JP6974216B2 - Lubricating oil composition for stern pipes - Google Patents

Description

The present invention relates to a lubricating oil composition for stern pipes.

Conventionally, fatty acid ester-based lubricating oils have been used as hydraulic hydraulic oils used in flood control equipment and the like, which are required to have flame retardancy and biodegradability from the viewpoints of safety, hygiene, environmental friendliness, and the like.

In recent years, marine pollution of lubricants leaked from ships has become a problem. In particular, the stern pipe lubricates the bearing of the screw shaft, so that the inside of the pipe is filled with lubricating oil. Due to the structure of the stern pipe, it is difficult to completely prevent the leakage of lubricating oil. Therefore, there are an increasing number of cases where a biodegradable fatty acid ester-based lubricating oil is used for a device in contact with seawater in a ship. Also, depending on the sea area, the use of this lubricant may be obligatory.
Further, the fatty acid ester-based lubricating oil used for equipment for ships is required to have excellent hydrolysis stability and rust preventive property against seawater because seawater is mixed with the lubricating oil.

As a fatty acid ester-based lubricating oil having excellent hydrolysis stability and rust-preventive properties, a fatty acid ester-based lubricating oil containing a specific amount of a fatty acid ester and a specific rust inhibitor and having a kinematic viscosity at 40 ° C. of 10 to 600 mm ² / s. The oil composition is disclosed (see, for example, Patent Document 1).

Fatty acid ester-based lubricating oils tend to be inferior in hydrolysis stability (hydrolysis resistance) to mineral oil-based lubricating oils. In order to use the fatty acid ester-based lubricating oil in the same manner as the mineral oil-based lubricating oil under high temperature conditions for a long period of time, it is desired to improve the hydrolysis stability.
For example, water-soluble alkylene glycol and / or polyalkylene glycol, water-soluble thickener, and water-soluble rust preventive for the purpose of having lubricity, rust preventiveness, biodegradability, etc. equivalent to those of mineral oil-based lubricating oil. Lubricating oils for ship bearing propulsion units containing each agent in a specific amount have been proposed (see, for example, Patent Document 2).

JP-A-2017-165912 Japanese Unexamined Patent Publication No. 2006-265345

However, the fatty acid ester-based lubricating oil has a high polarity and has a property of being easily adsorbed on the metal surface as compared with the mineral oil-based lubricating oil, so that it inhibits the adsorption of additives such as rust preventives contained in the lubricating oil. Therefore, in order to increase the adsorptive power of the additive to the metal surface, it is necessary to increase the concentration of the additive in the fatty acid ester-based lubricating oil as compared with the mineral oil-based lubricating oil. The addition of a rust preventive having a high adsorptive power and a rust preventive having a high concentration tends to reduce the hydrolysis stability of the fatty acid ester. Therefore, in the prior art described in Patent Documents 1 and 2, it is difficult to achieve both rust preventive properties and hydrolysis stability to the extent that they can withstand use in ship devices such as stern pipes.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a lubricating oil composition for a stern pipe having excellent hydrolysis stability and rust preventive property.

As a result of diligent research to solve the above problems, the present inventor hydrolyzes the base oil by containing a specific amount of alkenyl succinic acid half ester and a specific amount of N-oleoyl sarcosine. We have found that both stability and rust preventive properties are improved, and based on this finding, we have completed the present invention.
That is, the means for solving the above problems include the following embodiments.

<1>
Base oil and
Antioxidants and
With 0.05% by mass to 0.3% by mass of alkenyl succinic acid half ester based on the total amount of the composition,
0.03% by mass to 0.15% by mass of N-oleoyl sarcosine based on the total amount of the composition,
Lubricating oil composition for stern pipes containing.
<2> The lubricating oil composition for a stern tube according to <1>, wherein the content of the alkenyl succinic acid half ester is 0.08% by mass to 0.15% by mass based on the total amount of the composition.

INDUSTRIAL APPLICABILITY According to the present invention, a lubricating oil composition for a stern pipe having excellent hydrolysis stability and rust preventive property is provided.

Hereinafter, embodiments for carrying out the present invention will be described in detail.
In the present specification, "~" indicating a numerical range represents a range including numerical values described as the upper limit and the lower limit thereof, respectively. Further, when the unit is described only for the upper limit value in the numerical range represented by "~", it means that the lower limit value is also the same unit.
In the numerical range described stepwise in the present specification, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described in another stepwise description.
In the present specification, the content or content of each component in the composition is the same as that in the case where a plurality of substances corresponding to each component are present in the composition, unless otherwise specified. It means the total content or content of substances.
As used herein, a combination of preferred embodiments is a more preferred embodiment.

<< Lubricating oil composition for stern pipe >>
The lubricating oil composition for stern pipes of the present invention (hereinafter, also simply referred to as “lubricating oil composition”) contains a base oil, an antioxidant, and 0.05% by mass to 0.3% by mass based on the total amount of the composition. Alkenyl succinic acid half ester and 0.03% by mass to 0.15% by mass of N-oleoyl sarcosine based on the total amount of the composition.
The lubricating oil composition is excellent in hydrolysis stability and rust preventive property by containing a base oil, a specific amount of alkenylsuccinic acid half ester and a specific amount of N-oleoyl sarcosine.
The reason for this is not clear, but it is presumed as follows.

Generally, alkenyl succinic acid half ester and N-oleoyl sarcosine are used as rust preventives. Comparing the molecular structures of alkenyl succinic acid half ester and N-oleoyl sarcosin, it is speculated that alkenyl succinic acid half ester has more polar groups in the molecule, so that it is easily adsorbed on the metal surface and has stronger rust preventive property. Will be done.
Further, the alkenyl succinic acid half ester is ionized in the presence of water and reacts with a metal such as iron to form a metal salt adsorption film on the metal surface, so that it can exhibit rust preventive properties. ..
Similar to the alkenyl succinic acid half ester, N-oleoyl sarcosine has an anti-emulsifying property in addition to exhibiting a rust preventive property by forming an adsorption film of a metal salt on the metal surface. When water is mixed in the lubricating oil composition, N-oleoyl sarcosine separates the water from the oil component, so that the ionization of the alkenyl succinic acid half ester is promoted, and it is presumed that the rust preventive property is further exhibited.
Further, when the amount of the alkenyl succinic acid half ester in the lubricating oil composition is a specific amount, the acid value in the composition is unlikely to increase and the hydrolysis of the alkenyl succinic acid half ester is also suppressed, so that the hydrolysis stability is improved. Is also excellent.
Hereinafter, details of each component contained in the lubricating oil composition of the present invention will be described.

<Base oil>
The lubricating oil composition of the present invention contains a base oil.
The base oil is not particularly limited, and may be, for example, a mineral oil, a synthetic oil, or a mixed oil thereof.
Examples of the mineral oil include those obtained by refining the lubricating oil distillate of crude oil by appropriately combining refining methods such as solvent refining, hydrogenation refining, hydrogenation decomposition refining, and hydrogenation dewaxing. In addition, highly refined paraffin-based mineral oil obtained by subjecting hydrogenated refined oil, catalyst isomerized oil, or the like to a treatment such as solvent dewaxing or hydrogenation dewaxing can be mentioned.

Examples of the synthetic oil include ether compounds such as alkyldiphenyl ether, fatty acid esters such as diesters, polyol esters and complex-type polyol esters, synthetic hydrocarbons such as polyalphaolefins, and alkylnaphthalene.
Among these, the base oil is preferably a synthetic oil, and more preferably a fatty acid ester from the viewpoint of excellent oil-water separability.

Fatty acid esters can be obtained by the reaction of alcohols with fatty acids. The fatty acid ester may be used alone or in combination of two or more.

The alcohol used in the reaction of the fatty acid ester may be a monohydric alcohol or a polyhydric alcohol having two or more hydroxyl groups in one molecule.
Specific examples of alcohols include oleyl alcohol, lauryl alcohol, methanol, ethanol, pentanol, hexanol, ethylene glycol, propylene glycol, glycerol, neopentyl glycol, trimethylolmethane, trimethylolethane, trimethylolpropane, and trimethylolbutane. 1,2,6-hexanetriol, pentaerythritol, dipentaerythritol and the like can be mentioned.
Among these, the alcohol is preferably a polyhydric alcohol, and more preferably at least one of a trihydric alcohol and a polyhydric alcohol having a neopentyl structure (hereinafter, also referred to as "neopentyl polyol"). ..
Examples of the neopentyl polyol include neopentyl glycol, trimethylolpropane, pentaerythritol, dipentaerythritol and the like.

The fatty acid used for the synthesis of the fatty acid ester is not particularly limited, and may be a saturated or unsaturated fatty acid, or a linear or branched fatty acid.
Specific examples of fatty acids include butanoic acid, pentanoic acid, hexanoic acid, heptanic acid, octanoic acid, nonanoic acid, decanoic acid, dodecanoic acid, myristic acid, pentadecic acid, palmitic acid, margaric acid, stearic acid, and eikosanoic acid. , Docosanoic acid, palmitoleic acid, oleic acid, suberic acid, ricinoleic acid, azelaic acid, sebasic acid and the like.
Among these, from the viewpoint of hydrolysis stability, the fatty acid is preferably a saturated or unsaturated long-chain fatty acid having 11 or more carbon atoms, and is a saturated or unsaturated long-chain fatty acid having 11 to 20 carbon atoms. It is more preferably a fatty acid.

The fatty acid ester is an ester of an alcohol and a fatty acid as described above, and when the alcohol is a dihydric or higher alcohol, the fatty acid for forming one ester molecule may be a single type fatty acid. It may be a plurality of fatty acids.
For example, the fatty acid forming an ester with a hexavalent alcohol may be a mixture of a linear fatty acid having 8 carbon atoms and a branched chain fatty acid having 6 carbon atoms, or only a linear fatty acid having 8 carbon atoms. May be.

From the viewpoint of hydrolysis stability, the fatty acid ester is preferably a mixture of a neopentyl polyol and a saturated fatty acid, and a trivalent alcohol and an unsaturated fatty acid, and is saturated with the neopentyl polyol. It is an ester of a long-chain fatty acid having 11 or more carbon atoms or an ester of a neopentyl polyol and a saturated fatty acid of a branched chain, and a mixture of a trivalent alcohol and an unsaturated long-chain fatty acid having 11 or more carbon atoms. More preferably, it is a mixture of pentaerythritol and a saturated long-chain fatty acid having 11 or more carbon atoms, and a mixture of glycerol and oleic acid.

The acid value of the fatty acid ester is preferably 0.2 mgKOH / g or less. When the acid value of the fatty acid ester is 0.2 mgKOH / g or less, the hydrolysis stability is further excellent.
From the viewpoint of hydrolysis stability, the acid value of the fatty acid ester is more preferably 0.1 mgKOH / g or less, still more preferably 0.05 mgKOH / g or less.

The content of the base oil is preferably 97% by mass to 99.5% by mass, more preferably 98% by mass to 99.5% by mass, based on the total mass of the composition.

The base oil preferably has a kinematic viscosity at 40 ° C. is 10mm ² / s~600mm ² / ^s, and more preferably 20mm ² / s~200mm 2 / s.
When the kinematic viscosity of the base oil at 40 ° C. is 10 mm ² / s or more, lubricity as a lubricating oil can be obtained, and when it is 600 mm ² / s or less, high biodegradability can be obtained.
The 40 ° C. kinematic viscosity is a value measured based on the JIS K 2283: 2000 kinematic viscosity test method.

<Antioxidant>
The lubricating oil composition of the present invention contains at least an antioxidant.
Examples of the antioxidant include alkylphenols such as 2,6-di-tert-butyl-p-cresol, bisphenols such as 4,4'-methylenebis- (2,6-di-t-butylphenol), and n-octadecyl-3. -(4'-Hydroxy-3', 5'-di-t-butylphenol) Phenolic compounds such as propionate, aromatic amine compounds such as naphthylamine and dialkyldiphenylamine can be mentioned.
Among these, from the viewpoint of lubricity, the antioxidant is preferably an aromatic amine compound, and more preferably a phenolic compound, naphthylamine or dialkyldiphenylamine.
The antioxidant may be used alone or in combination of two or more.

The content of the antioxidant is preferably 0.3% by mass to 5% by mass, more preferably 0.5% by mass to 3% by mass, based on the total mass of the lubricating oil composition. ..

<Rust preventive agent>
The lubricating oil composition of the present invention contains 0.05% by mass to 0.3% by mass of an alkenyl succinic acid half ester based on the total amount of the composition and 0.03% by mass to 0.15% by mass based on the total amount of the composition. Contains at least N-oleoyl succinic acid.
Since the lubricating oil composition contains a specific amount of alkenyl succinic acid half ester and a specific amount of N-oleoyl sarcosine, it is excellent in hydrolysis stability and rust preventive property.

From the viewpoint of achieving both hydrolysis stability and rust preventive property, the content of the alkenyl succinic acid half ester is preferably 0.05% by mass to 0.2% by mass based on the total amount of the composition, preferably 0.08% by mass. More preferably, it is% to 0.15% by mass.

From the viewpoint of achieving both hydrolysis stability and rust preventive property, the content of N-oleoyl sarcosine is preferably 0.01% by mass to 0.15% by mass based on the total amount of the composition, preferably 0.05% by mass. More preferably, it is% to 0.15% by mass.

From the viewpoint of achieving both hydrolysis stability and rust preventive property, the content of the alkenyl succinic acid half ester is 0.05% by mass to 0.2% by mass (more preferably 0.08) based on the total amount of the composition. The content of N-oleoyl sarcosine is 0.01% by mass to 0.15% by mass (more preferably 0.05) based on the total amount of the composition. It is preferably from% by mass to 0.15% by mass).

From the viewpoint of achieving both hydrolysis stability and rust preventive property, the content ratio of N-oleoyl sarcosine and alkenyl succinic acid half ester is preferably 1: 1 to 1:10 on a mass basis. : 1 to 1: 6 is more preferable.

(Other ingredients)
The lubricating oil composition of the present invention contains, if necessary, an appropriate amount of components other than the base oil, the antioxidant, the alkenyl succinic acid half ester, and N-oleoyl sarcosine (hereinafter, also referred to as "other components"). You may be doing it.
Examples of other components include components used in ordinary lubricating oil compositions, such as extreme pressure agents, alkenyl succinic acid half esters, and rust inhibitors other than N-oleoyl sarcosin (hereinafter, also referred to as “other rust inhibitors”). ), Various additives such as corrosion inhibitors and antifoaming agents.

Examples of the extreme pressure agent include tricresyl phosphate, olefin sulfide and the like.

Examples of other rust preventives include alkenyl succinic acid and its derivatives, esters such as sorbitan monoolate, wax oxides, neutral barium sulfonate, sorbitan triol, paraffin or other amine compounds.

Examples of the corrosion inhibitor include dialkyldithiophosphate, benzotriazole and its derivatives, 1,3,4-thiadiazole polysulfide, 1,3,4-thiazolyl-2,5-bisalkyldithiocarbamate and the like.

Examples of the defoaming agent include polydimethylsiloxane and the like.

<Characteristics of lubricating oil composition>
The lubricating oil composition preferably has a kinematic viscosity of 40 ° C. is 10mm ² / s~600mm ² / ^s, and more preferably 20mm ² / s~200mm 2 / s. If the kinematic viscosity of the lubricating oil composition at 40 ° C. is 10 mm ² / s or more, lubricity as a lubricating oil can be obtained, ^{and if it is 600 mm 2} / s or less, high biodegradability can be obtained.
The 40 ° C. kinematic viscosity is a value measured based on the JIS K 2283: 2000 kinematic viscosity test method.

The viscosity index of the lubricating oil composition is preferably 150 or more, more preferably 170 or more, and even more preferably 190 or more.

<Preparation method of lubricating oil composition>
As a method for preparing the lubricating oil composition, in addition to the base oil, the antioxidant, the alkenyl succinic acid half ester and the N-oleoyl sarcosine, various additives may be appropriately mixed as needed.
The mixing order of the base oil, the antioxidant, the alkenyl succinic acid half ester and N-oleoyl sarcosine, and various additives is not particularly limited, and may be sequentially mixed with the base oil.

Next, the present invention will be specifically described with reference to Examples. The present invention is not limited to these examples.

(Examples 1 to 4 and Comparative Examples 1 to 12)
In Examples and Comparative Examples, the base oil and the additive were mixed at the blending ratios (% by mass) shown in Tables 1 and 2 below to prepare a lubricating oil composition.
The following performance evaluation was performed using each of the obtained lubricating oil compositions. The results are shown in Tables 1 and 2.

<Base oil>
-Saturation of 67 parts by mass of a fatty acid ester consisting of glycerol and oleic acid (initial acid value: 0.04 mgKOH / g, kinematic viscosity at 40 ° C.: 35.44 mm ² / s), pentaerythritol, dicarboxylic acid and 18 carbon atoms. Base oil mixed with 33 parts by mass of a fatty acid ester consisting of a fatty acid (initial acid value: 0.2 mgKOH / g, kinematic viscosity at 40 ° C.: 977 mm ^{2 / s).}

<Antioxidant>
-An antioxidant in which 0.5% by mass of alkylated phenyl α-naphthylamine and 0.25% by mass of tri (tert-butylphenyl) phosphate are mixed.

[evaluation]
<Hydrolyzed stability test>
Based on ASTM-D-2619, the hydrolysis stability test was carried out as follows.
After a mixture of the lubricating oil composition 7.5 × ¹⁰ -2 kg water 2.5 × ¹⁰ -2 kg prepared as a sample is mixed and put in a test container, the container was kept at 93 ° C., min The test was performed for 300 hours with 5 rotations.
After the test, the mixture was transferred to a centrifuge tube, rotated at 1500 rpm with a centrifuge, centrifuged for 20 minutes, separated into an oil phase and an aqueous phase, and the kinematic viscosity of the oil phase was measured at 40 ° C.
The viscosity change rate (%) was calculated from the following formula using the measured values of the 40 ° C. kinematic viscosity of the lubricating oil composition before the test and the oil phase after the test.

Viscosity change rate (%) = (measured value of 40 ° C kinematic viscosity of oil phase after test-40 ° C kinematic viscosity of lubricating oil composition before test) / 40 ° C kinematic viscosity of lubricating oil composition before test × 100

When the viscosity change rate was in the range of -10% to + 10%, it was judged that the hydrolysis stability was excellent. The smaller the viscosity change rate (closer to 0%), the better the hydrolysis stability.

<Rust prevention performance test>
A rust prevention performance test based on JIS-K-2510 (1998) was carried out as follows.
A polished steel round bar test piece (diameter 13.0 mm x length 81.0 mm) is immersed in a mixture of 300 ml of a lubricating oil composition prepared as a sample and 30 ml of artificial seawater at 60 ° C. for 24 hours. Then, the presence or absence of rust generated on the test piece was visually confirmed.
While the test piece was immersed in the mixed solution, the mixed solution was continuously stirred with a stirring rod.

-Evaluation criteria-
A; The surface of the test piece has 6 or less rust spots with a diameter of 1 mm or less, and is excellent in rust prevention.
B; There are more than 6 rust spots with a diameter of 1 mm or less on the surface of the test piece, but the rust is 5% or less of the surface of the test piece, and the rust preventive property is slightly inferior.
C; Rust is observed in a range exceeding 5% of the surface of the test piece, and the rust preventive property is inferior.

As shown in Table 1, the lubricating oil compositions of Examples 1 to 4 had a small rate of change in viscosity and were excellent in hydrolysis stability and rust preventive property.
On the other hand, as shown in Table 2, the lubricating oil compositions of Comparative Examples 1 to 12 were inferior in either hydrolysis stability or rust preventive property.
On the other hand, in Comparative Example 11 in which the content of N-oleoyl sarcosine exceeded 0.15% by mass, the rust preventive property was inferior. It is presumed that rust occurs because N-oleoyl sarcosine, which has a low rust preventive effect, inhibits the adsorption of alkenyl succinic acid half ester, which has a high rust preventive effect, on the metal surface.
Further, in Comparative Example 10 in which the content of the alkenyl succinic acid half ester exceeded 0.3% by mass, the hydrolysis stability was inferior.
Fatty acid esters are known to promote the hydrolysis reaction by acid. General rust preventives such as alkenyl succinic acid half ester have a high acid value, and when a large amount of alkenyl succinic acid half ester is added to the lubricating oil composition, the acid value of the lubricating oil composition is proportional to the addition amount. Is considered to increase, the hydrolysis reaction of the alkenyl succinic acid half ester is promoted, and the change in the viscosity of the composition becomes large. That is, it is presumed that hydrolysis stability cannot be obtained because the lubricating oil composition contains an alkenyl succinic acid half ester exceeding a predetermined amount.

From this, it can be seen that when the contents of each of the alkenyl succinic acid half ester and N-oleoyl sarcosine are within a predetermined range, both the hydrolysis stability and the rust preventive property are excellent.
From the above, the lubricating oil composition of the present invention is excellent in hydrolysis stability and rust preventive property.

Claims (2)

Base oil and
Antioxidants and
With 0.05% by mass to 0.3% by mass of alkenyl succinic acid half ester based on the total amount of the composition,
0.03% by mass to 0.15% by mass of N-oleoyl sarcosine based on the total amount of the composition,
Is a lubricating oil composition for stern pipes containing
The base oil is a fatty acid ester,
The content ratio of the N-oleoyl sarcosine to the alkenyl succinic acid half ester is 1: 1 to 1:10 on a mass basis.
Lubricating oil composition for stern pipes. The lubricating oil composition for a stern tube according to claim 1, wherein the content of the alkenyl succinic acid half ester is 0.08% by mass to 0.15% by mass based on the total amount of the composition.