Grease composition

Abstract

Provided is a grease composition that can be used in various environments and can achieve abrasion resistance and low dust-generation properties. The grease composition contains a thickener, a base oil, and a rust inhibitor. The thickener contains an alicyclic-aliphatic diurea. The base oil comprises an ether oil, or comprises an ether oil and a high-viscosity synthetic hydrocarbon oil having a kinematic viscosity at 40°C of 300-500 mm2 / s, and the ether oil content 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 90-150 mm2 / s, and the kinematic viscosity at -30°C is 60,000 mm2 / s or less. The rust inhibitor is a succinic acid-based rust inhibitor. In addition, the 60-stroke worked penetration of the grease composition measured in accordance with JIS K 2220 7 is 180-230.

Description

Grease composition

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

[0002] In general, drive components used in precision electronics manufacturing equipment, such as semiconductor manufacturing equipment, liquid crystal manufacturing equipment, and printed circuit board manufacturing equipment, as well as in machine tools and robotics applications, are required to have very low dust levels and be able to operate in a variety of environments, from low to high temperatures. Examples of such drive components include ball screws, linear guides, and servo motors. Among these, servo motors for robots are often used to drive joints, and they require compact size and high output to increase the axial speed and acceleration / deceleration of the joints. To achieve compactness, detectors and brakes are placed near rolling bearings. However, if some of the grease droplets inside the bearing adhere to the detector or brake, detection accuracy and braking performance will be reduced, so low dust-emission grease is required. Dust emission occurs when heat generated by the rotation of the rolling bearing and increased pressure inside the bearing cause some of the grease to evaporate or disperse and be released outside the bearing. Effective ways to suppress dust emission include increasing the apparent viscosity of the grease and reducing the amount of base oil in the grease. However, on the other hand, this can lead to insufficient supply of base oil to the rolling or sliding surfaces, which may result in excessive temperature rise of the bearing and damage such as surface roughening and wear of the rolling or 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 groups. Patent Document 2 discloses a grease composition which uses an ester oil with a low kinematic viscosity base oil.

[0003] JP 2004-352953 A JP 2018-188541 A

[0004] The grease composition described in Patent Document 1 contains a metal salt as a thickener, and therefore, if the grease composition splashes, 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 splashing. The present invention aims to provide a grease composition that can be used in a variety of environments and can achieve wear resistance and even lower dust generation.

[0005] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by a grease composition having the following configuration. That is, the present invention has the following configuration: [1] A grease composition containing a thickener, a base oil, and a rust inhibitor, wherein the thickener contains compounds represented by formula (1), formula (2), and formula (3), and 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) (wherein, 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 The present invention is based on a high-viscosity synthetic hydrocarbon oil having a kinematic viscosity of 90 to 150 mm / s and an ether oil, wherein the content of the ether oil is 80 mass% or more based on the total mass of the base oil, and the kinematic viscosity of the base oil at 40°C is 90 to 150 mm / s. 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, and the 60-stroke worked penetration measured in accordance with JIS K 2220 7 is 180 to 230. [2] Among the thickeners, R 1 The number of moles and R 3 The grease composition of [1], wherein the molar ratio of the number of moles of hydroxybenzoates to the number of moles of hydroxybenzoates is 40:60 to 60:40. [3] The grease composition of [1], further comprising an amine-based antioxidant.

[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.

[0007] <Base Oil> In the present invention, a high-viscosity synthetic hydrocarbon oil or an ether oil, such as alkyl diphenyl ether, is used as the base oil from the viewpoint of reducing dust generation due to evaporation of the base oil. Among these, it is preferable to use a base oil consisting of only 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 ether oils 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. As the high-viscosity synthetic hydrocarbon oil, a base oil having a kinematic viscosity at 40°C of 300 to 500 mm is used. 2 The base oil used in the present invention has a kinematic viscosity of 300 to 500 mm / s at 40°C, and is not particularly limited as long as it satisfies the range of 1 / s. Examples include poly-α-olefin (PAO), polybutene, ethylene-α-olefin copolymer, etc., and PAO or polybutene is preferred, with PAO being more preferred. 2 / s, 350 to 450 mm 2 The kinematic viscosity of the ether oil at 40°C is preferably 80 to 120 mm 2 / s, and 90 to 110 mm 2When 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. Furthermore, from the viewpoint of reducing dust generation due to evaporation of the base oil, the kinematic viscosity of the entire base oil at 40°C is preferably 90 mm 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 60,000 mm 2 / s or less, and 58,000 mm 2 The kinematic viscosity of the base oil at -30°C is preferably 20,000 mm / s or less. 2 / s or more, 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 therefore 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. 2 Representative examples of the divalent aromatic hydrocarbon group having 6 to 15 carbon atoms include those represented by the following structural formula: Of these, a diphenylmethane group is more preferred.

[0009]

[0010] R 3 The 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. Of the compounds represented by formula (1), formula (2), and formula (3), the thickener of the present invention preferably contains a diurea represented by formula (2). In the mixture of the 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, and 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 within the above range, and is, for example, preferably 13 to 17 mass%, and more preferably 14 to 16 mass%, based on the total mass of the composition. In this specification, the term "consistency" simply refers to the 60-stroke worked consistency measured in accordance with JIS K 2220 7.

[0011] <Rust Inhibitor> The rust inhibitor that can be used in the present invention is a succinic acid-based rust inhibitor from the viewpoint of low dust generation and wear resistance, with succinic anhydride being preferred, alkenyl succinic anhydride being more preferred, and succinic anhydride having an alkenyl group with 12 carbon atoms being 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] <Antioxidant> 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, or a mixture thereof. Of these, p,p'-dioctyldiphenylamine is particularly preferred. The inclusion of such an amine-based antioxidant provides excellent inhibition 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 this range, good oxidative degradation prevention effects can be obtained. On the other hand, the effect plateaus even if the content exceeds 1.0 mass%.

[0013] <Preparation of Grease Compositions> Examples 1 to 5, Comparative Examples 2 to 4, and Comparative Example 6: In the base oil shown in the table below, a predetermined amount of amine (a mixture of cyclohexylamine and stearylamine in the molar ratio shown in the table below) was reacted at a ratio of 1 mole of 4,4'-diphenylmethane diisocyanate (MDI) to 2 moles of amine, 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 on a three-roll mill to obtain a worked penetration at 60 strokes as measured in accordance with JIS K2220 7. The resulting mixture was adjusted to the value shown in the table below. Comparative Example 1: In the base oil shown in the table below, a predetermined amount of octylamine was reacted at a ratio of 1 mole of 4,4'-diphenylmethane diisocyanate (MDI) to 2 moles of amine, 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, a predetermined amount of amine (a mixture of cyclohexylamine and stearylamine in the molar ratio shown in the table below) was reacted at a ratio of 2 moles per mole of 4,4'-diphenylmethane diisocyanate (MDI), 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 on a three-roll mill to obtain a worked penetration of 250 at 60 strokes as measured in accordance with JIS K2220 7. In the examples and comparative examples, unless otherwise specified, the numbers in the table 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 a succinic anhydride having an alkenyl group with 12 carbon atoms.

[0014] <Test Methods 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 Corporation, 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 allowed to stand for 12 hours, and the weight loss rate was measured. [Evaluation Criteria] Weight loss rate: 0.80% or less...○ (pass) More than 0.80%...× (fail) 2. Apparent viscosity measurement (Evaluation of low dust generation) Using parallel plates with a diameter of 25 mm in a rheometer, the gap (distance between the measurement field and the parallel plates) was set to 0.01 mm, and the shear rate was measured at 3000 s -1 The apparent viscosity was measured at 0°C. [Evaluation criteria] Apparent viscosity 1.9 Pa·s or more... ◯ (pass) Less than 1.9 Pa·s... × (fail) 3. Abrasion resistance test (evaluation of abrasion resistance) A four-ball abrasion test was conducted in accordance with ASTM D 2266 at a temperature of 100°C, a load of 392 N, a rotation speed of 1200 rpm, and a test time of 1 hour, and the diameter of the wear scar on the steel ball after the test was measured. [Evaluation criteria] Wear scar diameter Less than 1000 μm... ◯ (pass) 1000 μm or more... × (fail) 4. Rust prevention test (evaluation of rust prevention) A rust prevention test was conducted in accordance with ASTM D 1743-73, and the state of rusting was judged. [Evaluation criteria] No rusting... ◯ (pass) Rusting... × (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 in accordance with JIS K2283. [Evaluation criteria] Kinematic viscosity of 60,000 mm 2 / s or less...〇(pass) 60000mm 2 Exceeds / s...× (fail)

[0015]

[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 thickeners, was unable to achieve satisfactory low dust generation. Comparative Example 2, which used only synthetic hydrocarbon oil, was unable to achieve satisfactory low dust generation. Kinematic viscosity 62.6 mm 2 In Comparative Example 3, which used a low-viscosity synthetic hydrocarbon oil of 154 mm / s, the low dust generation property was not satisfactory. 2 Comparative Example 4, which had a consistency of 1 / s, was unable to achieve satisfactory low temperature properties. Comparative Example 5, which had a consistency of 250, was unable to achieve satisfactory low dust generation properties. Comparative Example 6, which used an ester-based rust inhibitor, was unable to achieve 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 achieve satisfactory low dust generation properties, wear resistance, rust prevention properties, and low temperature properties.

[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, wherein the thickener contains compounds represented by formula (1), formula (2), and formula (3), and 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) (wherein, 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 The present invention is based on a high-viscosity synthetic hydrocarbon oil having a kinematic viscosity of 90 to 150 mm / s and an ether oil, wherein the content of the ether oil is 80 mass% or more based on the total mass of the base oil, and the kinematic viscosity of the base oil at 40°C is 90 to 150 mm / s. 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, and the 60-stroke worked penetration measured in accordance with JIS K 2220 7 is 180 to 230.

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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