Field of the Invention

This invention relates to a lubricating oil composition having excellent wear resistance.

Background of the Invention Greater fuel efficiency is demanded of automobiles from the standpoint of petroleum resource depletion and environmental protection. In particular, lubricating oil compositions with excellent performance are required as automobiles become lighter, engines improve in terms of energy efficiency, and drive trains improve in terms of driving force transmission.

For example, "Types of Additives and Performance (1): Anti-Wear Agents/Extreme Pressure Agents", R.J. Hartley et al., Tribologist, Vol. 40, No. 4, p. 326, 1995, notes the improvements in the wear resistance of iron materials in internal combustion engines when an anti-wear agent such as a zinc dialkyldithiophosphate is added to a lubricating oil for internal combustion engines.

The wear resistance of conventional lubricating oil compositions when used on aluminum and/or aluminum alloys, which are the main materials in engines, has not been studied sufficiently. In particular, with the reduction in size of engines in recent years, the materials that constitute the friction-bearing surface have a very large effect on wear resistance, and it has been found that excellent wear resistance is not always obtained for aluminum and/or aluminum alloys even when wear resistance for iron-based materials is high. Therefore, it is an object of the present invention to provide a novel lubricating oil composition having excellent wear resistance even when used on aluminum and/or aluminum alloys.

As a result of extensive research, the present inventors discovered that a lubricating oil composition containing specific components in specific amounts could achieve this object. Specifically, the present invention is the following.

Summary of the Invention

The present invention is a lubricating oil composition comprising a base oil, molybdenum dithiocarbamate, and a metal-based detergent, wherein the molybdenum dithiocarbamate content C _MO in terms of molybdenum atoms relative to the total amount of lubricating oil composition is greater than 200 ppm and 2,000 ppm or less, and the amount of sulfonated ash relative to the total amount of lubricating oil composition is less than 0.85% by mass.

The metal-based detergent preferably includes a calcium-based detergent and a magnesium-based detergent. The calcium-based detergent content Cc _a in terms of calcium atoms relative to the total amount of lubricating oil composition may be from 100 ppm to 2,000 ppm.

The magnesium-based detergent content C _Mg in terms of magnesium atoms relative to the total amount of lubricating oil composition may be from 50 ppm to 1,000 ppm.

(C _Mg +C _Mo /2)/Cca may be from 0.4 to 1.2.

The lubricating oil composition may further comprise a zinc dialkyldithiophosphate. The lubricating oil composition may be used to lubricate a sliding surface containing aluminum and/or an aluminum alloy.

Detailed Description of the Invention

The present invention is able to provide a novel lubricating oil composition having excellent wear resistance even when used on aluminum and/or aluminum alloys.

The following is a description of the components, amounts of components, physical characteristics and properties, production method, and applications for a lubricating oil composition of the present invention.

When an upper limit value and a lower limit value are mentioned for a certain numerical range, all combinations of numerical ranges including these values are included therein. Also, "from numerical value A to numerical value B" means "numerical value A or more and numerical value B or less." Here, "or more" and "or less" can be read to mean "greater than" and "less than."

The kinematic viscosities in the present invention are values measured in accordance with JIS K2283: 2000.

The lubricating oil composition contains a base oil, a metal-based detergent, and molybdenum dithiocarbamate. The lubricating oil composition preferably contains a zinc dialkyldithiophosphate. The lubricating oil composition may also contain other components.

There are no particular restrictions on the base oil, and any mineral oil, synthetic oil, animal or plant oil, or combination thereof commonly used in a lubricating oil composition can be selected. Specific examples include base oils belonging to Group 1, Group 2, Group 3, and Group 4 of the API (American Petroleum Institute) base oil categories, which can be used alone or in a mixture. Group 1 base oils include paraffinic mineral oils obtained by an appropriate combination of refining methods such as solvent refining, hydrorefining, and dewaxing performed on lubricating oil fractions obtained from atmospheric distillation of crude oil.

Group 2 base oils include paraffinic mineral oils obtained by an appropriate combination of refining methods such as hydrorefining and dewaxing performed on lubricating oil fractions obtained from atmospheric distillation of crude oil.

Group 3 base oils and Group 2 base oils include paraffinic mineral oils produced by a high degree of hydrorefining performed on lubricating oil fractions obtained from the atmospheric distillation of crude oil, base oils refined using the Isodewax process which dewaxes and substitutes the wax produced by the dewaxing process with isoparaffins, and gas-to-liquid (GTL) oils synthesized using the Fischer-Tropsch method of converting natural gas to liquid fuel. Use of these base oils is preferred. GTL base oils have a very low sulfur content and aromatic content as well as a very high paraffin ratio compared to mineral-oil base oils refined from crude oil. As a result, they have excellent oxidative stability and experience extremely low evaporation loss. Use of these as the base oil is especially preferred.

Examples of synthetic oils include polyolefins, dibasic acid diesters, trimellitic acid triesters, polyol esters, alkylbenzenes, alkylnaphthalenes, polyoxyalkylene glycols, polyoxyalkylene glycol esters, polyoxyalkylene glycol ethers, polyphenyl ethers, dialkyldiphenyl ethers, fluorine-containing compounds (perfluoropolyethers, fluorinated polyolefins, etc.), and silicone. The polyolefins include polymers of various olefins or hydrides of these. Any polyolefin can be used, and examples include ethylene, propylene, butene, and a-olefins with five or more carbon atoms. In the production of a polyolefin, one type of olefin or a combination of two or more types can be used. Especially preferred are the polyolefins known as poly-a-olefins (PAOs), which are Group 4 base oils.

Any component common in the art can be used as the metal-based detergent. Examples of metal-based detergents include alkali metal-based detergents (alkali metal sulfonates, alkali metal phenates, and alkali metal salicylates) and alkaline earth metal-based detergents (alkaline earth metal sulfonates, alkaline earth metal phenates, and alkaline earth metal salicylates). These metal- based detergents can be used alone or in combinations of two or more.

The metal-based detergent preferably includes a calcium-based detergent and/or a magnesium-based detergent. The calcium-based detergent is preferably calcium salicylate. The magnesium-based detergent is preferably magnesium sulfonate.

Calcium salicylate and magnesium sulfonate are preferred forms of the metal-based detergents. These metal- based detergents will be described in detail, but the metal- based detergents are not limited to these examples.

Any calcium salicylate common in the art can be used.

An example is the compound represented by formula (1) below. In this formula, R can be a hydrocarbon group having from 4 to 30 carbon atoms, but a linear or branched alkyl group having from 6 to 18 carbon atoms is preferred.

Any magnesium sulfonate common in the art can be used. An example is the compound represented by formula (2) below.

In this formula, R can be a hydrocarbon group having from 4 to 30 carbon atoms, but a linear or branched alkyl group having from 6 to 18 carbon atoms is preferred.

Any molybdenum dithiocarbamate (MoDTC) common in the art can be used. An example is the compound represented by formula (3) below.

In this formula, R1 to R4 represent an alkyl group, and XI to X4 represent an oxygen atom or a sulfur atom. More specifically, in this formula, alkyl groups Rl, R2, R3 and R4 are each independently a lipophilic group having from 2 to 30 carbon atoms.

Here, the molybdenum dithiocarbamate is preferably a compound represented by formula (4) below.

In this formula, Rl to R4 represent an alkyl group. More specifically, alkyl groups Rl, R2, R3 and R4 are each independently a lipophilic group having from 2 to 30 carbon atoms.

Any zinc dialkyldithiophosphate common in the art can be used. It is typically a compound represented by formula (5) below.

In this formula, R ^a , R ^b , R ^c and R ^d each independently represent a hydrocarbon group having from 3 to 24 carbon atoms. Preferred examples of hydrocarbon groups include linear or branched alkyl groups having from 3 to 24 carbon atoms, linear or branched alkenyl groups having from 3 to 24 carbon atoms, cycloalkyl groups or linear or branched alkylcycloalkyl groups having from 5 to 13 carbon atoms, aryl groups or linear or branched alkylaryl groups having from 6 to 18 carbon atoms, and arylalkyl groups having from 7 to 19 carbon atoms. These alkyl groups and alkenyl groups may be primary, secondary or tertiary groups.

Specific examples of zinc dialkyldithiophosphates include zinc diisopropyl dithiophosphate, zinc diisobutyl dithiophosphate, zinc di-sec-butyl dithiophosphate, zinc di- sec-pentyl dithiophosphate, zinc di-n-hexyl dithiophosphate, zinc di-sec-hexyl dithiophosphate, zinc di-octyl dithiophosphate, zinc di-2-ethylhexyl dithiophosphate, zinc di-n-decyldithiophosphate, zinc di-n-dodecyl dithiophosphate, zinc diisotridecyl dithiophosphate, and any combinations and mixtures thereof. These anti-wear agents can be used alone or in combinations of two or more.

Depending on the intended application, the lubricating oil composition may also contain other components common in the art in addition to those described above. Examples of these other components include additives such as dispersants, defoamers, pour point depressants, metal deactivators, antioxidants, and viscosity index improvers. The lubricating oil composition may also contain a detergent or anti-wear agent other than the components described above.

The base oil content relative to the total amount of lubricating oil composition is preferably from 50 to 95% by mass, more preferably from 60 to 90% by mass, and even more preferably from 70 to 85% by mass.

The metal-based detergent content relative to the total amount of lubricating oil composition may be determined in terms of metal atoms and, for example, is preferably from 0.05 to 0.5% by mass, more preferably from 0.1 to 0.4% by mass, and even more preferably from 0.13 to 0.25% by mass.

Preferred embodiments of the metal-based detergent are calcium salicylate and magnesium sulfonate, and the specific content of these metal-based detergents will now be explained.

The calcium salicylate content Cc _a relative to the total amount of lubricating oil composition in terms of calcium atoms is preferably from 100 to 2,000 ppm, more preferably from 500 to 1,800 ppm, even more preferably from 700 to 1,500 ppm, and still more preferably from 900 to 1,400 ppm.

The magnesium sulfonate content C _Mg relative to the total amount of lubricating oil composition in terms of magnesium atoms is preferably 50 to 1,000 ppm, more preferably from 200 to 800 ppm, and even more preferably from 300 to 600 ppm.

The molybdenum dithiocarbamate content C _MO relative to the total amount of lubricating oil composition in terms of molybdenum atoms is preferably more than 200 ppm and 2,000 ppm or less, more preferably from 250 ppm to 1,700 ppm, even more preferably from 300 to 1,500 ppm, and still more preferably from 400 to 1,200 ppm. When the amount of molybdenum dithiocarbamate is within this range, the wear resistance of aluminum and aluminum alloys can be improved while maintaining excellent fuel economy.

The ratio (C _Mg +C _Mo /2) /Cca is preferably from 0.4 to 1.2 (that is, 0.35 or more and less than 1.25), and more preferably from 0.4 to 0.9 (that is, 0.35 or more and less than 0.95).

The total amount of Cca , CMg , and CMO ( Cca + CMg + CMO ) is preferably from 1,000 to 4,000 ppm, more preferably from 1,500 to 3,000 ppm, even more preferably from 1,700 to 3,000 ppm, and still more preferably from 1,800 to 2,750 ppm.

The zinc dialkyldithiophosphate content Czn relative to the total amount of lubricating oil composition in terms of phosphorus atoms is preferably from 200 to 2,000 ppm, more preferably from 300 to 1,500 ppm, and even more preferably from 500 to 1,000 ppm.

The balance may be other components. The amount of other components relative to the total amount of lubricating oil composition may be 1% by mass or more, 3% by mass or more, or 5% by mass or more, and 25% by mass or less, 20% by mass or less, or 15% by mass or less.

The amount of sulfated ash relative to the total amount of lubricating oil composition is preferably less than 0.85% by mass or 0.84% by mass or less. When the amount of sulfated ash is within this range, the effects of the present invention increase and the engine complies with emission regulations. There are no particular restrictions on the lower limit value, which can be 0.1% by mass, 0.3% by mass, or 0.5% by mass.

The sulfated ash content can be measured using the method specified in JIS K 2272. The sulfated ash content can be adjusted by changing, for example, the amount of the metal-based detergent that is used.

Wear resistance is evaluated with a Falex block-on- ring friction tester (LFW-1) using a ring made of alloy steel (AISI 4620) and a block of aluminum alloy (AC8A-T6). The testing conditions include a ring rotation speed of 1,000 rpm, a load of 200 N, an oil temperature of 80°C, and an operating time of 15 minutes after applying a load of 200 N. The width (mm) of the wear on the block is measured after the test.

In terms of wear resistance, a wear width on the block after testing of 5 mm or less is preferred, and of 4.5 mm or less is especially preferred. When the wear resistance is within this range, a reduced size engine has sufficient durability.

The lubricating oil composition can be produced using any method common in the art. The components may be mixed together as appropriate, and there are no particular restrictions on the order in which the components are mixed together. The additives may be added in the form of an additive package containing a mixture of different additives.

A lubricating oil composition of the present invention can improve the balance between cleanliness, fuel economy, and wear resistance (especially wear resistance of aluminum and/or aluminum alloys). A lubricating oil composition of the present invention is suitable for use in gasoline engines with exhaust gas regulating measures (equipped with a GPF or gasoline particulate filter), and gasoline engines compatible with low sulfated ash engine oils comparable to the ACEA C2, C3, and C5 Mid SAPS categories in Europe (low sulfated ash engine oil standards for gasoline engine vehicles and diesel engine vehicles compatible with catalysts and GPF/DPF devices). A lubricating oil composition of the present invention is a low-viscosity engine oil with SAE viscosity grades 0W-20, OW-16, and OW-8, which are suitable for use in an engine with high fuel efficiency.

There are no particular restrictions on applications for these lubricating oil compositions, and they can be used as lubricating oils in a wide range of machinery. For example, they can be used to lubricate rotating components and sliding components in vehicles and production machinery. These lubricating oil compositions are preferably used as lubricating oils for the sliding surfaces of components containing aluminum and/or aluminum alloys (or an internal combustion engine containing these metal materials in its components).

Examples

The following ingredients were mixed together in the amounts (% by mass) shown in the tables to produce the lubricating oil compositions in the examples and comparative examples. The SAE viscosity grade of each example is 0W-20.

• Base Oil - GTL Base Oil

• Viscosity Index Improver - Polymethacrylate

• Metal-Based Detergent A - Calcium-Based Detergent:

Hyperbasic Calcium Salicylate

• Metal-Based Detergent B - Magnesium-Based Detergent:

Hyperbasic Magnesium Sulfonate

• Antiwear Agent - Zinc Dialkyldithiophosphate

• Friction Modifier - Molybdenum Dithiocarbamate • Ashless Dispersant - Boron-Free Dispersant: Alkenyl Succinimide; Boron-Containing Dispersant: Alkenyl Succinimide

• Antioxidant - Mixture of Amine-Based Antioxidant and Phenol-Based Antioxidant

• Defoamer - Kerosene Solution Containing 3% by Mass Di ethylpolysiloxane (DCF)

The amount of metal-based detergent and friction modifier in each lubricating oil composition is expressed as the amount of calcium, magnesium, or molybdenum (mass ppm) in the metal component of these agents relative to the total mass of the lubricating oil composition.

For other additives, refer to the general amounts added, which relative to the total mass of the lubricating oil composition are a nitrogen equivalent of 500 to 1,500 ppm (boron equivalent of 0 to 200 ppm) in the case of ashless dispersants, a zinc equivalent of 500 to 1,200 ppm in the case of anti-wear agents, and a silicon equivalent of 3 to 20 ppm in the case of defoamers. The amount of viscosity index improver is 20% by mass or less, and the amount of antioxidant is 5% by mass or less.

The equivalent amounts for each component are measured in accordance with well-known methods. For example, JPI-5S-38 is used for calcium, magnesium and molybdenum, and JIS K 2609 is used for nitrogen.

The sulfonated ash was used in each lubricating oil composition as shown in the tables.

A wear resistance test was performed using the method described above. The width (mm) of the wear in each block after the test was completed is shown in the table. As for the evaluation standards, when the wear width was 4.5 mm or less, an evaluation of n was assigned. When the wear width was 5.0 mm or less, an evaluation of ; was assigned. When the wear width was greater than 5.0 mm, an evaluation of x was assigned.

Table 1

Table 2