Grease composition

Abstract

Provided is a grease composition containing a base oil (A), a urea-based thickener (B), and a metal salt of a fatty acid (C). The urea-based thickener (B) contains one or more selected from diurea compounds represented by general formula (b1): R1-NHCONH-R3-NHCONH-R2 [in the general formula (b1), R1 and R2 each independently represent a monovalent aliphatic hydrocarbon group having 6 to 10 carbon atoms; R1 and R2 may be the same or different from each other; R3 represents a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms]. The content of the metal salt of a fatty acid (C) is 0.3 mass% or more based on the total amount of the grease composition, and the grease composition exhibits excellent shear stability even under conditions where there is water intrusion.

Description

Grease composition

[0001] This invention relates to a grease composition.

[0002] Grease compositions are easier to seal than lubricating oils, and allow for miniaturization and weight reduction of the machinery to which they are applied. For this reason, they have long been widely used for lubricating various sliding parts in automobiles, electrical equipment, industrial machinery, and other industrial equipment. Hub bearings (hub unit bearings) mounted on the wheels of automobiles and other vehicles are components that support the wheels and allow them to rotate smoothly. Since automobile hub unit bearings are components that rotate continuously, fluid lubricating oil compositions cannot be used, so semi-solid grease compositions are used as lubricants. Furthermore, hub unit bearings are required to maintain stable lubrication even in environments where water is present, so that they can continue to function even if rainwater enters them.

[0003] For example, Patent Document 1 discloses a grease composition that exhibits excellent adhesion to resin sliding surfaces and excellent lubricity, even in environments where it is likely to come into contact with water.

[0004] Japanese Patent Publication No. 2020-15876

[0005] However, the technology described in Patent Document 1 does not adequately consider shear stability in environments where water is present.

[0006] Therefore, the object of the present invention is to provide a grease composition that exhibits excellent shear stability even in environments where water is present.

[0007] The present invention provides the following [1] to [2]. [1] A base oil (A), a urea-based thickener (B), and a fatty acid metal salt (C), wherein the urea-based thickener (B) comprises one or more diurea compounds selected from those represented by the following general formula (b1), R １ -NHCONH-R ３ -NHCONH-R ２ (b1) [In the above general formula (b1), R １ and R ２ Each of these independently represents a monovalent chain hydrocarbon group having 6 to 10 carbon atoms.１ and R ２ may be the same or different from each other. R ３ represents a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms.] The grease composition, wherein a content of the fatty acid metal salt (C) is 0.3% by mass or more based on a total amount of the grease composition. [2] A method for producing a grease composition, comprising a step of blending a base oil (A), a urea-based thickener (B), and a fatty acid metal salt (C), wherein the urea-based thickener (B) comprises one or more selected from diurea compounds represented by the following general formula (b1), R １ -NHCONH-R ３ -NHCONH-R ２     (b1) [In the general formula (b1), R １ and R ２ each independently represent a monovalent chain hydrocarbon group having 6 to 10 carbon atoms. R １ and R ２ may be the same or different from each other. R ３ represents a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms.] The method for producing a grease composition, wherein a blending amount of the fatty acid metal salt (C) is 0.3% by mass or more based on a total amount of the grease composition.

[0008] According to the present invention, it is possible to provide a grease composition excellent in shear stability even under an environment where water is mixed therein.

[0009] The upper limit values and lower limit values of the numerical ranges described in the present specification can be combined arbitrarily. For example, when "A to B" and "C to D" are described as numerical ranges, the numerical ranges of "A to D" and "C to B" are also included in the scope of the present invention. In addition, unless otherwise specified, the numerical range "lower limit value to upper limit value" described in the present specification means not less than the lower limit value and not more than the upper limit value.

[0010] [Aspect of Grease Composition] The grease composition of the present embodiment is a grease composition containing a base oil (A), a urea-based thickener (B), and a fatty acid metal salt (C), wherein the urea-based thickener (B) comprises one or more selected from diurea compounds represented by the following general formula (b1), R １-NHCONH-R ３ -NHCONH-R ２ (b1) [In the above general formula (b1), R １ and R ２ Each of these independently represents a monovalent chain hydrocarbon group having 6 to 10 carbon atoms. １ and R ２ They may be the same or they may be different from one another. ３ This represents a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms. The grease composition is such that the content of the fatty acid metal salt (C) is 0.3% by mass or more on a basis of the total amount of the grease composition.

[0011] The inventors diligently conducted research to solve the above problems. As a result, they discovered that by containing a specific urea-based thickener and a specific amount of fatty acid metal salt in the grease composition, it repels water and makes it difficult for water to penetrate the grease composition, thus providing excellent shear stability even in environments where water is present, and thus completed the present invention.

[0012] In the following explanation, "base oil (A)", "urea-based thickener (B)", and "fatty acid metal salt (C)" will also be referred to as "component (A)", "component (B)", and "component (C)", respectively.

[0013] In the grease composition of this embodiment, the total content of component (A), component (B), and component (C) is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more, based on the total amount (100% by mass) of the grease composition. Also, it is usually 100% by mass or less, preferably less than 100% by mass, more preferably 99% by mass or less, and even more preferably 98% by mass or less. The grease composition of this embodiment may contain other components other than component (A), component (B), and component (C) as long as they do not impair the effects of the present invention.

[0014] The components included in the grease composition of this embodiment will be described in detail below.

[0015] <Base oil (A)> The grease composition of this embodiment contains base oil (A).

[0016] The base oil (A) preferably contains poly-α-olefin (hereinafter also referred to as "PAO") (A1). By including PAO (A1) in the base oil (A), the evaporability of the mixed base oil can be reduced. Examples of PAO (A1) include polybutene, polyisobutylene, 1-decene oligomer, and ethylene-propylene copolymer, as well as their hydrogenated products. PAO (A1) may be used alone or in combination of two or more types.

[0017] PAO(A1) preferably includes one or more selected from the group consisting of low viscosity PAO(A1-1) and high viscosity PAO(A1-2). These may be used individually or in combination of two or more.

[0018] In the grease composition of this embodiment, the kinematic viscosity of PAO(A1) at 40°C is preferably 10 mm². ２ / s or more 700mm ２ / s or less, more preferably 20 mm ２ / s or more 600mm ２ / s or less, more preferably 30 mm ２ / s or more 500mm ２ It is less than or equal to / s. In the grease composition of this embodiment, the viscosity index of PAO(A1) is preferably 100 or more, more preferably 110 or more, and even more preferably 120 or more.

[0019] In the grease composition of this embodiment, the content of PAO(A1) in the base oil (A) is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more, based on the total amount of base oil (A), from the viewpoint of reducing the evaporability of the mixed base oil.

[0020] <<Low Viscosity PAO (A1-1)>> As for the low viscosity PAO (A1-1), any PAO with a kinematic viscosity at 40°C within a predetermined range can be used without particular limitations. In the grease composition of this embodiment, the kinematic viscosity at 40°C of the low viscosity PAO (A1-1) is preferably 10 mm². ２ / s or more 70mm ２ / s or less, more preferably 20 mm ２ / s or more 60mm ２ / s or less, more preferably 30 mm ２ / s or more 50mm ２ / s or less, more preferably 40 mm ２ / s or more 48mm ２ It is less than or equal to / s. If the kinematic viscosity of the low viscosity PAO (A1-1) at 40°C is within the above range, the effects of the present invention can be more easily improved. In the grease composition of this embodiment, the viscosity index of the low viscosity PAO (A1-1) is preferably 110 or higher, more preferably 120 or higher, and even more preferably 130 or higher. If the viscosity index of the low viscosity PAO (A1-1) is 110 or higher, the effects of the present invention can be more easily improved.

[0021] <<High-viscosity PAO (A1-2)>> As for the high-viscosity PAO (A1-2), any PAO with a kinematic viscosity at 40°C within a predetermined range can be used without particular limitation. In the grease composition of this embodiment, the kinematic viscosity at 40°C of the high-viscosity PAO (A1-2) is preferably 200 mm. ２ / s or more 700mm ２ / s or less, more preferably 150 mm ２ / s or more 600mm ２ / s or less, more preferably 300 mm ２ / s or more 500mm ２ / s or less, more preferably 350 mm ２ / s or more 450mm ２ It is less than or equal to / s. If the kinematic viscosity of the high viscosity PAO (A1-2) at 40°C is within the above range, the effects of the present invention can be more easily improved. In the grease composition of this embodiment, the viscosity index of the high viscosity PAO (A1-2) is preferably 120 or higher, more preferably 130 or higher, and even more preferably 140 or higher. If the viscosity index of the high viscosity PAO (A1-2) is 120 or higher, the effects of the present invention can be more easily improved.

[0022] In the grease composition of this embodiment, the base oil (A) may contain a base oil other than PAO(A1). Examples of such other base oils include one or more selected from mineral oil and synthetic oils other than PAO(A1).

[0023] Examples of mineral oils include atmospheric residue obtained by atmospheric distillation of crude oil such as paraffinic crude oil, intermediate crude oil, and naphthenic crude oil; distillate obtained by vacuum distillation of the atmospheric residue; and mineral oil obtained by subjecting the distillate to one or more refining treatments such as solvent dewaxing, solvent extraction, hydrotrining, hydrocracking, advanced hydrocracking, solvent dewaxing, catalytic dewaxing, and hydroisomerization dewaxing.

[0024] Other synthetic oils besides PAO include, for example, normal paraffins, isoparaffins, aromatic oils, ether oils, ester oils, and synthetic oils obtained by isomerizing waxes produced by the Fischer-Tropsch process (GTL waxes). These may be used individually or in combination of two or more.

[0025] Examples of aromatic oils include alkylbenzenes such as monoalkylbenzene and dialkylbenzene; alkylnaphthalenes such as monoalkylnaphthalene, dialkylnaphthalene, and polyalkylnaphthalene; and so on.

[0026] Examples of ether-based oils include polyglycols such as polyethylene glycol, polypropylene glycol, polyethylene glycol monoether, and polypropylene glycol monoether; phenyl ether-based oils such as monoalkyltriphenyl ether, alkyldiphenyl ether, dialkyldiphenyl ether, pentaphenyl ether, tetraphenyl ether, monoalkyltetraphenyl ether, and dialkyltetraphenyl ether; and so on. Examples of ester-based oils include one or more selected from diester-based oils, aromatic ester-based oils, polyol-based ester-based oils, and complex ester-based oils. Examples of diester-based oils include dibutyl sebacate, dioctyl sebacate, di-2-ethylhexyl sebacate, dioctyl adipate, diisodecyl adipate, ditridecyl adipate, ditridecyl glutarate, and methylacetyl ricinolate. Examples of aromatic ester-based oils include trioctyl trimellitate, tridecyl trimellitate, and tetraoctyl pyromelitate. Examples of the polyol ester oils include trimethylolpropane caprylate, trimethylolpropane veralgonate, pentaerythritol-2-ethylhexanoate, and pentaerythritol veralgonate. Examples of the complex ester oils include oligoesters of polyhydric alcohols and mixed fatty acids of dibasic and monobasic acids. These may be used individually or in combination of two or more.

[0027] In the grease composition of this embodiment, the kinematic viscosity of the base oil (A) at 40°C is preferably 20 mm². ２ / s or more 80mm ２ / s or less, more preferably 30 mm ２ / s or more 70mm ２ / s or less, more preferably 40 mm ２ / s or more 65mm ２ / s or less, more preferably 50 mm ２ / s or more 65mm ２The viscosity index is less than or equal to / s. In the grease composition of this embodiment, the viscosity index of the base oil (A) is preferably 100 or higher, more preferably 110 or higher, and even more preferably 120 or higher. In this specification, the kinematic viscosity at 40°C, the kinematic viscosity at 100°C, and the viscosity index refer to values ​​measured or calculated in accordance with JIS K2283:2000.

[0028] In the grease composition of this embodiment, the base oil (A) content is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, based on the total amount (100% by mass) of the grease composition, and also preferably 95% by mass or less, more preferably 93% by mass or less, even more preferably 90% by mass or less, and even more preferably 88% by mass or less.

[0029] <Urea-based thickener (B)> The grease composition of this embodiment contains a urea-based thickener (B). Furthermore, the urea-based thickener (B) includes one or more diurea compounds selected from those represented by the following general formula (b1). １ -NHCONH-R ３ -NHCONH-R ２ (b1) [In the above general formula (b1), R １ and R ２ Each of these independently represents a monovalent chain hydrocarbon group having 6 to 10 carbon atoms. １ and R ２ They may be the same or they may be different from one another. ３ This represents a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms. The grease composition of this embodiment contains one or more diurea compounds selected from those represented by general formula (b1) as a urea-based thickener (B), which repels water and makes it difficult for water to penetrate into the grease composition, thus providing excellent shear stability even in environments where water is present.

[0030] From the viewpoint of further ensuring shear stability in environments where water is present, the content of the diurea compound represented by the general formula (b1) in the grease composition of this embodiment is preferably 50% to 100% by mass, more preferably 60% to 100% by mass, even more preferably 70% to 100% by mass, even more preferably 80% to 100% by mass, even more preferably 90% to 100% by mass, and even more preferably 95% to 100% by mass, based on the total amount (100% by mass) of the urea thickener (B).

[0031] R in the above general formula (b1) １ and R ２ The number of carbon atoms in the monovalent chain hydrocarbon group that can be selected is 6 to 10, preferably 6 to 8. １ and R ２ Examples of monovalent chain hydrocarbon groups that can be selected include saturated or unsaturated monovalent chain hydrocarbon groups, but saturated chain hydrocarbon groups are preferred.

[0032] Examples of monovalent saturated hydrocarbon groups include linear or branched alkyl groups having 6 to 10 carbon atoms, specifically hexyl, heptyl, octyl, nonyl, and decyl groups. The monovalent saturated hydrocarbon group may be linear or branched. Among these, the octyl group is preferred.

[0033] R in the above general formula (b1) ３ The number of carbon atoms in the divalent aromatic hydrocarbon group that can be selected is 6 to 18, preferably 6 to 15, and more preferably 6 to 13. ３ Examples of divalent aromatic hydrocarbon groups that can be selected include phenylene group, diphenylmethylene group, diphenylethylene group, diphenylpropylene group, methylphenylene group, dimethylphenylene group, and ethylphenylene group. Among these, phenylene group, diphenylmethylene group, diphenylethylene group, or diphenylpropylene group are preferred, and diphenylmethylene group is more preferred.

[0034] In the grease composition of this embodiment, the content of the urea-based thickener (B) is preferably 1.0 to 20.0% by mass, more preferably 3.0 to 19.0% by mass, even more preferably 5.0 to 18.0% by mass, even more preferably 7.0 to 16.0% by mass, and still more preferably 9.0% to 15.0% by mass, based on the total amount (100% by mass) of the grease composition, from the viewpoint of making the hardness of the grease within an appropriate range.

[0035] [Requirement (I)] From the viewpoint of further improving the effects of the present invention, it is preferable that the particles containing the urea-based thickener (B) in the grease composition of this embodiment satisfy the following requirement (I). Requirement (I): The arithmetic mean particle diameter on an area basis when the particles are measured by laser diffraction / scattering is 2.0 μm or less.

[0036] The above requirement (I) can also be considered a parameter indicating the state of aggregation of the urea-based thickener (B) in the grease composition. Here, the "particles containing the urea-based thickener (B)" to be measured by laser diffraction / scattering refers to particles formed by the aggregation of the urea-based thickener (B) contained in the grease composition. Although the grease composition may contain additives other than the urea-based thickener (B), the arithmetic mean particle size specified in the above requirement (I) can be obtained by measuring a grease composition prepared under the same conditions without the additive using laser diffraction / scattering. However, if the additive is liquid at room temperature (25°C) or dissolves in the base oil (A), the grease composition containing the additive may also be used as the measurement target.

[0037] Urea-based thickeners (B) are usually obtained by reacting an isocyanate compound with a monoamine, but because the reaction rate is very fast, the urea-based thickener (B) tends to aggregate, and large particles (micelle particles, so-called "clumps") are easily generated in excess. It is presumed that by refining the arithmetic mean particle size specified in requirement (I) above to 2.0 μm or less, the particles containing the urea-based thickener (B) become easier to penetrate into the lubricating area (friction surface) and are also more difficult to remove from the lubricating area, thereby improving the retention capacity of the grease composition in the lubricating area. From the above viewpoint, in the grease composition of this embodiment, the arithmetic mean particle size defined in requirement (I) above is preferably 1.5 μm or less, more preferably 1.0 μm or less, even more preferably 0.9 μm or less, even more preferably 0.8 μm or less, even more preferably 0.7 μm or less, even more preferably 0.6 μm or less, even more preferably 0.5 μm or less, and even more preferably 0.4 μm or less. Also, it is usually 0.01 μm or more.

[0038] [Requirement (II)] From the viewpoint of further improving the effects of the present invention, it is preferable that the particles containing the urea-based thickener (B) in the grease composition of this embodiment further satisfy the following requirement (II). Requirement (II): The specific surface area of ​​the particles when measured by laser diffraction / scattering method is 0.5 × 10 ５ cm ２ / cm ３ That's all.

[0039] The specific surface area specified in requirement (II) above is a secondary indicator of the state of particle refinement of the urea-based thickener (B) particles in the grease composition and the presence of large particles (clumps). That is, satisfying requirement (I) above and further satisfying requirement (II) above indicates that the state of particle refinement of the urea-based thickener (B) particles in the grease composition is better and the presence of large particles (clumps) is more suppressed. From the above viewpoint, the specific surface area specified in requirement (II) above is preferably 0.7 × 10⁻⁶. ５ cm ２ / cm ３ More preferably 0.8 × 10 ５cm ２ / cm ３ or more, more preferably 1.2×10 ５ cm ２ / cm ３ or more, even more preferably 1.5×10 ５ cm ２ / cm ３ or more, still more preferably 1.8×10 ５ cm ２ / cm ３ or more, particularly preferably 2.0×10 ５ cm ２ / cm ３ or more. The specific surface area is usually 1.0×10 ６ cm ２ / cm ３ or less.

[0040] The values defined by the above requirement (I), and further by the above requirement (II), can be adjusted mainly by the production conditions of the urea-based thickener (B).

[0041] [Method for Producing Urea-based Thickener (B)] The urea-based thickener (B) can generally be obtained by reacting an isocyanate compound with a monoamine. The reaction is preferably carried out by adding solution β, in which the monoamine is dissolved in the base oil (A), to heated solution α obtained by dissolving the isocyanate compound in the above-mentioned base oil (A). For example, when synthesizing the compound represented by the general formula (b1), as the isocyanate compound, R in the general formula (b1) ３ a diisocyanate having a group corresponding to the divalent aromatic hydrocarbon group represented by is used, and as the monoamine, R １ and R ２ By using an amine having a group corresponding to the monovalent hydrocarbon group represented by , the desired urea-based thickener (B) can be synthesized by the above method.

[0042] Furthermore, from the viewpoint of micronizing the urea-based thickener (B) in the grease composition so as to satisfy the above requirement (I), preferably requirement (II), it is preferable that the grease composition of this embodiment be manufactured by carrying out a grease formation reaction while applying a high shear rate to the urea-based thickener (B) or its precursor in the base oil (A). Alternatively, the grease formation reaction can be carried out by applying a predetermined high shear rate after the base oil (A) has been made into a mixed base oil. High-speed shearing can be carried out in a manufacturing apparatus or the like equipped with a high-speed rotating part inside the container. It is applied to the mixed liquid in the gap between the high-speed rotating part and the inner wall of the container. The gap between the high-speed rotating part and the inner wall of the container may be constant (uniform) in all parts, or it may be a non-uniform structure. Such a gap may be adjusted by changing the diameter of the high-speed rotating part in the direction of rotation axis, or by making the high-speed rotating part frustoconical and moving this high-speed rotating part up and down relative to the inner wall of the reaction vessel which has a taper. Furthermore, the larger gaps may be given an extrusion capability by creating a screw or spiral shape with continuous inclination. Note that when manufacturing using equipment arranged in the rotational direction, the larger gaps can be given an extrusion capability similar to a screw by inclining them with respect to the rotation axis.

[0043] From the viewpoint of applying uniform high-speed shear, the shearing time is preferably 0.1 seconds or longer, and more preferably 1 second or longer.

[0044] The temperature inside the manufacturing apparatus is preferably 40°C or higher, more preferably 50°C or higher, and even more preferably 60°C or higher, as this makes it less likely for isocyanates and amines, which are precursors of thickeners, to precipitate from the base oil, resulting in excellent dispersibility and reaction rate. Furthermore, the temperature inside the manufacturing apparatus is preferably 200°C or lower, more preferably 190°C or lower, and even more preferably 180°C or lower, from the viewpoint of preventing deterioration of the base oil and appropriately controlling the reaction rate.

[0045] To produce a grease containing a urea-based thickener (B), a grease base material containing the urea-based thickener (B) can be produced by respectively introducing solution α and solution β, which are grease raw materials, and rotating a rotor at a high speed. Even if a fatty acid metal salt (C) is blended into the obtained grease base material, the effect of the fatty acid metal salt (C) is less likely to be inhibited, and the urea-based thickener (B) in the grease composition can be micronized such that the above requirement (I) is preferably satisfied, and more preferably the above requirement (II) is satisfied.

[0046] As a high-speed rotation condition for the rotor, the shear rate applied to the grease raw material is preferably 10 ２ s －１ or more, more preferably 10 ３ s －１ or more, still more preferably 10 ４ s －１ or more. The higher the shear rate, the more improved the dispersion state of the urea-based thickener (B), and a more uniform grease composition can be obtained. Further, from the viewpoints of device safety, heat generation due to shearing and the like and heat removal, the shear rate is preferably 10 ７ s －１ or less. Such a shear rate can be imparted by introducing the mixed liquid into a production apparatus that generates shear through relative motion between opposing wall surfaces.

[0047] In the shearing when the rotor rotates at high speed, the ratio (Max / Min) of the maximum shear rate (Max) to the minimum shear rate (Min) is preferably 100 or less, more preferably 50 or less, and still more preferably 10 or less. When the shear rate applied to the mixed liquid is as uniform as possible, the urea-based thickener (B) and its precursor in the grease composition are easily micronized, resulting in a more uniform grease structure.

[0048] Here, the maximum shear rate (Max) is the highest shear rate applied to the mixture, and the minimum shear rate (Min) is the lowest shear rate applied to the mixture, as defined below: • Maximum shear rate (Max) = (Linear velocity of the surface of the high-speed rotating part at the point where the gap between the surface of the high-speed rotating part and the inner wall of the container is smallest / said gap) • Minimum shear rate (Min) = (Linear velocity of the surface of the high-speed rotating part at the point where the gap between the surface of the high-speed rotating part and the inner wall of the container is largest / said gap)

[0049] <Fatty acid metal salt (C)> The grease composition of this embodiment contains a fatty acid metal salt (C). By containing a fatty acid metal salt (C), the grease composition of this embodiment exhibits excellent shear stability even in environments where water is present.

[0050] The fatty acid metal salt (C) content is 0.3% by mass or more based on the total amount of the grease composition. A fatty acid metal salt (C) content of 0.3% by mass or more based on the total amount of the grease composition allows the fatty acid metal salt (C) to repel water, making it difficult for water to penetrate the grease composition. Therefore, a grease composition with excellent shear stability can be obtained even in environments where water is present. If the fatty acid metal salt (C) content is too high, the rust prevention properties may be insufficient. Therefore, the fatty acid metal salt (C) content is 0.3% by mass or more based on the total amount of the grease composition, and from the viewpoint of balancing shear stability and rust prevention in a humid environment, it is preferably 0.3% by mass or more and 10% by mass or less, more preferably 0.4% by mass or more and 8% by mass or less, even more preferably 0.4% by mass or more and 7% by mass or less, and even more preferably 0.5% by mass or more and 6% by mass or less.

[0051] The metal contained in the fatty acid metal salt (C) is not particularly limited, but it is preferably one or more metals selected from zinc (Zn), calcium (Ca), magnesium (Mg), and aluminum (Al). Examples of fatty acid metal salts (C) include fatty acid zinc salts, fatty acid calcium salts, fatty acid magnesium salts, and fatty acid aluminum salts. These may be one type or two or more types may be used in combination. Among these, fatty acid zinc salts are preferred.

[0052] The fatty acid constituting the fatty acid metal salt (C) may be a monobasic acid or a polybasic acid. Furthermore, the fatty acid constituting the fatty acid metal salt (C) may be a saturated fatty acid or an unsaturated fatty acid. Also, the fatty acid constituting the fatty acid metal salt (C) may be linear or branched. The number of carbon atoms in the fatty acid constituting the fatty acid metal salt (C) is preferably 8 to 30, more preferably 12 to 24, and even more preferably 14 to 20.

[0053] Examples of monobasic acids (saturated fatty acids) include octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, nonadecanoic acid, eicosanoic acid, henicosanoic acid, docosanoic acid, tricosanoic acid, tetracosanoic acid, pentacosanoic acid, hexacosanoic acid, heptacosanoic acid, octacosanoic acid, nonacosanoic acid, and triacontanoic acid. Examples of monobasic acids (unsaturated fatty acids) include octenic acid, nonenic acid, 10-hydroxy-2-decenoic acid, undecenoic acid, dodecenoic acid, tridecenoic acid, tetradecenoic acid, pentadecenoic acid, hexadecenoic acid, heptadecenoic acid, octadecenoic acid, nonadecenoic acid, eicosenoic acid, henicosenoic acid, docosenoic acid, tricosenoic acid, tetracosenoic acid, pentacosenoic acid, hexacosenoic acid, heptacosenoic acid, octacosenoic acid, nonacosenoic acid, and triaconthenic acid. Examples of polybasic acids (saturated fatty acids) include octanodioic acid, nonanedioic acid, decanedioic acid, undecanedioic acid, dodecanedioic acid, tridecanedioic acid, tetradecanedioic acid, pentadecanedioic acid, hexadecanedioic acid, heptadecanedioic acid, octadecanedioic acid, nonadecanedioic acid, eicosanedioic acid, henicosandioic acid, docosanedioic acid, tricosanedioic acid, tetracosanedioic acid, pentacosanedioic acid, hexacosanedioic acid, heptacosanedioic acid, octacosanedioic acid, nonacosanedioic acid, and triacontanedioic acid. Examples of polybasic acids (unsaturated fatty acids) include octenodioic acid, nonendioic acid, decendioic acid, undecendioic acid, dodecendioic acid, tridecendioic acid, tetradecendioic acid, pentadecendioic acid, hexadecenodioic acid, heptadecenodioic acid, octadecendioic acid, nonadecenodioic acid, eicosendioic acid, henicosendioic acid, docosendioic acid, tricosendioic acid, tetracosendioic acid, pentacosendioic acid, hexacosendioic acid, heptacosendioic acid, octacosendioic acid, nonacosendioic acid, and triacontenioic acid. Among these, octadecanoic acid (stearic acid) is preferred.

[0054] In the grease composition of this embodiment, the content of metal atoms derived from the fatty acid metal salt (C) is preferably 0.010% to 0.700% by mass, more preferably 0.020% to 0.650% by mass, and even more preferably 0.030% to 0.550% by mass, based on the total amount (100% by mass) of the grease composition, from the viewpoint of balancing shear stability and rust prevention in a humid environment. When the fatty acid metal salt (C) contains two or more metals, it is preferable that the total content be within the above range. In this specification, the content of metal atoms refers to the value measured in accordance with JPI-5S-38-03.

[0055] The content ratio [(B) / (C)] of the urea-based thickener (B) to the fatty acid metal salt (C) is preferably 1.0 to 40.0, more preferably 1.5 to 35.0, and even more preferably 2.0 to 30.0, in terms of mass ratio, from the viewpoint of balancing shear stability and rust prevention in a humid environment.

[0056] <Additive (D)> The grease composition of this embodiment may contain additive (D) other than components (B) and (C) that are commonly used in greases, as long as the effects of the present invention are not impaired. Examples of additive (D) include antioxidants, rust inhibitors, wear inhibitors, corrosion inhibitors, etc. Additive (D) may be used individually or in combination of two or more. The grease composition of this embodiment preferably contains one or more additives (D) selected from antioxidants, rust inhibitors, wear inhibitors, and corrosion inhibitors.

[0057] - Antioxidants - Examples of antioxidants include amine-based antioxidants and phenol-based antioxidants. Among these, amine-based antioxidants are preferred. Examples of amine-based antioxidants include diphenylamine compounds and naphthylamine compounds. Among these, diphenylamine compounds are preferred. Examples of diphenylamine compounds include monoalkyldiphenylamine compounds having one C1-C30 alkyl group, such as monooctyldiphenylamine and monononyldiphenylamine; dialkyldiphenylamine compounds having two C1-C30 alkyl groups, such as 4,4'-dibutyldiphenylamine, 4,4'-dipentyldiphenylamine, 4,4'-dihexyldiphenylamine, 4,4'-diheptyldiphenylamine, 4,4'-dioctyldiphenylamine, and 4,4'-dinonyldiphenylamine; polyalkyldiphenylamine compounds having three or more C1-C30 alkyl groups, such as tetrabutyldiphenylamine, tetrahexyldiphenylamine, tetraoctyldiphenylamine, and tetranonyldiphenylamine; and 4,4'-bis(α,α-dimethylbenzyl)diphenylamine. Among these, 4,4'-dioctyldiphenylamine is preferred. Examples of naphthylamine compounds include 1-naphthylamine, phenyl-1-naphthylamine, butylphenyl-1-naphthylamine, pentylphenyl-1-naphthylamine, hexylphenyl-1-naphthylamine, heptylphenyl-1-naphthylamine, octylphenyl-1-naphthylamine, nonylphenyl-1-naphthylamine, decylphenyl-1-naphthylamine, and dodecylphenyl-1-naphthylamine.Examples of phenolic antioxidants include 2,6-di-t-butyl-4-methylphenol, 2,6-di-t-butyl-4-ethylphenol, 2,4,6-tri-t-butylphenol, 2,6-di-t-butyl-4-hydroxymethylphenol, 2,6-di-t-butylphenol, 2,4-dimethyl-6-t-butylphenol, 2,6-di-t-butyl-4-(N,N-dimethylaminomethyl)phenol, 2,6-di-t-amyl-4-methylphenol, and n-octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propio Examples include monocyclic phenolic compounds such as nates, and polycyclic phenolic compounds such as 4,4'-methylenebis(2,6-di-t-butylphenol), 4,4'-isopropylidenebis(2,6-di-t-butylphenol), 2,2'-methylenebis(4-methyl-6-t-butylphenol), 4,4'-bis(2,6-di-t-butylphenol), 4,4'-bis(2-methyl-6-t-butylphenol), 2,2'-methylenebis(4-ethyl-6-t-butylphenol), and 4,4'-butylidenebis(3-methyl-6-t-butylphenol). These may be used individually or in combination of two or more.

[0058] - Rust Inhibitors - Examples of rust inhibitors include ester-based rust inhibitors, carboxylic acid-based rust inhibitors, zinc stearate, thiadiazole and its derivatives, benzotriazole and its derivatives, fatty acid soaps, alkyl sulfonates, fatty acid amines, oxidized paraffins, alkyl polyoxyethylene ethers, etc. Examples of ester-based rust inhibitors include glycerin monooleate, glycerin dioleate, glycerin trioleate, alkenyl succinate half-ester, alkenyl succinate polyhydric alcohol ester, etc. Examples of carboxylic acid-based rust inhibitors include octanoic acid, heptanoic acid, nonanoic acid, etc. Among these, carboxylic acid-based rust inhibitors are preferred, and octanoic acid is more preferred. These may be used individually or in combination of two or more.

[0059] - Wear-resistant agents - Examples of wear-resistant agents include zinc-containing compounds such as zinc dialkyldithiophosphate (ZnDTP), zinc dithiocarbamate (ZnDTC), and zinc phosphate; sulfur-containing compounds such as disulfides, sulfurized olefins, sulfurized oils and fats, sulfurized esters, thiocarbonates, thiocarbamates, and polysulfides; phosphorus-containing compounds such as phosphite esters, phosphate esters, phosphonic acid esters, and their amine salts or metal salts; and sulfur and phosphorus-containing wear-resistant agents such as thiophosphite esters, thiophosphate esters, thiophosphonic acid esters, and their amine salts or metal salts.

[0060] -Corrosion Inhibitors- Examples of corrosion inhibitors include benzotriazole compounds and thiazole compounds.

[0061] In the grease composition of this embodiment, the content of additive (D) is preferably 0.01% to 15% by mass, more preferably 0.05% to 13% by mass, even more preferably 0.10% to 12% by mass, and even more preferably 0.50% to 10% by mass, based on the total amount (100% by mass) of the grease composition.

[0062] [Physical Properties of the Grease Composition] <Divisibility> The divisibility (1 / 2) of the grease composition of this embodiment is preferably 175 to 385, more preferably 220 to 385, even more preferably 220 to 340, and even more preferably 265 to 295, from the viewpoint of ensuring that the grease composition maintains an appropriate hardness even in environments where water is present. In this specification, divisibility refers to the value measured at 25°C in accordance with JIS K2220:2013 (Clause 7).

[0063] <Shear Stability> The shear stability of the grease composition of this embodiment can be evaluated by the change in the mixed consistency in the roll stability test, which is measured and calculated by the method described in the examples below. The change in the mixed consistency in the roll stability test is preferably 50 or less, more preferably 40 or less, and even more preferably 30 or less. The change in the mixed consistency in the water-containing roll stability test is preferably 50 or less, more preferably 40 or less, and even more preferably 35 or less.

[0064] <Rust Prevention> The rust prevention properties of the grease composition of this embodiment can be evaluated by performing a rust prevention test according to the method described in the examples below. From the viewpoint of rust prevention, it is preferable that the grease composition of this embodiment does not cause corrosion when evaluated according to the method described in the examples below. In this specification, the rust prevention properties of the grease composition refer to the value evaluated under 1% saline solution conditions in accordance with the German standard DIN 51802:EMCOR rust prevention test.

[0065] [Method for producing the grease composition] The method for producing the grease composition of the present invention comprises the step of blending a base oil (A), a urea-based thickener (B), and a fatty acid metal salt (C), wherein the urea-based thickener (B) comprises one or more diurea compounds selected from those represented by the following general formula (b1), R １ -NHCONH-R ３ -NHCONH-R ２ (b1) [In the above general formula (b1), R １ and R ２ Each of these independently represents a monovalent chain hydrocarbon group having 6 to 10 carbon atoms. １ and R ２ They may be the same or they may be different from one another. ３ This represents a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms. The method for producing a grease composition is such that the amount of the fatty acid metal salt (C) blended is 0.3% by mass or more based on the total amount of the grease composition.

[0066] As an example of the above manufacturing method, the diurea compound represented by the above general formula (b1) can usually be obtained by reacting a diisocyanate with a monoamine. In this reaction, it is preferable to add a base oil in which diisocyanate is dissolved in PAO (A1) while heating and stirring the monoamine-containing base oil obtained by mixing a monoamine with the above PAO (A1) and heating and dissolving it. For example, when synthesizing the diurea compound represented by the above general formula (b1), the diisocyanate is R in the above general formula (b1). ３ A diisocyanate having a group corresponding to the divalent aromatic hydrocarbon group shown is used, and as the monoamine, R １ and R ２ A desired diurea compound can be synthesized by the above method using an amine having a group corresponding to the monovalent chain hydrocarbon group shown. During the above process, for example, before raising the temperature to a high temperature, a fatty acid metal salt (C) can be added. Alternatively, after the above process, a fatty acid metal salt (C) can be added to the base grease. Furthermore, if necessary, an additive (D) may be added after the above process. The preferred embodiments of the base oil (A), thickener (B), fatty acid metal salt (C), and additive (D) are as described above. The amounts and ratios of the base oil (A), thickener (B), fatty acid metal salt (C), and additive (D) are preferably amounts corresponding to the preferred contents of the base oil (A), thickener (B), fatty acid metal salt (C), and additive (D) as described above.

[0067] [Uses of the Grease Composition] The grease composition of the present invention can be suitably used even in environments where water is present. Fields of equipment in which the grease composition of the present invention can be suitably used include the railway, bicycle, automobile, office equipment, machine tool, wind turbine, construction, agricultural machinery, or industrial robot fields. Lubrication parts in automotive equipment in which the grease composition of the present invention can be suitably used include, for example, bearing parts in equipment such as radiator fan motors, fan couplings, alternators, idler pulleys, hub units, water pumps, power windows, wipers, electric power steering, drive motor flywheels, ball joints, wheel bearings, spline sections, and constant velocity joints; bearing parts, gear sections, and sliding parts in equipment such as door locks, door hinges, and clutch boosters; and more specifically, railway vehicles, main motors, hub units, electric power steering, drive motor flywheels, ball joints, wheel bearings, spline sections, constant velocity joints, clutch boosters, servo motors, blade bearings, or bearing parts of generators. The grease composition of this embodiment can be suitably used for lubricating hub bearings.

[0068] Examples of lubrication parts in equipment in the office equipment field where the grease composition of this embodiment can be suitably used include, for example, fixing rolls in equipment such as printers, bearings and gear parts in equipment such as polygon motors. Examples of lubrication parts in equipment in the machine tool field where the grease composition of the present invention can be suitably used include, for example, spindles, servo motors, and bearing parts in reduction gears of machine robots. Examples of lubrication parts in equipment in the wind turbine field where the grease composition of the present invention can be suitably used include, for example, blade bearings and bearing parts of generators. Examples of lubrication parts in equipment in the construction or agricultural machinery field where the grease composition of the present invention can be suitably used include, for example, ball joints, bearing parts such as spline sections, gear parts and sliding parts.

[0069] [One aspect of the present invention provided] According to one aspect of the present invention, the following [1] to [8] are provided. [1] A base oil (A), a urea-based thickener (B), and a fatty acid metal salt (C), wherein the urea-based thickener (B) comprises one or more diurea compounds selected from those represented by the following general formula (b1), R １ -NHCONH-R ３ -NHCONH-R ２ (b1) [In the above general formula (b1), R １ and R ２ Each of these independently represents a monovalent chain hydrocarbon group having 6 to 10 carbon atoms. １ and R ２ They may be the same or they may be different from one another. ３ [1] represents a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms. [2] A grease composition in which the content of the fatty acid metal salt (C) is 0.3% by mass or more on a basis of the total amount of the grease composition. [3] The grease composition according to [1], wherein the fatty acid contained in the fatty acid metal salt (C) is stearic acid. [4] The grease composition according to [1] or [2], wherein the metal contained in the fatty acid metal salt (C) is one or more selected from zinc (Zn), calcium (Ca), magnesium (Mg), and aluminum (Al). [5] The grease composition according to any one of [1] to [3], wherein the base oil (A) contains poly-α-olefin (PAO). [6] The grease composition according to any one of [1] to [4], wherein the miscible consistency at 25°C is 265 to 295. [7] The grease composition according to any one of [1] to [5], which is used in an environment where water is present. [7] A grease composition according to any one of [1] to [6] above, used for lubricating a hub bearing. [8] A grease composition comprising the step of blending a base oil (A), a urea-based thickener (B), and a fatty acid metal salt (C), wherein the urea-based thickener (B) comprises one or more diurea compounds selected from those represented by the following general formula (b1), R １ -NHCONH-R ３ -NHCONH-R ２ (b1) [In the above general formula (b1), R１ and R ２ Each of these independently represents a monovalent chain hydrocarbon group having 6 to 10 carbon atoms. １ and R ２ They may be the same or they may be different from one another. ３ This represents a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms. A method for producing a grease composition, wherein the amount of the fatty acid metal salt (C) blended is 0.3% by mass or more based on the total amount of the grease composition.

[0070] The present invention will be specifically described by the following embodiments. However, the present invention is not limited to the following embodiments.

[0071] [Method for measuring physical properties] The properties of each raw material used in each example and comparative example, as well as the properties of the lubricating oil compositions in each example and comparative example, were measured according to the following procedure.

[0072] (1) The kinematic viscosity at 40°C and viscosity index of the base oil (A) used in the preparation of the grease composition were measured in accordance with JIS K2283:2000.

[0073] (2) Mixing consistency (1 / 2) The mixing consistency of each grease composition was measured at 25°C in accordance with JIS K2220:2013 (Clause 7).

[0074] (3) Content of zinc atoms, calcium atoms, magnesium atoms, and aluminum atoms The content of zinc atoms, calcium atoms, magnesium atoms, and aluminum atoms was measured in accordance with JPI-5S-38-03.

[0075] [Examples 1-10 and Comparative Examples 1-4] Grease compositions for Examples 1-10 and Comparative Examples 1-4 were prepared using the methods described below, and these grease compositions were evaluated as described later.

[0076] The components included in Examples 1 to 10 and Comparative Examples 1 to 4 are as follows:

[0077] <Base oil (A)> Low viscosity PAO (A1-1) (Poly-α-olefin (PAO), kinematic viscosity at 40°C: 46.4 mm) ２( / s, viscosity index: 136) High viscosity PAO (A1-2) (poly-α-olefin (PAO), kinematic viscosity at 40°C: 396 mmHg) ２ / s, viscosity index: 147)

[0078] <Fatty Acid Metal Salts (C)> • Fatty Acid Metal Salt (C1): Zinc Stearate (Zinc atom content: 10.07% by mass) • Fatty Acid Metal Salt (C2): Calcium Stearate (Calcium atom content: 6.75% by mass) • Fatty Acid Metal Salt (C3): Magnesium Stearate (Magnesium atom content: 3.84% by mass) • Fatty Acid Metal Salt (C4): Aluminum Stearate (Aluminum atom content: 10.3% by mass)

[0079] <Additive (D)> The following components were used as additive (D).

[0080] - Antioxidants - Antioxidant (D1): Amine-based antioxidant (4,4'-dioctyldiphenylamine)

[0081] - Rust Inhibitors - • Rust Inhibitor (D2-1): Carboxylic Acid-based Rust Inhibitor (Product Name: K-CORR (Registered Trademark) G-1340, manufactured by KING INDUSTRIES) • Rust Inhibitor (D2-2): Carboxylic Acid-based Rust Inhibitor (Octanoic Acid)

[0082] - Wear-resistant agents - • Wear-resistant agent (D3-1): Bis(N,N-diamyldithiocarbamate) zinc (product name: VANLUBE® AZ ZnDTC, manufactured by Vanderbilt Chemicals) • Wear-resistant agent (D3-2): Aromatic phosphate ester (product name: ADEKA Ecoroyal AWP-3000, manufactured by ADEKA Corporation)

[0083] -Corrosion Inhibitor- •Corrosion Inhibitor (D4): 2,5-bis[(1,1,3,3-tetramethylbutyl)dithio]-1,3,4-thiadiazole

[0084] (Example 1) (1) Synthesis of Urea Grease Solution α was prepared by adding 6.71 parts by mass of diphenylmethane-4,4'-diisocyanate (MDI) to a mixed base oil of 34.82 parts by mass of low viscosity PAO (A1-1) and 3.87 parts by mass of high viscosity PAO (A1-2) heated to 80°C. Solution β was prepared by adding 6.86 parts by mass of octylamine to a mixed base oil of 34.69 parts by mass of low viscosity PAO (A1-1) and 3.85 parts by mass of high viscosity PAO (A1-2) heated separately to 80°C. Then, while stirring solution β heated to 80°C, solution α heated to 80°C was added and the stirring blade was rotated. Then, while continuing to stir, a fatty acid metal salt (C) was added, the temperature was raised to 170°C (annealing), and it was held for 1 hour to produce urea grease (b1). Furthermore, the urea-based thickener (B) contained in the obtained urea grease is R in the general formula (b1) above. １ and R ２ However, it is an octyl group, R ３ This corresponds to a compound in which the diphenylmethylene group is present. (2) Preparation of the grease composition Next, the urea grease (b1), which had been cooled to 100°C by natural cooling, was mixed with each component of additive (D) in the amounts shown in Table 1 to obtain the grease composition of Example 1.

[0085] (Examples 2-9 and Comparative Examples 1-2) The grease compositions of Examples 2-9 and Comparative Examples 1-2 were prepared in the same manner as in Example 1, except that the components and their contents were changed in the grease composition of Example 1 as shown in Tables 1-3.

[0086] (Example 10) The grease composition of Example 10 was prepared in the same manner as in Example 1, except that the annealing temperature was changed to 160°C and the components and their contents were changed as shown in Table 2. The urea-based thickener (B) contained in the obtained urea grease is R in the general formula (b1) above. １ and R ２ However, it is an octyl group or a stearyl group, R ３This corresponds to a compound with a diphenylmethylene group. Furthermore, the molar ratio of octylamine to stearylamine used as a raw material (octylamine / stearylamine) is 9 / 1.

[0087] (Comparative Example 3) A grease composition for Comparative Example 3 was prepared in the same manner as in Example 1, except that the annealing temperature was changed to 160°C and the components and their contents were changed as shown in Table 3. The urea-based thickener (B) contained in the obtained urea grease was R in the general formula (b1) above. １ and R ２ However, it is an octyl group or a stearyl group, R ３ This corresponds to a compound with a diphenylmethylene group. Furthermore, the molar ratio of octylamine to stearylamine used as a raw material (octylamine / stearylamine) is 9 / 1.

[0088] (Comparative Example 4) A grease composition for Comparative Example 4 was prepared in the same manner as in Example 1, except that the annealing temperature was changed to 180°C and the components and their contents were changed as shown in Table 3. The urea-based thickener (B) contained in the obtained urea grease was R in the general formula (b1) above. １ and R ２ However, it is a stearyl group or a cyclohexyl group, R ３ This corresponds to a compound with a diphenylmethylene group. Furthermore, the molar ratio of stearylamine and cyclohexylamine used as raw materials (stearylamine / cyclohexylamine) is 6 / 4.

[0089] [Evaluation of Shear Stability] For the grease compositions of Examples 1 to 10 and Comparative Examples 1 to 4, the change in consistency was measured in accordance with ASTM D 1831 by subtracting the consistency before the roll stability test from the consistency after the roll stability test. However, the temperature and time were changed to 80°C and 50 hours. In addition, a water-containing roll stability test was also performed by adding 10% water to the grease composition and applying shear. The change in consistency with water was measured by subtracting the consistency before the water-containing roll stability test from the consistency after the water-containing roll stability test. In both the roll stability test and the water-containing roll stability test, a change in consistency of 50 or less was evaluated as indicating excellent shear stability.

[0090] The results are shown in Tables 1 to 3.

[0091]

[0092]

[0093]

[0094] Tables 1 and 2 show that the grease compositions of Examples 1 to 10 exhibit excellent shear stability even in environments where water is present.

[0095] [Evaluation of Rust Prevention] The rust prevention properties of the grease compositions of Examples 1 to 10 were evaluated. In accordance with the German standard DIN 51802:EMCOR rust prevention test, the rust prevention properties of each grease composition of Examples 1 to 10 were evaluated by whether or not corrosion occurred under the condition of 1% saline solution. If no corrosion occurred, the rust prevention properties were judged to be good.

[0096] All of the grease compositions in Examples 1 to 10 were found not to cause corrosion and exhibited excellent rust prevention properties.

Claims

1. A compound comprising a base oil (A), a urea-based thickener (B), and a fatty acid metal salt (C), wherein the urea-based thickener (B) comprises one or more diurea compounds selected from those represented by the following general formula (b1), R １ -NHCONH-R ３ -NHCONH-R ２ (b1) [In the above general formula (b1), R １ and R ２ Each of these independently represents a monovalent chain hydrocarbon group having 6 to 10 carbon atoms. １ and R ２ They may be the same or they may be different from one another. ３ This represents a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms. The grease composition wherein the content of the fatty acid metal salt (C) is 0.3% by mass or more on a basis of the total amount of the grease composition.

2. The grease composition according to claim 1, wherein the fatty acid contained in the fatty acid metal salt (C) is stearic acid.

3. The grease composition according to claim 1 or 2, wherein the metal contained in the fatty acid metal salt (C) is one or more selected from zinc (Zn), calcium (Ca), magnesium (Mg), and aluminum (Al).

4. The grease composition according to any one of claims 1 to 3, wherein the base oil (A) comprises poly-α-olefin (PAO).

5. The grease composition according to any one of claims 1 to 4, wherein the miscible consistency at 25°C is 265 to 295.

6. A grease composition according to any one of claims 1 to 5, for use in an environment where water is present.

7. A grease composition according to any one of claims 1 to 6, used for lubricating hub bearings.

8. A method for producing a grease composition, comprising a step of blending a base oil (A), a urea-based thickener (B), and a fatty acid metal salt (C), wherein the urea-based thickener (B) comprises one or more selected from diurea compounds represented by the following general formula (b1): R １ -NHCONH-R ３ -NHCONH-R ２     (b1) [In the above general formula (b1), R １ and R ２ each independently represent a monovalent chain hydrocarbon group having 6 to 10 carbon atoms. R １ and R ２ may be the same or different from each other. R ３ represents a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms.] wherein the blending amount of the fatty acid metal salt (C) is 0.3% by mass or more based on the total amount of the grease composition.

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