Grease composition

Abstract

To provide a grease composition having low torque.SOLUTION: A grease composition comprises a base oil (A) and a thickener (B), wherein when a minor axis and a major axis of the thickener (B) in the grease composition are measured using a dielectric constant observation system of a scanning electron microscope, an aspect ratio (minor axis / major axis) of the thickener (B) is less than 0.23.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a grease composition. [Background technology]

[0002] Grease is a semi-solid lubricant made by dispersing a solid, highly lipophilic thickener in a base oil. Grease adheres more easily to lubricated parts and is less likely to leak out than lubricating oil. Therefore, using grease can simplify the mechanical structure of the lubrication system. Grease also leaks less than lubricating oil, creating a cleaner environment, and the replenishment interval can be shortened compared to lubricating oil. Grease is mainly used to lubricate machine elements such as rolling bearings, plain bearings, ball screws, linear guides, and gears. Rolling bearings are widely used in machine tool spindles, railroad car carriages, engine accessories such as automobile alternators, constant velocity joints, and wheels.

[0003] In response to recent demands for energy conservation and higher efficiency, there is a demand for reducing bearing rotational torque. For example, Patent Document 1 discloses a grease composition in which the relative surface area of ​​the thickener calculated from the particle size distribution of the thickener measured by laser diffraction is equal to or greater than a specific value, and discloses that this torque composition can reduce torque caused by stirring resistance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2016-204623 Summary of the Invention [Problem to be solved by the invention]

[0005] Demands for energy savings and higher efficiency are increasing, and even higher levels of torque reduction are required.

[0006] The laser diffraction / scattering method disclosed in Patent Document 1 is a method that can easily measure particle size, but the basic assumption used to calculate particle size distribution is that all distributions are the same as those when the particles to be measured are spherical, so there is a problem that the particle size cannot be measured appropriately if the particles to be measured are not spherical but rather long or thin.General thickeners are not spherical, so the particle size of thickener particles cannot be accurately measured using the laser diffraction / scattering method.

[0007] Furthermore, although it is possible to observe the size and shape of the thickener alone using an electron microscope, it is difficult to observe the size and shape of the thickener in a grease composition because the base oil evaporates in a vacuum.

[0008] If the size and shape of the thickener in the grease composition cannot be properly evaluated, the resulting grease composition may not achieve the desired effects even if the strength of shear force during production of the grease composition is controlled so as to satisfy specific parameters.

[0009] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a grease composition with low torque. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention employs the following configuration. [1] A grease composition containing a base oil (A) and a thickener (B), A grease composition, wherein, when the minor axis and major axis of the thickener (B) in the grease composition are measured using a dielectric constant observation system of a scanning electron microscope, the aspect ratio (minor axis / major axis) of the thickener (B) is less than 0.23. [2] The grease composition according to [1], wherein the thickener (B) is a urea-based thickener (B1). [3] The grease composition according to [2], wherein the urea-based thickener (B1) is a diurea compound. [4] The grease composition according to any one of [1] to [3], wherein the content of the thickener (B) is 5% by mass or more relative to 100% by mass of the total amount of the grease composition. [5] The grease composition according to any one of [1] to [4], wherein the aspect ratio of the thickener (B) is 0.21 or less. [Effects of the Invention]

[0011] According to the present invention, a grease composition with low torque can be provided. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is an image of the grease composition of Example 1 obtained using a scanning electron microscope dielectric observation system. [Figure 2] 1 is an image of the grease composition of Comparative Example 1 obtained using a dielectric constant observation system of a scanning electron microscope. [Figure 3] 1 is an image of the grease composition of Comparative Example 2 obtained using a scanning electron microscope dielectric constant observation system. [Figure 4] 1 is an image of the grease composition of Comparative Example 3 obtained using a dielectric constant observation system of a scanning electron microscope. DETAILED DESCRIPTION OF THE INVENTION

[0013] (Grease composition) The grease composition of the present embodiment contains a base oil (A) and a thickener (B). In the grease composition of the present embodiment, when the minor axis and major axis of the thickener (B) in the grease composition are measured under the following measurement conditions, the aspect ratio (minor axis / major axis) of the thickener (B) is less than 0.23. [Measurement conditions] Measurement equipment: Scanning electron microscope dielectric constant observation system Acceleration voltage: 3 to 20 keV Irradiation current: 10~20pA Observation magnification: 10,000 to 20,000 times

[0014] Specifically, the grease composition is observed using a dielectric constant observation system of a scanning electron microscope owned by the National Institute of Advanced Industrial Science and Technology. As described in Reference 1 below, the scanning electron microscope dielectric observation system is a system that can directly visualize solution samples at room temperature and pressure with nano-scale resolution and measure the size and shape of aggregates of individual compounds contained in the sample at the nanoscale. Document 1: Scientific Reports, 2017 Feb 23, 23:7:43025. doi:10.1038 / srep43025

[0015] The specific measurement procedure is as follows. First, a small amount of the grease composition is taken on the tip of a pointed object such as a toothpick, and about 0.1 mg of the grease composition is applied to the silicon nitride thin film window material of a dedicated sample holder. The holder with the grease composition attached is set in a centrifuge and the grease composition is adjusted to a thickness of 10 μm or less at 5,000 to 10,000 rpm for 1 minute, and then introduced into the device. Since the measurement conditions depend on the thickness of the grease composition, the accelerating voltage is adjusted to 3.0 to 20.0 kV and the probe current is adjusted to 10 to 20 pA, respectively, to enable observation of the thickener. The observation range is approximately 1.2 x 10 2 μm 2 The observation image is an 8-bit grayscale image of 1280 × 960 pixels.

[0016] The image obtained using the scanning electron microscope dielectric observation system is analyzed using image analysis software (Media Cybernetics' "Image-Pro 10") to extract and digitize the area corresponding to the thickener (dark area). The extracted area is approximated as an ellipse using the measurement function of the image analysis software, and the "area: width (minor axis)" and "area: length (major axis)" are measured to calculate the aspect ratio (minor axis / major axis).

[0017] The aspect ratio (minor axis / major axis) of the thickener (B) in the grease composition of this embodiment is less than 0.23, preferably 0.22 or less, and more preferably 0.21 or less. A low aspect ratio of the thickener (B) in the grease composition means that the thickener (B) is dispersed in the grease composition in an elongated form. When the thickener present in the grease is elongated, a long skeleton is formed inside the grease, increasing the rigidity of the grease and suppressing flow, similar to how the rigidity of concrete increases when rebar is placed inside the grease. When the grease composition is used in a bearing and the fluidity is suppressed during rotation, agitation of the grease in the bearing is reduced, thereby reducing unnecessary agitation resistance. As a result, torque can be reduced. When the aspect ratio of the thickener (B) in the grease composition of this embodiment is less than 0.23, the torque decreases. When the aspect ratio of the thickener (B) is equal to or less than the above-mentioned preferable value, the torque decreases further.

[0018] The aspect ratio of the thickener (B) in the grease composition of this embodiment can be controlled by adjusting the combination and contents of the base oil (A) and the thickener (B), as well as adjusting the homogenization time by the three-roll mill treatment in the production process of the grease composition of this embodiment.

[0019] <Base oil (A)> The grease composition of the present embodiment contains a base oil (A). The kinematic viscosity of base oil (A) at 40°C is 20mm 2 / s or more is preferable, 30 mm 2 / s or more is preferable, 40 mm 2 / s or more is even more preferable. The kinematic viscosity of base oil (A) at 40°C is 100mm 2 / s or less is preferable, 70 mm 2 / s or less is preferable, and 50 mm 2 / s or less is even more preferable.

[0020] When the kinematic viscosity at 40°C of the base oil (A) of the grease composition of the present embodiment is equal to or greater than the above-mentioned preferable lower limit, the lubricity of the grease composition is improved, the effects of using the grease composition are more fully obtained, and the torque reduction is further improved. When the kinematic viscosity at 40°C of the base oil (A) of the grease composition of this embodiment is not more than the above preferred upper limit, the viscous resistance caused by the grease composition is reduced, and torque reduction is further improved.

[0021] For example, the kinematic viscosity of base oil (A) at 40°C is 20mm 2 / s or more 100mm 2 / s or less is preferable, 30 mm 2 / s or more 70mm 2 / s or less is preferable, and 40 mm 2 / s or more 50mm 2 / s or less is even more preferable.

[0022] In this specification, the kinematic viscosity at 40°C means the kinematic viscosity at 40°C measured in accordance with JIS K2283:2000.

[0023] The base oil (A) of the grease composition of this embodiment may be a mineral oil or a synthetic oil.

[0024] <Mineral oil> As the mineral oil, a distillate oil obtained by atmospheric distillation of crude oil can be used. In addition, a lubricating oil fraction obtained by further vacuum distillation of the distillate oil and then refining the distillate oil through various refining processes can also be used. The refining process may be a suitable combination of hydrorefining, solvent extraction, solvent dewaxing, hydrodewaxing, sulfuric acid washing, clay treatment, etc. Mineral oil can be obtained by combining these refining processes in a suitable order. Furthermore, a mixture of a plurality of refined oils with different properties obtained by subjecting different crude oils or distillate oils to a combination of different refining processes may also be used.

[0025] As the mineral oil, API base oil classification Group I base oil (hereinafter referred to as "API Group I base oil"), Group II base oil (hereinafter referred to as "API Group II base oil"), or Group III base oil (hereinafter referred to as "API Group III base oil"), or a mixture thereof, can be used. API Group I base oils are mineral base oils having a sulfur content greater than 0.03 wt.% and / or a saturates content less than 90 wt.% and a viscosity index greater than or equal to 80 and less than 120. API Group II base oils are mineral base oils having a sulfur content of 0.03% by weight or less, a saturates content of 90% by weight or more, and a viscosity index of 80 or greater but less than 120. API Group III base oils are mineral base oils having a sulfur content of 0.03% by weight or less, a saturates content of 90% by weight or more, and a viscosity index of 120 or greater.

[0026] The base oil (A) of the grease composition of this embodiment may be a single mineral oil or a mixture of multiple mineral oils, the API classifications of which may be the same or different.

[0027] ≪Synthetic oil≫ Examples of synthetic oils include polyolefins such as poly-α-olefins, ester base oils such as diesters and polyol esters, polyalkylene glycols, alkylbenzenes, and alkylnaphthalenes. Among the above synthetic oils, polyolefins are preferred, and poly-α-olefins (PAOs) are more preferred, from the viewpoints of availability, cost, viscosity characteristics, and oxidation stability. As the base oil (A) of the grease composition of this embodiment, one synthetic oil may be used alone, or a mixture of multiple synthetic oils may be used.

[0028] As the base oil (A) of the grease composition of this embodiment, either a mineral oil or a synthetic oil may be used, or a mixture of a mineral oil and a synthetic oil may be used. The base oil (A) of the grease composition of this embodiment preferably contains a synthetic oil, and more preferably contains a poly-α-olefin.

[0029] The content of the base oil (A) in the grease composition of this embodiment is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and particularly preferably 80% by mass or more, based on the total amount of the grease composition. On the other hand, the content of the base oil (A) in the grease composition of this embodiment is preferably 95 mass % or less, and more preferably 90 mass % or less, based on the total amount of the grease composition. For example, the content of base oil (A) in the grease composition of this embodiment is preferably 50% by mass or more and 95% by mass or less, more preferably 60% by mass or more and 95% by mass or less, even more preferably 70% by mass or more and 95% by mass or less, and particularly preferably 80% by mass or more and 90% by mass or less, based on the total amount of the grease composition.

[0030] <Thickener (B)> The grease composition of this embodiment contains a thickener (B). Specific examples of the thickener (B) include urea-based thickeners (B1) and metal soap-based thickeners (B2).

[0031] <Urea-based thickener (B1)> Examples of the urea-based thickener (B1) (hereinafter also referred to as "component (B1)") include diurea compounds and polyurea compounds. A diurea compound is a compound obtained by reacting a diisocyanate with a monoamine, and has two urea groups (-NH-CO-NH-). In this specification, a polyurea compound refers to a compound obtained by reacting a diisocyanate with a monoamine or diamine, and having three or more urea groups (—NH—CO—NH—).

[0032] Diisocyanates Diisocyanates are compounds in which two hydrogen atoms of a hydrocarbon are replaced with an isocyanate group (-N=C=O). The hydrocarbon may be a cyclic hydrocarbon or a chain hydrocarbon, and may be an aromatic hydrocarbon or an aliphatic hydrocarbon. The number of carbon atoms in the hydrocarbon is preferably 4 to 20, and more preferably 8 to 18. In the present invention, "4 to 20 carbon atoms" means having 4 or more and 20 or less carbon atoms.

[0033] Specific preferred examples of diisocyanates include phenylene diisocyanate, tolylene diisocyanate, biphenyl diisocyanate (diphenyl diisocyanate), diphenylmethane-4,4'-diisocyanate (MDI), octadecane diisocyanate, decane diisocyanate, and hexane diisocyanate. The diisocyanates may be used singly or in combination of two or more.

[0034] Monoamines A monoamine is a compound that contains one amino group per molecule. Preferred monoamines include octylamine, dodecylamine, hexadecylamine, stearylamine (octadecylamine), oleylamine, aniline, p-toluidine, and cyclohexylamine. The monoamine may be a cyclic amine or a chain amine, and may also be an alicyclic amine, an aromatic amine, or an aliphatic amine. The monoamine preferably has 4 to 20 carbon atoms, and more preferably 8 to 18 carbon atoms.

[0035] Diamine A diamine is a compound that has two amino groups in one molecule. Preferred diamines include ethylenediamine, propanediamine, butanediamine, hexanediamine, octanediamine, phenylenediamine, tolylenediamine, xylenediamine, and diaminodiphenylmethane. The diamine may be a cyclic amine or a chain amine, and may also be an alicyclic amine, an aromatic amine, or an aliphatic amine. The diamine preferably has 4 to 20 carbon atoms, and more preferably 8 to 18 carbon atoms.

[0036] The component (B1) may be used alone or in combination of two or more. Of the above, diurea compounds are preferred as the component (B1). The diurea compound is preferably a compound obtained by reacting a diisocyanate having an aromatic hydrocarbon group with a monoamine. As the diisocyanate having an aromatic hydrocarbon group, diphenylmethane-4,4'-diisocyanate (MDI) is preferred. The monoamine is preferably an alicyclic amine or an aliphatic amine.

[0037] <Metal soap-based thickener (B2)> The metal soap-based thickener (B2) (hereinafter also referred to as "component (B2)") includes simple soaps and complex soaps. The simple soap is a metallic soap obtained by saponifying a fatty acid or fat with an alkali metal hydroxide or alkaline earth metal hydroxide. Complex soap is a compound soap that combines the fatty acids used in simple soap with organic acids of different molecular structures. The fatty acid may be a fatty acid derivative having a hydroxy group or the like. The fatty acid is preferably a monovalent or divalent aliphatic carboxylic acid. The fatty acid is preferably an aliphatic carboxylic acid having 6 to 20 carbon atoms, more preferably a monovalent aliphatic carboxylic acid having 12 to 20 carbon atoms or a divalent aliphatic carboxylic acid having 6 to 14 carbon atoms. Among the above, the fatty acid is preferably a monovalent aliphatic carboxylic acid containing one hydroxy group. As the organic acid to be combined with the fatty acid in the complex soap, a dibasic acid such as acetic acid, azelaic acid or sebacic acid, or benzoic acid is preferred.

[0038] The metal for the metal soap thickener may be an alkali metal such as lithium or sodium, an alkaline earth metal such as calcium, or an amphoteric metal such as aluminum. The component (B2) may be used alone or in combination of two or more.

[0039] <Other thickeners (B3)> Specific examples of other thickeners (B3) (hereinafter also referred to as "component (B3)") include inorganic thickeners such as bentonite and silica gel. The component (B3) may be used alone or in combination of two or more.

[0040] As the thickener (B) of the grease composition of this embodiment, any one of the components (B1), (B2), and (B3) may be used, or a mixture of two or more of the components (B1), (B2), and (B3) may be used. The thickener (B) of the grease composition of this embodiment is preferably component (B1) from the viewpoint of heat resistance, and more preferably a diurea compound.

[0041] The proportion of the (B1) component in the thickener (B) of the grease composition of this embodiment is preferably 80 mass % or more, more preferably 90 mass % or more, based on the total amount of the thickener (B), and even more preferably 100 mass %, i.e., it is composed solely of the (B1) component. In one embodiment, the grease composition does not include a grease composition containing components (B2) and (B3) as the thickener (B).

[0042] The content of the thickener (B) in the grease composition of this embodiment is preferably 5% by mass or more, and more preferably 10% by mass or more, based on the total amount of the grease composition. On the other hand, the content of the thickener (B) in the grease composition of this embodiment is preferably 30% by mass or less, and more preferably 20% by mass or less, based on the total amount of the grease composition. For example, the content of the thickener (B) in the grease composition of this embodiment is preferably 5% by mass or more and 30% by mass or less, and more preferably 10% by mass or more and 20% by mass or less, based on the total amount of the grease composition.

[0043] When the content of the thickener (B) in the grease composition of this embodiment is within the above-mentioned preferred range, the aspect ratio of the thickener (B) in the grease composition can be more easily controlled to less than 0.23.

[0044] <Optional ingredients> The grease composition of this embodiment may contain optional components other than the base oil (A) and thickener (B), such as solid lubricants, antiwear or extreme pressure agents, antioxidants, oiliness agents, rust inhibitors, and corrosion inhibitors.

[0045] Examples of solid lubricants include graphite, graphite fluoride, melamine cyanurate, polytetrafluoroethylene, molybdenum disulfide, antimony sulfide, boron nitride, and alkaline (earth) metal borates. When the grease composition contains a solid lubricant, the content thereof is, for example, 0.1 to 20 mass% relative to the total amount of the grease composition. One type of solid lubricant may be used alone, or multiple solid lubricants may be used in combination.

[0046] Examples of anti-wear agents or extreme pressure agents include organic zinc compounds such as zinc dialkyldithiophosphate and zinc dialkyldithiocarbamate; sulfur-containing compounds such as molybdenum dialkyldithiocarbamate, dihydrocarbyl polysulfide, sulfurized esters, thiazole compounds, and thiadiazole compounds; and phosphorus-based extreme pressure agents such as phosphate esters, acid phosphate esters, amine salts of acid phosphate esters, and phosphites. When the grease composition contains an anti-wear agent or extreme pressure agent, the content thereof is, for example, 0.1 to 10 mass% based on the total amount of the grease composition. One type of anti-wear agent or extreme pressure agent may be used alone, or multiple anti-wear agents or extreme pressure agents may be used in combination.

[0047] Examples of antioxidants include phenolic compounds such as 2,6-di-t-butylphenol and 2,6-di-t-butyl-p-cresol; and amine compounds such as diphenylamine, dialkyldiphenylamine, phenyl-α-naphthylamine, and p-alkylphenyl-α-naphthylamine. When the grease composition contains an antioxidant, the content thereof is, for example, 0.5 to 10 mass% relative to the total amount of the grease composition. One type of antioxidant may be used alone, or multiple antioxidants may be used in combination.

[0048] Examples of oily agents include amines such as laurylamine, myristylamine, palmitylamine, stearylamine, and oleylamine; higher alcohols such as lauryl alcohol, myristyl alcohol, palmityl alcohol, stearyl alcohol, and oleyl alcohol; higher fatty acids such as lauric acid, myristic acid, palmitic acid, stearic acid, and oleic acid; fatty acid esters such as methyl laurate, methyl myristate, methyl palmitate, methyl stearate, and methyl oleate; and fats and oils such as glycerin oleate and glycerin stearate. When the grease composition contains an oily agent, the content thereof is, for example, 0.01 to 5% by mass relative to the total amount of the grease composition. One oily agent may be used alone, or multiple oily agents may be used in combination.

[0049] Examples of rust inhibitors include amines, neutral or overbased petroleum-based or synthetic oil-based metal sulfonates, metal carboxylates, esters, phosphoric acid, phosphates, etc. When the grease composition contains a rust inhibitor, the content thereof is, for example, 0.005 to 5 mass% relative to the total amount of the grease composition. One type of rust inhibitor may be used alone, or multiple rust inhibitors may be used in combination.

[0050] As the corrosion inhibitor, for example, known corrosion inhibitors such as benzotriazole-based compounds, tolyltriazole-based compounds, thiadiazole-based compounds, and imidazole-based compounds can be used. When the grease composition contains a corrosion inhibitor, the content thereof is, for example, 0.01 to 10 mass% relative to the total amount of the grease composition. The corrosion inhibitor may be used alone, or multiple corrosion inhibitors may be used in combination.

[0051] (Method for producing grease composition) The method for producing the grease composition of the present embodiment includes a mixing step of mixing the base oil (A) and the thickener (B) to obtain a mixture, and a kneading step of kneading the mixture obtained in the mixing step with a roll mill.

[0052] <Mixing process> The mixing step is a step of mixing the base oil (A) and the thickener (B). The mixing step can be carried out using, for example, a magnetic stirrer, or by hand. The mixing step is preferably carried out under heating, preferably at a heating temperature of 50 to 80°C, more preferably 60 to 65°C.

[0053] <Kneading process> The kneading step is a step in which the mixture obtained in the mixing step is kneaded in a roll mill. In the kneading step, the grease composition can be kneaded so that the aspect ratio of the thickener (B) in the grease composition is less than 0.23.

[0054] The particles in the mixture are crushed to a certain particle size by kneading, but if further kneading is performed in this state, the particles that have been crushed to a certain particle size will gather together again and re-agglomerate. Therefore, in order to control the aspect ratio of the thickener (B) in the grease composition to be less than 0.23, it is not enough to simply increase the load in the kneading step; it is important to appropriately control the production conditions in the kneading step.

[0055] The kneading process is carried out using a three-roll mill, which can be hydraulic or non-hydraulic. A non-hydraulic three-roll mill is a device that pulverizes, kneads, disperses, and degasses materials by controlling the gap between the rolls and compressing the material by forcing it into the narrow gap between the rolls, and by shearing it due to the difference in roll speed. On the other hand, a hydraulic three-roll mill (hereinafter also referred to as a "hydraulic roll") is a device that can press rolls together using hydraulic force, and unlike the non-hydraulic three-roll mill described above, it is a device that can more precisely control the load on the material to be kneaded.

[0056] <Optional process> The method for producing a grease composition of this embodiment may include optional steps in addition to the mixing step and the kneading step. The optional steps include, before the above-mentioned mixing step, a preparation step of preparing a synthesis material (B0) for synthesizing a thickener (B), a synthesis step of reacting the synthesis material (B0) in the base oil (A) to synthesize the thickener (B), and a cooling step of cooling the mixture obtained in the mixing step.

[0057] ≪Preparation process≫ The preparation step is a step of preparing a synthesis material (B0) for synthesizing the thickener (B) before the above-mentioned mixing step. Specific examples of the synthesis material (B0) include diisocyanates and monoamines or diamines used to synthesize the component (B1) described above.

[0058] ≪Synthesis process≫ The synthesis step is a step of synthesizing a thickener (B) by reacting a synthesis material (B0) in a base oil (A). The dispersibility of the thickener (B) is improved by synthesizing the thickener (B) by reacting the synthetic material (B0) in the base oil (A) rather than preparing the base oil (A) and the thickener (B) separately and mixing them. In this case, the synthesis process and the mixing process are carried out simultaneously. The synthesis step is preferably a step of synthesizing a urea-based thickener (B1) by reacting an isocyanate with an amine, and more preferably a step of synthesizing a diurea compound by reacting a diisocyanate with a monoamine.

[0059] The synthesis step is preferably carried out under heating, as in the mixing step, with the heating temperature being preferably 50 to 80°C, more preferably 60 to 65°C.

[0060] ≪Cooling process≫ The cooling step is a step of cooling the mixture obtained in the mixing step. The mixture may be cooled using a cooler or at room temperature (25°C).

[0061] A preferred embodiment of the method for producing the grease composition of this embodiment is as follows. A preparation step of preparing a base oil (A), an isocyanate, and an amine; a synthesis step of synthesizing a urea-based thickener (B1) by reacting the isocyanate with the amine in the base oil (A); a mixing step of mixing the base oil (A) with the urea-based thickener (B1) obtained in the synthesis step; a cooling step of cooling the mixture obtained in the mixing step; and a kneading step of kneading the mixture obtained in the cooling step using a non-hydraulic three-roll mill. In the kneading step, the mixture is kneaded so that the aspect ratio of the thickener (B) in the mixture is less than 0.23. [Example]

[0062] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0063] <Formulation of grease composition> The grease composition of Example 1 and the grease compositions of Comparative Examples 1 to 3 were prepared by blending a base oil (A) and a thickener (B) in the blending ratios shown in Table 1. The "components" in Table 1 indicate the blending ratio (mass %) relative to the total amount of the grease composition. The obtained grease compositions of each example were evaluated as follows. The evaluation results are shown in Table 1 and Figures 1 to 4.

[0064] (1) Base oil (A) (A)-1: Poly-α-olefin (40°C kinematic viscosity = 48 mm 2 / s)

[0065] (2) Thickener (B) (B1)-1: Diurea compound (a diurea compound obtained by the reaction of diphenylmethane-4,4'-diisocyanate (MDI) with octylamine) (B1)-2: Diurea compound (a diurea compound obtained by the reaction of diphenylmethane-4,4'-diisocyanate (MDI) with cyclohexylamine) (B1)-3: Diurea compound (a diurea compound obtained by the reaction of diphenylmethane-4,4'-diisocyanate (MDI) with octadecylamine)

[0066] <Production of grease composition> (Grease composition of Example 1) ·Preparation process~cooling process Diphenylmethane-4,4'-diisocyanate (MDI) and octylamine, the raw materials for thickener (B1)-1, were prepared so that the blending ratio of thickener (B1)-1 was the blending ratio shown in Table 1. Base oil (A)-1 was prepared so that the blending ratio was the blending ratio shown in Table 1, and divided into two stainless steel containers. Diphenylmethane-4,4'-diisocyanate (MDI) was added to one of the stainless steel containers containing base oil (A)-1, heated to 60-65°C, and stirred with a magnetic stirrer to obtain mixed solution P. Octylamine was added to the other stainless steel container, heated to 60-65°C, and stirred with a magnetic stirrer to obtain mixed solution Q. Next, the mixed solution P and the mixed solution Q were mixed and stirred with a magnetic stirrer at 60 to 65°C, whereby diphenylmethane-4,4'-diisocyanate (MDI) and octylamine were reacted in the base oil (A)-1 to synthesize the thickener (B1)-1, while the base oil (A)-1 and the thickener (B1)-1 were mixed. The mixture was then cooled to room temperature, yielding a semi-solid composition.

[0067] · Mixing process The resulting semi-solid composition was kneaded twice using a non-hydraulic three-roll mill under the following production conditions to prepare the grease composition of Comparative Example 1. ≪Manufacturing conditions≫ Shear rate: 1.4 x 10 between the first and second rolls 3 / s, 1.2 × 10 between the second and third rolls 4 / s Distance between rolls: 0.15 mm between the first and second rolls, 0.05 mm between the second and third rolls

[0068] (Grease composition of Comparative Example 1) A grease composition of Comparative Example 1 was prepared in the same manner as in Example 1, except that the kneading step was changed as follows. · Mixing process The resulting semi-solid composition was kneaded twice using a hydraulic three-roll mill under the following production conditions to prepare the grease composition of Example 1. ≪Manufacturing conditions≫ Roll clamping pressure: 4MPa Shear rate: 5.8 x 10 between the first and second rolls 5 / s, 8.1 x 10 between the second and third rolls 5 / s

[0069] (Grease composition of Comparative Example 2) A grease composition of Comparative Example 2 was prepared in the same manner as in Example 1, except that the thickener (B1)-1 was changed to the thickener (B1)-2.

[0070] (Grease composition of Comparative Example 3) A grease composition of Comparative Example 3 was prepared in the same manner as in Example 1, except that the thickener (B1)-1 was changed to the thickener (B1)-3.

[0071] [Consistency evaluation] The worked penetration of each grease composition measured in accordance with JIS K2220:2013 is shown in Table 1.

[0072] [Aspect ratio measurement] Each grease composition was observed using a dielectric constant observation system on a scanning electron microscope owned by the National Institute of Advanced Industrial Science and Technology. A small amount of each grease composition was placed on the tip of a toothpick, and 0.1 mg of each was attached to the silicon nitride thin film window material of a dedicated sample holder. The holder with the grease composition attached was set in a centrifuge and the grease composition was adjusted to a thickness of 10 μm or less at 5,000 to 10,000 rpm for 1 minute, and then introduced into the device. Since the measurement conditions depend on the thickness of the grease composition, the accelerating voltage was adjusted to 3.0 to 20.0 kV and the probe current to 10 to 20 pA, respectively, to enable observation of the thickener. The observation range was approximately 1.2 x 10 2 μm 2 The observed image was an 8-bit grayscale image of 1280 × 960 pixels. Device name: Scanning electron microscope dielectric constant observation system Acceleration voltage: 3 to 20 keV Irradiation current: 10~20pA Observation magnification: 10,000 to 20,000 times

[0073] The observation image obtained using the dielectric observation system of the scanning electron microscope was used to extract and digitize the area corresponding to the thickener (dark area) using image analysis software ("Image-Pro 10" manufactured by Media Cybernetics). The extracted area was approximated as an ellipse using the measurement function of the image analysis software, and the "area: width (minor axis)" and "area: length (major axis)" were measured to calculate the aspect ratio (major axis / minor axis).

[0074] The images obtained above are shown in Figures 1 to 4. Figure 1 is an image of the grease composition of Example 1. Figure 2 is an image of the grease composition of Comparative Example 1. Figure 3 is an image of the grease composition of Comparative Example 2. Figure 4 is an image of the grease composition of Comparative Example 3.

[0075] [Torque measurement] Each bearing sample was created by filling 0.25 g (2 g total) of each grease composition into the cage at eight locations between the balls of a 6204 ball bearing and sealing with a rubber seal. An axial load of 50 N and a radial load of 50 N were applied, and the inner ring was rotated at 2000 rpm at room temperature. The tangential force acting on the housing was measured with a load cell to determine the torque (mN m) of each grease composition. The bearing torque was measured 30 minutes after the start of rotation. The results are shown in Table 1.

[0076] [Table 1]

[0077] As shown in Table 1, it was confirmed that the grease compositions of the examples in which the aspect ratio of the thickener (B) was less than 0.23 could reduce torque compared to the grease compositions of comparative examples 1 to 3 in which the aspect ratio of the thickener (B) was 0.23 or more.

Claims

1. A grease composition containing a base oil (A) and a thickener (B), A grease composition, wherein, when the minor axis and major axis of the thickener (B) in the grease composition are measured using a dielectric constant observation system of a scanning electron microscope, the aspect ratio (minor axis / major axis) of the thickener (B) is less than 0.

23.

2. 2. The grease composition according to claim 1, wherein the thickener (B) is a urea-based thickener (B1).

3. The grease composition according to claim 2, wherein the urea-based thickener (B1) is a diurea compound.

4. 3. The grease composition according to claim 1, wherein the content of the thickener (B) is 5% by mass or more relative to 100% by mass of the total amount of the grease composition.

5. 3. The grease composition according to claim 1, wherein the thickener (B) has an aspect ratio of 0.21 or less.

Images