Method for manufacturing a magnetic disk and lubricant solution

Abstract

The present invention provides a method for producing a magnetic disk, the method using a fluorine-based solvent that exhibits excellent solubility of a highly polar perfluoropolyether compound, while having a low global warming potential. The above are achieved by means of a method for producing a magnetic disk, the method comprising a step in which a lubricant solution that contains a lubricant and a hydrofluoroether that has a structure of formula (A) and a global warming potential (100 years) of less than 1000 is applied to a magnetic disk base material. (In formula (A), Ra represents F, CF2-Re or CF3; Rb represents O-Rd or C(-Rf)3; Rc represents H, F or CF3; each of Re and Rd independently represents a hydrocarbon group which may be partially substituted by a fluorine atom, wherein at least one carbon atom in the main chain may be substituted by an oxygen atom; each Rf independently represents H, F or a hydrocarbon group which may be partially substituted by a fluorine atom; and with respect to the hydrocarbon group which may be partially substituted by a fluorine atom, at least one carbon atom in the main chain may be substituted by an oxygen atom.)

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a magnetic disk and a lubricant solution.

Background Art

[0002] In a magnetic disk in a magnetic recording and reproducing apparatus, generally, an underlayer, a magnetic layer, a protective layer, and a lubricating layer are formed in this order on a non-magnetic substrate. As a method for forming the lubricating layer, a method of applying by dipping using a solution in which a lubricant is diluted with a fluorine-based solvent is mainstream. In recent years, as the lubricant, a highly polar perfluoropolyether compound having a functional group such as a hydroxyl group, an aromatic ring, or a phosphazene at the end of a perfluoropolyether backbone tends to be used.

[0003] The solvent for diluting the lubricant should have sufficient solubility to dissolve the lubricant, be liquid at room temperature, and have high volatility for forming a uniform film. Also, from the viewpoint of safety in the manufacturing process, it is desirable to be non-flammable. Conventionally, as fluorine-based solvents for diluting the lubricant of a magnetic disk, Vertrel (registered trademark) XF which is an HFC (hydrofluorocarbon) and Novec (registered trademark) 7100 which is an HFE (hydrofluoroether) are used.

[0004] For example, Patent Document 1 discloses that a perfluoropolyether compound having a perfluorotrimethyleneoxy repeating unit in the main chain and a perfluoropolyether compound having a cyclic triphosphazene structure are dissolved in Vertrel XF to prepare a lubricant coating solution, and a magnetic disk substrate is immersed in the lubricant coating solution to form a lubricating layer.

[0005] Patent Document 2 discloses that a magnetic disk is immersed in a solution in which a lubricant containing a phosphazene compound is dissolved in perfluorohexyl methyl ether (HFE-7100) to form a lubricating layer.

[0006] Patent Document 3 discloses that a perfluoropolyether-based lubricant having a cyclic triphosphazene end group in the molecule was diluted using HFE-7100 as a solvent and applied onto a protective layer by dip coating method.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, conventional fluorine-based solvents as described above have a high global warming potential (GWP), and thus have a large environmental impact, or have insufficient solubility in solvents for highly polar perfluoropolyether-based lubricants that tend to be used as lubricants in recent years, leaving room for improvement.

[0009] One aspect of the present invention aims to provide a method for manufacturing a magnetic disk and a lubricant solution using a fluorine-based solvent having a low global warming potential and excellent solubility for highly polar perfluoropolyether-based lubricants.

Means for Solving the Problems

[0010] That is, one embodiment of the present invention includes the following configurations.

[0011] A method for manufacturing a magnetic disk according to an embodiment of the present invention is a method for manufacturing a magnetic disk, which includes a lubricant application step of applying a lubricant solution containing a perfluoropolyether-based lubricant to the surface of the magnetic disk, wherein the solvent used in the lubricant solution has a structure represented by the following formula (A) and has a global warming potential (GWP) 100-year value of less than 1000, and contains hydrofluoroether (HFE).

Chemical formula

[0012] Further, a lubricant solution according to an embodiment of the present invention is a lubricant solution containing a perfluoropolyether-based lubricant, wherein the solvent used in the lubricant solution has a structure represented by the following formula (A) and has a global warming potential 100-year value of less than 1000, and contains hydrofluoroether.

Chemical formula

Advantages of the Invention

[0013] According to one aspect of the present invention, it is possible to provide a method for manufacturing a magnetic disk and a lubricant solution using a fluorine-based solvent that has a low global warming potential and excellent solubility in a solvent of a highly polar perfluoropolyether-based lubricant.)

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0015] Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited thereto, and various modifications are possible within the described range. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. Unless otherwise specified in this specification, "A to B" representing a numerical range is intended to mean "A or more and B or less".)

[0016] 〔1〕Method for Manufacturing a Magnetic Disk Conventionally, as fluorinated solvents for dissolving lubricants for magnetic disks, Vertrel (registered trademark, hereinafter the same in this specification) XF, which is the aforementioned hydrofluorocarbon (hereinafter sometimes referred to as "HFC" in this specification), and Novec (registered trademark, hereinafter the same in this specification) 7100 (HFE-7100), which is a hydrofluoroether (hereinafter sometimes referred to as "HFE" in this specification), have been used. However, although Vertrel XF has good solubility for highly polar perfluoropolyether-based lubricants, it has a high global warming potential (hereinafter sometimes referred to as "GWP" in this specification) and a large environmental load. On the other hand, although HFE generally has a low GWP, its solubility for highly polar perfluoropolyether-based lubricants is not sufficient. Therefore, in recent years, using Vertrel XF has been the only way as a fluorinated solvent for dissolving lubricants for magnetic disks.

[0017] During the study of solvents for perfluoropolyether-based lubricants, the inventor used one of the HFEs that was considered to be unable to sufficiently dissolve highly polar perfluoropolyether-based lubricants. Surprisingly, it was found that it was able to dissolve highly polar perfluoropolyether-based lubricants. As a result of further study based on such findings, the inventor found that HFEs having a specific structure in the molecule have high solubility for highly polar perfluoropolyether-based lubricants in the HFEs and a low GWP, and thus can be suitably used as solvents for perfluoropolyether-based lubricants, leading to the completion of the present invention.

[0018] That is, a method for manufacturing a magnetic disk according to an embodiment of the present invention is a method for manufacturing a magnetic disk including a lubricant application step of applying a lubricant solution containing a perfluoropolyether-based lubricant to the surface of the magnetic disk, wherein the solvent used in the lubricant solution contains an HFE having the structure of the following formula (A) and a GWP 100-year value of less than 1000.

Chemical formula

[0019] 〔1.1〕Solvent used in the lubricant solution In one embodiment of the present invention, the solvent used in the lubricant solution contains HFE having the structure of the above formula (A) and a GWP 100-year value of less than 1000. According to such a configuration, a method for manufacturing a magnetic disk and a lubricant solution using a fluorine-based solvent having a low GWP and excellent solubility in a solvent of a highly polar perfluoropolyether-based lubricant can be provided. Furthermore, the solvent is as excellent in volatility as Vertrel XF currently mainly used and can form a uniform lubricating layer. Furthermore, the present inventors have found that according to the solvent having the above configuration, there is an additional effect that the adsorptivity of the lubricating layer to the magnetic disk is improved. In addition, according to the solvent having the above configuration, an effect has also been found that the contact angles with respect to water and n-hexadecane in the lubricating layer are high and the surface energy of the lubricating layer is small. A lubricating layer having high contact angles with respect to water and n-hexadecane and a small surface energy of the lubricating layer has an advantage that it can prevent contamination of the magnetic disk surface.)

[0020] Here, HFE refers to a compound containing an ether structure having a hydrogen atom partially substituted by a fluorine atom. The HFE may have the structure of the following formula (A).

Chemical formula

[0021] If it is an HFE having the structure represented by general formula (A) in the molecule, it can dissolve a highly polar perfluoropolyether-based lubricant. This is because the hydrogen atom bonded to the carbon atom bonded to Ra, Rb, and Rc in general formula (A) is biased toward a positive charge by being surrounded by Ra, Rb, and Rc that can contain many fluorine atoms. It is presumed that this is because the hydrogen atom forms a hydrogen bond with the polar group of the highly polar perfluoropolyether-based lubricant, improving the affinity between the lubricant and HFE.)

[0022] The HFE is not particularly limited as long as it has the above structure. For example, Rd-O-CH2F, Rd-O-CHF2, Rd-O-CHFCF3, Rd-O-CH2CF2-Re, Rd-O-CHFCF2-Re, Rd-O-CH(CF3)CF2-Re, Rd-O-CH2CF3, Rd-O-CH(CF3)2, C(-Rf)3-CH2F, C(-Rf)3-CHF2, C(-Rf)3-CHFCF3, C(-Rf)3-CH2CF2-Re, C(-Rf)3-CHFCF2-Re, C(-Rf)3-CH(CF3)CF2-Re, C(-Rf)3-CH2CF3, C(-Rf)3-CH(CF3)2 can be mentioned.)

[0023] Here, Re and Rd are each independently a hydrocarbon group having 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms, still more preferably 1 to 3 carbon atoms, which may be partially substituted by fluorine atoms. At least one of the carbon atoms in the main chain may be substituted by an oxygen atom. Here, when at least one of the carbon atoms in the main chain is substituted by an oxygen atom, the substituted oxygen atom is also regarded as a carbon atom and counted as the number of carbon atoms in the hydrocarbon group (the same applies to Rf below).

[0024] Each Rf independently represents a hydrocarbon group which may be partially substituted by fluorine atoms, H, or F. The hydrocarbon group which may be partially substituted by fluorine atoms may have at least one of the carbon atoms in the main chain substituted by an oxygen atom. In other embodiments, at least one of Rf is a hydrocarbon group which may be partially substituted by fluorine atoms, and at least one of the carbon atoms in the main chain may be substituted by an oxygen atom.

[0025] Also, each Rf independently represents a hydrocarbon group having 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms, still more preferably 1 to 3 carbon atoms, which may be partially substituted by fluorine atoms, H, or F. The hydrocarbon group which may be partially substituted by fluorine atoms may have at least one of the carbon atoms in the main chain substituted by an oxygen atom. In other embodiments, at least one of Rf is a hydrocarbon group having 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms, still more preferably 1 to 3 carbon atoms, which may be partially substituted by fluorine atoms, and at least one of the carbon atoms in the main chain may be substituted by an oxygen atom. Among them, it is more preferable that one of Rf is a hydrocarbon group which may be partially substituted by fluorine atoms and at least one of the carbon atoms in the main chain may be substituted by an oxygen atom, and the other two of Rf are each independently either H or F. The aforementioned HFE can be used alone or in combination of two or more.

[0026] As a more specific example of the HFE, for example, 1,1,2,2 - tetrafluoroethyl 2,2,2 - trifluoroethyl ether, 1,1,2,3,3,3 - hexafluoropropyl methyl ether, 1,1,1,3,3,3 - hexafluoro - 2 - methoxypropane (hexafluoroisopropyl methyl ether), methyl 2,2,3,3,3 - pentafluoropropyl ether, ethyl 1,1,2,2 - tetrafluoroethyl ether, ethyl 1,1,2,3,3,3 - hexafluoropropyl ether, etc. may be mentioned.

[0027] In the present embodiment, the HFE is a compound having a GWP100 - year value of less than 1000. In this specification, "GWP" is the GWP according to the IPCC Fifth Assessment Report, and it is a value estimated as the ratio of the integrated value of the radiative energy given to the Earth within a certain period (for example, 100 years) when a unit mass (for example, 1 kg) of greenhouse gas is emitted into the atmosphere, relative to carbon dioxide. Therefore, the larger the GWP value, the greater the negative impact on global warming, and the smaller the GWP value, the smaller the negative impact on global warming. GWPs with numerical values based on different time scales of 20 years, 100 years, and 500 years have been published, but generally, the GWP100 - year value is used.

[0028] In the present embodiment, the GWP100 - year value of the HFE is preferably less than 1000, more preferably less than 900, still more preferably less than 800, even more preferably less than 700, and most preferably less than 600.

[0029] The boiling point of the HFE is preferably 30°C to 100°C, more preferably 35°C to 90°C, and even more preferably 40°C to 80°C. If the boiling point of the HFE is 100°C or lower, it is preferable because the drying property of the solvent after application to the disk is excellent. Also, if the boiling point of the HFE is 30°C or higher, it is preferable because there is little significant change in the concentration of the solution containing the lubricant due to evaporation of the solvent.

[0030] The HFE is preferably nonflammable from the viewpoint of the safety of the manufacturing process. Here, in this specification, "nonflammable" refers to the standard based on JIS method K2265.

[0031] More preferably, the HFE has three or more carbon-hydrogen bonds. As a result, since it is liquid at room temperature, it is suitable for the dipping method, and furthermore, the 100-year value of the global warming potential is likely to be low.

[0032] In one embodiment of the present invention, the solvent used in the lubricant solution may contain the HFE, but may contain other solvents as long as it does not adversely affect the effects of the present invention. As the other solvent, for example, an organic solvent not containing a fluorine atom can be used. Examples of the organic solvent not containing a fluorine atom include alcohols such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol, t-butanol, and n-butanol; ketones; ethers; dimethyl sulfoxide; dimethylformamide, and the like. Alternatively, even when containing HFC, according to one embodiment of the present invention, the GWP as a whole can be reduced. The content of the other solvent is not limited to this, but is preferably 30% by weight or less, more preferably 20% by weight or less, still more preferably 10% by weight or less, and particularly preferably 5% by weight or less based on the total amount of the solvent.

[0033] [1.2] Perfluoropolyether-based lubricant In one embodiment of the present invention, the perfluoropolyether-based lubricant used as the lubricant preferably contains a perfluoropolyether compound having the structure of the following formula (1). -(CF2) x (CF(CF3)) y O(CF2O) z (CF2CF2O) l (CF2CF2CF2O) m (CF2CF2CF2CF2O) n (CF(CF3)CF2O) o -(CF(CF3)) y (CF2)x - ···(1) In formula (1), x is a real number from 0 to 3, y is a real number from 0 to 1, z, l, m, n, o are each real numbers from 0 to 15, provided that either one of x and y is a real number of 1 or more, and at least one of z, l, m, n, o is a real number of 1 or more.

[0034] As the above formula (1), for example, the Demnum skeleton: -CF2CF2O-(CF2CF2CF2O) m CF2CF2-, the Fomblin skeleton: -CF2O-(CF2O) z (CF2CF2O) l CF2-, the C2 skeleton: -CF2O-(CF2CF2O) l CF2-, the C4 skeleton: -CF2CF2CF2O-(CF2CF2CF2CF2O) n CF2CF2CF2-, the Krytox skeleton: CF(CF3)O-(CF(CF3)CF2O) o CF(CF3)- etc. may be mentioned. In the above skeleton, z, l, m, n, o are real numbers from 1 to 15. In the Fomblin skeleton, CF2O and CF2CF2O may be randomly repeated.

[0035] It is preferable that the above perfluoropolyether compound has at least one structure represented by formula (1) in the molecule. That is, the above perfluoropolyether compound may have two or more structures represented by formula (1) in the molecule. In that case, two or more of the structures represented by formula (1) may be bonded via an arbitrary organic group. Examples of the organic group include an aliphatic hydrocarbon group, an aromatic hydrocarbon group, etc. The aliphatic hydrocarbon group and the aromatic hydrocarbon group may have an ether bond and / or a hydroxyl group.

[0036] For example, the above perfluoropolyether compound is represented by the following formula (2). R 1 -R 2 -R 3 ···(2) In formula (2), R 2is an organic group having a perfluoropolyether backbone. R 2 is, for example, a perfluoropolyether backbone represented by the above formula (1), and two or more structures represented by the formula (1) may be bonded via an arbitrary organic group as described above.

[0037] R 1 and R 3 are each independently an organic group having a fluorine atom, a hydroxyl group, a halogenated alkyl group, an alkoxy group, a carboxyl group, an amino group, an ester group, an amide group, an aryl group, or a phosphazene at the terminal. For example, R 1 and R 3 are each independently -F, -CH2OH, -CH2OCH2CH(OH)CH2OH, -CH2OCH2CH(OH)CH2OCH2CH(OH)CH2OH, -CH2O(CH2) g OH, -CH2OCH2CH(OH)CH2OC 12 H9O, -CH2OCH2CH(OH)CH2OC 10 H7, or CH2OCH2CH(OH)CH2OC6H4-R 4 Here, g is a real number from 1 to 10, and R 4 includes a hydrogen atom, a hydroxyl group, an alkoxy group having 1 to 4 carbon atoms, an amino group, an amide residue, etc. R 4 is preferably a hydroxyl group or an alkoxy group.

[0038] In addition, examples of the perfluoropolyether compound in which two or more perfluoropolyether backbones are bonded via an arbitrary organic group include, for example, a compound represented by the following formula (4).

[0039] R 1 -R 5 -R 6 -R 7 -R 3 ···(4) R 5 and R 7 are organic groups having a perfluoropolyether backbone, for example, a perfluoropolyether backbone represented by the above formula (1).

[0040] R 6 is an arbitrary organic group, and examples thereof include an aliphatic hydrocarbon group, an aromatic hydrocarbon group, etc. The aliphatic hydrocarbon group and the aromatic hydrocarbon group may have an ether bond and / or a hydroxyl group.

[0041] R 1 and R 3 are organic groups similar to those in formula (2).

[0042] The number average molecular weight of the perfluoropolyether compound is not particularly limited, but is preferably 500 to 6000, more preferably 700 to 4000. Also, the number of hydroxyl groups in one molecule of the perfluoropolyether compound is not limited, but is preferably 1 to 10, more preferably 2 to 8, and even more preferably 4 to 8. Here, in this specification, the number average molecular weight of the perfluoropolyether compound is measured by 19 F-NMR using JEOL JNM-ECX400. In the measurement of NMR, the sample itself is used for measurement without diluting the sample with a solvent. As the reference of the chemical shift, a known peak that is part of the skeletal structure of the perfluoropolyether compound is used as a substitute.

[0043] The perfluoropolyether compound may be a perfluoropolyether compound that satisfies the following formula (3). N OH / (Mn / 1500)≧2 ···(3) In formula (3), N OH represents the number of hydroxyl groups in one molecule of the perfluoropolyether compound, and Mn represents the number average molecular weight of the perfluoropolyether compound.

[0044] The solvent described in [1.1] can be suitably used for any perfluoropolyether-based lubricant, and in particular, it can be suitably used for a highly polar perfluoropolyether compound satisfying, for example, formula (3). Generally, a highly polar perfluoropolyether compound satisfying, for example, formula (3) has low solubility in HFE, but is highly soluble in the solvent described in [1.1], so the solvent described in [1.1] is very effective.

[0045] In one embodiment of the present invention, the perfluoropolyether compound may be used alone or in combination of two or more.

[0046] 〔1.3〕Lubricant application step The method for manufacturing a magnetic disk according to one embodiment of the present invention includes a lubricant application step of applying a lubricant solution containing the aforementioned perfluoropolyether-based lubricant and using the aforementioned solvent as a solvent to the surface of the magnetic disk. Here, the lubricant solution may be a solution in which the aforementioned perfluoropolyether-based lubricant is dissolved in the aforementioned solvent. The lubricant solution can be used as a lubricant for a recording medium for improving the sliding characteristics of the magnetic disk.

[0047] The concentration of the perfluoropolyether-based lubricant in the lubricant solution is preferably 0.001% by weight to 1.0% by weight, more preferably 0.003% by weight to 0.5% by weight, and even more preferably 0.005% by weight to 0.3% by weight. When the concentration of the perfluoropolyether-based lubricant is 0.001% by weight or more, the surface can be inactivated by coating the disk with perfluoropolyether, and the sliding characteristics can be ensured, which is preferable. Also, when it is 1.0% by weight or less, the coating film becomes thin, which is preferable.

[0048] The lubricant solution only needs to contain the perfluoropolyether-based lubricant and the solvent, and it is more preferably composed of the perfluoropolyether-based lubricant and the solvent, but may contain other components. Examples of the other components include lubricants other than the perfluoropolyether-based lubricant, hydrocarbon-based lubricants, fatty acid ester-based lubricants, and the like. The content of the other components is, for example, 10% by weight or less based on the total weight of the lubricant solution.

[0049] In this step, the lubricant solution is applied to the surface of the magnetic disk. Here, the magnetic disk includes, for example, a recording layer 4, a protective layer 3, and a lubricating layer 2 disposed on a non-magnetic substrate 8 as shown in the magnetic disk 1 in FIG. 1. The lubricating layer 2 contains the aforementioned lubricant.

[0050] Alternatively, the magnetic disk can include, as shown in the magnetic disk 1 in FIG. 2, a lower layer 5 disposed under the recording layer 4, one or more soft magnetic lower layers 6 disposed under the lower layer 5, and an adhesive layer 7 disposed under the one or more soft magnetic lower layers 6.

[0051] In this step, the lubricant solution is applied to the surface of the protective layer of the magnetic disk on which at least the recording layer and the protective layer are formed on the non-magnetic substrate to form a lubricating layer.

[0052] In this step, the method of applying the lubricant solution to the surface of the magnetic disk is not limited to this, and examples thereof include a dip method, a spin coating method, a spray method, a paper coating method, and the like. Among them, the dip method is more preferable.

[0053] The temperature of the lubricant solution when applying it to the surface of the magnetic disk is not particularly limited, but from the viewpoint of minimizing the change in the concentration of the lubricant solution in order to uniformly apply the film thickness of the lubricant, the temperature of the lubricant solution during application is preferably 10°C to 40°C.

[0054] Further, after applying the lubricant solution to the surface of the protective layer, ultraviolet irradiation or heat treatment may be performed. By performing ultraviolet irradiation or heat treatment, a stronger bond can be formed between the lubricating layer and the protective layer, and evaporation of the lubricant due to heating can be prevented. When performing ultraviolet irradiation, it is preferable to use ultraviolet light having a wavelength of 185 nm or 254 nm as the main wavelength in order to activate the interface between the lubricant and the protective layer without affecting the deep parts of the lubricating layer and the protective layer. When performing heat treatment, the temperature is preferably 60 to 170°C, more preferably 80 to 170°C, and even more preferably 80 to 150°C.

[0055] In the dipping method, for example, the lubricant solution can be applied to the surface of the magnetic disk by immersing the magnetic disk in the lubricant solution and then pulling it out. At this time, the immersion time of the magnetic disk is not particularly limited, but is, for example, 1 minute to 10 minutes. Also, the pulling-out speed of the magnetic disk after immersion is not particularly limited, but is, for example, 0.5 mm / second to 5 mm / second.

[0056] [1.4] Other Processes The method for manufacturing a magnetic disk according to an embodiment of the present invention may further include a process for manufacturing a perfluoropolyether-based lubricant, a process for preparing the lubricant solution, a process for forming a recording layer on a non-magnetic substrate, a process for forming a protective layer on the recording layer, and the like.

[0057] Each layer of the magnetic disk other than the lubricating layer can include materials known in the art as being suitable for individual layers of the magnetic disk. For example, as materials for the recording layer, there can be mentioned alloys obtained by adding chromium, platinum, tantalum, etc. to elements capable of forming ferromagnetic bodies such as iron, cobalt, nickel, etc., or oxides thereof. Also, as materials for the protective layer, for example, carbon, Si3N4, SiC, SiO2, etc. can be mentioned. As materials for the non-magnetic substrate, for example, aluminum alloys, glass, polycarbonate, etc. can be mentioned.

[0058] The method for preparing the lubricant solution is not particularly limited either. For example, it can be prepared by dissolving the aforementioned perfluoropolyether-based lubricant in the solvent. Further, the HFE used in the solvent can be one produced by a conventionally known method or a commercially available product. The method for producing the perfluoropolyether-based lubricant is not particularly limited either, and it can be produced by appropriately selecting a conventionally known method.

[0059] [2] Lubricant solution One aspect of the present invention includes a lubricant solution containing a perfluoropolyether-based lubricant, wherein the solvent used in the lubricant solution has a structure represented by the following formula (A) and contains an HFE with a GWP 100-year value of less than 1000. [Chemical formula] (In formula (A), Ra represents any one of F, CF2-Re, and CF3. Rb represents any one of O-Rd and C(-Rf)3. Rc represents any one of H, F, and CF3. Re and Rd are each independently a hydrocarbon group that may be partially substituted by fluorine atoms, and at least one of the carbon atoms in the main chain may be substituted by an oxygen atom. Rf is each independently a hydrocarbon group that may be partially substituted by H, F, and fluorine atoms, and at least one of the carbon atoms in the main chain may be substituted by an oxygen atom.)

[0060] The perfluoropolyether-based lubricant, the solvent, and the lubricant solution are as described in the above [1].

[0061] The lubricant solution can be used as a lubricant for a recording medium for improving the sliding characteristics of a magnetic disk. Further, in addition to magnetic disks, it can also be used as a lubricant for a recording medium in other recording devices where sliding occurs between a recording medium such as a magnetic tape and a head. Furthermore, it can be used not only in recording devices but also as a lubricant for devices having sliding parts.

[0062] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims. Embodiments obtained by appropriately combining technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0063] 〔Summary〕 One embodiment of the present invention includes the following configuration. 〔1〕A method for manufacturing a magnetic disk, comprising a lubricant application step of applying a lubricant solution containing a perfluoropolyether-based lubricant to the surface of the magnetic disk, wherein the solvent used in the lubricant solution has a structure represented by the following formula (A) and a global warming potential value over 100 years of less than 1000, and contains a hydrofluoroether.

Chemical formula

Chemical formula

Examples

[0064] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. All evaluation results are shown in Table 1 below.

[0065] 〔Solvent〕 The solvents used in the lubricant solutions in the examples and comparative examples are shown below. In Table 1, Ra, Rb, and Rc represent Ra, Rb, and Rc in formula (A). For Rb, when Rb is O-Rd, it is described as "O", and when Rb is C(-Rf)3, it is described as "C". Solvent 1: 1,1,2,2-Tetrafluoroethyl 2,2,2-trifluoroethyl ether (CAS No. 406-78-0, manufactured by Tokyo Chemical Industry Co., Ltd.) Solvent 2: 1,1,2,3,3,3-Hexafluoropropyl methyl ether (CAS No. 382-34-3, manufactured by Tokyo Chemical Industry Co., Ltd.) Solvent 3: 1,1,1,3,3,3-Hexafluoro-2-methoxypropane (hexafluoroisopropyl methyl ether) (CAS No. 13171-18-1, manufactured by Halocarbon) Solvent 4: Methyl 2,2,3,3,3-pentafluoropropyl ether (CAS No. 378-16-5, manufactured by Tokyo Chemical Industry Co., Ltd.) Solvent 5: Ethyl 1,1,2,2 - tetrafluoroethyl ether (CAS No. 512 - 51 - 6, manufactured by Tokyo Chemical Industry Co., Ltd.) Solvent 6: Ethyl 1,1,2,3,3,3 - hexafluoropropyl ether (CAS No. 380 - 34 - 7, manufactured by Tokyo Chemical Industry Co., Ltd.) Solvent 7: 1,1,1,2,3,4,4,5,5,5 - decafluoropentane (manufactured by Mitsui - Chemours Fluoro Products Co., Ltd., Vertrel - XF) Solvent 8: Mixture of methyl nonafluorobutyl ether and methyl nonafluoro - isobutyl ether (manufactured by 3M, Novec 7100) Solvent 9: Mixture of ethyl nonafluorobutyl ether and ethyl nonafluoro - isobutyl ether (manufactured by 3M, Novec 7200) Solvent 10: 2,2,2 - trifluoroethanol (manufactured by Tosoh - F - Tech Co., Ltd.).

[0066] 〔Perfluoropolyether - based lubricant〕 Perfluoropolyether compound having the structure of the following formula (B) (manufactured by MORESCO Corporation)

Chemical formula

[0067] 〔Evaluation method〕 Regarding the evaluation methods of the lubricant solutions and lubricating layers prepared in the examples and comparative examples, they will be described below.

[0068] (Solubility evaluation of lubricant) Regarding the lubricant solutions obtained in the examples and comparative examples, the dissolution state of the perfluoropolyether - based lubricant was visually confirmed. The evaluation criteria are as follows. Good: The perfluoropolyether - based lubricant is dissolved in the solvent. Poor: The perfluoropolyether - based lubricant is not dissolved in the solvent.

[0069] (Measurement of volatility) The evaluation of volatility was carried out according to the following procedures (1) to (4): (1) A petri dish with a diameter of 28 mm and a depth of 15 mm was placed on an electronic balance with a wind guard, 2 ml of the solvent was poured into the petri dish, and it was left standing at room temperature (20°C to 25°C, the same hereinafter in this specification); (2) The weight of the solvent was measured at the time points when 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, and 30 minutes had elapsed since the addition of the solvent; (3) The weight reduction amount per unit time was calculated, and the average volume reduction rate (ml / min) was calculated from the calculated weight reduction amount and the density of the solvent; (4) The average volume reduction rate of Comparative Example 1 using Vertrel-XF as the solvent was set to 1.0, and the relative volume reduction rate was calculated from the average volume reduction rate calculated in (3). The average volume reduction rate of Vertrel-XF was 0.028 ml / min.

[0070] (Measurement of the film thickness of the lubricant coating film) The measurement of the film thickness of the lubricant layer coating film formed by applying the lubricant solution was carried out according to the following procedures (1) to (3): (1) A 2.5-inch magnetic disk was immersed in the lubricant solution for 3 minutes, and the magnetic disk was pulled up vertically upward from the solution at a pulling speed of 1 mm / second with the pulling direction parallel to the magnetic disk surface to form a lubricant layer coating film; (2) Using FT-IR (VERTEX70 manufactured by Bruker), the IR intensities at three points on the magnetic disk surface where the distance from the center of the magnetic disk was 15 mm (indicated as "ID" in Table 1), 20 mm (indicated as "MD" in Table 1), and 25 mm (indicated as "OD" in Table 1) were measured, and the film thicknesses at these three points were calculated from the calibration curve between the film thickness measured by the ellipsometer and the IR intensity; (3) The state of the lubricant coating film was visually confirmed. If there were abnormalities such as the appearance of droplets, it was determined that the measurement could not be performed, and the film thickness was set to "≧14.0".

[0071] (Measurement of the contact angle of the lubricant coating film) The contact angle of the lubricant coating film was measured according to the following procedures (1) to (3): (1) A 2.5-inch magnetic disk was immersed in a lubricant solution for 3 minutes, and then the disk was pulled vertically upward from the solution at a pulling speed of 1 mm / second with the pulling direction parallel to the magnetic disk surface to form a lubricant coating film with a film thickness of about 13 Å. The film thickness was measured in the same manner as the measurement of the film thickness of the lubricant coating film, and the average value of the measured film thickness was taken as the film thickness; (2) After leaving the magnetic disk with the lubricant coating film formed thereon standing at room temperature for 2 weeks, 2 μL of water and 2 μL of n-hexadecane were each dropped, and the contact angle 60 seconds after the dropping was measured using an automatic contact angle meter DM500 (manufactured by Kyowa Interface Science Co., Ltd.). In order to make the film thickness of the lubricant coating film about 13 Å, the lubricant concentration was adjusted according to the solvent.

[0072] (Calculation of surface energy) From the values of the contact angle θ of water with respect to the lubricant coating film and the contact angle θ of n-hexadecane with respect to the lubricant coating film obtained by the measurement of the contact angle, the dispersion component γ was calculated by the Kaelble-Uy method (specifically, the following formula): d , the polar component γ p , and the surface energy γ were calculated. [Number] In the above formula, γ L is the surface energy of the liquid, and γ S is the surface energy of the solid.

[0073] (Adsorption evaluation) A magnetic disk on which a lubricant coating film was prepared in the same manner as the measurement of the contact angle was immersed in Vertrel-XF for 5 minutes, and then pulled vertically upward at 1 mm / second with the pulling direction parallel to the magnetic disk surface for cleaning, and the film thickness of the lubricant coating film remaining on the magnetic disk was measured. The film thickness of the lubricant coating film was measured using FT-IR (manufactured by Bruker, VERTEX70).

[0074] [Example 1] The perfluoropolyether compound was dissolved in Solvent 1 at room temperature to a concentration of 1000 ppm by mass to prepare a lubricant solution. The solubility of the lubricant in the obtained lubricant solution was evaluated. The volatility was evaluated using Solvent 1 as it was.

[0075] 〔Examples 2 and 3〕 Lubricant solutions of Examples 2 and 3 were prepared and the solubility of the lubricant was evaluated in the same manner as in Example 1, except that Solvent 1 was changed to Solvent 2 and Solvent 3, respectively. For Solvent 3, the film thickness was also evaluated. The volatility was evaluated using Solvent 2 and Solvent 3 as they were.

[0076] Separately, a lubricant solution obtained in the same manner as in Example 1 was prepared, except that the perfluoropolyether compound was dissolved in Solvent 3 to a concentration of 500 ppm by mass. Using this separately prepared lubricant solution, a lubricating layer coating film was formed, and for the obtained lubricant coating film, as Example 3, adsorption evaluation, measurement of contact angle, and calculation of surface energy were performed.

[0077] 〔Examples 4 to 6〕 Lubricant solutions of Examples 4 to 6 were prepared and the solubility of the lubricant was evaluated in the same manner as in Example 1, except that Solvent 1 was changed to Solvents 4 to 6, respectively. The volatility was evaluated using Solvents 4 to 6 as they were.

[0078] 〔Comparative Example 1〕 A lubricant solution of Comparative Example 1 was prepared and the solubility of the lubricant and the film thickness were measured in the same manner as in Example 1, except that Solvent 1 was changed to Solvent 7. The volatility was evaluated using Solvent 7 as it was.

[0079] Separately, a lubricant solution obtained in the same manner as in Example 1 was prepared, except that the perfluoropolyether compound was dissolved in Solvent 7 to a concentration of 500 ppm by mass. Using this separately prepared lubricant solution, a lubricating layer coating film was formed, and for the obtained lubricant coating film, measurement of contact angle, calculation of surface energy, and adsorption evaluation were performed.

[0080] 〔Comparative Examples 2 to 4〕 Lubricant solutions of Comparative Examples 2 to 4 were prepared in the same manner as in Example 1, except that Solvent 1 was changed to Solvents 8 to 10, respectively, and the solubility evaluation and evaporation property evaluation of the lubricant were performed. For Solvent 10 (Comparative Example 4), measurement of film thickness, measurement of contact angle, calculation of surface energy, and adsorption property evaluation were performed. The evaporation property was evaluated using Solvents 8 to 10 as they were.

[0081]

Table 1

[0082] 〔Results〕 As shown in Table 1, the solvents used in Examples 1 to 6 had a low GWP of less than 1000 and a small load on global warming. Further, the solvents used in Examples 1 to 6 were HFEs, similar to the solvents used in Comparative Examples 2 to 3, but surprisingly, it was shown that they could dissolve a highly polar perfluoropolyether-based lubricant. Thus, it can be seen that the solvents used in Examples 1 to 6 have a low GWP and excellent solubility of the highly polar perfluoropolyether-based lubricant in the solvent.

[0083] In contrast, Vertrel XF of Comparative Example 1, which is currently mainly used, is excellent in the solubility of the highly polar perfluoropolyether-based lubricant but has a large GWP. Further, the HFEs used in Comparative Examples 2 to 3, which do not have the structure of formula (A), have a small GWP but are difficult to dissolve the highly polar perfluoropolyether-based lubricant.

[0084] Furthermore, the solvents used in Examples 1 to 6 had an evaporation property within the range of 1.0 ± 0.5 based on Vertrel XF of Comparative Example 1, which is currently mainly used. Since these solvents evaporate very quickly, they can be used without problems as the solvent of the lubricant solution within the above range. On the other hand, for the solvent of Comparative Example 4, which is not an HFE, the evaporation property was 0.2, and it was found that the evaporation rate was slower compared to Examples 1 to 6 and Comparative Example 1.

[0085] In Example 3, it was also shown that the variation in film thickness at three points from the center to the outside of the formed lubricating layer coating film on the magnetic disk was small and was comparable to the variation when Vertrel XF of Comparative Example 1 was used. On the other hand, in Comparative Example 4 using a solvent that is not an HFE, generation of droplets was observed on the outer diameter (OD) of the magnetic disk, and film thickness measurement could not be performed. Therefore, Comparative Example 4 cannot be used as a lubricant solution. It should be noted that there is a correlation between volatility and variation in film thickness. When the volatility is high, the solution adhering to the disk lifted from the lubricant solution evaporates immediately, and the lubricant solution does not drip and accumulate at the lower part of the disk, so that the film thickness becomes uniform. In Examples 1, 2, and 4 to 6, the variation in film thickness at three points from the center to the outside of the magnetic disk was not measured, but since the volatility is comparable to that of Example 3, it is predicted that results comparable to those of Example 3 will be obtained.

[0086] Furthermore, in the adsorption evaluation, Example 3 showed a smaller change in film thickness before and after cleaning compared to Comparative Examples 1 and 4. That is, it was shown that the lubricating layer formed in Example 3 had a high adsorption property to the magnetic disk. Furthermore, in Example 3, it was shown that the contact angle with water was particularly high and the surface energy was low compared to Comparative Examples 1 and 4. That is, it was found that the lubricating layer formed in Example 3 can better prevent contamination of the magnetic disk surface.

Industrial Applicability

[0087] According to the method for manufacturing a magnetic disk and the lubricant solution according to an embodiment of the present invention, it is possible to provide a method for manufacturing a magnetic disk and a lubricant solution using a fluorine-based solvent having a low GWP and excellent solubility of a highly polar perfluoropolyether-based lubricant in the solvent. Therefore, it can be advantageously used in the manufacture of magnetic disks.

[0088] In addition, the HFE used in the method for manufacturing a magnetic disk and the lubricant solution according to an embodiment of the present invention has a low GWP and a small load on the earth. By using a solvent with a low GWP for the entire HDD industry, the negative impact of global warming can be minimized. Thereby, it can contribute to the achievement of Goal 13, "Take urgent action to combat climate change", of the Sustainable Development Goals (SDGs).

Explanation of symbols

[0089] 1 Magnetic disk 2 Lubricating layer 3 Protective layer 4 Recording layer 5 Lower layer 6 Soft magnetic lower layer 7 Adhesive layer 8 Non-magnetic substrate

Claims

1. A method for manufacturing a magnetic disk, comprising a lubricant application step of applying a lubricant solution containing a perfluoropolyether-based lubricant to the surface of the magnetic disk, wherein the solvent used in the lubricant solution contains a hydrofluoroether having a structure represented by the following formula (A) and a 100-year global warming potential value of less than 1000, the hydrofluoroether is contained in an amount exceeding 70% by weight based on the total amount of the solvent, the perfluoropolyether-based lubricant contains a perfluoropolyether compound satisfying the following formula (3), a method for manufacturing a magnetic disk. 【Chemical 1】 (In formula (A), Ra is F, CF ２ -Re or CF ３ . Rb represents either O-Rd or C(-Rf) ３ . Rc represents either H, F, or CF ３ . Re and Rd are each independently a hydrocarbon group that may be partially substituted by fluorine atoms, and at least one of the carbon atoms in the main chain may be substituted by an oxygen atom. Rf represents either a hydrocarbon group that may be partially substituted by fluorine atoms, H, or F, and in the hydrocarbon group that may be partially substituted by the fluorine atoms, at least one of the carbon atoms in the main chain may be substituted by an oxygen atom.) N OH / (Mn / 1500) ≧ 2... (3) (In formula (3), N OH represents the number of hydroxyl groups in one molecule of the perfluoropolyether compound, and Mn represents the number average molecular weight of the perfluoropolyether compound.)

2. A method for manufacturing a magnetic disk, comprising a lubricant application step of applying a lubricant solution containing a perfluoropolyether-based lubricant to the surface of the magnetic disk, wherein the solvent used in the lubricant solution contains a hydrofluoroether having a structure represented by the following formula (A) and a 100-year global warming potential value of less than 1000 (however, excluding 1,1,1,3,3,3-hexafluoroisopropyl methyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, and 1,1,2,3,3,3-hexafluoropropyl methyl ether). A method for manufacturing a magnetic disk. [Chemical Formula 2] (In formula (A), Ra represents any one of F, CF 2 - Re, and CF 3. Rb represents any one of O - Rd and C(-Rf) 3. Rc represents any one of H, F, and CF 3. Re and Rd are each independently a hydrocarbon group that may be partially substituted by fluorine atoms and at least one of the carbon atoms in the main chain may be substituted by an oxygen atom. Rf represents any one of a hydrocarbon group that may be partially substituted by fluorine atoms, H, and F, and the hydrocarbon group that may be partially substituted by fluorine atoms may have at least one of the carbon atoms in the main chain substituted by an oxygen atom.) **Claim 3** A method for manufacturing a magnetic disk, comprising a lubricant application step of applying a lubricant solution containing a perfluoropolyether-based lubricant to the surface of the magnetic disk, wherein the solvent used in the lubricant solution has a structure represented by the following formula (A) and a 100-year global warming potential value of less than 1000, and contains a hydrofluoroether. 【Chemical Formula 3】 (In formula (A), Ra represents any one of F, CF₂-Re, and CF₃. Rb represents any one of O-Rd and C(-Rf)₃. Rc represents either H or F. Re is a hydrocarbon group that may be partially substituted by fluorine atoms, and at least one of the carbon atoms in the main chain may be substituted by an oxygen atom. Rd is a hydrocarbon group. Rf is independently either OCH₂CH₃ or F.) **Claim 4** The manufacturing method according to any one of claims 1 to 3, wherein the solvent has a boiling point of 30°C to 100°C and is non-flammable. **Claim 5** The manufacturing method according to any one of claims 1 to 3, wherein the hydrofluoroether has three or more carbon-hydrogen bonds. **Claim 6** The manufacturing method according to any one of claims 1 to 3, wherein the perfluoropolyether-based lubricant contains a perfluoropolyether compound having a structure represented by the following formula (1). -(CF ２ ) ｘ (CF(CF ３ )) ｙ O(CF ２ O) ｚ (CF ２ CF ２ O) ｌ (CF ２ CF ２ CF ２ O) ｍ (CF ２ CF ２ CF ２ CF ２ O) ｎ (CF(CF ３ )CF ２ O) ｏ -(CF(CF ３ )) ｙ (CF ２ ) ｘ -...(1) (In formula (1), x is a real number from 0 to 3, y is a real number from 0 to 1, z, l, m, n, o are each real numbers from 0 to 15, provided that either x or y is a real number of 1 or more, and at least one of z, l, m, n, o is a real number of 1 or more.) **Claim 7** The manufacturing method according to any one of claims 1 to 3, wherein the perfluoropolyether-based lubricant is a perfluoropolyether compound having a structure represented by the following formula (2). R １ -R ２ -R ３ ... (2) (In formula (2), R ２ is an organic group having a perfluoropolyether skeleton, and R １ and R ３ are each independently an organic group having a fluorine atom, a hydroxyl group, a halogenated alkyl group, an alkoxy group, a carboxyl group, an amino group, an ester group, an amide group, a phosphazene or an aryl group at the terminal.) **Claim 8** The manufacturing method according to claim 2 or 3, wherein the perfluoropolyether-based lubricant contains a perfluoropolyether compound satisfying the following formula (3). N OH / (Mn / 1500) ≥ 2... (3) (In formula (3), N OH represents the number of hydroxyl groups in one molecule of the perfluoropolyether compound, and Mn represents the number average molecular weight of the perfluoropolyether compound.) **Claim 9** A lubricant solution containing a perfluoropolyether-based lubricant, wherein the solvent used in the lubricant solution contains a hydrofluoroether having the structure of the following formula (A) and having a global warming potential value of less than 1000 for 100 years, wherein the hydrofluoroether is contained in an amount exceeding 70% by weight based on the total amount of the solvent, and the perfluoropolyether-based lubricant contains a perfluoropolyether compound satisfying the following formula (3), the lubricant solution. 【Chemical Formula 4】 (In formula (A), Ra is F, CF ２ -Re or CF ３ . Rb represents either O-Rd or C(-Rf) ３ . Rc represents either H, F or CF ３ . Re and Rd are each independently a hydrocarbon group which may be partially substituted by fluorine atoms and at least one of the carbon atoms in the main chain may be substituted by an oxygen atom. Rf represents either a hydrocarbon group which may be partially substituted by fluorine atoms, H, or F, and the hydrocarbon group which may be partially substituted by the fluorine atoms may have at least one of the carbon atoms in the main chain substituted by an oxygen atom.) N OH / (Mn / 1500) ≥ 2 ··· (3) (In formula (3), N OH represents the number of hydroxyl groups in one molecule of the perfluoropolyether compound, and Mn represents the number average molecular weight of the perfluoropolyether compound.)

10. A lubricant solution containing a perfluoropolyether-based lubricant, wherein the solvent used in the lubricant solution contains a hydrofluoroether having the structure of the following formula (A) and having a global warming potential value of less than 1000 for 100 years (however, 1,1,1,3,3,3-hexafluoroisopropyl methyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, and 1,1,2,3,3,3-hexafluoropropyl methyl ether are excluded), the lubricant solution. 【Chemical Formula 5】 (In formula (A), Ra represents any one of F, CF 2 -Re and CF 3. Rb represents any one of O-Rd and C(-Rf) 3. Rc represents any one of H, F and CF 3. Re and Rd are each independently a hydrocarbon group that may be partially substituted by fluorine atoms, and at least one of the carbon atoms in the main chain may be substituted by an oxygen atom. Rf represents any one of a hydrocarbon group that may be partially substituted by fluorine atoms, H, and F, and the hydrocarbon group that may be partially substituted by fluorine atoms may have at least one of the carbon atoms in the main chain substituted by an oxygen atom.)

11. A lubricant solution containing a perfluoropolyether-based lubricant, wherein the solvent used in the lubricant solution contains a hydrofluoroether having the structure of the following formula (A) and having a global warming potential value of less than 1000 for 100 years, the lubricant solution. 【Chemical Formula 6】 (In formula (A), Ra represents any one of F, CF2-Re, and CF3. Rb represents any one of O-Rd and C(-Rf)3. Rc represents either H or F. Re is a hydrocarbon group that may be partially substituted by fluorine atoms, and at least one of the carbon atoms in the main chain may be substituted by an oxygen atom. Rd is a hydrocarbon group. Rf is independently either OCH2CH3 or F.)

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