TW202342707A - Lubricating oil composition, flash point improver, and flash point improving method - Google Patents

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 DEG C, of 0.835 g/cm3 or less. Requirement (4): Having a kinematic viscosity, at 40 DEG 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 increasing agent and flash point increasing method

Field of invention The present invention relates to lubricating oil compositions, flash point increasing agents and flash point increasing methods. More specifically, the present invention relates to a lubricating oil composition, a flash point increasing agent for lubricating oil base oil, and a method for increasing the flash point of lubricating oil base oil.

Background technology From the viewpoint of improving safety, various methods of increasing the flash point of oils have been proposed in the past. For example, Patent Document 1 proposes a method of increasing the flash point of the ester oil by mixing an ester oil with a flash point of 220° C. or higher and an antioxidant with a molecular weight of 300 or higher.

Prior technical literature patent documents Patent Document 1: Japanese Patent Application Publication No. 2021-175769

Summary of the Invention Problems to be Solved by the Invention However, improvement in the flash point may be required not only for ester oils but also for other oils. The inventor of this case conducted careful research on improving the flash point of a paraffin-rich lubricating base oil. The paraffin-rich lubricating base oil has a viscosity index of 120 or more, and the % obtained by ring analysis (ndM method) C _P is above 85, the density at 15°C is below 0.835g/cm ³ and has a specific kinematic viscosity. However, the method proposed in Patent Document 1 is a method for improving the flash point of ester oil, and methods for improving the flash point of paraffin-rich lubricating base oils such as those mentioned above have not yet been fully explored.

Therefore, an object of the present invention is to provide a high flash point lubricating oil composition using a paraffin-rich lubricating oil base oil, a flash point improving agent for the lubricating oil base oil, and a method for increasing the flash point of the lubricating oil base oil, and This paraffin-rich lubricating base oil has a viscosity index of 120 or more, a % _CP of 85 or more by ring analysis (ndM method), a density of 0.835g/ ^cm3 or less at 15°C, and a specific kinematic viscosity. .

Means for Solving the Problems According to the present invention, the following [1] to [3] can be provided. [1] A lubricating oil composition containing a lubricating oil base oil (X), a diphenylamine-based antioxidant (A), a naphthylamine-based antioxidant (B), and a phosphorus-containing phenolic antioxidant (C), and the aforementioned lubricating oil composition Oil-based oil (X) meets the following requirements (1)~(4): ． Requirement (1): Viscosity index is above 120; . Requirement (2): % _CP obtained by ring analysis (ndM method) is 85 or more; . Requirement (3): The density at 15℃ is below 0.835g/ ^cm3 ; . Requirement (4): The kinematic viscosity at 40°C is 28.8 mm ² /s or more; the content ratio of the aforementioned naphthylamine antioxidant (B) and the aforementioned diphenylamine antioxidant (A) [(B)/(A) ] is 2.0 or more in mass ratio, and the content ratio [(C)/(B)] of the phosphorus-containing phenolic antioxidant (C) and the naphthylamine antioxidant (B) is 0.15 or less in mass ratio. [2] A flash point increaser for lubricating base oils, containing a diphenylamine antioxidant (A), a naphthylamine antioxidant (B), and a phosphorus-containing phenolic antioxidant (C), and the naphthylamine antioxidant is The content ratio [(B)/(A)] of the oxidizing agent (B) and the aforementioned diphenylamine-based antioxidant (A) is 2.0 or more in terms of mass ratio, and the aforementioned phosphorus-containing phenolic antioxidant (C) and the aforementioned naphthylamine-based antioxidant are The content ratio [(C)/(B)] of the antioxidant (B) is 0.15 or less in terms of mass ratio. [3] A method for increasing the flash point of a lubricating oil base oil, which is to blend the lubricating oil base oil (X) that meets the following requirements (1) to (4) with a flash point increasing agent such as the above [2] to increase the aforementioned Flash point of lubricating base oil (X): ． Requirement (1): Viscosity index is above 120; . Requirement (2): % _CP obtained by ring analysis (ndM method) is 85 or more; . Requirement (3): The density at 15℃ is below 0.835g/ ^cm3 ; . Requirement (4): The kinematic viscosity at 40°C is 28.8mm ² /s or above.

Effects of the Invention According to the present invention, it is possible to provide a high flash point lubricating oil composition using a paraffin-rich lubricating oil base oil, a flash point improving agent for the lubricating oil base oil, and a method for increasing the flash point of the lubricating oil base oil, and This paraffin-rich lubricating base oil has a viscosity index of 120 or more, a % _CP of 85 or more by ring analysis (ndM method), a density of 0.835g/ ^cm3 or less at 15°C, and a specific kinematic viscosity. .

Form used to implement the invention The upper and lower limits of the numerical ranges described in this specification can be combined arbitrarily. For example, when the numerical ranges are described as "A~B" and "C~D", the numerical ranges of "A~D" and "C~B" are also included in the scope of the present invention. In addition, the numerical range "lower limit to upper limit" described in this specification means above the lower limit and below the upper limit unless otherwise stated in advance. In addition, in this specification, the numerical value of the Example is a numerical value which can be used as an upper limit value or a lower limit value.

[Mode of Lubricating Oil Composition] The lubricating oil composition of this embodiment contains a lubricating oil base oil (X), a diphenylamine-based antioxidant (A), a naphthylamine-based antioxidant (B), and a phosphorus-containing phenolic antioxidant. Oxidizing agent (C). The lubricating base oil (X) satisfies the following requirements (1) to (4). ． Requirement (1): Viscosity index is above 120. ． Requirement (2): %C _P obtained by ring analysis (ndM method) is 85 or more. ． Requirement (3): The density at 15°C is 0.835g/ ^cm3 or less. ． Requirement (4): The kinematic viscosity at 40°C is 28.8mm ² /s or above. The content ratio [(B)/(A)] of the naphthylamine-based antioxidant (B) and the diphenylamine-based antioxidant (A) is 2.0 or more in terms of mass ratio. Moreover, the content ratio [(C)/(B)] of the phosphorus-containing phenolic antioxidant (C) and the naphthylamine-based antioxidant (B) is 0.15 or less in terms of mass ratio.

The inventor of the present invention conducted careful research to solve the above-mentioned problems. As a result, it was found that the following (I) to (III) are important in increasing the flash point of the lubricating base oil (X). (I) Used in combination with diphenylamine antioxidant (A), naphthylamine antioxidant (B) and phosphorus-containing phenolic antioxidant (C). (II) The content ratio [(B)/(A)] of the naphthylamine-based antioxidant (B) and the diphenylamine-based antioxidant (A) is 2.0 or more in terms of mass ratio. (III) The content ratio [(C)/(B)] of the phosphorus-containing phenolic antioxidant (C) and the naphthylamine antioxidant (B) is 0.15 or less in terms of mass ratio.

The mechanism by which the flash point of the lubricating base oil (X) increases is not yet clear, but we speculate that this is because, for example, if the above (I) to (III) are satisfied, diphenylamine-based antioxidants (A), naphthylamine-based antioxidants ( This is caused by some interaction between B) and the phosphorus-containing phenolic antioxidant (C), which also has some impact on the flash point of the lubricating base oil (X).

In addition, in the subsequent description, "lubricating base oil (X)", "diphenylamine antioxidant (A)", "naphthylamine antioxidant (B)", "phosphorus-containing phenolic antioxidant ( C)" are respectively referred to as "ingredient (X)", "ingredient (A)", "ingredient (B)" and "ingredient (C)".

The lubricating oil composition of this embodiment may be composed of only "component (X)", "component (A)", "component (B)" and "component (C)", or within the scope of the present invention. Contains ingredients other than "Ingredient (X)", "Ingredient (A)", "Ingredient (B)" and "Ingredient (C)". In the lubricating oil composition of this embodiment, based on the total amount of the lubricating oil composition, "component (X)", "component (A)", "component (B)" and "component (C)" The total content is preferably 80 mass% or more, preferably 85 mass% or more, and more preferably 90 mass% or more.

Hereinafter, each component constituting the lubricating oil composition of this embodiment will be described in detail.

<Lubricating base oil (X)> Lubricating base oil (X) satisfies the following requirements (1) to (4). ． Requirement (1): Viscosity index is above 120. ． Requirement (2): %C _P obtained by ring analysis (ndM method) is 85 or more. ． Requirement (3): The density at 15°C is 0.835g/ ^cm3 or less. ． Requirement (4): The kinematic viscosity at 40°C is 28.8mm ² /s or above.

In this specification, the kinematic viscosity at 40°C specified in requirement (4) (hereinafter also referred to as "40°C kinematic viscosity") and the viscosity index specified in requirement (1) mean compliance with JIS K2283:2000 Measured and calculated values. In addition, in this specification, % _CP specified in requirement (2) means a value calculated by ring analysis (ndM method) in compliance with ASTM D3238:1995. In addition, in this specification, the density at 15°C specified in requirement (3) means that it is measured in accordance with JIS K 2249-1: 2011 (Crude oil and petroleum products - Density determination method - Part 1: Vibration method) value.

Examples of the lubricating base oil (X) include the following base oils: a distillate oil obtained by subjecting an atmospheric pressure residual oil obtained by normal pressure distillation of paraffin crude oil to further distillation under reduced pressure, and hydrogenolyzing the distillate oil. The bottom oil is obtained, and then the base oil is obtained by subjecting the bottom oil to at least one of hydroisomerization, dewaxing and hydrorefining. In addition, the following base oils may also be mentioned: those obtained by subjecting at least one of hydroisomerization, dewaxing and hydrorefining to one or more raw material oils selected from the group consisting of high-wax distillate oil, pine wax and GTL wax. base oil. The base oil may be a single type, or a mixture of two or more base oils. In addition, when using a mixed base oil, the mixed base oil only needs to satisfy requirements (1) to (4).

Here, from the viewpoint of easily further improving the effect of the present invention, the density specified in requirement (3) at 15°C is preferably 0.835g/ ^cm3 or less, preferably 0.832g/ ^cm3 or less, and more preferably 0.830g/ ^cm3 or less, more preferably 0.828g/ ^cm3 or less. In addition, it is preferably 0.815g/cm ³ or more.

Furthermore, from the viewpoint of making it easier to further enhance the effect of the present invention and from the viewpoint of making it easier to increase the flash point of the lubricating base oil (X) itself, the kinematic viscosity at 40°C specified in requirement (4) (hereinafter also referred to as " The "40°C dynamic viscosity") is preferably 30.0mm ² /s or more, preferably 35.0mm ² /s or more, and more preferably 41.4mm ² /s or more. Moreover, from the viewpoint of easily further improving the effect of the present invention, it is preferably 50.6 mm ² /s or less, preferably 48.0 mm ² /s or less, and more preferably 46.0 mm ² /s or less.

In addition, there is no special limit on the upper limit of the viscosity index specified in requirement (1), for example, it is below 180. In addition, the % _CP specified in requirement (2) is 85 or more, preferably 87 or more, and preferably 90 or more. The upper limit is not particularly limited, for example, it is 100 or less.

The flash point of the lubricating base oil (X) is usually 230°C or higher, preferably 235°C or higher, preferably 240°C or higher, more preferably 245°C or higher. In this specification, the flash point refers to the value measured using the Kirschner open cup (COC) method in compliance with JIS K2265-4:2007.

In the lubricating oil composition of this embodiment, based on the total amount of the lubricating oil composition, the content of the lubricating oil base oil (X) is preferably 90.0 mass% or more, preferably 93.0 mass% or more, and more preferably More than 95.0 mass%. Moreover, it is preferable that it is 99.7 mass % or less.

＜Lubricating base oil (X’)＞ The lubricating oil composition of this embodiment may further contain a lubricating base oil (X') that is inconsistent with the lubricating base oil (X). The lubricating base oil (X') may be selected from the group consisting of mineral oils that do not meet at least one of the requirements (1) to (4) and synthesis of at least one of the requirements (1) to (4). Oils form more than one type in the group. However, from the viewpoint of easily further improving the effect of the present invention, the content of the lubricating base oil (X') is preferably small. Specifically, the content of the lubricating base oil (X') should be less than 50 parts by mass relative to 100 parts by mass of the lubricating base oil (X), preferably less than 30 parts by mass, more preferably less than 10 parts by mass, and then change. Preferably, it is less than 1 part by mass, and more preferably, it is less than 0.1 part by mass.

＜Diphenylamine-based antioxidant (A)＞ The lubricating oil composition of this embodiment contains diphenylamine-based antioxidant (A). When the diphenylamine-based antioxidant (A) is not contained, the effect of the present invention cannot be exerted.

As the diphenylamine-based antioxidant (A), a diphenylamine-based antioxidant generally used as an antioxidant for lubricating oil compositions can be used. One type of diphenylamine-based antioxidant (A) may be used alone, or two or more types may be used in combination.

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

[Chemical formula 1]

In the above general formula (a1), R ^a1 and R ^a2 are each independently an alkyl group having 1 to 30 carbon atoms. If the carbon number of the alkyl group is 1 to 30, the effect of the present invention can be easily improved. From the viewpoint of easily further improving the effect of the present invention, the carbon numbers of the alkyl groups that can be selected as R ^a1 and R ^a2 are each independently preferably 1 to 20, preferably 4 to 16, and more preferably 4 to 14. Specific examples of the alkyl groups that can be used as R ^a1 and R ^a2 include: methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, Twelve bases, thirteen bases, fourteen bases, fifteen bases, sixteen bases, seventeen bases, eighteen bases, nineteen bases, twenty bases, twenty-one bases, twenty-two bases, twenty-three bases , twenty-four bases, twenty-five bases, twenty-six bases, twenty-seven bases, twenty-eight bases, twenty-nine bases, thirty bases, etc. These may be linear or branched.

In the above general formula (a1), na1 and na2 are each independently an integer from 1 to 5. From the viewpoint of easily further improving the effect of the present invention, na1 and na2 are each independently preferably 1 to 3, preferably 1 to 2, and more preferably 1.

One type of compound (A1) may be used alone, or two or more types may be used in combination.

＜Naphthylamine antioxidant (B)＞ The lubricating oil composition of this embodiment contains naphthylamine-based antioxidant (B). When the naphthylamine-based antioxidant (B) is not included, the effect of the present invention cannot be exerted.

As the naphthylamine-based antioxidant (B), those generally used as antioxidants for lubricating oil compositions can be used. One type of naphthylamine-based antioxidant (B) may be used alone, or two or more types may be used in combination.

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

[Chemical formula 2]

In the above general formula (b1), R ^b1 is an alkyl group having 1 to 30 carbon atoms. If the carbon number of the alkyl group is 1 to 30, the effect of the present invention can be easily improved. From the viewpoint of easily further improving the effect of the present invention, the carbon number of the alkyl group that can be selected as R ^b1 is preferably 1 to 20 independently, preferably 4 to 16, and more preferably 4 to 14. Specific examples of the alkyl group that can be used as R ^b1 include those previously exemplified as the alkyl groups that can be used as R ^a1 and R ^a2 . The alkyl group may be linear or branched.

In the above general formula (b1), nb1 is an integer from 1 to 5. From the viewpoint of easily further improving the effect of the present invention, nb1 is preferably 1 to 3, more preferably 1 to 2, and more preferably 1.

One type of compound (B1) may be used alone, or two or more types may be used in combination.

＜Phosphorus-containing phenolic antioxidant (C)＞ The lubricating oil composition of this embodiment contains a phosphorus-containing phenolic antioxidant (C). When the phosphorus-containing phenolic antioxidant (C) is not included, the effect of the present invention cannot be exerted.

As the phosphorus-containing phenolic antioxidant (C), those generally used as antioxidants for lubricating oil compositions can be used. One type of phosphorus-containing phenolic antioxidant (C) may be used alone, or two or more types may be used in combination.

Here, in the lubricating oil composition of this embodiment, from the viewpoint of easily further improving the effect of the present invention, the phosphorus-containing phenolic antioxidant (C) preferably contains the compound (C1) represented by the following general formula (c1) ). From the same point of view, based on the total amount of phosphorus-containing phenolic antioxidant (C), the content of compound (C1) in phosphorus-containing phenolic antioxidant (C) is preferably 50 mass% to 100 mass% , preferably 60 mass% to 100 mass%, more preferably 70 mass% to 100 mass%, still more preferably 80 mass% to 100 mass%, still more preferably 90 mass% to 100 mass%, and more preferably Preferably, it is 95% by mass to 100% by mass.

[Chemical formula 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. If the carbon number of the alkyl group is 1 to 30, the effect of the present invention can be easily further improved. Examples of alkyl groups that can be used as R ^c1 , R ^c2 , R ^c3 and R ^c4 are the same as the alkyl groups that can be used as R ^a1 and R ^a2 above. However, from the viewpoint of easily further improving the effect of the present invention, the carbon numbers of the alkyl groups that can be selected as R ^c1 , R ^c2 , R ^c3 and R ^c4 are each independently preferably 1 to 20, preferably 1 to 10, more preferably The best value is 1~6. Here, from the viewpoint of easily further improving the effects of the present invention, the compound (C1) preferably has a hindered phenol skeleton. Therefore, the alkyl group that can be selected as R ^c1 and R ^c2 is preferably a branched alkyl group, preferably a branched alkyl group with 1 to 6 carbon atoms, and more preferably a tertiary butyl group.

In the above general formula (c1), R ^c5 is an alkylene group having 1 to 5 carbon atoms. From the viewpoint of easily further improving the effect of the present invention, the carbon number of the alkylene group that can be selected as R ^c5 is preferably 1 to 4, preferably 1 to 3, more preferably 1 to 2, and still more preferably 1. Specific examples of the alkylene group that can be used as R ^c5 include linear alkylene groups such as methylene, ethylene, n-propylene, n-butylene, and n-pentylene; isopropyl, isobutyl Branched alkylene groups such as secondary butylene group, tertiary butylene group, isopentyl group, neopentyl group, etc. Among these, methylene is preferred.

Compound (C1) may be used individually by 1 type, and may be used in combination of 2 or more types.

＜Phosphorus-free phenolic antioxidant (D)＞ From the viewpoint of easily further improving the effect of the present invention, the lubricating oil composition of this embodiment preferably contains a phosphorus-free phenolic antioxidant (D).

As the phosphorus-free phenolic antioxidant (D), a phosphorus-free phenolic antioxidant generally used as an antioxidant for lubricating oil compositions can be used. One type of phosphorus-free phenolic antioxidant (D) may be used alone, or two or more types may be used in combination.

Here, in the lubricating oil composition of this embodiment, from the viewpoint of easily further improving the effect of the present invention, the phosphorus-free phenolic antioxidant (D) preferably contains a compound represented by the following general formula (d1) ( D1). From the same point of view, based on the total amount of phosphorus-free phenolic antioxidant (D), the content of compound (D1) in phosphorus-free phenolic antioxidant (D) is preferably 50% by mass to 100% by mass. Mass %, preferably 60 mass % to 100 mass %, more preferably 70 mass % to 100 mass %, still more preferably 80 mass % to 100 mass %, more preferably 90 mass % to 100 mass %, and Even more preferably, it is 95% by mass to 100% by mass.

[Chemical formula 4]

In the above formula (d1), R ^d1 is an alkylene group having 1 to 5 carbon atoms. From the viewpoint of easily further improving the effect of the present invention, the carbon number of the alkylene group that can be selected as R ^d1 is preferably 1 to 4, preferably 1 to 3, and more preferably 1 to 2. Specific examples of the alkylene group that can be used as R ^d1 include: linear alkylene groups such as methylene, ethylene, n-propyl, n-butyl, n-pentyl, etc.; isopropyl, isobutyl Branched alkylene groups such as secondary butylene group, tertiary butylene group, isopentyl group, neopentyl group, etc.

In the above formula (d1), R ^d2 is an alkyl group having 1 to 25 carbon atoms. From the viewpoint of easily further improving the effect of the present invention, the carbon number of the alkyl group that can be selected as R ^d2 is preferably 2 or more, preferably 4 or more, and more preferably 6 or more. Moreover, it is preferably 20 or less, more preferably 15 or less, more preferably 10 or less. The upper and lower limits of these numerical ranges may be combined in any combination. Specifically, it is preferably 2 to 20, more preferably 4 to 15, and more preferably 6 to 10. Specific examples of the alkyl group that can be used as R ^d2 include: methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, and dodecyl , thirteen bases, fourteen bases, fifteen bases, sixteen bases, seventeen bases, eighteen bases, nineteen bases, twenty bases, twenty-one bases, twenty-two bases, twenty-three bases, twenty Four bases, twenty-five bases, etc. These may be linear or branched.

One type of compound (D1) may be used alone, or two or more types may be used in combination.

＜Content ratio of component (B) and component (A) [(B)/(A)]＞ The lubricating oil composition of this embodiment must have a content ratio [(B)/(A)] of naphthylamine-based antioxidant (B) and diphenylamine-based antioxidant (A) of 2.0 or more in terms of mass ratio. When [(B)/(A)] is less than 2.0, the effect of the present invention cannot be exerted. Here, from the viewpoint of easily further improving the effect of the present invention, the mass ratio of [(B)/(A)] is preferably 2.1 or more, preferably 2.2 or more, and more preferably 2.3 or more. Furthermore, it is preferably 3.5 or less, more preferably 3.2 or less, more preferably 3.0 or less. The upper and lower limits of these numerical ranges may be combined in any combination. Specifically, it is preferably 2.1 to 3.5, more preferably 2.2 to 3.2, and more preferably 2.3 to 3.0.

＜Content ratio of component (C) and component (B) [(C)/(B)]＞ The lubricating oil composition of this embodiment must be such that the content ratio [(C)/(B)] of the phosphorus-containing phenolic antioxidant (C) and the naphthylamine antioxidant (B) is 0.15 or less in terms of mass ratio. When [(C)/(B)] is greater than 0.15, the effect of the present invention cannot be exerted. Here, from the viewpoint of easily further improving the effect of the present invention, the mass ratio of [(C)/(B)] is preferably 0.14 or less, preferably 0.12 or less, and more preferably 0.10 or less. Furthermore, it is preferably 0.03 or more, more preferably 0.04 or more, more preferably 0.05 or more. The upper and lower limits of these numerical ranges may be combined in any combination. Specifically, it is preferably 0.03~0.14, more preferably 0.04~0.12, more preferably 0.05~0.10.

＜Total content of component (A), component (B) and component (C)＞ The lubricating oil composition of this embodiment is based on the total amount of the lubricating oil composition. The total of diphenylamine antioxidant (A), naphthylamine antioxidant (B) and phosphorus-containing phenolic antioxidant (C) The content is preferably 0.30% by mass or more. When the total content is within this range, the effect of the present invention can be easily improved. Here, from the viewpoint of easily further improving the effect of the present invention, the total content is preferably 0.60 mass% or more, preferably 0.80 mass% or more, and more preferably 1.0 mass% or more. Moreover, from the viewpoint of suppressing excessive addition of component (A), component (B), and component (C) and obtaining the effect of matching the addition amount, it is preferably 5.0 mass% or less, preferably 4.0 mass% or less, and more preferably It is 3.0 mass% or less. The upper and lower limits of these numerical ranges may be combined in any combination. Specifically, the content is preferably 0.60 mass% to 5.0 mass%, more preferably 0.80 mass% to 4.0 mass%, and more preferably 1.0 mass% to 3.0 mass%.

＜Content of ingredient (A)＞ In the lubricating oil composition of this embodiment, from the viewpoint of easily further improving the effect of the present invention, the content of the diphenylamine-based antioxidant (A) is preferably 0.08 mass % based on the total amount of the lubricating oil composition. ~1.5 mass%, preferably 0.10 mass% to 1.0 mass%, more preferably 0.20 mass% to 0.80 mass%.

＜Content of ingredient (B)＞ In the lubricating oil composition of this embodiment, from the viewpoint of easily further improving the effect of the present invention, the content of the naphthylamine-based antioxidant (B) is preferably 0.22 mass % based on the total amount of the lubricating oil composition. ~3.1 mass%, preferably 0.40 mass% to 2.5 mass%, more preferably 0.60 mass% to 2.0 mass%.

＜Content of ingredient (C)＞ In the lubricating oil composition of this embodiment, from the viewpoint of easily further improving the effect of the present invention, the content of the phosphorus-containing phenolic antioxidant (C) is preferably 0.005 based on the total amount of the lubricating oil composition. Mass% ~ 0.40 mass%, preferably 0.010 mass% ~ 0.30 mass%, more preferably 0.015 mass% ~ 0.20 mass%.

＜Content of ingredient (D)＞ When the lubricating oil composition of the present embodiment contains a phosphorus-free phenolic antioxidant (D), from the viewpoint of easily further improving the effect of the present invention, based on the total amount of the lubricating oil composition, the phosphorus-free phenolic antioxidant (D) The content of the phenolic antioxidant (D) is preferably 0.40 mass% to 5.0 mass%, preferably 0.90 mass% to 4.0 mass%, and more preferably 1.5 mass% to 3.0 mass%.

<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), compared to the diphenylamine-based antioxidant (A), the naphthylamine-based antioxidant (B), and the phosphorus-containing phenolic antioxidant The total content of (C) of phosphorus-free phenolic antioxidant (D) [(D)/{(A)+(B)+(C)}] should be 0.50~10.0 in terms of mass ratio, which is relatively The optimal range is 0.70~8.0, and the more optimal range is 0.80~6.0.

＜Additives for lubricating oil＞ The lubricating oil composition of this embodiment may also contain lubricating oil additives other than components (A) to (D) within a range that does not impair the effects of the present invention. Examples of additives for lubricating oil include extreme pressure agents, cleaning and dispersing agents, pour point depressants, viscosity index improvers, rust inhibitors, metal deactivators, defoaming agents and friction modifiers. These lubricating oil additives may be used individually by one type, or two or more types may be used in combination.

[Physical properties of lubricating oil composition] The flash point of the lubricating oil composition of this embodiment is preferably 250°C or higher, preferably 260°C or higher, more preferably 270°C or higher, still more preferably 280°C or higher. In this specification, the flash point refers to the value measured using the Kirschner open cup (COC) method in compliance with JIS K2265-4:2007.

[Production method of lubricating oil composition] The method of producing the lubricating oil composition of this embodiment is not particularly limited. For example, the manufacturing method of the lubricating oil composition of this embodiment includes combining a lubricating oil base oil (X), a diphenylamine-based antioxidant (A), a naphthylamine-based antioxidant (B), and a phosphorus-containing phenolic antioxidant (C). ) to carry out the mixing step, and the aforementioned lubricating base oil (X) meets the following requirements (1)~(4): ． Requirement (1): Viscosity index is above 120; . Requirement (2): % _CP obtained by ring analysis (ndM method) is 85 or more; . Requirement (3): The density at 15℃ is below 0.835g/ ^cm3 ; . Requirement (4): The kinematic viscosity at 40°C is 28.8 mm ² /s or more; and the following steps are included: The content ratio of the aforementioned naphthylamine antioxidant (B) and the aforementioned diphenylamine antioxidant (A) [(B )/(A)] is adjusted to a mass ratio of 2.0 or more, and the content ratio of the phosphorus-containing phenolic antioxidant (C) and the naphthylamine antioxidant (B) [(C)/(B)] Adjust to a mass ratio of 0.15 or less.

If necessary, the manufacturing method may further include the step of blending a phosphorus-free phenolic antioxidant (D). In addition, the manufacturing method may further include the step of blending the above lubricating oil additives if necessary. The method of mixing each component is not particularly limited, and an example is a method of blending each component into lubricating base oil (X). In addition, each component may be mixed with a diluting oil or the like to form a solution (dispersion). After blending the ingredients, it is advisable to stir them using known methods to evenly disperse them. In addition, ideal aspects of the lubricating base oil (X), component (A), component (B), component (C), and component (D) are as described above. In addition, the blending amounts and blending ratios of the lubricating base oil (X), component (A), component (B), component (C), and component (D) are preferably set to correspond to the above-mentioned lubricating base oil (X). ), the ideal content and blending ratio of component (A), component (B), component (C) and component (D).

[Use of lubricating oil composition] The lubricating oil composition of this embodiment is suitable as an industrial equipment oil. The industrial equipment oil should include: hydraulic operating oil; turbine oil; compressor oils such as rotary air compressor oil and reciprocating air compressor oil; working machine oil; gear oil, etc. Preferred examples include: turbine oil ; Compressor oils such as rotary air compressor oil and reciprocating air compressor oil, preferably turbine oil. Therefore, this embodiment provides a method of using the above lubricating oil composition as hydraulic oil, turbine oil, compressor oil, machine oil, or gear oil. Furthermore, this embodiment provides a method of using the lubricating oil composition as turbine oil or compressor oil. Furthermore, this embodiment provides a method of using the above lubricating oil composition as turbine oil.

[Flash point enhancer] This embodiment also provides the following flash point improving agent for lubricating base oil. A flash point increaser for lubricating oil base oil, containing diphenylamine antioxidant (A), naphthylamine antioxidant (B) and phosphorus-containing phenolic antioxidant (C), and The content ratio [(B)/(A)] of naphthylamine-based antioxidant (B) and diphenylamine-based antioxidant (A) is 2.0 or more in terms of mass ratio, The content ratio [(C)/(B)] of the phosphorus-containing phenolic antioxidant (C) and the naphthylamine antioxidant (B) is 0.15 or less in terms of mass ratio.

From the viewpoint of making it easier to further increase the flash point of the lubricating base oil, it is preferable that the flash point increasing agent for lubricating base oil further contains a phosphorus-free phenolic antioxidant (D).

The above-mentioned flash point increasing agent for lubricating base oil is particularly suitable for increasing the flash point of lubricating base oil (X) that meets the following requirements (1) to (4). ． Requirement (1): Viscosity index is above 120. ． Requirement (2): %C _P obtained by ring analysis (ndM method) is 85 or more. ． Requirement (3): The density at 15°C is 0.835g/ ^cm3 or less. ． Requirement (4): The kinematic viscosity at 40°C is 28.8mm ² /s or above.

In addition, in the flash point improver for lubricating base oil according to this embodiment, the ideal aspects of the lubricating base oil (X), component (A), component (B), component (C) and component (D) are as follows: above. Furthermore, in the flash point improving agent for lubricating base oil of this embodiment, the ideal content ratio of the lubricating base oil (X), component (A), component (B), component (C), and component (D) is as follows: above.

The flash point increaser for lubricating base oil according to this embodiment can increase the flash point of the lubricating base oil (X) whose flash point is in the range of 235°C or higher (preferably 240°C or higher). It is ideal to increase the flash point of the lubricating base oil (X). 10°C or above, preferably 15°C or above.

[Method for improving flash point] This embodiment provides a method for improving the flash point of lubricating oil base oil, which is to blend the lubricating oil base oil (X) that meets the following requirements (1) to (4) with the above flash point increasing method. Agent to increase the flash point of lubricating base oil (X). ． Requirement (1): Viscosity index is above 120. ． Requirement (2): %C _P obtained by ring analysis (ndM method) is 85 or more. ． Requirement (3): The density at 15°C is 0.835g/ ^cm3 or less. ． Requirement (4): The kinematic viscosity at 40°C is 28.8mm ² /s or above.

In addition, in the method for improving the flash point of a lubricating base oil according to this embodiment, the ideal aspects of the lubricating base oil (X), component (A), component (B), component (C), and component (D) are as follows: above. Furthermore, in the method for improving the flash point of a lubricating base oil according to this embodiment, the ideal content ratios of the lubricating base oil (X), component (A), component (B), component (C), and component (D) are as follows: above.

According to the method of increasing the flash point of a lubricating base oil according to this embodiment, the flash point of the lubricating base oil (X) can be increased, for example, in the range of a flash point of 235°C or higher (preferably 240°C or higher). It is ideal to increase the flash point of the lubricating base oil (X). 10°C or above, preferably 15°C or above.

[composition] Furthermore, this embodiment also provides the following composition. A composition containing diphenylamine antioxidant (A), naphthylamine antioxidant (B) and phosphorus-containing phenolic antioxidant (C), and The content ratio [(B)/(A)] of naphthylamine-based antioxidant (B) and diphenylamine-based antioxidant (A) is 2.0 or more in terms of mass ratio, The content ratio [(C)/(B)] of the phosphorus-containing phenolic antioxidant (C) and the naphthylamine antioxidant (B) is 0.15 or less in terms of mass ratio. In addition, in the composition of this embodiment, ideal aspects of the lubricating base oil (X), component (A), component (B), component (C), and component (D) are as described above. Moreover, in the composition of this embodiment, the ideal content ratio of the lubricating base oil (X), component (A), component (B), component (C), and component (D) is as described above. In addition, this embodiment also provides a method of increasing the flash point of the lubricating base oil (X) using the above composition. Furthermore, this embodiment also provides a use of the above composition, which is used to increase the flash point of the lubricating base oil (X). According to the method and use of this embodiment, for example, the flash point of the lubricating base oil (X) whose flash point is in the range of 235°C or higher (preferably 240°C or higher) can be increased, preferably by 10°C or higher, preferably 10°C or higher. is above 15℃.

[Aspect of the present invention provided] An aspect of the present invention provides the following [1] to [11]. [1] A lubricating oil composition containing a lubricating oil base oil (X), a diphenylamine-based antioxidant (A), a naphthylamine-based antioxidant (B), and a phosphorus-containing phenolic antioxidant (C), and the aforementioned lubricating oil composition Oil-based oil (X) meets the following requirements (1)~(4): ． Requirement (1): Viscosity index is above 120; . Requirement (2): % _CP obtained by ring analysis (ndM method) is 85 or more; . Requirement (3): The density at 15℃ is below 0.835g/ ^cm3 ; . Requirement (4): The kinematic viscosity at 40°C is 28.8 mm ² /s or more; the content ratio of the aforementioned naphthylamine antioxidant (B) and the aforementioned diphenylamine antioxidant (A) [(B)/(A) ] is 2.0 or more in mass ratio, and the content ratio [(C)/(B)] of the phosphorus-containing phenolic antioxidant (C) and the naphthylamine antioxidant (B) is 0.15 or less in mass ratio. [2] The lubricating oil composition of [1] above, wherein the diphenylamine-based antioxidant (A) contains a compound (A1) represented by the following general formula (a1): [Chemical Formula 5] [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 antioxidant (B) contains a compound (B1) represented by the following general formula (b1): [Chemical Formula 6] [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 [1] to [3] above, wherein the phosphorus-containing phenolic antioxidant (C) contains a compound (C1) represented by the following general formula (c1): [ Chemical formula 7] [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; R ^c5 is an alkylene group having 1 to 5 carbon atoms]. [5] The lubricating oil composition according to any one of the above [1] to [4], which further contains a phosphorus-free phenolic antioxidant (D). [6] The lubricating oil composition of [5] above, wherein the phosphorus-free phenolic antioxidant (D) contains a compound (D1) represented by the following general formula (d1): [Chemical Formula 8] [In the above formula (d1), R ^d1 is an alkylene group having 1 to 5 carbon atoms; R ^d2 is an alkyl group having 1 to 25 carbon atoms]. [7] The lubricating oil composition according to any one of [1] to [6] above, wherein based on the total amount of the lubricating oil composition, the diphenylamine-based antioxidant (A), the naphthylamine-based antioxidant The total content of the antioxidant (B) and the aforementioned phosphorus-containing phenolic antioxidant (C) is 0.30% by mass or more. [8] A flash point increaser for lubricating base oils, containing a diphenylamine antioxidant (A), a naphthylamine antioxidant (B), and a phosphorus-containing phenolic antioxidant (C), and the naphthylamine antioxidant is The content ratio [(B)/(A)] of the oxidizing agent (B) and the aforementioned diphenylamine-based antioxidant (A) is 2.0 or more in terms of mass ratio, and the aforementioned phosphorus-containing phenolic antioxidant (C) and the aforementioned naphthylamine-based antioxidant are The content ratio [(C)/(B)] of the antioxidant (B) is 0.15 or less in terms of mass ratio. [9] The flash point increaser for lubricating base oils as described in [8] above, which further contains a phosphorus-free phenolic antioxidant (D). [10] The flash point increasing agent as described in [8] or [9] above, wherein the lubricating base oil is a lubricating base oil (X) that satisfies the following requirements (1) to (4), and the flash point is increased The agent system is for use in the aforementioned lubricating oil base oil (X): ． Requirement (1): Viscosity index is above 120; . Requirement (2): % _CP obtained by ring analysis (ndM method) is 85 or more; . Requirement (3): The density at 15℃ is below 0.835g/ ^cm3 ; . Requirement (4): The kinematic viscosity at 40°C is 28.8mm ² /s or above. [11] A method for increasing the flash point of lubricating oil base oil, which is to blend any one of the above [8] to [10] with lubricating oil base oil (X) that meets the following requirements (1) to (4) A flash point increasing agent is used to increase the flash point of the aforementioned lubricating oil base oil (X): ． Requirement (1): Viscosity index is above 120; . Requirement (2): % _CP obtained by ring analysis (ndM method) is 85 or more; . Requirement (3): The density at 15℃ is below 0.835g/ ^cm3 ; . Requirement (4): The kinematic viscosity at 40°C is 28.8mm ² /s or above.

Example The present invention is specifically illustrated using the following examples. However, the present invention is not limited to the following examples.

[Measurement method of various physical property values] The various properties of the base oil used in each example and each comparative example were measured in accordance with the following procedures. (1) The 40°C dynamic viscosity and viscosity index are measured and calculated in accordance with JIS K2283:2000. (2) % _CP is calculated by ring analysis (ndM method) in accordance with ASTM D3238:1995. (3) The density at 15°C is measured in accordance with JIS K 2249-1: 2011 (Crude oil and petroleum products - Density determination method - Part 1: Vibration method).

[Examples 1 to 7, Comparative Examples 1 to 2, Reference Examples 1 to 3] The following components were mixed to prepare lubricating oil compositions having the compositions shown in Tables 2 to 4. In addition, the numerical unit of the blend composition in Tables 2 to 4 is "mass %".

＜Lubricating base oil (X)＞ In this embodiment, lubricating base oil (X1) and lubricating base oil (X2) are used, which are base oils belonging to Group III of 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 lubricating base oil (X1) and the lubricating base oil (X2) used in Reference Example 2. Table 1 also shows the properties of the lubricating base oil (X') used in Reference Example 3. Lubricant base oil (X’) is a base oil belonging to Group II of API (American Petroleum Institute).

[Table 1]

<Diphenylamine-based antioxidant (A)> Dioctyldiphenylamine is used. Dioctyldiphenylamine is a compound in which R ^a1 and R ^a2 in the general formula (a1) are octyl groups, and na1=na2=1, which is consistent with compound (A1).

<Naphthylamine-based antioxidant (B)> Octylphenyl-1-naphthylamine was used. In octylphenyl-1-naphthylamine, R ^b1 in the general formula (b1) is octyl, and nb1=1, which is consistent with compound (B1).

<Phosphorus-containing phenolic antioxidant (C)> Use 3,5-di-tertiary butyl-4-hydroxybenzylisophosphite ethyl ester. 3,5-Di-tertiary butyl-4-hydroxybenzylisophosphite ethyl ester in the general formula (c1), R ^c1 and R ^c2 are tertiary butyl, R ^c3 and R ^c4 are ethyl, R ^c5 is methylene, consistent with compound (C1).

<Phosphorus-free phenolic antioxidant (D)> Use 3,5-bis(1,1-dimethylethyl)-4-hydroxyphenylpropionic acid alkyl ester. 3,5-Bis(1,1-dimethylethyl)-4-hydroxyphenylpropionic acid alkyl ester is a general formula (d1) in which R ^d1 is an alkylene group with a carbon number of 2, and R ^d2 is a carbon number. The alkyl group of 8 is consistent with compound (D1).

＜Evaluation＞ Before the test, the flash points of the lubricating base oils of Reference Examples 1 to 3 were measured. In this example, the flash point was measured using the Kirschner open cup (COC) method in compliance 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 in the same manner. Furthermore, for the lubricating oil compositions of Examples 1 to 3 and Comparative Example 1, the flash point increase range relative to the flash point of the lubricating oil base oil (X) of Reference Example 1 was calculated. Moreover, regarding the lubricating oil compositions of Examples 4 to 7, the flash point increase range with respect to the flash point of the lubricating oil base oil (X) of Reference Example 2 was calculated. For the lubricating oil composition of Comparative Example 2, the flash point increase range with respect to the flash point of the lubricating oil base oil (X') of Reference Example 3 was calculated. In addition, those with a flash point rise of 10°C or more are considered qualified. The evaluation results are shown in Tables 2 to 4.

[Table 2]

[table 3]

[Table 4]

As can be seen from Table 2, the flash point of the lubricating oil compositions of Examples 1 to 3 is increased by more than 10°C from the lubricating oil base oil of Reference Example 1, which is the benchmark. In contrast, it can be seen that in the lubricating oil composition of Comparative Example 1, the content ratio [(B)/(A)] of the naphthylamine-based antioxidant (B) and the diphenylamine-based antioxidant (A) is less than 2.0 in terms of mass ratio. Furthermore, the content ratio [(C)/(B)] of the phosphorus-containing phenolic antioxidant (C) and the naphthylamine antioxidant (B) is greater than 0.15 in terms of mass ratio, so its flash point does not follow the reference as a benchmark. The lubricating base oil in Example 1 was fully increased. Moreover, as can be seen from Table 3, the flash points of the lubricating oil compositions of Examples 4 to 7 are increased by more than 10°C from the lubricating oil base oil of Reference Example 2, which is the standard. In addition, as can be seen from Table 4, although the lubricating oil composition of Comparative Example 2 has the same antioxidant structure as the lubricating oil composition of Example 7, its flash point is still different from that of the lubricating oil of Reference Example 3. The base oil is fully improved. It can be seen from this that even if the lubricating base oil (X') that does not meet the requirements (1) to (4) is blended with diphenylamine-based antioxidant (A), naphthylamine-based antioxidant (B), and phosphorus-containing phenol-based Antioxidant (C) and phosphorus-free phenolic antioxidant (D), and adjust the content ratio [(B)/(A)] of naphthylamine antioxidant (B) and diphenylamine antioxidant (A) In order to be 2.0 or more in terms of mass ratio, the content ratio [(C)/(B)] of the phosphorus-containing phenolic antioxidant (C) and the naphthylamine-based antioxidant (B) is adjusted to 0.15 in terms of mass ratio. Below this, the flash point cannot be sufficiently improved.

(without)

Claims (11)

A lubricating oil composition containing a lubricating oil base oil (X), a diphenylamine-based antioxidant (A), a naphthylamine-based antioxidant (B), and a phosphorus-containing phenolic antioxidant (C), and the aforementioned lubricating oil base oil (X) Meet the following requirements (1)~(4): ． Requirement (1): Viscosity index is above 120; . Requirement (2): % _CP obtained by ring analysis (ndM method) is 85 or more; . Requirement (3): The density at 15℃ is below 0.835g/ ^cm3 ; . Requirement (4): The kinematic viscosity at 40°C is 28.8 mm ² /s or more; the content ratio of the aforementioned naphthylamine antioxidant (B) and the aforementioned diphenylamine antioxidant (A) [(B)/(A) ] is 2.0 or more in mass ratio, and the content ratio [(C)/(B)] of the phosphorus-containing phenolic antioxidant (C) and the naphthylamine antioxidant (B) is 0.15 or less in mass ratio. The lubricating oil composition of claim 1, wherein the diphenylamine antioxidant (A) includes a compound (A1) represented by the following general formula (a1): [Chemical Formula 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]. The lubricating oil composition of claim 1 or 2, wherein the naphthylamine antioxidant (B) includes a compound (B1) represented by the following general formula (b1): [Chemical Formula 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]. The lubricating oil composition according to any one of claims 1 to 3, wherein the phosphorus-containing phenolic antioxidant (C) includes a compound (C1) represented by the following general formula (c1): [Chemical Formula 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; R ^c5 is an alkylene group having 1 to 5 carbon atoms]. The lubricating oil composition according to any one of claims 1 to 4, which further contains a phosphorus-free phenolic antioxidant (D). The lubricating oil composition of claim 5, wherein the phosphorus-free phenolic antioxidant (D) contains a compound (D1) represented by the following general formula (d1): [Chemical Formula 4] [In the above formula (d1), R ^d1 is an alkylene group having 1 to 5 carbon atoms; R ^d2 is an alkyl group having 1 to 25 carbon atoms]. The lubricating oil composition according to any one of claims 1 to 6, wherein based on the total amount of the lubricating oil composition, the aforementioned diphenylamine antioxidant (A), the aforementioned naphthylamine antioxidant (B) and The total content of the aforementioned phosphorus-containing phenolic antioxidant (C) is 0.30% by mass or more. A flash point increaser for lubricating oil base oil, containing diphenylamine antioxidant (A), naphthylamine antioxidant (B) and phosphorus-containing phenolic antioxidant (C), and The content ratio [(B)/(A)] of the aforementioned naphthylamine-based antioxidant (B) and the aforementioned diphenylamine-based antioxidant (A) is 2.0 or more in terms of mass ratio, The content ratio [(C)/(B)] of the phosphorus-containing phenolic antioxidant (C) and the naphthylamine antioxidant (B) is 0.15 or less in terms of mass ratio. For example, the flash point enhancer for lubricating oil base oil in claim 8 further contains a phosphorus-free phenolic antioxidant (D). Such as the flash point increasing agent of claim 8 or 9, wherein the aforementioned lubricating oil base oil is a lubricating oil base oil (X) that meets the following requirements (1) to (4), and the aforementioned flash point increasing agent is for use in the aforementioned Lubricant base oil (X): ． Requirement (1): Viscosity index is above 120; . Requirement (2): % _CP obtained by ring analysis (ndM method) is 85 or more; . Requirement (3): The density at 15℃ is below 0.835g/ ^cm3 ; . Requirement (4): The kinematic viscosity at 40°C is 28.8mm ² /s or above. A method for increasing the flash point of lubricating oil base oil, which is to blend the lubricating oil base oil (X) that meets the following requirements (1) to (4) with a flash point increasing agent according to any one of claims 8 to 10. To increase the flash point of the aforementioned lubricant base oil (X): ． Requirement (1): Viscosity index is above 120; . Requirement (2): % _CP obtained by ring analysis (ndM method) is 85 or more; . Requirement (3): The density at 15℃ is below 0.835g/ ^cm3 ; . Requirement (4): The kinematic viscosity at 40°C is 28.8mm ² /s or above.