JP7493373B2 - Lubricating Oil Composition - Google Patents

Description

The present invention relates to a lubricating oil composition.

2. Description of the Related Art Zinc dialkyldithiophosphates are widely used in lubricating oil compositions from the viewpoint of imparting antioxidant properties, antiwear properties, and the like.
As described above, zinc dialkyldithiophosphates are excellent in that they can impart antioxidant and antiwear properties to a lubricating oil composition, but they also have an aspect that they are prone to cause sludge formation due to thermal oxidation, etc. Therefore, various methods have been adopted to suppress sludge originating from zinc dialkyldithiophosphates.

For example, Patent Document 1 describes the incorporation of an overbased metal salicylate in an industrial hydraulic oil composition to suppress sludge derived from zinc dialkyldithiophosphate. It also describes that the metal component constituting the overbased metal salicylate is an alkaline earth metal such as calcium or magnesium, preferably calcium.

JP 2016-089043 A

However, lubricating oil compositions tend to gradually deteriorate over time and to become darker in color. Therefore, in order to easily grasp the deterioration state of a lubricating oil composition, a deterioration determination method utilizing a change in the hue of the lubricating oil composition is widely used in the management of machines and equipment that use the lubricating oil composition.
However, while lubricating oil compositions containing zinc dialkyldithiophosphate tend to deteriorate in hue, the performance of the lubricating oil composition may be maintained even after the hue deteriorates, and therefore there is a problem that the deterioration state cannot be determined in general based on the change in hue alone.

In addition, when managing machines and equipment that use lubricating oil compositions, the state of contamination and the occurrence of precipitates are often visually confirmed. However, if the color of the lubricating oil composition deteriorates early, the visibility of the state of contamination and the occurrence of precipitates in the lubricating oil composition deteriorates, and it becomes impossible to visually grasp the state of contamination and the occurrence of precipitates. This may result in the shutdown of the machines and equipment.

The inventors therefore considered mitigating the deterioration of the color of a lubricating oil composition containing zinc dialkyldithiophosphate over time. This would extend the period during which the contamination status and precipitate occurrence status of the lubricating oil composition can be properly observed visually, and would reduce the risk of machines and equipment being shut down due to inability to visually detect the contamination status and precipitate occurrence status. In addition, mitigating the deterioration of the color of a lubricating oil composition can be said to at least suppress oxidative deterioration of the lubricating oil composition, and is therefore a desirable measure for the lubricating oil composition.

The present invention aims to provide a lubricating oil composition containing zinc dialkyldithiophosphate, which exhibits gradual deterioration in color over time.

The present inventors have conducted extensive research to solve the above problems and have completed the following invention.
That is, the present invention relates to the following [1] to [6].
[1] A lubricating oil composition comprising a base oil (A), a zinc dialkyldithiophosphate (B), and a sodium-based detergent (C),
The zinc atom content is 100 ppm by mass to 2,000 ppm by mass based on the total amount of the lubricating oil composition;
A lubricating oil composition having a sodium atom content of 5 ppm by mass to 1,000 ppm by mass based on the total amount of the lubricating oil composition.
[2] The lubricating oil composition according to [1], wherein the content ratio of zinc atoms (Zn) in the lubricating oil composition to sodium atoms (Na) in the lubricating oil composition [(Zn)/(Na)] is 0.050 to 50 in mass ratio.
[3] The lubricating oil composition according to [1] or [2], wherein the content of magnesium atoms is less than 30 ppm by mass based on the total amount of the lubricating oil composition.
[4] The lubricating oil composition according to any one of [1] to [3], wherein the calcium atom content is less than 30 ppm by mass based on the total amount of the lubricating oil composition.
[5] The lubricating oil composition according to any one of [1] to [4], wherein the ASTM color after an ISOT test in accordance with JIS K 2514-1:2013 is carried out at 150°C for 168 hours using copper pieces and iron pieces as a catalyst is 1.0 or less.
[6] The lubricating oil composition according to any one of [1] to [5], wherein the base oil (A) has a kinematic viscosity at 40° C. of 9.00 mm ² /s to 165 mm ² /s.

According to the present invention, it is possible to provide a lubricating oil composition containing zinc dialkyldithiophosphate, which exhibits gradual deterioration in color over time.

In this specification, for preferred numerical ranges (e.g., ranges of content, etc.), the lower limit and upper limit values described in stages can be independently combined. For example, from the description "preferably 10 to 90, more preferably 30 to 60", the "preferable lower limit (10)" and the "more preferable upper limit (60)" can be combined to form "10 to 60".
In this specification, the numerical values in the examples are numerical values that can be used as upper or lower limits.
In this specification, a numerical range described as "A to B" means "A or more and B or less," unless otherwise specified.

[Embodiments of the lubricating oil composition of the present invention]
The lubricating oil composition of the present invention is a lubricating oil composition containing a base oil (A), a zinc dialkyldithiophosphate (B), and a sodium-based detergent (C),
The zinc atom content is 100 ppm by mass to 2,000 ppm by mass based on the total amount of the lubricating oil composition;
The lubricating oil composition has a sodium atom content of 5 ppm by mass to 1,000 ppm by mass based on the total amount of the lubricating oil composition.

The present inventors have conducted extensive research into lubricating oil compositions containing zinc dialkyldithiophosphate (hereinafter also referred to as "ZnDTP") in order to moderate the deterioration of color over time. As a result, they have found that a lubricating oil composition using a combination of ZnDTP and a sodium-based detergent, with the zinc atom content and the sodium atom content each adjusted to a specific range, can moderate the deterioration of color over time.
According to the study by the present inventors, when ZnDTP and a sodium-based detergent are blended alone in a lubricating oil composition without combining them, it is found that the color of the composition tends to deteriorate quickly over time. In particular, when a sodium-based detergent is blended alone, the deterioration of the color of the composition over time is remarkable.
However, it has been unexpectedly found that when ZnDTP and a sodium-based detergent are combined and incorporated into a lubricating oil composition, the deterioration of color over time is extremely gradual.
Although the detailed mechanism of this phenomenon is not clear, it is believed that at least the deterioration of the color of the lubricating oil composition caused by ZnDTP is suppressed by the sodium-based detergent, and the deterioration of the color caused by the sodium-based detergent is suppressed by ZnDTP. In other words, the interaction between ZnDTP and the sodium-based detergent can suppress the early deterioration of the color that occurs when ZnDTP and the sodium-based detergent are each blended alone into the lubricating oil composition, and it is presumed that the effect of the present invention is exerted.
The effects of the present invention are not achieved when the sodium-based detergent is replaced with a calcium-based detergent or a magnesium-based detergent.

In the following description, “base oil (A)”, “ZnDTP (B)”, and “sodium-based detergent (C)” will also be referred to as “component (A)”, “component (B)”, and “component (C)”, respectively.
The lubricating oil composition of one embodiment of the present invention may be composed only of "component (A)", "component (B)", and "component (C)". However, it may also contain other components in addition to "component (A)", "component (B)", and "component (C)" as long as the effects of the present invention are not impaired.
In one embodiment of the present invention, from the viewpoint of making it easier to exert the effects of the present invention, the total content of components (A), (B), and (C) is preferably 70.0 mass % to 100 mass %, more preferably 80.0 mass % to 100 mass %, even more preferably 90.0 mass % to 100 mass %, and still more preferably 95.0 mass % to 100 mass %, based on the total amount of the lubricating oil composition.

The base oil (A), ZnDTP (B), and sodium-based detergent (C), as well as other additives, are described in detail below.

<Base oil (A)>
The lubricating oil composition of the present invention contains a base oil (A).
As the base oil (A), one or more types selected from mineral oils and synthetic oils conventionally used as base oils for lubricating oils can be used without particular limitation.

Examples of mineral oils include atmospheric residual oils obtained by atmospheric distillation of crude oils such as paraffinic crude oil, intermediate base crude oil, or naphthenic crude oil; distillate oils obtained by vacuum distillation of these atmospheric residual oils; and mineral oils obtained by subjecting the distillate oils to one or more refining processes such as solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, and hydrorefining.

Examples of synthetic oils include poly-α-olefins such as α-olefin homopolymers and α-olefin copolymers (for example, α-olefin copolymers having 8 to 14 carbon atoms, such as ethylene-α-olefin copolymers); isoparaffins; various esters such as polyol esters and dibasic acid esters; various ethers such as polyphenyl ether; polyalkylene glycols; alkylbenzenes; alkylnaphthalenes; and GTL base oils obtained by isomerizing wax (gas-to-liquid (GTL) wax) produced from natural gas by the Fischer-Tropsch process or the like.

The base oil (A) may be a mineral oil, either alone or in combination with multiple types of oil, or a synthetic oil, either alone or in combination with multiple types of oil. Also, one or more mineral oils may be used in combination with one or more synthetic oils.

From the viewpoint of further improving the oxidation stability of the lubricating oil composition, the base oil (A) is preferably one or more selected from base oils classified into Groups II, III, and IV in the base oil category of the American Petroleum Institute (API), and more preferably one or more selected from base oils classified into Groups II and III.

The kinematic viscosity of base oil (A) at 40° C. (hereinafter also referred to as "40° C. kinematic viscosity") is preferably 8.00 mm ² /s to 150 mm ² /s, more preferably 10.0 mm ² /s to 120 mm ² /s, and even more preferably 15.0 mm ² /s to 100 mm ² /s.
When the base oil (A) has a 40° C. kinematic viscosity of 8.00 mm ² /s or more, it is easy to obtain a lubricating oil composition having a high flash point and excellent lubricating performance.
Furthermore, when the base oil (A) has a 40° C. kinetic viscosity of 150 mm ² /s or less, the viscous resistance at low temperatures does not become so large, which tends to improve the operation of machinery.

The viscosity index of the base oil (A) is preferably 80 or more, more preferably 90 or more, and even more preferably 100 or more. When the viscosity index of the base oil (A) is within the above range, it is possible to suppress viscosity changes due to temperature changes, making it easier to form an oil film at high temperatures, and it is easy to improve wear resistance.

When base oil (A) is a mixed base oil containing two or more types of base oils, it is preferable that the 40°C kinematic viscosity and viscosity index of the mixed base oil are within the above ranges.

In this specification, the 40°C kinematic viscosity and viscosity index refer to values measured or calculated in accordance with JIS K 2283:2000.

In one embodiment of the lubricating oil composition of the present invention, the content of base oil (A) is preferably 80.0% by mass to 99.84% by mass, more preferably 85.0% by mass to 99.80% by mass, and even more preferably 90.0% by mass to 99.50% by mass, based on the total amount of the lubricating oil composition, from the viewpoint of making it easier to exert the effects of the present invention.

<ZnDTP(B)>
The lubricating oil composition of the present invention contains ZnDTP (B).
By including ZnDTP (B) in the lubricating oil composition, antioxidant properties and antiwear properties are imparted to the lubricating oil composition.
If the lubricating oil composition does not contain ZnDTP (B), the effect of the present invention achieved by combining ZnDTP (B) with the sodium-based detergent (C) is not achieved.

As a preferred example of the ZnDTP (B) used in the lubricating oil composition of one embodiment of the present invention, one represented by the following general formula (b1) can be mentioned.

In the above general formula (b1), R ¹¹ to R ¹⁴ each independently represent a primary or secondary alkyl group having 3 to 22 carbon atoms, or an alkylaryl group substituted with an alkyl group having 3 to 18 carbon atoms.

Examples of the primary or secondary alkyl group having 3 to 22 carbon atoms which may be selected as R ¹¹ to R ¹⁴ include a primary or secondary propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, dodecyl group, tetradecyl group, hexadecyl group, octadecyl group, icosyl group, and ethylhexyl group.
Examples of the alkylaryl group substituted with an alkyl group having 3 to 18 carbon atoms which can be selected as R ¹¹ to R ¹⁴ include a propylphenyl group, a pentylphenyl group, an octylphenyl group, a nonylphenyl group, and a dodecylphenyl group.

When the compound represented by the above general formula (b1) is used as ZnDTP (B), the compound may be used alone or in combination of two or more kinds.
Here, in the lubricating oil composition of one embodiment of the present invention, when a compound represented by the above general formula (b1) is used as ZnDTP (B), it is preferable to use a primary zinc dialkyldithiophosphate having at least a primary alkyl group (primary alkyl ZnDTP), and it is more preferable to use a primary alkyl ZnDTP alone.
When a primary alkyl ZnDTP and a secondary zinc dialkyldithiophosphate having a secondary alkyl group (secondary alkyl ZnDTP) are used in combination, the content ratio of the primary alkyl ZnDTP to the secondary alkyl ZnDTP [(primary alkyl ZnDTP)/(secondary alkyl ZnDTP)] is preferably 50/50 to 99/1, more preferably 60/40 to 95/5, and even more preferably 70/30 to 90/10, by mass ratio.

In one embodiment of the lubricating oil composition of the present invention, the content of zinc atoms derived from ZnDTP(B) is preferably 100 ppm by mass to 2,000 ppm by mass, more preferably 110 ppm by mass to 1,900 ppm by mass, and even more preferably 120 ppm by mass to 1,800 ppm by mass, based on the total amount of the lubricating oil composition, from the viewpoint of making it easier to exert the effects of the present invention.

In addition, in the lubricating oil composition of one embodiment of the present invention, the content of ZnDTP(B) may be adjusted so that the content of zinc atoms derived from ZnDTP(B) falls within the above range. The content of ZnDTP(B) is preferably 0.11 mass% to 2.3 mass%, more preferably 0.13 mass% to 2.2 mass%, and even more preferably 0.14 mass% to 2.1 mass%, based on the total amount of the lubricating oil composition.

<Sodium-Based Detergent (C)>
The lubricating oil composition of the present invention contains a sodium-based detergent (C).
By including the sodium-based detergent (C) in the lubricating oil composition, detergency and other properties are imparted to the lubricating oil composition.
If the lubricating oil composition does not contain the sodium-based detergent (C), the effect of the present invention achieved by combining ZnDTP (B) with the sodium-based detergent (C) will not be achieved.

Examples of the sodium-based detergent (C) include sodium salts such as sodium sulfonate, sodium phenate, and sodium salicylate.
Among these, sodium sulfonate is preferred from the viewpoint of making it easier to exhibit the effects of the present invention.

As the sodium sulfonate, a compound represented by the following general formula (c1) is preferable.
As the sodium phenate, a compound represented by the following general formula (c2) is preferable.
As the sodium salicylate, a compound represented by the following general formula (c3) is preferable.
The sodium-based detergent (C) may be used alone or in combination of two or more kinds.

In the above general formulas (c1) to (c3), R is a hydrogen atom or a hydrocarbon group having 1 to 18 carbon atoms. In addition, in the above general formula (c2), q is an integer of 0 or more, and preferably an integer of 0 to 3.
Examples of the hydrocarbon group that can be selected as R include an alkyl group having 1 to 18 carbon atoms, an alkenyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 18 ring carbon atoms, an aryl group having 6 to 18 ring carbon atoms, an alkylaryl group having 7 to 18 carbon atoms, and an arylalkyl group having 7 to 18 carbon atoms.

The sodium-based detergent (C) may be neutral, basic, or overbased. From the viewpoint of making it easier to improve the base number retention of the lubricating oil composition, the sodium-based detergent (C) is preferably basic or overbased, and more preferably overbased.
In this specification, the basic or overbased metal-based detergent means a detergent obtained by reacting a metal with an acidic organic compound and containing a metal in excess of the stoichiometric amount required for neutralizing the metal with the acidic organic compound. That is, when the total chemical equivalent of the metal in the metal-based detergent is taken as the "metal ratio" relative to the chemical equivalent of the metal in the metal salt (neutral salt) obtained by reacting the metal with the acidic organic compound according to the stoichiometric amount required for neutralization, the metal ratio of the basic or overbased metal-based detergent is greater than 1. The metal ratio of the basic or overbased metal-based detergent used in this embodiment is preferably greater than 1.3, more preferably 5 to 30, and even more preferably 7 to 22.
In this specification, in accordance with JIS K 2501:2003, a base number measured by the perchloric acid method of less than 50 mgKOH/g is defined as "neutral," a base number of 50 mgKOH/g or more but less than 150 mgKOH/g is defined as "basic," and a base number of 150 mgKOH/g or more is defined as "overbased."

The base number of the sodium-based detergent (C) is preferably 5 mgKOH/g or more, more preferably 100 mgKOH/g or more, even more preferably 200 mgKOH/g or more, even more preferably 300 mgKOH/g or more, even more preferably 350 mgKOH/g or more, even more preferably 400 mgKOH/g or more, and is preferably 600 mgKOH/g or less, more preferably 550 mgKOH/g or less, even more preferably 500 mgKOH/g or less.

In one embodiment of the lubricating oil composition of the present invention, the content of sodium atoms derived from the sodium-based detergent (C) is preferably 5 ppm by mass to 1,000 ppm by mass, more preferably 10 ppm by mass to 980 ppm by mass, and even more preferably 15 ppm by mass to 970 ppm by mass, based on the total amount of the lubricating oil composition, from the viewpoint of making it easier to exert the effects of the present invention.

In the lubricating oil composition of one embodiment of the present invention, the content of the sodium-based detergent (C) may be adjusted so that the content of sodium atoms derived from the sodium-based detergent (C) falls within the above range. The content of the sodium-based detergent (C) is preferably 0.01 mass% to 0.53 mass%, more preferably 0.01 mass% to 0.52 mass%, and even more preferably 0.01 mass% to 0.51 mass%, based on the total amount of the lubricating oil composition.

<Other additives>
The lubricating oil composition of one embodiment of the present invention may contain lubricating oil additives other than component (B) and component (C) to the extent that the effects of the present invention are not impaired.
Examples of the lubricating oil additives include antioxidants, viscosity index improvers, pour point depressants, rust inhibitors, metal deactivators, antifoam agents, extreme pressure agents, antiwear agents, oiliness agents, and metal-based detergents (C') other than the sodium-based detergents (C).
These lubricating oil additives may be used alone or in combination of two or more.
In this specification, the additives such as the viscosity index improver and the antifoaming agent may be in the form of a solution diluted and dissolved in a part of the above-mentioned base oil (A) in consideration of handling properties and solubility in the base oil (A). In such a case, in this specification, the above-mentioned content of the additives such as the antifoaming agent and the viscosity index improver means the content in terms of active ingredients (resin content) excluding the diluent oil.

(Antioxidant)
Examples of the antioxidant include amine-based antioxidants and phenol-based antioxidants. These may be used alone or in combination of two or more.

Examples of amine-based antioxidants include monoalkyldiphenylamine-based compounds such as monooctyldiphenylamine and monononyldiphenylamine; dialkyldiphenylamine-based compounds such as 4,4'-dibutyldiphenylamine, 4,4'-dipentyldiphenylamine, 4,4'-dihexyldiphenylamine, 4,4'-diheptyldiphenylamine, 4,4'-dioctyldiphenylamine, 4,4'-dinonyldiphenylamine, and monobutylphenylmonoctylphenylamine; tetrabutyldiphenylamine, Examples of suitable compounds include polyalkyldiphenylamine compounds such as tetraphenylamine, tetrahexyldiphenylamine, tetraoctyldiphenylamine, and tetranonyldiphenylamine; and naphthylamine compounds such as α-naphthylamine, phenyl-α-naphthylamine, butylphenyl-α-naphthylamine, pentylphenyl-α-naphthylamine, hexylphenyl-α-naphthylamine, heptylphenyl-α-naphthylamine, octylphenyl-α-naphthylamine, and nonylphenyl-α-naphthylamine.

Examples of phenol-based antioxidants include monophenol-based compounds such as 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-ethylphenol, and octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; and diphenol-based compounds such as 4,4'-methylenebis(2,6-di-tert-butylphenol) and 2,2'-methylenebis(4-ethyl-6-tert-butylphenol).

When the lubricating oil composition of one embodiment of the present invention contains an antioxidant, the content of the antioxidant should be the minimum amount necessary to maintain oxidation stability, and is preferably 0.01 mass % to 1.5 mass %, more preferably 0.1 mass % to 1 mass %, based on the total amount of the lubricating oil composition.

(Viscosity index improver)
Examples of viscosity index improvers include polymers such as non-dispersed polymethacrylate, dispersed polymethacrylate, olefin copolymers (e.g., ethylene-propylene copolymers, etc.), dispersed olefin copolymers, styrene copolymers (e.g., styrene-diene copolymers, styrene-isoprene copolymers, etc.), etc. These may be used alone or in combination of two or more.
When the lubricating oil composition of one embodiment of the present invention contains a viscosity index improver, the content of the viscosity index improver, calculated as the resin content, based on the total amount of the lubricating oil composition is preferably 0.01 to 10 mass %, more preferably 0.02 to 7 mass %, and even more preferably 0.03 to 5 mass %.

(Pour Point Depressants)
Examples of pour point depressants include polymethacrylates having a mass average molecular weight of about 50,000 to 150,000. These may be used alone or in combination of two or more.
When the lubricating oil composition of one embodiment of the present invention contains a pour point depressant, the content of the pour point depressant is preferably 0.01 to 5 mass %, more preferably 0.02 to 2 mass %, based on the total amount of the lubricating oil composition.

(anti-rust)
Examples of the rust inhibitor include alkylbenzene sulfonate, dinonylnaphthalene sulfonate, organic phosphite ester, organic phosphate ester, alkenyl succinate ester, alkenyl succinic acid polyhydric alcohol ester, etc. These may be used alone or in combination of two or more.
When the lubricating oil composition of one embodiment of the present invention contains a rust inhibitor, the content of the rust inhibitor is preferably 0.01 to 10.0 mass %, more preferably 0.03 to 5.0 mass %, based on the total amount of the lubricating oil composition.

(Metal Deactivators)
Examples of the metal deactivator include benzotriazole-based compounds, tolyltriazole-based compounds, thiadiazole-based compounds, imidazole-based compounds, pyrimidine-based compounds, etc. These may be used alone or in combination of two or more.
When the lubricating oil composition of one embodiment of the present invention contains a metal deactivator, the content of the metal deactivator is preferably 0.01 to 5.0 mass %, more preferably 0.03 to 3.0 mass %, based on the total amount of the lubricating oil composition.

(Antifoaming agent)
Examples of the defoaming agent include silicone-based defoaming agents, fluorine-based defoaming agents such as fluorosilicone oil and fluoroalkyl ether, polyacrylate-based defoaming agents, etc. These may be used alone or in combination of two or more.
When the lubricating oil composition of one embodiment of the present invention contains an antifoaming agent, the content of the antifoaming agent in terms of the resin content is preferably 0.0001 to 0.20 mass %, more preferably 0.0005 to 0.10 mass %, based on the total amount of the lubricating oil composition.

(Extreme pressure agent or anti-wear agent)
The lubricating oil composition of one embodiment of the present invention may contain one or more selected from the group consisting of extreme pressure agents and antiwear agents. From the viewpoint of making it easier to exert the effects of the present invention, however, it is preferable that the content of one or more selected from the group consisting of extreme pressure agents and antiwear agents is small.
Examples of the extreme pressure agent and antiwear agent include organometallic compounds, sulfur compounds, phosphorus compounds, and sulfur-phosphorus compounds that do not fall under the category of component (B).

Examples of organometallic compounds include organomolybdenum compounds such as molybdenum dialkyldithiocarbamate (MoDTC) and molybdenum dialkyldithiophosphate (MoDTP), as well as organozinc compounds other than component (B), such as zinc dialkyldithiocarbamate (ZnDTC).

Examples of sulfur-based compounds include sulfurized oils and fats, sulfurized fatty acids, sulfurized esters, sulfurized olefins, monosulfides, polysulfides, dihydrocarbyl sulfides, thiadiazole compounds, alkylthiocarbamoyl compounds, thiocarbamate compounds, thioterpene compounds, and dialkylthiodipropionate compounds.

Examples of phosphorus compounds include phosphate esters such as aryl phosphate, alkyl phosphate, alkenyl phosphate, and alkylaryl phosphate; phosphite esters such as aryl hydrogen phosphite, alkyl hydrogen phosphite, aryl phosphite, alkyl phosphite, alkenyl phosphite, and aryl alkyl phosphite; and amine salts thereof.

Examples of sulfur-phosphorus compounds include monoalkylthiophosphates, dialkyldithiophosphates, trialkyltrithiophosphates, and amine salts thereof.

In the lubricating oil composition of one embodiment of the present invention, the content of one or more selected from the group consisting of extreme pressure agents and antiwear agents is usually about 0.05 to 10 mass %, preferably 0.1 to 5 mass %, based on the total amount of the lubricating oil composition.
However, from the viewpoint of ensuring oxidation stability, suppressing sludge generation, and suppressing color deterioration, among phosphorus-based compounds, the content of acidic phosphoric acid esters such as monoaryl acid phosphate, diaryl acid phosphate, monoalkyl acid phosphate, dialkyl acid phosphate, monoalkenyl acid phosphate, dialkenyl acid phosphate, etc.; acidic phosphorous acid esters such as monoalkyl acid phosphite, dialkyl acid phosphite, monoalkenyl acid phosphite, dialkenyl acid phosphite; and their amine salts is preferably small.Specifically, based on the total amount of lubricating oil composition, the content is preferably less than 0.01 mass%, more preferably less than 0.001 mass%, and even more preferably does not contain these phosphorus-based compounds.

(Oil-based agent)
Examples of oily agents include fatty alcohols; fatty acid compounds such as fatty acids and fatty acid metal salts; ester compounds such as polyol esters, sorbitan esters, and glycerides; and amine compounds such as fatty amines.
From the viewpoint of the effect of adding the oiliness agent, the content thereof is usually 0.1 to 10 mass %, preferably 0.5 to 5 mass %, based on the total amount of the lubricating oil composition.

(Metal-based detergent (C') other than sodium-based detergent (C))
The lubricating oil composition of one embodiment of the present invention may contain a metal-based detergent (C') other than the sodium-based detergent (C). However, from the viewpoint of making it easier to exert the effects of the present invention, it is preferable that the content of the metal-based detergent (C') other than the sodium-based detergent (C) is small.
Examples of the metal-based detergent (C') other than the sodium-based detergent (C) include magnesium-based detergents and calcium-based detergents.

Magnesium-based detergents include magnesium salts such as magnesium sulfonate, magnesium phenate, magnesium salicylate, etc. Additionally, magnesium-based detergents may be neutral, basic, or overbased.
Calcium-based detergents include calcium salts such as calcium sulfonate, calcium phenate, calcium salicylate, etc. Calcium-based detergents may be neutral, basic, or overbased.

The lubricating oil composition of one embodiment of the present invention preferably has a low content of metal atoms derived from metal-based detergents (C') other than the sodium-based detergent (C), and preferably contains less than 30 ppm by mass, more preferably less than 20 ppm by mass, even more preferably less than 10 ppm by mass, still more preferably less than 1 ppm by mass, and even more preferably contains no magnesium atoms derived from magnesium-based detergents, based on the total amount of the lubricating oil composition.
The lubricating oil composition of one embodiment of the present invention preferably has a low content of magnesium atoms derived from magnesium-based detergents, and preferably contains less than 30 ppm by mass, more preferably less than 20 ppm by mass, even more preferably less than 10 ppm by mass, still more preferably less than 1 ppm by mass, and even more preferably contains no magnesium atoms derived from magnesium-based detergents, based on the total amount of the lubricating oil composition.
Furthermore, the lubricating oil composition of one embodiment of the present invention preferably has a low content of calcium atoms derived from calcium-based detergents, and preferably contains less than 30 ppm by mass, more preferably less than 20 ppm by mass, even more preferably less than 10 ppm by mass, still more preferably less than 1 ppm by mass, and even more preferably contains no calcium atoms derived from calcium-based detergents, based on the total amount of the lubricating oil composition.

[Physical properties of lubricating oil composition]
<Kinematic viscosity at 40°C, viscosity index>
The lubricating oil composition of one embodiment of the present invention preferably has a 40° C. kinematic viscosity of 9.00 mm ² /s to 165 mm ² /s, more preferably 20.0 mm ² /s to 120 mm ² /s, and even more preferably 25.0 mm ² /s to 100 mm ² /s.
When the 40°C kinematic viscosity of the lubricating oil composition is 9.00 ^mm2 /s or more, the lubricating oil composition has a high flash point and is easy to have excellent lubricating performance. Also, when the 40°C kinematic viscosity of the base oil (A) is 165 ^mm2 /s or less, the viscous resistance at low temperatures is not so large, and the operation of the machine is easy to be improved.
The lubricating oil composition of one embodiment of the present invention preferably has a viscosity index of 80 or greater, more preferably 90 or greater, and even more preferably 100 or greater.
The 40° C. kinematic viscosity and viscosity index refer to values measured or calculated in accordance with JIS K 2283:2000.

<Zinc atom content>
The lubricating oil composition of the present invention has a zinc atom content of 100 ppm by mass to 2,000 ppm by mass based on the total amount of the lubricating oil composition.
If the zinc atom content is less than 100 ppm by mass, the antioxidant and antiwear properties are poor and the effects of the present invention are difficult to achieve.If the zinc atom content is more than 2,000 ppm by mass, the effects of the present invention are also difficult to achieve.
From the viewpoint of making it easier to exert the effects of the present invention, and further from the viewpoint of preparing a lubricating oil composition excellent in antioxidant and antiwear properties, the zinc atom content in the lubricating oil composition of one embodiment of the present invention is preferably 110 ppm by mass to 1,900 ppm by mass, and more preferably 120 ppm by mass to 1,800 ppm by mass, based on the total amount of the lubricating oil composition.
In this specification, the zinc atom content of the lubricating oil composition means the value measured in accordance with ASTM D4951.

<Sodium atom content>
The lubricating oil composition of the present invention has a sodium atom content of 5 ppm by mass to 1,000 ppm by mass based on the total amount of the lubricating oil composition.
If the sodium atom content is less than 5 ppm by mass, the lubricating oil composition will have poor detergency and the effects of the present invention will be difficult to achieve.If the sodium atom content exceeds 1,000 ppm by mass, the effects of the present invention will also be difficult to achieve.
From the viewpoint of making it easier to exert the effects of the present invention, and further from the viewpoint of preparing a lubricating oil composition with excellent detergency, the sodium atom content of the lubricating oil composition of one embodiment of the present invention is preferably from 10 ppm by mass to 980 ppm by mass, and more preferably from 15 ppm by mass to 970 ppm by mass, based on the total amount of the lubricating oil composition.
In this specification, the sodium atom content of the lubricating oil composition means the value measured in accordance with ASTM D4951.

<Ratio of Zinc Atomic Content to Sodium Atomic Content>
In the lubricating oil composition of one embodiment of the present invention, the ratio of the zinc atom content to the sodium atom content [(Zn)/(Na)], in terms of making it easier to exhibit the effects of the present invention, is preferably 0.050 to 50, more preferably 0.080 to 30, and even more preferably 0.10 to 20, in mass ratio.

<Magnesium atom content>
In the lubricating oil composition of one embodiment of the present invention, the magnesium atom content, based on the total amount of the lubricating oil composition, from the viewpoint of making it easier to exhibit the effects of the present invention, is preferably less than 30 ppm by mass, more preferably less than 20 ppm by mass, even more preferably less than 10 ppm by mass, still more preferably less than 1 ppm by mass, and even more preferably the lubricating oil composition does not contain any magnesium atoms.
In this specification, the magnesium atom content of the lubricating oil composition means the value measured in accordance with ASTM D4951.

<Calcium atom content>
In the lubricating oil composition of one embodiment of the present invention, the calcium atom content, based on the total amount of the lubricating oil composition, from the viewpoint of making it easier to exhibit the effects of the present invention, is preferably less than 30 ppm by mass, more preferably less than 20 ppm by mass, even more preferably less than 10 ppm by mass, still more preferably less than 1 ppm by mass, and even more preferably the lubricating oil composition contains no calcium atoms.
In this specification, the calcium atom content of the lubricating oil composition means the value measured in accordance with ASTM D4951.

<ASTM color after ISOT test>
In the lubricating oil composition of one embodiment of the present invention, after adding copper pieces and iron pieces as a catalyst and carrying out an ISOT test in accordance with JIS K 2514-1:2013 at 150°C for 168 hours, the ASTM color is preferably 1.0 or less, more preferably 0.5 or less.

[Method of producing lubricating oil composition]
The method for producing the lubricating oil composition of the present invention is not particularly limited.
For example, one embodiment of the present invention relates to a method for producing a lubricating oil composition, which comprises a step of mixing a base oil (A), ZnDTP (B), and a sodium-based detergent (C).
The method of mixing the above components is not particularly limited, and may be, for example, a method having a step of blending component (B) and component (C) with base oil (A). Component (B) and component (C) may be blended simultaneously with base oil (A) or separately. The same applies to other components other than component (B) and component (C). Each component may be blended after being made into a solution (dispersion) by adding a diluent oil or the like. After blending each component, it is preferable to stir and uniformly disperse it by a known method.

[Uses of the lubricating oil composition]
The lubricating oil composition of the present invention exhibits a gradual deterioration in color over time, and is therefore suitable for use in machines and equipment that employ visual inspection to check for contamination and the occurrence of precipitates, etc. The composition also exhibits excellent oxidation stability.
Therefore, for example, it can be suitably used as hydraulic oil, compressor oil, gear oil, cutting oil, machine tool oil, refrigeration oil, turbine oil, internal combustion oil, transmission oil, etc., and is particularly suitable for use as a hydraulic oil.

The present invention will be described in detail with reference to the following examples, but the present invention is not limited to these examples.

[Methods for measuring various physical properties]
The physical properties of the base oils and lubricating oil compositions used in each of the Examples and Comparative Examples were measured according to the procedures described below.
(1) Kinematic Viscosity and Viscosity Index The 40° C. kinematic viscosity and viscosity index were measured and calculated in accordance with JIS K2283:2000.
(2) Atomic Amount of Sodium and Atomic Amount of Zinc The atomic amounts of calcium, magnesium, sodium and zinc in the lubricating oil composition were measured in accordance with ASTM D4951.

[Examples 1 to 11 and Comparative Examples 1 to 7]
The base oils and various additives shown below were thoroughly mixed in the amounts (mass %) shown in Table 1 to prepare respective lubricating oil compositions.
Details of the base oils and various additives used in Examples 1 to 11 and Comparative Examples 1 to 7 are as follows.

<Base oil (A)>
Mineral oil belonging to API category Group II (kinematic viscosity at 40° C.=30.6 mm ² /s, viscosity index=104) was used.

<Zinc dialkyldithiophosphate (B)>
A primary zinc dialkyldithiophosphate in which R ¹¹ to R ¹⁴ in the above general formula (b1) are 2-ethylhexyl groups (primary alkyl groups) was used.
Zinc atom content: 8.90% by mass, phosphorus atom content: 7.40% by mass, sulfur atom content: 15.0% by mass
In Table 1, zinc dialkyldithiophosphate (B) is abbreviated as "ZnDTP."

<Sodium-based detergent (C) and metal-based detergent (C') other than sodium-based detergent>
Na sulfonate (base number: 448 mg KOH/g, sodium atom content: 19.5% by mass)
Ca sulfonate (base number: 307 mg KOH/g, calcium atom content: 11.9% by mass)
Mg sulfonate (base number: 308 mg KOH/g, magnesium atom content: 9.4% by mass)
The base number of the sodium-based detergent (C) and the metal-based detergent (C') other than the sodium-based detergent was measured by a perchloric acid method in accordance with JIS K 2501-9:2003.

[evaluation]
<ISOT Test>
Copper pieces and iron pieces were added as catalysts to the test oil (lubricating oil composition), and the test oil was subjected to forced deterioration by carrying out an ISOT test in accordance with JIS K 2514-1: 2013. The test temperature was 150°C, and the ASTM color (JIS K 2580: 2003) of the test oil was measured before the start of the ISOT test, 72 hours after the start of the ISOT test, and 168 hours after the start of the ISOT test.
Sample oils whose ASTM color was 1.0 or less (L1.0) were judged to have "no deterioration in color," and sample oils whose ASTM color was greater than 1.0 (L1.5, L2.0, etc.) were judged to have "deterioration in color."

<Base Number>
The base number of the test oil before the start of the ISOT test (B _0h ), the base number of the test oil 72 hours after the start of the ISOT test (B _72h ), and the base number of the test oil 168 hours after the start of the ISOT test (B _168h ) were measured by the hydrochloric acid method in accordance with JIS K 2501-8:2003.
Then, "base number maintenance rate S _72h (%) after 72 hours from the start of the ISOT test" and "base number maintenance rate S _168h (%) after 168 hours from the start of the ISOT test" were calculated according to the following formula.
_S72h (%) = {( _B72h ) / ( _B0h )} × 100
S _168h (%) = {(B _168h ) / (B _0h )} × 100

The results are shown in Table 1.

The following can be seen from Table 1.
The lubricating oil compositions of Examples 1 to 11 showed no deterioration in color even after 168 hours had elapsed since the start of the ISOT test.
In contrast, in Comparative Examples 1 and 2, which contained ZnDTP but no Na sulfonate, deterioration in hue was observed 72 hours after the start of the ISOT test.
Also, in Comparative Examples 3 and 4, which contained Na sulfonate but no ZnDTP, deterioration in hue was observed 72 hours after the start of the ISOT test.
Furthermore, in Comparative Examples 5 and 6 in which Ca sulfonate was used instead of Na sulfonate, and Comparative Example 7 in which Mg sulfonate was used instead of Na sulfonate, deterioration in hue was observed 72 hours after the start of the ISOT test.

Claims (4)

A lubricating oil composition comprising a base oil (A), a zinc dialkyldithiophosphate (B), and a sodium-based detergent (C),
The base oil (A) has a kinematic viscosity at 40° C. of 9.00 mm ² /s to 165 mm ² /s;
The calcium atom content is less than 30 ppm by mass based on the total amount of the lubricating oil composition;
The zinc atom content is 100 ppm by mass to 2,000 ppm by mass based on the total amount of the lubricating oil composition;
The sodium atom content is 5 ppm by mass to 1,000 ppm by mass based on the total amount of the lubricating oil composition;
The sodium-based detergent (C) is a sodium sulfonate,
The base number of the sodium-based detergent (C) is 300 mgKOH/g or more,
A lubricating oil composition for hydraulic oil , wherein the ratio of the zinc atom content to the sodium atom content [(Zn)/(Na)] is 30 or less in mass ratio. 2. The lubricating oil composition according to claim 1, wherein the content ratio of zinc atoms (Zn) in the lubricating oil composition to sodium atoms (Na) in the lubricating oil composition [(Zn)/(Na)] is, in mass ratio, 0.050 to 30 . The lubricating oil composition according to claim 1 or 2, wherein the content of magnesium atoms is less than 30 ppm by mass based on the total amount of the lubricating oil composition. The lubricating oil composition according to any one of claims 1 to 3 , wherein the ASTM color after an ISOT test in accordance with JIS K 2514-1:2013 is carried out at 150°C for 168 hours using copper pieces and iron pieces as catalysts is 1.0 or less.