JP6845092B2 - Lubricating oil composition for shock absorber - Google Patents

Description

The present invention relates to a lubricant composition for a shock absorber.

The shock absorber is installed between the car body of the passenger car and the tires, and has a function of buffering the vibration of the car body due to the unevenness of the road surface, the shaking generated at the time of sudden acceleration or sudden braking, and the like. Therefore, the lubricating oil composition used for the shock absorber has lubricity, an anti-friction agent, and heat at the sliding parts (piston rod, oil seal, sliding part between the piston band and the cylinder, etc.) in the shock absorber. -Characteristics as a lubricant such as antioxidant properties are required.

As a lubricating oil composition for a shock absorber, a lubricating oil base oil containing various additives is disclosed (see, for example, Patent Documents 1 and 2).

Japanese Unexamined Patent Publication No. 2009-0133380 Japanese Unexamined Patent Publication No. 2013-199535

By the way, in the shock absorber lubricating oil composition, the frictional force (static frictional force) before starting to move is improved from the viewpoint of improving the steering stability from a low temperature (for example, −40 ° C.) to a high temperature (for example, 80 ° C.). On the other hand, from the viewpoint of improving the riding comfort, it is required to reduce the frictional force (dynamic frictional force) after starting to move. However, when the conventional lubricating oil composition is applied to the shock absorber, there is a problem that even if the dynamic friction force can be reduced, the static friction force is also reduced in conjunction with it.

Therefore, the present invention provides a lubricating oil composition for a shock absorber, which can reduce the dynamic friction force while increasing the static friction force from a low temperature to a high temperature at a sliding portion, and further has excellent low temperature characteristics and thermal stability. The main purpose is to do.

As a result of diligent studies to achieve the above object, the present inventors add a specific additive to a specific lubricating oil base oil to increase the static friction force and reduce the dynamic friction force at the sliding portion. Further, they have found that low temperature characteristics and thermal stability can be improved, and have completed the present invention.

That is, the present invention uses the lubricating oil compositions shown in the following [1] to [4], the use (application) of the composition shown in the following [5], and the use for producing the composition shown in the following [6]. (Application) is provided.

［式（１）中、Ｒ^１１〜Ｒ^１４は、それぞれ独立に第一級アルキル基を示す。］
［２］緩衝器用潤滑油組成物の−４０℃におけるＢＦ粘度が１，５００ｍＰａ・ｓ以下である、［１］に記載の緩衝器用潤滑油組成物。
［３］緩衝器用潤滑油組成物の１００℃における動粘度が２．０〜３．５ｍｍ^２／ｓである、［１］又は［２］に記載の緩衝器用潤滑油組成物。
［４］ジアルキルジチオリン酸亜鉛が、炭素数６〜１０の第一級アルキル基を含む、［１］〜［３］のいずれかに記載の緩衝器用潤滑油組成物。
［５］組成物の緩衝器用潤滑油としての使用（応用）であって、組成物が、１００℃における動粘度が０．１〜５．０ｍｍ^２／ｓである鉱油系基油と、組成物全量を基準として、重量平均分子量が８０，０００〜２００，０００であるポリ（メタ）アクリレート０．５〜５．０質量％と、数平均分子量が５００〜５，０００であるポリブテン０．０５〜１．０質量％と、下記一般式（１）で表されるジアルキルジチオリン酸亜鉛０．３〜１．０質量％と、トリアゾール誘導体０．０５〜０．７質量％と、を含有し、ポリブテンの数平均分子量に対する、ポリ（メタ）アクリレートの重量平均分子量の比が５０〜２５０である、使用（応用）。

［式（１）中、Ｒ^１１〜Ｒ^１４は、それぞれ独立に第一級アルキル基を示す。］
［６］組成物の緩衝器用潤滑油の製造のための使用（応用）であって、組成物が、１００℃における動粘度が０．１〜５．０ｍｍ^２／ｓである鉱油系基油と、組成物全量を基準として、重量平均分子量が８０，０００〜２００，０００であるポリ（メタ）アクリレート０．５〜５．０質量％と、数平均分子量が５００〜５，０００であるポリブテン０．０５〜１．０質量％と、下記一般式（１）で表されるジアルキルジチオリン酸亜鉛０．３〜１．０質量％と、トリアゾール誘導体０．０５〜０．７質量％と、を含有し、ポリブテンの数平均分子量に対する、ポリ（メタ）アクリレートの重量平均分子量の比が５０〜２５０である、使用（応用）。

［式（１）中、Ｒ^１１〜Ｒ^１４は、それぞれ独立に第一級アルキル基を示す。］ [1] Mineral oil-based base oil having a kinematic viscosity at 100 ° C. of 0.1 to 5.0 mm ² / s, and poly (meth) having a weight average molecular weight of 80,000 to 200,000 based on the total amount of the composition. ) Acrylate 0.5 to 5.0% by mass, polybutene having a number average molecular weight of 500 to 5,000, 0.05 to 1.0% by mass, and zinc dialkyldithiophosphate represented by the following general formula (1). It contains 0.3 to 1.0% by mass and 0.05 to 0.7% by mass of a triazole derivative, and the ratio of the weight average molecular weight of poly (meth) acrylate to the number average molecular weight of polybutene is 50 to 250. Lubricating oil composition for shock absorbers.

[In formula (1), R ^{11 to} R ¹⁴ each independently represent a primary alkyl group. ]
[2] The lubricating oil composition for a shock absorber according to [1], wherein the BF viscosity of the lubricating oil composition for a shock absorber at −40 ° C. is 1,500 mPa · s or less.
[3] The lubricating oil composition for a shock absorber according to [1] or [2], wherein the kinematic viscosity of the lubricating oil composition for a shock absorber at 100 ° C. is 2.0 to 3.5 mm ^{2 / s.}
[4] The lubricating oil composition for a shock absorber according to any one of [1] to [3], wherein zinc dialkyldithiophosphate contains a primary alkyl group having 6 to 10 carbon atoms.
[5] Use (application) of the composition as a lubricating oil for a shock absorber, wherein the composition is a mineral oil-based base oil having a ^{kinematic viscosity at 100 ° C. of 0.1 to 5.0 mm 2 / s, and the composition.} Based on the total amount, 0.5 to 5.0% by mass of poly (meth) acrylate having a weight average molecular weight of 80,000 to 200,000 and polybutene 0.05 to 5,000 having a number average molecular weight of 500 to 5,000. Polybutene containing 1.0% by mass, 0.3 to 1.0% by mass of zinc dialkyldithiophosphate represented by the following general formula (1), and 0.05 to 0.7% by mass of a triazole derivative. The ratio of the weight average molecular weight of the poly (meth) acrylate to the number average molecular weight of is 50 to 250, used (application).

[In formula (1), R ^{11 to} R ¹⁴ each independently represent a primary alkyl group. ]
[6] Use (application) for producing a lubricating oil for a shock absorber of the composition, wherein the composition is a mineral oil-based base oil having a ^{kinematic viscosity at 100 ° C. of 0.1 to 5.0 mm 2 / s.} , 0.5 to 5.0% by mass of poly (meth) acrylate having a weight average molecular weight of 80,000 to 200,000 and polybutene 0 having a number average molecular weight of 500 to 5,000 based on the total amount of the composition. .05 to 1.0% by mass, 0.3 to 1.0% by mass of zinc dialkyldithiophosphate represented by the following general formula (1), and 0.05 to 0.7% by mass of a triazole derivative. However, the ratio of the weight average molecular weight of poly (meth) acrylate to the number average molecular weight of polybutene is 50 to 250, which is used (application).

[In formula (1), R ^{11 to} R ¹⁴ each independently represent a primary alkyl group. ]

According to the present invention, there is provided a lubricating oil composition for a shock absorber which can reduce the dynamic friction force while increasing the static friction force from a low temperature to a high temperature in a sliding portion, and further has excellent low temperature characteristics and thermal stability. can do.

Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments.

The lubricating oil composition for a shock absorber according to an embodiment contains a specific lubricating oil base oil, a specific viscosity modifier, a specific zinc dialkyldithiophosphate, and a specific triazole derivative.

<Mineral oil-based base oil>
The lubricating oil composition for a shock absorber of the present embodiment contains a mineral oil-based base oil having a ^{kinematic viscosity of 0.1 to 5.0 mm 2 / s at 100 ° C.} As the mineral oil-based base oil, if the kinematic viscosity at 100 ° C. is 0.1 to 5.0 mm ² / s, the base oil used in the ordinary lubricating oil field can be used.

Examples of the mineral oil-based base oil include kerosene distillates obtained by distilling paraffin-based, naphthen-based, or aromatic crude oil; normal paraffins obtained by extraction operations from kerosene distillates; and paraffin-based, naphthen-based, and paraffin-based, naphthen-based oils. Alternatively, a lubricating oil distillate obtained by distilling an aromatic crude oil, or a wax such as slack wax obtained by a dewaxing step of the lubricating oil and / or a Fisher Tropsch wax obtained by a gastre liquid (GTL) process or the like. Using synthetic wax such as GTL wax as a raw material, one purification process such as solvent removal, solvent extraction, hydrocracking, hydroisomerization, solvent dewaxing, contact dewaxing, hydrogen purification, sulfuric acid cleaning, and white clay treatment. Alternatively, examples thereof include paraffin-based mineral oil, naphthen-based mineral oil, normal paraffin-based base oil, isoparaffin-based base oil, and aromatic-based base oil refined by appropriately combining two or more of them. One of these mineral oil-based base oils may be used alone, or two or more of them may be used in combination at any ratio. Further, it may be used in combination with one or more of the synthetic base oils described later in an arbitrary ratio.

The kinematic viscosity of the mineral oil-based base oil at 100 ° C. is 0.1 to 5.0 mm ² / s. The kinematic viscosity at 100 ° C. is preferably 0.5 mm ² / s or more, more preferably 1 mm ² / s or more, and further preferably 1.5 mm ² / s or more. The kinematic viscosity at 100 ° C. is preferably 4 mm ² / s or less, more preferably 3.5 mm ² / s or less, and further preferably 3 mm ² / s or less. When the kinematic viscosity at 100 ° C. is within the above range, the proper viscosity of the mineral oil-based base oil can be ensured, and a good oil film tends to be obtained in the actual operating temperature range.

The kinematic viscosity of the mineral oil-based base oil at 40 ° C. is not particularly limited, but is preferably 4 to 10 mm ² / s. The kinematic viscosity at 40 ° C. is more preferably 5 mm ² / s or more, further preferably 6 mm ² / s or more, and particularly preferably 7 mm ² / s or more. The kinematic viscosity at 40 ° C. is more preferably 9.5 mm ² / s or less, further preferably 9.2 mm ² / s or less, and particularly preferably 9 mm ² / s or less. When the kinematic viscosity at 40 ° C. is within the above range, the proper viscosity of the mineral oil-based base oil can be ensured, and a good oil film tends to be obtained in the actual operating temperature range.

The viscosity index of the mineral oil-based base oil is not particularly limited, but is preferably 60 or more, more preferably 80 or more, and further preferably 90 or more. When the viscosity index is within the above range, the stability of the viscosity with respect to the external temperature is ensured, so that the oil film tends to be stably formed even with the change of the external temperature during use. The upper limit of the viscosity index of the mineral oil-based base oil is not particularly limited, but may be, for example, 150 or less.

The kinematic viscosity and viscosity index at 40 ° C. and 100 ° C. in the present specification mean values measured in accordance with JIS K2283 “Crude oil and petroleum products-kinematic viscosity test method and viscosity index calculation method”, respectively.

The pour point of the mineral oil-based base oil is not particularly limited, but may be −20 ° C. or lower, −30 ° C. or lower, or −40 ° C. or lower. The pour point in the present specification means a value measured in accordance with JIS K2269 “Pour point of crude oil and petroleum products and test method for clouding point of petroleum products”.

The flash point of the mineral oil-based base oil is not particularly limited, but may be 130 ° C. or higher, 140 ° C. or higher, or 150 ° C. or higher. The flash point in the present specification means a value measured in accordance with JIS K2265-4 "How to obtain a flash point-Part 4: Cleveland opening method".

<Additives for lubricating oil>
[Poly (meth) acrylate]
The lubricant composition for a shock absorber of the present embodiment contains a poly (meth) acrylate having a weight average molecular weight of 80,000 to 200,000. Poly (meth) acrylate is a lubricating oil additive that can act as a viscosity modifier. By containing the poly (meth) acrylate in the lubricating oil composition, it is possible to improve the static friction force and reduce the dynamic friction force of the lubricating oil composition at a low temperature. In addition, poly (meth) acrylate means polyacrylate or polymethacrylate.

As the poly (meth) acrylate, poly (meth) acrylate used as a viscosity modifier in the usual lubricating oil field can be used. As the poly (meth) acrylate, one type may be used alone or two or more types may be used in combination at an arbitrary ratio as long as the weight average molecular weight satisfies the above conditions.

The poly (meth) acrylate may be a non-dispersive poly (meth) acrylate. The "non-dispersive" poly (meth) acrylate means a poly (meth) acrylate having no polar group such as a hydroxyl group, an amino group, or an amide group in the side chain. The non-dispersive poly (meth) acrylate may be, for example, a polymer of a monomer represented by the general formula (A-1).

In the formula (A-1), R ¹ represents a hydrogen atom or a methyl group, and R ² represents a linear or branched hydrocarbon group having 1 to 30 carbon atoms.

Examples of the hydrocarbon group having 1 to 30 carbon atoms represented by R ^2, for example, a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, heptyl group, octyl group, nonyl group, decyl group, Decyl group, undecyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group, octadecyl group, nonadecyl group, icosyl group, henicosyl group, docosyl group, tricosyl group, tetracosyl group, pentacosyl group, hexacosyl group. , Heptacosyl group, octacosyl group, nonacosyl group, triacontyl group and other alkyl groups (these alkyl groups may be linear or branched) and the like.

As the poly (meth) acrylate, a commercially available product may be used as it is, or a product produced by a known method may be used. Examples of the method for producing a poly (meth) acrylate include a method in which a monomer represented by the general formula (A-1) is subjected to radical solution polymerization in the presence of a polymerization initiator such as benzoyl peroxide.

The weight average molecular weight (Mw) of the poly (meth) acrylate is 80,000 to 200,000. The weight average molecular weight is preferably 85,000 or more, more preferably 90,000 or more, still more preferably 100,000 or more. When the weight average molecular weight is 80,000 or more, the viscosity index of the lubricating oil composition can be effectively improved. The weight average molecular weight is preferably 190,000 or less, more preferably 180,000 or less, still more preferably 170,000 or less. When the weight average molecular weight is 200,000 or less, the viscosity index of the lubricating oil composition can be improved and the shear stability can be improved. The weight average amount means a value measured by a gel permeation chromatography (GPC) method and converted based on a standard polystyrene calibration curve.

The ratio of the weight average molecular weight of the poly (meth) acrylate to the number average molecular weight of the polybutene described later (weight average molecular weight of the poly (meth) acrylate / number average molecular weight of the polybutene) is 50 to 250. The ratio is preferably 52 or more, more preferably 55 or more, still more preferably 60 or more. The ratio is preferably 220 or less, more preferably 200 or less, still more preferably 180 or less. When the ratio is within the above range, the friction characteristics of the lubricating oil composition tend to be improved.

The content of the poly (meth) acrylate is 0.5 to 5.0% by mass based on the total amount of the composition. The content of the poly (meth) acrylate is preferably 1.0% by mass or more, more preferably 1.2% by mass or more, and further preferably 1.5% by mass or more. The content of the poly (meth) acrylate is preferably 4.5% by mass or less, more preferably 4.0% by mass or less, still more preferably 3.5% by mass or less. When the content range of the poly (meth) acrylate is within the above range, the dynamic friction force can be reduced while increasing the static friction force of the lubricating oil composition at a low temperature.

[Polybuten]
The lubricant composition for a shock absorber of the present embodiment contains polybutene having a number average molecular weight of 500 to 5,000. Polybutene, like poly (meth) acrylate, is a lubricating oil additive that can act as a viscosity modifier. By including polybutene in the lubricating oil composition, tackiness (adhesiveness) is imparted and wettability tends to be improved. As a result, the oil film responsiveness of the sliding portion of the shock absorber can be improved, and the static friction force (steering stability) can be improved. As long as the number average molecular weight satisfies the above conditions, one type of polybutene may be used alone, or two or more types may be used in combination at any ratio.

Polybutene is a polymer obtained by polymerizing butenes having a double bond. The polybutene may be, for example, a polymer represented by the following general formula (X).

In formula (X), n represents an integer of 5 to 90.

As the polybutene, a commercially available product may be used as it is, or a product produced by a known method may be used. Examples of the method for producing polybutene include a method in which butadiene is removed from the C4 distillate produced by naphtha decomposition and polymerized using an acid catalyst.

The number average molecular weight (Mn) of polybutene is 500 to 5,000. The number average molecular weight is preferably 550 or more, more preferably 700 or more, still more preferably 900 or more. The number average molecular weight is preferably 4,000 or less, more preferably 3,000 or less, still more preferably 2,700 or less. When the number average molecular weight is in such a range, it is possible to optimize the static friction force at the sliding portion. The number average molecular weight means a value measured by a vapor pressure type molecular weight measurement (VPO) method.

The content of polybutene is 0.05 to 1.0% by mass based on the total amount of the composition. The content of polybutene is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and further preferably 0.4% by mass or more. The content of polybutene is preferably 0.9% by mass or less, more preferably 0.8% by mass or less, still more preferably 0.6% by mass or less. When the range of the content of polybutene is within the above range, the static frictional force of the lubricating oil composition can be improved.

The total content of the poly (meth) acrylate and polybutene may be 0.55 to 6.0% by mass based on the total amount of the composition. The total content of the poly (meth) acrylate and polybutene may be 1.0% by mass or more, 1.5% by mass or more, or 2.0% by mass or more, and 5.0% by mass or less. It may be 4.0% by mass or less, or 3.0% by mass or less.

[Zinc dialkyldithiophosphate]
The lubricating oil composition for a shock absorber of the present embodiment contains zinc dialkyldithiophosphate represented by the following general formula (1). By including such zinc dialkyldithiophosphate in the lubricating oil composition, it is possible to improve the frictional characteristics and thermal stability of the lubricating oil composition. As long as the zinc dialkyldithiophosphate is represented by the general formula (1), one type may be used alone, or two or more types may be used in combination at an arbitrary ratio.

In formula (1), R ^{11 to} R ¹⁴ each independently represent a primary alkyl (primary alkyl) group. Here, the primary alkyl group is an alkyl group represented by the following general formula (1A). R ^{11 to} R ¹⁴ may be the same as each other or may be different from each other.

In formula (1A), R ¹⁵ represents a hydrogen atom or a linear or branched alkyl group.

Examples of the primary alkyl group (alkyl group represented by the general formula (1A)) include a methyl group, an ethyl group, an n-propyl group, an n-butyl group, an n-pentyl group, an n-hexyl group and n. -Heptyl group, n-octyl group, n-nonyl group, n-decyl group, isoamyl group, 2-methylbutyl group, 2,3-dimethylbutyl group and the like can be mentioned.

The zinc dialkyldithiophosphate preferably contains a primary alkyl group having 6 to 10 carbon atoms as a primary alkyl group, more preferably contains a primary alkyl group having 7 to 9 carbon atoms, and has 7 to 9 carbon atoms. It is more preferable to contain 8 primary alkyl groups. Since zinc dialkyldithiophosphate contains a primary alkyl group having 6 to 10 carbon atoms, the frictional properties and thermal stability of the lubricating oil composition tend to be more excellent.

The lubricating oil composition for a shock absorber of the present embodiment contains zinc dialkyldithiophosphate represented by the general formula (1) and zinc dialkyldithiophosphate represented by the general formula (2) as zinc dialkyldithiophosphate. You may.

In formula (2), R ^{21 to} R ²⁴ each independently represent a secondary alkyl (secondary alkyl) group. Here, the secondary alkyl group is an alkyl group represented by the following general formula (2A). R ^{21 to} R ²⁴ may be the same as each other or may be different from each other.

In formula (2A), R ²⁵ and R ²⁶ represent linear or branched alkyl groups.

Examples of the secondary alkyl group (alkyl group represented by the general formula (2A)) include an isopropyl group, a sec-butyl group, a 1-ethylpropyl group and the like.

The content of zinc dialkyldithiophosphate represented by the general formula (2) may be 40% by mass or less, 30% by mass or less, or 25% by mass or less based on the total amount of zinc dialkyldithiophosphate.

As the zinc dialkyldithiophosphate represented by the general formula (1) and the general formula (2), a commercially available product may be used as it is, or a product produced by a known method may be used.

The content of zinc dialkyldithiophosphate is 0.3 to 1.0% by mass based on the total amount of the composition. The content of zinc dialkyldithiophosphate is preferably 0.4% by mass or more, more preferably 0.6% by mass or more, still more preferably 0.7% by mass or more. The content of zinc dialkyldithiophosphate is preferably 0.97% by mass or less, more preferably 0.95% by mass or less, still more preferably 0.9% by mass or less. When the content of zinc dialkyldithiophosphate is within the above range, the frictional properties and thermal stability of the lubricating oil composition tend to be excellent.

[Triazole derivative]
The lubricant composition for a shock absorber of the present embodiment contains a triazole derivative. By including the triazole derivative in the lubricating oil composition, it is possible to improve the static friction force and reduce the dynamic friction force of the lubricating oil composition at a high temperature. As the triazole derivative, one type may be used alone, or two or more types may be used in combination at an arbitrary ratio.

The triazole derivative may be a benzotriazole derivative. Examples of the benzotriazole derivative include a compound represented by the general formula (3), a compound represented by the general formula (4), and the like.

In formulas (3) and (4), R ³¹ and R ⁴¹ represent a hydrogen atom or a methyl group, and R ³² and R ⁴² have 1 to 20 carbon atoms containing a hydrogen atom, a hydroxyl group, or a nitrogen atom or an oxygen atom. Shows the basis of. R ³² and R ⁴² are preferably groups having 10 to 20 carbon atoms containing a nitrogen atom.

As the triazole derivative, a commercially available product may be used as it is, or a product produced by a known method may be used.

The content of the triazole derivative is 0.05 to 0.7% by mass based on the total amount of the composition. The content of the triazole derivative is preferably 0.07% by mass or more, more preferably 0.09% by mass or more, and further preferably 0.1% by mass or more. The content of the triazole derivative is preferably 0.6% by mass or less, more preferably 0.55% by mass or less, still more preferably 0.5% by mass or less. When the content of the triazole derivative is within the above range, the dynamic friction force can be reduced while increasing the static friction force of the lubricating oil composition at a high temperature.

[Esters of fatty acids and polyhydric alcohols]
The lubricating oil composition for a shock absorber of the present embodiment may further contain an ester composed of a fatty acid and a polyhydric alcohol (hereinafter, may be simply referred to as "ester").

The fatty acid constituting the ester may be, for example, a fatty acid having a linear or branched alkyl group or alkenyl group having 6 to 30 carbon atoms. The alkyl or alkenyl group preferably has 8 to 24 carbon atoms, more preferably 10 to 20 carbon atoms. One of these fatty acids may be used alone, or two or more of these fatty acids may be used in combination at any ratio.

Examples of fatty acids include oleic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid and the like.

The polyhydric alcohol constituting the ester may be, for example, a 2-6 valent aliphatic alcohol having 2 to 8 carbon atoms. The polyhydric alcohol preferably has 2 to 6 carbon atoms, more preferably 3 to 5 carbon atoms. The valence of the polyhydric alcohol is preferably 2 to 4 valences, more preferably trihydric or tetravalent. One of these polyhydric alcohols may be used alone, or two or more of these polyhydric alcohols may be used in combination at any ratio.

Examples of the polyhydric alcohol include ethylene glycol, propylene glycol, sorbitan, glycerol, pentaerythritol and the like.

Examples of the ester include a partial ester of oleic acid and a polyhydric alcohol such as sorbitan, glycerol, and pentaerythritol, that is, sorbitan monooleate, glycerol monooleate, pentaerythritol monooleate, and the like. One of these esters may be used alone, or two or more of these esters may be used in combination at any ratio.

The ester may be a partial ester in which some of the hydroxyl groups of the polyhydric alcohol are not esterified, or a complete ester in which all of the hydroxyl groups of the polyhydric alcohol are esterified. The ester is preferably a partial ester from the viewpoint of frictional properties.

As the ester, a commercially available product may be used as it is, or an ester produced by a known method may be used.

The ester content may be, for example, 0.1 to 1.0% by mass based on the total amount of the composition.

[Fatty acid amide]
The lubricant composition for a shock absorber of the present embodiment may further contain a fatty acid amide. The fatty acid amide may be, for example, a fatty acid amide composed of a fatty acid and a polyalkylene polyamine represented by the following general formula (E).
H ₂ N- ( ^RE1- NH) _m- H (E)

Wherein ^{(E), R E1} is an alkylene group having 2 to 4 carbon atoms, m represents an integer of 2 to 6.

The fatty acid constituting the fatty acid amide may be, for example, a fatty acid having a linear or branched alkyl group or alkenyl group having 6 to 30 carbon atoms. The alkyl or alkenyl group preferably has 8 to 24 carbon atoms, more preferably 10 to 20 carbon atoms. These fatty acids may be used alone or in combination of two or more at any ratio.

Examples of fatty acids include oleic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid and the like.

Examples of the polyalkylene polyamine represented by the general formula (E) constituting the fatty acid amide include diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, hexaethyleneheptamine, tetrapropylenepentamine, and hexabutylenehepta. Min and the like can be mentioned. One of these polyalkylene polyamines may be used alone, or two or more thereof may be used in combination at any ratio.

Examples of the fatty acid amide include an amide of isostearic acid and tetraethylenepentamine. One type of fatty acid amide may be used alone, or two or more types may be used in combination at any ratio.

As the fatty acid amide, a commercially available product may be used as it is, or a fatty acid amide produced by a known method may be used.

The content of fatty acid amide may be, for example, 0.1 to 0.5% by mass based on the total amount of the composition.

[Amine-based antioxidant]
The lubricant composition for a shock absorber of the present embodiment may further contain an amine-based antioxidant. The amine-based antioxidant is not particularly limited, and those used in the ordinary lubricating oil field can be used.

Examples of the amine-based antioxidant include (p, p') -alkylated diphenylamine represented by the following general formula (A), alkylated phenyl-α-naphthylamine represented by the following general formula (B), and the like. Can be mentioned. One of these amine-based antioxidants may be used alone, or two or more thereof may be used in combination at any ratio.

In the formula (A), ^RA1 and ^RA2 each independently represent an alkyl group having 1 to 20 carbon atoms. The carbon number of the alkyl group as R ^A1 and ^{R A2} is preferably 3 to 12, more preferably 4 to 8. ^RA1 and ^RA2 may be the same as or different from each other.

In the formula (B), ^RB1 represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms. The carbon number of the alkyl group as R ^B1 is preferably 6-20, more preferably 8-18.

The content of the amine-based antioxidant may be, for example, 0.1 to 0.5% by mass based on the total amount of the composition.

[Defoamer]
The lubricant composition for a shock absorber of the present embodiment may further contain an antifoaming agent. The defoaming agent is not particularly limited, and those used in the ordinary lubricating oil field can be used.

Examples of the defoaming agent include silicone oil, an alkenyl succinic acid derivative, and a polyhydroxy fatty alcohol which may have an alkyl halide group having a kinematic viscosity at 25 ° C. of 100 to 1,000,000 mm ^{2 / s.} Examples thereof include esters with long-chain fatty acids, esters with methyl salicylate and o-hydroxybenzyl alcohol, and the like.

The content of the defoaming agent may be, for example, 0.1 to 100 mass ppm based on the total amount of the composition.

[Other additives]
The lubricant composition for a shock absorber of the present embodiment may further contain any commonly used lubricant additive, depending on its purpose. Examples of such additives include metal-based detergents, rust inhibitors, anti-emulsifiers, metal inactivating agents and the like.

Examples of the metal-based cleaning agent include sulfonate-based cleaning agents, salicylate-based cleaning agents, phenate-based cleaning agents, and any of positive salts, basic salts, and hyperbasic salts with alkali metals or alkaline earth metals. Can also be blended.

Examples of the rust preventive include petroleum sulfonate, alkylbenzene sulfonate, dinonylnaphthalene sulfonate, alkenyl succinic acid ester, polyhydric alcohol ester and the like.

Examples of the anti-emulsifier include polyalkylene glycol-based nonionic surfactants such as polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, and polyoxyethylene alkyl naphthyl ether.

When these other additives are used, their respective contents may be 0.01 to 20% by mass based on the total amount of the composition.

The kinematic viscosity of the lubricating oil composition for a shock absorber of the present embodiment at 100 ° C. is preferably 2.0 to 3.5 mm ² / s. The kinematic viscosity at 100 ° C. is more preferably 2.5 mm ² / s or more, further preferably 2.8 mm ² / s or more, and particularly preferably 3.0 mm ² / s or more. The kinematic viscosity at 100 ° C. is more preferably 3.4 mm ² / s or less, further preferably 3.3 mm ² / s or less, and particularly preferably 3.2 mm ² / s or less. When the kinematic viscosity at 100 ° C. is within the above range, the proper viscosity of the lubricating oil composition can be ensured, and a good oil film tends to be obtained in the actual operating temperature range.

The BF viscosity of the lubricating oil composition for a shock absorber of this embodiment at −40 ° C. is 1,500 mPa · s or less. The BF viscosity at −40 ° C. is preferably 1,400 mPa · s or less, more preferably 1,350 mPa · s or less, still more preferably 1,300 mPa · s or less. When the BF viscosity at −40 ° C. is 1,500 mPa · s or less, the low temperature characteristics of the lubricating oil composition tend to be excellent. The BF viscosity at −40 ° C. may be, for example, 800 mPa · s or more. The BF viscosity at −40 ° C. in the present specification means a value measured according to ASTM D 2983.

According to the present invention, there is provided a lubricating oil composition for a shock absorber which can reduce the dynamic friction force while increasing the static friction force from a low temperature to a high temperature in a sliding portion, and further has excellent low temperature characteristics and thermal stability. Will be done. By applying such a lubricating oil composition to a shock absorber, excellent steering stability and ride quality can be obtained.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

[Preparation of lubricating oil composition]
(Examples 1 to 8 and Comparative Examples 1 to 6)
As shown in Tables 1 and 2, the lubricating oil compositions of Examples 1 to 8 and Comparative Examples 1 to 6, respectively, were prepared. When preparing the lubricating oil composition, the content of poly (meth) acrylate is mainly adjusted so that the ^{kinematic viscosity at 100 ° C. is within the range of 3.1 to 3.4 mm 2 / s.} did. The obtained lubricating oil composition was examined for viscosity characteristics, low temperature characteristics, friction characteristics, thermal stability and the like.

Details of each component shown in Tables 1 and 2 are as follows.

<Mineral oil-based base oil>
X-1: Hydrorefined mineral oil (GpII) (40 ° C. kinematic viscosity: 7.71 mm ² / s, 100 ° C. kinematic viscosity: 2.254 mm ² / s, viscosity index: 99, pour point: -42 ° C, flash point 162 ° C)
X-2: Hydrodesulfurized mineral oil (GpII) (40 ° C. kinematic viscosity: 8.854 mm ² / s, 100 ° C. kinematic viscosity: 2.464 mm ² / s, viscosity index: 100, pour point: -42.5 ° C., Flash point: 168 ° C)

<Poly (meta) acrylate>
A-1: Non-dispersive polymethacrylate, manufactured by Evonik Japan, VISCOPLEX 12-419 (weight average molecular weight: 170,000)
A-2: Non-dispersive polymethacrylate, manufactured by Evonik Japan, VISCOPLEX 12-205 (weight average molecular weight: 100,000)
a-1: Non-dispersive polymethacrylate, manufactured by Sanyo Chemical Industries, Ltd., Accluve V815 (weight average molecular weight: 20,000)

<Polybuden>
B-1: Polybuden, manufactured by NOF Corporation, NOF Polybuden 015N (number average molecular weight: 580, 40 ° C kinematic viscosity: 650 mm ² / s, 100 ° C kinematic viscosity: 35 mm ² / s, pour point: -25 ° C)
B-2: Polybuden, manufactured by NOF Corporation, NOF Polybuden 10N (number average molecular weight: 1,000, 40 ° C kinematic viscosity: 9,000 mm ² / s, 100 ° C kinematic viscosity: 270 mm ² / s, pour point: -10 ° C)
B-3: polybutene, manufactured by NOF Corporation, NOF polybutene 200 N (number average molecular weight: 2,650,40 ℃ kinematic viscosity: 170,000mm ² / s, 100 ℃ kinematic viscosity: 4,500 mm ² / s, flow Point: 15 ° C)

<Zinc dialkyldithiophosphate>
C-1: (Compound ^R 11 ^{to R 14} is a primary alkyl group of 8 carbon atoms in the general formula (1)) zinc dialkyldithiophosphate, Oronite Co., OLOA 269R (zinc content: 9.0 Mass%, phosphorus content: 7.4% by mass, sulfur content: 15.0% by mass)
C-2: zinc dialkyldithiophosphate (the general formula ^R 11 ^{to R 14} is a primary alkyl group of 4 carbon atoms compound (70 wt%) and ^R 11 ^{to R 14} is a 5 carbon atoms (1) A mixture of a compound (10% by mass) which is a primary alkyl group and a compound (20% by mass) which is a primary alkyl group having ^{R 11 to} R ^{14 having 8 carbon atoms), manufactured by Oronite, OLOA 267 (zinc).} Content: 8.5% by mass, phosphorus content: 7.5% by mass, sulfur content: 15.0% by mass)
c-1: zinc dialkyldithiophosphate (the general formula ^R 21 ^{to R 24} are secondary alkyl groups having 4 carbon atoms compound (90 wt%) and ^R 21 ^{to R 24} is 6 carbons (2) A mixture with a compound (10% by mass) which is a secondary alkyl group), manufactured by Oronite, OLOA 267 (zinc content: 8.5% by mass, phosphorus content: 7.5% by mass, sulfur content: 15). .0% by mass)

<Triazole derivative>
D-1: N, N-bis (2-ethylhexyl) -4-methyl-1H-benzotriazole-1-methaneamine, manufactured by BASF, IRGAMET 39

<Ester of fatty acid and polyhydric alcohol>
E-1: Pentaerythritol monooleate, manufactured by Kao Corporation, Exepearl PE-MO

<Fatty acid amide>
F-1: Reactant of isostearic acid and tetraethylenepentamine, manufactured by Oronite, OLOA 340D (nitrogen content: 6.2% by mass)

<Antioxidant>
G-1: Monobutylphenyl monooctylphenylamine, manufactured by BASF, IRGANOX L57 (nitrogen content: 4.5% by mass)

<Defoamer>
H-1: Polyalkylhaloalkylsiloxane (100%), manufactured by Toray Dow Corning Co., Ltd., FS 1265 (300 cS) (25 ° C. kinematic viscosity: 270 to 330 mm ² / s, specific gravity (25 ° C.): 1.22-1 .32, Refractive index (25 ° C): 1.378 to 1.383)

The elemental content of each component was determined by ICP elemental analysis.

(1) Viscosity characteristics The kinematic viscosity of each lubricating oil composition at 100 ° C. was measured according to JIS K2283.

(2) Low temperature characteristics The BF viscosity of each lubricating oil composition at −40 ° C. was measured according to ASTM D 2983. In this test, the smaller the value of BF viscosity (for example, 1,500 mPa · s or less), the better the low temperature characteristics.

(3) Friction characteristics-1
Using an MTM (Mini Traction Machine) tester (manufactured by PCS Instruments), the friction characteristics of each lubricating oil composition at a constant load and slip ratio were calculated as a friction coefficient (μ). The test conditions are shown below. In this test, the higher the coefficient of friction (for example, 0.060 or more), the better the riding comfort.
Rolling speed: 200 mm / s
Load: 31N
Slip rate: 50%
Oil temperature 60 ° C

(4) Friction characteristics-2
For each lubricating oil composition, a Bowden test (Bowden type reciprocating dynamic friction test) was performed under the following measurement conditions, and the static friction coefficient (μs) at the start of the 10th measurement and the dynamic friction coefficient (μd) at the 10th measurement were measured. The higher the coefficient of static friction (μs) at the start of the 10th measurement (for example, 0.135 or more), the better the steering stability. If the static friction coefficient (μs) is too high (for example, more than 0.145), the steering feeling tends to be hard. Therefore, the static friction coefficient (μs) is in a specific range (for example, 0.135 or more and 0.145 or less). ) Is preferable. Further, the lower the coefficient of dynamic friction (μd) at the 10th measurement (for example, 0.075 or less), the better the riding comfort. If the dynamic friction coefficient (μd) is too low (for example, less than 0.065), the sense of stability tends to be lost. Therefore, the dynamic friction coefficient (μd) is set in a specific range (for example, 0.065 or more and 0.075 or less). ) Is preferable.
Test piece: SUJ-2 ball / chrome-plated steel plate Load: 9.8N
Slip speed: 4 mm / s (stroke: 10 mm)
Oil temperature: 25 ° C or 80 ° C
Number of measurements: 20th

(5) Thermal Stability 100 mL of the lubricating oil composition collected in a beaker was heated at 150 ° C. for 48 hours in an air constant temperature bath. The hue and the presence or absence of sludge were evaluated for the heated lubricating oil composition. Hue was evaluated according to ASTM D156. The smaller the hue (for example, 5.0 or less), the better the thermal stability. The presence or absence of sludge was visually evaluated.

As shown in Tables 1 and 2, the lubricating oil compositions of Examples 1 to 8 are superior to the lubricating oil compositions of Comparative Examples 1 to 6 in terms of viscosity characteristics, low temperature characteristics, friction characteristics, and thermal stability. Was there. From these results, the lubricating oil composition for a shock absorber of the present invention can reduce the dynamic friction force while increasing the static friction force from low temperature to high temperature at the sliding portion, and further, low temperature characteristics and thermal stability. It was confirmed that it was excellent.

Claims (4)

Mineral oil-based base oil having a kinematic viscosity of 0.1 to 5.0 mm ^{2 / s at 100 ° C.}
Based on the total amount of composition
With 0.5 to 5.0% by mass of poly (meth) acrylate having a weight average molecular weight of 80,000 to 200,000,
Polybutene with a number average molecular weight of 500 to 5,000, 0.05 to 1.0% by mass,
Zinc dialkyldithiophosphate represented by the following general formula (1) is 0.3 to 1.0% by mass, and
Triazole derivative 0.05-0.7% by mass,
Contains,
The ratio of the weight average molecular weight of the poly (meth) acrylate to the number average molecular weight of the polybutene is 50 to 250.
Lubricating oil composition for shock absorbers.

[In formula (1), R ^{11 to} R ¹⁴ each independently represent a primary alkyl group. ] The BF viscosity of the buffer lubricating oil composition at −40 ° C. is 1,500 mPa · s or less.
The lubricating oil composition for a shock absorber according to claim 1. The kinematic viscosity of the buffer lubricating oil composition at 100 ° C. is 2.0 to 3.5 mm ² / s.
The lubricating oil composition for a shock absorber according to claim 1 or 2. The zinc dialkyldithiophosphate contains a primary alkyl group having 6 to 10 carbon atoms.
The lubricating oil composition for a shock absorber according to any one of claims 1 to 3.