Lubricating oil composition

Abstract

To provide a lubricant composition excellent in oxidation stability.SOLUTION: A lubricant composition contains a lubricant base oil, a hindered amine compound with a 2,2,6,6-tetraalkyl-4-piperidyl group, and copper (I) dialkyl dithiophosphate represented by the general formula (1) in the figure. The lubricant base oil comprises a hydrogenated refined mineral oil with a sulfur content of 300 mass ppm or less based on the total amount of the hydrogenated refined mineral oil. [In the formula (1), R1 and R2 each independently represent an alkyl group having 2 to 18 carbon atoms.]SELECTED DRAWING: None

Description

[Technical field]

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

[0002] Conventionally, lubricating oil or grease is used in hydraulic equipment, internal combustion engines, automatic transmissions, etc., to facilitate their operation. In hydraulic equipment such as construction machinery, injection molding machines, and presses, the mechanical elements of the hydraulic equipment are operated under severe conditions due to the increase in speed, pressure, and size. Therefore, the lubricating oil (especially hydraulic oil) used in these hydraulic equipment is required to have excellent lubricating performance that can ensure sufficient mechanical life for a long period of time even when used under high pressure, high speed, high load, and high temperature.

[0003] In order to use hydraulic equipment stably for a long time, stability against oxidation (oxidation stability) is important. Furthermore, from the perspective of reducing environmental impact in recent years, it is important for hydraulic oils to have a long life in order to reduce the amount of waste oil.

[0004] A lubricating oil composition as a hydraulic oil generally contains a lubricating base oil and additives selected according to the required performance as described above. For example, Patent Documents 1 to 3 disclose lubricating oil compositions containing various additives. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 3-045695 [Patent Document 2] JP 2009-197135 A [Patent Document 3] Special Publication No. 2012-516384 Summary of the Invention [Problem to be solved by the invention]

[0006] However, conventional lubricating oil compositions do not have sufficient oxidation stability and there is still room for improvement.

[0007] Therefore, an object of the present invention is to provide a lubricating oil composition that has excellent oxidation stability. [Means for solving the problem]

[0008] As a result of intensive research aimed at achieving the above-mentioned object, the present inventors have found that oxidation stability can be improved by combining a specified hydrorefined mineral oil, a specified copper(I) dialkyldithiophosphate, and a specified hindered amine compound, and have thus completed the present invention.

[0009] One aspect of the present invention relates to a lubricating oil composition. The lubricating oil composition contains a lubricating base oil, a hindered amine compound having a 2,2,6,6-tetraalkyl-4-piperidyl group, and a copper dialkyldithiophosphate (I) represented by the following general formula (1). The lubricating base oil contains a hydrorefined mineral oil having a sulfur content of 300 mass ppm or less based on the total amount of the hydrorefined mineral oil. Lubricating oil compositions containing such components tend to have excellent oxidation stability. [ka] [In formula (1), R 1 and R 2 each independently represents an alkyl group having 2 to 18 carbon atoms.]

[0010] The lubricating oil composition may further contain an organic phosphorus-containing sulfide compound represented by the following general formula (4). [ka] [In formula (4), R 41 , R 42 , R 43 , and R 44 each independently represents an alkyl group having 2 to 18 carbon atoms, and n4 represents 1 to 4.

[0011] In this specification, the sulfur content in the hydrorefined mineral oil means a value measured in accordance with JIS K 2541-6:2013.

[0012] The lubricating oil composition may be, for example, a hydraulic oil. Another aspect of the present invention relates to the use (application) of the composition as a hydraulic oil. Another aspect of the present invention relates to the use (application) of the composition for the manufacture of the composition. The composition contains a lubricating base oil, a hindered amine compound having a 2,2,6,6-tetraalkyl-4-piperidyl group, and a copper(I) dialkyldithiophosphate represented by general formula (1). The lubricating base oil contains a hydrotreated mineral oil having a sulfur content of 300 mass ppm or less in the total amount of the hydrotreated mineral oil. Effect of the Invention

[0013] According to the present invention, there is provided a lubricating oil composition having excellent oxidation stability. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, embodiments of the present invention will be described in detail, however, the present invention is not limited to the following embodiments.

[0015] In this specification, a numerical range indicated using "~" indicates a range including the numerical values ​​described before and after "~" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this specification, the upper limit or lower limit of a numerical range of a certain stage may be replaced with the upper limit or lower limit of a numerical range of another stage. In addition, in the numerical ranges described in this specification, the upper limit or lower limit of the numerical range may be replaced with a value shown in the examples.

[0016] In this specification, unless otherwise specified, the materials exemplified below may be used alone or in combination of two or more within the range corresponding to the conditions. When a plurality of substances corresponding to each component are present in the lubricating oil composition, the content of each component in the lubricating oil composition means the total amount of the plurality of substances present in the lubricating oil composition, unless otherwise specified.

[0017] In this specification, unless otherwise specified, the content of nitrogen in a component containing nitrogen as a constituent element means a value measured by a chemiluminescence method in accordance with JIS K 2609. Furthermore, unless otherwise specified, the content of phosphorus in a component containing phosphorus as a constituent element means a value measured by inductively coupled plasma atomic emission spectrometry (intensity ratio method (internal standard method)) in accordance with JIS K 0116.

[0018] The nitrogen content of the component containing nitrogen as a constituent element based on the total amount of the lubricating oil composition can be calculated from the nitrogen content and the amount of the component, and can also be determined by applying the chemiluminescence method to the lubricating oil composition. The phosphorus content of the component containing phosphorus as a constituent element based on the total amount of the lubricating oil composition can be calculated from the phosphorus content and the amount of the component, and can also be determined by applying the inductively coupled plasma atomic emission spectrometry to the lubricating oil composition.

[0019] [Lubricating oil composition] The lubricating oil composition contains a specific lubricating oil base oil, a hindered amine compound having a 2,2,6,6-tetraalkyl-4-piperidyl group (hereinafter, sometimes simply referred to as a "hindered amine compound"), and a dialkyldithiophosphate copper(I) represented by general formula (1) (hereinafter, sometimes simply referred to as "dialkyldithiophosphate copper(I)"). The lubricating oil composition may further contain an organic phosphorus-containing sulfide compound represented by general formula (4) (hereinafter, sometimes simply referred to as an "organic phosphorus-containing sulfide compound").

[0020] <Lubricant base oil> The lubricating base oil comprises a hydrorefined mineral oil having a sulfur content of 300 ppm by mass or less based on the total amount of the hydrorefined mineral oil.

[0021] Examples of hydrorefined mineral oils of the present embodiment include paraffinic base oils and naphthenic base oils obtained by applying at least hydrorefining to a lubricating oil fraction obtained by atmospheric or reduced pressure distillation of crude oil. In addition to hydrorefining, the refining method may further include one or more of solvent deasphalting, solvent extraction, solvent dewaxing, catalytic dewaxing, sulfuric acid washing, clay treatment, etc.

[0022] API base oil classification Group II base oil (hereinafter sometimes referred to as "API Group II base oil") and Group III base oil (hereinafter sometimes referred to as "API Group III base oil") are usually produced through a refining means such as hydrorefining. API Group II base oil is a mineral base oil having a sulfur content of 0.03 mass% (300 mass ppm) or less, a saturate content of 90 mass% or more, and a viscosity index of 80 or more and less than 120. API Group III base oil is a mineral base oil having a sulfur content of 0.03 mass% (300 mass ppm) or less, a saturate content of 90 mass% or more, and a viscosity index of 120 or more. Therefore, the hydrorefined mineral oil of this embodiment may be API Group II base oil or API Group III base oil.

[0023] The hydrorefined mineral oil of the present embodiment may be one type of hydrorefined mineral oil, or may be a mixed base oil consisting of two or more types of hydrorefined mineral oils. The mixed base oil containing two or more types of hydrorefined mineral oils may be a mixed base oil consisting of hydrorefined mineral oils of the same API classification, or may be a mixed base oil consisting of hydrorefined mineral oils of different API classifications. From the viewpoint of further enhancing the oxidation stability, the hydrorefined mineral oil is preferably a mixed base oil consisting of one type of API Group III base oil or two or more types of API Group III base oils.

[0024] The sulfur content in the total amount of the hydrorefined mineral oil of this embodiment is 300 ppm by mass or less from the viewpoint of enhancing oxidation stability. The sulfur content in the hydrorefined mineral oil is preferably 100 ppm by mass or less, more preferably 50 ppm by mass or less, and even more preferably 10 ppm by mass or less.

[0025] The hydrotreated mineral oil of this embodiment is the main component of the lubricating base oil. The content of the hydrotreated mineral oil may be, for example, 70 mass% or more, 80 mass% or more, 90 mass% or more, or 95 mass% or more based on the total amount of the lubricating base oil. The lubricating base oil may be composed only of hydrotreated mineral oil.

[0026] In addition to hydrorefined mineral oil, the lubricating base oil may contain other base oils as long as the effects of the present invention are not impaired. Examples of other base oils include API base oil classification Group I base oil (hereinafter, sometimes referred to as "API Group I base oil"), Group IV base oil (hereinafter, sometimes referred to as "API Group IV base oil"), and Group V base oil (hereinafter, sometimes referred to as "API Group V base oil"). API Group I base oil is a mineral base oil having a sulfur content of more than 0.03 mass% (300 mass ppm) and / or a saturate content of less than 90 mass%, and a viscosity index of 80 or more and less than 120. API Group IV base oil is a poly-α-olefin (PAO) base oil. API Group V base oil is a base oil other than API Group I base oil, API Group II base oil, API Group III base oil, and API Group IV base oil, and a preferred example thereof is an ester-based base oil.

[0027] Examples of API Group IV base oils include ethylene-propylene copolymers, polybutene, 1-octene oligomers, 1-decene oligomers, and hydrogenated versions of these.

[0028] Examples of API Group V base oils include monoesters (e.g., butyl stearate, octyl laurate, 2-ethylhexyl oleate, etc.), diesters (e.g., ditridecyl glutarate, bis(2-ethylhexyl) adipate, diisodecyl adipate, ditridecyl adipate, bis(2-ethylhexyl) sebacate, etc.), polyesters (e.g., trimellitic acid esters, etc.), and polyol esters (e.g., trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol-2-ethylhexanoate, pentaerythritol pelargonate, etc.).

[0029] The kinetic viscosity of the lubricating base oil (all base oils) at 100°C is preferably 2.0 mmHg or less from the viewpoint of enhancing wear resistance and fatigue resistance. 2 / s or more, more preferably 4.0 mm 2 / s or more, and from the viewpoint of reducing pumping resistance and enhancing energy saving, it is preferably 17.0 mm 2 / s or less, preferably 12.5 mm 2 In one embodiment, the kinematic viscosity of the lubricating base oil (all base oils) at 100° C. is 2.0 to 17.0 mm 2 / s or 4.0~12.5mm 2 / s.

[0030] The kinetic viscosity of the lubricating base oil (all base oils) at 40°C is preferably 10 mm 2 / s or more, preferably 20 mm 2 / s or more, and from the viewpoint of reducing pumping resistance and enhancing energy saving, preferably 150 mm 2 / s or less, preferably 100 mm 2 In one embodiment, the kinematic viscosity of the lubricating base oil (all base oils) at 40° C. is 10 to 150 mm 2 / s or 20~100mm 2 / s.

[0031] From the viewpoint of low-temperature fluidity and energy saving, the viscosity index of the lubricating base oil (total base oil) is preferably 80 or more, more preferably 90 or more. In one embodiment, the viscosity index of the lubricating base oil (total base oil) may be 100 or more, 110 or more, or 120 or more. The upper limit of the viscosity index of the lubricating base oil (total base oil) is not particularly limited, but is usually 150 or less, for example, 145 or less.

[0032] In this specification, the kinematic viscosity at 100° C. or 40° C. means the kinematic viscosity at 100° C. or 40° C. measured in accordance with JIS K 2283:2000. Also, the viscosity index means the viscosity index measured in accordance with JIS K 2283:2000.

[0033] From the viewpoint of further enhancing oxidation stability, the sulfur content in the lubricating base oil (total base oil) is preferably 300 ppm by mass or less, more preferably 100 ppm by mass or less, even more preferably 50 ppm by mass or less, and particularly preferably 10 ppm by mass or less.

[0034] From the viewpoint of low-temperature fluidity of the entire lubricating oil composition, the pour point of the lubricating base oil (all base oils) is preferably −10° C. or less, more preferably −12.5° C. or less, even more preferably −15° C. or less, particularly preferably −17.5° C. or less, and most preferably −20.0° C. or less. In this specification, pour point means the pour point measured in accordance with JIS K 2269:1987.

[0035] The lubricating base oil (total base oil) is the main component of the lubricating oil composition and constitutes the remainder of the content of the additives described below. The content of the lubricating base oil (total base oil) may be, for example, 70 mass% or more, 80 mass% or more, 90 mass% or more, or 95 mass% or more based on the total amount of the lubricating oil composition.

[0036] <Hindered amine compounds> The hindered amine compound is an amine compound having a sterically hindered (hindered) substituent (e.g., a hydrocarbon group) at least on one of the adjacent positions of the amine in the amine skeleton. As the hindered amine compound, a compound called HALS (Hindered Amine Light Stabilizers) can be preferably used. The hindered amine compound is preferably a compound represented by the following general formula (2A) or the following general formula (2B), more preferably a compound represented by the following general formula (2A). The hindered amine compound can act, for example, as an antioxidant.

[0037] [ka] [In formula (2A), R 11 , R 12 , R 13 , and R 14 each independently represents an alkyl group having 1 to 4 carbon atoms; 1 represents a monovalent organic group.

[0038] R 11 , R 12 , R 13 , and R 14 R may be a linear alkyl group or a branched alkyl group. 11 , R 12 , R 13 , and R 14 R are preferably the same alkyl group. 11 , R 12 , R 13 , and R 14 is preferably a methyl group. That is, in one embodiment, the hindered amine compound may be a compound having a 2,2,6,6-tetramethyl-4-piperidyl group.

[0039] X 1 Examples of the monovalent organic group as the aryl group include an acyloxy group (R 15 COO-), alkoxy group (R 15 O-), alkylamino group (R15 NH-), acylamino group (R 15 CONH-) etc. 15 R represents an alkyl group having 1 to 25 carbon atoms. 15 The alkyl group may be a linear alkyl group or a branched alkyl group. The number of carbon atoms in the alkyl group is 1 to 25, and may be 2 or more, 5 or more, 8 or more, or 10 or more, and may be 22 or less, 20 or less, 18 or less, or 16 or less.

[0040] In one embodiment, the compound represented by general formula (2A) may be a compound represented by the following general formula (3).

[0041] [ka] [In formula (3), R 11 , R 12 , R 13 , R 14 , and R 15 has the same meaning as above.]

[0042] The compound represented by general formula (3) can be obtained, for example, by reacting an alcohol represented by the following general formula (3a) with a carboxylic acid represented by the following general formula (3b).

[0043] [ka]

[0044] [ka] [In formula (2B), R 11 , R 12 , R 13 , and R 14 is the same as above. X 2 represents a divalent organic group.

[0045] X 2Examples of the divalent organic group as the alkyl group include a hydrocarbylene bis(carbonyloxy) group (-OOC-R 16 -COO-), hydrocarbylenediamino group (-HN-R 16 -NH-), hydrocarbylene bis(carbonylamino) group (-HNCO-R 16 -CONH-) etc. 16 represents a hydrocarbylene group having 1 to 30 carbon atoms, which may be an alkylene group. The hydrocarbylene group may have 1 to 24 or 1 to 20 carbon atoms.

[0046] From the viewpoint of enhancing oxidation stability, the content of the hindered amine compound is preferably 10 to 400 ppm by mass in terms of nitrogen element based on the total amount of the lubricating oil composition. The content of the hindered amine compound is more preferably 20 ppm by mass or more, even more preferably 30 ppm by mass or more, particularly preferably 40 ppm by mass or more, more preferably 300 ppm by mass or less, even more preferably 250 ppm by mass or less, and particularly preferably 200 ppm by mass or less, based on the total amount of the lubricating oil composition. In one embodiment, the content of the hindered amine compound is more preferably 20 to 300 ppm by mass, even more preferably 30 to 250 ppm by mass, and particularly preferably 40 to 200 ppm by mass in terms of nitrogen element based on the total amount of the lubricating oil composition.

[0047] <Copper(I) dialkyldithiophosphate> Copper dialkyldithiophosphate (I) is a compound represented by the following general formula (1): Copper dialkyldithiophosphate (I) can act, for example, as an antioxidant, an antiwear agent, and the like.

[0048] [ka] [In formula (1), R 1 and R 2 each independently represents an alkyl group having 2 to 18 carbon atoms.]

[0049] R1 and R 2 The alkyl group may be a linear alkyl group or a branched alkyl group. The number of carbon atoms in the alkyl group is 2 to 18, and from the viewpoint of solubility, it is preferably 3 or more, more preferably 4 or more, and from the viewpoint of low-temperature fluidity, it is preferably 15 or less, more preferably 12 or less.

[0050] The compound represented by general formula (1) can be obtained, for example, by reacting a compound represented by the following general formula (1a) (dialkyldithiophosphate compound) with a copper compound.

[0051] [ka] [In formula (1a), R 1 and R 2 has the same meaning as above.]

[0052] The compound represented by the general formula (1a) can be, for example, R 1 and R 2 It can be synthesized by reacting an alcohol having the corresponding alkyl group with diphosphorus pentasulfide (P2S5).

[0053] Examples of the copper compound include copper(I) compounds and copper(II) compounds. Examples of the copper(I) compound include organic acid salts of copper(I) (monovalent fatty acid salts of copper such as acetate), inorganic salts of copper(I) (copper(I) oxide, copper(I) hydroxide, copper(I) chloride, etc.). Examples of the copper(II) compound include organic acid salts of copper(II) (monovalent fatty acid salts of copper such as acetate), inorganic salts of copper(II) (copper(II) oxide, copper(II) hydroxide, copper(II) chloride, etc.). These copper compounds may contain water of hydration. Commercially available copper compounds can be used.

[0054] The reaction between the compound represented by general formula (1a) and the copper compound can be carried out by mixing an organic solvent solution of the compound represented by general formula (1a) with the copper compound. The organic solvent is not particularly limited as long as it can dissolve the compound represented by general formula (1a), and any commonly used organic solvent can be used. The organic solvent may be one type of organic solvent alone, or two or more types of organic solvents may be used in combination.

[0055] When a copper (I) compound is used as the copper compound, a compound represented by general formula (1) (copper (I) dialkyldithiophosphate) can be obtained by reacting a compound represented by general formula (1a) with a copper (I) compound. The molar ratio of the compound represented by general formula (1a) to copper (I) ions (compound represented by general formula (1a):copper (I) ions) can be, for example, about 1:1. The reaction temperature can be, for example, 25 to 80°C. The reaction time can be, for example, 1 to 4 hours. The reaction atmosphere is not particularly limited and can be an air atmosphere.

[0056] On the other hand, when a copper(II) compound is used as the copper compound, the inventors have found that the reaction between the compound represented by general formula (1a) and the copper(II) compound mainly produces a mixture of the compound represented by general formula (1) (copper(I) dialkyldithiophosphate) and the compound represented by general formula (1A) (dialkylphosphonothioyl sulfide compound, a compound corresponding to the compound represented by general formula (4) described below).

[0057] [ka] [In formula (1A), R 1 and R 2 has the same meaning as above. n1 represents 1 to 4.]

[0058] n1 is 1 to 4, and preferably 2. The organic phosphorus-containing sulfide compound may be used alone in which n1 is any one of 1 to 4, or may be used as a mixture containing at least two compounds selected from the group consisting of compounds in which n1 is 1, compounds in which n1 is 2, compounds in which n1 is 3, and compounds in which n1 is 4. In the mixture, the compound in which n1 is 2 may be the main component.

[0059] When a copper (II) compound is used as the copper compound, the molar ratio of the compound represented by the general formula (1a) to the copper (II) ion (compound represented by the general formula (1a):copper (II) ion) can be, for example, about 2:1. The copper (II) compound may be used in a small excess amount relative to the compound represented by the general formula (1a), and the molar ratio of the compound represented by the general formula (1a) to the copper (II) ion may be, for example, 1.5 to 1.9:1. The reaction temperature may be, for example, 25 to 80°C. The reaction time may be, for example, 1 to 4 hours. The reaction atmosphere is not particularly limited and may be an air atmosphere.

[0060] In the process of producing a mixture of a compound represented by general formula (1) and a compound represented by general formula (1A), a reaction mechanism via copper(II) dialkyldithiophosphate, which is a compound represented by the following general formula (1X), is also assumed. Therefore, the mixture may contain the compound represented by general formula (1X) (copper(II) dialkyldithiophosphate).

[0061] [ka] [In formula (1X), R 1 and R 2 has the same meaning as above.]

[0062] The copper dialkyldithiophosphate (I) may be used as a mixture of the compound represented by the general formula (1) and the compound represented by the general formula (1A). The copper dialkyldithiophosphate (I) may be used after isolating the compound represented by the general formula (1) from the mixture by a normal purification procedure (e.g., silica gel column chromatography, etc.). The isolated compound represented by the general formula (1A) may be used as an organic phosphorus-containing sulfide compound described below.

[0063] The content of copper dialkyl dithiophosphate (I) is preferably 50 to 500 mass ppm in terms of phosphorus element based on the total amount of the lubricating oil composition, from the viewpoint of enhancing oxidation stability by combination with the hindered amine compound. The content of copper dialkyl dithiophosphate (I) is more preferably 100 mass ppm or more, even more preferably 150 mass ppm or more, particularly preferably 200 mass ppm or more, more preferably 400 mass ppm or less, even more preferably 300 mass ppm or less, particularly preferably 250 mass ppm or less, based on the total amount of the lubricating oil composition, in terms of phosphorus element. In one embodiment, the content of copper dialkyl dithiophosphate (I) is more preferably 50 to 400 mass ppm, even more preferably 100 to 250 mass ppm, particularly preferably 150 to 200 mass ppm in terms of phosphorus element based on the total amount of the lubricating oil composition.

[0064] <Organophosphorus-containing sulfide compounds> The organic phosphorus-containing sulfide compound is a compound represented by the following general formula (4), which is a dialkylphosphonothioyl sulfide compound. The organic phosphorus-containing sulfide compound can act, for example, as an antioxidant, an antiwear agent, etc.

[0065] [ka] [In formula (4), R 41 , R 42 , R 43 , and R 44each independently represents an alkyl group having 2 to 18 carbon atoms, and n4 represents 1 to 4.

[0066] R 41 , R 42 , R 43 , and R 44 The alkyl group of R 1 and R 2 Examples of the alkyl group include those shown in R 41 , R 42 , R 43 , and R 44 Preferred examples of the alkyl group of R 1 and R 2 The alkyl group may be the same as the preferred examples of the alkyl group.

[0067] n4 is 1 to 4, and preferably 2. The organic phosphorus-containing sulfide compound may be a compound in which n4 is 1 to 4, and may be used alone, or may be used as a mixture containing at least two compounds selected from the group consisting of a compound in which n4 is 1, a compound in which n4 is 2, a compound in which n4 is 3, and a compound in which n4 is 4. In the mixture, the compound in which n4 is 2 may be the main component.

[0068] The compound represented by general formula (4) may be, for example, a compound represented by the following general formula (4A): The compound represented by general formula (4A) can be obtained by reacting a compound represented by the following general formula (4a) (dialkyldithiophosphate compound) with an oxidizing agent such as hydrogen peroxide or iodine.

[0069] [ka] [In formula (1A), R 41 , R 42 , and n4 are as defined above.]

[0070] [ka] [In formula (4a), R 41 and R42 has the same meaning as above.]

[0071] The compound represented by the general formula (4a) can be prepared, for example, by the same method as in the preparation of the compound represented by the general formula (1a) above, by adding R 41 and R 42 It can be synthesized by reacting an alcohol having the corresponding alkyl group with diphosphorus pentasulfide (P2S5).

[0072] The reaction between the compound represented by general formula (4a) and the oxidizing agent can be carried out by adding the oxidizing agent to an organic solvent solution of the compound represented by general formula (4a). The organic solvent is not particularly limited as long as it can dissolve the compound represented by general formula (4a), and any commonly used organic solvent can be used. The organic solvent may be one type of organic solvent alone, or two or more types of organic solvents may be used in combination.

[0073] When the compound represented by the general formula (4a) is reacted with an oxidizing agent, the molar ratio of the compound represented by the general formula (4a) to the oxidizing agent can be, for example, about 2:1. The oxidizing agent may be used in a small excess amount relative to the compound represented by the general formula (4a), and the molar ratio of the compound represented by the general formula (4a) to the oxidizing agent may be, for example, 1.5 to 1.9:1. The reaction temperature may be, for example, 25 to 80°C. The reaction time may be, for example, 1 to 4 hours. The reaction atmosphere is not particularly limited and may be an air atmosphere.

[0074] When the dialkyldithiophosphate copper (I) and the organic phosphorus-containing sulfide compound are used in combination, the content of the organic phosphorus-containing sulfide compound is preferably 50 to 300 mass ppm in terms of phosphorus element based on the total amount of the lubricating oil composition from the viewpoint of enhancing oxidation stability. The content of the organic phosphorus-containing sulfide compound is more preferably 70 mass ppm or more, more preferably 90 mass ppm or more, more preferably 200 mass ppm or less, and even more preferably 150 mass ppm or less, based on the total amount of the lubricating oil composition. In one embodiment, the content of the organic phosphorus-containing sulfide compound is more preferably 50 to 250 mass ppm, more preferably 90 to 150 mass ppm in terms of phosphorus element based on the total amount of the lubricating oil composition.

[0075] The ratio of the content of the organic phosphorus-containing sulfide compound to the content of the copper dialkyl dithiophosphate (I) (content of the organic phosphorus-containing sulfide compound in phosphorus element conversion / content of the copper dialkyl dithiophosphate (I) in phosphorus element conversion) is preferably 0.5 to 3, more preferably 0.7 or more, even more preferably 0.9 or more, more preferably 2 or less, even more preferably 1.5 or less. In one embodiment, the ratio of the content of the organic phosphorus-containing sulfide compound to the content of the copper dialkyl dithiophosphate (I) (phosphorus element conversion) is more preferably 0.5 to 2, even more preferably 0.9 to 1.5.

[0076] <Other additives> The lubricating oil composition may further contain other additives, such as metal deactivators, corrosion inhibitors, antiwear agents or extreme pressure agents (excluding copper(I) dialkyldithiophosphate and organic phosphorus-containing sulfide compounds), friction modifiers, antioxidants (excluding hindered amine compounds, copper(I) dialkyldithiophosphate and organic phosphorus-containing sulfide compounds), metal detergents, viscosity index modifiers (pour point depressants), rust inhibitors, antifoaming agents, demulsifiers, colorants, etc.

[0077] Examples of metal deactivators include known metal deactivators such as imidazoline, pyrimidine derivatives, alkyl thiadiazole, mercaptobenzothiazole, benzotriazole and its derivatives, 1,3,4-thiadiazole polysulfide, 1,3,4-thiadiazolyl-2,5-bisdialkyldithiocarbamate, 2-(alkyldithio)benzimidazole, β-(o-carboxybenzylthio)propioninitrile, etc. When the lubricating oil composition contains a metal deactivator, the content thereof may be, for example, 0.005 to 1 mass% based on the total amount of the lubricating oil composition.

[0078] Examples of the corrosion inhibitor include known corrosion inhibitors such as benzotriazole-based compounds, tolyltriazole-based compounds, thiadiazole-based compounds, imidazole-based compounds, etc. When the lubricating oil composition contains a corrosion inhibitor, the content thereof may be, for example, 0.005 to 5 mass% based on the total amount of the lubricating oil composition.

[0079] Examples of antiwear agents or extreme pressure agents include known phosphorus-based, sulfur-based, or phosphorus-sulfur-based antiwear agents or extreme pressure agents, such as phosphites, thiophosphites, dithiophosphites, trithiophosphites, phosphates, thiophosphates, dithiophosphates (excluding copper dialkyldithiophosphate (I) and organic phosphorus-containing sulfide compounds), trithiophosphates, amine salts thereof, metal salts thereof (excluding copper dialkyldithiophosphate (I)), derivatives thereof (excluding organic phosphorus-containing sulfide compounds), thiadiazole compounds, sulfurized oils and fats, sulfurized fatty acids, sulfurized esters, sulfurized olefins, dihydrocarbyl (poly)sulfides, alkylthiocarbamoyl compounds, thiocarbamate compounds, thioterpene compounds, dialkylthiodipropionate compounds, sulfurized mineral oils, and zinc dithiocarbamate. Examples of antiwear agents or extreme pressure agents include zinc dialkyldithiophosphate compounds (ZnDTP), which are zinc salts of dithiophosphate esters. The lubricating oil composition may or may not contain antiwear agents or extreme pressure agents other than copper dialkyldithiophosphate (I) and organic phosphorus-containing sulfide compounds. The total content of copper dialkyldithiophosphate (I), organic phosphorus-containing sulfide compounds, and other antiwear agents or extreme pressure agents may be 30 to 500 mass ppm in terms of phosphorus element based on the total amount of the lubricating oil composition.

[0080] Examples of the friction modifier include known friction modifiers such as ashless friction modifiers such as ester-based, amine-based, amide-based, and glycol-based friction modifiers, and metal-based friction modifiers such as molybdenum dithiocarbamate (MoDTC) and molybdenum dithiophosphate (MoDTP). When the lubricating oil composition contains a friction modifier, the content thereof may be, for example, 0.015 to 5 mass% based on the total amount of the lubricating oil composition.

[0081] Examples of the antioxidant include known antioxidants such as ashless antioxidants such as phenolic (hindered phenolic) compounds and amine compounds, and metal-based antioxidants such as copper compounds and molybdenum compounds. The hindered phenolic compound is a phenolic compound having a sterically hindered (hindered) substituent (e.g., t-butyl group, etc.) on at least one carbon atom adjacent to a hydroxyl group in a phenol as a parent skeleton. Examples of the phenolic (hindered phenolic) compound include 2,6-di-tert-butylcresol, 4,4'-methylenebis(2,6-di-tert-butylphenol), 4,4'-bis(2,6-di-tert-butylphenol), etc. Examples of the amine compound include phenyl-α-naphthylamine, alkylphenyl-α-naphthylamine, dialkyldiphenylamine, diphenylamine, etc. The lubricating oil composition may or may not contain an antioxidant other than the hindered amine compound, copper(I) dialkyldithiophosphate, and organic phosphorus-containing sulfide compound. When the lubricating oil composition contains an antioxidant other than the hindered amine compound, copper(I) dialkyldithiophosphate, and organic phosphorus-containing sulfide compound, the content thereof may be, for example, 0.01 to 3 mass% based on the total amount of the lubricating oil composition.

[0082] Examples of the metallic detergent include neutral salts such as sulfonates, phenates, and salicylates of alkali metals or alkaline earth metals, basic salts obtained by heating neutral salts with hydroxides, oxides, etc. of alkali metals or alkaline earth metals in the presence of water, and overbased salts obtained by reacting neutral salts with bases such as hydroxides of alkali metals or alkaline earth metals in the presence of carbon dioxide gas or boric acid or borate. Examples of the alkaline metals include sodium and potassium. Examples of the alkaline earth metals include magnesium, calcium, barium, etc. When the lubricating oil composition contains a metallic detergent, the content thereof may be, for example, 0.01 to 0.50 mass% in terms of metal elements (alkali metal elements and alkaline earth metal elements) based on the total amount of the lubricating oil composition.

[0083] Examples of the viscosity index modifier (pour point depressant) include known viscosity index modifiers (pour point depressants) such as non-dispersant or dispersant poly(meth)acrylate, (meth)acrylate-olefin copolymer, non-dispersant or dispersant ethylene-α-olefin copolymer or its hydrogenated product, polyisobutylene or its hydrogenated product, styrene-diene hydrogenated copolymer, styrene-maleic anhydride ester copolymer, polyalkylstyrene, etc. In this specification, (meth)acrylate means acrylate or its corresponding methacrylate. The same applies to other similar expressions. When the lubricating oil composition contains a viscosity index modifier (pour point depressant), the content thereof may be, for example, 0.005 to 2 mass% based on the total amount of the lubricating oil composition.

[0084] Examples of the rust inhibitor include known rust inhibitors such as petroleum sulfonates, alkylbenzene sulfonates, dinonylnaphthalene sulfonates, alkenyl succinic acid esters, polyhydric alcohol esters, etc. When the lubricating oil composition contains a rust inhibitor, the content thereof may be, for example, 0.005 to 5 mass% based on the total amount of the lubricating oil composition.

[0085] Examples of the antifoaming agent include known antifoaming agents such as silicone, fluorosilicone, fluoroalkyl ether, etc. When the lubricating oil composition contains an antifoaming agent, the content thereof may be, for example, 0.0005 to 0.02 mass% based on the total amount of the lubricating oil composition.

[0086] Examples of the demulsifier include known demulsifiers such as polyalkylene glycol nonionic surfactants, etc. When the lubricating oil composition contains a demulsifier, the content thereof may be, for example, 0.001 to 5 mass% based on the total amount of the lubricating oil composition.

[0087] Examples of the colorant include known colorants such as azo compounds.

[0088] <Lubricating oil composition> From the viewpoint of enhancing wear resistance, the lubricating oil composition preferably has a kinematic viscosity at 40° C. of 10 mm 2 / s or more, preferably 20 mm 2 / s or more, more preferably 30 mm 2 / s or more, and from the viewpoint of improving energy saving, it is preferably 150 mm 2 / s or less, preferably 100 mm 2 / s or less, more preferably 50 mm 2 In one embodiment, the kinematic viscosity of the lubricating oil composition at 40° C. is 10 to 150 mm 2 / s, 20~100mm 2 / s, or 30~50mm 2 / s.

[0089] The lubricating oil composition preferably has a kinematic viscosity at 100° C. of 2.0 mmHg or less from the viewpoint of enhancing wear resistance. 2 / s or more, more preferably 4.0 mm 2 / s or more, more preferably 5.0 mm 2 / s or more, and from the viewpoint of improving energy saving, preferably 17.0 mm 2 / s or less, preferably 12.5 mm 2 / s or less, more preferably 8.0 mm 2 In one embodiment, the lubricating oil composition has a kinematic viscosity at 100° C. of 2.0 to 17.0 mm / s or less. 2 / s, 4.0~12.5mm 2 / s, or 5.0~8.0mm 2 / s.

[0090] From the viewpoint of enhancing energy saving, the viscosity index of the lubricating oil composition is preferably at least 80, more preferably at least 100. There is no particular upper limit to the viscosity index of the lubricating oil composition, but it is usually 300 or less.

[0091] The lubricating oil composition may be, for example, a hydraulic oil. The mechanism of oxidation in the environment in which hydraulic oil is used is different from the mechanism of oxidation in the environment in which engine oil or transmission oil is used. The temperature of engine oil is about 170 to 180°C even in the piston and cylinder, which are the hottest, and it is known that the oxidative deterioration of engine oil is caused by the generation of peroxide radicals accompanying combustion. In contrast, hydraulic oil is generally pressurized by a hydraulic pump such as a vane pump or a piston pump and supplied to a hydraulic device (for example, a hydraulic cylinder, etc.). The discharge pressure of a gear pump that supplies oil to an internal combustion engine or a transmission is about 1.5 MPa at most, but the discharge pressure of a hydraulic pump used in a hydraulic device can be, for example, 5 MPa or more, up to about 20 MPa in the case of a vane pump, and can be, for example, 10 MPa or more, up to about 35 MPa in the case of a piston pump used for higher pressure applications. Hydraulic oil pressurized to such high pressure tends to easily undergo oxidative deterioration even when the bulk temperature is relatively low. The lubricating oil composition of the present embodiment exhibits high oxidation stability even under pumping conditions at such high discharge pressures, for example, 5 MPa or more, 15 MPa or more, or 35 MPa or more, and it is possible to extend the life of the lubricating oil composition even under such high pressure conditions. The upper limit of the discharge pressure of the hydraulic pump is not particularly limited, but may be, for example, 50 MPa or less or 40 MPa or less. EXAMPLES

[0092] The present invention will be specifically described below based on examples, but the present invention is not limited to these.

[0093] (Examples 1 to 6 and Comparative Examples 1 to 6) [Preparation of lubricating oil composition] Using the lubricating oil base oil and additives shown below, lubricating oil compositions of Examples 1 to 6 and Comparative Examples 1 to 6 having the compositions shown in Tables 1 and 2 were prepared. In the tables, the content of each component is based on the total amount of the lubricating oil composition (100 mass%). In the tables, mass ppm (N) means the content of the hindered amine compound in terms of nitrogen element based on the total amount of the lubricating oil composition, and mass ppm (P) means the content of the dialkyldithiophosphate copper (I), the organic phosphorus-containing sulfide compound, and the phosphorus-sulfur-based wear inhibitor (ZnDTP) in terms of phosphorus element based on the total amount of the lubricating oil composition.

[0094] In the table, the N concentration in the oil means the nitrogen element content in the lubricating oil composition based on the total amount of the lubricating oil composition, and can be calculated from the nitrogen element content and the charged amount of the components containing nitrogen element as a constituent element. The N concentration in the oil is mainly derived from the hindered amine compound and the corrosion inhibitor.

[0095] In the table, the P concentration in the oil means the content of phosphorus in the lubricating oil composition based on the total amount of the lubricating oil composition, and can be calculated from the content of phosphorus in the components containing phosphorus as a constituent element and the charged amount. The P concentration in the oil is mainly derived from copper(I) dialkyldithiophosphate, organic phosphorus-containing sulfide compounds, and ZnDTP.

[0096] <(A) Component: Lubricant base oil> A-1: API Group III base oil (Kinematic viscosity (40℃): 46.07mm 2 / s, kinematic viscosity (100℃): 7.54mm 2 / s, viscosity index: 120, sulfur content: less than 10 ppm by mass, aromatic content: 0.0% by mass A-2: API Group II base oil (Kinematic viscosity (40℃): 45.99mm 2 / s, kinematic viscosity (100℃): 6.93mm 2 / s, viscosity index: 100, sulfur content: less than 10 ppm by mass, aromatic content: 0.0% by mass A-3: API Group I base oil (Kinematic viscosity (40℃): 46.87mm 2 / s, kinematic viscosity (100℃): 6.90mm 2 / s, viscosity index: 104, sulfur content: 0.15% by mass, aromatic content: 26.8% by mass)

[0097] <Component (B): Hindered amine compound> B-1: In the above general formula (3), R 11 , R 12 , R 13 , and R 14 is a methyl group, and R 15 is a linear alkyl group having 11 carbon atoms (a group obtained by removing the carboxylic acid group from dodecanoic acid) (molecular weight: 339, nitrogen element content: 4.1% by mass)

[0098] <(b) Ingredient: Phenolic compound (ashless antioxidant)> b-1: 2,6-di-tert-butylcresol

[0099] <Component (C1): Copper(I) dialkyldithiophosphate> C1-1: In the above general formula (1), R 1 and R 2 Copper(I) dialkyldithiophosphate (phosphorus content: 7.4% by mass) in which the 2-ethylhexyl group is Phosphorus pentasulfide (P2S5) 0.1 mol (38.2 g) and 2-ethylhexyl alcohol (C8H 17 0.4 mol (52.0 g) of di-2-ethylhexyl dithiophosphoric acid was collected in a flask and stirred at 70°C for 15 hours. After the stirring was completed, 0.2 mol (70.8 g) of di-2-ethylhexyl dithiophosphoric acid was obtained as a reaction product. Next, 0.1 mol (35.4 g) of di-2-ethylhexyl dithiophosphoric acid was collected in a beaker and dissolved in 150 mL of hexane. To this solution was added an aqueous solution of copper(I) acetate prepared by dissolving 0.1 mol (12.3 g) of copper(I) acetate in 150 mL of water, and the mixture was stirred at 70°C for 1 hour. The hexane layer and the water layer were separated using a separatory funnel, and the hexane layer was washed twice with 150 mL of water. The hexane was distilled off using an evaporator to obtain the target product. 31 Analysis by PNMR revealed that the main component was the title compound.

[0100] <Component (C2): Organic phosphorus-containing sulfide compound> C2-1: In the above general formula (4), R 41 , R 42 , R 43 , and R 44 Compounds in which n is a 2-ethylhexyl group and n4 is 1 to 4 (phosphorus content: 8.8% by mass) Di-2-ethylhexyl dithiophosphoric acid was obtained in the same manner as above. 0.1 mol (35.4 g) of di-2-ethylhexyl dithiophosphoric acid was collected in a beaker and dissolved in 150 mL of hexane. 7 g of hydrogen peroxide (30%) was added to this solution and stirred at room temperature (25°C) for 2 hours. After stirring was completed, the hexane layer and the water layer were separated using a separatory funnel, and the hexane layer was washed twice with 150 mL of water. The hexane was distilled off using an evaporator to obtain the target product. 31 Analysis by PNMR revealed that the main component was the title compound.

[0101] <Component (C3): Mixture of copper(I) dialkyldithiophosphate and organic phosphorus-containing sulfide compound> C3-1: A mixture of C1-1 and C2-1 Di-2-ethylhexyl dithiophosphoric acid was obtained in the same manner as above. 0.1 mol (35.4 g) of di-2-ethylhexyl dithiophosphoric acid was collected in a beaker and dissolved in 150 mL of hexane. To this solution was added an aqueous solution of copper (II) acetate prepared by dissolving 0.05 mol (9.1 g) of copper (II) acetate monohydrate in 150 mL of water, and the mixture was stirred at 70°C for 1 hour. The hexane layer and the water layer were separated using a separatory funnel, and the hexane layer was washed twice with 150 mL of water. The hexane was distilled off using an evaporator to obtain the target product. 31 Analysis by PNMR revealed that the main components were the above-mentioned mixtures. The proportion of C1-1 in the mixture C3-1 was 55 mass %, and the proportion of C2-1 in the mixture was 45 mass %.

[0102] <Component (c): Phosphorus-sulfur anti-wear agent (ZnDTP)> c-1: In the following general formula (5), R 51 , R52 , R 53 , and R 54 A compound in which R is a 2-ethylhexyl group (phosphorus element content: 8.0% by mass)

[0103] [Chemical formula]

[0104] <(E) component: Corrosion inhibitor> ·D-1: Tolyltriazole derivative (nitrogen element content: 14.5% by mass) [Evaluation of lubricating oil composition]

[0105] <RPVOT test> In accordance with the "Rotating Pressure Vessel Oxidation Stability Test Method" in JIS K 2514-3:2013, the RPVOT test was conducted on the lubricating oil compositions of Examples 1 to 6 and Comparative Examples 1 to 6. The results are shown in Table 1.

[0106] [Table 1]

[0107] [Table 2]

[0108] As shown in Tables 1 and 2, the lubricating oil compositions of Examples 1 to 6, which are combinations of a hindered amine compound and copper(I) dialkyldithiophosphate, were excellent in the results of the RPVOT test.

[0109] On the other hand, Comparative Example 1 containing a lubricating base oil containing a hydrorefined mineral oil in which the sulfur content in the total amount of the hydrorefined mineral oil exceeded 300 ppm by mass was inferior in the results of the RPVOT test.

[0110] In addition, Comparative Examples 2 and 3, which contained only copper(I) dialkyldithiophosphate and did not contain a hindered amine compound, showed poor results in the RPVOT test. In addition, Comparative Example 4, which contained only a hindered amine compound and did not contain copper(I) dialkyldithiophosphate, also showed poor results in the RPVOT test.

[0111] The combination of a phenolic compound commonly used as an antioxidant with copper(I) dialkyldithiophosphate in Comparative Example 5 also showed poor results in the RPVOT test, as did the combination of such a phenolic compound with ZnDTP in Comparative Example 6.

[0112] From the above, it was found that the oxidation stability was improved by combining an organic phosphorus-containing sulfide compound having a specific structure with a hindered amine compound having a specific group. These results confirmed that the lubricating oil composition of the present invention has excellent oxidation stability.

Claims

1. A lubricating oil base oil; a hindered amine compound having a 2,2,6,6-tetraalkyl-4-piperidyl group; Copper dialkyldithiophosphate (I) represented by the following general formula (1), Contains The lubricating oil composition, wherein the lubricating base oil comprises a hydrorefined mineral oil having a sulfur content of 300 ppm by mass or less based on the total amount of the hydrorefined mineral oil. 【Chemistry 1】 [In formula (1), R １ and R ２ each independently represents an alkyl group having 2 to 18 carbon atoms.

2. The lubricating oil composition according to claim 1, further comprising an organic phosphorus-containing sulfide compound represented by the following general formula (4): 【Chemistry 2】 [In formula (4), R ４１ , R ４２ , R ４３ , and R ４４ each independently represents an alkyl group having 2 to 18 carbon atoms, and n4 represents 1 to 4.

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