Grease composition for speed reducer and speed reducer for robot

Abstract

To provide a grease composition capable of achieving both efficiency and durability of a speed reducer and a speed reducer for robots containing the same.SOLUTION: A grease composition for speed reducers comprises a thickener and a base oil, wherein the thickener is a Li soap, the base oil comprises poly-α-olefin and polyisobutylene, and the content of polyisobutylene is 4 to 12 mass% based on the total mass of the base oil.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a grease composition for a reducer and a reducer for a robot in which the grease composition for a reducer is packed. [Background technology]

[0002] Reducers used in industrial robots and the like have the role of converting the power of electric motors, which have high rotational speeds and low torque, into low speeds and high torque, and are also necessary for making robot joints smaller and lighter, and are generally lubricated with oil or grease. Reducers include planetary gear reducers, Harmonic Drive (registered trademark) reducers (wave gear reducers), Cyclo reducers (registered trademark), precision RV reducers (internal planetary gear reducers), ball reducers, etc., each with its own unique structure and characteristics such as reduction ratio and operating efficiency (Non-Patent Document 1). A known reducer for robots is one that uses a strain wave gear mechanism. Strain wave gear reducers are small, lightweight, and highly efficient, and are therefore widely used as reducers for robots (Non-Patent Document 2). In recent years, with the advancement of performance and miniaturization of robot reducers, there has been an increasing demand for higher efficiency, higher torque, and longer life for reducers, resulting in an increasing load on lubricated parts. Various lubricant compositions have been proposed to improve the efficiency of reducers. For example, Patent Document 1 proposes a lubricant composition that improves reducer efficiency by adding a component with a high friction-reducing effect. Patent Document 2 also proposes a lubricant composition that softens when subjected to shear, thereby exhibiting fluidity and improving reducer efficiency. However, in the case of reducers that have a mechanism that makes it difficult to retain a lubricant composition or grease composition in the lubricated parts, such as wave gear reducers, the lubricant is dissipated from the lubricated parts, and conventional lubricant compositions such as those disclosed in Patent Document 1 or Patent Document 2 cannot maintain high efficiency over a long period of time. Furthermore, poor lubrication results in a short lifespan of the reducer. Therefore, there is a demand for lubricant compositions and grease compositions that can achieve both high efficiency and long lifespan (durability) for robot reducers. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-339411 [Patent Document 2] Japanese Patent Application Publication No. 2019-178278 [Non-patent literature]

[0004] [Non-Patent Document 1] "Fundamentals and Applications of Lubricating Grease", edited by the Grease Research Group of the Japanese Society of Tribologists, Yokendo, pp. 197-198, 2020 [Non-patent document 2] "Latest Technology Trends of Harmonic Drive (Registered Trademark)", Journal of the Robotics Society of Japan, Vol. 21, No. 1, pp. 19-21, 2003 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention aims to provide a grease composition that can improve the performance and life of robot reducers, achieving both efficiency and durability of the reducer, something that has not been achieved with conventional lubricant compositions, and also to provide a robot reducer containing the grease composition. [Means for solving the problem]

[0006] As a result of extensive research, the present inventors have discovered that a grease composition containing a specific amount of polyisobutylene in a base oil can achieve both efficiency and durability of a reducer. The present invention has been made based on this discovery and provides the following grease composition for a reducer and a robot reducer using the same. [1] A grease composition for a reducer containing a thickener and a base oil, The thickener is Li soap, the base oil comprises a poly-α-olefin and a polyisobutylene; The grease composition for a reducer as described above, wherein the content of polyisobutylene is 4 to 12 mass % based on the total mass of the base oil. [2] The grease composition for a reducer according to [1], wherein the viscosity average molecular weight of the polyisobutylene is 30,000 to 60,000. [3] The kinematic viscosity of the base oil at 100°C is 5 to 20 mm 2 The grease composition for a reducer according to [1] or [2], wherein [4] The grease composition for a reducer according to any one of [1] to [3], wherein the base oil further contains an ester oil. [5] The grease composition for a reducer according to any one of [1] to [4], further comprising at least one additive selected from the group consisting of a friction modifier, an antioxidant, and a rust inhibitor. [6] A reducer for a robot, in which the grease composition according to any one of [1] to [5] is packed. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a grease composition that can achieve both efficiency and durability of a reducer, and therefore a robot reducer containing this grease composition has high efficiency and a long life. DETAILED DESCRIPTION OF THE INVENTION

[0008] [Grease composition for reducers] <Thickener> The thickener used in the present invention is Li soap. Examples of Li soaps include lithium 12-hydroxystearate (Li-(12OH)St), lithium stearate (Li-St), and Li complex soaps. Examples of Li complex soaps include complexes of lithium salts of aliphatic carboxylic acids such as stearic acid and 12-hydroxystearic acid with lithium salts of dibasic acids. Examples of dibasic acids include succinic acid, malonic acid, adipic acid, pimelic acid, azelaic acid, and sebacic acid, with azelaic acid and sebacic acid being preferred. A particularly preferred Li complex soap is a mixture of azelaic acid and lithium hydroxide salt and a 12-hydroxystearic acid and lithium hydroxide salt. Among the Li soaps, lithium 12-hydroxystearate (Li-(12OH)St) is preferred because it can be thickened with a small amount of thickener and has excellent fluidity. The content of the thickener is preferably 3 to 15 mass % and more preferably 3 to 10 mass % based on the total mass of the composition. By having the content of the thickener in this range, the grease composition can be given an appropriate hardness and leakage from seal parts can be prevented.

[0009] <Base oil> In the present invention, the base oil comprises a poly-α-olefin and a polyisobutylene. Specific examples of poly-α-olefins include those obtained by polymerizing one or more types of α-olefins. Examples of α-olefins include α-olefins produced using ethylene, propylene, butene, derivatives thereof, etc. as raw materials, and α-olefins having 6 to 18 carbon atoms (e.g., 1-decene, 1-dodecene, etc.) are preferred. The poly-α-olefin is particularly preferably an oligomer of 1-decene or 1-dodecene. The content of the poly-α-olefin in the base oil is preferably 30 to 80 mass %, more preferably 40 to 70 mass %, based on the total mass of the base oil. The polyisobutylene preferably has a viscosity average molecular weight of 30,000 to 60,000, more preferably 40,000 to 60,000. In this specification, the viscosity average molecular weight refers to a value measured by size exclusion chromatography (SEC) using standard polystyrene in accordance with JIS K 7252-1. The polyisobutylene content is 4 to 12 mass %, preferably 4 to 10 mass %, based on the total mass of the base oil. By setting the polyisobutylene content in the base oil within this range, the kinematic viscosity of the mixed oil base oil can be appropriately increased, thereby improving the durability of the reducer, and the efficiency and durability of the reducer can be improved without making the kinematic viscosity of the mixed oil too high. The base oil of the present invention may further contain other base oils in addition to poly-α-olefins and polyisobutylenes. Examples of other base oils include ester oils, mineral oils, and ether oils, with ester oils being preferred. Examples of ester oils include diesters and polyol esters (e.g., trimethylolpropane esters, pentaerythritol esters, and dipentaerythritol esters), with diesters being preferred. The content of the ester oil is preferably 10 to 40 mass %, more preferably 20 to 40 mass %, based on the total mass of the base oil. The content of the base oil in the grease composition is preferably 75 to 95 mass %, and more preferably 80 to 90 mass %, based on the total mass of the composition. When the content of the base oil is within this range, the fluidity of the grease composition is good, a sufficient lubricating effect is obtained, and the grease composition can be easily retained at the lubricated parts. The kinematic viscosity of the entire base oil of the present invention at 100°C is 5 to 20 mm 2 / s is preferable, and 5 to 18 mm 2 / s is more preferable, and 8 to 16 mm 2 / s. When the kinematic viscosity of the base oil mixture is in this range, the durability of the reducer can be improved, and the efficiency and durability of the reducer can be improved. In this specification, the kinematic viscosity of the base oil at 100°C is a value measured by a method in accordance with JIS K 2283.

[0010] <Additives> The grease composition of the present invention may contain various additives as needed, such as antioxidants, rust inhibitors, oiliness agents, corrosion inhibitors, anti-wear agents, extreme pressure agents, friction modifiers, solid lubricants, etc. Examples of antioxidants include amine-based antioxidants (e.g., diphenylamine, phenyl-α-naphthylamine, and alkylated products thereof), phenol-based antioxidants (e.g., hindered phenols such as 2,6-di-t-butyl-p-cresol, pentaerythritol-tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], and octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate), and quinoline-based antioxidants (e.g., 2,2,4-trimethyl-1,2 dihydroquinoline polymers), and amine-based antioxidants are preferred. Examples of rust inhibitors include carboxylic acid inhibitors (for example, lower fatty acids such as alkenylsuccinic acid, higher fatty acids such as naphthenic acid and lanolin fatty acid, salts thereof (alkali metal salts such as sodium salts; alkaline earth metal salts such as calcium salts and magnesium salts; aluminum salts; zinc salts; amine salts, etc.), anhydrides, and esters), and sulfonic acid inhibitors (for example, sulfonates (alkali metal salts such as sodium salts; alkaline earth metal salts such as calcium salts and barium salts; zinc salts, etc.)), with sulfonic acid inhibitors being preferred. Examples of oily agents include fatty acids, fatty acid esters, and phosphate esters. Corrosion inhibitors include benzotriazoles. Examples of friction modifiers include phosphorus-based (e.g., tricresyl phosphate, tri-2-ethylhexyl phosphate), sulfur-based (e.g., dibenzyl disulfide, various polysulfides), sulfur-phosphorus-based (e.g., triphenyl phosphorothioate), and organometallic-based (e.g., metal salts of dialkyldithiophosphate (Zn salt, Mo salt, Sb salt, Bi salt, etc.), and metal salts of dialkyldithiocarbamic acid (Zn salt, Mo salt, Sb salt, Ni salt, Cu salt, Bi salt, etc.)), with sulfur-phosphorus-based or organometallic-based being preferred. These friction modifiers can also be used as anti-wear agents or extreme pressure agents. Solid lubricants include molybdenum disulfide, graphite, polytetrafluoroethylene (PTFE), and melamine cyanurate (MCA). The content of the antioxidant is preferably 0.1 to 5.0 mass%, more preferably 0.1 to 3.0 mass%, and even more preferably 0.1 to 2.0 mass%, based on the total mass of the grease composition. The content of the rust inhibitor is preferably 0.1 to 5.0 mass%, more preferably 0.5 to 4.0 mass%, and even more preferably 1.0 to 3.0 mass%, based on the total mass of the grease composition. The content of the friction modifier is preferably 0.1 to 10.0 mass%, more preferably 0.5 to 8.0 mass%, and even more preferably 1.0 to 6.0 mass%, based on the total mass of the grease composition. These additives may be used alone or in combination of two or more. From the viewpoint of further improving various performances, the grease composition of the present invention preferably contains at least one additive selected from the group consisting of antioxidants, rust inhibitors, and friction modifiers, and more preferably contains an antioxidant, rust inhibitor, and friction modifier. It is also preferable to contain a combination of molybdenum dialkyldithiocarbamate, molybdenum dialkyldithiophosphate, zinc dialkyldithiophosphate, and a mixture of a sulfurized olefin and a phosphate ester as the friction modifier. It is particularly preferable that the grease composition of the present invention contain, as additives, N-phenyl-1-naphthylamine as the antioxidant, a calcium salt of an alkyl aromatic sulfonic acid as the rust inhibitor, and a mixture of molybdenum dialkyldithiocarbamate, molybdenum dialkyldithiophosphate, zinc dialkyldithiophosphate, and a mixture of a sulfurized olefin and a phosphate ester as the friction modifier. In the grease composition of the present invention, the total content of these additives is preferably 0.1 to 15 mass %, more preferably 0.1 to 10 mass %, based on the total mass of the grease composition.

[0011] The grease composition of the present invention is, among others, A grease composition for a reducer, comprising a thickener, a base oil, and an additive, The thickener is Li soap, the base oil comprises poly-α-olefin, polyisobutylene, and ester oil; The viscosity average molecular weight of the polyisobutylene is 30,000 to 60,000, The polyisobutylene content is 4 to 12 mass% based on the total mass of the base oil, The kinematic viscosity of the base oil at 100°C is 5 to 20 mm 2 / s, The grease composition for a reducer preferably contains an antioxidant, a rust inhibitor, and a friction modifier as the additives. In this embodiment, it is more preferred that the additive contains N-phenyl-1-naphthylamine as an antioxidant, a calcium salt of an alkyl aromatic sulfonic acid as a rust inhibitor, and molybdenum dialkyldithiocarbamate, molybdenum dialkyldithiophosphate, zinc dialkyldithiophosphate, and a mixture of a sulfurized olefin and a phosphate ester as a friction modifier. In particular, in this embodiment, the grease composition is preferably a grease composition for a reducer in a robot.

[0012] [Reducer] The reducer of the present invention is a robot reducer filled with the grease composition of the present invention. The robot reducer may be a wave gear reducer. Such a robot reducer filled with the grease composition of the present invention can more effectively exhibit the effects of the present invention, i.e., can be a robot reducer with high efficiency and long life. [Example]

[0013] Preparation of the Grease Composition The components shown in Table 1 were mixed in the proportions shown in Table 1 to prepare grease compositions of Examples 1 to 5 and Comparative Examples 1 to 3. The thickeners, base oils, and additives in the table are as follows. Note that, unless otherwise specified, the component numbers in the table represent mass % based on the total mass of the composition. <Thickener> Li soap: Li hydroxystearate obtained by reacting 12-hydroxystearic acid with an aqueous solution of lithium hydroxide in a base oil, then heating it to 200°C and cooling it to below 100°C. <Base oil> Polyisobutylene A: Viscosity average molecular weight 30,000 (trade name: Tetrax 3T, manufactured by ENEOS Corporation) Polyisobutylene B: Viscosity average molecular weight 50,000 (trade name: Tetrax 5T, manufactured by ENEOS Corporation) Polyisobutylene C: Viscosity average molecular weight 60,000 (trade name: Tetrax 6T, manufactured by ENEOS Corporation) PAO (poly-α-olefin): kinematic viscosity at 100°C: 4.0 mm2 / s Ester oil (diester): kinematic viscosity at 100°C 3.2mm 2 / s Mineral oil (mixture of paraffinic and naphthenic oils): kinematic viscosity at 100°C 7.7mm 2 / s <Additives> - Friction modifier - (Mo series) For the Mo system, the following molybdenum dialkyldithiocarbamate and molybdenum dialkyldithiophosphate were used in a ratio (mass ratio) of 1:3. Molybdenum dialkyldithiocarbamate (trade name: MOLYVAN 822NT, manufactured by Vanderbilt Chemicals, LLC) Molybdenum dialkyldithiophosphate (trade name: MOLYVAN L, manufactured by Vanderbilt Chemicals, LLC) (Zn-based) Zinc dialkyldithiophosphate (trade name: LUBRIZOL 1395, manufactured by LUBRIZOL) (SP type) A mixture of sulfurized olefin and phosphate ester (trade name: LUBRIZOL 5034A, manufactured by LUBRIZOL) - Antioxidant - N-phenyl-1-naphthylamine (trade name: Nocrac PA, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) - Rust inhibitor - Calcium salt of alkyl aromatic sulfonic acid (trade name: ALOX 165, manufactured by LUBRIZOL) The worked penetration of the grease compositions of the examples and comparative examples was measured by a method in accordance with JIS K 2220 7. The kinematic viscosity of the base oil was measured at a temperature of 100°C in accordance with JIS K 2283.

[0014] Performance Evaluation Test The prepared grease composition was filled into a strain wave gear reducer and subjected to an efficiency test, heat generation test, and life test. The results are shown in Table 1. [Efficiency test] The prepared grease compositions were tested under the following test conditions to measure efficiency (actual output torque when the output torque (theoretical value) when 100% of the torque of the input shaft is output is taken as 100). <Test conditions> Test temperature: 25℃ Load torque: 90Nm Input speed: 2000 rpm <Evaluation criteria> Efficiency is 73% or more ◎ (pass) Efficiency is between 65% and 73%: 〇 (pass) Efficiency less than 65% × (fail) [Pyrogenicity test] The prepared grease compositions were tested under the following test conditions, and the internal temperature of the reducer was measured after the test. <Test conditions> Test temperature: 25℃ Exam time: 9 hours Load torque: 220Nm Input speed: 3000 rpm <Evaluation criteria> Reducer internal temperature is 75°C or less. 〇 (Pass) The internal temperature of the reducer is higher than 75°C. × (Fail) [Life (durability) test] The prepared grease compositions were tested under the following test conditions, and the time until the internal parts were damaged (life time) was measured. <Test conditions> Test temperature: 25℃ Load torque: 220Nm Input speed: 3000 rpm <Evaluation criteria> The life was evaluated as a relative life ratio when the life of Comparative Example 1 was set to 1.0. Relative life ratio is 2.5 or more ◎ (pass) Relative life ratio is 1.5 or more and less than 2.5: 〇 (pass) Relative life ratio less than 1.5 × (fail)

[0015] [Table 1]

Claims

1. A grease composition for a reducer containing a thickener and a base oil, The thickener is Li soap, the base oil comprises a poly-α-olefin and a polyisobutylene; The grease composition for a reducer as described above, wherein the content of polyisobutylene is 4 to 12 mass % based on the total mass of the base oil.

2. 2. The grease composition for a reducer according to claim 1, wherein the viscosity average molecular weight of the polyisobutylene is 30,000 to 60,000.

3. The kinematic viscosity of the base oil at 100°C is 5 to 20 mm 2 The grease composition for a reducer according to claim 1, wherein the grease composition is 0.01g / s.

4. The grease composition for a reducer according to claim 1, wherein the base oil further contains an ester oil.

5. The grease composition for a reducer according to claim 1, further comprising at least one additive selected from the group consisting of an antioxidant, a rust inhibitor, and a friction modifier.

6. A reducer for a robot in which the grease composition according to any one of claims 1 to 5 is packed.

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