnetic recording layer were formed in sequence. First, using a target of Co-20Fe-5Zr-5Ta {Fe content 20 at%, Zr content 5 at%, Ta content 5 at%, the balance Co} at a substrate temperature of 100 °C or lower, a first soft magnetic recording layer with a layer thickness of 25 nm was deposited. Next, an intermediate layer consisting of Ru with a layer thickness of 0.7 nm was formed. Then, a second soft magnetic recording layer consisting of Co-20Fe-5Zr-5Ta with a layer thickness of 25 nm was deposited.

[0083] Next, a 5-nm thick seed layer was formed on the soft magnetic underlayer using a Ni-6W {W content 6 at%, the balance Ni} target by sputtering method.

[0084] After that, on the seed layer, as the first orientation control layer, a Ru layer with a layer thickness of 10 nm was deposited at a sputtering pressure of 0.8 Pa by sputtering method. Next, on the first orientation control layer, as the second orientation control layer, a Ru layer with a layer thickness of 10 nm was formed at a sputtering pressure of 1.5 Pa by sputtering method.

[0085] Subsequently, by sputtering method, a first magnetic recording layer consisting of 91(Co15Cr16Pt)-6(SiO2)-3(TiO2) {an alloy of Cr content 15 at%, Pt content 16 at%, the balance Co of 91 mol%, SiO2 of 6 mol%, and TiO2 of 3 mol%} was formed on the second orientation control layer to a layer thickness of 9 nm. The sputtering pressure here was set to 2 Pa.

[0086] Next, by means of sputtering, a non-magnetic recording layer composed of 88(Co30Cr)-12(TiO2) {an alloy with 30 atomic% Cr content, the balance being Co, 88 mol%, and TiO2 12 mol%} was formed on the first magnetic recording layer to a layer thickness of 0.3 nm.

[0087] Thereafter, by means of sputtering, a second magnetic recording layer composed of 92(Co11Cr18Pt)-5(SiO2)-3(TiO2) {an alloy with 11 atomic% Cr content, 18 atomic% Pt content, the balance being Co, 92 mol%, SiO2 5 mol%, and TiO2 3 mol%} was formed on the non-magnetic recording layer to a layer thickness of 6 nm. The sputtering pressure here was 2 Pa.

[0088] Thereafter, by means of sputtering, a non-magnetic recording layer made of Ru was formed on the second magnetic recording layer to a layer thickness of 0.3 nm.

[0089] Next, by means of sputtering, using a target composed of Co-20Cr-14Pt-3B {20 atomic% Cr content, 14 atomic% Pt content, 3 atomic% B content, the balance being Co}, the third magnetic recording layer was formed to a layer thickness of 7 nm with a sputtering pressure of 0.6 Pa.

[0090] On the surface of the third magnetic recording layer, using vaporized toluene as the source gas, a hydrogenated carbon film was formed as a protective layer by means of ion beam evaporation. When forming the hydrogenated carbon film, first, the gas flow rate of the source gas supplied to the film formation chamber was set to 2.9 SCCM, and the reaction pressure was set to 0.2 Pa. Further, the cathode power, which is the excitation source of the source gas, was set to 225 W (AC22.5 V, 10 A). Then, the voltage between the cathode electrode and the anode electrode covering it was set to 75 V, the current was set to 1650 mA, the ion acceleration voltage was set to 200 V, the current was set to 180 mA, and the film formation time was set to 1.5 seconds, and the hydrogenated carbon film was formed to a thickness of 3.5 nm. After the formation of the hydrogenated carbon film, the supply of the source gas was stopped, and the inside of the film formation chamber was evacuated for 2 seconds.

[0091] Next, with a gas flow rate of 2 SCCM and a reaction pressure of 5 Pa, nitrogen gas was supplied into the film formation chamber. Then, the cathode power was set to 128 W (AC 16 V, 8 A), the voltage between the cathode electrode and the anode electrode was 75 V, the current was 1000 mA, the ion acceleration voltage was 200 V, the current was 90 mA, the treatment time was 1 second, and nitrogen ions formed from nitrogen gas were irradiated onto the surface of the hydrocarbon film and exposed to nitrogen plasma. As a result, the surface of the hydrocarbon film was dehydrogenated and nitrided.

[0092] Next, D5OH(XS) (structural formula (i) below, manufactured by Matsumura Petrochemical Research Institute (MORESCO)) as the first lubricant was dissolved in Vertrel XF (trade name, manufactured by Mitsui DuPont Fluorochemicals) to obtain a solution for forming the first lubricating layer. The concentration of the compound contained in the solution for forming the first lubricating layer was 0.3 mass%.

[0093]

Chemical formula

[0094] Next, using the dip method, the solution for forming the first lubricating layer was applied onto the protective layer. That is, the laminate on which each layer up to the protective layer was formed was immersed in the solution for forming the first lubricating layer placed in the dipping tank of the dip coating apparatus, and then the laminate was pulled up from the dipping tank at a constant speed. In this way, the solution for forming the first lubricating layer was applied onto the surface on the protective layer so that the layer thickness of the first lubricating layer became 7 Å. Then, by drying the surface onto which the solution for forming the first lubricating layer was applied, the first lubricating layer was formed on the surface of the laminate.

[0095] Next, the second lubricant of the following structural formula (ii) was dissolved in HFE7200 (trade name, manufactured by 3M) to obtain a solution for forming the second lubricating layer. The concentration of the compound contained in the solution for forming the second lubricating layer was 0.3 mass%. Note that HFE7200 can dissolve the second lubricant of the following structural formula, but cannot dissolve the first lubricant D5OH(XS).

[0096]

Chemical formula

[0097] Next, using the dip method, a second lubricant was applied to the surface of the laminate on which the first lubricating layer was formed. The layer thickness of the second lubricating layer was set to 7 Å. Then, by drying the surface to which the solution for forming the second lubricating layer was applied, a second lubricating layer was formed on the surface of the laminate on which the first lubricating layer was formed.

[0098] Next, the surface of the laminate on which the first lubricating layer and the second lubricating layer were formed was burnished with a polishing tape. For this polishing tape, Sumitomo 3M Limited's product with model number DQ3 using Al2O3 with a particle size of 0.3 μm as the abrasive was used. The burnishing conditions were a rotational speed of the laminate of 1000 rpm and a processing time of 3 seconds.

[0099] Next, ultraviolet irradiation was performed on the surface of the laminate on which the first lubricating layer and the second lubricating layer were formed. An ultraviolet lamp manufactured byUSHIO Inc. was used for the ultraviolet irradiation, and the irradiation time was set to 10 seconds in a nitrogen gas atmosphere.

[0100] Next, heat treatment was performed on the surface of the laminate on which the first lubricating layer and the second lubricating layer were formed. The heat treatment was carried out at 120 °C for 1200 seconds in a nitrogen gas atmosphere. By heat-treating the surface of the laminate on which the first lubricating layer and the second lubricating layer were formed, the second lubricating layer was removed from the surface of the first lubricating layer, and a lubricating layer composed of the first lubricating layer was formed. As a result, a magnetic recording medium in which 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 carbon nitride film (protective layer), and a lubricating layer were laminated in this order on both sides of a glass substrate was manufactured.

[0101] [Evaluation of Lubricating Layer] The laminate after ultraviolet irradiation and heat treatment was analyzed by ESCA, and it was confirmed that the first lubricating layer with a layer thickness of 7 Å remained and the second lubricating layer was removed.

[0102] (Coating rate of the lubricating layer) The coating rate of the lubricating layer of the produced magnetic recording medium was measured. The coating rate was measured by immersing the magnetic recording medium after forming the lubricating layer in a fluorocarbon solvent for 5 minutes, measuring the absorbance near 1270 cm-1 before and after immersion at the same position of the same medium by ESCA, and taking the percentage of the ratio ((absorbance after immersion / absorbance before immersion) × 100). As the fluorocarbon solvent, Vertrel XF (trade name, manufactured by Mitsui DuPont Fluorochemical Co., Ltd.) was used. The coating rate of the lubricating layer of the produced magnetic recording medium was 80%.

[0103] (TA (thermal asperity) glide evaluation) The TA glide evaluation of the produced magnetic recording medium was performed. An MR head was used as the inspection head for the TA glide evaluation. The TA glide evaluation is a method of detecting the phenomenon that the signal waveform reproduced from the MR head fluctuates due to the frictional heat generated when the MR head collides with the protrusions on the surface of the magnetic recording medium, that is, detecting the thermal asperity TA, and evaluating the smoothness of the surface of the magnetic recording medium from the number of occurrences of the signal (TA count). The smaller the TA count, the higher the smoothness of the surface of the magnetic recording medium. The average TA count per surface of 100 produced magnetic recording media was 7.

[0104] Table 1 shows the treatment conditions of the second lubricant and the evaluation results of the lubricating layer in Example 1.

[0105] <Examples 2 to 11, Comparative Examples 1 to 4> Magnetic recording media were produced and evaluated in the same manner as in Example 1, except that the production conditions of the first lubricant and the second lubricant and the treatment conditions of the second lubricant were changed to the values shown in Table 1. The production conditions and evaluation results are shown in Table 1. Note that D4OH and D4OH(s) (both trade names: manufactured by Matsumura Petrochemical Research Institute (MORESCO)), which were used as the first lubricant and the second lubricant in any of Examples 2 to 11 and Comparative Examples 1 to 4, have the following structural formula (iii), and the structural formula (iv) is as follows. The average molecular weight of D4OH is 2000, and the average molecular weight of D4OH(s) was adjusted to be 1600.

[0106] Structural formulas of D4OH and D4OH(s): CH2(OH)CH(OH)CH2OCH2CF2CF2(OCF2CF2CF2) m OCF2CF2CH2OCH2CH(OH)CH2OH ···(iii) (m is a positive integer)

[0107] Structural formula (iv):

Chemical formula

[0108] In Comparative Example 5, for the removal of the second lubricant, ultraviolet irradiation and heat treatment (dry treatment) were not performed, and cleaning with a solvent (wet treatment) was used. HFE7200 was used as the solvent, and spin cleaning was used for cleaning.

[0109]

Table 1

[0110]

Table 2

[0111] From Table 1 and Table 2, in each example, the coverage rate of the lubricating layer was 74% or more, and the TA count was 10 or more. On the other hand, in each comparative example, the TA count was 15 or more. Therefore, by using the manufacturing method of the magnetic recording medium according to this embodiment, removing the second lubricant by ultraviolet irradiation or heat treatment and forming a lubricating layer, it can be said that foreign substances on the surface of the magnetic recording medium are efficiently removed, and a magnetic recording medium with a high coverage rate by the lubricating layer can be obtained.

Explanation of symbols

[0112] 1 Magnetic recording medium 11 Laminate (substrate to be laminated) 12 Lubricating layer 21 Abrasive 31 Ultraviolet irradiation 32 Heat treatment 40, 40A, 40B polishing tapes 41 Support 42 Abrasive layer 111 Substrate 112 Magnetic recording layer 113 Protective layer 121 First lubricant 122 Second lubricant 421 Abrasive grains 422 Binder 50 Burnishing device 521 Pair of polishing tape pressing means 522 Pair of polishing tape running systems 521A First polishing tape pressing means 521B Second polishing tape pressing means 522A First polishing tape running system 522B Second polishing tape running system S Polishing surface

Claims

1. A method for manufacturing a magnetic recording medium, comprising forming a lubricating layer on a laminate having a magnetic recording layer and a protective layer laminated in this order on a substrate, the method comprising the steps of: applying a first lubricant and a second lubricant onto the laminate; a step of burnishing the surface of the laminate to which the first lubricant and the second lubricant have been applied, using an abrasive; removing the second lubricant on the laminate; Including, the average molecular weight of the first lubricant is higher than the average molecular weight of the second lubricant; the polarity of the first lubricant is higher than the polarity of the second lubricant; The burnishing step includes a step of pressing an abrasive-containing tape against the surface of the laminate and rubbing the surface, A method for manufacturing a magnetic recording medium, wherein the step of removing the second lubricant includes a step of irradiating the laminate to which the first lubricant and the second lubricant have been applied with ultraviolet light, or a step of heat-treating the laminate to which the first lubricant and the second lubricant have been applied.

2. 2. The method for producing a magnetic recording medium according to claim 1, wherein the second lubricant has an average molecular weight of 300 to 1000 and contains no more than two polar groups.

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

4. 3. The method for producing a magnetic recording medium according to claim 1, wherein the film thickness of the first lubricant applied onto the laminate is set to 5 Å to 10 Å, and the film thickness of the second lubricant is set to 5 Å to 20 Å.

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

6. 3. The method for producing a magnetic recording medium according to claim 1, wherein the heat treatment is carried out in an inert gas atmosphere.

Images