Grease composition

Abstract

To provide a grease composition having low torque as well as excellent shear stability in environments where water is present. This grease composition contains a base oil, a diurea thickener, and a compound having at least one amide bond. The mass ratio of the diurea thickener and the compound having at least one amide bond is 55-95:45-5.

Description

Grease composition

[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.

[0002] In recent years, from the perspective of reducing power consumption, there has been a demand for higher efficiency in electrical equipment and machine parts used in various industries, including automobiles. Various studies have been conducted on weight reduction of parts, structural improvements, and grease improvements. One important method for increasing efficiency is reducing bearing torque. Conventional methods for reducing grease torque 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, 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 and thus reduces torque. However, this can 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. Also, softening the grease makes it easier for the grease to leak out, which also reduces the lubrication life and prevents the bearing from reaching its full lifespan. Furthermore, although aliphatic diureas composed of MDI and octylamine have low torque, it has been reported that they became fluid when tested under conditions of 10% by mass moisture content using a testing machine (ASTM D 1831) for evaluating mechanical shear stability (Non-Patent Literature 3). Greases used in axle bearings of automobiles are subject to water contamination from rainwater and driving on rough roads, and are also subjected to shear, so excellent moisture shear stability is required. Greases used in work roll bearings of hot rolling mills in steelmaking facilities are exposed to large amounts of cooling water and are subjected to strong shear, so excellent moisture shear stability is required. Greases used in rack and pinion gears of automobiles, worm gears in electric power steering, and worm gears in power window motors are subject to water contamination depending on weather conditions and are subjected to shear, so excellent moisture shear stability is required. In addition to the above, greases used in parts that are subjected to shear and may be exposed to water contamination and high humidity are required to have excellent moisture shear stability. Various studies have been conducted to address these water resistance issues.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 cannot be said to be sufficiently effective in terms of low torque properties and water-containing shear stability, and further improvements are needed.

[0003] Japanese Patent Publication No. 2002-053884 Japanese Patent Publication No. 2016-121336

[0004] Tribologist, Vol. 54, No. 9, 2009, pp. 580-585; Tribologist, Vol. 66, No. 8, 2021, pp. 646-655; Tribologist, Vol. 35, No. 5, 1990, pp. 343-348.

[0005] Therefore, the object of the present invention is to provide a grease composition that has low torque properties and excellent shear stability in environments where water is present.

[0006] As a result of diligent research, the present inventors have found that the above problem 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 configuration: [1] 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 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) (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 R6 may be the same as or different from each other, and is an aliphatic hydrocarbon group having 8 to 20 carbon atoms or an aliphatic hydrocarbon group having 8 to 20 carbon atoms and 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) [3] The total mass of the diurea 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, and the grease composition according to [1] or [2]. [4] The grease composition according to any one of [1] to [3], wherein the diurea 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 as or different from each other, and is 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 used for an axle of an automobile or an axle of a steelmaking facility.

[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.

[0008] <Base Oil> In the present invention, the type of base oil is not particularly limited. It may be mineral oil, synthetic oil, or a mixture thereof. Examples of mineral oil include paraffinic mineral oil, naphthenic mineral oil, a mixture of paraffinic mineral oil and naphthenic mineral oil, refined paraffinic mineral oil, and refined naphthenic mineral oil. Examples of synthetic oil include synthetic hydrocarbon oils represented by poly-α-olefin (PAO) and polybutene, ether-based synthetic oils represented by alkyl diphenyl ether and polypropylene glycol, ester-based synthetic oils represented by diester and polyol ester, silicone oil, fluorinated oil, and various other synthetic oils. Synthetic oil may also be so-called biomass oil, which is produced using biological resources derived from plants and animals as raw materials. For example, biomass ester oil synthesized from various fatty acids and alcohols derived from vegetable oil, or biomass hydrocarbon oil using vegetable oils such as palm oil, corn oil, and soybean oil can 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, resulting in superior low torque properties. 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 has 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 to 150 mm at 40°C. 2This means that the kinematic viscosity is / s, and low viscosity base oils have a kinematic viscosity of 5 to 40 mm at 40°C. 2 This means that it is / s. In the present invention, the kinematic viscosity of the entire base oil at 40°C is not particularly limited, but is 15 to 200 mm. 2 It is preferable that the value be / s, and the value is 15 to 150 mm. 2 It is more preferable that the value be / s, and the range is 30 to 100 mm. 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 by a 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 the base oil content within this range results in excellent grease fluidity and leak resistance.

[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 (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). 1 -NHCONH-R 2 -NHCONH-R 3 (I) In equation (I), R 2The 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. 1 and R 3 These may be the same or different groups, and are linear or branched alkyl groups having 5 to 30 carbon atoms, aryl groups having 6 to 7 carbon atoms, or cyclohexyl groups. 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 content of the 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 means the 60-compound consistency measured according to JIS K 2220 7. The content of the thickener may be any amount that can adjust the consistency 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 thickener to the compound having an amide bond (diurea thickener: compound having an amide bond) is 55 to 95:45 to 5, preferably 60 to 90:40 to 10, and more preferably 65 to 88:35 to 12. By using a diurea thickener and a compound having an amide bond in such a mass ratio, the shear stability when water is present is particularly excellent. When water is mixed into a grease composition containing a diurea compound as a thickener, if shear is applied while water is present, the grease may soften, preventing the desired grease function from being performed, or it may easily leak out of the parts where the grease 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 good 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, which changes the crystalline properties of the diurea compound and contributes to the improvement of shear stability when water is present. 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. Note that 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 water is present is poor. In the preparation of the grease composition of the present invention, the compound having an amide bond may be added at the same time as when the diurea compound is obtained by reacting the isocyanate and the amine, or it may be added after the diurea compound has been obtained by reacting the isocyanate and the amine. In the present invention, it is preferable to add the compound having an amide bond after obtaining a diurea compound by reacting an isocyanate with an amine.

[0011] The compounds having an amide bond are preferably those represented by formula (1), formula (2), or formula (3). Formula (1) In 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 3 These 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) 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. 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)

[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 even more preferably a compound represented by formula (4), formula (5), or formula (6), and particularly preferably a compound represented by formula (5) or formula (6). Formula (4) Formula (5) Formula (6)

[0013] The content of the compound having an amide bond 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 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 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 further 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. Examples of 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 such as Ca, Ba, Mg, Al, Zn, and Na of fatty acids, dibasic acids, naphthenic acid, lanolin fatty acid, and alkenyl succinic acid; sulfonates such as Ba salt, Ca salt, Zn salt, and Na salt of sulfonic acid; sodium nitrite, sodium molybdate, etc.; and esters such as sorbitan trioleate and sorbitan monooleate. 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. Metal corrosion inhibitors include benzotriazole or its derivatives, 2(3H)-benzothiazole thione, 2,5-bis(alkyldithio)-1,3,4-thiadiazole, and zinc oxide. Oily agents include fatty acids and fatty acid esters. Anti-wear agents include phosphorus compounds such as amine phosphates and tricresyl phosphates. Examples of extreme pressure additives 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, and Bi, and salts of dialkyldithiocarbamic acid with Zn, Mo, Sb, and Bi; and ashless dithiocarbamates and ashless dithiophosphates. 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 content of the antioxidant 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 an antioxidant in such amounts provides good heat resistance. The total content of additives is preferably, for example, 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.

[0016] [Preparation of Test Greases] 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 mm 2 / s (Product name: Rikemar R-886N, manufactured by Riken Vitamin Co., Ltd.) Ether oil A: Kinematic viscosity at 40°C 100 mm 2 / s (Product name: Moresco High Lube LB-100, manufactured by Moresco) ・Mineral oil A: Kinematic viscosity at 40°C 100 mm 2 / s (Product name: Super Oil K-100, manufactured by ENEOS Corporation) <Thickener> - Diurea compound A: Aliphatic diurea-diurea compound obtained using octylamine as the amine B: Aliphatic diurea-diurea compound obtained using stearylamine as the amine C: Aliphatic diurea-diurea compound obtained using octylamine and stearylamine as amines in a molar ratio of octylamine:stearylamine = 7:3 D: Alicyclic aliphatic diurea-diurea compound obtained using cyclohexylamine and stearylamine as amines in a molar ratio of cyclohexylamine:stearylamine = 3:7 E: Aromatic diurea obtained using p-toluidine as the amine <Compound having at least one amide bond> - N-lauroyl-L-glutamic acid dibutylamide (compound of formula (5), product 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 (trade name: NAA-45, manufactured by NOF Corporation)

[0017] [Test Methods and Evaluation Methods] (1) Water-containing Shear Stability (Water-containing Roll Stability Test) For the grease compositions of the examples and comparative examples, tests were conducted in accordance with ASTM D 1831, and the consistency after the test was measured. (Test Conditions) Grease filling amount: 45 g Ion-exchanged water: 5 g Rotation speed: 165 rpm Test temperature: 40 °C Test time: 168 hours (Judgment Criteria) Consistency after the test is 350 or less: ◎ (Pass) Consistency after the test exceeds 350 and is less than 400: ○ (Pass) Consistency after the test is 400 or more: × (Fail) (2) Low Torque Property (Bearing Torque Test) The grease composition was filled into a rolling bearing, the inner ring was rotated under the following conditions, and the torque value applied to the outer ring of the bearing 60 minutes after rotation was measured. (Test Conditions) Bearing type: Deep groove ball bearing 6204 Test temperature: Room temperature Rotation speed: 1000 rpm Test load: Axial load 400 N, Radial load 0 N Grease filling amount: 1.0 g (Judgment Criteria) Bearing torque is 0.040 Nm or less: ◎ (Pass) Bearing torque exceeds 0.040 Nm and is 0.060 Nm or less: 〇 (Pass) Bearing torque exceeds 0.060 Nm: × (Fail) (Comprehensive Evaluation) All tests are passed: 〇 (Pass) Any one of the tests fails: × (Fail)

[0018]

[0019]

Claims

1. A grease composition comprising 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 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 is 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 urea-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 as or different from each other, and is a linear or branched alkyl group having 5 to 22 carbon atoms or a cyclohexyl group.) 5. A grease composition according to any one of claims 1 to 4, which is for use in axle bearings of automobiles or bearings for steelmaking equipment.

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