GREASE COMPOSITION FOR SPEED REDUCER PART OF ON-VEHICLE ELECTRIC COMPONENT

Abstract

The invention provides a grease composition for a speed reducer part of an on-vehicle electric component, the grease composition containing a base oil and a thickener, wherein the base oil is poly-α-olefin or a mixed oil of poly-α-olefin and mineral oil having a kinematic viscosity of 4 to 19 mm.sup.2/s at 100° C. and a pour point of −30° C. or lower, the thickener is a mixture of a diurea compound expressed by formula (1) and a diurea compound expressed by formula (2)

R.sub.1—NHCONH—R.sub.2—NHCONH—R.sub.1  (1)

R.sub.3—NHCONH—R.sub.2—NHCONH—R.sub.3  (2)

wherein R.sub.1 is a straight-chain alkyl group having 8 or 18 carbon atoms, R.sub.2 is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, and R.sub.3 is an aryl group having 6 to 7 carbon atoms, and a penetration of the grease composition is 220 to 280.

Claims

1. A grease composition for a speed reducer part of an on-vehicle electric component, the grease composition containing a base oil and a thickener, wherein the base oil is poly-α-olefin or a mixed oil of poly-α-olefin and mineral oil having a kinematic viscosity of 4 to 19 mm.sup.2/s at 100° C. and a pour point of −30° C. or lower, the thickener is a mixture of a diurea compound expressed by formula (1) and a diurea compound expressed by formula (2)
R.sub.1—NHCONH—R.sub.2—NHCONH—R.sub.1  (1)
R.sub.3—NHCONH—R.sub.2—NHCONH—R.sub.3  (2) wherein R.sub.1 is a straight-chain alkyl group having 8 or 18 carbon atoms, R.sub.2 is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, and R.sub.3 is an aryl group having 6 to 7 carbon atoms, and a penetration of the grease composition is 220 to 280.

2. The grease composition according to claim 1, wherein a mixed ratio of the diurea compounds is (1):(2)=9:1 to 5:5 in mass ratio.

3. The grease composition according to claim 1, wherein the on-vehicle electric component is an opening-closing body drive motor, a wiper motor, a power seat motor, or a door mirror motor.

Description

DESCRIPTION OF EMBODIMENT

[Mixture of Aliphatic Diurea and Aromatic Diurea]

[0012] A thickener used in a grease composition of the present invention is a mixture of a diurea compound expressed by formula (1) below and a diurea compound expressed by formula (2) below.

R.sub.1—NHCONH—R.sub.2—NHCONH—R.sub.1  (1)

R.sub.3—NHCONH—R.sub.2—NHCONH—R.sub.3  (2)

(in the formulae, R.sub.1 is a straight-chain alkyl group independently having 8 or 18 carbon atoms, R.sub.2 is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, and R.sub.3 is an aryl group having 6 to 7 carbon atoms)

[0013] The compound of formula (1) may be a compound in which both R.sub.1 are a straight-chain alkyl group having 8 carbon atoms, both R.sub.1 are a straight-chain alkyl group having 18 carbon atoms, or one R.sub.1 is a straight-chain alkyl group having 8 carbon atoms while the other R.sub.1 is a straight-chain alkyl group having 18 carbon atoms. The compound of formula (1) is preferably the compound in which both R.sub.1 are the straight-chain alkyl group having 8 carbon atoms from the viewpoint of adhesiveness.

[0014] The compound of formula (2) is preferably a compound in which R.sub.3 is a tolyl group.

[0015] The R.sub.2 in formula (1) and formula (2) is preferably a group derived from tolylene diisocyanate or diphenylmethane-4,4′-diisocyanate, more preferably the group derived from diphenylmethane-4,4′-diisocyanate.

[0016] The compound of formula (1) is more preferably a compound in which R.sub.1 is the straight-chain alkyl group having 8 carbon atoms and R.sub.2 is the group derived from diphenylmethane-4,4′-diisocyanate. The compound of formula (2) is more preferably a compound in which R.sub.3 is the tolyl group and R.sub.2 is the group derived from diphenylmethane-4,4′-diisocyanate. A mixture of these compounds is most preferable.

[0017] A diurea-based thickener is generally obtained by reacting isocyanate and amine that are raw materials in a base oil. The thickener of the present invention can be obtained by separately preparing the diurea compound (belonging to so called “aliphatic diurea”) that is expressed by formula (1) and in which the raw material amine is octylamine and/or stearylamine and the diurea compound (belonging to so-called “aromatic diurea”) that is expressed by formula (2) and in which the raw material amine is aromatic amine in the base oil and then mixing the prepared compounds. The thickener of the present invention is different from a thickener obtained by reacting a mixture of aliphatic amine and aromatic amine with isocyanate.

[0018] A mass ratio between the diurea compound expressed by formula (1) and the diurea compound expressed by formula (2) is preferably (1):(2)=9:1 to 5:5, more preferably 9:1 to 7:3, even more preferably 9:1 to 8:2. The mass ratio being within such a range is preferable because, in such a case, the grease has excellent adhesiveness to a speed reducer part under a high-speed condition.

[0019] The content of the thickener in the grease composition of the present invention is preferably 5 to 30 mass %, more preferably 5 to 20 mass %, and even more preferably 8 to 20 mass %. The content of the thickener being within such a range is preferable because, in such a case, the adhesiveness is good.

[0020] The composition of the present invention preferably includes no thickener other than the mixture described above.

[Poly-α-Olefin or Mixed Oil of Poly-α-Olefin and Mineral Oil]

[0021] The base oil used in the grease composition of the present invention is PAO alone or a mixed oil of PAO and mineral oil.

[0022] The kinematic viscosity of the base oil at 100° C. is 4 to 19 mm.sup.2/s, preferably 6 to 15 mm.sup.2/s, more preferably 8 to 15 mm.sup.2/s. When the kinematic viscosity of the base oil at 100° C. is 4 mm.sup.2/s or more, a grease composition with excellent heat resistance can be obtained. When the kinematic viscosity of the base oil at 100° C. is 19 mm.sup.2/s or less, a grease composition with an excellent low-temperature property can be obtained. Particularly, when the kinematic viscosity of the base oil is 6 to 15 mm.sup.2/s or 8 to 15 mm.sup.2/s, it is possible to obtain the grease composition with both of acceptable low-temperature performance and acceptable heat resistance. In the case of the mixed oil, the kinematic viscosity of each of PAO and the mineral oil is not limited to particular viscosity as long as the kinematic viscosity of the whole base oil is within the aforementioned range. However, using PAO with kinematic viscosity of 4 to 100 mm.sup.2/s at 100° C. and mineral oil with kinematic viscosity of 6 to 15 mm.sup.2/s at 100° C. together can achieve an excellent low-temperature property and is thus preferable.

[0023] The pour point of the base oil is −30° C. or lower. When the pour point of the base oil is −30° C. or lower, a grease composition with an excellent low-temperature property can be obtained.

[0024] When the base oil of the present invention is the mixed oil of PAO and the mineral oil, the proportion of each oil is not limited to a particular proportion as long as the kinematic viscosity at 100° C. and the pour point are within the aforementioned ranges. In the case of the mixed oil, PAO:mineral oil (mass ratio) is more preferably 9:1 to 5:5, even more preferably 9:1 to 6:4. The mass ratio being within such a range is preferable because, in such a case, the low-temperature property is excellent.

[0025] The content of the base oil in the grease composition of the present invention is preferably 70 to 90 mass %, more preferably 80 to 90 mass %, even more preferably 80 to 90 mass %. The content of the base oil being within such a range is preferable because, in such a case, the low-temperature property is excellent.

[Other Additives]

[0026] The grease composition of the present invention may contain additives normally used in grease as necessary. When the grease composition of the present invention contains additives, the content of the additives is normally 0.5 to 35 mass %, preferably 5 to 25 mass %, more preferably 0.5 to 5% based on the total amount of the grease composition. Such additives include an inorganic passivator, an antioxidant, antirust agent, a metal corrosion inhibitor, an oiliness agent, an antiwear agent, an extreme pressure agent, and solid lubricant. The grease composition preferably contains the antioxidant and the antirust agent among these additives. The inorganic passivator specifically includes sodium nitrite and the like.

[0027] The antioxidant includes amine-based, phenol-based, quinoline-based, and sulfur-based antioxidants, zinc dithiophosphate, and the like. The antioxidant is preferably the amine-based or phenol-based antioxidant.

[0028] The antirust agent includes zinc-based, carboxylic acid-based, carboxylate salt-based, succinic acid-based, amine-based, and sulfonate salt-based antirust agents. The antirust agent is preferably the succinic acid-based antirust agent, more preferably a succinic anhydride, particularly preferably an alkenyl succinic anhydride (for example, succinic anhydride including an alkenyl group having 12 carbon atoms).

[0029] The metal corrosion inhibitor includes thiadiazole-based, benzimidazole-based, and benzotriazole-based metal corrosion inhibitors.

[0030] The oiliness agent includes an aliphatic acid, a fatty acid ester, and a phosphoric acid ester.

[0031] The antiwear agent and the extreme pressure agent include phosphorus-based, sulfur-based, and organic metal-based agents.

[0032] The solid lubricant includes a metal oxide salt, molybdenum disulfide, polytetrafluoroethylene, melamine cyanurate, and graphite.

[0033] The grease composition preferably contains no viscosity increaser as the additives.

[Penetration]

[0034] The penetration of the grease composition of the present invention is 220 to 280, preferably 235 to 265. Setting the penetration to 220 or more enables obtaining of a grease composition with an excellent low-temperature property and setting the penetration to 280 or less enables obtaining of a grease composition with excellent adhesiveness under a high-speed condition. Note that the term “penetration” in the present specification refers to a 60-stroke worked penetration. The penetration can be measured according to JIS K2220 7.

[0035] Among such grease compositions, a grease composition in which

[0036] a base oil is poly-α-olefin or the mixed oil of poly-α-olefin and the mineral oil having a kinematic viscosity of 13.6 mm.sup.2/s at 100° C. and a pour point of −30° C. or lower,

[0037] a thickener is the mixture of the compound of formula (1) in which R.sub.1 is the straight-chain alkyl group having 8 carbon atoms and R.sub.2 is the group derived from diphenylmethane-4,4′-diisocyanate and the compound of formula (2) in which R.sub.3 is the tolyl group and R.sub.2 is the group derived from diphenylmethane-4,4′-diisocyanate, where the mixing ratio is (1):(2)=9:1 in mass ratio, and

[0038] the penetration of the grease composition is 250

is preferable because this grease composition has a good balance of the low-temperature property, the adhesiveness under the high-speed condition, and the heat resistance (therefore, lubrication life). It is particularly preferable that this grease composition further contains 0.5 mass % of the phenol-based antioxidant as the antioxidant and 0.5 mass % of the succinic anhydride including the alkenyl group having 12 carbon atoms as the antirust agent.

[0039] The grease composition of the present invention can be used in a speed reducer part of an on-vehicle electric component, for example, an opening-closing body drive motor, a wiper motor, a power seat motor, or a door mirror motor. Materials forming these members may be resin or metal. The resin includes polyacetal (POM), aliphatic polyamide (PA6, PA66, and the like), aromatic polyamide (PA6T, PAST, and the like), polyphenylene sulfide (PPS), and the like. The metal includes steel, copper alloys (brass and the like), and the like. A combination of polyacetal and steel is preferable from the viewpoint of accuracy of dimensions, lubricating property, and cost.

EXAMPLES

[0040] Base oils used to prepare grease compositions of Examples and Comparative Examples are as follows. [0041] Poly-α-olefin A (“PAO-A”): Kinematic viscosity at 100° C. is 100.0 mm.sup.2/s, pour point is −30° C. [0042] Poly-α-olefin B (“PAO-B”): Kinematic viscosity at 100° C. is 8.0 mm.sup.2/s, pour point is −55° C. [0043] Poly-α-olefin C (“PAO-C”): Kinematic viscosity at 100° C. is 4.0 mm.sup.2/s, pour point is −65° C. [0044] Poly-α-olefin D (“PAO-D”): Kinematic viscosity at 100° C. is 2.0 mm.sup.2/s, pour point is −65° C. [0045] Mineral oil A (“MO-A”): Kinematic viscosity at 100° C. is 11.2 mm.sup.2/s, pour point is −15.0° C. [0046] Mineral oil B (“MO-B”): Kinematic viscosity at 100° C. is 31.6 mm.sup.2/s, pour point is −12.5° C.

Preparation Example 1 Preparation of Grease Composition in which Thickener is Aliphatic Diurea

[0047] 4,4′-diphenylmethane diisocyanate and octylamine were reacted at a ratio of 1 mol to 2 mol in the base oil and were cooled to form a base grease.

[0048] A phenol-based antioxidant (product name IRGANOX L135, manufactured by BASF Japan Ltd.) 0.5% and an alkenyl succinic anhydride (succinic anhydride including an alkenyl group having 12 carbon atoms) (product name DSA, manufactured by Sanyo Chemical Industries, Ltd.) 0.5% were added to the base grease as the antioxidant and the antirust agent, respectively, and were kneaded with a triple roll mill to prepare a grease composition with a predetermined penetration.

Preparation Example 2 Preparation of Grease Composition in which Thickener is Aromatic Diurea

[0049] A grease composition was prepared as in Preparation Example 1 except for the point that p-toluidine was used instead of octylamine.

Preparation Example 3 Preparation of Grease Composition in which Thickener is Mixture of Aliphatic Diurea and Aromatic Diurea

[0050] The base grease obtained in Preparation Example 1 and the base grease obtained in Preparation Example 2 were mixed to prepare a base grease in which the thickener was a mixture of aliphatic diurea and aromatic diurea.

[0051] A phenol-based antioxidant (product name IRGANOX L135, manufactured by BASF Japan Ltd.) 0.5% and an alkenyl succinic anhydride (succinic anhydride including an alkenyl group having 12 carbon atoms) (product name DSA, manufactured by Sanyo Chemical Industries, Ltd.) 0.5% were added to the base grease as the antioxidant and the antirust agent, respectively, and were kneaded with a triple roll mill to prepare a grease composition with a predetermined penetration.

[0052] The mass % of the thickener in each composition was as illustrated in Tables 1 and 2. The balance is the base oil.

[0053] Note that the kinematic viscosity of each base oil at 100° C. was measured according to JIS K2220 23. The pour point of each base oil was measured according to JIS K2269. The penetration of each grease composition was measured according to JIS K2220 7.

[0054] The grease compositions obtained above were tested and evaluated in methods described below.

<Evaluation of Adhesiveness by Ring-On-Ring Test>

[0055] Test Method

[0056] Sample grease was applied at an even thickness on a surface of a ring A, a ring B was placed on the ring A, the rings A and B were rotated at the specified number of revolutions, and then an amount of grease dispersed from the ring surface was measured.

[0057] Test Conditions

[0058] Ring A [0059] Material: polyacetal (φ50 mm) [0060] Number of revolutions: 400 rpm (V=62.8 m/min)

[0061] Ring B [0062] Material: steel (φ25 mm) [0063] Number of revolutions: 800 rpm (V=62.8 m/min)

[0064] Load: 10 N (10.7 MPa)

[0065] Test temperature: 25° C.

[0066] Measurement Item

Dispersion rate (%)=grease dispersion amount (mg)/grease application amount (mg)

[0067] Criteria [0068] Excellent Adhesiveness accepted: dispersion rate less than 20% [0069] Good Adhesiveness accepted: dispersion rate less than 25% [0070] Poor Adhesiveness failed: dispersion rate 25% or more [0071] Very poor Adhesiveness failed: dispersion rate 30% or more

<Evaluation of Low-Temperature Property by Rheometer Test>

[0072] Test Method

[0073] Sample grease was sandwiched between a cone and a plate and cooled to specified temperature. Then, the cone was rotated and maximum shear stress applied to the plate was measured.

[0074] Test Conditions [0075] Measurement temperature: −40° C. [0076] Shear rate: 0.1 to 100 s.sup.−1

[0077] Evaluation Item

[0078] Maximum shear stress at shear rate of 10 s.sup.−1 or less.

[0079] Criteria [0080] Excellent Low-temperature property accepted: maximum shear stress less than 20000 Pa [0081] Good Low-temperature property accepted: maximum shear stress less than 30000 Pa [0082] Poor Low-temperature property failed: maximum shear stress 30000 Pa or more [0083] Very poor Low-temperature property failed: maximum shear stress 40000 Pa or more

<Evaluation of Heat Resistance by High-Temperature Thin-Film Test>

[0084] Test Method

[0085] Grease was evenly applied to a steel plate at a thickness of 2 mm and left to stand in a constant temperature bath at specified temperature for specified time, and then an evaporation amount of the grease was measured.

[0086] Test Condition [0087] Test temperature: 120° C. [0088] Test time: 250 h

[0089] Criteria [0090] Excellent Heat resistance accepted: evaporation amount less than 2.0 mass % [0091] Good Heat resistance accepted: evaporation amount less than 3.0 mass % [0092] Poor Heat resistance failed: evaporation amount 3.0 mass % or more [0093] Very poor Heat resistance failed: evaporation amount 4.0 mass % or more

[0094] Results are illustrated in Tables 1 and 2.

TABLE-US-00001 TABLE 1 Example 1 2 3 4 5 6 7 Thickener Aliphatic diurea, mass ratio 90 90 90 90 90 90 50 Aromatic diurea, mass ratio 10 10 10 10 10 10 50 Mass %   16.0   13.5   11.0   13.5   13.5   13.5   18.0 Base oil PAO type PAO-A PAO-A PAO-A PAO-A PAO-A PAO-A PAO-A mass ratio 20 20 20 — 30 20 20 PAO-B PAO-B PAO-B PAO-B PAO-B PAO-B PAO-B 60 60 60 — 50 80 60 PAO-C PAO-C PAO-C PAO-C PAO-C PAO-C PAO-C — — — 100  — — — PAO-D PAO-D PAO-D PAO-D PAO-D PAO-D PAO-D — — — — — — — Mineral oil type MO-A MO-A MO-A MO-A MO-A MO-A MO-A mass ratio 20 20 20 — 20 — 20 MO-B MO-B MO-B MO-B MO-B MO-B MO-B — — — — — — — Kinematic viscosity, mm.sup.2/s   13.6   13.6   13.6   4.0   19.0   13.6   13.6 Pour point, ° C.  −30.0  −30.0  −30.0  −65.0  −30.0  −45.0  −30.0 Penetration 220  250  280  250  250  250  250  Adhesiveness Excellent Excellent Good Good Excellent Excellent Good Low-temperature property Good Excellent Excellent Excellent Good Excellent Good Heat resistance Excellent Excellent Good Good Excellent Excellent Excellent

TABLE-US-00002 TABLE 2 Comparative Example 1 2 3 4 5 6 7 8 Thickener Aliphatic diurea, mass ratio 100   0 90 90 90 90 90 90 Aromatic diurea, mass ratio  0 100  10 10 10 10 10 10 Mass %   10.0   20.0   18.0   10.0   13.5   13.5   13.5   13.5 Base oil PAO type PAO-A PAO-A PAO-A PAO-A PAO-A PAO-A PAO-A PAO-A mass ratio 20 20 20 20 — 30 10 — PAO-B PAO-B PAO-B PAO-B PAO-B PAO-B PAO-B PAO-B 60 60 60 60 — 45 40 — PAO-C PAO-C PAO-C PAO-C PAO-C PAO-C PAO-C PAO-C — — — — 50  5 — — PAO-D PAO-D PAO-D PAO-D PAO-D PAO-D PAO-D PAO-D — — — — 50 — — — Mineral oil type MO-A MO-A MO-A MO-A MO-A MO-A MO-A MO-A mass ratio 20 20 20 20 — 20 40 80 MO-B MO-B MO-B MO-B MO-B MO-B MO-B MO-B — — — — — — 10 20 Kinematic viscosity mm.sup.2/s   13.6   13.6   13.6   13.6   3.0   20.0   13.6   13.6 Pour point, ° C.  −30.0  −30.0  −30.0  −30.0   −65.0>  −30.0  −25.0  −12.5 Penetration 250  250  200  300  250  250  250  250  Adhesiveness Very poor Very poor Excellent Poor Good Excellent Excellent Good Low-temperature property Excellent Poor Poor Excellent Excellent Poor Poor Very poor Heat resistance Excellent Excellent Excellent Good Poor Excellent Poor Very poor