JP2018123240A - Lubricant composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lubricant composition interposed between a DLC coated surface and another metal member (particularly a steel material) in a sliding member, which has a better friction reducing effect and has better abrasion resistance than a conventional lubricant composition containing a friction modifier of molybdenum.SOLUTION: A lubricant composition of the present invention comprises a lubricant base oil, (A) molybdenum dialkyl dithiophosphate and (B) zinc dialkyl dithiophosphate. The amount of phosphorus is from 300 to 1500 mass.ppm based on a total mass of the lubricant composition.SELECTED DRAWING: None

Description

  The present invention relates to a lubricating oil composition, and more particularly to a lubricating oil composition for a sliding member, particularly a lubricating oil composition for a sliding member of an internal combustion engine.

  Lubricating oil compositions are widely used in the automotive field such as for internal combustion engines, automatic transmissions, and gear oils. In recent years, there has been a demand for lowering the viscosity of lubricating oil compositions in order to improve fuel efficiency, but there is a problem that the friction cannot be reduced sufficiently because the oil film becomes thinner and boundary friction increases due to the lowering of viscosity. . Friction reduction is important for improving fuel efficiency, and for this reason, surface modification technology for sliding members has attracted attention. For example, various hard films have been studied as a countermeasure for reducing friction and wear of sliding parts, and various developments using diamond-like carbon (hereinafter abbreviated as DLC) films have been attempted. For example, it has been studied to obtain a higher friction reduction effect by optimizing the combination of the DLC film and the lubricating oil composition interposed in the sliding portion.

  Patent Document 1 describes a lubricating oil composition that uses an oil-soluble organomolybdenum friction modifier and active sulfur as a surface active sulfur donor component to improve friction and wear resistance of the DLC coating. Molybdenum dithiocarbamate is used as an oil-soluble organic molybdenum friction modifier. Patent Document 2 describes that friction is reduced by using a coating surface coated with DLC doped with a specific element and an oil-soluble molybdenum compound having a chemical structure composed of a trinuclear body of Mo. Yes. Further, Patent Document 3 describes a lubricating oil composition essentially containing molybdenum dithiophosphate and an amine or amide friction modifier, and the lubricating oil composition is a DLC film, particularly hydrogenated amorphous carbon. It has been described that it has low friction and wear resistance against a DLC film comprising:

JP-T-2014-513173 JP 2014-224239 A JP 2006-216653 A

  However, a lubricating oil composition containing molybdenum dithiocarbamate or Mo trinuclear structure compound as a friction modifier is not yet sufficient in friction reduction effect. In addition, a lubricating oil composition containing molybdenum dithiocarbamate is effective in sliding contact between a steel material and a steel material, but there is a problem that the amount of wear increases in sliding contact between the DLC film and the steel material. Furthermore, when a lubricating oil composition containing an amine-based or amide-based friction modifier in the amount described in the examples of Patent Document 3 is used on the DLC film surface containing boron, the friction coefficient is high and the wear amount is large. There is a problem of becoming.

  In view of the above circumstances, the present invention is a lubricating oil composition interposed between a DLC coating surface and another metal member (particularly steel) in a sliding member, and includes a conventional molybdenum friction modifier. An object of the present invention is to provide a lubricating oil composition that has a more excellent friction reducing effect than the lubricating oil composition and has both good wear resistance.

  As a result of diligent investigations to solve the above problems, the present inventors have found that a lubricating oil composition containing molybdenum dialkyldithiophosphate and zinc dialkyldithiophosphate can achieve the above problems, and has achieved the present invention. It was.

  That is, the present invention contains a lubricating base oil, (A) molybdenum dialkyldithiophosphate, and (B) zinc dialkyldithiophosphate, and the amount of phosphorus with respect to the total mass of the lubricating oil composition is 300-1500 mass. Provided is a lubricating oil composition characterized by being in ppm.

Furthermore, the present invention provides a lubricating oil composition further having at least one of the following features (a) to (h).
(A) (A ′) at least one selected from the group consisting of an amine friction modifier and an amide friction modifier in an amount that is less than 0.1 mass% with respect to the total mass of the lubricating oil composition The lubricating oil composition comprising or none.
(B) The amount of the component (A) is 400 to 1300 ppm by mass with respect to the mass of the entire lubricating oil composition as the amount of molybdenum, and the amount of the component (B) is a lubricating oil composition as the amount of phosphorus. The said lubricating oil composition which is 200-1000 mass ppm with respect to the mass of the whole thing.
(C) A lubricating oil composition for lubricating a diamond-like carbon (DLC) film.
(D) a pair of sliding members having opposing sliding surfaces that can move relative to each other, wherein at least one sliding surface comprises a surface covered with a diamond-like carbon (DLC) film; A lubricating oil composition for lubricating an opposing sliding surface.
(E) The lubricating oil composition of (c) or (d), wherein DLC has boron.
(F) The lubricating oil composition having a high temperature high shear viscosity (HTHS viscosity) at 150 ° C. of 1.4 to 2.9 mPa · s.
(G) The lubricating oil composition having a kinematic viscosity at 100 ° C. of 9.3 mm ² / s or less.
(H) The lubricating oil composition for internal combustion engines.

  The sliding member in the present invention means a pair of members having opposed sliding surfaces that can move relative to each other such as a shaft and a bearing, and a piston and a liner. In the above (d), the sliding member formed of a surface in which at least one sliding surface is coated with a diamond-like carbon (DLC) film is a surface in sliding contact with a mating member in one of a pair of opposing members. It means that it is covered with a DLC film. The lubricating oil composition for lubricating the opposing sliding surfaces means that the lubricating oil composition is used for lubricating between the opposing sliding surfaces of a pair of members. The lubricating oil composition may be interposed between the opposing sliding surfaces.

  The lubricating oil composition of the present invention can reduce the coefficient of friction that occurs between sliding surfaces. In particular, compared with a lubricating oil composition containing only molybdenum dithiocarbamate or Mo trinuclear structure compound as a friction modifier between the sliding surfaces of the DLC coating surface and other metal members (particularly steel). A lower coefficient of friction can be given, and the wear resistance is also excellent. The lubricating oil composition of the present invention can be suitably used particularly as a lubricating oil composition for internal combustion engines.

FIG. 1 is a schematic diagram of a block-on-ring friction test.

  Hereinafter, the lubricating oil composition of the present invention will be described in more detail.

As the lubricating base oil, a conventionally known lubricating base oil can be used, and it may be a mineral oil, a synthetic oil, or a mixed oil thereof. As mineral base oils, lubricating oil fractions obtained by subjecting crude oil to atmospheric distillation and reduced pressure distillation are subjected to solvent deburring, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, hydrorefining, sulfuric acid There are lubricating base oils obtained by isomerizing and dewaxing waxes obtained by solvent dewaxing, such as paraffinic and naphthenic lubricating base oils, which are refined by appropriate combination of washing, refining treatment such as clay, etc. Can be mentioned. The kinematic viscosity at 100 ° C. of the mineral oil base oil is not particularly limited, but in order to obtain a lubricating oil composition having a low viscosity, it is preferably 1 to 6 mm ² / s, more preferably ^{2 to} 6 mm ² / s.

As the synthetic base oil, isoparaffin, alkylbenzene, alkylnaphthalene, monoester, diester, polyol ester, polyoxyalkylene glycol, dialkyldiphenyl ether, and polyphenyl ether can be used. Furthermore, GTL (Gas to Liquid) base oil, ATL (Asphalt to Liquid) base oil, BTL (Biomass to Liquid) base oil and CTL (Coal to Liquid) base oil can be used, and the process of using this as a raw material is U.S. Pat. No. 4,594,172 and US Pat. 4, 943, 672. The kinematic viscosity of the synthetic base oil is not particularly limited. It is also possible to use a poly α-olefin or α-olefin copolymer having a kinematic viscosity at 100 ° C. of less than 6 mm ² / s or more than 80 mm ² / s. To obtain a lubricating oil composition having a low viscosity, kinematic viscosity of synthetic base oils is preferably from 1 to 6 mm ² / s, and more preferably 2 to 6 mm ² / s.

  The base oils that can be used in combination may be used singly or in combination of two or more. When using two or more, use of two or more mineral base oils, use of two or more synthetic base oils, and use of one or more mineral base oils and one or more synthetic base oils Is possible.

Further, in order to obtain a lubricating oil composition having a low viscosity, as a whole lubricating base oil, kinematic viscosity 1 to 6 mm ² / s at 100 ° C., preferably from 2 to 6 mm ² / s, particularly 2.5 Preferably it has ˜6 mm ² / s.

(A) Molybdenum dialkyldithiophosphate The present invention is characterized in that the lubricating oil composition essentially contains molybdenum dialkyldithiophosphate (MoDTP). MoDTP is, for example, a compound represented by the following (1).
Conventionally, friction modifiers include organic molybdenum compounds, complexes of molybdenum compounds with sulfur-containing organic compounds or other organic compounds, and complexes of sulfur-containing molybdenum compounds such as sulfurized molybdic acid with alkenyl succinimides. It has been. As the organic molybdenum compound, molybdenum dialkyldithiophosphate (MoDTP) and molybdenum dithiocarbamate (MoDTC) are known, and among them, molybdenum dithiocarbamate (MoDTC) has been suitably used. This is because MoDTP has phosphorus as shown in the above formula (1). Since phosphorus poisons the exhaust gas purification three-way catalyst, the phosphorus content in the lubricating oil composition is regulated. Conventionally, an organophosphorus compound has often been added to a lubricating oil composition as an antiwear agent, and molybdenum dithiophosphate should be avoided in order to reduce the amount of phosphorus contained in the lubricating oil composition. It was done. From these points, conventionally, molybdenum dithiocarbamate (MoDTC) has been generally used as a friction modifier. However, as described above, the lubricating oil composition containing molybdenum dithiocarbamate (MoDTC) has a problem that large wear occurs between the sliding surface between the DLC coating surface and the steel material. Also, the friction reducing effect is not sufficient. On the other hand, the lubricating oil composition containing molybdenum dithiophosphate has an excellent friction reducing effect on the sliding surface having the DLC film, and also has wear resistance compared to the lubricating oil composition containing molybdenum dithiocarbamate. It can be improved.

  The lubricating oil composition of the present invention contains molybdenum dialkyldithiophosphate and zinc dialkyldithiophosphate as described above. The total amount of phosphorus contained in the lubricating oil composition is 300 mass ppm to 1500 mass ppm, preferably 400 to 1400 mass ppm, more preferably 500 to 1300 mass ppm, based on the total mass of the lubricating oil composition. Especially preferably, it is 600-1200 mass ppm, Most preferably, it is 600-1000 mass ppm. Combining molybdenum dialkyldithiophosphate and zinc dialkyldithiophosphate in an amount such that the total amount of phosphorus is within the above range improves the friction reduction effect between the sliding surfaces without causing catalyst poisoning and is excellent. Both wear resistance can be achieved.

In the said General formula (1), R is a C1-C30 monovalent hydrocarbon group mutually independently. The hydrocarbon group may be linear or branched. Examples of the monovalent hydrocarbon group include a linear or branched alkyl group having 1 to 30 carbon atoms; an alkenyl group having 2 to 30 carbon atoms; a cycloalkyl group having 4 to 30 carbon atoms; and an aryl having 6 to 30 carbon atoms. A group, an alkylaryl group or an arylalkyl group. In the arylalkyl group, the bonding position of the alkyl group is arbitrary. More specifically, examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, and a tridecyl group. A tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, and the like, and branched alkyl groups thereof. Particularly, an alkyl group having 3 to 8 carbon atoms is preferable. X ₁ and X ₂ are an oxygen atom or a sulfur atom, preferably an oxygen atom. Y ₁ and Y ₂ are an oxygen atom or a sulfur atom, preferably a sulfur atom.

  The amount of the (A) MoDTP in the lubricating oil composition of the present invention is 400 to 1300 ppm by mass, preferably 500 to 1200 ppm by mass, more preferably 600 to 1100 ppm by mass as the amount of molybdenum relative to the total mass of the lubricating oil composition. The amount is particularly preferably 650 to 1050 mass ppm. If the amount of MoDTP is less than the above lower limit, the effect of reducing friction between sliding surfaces cannot be sufficiently obtained. Further, if the amount of MoDTP exceeds the above upper limit, wear increases between the sliding surfaces, which is not preferable.

  The lubricating oil composition of the present invention comprises the above-mentioned molybdenum dialkyldithiophosphate containing, as optional components, a conventionally known molybdenum friction modifier other than (A), such as molybdenum dithiocarbamate (MoDTC) and molybdenum trinuclear compound. (MoDTP) and can be contained. The blending amount of the molybdenum-based friction modifier other than (A) may be in a range that does not impair the friction reduction effect and wear resistance exhibited by the present invention, and may be appropriately adjusted in a range that does not exceed the amount of MoDTP.

  As described above, in the lubricating oil composition containing only conventional molybdenum dithiocarbamate (MoDTC), the friction reduction effect is insufficient between the sliding surface between the DLC coating surface and the steel material, and large wear occurs. . However, by using MoDTC together with MoDTP, it is possible to further reduce friction between the sliding surface between the DLC coating surface and the steel material and to reduce wear. The blending amount of MoDTC is preferably 100 ppm by mass or less, preferably 70 ppm by mass or less, more preferably 50 ppm by mass or less, as the amount of molybdenum derived from MoDTC with respect to the total mass of the lubricating oil composition. Is good. The lower limit is not particularly limited, but is an amount that is 1 mass ppm or more, preferably 5 mass ppm or more, particularly preferably 10 mass ppm or more. If the amount of MoDTC exceeds the above upper limit value, wear between the sliding surfaces may be increased, which is not preferable.

  Molybdenum trinuclear compounds can also be included in conjunction with MoDTP. Thereby, compared with the lubricating oil composition containing only a molybdenum trinuclear compound, the friction between sliding surfaces can be reduced more. However, a lubricating oil composition containing a molybdenum trinuclear compound may be worn significantly even when used in combination with MoDTP. Therefore, when a molybdenum trinuclear compound is included, the amount should be very small as long as the effects of the present invention are not impaired. More specifically, the molybdenum amount derived from molybdenum dithiocarbamate relative to the total mass of the lubricating oil composition is less than 50 ppm by mass, preferably 40 ppm by mass or less, and more preferably 20 ppm by mass or less. The lower limit is not particularly limited. For example, it may be contained in an amount of 1 ppm by mass or more, further 5 ppm by mass or more, and more preferably 10 ppm by mass or more.

(A ′) Amide friction modifier and amine friction modifier In addition to the above, the lubricating oil composition of the present invention further contains at least one selected from amide friction modifiers and amine friction modifiers in less than a specific amount. It may be included or none of these may be included. In the case of containing an amide friction modifier or an amine friction modifier, the total content is preferably less than 0.1% by mass, more preferably less than 0.05% by mass, based on the total amount of the lubricating oil composition. Yes, more preferably less than 0.01% by mass. When a lubricating oil composition containing an amide friction modifier or an amine friction modifier in the above content or more is used particularly for a DLC film doped with boron, it is preferable because the friction coefficient is increased and wear is increased. Absent. The content of the amide-based friction modifier and the amine-based friction modifier is preferably as small as possible, and the most preferable is an embodiment that does not contain any of them.

  Any conventionally known amine-based friction modifier and amide-based friction modifier may be used. For example, methylamine, ethylamine, propylamine, etc., alkyl having 1 to 30 carbon atoms, preferably 4 to 28 carbon atoms, more preferably 6 to 25 carbon atoms, and having a linear or branched alkyl group An alkenylamine having an alkenyl group having 2 to 30 carbon atoms, preferably 4 to 28 carbon atoms, more preferably 6 to 25 carbon atoms, and may be branched, such as ethenylamine, propenylamine, and oleylamine; An alicyclic amine such as cyclohexylamine; an alkylenediamine having an alkylene group having 1 to 30 carbon atoms such as butylenediamine; a polyamine such as pentaethylenehexamine; and a mixture thereof. Examples of the amide friction modifier include, for example, ethanoic acid amide, propanoic acid amide, etc., having 1 to 30 carbon atoms, preferably 4 to 28 carbon atoms, more preferably 6 to 25 carbon atoms, Saturated fatty acid amide having a branched alkyl group; oleic acid amide, erucic acid amide, etc., having 2 to 30 carbon atoms, preferably 4 to 28 carbon atoms, more preferably 6 to 25 carbon atoms, and having a branch And unsaturated fatty acid amides having alkenyl groups which may be present; and mixtures thereof.

(B) Zinc Dialkyldithiophosphate The lubricating oil composition of the present invention contains zinc dialkyldithiophosphate (ZnDTP (also referred to as ZDDP)). This compound is known as an antiwear agent for lubricating oil compositions and is represented by the following formula (2).
In the above formula, R ¹ and R ² may be the same as or different from each other, and are each a hydrogen atom or a monovalent hydrocarbon group having 1 to 26 carbon atoms. The monovalent hydrocarbon group includes a primary (primary) or secondary (secondary) alkyl group having 1 to 26 carbon atoms; an alkenyl group having 2 to 26 carbon atoms; a cycloalkyl group having 6 to 26 carbon atoms; carbon A hydrocarbon group containing an aryl group, an alkylaryl group or an arylalkyl group of formula 6 to 26; or an ester bond, an ether bond, an alcohol group or a carboxyl group. R ¹ and R ² are preferably a primary or secondary alkyl group having 2 to 12 carbon atoms, a cycloalkyl group having 8 to 18 carbon atoms, and an alkylaryl group having 8 to 18 carbon atoms, They may be the same or different. In particular, zinc dialkyldithiophosphate is preferable, and the primary alkyl group preferably has 3 to 12 carbon atoms, more preferably 4 to 10 carbon atoms. The secondary alkyl group preferably has 3 to 12 carbon atoms, more preferably 3 to 10 carbon atoms. Further, zinc dithiocarbamate (ZnDTC) may be used in combination.

  The amount of the zinc dialkyldithiophosphate in the lubricating oil composition is such that the total amount of phosphorus with respect to the total mass of the lubricating oil composition satisfies the above range. Preferably, the amount of phosphorus derived from ZnDTP with respect to the total mass of the lubricating oil composition is 200 to 1000 ppm by mass, preferably 300 to 900 ppm by mass, more preferably 350 to 850 ppm by mass, It is particularly preferable that the amount be 400 to 800 mass ppm. By containing the zinc dialkyldithiophosphate in an amount in the above range, both the improvement of the friction reduction effect between the sliding surfaces and the excellent wear resistance can be achieved without causing catalyst poisoning. In the lubricating oil composition of the present invention, one kind of zinc dialkyldithiophosphate having a primary alkyl group (Pri-ZnDTP) and zinc dialkyldithiophosphate having a secondary alkyl group (Sec-ZnDTP) is used alone. These may be used, or two or more of these may be mixed and used. The mixing ratio in the case of mixing and using is not particularly limited. By combining with molybdenum dialkyldithiophosphate, even if any of Pri-ZnDTP and Sec-ZnDTP is used, an excellent friction reduction effect and wear resistance can be achieved at the same time. Although not limited, an embodiment in which Sec-ZnDTP is essential is particularly preferable, and an amount in which the amount of phosphorus derived from Sec-ZnDTP with respect to the mass of the entire lubricating oil composition is 200 to 1000 ppm by mass is preferable, and more preferable. Is preferably in an amount of 250 to 900 ppm by mass, particularly preferably 300 to 800 ppm by mass.

Further, in combination with zinc dialkyldithiophosphate, at least one selected from phosphates represented by the following formula (3), (4) or (5), phosphite-based phosphorus compounds, and metal salts and amine salts thereof. These compounds can also be used. However, the amount of these compounds is limited to an amount in which the total mass of phosphorus in the entire lubricating oil composition satisfies the above range. For example, it is preferably less than 0.1% by weight, more preferably less than 0.05% by weight, still more preferably less than 0.01% by weight, and most preferably not contained at all, based on the total amount of the lubricating oil composition. .
In the general formula (3), R ³ is a monovalent hydrocarbon group having 1 to 30 carbon atoms, and R ⁴ and R ⁵ are independently a hydrogen atom or a monovalent hydrocarbon group having 1 to 30 carbon atoms. And m is 0 or 1.
In the general formula (4), R ⁶ is a monovalent hydrocarbon group having 1 to 30 carbon atoms, and R ⁷ and R ⁸ are each independently a hydrogen atom or a monovalent hydrocarbon group having 1 to 30 carbon atoms. , N is 0 or 1.
In the general formula (5), R ⁶ is as described above.

In the general formulas (3), (4) and (5), examples of the monovalent hydrocarbon group having 1 to 30 carbon atoms represented by R ^{3 to} R ⁸ include an alkyl group, a cycloalkyl group, and an alkenyl group. , Alkyl-substituted cycloalkyl groups, aryl groups, alkyl-substituted aryl groups, and arylalkyl groups. In particular, an alkyl group having 1 to 30 carbon atoms or an aryl group having 6 to 24 carbon atoms is preferable, more preferably an alkyl group having 3 to 18 carbon atoms, and most preferably an alkyl group having 4 to 15 carbon atoms. It is.

  Examples of the phosphorus compound represented by the general formula (3) include phosphorous acid monoester having one hydrocarbon group having 1 to 30 carbon atoms and (hydrocarbyl) phosphonous acid; A phosphite diester having two hydrocarbon groups, a monothiophosphite diester, and a (hydrocarbyl) phosphonous monoester; a phosphite triester having three hydrocarbon groups having 1 to 30 carbon atoms, and (Hydrocarbyl) phosphonous acid diesters; and mixtures thereof.

  As described above, the lubricating oil composition of the present invention essentially comprises a lubricating base oil, (A) molybdenum dialkyldithiophosphate, and (B) zinc dialkyldithiophosphate. The amide friction modifier and the amine friction modifier can be further contained in less than the specific amount described above, but most preferably they are not included. Furthermore, in addition to these, as an optional component, one or more selected from (C) a viscosity index improver, (D) an ashless dispersant, and (E) a metal detergent may be included.

(C) Viscosity index improver As the viscosity index improver, for example, a polymer or copolymer of one or more monomers selected from various methacrylic acid esters, or a hydride thereof, a so-called non-dispersion type Viscosity index improver, or so-called dispersed viscosity index improver copolymerized with various methacrylic esters containing nitrogen compounds, non-dispersed or dispersed ethylene-α-olefin copolymer (as α-olefin, propylene, 1-butene, 1-pentene, etc.), or hydrides thereof, polyisobutenes or hydrides thereof, hydrides of styrene-diene copolymers, styrene-maleic anhydride ester copolymers, star-shaped isoprene, and the like Examples thereof include alkyl styrene. Further, a comb polymer containing at least a repeating unit based on a polyolefin macromer and a repeating unit based on an alkyl (meth) acrylate having an alkyl group having 1 to 30 carbon atoms in the main chain can also be used.

  The molecular weight of the viscosity index improver needs to be selected in consideration of the shear stability of the lubricating oil composition. For example, the weight average molecular weight of the viscosity index improver is usually 5,000 to 1,000,000, preferably 100,000 to 900,000 in the case of dispersed and non-dispersed polymethacrylates. Or, in the case of a hydride thereof, usually 800 to 5,000, preferably 1,000 to 4,000, and in the case of an ethylene-α-olefin copolymer or a hydride thereof, usually 800 to 500,000, preferably 3,000-200,000 is used.

Among the viscosity index improvers, when an ethylene-α-olefin copolymer or a hydride thereof is used, a lubricating oil composition particularly excellent in shear stability can be obtained. One or two or more compounds arbitrarily selected from the above viscosity index improvers can be contained in any amount.
The content of the viscosity index improver in the lubricating oil composition is 0.01 to 20% by mass, preferably 0.02 to 10% by mass, more preferably 0.05 to 5% by mass, based on the total amount of the composition. is there.

(D) Ashless Dispersant The lubricant composition of the present invention can further contain an ashless dispersant. A conventionally known ashless dispersant may be used and is not particularly limited. For example, a nitrogen-containing compound or derivative thereof having at least one alkyl group or alkenyl group having a straight chain structure or a branched structure having 40 to 400 carbon atoms, or a succinimide and a modified product thereof can be used. . Ashless dispersants may be used alone or in combination of two or more. A borated ashless dispersant can also be used. The boronated ashless dispersant is a borated version of any ashless dispersant used in lubricating oils. Boronation is generally performed by allowing boric acid to act on an imide compound to neutralize part or all of the remaining amino group and / or imino group.

  Carbon number of the said alkyl group or alkenyl group becomes like this. Preferably it is 40-400, More preferably, it is 60-350. When the carbon number of the alkyl group and the alkenyl group is less than the lower limit, the solubility of the compound in the lubricating base oil tends to decrease. Moreover, when the carbon number of an alkyl group and an alkenyl group exceeds the said upper limit, it exists in the tendency for the low-temperature fluidity | liquidity of a lubricating oil composition to deteriorate. The alkyl group and alkenyl group may have a straight chain structure or a branched structure. Preferable embodiments include, for example, oligomers of olefins such as propylene, 1-butene and isobutene, branched alkyl groups or branched alkenyl groups derived from ethylene and propylene co-oligomers.

  The succinimide is a reaction product of one end of a polyamine and succinic anhydride, a so-called monotype succinimide, and a reaction product of both ends of the polyamine and succinic anhydride. And succinimide. The lubricating oil composition of the present invention may contain one of monotype and bistype, or may contain both.

  The modified product of the succinimide is, for example, a product obtained by modifying succinimide with a boron compound (hereinafter sometimes referred to as a boronated succinimide). Modifying with a boron compound means boronation. A boronated succinimide may be used individually by 1 type, or may use 2 or more types together. When used in combination, it may be a combination of two or more of boronated succinimides. Moreover, both a monotype and a bis type may be included, the combined use of monotypes, or the combined use of bistypes may be sufficient. A boronated succinimide and a non-borated succinimide may be used in combination.

  For example, methods for producing a boronated succinimide are disclosed in JP-B-42-8013 and JP-A-42-8014, JP-A-51-52381, JP-A-51-130408, and the like. And the like. Specifically, for example, a boron compound such as boric acid, boric acid ester, or boric acid salt is added to polyamine and succinic anhydride (derivative) to organic solvents such as alcohols, hexane and xylene, light lubricating oil base oil, etc. It can be obtained by mixing and heat-treating under appropriate conditions. The boron content contained in the boronated succinimide thus obtained can usually be 0.1 to 4% by mass. In the present invention, a boron-modified compound of an alkenyl succinimide compound (boronated succinimide) is particularly preferable because of excellent heat resistance, antioxidant properties, and antiwear properties.

  The boron content contained in the borated ashless dispersant is not particularly limited. Usually, it is 0.1 to 3% by mass relative to the mass of the ashless dispersant. As one aspect of the present invention, the boron content in the ashless dispersant is preferably 0.2% by mass or more, more preferably 0.4% by mass or more, and preferably 2.5% by mass or less. More preferably, it is 2.3 mass% or less, More preferably, it is 2.0 mass% or less. The boronated ashless dispersant is preferably a boronated succinimide, and particularly preferably a boronated bissuccinimide.

  The borated ashless dispersant has a boron / nitrogen mass ratio (B / N ratio) of 0.1 or more, preferably 0.2 or more, preferably less than 1.0, more preferably 0.8 or less. What has is preferable.

  The content of the ashless dispersant may be appropriately adjusted. For example, the content of the ashless dispersant is preferably 0.01 to 20% by mass, and more preferably 0.1 to 10% by mass with respect to the mass of the entire lubricating oil composition. It is. If the content of the ashless dispersant is less than the above lower limit, the sludge dispersibility may be insufficient. Moreover, when content exceeds the said upper limit, there exists a possibility of deteriorating a specific rubber material or making low temperature fluidity worse.

(E) Metal detergent The metal detergent includes a detergent having an alkali metal or an alkaline earth metal. Examples include, but are not limited to, sulfonates containing alkali metals or alkaline earth metals, salicylates containing alkali metals or alkaline earth metals, and phenates containing alkali metals or alkaline earth metals. Examples of the alkali metal or alkaline earth metal include, but are not limited to, magnesium, barium, sodium, and calcium.

  More specifically, calcium sulfonate, magnesium sulfonate, calcium salicylate, magnesium salicylate, calcium phenate, and magnesium phenate are preferably used. A metal detergent may be used individually by 1 type, or may use 2 or more types together. The amount of alkali metal or alkaline earth metal contained in the metal detergent is not limited, but is preferably 0.1 to 20% by mass, more preferably 0.5 to 15% by mass, and 1.0 to 15%. More preferred is mass%.

  The metal detergent is not limited, but preferably has a total base number of 20 to 600 mgKOH / g, more preferably 50 to 500 mgKOH / g, further preferably 100 to 450 mgKOH / g, particularly preferably 150 to 400 mgKOH / g. g. Thereby, the acid neutralization property, high temperature cleanliness property, and rust prevention property which are required for lubricating oil are securable.

  The metal detergent may be contained in the lubricating oil composition at an arbitrary ratio. For example, it is 0.01-5 mass%, More preferably, it is 0.1-4 mass%, More preferably, it is 0.2-3 mass%.

  The lubricating oil composition of the present invention may further contain other additives other than those described above. Examples include oiliness agents, rust inhibitors, antioxidants, extreme pressure agents, corrosion inhibitors, metal deactivators, pour point depressants, antifoaming agents, colorants, and package additives for automatic transmission oils. . Various package additives for lubricating oils containing at least one of these can also be added. However, when using an additive having phosphorus, the total amount of phosphorus with respect to the total mass of the lubricating oil composition is 300 to 1500 mass ppm, preferably 400 to 1400 mass ppm, more preferably 500 to 1300 mass ppm, especially It is preferably adjusted within a range of 600 to 1200 ppm by mass, and most preferably 600 to 1000 ppm by mass.

  The high temperature high shear viscosity (HTHS viscosity) at 150 ° C. of the lubricating oil composition of the present invention is not limited, but is preferably 1.4 to 2.9 mPa.s. s, more preferably 1.7 to 2.6 mPa.s. s.

Kinematic viscosity at 100 ° C. of the lubricating oil composition of the present invention, but are not limited, is preferably 3~9.3mm ² / s, to be 3~8.2mm ² / s More preferably, it is 4 to 8.2 mm < ² > / s. When the kinematic viscosity at 100 ° C. of the lubricating oil composition is less than the above lower limit value, the friction coefficient may not be sufficiently ensured. On the other hand, if it exceeds the above upper limit value, the viscous resistance increases and the fuel consumption deteriorates.

  The viscosity index of the lubricating oil composition of the present invention is not limited, but is preferably 120 or more, and more preferably 160 or more. If the viscosity index of the lubricating oil composition is less than the above lower limit, the low temperature characteristics may not be sufficiently secured. The upper limit is not limited, but is preferably 250.

  The lubricating oil composition of the present invention has an excellent friction reducing effect and also has excellent wear resistance, despite the fact that the viscosity is reduced. The lubricating oil composition of the present invention is suitably used as an oil agent that intervenes between sliding surfaces in a sliding member. Moreover, the lubricating oil composition of the present invention functions suitably for lubricating diamond-like carbon (DLC) films. In particular, in a sliding member having a diamond-like carbon (DLC) film on at least one sliding surface, the lubricating oil composition of the present invention is provided between the DLC coating surface and the sliding surface of another metal member (particularly steel). By interposing an object, friction between the sliding surfaces can be further reduced, and excellent wear resistance can be provided. That is, a particularly preferred embodiment in the present invention is a combination of a diamond-like carbon (DLC) film and the above lubricating oil composition.

  The diamond-like carbon (DLC) film according to the present invention has an amorphous structure and may be a conventionally known DLC film. The DLC film is formed on at least one sliding surface of the sliding member. The DLC film is preferably doped with a predetermined element. Examples of the element include boron (B), titanium (Ti), vanadium (V), and molybdenum (Mo), and boron is particularly preferable. A further preferred embodiment of the present invention is a combination of a DLC film doped with boron and the above lubricating oil composition, thereby achieving both a superior friction reduction effect and wear resistance.

  The amount of boron is preferably 1 to 30%, more preferably 4 to 25% when the entire DLC film is 100 atomic%. If the amount of boron is less than the lower limit, the friction reducing effect and the wear resistance may be insufficient. Further, if the amount of boron exceeds the above upper limit value, a good DLC film may not be formed.

  The DLC film according to the present invention may be a so-called hydrogen-free DLC that does not contain hydrogen, but a DLC containing hydrogen is preferable because a friction reducing effect can be easily obtained. The amount of hydrogen is preferably 0 to 25%, 5 to 25%, 10 to 22%, and more preferably 15 to 20% when the entire film is 100 atomic%. As the amount of hydrogen in the DLC film increases, the low friction characteristics tend to be improved. However, if the amount of hydrogen is too large, the DLC film may become excessively soft and wear resistance may be reduced.

  The DLC film in the present invention may contain a modifying element or an inevitable impurity that improves its sliding characteristics. Examples of the element include O, Al, Mn, Si, Cr, W, and Ni. The content of these elements is not particularly limited, and may be adjusted as long as the effects of the present invention are not impaired. In particular, it is good that it is less than 8 atomic%, further less than 4 atomic%. The composition of the DLC film may be homogeneous, slightly changed, or even gradient with respect to its thickness direction.

  The base material on which the DLC film is formed (that is, the base material of the sliding member) is not particularly limited, but the DLC film is preferably harder than the base material and has a smaller elastic modulus than the base material. As a result, the wear resistance, toughness, impact resistance, etc. of the DLC coated surface can be improved. For example, the DLC film according to the present invention preferably has a hardness of 10 to 30 GPa, more preferably 14 to 25 GPa. If the hardness is too low, the wear resistance is lowered, and if the hardness is too high, the DLC film is liable to crack. From the same viewpoint, the elastic modulus of the DLC film is preferably, for example, 100 to 200 GPa, 110 to 190 GPa, 120 to 180 GPa, and further 130 to 170 GPa.

The DLC film may be formed by a conventionally known method. For example, it is possible to follow the method described in JP 2014-224239 A. Specifically, a sputtering method, particularly an unbalanced magnetron sputtering (UBMS) method is preferable, and a dense DLC film can be formed efficiently. Before forming the DLC film, it is preferable to evacuate the chamber to 10 ⁻⁵ Pa or less, or introduce hydrogen gas into the chamber to remove oxygen and moisture remaining in the chamber before film formation. The amount of hydrogen gas introduced may be adjusted according to the amount of H in the DLC film.

As the sputtering gas, for example, one or more of rare gases such as argon (Ar) gas, helium (He) gas, and nitrogen (N ₂ ) gas can be used. As the H-containing gas, one or more hydrocarbon-based gases such as methane (CH ₄ ), acetylene (C ₂ H ₂ ), and benzene (C ₆ H ₆ ) can be used. The gas flow rate, the DLC film deposition temperature, and the like may be appropriately selected according to a conventionally known method.

  The lubricating oil composition of the present invention can be applied to sliding parts in a wide variety of machines. In particular, a sliding machine including the lubricating oil composition of the present invention and a sliding member coated with a DLC film (particularly, a boron-containing DLC film) has a very low coefficient of friction between the sliding surfaces and is resistant to damage. Since it is excellent in wear, it is suitable for applications that require a reduction in mechanical loss due to sliding. For example, pistons, piston rings, piston pins, crankshafts, gears, rotors, rotor housings, cams, valve lifters, and the like. The lubricating oil composition of the present invention can be suitably used particularly for an internal combustion engine.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated in detail, this invention is not restrict | limited to the following Example.

In the following examples and comparative examples, the following evaluation materials for block-on-ring friction tests were prepared as test materials to be sliding members.
As a base material, a block-shaped (6.3 mm × 15.7 mm × 10.1 mm) steel material (SUS440C) subjected to quenching treatment was prepared. A DLC film was formed on the mirror-finished surface (surface roughness Rzjis 0.1 μm / sliding surface) of the steel material by using an unbalanced magnetron sputtering apparatus (UBMS504 manufactured by Kobe Steel, Ltd.). In order to form a DLC film doped with boron, B ₄ C was used as a doping target. The DLC film was formed by sputtering according to the method described in Japanese Patent Application Laid-Open No. 2014-224239. Thus, an evaluation material on which a DLC film (including hydrogen) doped with boron was formed was obtained. The thickness of each DLC film was about 2 μm. As for the composition of the obtained film, the boron content in the DLC film doped with boron was 6% as the boron content when the entire film was taken as 100 atomic%.

  Furthermore, as an evaluation material not coated with a DLC film, FALEX standard test pieces (hardness RC58-63) made of steel (SAE4620) are prepared as ring test pieces, and FALEEX made of steel (SAE O1) as block test pieces. A standard test piece (hardness RC58-63) was also prepared.

  In the following table, a test piece coated with a DLC film doped with boron is represented as “B-DLC”, and a test piece (steel material) not coated with the DLC film is represented as “Steel”.

Each component which comprises the lubricating oil composition of an Example and a comparative example is as follows.

・ Lubricant base oil GTL-derived base oil (100 ° C. kinematic viscosity = 4.1 mm ² / s, VI = 127)

(A) Molybdenum dialkyldithiophosphate (MoDTP)
Molybdenum content 9% by mass, represented by the above formula (1), X ₁ and X ₂ are oxygen atoms, Y ₁ and Y ₂ are sulfur atoms, and R is a monovalent hydrocarbon group having 8 carbon atoms. A compound.

Friction modifier other than the above (A) Molybdenum dithiocarbamate MoDTC (molybdenum content 10% by mass)
・ Mo trinuclear compound (Molybdenum content 5.5% by mass)
・ Oleylamine ・ Oleic acid amide

(B) Zinc dialkyldithiophosphate
・ Pri-ZnDTP (zinc dialkyldithiophosphate having a primary alkyl group)
Sec-ZnDTP (zinc dialkyldithiophosphate having a secondary alkyl group)
(B ′) Acidic phosphate ester A mixture of compounds represented by the following formula, wherein R ⁶ is a 2-ethylhexyl group and n is 1 or 2.

(C) Metal detergent ・ Ca salicylate (total base number 180 mgKOH / g, Ca content 6.3 mass%)
Mg sulfonate (total base number 400 mg KOH / g, Mg content 9.4 mass%)

(D) Ashless dispersant ・ Borated succinimide (B content 0.7 mass%, N content 2.0 mass%)
・ Non-borated succinimide (N content: 1.0% by mass)
(E) Viscosity index improver
・ Polymethacrylate (Mw = 300,000)
(F) Other additive packages
・ Antioxidants: phenolic antioxidants, amine antioxidants ・ Antifoaming agents: dimethyl silicone

[Examples 1-14 and Comparative Examples 1-5]
A lubricating oil composition was prepared by mixing the components described above in the compositions and amounts shown in the table.
Each amount described in the table will be described below.
The amount of the molybdenum-based friction modifier is ppm by mass with respect to the total amount of the lubricating oil composition converted to the molybdenum content. About MoDTP, mass ppm of the amount of phosphorus derived from MoDTP with respect to the total amount of the lubricating oil composition is also described.
The amount of zinc dialkyldithiophosphate is ppm by weight of the amount of phosphorus derived from the zinc dialkyldithiophosphate relative to the total amount of the lubricating oil composition.
The amount of oleylamine, oleic amide, and acidic phosphate ester is mass% based on the total amount of the lubricating oil composition.
The amount of the metal detergent is mass% with respect to the total amount of the lubricating oil composition in terms of calcium and magnesium contents.
The amount of the ashless dispersant is ppm by mass with respect to the total amount of the lubricating oil composition converted to the amount of boron, and ppm by mass with respect to the total amount of the lubricating oil composition converted to the amount of nitrogen.
In the table, the total mass ppm of phosphorus with respect to the total amount of the lubricating oil composition is also described.

The following tests were conducted on these lubricating oil compositions. The results are shown in the table.
(1) The kinematic viscosity (KV100) at 100 ° C. was measured according to ASTM D445. (2) The high temperature high shear viscosity (HTHS viscosity) at 150 ° C. was measured according to ASTM D4683.
(3) Measurement of minimum friction coefficient Block test piece having a sliding surface width of 6 mm (test piece covered with DLC film or test piece not covered with DLC film (standard specimen made of FALEX (steel material (SAE O1))) Hardness RC58-63)) and a ring test piece made of steel having an outer diameter of 35 mm and a width of 9 mm (standard test piece made of FALEEX (hardness RC58-63) made of steel (SAE4620)) A block-on-ring friction test is shown in Fig. 1. The block-on-ring friction test is schematically shown in Fig. 1. The test load is 294 N, the sliding speed is 0.3 m / s, and the oil temperature is 80 ° C (constant). A block-on-ring friction test was performed for 30 minutes, and the minimum friction coefficient in 30 minutes was defined as the minimum friction coefficient in the test.
(4) Evaluation of wear amount For each of the block test pieces before and after the block on-ring friction test, the surface roughness is measured with a surface roughness meter (SURFTEST SV-3200, manufactured by Mitutoyo Corporation). The amount of wear was calculated. The amount of wear was measured at a total of three locations, one in the center of the sliding trace and two in the central portion of 1 mm from both ends of the sliding trace, and the average value was taken as the amount of wear in this test.

As shown in Comparative Example 2, in the lubricating oil composition containing only molybdenum dithiocarbamate (MoDTC), the friction reducing effect is insufficient between the sliding surface between the DLC coating surface and the steel material, and large wear occurs. End up. As shown in Comparative Example 1, the lubricating oil composition containing only the molybdenum trinuclear compound has a large friction between the sliding surfaces. Further, large wear occurs between the sliding surfaces of the DLC coating surface and the steel material. Further, as shown in Comparative Example 3, in the lubricating oil composition containing only the molybdenum trinuclear compound, the friction between the sliding surfaces is large even if the amount of the molybdenum trinuclear compound is reduced. Furthermore, as shown in Comparative Examples 6 to 8, in the lubricating oil composition containing an amino friction modifier or an amide friction modifier in the amount described in the examples of Patent Document 3, the sliding between the B-DLC coating surface and the steel material is performed. The friction coefficient between the moving surfaces is high and the amount of wear is large.
On the other hand, as shown in Tables 1 and 2, the lubricating oil composition of the present invention is excellent not only between the sliding surfaces between the steel materials and the steel materials, but also between the sliding surfaces between the B-DLC coating surface and the steel materials. In addition, a friction reducing effect can be given, and wear resistance can be improved.

  The lubricating oil composition of the present invention contains only molybdenum dithiocarbamate or Mo trinuclear structure compound as a friction modifier, especially between the sliding surfaces of the DLC coating surface and other metal members (especially steel materials). Compared to the lubricating oil composition, a lower coefficient of friction can be given, and the wear resistance is also excellent. The lubricating oil composition of the present invention is particularly preferably used as a lubricating oil composition for internal combustion engines.

DESCRIPTION OF SYMBOLS 1 Load 2 Block test piece 3 Ring test piece 4 Lubricating oil composition

Claims (9)

  It contains a lubricating base oil, (A) molybdenum dialkyldithiophosphate, and (B) zinc dialkyldithiophosphate, and the amount of phosphorus relative to the total mass of the lubricating oil composition is 300 to 1500 mass ppm. A lubricating oil composition. (A ′) further containing at least one selected from the group consisting of an amine-based friction modifier and an amide-based friction modifier in an amount that is less than 0.1% by mass with respect to the total mass of the lubricating oil composition, or The lubricating oil composition according to claim 1, wherein none of them is contained.   The amount of the component (A) is 400 to 1300 ppm by mass with respect to the mass of the entire lubricating oil composition as the amount of molybdenum, and the amount of the component (B) is the total amount of the lubricating oil composition as the amount of phosphorus. The lubricating oil composition of Claim 1 or 2 which is 200-1000 mass ppm with respect to mass.   The lubricating oil composition according to any one of claims 1 to 3, which is used for lubricating a diamond-like carbon (DLC) film.   A pair of sliding members having opposed sliding surfaces that can move relative to each other, wherein at least one sliding surface is a surface covered with a diamond-like carbon (DLC) film. The lubricating oil composition according to any one of claims 1 to 3, wherein the lubricating oil composition is used for lubrication.   The lubricating oil composition according to claim 4 or 5, wherein the DLC film contains boron.   The lubricating oil composition according to any one of claims 1 to 6, which has a high temperature high shear viscosity (HTHS viscosity) at 150 ° C of 1.4 to 2.9 mPa · s. The lubricating oil composition according to claim 1, which has a kinematic viscosity at 100 ° C. of 9.3 mm ² / s or less.   The lubricating oil composition according to any one of claims 1 to 8, which is used for an internal combustion engine.