Grease composition and rolling bearings containing same

Abstract

PROBLEM TO BE SOLVED: To provide a grease composition which exhibits excellent friction and wear resistance characteristics and realizes a long service life even in high-temperature and high-speed-rotation environments. SOLUTION: A grease composition containing a synthetic hydrocarbon oil, a urea-based thickener, and an extreme pressure additive, in which the extreme pressure additive is at least one selected from the group consisting of alkenyl acid phosphates and trialkyl trithiophosphites and the grease composition is free from metal stearates and amide compounds.

Description

Grease composition and rolling bearing containing it

[0001] The present invention relates to a grease composition, a bearing containing the grease, and a motor equipped with the bearing.

[0002] In the field of grease and lubricant technology, load-bearing additives such as anti-wear agents and extreme pressure additives that adsorb to sliding surfaces and contribute to the formation of a strong protective film are used to improve resistance to wear, seizure, and flaking (peeling) in bearings and other applications to which they are applied. For example, in decoupler bearings and AC servo motor bearings, fretting wear is likely to occur on the rolling element surface and transfer surface due to the repeated minute reciprocating motion of the support shaft. Therefore, to improve fretting resistance, a lubricant composition has been proposed in which a metal stearate salt, a phosphate ester, and at least one selected from sulfonate-based metal salts and salicylate-based metal salts are added to the lubricant (Patent Document 1). Furthermore, a grease composition containing a diurea compound, an amide compound, and a thiophosphite compound has been proposed to improve resistance to flaking (peeling) that occurs during reciprocating sliding under various high loads (Patent Document 2).

[0003] Patent No. 6119438 Patent No. 7448359

[0004] In recent years, there has been a demand for grease compositions that can achieve friction and wear resistance even in high-temperature environments, in response to the miniaturization and high-speed rotation of bearings, as well as the heat generated from surrounding equipment associated with these processes. Furthermore, there is a demand for grease compositions that can enable long-term rotation and extend the lifespan of the bearings to which they are applied, not only in high-temperature but also high-speed environments.

[0005] The present invention aims to provide a grease composition that exhibits excellent friction and wear resistance characteristics and achieves a long service life even in high-temperature and high-speed rotation environments. Furthermore, the present invention aims to provide a rolling bearing equipped with the grease composition and a motor equipped with the same.

[0006] One aspect of the present invention is a grease composition containing a synthetic hydrocarbon oil, a urea-based thickener, and an extreme pressure additive, wherein the extreme pressure additive is at least one selected from the group consisting of alkenyl acid phosphates represented by the following formula (1) and trialkyltrithiophosphites represented by the following formula (2), (R １ -O) ｎ -P(=O)-(OH) ３－ｎ ...Formula (1) (R ２ -S) ３ -P...Formula (2) (In formula (1), R １ R represents an alkenyl group having 8 to 30 carbon atoms, and n represents 1 or 2. In formula (2), R ２ (wherein represents an alkyl group having 8 to 30 carbon atoms.) The grease composition relates to a grease composition that does not contain metal stearate salts and amide compounds. Furthermore, the present invention relates to a rolling bearing in which the grease composition is sealed, and a motor equipped with the rolling bearing.

[0007] This is a schematic diagram illustrating an example of the structure of a rolling bearing according to the present invention. This is a schematic diagram illustrating an example of the structure of a motor according to the present invention.

[0008] The inventors of this invention have investigated grease compositions containing extreme pressure additives to address the challenges of improving friction and wear resistance in high-temperature environments and extending the lifespan in high-speed rotation environments, particularly for grease compositions applied to rotating bearings. They have discovered for the first time that by incorporating specific extreme pressure additives such as alkenyl acid phosphates and trialkyltrithiophosphites, it is possible to achieve approximately twice the lifespan compared to compounds with similar structures. The lubricant compositions and grease compositions proposed in the aforementioned Patent Documents 1 and 2 aim to solve problems such as fretting wear and flaking (peeling) that occur during reciprocating sliding by forming a strong protective film by using metal stearate salts in combination, or by aiming for a synergistic thickening effect between amide compounds and urea grease. However, these documents do not discuss the rotational sliding (a form of sliding that rotates continuously in one direction) that is the subject of this invention. Furthermore, when lubricant compositions and the like disclosed in these documents use metal stearate salts and amide compounds as essential components, there are concerns that applying lubricant compositions and the like containing these to the rotating sliding bearings targeted by the present invention may result in deterioration of sound quality, increased torque fluctuations, and inability to form a stable oil film, leading to a shortened lifespan. The present invention will be described in detail below.

[0009] [Grease Composition] The grease composition according to the present invention comprises a synthetic hydrocarbon oil as a base oil, a urea-based thickener, and at least one extreme pressure additive selected from the group consisting of alkenyl acid phosphates and trialkyltrithiophosphites. The grease composition of the present invention will be described below.

[0010] <Base Oil> In the grease composition sealed in the rolling bearing according to this embodiment, a synthetic hydrocarbon oil is used as the base oil. Examples of the synthetic hydrocarbon oil include normal paraffin, isoparaffin, polybutene, polyisobutylene, 1-decene oligomer, and polyalphaolefins (PAOs) such as 1-decene and ethylene co-oligomer. The viscosity of the synthetic hydrocarbon oil used in the present invention is not particularly limited, but for example, the kinematic viscosity at 40°C is 20 to 150 mmHg.２ Those within the range of / s can be used.

[0011] In the grease composition of the present invention, within a range not impairing the effects of the present invention, base oils other than the above synthetic hydrocarbon oils, for example, synthetic oils such as ether-based synthetic oils and ester-based synthetic oils may be used in combination. However, since mineral oils have a lower viscosity index than the synthetic hydrocarbon oils used in the present invention, the change in viscosity accompanying temperature changes is large. That is, in a low-temperature environment, the increase in base oil viscosity is relatively large, leading to grease hardening, resulting in high torque and making it difficult for the bearing to rotate at high speed. Also, in a high-temperature environment, the decrease in base oil viscosity is relatively large, which may cause the oil film to become thin and reduce lubricity. Furthermore, mineral oils have a higher compatibility with additives than synthetic hydrocarbon oils, and there is a possibility that the effects of extreme pressure additives that interact with metals, etc., are difficult to obtain. From these viewpoints, it is desirable to avoid using mineral oils in combination.

[0012] The above base oil can be included, for example, at a ratio of 70% by mass or more based on the total mass of the grease composition of the present invention, and can be made to contain the above base oil at a ratio of 70% to 90% by mass based on the total mass of the grease composition.

[0013] <Thickener> In the grease composition of the present invention, a urea-based thickener is used as the thickener. Urea compounds are excellent in both heat resistance and water resistance, and particularly have good stability at high temperatures, so they are preferably used as thickeners in applications under high-temperature environments. As the urea-based thickener, urea compounds such as diurea compounds, triurea compounds, and polyurea compounds can be used. As these urea-based thickeners, conventionally known urea compounds can be used.

[0014] As an example of the diurea compound used in the urea-based thickener, a diurea compound represented by the following formula (3) can be mentioned. R ３ -NHCONH-R ４ -NHCONH-R ５ ... Formula (3) In the above formula (3), R ３ and R ５Each independently represents a monovalent aliphatic hydrocarbon group, a monovalent alicyclic hydrocarbon group, or a monovalent aromatic hydrocarbon group, and R ３ and R ５ At least one of them represents a monovalent aliphatic hydrocarbon group or a monovalent alicyclic hydrocarbon group. For example, R ３ and R ５ One of them may represent an aliphatic hydrocarbon group, and the other may represent a monovalent alicyclic hydrocarbon group or a monovalent aromatic hydrocarbon group, or R ３ and R ５ One of them may represent an aliphatic hydrocarbon group, and the other may represent a monovalent aromatic hydrocarbon group. ４ represents a divalent aromatic hydrocarbon group. Note that the diurea compound represented by formula (3) may also be in the form of a mixture of multiple types, for example, R ３ and R ５ Compounds in which both represent a monovalent aliphatic hydrocarbon group, and R ３ and R ５ Compounds in which both represent monovalent aromatic hydrocarbon groups, and R ３ and R ５ This can be a mixture of compounds in which one of the compounds represents an aliphatic hydrocarbon group and the other represents a monovalent aromatic hydrocarbon group.

[0015] Examples of the monovalent aliphatic hydrocarbon group include linear or branched saturated or unsaturated alkyl groups having 6 to 26 carbon atoms. Examples of the monovalent alicyclic hydrocarbon group include cycloalkyl groups having 5 to 12 carbon atoms. Examples of the aromatic hydrocarbon group include monovalent or divalent aromatic hydrocarbon groups having 6 to 20 carbon atoms.

[0016] Urea compounds used as urea thickeners can be synthesized using amine compounds and isocyanate compounds. Examples of amine compounds include aliphatic amines such as hexylamine, octylamine, dodecylamine, hexadecylamine, octadecylamine (stearylamine), behenylamine, and oleylamine, as well as alicyclic amines such as cyclohexylamine, and aromatic amines such as aniline, p-toluidine, and ethoxyphenylamine. Two or more of these amine compounds can be used in combination when synthesizing urea compounds. Examples of isocyanate compounds include aromatic diisocyanates such as phenylenediisocyanate, tolylenediisocyanate (TDI), diphenyldiisocyanate, diphenylmethanediisocyanate (MDI), and dimethylbiphenyldiisocyanate (TODI), and aliphatic diisocyanates such as octadecanediisocyanate, decanediisocyanate, and hexanediisocyanate. Furthermore, when aromatic diurea compounds obtained using aromatic monoamines and aromatic diisocyanates as amine raw materials are used as urea-based thickeners, there is a risk of abnormal noise generation, so their use should be carefully considered.

[0017] The above-mentioned urea-based thickener (urea compound) can be blended in such an amount as, for example, 10 to 20% by mass relative to the total amount of the grease composition of the present invention.

[0018] <Extreme pressure additive (compounds represented by formulas (1) and (2))> In the grease composition of the present invention, at least one selected from the group consisting of alkenyl acid phosphate represented by the following formula (1) and trialkyltrithiophospite represented by the following formula (2) is used as an extreme pressure additive. (R １ -O) ｎ -P(=O)-(OH) ３－ｎ ...Formula (1) In formula (1), R １ (R) represents an alkenyl group having 8 to 30 carbon atoms, and n represents 1 or 2. ２ -S) ３ -P...Formula (2) In formula (2), R２ This represents an alkyl group having 8 to 30 carbon atoms.

[0019] The above R １ The alkenyl group having 8 to 30 carbon atoms, represented by , may be linear or branched. Examples include octenyl, nonenyl, decenyl, undecenyl, dodecenyl, tridecenyl, tetradecenyl, pentadecenyl, hexadecenyl, heptadecenyl, octadecenyl, nonadecenyl, eicocenyl, henicocenyl, heneicocenyl, dococenyl, tricoesenyl, tetracocenyl, pentacocenyl, hexacocenyl, heptacocenyl, octacocenyl, nonacocenyl, and triacontenyl groups. Furthermore, the position of the unsaturated bond (double bond) in the alkenyl group is not particularly limited. Among these alkenyl groups, examples include the octenyl group, nonenyl group, decenyl group, or octadecenyl group such as the oleyl group, with the oleyl group being particularly noteworthy.

[0020] Also, n represents 1 or 2, and if n is 2, multiple R １ They may be the same or different. They may also be a mixture.

[0021] The above R ２ The alkyl group having 8 to 30 carbon atoms, represented by , may be linear or branched, and examples include the octyl group, nonyl group, decyl group, undecyl group, dodecyl group (lauryl group), tridecyl group, tetradecyl group (myristyl group), pentadecyl group, hexadecyl group (palmityl group), heptadecyl group, octadecyl group (stearyl group), nonadecyl group, eicosyl group, henicosyl group, heneicosyl group, docosyl group, tricosyl group, tetracosyl group, pentacosyl group, hexacosyl group, heptacosyl group, octacosyl group, nonacosyl group, and triacontyl group. Among these alkyl groups, examples include the octyl group, nonyl group, decyl group, lauryl group, palmityl group, stearyl group, etc., and among these, the lauryl group is particularly noteworthy.

[0022] Among these, oleyl acid phosphate can be mentioned as the alkenyl acid phosphate, and trilauryl trithiophosphite can be mentioned as the trialkyl trithiophosphite.

[0023] The specific extreme pressure additives represented by the above formulas (1) and (2) can be blended so as to be, for example, 0.1 to 10% by mass based on the total amount of the grease composition of the present invention.

[0024] In the grease composition of the present invention, extreme pressure additives other than the above usually used in grease compositions may be used within a range not impairing the effects of the present invention. For example, phosphorus compounds such as phosphate esters, phosphite esters, and phosphate ester amine salts other than the above, sulfur compounds such as sulfides and disulfides, chlorine compounds such as chlorinated paraffins and chlorinated diphenyls, and metal salts of sulfur compounds such as zinc dialkyldithiophosphate and molybdenum dialkyldithiocarbamate can be mentioned.

[0025] The grease composition of the present invention may contain other components described later in addition to the above components. However, when it is in a form containing a metal stearate or an amide compound listed in Patent Document 1 or Patent Document 2, it is not desirable because it may cause a reduction in life.

[0026] <Other Additives> The grease composition of the present invention can contain additives usually used in grease compositions as necessary within a range not impairing the effects of the present invention. Examples of such additives include antioxidants, metal deactivators, friction inhibitors (antiwear agents), rust preventives, oiliness improvers, viscosity index improvers, thickeners, etc. (however, the above-mentioned metal stearates and amide compounds are not included). When these other additives are included, the addition amount (total amount) is usually 0.1 to 10% by mass based on the total amount of the grease composition.

[0027] For example, the above antioxidants include octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, pentaerythritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], 2,4-bis-(n-octylthio)-6-(4-hydroxy-3,5-di-t-butylanilino)-1,3,5-triazine, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, triethylene glycol-bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate], 1,6-hexanediol-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], 2,2- Examples of antioxidants include hindered phenol-based antioxidants such as o-diethylenebis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] and N,N'-hexamethylenebis(3,5-di-t-butyl-4-hydroxyhydrocinnamide)octyl-3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid; other phenol-based antioxidants such as 2,6-di-t-butyl-4-methylphenol and 4,4-methylenebis(2,6-di-t-butylphenol); and amine-based antioxidants such as diphenylamine, alkylated diphenylamine, triphenylamine, hindered amine, phenyl-α-naphthylamine, alkylated phenyl-α-naphthylamine, phenothiazine, and alkylated phenothiazine.

[0028] Examples of metal deactivators include benzotriazole compounds such as benzotriazole, 1-[N,N-bis(2-ethylhexyl)aminomethyl]-benzotriazole, and 1-[N,N-bis(2-ethylhexyl)aminomethyl]-4-methylbenzotriazole; thiadiazole compounds such as thiadiazole, 2-mercaptothiadiazole, and 2,5-bis(alkyldithio)-1,3,4-thiadiazole; benzimidazole compounds such as benzimidazole, 2-mercaptobenzimidazole, and 2-(decyldithio)-benzimidazole; and sodium nitrite.

[0029] Other examples of friction inhibitors (wear-resistant agents) include tricresyl phosphates and polymer esters. Examples of polymer esters include esters of aliphatic monocarboxylic acids and dicarboxylic acids with polyhydric alcohols. Specific examples of polymer esters include, but are not limited to, the PRIOLUBE® series manufactured by Croda Japan Co., Ltd.

[0030] The grease composition of the present invention can be obtained by blending the aforementioned synthetic hydrocarbon oil, a urea-based thickener, at least one extreme pressure additive selected from the group consisting of alkenyl acid phosphate and trialkyltrithiophosphite, and optionally other additives. Alternatively, for example, a grease composition can be obtained by blending a urea-based grease (base grease) consisting of the aforementioned synthetic hydrocarbon oil and urea-based thickener with at least one extreme pressure additive selected from the group consisting of alkenyl acid phosphate and trialkyltrithiophosphite, and optionally other additives. Typically, the content of the thickener relative to the base grease is about 10 to 30% by mass, and for example, the content of the diurea compound (urea-based thickener) relative to the above-mentioned urea-based grease can be, for example, about 10 to 25% by mass or about 10 to 20% by mass.

[0031] [Rolling Bearings] The present invention also covers embodiments of rolling bearings in which the aforementioned grease composition is sealed. Preferred embodiments of the rolling bearing according to the present invention will be described in detail below with reference to the attached drawings. However, the present invention is not limited to the following embodiments.

[0032] Figure 1 is a radial cross-sectional view of a rolling bearing 10 according to a preferred embodiment of the present invention. The rolling bearing 10 has a basic structure similar to that of a conventional rolling bearing, and comprises an annular inner ring 11, an outer ring 12, a plurality of rolling elements 13, a cage 14, and a sealing member 15. The inner ring 11 is a cylindrical structure installed coaxially with the central axis on the outer circumference of a shaft (not shown). The outer ring 12 is a cylindrical structure arranged coaxially with the inner ring 11 on the outer circumference of the inner ring 11. Each of the plurality of rolling elements 13 is a ball arranged in a raceway within an annular bearing space 16 formed between the inner ring 11 and the outer ring 12. In other words, the rolling bearing 10 in this embodiment is a ball bearing. The cage 14 is arranged within the raceway and holds the plurality of rolling elements 13. The cage 14 is an annular body installed coaxially with the central axis of the shaft, and has a structure in which a rolling element 13 is housed in each pocket on one side in the direction of the central axis. The rolling elements 13 are held by the cage 14 at predetermined intervals in the circumferential direction of the inner ring 11 and the outer ring 12, preventing the rolling elements 13 from falling out or contacting adjacent rolling elements 13. The shape (crown-shaped, corrugated, etc.) and material (steel plate, resin, etc.) of the cage 14 are arbitrary and are not limited to a specific shape or material. The sealing member 15 is fixed to the inner circumferential surface of the outer ring 12 and extends toward the inner ring 11, sealing the bearing space 16. The bearing space 16 sealed by the sealing member 15 is filled with a grease composition G. That is, the grease composition G is held between the inner ring 11 and the outer ring 12. The grease composition G is the grease composition of the present invention described above. The amount of grease G sealed inside the bearing space 16 can be, for example, 5 to 50% of its volume. The sealing member 15 is formed of, for example, a steel plate or rubber, and examples include a steel plate shield that does not contact the outer circumference of the inner ring 11, and a non-contact type rubber seal that does not contact the outer circumference of the inner ring 11. In the present invention, either the steel plate shield or the non-contact type rubber seal can be used as the sealing member. Although this figure shows an embodiment that includes a sealing member 15, the rolling bearing of the present invention also includes embodiments of rolling bearings that do not include a sealing member.In the rolling bearing 10 having the above configuration, the grease composition G acts to reduce friction between the rolling elements 13 and the cage 14, and between the rolling elements 13 and the inner ring 11 to the outer ring 12. By reducing friction, friction torque is reduced and the generation of frictional heat is suppressed, promoting the smooth rotation of the inner ring 11 and the outer ring 12. As can be seen from the configuration shown in Figure 1, the grease composition G sealed in the rolling bearing 10 lubricates the space between the rolling elements 13 and the inner ring 11 to the outer ring 12 when the rolling bearing 10 rotates.

[0033] The rolling bearing in the present invention is not particularly limited in size or operating conditions, but can be applied as a small rolling bearing, for example, with an outer diameter of 22 mm or less, or even 10 mm or less. It can also be applied as a rolling bearing used in a rotation environment with a dmn value of 500,000 to 2,000,000. The rolling bearing of the present invention can be used as a rolling bearing in motors (e.g., fan motors, cleaner motors) used in automobiles, home appliances, information equipment, etc.

[0034] [Motor] As an example, Figure 2 will describe in detail an embodiment of a motor equipped with rolling bearings according to this embodiment, but the present invention is not limited to the following embodiments.

[0035] Figure 2 is a cross-sectional view in the shaft direction of a motor according to one embodiment of the present invention. The motor 20 has a basic structure similar to that of a conventional motor and consists of a housing 21, a stator 22, a coil 23, a rotor magnet 24, a shaft 25, and a rolling bearing 26 that supports the shaft 25. The motor 20 generates a magnetic force by passing an electric current supplied from a power source (not shown above) via a drive circuit through the coil 23 wound around the stator 22, which causes the rotor magnet 24 to rotate, and the rotation is transmitted to an external rotating body through the shaft 25.

[0036] The present invention is not limited to the embodiments or specific examples described herein, and various modifications and variations are possible within the scope of the technical idea described in the claims.

[0037] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited thereto.

[0038] [Test Example 1] Grease compositions Examples 1 to 12 were prepared with the compositions shown in Table 1 below, and various evaluations were carried out according to the procedure described later. In the following explanation, the example numbers of the grease compositions will also be used as the example numbers of the ball bearings in which they were sealed, as well as the example numbers of the evaluations for each test. The details and abbreviations of each component used in the preparation of the grease compositions are as follows: <Base Oil> ・PAO: Polyalphaolefin [Kinematic viscosity at 40°C: 48 mm] ２ / s] The amount of base oil added is the remainder of the thickener and extreme pressure additive listed below. <Thickener> ・Diurea compound: Alicyclic-aliphatic diurea compound (a diurea compound obtained by reacting a mixture of alicyclic amine and aliphatic amine with a diisocyanate compound) The thickener was added to a total of 12% by mass based on the total mass of each grease composition (100% by mass). <Extreme Pressure Additives> ・ZnDTP: Zinc dialkyldithiophosphate ・TPPT: Triphenyl phosphorothioate, trilauryl phosphite, oleyl acid phosphite, dioleyl hydrogen phosphite, tetracosyl acid phosphate, dilauryl hydrogen phosphite, tris(2-ethylhexyl) phosphite, trilauryl trithiophosphite, isotridecyl acid phosphate The above extreme pressure additives were added in such a way that their content was 2 to 4% by mass of the total grease composition (see Table 1).

[0039] <Various Evaluations> (1) Friction Characteristics Evaluation (Metal-to-Metal: Friction Test) A metal-to-metal friction and wear test was conducted using an Optimol vibration friction tester (product name: SRV). The test was performed using a ball-on-disk method, with a ball (material: SUJ2, φ10 mm) and a disc (material: SUJ2, φ24 mm). The test conditions were a load of 100 N, a measurement temperature of 120 °C, a sliding distance of 1 mm, a vibration frequency of 50 Hz, and a test time of 2 hours. 5 mg of each grease composition was supplied at the start of the test. During the test, the coefficient of friction was measured over time, and the average value of the coefficient of friction during the last 10 seconds of the test (2 hours) was used for evaluation according to the following criteria. After the test, the area of ​​the wear marks on the disc from the ball was measured, and the amount of wear (ball) [mm] was determined. ２ The following criteria were used to evaluate the product (average value for N=3): <Criteria: Friction coefficient> A: 0.100 or less B: Greater than 0.100 and 0.110 or less C: Greater than 0.110 and 0.120 or less D: Greater than 0.120 <Criteria: Wear amount> A: 325 mm ２ 350mm or more ２ Less than B: 350mm ２ 375mm or more ２ Less than C: 375mm ２ 400mm or more ２ Less than D: 400 mm ２ That's all.

[0040] (2) Durability Evaluation (High Temperature High Speed ​​Life Test) Each grease composition was sealed in a steel-shielded ball bearing (inner diameter 3 mm, outer diameter 8 mm, width 4 mm) at a concentration of 25% to 35% of the bearing volume. This ball bearing was set in a housing, and a preload of 8 N was applied to the outer ring from the axial direction. Then, a shaft was inserted into the inner diameter of the bearing and connected to the rotating shaft of a test motor so that the ball bearing could rotate the inner ring. Next, the housing was heated to 90°C, and the ball bearing was rotated at a test temperature of 90°C and a rotation speed of 250,000 rpm, and the time until the ball bearing stopped was measured. The stopping condition was defined as the point when the torque increased and the rotation speed decreased by 10% below the specified value, and the test time until stopping was defined as the high temperature high speed life (hrs). Each grease composition was tested three times, the average value was calculated, and it was evaluated according to the following criteria. <Criteria for evaluation> A: High-temperature high-speed lifespan of 300 hours or more B: High-temperature high-speed lifespan of 200 hours or more but less than 300 hours C: High-temperature high-speed lifespan of less than 200 hours

[0041]

[0042] As shown in Table 1, the grease compositions in Example 5: containing alkenyl acid phosphate (oleyl acid phosphate) and Example 11: containing trialkyltrithiophosphite (trilauryltrithiophosphite) achieved a low coefficient of friction and low wear, as well as approximately twice the high-temperature, high-speed life compared to other grease compositions.

[0043] [Test Example 2] In order to examine the suitability of combining metal stearate and amide compounds, comparative examples 1 to 6 of grease compositions were prepared by further adding metal stearate (calcium stearate) and amide compounds (oleic acid amide) to the grease compositions of Examples 5 and 11 described above (the content of these components was 1 to 2% by mass relative to the total grease composition, similar to the extreme pressure additives (see Table 2)). High-temperature, high-speed life tests were conducted on these comparative examples' compositions according to the procedure in [(2) Durability Evaluation (High-Temperature High-Speed ​​Life Test)] described above, and the durability was evaluated according to the judgment criteria. The formulations of comparative examples 1 to 6 and the results of the durability evaluation are shown in Table 2.

[0044]

[0045] As shown in Table 2, when metal stearate salts or amide compounds were added to the grease compositions of Examples 5 and 11, which had achieved high temperature and high lifespan, the durability was significantly impaired.

[0046] Although the best embodiment has been described in detail above, the present invention is not limited to the above embodiment, and any modifications, improvements, etc. that can achieve the objectives of the present invention are included in the present invention.

[0047] 10...Rolling bearing, 11...Inner ring, 12...Outer ring, 13...Rolling element, 14...Cage, 15...Seal member, 16...Bearing space, 20...Motor, 21...Housing, 22...Stator, 23...Coil, 24...Rotor magnet, 25...Shaft, 26...Bearing

Claims

1. A grease composition containing a synthetic hydrocarbon oil, a urea thickener, and an extreme pressure additive, wherein the extreme pressure additive is at least one selected from the group consisting of an alkenyl acid phosphate represented by the following formula (1) and a trialkyltrithiophosphite represented by the following formula (2), (R １ -O) ｎ -P(=O)-(OH) ３－ｎ ... Formula (1) (R ２ -S) ３ -P ... Formula (2) (In Formula (1), R １ represents an alkenyl group having 8 to 30 carbon atoms, and n represents 1 or 2. In Formula (2), R ２ represents an alkyl group having 8 to 30 carbon atoms.) ） The grease composition described above is a grease composition that does not contain metal stearate salts and amide compounds.

2. The grease composition according to claim 1, wherein the alkenyl acid phosphate is oleyl acid phosphate and the trialkyltrithiophosphite is trilauryltrithiophosphite.

3. The grease composition according to claim 1, which is a grease composition for rolling bearings with an outer diameter of 22 mm or less.

4. The grease composition according to claim 1, which is a rolling bearing grease used in a rotating environment where the dmn value is 500,000 or more and 2,000,000 or less.

5. A rolling bearing containing the grease composition described in any one of claims 1 to 4.

6. A motor comprising the rolling bearing described in claim 5.

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