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) a base oil; (B) an imide compound; (C) a calcium-based detergent; (D) a polymer component having a mass average molecular weight (Mw) in a range of from 10,000 to 50,000, and comprises a polyolefin and/or a polymethacrylate; and (E) a zinc dithiophosphate, wherein the imide compound (B) comprises non-boron-modified succinic acid imide compound (B1) comprising a succinic acid monoimide of formula (b-1) and/or a succinic acid bisimide of 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) in a range of from 500 to 4,000, R.sup.B, R.sup.B1, and R.sup.B2 are each independently an alkylene group having 2 to 5 carbon atoms, R.sup.C is an alkyl group having 1 to 10 carbon atoms or a group represented by (AO).sub.n-H, A is an alkylene group having 2 to 4 carbon atoms, and n being an integer in a range of from 1 to 10, x1 is an integer in a range of from 1 to 10, and x2 is an integer in a range of from 1 to 10.

2. The composition of claim 1, wherein the imide compound (B) further comprises a boron-modified succinic acid imide (B2) compound a boron-modified succinic acid monoimide and/or a boron-modified of succinic acid bisimide, and wherein the boron-modified succinic acid imide compound (B2) comprises no more than 0.020 mass % of boron atoms, based on total lubricating oil composition mass.

3. The composition of claim 2, wherein a (B2)/(B1) mass ratio, of the boron atoms in the boron-modified succinic acid imide compound (B2) to the nitrogen atoms in the imide compound (B1), is not more than 1.0.

4. The composition of claim 1, wherein a (E)/(B) mass ratio, of the phosphorus atoms in the zinc dithiophosphate (E) to the nitrogen atoms in the imide compound (B), is in a range of from 0.5 to 5.0.

5. The composition of claim 1, having a content of nitrogen atoms in a range of from 0.010% to 0.10 mass %, based on total lubricating oil composition mass.

6. The composition of claim 1, wherein the calcium-based detergent (C) is a calcium sulfonate.

7. The composition of claim 1, having a kinematic viscosity at 100? C. in a range of from 4.0 to less than 20.0 mm.sup.2/s.

8. A method for producing the lubricating oil composition of claim 1, the method comprising: mixing the base oil (A), the imide compound (B), the calcium-based detergent (C), the polymer component (D), and the zinc dithiophosphate (E).

9. The composition of claim 1, comprising no non-capped succinic acid imide compound.

10. The composition of claim 1, wherein the imide compound (B) having no active amine hydrogen.

11. The composition of claim 1, comprising no boron-containing benzylamine.

12. The composition of claim 1, comprising no benzylamine compound.

13. The composition of claim 1, wherein R.sup.C in the imide compound (B) is the alkyl group having 1 to 10 carbon atoms.

14. The composition of claim 1, wherein R.sup.C in the imide compound (B) is the group represented by (AO).sub.n-H.

15. The composition of claim 1, wherein the R.sup.C in the imide compound (B) is a methyl, ethyl, propyl, butyl, pentyl, hexyl group, heptyl, octyl group, 1,1-dimethylhexyl, 2-ethylhexyl, nonyl, 1,1-dimethylheptyl, or decyl group.

16. The composition of claim 1, comprising no boron-containing ash-free dispersant.

17. The composition of claim 1, having a boron atom content of no more than 0.008%, based on total composition amount.

18. The composition of claim 1, having a boron atom content of no more than 0.006%, based on total composition amount.

19. The composition of claim 1, having a boron atom content of no more than 0.001%, based on total composition amount.

20. The composition of claim 1, having a boron atom content of 0.00%, based on total composition amount.

Description

EXAMPLES

(1) 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.

(2) [40? C. Kinematic Viscosity, 100? C. Kinematic Viscosity, and Viscosity Index]

(3) 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.

(4) [150? C. HTHS Viscosity]

(5) The 150? C. HTHS viscosity was measured or calculated in accordance with JPI-5S-36-03.

(6) [Contents of Boron Atoms, Calcium Atoms, Phosphorus Atoms and Zinc Atoms]

(7) The contents of boron atoms, calcium atoms, phosphorus atoms and zinc atoms were measured in accordance with JPI-5S-38-03.

(8) [Content of Nitrogen Atoms]

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

(10) 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.

(11) [Atomic Content Ratio]

(12) 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).

(13) 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).

(14) <Base Number>

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

(16) [Examples 1 to 9 and Comparative Examples 1 to 4]

(17) The following components were thoroughly mixed in the amounts shown in Tables 1 to 3 to obtain lubricating oil compositions.

(18) Details of the components used in Examples 1 to 9 and Comparative Examples 1 to 4 are as follows.

(19) <Base Oil (A)> 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) 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)
<Imide compound (B)> 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) 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) Non-capped succinic acid imide compound (B): unmodified alkenyl succinic acid bisimide (non-capped succinic acid bisimide (B2) 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)
<Calcium-Based Detergent (C)> 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)
<Polymer Component (D)> 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) Polymer component (D1-2): poly-?-olefin (PAO, mass average molecular weight (Mw): 16,000) Polymer component (D2): polymethacrylate (PMA, mass average molecular weight (Mw): 35,000) 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)

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

(21) <Zinc Dithiophosphate (E)>

(22) ZnDTP: Zinc secondary dialkyldithiophosphate (the content of phosphorus atoms: 7.1% by mass)
<Other Component> Antioxidant: alkyl-substituted diphenylamine antioxidant

(23) 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.

(24) The following evaluations were performed on the resulting lubricating oil compositions. The results are shown in Tables 1 to 3 below.

(25) [Evaluation of Wear Resistance]

(26) 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 ?m. Test apparatus: Falex Block-on-Ring test machine (manufactured by Falex Corporation) Ring: Falex S-10 Test-Ring (SAE 4620 steel) Block: Falex H-60 Test-Block (SAE 01 steel) Oil temp.: 100? C. Load: 294 N Speed: 250 rpm Test time: 60 min Amount of oil: 120 mL
[Evaluation of Oil Film Retention]

(27) 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. Test apparatus: EHD2 (manufactured by PCS Instruments) Test specimen: steel ball (diameter: 7.5 mm) Disk: glass disc coated with SiO.sub.2/Cr Oil temp.: 80? C. Load: 20 N (surface pressure: 0.5 GPa) Speed: 100 mm/s Slide-roll ratio (SRR): 200%

(28) 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) ?m 378 385 401 387 389 Oil film retention (EHL oil nm 21.1 24.3 21.6 19.7 21.8 film thickness)

(29) 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) ?m 382 380 384 380 Oil film retention (EHL oil nm 22.6 17.0 18.8 18.9 film thickness)

(30) 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) ?m 414 433 410 400 Oil film retention (EHL oil nm 18.1 18.2 15.3 15.5 film thickness)

(31) 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.

(32) 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.

(33) 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.