Ionic liquid and lubricant composition

Abstract

Provision of ionic liquids that can maintain low friction for a long period even under high load conditions. The present invention provides an ionic liquid having a nitrogen-containing coordination compound having a specific structure as a cation and a boron-containing coordination compound having a specific structure as an anion.

Description

[Technical Field]

[0001] The present invention relates to an ionic liquid and a lubricant composition. [Background technology]

[0002] Reducing energy loss through lower friction is important in all industrial fields, including the automotive industry. For example, 10% of the total energy consumed in an automobile comes from engine friction loss, which directly affects fuel efficiency. Improving fuel efficiency also leads to reduced fossil fuel consumption and reduced carbon dioxide emissions.

[0003] Methods for improving fuel economy by reducing friction include (i) reducing friction loss in the hydrodynamic lubrication region by reducing the viscosity of the base oil, and (ii) reducing friction loss in the boundary region by developing and incorporating friction modifiers. However, there are limitations to reducing viscosity because the base oil tends to evaporate easily due to its low molecular weight.

[0004] Therefore, lubricating oil compositions using friction modifiers such as molybdenum dialkyldithiocarbamate (MoDTC) have been proposed (see Patent Document 1). However, although the use of MoDTC is effective in reducing friction, it has the problem of poor durability.

[0005] Given this situation, there are high expectations for the development of lubricants with excellent thermal stability and low friction, from the perspective of economical operation of machinery and reducing environmental impact.

[0006] Ionic liquids are defined as those consisting of a combination of anions and cations and having a melting point of 100°C or below 150°C. Due to their unique basic physical properties such as low vapor pressure and high thermal stability, their application as lubricants has been investigated, and they are expected to be usable in high-temperature environments exceeding 200°C, such as gas turbines, and in high-vacuum environments such as space (see Non-Patent Documents 1 and 2).

[0007] Furthermore, ionic liquids often contain fluorine, phosphorus, and sulfur as constituent elements. These elements are also found in common extreme pressure agents and wear reducers, and are expected to undergo chemical reactions due to friction, forming a reaction film and exhibiting high boundary lubrication capabilities. Non-Patent Documents 3 and 4 describe that friction between steels causes a tribochemical reaction due to the anionic structure of the ionic liquid, forming a composite film of iron fluoride and iron sulfide on the outermost surface, thereby exhibiting good friction properties and wear resistance.

[0008] Patent Document 2 describes that in a ball-on-disc friction test between aluminum (AA2024) and steel (100Cr6), borate-based ionic liquids (ionic liquids with anions such as bis(mandelato)borate and bis(oxalato)borate) exhibit friction properties superior to those of commercially available engine oil (5W30).Non-Patent Document 5 also describes that adding a borate-based ionic liquid (bis(salicylate)borate anion) to PEG reduces the coefficient of friction. Phosphonium salts with bis(oxalato)borate or bis(mandelato)borate as anions exhibit excellent properties under low load conditions. However, under high load friction conditions, although they exhibit a low friction coefficient immediately after the start of the test, the friction coefficient increases with subsequent sliding, making them only useful for short-term low friction and low wear.

[0009] On the other hand, automobile engine oils, gear lubricants, etc. are required to exhibit low friction over long periods under high pressure conditions (high load conditions).

[0010] Therefore, there is a current demand for lubricants that can maintain low friction for a long period of time even under high load conditions. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-197393 [Patent Document 2] Patent No. 5920900 [Non-patent literature]

[0012] [Non-Patent Document 1] Chengfeng Ye, Weimin Liu, Yunaxia Chen and Laigui, “Room-temperature ionic liquid: a novel versatile lubricant” Chem.Commun., 2001,P.2244-2245 [Non-patent document 2] Akihito Suzuki, Yoshihiro Shinka, Masabumi Masuko, “Tribology Characteristics of Imidazolium-based Room Temperature Ionic Liquids Under High Vacuum” Tribol Lett(2007) 27 P.307-313 [Non-patent document 3] Qiming Lu, Haizhong Wang, Chengfeng Ye, Weimin Liu, Qunji Xue “Room temperature ionic liquid 1-ethyl-3-hexylimidazolium-bis(trifluoromethylsulfonyl)-imide as lubricant for steel-steel contact” Tribology International 37 (2004) 547-552 [Non-patent document 4] Hideto Uemura, Takeru Chiba, Tomoo Kubo, Hidetaka Nanao, Ichiro Minami, Masayuki Mori, "Relationship between the Lubrication Properties and Ionic Structure of Imidazolium Ionic Liquids," Tribologist, Vol. 51, No. 11 (2006), pp. 826-834 [Non-patent document 5] Rashi Gusain, Raghuvir Singh, KLN Sivakumar and Om P. Khatri “Halogen-free imidazolium / ammonium bis(salicylato)borate ionic liquids as high performance lubricant additives” RSC Adv., 2014, 4, 1293-1301 Summary of the Invention [Problem to be solved by the invention]

[0013] The present invention has been proposed in view of the above-described conventional situation, and aims to provide an ionic liquid that can maintain low friction for a long period even under high load conditions, and a lubricant composition using the ionic liquid. [Means for solving the problem]

[0014] The means for solving the above problems are as follows, namely, the following [1] to [4]. [1] A lubricant composition characterized by containing an ionic liquid having a cation represented by the following general formula (B) and an anion represented by the following general formula (C): [ka] However, in the general formula (B), R 5 , R 6 , and R 7 R each independently represents a linear or branched alkyl group having 1 to 22 carbon atoms. 8 is a linear or branched alkyl group having 1 to 22 carbon atoms, or -C n H 2n represents —OH (n represents an integer of 1 to 22). However, in the general formula (C), R 9 R represents a linear or branched alkyl group having 1 to 22 carbon atoms. 10is a hydrogen atom or a linear or branched alkyl group having 1 to 22 carbon atoms (wherein R 10 is a hydrogen atom, R 9 represents a straight-chain or branched alkyl group having 3 to 9 carbon atoms. [2] In the general formula (C), R 9 represents a linear or branched alkyl group having 1 to 10 carbon atoms. 10 represents a hydrogen atom or a linear or branched alkyl group having 1 to 10 carbon atoms (wherein R 10 is a hydrogen atom, R 9 is a linear or branched alkyl group having 3 to 9 carbon atoms), the lubricant composition according to [1]. [3] The lubricant composition according to [1] or [2], further comprising a base oil. [4] The lubricant composition according to [3], wherein the base oil is at least one of a poly-α-olefin and a polyol ester. In addition, the present specification states the following <1> from <7> The present invention also discloses the following. <1> The ionic liquid is characterized by having either a cation represented by the following general formula (A) or a cation represented by the following general formula (B), and an anion represented by the following general formula (C). [ka] However, in the general formula (A), R 1 , R 2 , R 3 , and R 4 each independently represents a linear or branched alkyl group having 4 to 18 carbon atoms. However, in the general formula (B), R 5 , R 6 , and R 7 R each independently represents a linear or branched alkyl group having 1 to 22 carbon atoms. 8 is a linear or branched alkyl group having 1 to 22 carbon atoms, or -C n H 2n represents —OH (n represents an integer of 1 to 22). However, in the general formula (C), R 9 R represents a linear or branched alkyl group having 1 to 22 carbon atoms. 10 represents a hydrogen atom or a linear or branched alkyl group having 1 to 22 carbon atoms. <2> The anion represented by the general formula (C) is an anion represented by the following general formula (C-1): <1> The ionic liquid is as described in [ka] However, in the general formula (C-1), R 9 represents a linear or branched alkyl group having 1 to 22 carbon atoms. <3> The anion represented by the general formula (C-1) is an anion represented by the following structural formula (C-2): <2> The ionic liquid is as described in [ka] <4> The lubricant <1> from <3> The ionic liquid is any one of the above. <5> The aforementioned <1> from <4> 1. A lubricant composition comprising the ionic liquid according to any one of claims 1 to 9. <6> The above-mentioned compound further containing a base oil <5> The lubricant composition according to claim 1, <7> The base oil is at least one of a poly-α-olefin and a polyol ester. <6> The lubricant composition according to claim 1, [Effects of the Invention]

[0015] According to the present invention, it is possible to provide an ionic liquid that can maintain low friction for a long period even under high load conditions, and a lubricant composition using the ionic liquid. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a graph showing the results of friction tests on the materials of Examples 1 and 2 and Comparative Examples 1 to 5. [Figure 2]FIG. 2 is a graph showing the friction test results for the materials of Examples 2 and 3 and Comparative Examples 1 and 4. [Figure 3] FIG. 3 is a graph showing the results of a friction test when the ionic liquid of Example 1 was mixed with a base oil. DETAILED DESCRIPTION OF THE INVENTION

[0017] (ionic liquid) The ionic liquid of the present invention has either a cation represented by the following general formula (A) or a cation represented by the following general formula (B), and an anion represented by the following general formula (C).

[0018] <Cation represented by general formula (A)> [ka]

[0019] However, in the general formula (A), R 1 , R 2 , R 3 , and R 4 each independently represents a linear or branched alkyl group having 4 to 18 carbon atoms.

[0020] Examples of the alkyl group having 4 to 18 carbon atoms include an n-butyl group, a sec-butyl group, a tert-butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, and a heptadecyl group.

[0021] R in the general formula (A) 1 , R 2 , R 3 , and R 4 Examples of the combination include the following: R 1 , R 2 , and R 3 are each independently a linear or branched alkyl group having 4 to 10 carbon atoms, and R4 is a linear or branched alkyl group having 11 to 18 carbon atoms. Also, R 1 , R 2 , and R 3 are each independently a linear or branched alkyl group having 4 to 8 carbon atoms, and R 4 is a linear or branched alkyl group having 12 to 16 carbon atoms.

[0022] <Cation represented by general formula (B)> [ka]

[0023] However, in the general formula (B), R 5 , R 6 , and R 7 R each independently represents a linear or branched alkyl group having 1 to 22 carbon atoms. 8 is a linear or branched alkyl group having 1 to 22 carbon atoms, or -C n H 2n represents —OH (n represents an integer of 1 to 22).

[0024] Examples of the general formula (B) include the following general formula (B-1). [ka]

[0025] However, in the general formula (B), R 5 , R 6 , and R 7 each independently represents a linear or branched alkyl group having 1 to 22 carbon atoms; and n represents an integer of 1 to 22.

[0026] Examples of the alkyl group having 1 to 22 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, a tert-butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, a nonadecyl group, an eicosyl group, a heneicosyl group, and a docosyl group.

[0027] n is 1 to 22, preferably 1 to 18, more preferably 2 to 15, even more preferably 2 to 10, and particularly preferably 2 to 8. Said-C n H 2n -C in -OH n H 2n The - group may have a linear or branched structure.

[0028] R 8 The alkyl group having 1 to 22 carbon atoms and having a linear or branched structure in A linear or branched alkyl group having 1 to 22 carbon atoms is preferred, a linear or branched alkyl group having 1 to 18 carbon atoms is more preferred, a linear or branched alkyl group having 2 to 10 carbon atoms is even more preferred, and a linear or branched alkyl group having 2 to 8 carbon atoms is particularly preferred.

[0029] R in the general formula (B) 5 , R 6 , and R 7 Examples of the combination include the following: R 5 , and R 6 are each independently a linear or branched alkyl group having 1 to 10 carbon atoms, and R 7 is a linear or branched alkyl group having 11 to 22 carbon atoms. Also, R 5 , and R 6 are each independently a linear or branched alkyl group having 1 to 6 carbon atoms, and R 7is a linear or branched alkyl group having 14 to 22 carbon atoms. Also, R 5 , and R 6 are each independently a linear or branched alkyl group having 1 to 3 carbon atoms, and R 7 is a linear or branched alkyl group having 16 to 20 carbon atoms.

[0030] <Anion Represented by General Formula (C)> [ka]

[0031] However, in the general formula (C), R 9 R represents a linear or branched alkyl group having 1 to 22 carbon atoms. 10 represents a hydrogen atom or a linear or branched alkyl group having 1 to 22 carbon atoms.

[0032] Examples of the general formula (C) include the following general formula (C-1). [ka]

[0033] However, in the general formula (C-1), R 9 represents a linear or branched alkyl group having 1 to 22 carbon atoms.

[0034] The alkyl group has 1 to 22 carbon atoms, preferably 1 to 15 carbon atoms, more preferably 2 to 10 carbon atoms, and even more preferably 3 to 9 carbon atoms.

[0035] Examples of the alkyl group having 1 to 22 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, a tert-butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, a nonadecyl group, an eicosyl group, a heneicosyl group, and a docosyl group.

[0036] As the anion represented by the general formula (C), an anion represented by the following structural formula (C-2) is particularly preferred. [ka]

[0037] The ionic liquid can maintain low friction for a long period even under high load conditions, and can therefore be used as a lubricant by itself.

[0038] (Lubricant composition) The lubricant composition of the present invention contains at least the ionic liquid of the present invention, preferably a base oil, and may further contain other components as required.

[0039] <Ionic liquid> The content of the ionic liquid in the lubricant composition is not particularly limited and can be selected appropriately depending on the purpose, but is preferably 0.1% by mass or more and 100% by mass or less, more preferably 1% by mass or more and 70% by mass or less, even more preferably 5% by mass or more and 70% by mass or less, and particularly preferably 7% by mass or more and 70% by mass or less, relative to the base oil.

[0040] <Base oil> The base oil is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include vegetable oil, mineral oil, synthetic hydrocarbon oil, ester-based synthetic oil, ether-based synthetic oil, glycol-based synthetic oil, etc. These may be used alone or in combination of two or more. Among these, synthetic hydrocarbon oils are preferred because they are general-purpose base oils, and ester-based synthetic oils are preferred because they easily dissolve the ionic liquid.

[0041] <<Vegetable oil>> Examples of the vegetable oil include rapeseed oil, soybean oil, castor oil, palm oil, sunflower oil, safflower oil, corn oil, meadowfoam oil, rice bran oil, olive oil, and jojoba oil.

[0042] <<Mineral oil>> The mineral oils are classified according to the refining method, and examples thereof include mineral oils containing 0.5 to 10% wax. Preferred examples include mineral oils with low pour points and high viscosity indexes, and more specifically, examples include highly refined oils (mainly isoparaffin) produced by hydrocracking refining.

[0043] <<Synthetic hydrocarbon oil>> Examples of the synthetic hydrocarbon oil include poly-α-olefin (PAO), ethylene-α-olefin copolymer, polybutene, alkylbenzene, and alkylnaphthalene.

[0044] Examples of the poly-α-olefin include low-molecular-weight oligomers of olefins having a carbon number of 8 to 12. Such poly-α-olefins can be produced by known methods, such as cationic polymerization using a Ziegler catalyst, a Lewis acid, or the like, thermal polymerization, or radical polymerization.

[0045] The ethylene-α-olefin copolymer may be, for example, an ethylene-propylene oligomer obtained by polymerizing ethylene and propylene using a Ziegler catalyst, a metallocene catalyst, or the like.

[0046] Examples of the alkylbenzene and alkylnaphthalene include dialkylbenzenes and dialkylnaphthalenes having 6 to 14 carbon atoms. Such alkylbenzenes and alkylnaphthalenes can be produced, for example, by a Friedel-Crafts alkylation reaction between benzene or naphthalene and an olefin (a linear olefin, a branched olefin, or a combination thereof).

[0047] <<Ester-based synthetic oil>> Examples of the ester-based synthetic oil include diesters, polyol esters, and aromatic esters.

[0048] The diesters are synthetic oils made, for example, from dibasic acids and alcohols, or from diols and monobasic acids or mixtures of acids.

[0049] The polyol ester is a synthetic oil produced from, for example, a polyhydric alcohol (diol, triol (e.g., trimethylolpropane), tetraol (e.g., pentaerythritol), hexaol (e.g., dipentaerythritol), etc.) and a monobasic acid or acid mixture. Examples of the polyol ester include aliphatic polyol esters such as trimethylolpropane triheptanoate, trimethylolpropane tripelargonate, pentaerythritol tetraheptanoate, and pentaerythritol tetraoleate neopentyl polyol.

[0050] <<Ether-based synthetic oil>> Examples of the ether-based synthetic oil include alkyl diphenyl ether.

[0051] <<Glycol-based synthetic oil>> Examples of the glycol-based synthetic oil include polyethylene glycol and polypropylene glycol.

[0052] <Other ingredients> Examples of the other components include solid lubricants, antioxidants, extreme pressure agents, rust inhibitors, corrosion inhibitors, viscosity index improvers, and oiliness agents.

[0053] Examples of the solid lubricant include polytetrafluoroethylene (PTFE), sodium sebacate, carbon black, graphite, molybdenum disulfide, and organic molybdenum. , graphite, boron nitride, silane nitride, etc.

[0054] Examples of the antioxidant include phenol-based antioxidants (e.g., 2,6-di-t-butyl-4-methylphenol, 4,4'-methylenebis(2,6-di-t-butylphenol) and the like), and amine-based antioxidants (e.g., alkyldiphenylamines (the alkyl group has 4 to 20 carbon atoms), triphenylamine, phenyl-α-naphthylamine, phenothiazine, alkylated phenyl-α-naphthylamine, phenithiazine, alkylated phenothiazine and the like).

[0055] Examples of the extreme pressure additives include phosphorus-based compounds (e.g., acid phosphate esters, phosphites, acid phosphate amine salts, etc.), sulfur-based compounds (e.g., sulfides, disulfides, etc.), chlorine-based compounds (e.g., chlorinated paraffin, chlorinated diphenyl, etc.), and metal organic compounds (e.g., zinc dialkyldithiophosphate (ZnDTP), molybdenum dialkyldithiocarbamate (MoDTP), etc.).

[0056] Examples of the rust inhibitor include fatty acids, fatty acid soaps, alkyl sulfonates, fatty acid amines, oxidized paraffins, and polyoxyethylene alkyl ethers.

[0057] Examples of the corrosion inhibitor include benzotriazole, benzimidazole, and thiadiazole.

[0058] Examples of the viscosity index improver include polymethacrylate, ethylene-propylene copolymer, polyisobutylene, polyalkylstyrene, and hydrogenated styrene-isoprene copolymer.

[0059] Examples of the oily agent include fatty acids, higher alcohols, polyhydric alcohols, polyhydric alcohol esters, aliphatic esters, aliphatic amines, and fatty acid monoglycerides.

[0060] The lubricant composition may be an oil-based lubricant composition, or an emulsion-type water-soluble lubricant composition in which a lubricant is dispersed in an aqueous dispersion medium.

[0061] The emulsion-type water-soluble lubricant composition is prepared by dispersing the above-mentioned lubricant in an aqueous dispersion medium by a known method.

[0062] Examples of the aqueous dispersion medium include water (purified water), alcohol, and mixtures thereof.

[0063] The lubricant composition can be used in a wide range of industrial fields. Specific applications include, for example, gear oil, hydraulic oil, engine oil (two-cycle engine oil, gasoline engine oil, diesel engine oil, etc.), grease, cutting oil, grinding oil, punching oil, drawing oil, press oil, drawing oil, rolling oil, forging oil, slideway oil, electrical insulating oil, turbine oil, gear oil, air compressor oil, compressor oil, vacuum pump oil, bearing oil, heat transfer oil, mist oil, refrigeration oil, and rock drill oil. Preferred examples include gear oil, hydraulic oil, and engine oil used in automobiles or industry, metalworking oil, cutting oil, rolling oil, and chainsaw oil used in industrial processing of metal products, and grease. [Example]

[0064] Examples of the present invention will be described below, but the present invention is not limited to these examples in any way.

[0065] Example 1 <Synthesis of bis(2-hydroxyoctanoate)borate trihexyltetradecylphosphonium salt> [ka]

[0066] A 200 ml three-neck flask equipped with a condenser, thermometer, and stirrer was charged with 1.24 g (20 mmol) of boric acid (Wako Pure Chemical Industries, Ltd.), 0.74 g (10 mmol) of lithium carbonate (Wako Pure Chemical Industries, Ltd.), and 100 g of distilled water, and the mixture was stirred until homogeneous. Subsequently, 6.40 g (40 mmol) of powdered 2-hydroxyoctanoic acid (Tokyo Chemical Industry Co., Ltd.) was gradually added to the aqueous solution. The mixture was stirred at 60°C for 2 hours to prepare a lithium bis(2-hydroxyoctanoate)borate dispersion. After cooling the dispersion to room temperature, 6.77 g of trihexyltetradecylphosphonium bromide (Aldrich) was added and the mixture was stirred at room temperature for 18 hours. After the reaction was complete, 50 mL of methylene chloride was added, and the organic layer was washed 10 times with water. The resulting organic layer was evaporated and dried in a vacuum oven at 80°C for 24 hours, yielding 9.6 g (yield 99%) of the target ionic liquid, which was pale brown and transparent. The H-NMR (Proton Nuclear Magnetic Resonance) of the synthesized sample in deuterated DMSO gave values ​​of 3.9 ppm (m, 2H), 1.7-1.2 ppm (m, 64H), and 0.85 ppm (t, 18H). The B-NMR (Boron Nuclear Magnetic Resonance) in the same solvent was 10.9 ppm, confirming the structure of the target ionic liquid. Synthesis was confirmed by ion chromatography, which showed that the bromide ion content was significantly reduced to less than 1% compared to the starting phosphonium salt.

[0067] Example 2 <Bis(2-hydroxyoctanoate)borate·dimethyloctadecyl(6-hydroxy)hexylammonium salt> [ka]

[0068] A 100 ml three-neck flask equipped with a condenser, thermometer, and stirrer was charged with 10.2 g (30.6 mmol) of 1-bromooctadecane (Tokyo Chemical Industry Co., Ltd.), 3.58 g (24.6 mmol) of 6-dimethylamino-1-hexanol (Tokyo Chemical Industry Co., Ltd.), and 14 g of acetonitrile (Wako Pure Chemical Industries, Ltd.), and the mixture was stirred at 80°C for 6 hours. After the reaction, the mixture was reprecipitated in hexane, filtered, washed twice with hexane, and dried under reduced pressure at 40°C for 12 hours, yielding 11 g of dimethyloctadecyl(6-hydroxy)hexylammonium bromide in a 92% yield. This was added to a dispersion solution of lithium bis(2-hydroxyoctanoate)borate prepared under the same conditions as in Example 1 so that the borate was in excess of 1.2 equivalents, and salt exchange reaction and purification were carried out under the same conditions to obtain bis(2-hydroxyoctanoate)borate dimethicone. The octadecyl(6-hydroxy)hexylammonium salt was obtained in 99% yield. The H-NMR (Proton Nuclear Magnetic Resonance) of the synthesized sample in deuterated DMSO gave values ​​of 3.9 ppm (m, 2H), 3.2 ppm (m, 4H), 2.9-3 ppm (s, 6H), 1.7-1.2 ppm (m, 60H), and 0.85 ppm (t, 9H). The B-NMR (Boron Nuclear Magnetic Resonance) in the same solvent was 10.9 ppm, confirming the structure of the target ionic liquid.

[0069] Example 3 <Bis(2-hydroxyoctanoate)borate·dimethylhexyloctadecylammonium salt> [ka]

[0070] A 100 ml three-neck flask equipped with a condenser, thermometer, and stirrer was charged with 40.0 g of 1-bromooctadecane (Tokyo Chemical Industry Co., Ltd.), 12.9 g of dimethylhexylamine (Tokyo Chemical Industry Co., Ltd.), and 53 g of acetonitrile (Wako Pure Chemical Industries, Ltd.), and the mixture was stirred at 80°C for 3 hours. After the reaction, the mixture was reprecipitated in hexane, filtered, washed twice with hexane, and dried under reduced pressure at 50°C for 12 hours, yielding 32.8 g of dimethyloctadecylhexylammonium bromide in a 71% yield. A 200 ml three-neck flask equipped with a condenser, thermometer, and stirrer was charged with 1.55 g of boric acid (manufactured by Wako Pure Chemical Industries, Ltd.), 0.92 g of lithium carbonate (manufactured by Wako Pure Chemical Industries, Ltd.), and 100 g of distilled water, and the mixture was stirred until homogeneous. Then, 8.01 g of powdered 2-hydroxyethyloctanoic acid (manufactured by Tokyo Chemical Industry Co., Ltd.) was gradually added, and the mixture was stirred at 60°C for 2 hours to prepare a dispersion solution of lithium bis(2-hydroxyoctanoate)borate. After cooling the dispersion to room temperature, 9.27 g of the synthesized dimethyloctadecylhexylammonium bromide salt was added to the dispersion and stirred at room temperature for 18 hours. After the reaction was completed, 50 mL of methylene chloride was added, and the organic layer was washed 10 times with water. The resulting organic layer was evaporated and dried in a vacuum oven at 80°C for 12 hours, yielding 13.5 g (95% yield) of the colorless, transparent target ionic liquid. The synthesized sample was analyzed by H-NMR (Proton Nuclear Magnetic Resonance) in deuterated DMSO, and the peaks were 4.0-3.9 ppm (m, 2H), 3.2 ppm (m, 4H), 3-2.9 ppm (s, 6H), 1.7-1.2 ppm (m, 60H), and 0.85 ppm (m, 12H), confirming the structure of the target ionic liquid. Furthermore, ion chromatography confirmed the synthesis by revealing that the bromide ion content was significantly reduced to less than 1% compared to the starting ammonium salt.

[0071] (Comparative Example 1) <Bis(oxalato)borate trihexyltetradecylphosphonium> Bis(oxalato)borate trihexyltetradecylphosphonium represented by the following structural formula was synthesized with reference to Example 8 of Japanese Patent No. 5920900. [ka]

[0072] (Comparative Example 2) <Bis(mandelato)borate trihexyltetradecylphosphonium> Bis(mandelato)borate trihexyltetradecylphosphonium represented by the following structural formula was synthesized with reference to Example 3 of Japanese Patent No. 5920900. [ka]

[0073] (Comparative Example 3) 1-Butyl-3-methylimidazolium trifluoro(trifluoromethyl)borate 1-Butyl-3-methylimidazolium trifluoro(trifluoromethyl)borate (manufactured by Tokyo Chemical Industry Co., Ltd.) represented by the following structural formula was used. [ka]

[0074] Comparative Example 4 <PAO(ポリ-α-オレフィン)> The base oil used was SpectraSyn Plus6 (PAO (poly-α-olefin) manufactured by ExxonMobil Corporation).

[0075] (Comparative Example 5) <POE(ポリオールエステル)> Radialube 7364 (POE (polyol ester)) manufactured by Oleon was used as the base oil.

[0076] 〔evaluation〕 The substances of Examples 1 to 3 and Comparative Examples 1 to 5 were subjected to the following tests.

[0077] <Friction test (high load conditions)> The high-load friction test was carried out using a vibration friction tester (product name: SRV5) manufactured by Optimol. The test was carried out using a cylinder-on-disc system. The cylinder (material: SUJ2, φ15 mm) The friction test conditions were as follows: The load was 400 N (Hertz pressure: 0.3 GPa), the measurement temperature was 80°C, the sliding distance was 1,000 μm, and the vibration frequency was 50 Hz.

[0078] The results are shown in Figures 1 and 2. When Example 1, in which the cation was a phosphonium salt, was measured, a low coefficient of friction was observed from the beginning of the measurement, and no increase in the coefficient of friction was observed up to 1,800 seconds. When Example 2, in which the cation is an ammonium salt having a hydroxyl group, was measured, it showed a lower coefficient of friction than Example 1, and no increase in the coefficient of friction was observed up to 1,800 seconds. When Example 3, in which the cation was an ammonium salt having four alkyl groups, was measured, it showed a lower coefficient of friction than Example 1, and no increase in the coefficient of friction was observed up to 1,800 seconds. In Examples 1 to 3, the friction coefficients were stable after the friction reduction. Furthermore, in Example 3, the friction was reduced in a shorter time than in Example 2 after the start of the test. Comparative Example 1, in which the hexyl group in the borate structure of Example 1 was replaced with a carbonyl group, showed a favorable low coefficient of friction before 800 seconds had elapsed. However, after 800 seconds had elapsed, the coefficient of friction rose significantly beyond that of Examples 1 to 3. In other words, it was found that the low friction could not be maintained and that this example was unsuitable for long-term use. In Comparative Example 2, in which the hexyl group in the borate structure of Example 1 was replaced with a phenyl group, the friction coefficient was large immediately after the start of the evaluation, and this state was maintained. In Comparative Example 3, which was a general ionic liquid, the coefficient of friction was large immediately after the start of the test, and this state was maintained, just like in Comparative Example 2. The PAO (Comparative Example 4) had an even higher coefficient of friction than the comparative examples 1-3. When the base oil of Comparative Example 5, which is a general base oil, was measured, it showed a friction coefficient greater than those of Examples 1 to 3. On the other hand, it was about the same as those of Comparative Examples 2 and 3. From the above, it was found that the ionic liquid of the present invention exhibits a lower friction coefficient than Comparative Examples 2 and 3, and also has a lower friction coefficient than the base oils of Comparative Examples 4 and 5, and is therefore useful as a lubricant for use in base oils to reduce friction. Furthermore, it was found that the ionic liquid of the present invention can maintain a low coefficient of friction for a long period of time under high load conditions, compared to the ionic liquid of Comparative Example 1.

[0079] <Thermophysical properties / Solubility> The thermal properties, solubility, etc. of the materials of Examples 1 to 3 and Comparative Examples 1 to 3 are summarized in Table 1. All substances are liquid at room temperature and are ionic liquids based on their chemical structure. In Examples 1 to 3, the thermal decomposition temperatures (5% weight loss temperatures) were all 200°C or higher, which is within a practical range. Generally, the lower the viscosity, the more preferable it is, as long as it is compatible with wear resistance. This Example is within the practical range. All Examples exhibited solubility in the base oil POE (=Comparative Example 5), and Example 1 exhibited solubility in base oil GpI, and Example 3 exhibited solubility in base oil GpIV.

[0080] [Table 1]

[0081] *1: Solubility was evaluated by adding 1 part by mass to 100 parts by mass of each base oil (POE, GpI, GpIV). "○" indicates that it dissolved, and "×" indicates that it did not dissolve. *2: Base oil GpI and GpIV are defined by API standards. *3: As the base oil GpIV, SpectraSyn4 (SpectraSyn 4, ExxonMobil) was used.

[0082] The 5% thermal decomposition temperature was determined by TG / DTA measurement. In the TG / DTA measurement, EXSTAR6000 manufactured by Seiko Instruments Inc. was used, and the measurement was carried out in the temperature range of 30°C - 600°C at a heating rate of 10°C / min while introducing air at a flow rate of 200 ml / min.

[0083] <Addition to POE> The ionic liquid of Example 1 having a friction reduction effect was mixed with the oil of Comparative Example 5 which is the base oil, and the change over time of the friction coefficient was evaluated. The results are shown in Figure 3. In the range of 10 mass% - 50 mass% evaluated this time, the friction reduction effect could be confirmed, and the effect could be maintained until 1,800 seconds of evaluation. Note that 10 mass% in Figure 3 means that 10 parts by mass of the ionic liquid of Example 1 was added to 90 parts by mass of the base oil.

Industrial Applicability

[0084] The ionic liquid of the present invention can be suitably used as a lubricant because it can maintain low friction properties for a long time even under high load conditions. In addition, the lubricant composition of the present invention can be widely used in various industrial fields such as the automotive field and the industrial field.

Claims

1. A lubricant composition comprising an ionic liquid having a cation represented by the following general formula (B) and an anion represented by the following general formula (C): 【Chemical 1】 However, in the general formula (B), R ５ , R ６ , and R ７ R each independently represents a linear or branched alkyl group having 1 to 22 carbon atoms. ８ represents a linear or branched alkyl group having 1 to 22 carbon atoms, or -C ｎ H ２ｎ -OH (n is an integer of 1 to 22). However, in the general formula (C), R ９ represents a linear or branched alkyl group having 1 to 10 carbon atoms. １０ represents a linear or branched alkyl group having 1 to 10 carbon atoms.

2. The lubricant composition of claim 1 further comprising a base oil.

3. 3. The lubricant composition according to claim 2, wherein the base oil is at least one of a poly-α-olefin and a polyol ester.

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