JP2016037528A - Lubricant composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lubricant composition that has a small coefficient of friction between a rubber material and metal, large friction energy, and furthermore excellent oxidation stability.SOLUTION: The lubricant composition is obtained by blending at least one selected from acid phosphate esters represented by following formulas (1) and (2), and an antioxidant into a base oil. (In the respective formulas, R, R, and Rare all alkyl groups. At least either of Rand R, and Rhave carbon numbers of 20 to 30.)SELECTED DRAWING: None

Description

  The present invention relates to a lubricating oil composition, for example, a lubricating oil composition for shock absorbers used in automobiles and industrial machines and devices.

The shock absorber is installed at a portion connecting the tire and the vehicle body of the passenger car, and plays a role of attenuating the shaking of the vehicle body caused by road surface unevenness and increase / decrease in vehicle speed. Therefore, riding comfort is greatly influenced by the performance of the shock absorber.
The friction (friction) of the shock absorber is mainly generated in the oil seal (rubber material) and the rod (chrome plating) part. Therefore, it is a very important issue to improve the friction characteristics generated between the rubber material and the chrome plating. In addition, in order to move smoothly when the rod of the shock absorber expands and contracts, it is required that the absolute value of rubber friction (rubber material-metal friction coefficient) is small.
So far, evaluation of the friction characteristics based on the absolute value of rubber friction has been carried out, and shock absorber oils having small parameters have been developed (see Non-Patent Documents 1 and 2).

Proceedings of the Japan Petroleum Institute Petroleum Product Discussion Meeting, 96 pages (December 2009) Tribologist, 567, Vol. 56, No. 9 (2011)

  However, the frictional characteristics cannot be sufficiently evaluated only by the absolute value of the rubber friction as described in Non-Patent Documents 1 and 2, and it has not been easy to develop a lubricating oil having excellent frictional characteristics. . On the other hand, it has been found that it is also important that the work of friction (friction energy; also referred to as friction energy) is large in order to attenuate the shaking of the vehicle body. In addition, since the shock absorber is not replaced, it is generally used continuously for 5 to 10 years. For this reason, the lubricating oil for the shock absorber is required to have high oxidation stability.

  An object of the present invention is to provide a lubricating oil composition having a small coefficient of friction between a rubber material and a metal, a large friction energy, and excellent oxidation stability.

In order to solve the above problems, the present invention provides the following lubricating oil composition.
[1] A lubricating oil comprising a base oil blended with at least one of acidic phosphate esters represented by the following formula (1) and the following formula (2), and an antioxidant. Composition.

（上記各式において、Ｒ^１、Ｒ^２及びＲ^３はいずれもアルキル基である。Ｒ^１及びＲ^２の少なくともいずれか一方、並びにＲ^３の炭素数は２０以上３０以下である。）
〔２〕上記〔１〕に記載の潤滑油組成物において、前記Ｒ^１及びＲ^２のうち少なくともいずれか１つが側鎖を有することを特徴とする潤滑油組成物。
〔３〕上記〔１〕に記載の潤滑油組成物において、前記Ｒ^３が側鎖を有することを特徴とする潤滑油組成物。
〔４〕上記〔２〕又は〔３〕に記載の潤滑油組成物において、前記側鎖の炭素数が６以上１８以下であることを特徴とする潤滑油組成物。
〔５〕上記〔１〕から〔４〕までのいずれか１つに記載の潤滑油組成物において、前記酸化防止剤がフェノール系酸化防止剤、アミン系酸化防止剤、及び硫黄系酸化防止剤のうち少なくともいずれか１種であることを特徴とする潤滑油組成物。
〔６〕上記〔１〕から〔５〕までのいずれか１つに記載の潤滑油組成物において、前記酸性リン酸エステルを、組成物全量基準で０．０１質量％以上３質量％以下配合してなることを特徴とする潤滑油組成物。
〔７〕上記〔１〕から〔６〕までのいずれか１つに記載の潤滑油組成物において、当該組成物が緩衝器用であることを特徴とする潤滑油組成物。
〔８〕上記〔７〕に記載の潤滑油組成物において、前記緩衝器が四輪自動車用であることを特徴とする潤滑油組成物。

(In each of the above formulas, R ¹ , R ² and R ³ are all alkyl groups. At least one of R ¹ and R ² , and R ³ has 20 to 30 carbon atoms.)
[2] The lubricating oil composition according to [1], wherein at least one of R ¹ and R ² has a side chain.
[3] The lubricating oil composition according to [1], wherein R ³ has a side chain.
[4] The lubricating oil composition according to the above [2] or [3], wherein the side chain has 6 to 18 carbon atoms.
[5] The lubricating oil composition according to any one of [1] to [4], wherein the antioxidant is a phenol-based antioxidant, an amine-based antioxidant, or a sulfur-based antioxidant. A lubricating oil composition comprising at least one of them.
[6] In the lubricating oil composition according to any one of [1] to [5], the acidic phosphate ester is blended in an amount of 0.01% by mass to 3% by mass based on the total amount of the composition. A lubricating oil composition characterized by comprising:
[7] The lubricating oil composition according to any one of [1] to [6], wherein the composition is for a shock absorber.
[8] The lubricating oil composition according to the above [7], wherein the shock absorber is for a four-wheeled vehicle.

  According to the present invention, it is possible to provide a lubricating oil composition having a small friction coefficient between a rubber material and a metal, a large friction energy, and excellent oxidation stability.

The figure which showed typically an example of the ditetracosyl acid phosphate. The figure which showed typically an example of the dioctacyl acid phosphate. The figure which showed typically an example of the distearyl acid phosphate. The figure which shows the friction test apparatus in an Example. The figure which shows an example of the Lissajous waveform obtained with the friction test apparatus.

  The lubricating oil composition in the present embodiment (hereinafter also referred to as “the present composition”) is characterized in that a predetermined acidic phosphate ester and an antioxidant are blended with a base oil. Hereinafter, the composition will be described in detail.

[Base oil]
The base oil used in the present composition is not particularly limited, and may be at least one of mineral oil and synthetic oil, that is, each may be used alone or in combination of two or more, or mineral oil and synthetic oil may be used in combination. .
If it is for shock absorbers, it is preferable to use a base oil having a kinematic viscosity at 40 ° C. of about 5 mm ² / s or more and 40 mm ² / s or less in order to maintain good friction characteristics.
Further, the pour point, which is an index of the low temperature fluidity of the base oil, is not particularly limited, but is preferably −10 ° C. or lower, particularly preferably −15 ° C. or lower.

Examples of such mineral oil include naphthenic mineral oil, paraffinic mineral oil, GTL WAX, and the like. Specific examples include light neutral oil, medium neutral oil, heavy neutral oil, bright stock and the like by solvent refining or hydrogenation refining.
On the other hand, as synthetic oil, polybutene or a hydride thereof, polyalphaolefin (1-octene oligomer, 1-decene oligomer, etc.), alkylbenzene, polyol ester, dibasic acid ester, polyoxyalkylene glycol, polyoxyalkylene glycol ester, Examples include polyoxyalkylene glycol ethers, hindered esters, and silicone oils.

[Acid phosphate ester]
The acidic phosphate ester blended in the present composition is represented by the following formula (1) and the following formula (2).

In the above formulas, R ¹ , R ² and R ³ are all alkyl groups. At least one of R ¹ and R ² and R ³ has 20 or more and 30 or less carbon atoms.
Examples of the alkyl group having 20 to 30 carbon atoms include an eicosyl group, a heneicosyl group, a docosyl group, a tricosyl group, a tetracosyl group, a pentacosyl group, a hexacosyl group, a heptacosyl group, an octacosyl group, a nonacosyl group, and a triacontyl group. Can be mentioned.
Examples of the acidic phosphate esters of the above formulas (1) and (2) include, for example, when R ^{1 to} R ³ are a tetracosyl group or an octacosyl group, tetracosyl acid phosphate, ditetracosyl acid phosphate, octacosyl. Acid phosphate, dioctacyl acid phosphate, etc. are mentioned. For reference, FIGS. 1 and 2 schematically show examples of ditetracosyl acid phosphate and dioctacyl acid phosphate.
When the acidic phosphate ester has an alkyl group having 20 or more carbon atoms, the friction coefficient and the friction energy can be effectively improved. In addition, the oxidation stability is improved by the presence of such an acidic phosphate ester.
Furthermore, it is preferable that the above-described alkyl group has 30 or less carbon atoms because the solubility in the base oil can be ensured. The above-described alkyl group preferably has 20 to 26 carbon atoms, more preferably 20 to 24 carbon atoms.
On the other hand, if the number of carbon atoms of the alkyl group is below the above lower limit, the friction coefficient increases, and an increase in friction energy cannot be expected. For example, FIG. 3 schematically shows an example of distearyl acid phosphate, but since the number of carbon atoms of the alkyl group is small, the friction coefficient is large and the friction energy is small.

The alkyl groups in formula (1) and formula (2) may be linear, but having a side chain is desirable from the viewpoint of reducing the friction coefficient and increasing the friction energy. Furthermore, the side chain becomes a steric hindrance and the oxidation stability is improved. That is, in Formula (1), it is preferable that at least one of R ¹ and R ² has a side chain. In the formula (2), it is preferred that R ³ has a side chain. Further, the number of carbon atoms in the side chain is preferably 6 or more and 18 or less. It is preferable that the number of carbons in the side chain is 6 or more from the viewpoint of reducing the friction coefficient and increasing the friction energy. Further, it is preferable that the side chain has 18 or less carbon atoms because the solubility in the base oil is improved.
From the viewpoints of reducing the friction coefficient, increasing the frictional energy, and oxidation stability, the acidic phosphate ester of the formula (1) is preferable to the acidic phosphate ester of the formula (2).

  In the present composition, the acidic phosphate ester is preferably blended in an amount of 0.01% by mass or more and 3% by mass or less based on the total amount of the composition with respect to the base oil. The content is more preferably no greater than mass%, and even more preferably no less than 0.2 mass% and no greater than 1 mass%. When the compounding amount of the acidic phosphate is 0.01% by mass or more, it is preferable not only from the viewpoint of reducing the friction coefficient and increasing the friction energy, but also from the viewpoint of oxidation stability. Moreover, since the solubility to base oil can be ensured that the compounding quantity of acidic phosphate ester is 3 mass% or less, it is preferable.

[Antioxidant]
The composition further contains an antioxidant. The above-mentioned predetermined acidic phosphoric acid ester also has an effect of improving the oxidation stability, but it exhibits exceptional oxidation stability by using an antioxidant together.
As the antioxidant, at least one of amine-based antioxidants, phenol-based antioxidants, and sulfur-based antioxidants can be preferably used. These antioxidants can be used individually by 1 type or in combination of 2 or more types.
Examples of the amine antioxidant include monoalkyl diphenylamine compounds such as monooctyl diphenylamine and monononyl diphenylamine, 4,4′-dibutyldiphenylamine, 4,4′-dipentyldiphenylamine, 4,4′-dihexyldiphenylamine, 4 , 4′-diheptyldiphenylamine, 4,4′-dioctyldiphenylamine, dialkyldiphenylamine compounds such as 4,4′-dinonyldiphenylamine, polyalkyl such as tetrabutyldiphenylamine, tetrahexyldiphenylamine, tetraoctyldiphenylamine, tetranonyldiphenylamine Diphenylamine compounds, α-naphthylamine, phenyl-α-naphthylamine, butylphenyl-α-naphthylamine, pentylphenyl-α-na Ethylamine, hexyl phenyl -α- naphthylamine, heptylphenyl -α- naphthylamine, octylphenyl -α- naphthylamine, and naphthylamine-based compounds such as nonylphenyl -α- naphthylamine.

Examples of the phenolic antioxidant include monophenolic compounds such as 2,6-di-tert-butyl-4-methylphenol and 2,6-di-tert-butyl-4-ethylphenol, 4,4 ′ Examples include diphenolic compounds such as -methylenebis (2,6-di-tert-butylphenol) and 2,2'-methylenebis (4-ethyl-6-tert-butylphenol).
Examples of the sulfur-based antioxidant include 2,6-di-tert-butyl-4- (4,6-bis (octylthio) -1,3,5-triazin-2-ylamino) phenol, phosphorus pentasulfide and Examples thereof include thioterpene compounds such as a reaction product with pinene, and dialkylthiodipropionates such as dilauryl thiodipropionate and distearyl thiodipropionate.
The blending amount of these antioxidants is about 0.01% by mass or more and 10% by mass or less, and preferably about 0.03% by mass or more and 5% by mass or less based on the total amount of the present composition.

In the present invention, “a lubricating oil composition comprising a base oil containing a predetermined acidic phosphate ester and an antioxidant” includes “a base oil containing a predetermined acidic phosphate ester and Not only the “lubricating oil composition containing an antioxidant” but also at least one component of “base oil”, “predetermined acidic phosphate ester” and “antioxidant”, the component is modified. A modified product and a composition containing a reaction product after the component has reacted are also included.
[Other ingredients]
In the present composition, other additives such as a viscosity index improver, a pour point depressant, an antiwear agent, a friction modifier, a metal detergent, as necessary, as long as the effects of the present invention are not impaired. Ashless dispersants, rust inhibitors, metal deactivators, antifoaming agents, and the like may be blended. In addition, the present composition containing each additive includes a modified product obtained by modifying the additive, and a composition containing a reaction product after the additive has reacted.

Examples of the viscosity index improver include polymethacrylate, dispersed polymethacrylate, olefin copolymer (for example, ethylene-propylene copolymer), dispersed olefin copolymer, styrene copolymer (for example, styrene- Diene copolymer, styrene-isoprene copolymer, etc.). The blending amount of the viscosity index improver is about 0.5% by mass or more and 15% by mass or less based on the total amount of the present composition from the viewpoint of blending effect.
As the pour point depressant, for example, polymethacrylate having a mass average molecular weight of about 10,000 to 150,000 is used. A preferable blending amount of the pour point depressant is about 0.01% by mass or more and 10% by mass or less based on the total amount of the composition.

Examples of the antiwear agent include sulfur type antiwear agents such as thiophosphate metal salts (Zn, Pb, Sb, etc.) and thiocarbamic acid metal salts (Zn, etc.), phosphate esters (tricresyl phosphate), etc. Phosphorous wear inhibitors can be mentioned. A preferable blending amount of the antiwear agent is about 0.05% by mass or more and 5% by mass or less based on the total amount of the composition.
Examples of the friction modifier include polyhydric alcohol partial esters such as neopentyl glycol monolaurate, trimethylolpropane monolaurate, and glycerin monooleate (oleic acid monoglyceride). A preferable blending amount of the friction modifier is about 0.05% by mass or more and 4% by mass or less based on the total amount of the composition.

The metal detergent is preferably at least one of metal salicylate, metal phenate and metal sulfonate. As the metal, an alkaline earth metal is preferable, and Ca is more preferable. From the viewpoint of maintaining cleanliness, Ca salicylate is particularly preferable. As the metal-based detergent, in order to maintain the cleanliness of the present composition, the base number by the hydrochloric acid method is preferably 100 mgKOH / g or more and 250 mgKOH / g or less. As a compounding quantity of a metal type detergent, it is preferable that they are 60 mass ppm or more and 6000 mass ppm or less in conversion of a metal quantity standard and metal amount.
Examples of the ashless dispersant include succinimides, boron-containing succinimides, benzylamines, boron-containing benzylamines, succinic esters, monovalent or divalent typified by fatty acids or succinic acid. Examples thereof include amides of carboxylic acids. A preferable blending amount of the ashless dispersant is about 0.1% by mass or more and 20% by mass or less based on the total amount of the present composition.

Examples of the rust inhibitor include fatty acid, alkenyl succinic acid half ester, fatty acid soap, alkyl sulfonate, polyhydric alcohol fatty acid ester, fatty acid amide, oxidized paraffin, alkyl polyoxyethylene ether and the like. The preferable compounding quantity of a rust preventive agent is about 0.01 mass% or more and 3 mass% or less on the basis of this composition whole quantity.
As the metal deactivator, for example, benzotriazole, thiadiazole and the like are used alone or in combination of two or more. A preferable compounding amount of the metal deactivator is about 0.01% by mass or more and 5% by mass or less based on the total amount of the present composition.

  As the antifoaming agent, for example, a silicone compound, an ester compound, or the like is used alone or in combination of two or more. A preferable blending amount of the antifoaming agent is about 0.05% by mass or more and 5% by mass or less based on the total amount of the composition.

Since the present composition is formed by blending an acidic phosphate ester having a predetermined structure and an antioxidant, the friction coefficient between the rubber material and the metal is small, the friction energy is large, and the oxidation stability is also excellent. Therefore, it is preferable for a shock absorber, and particularly suitable for a shock absorber of a four-wheeled vehicle (passenger car, bus, truck, etc.) where ride comfort is important.
In addition, this composition can be preferably applied also to the shock absorber for two wheels, and also can be applied preferably as a hydraulic fluid.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further more concretely, this invention is not limited at all by these examples. The properties and performance of the lubricating oil composition (sample oil) in each example were determined by the following methods.

(1) Kinematic viscosity at 40 ° C. Measured according to JIS K 2283.
(2) 40 ° C. Kinematic Viscosity Increase Rate After performing the ISOT test (JIS K 2514 compliant: 130 ° C., 24 hours), the 40 ° C. kinematic viscosity was measured, and the increase rate (%) relative to the 40 ° C. kinematic viscosity before the ISOT test. Asked.

(3) Friction coefficient and friction energy The friction coefficient between rubber and metal (dynamic friction coefficient) and friction energy were determined by the test apparatus shown in FIG. Specifically, as shown in FIG. 4, a Lissajous waveform was recorded by reciprocatingly sliding a rubber and a Cr (chromium) plated steel plate with a predetermined load while pressing the sample oil. FIG. 5 shows an example of a Lissajous waveform. The friction coefficient (μ) was determined from the maximum value of the frictional force, and the area of the Lissajous waveform (the product of the amplitude and the frictional force, which corresponds to the work amount) was determined as the frictional energy.
The test conditions are as follows.
Temperature: 30 ° C
Amplitude: ± 0.4 mm (sine wave)
Load: 3kgf (29.4N)
Upper test piece: NBR (nitrile rubber)
Lower test piece: Hard Cr plated steel plate Excitation frequency: 5Hz
Sample oil volume: 100 mL

[Examples 1-2, Comparative Examples 1-12]
Each sample oil was prepared according to the composition shown in Tables 1 and 2. About each sample oil, the property and performance were evaluated by the above-mentioned method. The results are also shown in Tables 1 and 2.

1) Base oil: paraffinic mineral oil (60 N, 40 ° C. kinematic viscosity 7.8 mm ² / s)
2) Antioxidant: DBPC (2,6-di-tert-butyl-p-cresol)
3) Acid phosphate ester amine salt: The alkyl group of phosphate ester is mainly monoethyl group and monomethyl group)
4) ZnDTP: primary alkyl group type having 12 carbon atoms 5) ZnDTP: primary alkyl group type having 6 carbon atoms (having some isopropyl and isobutyl groups)

〔Evaluation results〕
As can be seen from Examples 1 and 2, the sample oil blended with a predetermined acidic phosphate ester and an antioxidant has a small coefficient of friction between the rubber material and the metal, a large friction energy, and excellent oxidation stability. I understand that. Therefore, according to the present invention, it can be understood that a shock absorber oil that is excellent in ride comfort and can be used for a long period of time can be provided.
On the other hand, the sample oil of each comparative example is a blend of various oily agents, phosphorus extreme pressure agents, etc., all satisfying all of the friction coefficient, friction energy, and oxidation stability at the same time. It is not possible. For example, Comparative Examples 2, 3, 5, and 10 are inferior in oxidation stability even though the same amount of the same antioxidant as in Examples 1 and 2 is blended. Comparative Example 12 is a blend of an acidic phosphoric diester having an alkyl group with a relatively large number of carbon atoms, but the carbon number of the alkyl group is still 18 and the lower limit of the carbon number of the alkyl group in the present invention is Since it is less than the value, the coefficient of friction is larger than in the case of the base oil alone (Comparative Example 1: only antioxidant) and almost no increase in friction energy is observed.

Claims (8)

A lubricating oil composition comprising a base oil and at least one of acidic phosphate esters represented by the following formula (1) and the following formula (2) and an antioxidant.

(In each of the above formulas, R ¹ , R ² and R ³ are all alkyl groups. At least one of R ¹ and R ² , and R ³ has 20 to 30 carbon atoms.) The lubricating oil composition according to claim 1, wherein
A lubricating oil composition, wherein at least one of R ¹ and R ² has a side chain. The lubricating oil composition according to claim 1, wherein
The lubricating oil composition, wherein R ³ has a side chain. In the lubricating oil composition according to claim 2 or claim 3,
The lubricating oil composition, wherein the side chain has 6 to 18 carbon atoms. In the lubricating oil composition according to any one of claims 1 to 4,
The lubricating oil composition, wherein the antioxidant is at least one of a phenol-based antioxidant, an amine-based antioxidant, and a sulfur-based antioxidant. In the lubricating oil composition according to any one of claims 1 to 5,
A lubricating oil composition comprising the acidic phosphate ester blended in an amount of 0.01% by mass to 3% by mass based on the total amount of the composition. In the lubricating oil composition according to any one of claims 1 to 6,
A lubricating oil composition, wherein the composition is for a shock absorber. The lubricating oil composition according to claim 7,
The lubricating oil composition, wherein the shock absorber is for a four-wheeled vehicle.

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