AU694122B2

AU694122B2 - Lubricating oil composition

Info

Publication number: AU694122B2
Application number: AU69595/94A
Authority: AU
Inventors: Katsuya Arai; Satoshi Asano; Sadao Wada
Original assignee: Tonen Corp
Current assignee: Tonen General Sekiyu KK
Priority date: 1993-05-27
Filing date: 1994-05-27
Publication date: 1998-07-16
Anticipated expiration: 2014-05-27
Also published as: JPH06336592A; CA2163206A1; NO313012B1; DE69411563T2; CA2163206C; WO1994028095A1; EP0700425A4; AU6959594A; JP3613530B2; NO954709L; DE69411563D1; EP0700425B1; EP0700425A1; NO954709D0

Description

SWO 94/28095 PCT/US94/06002 1- LUBRICATING OIL COMPOSITION BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel lubricating oil composition, in particular, a lubricating oil composition having improved friction reducing properties and wear resistance and suitable for use as a lubricating oil for internal combustion engines, autoi matic transmissions, suspension and power steering wheels, particularly as a lubricating oil for internal combustion engines.

I 2. Description of the Related Art i Lubricating oils are usually used for smoothing the operation of internal combustion engines, driving mechanisms such as automatic transmissions, suspensions and power stearings, and gears. Particularly, engine oils are effective in lubricating mainly sliding parts such as a piston ring and a cylinder liner, bearings of a crank shaft or a connecting rod, and valve trains including cams and valve i lifters; in cooling the engine; in cleaning and dispersing combustion products; and in preventing rust formation and corrosion.

Thus, various functions are required of the engine oils and, recently, even better functions are being demanded as the required performance and engine output become higher and higher and the operation conditions more severe. Under these circumstances, additives such as a corrosion inhibitor, metallic detergent, ashless dispersant and antioxidant are incorporated into the engine oil in order to satisfy such requirements.

It is an important basic function of an engine oil to drive the engine smoothly and to prevent wear and seizure under any given condition. In the lubricated parts of an engine, a fluid lubrication state is mostly realized. However, in the valve train and the top and the bottom dead centers of a piston, a boundary lubrication state is L L Y WO 94/28095 PCTIUS94/06002 2 apt to occur. In such a boundary lubrication, wear is usually prevented by addition of zinc dithiophosphate (ZnDTP) or zinc dithiocarbamate (ZnDTC).

Since the energy loss in the friction parts in which the lubricating oil participates is high in the engine, a friction modifier (FM) is added to the lubricating oil in order to minimize the friction loss and improve the fuel consumption. As the friction modifiers, extreme-pressure additives such as molybdenum compounds and phosphoric esters and oiliness improvers such as fatty acid esters and alkylamines are usually used.

However, when a combination of the antiwear agent with the 3 friction modifier is used, the functions of both of them are not fully I iexhibited because of their competitive adsorption onto the metal surface. More specifically, ZnDTP and ZnDTC protect the metal surface from wear due to metal/metal contact by forming a protective film thereon, while the friction modifier also forms a low-friction film by 4j the adsorption onto the metal surface, by the reaction therewith or by the formation of a polymer on the metal surface to reduce the friction. Therefore, when both ZnDTP or ZnDTC and the friction modifier are added to the lubricating oil, the adsorption of ZnDTP and ZnDTC is reduced in amount by the competitive adsorption onto the metal surface to reduce the wear resistance or no sufficient friction-reducing effect can be obtained even by the addition of the friction modifier.

On the other hand, an interaction between ZnDTP or ZnDTC and some detergent-dispersant is apt to occur to reduce the wear resis- Stance. Further, other additives such as the detergent-dispersant might exert an influence on the effect of the friction modifier.

Thus, the selection of other additives such as the -detergentdispersant and the concentration thereof must be taken into consideration.

The present invention has been completed after investigations made for the purpose of providing a lubricating oil composition having improved friction reduction and antiwear properties and suitable for I Y II C- 3 use as a lubricating oil for internal combustion engines, automatic transmissions, suspension and power steering wheels, particularly as a lubricating oil for internal combustion engines.

SUMMARY OF THE INVENTION After intensive investigations made for the purpose of developing a lubricating oil composition having the above-described excellent properties, the inventors have found that the above purpose can be attained with a lubricating oil composition comprising zinc dialkyl dithiophosphates, mainly one having secondary alkyl groups, a i calcium sulfonate and a calcium salicylate as a metallic detergent and sulfurized oxymolybdenum dithiocarbamate in specified proportions.

The present invention has been completed on the basis of this finding.

Specifically, the present invention provides a lubricating oil composition comprising a base oil containing from 0.04 to 0.12% by weight (in terms of phosphorus), based on the whole composii tion, of a zinc dialkyl dithiophosphate containing 50 to 100% by weight (in terms of phosphorus), based on the total phosphorus content, of a zinc dialkyl dithiophosphate having secondary alkyl groups and 50 to 0% by weight (in terms of phosphorus), based on the total phosphorus content, of a zinc dialkyl dithiophosphate having primary alkyl groups, 1.0 to 3.0% by weight of a calcium sulfonate and 0.3 to 2.5% by weight of a calcium salicylate, and 50 to 2,000 ppm (in terms of molybdenum) of a sulfurized oxymolybdenum dithiocarbamate containing at least one hydrocarbon group having 8 to 23 carbon atoms, wherein the oil composition is characterized by having a total base Snumber of 2 to 13.

DETAILED DESCRIPTION OF THE INVENTION The base oil usable as the major component in the lubricating oil composition of the present invention is not particularly limited.

Base oils are those usually used in ordinary lubricating oils, such as mineral oils and synthetic oils.

I ~L I 1- II .i WO 94/28095 PCT/US94i06002 4 The mineral oils include, for example, 60 neutral oil, 100 neutral oil, 150 neutral oil, 300 neutral oil and 500 neutral oil obtained by solvent refining or hydrotreating; and low pour point base oils prepared by removing a wax from these base oils so as to improve the low-temperature fluidity. They may be used either singly or in the form of a mixture of two or more of them in a proper ratio.

The synthetic oils include, for example, poly-a-olefin oligomers, diesters, polyol esters and polyglycol esters. They are usable either singly or in the form of a mixture. They are also usable in the form of a mixture with the above-described mineral oil.

The mixing weight ratio of the synthetic oil to the mineral oil is, for example, 80:20 to 20:80.

A suitable base oil usable in the composition of the present invention is one having a viscosity in the range of 3 to 20 cSt at 100 0 C. Particularly preferred are hydrocracked products and/or wax isomerized product containing 3.0% by weight or below of an aromatic component and having a sulfur content of 50 ppm or below and a nitrogen content of 50 ppm or below.

In the composition of the present invention, the component is zinc dialkyl dithiophosphate (ZnDTP). ZnDTP comprises ZnDTP having secondary alkyl groups and ZnDTP having primary alkyl groups in such a proportion that the content of the phosphorus therein is 50 to 100% by weight and 50 to 0% by weight, respectively, based on the total phosphorus content. By using such a ZnDTP, the object of the present invention can be effectively attained.

The ZnDTP having secondary alkyl groups include those of the following general formula: R1o RI -S--Zn 2 2 WO 94/28095 PCT/US94/06002 5 The groups R 1 and R 2 in the general formula each represent a secondary alkyl group having 3 to 25 carbon atoms, such as propyl, butyl, pentyl, hexyl, cyclohexyl, octyl, decyl, dodecyl, pentadecyl or octadecyl group. They may be the same or different.

On the other hand, the ZnDTP having primary alkyl groups include, for example, those of the following general formula: S--Zn (2

J

2 The groups R 3 and R 4 in the general formula each represent a primary alkyl group having 8 to 25 carbon atoms, such as octyl, decyl, lauryl, myristyl, palmityl, stearyl or eicosyl group. They may be the same or different.

In the composition of the present invention, the amount of ZnDTP used as the component must be 0.04 to 0.12% by weight (in terms of phosphorus) based on the whole composition. When the amount of phosphorus is below 0.05% by weight, the wear resistance is insufficient and, when it is above 0.12% by weight, there is no further significant improvement in wear resistance.

The composition of the present invention contains a calcium sulfonate and a calcium salicylate as the metallic detergent The amount of the calcium sulfonate must be 1.0 to 3.0% by weight based on the whole composition. When the amount of calcium sulfonate is below by weight, the detergency is insufficient and when it is above by weight, the detergency effect is not further increased and the ash content is increased unfavorably. On the other hand, the calcium salicylate must be contained in an amount of 0.3 to 2.5% by weight based on the whole composition. When it is below 0.3% by weight, no sufficient friction reducing properties can be obtained and, when it exceeds 2.5% by weight, the wear resistance is reduced and the ash content is increased unfavorably.

WO 94/28095 PCT/US94/06002 6 The calcium salicylates are, for example, those of the following general formula: COO-Ca-OOC ii O R 0 )-R5[3] OH HO In the general formula R 5 represents a linear, branched or cyclic alkyl group having 8 to 23 carbon atoms, such as octyl, nonyl, decyl, dodecyl, pentadecyl, octadecyl or eicosyl group.

I A sulfurized oxymolybdenum dithiocarbamate (MoDTC) having a i hydrocarbon group having 8 to 23 carbon atoms is contained as the component in the composition of the present invention. MoDTC has a structure of the following general formula: R6 7 N-C-S -M02Snm0n (4) [i 2 IThe groups R 6 and R 7 in the above general formula each represent a hydrocarbon group having 8 to 23 carbon atoms. The hydrocarbon groups having 8 to 23 carbon atoms include linear and H branched alkyl and alkenyl groups having 8 to 23 carbon atoms, and cycloalkyl, aryl alkylaryl and arylalkyl groups having 8 to 23 carbon 1 atoms. Examples of them include 2-ethyl-hexyl, n-cctyl, nonyl, decyl, lauryl, tridecyl, palmityl, stearyl, oleyl, eicosyl, butylphenyl and nonylphenyl groups. R 6 and R 7 may be the same or different, and m and n are positive integers such that the sum of them is 4.

In the composition of the present invention, MoDTC used as the component may be used either singly or in combination of two or more of them. The amount of MoDTC is in the range of 50 to 2,000 ppm (in terms of molybdenum), preferably 100 to 1,000 ppm, based on the whole composition. When the amount of molybdenum is below 50 ppm, no sufficient low-frictional properties can be obtained and when it is c i slll-\m~rOCLap-*-~g ~iqLi C f~ i WO 94/28095 PCT/US94/06002 -7above 2,000 ppm, the frictional properties are not further significantly improved.

The total base number of the composition of the present invention must be 2 to 13, preferably 4 to 9. The base number is determined according to JIS K 2501 (the unit of the total base number being mgKOH/g).

The total base number of the composition of the present invention can be suitably controlled with a calcium sulfonate having a I total base number (TBN) of 200 to 300 or a calcium sulfonate having a total base number (TBN) of 10 to 100.

The lubricating oil composition of the present invention may contain suitable additives usually incorporated into lubricating oils, such as an ashless detergent-dispersant, viscosity index improver, pour point depressant, antioxidant, rust inhibitor, corrosion inhibitor, antifoaming agent and other antiwear agent and friction modifier, so far as the object of the present invention is not disturbed thereby.

sI The ashless detergent-dispersant include, for example, I succinimides, succinamides, benzylamines and their boron derivatives and esters. They are used in an amount of usually 0.5 to 7% by weight, based on the whole composition.

The viscosity index improvers include, for example, polymethacrylates, polyisobutylenes, ethylene/propylene copolymers and hydrogenated styrene/butadiene copolymers. They are used in an amount of usually 0.5 to 35% by weight, based on the whole composition. The antioxidants include, for example, amine antioxidants such as alkylated diphenylamines, phenyl-a-naphthylamines and alkylated a-naphthylamines, and phenolic antioxidants such as 2,6-di-t-butyl-4methylphenol and 4,4'-methylenebis(2,6-di-t-butylphenol). They are used in an amount of usually 0.05 to 2% by weight, based on the whole composition.

.11C 971~ IIP1~DllBd*- V~ =ICII t I. I WO 94/28095 PCT/US94/06002 8 The rust inhibitors include, for example, alkenylsuccinic acids and partial esters thereof. The corrosion inhibitors include, for example, benzotriazole and benzimidazole. The antifoaming agents include, for example, dimethylpolysiloxanes and polyacrylates. They can be suitably incorporated into the composition.

The following Examples will further illustrate the present invention and do not limit the invention.

I Examples 1 to 8 and Comparative Examples 1 to The coefficient of friction and wear track diameter of the lubricating oil composition were determined as follows: Coefficient of friction !The efficient of friction was determined by the LFW-1 test Sunder the conditions of 270 rpm, 30 kgf, 120 0 C and 10 minutes.

I Wear track diameter (mm): The wear track diameter was determined by the Shell four-ball friction test under the conditions of 1,800 rpm, 20 kgf, 90"C and minutes.

Base oil 150N-1 (having viscosity at 100°C of 5.7 mm 2 /s, i aromatic component content of 4.1 wt%, sulfur content of 11.0 ppm and i nitrogen content of 89.0 ppm) or 150N-2 (having viscosity at 100 0 C of mm 2 aromatic component content of 0.5 wt%, sulfur content of ppm and nitrogen content of 0.1 ppm) was used.

Each of the lubricating oil compositions listed in Table 1 was prepared from the base oil, and the coefficient of friction (p) and the wear track diameter (mm) were determined. The results are given in Tables 1-1 and 1-2.

-~1 TABLE 1-1 Example Example Example Example Example Example Example Example 1 2 3 4 5 6 7 8 Base 1501N-1 balance balance balance balance balance balance balance Oil 1501N-2 balance Sec. C 3

C

6 -ZnDTP 1.0 0.6 0.6 0.9 1.0 1.0 0.6 (P content wt%) (0.091 (0.05) (0.05) (0.08) (0.09) (0.09) (0.05) (0.091 Pric. C 12 -ZnIrP -0.9 0.18 (P content wt%l (0.05) (0.01) Component Ca sulfonate

(C

16 20 (TBN300) 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Ca salicylate

(C

16 20 (TBN7O) 2.5 2.5 1 2.5 2.5 2.5 Ca salicylate

(C

16 20 (TBN1O) 2.5 CB-MoDTC (No 500PPM) 1.0

C

1 8 -MoDTC IWO 500 ppm) 1.0 1.0 1.0 1.0 1.0 Total base number of composition 6 6 6 6 5 6 5 6 coefficient of friction 0.040 0.3 0.039 0.036 0.039 0.029 0.027 0.030 Evaluation wear track _______diameter (mm) 0.51 0.53 1-0.54- 0.50 0.48 0.49 0.52 0.46 7-, TABLE 1-2 Comparative Comparative Comn~arative Comparative Comparative Example 1 Example 2 Example 3 Example 4 Example Base 150N-1 balance balance balance Oil 150N-2 balance balance Sec. C 3

/C

6 -ZnDTP 1.0 1.0 0.3 1.0 0.3 (P content wt%) 10.09) (0.09) (0.025) (0.09) (0.025L_ Pri. C 12 -ZnDTP 1.2 1.2 (P content wt%) (0.066) (0.066) component Ca sulfonate

(C

16 20 (TBN300) 1.0 1.0 1.0 1.0 Ca salicylate

(C

16 20 (TBN7O) 3.0 3.0 -3.0 Ca salicylate

(C

16 20 (TBN1O) 3.0 CB- MODTC (Mo 500 ppm) 1.0

C

18

-MODTC

500 ppm) Total base number of composition 5 5 3 5 coefficient of friction (gi) 0.040 0.098 0.043 0.093 0.056 Evaluation wear track _______-diameter (mm) 0.65 0.73 0.74 0.70 0.71 1.

TABLE 1-2 (continued) Comparative V I A Comparative V- 17 Comparative V 1 0 Comparative 'I el Comparative T 4 nsc~aa.,,w.. LJ flIIIIJ~ r £AcI*IltL C) OhISltl p e.Aahaumie IeU I 1i znml1 Base Oil I m" 1-1 t- I a +nc I) a ance.balanc I 150N-2 Component (wt%) Sec. C 3

/C

6 -ZnDTP 0.73 1.0 1.67 0.11 £LS-ontent wtl (0.066) (0.091 (0.15) (0.01) 10.09) Pri. C 12 -ZnDTP 0.45 1.45 (P content wt%I (0.025) (0.08 Ca sulfonate

(C

16 2 0 (TBN300) 1.0 3.5 1.0 1.0 Ca salicylate

(C

1 6.

20 (TBN7O) 3.0 2.0 3.0 3.0 0.1 Ca salicylate

(C

16 -2 0 (TBN1O)

C

8 -MoDTC (Mo 500 ppm) 1.0 1 1.0 1.0 1.0

C

18

-MDTC

(Mo 500 nnm I Total base number of composition 5 12 5 5 3 coefficient of friction 0.057 0.078 0.055 0.047 0.055 Evaluation wear track diameter (mm) 0.63 0.70 0.57 0.79 0.61 11__I 1 _I '"F~r*;nu;nrepmrr- WO 94/28095 PCT/US94!06002 12 As can be seen from a comparison of the data in Table 1-1 vs.

Table 1-2, the oil composition according to the invention provides significantly improved coefficient of function, wear track diameter or both over the comparative composition set forth in Table 1-2.

The lubricating oil composition of the present invention has excellent antiwear properties and also excellent friction reducing properties, and is suitable for use as a lubricating oil for, for example, internal combustion engines, automatic transmissions, suspensions and power steering wheels, particularly as a lubricating oil for internal combustion engines.

Claims

1. A lubricating oil composition comprising a base oil containing 0.04 to 0.12% by weight in terms of phosphorus, based on the whole cop isition, of a zinc dialkyl dithiophosphate containing to 100% by weight in terms of phosphorus, based on the total phosphorus content, of a zinc dialkyl dithiophosphate having secondary alkyl -roups and 50 to 0% by weight in terms of phosphorus, based on the total phosphorus content, of a zinc dialkyl dithiophosphate having primary alkyl groups, 1.0 to 3.0% by weight of a calcium sulfonate and 0.3 to 2.5% by weight of a calcium salicylate, and 50 to 2000 ppm in terms of molybdenum of a sulfurized oxymolybdenum dithio- carbamate containing at least one hydrocarbyl group having 8 to 23 carbon atoms, wherein the oil composition is characterized by having a total base number of 2 to 13.

2. The oil composition of claim 1, wherein the base oil is a hydrocracked oil and/or a wax isomerized oil containing 3.0% by weight or below of an aromatic component and having a sulfur content of ppm or below and a nitrogen content of 50 ppm or below.

3. The oil composition of claim 1, wherein the zinc dialkyl dithiophosphate having secondary alkyl groups has the general formula: iR 1 II P-S--Zn SR 2 0 2 wherein R 1 and R 2 are each independently a secondary alkyl group having 3 to 25 carbon atoms.

4. The oil composition of claim 1, wherein the zinc di- alkyldithiophosphate having primary alkyl groups has the formula: WO 94/28095 PCT/US94/06002 14 [R -S Zn [2] [R4° wherein R 3 and R 4 are each independently a primary alkyl group having 8 to 25 carbon atoms. The oil composition of claim 1, wherein the calcium salicylate has the formula: SCOO-Ca-OOC R 0 0 R OH HO wherein R 5 is a linear, branched or cyclic alkyl group having 8 to 23 carbon atoms.

6. The oil composition of claim 1, wherein the sulfurized oxymolybdenum dithiocarbamate has the formula: m- -S--MO2S n LR 7 2 where R 6 and R 7 are each independently a hydrocarbyl group having 8 to 23 carbon atoms and the sum of m n is 4. ~d state is mostly realized. However, in the valve train and the top and the bottom dead centers of a piston, a boundary lubrication state is IF *i I I INTERNATIONAL SEARCH REPORT International application No. PCT/US94/06002 A. CLASSIFICATION OF SUBJECT MATTER :C10M 135/18, 129/54, 12V976 US CL 252/32.7E, 39, 42.7, 56R According to International Patent Classification (IPC) or to both national classification and IPC B. FIELDS SEARCHED Minimum documentation searched (classification system followed by classification symbols) U.S. 252/42.7, 56R Documentation searched other than minimum documentation to the extent that such documents are included in the fields searched Electronic data base consulted during the international search (name of data base and, where practicable, search terms used) APS: Search terms: sulfurized oxymolybdenum dithiocarbamate, calcium sulfonate, calcium salicylate, lubricant C. DOCUMENTS CONSIDERED TO "E RELEVANT Category* Citation of document, with indication, where appropriate, of the relevant passages Relevant to claim No. Y,P US,A, 5,281,347 (Igarashi et al) 25 January 1994, see col. 1-6 3, lines 39-52 and col. 4, lines 3-16. Y US,A, 4,832,867 (Seiki et al) 23 May 1989, see col. 5, lines 1-6

10-38 and col. 6, lines 8-17. A US,A, 4,832,857 (Hunt et al) 23 May 1989, see col. 4, lines 1-6

42-46. A US,A, 3,840,463 (Froeschmann et al) 08 October 1974, see 1-6 col. 1, lines 54-69 and claims. D Further documents are listed in the continuation of Box C. See patent family annex. S Special categories of cited documents: later document published after the international filing date or priority date and not in conflict with the application but cited to understand the A' document defining the general state of the art which is not considered principle or theory underlying the invention to be of particular relevance rlir document publishedonorafter in ationa inX document of particuar relvanc the claimed invention cannot be rlir document published on or after e international iling date considered novel or cannot be considered to involve an inventive step document which may throw doubts on priority claim(s) or which is when the document is taken alone cited to establish the publication date of another citation or other special reason (as specified) "Y document of particular relevance; the cla led invention cannot be considered to involve an inventive sic.p when the document is document referring to an oral disclosure. use, exhibition or other combined with one or more other such documents, such combination means being obvious to a person skilled in the art document published prior to the international filing date but later than document member of the same patent family the priority date claimed Date of the actual completion of the international search 02 SEPTEMBER 1994 Name and mailing address of the ISAIUS Commiussioner of Patents and Trademarks Box PCT Washington, D.C. 20231 Facsimile No. (703) 305-3230 Form PCT/ISA/210 (second sheet)(July 1992)* Date of mailing of the international search report SEP 2 7 994 i 1 rr -FC-C-I