Lubricating oil composition

Abstract

To provide a lubricating oil composition capable of suppressing oxidative deterioration of a lubricating base oil while using a component different from a component conventionally used as an antioxidant.SOLUTION: The lubricant composition comprises a lubricant base oil and a compound represented by general formula (1): Wherein, in formula (1), R1 and R2 each independently represent hydrogen or the like; An antioxidant comprising a mercaptothiazole zinc compound represented by the following formula (1): SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] 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 life 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 the oxidized deterioration, it is common to use a combination of the lubricating base oil and an antioxidant.

[0003] As such antioxidants, phenol-based antioxidants and amine-based antioxidants are generally used (for example, JP 2023-049434 A (Patent Document 1) describes amine-based antioxidants and phenol-based antioxidants as antioxidants to be blended in lubricating oil compositions).

[0004] In the field of lubricating oil compositions, from the viewpoint of designing an appropriate composition depending on the application, etc., there is a demand for the development of new compositions that can prevent oxidative degradation of lubricating base oils while utilizing components different from those conventionally used as antioxidants. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2023-049434 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in view of the problems associated with the prior art, and has as its object to provide a lubricating oil composition that is capable of suppressing oxidative degradation of a lubricating base oil while utilizing a component that is different from components that have conventionally been used as antioxidants. [Means for solving the problem]

[0007] As a result of extensive research conducted by the present inventors in order to achieve the above-mentioned object, they discovered that by making a lubricating oil composition contain a lubricating base oil and an antioxidant consisting of a mercaptothiazole zinc-based compound represented by the following general formula (1), it is possible to suppress oxidative degradation of the composition, and thus completed the present invention.

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

[0009] [1] a lubricating base oil; The following general formula (1):

[0010] [ka]

[0011] [In formula (1), R 1 and R 2 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, or R 1 and R 2 may form a cyclic structure having 3 to 8 ring members together with the carbon atom to which they are attached, The cyclic structure may contain, as a constituent atom, at least one heteroatom selected from the group consisting of an oxygen atom, a nitrogen atom, and a sulfur atom, and may have a substituent. an antioxidant comprising a mercaptothiazole zinc compound represented by the formula: A lubricating oil composition comprising:

[0012] [2] The antioxidant is represented by the following general formula (2):

[0013] [ka]

[0014] [In formula (2), R 3 each independently represents one selected from the group consisting of a hydrogen atom and an alkyl group having 1 to 8 carbon atoms, R 4 each independently represents one selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, and an aryl group which may have at least one substituent selected from the group consisting of an alkyl group and an alkoxy group and which has a total of 6 to 12 carbon atoms including the carbon atoms of the substituent; R 5 each independently represents one selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, and an alkoxy group having 1 to 8 carbon atoms; n is an integer between 1 and 5. The lubricating oil composition according to [1], further comprising a pyridine imine compound represented by the formula:

[0015] [3] The lubricating oil composition according to [1] or [2], wherein the lubricating base oil is at least one selected from the group consisting of ester-based base oils and hydrocarbon-based base oils.

[0016] [4] The lubricating oil composition according to [2], wherein the lubricating base oil is a hydrocarbon base oil.

[0017] Although the reason why the lubricating oil composition of the present invention achieves the above object is not entirely clear, the present inventors speculate as follows.

[0018] In the present invention, to prevent oxidative degradation of a lubricating base oil, an antioxidant comprising a mercaptothiazole zinc compound represented by the general formula (1) (preferably, an antioxidant further comprising a pyridine imine compound represented by the general formula (2) in addition to the mercaptothiazole zinc compound as described in [1] above) is used in combination with a lubricating base oil. First, the oxidation reaction of a typical lubricating oil composition will be described. Generally, in a lubricating oil composition, the oxidation reaction that causes degradation of the lubricating base oil is thought to occur as follows. Specifically, when an external stimulus such as light or heat is applied to the lubricating oil composition, radicals of the components constituting the base oil (lubricating base oil) in the lubricating oil composition are first generated. When oxygen molecules come into contact with the radicals generated in this way, the oxygen molecules are added to the radicals, generating peroxy radicals. The generated peroxy radicals then attack the unreacted components of the base oil. This attack generates hydroperoxides in the system, and also generates radicals from the attacked base oil components, which then react with oxygen molecules to generate hydroperoxy radicals. In this way, radical proliferation reactions occur continuously (chain reactions) in the composition. Note that this radical proliferation reaction stops when oxygen-containing compounds such as alcohols, ketones, and carboxylic acids are produced during the reaction, but in other cases, it basically continues continuously (chain reactions). The radical proliferation reaction (negative chain reactions) thus caused accelerates the oxidative degradation of the lubricating base oil.

[0019] Next, a general zinc complex will be described. It has been known for some time that zinc-bipyridyl complexes, which are one type of zinc complex, can efficiently induce the disproportionation of superoxide, an oxidizing species, and decompose it into oxygen molecules and peroxide, which has lower oxidizing activity than superoxide (see, for example, Angew. Chem. Int. Engl., "Superoxide disproportionation driven by zinc complexes with various steric and electrostatic properties," 2013, vol. 52, pp. 12293-12297 (Reference 1)). However, Reference 1 does not disclose any mercaptothiazole zinc compounds. Thus, while it has been known that zinc-bipyridyl complexes can be used to disproportionate superoxide, an oxidizing species, and induce its decomposition, there have been no reports to date of using mercaptothiazole zinc compounds (or even of using a mixture of mercaptothiazole zinc compounds and pyridine imine compounds) to suppress oxidative degradation of lubricating oil compositions.

[0020] Under these circumstances, the present inventors have conducted extensive research and found that the use of the mercaptothiazole zinc-based compound as an antioxidant can highly inhibit the above-mentioned oxidation reaction (deterioration reaction). Furthermore, as demonstrated in the Examples section, the present inventors have further researched and confirmed that when the mercaptothiazole zinc-based compound and the pyridine imine compound are used in combination as antioxidants, oxidation degradation can be inhibited to a higher level than conventionally known amine-based antioxidants, particularly when the lubricating oil base oil is composed of a hydrocarbon base oil. Thus, in the present invention, at least a mercaptothiazole zinc-based compound is used as an antioxidant to inhibit oxidation reactions (deterioration reactions), i.e., to exert the effect of decomposing one or more oxidizing active species by themselves or between molecules, thereby making it possible to achieve the desired effect (the effect of inhibiting oxidation degradation of the base oil in the composition).

[0021] Although the reason why the use of a mercaptothiazole zinc compound makes it possible to suppress oxidation reactions (deterioration reactions) is not entirely clear, the inventors speculate that by using a mercaptothiazole zinc compound as an antioxidant (or, in some cases, by using a mercaptothiazole zinc compound in combination with a pyridine imine compound), the property of zinc to decompose oxidatively active species can be efficiently utilized, thereby making it possible to efficiently induce decomposition reactions of peroxy radicals and the like, thereby making it possible to suppress oxidative deterioration of the lubricating oil composition. [Effects of the Invention]

[0022] According to the present invention, it is possible to provide a lubricating oil composition that is capable of suppressing oxidative degradation of a lubricating base oil while utilizing a component that is different from components that have conventionally been used as antioxidants. DETAILED DESCRIPTION OF THE INVENTION

[0023] 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.

[0024] [Lubricating oil composition] The lubricating oil composition of the present invention comprises: a lubricating base oil; The following general formula (1):

[0025] [ka]

[0026] [In formula (1), R 1 and R 2each 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, or R 1 and R 2 may form a cyclic structure having 3 to 8 ring members together with the carbon atom to which they are attached, The cyclic structure may contain, as a constituent atom, at least one heteroatom selected from the group consisting of an oxygen atom, a nitrogen atom, and a sulfur atom, and may have a substituent. an antioxidant comprising a mercaptothiazole zinc compound represented by the formula: The present invention is characterized in that it contains:

[0027] <Antioxidants> The antioxidant according to the present invention comprises a mercaptothiazole zinc compound represented by the general formula (1). Thus, the antioxidant according to the present invention contains the mercaptothiazole zinc compound as an essential component.

[0028] R in the general formula (1) 1 and R 2 As described above, 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, or R 1 and R 2 may form a ring structure having 3 to 8 ring members together with the carbon atom to which they are attached. 1 and R 2 form a cyclic structure together with the carbon atom to which they are attached, the cyclic structure may contain at least one heteroatom selected from the group consisting of oxygen atom, nitrogen atom and sulfur atom as a constituent atom, and may have a substituent.

[0029] Such an R1 ~R 2 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.

[0030] Also, such R 1 ~R 2 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, those having 1 to 10 carbon atoms (more preferably 1 to 6, even more preferably 1 to 4, particularly preferably 1 to 3, and most preferably 1 to 2) are preferred from the viewpoint of ease of compound synthesis.

[0031] Such an R 1 ~R 2The 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).

[0032] Also, such R 1 ~R 2 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.

[0033] R in the general formula (1) 1 and R 2 are those (R 1 and R 2 ) may form a cyclic structure having 3 to 8 ring members together with the carbon atom to which it is bonded, and in this case (when a cyclic structure is formed), the cyclic structure may contain at least one heteroatom selected from the group consisting of oxygen atoms, nitrogen atoms, and sulfur atoms as a constituent atom, and may have a substituent. 1 and R 2 However, those (R 1 and R 2 ) together with the carbon atom to which it is attached to form a ring structure, the ring structure is 1 and R 2 The ring structure contains a carbon-carbon double bond of a thiazole compound to which R is bonded (substituted), and contains at least carbon atoms as constituent atoms of the ring (ring member atoms). Furthermore, such a cyclic structure may contain, in addition to carbon atoms as constituent atoms of the ring, at least one heteroatom selected from the group consisting of oxygen atoms, nitrogen atoms, and sulfur atoms. Furthermore, the number of ring members (total number of atoms constituting the ring) of such a cyclic structure is 3 to 8, more preferably 4 to 7, and even more preferably 5 to 6. Thus, the cyclic structure is more preferably a 5-membered or 6-membered ring. By setting the number of ring members (total number of atoms constituting the ring) within the above-mentioned numerical range, the stability of the ring structure is maintained to a high degree compared to when the number of ring members is outside the above-mentioned numerical range. Furthermore, such R 1 and R 2However, when they form a cyclic structure together with the carbon atoms to which they are bonded, the cyclic structure may have a substituent. Such a substituent is not particularly limited, but is preferably an alkyl group having 1 to 18 carbon atoms (more preferably 1 to 16, particularly preferably 1 to 14, and most preferably 1 to 12), with the aforementioned alkyl groups being more preferred. These alkyl groups may be linear or branched. The cyclic structure may also have no substituent (i.e., all groups (atoms) bonded to the cyclic structure may be hydrogen atoms). Furthermore, such cyclic structures are not particularly limited, but examples thereof include an epoxy ring, a thiirane ring, a cyclopropane ring, an oxetane ring, a cyclopentane ring, a cyclopentene ring, a furan ring, a dihydrofuran ring, a pyrrole ring, a thiophene ring, a pyrazole ring, an imidazole ring, an oxazole ring, a thiazole ring, a benzene ring, a pyridine ring, a pyran ring, a piperidine ring, a cycloheptane ring, and a cyclooctane ring, each of which may have a substituent. Furthermore, the cyclic structures exemplified above may be used as a basic skeleton, and a structure in which the double bonds in the skeleton are appropriately hydrogenated may be used as the cyclic structure, for example, a cyclohexane ring, a cyclohexadiene ring, etc., which are hydrogenated products of a benzene ring, may be used as the cyclic structure. Furthermore, the cyclic structures exemplified above may be used as a basic skeleton, and a structure in which the hydrogen atoms bonded to the skeleton are appropriately dehydrogenated may be used as the cyclic structure, for example, a cyclooctene ring, a cyclooctadiene ring, etc., which are dehydrogenated products of a cyclooctane ring, may be used as the cyclic structure.

[0034] In addition, R in the general formula (1) 1 and R 2 However, those (R 1 and R 2When the cyclic structure is formed together with the carbon atom to which R 1 is bonded, the cyclic structure is preferably an aromatic ring which may have a substituent, from the viewpoint of improving oxidation resistance. It is more preferably a benzene ring, pyridine ring, furan ring, pyrrole ring, thiophene ring, pyrazole ring, imidazole ring, oxazole ring, or thiazole ring, each of which may have a substituent. It is even more preferably a benzene ring, pyridine ring, or furan ring, each of which may have a substituent. It is even more preferably a benzene ring which may have a substituent. It is preferable that the substituent is an alkyl group having 1 to 18 carbon atoms (more preferably 1 to 16, particularly preferably 1 to 14, and most preferably 1 to 12) from the viewpoint of affinity with the base oil. This alkyl group may have a linear or branched structure. Among these, the substituent is more preferably a methyl group, an ethyl group, a butyl group, a hexyl group, an octyl group, a decyl group, or a dodecyl group, and more preferably a methyl group. Furthermore, when R 1 in the general formula (1) 1 and R 2 However, those (R 1 and R 2 ) together with the carbon atom to which it is bonded to form the cyclic structure, the cyclic structure is particularly preferably unsubstituted (having no substituents).

[0035] In addition, such R 1 ~R 2 As for the group, taking into consideration the availability, etc., the above-mentioned groups or R 1 and R 2 There are no particular limitations as long as the ring structure is appropriately selected from the ring structures formed by the carbon atoms to which they are bonded. 1 ~R 2 When R is a structure other than the above-mentioned cyclic structure, it is easier to obtain and synthesize it, and therefore, it is preferable to use R 1 ~R 2are each independently preferably a hydrogen atom, the alkyl group, the aryl group, or the aralkyl group, more preferably a hydrogen atom or the alkyl group, and further preferably a hydrogen atom, a methyl group, or an ethyl group; and R 1 ~R 2 It is particularly preferable that all of R are hydrogen atoms. 1 ~R 2 From the viewpoint of availability, R 1 and R 2 form the aforementioned cyclic structure together with the carbon atom to which they are bonded, and the cyclic structure is further preferably an aromatic ring which may have a substituent, particularly preferably a benzene ring which may have a substituent, a pyridine ring which may have a substituent, or a furan ring, and most preferably a benzene ring which may have a substituent.

[0036] Furthermore, in terms of improving oxidation resistance, the mercaptothiazole zinc compound represented by the general formula (1) is preferably a compound represented by the general formula (1) below, wherein R 1 and R 2 However, compounds in which they form a cyclic structure together with the carbon atom to which they are bonded and all of the constituent atoms of the ring are carbon atoms (this cyclic structure may have a substituent) are more preferred, and among these, from the viewpoint of availability, compounds represented by the following general formula (10):

[0037] [ka]

[0038] [In formula (10), R 10 each independently represents at least one selected from the group consisting of a hydrogen atom and an alkyl group having 1 to 8 carbon atoms (more preferably 1 to 4, particularly preferably 1 to 3, and most preferably 1 to 2). It is more preferable that the compound is a mercaptothiazole zinc compound (mercaptobenzothiazole zinc compound) represented by the formula (10). 10are each independently more preferably a hydrogen atom or the alkyl group, and even more preferably a hydrogen atom or a methyl group; R 10 are particularly preferably hydrogen atoms.

[0039] Furthermore, as the mercaptothiazole zinc-based compound represented by the general formula (1), from the viewpoint of availability and the like, 2-mercaptobenzothiazole zinc, 2-mercapto-5-methylbenzothiazole zinc, 2-mercapto-5-methoxybenzothiazole zinc, and 2-mercapto-5-chlorobenzothiazole zinc are preferred, 2-mercaptobenzothiazole zinc, 2-mercapto-5-methylbenzothiazole zinc, and 2-mercapto-5-methoxybenzothiazole zinc are more preferred, and 2-mercaptobenzothiazole zinc is particularly preferred.

[0040] The method for producing such a mercaptothiazole zinc compound represented by the general formula (1) is not particularly limited, and a desired design (e.g., R 1 and R 2 A known method may be appropriately adopted depending on the type of mercaptothiazole zinc compound represented by the general formula (1). In addition, commercially available products may be appropriately used as the mercaptothiazole zinc compound represented by the general formula (1).

[0041] The mercaptothiazole zinc-based compound represented by the general formula (1) can be formed as a reaction product of mercaptothiazole and a zinc salt. For example, a mixture of mercaptothiazole and a zinc salt can be added to a lubricating base oil and heated and mixed to react the mercaptothiazole and the zinc salt in the system, thereby producing and using the mercaptothiazole zinc-based compound represented by the general formula (1) consisting of a reaction product of mercaptothiazole and a zinc salt. Thus, a mixture of mercaptothiazole and a zinc salt can be used to incorporate the mercaptothiazole zinc-based compound represented by the general formula (1) into the system. When using such a mixture, the zinc salt that can be used (the zinc salt that can be used as a raw material for the mercaptothiazole zinc-based compound) is not particularly limited as long as it contains divalent zinc, but at least one compound selected from the group consisting of zinc fatty acid, zinc halide, zinc nitrate, zinc sulfate, zinc oxide, zinc sulfide, and zinc phosphate is preferred. Suitable examples of such zinc salts include zinc fluoride, zinc chloride, zinc bromide, zinc iodide, zinc nitrate, zinc sulfate, zinc oxide, zinc sulfide, zinc phosphate, zinc acetate, zinc propionate, zinc butanoate, zinc hexanoate, zinc adipate, zinc octanoate, zinc 2-ethylhexanoate, zinc benzoate, zinc cyclohexanoate, and zinc naphthenate. From the viewpoint of availability, zinc halides and zinc fatty acids are preferred, with zinc chloride, zinc acetate, zinc 2-ethylhexanoate, and zinc naphthenate being more preferred. Among these, zinc acetate, zinc 2-ethylhexanoate, and zinc naphthenate are even more preferred from the viewpoint of achieving higher solubility in lubricating base oils. The conditions employed for preparing the reaction product of mercaptothiazole (also known as 2-thiazolethiol) and a zinc salt are not particularly limited, and conditions may be appropriately selected so that a mercaptothiazole-based zinc compound represented by the general formula (1) is formed from mercaptothiazole and a zinc salt. Here, depending on the type of zinc salt, the mercaptothiazole and the zinc salt may be reacted by simply mixing them.

[0042] The antioxidant according to the present invention may contain the mercaptothiazole zinc compound represented by the general formula (1) above. However, when the lubricating base oil is a hydrocarbon base oil in particular, the antioxidant can exhibit a higher level of oxidation performance. Therefore, it is preferable to use the antioxidant containing the mercaptothiazole zinc compound and a compound represented by the following general formula (2):

[0043] [ka]

[0044] [In formula (2), R 3 each independently represents one selected from the group consisting of a hydrogen atom and an alkyl group having 1 to 8 carbon atoms, R 4 each independently represents one selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, and an aryl group which may have at least one substituent selected from the group consisting of an alkyl group and an alkoxy group and which has a total of 6 to 12 carbon atoms including the carbon atoms of the substituent; R 5 each independently represents one selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, and an alkoxy group having 1 to 8 carbon atoms; n is an integer between 1 and 5. In other words, from the viewpoint of enabling the antioxidant according to the present invention to exhibit a higher level of oxidation performance depending on the type of lubricating base oil, it is preferable to use a combination of the mercaptothiazole zinc compound represented by the general formula (1) and the pyridine imine compound represented by the general formula (2) (i.e., to use a mixture of the mercaptothiazole zinc compound represented by the general formula (1) and the pyridine imine compound represented by the general formula (2)).

[0045] R in the formula (2) 3 The compound may contain (5-n) of these R (n is an integer (natural number) of 1 to 5). 3When R is present in a compound, 3 each independently represents at least one selected from the group consisting of a hydrogen atom and an alkyl group having 1 to 8 carbon atoms (R 3 If there are multiple (n is 3 or less), R 3 may be the same or different).

[0046] Such an R 3 The alkyl group that can be selected as R has a carbon number of 1 to 8 (more preferably 1 to 6, even more preferably 1 to 4, particularly preferably 1 to 3, and most preferably 1 to 2). When the carbon number is equal to or less than the upper limit, a higher effect can be obtained in terms of solubility in base oil and ease of synthesis compared to when the carbon number exceeds the upper limit. In addition, such R 3 The alkyl group having 1 to 8 carbon atoms that can be selected as the alkyl group may be any of linear, branched, and cyclic, and is not particularly limited. However, from the viewpoint of ease of synthesis, linear alkyl groups and / or branched alkyl groups are preferred.

[0047] Furthermore, R in equation (2) 3 From the viewpoint of ease of compound synthesis, each of the groups is preferably a hydrogen atom, a methyl group, an ethyl group, a propyl group, or an isopropyl group, more preferably a hydrogen atom, a methyl group, an ethyl group, or a propyl group, even more preferably a hydrogen atom, a methyl group, or an ethyl group, particularly preferably a hydrogen atom or a methyl group, and most preferably a hydrogen atom.

[0048] In addition, R in the formula (2) 4 The compound contains n Rs (n is an integer (natural number) between 1 and 5). 4 each independently represents at least one selected from the group consisting of a hydrogen atom; an alkyl group having 1 to 8 carbon atoms; and an aryl group which may have at least one substituent selected from the group consisting of an alkyl group and an alkoxy group and which has a total of 6 to 12 carbon atoms including the carbon atoms of the substituent (R4 If there are multiple (n is 2 or more), R 4 may be the same or different).

[0049] Such an R 4 The alkyl group that can be selected as R has a carbon number of 1 to 8 (more preferably 1 to 6, even more preferably 1 to 4, particularly preferably 1 to 3, and most preferably 1 to 2). When the carbon number is equal to or less than the upper limit, a higher effect can be obtained in terms of solubility in base oil and ease of synthesis compared to when the carbon number exceeds the upper limit. In addition, such R 4 The alkyl group having 1 to 8 carbon atoms that can be selected as may be any of linear, branched, and cyclic alkyl groups, and is not particularly limited. However, from the viewpoint of ease of synthesis, a linear alkyl group is preferred, and among these, a methyl group, an ethyl group, or a propyl group is more preferred, a methyl group or an ethyl group is even more preferred, and a methyl group is particularly preferred.

[0050] Such an R 4 The aryl group that can be selected as the aryl group is an aryl group that may have at least one substituent selected from the group consisting of an alkyl group and an alkoxy group and has a total carbon number of 6 to 12 (more preferably 6 to 8), including the carbon number of the substituent. By setting the carbon number of such an aryl group to the above upper limit or less, it is possible to make the resulting compound excellent in solubility in base oil and easy to synthesize.

[0051] In addition, R in such formula (2) 4From the viewpoint of ease of synthesis, each of R is preferably independently a linear alkyl group; or an aryl group which may have at least one substituent selected from the group consisting of alkyl groups and alkoxy groups and which has a total of 6 to 12 carbon atoms including the carbon atoms of the substituent; among these, methyl, ethyl, propyl, phenyl, or p-alkoxyphenyl groups having a total of 6 to 8 carbon atoms are preferred, methyl, ethyl, phenyl, or p-methoxyphenyl groups are more preferred, methyl, phenyl, or p-methoxyphenyl groups are even more preferred, methyl or p-methoxyphenyl groups are particularly preferred, and methyl groups are most preferred. Note that from the viewpoint of ease of availability of raw materials during production, etc., R in the formula (2) is 4 A preferred example of the group is a hydrogen atom.

[0052] In addition, R in the formula (2) 5 The alkyl group that can be selected as R has a carbon number of 1 to 8 (more preferably 1 to 6, even more preferably 1 to 4, particularly preferably 1 to 3, and most preferably 1 to 2). When the carbon number is equal to or less than the upper limit, a higher effect can be obtained in terms of ease of availability of raw materials compared to when the carbon number exceeds the upper limit. 5 The alkyl group having 1 to 8 carbon atoms that can be selected as the alkyl group is not particularly limited and may be any of linear, branched, and cyclic groups. From the viewpoint of easy availability of raw materials, among these, a methyl group, an ethyl group, a propyl group, and an isopropyl group are more preferable, and a methyl group is particularly preferable.

[0053] In addition, R in the formula (2) 5 The alkoxy group that can be selected as R has a carbon number of 1 to 8 (more preferably 1 to 6, even more preferably 1 to 4, particularly preferably 1 to 3, and most preferably 1 to 2). When the carbon number is equal to or less than the upper limit, a higher effect can be obtained in terms of ease of availability of raw materials compared to when the carbon number exceeds the upper limit. 5The alkoxy group having 1 to 8 carbon atoms that can be selected as is not particularly limited, but from the viewpoint of easy availability of raw materials, among them, a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, a butoxy group, or an isobutoxy group is more preferable, a methoxy group, an ethoxy group, or a propoxy group is even more preferable, and a methoxy group is particularly preferable.

[0054] In addition, R in the formula (2) 5 From the viewpoint of availability of raw materials, each of the groups is more preferably a hydrogen atom, a methyl group, an ethyl group, a propyl group, an isopropyl group, or a methoxy group, and particularly preferably a hydrogen atom, a methyl group, an isopropyl group, or a methoxy group.

[0055] In addition, R in the formula (2) 5 is a substituent other than a hydrogen atom, the substitution position of the group on the benzene ring is arbitrary. However, since the 2nd, 4th, and 6th positions of the benzene ring have a large electronic influence on the adjacent nitrogen atom, if you want to increase the electron density, the substituent R 5 is particularly preferably an electron-donating substituent such as an alkyl group or an alkoxy group.

[0056] In the formula (2), n is an integer of 1 to 5 (here, a natural number), preferably an integer of 1 to 3, more preferably 1 or 2. Note that n is R 3 (In formula (2), the substituent other than the formula: -CR 4 The number of groups containing the structure represented by =N-) bonded (R 3 The number of substituents other than those on the pyridine ring is shown. 3 Substituents other than (formula: -CR 4 The substitution position of the group containing the structure represented by =N-) on the pyridine ring is not particularly limited and can be any position, but in order to further improve the interaction with zinc in the mercaptothiazole zinc compound, it is preferable to have a group containing the formula: -CR 4A group containing a structure represented by =N- (R 3 It is particularly preferred to place a substituent other than

[0057] In addition, a suitable example (a suitable embodiment) of the pyridine imine compound represented by the general formula (2) is not particularly limited, but for example, it is represented by the formula (2), n is 1 or 2, and R 3 are all hydrogen atoms, and R 4 are each independently one selected from the group consisting of a methyl group, a phenyl group, and a p-methoxyphenyl group (more preferably a methyl group), and R 5 are each independently one selected from the group consisting of a hydrogen atom, a methyl group, an ethyl group, a propyl group, an isopropyl group, a methoxy group and an ethoxy group.

[0058] The pyridine imine compound represented by the general formula (2) includes compounds represented by the following general formulas (3) to (4):

[0059] [ka]

[0060] Among them, the compound represented by general formula (4) is more preferable. 3 , R 4 and R 5 are R in the formula (2) 3 , R 4 and R 5 and the preferred examples thereof are also the same. Therefore, for example, 3 are all hydrogen atoms, and R 4 are each independently one selected from the group consisting of a methyl group, a phenyl group, and a p-methoxyphenyl group, and R 5are each independently one selected from the group consisting of a hydrogen atom, a methyl group, an ethyl group, a propyl group, an isopropyl group, a methoxy group and an ethoxy group.

[0061] As the pyridine imine compound represented by the general formula (2), for example, compounds represented by the following formulae (a) to (m) can be given as suitable examples.

[0062] [ka]

[0063] The method for producing such a pyridineimine compound represented by general formula (2) may be any known synthesis method that can be appropriately applied to produce the structure represented by general formula (2), and is not particularly limited. For example, a compound represented by the following general formula (5):

[0064] [ka]

[0065] [R in formula (5)] 3 , R 4 and n are R in the formula (2), 3 , R 4 and n.] (e.g., 2-formylpyridine, 2-acetylpyridine, 2,6-diacetylpyridine, 2-formylpyridine, 2,6-diphenylpyridine, 2,6-di(4-methoxyphenyl)pyridine, etc.) and a carbonyl compound represented by the following general formula (6):

[0066] [ka]

[0067] [R in formula (6)] 5 is R in the formula (1) 5 is equivalent to.] Preferably, the carbonyl compound is synthesized by a condensation reaction with an aniline compound represented by the formula (e.g., 2,4-dimethylaniline, 2,6-diisopropylaniline, 4-methoxy-2-methylaniline, 2,6-dimethylaniline, etc.). A suitable synthesis method using such a condensation reaction is, for example, dissolving the carbonyl compound and the aniline compound in a solvent such as toluene, ethanol, THF, or DMF and then subjecting them to a condensation reaction under heating and reflux conditions. An acid catalyst may be used as needed, taking into consideration the types of the carbonyl compound and the aniline compound. To efficiently promote the condensation reaction under heating and reflux conditions, it is preferable to use a dehydration apparatus such as a Dean-Stark apparatus. When using such a synthesis method, the product may precipitate as a precipitate depending on the compatibility between the produced compound and the solvent used. In such a case, the precipitate can be filtered and then washed with an appropriate solvent, enabling efficient purification. In addition, when the produced compound is soluble in the solvent used in the synthesis, it may be purified by means of recrystallization using an appropriate solvent, separation by column chromatography, etc. As described above, the method for purifying the produced compound is not particularly limited, and known methods such as purification by recrystallization can be appropriately used depending on the type of compound, etc.

[0068] Furthermore, the antioxidant according to the present invention is not particularly limited as long as it is made of the mercaptothiazole zinc-based compound, and may be, for example, made up of only the mercaptothiazole zinc-based compound, or made up of only a mixture of the mercaptothiazole zinc-based compound and the pyridine imine compound. However, in addition to the mercaptothiazole zinc-based compound and / or the pyridine imine compound, known antioxidants (for example, antioxidants described in JP 2022-158124 A (aromatic amine antioxidants, hindered amine antioxidants, phenolic antioxidants, etc.)) may also be used in combination, as long as the effects of the present invention are not impaired.

[0069] <Lubricant base oil> The lubricating base oil is not particularly limited, and any base oil known in the field of lubricating oil compositions can be used as appropriate. For example, a mineral base oil, a synthetic base oil, or a mixture thereof can be used.

[0070] Examples of the mineral oil base oil include paraffinic mineral oils, normal paraffinic base oils, isoparaffinic base oils, and naphthenic base oils, which are obtained by refining a lubricating oil fraction obtained by atmospheric distillation and / or vacuum distillation of crude oil, through one or a combination of two or more refining processes selected from solvent deasphalting, solvent extraction, hydrocracking, hydroisomerization, solvent dewaxing, catalytic dewaxing, solvent refining, hydrorefining, chemical washing, clay treatment, and the like; and mixtures of two or more of these.

[0071] Further, examples of the mineral oil-based base oil include base oils obtained by using any of the following (1) to (8) as a stock oil, refining the stock oil and / or a lubricating oil fraction recovered from the stock oil by a predetermined refining method, and recovering the lubricating oil fraction. (1) Distillates obtained by atmospheric distillation of paraffinic and / or mixed crude oils (2) Vacuum distillate (WVGO) from atmospheric residue of paraffinic and / or mixed crude oils (3) Waxes obtained by lubricating oil dewaxing processes (slack wax, etc.), and / or synthetic waxes obtained by the Fischer-Tropsch (FT) process, Gas-to-Liquid (GTL) process, etc. (FT wax, GTL wax, etc.) (4) Mild hydrocracking oil selected from the raw oils (1) to (3), and / or a mild hydrocracking oil of a mixture of two or more selected from the raw oils (1) to (3). (5) A mixed oil of two or more kinds selected from the raw material oils (1) to (4) (6) Deasphalted oil (DAO) of feedstock (1), (2), (3), (4) or (5) (7) Mild hydrocracking oil (MHC) of raw oil (6) (8) A mixed oil of two or more kinds selected from the raw material oils (1) to (7).

[0072] Preferred examples of the above-mentioned predetermined refining method include hydrorefining such as hydrocracking and hydrofinishing; solvent refining such as furfural solvent extraction; dewaxing such as solvent dewaxing and catalytic dewaxing; clay refining using acid clay or activated clay; and chemical (acid or alkali) washing such as sulfuric acid washing and caustic soda washing. One of these refining methods may be used alone, or two or more may be used in combination. When two or more refining methods are combined, the order in which they are used is not particularly limited and can be selected as appropriate.

[0073] Particularly preferred examples of mineral base oils include the following base oils (9) or (10) obtained by subjecting a stock oil selected from the above (1) to (8) or a lubricating oil fraction recovered from the stock oil to a predetermined treatment. (9) A hydrocracked base oil obtained by hydrocracking a feedstock oil selected from the above (1) to (8) or a lubricating oil fraction recovered from the feedstock oil, and subjecting the resulting product or the lubricating oil fraction recovered from the product by distillation or the like to a dewaxing treatment such as solvent dewaxing or catalytic dewaxing, or by distilling the dewaxing treatment followed by distillation. (10) A hydroisomerized base oil obtained by hydroisomerizing a feedstock oil selected from the above (1) to (8) or a lubricating oil fraction recovered from the feedstock oil, and then subjecting the resulting product or a lubricating oil fraction recovered from the product by distillation or the like to a dewaxing treatment such as solvent dewaxing or catalytic dewaxing, or by distilling the dewaxing treatment followed by distillation (it is more preferable to use a base oil produced by subjecting the dewaxing process to a catalytic dewaxing process).

[0074] In obtaining the mineral base oil (9) or (10) above, a solvent refining treatment and / or hydrofinishing treatment step may be further carried out at an appropriate stage, if necessary.

[0075] The mineral base oil may be a Group I base oil (hereinafter sometimes referred to as "API Group I base oil"), a Group II base oil (hereinafter sometimes referred to as "API Group II base oil"), or a Group III base oil (hereinafter sometimes referred to as "API Group III base oil"), or a blended base oil obtained by combining these. API Group I base oils are mineral base oils having a sulfur content of more than 0.03 mass% and / or a saturates content of less than 90 mass%, and a viscosity index of 80 or greater but less than 120. API Group II base oils are mineral base oils having a sulfur content of 0.03 mass% or less, a saturates content of 90 mass% or greater, and a viscosity index of 80 or greater but less than 120. API Group III base oils are mineral base oils having a sulfur content of 0.03 mass% or less, a saturates content of 90 mass% or greater, and a viscosity index of 120 or greater. API Group I base oils are typically produced through a solvent refining process, while API Group II and Group III base oils are typically produced through a hydrocracking process. In this specification, viscosity index refers to a viscosity index measured in accordance with JIS K 2283-2000. In this specification, the "sulfur content in the lubricating base oil" refers to a value measured in accordance with JIS K 2541-2003. In this specification, the "saturates content in the lubricating base oil" refers to a value measured in accordance with ASTM D 2007-93.

[0076] Suitable examples of the synthetic base oil include hydrocarbon synthetic oils and ester base oils. Examples of such synthetic base oils include API Group IV base oils (poly-α-olefin base oils, hereinafter sometimes referred to as "API Group IV base oils." Such base oils (hydrocarbon synthetic oils) are suitable hydrocarbon base oils), API Group V base oils (hereinafter sometimes referred to as "API Group V base oils." Such base oils include ester base oils), and mixed base oils obtained by combining these.

[0077] Suitable examples of API Group IV base oils include hydrocarbon base oils (hydrocarbon synthetic oils) made from oligomers and cooligomers of α-olefins having 2 to 32 carbon atoms (preferably 6 to 16 carbon atoms) and hydrogenation products thereof, such as ethylene-propylene copolymers, polybutene, 1-octene oligomers, 1-decene oligomers, and hydrogenation products thereof.

[0078] Preferred examples of the API Group V base oil include ester-based base oils such as monoesters (e.g., butyl stearate, octyl laurate, 2-ethylhexyl oleate, etc.); diesters (e.g., ditridecyl glutarate, di-2-ethylhexyl adipate, diisodecyl adipate, ditridecyl adipate, di-2-ethylhexyl sebacate, etc.); polyesters (e.g., trimellitic esters, etc.); and polyol esters (e.g., trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol-2-ethylhexanoate, pentaerythritol pelargonate, etc.). Other examples of conventional API Group V base oils include aromatic synthetic base oils such as alkylbenzenes, alkylnaphthalenes, dialkyldiphenyl ethers, and polyphenyl ethers. Among these API Group V base oils, the ester-based base oils are more preferred due to their availability.

[0079] Among these lubricating base oils, the ester-based base oils and / or hydrocarbon-based base oils are preferred because the antioxidant of the present invention can provide better antioxidant performance. Furthermore, when the antioxidant is composed of the mercaptothiazole zinc compound represented by the general formula (1) and the pyridine imine compound represented by the general formula (2), a higher level of antioxidant performance can be achieved, so it is preferred to use the hydrocarbon base oils in combination.

[0080] The "hydrocarbon base oil" referred to herein can be any hydrocarbon base oil commonly used in the field of lubricants, such as mineral hydrocarbon oils, synthetic hydrocarbon oils, or a mixture of both. From the standpoint of availability, API Group I, II, III, and IV base oils are preferred as such hydrocarbon base oils. Among these, API Group III and API Group IV base oils are particularly high-performance base oils, and their long-term use is extremely important. Using the antioxidant of the present invention in combination with these base oils is an effective means of extending the life of the base oil while enabling the design of an appropriate composition depending on the application. For these reasons, API Group III and API Group IV base oils are more preferred as the hydrocarbon base oil.

[0081] <About additives> The lubricating oil composition of the present invention may contain the lubricating base oil and the antioxidant consisting of the mercaptothiazole zinc 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.

[0082] 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 (known extreme pressure agents) such as metal thiocarbamate salts (e.g., salts of various metals such as Mo, Zn, Pb, and Sb), and disulfides; metal dithiophosphate salts (e.g., salts of various metals such as Zn, Pb, Sb, and Mo), and diazonium compounds. Examples of suitable additives include known antiwear agents such as known phosphorus-based and phosphorus-sulfur-based additives, such as metal alkyl phosphates (e.g., salts of various metals such as Zn, Pb, Sb, and Mo), phosphate esters, phosphites, 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.

[0083] <About the composition> In the lubricating oil composition of the present invention, the content of the lubricating base oil is not particularly limited, but is preferably 70% by mass or more (more preferably 80% by mass or more, even more preferably 95% by mass or more, and particularly preferably 99% by mass or more) based on the total amount of the composition. When the content of the lubricating base oil is equal to or greater than the lower limit, a more excellent effect can be obtained in terms of the dissolution stability of the additives when the additives are used, compared to when the content is less than the lower limit.

[0084] The content of the mercaptothiazole zinc-based compound (compound represented by the general formula (1)) used as the antioxidant is preferably 0.1 micromoles to 10 millimoles (more preferably 0.3 micromoles to 9 millimoles, and even more preferably 0.5 micromoles to 8 millimoles) per gram of the lubricating base oil. By setting the content of such mercaptothiazole zinc-based compound at or above the lower limit, even higher antioxidant performance can be achieved. On the other hand, by setting the content at or below the upper limit, even greater effectiveness can be achieved in terms of achieving high antioxidant performance economically. Conventionally known antioxidants basically achieve antioxidant effects through equivalent reactions, and depending on the type of antioxidant, large amounts must be added to maintain antioxidant function over a long period of time. However, when the antioxidant comprising the mercaptothiazole zinc-based compound according to the present invention is used, it is possible to suppress oxidative degradation over a long period of time even when a relatively small amount is used.

[0085] The content of the mercaptothiazole zinc compound used as the antioxidant is preferably 1 ppm by mass to 10% by mass (more preferably 1.5 ppm by mass to 9% by mass, and even more preferably 2 ppm by mass to 8% by mass) based on the total amount of the composition. By setting the content of the mercaptothiazole zinc compound relative to the total amount of the composition to be equal to or greater than the lower limit, a higher level of antioxidant performance can be obtained, while by setting it to be equal to or less than the upper limit, an even higher effect can be obtained in terms of obtaining high antioxidant performance economically.

[0086] Furthermore, when the antioxidant is composed of the mercaptothiazole zinc compound and the pyridine imine compound, the content of the pyridine imine compound is preferably 1 ppm by mass to 10% by mass (more preferably 1.5 ppm by mass to 9% by mass, and even more preferably 2 ppm by mass to 8% by mass) based on the total amount of the composition. By setting the content of such pyridine imine compound at or above the lower limit, a higher effect in terms of antioxidant performance tends to be obtained, while by setting it at or below the upper limit, a higher effect in terms of high antioxidant performance tends to be obtained economically.

[0087] Furthermore, when the antioxidant is composed of the mercaptothiazole zinc compound and the pyridine imine compound (when the mercaptothiazole zinc compound is used in combination with the pyridine imine compound), the content of the pyridine imine compound is preferably 0.1 to 10 moles (more preferably 0.5 to 1.5 moles) per mole of the mercaptothiazole zinc compound. By setting the content of such pyridine imine compound at or above the lower limit and at or below the upper limit, a higher combined antioxidant effect tends to be obtained economically.

[0088] 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.

[0089] <Preferred embodiments of the lubricating oil composition of the present invention> Preferred embodiments of the composition of the present invention (preferable combinations of components of the composition, etc.) will be briefly described below.

[0090] A preferred embodiment of the composition of the present invention is, for example, a composition containing an ester-based base oil as a lubricating base oil and an antioxidant consisting of the mercaptothiazole zinc-based compound (which may contain other additives as needed).In this way, in a composition in which the lubricating base oil is an ester-based base oil, even when the mercaptothiazole zinc-based compound is used alone, it is possible to exhibit sufficiently excellent antioxidant performance, and the design of the composition can be made simpler.

[0091] Another preferred embodiment of the lubricating oil composition of the present invention is, for example, a composition containing a hydrocarbon base oil as a lubricating base oil and an antioxidant consisting of a mixture of the mercaptothiazole zinc compound and the pyridine imine compound (which may contain other additives as needed). In this way, in a composition in which the lubricating base oil is a hydrocarbon base oil, using the mixture as an antioxidant makes it possible to more reliably achieve a higher level of antioxidant performance.

[0092] The preferred embodiments of the lubricating oil composition of the present invention have been described above. However, the lubricating oil composition of the present invention is not limited to the preferred embodiments described above, and other conditions are not particularly limited as long as it contains the lubricating base oil and the antioxidant comprising the mercaptothiazole zinc-based compound. [Example]

[0093] 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.

[0094] <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).

[0095] <About antioxidants> In the following examples and comparative examples, the components used as antioxidants are explained below. (I) Components used as antioxidants in the examples Zinc mercaptothiazole compounds: Zinc 2-mercaptobenzothiazole (manufactured by Tokyo Chemical Industry Co., Ltd.; also known as zinc 2-mercaptobenzothiazole) Pyridinimine compound: a compound represented by the following formula (k) (pyridinimine compound (k) obtained in Synthesis Example 1 below)

[0096] [ka]

[0097] (II) Components used as antioxidants in comparative examples Amine antioxidant: diphenylamine (manufactured by Tokyo Chemical Industry Co., Ltd., used in Comparative Example 2 as a conventionally known antioxidant).

[0098] (Synthesis Example 1: Synthesis of pyridine imine compound (k)) The compound represented by the formula (k) (pyridine imine compound (k)) was synthesized as follows. Specifically, dry toluene (60 ml) was first introduced into a 100 ml recovery flask under a nitrogen atmosphere, followed by the addition of 4-methoxy-2-methylaniline (2.0893 g, 15.3 mmol, manufactured by Tokyo Chemical Industry Co., Ltd.), 2,6-diacetylpyridine (1.2429 g, 7.6 mmol, manufactured by Tokyo Chemical Industry Co., Ltd.), and a catalytic amount (2 mg) of paratoluenesulfonic acid to obtain a mixed solution. Next, the mixed solution in the recovery flask was heated with stirring using a Dean-Stark water separator, and this heating and refluxing process was carried out for 24 hours to obtain a reaction solution. The reaction solution was then concentrated to dryness to obtain a crude solid (2.8241 g). Next, 2 g of the resulting crude solid was weighed out and washed with absolute ethanol (30 ml). The ethanol-insoluble solid was then filtered off, and the solid was further washed with ethanol. The remaining solid was then thoroughly dried to obtain a compound represented by the above formula (k) (pyridinimine compound (k)) in a yield of 50%. The structure of the obtained compound was identified by NMR measurement, and it was confirmed that the obtained solid was indeed pyridinimine compound (k). The results of the NMR measurement are shown below.

[0099] (NMR measurement results) 1 H-NMR(500MHz,1,2-CD2Cl4):2.13 (S,6H),2.36(s,6H),3.01(s,6H),6.63(d,J=7Hz,2H),6.76 and 6.76(d,J=7Hz,2H),6.81 and 6.82(s,2H),7.89(dd,J=8Hz,1H),8.38(d,J=7Hz,2H) 13 C-NMR (500MHz, 1,2-CD2Cl4):16.3,18.1,55.4,111.2,115.9,119.2,122.0,129.2,136.6,142.9,155.4,155.8,167.0.

[0100] <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.

[0101] [Measurement procedure for evaluation test] First, approximately 2.5 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 sampling the sample during precise weighing is described in each Example. 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. 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. 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 indicates a higher antioxidant performance. For the samples of the lubricating oil compositions obtained in Examples 1 and 2, the pressure did not reach the end-point pressure even after a long time had passed, and the percentage of pressure drop from the maximum achieved pressure (hereinafter sometimes simply referred to as "dropped pressure") at the time shown in Tables 1 and 2 (Example 1: 36,067 seconds (10.02 hours), Example 2: 33,201 (9.22 hours)) was 3.5% (Example 1) and 3.0% (Example 2), respectively. Taking this percentage of pressure drop into consideration, the test was terminated with the time shown in Tables 1 and 2 as the end-point. The measurement results for the lubricating oil compositions obtained in each Example, etc., for each type of base oil are shown in Tables 1 and 2, respectively.

[0102] Table 1 also shows, as an index of antioxidant performance, the multiplication factor ([measurement time of each example, etc.] / [measurement time of Comparative Example 1 (reference value)]) of the measurement time (time to the endpoint) of the composition of Comparative Example 1 (consisting only of base oil) as the reference (1x) for the composition of Comparative Example 1 and Comparative Example 2, which use the same base oil. Similarly, Table 2 also shows the multiplication factor ([measurement time of Example 2] / [measurement time of Comparative Example 3 (reference value)]) of the measurement time (time to the endpoint) of the composition of Comparative Example 3, which uses the same base oil. The multiplication factors listed in Examples 1 and 2 are those when the tests were forcibly stopped. Therefore, they are multiplication factors at intermediate stages and are actually much higher than the listed values.

[0103] Example 1 To the hydrocarbon base oil (6.0217 g), zinc 2-mercaptobenzothiazole (7.2 mg, manufactured by Tokyo Chemical Industry Co., Ltd.) and pyridine imine compound (k) (9.7 mg, prepared in Synthesis Example 1) were added as antioxidants, and the mixture was heated to 100°C with a heat gun to obtain a lubricating oil composition. The mixture (lubricating oil composition) thus obtained was thoroughly stirred and sampled, and the obtained sample was subjected to an oxidation stability tester to evaluate the antioxidant performance. The content of the mercaptothiazole zinc compound (zinc 2-mercaptobenzothiazole) per 1 g of lubricating base oil was 3.0 μmol / g (1.19 mg / g), and the content of the pyridine imine compound (k) per 1 g of lubricating base oil was 4.0 μmol / g (1.61 mg / g), and the molar ratio thereof ([mercaptothiazole zinc compound]:[pyridine imine compound (k)]) was 1:1.3.

[0104] (Comparative Example 1) The hydrocarbon base oil was used as it was without adding any antioxidant, and was regarded as a lubricating oil composition for comparison. Note that a commercially available hydrocarbon base oil (manufactured by INEOS) was sampled, and the obtained sample was subjected to an oxidation stability tester to evaluate the antioxidant performance.

[0105] (Comparative Example 2) The hydrocarbon base oil (8.4258 g) was mixed with diphenylamine (4.3 mg, manufactured by Tokyo Chemical Industry Co., Ltd.), an amine-based antioxidant, as a comparative antioxidant component, to obtain a mixed liquid, which was used as a lubricating oil composition. The mixed liquid (lubricating oil composition) thus obtained was thoroughly stirred and sampled, and the obtained sample was subjected to an oxidation stability tester to evaluate the antioxidant performance. The content of the antioxidant (amine-based antioxidant) per 1 g of lubricating oil base oil was 3.0 μmol / g.

[0106] [Table 1]

[0107] As is clear from the results shown in Table 1, when the antioxidant was a mixture of zinc 2-mercaptobenzothiazole and pyridine imine compound (k) (Example 1), the pressure drop remained at 3.5% even after the measurement time of 36,067 seconds (11 times the time of Comparative Example 1), and it was confirmed that the composition exhibited extremely high antioxidant performance even when compared with the composition obtained in Comparative Example 2 (a system using a known antioxidant).

[0108] Example 2 Zinc 2-mercaptobenzothiazole (14.2 mg) was added as an antioxidant to the ester-based base oil (11.5738 g), and the mixture was heated to 100°C with a heat gun to obtain a lubricating oil composition. The mixture (lubricating oil composition) thus obtained was thoroughly stirred and sampled, and the obtained sample was subjected to an oxidation stability tester to evaluate the antioxidant performance. The content of the zinc mercaptothiazole compound (zinc 2-mercaptobenzothiazole) per 1 g of lubricating oil base oil was 3.1 μmol / g (1.23 mg / g).

[0109] (Comparative Example 3) The ester-based base oil was used as a comparative lubricating oil composition without adding any antioxidant (e.g., mercaptothiazole zinc compound). A commercially available ester-based base oil (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was sampled, and the obtained sample was subjected to an oxidation stability tester to evaluate the antioxidant performance.

[0110] [Table 2]

[0111] As is clear from the results shown in Table 2, in a system using an ester-based base oil, the time required for the pressure drop to reach 10% was 9,181 seconds when the base oil itself was used without an antioxidant (Comparative Example 3), whereas for the composition obtained in Example 2, which used zinc 2-mercaptobenzothiazole as the antioxidant, the pressure drop remained at 3.0% even after 33,201 seconds (about four times the time of Comparative Example 3). These results demonstrate that the use of a zinc mercaptothiazole-based compound (zinc 2-mercaptobenzothiazole) as an antioxidant can suppress oxidative degradation of base oil.

[0112] As explained above, the results shown in Tables 1 and 2 reveal that when zinc 2-mercaptobenzothiazole is used as an antioxidant, it is possible to suppress oxidative degradation of base oil. Furthermore, it was confirmed that when the antioxidant is a mixture of a zinc mercaptothiazole compound (zinc 2-mercaptobenzothiazole) and a pyridine imine compound (see Example 1), when the base oil is a hydrocarbon base oil, it is possible to achieve extremely high antioxidant performance compared to conventional antioxidants (amine antioxidants). [Industrial Applicability]

[0113] As explained above, according to the present invention, it is possible to provide a lubricating oil composition that can suppress oxidative degradation of a lubricating base oil while utilizing a component different from components conventionally used as antioxidants. 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, etc.).

Claims

1. a lubricating base oil; The following general formula (1): 【Chemistry 1】 [In formula (1), R １ and R ２ 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, or R １ and R ２ may form a cyclic structure having 3 to 8 ring members together with the carbon atom to which they are attached, The cyclic structure may contain, as a constituent atom, at least one heteroatom selected from the group consisting of an oxygen atom, a nitrogen atom, and a sulfur atom, and may have a substituent. an antioxidant comprising a mercaptothiazole zinc compound represented by the formula: A lubricating oil composition comprising:

2. The antioxidant is represented by the following general formula (2): 【Chemistry 2】 [In formula (2), R ３ each independently represents one selected from the group consisting of a hydrogen atom and an alkyl group having 1 to 8 carbon atoms, R ４ each independently represents one selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, and an aryl group which may have at least one substituent selected from the group consisting of an alkyl group and an alkoxy group and which has a total of 6 to 12 carbon atoms including the carbon atoms of the substituent; R ５ each independently represents one selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, and an alkoxy group having 1 to 8 carbon atoms; n represents an integer of 1 or more and 5 or less.

2. The lubricating oil composition according to claim 1, further comprising a pyridine imine compound represented by the formula:

3. 2. The lubricating oil composition according to claim 1, wherein the lubricating base oil is at least one selected from the group consisting of ester-based base oils and hydrocarbon-based base oils.

4. 3. The lubricating oil composition according to claim 2, wherein the lubricating base oil is a hydrocarbon base oil.

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