Internal-combustion engine lubrican composition

Abstract

 [PROBLEMS TO BE SOLVED BY THE INVENTION]
To provide a lubricating oil composition excellent in cleanability at high temperature around a piston in spite of its superlow-ash composition substantially free of ashes derived from a metal·base dergent, which cannot be realized by conventional techniques.
[MEANS FOR SOLVING THE PROBLEMS]
The lubricating oil composition for internal combustion engines, containing the GCD550°C + heavy fraction at 6% by volume or more, and having a sulfated ash content of 0.6% by mass or less and content of an additive containing a boron-base compound of 0.02% by mass or more as boron.

Description

[FIELD OF THE INVENTION]

[0001] The present invention relates to a lubricating oil composition for internal combustion engines, more particularly a lubricating oil composition for internal combustion engines having a superlow-ash oil composition suitable for diesel engines equipped with an exhaust gas post-treatment device, e.g., diesel particulate filter (DPF) or catalytic system for simultaneously abating particulate matter and NOx (DPNR).

[DESCRIPTION OF THE PRIOR ART]

[0002] Recently, regulations on exhaust gases from internal combustion engines have been increasingly stringent for strengthened environmental preservation measures. For exhaust gases from diesel engines, in particular, abatement of nitrogen oxides (NOx) and particulate matter (PM) is an inevitable challenge.
Some of the measures against NOx and PM emissions include exhaust gas recycling (EGR), delayed fuel injection timing, increased pressure of fuel to be injected, improved combustor shapes, and incorporation of exhaust gas post-treatment devices, for which oxidation catalysts and DPF have been developed.

[0003] However, lubricating oils for diesel engines generally contain a metal-base detergent and ashless dispersant as essential components, which may cause troubles, e.g., clogging and malfunctions of DPFs by a metal in oils. Reducing metal content may cause insufficient cleaning of engines.

[0004]  Therefore, a number of low-ash oil compositions have been proposed for exhaust gas post-treatment devices, e.g., DPFs. For example, Prior Art 1 (JP-A-8-253782, Patent Document 1) discloses a lubricating oil composition for diesel engines, having a sulfated ash content of 1.5% by mass or less, wherein the composition comprises a lubricating base oil incorporated with additives of (a) boron-containing low-ash dispersant, (b) metal-base detergent agent and, as required, (c) ester of an aromatic carboxylic acid containing hydroxyl group and hydroxyl compound and/or boron-containing compound in a [B]/[M] mass ratio of 0.15 or more ([B]: boron content in the composition and [M]: content of total metals based on the metal-base detergent(s) in the composition).
However, the composition is considered not to achieve sufficient reduction of metals judging from the description saying that it needs 0.18% by mass of calcium.

[0005] Prior Art 2 (JP-A-9-111275, Patent Document 2) discusses that a combination of specific metal-base detergent and ashless dispersant achieves good characteristics, e.g., cleanability, for a lubricating oil having an ash content of 0.4 to 0.8% by mass. However, it still needs 0.07% of a metal-base detergent component to keep its cleanability. Prior Art 3 (JP-A-2002-60776, Patent Document 3) reduces the ash content in a low-sulfur oil composition incorporated with a Mo compound. This technique, however, aims at improved combustion of PM, and fails to achieve a superlow ash content viewed from prevention of DPF clogging, because it contains a metallic component derived from a metal-base detergent at around 0.2%.

[0006] Prior Art 4 (JP-A-2004-35652, Patent Document 4) intends to secure good cleanability at a low ash content by use of specific calcium salicylate. However, it needs at least 0.03% by mass of calcium, as is the case with the conventional technique, and fails to sufficiently reduce an ash content to a low level.
Under these situations, there are strong demands for oil compositions of lower ash content viewed from extending DPF serviceability, in consideration of exhaust gas regulations becoming increasingly stringent and future regulations on sub-micron particles.

[0007] Each of the prior art techniques cited above, however, intends to secure low ash content and cleanability at high temperature by optimizing an additive composition, as discussed above. There are invariably limits for them to reduce the ash content to a very low level to an extent that the oil composition is substantially free of ashes derived from a metal-base detergent while securing cleanability at high temperature.

[0008] The inventors of the present invention have proposed a diesel engine oil composition which can secure low ash content and cleanability at high temperature by use of a heavy fraction having a GCD boiling temperature of 550°C or higher (hereinafter referred to as the GCD550°C + heavy fraction) contained at 6% by volume or more, instead of optimizing an additive composition (Prior Art 5, (JP-A-2003-201496, Patent Document 5).

[0009] On the other hand, fuel consumption has been regulated to abate CO₂ emissions for preventing global warming, and low-viscosity lubricating oil of reduced viscous resistance has been demanded as an engine oil capable of contributing to fuel saving. The 5W-20 grade oil, whose viscosity is reduced to a lowest level at high temperature and high shear rate, has been spreading from the age of SJ/GF-2. More recently, the 0W-20 grade oil, which has a reduced viscosity not only at high temperature but also at low temperature to improve fuel economy, has been spreading. The major Japanese automakers have been adopting the OW-20 grade oil, which has the lowest-viscosity multi-grade oil specified by SAE J300.

[0010] Under these situations, the markets have been strongly demanding reduction of ashes by further reducing sulfated ash content and, at the same time, improved cleanability not only for a carbonaceous component deposited on a piston but also for a deposited lacquer component.
Patent Document 1: JP-A-8-253782
Patent Document 2: JP-A-9-111275
Patent Document 3: JP-A-2002-60776
Patent Document 4: JP-A-2004-35652
Patent Document 5: JP-A-2003-201496

[DISCLOSURE OF THE INVENTION]

[PROBLEMS TO BE SOLVED BY THE INVENTION]

[0011] Under the development situations described above, it is an object of the present invention to provide a lubricating oil composition of superlow ash content, substantially free of ashes derived from a metal-base detergent and, at the same time, of improved cleanability not only for a carbonaceous component deposited on a piston but also for a lacquer component deposited on lower-temperature portions in engines, which cannot be realized by conventional techniques which attempt only optimization of an additive composition.

[MEANS FOR SOLVING THE PROBLEMS]

[0012] The inventors of the present invention have found, after having extensively studied to solve the above problems, that a superlow-ash lubricating oil composition for internal combustion engines, substantially free of metal derived from a metal-base detergent or containing the metal at a very low content, can exhibit cleanability not only for a carbonaceous component deposited on a piston but also for a lacquer component deposited on lower-temperature portions in engines, in spite of its low viscosity, by incorporating the GCD550°C + heavy fraction at 6% by mass or more and, at the same time, a specific boron-base additive, achieving the present invention based on the above findings.

[0013] The present invention provides a lubricating oil composition for internal combustion engines, characterized by containing the GCD550°C + heavy fraction at 6% by volume or more, and having a sulfated ash content of 0.6% by mass or less and content of an additive containing a boron-base compound of 0.02% by mass or more as boron.

[0014] The present invention provides a lubricating oil composition for internal combustion engines, containing, as essential components, the GCD550°C + heavy fraction at 6% by volume or more and an additive containing a boron-base compound at 0.02% by mass or more as boron. It includes more preferable embodiments 1) to 8) described below.

[0015] 

1) The above lubricating oil composition of low viscosity for internal combustion engines, falling under the SAE viscosity grade of 0W-20, 0W-30, 5W-20, 5W-30 or 10W-30, preferably 0W-20, 0W-30, 5W-20 or 5W-30.

2) The above lubricating oil composition for internal combustion engines, having a viscosity of below 2.6 mPa·s at a high temperature of 150°C and high shear rate of 10⁶ s^-1, (hereinafter referred to as high temperature, high shear rate viscosity or HTHS viscosity).

3) The above lubricating oil composition for internal combustion engines, whose base oil is a mineral oil and/or a mixture of synthetic oil and high-boiling oil.

4) The above lubricating oil composition for internal combustion engines, wherein the additive containing a boron-base compound is a hydrated alkali metal borate dispersed in the base oil.

5) The above lubricating oil composition for internal combustion engines, wherein the additive containing a boron-base compound is boron-containing polyalkenyl succinimide.

6) The above lubricating oil composition for internal combustion engines, containing the metal derived from the metal-base detergent at 0.1% by mass or less, preferably 0.01% by mass or less.

7) The above lubricant oil composition for internal combustion engines, additionally containing at least one species of additive selected from the group consisting of ashless dispersant containing no boron, wear inhibitor, oxidation inhibitor, viscosity index improver, pour-point depressant, corrosion inhibitor and defoaming agent at an effective content.

8) The above lubricating oil composition for internal combustion engines, wherein the oxidation inhibitor is at least one species selected from the group consisting of phenol-base and amine-base ones.

[ADVANTAGES OF THE INVENTION]

[0016] The lubricating oil composition of the present invention exhibits a notable effect for improving cleanability at high temperature in spite of its superlow-ash composition substantially free of a metal-base detergent , as discussed above.
Moreover, the present invention provides a suitable engine oil for diesel engines quipped with an exhaust gas post-treatment device, e.g., DPF, because it can prevent clogging of the DPF with ashes.
Still more, the present invention provides a lubricating oil composition excellent in cleanability at high temperature in spite of its low viscosity and superlow-ash composition substantially free of a metal-base detergent.

[BEST MODE FOR CARRYING OUT THE INVENTION]

Lubricating oil composition for internal combustion engines

[0017] The lubricating oil composition of the present invention for internal combustion engines has the following characteristics:

(1) containing the GCD550°C + heavy fraction at 6% by volume or more,

(2) having a sulfated ash content of 0.6% by mass or less, and

(3) having a content of additive containing a boron-base compound of 0.02% by mass or more as boron.

[0018] The lubricating oil composition for internal combustion engines is achieved by incorporating a lubricating oil with a base oil of high boiling point and an additive containing a boron-base compound, while using substantially no metal-base detergent.

[0019] The present invention can provide a lubricating oil composition for internal combustion engines, having an SAE viscosity grade of 0W-20, 0W-30, 5W-20, 5W-30 or 10W-30, preferably 0W-20, 0W-30, 5W-20 or 5W-30.
Moreover, the present invention can provide a low-viscosity lubricating oil composition for internal combustion engines, having an HTHS viscosity of below 2.6 mPa·s at 150°C and a shear rate of 10⁶ s^-1.

[0020] The above characteristic (1) of "containing the GCD550°C + heavy fraction at 6% by volume or more" means that the composition can exhibit a notable effect of improving cleanability at high temperature when it contains the fraction at 6% by volume or more. The critical content has been confirmed by the panel coking test for measuring deposit formed, the results indicating that the effect sharply decreasing when the content is below 6% by volume. The upper content level is 50% by volume, preferably 25% by volume. At above 50% by volume, the viscosity-related properties at low temperature, cold startability and fuel economy may deteriorate.
The "GCD550°C + heavy fraction" is determined by gas chromatography carried out by a procedure under conditions described later in Examples.

[0021] The function of the GCD550°C + heavy fraction is not fully substantiated, but conceivably comes from its function of cleaning carbonaceous substance deposited on, e.g., upper portion of piston.

[0022] The above characteristic (2) is a sulfated ash content of 0.6% by mass or less, preferably 0.5% by mass or less.
The sulfated ash content means a constant mass of char resulting from combustion of sample oil, after it is treated with sulfuric acid under heating. The procedure for determining the sulfated ash content is described later in Examples. It is generally derived from a metal in a metal-base additive contained in a lubricating oil composition. It is necessary to limit it to 1.0% by mass, because a DPF tends to be clogged with ashes when a lubricating oil composition has a sulfated ash content exceeding 1.0% by mass. The present invention can further reduce the content to 0.6% by mass or less to provide a lubricating oil composition of superlow ash content.

[0023] The characteristic (3) is a content of additive containing a boron-base compound of 0.02% by mass or more as boron.
Incorporation of the lubricating oil composition with a boron-base compound at a specific content, i.e., 0.02% by mass or more as boron, notably improves cleanability of removing deposited lacquer, determined by the hot tube test carried out at 290°C. This characteristic, coupled with the characteristic (1) of containing the GCD550°C + heavy fraction at 6% by volume or more, secures cleanability at high temperature over a wider range.

[0024] The upper limit of a boron-base compound is set at 0.2% by mass as boron, preferably 0.1% by mass, because increasing boron content beyond the above level will lead to increased ash content.
Examples of the boron-base compounds include boron-containing polyalkenyl succinimide and borate of an alkaline metal, which are described later in detail.

Lubricating base oil

[0025] A lubricating base oil as a component of the lubricating oil composition of the present invention contains a high-boiling fraction having fluidity at high temperature at a specific content. More specifically, it contains the GCD550°C + heavy fraction at 6% by volume or more based on the lubricating oil composition.

[0026] The base oil having the specific properties can be produced by blending various base stocks. The base stock is not limited so long as it has a given fraction. It may be a mineral base oil, synthetic base oil, hydroisomerized/isomerized dewaxed base oil, gas-to-liquid (GTL) base oil, asphalt-to-liquid (ATL) base oil, vegetable base oil or a mixture thereof.

[0027] Next, the lubricating base oil for the present invention is described more specifically.
The mineral base oil is produced by treating a lubricating oil fraction as a vacuum distillate from a paraffinic, intermediate or naphthenic crude. The treatment methods include solvent refining, hydrocracking, hydrogenation, hydrorefining, catalytic dewaxing and clay treatment. The mineral base oils useful for the present invention include solvent-refined raffinate or hydrotreated oil treated by one or more of the above methods; vacuum residue treated by solvent deasphalting and then by one or more of the above methods; isomerized wax; hydroisomerized/isomerized dewaxed oil; gas-to-liquid (GTL) oil; asphalt-to-liquid (ATL) oil; and a mixture thereof.
The solvent refining may use an aromatic extraction solvent, e.g., phenol, fulfural, or N-methylpyrrolidone. The solvent dewaxing may use a solvent, e.g., liquefied propane or MEK/toluene. The catalytic dewaxing may use a dewaxing catalyst, e.g., shape-selective zeolite.

[0028] The base oil for the present invention may be composed of, totally or partly, hydrodewaxed oil, mixed hydroisomerized/catalytic (or solvent) dewaxed base stock, mixed GTL base stock or a mixture thereof, preferably mixed GTL base stock.
Similarly, a lubricating oil fraction isolated from a liquid product from an ATL process which treats heavy residue component, e.g., asphalt, may be also used.
The above-described refined mineral oil, hydroisomerized/isomerized dewaxed base oil, GTL base oil and ATL base oil include light or medium neutral oil. These base oils can be adequately blended to satisfy the required properties, in order to produce the desired base oil for the present invention.

[0029] Examples of synthetic base oils include:

poly-α-olefin oligomers (PAOs) (e.g., poly(1-hexene), poly(1-octene), poly(1-decen) and a mixture thereof);

polybutenes;

alkylbenzenes (e.g., dodecylbenzene, tetradecylbenzene, di(2-ethylhexyl)benzene and dinonyl benzene);

polyphenyls (e.g., biphenyl and alkylated polyphenyls);

alkylated diphenyl ether and alkylated diphenyl sulfide and derivatives thereof;

esters of dicarboxylic acid (e.g., phthalic acid, succinic acid, alkyl succicnic acid, alkenyl succinic acid, maleic acid, azelaic acid, suberic acid, sebacid acid, fumaric acid, adipic acid or linoleic acid dimer) and alcohol (e.g., butyl alcohol, hexyl alcohol, 2-ethylhecyl alcohol, isodecyl alcohol, dodecyl alcohol, ethylene glycol, diethylene glycol monoether, or propylene glycol);

esters of monocarboxylic acid of 4 to 20 carbon atoms and polyol (e.g., neopentyl glycol, trimethylolpropane, pentaerythritol, dipentaerythritol, or tripentaerythritol); and

polyoxyalkylene glycol, polyoxyalkylene glycol esters, polyoxyalkylene glycol ethers, phosphoric acid esters and silicone oil.

[0030] Specific examples of the -α-olefin oligomer (PAO) include homopolymers of α-olefin of 6 to 12 carbon atoms (e.g., 1-hexene, 1-octene and 1-decene polymers described above), and copolymers of mixed monomers, having a kinematic viscosity of 2 to 3000 mm²/s at 100°C. Moreover, a liquid copolymer of ethylene and an α-olefin may be used as a base oil, selected from commercial viscosity grades of 8, 10, 20, 40, 100, 150, 600, 2000 mm²/s at 100°C, and so forth.

[0031] Examples of the polyol esters include those of hindered alcohol of 5 to 30 carbon atoms and fatty acid. The hindered alcohols include neopentyl glycol, 2,2-diethylpropane-1,3-diol, 2,2-dibutylpropane-1,3-diol, 2-methyl-2-propylpropane-1,3-diol, 2-ethyl-2-butylpropane-1,3-diol, trimethylol ethane, trimethylol propane, ditrimethylol propane, tritrimethylol propane, tetratrimethylol propane, pentaerythritol, dipentaerythritol, tripentaerythritol, tetrapentaerythritol and pentapentaerythritol. They may be used either individually or in combination. The preferable hindered alcohols have 5 to 20 carbon atoms, and the particularly preferable ones include trimethylol propane, ditrimethylol propane, tritrimethylol propane, pentaerythritol, dipentaerythritol and tripentaerythritol.

[0032] Examples of the fatty acids include linear or branched ones of 4 to 20 carbon atoms. The linear fatty acids include n-butanoic acid, n-pentanoic acid, n-hexanoic acid, n-heptanoic acid, n-octanoic aicd, n-nonanoic acid, n-decanoic acid, n-undecanoic acid, n-dodecanoic acid, n-tridecanoic acid, n-tetradecanoic acid, n-pentadecanoic acid, n-hexadecanoic acid, n-heptadecanoic acid, n-octadecanoic acid, n-nonadecanoic acid and eicosanic acid. They may be used either individually or in combination. Examples of the branched fatty acids include 2-methylpropanoic acid, 2-methylbutanoic acid, 3-methylbutanoic acid, 2,2-di-methylpropanoic acid, 2-ethylbutanoic acid, 2,2-dimethylbutanoic acid, 2,3-dimethylbutanoic acid, 2-ethylpentanoic acid, 2,2-dimethylpentanoic acid, 2-ethyl-2-methylbutanoic acid, 3-methylhexanoic acid, 2-methylheptanoic acid, 2-ethylhexanoic acid, 2-propylpentanoic acid, 2,2-dimethylhexanoic acid, 2-ethyl-2-methylpentanoic acid, 2-methyloctanoic acid, 2,2-dimethylheptanoic acid, 2-ethylheptanoic acid, 2-methylnonanoic acid, 2,2-dimethyloctanoic acid, 2-ethyloctanoic acid, 2-methyldecanoic acid, 3-methyldecanoic acid, 4-methyldecanoic acid, 5-methyldecanoic acid, 6-methyldecanoic acid, 7-methyldecanoic acid, 6-ethylnonanoic acid, 3-methylundecanoic acid, 2-methyldodecanoic acid, 2-methyltridecanoic acid, 2-methyltridecanoic acid, 2-methyltetradecanoic acid, 4-methyltetradecanoic acid, 2-ethyltetradecanoic acid, 2-propyltetradecanoic acid, 2-pentylnonanoic acid, 2-hexyldecanoic acid, 2-ethylhexadecanoic acid, 2-butyltetradecanoic acid, 2-heptylundecanoic acid, 3-methylnonadecanoic acid and 2-methyloctadecanoic acid. They may be used either individually or in combination. The preferable fatty acids include those of 4 to 18 carbon atoms, particularly preferably 8 to 18 carbon atoms.

[0033] The hindered ester can be produced by conventional method, e.g., (a) direct esterification in which a polyol and fatty acid is dehydrated/condensed in the absence of catalyst or in the presence of acidic catalyst, (2) reaction of a fatty acid chloride with a polyol, or (3) transesterification between a lower alcohol/fatty acid ester and polyol ester.

[0034] Examples of the polyol esters include the following compounds, wherein neopentyl glycol, trimethylol propane, dimethylol propane, pentaerythritol, dipentaerythritol and tripentaerythritol are abbreviated by respective NPG, TMP, DTMP, PE, DPE and TPE.

[0035] NPG di(n-butanoate), NPG di(n-pentanoate), NPG di(n-hexanoate), NPG di(n-heptanoate), NPG di(n-octanoate), NPG di(n-ethylhexanoate), NPG di(n-nonanoate), NPG di(isononanoate), NPG di(n-decanoate), NPG di(n-undecanoate), NPG di(n-dodecanoate), NPG di(n-tridecanoate), NPG di(n-tetradecanoate), NPG di(n-pentadecanoate), NPG di(n-hexadecanoate), NPG di(n-heptadecanoate), NPG di(n-octadecanoate), NPG di(n-nonadecanoate), NPG di(n-eicosanoate), NPG di(2,2-dimethyl octanoate), NPG di(2-methyl decanoate), NPG di(3-methyl hendecanoate), NPG di(2-methyl dodecanoate), NPG di(2-methyl tridecanoate), NPG di(2-methyl tetradecanoate), NPG di(2-propyl decanoate), NPG di(2-pentylnonanoate), NPG di(2-hexyl decanoate), NPG di(2-ethyl hexadecanoate), NPG di(2-ethyl tetraoctanoate), TMP tri(n-butanoate), TMP tri(n-pentanoate), TMP tri(n-hexanoate), TMP tri(n-heptanoate), TMP tri(n-octanoate), TMP tri(n-nonanoate), TMP tri(n-decanoate), TMP tri(n-dodecanoate), TMP tri(n-tridecanoate), TMP tri(n-tetradecanoate), TMP tri(n-pentadecanoate), TMP tri(n-hexadecanoate), TMP tri(n-heptadecanoate), TMP tri(n-octadecanoate), TMP tri(n-nonadecanoate), TMP tri(n-eicosanoate), TMP tri(2,2-dimethyl octanoate), TMP tri(2-methyl decanoate), TMP tri(2-methyl dodecanoate), TMP tri(2-methyl tridecanoate), TMP tri(2-ethyl tetradecanoate), TMP tri(2-ethyl hexadecanoate), TMP tri(2-heptyldecanoate), TMP tri(2-ethyl octadecanoate), TMP tri(3-methyl nonadecanoate), DTMP tetra(n-butanoate), DTMP tetra(n-pentanoate), DTMP tetra(n-hexanoate), DTMP tetra(n-heptanoate), DTMP tetra(n-octanoate), DTMP tetra(n-nonanoate), DTMP tetra(n-decanoate), DTMP tetra(n-dodecanoate), DTMP tetra(n-octadecanoate), PE tetra(n-butanoate), PE tetra(n-pentanoate), PE tetra(n-hexanoate), PE tetra(n-heptanoate), PE tetra(n-octanoate), PE tetra(n-nonanoate), PE tetra(n-decanoate), a mixture of PE tetra (n-pentanoate), PE tetra (isopentanoate), PE tetra (n-hexanoate) and PE tetra (n-butanoate), PE tetra(n-dodecanoate), PE tetra(n-tridecanoate), PE tetra(n-tetradecanoate), PE tetra(n-pentadecanoate), PE tetra(n-hexadecanoate), PE tetra(n-heptadecanoate), PE tetra(n-octadecanoate), PE tetra(n-nonadecanoate), PE tetra(n-eicosanoate), PE tetra(2,2-dimethyl octanoate), PE tetra(2-methyl decanoate), PE tetra(2-methyl dodecanoate), PE tetra(2-methyl tridecanoate), PE tetra(2-methyl tetradecanoate), PE tetra(2-ethyl tetradecanoate), PE tetra(2-propyl decanoate), PE tetra(2-hexyl decanoate), PE tetra(2-ethyl hexadecanoate) and PE tetra(2-butylethyl tetradecanoate).
Examples of vegetable base oil include ricinus and copra oil.

[0036] The base oil for the lubricant oil composition of the present invention for internal combustion engines can be produced from the above-described base stocks, which may be used either individually or in combination in such a way to secure desired properties, e.g., kinematic viscosity of 2 to 15 mm²/s at 100°C, preferably 3 to 13 mm²/s, and GCD550°C + heavy fraction content of 6 to 50% by volume, inclusive, based on the lubricating oil composition, preferably 25% by volume or less, more preferably 20% by volume or less.

[0037] The present invention can provide a low-viscosity lubricating oil composition having an SAE viscosity grade of 0W-20, 0W-30, 5W-20, 5W-30 10W-30 or the like by adequately selecting one or more lubricant base oils. Moreover, it can provide a lubricating oil composition having an HTHS viscosity of below 2.6 mPa·s.
The above viscosity grade is based on the specification SAE J300 (SAE: US's Society of Automotive Engineers).

Boron-base additive

[0038] Examples of the additive containing a boron-base compound as a component of the lubricating oil composition of the present invention for internal combustion engines include boron-containing dispersants based on polyalkenyl succinimide and additives based on potassium borate.

[0039] Boron-containing dispersants based on polyalkenyl succinimide are produced by treating a mono or bis type polyalkenyl succinimide, represented by the respective general formulae (1) and (2), with a boron compound. These mono and bis succinimide types may be used in combination.

[0040] 

[0041] 

[0042] The boron compounds include boric acid, boric anhydride, boron oxide, halogenated boron, boric acid ester and so forth.
In the above general formulae, R¹, R³ and R⁵ are each a polyalkenyl group, preferably polybutenyl group, having a number-average molecular weight of 800 to 2600, preferably 900 to 2400, which may be the same or different; R² and R⁴ are each an alkylene group of 2 to 5 carbon atoms, which may be the same or different; and X is an integer of 1 to 10.

[0043] The mono and bis type polyalkenyl succinimides are generally produced by the reaction between a polybutenyl succinic anhydride and polyamine, the former being produced by the reaction between polybutene and maleic anhydride. Examples of the polyamine include single diamines, e.g., ethylenediamine, propylenediamine, butylenediamine and pentylenediamine; and polyalkyene polyamines, e.g., diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, di(methylethylene)triamine, dibutylenetriamine, tributylenetetramine and pentapentylenehexamoine.
The boron-containing dispersant based on polyalkenyl succinimide preferably contains boron at 0.2% by mass or more. Each of the mono type represented by the general formula (1) and bis type represented by the general formula (2) may be used, the latter being more preferable.

[0044] Next, the additive based on borate of an alkaline metal, containing a hydrated borate of an alkaline metal, can be represented by the following general formula:

        M₂O·XB₂O₃·yH₂O

wherein, M is an alkaline metal; "x" is 2.5 to 4.5; and "y" is 1.0 to 4.8. More specifically, examples of the compound include hydrated lithium borate, hydrated sodium borate, hydrated potassium borate, hydrated rubidium borate and hydrated cesium borate, of which hydrated potassium borate and hydrated sodium borate are more preferable, and hydrated potassium borate is particularly preferable.
The hydrated borate generally has an average particle diameter of 1 µm or less.
The alkaline metal borate for the present invention preferably has a boron/alkaline metal ratio in a range from about 2.5/1 to 4.5/1.

[0045] A dispersion of hydrated alkaline metal borate in oil is generally produced by a process comprising steps for forming a solution of the alkaline metal hydroxide and boric acid in deionized water in the presence of an optional small quantity of alkaline metal carbonate; for incorporating the solution in a lubricant oil composition composed of a lubricant oil, dispersant and optional additive(s) to form an emulsion; and for dehydrating the emulsion.

[0046] The present invention may also use a dispersion of fine particles of alkaline metal borate produced by a process comprising steps for carbonating an alkaline or alkaline-earth, neutral sulfonate in the presence of an alkaline metal hydroxide to form the ultrabasic sulfonate; and for reacting boric acid with the resulting sulfonate. The carbonation process may be carried out in the presence of an ashless dispersant, e.g., succinimide. The more preferable hydrated alkaline metal borate for the composition component are potassium borate and sodium borate in the form of dispersion, produced using neutral calcium sulfonate or an ashless dispersant, e.g., succinimide. The hydrated alkaline metal borates may be used either individually or in combination.

[0047] The boron-base additive for the lubricating oil composition of the present invention for internal combustion engines may be the above-described boron-containing polyalkenyl succinimide, borate of an alkaline metal or a mixture thereof, of which the additive of borate of an alkaline metal is particularly preferable. The boron-base additive is incorporated at least at 0.02% by mass based on the whole lubricant oil composition. At a lower content, the composition may have insufficient cleanability, as demonstrated in Examples and Comparative Examples. The upper limit is preferably set at 0.2% by mass, above which sulfated ash content increases to possibly clog a DPF and viscosity-related properties of the composition may be deteriorated by the succinimide component.

Metal-base detergent

[0048] The lubricating oil composition of the present invention for internal combustion engines can be structured to exhibit sufficient cleanability at high temperature in the absence of a metal-base cleaning agent as a constituent, but will have improved cleanability in the presence of a detergent without substantially increasing sulfated ash content so long as it is incorporated at 0.1% by mass or less, preferably 0.01% by mass or less.
The useful metal-base detergent is an alkaline-earth metal sulfonate, alkaline-earth salicylate, alkaline-earth phenate or a mixture thereof. An alkaline-earth sulfonate is a salt of sulfonic acid with an alkaline-earth metal, e.g., long-chain alkylbenzene, alkylnaphthalene or the like.

[0049] An alkaline-earth salicylate is a salt of alkylsalicylic acid, which may be sulfided, with an alkaline-earth metal.
An alkaline-earth phenate is a salt of alkylphenol, which may be sulfided, with an alkaline-earth metal.
The alkaline-earth metals for the sulfonate, salicylate and phenate include calcium, magnesium, barium and so forth, of which calcium is more preferable. The alkaline-earth metal salt may be neutral or basic.

Other additives

[0050] The lubricating oil composition of the present invention for internal combustion engines is required to satisfy diversified requirements, and may be incorporated with one or more additives described below within limits not harmful to the object of the present invention.
Non-boron-base dispersants include those containing succinimide, succinamide, benzylamine, succinic acid ester, succinic acid ester/amide or the like, of which succinimide-base one is more preferable. A succinimide-base dispersant is incorporated at 0.001 to 0.5% by mass based on the whole composition, preferably 0.04 to 0.2% by mass.

[0051] The wear inhibitors useful for the present invention generally include zinc dithiophosphate, a metallic salt of dithiophosphoric acid (Sb, Mo or the like), metallic salt of dithiocarbamic acid (Zn, Sb, Mo or the like), metallic salt of naphthenic acid, metallic salt of fatty acid, boron compound, phosphoric acid ester, phosphorous acid ester, amine salt of phosphoric acid, metallic salt of phosphoric acid, metallic salt of phosphoric acid ester, metallic acid of phosphorous acid ester and so forth. It is incorporated generally at 0.1 to 5% by mass. Of these compounds, zinc dialkyl dithiophosphate is more preferable. The wear inhibitor is incorporated at 0.01% by mass or more as phosphorus based on the whole composition, particularly preferably 0.05 to 0.2% by mass.

[0052] The oxidation inhibitors useful for the present invention generally include amine-base ones, e.g., alkylated diphenylamine, phenyl-α-naphthylamine and alkylated phenyl-α-naphthylamine; phenol-base ones, e.g., 2,6-di-t-butylphenol, 4,4'-methylenebis(2,6-di-t-butylphenol and isooctyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate; sulfur-base ones, e.g., dilauryl-3,3'-thiodipropionate; phosphorus-base ones, e.g., phosphite; molybdenum-base ones; and zinc dithiophosphate, of which an amine-base one, phenol-base one and mixture thereof are more preferable. The oxidation inhibitor is incorporated generally at 0.04 to 5% by mass.

[0053] The viscosity index improvers useful for the present invention generally include polymethacrylate, which may be in the form of dispersion, olefin copolymer (polyisobutylene/propylene or ethylene/propylene copolymer), which may be in the form of dispersion, polyalkylstyrene, hydrogenated styrene/butadiene copolymer, styrene/maleic anhydride ester copolymer and star-shape isoprene, of which an olefin copolymer (polyisobutylene/propylene or ethylene/propylene copolymer) is more preferable. Particularly preferable one is a polyisobutylene/propylene or ethylene/propylene copolymer having a GPC-determined weight-average molecular weight of 100,000 or more as polystyrene. A dispersion type olefin copolymer is the one having oxygen or nitrogen in the molecular structure. The viscosity index improver is incorporated generally at 0.01 to 30% by mass.

[0054] The pour point depressants useful for the present invention generally include ethylene/vinyl acetate copolymer, condensate of chlorinated paraffin and naphthalene, condensate of chlorinated paraffin and phenol, polymethacrylate and polyalkylstyrene, of which polymethacrylate is particularly preferable. The pour point depressant is incorporated generally at 0.01 to 5% by mass.

[0055] The friction-reducing agents useful for the present invention include organomolybdenum-base compound, fatty acid, higher alcohol, fatty acid ester, oil or fat, amine, amide, ether, sulfide ester, phosphoric acid ester, phosphorous acid ester and amine salt of phosphoric acid ester. The friction-reducing agent is incorporated generally at 0.05 to 3% by mass.

[0056] The extreme pressure agents useful for the present invention generally include ashless sulfide, sulfided oil or fat, phosphoric acid ester, phosphrous acid ester and amine salt of phosphoric acid ester. The extreme pressure agent is incorporated generally at 0.05 to 3% by mass.

[0057] The corrosion inhibitors useful for the present invention include benzotriazole, triazole derivative, benzotriazole derivative, thiazole, thiazole derivative, thiadiazole and thiadiazole derivative. The corrosion inhibitor is incorporated at 0.001 to 3% by mass.

[0058] The rust inhibitors useful for the present invention include fatty acid, alkenylsuccinic acid half-ester, fatty acid soap, alkylsulfonate, polyhydric alcohol/fatty acid ester, fatty acid amine, oxidized paraffin and alkylpolyoxyethylene ether. The rust inhibitor is incorporated generally at 0.01 to 3% by mass.

[0059] The defoaming agents useful for the present invention include dimethyl polysiloxane and polyacrylate. The defoamiong agent is incorporated generally at a very low content, e.g., about 0.002% by mass.

[0060] The lubricant oil composition of the present invention for internal combustion engines may be incorporated with another additive, e.g., colorant, as required.

[Examples]

[0061] Next, the present invention is described in more detail by Examples and Comparative Examples, which by no means limit the present invention.
The base oils for the lubricating oil compositions, additives and methods for evaluating the compositions used in Examples and Comparative Examples are described below.
In Examples and Comparative Examples, "%" means % by mass, unless otherwise stated.

I. Lubricating base oils

[0062] 

1. Mineral base oil: having a kinematic viscosity of 4.5 mm²/s at 100°C

2. Synthetic base oil 1: Poly-α-olefin Synthetic base oil 2: Trimethylol propane/C₁₈ acid ester

II. Additives

[0063] 

(1) Viscosity index improver: Olefin copolymer

(2) Pour point depressant: Polymethacrylate

(3) Defoaming agent: silicone-base defoaming agent

(4) DI package: Metallic cleaning agent, oxidation inhibitor, ashless dispersant and wear inhibitor

(5) Boron-base additives .
Boron-base additive 1: Boron-containing polybutenyl succinimide (boron content: 1.4%)
Boron-base additive 2: Potassium borate-base additive (boron content: 6.8%), with potassium borate dispersed in a system composed of ashless and calcium-base dispersants

(6) No-boron-base dispersant: Succinimide-base ashless dispersant

III. Evaluation methods

1. GCD550°C + heavy fraction

[0064] A standard straight-run hydrocarbon sample of known distillation properties is analyzed by gas chromatography under the following conditions to find a retention time at which the component boiling at 550°C is distilled off, and the analysis is continued to find the GCD550°C + heavy fraction, which is defined as the integrated fractions distilled off thereafter.
Column: HT-5
Length: 6 m
Inner diameter: 0.53 mm
Film thickness: 0.1 µm
Carrier gas: Helium
Detector: FID
Initial temperature: 50°C
Heating rate: 10°C/minute
Final temperature: 450°C
Solvent: Carbon disulfide
Amount injected: 2 µL

2. Deposited amount in the panel coking test

[0065] A sample incorporated with commercial carbon black at 3% is dropped at 1.0 g/hour onto a sloping panel under conditions of slope angle: 8°, panel temperature: 310°C and test time: 3 hours. The sample is charred on the panel to form the deposit, which is treated with petroleum ether to extract the oil remaining in the deposit. Amount of the deposit is determined from the panel differential weight before and after the test.

3. Sulfated ash content

[0066] Determined in accordance with ASTM D-874

4. Hot tube test (carried out in accordance with JPI-5S-55-99)

[0067] A sample oil and air are passed into a glass tube (inner diameter: 2 mm) at respective 3 mL/hour and 10 mL/hour, while the tube temperature is kept at 280 or 290°C. Color of the lacquer attaching to the tube is compared with the color standard to evaluate the sample according to the following standards, transparent: 10 points and black: 0 points. The higher the point number, the higher performance the sample has.

Example 1

[0068] The base oil composed of 78.8% of the mineral base oil and 5.1% of the synthetic base oil 1 was incorporated with the DI package (free of a metallic cleaning agent) at 10.1%, viscosity index improver at 5.1%, pour point depressant at 0.1%, defoaming agent at 0.02% and boron-base additive 1 at 0.8% to form Sample (A) of superlow-ash composition, containing the GCD550°C + heavy fraction at 8.0% by volume, boron at 0.02% and sulfated ash content at 0.34%. It had an HTHS viscosity of 3.2 mPa·s at 150°C, and fell under the SAE viscosity grade of 5W-30. Sample (A) was subjected to the hot tube test (carried out at 280°C for 16 hours or 290°C for 16 hours) and panel coking test. The results are given in Table 1. These results indicate that Sample (A) is excellent in cleanability at high temperature and cleanability with lacquer preventing it from depositing on a piston at a low-temperature portion.

Example 2

[0069] Sample (B) was prepared in the same manner as in Example 1 for preparing Sample (A), except that the boron-base additive 1 was replaced by the boron-base additive 2 which was incorporated at 0.2%. Its composition is given in Table 1. The results of the hot tube test and panel coking test are also given in the table.

Example 3

[0070] Sample (C) was prepared in the same manner as in Example 1 for preparing Sample (A), except that the synthetic base oil 1 was replaced by the synthetic base oil 2 which was incorporated at 9%. Its composition is given in Table 1. The results of the hot tube test and panel coking test are also given in the table.

Example 4

[0071] Sample (D) was prepared in the same manner as in Example 1 for preparing Sample (A), except that the synthetic base oil 1 was replaced by the synthetic base oil 2 which was incorporated at 15%. Its composition is given in Table 1. The results of the hot tube test and panel coking test are also given in the table.

Comparative Examples 1 to 5

[0072] Sample oils (a) to (e) were prepared in respective Comparative Examples 1 to 5 using the base oils and additives to have compositions given in Table 1. Each of these samples lacks at least one of the compositional properties which the present invention requires or has a component out of a content range which the present invention specifies. They were found to fail simultaneously pass the hot tube and panel coking tests, as shown in Table 1, and were notably inferior in performance to the samples of the present invention. Sample (a) prepared in Comparative Example 1, although containing the GCD550°C + heavy fraction at 7.6% by volume, contained no boron-base additive. It had the deposited amount sufficiently decreased in the panel coking test, but had the deposited lacquer of black in color in the hot tube test carried out at 290°C, resulting in an evaluation point of 1.0.

[0073] Each of Samples (b) and (c), prepared in respective Comparative Examples 2 and 3, contained the GCD550°C + heavy fraction at respective 3.6 and 3.7% by volume, and produced an excessive amount of the deposit in the panel coking test.

[0074] Sample (e) prepared in Comparative Example 5 contained the GCD550°C + heavy fraction at 5.5% by volume, and produced a large amount of the deposit in the panel coking test. On the other hand, Sample (d) prepared in Comparative Example 4, although containing GCD550°C + heavy fraction at a content reaching 8.0% by volume, showed a very low evaluation point in the hot tube test carried out at 290°C because of absence of boron (which should be contained at least at 0.02% by mass):

[0075] 

[0076] It is thus found by Examples and Comparative Examples that the sample oil simultaneously satisfying the GCD550°C + heavy fraction content of 6% by volume or more, sulfated ash content of 0.6% by mass or less and boron content of at least 0.02% by mass as the compositional properties can have a high evaluation point in the hot tube tests carried out at 280 and 290°C, and greatly suppressed formation of the deposit in the panel coking test. As such, it exhibits high cleanability in spite of its superlow ash composition and brings very notable effects.

Claims

1. A lubricating oil composition for internal combustion engines, containing a heavy fraction having a GCD boiling temperature of 550°C or higher at 6% by volume or more, and having a sulfated ash content of 0.6% by mass or less and content of an additive containing a boron-base compound of 0.02% by mass or more as boron.

2. The lubricating oil composition for internal combustion engines according to Claim 1 falling under the SAE viscosity grade of 0W-20, 0W-30, 5W-20, 5W-30 or 10W-30.

3. The lubricating oil composition for internal combustion engines, according to Claim 1 or 2 containing a metal derived from the metal-base detergent at 0.01% by mass or less.

4. The lubricating oil composition for internal combustion engines according to one of Claims 1 to 3 containing at least one additive species selected from the group consisting of ashless dispersant containing no boron, wear inhibitor, ashless oxidation inhibitor, viscosity index improver, pour-point depressant and defoaming agent at an effective content.