JP5414513B2 - System lubricant composition for crosshead type diesel engine - Google Patents

Description

  The present invention relates to a system lubricant composition for a crosshead type diesel engine.

Crosshead diesel engines use cylinder oil that lubricates between the cylinder and piston, and system oil that controls lubrication and cooling of other parts. The cylinder oil is required to have a proper viscosity necessary for lubrication between the cylinder and the piston (piston ring) and a function of maintaining cleanliness necessary for proper movement of the piston and piston ring. Furthermore, this engine has a problem of cylinder corrosion due to acidic components such as sulfuric acid generated by combustion because high sulfur fuel is usually used because of its economic efficiency. In order to prevent this problem, the cylinder oil must have a function of neutralizing acidic components such as sulfuric acid to prevent corrosion.
On the other hand, system oil, unlike ordinary diesel engine oil, does not come into contact with combustion gas, is stored in a tank, and is supplied to bearings and the like by a circulation pump for lubrication and cooling. Since it is used over a long period of time, it is required to maintain an appropriate viscosity for a long period of time (for example, Patent Document 1). However, in the marine crosshead type engine, there is a problem that the viscosity of the system oil is increased by mixing the drip oil of the cylinder oil, and it has been a long-standing problem how to suppress the increase in the viscosity. In particular, due to the recent increase in environmental problems, it has become important to prevent deterioration in fuel consumption due to increased friction loss at the bearing portion due to increased viscosity and reduction in heat exchange efficiency on the piston cooling surface. It was.

JP 2002-275491 A

  It is an object of the present invention to provide a system lubricating oil composition for a crosshead type diesel engine that can prevent deterioration in fuel consumption by suppressing an increase in viscosity.

As a result of intensive studies to solve the above problems, the inventors of the present invention can balance the increase in the viscosity due to the drip oil and the decrease in the viscosity due to thermal decomposition of the polymer by adding the specific polymer. The present invention has been completed by finding that it is effective as a system lubricant composition for a crosshead type diesel engine.
Specifically, piston cooling is achieved by blending a lubricating oil base oil with a star polymer having a vinyl aromatic hydrocarbon structure in the molecule that has excellent shear stability but is easily decomposed by heat. On the surface, the polymer decomposes to lower the viscosity of the system oil, offset the increase in viscosity due to the cylinder drip oil mixing, and suppress the deterioration of fuel consumption.

That is, the present invention provides a base number of 4 to 20 mgKOH / g, 100 based on mineral oil and / or synthetic oil and containing (A) a star polymer having a vinyl aromatic hydrocarbon structure in the molecule. The present invention relates to a system lubricating oil composition for a crosshead type diesel engine, wherein the kinematic viscosity at ° C is 7.5 to 15.0 mm ² / s.

Further, in the present invention, the component (A) is a compound having a structure in which a diene polymer or copolymer radially extends from a vinyl aromatic hydrocarbon nucleus located at the center of the molecule. The present invention relates to a system lubricant composition for a head type diesel engine.
The present invention also relates to the system lubricating oil composition for a crosshead type diesel engine as described above, wherein the vinyl aromatic hydrocarbon is divinylbenzene.
The present invention also relates to the system lubricating oil composition for a crosshead type diesel engine as described above, wherein the diene polymer or copolymer is polyisoprene or isoprene-styrene copolymer.

Further, the present invention further comprises at least one selected from (B) a metal-based detergent, (C) a zinc dialkyldithiophosphate, (D) a rust inhibitor and (E) an ashless dispersant. The present invention relates to a system lubricant composition for a crosshead type diesel engine as described above.
The present invention also relates to the system lubricating oil composition for a crosshead type diesel engine described above, wherein the base oil has a kinematic viscosity at 100 ° C. of 3.5 to 9.3 mm ² / s.

  By using the system lubricating oil composition for a crosshead type diesel engine of the present invention, an increase in the viscosity of the system oil is suppressed, and as a result, deterioration of fuel consumption can be prevented.

Hereinafter, the present invention will be described in detail.
The lubricating base oil used in the system lubricating oil composition for a crosshead type diesel engine of the present invention (hereinafter referred to as the lubricating oil composition of the present invention) is not particularly limited, and mineral oil, synthetic oil or a mixture thereof is used. can do.

  Specifically, as the mineral base oil, the lubricating oil fraction obtained by subjecting the crude oil to atmospheric distillation obtained under reduced pressure is subjected to solvent removal, solvent extraction, hydrocracking, Produced by one or more processes such as solvent dewaxing, hydrorefining, etc., or by a method of isomerizing GTL WAX (Gas Liquid Wax) produced by wax isomerized mineral oil, Fischer-Tropsch process, etc. Lubricating oil base oil and the like can be exemplified.

  Specific examples of synthetic base oil include polybutene or hydrides thereof; poly α-olefins such as 1-octene oligomers and 1-decene oligomers or hydrides thereof; ethylene and α-olefins having 3 to 30 carbon atoms Copolymer with ditridecyl glutarate, di-2-ethylhexyl adipate, diisodecyl adipate, ditridecyl adipate, di-2-ethylhexyl sebacate and the like; trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol Polyol esters such as 2-ethylhexanoate and pentaerythritol pelargonate; Copolymers of dicarboxylic acids such as dibutyl maleate and α-olefins having 2 to 30 carbon atoms; Alkyl naphthalene, alkyl benzene, aromatic ester The aromatic synthetic oils or mixtures thereof etc. and the like can be exemplified.

  As the lubricating base oil used in the lubricating oil composition of the present invention, a mineral base oil or a synthetic base oil may be used alone or in combination of two or more, or a mineral oil base oil may be used. One type or two or more types of base oils and one or more types of synthetic base oils can be mixed and used.

Kinematic viscosity at 100 ° C. of the lubricating base oil of the present invention is preferably 9.3 mm ² / s or less, more preferably 8.5 mm ² / s, more preferably not more than 8.0 mm ² / s. On the other hand, the kinematic viscosity at 100 ° C. is preferably 3.5 mm ² / s or more, more preferably 3.8 mm ² / s or more, and still more preferably 4.0 mm ² / s or more. The kinematic viscosity at 100 ° C. here refers to the kinematic viscosity at 100 ° C. as defined in ASTM D-445. When the kinematic viscosity at 100 ° C. of the lubricating base oil exceeds 9.3 mm ² / s, there is a possibility that the viscosity increase inhibiting effect when cylinder drip oil is mixed may not be recognized because the viscosity decrease is small. If it is less than ² / s, the viscosity drop is too great, so that the oil film forming ability of the bearing is lowered and seizure may occur.

The kinematic viscosity at 40 ° C. of the lubricating base oil according to the present invention is not particularly limited, but is preferably 150 mm ² / s or less, more preferably 120 mm ² / s or less, and still more preferably 90 mm ² / s or less. On the other hand, the kinematic viscosity at 40 ° C. is preferably 15 mm ² / s or more, more preferably 20 mm ² / s or more, and further preferably 25 mm ² / s or more. When the kinematic viscosity at 40 ° C. of the lubricating base oil exceeds 200 mm ² / s, there is a possibility that the increase in viscosity when cylinder drip oil is mixed may not be observed because the viscosity is small, and less than 50 mm ² / s. In this case, since the decrease in viscosity is too large, the oil film forming ability of the bearing is decreased, and seizure may occur.

The viscosity index of the lubricating base oil according to the present invention is preferably 85 or more, more preferably 90 or more, and still more preferably 95 or more. The upper limit of the viscosity index is not particularly limited, and normal paraffin, slack wax, GTL wax, etc., or isoparaffin mineral oil obtained by isomerizing these can also be used.
In addition, the viscosity index as used in the field of this invention means the viscosity index measured based on JISK2283-1993.

  The lubricating oil composition of the present invention contains (A) a star polymer having a vinyl aromatic hydrocarbon structure in the molecule as an essential component. Specifically, the star polymer having a vinyl aromatic hydrocarbon structure in the molecule means a polymer polymer or copolymer arm of a large number (two or more) of diene from the nucleus of the vinyl aromatic hydrocarbon located at the center of the molecule ( (Arm) is a compound having a radially extending structure.

  The vinyl aromatic hydrocarbons located at the center of the molecule include divinylbenzene, trivinylbenzene, tetravinylbenzene, divinylortho-, meta- or para-xylene, trivinylortho-, meta- or para-xylene, tetravinyl. Ortho-, meta- or para-xylene, divinylnaphthalene, divinylethylbenzene, divinylbiphenyl, diisobutenylbenzene, diisopropenylbenzene, diisopropenylbiphenyl and the like can be mentioned. Of these, divinylbenzene is preferred.

The diene monomer constituting the diene polymer or copolymer preferably has 4 to 12 carbon atoms, specifically 1,3-butadiene, isoprene, piperylene, methylpentadiene, phenylbutadiene, 3,4-dimethyl- Examples include 1,3-hexadiene and 4,5-diethyl-1,3-octadiene. Of these, 1,3-butadiene and isoprene are preferred.
Examples of the diene polymer or copolymer serving as an arm of the star polymer include diene homopolymers such as polyisoprene and diene comopolymers such as isoprene-butadiene copolymer. Further, it may be a copolymer of diene and another monomer other than diene (for example, isoprene / styrene copolymer). The copolymer may be a random copolymer or a block copolymer.

In the present invention, the weight average molecular weight (M _w ) of the star polymer having a vinyl aromatic hydrocarbon structure in the molecule used as the component (A) is preferably 10,000 or more, more preferably 50,000. Or more, more preferably 100,000 or more. Moreover, it is preferable that it is 1,000,000 or less, More preferably, it is 800,000 or less, More preferably, it is 500,000 or less. When the weight average molecular weight is less than 10,000, not only the viscosity adjustment effect may not be sufficiently exhibited, but also the cost may increase, and when the weight average molecular weight exceeds 1,000,000. Since the shear stability is poor, the viscosity adjusting effect may not be exhibited in the same manner.

The PSSI (Permanent Cysability Index) of the star polymer having a vinyl aromatic hydrocarbon structure in the molecule used in the present invention is preferably 1 to 40, more preferably 1 to 35, still more preferably 1 to 30, particularly Preferably it is 1-25. When PSSI exceeds 40, since shear stability is bad, there exists a possibility that the viscosity adjustment effect cannot fully be exhibited. Moreover, when PSSI is less than 1, there exists a possibility that the viscosity adjustment effect cannot be exhibited similarly.
The “PSSI” referred to here conforms to ASTM D 6022-01 (Standard Practice for Calculation of Permanent Shear Stability Index) and conforms to ASTM D 6278-02 (Test Metohd for Shear Stability of Polymer Containing Fluids Using a European Diesel). It means the permanent shear stability index of the polymer calculated based on the data measured by the Injector Apparatus).

  The content of the component (A) in the lubricating oil composition of the present invention is preferably 1 to 20% by mass, more preferably 2 to 15% by mass, further preferably 3 to 12% by mass, based on the total amount of the composition. Most preferably, it is 4-10 mass%. When the content is less than 1% by mass, the viscosity adjustment effect may not be sufficiently exhibited. When the content exceeds 20% by mass, deposits are generated due to deterioration of the polymer and the cleanliness deteriorates. There is a fear.

  The lubricating oil composition of the present invention further contains at least one selected from (B) a metal-based detergent, (C) a zinc dialkyldithiophosphate, (D) a rust inhibitor and (E) an ashless dispersant. It is preferable.

  (B) As a metal detergent, use one or more metal detergents selected from phenate detergents, sulfonate detergents, salicylate detergents, carboxylate detergents and phosphonate detergents. Can do.

The phenate metal detergent contains, for example, an alkylphenol having a structure represented by the following formulas (1) to (3), an alkylphenol sulfide, an alkaline earth metal salt of a Mannich reaction product of an alkylphenol, or a (over) basic salt thereof. It is a phenate metal detergent.
Examples of the alkaline earth metal include magnesium, barium, and calcium. Magnesium or calcium is preferable, and calcium is particularly preferable.

In the general formula ^{(1) ~ (3),} R 1, R 2, R 3, R 4, R 5, R 6 and ^{R 7,} which may be different from each other in the same 4 to 30 carbon atoms, preferably Represents a 6-18 linear or branched alkyl group. If the carbon number is shorter than 4, the solubility in the lubricating base oil may be poor. If the carbon number is longer than 30, the production is difficult and the heat resistance may be poor. Specific examples of R ^{1 to} R ⁷ include butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, Heptadecyl group, octadecyl group, nonadecyl group, icosyl group, heicosyl group, docosyl group, tricosyl group, tetracosyl group, pentacosyl group, hexacosyl group, heptacosyl group, octacosyl group, nonacosyl group, triacontyl group, etc. But it may be branched. These may also be primary alkyl groups, secondary alkyl groups or tertiary alkyl groups.
M ¹ , M ² and M ³ each represent an alkaline earth metal, preferably calcium and / or magnesium, x, y and z each independently represent an integer of 1 to 3, and m represents 0, 1 or 2 , N represents 0 or 1.

  As the sulfonate detergent, an alkali metal salt or alkaline earth metal salt of an alkyl aromatic sulfonic acid obtained by sulfonating an alkyl aromatic compound having a molecular weight of 300 or more, preferably 400 to 700, and / or ( Per) basic salts can be used. Examples of the alkali metal or alkaline earth metal include sodium, potassium, magnesium, barium, and calcium. Magnesium and / or calcium are preferable, and calcium is particularly preferably used.

  Specific examples of the alkyl aromatic sulfonic acid include so-called petroleum sulfonic acid and synthetic sulfonic acid. As the petroleum sulfonic acid here, generally used is a product obtained by sulfonating an alkyl aromatic compound of a lubricating oil fraction of mineral oil, or so-called mahoganic acid produced as a by-product when white oil is produced. In addition, as the synthetic sulfonic acid, for example, a sulfonated alkylbenzene having a linear or branched alkyl group, which is obtained as a by-product from an alkylbenzene production plant that is a raw material of a detergent or is obtained by alkylating polyolefin with benzene, is obtained. Or those obtained by sulfonating alkylnaphthalene such as dinonylnaphthalene. The sulfonating agent for sulfonating these alkyl aromatic compounds is not particularly limited, but usually fuming sulfuric acid or anhydrous sulfuric acid is used.

  The salicylate-based detergent is an alkali metal or alkaline earth metal salicylate having one hydrocarbon group having 1 to 19 carbon atoms and / or (over) basic salt thereof, 1 hydrocarbon group having 20 to 40 carbon atoms. Alkali metal or alkaline earth metal salicylate and / or (over) basic salt thereof, alkali metal or alkaline earth metal salicylate having two or more hydrocarbon groups having 1 to 40 carbon atoms and / or ( Per) basic salts (these hydrocarbon groups may be the same or different). In these, it is desirable to use the alkali metal or alkaline-earth metal salicylate which has one C8-C19 hydrocarbon group, and / or its (over) basic salt from the point which is excellent in low-temperature fluidity | liquidity. Examples of the alkali metal or alkaline earth metal include sodium, potassium, magnesium, barium, and calcium. Magnesium and / or calcium are preferable, and calcium is particularly preferably used.

The base number of the metal detergent (B) used in the present invention is preferably in the range of 50 to 500 mgKOH / g, more preferably in the range of 100 to 450 mgKOH / g, and 150 to 350 mgKOH / g. More preferably, it is the range. If the base number of the metal detergent is less than 50 mgKOH / g, there is a risk that corrosion wear will increase due to insufficient acid neutralization, and if it exceeds 500 mgKOH / g, there may be a problem in solubility. There is.
The base number referred to here is 7. JIS K2501 “Petroleum products and lubricating oils-Neutralization number test method”. Means the base number measured by the perchloric acid method according to the above.

(B) The metal ratio of the metallic detergent is not particularly limited, but the lower limit is 1 or more, preferably 2 or more, particularly preferably 2.5 or more, and the upper limit is preferably 20 or less, more preferably 15 or less, particularly preferably. Is preferably 10 or less.
The metal ratio referred to here is represented by (B) the valence of the metal element in the metal-based detergent × metal element content (mol%) / soap group content (mol%). Alkaline earth metals such as calcium and magnesium and soap groups mean phenol groups.

  In the composition of the present invention, when the (B) metal detergent is used, the content is usually 0.5 to 15% by mass, preferably 1 to 12% by mass, particularly preferably based on the total amount of the composition. 1.5 to 10% by mass.

The lubricating oil composition of the present invention preferably contains (C) zinc dialkyldithiophosphate represented by the following general formula (4).

In formula (4), R ¹ , R ² , R ³ and R ⁴ may be the same or different, and each independently represents an alkyl group having 1 to 30 carbon atoms or an alkylaryl group having 7 to 30 carbon atoms. Yes, the alkyl group may be linear or branched, and may be primary or secondary.

In addition, as a manufacturing method of (C) component dithiophosphate zinc, the conventional arbitrary methods are employable and it does not restrict | limit in particular. For example, it can be synthesized by reacting an alcohol having an alkyl group corresponding to R ¹ , R ² , R ³ and R ⁴ with diphosphorus pentasulfide to produce dithiophosphoric acid and neutralizing it with zinc oxide. it can.

  In the lubricating oil composition of the present invention, when (C) zinc dithiophosphate is used, its content is preferably 0.005 to 0.12% by mass as phosphorus element content based on the total amount of the composition. More preferably, it is 0.01-0.10 mass%, More preferably, it is 0.02-0.08 mass%. If it is less than 0.005% by mass, the extreme pressure and gear characteristics required for system oil cannot be obtained, and if it exceeds 0.12% by mass, the seal ring and oil slaver ring of the bearing and stuffing box may be corroded. is there.

The lubricating oil composition of the present invention preferably contains (D) a rust inhibitor.
Examples of the rust preventive include sulfonates (salts such as sodium, calcium and barium), succinic acid derivatives, organic acid esters such as fatty acid esters and sorbitan acid esters, and carboxylates (sodium such as stearic acid and naphthenic acid). , Magnesium, barium, zinc, etc.), polyhydric alcohol partial esters such as sorbitan monoester and pentaerythritol monoester, oxidized paraffin (oxidized wax), carboxylic acid, phosphate ester and the like, and sulfonate is preferred.

  In the lubricating oil composition of the present invention, when (D) a rust inhibitor is used, its content is preferably 0.005 to 5% by mass based on the total amount of the composition.

The lubricating oil composition of the present invention preferably contains (E) an ashless dispersant.
As the ashless dispersant, any ashless dispersant used in lubricating oils can be used. For example, a linear or branched alkyl group or alkenyl group having 40 to 400 carbon atoms, preferably 60 to 350 carbon atoms, is included in the molecule. Examples thereof include at least one succinimide, benzylamine, polyamine, and modified products thereof.
The alkyl group or alkenyl group may be linear or branched, but preferred examples include those derived from olefin oligomers such as propylene, 1-butene and isobutylene, and copolymers derived from ethylene and propylene. Examples thereof include a branched alkyl group and a branched alkenyl group.

In these, the succinimide shown by the following Formula or its boron modified product is preferable.

In the formula (5), R ¹ represents an alkyl group or alkenyl group having 40 to 400 carbon atoms, preferably 60 to 350 carbon atoms, and h represents an integer of 1 to 5, preferably 2 to 4. On the other hand, in formula (6), R ² and R ³ each independently represent an alkyl group or alkenyl group having 40 to 400 carbon atoms, preferably 60 to 350 carbon atoms, and particularly preferably a polybutenyl group. I represents an integer of 0 to 4, preferably 1 to 3.

  In the lubricating oil composition of the present invention, when an ashless dispersant is used, the content thereof is preferably 1 to 8% by mass based on the total amount of the composition.

  The lubricating oil composition of the present invention is an optional component commonly used in lubricating oils depending on its purpose in order to further improve its performance or to add other required performance in addition to the above configuration. Further additives can be added. Examples of such additives include additives such as antioxidants, extreme pressure agents, corrosion inhibitors, demulsifiers, metal deactivators, pour point depressants, and antifoaming agents.

As antioxidants, phenolic antioxidants such as DBPC, bisphenol and hindered phenol, amine antioxidants such as diphenylamine and N-phenyl-α-naphthylamine, and metal antioxidants such as copper and molybdenum Is mentioned.
In the lubricating oil composition of the present invention, when an antioxidant is used, its content is preferably 0.05 to 5% by mass based on the total amount of the composition.

As the extreme pressure agent, any extreme pressure agent / antiwear agent used for lubricating oil can be used. For example, sulfur-based, phosphorus-based, sulfur-phosphorus extreme pressure agents and the like can be used. Specifically, phosphites, thiophosphites, dithiophosphites, trithiophosphites Esters, phosphate esters, thiophosphate esters, dithiophosphate esters, trithiophosphate esters, amine salts thereof, metal salts thereof, derivatives thereof, dithiocarbamate, zinc dithiocarbamate, molybdenum dithiocarbamate, disulfide , Polysulfides, sulfurized olefins, sulfurized fats and oils, and the like.
In the lubricating oil composition of the present invention, when an extreme pressure agent is used, the content thereof is preferably 0.05 to 5% by mass based on the total amount of the composition.

  Examples of the corrosion inhibitor include benzotriazole, tolyltriazole, thiadiazole, and imidazole compounds.

  Examples of the demulsifier include polyalkylene glycol nonionic surfactants such as polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, and polyoxyethylene alkyl naphthyl ether.

  Examples of metal deactivators include imidazoline, pyrimidine derivatives, alkylthiadiazoles, mercaptobenzothiazoles, benzotriazoles or derivatives thereof, 1,3,4-thiadiazole polysulfide, 1,3,4-thiadiazolyl-2,5-bis. Examples thereof include dialkyl dithiocarbamate, 2- (alkyldithio) benzimidazole, β- (o-carboxybenzylthio) propiononitrile.

  As the pour point depressant, for example, a polymethacrylate polymer compatible with the lubricating base oil to be used can be used.

Examples of antifoaming agents include silicone oils having a kinematic viscosity at 25 ° C. of 100 to 100,000 mm ² / s, alkenyl succinic acid derivatives, esters of polyhydroxy aliphatic alcohols and long chain fatty acids, methyl salicylates and o- Hydroxybenzyl alcohol, aluminum stearate, potassium oleate, N-dialkyl-allylamine nitroaminoalkanol, aromatic amine salt of isoamyl octyl phosphate, alkylalkylene diphosphate, metal derivative of thioether, metal derivative of disulfide, aliphatic hydrocarbon Fluorine compounds, triethylsilane, dichlorosilane, alkylphenyl polyethylene glycol ether sulfide, fluoroalkyl ether and the like can be mentioned.

  When these additives are contained in the lubricating oil composition of the present invention, the content is based on the total amount of the composition, and is usually 0.005 to 5% by mass for the corrosion inhibitor, the rust inhibitor, and the demulsifier, The metal deactivator is usually selected from the range of 0.005 to 1% by mass, and the antifoaming agent is usually selected from the range of 0.0005 to 1% by mass.

Incidentally, the kinematic viscosity at 100 ° C. of the lubricating oil composition of the present invention is required to be 7.5 mm ² / s or more, preferably 9.3 mm ² / s or more, more preferably 10 mm ² / s or more is there. The kinematic viscosity at 100 ° C. of the lubricating oil composition of the present invention is required to be 15.0 mm ² / s or less, preferably 14.5 mm ² / s or less, more preferably 12.5 mm ² / s or less. It is. When the kinematic viscosity at 100 ° C. is less than 7.5 mm ² / s, the oil film forming ability is insufficient and the bearing may be seized. On the other hand, if it exceeds 15.0 mm ² / s, cooling of the piston cooling surface is insufficient, which may cause burning of the piston, and may increase fuel consumption due to increased friction loss.

  Further, the base number of the lubricating oil composition of the present invention is required to be 4 to 20 mgKOH / g, the lower limit is preferably 5 mgKOH / g or more, more preferably 5.5 mgKOH / g or more, and the upper limit is preferably Is 15 mg KOH / g or less, more preferably 10 mg KOH / g or less. When the base number is less than 4 mgKOH / g, the cleanliness may be insufficient, and when the base number exceeds 20 mgKOH / g, the contaminated contaminants may be difficult to remove with a cleaner.

  The lubricating oil composition of the present invention is not only used as a system oil for a crosshead type diesel engine, but also for a trunk piston type diesel engine, a gasoline engine for two-wheeled vehicles, four-wheeled vehicles, for power generation, cogeneration, etc., diesel It can also be suitably used for engines, gas engines and the like.

  Hereinafter, the content of the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these.

(Examples 1-9, Comparative Examples 1-4)
The lubricating oil compositions (Examples 1 to 9) of the present invention shown in Table 1 and comparative lubricating oil compositions (Comparative Examples 1 to 4) were prepared. About the obtained composition, the hot tube test was implemented and the result was similarly shown in Table 1. For Examples 1 to 7 and Comparative Examples 1, 3, and 4, the amount of the polymer compound added so that the kinematic viscosity at 100 ° C. of the composition with the additive added was 11.5 mm ² / s. And the blending ratio of the base oil was adjusted.

(Base oil)
Base oil A: 100 neutral (kinematic viscosity @ 100 ° C .: 4.42 mm ² / s)
Base oil B: 250 neutral (kinematic viscosity @ 100 ° C .: 7.12 mm ² / s)
Base oil C: 500 neutral (kinematic viscosity @ 100 ° C: 10.8 mm ² / s)
Base oil D: 150 bright stock (kinematic viscosity @ 100 ° C: 31.7 mm ² / s)
(Additive)
(1) Polymer compound A-1: Polyisoprene star polymer (polymer of polyisoprene bonded as an arm to divinylbenzene, PSSI = 2)
A-2: Polyisoprene / polystyrene star polymer (polymer of divinylbenzene bonded with isoprene / styrene copolymer as an arm. PSSI = 25)
PMA: Polymethacrylate (PSSI = 5)
PB: Polybutene (molecular weight 800)
(2) Additives other than polymer compounds B-1: Metal-based detergent (overbased calcium phenate: base number 255 mgKOH / g, Ca content 9.25% by mass)
B-2: Metal-based detergent (overbased calcium salicylate: base number 170 mg KOH / g, Ca content 6.2% by mass)
Zinc dialkyldithiophosphate: primary zinc dialkyldithiophosphate (alkyl = 2-ethylhexyl, P content 7.4% by mass)
Rust preventive agent: neutral calcium sulfonate (base number 20 mg KOH / g, Ca content 2.35% by mass)
Ashless dispersant: Alkenyl succinimide (bis type, nitrogen content: 1% by mass)
Other additives (antioxidants, extreme pressure agents, pour point depressants, antifoaming agents, etc.)

(Hot tube test)
It implemented based on JPI-5S-55-99. The test temperature is set to 250 ° C., the oil flowing out from each glass tube is collected, and the viscosity thereof is measured by an automatic capillary viscometer (CACV) manufactured by Cannon. For the six sample oils, the following two cases were tested.
A) 100% new oil
B) A mixture of 15% by mass of cylinder drip oil collected from a crosshead type diesel engine mounted in VLCC (Middle East to Japan) with 85% of new oil. The properties of the cylinder drip oil are as follows: kinematic viscosity (100 ° C.): 28.1 mm ² / s, acid value: 7.5 mgKOH / g, base number (perchloric acid method): 24.1 mgKOH / g, pentane insoluble matter (A Method): 6.0% by mass.

  As is clear from the results in Table 1, the lubricating oil composition of the present invention is not different from the comparative oil in viscosity change when tested with 100% fresh oil, but when mixed with cylinder drip oil, It can be seen that the increase in viscosity is small compared to the comparative oil.

  The lubricating oil composition of the present invention is excellent in fuel efficiency because of little increase in viscosity even when cylinder drip oil is mixed, and exhibits particularly excellent effects as a system lubricating oil composition for a crosshead type diesel engine. To do.

Claims (6)

A base oil based on mineral oil and / or synthetic oil and containing (A) a star polymer having a vinyl aromatic hydrocarbon structure in the molecule, a base number of 4 to 20 mgKOH / g, and a kinematic viscosity at 100 ° C. of 7 A system lubricating oil composition for a crosshead type diesel engine, characterized in that it is 5 to 15.0 mm ² / s.   The crosshead type according to claim 1, wherein the component (A) is a compound having a structure in which a diene polymer or copolymer is radially extended from a vinyl aromatic hydrocarbon nucleus located at the center of the molecule. System lubricant composition for diesel engines.   The system lubricating oil composition for a crosshead type diesel engine according to claim 1 or 2, wherein the vinyl aromatic hydrocarbon is divinylbenzene.   The system lubricating oil composition for a crosshead type diesel engine according to any one of claims 1 to 3, wherein the diene polymer or copolymer is polyisoprene or isoprene-styrene copolymer.   Furthermore, at least 1 sort (s) chosen from (B) metal type detergent, (C) zinc dialkyl dithiophosphate, (D) rust preventive agent, and (E) ashless dispersant is contained, The 1-4 characterized by the above-mentioned. A system lubricating oil composition for a crosshead type diesel engine according to any one of the above. The system lubricating oil composition for a crosshead type diesel engine according to any one of claims 1 to 5, wherein the base oil has a kinematic viscosity at 100 ° C of 3.5 to 9.3 mm ² / s.