Lubricating oil composition

Abstract

To provide a lubricating oil composition capable of suppressing the oxidative deterioration of a hydrocarbon-based base oil contained as a lubricating base oil at a high level.SOLUTION: A hydrocarbon-based base oil; [In the formula (1), R1 to R3 each independently represent hydrogen or the like. The lubricating oil composition is characterized in that the content of the guanidine compound is 0.40 mass% or less based on the total amount of the composition.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Conventionally, lubricating oil compositions have been used in various mechanical devices having moving parts, in order to reduce the friction and wear of the components constituting the moving parts, and to improve the energy saving and lifespan of the devices.In such lubricating oil compositions, the lubricating base oil, which is an essential component, is oxidized and deteriorated when it comes into contact with air, so that in order to suppress this oxidized deterioration, it is common to use a combination of the lubricating base oil and an antioxidant, and various combinations of such base oils and antioxidants have been studied.

[0003] For example, Japanese Patent Laid-Open Publication No. 01-123896 (Patent Document 1) discloses an ester-based lubricating oil composition in which the base oil is an ester-based base oil made from an unsaturated fatty acid polyol ester, and the ester-based base oil contains 0.5 to 2.8 wt % of N-phenyl-α-naphthylamine, 2,6-di-tert-butyl-dimethylamino-p-cresol or 1,3-diphenylguanidine and 0.1 to 0.8 wt % of 4,4-butylidene-bis(3-methyl-6-tert-butyl-phenol). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 01-123896 Summary of the Invention [Problem to be solved by the invention]

[0005] However, Patent Document 1 merely discloses the use of a specific compound in combination as an antioxidant for a specific ester-based base oil, and does not disclose the use of any one of the compounds disclosed in the same document as an antioxidant for other types of base oil.

[0006] The present invention has been made in view of the problems of the prior art, and has as its object to provide a lubricating oil composition that is capable of suppressing, at a high level, the oxidative degradation of a hydrocarbon base oil contained as a lubricating oil base oil. [Means for solving the problem]

[0007] As a result of intensive research to achieve the above object, the present inventors have discovered that by forming a lubricating oil composition containing a hydrocarbon base oil and a guanidine compound represented by the following general formula (1) and by limiting the content of the guanidine compound to 0.40 mass% or less based on the total amount of the composition, it is possible to highly inhibit oxidative degradation of the hydrocarbon base oil contained as the lubricating oil base oil, and have thus completed the present invention. Thus, the present inventors have surprisingly discovered that when a lubricating oil base oil contains a hydrocarbon base oil, by using a specific amount or less of the guanidine compound represented by the following general formula (1) as an antioxidant, it is possible to highly inhibit the oxidation reaction (deterioration reaction) of the base oil in the composition, and have thus completed the present invention.

[0008] That is, the present invention provides the following aspects.

[0009] [1] A hydrocarbon base oil; The following general formula (1):

[0010] [ka]

[0011] [In formula (1), R 1 ~R 3each independently represents one selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, an aryl group having 6 to 24 carbon atoms which may have a substituent, and an aralkyl group having 7 to 25 carbon atoms which may have a substituent. an antioxidant consisting of a guanidine-based compound represented by the formula: and A lubricating oil composition, wherein the content of the guanidine compound is 0.40 mass % or less based on the total amount of the composition.

[0012] [2] The lubricating oil composition according to [1], wherein the content of the guanidine compound is 0.15 mass % or less based on the total amount of the composition.

[0013] [3] In the formula (1), R 1 and R 3 each independently represents one selected from the group consisting of a phenyl group and a substituted phenyl group, and R 2 The lubricating oil composition according to [1] or [2], wherein represents one member selected from the group consisting of a hydrogen atom and an alkyl group having 1 to 8 carbon atoms. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a lubricating oil composition containing a hydrocarbon base oil, which is capable of suppressing oxidative degradation of the hydrocarbon base oil contained as the lubricating oil base oil at a high level. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention will be described in detail below with reference to preferred embodiments. In this specification, unless otherwise specified, the expression "X to Y" for numerical values ​​X and Y means "X or more and Y or less." In such an expression, when a unit is assigned only to the numerical value Y, the unit also applies to the numerical value X.

[0016] The lubricating oil composition of the present invention comprises: a hydrocarbon base oil; The following general formula (1):

[0017] [ka]

[0018] [In formula (1), R 1 ~R 3 each independently represents one selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, an aryl group having 6 to 24 carbon atoms which may have a substituent, and an aralkyl group having 7 to 25 carbon atoms which may have a substituent. an antioxidant consisting of a guanidine-based compound represented by the formula: and The lubricating oil composition of the present invention is characterized in that the content of the guanidine compound is 0.40 mass% or less based on the total amount of the composition. Thus, the lubricating oil composition of the present invention comprises a lubricating base oil and an antioxidant comprising the guanidine compound.

[0019] <Antioxidants> The antioxidant according to the present invention may be any guanidine-based compound represented by the general formula (1). 1 ~R 3 are each independently one selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, an aryl group having 6 to 24 carbon atoms which may have a substituent, and an aralkyl group having 7 to 25 carbon atoms which may have a substituent.

[0020] Such an R 1 ~R 3 The alkyl group that can be selected as the alkyl group has 1 to 18 carbon atoms. By setting the number of carbon atoms in such an alkyl group to the above upper limit or less, it is possible to obtain an excellent balance between solubility in the base oil and antioxidant effect. By appropriately selecting the number of carbon atoms in such an alkyl group within the above upper limit or less, it is possible to easily adjust the solubility in the base oil depending on the type of base oil, and thereby easily maintain a high level of solubility in the base oil.

[0021] Also, such R 1 ~R 3 The alkyl group having 1 to 18 carbon atoms that can be selected as the alkyl group is not particularly limited, but suitable examples include linear alkyl groups such as methyl, ethyl, propyl, butyl, hexyl, octyl, decyl, dodecyl, hexadecyl, and octadecyl; branched alkyl groups such as isopropyl, isobutyl, tertiary butyl, isohexyl, and 2-ethylhexyl; and cyclic alkyl groups having a ring structure as the main structure, such as cyclopentyl and cyclohexyl. Of these, linear alkyl groups are preferred from the viewpoint of easy availability of raw materials. Furthermore, among such linear alkyl groups having 1 to 18 carbon atoms, those having 1 to 12 carbon atoms (more preferably 1 to 8 carbon atoms) are more preferred from the viewpoint of ease of compound synthesis and availability of synthetic raw materials.

[0022] Such an R 1 ~R 3The optionally substituted aryl group that can be selected as (C1) has 6 to 24 carbon atoms. By appropriately selecting the number of carbon atoms of such an aryl group within the range not exceeding the above upper limit, the solubility in the base oil can be easily adjusted depending on the type of base oil, thereby making it possible to easily maintain a high level of solubility in the base oil. The optionally substituted aryl group having 6 to 24 carbon atoms is not particularly limited, but suitable examples include a phenyl group, a tolyl group, a naphthyl group, and a xylyl group. Furthermore, when such an aryl group has a substituent, the substituent is preferably an alkyl group having 1 to 18 carbon atoms. Furthermore, among such optionally substituted aryl groups having 6 to 24 carbon atoms, a phenyl group or a phenyl group having a substituent is preferred, with a phenyl group, a toluyl group (tolyl group), or a xylyl group being particularly preferred. When the aryl group is a toluyl group or a xylyl group, the substitution position of the methyl group is optional. In addition, in such an aryl group having 6 to 24 carbon atoms which may have a substituent, the type of the substituent on the aryl group, the position at which the substituent is substituted, and the like may be appropriately changed depending on the solubility in the base oil used (desired solubility).

[0023] Also, such R 1 ~R 3 The optionally substituted aralkyl group that can be selected as (C1) has 7 to 25 carbon atoms. By appropriately selecting the number of carbon atoms of such an aralkyl group within the range not exceeding the above upper limit, it is possible to adjust the solubility in the base oil depending on the type of base oil, thereby making it possible to easily maintain a high level of solubility in the base oil. Furthermore, such an optionally substituted aralkyl group having 7 to 25 carbon atoms is not particularly limited, but suitable examples include aralkyl groups such as a benzyl group, a phenethyl group, and a phenylpropyl group. When such an aralkyl group has a substituent, the substituent is preferably an alkyl group having 1 to 18 carbon atoms.

[0024] Such an R 1 ~R 3 The group selected as R may be appropriately selected from among a hydrogen atom, the alkyl group, the aryl group, and the aralkyl group from the viewpoints of availability of the raw material compound and solubility in the finally obtained guanidine compound base oil (base oil to be combined), among others. Among these, from the viewpoint of availability of the guanidine compound itself, R 1 and R 3 each independently represents one selected from the group consisting of a phenyl group and a substituted phenyl group (more preferably a substituted phenyl group), and R 2 It is preferable that R represents one selected from the group consisting of a hydrogen atom and an alkyl group having 1 to 8 carbon atoms. 1 and R 3 are each independently a toluyl group or a xylyl group, and R 2 is more preferably a hydrogen atom, a methyl group, or an ethyl group, and particularly preferably a hydrogen atom.

[0025] The method for preparing the guanidine compound is not particularly limited, and known methods can be appropriately adopted. For example, the method described in Reference 1 (Yokohama National University, Faculty of Education Bulletin IV, Natural Sciences 2018, Vol. 1, p. 63) can be used. Specific methods for preparing the guanidine compound include, for example, a synthesis method in which an amine compound such as a primary amine is added to a carbodiimide compound. The carbodiimide compound used in such a method can be synthesized by a dehydration reaction of a urea compound, but it is preferable to use a commercially available product. Examples of carbodiimide compounds include dicyclohexylcarbodiimide, diisopropylcarbodiimide, 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide, N-tertiary butyl-N'-ethylcarbodiimide, N,N'-ditertiary butylcarbodiimide, N,N'-diorthotolylcarbodiimide, and N,N'-diparatolylcarbodiimide. Examples of the primary amine include methylamine, ethylamine, propylamine, butylamine, hexylamine, cyclohexylamine, aniline, benzylamine, toluidine, and xylylamine. The position of the substituent in toluidine and xylylamine is optional. In addition to the primary amines, cyclic secondary amines such as unsubstituted ammonia and morpholine can also be used as the amine compound. When employing such a method, the reaction conditions are not particularly limited. For example, by reacting the carbodiimide with the amine compound in the presence of a strong base, a guanidine compound of desired design can be synthesized depending on the structure of the raw material used.

[0026] In addition to the guanidine compounds synthesized as described above, commercially available products can also be used as the guanidine compounds. Specific examples include diphenylguanidine, ditolylguanidine, dibiphenylguanidine, triphenylguanidine, tritolylguanidine, dicumenylguanidine, 1,1,3,3-tetramethylguanidine, and N,N'-dicyclohexyl-4-morpholinecarbodiimide. Salts of these compounds with acidic compounds such as hydrochloric acid and sulfuric acid can also be suitably used.

[0027] Furthermore, the antioxidant according to the present invention may contain the guanidine compound, and may be used in combination with a known antioxidant (for example, an antioxidant described in JP 2022-158124 A (an aromatic amine antioxidant, a hindered amine antioxidant, a phenolic antioxidant, etc.)) within a range that does not impair the effects of the present invention. Thus, in the present invention, depending on the application and design of the composition, the antioxidant used may consist solely of the guanidine compound, or may be a mixture (combined) of the guanidine compound and another known antioxidant.

[0028] <Hydrocarbon base oil> The lubricating oil composition of the present invention contains a hydrocarbon base oil (hydrocarbon lubricating base oil) as a lubricating base oil. By using the antioxidant in such a hydrocarbon base oil, it is possible to achieve excellent antioxidant performance.

[0029] The "hydrocarbon base oil" used herein may be any hydrocarbon base oil commonly used in the field of lubricants, and specific examples of the hydrocarbon base oil include mineral hydrocarbon oils, synthetic hydrocarbon oils, and mixtures of both.

[0030] Examples of such mineral hydrocarbon oils include paraffinic mineral oils, naphthenic mineral oils, normal paraffinic base oils, isoparaffinic base oils, and aromatic base oils, which are obtained by using waxes such as slack wax obtained by the lubricant oil dewaxing process and / or synthetic waxes such as Fischer-Tropsch wax and GTL wax obtained by the gas-to-liquid (GTL) process as raw materials, and refining them by one or a suitable combination of two or more refining processes such as solvent deasphalting, solvent extraction, hydrocracking, hydroisomerization, solvent dewaxing, catalytic dewaxing, hydrorefining, sulfuric acid washing, and clay treatment. These mineral base oils may be used alone or in any combination of two or more types. As such mineral base oils, any of those classified as API base oil classification Group I, II, and III base oils can be suitably used. Among such mineral base oils, API base oil classification Group III base oils (hereinafter sometimes referred to as "API Group III base oils") can be more suitably used from the viewpoint of being able to achieve a higher viscosity index.

[0031] Examples of synthetic hydrocarbon oils include poly-α-olefins or hydrogenated products thereof; olefin oligomers or hydrogenated products thereof, such as propylene oligomer, isobutylene oligomer, polybutene, 1-octene oligomer, 1-decene oligomer, and ethylene-propylene oligomer; alkylbenzene; and alkylnaphthalene. These synthetic hydrocarbon oils may be used alone or in combination of two or more in any ratio.

[0032] As the synthetic hydrocarbon oil, API Group IV base oils (poly-α-olefin base oils, hereinafter sometimes referred to as "API Group IV base oils") can be suitably used.

[0033] Furthermore, as the hydrocarbon base oil according to the present invention, API Group III base oils and API Group IV base oils are more preferred because they provide higher oxidation stability.

[0034] <About additives> The lubricating oil composition of the present invention may contain the hydrocarbon base oil and the antioxidant consisting of the guanidine compound. Depending on the application, etc., known additives used in the field of lubricating oil compositions can be appropriately used within the scope that does not impair the effects of the present invention. Such additives are not particularly limited, but examples thereof include ashless dispersants, metal-based detergents, friction modifiers, antiwear agents, extreme pressure agents, viscosity index improvers, pour point depressants, corrosion inhibitors, rust inhibitors, metal deactivators, demulsifiers, antifoaming agents, and colorants. In addition, as such additives, for example, various additives described in International Publication No. 2017 / 073748, JP 2020-76004 A, International Publication No. 2020 / 095970, JP 2022-158124 A, JP 2022-090378 A, etc. can be appropriately used.

[0035] Such additives are not particularly limited, but examples thereof include known ashless dispersants such as succinimide-based ashless dispersants; known metal-based detergents such as alkali or alkaline earth metal alkyl salicylates, alkali or alkaline earth metal alkylbenzene sulfonates, and alkali or alkaline earth metal alkylphenates; known friction modifiers such as oiliness agent-based friction modifiers, organic molybdenum compounds, organic boron compounds such as alkyl mercaptyl borates, graphite, molybdenum disulfide, antimony sulfide, boron compounds, and polytetrafluoroethylene; known sulfur-based additives such as metal thiocarbamate salts (salts of various metals such as Mo, Zn, Pb, and Sb), and disulfides; and metal dithiophosphate salts (salts of various metals such as Mo, Zn, Pb, and Sb). Examples of suitable additives include known antiwear agents such as known phosphorus-based and phosphorus-sulfur-based additives, such as salts of various metals such as methyl acrylate, methyl methacrylate, methyl acrylate, phosphate esters, phosphite esters, and amine salts of phosphoric acid partial esters; known viscosity index improvers such as dispersant or non-dispersant poly(meth)acrylates (dispersant or non-dispersant polyalkyl(meth)acrylates), non-dispersant or dispersant ethylene-α-olefin copolymers and hydrogenated products thereof, polyisobutylene and hydrogenated products thereof, hydrogenated products of styrene-diene copolymers, styrene-maleic anhydride ester copolymers, and polyalkylstyrenes; known pour point depressants such as polymethacrylate polymers and ethylene vinyl acetate; and known metal deactivators such as tolyltriazole or its derivatives.

[0036] <About the composition> In the lubricating oil composition of the present invention, the content of the guanidine compound (compound represented by the general formula (1)) used as the antioxidant is 0.40 mass% or less based on the total amount of the composition. If the content exceeds 0.40 mass%, excessive precipitation at room temperature may occur, potentially causing clogging of filters, etc., during actual use of the lubricating oil. Furthermore, since a higher effect can be obtained with a small amount of addition, the content of the guanidine compound (compound represented by the general formula (1)) is preferably 0.30 mass% or less based on the total amount of the composition, more preferably 1.0 ppm by mass or more and 0.30 mass% or less, and particularly preferably 1.5 ppm by mass or more and 0.15 mass% or less. From the viewpoint of achieving even higher antioxidant performance, the lower limit of the content of the guanidine compound is more preferably 2.0 ppm by mass (more preferably 10 ppm by mass, and particularly preferably 100 ppm by mass) based on the total amount of the composition.

[0037] The content of the guanidine compound (compound represented by the general formula (1)) used as the antioxidant is preferably 0.01 to 17 micromoles (more preferably 0.02 to 13 micromoles, and even more preferably 0.3 to 7 micromoles) per gram of the lubricating base oil. By setting the content of such a guanidine compound at or above the lower limit, a higher level of antioxidant performance can be obtained. On the other hand, by setting the content at or below the upper limit, an even higher level of antioxidant performance can be obtained economically. Conventionally known antioxidants essentially achieve antioxidant protection through an equivalent reaction, and depending on the type of antioxidant, large amounts have had to be added to maintain antioxidant function over a long period of time. However, when the antioxidant comprising the guanidine compound according to the present invention is used, it is possible to suppress oxidative degradation over a long period of time, even with the use of a relatively small amount, although the reason for this is not entirely clear.

[0038] In addition, in the lubricating oil composition of the present invention, the content of the lubricating base oil is not particularly limited, but is preferably 70 mass% or more (more preferably 80 mass% or more, even more preferably 95 mass% or more, and particularly preferably 99 mass% or more) based on the total amount of the composition. When the content of such lubricating base oil is equal to or greater than the lower limit, a more excellent effect can be obtained in terms of the solubility stability of the additives when the additives are used, compared to when the content is less than the lower limit.

[0039] Furthermore, when the lubricating oil composition of the present invention contains the other additives (such as ashless dispersants, metallic detergents, friction modifiers, antiwear agents, extreme pressure agents, viscosity index improvers, pour point depressants, corrosion inhibitors, rust inhibitors, metal deactivators, demulsifiers, antifoaming agents, and colorants), the amount of each additive may be appropriately selected depending on the intended use of the composition, as long as it does not impair the effects of the present invention. For example, when one or more of an ashless dispersant, a viscosity index improver, and a pour point depressant are used as the additive, the content of each additive may be 0.01 to 20 mass% based on the total amount of the composition. For example, when a metallic detergent is used as the additive, the content may be 0.001 to 5.0 mass% based on the total amount of the composition in terms of metal element. Furthermore, when the additives include one or more of a friction modifier, an antiwear agent, and an extreme pressure agent, the content thereof may be 0.05 to 5.0 mass% of the total composition. When the additives include one or more of a corrosion inhibitor, a rust inhibitor, and an anti-emulsifier, the content thereof may be 0.005 to 5 mass% of the total composition. When the additives include a metal deactivator, the content thereof may be 0.005 to 1 mass% of the total composition. When the additives include an anti-foaming agent, the content thereof may be 0.0001 to 0.1 mass% of the total composition. [Example]

[0040] The present invention will be described in more detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0041] <About lubricant base oil> In the following examples, the components used as the lubricating base oil are described below. Hydrocarbon base oil: Polyalphaolefin (manufactured by INEOS, product name: Durasyn 164, abbreviation: PAO, API Group IV base oil) Ester base oil: Tetraester of pentaerythritol with 2-ethylhexanoic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., API Group V base oil).

[0042] <Evaluation tests of the properties of the compositions obtained in each example> The lubricating oil compositions obtained in each example were used, and tests were conducted using an oxidation stability tester RapidOxy (manufactured by Anton Paar) as the measuring device, employing the following measurement procedures (conditions), to evaluate the antioxidant performance of the lubricating oil compositions.

[0043] [Measurement procedure for evaluation test] First, approximately 5 g of the lubricating oil composition was placed in a glass dish for the measuring device and precisely weighed out. This was used as a sample (the method for precisely weighing the sample is described in each Example, etc. The mass of the precisely weighed lubricating oil composition (sample mass) is listed for each Example in Table 1). Next, the glass dish containing the sample (test lubricating oil composition) was placed in the measuring device and sealed, and the device was then filled with pure oxygen (G2 grade) at room temperature (25°C) at a pressure of 700 kPa. After pressurizing the device by introducing pure oxygen (G2 grade) in this way, the test was started once the pressure inside the device stabilized. The temperature inside the device was raised to 150°C and maintained at 150°C, and the time from the start of the test until the pressure inside the device reached a pressure 10% lower than the maximum pressure was measured (the time was measured with the point at which the pressure reached 10% lower than the maximum pressure as the end point). From this measurement, a longer measured time can be evaluated as having better antioxidant performance. In the lubricating oil composition samples obtained in Example 2 and Comparative Example 3, the pressure did not reach the end point even after a longer time compared to the other comparative examples, and so the test was terminated at the time shown in Table 1 (31,314 seconds for Example 2 and 32,490 seconds for Comparative Example 3). In Example 2, the pressure drop from the maximum ultimate pressure was 4.2% even after 31,314 seconds, while in Comparative Example 3, the pressure drop from the maximum ultimate pressure was 3.3% after 32,490 seconds. The measurement results are shown in Table 1. For comparison with Comparative Example 3, the time (14,640 seconds) required for the pressure drop from the maximum ultimate pressure measured in the test of Example 1 to reach 3.3% is also shown in Table 1.

[0044] Table 1 also shows, as an index of antioxidant performance, the multiplication factor ([measurement time until the pressure of the composition of Example 1 reaches 3.3%] / [measurement time of Comparative Example 1 (reference value)]) of the measurement time (time until the pressure of the composition of Comparative Example 1, which uses the same base oil, relative to the measurement time (time until the end point) of the composition of Comparative Example 1 (which consists only of base oil) as the reference (1). Similarly, Table 1 also shows the multiplication factor ([measurement time of Comparative Example 3] / [measurement time of Comparative Example 2 (reference value)]) of the measurement time (time until the end point: measurement time until the pressure of the composition of Comparative Example 3, which uses the same base oil, relative to the measurement time (time until the end point) of the composition of Comparative Example 2 (which consists only of base oil) as the reference (1). Furthermore, in this specification, such multiplication factor is used as an index of the effect of extending the life of the base oil.

[0045] Example 1 1,3-diorthotolylguanidine (7.7 mg, manufactured by Tokyo Chemical Industry Co., Ltd.) was added to the hydrocarbon base oil (10.7267 g, manufactured by INEOS) and heated to 100°C with a heat gun to dissolve, obtaining a mixture, which was used as a lubricating oil composition. Immediately after the heating and dissolving step, a test sample was weighed from the mixture (lubricating oil composition), and the obtained sample was subjected to an oxidation stability tester to evaluate antioxidant performance. Furthermore, in the obtained lubricating oil composition, the content of the guanidine-based compound per 1 g of lubricating base oil was 3.0 μmol / g (0.72 mg / g), and the content of the guanidine-based compound relative to the total amount of the composition was 0.072 mass%.

[0046] Example 2 1,3-Diorthotolylguanidine (16.1 mg, manufactured by Tokyo Chemical Industry Co., Ltd.) was added to the hydrocarbon base oil (9.9697 g, manufactured by INEOS) and heated to 100°C with a heat gun to dissolve, obtaining a mixed solution, which was used as a lubricating oil composition. Immediately after the heating and dissolving step, a test sample was weighed from the mixed solution (lubricating oil composition), and the obtained sample was subjected to an oxidation stability tester to evaluate antioxidant performance. Furthermore, in the obtained lubricating oil composition, the content of the guanidine-based compound per 1 g of lubricating base oil was 6.0 μmol / g (1.64 mg / g), and the content of the guanidine-based compound relative to the total amount of the composition was 0.14 mass%.

[0047] (Comparative Example 1) The guanidine compound (1,3-diorthotolylguanidine) was not used, and only the hydrocarbon base oil (manufactured by INEOS) was used as a comparative lubricating oil composition. The commercially available hydrocarbon base oil (manufactured by INEOS) was sampled at room temperature (about 25°C), and the obtained sample was subjected to an oxidation stability tester to evaluate the antioxidant performance.

[0048] (Comparative Example 2) The guanidine compound (1,3-diorthotolylguanidine) was not used, and only the ester base oil (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used as a comparative lubricating oil composition. The commercially available ester base oil (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was sampled at room temperature (about 25°C), and the obtained sample was subjected to an oxidation stability tester to evaluate the antioxidant performance.

[0049] (Comparative Example 3) 1,3-diorthotolylguanidine (7.3 mg, manufactured by Tokyo Chemical Industry Co., Ltd.) was added to the ester base oil (9.9844 g, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and heated to 100°C with a heat gun to dissolve, obtaining a mixture, which was used as a comparative lubricating oil composition. Immediately after the heating and dissolving step, a test sample was weighed from the mixture (comparative lubricating oil composition), and the obtained sample was subjected to an oxidation stability tester to evaluate antioxidant performance. In the comparative lubricating oil composition, the content of the guanidine-based compound per 1 g of ester base oil was 3.0 μmol / g (0.72 mg / g), and the content of the guanidine-based compound relative to the total amount of the composition was 0.073% by mass.

[0050] [Table 1]

[0051] As is clear from the results shown in Table 1, when the guanidine compound represented by the general formula (1) was combined with a hydrocarbon-based base oil (Examples 1 and 2), higher antioxidant performance was obtained compared to when an ester-based base oil was combined with a guanidine compound (Comparative Example 3). In this regard, first, when only a hydrocarbon-based base oil was used (Comparative Example 1), the time until the pressure drop rate (pressure reduction rate) reached 10% was 3,347 seconds, whereas when only an ester-based base oil was used (Comparative Example 2), the time until the pressure reduction rate reached 10% was 9,181 seconds. This indicates that the hydrocarbon-based base oil has a shorter time until the pressure reduction rate reaches 10% than the ester-based base oil, and therefore a faster rate of oxidative degradation. In other words, comparing Comparative Example 1 and Comparative Example 2, it can be understood that the hydrocarbon-based base oil is a base oil that is more susceptible to oxidative degradation than the ester-based base oil. Next, for the composition obtained in Comparative Example 3 containing an ester base oil and 3.0 μmol / g of a guanidine compound, the time until the pressure reduction rate reached 3.3% was 32,490 seconds. Therefore, the multiplier (hereinafter, this multiplier will be considered as the "life extension rate") was calculated based on the time until the pressure reduction rate of the base oil reached 10% (the end point time of Comparative Example 2). It was found that the life extension rate of the ester base oil was approximately 3.5 times (= 32,490 / 9,181) in Comparative Example 3. In contrast, for the composition obtained in Example 1 containing a hydrocarbon base oil and 3.0 μmol / g (the same proportion as in Comparative Example 3) of a guanidine compound, the time until the pressure reduction rate reached 3.3% was 14,640 seconds. When the multiplier (life extension rate) was calculated based on the time until the pressure reduction rate of the base oil reached 10%, it was found that the life extension rate of the hydrocarbon base oil in Example 1 was 4.4 times (= 14,640 / 3,347). Taking into consideration the elongation rate and the rate of oxidative degradation of the base oil itself, the results shown in Table 1 clearly show that the antioxidant effect of the guanidine compound on hydrocarbon base oils is higher than that on ester base oils, and it was found that the present invention can achieve higher antioxidant performance. [Industrial Applicability]

[0052] As described above, the present invention provides a lubricating oil composition that can highly inhibit the oxidative degradation of a hydrocarbon base oil contained as a lubricating base oil. Therefore, the lubricating oil composition of the present invention is useful as a composition for lubricating the moving parts of various mechanical devices having moving parts (e.g., internal combustion engines).

Claims

1. a hydrocarbon base oil; The following general formula (1): 【Chemistry 1】 [In formula (1), R １ ~R ３ each independently represents one selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, an aryl group having 6 to 24 carbon atoms which may have a substituent, and an aralkyl group having 7 to 25 carbon atoms which may have a substituent. an antioxidant consisting of a guanidine-based compound represented by the formula: and A lubricating oil composition characterized in that the content of the guanidine compound is 0.40 mass % or less based on the total amount of the composition.

2. 2. The lubricating oil composition according to claim 1, wherein the content of the guanidine compound is 0.15 mass % or less based on the total amount of the composition.

3. In the formula (1), R １ and R ３ each independently represents one selected from the group consisting of a phenyl group and a substituted phenyl group, and R ２ 2. The lubricating oil composition according to claim 1, wherein represents one member selected from the group consisting of a hydrogen atom and an alkyl group having 1 to 8 carbon atoms.

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