Lubricating oil composition

Abstract

To provide a lubricating oil composition excellent in oxidation stability.SOLUTION: A lubricating oil composition includes a base oil and an antioxidant containing a phenolic compound, a naphthylamine compound, a diphenylamine compound, and a phosphite compound. In the lubricating oil composition, a ratio of a content of the phenolic compound to a content of the whole antioxidant by mass is 0.05 or more and 0.30 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a lubricating oil composition. [Background technology]

[0002] Lubricating oil compositions used in equipment such as turbines, compressors, and hydraulic systems are susceptible to oxidative degradation, especially in high-temperature environments. Therefore, various developments are being undertaken to improve the oxidative stability of these lubricating oil compositions.

[0003] For example, Patent Document 1 proposes "a lubricating oil composition for rotary gas compressors characterized by containing a lubricating oil base oil with a viscosity index of 120 or higher, phenyl-α-naphthylamine or a derivative thereof, p,p'-dialkyldiphenylamine or a derivative thereof, and a viscosity index improver." [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2011-162629 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] In recent years, there has been a growing demand for further improvements in the oxidation stability of lubricating oil compositions. The object of this disclosure is to provide a lubricating oil composition that exhibits excellent oxidation stability. [Means for solving the problem]

[0006] The means to solve the above problems include the following: <1> Base oil and, It contains antioxidants including phenol compounds, naphthylamine compounds, diphenylamine compounds, and phosphite compounds, A lubricating oil composition in which the ratio of the content of the phenolic compound to the content of the entire antioxidant is 0.05 or more and 0.30 or less on a mass basis. <2> The lubricating oil composition according to <1>, wherein the content of the phenolic compound with respect to the entire lubricating oil composition is 0.05% by mass or more and 0.5% by mass or less. <3> The lubricating oil composition according to <1> or <2>, wherein the phenolic compound is a compound represented by the following formula (A).

[0007]

Chemical formula

[0008] (In the above formula (A), R1 is an alkylene group having 1 to 4 carbon atoms, and R2 is an alkyl group having 1 to 16 carbon atoms.)

[0009] <4> The lubricating oil composition according to any one of <1> to <3>, wherein the phosphite compound is a compound represented by the following formula (D).

[0010]

Chemical formula

[0011] (In formula (D), R6 and R7 each independently represent an alkyl group having 1 to 12 carbon atoms.)

Advantages of the Invention

[0012] According to the present disclosure, a lubricating oil composition having excellent oxidation stability is provided.

Modes for Carrying Out the Invention

[0013] Hereinafter, embodiments which are an example of the present disclosure will be described. These descriptions and examples are illustrative of the embodiments and do not limit the scope of the invention. In numerical ranges described stepwise within this specification, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described stepwise. Furthermore, in numerical ranges described within this specification, the upper or lower limit of that range may be replaced with the values ​​shown in the examples. In this specification, the symbol "~" representing a numerical range indicates a range that includes the values ​​specified as its upper and lower limits, respectively. Furthermore, if only the unit is specified for the upper limit of a numerical range represented by "~", it means that the lower limit also has the same unit.

[0014] Each component may contain multiple types of the relevant substance. When referring to the amount of each component in a composition, if there are multiple substances corresponding to each component in the composition, unless otherwise specified, it refers to the total amount of those multiple substances present in the composition.

[0015] <Lubricating oil composition> The lubricating oil composition according to this disclosure comprises a base oil and an antioxidant containing a phenol compound, a naphthylamine compound, a diphenylamine compound, and a phosphite compound, wherein the ratio of the content of the phenol compound to the total content of the antioxidant is 0.05 or more and 0.30 or less by mass.

[0016] The lubricating oil composition according to this disclosure exhibits excellent oxidation stability due to the above-described composition. The reason for this is not entirely clear, but it is presumed that the combination of phenol compounds, naphthylamine compounds, diphenylamine compounds, and phosphite compounds as antioxidants improves the antioxidant capacity of the antioxidants through the interaction of each compound. Furthermore, it is presumed that setting the ratio of the phenol compound content to the total antioxidant content to 0.05 or more and 0.30 or less by mass strengthens the interaction of each compound, thereby further improving the antioxidant capacity of the antioxidants. The lubricating oil composition relating to this disclosure will be described in detail below.

[0017] (Base oil) The lubricating oil composition according to the present disclosure contains a base oil. The base oil is not particularly limited, and examples thereof include mineral oil-based lubricating oil base oils, synthetic lubricating oil base oils, and mixtures thereof. Examples of the mineral oil-based lubricating oil base oil include those obtained by appropriately combining refining methods such as solvent refining, hydrorefining, hydrocracking refining, and hydrodewaxing of the lubricating oil fraction of crude oil. Examples of the synthetic lubricating oil base oil include α-olefin oligomers; base oils produced from wax obtained by Fischer-Tropsch synthesis using natural gas such as methane as a raw material; and the like.

[0018] [[ID=HID=10]]The content of the base oil is preferably 97% by mass to 99.5% by mass, and more preferably 98% by mass to 99.5% by mass, based on the total mass of the composition.

[0019] The base oil has a kinematic viscosity at 40 °C (also referred to as the 40 °C kinematic viscosity) of 2 mm 2 / s to 500 mm 2 / s, preferably 2 mm 2 / s to 60 mm 2 / s, more preferably. When the kinematic viscosity of the base oil at 40 °C is 2 mm 2 / s or more, lubricity as a lubricating oil can be obtained, and when it is 500 mm 2 / s or less, the flow resistance and stirring resistance are reduced, and power loss and the like are suppressed.

[0020] The base oil has a kinematic viscosity at 100 °C (also referred to as the 100 °C kinematic viscosity) of 1 mm [[ID=3HID=33]] 2 / s to 20 mm 2 / s, preferably 2 mm 2 / s to 10 mm 2 / s, more preferably. The 40 °C kinematic viscosity and the 100 °C kinematic viscosity are values measured based on the JIS K 2283:2000 kinematic viscosity test method.

[0021] (Antioxidant) The lubricating oil composition according to the present disclosure contains an antioxidant. The antioxidants include phenol compounds, naphthylamine compounds, diphenylamine compounds, and phosphite compounds.

[0022] The content of antioxidants relative to the total mass of the lubricating oil composition is preferably 0.1% by mass or more and 5% by mass or less, more preferably 0.5% by mass or more and 2% by mass or less, and even more preferably 1.0% by mass or more and 1.5% by mass or less.

[0023] -Phenol compounds- A phenolic compound is a compound that has a benzene ring and a phenolic hydroxyl group. From the viewpoint of improving the oxidation stability of the lubricating oil composition, the phenol compound is preferably a hindered phenol compound.

[0024] Here, a hindered phenol compound is a phenol compound in which a hydrogen atom on the benzene ring is substituted with a bulky substituent such as a tert-butyl group. The bulky substituent included in the hindered phenol compound is preferably a tert-butyl group. From the viewpoint of improving the oxidative stability of the lubricating oil composition, the number of tert-butyl groups bonded to the benzene ring of the hindered phenol compound is preferably one to three per molecule of the hindered phenol compound, more preferably one or two, and even more preferably two. From the viewpoint of improving the oxidation stability of the lubricating oil composition, it is preferable that two tert-butyl groups bonded to the benzene ring of the hindered phenol compound are present at the ortho position of the phenolic hydroxyl group.

[0025] From the viewpoint of improving the oxidation stability of the lubricating oil composition, it is preferable that the hindered phenol compound has a substituent at the para position of the phenolic hydroxyl group. Substituents located at the para position of a phenolic hydroxyl group include, for example, linear or branched aliphatic hydrocarbon groups; aromatic hydrocarbon groups; and -R A1-COO-R A2 The group represented by (R A1 R is an alkylene group, A2 Examples include: (is an alkyl group); From the viewpoint of improving the oxidation stability of lubricating oil compositions, the substituent located at the para position of the phenolic hydroxyl group of a hindered phenol compound is -R A1 -COO-R A2 It is preferable that the functional group is represented by .

[0026] The phenol compound is preferably a hindered phenol compound represented by the following formula (A).

[0027] [ka]

[0028] (In formula (A) above, R1 is a linear or branched alkylene group having 1 to 5 carbon atoms, and R2 is a linear or branched alkyl group having 1 to 25 carbon atoms.)

[0029] By using a hindered phenol compound represented by formula (A) above as the phenol compound, the oxidation stability of the lubricating oil composition is further improved. The reason for this is not entirely clear, but it is presumed that the alkyl group represented by R2 in formula (A) above strengthens the interaction with naphthylamine compounds and diphenylamine compounds, thereby further improving the antioxidant capacity.

[0030] Specific examples of alkylene groups represented by R1 include methylene groups, ethylene groups, n-propylene groups, and n-butylene groups.

[0031] From the viewpoint of improving the oxidation stability of the lubricating oil composition, R1 is preferably an alkylene group having 1 to 4 carbon atoms, more preferably an alkylene group having 1 to 3 carbon atoms, and even more preferably an alkylene group having 1 or 2 carbon atoms.

[0032] Specific examples of alkyl groups represented by R2 include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, tert-butyl group, n-pentyl group, isopentyl group, neopentyl group, tert-pentyl group, 2-methylbutyl group, n-hexyl group, isohexyl group, 3-methylpentyl group, ethylbutyl group, n-heptyl group, 2-methylhexyl group, n-octyl group, 2-ethylhexyl group, 3-methylheptyl group, n-nonyl group, methyloctyl group, ethylheptyl group, n-decyl group, n-undecyl group, n-dodecyl group, and n-tetradecyl group.

[0033] From the viewpoint of improving the oxidation stability of the lubricating oil composition, R2 is preferably an alkyl group having 2 to 20 carbon atoms, more preferably an alkyl group having 4 to 15 carbon atoms, and even more preferably an alkyl group having 6 to 10 carbon atoms.

[0034] Table 1 below illustrates, but is not limited to, specific examples of hindered phenol compounds represented by general formula (A). In Table 1, R1 and R2 represent specific examples of R1 and R2 in general formula (A).

[0035] [Table 1]

[0036] The phenolic compound may be included individually or in combination of two or more types.

[0037] It is preferable that the content of the phenol compound relative to the entire lubricating oil composition is 0.05% by mass or more and 0.5% by mass or less.

[0038] By setting the content of phenol compounds in the lubricating oil composition to 0.05% by mass or more and 0.5% by mass or less, the oxidation stability of the lubricating oil composition is further improved. The reason for this is not entirely clear, but it is presumed that this is because it strengthens the interaction between phenol compounds and naphthylamine compounds and diphenylamine compounds, thereby further improving the antioxidant capacity.

[0039] The content of the phenol compound in the lubricating oil composition is more preferably 0.07% by mass or more and 0.45% by mass or less, and even more preferably 0.10% by mass or more and 0.40% by mass or less.

[0040] The lubricating oil composition relating to this disclosure has a ratio of the content of phenolic compounds to the total content of antioxidants (i.e., "content of phenolic compounds / total content of antioxidants") of 0.05 or more and 0.30 or less by mass.

[0041] The ratio of the phenol compound content to the total antioxidant content is more preferably 0.07 to 0.30 by mass, even more preferably 0.08 to 0.28, and particularly preferably 0.08 to 0.27.

[0042] -Naphthylamine compounds- Naphthylamine compounds are amines that contain a naphthalene ring. Examples of naphthylamine compounds include those represented by the following general formula (B).

[0043] [ka]

[0044] In general formula (B), R3 represents a linear or branched alkyl group having 1 to 16 carbon atoms.

[0045] Specific examples of linear or branched alkyl groups represented by R3 include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, tert-butyl group, n-pentyl group, isopentyl group, neopentyl group, tert-pentyl group, 2-methylbutyl group, n-hexyl group, isohexyl group, 3-methylpentyl group, ethylbutyl group, n-heptyl group, 2-methylhexyl group, n-octyl group, tert-octyl group, 2-ethylhexyl group, 3-methylheptyl group, n-nonyl group, methyloctyl group, ethylheptyl group, n-decyl group, n-undecyl group, n-dodecyl group, and n-tetradecyl group.

[0046] R3 is preferably a linear or branched alkyl group having 4 to 8 carbon atoms.

[0047] Examples of naphthylamine compounds include octylated phenyl α-naphthylamine (compounds in which R3 in general formula (B) is an octyl group).

[0048] The naphthylamine compound may be included alone or in combination of two or more types.

[0049] The ratio of the naphthylamine compound content to the total antioxidant content (i.e., "naphthylamine compound content / total antioxidant content") is preferably 0.05 or more and 0.50 or less by mass, more preferably 0.10 or more and 0.35 or less, and even more preferably 0.15 or more and 0.31 or less.

[0050] -Diphenylamine compounds- Diphenylamine compounds are amines that have an amino group bonded to two benzene rings. Furthermore, the two benzene rings in the diphenylamine compound are each independently bonded to the amino group (in other words, the two benzene rings exist in an unfused state).

[0051] Examples of diphenylamine compounds include those represented by the following general formula (C).

[0052] [ka]

[0053] In general formula (C), R4 and R5 each independently represent a hydrogen atom or a linear or branched alkyl group having 1 to 16 carbon atoms. R4 and R5 may be the same or different.

[0054] Specific examples of linear or branched alkyl groups represented by R4 and R5 include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, tert-butyl group, n-pentyl group, isopentyl group, neopentyl group, tert-pentyl group, 2-methylbutyl group, n-hexyl group, isohexyl group, 3-methylpentyl group, ethylbutyl group, n-heptyl group, 2-methylhexyl group, n-octyl group, isooctyl group, tert-octyl group, 2-ethylhexyl group, 3-methylheptyl group, n-nonyl group, methyloctyl group, ethylheptyl group, n-decyl group, n-undecyl group, n-dodecyl group, and n-tetradecyl group.

[0055] R4 and R5 are preferably hydrogen atoms or linear or branched alkyl groups having 3 to 9 carbon atoms, and more preferably hydrogen atoms or linear or branched alkyl groups having 4 to 8 carbon atoms.

[0056] Table 2 below shows, but is not limited to, specific examples of diphenylamine compounds represented by general formula (C). In Table 2, R4 and R5 represent specific examples of R4 and R5 in general formula (C).

[0057] [Table 2]

[0058] In Table 2, "butyl group" means "n-butyl group, isobutyl group, or tert-butyl group." In Table 2, the term "octyl group" refers to "n-octyl group, isooctyl group, or tert-octyl group." Furthermore, the substitution positions of R4 and R5 on the benzene ring include all three positions of the amino group: ortho, meta, and para.

[0059] The above-mentioned diphenylamine compounds may be included individually or in combination of two or more types.

[0060] The ratio of the content of the diphenylamine compound to the total content of the antioxidant (i.e., "content of the diphenylamine compound / total content of the antioxidant") is preferably 0.10 or more and 0.80 or less by mass, more preferably 0.20 or more and 0.70 or less, and even more preferably 0.30 or more and 0.60 or less.

[0061] -Phosphite compounds- In this disclosure, "phosphite compound" means a phosphite ester. Any known phosphite compound can be used without any particular limitations. Examples of phosphite compounds include trialkyl esters of phosphite such as tris(2-ethylhexyl-3-mercaptopropionate) phosphite, triphenyl phosphite, trioctadecyl phosphite, tristearyl phosphite, trilauryl trithiophosphite, triisooctyl phosphite, tris(nonylphenyl) phosphite, tricresyl phosphite, and diphenylisodecyl phosphite; dialkyl esters of phosphite; and monoalkyl esters of phosphite.

[0062] Tris(alkylphenyl)phosphite is preferred as the phosphite compound. Examples of tris(alkylphenyl)phosphites include compounds represented by the following formula (D).

[0063] [ka]

[0064] In formula (D), R6 and R7 each independently represent an alkyl group having 1 to 12 carbon atoms. In formula (D), R6 and R7 are preferably alkyl groups having 2 to 6 carbon atoms, from the viewpoint of oxidation stability.

[0065] Examples of alkyl groups represented by R6 and R7 in formula (D) include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, tert-butyl group, n-pentyl group, isopentyl group, neopentyl group, and tert-pentyl group. From the viewpoint of improving the oxidation stability of the lubricating oil composition, the alkyl groups represented by R6 and R7 in formula (D) are preferably tert-butyl groups. From the viewpoint of improving the oxidation stability of the lubricating oil composition, among the tris(alkylphenyl)phosphites represented by formula (D), the compound represented by the following formula (D-1) is preferred.

[0066] [ka]

[0067] The ratio of the phosphite compound content to the total antioxidant content (i.e., "phosphite compound content / total antioxidant content") is preferably 0.05 to 0.50 by mass, more preferably 0.10 to 0.30, and even more preferably 0.12 to 0.20.

[0068] -Other antioxidants- The antioxidant may, if necessary, include other antioxidants other than phenol compounds, naphthylamine compounds, and diphenylamine compounds. Other antioxidants include, for example, phosphorus-based antioxidants other than phosphite compounds (such as zinc dialkyldithiophosphate), sulfur-based antioxidants, and metal-based antioxidants.

[0069] (Other additives) The lubricating oil composition relating to this disclosure may contain other additives in addition to the base oil and antioxidant. Other additives include common lubricant additives such as rust inhibitors, corrosion inhibitors, pour point depressants, extreme pressure additives, metal deactivators, oiliness agents, defoamers, and detergent dispersants.

[0070] Examples of rust inhibitors include aliphatic amines, metal organic sulfonates, metal organic phosphates, alkenyl succinates, and polyhydric alcohol esters. Examples of corrosion inhibitors include benzotriazole compounds, thiadiazole compounds, and imidazole compounds. Examples of pour point depressants include polymethacrylate, polyisobutylene, and polystyrene. Examples of extreme pressure agents include phosphorus-based extreme pressure agents and phosphorothionates. Preferably, phosphorus-based extreme pressure agents include orthophosphate esters, acidic phosphorus esters, amine salts of acidic phosphorus esters, chlorinated phosphorus esters, and phosphite esters. Examples of metal deactivators include benzotriazole or its derivatives. Examples of oily agents include ester oily agents, alcohol oily agents, and ether oily agents. Examples of defoaming agents include acrylate-based defoaming agents such as polyacrylates, and siloxane-based defoaming agents such as alkylpolysiloxanes. Examples of cleaning and dispersing agents include metal-based cleaning agents such as sulfonates, phenates, and salicylates, and ashless dispersing agents such as succinimide.

[0071] <Application> The lubricating oil composition according to this disclosure has excellent oxidation stability and can be suitably used in various compressors, for example. In particular, it is extremely useful as a lubricant for rotary compressors.

[0072] <Method for preparing a lubricating oil composition> The lubricating oil composition can be prepared by mixing a base oil, an antioxidant, and other additives as needed. The mixing order of the base oil, antioxidants, and other additives is not particularly limited, and they may be mixed sequentially with the base oil. [Examples]

[0073] Examples are described below, but the present invention is not limited in any way to these examples.

[0074] <Examples 1-6, Comparative Examples 1-4> Lubricating oil compositions were prepared by mixing base oil, antioxidants, and other additives in the proportions (volume %) or mass %) shown in Table 3 below. Note that the base oil blending ratios in Table 3 represent the ratio of the volume of base oil component 1, base oil component 2, or base oil component 3 to the total volume of base oil. The antioxidant blending ratios in Table 3 represent the ratio of the mass of each compound to the total mass of the lubricating oil composition. The proportions of other additives in Table 3 indicate the ratio of the mass of each other additive to the total mass of the lubricating oil composition. The ratio of the base oil mass to the total mass of the lubricating oil composition is the residue in the lubricating oil composition excluding antioxidants and other additives.

[0075] The following performance evaluations were performed using each of the obtained lubricating oil compositions. The results are shown in Table 3. (Oxidative stability: RPVOT test) The lubricating oil oxidation stability test (RPVOT) was conducted in accordance with the Japanese Industrial Standard JIS K2514-3 (2013). The numbers in the table represent the time (minutes) required for the pressure to drop; a higher number indicates higher oxidation stability. A score of 1400 minutes or more is considered a passing score.

[0076] [Table 3]

[0077] Details of the abbreviations in Table 3 are described below. (Base oil (BO)) • Base oil component 1: Hydrocracked mineral oil (mineral oil-based lubricant base oil) 40℃ kinematic viscosity: 35.11mm 2 / s, 100℃ kinematic viscosity: 6.314mm 2 Viscosity index: 131, Density at 15°C: 0.843 g / cm³ 3 • Base oil component 2: Hydrogenated refined mineral oil (mineral oil-based lubricant base oil) 40℃ kinematic viscosity: 15.46mm 2 / s, 100℃ kinematic viscosity: 3.511mm 2 Viscosity index: 105, Density at 15°C: 0.8517 g / cm³ 3 • Base oil component 3: Hydrogenated refined mineral oil (mineral oil-based lubricant base oil) 40℃ kinematic viscosity: 32.25mm 2 / s, 100℃ kinematic viscosity: 5.577mm 2 Viscosity index: 111, Density at 15°C: 0.8599 g / cm³ 3

[0078] (Antioxidant) • Phenol compounds: Hindered phenol compounds in formula (A) where R1 is a C2 alkylene group and R2 is a C8 alkyl group. Specifically, the hindered phenol compounds shown in formula (A-1) below.

[0079] [ka]

[0080] • Naphthylamine compound: Octylated phenyl-α-naphthylamine Compounds in which R3 in the above general formula (B) is an octyl group • Diphenylamine compounds: Alkylated diphenylamines A mixture of compounds in which R4 and R5 in the above general formula (C) are butyl groups or octyl groups. • Phosphite compound: Tris(2,4-t-butylphenyl)phosphite (i.e., the compound represented by formula (D-1))

[0081] (Other additives) • Pour point depressant • Rust inhibitor ·Metal deactivator • Antifoaming agent

[0082] From the above results, it can be seen that the lubricating oil composition of this embodiment has excellent oxidation stability.

Claims

1. Base oil and, It contains antioxidants including phenol compounds, naphthylamine compounds, diphenylamine compounds, and phosphite compounds, The ratio of the content of the phenol compound to the total content of the antioxidant is 0.05 or more and 0.30 or less by mass. A lubricating oil composition comprising only a hindered phenol compound represented by the following formula (A) as the phenol compound. 【Chemistry 1】 (In formula (A), R １ R is an alkylene group having 1 to 4 carbon atoms, ２ (This refers to an alkyl group having 1 to 16 carbon atoms.)

2. The lubricating oil composition according to claim 1, wherein the content of the phenol compound relative to the entire lubricating oil composition is 0.05% by mass or more and 0.5% by mass or less.

3. The lubricating oil composition according to claim 1 or claim 2, wherein the phosphite compound is a compound represented by the following formula (D). 【Chemistry 2】 (In formula (D), R ６ and R ７ Each of these independently represents an alkyl group having 1 to 12 carbon atoms.

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