Lubricating oil composition

Abstract

The objective is to provide a lubricating oil composition that has low volatility and excellent anti-foaming properties under reduced pressure. [Solution] The present invention relates to a lubricating oil composition comprising an ionic liquid (X) consisting of an anion (A) and a cation (B), wherein the anion (A) is at least one anion selected from the group consisting of alkyl carboxylate anions, alkyl sulfonate anions, dialkyl phosphate anions, dicyanamide anions, and thiocyanate anions, the water content in the lubricating oil composition is 50 ppm or less, and the viscosity of the lubricating oil composition at 25°C is 15 to 370 mPa·s.

Description

Technical Field

[0001] The present invention relates to a lubricating oil composition.

Background Art

[0002] In recent years, materials used in a vacuum environment such as in the aerospace field and the manufacturing process of organic ELs have become important. Lubricating oils used in a vacuum are particularly required to be low-volatile in the manufacturing process. As materials with low volatility even in a high vacuum, Patent Document 1 shows perfluoropolyether (PFPE) and other low-volatile fluids, Patent Document 2 shows silicone-modified ionic liquids, and Patent Document 3 shows ionic liquids using bis(trifluoromethanesulfonyl)imide anions.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Disclosure of the Invention

Problems to be Solved by the Invention

[0004] However, any of the materials in Patent Documents 1 to 3 including PFPE has a problem that the volatility is high and the bubbles generated under reduced pressure do not break for a long time. An object of the present invention is to provide a lubricating oil composition having low volatility and excellent defoaming properties under reduced pressure.

Means for Solving the Problems

[0005] As a result of intensive studies to solve the above problems, the present inventors have reached the present invention. In other words, the present invention is a lubricating oil composition comprising an ionic liquid (X) consisting of an anion (A) and a cation (B), wherein the anion (A) is at least one anion selected from the group consisting of alkyl carboxylic acid anions, alkyl sulfonate anions, dialkyl phosphate anions, dicyanamide anions, and thiocyanate anions, the water content in the lubricating oil composition is 50 ppm or less, and the viscosity of the lubricating oil composition at 25°C is 15 to 370 mPa·s. [Effects of the Invention]

[0006] The lubricating oil composition of the present invention exhibits low volatility and excellent anti-foaming properties under reduced pressure. [Modes for carrying out the invention]

[0007] The present invention will be described in detail below.

[0008] The lubricating oil composition of the present invention is a lubricating oil composition comprising an ionic liquid (X) consisting of an anion (A) and a cation (B). In this invention, an ionic liquid refers to a molten salt formed by combining an anion (A) and a cation (B), and is a liquid salt with a melting point of 100°C or lower.

[0009] Anion (A) is at least one anion selected from the group consisting of alkyl carboxylate anions, alkyl sulfonate anions, dialkyl phosphate anions, dicyanamide anions, and thiocyanate anions.

[0010] Preferably, the alkyl carboxylate anion has 1 to 30 carbon atoms. Specifically, examples include acetate anion, propionate anion, butanoate anion, pentanoate anion, hexanoate anion, heptanoate anion, octanoate anion, nonanoate anion, decanoate anion, dodecanoate anion, tetradecanoate anion, pentadecanoate anion, hexadecanate anion, heptadecanate anion, octadecanoate anion, eicosanate anion, docosanate anion, tetracosanate anion, and triacontanoate anion. From the viewpoint of resistance to frictional degradation, alkyl carboxylate anions have 1 to 10 carbon atoms, and most preferably alkyl carboxylate anions have 1 to 4 carbon atoms.

[0011] Preferably, the alkyl sulfonate anion is an alkyl sulfonate anion having 1 to 30 carbon atoms, specifically including methanesulfonate anion, ethanesulfonate anion, propanesulfonate anion, butanesulfonate anion, pentanesulfonate anion, hexanesulfonate anion, heptanesulfonate anion, octanesulfonate anion, nonanesulfonate anion, decanesulfonate anion, dodecanesulfonate anion, tetradecanesulfonate anion, pentadecanesulfonate anion, hexadecanesulfonate anion, heptadecanesulfonate anion, octadecanesulfonate anion, and triacontanesulfonate anion. From the viewpoint of resistance to frictional degradation, alkyl sulfonate anions having 1 to 10 carbon atoms are even more preferable, and alkyl sulfonate anions having 1 to 4 carbon atoms are most preferable.

[0012] Preferably, dialkyl phosphate anions have 1 to 30 carbon atoms, specifically dimethyl phosphate anions, diethyl phosphate anions, dipropyl phosphate anions, and dibutyl phosphate anions. From the viewpoint of resistance to friction degradation, dialkyl phosphate anions have 1 to 10 carbon atoms, and most preferably, dialkyl phosphate anions have 1 to 4 carbon atoms.

[0013] Among the anions (A), from the viewpoint of anti-friction decomposition properties, at least one anion selected from the group consisting of an alkylsulfonic acid anion, a dicyanamide anion, and a thiocyanate anion is preferable, and more preferably a methanesulfonic acid anion, a dicyanamide anion, and a thiocyanate anion.

[0014] The cation (B) is not particularly limited, and among known cations, a cation capable of forming an ionic liquid with the anion (A) can be used. Examples of known cations include an ammonium cation, a primary ammonium cation, a secondary ammonium cation, a tertiary ammonium cation, a quaternary ammonium cation, and an imidazolium cation.

[0015] Examples of the ammonium cation include an unsubstituted ammonium cation.

[0016] Examples of the primary ammonium cation include ammonium cations having 1 to 3 carbon atoms (such as methylammonium, ethylammonium, propylammonium, and isopropylammonium) cations.

[0017] Examples of the secondary ammonium cation include ammonium cations having 2 to 6 carbon atoms (such as dimethylammonium, diethylammonium, methylethylammonium, methylpropylammonium, and methylisopropylammonium) cations.

[0018] Examples of the tertiary ammonium cation include ammonium cations having 3 to 9 carbon atoms (such as trimethylammonium, triethylammonium, dimethylethylammonium, dimethylpropylammonium, and dimethylisopropylammonium) cations.

[0019] Examples of the quaternary ammonium cation include acyclic quaternary ammonium cations (cations represented by the following general formula (1)) and cyclic quaternary ammonium cations (N,N-dimethylmorpholinium cation, N-ethyl-N-methylmorpholinium cation), etc.

[0020] [Chemical formula] [In general formula (1), R1 to R4 each independently represent a linear or branched alkyl group having 1 to 10 carbon atoms.]

[0021] Preferred examples of the acyclic quaternary ammonium cation represented by the general formula (1) include didecyldimethylammonium cation, didecyldiethylammonium cation, tetramethylammonium cation, tetraethylammonium cation, trioctylmethylammonium, and trioctylethylammonium, etc.

[0022] Examples of the imidazolium cation include cations represented by the following general formula (2) and cations represented by general formula (3), etc.

[0023] [Chemical formula] [In general formula (2), R5 and R7 each independently represent a linear or branched alkyl group having 1 to 10 carbon atoms, and R6, R8, and R9 represent a hydrogen atom or a linear or branched alkyl group having 1 to 10 carbon atoms.]

[0024] [Chemical formula] [In general formula (3), R 10 , R 12 each independently represent a linear or branched alkyl group having 1 to 10 carbon atoms, R 11 represents a hydrogen atom or a linear or branched alkyl group having 1 to 10 carbon atoms, R 13, R 14 Each of these independently represents a linear or branched alkyl group having 1 to 10 carbon atoms. Furthermore, R 10 ~R 14 Some or all of these may be bonded together in groups of 2 to 4 to form a 2- to 4-valent group, creating a heterocycle with the nitrogen atom.

[0025] Specific examples of the above general formulas (2) and (3) include cations such as 1,2,3,4-tetramethylimidazolinium, 1,3,4-trimethyl-2-ethylimidazolinium, 1,3-dimethyl-2,4-diethylimidazolinium, 1,2-dimethyl-3,4-diethylimidazolinium, 1,3-dimethylimidazolium, 1,3-diethylimidazolium, 1-ethyl-3-methylimidazolium, and 1,2,3-trimethylimidazolium.

[0026] The cation (B) is preferably a quaternary ammonium cation and / or an imidazolium cation from the viewpoint of corrosiveness, more preferably at least one cation selected from the group consisting of a cation represented by general formula (1), a cation represented by general formula (2), and a cation represented by general formula (3), and even more preferably 1-ethyl-3-methylimidazolium.

[0027] The lubricating oil composition of the present invention may contain an ionic liquid (Y) comprising an anion other than anion (A) and a cation (B). The cation (B) is not particularly limited, and any known cation that can form an ionic liquid when salted with an anion other than anion (A) can be used.

[0028] Other than the aforementioned anion (A), known anions can be used, such as inorganic strong acids (a1), halogen atom-substituted alkyl group-containing strong acids (a2), halogen atom-containing sulfonylimides (a3), halogen atom-containing sulfonylmethides (a4), halogen atom-containing carboxylic acid amides (a5), nitrile-containing methides (a6), and halogen atom-containing alkylamines (a7), which are anions obtained by removing a hydrogen atom from an acid. The anions may also be a mixture of two or more types.

[0029] Examples of the inorganic strong acid (a1) include hydrofluoric acid, hydrochloric acid, sulfuric acid, phosphoric acid, HClO4, HBF4, HPF6, HAsF6, HSbF6, and fluorosulfonic acid.

[0030] Examples of the halogen atom-substituted alkyl group-containing strong acid (a2) include trifluoromethanesulfonic acid, pentafluoroethanesulfonic acid, heptafluoropropanesulfonic acid, trichloromethanesulfonic acid, pentachloropropanesulfonic acid, heptachlorobutanesulfonic acid, trifluoroacetic acid, pentafluoropropionic acid, pentafluorobutanoic acid, trichloroacetic acid, pentachloropropionic acid, and heptachlorobutanoic acid.

[0031] Examples of the halogen atom-containing sulfonylimide (a3) ​​include bis(fluoromethanesulfonyl)imide and bis(fluoromethanesulfonyl)imide.

[0032] Examples of the halogen atom-containing sulfonylmethide (a4) include tris(trifluoromethanesulfonyl)methide.

[0033] Examples of the halogen atom-containing carboxylic acid amide (a5) include bis(trifluoroacetyl)amide and the like.

[0034] Examples of the nitrile-containing methide (a6) include HC(CN)3.

[0035] Examples of the halogen atom-containing alkylamine (a7) include HN(CF3)2.

[0036] In the present invention, the method for producing the ionic liquid (X) and the ionic liquid (Y) is not particularly limited, but examples include the method described in J.Am.Chem.Soc., 69, 2269 (1947), U.S. Patent No. 4,892,944, etc. (a method of quaternizing a tertiary amine with a carbonate ester and then exchanging the salt).

[0037] The lubricating oil composition of the present invention may also contain, as components other than the ionic liquid (X) and ionic liquid (Y), a surfactant (C), a polymer (D), an inorganic substance (E), or a combination thereof. Including these can improve the anti-foaming effect under reduced pressure.

[0038] The surfactant (C) is preferably a nonionic surfactant, and by using a nonionic surfactant, good foam-breaking properties under reduced pressure can be achieved. Examples of the aforementioned nonionic surfactants include "Noptam 740A," "SN Deformer 260," "Nopco 1407-H," "SN Deformer 180," and "SN Deformer 1407K" from Sunopco Corporation; "Pronal C-448" and "Pronal EX-300" from Toho Chemical Co., Ltd.; "Neoclair TO-1" and "Neoclair TO-2" from Takemoto Oil & Fat Co., Ltd.; and "Acetylenel EL," "Acetylenel EH," "Acetylenel E40," and "Acetylenel E100" from Kawaken Fine Chemical Co., Ltd.

[0039] The polymer (D) can be at least one polymer selected from acrylic polymers, urethane polymers, and epoxy polymers. Of these, acrylic polymers are preferred from the viewpoint of heat resistance and dispersibility in lubricating oil compositions.

[0040] Examples of the inorganic substance (E) include kaolin, talc, silica, titanium dioxide, calcium carbonate, and bentonite. Of these, silica (e.g., fumed silica) is preferred from the viewpoint of anti-foaming properties.

[0041] The lubricating oil composition of the present invention may also contain components other than the ionic liquid (X) and the ionic liquid (Y), such as an antifoaming agent (F).

[0042] The defoaming agent (F) can preferably be a defoaming agent which is a mixture of silicone and hydrophobic fine particles, or an amide-based defoaming agent. The defoaming agent for the mixture of silicone and hydrophobic fine particles is "BYK-011", "BYK-012", "BYK-014", "BYK-015", "BYK-017", "BYK-018", "BYK-019", "BYK-021", "BYK-022", "BYK-023", "BYK-024", "BYK-025", "BYK-028", "BYK-038", "BYK-039", "BYK-044", "BYK- 093", "BYK-094", "BYK-1610", "BYK-1611", "BYK-1615", "BYK-1617", "BYK-1640", "BYK-1650", "BYK-1710", "BYK-1711 ", "BYK-1719", "BYK-1723", "BYK-1724", "BYK-1730", "BYK-1740", "BYK-1770", "BYK-1780", "BYK-1781", "BYK-1785", " BYK-1786, BYK-1798; Sunopco Corporation's "SN Deformer 121N", "SN Deformer 1311", "SN Deformer 1312", "SN Deformer 1313", "SN Deformer 1314", "SN Deformer 1315", "SN Deformer 1316", "SN Deformer 154", "SN Deformer 154S", "SN Deformer 180", "SN Deformer 265", "SN Deformer Examples include "-317", "SN Deformer 380", "SN Deformer 381", "SN Deformer 391", "SN Deformer 393", "SN Deformer 395", "SN Deformer 399", "SN Deformer 5016", "Nopco DF-122-NS", "Noptum 3590", "Noptum 6030PC", "Noptum 777-F", "Noptum 8000PC", "Noptum 8034-F", and "Noptum 8034-LF". Examples of the aforementioned amide-based defoaming agents include "SN Deformer 1044" and "SN Deformer 5013" manufactured by Sunopco Corporation.

[0043] The lubricating oil composition of the present invention can be obtained by mixing an ionic liquid (X), optionally an ionic liquid (Y), a surfactant (C), a polymer (D), an inorganic substance (E), and an antifoaming agent (F), etc. Methods of mixing include mixing each component using a suitable mixer (such as a kneader). Furthermore, when mixing polymer (D), a lubricating oil composition in which polymer (D) is dispersed may be obtained by mixing monomers that serve as raw materials for polymer (D) with the ionic liquid (X) and then polymerizing them. Alternatively, a lubricating oil composition in which polymer (D) is dispersed may be obtained by mixing a low-molecular-weight polymer of polymer (D) with the ionic liquid (X) and then polymerizing it further.

[0044] The lubricating oil composition of the present invention preferably contains 95% by weight or more of the ionic liquid (X). Containing 95% by weight or more of the ionic liquid (X) results in a lubricating oil composition with low volatility. From the viewpoint of anti-foaming properties under reduced pressure, the content of the ionic liquid (X) in the lubricating oil composition is more preferably 98% by weight or more, more preferably 99% by weight or more, and particularly preferably 100% by weight. Note that the lubricating oil composition of the present invention may also use the ionic liquid (X) as is.

[0045] If the lubricating oil composition contains components other than the ionic liquid (X), the content of the components other than the ionic liquid (X) in the lubricating oil composition is preferably 5% by weight or less, more preferably 2% by weight or less, and particularly preferably 1% by weight or less. By limiting the content of the components other than the ionic liquid (X) to 5% by weight or less, a lubricating oil composition with optimal viscosity is obtained.

[0046] The viscosity of the lubricating oil composition of the present invention is 15 to 370 mPa·s at 25°C, preferably 15 to 280 mPa·s, and more preferably 15 to 180 mPa·s. If the viscosity is less than 15 mPa·s, the volatility under reduced pressure increases, and if it is greater than 370 mPa·s, the anti-foaming properties under reduced pressure deteriorate. The viscosity can be reduced by using cations with alkyl chain lengths that disrupt the symmetry of the cation structure or cations with alkyl groups that have been introduced into alkyl groups, and the viscosity can be increased by using cations with long-chain alkyl groups of octyl or longer, or by adding a non-volatile liquid with higher viscosity. The viscosity of the lubricating oil composition can be measured using an E-type viscometer with a 1°34' × R24 cone rotor at a rotation speed of 3 to 60 rpm after adjusting the sample to 25°C.

[0047] The water content of the lubricating oil composition is 50 ppm or less. If the water content of the lubricating oil composition exceeds 50 ppm, outgassing may occur under reduced pressure. The water content in the lubricating oil composition was measured using a Karl Fischer moisture meter. [Examples]

[0048] The following describes embodiments of the present invention, but the present invention is not limited to these embodiments. In the following, "parts" refers to parts by weight.

[0049] <Example 1> A solution of 135 parts (1.5 moles) of dimethyl carbonate dissolved in 192 parts of methanol was added to a stirred autoclave, and 96 parts (1.0 mole) of 1-ethylimidazole was added dropwise using a dropper funnel. The mixture was then stirred at 130°C for 40 hours to obtain 1-ethyl-3-methylimidazolium methyl carbonate salt. After cooling to 20°C, 96 parts (1.0 mole) of methanesulfonic acid was added, and after the generation of carbon dioxide gas subsided, the mixture was heated to 110°C under a reduced pressure of 1.0 kPa to remove the dimethyl carbonate and methanol, thereby obtaining a pale yellow 1-ethyl-3-methylimidazolium methanesulfonate. The obtained 1-ethyl-3-methylimidazolium methanesulfonate was used as lubricating oil composition Z-1.

[0050] <Example 2> 147 parts (1.0 mol) of 1-ethyl-3-methylimidazolium chloride and 89 parts (1.0 mol) of sodium dicyanamide were dissolved in 200 parts methanol and stirred for 10 minutes. The mixture was then heated to 60°C under a reduced pressure of 1.0 kPa to remove the methanol solvent, and after returning to room temperature, 1600 parts of dehydrated acetone were added to precipitate sodium chloride. After removing the precipitated sodium chloride by filtration, the mixture was heated to 70°C under a reduced pressure of 1.0 kPa to remove the acetone solvent, yielding a pale yellow 1-ethyl-3-methylimidazolium dicyanamide salt. The obtained 1-ethyl-3-methylimidazolium dicyanamide salt was used as lubricating oil composition Z-2.

[0051] <Example 3> 1-ethyl-3-methylimidazolium methyl carbonate salt was obtained by the same procedure as in Example 1. Next, a solution of 76 parts (1.0 mol) of ammonium thiocyanate dissolved in 76 parts of deionized water was added, generating carbon dioxide gas, and then white ammonium carbonate precipitated. After removing the precipitated ammonium carbonate by filtration, the mixture was heated to 110°C under a reduced pressure of 1.0 kPa while passing nitrogen gas at a rate of 0.1 mL / min to remove dimethyl carbonate, methanol, and deionized water, yielding a pale yellow 1-ethyl-3-methylimidazolium thiocyanate salt. The obtained 1-ethyl-3-methylimidazolium thiocyanate salt was used as lubricating oil composition Z-3.

[0052] <Example 4> 1-ethyl-3-methylimidazolium methyl carbonate salt was obtained by the same procedure as in Example 1. Next, 60 parts (1.0 mol) of acetic acid were added, and carbon dioxide gas was generated. After the generation of carbon dioxide gas subsided, the mixture was heated to 110°C under a reduced pressure of 1.0 kPa to remove dimethyl carbonate and methanol, yielding a pale yellow 1-ethyl-3-methylimidazolium acetate. The obtained 1-ethyl-3-methylimidazolium acetate was used as lubricating oil composition Z-4.

[0053] <Example 5> Lubricating oil composition Z-5 was obtained by adding 1 part of antifoaming agent F-1 to 99 parts of 1-ethyl-3-methylimidazolium methanesulfonate obtained in Example 1 and mixing.

[0054] <Example 6> Lubricating oil composition Z-6 was obtained by adding 1 part surfactant C-1 to 99 parts of the 1-ethyl-3-methylimidazolium thiocyanate salt obtained in Example 3 and mixing.

[0055] <Example 7> 311 parts (1.0 mol) of didecylmethylamine, 90 parts (1.0 mol) of dimethyl carbonate, and 64 parts of methanol as a solvent were charged into a stirred autoclave and reacted at 110°C for 12 hours to obtain didecyldimethylammonium methyl carbonate salt. Next, a solution of 76 parts (1.0 mol) of ammonium thiocyanate dissolved in 152 parts of methanol was added, generating carbon dioxide gas. The mixture was then stirred at 90°C for 4 hours to decompose and remove ammonium carbonate. The mixture was heated to 110°C under a reduced pressure of 1.0 kPa while passing nitrogen gas at a rate of 0.1 mL / min to remove the methanol solvent and ion-exchanged water, yielding a pale yellow didecyldimethylammonium thiocyanate salt. 4.9 parts of the obtained didecyldimethylammonium thiocyanate salt and 0.1 parts of fumed silica (AEROSIL200) were kneaded for 300 seconds at a rotational speed of 2000 rpm using an Awatori Neritaro (ARE-310, manufactured by Shinky Co., Ltd.). Next, 95 parts of the 1-ethyl-3-methylimidazolium methanesulfonate obtained in Example 1 were added and kneaded for 120 seconds at a rotational speed of 2000 rpm to obtain lubricating oil composition Z-7.

[0056] <Example 8> 99 parts of 1-ethyl-3-methylimidazolium methanesulfonate obtained in Example 1 were added to 0.98 parts of methyl methacrylate and 0.02 parts of 2,2'-azobis(2,4-dimethylvaleronitrile), and nitrogen was passed through at 20 mL / min for 5 minutes. Then, radical polymerization was carried out at 80°C for 6 hours under a nitrogen atmosphere to obtain lubricating oil composition Z-8 in which polymethyl methacrylate was dispersed. 5 g of the obtained lubricating oil composition Z-8 was poured into 100 g of methanol, and the resulting precipitate was recovered by suction filtration. The recovered precipitate was dissolved in THF, and the weight-average molecular weight was measured by GPC (polystyrene equivalent) using THF as the eluent, and it was found to be 70,000.

[0057] The measurement conditions for weight-average molecular weight in this invention are as follows: Device: HLC-8320 [Manufactured by Tosoh Corporation] Column: TSK GEL GMH6 (2 pieces) [Manufactured by Tosoh Corporation] Measurement temperature: 40℃ Sample solution: 0.25% by weight tetrahydrofuran (THF) solution Mobile phase: THF (contains no polymerization inhibitors) Solution injection volume: 100μL Detection device: Refractive index detector Reference material: Standard polystyrene (TSKstandard POLYSTYRENE)

[0058] <Example 9> A pale yellow 1-ethyl-3-methylimidazolium methanesulfonate was obtained by the same procedure as in Example 1. An appropriate amount of deionized water was added to the obtained 1-ethyl-3-methylimidazolium methanesulfonate and stirred to obtain lubricating oil composition Z-9 with a water content of 45 ppm.

[0059] <Example 10> Lubricating oil composition Z-10 was obtained by adding 1 part surfactant C-2 to 99 parts of 1-ethyl-3-methylimidazolium methanesulfonate obtained in Example 1 and mixing.

[0060] <Example 11> Lubricating oil composition Z-11 was obtained by adding 1 part of antifoaming agent F-2 to 99 parts of 1-ethyl-3-methylimidazolium methanesulfonate obtained in Example 1 and mixing.

[0061] <Example 12> Lubricating oil composition Z-12 was obtained by adding 1 part of antifoaming agent F-3 to 99 parts of 1-ethyl-3-methylimidazolium methanesulfonate obtained in Example 1 and mixing.

[0062] <Example 13> To 99 parts of 1-ethyl-3-methylimidazolium methanesulfonate obtained in Example 1, 0.98 parts of polyethylene glycol methacrylate manufactured by Sigma-Aldrich and 0.15 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) were added, and nitrogen was passed through at 20 mL / min for 5 minutes. Then, radical polymerization was carried out at 110°C for 2 hours under a nitrogen atmosphere to obtain lubricating oil composition Z-13 in which polyethylene glycol methacrylate was dispersed. 5 g of the obtained lubricating oil composition Z-13 was poured into 100 g of methanol, and the resulting precipitate was recovered by suction filtration. The recovered precipitate was dissolved in THF, and the weight-average molecular weight was measured by GPC (polystyrene equivalent) using THF as the eluent, and it was found to be 5000.

[0063] <Example 14> A column (DuPont, AmberLite ILA-402) packed with 1000 ml of strongly basic anion exchange resin pretreated to the thiocyanate (SCN-) form was passed through 404 parts (1.0 mol) of trioctylmethylammonium chloride dissolved in 1200 parts of anhydrous methanol solution. Subsequently, the column was heated to 110°C under a reduced pressure of 1.0 kPa to remove methanol, thereby obtaining trioctylmethylammonium thiocyanate salt. The obtained trioctylmethylammonium thiocyanate salt was used as lubricating oil composition Z-14.

[0064] <Example 15> In a round-bottom flask, 404 parts (1.0 mol) of trioctylmethylammonium chloride, 1000 parts (1.2 mol) of anion exchange resin (DuPont, AmberLite IRA-400(OH)), and 1200 parts of methanol were charged and stirred at room temperature for 3 hours to obtain a methanol solution of trioctylmethylammonium hydroxide. After filtering off the ion exchange resin, 60 parts (1.0 mol) of acetic acid were added dropwise, and stirring continued at room temperature for another hour. Then, the mixture was heated to 110°C under a reduced pressure of 1.0 kPa to remove the methanol and obtain trioctylmethylammonium acetate. The obtained trioctylmethylammonium acetate was used as lubricating oil composition Z-15.

[0065] <Example 16> To 94 parts of 1-ethyl-3-methylimidazolium methanesulfonate obtained in Example 1, 5.88 parts of polyethylene glycol methacrylate manufactured by Sigma-Aldrich and 0.90 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) were added, and nitrogen was passed through at 20 mL / min for 5 minutes. Then, radical polymerization was carried out at 110°C for 2 hours under a nitrogen atmosphere to obtain lubricating oil composition Z-16 in which polyethylene glycol methacrylate was dispersed. 5 g of the obtained lubricating oil composition Z-16 was poured into 100 g of methanol, and the resulting precipitate was recovered by suction filtration. The recovered precipitate was dissolved in THF, and the weight-average molecular weight was measured by GPC (polystyrene equivalent) using THF as the eluent, and it was found to be 5000.

[0066] <Example 17> Lubricating oil composition Z-17 was obtained by adding 1 part of siloxanediamine antifoaming agent F-4 to 99 parts of 1-ethyl-3-methylimidazolium methanesulfonate obtained in Example 1 and mixing.

[0067] <Example 18> Lubricating oil composition Z-18 was obtained by adding 1 part of glycerin ester antifoaming agent F-5 to 99 parts of 1-ethyl-3-methylimidazolium methanesulfonate obtained in Example 1 and mixing.

[0068] <Example 19> 1-ethyl-3-methylimidazolium methyl carbonate salt was obtained by the same procedure as in Example 1. When 126 parts (1.0 molar part) of dimethyl phosphoric acid were added to the obtained 1-ethyl-3-methylimidazolium methyl carbonate salt, carbon dioxide gas was generated. After the generation of carbon dioxide gas subsided, the mixture was heated to 110°C under a reduced pressure of 1.0 kPa to remove dimethyl carbonate and methanol, thereby obtaining a pale yellow 1-ethyl-3-methylimidazolium dimethyl phosphate salt. The obtained 1-ethyl-3-methylimidazolium dimethyl phosphate salt was used as lubricating oil composition Z-19.

[0069] <Comparative Example 1> 1-ethyl-3-methylimidazolium methyl carbonate salt was obtained by the same procedure as in Example 1. Next, 210 parts (1.0 molar part) of dibutyl phosphate were added, and carbon dioxide gas was generated. After the generation of carbon dioxide gas subsided, the mixture was heated to 110°C under a reduced pressure of 1.0 kPa to remove dimethyl carbonate and methanol, thereby obtaining pale yellow 1-ethyl-3-methylimidazolium dibutyl phosphate. The obtained 1-ethyl-3-methylimidazolium dibutyl phosphate was used as lubricating oil composition Z'-1.

[0070] <Comparative Example 2> Didecyldimethylammonium thiocyanate salt was obtained by the same procedure as in Example 7. The obtained didecyldimethylammonium thiocyanate salt was used as lubricating oil composition Z'-2.

[0071] <Comparative Example 3> A commercially available 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt (manufactured by Tokyo Chemical Industry Co., Ltd.) was used as lubricant composition Z'-3.

[0072] <Comparative Example 4> A pale yellow 1-ethyl-3-methylimidazolium methanesulfonate was obtained by the same procedure as in Example 1. An appropriate amount of deionized water was added to the obtained 1-ethyl-3-methylimidazolium methanesulfonate and stirred to obtain lubricating oil composition Z'-4 with a water content of 75 ppm.

[0073] The lubricating oil compositions of Examples 1-19 and Comparative Examples 1-4 were evaluated for water content, viscosity, volatility (weight loss rate), defoaming properties under reduced pressure (defoaming time), gas-out properties, and corrosiveness (immersion test) using the following test methods. The results are shown in Tables 1-3.

[0074] [Table 1]

[0075] [Table 2]

[0076] [Table 3]

[0077] The ionic liquids and other additives shown in Tables 1-3 are as follows: EMI-MSA: 1-ethyl-3-methylimidazolium methanesulfonate EMI-DCA: 1-ethyl-3-methylimidazolium dicyanamide salt EMI-SCN: 1-ethyl-3-methylimidazolium thiocyanate salt EMI-AcO: 1-ethyl-3-methylimidazolium acetate EMI-DBP: 1-Ethyl-3-methylimidazolium dibutyl phosphate DDA-SCN: Didecyldimethylammonium thiocyanate salt TOMA-AcO: Trioctylmethylammonium acetate TOMA-SCN: Trioctylmethylammonium thiocyanate salt EMI-DMP: 1-ethyl-3-methylimidazolium dimethyl phosphate EMI-TFSI: 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt Nonionic surfactant C-1: "Noptam 740A" manufactured by Sunopco Corporation. Nonionic surfactant C-2: "SN Deformer 260" manufactured by Sunopco Co., Ltd. PEGMA: Polyethylene glycol methacrylate with a weight-average molecular weight of 5000. PMMA: Polymethyl methacrylate with a weight-average molecular weight of 70,000 SiO2: Evonik AEROSIL200 Antifoaming agent F-1: "SN Deformer 399" manufactured by Sunopco Co., Ltd. Antifoaming agent F-2: "SN Deformer 381" manufactured by Sunopco Co., Ltd. Antifoaming agent F-3: "Noptam 777-F" manufactured by Sunopco Corporation. Antifoaming agent F-4: "X-22-1660B-3" manufactured by Shin-Etsu Chemical Co., Ltd. Antifoaming agent F-5: "Nopco 1407-H" manufactured by Sunopco Co., Ltd.

[0078] <Water content> The moisture content of the lubricating oil composition was determined by measuring the obtained lubricating oil composition with a Karl Fischer moisture meter (MKS-500, manufactured by Kyoto Electronics Manufacturing Co., Ltd.).

[0079] <Viscosity> The obtained lubricating oil composition was adjusted to 25°C, and the viscosity of the lubricating oil composition was measured using an E-type viscometer with a 1°34' × R24 cone rotor at rotational speeds of 3 to 60 rpm.

[0080] <Volatility [Weight loss rate (before friction test)]> The obtained lubricating oil composition and aluminum cup were left to stand overnight in a dry environment at 17°C with a dew point of -50°C. The weight of the aluminum cup was then weighed using a high-precision analytical balance (denoted as Wt). Next, approximately 10 mg of the lubricating oil composition was added to the weighed aluminum cup, spreading it evenly across the bottom surface of the cup. The weight of this evaluation sample was then weighed using a high-precision analytical balance (denoted as Wb). The evaluation sample was placed in a vacuum desiccator (MVD-300N, manufactured by AS ONE Corporation), and the pressure was reduced to 1.0 kPa for 1 hour. After 1 hour, the vacuum desiccator was gradually depressurized and the evaluation sample was recovered. The weight of the evaluation sample was then weighed using a high-precision analytical balance (denoted as Wa). The weight loss rate was calculated as follows: Weight loss rate = (Wb - Wa) / (Wb - Wt) × 100 (%).

[0081] <Volatility [Weight loss rate (after friction test)]> The obtained lubricating oil composition and aluminum cup were left to stand overnight in a dry environment at 17°C with a dew point of -50°C, and the weight of the aluminum cup was weighed using a high-precision analytical balance (this is denoted as Wt). 1 g of the lubricating oil composition and three Φ10 mm zirconia balls were added to the dedicated container of the Awatori Rentaro vacuum type (ARV-310P, manufactured by Thinky Co., Ltd.), and the Awatori Rentaro was stirred at 10 kPa, a rotation speed of 2000 rpm, and for 120 seconds. Next, approximately 10 mg of the lubricating oil composition after the friction test was added to the weighed aluminum cup so that it spread evenly across the entire bottom surface of the cup, and the weight of this evaluation sample was weighed using a high-precision analytical balance (this is denoted as Wb). The evaluation sample was placed in a vacuum desiccator (MVD-300N, manufactured by AS ONE Corporation), and then left to stand for 1 hour under reduced pressure of 1.0 kPa. After standing for one hour, the vacuum desiccator was gradually depressurized and the evaluation samples were collected. The weight of the evaluation samples was weighed using a high-precision analytical balance (denoted as Wa). The weight loss rate was calculated as follows: Weight loss rate = (Wb-Wa) / (Wb-Wt) × 100 (%).

[0082] <Volatility [Weight Loss Rate (Difference)]> The difference between the weight loss rate (after friction test) and the weight loss rate (before friction test) was defined as the weight loss rate (difference).

[0083] <Foam-breaking properties (defoaming time) under reduced pressure> The obtained lubricating oil composition was left to stand overnight in a dry environment at 17°C with a dew point of -50°C. Then, dry air was passed through the lubricating oil composition at a flow rate of 50 mL / min for 10 minutes. After the air was passed through, the lubricating oil composition was left to stand for 1 hour, then 25 mL was transferred to a 50 mL beaker without creating bubbles, and the beaker was placed in a vacuum desiccator (MVD-300N, manufactured by AS ONE Corporation) and the pressure was reduced to 1.0 kPa. The time immediately after the start of the pressure reduction was defined as the start time, and it was visually confirmed that no new bubbles were generated for 10 minutes after the last bubble disappeared. The time when the last bubble disappeared was defined as the end time, and the time taken from start to end was defined as the defoaming time.

[0084] <Outgassing> Compliant with ASTM E595, under vacuum conditions (7 × 10 -3 The test was conducted under the following conditions (Pa or less): heating temperature: 125°C, holding time: 24 hours, and exhaust gas cooling temperature: 25°C. Outgassing from the lubricating oil composition was measured under these test conditions. If the total mass loss ratio (TML) calculated from the measurement results was 1.0% or less, and the collected volatile condensable material ratio (CVCM) was 0.1% or less, it was marked as "○". If the TML exceeds 1.0% or the CVCM exceeds 0.1%, it was marked with "×". If the TML exceeds 1% or the CVCM exceeds 0.1%, it can be said that outgassing is occurring.

[0085] <Corrosion (immersion test)> The obtained lubricating oil composition was left to stand overnight in a dry environment at 17°C with a dew point of -50°C. Then it was moved to a glove box under an argon atmosphere (dew point -70°C) and left to stand until the dew point in the glove box recovered to -70°C. Next, a SUS plate (material: SUS304, 1 mm thick x 20 mm long x 40 mm wide) was polished in accordance with JIS K2246:2018 to prepare a test specimen. The prepared test specimen was immersed in the lubricating oil composition and left to stand for one week, and the appearance of the test specimen surface was evaluated visually in the following two stages. ○: No discoloration or deposits on the surface of the test specimen. ×: Discoloration or adhesion of substances on the surface of the test specimen

[0086] The results shown in Tables 1 and 2 indicate that the lubricating oil composition of the present invention exhibits excellent volatility and anti-foaming properties under reduced pressure, as well as good corrosiveness and no outgassing. On the other hand, as shown in the results in Table 3, comparative example 4, in which the water content in the lubricating oil composition exceeded 50 ppm, exhibited gas outflow. Furthermore, Comparative Examples 1 and 2, whose lubricating oil compositions had a viscosity exceeding 370 mPa·s at 25°C, exhibited poor defoaming properties under reduced pressure. Furthermore, Comparative Examples 1 and 3, which are ionic liquids composed of at least one anion other than an anion selected from the group consisting of alkyl carboxylate anions, alkyl sulfonate anions, dicyanamide anions, and thiocyanate anions, exhibited poor volatility. [Industrial applicability]

[0087] The lubricating oil composition of the present invention functions as a cutting oil and, because it contains an ionic liquid, also has high conductivity and is useful as a heat transfer medium.

Claims

1. A lubricating oil composition comprising an ionic liquid (X) consisting of an anion (A) and a cation (B), The anion (A) is at least one anion selected from the group consisting of alkyl carboxylate anions, alkyl sulfonate anions, dialkyl phosphate anions, dicyanamide anions, and thiocyanate anions. The water content in the lubricating oil composition is 50 ppm or less. The lubricating oil composition having a viscosity of 15 to 370 mPa·s at 25°C.

2. The lubricating oil composition according to claim 1, wherein the cation (B) is a quaternary ammonium cation and / or an imidazolium cation.

3. The lubricating oil composition according to claim 2, wherein the imidazolium cation is 1-ethyl-3-methylimidazolium.

4. The lubricating oil composition according to claim 1, wherein the lubricating oil composition contains 95% by weight or more of an ionic liquid (X).

5. Furthermore, the lubricating oil composition according to claim 1 further comprises a surfactant (C), a polymer (D), an inorganic substance (E), or a combination thereof.

6. The lubricating oil composition according to claim 5, wherein the surfactant (C) is a nonionic surfactant.

7. The lubricating oil composition according to claim 5, wherein the polymer (D) is an acrylic polymer.

8. The lubricating oil composition according to claim 5, wherein the inorganic substance (E) is silica.

Images