Grease composition

Abstract

To provide a grease composition that can be used in various environments and can achieve wear resistance and low dust generation.SOLUTION: A grease composition comprises a thickener, a base oil, and a rust inhibitor, wherein the thickener comprises alicyclic-aliphatic diurea, the base oil consists of an ether oil or consists of a high-viscosity synthetic hydrocarbon oil having a kinematic viscosity at 40°C of 300 to 500 mm2 / s and an ether oil, a content of the ether oil is 80 mass% or more based on a total mass of the base oil, a kinematic viscosity of the base oil at 40°C is 90 to 150 mm2 / s, and a kinematic viscosity at -30°C is 60000 mm2 / s or less, the rust inhibitor is a succinic acid-based rust inhibitor, and a 60-stroke worked penetration measured in accordance with JIS K 2220 7. is 180 to 230.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] In general, drive parts used in precision electronic device manufacturing equipment such as semiconductor manufacturing equipment, liquid crystal manufacturing equipment, and printed circuit board manufacturing equipment, as well as machine tools and robotics applications, are required to be extremely dust-free and capable of operating in a variety of environments, from low to high temperatures. Examples of such drive parts include ball screws, linear guides, and servo motors. Of these, servo motors for robots are often used to drive joints, and so they need to be small and have high output in order to increase the axial speed and acceleration / deceleration of the joints.To achieve miniaturization, detectors and brakes are placed near the rolling bearings, but if some of the grease droplets inside the bearings adhere to the detectors or brakes, this will reduce detection accuracy and braking performance, so the grease needs to be low-dust generating. Dust generation occurs when heat generated by the rotation of a rolling bearing and an increase in pressure inside the bearing cause some of the grease to evaporate or scatter and be released outside the bearing. Effective ways to suppress dust generation are to increase the apparent viscosity of the grease or to reduce the amount of base oil in the grease. However, on the other hand, the supply of base oil to the rolling and sliding surfaces is likely to be insufficient, which may result in excessive temperature rise of the bearing and damage such as surface roughening and wear of the rolling and sliding surfaces. Patent Document 1 discloses a grease composition containing a base oil having a predetermined kinematic viscosity and 15 to 30 mass % of a predetermined fibrous thickener, which is a lithium salt of a fatty acid having 10 or more carbon atoms and no hydroxyl group. Patent Document 2 discloses a grease composition using an ester oil with a low kinematic viscosity as the base oil. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-352953 [Patent Document 2] JP 2018-188541 A Summary of the Invention [Problem to be solved by the invention]

[0004] The grease composition described in Patent Document 1 contains a metal salt as a thickener, and therefore, if the grease composition scatters, it may adhere to precision electronic devices such as semiconductor devices, causing malfunctions.The grease composition described in Patent Document 2 has insufficient low dust generation properties because the base oil has a low kinematic viscosity and the ester oil is hydrolyzed to a low molecular weight, which makes the base oil prone to evaporation and the grease prone to scattering. An object of the present invention is to provide a grease composition that can be used in a variety of environments and that can achieve wear resistance and even lower dust generation. [Means for solving the problem]

[0005] As a result of extensive research, the present inventors have found that the above problems can be solved by a grease composition having the following composition. That is, the present invention has the following configuration. [1] A grease composition containing a thickener, a base oil, and a rust inhibitor, The thickener comprises compounds represented by formula (1), formula (2), and formula (3), R 1 -NHCONH-R 2 -NHCONH-R 1 (1) R 1 -NHCONH-R 2 -NHCONH-R 3 (2) R 3 -NHCONH-R 2 -NHCONH-R 3 (3) (In the formula, R 1 is a cyclohexyl group, and R 2 is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, and R 3is an alkyl group having 6 to 30 carbon atoms. The base oil is an ether oil or has a kinematic viscosity of 300 to 500 mm at 40°C. 2 / s high viscosity synthetic hydrocarbon oil and ether oil, The content of the ether oil is 80 mass% or more based on the total mass of the base oil, The kinematic viscosity of the base oil at 40°C is 90 to 150 mm 2 / s, and the kinematic viscosity at -30°C is 60,000 mm 2 / s or less, The rust inhibitor is a succinic acid-based rust inhibitor, The grease composition has a 60-stroke worked penetration of 180 to 230 as measured in accordance with JIS K 2220 7. [2] Thickener, R 1 and R 3 The grease composition according to [1], wherein the molar ratio of the number of moles of the grease to the number of moles of the grease is 40:60 to 60:40. [3] The grease composition according to [1], further comprising an amine-based antioxidant. [Effects of the Invention]

[0006] The present invention can provide a grease composition that can be used in a variety of environments and that can achieve wear resistance and even lower dust generation. DETAILED DESCRIPTION OF THE INVENTION

[0007] <Base oil> In the present invention, a high-viscosity synthetic hydrocarbon oil or an ether oil, typically an alkyl diphenyl ether, is used as the base oil from the viewpoint of reducing dust generation due to evaporation of the base oil. Of these, it is preferable to use a base oil consisting of only an ether oil or a base oil consisting of a mixture of a high-viscosity synthetic hydrocarbon oil and an ether oil, and it is more preferable to use a base oil consisting of a mixture of a high-viscosity synthetic hydrocarbon oil and an ether oil. Examples of the ether oil include alkyl diphenyl ether, polyphenyl ether oil, alkyl triphenyl ether oil, and alkyl tetraphenyl ether oil, with alkyl diphenyl ether being preferred, and monoalkyl diphenyl ether oil, dialkyl diphenyl ether oil, and trialkyl diphenyl ether oil being more preferred. High viscosity synthetic hydrocarbon oils have a kinematic viscosity of 300 to 500 mm at 40°C. 2 As long as the range of / s is satisfied, there are no particular limitations, but examples include poly-α-olefin (PAO), polybutene, ethylene-α-olefin copolymer, etc., with PAO or polybutene being preferred, and PAO being more preferred. In the base oil used in the present invention, from the viewpoint of reducing dust generation due to evaporation of the base oil, the kinematic viscosity of the synthetic hydrocarbon oil at 40°C is 300 to 500 mm 2 / s, 350~450mm 2 The kinematic viscosity of the ether oil at 40°C is preferably 80 to 120 mm 2 / s is preferable, and 90 to 110 mm 2 / s is more preferable. When the base oil of the present invention is a mixture of a synthetic hydrocarbon oil and an ether oil, the mass ratio of the synthetic hydrocarbon oil to the ether oil is preferably synthetic hydrocarbon oil:ether oil=2:98 to 20:80, more preferably 5:95 to 15:85, from the viewpoint of reducing dust generation due to evaporation of the base oil. In addition, in order to reduce dust generation due to evaporation of the base oil, the kinematic viscosity of the entire base oil at 40°C is set to 90mm 2 / s or more, and 95 mm 2 From the viewpoint of maintaining fluidity at low temperatures, the kinematic viscosity of the entire base oil at 40°C is preferably 150 mm / s or more. 2 / s or less, and 140 mm 2 / s or less, and the kinematic viscosity of the base oil at -30°C is preferably 60000 mm 2 / s or less, 58000mm 2 The kinematic viscosity of the base oil at -30°C is preferably 20,000 mm / s or less. 2 / s or more is preferable, and 25,000 mm 2 / s or more is more preferable. In this specification, the kinematic viscosity is a value measured in accordance with JIS K2283. From the viewpoint of reducing dust generation due to evaporation of the base oil, the content of the base oil in the grease composition of the present invention is preferably 75 to 90 mass %, more preferably 80 to 87 mass %, and even more preferably 83 to 87 mass %, based on the total mass of the composition.

[0008] <Thickener> The fluidity of the grease composition filled in the bearing varies depending on the type of thickener, and the thickener can have a significant effect on the apparent viscosity of the grease. The thickener used in the present invention is an alicyclic-aliphatic diurea, which is a mixture of compounds represented by the following formulas (1), (2), and (3): R 1 -NHCONH-R 2 -NHCONH-R 1 (1) R 1 -NHCONH-R 2 -NHCONH-R 3 (2) R 3 -NHCONH-R 2 -NHCONH-R 3 (3) In the formula, R 1 is a cyclohexyl group, and R 2 is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, and R 3 is an alkyl group having 6 to 30 carbon atoms. R 2 Representative examples of the divalent aromatic hydrocarbon group having 6 to 15 carbon atoms include those represented by the following structural formulas: Of these, a diphenylmethane group is more preferred.

[0009] [ka]

[0010] R 3The alkyl group having 6 to 30 carbon atoms is preferably a linear alkyl group having 8 to 18 carbon atoms, more preferably a linear alkyl group having 12 to 18 carbon atoms, and particularly preferably a linear alkyl group having 18 carbon atoms. The thickener of the present invention preferably contains a diurea represented by formula (2) among the compounds represented by formula (1), formula (2), and formula (3). In the mixture of compounds represented by formula (1), formula (2), and formula (3), R 1 The cyclohexyl group and R 3 The molar ratio of the alkyl groups having 6 to 30 carbon atoms is preferably 40:60 to 60:40, and more preferably 45:55 to 55:45. From the viewpoint of reducing dust generation due to scattering of the grease, the grease composition of the present invention preferably has a consistency of 180 to 230, more preferably 190 to 230. The content of the thickener in the grease composition of the present invention may be any amount suitable for adjusting the consistency to within the above range, and is, for example, preferably 13 to 17 mass %, more preferably 14 to 16 mass %, based on the total mass of the composition. In this specification, when simply referring to "consistency," it refers to the 60-stroke worked consistency measured in accordance with JIS K 2220 7.

[0011] <Rust inhibitor> The rust inhibitors that can be used in the present invention are succinic acid-based rust inhibitors from the viewpoint of low dust generation and abrasion resistance, and succinic anhydride is preferred, alkenylsuccinic anhydride is more preferred, and succinic anhydride having an alkenyl group with 12 carbon atoms is particularly preferred. In the grease composition of the present invention, the content of the rust inhibitor is preferably 0.1 to 1.0 mass%, more preferably 0.1 to 0.8 mass%, and even more preferably 0.1 to 0.5 mass%. By including the rust inhibitor in such a range, a good rust prevention effect can be obtained. On the other hand, if the content exceeds 1.0 mass%, the effect will plateau.

[0012] <Antioxidants> The grease composition of the present invention may further contain an amine-based antioxidant. The amine-based antioxidant that can be used in the present invention is preferably selected from the group consisting of p,p'-dioctyldiphenylamine, N-phenyl-α-naphthylamine, alkylated phenyl-α-naphthylamine, and mixtures thereof. Of these, p,p'-dioctyldiphenylamine is particularly preferred. The inclusion of such an amine-based antioxidant provides excellent suppression of base oil degradation at high temperatures. The content of the amine-based antioxidant in the grease composition of the present invention is preferably 0.1 to 1.0 mass%, more preferably 0.1 to 0.8 mass%, and even more preferably 0.1 to 0.5 mass%, based on the total mass of the composition. By including the amine-based antioxidant in such a range, a good effect of preventing oxidative degradation can be obtained. On the other hand, if the content exceeds 1.0 mass%, the effect will plateau. [Example]

[0013] <Preparation of grease composition> Examples 1 to 5, Comparative Examples 2 to 4, and Comparative Example 6 In the base oil shown in the table below, 1 mole of 4,4'-diphenylmethane diisocyanate (MDI) was reacted with 2 moles of amine (a mixture of cyclohexylamine and stearylamine in the molar ratio shown in the table below), and the reaction mixture was heated and cooled to obtain a base grease. This base grease was diluted with additional base oil, and the additives shown in the table below were added. The mixture was then kneaded on a three-roll mill to adjust the worked penetration at 60 strokes, as measured according to JIS K2220 7, to the value shown in the table below. Comparison Example 1 In the base oil shown in the table below, 1 mole of 4,4'-diphenylmethane diisocyanate (MDI) was reacted with 2 moles of octylamine in a predetermined amount, and the mixture was heated and cooled to obtain a base grease. Using this base grease, the grease composition of Comparative Example 1 was obtained using the same procedure as above. Comparative Example 5 In the base oil shown in the table below, 1 mole of 4,4'-diphenylmethane diisocyanate (MDI) was reacted with 2 moles of amine (a mixture of cyclohexylamine and stearylamine in the molar ratio shown in the table below), and the mixture was heated and cooled to obtain a base grease. This base grease was diluted with additional base oil, and the additives shown in the table below were added. The mixture was kneaded in a three-roll mill to obtain a worked penetration of 250 after 60 strokes, as measured according to JIS K2220 7. In the examples and comparative examples, unless otherwise specified, the numbers in the tables below represent mass % based on the total mass of the composition. In the table below, the alkyl diphenyl ether oil is a mixture of dialkyl diphenyl ether oil and trialkyl diphenyl ether oil, and the alkenyl succinic anhydride is succinic anhydride having an alkenyl group with 12 carbon atoms.

[0014] <Testing and evaluation methods> The obtained grease compositions of the Examples and Comparative Examples were evaluated by the following test methods and test conditions. 1. Thermogravimetry (TG) (evaluation of low dust generation) Using a Thermo plus EVO TG 8120 manufactured by Rigaku, the temperature was raised to 120°C at a rate of 10°C / min while introducing air at a flow rate of 200 ml / min, and the sample was then left to stand for 12 hours, after which the weight loss rate was measured. [Evaluation criteria] Weight reduction rate 0.80% or less...〇(Pass) Exceeding 0.80%...×(Fail) 2. Apparent viscosity measurement (evaluation of low dust generation) The rheometer uses parallel plates with a diameter of 25 mm, the gap (the distance between the measurement field and the parallel plates) is set to 0.01 mm, and the shear rate is 3000 s -1 The apparent viscosity was measured at this time. [Evaluation criteria] Apparent viscosity 1.9 Pa·s or more....Good (passed) Less than 1.9 Pa·s: × (fail) 3. Abrasion resistance test (evaluation of abrasion resistance) A four-ball wear test was conducted in accordance with ASTM D 2266 at a temperature of 100°C, a load of 392N, a rotation speed of 1200 rpm, and a test time of 1 hour, and the diameter of the wear scar on the steel balls after the test was measured. [Evaluation criteria] Wear scar diameter less than 1000 μm: Good (passed) 1000μm or more...×(Fail) 4. Rust prevention test (evaluation of rust prevention) A rust prevention test was carried out in accordance with ASTM D 1743-73 to determine the state of rust formation. [Evaluation criteria] No rusting.....〇 (passed) Rust present...× (fail) 5. Low temperature properties (evaluation of low temperature fluidity) The kinematic viscosity of the base oil was measured at a constant temperature of -30°C according to JIS K2283. [Evaluation criteria] Dynamic viscosity is 60,000 mm 2 / s or less...〇(Pass) 60,000mm 2 / s exceeded...×(fail)

[0015] [Table 1]

[0016] The grease compositions of Examples 1 to 5 passed all of the tests for low dust generation, wear resistance, rust prevention, and low-temperature properties. Comparative Example 1, which used octylamine and MDI as the thickener, was not satisfactory in terms of low dust generation. Comparative Example 2, in which only synthetic hydrocarbon oil was used, was not satisfactory in terms of low dust generation. Kinematic viscosity 62.6mm 2 Comparative Example 3, which used a low-viscosity synthetic hydrocarbon oil of 1 / s, was not satisfactory in terms of low dust generation. The kinematic viscosity of the base oil at 40°C is 154mm 2 Comparative Example 4, in which the temperature was 100°C / s, was not satisfactory in terms of low temperature properties. Comparative Example 5, which had a consistency of 250, did not satisfy the requirement for low dust generation. Comparative Example 6, which used an ester-based rust inhibitor, was unable to provide satisfactory wear resistance and rust prevention properties. From the above, it can be said that the grease composition having the specific configuration of the present invention can satisfy all of the requirements for low dust generation, wear resistance, rust prevention, and low-temperature properties. [Industrial Applicability]

[0017] The low-dust-generation grease of the present invention is a grease composition that can be used in a variety of environments and achieves wear resistance and even lower dust generation, and therefore can be suitably used for linear motion parts such as ball screws and linear guides, bearings for servo motors, etc.

Claims

1. A grease composition containing a thickener, a base oil, and a rust inhibitor, The thickener comprises compounds represented by formula (1), formula (2), and formula (3), R 1 -NHGNH-R 2 -NHGNH-R 1 (1) R 1 -NHGNH-R 2 -NHGNH-R 3 (2) R 3 -NHGNH-R 2 -NHGNH-R 3 (3) (In the formula, R 1 is a cyclohexyl group, and R 2 is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, and R 3 is an alkyl group having 6 to 30 carbon atoms. The base oil is an ether oil or has a kinematic viscosity of 300 to 500 mm at 40°C. 2 / s high viscosity synthetic hydrocarbon oil and ether oil, The content of the ether oil is 80% by mass or more based on the total mass of the base oil, The kinematic viscosity of the base oil at 40°C is 90 to 150 mm 2 / s, and the kinematic viscosity at -30°C is 60,000 mm 2 / s or less, The rust inhibitor is a succinic acid-based rust inhibitor, The grease composition has a 60-stroke worked penetration of 180 to 230 as measured in accordance with JIS K 2220 7.

2. Among thickeners, R 1 The number of moles and R 3 The grease composition according to claim 1, wherein the molar ratio of the number of moles of the hydroxybenzoates to the number of moles of the hydroxybenzoates is 40:60 to 60:

40.

3. The grease composition according to claim 1, further comprising an amine-based antioxidant.

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