JP2000026879A - Lubricating oil composition for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low-fuel-consumption lubricating oil compsn. for internal combustion engines which is excellent in reducing the friction loss of automotive internal combustion engines and is esp. suitable as a diesel engine oil or a gasoline engine oil. SOLUTION: This compsn. is prepd. by compounding a base oil comprising a mineral oil and/or a synthetic lubricating oil with, based on the compsn., 0.5-40 wt.% partial ester of a polyhydric alcohol, provided (A) the polyhydric alcohol has at least 4 hydroxyl groups in one molecule and (B) the partial ester has a hydroxyl value of 30 mgKOH/g or higher and an ester value of 50 mgKOH/g or higher.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lubricating oil composition for an internal combustion engine, and more particularly, to a lubricating oil composition for an internal combustion engine which is excellent in reducing friction loss to an internal combustion engine of an automobile and is particularly suitable as a diesel engine oil or a gasoline engine oil. The present invention relates to a fuel-saving lubricating oil composition.

[0002]

2. Description of the Related Art Generally, an engine having a sliding portion is provided.
Lubricating oil is used in internal combustion engines, automatic transmissions, shock absorbers, drive system devices such as power steering, gears, and the like in order to facilitate their operations. In particular, lubricating oil for internal combustion engines mainly lubricates various sliding parts such as piston rings and cylinder liners, bearings for crankshafts and connecting rods, and valve mechanisms including cams and pallet lifters, as well as cooling and combustion generation in the engine. It acts to clean and disperse things and prevent rust and corrosion. As described above, lubricating oils for internal combustion engines are required to have various performances, and in recent years, advanced performances have been required in accordance with higher performance, higher output, and more severe operating conditions of internal combustion engines. I have.
Therefore, various additives for satisfying such required performance, for example, an antiwear agent, a metal detergent, an ashless dispersant, an antioxidant, and the like are blended in the lubricating oil for an internal combustion engine. As a basic function of a lubricating oil for an internal combustion engine, it is important to make the engine operate smoothly, particularly under all conditions, to prevent wear and seizure. Most of the engine lubrication part is in a fluid lubrication state, but it tends to be in a boundary lubrication state at the valve operating system or at the top and bottom dead center of the piston. It is provided by addition. By the way, in an internal combustion engine, since the energy loss in a friction portion involving lubricating oil is large, as a measure to reduce friction loss and fuel consumption, for example, as shown in JP-B-3-23595, a friction reducing agent is used. Initially, lubricating oils that combine various additives are used. Automotive internal combustion engines have a wide range of oil temperatures, speeds,
The lubricating oil for an internal combustion engine is required to have excellent friction characteristics under a wide range of operating conditions in order to operate under a load and thus further improve fuel efficiency.

Conventionally, in order to lower the friction coefficient of lubricating oil, an organic molybdenum compound has been added, and a combination of an organic molybdenum compound and a metallic detergent (for example, Japanese Patent Publication No. 6-62).
983), or a combination of an organic molybdenum compound and a sulfur-based compound (for example, Japanese Patent Publication No. 5-83599). Examples of the friction reducing agent other than the organic molybdenum compound include a combination of a glycerol partial ester of a fatty acid and an organic copper compound (for example, Japanese Patent Publication No. 3-77837), a pentaerythritol ester and a succinimide or dithiophosphoric acid. A combination with zinc (for example, JP-A-55-80494 and JP-A-55-82195) has been proposed.
However, in a diesel engine, unlike a gasoline engine, a large amount of soot produced by incomplete combustion of light oil is mixed into engine oil. It is said that this soot has an activity of adsorbing a polar additive in oil and scraping off a film formed on a friction surface because of its surface activity. Therefore, under such severe frictional conditions that soot is mixed in oil, the mode of action as a friction reducing agent is significantly different from that of gasoline engines, and conventional friction reducing agents, that is, organic molybdenum compounds, amines,
It is said that amides, phosphate esters and the like do not show a sufficient effect on reducing fuel consumption of diesel engines.
For this reason, in order to improve the fuel-saving performance of a diesel engine, only a slight blending of an alkali metal borate hydrate (for example, Japanese Patent Publication No. 1-48319) has been proposed. On the other hand, lowering the viscosity of lubricating oils is also known to be effective as a means of improving fuel efficiency, and a viscosity index improver such as polymethacrylate or ethylene-propylene copolymer was added to the low-viscosity lubricating oil. Multi-grade diesel engine oils are commonly used. However, the fuel efficiency reduction effect of a multi-grade diesel engine oil to which only these viscosity index improvers were added was insignificant and could not be said to be sufficient. For this reason, there has been a strong demand for the technical development of a lubricating oil composition for an internal combustion engine that exhibits a sufficient fuel consumption reduction effect not only in a gasoline engine but also in a diesel engine.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a fuel-saving lubricating oil composition for an internal combustion engine which is excellent in friction loss reduction of an internal combustion engine of an automobile and is particularly suitable as a diesel engine oil or a gasoline engine oil. It is in.

[0005]

Means for Solving the Problems The present inventors have made intensive studies to overcome the problems of the prior art, and as a result, have prepared a lubricating oil composition containing a partial ester of a polyhydric alcohol. It has been found that a low coefficient of friction can be obtained even under lubricating conditions in which is mixed. The present invention has been completed based on these findings.

That is, according to the present invention, a base oil composed of mineral oil and / or synthetic lubricating oil is added in an amount of 0.1% based on the total amount of the composition.
A lubricating oil composition containing 5 to 40% by weight of a partial ester of a polyhydric alcohol, wherein (A) the polyhydric alcohol has four or more hydroxyl groups in one molecule, and (B) the polyhydric alcohol has The partial ester of a dihydric alcohol has a hydroxyl value of 30 m
A lubricating oil composition having a gKOH / g or more and an ester value of 50 mgKOH / g or more is provided. Further, according to the present invention, there is provided the above lubricating oil composition, wherein the polyhydric alcohol partial ester is a sorbitan fatty acid partial ester.

The present invention relates to a fuel-saving lubricating oil composition for an internal combustion engine containing a partial ester of a polyhydric alcohol, as described above.
The following are included: (1) The lubricating oil composition as described above, wherein the partial ester of a polyhydric alcohol has a kinematic viscosity at 100 ° C. of 0.5 to 50 mm ² / s. (2) The lubricating oil composition as described above, wherein the acid component as a raw material of the partial ester of the polyhydric alcohol is a fatty acid. (3) The lubricating oil composition according to (2), wherein the fatty acid is a saturated fatty acid or an unsaturated fatty acid having 12 to 24 carbon atoms. (4) The partial ester of the polyhydric alcohol has a hydroxyl value of 150 to 250 mgKOH / g and an ester value of 10
The lubricating oil composition as described above, wherein the amount is from 0 to 200 mgKOH / g. (5) The lubricating oil composition as described above, wherein the polyhydric alcohol is at least one selected from pentaerythritol, dipentaerythritol, tripentaerythritol, ditrimethylolpropane, sorbitol, sorbitan, and a mixture thereof. .

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. 1. Lubricating Base Oil The base oil used in the lubricating oil composition of the present invention is not particularly limited, and any base oil generally used as a lubricating base oil can be used. That is, those which correspond to these include mineral oil, synthetic lubricating oil, or a mixed oil thereof.

As the mineral oil, a solvent-refined raffinate and a lubricating oil raw material obtained by treating a lubricating oil raw material derived from atmospheric or reduced pressure distillation of a crude oil with an aromatic extraction solvent such as phenol, furfural and N-methylpyrrolidone are used. Hydrotreated oil obtained by contacting hydrogen under hydrotreating conditions in the presence of a hydrotreating catalyst, isomers obtained by contacting wax with hydrogen under isomeric conditions in the presence of a catalyst for isomerization And a lubricating oil fraction obtained by combining a solvent purification step, a hydrotreating step, an isomerization step, and the like. In any of the production methods, steps such as a dewaxing step, a hydrofinishing step, and a clay treatment step can be arbitrarily adopted by a conventional method. Specific examples of the mineral oil include light neutral oil, medium neutral oil, heavy neutral oil, bright stock, and the like. The base oil can be adjusted by appropriately mixing so as to satisfy required properties.

Examples of the synthetic lubricating oil include poly-α-olefin, α-olefin oligomer, polybutene, alkylbenzene, polyol ester, dibasic acid ester, polyoxyalkylene glycol, polyoxyalkylene glycol ether, silicone oil and the like. be able to.

These base oils can be used alone or in combination of two or more, and mineral oil and synthetic oil may be used in combination. The base oil used in the present invention is usually ^{2 to 20} mm 2/100 ° C.
s with a kinematic viscosity of 3 to 15 mm ² / s
Range. If the kinematic viscosity of the lubricating base oil is too high, the stirring resistance will increase, and the friction coefficient in the fluid lubrication region will increase, and the fuel-saving characteristics will deteriorate. There is a problem in that wear increases in sliding parts such as a valve train, a piston, a ring, and a bearing.

2. Partial Ester of Polyhydric Alcohol In the lubricating oil composition of the present invention, the partial ester of polyhydric alcohol blended as an essential component is, as described below, a specific polyhydric alcohol component as a raw material, It is important that the valency and the ester number are above a certain value.

The polyhydric alcohol component used as the raw material of the partial ester of the polyhydric alcohol used in the present invention must have four or more hydroxyl groups in one molecule. Examples of such a polyhydric alcohol component having four or more hydroxyl groups in one molecule include pentaerythritol, dipentaerythritol, tripentaerythritol, ditrimethylolpropane, sorbitol, and sorbitol in which sorbitol is intramolecularly dehydrated. And these one
Seeds may be used, or two or more kinds may be appropriately mixed and used. Among them, sorbitan is preferably used. In the case of a trihydric polyhydric alcohol having less than 4 hydroxyl groups in one molecule, for example, a low coefficient of friction cannot be obtained under lubricating conditions containing soot, and the object of the present invention cannot be achieved.

The acid component as a raw material of the partial ester of the polyhydric alcohol used in the present invention preferably has 3 to 3 carbon atoms.
A saturated fatty acid or unsaturated fatty acid having 24 carbon atoms is used, and a saturated fatty acid or unsaturated fatty acid having 12 to 18 carbon atoms is more preferable. Further preferred fatty acids include, for example, lauric acid, tridecylic acid, myristic acid,
Examples include pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, and stearic acid. If the fatty acid has a short chain length, a low coefficient of friction may not be obtained under lubricating conditions in which soot is mixed, and compatibility and stability in a lubricating oil may be reduced.

In the lubricating oil composition of the present invention, the partial ester of a polyhydric alcohol used as an essential friction-reducing component must have a hydroxyl value of 30 mg KOH / g or more and an ester value of 50 mg KOH / g or more, and is preferable. Has a hydroxyl value of 150 to 250 mg.
KOH / g, ester value of 100 to 200 mg KOH /
g. The hydroxyl value and ester value are determined according to JIS.
It is measured according to K0070. A hydroxyl value of less than 30 mg KOH / g and an ester value of 50 mg K
If it is less than OH / g, a low coefficient of friction cannot be obtained under lubricating conditions in which soot is mixed. Although the theory that partial esters exhibit low friction properties under soot-containing lubrication conditions has not yet been clarified, the ester groups and alcohol groups in the partial esters of polyhydric alcohols, which are friction reducers, are transferred to metal surfaces. In addition, the acid component of the raw material influences the molecular film thickness of the adsorption, and as a result, the partial ester shows lower friction characteristics than the full ester or full alcohol.

In the lubricating oil composition of the present invention, the content of the partial ester of the polyhydric alcohol is based on the total amount of the composition.
It is 0.5 to 40% by weight, preferably 5 to 20% by weight. If the content is less than 0.5% by weight, a low coefficient of friction cannot be obtained under lubricating conditions in which soot is mixed. On the other hand, if it exceeds 40% by weight, no improvement in the friction reducing effect can be obtained, but rather the seal rubber compatibility and the like deteriorate, which is not preferable. Since the partial ester of polyhydric alcohol is also used as a base oil, the kinematic viscosity at 100 ° C. is desirably 0.5 to 50 mm ² / s. 100
If the kinematic viscosity at 0 ° C. is less than 0.5 mm ² / s, there is a problem that wear increases in sliding parts such as a valve train of an internal combustion engine, a piston, a ring and a bearing, and oil consumption may increase. On the contrary, the kinematic viscosity at 100 ° C. is 5
If it exceeds 0 mm ² / s, there is a possibility that compatibility with other base oils may become a problem, and further, the stirring resistance becomes large,
Further, the friction coefficient in the fluid lubrication region is increased, and there is a disadvantage that the fuel-saving characteristics are deteriorated.

Further, as the partial ester of the polyhydric alcohol, as described above in connection with the raw material component, a sorbitan fatty acid partial ester is preferably used. In particular, the acyl group is preferably a carboxylic acid having 3 to 24 carbon atoms, among which a partial ester of a saturated fatty acid or unsaturated fatty acid is preferably used, and more preferably a partial ester of a saturated fatty acid or unsaturated fatty acid having 12 to 18 carbon atoms. Used. One type of fatty acid may be used, or two or more types may be appropriately mixed. As the sorbitan fatty acid partial ester, a mono-, di-, or triester is used, and these may be used alone or in an appropriate combination of two or more.

3. Other Additive Components The lubricating oil composition of the present invention contains a partial ester of the above-mentioned polyhydric alcohol as an essential component in the lubricating base oil. In order to secure the performance adapted to them, various additives such as viscosity index improver, pour point depressant, ashless dispersant, metal detergent, antioxidant, friction A reducing agent, an antiwear agent, an extreme pressure agent, a metal deactivator, a rust inhibitor, an antifoaming agent, a corrosion inhibitor, a coloring agent, and the like can be appropriately added as long as the object of the invention is not impaired.

Examples of the viscosity index improver include polymethacrylates, olefin copolymers (polyisobutylenes, ethylene-propylene copolymers), polyalkylstyrenes, styrene-butadiene hydrogenated copolymers, and styrene-maleic anhydride. Ester copolymers and the like are mentioned, and these are usually used at a ratio of 1 to 30% by weight.

As a pour point depressant, generally, ethylene-
Vinyl acetate copolymer, condensate of chlorinated paraffin and naphthalene, condensate of chlorinated paraffin and phenol,
Examples thereof include polymethacrylate and polyalkylstyrene, and among them, polymethacrylate is preferably used. These are usually used at a ratio of 0.01 to 5% by weight.

Examples of the ashless dispersant include polyalkenylsuccinimide-based, polyalkenylsuccinamide-based, benzylamine-based, succinic ester-based, succinic ester-amide-based, and boron-containing ashless dispersants.
Among them, polyalkenyl succinimide (polybutenyl succinimide) is preferably used. These are usually used at a ratio of 0.1 to 15% by weight.

As the metal detergent, Ca, Mg, Ba,
Na and other sulfonate-based, phenate-based, salicylate-based, and phosphonate-based ones.
It is used in a proportion of from 0.5 to 5% by weight.

Examples of the antioxidant include amine antioxidants such as alkylated diphenylamine, phenyl-α-naphthylamine and alkylated phenyl-α-naphthylamine; 2,6-ditert-butylphenol;
Phenolic antioxidants such as 4,4'-methylenebis- (2,6-ditert-butylphenol); sulfur-based antioxidants such as dilauryl-3,3'-thiodipropionate; and phosphorus-based oxidation such as phosphite. Inhibitors Further, zinc dithiophosphate and the like can be mentioned, and among them, amine antioxidants and phenolic antioxidants are preferably used. These are usually used at a ratio of 0.05 to 5% by weight.

As the friction reducing agent, in addition to the partial ester of the polyhydric alcohol which is an essential component, for example, organic molybdenum compounds, fatty acids, higher alcohols, fatty acid esters, oils and fats, amines, amides, sulfurized esters, phosphoric acid Examples include esters, phosphites, and phosphate amine salts. These are usually used at a ratio of 0.05 to 3% by weight.

As the antiwear agent, generally, zinc dithiophosphate, metal dithiophosphate (Pb, Sb, Mo, etc.), metal dithiocarbamate (Zn, Pb, Sb, Mo, etc.), metal naphthenate (Pb, etc.) And metal salts of fatty acids (such as Pb), boron compounds, phosphate esters, phosphite esters, phosphate amine salts, and the like. Of these, zinc dithiophosphate is preferably used. These are usually used at a ratio of 0.1 to 5% by weight.

Examples of extreme pressure agents generally include ashless sulfide compounds, sulfurized oils and fats, phosphate esters, phosphite esters, phosphate ester amine salts, and the like.
Usually, it is used in a ratio of 0.05 to 3% by weight.

Examples of the metal deactivator include benzotriazole, a triazole derivative, a benzotriazole derivative, a thiadiazole derivative and the like, and these are usually used at a ratio of 0.001 to 3% by weight.

Examples of the rust preventive include fatty acids, alkenyl succinic acid half esters, fatty acid soaps, alkyl sulfonates, polyhydric alcohol fatty acid esters, fatty acid amines, paraffin oxide, and alkyl polyoxyethylene ether. Is usually 0.01 to 3
Used in percentages by weight.

Examples of the antifoaming agent include dimethylpolysiloxane, polyacrylate and the like, and usually, a very small amount, for example, about 0.002% by weight is added. Furthermore,
In the lubricating oil composition of the present invention, other additives such as a corrosion inhibitor and a coloring agent can be used as desired.

[0030]

Next, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not particularly limited to these examples. The friction coefficient in the examples and comparative examples was measured using a reciprocating (SRV) friction tester, and a friction test was performed under the following test conditions. Test conditions-Test piece (friction material): SUJ-2-Plate: 24 mm diameter x 7 mm-Cylinder: 15 mm diameter x 22 mm-Temperature: 80 ° C-Load: 150 N-Amplitude: 1.5 mm-Frequency: 50 Hz-Test time : 30 minutes

Examples 1 to 3 In Example 1, a solvent-refined paraffinic mineral oil (viscosity at 100 ° C .: 5.8 mm ² / s) was used as a lubricating base oil, and a partial ester of a polyhydric alcohol was used. Hydroxyl value of sorbitan dioleate as a main component is 1
95 mgKOH / g, ester value 150 mgKOH /
g and lubricating oil compositions containing the types and amounts of each additive component shown in Table 1 were prepared, and the friction coefficient was measured. In Examples 2 and 3, in addition to the composition of Example 1, carbon black (trade name: MA-11, manufactured by Mitsubishi Chemical Corporation, average particle size: 29 nm) supposed to further simulate soot in oil was used. 1.0% by weight in Example 2 and 3% by weight in Example 2 were added to prepare a lubricating oil composition, and the friction coefficient was measured. Table 1 shows the results.

[0032]

[Table 1]

Comparative Examples 1 to 9 Lubricating oil compositions were prepared by blending the lubricating base oil components, additive components and carbon black shown in Table 1 in the proportions shown in the same table. Comparative Examples 1 to 9 do not contain a partial ester of a polyhydric alcohol, and Comparative Examples 7 to 9 have a C ₈ / C _{10 of} trimethylolpropane that is a trihydric alcohol instead of a partial ester of a polyhydric alcohol. Contains acid full esters. Table 2 shows the results of measuring the coefficient of friction in the same manner as in Examples 1 to 3.

[0034]

[Table 2]

From the results of the above Examples and Comparative Examples, the lubricating oil composition containing a specific ester of a polyhydric alcohol in the lubricating base oil has a reduced coefficient of friction and further simulates soot. It was also found that the lubricating oil composition to which the carbon black was added also reduced the coefficient of friction.

[0036]

The lubricating oil composition of the present invention contains, as an essential component, a partial ester of a specific polyhydric alcohol, and is excellent in reducing friction loss to an internal combustion engine of an automobile. It can be suitably used as a fuel-saving lubricating oil composition for an engine, particularly as a diesel engine oil or a gasoline engine oil.

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Claims (2)

[Claims] A lubricating oil composition comprising a base oil composed of mineral oil and / or synthetic lubricating oil and 0.5 to 40% by weight, based on the total amount of the composition, of a partial ester of a polyhydric alcohol, A) The polyhydric alcohol has four or more hydroxyl groups in one molecule, and (B) the partial ester of the polyhydric alcohol has a hydroxyl value of 30 mgKOH / g or more and an ester value of 50 mgKOH / g or more. , A lubricating oil composition. 2. The lubricating oil composition according to claim 1, wherein the polyhydric alcohol partial ester is a sorbitan fatty acid partial ester.