WO2022039105A1 - Lubricating oil composition, shock absorber, and method for using lubricating oil composition - Google Patents

Abstract

Provided is a lubricating oil composition used for lubricating shock absorbers and comprising a base oil (A), a polyalkyl (meth)acrylate (B) having a weight-average molecular weight of 150,000-900,000, and an olefin copolymer (C) having a weight-average molecular weight of not more than 100,000.

Description

Lubricating oil composition, shock absorber, and how to use the lubricating oil composition

The present invention relates to a lubricating oil composition, a shock absorber using the lubricating oil composition, and a method of using the lubricating oil composition.

The shock absorber (shock absorber) is used by filling it with a lubricant composition for a shock absorber to generate a damping force that damps the vibration of the vehicle body, and optimizes the friction characteristics of the sliding parts to improve the riding comfort of the vehicle body. It is a mechanism mounted on the vehicle body for the purpose of controlling and suppressing frictional wear of sliding parts to ensure durability.
Various buffer lubricating oil compositions that can be suitably used for such shock absorbers have been developed.
For example, Patent Document 1 describes a non-dispersive poly (meth) acrylate-based viscosity modifier having a weight average molecular weight of 30,000 to 200,000 in a lubricating base oil having a predetermined kinematic viscosity, a primary dialkyl. An invention relating to a lubricant composition for a shock absorber containing zinc dithiophosphate and secondary zinc dialkyldithiophosphate in a predetermined content ratio is disclosed.

Japanese Unexamined Patent Publication No. 2018-203953

According to the studies by the present inventors, it was found that the lubricating oil composition described in Patent Document 1 has an insufficient effect of suppressing cavitation. Further, there is a demand for a lubricating oil composition used for lubricating a shock absorber having improved characteristics such as low temperature startability and shear stability as well as an effect of suppressing cavitation.

The present invention provides a lubricating oil composition used for lubricating a shock absorber, which contains a base oil, a polyalkyl (meth) acrylate having a predetermined weight average molecular weight, and an olefin copolymer having a predetermined weight average molecular weight. .. Specifically, the present invention provides the following aspects [1] to [10].
[1] A base oil (A), a polyalkyl (meth) acrylate (B) having a weight average molecular weight of 150,000 to 900,000, and an olefin copolymer (C) having a weight average molecular weight of 100,000 or less. A lubricating oil composition that contains and is used to lubricate shock absorbers.
[2] The lubricating oil composition according to the above [1], wherein the total content of the component (B) and the component (C) is 20.0% by mass or less based on the total amount of the lubricating oil composition.
[3] The content ratio [(B) / (C)] of the component (B) to the component (C) is 1/99 to 90/10 in terms of mass ratio, as described above [1] or [2]. The lubricating oil composition according to.
[4] The item according to any one of [1] to [3] above, wherein the content of the component (B) is 0.1 to 10.0% by mass based on the total amount of the lubricating oil composition. Lubricating oil composition.
[5] The item according to any one of [1] to [4] above, wherein the content of the component (C) is 0.1 to 10.0% by mass based on the total amount of the lubricating oil composition. Lubricating oil composition.
[6] The lubricating oil composition according to any one of the above [1] to [5], wherein the weight average molecular weight of the component (C) is 8,000 or more and 100,000 or less.
[7] The lubricating oil composition according to any one of the above [1] to [6], wherein the component (C) contains an ethylene propylene copolymer (C1).
[8] The item according to any one of [1] to [7] above, wherein the total content of the components (A) to (C) is 80 to 100% by mass based on the total amount of the lubricating oil composition. Lubricating oil composition.
[9] The lubricating oil composition according to any one of the above [1] to [8], wherein the BF viscosity of the lubricating oil composition at −40 ° C. is 1500 mPa · s or less.
[10] Use of a lubricating oil composition for applying the lubricating oil composition according to any one of the above [1] to [9] to lubricate a shock absorber.

The lubricating oil composition of one preferred embodiment of the present invention is excellent in properties such as low temperature startability, shear stability, and cavitation suppressing effect, and a particularly suitable one aspect of the lubricating oil composition is low temperature startability. Since it is excellent in all of the shear stability and the effect of suppressing cavitation, it can be suitably applied to the lubrication of a shock absorber.

It is a schematic diagram of the test apparatus for evaluating the effect of suppressing cavitation.

As used herein, kinematic viscosity and viscosity index mean values measured or calculated in accordance with JIS K2283: 2000.
In the present specification, the weight average molecular weight (Mw) and the number average molecular weight (Mn) are values in terms of standard polystyrene measured by a gel permeation chromatography (GPC) method, and are specifically described in Examples. Means the value measured by the method.

For the numerical range described in the present specification, the upper limit value and the lower limit value can be arbitrarily combined. For example, when the numerical range is described as "preferably 30 to 100, more preferably 40 to 80", the range of "30 to 80" and the range of "40 to 100" are also described in the present specification. It is included in the numerical range. Further, for example, when the numerical range is described as "preferably 30 or more, more preferably 40 or more, preferably 100 or less, more preferably 80 or less", it is referred to as "30 to 80". The range and the range of "40-100" are also included in the numerical range described herein.
In addition, as the numerical range described in the present specification, for example, the description of "60 to 100" means that the range is "60 or more and 100 or less".

[Structure of lubricating oil composition]
The lubricating oil composition of the present invention contains a base oil (A), a polyalkyl (meth) acrylate (B) having a weight average molecular weight of 150,000 to 900,000, and an olefin having a weight average molecular weight of 100,000 or less. Contains the polymer (C).
Various properties are required for the lubricating oil composition in which the shock absorber is used. As one of such characteristics, the effect of suppressing cavitation is required. Cavitation is a physical phenomenon in which bubbles are generated and disappear in a short time due to a pressure difference in the flow of a lubricating oil composition, and is a factor that causes a decrease in the responsiveness of the shock absorber and noise. For example, when cavitation occurs in a shock absorber mounted on a vehicle, it affects the ride quality of the vehicle or the like.
Further, the lubricating oil composition in which the shock absorber is used is required to have not only the effect of suppressing cavitation but also the characteristics such as low temperature startability and shear stability.

The present inventors have diligently studied in order to obtain a lubricating oil composition capable of improving these properties in a well-balanced manner, and as a result, polyalkyl (meth) acrylate (B) and an olefin copolymer having a predetermined weight average molecular weight ( C) was found to be useful in combination.
That is, the component (B) is a factor that can improve the cavitation suppressing effect and the low temperature startability, but is a factor that causes a decrease in the shear stability, while the component (C) is a factor that suppresses the cavitation and the shear stability. Although it is a factor that can improve the property, it has been found by the studies of the present inventors that it is a factor that causes a decrease in low-temperature startability.
Therefore, the present inventors have found that by using the components (B) and (C) in combination, a lubricating oil composition having a well-balanced improvement in low temperature startability, shear stability, and cavitation suppressing effect can be obtained. Got The present invention has been completed based on this finding.

In the lubricating oil composition of one aspect of the present invention, the components (B) and the component (C) are used from the viewpoint of providing a lubricating oil composition having improved low temperature startability, shear stability, and cavitation suppressing effect in a well-balanced manner. The content ratio [(B) / (C)] is preferably 1/99 to 90/10, more preferably 5/85 to 80/20, and more preferably 10/90 to 70/30 in terms of mass ratio. , More preferably 15/85 to 60/40, even more preferably 20/80 to 50/50, and particularly preferably 25/75 to 45/55.

Further, in the lubricating oil composition of one aspect of the present invention, the total content of the component (B) and the component (C) is based on the total amount (100% by mass) of the lubricating oil composition, and has low-temperature startability and shear stability. From the viewpoint of obtaining a lubricating oil composition having a good balance of properties, it is preferably 20.0% by mass or less, more preferably 16.0% by mass or less, still more preferably 10.0% by mass or less, still more preferably 8. It is 0.0% by mass or less, particularly preferably 6.0% by mass or less, and from the viewpoint of further improving the effect of suppressing cavitation, it is preferably 0.2% by mass or more, more preferably 0.6% by mass or more. It is more preferably 1.0% by mass or more, still more preferably 1.6% by mass or more, and particularly preferably 2.0% by mass or more.

In consideration of handleability and solubility with the component (A), the components (B) and (C) are often marketed in the form of a solution dissolved in a diluted oil.
However, in the present specification, the content of the component (B) and (C) is the resin constituting the component (B) or (C) excluding the mass of the diluted oil in the solution diluted with the diluted oil. It is the content converted into minutes.

The lubricating oil composition of one aspect of the present invention may further contain additives for lubricating oil other than the components (B) to (C).
However, in the lubricating oil composition of one aspect of the present invention, the total content of the components (A) to (C) is determined from the viewpoint of making the lubricating oil composition further improved in the effect of suppressing cavitation and the low temperature startability. Based on the total amount (100% by mass) of the lubricating oil composition, it is preferably 80 to 100% by mass, more preferably 85 to 100% by mass, still more preferably 90 to 100% by mass, still more preferably 95 to 100% by mass. Particularly preferably, it is 98 to 100% by mass, and more than 98.5% by mass and 100% by mass or less, 99.0% by mass and 100% by mass or less, 99.5% by mass and 100% by mass or less, or 99. It may be more than 7% by mass and 100% by mass or less.

Hereinafter, details of each component contained in the lubricating oil composition of one aspect of the present invention will be described.

<Ingredient (A): Base oil>
Examples of the base oil as the component (A) used in one embodiment of the present invention include one or more selected from mineral oils and synthetic oils.
Mineral oils include, for example, normal pressure residual oil obtained by atmospheric distillation of crude oils such as paraffin crude oil, intermediate base crude oil, and naphthenic crude oil; and distillate oil obtained by vacuum distillation of these normal pressure residual oils. ; Refined oil obtained by subjecting the distillate oil to one or more refining treatments such as solvent removal, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, and hydrorefining; and the like.

Examples of the synthetic oil include polyα-olefins such as α-olefin homopolymers; isoparaffin; polyalkylene glycols; ester oils such as polyol esters, dibasic acid esters and phosphate esters; ether oils such as polyphenyl ethers. Oil; Alkylbenzene; Alkylnaphthalene; Synthetic oil (GTL) obtained by isomerizing a wax (GTL wax (Gas To Liquids WAX)) produced from natural gas by the Fischer-Tropsch method or the like can be mentioned.

Among these, the component (A) used in one embodiment of the present invention includes mineral oils classified into Group 2 and Group 3 of the API (American Petroleum Institute) base oil category, and one or more selected from synthetic oils. Is preferable.

The kinematic viscosity of the component (A) used in one aspect of the present invention at 40 ° C. is preferably 3.0 to 100 mm ² / s, more preferably 4.0 to 70 mm ² / s, still more preferably 5.0 to 40 mm. It is ² / s, more preferably 5.5 to 30 mm ² / s, and particularly preferably 6.0 to 20 mm ² / s.

The viscosity index of the component (A) used in one aspect of the present invention is appropriately set according to the use of the lubricating oil composition, but is preferably 70 or more, more preferably 80 or more, still more preferably 90 or more. It is even more preferably 100 or more, and particularly preferably 105 or more.
In one aspect of the present invention, when a mixed oil in which two or more kinds of base oils are combined is used as the component (A), the kinematic viscosity and the viscosity index of the mixed oil are preferably in the above ranges.

In the lubricating oil composition of one aspect of the present invention, the content of the component (A) is preferably 60% by mass or more, more preferably 70% by mass or more, based on the total amount (100% by mass) of the lubricating oil composition. , More preferably 75% by mass or more, further preferably 80% by mass or more, still more preferably 85% by mass or more, particularly preferably 90% by mass or more, and preferably 99.8% by mass or less, more preferably. It is 99.5% by mass or less, more preferably 99.0% by mass or less, still more preferably 98.5% by mass or less, and particularly preferably 98.0% by mass or less.

<Component (B): Polyalkyl (meth) acrylate>
The lubricating oil composition of the present invention contains a polyalkyl (meth) acrylate having a weight average molecular weight (Mw) of 150,000 to 900,000 as the component (B). If Mw is less than 150,000, the effect of suppressing cavitation is less likely to be exhibited. Further, when Mw is larger than 900,000, it tends to be difficult to achieve both the cavitation suppressing effect and the shear stability. Since the component (C) described later is used in combination with the component (B), the lubricating oil composition can be adjusted to have good shear stability.

The weight average molecular weight (Mw) of the polyalkyl (meth) acrylate used as the component (B) in one aspect of the present invention is 150,000 or more, but the lubricating oil has further improved the effect of suppressing cavitation and the low temperature startability. From the viewpoint of the composition, it is preferably 200,000 or more, more preferably 250,000 or more, more preferably 260,000 or more, more preferably 270,000 or more, more preferably 300,000 or more, still more preferably 320. 000 or more, more preferably 350,000 or more, still more preferably 370,000 or more, still more preferably 400,000 or more, still more preferably 420,000 or more, still more preferably 450,000 or more, still more preferably. It is 470,000 or more, more preferably 500,000 or more, particularly preferably 520,000 or more, and 900,000 or less, but from the viewpoint of obtaining a lubricating oil composition having better shear stability. It is preferably 850,000 or less, more preferably 800,000 or less, more preferably 750,000 or less, still more preferably 700,000 or less, still more preferably 650,000 or less, and particularly preferably 600,000 or less. ..

In the lubricating oil composition of one aspect of the present invention, the content of the component (B) is based on the total amount (100% by mass) of the lubricating oil composition, and the lubricating effect of suppressing cavitation and the low-temperature startability are further improved. From the viewpoint of making an oil composition, it is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, still more preferably 0.3% by mass or more, still more preferably 0.5% by mass or more, and particularly preferably. Is 0.7% by mass or more, and is preferably 10.0% by mass or less, more preferably 8.0% by mass or less, still more preferably, from the viewpoint of obtaining a lubricating oil composition having better shear stability. Is 5.0% by mass or less, more preferably 3.0% by mass or less, and particularly preferably 2.0% by mass or less.

The component (B) used in one embodiment of the present invention may be a polymer having a structural unit derived from an alkyl acrylate or an alkyl methacrylate (hereinafter collectively referred to as “alkyl (meth) acrylate”), and may be an alkyl (meth). ) It may be a copolymer having a structural unit derived from a monomer other than acrylate.
The number of carbon atoms of the alkyl group contained in the alkyl (meth) acrylate may be 1 or more, 3 or more, 5 or more, or 10 or more, and may be 60 or less, 40 or less, 30 or less, or 20 or less.

In the component (B) used in one embodiment of the present invention, the content of the structural unit derived from the alkyl (meth) acrylate is 10 mol% or more based on the total amount (100 mol%) of the structural unit of the component (B). It may be 30 mol% or more, 50 mol% or more, 60 mol% or more, 70 mol% or more, 80 mol% or more, 90 mol% or more, 95 mol% or more, or 99 mol% or more.

≪Comb-shaped polymer≫
The component (B) used in one embodiment of the present invention may be a comb-shaped polymer.
The comb-shaped polymer used as the component (B) in one aspect of the present invention may be a polymer having a structure having a large number of three-pronged branch points in the main chain having high molecular weight side chains.

The SSI (shear stability index) of the comb polymer used as the component (B) in one aspect of the present invention is preferably 100 or less, more preferably 80 or less, still more preferably 70 or less, still more preferably 60 or less, particularly. It is preferably 50 or less.
Further, the SSI of the comb polymer is not particularly limited to the lower limit value, but is usually 0.1 or more.

In the present specification, the SSI (shear stability index) indicates the decrease in viscosity due to shearing derived from the polymer component as a percentage, and is a value measured in accordance with JPI-5S-29-06. More specifically, it is a value calculated from the following formula (1).
-Calculation formula (1): SSI (%) = (Kv ₀ -Kv ₁ ) / (Kv ₀ -Kv _oil ) x 100
In the above formula (1), Kv ₀ is the value of the kinematic viscosity of the sample oil obtained by diluting the polymer component with mineral oil at 100 ° C., and Kv ₁ is the sample oil obtained by diluting the polymer component with mineral oil. It is the value of the kinematic viscosity at 100 ° C. after irradiation with ultrasonic waves for 30 minutes according to the output method according to the procedure of 5S-29-06. Further, Kv _oil is a value of the kinematic viscosity of the mineral oil used for diluting the polymer component at 100 ° C.

The SSI value of the comb polymer varies depending on its structure. Specifically, there is a tendency shown below, and the value of SSI of the comb-shaped polymer can be easily adjusted by considering these matters. The following items are just examples and can be adjusted by considering items other than these items.
-The side chain of the comb-shaped polymer is composed of a macromonomer (x1), and the content of the structural unit (X1) derived from the macromonomer (x1) is 0.5 based on the total amount (100 mol%) of the structural unit. Comb-shaped polymers of mol% or more tend to have lower SSI values.
-The larger the molecular weight of the macromonomer (x1) constituting the side chain of the comb-shaped polymer, the lower the SSI value tends to be.

The comb-shaped polymer used as the component (B) in one aspect of the present invention is preferably a polymer having at least a structural unit (X1) derived from the macromonomer (x1). This structural unit (X1) corresponds to the above-mentioned "high molecular weight side chain".
In the present specification, the above-mentioned "macromonomer (x1)" means a high molecular weight monomer having a polymerizable functional group, and is preferably a high molecular weight monomer having a polymerizable functional group at the terminal. ..

In the comb polymer used as the component (B) in one aspect of the present invention, the content of the constituent unit (X1) is preferably 0.5 to 20 mol based on the total amount (100 mol%) of the constituent units of the comb polymer. %, More preferably 0.7 to 10 mol%, still more preferably 0.9 to 5 mol%.
In the present specification, the content of the constituent unit of the comb-shaped polymer means a value calculated by analyzing the ¹³ C-NMR quantitative spectrum.

The number average molecular weight (Mn) of the macromonomer (x1) is preferably 300 or more, more preferably 400 or more, still more preferably 500 or more, and preferably 100,000 or less, more preferably 50,000 or less. , More preferably 20,000 or less.
That is, the number average molecular weight (Mn) of the macromonomer (x1) is preferably 300 to 100,000, more preferably 400 to 50,000, and even more preferably 500 to 20,000.

Examples of the polymerizable functional group of the macromonomer (x1) include an acryloyl group (CH ₂ = CH-COO-), a methacryloyl group (CH ₂ = CCH ₃ -COO-), and an ethenyl group (CH ₂ = CH-). , Vinyl ether group (CH ₂ = CH-O-), allyl group (CH ₂ = CH-CH _2- ), allyl ether group (CH ₂ = CH-CH ₂ -O-), CH ₂ = CH-CONH- Examples thereof include a group represented by _CH2 = CCH3-CONH-.

The macromonomer (x1) may have, for example, one or more repeating units represented by the following general formulas (i) to (iii) in addition to the above-mentioned polymerizable functional group.

In the above general formula (i), R ^b1 is a linear or branched alkylene group having 1 to 10 carbon atoms.
In the above general formula (ii), R ^b2 is a linear or branched alkylene group having 2 to 4 carbon atoms.
In the above general formula (iii), R ^b3 is a hydrogen atom or a methyl group. R ^b4 is a linear or branched alkyl group having 1 to 10 carbon atoms.
When each of the plurality of repeating units represented by the above general formulas (i) to (iii) is provided, the plurality of R ^b1 , R ^b2 , R ^b3 , and R ^b4 may be the same. They may be different from each other.

In one aspect of the present invention, the macromonomer (x1) is preferably a polymer having a repeating unit represented by the general formula (i), and R ^b1 in the general formula (i) is 1,2. -A polymer having a repeating unit (X1-1) which is at least one of a butylene group and a 1,4-butylene group is more preferable.

The content of the repeating unit (X1-1) is preferably 1 to 100 mol%, more preferably 20 to 95 mol%, still more preferably, based on the total amount (100 mol%) of the constituent units of the macromonomer (x1). Is 40 to 90 mol%, more preferably 50 to 80 mol%.

When the macromonomer (x1) is a copolymer having two or more repeating units selected from the general formulas (i) to (iii), the form of copolymerization is a block copolymer. It may be a random copolymer or a random copolymer.

The comb-shaped polymer used as the component (B) in one aspect of the present invention may be a homopolymer consisting of only a structural unit (X1) derived from one type of macromonomer (x1), or two or more types of macromonomers (x1). It may be a copolymer having a structural unit (X1) derived from.
Further, the comb-shaped polymer used as the component (B) in one aspect of the present invention has a structural unit (X1) derived from the macromonomer (x1) and a structural unit (X2) derived from a monomer other than the macromonomer (x1). ) May be a copolymer.
As a specific structure of such a comb-shaped polymer, a main chain containing a structural unit (X2) derived from a monomer (x2) is opposed to a side chain containing a structural unit (X1) derived from a macromonomer (x1). A copolymer having the above is preferable.

Examples of the monomer (x2) include an alkyl (meth) acrylate, a nitrogen atom-containing vinyl monomer, a hydroxyl group-containing vinyl monomer, a phosphorus atom-containing monomer, an aliphatic hydrocarbon-based vinyl monomer, and an alicyclic type. Hydrocarbon-based vinyl monomers, vinyl esters, vinyl ethers, vinyl ketones, epoxy group-containing vinyl monomers, halogen element-containing vinyl monomers, unsaturated polycarboxylic acid esters, (di) alkyl fumarate, ( D) Alkyl maleate, aromatic hydrocarbon-based vinyl monomer and the like can be mentioned.

The monomer (x2) is preferably a monomer other than the phosphorus atom-containing monomer and the aromatic hydrocarbon-based vinyl monomer, and the monomer represented by the following general formula (a1), alkyl (meth). ) It is more preferable to contain at least one selected from acrylate and a hydroxyl group-containing vinyl monomer, and further preferably to contain at least a hydroxyl group-containing vinyl monomer (x2-d).

In the above general formula (a1), R ^b11 is a hydrogen atom or a methyl group.
R ^b12 is a single bond, a linear or branched alkylene group having 1 to 10 carbon atoms, -O-, or -NH-.
R ^b13 is a linear or branched alkylene group having 2 to 4 carbon atoms. Further, n represents an integer of 1 or more (preferably an integer of 1 to 20, more preferably an integer of 1 to 5). When n is an integer of 2 or more, the plurality of R ^b13s may be the same or different, and the (R ^b13 O) _n portion may be a random bond or a block bond.
R ^b14 is a linear or branched alkyl group having 1 to 60 carbon atoms (preferably 10 to 50, more preferably 20 to 40).

<Olefin copolymer (C)>
The lubricating oil composition of the present invention contains an olefin copolymer having a weight average molecular weight (Mw) of 100,000 or less as the component (C). By using the olefin copolymer in the range of Mw in combination with the component (B), a lubricating oil composition having an improved cavitation suppressing effect and shear stability can be obtained. Since the above-mentioned component (B) is used in combination with the component (C), the lubricating oil composition can be adjusted to have good low-temperature startability.

The weight average molecular weight (Mw) of the olefin copolymer used as the component (C) in one aspect of the present invention is 100,000 or less, but the low temperature startability and shear stability are improved while further improving the effect of suppressing cavitation. From the viewpoint of obtaining a better lubricating oil composition, preferably 80,000 or less, more preferably 70,000 or less, more preferably 60,000 or less, still more preferably 40,000 or less, still more preferably 30. It is 000 or less, particularly preferably 25,000 or less.
The weight average molecular weight (Mw) of the olefin copolymer as the component (C) is 500 or more, 1,000 or more, 3,000 or more, 5,000 or more, 7,000 or more, 8,000 or more, 8. It may be over 000, 8,000 or more, 9,000 or more, 9,500 or more, 10,000 or more, 11,000 or more, 12,000 or more, or 13,000 or more.

In the lubricating oil composition of one aspect of the present invention, the content of the component (C) is based on the total amount (100% by mass) of the lubricating oil composition, and the effect of suppressing cavitation and the shear stability are further improved. From the viewpoint of making an oil composition, it is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, still more preferably 0.5% by mass or more, still more preferably 0.8% by mass or more, and particularly preferably. Is 1.0% by mass or more, and is preferably 10.0% by mass or less, more preferably 8.0% by mass or less, still more preferably, from the viewpoint of obtaining a lubricating oil composition having better low-temperature startability. Is 5.0% by mass or less, more preferably 4.0% by mass or less, particularly preferably 3.0% by mass or less, and further, 2.5% by mass or less, or 2.0% by mass or less. ..

The component (C) used in one embodiment of the present invention is a copolymer having a structural unit derived from a monomer having an alkenyl group, and is, for example, a copolymer having 2 to 20 carbon atoms (preferably 2 to 16 carbon atoms, more preferably 2 to 16 carbon atoms). Examples thereof include the α-olefin copolymers of 2 to 14), and more specifically, the ethylene-α-olefin copolymer is preferable.
The number of carbon atoms of the α-olefin constituting the ethylene-α-olefin copolymer is preferably 3 to 20, more preferably 3 to 16, still more preferably 3 to 14, and even more preferably 3. ~ 6, particularly preferably 3.

The component (C) used in one aspect of the present invention may be a dispersed olefin-based copolymer.
As the dispersed olefin-based copolymer, a copolymer obtained by graft-polymerizing the above-mentioned ethylene-α-olefin copolymer with maleic acid, N-vinylpyrrolidone, N-vinylimidazole, glycidyl acrylate and the like. Can be mentioned.

Further, the component (C) used in one embodiment of the present invention may be a copolymer having a structural unit derived from a monomer having an alkenyl group and further having a structural unit derived from an aromatic monomer. Examples of such an olefin-based copolymer include styrene-based copolymers such as a styrene-diene copolymer and a styrene-isoprene copolymer.

Among these, the component (C) used in one aspect of the present invention may contain an ethylene propylene copolymer (C1) from the viewpoint of obtaining a lubricating oil composition having an effect of suppressing cavitation and improved shear stability. preferable.
In the lubricating oil composition of one aspect of the present invention, the content ratio of the component (C1) is preferably 30 to 100% by mass with respect to the total amount (100% by mass) of the component (C) contained in the lubricating oil composition. %, More preferably 50 to 100% by mass, still more preferably 70 to 100% by mass, still more preferably 80 to 100% by mass, and particularly preferably 90 to 100% by mass.

<Additives for lubricating oil>
The lubricating oil composition of one aspect of the present invention may further contain an additive for lubricating oil other than the component (B) and the component (C), if necessary, as long as the effect of the present invention is not impaired. ..
Examples of such additives for lubricating oil include antioxidants such as phenol-based antioxidants and amino-based antioxidants; metal-based detergents such as metal sulfonates, metal salicylates, and metal phenates; alkenyl succinate imide and the like. Ash-free dispersant; Molybdenum-based friction modifier, fatty acid ester, fatty acid, friction modifier such as aliphatic alcohol; Abrasion resistant agent such as zinc dithiophosphate; Phosphorus-based extreme pressure agent, sulfur-based extreme pressure agent, sulfur- Extreme pressure agents such as phosphorus-based extreme pressure agents; defoaming agents such as silicone-based defoaming agents; metal inactivating agents such as benzotriazole-based compounds; rust preventives; antistatic agents; and the like.
These lubricant additives may be used alone or in combination of two or more.

The content of each of these additives for lubricating oil can be appropriately prepared within a range that does not impair the effects of the present invention, but each addition is based on the total amount (100% by mass) of the lubricating oil composition. Independently for each agent, it is usually 0.001 to 15% by mass, preferably 0.005 to 10% by mass, and more preferably 0.01 to 5% by mass.

<Manufacturing method of lubricating oil composition>
The method for producing the lubricating oil composition according to one aspect of the present invention is not particularly limited, but from the viewpoint of productivity, the component (A) includes the component (B) and the component (C), and if necessary. , It is preferable that the method has a step of blending other additives for lubricating oil.
The resin components such as the component (B) and the component (C) are in the form of a solution dissolved in the diluted oil from the viewpoint of compatibility with the component (A), and the solution is blended with the component (A). Is preferable.

[Characteristics of lubricating oil composition]
The kinematic viscosity of the lubricating oil composition of one aspect of the present invention at 40 ° C. is preferably 5.0 to 130 mm ² / s, more preferably 6.5 to 100 mm ² / s, still more preferably 8.0 to 100 mm ² . / S, more preferably 10.0 to 60 mm ² / s, and particularly preferably 11.0 to 40 mm ² / s.

The kinematic viscosity of the lubricating oil composition of one aspect of the present invention at 100 ° C. is preferably 2.0 to 30 mm ² / s, more preferably 2.3 to 20 mm ² / s, still more preferably 2.6 to 15 mm ² . / S, more preferably 3.0 to 10 mm ² / s, and particularly preferably 3.2 to 7.0 mm ² / s.

The kinematic viscosity of the lubricating oil composition of one aspect of the present invention at 150 ° C. is preferably 1.0 to 20 mm ² / s, more preferably 1.2 to 10 mm ² / s, and even more preferably 1.4 to 7. It is 0 mm ² / s, more preferably 1.6 to 5.0 mm ² / s, and particularly preferably 1.8 to 3.0 mm ² / s.

The viscosity index of the lubricating oil composition according to one aspect of the present invention is preferably 100 or more, more preferably 120 or more, still more preferably 140 or more, still more preferably 160 or more, and particularly preferably 180 or more.

The BF viscosity (Brookfield viscosity) of the lubricating oil composition according to one aspect of the present invention at −40 ° C. is preferably 1500 mPa · s or less, more preferably 1400 mPa, from the viewpoint of obtaining a lubricating oil composition having good low-temperature startability. -S or less, more preferably 1300 mPa · s or less, still more preferably 1200 mPa · s or less, preferably 100 mPa · s or more, more preferably 300 mPa · s or more, still more preferably 500 mPa · s or more, still more. It is preferably 700 mPa · s or more.
In this specification, the BF viscosity means a value measured according to ASTM D2983-09.

The rate of decrease in kinematic viscosity calculated according to the method described in Examples described later for the lubricating oil composition of one aspect of the present invention is preferably 11 from the viewpoint of obtaining a lubricating oil composition having good shear stability. It is less than 0.0%, more preferably less than 10.5%, even more preferably less than 10.0%, still more preferably less than 9.5%.

The value of the cavitation coefficient calculated according to the method described in Examples described later for the lubricating oil composition of one aspect of the present invention is preferably from the viewpoint of obtaining a lubricating oil composition having an excellent effect of suppressing cavitation. It is 0.45 or less, more preferably 0.44 or less, still more preferably 0.43 or less, and usually 0.40 or more.

[Characteristics and applications of lubricating oil composition]
The lubricating oil composition of one aspect of the present invention has excellent properties such as low temperature startability, shear stability, and cavitation suppressing effect.
Therefore, the lubricating oil composition according to one aspect of the present invention can be suitably used for lubricating a shock absorber, and more specifically, it can be used for both a double-cylinder shock absorber and a single-cylinder shock absorber. , Can be suitably used for both two-wheeled and four-wheeled shock absorbers.
Considering these properties of the lubricating oil composition of one aspect of the present invention, the present invention may also provide the following [1] and [2].
[1] A shock absorber filled with the above-mentioned lubricating oil composition according to one aspect of the present invention.
[2] Use of a lubricating oil composition, which applies the above-mentioned lubricating oil composition of one aspect of the present invention to lubricate a shock absorber.

Next, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples. The methods for measuring various physical properties are as follows.

(1) Kinematic viscosity, viscosity index Measured and calculated according to JIS K2283: 2000.
(2) Weight average molecular weight (Mw)
It was measured under the following conditions using a gel permeation chromatograph device (manufactured by Agilent, "1260 type HPLC"), and the value measured in terms of standard polystyrene was used.
(Measurement condition)
-Column: Two "Shodex LF404" are connected in sequence.
-Column temperature: 35 ° C
・ Developing solvent: Chloroform ・ Flow rate: 0.3 mL / min

Example 1, Comparative Examples 1 to 8
Various additives were blended with the base oil according to the types and blending amounts shown in Table 1, and lubricating oil compositions were prepared respectively. The blending amounts of the various additives shown in Table 1 are the blending amounts in terms of active ingredients (solid content equivalent) excluding the mass of the diluted oil, even if they are blended in a state of being dissolved in the diluted oil. It is described.
The details of the base oil and various additives used for preparing each lubricating oil composition are as follows.

<Base oil>
"Paraffin-based mineral oil": 40 ° C. kinematic viscosity = 7.1 mm ² / s, 100 ° C. kinematic viscosity = 2.17 mm ² / s, viscosity index = 109, 15 ° C. density = 0.82 g / cm ³ , paraffin System mineral oil.
<PMA>
"PMA (550,000)": Polyalkyl (meth) acrylate having a weight average molecular weight (Mw) = 550,000.
"PMA (29,000)": Polyalkyl (meth) acrylate having a weight average molecular weight (Mw) of 29,000.
"PMA (140,000)": Polyalkyl (meth) acrylate having a weight average molecular weight (Mw) = 140,000.
<OCP>
"OCP (17,000)": Ethylene propylene copolymer having a weight average molecular weight (Mw) of 17,000.
"OCP (780,000)": An olefin copolymer having a weight average molecular weight (Mw) = 780,000.

The prepared lubricating oil composition was measured or calculated for 40 ° C. kinematic viscosity, 100 ° C. kinematic viscosity, 150 ° C. kinematic viscosity, and viscosity index, and the following measurements or evaluations were performed. These results are shown in Table 1.

(1) Evaluation of low temperature startability The BF viscosity at −40 ° C. was measured according to ASTM D2983-09.
It can be said that the lower the BF viscosity is, the more excellent the low temperature startability is, and when the BF viscosity at −40 ° C. is 1500 mPa · s or less, it is determined that the lubricating oil composition is excellent in low temperature startability. ..

(2) Evaluation of shear stability The shear test is based on the ultrasonic A method (JPI-5S-29), and the prepared lubricating oil composition is used as the sample oil, and ultrasonic waves are applied to 30 mL of the sample oil at 25 ° C. Was irradiated for 60 minutes. The output voltage of the ultrasonic wave is 30 mL of standard oil whose kinematic viscosity has been measured in advance at 40 ° C., and the output voltage has a decrease rate of 40 ° C. Adopted the value.
Then, the kinematic viscosity of the sample oil at 40 ° C. before and after the shear test was measured, the rate of decrease in kinematic viscosity was calculated from the following formula, and the shear stability was evaluated.
-Decrease rate of kinematic viscosity (%) = ([40 ° C kinematic viscosity of sample oil before shear test]-[40 ° C kinematic viscosity of sample oil after shear test]) / [40 ° C dynamic of sample oil before shear test] Viscosity] x 100
It can be said that the smaller the value of the kinematic viscosity reduction rate is, the more excellent the shear stability is, and when the value of the kinematic viscosity reduction rate is less than 11.0%, the lubricating oil is excellent in shear stability. It was judged to be a composition.

(3) Evaluation of Cavitation Suppressing Effect FIG. 1 is a schematic diagram of a test device for evaluating the cavitation suppressing effect. The test apparatus 1 shown in FIG. 1 includes an oil tank 11 for storing the sample oil to be evaluated, a pump 12 for circulating the sample oil, a heater 13 for adjusting the temperature of the sample oil, a flow meter 14 for controlling the flow velocity of the sample oil, and a sample. Valves 15a, 15b, 15c for controlling oil flow, observation tank 16 with sapphire observation windows on the sides and an orifice 16a with a diameter of 1 mm at the upstream inlet, and pressure on the upstream and downstream sides of the observation tank, respectively. It has a total of 17a, 17b, and a thermoelectric pair 18.
First, the prepared lubricating oil composition is filled in the oil tank 11 as sample oil, the valves 15a, 15b, and 15c are fully opened, the pump 12 and the heater 13 are operated, and along the flow path 1 and the flow path 2. The observation tank 16 was also filled with the sample oil while circulating the sample oil. Then, the state in which the temperature of the sample oil reached 150 ° C. and was stabilized was set as the initial state.
From the initial state, the valve 15c is gradually closed from the fully open state, the flow along the flow path 2 of the sample oil is restricted, and the state where the pressure gauge 17a on the upstream side shows "0.5 MPa" is set as the starting point. , The valve 15a on the upstream side and the valve 15b on the downstream side were adjusted, and the pressure was gradually increased until the pressure gauge 17a on the upstream side showed "5.0 MPa". In the process of pressurizing, the degree of cavitation is visually observed through the transparent window of the observation tank 16 based on the cavitation score for which the standard is set in advance according to the degree of cavitation, and cavitation. The upstream pressure Pu indicated by the upstream pressure gauge 17a and the downstream pressure Pd indicated by the downstream pressure gauge 17b at the point where the score was "5" were confirmed, and the cavitation coefficient was calculated.
The above cavitation score is evaluated in 11 steps in 1 increments, with "0" for non-occurrence of cavitation and "10" for the maximum occurrence of cavitation, and the standard for each step is cavitation. Based on what is predetermined according to the degree of occurrence.
The cavitation coefficient was calculated from the following formula, and the values are shown in Table 1.
・ Cavitation coefficient = (Pd + atmospheric pressure) / (Pu-Pd)
(In the above formula, Pu is the upstream pressure (unit: Pa), and Pd is the downstream pressure (unit: Pa).)
It can be said that the smaller the cavitation coefficient calculated from the above formula is, the higher the cavitation suppressing effect is, and when the cavitation coefficient value is 0.45 or less, the lubricating oil composition is excellent in the cavitation suppressing effect. I judged it to be a thing.
If cavitation with a cavitation score of "5" or higher has already occurred at the starting point where the upstream pressure is 0.5 MPa, it is assumed that cavitation is always occurring, and "F" in Table 1. It is described as.

From Table 1, the lubricating oil composition prepared in Example 1 was excellent in low temperature startability and shear stability, and also had a high effect of suppressing cavitation. On the other hand, the lubricating oil compositions prepared in Comparative Examples 1 to 8 were inferior in any of the low temperature startability, shear stability, and cavitation suppressing effect.

1 Test equipment 11 Oil tank 12 Pump 13 Heater 14 Flow meter 15a, 15b, 15c Valve 16 Observation tank 16a Orifice 17a, 17b Pressure gauge 18 Thermocouple

Claims (10)

It contains a base oil (A), a polyalkyl (meth) acrylate (B) having a weight average molecular weight of 150,000 to 900,000, and an olefin copolymer (C) having a weight average molecular weight of 100,000 or less. A lubricating oil composition used to lubricate shock absorbers. The lubricating oil composition according to claim 1, wherein the total content of the component (B) and the component (C) is 20.0% by mass or less based on the total amount of the lubricating oil composition. The lubricating oil composition according to claim 1 or 2, wherein the content ratio [(B) / (C)] of the component (B) to the component (C) is 1/99 to 90/10 in terms of mass ratio. thing. The lubricating oil composition according to any one of claims 1 to 3, wherein the content of the component (B) is 0.1 to 10.0% by mass based on the total amount of the lubricating oil composition. The lubricating oil composition according to any one of claims 1 to 4, wherein the content of the component (C) is 0.1 to 10.0% by mass based on the total amount of the lubricating oil composition. The lubricating oil composition according to any one of claims 1 to 5, wherein the weight average molecular weight of the component (C) is 8,000 or more and 100,000 or less. The lubricating oil composition according to any one of claims 1 to 6, wherein the component (C) contains an ethylene propylene copolymer (C1). The lubricating oil composition according to any one of claims 1 to 7, wherein the total content of the components (A) to (C) is 80 to 100% by mass based on the total amount of the lubricating oil composition. The lubricating oil composition according to any one of claims 1 to 8, wherein the BF viscosity of the lubricating oil composition at −40 ° C. is 1500 mPa · s or less. Use of a lubricating oil composition, wherein the lubricating oil composition according to any one of claims 1 to 9 is applied to lubricate a shock absorber.

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