Grease base oil

Abstract

Provided is a grease base oil that has excellent compatibility with respect to a nonpolar polymer material and has excellent water resistance, heat resistance, and low temperature fluidity. This grease base oil contains a polyalkylene glycol-based compound represented by formula (1).　(1): R1O-(EO)m-(PO)n-R2 (In formula (1), R1 represents an alkyl group having 1-3 carbon atoms, R2 represents a methyl group or hydrogen, EO represents an oxyethylene group, PO represents an oxypropylene group, EO and PO are randomly added, m represents the average addition mole number of EO and is 1-8, n represents the average addition mole number of PO and is 5-30, and the mass ratio of EO and PO is EO:PO=10:90 to 20:80.)

Description

Grease base oil

[0001] The present invention relates to a grease base oil that has excellent compatibility with non-polar polymeric materials.

[0002] Grease is used in the lubrication of various mechanical parts, such as gears, in automobile parts, home appliances, electronic information devices, and office automation equipment. To prevent the grease from leaking to other parts or to prevent the intrusion of foreign matter such as water from the outside, sealants are sometimes installed in the lubrication areas. Nitrile rubber (NBR) is generally widely used as a sealant due to its oil resistance, processability, and low cost. However, NBR is prone to degradation in high and low temperature environments, which can lead to the intrusion of foreign matter such as water, resulting in poor lubrication and rust, shortening the lifespan of mechanical parts. Therefore, ethylene propylene diene rubber (EPDM), which has excellent cold resistance, ozone resistance, heat resistance, and water resistance, is widely used, although it has slightly inferior oil resistance to NBR. Styrene butadiene rubber (SBR) is also widely used as a sealant. Furthermore, while many resin materials are used in automotive parts, in recent years, polypropylene (PP), which emits less CO2 during production than other resin materials, has attracted attention in light of CO2 reduction efforts, and its range of applications is expected to expand. Meanwhile, hydrocarbon oils such as mineral oil and poly-α-olefins, which are commonly used as grease base oils, tend to corrode non-polar polymeric materials such as EPDM, SBR, and PP, so polyalkylene glycol-based compounds are widely used instead. However, the required operating temperature range is becoming more stringent every year, and conventional polyalkylene glycol-based compounds lack heat resistance at high temperatures, causing the oil to evaporate and the grease to lose its lubricity, and at low temperatures, due to their high pour points, causing the grease to lose significant fluidity. Therefore, improving heat resistance and low-temperature fluidity is urgently needed. Patent Document 1 discloses a grease base oil that is excellent in water resistance and low volatility, and also has excellent corrosion resistance to rubbers such as EPDM and SBR. The chromatogram obtained by gel permeation chromatography satisfies a specific relationship and is represented by formula (1). However, in order to satisfy the recent demands for environmental temperatures in use, there is room for further improvement in heat resistance and low-temperature fluidity.

[0003] Japanese Patent Application Laid-Open No. 2019-073647

[0004] An object of the present invention is to provide a grease base oil that has excellent compatibility with non-polar polymeric materials and is excellent in water resistance, heat resistance, and low-temperature fluidity.

[0005] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by a grease base oil using a polyalkylene glycol-based compound having a specific terminal structure and a specific ratio and arrangement of oxyethylene groups and oxypropylene groups. That is, the present invention has the following configurations. [1] A grease base oil containing a polyalkylene glycol-based compound represented by formula (1). R 1 O-(EO) m - (PO) n -R 2 (1) (In formula (1), R 1 represents an alkyl group having 1 to 3 carbon atoms, and R 2 represents a methyl group or hydrogen, EO represents an oxyethylene group, PO represents an oxypropylene group, EO and PO are added randomly, m represents the average number of moles of EO added and is a number from 1 to 8, n represents the average number of moles of PO added and is a number from 5 to 30, and the mass ratio of EO to PO is EO:PO=10:90 to 20:80. [2] The grease base oil of [1], wherein the mass average molecular weight of the polyalkylene glycol compound is 500 to 2000. [3] A grease base oil having a kinematic viscosity at 100°C of 4 to 20 mm 2 [4] The grease base oil of any of [1] to [3], having a pour point of -50°C or lower. [5] The grease base oil of any of [1] to [4], having water resistance. [6] The grease base oil of any of [1] to [5], for use in a machine part having a member made of at least one non-polar polymer material selected from the group consisting of ethylene propylene diene rubber (EPDM), styrene butadiene rubber (SBR), and polypropylene resin (PP).

[0006] According to the present invention, it is possible to provide a grease base oil that has excellent compatibility with non-polar polymeric materials, and is excellent in water resistance, heat resistance, and low-temperature fluidity.

[0007] The grease base oil of the present invention contains a polyalkylene glycol compound represented by formula (1). 1 O-(EO) m - (PO) n -R 2 (1) In formula (1), R 1 represents an alkyl group having 1 to 3 carbon atoms. Examples of the alkyl group having 1 to 3 carbon atoms include a methyl group, an ethyl group, an n-propyl group, and an i-propyl group, and these may be used alone or in combination of two or more. R 1 By making R an alkyl group having 1 to 3 carbon atoms, it is possible to improve heat resistance and compatibility with non-polar polymeric materials. 1 is preferably a methyl group or an ethyl group, and more preferably a methyl group. 2 represents a methyl group or hydrogen. 2 is preferably a methyl group. EO represents an oxyethylene group, and PO represents an oxypropylene group, with the oxyethylene groups (EO) and oxypropylene groups (PO) being added randomly. The random addition of EO and PO makes it possible to obtain a grease base oil with even better low-temperature fluidity.

[0008] m represents the average number of moles of oxyethylene groups (EO) added (i.e., the average number of repetitions of oxyethylene groups) and is a number from 1 to 8. m is preferably 2 to 7, and more preferably 3 to 5. When m is in this range, heat resistance and low-temperature fluidity are improved. n represents the average number of moles of oxypropylene groups (PO) added (i.e., the average number of repetitions of oxypropylene groups) and is a number from 5 to 30. n is preferably 5 to 25, and more preferably 10 to 20. When n is in this range, heat resistance and low-temperature fluidity are improved. The mass ratio of EO to PO, EO:PO, is 10:90 to 20:80. That is, based on the total mass of the oxyethylene groups (EO) and the oxypropylene groups (PO) contained in formula (1), the mass of EO is 10 to 20%, and the mass of PO is 80 to 90%. An EO ratio of 10 to 20% enables excellent compatibility with non-polar polymeric materials and excellent water resistance to be obtained. As represented by formula (1), by using a polyalkylene glycol compound that is both end- and / or one-end-capped and in which the chain length of the alkyl group at the capped end is a specific length, it is possible to obtain a grease base oil that is excellent in compatibility with non-polar resins and that simultaneously achieves improved water resistance, heat resistance, and low-temperature fluidity.

[0009] The weight average molecular weight of the polyalkylene glycol compound represented by formula (1) is preferably 500 to 2000, more preferably 700 to 1800, and even more preferably 900 to 1600. When the weight average molecular weight of the polyalkylene glycol compound represented by formula (1) is within this range, the heat resistance and low-temperature fluidity are improved. In this specification, the weight average molecular weight is a value measured by gel permeation chromatography (GPC). That is, in this specification, the mass average molecular weight can be determined in GPC using a SHODEX (registered trademark) GPC101 dedicated GPC system as the system, in which a SHODEX RI-71s differential refractometer, a SHODEX KF-G guard column, and three SHODEX KF804L columns are mounted in series, with tetrahydrofuran as a developing solvent flowing at a flow rate of 1 ml / min at a column temperature of 40°C, injecting 0.1 ml of a 0.1 mass % tetrahydrofuran solution of the obtained reaction product, and using a BORWIN GPC calculation program to obtain a chromatogram represented by refractive index intensity and elution time.

[0010] The polyalkylene glycol compound of formula (1) can be produced by the following method. That is, an alcohol initiator and potassium hydroxide as a catalyst are charged into an autoclave, the air in the autoclave is replaced with dry nitrogen, and the catalyst is completely dissolved at 140°C while stirring. Next, a mixture of ethylene oxide and propylene oxide is added dropwise using a dropping device, and after completion of the dropwise addition, the reaction is carried out at 140°C for 2 hours. Next, potassium hydroxide is charged, and the autoclave is replaced with dry nitrogen. Then, methyl chloride is pressure-charged at a temperature of 80 to 130°C and the reaction is carried out for 5 hours. Thereafter, the reaction composition (containing the compound of formula (1) produced) is removed from the autoclave, neutralized with hydrochloric acid to a pH of 6 to 7, and dehydrated at 100°C under a reduced pressure of -0.095 MPa (50 mmHg) for 1 hour to remove the contained water. The product can then be produced by filtration to remove the salt produced by the dehydration.

[0011] The grease base oil of the present invention preferably contains a polyalkylene glycol compound represented by the following formula (1): 1 O-(EO) m - (PO) n -R 2 (1) (In formula (1), R 1 represents a methyl group or an ethyl group, R 2 represents a methyl group, EO represents an oxyethylene group, PO represents an oxypropylene group, EO and PO are added randomly, m represents the average number of moles of EO added and is a number from 3 to 5, n represents the average number of moles of PO added and is a number from 10 to 20, and the mass ratio of EO to PO is EO:PO=10:90 to 20:80. In this embodiment, the kinematic viscosity of the base oil at 100° C. is 4 to 10 mm 2 In this embodiment, the pour point is preferably −50° C. or lower, and more preferably −55° C. or lower.

[0012] The grease base oil of the present invention may contain only the polyalkylene glycol compound of formula (1), or may be a mixture of the polyalkylene glycol compound of formula (1) with another grease base oil. The grease base oil of the present invention preferably uses an ester oil as the other base oil. Examples of ester oils include diesters and polyol esters (e.g., trimethylolpropane esters, pentaerythritol esters, and dipentaerythritol esters), with polyol esters being preferred. By using a combination of the polyalkylene glycol compound of formula (1) and an ester oil as the base oil, a grease base oil having excellent compatibility with non-polar polymeric materials and excellent heat resistance can be obtained. The content of the polyalkylene glycol compound of formula (1) is preferably 30% by mass or more, more preferably 50% by mass or more, even more preferably 60% by mass or more, and even more preferably 80% by mass or more, based on the total mass of the grease base oil. By including the polyalkylene glycol compound of formula (1) in such an amount, it is possible to obtain a grease base oil that is excellent in compatibility with non-polar polymeric materials, and that is excellent in water resistance, heat resistance, and low-temperature fluidity.

[0013] The grease base oil of the present invention contains a polyalkylene glycol compound of formula (1) and, if necessary, other grease base oils, and may further contain additives to form a lubricant. Any additives commonly used in grease compositions can be added as needed. Examples include antioxidants, rust inhibitors, corrosion inhibitors, oiliness agents, viscosity index improvers, extreme pressure agents, friction modifiers, etc. Examples of antioxidants include amine-based, phenol-based, quinoline-based, and sulfur-based antioxidants, with amine-based or quinoline-based antioxidants being preferred. Examples of rust inhibitors include zinc-based, carboxylic acid-based, carboxylate-based, succinic acid-based, amine-based, sulfonate-based, and naphthenic acid-based inhibitors, with amine-based or naphthenic acid-based inhibitors being preferred, and mixtures thereof being even more preferred. Examples of corrosion inhibitors include thiadiazole-based, benzimidazole-based, and benzotriazole-based inhibitors. Examples of oiliness agents include fatty acids, fatty acid esters, and phosphate esters. The content of the additive is preferably 0.1 to 10 mass %, more preferably 0.3 to 5 mass %, and even more preferably 0.5 to 3 mass %, based on the total mass of the lubricant.

[0014] The kinematic viscosity of the polyalkylene glycol compound represented by formula (1) at 100°C is 4 to 20 mm 2 / s, and 4 to 15 mm 2 / s is more preferable, and 4 to 10 mm 2 The kinematic viscosity of the grease base oil of the present invention at 100°C is preferably 4 to 20 mm / s. 2 / s, and 4 to 15 mm 2 / s is more preferable, and 4 to 10 mm 2 / s. When the kinematic viscosity at 100°C of the polyalkylene glycol-based compound or base oil of formula (1) is in this range, the fluidity of the grease base oil at low temperatures is improved, evaporation at high temperatures is prevented, and stable lubrication can be ensured. In this specification, the kinematic viscosity is a value measured in accordance with JIS K2283:2000. The polyalkylene glycol-based compound represented by formula (1) preferably has low-temperature fluidity and a pour point of -50°C or lower. In addition, the grease base oil of the present invention preferably has low-temperature fluidity and a pour point of -50°C or lower. In this specification, the pour point is a value measured in accordance with JIS K2269:1987. Furthermore, the polyalkylene glycol-based compound represented by formula (1) and the grease base oil preferably have heat resistance. The polyalkylene glycol-based compound represented by formula (1) preferably has water resistance. In addition, the grease base oil of the present invention preferably has water resistance. That is, it is preferable that the polyalkylene glycol compound represented by formula (1) or the grease base oil is immiscible with water.

[0015] The grease base oil of the present invention can be used around nonpolar polymeric materials such as ethylene propylene diene rubber (EPDM), styrene butadiene rubber (SBR), and polypropylene resin (PP). In other words, the grease base oil of the present invention can be used for machine parts equipped with components made of nonpolar polymeric materials (e.g., sealing materials made of at least one nonpolar polymeric material selected from the group consisting of EPDM and SBR, and components made of PP), and can be used in direct contact with the nonpolar polymeric materials. Even when used in this condition, the grease base oil of the present invention can maintain the functionality of components made of these materials without corroding the nonpolar polymeric materials.

[0016] Preparation of Grease Base Oils The grease base oils of Examples 1 to 5 and Comparative Examples 1 to 5 were prepared by the following method. The composition of each grease base oil is shown in Tables 1 and 2. Example 1: 80 g of methanol and 2.4 g of potassium hydroxide as a catalyst were charged into an autoclave. The air in the autoclave was replaced with dry nitrogen, and the catalyst was completely dissolved at 140°C while stirring. Next, a mixture of 230 g of ethylene oxide and 2,060 g of propylene oxide was added dropwise using a dropping device, and the reaction was carried out for 2 hours at 140°C. Next, 168 g of potassium hydroxide was charged, and the autoclave was replaced with dry nitrogen. 153 g of methyl chloride was then added under pressure at a temperature of 80 to 130°C, and the reaction was carried out for 5 hours. The reaction composition was then removed from the autoclave, neutralized with hydrochloric acid to a pH of 6 to 7, and dehydrated for 1 hour at 100°C under a reduced pressure of -0.095 MPa (50 mmHg) to remove the contained water. Further, filtration was carried out to remove salts generated by dehydration, yielding the grease base oil of Example 1. Example 2: 80 g of methanol and 2.4 g of potassium hydroxide as a catalyst were charged into an autoclave. The air in the autoclave was replaced with dry nitrogen, and the catalyst was completely dissolved at 140°C while stirring. Next, a mixture of 496 g of ethylene oxide and 1,888 g of propylene oxide was added dropwise using a dropping device, and the reaction was carried out for 2 hours at 140°C after completion of the dropwise addition. Next, 168 g of potassium hydroxide was charged, and the autoclave was replaced with dry nitrogen. Then, 159 g of methyl chloride was added under pressure at a temperature of 80 to 130°C, and the reaction was carried out for 5 hours. The reaction composition was then removed from the autoclave, neutralized with hydrochloric acid to a pH of 6 to 7, and dehydrated for 1 hour at 100°C under a reduced pressure of -0.095 MPa (50 mmHg) to remove the contained water. Further, filtration was carried out to remove salts generated by dehydration, yielding the grease base oil of Example 2. Example 3 50 g of methanol and 2.3 g of potassium hydroxide as a catalyst were charged into an autoclave, and after the air in the autoclave was replaced with dry nitrogen, the catalyst was completely dissolved with stirring at 140° C. Next, a mixture of 461 g of ethylene oxide and 1,797 g of propylene oxide was added dropwise using a dropping device, and after completion of the dropwise addition, the mixture was reacted at 140° C. for 2 hours.Next, 105 g of potassium hydroxide was charged into the autoclave, and the air inside the autoclave was replaced with dry nitrogen. Then, 149 g of methyl chloride was added under pressure at 80 to 130°C and reacted for 5 hours. The reaction composition was then removed from the autoclave, neutralized with hydrochloric acid to a pH of 6 to 7, and dehydrated for 1 hour at 100°C under a reduced pressure of -0.095 MPa (50 mmHg) to remove the contained water. Filtration was then performed to remove the salt produced by dehydration, yielding the grease base oil of Example 3. Example 4: 100 g of ethanol and 2.2 g of potassium hydroxide as a catalyst were charged into the autoclave, and the air inside the autoclave was replaced with dry nitrogen. The catalyst was then completely dissolved at 140°C while stirring. Next, a mixture of 412 g of ethylene oxide and 1641 g of propylene oxide was added dropwise using a dropping device, and the mixture was reacted for 2 hours at 140°C after completion of the dropwise addition. Next, 146 g of potassium hydroxide was charged into the autoclave, and the air inside the autoclave was purged with dry nitrogen. Then, 139 g of methyl chloride was added under pressure at 80 to 130°C and reacted for 5 hours. The reaction composition was then removed from the autoclave, neutralized with hydrochloric acid to a pH of 6 to 7, and dehydrated for 1 hour at 100°C under a reduced pressure of -0.095 MPa (50 mmHg) to remove the contained water. Filtration was then performed to remove the salt produced by dehydration, yielding the grease base oil of Example 4. Example 5: 120 g of n-propanol and 2.0 g of potassium hydroxide as a catalyst were charged into the autoclave, and the air inside the autoclave was purged with dry nitrogen. The catalyst was then completely dissolved at 140°C while stirring. Next, a mixture of 370 g of ethylene oxide and 1,475 g of propylene oxide was added dropwise using a dropping device, and the mixture was allowed to react for 2 hours at 140°C after the completion of the dropwise addition. Next, 134 g of potassium hydroxide was charged, and the autoclave was purged with dry nitrogen. Then, 127 g of methyl chloride was added under pressure at a temperature of 80 to 130°C, and the reaction was carried out for 5 hours. The reaction composition was then removed from the autoclave, neutralized with hydrochloric acid to a pH of 6 to 7, and dehydrated at 100°C under a reduced pressure of -0.095 MPa (50 mmHg) for 1 hour to remove contained water. Filtration was then carried out to remove salts produced by dehydration, and the grease base oil of Example 5 was obtained.

[0017] Comparative Example 1: 200 g of 1-butanol and 2.3 g of potassium hydroxide as a catalyst were charged into an autoclave. The air in the autoclave was replaced with dry nitrogen, and the catalyst was completely dissolved at 140°C while stirring. Next, 2,120 g of propylene oxide was added dropwise using a dropping device. After completion of the dropwise addition, the mixture was allowed to react for 2 hours at 140°C. The reaction composition was then removed from the autoclave, neutralized with hydrochloric acid to a pH of 6-7, and dehydrated for 1 hour at 100°C under a reduced pressure of -0.095 MPa (50 mmHg) to remove the contained water. Filtration was then performed to remove the salt generated by the dehydration, yielding the grease base oil of Comparative Example 1. Comparative Example 2: 200 g of 1-butanol and 2.3 g of potassium hydroxide as a catalyst were charged into an autoclave. The air in the autoclave was replaced with dry nitrogen, and the catalyst was completely dissolved at 140°C while stirring. Next, 2120 g of propylene oxide was added dropwise using a dropping device, and the mixture was allowed to react for 2 hours at 140°C. Next, 182 g of potassium hydroxide was charged, and the autoclave was purged with dry nitrogen. Then, 150 g of methyl chloride was added under pressure at a temperature of 80 to 130°C, and the reaction was allowed to proceed for 5 hours. The reaction composition was then removed from the autoclave, neutralized with hydrochloric acid to a pH of 6 to 7, and dehydrated at 100°C under a reduced pressure of -0.095 MPa (50 mmHg) for 1 hour to remove the contained water. Filtration was then performed to remove the salt produced by the dehydration, yielding the grease base oil of Comparative Example 2. <Comparative Example 3> 80 g of methanol and 2.5 g of potassium hydroxide as a catalyst were charged into the autoclave. After the air in the autoclave was purged with dry nitrogen, the catalyst was completely dissolved at 140°C with stirring. Next, a mixture of 716 g of ethylene oxide and 1,670 g of propylene oxide was added dropwise using a dropping device, and after completion of the dropwise addition, the mixture was allowed to react for 2 hours at 140°C. Next, 168 g of potassium hydroxide was charged, and the autoclave was purged with dry nitrogen. Then, 159 g of methyl chloride was added under pressure at a temperature of 80 to 130°C, and the reaction was allowed to proceed for 5 hours. The reaction composition was then removed from the autoclave, neutralized with hydrochloric acid to a pH of 6 to 7, and dehydrated for 1 hour at 100°C under a reduced pressure of -0.095 MPa (50 mmHg) to remove contained water. Filtration was then carried out to remove salts produced by dehydration, and the grease base oil of Comparative Example 3 was obtained.Comparative Example 4: 80 g of methanol and 2.5 g of potassium hydroxide as a catalyst were charged into an autoclave. The air in the autoclave was replaced with dry nitrogen, and the catalyst was completely dissolved at 140°C while stirring. Next, 496 g of ethylene oxide was added dropwise using a dropping device, and after completion of the dropwise addition, the reaction was carried out at 140°C for 1 hour. Next, 1,888 g of propylene oxide was added dropwise, and after completion of the dropwise addition, the reaction was carried out at 140°C for 2 hours. Next, 168 g of potassium hydroxide was charged, and the autoclave was replaced with dry nitrogen. Then, 159 g of methyl chloride was added under pressure at a temperature of 80 to 130°C, and the reaction was carried out for 5 hours. The reaction composition was then removed from the autoclave, neutralized with hydrochloric acid to a pH of 6 to 7, and dehydrated at 100°C under a reduced pressure of -0.095 MPa (50 mmHg) for 1 hour to remove the contained water. Filtration was then carried out to remove salts produced by the dehydration, and the grease base oil of Comparative Example 4 was obtained. Comparative Example 5: 180 g of 1-butanol and 2.0 g of potassium hydroxide as a catalyst were charged into an autoclave. The air in the autoclave was replaced with dry nitrogen, and the catalyst was completely dissolved at 140°C while stirring. Next, a mixture of 375 g of ethylene oxide and 1,455 g of propylene oxide was added dropwise using a dropping device, and the mixture was allowed to react for 2 hours at 140°C after completion of the dropwise addition. Next, 164 g of potassium hydroxide was charged, and the autoclave was replaced with dry nitrogen. Then, 130 g of methyl chloride was added under pressure at a temperature of 80 to 130°C, and the reaction was allowed to proceed for 5 hours. The reaction composition was then removed from the autoclave, neutralized with hydrochloric acid to a pH of 6 to 7, and dehydrated for 1 hour at 100°C under a reduced pressure of -0.095 MPa (50 mmHg) to remove the contained water. Filtration was then performed to remove the salt generated by the dehydration, yielding the grease base oil of Comparative Example 5.

[0018] Evaluation of Grease Base Oils The obtained grease base oils of the Examples and Comparative Examples were evaluated for water resistance, low-temperature fluidity, heat resistance, and rubber compatibility. The results are shown in Tables 1 and 2. In the following evaluation criteria, a rating of ⊚ or ◯ was considered acceptable. <Water Resistance> Equal amounts of the grease base oil and water were weighed into a glass container, stirred 10 times with a stirring rod, and allowed to stand at room temperature for 24 hours. The appearance was observed and the water resistance was evaluated using the following criteria. [Evaluation Criteria] The grease base oil and water are completely separated: ◯ The grease base oil and water are not completely separated: × <Low-Temperature Fluidity> A pour point test was conducted in accordance with JIS 2269:1987, and the low-temperature fluidity was evaluated using the following criteria. [Evaluation Criteria] The pour point of the grease base oil is -55°C or less: ⊚ The pour point of the grease base oil is greater than -55°C and less than -50°C: ○ The pour point of the grease base oil is greater than -50°C: × <Heat Resistance> 50g of grease base oil was placed in a 100mL beaker and allowed to stand at 120°C for 240 hours, after which the mass was measured to determine the amount of evaporation of the base oil, and heat resistance was evaluated using the following criteria. [Evaluation Criteria] The amount of evaporation of the grease base oil is 20% by mass or less: ○ The amount of evaporation of the grease base oil is greater than 20% by mass: × <Rubber Compatibility> Compatibility was evaluated in accordance with JIS K 6258:2016. No. 8 dumbbell EPDM rubber test pieces were used, and these test pieces were immersed in 100g of grease base oil at 100°C for 72 hours, after which the mass and volume were measured. The volume of the test piece was measured using the water displacement method. The change in mass and volume of the test piece before and after immersion was determined, and the suitability was evaluated using the following criteria. [Evaluation criteria] Mass change rate: The mass change rate of the test piece is less than 5%: ○ The mass change rate of the test piece is 5% or more: × Volume change rate: The volume change rate of the test piece is less than 5%: ○ The volume change rate of the test piece is 5% or more: ×

[0019]

[0020]

Claims

1. A grease base oil containing a polyalkylene glycol compound represented by formula (1). 1 O-(EO) m - (PO) n -R 2 (1) (In formula (1), R 1 represents an alkyl group having 1 to 3 carbon atoms, and R 2 represents a methyl group or hydrogen, EO represents an oxyethylene group, PO represents an oxypropylene group, EO and PO are added randomly, m represents the average number of moles of EO added and is a number from 1 to 8, n represents the average number of moles of PO added and is a number from 5 to 30, and the mass ratio of EO to PO is EO:PO=10:90 to 20:

80.

2. The grease base oil according to claim 1, wherein the polyalkylene glycol compound has a mass average molecular weight of 500 to 2,000.

3. Kinematic viscosity at 100°C is 4 to 20 mm 2 The grease base oil according to claim 1, wherein the grease base oil is 0.1 to 0.5 wt.

4. The grease base oil according to claim 1, having a pour point of -50°C or lower.

5. The grease base oil according to claim 1, which has water resistance.

6. The grease base oil according to any one of claims 1 to 5, which is for use in a machine part having a member made of at least one non-polar polymer material selected from the group consisting of ethylene propylene diene rubber (EPDM), styrene butadiene rubber (SBR), and polypropylene resin (PP).

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