JP2013072060A - Lubricating oil composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lubricating oil composition which has a low sulfur content and which is favorably employed for lubricating an internal combustion engine operated using a low sulfur hydrocarbon fuel particularly as a fuel for running.SOLUTION: The lubricating oil composition for the internal combustion engine has a sulfur content of 0.5 mass% or less and at least includes following components (a) to (e) dissolved or dispersed in a base oil: (a) an ashless dispersant being an alkenyl- or alkyl-succinimide or a derivative thereof; (b) an ashless dispersant being an alkenyl- or alkyl-succinic ester or a derivative thereof; (c) a molybdenum complex of a basic nitrogen-containing compound; (d) an alkaline earth metal-containing detergent having a total base number of 10-400 mg-KOH/g; and (e) an anti-wear agent.

Description

  The present invention relates to a lubricating oil composition useful for lubricating internal combustion engines such as diesel engines and gasoline engines. In particular, the present invention has a low sulfur content (about 0.5% by mass or less) that reduces friction during lubrication of an automobile internal combustion engine that uses a low-sulfur content hydrocarbon fuel and exhibits good high-temperature cleanliness. In particular, about 0.2% by weight or less).

  Sulfur content mixed in fuel such as gasoline and diesel fuel oil (light oil) used for the operation of the internal combustion engine is oxidized during combustion of the fuel to sulfur oxide such as sulfuric acid, and part of it is It mixes with the lubricating oil used for lubrication, and others are discharged | emitted as exhaust gas with combustion gas. Since sulfur oxides discharged into the atmosphere together with the exhaust gas cause air pollution, the sulfur content (sulfur content) contained in the fuel has been conventionally regulated. This regulation of sulfur was initially applied to gasoline, which is a fuel for gasoline engines, but it has also been applied to diesel fuel oil with a high sulfur content. In recent years, for diesel fuel oil, The upper limit of the sulfur content is 0.0010% by mass.

  As the sulfur content of fuel progresses, the amount of sulfur oxides, such as sulfuric acid, produced by the combustion of fuel decreases in the lubricating oil and is required to neutralize those sulfur oxides. The amount of overbased metal detergent (overbased metal-containing detergent) added in the lubricating oil can be reduced.

  It is also known that not only the fuel but also a part of the lubricating oil burns in the engine, and the combustion gas is discharged as a part of the exhaust gas. Therefore, it is preferable to reduce the sulfur content in the lubricating oil as low as possible. In addition, most of the lubricating oils for internal combustion engines that have been used in recent years are hydrocarbon oils of lubricating viscosity called base oils, and overbased metal-containing cleaners that are effective in neutralizing sulfur oxides mixed in lubricating oils. Dispersed in the base oil, antioxidants to prevent deterioration of base oils placed under high temperature, fuel residue (煤) of fuel, residue of base oil and metal-containing detergent Various kinds of dispersants such as an effective dispersing agent, an extreme pressure agent for preventing seizure between the piston and the cylinder, and a friction modifier (friction adjusting agent) for reducing friction generated between the piston and the cylinder It is supplied as a lubricating oil composition to which an additive component (lubricating oil additive) is added.

  The phosphorus content and metal content contained in the lubricating oil additive blended in the lubricating oil composition are also mixed into the exhaust gas as phosphorous oxide and metal oxide by the combustion of the lubricating oil composition. And it is known that the phosphorus oxide and the metal oxide in the exhaust gas poison the oxidation catalyst or the reduction catalyst filled in the exhaust gas treatment device and reduce the catalytic activity.

Therefore, in recent years, there has been an increasing demand for lowering the ash content, phosphorus content, and sulfur content of lubricating oils. As a lubricating oil that meets these requirements, Patent Document 1 discloses a lubricating oil composition suitable for lubricating an internal combustion engine using a fuel having a low sulfur content, particularly a diesel engine. The product is based on at least a base oil having a sulfur content of 0.1% by mass or less (preferably 0.03% by mass or less) based on the total mass of the composition
a) An ashless dispersant that is an alkenyl or alkyl succinimide or a derivative thereof is 0.01 to 0.3% by mass in terms of nitrogen content,
b) A metal-containing detergent (so-called metal detergent) having a sulfur content of 3% by mass or less and a total base number of 10 to 350 mgKOH / g is 0.1 to 1% by mass in terms of sulfated ash.
c) zinc dialkyldithiophosphate is 0.01 to 0.12% by weight in terms of phosphorus content, and d) 0.01 to 5% by mass of an antioxidant phenol compound and / or an antioxidant amine compound. ,
The amount of sulfated ash is in the range of 0.1 to 1% by weight, the phosphorus content is in the range of 0.01 to 0.1% by weight, based on the total weight of the composition, and The sulfur content is in the range of 0.01 to 0.3 mass%, the chlorine content is 40 mass ppm or less, and the organic acid metal salt contained in the metal-containing detergent is 0.2 in the composition. -7% by mass (preferably 0.5-5% by mass, more preferably 1.0-3% by mass). And in the Example described in this patent document 1, it is clarified that the lubricating oil composition having the above composition exhibits excellent high-temperature cleanliness when used as engine oil.
In addition, this patent document 1 describes that a molybdenum-containing compound can be used as a multifunctional additive that functions as a friction modifier, an antioxidant, and an antiwear agent in the lubricating oil composition. As a molybdenum-containing compound useful as such a multifunctional additive, there is a description in Patent Document 1, but conventionally, it contains or does not contain sulfurized oxymolybdenum dithiocarbamate, sulfurized oxymolybdenum dithiophosphate, and a sulfur content. Molybdenum complexes of succinimide are known.

  Patent Document 2 discloses a low ash, low phosphorus and low sulfur lubricating oil, in particular, an internal combustion engine lubricating oil (engine oil), a base oil, an ashless dispersant treated with ethylene carbonate, and a borate treated with no boric acid. A lubricating oil composition is described that incorporates an ash dispersant, a highly basic metal-containing detergent, and a phosphorus-containing compound. It is also described that this lubricating oil composition can further contain a molybdenum-succinimide complex. In the examples of Patent Document 2, it is clarified by experimental data that this lubricating oil composition exhibits excellent wear resistance as well as excellent oxidation stability.

Patent Document 3 discloses low-ash, low-phosphorus and low-sulfur engine oils such as boron-containing ashless dispersants, molybdenum-containing friction reducers, sulfonates, phenates, salicylates, and other metal-based cleaners. An engine lubricating oil composition to which an agent and zinc dithiophosphate are added is described. In this patent document 3, molybdenum diorganodithiocarbamate, molybdenum diorganodithiophosphate, molybdenum carboxylate, and Mo ₃ S ₇ (dtc) ₄ and Mo ₃ S ₄ (dtc) ₄ are represented as molybdenum-containing friction reducing agents. Trinuclear molybdenum compounds are illustrated. And about the lubricating oil composition of this patent document 3, the high temperature antioxidant property and friction reduction characteristic which were excellent in the lubricating oil composition using said trinuclear molybdenum compound as a molybdenum compound in the Example. It has been clarified by experimental data that

JP 2002-53888 A JP 2004-149802 A JP-T-2005-516106

As described above, it is already known that a molybdenum compound is effective as a friction modifier to be added to a lubricating oil composition. Among them, molybdenum diorganodithiocarbamate and molybdenum diorganodithiophosphate are generally used as molybdenum-containing friction modifiers, but the former contains sulfur (S) in the molecular structure, and the latter in the molecular structure. Since phosphorus (P) is contained, sulfur oxide gas and phosphorus oxide gas are generated by combustion of the lubricating oil composition when added to the lubricating oil composition, and poisoning of the catalyst of the exhaust gas treatment device Has the disadvantage of bringing Further, according to Patent Document _{3, Mo 3 S 7 (dtc} ) 4, Mo 3 S 4 (dtc) 4 friction effect trinuclear molybdenum compounds having excellent represented by (friction effects) clearly indicate the However, since this trinuclear molybdenum compound contains a sulfur atom coordinated to molybdenum in addition to the sulfur content contained in the molecular structure of “dtc (dithiocarbamate)” functioning as a ligand, The overall sulfur content is high and therefore is not preferred for promoting the low sulfur content of lubricating oil compositions.

The present invention is represented by molybdenum diorganodithiocarbamate, molybdenum diorganodithiophosphate, and Mo ₃ S ₇ (dtc) ₄ , Mo ₃ S ₄ (dtc) _4, which are known to exhibit an excellent friction relaxation effect than before. Instead of friction modifiers containing sulfur and phosphorus at a high rate, such as trinuclear molybdenum compounds, molybdenum containing friction relaxation that contains no sulfur or phosphorus or has relatively low sulfur and phosphorus content The purpose is to provide an agent.

As described above, it is already known that a molybdenum complex of a basic nitrogen compound such as a molybdenum-succinimide complex is also effective as a molybdenum-containing friction modifier.
According to the research of the inventors of the present invention, the friction relaxation action of this molybdenum complex of a basic nitrogen compound is known as an alkenyl or alkyl succinimide or a derivative thereof known as an ashless dispersant, and also as an ashless dispersant. The present inventors have found that when alkenyl or alkyl succinic acid esters or derivatives thereof are combined and added to a lubricating oil composition in a specific range of amounts, they are remarkably improved, and the present invention has been achieved. In addition, when the molybdenum complex of the above basic nitrogen compound is added to the lubricating oil composition in combination with succinimide or a derivative thereof (that is, when succinic acid ester or a derivative thereof is not further combined). It has been found that the high-temperature oxidation resistance of the lubricating oil composition is improved, but is hardly effective in reducing the friction coefficient.

The present invention resides in a lubricating oil composition for lubricating an internal combustion engine in which at least the following components a) to e) are dissolved or dispersed in a base oil and the sulfur content is 0.5% by mass or less. .
a) 0.5 to 5.0% by weight of an ashless dispersant which is an alkenyl or alkyl succinimide or a derivative thereof,
b) an ashless dispersant which is 0.5 to 5.0% by weight of an alkenyl or alkyl succinate or a derivative thereof;
c) Molybdenum complex of basic nitrogen compound in an amount of 50 to 1200 ppm by mass as molybdenum.
d) an alkaline earth metal-containing detergent having a total base number of 10 to 400 mg KOH / g in an amount of 0.05 to 1.0% by mass as the amount of alkaline earth metal, and e) 0.05 to 5.0 mass % Antiwear agent.

  The present invention also operates an internal combustion engine mounted on a vehicle for running on land that is operated using a fuel oil having a sulfur content of 0.001% by mass or less using the lubricating oil composition of the present invention. There is also a way.

Preferred embodiments of the lubricating oil composition of the present invention are described below.
(1) The sulfur content of the lubricating oil composition is 0.01 or more and 0.2% by mass.
(2) The sulfur content of the lubricating oil composition is 0.05 or more and 0.12% by mass or less.
(3) The lubricating oil composition contains a viscosity index improver, and the SAE viscosity grade is a multi-grade engine oil of 0W5, 0W10, 0W15, 0W20, 0W30, 5W20, 5W30, 10W20, or 10W30.
(4) The content of the ashless dispersant which is an alkenyl or alkyl succinimide or a derivative thereof as component a) is 1.0% by mass or more and 4.0% by mass or less.
(5) The content of the ashless dispersant which is an alkenyl or alkyl succinate of component b) or a derivative thereof is 1.0% by mass or more and 4.0% by mass or less.
(6) The mass ratio of the alkenyl or alkyl succinimide of component a) or an ashless dispersant that is a derivative thereof to the ashless dispersant that is an alkenyl or alkyl succinate of component b) or a derivative thereof is 1 : In the range of 4-4: 1.
(7) The molybdenum complex of the basic nitrogen compound of component c) contains sulfur in an amount not exceeding 1% by mass.
(8) The molybdenum complex of the basic nitrogen compound of component c) contains 0.05% by mass or more and 0.5% by mass or less of sulfur.
(9) The molybdenum complex of the basic nitrogen compound of component c) is a molybdenum complex of succinimide.
(10) The alkaline earth metal-containing detergent of component d) comprises an alkaline earth metal salicylate.
(11) The antiwear agent is zinc dialkyldithiophosphate.
(12) Contains an antioxidant.
(13) The lubricating oil composition is for lubricating an internal combustion engine operated using a fuel oil having a sulfur content of 0.001% by mass or less.

  The lubricating oil composition of the present invention comprises, as a friction modifier, a molybdenum complex of a basic nitrogen compound (which may contain a small amount of sulfur), an alkenyl or alkyl succinimide known as an ashless dispersant, The use of compositions thereof in combination with alkenyl or alkyl succinic acid esters or derivatives thereof, also known as ashless dispersants, in a specific range of amounts, reduces the sulfur content of lubricating oil compositions to low levels. Can be. On the other hand, the lubricating oil composition of the present invention exhibits an excellent friction relaxation action.

As the base oil in the lubricating oil composition of the present invention, mineral oil or synthetic oil having a kinematic viscosity at 100 ° C. of ² to 50 mm ² / s is usually used. Although there is no restriction | limiting in particular about the kind of this mineral oil or synthetic oil, or other properties, As a base oil, sulfur content needs to be 0.1 mass% or less. The sulfur content is desirably 0.03% by mass or less, and particularly desirably 0.005% by mass or less.

  The mineral oil-based base oil is preferably a mineral oil-based lubricating oil fraction that has been processed by appropriately combining processing methods such as solvent refining or hydrotreating, and is particularly highly hydrorefined base oil (for example, A base oil having a viscosity index of 100 to 150, an aromatic content of 5% by mass or less, and nitrogen and sulfur content of 50 ppm by mass or less is preferably used. In particular, a high viscosity index base oil (for example, viscosity index 140-160) obtained by hydroisomerization of slack wax or GTL wax is particularly preferably used.

  Synthetic oils (synthetic lubricating base oils) include, for example, poly-α-olefins, which are polymers of α-olefins having 3 to 12 carbon atoms, sebacic acid, azelaic acid, adipic acid represented by dioctyl sebacate, etc. Dialkyl diester which is an ester of a dibasic acid and an alcohol having 4 to 18 carbon atoms, polyol ester which is an ester of 1-trimethylolpropane or pentaerythritol and a monobasic acid having 3 to 18 carbon atoms, 9 to 40 carbon atoms And alkylbenzene having an alkyl group of In general, synthetic oils are substantially preferred for the lubricating oil composition of the present invention because they contain substantially no sulfur content, are excellent in oxidation stability and heat resistance, and produce little residual carbon and soot once burned.

  Mineral base oils and synthetic base oils can be used alone, but if desired, two or more mineral base oils or a combination of two or more synthetic base oils may be used. it can. Further, if desired, a mineral base oil and a synthetic base oil can be used in combination at any ratio.

  The lubricating oil composition of the present invention comprises at least two types of ashless dispersants: a) alkenyl or alkyl succinimide or a derivative thereof as component, and b) alkenyl or alkyl succinate or a derivative thereof as component Are contained in an amount in the range of 0.5 to 5.0% by mass (percent of the total amount of the lubricating oil composition), preferably in an amount in the range of 1.0 to 4.0% by mass. The ashless dispersant of component a) and the ashless dispersant of component b) are preferably in the range of 1: 4 to 4: 1, particularly preferably 1: 2 to 2: 1 by weight. Used in quantitative ratio.

  As the alkenyl or alkyl succinimide or derivative thereof as the component a), known alkenyl or alkyl succinimide or derivative thereof can be used. For example, alkenyl or alkyl succinimide derived from polyolefin or a derivative thereof is used. Exemplary succinimides include succinic anhydrides substituted with high molecular weight alkenyl or alkyl groups and polyalkylene polyamines containing an average of 4 to 10 (preferably 5 to 7) nitrogen atoms per molecule. It can obtain by reaction of. The high molecular weight alkenyl or alkyl group is preferably derived from a polybutene having a number average molecular weight of about 900 to 3000 (particularly a highly reactive polybutene having a vinylidene terminal).

  In the process of obtaining polybutenyl succinic anhydride by reaction of polybutene and maleic anhydride, a chlorination method using chlorine is often used. However, this method results in a large amount of chlorine (eg, about 2000 to 3000 ppm by mass) remaining in the succinimide final product. On the other hand, in the thermal reaction method using no chlorine, chlorine remaining in the final product can be suppressed to an extremely low level (for example, 0 to 30 ppm by mass). Therefore, in order to suppress the chlorine content in the lubricating oil composition to an amount in the range of 0 to 30 mass ppm, it is desirable to use succinimide from polybutenyl succinic anhydride obtained by a thermal reaction method. The succinimide can be further reacted with boric acid, alcohol, aldehyde, ketone, alkylphenol, cyclic carbonate, organic acid or the like to form a so-called modified succinimide. In particular, boron-containing alkenyl (or alkyl) succinimide obtained by reaction with boric acid or a boron compound has high thermal / oxidative stability and is advantageously used.

  As the alkenyl or alkyl succinic acid ester or derivative thereof as component b), known alkenyl or alkyl succinic acid esters or derivatives thereof can be used. For example, alkenyl or alkyl succinate derived from polyolefin or a derivative thereof is used. Typical succinic esters can be obtained by reaction of succinic anhydrides substituted with high molecular weight alkenyl or alkyl groups with alcohols containing 1 to 6 hydroxyl groups per molecule. The high molecular weight alkenyl or alkyl group is preferably derived from a polybutene having a number average molecular weight of about 900 to 3000 (particularly a highly reactive polybutene having a vinylidene terminal).

  The lubricating oil composition of the present invention has other ashless properties such as an alkenylbenzylamine ashless dispersant in addition to the ashless dispersant of component a) and the ashless dispersant of component b). A combination of dispersants can be used.

  The lubricating oil composition of the present invention contains, as component c), a molybdenum complex of a basic nitrogen compound, which is a known molybdenum-containing multifunctional dispersant, in an amount of 50 to 1200 ppm by mass as the amount of molybdenum. The molybdenum complex of the basic nitrogen compound may contain a small amount of sulfur.

  The molybdenum complex of the basic nitrogen compound functions mainly as an antioxidant, an antiwear agent or a friction modifier in the lubricating oil composition, and contributes to an improvement in cleanliness at high temperatures.

  As the molybdenum complex of the basic nitrogen compound, an oxymolybdenum complex that is a reaction product of an acidic molybdenum compound and a basic nitrogen compound is preferably used. Here, examples of the acidic molybdenum compound include molybdic acid, ammonium molybdate, and alkali metal molybdate. Examples of the basic nitrogen compound include succinimide, carboxylic acid amide, hydrocarbylamine, and Mannich base compound. Examples of molybdenum complexes of basic nitrogen compounds include molybdenum complexes of succinimides and molybdenum complexes of secondary aliphatic amines.

  Molybdenum complexes of basic nitrogen compounds can also be used as reaction products with small amounts of sulfur or sulfur compounds. In particular, a low-temperature sulfurization reaction product of an oxymolybdenum complex of succinimide is preferred. In view of the purpose of the lubricating oil composition of the present invention, it is not preferable to increase the sulfur content. Therefore, the sulfur content is preferably 10% by mass or less of the molybdenum content. A method for producing a sulfurized oxymolybdenum complex is described, for example, in Examples C to H of US Pat. No. 6,562,765 B1. In addition, although the molybdenum complex of a basic nitrogen compound is known especially as an antioxidant, as disclosed in the above-mentioned US Pat. No. 6,562,765 B1, it exhibits an action as a friction reducing agent.

  The lubricating oil composition of the present invention may further contain other molybdenum-containing compounds such as sulfurized oxymolybdenum dithiocarbamate, sulfurized oxymolybdenum dithiophosphate, and oxymolybdenum monoglyceride.

  In the lubricating oil composition of the present invention, as an ingredient d), an alkaline earth metal-containing detergent having a total base number of 10 to 400 mgKOH / g and an alkaline earth metal amount of 0.05 to 1.0% by mass Contained in an amount.

  As the alkaline earth metal-containing detergent having a total base number of 10 to 400 mgKOH / g in the lubricating oil composition of the present invention, known alkaline earth metal-containing detergents can be used, but particularly preferred. Is an alkyl salicylic acid calcium salt detergent. In this calcium alkylsalicylate detergent, the organic acid metal salt contained in the calcium alkylsalicylate detergent is 0.2 to 7% by mass (preferably 0.5 to 5% by mass, more preferably 1% in the composition). (0.0-3 mass%) is preferably present. Preferably, the alkyl salicylic acid calcium salt detergent contains a non-sulfurized alkyl salicylic acid calcium salt detergent having an alkyl group having 14 to 18 carbon atoms. A non-sulfurized alkyl salicylic acid calcium salt detergent having an alkyl group having 14 to 18 carbon atoms is combined with a non-sulfurized alkyl salicylic acid calcium salt detergent having an alkyl group having 20 to 28 carbon atoms. May be used. In the present invention, the non-sulfurized alkyl salicylic acid calcium salt detergent having an alkyl group having 14 to 18 carbon atoms is 90 mol% or more of the alkyl groups contained in the non-sulfurized alkyl salicylic acid calcium salt. It means a non-sulfurized alkyl salicylic acid calcium salt detergent which is an alkyl group having 14 to 18 carbon atoms. The same applies to the non-sulfurized alkyl salicylic acid calcium salt detergent having an alkyl group having 20 to 28 carbon atoms, and 90 mol% or more of the alkyl groups contained in the non-sulfurized alkyl salicylic acid calcium salt are carbon atoms. It means a non-sulfurized alkyl salicylic acid calcium salt detergent which is an alkyl group having a number of 20 to 28.

  The non-sulfurized calcium alkylsalicylate is preferably a calcium salt of alkylsalicylic acid produced by using a Kolbe-Schmidt reaction from an alkylphenol obtained by reacting an α-olefin having a predetermined number of carbon atoms with phenol. Usually, an overbased calcium salicylate with an increased total base number is further used as a calcium salicylate detergent by an overbasing step using slaked lime and carbon dioxide.

  There is also a method in which alkylphenol is directly neutralized to obtain a Ca salt, and calcium salicylic acid calcium salt is obtained directly in the carbonation step.

  In the above alkyl salicylic acid calcium salt detergent, the organic acid metal salt contained in the alkyl salicylic acid calcium salt detergent is 0.2 to 7% by mass (preferably 0.5 to 5% by mass, more preferably, in the composition). It is preferable to determine the type and amount of alkylsalicylic acid calcium salt detergent so that they are present (1.0 to 3% by mass). Alkyl salicylic acid calcium salt detergent is composed of an organic acid metal salt (generally called a soap component or soap) and a basic inorganic salt aggregated around the organic acid metal salt in an oily medium. An oily dispersion containing fine particles (eg, calcium carbonate fine particles) in a dispersed state (the content of the oily medium is usually about 30 to 50% by mass). If the amount of the organic acid metal salt in the lubricating oil composition is maintained at a certain level or more even if the addition amount of the calcium alkylsalicylate detergent is reduced to the lubricating oil composition, the lubricating oil composition The deterioration of the high temperature cleanliness (the ability to keep the inside of the engine clean in a high temperature environment) is not significant.

  On the other hand, as an alkaline earth metal-containing detergent, an organic acid having a carbon-nitrogen bond or an alkali metal salt or an alkaline earth metal salt of a phenol derivative can also be used. In general, by reacting an amine compound, a base number derived from basic nitrogen can be obtained, and a high base number can be obtained even at a low ash content, which is advantageous. For example, various metal salts such as aminocarboxylic acid metal salts are conceivable. In particular, non-sulfurized alkyl phenates (alkaline earth metal salts) having a Mannich base structure are effective. This compound is usually synthesized by Mannich reaction using alkylphenol, formaldehyde, amine or an amine compound, and the reaction product obtained by aminomethylation of the phenol ring is neutralized with a base such as calcium hydroxide to form a metal salt. Can be obtained.

  As the alkaline earth metal-containing detergent, petroleum sulfonic acid or sulfonate which is an alkaline earth metal salt of alkylbenzenesulfonic acid or alkyltoluenesulfonic acid can also be used.

  As alkaline earth metal-containing detergents, sulfurized phenates, ie, alkaline earth metal salts of sulfurized alkylphenols, can also be used.

  The lubricating oil composition of the present invention further contains 0.05 to 5.0% by mass of an antiwear agent as component e). Although it does not specifically limit as an antiwear agent, Generally, well-known sulfur type antiwear agent or phosphorus type antiwear agent is used. Examples of sulfur-based antiwear agents include sulfurized olefins, polysulfide compounds, sulfurized esters, sulfurized alcohols, sulfurized amides, sulfurized fats and oils, ashless dithiocarbamates, dithiocarbamates of metals other than molybdenum, mercaptothiadiazole, mercaptobenzothiazole, mercapto Mention may be made of thiazolines. Phosphorous wear inhibitors include phosphoric acid esters, phosphorous acid esters, thiophosphoric acid esters, dithiophosphoric acid esters, zinc salts of dialkyldithiophosphates, zinc dialkylthiophosphates, zinc dialkylphosphates that are amine salts or metal salts thereof. Can be mentioned.

  As the antiwear agent of the component e) in the lubricating oil composition of the present invention, it is preferable to use a zinc phosphate antiwear agent such as zinc dialkyldithiophosphate or zinc dihydrocarbylphosphate. The basic production methods and properties of these zinc phosphate antiwear agents are already known in detail. This zinc phosphate antiwear agent is used in the range of 0.01 to 0.12% by mass in terms of phosphorus content, but from the viewpoint of low phosphorus content and low sulfur content, 0.01 to 0.06 mass. It is preferably used in an amount in the range of%.

  It is desirable that the zinc dialkyldithiophosphate has an alkylaryl group containing an alkyl group having 3 to 18 carbon atoms or an alkyl group having 3 to 18 carbon atoms. Particularly preferred is an alkyl group derived from a secondary alcohol having 3 to 18 carbon atoms, or a primary alcohol having 3 to 18 carbon atoms and 3 to 18 carbon atoms, which is particularly effective for suppressing wear. Dialkyldithiophosphate zinc containing an alkyl group derived from a mixture of a secondary alcohol. Zinc dialkyldithiophosphates from primary alcohols tend to be excellent in heat resistance. These zinc dithiophosphates may be used alone, but are preferably used in a mixture mainly of a secondary alkyl group type and / or a primary alkyl group type.

The lubricating oil composition of the present invention further contains an antioxidant such as an antioxidant phenol compound and an antioxidant amine compound in the range of 0.01 to 5% by mass (preferably 0.1 to 3% by mass). It is preferable to include. In general, a low ash, low phosphorus and low sulfur lubricating oil composition has a low content of metal detergent and zinc dithiophosphate, and therefore tends to be deteriorated in high temperature cleanliness, oxidation stability or wear resistance. Therefore, it is preferable to add an antioxidant to maintain these performances. As the antioxidant, a diarylamine-based antioxidant and / or a hindered phenol-based antioxidant is preferable. These antioxidants are also effective in improving high temperature cleanability. In particular, diarylamine-based antioxidants are advantageous in this respect because they have a base number derived from nitrogen. On the other hand, hindered phenolic antioxidant is advantageous in prevention of the NO _x oxidation deterioration.

  Examples of hindered phenol antioxidants include 2,6-di-t-butyl-p-cresol, 4,4′-methylenebis (2,6-di-t-butylphenol), 4,4′-methylenebis. (6-t-butyl-o-cresol), 4,4′-isopropylidenebis (2,6-di-t-butylphenol), 4,4′-bis (2,6-di-t-butylphenol), 2,2'-methylenebis (4-methyl-6-tert-butylphenol), 4,4'-thiobis (2-methyl-6-tert-butylphenol), 2,2-thio-diethylenebis [3- (3 5-di-t-butyl-4-hydroxyphenyl) propionate], and octyl 3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, 3- (3,5-di-t- Butyl-4- It may be mentioned hindered phenols such as hydroxyphenyl) octadecyl propionate.

  Examples of diarylamine antioxidants include mixed alkyl diphenylamines having 4 to 9 carbon atoms, p, p′-dioctyldiphenylamine, phenyl-α-naphthylamine, phenyl-β-naphthylamine, alkylated α-naphthylamine, And diarylamines, such as alkylation-phenyl-alpha-naphthylamine, can be mentioned. The hindered phenol-based antioxidant and the diarylamine-based antioxidant can be used alone or in combination as desired. Moreover, you may use together oil-soluble antioxidant other than these.

On the other hand, addition of alkali metal borate hydrate is also effective in terms of imparting high temperature cleanliness or base number. Alkali metal borate hydrate represents a compound represented by the compounds synthesized by the methods described in US Pat. Nos. 3,929,650 and 4,089,790. For example, alkali metal or alkaline earth metal neutral sulfonate is carbonated in the presence of an alkali metal hydroxide to obtain an overbased sulfonate, and boric acid is reacted with this to disperse fine particles of alkali metal borate obtained (A desirable ashless dispersant such as succinimide is allowed to coexist during the carbonation reaction). Here, potassium, sodium, etc. are desirable as the alkali metal. Specific examples include a fine particle dispersion having a particle size of about 0.3 μm or less represented by a composition formula: KB ₃ O ₅ .H ₂ O dispersed in neutral calcium sulfonate and succinimide. From the viewpoint of water resistance, those obtained by replacing potassium with sodium are also used favorably.

  The lubricating oil composition of the present invention preferably further contains a viscosity index improver in an amount of 20% by mass or less (preferably in the range of 1 to 20% by mass). Examples of the viscosity index improver include polymer compounds such as polyalkyl methacrylate, ethylene-propylene copolymer, styrene-butadiene copolymer, and polyisoprene. Alternatively, a dispersion-type viscosity index improver or a multifunctional viscosity index improver that imparts dispersion performance to these polymer compounds can be used. These viscosity index improvers can be used alone, but any viscosity index improver may be used in combination of two or more.

  The lubricating oil composition of the present invention may further contain various auxiliary additives. Examples of such auxiliary additives include compounds such as benzotriazole compounds and thiadiazole compounds that function as metal deactivators. In addition, polyoxyalkylene nonionic surfactants such as polyoxyethylene alkylphenyl ethers functioning as rust inhibitors or demulsifiers and copolymers of ethylene oxide and propylene oxide can also be added. Various compounds that function as an antifoaming agent or pour point depressant can also be added. These auxiliary additives are preferably used in an amount of 3% by mass or less (particularly in the range of 0.001 to 3% by mass) with respect to the lubricating oil composition.

(1) Production of lubricating oil composition (test oil) Lubricating oil composition having a sulfur content of 0.5% by mass or less using the following base oil and additive components as a lubricating oil composition for performance evaluation The product was prepared according to the following recipe. The lubricating oil composition was adjusted to show a 5W30 viscosity grade (SAE viscosity grade) by the addition of a viscosity index improver.

(2) Base oil and additives 1) Base oil (mixture of 46:54 in mass ratio of base oil A and base oil B below)
Base oil A: hydrocracked base oil having a kinematic viscosity at 100 ° C. of 6.4 mm ² / s, a viscosity index of 132, a saturated component of 92% by mass, and a sulfur content of less than 0.001% by mass Base oil B : Hydrocracking base oil having a kinematic viscosity at 100 ° C. of 4.1 mm ² / s, a viscosity index of 127, a saturated component of 92% by mass, and a sulfur content of less than 0.001% by mass 2) Additives

Ashless Dispersant A: Ethylene carbonate reaction-treated succinimide dispersant (nitrogen content: 0.85% by mass, polyisobutenyl succinic anhydride formed by thermal reaction of polybutene having a number average molecular weight of about 2200 and maleic anhydride Next, about 2 mol of this polyisobutenyl succinic anhydride is reacted with a polyalkylene polyamine having an average number of nitrogen atoms of 6.5 (per molecule) to form a bis-type succinimide, which is finally converted into ethylene carbonate. Processed by reaction)
Ashless dispersant B: Succinic acid ester dispersant (TAN: 5 mg KOH / g, polybutene having a number average molecular weight of about 1000 and thermal reaction of maleic anhydride to form polyisobutenyl succinic anhydride, and then this polyisobutenyl succinic acid Alkenyl succinic acid ester obtained by reacting about 1.14 mol of anhydride with 1 mol of pentaerythritol)

Succinimide Mo complex: A compound (molybdenum content) obtained by reacting a small amount of sulfur with a molybdenum complex obtained by reacting a monotype alkenyl succinimide derived from polyisobutene having a number average molecular weight of about 1000 with molybdic acid. : 4.5 mass%, nitrogen content 2.1 mass%, sulfur content: 0.16 mass%)
MoDTC: oxymolybdenum dialkyldithiocarbamate (molybdenum content: 10% by mass, sulfur content: 11% by mass)

Calcium-containing detergent A: monoalkyl (carbon atoms: about 14-18) calcium salicylate (overbasing degree: 2.0, calcium content: 6.2% by mass, sulfur content: 0.12% by mass)
Calcium-containing detergent B: monoalkyl (carbon atom number: about 20 to 28) calcium salicylate (overbasing degree: 8.2, calcium content: 11.4% by mass, sulfur content: 0.17% by mass)
Calcium-containing detergent C: neutral type calcium sulfonate (calcium content: 2.4% by mass, sulfur content: 2.7% by mass)

  ZnDTP: zinc dialkyldithiophosphate (phosphorus content: 7.2% by mass, sulfur content: 14.4%, secondary alcohols having 4 and 6 carbon atoms are used as raw materials)

Antioxidant: Mixture of dialkyldiphenylamine antioxidant and hindered phenol propionate antioxidant Viscosity index improver (non-dispersed ethylene propylene copolymer, Paratone 8057)

(3) Measurement of friction coefficient Using a reciprocating friction tester (HFRR), the friction coefficient of the test oil was measured under the following measurement conditions.
Oil temperature: 105 ° C., load: 400 g, friction distance: 1000 μm, reciprocating cycle: 20 Hz, measurement time: 1 hour

(4) High-temperature deposit formation prevention ability The ability to prevent the formation of high-temperature deposits (deposits) of the test oil was evaluated using a hot tube tester (HTT) under the following measurement conditions. In addition, evaluation was performed by the score by the merit method (10 points perfect score). Therefore, the higher the score, the higher the ability to prevent high-temperature deposit formation.
A glass tube having an inner diameter of 2 mm was vertically arranged in the heater block, and test oil was supplied from the lower part of the glass tube at a flow rate of 0.31 cc / hour and air at a flow rate of 10 cc / minute. This operation was performed for 16 hours while maintaining the temperature of the heater at 280 ° C. Thereafter, the glass tube was removed from the heater block, washed with petroleum ether, dried, and the deposits adhering to the inner surface of the glass tube were observed and scored by the merit method.

(5) Composition and evaluation result of test oil The composition and evaluation result of the test oil are shown in Table 1 below.

Table 1 ────────────────────────────────────
Example 1 Comparative Example 1 Comparative Example 2
────────────────────────────────────
Ashless dispersant A
(Mass%) 3.0 5.5 3.0
Ashless dispersant B
(Mass%) 2.5-2.5
Succinimide Mo complex (Mo equivalent mass ppm) 220 220 −
MoDTC
(Mo equivalent mass ppm) − − 220
Calcium-containing detergent A
(Ca equivalent mass%) 0.19 0.19 0.19
Calcium-containing detergent B
(Ca equivalent mass%) 0.06 0.06 0.06
Calcium-containing detergent C
(Ca equivalent mass%) 0.01 0.01 0.01
ZnDTP
(Mass% in P) 0.04 0.04 0.04
Antioxidant (mass%) 1.0 1.0 1.0
Viscosity index improver (mass%) 5.0 5.0 5.0
Base oil Residual Residual Residual Residual Residue ────────────────────────────────────
Sulfur content (mass%) 0.11 0.11 0.13
────────────────────────────────────
Coefficient of friction 0.05 0.12 0.05
────────────────────────────────────
High temperature deposit generation score 7.5 7.5 5.5
────────────────────────────────────

  From the results shown in Table 1, the lubricating oil composition according to the present invention (the test oil of Example 1) combined the succinimide Mo complex with the succinimide dispersant (ashless dispersant A). Compared to a lubricating oil composition (test oil of Comparative Example 1) that was not combined with an ester dispersant (ashless dispersant B), the ability to prevent high temperature deposit formation was equivalent, but it clearly showed a low coefficient of friction. In comparison with the lubricating oil composition (test oil of Comparative Example 2) prepared by replacing the succinimide Mo complex with the same amount of MoDTC (oxymolybdenum dialkyldithiocarbamate), the test oil of Comparative Example 2 contained sulfur. The amount was increased and the friction coefficient was equivalent, but it was confirmed that the ability to prevent high-temperature deposit formation was inferior.

Claims (15)

A lubricating oil composition for lubricating an internal combustion engine having at least the following components a) to e) dissolved or dispersed in a base oil and having a sulfur content of 0.5% by mass or less:
a) 0.5 to 5.0% by weight of an ashless dispersant which is an alkenyl or alkyl succinimide or a derivative thereof,
b) an ashless dispersant which is 0.5 to 5.0% by weight of an alkenyl or alkyl succinate or a derivative thereof;
c) Molybdenum complex of basic nitrogen compound in an amount of 50 to 1200 ppm by mass as molybdenum.
d) an alkaline earth metal-containing detergent having a total base number of 10 to 400 mg KOH / g in an amount of 0.05 to 1.0% by mass as the amount of alkaline earth metal, and e) 0.05 to 5.0 mass % Antiwear agent.   The lubricating oil composition according to claim 1, wherein the sulfur content is in the range of 0.01 to 0.2 mass%.   The lubricating oil composition according to claim 1, wherein the sulfur content is in the range of 0.05 to 0.12 mass%.   The lubricating oil composition according to claim 1, which further contains a viscosity index improver and is a multigrade engine oil having a SAE viscosity grade of 0W5, 0W10, 0W15, 0W20, 0W30, 5W20, 5W30, 10W20, or 10W30.   The lubricating oil composition according to claim 1, wherein the content of the ashless dispersant which is an alkenyl or alkyl succinimide or a derivative thereof as component a) is 1.0 to 4.0% by mass.   The lubricating oil composition according to claim 1, wherein the content of the ashless dispersant which is an alkenyl or alkyl succinic acid ester of component b) or a derivative thereof is 1.0 to 4.0% by mass.   The mass ratio of the alkenyl or alkyl succinimide of component a) or an ashless dispersant that is a derivative thereof to the ashless dispersant of component b) alkenyl or alkyl succinate or a derivative thereof is 1: 4 to The lubricating oil composition of claim 1 in the range of 4: 1.   The lubricating oil composition according to claim 1, wherein the molybdenum complex of the basic nitrogen compound of component c) contains sulfur in an amount not exceeding 1% by mass.   The lubricating oil composition according to claim 1, wherein the molybdenum complex of the basic nitrogen compound of component c) contains 0.05 to 0.5% by mass of sulfur.   The lubricating oil composition according to claim 1, wherein the molybdenum complex of the basic nitrogen compound of component c) is a molybdenum complex of succinimide.   The lubricating oil composition of claim 1, wherein the alkaline earth metal-containing detergent of component d) comprises an alkaline earth metal salicylate.   The lubricating oil composition of claim 1, wherein the antiwear agent is a zinc dialkyldithiophosphate.   The lubricating oil composition according to claim 1, further comprising an antioxidant.   The lubricating oil composition according to claim 1, which is used for lubricating an internal combustion engine operated using a fuel oil having a sulfur content of 0.001% by mass or less.   A method for operating an internal combustion engine mounted on a vehicle for land travel, which is operated using fuel oil having a sulfur content of 0.001% by mass or less, using the lubricating oil composition according to claim 1.