Grease composition and grease-filled bearing

Abstract

The present invention provides a grease composition that prevents grease leakage and suppresses heat generation inside the bearing even under high-speed rotation conditions, and a grease-filled bearing containing the grease composition. [Solution] The grease composition 7 is sealed in the rolling bearing 1 and is a grease composition containing a base oil and a thickener, wherein the kinematic viscosity of the base oil at 40°C is 12 mm². 2 / s or more 26mm 2 The value is less than / s, at a temperature of 25°C, with a strain of 1 × 10⁻⁶. -5 ~5×10 -3 The maximum storage modulus at a frequency of 1 Hz is in the range of 6,000 Pa to 50,000 Pa.

Description

[Technical Field]

[0001] The present invention relates to a grease composition and a grease-filled bearing containing the grease composition, and more particularly to a grease composition used in machine tools and in bearings that support rotating shafts such as spindles that rotate at high speed. [Background technology]

[0002] For example, the spindle of a machine tool is preferably designed to rotate at high speed to increase machining efficiency, and various lubrication technologies are applied to its bearings. Suitable lubrication methods for high-speed spindles include, for example, air-oil lubrication and oil mist lubrication. However, these lubrication methods require ancillary equipment such as compressed air and oil supply devices, which contribute to increased initial and running costs of machine tools. In contrast, grease lubrication is a preferable lubrication method because it requires less maintenance.

[0003] By the way, rolling bearings for machine tool spindles, which are sealed with grease, require high-speed durability. At high rotational speeds, grease leakage to the outside of the bearing and heat generated by grease flow inside the bearing tend to shorten the bearing's lifespan.

[0004] For example, Patent Document 1 proposes a grease composition that prevents grease leakage by specifying the kinematic viscosity of the base oil at 40°C and the number of carbon atoms in the lithium soap thickener. Furthermore, Patent Document 2 proposes extending the lifespan of a bearing device lubricated by a grease composition by supplying compressed air at a lower temperature than the bearing from an external source to suppress the temperature rise of the bearing. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2006-199771 [Patent Document 2] Japanese Patent Publication No. 2018-169040 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, while the grease composition described in Patent Document 1 specifies the kinematic viscosity of the base oil and the number of carbon atoms in the lithium soap, even with the same composition, differences in the proportion of thickener in the total grease can lead to increased grease leakage and heat generation, potentially shortening the bearing's lifespan. Furthermore, while Patent Document 2 suppresses heat generation within the bearing, compressed air passes through the bearing, potentially leading to grease leakage and a shortened lifespan. Additionally, it requires a device and structure for supplying compressed air, which may increase manufacturing costs.

[0007] This invention has been made in view of these circumstances, and aims to provide a grease composition that can prevent grease leakage and suppress heat generation inside the bearing even under high-speed rotation conditions, and a grease-sealed bearing in which the grease composition is sealed. [Means for solving the problem]

[0008] The grease composition of the present invention is a grease composition for sealing in rolling bearings, comprising a base oil and a thickener, wherein the kinematic viscosity of the base oil at 40°C is 12 mm². 2 / s or more 26mm 2 The value is less than / s, at a temperature of 25°C, with a strain of 1 × 10⁻⁶. -5 ~5×10 -3 It is characterized in that the maximum value of the storage modulus at a frequency of 1 Hz is within the range of 6,000 Pa to 50,000 Pa.

[0009] The thickener is a diurea compound, barium soap, or lithium complex soap, and the content of the thickener relative to the total amount of the base oil and the thickener is 10% to 30% by mass.

[0010] The above-mentioned grease composition is further characterized by containing an antioxidant and a rust preventive agent.

[0011] The above-mentioned thickener is a diurea compound obtained by reacting a diisocyanate component with a monoamine component, the above-mentioned monoamine component is an aliphatic monoamine alone or a mixture with other monoamines, the content of the above-mentioned thickener relative to the total amount of the above-mentioned base oil and the above-mentioned thickener is 10% to 16% by mass, and the maximum value of the above-mentioned storage elastic modulus is within the range of 8000 Pa to 40000 Pa.

[0012] The grease-encased bearing of the present invention is a rolling bearing comprising an inner ring and an outer ring, a plurality of rolling elements interposed between the inner ring and the outer ring, a cage for holding the rolling elements, and a grease composition encapsulated in a bearing space between the inner ring and the outer ring, wherein the grease composition is the grease composition of the present invention.

[0013] The above-mentioned rolling bearing is a bearing for a machine tool spindle used at a rotational speed of 10000 min -1 or higher.

[0014] The above-mentioned rolling elements are rolling elements made of ceramics.

[0015] [[ID=二十一]] The above-mentioned rolling bearing is a bearing for a machine tool spindle used when the dm·n value (the product of the pitch circle diameter dm [unit: mm] of the rolling elements and the number of revolutions n of the raceway [unit: min -1 ) is 100×10 4 or higher.

[0016] The above-mentioned rolling bearing has a seal member for sealing the bearing space, the seal member is a seal member in which one end is fixed to one of the raceways of the inner ring and the outer ring, and the seal lip portion of the other end faces the other raceway in a non-contact manner, and the amount of grease encapsulated in the above-mentioned rolling bearing is 10% to 30% of the static space volume of the bearing inner space.

Advantages of the Invention

[0017] The grease composition of the present invention is enclosed in a rolling bearing and contains a base oil and a thickener. The kinematic viscosity of the base oil at 40°C is 12 mm 2 / s or more and 26 mm 2 / s or less, and at a temperature of 25°C and a strain of 1×10 -5 ~5×10 -3 , the maximum value of the storage modulus at a frequency of 1 Hz is in the range of 6000 Pa to 50000 Pa. Therefore, even under high-speed rotation conditions, leakage outside the bearing can be prevented and heat generation inside the bearing can be suppressed.

[0018] The grease-filled bearing of the present invention includes an inner ring, an outer ring, a plurality of rolling elements, a cage, and the grease composition of the present invention, and is preferably used as a bearing for a machine tool spindle used at a rotational speed of 10000 min -1 or higher.

Brief Description of the Drawings

[0019] [Figure 1] It is a cross-sectional view showing an angular ball bearing which is an example of the rolling bearing of the present invention. [Figure 2] It is a diagram showing a test using a rheometer. [Figure 3] It is a diagram showing a spindle using the angular ball bearing of the present invention.

Modes for Carrying Out the Invention

[0020] As a result of intensive studies on a grease composition for lubricating a rolling bearing used particularly under high-speed rotation conditions, the present inventors have found that the storage modulus of the grease composition is related to grease leakage and heat generation inside the bearing, and by setting the storage modulus within a predetermined range together with the kinematic viscosity of the base oil, it has been found that grease leakage can be prevented and bearing heat generation can be suppressed even under high-speed rotation conditions. The present invention is based on such findings.

[0021] An example of the rolling bearing of the present invention will be described with reference to Figure 1. Figure 1 is an axial cross-sectional view of an angular contact ball bearing. As shown in Figure 1, the angular contact ball bearing 1 is an angular contact ball bearing in which a bearing space in which balls 4 are held in a cage 5 between an inner ring 2 and an outer ring 3 is sealed by a seal member 6 fixed to a locking groove provided on the inner circumferential surface of the outer ring 3. The seal member 6 is a contact seal in which the inner diameter side seal lip portion contacts the seal groove. At least the area around the balls 4 is sealed with a grease composition 7. The straight line connecting the contact points between the balls 4 and the inner ring 2 and outer ring 3 has a contact angle α with respect to the radial direction, and can withstand radial loads and unidirectional axial loads. In the present invention, the grease composition of the present invention is sealed in the bearing space formed by the inner ring 2, the outer ring 3 and the balls 4.

[0022] Furthermore, a circumferential groove-shaped grease pocket is formed on the inner surface of the outer ring 3, providing an even greater protection against leakage of the grease composition.

[0023] In the angular contact ball bearing 1, the ferrous metal materials constituting the bearing members, namely the inner ring 2, outer ring 3, and balls 4, are any materials commonly used as bearing materials. Examples include high-carbon chromium bearing steel (SUJ1, SUJ2, SUJ3, SUJ4, SUJ5, etc.; ISO 683-17), carburized steel (SCr420, SCM420, etc.; ISO 683-5), stainless steel (SUS440C, etc.; ISO 16143-2), high-speed steel (M50, etc.), and cold-rolled steel.

[0024] Furthermore, the ball 4 can be made not only from iron-based metal materials but also from lightweight ceramic materials. Using ceramic materials is preferable because, for example, the increase in preload due to centrifugal force during high-speed rotation can be suppressed. Examples of ceramic materials include silicon nitride, silicon carbide, aluminum oxide (alumina), zirconium oxide (zirconia), sialon, and glass. Among these, silicon nitride is more preferable because of its excellent heat resistance.

[0025] The sealing member 6 may be made of metal or a rubber molded body alone, or it may be a composite of a rubber molded body and a metal plate, plastic plate, or ceramic plate. Due to its durability and ease of adhesion, a composite of a rubber molded body and a metal plate is preferred, as shown in Figure 1. Alternatively, as will be described later, it may be a non-contact seal.

[0026] The angular contact ball bearing 1 is suitable for use under high-speed rotation conditions, such as a rotational speed of 8000 min⁻¹. -1 The above, preferably 10,000 min -1 That concludes the explanation. Note that there is no particular upper limit to the rotational speed, but for example, 30,000 min⁻¹ -1 That is the case. Also, in terms of dm·n values, for example, if the dm·n value is 80 × 10 4 The above, preferably 100 × 10 4 That concludes the explanation. Note that there is no particular upper limit to the dm·n value, but for example, 250 × 10 4 That is the case.

[0027] In rolling bearings, during high-speed rotation, centrifugal force easily causes the grease composition to separate, and the thickener, which is agitated and sheared within the bearing, is destroyed, causing the grease composition to soften and making it easier for the grease composition to leak out of the bearing. Furthermore, during high-speed rotation, the heat generated by the grease flow inside the bearing tends to shorten the bearing's lifespan. In response to this, the present invention uses a base oil with relatively low viscosity and keeps the storage modulus of the grease composition within a predetermined range to prevent grease leakage and suppress bearing heat generation.

[0028] The grease composition of the present invention comprises a base oil and a thickener, with various additives added as needed. The grease composition has a strain of 1 × 10 at a temperature of 25°C. -5 ~5×10 -3 The maximum storage modulus at a frequency of 1 Hz is in the range of 6,000 Pa to 50,000 Pa.

[0029] Dynamic viscoelasticity is a method of evaluating viscoelasticity by applying vibrational (periodic) strain or stress to a linear viscoelastic material and measuring the resulting stress or strain. The viscoelasticity obtained in this way is called dynamic viscoelasticity, and the resulting modulus of elasticity is expressed in the form of a complex number. In this invention, the grease composition is used as the linear viscoelastic material.

[0030] If the modulus of elasticity in dynamic viscoelasticity is given by the complex modulus G* = G′ + iG″, then the real part G′ of the complex modulus G* corresponds to the storage modulus, and the imaginary part G″ corresponds to the loss modulus. The storage modulus G′ represents the elastic component of dynamic viscoelasticity. Specifically, it is the ratio of the elastic stress in phase with the strain generated when an external force is applied to the grease composition, and represents the energy that can be elastically stored from the external force received by the grease composition. On the other hand, the loss modulus G″ represents the viscous component of dynamic viscoelasticity. Specifically, it is the ratio of the strain in phase with a different phase when an external force is applied to the grease composition, and represents the energy that is dissipated as heat from the external force received by the grease composition.

[0031] Thus, the storage modulus can be considered an indicator of the dimensional stability of grease. Furthermore, even with the same grease, the storage modulus changes significantly with strain. In the case of grease, the storage modulus is high under low strain conditions, and under high strain conditions, viscosity takes over and the storage modulus decreases. This low strain (specifically, strain amount 1 × 10⁻⁶) -5 ~5×10 -3 By setting the maximum storage modulus in the bearing to an appropriate range of 6,000 Pa to 50,000 Pa, the grease composition exhibits appropriate dimensional stability even during high-speed rotation, thereby preventing grease leakage and suppressing bearing heat generation. The storage modulus is preferably 8,000 Pa to 40,000 Pa, but may also be 8,000 Pa to 20,000 Pa.

[0032] In this invention, the storage modulus is defined as a temperature of 25°C and a strain of 1 × 10⁻⁶. -5 ~5×10 -3The measurement is performed using a rheometer at a frequency of 1 Hz. Preferably, a rheometer with a parallel plate type cell, as shown in Figure 2, is used. Specific measurement conditions are shown in the examples.

[0033] The base oil used in the grease composition of the present invention has a kinematic viscosity of 12 mm² at 40°C (or the kinematic viscosity of the mixed oil in the case of a mixed oil). 2 / s or more 26mm 2 The kinematic viscosity is less than or equal to / s. Keeping it within this range makes it easier to suppress bearing heat generation and also makes it easier to suppress leakage outside the bearing even at high rotational speeds. In addition, it makes it easier to prevent grease evaporation degradation at high temperatures. The above kinematic viscosity is 15 mm 2 / s~22mm 2 / s is preferable.

[0034] As a base oil, any oil commonly used in rolling bearings can be used without particular restrictions. Examples include mineral oils such as paraffinic mineral oil and naphthenic mineral oil, synthetic hydrocarbon oils such as poly-α-olefin (PAO) oil and alkylbenzene oil, ester oils, ether oils, silicone oils, and fluorinated oils. These base oils may be used individually or in combination of two or more types.

[0035] Among the base oils mentioned above, it is preferable to use ester oil or a base oil mixed with ester oil, due to its compatibility with other extreme pressure additives and rust inhibitors that may be contained in the grease.

[0036] The thickener used in the grease composition of the present invention is not particularly limited, and general thickeners commonly used in the field of grease can be used. For example, soap-based thickeners such as metal soaps and complex metal soaps, and non-soap-based thickeners such as bentonite, silica gel, urea compounds, and urea-urethane compounds can be used. Examples of metal soaps include sodium soap, calcium soap, barium soap, aluminum soap, and lithium soap, while examples of urea compounds and urea-urethane compounds include diurea compounds, triurea compounds, tetraurea compounds, other polyurea compounds, and diurethane compounds.

[0037] Diurea compounds are obtained by reacting a diisocyanate component with a monoamine component. Examples of diisocyanate components include phenylenediisocyanate and diphenylmethane diisocyanate (MDI). Examples of monoamine components include alicyclic monoamines such as cyclohexylamine, aromatic monoamines such as p-toluidine, and aliphatic monoamines such as octylamine.

[0038] Among the thickeners mentioned above, it is preferable to use aliphatic diurea compounds alone or in mixtures with others, as this makes it easier to set the storage modulus within the desired range. Examples of the latter include diurea compounds (also referred to as fatty-alicyclic diureas) that use aliphatic monoamines and alicyclic monoamines as monoamine components, and diurea compounds (also referred to as fatty-aromatic diureas) that use aliphatic monoamines and aromatic monoamines.

[0039] The above-mentioned thickener is preferably contained in an amount of 5% to 30% by mass relative to the total amount of the base oil and the thickener, and is more likely to be contained in an amount of 10% to 30% by mass, as this makes it easier to set the storage modulus within the desired range. For example, in the case of diurea-based thickeners, it is more preferable to contain 10% to 20% by mass, and may also be 10% to 16% by mass.

[0040] Furthermore, the grease composition of the present invention may contain other additives, to the extent that they do not impair the objectives of the present invention. Examples include antioxidants such as amine-based, phenol-based, and sulfur-based compounds, rust inhibitors such as sulfonates, and oily agents such as esters and alcohols.

[0041] The amount of antioxidant added is preferably 0.1% by mass or more and less than 3% by mass relative to the total amount of the base grease (100% by mass) consisting of the base oil and thickener. Within this range, oxidative degradation of the grease can be suppressed, and a decrease in lubrication performance can be prevented. Examples of antioxidants include amine-based antioxidants such as phenyl-1-naphthylamine, phenyl-2-naphthylamine, diphenyl-p-phenylenediamine, dipyridylamine, phenothiazine, N-methylphenothiazine, N-ethylphenothiazine, 3,7-dioctylphenothiazine, p,p'-dioctyldiphenylamine, and N,N'-diisopropyl-p-phenylenediamine, as well as phenol-based antioxidants such as 2,2'-methylenebis(6-tert-butyl-4-methylphenol). These antioxidants may be used individually or in combination of two or more. It is preferable to use amine-based antioxidants as the antioxidant.

[0042] The type of rust inhibitor is not particularly limited, and can be used, including ester-based rust inhibitors, sulfonate-based rust inhibitors, linear fatty acids such as lauric acid and stearic acid, or carboxylic acid-based rust inhibitors such as succinic acid and alkyl succinic acid, carboxylic acid salt-based rust inhibitors such as fatty acids and metal salts (cobalt, manganese, zinc) of naphthenic acid, and amine-based rust inhibitors such as alkoxyphenylamine. Among these rust inhibitors, it is preferable to use at least one selected from ester-based rust inhibitors and sulfonate-based rust inhibitors. As ester-based rust inhibitors, partial esters of polyhydric alcohols such as sorbitan, sorbitol, pentaerythritol, sucrose, and glycerin with carboxylic acids such as oleic acid and lauric acid, or succinic acid half-esters such as alkyl succinic acid half-esters and alkenyl succinic acid half-esters can be used. These ester-based rust inhibitors may be used alone or in combination of two or more.

[0043] The amount of rust inhibitor added is preferably 0.1% by mass or more and less than 3% by mass relative to the total amount of the base grease (100% by mass) consisting of the base oil and thickener.

[0044] In the present invention, the grease composition preferably contains an antioxidant and a rust inhibitor as additives. By adding these additives, the storage modulus can be easily adjusted to a desired range, and as shown in the examples described later, the storage modulus can be reduced by adding, for example, a sulfonate-based rust inhibitor.

[0045] The consistency of the above grease composition (ISO 2137) is preferably in the range of 200 to 350. If the consistency is less than 200, oil separation is poor and lubrication may be inadequate. On the other hand, if the consistency exceeds 350, the grease becomes soft and easily leaks out of the bearing, which is undesirable. The above consistency is more preferably in the range of 250 to 340.

[0046] In the grease-filled bearing of the present invention, the amount of grease filled is preferably 10% to 40% (volume ratio) of the static space volume in the bearing's internal space. If it is less than 10% by volume, the amount of grease necessary for lubrication will be insufficient and it will easily be depleted, and if it exceeds 40% by volume, it will be more prone to heat generation due to increased torque caused by agitation. Here, the static space volume is the volume of space in the space between the inner ring, outer ring, and seal member that the rolling elements and cage do not pass through when the bearing rotates. The amount of grease filled may be 10% to 30% of the static space volume in the bearing's internal space, or it may be 10% to 20%.

[0047] In the angular contact ball bearing 1 shown in Figure 1, a contact seal is used as the sealing member, but a non-contact seal with a gap between the seal lip portion and the opposing raceway ring portion may also be used. For example, a seal groove may be provided on the raceway ring portion (e.g., the outer circumferential surface of the inner ring) opposite the seal lip portion of the sealing member, and a simple labyrinth may be formed between the seal lip portion and the seal groove. The grease composition of the present invention has a storage modulus within a predetermined range and can prevent grease leakage even in non-contact seals.

[0048] In addition to the angular contact ball bearing shown in Figure 1, other types of rolling bearings that can be used in the present invention include deep groove ball bearings, cylindrical roller bearings, tapered roller bearings, self-aligning roller bearings, needle roller bearings, thrust cylindrical roller bearings, thrust tapered roller bearings, thrust needle roller bearings, and thrust self-aligning roller bearings.

[0049] Figure 3 shows an example of a spindle device for a machine tool spindle using the angular contact ball bearings shown in Figure 1. As shown in Figure 3, the spindle device 11 has two rows of angular contact ball bearings 1 on the front side and a single row of cylindrical roller bearings 15 on the rear side, and is a high-speed specification driven by a built-in motor 12 equipped with a stator 13 and rotor 14 located in the center. The rotating shaft driven by the built-in motor 12 is supported by the angular contact ball bearings 1 and the cylindrical roller bearings 15. The cylindrical roller bearing 15 consists of an inner ring 16, an outer ring 17, cylindrical rollers 18, and a cage 19. For bearing preloading, for example, a fixed-position preloading method is employed. In the fixed-position preloading method, there is a concern about heat generation, but a grease composition with physical properties within a specific range of the base oil viscosity of the grease and the storage modulus measured by a rheometer is used, so that it can be operated at a low temperature rise without leakage outside the bearing. [Examples]

[0050] The present invention will be specifically described by examples and comparative examples, but the invention is not limited in any way by these examples.

[0051] Examples 1-5, Comparative Examples 1-8 Thirteen test greases were prepared, as listed in Tables 1 and 2. Tables 1 and 2 show the kinematic viscosity at 40°C, the type of thickener, and the amount of thickener relative to the base grease for each test grease. Note that each grease composition in Examples 1 to 5 contains antioxidants and rust inhibitors as additives.

[0052] <Measurement of Storage Modulus> The storage modulus was measured using a viscoelasticity measuring device (HAAKE MARS). Each test grease G was sandwiched between two parallel disc plates 8 with a diameter of φ25 mm, with a thickness of 1 mm, as shown in Figure 2. For each test grease, a periodic strain was applied by rotating the upper plate 9 to induce vibration, and the shear stress as the response was measured. The measurement conditions are shown below. Frequency: 1Hz Strain amount: 1 × 10 -5 ~5×10 -3 Temperature: 25℃

[0053] From the following formula, frequency 1 Hz, strain 1 × 10⁻⁶ -5 ~5×10 -3 The maximum storage modulus G′ at a temperature of 25°C was determined. The results are shown in Tables 1 and 2. G' = (σ0 / γ0)cosδ Here, σ0 represents the stress at t=0, γ0 represents the strain at t=0, and δ represents the phase difference (the difference in response time when strain is applied).

[0054] <Bearing Test> A test bearing was fabricated by sealing the test grease into a 20mm inner diameter deep groove ball bearing 6204LLB (non-contact seal). The test conditions were an ambient temperature of 25°C and a rotational speed of 10,000 min⁻¹. -1 The axial load Fa and radial load Fr were set to 67N, and the grease filling amount was set to 30% of the stationary space volume inside the bearing. The bearing was then rotated for 24 hours. This test observed the heat generated during churning, a condition in which the bearing torque fluctuates due to grease movement caused by agitation. The evaluation items for this test were the temperature measured during bearing operation and the presence or absence of leakage from the bearing. For temperature, "A" was assigned if the outer ring temperature remained below 60°C, and "B" if it exceeded 60°C. For leakage from the bearing, the appearance was observed after operation. "A" was assigned if no test grease leaked from the seal groove, and "B" if leakage occurred. The results are shown in Tables 1 and 2.

[0055] <High-temperature storage test> The weight loss of a predetermined amount (approximately 1 g) of grease composition was measured after being left at a high temperature of 120°C for 100 hours. A weight loss of less than 20% by mass was classified as "A," and a weight loss of 20% by mass or more was classified as "B." The results are shown in Tables 1 and 2.

[0056] [Table 1]

[0057] [Table 2]

[0058] As shown in Table 1, the kinematic viscosity of the base oil at 40°C is 12 mm². 2 / s or more 26mm 2 Examples 1 to 5, which used grease compositions with a storage modulus of elasticity of 6000 Pa to 50000 Pa measured above and a storage modulus of elasticity of 6000 Pa or less, maintained a bearing temperature of 60°C or less during operation, showed no leakage outside the bearing, and exhibited a weight loss of less than 20% by mass due to high-temperature storage.

[0059] On the other hand, Comparative Examples 1 and 7-8, which had the same kinematic viscosity at 40°C as the Examples but a higher storage modulus, experienced a greater temperature rise during operation, with bearing temperatures exceeding 60°C. It is thought that the higher storage modulus made it easier to maintain the shape of the grease composition, increasing the resistance when the balls overcome the grease composition on the raceway surface, resulting in higher torque and increased heat generation.

[0060] Note that the difference between Example 5 and Comparative Example 8 is the presence or absence of a sulfonate-based rust inhibitor as an additive; in Example 5, the sulfonate-based rust inhibitor is added. In Example 5, the inclusion of the sulfonate-based rust inhibitor resulted in a lower storage modulus compared to Comparative Example 8, and consequently, improved heating characteristics. Furthermore, the difference between Example 2 and Comparative Example 7 is the amount of thickener; in Example 2, the amount of thickener influenced the storage modulus to be within an appropriate range, and consequently, improved heating characteristics.

[0061] Furthermore, leakage outside the bearing was observed in the grease compositions of Comparative Examples 3 and 4, where the storage modulus of elasticity was 2500 Pa or less. The test bearings were non-contact seals, and the influence of the shape retention of the grease composition is considered to be particularly significant. Additionally, the kinematic viscosity of the base oil in Comparative Examples 5 and 6 at 40°C was 5 mm². 2 In the grease composition of / s, a weight loss of 20% or more by mass occurred when left at high temperatures.

[0062] Thus, the grease compositions of Comparative Examples 1 to 8 are more likely to have increased surface pressure due to increased heat generation and grease leakage compared to the grease compositions of Examples 1 to 5, and are therefore more likely to have a shorter bearing life.

[0063] Based on the above temperature rise characteristics, grease leakage from the bearings, and weight loss during high-temperature storage, the kinematic viscosity of the base oil at 40°C is 15 mmHg. 2 / s~26mm 2 At / s, the maximum storage modulus measured under the above conditions is preferably in the range of 8000 Pa to 50000 Pa. On the other hand, even if the storage modulus is within this range, if the kinematic viscosity of the base oil at 40°C is relatively high (for example, Comparative Example 2), heat generation is large, and as a result, the surface pressure is expected to be high. [Industrial applicability]

[0064] The grease composition of the present invention is suitable for use as a grease for rolling bearings used under high-speed rotation conditions because it prevents grease leakage outside the bearing even under high-speed rotation conditions, allows for operation at low temperatures, and extends the lifespan. Specifically, it is suitable as a grease for rolling bearings in machine tool spindle devices. [Explanation of Symbols]

[0065] 1. Angular contact ball bearing 2 Inner ring 3 Outer ring 4 Balls (rolling elements) 5 Cage 6. Sealing member 7. Grease Composition 8 Rheometer 9. Top plate 10 Lower plate 11 Spindle device 12. Built-in motor 13 status 14 rotors 15 Cylindrical roller bearings 16 Inner circle 17 Outer ring 18 cylindrical rollers 19 Cage

Claims

1. A grease composition that is sealed in a rolling bearing and contains a base oil and a thickener, The kinematic viscosity of the base oil at 40°C is 12 mm². ２ / s or more 26mm ２ The value is less than or equal to / s, at a temperature of 25°C, with a strain of 1 × 10⁻⁶. －５ ~5 x 10 －３ A grease composition characterized in that the maximum value of the storage modulus at a frequency of 1 Hz is in the range of 6,000 Pa to 50,000 Pa.

2. The grease composition according to claim 1, characterized in that the thickener is a diurea compound, barium soap, or lithium complex soap, and the content of the thickener relative to the total amount of the base oil and the thickener is 10% to 30% by mass.

3. The grease composition according to claim 1 or 2, further comprising an antioxidant and a rust inhibitor.

4. The thickener is a diurea compound obtained by reacting a diisocyanate component with a monoamine component, the monoamine component is an aliphatic monoamine alone or a mixture with other monoamines, and the content of the thickener relative to the total amount of the base oil and the thickener is 10% to 16% by mass. The grease composition according to claim 1, characterized in that the maximum value of the storage modulus is in the range of 8,000 Pa to 40,000 Pa.

5. A rolling bearing comprising an inner ring and an outer ring, a plurality of rolling elements interposed between the inner ring and the outer ring, a cage for holding the rolling elements, and a grease composition sealed in the bearing space between the inner ring and the outer ring, A grease-filled bearing characterized in that the grease composition is the grease composition according to claim 1 or claim 2.

6. The aforementioned rolling bearing rotates at a speed of 10,000 min －１ The grease-filled bearing according to claim 5, characterized in that it is a bearing for the spindle of a machine tool used as described above.

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