Grease composition and method for suppressing decomposition of water-soluble cutting oil

Abstract

Provided is a grease composition capable of suppressing decomposition of water-soluble cutting oil, even if admixed in a cutting oil tank, while having a prescribed consistency. This grease composition contains a base oil (A), a thickener (B), a decomposition-preventing agent (C), and an imide compound (D).

Description

Grease composition and method for inhibiting decay of water-soluble cutting oil

[0001] The present invention relates to a grease composition and a method for inhibiting putrefaction of a water-soluble cutting oil.

[0002] Machine tools have sliding surfaces for moving tools, workpieces, etc. in any direction, and grease is used to smooth the sliding motion. However, if grease gets into a water-soluble cutting oil tank (hereinafter referred to as "cutting oil tank") installed in the machine tool, there is a problem that the quality of the water-soluble cutting oil is easily deteriorated. In view of this problem, for example, Patent Document 1 discloses an antibacterial grease containing antibacterial zeolite.

[0003] Japanese Patent Application Publication No. 5-98278

[0004] Conventionally, the use period of water-soluble cutting oil has been extended by quickly separating grease from the water-soluble cutting oil and inhibiting bacterial growth in the cutting oil tank. However, in recent years, cutting oil tanks have increasingly been equipped without oil skimmers, which are other oil separation devices, and the problem of deterioration in the quality of water-soluble cutting oil due to grease contamination has become a major issue. Furthermore, the zeolite described in Patent Document 1 has a disadvantage in terms of material cost. Under these circumstances, there is a need for a grease composition that has a predetermined consistency and can inhibit the spoilage of water-soluble cutting oil even when mixed into a cutting oil tank.

[0005] The present invention provides the following aspects [1] to

[11] . [1] A grease composition containing a base oil (A), a thickener (B), an antiseptic (C), and an imide compound (D). [2] The grease composition according to [1], wherein the antiseptic (C) comprises one or more compounds selected from the group consisting of a dithiocarbamate-type compound (C1) represented by the following general formula (c-1), a 1-hydroxy-2-pyridone-type compound (C2) represented by the following general formula (c-2), a salicylic acid-type compound (C3) represented by the following general formula (c-3), and an alicyclic monoamine compound (C4). (In the above general formula (1), M represents a single bond or a metal atom selected from the group consisting of sodium (Na), potassium (K), bismuth (Bi), copper (Cu), iron (Fe), nickel (Ni), selenium (Se), zinc (Zn), cadmium (Cd), calcium (Ca), tellurium (Te), and zirconium (Zr), and R １ and R ２ each independently represents an alkyl group having 1 to 20 carbon atoms, and a represents the valence of the metal atom when M is a metal atom, and is 2 when M is a single bond. (In the above general formula (2), R ３ represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and R ４ represents an alkyl group having 1 to 20 carbon atoms, and X ＋ represents an organic base, an alkali metal ion, an ammonium ion, or a divalent to tetravalent cation. (In the above general formula (3), R ５ represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms.) [3] The grease composition according to [1] or [2], wherein the imide compound (D) comprises at least one compound selected from the group consisting of a bisimide compound (D1) represented by the following general formula (4) and a monoimide compound (D2) represented by the following general formula (5): (In the above general formulas (4) and (5), R ８ , R ９ and R １０are each independently a polybutenyl group or a polyisobutenyl group, each A is independently an alkylene group having 2 to 5 carbon atoms, and m is an integer of 2 to 6.) [4] The grease composition according to any one of [1] to [3], wherein the content of the antiseptic agent (C) is 0.01 to 5.0 mass% based on the total amount of the grease composition. [5] The grease composition according to any one of [1] to [4], wherein the content of the imide compound (D) is 0.01 to 5.0 mass% based on the total amount of the grease composition. [6] The grease composition according to any one of [1] to [5], wherein the content ratio of the antiseptic agent (C) to the imide compound (D) [(C) / (D)] is 0.1 to 5.0 by mass. [7] The grease composition according to any one of [1] to [6], wherein the base oil (A) comprises a mineral oil. [8] The grease composition according to any one of [1] to [7], wherein the thickener (B) comprises a urea-based thickener. [9] The grease composition according to any one of [1] to [8], which is used for lubricating a mechanical device to which a water-soluble cutting oil is applied.

[10] A grease composition obtained by blending a grease containing a base oil (A) and a thickener (B), with an anti-corrosion agent (C) and an imide compound (D).

[11] A method for inhibiting corrosion of a water-soluble cutting oil, which comprises using the grease composition according to any one of [1] to [8], for lubricating a mechanical device.

[0006] The grease composition of a preferred embodiment of the present invention has an appropriate consistency and excellent corrosion resistance. Therefore, the grease composition of the present invention can be suitably used for lubricating sliding parts of various mechanical devices. Furthermore, according to another embodiment of the present invention, there is provided a method for inhibiting corrosion of a water-soluble cutting oil.

[0007] Regarding the numerical ranges described herein, the upper and lower limits can be arbitrarily combined. For example, when a numerical range is described as "preferably 30 to 100, more preferably 40 to 80," the ranges "30 to 80" and "40 to 100" are also included in the numerical ranges described herein. Furthermore, when a numerical range is described as "preferably 30 or more, more preferably 40 or more, and preferably 100 or less, more preferably 80 or less," the ranges "30 to 80" and "40 to 100" are also included in the numerical ranges described herein. In addition, the numerical ranges described herein mean, for example, a range of "60 or more (more than 60 or 60) and 100 or less (less than 100 or 100)." Furthermore, when specifying the upper and lower limits described herein, the numerical range from the lower limit to the upper limit can be specified by appropriately selecting from the respective options and combining them arbitrarily. In addition, multiple combinations of the various requirements described as preferred aspects of the present specification can be used.

[0008] [Configuration of Grease Composition] The grease composition of the present invention contains a base oil (A) (hereinafter also referred to as "component (A)"), a thickener (B) (hereinafter also referred to as "component (B)"), an antiseptic (C) (hereinafter also referred to as "component (C)"), and an imide compound (D) (hereinafter also referred to as "component (D)"). The grease composition of one embodiment of the present invention is obtained by blending the antiseptic (C) and the imide compound (D) with a grease containing the base oil (A) and the thickener (B). The specific configuration of the grease composition will be described below.

[0009] <Component (A): Base Oil> The base oil (A) may be any base oil commonly used in grease compositions, for example, it may be a mineral oil, a synthetic oil, or a mixture of a mineral oil and a synthetic oil. The grease composition of one embodiment of the present invention may contain a mineral oil, since it contains the component (C) described below. That is, compared to synthetic oils, mineral oils contain trace amounts of impurities, etc., and there is a high risk of disrupting the balance of the water-soluble cutting oil. Therefore, if a grease composition containing mineral oil is mixed into a cutting oil tank, it is thought that the quality of the water-soluble cutting oil will deteriorate. However, according to the present invention, by including the anticorrosive agent of component (C), it is possible to suppress the spoilage of the water-soluble cutting oil even if the base oil (A) contains mineral oil.

[0010] Examples of mineral oils include atmospheric residues obtained by atmospheric distillation of crude oils such as paraffinic crude oil, intermediate crude oil, and naphthenic crude oil; distillates obtained by vacuum distillation of these atmospheric residues; and refined 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.

[0011] Examples of synthetic oils include poly-α-olefins such as α-olefins, homopolymers thereof, and α-olefin copolymers (for example, α-olefin copolymers having 8 to 14 carbon atoms, such as ethylene-α-olefin copolymers); isoparaffins; polyalkylene glycols; ester oils such as polyol esters, dibasic acid esters, and phosphate esters; ether oils such as polyphenyl ethers; alkylbenzenes; alkylnaphthalenes; synthetic oils (GTL) obtained by isomerizing wax produced from natural gas by the Fischer-Tropsch process or the like (GTL wax (Gas To Liquids WAX)); synthetic oils (CTL) obtained by isomerizing wax produced from coal by the Fischer-Tropsch process or the like (CTL wax (Coal To Liquids WAX)); and wax produced from biomass by the Fischer-Tropsch process or the like (BTL wax (Biomass To Liquids WAX)). Examples of suitable oils include synthetic oils (BTL) obtained by isomerizing waxes and waxes.

[0012] The kinematic viscosity at 40°C of the base oil (A) used in one embodiment of the present invention is preferably 500 mm ２ / s or less, more preferably 400 mm ２ / s or less, more preferably 300 mm ２ / s or less, particularly preferably 200 mm ２ On the other hand, from the viewpoint of the required lubrication performance, it is preferably 30 mm ２ / s or more, more preferably 50 mm ２ / s or more, more preferably 100 mm ２ / s or more, particularly preferably 150 mm ２ / s or more.

[0013] The viscosity index of the base oil (A) used in one embodiment of the present invention is preferably 70 or more, more preferably 80 or more, even more preferably 90 or more, and particularly preferably 100 or more. In one embodiment of the present invention, when a mixed oil combining two or more base oils is used as component (A), the kinematic viscosity and viscosity index of the mixed oil are preferably within the above-mentioned ranges. Therefore, the mixed oil may be prepared by combining a low-viscosity base oil and a high-viscosity base oil so that the mixed oil has a kinematic viscosity and viscosity index within the above-mentioned ranges. The mixed oil may be a mixed oil combining two or more base oils whose kinematic viscosity and viscosity index at 100°C fall within the above-mentioned ranges, or a mixed oil combining a base oil whose kinematic viscosity and viscosity index at 100°C fall within the above-mentioned ranges with a base oil that does not fall within the above-mentioned ranges. It may also be a mixed oil adjusted to fall within the above-mentioned ranges by combining a low-viscosity base oil and a high-viscosity base oil whose kinematic viscosity and viscosity index at 100°C do not fall within the above-mentioned ranges. In this specification, the kinematic viscosity and viscosity index refer to values ​​measured or calculated in accordance with JIS K2283:2000.

[0014] In the grease composition of one embodiment of the present invention, the content of the base oil (A) is, based on the total amount (100 mass%) of the grease composition, usually 55 mass% or more, preferably 60 mass% or more, more preferably 65 mass% or more, even more preferably 70 mass% or more, still more preferably 75 mass% or more, particularly preferably 80 mass% or more, and is preferably 99.9 mass% or less, more preferably 95 mass% or less, even more preferably 90 mass% or less.

[0015] <Component (B): Thickener> The grease composition of the present invention contains a thickener (B) to impart a desired hardness to the grease composition. The thickener (B) used in one embodiment of the present invention may be a urea-based thickener or a soap-based thickener. Furthermore, the grease composition of one embodiment of the present invention may use one or more thickeners selected from the group consisting of bentonite, silica, polytetrafluoroethylene (PTFE), and cellulose nanofibers. From the viewpoint of heat resistance, the grease composition of one embodiment of the present invention preferably contains a urea-based thickener. Note that the thickener (B) may be used alone or in combination of two or more types. The urea-based thickener and the soap-based thickener used in one embodiment of the present invention are described below.

[0016] (Urea-based thickener) The urea-based thickener may be any compound having a urea bond, but a diurea having two urea bonds is preferred, and a compound represented by the following general formula (b1) is more preferred. １ -NHCONH-R ３ -NHCONH-R ２ (b1) The urea-based thickener used in one embodiment of the present invention may consist of one type or may be a mixture of two or more types.

[0017] In the above general formula (b1), R １ and R ２ each independently represents a monovalent hydrocarbon group having 6 to 24 carbon atoms; R １ and R ２ may be the same or different from each other. ３represents a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms.

[0018] R in the general formula (b1) １ and R ２ The number of carbon atoms of the monovalent hydrocarbon group that can be selected as R is 6 to 24, preferably 6 to 20, and more preferably 6 to 18. １ and R ２ Examples of the monovalent hydrocarbon group that can be selected as aryl include a saturated or unsaturated monovalent chain hydrocarbon group, a saturated or unsaturated monovalent alicyclic hydrocarbon group, and a monovalent aromatic hydrocarbon group, and a saturated or unsaturated monovalent chain hydrocarbon group or a saturated or unsaturated monovalent alicyclic hydrocarbon group is preferred.

[0019] Examples of the monovalent saturated chain hydrocarbon group include linear or branched alkyl groups having 6 to 24 carbon atoms, and specific examples thereof include 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, an octadecenyl group, a nonadecyl group, and an icosyl group. Examples of the monovalent unsaturated chain hydrocarbon group include linear or branched alkenyl groups having 6 to 24 carbon atoms, and specific examples thereof include a hexenyl group, a heptenyl group, an octenyl group, a nonenyl group, a decenyl group, a dodecenyl group, a tridecenyl group, a tetradecenyl group, a pentadecenyl group, a hexadecenyl group, an octadecenyl group, a nonadecenyl group, an icosenyl group, an oleyl group, a geranyl group, a farnesyl group, and a linoleyl group.

[0020] Examples of the monovalent saturated alicyclic hydrocarbon group include cycloalkyl groups such as a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, and a cyclononyl group; and cycloalkyl groups substituted with an alkyl group having 1 to 6 carbon atoms, such as a methylcyclohexyl group, a dimethylcyclohexyl group, an ethylcyclohexyl group, a diethylcyclohexyl group, a propylcyclohexyl group, an isopropylcyclohexyl group, a 1-methyl-propylcyclohexyl group, a butylcyclohexyl group, a pentylcyclohexyl group, a pentyl-methylcyclohexyl group, and a hexylcyclohexyl group.

[0021] Examples of the monovalent unsaturated alicyclic hydrocarbon group include cycloalkenyl groups such as a cyclohexenyl group, a cycloheptenyl group, and a cyclooctenyl group; and cycloalkenyl groups substituted with an alkyl group having 1 to 6 carbon atoms, such as a methylcyclohexenyl group, a dimethylcyclohexenyl group, an ethylcyclohexenyl group, a diethylcyclohexenyl group, and a propylcyclohexenyl group.

[0022] Examples of the monovalent aromatic hydrocarbon group include a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a diphenylmethyl group, a diphenylethyl group, a diphenylpropyl group, a methylphenyl group, a dimethylphenyl group, an ethylphenyl group, and a propylphenyl group.

[0023] R in the general formula (b1) ３ The carbon number of the divalent aromatic hydrocarbon group that can be selected as R is 6 to 18, preferably 6 to 15, and more preferably 6 to 13. ３ Examples of the divalent aromatic hydrocarbon group that can be selected as aryl include a phenylene group, a diphenylmethylene group, a diphenylethylene group, a diphenylpropylene group, a methylphenylene group, a dimethylphenylene group, an ethylphenylene group, etc. Among these, a phenylene group, a diphenylmethylene group, a diphenylethylene group, or a diphenylpropylene group is preferred, and a diphenylmethylene group is more preferred.

[0024] (Soap-based thickener) The soap-based thickener may be a metal soap made of a metal salt of a monovalent fatty acid, or a metal complex soap made of a metal salt of a monovalent fatty acid and a metal salt of a divalent fatty acid. Examples of metal soaps include lithium soap, calcium soap, sodium soap, barium soap, and aluminum soap. Examples of metal complex soaps include lithium complex soap, calcium complex soap, barium complex soap, and aluminum complex soap.

[0025] Examples of monovalent fatty acids that constitute metal soaps and metal complex soaps include lauric acid, tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, margaric acid, stearic acid, nonadecylic acid, arachidic acid, behenic acid, lignoceric acid, tallow fatty acid, 9-hydroxystearic acid, 10-hydroxystearic acid, 12-hydroxystearic acid, 9,10-hydroxystearic acid, ricinoleic acid, and ricinoleidic acid, and monovalent saturated fatty acids having 12 to 24 carbon atoms (preferably 12 to 18, more preferably 14 to 18) are preferred.

[0026] Examples of divalent fatty acids that constitute metal complex soaps include succinic acid, malonic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid.

[0027] In the grease composition of one embodiment of the present invention, the content of the thickener (B) is, based on the total amount (100 mass%) of the grease composition, preferably 0.01 mass% or more, more preferably 0.1 mass% or more, even more preferably 1 mass% or more, and may be 3 mass% or more or 5 mass% or more. On the other hand, the content of the thickener (B) is, based on the total amount (100 mass%) of the grease composition, preferably 40 mass% or less, more preferably 30 mass% or less, even more preferably 25 mass% or less, still more preferably 15 mass% or less, and particularly preferably 10 mass% or less.

[0028] <Component (C): Antiseptic> The grease composition of the present invention contains an antiseptic (C). As mentioned above, grease contamination can lead to bacterial proliferation in cutting oil tanks, resulting in deterioration of the quality of water-soluble cutting oils. In response to this problem, the present inventors discovered that by including as component (C) one or more compounds selected from the group consisting of dithiocarbamate-type compounds (C1) represented by the following general formula (c-1), 1-hydroxy-2-pyridone-type compounds (C2) represented by the following general formula (c-2), salicylic acid-type compounds (C3) represented by the following general formula (c-3), and alicyclic monoamine compounds (C4), the spoilage of water-soluble cutting oils can be inhibited. Each compound constituting component (C) is described below.

[0029] (Dithiocarbamate Compound (C1)) The grease composition of one embodiment of the present invention contains, as component (C), a dithiocarbamate compound (C1) represented by the following general formula (c-1).

[0030] In the general formula (c-1) above, M represents a single bond or a metal atom selected from the group consisting of sodium (Na), potassium (K), bismuth (Bi), copper (Cu), iron (Fe), nickel (Ni), selenium (Se), zinc (Zn), cadmium (Cd), calcium (Ca), tellurium (Te), and zirconium (Zr).

[0031] R １ and R ２ R each independently represents an alkyl group having 1 to 20 carbon atoms. The alkyl group may be linear or branched. １ and R ２ The number of carbon atoms in the alkyl group that can be selected as the alkyl group is preferably 2 to 12, more preferably 3 to 10, and even more preferably 4 to 8. Having the alkyl group with a specific number of carbon atoms can improve the corrosion resistance of the water-soluble cutting oil. Examples of alkyl groups having 1 to 20 carbon atoms include methyl, ethyl, propyl groups such as n-propyl and isopropyl, butyl groups such as n-butyl, isobutyl, s-butyl and t-butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, and icosyl groups. The above groups also include structural isomers.

[0032] In the general formula (c-1), when M is a metal atom, a represents the valence of the metal atom, and when M is a single bond, a represents 2. For example, when M is a divalent metal atom such as zinc (Zn), a represents 2.

[0033] In one embodiment of the present invention, the dithiocarbamate compound (C1) represented by the above general formula (c-1) may be, for example, tetrabutylthiuram disulfide (Butyl Tuads), zinc diamyldithiocarbamate (ZnDTC), zinc dimethyldithiocarbamate, sodium dimethyldithiocarbamate, potassium dimethyldithiocarbamate, bismuth dimethyldithiocarbamate, copper dimethyldithiocarbamate, iron(II) dimethyldithiocarbamate, nickel dimethyldithiocarbamate, selenium dimethyldithiocarbamate, zinc ethyldithiocarbamate, cadmium ethyldithiocarbamate, calcium ethyldithiocarbamate, iron(II) diethyldithiocarbamate, iron(III) diethyldithiocarbamate, nickel diethyldithiocarbamate, tellurium(II) diethyldithiocarbamate, zirconium diethyldithiocarbamate, tellurium(IV) diethyldithiocarbamate, and the like.

[0034] In the grease composition of one embodiment of the present invention, the content of the dithiocarbamate compound (C1) is preferably 0.6 mass% or more, more preferably 0.7 mass% or more, even more preferably 0.8 mass% or more, and even more preferably 1.0 mass% or more, based on the total amount (100 mass%) of the grease composition, from the viewpoint of improving the putrefaction resistance of the water-soluble cutting oil. Furthermore, from the viewpoint of maintaining good lubricating performance of the grease composition, the content of the dithiocarbamate compound (C1) is preferably 5.0 mass% or less, 4.0 mass% or less, 3.0 mass% or less, 2.5 mass% or less, 2.0 mass% or less, or 1.5 mass% or less, based on the total amount (100 mass%) of the grease composition.

[0035] In the grease composition of one embodiment of the present invention, the content ratio [(C1) / (D)] of the dithiocarbamate compound (C1) to the imide compound (D) described below is, in terms of mass ratio, preferably 0.1 or more, more preferably 0.5 or more, even more preferably 0.8 or more, and still more preferably 1.2 or more, from the viewpoints mentioned above, from the viewpoint of achieving a good balance between improving the putrefaction resistance of the water-soluble cutting oil and inhibiting hardening of the grease composition, and is also preferably 5.0 or less, more preferably 3.0 or less, and even more preferably 2.0 or less. Furthermore, the grease composition of one embodiment of the present invention does not include one in which the above ratio is 1.0.

[0036] (1-Hydroxy-2-pyridone Compound (C2)) The grease composition of one embodiment of the present invention contains, as component (C), a 1-hydroxy-2-pyridone compound (C2) represented by the following general formula (c-2).

[0037] In the above general formula (c-2), R ３ represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms. The alkyl group may be linear or branched. ３ The number of carbon atoms in the alkyl group that can be selected as is preferably 1 to 6, more preferably 1 to 4, and even more preferably 1. Examples of alkyl groups having 1 to 8 carbon atoms include methyl, ethyl, propyl groups such as n-propyl and isopropyl, butyl groups such as n-butyl, isobutyl, s-butyl and t-butyl, pentyl, hexyl, heptyl, and octyl. The above groups also include structural isomers.

[0038] In the above general formula (c-2), R ４ represents an alkyl group having 1 to 20 carbon atoms. The alkyl group may be linear or branched. ４ The number of carbon atoms in the alkyl group that can be selected as is preferably 4 to 18, more preferably 6 to 14, and even more preferably 8 to 12. Specific examples of alkyl groups having 1 to 20 carbon atoms are as described above.

[0039] In the general formula (c-2), X ＋represents an organic base, an alkali metal ion, an ammonium ion, or a divalent to tetravalent cation.

[0040] The 1-hydroxy-2-pyridone compound (C2) is used as a salt, and can be suitably used as a salt with, for example, an organic amine. Specific examples include ethanolamine, diethanolamine, N-ethylethanolamine, N-methyldiethanolamine, triethanolamine, diethylaminoethanol, 2-amino-2-methyl-n-propanol, dimethylaminopropanol, 2-amino-2-methylpropanediol, triisopropanolamine, ethylenediamine, hexamethylenediamine, morpholine, piperidine, cyclohexylamine, tributylamine, dodecylamine, N,N-dimethyldodecylamine, stearylamine, oleylamine, benzylamine, dibenzylamine, N-ethylbenzylamine, dimethylstearylamine, N-methylmorpholine, N-methylpiperazine, 4-methylcyclohexylamine, and N-hydroxyethylmorpholine.

[0041] The 1-hydroxy-2-pyridone compound (C2) may also be a salt with an inorganic ion, and can be used as a salt with a divalent to tetravalent cation, such as an alkali metal salt such as a sodium salt or a potassium salt; an ammonium salt; or a magnesium salt, a calcium salt, a zinc salt, an aluminum salt, or a zirconium salt.

[0042] In one embodiment of the present invention, specific examples of the 1-hydroxy-2-pyridone-type compound (C2) represented by the above general formula (c-2) include 1-hydroxy-4-methyl-6-cyclohexyl-2-pyridone, 1-hydroxy-4-methyl-6-(methyl-cyclohexyl)-2-pyridone, 1-hydroxy-4-methyl-6-(2-bicyclo[2,2,1]heptyl)-2-pyridone, and the monoethanolamine salt of 1-hydroxy-4-methyl-6-(2,4,4-trimethylpentyl)-2-pyridone. Among these, the monoethanolamine salt of 1-hydroxy-4-methyl-6-(2,4,4-trimethylpentyl)-2-pyridone (piroctone olamine) is more preferred. In another embodiment of the present invention, the antiseptic agent of component (C) may be a mixture of piroctone olamine and phenoxyethanol.

[0043] In the grease composition of one embodiment of the present invention, the content of the 1-hydroxy-2-pyridone compound (C2) is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, even more preferably 0.1% by mass or more, and even more preferably 0.3% by mass or more, based on the total amount (100% by mass) of the grease composition, from the viewpoint of improving the putrefaction resistance of the water-soluble cutting oil. Furthermore, from the viewpoint of maintaining good lubricating performance of the grease composition, the content of the 1-hydroxy-2-pyridone compound (C2) is preferably 5.0% by mass or less, 4.0% by mass or less, 3.0% by mass or less, 2.5% by mass or less, 2.0% by mass or less, or 1.5% by mass or less, based on the total amount (100% by mass) of the grease composition.

[0044] In the grease composition of one embodiment of the present invention, the content ratio [(C2) / (D)] of the 1-hydroxy-2-pyridone compound (C2) to the imide compound (D) described below is, in terms of mass ratio, preferably 0.1 or more, more preferably 0.3 or more, and even more preferably 0.5 or more, from the viewpoint of achieving a good balance between improving the putrefaction resistance of the water-soluble cutting oil and inhibiting hardening of the grease composition; and from the same viewpoint as above, is preferably 2.0 or less, more preferably 1.0 or less, and even more preferably 0.75 or less.

[0045] (Salicylic Acid Type Compound (C3)) The grease composition of one embodiment of the present invention contains, as component (C), a salicylic acid type compound (C3) represented by the following general formula (c-3).

[0046] In the above general formula (c-3), R ５ represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms. The alkyl group may be linear or branched. ５ The number of carbon atoms in the alkyl group that can be selected as is preferably 1 to 6, more preferably 1 to 4, and even more preferably 1. Specific examples of alkyl groups having 1 to 8 carbon atoms are as described above.

[0047] In one embodiment of the present invention, specific examples of the salicylic acid type compound (C3) represented by the above general formula (c-3) include salicylic acid, methyl salicylate, ethyl salicylate, pentyl salicylate, butyl salicylate, isobutyl salicylate, pentyl salicylate, hexyl salicylate, heptyl salicylate, and octyl salicylate.

[0048] In the grease composition of one embodiment of the present invention, the content of the salicylic acid type compound (C3) is preferably 0.1 mass% or more, 0.3 mass% or more, 0.5 mass% or more, 0.7 mass% or more, or 1.0 mass% or more, based on the total amount (100 mass%) of the grease composition, from the viewpoint of improving the putrefaction resistance of the water-soluble cutting oil. Furthermore, the content of the salicylic acid type compound (C3) is preferably 5.0 mass% or less, 4.0 mass% or less, 3.0 mass% or less, 2.5 mass% or less, 2.0 mass% or less, or 1.5 mass% or less, based on the total amount (100 mass%) of the grease composition, from the viewpoint of maintaining good lubricating performance of the grease composition.

[0049] In the grease composition of one embodiment of the present invention, the content ratio [(C3) / (D)] of the salicylic acid type compound (C3) to the imide compound (D) described below is, in terms of mass ratio, preferably 0.1 or more, more preferably 0.3 or more, and even more preferably 0.5 or more, from the viewpoint of achieving a good balance between improving the putrefaction resistance of the water-soluble cutting oil and inhibiting hardening of the grease composition; and from the same viewpoint as above, is preferably 2.0 or less, more preferably 1.5 or less, and even more preferably 1.0 or less.

[0050] (Alicyclic Monoamine Compound (C4)) The grease composition of one embodiment of the present invention contains an alicyclic monoamine compound (C4) as component (C). The alicyclic monoamine compound (C4) includes one or more compounds selected from the group consisting of primary monoamine compounds represented by the following general formula (i), secondary monoamine compounds represented by the following general formula (ii), and tertiary monoamine compounds represented by the following general formula (iii):

[0051] In the above general formulas (i) to (iii), R ｃ－４ each independently represents a cycloalkyl group having 3 to 8 carbon atoms. The cycloalkyl group preferably has 4 to 8 carbon atoms, more preferably 5 to 8 carbon atoms, and even more preferably 6 to 8 carbon atoms.

[0052] The grease composition of one embodiment of the present invention contains a secondary monoamine compound represented by the general formula (ii) above as the alicyclic monoamine compound (C4). Specific examples of the secondary monoamine compound include dicyclopropylamine, dicyclobutylamine, dicyclopentylamine, dicyclohexylamine, dicycloheptylamine, and dicyclooctylamine.

[0053] In the grease composition of one embodiment of the present invention, the content of the alicyclic monoamine compound (C4) is preferably 0.1 mass % or more, 0.3 mass % or more, 0.5 mass % or more, 0.7 mass % or more, or 1.0 mass % or more, based on the total amount (100 mass %) of the grease composition, from the viewpoint of improving the putrefaction resistance of the water-soluble cutting oil. Furthermore, the content of the alicyclic monoamine compound (C4) is preferably 5.0 mass % or less, 4.0 mass % or less, 3.0 mass % or less, 2.5 mass % or less, 2.0 mass % or less, or 1.5 mass % or less, based on the total amount (100 mass %) of the grease composition, from the viewpoint of maintaining good lubricating performance of the grease composition.

[0054] In the grease composition of one embodiment of the present invention, the content ratio [(C4) / (D)] of the alicyclic monoamine compound (C4) to the imide compound (D) described below, expressed as a mass ratio, is preferably 0.1 or more, more preferably 0.3 or more, and even more preferably 0.5 or more, from the viewpoint of achieving a good balance between improving the putrefaction resistance of the water-soluble cutting oil and inhibiting hardening of the grease composition; and from the same viewpoint as above, is preferably 2.0 or less, more preferably 1.5 or less, and even more preferably 1.0 or less.

[0055] In the grease composition of one embodiment of the present invention, the content of the anticorrosive agent (C) is preferably 0.01 mass% or more, 0.05 mass% or more, 0.1 mass% or more, 0.3 mass% or more, 0.5 mass% or more, or 1.0 mass% or more based on the total amount (100 mass%) of the grease composition from the viewpoint of improving the anticorrosion properties of the water-soluble cutting oil. Furthermore, the content of the anticorrosive agent (C) is preferably 5.0 mass% or less, 4.0 mass% or less, 3.0 mass% or less, 2.5 mass% or less, 2.0 mass% or less, or 1.5 mass% or less based on the total amount (100 mass%) of the grease composition from the viewpoint of maintaining good lubrication performance of the grease composition.

[0056] <Component (D): Imide Compound> The grease composition of the present invention contains an imide compound (D). As described above, according to the present invention, by incorporating an antiseptic (C) into the grease composition, deterioration of the quality of the water-soluble cutting oil can be suppressed. However, it was found that incorporating an antiseptic (C) into the grease composition causes a secondary problem of hardening of the grease composition. Therefore, the present inventors conducted further studies and found that hardening of the grease composition can be suppressed by further incorporating, as component (D), one or more imide compounds (D) selected from the group consisting of bisimide compounds (D1) represented by the following general formula (d-1) and monoimide compounds (D2) represented by the following general formula (d-2).

[0057]

[0058] In the above general formulas (d-1) and (d-2), R ８ , R ９ and R １０ are each independently a polybutenyl group or a polyisobutenyl group, and the number average molecular weight (Mn) thereof is 900 to 2,500.

[0059] In the above general formulas (d-1) and (d-2), each A is independently an alkylene group having 2 to 5 carbon atoms. The number of carbon atoms of the alkylene group that can be selected as A is preferably 2 to 4. Examples of the alkylene group having 2 to 5 carbon atoms include various propylene groups such as 1,1-ethylene group, 1,2-ethylene group, 1,3-propylene, 1,2-propylene, and 2,2-propylene, as well as butylene and pentylene groups. The above groups also include structural isomers.

[0060] In the above general formulae (d-1) and (d-2), m is an integer of 2 to 6, preferably 2 to 5, and more preferably 2 to 4.

[0061] Furthermore, the imide compound (D) represented by the general formulas (d-1) and (d-2) above may be a modified succinimide reacted with one or more selected from a boron compound, an alcohol, an aldehyde, a ketone, an alkylphenol, a cyclic carbonate, an epoxy compound, and an organic acid, or may be an unmodified succinimide. In one embodiment of the present invention, the imide compound (D) includes an unmodified succinimide. In another embodiment of the present invention, the imide compound (D) includes a non-boron-modified succinimide.

[0062] In addition, in the grease composition of one embodiment of the present invention, the content of boron atoms derived from the imide compound (D) is less than 2 ppm by mass, less than 1 ppm by mass, less than 0.1 ppm by mass, less than 0.05 ppm by mass, or less than 0.01 ppm by mass, based on the total amount of the grease composition, and is preferably 0 ppm by mass.

[0063] In the grease composition of one embodiment of the present invention, the content of the imide compound (D) is preferably 0.01 mass% or more, 0.05 mass% or more, 0.1 mass% or more, 0.3 mass% or more, 0.5 mass% or more, or 1.0 mass% or more, based on the total amount (100 mass%) of the grease composition, from the viewpoint of suppressing hardening of the grease composition. Furthermore, the content of the imide compound (D) is preferably 5.0 mass% or less, 4.0 mass% or less, 3.0 mass% or less, 2.5 mass% or less, 2.0 mass% or less, or 1.5 mass% or less, based on the total amount (100 mass%) of the grease composition, from the viewpoint of maintaining good lubricating performance of the grease composition.

[0064] In the grease composition of one embodiment of the present invention, the content ratio of the anticorrosive agent (C) to the imide compound (D) [(C) / (D)] is, in mass ratio, preferably 0.1 or more, more preferably 0.3 or more, and even more preferably 0.5 or more, from the viewpoint of achieving a good balance between improving the putrefaction resistance of the water-soluble cutting oil and inhibiting hardening of the grease composition, and from the same viewpoint as above, is preferably 5.0 or less, more preferably 3.0 or less, and even more preferably 1.5 or less. Furthermore, the grease composition of one embodiment of the present invention does not include one in which the above ratio is 1.0.

[0065] <General-Purpose Additives> The grease composition of one embodiment of the present invention may contain general-purpose additives that are typically contained in grease compositions, or may not contain such general-purpose additives, as long as the effects of the present invention are not impaired. Examples of general-purpose additives include extreme pressure agents, antiwear agents, rust inhibitors, antioxidants, solid lubricants, thickeners, corrosion inhibitors, metal deactivators, and oiliness agents. These general-purpose additives can be used alone or in combination. Furthermore, the grease composition of one embodiment of the present invention may use a package additive containing a combination of these general-purpose additives.

[0066] Examples of extreme pressure agents include sulfur compounds such as sulfurized fats and oils, sulfurized olefins, polysulfides, thiophosphates, thioterpenes, and dialkylthiodipropionates; phosphate esters such as tricresyl phosphate; phosphite esters such as triphenyl phosphite; and polycarboxylates.

[0067] Examples of anti-wear agents include sulfur compounds such as sulfurized olefins, dialkyl polysulfides, diaryl alkyl polysulfides, and diaryl polysulfides; phosphorus compounds such as phosphate esters, thiophosphate esters, phosphites, alkyl hydrogen phosphites, phosphate ester amine salts, and phosphites ester amine salts; and ashless anti-wear agents such as amine compounds, fatty acid esters, fatty acid amides, fatty acids, aliphatic alcohols, aliphatic ethers, urea compounds, hydrazide compounds, and polycarboxylates.

[0068] Examples of the rust inhibitor include carboxylic acid-based rust inhibitors such as alkenyl succinic acid polyhydric alcohol esters, zinc stearate, thiadiazole and its derivatives, and benzotriazole and its derivatives.

[0069] Examples of the antioxidant include amine-based antioxidants such as alkylated diphenylamine, phenyl-α-naphthylamine, and alkylated-α-naphthylamine; and phenol-based antioxidants such as 2,6-di-t-butyl-4-methylphenol and 4,4′-methylenebis(2,6-di-t-butylphenol).

[0070] Examples of solid lubricants include PTFE, graphite, metal oxides, boron nitride, melamine cyanurate (MCA), and molybdenum disulfide.

[0071] Examples of thickeners include polymethacrylate (PMA), olefin copolymer (OCP), polyalkylstyrene (PAS), and styrene-diene copolymer (SCP).

[0072] Examples of the corrosion inhibitor include benzotriazole compounds and thiazole compounds.

[0073] Examples of the metal deactivator include benzotriazole compounds.

[0074] Examples of oily agents include higher fatty acids, alcohols, esters, and oils and fats.

[0075] The amount of each of these general-purpose additives to be added is set appropriately depending on the type of additive, but each is independently usually 0 to 10 mass %, preferably 0 to 7 mass %, more preferably 0 to 5 mass %, and even more preferably 0 to 2 mass %, based on the total amount (100 mass %) of the grease composition.

[0076] In one embodiment of the present invention, from the viewpoint of preparing a lubricating oil composition that can improve the putrefaction resistance of a water-soluble cutting oil, the content of the molybdenum compound having a dithiocarbamate structure (—N—C(═S)—S—) in the molecule is less than 0.01 mass %, less than 0.005 mass %, less than 0.001 mass %, or less than 0.0001 mass %, and preferably 0 mass %, based on the total amount (100 mass %) of the grease composition.

[0077] Furthermore, from the viewpoint of preparing a lubricating oil composition that can improve the putrefaction resistance of a water-soluble cutting oil, the content of the molybdenum compound having a dithiocarbamate structure (—N—C(═S)—S—) in the molecule is less than 2 ppm by mass, less than 1 ppm by mass, less than 0.1 ppm by mass, less than 0.05 ppm by mass, less than 0.01 ppm by mass, and preferably 0 ppm by mass, based on the total amount of the grease composition, in terms of molybdenum atoms.

[0078] In one embodiment of the present invention, from the viewpoint of preparing a lubricating oil composition that can improve the putrefaction resistance of a water-soluble cutting oil, the content of the molybdenum compound having a dithiophosphate structure (-P(=S)-S-) in the molecule is less than 0.01 mass %, less than 0.005 mass %, less than 0.001 mass %, or less than 0.0001 mass %, and preferably 0 mass %, based on the total amount (100 mass %) of the grease composition.

[0079] Furthermore, from the viewpoint of preparing a lubricating oil composition that can improve the putrefaction resistance of a water-soluble cutting oil, the content of the molybdenum compound having a dithiophosphate structure (-P(=S)-S-) in the molecule, converted into molybdenum atoms, is less than 2 ppm by mass, less than 1 ppm by mass, less than 0.1 ppm by mass, less than 0.05 ppm by mass, or less than 0.01 ppm by mass, and preferably 0 ppm by mass, based on the total amount of the grease composition.

[0080] [Method for Producing Grease Composition] The method for producing the grease composition of one embodiment of the present invention is not particularly limited and can be produced according to known methods, but examples include a production method having the following steps (1) and (2). Step (1): A step of blending raw materials for a thickener (B) with a base oil (A) to synthesize the thickener (B) and obtain a grease base material. Step (2): A step of blending an antiseptic (C) and an imide compound (D) with the grease base material to obtain a grease composition. Note that general-purpose additives other than components (C) and (D) may be added when preparing the grease base material in step (1), or may be added in step (2).

[0081] [Properties of Grease Composition] The consistency of the grease composition of the present invention is a value based on the "spreading consistency" measured by the method described in the Examples below. In one embodiment of the present invention, the initial consistency of the grease composition is preferably 300 or more, more preferably 350 or more, even more preferably 380 or more, and even more preferably 410 or more. There is no particular upper limit, but it may be, for example, 500. In one embodiment of the present invention, the consistency of the grease composition after storage for 14 weeks at 30°C and 98% humidity is preferably 300 or more, more preferably 325 or more, even more preferably 350 or more, and even more preferably 375 or more. In one embodiment of the present invention, the change in consistency (%) from the initial consistency after storage for 14 weeks under the above conditions (hereinafter referred to as "consistency change") is preferably -20% or less, more preferably -18% or less, and even more preferably -15% or less. In this specification, the consistency change is calculated as follows. Percentage of change in consistency = (consistency after 14 weeks - initial consistency) / initial consistency x 100

[0082] [Uses of the Grease Composition] As described above, the grease composition of one embodiment of the present invention can suppress deterioration of the quality of water-soluble cutting oil even when mixed with the water-soluble cutting oil. Therefore, the present invention also provides the following embodiments. A grease composition used for lubricating a mechanical device to which a water-soluble cutting oil is applied. A method for suppressing spoilage of a water-soluble cutting oil, comprising using the grease composition of one embodiment of the present invention for lubricating a mechanical device.

[0083] In addition, the grease composition of one embodiment of the present invention can be used without limitation for the lubrication of various other mechanical devices. In particular, because the grease composition of one embodiment of the present invention has the above-mentioned properties, it can be suitably used for the lubrication of mechanical devices that are wet or prone to wetness. Examples of such mechanical devices include machine tools equipped with various mechanical components, such as bearings and gears. More specific examples include various bearings such as plain bearings, rolling bearings, oil-impregnated bearings, and fluid dynamic bearings, gears, internal combustion engines, brakes, torque transmission device parts, fluid couplings, compression device parts, chains, hydraulic device parts, vacuum pump device parts, watch parts, hard disk drive parts, refrigeration machine parts, cutting machine parts, rolling mill parts, drawing and drawing machine parts, rolling machine parts, forging machine parts, heat treatment machine parts, heat transfer medium parts, cleaning machine parts, shock absorber machine parts, sealing device parts, construction machinery parts, agricultural machinery parts, ball screws, sliding screws, linear guides, etc.

[0084] Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples in any way.

[0085] [Screening test of anti-corrosion agents] Grease compositions were prepared by adding various components to a grease containing the following base oil (mineral oil) and urea-based thickener according to the formulations shown in Table 1. Thereafter, a corrosion resistance test was carried out by the following method.

[0086] <Component (A): Base oil> Mineral oil (40°C kinematic viscosity: 170.9mm ２ / s, viscosity index: 105) <Component (B): Thickener> Urea-based thickener (1.96% by mass in the base grease) <Candidate component for anti-corrosion agent> Zinc diamyldithiocarbamate (ZnDTC) ・Piroctone olamine Mixtures of piroctone olamine and 2-phenoxyethanol (1) and (2) In Table 1, "Mixture of Piroctone Olamine and 2-phenoxyethanol (1)" is a mixture of piroctone olamine and 2-phenoxyethanol at a ratio of 5:95, and "Mixture of Piroctone Olamine and 2-phenoxyethanol (2)" is a mixture of piroctone olamine and 2-phenoxyethanol at a ratio of 10:90. Tetrabutyl thiuram disulfide (Butyl Tuads) Salicylic acid ・Dicyclohexylamine ・tert-Alkyl (C=16-22) amine ・2,2'-(cyclohexylimino)bisethanol O-(2-aminopropyl)-O'-(2-methoxyethyl) polypropylene glycol Poly(propylene glycol) diamine ・2-phenylethyl alcohol ・2-phenoxyethanol ・Methylene bis(dibutyldithiocarbamate) <Other additives> ・Corrosion inhibitor (thiadiazole) ・Extreme pressure agent, anti-wear agent (phosphate ester, polycarboxylate) ・Oil agent (castor oil)

[0087] (Septic Resistance Test) 1 g of the prepared grease composition, 3 g of cutting chips (FC250), and 3 g of Cast Iron Chips (as defined in ASTM D4627) were added to 100 mL of 30-fold diluted water-soluble cutting oil. Then, 3 g of Cast Iron Chips (as defined in ASTM D4627), 1 mL of Putrefactive Solution A shown below, and 0.2 mL of Putrefactive Solution B were added to an Erlenmeyer flask, and shaking culture was started under conditions of 30 ° C. and 150 rpm. During the culture period, Putrefactive Solution A (1 mL) and Putrefactive Solution B (0.2 mL) were added every 7 days. Then, just before the addition of Putrefactive Solution A and Putrefactive Solution B every 7 days, the viable cell count in the liquid in the Erlenmeyer flask was measured, and the viable cell count was 1.0 × 10 ７The lifespan of the water-soluble cutting fluid was determined when the cell count reached 100 cells / mL. (Details of Putrefactive Solutions A and B) Putrefactive Solution A: Putrefactive emulsion-type water-soluble cutting fluid was added with Merck's "Tryptic Soy Broth 105459" and cultured with shaking for 24 hours to activate the fluid. Putrefactive Solution B: Putrefactive emulsion-type water-soluble cutting fluid was added to a medium containing Sigma-Aldrich's "Potato Dextrose Broth P6685" with tartaric acid added to adjust the pH to 3.5, and cultured with shaking for 48 hours to activate the fluid. The shake culture conditions for preparing Putrefactive Solutions A and B were 30°C, 150 rpm, and an environment with the addition of 3 g of Cast Iron Chips as specified in ASTM D4627. The evaluation was based on the lifespan (4 weeks) of the water-soluble cutting oil when cultured under the same conditions as above without adding the grease composition, and was rated on a three-point scale of A to C based on the following. The results are shown in Table 1. A: Longer than the standard (4 weeks) B: Equivalent to the standard (4 weeks) C: Shorter than the standard (4 weeks)

[0088]

[0089] Examples 1-2, Comparative Examples 1-5 Grease compositions were prepared by adding various components to the grease used in the above [Screening Test for Anticorrosive Agents] according to the formulations shown in Table 2 below. A decay resistance test was then conducted in the same manner as in the above [Screening Test for Anticorrosive Agents]. A consistency change measurement test was also conducted in the following manner. The following components (A), (B), (C), and (C)' were the same as those used in the above [Screening Test for Anticorrosive Agents].

[0090] <Component (A): Base oil> - Mineral oil <Component (B): Thickener> - Urea-based thickener <Component (C): Anti-corrosion agent> - Zinc diamyldithiocarbamate, piroctone olamine <Component (C)': Ashless antioxidant> - Methylene bis(dibutyldithiocarbamate) <Component (D): Imide compound> - Succinimide (non-boron-modified) <Other additives> - Corrosion inhibitor (thiadiazole) - Extreme pressure agent, anti-wear agent (phosphate ester, polycarboxylate) - Oiliness agent (castor oil)

[0091] (Consistency Change Measurement Test) The spreading consistency was measured using the following method. That is, an arbitrary amount of grease composition was applied to a metal plate at room temperature, and then an acrylic plate with a 500 g weight attached thereon was placed on top of the metal plate. The acrylic plate was then dropped to sandwich the grease composition and compressed for 5 seconds, and the spreading (diameter) of the grease composition was measured. Thereafter, a calibration curve was created using three or more greases with known consistency, and the consistency of the grease composition was calculated. The initial consistency and the consistency after 14 weeks of storage at 30°C and 98% humidity were measured, and the consistency change rate (%) was calculated based on these. The evaluation was based on the consistency change rate (-18%) of the grease composition of Comparative Example 1, which did not contain components (C) and (D), and was evaluated on a three-level scale (A to C) based on the following criteria. The results are shown in Table 2. A: The rate of change is smaller than the standard (-18%). B: The rate of change is the same as the standard (-18%). C: The rate of change is larger than the standard (-18%).

[0092] (Overall Evaluation) A sample that was evaluated as C in either the decay resistance test or the consistency change measurement test was determined as "failed," and the rest were determined as "passed."

[0093]

[0094] It was found from Table 1 that a grease composition containing a specific anticorrosive (C) can inhibit the putrefaction of a water-soluble cutting oil in a putrefaction resistance test. Also, it was found from Table 2 that a grease composition containing a specific imide compound (D) in addition to the specific anticorrosive (C) can not only inhibit the putrefaction of a water-soluble cutting oil in a putrefaction resistance test, but also has a small rate of change in consistency and an appropriate hardness.

Claims

1. A grease composition containing a base oil (A), a thickener (B), a corrosion inhibitor (C), and an imide compound (D).

2. The grease composition according to claim 1, wherein the anti-corrosion agent (C) comprises one or more compounds selected from the group consisting of dithiocarbamate compounds (C1) represented by the following general formula (c-1), 1-hydroxy-2-pyridone compounds (C2) represented by the following general formula (c-2), salicylic acid compounds (C3) represented by the following general formula (c-3), and alicyclic monoamine compounds (C4). (In the above general formula (1), M represents a single bond or a metal atom selected from the group consisting of sodium (Na), potassium (K), bismuth (Bi), copper (Cu), iron (Fe), nickel (Ni), selenium (Se), zinc (Zn), cadmium (Cd), calcium (Ca), tellurium (Te), and zirconium (Zr), and R １ and R ２ each independently represents an alkyl group having 1 to 20 carbon atoms, and a represents the valence of the metal atom when M is a metal atom, and is 2 when M is a single bond. (In the above general formula (2), R ３ represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and R ４ represents an alkyl group having 1 to 20 carbon atoms, and X ＋ represents an organic base, an alkali metal ion, an ammonium ion, or a divalent to tetravalent cation. (In the above general formula (3), R ５ represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms.

3. The grease composition according to claim 1 or 2, wherein the imide compound (D) comprises at least one compound selected from the group consisting of a bisimide compound (D1) represented by the following general formula (4) and a monoimide compound (D2) represented by the following general formula (5): (In the above general formulas (4) and (5), R ８ , R ９ and R １０ are each independently a polybutenyl group or a polyisobutenyl group, each A is independently an alkylene group having 2 to 5 carbon atoms, and m is an integer of 2 to 6.

4. A grease composition according to any one of claims 1 to 3, wherein the content of the anticorrosive agent (C) is 0.01 to 5.0 mass% based on the total amount of the grease composition.

5. A grease composition according to any one of claims 1 to 4, wherein the content of the imide compound (D) is 0.01 to 5.0 mass% based on the total amount of the grease composition.

6. A grease composition according to any one of claims 1 to 5, wherein the content ratio of the anti-corrosion agent (C) to the imide compound (D) [(C) / (D)] is 0.1 to 5.0 by mass.

7. A grease composition according to any one of claims 1 to 6, wherein the base oil (A) comprises a mineral oil.

8. A grease composition according to any one of claims 1 to 7, wherein the thickener (B) comprises a urea-based thickener.

9. The grease composition according to any one of claims 1 to 8, which is used to lubricate mechanical devices to which water-soluble cutting oil is applied.

10. A grease composition comprising a grease containing a base oil (A) and a thickener (B), and further containing an anticorrosive agent (C) and an imide compound (D).

11. A method for inhibiting decay of water-soluble cutting oil, comprising using the grease composition according to any one of claims 1 to 8 for lubricating mechanical equipment.

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