JP6223231B2 - Engine oil composition - Google Patents

Description

  The present invention relates to an engine oil composition that exhibits excellent fuel economy performance, and particularly to an engine oil composition that is suitably used for a diesel engine.

In recent years, global warming has become a global problem, and reduction of CO ₂ contained in automobile exhaust gas has been strongly demanded. In order to reduce the CO ₂ emission amount of an automobile, it is extremely effective to enable a longer distance traveling with limited fuel, that is, to improve the fuel saving performance of the automobile. It is known that not only the improvement of the internal combustion engine hardware but also the improvement of the engine oil, which is the lubricating oil, contributes greatly in improving the fuel efficiency of automobiles.

  As a fuel efficiency improvement technology for engine oil, engine oil is known in which the friction coefficient in the boundary lubrication region where oil film is thin and metal-to-metal contact is reduced by blending a friction modifier such as an organic molybdenum compound. (For example, see (Patent Document 1) and (Patent Document 2)).

  In addition, improving the viscosity characteristics of engine oil is also an effective technique for improving fuel economy, and in recent years, by using a specific viscosity index improver alone or in combination, a high fuel efficiency can be achieved. An engine oil composition imparted with performance has been disclosed (for example, see (Patent Document 3), (Patent Document 4), and (Patent Document 5)).

JP-A-8-302378 (Claims) JP 2001-348591 A (Claims) Japanese Patent Laying-Open No. 2011-21056 (Claims) JP-A-10-53788 (Claims) Japanese Patent Application No. 2008-68415 (Claims)

  However, there is still a great demand for fuel economy performance of engine oil, and it cannot be said that the existing technology is sufficient.

  Among gasoline engine oils, low-viscosity oils such as 5W-20 and 0W-20 with SAE viscosity grades defined in SAE J300 are widely marketed as fuel-saving oils. In contrast, diesel engines have higher in-cylinder pressure than gasoline engines and are frequently used under high loads. Therefore, excessive oil viscosity reduction aimed at reducing friction in the fluid lubrication area is There is a problem that the fuel-saving effect that can be exhibited in a gasoline engine cannot be sufficiently obtained because there is a concern that the wear resistance is deteriorated due to insufficient strength, the durability of the engine is adversely affected, and the friction is increased in the boundary lubrication region. Therefore, in order to obtain a friction reduction effect in a high fluid lubrication region in diesel engine oil, a viscous resistance reduction technique that does not depend on excessively low viscosity is required.

  On the other hand, organic molybdenum compounds widely applied in gasoline engine oils as friction reducing technology in the boundary lubrication region are sufficiently effective for diesel engines with a large amount of soot generation because their effects are significantly hindered by soot contamination. May not be obtained. Furthermore, since the organomolybdenum compound containing a metal element causes ash, it is known to adversely affect the life of exhaust gas aftertreatment devices such as DPF (Diesel Particulate Filter). In recent diesel engines, due to strict exhaust gas regulations, it has become essential to maintain the long-term performance of exhaust gas aftertreatment devices. is there. Therefore, among the ashless friction modifiers that do not contain a metal element, it is necessary to select a compound that exhibits an excellent friction reducing effect in place of the organic molybdenum compound. Here, diesel engines have a higher compression ratio and higher combustion temperatures than gasoline engines, so pistons and cylinder liners are also exposed to relatively high temperatures, which is a higher temperature for friction modifiers for diesel engine oils. It is required to exert an effect under conditions. However, the conventional ashless type friction modifier cannot maintain the adsorption activity to the metal surface under such severe conditions, and there is a problem that it is difficult to obtain a friction reducing effect. Under such circumstances, development of an ashless friction modifier that exhibits an excellent friction reducing effect even under high temperature conditions has been eagerly desired.

  In view of the above background, an object of the present invention is to provide an engine oil composition that has high fuel-saving performance and is particularly suitable for use in a diesel engine.

  In such a situation, as a result of earnestly examining the engine oil composition excellent in fuel saving performance, a viscosity index improver having a specific structure is combined in a specific content, and as a friction modifier It has been found that by including a polymer compound containing a specific structure as a structural unit, an engine oil composition exhibiting an extremely excellent fuel saving effect can be obtained, and the present invention has been completed.

That is, the present invention has a star structure in which a polymer chain is branched from the center of a polymer as the first viscosity index improver (A), and the polymer chain is composed of a vinyl aromatic compound monomer and a conjugated diene monomer. A star polymer having a weight average molecular weight of 100,000 to 1,000,000, which is a polymer chain obtained by copolymerization and hydrogenation;
(B) As a second viscosity index improver, a polyalkyl (meth) acrylate having a weight average molecular weight of 200,000 to 600,000,
(C) As a friction modifier, the following (C-1) to (C-4):
(C-1) a polyalkylene glycol in which the alkylene group is a linear or branched hydrocarbon group having 1 to 30 carbon atoms,
(C-2) a dicarboxylic acid having a linear or branched hydrocarbon group having 1 to 30 carbon atoms,
(C-3) linear or branched polyolefin,
(C-4) a monomer for linking the above (C-1), (C-2) or (C-3),
Among structural units derived from (C-1), structural units derived from (C-2), and structural units derived from (C-3), or (C-1) A structural unit derived from (C-2), a structural unit derived from (C-3), a structural unit derived from (C-4), and a weight average molecular weight of 500 to A polymer compound that is 20,000;
Containing
The content (M _A ) of the (A) star polymer is 0.10 to 2.00% by mass with respect to the total mass of the engine oil composition,
The (B) content of the polyalkyl (meth) acrylate _{(M B)} is a 0.50 to 6.00% by weight relative to the total weight engine oil composition,
The content of the polymer compound (C) is 0.01 to 10% by mass with respect to the total mass of the engine oil composition,
The ratio (M _A / M _B ) of the content (M _A ) of the (A) star polymer to the content (M _B ) of the (B) polyalkyl (meth) acrylate is 0.10 to 1.00 And
The viscosity index of the engine oil composition is 185 to 230;
The engine oil composition characterized by the above is provided.

  ADVANTAGE OF THE INVENTION According to this invention, the engine oil composition excellent in fuel-saving performance, especially the engine oil composition used suitably for a diesel engine can be provided.

  The engine oil composition of the present invention comprises a base oil and various additives. The engine oil composition of the present invention contains (A) a star polymer and (B) polyalkyl (meth) acrylate as a viscosity index improver, and (C) as a friction modifier. Contains a polymer compound.

  There is no restriction | limiting in particular as a base oil contained in the engine oil composition of this invention, 1 type, or 2 or more types chosen from a mineral base oil and a synthetic base oil are used. The base oil may be a mixture of a mineral base oil and a synthetic base oil.

  Examples of the mineral base oil include those obtained by refining a lubricating oil fraction of crude oil by appropriately combining purification methods such as solvent refining, hydrorefining, hydrocracking refining, and hydrodewaxing. The base oil having a viscosity index of 125 or more, which will be described later, is a highly refined paraffinic mineral oil (hydrorefined oil, catalytic isomerized oil, etc., which has been subjected to treatment such as solvent dewaxing or hydrodewaxing ( High viscosity index mineral oil base oil) and the like.

  Examples of synthetic base oils include isoparaffins, α-olefin oligomers, dialkyl diesters, polyols, alkylbenzenes, polyglycols, and phenyl ethers synthesized from natural gas such as methane.

The property of the base oil is not particularly limited as long as it is a property of a normal engine oil composition, but in order to obtain an engine oil composition with more excellent fuel economy, kinematic viscosity at 100 ° C. (JIS-K −2283 (ASTM D445)) is preferably ³ to 12 mm ² / s, and the viscosity index (JIS K 2283 (ASTM D2270)) is preferably 120 or more, the kinematic viscosity at 100 ° C. is 3 to 7 mm ² / s, and the viscosity index is It is particularly preferably 125 or more, more preferably a 100 ° C. kinematic viscosity of 3.5 to 5.0 mm ² / s and a viscosity index of 130 or more. Base oils with such properties are Group II base oils (Sulfur content 0.03% by mass or less, saturation content 90% by mass or more, viscosity index 80 to less than 120) according to American Oil Association (API) base oil classification Base group oil) and Group III base oil (sulfur content 0.03% by mass or less, saturation content 90% by mass or more, viscosity index 120 or more) may be mixed and adjusted to the above properties, Base oils belonging to group III or higher are preferred in that they exhibit high fuel efficiency.

  The engine oil composition of the present invention contains (A) a star polymer that functions as a viscosity index improver and (B) a polyalkyl (meth) acrylate.

  (A) The star polymer has a so-called star structure in which a polymer chain is branched from the center of the polymer. That is, the (A) star polymer has a structure in which a polymer chain is bonded to the center of the polymer. The polymer chain of the (A) star polymer is a polymer chain obtained by copolymerization and hydrogenation of a vinyl aromatic compound monomer and a conjugated diene monomer.

  (A) As the star polymer, one or more monomers selected from vinyl aromatic compound monomers and one or more monomers selected from conjugated diene monomers are copolymerized to form a vinyl aromatic compound monomer and a conjugated diene monomer. And a copolymer obtained by reacting this copolymer with a polyalkenyl coupling agent and then subjecting it to a hydrogenation treatment. The (A) star polymer thus obtained reacts with a copolymer of a vinyl aromatic compound monomer and a conjugated diene monomer, and is further subjected to a hydrogenation treatment to a structural site derived from a polyalkenyl coupling agent or The structural part derived from the polyalkenyl coupling agent after the hydrogenation treatment and a part of the copolymer of the vinyl aromatic compound monomer and the conjugated diene monomer are (A) the central part of the star polymer. The polymer chain obtained by copolymerization and hydrogenation of a vinyl aromatic compound monomer and a conjugated diene monomer is branched.

  The vinyl aromatic compound monomer is an aromatic compound having a vinyl group or an alkylated product thereof, and examples thereof include styrene, methylstyrene, ethylstyrene, vinylnaphthalene, and alkylated products thereof. Of these, styrene is preferred as the vinyl aromatic compound monomer.

  Conjugated diene monomers include butadiene, isoprene, 2-methyl-butadiene, 2,3-dimethyl-butadiene, 2-ethyl-butadiene, 2,3-diethyl-butadiene, pentadiene, 2-methyl-pentadiene, 3-methyl- Examples thereof include conjugated dienes such as pentadiene. Of these, butadiene and isoprene are preferred as the conjugated diene monomer.

  In copolymerizing the vinyl aromatic compound monomer and the conjugated diene monomer, the copolymerization ratio of the vinyl aromatic compound monomer is preferably 5 to 30% by mass, particularly preferably 5 to 5% by mass based on the total mass of the monomers. The copolymerization ratio of the conjugated diene monomer is preferably 65 to 95% by mass, particularly preferably 75 to 95% by mass, based on the total mass of the monomers.

  Polyalkenyl coupling agents include polyalkenyl aliphatic compounds such as polyvinyl acetylene, polyallyl acetylene, diacetylene, dimethacrylate, divinylbenzene, trivinylbenzene, tetravinylbenzene, divinyl o-xylene, m-xylene, p -Xylene, trivinyl-o-xylene, trivinyl-m-xylene, trivinyl-p-xylene, tetravinyl-o-xylene, tetravinyl-m-xylene, tetravinyl-p-xylene, divinylnaphthalene, divinylethylbenzene, divinylbiphenyl Polyalkenyl aromatic compounds such as diisobutenylbenzene, diisopropenylbenzene, diisopropenylbiphenyl and the like are preferable, and polyalkenyl aromatic compounds are preferable, and divinyl It is a benzene.

  (A) As a star polymer, a polymer chain is a styrene-butadiene-isoprene star polymer whose polymer chain is a polymer chain obtained by copolymerization and hydrogenation of styrene, butadiene and isoprene, and a polymer chain is styrene and isoprene. And a styrene-isoprene star polymer which is a polymer chain obtained by copolymerization and hydrogenation. A styrene-butadiene-isoprene star polymer is obtained by copolymerizing styrene with butadiene and isoprene to obtain a copolymer, then reacting the copolymer with a polyalkenyl coupling agent such as divinylbenzene, and further hydrogenating. It is obtained by processing. The styrene-isoprene star polymer is obtained by copolymerizing styrene and isoprene to obtain a copolymer, and then reacting the copolymer with a polyalkenyl coupling agent such as divinylbenzene, followed by hydrogenation treatment. It was obtained. Such styrene-butadiene-isoprene star polymers or styrene-isoprene star polymers contain divinylbenzene in the center of the molecular structure.

  The (A) star polymer according to the engine oil composition of the present invention is obtained by copolymerizing a vinyl aromatic compound monomer and a conjugated diene monomer and then reacting with a polyalkenyl coupling agent, followed by hydrogenation treatment. Therefore, although there are few unsaturated bonds derived from a conjugated diene, you may have an unsaturated bond derived from a conjugated diene. (A) The degree of unsaturation derived from the conjugated diene in the star polymer is preferably lower, and the repeating unit based on the conjugated diene having an unsaturated bond is 20% by mass relative to the total amount of repeating units based on the conjugated diene. The content is particularly preferably 10% by mass or less, more preferably 5% by mass or less.

  (A) A star polymer has a structure in which a polymer chain consisting of a hydrogenated product of a copolymer of a vinyl aromatic compound monomer and a conjugated diene monomer is branched from the center of the polymer, a so-called “star structure”. Have. (A) The number of polymer chains of the star polymer is 3 or more, preferably 5 or more, and particularly preferably 7 or more. (A) By setting the number of polymer chains of the star polymer to 5 or more, the weight average molecular weight tends to be in the range described later, and good shear stability tends to be easily obtained.

  (A) The weight average molecular weight of the star polymer is 100,000 to 1,000,000, preferably 150,000 to 800,000, particularly preferably 400,000 to 700,000, more preferably 500,000 to 700,000. If the weight average molecular weight of the star polymer is less than the above range, a thickening effect as a viscosity index improver cannot be sufficiently obtained, and if it exceeds the above range, sufficient shear stability cannot be obtained, and long-term When used, engine oil may cause a decrease in viscosity due to shearing, and wear resistance or seizure resistance may decrease. The “weight average molecular weight” as used herein refers to equipment: TOSOH HLC-8020, column: TSKgel GMHHR-M, detector: suggested refraction detector, mobile phase: THF, flow rate: 1 ml / min, sample Concentration: about 1.0 mass% / Vol% THF, injection amount: Refers to a polystyrene equivalent value measured by 50 μl.

  (A) The star polymer may be a single type or a combination of two or more types.

(B) A polyalkyl (meth) acrylate is a polymer having a structural unit represented by the following formula (1).
Formula (1):

(In the formula (1), R ¹ is hydrogen or a methyl group, and R ² is a linear alkyl group having 1 to 50 carbon atoms or an alkyl group having a branched chain.)

(B) A polyalkyl (meth) acrylate is a polymer having a structural unit represented by the formula (1). That is, the (B) polyalkyl (meth) acrylate may be a polymer having only a methacrylic acid ester or an acrylic acid ester as a monomer, that is, a polymer consisting only of the structural unit represented by the formula (1), Or the copolymer which has a structural unit other than the structural unit shown in Formula (1) may be sufficient as the copolymer of a methacrylic acid ester and acrylic acid ester, and another monomer, ie, a structure. (B) The polyalkyl (meth) acrylates may have the same or different R ^{1 of the} structural unit represented by the formula (1) in the polymer. (B) The polyalkyl (meth) acrylate may be a dispersion type having a polar group such as an amino group or a sulfonic acid group, or a non-dispersion type having no such group.

  (B) The weight average molecular weight of polyalkyl (meth) acrylate is 200,000-600,000, Preferably it is 250,000-500,000, Most preferably, it is 300,000-450,000. When the weight average molecular weight of the polyalkyl (meth) acrylate is less than the above range, the effect of improving the viscosity index is lowered, so that a sufficient fuel saving effect cannot be obtained. Insufficient shear stability, engine oil may decrease in viscosity due to shear over a long period of use, may reduce wear resistance or seizure resistance, and may adversely affect the coking resistance of the engine oil composition There is.

  (B) The polyalkyl (meth) acrylate may be a single type or a combination of two or more types.

  In the engine oil composition of the present invention, the content of the (A) star polymer is 0.10 to 2.00% by mass, preferably 0.20 to 1.50% by mass with respect to the total mass of the engine oil composition. %, Particularly preferably 0.25 to 1.25% by mass, still more preferably 0.30 to 1.00% by mass. (A) Star polymers exhibit very good shear stability. (A) When the content of the star polymer is less than the above range, since the blending amount of (B) polyalkyl (meth) acrylate which is inferior in shear stability is relatively increased, the shear stability of the engine oil composition Low. The (A) star polymer has a lower viscosity index improvement effect than the (B) polyalkyl (meth) acrylate, and also reduces the high-temperature high-shear viscosity in the effective region that greatly affects the fuel efficiency. (A) If the content of the star polymer exceeds the above range, the viscosity of the engine oil composition will be unnecessarily high. Since the amount of (meth) acrylate is reduced, the viscosity index specified in the engine oil composition of the present invention is not satisfied, and the value of high-temperature high-shear viscosity in the effective region is also increased, so that the fuel saving effect cannot be sufficiently exhibited. .

  In the engine oil composition of the present invention, the content of (B) polyalkyl (meth) acrylate is 0.50 to 6.00% by mass, preferably 0.70 to 4%, based on the total mass of the engine oil composition. .50% by mass, particularly preferably 0.85 to 3.00% by mass, and further preferably 1.00 to 2.00% by mass. In general, (B) polyalkyl (meth) acrylate is excellent in the effect of improving the viscosity index, but tends to be inferior in shear stability and anti-caulking performance. (B) When content of polyalkyl (meth) acrylate is less than the said range, the viscosity index prescribed | regulated to the engine oil composition of this invention cannot be satisfy | filled, and a fuel-saving effect cannot fully be expressed. In addition, if the content of (B) polyalkyl (meth) acrylate exceeds the above range, the viscosity of the engine oil composition becomes unnecessarily high and fuel saving performance cannot be obtained, and shear stability and anti-caulking performance are obtained. There is a risk of adversely affecting practical performance.

  In addition, when (A) star polymer or (B) polyalkyl (meth) acrylate is diluted with diluent oil, (A) star polymer or (B) polyalkyl in the engine oil composition of the present invention. Content of (meth) acrylate means content in the amount of active ingredients (polymer amount) except dilution oil.

In the engine oil composition of the present invention, the content of (A) star polymers relative to the total weight engine oil composition and M _A% by weight, content of the total weight engine oil composition (B) polyalkyl (meth) acrylate If the amount was _{M B} mass%, (B) the ratio of the polyalkyl (meth) content of (a) the star polymer to the content of acrylate _(M a / _{M B)} is 0.10 to 1.00 And preferably 0.12 to 0.75, particularly preferably 0.15 to 0.50. When the content ratio (M _A / M _B ) is in the above range, the engine oil composition is excellent in shear stability while ensuring the viscosity index of the engine oil composition of the present invention. It becomes easy to obtain.

  The engine oil composition of the present invention contains (A) a star polymer and (B) polyalkyl (meth) acrylate as essential components as a viscosity index improver, and further contains other viscosity index improvers as necessary. It can also be contained. Examples of other viscosity index improvers include various known viscosities such as olefin copolymers, polyisobutylenes, polyalkylstyrenes, styrene-maleic anhydride copolymers, and those containing a dispersing group in them. An index improver is mentioned. However, if the content of the other viscosity index improvers is too large, it may adversely affect fuel efficiency, so it is desirable to keep the content to a minimum. The amount is preferably 5% by mass or less, particularly preferably 2% by mass or less, based on the total amount of (A) the star polymer and (B) polyalkyl (meth) acrylate.

In addition to the viscosity index improver, the engine oil composition of the present invention further contains (C) a polymer compound that acts as a friction modifier as an essential additive.
(C) The polymer compound is (i) a polymer compound having a structural unit derived from (C-1), a structural unit derived from (C-2), and a structural unit derived from (C-3), or (ii) A polymer compound having a structural unit derived from (C-1), a structural unit derived from (C-2), a structural unit derived from (C-3), and a structural unit derived from (C-4). And a polymer compound having a weight average molecular weight of 100 to 20,000. (C) The polymer compound may be one of (i) and (ii) or a combination of two. In the present invention, the structural unit derived from (C-1) polyalkylene glycol refers to a reaction residue after (C-1) polyalkylene glycol has reacted with another constituent material of the polymer compound. For example, when (C-1) a polyalkylene glycol and a dicarboxylic acid are reacted to form an ester, the polyalkylene glycol reaction residue in such an ester is a structure derived from (C-1) polyalkylene glycol. Unit. Similarly, the structural unit derived from (C-2) dicarboxylic acid is a reaction residue after (C-2) dicarboxylic acid has reacted with another constituent material of the polymer compound, and (C- 3) The structural unit derived from polyolefin is a reaction residue after (C-3) polyolefin reacts with other constituent materials of the polymer compound, and (C-4) the above (C-1), The structural unit derived from the monomer used to link (C-2) or (C-3) is (C-4) the above (C-1), (C-2) or (C-3). It is a reaction residue after the monomer used for linking reacts with another constituent material of the polymer compound. In addition, (C) the following (C-1) to (C-4): (C-1) a polyalkylene glycol in which the alkylene group is a linear or branched hydrocarbon group having 1 to 30 carbon atoms, (C -2) a dicarboxylic acid having a linear or branched hydrocarbon group having 1 to 30 carbon atoms, (C-3) a linear or branched polyolefin, (C-4) the above (C-1), Among the structural units derived from the monomer for linking (C-2) or (C-3), the structural unit derived from (C-1), the structural unit derived from (C-2), and (C -3) or a structural unit derived from (C-1), a structural unit derived from (C-2), a structural unit derived from (C-3), and (C-4) ) And a polymer compound having a weight average molecular weight of 500 to 20,000 is represented by “(C) Rimmer compound "also described.

(C-1) to (C-4) are as follows.
(C-1) is a polyalkylene glycol in which the alkylene group is a linear or branched hydrocarbon group having 1 to 30 carbon atoms,
(C-2) is a dicarboxylic acid having a linear or branched hydrocarbon group having 1 to 30 carbon atoms,
(C-3) is a linear or branched polyolefin,
(C-4) is a monomer used to link (C-1), (C-2) or (C-3).

  (C-1) The polyalkylene glycol in which the alkylene group is a linear or branched hydrocarbon group having 1 to 30 carbon atoms is obtained by polymerizing alkylene glycol. The alkylene group in the polyalkylene glycol according to (C-1) may be a linear hydrocarbon group or a branched hydrocarbon group, and the alkylene group has 1 to 30 carbon atoms. , Preferably it is 1-10, More preferably, it is 2-5. Further, the alkylene group constituting the polyalkylene glycol according to (C-1) may be one type or a combination of two or more types, that is, the polyalkylene glycol according to (C-1) It may be obtained by using one kind of alkylene glycol as a raw material or may be obtained by using two or more kinds of alkylene glycol. The alkylene glycol (polyalkylene glycol polymerization raw material) according to (C-1) is preferably ethylene glycol, propylene glycol, or a mixture thereof, and particularly preferably ethylene glycol. The degree of polymerization of the alkylene glycol of the polyalkylene glycol according to (C-1) is preferably 2 to 50, more preferably 3 to 40, particularly preferably 3 to 30, and most preferably 3 to 25. . If the degree of polymerization is larger than the preferred range, the solubility of the polymer compound (C) in the engine oil may not be ensured, whereas if it is small, a sufficient friction reduction effect may not be expected. In addition, the polyalkylene glycol according to (C-1) may be a combination of a plurality of polyalkylene glycol structural units having different degrees of polymerization as long as they are within the range of these preferable degrees of polymerization.

  (C-2) The dicarboxylic acid having a linear or branched hydrocarbon group having 1 to 30 carbon atoms may have either a saturated hydrocarbon group or an unsaturated hydrocarbon group. The carbon number of the hydrocarbon group of the dicarboxylic acid according to (C-2) is 1 to 30, preferably 2 to 20. As the dicarboxylic acid according to (C-2), oxalic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid and the like are preferable as those having a saturated hydrocarbon group. Examples of those having an unsaturated hydrocarbon group include maleic acid and the like, and particularly preferred are succinic acid, glutaric acid, adipic acid, pimelic acid and maleic acid, and most preferred are succinic acid and adipine. Acid, maleic acid. The structural unit derived from (C-2) is preferably present in the polymer compound by forming an ester bond with the structural unit derived from (C-1) in the polymer compound. Moreover, a polyolefin structural unit can also be introduce | transduced in a (C) polymer compound by using the dicarboxylic acid made into polyolefin as the dicarboxylic acid which concerns on (C-2). A preferred form of the structural unit derived from (C-2) is polyisobutylene succinic anhydride obtained by reacting polyisobutylene with maleic anhydride.

  (C-3) The linear or branched polyolefin is incorporated into the (C) polymer compound in order to ensure solubility in engine oil. The polyolefin according to (C-3) is obtained by polymerizing a linear or branched olefin. The olefin to be a polymerization raw material (monomer) of the polyolefin according to (C-3) may be a linear olefin or an olefin having a branched structure, and the olefin has 2 to 6 carbon atoms, preferably Is 3-5. In addition, the olefin that is a polymerization raw material of the polyolefin according to (C-3) may be one kind or a combination of two or more kinds, that is, the polyolefin according to (C-3) It may be obtained using olefin as a raw material or may be obtained using two or more olefins. Examples of the polyolefin according to (C-3) include polyethylene, polypropylene, polybutylene, polyisobutylene, and the like, preferably polyisobutylene. The molecular weight of the polyolefin according to (C-3) is preferably 200 to 10,000, more preferably 400 to 8000, still more preferably 600 to 6000, and most preferably 800 to 4000. When the molecular weight is smaller than these, the polymer compound (C) may not be dissolved in the engine oil. Conversely, when the molecular weight is large, there is a possibility that a sufficient friction reducing effect cannot be obtained. In addition, the polyolefin which concerns on (C-3) may be integrated in the (C) polymer compound as the above-mentioned polyolefin-ized dicarboxylic acid structural unit.

  (C) The polymer compound optionally includes structural units derived from the monomer (C-4) for linking individual structural units derived from (C-1), (C-2) or (C-3). Have. Examples of the monomer according to (C-4) include polyols, and preferable polyols include glycerol, neopentyl glycol, trimethylol ethane, trimethylol butane, pentaerythritol, dipentaerythritol, tripentaerythritol, and the like. Of these, glycerol is particularly preferred.

  In addition, as a manufacturing method of the polymer compound which has such a structural unit, the manufacturing method described in the special table | surface 2013-521369 grade | etc., Is mentioned, for example.

  (C) The weight average molecular weight of the polymer compound is 500 to 20,000, preferably 600 to 20,000, more preferably 700 to 18,000, still more preferably 1500 to 16,000, and still more preferably 4000 to 14. 1,000, most preferably 5,000 to 11,000. When the weight average molecular weight of the (C) polymer compound is outside these ranges, not only a sufficient friction reducing effect can be obtained, but also the solubility of the (C) polymer compound in the engine oil may not be ensured.

  In the engine oil composition of the present invention, the content of the polymer compound (C) is 0.01 to 10.0% by mass, preferably 0.03 to 5.0% by mass, based on the total amount of the engine oil composition. More preferably, it is 0.05-2.5 mass%, Most preferably, it is 0.1-1.5 mass%. (C) When the content of the polymer compound is within the above range, an excellent friction reducing effect can be obtained. When the content of the (C) polymer compound is less than the above range, a sufficient effect cannot be expected. Conversely, when the content is excessive from the above range, an effect commensurate with the content cannot be expected. This is not preferable because it may not dissolve in engine oil.

  In addition to the viscosity index improver and the friction modifier, the engine oil composition of the present invention can further contain various additives as necessary.

  The engine oil composition of the present invention can contain an ashless dispersant. Examples of the ashless dispersant include succinimide dispersants represented by the following general formula (2) or general formula (3). Examples of the ashless dispersant include boron-modified succinimides represented by the following general formula (2) or general formula (3).

General formula (2):

General formula (3):

In General Formula (2) and General Formula (3), R ¹ and R ³ are alkyl groups or alkenyl groups, preferably polybutenyl groups, and have a weight average molecular weight of 300 to 10,000, preferably 500 to 8000, more preferably 800 to 6000. R ¹ and R ³ may be the same or different. R ² is an alkylene group having 2 to 5 carbon atoms, and preferably 2 or 3 carbon atoms. n is an integer of 1-10. The weight average molecular weight of the dispersant represented by the general formula (2) or the general formula (3) is preferably 500 to 20000, more preferably 1000 to 15000, still more preferably 3000 to 13000, and most preferably 4000. -10000. By setting the weight average molecular weight of the dispersant within the above range, sufficient dispersibility as a diesel engine oil can be obtained.

  As the ashless dispersant, one or more of the succinimide dispersant represented by the general formula (2) and the succinimide dispersant represented by the general formula (3), and the general formula One or two or more of boron-modified succinimide dispersants represented by (2) and boron-modified succinimide dispersants represented by general formula (3) A combination of In order to ensure the high heat resistance required for diesel engine oil, it is preferable to blend boron-modified succinimide.

  Although content in particular of a succinimide type dispersing agent is not restrict | limited, Preferably it is 100-2000 mass ppm as an amount of nitrogen elements with respect to engine oil composition total mass, More preferably, it is 300-1500 mass ppm. Further, when boron-modified succinimide is used as the succinimide dispersant, the amount of boron element is preferably 50 to 2000 mass ppm, more preferably 75 to 1000 mass, relative to the total mass of the engine oil composition. It is preferable to contain ppm, more preferably 100 to 500 ppm by mass, and most preferably 150 to 400 ppm by mass. Since the succinimide dispersant is extremely viscous and adversely affects the viscosity characteristics of the engine oil composition, it is desirable to keep its content to a minimum in order to maintain high fuel efficiency.

  The engine oil composition of the present invention can contain zinc dialkyldithiophosphate. When the engine oil composition contains zinc dialkyldithiophosphate, the wear prevention performance is enhanced. The alkyl group of zinc dialkyldithiophosphate has one derived from a primary alcohol, one derived from a secondary alcohol, or one derived from both a primary alcohol and one derived from a secondary alcohol. There may be. Although there is no restriction | limiting in particular in carbon number of an alkyl group, 3-12 are preferable at the point from which abrasion prevention performance becomes high.

  The content of the zinc dialkyldithiophosphate in the engine oil composition of the present invention is preferably 0.01 to 0.20% by mass, particularly preferably 0. 0% in terms of phosphorus element with respect to the total mass of the engine oil composition. It is 03-0.14 mass%. If the content of zinc dialkyldithiophosphate is less than the above range, the expected antiwear property may not be obtained sufficiently, and if it exceeds the above range, the sulfuric acid produced from the decomposition product of the engine oil may cause It may adversely affect oxidative stability.

  The engine oil composition of the present invention can contain a metallic detergent. Examples of the metal detergent include alkaline earth metal salicylate, alkaline earth metal sulfonate, alkaline earth metal phenate and the like, and these may be used alone or in combination of two or more. As the metallic detergent, it is preferable to blend alkaline earth metal salicylate in order to achieve both long life of engine oil and reduction of friction.

  The engine oil composition of the present invention can contain an antioxidant. Examples of antioxidants include phenolic antioxidants, amine-based antioxidants, organic molybdenum-based antioxidants, and the like. These may be used alone or in combination of two or more. Good. Examples of phenolic antioxidants include alkylphenols such as 2,6-di-tert-butyl-p-cresol, bisphenols such as 4,4′-methylenebis- (2,6-di-t-butylphenol), Examples include phenolic compounds such as n-octadecyl-3- (4′-hydroxy-3 ′, 5′-di-tert-butylphenol) propionate. Examples of amine-based antioxidants include aromatic amine compounds such as naphthylamines and dialkyldiphenylamines. Examples of the organic molybdenum-based antioxidant include organic molybdenum compounds such as molybdenum amine. The content of the antioxidant in the engine oil composition of the present invention is preferably 0.05 to 5.0 mass%, particularly preferably 0.5 to 3.0 mass%, based on the total mass of the engine oil composition. %.

  The engine oil composition of the present invention can optionally further contain other friction modifiers. Examples of the friction modifier include organic molybdenum compounds and ashless friction modifiers. Examples of the organic molybdenum compound include molybdenum dithiophosphate, molybdenum dithiocarbamate, molybdate amine compound, molybdenum long chain aliphatic amine compound, and the like. The content of the organomolybdenum compound in the engine oil composition of the present invention is preferably 100 to 1,200 mass ppm in terms of molybdenum element amount with respect to the total mass of the engine oil composition. Examples of the ashless friction modifier include long-chain aliphatic amines, long-chain fatty acid esters, long-chain aliphatic alcohols, amide compounds of aliphatic amines and fatty acids, and aliphatic polyglyceryl ethers. However, in a diesel engine, an ashless friction modifier is more preferable because an organic molybdenum compound may not exhibit a satisfactory effect due to the influence of soot mixed therein. Further, the engine oil composition of the present invention can optionally contain other friction modifiers as described above, but if the content is too large, the (C) polymer according to the engine oil composition of the present invention The content of other friction modifiers as described above should be kept to a minimum because there is a possibility of inhibiting the action of the compound as a friction modifier, and preferably 3% relative to the total mass of the engine oil composition. It is not more than mass%, preferably not more than 2 mass%, more preferably not more than 1.5 mass%, most preferably not more than 1 mass%.

  The engine oil composition of the present invention contains various additives effective for imparting engine oil performance, such as a metal deactivator, a rust inhibitor, a pour point depressant, and a defoaming agent, as necessary. be able to.

  The engine oil composition of the present invention comprises a base oil, (A) a star polymer, (B) a polyalkyl (meth) acrylate and a (C) polymer compound, and various additives that are added as necessary. The mixing order is not particularly limited.

The viscosity index of the engine oil composition of the present invention is 185 to 230, preferably 187 to 225, particularly preferably 190 to 215.
The kinematic viscosity (JIS-K-2283 (ASTM D445)) at 40 ° C. of the engine oil composition of the present invention is preferably 10 to 70 mm ² / s, particularly preferably 20 to 60 mm ² / s, and further preferably 30 to 30— 55 mm ² / s. The kinematic viscosity (JIS-K-2283 (ASTM D445)) at 100 ° C. of the engine oil composition of the present invention is preferably 5.6 to 12.5 mm ² / s, particularly preferably 8.5 to 11.5 mm. ² / s, more preferably 9.3 to 11.0 mm ² / s.
The engine oil composition of the present invention exhibits an excellent effect among SAE viscosity grades defined in SAE J300, particularly at 0W-30 or 5W-30. In the engine oil composition of the present invention, the content of the viscosity index improver is adjusted so as to conform to the SAE viscosity grade within the range of the content defined in the engine oil composition of the present invention.

  The engine oil composition of the present invention is applied to various engine engines, and is used for, for example, gasoline engine engines, diesel engine engines, gas engine engines, etc. Demonstrates great fuel efficiency.

  Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

(Examples, comparative examples, reference examples)
Each example, reference example and comparative example are engine oil compositions obtained by mixing the base oil and additives shown below so as to have the contents shown in Tables 1 and 2. In the table, “mass%” or “mass ppm” means mass% or mass ppm relative to the total mass of the engine oil composition. Each engine oil composition meets the requirements of 0W-30 or 5W-30 in the SAE viscosity grade, and oil after ASTM D6278-07 shear test which is a requirement of JASO DH-2 standard which is a domestic diesel engine oil standard The kinematic viscosity at 100 ° C. is adjusted to be 9.3 mm ² / s or more. Further, the high-temperature high-shear viscosity at 150 ° C. shear rate of 1 × 10 ⁶ is adjusted to be 3.0 mPa · s or more. In the preparation of each example, reference example and comparative example, the content of the viscosity index improver was taken into consideration so as to minimize the amount required to satisfy the above-mentioned conditions in consideration of the influence on the fuel saving performance.

<Used base oil and additives>
(1) Base oil Hydrocracked mineral base oil (Group III base oil): 100 ° C. kinematic viscosity 4.1 mm ² / s, viscosity index 134
(2) Viscosity index improver / Viscosity index improver A
Star polymer containing divinylbenzene in the center of the molecular structure and having a polymer chain obtained by copolymerization and hydrogenation of styrene, isoprene and butadiene: weight average molecular weight = 595,000, the amount of active ingredients excluding diluent oil is 11 It was 0.0 mass%.
・ Viscosity index improver B
Polyalkyl methacrylate: weight average molecular weight = 440,000, the amount of active ingredients excluding diluent oil was 19.7% by mass.
・ Viscosity index improver C
Ethylene / propylene copolymer: weight average molecular weight = 180,000, the amount of active ingredients excluding diluent oil was 12.0% by mass.
(3) Friction modifier / friction modifier 1 ((C) polymer compound)
A polymer compound having a weight average molecular weight of 7,300 having a structural unit derived from polyethylene glycol (a mixture having a polymerization degree of ethylene glycol of 6 to 20), adipic acid, and polyisobutylene (weight average molecular weight 2,260). The molar ratio occupied by each of the structural units derived from polyethylene glycol and adipic acid in the polymer compound was about 8%, and the molar ratio occupied by polyisobutylene was about 92%.
・ Friction modifier 2
Sulfurized oxymolybdenum dithiocarbamate, molybdenum content: 10.2% by mass.
・ Friction modifier 3
Glycerol monooleate
・ Friction modifier 4
Glycerin oleyl ether and friction modifier 5
Oleic acid diethanolamide (4) antiwear agent Zinc dialkyldithiophosphate having a secondary type alkyl group and a primary type alkyl group was used as an antiwear agent.
(5) Dispersant / Dispersant A: Alkenyl succinimide represented by the general formula (3), weight average molecular weight = 7,370, nitrogen content = 1.1 mass%, does not contain boron.
Dispersant B: Boron-modified alkenyl succinimide represented by general formula (3), weight average molecular weight = 4,380, nitrogen content = 1.4 mass%, boron content = 0.5 mass %.
(6) Metal type detergent / detergent A: calcium salicylate, base number = 170 mgKOH / g.
Cleaner B: calcium phenate, base number = 255 mg KOH / g.
In addition, a base number here is a value measured according to JIS-K-2501-6.
(7) Other additives Including phenol type antioxidant, pour point depressant, silicone antifoaming agent.

<Evaluation method>
The evaluation test method is as follows.
(1) SAE viscosity grade The viscosity grade prescribed | regulated by SAE J300 was determined.
(2) Kinematic viscosity According to JIS K 2283 (ASTM D445), the kinematic viscosity and viscosity index at 40 ° C. and 100 ° C. were measured.
(3) Viscosity index Calculated according to JIS K 2283 (ASTM D2270).
(4) High temperature high shear viscosity at a temperature of 100 ° C. and a shear rate of 1 × 10 ⁶ / s was measured according to ASTM D6616-07.
(5) High temperature high shear viscosity at a temperature of 150 ° C. and a shear rate of 1 × 10 ⁶ / s was measured according to ASTM D4683.
(6) High temperature high shear viscosity at a temperature of 150 ° C. and a shear rate of 1 × 10 ⁷ / s was measured using a USV (The Ultra Shear Viscometer) manufactured by PCS Instruments.
(7) Kinematic viscosity at 100 ° C. after shear test ASTM D6278-07 (Standard Test Method for Shear Stability of Polymer Containing Fluids Using a European Diesel Oil Test) The kinematic viscosity was measured.
(8) PSSI of viscosity index improver mixture
PSSI of the viscosity index improver mixture was calculated according to ASTM D6022-01 from the results of the 100 ° C. kinematic viscosity after the shear test described in (7) above.

<Evaluation test of fuel efficiency of engine oil composition>
・ Test condition 1
The fuel economy performance of the engine oil composition was evaluated by a bench fuel economy test using a 4,600cc diesel engine in Japan. Test conditions were set with reference to the Ministry of Land, Infrastructure, Transport and Tourism 10.15 mode. The result shown in Table 1 is the fuel efficiency improvement rate (%) when the result of Comparative Example 5 is used as a reference.
・ Test condition 2
It was evaluated by a bench fuel consumption test using a 4,000cc diesel engine in Japan. Test conditions were set with reference to the Ministry of Land, Infrastructure, Transport and Tourism JE05 mode. The result shown in Table 2 is the fuel efficiency improvement rate (%) with respect to Reference Example 1.

<Friction test>
The friction reduction effect of the engine oil composition was measured using a Mini Traction Machine manufactured by PCS Instruments, which is a ball-on-disk friction tester. The test piece was a 3/4 inch steel ball and a 46 mm diameter steel disc test piece, and the friction test was conducted for 1 hour under the conditions of oil temperature 120 ° C., load 30 N, slip rate 50%, pull-in speed 0.05 mm / s. The traction coefficient was measured at 10 second intervals during the test. The friction reduction effect was evaluated by comparing the average traction coefficient for 10 minutes after the start of friction and for the last 10 minutes (50 to 60 minutes after the start).

<Coking resistance test>
According to the panel coking test method (Fed-791B), the coking weight was measured. The oil temperature was set to 100 ° C. and the test piece panel temperature was set to 300 ° C. The cycle of splash for 15 seconds and then stopped for 45 seconds was repeated for 3 hours, and then the amount of deposit (mg) attached to the test piece panel was measured.

First, in Table 1, the (A) star polymer and (B) polyalkyl (meth) acrylate of the viscosity index improver according to the present invention, without containing the (C) polymer compound according to the present invention, The result of having evaluated the engine oil composition which mix | blended the viscosity index improver ethylene propylene copolymer etc. in combination is shown. As can be seen from these results, as shown in Reference Examples 1 to 4, as a viscosity index improver, (A) a star polymer, which is a viscosity index improver essential in the engine oil composition of the present invention, and (B) An engine oil composition containing both polyalkyl (meth) acrylates and blending amounts and blending ratios M _A / M _B within the range specified in the present invention does not contain both, and only ethylene / propylene copolymer Engine oil composition of Reference Example 5 containing: (A) Engine oil composition of Reference Example 6 containing only (B) polyalkyl (meth) acrylate without containing star polymer, and (A) Star Compared to any of the engine oil compositions of Reference Example 7 that do not contain a type polymer (B) and contain a polyalkyl (meth) acrylate and an ethylene / propylene copolymer, It can be seen that Ku value of high-temperature high-shear viscosity of 100 ° C. · shear rate 10 6 ^{/ s} and 0.99 ° C. · shear rate 10 7 ^{/ s,} which is known to correlation is significantly lower. The correlation between fuel efficiency and these high-temperature and high-shear viscosities is described in Tribology Series 10 Lubrication of Internal Combustion Engines (Yokoshobo), JSAE 20008815 (2008) and the like. And also in the actual fuel-consumption test result, the reference example 1 showed the very outstanding fuel-saving performance compared with any of the reference examples 5-7. Further, as shown in Comparative Examples 8 and 9, the (A) star polymer and (B) be a polyalkyl (meth) acrylate together engine oil composition containing, both compounding ratio of M _{A /} M _B If the present invention does not fall within the specified range, either high temperature high shear viscosity value of 100 ° C./shear rate 10 ⁶ / s or 150 ° C./shear rate 10 ⁷ / s is described in the reference examples 1 to 4. Since it becomes high compared with the oil composition, the excellent fuel saving performance of the present invention cannot be expected. Further, the engine oil composition of Comparative Example 10 containing only (A) a star polymer as a viscosity index improver and not containing (B) a polyalkyl (meth) acrylate is also defined in the engine oil composition of the present invention. The high-temperature high-shear viscosity value at 100 ° C. and a shear rate of 10 ⁶ / s is higher than that of the engine oil composition of the example, so that a fuel saving effect cannot be expected.

  Next, in Table 2, the engine oil composition of Reference Example 1 and the engine oil composition of Reference Example 1 were further added with the friction modifier 1 corresponding to the polymer compound (C) according to the present invention as a friction modifier. An evaluation result is shown about Comparative Examples 1-4 which mix | blended the conventional friction modifier as a friction modifier with the engine oil composition of Example 1 and Reference Example 1 further. First, the shear viscosity shows the same level result for any engine oil composition. However, Reference Example 1 in which no friction modifier is blended is inferior to Example 1 in friction reduction effect, and Comparative Examples 1 to 4 show a slight friction reduction as compared to Reference Example 1, but in the latter half of the test time, the friction coefficient It is understood that the activity as a friction modifier cannot be maintained. On the other hand, Example 1 in which the polymer compound (C) according to the present invention was blended was an ashless friction modifier, but the friction reduction effect superior to that of Comparative Example 1 in which MoDTC was blended over the entire test time. It can be seen that Further, as shown in Table 2, also in the bench fuel consumption test using the actual engine, Example 1 shows further improved fuel consumption improvement over Reference Example 1, and Comparative Example 1 containing MoDTC as a friction modifier is also included. The result was higher. From the above, it is clear that the engine oil composition containing (C) in addition to (A) and (B) exhibits a further excellent fuel economy effect.

  According to the present invention, an engine oil composition having high fuel saving performance can be provided.

Claims (5)

(A) As a first viscosity index improver, it has a star structure in which a polymer chain is branched from the center of the polymer, and the polymer chain is obtained by copolymerization and hydrogenation of a vinyl aromatic compound monomer and a conjugated diene monomer. A star polymer having a polymer chain and a weight average molecular weight of 100,000 to 1,000,000;
(B) As a second viscosity index improver, a polyalkyl (meth) acrylate having a weight average molecular weight of 200,000 to 600,000,
(C) As a friction modifier, the following (C-1) to (C-4):
(C-1) a polyalkylene glycol in which the alkylene group is a linear or branched hydrocarbon group having 1 to 30 carbon atoms,
(C-2) a dicarboxylic acid having a linear or branched hydrocarbon group having 1 to 30 carbon atoms,
(C-3) linear or branched polyolefin,
(C-4) a monomer for linking the above (C-1), (C-2) or (C-3),
Among structural units derived from (C-1), structural units derived from (C-2), and structural units derived from (C-3), or (C-1) A structural unit derived from (C-2), a structural unit derived from (C-3), a structural unit derived from (C-4), and a weight average molecular weight of 500 to A polymer compound that is 20,000;
Containing
The content (M _A ) of the (A) star polymer is 0.10 to 2.00% by mass with respect to the total mass of the engine oil composition,
The (B) content of the polyalkyl (meth) acrylate _{(M B)} is a 0.50 to 6.00% by weight relative to the total weight engine oil composition,
The content of the polymer compound (C) is 0.01 to 10% by mass with respect to the total mass of the engine oil composition,
The ratio (M _A / M _B ) of the content (M _A ) of the (A) star polymer to the content (M _B ) of the (B) polyalkyl (meth) acrylate is 0.10 to 1.00 And
The viscosity index of the engine oil composition is 185 to 230;
An engine oil composition characterized by the above.   The engine oil according to claim 1, wherein the vinyl aromatic compound monomer in the (A) star polymer is styrene, and the conjugated diene monomer is isoprene or butadiene, or a combination of isoprene and butadiene. Composition.   (C-1) of the (C) polymer compound is one or more selected from polyethylene glycol and polypropylene glycol, (C-2) is one or more selected from succinic acid, adipic acid and maleic acid, (C-3 ) Is a polyisobutylene. The engine oil composition according to claim 1 or 2, wherein:   The engine oil composition according to any one of claims 1 to 3, wherein (C-1) of the polymer compound (C) is polyethylene glycol having a polymerization degree of 2 to 50, and (C-2) is adipic acid. object.   The engine oil composition according to any one of claims 1 to 4, wherein the engine oil composition is a diesel engine oil composition of SAW viscosity grade of 0W-30, 5W-30, or 10W-30.