LUBRICATING OIL COMPOSITION

Abstract

There is provided a lubricating oil composition which is excellent in the wear resistance and the oil film retention even when the viscosity of the composition is lowered. The lubricating oil composition comprises: a base oil (A); an imide compound (B); a calcium-based detergent (C); a polymer component (D); and a zinc dithiophosphate (E), wherein the imide compound (B) comprises at least one non-boron-modified succinic acid imide compound (Bx) selected from a succinic acid monoimide (B1x) represented by general formula (b-1) and a succinic acid bisimide (B2x) represented by general formula (b-2), and wherein the polymer compound (D) has a mass average molecular weight (Mw) of not less than 10,000 and not more than 50,000, and comprises at least one selected from an olefin polymer (D1) and a polymethacrylate (D2).

Claims

1. A lubricating oil composition, comprising: a base oil; an imide compound; a calcium-based detergent; a polymer component; and a zinc dithiophosphate, wherein the imide compound comprises at least one non-boron-modified succinic acid imide compound selected from the group consisting of a succinic acid monoimide represented by the following general formula (b-1) and a succinic acid bisimide represented by the following general formula (b-2): ##STR00009## wherein R.sup.A, R.sup.A1, and R.sup.A2 are each independently an alkenyl group having a mass average molecular weight (Mw) of 500 to 4,000, wherein R.sup.B, R.sup.B1, and R.sup.B2 are each independently an alkylene group having 2 to 5 carbon atoms, wherein R.sup.C is an alkyl group having 1 to 10 carbon atoms or a group represented by —(AO).sub.n-H where A represents an alkylene group having 2 to 4 carbon atoms, and n represents an integer of 1 to 10, and wherein x1 is an integer of 1 to 10, and x2 is an integer of 1 to 10, and wherein the polymer component has a mass average molecular weight (Mw) of not less than 10,000 and not more than 50,000, and comprises at least one selected from the group consisting of an olefin polymer and a polymethacrylate.

2. The lubricating oil composition to of claim 1, wherein the imide compound further comprises at least one boron-modified succinic acid imide compound selected from the group consisting of a boron-modified product of the succinic acid monoimide and a boron-modified product of the succinic acid bisimide, and wherein the content of boron atoms derived from the boron-modified succinic acid imide compound is not more than 0.020% by mass based on the total amount of the lubricating oil composition.

3. The lubricating oil composition of claim 2, wherein the mass ratio of the content of boron atoms derived from the boron-modified succinic acid imide compound to the content of nitrogen atoms derived from the imide compound is not more than 1.0.

4. The lubricating oil composition of claim 1, wherein the mass ratio of the content of phosphorus atoms derived from the zinc dithiophosphate to the content of nitrogen atoms derived from the imide compound is not less than 0.5 and not more than 5.0.

5. The lubricating oil composition of claim 1, wherein the content of nitrogen atoms is not less than 0.010% by mass and not more than 0.10% by mass based on the total amount of the lubricating oil composition.

6. The lubricating oil composition of claim 1, wherein the calcium-based detergent is a calcium sulfonate.

7. The lubricating oil composition of claim 1, wherein the kinematic viscosity of the composition at 100° C. is not less than 4.0 mm.sup.2/s and is less than 20.0 mm.sup.2/s.

8. (canceled)

9. A method for producing a lubricating oil composition, the method comprising: mixing a base oil, an imide compound, a calcium-based detergent, a polymer component, and a zinc dithiophosphate, wherein the imide compound comprises at least one non-boron-modified succinic acid imide compound selected from the group consisting of a succinic acid monoimide represented by the following general formula (b-1) and a succinic acid bisimide represented by the following general formula (b-2): ##STR00010## wherein R.sup.A, R.sup.A1, and R.sup.A2 are each independently an alkenyl group having a mass average molecular weight (Mw) of 500 to 4,000, wherein R.sup.B, R.sup.B1, and R.sup.B2 are each independently an alkylene group having 2 to 5 carbon atoms, wherein R.sup.C is an alkyl group having 1 to 10 carbon atoms or a group represented by —(AO).sub.n-H where A represents an alkylene group having 2 to 4 carbon atoms, and n represents an integer of 1 to 10, wherein x1 is an integer of 1 to 10, and x2 is an integer of 1 to 10, and wherein the polymer component has a mass average molecular weight (Mw) of not less than 10,000 and not more than 50,000, and comprises at least one selected from the group consisting of an olefin polymer and a polymethacrylate.

Description

EXAMPLES

[0199] The following examples illustrate the present invention in greater detail and are not intended to limit the scope of the invention. Various properties and parameters of lubricating oil compositions and their components, used in Examples and Comparative Examples, were measured by the following methods.

[0200] [40° C. Kinematic Viscosity, 100° C. Kinematic Viscosity, and Viscosity Index]

[0201] The 40° C. kinematic viscosity, the 100° C. kinematic viscosity, and the viscosity index were measured or calculated in accordance with JIS K 2283:2000.

[0202] [150° C. HTHS Viscosity]

[0203] The 150° C. HTHS viscosity was measured or calculated in accordance with JPI-5S-36-03.

[0204] [Contents of Boron Atoms, Calcium Atoms, Phosphorus Atoms and Zinc Atoms]

[0205] The contents of boron atoms, calcium atoms, phosphorus atoms and zinc atoms were measured in accordance with JPI-5S-38-03.

[0206] [Content of Nitrogen Atoms]

[0207] The content of nitrogen atoms (total amount measured) was measured in accordance with JIS K 2609:1998.

[0208] The measured content of nitrogen atoms includes the content of nitrogen atoms derived from an antioxidant. Therefore, the theoretical value was calculated from the content of the imide compound and from the content of nitrogen atoms in the imide compound.

[0209] [Atomic Content Ratio]

[0210] From the contents of various atoms determined above, the ratio [(By-B)/(B-N)] of the content of boron atoms (By-B) derived from the boron-modified succinic acid imide compound (By) to the content of nitrogen atoms (B-N) derived from the imide compound (B) was calculated by dividing the content of boron atoms (By-B) by the content of nitrogen atoms (B-N).

[0211] Further, from the contents of various atoms determined above, the ratio [(E-P)/(B-N)] of the content of phosphorus atoms (E-P) derived from the zinc dithiophosphate (E) to the content of nitrogen atoms (B-N) derived from the imide compound (B) was calculated by dividing the content of phosphorus atoms (E-P) by the content of nitrogen atoms (B-N).

[0212] <Base Number>

[0213] The base number of the calcium-based detergent (C) was measured by the perchloric acid method in accordance with JIS K 2501:2003.

[0214] [Examples 1 to 9 and Comparative Examples 1 to 4]

[0215] The following components were thoroughly mixed in the amounts shown in Tables 1 to 3 to obtain lubricating oil compositions.

[0216] Details of the components used in Examples 1 to 9 and Comparative Examples 1 to 4 are as follows.

[0217] <Base Oil (A)>

[0218] Base oil (A1): mineral oil (API Base Oil Category: Group III, 40° C. kinematic viscosity: 32.7 mm.sup.2/s, 100° C. kinematic viscosity: 6.0 mm.sup.2/s, viscosity index: 132)

[0219] Base oil (A2): mineral oil (API Base Oil Category: Group II, 40° C. kinematic viscosity: 88.7 mm.sup.2/s, 100° C. kinematic viscosity: 10.2 mm.sup.2/s, viscosity index: 96)

[0220] <Imide compound (B)>

[0221] Non-boron-modified succinic acid imide compound (Bx): capped non-boron-modified alkenyl succinic acid bisimide (succinic acid bisimide (B2x) represented by the general formula (b-2). In the general formula (b-2), R.sup.A1 and R.sup.A2 are each a polybutenyl group having a mass average molecular weight (Mw) of 2,300, R.sup.B1 and R.sup.B2 are each an ethylene group, R.sup.C is a group represented by —CH.sub.2CH.sub.2OCH.sub.2CH.sub.2OH, and x2 is 5. The content of nitrogen atoms: 1.0% by mass)

[0222] Boron-modified succinic acid imide compound (By): capped boron-modified alkenyl succinic acid imide (polybutene backbone, the content of nitrogen atoms: 2.3% by mass, the content of boron atoms: 1.9% by mass)

[0223] Non-capped succinic acid imide compound (B′): unmodified alkenyl succinic acid bisimide (non-capped succinic acid bisimide (B′2) represented by the general formula (ii). In the general formula (ii), R.sup.A1 and R.sup.A2 are each a polybutenyl group having a mass average molecular weight (Mw) of 950, R.sup.B1 and R.sup.B2 are each an ethylene group, and x2 is 3. The content of nitrogen atoms: 1.9% by mass)

[0224] <Calcium-Based Detergent (C)>

[0225] Calcium-based detergent (C1): calcium sulfonate with a branched alkyl group having a branched chain of a butyl group and having 16 carbon atoms (including the number of the carbon atoms of the branched chain) (base number: 300 mgKOH/g, the content of calcium atoms: 11.6% by mass)

[0226] <Polymer Component (D)>

[0227] Polymer component (D1-1): ethylene-propylene copolymer (product name: LUCANT HC-2000 (registered trademark), manufactured by Mitsui Chemicals, Inc., mass average molecular weight (Mw): 14,000)

[0228] Polymer component (D1-2): poly-α-olefin (PAO, mass average molecular weight (Mw): 16,000)

[0229] Polymer component (D2): polymethacrylate (PMA, mass average molecular weight (Mw): 35,000)

[0230] Polymer component (D3): ethylene-propylene copolymer (product name: LUCANT HC-600 (registered trademark), manufactured by Mitsui Chemicals, Inc., mass average molecular weight (Mw): 7,000)

[0231] The mass average molecular weights (Mw) of the polymer components (D) were measured by gel permeation chromatography, followed by calculation in terms of polystyrene.

[0232] <Zinc Dithiophosphate (E)>

[0233] ZnDTP: Zinc secondary dialkyldithiophosphate (the content of phosphorus atoms: 7.1% by mass)

[0234] <Other Component>

[0235] Antioxidant: alkyl-substituted diphenylamine antioxidant

[0236] The following physical properties and the contents of elements were determined for the resulting lubricating oil compositions. The results are shown in Tables 1 to 3 below.

[0237] The following evaluations were performed on the resulting lubricating oil compositions. The results are shown in Tables 1 to 3 below.

[0238] [Evaluation of Wear Resistance]

[0239] Using a Falex Block-on-Ring wear resistance test machine (LFW-1), a test specimen was subjected to a wear resistance test using each of the resulting lubricating oil compositions under the following conditions, and the wear width of the test specimen was measured. The lubricating oil composition was rated as excellent in the wear resistance when the wear width of the test specimen was not more than 410 μm.

[0240] Test apparatus: Falex Block-on-Ring test machine (manufactured by Falex Corporation)

[0241] Ring: Falex S-10 Test-Ring (SAE 4620 steel)

[0242] Block: Falex H-60 Test-Block (SAE 01 steel)

[0243] Oil temp.: 100° C.

[0244] Load: 294 N

[0245] Speed: 250 rpm

[0246] Test time: 60 min

[0247] Amount of oil: 120 mL

[0248] [Evaluation of Oil Film Retention]

[0249] The thickness of an oil film of each of the resulting lubricating oil compositions was measured under the following conditions. The thickness of the oil film was measured three times under the same conditions, and the average of the three measured values was taken as the EHL oil film thickness of the lubricating oil composition. The lubricating oil composition was rated as excellent in the oil film retention when the EHL oil film thickness was not less than 17.0 nm.

[0250] Test apparatus: EHD2 (manufactured by PCS Instruments)

[0251] Test specimen: steel ball (diameter: 7.5 mm)

[0252] Disk: glass disc coated with SiO.sub.2/Cr

[0253] Oil temp.: 80° C.

[0254] Load: 20 N (surface pressure: 0.5 GPa)

[0255] Speed: 100 mm/s

[0256] Slide-roll ratio (SRR): 200%

TABLE-US-00001 TABLE 1 Examples Components (unit) 1 2 3 4 5 Base oil (A) Base oil (A1) mass % 80.95 82.45 79.45 81.18 81.45 Base oil (A2) mass % 12.00 12.00 12.00 12.00 12.00 Imide compound (B) Non-boron-modified succinic mass % 3.00 1.50 4.50 2.50 3.00 acid imide compound (Bx) Boron-modified succinic acid mass % — — — 0.27 — imide compound (By) Non-capped succinic acid mass % — — — — — imide compound (B′) Calcium-based detergent (C) Calcium-based detergent (C1) mass % 1.71 1.71 1.71 1.71 1.71 Polymer component (D) Polymer component (D1-1) mass % 1.00 1.00 1.00 1.00 0.50 Polymer component (D1-2) mass % — — — — — Polymer component (D2) mass % — — — — — Polymer component (D3) mass % — — — — — Zinc dithiophosphate (E) ZnDTP mass % 0.84 0.84 0.84 0.84 0.84 Other component Antioxidant mass % 0.50 0.50 0.50 0.50 0.50 Total mass % 100 100 100 100 100 lubricating oil Physical 40° C. kinematic viscosity mm.sup.2/s 46.0 43.1 49.3 45.3 43.3 composition properties 100° C. kinematic viscosity mm.sup.2/s 7.8 7.4 8.2 7.7 7.4 150° C. HTHS viscosity mPa .Math. s 2.6 2.5 2.7 2.6 2.5 viscosity index — 139 138 140 139 137 Content of Boron (By-B) derived from mass % 0.00 0.00 0.00 0.005 0.00 atoms in imide compound (By) lubricating Calcium derived from mass % 0.20 0.20 0.20 0.20 0.20 oil calcium-based detergent (C1) composition Phosphorus (E-P) derived mass % 0.060 0.060 0.060 0.060 0.060 from zinc dithiophosphate (E) Zinc derived from zinc mass % 0.070 0.070 0.070 0.070 0.070 dithiophosphate (E) Nitrogen (total amount measured) mass % 0.045 0.030 0.060 0.045 0.045 Theoretical value Nitrogen derived from imide mass % 0.030 0.015 0.045 0.030 0.030 compound (Bx), (By), (B′) Atomic content ratio Ratio [(By-B)/(B-N)] — 0.0 0.0 0.0 0.2 0.0 Ratio [(E-P)/(B-N)] — 2.0 3.0 1.5 2.0 2.0 Evaluation results Wear resistance (wear width) μm 378 385 401 387 389 Oil film retention (EHL oil nm 21.1 24.3 21.6 19.7 21.8 film thickness)

TABLE-US-00002 TABLE 2 Examples Components (unit) 6 7 8 9 Base oil (A) Base oil (A1) mass % 81.25 80.95 81.25 80.67 Base oil (A2) mass % 12.00 12.00 12.00 12.00 Imide compound (B) Non-boron-modified succinic mass % 3.00 3.00 3.00 3.00 acid imide compound (Bx) Boron-modified succinic mass % — — — — acid imide compound (By) Non-capped succinic acid mass % — — — — imide compound (B′) Calcium-based detergent (C) Calcium-based detergent (C1) mass % 1.71 1.71 1.71 1.71 Polymer component (D) Polymer component (D1-1) mass % 0.70 — — 1.00 Polymer component (D1-2) mass % — 1.00 — — Polymer component (D2) mass % — — 0.70 — Polymer component (D3) mass % — — — — Zinc dithiophosphate (E) ZnDTP mass % 0.84 0.84 0.84 1.12 Other component Antioxidant mass % 0.50 0.50 0.50 0.50 Total mass % 100 100 100 100 lubricating oil Physical 40° C. kinematic viscosity mm.sup.2/s 44.4 42.4 42.3 46.0 composition properties 100° C. kinematic viscosity mm.sup.2/s 7.6 7.3 7.4 7.8 150° C. HTHS viscosity mPa .Math. s 2.5 2.4 2.5 2.6 viscosity index — 138 136 141 139 Content of Boron (By-B) derived from mass % 0.00 0.00 0.00 0.00 atoms in imide compound (By) lubricating Calcium derived from mass % 0.20 0.20 0.20 0.20 oil calcium-based detergent (C1) composition Phosphorus (E-P) derived mass % 0.060 0.060 0.060 0.080 from zinc dithiophosphate (E) Zinc derived from zinc mass % 0.070 0.070 0.070 0.070 dithiophosphate (E) Nitrogen (total amount measured) mass % 0.045 0.045 0.045 0.045 Theoretical value Nitrogen derived from imide mass % 0.030 0.030 0.030 0.030 compound (Bx), (By), (B′) Atomic content ratio Ratio [(By-B)/(B-N)] — 0.0 0.0 0.0 0.0 Ratio [(E-P)/(B-N)] — 2.0 2.0 2.0 2.0 Evaluation results Wear resistance (wear width) μm 382 380 384 380 Oil film retention (EHL oil nm 22.6 17.0 18.8 18.9 film thickness)

TABLE-US-00003 TABLE 3 Comp. Examples Components (unit) 1 2 3 4 Base oil (A) Base oil (A1) mass % 82.24 82.41 81.95 80.67 Base oil (A2) mass % 12.00 12.00 12.00 12.00 Imide compound (B) Non-boron-modified succinic mass % — — 3.00 3.00 acid imide compound (Bx) Boron-modified succinic acid mass % 1.71 — — — imide compound (By) Non-capped succinic acid mass % — 1.54 — — imide compound (B′) Calcium-based detergent (C) Calcium-based detergent (C1) mass % 1.71 1.71 1.71 1.71 Polymer component (D) Polymer component (D1-1) mass % 1.00 1.00 — — Polymer component (D1-2) mass % — — — — Polymer component (D2) mass % — — — — Polymer component (D3) mass % — — — 1.00 Zinc dithiophosphate (E) ZnDTP mass % 0.84 0.84 0.84 1.12 Other component Antioxidant mass % 0.50 0.50 0.50 0.50 Total mass % 100 100 100 100 lubricating oil Physical 40° C. kinematic viscosity mm.sup.2/s 42.5 43.1 40.8 44.5 composition properties 100° C. kinematic viscosity mm.sup.2/s 7.3 7.4 7.1 7.6 150° C. HTHS viscosity mPa .Math. s 2.5 2.5 2.4 2.6 viscosity index — 137 137 135 138 Content of Boron (By-B) derived from mass % 0.040 0.00 0.00 0.00 atoms in imide compound (By) lubricating Calcium derived from mass % 0.20 0.20 0.20 0.20 oil calcium-based detergent (C1) composition Phosphorus (E-P) derived mass % 0.060 0.060 0.060 0.060 from zinc dithiophosphate (E) Zinc derived from zinc mass % 0.070 0.070 0.070 0.070 dithiophosphate (E) Nitrogen (total amount measured) mass % 0.045 0.045 0.045 0.045 Theoretical value Nitrogen derived from imide mass % 0.030 0.030 0.030 0.030 compound (Bx), (By), (B′) Atomic content ratio Ratio [(By-B)/(B-N)] — 1.3 0.0 0.0 0.0 Ratio [(E-P)/(B-N)] — 2.0 2.0 2.0 2.0 Evaluation results Wear resistance (wear width) μm 414 433 410 400 Oil film retention (EHL oil nm 18.1 18.2 15.3 15.5 film thickness)

[0257] The lubricating oil compositions of Examples 1 to 9, which satisfy all the features of the present invention, were found to be excellent in the wear resistance and the oil film retention.

[0258] On the other hand, the lubricating oil composition of Comparative Example 1, which does not contain the non-boron-modified succinic acid imide compound (Bx) and solely contains the boron-modified succinic acid imide compound (By) as the imide compound (B), and the lubricating oil composition of Comparative Example 2, which solely contains the non-capped imide compound (B′) as the imide compound (B), were found to be poor in the wear resistance.

[0259] The lubricating oil composition of Comparative Example 3 which does not contain the polymer component (D), and the lubricating oil composition of Comparative Example 4 which contains a polymer component (D) having a mass average molecular weight (Mw) of less than 10,000 were found to be poor in the oil film retention.