LUBRICATING OIL COMPOSITION AND METHOD FOR PRODUCING LUBRICATING OIL COMPOSITION

Abstract

Provided is a lubricating oil composition containing a base oil (A); a molybdenum dithiophosphate (B1) in an amount of 400 ppm by mass or more as expressed in terms of a molybdenum atom; an organic metal-based detergent (C1) containing a metal atom selected from an alkali metal atom and an alkaline earth metal atom in an amount of 1,400 ppm by mass or less as expressed in terms of the metal atom; and a hindered amine-based antioxidant (D1) in an amount of 900 ppm by mass or more as expressed in terms of a nitrogen atom, with a sulfated ash content being 0.70% by mass or less. The lubricating oil composition may be one in which the detergency, the wear resistance, and the friction-reducing effect are improved with a well balance while reducing the ash content.

Description

TECHNICAL FIELD

The present invention relates to a lubricating oil composition and a method for producing the lubricating oil composition.

BACKGROUND ART

In recent years, the environmental regulation on a global scale is becoming severe more and more, and the circumstances surrounding automobiles are getting severe from the aspects of fuel consumption regulations, exhaust gas regulations, and so on. In particular, an improvement of fuel consumption performance of vehicles, such as automobiles, is a big issue. As one means for solving that issue, lower friction properties of a lubricating oil composition for an internal combustion engine to be used for vehicles are demanded.

In order to provide a lubricating oil composition having a reduced coefficient of friction, a friction modifier, such as an organic molybdenum compound, is generally used.

For example, PTL 1 discloses an engine oil composition obtained by blending a base oil with predetermined amounts of an organic molybdenum compound, a boron-based succinimide, and an alkaline earth metal salt of salicylic acid.

PTL 1 describes that the foregoing engine oil composition is capable of taking an effect to steadily reduce the friction loss of an engine for a long period of time.

CITATION LIST

Patent Literature

PTL 1: JP 5-163497 A

SUMMARY OF INVENTION

Technical Problem

Now, from the viewpoint of air pollution control, it is demanded to reduce nitrogen oxides (NOx) or particulate emissions (particulates) in a diesel engine exhaust gas. As countermeasures thereto, the development of an exhaust gas postprocessing device using a three-way catalyst, an oxidation catalyst, a diesel particulate filter, etc. is being advanced.

In addition, in recent years, in order to improve the fuel consumption performance, the development of a direct-injection gasoline engine mounted with a supercharger, such as a turbocharger, is being advanced. Similar to the case of diesel engine, soot, such as a particulate matter (PM), which is contained in an exhaust gas, is generated due to direction injection of a gasoline engine. Accordingly, even in the gasoline engine, it is necessary to install an exhaust gas postprocessing device, such as gasoline particulate filter.

However, in the case where a lubricating oil composition for an internal combustion engine containing a metal-based detergent is used for an engine mounted with such an exhaust gas postprocessing device, there is a concern that a metal component derived from the metal-based detergent, etc. is accumulated in the interior of the film in the exhaust gas postprocessing device, thereby causing clogging of the filter or reduction of the catalytic activity.

In order to avoid the foregoing problem, it is necessary to reduce the ash content of the lubricating oil composition. However, the reduction of the content of the metal-based detergent causes a lowering of the base number, whereby worsening of detergency is liable to be resulted, and coking (a phenomenon in which the lubricating oil composition is carbonized and denatured to form a carbide) is also possibly generated.

In addition, according to investigations made by the present inventors, it was noted that in the lubricating oil composition for an internal combustion engine containing a lot of the metal-based detergent, the coefficient of friction against an engine member is liable to rise, thereby possibly causing a lowering of the friction-reducing effect.

Accordingly, there is demanded a lubricating oil composition for an internal combustion engine having a low ash content while making both the detergency and the friction-reducing effect good.

The engine oil composition described in PTL 1 is originally not one having a low ash content. In addition, in PTL 1, the issue of worsening of detergency following a reduction of the ash content of the disclosed engine oil composition is not reviewed.

Furthermore, a lubricating oil composition which is used for vehicles, etc. is also required to have wear resistance while smoothly lubricating a sliding mechanism provided with a piston ring and a liner.

In general, in order to obtain a lubricating oil composition with good wear resistance, an anti-wear agent, such as a zinc dithiophosphate (ZnDTP), is used. The anti-wear agent forms a film on the metal surface through adsorption onto the metal surface of the sliding member, reaction with a metal atom on the surface, production of a polymer on the metal surface, and so on, thereby contributing to an improvement of the wear resistance.

However, when the content of ZnDTP in the lubricating oil composition increases, the friction-reducing effect of the lubricating oil composition tends to be lowered.

Accordingly, there is also demanded a lubricating oil composition capable of keeping a good friction-reducing effect while improving the wear resistance.

In view of the aforementioned circumstances, the present invention has been made, and an object thereof is to provide a lubricating oil composition in which the detergency, the wear resistance, and the friction-reducing effect are improved with a well balance while reducing the ash content; and a method for producing the lubricating oil composition.

Solution to Problem

The present inventors have found that the aforementioned problem can be solved by a lubricating oil composition in which the sulfated ash content is controlled to a predetermined value or less, the lubricating oil composition containing a base oil as well as a molybdenum dithiophosphate, an organic metal-based detergent, and a hindered amine-based antioxidant, and further, the contents of these three components being controlled to predetermined ranges, respectively, thereby leading to accomplishment of the present invention.

Specifically, the present invention provides the following [1] to [3]. [1] A lubricating oil composition containing:

a base oil (A);

a molybdenum dithiophosphate (B1) in an amount of 400 ppm by mass or more as expressed in terms of a molybdenum atom;

an organic metal-based detergent (C1) containing a metal atom selected from an alkali metal atom and an alkaline earth metal atom in an amount of 1,400 ppm by mass or less as expressed in terms of the metal atom; and

a hindered amine-based antioxidant (D1) in an amount of 900 ppm by mass or more as expressed in terms of a nitrogen atom,

with a sulfated ash content being 0.70% by mass or less.

[2] A method of use of a lubricating oil composition, using the lubricating oil composition as set forth in the above [1] for an internal combustion engine provided with an exhaust gas postprocessing device.
[3] A method for producing a lubricating oil composition, including the following step (I):

step (I): a step of blending

a base oil (A);

a molybdenum dithiophosphate (B1) in an amount of 400 ppm by mass or more as expressed in terms of a molybdenum atom;

an organic metal-based detergent (C1) containing a metal atom selected from an alkali metal atom and an alkaline earth metal atom in an amount of 1,400 ppm by mass or less as expressed in terms of the metal atom; and

a hindered amine-based antioxidant (D1) in an amount of 900 ppm by mass or more as expressed in terms of a nitrogen atom,

to obtain a lubricating oil composition having a sulfated ash content of 0.70% by mass or less.

Advantageous Effects of Invention

The lubricating oil composition of the present invention is excellent in all of detergency, wear resistance, and friction-reducing effect while reducing the ash content.

DESCRIPTION OF EMBODIMENTS

In the present specification, the wording “alkali metal atom” refers to a lithium atom (Li), a sodium atom (Na), a potassium atom (K), a rubidium atom (Rb), a cesium atom (Cs), and a francium atom (Fr).

In addition, the wording “alkaline earth metal atom” refers to a beryllium atom (Be), a magnesium atom (Mg), a calcium atom (Ca), a strontium atom (Sr), and a barium atom (Ba).

In the present specification, the content of each atom means a value measured in conformity with the following standards.

Molybdenum atom (Mo), calcium atom (Ca), boron atom (B), potassium atom (K), zinc atom (Zn), and phosphorus atom (P): measured in conformity with JPI-5S-38-92

Sulfur atom (S): measured in conformity with JIS K2541-6

Nitrogen atom (N): measured in conformity with JIS K2609

[Lubricating Oil Composition]

The lubricating oil composition of the present invention contains a base oil (A), a molybdenum dithiophosphate (MoDTP) (B1), an organic metal-based detergent (C1), and a hindered amine-based antioxidant (D1).

The lubricating oil composition of the present invention is a lubricating oil composition having a low ash content, in which the sulfated ash content is controlled to 0.70% by mass or less. The sulfated ash content can be controlled to be low by reducing the content of the organic metal-based detergent (C1) or a metal-based compound, such as ZnDTP, in the lubricating oil composition.

The lubricating oil composition of the present invention is one having a low ash content, in which the content of the organic metal-based detergent (C1) or the metal-based compound, such as ZnDTP, is reduced, and therefore, even when used for an engine installed with an exhaust gas postprocessing device, a harmful effect, such as clogging of the filter or a reduction of the catalytic activity, can be prevented from occurring.

In a usual case, when the content of the organic metal-based detergent (C1) is reduced, the base number of the obtained lubricating oil composition is lowered, worsening of detergency is brought, and coking is also possibly generated.

In contrast, the lubricating oil composition of the present invention contains a hindered amine-based antioxidant (D1) as an antioxidant, and therefore, even when the content of the organic metal-based detergent (C1) is low, the detergency can be kept good, and the generation of coking can be inhibited, too.

In addition, a lubricating oil composition capable of revealing an excellent friction-reducing effect can be provided by reducing the content of the organic metal-based detergent (C1) or the metal-based compound, such as ZnDTP, and controlling the sulfated ash content to 0.70% by mass or less.

However, in the lubricating oil composition of the present invention, it becomes possible to achieve a more improvement of the friction-reducing effect by not only reducing the content of the organic metal-based detergent (C1) or ZnDTP and controlling the sulfated ash content to 0.70% by mass or less, but also containing the molybdenum dithiophosphate (B1) as a molybdenum-based compound.

In the lubricating oil composition containing the aforementioned components and having reduced content of the metal-based compound, the wear resistance of the lubricating oil composition can be effectively improved by using the molybdenum dithiophosphate (B1), even when the content of ZnDTP is reduced.

Namely, in the lubricating oil composition of the present invention, the lubricating oil composition may become one in which the detergency, the wear resistance, and the friction-reducing effect are improved with a well balance by not only controlling the sulfated ash content to 0.70% by mass or less but also jointly using the molybdenum dithiophosphate (B1), the organic metal-based detergent (C1), and the hindered amine-based antioxidant (D1) in the predetermined contents.

From the aforementioned viewpoints, the sulfated ash content of the lubricating oil composition of one embodiment in the present invention is preferably 0.60% by mass or less, more preferably 0.55% by mass or less, still more preferably 0.50% by mass or less, yet still more preferably 0.40% by mass or less, and especially preferably 0.38% by mass or less on the basis of the whole amount (100% by mass) of the lubricating oil composition.

Taking into consideration the contents of the components (B1) and (C1), the sulfated ash content of the lubricating oil composition of one embodiment in the present invention is preferably 0.06% by mass or more, more preferably 0.10% by mass or more, still more preferably 0.15% by mass or more, yet still more preferably 0.20% by mass or more, and especially preferably 0.22% by mass or more on the basis of the whole amount (100% by mass) of the lubricating oil composition.

In the present specification, the sulfated ash content means a value measured in conformity with JIS K2272.

Though the lubricating oil composition of the present invention contains the molybdenum dithiophosphate (B1) as a molybdenum-based compound (B), it may further contain a molybdenum dithiocarbamate (MoDTC) (B2).

Though the lubricating oil composition of the present invention contains the organic metal-based detergent (C1) as a detergent (C), it preferably further contains an alkali metal borate (C2), and it may contain an ashless detergent (C3).

Though the lubricating oil composition of the present invention contains the hindered amine-based antioxidant (D1) as an antioxidant (D), it may further contain an antioxidant (D2) other than the component (D1).

The lubricating oil composition of one embodiment in the present invention may further contain a zinc dithiophosphate (ZnDTP) (E1) as an anti-wear agent (E).

The lubricating oil composition of one embodiment in the present invention may contain other additives for lubricating oil, which are not corresponding to the aforementioned components, such as a friction modifier, a viscosity index improver, an extreme pressure agent, a metal deactivator, a pour-point depressant, a rust inhibitor, and an anti-foaming agent, within a range where the effects of the present invention are not impaired.

In the lubricating oil composition of one embodiment in the present invention, a total blending amount of the component (A), the component (B1), the component (C1), and the component (D1) is preferably 70% by mass or more, more preferably 75% by mass or more, and still more preferably 80% by mass or more, and it is typically 100% by mass or less, more preferably 99.9% by mass or less, and still more preferably 99.0% by mass or less, on the basis of the whole amount (100% by mass) of the lubricating oil composition.

In the lubricating oil composition of one embodiment in the present invention, a total blending amount of the base oil (A), the molybdenum-based compound (B) containing the component (B1), the detergent (C) containing the component (C1), an antioxidant (D) containing the component (D1), and the anti-wear agent (E) containing the component (E1) is preferably 73% by mass or more, more preferably 77% by mass or more, and still more preferably 83% by mass or more, and it is typically 100% by mass or less, more preferably 99.9% by mass or less, and still more preferably 99.0% by mass or less, on the basis of the whole amount (100% by mass) of the lubricating oil composition.

Each of the components which are contained in the lubricating oil composition of one embodiment in the present invention is hereunder described.

<Base Oil (A)>

The base oil (A) which is contained in the lubricating oil composition of one embodiment in the present invention may be a mineral oil, or may be a synthetic oil, and a mixed oil of a mineral oil and a synthetic oil may also be used.

Examples of the mineral oil include topped crudes obtained by subjecting a crude oil, such as a paraffinic mineral oil, an intermediate-based mineral oil, and a naphthenic mineral oil, to atmospheric distillation; distillates obtained by subjecting such a topped crude to distillation under reduced pressure; mineral oils resulting from subjecting the distillate to one or more treatments of solvent deasphalting, solvent extraction, hydro-cracking, solvent dewaxing, catalytic dewaxing, hydrorefining, and so on; and mineral oils obtained by isomerizing a wax (GTL wax (gas to liquids wax)) produced by the Fischer-Tropsch process or the like.

These mineral oils may be used either alone or in combination of two or more thereof.

Of those, a mineral oil having been subjected to one or more treatments of solvent deasphalting, solvent extraction, hydro-cracking, solvent dewaxing, catalytic dewaxing, hydrorefining, and so on and a mineral oil obtained by isomerizing a GTL wax are preferred as the mineral oil which is used in one embodiment of the present invention; a mineral oil classified into Group 2 or Group 3 of the base stock categories of the API (American Petroleum Institute) and a mineral oil obtained by isomerizing a GTL wax are more preferred; and a mineral oil classified into the foregoing Group 3 and a mineral oil obtained by isomerizing a GTL wax are still more preferred.

Examples of the synthetic oil include a poly-α-olefin, such as an α-olefin homopolymer or an α-olefin copolymer (for example, an α-olefin copolymer having a carbon number of 8 to 14, such as an ethylene-α-olefin copolymer); an isoparaffin; various esters, such as a polyol ester and a dibasic acid ester; various ethers, such as a polyphenyl ether; a polyalkylene glycol; an alkyl benzene; an alkyl naphthalene; and a synthetic oil obtained by isomerizing a wax (GTL wax) produced by the Fischer-Tropsch process or the like.

These synthetic oils may be used either alone or in combination of two or more thereof.

Of those, one or more synthetic oils selected from a poly-α-olefin, various esters, and a polyalkylene glycol are preferred as the synthetic oil which is used in one embodiment of the present invention, and a poly-α-olefin is more preferred.

A kinematic viscosity at 100° C. of the base oil (A) is preferably 2.0 to 20.0 mm²/s, more preferably 2.0 to 15.0 mm²/s, still more preferably 2.0 to 7.0 mm²/s, and yet still more preferably 2.0 to 5.0 mm²/s.

When the kinematic viscosity at 100° C. of the base oil (A) is 2.0 mm²/s or more, an evaporation loss is small, and hence, such is preferred. On the other hand, when the kinematic viscosity at 100° C. of the base oil (A) is 20.0 mm²/s or less, a power loss to be caused due to viscous resistance can be suppressed, and a fuel consumption improving effect is obtained, and hence, such is preferred.

From the viewpoint of not only suppression of a change in viscosity to be caused due to a change in temperature but also an improvement of fuel saving properties, a viscosity index of the base oil (A) is preferably 80 or more, more preferably 100 or more, and still more preferably 120 or more.

In the present specification, the “kinematic viscosity at 100° C.” and the “viscosity index” mean values measured and calculated in conformity with JIS K2283, respectively.

In the case where the base oil (A) is a mixed oil of two or more selected from a mineral oil and a synthetic oil, it is preferred that the kinematic viscosity and the viscosity index of the mixed oil fall within the aforementioned ranges, respectively.

In the lubricating oil composition of one embodiment in the present invention, the content of the base oil (A) is preferably 60% by mass or more, more preferably 65% by mass or more, still more preferably 70% by mass or more, and yet still more preferably 75% by mass or more, and it is preferably 99% by mass or less, and more preferably 95% by mass or less, on the basis of the whole amount (100% by mass) of the lubricating oil composition.

<Molybdenum Dithiophosphate (B1)>

The lubricating oil composition of the present invention contains the molybdenum dithiophosphate (MoDTP) (B1) as the molybdenum-based compound (B).

According to the investigations made by the present inventors, in the lubricating oil composition having a low ash content, in which the content of the organic metal-based detergent (C1) is reduced, it has been noted that the friction-reducing effect may be more improved by containing MoDTP, as compared with the case of using alone other molybdenum-based compound, such as MoDTC.

It may be conjectured that a film formed of the MoDTP-containing lubricating oil composition having a low ash content is firm as compared with a film formed using MoDTC.

In general, in order to improve the wear resistance, there is frequently found a case of using a zinc dithiophosphate (ZnDTP) that is the anti-wear agent.

However, according to the investigations made by the present inventors, in the lubricating oil composition having a low ash content, it has been noted that in the case of using alone only MoDTP without using the anti-wear agent, such as ZnDTP, the effect for improving the wear resistance is large even in comparison with the case of using only ZnDTP.

As mentioned above, when the content of ZnDTP in the lubricating oil composition is increased, there is a tendency that the friction-reducing effect of the lubricating oil composition is lowered.

Provisionally, in order to suppress a lowering of the friction-reducing effect, when MoDTC that is the friction modifier is used in combination with ZnDTP, competitive adsorption is generated on the metal surface of the engine member, and the formation of a film due to the both components is insufficient, and as a result, the wear resistance or the friction-reducing effect is occasionally worsened.

In contrast, even in the case of using alone MoDTP without using ZnDTP or the like, or even in the case of using MoDTP in combination with ZnDTP, the wear resistance and the friction-reducing effect can be improved with a well balance by using MoDTP.

In the lubricating oil composition of the present invention, from the viewpoint of providing a lubricating oil composition which is improved in both the wear resistance and the friction-reducing effect, the content of the component (B1) as expressed in terms of a molybdenum atom is 400 ppm by mass or more, preferably 500 ppm by mass or more, more preferably 600 ppm by mass or more, still more preferably 700 ppm by mass or more, yet still more preferably 800 ppm by mass or more, and especially preferably 900 ppm or more on the basis of the whole amount (100% by mass) of the lubricating oil composition.

From the viewpoint of controlling the sulfated ash content of the obtained lubricating oil composition to the aforementioned range, the content of the component (B1) as expressed in terms of a molybdenum atom is preferably 2,000 ppm by mass or less, more preferably 1,800 ppm by mass or less, still more preferably 1,500 ppm by mass or less, and yet still more preferably 1,300 ppm by mass or less on the basis of the whole amount (100% by mass) of the lubricating oil composition.

In the lubricating oil composition of one embodiment in the present invention, though the blending amount of the component (B1) may be controlled such that the content as expressed in terms of a molybdenum atom falls within the aforementioned range, it is preferably 0.40 to 2.60% by mass, more preferably 0.50 to 2.40% by mass, still more preferably 0.50 to 2.00% by mass, yet still more preferably 0.50 to 1.80% by mass, and especially preferably 0.55 to 1.60% by mass on the basis of the whole amount (100% by mass) of the lubricating oil composition.

As the molybdenum dithiophosphate (B1), a compound represented by the following general formula (b1-1) and a compound represented by the following general formula (31-2) are preferred.

In the present invention, the molybdenum dithiophosphate (B1) may be used either alone or in combination of two or more thereof.

In the general formulae (b1-1) and (b1-2), R¹ to R⁴ each independently represent a hydrocarbon group, and may be the same as or different from each other.

X¹ to X⁸ each independently represent an oxygen atom or a sulfur atom, and may be the same as or different from each other, provided that at least two of X¹ to X⁸ in the formula (b1-1) are a sulfur atom.

In one embodiment of the present invention, in the general formula (b1-1), it is preferred that X¹ and X² are an oxygen atom, and X³ to X⁸ are a sulfur atom.

In the general formula (b1-2), it is preferred that X¹ and X² are an oxygen atom, and X³ and X⁴ are a sulfur atom.

In the general formula (b1-1), from the viewpoint of improving the solubility in the base oil (A), a molar ratio of a sulfur atom to an oxygen atom [sulfur atom/oxygen atom] in X¹ to X⁸ is preferably 1/4 to 4/1, and more preferably 1/3 to 3/1.

In the general formula (b1-2), from the same viewpoint, a molar ratio of a sulfur atom to an oxygen atom [sulfur atom/oxygen atom] in X¹ to X⁴ is preferably 1/3 to 3/1, and more preferably L5/2.5 to 2.5/L5.

The carbon number of the hydrocarbon group which may be selected as R¹ to R⁴ is preferably 1 to 20, more preferably 5 to 18, still more preferably 5 to 16, and yet still more preferably 5 to 12.

Specifically, examples of the hydrocarbon group which may be selected as R¹ to R⁴ include an alkyl group, such as a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, and an octadecyl group; an alkenyl group, such as an octenyl group, a nonenyl group, a decenyl group, a undecenyl group, a dodecenyl group, a tridecenyl group, a tetradecenyl group, and a pentadecenyl group; a cycloalkyl group, such as a cyclohexyl group, a dimethylcyclohexyl group, an ethylcyclohexyl group, a methylcyclohexylmethyl group, a cyclohexylethyl group, a propylcyclohexyl group, a butylcyclohexyl group, and a heptylcyclohexyl group; an aryl group, such as a phenyl group, a naphthyl group, an anthracenyl group, a biphenyl group, and a terphenyl group; an alkylaryl group, such as a tolyl group, a dimethylphenyl group, a butylphenyl group, a nonylphenyl group, a methylbenzyl group, and a dimethylnaphthyl group; and an arylalkyl group, such as a phenylmethyl group, a phenylethyl group, and a diphenylmethyl group.

<Molybdenum Dithiocarbamate (B2)>

However, the lubricating oil composition of one embodiment in the present invention may contain, as the molybdenum-based compound (B), a molybdenum dithiocarbamate (MoDTC) (B2) together with the molybdenum dithiophosphate (MoDTP) (B1).

When MoDTC is jointly used together with MoDTP without being used alone, a lubricating oil composition which is excellent in the wear resistance and the friction-reducing effect can be provided.

In the lubricating oil composition of one embodiment in the present invention, the content of the component (B2) as expressed in terms of a molybdenum atom is preferably 0 to 1,300 ppm by mass, more preferably 0 to 800 ppm by mass, still more preferably 0 to 600 ppm by mass, and yet still more preferably 0 to 500 ppm by mass on the basis of the whole amount (100% by mass) of the lubricating oil composition.

In the lubricating oil composition of one embodiment in the present invention, though the blending amount of the component (B2) may be controlled such that the content as expressed in terms of a molybdenum atom falls within the aforementioned range, it is preferably 0 to 1.60% by mass, more preferably 0 to 1.00% by mass, still more preferably 0 to 0.80% by mass, and yet still more preferably 0 to 0.70% by mass on the basis of the whole amount (100% by mass) of the lubricating oil composition.

A content ratio of the component (B2) as expressed in terms of a molybdenum atom is preferably 0 to 150 parts by mass, more preferably 0 to 100 parts by mass, still more preferably 0 to 80 parts by mass, and yet still more preferably 0 to 40 parts by mass on the basis of 100 parts by mass of the whole amount of the component (B1) as expressed in terms of a molybdenum atom.

Examples of the molybdenum dithiocarbamate (B2) include a binuclear molybdenum dithiocarbamate (B21) having two molybdenum atoms in one molecule thereof; and a trinuclear molybdenum dithiocarbamate (B22) having three molybdenum atoms in one molecule thereof.

In the present invention, the molybdenum dithiocarbamate (B2) may be used either alone or in combination of two or more thereof.

In the lubricating oil composition of one embodiment in the present invention, in the case of containing both the component (B21) and the component (B22), from the viewpoint of providing a lubricating oil composition which is excellent in the wear resistance and the friction-reducing effect, a content ratio of the component (B21) to the component (B22) [(B21)/(B22)] is preferably 0.1/1 to 5/1, more preferably 0.2/1 to 4/1, still more preferably 0.3/1 to 3/1, and yet still more preferably 0.4/1 to 2/1 in terms of a mass ratio.

The content ratio of the component (B21) to the component (B22) [(B21)/(B22)] is preferably 0.1/1 to 5/1, more preferably 0.2/1 to 4/1, still more preferably 0.3/1 to 3/1, and yet still more preferably 0.4/1 to 2/1 in a ratio as expressed in terms of a molybdenum atom.

As the binuclear molybdenum dithiocarbamate (B21), a compound represented by the following general formula (b21-1) and a compound represented by the following general formula (b21-2) are preferred.

In the general formulae (b21-1) and (b21-2), R¹¹ to R¹⁴ each independently represent a hydrocarbon group, and may be the same as or different from each other.

X¹¹ to X¹⁸ each independently represent an oxygen atom or a sulfur atom, and may be the same as or different from each other, provided that at least two of X¹¹ to X¹⁸ in the formula (b21-1) are a sulfur atom.

In one embodiment of the present invention, in the general formula (b21-1), it is preferred that X¹¹ and X¹² are an oxygen atom, and X¹³ to X¹⁸ are a sulfur atom.

In the general formula (b21-2), it is preferred that X¹¹ to X¹⁴ are an oxygen atom.

In the general formula (b21-1), from the viewpoint of improving the solubility in the base oil (A), a molar ratio of a sulfur atom to an oxygen atom [sulfur atom/oxygen atom] in X¹¹ to X¹⁸ is preferably 1/4 to 4/1, and more preferably 1/3 to 3/1.

The carbon number of the hydrocarbon group which may be selected as to R¹¹ is preferably 7 to 22, more preferably 7 to 18, still more preferably 7 to 14, and yet still more preferably 8 to 13.

As the specific hydrocarbon group which may be selected as R¹¹ to R¹⁴ in the general formulae (b21-1) and (b21-2), the same hydrocarbon groups as those which may be selected as R¹ to R⁴ in the general formula (b1-1) or (b1-2) are exemplified.

As the trinuclear molybdenum dithiocarbamate (B22), a compound represented by the following general formula (b22-1) is preferred.

Mo₃S_kE_mL_nA_pQ_z  (b22-1)

In the general formula (b22-1), k is an integer of 1 or more; m is an integer of 0 or more; and (k+m) is an integer of 4 to 10, and preferably an integer of 4 to 7. n is an integer of 1 to 4; and p is an integer of 0 or more. z is an integer of 0 to 5, inclusive of a non-stoichiometric value.

E's are each independently an oxygen atom or a selenium atom, and for example, are one capable of substituting sulfur in a core as mentioned later.

L's are each independently an anionic ligand having a carbon atom-containing organic group; a sum total of carbon atoms of the organic group in each of the ligands is 14 or more; and the respective ligands may be the same as or different from each other.

A's are each independently an anion other than L.

Q's are each independently a compound capable of providing a neutral electron and are existent for the purpose of fulfilling a vacant coordination site on the trinuclear molybdenum compound.

A sum total of carbon atoms of the organic group in the anionic ligand(s) represented by L is preferably 14 to 50, more preferably 16 to 30, and still more preferably 18 to 24.

As L, a monoanionic ligand that is a monovalent anionic ligand is preferred, and specifically, ligands represented by the following general formulae (i) to (iv) are more preferred.

In the general formula (b22-1), the anionic ligand which is selected as L is preferably a ligand represented by the following general formula (iv).

In the general formula (b22-1), it is preferred that all of the anionic ligands selected as L are the same, and it is more preferred that all of the anionic ligands selected as L are a ligand represented by the following general formula (iv).

In the general formulae (i) to (iv), X³¹ to X³⁷ and Y are each independently an oxygen atom or a sulfur atom, and may be the same as or different from each other.

In the general formulae (i) to (iv), R³¹ to R³⁵ are each independently an organic group, and may be the same as or different from each other.

The carbon number of each of the organic groups which may be selected as R³¹, R³², and R³³ is preferably 14 to 50, more preferably 16 to 30, and still more preferably 18 to 24.

The total carbon number of the two organic groups which may be selected as R³⁴ and R³⁵ in the formula (iv) is preferably 14 to 50, more preferably 16 to 30, and still more preferably 18 to 24.

The carbon number of each of the organic groups which may be selected as R³⁴ and R³⁵ is preferably 7 to 30, more preferably 7 to 20, and still more preferably 8 to 13.

Though the organic group of R³⁴ and the organic group of R³⁵ may be the same as or different from each other, they are preferably different from each other. In addition, though the carbon number of the organic group of R³⁴ and the carbon number of the organic group of R³⁵ may be the same as or different from each other, they are preferably different from each other.

Examples of the organic group which is selected as R³¹ to R³⁵ include a hydrocarbyl group, such as an alkyl group, an aryl group, a substituted aryl group, and an ether group.

The term “hydrocarbyl” refers to a substituent having a carbon atom directly bonded to the remainder of the ligand, and is predominantly hydrocarbyl in characteristics in the scope of the present embodiment. Such substituents include the following.

1. Hydrocarbon Substituent:

Examples of the hydrocarbon substituent include an aliphatic substituent, such as alkyl and alkenyl; an alicyclic substituent, such as cycloalkyl and cycloalkenyl; an aromatic-, aliphatic-, or alicyclic-substituted aromatic nucleus; and a cyclic group in which the ring is completed through another portion of the ligand (that is, any two indicated substituents may together form an alicyclic group).

2. Substituted Hydrocarbon Substituent;

Examples of the substituted hydrocarbon group include those in which the aforementioned hydrocarbon substituent is substituted with a non-hydrocarbon group which does not change the characteristics of the hydrocarbyl. In particular, examples of the non-hydrocarbon group include a halogen group, such as chloro and fluoro, an amino group, an alkoxy group, a mercapto group, an alkylmercapto group, a nitro group, a nitroso group, and a sulfoxy group.

In the general formula (b22-1), as the anionic ligand which is selected as L, ligands derived from an alkylxanthogenate, a carboxylate, a dialkyldithiocarbamate, or a mixture thereof are preferred, and ligands derived from a dialkyldithiocarbamate are more preferred.

In the general formula (b22-1), the anion which may be selected as A may be either a monovalent anion or a divalent anion, and examples of the anion which may be selected as A include a disulfide, a hydroxide, an alkoxide, an amide, a thiocyanate, and derivatives thereof.

In the general formula (b22-1), examples of Q include water, an amine, an alcohol, an ether, and a phosphine. Though Q's may be the same as or different from each other, they are preferably the same as each other.

As the component (B22), the compound represented by the general formula (b22-1), in which k is an integer of 4 to 7; n is 1 or 2; L is a monoanionic ligand; p is an integer of imparting electrical neutrality to the compound based on an anionic charge in A; and m and z are each 0 is preferred; and a compound represented by the general formula (b22-1) in which k is an integer of 4 to 7; L is a monoanionic ligand; n is 4; and p, m, and z are each 0 is more preferred.

As the component (B22), for example, a compound having a core represented by the following formula (IV-A) or (IV-B) is preferred. Each core has a net electrical charge of +4. Such a core is surrounded by an anionic ligand and an optionally existing anion other than the anionic ligand.

Formation of the trinuclear molybdenum-sulfur compound requires selection of an appropriate anionic ligand (L) and other anion (A), depending on, for example, the number of sulfur and E atoms present in the core, i.e., the total anionic charge constituted of a sulfur atom, an E atom, if present, L, and A, if present, must be −4.

In the case where the anionic charge exceeds −4, the trinuclear molybdenum-sulfur compound may also contain a cation other than molybdenum, for example, an (alkyl)ammonium, an amine, or sodium. A preferred embodiment of the anionic ligand (L) and other anion (A) is a constitution having four monoanionic ligands.

The molybdenum-sulfur cores, for example, the structures represented by the aforementioned (IV-A) and (IV-B), may be interconnected by means of one or more multidentate ligands, i.e., a ligand having more than one functional group capable of binding to a molybdenum atom to form oligomers.

<Other Molybdenum-Based Compound (B3)>

The lubricating oil composition of one embodiment in the present invention may contain, as the molybdenum-based compound (B), a molybdenum-based compound (B3) other than the components (B1) and (B2) within a range where the effects of the present invention are not impaired.

Examples of such other molybdenum-based compound (B3) include an amine salt of molybdic acid; and a molybdenum amine complex obtained through a reaction of molybdenum trioxide and/or molybdic acid and an amine compound.

A content ratio of the component (B3) as expressed in terms of a molybdenum atom is typically 0 to 80 parts by mass, preferably 0 to 50 parts by mass, still more preferably 0 to 30 parts by mass, yet still more preferably 0 to 10 parts by mass, and even yet still more preferably 0 to 3 parts by mass on the basis of the whole amount of 100 parts by mass of the component (B1) as expressed in terms of a molybdenum atom.

<Organic Metal-Based Detergent (C1)>

The lubricating oil composition of the present invention contains, as the detergent (C), the organic metal-based detergent (C1) containing a metal atom selected from an alkali metal atom and an alkaline earth metal atom.

The “organic metal-based detergent” as referred to herein means a compound containing at least a carbon atom and a hydrogen atom together with an alkali metal atom and/or an alkaline earth metal atom, and the foregoing compound may further contain a hetero atom, such as an oxygen atom, a sulfur atom, and a nitrogen atom.

In the lubricating oil composition of the present invention, the content of the organic metal-based detergent (C1) as expressed in terms of a metal atom is controlled to 1,400 ppm by mass or less, whereby it is contemplated to reduce the ash content of the lubricating oil composition.

When the foregoing content is more than 1,400 ppm by mass, not only it is difficult to use the obtained lubricating oil composition for an engine installed with an exhaust gas postprocessing device, but also a value of a coefficient of friction of the lubricating oil composition is large, so that the lubricating oil composition is inferior in the friction-reducing effect.

In the lubricating oil composition of the present invention, though the content of the organic metal-based detergent (C1) as the detergent (C) is reduced, in view of the matter that the lubricating oil composition contains, as the antioxidant (D), the hindered amine-based antioxidant (D1) as mentioned later, it keeps good detergency.

In the lubricating oil composition of the present invention, though the content of the component (C1) as expressed in terms of a metal atom is 1,400 ppm by mass or less on the basis of the whole amount (100% by mass) of the lubricating oil composition, from the viewpoint of more revealing the friction-reducing effect, it is preferably 1,250 ppm by mass or less, more preferably 1,100 ppm by mass or less, still more preferably 1,000 ppm by mass or less, yet still more preferably 800 ppm by mass or less, and especially preferably 600 ppm by mass or less.

From the viewpoint of providing a lubricating oil composition with improved detergency, the content of the component (C1) as expressed in terms of a metal atom is preferably 50 ppm by mass or more, more preferably 70 ppm by mass or more, still more preferably 100 ppm by mass or more, yet still more preferably 150 ppm by mass or more, and especially preferably 200 ppm by mass or more on the basis of the whole amount (100% by mass) of the lubricating oil composition.

In the lubricating oil composition of one embodiment in the present invention, though the blending amount of the component (C1) may be controlled such that the content as expressed in terms of a metal atom falls within the aforementioned range, it is preferably 0.01 to 2.8% by mass, more preferably 0.05 to 2.5% by mass, and still more preferably 0.10 to 2.1% by mass on the basis of the whole amount (100 mass %) of the lubricating oil composition.

As the metal atom which is contained in the organic metal-based detergent (C1), from the viewpoint of an improvement of detergency, a sodium atom, a calcium atom, a magnesium atom, and a barium atom are preferred; a calcium atom and a magnesium atom are more preferred; and a calcium atom is still more preferred.

Namely, it is preferred that the organic metal-based detergent (C1) contains a calcium-based detergent.

The content of the calcium-based detergent in the organic metal-based detergent (C1) is preferably 70 to 100% by mass, more preferably 80 to 100% by mass, still more preferably 90 to 100% by mass, and yet still more preferably 95 to 100% by mass on the basis of the whole amount (100% by mass) of the organic metal-based detergent (C1) which is contained in the lubricating oil composition.

The organic metal-based detergent (C1) may be used either alone or in combination of two or more thereof.

As the organic metal-based detergent (C1) which is used in one embodiment of the present invention, at least one selected from a metal salicylate, a metal phenate, and a metal sulfonate, each containing a metal atom selected from an alkali metal atom and an alkaline earth metal atom, is preferred; and a mixture of a metal sulfonate and at least one selected from a metal salicylate and a metal phenate is more preferred. The foregoing mixture is preferably a mixture of a metal sulfonate and a metal salicylate.

The metal salicylate which is used in one embodiment of the present invention is preferably a compound represented by the following general formula (c1-1); the metal phenate is preferably a compound represented by the following general formula (c1-2); and the metal sulfonate is preferably a compound represented by the following general formula (c1-3).

In the general formulae (c1-1) to (c1-3), M is a metal atom selected from an alkali metal atom and an alkaline earth metal atom; preferably a sodium atom, a calcium atom, a magnesium atom, or a barium atom; more preferably a calcium atom or a magnesium atom; and still more preferably a calcium atom.

M′ is an alkaline earth metal atom; preferably a calcium atom, a magnesium atom, or a barium atom; more preferably a calcium atom or a magnesium atom; and still more preferably a calcium atom.

p is a valence of M and is 1 or 2.

q is an integer of 0 or more, preferably an integer of 0 to 3, and more preferably 1 or 2.

R is a hydrogen atom or a hydrocarbon group having a carbon number of 1 to 18.

Examples of the hydrocarbon group which may be selected as R include an alkyl group having a carbon number of 1 to 18, an alkenyl group having a carbon number of 1 to 18, a cycloalkyl group having ring carbon atoms of 3 to 18, an aryl group having ring carbon atoms of 6 to 18, an alkylaryl group having a carbon number of 7 to 18, and an arylalkyl group having a carbon number of 7 to 18.

The organic metal-based detergent (C1) may be any of a neutral salt, a basic salt, an overbased salt, and a mixture thereof.

In the case where a mixture of a neutral salt and at least one selected from a basic salt and an overbased salt is used as the organic metal-based detergent (C1), a ratio of the neutral salt to at least one selected from the basic salt and the overbased salt [(neutral salt)/((over)basic salt)] is preferably 1/99 to 99/1, more preferably 10/99 to 90/10, and still more preferably 20/80 to 80/20.

In the case where the organic metal-based detergent (C1) is a neutral salt, a base number of the neutral salt is preferably 0 to 30 mgKOH/g, more preferably 0 to 25 mgKOH/g, and still more preferably 0 to 20 mgKOH/g.

In the case where the organic metal-based detergent (C1) is a basic salt or an overbased salt, a base number of the basic salt or overbased salt is preferably 100 to 600 mgKOH/g, more preferably 120 to 550 mgKOH/g, still more preferably 160 to 500 mgKOH/g, and yet still more preferably 200 to 450 mgKOH/g.

In the present specification, the “base number” means a base number as measured by the perchloric acid method in conformity with JIS K2501, Section 7: “Petroleum products and lubricating oils-neutralization number test method”.

<Alkali Metal Borate (C2)>

From the viewpoint of providing a lubricating oil composition with more improved detergency, it is preferred that the lubricating oil composition of one embodiment in the present invention further contains an alkali metal borate (C2) as the detergent (C).

In the lubricating oil composition of one embodiment in the present invention, the content of the component (C2) as expressed in terms of a boron atom is preferably 50 to 1,000 ppm by mass, more preferably 60 to 700 ppm by mass, still more preferably 70 to 500 ppm by mass, and yet still more preferably 80 to 200 ppm by mass on the basis of the whole amount (100% by mass) of the lubricating oil composition.

A content ratio of the component (C2) as expressed in terms of a boron atom is preferably 0 to 100 parts by mass, more preferably 1 to 80 parts by mass, still more preferably 3 to 50 parts by mass, and yet still more preferably 5 to 40 parts by mass on the basis of 100 parts by mass of the whole amount of the component (C1) as expressed in terms of a metal atom.

In the lubricating oil composition of one embodiment in the present invention, though the blending amount of the component (C2) may be controlled such that the content as expressed in terms of a boron atom falls within the aforementioned range, it is preferably 0.01 to 2.0% by mass, more preferably 0.03 to 1.5% by mass, and still more preferably 0.05 to 1.0% by mass on the basis of the whole amount (100% by mass) of the lubricating oil composition.

From the viewpoint of an improvement of detergency, a potassium atom or a sodium atom is preferred as the alkali metal atom which is contained in the alkali metal borate (C2), and a potassium atom is more preferred.

The borate is an electrically positive compound (salt) containing boron and oxygen and being optionally hydrated. Examples of the borate include a salt of a boric acid ion (BO₃³⁻) and a salt of a metaboric acid ion (BO₂⁻). The boric acid ion (BO₃³⁻) may form various polymer ions, for example, a triboric acid ion (B₃O₅⁻), a tetraboric acid ion (B₄O₇²⁻), and a pentaboric acid ion (B₅O₈⁻).

Examples of the alkali metal borate (C2) include sodium tetraborate, sodium pentaborate, sodium hexaborate, sodium octaborate, sodium diborate, potassium metaborate, potassium triborate, potassium tetraborate, potassium pentaborate, potassium hexaborate, and potassium octaborate, and an alkali metal borate represented by the following general formula (c2-1) is preferred.

M″O_1/2.mBO_3/2  General formula (c2-1):

In the general formula (c2-1), M″ represents an alkali metal atom and is preferably a potassium atom or a sodium atom, and more preferably a potassium atom; and m represents a number of 2.5 to 4.5.

The alkali metal borate (C2) which is used in one embodiment of the present invention may be a hydrate.

Examples of the hydrate of the alkali metal borate include Na₂B₄O₇.10H₂O, NaBO₂.4H₂O, KB₃O₅.4H₂O, K₂B₄O₇.5H₂O, K₉B₄O₇.8H₂O, and KB₅O₈.4H₂O, and an alkali metal borate hydrate represented by the following general formula (c2-2) is preferred.

M″O_1/2.mBO_3/2.nH₂O  General formula (c2-2):

In the general formula (c2-2), M″ and m are the same as those in the aforementioned general formula (c2-1); and n represents a number of 0.5 to 2.4.

A ratio of the boron atom and the alkali metal atom [(boron atom)/(alkali metal atom)] in the alkali metal borate (C2) is preferably 0.1/1 or more, more preferably 0.3/1 or more, still more preferably 0.5/1 or more, and yet still more preferably 0.7/1 or more, and it is preferably 5/1 or less, more preferably 4.5/1 or less, still more preferably 3.25/1 or less, and yet still more preferably 2.8/1 or less.

The alkali metal borate (C2) which is used in one embodiment of the present invention may be used either alone or in combination of two or more thereof.

Of those, from the viewpoint of an improvement of detergency and the viewpoint of solubility in the base oil (A), potassium triborate (KB₃O₅⁻) and its hydrate (KB₃O₅⁻.nH₂O (n is a number of 0.5 to 2.4)) are preferred as the alkali metal borate (C2).

<Ashless Detergent (C3)>

The lubricating oil composition of one embodiment in the present invention may further contain an ashless detergent (C3) as the detergent (C).

The blending amount of the component (C3) is preferably 0 to 10.0% by mass, more preferably 0.1 to 8.0% by mass, and still more preferably 0.5 to 6.0% by mass on the basis of the whole amount (100% by mass) of the lubricating oil composition.

In the present invention, the ashless detergent (C3) may be used either alone or in combination of two or more thereof.

An alkenylsuccinimide (C31) and a boronated alkenylsuccinimide (C32) are preferred as the ashless detergent (C3).

Examples of the alkenylsuccinimide (C31) include an alkenylsuccinic acid monoimide represented by the following general formula (c3-1) and an alkenylsuccinic acid bisimide represented by the following general formula (c3-2).

Furthermore, a modified polybutenyl succinimide obtained through a reaction of a compound represented by the following general formula (c3-1) or (c3-2) and one or more selected from an alcohol, an aldehyde, a ketone, an alkylphenol, a cyclic carbonate, an epoxy compound, an organic acid, and so on can also be used as the polybutenyl succinimide (C31).

Examples of the boronated alkenylsuccinimide include a boronated compound of an alkenylsuccinimide represented by the following general formula (c3-1) or (c3-2).

In the general formulae (c3-1) and (c3-2), R^A, R^A1, and R^A2 are each independently an alkenyl group having a weight average molecular weight (Mw) of 500 to 3,000 (preferably 1,000 to 3,000).

R^B, R^B1, and R^B2 are each independently an alkylene group having a carbon number of 2 to 5.

x1 is an integer of 1 to 10, preferably an integer of 2 to 5, and more preferably 3 or 4.

x2 is an integer of 0 to 10, preferably an integer of 1 to 4, and more preferably 2 or 3.

Examples of the alkenyl group that may be selected as R^A, R^A1, and R^A2 include a polybutenyl group, a polyisobutenyl group, and an ethylene-propylene copolymer. Of those, a polybutenyl group or a polyisobutenyl group is preferred.

The alkenylsuccinimide (C31) can be, for example, produced by allowing an alkenylsuccinic anhydride which is obtained through a reaction of a polyolefin and maleic anhydride to react with a polyamine.

Examples of the polyolefin include polymers which are obtained through polymerization of one or more selected from an α-olefin having a carbon number of 2 to 8, and a copolymer of isobutene and 1-butene is preferred.

Examples of the polyamine include a single diamine, such as ethylenediamine, propylenediamine, butylenediamine, and pentylenediamine;

a polyalkylenepolyamine, such as diethylenetriamine, triethylenetetr amine, tetraethylenepentamine, pentaethylenehexamine, di(methylethylene)triamine, dibutylenetriamine, tributylenetetramine, and pentapentylenehexamine; and a piperazine derivative, such as aminoethylpiperazine.

The boronated alkenylsuccinimide (C32) can be, for example, produced by allowing an alkenylsuccinic anhydride which is obtained through a reaction of the aforementioned polyolefin and maleic anhydride to react with the aforementioned polyamine and a boron compound.

Examples of the boron compound include boron oxide, a boron halide, boric acid, boric anhydride, a boric acid ester, and an ammonium salt of boric acid.

In one embodiment of the present invention, from the viewpoint of improving the detergency, a ratio of the boron atom and the nitrogen atom constituting the boronated alkenylsuccinimide (C32) [B/N] is preferably 0.5 or more, more preferably 0.6 or more, still more preferably 0.8 or more, and yet still more preferably 0.9 or more.

In the lubricating oil composition of one embodiment in the present invention, the content of the alkenylsuccinimide-based compound (C31) as expressed in terms of a nitrogen atom is preferably 10 to 3,000 ppm by mass, more preferably 50 to 2,000 ppm by mass, still more preferably 100 to 1,400 ppm by mass, and yet still more preferably 200 to 1,200 ppm by mass on the basis of the whole amount (100% by mass) of the lubricating oil composition.

In the lubricating oil composition of one embodiment in the present invention, the content of the boronated alkenylsuccinimide (C32) as expressed in terms of a boron atom is preferably 10 to 1,000 ppm by mass, more preferably 30 to 700 ppm by mass, still more preferably 50 to 500 ppm by mass, and yet still more preferably 100 to 400 ppm by mass on the basis of the whole amount (100% by mass) of the lubricating oil composition.

The content of the boronated alkenylsuccinimide (C32) as expressed in terms of a nitrogen atom is preferably 10 to 1,000 ppm by mass, more preferably 30 to 700 ppm by mass, still more preferably 50 to 500 ppm by mass, and yet still more preferably 100 to 400 ppm by mass on the basis of the whole amount (100% by mass) of the lubricating oil composition.

In the lubricating oil composition of one embodiment in the present invention, it is preferred that the ash-free detergent (C3) contains both the alkenylsuccinimide (C31) and the boronated alkenylsuccinimide (C32).

A ratio of the content of the boronated alkenylsuccinimide (C32) as expressed in terms of a boron atom to the content of the alkenylsuccinimide (C31) as expressed in terms of a nitrogen atom [(C32)/(C31)] is preferably 0.5 to 5, more preferably 0.7 to 3, still more preferably 0.8 to 2, and yet still more preferably 0.9 to 1.5.

<Hindered Amine-Based Antioxidant (D1)>

The lubricating oil composition of the present invention contains, as the antioxidant (D), the hindered amine-based antioxidant (D1) in an amount of 900 ppm by mass or more as expressed in terms of a nitrogen atom.

In the lubricating oil composition of the present invention, though the content of the organic metal-based detergent (C1) as expressed in terms of a metal atom is controlled to 1,400 ppm by mass or less, the detergency is improved by containing the hindered amine-based antioxidant (D1).

The hindered amine-based antioxidant (D1) does not contain a metal atom, and therefore, it contributes to an improvement of the oxidation prevention performance without raising the sulfated ash content of the lubricating oil composition, whereby the oxidation deterioration of the lubricating oil composition following the use may be inhibited. Namely, owing to the oxidation prevention performance which the component (D1) possesses, the formation of a sludge following the use can be reduced, and the detergency can be kept good. The maintainability of this detergency is effective as compared with the case of using the aforementioned ash-free detergent (C3).

In the lubricating oil composition of the present invention, the content of the component (D1) as expressed in terms of a nitrogen atom is 900 ppm by mass or more, preferably 950 ppm by mass or more, more preferably 1,000 ppm by mass or more, still more preferably 1,100 ppm by mass or more, and yet still more preferably 1,200 ppm by mass or more, and it is preferably 2,000 ppm by mass or less, more preferably 1,800 ppm by mass or less, still more preferably 1,600 ppm by mass or less, and yet still more preferably 1,500 ppm by mass or less, on the basis of the whole amount (100% by mass) of the lubricating oil composition.

In the lubricating oil composition of one embodiment in the present invention, though the blending amount of the component (D1) may be controlled such that the content as expressed in terms of a nitrogen atom falls within the aforementioned range, it is preferably 2.10 to 5.00% by mass, more preferably 2.30 to 4.70% by mass, still more preferably 2.50 to 4.50% by mass, and yet still more preferably 2.80 to 4.20% by mass on the basis of the whole amount (100% by mass) of the lubricating oil composition.

The hindered amine-based antioxidant (D1) which is used in the present invention may be an antioxidant containing a structure represented by the following formula (d).

The hindered amine-based antioxidant (D1) may be used either alone or in combination of two or more thereof.

In the formula (d), *1 and *2 each represent a bonding position to other atom.

More specifically, the hindered amine-based antioxidant (D1) is preferably a compound represented by the following general formula (d-1) or a compound represented by the following general formula (d-2), and more preferably a compound represented by the following general formula (d-3) or a compound represented by the following general formula (d-4).

In the general formulae (d-1) to (d-4), R^D1's are each independently a hydrogen atom or an alkyl group having a carbon number of 1 to 10, and preferably a hydrogen atom or an alkyl group having a carbon number of 1 to 3.

In the general formula (d-1), R^D2 is a hydrogen atom, an alkyl group having a carbon number of 1 to 20, a cycloalkyl group having ring carbon atoms of 6 to 18, an aryl group having ring carbon atoms of 6 to 18, a hydroxy group, an amino group, or a group represented by —O—CO—R′ (R′ is a hydrogen atom or an alkyl group having a carbon number of 1 to 20).

In the general formula (d-2), Z is an alkylene group having 1 to 20 carbon atoms, a cycloalkylene group having ring carbon atoms of 6 to 18, an arylene group having ring carbon atoms of 6 to 18, an oxygen atom, a sulfur atom, or a group represented by —O—CO—(CH₂)_n—CO—O— (n is an integer of 1 to 20).

In the general formula (d-3), R′ is a hydrogen atom or an alkyl group having a carbon number of 1 to 20.

In the general formula (d-4), n is an integer of 1 to 20.

<Antioxidant (D2) Other than Component (D1)>

From the viewpoint of providing a lubricating oil composition with improved oxidation stability, the lubricating oil composition of one embodiment in the present invention may further contain an antioxidant (D2) other than the component (D1) as the antioxidant (D).

In the lubricating oil composition of one embodiment in the present invention, the blending amount of the component (D2) is preferably 0 to 8.0% by mass, more preferably 0.05 to 6.0% by mass, still more preferably 0.1 to 4.5% by mass, and yet still more preferably 0.3 to 3.0% by mass on the basis of the whole amount (100% by mass) of the lubricating oil composition.

A content ratio of the component (D2) is preferably 0 to 100 parts by mass, more preferably 1 to 80 parts by mass, still more preferably 5 to 60 parts by mass, and yet still more preferably 10 to 50 parts by mass on the basis of 100 parts by mass of the whole amount of the component (D1).

Examples of the antioxidant (D2) include a phenol-based antioxidant, an amine-based antioxidant other than the component (D1), a sulfur-based antioxidant, and a phosphorus-based antioxidant.

The antioxidant (D2) may be used either alone or in combination of two or more thereof.

Examples of the phenol-based antioxidant include a monophenol-based antioxidant, such as 2,6-di-tert-butylphenol, 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-ethylphenol, isooctyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and benzenepropanoic acid, 3,5-bis(1,1-dimethylethyl)-4-hydroxy, C7-C9 side chain alkyl ester; a diphenol-based antioxidant, such as 4,4′-methylenebis(2,6-di-tert-butylphenol) and 2,2′-methylenebis(4-ethyl-6-tert-butylphenol); and a hindered phenol-based antioxidant other than the component (D1).

Examples of the amine-based antioxidant other than the component (D1) include a diphenylamine-based antioxidant, such as diphenylamine and an alkylated diphenylamine having an alkyl group having a carbon number of 3 to 20; and a naphthylamine-based antioxidant, such as α-naphthylamine, phenyl-α-naphthylamine, and a substituted phenyl-α-naphthylamine having an alkyl group having a carbon number of 3 to 20.

Examples of the sulfur-based antioxidant include dilauryl-3,3′-thiodipropionate.

Examples of the phosphorus-based antioxidant include a phosphite.

Of those, from the viewpoint of providing a lubricating oil composition with improved oxidation stability, the component (D2) preferably contains one or more selected from a phenol-based antioxidant (D21) and an amine-based antioxidant (D22) other than the component (D1), and more preferably contains both the phenol-based antioxidant (D21) and the amine-based antioxidant (D22) other than the component (D1).

In the case where the component (D2) contains both the component (D21) and the component (D22), from the viewpoint of providing a lubricating oil composition with improved oxidation stability, a content ratio of the component (D21) to the component (D22) [(D21)/(D22)] is preferably 0.1/1 to 1.0/1, more preferably 0.2/1 to 0.9/1, and still more preferably 0.3/1 to 0.8/1 in terms of a mass ratio.

<Zinc Dithiophosphate (E1)>

The lubricating oil composition of one embodiment in the present invention may further contain a zinc dithiophosphate (ZnDTP) (E1) as the anti-wear agent (E).

As mentioned above, when ZnDTP and MoDTC are jointly used, a film of phosphorus is formed on the metal surface of the engine member, and a film of molybdenum sulfide is further formed on the foregoing film of phosphorus, whereby the wear resistance and the friction-reducing effect are obtained; however, such joint use is insufficient for realizing the fuel saving properties which will be required on a higher level in the future.

On the other hand, in the lubricating oil composition of the present invention, in the case of further containing ZnDTP, a firmer film of phosphorus derived from ZnDTP and a film of molybdenum sulfide derived from MoDTP can be formed. In addition, in the lubricating oil composition of the present invention, it is possible to control the content of ZnDTP to a low level, and therefore, the wear resistance and the friction-reducing effect can be more improved with a well balance.

Accordingly, in the lubrication oil composition of one embodiment in the present invention, even when ZnDTP is further contained, the wear resistance can be more improved without lowering the friction-reducing effect.

In the lubricating oil composition of one embodiment in the present invention, the content of the component (E1) as expressed in terms of a zinc atom is preferably 100 to 700 ppm by mass, more preferably 150 to 650 ppm by mass, still more preferably 200 to 600 ppm by mass, and yet still more preferably 250 to 550 ppm by mass on the basis of the whole amount (100% by mass) of the lubricating oil composition.

When the foregoing content is 100 ppm by mass or more, a lubricating oil composition with more improved wear resistance can be provided. In addition, where the foregoing content is 700 ppm by mass or less, a lowering of the friction-reducing effect of the obtained lubricating oil composition can be inhibited.

In the lubricating oil composition of one embodiment in the present invention, though the blending amount of the component (E1) may be controlled such that the content as expressed in terms of a zinc atom falls within the aforementioned range, it is preferably 0.01 to 1.00% by mass, more preferably 0.05 to 0.90% by mass, still more preferably 0.1 to 0.85% by mass, and yet still more preferably 0.2 to 0.80% by mass on the basis of the whole amount (100% by mass) of the lubricating oil composition.

A content ratio of the component (E1) as expressed in terms of a phosphorus atom is preferably 0 to 300 parts by mass, more preferably 0 to 200 parts by mass, still more preferably 0 to 100 parts by mass, and yet still more preferably 0 to 80 parts by mass on the basis of 100 parts by mass of the whole amount of the component (B1) as expressed in terms of a phosphorus atom.

The zinc dithiophosphate (E1) is preferably a compound represented by the following general formula (e-1).

The zinc dithiophosphate (E1) may be used either alone or in combination of two or more thereof.

In the formula (e-1), R^E1 to R^E1 each independently represent a hydrocarbon group, and may be the same as or different from each other.

The carbon number of the hydrocarbon group which may be selected as R^E1 to R^E4 is preferably 1 to 20, more preferably 1 to 16, still more preferably 3 to 12, and yet still more preferably 3 to 10.

Though examples of the specific hydrocarbon group which may be selected as R^E1 to R^E4 include the same hydrocarbon groups as those for the hydrocarbon group which may be selected as R¹ to R⁴ in the aforementioned general formula (b1-1) or (b1-2), an alkyl group is preferred, and a primary or secondary alkyl group is more preferred.

<Other Additives for Lubricating Oil>

The lubricating oil composition of one embodiment in the present invention may contain other additives for lubricating oil, which are not corresponding to the aforementioned components, such as an ashless friction modifier, an anti-wear agent, an extreme pressure agent, a viscosity index improver, a metal deactivator, a pour-point depressant, a rust inhibitor, and an anti-foaming agent, within a range where the effects of the present invention are not impaired.

Each of these additives for lubricating oil may be used either alone or in combination of two or more thereof.

Though the content of each of these additives for lubricating oil may be suitably controlled within a range where the effects of the present invention are impaired, it is typically 0.001 to 15% by mass, preferably 0.005 to 10% by mass, and more preferably 0.01 to 8% by mass on the basis of the whole amount (100% by mass) of the lubricating oil composition.

In the lubricating oil composition of one embodiment in the present invention, a total content of these additives for lubricating oil is preferably 0 to 25% by mass, more preferably 0 to 20% by mass, and still more preferably 0 to 15% by mass on the basis of the whole amount (100% by mass) of the lubricating oil composition.

In the present specification, there is a case where the additive, such as a viscosity index improver and an anti-foaming agent, is blended in a form of a solution dissolved in a diluent oil, such as a mineral oil, a synthetic oil, and a light oil, with other components taking into consideration handling properties or solubility in the base oil (A). In such a case, in the present specification, the aforementioned content of the additive, such as an anti-foaming agent and a viscosity index improver, means the content as expressed in terms of active components (expressed in terms of a resin content) from which the diluent oil has been eliminated.

Examples of the ashless friction modifier include an aliphatic amine, a fatty acid ester, a fatty acid amide, a fatty acid, an aliphatic alcohol, and an aliphatic ether, each having at least one alkyl group or alkenyl group having a carbon number of 6 to 30, especially a linear alkyl group or linear alkenyl group having a carbon number of 6 to 30, in a molecule thereof.

Examples of the anti-wear agent or the extreme pressure agent other than the aforementioned components include zinc phosphate; a sulfur-containing compound, such as zinc dithiocarbamate, a disulfide, a sulfurized olefin, sulfurized oils and fats, a sulfurized ester, a thiocarbonate, a thiocarbamate, and a polysulfide; a phosphorus-containing compound, such as a phosphite ester, a phosphate ester, a phosphonate ester, and an amine salt or metal salt thereof; and a sulfur- and phosphorus-containing anti-wear agent, such as a thiophosphite ester, a thiophosphate ester, a thiophosphonate ester, and an amine salt or metal salt thereof.

Examples of the viscosity index improver include a polymethacrylate, a dispersion type polymethacrylate, an olefinic copolymer (for example, an ethylene-propylene copolymer), a dispersion type olefinic copolymer, and a styrenic copolymer (for example, a styrene-diene copolymer and a styrene-isoprene copolymer).

The structure of the viscosity index improver may be either linear or branched. In addition, the viscosity index improver which is used in the present invention may be a polymer having a specified structure, such as a comb-type polymer having a structure having a large number of trigeminal branch points from which a high-molecular weight side chain comes out in a main chain thereof; and a star-shaped polymer which is a kind of branched polymer and has a structure in which three or more chain polymers are bonded at one point.

Though a mass average molecular weight (Mw) of such a viscosity index improver is typically 500 to 1,000,000, preferably 5,000 to 800,000, and more preferably 10,000 to 600,000, it is suitably set according to the kind of the polymer.

SSI (shear stability index) of the resin content constituting the viscosity index improver is preferably 1 to 30.

The value of SSI represents an ability to resist decomposition of the resin content constituting the viscosity index improver. As the value of SSI is higher, the resin content is more unstable and decomposed more easily under shear.

In the present specification, the SSI of the resin content constituting the viscosity index improver means a value as measured in conformity with ASTM D6278.

Examples of the metal deactivator include a benzotriazole-based compound, a tolyltriazole-based compound, a thiadiazole-based compound, an imidazole-based compound, and a pyrimidine-based compound.

Examples of the pour-point depressant include an ethylene-vinyl acetate copolymer, a condensate of a chlorinated paraffin and naphthalene, a condensate of a chlorinated paraffin and phenol, a polymethacrylate, and a polyalkylstyrene.

Examples of the rust inhibitor include a petroleum sulfonate, an alkylbenzene sulfonate, dinonylnaphthalene sulfonate, an alkenylsuccinic ester, and a polyhydric alcohol ester.

Examples of the anti-foaming agent include silicone oil, fluorosilicone oil, and a fluoroalkyl ether.

[Various Properties of Lubricating Oil Composition]

The content of the molybdenum atom in the lubricating oil composition of one embodiment in the present invention is preferably 400 to 3,000 ppm by mass, more preferably 500 to 2,500 ppm by mass, still more preferably 700 to 2,000 ppm by mass, yet still more preferably 800 to 1,800 ppm by mass, and especially preferably 900 to 1,500 ppm by mass on the basis of the whole amount (100% by mass) of the lubricating oil composition.

The content of the calcium atom in the lubricating oil composition of one embodiment in the present invention is preferably 50 to 1,400 ppm by mass, more preferably 60 to 1,250 ppm by mass, still more preferably 70 to 1,100 ppm by mass, yet still more preferably 80 to 1,000 ppm by mass, even yet still more preferably 90 to 800 ppm by pass, and especially preferably 100 to 600 ppm by mass on the basis of the whole amount (100% by mass) of the lubricating oil composition.

The content of the phosphorus atom in the lubrication oil composition of one embodiment in the present invention is preferably 200 to 1,100 ppm by mass, more preferably 300 to 1,000 ppm by mass, still more preferably 400 to 900 ppm by mass, and yet still more preferably 500 to 850 ppm by mass on the basis of the whole amount (100% by mass) of the lubricating oil composition.

A kinematic viscosity at 100° C. of the lubricating oil composition of one embodiment in the present invention is preferably 3 to 20 mm²/s, more preferably 3 to 10 mm²/s, and still more preferably 5 to 8 mm²/s.

A viscosity index of the lubricating oil composition of one embodiment in the present invention is preferably 100 or more, more preferably 120 or more, and still more preferably 130 or more.

[Application of Lubricating Oil Composition]

The lubricating oil composition of one embodiment in the present invention can be preferably used as a lubricating oil for internal combustion engine, such as a gasoline engine, a diesel engine, and a gas engine, of an automobile, e.g., a two-wheeled vehicle and a four-wheeled vehicle, a power generator, and a ship. In particular, because of a low sulfated ash content, the lubricating oil composition of one embodiment in the present invention is suitable as a lubricating oil composition for internal combustion engine provided with an exhaust gas postprocessing device (particularly, a particulate filter or an exhaust gas cleaning device).

Namely, the present invention is also able to provide a method of use of a lubricating oil composition, using the foregoing lubricating oil composition for an internal combustion engine provided with an exhaust gas postprocessing device.

As the internal combustion engine using the lubricating oil composition of the present invention, for example, a direct-injection gasoline engine (namely, a downsizing engine) mounted with a supercharger, such as a supercharger and a turbocharger, and a diesel engine are preferred.

In addition, the lubricating oil composition of one embodiment in the present invention is also useful as a lubricating oil composition for internal combustion engine capable of sufficiently coping with the exhaust gas regulations in the future.

The lubricating oil composition of one embodiment in the present invention is suitably used for lubricating each component of such an internal combustion engine upon filling in the internal combustion engine, particularly, a diesel engine provided with an exhaust gas postprocessing device.

[Production Method of Lubricating Oil Composition]

The present invention also provides a method for producing a lubricating oil composition having a sulfated ash content of 0.70% by mass or less.

Specifically, the method for producing a lubricating oil composition of the present invention includes the following step (I);

step (I); a step of blending

a base oil (A);

a molybdenum dithiophosphate (B1) in an amount of 400 ppm by mass or more as expressed in terms of a molybdenum atom;

an organic metal-based detergent (C1) containing a metal atom selected from an alkali metal atom and an alkaline earth metal atom in an amount of 1,400 ppm by mass or less as expressed in terms of the metal atom; and

a hindered amine-based antioxidant (D1) in an amount of 900 ppm by mass or more as expressed in terms of a nitrogen atom,

to obtain a lubricating oil composition having a sulfated ash content of 0.70% by mass or less.

The components (A), (B1), (C1), and (D1) which are blended in the step (I) are the same as the respective components contained in the aforementioned lubricating oil composition of the present invention, and the kinds of suitable components and contents of the respective components are also the same as those mentioned above.

The aforementioned components other than these components may be blended in this step.

Each of the components which are blended in the step (I) may be blended after being formed in a solution (dispersion) upon addition with a diluent oil or the like.

It is preferred that after blending the respective components, the blend is stirred and uniformly dispersed.

Properties (e.g., sulfated ash content, contents of various atoms, kinematic viscosity, and viscosity index) of the lubricating oil composition obtained through the step (I) are the same as those in the lubrication oil composition of the present invention as mentioned above.

EXAMPLES

The present invention is hereunder described in more detail by reference to Examples, but it should be construed that the present invention is by no means limited by these Examples. Various physical properties values of the respective components used in the Examples and Comparative Examples and the obtained lubricating oil compositions were measured in conformity with the following methods.

<Kinematic Viscosity at 40° C. and 100° C.>

The measurement was performed in conformity with JIS K 2283.

<Viscosity Index>

The measurement was performed in conformity with JIS K 2283.

<Aromatic Content (% C_A) and Paraffin Content (% C_P)>

The measurement was performed by the ring analysis of ASTM D-3238 (n-d-M method).

<NOACK Value>

The measurement was performed in conformity with JPI-5S-41-2004.

<Content of Sulfur Atom>

The measurement was performed in conformity with JIS K2541-6.

<Contents of Molybdenum Atom, Calcium Atom, Boron Atom, Potassium Atom, Zinc Atom, and Phosphorus Atom>

The measurement was performed in conformity with JPI-55-38-92.

<Content of Nitrogen Atom>

The measurement was performed in conformity with JIS K2609.

<Sulfated Ash Content>

The measurement was performed in conformity with JIS K2272.

<Base Number (Perchloric Acid Method or Hydrochloric Acid Method)>

The measurement was performed in conformity with JIS K2501.

<SSI (Shear Stability Index)>

The measurement was performed in conformity with ASTM D6278.

<Mass Average Molecular Weight (Mw) and Number Average Molecular Weight (Mn)>

The measurement was performed using a gel permeation chromatograph (“1260 Model HPLC”, manufactured by Agilent) under the following conditions, and values as expressed in terms of standard polystyrene were used.

(Measurement Conditions)

Column: One in which two of “Shodex LF404” are successively connected to each other

Column temperature: 35° C.

Developing solvent: Chloroform

Flow rate: 0.3 mL/min

Examples 1 to 13 and Comparative Examples 1 to 6

A base oil and various additives as shown below were added in blending amounts shown in Tables 1 to 3 and thoroughly mixed to prepare lubricating oil compositions, respectively.

Details of the base oil and the various additives used in the Examples and Comparative Examples are shown below.

<Base Oil>

“Hydrorefined Mineral Oil (1)”;

Mineral oil classified into Group 3 of the API Base Oil Categories, having a kinematic viscosity at 40° C. of 18.5 mm²/s, a kinematic viscosity at 100° C. of 4.15 mm²/s, and a viscosity index of 133. % C_A=0.1 or less, % C_P=89.5, content of sulfur atom=less than 5 ppm by mass, NOACK value=13.8% by mass; corresponding to the component (A).

<Molybdenum-Based Compound>

“MoDTP (1)”:

ADEKA SAKURA-LUBE 310G (manufactured by Adeka Corporation) having a content of molybdenum atom of 8.5% by mass, a content of phosphorus atom of 5.5% by mass, and a content of sulfur atom of 13.0% by mass, which is a binuclear molybdenum dialkyldithiophosphate represented by the general formula (b1-1), in which X¹ and X² are an oxygen atom, X³ to X⁸ are a sulfur atom, and R¹ to R⁴ are each independently a hydrocarbon group; corresponding to the component (B1).

“MoDTC (1)”;

ADEKA SAKURA-LUBE 515 (manufactured by Adeka Corporation) having a content of molybdenum atom of 10.0% by mass and a content of sulfur atom of 11.5% by mass, which is a binuclear molybdenum dialkyldithiocarbamate represented by the general formula (b21-2), in which X¹¹ to X¹⁴ are an oxygen atom, and R¹¹ to R¹⁴ are each independently a hydrocarbon group having a carbon number of 8 or 13; corresponding to the component (B21).

“MoDTC (2)”;

Infineum C9455B (manufactured by Infineum) having a content of molybdenum atom of 5.5% by mass and a content of sulfur atom of 9.9% by mass, which is a trinuclear molybdenum dithiocarbamate represented by the general formula (b22-1); corresponding to the component (B22).

<Detergent>

Organic Metal-Based Detergent (1);

Overbased calcium salicylate having a base number (perchloric acid method) of 225 mgKOH/g, a content of calcium atom of 7.8% by mass, and a content of sulfur atom of 0.15% by mass; corresponding to the component (C1).

Organic Metal-Based Detergent (2):

Neutral calcium sulfonate having a base number (perchloric acid method) of 17 mgKOH/g, a content of calcium atom of 2.15% by mass, and a content of sulfur atom of 3.44% by mass; corresponding to the component (C1).

Potassium Borate Hydrate:

A product name “OLOA9750”, manufactured by Oronite Japan Ltd., which is a compound represented by the general formula (c2-2), in which M″ is a potassium atom, having a base number (perchloric acid method) of 125 mgKOH/g, a content of boron atom of 6.8% by mass, and a content of nitrogen atom of 0.22% by mass; corresponding to the component (C2).

Ashless Detergent (1):

Polybutenyl group-containing polybutenyl succinic bisimide having a number average molecular weight 2,300 (a compound represented by the general formula (c3-2)) and having a content of nitrogen atom of 0.99% by mass; corresponding to the compound (C3).

Ashless Detergent (2):

Polybutenyl group-containing polybutenyl succinic monoimide borate having a number average molecular weight of 1,000 (a boronated compound of a compound represented by the general formula (c3-1)) having a content of boron atom of 1.30% by mass and a content of nitrogen atom of 1.23% by mass; corresponding to the component (C3).

<Antioxidant>

Hindered Amine-Based Antioxidant (1):

A product name “XPDL-590”, manufactured by BASF SE that is 2,2,6,6-tetramethylpiperidin-4-yl dodecanoate (a compound represented by the general formula (d-3), in which R^D1 is a hydrogen atom, and R′ is an undecyl group) having a content of nitrogen atom of 4.13% by mass; corresponding to the component (D1).

Phenol-Based Antioxidant (1):

Benzenepropanoic acid, 3,5-bis(1,1-dimethylethyl)-4-hydroxy, C7-C9 side chain alkyl ester; corresponding to the component (D2).

Amine-Based Antioxidant (1):

Bis(4-nonylphenyl)amine having a content of nitrogen atom of 3.5% by mass; corresponding to the component (D2).

<Anti-Wear Agent>

ZnDTP (1):

Zinc dialkyldithiophosphate (a mixture of a compound represented by the general formula (e-1), in which R^E1 to R^E4 are a secondary propyl group and a compound represented by the general formula (e-1), in which R^E1 to R^E4 are a secondary hexyl group) having a content of zinc atom of 7.85% by mass, a content of phosphorus atom of 7.2% by mass, and a content of sulfur atom of 14.4% by mass; corresponding to the component (E1).

<Friction Modifier>

Ashless Friction Modifier:

Oleyl Diethanolamine

<Viscosity Index Improver>

PMA:

Polyalkyl (meth)acrylate having a mass average molecular weight of 380,000 and an SSI of 20.

<Other Additives>

Other Additives:

Mixture of a metal deactivator, a pour-point depressant, and an anti-foaming agent.

With respect to the lubricating oil compositions prepared in the Examples and Comparative Examples, the calcium atom (Ca) content, the phosphorus atom (P) content, the molybdenum atom (Mo) content, the base number (hydrochloric acid method), and the sulfated ash content were measured in conformity with the aforementioned methods. Then, using each of the lubricating oil compositions, the following tests were performed. These results are shown in Tables 1 to 3.

<NOx Blowing Test>

(1) NOx Blowing Test:

100 g of each of the lubricating oil compositions prepared in the Examples and Comparative Examples was heated to 140° C. A mixed gas obtained by mixing air at a flow rate of 100 mL/min and an NO gas at a flow rate of 100 mL/min, produced by diluting nitrogen monoxide (NO) with nitrogen (NO concentration: 8,000 ppm by volume) was introduced into the lubricating oil composition for 72 hours. There were thus obtained NOx-degraded oils, respectively.

(2) Measurement of Base Number of NOx-Degraded Oil:

Using the NOx-degraded oil obtained in the above (1), a base number (hydrochloric acid method) after the test was measured by the hydrochloric acid method in conformity with JIS K2501. Then, a reduction amount in the base number before and after the test was also calculated.

(3) Hot Tube Test of NOx-Degraded Oil:

A test oil having 1% by mass of 1-ethyl-4-nitrobenzene was prepared by adding 1-ethyl-4-nitrobenzene to the NOx-degraded oil obtained in the above (1).

Then, a glass tube having an inside diameter of 2 mm was set vertically in a heater block; 0.3 mL/hr of the prepared test oil and 10 mL/min of air were sent, respectively from a lower part of the glass tube; and a hot tube test was performed for 16 hours while keeping the temperature of the heater part at 240° C.

After the hot tube test was performed for 16 hours, the attachment state of a deposit attached in the interior of the glass tube was evaluated at 0.5 increments in a range of from Score 0 (colored black) to Score 10 (colorless: no deposit). As for the ratings, it may be said that as the numerical value is larger, a lubricating oil composition having a smaller volume of the deposit and more excellent detergency is provided. In the present Example, though the case where the rating is 5.0 or more was judged to be acceptable, the rating is preferably 6.0 or more.

In addition, whether or not the deposit was attached to the upper part of the glass tube after performing the hot tube test for 16 hours was also observed.

<Falex Wear Test>

A Falex tester was used, and AISIC1137/SAE3135 was used as a pin/block. The pin/block was set in the Falex tester; 60 g of the lubricating oil composition that is objective to the test was introduced into the inside of a test vessel; and the test vessel was set at a rotation number of 600 rpm, an oil temperature of 80° C., and a load of 1,340 N, thereby measuring a block wear amount (mg) and a pin wear amount (mg). A numerical value described as “Falex wear test: wear amount” in Tables 1 to 3 is a value of a total wear amount of the block wear amount and the pin wear amount.

<TE77 Reciprocating Friction Test>

A “high speed reciprocating friction machine TE77” (manufactured by Phoenix Tribology Ltd.) was used, and a test plate (material: FC250, shape: 58 mm in length×20 mm in width×4 mm in thickness) and a test cylinder pin (material: SUJ-2, shape: 6 mm in diameter×14 mm in length) were used.

Before the test, an oil temperature of the lubricating oil composition that is objective to the test was set to 80° C., and a running-in operation was performed for 60 minutes under conditions at an amplitude of 8 mm, a frequency of 20 Hz, and a load of 10 N to 200 N.

Then, a coefficient of friction was measured under conditions at an amplitude of 8 mm, a frequency of 20 Hz, an oil temperature of 80° C., and a load of 80 N.

It may be said that as the value of the coefficient of friction is smaller, a lubricating oil composition having a more excellent friction-reducing effect is provided.

TABLE 1
				Com-	Com-
				par-	par-
				ative	ative
	Exam-	Exam-	Exam-	Exam-	Exam-
Composition of lubricating oil composition	ple 1	ple 2	ple 3	ple 1	ple 2
Component	Hydrorefined	Blending amount	80.30	80.55	80.15	79.95	79.55
(A)	mineral oil (1)	(% by mass)
Component	MoDTP (1)	Blending amount	1.20	0.95	1.20	0.00	0.00
(B1)		(% by mass)
		Expressed in terms	1020	808	1020	—	—
		of Mo
		(ppm by mass)
		Expressed in terms	660	523	660	—	—
		of P
		(ppm by mass)
Component	MoDTC (1)	Blending amount	0.00	0.00	0.00	1.00	1.00
(B2)		(% by mass)
		Expressed in terms	—	—	—	1000	1000
		of Mo
		(ppm by mass)
	MoDTC (2)	Blending amount	0.00	0.00	0.00	0.40	0.40
		(% by mass)
		Expressed in terms	—	—	—	220	220
		of Mo
		(ppm by mass)
Component	Organic	Blending amount	0.40	0.40	0.40	0.40	0.40
(C1)	metal-based	(% by mass)
	detergent (1)	Expressed in terms	312	312	312	312	312
		of Ca
		(ppm by mass)
	Organic	Blending amount	0.00	0.00	0.00	0.00	0.00
	metal-based	(% by mass)
	detergent (2)	Expressed in terms	—	—	—	—	—
		of Ca
		(ppm by mass)
Component	Potassium borate	Blending amount	0.00	0.00	0.15	0.15	0.15
(C2)	hydrate (1)	(% by mass)
		Expressed in terms	—	—	102	102	102
		of B
		(ppm by mass)
Component	Ashless	Blending amount	2.50	2.50	2.50	2.50	2.50
(C3)	detergent (1)	(% by mass)
	Ashless	Blending amount	2.00	2.00	2.00	2.00	2.00
	detergent (2)	(% by mass)
Component	Hindered	Blending amount	3.00	3.00	3.00	3.00	3.00
(D1)	amine-based	(% by mass)
	antioxidant (1)	Expressed in terms	1239	1239	1239	1239	1239
		of N
		(ppm by mass)
Component	Phenol-based	Blending amount	0.50	0.50	0.50	0.50	0.50
(D2)	antioxidant (1)	(% by mass)
	Amine-based	Blending amount	0.80	0.80	0.80	0.80	0.80
	antioxidant (1)	(% by mass)
Component	ZnDTP (1)	Blending amount	0.00	0.00	0.00	0.00	0.40
(E1)		(% by mass)
		Expressed in terms	—	—	—	—	314
		of Zn
		(ppm by mass)
		Expressed in terms	—	—	—	—	288
		of P
		(ppm by mass)
Additives	Ashless friction	Blending amount	—	—	—	—	—
	modifier	(% by mass)
	PMA	Blending amount	9.00	9.00	9.00	9.00	9.00
		(% by mass)
	Other additives	Blending amount	0.30	0.30	0.30	0.30	0.30
		(% by mass)
Properties	Ca content	ppm by mass	312	312	312	312	312
of	P Content	ppm by mass	660	523	660	0	288
lubricating	Mo content	ppm by mass	1020	808	1020	1220	1220
oil	Base number	mgKOH/g	6.23	6.23	6.37	6.32	6.32
composition	(hydrochloric
	acid method)
	Sulfated ash	% by mass	0.36	0.35	0.37	0.21	0.21
	content
NOx	Base number after	mgKOH/g	3.59	3.46	3.52	3.62	3.54
blowing	test (hydrochloric
test	acid method)
	Reduction amount	mgKOH/g	2.64	2.77	2.85	2.70	2.78
	of base number
	before and
	after the test
	Merit ratings of hot tube test	6.0	6.0	7.0	7.0	7.0
	Presence or absence of attachment	No	No	No	No	No
	of deposit in the upper
	part of glass tube
Falex wear test:	mg	5.4	7.2	5.2	14.6	12.5
wear amount
TE77 reciprocating	—	0.016	0.018	0.013	0.042	0.043
friction test:
coefficient
of friction

TABLE 2
	Com-				Com-	Com-		Com-
	par-				par-	par-		par-
	ative				ative	ative		ative
	Exam-	Exam-	Exam-	Exam-	Exam-	Exam-	Exam-	Exam-
Composition of lubricating oil composition	ple 3	ple 4	ple 5	ple 6	ple 4	ple 5	ple 7	ple 6
Component	Hydrorefined	Blending amount	80.70	80.56	77.80	79.00	78.35	77.30	79.50	80.50
(A)	mineral oil (1)	(% by mass)
Component	MoDTP (1)	Blending amount	1.20	1.20	0.85	1.20	1.20	1.20	0.85	0.85
(B1)		(% by mass)
		Expressed in terms	1020	1020	723	1020	1020	1020	723	723
		of Mo
		(ppm by mass)
		Expressed in terms	660	660	468	660	660	660	468	468
		of P
		(ppm by mass)
Component	MoDTC (1)	Blending amount	0.00	0.00	0.20	0.00	0.00	0.00	0.20	0.20
(B2)		(% by mass)
		Expressed in terms	—	—	200	—	—	—	200	200
		of Mo
		(ppm by mass)
	MoDTC (2)	Blending amount	0.00	0.00	0.40	0.40	0.40	0.40	0.40	0.40
		(% by mass)
		Expressed in terms	—	—	220	220	220	220	220	220
		of Mo
		(ppm by mass)
Component	Organic	Blending amount	0.00	0.14	0.00	1.30	1.95	3.00	0.40	0.40
(C1)	metal-based	(% by mass)
	detergent (1)	Expressed in terms	—	109	—	1014	1521	2340	312	312
		of Ca
		(ppm by mass)
	Organic	Blending amount	0.00	0.00	2.10	0.00	0.00	0.00	0.00	0.00
	metal-based	(% by mass)
	detergent (2)	Expressed in terms	—	—	452	—	—	—	—	—
		of Ca
		(ppm by mass)
Component	Potassium borate	Blending amount	0.00	0.00	0.15	0.00	0.00	0.00	0.15	0.15
(C2)	hydrate (1)	(% by mass)
		Expressed in terms	—	—	102	—	—	—	102	102
		of B
		(ppm by mass)
Component	Ashless	Blending amount	2.50	2.50	2.50	2.50	2.50	2.50	2.50	2.50
(C3)	detergent (1)	(% by mass)
	Ashless	Blending amount	2.00	2.00	2.00	2.00	2.00	2.00	2.00	2.00
	detergent (2)	(% by mass)
Component	Hindered	Blending amount	3.00	3.00	3.00	3.00	3.00	3.00	3.00	2.00
(D1)	amine-based	(% by mass)
	antioxidant (1)	Expressed in terms	1239	1239	1239	1239	1239	1239	1239	826
		of N
		(ppm by mass)
Component	Phenol-based	Blending amount	0.50	0.50	0.50	0.50	0.50	0.50	0.50	0.50
(D2)	antioxidant (1)	(% by mass)
	Amine-based	Blending amount	0.80	0.80	0.80	0.80	0.80	0.80	0.80	0.80
	antioxidant (1)	(% by mass)
Component	ZnDTP (1)	Blending amount	0.00	0.00	0.40	0.00	0.00	0.00	0.40	0.40
(E1)		(% by mass)
		Expressed in terms	—	—	314	—	—	—	314	314
		of Zn
		(ppm by mass)
		Expressed in terms	—	—	288	—	—	—	288	288
		of P
		(ppm by mass)
Additives	Ashless friction	Blending amount	—	—	—	—	—	—	—	—
	modifier	(% by mass)
	PMA	Blending amount	9.00	9.00	9.00	9.00	9.00	9.00	9.00	9.00
		(% by mass)
	Other additives	Blending amount	0.30	0.30	0.30	0.30	0.30	0.30	0.30	0.30
		(% by mass)
Properties	Ca content	ppm by mass	0	109	452	1014	1521	2340	312	312
of	P Content	ppm by mass	660	660	756	660	660	660	756	756
lubricating	Mo content	ppm by mass	1020	1020	1143	1240	1240	1240	1143	1143
oil	Base number	mgKOH/g	5.63	5.82	6.44	7.90	9.02	10.93	6.22	4.65
composition	(hydrochloric
	acid method)
	Sulfated ash	% by mass	0.35	0.36	0.37	0.50	0.72	1.01	0.36	0.36
	content
NOx	Base number after	mgKOH/g	2.95	3.13	3.21	5.07	(*)	(*)	3.81	1.83
blowing	test (hydrochloric
test	acid method)
	Reduction amount	mgKOH/g	2.68	2.69	3.23	2.83	(*)	(*)	2.41	2.82
	of base number
	before and
	after the test
	Merit ratings of hot tube test	6.0	6.0	7.0	7.5	8.0	8.5	7.0	4.5
	Presence or absence of attachment	Yes	No	No	No	No	No	No	No
	of deposit in the upper
	part of glass tube
Falex wear test:	mg	5.3	5.5	3.3	5.4	(*)	(*)	2.8	2.9
wear amount
TE77 reciprocating	—	0.014	0.015	0.015	0.020	0.033	0.038	0.016	0.015
friction test:
coefficient
of friction
(*) not measured

TABLE 3
	Exam-	Exam-	Exam-	Exam-	Exam-	Exam-
Composition of lubricating oil composition	ple 8	ple 9	ple 10	ple 11	ple 12	ple 13
Component	Hydrorefined	Blending amount	79.90	79.75	79.05	79.25	79.00	79.05
(A)	mineral oil (1)	(% by mass)
Component	MoDTP (1)	Blending amount	1.20	1.20	0.50	0.50	0.85	0.85
(B1)		(% by mass)
		Expressed in terms	1020	1020	425	425	723	723
		of Mo
		(ppm by mass)
		Expressed in terms	660	660	275	275	468	468
		of P
		(ppm by mass)
Component	MoDTC (1)	Blending amount	0.00	0.00	1.00	0.50	0.20	0.20
(B2)		(% by mass)
		Expressed in terms	—	—	1000	500	200	200
		of Mo
		(ppm by mass)
	MoDTC (2)	Blending amount	0.40	0.40	0.40	0.40	0.40	0.40
		(% by mass)
		Expressed in terms	220	220	220	220	220	220
		of Mo
		(ppm by mass)
Component	Organic	Blending amount	0.40	0.40	0.40	0.40	0.40	0.40
(C1)	metal-based	(% by mass)
	detergent (1)	Expressed in terms	312	312	312	312	312	312
		of Ca
		(ppm by mass)
	Organic	Blending amount	0.00	0.00	0.00	0.00	0.00	0.00
	metal-based	(% by mass)
	detergent (2)	Expressed in terms	—	—	—	—	—	—
		of Ca
		(ppm by mass)
Component	Potassium borate	Blending amount	0.00	0.15	0.15	0.15	0.15	0.00
(C2)	hydrate (1)	(% by mass)
		Expressed in terms	—	102	102	102	102	—
		of B
		(ppm by mass)
Component	Ashless	Blending amount	2.50	2.50	2.50	2.50	2.50	2.50
(C3)	detergent (1)	(% by mass)
	Ashless	Blending amount	2.00	2.00	2.00	2.00	2.00	2.00
	detergent (2)	(% by mass)
Component	Hindered	Blending amount	3.00	3.00	3.00	3.00	3.00	3.00
(D1)	amine-based	(% by mass)
	antioxidant (1)	Expressed in terms	1239	1239	1239	1239	1239	1239
		of N
		(ppm by mass)
Component	Phenol-based	Blending amount	0.50	0.50	0.50	0.50	0.50	0.50
(D2)	antioxidant (1)	(% by mass)
	Amine-based	Blending amount	0.80	0.80	0.80	0.80	0.80	0.80
	antioxidant (1)	(% by mass)
Component	ZnDTP (1)	Blending amount	0.00	0.00	0.40	0.70	0.40	1.00
(E1)		(% by mass)
		Expressed in terms	—	—	314	550	314	785
		of Zn
		(ppm by mass)
		Expressed in terms	—	—	288	504	288	720
		of P
		(ppm by mass)
Additives	Ashless friction	Blending amount	—	—	—	—	0.50	—
	modifier	(% by mass)
	PMA	Blending amount	9.00	9.00	9.00	9.00	9.00	9.00
		(% by mass)
	Other additives	Blending amount	0.30	0.30	0.30	0.30	0.30	0.30
		(% by mass)
Properties	Ca content	ppm by mass	312	312	312	312	312	312
of	P Content	ppm by mass	660	660	563	779	756	1188
lubricating	Mo content	ppm by mass	1240	1240	1645	1145	1143	1143
oil	Base number	mgKOH/g	6.23	6.34	6.34	6.44	6.53	6.63
composition	(hydrochloric
	acid method)
	Sulfated ash	% by mass	0.36	0.37	0.41	0.37	0.38	0.40
	content
NOx	Base number after	mgKOH/g	3.66	3.61	3.82	4.02	3.74	4.03
blowing	test (hydrochloric
test	acid method)
	Reduction amount	mgKOH/g	2.57	2.73	2.52	2.42	2.79	2.60
	of base number
	before and
	after the test
	Merit ratings of hot tube test	6.0	7.0	7.0	7.0	7.0	6.0
	Presence or absence of attachment	No	No	No	No	No	No
	of deposit in the upper
	part of glass tube
Falex wear test:	mg	4.6	4.8	2.6	2.0	3.1	1.8
wear amount
TE77 reciprocating	—	0.013	0.013	0.020	0.019	0.011	0.030
friction test:
coefficient
of friction

The results from Tables 1 to 3 revealed that the lubricating oil compositions prepared in Examples 1 to 13 are excellent in the detergency, the wear resistance, and the friction-reducing effect with a well balance while reducing the ash content, as compared with the lubricating oil compositions prepared in Comparative Examples 1 to 6.

Claims

1. A lubricating oil composition, comprising:

(A) a base oil (A);

(B1) a molybdenum dithiophosphate (B1) in an amount of 400 ppm by mass or more as expressed in terms of a molybdenum atom;

(C1) an organic metal-based detergent (C1) comprising a metal atom selected from the group consisting of an alkali metal atom and an alkaline earth metal atom in an amount of 1,400 ppm by mass or less as expressed in terms of the metal atom; and

(D1) a hindered amine-based antioxidant (D1) in an amount of 900 ppm by mass or more as expressed in terms of a nitrogen atom,

wherein a sulfated ash content of the lubricating oil composition is 0.70% by mass or less.

2. The lubricating oil composition according to claim 1,

wherein a content of a molybdenum dithiocarbamate (B2), as expressed in terms of a molybdenum atom, is 600 ppm by mass or less on the basis of the whole amount of the lubricating oil composition.

3. The lubricating oil composition according to claim 1, further comprising:

(E1) a zinc dithiophosphate (E1).

4. The lubricating oil composition according to claim 3, wherein a content of the component (E1) as expressed in terms of a zinc atom is from 100 to 700 ppm by mass on the basis of the whole amount of the lubricating oil composition.

5. The lubricating oil composition according to claim 1, further comprising:

(C2) an alkali metal borate (C2).

6. The lubricating oil composition according to claim 1, wherein the content of a phosphorus atom is from 200 to 1,100 ppm by mass on the basis of the whole amount of the lubricating oil composition.

7. The lubricating oil composition according to claim 1, wherein the content of the component (B1) as expressed in terms of a molybdenum atom is from 400 to 2,000 ppm by mass on the basis of the whole amount of the lubricating oil composition.

8. The lubricating oil composition according to claim 1, wherein the component (C1) comprises a calcium-based detergent.

9. The lubricating oil composition according to claim 1, wherein the content of the component (C1) as expressed in terms of a metal atom is from 100 to 1,100 ppm by mass on the basis of the whole amount of the lubricating oil composition.

10. The lubricating oil composition according to claim 1, wherein the content of the component (D1) as expressed in terms of a nitrogen atom is from 900 to 2,000 ppm by mass on the basis of the whole amount of the lubricating oil composition.

11. The lubricating oil composition according to claim 1, wherein a sulfated ash content is from 0.06 to 0.50% by mass on the basis of the whole amount of the lubricating oil composition.

12. The lubricating oil composition according to claim 1, wherein a content of the component (A) is 60% by mass or more on the basis of the whole amount of the lubricating oil composition.

13. The lubricating oil composition according to claim 1, wherein a total blending amount of the component (A), the component (B1), the component (C1), and the component (D1) is 70% by mass or more on the basis of the whole amount of the lubricating oil composition.

14. A method, comprising lubricating an internal combustion engine provided with an exhaust gas postprocessing device with the lubricating oil composition of claim 1.

15. A method for producing a lubricating oil composition, the method comprising blending:

(A) a base oil (A);

(B1) a molybdenum dithiophosphate (B1) in an amount of 400 ppm by mass or more as expressed in terms of a molybdenum atom;

(C1) an organic metal-based detergent (C1) comprising a metal atom selected from the group consisting of an alkali metal atom and an alkaline earth metal atom in an amount of 1,400 ppm by mass or less as expressed in terms of the metal atom; and

(D1) a hindered amine-based antioxidant (D1) in an amount of 900 ppm by mass or more as expressed in terms of a nitrogen atom,

to obtain a lubricating oil composition having a sulfated ash content of 0.70% by mass or less.