Grease composition, method for producing grease composition, and method for lubricating axle

Abstract

To provide a grease composition having high shear stability.SOLUTION: A grease composition contains a base oil and a thickener, wherein the thickener has an arithmetic mean particle diameter on an area basis of 2.0 μm or less as measured by a laser analysis / scattering method, and the grease composition is obtained by holding a mixture of the base oil and the thickener at a holding temperature of 155°C or higher and 185°C or lower for 30 minutes or more and 120 minutes or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a grease composition, a method for making the grease composition, and a method for lubricating an axle with the grease composition. [Background technology]

[0002] Grease compositions are easier to seal than lubricating oils and allow for the miniaturization and weight reduction of machines to which they are applied, and therefore have been widely used for the lubrication of various sliding parts in automobiles, electrical equipment, industrial machinery, and other machinery.

[0003] Patent Document 1 discloses a method for producing a urea grease having a twisted micellar fiber structure, which comprises adding a diisocyanate and an aromatic monoamine to a base oil and maintaining the mixture at a temperature of 20 to 120°C to allow the reaction, separately adding a diisocyanate and an aliphatic monoamine to a base oil and maintaining the mixture at a temperature of 20 to 120°C to allow the reaction, mixing the two reaction compositions while maintaining the temperature at 60 to 150°C, raising the temperature to 170 to 200°C at a rate of 0.3°C per minute or more, and maintaining the temperature within the range for 0 to 180 minutes. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 62-290797 Summary of the Invention [Problem to be solved by the invention]

[0005] For example, in high-speed rotation situations such as railroad axles, the grease is subjected to high shear forces and the temperatures in the area where the grease is used are very high. Due to these high shear forces and high temperatures, axle greases are required to have high shear stability.

[0006] An object of one aspect of the present invention is to provide a grease composition having high shear stability. [Means for solving the problem]

[0007] As a result of extensive research aimed at solving the above-mentioned problems, the present inventors discovered for the first time that a grease composition having high shear stability can be obtained by heat-treating a grease composition containing thickener particles having an arithmetic mean particle diameter of 2.0 μm or less on an area basis as measured by laser analysis and scattering at a specific temperature for a specific period of time, thereby completing the present invention. That is, in order to solve the above-mentioned problems, a grease composition according to one embodiment of the present invention comprises a base oil and a thickener, the thickener having an arithmetic mean particle diameter of 2.0 μm or less on an area basis as measured by laser analysis and scattering, and the grease composition is obtained by holding a mixture of the base oil and the thickener at a holding temperature of 155°C or higher and 185°C or lower for 30 minutes or longer and 120 minutes or shorter.

[0008] In order to solve the above-mentioned problems, a method for producing a grease composition according to one embodiment of the present invention includes the steps of obtaining a mixture of a base oil and a thickener, and holding the mixture at a temperature of 155°C or higher and 185°C or lower for 30 minutes or longer and 120 minutes or shorter, wherein the thickener has an arithmetic mean particle size of 2.0 μm or smaller on an area basis as measured by laser diffraction / scattering. [Effects of the Invention]

[0009] According to one aspect of the present invention, a grease composition having high shear stability can be realized. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic cross-sectional view of a grease production apparatus used in one embodiment of the present invention. [Figure 2] 2 is a schematic diagram of a cross section of a first concave-convex portion on the container body side of the grease production apparatus of FIG. 1, taken in a direction perpendicular to the rotation axis. DETAILED DESCRIPTION OF THE INVENTION

[0011] One embodiment of the present invention will be described in detail below. In this specification, unless otherwise specified, the expression "A to B" representing a range of numerical values ​​means "A or more and B or less."

[0012] [1. Grease composition] A grease composition according to one embodiment of the present invention contains a base oil and a thickener, wherein the thickener has an arithmetic mean particle size on an area basis measured by laser diffraction / scattering method of 2.0 μm or less, and is obtained by holding a mixture of the base oil and the thickener at a holding temperature of 155°C or more and 185°C or less for 30 minutes or more and 120 minutes or less.

[0013] In a grease composition according to one embodiment of the present invention, the thickener particles in the grease composition satisfy the following requirements (I) and (II). Requirement (I): The arithmetic mean particle size (sometimes simply abbreviated as "particle size") on an area basis when the particles are measured by a laser diffraction / scattering method is 2.0 μm or less. Requirement (II): The mixture of base oil and thickener is obtained by holding the mixture at a temperature of 155°C or higher and 185°C or lower for 30 minutes or longer and 120 minutes or shorter.

[0014] By satisfying the requirements (I) and (II), a grease composition having high shear stability can be realized, and further, by satisfying the requirement (I), a grease composition having excellent performance at low temperatures (-40°C) (hereinafter also referred to as "low-temperature properties") can be obtained.

[0015] Such effects will also contribute to achieving, for example, Goal 9 of the United Nations' Sustainable Development Goals (SDGs), which is "Build resilient infrastructure, promote inclusive and sustainable industrialization, and promote innovation and resilience."

[0016] Here, requirement (I) can be considered a parameter indicating the state of aggregation of the thickener in the grease composition. Here, the "thickener particles" to be measured by the laser diffraction / scattering method refer to particles formed by aggregation of the thickener contained in the grease composition. If the grease composition contains additives other than the thickener, the particle size specified in requirement (I) can be obtained by measuring a grease composition prepared under the same conditions but without the additive by the laser diffraction / scattering method. However, if the additive is liquid at room temperature (25°C) or dissolves in the base oil, the grease composition containing the additive may also be used as the measurement target.

[0017] By miniaturizing the particle size specified in the above requirement (I) to 2.0 μm or less, a grease composition with high shear stability can be obtained.

[0018] Furthermore, by miniaturizing the particle diameter specified in the above requirement (I) to 2.0 μm or less, a grease composition with excellent low-temperature properties can be obtained. This effect is presumably due to the fact that by miniaturizing the particle diameter specified in the above requirement (I) to 2.0 μm or less, particles containing a thickener can easily penetrate into lubricated parts (friction surfaces) and are less likely to be removed from the lubricated parts, even at low temperatures where the viscosity of the base oil increases. This improves the retention of the grease composition in the lubricated parts, thereby reducing torque at startup and improving seizure life. Furthermore, by miniaturizing the particle diameter specified in the above requirement (I) to 2.0 μm or less, the retention of the base oil by the particles is improved. This is presumably due to the improved effect of spreading the base oil throughout the lubricated parts (friction surfaces).

[0019] From the above viewpoints, in a grease composition according to one embodiment of the present invention, the particle size specified in requirement (I) is preferably 1.5 μm or less, more preferably 1.0 μm or less, even more preferably 0.9 μm or less, still more preferably 0.8 μm or less, even more preferably 0.7 μm or less, still more preferably 0.6 μm or less, even more preferably 0.5 μm or less, and still more preferably 0.4 μm or less. There is no particular lower limit to the particle size specified in requirement (I), and it is, for example, 0.01 μm or more.

[0020] In this specification, the particle size value specified in the above requirement (I) is a value measured by the method described in the Examples below. The particle size value specified in the above requirement (I) can be adjusted mainly by the manufacturing conditions of the thickener.

[0021] <Base oil> The base oil contained in the grease composition according to one embodiment of the present invention is not particularly limited, and examples thereof include mineral oil and synthetic oil.

[0022] The mineral oil is not particularly limited, and examples thereof include those obtained by methods commonly used in the lubricant manufacturing process in the petroleum refining industry (for example, lubricant fractions obtained by distilling crude oil from atmospheric pressure to vacuum and then refining the fraction by one or more of solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, hydrorefining, sulfuric acid washing, clay treatment, etc.). Specific examples of hydrocarbon oils include turbine oil, spindle oil, machine oil, etc.

[0023] Synthetic oils are not particularly limited and include, for example: (1) Hydrocarbon oils (e.g., poly-α-olefins such as polybutene, 1-octene oligomer, 1-decene oligomer, etc., or hydrogenated products thereof (including α-olefin copolymers); alkyl aromatic compounds such as alkylnaphthalenes and alkylbenzenes; alicyclic compounds), (2) Ester oils (e.g., diesters such as ditridecyl glutarate, di-2-ethylhexyl adipate, diisodecyl adipate, ditridecyl adipate, and di-3-ethylhexyl sebacate; polyol esters such as trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol-2-ethylhexanoate, and pentaerythritol pelargonate; aromatic esters such as phthalates, trimellitates, and pyromellitates), (3) Polyether oils (e.g., polyglycols; polyoxyalkylene glycols; polyphenyl ethers, alkyl diphenyl ethers; dialkyl diphenyl ethers, and other phenyl ethers); (4) Phosphorus compound-based oils (e.g., aromatic phosphate esters), (5) Silicon compound-based oils (e.g., silicone), and (6) Halogenated oils (for example, fluorinated polyethers).

[0024] These may be used alone or in combination as a mixture of two or more.

[0025] As the base oil, synthetic oils are preferred from the viewpoints of improving fluidity at low temperatures, ensuring fuel economy, low volatility, and temperature rise resistance, and among synthetic oils, poly-α-olefins (PAOs) are particularly preferred.

[0026] The base oil contained in the grease composition according to one embodiment of the present invention is a mixed base oil (hereinafter also referred to as "mixed base oil (A)") containing the following two types of synthetic oils from the viewpoint of temperature rise resistance, and has a kinematic viscosity at 40°C of 35mm: 2 / s or more and a viscosity index of 140 or more: 40℃ kinematic viscosity 200mm 2 / s or more, 600mm 2 / s or less high viscosity synthetic oil (A1), - 40℃ kinematic viscosity 5.0mm 2 / s or more, 110mm 2 / s or less low viscosity synthetic oil (A2).

[0027] The kinematic viscosity of the mixed base oil (A) at 40°C is 35mm 2 / s or more, the grease composition can achieve sufficient wear resistance and fatigue life, etc. Furthermore, when the base oil mixture (A) has a viscosity index of 140 or more, it is possible to easily suppress changes in the kinematic viscosity of the base oil mixture (A) due to temperature changes.

[0028] From the viewpoint of the temperature rise resistance of the grease composition, the kinematic viscosity at 40°C of the mixed base oil (A) is 40mm 2 / s or more is more preferable, and 45 mm 2 / s or more is more preferable, and 50 mm 2 From the viewpoint of making it easier to exhibit the effects of the present invention, the kinematic viscosity at 40°C of the mixed base oil (A) is more preferably 75 mm / s or more. 2 / s or less is more preferable, and 70 mm 2 / s or less is more preferable, and 65 mm 2 / s or less is more preferable.

[0029] The viscosity index of the mixed base oil (A) is preferably 110 or more, more preferably 120 or more, and even more preferably 130 or more.

[0030] Furthermore, the mixed base oil (A) has a kinematic viscosity of 7.0 mm at 100°C. 2 / s or more is preferable, and 8.0 mm 2 / s or more is more preferable, and 9.0 mm 2 It is more preferable that the kinematic viscosity at 100°C is 11 mm / s or more. 2 / s or less is preferable, and 10 mm 2 / s or less is more preferable, and 9.5 mm 2 / s or less is more preferable.

[0031] In this specification, the 40°C kinematic viscosity, 100°C kinematic viscosity, and viscosity index are values ​​measured or calculated in accordance with JIS K2283:2000.

[0032] (High viscosity synthetic oil (A1)) The high viscosity synthetic oil (A1) (hereinafter also referred to as "base oil (A1)") has a kinematic viscosity of 200 mm at 40°C. 2 / s or more, 600mm 2 / s or less, the kinematic viscosity of the mixed base oil (A) is maintained high, which contributes to improving the wear resistance and fatigue life of the grease composition.

[0033] In order to further improve the wear resistance and fatigue life, the kinematic viscosity at 40°C of the base oil (A1) is 250mm 2 / s or more is preferable, and 300 mm 2 / s or more is more preferable, and 350 mm 2 The kinematic viscosity of the base oil (A1) at 40°C is more preferably 550 mm / s or more. 2 / s or less is preferable, and 500 mm 2 / s or less is more preferable, and 450 mm 2 / s or less is more preferable.

[0034] As the base oil (A1), any known synthetic oil that has been used as a lubricating base oil can be used without any particular limitation, as long as its kinematic viscosity at 40°C falls within the above range.

[0035] Examples of the base oil (A1) include hydrocarbon oils, aromatic oils, ester oils, ether oils, and GTL (Gas To Liquids) base oils obtained by hydroisomerization dewaxing wax produced from natural gas by the Fischer-Tropsch process, etc. These may be used alone or in combination of two or more.

[0036] Examples of hydrocarbon oils include normal paraffin, isoparaffin, polybutene, polyisobutylene, 1-decene oligomer, 1-decene and ethylene co-oligomer and other poly-α-olefins, and hydrogenated products thereof.

[0037] Examples of aromatic oils include alkylbenzenes such as monoalkylbenzenes and dialkylbenzenes; alkylnaphthalenes such as monoalkylnaphthalenes, dialkylnaphthalenes, and polyalkylnaphthalenes; and the like.

[0038] Examples of ester oils include diester oils such as dibutyl sebacate, di-2-ethylhexyl sebacate, dioctyl adipate, diisodecyl adipate, ditridecyl adipate, ditridecyl glutarate, and methyl acetyl ricinoleate; aromatic ester oils such as trioctyl trimellitate, tridecyl trimellitate, and tetraoctyl pyromellitate; polyol ester oils such as trimethylolpropane caprylate, trimethylolpropane bellargonate, pentaerythritol-2-ethylhexanoate, and pentaerythritol bellargonate; and complex ester oils such as oligoesters of polyhydric alcohols and mixed fatty acids of dibasic and monobasic acids.

[0039] Examples of ether-based oils include polyglycols such as polyethylene glycol, polypropylene glycol, polyethylene glycol monoether, and polypropylene glycol monoether; and phenyl ether-based oils such as monoalkyl triphenyl ether, alkyl diphenyl ether, dialkyl diphenyl ether, pentaphenyl ether, tetraphenyl ether, monoalkyl tetraphenyl ether, and dialkyl tetraphenyl ether.

[0040] Among these, hydrocarbon oils are preferred, and poly-α-olefins are more preferred.

[0041] The kinematic viscosity of the base oil (A1) at 100°C is 10 mm2 / s or more, 70mm 2 / s or less is preferable, and 25 mm 2 / s or more, 55mm 2 The viscosity index of the base oil (A1) is preferably 100 or more and 300 or less, and more preferably 120 or more and 250 or less.

[0042] Commercially available base oils (A1) include "Spectrasyn 40" manufactured by Exxon Mobil Corporation.

[0043] (Low viscosity synthetic oil (A2)) The low viscosity synthetic oil (A2) (hereinafter referred to as "base oil (A2)") has a kinematic viscosity of 5.0 mm at 40°C. 2 / s or more, 110mm 2 / s or less, the viscosity of the mixed oil can be adjusted.

[0044] The kinematic viscosity of base oil (A2) at 40°C is 6.0 mm 2 / s or more is preferable, and 7.0 mm 2 / s or more is more preferable, and 8.0 mm 2 / s or more is more preferable, and 10.0 mm 2 / s or more is more preferable, and 20.0 mm 2 / s or more is more preferable, and 25.0 mm 2 The kinematic viscosity at 40°C of the base oil (A2) is more preferably 90.0 mm / s or more. 2 / s or less is preferable, and 80.0 mm 2 / s or less is more preferable, and 75.0 mm 2 / s or less is more preferable, and 70.0 mm 2 / s or less is more preferable, and 50.0 mm 2 / s or less is more preferable, and 40.0 mm 2 / s or less is more preferable.

[0045] As the base oil (A2), any known synthetic oil used as a lubricating base oil can be used without particular limitation, as long as its kinematic viscosity at 40°C falls within the above range. For example, the hydrocarbon oils exemplified as the base oil (A1) can be used. The base oil (A2) can be used singly or in combination of two or more.

[0046] The kinematic viscosity of the base oil (A2) at 100°C is set to 2.0 mm from the viewpoint of high low-temperature fluidity, low viscosity and low evaporation. 2 / s or more, 10.0mm 2 / s or less is preferable, and 4.0 mm 2 / s or more, 8.0mm 2 / s or less is more preferable.

[0047] The viscosity index of the base oil (A2) is preferably 80 or more, more preferably 90 or more, even more preferably 100 or more, still more preferably 110 or more, and still more preferably 120 or more. There is no particular upper limit, but it is, for example, 200.

[0048] Commercially available base oils (A2) include "DURASYN 168" manufactured by INEOS Corporation.

[0049] (Content of base oils (A1) to (A2)) The kinematic viscosity of the mixed base oil (A) at 40°C is 35mm 2 The contents of the base oils (A1) and (A2) may be appropriately adjusted so that the viscosity is 1 / s or more and the viscosity index is 140 or more.

[0050] For example, from the viewpoint of improving the wear resistance and fatigue life of the grease composition, the content of the base oil (A1) is preferably 5 to 35 parts by mass, and more preferably 10 to 20 parts by mass, when the total amount of the mixed base oil (A) is 100 parts by mass.

[0051] In addition, from the viewpoint of making it easier to exhibit the effects of the present invention, the content of the base oil (A2) is preferably 65 to 95 parts by mass, and more preferably 80 to 90 parts by mass, when the total amount of the mixed base oil (A) is 100 parts by mass.

[0052] In the grease composition according to one embodiment of the present invention, the content of the base oil (A1) is preferably 3 to 15 mass %, more preferably 5 to 10 mass %, based on the total amount of the grease composition. When the content of the base oil (A1) is within the above range, it is easy to maintain a high kinematic viscosity of the grease composition, and it is easy to prepare a grease composition that is excellent in wear resistance and fatigue life.

[0053] In the grease composition according to one aspect of the present invention, the content of the base oil (A2) is preferably 50% by mass to 75% by mass, and more preferably 60% by mass to 70% by mass, based on the total amount of the grease composition, from the viewpoint of making it easier to exhibit the effects of the present invention.

[0054] Regarding the content ratio of the base oil (A1) and the base oil (A2) in the mixed base oil (A), it is preferable to blend the base oil (A1) and the base oil (A2) so that the ratio of the base oil with a lower molecular weight is reduced, so as to achieve low viscosity but low evaporation, and from the viewpoint of aggressiveness to rubber. For example, in the case of the combination of base oil (A1) and base oil (A2) used in the examples described later, it is preferable to blend them so that the ratio of the low molecular weight base oil (A1) is reduced.

[0055] <Thickener> The thickener contained in the grease composition according to one embodiment of the present invention may be a conventionally known substance used to adjust the viscosity of a base oil to make it semi-solid, such as a soap-based thickener or a non-soap-based thickener.

[0056] The soap-based thickener is not particularly limited, and examples thereof include metallic soaps such as lithium and calcium soaps, and metal complex soaps such as lithium and calcium soaps.

[0057] The non-soap thickener is not particularly limited, and examples thereof include urea thickeners such as aromatic diurea, aliphatic diurea, alicyclic diurea, triurea, and polyurea; organic thickeners such as sodium terephthalamate and polytetrafluoroethylene (PTFE); and inorganic thickeners such as organo-bentonite, graphite, and silica gel.

[0058] These thickeners can be synthesized by known methods.

[0059] From the viewpoint of heat resistance and long life, the thickener is preferably a urea-based thickener.

[0060] (Urea-based thickener) The urea-based thickener may be any compound having a urea bond, but a diurea compound having two urea bonds is preferred, and a diurea compound represented by the following general formula (b1) is more preferred. R 1 -NHCONH-R 3 -NHCONH-R 2 (b1) In the general formula (b1), R 1 and R 2 R each independently represents a monovalent hydrocarbon group having 6 to 24 carbon atoms. 1 and R 2 may be the same or different from each other. 3 represents a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms.

[0061] R in the general formula (b1) 1 and R 2 The number of carbon atoms in the monovalent hydrocarbon group that can be selected as R is 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 include a saturated or unsaturated monovalent chain hydrocarbon group, a saturated or unsaturated monovalent alicyclic hydrocarbon group, and a monovalent aromatic hydrocarbon group.

[0062] 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.

[0063] Examples of monovalent unsaturated chain hydrocarbon groups include straight-chain or branched-chain alkenyl groups having 6 to 24 carbon atoms, specifically hexenyl, heptenyl, octenyl, nonenyl, decenyl, undecenyl, dodecenyl, tridecenyl, tetradecenyl, pentadecenyl, hexadecenyl, heptadecenyl, octadecenyl, nonadecenyl, icosenyl, oleyl, geranyl, farnesyl, linoleyl, etc. The monovalent saturated chain hydrocarbon groups and monovalent unsaturated chain hydrocarbon groups may be straight-chain or branched.

[0064] 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 (preferably a cyclohexyl group substituted with an alkyl group having 1 to 6 carbon atoms).

[0065] 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 (preferably a cyclohexenyl group substituted with an alkyl group having 1 to 6 carbon atoms).

[0066] 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.

[0067] R in the general formula (b1) 3 The carbon number of the divalent aromatic hydrocarbon group that can be selected as R is preferably 6 to 15, and more preferably 6 to 13. 3 Examples of the divalent aromatic hydrocarbon group that can be selected as 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.

[0068] The urea-based thickener contained in the grease composition according to one embodiment of the present invention may consist of one type or may be a mixture of two or more types.

[0069] <Method for manufacturing urea-based thickeners> The urea-based thickener can be obtained, for example, by reacting an isocyanate compound with a monoamine. The reaction is preferably carried out by adding a solution β obtained by dissolving a monoamine in a base oil to a heated solution α obtained by dissolving an isocyanate compound in the base oil. For example, when synthesizing a compound represented by the general formula (b1), the isocyanate compound may be a compound represented by the general formula (b1) R 3 A diisocyanate having a group corresponding to a divalent aromatic hydrocarbon group represented by the formula: 1 and R 2 The desired urea-based thickener can be synthesized by the above method using an amine having a group corresponding to the monovalent hydrocarbon group represented by the following formula:

[0070] R in the general formula (b1) 3 Examples of diisocyanates having a group corresponding to the divalent aromatic hydrocarbon group represented by the formula (I) include diphenylmethane-4,4'-diisocyanate (MDI), etc. One type of diisocyanate may be used alone, or two or more types may be used in combination.

[0071] R in the general formula (b1) 1 and R 2 Examples of monoamines having a group corresponding to the monovalent hydrocarbon group represented by the formula include octylamine, stearylamine, etc. One type of monoamine may be used alone, or two or more types may be used in combination.

[0072] There are no particular limitations on the combination of diisocyanate and monoamine as long as it is a combination that can produce a reaction product of an isocyanate compound and a monoamine. However, it is preferable to use diphenylmethane-4,4'-diisocyanate (MDI) as the diisocyanate and a combination of octylamine and stearylamine as the monoamine.

[0073] When octylamine and stearylamine are used in combination as monoamines, from the viewpoint of heat resistance, the molar ratio of octylamine to stearylamine (octylamine:stearylamine) to be reacted with an isocyanate compound is preferably 8:2 or more, more preferably 8.5:1.5 or more. Furthermore, from the viewpoint of low-temperature fluidity, the molar ratio of octylamine to stearylamine (octylamine:stearylamine) to be reacted with an isocyanate compound is preferably 9.8:0.2 or less, more preferably 9.5:0.5 or less.

[0074] <Manufacturing method of grease base material> In order to make the thickener in the grease composition finer so as to satisfy the requirement (I), the raw materials of the grease base material are 2 s -1 It is preferable to obtain a grease base material as a mixture in which thickener particles are dispersed in a base oil by applying a shear force of at least this magnitude. For example, it is preferable to produce the grease base material using a grease production apparatus such as that shown in [1] below. In this specification, the term "grease base material" refers to a mixture of a base oil and a thickener, which does not contain any additives. [1] A container body having an inlet portion into which raw materials for a grease base material are introduced and an outlet portion from which the grease is discharged to the outside; a rotor having a rotation axis in the axial direction of the inner periphery of the container body and rotatably provided inside the container body, The rotor is (i) along the surface of the rotor, concaves and convexes are alternately provided, and the concaves and convexes are inclined with respect to the rotation axis; (ii) A grease production device comprising a first uneven portion having a feeding capability from the introduction portion in the direction of the discharge portion.

[0075] The grease production apparatus described in [1] above will be explained. Unless otherwise specified, the "preferred" provisions described below are aspects from the viewpoint of finely granulating the thickener in the grease composition so as to satisfy the requirement (I) and further the requirement (II).

[0076] Figure 1 is a schematic cross-sectional view of the grease production apparatus [1] that can be used in one embodiment of the present invention. The grease production apparatus 1 shown in Figure 1 includes a container body 2 into which grease raw materials are introduced, and a rotor 3 that has a rotating shaft 12 on the central axis of the inner periphery of the container body 2 and rotates around the rotating shaft 12 as its central axis.

[0077] The rotor 3 rotates at high speed around the rotary shaft 12 as the central axis, and applies a high shear force to the grease raw material inside the container body 2. This produces grease containing a thickener.

[0078] As shown in Fig. 1, the container body 2 is preferably partitioned into, in order from the upstream side, an introduction section 4, a retention section 5, a first inner circumferential surface 6, a second inner circumferential surface 7, and a discharge section 8. As shown in Fig. 1, the container body 2 preferably has a truncated conical inner circumferential surface whose inner diameter gradually increases from the introduction section 4 toward the discharge section 8. The introduction section 4, which is one end of the container body 2, is equipped with a plurality of solution introduction pipes 4A, 4B for introducing the grease raw material from the outside of the container body 2.

[0079] The retention section 5 is located downstream of the introduction section 4 and is a space for temporarily retaining the grease raw material introduced from the introduction section 4. If the grease raw material remains in this retention section 5 for a long time, the grease adhering to the inner circumferential surface of the retention section 5 will form large lumps, so it is preferable to transport the grease raw material downstream to the first inner circumferential surface 6 in as short a time as possible. It is even more preferable to transport the grease raw material directly to the first inner circumferential surface 6 without passing through the retention section 5.

[0080] The first inner circumferential surface 6 is disposed in a downstream portion adjacent to the retention portion 5, and the second inner circumferential surface 7 is disposed in a downstream portion adjacent to the first inner circumferential surface 6. As will be described in detail later, providing a first uneven portion 9 on the first inner circumferential surface 6 and a second uneven portion 10 on the second inner circumferential surface 7 is preferable in order to make the first inner circumferential surface 6 and the second inner circumferential surface 7 function as high shear portions that apply high shear force to the grease raw material or the grease.

[0081] The discharge part 8, which is the other end of the container body 2, is a part that discharges the grease stirred between the first inner circumferential surface 6 and the second inner circumferential surface 7, and is provided with a discharge port 11 that discharges the grease. The discharge port 11 is formed in a direction perpendicular or substantially perpendicular to the rotation axis 12. This allows the grease to be discharged from the discharge port 11 in a direction perpendicular or substantially perpendicular to the rotation axis 12. However, the discharge port 11 does not necessarily have to be perpendicular to the rotation axis 12, and may be formed in a direction parallel or substantially parallel to the rotation axis 12.

[0082] The rotor 3 is rotatably mounted around the central axis of the truncated cone-shaped inner peripheral surface of the vessel body 2 as a rotation axis 12, and rotates counterclockwise when the vessel body 2 is viewed from the upstream to the downstream as shown in Figure 1. The rotor 3 has an outer peripheral surface that expands in accordance with the expansion of the inner diameter of the truncated cone of the vessel body 2, and a constant gap is maintained between the outer peripheral surface of the rotor 3 and the inner peripheral surface of the truncated cone of the vessel body 2.

[0083] The outer peripheral surface of the rotor 3 is provided with a first rotor uneven portion 13, in which unevenness is alternately provided along the surface of the rotor 3. The first rotor uneven portion 13 is inclined with respect to the rotation axis 12 of the rotor 3 in the direction from the introduction portion 4 to the discharge portion 8, and has the ability to feed from the introduction portion 4 to the discharge portion 8. In other words, the first rotor uneven portion 13 is inclined in a direction that pushes the solution downstream when the rotor 3 rotates in the direction shown in FIG.

[0084] The difference in level between the recesses 13A and the protrusions 13B of the first uneven portion 13 of the rotor is preferably 0.3 to 30, more preferably 0.5 to 15, and even more preferably 2 to 7, when the diameter of the recesses 13A on the outer peripheral surface of the rotor 3 is taken as 100. The number of protrusions 13B of the first uneven portion 13 of the rotor in the circumferential direction is preferably 2 to 1000, more preferably 6 to 500, and even more preferably 12 to 200.

[0085] The ratio of the width of the convex portion 13B of the first uneven portion 13 of the rotor to the width of the concave portion 13A in a cross section perpendicular to the rotation axis 12 of the rotor 3 (width of convex portion / width of concave portion) is preferably 0.01 to 100, more preferably 0.1 to 10, and even more preferably 0.5 to 2.

[0086] The inclination angle of the first uneven portion 13 of the rotor with respect to the rotation axis 12 is preferably 2 to 85 degrees, more preferably 3 to 45 degrees, and even more preferably 5 to 20 degrees.

[0087] The first inner circumferential surface 6 of the container body 2 is preferably provided with a first uneven portion 9 having a plurality of unevennesses formed along the inner circumferential surface. Furthermore, the unevenness of the first uneven portion 9 on the container body 2 side is preferably inclined in the opposite direction to the first uneven portion 13 of the rotor. In other words, the plurality of unevennesses of the first uneven portion 9 on the container body 2 side are preferably inclined in a direction that pushes the solution downstream when the rotation shaft 12 of the rotor 3 rotates in the direction shown in FIG. 1. The stirring capacity and discharge capacity are further enhanced by the first uneven portion 9 having a plurality of unevennesses provided on the first inner circumferential surface 6 of the container body 2.

[0088] The depth of the recesses and projections of the first recessed and projected portion 9 on the container body 2 side is preferably 0.2 to 30, more preferably 0.5 to 15, and even more preferably 1 to 5, when the inner diameter (diameter) of the container is taken as 100. The number of recesses and projections of the first recessed and projected portion 9 on the container body 2 side is preferably 2 to 1,000, more preferably 6 to 500, and even more preferably 12 to 200.

[0089] The ratio of the width of the recesses of the first uneven portion 9 on the container body 2 side to the width of the protrusions between the grooves [width of recesses / width of protrusions] is preferably 0.01 to 100, more preferably 0.1 to 10, and even more preferably 0.5 to 2 or less.

[0090] The inclination angle of the concaves and convexes of the first concave-convex portion 9 on the container body 2 side with respect to the rotation axis 12 is preferably 2 to 85 degrees, more preferably 3 to 45 degrees, and even more preferably 5 to 20 degrees. By providing the first concave-convex portion 9 on the first inner circumferential surface 6 of the container body 2, the first inner circumferential surface 6 can function as a shearing portion that applies a high shear force to the grease raw material or the grease, but the first concave-convex portion 9 is not necessarily provided.

[0091] It is preferable that a second rotor uneven portion 14, in which unevenness is alternately provided along the surface of the rotor 3, is provided on the outer peripheral surface of the downstream portion of the first rotor uneven portion 13. The second rotor uneven portion 14 is inclined with respect to the rotation axis 12 of the rotor 3, and has the ability to suppress the feed of the solution by pushing it back upstream from the inlet portion 4 toward the outlet portion 8.

[0092] The step height of the second uneven portion 14 of the rotor is preferably 0.3 to 30, more preferably 0.5 to 15, and even more preferably 2 to 7, where the diameter of the recess on the outer peripheral surface of the rotor 3 is taken as 100. The number of protrusions of the second uneven portion 14 of the rotor in the circumferential direction is preferably 2 to 1000, more preferably 6 to 500, and even more preferably 12 to 200.

[0093] The ratio of the width of the convex portion to the width of the concave portion of the second uneven portion 14 of the rotor in a cross section perpendicular to the rotation axis of the rotor 3 [convex portion width / concave portion width] is preferably 0.01 to 100, more preferably 0.1 to 10, and even more preferably 0.5 to 2. The tilt angle of the second uneven portion 14 of the rotor with respect to the rotation axis 12 is preferably 2 to 85 degrees, more preferably 3 to 45 degrees, and even more preferably 5 to 20 degrees.

[0094] The second inner circumferential surface 7 of the container body 2 preferably has a second uneven portion 10 formed with multiple unevennesses adjacent to the downstream portion of the unevennesses in the first uneven portion 9 on the container body 2 side. Multiple unevennesses are preferably formed on the inner circumferential surface of the container body 2, and each unevenness is preferably inclined in the opposite direction to the inclination direction of the second uneven portion 14 of the rotor. That is, the multiple unevennesses of the second uneven portion 10 on the container body 2 side are preferably inclined in a direction that pushes the solution back upstream when the rotation shaft 12 of the rotor 3 rotates in the direction shown in FIG. 1 . The unevenness of the second uneven portion 10 on the second inner circumferential surface 7 of the container body 2 further enhances the stirring ability. Furthermore, the second inner circumferential surface 7 of the container body can function as a shearing portion that applies high shear force to the grease raw material or grease.

[0095] The depth of the recesses of the second uneven portion 10 on the container body 2 side is preferably 0.2 to 30, more preferably 0.5 to 15, and even more preferably 1 to 5, when the inner diameter (diameter) of the container body 2 is taken as 100. The number of recesses of the second uneven portion 10 on the container body 2 side is preferably 2 to 1,000, more preferably 6 to 500, and even more preferably 12 to 200.

[0096] The ratio of the width of the convex portions to the width of the concave portions of the second concave-convex portion 10 on the container body 2 side in a cross section perpendicular to the rotation axis 12 of the rotor 3 [convex portion width / concave portion width] is preferably 0.01 to 100, more preferably 0.1 to 10, and even more preferably 0.5 to 2. The inclination angle of the second concave-convex portion 10 on the container body 2 side with respect to the rotation axis 12 is preferably 2 to 85 degrees, more preferably 3 to 45 degrees, and even more preferably 5 to 20 degrees. The ratio of the length of the first concave-convex portion 9 on the container body 2 side to the length of the second concave-convex portion 10 on the container body 2 side [first concave-convex portion length / second concave-convex portion length] is preferably 2 / 1 to 20 / 1.

[0097] 2 is a cross-sectional view of the first uneven portion 9 on the container body 2 side of the grease production apparatus 1, taken in a direction perpendicular to the rotation axis 12. The first uneven portion 13 of the rotor shown in FIG. 2 is provided with a plurality of scrapers 15 whose tips protrude toward the inner circumferential surface of the container body 2 beyond the tips of the protruding portions 13B of the first uneven portion 13. Although not shown, the second uneven portion 14 is also provided with a plurality of scrapers whose tips protrude toward the inner circumferential surface of the container body 2, similar to the first uneven portion 13. The scrapers 15 scrape off grease adhering to the first uneven portion 9 on the container body 2 side and the inner circumferential surfaces of the second uneven portion 10 on the container body 2 side. It is preferable that the ratio [R2 / R1] of the radius (R2) of the tip of the scraper 15 to the radius (R1) of the tip of the convex portion 13B of the rotor's first uneven portion 13 is greater than 1.005 and less than 2.0, with respect to the protrusion of the tip of the scraper 15 relative to the protrusion of the convex portion 13B.

[0098] The number of scrapers 15 is preferably 2 to 500, more preferably 2 to 50, and even more preferably 2 to 10. Although the grease production apparatus 1 shown in Fig. 2 is provided with scrapers 15, it may not be provided with scrapers 15, or scrapers 15 may be provided intermittently.

[0099] The grease manufacturing apparatus described in [1] above is disclosed, for example, in Japanese Patent Application Laid-Open No. 2021-161296 as grease manufacturing apparatus 1.

[0100] As an example, a case will be described in which a grease base material containing a urea-based thickener is produced by the grease production apparatus 1, which is one embodiment of the grease production apparatus described in [1] above.

[0101] When a grease base material containing a urea-based thickener is produced using the grease production apparatus 1, the grease base material containing a urea-based thickener can be produced by introducing the aforementioned raw materials for the grease base material, solutions α and β, respectively, through solution inlet pipes 4A and 4B of the inlet portion 4 of the container body 2 and rotating the rotor 3 at high speed. Then, even when additives are blended into the grease base material obtained in this manner, the urea-based thickener in the grease composition can be made fine so as to satisfy the requirement (I) above.

[0102] As a condition for the high speed rotation of the rotor 3, the shear force applied to the raw material of the grease base material is a shear rate of 10 2 s -1 It is preferable that the number is 10 or more. 3 s -1 More preferably, it is 10 or more. 4 s -1 The upper limit of the shear rate is not particularly limited, and is, for example, 10 7 s -1 The following is the result.

[0103] Furthermore, the ratio (Max / Min) of the maximum shear rate (Max) to the minimum shear rate (Min) during shear when the rotor 3 rotates at high speed is preferably 100 or less, more preferably 50 or less, and even more preferably 10 or less. By making the shear rate for the mixed liquid as uniform as possible, it becomes easier to micronize the urea-based thickener and its precursor in the grease composition, resulting in a more uniform grease structure.

[0104] Here, the maximum shear rate (Max) is the highest shear rate applied to the mixed liquid, and the minimum shear rate (Min) is the lowest shear rate applied to the mixed liquid, and is defined as follows: Maximum shear rate (Max) = (linear velocity of the tip of the convex portion 13B of the first uneven portion 13 of the rotor) / (gap A1 between the tip of the convex portion 13B of the first uneven portion 13 of the rotor and the convex portion of the first uneven portion 9 of the first inner circumferential surface 6 of the container body 2) Minimum shear rate (Min) = (linear velocity of recess 13A of first uneven portion 13 of rotor) / (gap A2 between recess 13A of first uneven portion 13 of rotor and recess of first uneven portion 9 of first inner circumferential surface 6 of container body 2)

[0105] Furthermore, the grease base is heat-treated (also referred to as "annealed") at a holding temperature of 155°C or higher and 185°C or lower for a holding time of 30 minutes or longer and 120 minutes or shorter so as to satisfy the requirement (II). A grease composition containing a grease base that has been heat-treated at the above-mentioned specific holding temperature and specific holding time will have high shear stability. Here, in this specification, the "holding temperature" refers to the product temperature of the grease base, and the "holding time" refers to the length of time during which the product temperature of the grease base is held at a predetermined holding temperature, and refers to the length of time from when the product temperature of the grease base reaches the predetermined holding temperature to when the heat treatment is stopped.

[0106] As for the heat treatment conditions, from the viewpoint of further improving shear stability, the holding temperature is preferably 160°C or higher, more preferably 165°C or higher, more preferably 170°C or higher, and even more preferably 175°C or higher.

[0107] Furthermore, from the viewpoint of achieving a homogeneous heat treatment of the thickener, the temperature is more preferably maintained for 60 minutes or more and 120 minutes or less.

[0108] The heat treatment can be carried out by holding the grease base material in a conventionally known device capable of maintaining the interior at a predetermined temperature for a predetermined period of time, such as a reaction vessel, a mixing vessel, a planetary mixer, an autoclave, a contactor, a kneader, etc.

[0109] The method for producing the grease base is not limited to the above-mentioned method, and the grease base may be produced by a method other than the above-mentioned methods as long as the method can finely refine the thickener in the grease composition so as to satisfy the requirement (I).

[0110] <Content of each ingredient> From the viewpoint of extending the service life, the content of the base oil in the grease composition according to one embodiment of the present invention is, based on the total amount (100 mass%) of the grease composition, preferably 50 mass% or more, more preferably 55 mass% or more, even more preferably 60 mass% or more, still more preferably 65 mass% or more, and is preferably 98.5 mass% or less, more preferably 97 mass% or less, even more preferably 95 mass% or less, and still more preferably 93 mass% or less.

[0111] The content of the thickener in the grease composition according to one embodiment of the present invention is, from the viewpoint of ease of adjusting the worked penetration of the resulting grease composition, preferably 1.0% by mass or more, more preferably 1.5% by mass or more, even more preferably 2.0% by mass or more, even more preferably 2.5% by mass or more, and even more preferably 4.0% by mass or more, based on the total amount (100% by mass) of the grease composition. From the viewpoint of the lubricity and low-temperature properties of the resulting grease composition, the content of the thickener is preferably 15.0% by mass or less, more preferably 13.0% by mass or less, even more preferably 10.0% by mass or less, even more preferably 8.0% by mass or less, even more preferably 7.0% by mass or less, and even more preferably 5.0% by mass or less, based on the total amount (100% by mass) of the grease composition.

[0112] The total content of the base oil and thickener in the grease composition according to one embodiment of the present invention (i.e., the content of the grease base material) is preferably 60% by mass or more, more preferably 70% by mass or more, 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. The upper limit of the total content of the base oil and thickener is, for example, 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 according to one embodiment of the present invention may contain components other than the base oil and thickener, as long as the effects of the present invention are not impaired.

[0113] <Other ingredients> The grease composition according to one embodiment of the present invention may further contain, if desired, additives commonly used in grease compositions, such as oiliness agents, antioxidants, synthetic waxes, thickeners, rust inhibitors, dispersants, metal deactivators, extreme pressure agents, and wear reducers.

[0114] Examples of oily agents include fatty alcohols; fatty acid compounds such as fatty acids and fatty acid metal salts; ester compounds such as fatty acid esters, polyol esters, sorbitan esters, and glycerides; amine compounds such as fatty amines; and amide compounds.

[0115] Examples of the antioxidant include amine-based antioxidants such as diphenylamine-based compounds (e.g., dioctyldiphenylamine) and naphthylamine-based compounds; and phenol-based antioxidants such as monocyclic phenol-based compounds and polycyclic phenol-based compounds.

[0116] Examples of synthetic waxes include polyethylene wax, polypropylene wax, copolymer waxes such as ethylene-propylene-hexene-vinyl acetate and acrylic acid; hydrocarbon waxes such as Fischer-Tropsch wax and polymethylene wax; and synthetic amide wax.

[0117] Examples of thickeners include polymethacrylate (PMA), olefin copolymer (OCP), polyalkylstyrene (PAS), and styrene-diene copolymer (SCP).

[0118] Examples of the rust inhibitor include carboxylic acid-based rust inhibitors such as alkenyl succinic acid polyhydric alcohol esters; thiadiazole and its derivatives; benzotriazole and its derivatives; metal sulfonates such as barium sulfonate; and fatty acid ester-based rust inhibitors such as sorbitan monooleate.

[0119] Examples of the dispersant include ashless dispersants such as calcium sulfonate, succinimide, and boron-based succinimide.

[0120] Examples of the metal deactivator include benzotriazole compounds.

[0121] Examples of extreme pressure agents include thiocarbamic acids such as zinc dialkyldithiophosphate (ZnDTP), molybdenum dialkyldithiophosphate, ashless dithiocarbamates, zinc dithiocarbamates, and molybdenum dithiocarbamate (MoDTC); sulfur compounds such as sulfurized oils and fats, sulfurized olefins, polysulfides, thiophosphoric acids, thioterpenes, and dialkylthiodipropionates; phosphate esters such as tricresyl phosphate and molybdenum dithiophosphate (MoDTP); and phosphite esters such as triphenyl phosphite.

[0122] Examples of the wear reducer include phosphate esters and dithiocarbamate esters.

[0123] When the grease composition according to one embodiment of the present invention contains additives, the content of each additive is independently 0.01 to 20 mass%, preferably 0.01 to 15 mass%, more preferably 0.01 to 10 mass%, and even more preferably 0.01 to 7 mass%, based on the total amount (100 mass%) of the grease composition.

[0124] These additives may be used singly or as a mixture of two or more kinds.

[0125] <Properties of grease composition> (Change in consistency) A grease composition according to one embodiment of the present invention has a consistency change of 0 or more and less than +60 in a roll stability test measured after applying shear under the specified conditions (80°C, 50 hours) using a testing machine conforming to ASTM D1831. Such a grease composition can be said to have sufficiently high shear stability. Since the smaller the consistency change, the higher the shear stability, the consistency change is preferably +55 or less, more preferably +50 or less, even more preferably +40 or less, and still more preferably +30 or less.

[0126] (Worked penetration) From the viewpoint of fluidity, the grease composition according to one embodiment of the present invention preferably has a worked penetration at 25°C of 240 or more, preferably 260 or more, and more preferably 265 or more. From the viewpoint of leak resistance, the worked penetration at 25°C is preferably 450 or less, and more preferably 340 or less. In this specification, the worked penetration of the grease composition means a value measured at 25°C and 60 W according to the method described in JIS K2220.7.

[0127] (dropping point) From the viewpoint of heat resistance, the grease composition according to one embodiment of the present invention preferably has a dropping point of 100 or higher, more preferably 120 or higher, more preferably 150 or higher, even more preferably 180 or higher, and even more preferably 190 or higher. Furthermore, although not particularly limited, the dropping point may be 300 or lower. In this specification, the dropping point of the grease composition means a value measured in accordance with JIS K2220:2013.

[0128] (low temperature torque) From the viewpoint of achieving excellent low-temperature properties, the grease composition according to one embodiment of the present invention preferably has a starting torque at low temperatures of 600 or less, more preferably 580 or less. Furthermore, the running torque at low temperatures is preferably 460 or less, more preferably 450 or less. A grease composition having a starting torque and running torque within the above ranges at low temperatures can be said to have excellent low-temperature properties. In this specification, the low-temperature torque of a grease composition refers to the starting torque (unit: mN m) and running torque (unit: mN m) determined at a temperature of -40°C in accordance with JIS K2220:2013. The starting torque is the torque required to output power from a stationary state, and the smaller the torque, the better. The running torque is the torque required to continuously output power, and the smaller the torque, the better.

[0129] <Applications of grease compositions> The grease composition according to one embodiment of the present invention has high shear stability and is therefore suitable for use in lubricating rolling bearings and sliding parts of various devices, and is particularly suitable for use in roller bearings, self-aligning bearings, roller-type linear motion devices, and the like.

[0130] The grease composition according to one embodiment of the present invention can be suitably used in the fields of equipment such as railway vehicles, automobiles, office equipment, machine tools, wind turbines, construction equipment, agricultural machinery, and industrial robots. Among these, the grease composition can be suitably used for lubricating the axles of railway vehicles (particularly Shinkansen bullet trains), which are subject to high rotational speeds and therefore require extremely high shear stability. It can also be suitably used in electric motors.

[0131] Examples of lubricated parts in equipment in the field of railway vehicles that can be suitably used with the grease composition according to one embodiment of the present invention include axle parts.

[0132] Examples of lubricating parts in devices in the automotive field that can suitably use the grease composition according to one embodiment of the present invention include bearing parts in devices such as radiator fan motors, fan couplings, alternators, idler pulleys, hub units, water pumps, power windows, wipers, electric power steering, electric drive motor flywheels, ball joints, wheel bearings, spline parts, constant velocity joints, etc.; bearing parts, gear parts, and sliding parts in devices such as door locks, door hinges, and clutch boosters, etc. More specific examples include bearing parts of hub units, electric power steering, electric drive motor flywheels, ball joints, wheel bearings, spline parts, constant velocity joints, clutch boosters, servo motors, blade bearings, and generators.

[0133] Examples of lubricating parts in devices in the field of office equipment for which the grease composition according to one embodiment of the present invention can be suitably used include fuser rolls in devices such as printers, and bearings and gear parts in devices such as polygon motors.

[0134] Examples of lubricated parts within equipment in the field of machine tools for which the grease composition according to one embodiment of the present invention can be suitably used include bearing parts within reducers of spindles, servo motors, machine tool robots, and the like.

[0135] Examples of lubricating parts in equipment in the wind turbine field that can be suitably used with the grease composition according to one embodiment of the present invention include bearing parts such as main bearings, blade bearings, and generators.

[0136] Examples of lubricated parts within equipment in the fields of construction or agricultural machinery for which the grease composition according to one embodiment of the present invention can be suitably used include bearing parts such as ball joints and spline parts, gear parts, and sliding parts.

[0137] [2. Method for producing grease composition] A method for producing a grease composition according to one embodiment of the present invention includes the following steps (1) and (2), wherein the thickener has an arithmetic mean particle size on an area basis measured by a laser diffraction / scattering method of 2.0 μm or less: Step (1): obtaining a mixture of the base oil and the thickener; Step (2): A step of holding the mixture at a holding temperature of 155°C or higher and 185°C or lower for 30 minutes or longer and 120 minutes or shorter.

[0138] According to the method for producing a grease composition according to one aspect of the present invention, it is possible to produce a grease composition having high shear stability. According to the method for producing a grease composition according to one aspect of the present invention, it is possible to produce the grease composition according to the above-mentioned aspect of the present invention.

[0139] Steps (1) and (2) will be described below. <Process (1)> Step (1) is a step of obtaining a mixture of a base oil and a thickener. The mixture of a base oil and a thickener can be obtained by reacting raw materials for the thickener in the base oil. For example, a mixture of a base oil and a urea-based thickener can be obtained by reacting an isocyanate compound, which is a raw material for the urea-based thickener, with a monoamine in the base oil. The base oil and the thickener have already been explained in the section "1. Grease Composition" above, so the explanation will not be repeated here.

[0140] In step (1), from the viewpoint of finely pulverizing the urea-based thickener so as to satisfy the requirement (I) for the grease composition according to one embodiment of the present invention, the raw materials for the grease composition are subjected to a shear rate of 10 2 s -1 It is preferable to synthesize the thickener in the base oil while applying the above shear force, thereby obtaining a mixture in which thickener particles are dispersed in the base oil. For example, it is preferable to obtain a mixture in which thickener particles are dispersed in the base oil using a grease production apparatus such as that shown in [1] above. The method for obtaining a mixture of a base oil and a urea-based thickener using the grease production apparatus shown in [1] above has already been explained in the section "1. Grease composition" above, so the explanation will not be repeated here.

[0141] In step (1), the thickener may be synthesized by reacting an isocyanate compound with a monoamine in the base oil. In this case, the monoamine is preferably octylamine and stearylamine. From the viewpoint of improving shear stability, the molar ratio of octylamine to stearylamine (octylamine:stearylamine) to be reacted with the isocyanate compound is preferably 8:2 or more, more preferably 8.5:1.5 or more. Furthermore, from the viewpoint of low-temperature fluidity, the molar ratio of octylamine to stearylamine (octylamine:stearylamine) to be reacted with the isocyanate compound is preferably 9.8:0.2 or less, more preferably 9.5:0.5 or less.

[0142] <Process (2)> Step (2) is a step of holding the mixture obtained in step (1) at a holding temperature of 155°C or higher and 185°C or lower for 30 minutes or longer and 120 minutes or shorter. By undergoing step (2), a grease composition with high shear stability can be produced. Step (2) is also called a heat treatment step or an annealing step.

[0143] The holding temperature and holding time in the heat treatment in step (2), as well as the heat treatment method, have already been explained in the section "1. Grease composition" above, and therefore will not be explained again here.

[0144] In step (2), the mixture of base oil and thickener is heated to increase its temperature until it reaches a predetermined holding temperature. From the viewpoint of production efficiency, the temperature increase rate is preferably 0.5°C per minute or more, more preferably 0.8°C per minute or more. From the viewpoint of uniform heat treatment, the temperature increase rate is preferably 2.0°C per minute or less, more preferably 1.5°C per minute or less.

[0145] In step (2), the heat treatment is preferably carried out while stirring the mixture of base oil and thickener during the heating period until the product temperature of the mixture of base oil and thickener reaches a predetermined holding temperature, and during the holding period after the product temperature of the mixture of base oil and thickener reaches the predetermined holding temperature. This allows heat to be applied uniformly to the thickener. The stirring conditions can be such that the mixture of base oil and thickener is mixed uniformly. For example, the mixture of base oil and thickener can be mixed uniformly by stirring at a rotational speed of 1 rpm or more, preferably 30 rpm or more, using a stirring device such as a conventional planetary mixer.

[0146] <Other processes> The method for producing a grease composition according to one embodiment of the present invention may include steps other than the above-described steps (1) and (2). For example, it may include a step of cooling the mixture of base oil and thickener after step (1) to room temperature before carrying out step (2).

[0147] Furthermore, for example, if necessary, the method may include a step of blending one or more additives into the mixture of the base oil and the thickener after the completion of step (2). The temperature at which the additives are blended is preferably 15°C or higher and 100°C or lower.

[0148] After step (2), if necessary, it is preferable to include a step of milling the grease composition after the step of blending the additives. The milling can be carried out using a conventionally known device such as a roll mill or a homogenizer. This allows the thickener and additives to be uniformly dispersed.

[0149] The conditions for the milling treatment are not particularly limited, but when the milling treatment is carried out using a roll mill, for example, it is effective to carry out the treatment with a gap between the rolls of 5 to 20 μm.

[0150] 3. How to Lubricate the Axles A method for lubricating an axle with a grease composition according to one embodiment of the present invention is also included in the scope of the present invention. The grease composition according to one embodiment of the present invention in the method for lubricating an axle according to one embodiment of the present invention has already been described, so the description will not be repeated here. According to the method for lubricating an axle using the grease composition according to one embodiment of the present invention, the grease composition has high shear stability, and is therefore suitable as a method for lubricating axles that are exposed to high rotation, such as axles of railway vehicles.

[0151] 〔summary〕 According to one aspect of the present invention, the following [1] to [9] are provided. [1] A grease composition comprising a base oil and a thickener, wherein the thickener has an arithmetic mean particle size on an area basis measured by laser diffraction / scattering method of 2.0 μm or less, and obtained by holding a mixture of the base oil and the thickener at a holding temperature of 155°C or more and 185°C or less for 30 minutes or more and 120 minutes or less. [2] The grease composition according to [1], wherein the retention temperature is 175°C or higher and 185°C or lower. [3] The grease composition according to [1] or [2], wherein the thickener is a urea-based thickener that is a reaction product of an isocyanate compound and a monoamine, the monoamines being octylamine and stearylamine, and the molar ratio of the octylamine to the stearylamine that is reacted with the isocyanate compound is 8:2 or more and 9.8:0.2 or less. [4] The grease composition according to any one of [1] to [3], wherein the consistency change measured in a roll stability test after applying shear under the specified conditions (80°C, 50 hours) using a testing machine conforming to ASTM D1831 is 0 or more and less than +60. [5] A method for lubricating an axle with the grease composition according to any one of [1] to [4]. [6] A method for producing a grease composition, comprising: obtaining a mixture of a base oil and a thickener; and holding the mixture at a temperature of 155°C or higher and 185°C or lower for 30 minutes or longer and 120 minutes or shorter, wherein the thickener has an arithmetic mean particle size of 2.0 μm or smaller on an area basis as measured by a laser diffraction / scattering method. [7] The method for producing a grease composition according to [6], wherein the holding temperature is 175°C or higher and 185°C or lower. [8] In the step of obtaining a mixture of the base oil and the thickener, a shear rate of 10 2 s -1 The method for producing a grease composition according to [6] or [7], wherein the thickener is synthesized in the base oil while applying a shear force of at least 100 MPa to obtain the mixture in which particles of the thickener are dispersed in the base oil. [9] The method for producing a grease composition according to any one of [6] to [8], wherein in the step of obtaining a mixture of the base oil and the thickener, the thickener is synthesized by reacting an isocyanate compound with a monoamine in the base oil, the monoamines being octylamine and stearylamine, and the molar ratio of the octylamine to the stearylamine reacted with the isocyanate compound is 8:2 or more and 9.8:0.2 or less.

[0152] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in the embodiments are also included in the technical scope of the present invention. [Example]

[0153] The present invention will be specifically described with reference to the following examples, but the present invention is not limited to these examples.

[0154] [Various physical properties] The methods for measuring various physical properties were as follows. (1) Kinematic viscosity at 40°C, kinematic viscosity at 100°C, and viscosity index of base oil (mixed base oil) Measurements and calculations were made in accordance with JISK2283:2000.

[0155] (2) Calculation of particle size of urea-based thickener particles The particle size of particles containing a urea-based thickener in a grease composition was evaluated. Specifically, the urea grease synthesized in the examples was used as a measurement sample, and the particle size of the urea-based thickener particles was determined by the following procedure.

[0156] First, the measurement sample was vacuum-degassed and then loaded into a 1 mL syringe. 0.10 to 0.15 mL of the sample was extruded from the syringe, and the extruded sample was placed on the surface of a plate-shaped cell of a paste cell fixture. Next, another plate-shaped cell was placed on top of the sample, resulting in a measurement cell in which the sample was sandwiched between the two cells. Next, the area-based arithmetic mean particle diameter of the particles in the sample in the measurement cell was measured using a laser diffraction particle size analyzer (Shimadzu Corporation, product name: SALD-7500nano). Here, "area-based arithmetic mean particle diameter" refers to the arithmetic mean of the area-based particle size distribution. The area-based particle size distribution represents the frequency distribution of particle diameters across all particles being measured, expressed using the area calculated from the particle diameters (more specifically, the cross-sectional area of ​​particles having the particle diameters). The arithmetic mean of the area-based particle size distribution can be calculated using the following formula (1):

[0157]

number

[0158] (3) Dropping point of the grease composition Measurements were performed in accordance with JIS K2220:2013.

[0159] (4) Worked consistency of the grease composition Measurement was carried out according to the method described in JIS K2220.7 (25°C, 60W).

[0160] (5) Change in consistency during roll stability test Measurement was carried out according to the method described in ASTM D1831 (except that the temperature and time were changed to 80°C and 50 hours (h)).

[0161] [Raw materials] In the examples and comparative examples, the base oils and additives used as raw materials for preparing the grease compositions were as follows.

[0162] <Base oil (A)> Base oil (A) was prepared by blending and mixing the following base oils (A1) and (A2) in the amounts shown in Table 1. The kinematic viscosity at 40°C of the obtained base oil (A) was 59.49 mm 2 / s, and the kinematic viscosity at 100°C is 8.93 mm 2 / s and the viscosity index was 127 or more. High viscosity synthetic oil (A1) (poly-α-olefin (PAO), kinematic viscosity at 40°C: 396 mmHg 2 / s) (ExxonMobil, Sepctrasyn 40) Low viscosity synthetic oil (A2) (poly-α-olefin (PAO), kinematic viscosity at 40°C: 46.74 mm) 2 / s) (DURASYN168, manufactured by INEOS Corporation)

[0163] <Additives (dispersants)> Calcium sulfonate (Afton Chemical Company, HITEC614)

[0164] <Additives (rust inhibitors)> Barium sulfonate (King Industries, NA-SUL BSB) Sorbitan monooleate (Sorbitan sesquioleate, manufactured by Nippon Surfactant Industry Co., Ltd.)

[0165] <Additives (antioxidants)> Dioctyldiphenylamine (BASF, IRGANOX L57)

[0166] <Additives (extreme pressure agents)> Zinc dialkyldithiophosphate (ZnDTP) (Afton Chemical Company, HITEC7169) Molybdenum dithiocarbamate (MoDTC) (ADEKA, Sakuralube 600) Molybdenum dithiophosphate (MoDTP) (ADEKA, Sakuralube 300)

[0167] Example 1 (1) Synthesis of urea grease (b1) A base oil (A) obtained by mixing 10.0 parts by mass of base oil (A1) and 90.0 parts by mass of base oil (A2) based on the total amount of base oil (A) (100 parts by mass) was divided into three equal portions.

[0168] Next, 1 / 3 of the first base oil (A) was heated to 70°C, and 25.1 parts by mass of diphenylmethane-4,4'-diisocyanate (MDI) was added to the heated base oil based on the total amount (100 parts by mass) of the first base oil (A) to prepare solution α.

[0169] Furthermore, one-third of the second base oil (A) was heated to 70°C, and 23.1 parts by mass of octylamine and 5.4 parts by mass of stearinamine were added to the heated base oil, based on the total amount (100 parts by mass) of the second base oil (A), to prepare solution β.

[0170] Then, using the grease manufacturing apparatus 1 shown in FIG. 1, solution α heated to 70°C was introduced into the container body 2 at a flow rate of 150 L / h through the solution inlet pipe 4A, and solution β heated to 70°C was introduced into the container body 2 at a flow rate of 150 L / h through the solution inlet pipe 4B. While the rotor 3 was rotating, solution α and solution β were continuously introduced into the container body 2, thereby synthesizing a urea grease (b1) (grease base material).

[0171] The rotation speed of the rotor 3 of the grease manufacturing device 1 used was 8,000 rpm. The maximum shear rate (Max) was 10,500 s -1 The mixing was carried out with a ratio of the maximum shear rate (Max) to the minimum shear rate (Min) [Max / Min] set to 3.5. The molar ratio of octylamine to stearylamine used as raw materials was 90:10.

[0172] (2) Preparation of grease composition The urea grease (b1) synthesized above was allowed to cool naturally to room temperature, then transferred to a propeller-agitated atmospheric pressure reactor, heated at a temperature increase rate of 0.5 to 1.0°C per minute to the holding temperature listed in Table 1, and heat-treated at that holding temperature for 60 minutes. During this time, the urea grease was stirred at a rotation speed of 200 rpm inside the reactor. The additives listed in Table 1 were then added and stirred, and the mixture was subjected to roll mill processing under the following conditions to prepare a grease composition. <Roll mill processing conditions> The processing was carried out using a three-roll mill, S7x16 model RS400226, manufactured by Inoue Seisakusho Co., Ltd., with an inter-roll clearance of 5 to 20 μm.

[0173] [Examples 2 to 3, Comparative Examples 1 to 3] Grease compositions of Examples 2 and 3 and Comparative Examples 1 to 3 were prepared in the same manner as in Example 1, except that the holding temperature in the heat treatment conditions was set to the temperature shown in Table 1.

[0174] [Table 1]

[0175] <Evaluation results> The particle size of the urea-based thickener particles, the worked penetration of the grease composition, the dropping point of the grease composition, and the change in consistency in a roll stability test were measured for each of the grease compositions of Examples 1 to 3 and Comparative Examples 1 to 3. Grease compositions with a change in consistency of less than 60 in the roll stability test were evaluated as having good shear stability.

[0176] The results are shown in Table 2. In Table 2, for the results of the roll stability test, the values ​​in parentheses indicate the change in consistency in the roll stability test, and the values ​​to the left of the parentheses indicate the worked consistency after the test.

[0177] [Table 2]

[0178] The results shown in Tables 1 and 2 indicate that the grease compositions of Examples 1 to 3, which were obtained by holding a mixture of a base oil and a thickener having an arithmetic mean particle diameter of 2.0 μm or less on an area basis as measured by laser diffraction / scattering at a holding temperature of 155°C or higher and 185°C or lower for 30 minutes or longer and 120 minutes or shorter, had a consistency change of less than 60 in the roll stability test and had high shear stability. The grease composition of Example 3, which was held at 180°C, had a consistency change of 22 in the roll stability test and particularly high shear stability. [Industrial Applicability]

[0179] The present invention can be suitably used, for example, as a grease composition for railroad vehicle axles. [Explanation of symbols]

[0180] 1 grease manufacturing device, 2 container body, 3 rotor, 4 introduction section, 4A, 4B solution introduction pipe, 5 retention section, 6 first uneven section, 7 second uneven section, 8 discharge section, 9 first uneven section on container body side, 10 second uneven section on container body side, 11 discharge port, 12 rotating shaft, 13 first uneven section of rotor, 13A concave section, 13B convex section, 14 second uneven section of rotor, 15 scraper, A1, A2 gap

Claims

1. Contains a base oil and a thickener, The thickener has an arithmetic mean particle size on an area basis measured by a laser analysis / scattering method of 2.0 μm or less, A grease composition obtained by holding a mixture of the base oil and the thickener at a holding temperature of 155°C or higher and 185°C or lower for 30 minutes or longer and 120 minutes or shorter.

2. 2. The grease composition according to claim 1, wherein the holding temperature is 175°C or higher and 185°C or lower.

3. the thickener is a urea-based thickener that is a reaction product of an isocyanate compound and a monoamine, the monoamines are octylamine and stearylamine; 2. The grease composition according to claim 1, wherein the molar ratio of the octylamine to the stearylamine to be reacted with the isocyanate compound is 8:2 or more and 9.8:0.2 or less.

4. 2. The grease composition according to claim 1, wherein the consistency change measured in a roll stability test after applying shear under the specified conditions (80°C, 50 hours) using a testing machine in accordance with ASTM D1831 is 0 or more and less than +60.

5. A method for lubricating an axle with the grease composition according to any one of claims 1 to 4.

6. obtaining a mixture of base oil and thickener; holding the mixture at a holding temperature of 155°C or more and 185°C or less for 30 minutes or more and 120 minutes or less; Including, The method for producing a grease composition, wherein the thickener has an arithmetic mean particle diameter on an area basis measured by a laser analysis / scattering method of 2.0 μm or less.

7. The method for producing a grease composition according to claim 6, wherein the holding temperature is 175°C or higher and 185°C or lower.

8. In the step of obtaining a mixture of the base oil and the thickener, a shear rate of 10 ２ s －１ 7. The method for producing a grease composition according to claim 6, wherein the thickener is synthesized in the base oil while applying a shear force of at least 100 MPa to obtain the mixture in which particles of the thickener are dispersed in the base oil.

9. In the step of obtaining a mixture of the base oil and the thickener, the thickener is synthesized by reacting an isocyanate compound with a monoamine in the base oil; the monoamines are octylamine and stearylamine; 7. The method for producing a grease composition according to claim 6, wherein the molar ratio of the octylamine to the stearylamine to be reacted with the isocyanate compound is 8:2 or more and 9.8:0.2 or less.

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