EP3572485A1

EP3572485A1 - Lubricant composition

Info

Publication number: EP3572485A1
Application number: EP18742030.2A
Authority: EP
Inventors: Shota Inoue; Shinji Aoki
Original assignee: Idemitsu Kosan Co Ltd
Current assignee: Idemitsu Kosan Co Ltd
Priority date: 2017-01-19
Filing date: 2018-01-19
Publication date: 2019-11-27
Also published as: CN110168061B; US20190367834A1; CN110168061A; JP7058226B2; JPWO2018135645A1; EP3572485A4; WO2018135645A1

Abstract

The present invention provides a lubricating oil composition containing a base oil (A), zinc dithiophosphate (B), a metal sulfonate (C), and an ashless friction modifier (D) containing a boronated alkenyl succinimide (D1), which is to be used for a machine equipped with at least one of a wet type brake and a wet type clutch. The lubricating oil composition is not only excellent in oxidation stability but also favorable in an effect for suppressing the generation of squeal and braking properties, and is suitably applicable to machines equipped with a wet type brake or wet type clutch.

Description

Technical Field

The present invention relates to a lubricating oil composition.

Background Art

Hydraulic equipment to be mounted on a construction machinery, such as a hydraulic excavator, a crane, a wheel loader, and a bulldozer, is required to be operated at a high pressure, a high temperature, or a high speed, or under a high load. For that reason, a hydraulic fluid which is used in the hydraulic equipment for construction machinery is demanded to have wear resistance or oxidation stability such that even when used at a high pressure, a high temperature, or a high speed, or under a high load over a long period of time, it does not impair performances of the hydraulic equipment.
In addition, for lubrication of a wet type brake or a wet type clutch of a traction motor, a swing motor, etc., or a wet type disc brake-equipped winch, etc., equipped in these construction machineries, it is general that a hydraulic fluid which is used for the hydraulic equipment is also used.
For that reason, the hydraulic fluid which is used for construction machinery equipped with a wet type brake or a wet type clutch is required to have not only the aforementioned performances as the hydraulic fluid but also a lubricating performance for a wet type brake or a wet type clutch.
For that reason, in the hydraulic fluid which is used for construction machinery equipped with a wet type brake or a wet type clutch, a brake control or the like at the time of swinging is typically performed by increasing a friction coefficient required to be decreased to a certain extent from the standpoint of application to the hydraulic equipment.
For example, PTL 1 investigates a hydraulic fluid composition for construction machinery having excellent wear resistance and sludge generation suppression properties even under a high-temperature and high-pressure condition while it is a zinc-based one, having a low kinematic friction coefficient for controlling the actions at the time of starting or just before stop, and having a high static friction coefficient to such an extent that a brake performance by a wet type brake is not impaired.
In addition to that, PTL 1 discloses a hydraulic fluid composition for construction machinery containing a base oil, a zinc dialkyldithiophosphate, basic calcium salicylate, and an ashless friction modifier containing a nitrogen atom or an oxygen atom but not containing phosphorus atom in specified ranges.

Citation List

Patent Literature

PTL 1: JP 2014-218625 A

Summary of Invention

Technical Problem

Now, for the purpose of suppressing the sludge generation under a high-temperature and high-pressure condition, the hydraulic fluid composition for construction machinery as described in PTL 1 contains calcium salicylate as a dispersant. In the hydraulic fluid compositions specifically disclosed as the working examples, though an effect for suppressing the sludge generation due to the matter that it contains calcium salicylate is perceived, a ratio of a kinematic friction coefficient µ₀ just before stop to a kinematic friction coefficient µ_d during operation [µ₀/µ_d] is considerably low as 0.750 or less.
For that reason, the hydraulic fluid composition for construction machinery as described in PTL 1 involves such a concern that a problem of generation of squeal in the wet type clutch test or worsening of braking properties is caused, and it is not suited for an application to machines for which braking properties are particularly required as in a crane.
In view of the aforementioned problems, the present invention has been made, and an object thereof is to provide a lubricating oil composition which is not only excellent in oxidation stability but also favorable in an effect for suppressing the generation of squeal and braking properties, and which is suitably applicable to machines equipped with a wet type brake or a wet type clutch.

Solution to Problem

The present inventors have found that a lubricating oil composition containing zinc dithiophosphate and further containing a metal sulfonate and an ashless friction modifier containing a boronated alkenyl succinimide is able to solve the aforementioned problem, thereby leading to accomplishment of the present invention.
Specifically, the present invention relates to the following [1] to [3].

[1] A lubricating oil composition, which is to be used for a machine equipped with at least one of a wet type brake and a wet type clutch, containing a base oil (A), zinc dithiophosphate (B), a metal sulfonate (C), and an ashless friction modifier (D) containing a boronated alkenyl succinimide (D1).
[2] A machine equipped with at least one of a wet type brake and a wet type clutch, including the lubricating oil composition as set forth in the above [1].
[3] A method of using a lubricating oil composition, including using the lubricating oil composition as set forth in the above [1] for a machine equipped with at least one of a wet type brake and a wet type clutch.

Advantageous Effects of Invention

The lubricating oil composition of the present invention is not only excellent in oxidation stability but also favorable in an effect for suppressing the generation of squeal and braking properties. For that reason, it is suitably applicable to machines equipped with a wet type brake or wet type clutch.

Description of Embodiments

In this specification, the content of each of atoms means a value as measured in conformity with the following standards.

Zinc atom (Zn), calcium atom (Ca), boron atom (B), and phosphorus atom (P): Measured in conformity with JPI-5S-38-03.
Sulfur atom (S): Measured in conformity with JIS K2541-6.
Nitrogen atom (N): Measured in conformity with JIS K2609.

[Lubricating Oil Composition]

The lubricating oil composition of the present invention contains a base oil (A), zinc dithiophosphate (B), a metal sulfonate (C), and an ashless friction modifier (D) containing a boronated alkenyl succinimide (D1).
The lubricating oil composition of an embodiment of the present invention may further contain an antioxidant (E) according to the content of the zinc dithiophosphate (B).
The lubricating oil composition of an embodiment of the present invention may also contain other additives for lubricating oil not corresponding to the aforementioned components within a range where the effects of the present invention are not impaired.
In the lubricating oil composition of an embodiment of the present invention, the total content of the component (A), the component (B), the component (C), and the component (D) based on the total amount (100% by mass) of the lubricating oil composition is preferably 60% by mass or more, more preferably 70% by mass or more, still more preferably 75% by mass or more, and yet still more preferably 80% by mass or more, and it is typically 100% by mass or less, preferably 99.0% by mass or less, and more preferably 98.0% by mass or less.
In the lubricating oil composition of an embodiment of the present invention, the total content of the component (A), the component (B), the component (C), the component (D), and the component (E) based on the total amount (100% by mass) of the lubricating oil composition is preferably 65% by mass or more, more preferably 70% by mass or more, still more preferably 75% by mass or more, and yet still more preferably 80% by mass or more, and it is typically 100% by mass or less, preferably 99.5% by mass or less, and more preferably 99.0% by mass or less.
The lubricating oil composition of the present invention is one to be used for a machine equipped with at least one of a wet type brake and a wet type clutch.
As mentioned above, in a machine equipped with a wet type brake or a wet type clutch, it is general that a lubricating oil composition which is used for the hydraulic equipment is also used for a wet type brake or a wet type clutch of a traction motor or a swing motor, etc. with which the foregoing machine is equipped.
For that reason, the lubricating oil composition which is used for a machine equipped with a wet type brake or a wet type clutch is required to have not only excellent oxidation stability that is a performance as the hydraulic fluid but also such characteristics that a friction coefficient is high to a certain extent, and an effect for suppressing the generation of squeal or braking properties are favorable so as to make it applicable for lubrication of a wet type brake or a wet type clutch.
Now, in the lubricating oil composition as disclosed in PTL 1, etc., which is obtained by blending a metal salicylate as a dispersant together with a base oil and zinc dithiophosphate, a ratio of a kinematic friction coefficient µ₀ just before stop to a kinematic friction coefficient µ_d during operation [µ₀/µ_d] tends to become low. For example, in the lubricating oil compositions shown in the working examples of the PTL 1, the foregoing ratio [µ₀/µ_d] is considerably low as 0.750 or less.
As mentioned above, in such a lubricating oil composition, on the occasion when applied to a wet type brake or a wet type clutch, the generation of squeal or worsening of braking properties to be caused due to a decrease of the friction coefficient is feared. In particular, when applied to a machine for which braking properties are required, such as a crane and a winch, it is expected to be difficult for control of delicate movements of the winch.
On the other hand, in the lubricating oil composition of the present invention, in view of the fact that it contains, as a dispersant, the metal sulfonate (C) but not a metal salicylate, together with the base oil (A) and the zinc dithiophosphate (B) and further contains, as a friction modifier, the ashless friction modifier (D) containing the boronated alkenyl succinimide (D1) containing a nitrogen atom and an oxygen atom, not only excellent oxidation stability is kept, but also an effect for suppressing the generation of squeal is high, and braking properties are improved, too.
Each of the components which are contained in the lubricating oil composition of an embodiment of the present invention is hereunder described.

The base oil (A) which is contained in the lubricating oil composition of the present invention may be a mineral oil, may be a synthetic oil, or may be a mixed oil of a mineral oil and a synthetic oil.
Examples of the mineral oil include atmospheric residues obtained through atmospheric distillation of crude oils, such as paraffin-based crude oils, intermediate-base crude oils, and naphthene-based crude oils; distillates obtained through reduced-pressure distillation of such atmospheric residues; mineral oils obtained by purifying the distillates through one or more purification treatments, such as solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, and hydrorefining; and mineral oils (GTL) obtained by isomerizing a wax (GTL wax (Gas To Liquids WAX)) which is obtained by synthesis of a natural gas through the Fischer-Tropsch method, etc.
These mineral oils may be used alone or may be used in combination of two or more thereof.
Of these, as the mineral oil which is used in an embodiment of the present invention, it is preferred to contain a mineral oil having been subjected to one or more purification treatments, such as solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, and hydrorefining, or a mineral oil obtained by isomerizing a GTL wax.
As the mineral oil, it is preferred to contain a mineral oil grouped in Group 2 or Group 3 in the base oil category by API (American Petroleum Institute) or a mineral oil obtained by isomerizing a GTL wax; and it is more preferred to contain a mineral oil grouped in the foregoing Group 3 or a mineral oil obtained by isomerizing a GTL wax.
Examples of the synthetic oil include synthetic oils, such as poly-α-olefins, e.g., an α-olefin homopolymer and an α-olefin copolymer (for example, an α-olefin copolymer having 8 to 14 carbon atoms, e.g., an ethylene-α-olefin copolymer); isoparaffins; esters, e.g., a polyol ester and a dibasic acid ester; ethers, e.g., polyphenyl ether; polyalkylene glycols; alkylbenzenes; and alkylnaphthalenes.
These synthetic oils may be used alone or may be used in combination of two or more thereof.
Of these, as the synthetic oil which is used in an embodiment of the present invention, it is preferred to contain one or more synthetic oils selected from poly-α-olefins, various esters, and polyalkylene glycols.
A kinematic viscosity at 40°C of the base oil (A) is preferably 10 to 150 mm²/s, more preferably 12 to 120 mm²/s, and still more preferably 15 to 100 mm²/s.
A viscosity index of the base oil (A) is preferably 80 or more, more preferably 100 or more, and still more preferably 110 or more.
In this specification, the "kinematic viscosity at 40°C" and the "viscosity index" mean values as measured in conformity of JIS K2283.
In the case where the base oil (A) is a mixed oil of two or more selected from mineral oils and synthetic oils, the kinematic viscosity and the viscosity index of the mixed oil have to only fall within the aforementioned ranges, respectively.
In the lubricating oil composition of an embodiment of the present invention, the content of the base oil (A) based on the total amount (100% by mass) of the lubricating oil composition is typically 55% by mass or more, preferably 60% by mass or more, more preferably 65% by mass or more, still more preferably 70% by mass or more, and yet still more preferably 75% by mass or more, and it is preferably 98% by mass or less, more preferably 97% by mass or less, still more preferably 95% by mass or less, and yet still more preferably 93% by mass or less.

Since the lubricating oil composition of the present invention contains the zinc dithiophosphate (B), it improves wear resistance and oxidation stability and effectively suppresses metal wear and oxidation degradation generated following the use.
The zinc dithiophosphate (B) which is contained in the lubricating oil composition of an embodiment of the present invention is preferably a compound represented by the following general formula (b-1).
The zinc dithiophosphate (B) may be used alone or may be used in combination of two or more thereof.
In the formula (b-1), R¹ to R⁴ each independently represent a hydrocarbon group and may be the same as or different from each other.
Specific examples of the hydrocarbon group which may be selected as R¹ to R⁴ include alkyl groups, such as a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a 2-ethylhexyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, and an octadecyl group; alkenyl groups, such as an octenyl group, a nonenyl group, a decenyl group, an undecenyl group, a dodecenyl group, a tridecenyl group, a tetradecenyl group, and a pentadecenyl group; cycloalkyl groups, such as a cyclohexyl group, a dimethylcyclohexyl group, an ethylcyclohexyl group, a methylcyclohexylmethyl group, a cyclohexylethyl group, a propylcyclohexyl group, a butylcyclohexyl group, and a heptylcyclohexyl group; aryl groups, such as a phenyl group, a naphthyl group, an anthracenyl group, a biphenyl group, and a terphenyl group; alkylaryl groups, such as a tolyl group, a dimethylphenyl group, a butylphenyl group, a nonylphenyl group, a methylbenzyl group, and a dimethylnaphthyl group; and arylalkyl groups, such as a phenylmethyl group, a phenylethyl group, and a diphenylmethyl group.
Of these, an alkyl group is preferred as R¹ to R⁴.
Though the alkyl group may be either a linear alkyl group or a branched alkyl group, it is preferably a branched alkyl group.
The carbon number of the hydrocarbon group which may be selected as R¹ to R⁴ is preferably 1 to 20, more preferably 3 to 16, still more preferably 4 to 12, and yet still more preferably 5 to 10.
In the lubricating oil composition of an embodiment of the present invention, from the viewpoint of not only more improving the oxidation stability and enhancing the effect for suppressing the sludge deposition, but also providing a lubricating oil composition with excellent wear resistance, the content of the component (B) as expressed in terms of a zinc atom based on the total amount (100% by mass) of the lubricating oil composition is preferably 100 ppm by mass or more, more preferably 150 ppm by mass or more, still more preferably 200 ppm by mass or more, and yet still more preferably 250 ppm by mass or more, and from the viewpoint of more improving the wear resistance, it is even yet still more preferably 500 ppm by mass or more, and especially preferably 600 ppm by mass or more.
So long as the content of the component (B) as expressed in terms of a zinc atom is 500 ppm by mass or more, even when an antioxidant (E) as mentioned later is not separately blended, it becomes possible to prepare a lubricating oil composition having an effect for suppressing the sludge deposition.
From the viewpoint of providing a lubricating oil composition capable of regulating the friction coefficient to a predetermined value or more and suppressing evils, such as generation of squeal and worsening of braking properties, the content of the component (B) as expressed in terms of a zinc atom based on the total amount (100% by mass) of the lubricating oil composition is preferably 2,000 ppm by mass or less, more preferably 1,500 ppm by mass or less, still more preferably 1,200 ppm by mass or less, and yet still more preferably 1,000 ppm by mass or less.
In the lubricating oil composition of an embodiment of the present invention, as for the content (blending amount) of the component (B), though the content as expressed in terms of a zinc atom may be regulated so as to fall within the aforementioned range, it is typically 0.01 to 2.00% by mass, preferably 0.01 to 1.50% by mass, more preferably 0.01 to 1.00% by mass, still more preferably 0.05 to 0.90% by mass, yet still more preferably 0.10 to 0.85% by mass, and especially preferably 0.20 to 0.80% by mass based on the total amount (100% by mass) of the lubricating oil composition.

Since the lubricating oil composition of the present invention contains the metal sulfonate (C), not only the effect for improving the oxidation stability owing to addition of the component (B) is effectively revealed, but also evils, such as worsening of braking properties, can be suppressed.
From the aforementioned viewpoint, the metal sulfonate (C) is preferably a metal sulfonate containing a metal atom selected from alkali metals and an alkaline earth metals; and more preferably a metal sulfonate containing a metal atom selected from a sodium atom, a calcium atom, a magnesium atom, and a barium atom. In particular, from the viewpoint of providing a lubricating oil composition in which the friction coefficient in a high-speed region is appropriately increased, and the braking properties are more improved, it is still more preferred to contain calcium sulfonate.
In this specification, the "alkali metal atom" refers to a lithium atom (Li), a sodium atom (Na), a potassium atom (K), a rubidium atom (Rb), a cesium atom (Cs), and a francium atom (Fr).
The "alkaline earth metal atom" refers to a beryllium atom (Be), a magnesium atom (Mg), a calcium atom (Ca), a strontium atom (Sr), and a barium atom (Ba).
In the lubricating oil composition of an embodiment of the present invention, the content of the calcium sulfonate in the component (C) based on the total amount (100% by mass) of the component (C) which is contained in the lubricating oil composition is preferably 70 to 100% by mass, more preferably 80 to 100% by mass, still more preferably 90 to 100% by mass, and yet still more preferably 95 to 100% by mass.
The metal sulfonate (C) which is contained in the lubricating oil composition of an embodiment of the present invention is preferably a compound represented by the following general formula (c-1).
The metal sulfonate (C) may be used alone or may be used in combination of two or more thereof.

In the general formula (c-1), M is a metal atom; preferably an alkali metal or an alkaline earth metal; more preferably a sodium atom, a calcium atom, a magnesium atom, or a barium atom; still more preferably a calcium atom or a magnesium atom; and yet still more preferably a calcium atom.
p is a valence of M and is 1 or 2.

Examples of R include a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, an alkenyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 18 ring carbon atoms, an aryl group having 6 to 18 ring carbon atoms, an alkylaryl group having 7 to 18 carbon atoms, and an arylalkyl group having 7 to 18 carbon atoms.
Though the metal sulfonate (C) may be any of a neutral salt, a basic salt, an overbased salt, and a mixture thereof, it is preferred to contain an overbased salt.
In the case where the metal sulfonate (C) is a neutral salt, a base number of the neutral salt is preferably 0 to 30 mgKOH/g, more preferably 0 to 25 mgKOH/g, and still more preferably 0 to 20 mgKOH/g.
In the case where the metal sulfonate (C) is a basic salt or an overbased salt, a base number of the basic salt or overbased salt is preferably 100 to 600 mgKOH/g, more preferably 120 to 550 mgKOH/g, still more preferably 160 to 500 mgKOH/g, and yet still more preferably 200 to 480 mgKOH/g.
In this specification, the "base number" means a base number measured by the perchloric acid method in conformity with Item 7 of JIS K2501 "Petroleum Products and Lubricating Oils-Neutralization Number Testing Method."
In the lubricating oil composition of an embodiment of the present invention, from the viewpoint of providing a lubricating oil composition in which the friction coefficient in a high-speed region is appropriately increased, and the braking properties are improved, the content of the component (C) as expressed in terms of a metal atom based on the total amount (100% by mass) of the lubricating oil composition is preferably 200 ppm by mass or more, more preferably 300 ppm by mass or more, still more preferably 400 ppm by mass or more, yet still more preferably 500 ppm by mass or more, even yet still more preferably 1,000 ppm by mass or more, and even still more preferably 1,200 ppm by mass or more.
From the viewpoint of providing a lubricating oil composition which may more effectively suppress the generation of squeal, the content of the component (C) as expressed in terms of a metal atom based on the total amount (100% by mass) of the lubricating oil composition is preferably 4,000 ppm by mass or less, more preferably 3,500 ppm by mass or less, still more preferably 2,500 ppm by mass or less, and yet still more preferably 2,000 ppm by mass or less.
In the lubricating oil composition of an embodiment of the present invention, as for the content (blending amount) of the component (C), though the content as expressed in terms of a metal atom may be regulated so as to fall within the aforementioned range, it is preferably 0.01 to 3.0% by mass, more preferably 0.05 to 2.7% by mass, still more preferably 0.10 to 2.4% by mass, and yet still preferably 0.20 to 2.0% by mass based on the total amount (100% by mass) of the lubricating oil composition.
In the lubricating oil composition of an embodiment of the present invention, though a metal salicylate may be contained within a range where the effects of the present invention are not impaired, from the viewpoint of providing a lubricating oil composition in which the friction coefficient in a high-speed region is appropriately increased, and the braking properties are more improved, it is preferred that the content of the metal salicylate is low as far as possible.
Specifically, the content of the metal salicylate based on the total amount (100% by mass) of the lubricating oil composition is preferably less than 0.03% by mass, more preferably less than 0.01% by mass, still more preferably less than 0.001% by mass, and yet still more preferably less than 0.0001% by mass.
The content of the metal salicylate relative to the total amount (100% by mass) of the component (C) which is contained in the lubricating oil composition is preferably less than 10% by mass, more preferably less than 6% by mass, still more preferably less than 3% by mass, and yet still more preferably less than 1% by mass.

Since the lubricating oil composition of the present invention contains the ashless friction modifier (D) containing the boronated alkenyl succinimide (D1), not only the effect for improving the oxidation stability owing to addition of the component (B) is effectively revealed, but also evils, such as worsening of braking properties, can be suppressed.
In particular, in view of the fact that the component (D1) is contained, the effect for suppressing evils, such as generation of squeal and worsening of braking properties, may be conspicuously improved as compared with the case of using only the component (C).
In the lubricating oil composition of an embodiment of the present invention, from the viewpoint of not only more effectively revealing the effect for improving the oxidation stability owing to addition of the component (B) but also more suppressing evils, such as generation of squeal and worsening of braking properties, it is preferred that the component (D) contains the boronated alkenyl succinimide (D1) and an alkenyl group-containing unsaturated amine (D2).
A content ratio of the component (D1) to the component (D2) [(D1)/(D2)] is preferably 2 to 100, more preferably 3 to 80, still more preferably 4 to 60, yet still more preferably 5 to 50, and even yet still more preferably 7 to 40 in terms of a mass ratio.
When the aforementioned mass ratio [(D1)/(D2)] is 2 or more, the effect for suppressing worsening of braking properties is more readily revealed. On the other hand, when the mass ratio [(D1)/(D2)] is 100 or less, the effect for suppressing the generation of squeal is more readily revealed.
The lubricating oil composition of an embodiment of the present invention may contain, as the ashless friction modifier (C), other ashless friction modifier than the components (D1) and (D2) within a range where the effects of the present invention are not impaired.
However, in the lubricating oil composition of an embodiment of the present invention, the content of the component (D1) based on the total amount (100% by mass) of the component (D) which is contained in the lubricating oil composition is preferably 50% by mass or more, more preferably 60% by mass or more, still more preferably 70% by mass or more, and yet still more preferably 80% by mass or more.
In the lubricating oil composition of an embodiment of the present invention, the total content of the components (D1) and (D2) based on the total amount (100% by mass) of the component (D) which is contained in the lubricating oil composition is preferably 60 to 100% by mass, more preferably 70 to 100% by mass, still more preferably 80 to 100% by mass, and yet still more preferably 90 to 100% by mass.
In the lubricating oil composition of an embodiment of the present invention, the content (blending amount) of the component (D) based on the total amount (100% by mass) of the lubricating oil composition is preferably 0.05 to 7.0% by mass, more preferably 0.10 to 5.0% by mass, still more preferably 0.20 to 4.0% by mass, and yet still more preferably 0.30 to 3.2% by mass.
In the lubricating oil composition of an embodiment of the present invention, the content of a nitrogen atom derived from the component (D) based on the total amount (100% by mass) of the lubricating oil composition is preferably 15 to 900 ppm by mass, more preferably 40 to 700 ppm by mass, still more preferably 55 to 500 ppm by mass, and yet still more preferably 100 to 350 ppm by mass.

[Boronated Alkenyl Succinimide (D1)]

The boronated alkenyl succinimide (D1) which is used in the present invention is a boronated product of an alkenyl succinimide, and examples of the boronated product include boron oxide, a boron halide, boric acid, boric anhydride, a boric acid ester, and an ammonium salt of boric acid.
In an embodiment of the present invention, the boronated alkenyl succinimide (D1) is preferably a boronated product of a compound represented by the following general formula (d-11) or (d-12).
The component (D1) may also be a boronated product of polybutenyl succinimide obtained through a reaction between a compound represented by the following general formula (d-11) or (d-12) and at least one compound selected from an alcohol, an aldehyde, a ketone, an alkylphenol, a cyclic carbonate, an epoxy compound, and an organic acid.

In the general formulae (d-11) and (d-12), R^A, R^A1, and R^A2 are each independently an alkenyl group having a weight average molecular weight (Mw) of 500 to 3,000 (preferably 1,000 to 3,000).
R^B, R^B1, and R^B2 are each independently an alkylene group having 2 to 5 carbon atoms.
x1 is an integer of 1 to 10, preferably an integer of 2 to 5, and more preferably 3 or 4.
x2 is an integer of 0 to 10, preferably an integer of 1 to 4, and more preferably 2 or 3.

Examples of the alkenyl group which may be selected as R^A, R^A1, and R^A2 include a polybutenyl group, a polyisobutenyl group, and a group containing an ethylene-propylene unit. Of these, a polybutenyl group or a polyisobutenyl group is preferred.
The compound represented by the general formula (d-11) can be, for example, produced by allowing an alkenyl succinic anhydride obtained through a reaction between a polyolefin and maleic anhydride, to react with a polyamine.
Examples of the polyolefin include polymers obtained through polymerization of one or more compounds selected from α-olefins having 2 to 8 carbon atoms. Of these, a copolymer of isobutene and 1-butene is preferred.
Examples of the polyamine include simple diamines, such as ethylenediamine, propylenediamine, butylenediamine, and pentylenediamine; polyalkylenepolyamines, such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, di(methylethylene)triamine, dibutylenetriamine, tributylenetetramine, and pentapentylenehexamine; and piperazine derivatives, such as aminoethylpiperazine.
The compound represented by the general formula (d-12) can be, for example, produced by allowing an alkenyl succinic anhydride obtained through a reaction between the aforementioned polyolefin and maleic anhydride, to react with the aforementioned polyamine.
In the lubricating oil composition of an embodiment of the present invention, from the viewpoint of effectively suppressing evils, such as generation of squeal and worsening of braking properties, a mass ratio [B/N] of a boron atom to a nitrogen atom constituting the component (D1) is preferably 0.2 to 3.0, more preferably 0.4 to 2.5, still more preferably 0.6 to 2.0, and yet still more preferably 0.7 to 1.5.
In the lubricating oil composition of an embodiment of the present invention, the content of the component (D1) as expressed in terms of a boron atom based on the total amount (100% by mass) of the lubricating oil composition is preferably 30 to 600 ppm by mass, more preferably 50 to 500 ppm by mass, still more preferably 60 to 400 ppm by mass, and yet still more preferably 80 to 300 ppm by mass.
In the lubricating oil composition of an embodiment of the present invention, the content of the component (D1) as expressed in terms of a nitrogen atom based on the total amount (100% by mass) of the lubricating oil composition is preferably 10 to 800 ppm by mass, more preferably 30 to 600 ppm by mass, still more preferably 50 to 400 ppm by mass, and yet still more preferably 80 to 300 ppm by mass.
In the lubricating oil composition of an embodiment of the present invention, as for the content (blending amount) of the component (D1), though the content as expressed in terms of a boron atom may be regulated so as to fall within the aforementioned range, it is preferably 0.05 to 4.0% by mass, more preferably 0.10 to 3.0% by mass, still more preferably 0.20 to 2.5% by mass, and yet still more preferably 0.30 to 2.0% by mass based on the total amount (100% by mass) of the lubricating oil composition.

[Alkenyl Group-Containing Unsaturated Amine (D2)]

Examples of the alkenyl group-containing unsaturated amine (D2) which is used in an embodiment of the present invention include primary to tertiary unsaturated amines having 1 to 3 alkenyl groups.
The carbon number of the alkenyl group is preferably 2 to 30, more preferably 4 to 26, still more preferably 8 to 24, and yet still more preferably 10 to 20.
Though the alkenyl group may be either a linear alkenyl group or a branched alkenyl group, it is preferably a linear alkenyl group.
In an embodiment of the present invention, it is preferred that the unsaturated amine (D2) contains a primary unsaturated amine (D21) having an alkenyl group having 2 to 30 carbon atoms.
In the lubricating oil composition of an embodiment of the present invention, the content of the primary unsaturated amine (D21) in the component (D2) based on the total amount (100% by mass) of the component (D2) which is contained in the lubricating oil composition is preferably 70 to 100% by mass, more preferably 80 to 100% by mass, still more preferably 90 to 100% by mass, and yet still more preferably 95 to 100% by mass.
The primary unsaturated amine (D21) is preferably a compound represented by the following general formula (d-2).

H₂N-(CH₂)_z1-CH=CH-(CH₂)_z2-H (d-2)
In the general formula (d-2), z1 and z2 are each independently an integer of 0 or more, and (z1 + z2) is an integer of 0 to 28. (z1 + z2) is preferably 2 to 24, more preferably 6 to 22, and still more preferably 7 to 18.
In the lubricating oil composition of an embodiment of the present invention, the content of the component (D2) as expressed in terms of a nitrogen atom based on the total amount (100% by mass) of the lubricating oil composition is preferably 5 to 100 ppm by mass, more preferably 10 to 80 ppm by mass, still more preferably 15 to 60 ppm by mass, and yet still more preferably 20 to 50 ppm by mass.
In the lubricating oil composition of an embodiment of the present invention, as for the content (blending amount) of the component (D2), though the content as expressed in terms of a nitrogen atom may be regulated so as to fall within the aforementioned range, it is preferably 0.001 to 3.0% by mass, more preferably 0.005 to 2.0% by mass, still more preferably 0.01 to 1.5% by mass, and yet still more preferably 0.02 to 1.2% by mass based on the total amount (100% by mass) of the lubricating oil composition.

[Other Ashless Friction Modifier (D) than Components (D1) and (D2)]

The lubricating oil composition of an embodiment of the present invention may contain, as the ashless friction modifier (C), other ashless friction modifier than the components (D1) and (D2) within a range where the effects of the present invention are not impaired.
Examples of the other ashless friction modifier include an aliphatic amine having an alkyl group having 2 to 30 carbon atoms, other than the components (D1) and (D2); a compound having an alkenyl group or an alkyl group each having 2 to 30 carbon atoms, which is selected from a fatty acid ester, a fatty acid amide, a fatty acid, an aliphatic alcohol, and an aliphatic ether; a phosphoric acid ester; and a non-boronated alkenyl succinimide.
In the lubricating oil composition of an embodiment of the present invention, a non-boronated alkenyl succinimide may be contained within a range where the effects of the present invention are not impaired; however, it is preferred that the content of the non-boronated alkenyl succinimide is low.
Specifically, the content of the non-boronated alkenyl succinimide based on the total amount (100% by mass) of the component (D1) which is contained in the lubricating oil composition is preferably less than 10% by mass, more preferably less than 6% by mass, still more preferably less than 3% by mass, and yet still more preferably less than 1% by mass.

The lubricating oil composition of an embodiment of the present invention may further contain an antioxidant (E) according to the content of the zinc dithiophosphate (B).
Examples of the antioxidant (E) include a phenol-based antioxidant, an amine-based antioxidant, a molybdenum-based antioxidant, a sulfur-based antioxidant, and a phosphorus-based antioxidant.
In an embodiment of the present invention, the antioxidant (E) may be used alone or may be used in combination of two or more thereof.
Of these, in an embodiment of the present invention, from the viewpoint of more improving the oxidation stability, it is preferred that the antioxidant (E) contains a phenol-based antioxidant (E1) and an amine-based antioxidant (E2).
Examples of the phenol-based antioxidant (E1) include monophenol-based antioxidants, such as 2,6-di-t-butylphenol, 2,6-di-t-butyl-4-methylphenol, 2,6-di-t-butyl-4-ethylphenol, isooctyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, and octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate; diphenol-based antioxidants, such as 4,4'-methylenebis(2,6-di-t-butylphenol) and 2,2'-methylenebis(4-ethyl-6-t-butylphenol); and hindered phenol-based antioxidants.
The amine-based antioxidant (E2) is preferably an aromatic amine compound, and more preferably at least one selected from a diphenylamine compound and a naphthylamine-based compound.
Examples of the diphenylamine-based compound include monoalkyldiphenylamine-based compounds having one alkyl group having 1 to 30 carbon atoms (preferably 4 to 30 carbon atoms, and more preferably 8 to 30 carbon atoms), such as monooctyldiphenylamine and monononyldiphenylamine; dialkyldiphenylamine compounds having two alkyl groups having 1 to 30 carbon atoms (preferably 4 to 30 carbon atoms, and more preferably 8 to 30 carbon atoms), such as 4,4'-dibutyldiphenylamine, 4,4'-dipentyldiphenylamine, 4,4'-dihexyldiphenylamine, 4,4'-diheptyldiphenylamine, 4,4'-dioctyldiphenylamine, and 4,4'-dinonyldiphenylamine; polyalkyldiphenylamine-based compounds having three or more alkyl groups having 1 to 30 carbon atoms (preferably 4 to 30 carbon atoms, and more preferably 8 to 30 carbon atoms), such as tetrabutyldiphenylamine, tetrahexyldiphenylamine, tetraoctyldiphenylamine, and tetranonyldiphenylamine; and 4,4'-bis(α,α-dimethylbenzyl)diphenylamine.
Examples of the naphthylamine-based compound include 1-naphthylamine, phenyl-1-naphthylamine, butylphenyl-1-naphthylamine, pentylphenyl-1-naphthylamine, hexylphenyl-1-naphthylamine, heptylphenyl-1-naphthylamine, octylphenyl-1-naphthylamine, nonylphenyl-1-naphthylamine, decylphenyl-1-naphthylamine, and dodecylphenyl-1-naphthylamine.
Examples of the molybdenum-based antioxidant include a molybdenum amine complex obtained through a reaction between molybdenum trioxide and/or molybdic acid and an amine compound.
Examples of the sulfur-based antioxidant include dilauryl-3,3'-thiodipropionate.
Examples of the phosphorus-based antioxidant include a phosphite and diethyl 3,5-di-t-butyl-4-hydroxybenzylphosphonate.
In the lubricating oil composition of an embodiment of the present invention, from the viewpoint of more improving the oxidation stability, a mass ratio [(E1)/(E2)] of the component (E1) to the component (E2) is preferably 1/6 to 6/1, more preferably 1/5 to 5/1, still more preferably 1/4 to 4/1, and yet still more preferably 1/3.5 to 3.5/1.
In the lubricating oil composition of an embodiment of the present invention, the total content of the components (E1) and (E2) based on the total amount (100% by mass) of the component (E) which is contained in the lubricating oil composition is preferably 60 to 100% by mass, more preferably 70 to 100% by mass, still more preferably 80 to 100% by mass, and yet still more preferably 90 to 100% by mass.
In the lubricating oil composition of an embodiment of the present invention, the content (blending amount) of the component (E) based on the total amount (100% by mass) of the lubricating oil composition is preferably 0.01 to 10.0% by mass, more preferably 0.05 to 7.0% by mass, still more preferably 0.10 to 5.0% by mass, and yet still more preferably 0.20 to 3.0% by mass.
In the lubricating oil composition in which the content of the component (B) as expressed in terms of a zinc atom is 500 ppm by mass or more, even when the antioxidant (E) is not blended, the effect for suppressing the sludge deposition can be made high.
For that reason, the lubricating oil composition may not contain the antioxidant (E).

The lubricating oil composition of an embodiment of the present invention may contain other additives for lubricating oil not corresponding to the aforementioned components (B) to (E) within a range where the effects of the present invention are not impaired.
Examples of the other additives for lubricating oil include a viscosity index improver, a flow point depressant, an anti-wear agent, an extreme pressure agent, a metal-based friction modifier, a rust inhibitor, a metal deactivator, a demulsifier, and an anti-foaming agent.
Each of such additives for lubricating oil may be used alone or may be used in combination of two or more thereof.
Though the content of each of such additives for lubricating oil can be properly regulated within a range where the effects of the present invention are not impaired, it is typically 0.001 to 15% by mass, preferably 0.005 to 10% by mass, and more preferably 0.01 to 8% by mass based on the total amount (100% by mass) of the lubricating oil composition.
In this specification, taking into consideration handling properties and solubility in the base oil (A), the additive, such as a viscosity index improver and an anti-foaming agent, may be blended in a form of a solution having been diluted with and dissolved in a part of the based oil (A), with other components. In such a case, in this specification, the aforementioned content of the additive, such as an anti-foaming agent and a viscosity index improver, means the content as expressed in terms of the effective component excluding a diluent oil (expressed in terms of the resin content).
Examples of the viscosity index improver include polymers, such as a non-dispersant-type polymethacrylate, a dispersant-type polymethacrylate, an olefin-based copolymer (for example, an ethylene-propylene copolymer), a dispersant-type olefin-based copolymer, and a styrene-based copolymer (for example, a styrene-diene copolymer and a styrene-isoprene copolymer).
Though a weight average molecular weight (Mw) of such a viscosity index improver is typically 500 to 1,000,000, preferably 5,000 to 100,000, and more preferably 10,000 to 50,000, it is properly set according to the kind of the polymer.
In this specification, the weight average molecular weight (Mw) of each of the components is a value as expressed in terms of standard polystyrene as measured by means of gel permeation chromatography (GPC).
Examples of the flow point depressant include ethylene-vinyl acetate copolymers, condensation products of chloroparaffin and naphthalene, condensation products of chloroparaffin and phenol, polymethacrylates, and polyalkylstyrenes.
Examples of the anti-wear agent or the extreme pressure agent include zinc phosphate that is a phosphorus compound other than the component (B); sulfur-containing compounds, such as zinc dithiocarbamate, molybdenum dithiocarbamate, molybdenum dithiophosphate, disulfides, sulfurized olefins, sulfurized oils and fats, sulfurized esters, thiocarbonates, thiocarbamates, and polysulfides; phosphorus-containing compounds, such as phosphorous acid esters, phosphoric acid esters, phosphonic acid esters, and amine salts or metal salts thereof; and sulfur- and phosphorus-containing compounds, such as thiophosphorous acid esters, thiophosphoric acid esters, thiophosphonic acid esters, and amine salts or metal salts thereof.
Examples of the metal-based friction modifier include molybdenum-based friction modifiers, such as molybdenum dithiocarbamate (MoDTC), molybdenum dithiophosphate (MoDTP), and amine salts of molybdic acid.
Examples of the rust inhibitor include fatty acids, alkenylsuccinic acid half esters, fatty acid soaps, alkylsulfonic acid salts, polyhydric alcohol fatty acid esters, fatty acid amines, oxidized paraffins, and alkyl polyoxyethylene ethers.
Examples of the metal deactivator include benzotriazole-based compounds, tolyltriazole-based compounds, thiadiazole-based compounds, imidazole-based compounds, and pyrimidine-based compounds.
Examples of the demulsifier include anionic surfactants, such as sulfuric acid ester salts of castor oil and petroleum sulfonic acid salts; cationic surfactants, such as quaternary ammonium salts and imidazolines; polyoxyalkylene polyglycols and dicarboxylic acid esters thereof; and alkylene oxide adducts of an alkylphenol-formaldehyde polycondensate.
Examples of the anti-foaming agent include silicone oils, fluorosilicone oils, and fluoroalkyl ethers.

[Various Properties of Lubricating Oil Composition]

A kinematic viscosity at 40°C of the lubricating oil composition of an embodiment of the present invention is preferably 10 to 100 mm²/s, more preferably 13 to 75 mm²/s, and still more preferably 25 to 55 mm²/s.
A viscosity index of the lubricating oil composition of an embodiment of the present invention is preferably 100 or more, more preferably 120 or more, and still more preferably 130 or more.
The lubricating oil composition of the present invention not only has excellent oxidation stability but also is favorable in an effect for suppressing the generation of squeal and braking properties, and therefore, it is suitably applicable to machines equipped with at least one of a wet type brake and a wet type clutch.
With respect to the lubricating oil composition of an embodiment of the present invention, on the occasion of performing the "Test of Oxidation Stability of Lubricating Oils for Internal Combustion Engine" (ISOT) in conformity with JIS K2514-1 at a test temperature of 150°C for 168 hours, the amount of sludge generated after the test as measured in conformity with JIS B9931 is preferably less than 2.0 mg/100 mL, more preferably less than 1.5 mg/100 mL, and still more preferably less than 1.0 mg/100 mL.
It may be said that as the amount of sludge is lower, the lubricating oil composition has more excellent oxidation stability even at a high temperature.
In this specification, the aforementioned amount of sludge means a value as measured in conformity with the method described in the section of Examples as mentioned later.
With respect to the lubricating oil composition of an embodiment of the present invention, on the occasion of performing a high-pressure piston pump test with a high-pressure piston pump test apparatus (pump: BOSCH-REXROTH A2F10) in conformity with JCMAS P045 under a condition of a pump pressure of 35 MPa, a sample oil temperature of 80°C, and an air blowing amount of 1.0 L/h for 500 hours, the amount of sludge generated after the test as measured in conformity with JIS B9931 is preferably less than 3.0 mg/100 mL, more preferably less than 2.0 mg/100 mL, and still more preferably less than 1.0 mg/100 mL.
It may be said that as the amount of sludge is lower, the lubricating oil composition has more excellent oxidation stability even under a high pressure.
In this specification, the aforementioned amount of sludge means a value as measured in conformity with the method described in the section of Examples as mentioned later.
With respect to the lubricating oil composition of an embodiment of the present invention, on the occasion of measuring a kinematic friction coefficient at an oil temperature of 80°C under a load of 0.5 MPa by using a low-speed slip test apparatus in conformity with JASO M349, from the viewpoint of making the effect for suppressing the generation of squeal and the braking properties favorable, a ratio of a kinematic friction coefficient µ₁ at a rotational speed of 1 rpm to a kinematic friction coefficient µ₅₀ at a rotational speed of 50 rpm [µ₁/µ₅₀] is preferably 0.80 or more and less than 1.00, more preferably 0.80 or more and less than 0.95, and still more preferably 0.81 or more and less than 0.90.
The kinematic friction coefficient µ₁ at a rotational speed of 1 rpm is preferably 0.100 or more and less than 0.150, more preferably 0.105 or more and less than 0.140, and still more preferably 0.110 or more and less than 0.130.
The kinematic friction coefficient µ₁ can be considered to be a kinematic coefficient just before stop, whereas the kinematic friction coefficient µ₅₀ can be considered to be a kinematic coefficient during operation. The ratio [µ₁/µ₅₀] is a physical properties value serving as an index of the braking properties, and so long as it falls within the aforementioned range, it may be said that the braking properties are favorable.
In this specification, the aforementioned kinematic friction coefficient µ₁ and ratio [µ₁/µ₅₀] mean values as measured in conformity with the method described in the section of Examples as mentioned above.
With respect to the lubricating oil composition of an embodiment of the present invention, the wear amount of vanes and a cam ring as measured under a condition described in the section of Examples as mentioned later in conformity with ASTM D2882 on the occasion of driving a base pump (a product name: "V-104C", manufactured by Vickers) for 100 hours is preferably less than 40 mg, more preferably less than 36 mg, still more preferably less than 30 mg, and yet still more preferably less than 25 mg.

[Application of Lubricating Oil Composition]

Even if the lubricating oil composition of the present invention is applied for lubrication of a wet type brake or a wet type clutch, it is able to suppress the generation of squeal and to make the braking properties favorable, and therefore, it is preferred that the lubricating oil composition of the present invention is used for machines equipped with a wet type brake or a wet type clutch and used as a hydraulic fluid composition.
The machine is preferably a construction machinery, and more preferably a crane.
Examples of the construction machinery as referred to herein include cranes, such as a mobile crane, a stationary crane, and a derrick; excavators, such as a hydraulic excavator, a compact excavator, and a wheel type hydraulic excavator; land grading machines, such as a bulldozer; loaders, such as a wheel loader; transporting machines, such as a rough terrain hauler; compacting machines, such as a vibratory roller; dismantling machines, such as a breaker; foundation work machines, such as a pile driver and an earth auger; concrete/asphalt machines, such as a concrete pump vehicle; an elevating work platform, a paving machine, a shielding machine, a boring machine, and a snow blower.
Namely, since the lubricating oil composition of the present invention has excellent braking properties, it is preferably a hydraulic fluid composition which is used for construction machineries for which braking properties are especially required, and specifically, it is more preferably a hydraulic fluid composition which is used for cranes.
That is, the present invention may also provide the following machines and method of using a lubricating oil composition.

(1) A machine equipped with at least one of a wet type brake and a wet type clutch, using a lubricating oil composition containing a base oil (A), zinc dithiophosphate (B), a metal sulfonate (C), and an ashless friction modifier (D) containing a boronated alkenyl succinimide (D1).
(2) A method of using a lubricating oil composition, including using a lubricating oil composition containing a base oil (A), zinc dithiophosphate (B), a metal sulfonate (C), and an ashless friction modifier (D) containing a boronated alkenyl succinimide (D1) for a machine equipped with at least one of a wet type brake and a wet type clutch.

Preferred embodiments of the lubricating oil composition as prescribed in the above (1) and (2) are those as mentioned above.
The aforementioned machine is preferably a construction machinery, and more preferably a crane.

[Production Method of Lubricating Oil Composition]

The present invention also provides a production method of a lubricating oil composition, including the following step (I).
Step (I): A step of blending a base oil (A) with zinc dithiophosphate (B), a metal sulfonate (C), and an ashless friction modifier (D) containing a boronated alkenyl succinimide (D1).
The components (A), (B), (C), and (D) which are blended in the aforementioned step (I), and the component (E) and the other additives for lubricating oil, which are blended, as the need arises, are those as mentioned above, and the kinds of suitable components and the content of each of the components are also those as mentioned above.
In the present step, the other additives for lubricating oil than these components may also be blended at the same time.
Each of the components which are blended in the step (I) may be blended after being converted into a form of a solution (dispersion) upon addition with a diluent oil or the like. It is preferred that after blending the respective components, the blend is stirred and uniformly dispersed by a known method.

Examples

Next, the present invention is described in more detail by reference to Examples, but it should be construed that the present invention is by no means limited by these Examples. Various properties of the respective components used in the Examples and Comparative Examples and the obtained lubricating oil compositions were measured in conformity with the following methods.

Measured in conformity with JIS K2283.

Measured in conformity with JIS K2283.

Measured in conformity with JPI-5S-38-03.

Measured in conformity with JIS K2609.

Measured in conformity with JIS K2541-6.

Measured in conformity with JIS K2501.

A value obtained by performing the measurement with a gel permeation chromatograph ("1260 Type HPLC", manufactured by Agilent) under the following condition and expressing in terms of standard polystyrene was used.

(Measurement Condition)

Column: Two "Shodex LF404" columns connected in order
Column temperature: 35°C
Developing solvent: Chloroform
Flow rate: 0.3 mL/min

Examples 1 to 3 and Comparative Examples 1 to 3

The following mineral oil and various additives were added in blending amounts shown in Table 1 and thoroughly mixed to prepare lubricating oil compositions, respectively.
Details of the mineral oil and various additives used in the Examples and Comparative Examples are as follows.

(Component (A))

"Mineral oil": Mixed mineral oil of 100N mineral oil grouped in Group 3 and 500N mineral group in Group 2 by the API category ((100N mineral oil)/(500N mineral oil) = 86/14 (mass ratio)), kinematic viscosity at 40°C = 23.57 mm²/s, viscosity index = 118

(Component (B))

"ZnDTP": Zinc dialkyldithiophosphate (a compound represented by the general formula (b-1), wherein R¹ to R⁴ are each a 2-ethylhexyl group), content of zinc atom = 9.9% by mass, content of phosphorus atom = 8.0% by mass, content of sulfur atom = 16.6% by mass

(Component (C))

"Ca sulfonate": Overbased calcium sulfonate, base number (perchloric acid method) = 450 mgKOH/g, content of calcium atom = 20.0% by mass, content of sulfur atom = 1.4% by mass

(Component (D1))

"Boronated alkenyl succinimide": Boronated product of polybutenyl succinic monoimide having a polybutenyl group and having a number average molecular weight (Mn) of 1,000 (a boronated product of a compound represented by the general formula (d-11)), content of boron atom = 3.1% by mass, content of nitrogen atom = 3.8% by mass, mass ratio (B/N) of boron atom to nitrogen atom = 0.82

(Component (D2))

"Oleylamine": Primary unsaturated amine represented by the general formula (b-2), wherein z1 = z2 = 8, content of nitrogen atom = 5.2% by mass (Component (E1))
"Phenol-based antioxidant": 2,6-Di-t-butyl-4-methylphenol (DBPC)

(Component (E2))

"Amine-based antioxidant": Alkylated diphenylamine, content of nitrogen atom = 4.6% by mass

(Other additives)

"Viscosity index improver": Polymethacrylate having a weight average molecular weight (Mw) of 30,000 to 45,000
"Other additives": Mixed additive of a flow point depressant, an extreme pressure agent, a rust inhibitor, a copper deactivator, a demulsifier, and an anti-foaming agent

With respect to the lubricating oil compositions prepared in the Examples and Comparative Examples, the following tests were performed. The results thereof are shown in Table 1.

(1) Test of Oxidation Stability of Lubricating Oils for Internal Combustion Engine (ISOT)

The test of oxidation stability of lubricating oils for internal combustion engine (ISOT) in conformity with JIS K2514-1 was performed at a test temperature of 150°C for 168 hours. Then, the amount of sludge generated after the test (mg/100 mL) was measured in conformity with JIS B9931.

(2) High-Pressure Piston Pump Test

The high-pressure piston pump test with a high-pressure piston pump test apparatus (pump: BOSCH-REXROTH A2F10) in conformity with JCMAS P045 was performed under a condition of a pump pressure of 35 MPa, a sample oil temperature of 80°C, and an air blowing amount of 1.0 L/h for 500 hours. Then, the amount of sludge generated after the test (mg/100 mL) was measured in conformity with JIS B9931.

(3) Low-Speed Slip Friction Test

A kinematic friction coefficient µ₁ at a rotational speed of 1 rpm and a kinematic friction coefficient µ₅₀ at a rotational speed of 50 rpm were measured with a low-speed slip test apparatus (a product name: "L.V.F.A", manufactured by Automax Co., Ltd.) in conformity with JASO M349-12 under a condition of an oil temperature of 80°C and a load of 0.5 MPa. Then, a ratio of the kinematic friction coefficient µ₁ to the kinematic friction coefficient µ₅₀ [µ₁/µ₅₀] was calculated.

(4) Vane Pump Wear Test

Using a vane pump (a product name: "V-104C", manufactured by Vickers), on the occasion of driving for 100 hours in conformity with ASTM D2882 under a condition of a pump pressure of 13.8 MPa, an oil temperature of 66°C, a rotational speed of 1,200 rpm, a sample oil amount of 60 L, and a flow rate of 25 L/min, the wear amount (unit: mg) of vanes and a cam ring was measured.
From Table 1, the lubricating oil compositions prepared in Examples 1 to 3 are low in the amount of sludge in the ISOT and the high-pressure piston pump test, and therefore, it may be said that the lubricating oil compositions prepared in Examples 1 to 3 are high in the oxidation stability at a high temperature and a high pressure. In addition, in the lubricating oil compositions prepared in Examples 1 to 3, in view of the fact that the µ₁/µ₅₀ value is 0.80 or more and less than 1.00, it may be said that the effect for suppressing the generation of squeal is high, and the braking properties are favorable. Furthermore, the lubricating oil compositions prepared in Examples 1 to 3 are also excellent in the wear resistance.
On the other hand, in the lubricating oil compositions prepared in Comparative Examples 1 to 3, since the µ₁/µ₅₀ value is low, it may be said that the squeal is liable to be generated, and the braking properties are problematic; and in addition, there were brought such results that the wear resistance is inferior as compared with Examples 1 to 3.

Claims

A lubricating oil composition, which is to be used for a machine equipped with at least one of a wet type brake and a wet type clutch, comprising a base oil (A), zinc dithiophosphate (B), a metal sulfonate (C), and an ashless friction modifier (D) containing a boronated alkenyl succinimide (D1).
The lubricating oil composition according to claim 1, wherein the content of the component (B) as expressed in terms of a zinc atom based on the total amount of the lubricating oil composition is from 100 to 2,000 ppm by mass.
The lubricating oil composition according to claim 1, wherein the content of the component (B) as expressed in terms of a zinc atom based on the total amount of the lubricating oil composition is from 500 to 1,500 ppm by mass.
The lubricating oil composition according to any one of claims 1 to 3, wherein the component (C) contains calcium sulfonate.
The lubricating oil composition according to any one of claims 1 to 4, wherein the content of the component (C) as expressed in terms of a metal atom based on the total amount of the lubricating oil composition is from 200 to 4,000 ppm by mass.
The lubricating oil composition according to any one of claims 1 to 4, wherein the content of the component (C) as expressed in terms of a metal atom based on the total amount of the lubricating oil composition is from 1,000 to 3,500 ppm by mass.
The lubricating oil composition according to any one of claims 1 to 6, wherein the content of a metal salicylate based on the total amount of the lubricating oil composition is less than 0.03% by mass.
The lubricating oil composition according to any one of claims 1 to 7, wherein the component (D1) is a boronated product of a compound represented by the following general formula (d-11) or (d-12):

wherein,
R^A, R^A1, and R^A2 are each independently an alkenyl group having a weight average molecular weight (Mw) of 500 to 3,000;

R^B, R^B1, and R^B2 are each independently an alkylene group having 2 to 5 carbon atoms; and

x1 is an integer of 1 to 10, and x2 is an integer of 0 to 10.
The lubricating oil composition according to any one of claims 1 to 8, wherein a mass ratio [B/N] of a boron atom to a nitrogen atom constituting the component (D1) is from 0.2 to 3.0.
The lubricating oil composition according to any one of claims 1 to 9, wherein the content of the component (D1) as expressed in terms of a boron atom based on the total amount of the lubricating oil composition is from 30 to 600 ppm by mass.
The lubricating oil composition according to any one of claims 1 to 10, wherein the component (D) contains the component (D1) and an alkenyl group-containing unsaturated amine (D2).
The lubricating oil composition according to claim 11, wherein a content ratio of the component (D1) to the component (D2) [(D1)/(D2)] is from 2 to 100 in terms of a mass ratio.
The lubricating oil composition according to any one of claims 1 to 12, wherein on the occasion of measuring a kinematic friction coefficient at an oil temperature of 80°C under a load of 0.5 MPa by using a low-speed slip test apparatus in conformity with JASO M349, a ratio of a kinematic friction coefficient µ₁ at a rotational speed of 1 rpm to a kinematic friction coefficient µ₅₀ at a rotational speed of 50 rpm [µ₁/µ₅₀] is 0.80 or more and less than 1.00.
A machine equipped with at least one of a wet type brake and a wet type clutch, comprising the lubricating oil composition according to any one of claims 1 to 13.
A method of using a lubricating oil composition, comprising using the lubricating oil composition according to any one of claims 1 to 13 for a machine equipped with at least one of a wet type brake and a wet type clutch.