JP6754612B2 - Gas engine oil composition - Google Patents

Description

The present invention relates to a gas engine oil composition.

In recent years, gas engine peat pump systems have been developed and put into practical use for air conditioning in houses and buildings. In this system, a gas engine that uses natural gas, liquefied petroleum gas (LPG), or the like as fuel is generally used. The gas engine system has good combustibility, produces less combustion residue, and has less dirt in the combustion chamber. However, since the combustion temperature is higher than that of a gasoline engine or a diesel engine, a large amount of NOx is generated due to high temperature oxidation. Therefore, the NOx concentration in the blow-by gas is high, and the engine used is in continuous operation with a high load, which is a harsh usage condition for the lubricating oil.
Engine oils used in gas engines such as these gas engine systems (hereinafter, may be referred to as "gas engine oil composition" and "gas engine oil") may be excellent in oxidation stability and abrasion resistance. Required. In addition, since maintenance and inspection work will increase due to the spread of gas engine systems, improvement of maintenance such as simplification of inspection and extension of maintenance period and extension of refueling time of gas engine oil used will be issues. There is.

Conventionally, in order to extend the life of gas engine oil, salicylate, a hyperbasic calcium-based cleaning agent, has been adopted as a metal-type cleaning agent, and zinc dialkyldithiophosphate containing a secondary alkyl group has been used as an anti-wear agent (for example,). , Patent Documents 1 and 2), amine-based antioxidants and hindered phenol-based antioxidants (see, for example, Patent Document 3) as antioxidants, and succinimide-based dispersions as ashless dispersants. Agents (see, for example, Patent Document 4) have been adopted respectively.

Japanese Unexamined Patent Publication No. 7-258678 Japanese Unexamined Patent Publication No. 9-71795 Japanese Unexamined Patent Publication No. 2004-107556 Japanese Unexamined Patent Publication No. 2005-220199

The present inventors have found the following problems in engine oils for long-life gas heat pumps.
-In the oxidation stability test using NOx gas, the kinematic viscosity may increase sharply even though the base value, which is an index of long life, remains.
-Some of the engines used in gas heat pump systems are used at relatively low temperatures, and some of them do not have excellent wear resistance when operated at low temperatures.
In order to solve these problems, the present inventors have studied to provide a gas engine oil composition having an excellent effect of suppressing an increase in kinematic viscosity and an excellent wear suppressing property at a low temperature.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a gas engine oil composition having an excellent effect of suppressing increase in kinematic viscosity and an excellent ability to suppress wear at low temperatures.

As a result of diligent studies to solve the above problems, the present inventors have contained specific amounts of boron-modified alkenylsuccinimide as an ashless dispersant and zinc dialkyldithiophosphate as an anti-wear agent, and further, these By containing the components in a specific ratio, containing a specific amount of a specific alkaline earth metal salicylate as a metal-type cleaning agent, and containing a specific phenolic antioxidant and an amine-based antioxidant as an antioxidant. The present invention has been completed by finding a gas engine oil composition capable of suppressing an increase in kinematic viscosity by an oxidation stability test under a NOx usage environment and ensuring abrasion resistance at a low temperature.
That is, the following inventions are provided in order to achieve the above object.

<1> Base oil and
An ashless dispersant selected from boron-modified alkenyl succinimide having a polybutenyl group having a number average molecular weight of 1000 to 2000 and a weight average molecular weight of 5000 to 6000.
An anti-wear agent selected from zinc dialkyl dithiophosphate having a secondary alkyl group having 3 to 6 carbon atoms and zinc dialkyl dithiophosphate having a primary alkyl group having 8 or more carbon atoms, respectively.
A metal-type cleaning agent selected from alkaline earth metal salicylates having a base value of 200 to 250 mgKOH / g, and
Contains antioxidants selected from phenolic antioxidants and amine antioxidants, respectively.
The mass ratio (B1 / N1) of the amount of boron (B1) and the amount of nitrogen (N1) derived from the ashless dispersant in the total amount of the composition is 0.3 to 0.6.
The mass ratio (P1 / N1) of the amount of phosphorus (P1) derived from the anti-wear agent and the amount of nitrogen (N1) derived from the ashless dispersant in the total amount of the composition is 0.5 to 1.0.
A gas engine oil composition having a total sulfate ash content of 1.0 to 1.5% by mass.

According to the present invention, it is possible to obtain a gas engine oil composition having an excellent effect of suppressing an increase in kinematic viscosity and an excellent effect of suppressing wear at a low temperature.

Hereinafter, an example of the embodiment of the present invention will be described in detail. In the present specification, "~" representing a numerical range represents a range including the upper and lower limit numerical values.
Further, when the unit is described only for the upper limit value in the numerical range, it means that the lower limit value is also the same unit as the upper limit value.
The gas engine oil composition of the present invention
Base oil and
An ashless dispersant selected from boron-modified alkenyl succinimide having a polybutenyl group having a number average molecular weight of 1000 to 2000 and a weight average molecular weight of 5000 to 6000.
An anti-wear agent selected from zinc dialkyl dithiophosphate having a secondary alkyl group having 3 to 6 carbon atoms and zinc dialkyl dithiophosphate having a primary alkyl group having 8 or more carbon atoms, respectively.
A metal-type cleaning agent selected from alkaline earth metal salicylates having a base value of 200 to 250 mgKOH / g, and
Antioxidants selected from phenolic antioxidants and amine antioxidants, respectively,
Contains,
The mass ratio (B1 / N1) of the amount of boron (B1) and the amount of nitrogen (N1) derived from the ashless dispersant in the total amount of the composition is 0.3 to 0.6.
The mass ratio (P1 / N1) of the amount of phosphorus (P1) derived from the anti-wear agent and the amount of nitrogen (N1) derived from the ashless dispersant in the total amount of the composition is 0.5 to 1.0.
The total amount of sulfated ash in the composition is 1.0 to 1.5% by mass.
Hereinafter, the constituent components, physical properties, etc. of the gas engine oil composition of the present invention will be specifically described.

1. 1. Base oil The base oil contained in the gas engine oil composition of the present invention is not particularly limited as long as it exhibits the effect of the present invention when a gas engine oil is prepared by adding a predetermined additive, and is a mineral oil. One kind or two or more kinds selected from system base oil and synthetic base oil can be used. The base oil may be a mixture of a mineral oil-based base oil and a synthetic base oil.
Examples of the mineral oil-based base oil include those obtained by refining a lubricating oil distillate of crude oil by appropriately combining refining methods such as solvent refining, hydrogenation refining, hydrogenation decomposition refining, and hydrogenation dewaxing. The base oil having a viscosity index of 125 or more, which will be described later, is a highly refined paraffinic mineral oil obtained by subjecting hydrorefined oil, catalytic isomerized oil, or the like to solvent dewaxing or hydrodewaxing. High viscosity index mineral oil-based lubricating oil base oil) and the like.
Examples of the synthetic base oil include isoparaffin, α-olefin oligomer, dialkyldiesters, polyols, alkylbenzenes, polyglycols, phenyl ethers and the like, which are synthesized from natural gas such as methane.

The properties of the base oil are not particularly limited as long as the effects of the present invention are obtained when a gas engine oil is prepared by adding a predetermined additive, but the kinematic viscosity at 100 ° C. (JIS-K-2283: 2000 (ASTM)). D445)) is preferably ³ to 12 mm ² / s, viscosity index (JIS K 2283: 2000 (ASTM D2270)) is preferably 120 or more, kinematic viscosity at 100 ° C. is 3 to 7 mm ² / s, viscosity index is It is particularly preferably 125 or more.
Base oils with such properties are classified by the American Petroleum Association (API) as group II base oils (sulfur content 0.03% by mass or less, saturation content 90% by mass or more, viscosity index 80 or more and less than 120). (Base oil having a viscosity index of 120 or more) and Group III base oil (base oil having a sulfur content of 0.03% by mass or less, a saturation content of 90% by mass or more, and a viscosity index of 120 or more) are mixed and matched to the above properties. Although it may be present, base oils belonging to Group III or higher categories are preferable in that they exhibit high oxidation stability performance.

2. 2. Ash-free dispersant The gas engine oil composition of the present invention contains boron-modified alkenyl succinimide (hereinafter, may be simply referred to as “dispersant”) as an ash-free dispersant. In the present invention, a boron-modified alkenyl succinimide having a polybutenyl group having a number average molecular weight (Mn) of 1000 to 2000 and a weight average molecular weight (Mw) of 5000 to 6000 is used. Two or more kinds of boron-modified alkenyl succinimide having the above physical properties may be blended.

The boron-containing alkenyl succinimide having the above physical properties used in the gas engine oil composition of the present invention may be any one type or may be mixed and used, but has cleanliness and oxidative stability. It is preferable to use a screw type having excellent wear resistance. For example, a bis type obtained by boron-denaturing an alkenyl succinimide represented by the following general formula (1) can be mentioned.

In the general formula (1), R ¹ and R ³ independently represent an alkyl group or an alkenyl group, and at least one of R ¹ and R ³ is a polybutenyl group, and the number average molecular weight of the polybutenyl group is 1000 to 2000. Yes, preferably 1000-1500. R ¹ and R ³ may be polybutenyl groups having the same structure or may be different from each other.
R ² is preferably an alkylene group having 2 to 5 carbon atoms, and more preferably an alkylene group having 2 or 3 carbon atoms. n is preferably an integer of 1-10.

The weight average molecular weight of the dispersant obtained by boron-modifying the alkenyl succinimide represented by the general formula (1) is 5000 to 6000, preferably 5000 to 5700. Sufficient dispersibility as a gas engine oil can be obtained by setting the number average molecular weight of the polybutenyl group of the dispersant and the weight average molecular weight of the dispersant within the above ranges. For example, when the weight average molecular weight is in the range of 5000 to 6000, it is possible to suppress a rapid increase in kinematic viscosity in an oxidation test using NOx gas.

The number average molecular weight and the weight average molecular weight are values converted to standard polystyrene for molecular weight calculation measured by gel permeation chromatography (GPC) under the following conditions.
<Conditions>
Equipment: Shodex GPC-101 (manufactured by Showa Denko KK), Column: Three Shodex GPC LF-804 (manufactured by Showa Denko KK), Detector: Differential refractometer, Mobile phase: THF (tetrahydrofuran), Flow rate: 1 ml / min, sample concentration: about 1.0 mass% / vol% THF, injection volume: 100 μL

The amount of boron (B1) in the boron-modified alkenyl succinimide is preferably 0.1 to 1.5% by mass, more preferably 0.2 to 1.0% by mass, and 0. More preferably, it is 3 to 0.8% by mass.
Further, the amount of nitrogen (N1) in the boron-modified alkenyl succinimide is preferably 1.0 to 2.5% by mass, more preferably 1.4 to 2.0% by mass.
For example, the effect of the present invention (inhibition of increase in kinematic viscosity) is obtained by setting either or preferably both the amount of boron (B1) and the amount of nitrogen (N1) of the boron-modified alkenyl succinimide to be used within the above preferable ranges. , Wear suppression property at low temperature) is easily obtained, and the sudden increase in kinematic viscosity is suppressed.

The gas engine oil composition of the present invention contains the above-mentioned boron-modified alkenyl succinimide as the total amount, preferably 0.08 to 0.20% by mass in terms of nitrogen concentration, based on the total amount of the composition. Is contained in an amount of 0.10 to 0.15% by mass, particularly preferably 0.1 to 0.13% by mass.
Further, in the gas engine oil composition of the present invention, the total amount of boron-modified alkenyl succinimide is preferably 0.02 to 0.10% by mass, more preferably 0, in terms of boron concentration, based on the total amount of the composition. Contains .04 to 0.065% by mass.

Then, in the gas engine oil composition of the present invention, the mass ratio (B1 / N1) of the amount of boron (B1) and the amount of nitrogen (N1) derived from the boron-modified alkenyl succinimide satisfies the following formula (I). Must be contained in.
0.3 ≤ B1 / N1 ≤ 0.6 Equation (I)
B1: Boron-modified alkenyl Succinimide-derived boron amount (% by mass)
N1: Amount of nitrogen derived from boron-modified alkenyl succinimide (% by mass)
If the mass ratio (B1 / N1) of the amount of boron (B1) derived from boron-modified alkenyl succinimide to the amount of nitrogen (N1) in the entire gas engine oil composition is within the range of 0.3 to 0.6. The sudden increase in kinematic viscosity is suppressed.

3. 3. Anti-Abrasion Agent The gas engine oil composition of the present invention contains zinc dialkyldithiophosphate as an anti-wear agent. In the present invention, as an anti-wear agent, zinc dialkyl dithiophosphate having a secondary alkyl group having 3 to 6 carbon atoms and zinc dialkyl dithiophosphate having a primary alkyl group having 8 or more carbon atoms are contained and composed. The mass ratio (P1 / N1) of the amount of phosphorus (P1) derived from zinc dialkyldithiophosphate to the amount of nitrogen (N1) in the whole product is 0.5 to 1.0.
Examples of zinc dialkyldithiophosphate used in the gas engine oil composition of the present invention include compounds having a structure represented by the following general formula (2).

In R ^{4 to} R ⁷ , the carbon atom bonded to the oxygen atom is a primary (primary) type or secondary (secondary) type alkyl group, which may be the same or different, and may be linear or branched. You may. The number of carbon atoms is preferably 2 to 18, more preferably 3 to 12, and even more preferably 3 to 8.
The zinc dialkyl dithiophosphate used in the gas engine oil composition of the present invention includes zinc dialkyl dithiophosphate having a secondary alkyl group having 3 to 6 carbon atoms and dialkyl dithiophosphate having a primary alkyl group having 8 or more carbon atoms. Use with zinc acid.

As the zinc dialkyldithiophosphate having a secondary alkyl group having 3 to 6 carbon atoms, at least one of R ^{4 to} R ⁷ in the general formula (2) may have 3 to 6 carbon atoms, for example, the carbon number. It may have only a secondary type having 3 to 6 carbon atoms, or it may be a mixed system of a secondary type having 3 to 6 carbon atoms and a primary type having 3 to 8 carbon atoms. Further, it is preferable to use a mixed system of a secondary type having 3 to 5 carbon atoms and a primary type having 3 to 8 carbon atoms, and a mixed system of a secondary type having 3 to 4 carbon atoms and a primary type having 3 to 6 carbon atoms. It is preferable to have. Further, these may be one kind alone or a combination of two or more kinds.

As the zinc dialkyldithiophosphate having a primary alkyl group having 8 or more carbon atoms, at least one of R ^{4 to} R ⁷ in the general formula (2) may be a primary alkyl group having 8 or more carbon atoms. For example, it may have only a primary type having 8 or more carbon atoms. Further, these may be one kind alone or a combination of two or more kinds.

In the case of zinc dialkyldithiophosphate having a secondary alkyl group having 3 to 6 carbon atoms and a primary alkyl group having 8 or more carbon atoms, "a secondary alkyl group having 3 to 6 carbon atoms can be used. As zinc dialkyldithiophosphate having both "zinc dialkyldithiophosphate having" and "zinc dialkyldithiophosphate having a primary alkyl group having 8 or more carbon atoms", one type can be used alone.

The gas engine oil composition of the present invention preferably contains the above zinc dialkyldithiophosphate in an amount of 0.01 to 0.10% by mass in terms of phosphorus concentration as the total amount, more preferably 0. Contains 06 to 0.09% by mass. When the content of the zinc dialkyldithiophosphate is 0.06% by mass or more, sufficient anti-wear properties can be obtained.

Further, in the gas engine oil composition of the present invention, the mass ratio (P1 / N1) of the phosphorus amount (P1) of zinc dialkyldithiophosphate and the nitrogen amount (N1) of boron-modified succinimide is the following general formula. It is necessary to satisfy (II).
0.5 ≤ P1 / N1 ≤ 1.0 Equation (II)
N1: Amount of nitrogen derived from boron-modified alkenyl succinimide (% by mass)
P1: Amount of phosphorus derived from zinc dialkyldithiophosphate (% by mass)
When this P1 / N1 ratio is in the range of 0.5 to 1.0, high wear resistance and oxidation stability can be obtained even at low temperatures, while it may be less than 0.5 or more than 1.0. Abrasion resistance and oxidation stability deteriorate even at low temperatures. This P1 / N1 ratio is preferably 0.6 to 0.8.

4. Metal-type cleaning agent The gas engine oil composition of the present invention contains a metal-type cleaning agent.
Examples of the metal-type cleaning agent generally include alkaline earth metal salicylate, alkaline earth metal sulfonate, alkaline earth metal phenate and the like, but in the present invention, in order to extend the life of the gas engine oil, a base is used. Alkaline earth metal salicylate having a value of 200 to 250 mgKOH / g is used. In particular, it preferably contains calcium salicylate. The base value of the alkaline earth metal salicylate in the gas engine oil composition of the present invention is 200 to 250 mgKOH / g by the perchloric acid method, preferably 200 to 230 mgKOH / g.
For example, when an alkaline earth metal salicylate having a base value of more than 250 mgKOH / g is used, the base value persistence becomes significantly worse, and when the base value is less than 200 mgKOH / g, in order to satisfy the target sulfate ash content, The amount of addition increases, leading to cost increase.

5. Antioxidant The gas engine oil composition of the present invention contains one or more phenolic antioxidants and one or more amine-based antioxidants as antioxidants.
As the phenol-based antioxidant, a hindered phenol-based antioxidant is preferable, and examples thereof include isooctyl-3- (3', 5'-di-tert-butyl-4'-hydroxyphenyl) propionate and n-octadecyl. -3- (3', 5'-di-tert-butyl-4'-hydroxyphenyl) propionate and the like are preferred.
Examples of the amine-based antioxidant include aromatic amine compounds such as naphthylamine-based antioxidants and diphenylamine-based antioxidants. Specific examples of the naphthylamine-based antioxidant include phenyl-α-naphthylamine and alkylated phenyl-α-naphthylamine. Specific examples of diphenylamine-based antioxidants include dialkyldiphenylamine.
However, the present invention is not limited by the above specific examples.

The total content of the antioxidant in the gas engine oil composition of the present invention is preferably 3.0 to 5.0% by mass, particularly preferably 4.0 to 4.0% by mass, based on the total mass of the gas engine oil composition. It is 4.5% by mass.
For example, if the total content of the antioxidant is 3.0% by mass or more, the remaining time of the base value, which is an index of longevity, becomes long, and if the content is 5.0% by mass or less, the cost Can be suppressed to prolong the remaining time of the base value.

6. Sulfuric acid ash content The amount of sulfuric acid ash content in the gas engine oil composition of the present invention is 1.0 to 1.5% by mass with respect to the total mass of the composition.
For example, when the amount of ash sulfate is small, the remaining time of the base value, which is an index of longevity, becomes significantly short, and when the amount of ash sulfate is large, the remaining time of the base value becomes long, but the combustion temperature is high. In, it is expected that the ash will stick to the engine piston and the like, causing engine trouble. When the amount of sulfated ash in the total amount of the composition is 1.0 to 1.5% by mass, the remaining time of the base value can be lengthened, and the possibility that the ash content sticks to the engine piston or the like can be suppressed.
The sulfuric acid ash content in the present invention is the ash content measured in accordance with the test method specified in JIS K-2272: 1998.

7. Other Additives The gas engine oil composition of the present invention may contain additives other than the above-mentioned components, if necessary. For example, a viscosity index improver can be contained.
Examples of the viscosity index improver include polymethacrylates, polyacrylates, olefin copolymers, polyisobutylenes, polyalkylstyrenes, styrene-butadiene hydride copolymers, styrene-isoprene hydride copolymers, and styrene-. Various known viscosity index improvers such as maleic anhydride copolymers or those containing a dispersing group may be used alone or in combination of two or more.
The preferred weight average molecular weight of the viscosity index improver is 100,000 to 1,000,000, more preferably 150,000 to 600,000. The content of the viscosity index improver in the gas engine oil composition of the present invention is preferably 0.5 to 15% by mass or less, more preferably 1.0 to 10% by mass or less.

In addition to the above, the gas engine oil composition of the present invention includes various additives effective for imparting gas engine oil performance, such as a metal inactivating agent, a rust preventive agent, a pour point lowering agent, and a defoamer. Can be contained as needed.

8. Properties of the composition It is preferable that the gas engine oil composition of the present invention is a multi-grade oil that can be used even at a low temperature while maintaining the lubrication performance at a high temperature. Specifically, the kinematic viscosity at 100 ° C. is preferably 9.3 to 12.5 mm ² / s, and the high temperature high shear viscosity (HTHS viscosity) at 150 ° C. is 2.9 mPa · s or more. The low temperature cranking viscosity (CCS viscosity) at −25 ° C. is preferably 7,000 mPa · s or less.

9. Applications The gas engine oil composition of the present invention can be suitably applied to, for example, an engine engine for a gas heat pump system. The gas engine oil composition of the present invention can be suitably applied not only to a gas engine for a gas heat pump system but also as a gas engine oil in a gas engine such as a cogeneration system.

Next, the present invention will be described in more detail with reference to Examples. The present invention is not limited by these examples.

[Preparation of gas engine oil composition]
As Examples and Comparative Examples, a gas engine oil composition was produced using the base oils and additives described below at the mixing ratios shown in Table 1 so that the viscosity grade was 10 W-30 grade of SAE J300 standard. .. The present invention is not limited by the materials (ingredients), formulations, properties, etc. of the following examples.

<Base oil, additives>
-Base oil (A): A mineral oil-based lubricating oil base oil having a kinematic viscosity at 100 ° C. of 6.276 mm ² / s and a viscosity index of 122 was used.

-Boron-modified alkenyl succinimide-free dispersant (B1): A polybutenyl group having a number average molecular weight of 1300, a weight average molecular weight of Mw5500, and a bis-type polyalkenyl succinimide treated with a boron compound was used. The amount of boron was 0.86% by mass and the amount of nitrogen was 1.7% by mass.
Ash-free dispersant (B2): A polybutenyl group having a number average molecular weight of 1300, a weight average molecular weight of Mw5100, and a bis-type polyalkenylsuccinimide treated with a boron compound was used. The amount of boron was 0.52% by mass and the amount of nitrogen was 1.5% by mass.
Ash-free dispersant (B3): A polybutenyl group having a number average molecular weight of 1300, a weight average molecular weight of Mw6000, and a bis-type polyalkenylsuccinimide treated with a boron compound was used. The amount of boron was 1.3% by mass and the amount of nitrogen was 1.45% by mass.
Ash-free dispersant (B4): A polybutenyl group having a number average molecular weight of 1000, a weight average molecular weight of Mw4400, and a monotype polyalkenylsuccinimide treated with a boron compound was used. The amount of boron was 1.8% by mass and the amount of nitrogen was 2.4% by mass.

(In the general formula ^{(2) R 4 ~R 7)} · zinc dialkyldithiophosphate alkyl group using zinc dialkyldithiophosphate having alkyl groups below as.
Anti-wear agent (C1): Zinc dialkyldithiophosphate having a secondary alkyl group having 3 carbon atoms and a secondary alkyl group having 6 carbon atoms was used.
Anti-wear agent (C2): Zinc dialkyldithiophosphate having a secondary alkyl group having 3 carbon atoms, a primary alkyl group having 4 carbon atoms, and a primary alkyl group having 5 carbon atoms was used.
Anti-wear agent (C3): Zinc dialkyldithiophosphate having a primary alkyl group having 8 carbon atoms was used.
Anti-wear agent (C4): Zinc dialkyldithiophosphate having a primary alkyl group having 4 carbon atoms and a primary alkyl group having 5 carbon atoms was used.

-Metal type cleaning agent (D): calcium salicylate, basic value (perchloric acid method: JIS K-2501: 2003-9) 225 mgKOH / g was used.
-Antioxidant A phenolic antioxidant (E1): isooctyl-3- (3', 5'-di-tert-butyl-4'-hydroxyphenyl) propionate was used.
Naphthylamine-based antioxidant (E2): Alkylated phenyl-α-naphthylamine was used.
Diphenylamine-based antioxidant (E3): Dialkyldiphenylamine was used.

<Characteristics>
・ Amount of boron (B1)
It is the amount of boron derived from the boron-modified alkenyl succinimide ashless dispersant contained in the gas engine oil composition.
・ Nitrogen amount (N1)
It is the amount of nitrogen derived from the boron-modified alkenyl succinimide ashless dispersant contained in the gas engine oil composition.
・ Phosphorus amount (P1)
It is the amount of phosphorus derived from zinc dithiophosphate contained in the gas engine oil composition.

Table 1 shows the formulations and properties of the gas engine oil compositions prepared in Examples and Comparative Examples.
The amount of boron derived from the ashless dispersant (B1) and the amount of phosphorus derived from zinc dithiophosphate (P1) are the lubricating oil-added element test method-inductively coupled specified in the JPI-5S-38 of the Petroleum Society, respectively. It is a value measured by plasma emission spectroscopic analysis. The nitrogen content (N1) is the result of measurement by the chemiluminescence method described in the crude oil and petroleum products-nitrogen content test method specified in JIS K2609.

[Evaluation]
The evaluation tests described below were performed on the compositions prepared in Examples and Comparative Examples, and the results are shown in Table 2.

<Evaluation test method>
-NOx bubbling test A glass test tube (described in JIS K6257 11.2), 200 g of gas engine oil composition was collected in an outer diameter of about 38 mm and a length of 300 mm, and four types of metal pieces used in ASTM D6594 were added as a catalyst. Immerse in an oil bath at 150 ° C. 100 ml / min of NO gas having a concentration of 8000 ppm and air are blown into the prepared gas engine oil composition, respectively. The gas engine oil composition after a lapse of a certain time (216 hours) was recovered, the kinematic viscosity was measured at 100 ° C. according to JIS K 2283, and the rate of change from the pre-test oil was calculated. At the same time, the potential difference optimization method (base value) based on JIS K 2501 was measured, and the retention rate of the remaining base components was calculated.
Whether or not the rate of change in kinematic viscosity of the gas engine oil composition at 100 ° C. is 120% or less and the residual base value retention rate is 15% or more is used as a criterion.

-ISOT test In accordance with the oxidation stability test of lubricating oil for internal combustion engines specified in JIS K 2514-1, after 96 hours of test time, measure the potential difference optimization method (base value) of oil in accordance with JIS K 2501. , The retention rate of the remaining base components was calculated.
The higher the remaining base value and retention rate, the better the oxidative stability.

・ Abrasion resistance test (shell walk test)
The wear mark diameter was evaluated according to the shell high-speed walk test method specified in ASTM D4172-94. The test conditions were evaluated at an oil temperature of 45 ° C. as a condition under a low temperature in addition to an oil temperature of 75 ° C. Other conditions were 1200 rpm and 60 minutes.
The smaller the wear mark diameter, the better the wear resistance. Whether or not the wear mark diameter is 0.48 mm or less is used as a criterion.

<Evaluation result>
(Example 1)
The increase in kinematic viscosity by the NOx bubbling test is a result within the judgment criteria, and no rapid increase in kinematic viscosity is observed. In addition, the wear prevention performance at low temperatures by the shell walk test is a result within the judgment criteria.

(Examples 2 and 3)
The increase in kinematic viscosity by the NOx bubbling test as in Example 1 is a result within the judgment criteria, and no rapid increase in kinematic viscosity is observed.

(Comparative Examples 1 and 2)
The B1 / N1 ratio exceeds 0.6, and the amount of increase in kinematic viscosity by the NOx bubbling test is out of the judgment standard.

(Comparative Example 3)
The P1 / N1 ratio exceeds 1.0, and the amount of increase in kinematic viscosity by the NOx bubbling test is out of the judgment standard.

(Comparative Examples 4 to 8)
Both the B1 / N1 ratio and the P1 / N1 ratio were the same as in Example 1, but a difference was observed in the wear prevention test results by the shell walk test depending on the type of wear inhibitor to be blended.
The anti-wear agent described in Comparative Example 4 has deteriorated anti-wear property at high temperature. In Comparative Example 5, the wear prevention property is good, but the oxidation stability by ISOT is inferior. The anti-wear agent of Comparative Example 6 is excellent in oxidative stability but inferior in anti-wear property. Comparative Example 7 and Comparative Example 8 are slightly inferior in anti-wear property.
On the other hand, in Example 1, by containing an anti-wear agent (C1) having excellent anti-wear properties and an anti-wear agent (C3) having excellent anti-oxidation performance, oxidation is performed while maintaining excellent anti-wear performance at low temperatures. A gas engine oil composition that maintains stable performance has been obtained.

Claims (2)

Base oil and
An ashless dispersant selected from boron-modified alkenyl succinimide having a polybutenyl group having a number average molecular weight of 1000 to 2000 and a weight average molecular weight of 5000 to 5700.
An anti-wear agent selected from zinc dialkyl dithiophosphate having a secondary alkyl group having 3 to 6 carbon atoms and zinc dialkyl dithiophosphate having a primary alkyl group having 8 or more carbon atoms, respectively.
A metal-type cleaning agent selected from alkaline earth metal salicylates having a base value of 200 to 250 mgKOH / g, and
Antioxidants selected from phenolic antioxidants and amine antioxidants, respectively,
Contains,
The mass ratio (B1 / N1) of the amount of boron (B1) and the amount of nitrogen (N1) derived from the ashless dispersant in the total amount of the composition is 0.3 to 0.6.
The mass ratio (P1 / N1) of the amount of phosphorus (P1) derived from the anti-wear agent and the amount of nitrogen (N1) derived from the ashless dispersant in the total amount of the composition is 0.5 to 1.0.
The total amount of the boron-modified alkenyl succinimide to the total amount of the composition is 0.04 to 0.065% by mass in terms of boron concentration.
The total amount of the boron-modified alkenyl succinimide with respect to the total amount of the composition was 0.10 to 0.15% by mass in terms of nitrogen concentration.
A gas engine oil composition having a total sulfate ash content of 1.0 to 1.5% by mass. The gas engine oil composition according to claim 1, which comprises two types of boron-modified alkenyl succinimide.