Lubricating Oil Composition, Method for Using Same, and Method for Producing Same

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

In recent years, along with the introduction of the concept of carbon neutrality, the utilization of a plant-derived raw material has started to progress. In the field of a lubricating oil, an investigation has been made on the use of a vegetable oil as a base oil.

In, for example, Patent Literature 1, as an animal and vegetable lubricating oil having a low-melting point property, a high viscosity, and high stability, there is a proposal of the following animal and vegetable lubricating oil: the content of an isolated trans-isomer in constituent fatty acids of a triglyceride is 40 mass % or more, and the oil has an iodine value of from 50 to 90.

PTL 1: JP 08-311466 A

In Patent Literature 1, however, only an investigation on a base oil has been made, and an investigation on a lubricating oil composition including additive formulation has not been made.

An object of the present invention is to provide a lubricating oil composition using a vegetable oil as a base oil, the composition being excellent in oxidation stability, and a method of using the composition and a method of producing the composition.

According to the present invention, there are provided the following items [1] to [3].

According to the present invention, the lubricating oil composition using a vegetable oil as a base oil, the composition being excellent in oxidation stability, and the method of using the composition and the method of producing the composition can be provided.

The upper limit values and lower limit values of numerical ranges described herein may be arbitrarily combined. For example, when the range of “from A to B” and the range of “from C to D” are described as numerical ranges, the numerical range of “from A to D” and the numerical range of “from C to B” are also included in the scope of the present invention.

In addition, the numerical range of “from a lower limit value to an upper limit value” described herein means that a physical property value is the lower limit value or more and the upper limit value or less unless otherwise stated.

In addition, in this description, the numerical values of Examples are numerical values that may each be used as an upper limit value or a lower limit value.

A lubricating oil composition of this embodiment includes: a vegetable oil (A); a zinc dithiophosphate (B); and an amine-based antioxidant (C).

The total content of linoleic acid and linolenic acid among constituent fatty acids of the vegetable oil (A) is less than 20 mass % with respect to the total amount of the constituent fatty acids in the vegetable oil (A).

In addition, the content of the amine-based antioxidant (C) is 2.00 mass % or more with respect to the total amount of the lubricating oil composition.

In addition, when the lubricating oil composition further includes a phosphorus-free phenol-based antioxidant (D), the content of the phosphorus-free phenol-based antioxidant (D) is less than 2.00 mass % with respect to the total amount of the lubricating oil composition.

The inventor of the present invention has made extensive investigations with a view to solving the above-mentioned problem. As a result, the inventor has found that the following items (I) to (IV) are important in the preparation of a lubricating oil composition excellent in oxidation stability through use of a vegetable oil as a base oil:

Although the mechanism via which the lubricating oil composition of this embodiment is excellent in oxidation stability has not been elucidated, it is assumed that specific additive formulation satisfying the above-mentioned items (II) to (IV) exhibits an extremely excellent improving effect on the oxidation stability of a vegetable oil having a specific chemical structure satisfying the above-mentioned item (I) to make the oxidation stability of the lubricating oil composition excellent.

In the following description, the “vegetable oil (A),” the “zinc dithiophosphate (B),” the “amine-based antioxidant (C),” and the “phosphorus-free phenol-based antioxidant (D)” are also referred to as “component (A),” “component (B),” “component (C),” and “component (D),” respectively.

Although the lubricating oil composition of this embodiment may be formed only of the “component (A),” the “component (B),” and the “component (C),” the composition may or may not include the “component (D),” and one or more kinds selected from other components except the “component (A),” the “component (B),” the “component (C),” and the “component (D)” to the extent that the incorporation of such component does not deviate from the gist of the present invention.

In the lubricating oil composition of this embodiment, the total content of the “component (A),” the “component (B),” and the “component (C)” is preferably 35 mass % or more, more preferably 40 mass % or more, still more preferably 50 mass % or more, still further more preferably 60 mass % or more, yet still further more preferably 70 mass % or more, even more preferably 80 mass % or more, still even more preferably 90 mass % or more, yet still even more preferably 95 mass % or more with respect to the total amount of the lubricating oil composition.

The respective components for forming the lubricating oil composition of this embodiment are described in detail below.

The lubricating oil composition of this embodiment includes the vegetable oil (A) as a base oil.

The total content of linoleic acid and linolenic acid among the constituent fatty acids of the vegetable oil (A) is less than 20 mass % with respect to the total amount of the constituent fatty acids in the vegetable oil (A) (hereinafter also referred to as “requirement 1”).

When the total content of linoleic acid and linolenic acid is 20 mass % or more, the lubricating oil composition is liable to undergo oxidative degradation, and hence the oxidation stability of the lubricating oil composition is liable to be insufficient.

The term “constituent fatty acids of the vegetable oil (A)” means fatty acids in a compound for forming the vegetable oil in which the fatty acids and glycerin are ester-bonded to each other.

Herein, from the viewpoint of further facilitating an improvement in oxidation stability of the lubricating oil composition, the total content of linoleic acid and linolenic acid is preferably 18 mass % or less, more preferably 16 mass % or less, still more preferably 15 mass % or less with respect to the total amount of the constituent fatty acids in the vegetable oil (A).

In addition, from the viewpoint of further facilitating an improvement in oxidation stability of the lubricating oil composition, the content of oleic acid among the constituent fatty acids of the vegetable oil (A) is preferably 65 mass % or more with respect to the total amount of the constituent fatty acids in the vegetable oil (A) (hereinafter also referred to as “requirement 2”). From the same viewpoint, the content of oleic acid is more preferably 70 mass % or more, still more preferably 75 mass % or more with respect to the total amount of the constituent fatty acids in the vegetable oil (A). In addition, the content of oleic acid is typically less than 85 mass % with respect to the total amount of the constituent fatty acids in the vegetable oil (A).

In addition, from the viewpoint of further facilitating an improvement in oxidation stability of the lubricating oil composition, the content of a saturated fatty acid among the constituent fatty acids of the vegetable oil (A) is preferably 3 mass % or more with respect to the total amount of the constituent fatty acids in the vegetable oil (A) (hereinafter also referred to as “requirement 3”). The content is more preferably 4 mass % or more, still more preferably 5 mass % or more.

Examples of the saturated fatty acid that may be incorporated into the constituent fatty acids of the vegetable oil (A) include one or more kinds selected from the group consisting of: lauric acid; myristic acid; palmitic acid; stearic acid; arachidic acid; behenic acid; and lignoceric acid. A particularly typical example thereof is palmitic acid.

A method of measuring the fatty acid composition of the vegetable oil (A) is, for example, a method including: extracting a lipid from the vegetable oil (A) with an organic solvent; evaporating the organic solvent after the extraction; then preparing a fatty acid methyl ester from the resultant lipid; and subjecting the fatty acid methyl ester to gas chromatography mass spectrometry (GC-MS analysis).

Examples of the vegetable oil (A) to be used in this embodiment include: a raw oil obtained by squeezing and extracting a natural vegetable oil raw material; a refined oil obtained by subjecting the raw oil to various kinds of refining treatment, such as filtration for removing a floating impurity in the raw oil, degumming for removing a phospholipid or the like, deacidification for removing a free fatty acid, decolorization for removing coloring matter, and dewaxing for removing a wax content; and a modified oil and fat obtained by subjecting the refined oil to treatment, such as hardening, fractionation, ester exchange, or hydrogenation.

Specific examples of the vegetable oil (A) include: vegetable oils, such as olive oil, sunflower oil (preferably high-oleic type), Carthamus Tinctorius oil (preferably high-oleic type), safflower oil (preferably high-oleic type), palm oil, palm kernel oil, and coconut oil; and plant-derived base oils such as an estolide ester.

The vegetable oil (A) may be formed only of one kind of vegetable oil, or may be a mixed vegetable oil including two or more kinds of vegetable oils. When the vegetable oil (A) is a mixed vegetable oil, the mixed vegetable oil only needs to satisfy the above-mentioned requirement 1, and the mixed vegetable oil preferably further satisfies at least one of the above-mentioned requirement 2 or 3, and more preferably satisfies all of the above-mentioned requirements 1, 2, and 3.

In the lubricating oil composition of this embodiment, the content of the vegetable oil (A) is preferably 30 mass % or more, more preferably 40 mass % or more, still more preferably 50 mass % or more, still further more preferably 60 mass % or more, yet still further more preferably 70 mass % or more, even more preferably 80 mass % or more, still even more preferably 85 mass % or more, yet still even more preferably 90 mass % or more with respect to the total amount of the lubricating oil composition. In addition, from the viewpoint of room for the blending of additives, such as the component (B) and the component (C), the content of the vegetable oil (A) is preferably 97.9 mass % or less with respect to the total amount of the lubricating oil composition.

The lubricating oil composition of this embodiment includes the zinc dithiophosphate (B).

When the lubricating oil composition of this embodiment is free of the zinc dithiophosphate (B), the lubricating oil composition is liable to undergo oxidative degradation, and hence the oxidation stability of the lubricating oil composition is liable to be insufficient.

The zinc dithiophosphate (B) is preferably, for example, a compound represented by the following general formula (b-1):

That is, the zinc dithiophosphate (B) to be used in this embodiment is preferably a zinc dialkyldithiophosphate.

The cycloalkyl group and the aryl group that may each be selected as each of Rto Rmay be, for example, polycyclic groups, such as a decalyl group and a naphthyl group.

In addition, the monovalent hydrocarbon group that may be selected as each of Rto Rmay be a group having a substituent containing an oxygen atom and/or a nitrogen atom, such as a hydroxy group, a carboxy group, an amino group, an amide group, a nitro group, or a cyano group, or may be partially substituted with a nitrogen atom, an oxygen atom, a halogen atom, or the like. When the monovalent hydrocarbon group is a cycloalkyl group or an aryl group, the group may further have a substituent, such as an alkyl group or an alkenyl group.

Although the alkyl group and the alkenyl group that may each be selected as each of Rto Rmay be linear or branched, from the viewpoint of obtaining more excellent oxidation stability, each of the groups is preferably a primary or secondary group. Among them, a primary alkyl group or a secondary alkyl group is preferred, and a primary alkyl group is more preferred.

That is, the zinc dialkyldithiophosphate to be used in this embodiment is preferably a zinc dialkyldithiophosphate having a primary alkyl group or a secondary alkyl group, or a combination thereof, more preferably a primary zinc dialkyldithiophosphate or a secondary zinc dialkyldithiophosphate, or a combination thereof, still more preferably a primary zinc dialkyldithiophosphate.

From the viewpoint of improving the oxidation stability, when the monovalent hydrocarbon group is an alkyl group, the number of the carbon atoms of the hydrocarbon group represented by any one of Rto Ris preferably 1 or more, more preferably 2 or more, still more preferably 3 or more, and the upper limit thereof is preferably 24 or less, more preferably 18 or less, still more preferably 12 or less, still further more preferably 10 or less. When the monovalent hydrocarbon group is an alkenyl group, the number of the carbon atoms thereof is preferably 2 or more, more preferably 3 or more, and the upper limit thereof is preferably 24 or less, more preferably 18 or less, still more preferably 12 or less, still further more preferably 10 or less. In addition, when the monovalent hydrocarbon group is a cycloalkyl group, the number of the carbon atoms thereof is preferably 5 or more, and the upper limit thereof is preferably 20 or less. When the monovalent hydrocarbon group is an aryl group, the number of the carbon atoms thereof is preferably 6 or more, and the upper limit thereof is preferably 20 or less.

From the viewpoint of facilitating an improvement in oxidation stability of the lubricating oil composition, the content of the zinc dithiophosphate (B) is preferably 0.10 mass % or more, more preferably 0.20 mass % or more, still more preferably 0.30 mass % or more, still further more preferably 0.40 mass % or more, yet still further more preferably 0.50 mass % or more with respect to the total amount of the lubricating oil composition. In addition, from the viewpoint of suppressing sludge deposition, the content is preferably 1.00 mass % or less, more preferably 0.90 mass % or less, still more preferably 0.80 mass % or less. The zinc dithiophosphates (B) may be used alone or in combination thereof.

The lubricating oil composition of this embodiment includes the amine-based antioxidant (C). In addition, in the lubricating oil composition of this embodiment, the content of the amine-based antioxidant (C) needs to be 2.00 mass % or more with respect to the total amount of the lubricating oil composition.

When the content of the amine-based antioxidant (C) is less than 2.00 mass % with respect to the total amount of the lubricating oil composition, the lubricating oil composition is liable to undergo oxidative degradation, and hence the oxidation stability of the lubricating oil composition is liable to be insufficient.

Herein, from the viewpoint of further facilitating an improvement in oxidation stability of the lubricating oil composition, the content of the amine-based antioxidant (C) is preferably 3.00 mass % or more, more preferably 3.50 mass % or more, still more preferably 3.80 mass % or more with respect to the total amount of the lubricating oil composition.

In addition, from the viewpoint of appropriately facilitating an improvement in oxidation stability of the lubricating oil composition while suppressing excessive addition of the amine-based antioxidant (C), the content of the amine-based antioxidant (C) is preferably 8.00 mass % or less, more preferably 7.00 mass % or less, still more preferably 6.00 mass % or less with respect to the total amount of the lubricating oil composition.

An amine-based antioxidant generally used as an antioxidant for a lubricating oil composition may be used as the amine-based antioxidant (C).