Grease composition

Abstract

To provide a grease composition excellent in low-temperature startability.SOLUTION: An embodiment of the present invention is a grease composition containing a thickener, a base oil, and a polymethacrylate. The polymethacrylate is a comb-shaped polymer having a side chain, and has an average side chain carbon number of 14 to 22. It is preferable that the thickener includes a urea-based thickener or a soap-based thickener. The number average molecular weight (Mn) of the polymethacrylate is preferably 30,000 to 90,000.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a grease composition. [Background technology]

[0002] With advances in mechanical technology, the environments in which grease compositions are used are changing dramatically year by year, creating a demand for grease compositions that maintain excellent performance over a wide range of temperatures.

[0003] Conventionally, the performance of grease compositions in high-temperature environments has been improved by using thickeners and high-performance antioxidants with excellent thermal stability, but the performance of grease compositions in low-temperature environments has not been sufficient.

[0004] If the performance of a grease composition in a low-temperature environment is insufficient, the fluidity of the grease composition may be insufficient in the low-temperature environment, resulting in poor lubrication such as increased torque and increased fretting wear. Specifically, in applications such as wind power generation, when the power generation system is installed in a cold region or operated in winter, the grease composition applied to bearings, etc. may not exhibit sufficient lubrication, causing fretting or reducing power generation efficiency due to excessive torque. Furthermore, in applications such as electric vehicles, since there is almost no heat source such as an engine, parts such as bearings start operating immediately from a low-temperature state, and the grease composition may not exhibit sufficient lubrication, causing excessive operating torque and increasing energy loss due to friction.

[0005] In addition to the above applications, articles that can be used outdoors are always likely to be exposed to low-temperature environments. Therefore, there is a demand for grease compositions that have sufficient performance in low-temperature environments in a wide range of fields, such as construction machinery, railway vehicles, ships, and aircraft.

[0006] Prior art document 1 discloses a grease composition that has excellent durability at high temperatures and good operability at low temperatures, and that is made by adding a thickener to a mixed base oil that combines specific perfluoropolyether oils in an amount that accounts for 15 to 50% by weight of the total amount of the composition. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-91464 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the grease compositions according to the prior art do not have sufficient low-temperature startability, and there is room for improvement.

[0009] Therefore, an object of the present invention is to provide a grease composition that is excellent in low-temperature startability. [Means for solving the problem]

[0010] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by using a specific component.

[0011] One aspect of the present invention is a grease composition containing a thickener, a base oil, and a polymethacrylate. The polymethacrylate is a comb polymer having side chains, and has an average of 14 to 22 carbon atoms in the side chains. The thickener preferably includes a urea-based thickener or a soap-based thickener. The number average molecular weight (Mn) of the polymethacrylate is preferably 30,000 to 90,000. The base oil is preferably a mineral oil alone, a mixed oil containing a mineral oil and a GTL, or a mixed oil containing a mineral oil and a synthetic hydrocarbon oil. The content of the non-mineral oil other than the mineral oil is preferably 40.00 mass % or less based on the total amount of the base oil. The content of the polymethacrylate is preferably 0.10 to 7.00 mass % based on the total mass of the grease composition. [Effects of the Invention]

[0012] According to the present invention, a novel grease composition having excellent low-temperature startability is provided. DETAILED DESCRIPTION OF THE INVENTION

[0013] In this specification, when an upper limit value and a lower limit value are separately described, it is considered that a numerical range combining any upper limit value and any lower limit value is substantially disclosed.

[0014] Unless otherwise specified, all measurements are performed at room temperature (25°C).

[0015] The components, physical properties / properties, production method, applications, etc. of the grease composition will be described below, but the present invention is not limited thereto.

[0016] <<<Ingredients>>> The grease composition contains a base oil, a thickener, and a polymethacrylate. The grease composition may also contain other components. Each component will be described below.

[0017] <<Base oil>> The base oil is not particularly limited as long as it is one that is commonly used in grease compositions.

[0018] As the base oil, mineral oil, synthetic hydrocarbon oil (synthetic oil), animal and vegetable oil, and mixed oils thereof can be used as appropriate. Specific examples of the base oil include base oils belonging to groups 1 to 5 in the API (American Petroleum Institute) base oil category.

[0019] Examples of Group 1 base oils include paraffinic mineral oils obtained by atmospherically distilling crude oil to obtain a lubricating oil fraction and then subjecting it to an appropriate combination of refining procedures such as solvent refining, hydrorefining, and dewaxing. Examples of Group 2 base oils include paraffinic mineral oils obtained by subjecting lubricating oil fractions obtained by atmospheric distillation of crude oil to an appropriate combination of refining methods such as hydrocracking and dewaxing. Group 2 base oils refined by hydrorefining methods such as the Gulf Process have a total sulfur content of less than 10 ppm and an aromatic content of 5% or less. Examples of Group 3 base oils include paraffinic mineral oils produced by advanced hydrorefining of lubricating oil fractions obtained by atmospheric distillation of crude oil, base oils refined by the ISODEWAX process, which converts and dewaxes the wax produced in the dewaxing process into isoparaffins, and base oils refined by the MobilWAX isomerization process.

[0020] Examples of synthetic hydrocarbon oils include polyolefins, diesters of dibasic acids such as dioctyl sebacate, polyol esters, alkylbenzenes, alkylnaphthalenes, esters, polyoxyalkylene glycols, polyoxyalkylene glycol esters, polyoxyalkylene glycol ethers, polyphenyl ethers, dialkyldiphenyl ethers, fluorine-containing compounds (perfluoropolyethers, fluorinated polyolefins, etc.), and silicones. The polyolefins include polymers of various olefins and hydrogenated products thereof. Any olefin may be used, including, for example, ethylene, propylene, butene, and α-olefins having 5 or more carbon atoms. When producing polyolefins, one of the above olefins may be used alone, or two or more may be used in combination. The synthetic hydrocarbon oil is preferably poly-α-olefin (PAO), a Group 4 base oil.

[0021] The base oil may be what is known as GTL (Gas-to-Liquid). GTL is a base oil synthesized by the Fischer-Tropsch process, a technology for converting natural gas into liquid fuel. Compared to mineral oil refined from crude oil, GTL has extremely low sulfur and aromatic content and an extremely high paraffin composition ratio, so it tends to have excellent oxidation stability and very small evaporation loss.

[0022] The base oil preferably contains a mineral oil. More specifically, the base oil is preferably any one of (1) a mineral oil alone, (2) a mixed oil containing a mineral oil and GTL, or (3) a mixed oil containing a mineral oil and a synthetic hydrocarbon oil.

[0023] When the base oil contains a non-mineral oil (a base oil other than mineral oil), the content of the non-mineral oil is preferably 40.00 mass% or less or 35.00 mass% or less, and is preferably 10.00 mass% or more or 20.00 mass% or more, relative to the total amount of the base oil.

[0024] The content of the base oil in the grease composition is, for example, 75.00 mass % or more, 80.00 mass % or more, or 85.00 mass % or more relative to the total amount of the grease composition.

[0025] The kinematic viscosity of the base oil at 40°C is 160.0 mm 2 / s or more, 170.0mm 2 / s or more, or 180.0 mm 2 / s or more, and 200.0 mm 2 / s or less, 195.0mm 2 / s or less, or 190.0 mm 2 The kinematic viscosity is preferably 1 / s or less. The kinematic viscosity is measured, for example, in accordance with JIS K 2283.

[0026] <<Polymethacrylate>> Polymethacrylates are comb polymers with side chains.

[0027] The average number of carbon atoms in the side chains of the polymethacrylate is preferably 14 or more, or 15 or more, and preferably 22 or less, 20 or less, or 18 or less. By using such a polymethacrylate, the behavior in oil becomes appropriate, and it is thought that the viscosity increase at low temperatures is reduced while the viscosity increase effect at high temperatures is sufficiently maintained, and low-temperature properties are easily improved.

[0028] The average number of carbon atoms in the side chains of polymethacrylate can be determined by structural analysis using NMR. For example, 13 Using each measurement mode of C-NMR, the average number of carbon atoms in the side chains of polymethacrylate is calculated by the following procedure. DEPT135 is used to confirm the chemical shift position of the methylene group (-CH2-) derived from the side chain and the chemical shift position of the methyl group (-CH3). DEPT90 is used to confirm the chemical shift position of tertiary carbons derived from side chains. Note that if no tertiary carbons are present, a deuterium solvent peak may be detected. Quantification of quaternary carbons derived from side chains is performed by comparing the spectrum obtained with DEPT135 with the spectrum obtained by the inverse gated decoupling method. Using these carbon-derived chemical shifts as reference, the number of carbon atoms derived from the side chains of polymethacrylate was quantified using POMMIE, and then rounded off to the nearest tenth to account for any error. The average number of carbon atoms in the side chain structure of polymethacrylate (average side chain carbon number) was calculated as the average of these carbon numbers.

[0029] The number average molecular weight (Mn) of the polymethacrylate is preferably 30,000 or more, 32,000 or more, or 34,000 or more, and preferably 90,000 or less, 80,000 or less, or 70,000 or less. By setting the number average molecular weight of the polymethacrylate within this range, a grease composition with excellent low-temperature properties is easily obtained. The number average molecular weight is measured as the number average molecular weight converted into polystyrene using, for example, a Shodex GPC-101 high-performance liquid chromatograph manufactured by Showa Denko K.K.

[0030] The content of polymethacrylate (comb-shaped polymethacrylate having an average side chain carbon number within a specified range) in the grease composition is preferably 0.10 mass% or more, 0.15 mass% or more, or 0.20 mass% or more, and is preferably 10.00 mass% or less, 7.00 mass% or less, 3.00 mass% or less, or 1.00 mass% or less, relative to the total amount of the grease composition.

[0031] The kinematic viscosity at 40°C when the base oil and polymer are mixed is 160.0 mm 2 / s or more, 170.0mm 2 / s or more, or 180.0 mm 2 / s or more, and 270.0 mm 2 / s or less, 260.0mm 2 / s or less, or 250.0 mm 2 / s or less is preferable.

[0032] <<Thickener>> The thickener preferably includes a urea-based thickener or a soap-based thickener.

[0033] Examples of urea-based thickeners include diurea-based thickeners, tetraurea-based thickeners, and other polyurea-based thickeners (such as urea urethane).

[0034] As an example, various raw materials used in the synthesis reaction of a urea-based thickener are listed below.

[0035] The urea-based thickener is synthesized from, for example, an isocyanate-based compound such as diisocyanate and an amine-based compound such as a primary amine (primary amine, primary diamine, etc.). Furthermore, the raw material of the urea-based thickener may contain an alcohol-based compound such as monoalcohol.

[0036] Examples of diisocyanates include aliphatic diisocyanates, alicyclic diisocyanates, aromatic diisocyanates, etc. More specific examples include 4,4'-diphenylmethane diisocyanate (MDI), tolylene diisocyanate (TDI), naphthalene diisocyanate, p-phenylene diisocyanate, trans-1,4-cyclohexane diisocyanate (CHDI), 1,3-bis-(isocyanatomethyl-benzene), 4,4'-dicyclohexylmethane diisocyanate (H12MDI), 1,3-bis-(isocyanatomethyl)-cyclohexane (H6XDI), hexamethylene diisocyanate (HDI), 3-isocyanatomethyl-cyclohexane (H6XDI ... Examples include trimethyl-3,3,5'-trimethylcyclohexyl isocyanate (IPDI), phenylene diisocyanate, m-tetramethylxylene diisocyanate (m-TMXDI), p-tetramethylxylene diisocyanate (p-TMXDI), and in particular 4,4'-diphenylmethane diisocyanate (MDI), tolylene diisocyanate (TDI), trans-1,4-cyclohexane diisocyanate (CHDI), and 4,4'-dicyclohexylmethane diisocyanate (H12MDI).

[0037] The primary monoamine may be an aliphatic, alicyclic, or aromatic monoamine. Here, the aliphatic amine may be a saturated or unsaturated C8 to C24 aliphatic amine, branched or linear. Examples of the monoamine include octylamine, decylamine, dodecylamine, tetradecylamine, hexadecylamine, octadecylamine, oleylamine, aniline, p-toluidine, and cyclohexylamine.

[0038] Examples of primary diamines include aliphatic, alicyclic, and aromatic diamines, such as C2 to C12 diamines, including aliphatic diamines such as ethylenediamine, trimethylenediamine, tetramethylenediamine, hexamethylenediamine, octamethylenediamine, and decamethylenediamine, alicyclic diamines such as diaminocyclohexane, and aromatic diamines such as phenylenediamine, benzidine, diaminostilbene, and tolidine.

[0039] Examples of monoalcohols include aliphatic, alicyclic, and aromatic alcohols. The aliphatic alcohols used herein are saturated or unsaturated C8 to C24 aliphatic alcohols, both branched and linear. Specific examples include octyl alcohol, decyl alcohol, dodecyl alcohol, tetradecyl alcohol, hexadecyl alcohol, octadecyl alcohol, and oleyl alcohol. Examples of alicyclic alcohols include cyclohexyl alcohol. Examples of aromatic alcohols include benzyl alcohol, salicylic alcohol, phenethyl alcohol, cinnamyl alcohol, and hydrocinnamyl alcohol.

[0040] Soap-based thickeners are metal salts of fatty acids.

[0041] Examples of fatty acids constituting the soap-based thickener include butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, capric acid, lauric acid, myristic acid, pentadecylic acid, palmitic acid, margaric acid, stearic acid, crotonic acid, myristoleic acid, palmitoleic acid, sapienic acid, oleic acid, linoleic acid, linolenic acid, pinoleic acid, eleostearic acid, stearidonic acid, bosseopentaenoic acid, etc. These may be used alone or in combination.

[0042] Examples of metal elements constituting the soap-based thickener include alkali metals such as lithium, sodium, potassium, rubidium, and cesium; beryllium; magnesium; alkaline earth metals such as calcium, strontium, and barium; aluminum; and zinc. These may be used alone or in combination. The metal element is preferably an alkali metal, and more preferably lithium.

[0043] In the grease composition, the total content of the urea-based thickener and the soap-based thickener is preferably 1.00 mass% or more, 3.00 mass% or more, or 5.00 mass% or more, and is preferably 20.00 mass% or less, 15.00 mass% or less, or 10.00 mass% or less, based on the total grease composition.

[0044] <<Other ingredients>> Other components include additives such as antioxidants, rust inhibitors, oiliness agents, extreme pressure agents, anti-wear agents, solid lubricants, metal deactivators, polymers, metal detergents, non-metal detergents, and colorants.

[0045] The content of other components in the grease composition may be 20.00% by mass or less, 15.00% by mass or less, 10.00% by mass or less, or 5.00% by mass or less, based on the total amount of the grease composition.

[0046] <<<Quality / Property>>> <<Low temperature fluidity (strain amount)>> The amount of strain (low-temperature fluidity) of the grease composition at -20°C when the loss tangent (tanδ) is 1 is preferably 12.0% or less, 8.0% or less, 6.0% or less, 5.0% or less, 4.5% or less, 4.0% or less, 3.5% or less, or 3.0% or less. The amount of strain when the loss tangent (tanδ) is 1 is measured according to the following measurement procedure. (Measurement procedure) A dynamic viscoelasticity test is carried out under the conditions below to determine the amount of strain at which the loss tangent (tanδ) becomes 1. More specifically, the grease composition to be evaluated is sandwiched between the upper and lower plates of a dynamic viscoelasticity measuring device, and the upper plate is moved under the conditions below to measure the storage shear modulus G' and the loss shear modulus G''. The loss tangent (tanδ) is calculated using the following formula (1), and the amount of strain at which the loss tangent (tanδ) becomes 1 is evaluated as low-temperature fluidity. (Formula 1) Loss tangent: tanδ=G'' / G' G'' Loss modulus G' Storage modulus (Measurement conditions) Dynamic viscoelasticity measuring device: Rheometer DHR-2 (manufactured by TA-Instruments) Plate: φ25mm parallel plate Gap between plates: 0.1mm Temperature: -20℃ Measurement frequency: 1Hz Strain amount: 0.01 to 100.0%

[0047] <<Consistency>> The grease composition preferably has a consistency (worked consistency) of 175 to 475, 220 to 430, 265 to 385, or 265 to 340. The consistency is measured in accordance with JIS K 2220 7.

[0048] <<Low temperature torque (low temperature startability)>> The low-temperature torque (starting fluidity) of the grease composition at -20°C is preferably 60.00 mN·m or less, 55.00 mN·m or less, or 50.00 mN·m or less. With the low-temperature torque in this range, stable operation can be maintained even at low temperatures. The low-temperature torque (low-temperature starting performance) was measured according to the following measurement procedure. (Measurement procedure) Torque was measured by a test carried out under the following conditions. More specifically, a gap (0.1 mm) was set between the upper rotating plate and the lower fixed plate of the torque measuring device, and each grease composition was sandwiched between the gap and held in an environment of -20°C. After that, the shear rate was increased to 10 s -1 Under these conditions, measure the torque at startup. (Measurement conditions) Torque measurement device: Rheometer DHR-2 (manufactured by TA-Instruments) Plate: φ25mm parallel plate Gap between plates: 0.1mm Temperature: -20℃ Shear rate during measurement: 10 s -1 Low temperature torque reading: The maximum value read during 1 to 5 seconds from the start of measurement is used.

[0049] <<<Manufacturing method>>> As a method for producing the grease composition according to the present disclosure, a conventionally known method for producing a grease composition can be applied.

[0050] Examples of methods for producing the grease composition include a method in which a base oil, a thickener, and other ingredients are placed in a grease production vessel, stirred, and then homogenized using a disperser (e.g., a three-roll mill, etc.).

[0051] It is also possible to produce a grease composition by mixing a base oil, fatty acids and basic metal components (such as sodium hydroxide or lithium hydroxide) that are raw materials for the thickener, and other components in a grease production vessel, generating the thickener through a saponification reaction in the vessel, and then performing dehydration and homogenization by heating.

[0052] <<<Usage>>> The grease composition according to the present disclosure is applicable to a wide range of applications. The grease composition according to the present disclosure can be used for machinery, bearings, gears, and the like, and can also exhibit excellent performance under more severe conditions, particularly low-temperature environments. For example, in automobiles, the grease composition can be suitably used for lubricating various parts, such as engine peripherals such as starters, alternators, and various actuators, powertrains such as propeller shafts, constant velocity joints (CVJs), wheel bearings, and clutches, electric power steering (EPS), braking systems, ball joints, door hinges, handlebars, cooling fan motors, and brake expanders. Furthermore, the grease composition is also suitable for use in various high-load areas, such as construction machinery such as power shovels, bulldozers, and crane trucks, the steel industry, the paper industry, forestry machinery, agricultural machinery, chemical plants, power generation facilities, drying furnaces, copiers, railway vehicles, and threaded joints in seamless pipes. Other applications include hard disk bearings, plastic lubrication, and cartridge grease. [Example]

[0053] The grease composition according to the present invention will be described in detail below with reference to examples, but the present invention is not limited thereto in any way.

[0054] <<Raw materials>> <Base oil> Base oil A: Paraffinic mineral oil obtained by dewaxing solvent refining and belonging to Group 1 as classified by the American Petroleum Institute (API) (kinematic viscosity at 40°C: 99.82 mm 2 / s, viscosity index 98) and paraffinic mineral oil belonging to Group 1 (kinematic viscosity at 40°C 494.6 mm 2 / s, viscosity index 96) and naphthenic mineral oil belonging to Group 5 (kinematic viscosity at 40°C 521.3 mm 2 / s, viscosity index 5) in a mass ratio of 54%, 17%, and 29%. Base oil B: Paraffinic mineral oil belonging to Group 1, kinematic viscosity at 40°C: 494.6 mm 2 / s, viscosity index 96) and naphthenic mineral oil belonging to Group 5 (kinematic viscosity at 40°C 521.3 mm 2 / s, viscosity index 5) in a mass ratio of 60% to 40%. Base oil C: A GTL (gas-to-liquid) synthesized by the Fischer-Tropsch method, belonging to Group 3, with a kinematic viscosity of 44.02 mm at 40°C. 2 / s and a viscosity index of 140. Base oil D: A 1-decene-based polyalphaolefin obtained by hydrotreating a mixture of alphaolefins polymerized and oligomerized under acidic catalysis, belonging to Group 4, with a kinematic viscosity of 47.36 mm at 40°C. 2 / s and a viscosity index of 134.

[0055] <Comb-shaped polymethacrylate> As comb-type polymethacrylates, polymers A to H shown in Table 1 were prepared.

[0056] [Table 1]

[0057] Table 2 shows the kinematic viscosity (40°C) of the base oil alone and the kinematic viscosity (40°C) of the mixture of the base oil and polymethacrylate.

[0058] <<Preparation of grease composition>> Example 1 Diphenylmethane diisocyanate was reacted with a primary monoamine having 8 to 18 carbon atoms in base oil A to synthesize a diurea compound, and the mixture was further heated to 170°C with stirring to complete the reaction. The contents (mass%) of the diurea compound and base oil in the grease composition are as shown in Table 2. The mixture was then quickly cooled to 90°C, and a polymer was added in the blending ratio shown in Table 2. The mixture was stirred and mixed, and treated with a homogenizer to obtain a grease.

[0059] <Examples 2-11, Comparative Examples 1-4> Grease compositions according to Examples 2-11 and Comparative Examples 1-4 were prepared in the same manner as in Example 1, except that the base oil and polymethacrylate were changed to those shown in Table 2 (no polymethacrylate was used for Comparative Example 1) and the content (mass%) of each component in the grease composition was changed to the proportions shown in Table 2.

[0060] Example 12 Fatty acids and lithium hydroxide were saponified in base oil A to synthesize lithium soap, which was then dehydrated and heated to 220°C. The contents (mass%) of lithium soap and base oil in the grease composition are shown in Table 2. The mixture was then gradually cooled to 90°C, and polymers and additives were added in the blending ratios shown in Table 2. The mixture was then stirred and mixed, and treated with a homogenizer to obtain a grease.

[0061] <<Evaluation>> The grease compositions according to the examples and comparative examples were evaluated for low-temperature fluidity, worked penetration, and low-temperature startability according to the methods described above. The evaluation results are shown in Table 2.

[0062] [Table 2]

[0063] As described above, the grease composition according to the present invention is excellent in low-temperature starting performance and the like. [Industrial Applicability]

[0064] The grease composition according to the present invention has excellent low-temperature starting properties, and is therefore useful for application to devices and apparatuses that can be used in cold climates, and for application to electric vehicles.

Claims

1. Contains a thickener, a base oil, and a polymethacrylate, The polymethacrylate is a comb polymer having side chains, and the average number of carbon atoms in the side chains is 14 to 22.

2. The grease composition according to claim 1, wherein the thickener comprises a urea-based thickener or a soap-based thickener.

3. 2. The grease composition according to claim 1, wherein the polymethacrylate has a number average molecular weight (Mn) of 30,000 to 90,000.

4. 2. The grease composition according to claim 1, wherein the base oil is a mineral oil alone, a mixed oil containing a mineral oil and a GTL, or a mixed oil containing a mineral oil and a synthetic hydrocarbon oil.

5. 5. The grease composition according to claim 4, wherein the content of the non-mineral oil other than the mineral oil is 40.00 mass% or less based on the total amount of the base oil.

6. 2. The grease composition according to claim 1, wherein the content of the polymethacrylate is 0.10 to 7.00 mass % based on the total mass of the grease composition.

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