Lubricating oil composition

Abstract

An object of the present invention is to provide a lubricating oil composition having excellent cooling performance, a high flash point, a low pour point, and excellent electrical insulation properties. This object is solved by forming a lubricating oil composition containing a base oil (A), wherein the base oil (A) contains one or more synthetic oils (A1) selected from specific polyalkylene glycols having a specific number of polymerization units and specific polyvinyl ethers having a specific number of polymerization units.

Description

Technical Field

[0001] The present invention relates to a lubricating oil composition, for example, a lubricating oil composition for cooling an electric vehicle device. Background Art

[0002] In recent years, from the viewpoint of protecting the global environment, there has been a strong demand for carbon dioxide reduction. In the field of automobiles, efforts have also been made in the development of fuel-saving technologies, and the popularization of hybrid vehicles and electric vehicles (hereinafter, also referred to as "electric vehicles"), which are automobiles with excellent fuel consumption and environmental performance, is being promoted. The electric vehicle devices of electric vehicles require a cooling oil with excellent cooling performance and electrical insulation. In addition, in electric vehicles, there are also electric vehicles in the form of a gear reducer, and therefore these cooling oils need to have lubricity in addition to the above-mentioned performance.

[0003] As the cooling oil for electric vehicle devices, existing lubricating oil compositions such as automatic transmission fluid (hereinafter, also referred to as "ATF") and continuously variable transmission fluid (hereinafter, also referred to as "CVTF") are mainly used, and the development of various cooling oils to replace them is also underway.

[0004] For example, in Patent Document 1, as a lubricating oil composition for cooling an electric vehicle engine and its various parts, a lubricating oil composition containing at least one polyalkylene glycol obtained by polymerization or copolymerization of an alkylene oxide having 2 to 8 carbon atoms, preferably 2 to 4 carbon atoms, is proposed.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2020-512410 Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] However, it cannot be said that the cooling performance of the lubricating oil composition of Patent Document 1 is sufficient.

[0010] In addition, for the lubricating oil composition used in the cooling of electric vehicle devices, from the viewpoint of ensuring safety, a high flash point is required, and from the viewpoint of use in cold regions, a low pour point is also required. In addition, as described above, excellent electrical insulation is also required.

[0011] The present invention has been completed in view of the above problems and requirements, and an object thereof is to provide a lubricating oil composition having excellent cooling performance, a high flash point, a low pour point, and excellent electrical insulation properties.

[0012] Means for Solving the Problem

[0013] The present inventors repeatedly conducted in-depth studies and found that a lubricating oil composition containing one or more synthetic oils selected from polyalkylene glycols having a specific number of polymerization units and polyvinyl ethers having a specific number of polymerization units can solve the above problems, thus completing the present invention.

[0014] That is, the present invention relates to the following [1] to [4].

[0015] [1] A lubricating oil composition containing a base oil (A),

[0016] The above base oil (A) contains one or more synthetic oils (A1) selected from polyalkylene glycols having a structural unit represented by the following general formula (1) and polyvinyl ethers having a structural unit represented by the following general formula (2).

[0017] [Chemical Formula 1]

[0018]

[0019] [In the above general formula (1), R 1 and R 2 each independently represent a hydrogen atom or a monovalent hydrocarbon group having 1 to 18 carbon atoms. R 3 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. n is an integer of 3 to 5.]

[0020] [Chemical Formula 2]

[0021]

[0022] [In the above general formula (2), R 5 , R 6 and R 7 each independently represent a hydrogen atom or a monovalent hydrocarbon group having 1 to 8 carbon atoms. R 8 represents a divalent hydrocarbon group having 2 to 10 carbon atoms. R 9 represents a monovalent hydrocarbon group having 1 to 10 carbon atoms. m is 3 or 4. q is an integer of 0 to 10.]

[0023] [2] The lubricating oil composition according to the above [1], which is used for cooling an electric vehicle device.

[0024] [3] A method of use, wherein the lubricating oil composition according to [1] or [2] is used for cooling an electric vehicle device.

[0025] [4] A cooling system for cooling equipment for electric vehicles, which comprises the lubricating oil composition described in [1] or [2].

[0026] Advantages of the Invention

[0027] According to the present invention, a lubricating oil composition can be provided which has excellent cooling performance, a high flash point, a low pour point, and excellent electrical insulation. Detailed Embodiments

[0028] Hereinafter, embodiments of the present invention will be described in detail. It should be noted that the present invention is not limited to the following embodiments and can be implemented with any changes within the scope of its gist.

[0029] The upper and lower limit values of the numerical ranges described in this specification can be arbitrarily combined. For example, when “A to B” and “C to D” are described, the ranges of “A to D” and “C to B” are also included in the scope of the present invention as numerical ranges. In addition, the numerical range “lower limit value to upper limit value” described in this specification means above the lower limit value and below the upper limit value unless otherwise specified.

[0030] In addition, in this specification, the numerical values in the examples are numerical values that can be used as the upper limit value or the lower limit value.

[0031] [Scheme of Lubricating Oil Composition]

[0032] The lubricating oil composition of the present invention contains a base oil (A), and the base oil (A) contains one or more synthetic oils (A1) selected from polyalkylene glycols having a structural unit represented by the following general formula (1) and polyethylene vinyl ethers having a structural unit represented by the following general formula (2).

[0033] [Chemical Formula 3]

[0034]

[0035] [In the above general formula (1), R 1 and R 2 each independently represent a hydrogen atom or a monovalent hydrocarbon group having 1 to 18 carbon atoms. R 3 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. n is an integer of 3 to 5. ]

[0036] [Chemical Formula 4]

[0037]

[0038] [In the above general formula (2), R 5 , R 6 and R 7Each independently represents a hydrogen atom or a monovalent hydrocarbon group having 1 to 8 carbon atoms. R 8 represents a divalent hydrocarbon group having 2 to 10 carbon atoms. R 9 represents a monovalent hydrocarbon group having 1 to 10 carbon atoms. m is 3 or 4. q is an integer from 0 to 10.]

[0039] The inventors of the present invention conducted in-depth research to solve the above problems. As a result, it was found that trimer to pentamer polyalkylene glycols, and further polyethylene vinyl ethers of trimer or tetramer have excellent cooling performance, high flash point, low pour point, and excellent electrical insulation.

[0040] The lubricating oil composition of one embodiment of the present invention is preferably composed only of the base oil (A), but other components other than the base oil (A) may be contained within a range not impairing the effects of the present invention.

[0041] Specifically, in the lubricating oil composition of one embodiment of the present invention, from the viewpoint of more easily exhibiting the effects of the present invention, the content of the base oil (A) is preferably 30% by mass or more, more preferably 50% by mass or more, further preferably 60% by mass or more, still further preferably 70% by mass or more, yet further preferably 80% by mass or more, still preferably 90% by mass or more, still further preferably 95% by mass or more, still further preferably 99% by mass or more, based on the total amount of the lubricating oil composition. In addition, it is preferably 100% by mass or less.

[0042] The upper and lower limit values of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 30% by mass to 100% by mass, more preferably 50% by mass to 100% by mass, further preferably 60% by mass to 100% by mass, still further preferably 70% by mass to 100% by mass, yet further preferably 80% by mass to 100% by mass, still preferably 90% by mass to 100% by mass, still further preferably 95% by mass to 100% by mass, still further preferably 99% by mass to 100% by mass.

[0043] It should be noted that when the lubricating oil composition of one embodiment of the present invention is composed only of the base oil (A), the lubricating oil composition is also referred to as "lubricating oil base oil".

[0044] Hereinafter, the base oil (A) will be described in detail.

[0045] [Base oil (A)]

[0046] The lubricating oil composition of the present invention contains the base oil (A).

[0047] The base oil (A) contains one or more synthetic oils (A1) selected from polyalkylene glycols having a structural unit represented by the above general formula (1) and polyvinyl ethers having a structural unit represented by the above general formula (2).

[0048] That is, the base oil (A) may be used alone one or more selected from polyalkylene glycols having a structural unit represented by the above general formula (1), or may be used alone one or more selected from polyvinyl ethers having a structural unit represented by the above general formula (2). In addition, one or more selected from polyalkylene glycols having a structural unit represented by the above general formula (1) may be used in combination with one or more selected from polyvinyl ethers having a structural unit represented by the above general formula (2).

[0049] Here, from the viewpoint of more easily exerting the effects of the present invention, the content of the synthetic oil (A1) is preferably 30% by mass or more, more preferably 40% by mass or more, further preferably 45% by mass or more, and still more preferably 50% by mass or more, based on the total amount of the base oil (A). In addition, it is preferably 100% by mass or less.

[0050] The upper and lower limit values of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 30% by mass to 100% by mass, more preferably 40% by mass to 100% by mass, further preferably 45% by mass to 100% by mass, and still more preferably 50% by mass to 100% by mass.

[0051] In addition, from the viewpoint of more easily exerting the effects of the present invention, the content of the synthetic oil (A1) is preferably 30% by mass or more, more preferably 40% by mass or more, further preferably 45% by mass or more, and still more preferably 50% by mass or more, based on the total amount of the lubricating oil composition. In addition, it is preferably 100% by mass or less.

[0052] The upper and lower limit values of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 30% by mass to 100% by mass, more preferably 40% by mass to 100% by mass, further preferably 45% by mass to 100% by mass, and still more preferably 50% by mass to 100% by mass.

[0053] Hereinafter, the polyalkylene glycol (PAG) and polyvinyl ether (PVE) contained in the lubricating oil composition of the present invention will be described in detail.

[0054] <Polyalkylene glycol (PAG)>

[0055] As the polyalkylene glycol (hereinafter sometimes simply referred to as "PAG"), a polyalkylene glycol having a structural unit represented by the following general formula (1) is used. This PAG may be a homopolymer having only one kind of this structural unit, or may be a copolymer composed of two or more kinds in combination. As the copolymerization mode of this copolymer, there is no particular limitation, and it may be a block copolymer, a random copolymer, or a graft copolymer.

[0056] From the viewpoint of easily exhibiting the effects of the present invention, the content of the structural unit represented by the following general formula (1) is preferably 50% by mass or more, more preferably 60% by mass or more, further preferably 70% by mass or more, still further preferably 80% by mass or more, yet further preferably 90% by mass or more, and still more preferably 95% by mass or more, based on all the structural units of the PAG. In addition, it is preferably 100% by mass or less.

[0057] The upper limit value and the lower limit value of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 50% by mass to 100% by mass, more preferably 60% by mass to 100% by mass, further preferably 70% by mass to 100% by mass, still further preferably 80% by mass to 100% by mass, yet further preferably 90% by mass to 100% by mass, and still more preferably 95% by mass to 100% by mass.

[0058] In addition, one kind of this PAG can be used alone, or two or more kinds can be used in combination.

[0059] [Chemical formula 5]

[0060]

[0061] In the above general formula (1), R 1 and R 2 each independently represent a hydrogen atom or a monovalent hydrocarbon group having 1 to 18 carbon atoms. R 3 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. n is an integer of 3 to 5.

[0062] A plurality of R 3 present may be the same or different from each other.

[0063] In addition, R 1 and R 2 may be the same or different from each other.

[0064] (R 1 and R 2 )

[0065] R 1 and R 2 each independently represent a hydrogen atom or a monovalent hydrocarbon group having 1 to 18 carbon atoms.

[0066] When the number of carbon atoms in the hydrocarbon group exceeds 18, it is difficult to produce PAG with excellent cooling performance.

[0067] As the monovalent hydrocarbon group having 1 to 18 carbon atoms that can be selected as R 1 and R 2 For example, alkyl groups having 1 to 18 carbon atoms such as methyl, ethyl, various propyl groups, various butyl groups, various pentyl groups, various hexyl groups, various heptyl groups, various octyl groups, various nonyl groups, various decyl groups, various undecyl groups, various dodecyl groups, various tridecyl groups, various tetradecyl groups, various pentadecyl groups, various hexadecyl groups, various heptadecyl groups, and various octadecyl groups; cycloalkyl groups having 3 to 18 carbon atoms such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, various methylcyclohexyl groups, various ethylcyclohexyl groups, various dimethylcyclohexyl groups, and various trimethylcyclohexyl groups; aryl groups having 6 to 18 carbon atoms such as phenyl, naphthyl, various methylphenyl groups, various ethylphenyl groups, various dimethylphenyl groups, and various trimethylphenyl groups; aralkyl groups having 6 to 18 carbon atoms such as benzyl, various phenylethyl groups, and various methylbenzyl groups, etc.

[0068] It should be noted that in this specification, the expression "various X groups" includes all isomers considered to be X groups. For example, "various alkyl groups" means "linear or branched alkyl groups". For example, "various propyl groups" means "n-propyl, isopropyl". In addition, "various butyl groups" means "n-butyl, sec-butyl, isobutyl, tert-butyl".

[0069] From the viewpoint of easily improving the cooling performance of PAG, the monovalent hydrocarbon group having 1 to 18 carbon atoms that can be selected as R 1 and R 2 preferably has 1 to 10 carbon atoms, more preferably 1 to 6 carbon atoms, still more preferably 1 to 4 carbon atoms, even more preferably 1 to 3 carbon atoms, yet even more preferably 1 to 2 carbon atoms, and most preferably 1 carbon atom.

[0070] In addition, from the viewpoint of easily improving the cooling performance of PAG, the monovalent hydrocarbon group having 1 to 18 carbon atoms that can be selected as R 1 and R 2 is preferably an alkyl group. The alkyl group preferably has 1 to 10 carbon atoms, more preferably 1 to 6 carbon atoms, still more preferably 1 to 4 carbon atoms, even more preferably 1 to 3 carbon atoms, yet even more preferably 1 to 2 carbon atoms, and most preferably 1 carbon atom.

[0071] Here, from the viewpoint of easily further improving the volume resistivity, at least one of R 1 and R 2 is preferably a monovalent hydrocarbon group having 1 to 18 carbon atoms, and preferably at least one of R 1 and R 2Both are monovalent hydrocarbon groups having 1 to 18 carbon atoms. The preferred hydrocarbon groups and the number of carbon atoms at this time are as described above.

[0072] (R 3 )

[0073] R 3 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

[0074] When the number of carbon atoms in the alkyl group exceeds 4, it is difficult to produce a PAG having excellent cooling performance.

[0075] As the alkyl group having 1 to 4 carbon atoms that can be selected as R 3 , for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, and tert-butyl can be cited.

[0076] From the viewpoint of easily improving the cooling performance of PAG, the number of carbon atoms of the alkyl group that can be selected as R 3 is preferably 1 to 3, more preferably 1 to 2, and further preferably 1.

[0077] It should be noted that, from the viewpoint of the balance of the cooling performance, volume resistivity, and low-temperature fluidity of PAG, R 3 is preferably a hydrogen atom or a methyl group. In addition, from the viewpoint of improving the cooling performance, R 3 is preferably a hydrogen atom, and from the viewpoint of improving the volume resistivity and low-temperature fluidity, a methyl group is preferred.

[0078] (n)

[0079] n is an integer of 3 to 5.

[0080] In the above general formula (1), the value of n represents the number of polymerization units of PAG. In the present invention, it is characterized by using a trimer to pentamer of PAG.

[0081] If n is 2 or less, the flash point of PAG decreases and the electrical insulation also decreases. In addition, if n is 6 or more, the cooling performance of PAG decreases.

[0082] Here, from the viewpoint of improving the cooling performance of PAG, the value of n is preferably 3 to 4, more preferably 3. On the other hand, from the viewpoint of improving the flash point and electrical insulation of PAG, the value of n is preferably 4 to 5, more preferably 5.

[0083] In addition, from the viewpoint of producing a PAG having an excellent balance of cooling performance, flash point, and electrical insulation, the value of n is preferably 4.

[0084] (Molecular weight)

[0085] From the viewpoint of producing a PAG with more excellent cooling performance, the molecular weight of the PAG is preferably 150 or more, more preferably 160 or more, further preferably 180 or more, still further preferably 200 or more, and yet further preferably 220 or more. In addition, it is preferably 1100 or less, more preferably 800 or less, further preferably 500 or less, still further preferably 400 or less, and yet further preferably 336 or less.

[0086] The upper and lower limit values of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 150 to 1100, more preferably 160 to 800, further preferably 180 to 500, still further preferably 200 to 400, and yet further preferably 220 to 336.

[0087] <Polyvinyl ether (PVE)>

[0088] As the polyvinyl ether (hereinafter, sometimes simply referred to as "PVE"), a polyvinyl ether having a structural unit represented by the following general formula (2) is used. This PVE may be a homopolymer having only one kind of this structural unit, or may be a copolymer composed of two or more kinds in combination. As the copolymerization mode of this copolymer, there is no particular limitation, and it may be a block copolymer, a random copolymer, or a graft copolymer.

[0089] Based on the structural unit of the following general formula (2), it is preferably 50% by mass or more, more preferably 60% by mass or more, further preferably 70% by mass or more, still further preferably 80% by mass or more, and yet further preferably 90% by mass or more, and still more preferably 95% by mass or more. In addition, it is preferably 100% by mass or less.

[0090] The upper and lower limit values of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 50% by mass to 100% by mass, more preferably 60% by mass to 100% by mass, further preferably 70% by mass to 100% by mass, still further preferably 80% by mass to 100% by mass, and yet further preferably 90% by mass to 100% by mass, and still more preferably 95% by mass to 100% by mass.

[0091] In addition, this PVE may be used alone or in combination of two or more kinds.

[0092] [Chemical formula 6]

[0093]

[0094] In the above general formula (2), R 5 , R 6 and R 7 each independently represents a hydrogen atom or a monovalent hydrocarbon group having 1 to 8 carbon atoms. R8 represents a divalent hydrocarbon group having 2 to 10 carbon atoms. R 9 represents a monovalent hydrocarbon group having 1 to 10 carbon atoms. m is 3 or 4. q is an integer from 0 to 10.

[0095] The plurality of R present 5 may be the same or different from each other. Regarding the plurality of R present 6 、R 7 、R 8 and R 9 The same also applies.

[0096] In addition, R 5 、R 6 and R 7 may be the same or different from each other.

[0097] In addition, when q is 0, the bond between the carbon atom (C) in the above general formula (2) and -OR 9 is a single bond, and this carbon atom (C) is directly bonded to -OR 9 .

[0098] (R 5 、R 6 and R 7 )

[0099] R 5 、R 6 and R 7 each independently represents a hydrogen atom or a monovalent hydrocarbon group having 1 to 8 carbon atoms.

[0100] When the number of carbon atoms in the hydrocarbon group exceeds 8, it is difficult to produce a PVE having excellent cooling performance.

[0101] As the monovalent hydrocarbon group having 1 to 8 carbon atoms that can be selected as R 5 、R 6 and R 7 , for example, alkyl groups having 1 to 8 carbon atoms such as methyl, ethyl, various propyl groups, various butyl groups, various pentyl groups, various hexyl groups, various heptyl groups, various octyl groups; cycloalkyl groups having 3 to 8 carbon atoms such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, various methylcyclohexyl groups, various ethylcyclohexyl groups, various dimethylcyclohexyl groups; aryl groups having 6 to 8 carbon atoms such as phenyl, various methylphenyl groups, various ethylphenyl groups, various dimethylphenyl groups; aralkyl groups having 6 to 8 carbon atoms such as benzyl, various phenylethyl groups, various methylbenzyl groups, etc. can be cited.

[0102] From the viewpoint of easily improving the cooling performance of PVE, the R that can be selected 5 、R 6 and R 7The number of carbon atoms of the monovalent hydrocarbon group is preferably 1 to 6, more preferably 1 to 4, still more preferably 1 to 3, even more preferably 1 to 2, and yet even more preferably 1.

[0103] In addition, from the viewpoint of easily improving the cooling performance of PVE, R 5 , R 6 and R 7 The monovalent hydrocarbon group having 1 to 8 carbon atoms is preferably an alkyl group. The number of carbon atoms of the alkyl group is preferably 1 to 6, more preferably 1 to 4, still more preferably 1 to 3, even more preferably 1 to 2, and yet even more preferably 1.

[0104] Here, from the viewpoint of easily further improving the cooling performance of PVE, it is preferable that at least one of R 5 , R 6 and R 7 is a hydrogen atom, more preferably two or more are hydrogen atoms, and still more preferably all three are hydrogen atoms.

[0105] (R 8 )

[0106] R 8 Each independently represents a divalent hydrocarbon group having 2 to 10 carbon atoms.

[0107] When the number of carbon atoms of the hydrocarbon group exceeds 10, it is difficult to produce PVE with excellent cooling performance.

[0108] In addition, it is difficult to manufacture PVE having 1 carbon atom in the hydrocarbon group.

[0109] Examples of the divalent hydrocarbon group having 2 to 10 carbon atoms that can be selected as R 8 include alkylene groups having 2 to 10 carbon atoms such as ethylene, 1,2-propylene, 1,3-propylene, various butylene groups, various pentylene groups, various hexylene groups, various heptylene groups, various octylene groups, various nonylene groups, and various decylene groups; cycloalkylene groups having 3 to 10 carbon atoms such as cyclopropylene, cyclobutylene, cyclopentylene, cyclohexylene, methylcyclohexylene, ethylcyclohexylene, and dimethylcyclohexylene; divalent aromatic groups having 6 to 10 carbon atoms such as various phenylene groups, various methylphenylene groups, various ethylphenylene groups, various dimethylphenylene groups, and various naphthylene groups; divalent alkylaromatic groups having a monovalent bonding site in the alkyl part and the aromatic part of alkylaromatic hydrocarbons such as toluene, xylene, and ethylbenzene; divalent alkylaromatic groups having a bonding site in the alkyl part of alkylaromatic hydrocarbons such as xylene and diethylbenzene.

[0110] From the viewpoint of easily improving the cooling performance of PVE, R 8The divalent hydrocarbon group preferably has 2 to 8 carbon atoms, more preferably 2 to 6 carbon atoms, and even more preferably 2 to 4 carbon atoms.

[0111] In addition, from the viewpoint of easily improving the cooling performance of PVE, the divalent hydrocarbon group having 2 to 10 carbon atoms that can be selected as R 8 is preferably an alkylene group. From the viewpoint of the balance between improving the cooling performance of PVE and the volume resistivity, the alkylene group preferably has 2 to 8 carbon atoms, more preferably 2 to 6 carbon atoms, and even more preferably 2 to 4 carbon atoms.

[0112] (R 9 )

[0113] R 9 represents a monovalent hydrocarbon group having 1 to 10 carbon atoms.

[0114] When the number of carbon atoms of the hydrocarbon group exceeds 10, it is difficult to produce PVE with excellent cooling performance.

[0115] As the monovalent hydrocarbon group having 1 to 10 carbon atoms that can be selected as R 9 , for example, there can be mentioned alkyl groups having 1 to 10 carbon atoms such as methyl, ethyl, various propyl groups, various butyl groups, various pentyl groups, various hexyl groups, various heptyl groups, various octyl groups, various nonyl groups, and various decyl groups; cycloalkyl groups having 3 to 10 carbon atoms such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, various methylcyclohexyl groups, various ethylcyclohexyl groups, and various dimethylcyclohexyl groups; aryl groups having 6 to 10 carbon atoms such as phenyl, various methylphenyl groups, various ethylphenyl groups, and various dimethylphenyl groups; arylalkyl groups having 6 to 10 carbon atoms such as benzyl, various phenylethyl groups, various methylbenzyl groups, various phenylpropyl groups, and various phenylbutyl groups, etc.

[0116] From the viewpoint of easily improving the cooling performance of PVE, the monovalent hydrocarbon group that can be selected as R 9 preferably has 1 to 8 carbon atoms, more preferably 1 to 6 carbon atoms, even more preferably 1 to 4 carbon atoms, still more preferably 1 to 3 carbon atoms, yet more preferably 1 to 2 carbon atoms, and further preferably 1 carbon atom.

[0117] In addition, from the viewpoint of easily improving the cooling performance of PVE, the monovalent hydrocarbon group having 1 to 10 carbon atoms that can be selected as R 9 is preferably an alkyl group. The alkyl group preferably has 1 to 8 carbon atoms, more preferably 1 to 6 carbon atoms, even more preferably 1 to 4 carbon atoms, still more preferably 1 to 3 or less carbon atoms, yet more preferably 1 to 2 carbon atoms, and further preferably 1 carbon atom.

[0118] (q)

[0119] q is an integer from 0 to 10.

[0120] When q is an integer greater than 10, it is difficult to produce PVE with excellent cooling performance.

[0121] It should be noted that, from the viewpoint of easily improving the cooling performance of PVE, the value of q is preferably from 0 to 5, more preferably from 0 to 3, further preferably from 0 to 2, still further preferably from 0 to 1, and yet further preferably 0.

[0122] (m)

[0123] m is 3 or 4.

[0124] In the above general formula (2), the value of m represents the number of polymerization units of PVE. In the present invention, it is characterized by using trimer or tetramer PVE.

[0125] If m is 2 or less, the flash point of PVE decreases. In addition, if m is 5 or more, the cooling performance of PVE decreases.

[0126] Here, from the viewpoint of improving the cooling performance of PVE, the value of m is preferably 3. On the other hand, from the viewpoint of improving the flash point of PVE, the value of m is preferably 4.

[0127] (Terminal structure of PVE)

[0128] The terminal structure of PVE is not particularly limited, and examples thereof include a hydrogen atom or a monovalent group derived from a saturated hydrocarbon, ether, alcohol, ketone, amide, or nitrile.

[0129] It should be noted that the terminal of PVE refers to the * part in the following general formula (2).

[0130] [Chemical formula 7]

[0131]

[0132] (Molecular weight)

[0133] From the viewpoint of producing PVE with more excellent cooling performance, the molecular weight of PVE is preferably 176 or more. In addition, it is preferably 5000 or less, more preferably 3000 or less, further preferably 1000 or less, still further preferably 500 or less, and yet further preferably 234 or less.

[0134] The upper limit and the lower limit of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 176 to 5000, more preferably 176 to 3000, further preferably 176 to 1000, still further preferably 176 to 500, and yet further preferably 176 to 234.

[0135] (Base oil (A2) other than synthetic oil (A1))

[0136] In the lubricating oil composition of one embodiment of the present invention, the base oil (A) may contain other base oils (A2) (hereinafter, also simply referred to as "other base oils (A2)") other than the synthetic oil (A1).

[0137] From the viewpoint of exerting the performance of the synthetic oil (A1) and more easily exerting the effects of the present invention, the content of the other base oil (A2) is preferably 70% by mass or less, more preferably 60% by mass or less, and still more preferably 55% by mass or less based on the total amount of the base oil (A).

[0138] As the other base oil (A2), one or more selected from synthetic oils other than the synthetic oil (A1) and mineral oils can be used.

[0139] Examples of synthetic oils other than the synthetic oil (A1) include polyalphaolefins such as alpha-olefin homopolymers and alpha-olefin copolymers (such as ethylene-alpha-olefin copolymers and other alpha-olefin copolymers having 8 to 14 carbon atoms); isoparaffins; various esters such as polyol esters and dibasic acid esters; various ethers such as polyphenyl ethers (excluding PVE); alkylbenzenes; alkylnaphthalenes; GTL base oils obtained by isomerizing waxes (Gas To Liquid (GTL) waxes) produced from natural gas by the Fischer-Tropsch method, etc.

[0140] Examples of mineral oils include atmospheric residua obtained by subjecting crude oils such as paraffinic crude oils, intermediate-base crude oils, or naphthenic crude oils to atmospheric distillation; distillates obtained by subjecting these atmospheric residua to vacuum distillation; mineral oils obtained by subjecting the distillates to one or more refining treatments such as solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, and hydrorefining; and so on.

[0141] The other base oil (A2) can be used alone as a mineral oil or in combination of multiple mineral oils, or can be used alone as a synthetic oil other than the synthetic oil (A1) or in combination of multiple synthetic oils other than the synthetic oil (A1). Further, one or more mineral oils can be used in combination with one or more synthetic oils other than the synthetic oil (A1).

[0142] Here, as the other base oil (A2), mineral oil is preferred. By using the synthetic oil (A1) and mineral oil in combination, the cooling performance can be sufficiently ensured without significantly reducing the cooling performance, and the electrical insulation can be further improved, and a lubricating oil composition having an extremely excellent balance between the cooling performance and the electrical insulation can be prepared.

[0143] From the above viewpoints, as the content of the mineral oil, it is preferably 10% by mass or more, more preferably 30% by mass or more, and still more preferably 40% by mass or more based on the total amount of the base oil (A). In addition, it is preferably 70% by mass or less, more preferably 60% by mass or less. The upper limit value and the lower limit value of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 10% by mass to 70% by mass, more preferably 30% by mass to 60% by mass, and still more preferably 40% by mass to 60% by mass.

[0144] In addition, the content ratio of the synthetic oil (A1) to the mineral oil [(synthetic oil (A1)) / (mineral oil)] is preferably 30 / 70 or more, more preferably 40 / 60 or more in terms of mass ratio. In addition, it is preferably 90 / 10 or less, more preferably 70 / 30 or less, and still more preferably 60 / 40 or less. The upper limit value and the lower limit value of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 30 / 70 to 90 / 10, more preferably 40 / 60 to 70 / 30, and still more preferably 40 / 60 to 60 / 40.

[0145] In addition, from the viewpoint of more easily exerting the effects of the present invention, preferably, the content of one or more synthetic oils (A1') selected from PAGs in which n is an integer of 2 or less and PAGs in which n is an integer of 6 or more in the above general formula (1) (wherein R 1 , R 2 and R 3 are as described above.), and PVE in which m is an integer of 2 or less and PVE in which m is an integer of 5 or more in the above general formula (2) (wherein R 5 , R 6 , R 7 , R 8 and R 9 are as described above.) is small.

[0146] Specifically, the content of the synthetic oil (A1') is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, still more preferably 3 parts by mass or less, even more preferably 1 part by mass or less, and still more preferably 0 part by mass with respect to 100 parts by mass of the synthetic oil (A1).

[0147] [Properties of Base Oil (A)]

[0148] In one aspect of the present invention, the base oil (A) preferably satisfies the properties defined in the following conditions (1) to (8).

[0149] <Condition (1): Relative heat transfer coefficient>

[0150] In one aspect of the present invention, the relative heat transfer coefficient of the base oil (A) is preferably 1.01 or more (Condition (1)).

[0151] The relative heat transfer coefficient described above is the heat transfer coefficient when the heat transfer coefficient of the mineral oil (α) that satisfies the following conditions (α1) to (α4) at 20°C is set to 1.00.

[0152] · Condition (α1): The kinematic viscosity at 20°C is 7.06 mm 2 / s.

[0153] · Condition (α2): The specific heat at 20°C is 1.67 kJ / (kg·K).

[0154] · Condition (α3): The density at 20°C is 0.857 g / cm 3 .

[0155] · Condition (α4): The thermal conductivity at 20°C is 0.141 W / (m·K).

[0156] The heat transfer coefficient is an index of the ease of heat transfer between two substances (i.e., the base oil (A) and the object to be cooled). In condition (1), the heat transfer coefficient of the base oil (A) is defined as the relative heat transfer coefficient based on the heat transfer coefficient of the mineral oil (α). It can be said that the larger the relative heat transfer coefficient defined in condition (1), the better the cooling performance.

[0157] The heat transfer coefficient (Aα, unit: W / (m 2 ·K)) of the fluid at 20°C can be calculated according to the following formula (I).

[0158] [Mathematical formula 1]

[0159]

[0160] In the above formula (I), A D20 is the density of the fluid at 20°C (unit: g / cm 3 ). A C20 is the specific heat of the fluid at 20°C (unit: kJ / (kg·K)). A HC20 is the thermal conductivity of the fluid at 20°C (unit: W / (m·K)). A KV20 is the kinematic viscosity of the fluid at 20°C (unit: mm 2 / s).

[0161] Here, the relative heat transfer coefficient defined in condition (1) is more preferably 1.03 or more, further preferably 1.06 or more, and even more preferably 1.10 or more. Additionally, it is usually 1.50 or less.

[0162] The upper and lower limit values of these numerical ranges can be combined arbitrarily. Specifically, it is preferably 1.01 to 1.50, more preferably 1.03 to 1.50, further preferably 1.06 to 1.50, and still further preferably 1.10 to 1.50.

[0163] <Condition (2): Kinematic viscosity>

[0164] In one aspect of the present invention, the kinematic viscosity of the base oil (A) at 40 °C (hereinafter, also referred to as "40 °C kinematic viscosity") is preferably 6.00 mm 2 / s or less (Condition (2)). The lower the kinematic viscosity of the base oil (A), the higher the cooling performance. On the other hand, the flash point of the base oil (A) is more likely to decrease. However, in the present invention, by including the synthetic oil (A1), the base oil (A) has a low viscosity and a high flash point is ensured.

[0165] Here, the 40 °C kinematic viscosity of the base oil (A) specified in Condition (2) is more preferably 5.80 mm 2 / s or less, further preferably 5.60 mm 2 / s or less, still further preferably 5.40 mm 2 / s or less. In addition, it is usually 1.20 mm 2 / s or more.

[0166] The upper and lower limit values of these numerical ranges can be combined arbitrarily. Specifically, it is preferably 1.20 mm 2 / s to 6.00 mm 2 / s, more preferably 1.20 mm 2 / s to 5.80 mm 2 / s, further preferably 1.20 mm 2 / s to 5.60 mm 2 / s, still further preferably 1.20 mm 2 / s to 5.40 mm 2 / s.

[0167] In addition, in Condition (2), in addition to the 40 °C kinematic viscosity of the base oil (A), it is also preferable that the kinematic viscosity of the base oil (A) at 20 °C (hereinafter, also referred to as "20 °C kinematic viscosity") is a specified value or less. Specifically, it is preferably 11.0 mm 2 / s or less, more preferably 10.5 mm 2 / s or less, further preferably 10.0 mm 2 / s or less. In addition, it is usually 1.50 mm 2 / s or more.

[0168] The upper and lower limit values of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 1.50 mm 2 / s to 11.0 mm 2 / s, more preferably 1.50 mm 2 / s to 10.5 mm 2 / s, further preferably 1.50 mm 2 / s to 10.0 mm 2 / s.

[0169] It should be noted that in this specification, the kinematic viscosity at 40 °C and the kinematic viscosity at 20 °C of the base oil (A) are values measured or calculated in accordance with JIS K2283:2000.

[0170] <Condition (3): Specific heat>

[0171] In one aspect of the present invention, the base oil (A) preferably has a specific heat at 20 °C of 1.60 kJ / (kg·K) or more (Condition (3)). The greater the specific heat at 20 °C, the easier it is to improve the cooling performance of the base oil (A).

[0172] From the above viewpoints, the specific heat of the base oil (A) at 20 °C specified in Condition (3) is more preferably 1.62 kJ / (kg·K) or more, and further preferably 1.64 kJ / (kg·K) or more. Additionally, it is usually 1.75 kJ / (kg·K) or less.

[0173] The upper and lower limit values of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 1.60 kJ / (kg·K) to 1.75 kJ / (kg·K), more preferably 1.62 kJ / (kg·K) to 1.75 kJ / (kg·K), and further preferably 1.64 kJ / (kg·K) to 1.75 kJ / (kg·K).

[0174] It should be noted that in this specification, the specific heat of the base oil (A) at 20 °C refers to the value calculated by the following formula (f1) using the thermal conductivity measurement value and the thermal permeability measurement value measured by a thermal conductivity measurement device and the density at 20 °C measured by the method described later.

[0175] (Specific heat at 20 °C) = (Thermal permeability at 20 °C) 2 / {(Thermal conductivity at 20 °C) × (Density at 20 °C)} ···· (f1)

[0176] <Condition (4): Density>

[0177] In one aspect of the present invention, the base oil (A) preferably has a density at 20 °C of 0.840 g / cm 3As described above (Condition (4)), the greater the density at 20°C, the easier it is to improve the cooling performance of the base oil (A).

[0178] From the above viewpoints, the density of the base oil (A) specified in Condition (4) at 20°C is more preferably 0.850 g / cm 3 or more, further preferably 0.880 g / cm 3 or more, still further preferably 0.900 g / cm 3 or more. Additionally, it is usually 0.980 g / cm 3 or less.

[0179] The upper and lower limit values of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 0.840 g / cm 3 to 0.980 g / cm 3 , more preferably 0.850 g / cm 3 to 0.980 g / cm 3 , further preferably 0.880 g / cm 3 to 0.980 g / cm 3 , still further preferably 0.900 g / cm 3 to 0.980 g / cm 3 .

[0180] It should be noted that in this specification, the density of the base oil (A) at 20°C refers to the value measured in accordance with JIS K 2249-1:2011 (Crude oil and petroleum products - Method for determination of density - Part 1: Oscillation method).

[0181] <Condition (5): Thermal conductivity>

[0182] In one aspect of the present invention, the base oil (A) preferably has a thermal conductivity at 20°C of 0.135 W / (m·K) or more (Condition (5)). The greater the thermal conductivity at 20°C, the easier it is to improve the cooling performance of the base oil (A).

[0183] From the above viewpoints, the thermal conductivity of the base oil (A) specified in Condition (5) at 20°C is more preferably 0.140 W / (m·K) or more, further preferably 0.143 W / (m·K) or more, still further preferably 0.145 W / (m·K) or more, and yet further preferably 0.147 W / (m·K) or more. Additionally, it is usually 0.165 W / (m·K) or less.

[0184] The upper and lower limit values of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 0.135 W / (m·K) to 0.165 W / (m·K), more preferably 0.140 W / (m·K) to 0.165 W / (m·K), further preferably 0.143 W / (m·K) to 0.165 W / (m·K), still further preferably 0.145 W / (m·K) to 0.165 W / (m·K), and even further preferably 0.147 W / (m·K) to 0.165 W / (m·K).

[0185] It should be noted that in this specification, the thermal conductivity of the base oil (A) at 20°C refers to the thermal conductivity measured by a thermal conductivity measuring device.

[0186] <Condition (6): Volume resistivity>

[0187] In one embodiment of the present invention, the base oil (A) preferably has a volume resistivity of 1.00×10 8 Ω·m or more at 25°C (Condition (6)). The higher the volume resistivity, the more excellent the electrical insulation of the base oil (A).

[0188] Here, from the viewpoint of making the electrical insulation of the base oil (A) better, the volume resistivity of the base oil (A) at 25°C specified in Condition (6) is preferably 1.00×10 9 Ω·m or more, more preferably 5.00×10 9 Ω·m or more, and further preferably 8.00×10 9 Ω·m or more. In addition, it is usually 1.00×10 13 Ω·m or less.

[0189] The upper and lower limit values of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 1.00×10 8 Ω·m to 1.00×10 13 Ω·m, more preferably 1.00×10 9 Ω·m to 1.00×10 13 ·m, further preferably 5.00×10 9 Ω·m to 1.00×10 13 Ω·m, still further preferably 8.00×10 9 Ω·m to 1.00×10 13 Ω·m.

[0190] It should be noted that from the viewpoint of further increasing the volume resistivity of the base oil (A), the synthetic oil (A1) preferably contains the polyvinyl ether represented by the above general formula (2).

[0191] It should be noted that in this specification, the volume resistivity of base oil (A) at 25°C refers to the value measured under the conditions of a measurement temperature of 25°C and an applied voltage of 250V in accordance with JIS C 2101:1999.

[0192] <Condition (7): Flash point>

[0193] In one embodiment of the present invention, the flash point of base oil (A) is preferably 100°C or higher (Condition (7)). By setting the flash point of base oil (A) to 100°C or higher, it becomes difficult for base oil (A) to catch fire, and safety can be easily improved.

[0194] Here, the flash point specified in Condition (7) is preferably 110°C or higher, more preferably 120°C or higher, further preferably 130°C or higher, still further preferably 140°C or higher, and yet further preferably 150°C or higher. Additionally, it is usually 200°C or lower.

[0195] The upper and lower limit values of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 100°C to 200°C, more preferably 110°C to 200°C, further preferably 120°C to 200°C, still further preferably 130°C to 200°C, yet further preferably 140°C to 200°C, and even more preferably 150°C to 200°C.

[0196] It should be noted that in this specification, the flash point of base oil (A) refers to the value measured by the Cleveland Open Cup method (COC method) in accordance with JIS K 2265-4:2007.

[0197] <Condition (8): Pour point>

[0198] In one embodiment of the present invention, base oil (A) preferably has a pour point of -40°C or lower (Condition (8)). By setting the pour point of base oil (A) to -40°C or lower, it can withstand use in cold regions.

[0199] Here, the pour point specified in Condition (8) is more preferably -45°C or lower, further preferably -50°C or lower, still further preferably -55°C or lower, and yet further preferably -60°C or lower.

[0200] It should be noted that in this specification, the pour point of base oil (A) refers to the value measured in accordance with JIS K 2269:1987 (Test Method for Pour Point of Crude Oil and Petroleum Products and Cloud Point of Petroleum Products).

[0201] [Additive]

[0202] The lubricating oil composition of one embodiment of the present invention may contain additives such as antiwear agents, antioxidants, viscosity index improvers, rust inhibitors, metal deactivators, defoamers, and detergent-dispersants as needed within the range that does not impair the effects of the present invention.

[0203] These additives may be used singly or in combination of two or more.

[0204] There is no particular limitation on the total content of these additives, and it is, for example, about 0 to 20% by weight based on the total amount of the composition.

[0205] <Antiwear agent>

[0206] There is no particular limitation on the antiwear agent, and any antiwear agent can be appropriately selected from the antiwear agents conventionally used in lubricating oils. For example, when an electric motor and a gear reducer are used in combination in a hybrid vehicle or an electric vehicle, in order not to impair the electrical insulation as much as possible, it is preferable to use one or more selected from neutral phosphorus compounds, acidic phosphites or their amine salts, and sulfur compounds.

[0207] The content of the antiwear agent is not particularly limited, and it is, for example, about 0.01 to 5% by weight based on the total amount of the composition.

[0208] Examples of the neutral phosphorus compounds include aromatic neutral phosphates such as tricresyl phosphate, triphenyl phosphate, tris(dimethylphenyl) phosphate, trimethylphenylphenyl phosphate, tricresyl thiophosphate, and triphenyl thiophosphate; aliphatic neutral phosphates such as tributyl phosphate, tris(2-ethylhexyl) phosphate, tributoxy phosphate, and tributyl thiophosphate; aromatic neutral phosphites such as triphenyl phosphite, tricresyl phosphite, tris(nonylphenyl) phosphite, diphenylmono(2-ethylhexyl) phosphite, diphenylmonotridecyl phosphite, tricresyl thiophosphite, and triphenyl thiophosphite; and aliphatic neutral phosphites such as tributyl phosphite, trioctyl phosphite, tridecyl phosphite, tris(tridecyl) phosphite, trioleyl phosphite, tributyl thiophosphite, and trioctyl thiophosphite. They may be used singly or in combination of two or more.

[0209] As acidic phosphites, examples include aliphatic acidic phosphate amine salts such as di(2-ethylhexyl) acid phosphate amine salt, dilauryl acid phosphate amine salt, dioleyl acid phosphate amine salt; aliphatic acidic phosphites such as di(2-ethylhexyl) hydrogen phosphite, dilauryl hydrogen phosphite, dioleyl hydrogen phosphite and their amine salts; aromatic acidic phosphate amine salts such as diphenyl acid phosphate amine salt, xylenyl acid phosphate amine salt; aromatic acidic phosphites such as diphenyl hydrogen phosphite, xylenyl hydrogen phosphite and their amine salts; sulfur-containing acidic phosphate amine salts such as S-octylthioethyl acid phosphate amine salt, S-dodecylthioethyl acid phosphate amine salt; sulfur-containing acidic phosphites such as S-octylthioethyl hydrogen phosphite, S-dodecylthioethyl hydrogen phosphite and their amine salts, etc. They can be used alone or in combination of two or more.

[0210] As sulfur compounds, various sulfur compounds can be used. Specifically, examples include thiadiazole compounds, polysulfide compounds, dithiocarbamate compounds, sulfurized oil and fat compounds, and sulfurized olefin compounds, etc. They can be used alone or in combination of two or more.

[0211] <Antioxidant>

[0212] As an antioxidant, any antioxidant can be appropriately selected from known antioxidants conventionally used as antioxidants for lubricating oils. For example, amine antioxidants (diphenylamine-based, naphthylamine-based), phenolic antioxidants, molybdenum antioxidants, sulfur antioxidants, phosphorus antioxidants, etc. can be cited. The antioxidant can be used alone or in combination of two or more. The content of the antioxidant is not particularly limited, and is, for example, about 0.05 to 7% by weight based on the total amount of the composition.

[0213] <Viscosity index improver>

[0214] As a viscosity index improver, for example, poly(meth)acrylate, dispersed poly(meth)acrylate, olefin copolymers (such as ethylene-propylene copolymers, etc.), dispersed olefin copolymers, styrene copolymers (such as styrene-diene copolymers, styrene-isoprene copolymers, etc.) can be cited. The viscosity index improver can be used alone or in combination of two or more. The blending amount of the viscosity index improver (in terms of resin component conversion) is not particularly limited. For example, from the aspect of blending effect, it is 0.1% by weight or more and 10% by weight or less based on the total amount of the composition.

[0215] <Rust inhibitor>

[0216] As rust inhibitors, for example, fatty acids, half esters of alkenyl succinic acids, fatty acid soaps, alkyl sulfonates, fatty acid esters of polyhydric alcohols, fatty acid amides, oxidized paraffin, alkyl polyoxyethylene ethers, etc. can be cited. The rust inhibitor can be used alone or in combination of two or more. The preferred blending amount of the rust inhibitor is not particularly limited, and is about 0.01% by weight or more and 3% by weight or less based on the total amount of the composition.

[0217] <Metal deactivator>

[0218] As metal deactivators, for example, benzotriazole, triazole derivatives, benzotriazole derivatives, thiadiazole derivatives can be cited. The metal deactivator can be used alone or in combination of two or more. The content of the metal deactivator is not particularly limited, and is preferably 0.01 to 5% by weight based on the total amount of the composition.

[0219] <Defoamer>

[0220] As defoamers, for example, silicone-based compounds such as dimethylpolysiloxane, polyacrylates, etc. can be cited. The defoamer can be used alone or in combination of two or more. The content of the defoamer is not particularly limited, and is about 0.001% by weight or more and 0.5% by weight or less based on the total amount of the composition.

[0221] <Detergent-dispersant>

[0222] As detergent-dispersants, for example, succinimide compounds, boron-based imide compounds, amide-based compounds, etc. can be cited. The detergent-dispersant can be used alone or in combination of two or more. The content of the detergent-dispersant is not particularly limited, and is preferably 0.1 to 20% by weight based on the total amount of the composition.

[0223] [Properties of the lubricating oil composition]

[0224] The lubricating oil composition of one embodiment of the present invention preferably satisfies the above conditions (1) to (8) specified for the properties of the base oil (A). Regarding the preferred range, it is the same as the specification in the above conditions (1) to (8).

[0225] [Uses of the lubricating oil composition]

[0226] The lubricating oil composition of the present invention has excellent cooling performance, ensures electrical insulation, and also has a high flash point. In addition, lubricity is also ensured.

[0227] Therefore, the lubricating oil composition of the present invention can be suitably used as a cooling oil for cooling various equipment. In particular, it can be suitably used as a cooling oil for cooling the electric vehicle equipment of electric vehicles.

[0228] Specifically, for example, it can be suitably used as a cooling oil for cooling one or more electric vehicle devices selected from electric motors, generators, electrical storage devices, converters, inverters, engines, and transmissions.

[0229] It should be noted that the above electric motor can be a motor dedicated for driving or a motor that also serves as a generator.

[0230] The above generator listed as an electric vehicle device refers to a generator separately mounted from the motor that also serves as a generator.

[0231] Examples of the above electrical storage device include batteries and capacitors.

[0232] It should be noted that in one aspect of the present invention, there is provided a method of using the lubricating oil composition of the present invention for cooling electric vehicle devices provided in an electric vehicle. As the electric vehicle devices, as described above, one or more selected from electric motors, generators, electrical storage devices, converters, inverters, engines, and transmissions can be cited.

[0233] [Cooling System]

[0234] The lubricating oil composition of the present invention has excellent cooling performance, ensures electrical insulation, and has a high flash point. In addition, lubricity is also ensured.

[0235] The lubricating oil composition of the present invention has excellent cooling performance, ensures electrical insulation, and has a high flash point. In addition, lubricity is also ensured.

[0236] Therefore, the lubricating oil composition of the present invention lubricates the device and cools the device, for example, by circulating in various devices such as electric vehicle devices.

[0237] Here, in one aspect of the present invention, there is provided a cooling system for cooling electric vehicle devices, which includes the above lubricating oil composition of the present invention. As the electric vehicle devices, as described above, one or more selected from electric motors, generators, electrical storage devices, converters, inverters, engines, and transmissions can be cited.

[0238] The cooling system has a circulation path for circulating the above lubricating oil composition and a cooling target part. The above cooling target part is the above equipment (preferably the equipment for electric vehicles). The cooling method in the above cooling target part can be either a direct cooling method or an indirect cooling method, and is appropriately set according to the cooling method required by the above equipment (preferably the equipment for electric vehicles). It should be noted that the cooling system may further include a supply device for supplying the above lubricating oil composition to the above cooling target part via the above circulation path. In addition, it may also be that a sensor part for checking the temperature of the above cooling target part and a control device for controlling the operation of the above supply device according to the temperature checked by the sensor part are further provided.

[0239] In this specification, the "cooling system" refers to an "object" that includes at least the above circulation path and the above cooling target part and functions to cool the above cooling target part, and can also be referred to as a "device" that includes multiple structures and functions to cool the above cooling target part.

[0240] [Manufacturing method of lubricating oil composition]

[0241] The manufacturing method of the lubricating oil composition of the present invention is not particularly limited. The manufacturing method of the lubricating oil composition according to one embodiment includes a step of preparing a base oil (A), and the base oil (A) contains at least one synthetic oil (A1) selected from polyalkylene glycols having a structural unit represented by the above general formula (1) and polyvinyl ethers having a structural unit represented by the above general formula (2).

[0242] In addition, it may include a step of mixing additives in the base oil (A) as needed. The additives can be incorporated by any method, and the order and method of incorporation are not limited.

[0243] [One aspect of the present invention provided]

[0244] According to one aspect of the present invention, the following [1] to

[12] are provided.

[0245] [1] A lubricating oil composition containing a base oil (A),

[0246] The above base oil (A) contains at least one synthetic oil (A1) selected from polyalkylene glycols having a structural unit represented by the following general formula (1) and polyvinyl ethers having a structural unit represented by the following general formula (2).

[0247] [Chemical formula 8]

[0248]

[0249] [In the above general formula (1), R 1 and R2 Each independently represents a hydrogen atom or a monovalent hydrocarbon group having 1 to 18 carbon atoms. R 3 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. n is an integer of 3 to 5.]

[0250] [Chemical formula 9]

[0251]

[0252] [In the above general formula (2), R 5 , R 6 and R 7 each independently represents a hydrogen atom or a monovalent hydrocarbon group having 1 to 8 carbon atoms. R 8 represents a divalent hydrocarbon group having 2 to 10 carbon atoms. R 9 represents a monovalent hydrocarbon group having 1 to 10 carbon atoms. m is 3 or 4. q is an integer of 0 to 10.]

[0253] [2] The lubricating oil composition according to [1], wherein, in the above general formula (1), R 3 is methyl.

[0254] [3] The lubricating oil composition according to [1] or [2], wherein, in the above general formula (2), R 5 , R 6 and R 7 are hydrogen atoms,

[0255] R 9 is methyl,

[0256] q = 0.

[0257] [4] The lubricating oil composition according to any one of [1] to [3], wherein the content of the above synthetic oil (A1) is 30% by mass to 100% by mass based on the total amount of the above base oil (A).

[0258] [5] The lubricating oil composition according to any one of [1] to [4], having a relative heat transfer coefficient of 1.01 or more,

[0259] The above relative heat transfer coefficient is the heat transfer coefficient when the heat transfer coefficient at 20°C of a mineral oil (α) satisfying the following conditions (α1) to (α4) is set to 1.00.

[0260] · Condition (α1): The kinematic viscosity at 20°C is 7.06 mm 2 / s.

[0261] · Condition (α2): The specific heat at 20°C is 1.67 kJ / (kg·K).

[0262] ·Condition (α3): The density at 20 °C is 0.857 g / cm 3 .

[0263] ·Condition (α4): The thermal conductivity at 20 °C is 0.141 W / (m·K).

[0264] [6] The lubricating oil composition according to any one of [1] to [5], having a volume resistivity at 25 °C of 1.00×10 8 Ω·m or more.

[0265] [7] The lubricating oil composition according to any one of [1] to [6], having a flash point of 100 °C or more.

[0266] [8] The lubricating oil composition according to any one of [1] to [7], having a pour point of -40 °C or less.

[0267] [9] The lubricating oil composition according to any one of [1] to [8] is used for cooling an electric vehicle device.

[0268]

[10] The lubricating oil composition according to [9], wherein the electric vehicle device is one or more selected from a motor, a generator, a storage battery, a converter, an inverter, an engine, and a transmission.

[0269]

[11] A method of use, wherein the lubricating oil composition according to any one of [1] to

[10] is used for cooling an electric vehicle device.

[0270]

[12] A cooling system for cooling an electric vehicle device, comprising the lubricating oil composition according to any one of [1] to

[10] .

[0271] Examples

[0272] The present invention will be specifically described by the following examples, but the present invention is not limited to the following examples.

[0273] [Examples 1 to 9 and Comparative Examples 1 to 9]

[0274] Two kinds of the following various base oils were used alone or in combination as shown in Tables 1 to 3 as the lubricating oil compositions of Examples 1 to 9 and Comparative Examples 1 to 9.

[0275] <Polyalkylene glycol>

[0276] In the above general formula (1), R 1 , R 2 and R 3 Are five kinds of polypropylene glycols "PPG-2" to "PPG-6" with methyl groups and only different values of n.

[0277] · "PPG-2": n = 2, molecular weight = 162

[0278] · "PPG-3": n = 3, molecular weight = 220

[0279] · "PPG-4": n = 4, molecular weight = 278

[0280] · "PPG-5": n = 5, molecular weight = 336

[0281] · "PPG-6": n = 6, molecular weight = 394

[0282] <Polyvinyl ether>

[0283] In the above general formula (2), R 5 , R 6 and R 7 are hydrogen atoms, q = 0, R 9 is methyl, and there are 4 kinds of polyvinyl ethers "PVE(Me)-2" to "PVE(Me)-5" with different values of m.

[0284] · "PVE(Me)-2": m = 2, both ends are hydrogen atoms, molecular weight = 118

[0285] · "PVE(Me)-3": m = 3, both ends are hydrogen atoms, molecular weight = 176

[0286] · "PVE(Me)-4": m = 4, both ends are hydrogen atoms, molecular weight = 234

[0287] · "PVE(Me)-5": m = 5, both ends are hydrogen atoms, molecular weight = 292

[0288] <Ester>

[0289] · "Ester 1": 2-ethylhexyl oleate

[0290] · "Ester 2": di(2-ethylhexyl) azelate

[0291] <Mineral oil>

[0292] · "Mineral oil 1": Mineral oil equivalent to VG2

[0293] · "Mineral oil 2": Mineral oil equivalent to VG5, equivalent to the above mineral oil (α).

[0294] <Others>

[0295] · Ethylene glycol

[0296] · Water

[0297] [Methods for measuring various physical property values]

[0298] The measurements and calculations of the properties of the lubricating oil compositions of Examples 1 to 9 and Comparative Examples 1 to 9 were carried out according to the procedures shown below. It should be noted that in this example, since no additives other than the base oil were incorporated for the study, the properties of the lubricating oil compositions are also the properties of the base oil.

[0299] (1) Kinematic viscosity at 40 °C

[0300] It was measured in accordance with JIS K2283:2000.

[0301] (2) Kinematic viscosity at 20 °C

[0302] It was calculated using the measurement results of the kinematic viscosity at 40 °C and the kinematic viscosity at 100 measured in accordance with JIS K2283:2000.

[0303] (3) Density at 20 °C

[0304] It was measured in accordance with JIS K 2249-1:2011 (Crude oil and petroleum products - Methods for determination of density - Part 1: Oscillation method).

[0305] (4) Specific heat at 20 °C

[0306] The thermal conductivity measurement value and the thermal permeability measurement value were obtained by a thermal conductivity measurement device (manufactured by C-THERM Technology Co., Ltd., TCi), and calculated using the above formula (f1). The density at 20 °C was the value measured in the above (3).

[0307] (5) Thermal conductivity at 20 °C

[0308] The thermal conductivity was measured using a thermal conductivity measurement device (manufactured by C-THERM Technology Co., Ltd., TCi).

[0309] (6) Flash point

[0310] It was measured in accordance with JIS K 2265-4:2007 by the Cleveland open cup method (COC method).

[0311] (7) Volume resistivity at 25 °C

[0312] It was measured in accordance with JIS C2101:1999 under the conditions of a measurement temperature of 25 °C and an applied voltage of 250 V.

[0313] <Calculation of relative heat transfer coefficient>

[0314] Based on the density at 20°C, specific heat at 20°C, thermal conductivity at 20°C, and kinematic viscosity at 20°C obtained through the above measurements, the heat transfer coefficient at 20°C of the lubricating oil compositions of Examples 1 to 9 and Comparative Examples 1 to 9 was calculated using the above formula (I).

[0315] Then, the heat transfer coefficients of Examples 1 to 9, Comparative Examples 1 to 7, and Comparative Example 9 were calculated with the heat transfer coefficient of Comparative Example 8 (using mineral oil 2 equivalent to mineral oil (α)) set to 1.00, and taken as the relative heat transfer coefficients.

[0316] <Evaluation>

[0317] In this example, the passing criteria are as follows.

[0318] · Relative heat transfer coefficient: 1.01 or more

[0319] · Volume resistivity: 1.00×10 8 Ω·m or more

[0320] · Flash point: 100°C or more

[0321] · Pour point: -40°C or less

[0322] The results are shown in Tables 1 to 3.

[0323] [Table 1]

[0324] Table 1

[0325]

[0326] [Table 2]

[0327] Table 2

[0328]

[0329] [Table 3]

[0330]

[0331] From the results shown in Table 1, the following can be known.

[0332] As shown in Examples 1 to 3, it can be seen that in the above general formula (1), PAG with n values of 3 to 5 has excellent cooling performance, high flash point, low pour point, and excellent electrical insulation.

[0333] In contrast, it can be seen that in the above general formula (1), PAG with n = 2 has a low flash point and low volume resistivity, so the electrical insulation is poor. It can also be seen that in the above general formula (1), PAG with n = 6 has a low relative heat transfer coefficient and poor cooling performance.

[0334] In addition, based on the results shown in Table 2, the following can be known.

[0335] As shown in Examples 4 and 5, it can be known that in the above general formula (2), PVE with m value of 3 - 4 has excellent cooling performance, high flash point, low pour point, and excellent electrical insulation.

[0336] In contrast, it can be known that in the above general formula (2), PVE with m value of 2 has a low flash point. In addition, in the above general formula (2), PVE with n value of 5 has a low relative heat transfer coefficient and poor cooling performance.

[0337] Furthermore, based on the results shown in Table 3, the following can be known.

[0338] From the results shown in Examples 6 - 9, it can be known that a lubricating oil composition containing PAG with n value of 3 - 4 in the above general formula (1) and PVE with m value of 3 - 4 in the above general formula (2) has excellent cooling performance, high flash point, low pour point, and excellent electrical insulation.

[0339] In contrast, it can be known that in the cases of using only a specific ester oil (Comparative Examples 5 and 6), using only mineral oil (Comparative Examples 7 and 8), and using a mixture of ethylene glycol and water (Comparative Example 9), at least any one of the relative heat transfer coefficient, pour point, and volume resistivity does not meet the above qualified criteria.

Claims

1. A method for using a lubricating oil composition, which uses the lubricating oil composition for cooling an electric vehicle device, and the lubricating oil composition contains a base oil (A). The base oil (A) contains one or more synthetic oils (A1) selected from polyalkylene glycols having a structural unit represented by the following general formula (1) and trimers or tetramers of polyethylene vinyl ethers having a structural unit represented by the following general formula (2). In the general formula (1), R 1 and R 2 each independently represent a hydrogen atom or a monovalent hydrocarbon group having 1 to 18 carbon atoms, R 3 represents a methyl group, and n is an integer of 3 to 5. In the general formula (2), R 5 , R 6 and R 7 each independently represent a hydrogen atom or a monovalent hydrocarbon group having 1 to 8 carbon atoms, R 8 represents a divalent hydrocarbon group having 2 to 10 carbon atoms, R 9 represents a monovalent hydrocarbon group having 1 to 10 carbon atoms, m is 3 or 4, and q is an integer of 0 to 10.

2. The method for use according to claim 1. Wherein, In the general formula (2), R 5 , R 6 and R 7 are hydrogen atoms, R 9 is methyl, q＝0。 3. The method for use according to claim 1. Wherein, The content of the synthetic oil (A1) is 30% by mass to 100% by mass based on the total amount of the base oil (A).

4. The method for use according to claim 1, wherein the relative heat transfer coefficient of the lubricating oil composition is 1.01 or more. The relative heat transfer coefficient is the heat transfer coefficient when the heat transfer coefficient at 20 °C of a mineral oil (α) satisfying the following conditions (α1) to (α4) is set to 1.

00. ·Condition (α1): The kinematic viscosity at 20 °C is 7.06 mm 2 / s, · Condition (α2): The specific heat at 20 °C is 1.67 kJ / (kg·K). ·Condition (α3): The density at 20 °C is 0.857 g / cm 3 , · Condition (α4): The thermal conductivity at 20 °C is 0.141 W / (m·K).

5. According to the usage method described in claim 1, the volume resistivity of the lubricating oil composition at 25 °C is 1.00×10 8 Ω·m or more.

6. The method for use according to claim 1, wherein the flash point of the lubricating oil composition is 100 °C or more.

7. The method for using the lubricating oil composition according to claim 1, wherein the pour point of the lubricating oil composition is -40 °C or lower.

8. The method for use according to claim 1. Wherein, The content of the base oil (A) is 80% by mass to 100% by mass based on the total amount of the lubricating oil composition.

9. The method for use according to claim 1. Wherein, The content of the base oil (A) is 95% by mass to 100% by mass based on the total amount of the lubricating oil composition.

10. The method for use according to claim 1. Wherein, The content of the synthetic oil (A1) is 50% by mass to 100% by mass based on the total amount of the base oil (A).

11. The method for use according to claim 1. Wherein, The content of the structural unit represented by the following general formula (1) is 80% by mass to 100% by mass based on all the structural units of the polyalkylene glycol.

12. The method for use according to claim 1. Wherein, The content of the structural unit represented by the following general formula (1) is 95% by mass to 100% by mass based on all the structural units of the polyalkylene glycol.

13. The method for use according to claim 1. Wherein, The terminal structure of the polyethylene vinyl ether is a hydrogen atom.

14. The method for use according to claim 1. Wherein, The molecular weight of the polyethylene vinyl ether is 176 to 1000.

15. The method for use according to claim 1. Wherein, The molecular weight of the polyethylene vinyl ether is 176 to 500.

16. The method for use according to claim 1. Wherein, The base oil (A) further contains other base oils (A2).

17. The method for use according to claim 16. Wherein, The other base oil (A2) is a mineral oil.

18. The method for use according to claim 17. Among them, the content of the mineral oil is 10% by mass to 70% by mass based on the total amount of the base oil (A).

19. The method of use according to claim 1, wherein, The kinematic viscosity of the base oil (A) at 40 °C is 1.20 mm 2 / s to 6.00 mm 2 / s.

20. The method of use according to claim 1, wherein, the specific heat of the base oil (A) at 20°C is 1.60 kJ / (kg·K) to 1.75 kJ / (kg·K).

21. The method of use according to claim 1, wherein, The density of the base oil (A) at 20 °C is 0.840 g / cm 3 to 0.980 g / cm 3 .

22. The method of use according to claim 1, wherein, the thermal conductivity of the base oil (A) at 20°C is 0.135 W / (m·K) to 0.165 W / (m·K).

23. The method of use according to claim 1, wherein, The volume resistivity of the base oil (A) at 25 °C is 1.00×10 8 Ω·m to 1.00×10 13 Ω·m.

24. The method of use according to claim 1, wherein, the flash point of the base oil (A) is 100°C to 200°C.

25. The method of use according to claim 1, wherein, the pour point of the base oil (A) is -40°C or lower.

26. The method of use according to claim 1, wherein, the equipment for electric vehicles is one or more selected from the group consisting of an electric motor, a generator, a storage battery, a converter, an inverter, an engine, and a transmission.

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