JP2007131825A - Lubricating oil composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lubricating oil composition with a base oil comprising an oxygen-containing organic compound such as an ester base oil, improved in antioxidant ability. <P>SOLUTION: The lubricating oil composition comprises ≥90 wt.% of a base oil with a dielectric constant (at 25°C) of ≥2.5, 0.01-5 wt.% of an amine-based antioxidant and ≤0.1 wt.% of a phenolic antioxidant. In this composition, it is preferable that the base oil comprises a diester and/or a polyol ester and also contains 0.01-2 wt.% of at least one compound selected from epoxy compound, carbodiimide compound and triazole compound. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a lubricating oil composition having improved oxidation stability using a base oil having a high relative dielectric constant, particularly an oxygen-containing organic compound such as an ester base oil, as a base oil.

  Lubricating oil oxidizes and deteriorates due to the presence of oxygen and heat. Thereby, the target performance may not be exhibited. In recent years, the use environment of lubricating oil has become more severe, and oxidation stability is required more than ever. Various kinds of antioxidants are added to the lubricating oil according to the purpose, and a plurality of kinds of antioxidants are often used in combination. As antioxidants, phenolic, amine-based, sulfur-containing compounds, organic phosphorus compounds, and the like are known. In general, a synergistic effect is known in which it is better to use phenolic and amine antioxidants in combination than to use them alone.

Satoshi Watanabe; “Functions and Applications of Antioxidants” Lubrication Economy ‘03 Feb.

  When a base oil having a high relative dielectric constant, particularly an oxygen-containing organic compound such as an ester base oil, is used as the base oil, the oxidation cannot be sufficiently prevented. An object of the present invention is to provide a lubricating oil composition capable of sufficient oxidation prevention even when such a base oil is used.

  The lubricating oil composition according to the present invention comprises 95% by weight or more of a base oil having a relative dielectric constant (25 ° C.) of 2.5 or more and 0.01 to 5% by weight of an amine antioxidant, and is a phenolic antioxidant. The content of the agent is 0.1% by weight or less. The base oil preferably contains a diester and / or a polyol ester as a main component, and preferably contains 0.01 to 2% by weight of at least one selected from an epoxy compound, a carbodiimide compound and a triazole compound.

  When the present inventor uses a diester, a polyol ester or the like as a base oil, the amine antioxidant and the phenolic antioxidant are used simultaneously as the antioxidant, and only the amine antioxidant is used. It was found that the antioxidant ability is lower than that. In this case, excellent oxidation resistance can be obtained by using only an amine antioxidant without using a phenolic antioxidant. Moreover, oxidation resistance is further improved by using an epoxy compound, a carbodiimide compound and / or a triazole compound in combination with an amine-based antioxidant.

[Base Oil] The base oil of the present invention has a relative dielectric constant (25 ° C.) of 2.5 or more, and preferably 2.7 to 10, particularly 2.9 to 8.0. The kinematic viscosity (40 ° C.) of the base oil is preferably 2 to 300 cSt, particularly 3 to 200 cSt, and more preferably 4 to 100 cSt. The viscosity index of the base oil is preferably 0 to 250, particularly 20 to 200, and more preferably 40 to 180. The content of the base oil in the lubricating oil composition is preferably 90% by weight or more, particularly 95 to 99.9% by weight.

  The compound constituting the base oil is preferably composed mainly of an organic compound containing oxygen, particularly a compound composed only of oxygen, carbon, and hydrogen. Preferred compounds as the main component are compounds containing an ester or ether bond, and particularly compounds having a plurality of ester bonds, particularly those having 2 to 4 ester bonds such as diesters and polyol esters. The proportion of these main components in the base oil is preferably 50% by weight or more, particularly 80% by weight or more, and more preferably 90% by weight or more.

[Diester] The diester used in the base oil of the present invention is a compound obtained by esterifying a dicarboxylic acid and a monohydric alcohol. As the dicarboxylic acid, an aliphatic dibasic acid is preferable, and a linear or branched aliphatic dibasic acid having 6 to 12 carbon atoms is particularly preferable. Examples thereof include adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecadioic acid and the like. The monohydric alcohol is preferably an aliphatic monohydric alcohol, particularly a linear or branched aliphatic monohydric alcohol having 6 to 18 carbon atoms. Examples include hexyl alcohol, heptyl alcohol, octyl alcohol, nonyl alcohol, decyl alcohol, undecyl alcohol, lauryl alcohol, myristyl alcohol, cetyl alcohol, stearyl alcohol, and branched alcohols corresponding to these linear alcohols. .

  Preferred diesters include dioctyl adipate (DOA), diisononyl adipate (DINA), diisobutyl adipate (DIBA), dibutyl adipate (DBA), dioctyl azelate (DOZ), dioctyl suberate, dibutyl sebacate (DBS), dioctyl sebacate (DOS), methyl acetylricinolate (MAR-N), and the like. The diester preferably has a degree of purification having a total acid value of 0.1 mgKOH / g or less, preferably 0.05 mgKOH / g or less, and a hydroxyl value of 10 mgKOH / g or less, preferably 5 mgKOH / g or less.

[Polyol ester] The polyol ester used in the base oil of the present invention is a compound obtained by esterifying a monovalent carboxylic acid and a polyhydric alcohol. As the monovalent carboxylic acid, an aliphatic carboxylic acid is preferable, and a linear or branched aliphatic carboxylic acid having 4 to 18 carbon atoms is particularly preferable. Examples include butyric acid, caproic acid, heptanoic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, and branched acids corresponding to these linear acids. The polyhydric alcohol is preferably an aliphatic polyhydric alcohol, particularly a linear or branched aliphatic polyhydric alcohol having 4 to 18 carbon atoms. For example, in addition to neopentyl glycol, trimethylolpropane, pentaerythritol, butylethylpropanediol, and the like, polyalkylene glycols such as diethylene glycol and triethylene glycol can be used. The polyol ester preferably has a total acid value of 0.1 mgKOH / g or less, preferably 0.05 mgKOH / g or less, and a hydroxyl value of 10 mgKOH / g or less, preferably 5 mgKOH / g or less.

[Amine-based antioxidant] Examples of the amine-based antioxidant used in the present invention include (1) monoalkyldiphenylamines such as monooctyldiphenylamine and monononyldiphenylamine, (2) 4,4′-dibutyldiphenylamine, 4,4 Dialkyldiphenylamines such as' -dipentyldiphenylamine, 4,4'-dihexyldiphenylamine, 4,4'-diheptyldiphenylamine, 4,4'-dioctyldiphenylamine, 4,4'-dinonyldiphenylamine, (3) tetrabutyldiphenylamine Polyalkyldiphenylamines such as tetrahexyldiphenylamine, tetraoctyldiphenylamine, tetranonyldiphenylamine, (4) α-naphthylamine, phenyl-α-naphthylamine, butylphenyl-α-na Ethylamine, pentylphenyl -α- naphthylamine, hexylphenyl -α- naphthylamine, heptylphenyl -α- naphthylamine, octylphenyl -α- naphthylamine can include naphthylamine and nonyl phenyl -α- naphthylamine. A di (alkylphenyl) amine compound or an alkylphenylnaphthylamine compound, particularly a compound having an alkyl group having 4 to 24 carbon atoms, particularly 6 to 18 carbon atoms, is preferably used.

  These compounds may be used alone or in combination of two or more. The total amount of these compounds added is preferably 0.01 to 5% by weight, particularly 0.02 to 3% by weight, and more preferably 0.05 to 2% by weight.

[Phenolic Antioxidant] The phenolic antioxidant is a phenolic compound (an organic compound having a phenol group) having radical trapping ability. For example, 2,6-di-t-butylphenol, 2,6-di-t-butyl-4-methylphenol, 4,4'-methylenebis (2,6-di-t-butylphenol), 4,4'-butylidenebis (3
-Methyl-6-t-butylphenol), 2,2'-methylenebis (4-ethyl-6-t-butylphenol), 2,2'-methylenebis (4-methyl-6-t-butylphenol), 4,4 ' -Isopropylidenebisphenol, 2,4-dimethyl-6-tert-butylphenol, tetrakis [methylene-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate] methane, 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane, 1,3,5
-Trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxybenzyl) benzene, 2,6-di-tert-butyl-4-ethylphenol, 2,6-bis (2 '-Hydroxy-3'-t-butyl-5'-methylbenzyl) -4
-Methylphenol, bis [2- (2-hydroxy-5-methyl-3-t-butylbenzyl) -4-methyl-6-t-butylphenyl] terephthalate, triethylene glycol-bis [3- (3-t -Butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate].

  It is necessary that these compounds are not substantially added, and the content is preferably 0.1% by weight or less, particularly 0.03% by weight or less, and more preferably 0.01% by weight or less.

[Other Additives] In order to improve the oxidation stability, at least one selected from an epoxy compound, a carbodiimide compound and a triazole compound is contained in an amount of 0.01 to 2% by weight, particularly 0.02 to 1% by weight. It is preferable. Moreover, it is particularly preferable to add three types of epoxy compounds, carbodiimide compounds, and triazole compounds.

[Epoxy Compound] The epoxy compound is a compound having an epoxy group, and preferably has 4 to 60 carbon atoms, particularly 5 to 25 carbon atoms. The epoxy compound may be used alone or in combination of two or more, and is preferably contained in an amount of 0.01 to 2% by weight, particularly 0.02 to 1% by weight.

  Specifically, glycidyl ethers such as butyl glycidyl ether, 2-ethylhexyl glycidyl ether, trimethylolpropane polyglycidyl ether, neopentyl glycol diglycidyl ether, t-butylphenyl glycidyl ether, adipic acid glycidyl ester, 2-ethylhexane Examples thereof include glycidyl esters such as acid glycidyl ester, isononanoic acid glycidyl ester, and neodecanoic acid glycidyl ester, epoxidized fatty acid monoesters such as epoxidized methyl stearate, and epoxidized vegetable oils such as epoxidized soybean oil. Preferable epoxy compounds are glycidyl ethers represented by the following general formulas 1 and 2 or glycidyl esters represented by the following formula 3, and glycidyl esters are particularly preferable.

In the formula, R ₁ represents a hydrogen atom, a linear or branched alkyl group having 1 to 24 carbon atoms, or an alkylphenyl group having 1 to 24 carbon atoms.

In the formula, R ₂ represents a linear or branched alkylene group having 1 to 18 carbon atoms.

In the formula, R ₃ represents a linear or branched alkyl group having 1 to 24 carbon atoms or an alkylphenyl group having 1 to 24 carbon atoms.

[Carbodiimide Compound] The carbodiimide compound is represented by a general formula of R′—N═C═N—R ″. Here, R ′ and R ″ are hydrocarbon groups having 1 to 18 carbon atoms, which may be the same. May be different. R ′ and R ″ are preferably an alkyl-substituted phenyl group having 7 to 14 carbon atoms. Specific examples include 1,3-diisopropylcarbodiimide, 1,3-di-t-butyl-carbodiimide, and 1,3-dicyclohexyl. Carbodiimide, 1,3-di-p-tolylcarbodiimide, 1,3-bis- (2,6-diisopropylphenyl) carbodiimide, etc., preferably 1,3-diisopropylcarbodiimide, 1,3-di-p- These are tolyl carbodiimide and 1,3-bis- (2,6-diisopropylphenyl) carbodiimide, and the carbodiimide compound may be used alone or in combination of two or more, and is 0.01 to 2% by weight, particularly preferably 0.2% by weight. It is preferable to contain 02 to 1 weight%.

[Triazole Compound] As the triazole compound, benzotriazole and a benzotriazole derivative can be used. It is preferable to use a compound represented by the following general formula 4.

In the formula, R ₄ represents a hydrogen atom or a methyl group, and R ₅ represents a hydrogen atom or a group having 0 to 20 carbon atoms containing a nitrogen atom and / or an oxygen atom.

As the triazole compound, a benzotriazole derivative is preferable, and R ₂ is preferably a group having 5 to 20 carbon atoms containing a nitrogen atom. The triazole compound may be used alone or in combination of two or more, and is preferably contained in an amount of 0.01 to 2% by weight, particularly 0.02 to 1% by weight.

  Specifically, 2- (2′-hydroxy-5′-methylphenyl) benzotriazole, 2- (2′-hydroxy-3 ′, 5′-bis (α, α′-dimethylbenzyl) phenyl) -benzo Examples include triazole, 2- (2′-hydroxy-3 ′, 5′-di-t-butylphenyl) -benzotriazole, 1- (N, N-bis- (2-ethylhexyl) aminomethyl) benzotriazole and the like. .

[Other components] As required, detergent dispersant, antiwear agent, viscosity index improver, pour point depressant, ashless dispersant, metal deactivator, metal detergent, oiliness agent, surfactant Various additives such as an antifoaming agent, a friction modifier, a rust inhibitor, and a corrosion inhibitor can be blended depending on the application.

EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not interpreted limitedly by this Example.
In this example, the relative dielectric constant (25 ° C.) is JIS C2101, the kinematic viscosity and viscosity index are JIS K2283, the rotary cylinder oxidation stability (RBOT) is JIS K2514, the total acid value is JISK2501, and , Hydroxyl value is JIS
Measured by K0070.

  Dioctyl sebacate (DOS), ester of neopentyl glycol and capric acid (NPG-1), ester of pentaerythritol and heptanoic acid (PE-1) and polyalphaolefin (PAO) were used as the base oil. Each characteristic is summarized in Table 1.

As an additive,
DPA: 4,4′-dioctyldiphenylamine which is an amine antioxidant.
PANA: 4-octylphenylnaphthylamine which is an amine antioxidant.
Phe: Irganox L135 (manufactured by Ciba Specialty Chemicals), a phenolic antioxidant.
Epoxy compound: Neodecanoic acid glycidyl ester carbodiimide: 1,3-bis- (2,6-diisopropylphenyl) carbodiimide
BTA derivative: Irgamet 39 (Ciba Specialty Chemicals)
Was used.

  Sample oils of Examples 1 to 7 and Comparative Examples 1 to 9 were prepared by blending the base oil with additives in the blending amounts (% by weight) shown in Table 1. About these, the result of having evaluated oxidation stability by rotation cylinder type oxidation stability (RBOT) is shown according to Table 2.

When the present inventor uses a diester, a polyol ester or the like as a base oil, excellent oxidation resistance can be obtained by using only an amine-based antioxidant without using a phenol-based antioxidant. Moreover, oxidation resistance is further improved by using an epoxy compound, a carbodiimide compound and / or a triazole compound in combination with an amine-based antioxidant. Thereby, the lubricating oil composition according to the present invention can be used stably for a long period of time.

Claims (4)

95% by weight or more of a base oil having a relative dielectric constant (25 ° C.) of 2.5 or more, 0.01 to 5% by weight of an amine antioxidant, and 0.1% by weight of a phenolic antioxidant % Lubricating oil composition. The lubricating oil composition according to claim 1, wherein the base oil is mainly composed of a diester and / or a polyol ester. The lubricating oil composition according to claim 1, comprising 0.01 to 2% by weight of at least one selected from an epoxy compound, a carbodiimide compound and a triazole compound. Lubrication according to any one of claims 1 to 3, characterized in that it contains 0.05 to 2% by weight of an amine antioxidant and the content of phenolic antioxidant is not more than 0.1% by weight. Oil composition.