Grease composition and wheel bearing

Abstract

Provided are: a grease composition that improves surface starting point type detachment caused by insufficient oil film formation due to use of a base oil having low viscosity, can suppress fretting wear under minute vibration at a low temperature, and has low torque properties; and a wheel bearing in which the grease composition is sealed. This grease composition contains a base oil, a thickening agent, and an additive. The base oil is a mineral oil, a synthetic oil, or an oil mixture thereof. The kinematic viscosity of the base oil at 40°C is 18-60 mm2 / s. The additive contains a phosphite represented by formula (1) (in formula (1), R1 and R2 may be identical or different from each other, and each represent an alkyl group having 8-18 carbon atoms). The contained amount of the phosphite is 0.1-5.0 mass% based on the total mass of the composition.

Description

Grease composition and wheel bearings

[0001] The present invention relates to a grease composition that exhibits excellent peeling life due to surface-initiated peeling and fretting resistance at low temperatures, as well as low torque properties, and a wheel bearing containing the same.

[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, and various studies are being conducted, such as weight reduction of parts and structural improvements. One important method for increasing the efficiency of automobiles is to reduce the torque of the bearings in automobile wheels. Conventional methods for reducing the torque of grease include using a base oil with low kinematic viscosity (Non-Patent Literature 1) and softening the grease to reduce the stirring resistance of the grease. Lowering the kinematic viscosity of the base oil can reduce torque because it lowers the stirring resistance of the grease, but it can cause 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, automobiles are often transported by rail or truck, and during this transport, minute vibrations caused by rail joints and rough roads can occur, which can cause fretting wear on lubricated parts coated with grease. Particularly in low-temperature environments, the base oil of grease becomes less fluid, leading to insufficient grease flow into the lubricated area and making fretting wear more likely. Various studies have been conducted to address this problem. For example, Patent Document 1 discloses that, in addressing surface-initiated delamination, instead of using a base oil with high kinematic viscosity to form a sufficient oil film thickness, a grease composition using a diurea compound represented by the following formula as a thickener can effectively prevent direct contact between the lubricated surfaces and improve delamination resistance. 1 -NHCONH-R 2 -NHCONH-R 3 (In the formula, R 1 , R 3is a phenyl group and / or a cyclohexyl group, R 2 is a divalent hydrocarbon group having 6 to 15 carbon atoms, R 1 , R 3 the molar ratio of cyclohexyl groups to (cyclohexyl groups + phenyl groups) is 0.10 to 0.95. ) Further, as a countermeasure against surface-initiated flaking using additives, for example, Patent Document 2 discloses the use of oxides or carbonates of typical metals such as zinc oxide, sodium nitrite, sodium molybdate, sodium benzoate, sodium sebacate, and calcium carbonate. All of the above additives are solid additives, which increase the amount of solid components in the grease and cause an increase in stirring resistance, so that low torque properties cannot be sufficiently satisfied. As a grease composition excellent in fretting resistance, Patent Document 3 discloses a grease composition containing a thickener, a base oil, and an amine phosphate. However, these conventional grease compositions cannot be said to have sufficient effects on flaking resistance when a base oil with low kinematic viscosity is used for torque reduction and fretting resistance at low temperatures, and further improvement is required.

[0003] Japanese Patent Application Laid-Open No. 2008-222739, Japanese Patent Application Laid-Open No. 2013-35882, Japanese Patent Application Laid-Open No. 2014-118467

[0004] Hiroshi Ishikawa, "Technical Trends and Tribology of Hub Unit Bearings", Tribologist, Vol. 54, No. 9, 2009, pp. 580-585

[0005] An object of the present invention is to provide a grease composition that improves surface-initiated flaking caused by insufficient oil film formation due to the use of a low-viscosity base oil, can suppress fretting wear under micro-vibration at low temperatures, and has low torque properties. Another object of the present invention is to provide a wheel bearing in which the grease composition is enclosed.

[0006] As a result of intensive studies, the present inventors have found that the above problems can be solved by including a specific phosphite ester as an additive in a grease composition containing a base oil and a thickener. That is, the present invention has the following configurations. [1] A grease composition containing a base oil, a thickener, and an additive, wherein the base oil is a mineral oil, a synthetic oil, or a mixed oil thereof, and the kinematic viscosity of the base oil at 40°C is 18 to 60 mm 2 / s, and the additive comprises a phosphite ester represented by formula (1), (In formula (1), R 1 and R 2 may be the same or different from each other, and are each an alkyl group having 8 to 18 carbon atoms.) The grease composition, wherein the content of the phosphite ester is 0.1 to 5.0% by mass based on the total mass of the composition. [2] The grease composition according to [1], wherein the phosphite ester is at least one selected from the group consisting of dioleyl hydrogen phosphite, dilauryl hydrogen phosphite, and bis(2-ethylhexyl) hydrogen phosphite. [3] The grease composition according to [1] or [2], wherein the thickener is a diurea compound represented by formula (I). R 4 -NHCONH-R 3 -NHCONH-R 5 (I) (In formula (I), R 3 is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, R 4 and R 5 may be the same or different from each other, and are each an alkyl group having 6 to 30 carbon atoms, an aryl group having 6 or 7 carbon atoms, or a cyclohexyl group.) [4] In formula (I), R 4 and R 5 may be the same or different from each other, and are each an alkyl group having 6 to 30 carbon atoms or a cyclohexyl group, and R 4 and R 5In the grease composition according to [3], the mole number of alkyl groups having 6 to 30 carbon atoms is 10 to 100 mol% based on the total mole number of alkyl groups having 6 to 30 carbon atoms and cyclohexyl groups. [5] The grease composition according to any one of [1] to [4], further comprising a metal sulfonate organic salt represented by formula (2). [R 6 -SO3]2M (2) In formula (2), R 6 is an alkyl group, an alkenyl group, an alkylnaphthyl group, a dialkylnaphthyl group, an alkylphenyl group, or a petroleum high-boiling fraction residue; the alkyl or alkenyl is linear or branched, and has 2 to 22 carbon atoms; and M is Ca or Zn.) [6] The grease composition according to [5], wherein the content of the metal salt of the organic sulfonic acid is 0.1 to 10% by mass based on the total mass of the composition. [7] A wheel bearing enclosing the grease composition according to any one of [1] to [6].

[0007] According to the present invention, it is possible to provide a grease composition having low torque properties that improves surface-origin flaking caused by insufficient oil film formation due to the use of a low-viscosity base oil, and can suppress fretting wear under micro-vibration at low temperatures. Further, a wheel bearing enclosing the grease composition can be provided.

[0008] Figure 1 is a schematic diagram of a rolling four-ball test.

[0009] [Grease Composition] <Base Oil> The type of base oil used in the present invention is not particularly limited and may be mineral oil, synthetic oil, or a mixture of mineral oil and synthetic oil. 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 also be used. The base oil preferably contains synthetic hydrocarbon oil, and more preferably poly-α-olefin. The inclusion of poly-α-olefin in the base oil provides excellent low-temperature fluidity. Alternatively, the base oil may be a mixture of synthetic hydrocarbon oil and ester-based synthetic oil. The inclusion of synthetic hydrocarbon oil and ester-based synthetic oil provides excellent compatibility with sealing materials and heat resistance. 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. Even when the base oil is a mixture of poly-α-olefin and ester-based synthetic oil, the poly-α-olefin content is preferably within the above range. When the proportion of poly-α-olefin in the base oil is within the above range, low-temperature fluidity is improved, and low-temperature fretting resistance is excellent. When the base oil is a mixture of mineral oil and synthetic oil, the mixing ratio is not particularly limited. The mixing ratio can be selected as needed. When the base oil is a mixture of mineral oil and synthetic oil, the mineral oil content is preferably 50% by mass or less, based on the total mass of the base oil, from the viewpoint of low-temperature fluidity. The lower limit is not particularly limited, but is greater than 0% by mass and preferably 10% by mass or more.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. 2 This 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 this invention, the kinematic viscosity of the entire base oil at 40°C is 18 to 60 mm². 2 / s, 20-60 mm 2 It is preferable that it be / s, and 20 to 50 mm 2 It is more preferable that the kinematic viscosity is / s. Whether the base oil is a single type or a mixture of two or more types, 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 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. The base oil content in the grease composition of the present invention is preferably 60 to 95% by mass, more preferably 60 to 90% 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 ensures a sufficient amount of lubricating oil and provides excellent durability.

[0010] <Thickeners> The thickeners that can be used in the present invention are not particularly limited. Specifically, examples include soap-based thickeners represented by Li soap and complex Li soap, urea-based thickeners represented by diurea, inorganic thickeners represented by organic clay and silica, and organic thickeners represented by PTFE. In the present invention, it is preferable to use a diurea compound. A diurea compound is a reaction product of an isocyanate and an amine, and as the isocyanate, diphenylmethane diisocyanate (monomeric MDI), polymeric MDI which is a mixture of monomeric MDI and its polynuclear form, or tolylene diisocyanate (TDI) are preferred, and diphenylmethane diisocyanate is more preferred. As the isocyanate, it is also possible to use biomass raw materials derived from vegetable oils and fats, or so-called biomass isocyanates produced by clean energy. In the present invention, from the viewpoint of heat resistance, it is preferable to use a diurea compound represented by formula (I). R 4 -NHCONH-R 3 -NHCONH-R 5 (I) In equation (I), R 3 R is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, preferably a diphenylmethane group or a triylene group, and more preferably a diphenylmethane group. 4 and R 5 These may be the same or different groups, and are alkyl groups having 6 to 30 carbon atoms, aryl groups having 6 or 7 carbon atoms, or cyclohexyl groups. 4 and R 5 It is preferably an alkyl group or cyclohexyl group having 6 to 30 carbon atoms, R 4 and R 5 Both are alkyl groups with 6 to 30 carbon atoms (aliphatic diurea), or R 4 and R 5It is more preferable that one of the groups is an alkyl group having 6 to 30 carbon atoms and the other is a cyclohexyl group (alicyclic aliphatic diurea). As the alkyl group having 6 to 30 carbon atoms, a linear alkyl group having 8 to 20 carbon atoms is more preferable, a linear alkyl group having 8 to 18 carbon atoms is more preferable, and a linear alkyl group having 8 carbon atoms or a linear alkyl group having 18 carbon atoms is particularly preferable. As the aryl group having 6 or 7 carbon atoms, examples include a phenyl group and a tolyl group, with the phenyl group being preferred.

[0011] R 4 and R 5 When one of the groups is a cyclohexyl group, the other is preferably an alkyl group having 6 to 30 carbon atoms, and more preferably an alkyl group having 8 or 18 carbon atoms. Such diurea compounds (alicyclic aliphatic diureas) are so-called aliphatic diurea compounds (in formula (I), R) formed during the reaction of diisocyanate and monoamine. 4 and R 5 (In formula (I), R is a diurea compound in which all of the alkyl groups have 6 to 30 carbon atoms) and an alicyclic diurea compound (in formula (I), R 4 and R 5 (In formula (I), R is a cyclohexyl group in all diurea compounds) and alicyclic aliphatic diurea compounds (in formula (I), R 4 and R 5 It is a mixture of a diurea compound in which one of the atoms is an alkyl group having 6 to 30 carbon atoms and the other is a cyclohexyl group. Here, the diurea compound of formula (I) may be a mixture of compounds represented by the following formulas (I-1), (I-2), and (I-3). 4 -NHCONH-R 3 -NHCONH-R 4 (I-1) R 4 -NHCONH-R 3 -NHCONH-R 5 (I-2) R 5 -NHCONH-R 3 -NHCONH-R 5 (I-3) For example, in equation (I), R 4 R is an alkyl group having 6 to 30 carbon atoms, 5If is a cyclohexyl group, then in formulas (I-1), (I-2), and (I-3), R 3 R is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms. 4 R is an alkyl group having 6 to 30 carbon atoms. 5 is a cyclohexyl group. In such diurea compounds (alicyclic aliphatic diureas), the ratio of moles of C6-C30 alkyl groups to the total number of moles of C6-C30 alkyl groups and cyclohexyl groups [{(number of C6-C30 alkyl groups) / (number of C6-C30 alkyl groups + number of cyclohexyl groups)} × 100] is preferably 10-100 mol%, more preferably 10-80 mol%, and even more preferably 10-70 mol%. As the thickener of the present invention, alicyclic aliphatic diurea compounds or aliphatic diurea compounds are preferred, and alicyclic aliphatic diurea compounds are more preferred. In particular, in formula (I), R 4 and R 5 A diurea compound is preferred in which one of the members is a linear alkyl group having 18 carbon atoms and the other is a cyclohexyl group, and the ratio of the moles of the linear alkyl group having 18 carbon atoms to the total number of moles of the linear alkyl group having 18 carbon atoms and the cyclohexyl group is 10 to 30 mol%. Having the ratio of moles of the linear alkyl group having 18 carbon atoms in this range results in excellent peel resistance and low torque. From the viewpoint of low torque, the consistency of the grease composition of the present invention is preferably 220 to 350, more preferably 235 to 325, and even more preferably 240 to 315. In this specification, consistency means the 60-step blended consistency measured according to JIS K2220 7. The amount of thickener in the grease composition of the present invention varies depending on the type of thickener, but it should be an amount that can adjust the consistency to the above range, preferably 5 to 25% by mass, more preferably 8 to 20% by mass, and even more preferably 8 to 18% by mass, based on the total mass of the composition.

[0012] <Additives> The grease composition of the present invention contains a phosphite ester represented by formula (1). In formula (1), R 1and R 2 These are alkyl groups having 8 to 18 carbon atoms, which may be the same or different from each other. The alkyl groups having 8 to 18 carbon atoms may be linear or branched, but linear is preferred. Although not bound by any theory, it is believed that the grease composition of the present invention, by containing the phosphite ester represented by formula (1), forms a phosphate film on the metal contact surface of the lubricated part to which the grease is applied, and this film suppresses surface-initiated delamination and reduces fretting wear. The phosphite ester represented by formula (1) is preferably at least one selected from the group consisting of dioleyl hydrogen phosphite, dilauryl hydrogen phosphite, and bis(2-ethylhexyl) hydrogen phosphite. Among these, dioleyl hydrogen phosphite or bis(2-ethylhexyl) hydrogen phosphite is more preferred, and dioleyl hydrogen phosphite is even more preferred. The content of phosphite ester is 0.1 to 5.0% by mass, preferably 0.5 to 4.0% by mass, more preferably 0.5 to 3.0% by mass, and even more preferably 0.5 to 2.5% by mass, based on the total mass of the composition. Including phosphite ester within this range provides excellent fretting resistance.

[0013] The grease composition of the present invention preferably further contains an organic sulfonic acid metal salt represented by formula (2). [R 6 -SO3]2M (2) In formula (2), R 6The group is an alkyl group, an alkenyl group, an alkylnaphthyl group, a dialkylnaphthyl group, an alkylphenyl group, or a petroleum high-boiling fraction residue. The alkyl or alkenyl groups constituting these groups are linear or branched and have 2 to 22 carbon atoms. M is an alkaline earth metal or zinc, preferably calcium (Ca) or zinc (Zn). That is, the organic sulfonic acid metal salt is preferably a calcium salt of organic sulfonic acid or a zinc salt of organic sulfonic acid. By using a calcium salt of organic sulfonic acid or a zinc salt of organic sulfonic acid as the organic sulfonic acid metal salt, the peel resistance is further improved. Furthermore, it is believed that by including an organic sulfonic acid metal salt in addition to the phosphite ester represented by formula (1) as an additive in the grease composition of the present invention, the phosphate film formed on the contact surface by the phosphite ester represented by formula (1) becomes stronger, surface-initiated peeling is further suppressed, and fretting wear is further reduced. Examples of metal salts of organic sulfonic acid include calcium or zinc salts of alkylbenzenesulfonic acid, calcium or zinc salts of dinonylnaphthalenesulfonic acid, or highly basic salts thereof. Of these, the highly basic salt of the calcium salt of alkylbenzenesulfonic acid or the neutral salt of the zinc salt of dinonylnaphthalenesulfonic acid are preferred. The total base number (TBN) of the metal salt of organic sulfonic acid is preferably 0.1 to 500 mg KOH / g, more preferably 50 to 500 mg KOH / g for high basicity, and even more preferably 300 to 500 mg KOH / g from the viewpoint of peel resistance and rust prevention. In this specification, the base number is the value measured in accordance with JIS K 2501. The content of the metal salt of organic sulfonic acid is preferably 0.1 to 10.0% by mass, more preferably 0.5 to 7.0% by mass, and even more preferably 0.5 to 5.0% by mass, based on the total mass of the composition. The inclusion of organic sulfonic acid metal salts within this range provides excellent resistance to peeling and fretting.

[0014] <Other Additives> In addition to the phosphite ester represented by formula (1) and the organic sulfonic acid metal salt represented by formula (2) above, the grease composition of the present invention may further contain other additives. As for other additives, any additive commonly used in grease can be used as needed, and examples include rust inhibitors other than organic sulfonic acid metal salts, antioxidants, metal corrosion inhibitors, oiliness agents, and wear-resistant agents other than phosphite esters. Rust inhibitors: 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, Na, etc. of fatty acids, dibasic acids, naphthenic acid, lanolin fatty acid, alkenyl succinic acid; sulfonates; passivating agents such as sodium nitrite and sodium molybdate; esters and acids such as sorbitan trioleate and sorbitan monooleate. Antioxidants: Amine antioxidants: Phenyl α-naphthylamine, alkylated phenyl α-naphthylamine, alkylated diphenylamine, etc. Phenolic antioxidants: 2,6-di-tert-butyl-p-cresol, pentaerythrityl tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, etc. Corrosion inhibitors such as benzotriazole or its derivatives, 2(3H)-benzothiazole thion, 2,5-bis(alkyldithio)-1,3,4-thiadiazole, zinc oxide, etc. Oily agents such as fatty acids and fatty acid esters. Anti-wear agents such as sulfur compounds such as dibenzyl disulfide and various polysulfides. Sulfur-phosphorus compounds such as triphenylphosphorothionate. Organometallic compounds such as salts of dialkyldithiophosphate with Zn, Mo, Sb, Bi, etc., and salts of dialkyldithiocarbamic acid with Zn, Mo, Sb, Bi, etc. Others such as ashless dithiocarbamate and ashless dithiophosphorate. Of these, from the viewpoint that the bearing may be subjected to water, heat, and high loads, it is preferable to include rust inhibitors (preferably a mixture of fatty acid amine salts and zinc naphthenate), antioxidants (preferably amine antioxidants, more preferably alkylated diphenylamine), and / or anti-wear agents.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 other 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] [Wheel Bearings] The wheel bearings of the present invention are wheel bearings that contain the grease composition of the present invention. The wheel bearings are preferably ball bearings or roller bearings, and more preferably ball bearings. Wheel bearings containing the grease composition of the present invention exhibit excellent suppression of fretting wear under minute vibrations at low temperatures.

[0016] [Preparation of Test Greases] Grease compositions for the examples and comparative examples were prepared using the components shown in the table below. Specifically, a predetermined ratio of 2 moles of amine per 1 mole of diphenylmethane diisocyanate was reacted in a base oil, heated, cooled, and then kneaded using a three-roll mill to obtain a base grease. Additives were then added in the amounts shown in the table below, and base oil was further added to achieve the thickener amount shown in the table below to obtain the grease compositions of Examples 1 to 14 and Comparative Examples 1 to 6. All grease compositions were prepared so that the mixed consistency, measured according to the measurement method in accordance with JIS K2220 7., was 300. The kinematic viscosity of the base oil at 40°C was measured according to the measurement method in accordance with JIS K2283, and the base number was measured according to the measurement method in accordance with JIS K 2501. The base oil, thickener, and additives in the table are as follows. Unless otherwise specified, the numbers for the components in the table indicate the mass % of the total mass of the grease composition.

[0017] <Base Oil> Poly-alpha-olefin A: Kinematic viscosity at 40°C: 30 mm 2 / s Poly-α-olefin B: kinematic viscosity at 40°C 400 mm 2 / s • Mineral oil A: Kinematic viscosity at 40°C 40 mm 2 / s Ester oil A: kinematic viscosity 30 mm at 40°C2 / s <Thickeners> ・Thickener A: Alicyclic aliphatic diurea (molar ratio of cyclohexylamine to stearylamine is cyclohexylamine:stearylamine = 7:1) ・Thickener B: Alicyclic aliphatic diurea (molar ratio of cyclohexylamine to stearylamine is cyclohexylamine:stearylamine = 3:7) ・Thickener C: Aliphatic diurea (octylamine) ・Thickener D: Aliphatic diurea (stearylamine) <Phosphite esters> ・Phosphite ester A: Dioleyl hydrogen phosphite (Trade name: JP-218-OR, manufactured by Johoku Chemical Industry Co., Ltd.) ・Phosphite ester B: Bis(2-ethylhexyl) hydrogen phosphite (Trade name: JPE-208, manufactured by Johoku Chemical Industry Co., Ltd.) <Organosulfonic acid metal salts>・Ca sulfonate A: Calcium dodecylbenzenesulfonate (Trade name: Bryton C-400C, manufactured by LANXESS Solutions Ltd., base number 405 mg KOH / g) ・Ca sulfonate B: Calcium dinonylnaphthalenesulfonate (Trade name: NA-SUL 729, manufactured by KINGINDUSTRIES.INC, base number 0.26 mg KOH / g) ・Zinc sulfonate: Zinc dinonylnaphthalenesulfonate (Trade name: NA-SUL ZS-HT, manufactured by KINGINDUSTRIES.INC, base number 0.50 mg KOH / g) <Abrasion resistant agent> ・Tricresyl phosphate (TCP, manufactured by Daihachi Chemical Industry Co., Ltd.) ・Triphenyl phosphorothioate (IRGALUBE TPPT, manufactured by BASF) - Diphenylhydrogen phosphite (JP-260, manufactured by Johoku Chemical Industry Co., Ltd.) - Tertiary alkylamine-dimethyl phosphate (Vanlube 672, manufactured by Vanderbilt Chemicals, LLC)

[0018] [Test Method and Judgment] (1) Delamination resistance to surface-initiated delamination (Rolling 4-ball test) Three bearing steel balls with a diameter of 15 mm were prepared and placed in a cylindrical container with an inner diameter of 40 mm and a height of 14 mm, and the container was filled with approximately 20 g of test grease. As shown in Figure 1, one bearing steel ball with a diameter of 5 / 8 inch was placed in contact with these three steel balls and set in the testing machine. When a load was applied in the W direction in Figure 1 and the machine was rotated, the three lower steel balls rotated on their own axis while revolving around the earth. This was continued until delamination occurred. At this time, delamination occurred between the balls with the highest surface pressure. The lifespan was defined as the total number of contacts of the upper ball at the time delamination occurred. This was repeated 5 times to determine the L50 lifespan (the number of times at which 50% of the lifespan is reached). (Test conditions) Test steel balls: Grade 40 15 mm and Grade 200 5 / 8 inch bearing steel balls Test load: 250 kgf (5.6 GPa) Rotation speed: 1500 rpm Number of test repetitions: 5 (Judgment criteria) Total number of contacts 300 × 10 5 Rotation or better ◎ (Pass) 250 x 10 5 Rotation 300 x 10 5 Less than 10 rotations ○ (Pass) 250 x 10 5Less than rotation × (failure) (2) Fretting resistance at low temperatures (Fafnir test) The Fafnir test was performed according to the method in accordance with ASTM D 4170. Test grease was applied to the two sets of test thrust bearings described below, and the specified oscillating operation was performed to determine the amount of wear (mass reduction due to fretting wear). (Test conditions) Bearing: 51204 Thrust bearing load: 4000N (surface pressure: 1.9 GPa) Oscillation angle: ±3° Oscillation cycle: 3Hz Time: 12 hours Temperature: -30℃ Grease amount: 1.0g per bearing set Wear amount: Race mass reduction per bearing set (total mass reduction of test bearing races / 2) (Judgment criteria) Wear amount Less than 1.0mg ◎ (Pass) 1.0mg or more and less than 2.0mg ○ (Pass) 2.0mg or more × (Fail) (3) Low torque performance: Bearing torque test The grease composition was sealed in 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 30 minutes after rotation. (Test conditions) Bearing type: Angular contact ball bearing 7204B Test temperature: Room temperature Rotation speed: 1000 rpm Test load: Axial load 100 N Radial load 500 N Grease amount: 2.5 g (Judgment criteria) Bearing torque is 0.025 Nm or less ◎ (Pass) Bearing torque is greater than 0.025 Nm and 0.030 Nm or less ○ (Pass) Bearing torque is greater than 0.030 Nm × (Fail) (Overall evaluation) All tests passed ○ (Pass) Any of the tests failed × (Fail) The results are shown in Tables 1 and 2.

[0019]

[0020]

[0021] The greases of Examples 1 to 14 passed the rolling four-ball test, the Fafnir test, and the bearing torque test, demonstrating good results in low-temperature fretting resistance, peeling resistance, and low torque performance. In contrast, the grease compositions of Comparative Examples 1 and 2, which contained additives other than phosphite esters, showed poor low-temperature fretting resistance. Furthermore, the grease compositions of Comparative Examples 2 to 5, which contained phosphite esters other than the phosphite ester represented by formula (1) (diphenyl hydrogen phosphite, diethyl hydrogen phosphite) or tert-alkylamine-dimethyl phosphate, showed good low-temperature fretting resistance but poor peeling resistance. In addition, the kinematic viscosity of the base oil at 40°C was 70 mmHg. 2 The grease composition of Comparative Example 6, which was / s, had good peel resistance, but poor low-torque performance.

Claims

1. A grease composition containing a base oil, a thickener, and an additive, wherein the base oil is mineral oil, synthetic oil, or a mixture thereof, and the kinematic viscosity of the base oil at 40°C is 18 to 60 mmHg. 2 / s, and the additive contains a phosphite ester represented by formula (1), (In formula (1), R 1 and R 2 (These may be the same or different alkyl groups having 8 to 18 carbon atoms.) The grease composition wherein the content of the phosphite ester is 0.1 to 5.0% by mass, based on the total mass of the composition.

2. The grease composition according to claim 1, wherein the phosphite ester is at least one selected from the group consisting of dioleyl hydrogen phosphite, dilauryl hydrogen phosphite, and bis(2-ethylhexyl) hydrogen phosphite.

3. The grease composition according to claim 1, wherein the thickener is a diurea compound represented by formula (I): R 4 -NHCONH-R 3 -NHCONH-R 5   (I) (in formula (I), R 3 is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, R 4 and R 5 may be the same or different from each other, and are each an alkyl group having 6 to 30 carbon atoms, an aryl group having 6 or 7 carbon atoms, or a cyclohexyl group.) 4. In formula (I), R 4 and R 5 However, they may be the same or different, and are alkyl groups or cyclohexyl groups having 6 to 30 carbon atoms, R 4 and R 5 The grease composition according to claim 3, wherein the number of moles of alkyl groups having 6 to 30 carbon atoms relative to the total number of moles of alkyl groups having 6 to 30 carbon atoms and cyclohexyl groups is 10 to 100 mol%.

5. The grease composition according to claim 1, further comprising an organic sulfonic acid metal salt represented by formula (2). [R 6 -SO3]2M (2) (In formula (2), R 6 (where M is an alkyl group, alkenyl group, alkylnaphthyl group, dialkylnaphthyl group, alkylphenyl group, or petroleum high-boiling fraction residue, and the alkyl or alkenyl is linear or branched and has 2 to 22 carbon atoms. M is Ca or Zn.) 6. The grease composition according to claim 5, wherein the content of the metal salt of the organic sulfonic acid is 0.1 to 10% by mass, based on the total mass of the composition.

7. A wheel bearing containing the grease composition described in any one of claims 1 to 6.

Images