Lubricating oil composition, flash point improver, and flash point improving method

Abstract

This lubricating oil composition contains a lubricating oil base oil (X), a diphenylamine-based antioxidant (A), a naphthylamine-based antioxidant (B), and a phosphorus-containing phenol-based antioxidant (C). The lubricating oil base oil (X) satisfies requirements (1)-(4). · Requirement (1): Having a viscosity index of 120 or more. · Requirement (2): Having a %CP of 85 or more as determined through ring analysis (n-d-M method). · Requirement (3): Having a density, at 15°C, of 0.835 g / cm3 or less. · Requirement (4): Having a kinematic viscosity, at 40°C, of 28.8 mm2 / s or more.　The content ratio [(B) / (A)] of the naphthylamine-based antioxidant (B) to the diphenylamine-based antioxidant (A) is 2.0 or more in mass ratio. The content ratio [(C) / (B)] of the phosphorus-containing phenol-based antioxidant (C) to the naphthylamine-based antioxidant (B) is 0.15 or less in mass ratio.

Description

Lubricating oil composition, flash point improver, and flash point improvement method

[0001] The present invention relates to a lubricating oil composition, a flash point improver, and a method for improving the flash point of a lubricating base oil. More particularly, the present invention relates to a lubricating oil composition, a flash point improver for a lubricating base oil, and a method for improving the flash point of a lubricating base oil.

[0002] From the viewpoint of improving safety, various methods for improving the flash point of oils have been proposed. For example, Patent Document 1 proposes a method for improving the flash point of an ester oil by mixing an ester oil having a flash point of 220° C. or higher with an antioxidant having a molecular weight of 300 or higher.

[0003] Japanese Patent Application Laid-Open No. 2021-175769

[0004] Incidentally, improvement in flash point is required not only for ester oils but also for other oils. Ｐ is 85 or more, and the density at 15°C is 0.835 g / cm ３ The present inventors have conducted extensive research to improve the flash point of a paraffin-rich lubricating base oil having a kinematic viscosity of 1000 kJ / g or less and a specific kinematic viscosity of 1000 kJ / g or less. However, the method proposed in Patent Document 1 is a method for improving the flash point of an ester oil, and currently, methods for improving the flash point of such paraffin-rich lubricating base oils have not been fully investigated.

[0005] Therefore, the present invention provides a viscosity index of 120 or more and a % C value determined by ring analysis (ndM method). Ｐ is 85 or more, and the density at 15°C is 0.835 g / cm ３ The present invention addresses the problem of providing a high-flash point lubricating oil composition using a paraffin-rich lubricating base oil having a kinematic viscosity of 1000 ppm or less and a specific viscosity; a flash point improver for the lubricating base oil; and a method for improving the flash point of the lubricating base oil.

[0006] According to the present invention, the following [1] to [3] are provided. [1] A lubricating oil base oil (X), a diphenylamine-based antioxidant (A), a naphthylamine-based antioxidant (B), and a phosphorus-containing phenol-based antioxidant (C), wherein the lubricating oil base oil (X) satisfies the following requirements (1) to (4): Requirement (1): A viscosity index of 120 or more; Requirement (2): A % C by ring analysis (nd-M method) Ｐ Requirement (3): Density at 15°C is 0.835 g / cm ３ Requirement (4): The kinematic viscosity at 40°C is 28.8 mm ２ a content ratio [(B) / (A)] of the naphthylamine-based antioxidant (B) to the diphenylamine-based antioxidant (A) in terms of mass ratio is 2.0 or more, and a content ratio [(C) / (B)] of the phosphorus-containing phenol-based antioxidant (C) to the naphthylamine-based antioxidant (B) in terms of mass ratio is 0.15 or less. [2] A flash point improver for a lubricating base oil, comprising a diphenylamine antioxidant (A), a naphthylamine antioxidant (B), and a phosphorus-containing phenolic antioxidant (C), wherein the content ratio of the naphthylamine antioxidant (B) to the diphenylamine antioxidant (A) [(B) / (A)] is 2.0 or more by mass, and the content ratio of the phosphorus-containing phenolic antioxidant (C) to the naphthylamine antioxidant (B) [(C) / (B)] is 0.15 or less by mass. [3] A method for improving the flash point of a lubricating base oil, comprising blending the flash point improver described in [2] above with a lubricating base oil (X) that satisfies the following requirements (1) to (4), thereby improving the flash point of the lubricating base oil (X). Requirement (1): The viscosity index is 120 or more. Requirement (2): %C by ring analysis (nd-M method) Ｐ Requirement (3): Density at 15°C is 0.835 g / cm ３ Requirement (4): The kinematic viscosity at 40°C is 28.8 mm ２ / s or more.

[0007] According to the present invention, the viscosity index is 120 or more, and the % C by ring analysis (ndM method) Ｐis 85 or more, and the density at 15°C is 0.835 g / cm ３ The present invention also makes it possible to provide a high-flash point lubricating oil composition using a paraffin-rich lubricating base oil having a specific kinematic viscosity of or less, a flash point improver for the lubricating base oil, and a method for improving the flash point of the lubricating base oil.

[0008] The upper and lower limit values ​​of the numerical ranges described in this specification can be combined in any way. For example, when "A to B" and "C to D" are described as numerical ranges, the numerical ranges "A to D" and "C to B" are also included in the scope of the present invention. Furthermore, the numerical range "lower limit to upper limit" described in this specification means that the range is equal to or greater than the lower limit and equal to or less than the upper limit, unless otherwise specified. Furthermore, in this specification, the numerical values ​​in the examples are numerical values ​​that can be used as upper or lower limit values.

[0009] [Embodiments of Lubricating Oil Composition] The lubricating oil composition of this embodiment contains a lubricating base oil (X), a diphenylamine-based antioxidant (A), a naphthylamine-based antioxidant (B), and a phosphorus-containing phenol-based antioxidant (C). The lubricating base oil (X) satisfies the following requirements (1) to (4): Requirement (1): A viscosity index of 120 or more. Requirement (2): % C by ring analysis (nd-M method). Ｐ Requirement (3): Density at 15°C is 0.835 g / cm ３ Requirement (4): The kinematic viscosity at 40°C is 28.8 mm ２ / s or more. The content ratio of the naphthylamine-based antioxidant (B) to the diphenylamine-based antioxidant (A) [(B) / (A)] is, in mass ratio, 2.0 or more. The content ratio of the phosphorus-containing phenol-based antioxidant (C) to the naphthylamine-based antioxidant (B) [(C) / (B)] is, in mass ratio, 0.15 or less.

[0010] The present inventors have conducted extensive research to solve the above problems. As a result, they have discovered that the following (I) to (III) are important for improving the flash point of lubricating base oil (X): (I) using a combination of a diphenylamine-based antioxidant (A), a naphthylamine-based antioxidant (B), and a phosphorus-containing phenol-based antioxidant (C); (II) the content ratio of the naphthylamine-based antioxidant (B) to the diphenylamine-based antioxidant (A) [(B) / (A)] is 2.0 or more by mass; and (III) the content ratio of the phosphorus-containing phenol-based antioxidant (C) to the naphthylamine-based antioxidant (B) [(C) / (B)] is 0.15 or less by mass.

[0011] The mechanism by which the flash point of the lubricating base oil (X) is improved is not clear; however, it is presumed that, for example, by satisfying the above conditions (I) to (III), some kind of interaction occurs among the diphenylamine-based antioxidant (A), the naphthylamine-based antioxidant (B), and the phosphorus-containing phenol-based antioxidant (C), which has some effect on the flash point of the lubricating base oil (X).

[0012] In the following description, the “lubricating base oil (X),” “diphenylamine-based antioxidant (A),” “naphthylamine-based antioxidant (B),” and “phosphorus-containing phenol-based antioxidant (C)” will also be referred to as “component (X),” “component (A),” “component (B),” and “component (C),” respectively.

[0013] The lubricating oil composition of this embodiment may be composed only of "component (X)," "component (A)," "component (B)," and "component (C)," but may also contain components other than "component (X)," "component (A)," "component (B)," and "component (C)" within a range that does not deviate from the spirit of the present invention. In the lubricating oil composition of this embodiment, the total content of "component (X)," "component (A)," "component (B)," and "component (C)" is preferably 80 mass % or more, more preferably 85 mass % or more, and even more preferably 90 mass % or more, based on the total amount of the lubricating oil composition.

[0014] Each component constituting the lubricating oil composition of this embodiment will now be described in detail.

[0015] <Lubricant Base Oil (X)> The lubricant base oil (X) satisfies the following requirements (1) to (4): Requirement (1): A viscosity index of 120 or more; Requirement (2): A % C by ring analysis (ndM method) Ｐ Requirement (3): Density at 15°C is 0.835 g / cm ３ Requirement (4): The kinematic viscosity at 40°C is 28.8 mm ２ / s or more.

[0016] In this specification, the kinematic viscosity at 40°C (hereinafter also referred to as "40°C kinematic viscosity") specified in requirement (4) and the viscosity index specified in requirement (1) refer to values ​​measured and calculated in accordance with JIS K2283:2000. Ｐ means a value calculated by ring analysis (ndM method) in accordance with ASTM D3238: 1995. In addition, in this specification, the density at 15°C specified in requirement (3) means a value measured in accordance with JIS K 2249-1: 2011 (Crude oil and petroleum products - Determination of density - Part 1: Vibration method).

[0017] Examples of lubricating base oil (X) include base oils obtained by subjecting atmospheric residual oil obtained by atmospheric distillation of paraffinic crude oil to further vacuum distillation to obtain distillate, followed by hydrocracking to obtain bottom oil, and then subjecting the bottom oil to at least one of hydroisomerization dewaxing and hydrorefining. Other examples include base oils obtained by subjecting one or more feedstock oils selected from high-wax distillate oil, slack wax, and GTL wax to at least one of hydroisomerization dewaxing and hydrorefining. These base oils may be used alone, or may be a mixed base oil of two or more types. When a mixed base oil is used, it is sufficient that the mixed base oil satisfies the requirements (1) to (4).

[0018] Here, from the viewpoint of further improving the effects of the present invention, the density at 15°C specified in requirement (3) is preferably 0.835 g / cm ３ or less, more preferably 0.832 g / cm ３More preferably, 0.830 g / cm ３ More preferably, 0.828 g / cm or less ３ Preferably, the density is 0.815 g / cm or less. ３ That's all.

[0019] In addition, from the viewpoint of facilitating further improvement of the effects of the present invention and facilitating improvement of the flash point of the lubricating base oil (X) itself, the kinematic viscosity at 40 ° C. (hereinafter also referred to as “40 ° C. kinematic viscosity”) specified in requirement (4) is preferably 30.0 mm ２ / s or more, more preferably 35.0 mm ２ / s or more, more preferably 41.4 mm ２ In order to further improve the effects of the present invention, it is preferable that the ２ / s or less, more preferably 48.0 mm ２ / s or less, more preferably 46.0 mm ２ / s or less.

[0020] The upper limit of the viscosity index specified in the requirement (1) is not particularly limited, but is, for example, 180 or less. Ｐ is 85 or more, preferably 87 or more, more preferably 90 or more, and the upper limit is not particularly limited, but is, for example, 100 or less.

[0021] The flash point of the lubricating base oil (X) is usually 230° C. or higher, preferably 235° C. or higher, more preferably 240° C. or higher, and even more preferably 245° C. or higher. In this specification, the flash point refers to a value measured by the Cleveland Open Chamber (COC) method in accordance with JIS K2265-4:2007.

[0022] In the lubricating oil composition of this embodiment, the content of the lubricating base oil (X) is preferably 90.0 mass% or more, more preferably 93.0 mass% or more, and even more preferably 95.0 mass% or more, based on the total amount of the lubricating oil composition, and is preferably 99.7 mass% or less.

[0023] <Lubricant base oil (X')> The lubricant composition of this embodiment may further contain a lubricant base oil (X') that does not fall under the category of lubricant base oil (X). Examples of the lubricant base oil (X') include one or more selected from the group consisting of mineral oils that do not satisfy at least one of the requirements (1) to (4) and synthetic oils that do not satisfy at least one of the requirements (1) to (4). However, from the viewpoint of further improving the effects of the present invention, it is preferable that the content of the lubricant base oil (X') is low. Specifically, the content of the lubricant base oil (X') is preferably less than 50 parts by mass, more preferably less than 30% by mass, even more preferably less than 10 parts by mass, even more preferably less than 1 part by mass, and even more preferably less than 0.1 parts by mass, per 100 parts by mass of the lubricant base oil (X).

[0024] <Diphenylamine-Based Antioxidant (A)> The lubricating oil composition of this embodiment contains a diphenylamine-based antioxidant (A). If the diphenylamine-based antioxidant (A) is not contained, the effects of the present invention will not be achieved.

[0025] As the diphenylamine-based antioxidant (A), diphenylamine-based antioxidants generally used as antioxidants for lubricating oil compositions can be used. The diphenylamine-based antioxidants (A) may be used alone or in combination of two or more.

[0026] In the lubricating oil composition of this embodiment, the diphenylamine antioxidant (A) preferably contains a compound (A1) represented by the following general formula (a1), from the viewpoint of further improving the effects of the present invention. From the same viewpoint, the content of compound (A1) in the diphenylamine antioxidant (A) is preferably 50% by mass to 100% by mass, more preferably 60% by mass to 100% by mass, even more preferably 70% by mass to 100% by mass, still more preferably 80% by mass to 100% by mass, even more preferably 90% by mass to 100% by mass, and even more preferably 95% by mass to 100% by mass, based on the total amount of the diphenylamine antioxidant (A).

[0027]

[0028] In the above general formula (a1), R ａ１ and R ａ２ are each independently an alkyl group having 1 to 30 carbon atoms. When the alkyl group has 1 to 30 carbon atoms, the effects of the present invention are more likely to be improved. ａ１ and R ａ２ The number of carbon atoms in the alkyl groups that can be selected as R is preferably 1 to 20, more preferably 4 to 16, and even more preferably 4 to 14, from the viewpoint of further improving the effects of the present invention. ａ１ and R ａ２ Specific examples of alkyl groups that can be selected as include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, icosyl, henicosyl, docosyl, tricosyl, tetracosyl, pentacosyl, hexacosyl, heptacosyl, octacosyl, nonacosyl, triacontyl, etc. These may be linear or branched.

[0029] In the general formula (a1), na1 and na2 each independently represent an integer of 1 to 5. From the viewpoint of making it easier to improve the effects of the present invention, na1 and na2 each independently represent preferably an integer of 1 to 3, more preferably 1 or 2, and even more preferably 1.

[0030] The compound (A1) may be used alone or in combination of two or more.

[0031] <Naphthylamine-Based Antioxidant (B)> The lubricating oil composition of this embodiment contains a naphthylamine-based antioxidant (B). If the naphthylamine-based antioxidant (B) is not contained, the effects of the present invention will not be achieved.

[0032] As the naphthylamine-based antioxidant (B), naphthylamine-based antioxidants generally used as antioxidants for lubricating oil compositions can be used. The naphthylamine-based antioxidants (B) may be used alone or in combination of two or more.

[0033] In the lubricating oil composition of this embodiment, the naphthylamine antioxidant (B) preferably contains a compound (B1) represented by the following general formula (b1), from the viewpoint of further improving the effects of the present invention. From the same viewpoint, the content of compound (B1) in the naphthylamine antioxidant (B) is preferably 50% by mass to 100% by mass, more preferably 60% by mass to 100% by mass, even more preferably 70% by mass to 100% by mass, still more preferably 80% by mass to 100% by mass, even more preferably 90% by mass to 100% by mass, and even more preferably 95% by mass to 100% by mass, based on the total amount of the naphthylamine antioxidant (B).

[0034]

[0035] In the above general formula (b1), R ｂ１ is an alkyl group having 1 to 30 carbon atoms. When the alkyl group has 1 to 30 carbon atoms, the effects of the present invention are more likely to be improved. ｂ１ The number of carbon atoms in the alkyl groups that can be selected as R is preferably 1 to 20, more preferably 4 to 16, and even more preferably 4 to 14, from the viewpoint of further improving the effects of the present invention. ｂ１ Specific examples of alkyl groups that can be selected as R ａ１ and R ａ２ Examples of the alkyl group that can be selected from include those exemplified above. The alkyl group may be linear or branched.

[0036] In the above general formula (b1), nb1 is an integer of 1 to 5. From the viewpoint of making it easier to improve the effects of the present invention, nb1 is preferably 1 to 3, more preferably 1 or 2, and even more preferably 1.

[0037] The compound (B1) may be used alone or in combination of two or more.

[0038] <Phosphorus-containing phenolic antioxidant (C)> The lubricating oil composition of this embodiment contains a phosphorus-containing phenolic antioxidant (C). If the phosphorus-containing phenolic antioxidant (C) is not contained, the effects of the present invention will not be achieved.

[0039] The phosphorus-containing phenolic antioxidant (C) may be any phosphorus-containing phenolic antioxidant commonly used as an antioxidant for lubricating oil compositions. The phosphorus-containing phenolic antioxidant (C) may be used alone or in combination of two or more.

[0040] In the lubricating oil composition of this embodiment, the phosphorus-containing phenolic antioxidant (C) preferably contains a compound (C1) represented by the following general formula (c1), from the viewpoint of further improving the effects of the present invention. From the same viewpoint, the content of compound (C1) in the phosphorus-containing phenolic antioxidant (C) is preferably 50 to 100 mass%, more preferably 60 to 100 mass%, even more preferably 70 to 100 mass%, still more preferably 80 to 100 mass%, even more preferably 90 to 100 mass%, and even more preferably 95 to 100 mass%, based on the total amount of the phosphorus-containing phenolic antioxidant (C).

[0041]

[0042] In the above general formula (c1), R ｃ１ , R ｃ２ , R ｃ３ , and R ｃ４ are each independently a hydrogen atom or an alkyl group having 1 to 30 carbon atoms. When the alkyl group has 1 to 30 carbon atoms, the effects of the present invention are more likely to be improved. ｃ１ , R ｃ２ , R ｃ３ , and R ｃ４ The alkyl group that can be selected as R ａ１ and R ａ２ The alkyl groups are the same as those that can be selected as R ｃ１ , R ｃ２ , R ｃ３ , and R ｃ４The number of carbon atoms in the alkyl groups that can be selected as R is preferably 1 to 20, more preferably 1 to 10, and even more preferably 1 to 6, from the viewpoint of further improving the effects of the present invention. Here, from the viewpoint of further improving the effects of the present invention, it is preferable that the compound (C1) has a hindered phenol skeleton. Therefore, R ｃ１ and R ｃ２ The alkyl group that can be selected as is preferably a branched alkyl group, more preferably a branched alkyl group having 1 to 6 carbon atoms, and even more preferably a tert-butyl group.

[0043] In the above general formula (c1), R ｃ５ is an alkylene group having 1 to 5 carbon atoms. ｃ５ The number of carbon atoms in the alkylene group that can be selected as R is preferably 1 to 4, more preferably 1 to 3, even more preferably 1 to 2, and still more preferably 1, from the viewpoint of further improving the effects of the present invention. ｃ５ Specific examples of the alkylene group that can be selected as include linear alkylene groups such as methylene, ethylene, n-propylene, n-butylene, and n-pentylene; and branched alkylene groups such as isopropylene, isobutylene, sec-butylene, tert-butylene, isopentylene, and neopentylene. Of these, a methylene group is preferred.

[0044] The compound (C1) may be used alone or in combination of two or more.

[0045] <Phosphorus-Free Phenol-Based Antioxidant (D)> From the viewpoint of further enhancing the effects of the present invention, the lubricating oil composition of this embodiment preferably further contains a phosphorus-free phenol-based antioxidant (D).

[0046] The phosphorus-free phenolic antioxidant (D) may be any of the phosphorus-free phenolic antioxidants generally used as antioxidants for lubricating oil compositions. The phosphorus-free phenolic antioxidants (D) may be used alone or in combination of two or more.

[0047] In the lubricating oil composition of this embodiment, the phosphorus-free phenolic antioxidant (D) preferably contains a compound (D1) represented by the following general formula (d1), from the viewpoint of further improving the effects of the present invention. From the same viewpoint, the content of compound (D1) in the phosphorus-free phenolic antioxidant (D) is preferably 50% by mass to 100% by mass, more preferably 60% by mass to 100% by mass, even more preferably 70% by mass to 100% by mass, still more preferably 80% by mass to 100% by mass, even more preferably 90% by mass to 100% by mass, and even more preferably 95% by mass to 100% by mass, based on the total amount of the phosphorus-containing phenolic antioxidant (D).

[0048]

[0049] In the above formula (d1), R ｄ１ is an alkylene group having 1 to 5 carbon atoms. ｄ１ The number of carbon atoms in the alkylene group that can be selected as R is preferably 1 to 4, more preferably 1 to 3, and even more preferably 1 to 2, from the viewpoint of further improving the effects of the present invention. ｄ１ Specific examples of the alkylene group that can be selected as aryl include linear alkylene groups such as a methylene group, an ethylene group, an n-propylene group, an n-butylene group, and an n-pentylene group; and branched alkylene groups such as an isopropylene group, an isobutylene group, a sec-butylene group, a tert-butylene group, an isopentylene group, and a neopentylene group.

[0050] In the above formula (d1), R ｄ２ is an alkyl group having 1 to 25 carbon atoms. ｄ２ The number of carbon atoms in the alkyl group that can be selected as R is preferably 2 or more, more preferably 4 or more, and even more preferably 6 or more, from the viewpoint of making it easier to improve the effects of the present invention. It is also preferably 20 or less, more preferably 15 or less, and even more preferably 10 or less. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 2 to 20, more preferably 4 to 15, and even more preferably 6 to 10. ｄ２Specific examples of alkyl groups that can be selected as include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, icosyl, heniicosyl, docosyl, tricosyl, tetracosyl, and pentacosyl groups. These may be linear or branched.

[0051] The compound (D1) may be used alone or in combination of two or more.

[0052] <Ratio of Component (B) to Component (A) [(B) / (A)]> In the lubricating oil composition of this embodiment, the ratio of the naphthylamine-based antioxidant (B) to the diphenylamine-based antioxidant (A) [(B) / (A)], in mass ratio, must be 2.0 or greater. If [(B) / (A)] is less than 2.0, the effects of the present invention will not be achieved. Here, from the viewpoint of further improving the effects of the present invention, [(B) / (A)], in mass ratio, is preferably 2.1 or greater, more preferably 2.2 or greater, and even more preferably 2.3 or greater. It is also preferably 3.5 or less, more preferably 3.2 or less, and even more preferably 3.0 or less. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 2.1 to 3.5, more preferably 2.2 to 3.2, and even more preferably 2.3 to 3.0.

[0053] <Ratio of Component (C) to Component (B) [(C) / (B)]> In the lubricating oil composition of this embodiment, the ratio of the phosphorus-containing phenolic antioxidant (C) to the naphthylamine-based antioxidant (B) [(C) / (B)], in mass ratio, must be 0.15 or less. If [(C) / (B)] exceeds 0.15, the effects of the present invention will not be achieved. Here, from the viewpoint of further improving the effects of the present invention, [(C) / (B)], in mass ratio, is preferably 0.14 or less, more preferably 0.12 or less, and even more preferably 0.10 or less. It is also preferably 0.03 or more, more preferably 0.04 or more, and even more preferably 0.05 or more. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 0.03 to 0.14, more preferably 0.04 to 0.12, and even more preferably 0.05 to 0.10.

[0054] <Total Content of Component (A), Component (B), and Component (C)> In the lubricating oil composition of this embodiment, the total content of the diphenylamine antioxidant (A), the naphthylamine antioxidant (B), and the phosphorus-containing phenolic antioxidant (C) is preferably 0.30 mass% or more, based on the total amount of the lubricating oil composition. Having this total content within this range facilitates improving the effects of the present invention. Here, from the viewpoint of further facilitating improving the effects of the present invention, the total content is preferably 0.60 mass% or more, more preferably 0.80 mass% or more, and even more preferably 1.0 mass% or more. Furthermore, from the viewpoint of obtaining effects commensurate with the amounts added while suppressing excessive addition of component (A), component (B), and component (C), the total content is preferably 5.0 mass% or less, more preferably 4.0 mass% or less, and even more preferably 3.0 mass% or less. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, the content is preferably 0.60% by mass to 5.0% by mass, more preferably 0.80% by mass to 4.0% by mass, and even more preferably 1.0% by mass to 3.0% by mass.

[0055] <Content of Component (A)> In the lubricating oil composition of this embodiment, the content of the diphenylamine-based antioxidant (A) is preferably 0.08 mass % to 1.5 mass %, more preferably 0.10 mass % to 1.0 mass %, and even more preferably 0.20 mass % to 0.80 mass %, based on the total amount of the lubricating oil composition, from the viewpoint of making it easier to improve the effects of the present invention.

[0056] <Content of Component (B)> In the lubricating oil composition of this embodiment, the content of the naphthylamine-based antioxidant (B) is preferably 0.22 mass % to 3.1 mass %, more preferably 0.40 mass % to 2.5 mass %, and even more preferably 0.60 mass % to 2.0 mass %, based on the total amount of the lubricating oil composition, from the viewpoint of making it easier to improve the effects of the present invention.

[0057] <Content of Component (C)> In the lubricating oil composition of this embodiment, the content of the phosphorus-containing phenolic antioxidant (C) is preferably 0.005 to 0.40 mass %, more preferably 0.010 to 0.30 mass %, and even more preferably 0.015 to 0.20 mass %, based on the total amount of the lubricating oil composition, from the viewpoint of making it easier to improve the effects of the present invention.

[0058] <Content of Component (D)> When the lubricating oil composition of the present embodiment contains the phosphorus-free phenolic antioxidant (D), the content of the phosphorus-free phenolic antioxidant (D) is preferably 0.40 mass % to 5.0 mass %, more preferably 0.90 mass % to 4.0 mass %, and even more preferably 1.5 mass % to 3.0 mass %, based on the total amount of the lubricating oil composition, from the viewpoint of making it easier to improve the effects of the present invention.

[0059] <Content of Component (D) Relative to the Total Content of Component (A), Component (B), and Component (C)> When the lubricating oil composition of this embodiment contains the phosphorus-free phenolic antioxidant (D), the content of the phosphorus-free phenolic antioxidant (D) relative to the total content of the diphenylamine antioxidant (A), the naphthylamine antioxidant (B), and the phosphorus-containing phenolic antioxidant (C) [(D) / {(A)+(B)+(C)}] is preferably 0.50 to 10.0, more preferably 0.70 to 8.0, and even more preferably 0.80 to 6.0, in mass ratio.

[0060] <Lubricating Oil Additives> The lubricating oil composition of this embodiment may contain lubricating oil additives other than components (A) to (D) to the extent that the effects of the present invention are not impaired. Examples of such lubricating oil additives include extreme pressure agents, detergent-dispersants, pour point depressants, viscosity index improvers, rust inhibitors, metal deactivators, antifoaming agents, and friction modifiers. These lubricating oil additives may be used alone or in combination of two or more.

[0061] [Physical Properties of Lubricating Oil Composition] The lubricating oil composition of this embodiment preferably has a flash point of 250° C. or higher, more preferably 260° C. or higher, even more preferably 270° C. or higher, and still more preferably 280° C. or higher. In this specification, flash point refers to a value measured by the Cleveland Open Carbon (COC) method in accordance with JIS K2265-4:2007.

[0062] [Method for Producing Lubricating Oil Composition] The method for producing the lubricating oil composition of this embodiment is not particularly limited. For example, the method for producing the lubricating oil composition of this embodiment includes a step of mixing a lubricating base oil (X), a diphenylamine-based antioxidant (A), a naphthylamine-based antioxidant (B), and a phosphorus-containing phenol-based antioxidant (C), and the lubricating base oil (X) satisfies the following requirements (1) to (4): Requirement (1): A viscosity index of 120 or more; Requirement (2): A % C by ring analysis (nd-M method) Ｐ Requirement (3): Density at 15°C is 0.835 g / cm ３ Requirement (4): The kinematic viscosity at 40°C is 28.8 mm ２The method includes a step of adjusting the content ratio [(B) / (A)] of the naphthylamine-based antioxidant (B) to the diphenylamine-based antioxidant (A) to be 2.0 or more in mass ratio, and a step of adjusting the content ratio [(C) / (B)] of the phosphorus-containing phenol-based antioxidant (C) to the naphthylamine-based antioxidant (B) to be 0.15 or less in mass ratio.

[0063] The production method may further include a step of blending a phosphorus-free phenolic antioxidant (D) as needed. The production method may also include a step of blending the above-mentioned lubricating oil additive as needed. The method for mixing the components is not particularly limited, and examples include a method in which each component is blended with a lubricating base oil (X). The components may also be blended after adding a diluent oil or the like to form a solution (dispersion). After blending the components, it is preferable to uniformly disperse them by stirring using a known method. The preferred embodiments of the lubricating base oil (X), component (A), component (B), component (C), and component (D) are as described above. The blending amounts and blending ratios of the lubricating base oil (X), component (A), component (B), component (C), and component (D) are preferably blended in amounts and blending ratios corresponding to the preferred contents and content ratios of the lubricating base oil (X), component (A), component (B), component (C), and component (D) described above.

[0064] [Uses of Lubricating Oil Composition] The lubricating oil composition of this embodiment is preferably used as an industrial equipment oil. Preferred examples of the industrial equipment oil include hydraulic oil; turbine oil; compressor oils such as rotary air compressor oil and reciprocating air compressor oil; machine tool oil; gear oil, etc., more preferably turbine oil; compressor oils such as rotary air compressor oil and reciprocating air compressor oil, and even more preferably turbine oil. Therefore, this embodiment provides a method of using the lubricating oil composition as a hydraulic oil, turbine oil, compressor oil, machine tool oil, or gear oil. This embodiment also provides a method of using the lubricating oil composition as a turbine oil or compressor oil. This embodiment also provides a method of using the lubricating oil composition as a turbine oil.

[0065] [Flash Point Improver] This embodiment also provides the following flash point improver for a lubricating base oil: The flash point improver for a lubricating base oil contains a diphenylamine antioxidant (A), a naphthylamine antioxidant (B), and a phosphorus-containing phenolic antioxidant (C), wherein the content ratio of the naphthylamine antioxidant (B) to the diphenylamine antioxidant (A) [(B) / (A)] is 2.0 or more by mass, and the content ratio of the phosphorus-containing phenolic antioxidant (C) to the naphthylamine antioxidant (B) [(C) / (B)] is 0.15 or less by mass.

[0066] The flash point improver for lubricating base oils preferably further contains a phosphorus-free phenolic antioxidant (D) from the viewpoint of making it easier to improve the flash point of the lubricating base oil.

[0067] The flash point improver for lubricating base oils described above is particularly suitable for improving the flash point of lubricating base oil (X) that satisfies the following requirements (1) to (4): Requirement (1): A viscosity index of 120 or more; Requirement (2): A % C value determined by ring analysis (nd-M method) Ｐ Requirement (3): Density at 15°C is 0.835 g / cm ３ Requirement (4): The kinematic viscosity at 40°C is 28.8 mm ２ / s or more.

[0068] In the flash point improver for lubricating base oils of this embodiment, the preferred aspects of the lubricating base oil (X), component (A), component (B), component (C), and component (D) are as described above. In addition, in the flash point improver for lubricating base oils of this embodiment, the preferred content ratios of the lubricating base oil (X), component (A), component (B), component (C), and component (D) are as described above.

[0069] According to the flash point improver for lubricating base oils of this embodiment, for example, the flash point of lubricating base oil (X) having a flash point in the range of 235°C or higher (preferably 240°C or higher) can be improved by preferably 10°C or higher, more preferably 15°C or higher.

[0070] [Method for Improving Flash Point] In this embodiment, there is provided a method for improving the flash point of a lubricating base oil, in which the above-mentioned flash point improver is blended with a lubricating base oil (X) that satisfies the following requirements (1) to (4) to improve the flash point of the lubricating base oil (X). Requirement (1): The viscosity index is 120 or more. Requirement (2): The % C by ring analysis (nd-M method) is 120 or more. Ｐ Requirement (3): Density at 15°C is 0.835 g / cm ３ Requirement (4): The kinematic viscosity at 40°C is 28.8 mm ２ / s or more.

[0071] In the method for improving the flash point of a lubricating base oil of this embodiment, the preferred aspects of the lubricating base oil (X), component (A), component (B), component (C), and component (D) are as described above. In addition, in the method for improving the flash point of a lubricating base oil of this embodiment, the preferred content ratios of the lubricating base oil (X), component (A), component (B), component (C), and component (D) are as described above.

[0072] According to the method for improving the flash point of a lubricating base oil of this embodiment, for example, the flash point of a lubricating base oil (X) having a flash point in the range of 235°C or higher (preferably 240°C or higher) can be improved by preferably 10°C or higher, more preferably 15°C or higher.

[0073] [Composition] The present embodiment also provides the following composition: It contains a diphenylamine-based antioxidant (A), a naphthylamine-based antioxidant (B), and a phosphorus-containing phenol-based antioxidant (C), wherein the content ratio of the naphthylamine-based antioxidant (B) to the diphenylamine-based antioxidant (A) [(B) / (A)] is 2.0 or more by mass, and the content ratio of the phosphorus-containing phenol-based antioxidant (C) to the naphthylamine-based antioxidant (B) [(C) / (B)] is 0.15 or less by mass. In the composition of this embodiment, preferred aspects of the lubricating base oil (X), component (A), component (B), component (C), and component (D) are as described above. In the composition of this embodiment, preferred content ratios of the lubricating base oil (X), component (A), component (B), component (C), and component (D) are as described above. In addition, this embodiment also provides a method for improving the flash point of a lubricating base oil (X) using the above composition. Furthermore, this embodiment also provides the use of the above composition for improving the flash point of a lubricating base oil (X). According to the method and use of this embodiment, for example, the flash point of a lubricating base oil (X) having a flash point in the range of 235 ° C or higher (preferably 240 ° C or higher) can be improved by preferably 10 ° C or higher, more preferably 15 ° C or higher.

[0074] [One Aspect of the Present Invention Provided] In one aspect of the present invention, the following [1] to

[11] are provided. [1] A lubricating base oil (X), a diphenylamine-based antioxidant (A), a naphthylamine-based antioxidant (B), and a phosphorus-containing phenol-based antioxidant (C), wherein the lubricating base oil (X) satisfies the following requirements (1) to (4): Requirement (1): A viscosity index of 120 or more; Requirement (2): A % C by ring analysis (nd-M method) Ｐ Requirement (3): Density at 15°C is 0.835 g / cm ３ Requirement (4): The kinematic viscosity at 40°C is 28.8 mm ２ / s or more. A lubricating oil composition, wherein the content ratio [(B) / (A)] of the naphthylamine-based antioxidant (B) to the diphenylamine-based antioxidant (A) is 2.0 or more, in mass ratio, and the content ratio [(C) / (B)] of the phosphorus-containing phenol-based antioxidant (C) to the naphthylamine-based antioxidant (B) is 0.15 or less, in mass ratio. [2] The lubricating oil composition according to the above item [1], wherein the diphenylamine-based antioxidant (A) contains a compound (A1) represented by the following general formula (a1): [In the above general formula (a1), R ａ１ and R ａ２ are each independently an alkyl group having 1 to 30 carbon atoms. na1 and na2 are each independently an integer of 1 to 5.] [3] The lubricating oil composition according to the above [1] or [2], wherein the naphthylamine-based antioxidant (B) comprises a compound (B1) represented by the following general formula (b1): [In the above general formula (b1), R ｂ１ is an alkyl group having 1 to 30 carbon atoms. nb1 is an integer of 1 to 5.] [4] The lubricating oil composition according to any one of the above [1] to [3], wherein the phosphorus-containing phenolic antioxidant (C) comprises a compound (C1) represented by the following general formula (c1): [In the above general formula (c1), R ｃ１ , R ｃ２ , R ｃ３ , and R ｃ４ are each independently a hydrogen atom or an alkyl group having 1 to 30 carbon atoms. ｃ５ is an alkylene group having 1 to 5 carbon atoms.] [5] The lubricating oil composition according to any one of the above items [1] to [4], further comprising a non-phosphorus-containing phenolic antioxidant (D). [6] The lubricating oil composition according to the above item [5], wherein the non-phosphorus-containing phenolic antioxidant (D) comprises a compound (D1) represented by the following general formula (d1): [In the above formula (d1), R ｄ１ is an alkylene group having 1 to 5 carbon atoms. ｄ２is an alkyl group having 1 to 25 carbon atoms.] [7] The lubricating oil composition according to any one of [1] to [6] above, wherein the total content of the diphenylamine-based antioxidant (A), the naphthylamine-based antioxidant (B), and the phosphorus-containing phenol-based antioxidant (C) is 0.30 mass % or more based on the total amount of the lubricating oil composition. [8] A flash point improver for a lubricating base oil, comprising a diphenylamine-based antioxidant (A), a naphthylamine-based antioxidant (B), and a phosphorus-containing phenol-based antioxidant (C), wherein the content ratio [(B) / (A)] of the naphthylamine-based antioxidant (B) to the diphenylamine-based antioxidant (A) is 2.0 or more by mass, and the content ratio [(C) / (B)] of the phosphorus-containing phenol-based antioxidant (C) to the naphthylamine-based antioxidant (B) is 0.15 or less by mass. [9] The flash point improver for a lubricating base oil according to the above item [8], further comprising a phosphorus-free phenolic antioxidant (D).

[10] The flash point improver according to the above item [8] or [9], for use with the lubricating base oil (X), wherein the lubricating base oil is a lubricating base oil (X) that satisfies the following requirements (1) to (4): Requirement (1): A viscosity index of 120 or more. Requirement (2): % C by ring analysis (nd-M method). Ｐ Requirement (3): Density at 15°C is 0.835 g / cm ３ Requirement (4): The kinematic viscosity at 40°C is 28.8 mm ２

[11] A method for improving the flash point of a lubricating base oil, comprising blending a flash point improver according to any one of [8] to

[10] above with a lubricating base oil (X) that satisfies the following requirements (1) to (4), thereby improving the flash point of the lubricating base oil (X). Requirement (1): The viscosity index is 120 or more. Requirement (2): The % C by ring analysis (nd-M method) is 120 or more. Ｐ Requirement (3): Density at 15°C is 0.835 g / cm ３ Requirement (4): The kinematic viscosity at 40°C is 28.8 mm ２ / s or more.

[0075] The present invention will be specifically described with reference to the following examples, although the present invention is not limited to the following examples.

[0076] [Methods for measuring various physical properties] The properties of the base oils used in each example and each comparative example were measured according to the following procedures. (1) 40°C kinematic viscosity and viscosity index: Measured and calculated in accordance with JIS K2283:2000. (2) %C Ｐ It was calculated by ring analysis (ndM method) in accordance with ASTM D3238: 1995. (3) Density at 15°C It was measured in accordance with JIS K 2249-1: 2011 (Crude oil and petroleum products - Determination of density - Part 1: Vibration method).

[0077] [Examples 1 to 7, Comparative Examples 1 and 2, Reference Examples 1 to 3] The components listed below were mixed to prepare lubricating oil compositions having the compositions shown in Tables 2 to 4. The numerical units for the blended compositions in Tables 2 to 4 are "mass %."

[0078] <Lubricant base oil (X)> In this example, lubricant base oil (X1) and lubricant base oil (X2) were used, which are base oils belonging to Group III of the API (American Petroleum Institute) and have the properties shown in Table 1. Table 1 also shows the properties of the mixed base oil of the lubricant base oil (X1) and the lubricant base oil (X2) used in Reference Example 2. Table 1 also shows the properties of the lubricant base oil (X') used in Reference Example 3. The lubricant base oil (X') is a base oil belonging to Group II of the API (American Petroleum Institute).

[0079]

[0080] <Diphenylamine-based antioxidant (A)> Dioctyldiphenylamine was used. Dioctyldiphenylamine is a diphenylamine represented by the general formula (a1), R ａ１ and R ａ２ is an octyl group, na1 = na2 = 1, and corresponds to compound (A1).

[0081] <Naphthylamine-based antioxidant (B)> Octylphenyl-1-naphthylamine was used. Octylphenyl-1-naphthylamine is a compound represented by the general formula (b1), R ｂ１is an octyl group, nb1=1, and corresponds to compound (B1).

[0082] <Phosphorus-containing phenolic antioxidant (C)> Diethyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate was used. Diethyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate is a phenol represented by the general formula (c1), R ｃ１ and R ｃ２ is a tert-butyl group, and R ｃ３ and R ｃ４ is an ethyl group, and R ｃ５ is a methylene group, which corresponds to compound (C1).

[0083] <Phosphorus-free phenolic antioxidant (D)> Benzenepropanoic acid-3,5-bis(1,1-dimethylethyl)-4-hydroxyalkyl ester was used. Benzenepropanoic acid-3,5-bis(1,1-dimethylethyl)-4-hydroxyalkyl ester is a phenol represented by the general formula (d1), R ｄ１ is an alkylene group having 2 carbon atoms, R ｄ２ is an alkyl group having 8 carbon atoms, and corresponds to compound (D1).

[0084] <Evaluation> Prior to the test, the flash points of the lubricating base oils of Reference Examples 1 to 3 were measured. In this example, the flash points were measured by the Cleveland Open Crack (COC) method in accordance with JIS K2265-4:2007. Next, the flash points of the lubricating oil compositions of Examples 1 to 7 and Comparative Examples 1 and 2 were measured using the same method. Then, for the lubricating oil compositions of Examples 1 to 3 and Comparative Example 1, the increase in flash point relative to the flash point of the lubricating base oil (X) of Reference Example 1 was calculated. Furthermore, for the lubricating oil compositions of Examples 4 to 7, the increase in flash point relative to the flash point of the lubricating base oil (X) of Reference Example 2 was calculated. For the lubricating oil composition of Comparative Example 2, the increase in flash point relative to the flash point of the lubricating base oil (X') of Reference Example 3 was calculated. Then, compositions with an increase in flash point of 10°C or more were deemed to have passed. The evaluation results are shown in Tables 2 to 4.

[0085]

[0086]

[0087]

[0088] Table 2 shows that the lubricating oil compositions of Examples 1 to 3 have flash points that are 10°C or more higher than the reference lubricating oil base oil of Reference Example 1. In contrast, the lubricating oil composition of Comparative Example 1 has a content ratio [(B) / (A)] of the naphthylamine-based antioxidant (B) to the diphenylamine-based antioxidant (A) of less than 2.0 by mass, and a content ratio [(C) / (B)] of the phosphorus-containing phenol-based antioxidant (C) to the naphthylamine-based antioxidant (B) of more than 0.15 by mass, and therefore does not have a flash point that is sufficiently higher than the reference lubricating oil base oil of Reference Example 1. Furthermore, Table 3 shows that the lubricating oil compositions of Examples 4 to 7 have flash points that are 10°C or more higher than the reference lubricating oil base oil of Reference Example 2. It can be seen from Table 4 that the lubricating oil composition of Comparative Example 2, despite having the same antioxidant composition as the lubricating oil composition of Example 7, does not have a flash point sufficiently improved compared to the reference lubricating oil base oil of Reference Example 3. This shows that for lubricating base oil (X') that does not satisfy requirements (1) to (4), the flash point is not sufficiently improved even when a diphenylamine-based antioxidant (A), a naphthylamine-based antioxidant (B), a phosphorus-containing phenolic antioxidant (C), and a phosphorus-free phenolic antioxidant (D) are blended, the content ratio [(B) / (A)] of the naphthylamine-based antioxidant (B) to the diphenylamine-based antioxidant (A) is adjusted to 2.0 or more by mass, and the content ratio [(C) / (B)] of the phosphorus-containing phenolic antioxidant (C) to the naphthylamine-based antioxidant (B) is adjusted to 0.15 or less by mass.

Claims

1. A lubricating oil composition comprising a lubricating base oil (X), a diphenylamine-based antioxidant (A), a naphthylamine-based antioxidant (B), and a phosphorus-containing phenol-based antioxidant (C), The lubricating base oil (X) satisfies the following requirements (1) to (4): Requirement (1): The viscosity index is 120 or more. Requirement (2): %C by ring analysis (nd-M method) Ｐ is 85 or higher. Requirement (3): Density at 15°C is 0.835 g / cm ３ The following is the result. Requirement (4): Kinematic viscosity at 40 ° C. is 28.8 mm ２ / s or more. a content ratio of the naphthylamine-based antioxidant (B) to the diphenylamine-based antioxidant (A) [(B) / (A)] in terms of mass ratio is 2.0 or more; a content ratio [(C) / (B)] of the phosphorus-containing phenolic antioxidant (C) to the naphthylamine-based antioxidant (B) is 0.15 or less in mass ratio.

2. 2. The lubricating oil composition according to claim 1, wherein the diphenylamine-based antioxidant (A) comprises a compound (A1) represented by the following general formula (a1): 【Chemistry 1】 [In the above general formula (a1), R ａ１ and R ａ２ are each independently an alkyl group having 1 to 30 carbon atoms. na1 and na2 are each independently an integer of 1 to 5.

3. 3. The lubricating oil composition according to claim 1, wherein the naphthylamine-based antioxidant (B) comprises a compound (B1) represented by the following general formula (b1): 【Chemistry 2】 [In the above general formula (b1), R ｂ１ is an alkyl group having 1 to 30 carbon atoms. nb1 is an integer of 1 to 5.

4. 3. The lubricating oil composition according to claim 1, wherein the phosphorus-containing phenolic antioxidant (C) comprises a compound (C1) represented by the following general formula (c1): 【Transformation 3】 [In the above general formula (c1), R ｃ１ , R ｃ２ , R ｃ３ , and R ｃ４ are each independently a hydrogen atom or an alkyl group having 1 to 30 carbon atoms. ｃ５ is an alkylene group having 1 to 5 carbon atoms.

5. 3. The lubricating oil composition according to claim 1, further comprising a phosphorus-free phenolic antioxidant (D).

6. 6. The lubricating oil composition according to claim 5, wherein the phosphorus-free phenolic antioxidant (D) contains a compound (D1) represented by the following general formula (d1): 【Chemistry 4】 [In the above formula (d1), R ｄ１ is an alkylene group having 1 to 5 carbon atoms. ｄ２ is an alkyl group having 1 to 25 carbon atoms.

7. 3. The lubricating oil composition according to claim 1, wherein the total content of the diphenylamine-based antioxidant (A), the naphthylamine-based antioxidant (B), and the phosphorus-containing phenol-based antioxidant (C) is 0.30 mass% or more based on the total amount of the lubricating oil composition.

8. The composition contains a diphenylamine-based antioxidant (A), a naphthylamine-based antioxidant (B), and a phosphorus-containing phenol-based antioxidant (C), a content ratio of the naphthylamine-based antioxidant (B) to the diphenylamine-based antioxidant (A) [(B) / (A)] in terms of mass ratio is 2.0 or more; a content ratio [(C) / (B)] of the phosphorus-containing phenolic antioxidant (C) to the naphthylamine-based antioxidant (B) is 0.15 or less in mass ratio.

9. 9. The flash point improver for lubricating base oils according to claim 8, further comprising (D) a non-phosphorus-containing phenolic antioxidant.

10. The lubricating base oil is a lubricating base oil (X) that satisfies the following requirements (1) to (4), and the lubricating base oil (X) is used. The flash point improver according to claim 8 or 9. Requirement (1): The viscosity index is 120 or more. Requirement (2): %C by ring analysis (nd-M method) Ｐ is 85 or higher. Requirement (3): Density at 15°C is 0.835 g / cm ３ The following is the result. Requirement (4): Kinematic viscosity at 40 ° C. is 28.8 mm ２ / s or more.

11. The flash point improver according to claim 8 or 9 is blended with a lubricating base oil (X) satisfying the following requirements (1) to (4) to improve the flash point of the lubricating base oil (X). A method for improving the flash point of a lubricating base oil. Requirement (1): The viscosity index is 120 or more. Requirement (2): %C by ring analysis (nd-M method) Ｐ is 85 or higher. Requirement (3): Density at 15°C is 0.835 g / cm ３ The following is the result. Requirement (4): Kinematic viscosity at 40 ° C. is 28.8 mm ２ / s or more.

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