JP6325414B2 - Lubricating oil composition - Google Patents

Description

  The present invention relates to a lubricating oil composition. Specifically, the present invention relates to a lubricating oil composition based on a mineral oil having a high sulfur content.

Lubricating oils and greases are used for various industrial machines, internal combustion engines, automatic transmissions, and the like according to their applications. All of these lubricants gradually lose their original performance due to oxidative degradation due to oxygen in the air during use, thermal degradation due to temperature rise of the lubricant and contact with high temperature parts, etc., and replacement with new oil Must. It is important from the viewpoint of labor saving in maintenance management, resource saving, and prevention of environmental pollution to suppress the deterioration of the lubricating oil and to make the oil change interval as long as possible (long draining). Improvement of oxidation stability and thermal stability is the key to making the lubricating oil longer drain, and studies have been made on both the performance of the base oil (higher refining degree) and the additive blending technology.
Metal complexes such as phenol- or amine-based antioxidants that function as chain terminators, zinc dialkyldithiophosphates (ZDTP) and organic molybdenum compounds that function as peroxide decomposers to improve the oxidation stability of lubricating oils It is conventionally known to blend. On the other hand, metal complexes such as ZDTP have a problem that they are changed into components (sludge) that are insoluble in oil due to thermal decomposition, oxidative decomposition, hydrolysis, and the like, causing trouble. Therefore, it is conventionally known to blend an ashless sulfur compound that functions as a peroxide decomposer (Non-Patent Document 1) and to blend a phenolic antioxidant and an ashless sulfur compound ( Non-patent document 2).
The base oil for lubricating oils, which is formulated with these antioxidants and focuses on improving oxidative stability and thermal stability, is an API GrII group with low sulfur content and low aromaticity that has been highly purified by treatments such as hydrogenation. Oil, GrIII base oil and GTL base oil are mainly used. Synthetic lubricating oils such as polyalphaolefins, esters, and aromatic carboxylic acid esters are also used. Highly hydrogenated mineral oils and GTL base oils require special production equipment for production or refining, and synthetic oils are expensive and therefore cannot be used as lubricating base oils for general purposes.

G.H.Denison, P.C.Condit, Ind.Eng.Chem., 37 1102 (1945) Polymer Additive Handbook, CMC Publishing, p43 (2010)

  Mineral oil with a high sulfur content is relatively inexpensive and has a high supply ability, but has a drawback of low oxidation stability and thermal stability. The present invention provides a long-draining lubricating oil composition that improves the oxidative stability and thermal stability of a lubricating oil based on a mineral oil having a high sulfur content and enables long-term use.

  As a result of intensive studies on the above problems, the present inventors have completed the present invention.

  That is, the present invention includes that the mineral oil base oil having a sulfur content of 200 mass ppm or more contains [A] alkylated diphenylamine, [B] hindered phenol compound, and [C] sulfurized fatty acid ester. The lubricating oil composition is characterized.

  According to the present invention, it is possible to provide a long-draining lubricating oil composition that improves the oxidative stability and thermal stability of a lubricating oil based on a mineral oil having a high sulfur content and enables long-term use. It has become possible.

  Hereinafter, the present invention will be described in detail.

  The base oil according to the lubricating oil composition of the present invention is a mineral oil base oil.

As mineral base oils, lubricating oil fractions obtained by subjecting crude oil to atmospheric distillation and reduced pressure distillation are subjected to solvent deburring, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, hydrorefining, sulfuric acid Examples thereof include mineral base oils such as paraffinic and naphthenic oils that are refined by a single or a combination of two or more purification treatments such as washing and clay treatment.
These base oils may be used alone or in combination of two or more at any ratio.

The sulfur content of the mineral base oil is at least 200 ppm by mass, preferably at least 300 ppm by mass, and more preferably at least 500 ppm by mass. On the other hand, if the sulfur content is too high, oxidative degradation is promoted, so the content is preferably 0.75% by mass or less, and more preferably 0.5% by mass or less.
In addition, the sulfur content as used in the field of this invention means the value measured based on ASTM D4951.

Although there is no restriction | limiting in particular about the total aromatic content of mineral oil type base oil, Preferably it is 40 mass% or less, More preferably, it is 30 mass% or less. Although the total aromatic content may be 0% by mass, it is preferably 1% by mass or more, more preferably 5% by mass or more, and more preferably 10% by mass or more in terms of the solubility of the additive. preferable. When the total aromatic content of the base oil exceeds 40% by mass, oxidation stability is inferior, which is not preferable.
In addition, the said total aromatic content means the aromatic fraction content measured based on ASTM D2549 (aromatic fraction). Usually, this aromatic fraction includes alkylbenzene, alkylnaphthalene, anthracene, phenanthrene, alkylated products thereof, compounds in which four or more benzene rings are condensed, and heterogeneous compounds such as pyridines, quinolines, phenols, and naphthols. Compounds having aromatics are included.

Kinematic viscosity at 40 ° C. of the mineral base oil is preferably ^{2 mm} 2 / s or more, more preferably 10 mm ² / s or more, further preferably 30 mm ² / s or more. On the other hand, it is preferable that it is 460 mm < ² > / s or less, More preferably, it is 150 mm < ² > / s or less, More preferably, it is 70 mm < ² > / s or less.
When the kinematic viscosity at 40 ° C. of the mineral oil base oil exceeds 460 mm ² / s, the viscosity temperature characteristics and the low temperature viscosity characteristics deteriorate, and when it is less than 2 mm ² / s, the oil film formation at the lubrication point is insufficient. Therefore, the metal fatigue resistance and wear resistance are inferior, and the evaporation loss of the lubricating base oil is increased.

Although there is no special restriction | limiting in the viscosity index of mineral oil type base oil, 85 or more are preferable, 90 or more are more preferable, and 95 or more are further more preferable. On the other hand, 160 or less is preferable, 150 or less is more preferable, and 140 or less is more preferable.
When the viscosity index is lower than 85, viscosity temperature characteristics that can exhibit fuel saving performance cannot be obtained. On the other hand, when it exceeds 160, normal paraffin increases in the base oil, so that the viscosity at a low temperature increases rapidly.

  The lubricating oil composition of the present invention contains alkylated diphenylamine as the [A] component.

  The alkylated diphenylamine is preferably p, p′-dialkyldiphenylamine represented by the following general formula (1).

In the general formula (1), R ¹ and R ² may be the same or different, R ¹ represents hydrogen or an alkyl group having ^{1 to} 16 carbon atoms, and R ² represents an alkyl group having 1 to 16 carbon atoms. When both R ¹ and R ² are hydrogen atoms, they themselves may precipitate as sludge due to oxidation, while when the number of carbons exceeds 16, the proportion of functional groups in the molecule decreases, There is a risk that the antioxidant ability will be weakened.

Specific examples of the alkyl group having ^{1 to} 16 carbon atoms of R ¹ and R ² include, for example, methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, Examples include decyl group, undecyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group and the like (these alkyl groups may be linear or branched). Among these, as R ¹ and R ² , a branched alkyl group having 3 to 16 carbon atoms is preferable from the viewpoint of excellent solubility of the oxidation product itself in the base oil, and further an olefin having 3 or 4 carbon atoms, Alternatively, a branched alkyl group having 3 to 16 carbon atoms derived from the oligomer is more preferable. Specific examples of the olefin having 3 or 4 carbon atoms include propylene, 1-butene, 2-butene, isobutylene, and the like, but the solubility of its own oxidation product in a lubricating base oil is excellent. From the viewpoint, propylene or isobutylene is preferable.

When p, p′-dialkyldiphenylamine represented by the general formula (1) is used, R ¹ and R ² are isopropyl group derived from propylene, tert-butyl group derived from isobutylene, and two amounts of propylene. Branched hexyl group derived from the body, branched octyl group derived from the dimer of isobutylene, branched nonyl group derived from the trimer of propylene, branched dodecyl derived from the trimer of isobutylene A branched dodecyl group derived from a propylene tetramer or a branched pentadecyl group derived from a propylene pentamer is particularly preferred, a tert-butyl group derived from isobutylene, derived from a propylene dimer Branched hexyl groups, branched octyl groups derived from isobutylene dimers, and propylene trimers A branched nonyl group, a branched dodecyl group derived from a tetramer of a branched dodecyl or propylene derived from a trimer of isobutylene are particularly preferred.

  A commercially available product may be used as p, p'-dialkyldiphenylamine. Further, by reacting diphenylamine with an alkyl halide having 1 to 16 carbon atoms, an olefin having 2 to 16 carbon atoms, an olefin having 2 to 16 carbon atoms or an oligomer thereof with a Friedel-Crafts catalyst, It can be easily synthesized. Specifically, as the Friedel-Crafts catalyst at this time, for example, a metal halide or an acidic catalyst is used.

  As the alkylated diphenylamine, one type of compound may be used alone, or a mixture of two or more types of compounds in an arbitrary mixing ratio may be used.

The content of the component [A] is not particularly limited, but is preferably 0.01 to 10% by mass, more preferably 0.05 to 5% by mass, and still more preferably 0, based on the total amount of the composition. 0.1 to 1% by mass.
When the content of the component [A] is 0.01% by mass or more, sufficient antioxidant properties are obtained, and when it is 10% by mass or less, solubility in base oil is sufficiently obtained.

  The lubricating oil composition of the present invention contains a hindered phenol compound as the [B] component.

Specific examples of the hindered phenol compound include 4,4′-methylenebis (2,6-di-tert-butylphenol) and 4,4′-bis (2,6-di-tert-butylphenol). 4,4′-bis (2-methyl-6-tert-butylphenol), 2,2′-methylenebis (4-ethyl-6-tert-butylphenol), 2,2′-methylenebis (4-methyl-6- tert-butylphenol), 4,4′-butylidenebis (3-methyl-6-tert-butylphenol), 4,4′-isopropylidenebis (2,6-di-tert-butylphenol), 2,2′-methylenebis ( 4-methyl-6-nonylphenol), 2,2′-isobutylidenebis (4,6-dimethylphenol), 2,2′-methylenebis (4-methyl) Til-6-cyclohexylphenol), 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-ethylphenol, 2,4-dimethyl-6-tert-butylphenol, 2,6-di-tert-α-dimethylamino-p-cresol, 2,6-di-tert-butyl-4 (N, N′-dimethylaminomethylphenol), 4,4′-thiobis (2-methyl) -6-tert-butylphenol), 4,4'-thiobis (3-methyl-6-tert-butylphenol), 2,2'-thiobis (4-methyl-6-tert-butylphenol), bis (3-methyl- 4-hydroxy-5-tert-butylbenzyl) sulfide, bis (3,5-di-tert-butyl-4-hydroxybenzyl) sulfide 2,2′-thio-diethylenebis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], octyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) ) Propionate, tridecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, pentaerythrityl-tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate ], Octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, and mixtures thereof.
Among these, a hindered phenol compound having a molecular weight of 240 or more is more preferably used because it has a high decomposition temperature and exhibits its antioxidant effect even under higher temperature conditions.

The content of the component [B] is not particularly limited, but is preferably 0.01 to 10% by mass, more preferably 0.05 to 5% by mass, and still more preferably 0, based on the total amount of the composition. 0.1 to 1% by mass.
Sufficient antioxidant property is acquired by making content of a [B] component 0.01 mass% or more, and since solubility to a base oil is fully acquired as it is 10 mass% or less, it is preferable respectively.

  The lubricating oil composition of the present invention contains a sulfurized fatty acid ester as the [C] component.

  Sulfurized fatty acid ester refers to a compound obtained by sulfiding a fatty acid ester, and preferably includes a compound represented by the following general formula (2).

R ³ and R ⁴ in the general formula (2) each independently represent hydrogen or a linear or branched hydrocarbyl group having 1 to 24 carbon atoms, preferably 1 to 8 carbon atoms, and particularly preferably 1 to 4 carbon atoms. These may be the same or different. Specific examples include a hydrogen atom; an alkyl group such as a methyl group, an ethyl group, a propyl group, and a butyl group; and a cycloalkyl group such as a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group.
Among these, an alkyl group is preferable from the viewpoint of improving processability, and a methyl group and an ethyl group are particularly preferable.

In the above general formula (2), l, m, n and o are each independently an integer of 3 or more, and the sum of l and m and the sum of n and o are 8 to 16, preferably 10 to 14, respectively. .
If the sum of l and m and the sum of n and o are less than 8, the solubility is lowered. On the other hand, if it exceeds 16, the oxidation stability is lowered.

  X in the general formula (2) represents the number of sulfur bridges and is an integer of 1 or more. Although there is no restriction | limiting in particular in an upper limit, 7 or less are preferable, 5 or less are more preferable, and 3 or less are more preferable. If it exceeds 7, a tendency that the sulfurized fatty acid ester tends to become unstable is not preferable.

The sulfur compound represented by the general formula (2) is a sulfur bridge formed from an ester of an unsaturated fatty acid (for example, oleic acid) having 12 to 20, preferably 14 to 18 carbon atoms having one unsaturated bond in the molecule. Can be obtained. The raw material unsaturated fatty acid ester is preferably purified, but can be used even if it contains impurities. The content of impurities in the raw material is preferably 50% by mass or less, more preferably 30% by mass or less, and most preferably 10% by mass or less.
As the unsaturated fatty acid ester, oleic acid esters such as methyl oleate, ethyl oleate, and propyl oleate are preferable, and among them, a sulfur cross-linked product of methyl oleate is preferable because it exhibits an effective friction reducing effect.

The content of the component [C] is not particularly limited, but is preferably 0.01 to 10% by mass, more preferably 0.05 to 5% by mass, and still more preferably 0, based on the total amount of the composition. 0.1 to 1% by mass.
When the content of the component [C] is less than 0.01% by mass, a sufficient effect as an antioxidant cannot be obtained, and when it exceeds 10% by mass, the oxidation stability of the lubricating oil composition tends to decrease. Each of which is not preferable.

  The lubricating oil composition of the present invention preferably contains substantially no metal. By not containing a metal substantially, low sludge property is realizable.

  In the present invention, “substantially does not contain metal” means that it contains no metal at all or contains a very small amount so that the influence can be ignored even if it is contained. . More specifically, the metal content in the lubricating oil composition is preferably 50 ppm by mass or less, more preferably 20 ppm by mass or less, still more preferably 10 ppm by mass or less, particularly preferably 5 ppm by mass or less, Most preferably, it is 0 mass ppm.

  In general, the metal contained in the lubricating oil composition is usually derived from an additive. Examples of such an additive containing a metal include a metal detergent and a metal complex extreme pressure agent. Accordingly, the lubricating oil composition of the present invention is substantially free of such metal-containing additives.

  Examples of the metal detergent include alkali metal sulfonate or alkaline earth metal sulfonate, alkali metal phenate or alkaline earth metal phenate, and alkali metal salicylate or alkaline earth metal salicylate.

  Examples of the metal complex extreme pressure agent include a zinc dithiophosphate compound, a zinc dithiocarbamate compound, a molybdenum dithiophosphate, a molybdenum dithiocarbamate compound, and the like.

According to the lubricating oil composition of the present invention, a lubricating oil composition having excellent oxidation stability and low sludge property can be obtained by the above-described configuration. However, the lubricating oil composition has the performance required for the purpose of further enhancing its performance or as a lubricating oil composition. Further, for the purpose of imparting, known ashless lubricating oil additives can be added.
Examples of such additives include wetting agents such as diethylene glycol monoalkyl ether; film forming agents such as acrylic polymer, paraffin wax, microwax, slack wax, and polyolefin wax; water displacement agents such as fatty acid amine salts; Solid lubricants such as graphite, molybdenum disulfide, boron nitride, polyethylene powder; amines, alkanolamines, amides, carboxylic acids, carboxylates, sulfonates, phosphoric acids, phosphates, polyhydric alcohol partial esters, etc. Corrosion inhibitors; Metal deactivators such as benzotriazole and thiadiazole; Antifoaming agents such as methyl silicone, fluorosilicone and polyacrylate; Ashless dispersants such as alkenyl succinimide, benzylamine and polyalkenylamine aminoamide; etc. Is mentioned . The content when these known additives are used in combination is not particularly limited, but the amount is such that the total content of these known additives is 0.1 to 10% by mass based on the total amount of the lubricating oil composition. It is preferable to add.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
The base oils and additives used in the examples and comparative examples are as follows.

[Lubricant base oil]
Solvent refined base oil; sulfur content: 0.19% by mass, total aromatic content: 28.9% by mass, kinematic viscosity at 40 ° C .: 46 mm ² / s, viscosity index: 102

[Additive]
([A] component);
Alkylated diphenylamine A; manufactured by BASF Ltd. Product name: “IRGANOX L57”

([B] component);
Hindered phenol A; Ditertiary butyl paracresol Hindered phenol B; manufactured by BASF Corporation Product name: “IRGANOX L135”

([C] component)
Sulfurized fatty acid ester A; sulfurized methyl oleate (in general formula (1), R ¹ = R ² = CH ₃ , l + m = n + o = 14, x = 1 to 3), sulfur content 10% by mass
Sulfurized fatty acid ester B; methyl sulfide oleate (in general formula (1), R ¹ = R ² = CH ₃ , l + m = n + o = 14, x = 4 to 7), sulfur content 21% by mass

(Examples 1-4 and Comparative Examples 1-9)
Table 1 shows the blending amounts and performances of various lubricating base oils and additives. The addition amount (% by mass) of each additive is based on the total amount of the lubricating oil composition. About each obtained composition, oxidation stability was evaluated and the result was written together in Table 1.

(Oxidation stability test)
The rotary cylinder type oxidation stability test was conducted in accordance with JIS K2514. A container containing 5 g of sample oil and 5 ml of distilled water and containing a Cu coil as a catalyst was placed in the rotary cylinder, and oxygen was injected into the cylinder up to 620 kPa. In a thermostat, the cylinder was rotated at 100 revolutions per minute while maintaining the angle at 30 degrees, and the time (minutes) from when the oxygen pressure reached the maximum to 175 kPa was measured.

Claims (3)

A lubricating oil composition comprising [A] alkylated diphenylamine, [B] hindered phenolic compound, and [C] sulfurized fatty acid ester in a mineral oil base oil having a sulfur content of 200 ppm by mass or more. The lubricating oil composition is characterized in that the metal content in the composition is 50 mass ppm or less . [A] The lubricating oil composition according to claim 1, wherein the alkylated diphenylamine is p, p′-dialkyldiphenylamine represented by the following general formula (1).

(In the formula, R ¹ represents hydrogen or an alkyl group having ^{1 to} 16 carbon atoms, and R ² represents an alkyl group having 1 to 16 carbon atoms.) [C] The lubricating oil composition according to claim 1 or 2, wherein the sulfurized fatty acid ester is a compound represented by the following general formula (2).

(Wherein R ³ and R ⁴ each independently represent hydrogen or a hydrocarbyl group having 1 to 24 carbon atoms. L, m, n, and o are each independently an integer of 3 or more, and the sum of l and m and (The sum of n and o is individually 8 to 16. x represents the number of sulfur bridges and represents an integer of 1 or more.)