Grease composition

Abstract

The present invention provides a grease composition that exhibits low torque properties and excellent shear stability in environments where water is present. [Solution] A grease composition containing a base oil, a diurea-based thickener, and a compound having at least one amide bond, wherein the mass ratio of the diurea-based thickener to the compound having at least one amide bond is 55-95:45-5.

Description

[Technical Field]

[0001] The present invention relates to a grease composition that exhibits excellent low torque properties and is suitable for use in environments where water may be present and where shear stress is applied. [Background technology]

[0002] In recent years, from the perspective of reducing power consumption, there has been a demand for higher efficiency in electrical equipment and mechanical parts used in various industries, including automobiles. Various measures are being considered, such as reducing the weight of parts, improving the structure, and improving grease. One important method for increasing efficiency is reducing the torque of bearings. Conventional methods for reducing the torque of grease include using a base oil with low kinematic viscosity (Non-Patent Literature 1), softening the grease, or using a specific thickener to reduce the stirring resistance of the grease. Regarding specific thickeners, among diurea thickeners, it is known that aliphatic diureas consisting of diphenylmethane diisocyanate (MDI) and octylamine are particularly effective in reducing torque (Non-Patent Literature 2). Lowering the kinematic viscosity of the base oil reduces the stirring resistance of the grease, thereby reducing torque. However, this can also lead to surface peeling due to insufficient oil film formation and a decrease in lubrication life due to evaporation, preventing the bearing from reaching its full lifespan. Furthermore, making the grease softer makes it more prone to leaking out, which also reduces lubrication life and prevents the bearing from reaching its full lifespan. In addition, although aliphatic diureas consisting of MDI and octylamine have low torque, it has been reported that they become fluid when tested under conditions of 10% water content using a testing machine (ASTM D 1831) that evaluates mechanical shear stability (Non-Patent Literature 3). The grease used in the axle bearings of automobiles is subject to water contamination from rainwater and rough roads, as well as shear stress, so it is required to have excellent water-saturated shear stability. The grease used in the work roll bearings of hot rolling mills in steelmaking facilities is subjected to large amounts of cooling water and strong shear forces, so it is required to have excellent water-saturated shear stability. The grease used in automotive rack and pinion gears, electric power steering worm gears, and worm gears in power window motors is subject to water contamination and shear stress due to weather conditions, and therefore requires excellent water-saturated shear stability. In addition to the above, grease used in parts that are subjected to shear and may be exposed to water contamination or high humidity is required to have excellent water-saturated shear stability. Various studies have been conducted to address this water resistance problem. For example, a grease composition has been reported that uses a diurea-based thickener and contains one metal salt compound selected from the group consisting of basic metal sulfonates, basic metal salicylates, and basic metal phenates, as well as an anhydride of alkenyl succinic acid (Patent Document 1). In addition, a grease composition has been reported that uses a component with excellent water content, such as barium sulfate, as a thickener (Patent Document 2). However, these conventional grease compositions are not sufficiently effective in terms of low torque and water-containing shear stability, and further improvements are needed. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2002-053884 [Patent Document 2] Japanese Patent Publication No. 2016-121336 [Non-patent literature]

[0004] [Non-Patent Document 1] Tribologist, Vol. 54, No. 9, 2009, pp. 580-585. [Non-Patent Document 2] Tribologist, Vol. 66, No. 8, 2021, pp. 646-655 [Non-Patent Document 3] Tribologist, Vol. 35, No. 5, 1990, pp. 343-348

Summary of the Invention

Problems to be Solved by the Invention

[0005] Therefore, an object of the present invention is to provide a grease composition having low torque properties and excellent shear stability in an environment where water is mixed in.

Means for Solving the Problems

[0006] As a result of intensive studies, the present inventors have found that the above problems can be solved by combining a compound having an amide bond in a grease composition containing a base oil and a diurea compound as a thickener. That is, the present invention has the following configurations. [1] A grease composition containing a base oil, a diurea-based thickener, and a compound having at least one amide bond, where the mass ratio of the diurea-based thickener to the compound having at least one amide bond is 55 to 95:45 to 5. [2] The grease composition according to [1], wherein the compound having at least one amide bond is a compound represented by formula (1), formula (2), or formula (3). Formula (1) JPEG2026089426000001.jpg4654 (In formula (1), R 1 , R 2 , and R 3 may be the same as or different from each other and are aliphatic hydrocarbon groups having 1 to 20 carbon atoms.) Formula (2) JPEG2026089426000002.jpg2554 (In formula (2), R 4 and R 6 may be the same as or different from each other and are aliphatic hydrocarbon groups having 8 to 20 carbon atoms or aliphatic hydrocarbon groups having 8 to 20 carbon atoms and having a hydroxyl group. R 5 is an aliphatic hydrocarbon group having 2 to 10 carbon atoms or an aromatic hydrocarbon group having 6 to 15 carbon atoms.) Formula (3) JPEG2026089426000003.jpg4374[3] The total mass of the diurea-based thickener and the compound having at least one amide bond is more than 10% by mass based on the total mass of the grease composition, the grease composition according to [1] or [2]. [4] The grease composition according to any one of [1] to [3], wherein the diurea-based thickener is a compound represented by the formula (I). R 1 -NHCONH-R 2 -NHCONH-R 3 (I) (In the formula (I), R 2 is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, and R 1 and R 3 may be the same or different from each other, and are a linear or branched alkyl group having 5 to 22 carbon atoms or a cyclohexyl group.) [5] The grease composition according to any one of [1] to [4], which is for a shaft of an automobile axle or for a shaft of iron-making equipment.

Advantages of the Invention

[0007] According to the present invention, it is possible to provide a grease composition having low torque properties and excellent shear stability in an environment where water is mixed.

Modes for Carrying Out the Invention

[0008] <Base Oil> In the present invention, the type of the base oil is not particularly limited. It may be a mineral oil, a synthetic oil, or a mixed oil thereof. Examples of the mineral oil include paraffinic mineral oil, naphthenic mineral oil, a mixed oil of paraffinic mineral oil and naphthenic mineral oil, refined paraffinic mineral oil, and refined naphthenic mineral oil. Examples of synthetic oils include synthetic hydrocarbon oils such as poly-α-olefins (PAO) and polybutene, ether-based synthetic oils such as alkyl diphenyl ethers and polypropylene glycol, ester-based synthetic oils such as diesters and polyol esters, silicone oils, and fluorinated oils. Synthetic oils may also be so-called biomass oils, which are produced using biological resources derived from plants and animals as raw materials. For example, biomass ester oils synthesized from various fatty acids and alcohols derived from vegetable oils, or biomass hydrocarbon oils using vegetable oils such as palm oil, corn oil, and soybean oil can also be used. The base oil preferably contains synthetic hydrocarbon oil, and more preferably contains poly-α-olefin. The inclusion of poly-α-olefin in the base oil results in superior low-torque properties. When the base oil contains poly-α-olefin, the poly-α-olefin content is preferably 40% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more, based on the total mass of the base oil. When the proportion of poly-α-olefin in the base oil is within the above range, traction is reduced and low torque performance is excellent. When the base oil is a mixture of mineral oil and synthetic oil, the mixing ratio is not particularly limited and can be selected as needed. Furthermore, the base oil may be a combination of two or more synthetic oils or mineral oils. For example, a high-viscosity or medium-viscosity synthetic oil may be used in combination with a low-viscosity synthetic oil, a high-viscosity or medium-viscosity mineral oil may be used in combination with a low-viscosity synthetic oil, a high-viscosity or medium-viscosity synthetic oil may be used in combination with a low-viscosity mineral oil, or a low-viscosity synthetic oil may be used in combination with a low-viscosity mineral oil. In this specification, a high-viscosity base oil is defined as having a kinematic viscosity of 150 to 2000 mmHg at 40°C. 2 This means that the kinematic viscosity is / s, and medium viscosity base oils have a kinematic viscosity of 40-150 mm at 40°C. 2 This means that the kinematic viscosity is / s, and low viscosity base oils have a kinematic viscosity of 5-40 mm at 40°C. 2 It means something that is / s. In the present invention, the kinematic viscosity of the entire base oil at 40°C is not particularly limited, but is between 15 and 200 mm.2 It is preferable that the value be / s, and the length is 15-150 mm. 2 It is more preferable that it be / s, 30-100mm 2 It is even more preferable that the kinematic viscosity is / s. Whether the base oil is a single type or a mixed base oil containing two or more types of base oils, it is preferable that the kinematic viscosity of the entire base oil at 40°C is within the range described above. Having the kinematic viscosity of the entire base oil at 40°C within this range results in excellent lubrication life and low torque properties. In this specification, the kinematic viscosity of the base oil is a value measured according to the method in accordance with JIS K2283. In the grease composition of the present invention, the base oil content is preferably 50 to 95% by mass, more preferably 60 to 95% by mass, and even more preferably 70 to 90% by mass, based on the total mass of the composition. Having a base oil content within this range results in excellent fluidity and leak resistance of the grease.

[0009] <Thickener> In the grease composition of the present invention, the diurea compound (diurea-based thickener) used as a thickener is a reaction product of an isocyanate and an amine. The isocyanate is preferably diphenylmethane diisocyanate (monomeric MDI), polymeric MDI which is a mixture of monomeric MDI and its polynuclear form, or tolylene diisocyanate (TDI), with diphenylmethane diisocyanate being more preferred. As the isocyanate, it is also possible to use biomass raw materials derived from plant-based oils and fats, or so-called biomass isocyanates produced using clean energy. The diurea compound is preferably a compound represented by formula (I). R 1 -NHCONH-R 2 -NHCONH-R 3 (I) In formula (I), R 2 The group is preferably a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, more preferably a diphenylmethane group or a triylene group, and even more preferably a diphenylmethane group. R1 and R 3 These may be the same or different from each other, and are a linear or branched alkyl group having 5 to 30 carbon atoms, an aryl group having 6 to 7 carbon atoms, or a cyclohexyl group. 1 and R 3 These may be the same or different from each other, and are preferably linear or branched alkyl groups or cyclohexyl groups having 5 to 30 carbon atoms, more preferably linear or branched alkyl groups or cyclohexyl groups having 5 to 22 carbon atoms, and even more preferably linear alkyl groups having 8 to 18 carbon atoms. The amount of thickener in the grease composition of the present invention varies depending on the type of thickener. The consistency of the grease composition of the present invention is preferably 220 to 385, more preferably 235 to 325, and even more preferably 240 to 300. In this specification, consistency refers to the 60-compound consistency measured according to JIS K 2220 7. The amount of thickener should be such that the consistency can be adjusted to the above range, and is preferably 2 to 25%, more preferably 10 to 20% by mass, and even more preferably 10 to 18% by mass, based on the total mass of the composition.

[0010] <Compounds having at least one amide bond> The grease composition of the present invention contains a compound having at least one amide bond. Hereinafter, a compound having at least one amide bond may simply be referred to as a compound having an amide bond. In the grease composition of the present invention, the mass ratio of the diurea-based thickener to the compound having an amide bond (diurea-based thickener: compound having an amide bond) is 55-95:45-5, preferably 60-90:40-10, and more preferably 65-88:35-12. By using the diurea-based thickener and the compound having an amide bond in such a mass ratio, the shear stability when water-containing is particularly excellent. When water is mixed into a grease composition containing a diurea compound as a thickener, the grease may soften when shear is applied while it is saturated with water, resulting in a failure to perform the desired function of the grease or making it more prone to leaking from the parts in which it is used. In the grease composition of the present invention, by using a diurea compound as a thickener and a compound having an amide bond in the above-mentioned mass ratio, the shear stability is improved even when water is mixed into the grease composition. The reason for this is not entirely clear, but it is presumed that in a specific mass ratio combination of the diurea compound and the compound having an amide bond, the diurea compound and the compound having an amide bond form hydrogen bonds with each other, changing the crystal properties of the diurea compound and contributing to improved shear stability when saturated with water. In the grease composition of the present invention, the compound having an amide bond appears to play a role as an auxiliary agent for the diurea compound used as a thickener. However, when the diurea compound is used in combination with a compound that forms hydrogen bonds but does not have an amide bond, the effect of improving shear stability when saturated with water is poor. In preparing the grease composition of the present invention, the compound having an amide bond may be added simultaneously with the reaction of the isocyanate and the amine to obtain the diurea compound, or it may be added after the reaction of the isocyanate and the amine to obtain the diurea compound. In the present invention, it is preferable to add the compound having an amide bond after the reaction of the isocyanate and the amine to obtain the diurea compound.

[0011] The compounds having an amide bond are preferably those represented by formula (1), formula (2), or formula (3). Formula (1) JPEG2026089426000004.jpg4654In formula (1), R 1 , R 2 , and R 3 These may be identical or different from each other, and are aliphatic hydrocarbon groups having 1 to 20 carbon atoms. 1 , R 2 , and R 3These may be the same or different from each other, and are preferably linear or branched alkyl groups having 1 to 20 carbon atoms, and more preferably linear or branched alkyl groups having 1 to 12 carbon atoms. Formula (2) JPEG2026089426000005.jpg2554In formula (2), R 4 and R 6 These may be the same or different from each other, and are aliphatic hydrocarbon groups having 8 to 20 carbon atoms, or aliphatic hydrocarbon groups having 8 to 20 carbon atoms that have a hydroxyl group. 4 and R 6 These may be the same or different from each other, and are preferably linear or branched alkyl groups having 12 to 18 carbon atoms, or linear or branched alkyl groups having 12 to 18 carbon atoms having a hydroxyl group, and more preferably linear alkyl groups having 12 to 18 carbon atoms having a hydroxyl group. 5 R is an aliphatic hydrocarbon group having 2 to 10 carbon atoms, or an aromatic hydrocarbon group having 6 to 15 carbon atoms. 5 It is preferably an aromatic hydrocarbon group having 6 to 15 carbon atoms, and more preferably an aromatic hydrocarbon group having 8 to 12 carbon atoms. Formula (3) JPEG2026089426000006.jpg4374

[0012] The compound having an amide bond is more preferably a compound having two or more amide bonds, and even more preferably a compound represented by formula (1) or formula (2). The compound having an amide bond is more preferably a compound represented by formula (4), formula (5), or formula (6), and is particularly preferably a compound represented by formula (5) or formula (6). Formula (4) JPEG2026089426000007.jpg24170 formula (5) JPEG2026089426000008.jpg30102 formula (6) JPEG2026089426000009.jpg3677

[0013] The content of compounds having amide bonds is preferably 0.1 to 10.0% by mass, more preferably 0.5 to 10.0% by mass, and even more preferably 0.5 to 5.0% by mass, based on the total mass of the grease composition. In the grease composition of the present invention, the total mass of the diurea-based thickener and the compound having an amide bond is preferably more than 10% by mass, more preferably 11.5% by mass or more, and even more preferably 13.0% by mass or more, based on the total mass of the grease composition. The upper limit is preferably 25.0% by mass or less, more preferably 21.0% by mass or less, and even more preferably 18.0% by mass or less. By including the diurea-based thickener and the compound having an amide bond within this range, the fluidity, leak resistance, and shear stability when water-containing of the grease are improved.

[0014] <Additives> The grease composition of the present invention may use any additives commonly used in greases as needed. Examples of additives include rust inhibitors, antioxidants, metal corrosion inhibitors, lubricity agents, wear inhibitors, extreme pressure agents, and solid lubricants. Rust inhibitors include amine-based rust inhibitors; carboxylic acids and their derivatives such as alkenyl succinic anhydride, alkenyl succinic acid esters, and alkenyl succinic acid half-esters; metal salts or amine salts of fatty acids, dibasic acids, naphthenic acid, lanolin fatty acid, alkenyl succinic acid, etc., such as Ca, Ba, Mg, Al, Zn, and Na; sulfonates such as Ba salts, Ca salts, Zn salts, and Na salts of sulfonic acid; sodium nitrite, sodium molybdate, etc.; and esters such as sorbitan triolate and sorbitan monooleate. Examples of antioxidants include amine antioxidants such as phenyl α-naphthylamine, alkylated phenyl α-naphthylamine, and alkylated diphenylamine; and phenol antioxidants such as hindered phenols such as 2,6-di-tert-butyl-p-cresol, pentaerythrityl tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate. Examples of metal corrosion inhibitors include benzotriazole or its derivatives, 2(3H)-benzothiazolethion, 2,5-bis(alkyldithio)-1,3,4-thiadiazole, and zinc oxide. Examples of oily agents include fatty acids and fatty acid esters. Examples of wear-resistant agents include phosphorus-based compounds such as amine phosphates and tricresyl phosphates. Examples of extreme pressure agents include sulfur compounds such as sulfurized oils and fats, sulfurized olefins, dibenzyl disulfide, and various polysulfides; sulfur-phosphorus compounds such as triphenyl phosphorothionate; organometallic compounds such as salts of dialkyldithiophosphate with Zn, Mo, Sb, Bi, etc., and salts of dialkyldithiocarbamic acid with Zn, Mo, Sb, Bi, etc.; and ashless dithiocarbamates and ashless dithiophosphotes. Examples of solid lubricants include molybdenum disulfide, graphite, carbon black, PTFE, and melamine cyanurate (MCA). The grease composition of the present invention preferably contains, as an additive, a rust inhibitor, an antioxidant, an anti-wear agent, or an extreme pressure agent, from the viewpoint that the parts used may be subjected to water, heat, and high loads. The antioxidant content is preferably 0.1 to 7.0% by mass, more preferably 0.5 to 5.0% by mass, and even more preferably 0.5 to 3.0% by mass, based on the total mass of the composition. Including antioxidants in such amounts results in good heat resistance. The total content of the additives is preferably 0.1 to 10% by mass, more preferably 0.5 to 8% by mass, and even more preferably 0.5 to 7% by mass, based on the total mass of the composition.

[0015] The grease composition of the present invention is suitable for parts that are subjected to shear and may be exposed to water contamination and high humidity. Examples of such parts include axle bearings of automobiles, bearings for steelmaking equipment, rack and pinion gears and worm gears of electric power steering systems in automobiles, worm gears in power window motors, bearings for machine tools, bearings for engine accessories and electrical components of automobiles, axle bearings of railway vehicles, bearings for main motors and gearboxes, bearings for fan motors and ventilation fans in air conditioners, and bearings for wind turbines. The grease composition of the present invention is particularly suitable for axle bearings of automobiles or bearings for steelmaking equipment, where a large amount of water may be present. [Examples]

[0016] [Preparation of test grease] The grease compositions of the examples and comparative examples were prepared using the components shown in the table below. Specifically, after reacting diphenylmethane diisocyanate (1 mole) with a predetermined amine (2 moles) in a base oil, a compound having at least one amide bond or a compound that forms hydrogen bonds but does not have an amide bond was added, and the mixture was stirred, heated, and cooled to obtain a base grease. Then, additional base oil was added and the mixture was kneaded using a three-roll mill until the consistency measured according to JIS K2220 7. was 260, thus preparing the grease compositions of Examples 1 to 12 and Comparative Examples 1 to 8. The grease compositions of Comparative Examples 9 and 10 were prepared using the same procedure as above, so that the amounts of base oil, thickener, and compound having at least one amide bond were as shown in Table 1. The kinematic viscosity of the base oil at 40°C was measured according to JIS K2283. Unless otherwise specified, the units of the numerical values ​​in the table represent mass % of the total mass of the grease composition. <Base oil> • Poly-alpha-olefin A:PAO10, kinematic viscosity at 40°C: 62.1 mm² 2 / s • Ester oil A: Kinematic viscosity at 40°C 76.5 mmHg 2 / s (Product name: Rikemaru R-886N, manufactured by Riken Vitamin Co., Ltd.) Ether oil A: Kinematic viscosity at 40°C: 100 mm² 2 / s (Product name: Moresco High Lube LB-100, manufactured by Moresco) • Mineral oil A: Kinematic viscosity at 40°C 100 mmHg 2 / s (Product name: Super Oil K-100, manufactured by ENEOS Corporation) <Thickener> • Diurea compound A: Aliphatic diurea obtained using octylamine as the amine. • Diurea compound B: Aliphatic diurea obtained using stearylamine as the amine. • Diurea compound C: Aliphatic diurea obtained by using octylamine and stearylamine as amines in a molar ratio of octylamine:stearylamine = 7:3 • Diurea compound D: A cyclohexylamine and stearylamine were used as amines in a molar ratio of cyclohexylamine:stearylamine = 3:7 to obtain an alicyclic aliphatic diurea. • Diurea compound E: Aromatic diurea obtained using p-toluidine as the amine. <Compounds having at least one amide bond> • N-lauroyl-L-glutamic acid dibutylamide (compound of formula (5), trade name: GP-1, manufactured by Ajinomoto Healthy Supply Co., Ltd.) • N-2-ethylhexanoyl lauroyl-L-glutamic acid dibutylamide (compound of formula (6), trade name: EB-21, manufactured by Ajinomoto Healthy Supply Co., Ltd.) • Aspartame (compound of formula (3), manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) • N,N'-Xylylene-bis-12-hydroxystearylamide (compound of formula (4), trade name: ITHOWAX J-700, manufactured by Ito Oil Co., Ltd.) <Compounds that form hydrogen bonds but do not have amide bonds> • 12-Hydroxystearic acid (Trade name: 12-HSA-I, manufactured by JAYANT AGRO-ORGANICS) • Stearyl alcohol (product name: NAA-45, manufactured by NOF Corporation)

[0017] [Testing Methods and Evaluation Methods] (1) Water-containing shear stability (water-containing roll stability test) The grease compositions of the examples and comparative examples were tested in accordance with ASTM D 1831, and the consistency after testing was measured. (Test conditions) Grease quantity: 45g Ion-exchanged water: 5g Rotation speed: 165 rpm Test temperature: 40℃ Exam duration: 168 hours (Judgment criteria) Consistency after testing is 350 or less: ◎ (Pass) Consistency after testing: Over 350 but less than 400: ○ (Pass) Consistency after testing is 400 or higher: × (Fail) (2) Low torque (bearing torque test) A grease composition was sealed into a rolling bearing, and the inner ring was rotated under the following conditions. The torque value applied to the outer ring of the bearing was measured 60 minutes after rotation. (Test conditions) Bearing type: Deep groove ball bearing 6204 Test temperature: Room temperature Rotation speed: 1000 rpm Test load: Axial load 400N, Radial load 0N Grease content: 1.0g (Judgment criteria) Bearing torque is 0.040 Nm or less: ◎ (Pass) Bearing torque between 0.040 Nm and 0.060 Nm: ○ (Pass) Bearing torque exceeding 0.060 Nm: × (Fail) (comprehensive evaluation) Passed all exams: ○ (Passed) Failing any of the exams: × (Fail)

[0018] Table 1

[0019] Table 2

Claims

1. It contains a base oil, a diurea-based thickener, and a compound having at least one amide bond. A grease composition in which the mass ratio of a diurea-based thickener to a compound having at least one amide bond is 55 to 95:45 to 5.

2. The grease composition according to claim 1, wherein the compound having at least one amide bond is a compound represented by formula (1), formula (2), or formula (3). Formula (1) (In formula (1), R 1 , R 2 , and R 3 These are aliphatic hydrocarbon groups having 1 to 20 carbon atoms, and may be identical or different from each other. Formula (2) (In formula (2), R 4 and R 6 These may be the same or different from each other, and are aliphatic hydrocarbon groups having 8 to 20 carbon atoms, or aliphatic hydrocarbon groups having 8 to 20 carbon atoms and a hydroxyl group. 5 (This refers to an aliphatic hydrocarbon group having 2 to 10 carbon atoms, or an aromatic hydrocarbon group having 6 to 15 carbon atoms.) Formula (3)

3. The grease composition according to claim 1, wherein the total mass of the diurea-based thickener and the compound having at least one amide bond is greater than 10% by mass based on the total mass of the grease composition.

4. The grease composition according to claim 1, wherein the diurea-based thickener is a compound represented by formula (I). R 1 -NHGNH-R 2 -NHGNH-R 3 (I) (In formula (I), R 2 R is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms. 1 and R 3 These may be identical or different, and are linear or branched alkyl groups or cyclohexyl groups having 5 to 22 carbon atoms.

5. A grease composition according to any one of claims 1 to 4, for use in axle bearings of automobiles or bearings for steelmaking equipment.

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