Grease composition

Abstract

To provide a grease composition having excellent performance in a low-temperature environment.SOLUTION: One embodiment of the grease composition of the present invention is a grease comprising a thickener and a base oil, wherein a strain when a loss tangent shows 1 in a viscoelasticity test performed using a rheometer under conditions of a temperature of -20°C and a frequency of 1 Hz is 1.0 to 3.5%, and a noise generation time of +10 dB or more with respect to an average value of sound pressure from 5 seconds to 10 seconds after start-up under the wide-angle drive shaft test conditions described in this patent is 5.0 seconds or less. Also, the grease composition has a start-up torque in a range of 10.0 to 45.0 mN*m when measured using a rheometer under conditions of a temperature of -20°C and a shear rate of 10 s-1, and the base oil consists of one or more types selected from mineral oil and synthetic oil and has a kinematic viscosity at 40°C of 90 mm2 / s or more.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a grease composition, and particularly to a grease composition having excellent performance in a low-temperature environment for a wide range of mechanical parts such as rolling bearings, sliding bearings, and gears of various industrial machines and automotive parts.

Background Art

[0002] In parts used in various industrial machines including automobiles, the requirements for maintaining performance in a wide range from low temperature to high temperature and for quality stability have been accelerating year by year. So far, regarding countermeasures for high temperature, technologies related to various thickeners with excellent thermal stability and technologies combining synthetic oils and high-performance antioxidants have been disclosed, but there are still many problems regarding low-temperature properties. Specifically, at low temperatures, there are not a few cases where lubrication failure occurs, such as an increase in torque, generation of abnormal noise due to stick-slip, and further increase in fretting wear.

[0003] For example, in the application of wind power generation, when installed in extremely cold regions, the grease enclosed in bearings and the like cannot exhibit sufficient performance, and there are problems such as fretting wear and a decrease in power generation efficiency due to an increase in torque. In addition, in the automotive field, especially in recent years with the accelerating electrification, all parts, including the drive unit, are being operated and controlled by electric motors. Frictional losses and abnormal noises of each part are eliminated as much as possible, and low fuel consumption (low electricity cost) and quietness are aimed for. Particularly at low temperatures, in engine-equipped vehicles, the peripheral parts such as bearings warmed by the heat source generated when the engine is operating did not require low-temperature properties for the grease, but in electric vehicles, there are many cases where there is no heat source and immediate operation occurs, resulting in an increase in excessive operating torque and energy loss due to friction. Furthermore, due to the elimination of engine noise, the driving noise and operating noise of parts are more likely to be transmitted to the driver and passengers. Particularly at low temperatures, the enclosed grease cannot exhibit sufficient performance, and abnormal noises generated by metal-to-metal contact due to temporary stalling during startup or friction (stick-slip) with the seal material or boot material may be clearly observed. Thus, a grease composition having excellent performance at low temperatures is required.

[0004] Patent Document 1 discloses that a grease composition using a polyalphaolefin oil having a kinematic viscosity at 40 ° C of 25 mm 2 / s or less as a base oil has good performance.

[0005] Patent Document 2 discloses that by adjusting the types and mixing ratios of the base oil and the thickener used in the grease so that the storage elastic modulus measured using a rheometer under the conditions of a temperature of 25 ° C, a frequency of 10 Hz, and a strain amount of 100% is 500 to 100,000 Pa, the generation of the brake noise of the disc brake can be suppressed.

[0006] Patent Document 3 discloses that in four temperature ranges of temperatures of -40 ° C, -30 ° C, -20 ° C, and 20 ° C, when measured using a rheometer under the conditions of a frequency of 1 Hz and a strain amount of 0.003%, the storage elastic modulus is 120,000 Pa or less, and when the loss elastic modulus in the above temperature range at a frequency of 1 Hz is 27,000 Pa or less, by adjusting the types and mixing ratios of the base oil and the thickener used in the grease, when using a rolling bearing including an inner ring and an outer ring, a plurality of rolling elements interposed between the inner ring and the outer ring, and grease enclosed around the rolling elements, no abnormal noise occurs at low temperatures. Further, it discloses that no abnormal noise occurs in the above rolling bearing when the values fall within the ranges of the above storage elastic modulus and loss elastic modulus even in a temperature range of -40 ° C or lower.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, the grease composition described in Patent Document 1 cannot be expected to exhibit sufficient durability under high loads. Therefore, the grease composition described in Patent Document 1 cannot achieve both durability under high load usage conditions and performance at low temperatures.

[0009] In addition, the grease composition described in Patent Document 2 is intended to effectively suppress the occurrence of brake noise, and its performance at low temperatures may not be sufficient.

[0010] The kinematic viscosity at 40 °C of the base oil of the grease composition described in Patent Document 3 is 70 mm 2 / s or less, and verification has not been performed on grease compositions using a higher viscosity constituent oil. When using the above-mentioned oil, even in a grease composition having a predetermined dynamic elastic modulus, it may not be sufficient for abnormal noise. Although attention is paid to the storage elastic modulus and loss elastic modulus in the ultra-low strain region of 0.003%, since attention is not paid to the hardness of the grease and the yield point of the grease when a strong strain is applied, it may be insufficient as a low-temperature abnormal noise simulation test in cold weather.

[0011] The present invention has been made in view of such problems, and particularly aims to obtain a grease composition having excellent performance in a low-temperature environment for a wide range of mechanical parts such as rolling bearings, sliding bearings, and gears in various industrial machines and automotive parts.

Means for Solving the Problems

[0012] As a result of intensive research to achieve the above object, in a grease composition composed of a base oil and a thickener, a method for quantifying the behavior at low temperatures using a rheometer was used, and a grease composition that exhibits excellent performance when enclosed in a bearing or the like was found, and the present invention was completed.

[0013] One form of the present invention is a grease composition. In the grease composed of a thickener and a base oil, the strain amount at which the loss tangent measured using a rheometer under the conditions of a temperature of -20°C and a frequency of 1 Hz shows 1 is in the range of 1.0 to 3.5%, and the abnormal noise generation time of +10 dB or more with respect to the average value of the sound pressure between 5 seconds and 10 seconds from the start of operation under the following wide-angle drive shaft test conditions is preferably 5.0 seconds or less. (Wide-angle drive shaft test conditions) · Outer diameter of the outboard constant velocity joint: Fixed joint with an outer diameter of 89.8 mm · Diameter of the rolling elements of the outboard constant velocity joint is 19.03 mm · Angle: 35 degrees · Torque: 400 Nm · Rotational speed: 200 rpm · Temperature: -40°C, -30°C, -20°C · Measurement position of abnormal noise: 95 mm from the outboard constant velocity joint of the drive shaft · Frequency of abnormal noise: 5,700 - 5,900 Hz

[0014] The grease composition preferably has a starting torque in the range of 10.0 to 45.0 mN·m when measured using a rheometer under the conditions of a temperature of -20°C and a shear rate of 10 s -1 . The grease composition is preferably at least one selected from mineral oils and synthetic oils. The base oil preferably has a kinematic viscosity at 40°C of 90 mm 2 / s or more.

Advantages of the Invention

[0015] According to the present invention, in a grease composition composed of a base oil and a thickener, it is possible to provide a grease composition that exhibits excellent performance when enclosed in a bearing or the like by using a method for quantifying the behavior at low temperatures by a rheometer.

Embodiments for Carrying Out the Invention

[0016] In the following, when an upper limit value and a lower limit value are described separately, it is considered that a numerical range combining any upper limit value and any lower limit value is substantially disclosed.

[0017] In this specification, "low temperature" refers to temperatures such as 0°C or lower, -20°C or lower, -30°C or lower, -40°C or lower, etc.

[0018] The number average molecular weight can be measured using a known measurement method, for example, the gel permeation chromatography (GPC) method as the polystyrene equivalent molecular weight.

[0019] Hereinafter, the physical properties / characteristics, components, manufacturing method, uses, etc. of the grease composition according to the present disclosure will be described.

[0020] <<Physical Properties / Characteristics of Grease Composition>> <Amount of Strain at Low Temperature / Low Temperature Fluidity> The grease composition of the present disclosure has an amount of strain showing a loss tangent of 1 in the viscoelasticity test measured using a rheometer under the conditions of a temperature of -20°C and a frequency of 1 Hz in the range of 1.0 to 3.5%.

[0021] The loss tangent (tanδ) in the dynamic viscoelasticity measurement is represented by the ratio of the loss elastic modulus (G'', viscosity) to the storage elastic modulus (G', elasticity) (Equation 1). Also, generally, the storage elastic modulus (G') is a parameter corresponding to the elastic component and corresponds to the energy stored in the viscoelastic body out of the energy absorbed by the viscoelastic body when receiving an external force. The loss elastic modulus (G'') is a parameter corresponding to the viscous component and corresponds to the energy released to the outside as heat out of the energy absorbed by the viscoelastic body when receiving an external force. Therefore, it is considered that when using a grease with a large loss tangent, it is easy to absorb the kinetic energy (vibration, sound, etc.) of the external force and release it as heat energy. (Equation 1) Loss tangent: tanδ = G'' / G' G''... Loss elastic modulus G'... Storage elastic modulus

[0022] Here, the loss tangent is determined from the dynamic viscoelasticity test conducted under the following conditions. More specifically, with the grease to be evaluated sandwiched between the upper plate and the lower plate of the dynamic viscoelasticity measuring device, the storage shear modulus G' and the loss shear modulus G'' were measured when the upper plate was moved under the following conditions, and the loss tangent tanδ was calculated using Equation (1). Dynamic viscoelasticity measuring device: Rheometer DHR-2 (manufactured by TA Instruments) Plates: φ25 mm parallel plates Gap between plates: 0.1 mm Temperature: -20°C Measurement frequency: 1 Hz Strain amount: 0.01 to 100.0%

[0023] From the perspective of dynamic viscoelasticity, it is considered that the grease starts to flow when G', which indicates the degree of hardness of the gel (rubber elasticity) structure, becomes the same value as G'', which indicates the degree of liquidity. Also, the grease has a storage modulus that exceeds the loss modulus in the low strain region. When the external stress is weak, the grease shows a gel-like state formed by the internal thickener network.

[0024] Also, the grease shows the behavior in the gel (rubber elasticity) state in the region where G'>G'' at low strain, but at higher strain, the internal thickener network of the grease is reversibly oriented in the strain direction and shows a liquid-like behavior. At this point, G''>G' (tanδ>1).

[0025] In the present disclosure, for example, the following reasons are speculated as the effects that a grease composition having a loss tangent exceeding 1 at a low strain amount results in low torque during startup in a low-temperature environment and can prevent the generation of abnormal noises due to stick-slip.

[0026] When the base oil constituting the grease composition of the present disclosure is a synthetic oil, the thickening effect when the temperature is lowered to a low temperature is smaller than that of the grease composed only of mineral oil. Therefore, even when the temperature is lowered to a low temperature, the storage modulus related to the hardness of the grease does not increase so much. As a result, it is considered that the amount of strain required for the start of the flow of the grease at a low temperature (when the loss tangent tanδ = 1) is small.

[0027] When the grease composition of the present disclosure contains mineral oil and a thickener, the thickener and the thickener form a three-dimensional network by physical cross-linking through at least one or more of the following mechanisms (1) to (3). As a result, it is considered that the amount of strain required for the start of the flow of the grease under low temperature conditions (when the loss tangent tanδ = 1) is small. (1) Network via the crystal layer of the thickener and the added polymer (2) Network formed by hydrogen bonding or chemical bonding between the thickener and the added polymer (3) Network formed by entanglement of the polymer chains of the thickener and the added polymer

[0028] Since the grease composition of the present disclosure has the property of having an appropriate low strain amount when the loss tangent tanδ = 1, the thickener network in the grease is reversibly oriented in the strain direction and is likely to start flowing. That is, since the grease has a small resistance during low-temperature flow, the starting torque is small, and the lubricating performance such as suppression of abnormal noise caused by stick-slip and fretting wear can be exhibited because the intervention to the lubricating interface is improved.

[0029] From the above, it is considered that the grease composition in the present disclosure is excellent in the fluidity of the grease and the intervention to the lubricating interface in a low-temperature environment and can be applied to a wide range of sliding parts.

[0030] The low-temperature fluidity can be adjusted, for example, by changing the presence or absence of a thickener to be described later, its type and blending amount, changing the blending of a synthetic oil to be described later and its blending amount, and the like. For example, the low-temperature fluidity is improved by blending a thickener into a grease using mineral oil as a base oil. In addition, desired performance can also be achieved by blending a synthetic oil.

[0031] <Low-temperature startability> The grease composition of the present disclosure has a starting torque (low-temperature startability) in the range of 10.0 to 45.0 mN·m in a viscoelasticity test performed using a rheometer under the conditions of a temperature of -20°C and a shear rate of 10 s -1 .

[0032] The starting torque (low-temperature startability) is determined from the measurement performed under the following viscoelasticity test conditions. More specifically, a gap (0.1 mm) between an upper rotating plate and a lower fixed plate is set, each grease composition is sandwiched between the gaps, and after being held in an environment of -20°C, the torque at the start is measured under the condition that the shear rate is 10 s -1 . Torque measuring device at start: Rheometer DHR-2 (manufactured by TA-Instruments) Plate: φ25 mm parallel plate Gap between plates: 0.1 mm Temperature: -20°C Shear rate during measurement: 10 s -1 Reading value of starting torque: The reading value is taken 1 second after the start of measurement.

[0033] <Measurement of abnormal noise characteristics> The grease composition of the present disclosure has an abnormal noise generation time of +10 dB or more with respect to the average value of the sound pressure between 5 seconds and 10 seconds from the start of operation under the following wide-angle drive shaft test conditions of 5.0 seconds or less.

[0034] In this specification, abnormal noise refers to the abnormal noise generated when mechanical components such as rolling bearings, sliding bearings, gears, and constant velocity joints filled with grease are operated at low temperatures. More specifically, abnormal noise refers to a sound that is +10 dB or more relative to the average value of the stable sound pressure between 5 seconds and 10 seconds after the start of operation of the mechanical component at a frequency of 5,700 to 5,900 Hz. For example, in the case of the following wide-angle drive shaft test conditions. The sound pressure of the abnormal noise is not particularly limited as long as it is at a level that makes the driver of the vehicle, etc., feel uncomfortable. For example, 65 dB or more can be mentioned.

[0035] The above abnormal noise generation time is measured under the following [Wide-angle drive shaft test conditions] and [Abnormal noise measurement conditions] by enclosing the grease composition of this embodiment in the following evaluation joint.

[0036] In addition, in this embodiment, although it is described that the above abnormal noise generation time is 5.0 seconds or less, when the above abnormal noise generation time is 0.0 seconds, that is, when the above abnormal noise does not occur at all, it is also within the scope of the present invention.

[0037] [Evaluation joint] · Surface roughness Ra of the outer race of the outboard constant velocity joint: 0.7 - 0.9 μm · Outer diameter of the outboard constant velocity joint: Fixed joint with an outer diameter of 89.8 mm · Type of outboard constant velocity joint: Bifol field type joint · Diameter of the rolling elements of the outboard constant velocity joint: 19.03 mm · Number of rolling elements of the outboard constant velocity joint: 6 · Enclosed grease: Unused evaluation grease

[0038] [Wide-angle drive shaft test conditions] · Angle: 35 degrees · Torque: 400 Nm · Rotational speed: 200 rpm · Temperature: -40 °C, -30 °C, -20 °C

[0039] [Abnormal noise measurement conditions] · Abnormal noise measuring machine: NL-42A (manufactured by Lion Corporation) · Measurement position of abnormal noise: 95 mm from the outboard constant velocity joint of the drive shaft (constant velocity joint attached to the wheel side of the drive shaft) · Frequency of abnormal noise: 5,700 - 5,900 Hz · Timing of measurement start: Sound measurement was started simultaneously with the operation of the drive shaft test. · Measurement time of abnormal noise: 120 seconds

[0040] <Extreme pressure property> The grease composition of the present disclosure preferably has a welding load (extreme pressure property) obtained by a high-speed four-ball extreme pressure test of 2,452 N or more. Note that the extreme pressure property uses the value measured according to ASTM D2596.

[0041] <Consistency> The consistency of the grease composition of the present disclosure is preferably No. 000 to No. 4 (175 - 475), more preferably No. 00 to No. 3 (220 - 430), and even more preferably No. 0 to No. 2. When the consistency is 475 or less, the hardness of the grease composition can be sufficiently ensured, and leakage of the grease composition from mechanical parts can be suppressed. On the other hand, when the consistency is 175 or more, the grease composition can be prevented from becoming too hard, thereby improving the fluidity at low temperatures. Note that the consistency represents the physical hardness, and as the consistency, the value of the mixed consistency measured according to JIS K2220 7 is used.

[0042] <<Components of the grease composition>> The grease composition of the present disclosure is composed of a thickener and a base oil. In addition, the grease composition of the present disclosure may contain an additive. The base oil, thickener, and additive used in the grease composition of the present disclosure are not particularly limited, but will be described below respectively.

[0043] <Base oil> The base oil is not particularly limited, but it is preferably one or more selected from mineral oils and synthetic oils.

[0044] Mineral oil is a base oil obtained by refining crude oil (such as paraffinic crude oil, naphthenic crude oil, intermediate-base crude oil, etc.). Examples of mineral oil include paraffinic or naphthenic mineral oil obtained by appropriately combining one or more refining means such as solvent dewaxing, solvent extraction, hydrocracking, solvent deoiling, catalytic deoiling, hydrorefining, sulfuric acid washing, and clay treatment for the lubricating oil fraction obtained by atmospheric distillation and vacuum distillation of crude oil. Mineral oil can be used alone or in combination of two or more.

[0045] Examples of synthetic oils include polyalphaolefins (PAO), alpha-olefin copolymers, polybutene, alkylbenzene, polyol esters, dibasic acid esters, polyoxyalkylene glycols, polyoxyalkylene glycol esters, polyoxyalkylene glycol ethers, hindered esters, silicone oils, etc. Synthetic oils can be used alone or in combination of two or more.

[0046] It is also possible to combine mineral oil and synthetic oil as the base oil. In this case, the ratio of synthetic oil to mineral oil (content of mineral oil in the grease composition / content of synthetic oil in the grease composition) can be, for example, 0.1 to 10.0, 0.1 to 5.0, 0.2 to 1.5, or 0.3 to 1.2, etc.

[0047] The range of the kinematic viscosity of the base oil at 40 °C is not particularly limited, but it is preferably 90 mm 2 / s or more, more preferably 100 mm 2 / s or more, still more preferably 120 mm 2 / s or more, and particularly preferably 150 mm 2 / s or more. The upper limit value of the kinematic viscosity of the base oil at 40 °C is not particularly limited, but for example, 300 mm 2 / s, or 250 mm 2It is in [unit]. Here, for the kinematic viscosity at 40°C of these base oils, the value measured at 40°C in accordance with JIS K 2283 is used. The kinematic viscosity at 40°C of the base oil, when the base oil is a mixed oil, indicates the kinematic viscosity at 40°C of the mixed oil.

[0048] <Thickener> The thickener is not particularly limited, but metal soap-based thickeners such as tricalcium phosphate, alkali metal soaps, alkali metal complex soaps, alkaline earth metal soaps, alkaline earth metal complex soaps, etc., and urea-based thickeners such as triurea monourethane, diurea, tetraurea, etc. are preferred. Other thickeners include silica (silicon oxide) such as clay and silica aerogel, and fluororesins such as polytetrafluoroethylene. As the thickener, one kind or two or more kinds can be used in combination.

[0049] When the content of the thickener in the grease composition is based on the total amount of the grease composition being 100.00% by mass, it is preferably 1.00% by mass or more, 3.00% by mass or more, or 5.00% by mass or more, and is preferably 25.00% by mass or less, 20.00% by mass or less, or 15.00% by mass or less.

[0050] <Additive> Examples of the additive include conventionally known additives such as rust preventives, friction modifiers, antiwear agents, antioxidants, oiliness agents, extreme pressure agents, solid lubricants, metal deactivators, metal-based detergents, non-metal-based detergents, corrosion inhibitors, and colorants.

[0051] In addition, the grease composition of the present disclosure may contain a thickening agent as an additive, and may also contain a polymer as a thickening agent.

[0052] In the present disclosure, the polymer is a type of thickener and an additive compounded to increase the adhesiveness and viscosity of the grease composition. The structure of the polymer (such as the structure of the main skeleton, side chain, substituent, etc.) and physical properties (number average molecular weight, crystallization start temperature, etc.) can be appropriately changed so that the grease composition satisfies the desired performance. Examples of the polymer used as a thickener in the grease composition include thickeners such as polybutene-based, polyisobutylene-based, poly(meth)acrylate-based, and olefin copolymer-based thickeners. The poly(meth)acrylate-based polymer may be a dispersed poly(meth)acrylate, a non-dispersed poly(meth)acrylate, or a mixture thereof. For the non-dispersed poly(meth)acrylate and the dispersed poly(meth)acrylate, for example, those disclosed in JP-A-2022-044925 can be used. In particular, when the base oil is mineral oil, the grease composition preferably contains a polymer. The polymers can be used not only alone but also in combination of two or more.

[0053] The kinematic viscosity when the base oil and the polymer are mixed among the components constituting the grease composition is 90 mm 2 / s or more, 100 mm 2 / s or more, 120 mm 2 / s or more, or 150 mm 2 / s or more, and preferably 310 mm 2 / s or less, or 260 mm 2 / s or less.

[0054] The specific content of the polymer may be appropriately adjusted according to the type of the base oil, etc. For example, when the total amount of the grease composition is 100.00% by mass, it is preferably 5.00% by mass or less, 3.00% by mass or less, or 1.50% by mass or less. Also, the lower limit value of the polymer content can be, for example, 0.10% by mass, 0.20% by mass, or 0.30% by mass, etc. Note that the content of the polymer in the grease composition of the present disclosure may be less than 0.10% by mass, 0.05% by mass or less, 0.01% by mass or less, or 0.00% by mass.

[0055] <<Method for manufacturing grease composition>> The method for manufacturing a grease composition can be carried out according to a known method. For example, for the grease composition, each component (base oil, thickener, and additives added as necessary, etc.) may be appropriately mixed, and the mixing order is not particularly limited.

[0056] Also, for components such as thickeners, they may be obtained by blending the raw material components of the components into the base oil constituting the grease composition according to a conventionally known method and reacting the raw material components. For example, a method of forming a urea-based thickener by charging a base oil, an isocyanate component, and an amine component into a kettle and reacting the isocyanate component and the amine component in the base oil, or a method of forming a metal soap-based thickener by charging a base oil, a carboxylic acid component, and a basic metal component into a kettle and reacting the carboxylic acid component and the basic metal component in the base oil may be implemented.

[0057] <<Uses of grease composition>> Since the grease composition according to the present disclosure is excellent in performance at low temperatures and durability under high load usage conditions, etc., it can be applied to various uses, and is particularly preferably applicable to uses assumed to be used in a low temperature environment. More specifically, the grease composition according to the present disclosure can be preferably applied to a wide range of mechanical parts such as rolling bearings, sliding bearings, gears, etc. for automobiles, wind power generation, and other various industrial machines.

Examples

[0058] Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited by these Examples at all.

[0059] <<Raw materials>> The raw materials used in Examples 1 to 11 and Comparative Examples 1 to 4 of the present Example described in Tables 1 and 2 are as follows. In Tables 1 and 2, the blending amounts of each component are shown in parts by mass.

[0060] <Thickener> (Diurea) The diurea compound constituting the grease composition is obtained by reacting 4,4'-diphenylmethane diisocyanate with a linear primary amine in a base oil. (Lithium soap) The lithium soap constituting the grease composition is obtained by reacting 12-hydroxystearic acid with lithium hydroxide monohydrate in a base oil.

[0061] <Base oil> (Base oil A) A paraffinic mineral oil obtained by dewaxing solvent refining belonging to Group 1 classified by the American Petroleum Institute (API: American Petroleum Institute) (kinematic viscosity at 40°C is 99.82 mm 2 / s, viscosity index is 98), a paraffinic mineral oil belonging to Group 1 (kinematic viscosity at 40°C is 494.6 mm 2 / s, viscosity index is 96), and a naphthenic mineral oil belonging to Group 5 (kinematic viscosity at 40°C is 521.3 mm 2 / s, viscosity index is 5) are mixed in a mass ratio of 54%:17%:29%. (Base oil B) A paraffinic mineral oil belonging to Group 1 (kinematic viscosity at 40°C is 99.82 mm 2 / s, viscosity index is 98), a paraffinic mineral oil belonging to Group 1 (kinematic viscosity at 40°C is 494.6 mm 2 / s, viscosity index is 96), and a naphthenic mineral oil belonging to Group 5 (kinematic viscosity at 40°C is 521.3 mm 2 / s, viscosity index is 5) are mixed in a mass ratio of 41%:30%:29%. (Base oil C) A paraffinic mineral oil belonging to Group 1 with a kinematic viscosity at 40°C of 494.6 mm 2 / s, viscosity index is 96), and a naphthenic mineral oil belonging to Group 5 (kinematic viscosity at 40°C is 521.3 mm 2 / s, viscosity index is 5) are mixed in a mass ratio of 60%:40%. (Base oil D) Paraffinic mineral oil belonging to Group 1 with a kinematic viscosity at 40 °C of 494.6 mm 2 / s and a viscosity index of 96), and naphthenic mineral oil belonging to Group 5 (kinematic viscosity at 40 °C of 521.3 mm 2 / s and a viscosity index of 5) are mixed in a mass ratio of 41% to 59%. (Synthetic oil A) GTL (Gas to Liquid) synthesized by the Fischer-Tropsch method, belonging to Group 3, with a kinematic viscosity at 40 °C of 44.16 mm 2 / s and a viscosity index of 141.

[0062] <Thickener (polymer)> The polymers used as raw materials are listed below. (Polymer A) Non-dispersed polymethacrylate with a number average molecular weight of 14,000 (Polymer B) A mixture of non-dispersed polymethacrylates with number average molecular weights of 12,000 and 552,000, and the number average molecular weight of the whole polymer is 14,000. (Polymer C) (Polymer C) A mixture of non-dispersed polymethacrylates with number average molecular weights of 30,000 and 4,200,000, and the number average molecular weight of the whole polymer is 32,000. (Polymer D) Polymethacrylate with a number average molecular weight of 26,000 and a crystallization start temperature of -19.2 °C during DSC measurement (Polymer E) Polymethacrylate with a number average molecular weight of 35,000 and a crystallization start temperature of -14.4 °C during DSC measurement (Polymer F) Polymethacrylate with a number average molecular weight of 43,000 and a crystallization start temperature of -13.5 °C during DSC measurement (Polymer G) Polyisobutene with a number average molecular weight of 800 (Polymer H) Polyisobutene with a number average molecular weight of 2,900

[0063] <Other additives> As other additives, a rust inhibitor, a friction modifier, and an anti-wear agent were used. Specifically, calcium sulfonate, molybdenum dithiocarbamate, and zinc dialkyldithiophosphate were blended in an amount of 3.0 parts by mass based on 100 parts by mass of the entire grease composition so that the elemental ratio of Ca:Mo:Zn:S:P was 1.5:39.0:5.0:50.0:4.5.

[0064] <<Preparation of grease composition>> <Examples 1 to 6> The above diurea compound was synthesized in base oil A, and further heated to 170 °C with stirring to complete the reaction. Then, it was quickly cooled to 90 °C, and a polymer and additives were added at the blending ratios shown in Table 1, followed by stirring and mixing, and then treated with a homogenizer to obtain grease.

[0065] <Example 7> The above urea compound was synthesized in base oil B, and further heated to 170 °C with stirring to complete the reaction. Then, it was quickly cooled to 90 °C, and a polymer and additives were added at the blending ratios shown in Table 1, followed by stirring and mixing, and then treated with a homogenizer to obtain grease.

[0066] <Example 8> The above urea compound was synthesized in a mixed oil of base oil C and synthetic oil A, and further heated to 170 °C with stirring to complete the reaction. Then, it was quickly cooled to 90 °C, and additives were added at the blending ratios shown in Table 1, followed by stirring and mixing, and then treated with a homogenizer to obtain grease.

[0067] <Example 9> The above urea compound was synthesized in a mixed oil of base oil C and synthetic oil A, and further heated to 170 °C with stirring to complete the reaction. Then, it was quickly cooled to 90 °C, and a polymer and additives were added at the blending ratios shown in Table 1, followed by stirring and mixing, and then treated with a homogenizer to obtain grease.

[0068] <Example 10> The above urea compound was synthesized in a mixed oil of base oil D and synthetic oil A, and then heated to 170°C with stirring to complete the reaction. Thereafter, it was quickly cooled to 90°C, additives were added at the blending ratios shown in Table 1, stirred and mixed, and then treated with a homogenizer to obtain grease.

[0069] <Example 11> The above lithium soap was synthesized in base oil A, and after dehydration, it was heated to 220°C. Thereafter, it was gradually cooled to 90°C, a polymer and additives were added at the blending ratios shown in Table 1, stirred and mixed, and then treated with a homogenizer to obtain grease.

[0070] <Comparative Example 1> The above diurea compound was synthesized in base oil A, and then heated to 170°C with stirring to complete the reaction. Thereafter, it was quickly cooled to 90°C, additives were added at the blending ratios shown in Table 1, stirred and mixed, and then treated with a homogenizer to obtain grease.

[0071] <Comparative Examples 2 and 3> The above diurea compound was synthesized in base oil A, and then heated to 170°C with stirring to complete the reaction. Thereafter, it was quickly cooled to 90°C, a polymer and additives were added at the blending ratios shown in Table 1, stirred and mixed, and then treated with a homogenizer to obtain grease.

[0072] <Comparative Example 4> The above diurea compound was synthesized in synthetic oil A, and then heated to 170°C with stirring to complete the reaction. Thereafter, it was quickly cooled to 90°C, additives were added at the blending ratios shown in Table 1, stirred and mixed, and then treated with a homogenizer to obtain grease.

[0073] <<Measurement / Evaluation>> According to the method described above, the low-temperature fluidity, low-temperature starting property, consistency, and extreme pressure property of the grease composition were measured.

[0074] Also, under the wide-angle drive shaft test conditions described above, the abnormal noise occurrence time T of +10 dB or more with respect to the average value of the stable sound pressure from 5 seconds to 10 seconds after the start of operation at 5,700 to 5,900 Hz was measured and evaluated based on the following evaluation criteria. The measurement / evaluation results are shown in Table 1. (Evaluation Criteria for Wide-Angle Drive Shaft Test) A: T ≤ 5.0 seconds B: T > 5.0 seconds

[0075]

Table 1

[0076]

Table 2

[0077] Examples 1 to 11 described in Table 1 showed good low-temperature fluidity and low-temperature startability, and were also excellent in extreme pressure properties. Further, the abnormal noise occurrence time T of +10 dB or more with respect to the average value of the stable sound pressure from 5 seconds to 10 seconds after the start of operation under the wide-angle drive shaft test conditions was all 5.0 seconds or less. From the above, the grease compositions of the respective examples can achieve both low torque at low temperatures and durability under high load usage conditions, and it can be expected to suppress lubrication deficiencies such as abnormal noise generation due to stick-slip and further increase in fretting wear.

Industrial Applicability

[0078] The grease composition of the present invention uses a method for quantifying the behavior at low temperatures by a rheometer and exhibits excellent performance when enclosed in a bearing or the like. Therefore, since it is excellent in performance at low temperatures and durability under high load usage conditions, etc., it can be applied to various applications assumed to be used in low-temperature environments. More specifically, it can be preferably applied to a wide range of mechanical parts such as rolling bearings, sliding bearings, and gears for automobiles, wind power generation, and other various industrial machines.

Claims

1. A grease composition comprising a base oil and a thickener, wherein when the loss tangent in a viscoelasticity test performed using a rheometer under the conditions of a temperature of -20°C and a frequency of 1 Hz shows 1, the strain is 1.0 to 3.5%, and the abnormal noise generation time which is +10 dB or more with respect to the average value of the sound pressure between 5 seconds and 10 seconds from the start of operation under the following wide-angle drive shaft test conditions is 5.0 seconds or less. (Wide-angle drive shaft test conditions) - Fixed joint with an outer diameter of the outboard constant velocity joint: 89.8 mm - Diameter of the rolling elements of the outboard constant velocity joint: 19.03 mm - Angle: 35 degrees - Torque: 400 Nm - Rotational speed: 200 rpm - Temperatures: -40°C, -30°C, -20°C - Measurement position of abnormal noise: 95 mm from the outboard constant velocity joint of the drive shaft - Frequency of abnormal noise: 5,700 to 5,900 Hz

2. Temperature: -20°C, Shear rate: 10 s －１ The grease composition according to claim 1, wherein the starting torque in the viscoelasticity test carried out using a rheometer under the conditions of －１ is 10.0 to 45.0 mN·m.

3. The grease composition according to claim 1 or 2, wherein the base oil is one or more selected from mineral oils and synthetic oils.

4. The kinematic viscosity of the base oil at 40 °C is 90 mm ２ / s or more, the grease composition according to claim 1 or 2.

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