BACKGROUND OF THE INVENTION

Field of the Invention

The present invention concerns a novel lubricating oil composition and, more particularly, it relates to a lubricating oil composition which is suitable, for example, as engine oils (lubricat¬ ing oil for internal combustion engines), gear oils, automatic trans¬ mission fluids (ATF), power steering oils (PS oil), spindle oils, hydraulic fluids and industrial lubricating oils, excellent in wear resistance, exhibiting a low friction coefficient, capable of improv¬ ing fuel economy and with improved copper corrosion property, as well as a lubricating oil composition having the above-mentioned character¬ istics and capable of exhibiting a low friction coefficient already from an initial stage of operation (conditioning driving).

2. Description of the Related Art

An increase in the output of internal combustion engines such as automobile engines has caused individual parts of engines, for example valve train systems or cylinders, to be exposed to high temperatures. Moreover, the number of contacts per unit time of metal with each other has been increased, thus placing the internal combus¬ tion engine under severe operating conditions. Lubricating oils for internal combustion engines must function under severe conditions. With a reduction of size and increase in the performance which results in an increase in the number of revolutions and an increase in the output, engine oils are required to be versatile and possess high levels of performance.

As fundamental performances required for the engine oils, there can be mentioned reduction of friction, prevention of wear and seizure, reduction of thermal and oxidative degradation, detergency and dispersancy, inhibition of corrosion and cooling and sealing

functions, and use of various kinds of additives has been studied for satisfying such functions.

For instance, as a lubricating oil composition excellent, particularly, in the reduction of mechanical friction loss for 4-cycle engines, there has been proposed a lubricating oil composition com¬ prising a mineral oil and/or synthetic oil having a kinematic viscosity at 100°C of 3 to 20 cSt and blended therewith, (a) 0.2 to 5% by weight of sulfurized oxymolybdenum organophosphorodithioate (here¬ inafter referred to simply as MoDTP) and/or sulfurized oxymolybdenum dithiocarbamate (hereinafter referred simply as MoDTC), (b) 0.1 to 7% by weight of zinc dithiophosphate, (c) 0.1 to 20% by weight of calcium alkylbenzene sulfonate and (d) 1 to 15% by weight of alkenyl succinimide and/or boron compound derivative of alkenyl succinimide (Japanese Patent Publication No. 23595/1991). According to this lubricating oil composition, the friction coefficient in the mixed/boundary region can be reduced to about 1/3 of that for the conventional engine oil.

One of the important features of the lubricating oil is that it does not attack a metal within the engine during use. It is considered that corrosion may be caused by free sulfur, sulfur com¬ pounds or acidic substances. Since a copper plate is most sensitive to these substances, the corrosion of a copper plate when exposed to lubricating oil is evaluated as a measure of the corrosiveness of the lubricating oil. It is a common practice to add nitrogeneous metal deactivators, such as benzotriazole, to the lubricating oil for the purpose of reducing the copper corrosiveness. However, the addition of these metal deactivators in a large amount results in hardening of sealing rubbers. Further, if MoDTP or MoDTC is added in a relatively great amount as 0.2 to 5% by weight as disclosed in the above-cited patent publication for reducing the friction, it results in a problem of causing a strong corrosive effective to copper.

Further, a lubricating oil composition having an organo- molybdenum compound such as MoDTP or MoDTC added thereto involves a problem that a friction coefficient at an initial stage (during

conditioning driving) is high. Lubricating oil additives have an effect of reducing the boundary friction by adsorption to metal surface to form boundary lubricating film but the organomolybdenum compounds described above require a relatively long period of time until they are adsorbed on the metal surface to develop the friction reducing effect.

Accordingly, when a lubricating oil composition having the organomolybdenum compound added thereto is used as an engine oil, the effect of reducing the friction develops after running a distance of 2,000 to 3,000 km, although this depends on the running condition of automobiles. However, after the above-described running, the time for the development of the effect of the friction often overlaps with the time for the replacement of the engine oil. In such a case, an increase in the amount of addition of MoDTP or MoDTC does not lead to the development of the effect of reducing the friction at an earlier stage and rather increases the copper corrosiveness.

SUMMARY OF THE INVENTION

The present invention has been made under such circumstances with a view to provide a lubricating oil composition excellent in wear resistance, exhibiting low friction coefficient, capable of improving fuel economy, and with improved copper corrosiveness, as well as a lubricating oil composition having the foregoing characteristics and, in addition, capable of developing a low coefficient of friction from the initial stage of operation.

The present inventors have made earnest studies for develop¬ ing a lubricating oil composition having desired properties as described above, as a result, have noted that oxymolybdenum mono- glyceride or oxymolybdenum diethylate amide, not containing sulfur atoms in the molecule, does not increase the copper corrosiveness as in the case of MoDTP or MoDTC and have found that a lubricating oil composition of excellent wear resistance, exhibiting low coefficient of friction and with reduced copper corrosiveness can be obtained by combining the above-mentioned compound with a metal dithiocarbamate

having a secondary alkyl group and blending them each at a predeter¬ mined ratio to a lubricating oil basestock and, further, a lubricating oil composition having the foregoing characteristics and, in addition, capable of reducing the friction coefficient at the initial stage of driving can be obtained by further blending an organic amide compound at a predetermined ratio. The present invention has been accomplished based on such findings.

That is, the present invention provides a lubricating oil composition comprising a lubricating oil basestock and, based on the oil composition,

(A) 0.01 to 10% by weight of at least one of organomolybdenum com¬ pounds selected from oxymolybdenum monoglyceride and oxy¬ molybdenum diethylate amide, and

(B) 0.5 to 7% by weight of a metal dithiocarbamate represented by the general formula (1) :

R ¹ S S R ³

\ II II /

N - C - M - S - C - N (1)

/ \

R2

where M represents zinc, copper, nickel, iron, cadmium, silver, lead, antimony, tin or bismuth; R ¹ , R ² , R ³ and R ⁴ represent independently an oleophilic group of 1 to 30 carbon atoms in which at least one of the four oleophilic groups is a secondary oleophilic group. Another embodiment relates to a lubricating oil composition comprising a lubricating oil basestock and, based on the oil composition, 0.01 to 10% by weight of the ingredient (A) described above, 0.5 to 7% by weight of the ingredient (B) described above, and (C) 0.01 to 5% by weight of an organic amide compound.

DETAILED DESCRIPTION OF THE INVENTION

There is no particular restriction for the basestocks used in the lubricating oil composition according to the present invention and those proposed so far as the basestock for the lubricating oil, for example, mineral oils or synthetic oils can be used.

As the mineral oil, there can be mentioned, for example, 50 neutral oil, 100 neutral oil, 150 neutral oil, 300 neutral oil, 500 neutral oil and bright stock obtained by solvent refining or hydro- genation, which may be used alone or as a mixture of two or more of them at an appropriate ratio.

As the synthetic oil, there can be mentioned, for example, poly α-olefin oligomer, polybutene, alkylbenzene, alkyldiphenyl, polyol ester, polyglycol ester, dibasic acid ester, phosphoric acid ester and silicone oil, which may be used alone or as a mixture of two or more of them at an appropriate ratio. In addition, mineral oil and the synthetic oil described above may be used in admixture.

As the base oil used in the lubricating oil composition according to the present invention, those having a kinematic viscosity at a temperature of 100°C within a range from 3 to 20 mm ² /s, prefer¬ ably 4 to 15 mm ² /s are preferred.

As the ingredient (A) in the composition according to the present invention, oxymolybdenum monoglyceride or oxymolybdenum diethylate amide (hereinafter referred to "MoOxide type compound") is used. The oxymolybdenum monoglyceride is represented by the general formula (2):

O

II

R - C - O - CH - CH - CH

I I

O O (2)

\ / Mo

// \\ O O

while oxymolybdenum diethylate amide is represented by the general formula (3):

O CH2 - CH2 - O O

II / \ //

R - C - N Mo (3)

\ / \\

CH ₂ - CH - O O

In the general formulae (2) and (3), R is hydrogen atom, alkyl group of 1 to 20 carbon atoms, alkenyl group of 2 to 20 carbon atoms, cycloalkyl group of 6 to 26 carbon atoms, aryl group of 6 to 26 carbon atoms, alkylaryl or arylalkyl group of 7 to 26 carbon atoms or a hydrocarbon group containing ester bond, ether bond, alcohol group or carboxyl group. Preferred R is alkyl group of 6 to 18 carbon atoms, alkenyl group of 6 to 18 carbon atoms, cycloalkyl group or 12 to 24 carbon atoms or alkylaryl group of 12 to 24 carbon atoms. As preferred specific examples of them, there can be mentioned alkyl or alkenyl groups of 6 to 18 carbon atoms such as n-hexyl group, 2- ethylhexyl group, n-octyl group, nonyl group, decyl group, lauryl group, tridecyl group, oleyl group and linoleyl group, and alkylaryl group having an alkyl group of 3 to 18 carbon atoms such as nonyl- phenyl group.

The MoOxide type compound for the ingredient (A) may be used alone or two or more of them may be combined for use. Further, it is necessary that the blending amount is selected within a range from 0.01 to 10% by weight, preferably, 0.05 to 8% by weight based on the entire weight of the oil composition. No sufficient friction reducing effect can be obtained if the blending amount is less than 0.01% by weight whereas no corresponding improvement for the friction reducing effect can be observed if it exceeds 10% by weight.

As the ingredient (B) in the lubricating oil composition according to the present invention, a metal dithiocarbamate (herein¬ after referred to ^■ "M-DTC ^* ") represented by the general formula (1) is used.

R ¹ S S R ³

\ II II /

N - C - M - S - C - N ( 1 )

/ \

R ² R ⁴

In the above general formula (1), M is zinc, copper, nickel, iron, cadmium, silver, lead, antimony, tin or bismuth. Each of R ¹ , R ² , R ³ and R ⁴ is an oleophilic group of 1 to 30 carbon atoms in which at least one of them is a secondary oleophilic group, preferably, at least two of them are secondary oleophilic groups and the residue includes primary oleophilic groups. Further preferred oleophilic group are those in which at least three of them are secondary alkyl groups. Rl, R ² , R ³ and R ⁴ may be identical or different with each other.

As the oleophilic group of 1 to 30 carbon atoms, there can be mentioned for example, alkyl group of 1 to 30 carbon atoms, alkenyl group of 2 to 30 carbon atoms, cycloalkyl group of 6 to 30 carbon atoms, aryl group of 6 to 30 carbon atoms, alkylaryl group of 7 to 30 carbon atoms, arylalkyl group of 7 to 30 carbon atoms or hydrocarbon group having ester bond, ether bond, alcohol group or carboxyl group.

M-DTC represented by the general formula (1) in the oil composition according to the present invention having four oleophilic groups with the average number of carbon atoms between 1 and 5 are desirably reacted with an oil soluble amine compound for complexing treatment in order to increase the solubility to the lubricating oil basestock and improve the wear resistance. M-DTC having four oleophilic groups with an average number of carbon atoms of 1 (in which all the oleophilic groups are methyl) cannot provide a homo¬ geneous lubricating oil composition even if it is reacted with the oil soluble amine compound since the solubility of the resultant complex to the lubricating oil basestock is poor. Since M-DTC exhibits its function by adsorption to metal surface, no sufficient effect can be expected if it dissolves excessively but it will be quite useless unless it is soluble. The lower limit for the average number of carbon atoms of the oleophilic group is preferably two or more in view

of both functions of the solubility and the wear resistance. If the average number of carbon atoms of the four oleophilic groups is 5 or more, solubility to the lubricating oil basestock is satisfactory with no complexing treatment but it may be used after complexing if neces¬ sary.

In M-DTC, it is preferred that all the four oleophilic groups are identical hydrocarbon groups, more suitably, the four oleophilic groups are alkyl groups of 3 to 6 carbon atoms in view of easy produc¬ tion and wear resistance.

More preferred oleophilic group is alkyl group of 3 to 4 carbon atoms. For the metal atom (M), zinc is preferred in view of easy availability and wear resistance.

M-DTC can be produced by a known method. For instance, zinc diisopropyl dithiocarbamate can be produced by reacting diisopropyl- amine, carbon disulfide and sodium hydroxide to prepare sodium diisopropyl dithiocarbamate which is then reacted with zinc nitrate.

As the oil soluble amine compound used for complexing M-DTC, there can be mentioned, for example, ashless detergent dispersant such as polyalkenyl succinimide or alkylbenzylamine or alkylamine, alkyldi- amine and alkylpolyamine.

For previously forming a complex of M-DTC and the oil soluble amine compound, it is preferred to employ a method of adding both of them to a lubricating oil basestock at a ratio of providing a high concentration and heating them. For instance, when a lubricating oil composition containing 2 to 7% by weight of M-DTC and 2 to 25% by weight of oil soluble amine compound, at a ratio of 1 to 10 parts by weight of the oil soluble amine compound based on 1 part of weight of M-DTC is stirred at a temperature of 100 to 230°C, more preferably, 150 to 200°C, preferably for 1 to 60 minutes, more preferably, 1 to 30 minutes, both of the compounds form a complex which is uniformly dissolved in the lubricating oil basestock. As the heating tempera¬ ture is higher, they form a complex in a shorter period of time and

are dissolved more uniformly. A homogeneous lubricating oil composi¬ tion containing both of the compounds at a desired ratio can be obtained easily by diluting the resultant complex solution at high concentration with the lubricating oil basestock.

In the lubricating oil composition according to the present invention, M-DTC as the ingredient (B) may be used alone or as a combination of two or more of them. It is necessary to blend M-DTC by 0.5 to 7% by weight, preferably, 1 to 5% by weight based on the oil composition. No sufficient wear resistant effect can be obtained if the blending amount is less than 0.5% by weight, whereas the solu¬ bility tends to be lowered if it exceeds 7% by weight.

secM-DTC has a function of an extreme pressure agent, as well as a function as an antioxidant, a corrosion inhibitor or the like.

In the lubricating oil composition according to the present invention, the organic amide compound as the ingredient (C) can be used as required. The organic amide compound is a compound repre¬ sented by the general formula (4):

R5

R ⁷ - C - N < ⁴ >

R6

In the general formula (4), R ⁵ and R ⁶ each represents hydrogen atom, alkyl group of 1 to 20 carbon atoms, alkenyl groups of 2 to 20 carbon atoms, cycloalkyl group of 6 to 26 carbon atoms, aryl group of 6 to 26 carbon atoms, alkylaryl group or arylalkyl group of 7 to 26 carbon atoms or alkylene oxide group of 2 to 30 carbon atoms which may be identical or different with each other. R ⁷ represents hydrogen atom, alkyl group of 1 to 20 carbon atoms, alkenyl group of 2 to 20 carbon atoms, cycloalkyl group of 6 to 26 carbon atoms, aryl group of 6 to 26 carbon atoms, alkylaryl or arylalkyl group of 7 to 26 carbon atoms or hydrocarbon group containing ester bond, ether bond, alcohol group or carboxyl group.

The alkylene oxide group mentioned herein is a group repre¬ sented by general formula (5) or (6).

CH ₂ CHO 'n H

(5)

CHCH ₂ 0 H

(6)

R' wherein R' represents hydrogen atom or methyl group and n is an integer of 1 to 10.

Preferred R ⁵ and R ⁶ in the general formula (4) are hydrogen atom, alkyl group of 2 to 8 carbon atoms, cycloalkyl group of 8 to 14 carbon atoms, alkylaryl group of 8 to 14 carbon atoms, and alkylene oxide group in which n is 1 to 5. Preferred R ⁷ can include alkyl group of 6 to 18 carbon atoms, alkenyl group of 6 to 18 carbon atoms, cycloalkyl group of 12 to 24 carbon atoms and alkylaryl group of 12 to 24 carbon atoms. As specific examples of the organic amide compound, there can be mentioned, for example, oleamide or lauramide, which may be used alone or as a combination of two or more of them.

In the lubricating oil composition according to the present invention, the organic amide compound as the ingredient (C) is blended by 0.01 to 5% by weight, preferably, 0.05 to 2% by weight based on the oil composition. Blending of the organic amide compound can reduce the friction coefficient already from the initial stage of driving while suppressing the copper corrosiveness. No sufficient effect for reducing the friction coefficient from the initial stage of driving can be attained if the blending amount is less than 0.01% by weight, whereas no corresponding improvement for the effect can be recognized if the amount exceeds 5% by weight.

In the lubricating oil composition according to the present invention, there can be properly added various kinds of additives used

customarily in the lubricating oils, for example, other extreme pressure agents, ashless detergent dispersant, antioxidant, metallic detergent, metal deactivator, viscosity index improver, pour point depressor, rust inhibitor, antifoamer and corrosion inhibitor within such a range as not deteriorating the purpose of the present inven¬ tion.

For other extreme expressure agent, there can be mentioned, for example, organomolybdenum compounds such as MoDTC or MoDTP. However, if the amount of the organomolybdenum compound used is increased, the copper corrosion becomes conspicuous. As the ashless detergent dispersant, there can be mentioned, for example, succinimide, succinamide, benzylamine or ester type, as well as boron-containing ashless detergent dispersant can be used. They are used usually at a ratio of 0.5 to 7% by weight.

Further, as the antioxidant, there can be mentioned, for example, amine-based antioxidant such as alkylated diphenylamine, phenyl-α-naphthylamine, alkylated-α-naphthylamine, and phenolic antioxidant such as 2,6-di-tertiary-butylphenol, and 4,4'-methylene- bis-(2,6-di-tertiary-butylphenyl) and it is usually used at a ratio of 0.05 to 2.0% by weight.

As the metallic detergent, there can be mentioned, for example, Ca-sulfonate, Mg-sulfonate, Ba-sulfonate, Ca-phenate, Mg- phenate, Ba-phenate, Ca-salicylate, Mg-salicylate and Ba-salicylate which is generally used at a ratio of 0.1 to 5.0% by weight. As the metal deactivator, there can be mentioned, for example, benzotriazole, benzotriazole derivative, benzothiazole, benzothiazole derivative, triazole, triazole derivative, dithiocarbamate, dithiocarbamate derivative, indazole and indazole derivative, which may be used usually at a ratio of 0.005 to 0.3% by weight.

As the viscosity index improver, there can be mentioned, for example, polymethacrylate, polyisobutylene, ethylene-propylene co- polymer and styrene-butadiene hydrogenated copolymer type improver, which may be used usually at a ratio of 0.5 to 35% by weight.

• _*

Further, as the rust inhibitor, there can be mentioned, for example, alkenyl succinic acid or its partial ester and as the antifoamer, there can be mentioned, for example, dimethyl polysiloxane and poly- acrylate, which may be added properly.

The lubricating oil composition according to the present invention can be prepared by blending each of the various kinds of additives described above at a predetermined amount with a basestock and uniformly mixing them. The lubricating oil composition according to the present invention can be used suitably, for example, to auto¬ mobile engine oil, gear oils, ATF oils, PS oils, spindle oils, hydraulic fluids or industrial lubricating oils.

The present invention will now be described more in details by way of preferred examples but the invention is not restricted at all to such examples.

Examples 1-9 and Comparative Examples 1-3

The performance of the lubricating oil composition was determined by the method shown below.

1. Coefficient of Friction

The coefficient of friction was measured by using a reciprocal vibration friction tester (SRV). In the SRV tester, a steel ball of 1/2 inch diameter (SUJ-2 specified in JIS G-4805) was used as the upper test piece, and a steel disc (SUJ-2 specified in JIS G-4805) was used as the lower test piece. A sample oil was dropped on the lower test piece, a load was applied to the upper piece from the top, and the upper test piece was vibrated parallel to the lower test piece with the upper test piece being passed against the lower test piece. The lateral load applied to the lower test piece was measured to calculate the coefficient of friction (μ).

The coefficient of friction was measured twice, that is, 5 minutes and 20 minutes after the initiation of the vibration of the upper test piece. Testing conditions are as follows:

Load: 100N

Temperature: 130°C

Frequency: 8 Hz

Amplitude: 4 mm

2. Copper Corrosiveness

Corrosiveness was tested in accordance with JIS K2513 "Copper Strip Corrosion Test Method for Petroleum Products" at a test tempera¬ ture of 100°C for a test period of 8 hours by the test method, in which the state of discoloration of the copper strip was observed in accordance with "the Standard for Copper Corrosion" and the corrosive¬ ness was evaluated by subdivision symbols la-4c. The corrosiveness is lower as the numerical value of the subdivisional mark is smaller and the corrosiveness is increased in the alphabetical order.

Specific evaluation examples are as follows:

la: pale orange color which is substantially identical color with that of polished copper plate upon finishing,

lb: deep orange color, and

3a: reddish brown pattern on bronze color.

Examples 1-4, Comparative Examples 1-3

Lubricating oil compositions were prepared by blending 4% by weight of Ca-sulfonate, 5% by weight of succinimide, 0.5% by weight of alkylated diphenylamine, 0.3% by weight of 2,6-di-t-butylphenol and 0.02% by weight of 5-methyl-benzotriazole to a mineral oil (150 neutral mineral oil having kinematic viscosity at 100°C of 5.1 mm ² /s) based on the entire weight of the oil composition, and blending each

of the ingredients shown in Table 1, and the performances were evaluated. The results of measurement of properties are shown in Table 1.

Each of the ingredients are as shown below.

(1) MoOxide compound

0

II n - C ₆ H ₁₃ - c - 0 - CH - CH - CH

/ \ O O

\ /

Mo

// \\ 0 O

(2) MoDTC (Sakura-Lube® manufactured by Asahi Denka Kogyo K.K.)

(2EH) S 0 S C S (2EH)

\ II II / \ II II /

N - C - S - Mo Mo - S - C - N

/ \ / \

(2EH) S (2EH)

2EH : 2-ethylhexyl group, here and hereinafter

(3) MoDTP (Molyvan L® manufactured by R.T. Vanderbilt)

(2EH) - O S O S O S O - (2EH)

Ml II / \ II 11/

P - S - Mo Mo - S - P

/ \ / \

(2EH) - O S O - (2EH)

(4) sec-ZnDTC

R ¹ S S R ³

\ II II /

N - C - M - S - C - N

/ \

R ² R ⁴

wherein two groups of R^-R ⁴ are isopropyl groups and the residues are n-propyl group) .

(5) Ca-sulfonate

(6) Succinimide

PiB : polyisobutylene

TABLE 1

COMPARATIVE

EXAMPLES EXAMPLES

1 2 3 4 5 6 7 8 9 1 2 3

MoOxide (wt%) 0.7 3.0 0.7 3.0 0.7 3.0 0.7 0.7 0.7 0.7 0.3

MoDTC (wt%) ___ 0.3 i-C ₃ ZnDTC (wt%) 1.0 1.0 1.0 1.0 1.0 1.0 n-C ₃ ZnDTC (wt%) — — — 1.0 1.0 i-C ₃ /n-C ₃ ZnDTC 1.0 1.0 1.0 (wt%) (1)

1-methylnonyl 1.9 1.9 ZnDTC (wt%) i-C ₃ /s-C5ZnDTP — — _2# o (wt%) (2)

Oleamide (wt%) — 0.5 — — 0.5 0.5

Lauramide (wt%) — 0.5 —

Coefficient of Friction

After 5 minutes 0.12 0.12 0.05 0.06 0.12 0.12 0.06 0.13 0.07 0.14 0.14 0.13

After 20 minutes 0.06 0.05 0.05 0.04 0.06 0.06 0.06 0.07 0.06 0.10 0.09 0.11

Copper Corrosiveness la la la la la la la la la la la 3a

Notes: (1) iC ₃ /nC ₃ molar ratio is 1/1.

(2) Alkyl group comprises mixture of isopropyl group and secondary hexyl group.

The present invention can provide a lubricating oil composi¬ tion excellent in wear resistance, exhibiting a low coefficient of friction, capable of improving fuel economy and having improved copper corrosiveness, as well as a lubricating oil composition having the above-mentioned characteristics and, in addition, capable of attaining a low coefficient of friction already from the initial stage of driving.