Grease composition

Abstract

To provide a grease composition having a good operating property of a machine part in a low-temperature environment.SOLUTION: There is provided a grease composition, comprising: a base oil; a thickener; and 5 to 40 mass% of polyisobutylene having a weight average molecular weight of 50,000 or more in the composition, and a low temperature torque at -40°C is 300 mN m or less. A mass ratio of the base oil to the polyisobutylene (base oil vs polyisobutylene) is within a range of 90:10 to 70:30, and a viscosity index of a mixed base oil obtained by the base oil and polyisobutylene is 200 or more.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a grease composition using a high-viscosity base oil, which is suitable for mechanical parts, particularly mechanical parts used in a low-temperature environment such as automotive parts.

Background Art

[0002] Grease is often applied to mechanical parts such as gears and bearings to make the movement smooth and prevent corrosion and wear. For example, as a grease composition excellent in rust prevention and wear resistance, a grease composition containing an anti-wear agent, a thickener, a rust inhibitor, and polyisobutylene in a base oil has been developed (see Patent Document 1 below).

[0003] On the other hand, in recent years, various efforts have been made to reduce CO2 from the perspective of global environmental protection and SDGs. As one of them, in the automotive industry, there is a tendency to popularize HEV vehicles and EV vehicles. HEV vehicles and EV vehicles are extremely quiet vehicles with extremely small engine noise or no engine noise at all compared to conventional gasoline vehicles. In order to further reduce noise, it is expected that noise generated other than engine noise also needs to be reduced. Therefore, in such vehicles, it is expected that the noise reduction of various sounds that have not been regarded as a problem conventionally will be improved, and it is considered that the grease used for automotive parts is also required to have the property of operating the parts smoothly.

[0004] Grease generally becomes hard and has a large resistance at low temperatures, which may prevent the operation of mechanical parts. Since automotive parts are also used in a low-temperature environment, the grease used for them is required to have good operability even in a low-temperature range. In order to improve the operability in a low-temperature environment, the base oil is selected from a call-to-liquid or Group III base oil in the American Petroleum Institute classification, and the kinematic viscosity of the base oil is 3 mm 2 / s or more and 40 mm 2 / s or less at 100 °C, and a grease composition having a starting torque value of 400 mN·m or less at -40 °C has been developed (see Patent Document 2 below).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] Greases used for mechanical parts such as automotive parts are required to have operability in a wide temperature range. For example, lubricity to reliably operate mechanical parts even in a low-temperature environment of -40°C or lower is required, and high viscosity that remains in that part even at normal temperature (for example, kinematic viscosity at 40°C is 800 mm 2 / s or more) is also required. However, there has been a problem that it is difficult to achieve both of these points.

[0007] As a result of intensive research, the present inventor has found that by incorporating a specific polyisobutylene into the grease, the operability of mechanical parts in a low-temperature environment is improved, and the above problems can be solved.

[0008] Therefore, an object of the present invention is to provide a grease composition capable of improving the operability of mechanical parts even in a low-temperature environment of -40°C or lower. Furthermore, this grease composition has a high viscosity at normal temperature (for example, kinematic viscosity at 40°C is 800 mm 2 / s or more).

Means for Solving the Problems

[0009] A grease composition according to one aspect of the present invention includes a base oil, a thickener, and polyisobutylene having a weight average molecular weight of 50,000 or more and accounting for 5 to 40% by mass in the composition, and is characterized in that the low-temperature torque at -40°C is 300 mN·m or less.

[0010] In the grease composition of the above aspect, the mass ratio of the base oil to the polyisobutylene (base oil: polyisobutylene) is preferably in the range of 90:10 to 70:30, and the viscosity index of the mixed base oil of the base oil and the polyisobutylene is preferably 200 or more.

[0011] In the grease composition of the above aspect, it is preferable that the thickener is lithium soap at 15% by mass or less in the composition.

[0012] In the grease composition of the above aspect, the kinematic viscosity of the mixed base oil at 40 °C is preferably 800 mm 2 / s or more.

[0013] In the grease composition of the above aspect, the pour point of the mixed base oil is preferably -30 °C or lower.

Effect of the Invention

[0014] The grease composition of one aspect of the present invention can improve the operability of mechanical parts in a low-temperature environment by containing a specific polyisobutylene.

Mode for Carrying Out the Invention

[0015] Hereinafter, the present invention will be described based on one embodiment. However, the present invention is not limited to this embodiment.

[0016] <Grease Composition> The grease composition of one embodiment of the present invention (hereinafter, also referred to as the present grease composition) includes a base oil, a thickener, and a specific polyisobutylene, and has a low-temperature torque at -40 °C of 300 mN·m or less.

[0017] (Base Oil) The base oil of the present grease composition is not particularly limited, and those conventionally used in greases can be used. For example, mineral oil or synthetic oil can be used. Examples of synthetic oils include ether oil-based synthetic oils, ester-based synthetic oils, and hydrocarbon-based synthetic oils. Examples of ester oil-based synthetic oils include polyol ester oils, phosphate ester oils, polymer ester oils, aromatic ester oils, carbonate ester oils, diester oils, polyglycol oils, and the like. Among these, hydrocarbon-based synthetic oils are preferred, and examples include PAO (polyalphaolefin) oils. More specific examples include hydrocarbon-based synthetic oils such as PAO4 (kinematic viscosity at 100 °C is about 4 mm 2 / s) or PAO6 (kinematic viscosity at 100 °C is about 6 mm 2 / s). Examples of PAO6 include the product name "Synfluid PAO6 cSt" (manufactured by Chevron Phillips Chemical Company), the product name "SpectraSyn Plus6" (manufactured by Exxon Mobil), and examples of PAO4 include the product name "Synfluid PAO4 cSt" (manufactured by Chevron Phillips Chemical Company), the product name "SpectraSyn 4" (manufactured by Exxon Mobil), and the product name "SpectraSyn MaX3.5" (manufactured by Exxon Mobil).

[0018] The base oil may be used alone or in combination of two or more. For example, two or more types having different viscosities may be used in combination to form the base oil.

[0019] The kinematic viscosity of the base oil at 40 °C is not particularly limited, but is preferably 5 to 50 mm 2 / s, more preferably 10 to 40 mm 2 / s, and particularly preferably 15 to 35 mm 2 / s.

[0020] The kinematic viscosity of the base oil at 100 °C is not particularly limited, but is preferably 1 to 10 mm 2 / s, more preferably 2 to 8 mm 2 / s, and particularly preferably 3.5 to 6.5 mm 2 / s.

[0021] The viscosity index of the base oil is not particularly limited, but is preferably from 100 to 150, more preferably from 110 to 140, and particularly preferably from 120 to 135.

[0022] The pour point of the base oil is not particularly limited, but is preferably -50°C or lower, more preferably -55°C or lower, and particularly preferably -60°C or lower.

[0023] The flash point of the base oil is not particularly limited, but is preferably 220°C or higher, more preferably 230°C or higher, and particularly preferably 240°C or higher.

[0024] The base oil is not particularly limited, but can be contained in the grease composition in an amount of 50% by mass or more, preferably 60% by mass or more, more preferably 70% by mass or more. The upper limit is preferably 90% by mass or less.

[0025] (Thickener) The thickener of the grease composition is not particularly limited, and those conventionally used in greases can be used. For example, soap-based or non-soap-based thickeners can be used. Examples of soap-based thickeners include lithium soap, lithium complex soap, calcium soap, calcium complex soap, aluminum soap, aluminum complex soap, etc. Among them, lithium soap is preferred, and for example, either lithium stearate, lithium 12-hydroxystearate, or a mixture thereof is particularly preferred. Examples of non-soap-based thickeners include urea, sodium terephthalate, fluororesin, bentonite, silica gel, etc. The thickener may be used alone or in combination of two or more.

[0026] The thickener is not particularly limited, but can be contained in the grease composition in an amount of 15% by mass or less, preferably 10% by mass or less, more preferably 8% by mass or less. The lower limit is preferably 0.1% by mass or more.

[0027] (Polyisobutylene) The polyisobutylene in this grease composition is a polymer of isobutene, and those having a weight average molecular weight of 50,000 or more can be used. Further, the weight average molecular weight is preferably 200,000 or less, more preferably 150,000 or less, and particularly preferably 110,000 or less. As such polyisobutylene, commercially available products can be used. For example, product name "Oppanol B10N" (manufactured by BASF: weight average molecular weight 53,000), product name "Oppanol B15N" (manufactured by BASF: weight average molecular weight 108,000), etc. can be used.

[0028] The viscosity index of the polyisobutylene used in this grease composition is preferably in the range of 200 to 400, and more preferably in the range of 200 to 350.

[0029] Polyisobutylene is not particularly limited, but can be contained in this grease composition in a proportion of 5% by mass or more and 40% by mass or less, preferably 10% by mass or more and 30% by mass or less, more preferably 10% by mass or more and 25% by mass or less.

[0030] In this grease composition, the mass ratio of polyisobutylene to the base oil (base oil: polyisobutylene) is preferably in the range of 90:10 to 70:30, more preferably 88:12 to 73:27, and particularly preferably 86:14 to 75:25.

[0031] (Additives) This grease composition may contain additives as other components other than the above. Examples of the additives include antioxidants such as amine-based and phenol-based ones, rust preventives such as metal sulfonates and succinic acid-based ones, extreme pressure additives such as S-P-based, ZnDTP, and organic molybdenum, and solid lubricants such as MoS2, graphite, PTFE, and MCA.

[0032] When additives are to be incorporated, although not particularly limited, they can be incorporated in an amount of 3% by mass or less, preferably 1% by mass or less, more preferably 0.5% by mass or less in the grease composition.

[0033] (Low-temperature torque at -40°C) This grease composition has a low-temperature torque at -40°C of 300 mN·m or less. More preferably 250 mN·m or less, particularly preferably 200 mN·m or less. The low-temperature torque at -40°C can be measured in accordance with JIS K 2220 and can be adjusted, for example, by changing the content ratio of polyisobutylene.

[0034] Regarding the mixed solution of base oil and polyisobutylene as "mixed base oil", the physical property values of the mixed base oil are preferably as follows.

[0035] (Kinematic viscosity of the mixed base oil at 40°C) This grease composition preferably has a kinematic viscosity of the mixed base oil at 40°C of 800 mm 2 / s or more. More preferably 1500 mm 2 / s or more, particularly preferably 2000 mm 2 / s or more. The kinematic viscosity of the mixed base oil at 40°C can be measured in accordance with JIS K 2283 and can be adjusted, for example, by changing the content ratio of polyisobutylene.

[0036] (Kinematic viscosity of the mixed base oil at 100°C) This grease composition preferably has a kinematic viscosity of the mixed base oil at 100°C of 100 mm 2 / s or more. More preferably 110 mm 2 / s or more, particularly preferably 120 mm 2 / s or more. The kinematic viscosity of the mixed base oil at 100°C can be measured in accordance with JIS K 2283 and can be adjusted, for example, by changing the content ratio of polyisobutylene.

[0037] (Pour point) The pour point of the mixed base oil of this grease composition is preferably -30°C or lower. More preferably, it is -35°C or lower, and particularly preferably -40°C or lower. The pour point can be measured according to JIS K 2269 and can be adjusted, for example, by changing the content ratio of polyisobutylene.

[0038] (Viscosity index) The viscosity index of the mixed base oil of this grease composition is preferably 200 or higher. More preferably, it is 225 or higher, and particularly preferably 250 or higher. The viscosity index can be measured according to JIS K 2283 and can be adjusted, for example, by changing the content ratio of polyisobutylene.

[0039] (Manufacturing method) This grease composition can be manufactured by blending a base oil, a thickener, polyisobutylene, and, if necessary, an additive in the above-described content ratios and then milling them. The milling is not particularly limited, but can be carried out using a milling and dispersing treatment device such as a three-roll mill, a homogenizer, or a colloid mill.

[0040] The mixing is preferably carried out while heating and dissolving. The heating can be carried out while maintaining the temperature at which lithium soap dissolves, for example, preferably 200°C or higher, more preferably 220°C or higher, and particularly preferably 240°C or higher. The polyisobutylene having a weight average molecular weight of 50,000 or more used in this grease composition is difficult to mix due to its high viscosity. Therefore, it is preferable to mix and heat the base oil and polyisobutylene in advance to dissolve them.

[0041] (Applications) This grease composition can be suitably used for mechanical parts such as automotive parts and precision mechanical parts. Among them, it is suitable for automotive parts because of its excellent low-temperature torque. Examples of automotive parts include, for example, door locks, gear shift levers, window regulators, fan control levers, door mirrors, and the like. Examples of products other than automotive parts include, for example, home appliances such as air conditioners, controllers for gaming devices, electronic musical instruments such as electronic pianos, and welfare devices such as nursing bed lifting devices.

Example

[0042] Hereinafter, the present invention will be described based on an example. However, the present invention is not limited to this example.

[0043] In preparing the examples and comparative examples, the following materials were used.

[0044] <Base oil> 1-A: PAO6 (trade name "Synfluid PAO6 cSt" (manufactured by Chevron Phillips Chemical Company)) Kinematic viscosity at 40°C: 30.7 mm 2 / s Kinematic viscosity at 100°C: 5.8 mm 2 / s Viscosity index: 135 Pour point: -63°C

[0045] 1-B: PAO4 (trade name "Synfluid PAO4 cSt" (manufactured by Chevron Phillips Chemical Company)) Kinematic viscosity at 40°C: 17.4 mm 2 / s Kinematic viscosity at 100°C: 3.9 mm 2 / s Viscosity index: 124 Pour point: -68°C

[0046] <Thickener> 2-A: Lithium 12-hydroxystearate (manufactured by Katsuta Chemical Co., Ltd.) 2-B: Lithium stearate (manufactured by Katsuta Chemical Co., Ltd.)

[0047] <Polyisobutylene> 3-A: Polyisobutylene (trade name "Oppanol B15N" (manufactured by BASF)) Weight average molecular weight: 108,000

[0048] <Viscosity modifier> 4-A: Ethylene α-olefin oligomer (trade name "Lucant HC2000" (manufactured by Mitsui Chemicals)) Number average molecular weight: 3,400 4-B: Polybutene (trade name "ENEOS Polybutene Grade HV1900" (manufactured by ENEOS)) Number average molecular weight: 2,900

[0049] (Examples 1 to 3) Into a stainless steel cup, 168 g of PAO6 (1-A), 37.8 g of lithium 12-hydroxystearate (2-A), and 4.2 g of lithium stearate (2-B) were added, and the mixture was gradually heated with stirring until it was confirmed that lithium 12-hydroxystearate (2-A) and lithium stearate (2-B) were completely dissolved. Then, the heating was stopped, and while stirring, 90 g of PAO6 (1-A) was added dropwise and cooled to 150°C. Thereafter, it was left to cool to room temperature and milled with a three-roll mill to obtain a base grease.

[0050] On the other hand, into another stainless steel cup, 241.53 g of PAO6 (1-A) and 158.47 g of polyisobutylene (3-A) were added, and the mixture was heated to 200°C with stirring to dissolve it, thereby preparing a solution.

[0051] To 100 g of the base grease, the above solution and PAO6 (1-A) were blended in appropriate amounts, and the mixture was stirred while heating with a three-roll mill to prepare the grease compositions of Examples 1 to 3 having the blending ratios shown in Table 1 below.

[0052] (Examples 4 to 6) In Examples 1 to 3 above, grease compositions of Examples 4 to 6 were prepared in the same manner except that PAO6 (1-A) was changed to PAO4 (1-B).

[0053] (Comparative Example 1) Ethylene α-olefin oligomer (4-A) and PAO6 (1-A) were blended with the above base grease in the blending ratios shown in Table 1 below and mixed with a three-roll mill to prepare the grease composition of Comparative Example 2.

[0054] (Comparative Example 2) Polybutene (4-B) and PAO6 (1-A) were blended with the above base grease in the blending ratios shown in Table 1 below and mixed with a three-roll mill to prepare the grease composition of Comparative Example 1.

[0055]

Table 1

[0056] (Test) The following tests were conducted on the grease compositions of Examples 1 to 6 and Comparative Examples 1 and 2. The results of these tests are shown in Table 1 above.

[0057] <Consistency>[[]] The consistency was measured according to JIS K 2220 5.3. The consistency was adjusted to fall within the range of No. 2 grade of 280 ± 15.

[0058] <Low-temperature torque>[[]] The starting torque at -40 °C was measured according to JIS K 2220 5.14.

[0059] <Drop point>[[]] The drop point was measured according to JIS K 2220 5.4.

[0060] (Blended base oil) Only the base oil and polyisobutylene were mixed at the same blending ratios as in Examples 1 to 6 and Comparative Examples 1 and 2 to prepare a blended base oil, and the following physical property values were measured. The measured results are shown in Table 1 above.

[0061] <Kinematic viscosity>[[]] ​​​​The kinematic viscosity at 40°C and 100°C was measured in accordance with JIS K 2283.

[0062] <Viscosity index> The viscosity index was calculated in accordance with JIS K 2283.

[0063] <Pour point> The pour point was measured in accordance with JIS K 2269. The pour point was measured every 0.5°C.

[0064] (Results) Compared with the grease compositions of Comparative Examples 1 and 2, the grease compositions of Examples 1 to 6 had higher kinematic viscosities at 40°C and 100°C, but lower low-temperature torque and pour point at -40°C, and it was confirmed that the operability at low temperatures could be improved. Also, compared with the grease compositions of Comparative Examples 1 and 2, the grease compositions of Examples 1 to 6 had a higher viscosity index and less viscosity change due to temperature.

[0065] (Discussion) As a factor for Examples 1 to 6 having low torque in the low-temperature range, the movement of the grease packed in the bearing is presumed. Regarding the so-called churning phenomenon where the entire grease is agitated in the bearing, the grease in the bearing is extruded from the bearing and repositioned to the locations where only the amount necessary for lubricating the bearing is required, so-called channeling property was significantly improved, resulting in a decrease in torque. Therefore, it is considered that Examples 1 to 6 have lower torque at low temperatures compared with Comparative Examples 1 and 2.

Claims

1. A grease composition comprising a base oil, a thickener, and polyisobutylene having a weight average molecular weight of 50,000 or more and accounting for 5 to 40% by mass in the composition, and having a low-temperature torque at -40°C of 300 mN·m or less.

2. The grease composition according to claim 1, wherein the mass ratio of the base oil to the polyisobutylene (base oil: polyisobutylene) is in the range of 90:10 to 70:30, and the viscosity index of the mixed base oil of the base oil and the polyisobutylene is 200 or more.

3. The grease composition according to claim 2, wherein the thickener is lithium soap at 15% by mass or less in the composition.

4. The kinematic viscosity of the mixed base oil at 40°C is 800 mm ２ / s or more, and the grease composition according to claim 3.

5. The grease composition according to claim 4, wherein the pour point of the mixed base oil is -30°C or lower.

Images