JP6223312B2 - Lubricating oil composition - Google Patents

Description

  The present invention relates to a lubricating oil composition, and more particularly to a lubricating oil composition that is substantially free of a sulfur-containing metal complex and is more excellent in oxidation stability and low sludge than ever before.

Lubricating oil is used in various applications such as engine oil, drive system oil, turbine oil, hydraulic oil, and grease. In any of these uses, excellent oxidation resistance is required because of contact with peroxy radicals and peroxides, which are active species for oxidative degradation generated by heat, light, and the like. For these reasons, it is essential to add an antioxidant to the lubricating oil in order to prevent oxidative degradation.
Conventionally known as antioxidants for lubricating oils are chain terminators such as aromatic amine compounds and phenol compounds, and peroxide decomposers such as sulfur compounds and molybdenum compounds. In addition, the performance of various antioxidants varies depending on the operating temperature range, and a plurality of antioxidants are used in combination with the expectation of a synergistic effect (see, for example, Patent Document 1).
Ashless antioxidants such as aromatic amine compounds and phenolic compounds have the advantage of producing less sludge, but they are self-sacrificing and cannot be used to prevent deterioration of the lubricating oil over a long period of time. was there.
On the other hand, the peroxide resolution of sulfur-containing metal complexes such as zinc dialkyldithiophosphates and molybdenum compounds is known to act catalytically and can prevent oxidative degradation over a long period of time. However, they have problems such as sludge in the process of use and damage of equipment.
The sulfur compound functions as a peroxide decomposing agent in the same manner as the sulfur-containing metal complex. However, benzyl disulfide, which is a typical sulfur-based antioxidant, has problems such as low activity compared to sulfur-containing metal complexes. Moreover, when it used abundantly in order to acquire high activity, there existed a possibility of forming sludge.

JP 2010-242085 A

  The present invention provides a lubricating oil composition that achieves both excellent oxidation life and low sludge with a small addition amount, which is impossible to achieve with a combination of a conventional sulfur-based antioxidant and a chain terminator. It is the purpose. In particular, it is suitably used as a lubricating oil for machinery that has a low operating temperature and does not lubricate the combustion chamber.

  As a result of intensive studies on the above problems, the present inventors have completed the present invention.

（式中のｍ，ｎはそれぞれ個別に０または１を示す。） That is, the present invention is a lubricating oil composition comprising a lubricating base oil and a trisulfide compound represented by the following formula (1), wherein the lubricating oil is substantially free of a sulfur-containing metal complex. It is a composition.

(In the formula, m and n each independently represents 0 or 1.)

Moreover, this invention is the said lubricating oil composition characterized by the sulfur content of lubricating base oil being 10 mass ppm or less.
Moreover, this invention is said lubricating oil composition characterized by the content of the trisulfide compound represented by Formula (1) being 10-500 mass ppm as sulfur amount on the basis of the composition whole quantity.
Furthermore, the present invention is the above-described lubricating oil composition, which is used as a lubricating oil for machinery that does not lubricate the combustion chamber.

  The lubricating oil composition of the present invention is a lubricating oil composition that has both excellent oxidation life and low sludge properties, and exhibits its effect particularly when the operating temperature is low. Therefore, the operating temperature is low and the combustion chamber is lubricated. It is suitable as a lubricating oil for machinery that does not.

  Hereinafter, the present invention will be described in detail.

  Mineral oil, synthetic oil, and fats and oils are used as the lubricating base oil of the lubricating oil composition of the present invention. These may be a mixture.

  As mineral oil, for example, a lubricating oil fraction obtained by subjecting crude oil to atmospheric distillation and vacuum distillation is subjected to solvent removal, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, hydrorefining, sulfuric acid washing In addition, paraffinic mineral oil or naphthenic mineral oil refined by appropriately combining one or more refining treatments such as white clay treatment may be mentioned.

  Synthetic oils include, for example, propylene oligomer, polybutene, polyisobutylene, 1-octene oligomer, 1-decene oligomer, ethylene and propylene co-oligomer, ethylene and 1-octene co-oligomer, and ethylene and 1-decene. Poly α-olefin (PAO) such as co-oligomer or hydride thereof; isoparaffin; alkyl benzene such as monoalkylbenzene, dialkylbenzene, polyalkylbenzene; alkylnaphthalene such as monoalkylnaphthalene, dialkylnaphthalene, polyalkylnaphthalene; dioctyl adipate, di Dibasic acid esters such as 2-ethylhexyl adipate, diisodecyl adipate, ditridecyl adipate, di-2-ethylhexyl sebacate, ditridecyl glutarate; Tribasic acid esters such as limeric acid; polyol esters such as trimethylolpropane caprylate, trimethylolpropane pelargonate, trimethylolpropane oleate, pentaerythritol 2-ethylhexanoate, pentaerythritol pelargonate; polyethylene glycol, polypropylene glycol Polyglycols such as polyoxyethyleneoxypropylene glycol, polyethylene glycol monoether, polypropylene glycol monoether, polyoxyethyleneoxypropylene glycol monoether, polyethylene glycol diether, polypropylene glycol diether, polyoxyethyleneoxypropylene glycol diether; Monoalkyldiphenyl ether, dialkyldiphenyl Ethers, monoalkyl triphenyl ethers, dialkyl triphenyl ethers, tetraphenyl ethers, monoalkyl tetraphenyl ethers, dialkyl tetraphenyl ethers, phenyl ethers such as pentaphenyl ether; silicone oils; fluoroethers such as perfluoroethers, etc. These can be used alone or in combination of two or more.

  Examples of the fat include beef tallow, lard, soybean oil, rapeseed oil, rice bran oil, coconut oil, palm oil, palm kernel oil, hydrogenated products thereof, or a mixture of two or more of these.

The sulfur content of the lubricating base oil is preferably 10 mass ppm or less, more preferably 5 mass ppm or less, and most preferably 1 mass ppm or less. Oxidation stability can be further improved by making a sulfur content into 10 mass ppm or less.
In addition, the sulfur content as used in the field of this invention means the value measured by ICP.

The total aromatic content of the lubricating base oil is not particularly limited, but is preferably 25% by mass or less, more preferably 15% by mass or less, and more preferably 5% by mass or less from the viewpoint of oxidation stability. More preferably.
The total aromatic content referred to in the present invention is the total aromatic content measured by the Petroleum Institute method JPI-5S-49-97 “Petroleum products—hydrocarbon type test method—high performance liquid chromatograph”. means.

Kinematic viscosity at 40 ° C. of the lubricating base oil is not particularly limited but is preferably 1 to 100 mm ² / s, more preferably 5~80mm ² / s, more preferably 10 to 50 mm ² / s. When the kinematic viscosity at 40 ° C. is less than 1 mm ² / s, the lubricity is lowered, and the working environment is deteriorated due to generation of mist, which is not preferable.
In addition, the kinematic viscosity at 40 ° C. in the present invention refers to a value measured by a capillary viscometer method.

The viscosity index of the lubricating base oil according to the present invention is not particularly limited, but is preferably 100 or more, more preferably 110 or more, and still more preferably 120 or more. On the other hand, it is preferably 200 or less. By setting the viscosity index to 100 or more, the viscosity-temperature characteristics, thermal / oxidation stability, and volatilization prevention properties are improved, the friction coefficient tends to decrease, and the wear prevention properties tend to be improved. Moreover, it exists in the tendency for a low temperature viscosity characteristic to improve because a viscosity index shall be 200 or less.
In addition, the viscosity index as used in the field of this invention means the viscosity index measured based on JISK2283.

  The lubricating oil composition of the present invention contains a trisulfide compound represented by the following formula (1).

（式中のｍ，ｎはそれぞれ個別に０または１を示す。）

(In the formula, m and n each independently represents 0 or 1.)

  M and n in the above formula (1) are each independently 0 or 1. When m and n exceed 1, the amount of sulfur component per unit mass is decreased, and the antioxidant effect is decreased, which is not preferable.

  The trisulfide compound is a sulfide compound having 3 sulfur bridges. A sulfide compound having a sulfur bridge number of 2 or less is preferable because the oxidation stability of the lubricating oil composition is insufficient, and a sulfide compound having a sulfur bridge number of 4 or more tends to be unstable. Absent.

The manufacturing method of the sulfur compound represented by the said Formula (1) is not specifically limited, What is necessary is just to obtain these compounds as a product.
For example, it can be obtained as a sulfide (sulfurized olefin) of two molecules of a hydrocarbon compound (olefin) having one unsaturated bond in the molecular structure. Examples of such olefins include isobutene. The olefin to be bonded at this time may be the same compound or a different compound.

  The method for purifying the sulfur compound represented by the above formula (1) produced by sulfiding treatment of olefin as described above is not particularly limited, and any method can be used. Examples thereof include extraction by gel chromatography using silica gel.

  Specific examples of the sulfur compound represented by the formula (1) include bis (1,1,3,3-tetramethylbutyl) trisulfide.

  Although content in particular of the sulfur compound represented by said Formula (1) does not have a restriction | limiting, 10-500 mass ppm is preferable on the basis of a composition whole quantity as a sulfur element amount, 15-350 mass ppm is preferable, and 20-200. More preferred is ppm by mass. When the amount is less than 10 ppm by mass, a sufficient effect cannot be obtained, and when it exceeds 500 ppm by mass, the sludge resistance and corrosion resistance of the lubricating oil composition tend to decrease.

  The lubricating oil composition of the present invention is characterized by containing substantially no sulfur-containing metal complex. The lubricating oil composition of the present invention realizes low sludge properties by substantially not containing a sulfur-containing metal complex.

  The sulfur-containing metal complex broadly means a general complex of an organic compound containing a sulfur atom in the structure and a metal element. Examples of the sulfur-containing metal complex include zinc dithiophosphate compounds, zinc dithiocarbamate compounds, molybdenum dithiophosphate compounds, and molybdenum dithiocarbamate compounds.

［式（２）〜（５）中、Ｒ^１〜Ｒ^１６は同一でも異なっていてもよく、それぞれ炭素数１以上２０以下の炭化水素基を表し、Ｘ^１及びＸ^２はそれぞれ酸素原子又は硫黄原子を表す。］ A zinc dithiophosphate compound, a zinc dithiocarbamate compound, a molybdenum dithiophosphate compound and a molybdenum dithiocarbamate compound are compounds represented by the following general formulas (2) to (5), respectively.

[In the formulas (2) to (5), R ^{1 to} R ¹⁶ may be the same or different and each represents a hydrocarbon group having 1 to 20 carbon atoms, and X ¹ and X ² are each an oxygen atom or sulfur. Represents an atom. ]

In the present invention, “substantially does not contain a sulfur-containing metal complex” means that it contains no sulfur-containing metal complex or contains a very small amount so that the influence can be ignored even if it is contained. Say not.
More specifically, the content of the sulfur-containing metal complex is preferably 50 ppm by mass or less, more preferably 20 ppm by mass or less, and still more preferably 10 ppm by mass or less, based on the total amount of the metal element. Most preferably, it is 0 ppm by mass.

According to the lubricating oil composition of the present invention, a lubricating oil composition having excellent oxidation stability and low sludge property can be obtained by the above-described configuration. However, the lubricating oil composition has the performance required for the purpose of further enhancing its performance or as a lubricating oil composition. Further, for the purpose of imparting, known lubricating oil additives can be added.
Examples of such additives include antioxidants such as hindered phenols; metal detergents such as calcium sulfonate; wetting agents such as diethylene glycol monoalkyl ether; acrylic polymers, paraffin wax, microwax, slack wax, polyolefin wax, and the like. Film forming agent; water substitute agent such as fatty acid amine salt; solid lubricant such as graphite, fluorinated graphite, molybdenum disulfide, boron nitride, polyethylene powder; amine, alkanolamine, amide, carboxylic acid, carboxylate, sulfone Corrosion inhibitors such as acid salts, phosphoric acid, phosphates and partial esters of polyhydric alcohols; metal deactivators such as benzotriazole and thiadiazole; antifoaming agents such as methyl silicone, fluorosilicone and polyacrylate; Acid imide, Njiruamin, ashless dispersants such as polyalkenyl amines polyaminoamide; and the like. The content when these known additives are used in combination is not particularly limited, but the amount is such that the total content of these known additives is 0.1 to 10% by mass based on the total amount of the lubricating oil composition. It is preferable to add.

The kinematic viscosity of the lubricating oil composition of the present invention is not particularly limited, but the kinematic viscosity at 40 ° C. is preferably 100 mm ² / s or less, and 80 mm ² / s from the viewpoint of easy supply to the lubrication site. Or less, more preferably 50 mm ² / s or less.
Meanwhile, the kinematic viscosity at 40 ° C., preferably at ^{1 mm} 2 / s or more, more preferably ^{2 mm} 2 / s or more, and still more preferably ^{3 mm} 2 / s or more.

  Since the lubricating oil composition of the present invention can achieve both excellent oxidation life and low sludge properties, it can be suitably used in a wide range of applications. In particular, when the use temperature is low, such as 120 ° C. or less, the effect is more exhibited, and therefore, it can be suitably used as a machine lubricant that does not lubricate the combustion chamber.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
The base oils and additives used in the examples and comparative examples are as follows.

[Lubricant base oil]
Highly refined mineral base oil; total aromatic content: 0.3 mass%, sulfur content: 0 mass ppm, 40 ° C. kinematic viscosity: 35 mm ² / s, viscosity index: 120

トリスルフィド化合物Ｂ；下記式で表されるトリスルフィド化合物（式（１）においてｍ，ｎ＝０、硫黄量：４６質量％）

なお、トリスルフィド化合物Ａ、トリスルフィド化合物Ｂは、それぞれイソブテンを硫化して硫化オレフィンを得、この硫化オレフィンを、シリカゲルによるゲルクロマトグラフィで抽出した画分である。得られたトリスルフィド化合物Ａ、トリスルフィド化合物ＢはＣ^１３−ＮＭＲ、ＦＤ−ＭＳおよび元素分析にて同定した。 [Sulfur-based compound according to the present invention]
Trisulfide compound A; trisulfide compound represented by the following formula (in formula (1), m, n = 1, sulfur content: 30% by mass)

Trisulfide compound B; trisulfide compound represented by the following formula (in formula (1), m, n = 0, sulfur content: 46% by mass)

The trisulfide compound A and the trisulfide compound B are fractions obtained by sulfurizing isobutene to obtain a sulfurized olefin, and extracting the sulfurized olefin by gel chromatography using silica gel. Resulting trisulfide Compound A, trisulfide Compound B was identified by ^C 13 -NMR, FD-MS and elemental analysis.

スルフィド化合物ｂ；下記式で表されるスルフィド化合物の混合物（ｌ＝１〜５、硫黄量：２０質量％）

スルフィド化合物ｃ；ジベンジルジスルフィド（東京化成工業株式会社製、硫黄量：２６質量％）
スルフィド化合物ｄ；下記式で表される硫黄系化合物の混合物（硫黄量：１３質量％）

[Sulfur compounds other than the sulfur compounds according to the present invention]
(Sulfide compound);
Sulfide compound a; disulfide compound represented by the following formula (sulfur content: 22% by mass)

Sulfide compound b; a mixture of sulfide compounds represented by the following formula (l = 1 to 5, sulfur content: 20% by mass)

Sulfide compound c; dibenzyl disulfide (manufactured by Tokyo Chemical Industry Co., Ltd., sulfur content: 26% by mass)
Sulfide compound d; a mixture of sulfur compounds represented by the following formula (sulfur amount: 13% by mass)

(Sulfur-containing metal complex)
Zinc dithiophosphate compound; secC4 / secC6 ZDTP (Zn content 7.2 mass%, P content 6.2 mass%, S content 14.7 mass%)

(Examples 1-5 and Comparative Examples 1-8)
Table 1 shows the blending amounts and performances of various lubricating base oils and additives. The addition amount (% by mass) of each additive is based on the total amount of the lubricating oil composition.
About each composition, the oxidation stability and sludge prevention performance were evaluated by the peroxide decomposition | disassembly test shown below. This test is a test in which the peroxide decomposition effect of the additive can be directly evaluated by coexisting the additive and the peroxide and measuring the peroxide value after a certain time.

(Peroxide decomposition test)
A test oil is obtained by adding cumene hydroperoxide as a peroxide to a lubricating base oil so that the peroxide value is about 2000 mg / kg and further adding each additive as shown in Table 1. The test oil was stirred while being heated to 80 ° C., and the peroxide value of the test oil after a lapse of a certain time was measured to confirm how much the change was compared with the initial value. Further, the sample oil after 7 hours was visually observed to confirm the presence or absence of insoluble matter. The numerical values in the table are relative values with the state before the test started as 100.

Claims (3)

A lubricating oil composition comprising a lubricating base oil and a trisulfide compound represented by the following formula (1), wherein the content of the trisulfide compound represented by the formula (1) is an amount of sulfur based on the total amount of the composition A lubricating oil composition characterized by being 10 to 500 ppm by mass and containing substantially no sulfur-containing metal complex.

(In the formula, m and n each independently represents 0 or 1.)   The lubricating oil composition according to claim 1, wherein the lubricating base oil has a sulfur content of 10 ppm by mass or less. The lubricating oil composition according to claim 1 or 2, characterized in that use a combustion chamber as a machine lubricating oil without lubrication.