Biodegradable lubricating oil composition

Abstract

Provided is a biodegradable lubricating oil composition which is excellent in terms of biodegradability, lubricity (extreme pressure property), demulsibility, and friction-reducing property and is highly effective in friction reduction even in the presence of seawater. The biodegradable lubricating oil composition is characterized by comprising 100 parts by mass of a specific ester compound (A), 0.1-10.0 parts by mass of a specific poly(alkyl (meth)acrylate) (B), and 0.1-1.5 parts by mass of a specific acidic phosphoric acid ester amine salt (C).

Description

Biodegradable lubricating oil composition

[0001] The present disclosure relates to lubricating oil compositions that are biodegradable.

[0002] In recent years, new environmental protection initiatives have been progressing worldwide, and lubricants that can reduce environmental impact have become increasingly important. Biodegradable lubricants, which readily decompose in nature and have minimal impact on ecosystems even in the event of a leak, have attracted attention as a type of lubricant that can reduce environmental impact. For example, Patent Document 1 discloses a biodegradable lubricant composition suitable for gearboxes used in wind turbine generators, which comprises a base oil containing a complex ester of a specific linear saturated fatty acid and a linear aliphatic dicarboxylic acid with a polyhydric alcohol, and an ester of a linear saturated fatty acid with a polyhydric alcohol, and an acidic phosphate ester amine salt. Furthermore, many biodegradable lubricants are used as a countermeasure against leaks into rivers or oceans, and the use of biodegradable lubricants is mandatory in some applications and regions. For example, in Europe, the use of biodegradable lubricants is mandatory for two-cycle engine oils for outboard motors used in lake and marsh areas, and hydraulic oils for construction machinery used near rivers where drinking water is collected. As a lubricating oil for use near water, for example, Patent Document 2 discloses a biodegradable lubricating oil containing various additives blended with a base oil consisting of an alkylene oxide adduct of an alcohol having a valence of 1 to 8, with the alkylene oxide carbon number, the alkylene oxide adduct molar number, and the HLB value being within specific ranges. Furthermore, in recent years, the use of biodegradable lubricating oils has become mandatory for marine lubricating oils used on ships operating in U.S. waters. Stern tube bearing oils and thruster oils used in equipment operating in seawater may be contaminated with seawater, and demulsification properties are required to remove the seawater. As a lubricating oil with excellent demulsification properties, for example, Patent Document 3 discloses a biodegradable lubricating oil composition containing a base oil made of a complex ester of pentaerythritol, a specific linear fatty acid, and adipic acid, blended with an acidic phosphate ester amine salt, an amine-based antioxidant, and a phenol-based antioxidant. On the other hand, it is difficult to immediately stop operation of a ship even if seawater gets into the lubricating oil in its equipment, and the lubricating oil in the equipment may be used for a certain period of time with seawater mixed in, so it is necessary for the lubricating oil to perform sufficiently even when seawater gets mixed in. Furthermore, as fuel efficiency has been required for ships in recent years, it is desirable to be able to sufficiently reduce friction even when seawater gets mixed in.However, in the biodegradable lubricating oils of the above-mentioned prior art, sufficient consideration has not been given to the friction reduction properties when seawater is mixed in.

[0003] JP 2013-053227 A JP 2017-186529 A International Publication No. 2023 / 074424

[0004] An object of the present disclosure is to provide a biodegradable lubricating oil composition that is excellent in biodegradability, lubricity (extreme pressure properties), demulsibility, and friction-reducing properties, and that is also excellent in friction-reducing properties even in the presence of seawater.

[0005] As a result of intensive research to solve the above-mentioned problems, the present inventors have found that by blending a specific ester compound (A) of pentaerythritol with a specific linear fatty acid and adipic acid with a specific polyalkyl(meth)acrylate (B) and a specific acidic phosphate amine salt (C) in a specific ratio, a composition can be obtained that not only has excellent biodegradability, lubricity (extreme pressure properties), demulsibility, and friction-reducing properties, but also has excellent friction-reducing properties even in the presence of seawater, and have completed the present disclosure.

[0006] That is, the present disclosure provides the following: A biodegradable lubricating oil composition comprising 0.1 to 10.0 parts by mass of the following (B) polyalkyl(meth)acrylate and 0.1 to 1.5 parts by mass of the following (C) acidic phosphoric acid ester amine salt, relative to 100 parts by mass of the following (A) ester compound. (A): an ester compound of (a) pentaerythritol, (b) a straight-chain fatty acid having 14 to 22 carbon atoms, and (c) adipic acid, wherein the molar percentage of the component derived from the pentaerythritol (a) is 20 to 30 mol %, the molar percentage of the component derived from the straight-chain fatty acid having 14 to 22 carbon atoms (b) is 55 to 79 mol %, and the molar percentage of the component derived from the adipic acid (c) is 1 to 15 mol %, the molar ratio of the component derived from the adipic acid (c) to the component derived from the straight-chain fatty acid having 14 to 22 carbon atoms (b) is 0.02 to 0.25, and the hydroxyl value is 10 to 100 mgKOH / g; (B): a non-dispersed polyalkyl(meth)acrylate having a weight-average molecular weight of 20,000 to 800,000; and (C): an acidic phosphate amine salt represented by the following general formula (1):

[0007] (In general formula (1), n ​​is an integer of 1 or 2, R' is a linear alkyl group having 4 to 6 carbon atoms, and R'' is a hydrogen atom or an alkyl group having 11 to 14 carbon atoms.)

[0008] The biodegradable lubricating oil composition of the present disclosure is excellent in biodegradability, lubricity (extreme pressure properties), demulsibility, and friction-reducing properties, and also exhibits excellent friction-reducing properties even in the presence of seawater.

[0009] The biodegradable lubricating oil composition of the present disclosure will be described in detail below. In this specification, the biodegradable lubricating oil composition of the present disclosure may be simply referred to as the "lubricating oil composition of the present disclosure" or the "lubricating oil composition." In addition, in this disclosure, a numerical range defined using the symbol "to" includes both the upper and lower limits of the symbol "to." For example, "2 to 5" represents a range of 2 to 5. Furthermore, among the numerical values ​​described to explain this disclosure, numerical values ​​that may include decimal places are, unless otherwise specified, values ​​obtained by rounding off the digit that is one place smaller than the lowest digit included in the numerical value. Furthermore, in this disclosure, "(meth)acrylate" refers to at least one selected from the group consisting of acrylates and methacrylates. Furthermore, in this disclosure, the number of carbon atoms x may be simply represented as Cx. Furthermore, in this disclosure, when the term "friction reduction" is simply used, it refers to friction reduction under conditions where no additional material or foreign matter is mixed in, and is distinguished from "friction reduction in the presence of seawater."

[0010] The lubricating oil composition of the present disclosure contains (A) an ester compound as a base oil, and (B) a polyalkyl(meth)acrylate and (C) an acidic phosphate amine salt as additives, and may further contain other additives within the scope of the present disclosure. Each component contained in the lubricating oil composition of the present disclosure will be described in detail below.

[0011] <(A) Ester Compound> The (A) ester compound contained in the lubricating oil composition of the present disclosure is an ester compound of (a) pentaerythritol, (b) a straight-chain fatty acid having 14 to 22 carbon atoms, and (c) adipic acid.

[0012] The (A) ester compound has excellent oxidation stability and heat resistance because (a) pentaerythritol is used as the raw material alcohol.

[0013] The (A) ester compound uses (b) a straight-chain fatty acid having 14 to 22 carbon atoms and (c) adipic acid as raw carboxylic acids. By using (b) a straight-chain fatty acid having 14 to 22 carbon atoms (sometimes simply referred to as "(b) straight-chain fatty acid" in this disclosure), the lubricating oil composition of the present disclosure has excellent lubricity (extreme-pressure properties) and is prevented from becoming highly viscous. If the viscosity of the lubricating oil increases, the internal resistance of the lubricating oil itself may cause energy loss in equipment using the lubricating oil, which may result in poor fuel economy. Therefore, it is desirable to prevent the lubricating oil from becoming highly viscous. If a straight-chain fatty acid having fewer than 14 carbon atoms is used instead of the (b) straight-chain fatty acid, the resulting lubricating oil composition will have insufficient lubricity (extreme-pressure properties). From the perspective of improving the lubricating oil composition's lubricity (extreme-pressure properties), the (b) straight-chain fatty acid preferably contains at least a straight-chain fatty acid having 16 or more carbon atoms. On the other hand, if a straight-chain fatty acid having more than 22 carbon atoms is used instead of the (b) straight-chain fatty acid, the resulting lubricating oil composition is likely to have a high viscosity, and the ester compound produced may become solid and may not be usable as a lubricating oil. From the viewpoint of increasing the viscosity of the lubricating oil composition and suppressing solidification of the (A) ester compound, the (b) straight-chain fatty acid is preferably a straight-chain fatty acid having 20 or less carbon atoms.

[0014] The (b) straight-chain fatty acid is a straight-chain saturated fatty acid having 14 to 22 carbon atoms, a straight-chain unsaturated fatty acid having 14 to 22 carbon atoms, or a mixed fatty acid thereof. Furthermore, the (b) straight-chain fatty acid is preferably a monocarboxylic acid, in order to prevent the lubricating oil composition from becoming highly viscous. Examples of straight-chain saturated fatty acids having 14 to 22 carbon atoms include myristic acid, palmitic acid, stearic acid, arachidic acid, and behenic acid. Examples of straight-chain unsaturated fatty acids having 14 to 22 carbon atoms include myristoleic acid, palmitoleic acid, oleic acid, linoleic acid, linolenic acid, and erucic acid.

[0015] The (b) straight-chain fatty acid may contain one type alone, or may contain two or more types in combination from the viewpoint of ease of availability or ease of production. The (b) straight-chain fatty acid preferably contains a combination of a straight-chain saturated fatty acid and a straight-chain unsaturated fatty acid having 14 to 22 carbon atoms. In a mixed fatty acid of a straight-chain saturated fatty acid and a straight-chain unsaturated fatty acid having 14 to 22 carbon atoms (the total amount being 100% by mass), the straight-chain unsaturated fatty acid content is preferably 60% by mass or more, more preferably 65% ​​by mass or more, and even more preferably 70% by mass or more. The upper limit of the straight-chain unsaturated fatty acid content is not particularly limited, but is preferably 95% by mass or less.

[0016] Furthermore, the (b) straight-chain fatty acid preferably contains at least one selected from the group consisting of palmitoleic acid, oleic acid, linoleic acid, linolenic acid, and erucic acid, more preferably at least one selected from the group consisting of oleic acid, linoleic acid, and linolenic acid, and even more preferably at least oleic acid. When the (b) straight-chain fatty acid contains oleic acid, the content of oleic acid in 100% by mass of the (b) straight-chain fatty acid is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. The upper limit of the oleic acid content is not particularly limited, but may be, for example, 90% by mass or less, or 80% by mass or less.

[0017] The (A) ester compound further uses a dibasic acid (c) adipic acid as a raw carboxylic acid. By using adipic acid among dibasic acids, the lubricating oil composition of the present disclosure is more likely to exhibit the effects of various additives, and the oxidation stability and heat resistance of the (A) ester compound are improved. If succinic acid, which has a smaller carbon number, is used instead of adipic acid as a dibasic acid, the effects of various additives may be less likely to be exhibited. On the other hand, if sebacic acid, which has a larger carbon number, or maleic acid, which contains an unsaturated bond, is used instead of adipic acid, the oxidation stability or heat resistance of the resulting ester compound may be insufficient.

[0018] In the (A) ester compound, the molar percentage of the (a) pentaerythritol-derived component (sometimes referred to as "(a) mol%" in the present disclosure) is 20 to 30 mol%, the molar percentage of the (b) C14 to C22 linear fatty acid-derived component (sometimes referred to as "(b) mol%" in the present disclosure) is 55 to 79 mol%, and the molar percentage of the (c) adipic acid-derived component (sometimes referred to as "(c) mol%" in the present disclosure) is 1 to 15 mol%, provided that the sum of (a) mol%, (b) mol%, and (c) mol% ((a) mol% + (b) mol% + (c) mol%) is 100 mol%. In the (A) ester compound used in the present disclosure, the (a) pentaerythritol-derived component is a residue of (a) pentaerythritol, the (b) C14-22 straight-chain fatty acid-derived component is a residue of (b) C14-22 straight-chain fatty acid, and the (c) adipic acid-derived component is a residue of (c) adipic acid. When the ratios of (a) mol%, (b) mol%, and (c) mol% are within the above ranges, the lubricating oil composition of the present disclosure is prevented from increasing in viscosity and exhibits excellent biodegradability, demulsibility, lubricity (extreme pressure properties), and friction reduction properties. From these perspectives, the (a) mol% is preferably 21 to 28 mol%, more preferably 22 to 25 mol%. The (b) mol% is preferably 60 to 79 mol%, more preferably 68 to 75 mol%. (c) The mol % is preferably 2 to 10 mol %, more preferably 3 to 7 mol %.

[0019] In the (A) ester compound used in the present disclosure, the above "(a) mol %, " "(b) mol %, and "(c) mol %" refer to the mol content of the (A) ester compound. １ The molar amounts of the constituent components derived from each raw material were determined by H NMR analysis, and the values ​​were calculated from the determined molar amounts of the constituent components. １ The measurement conditions for H NMR are as follows: <Measurement conditions> Analytical equipment: １ H NMR Solvent: deuterated chloroform

[0020] The ester compound (A) obtained under the above measurement conditions １By analyzing the H NMR chart, the molar amount of each component of (A) the ester compound can be determined. Specifically, the following four peaks are used: Peak (I): 3.40 to 3.70 ppm = (a) hydrogen at the α-position of the unreacted hydroxyl group of pentaerythritol Peak (II): 4.00 to 4.20 ppm = (a) hydrogen at the α-position of the reacted hydroxyl group of pentaerythritol The total number of hydrogen atoms in peak (I) and peak (II) is eight. Peak (III): 0.85 to 0.90 ppm = (b) hydrogen atoms (3) bonded to the terminal carbon of a straight-chain fatty acid having 14 to 22 carbon atoms. Peak (IV): 2.25 to 2.35 ppm = (c) hydrogen atoms (4) at the α-position of the carbonyl group of adipic acid and (b) hydrogen atoms (2) at the α-position of the carbonyl group of a straight-chain fatty acid having 14 to 22 carbon atoms.

[0021] From the integrals of the above four peaks, (a) the number of moles of the component derived from pentaerythritol ((a) mol), (b) the number of moles of the component derived from a linear fatty acid having 14 to 22 carbon atoms ((b) mol), and (c) the number of moles of the component derived from adipic acid ((c) mol) can be calculated using the following formulas: (a) mol = {integral value of peak (I) + integral value of peak (II)} / 8 (b) mol = integral value of peak (III) / 3 (c) mol = [integral value of peak (IV) - {(b) mol x 2}] / 4

[0022] From the calculated (a) mol, (b) mol, and (c) mol, (a) mol%, (b) mol%, and (c) mol% can be calculated using the following formulas: (a) mol% = 100 x (a) mol / {(a) mol + (b) mol + (c) mol} (b) mol% = 100 x (b) mol / {(a) mol + (b) mol + (c) mol} (c) mol% = 100 x (c) mol / {(a) mol + (b) mol + (c) mol}

[0023] Furthermore, from the above (a) mol%, (b) mol%, and (c) mol%, the molar ratio of each constituent can be calculated using the following formulas: Molar ratio of the constituent component derived from adipic acid (c) to the constituent component derived from a straight-chain fatty acid having 14 to 22 carbon atoms (b) = (c) mol% / (b) mol% Molar ratio of the constituent component derived from adipic acid (c) to the constituent component derived from pentaerythritol (a) = (c) mol% / (a) mol% Molar ratio of the constituent component derived from a straight-chain fatty acid having 14 to 22 carbon atoms (b) to the constituent component derived from pentaerythritol (a) = (b) mol% / (a) mol%

[0024] In the (A) ester compound, the molar ratio of the (c) adipic acid-derived component to the (b) C14-22 linear fatty acid-derived component ((c) mol% / (b) mol%) is 0.02 to 0.25. When the (c) mol% / (b) mol% is 0.02 or more, the lubricating oil composition of the present disclosure has excellent rust-preventing properties, and when the (c) mol% / (b) mol% is 0.25 or less, viscosity increase is suppressed and biodegradability is excellent. From these viewpoints, the (c) mol% / (b) mol% is preferably 0.03 to 0.20, and more preferably 0.05 to 0.10.

[0025] In the (A) ester compound, the molar ratio of the (c) adipic acid-derived component to the (a) pentaerythritol-derived component ((c) mol% / (a) mol%) is preferably 0.05 to 0.55. In the lubricating oil composition of the present disclosure, when the (c) mol% / (a) mol% is 0.05 or more, rust prevention properties are improved, and when it is 0.55 or less, viscosity increase is suppressed. From these viewpoints, the (c) mol% / (a) mol% is more preferably 0.10 to 0.40, and even more preferably 0.15 to 0.30.

[0026] In the (A) ester compound, the molar ratio of (b) the component derived from a linear fatty acid having 14 to 22 carbon atoms to (a) the component derived from pentaerythritol ((b) mol% / (a) mol%) is preferably 2.0 to 4.0. In the lubricating oil composition of the present disclosure, when (b) mol / (a) mol) is 2.0 or more, an increase in viscosity is suppressed, and when it is 4.0 or less, rust prevention properties are improved. From these viewpoints, (b) mol% / (a) mol% is more preferably 2.3 to 3.8, and even more preferably 2.5 to 3.5.

[0027] The (A) ester compound has a hydroxyl value of 10 to 100 mgKOH / g. If the hydroxyl value of the ester exceeds 100 mgKOH / g, the lubricating oil composition may have poor lubricity (extreme pressure properties), demulsification properties, or friction reduction properties in the presence of seawater. If the hydroxyl value of the (A) ester compound is less than 10 mgKOH / g, the rust prevention properties may be poor. From these viewpoints, the hydroxyl value of the (A) ester compound is preferably 15 to 85 mgKOH / g, more preferably 15 to 75 mgKOH / g, and even more preferably 20 to 60 mgKOH / g.

[0028] The (A) ester compound preferably has an acid value of 10.0 mgKOH / g or less. When the (A) ester compound has an acid value of 10.0 mgKOH / g or less, deterioration of the lubricating oil composition's lubricity (extreme pressure properties) and oxidation stability can be suppressed. From this perspective, the acid value of the (A) ester compound is more preferably 5.0 mgKOH / g or less, even more preferably 3.0 mgKOH / g or less, and particularly preferably 1.5 mgKOH / g or less. The lower limit of the acid value of the (A) ester compound is not particularly limited, but may be 0.01 mgKOH / g or more from the viewpoint of ease of production. In the present disclosure, the acid value and hydroxyl value are measured in accordance with JIS K 0070.

[0029] (A) The ester compound has a kinematic viscosity at 40°C of 60 to 300 mm ２ (A) The ester compound preferably has a kinematic viscosity of 60 mm / s at 40°C. ２When the kinematic viscosity of the ester compound (A) is 300 mm / s or more at 40°C, the lubricating oil composition of the present disclosure has further improved lubricity (extreme pressure properties). ２ From this viewpoint, the kinematic viscosity at 40°C of the ester compound (A) is more preferably 70 to 200 mm / s. ２ / s, and more preferably 75 to 150 mm ２ / s.

[0030] (A) The ester compound has a kinematic viscosity at 100°C of 10 to 40 mm ２ (A) The ester compound preferably has a kinematic viscosity of 10 mm / s at 100°C. ２ When the kinematic viscosity of the ester compound (A) is 40 mm / s or more at 100°C, the lubricating oil composition of the present disclosure has further improved lubricity (extreme pressure properties). ２ From this viewpoint, the kinematic viscosity at 100°C of the ester compound (A) is more preferably 11 to 30 mm / s. ２ / s, and more preferably 12 to 22 mm ２ / s.

[0031] The (A) ester compound preferably has a viscosity index of 100 or more. When the (A) ester compound has a viscosity index of 100 or more, the lubricating oil composition of the present disclosure can suppress viscosity changes caused by temperature changes. From this perspective, the viscosity index of the (A) ester compound is more preferably 130 or more, and even more preferably 150 or more. There is no particular upper limit for the viscosity index of the (A) ester compound, but it is usually 250 or less. In the present disclosure, the kinematic viscosity at 40°C, the kinematic viscosity at 100°C, and the viscosity index are measured in accordance with JIS K 2283.

[0032] The (A) ester compound preferably has a flash point of 250°C or higher. When the (A) ester compound has a flash point of 250°C or higher, the lubricating oil composition of the present disclosure is more safely handled. From this perspective, the flash point of the (A) ester compound is more preferably 275°C or higher, and even more preferably 300°C or higher. The upper limit of the flash point of the (A) ester compound is not particularly limited, but is usually 400°C or lower. In the present disclosure, the flash point is measured using a Cleveland open cup (COC) in accordance with JIS K 2565.

[0033] <(B) Polyalkyl(meth)acrylate> The lubricating oil composition of the present disclosure contains (B) a non-dispersant polyalkyl(meth)acrylate having a weight average molecular weight of 20,000 to 800,000 (sometimes referred to as "(B) polyalkyl(meth)acrylate" in this disclosure). In the lubricating oil composition of the present disclosure, (B) polyalkyl(meth)acrylate is used as a viscosity modifier. Here, polyalkyl(meth)acrylate refers to at least one selected from the group consisting of polyalkyl acrylates and polyalkyl methacrylates. Furthermore, "non-dispersant" polyalkyl(meth)acrylate refers to a polyalkyl(meth)acrylate that does not have a polar group, such as a hydroxyl group, an amino group, or an amide group, on its side chain. Polyalkyl(meth)acrylates having the polar group on the side chain exhibit a detergent-dispersing effect when blended into a lubricating oil, and are therefore called "dispersant" polyalkyl(meth)acrylates, while polyalkyl(meth)acrylates not having the polar group on the side chain are not expected to exhibit a detergent-dispersing effect when blended into a lubricating oil, and are therefore called "non-dispersant" polyalkyl(meth)acrylates. The lubricating oil composition of the present disclosure contains a non-dispersant polyalkyl(meth)acrylate as the (B) polyalkyl(meth)acrylate, thereby achieving excellent friction reduction even in the presence of seawater. If a dispersant polyalkyl(meth)acrylate is used instead of a non-dispersant polyalkyl(meth)acrylate, sufficient friction reduction in the presence of seawater cannot be achieved.

[0034] The (B) polyalkyl(meth)acrylate may be, for example, a polymer of a monomer represented by the following general formula (2): The polymer may be a homopolymer using a single type of monomer represented by the following general formula (2), or a copolymer using two or more types of monomers represented by the following general formula (2).

[0035] (In general formula (2), R １ represents a hydrogen atom or a methyl group, R ２ represents a linear or branched alkyl group having 1 to 30 carbon atoms.

[0036] R in the above general formula (2) ２ Examples of the linear or branched alkyl group having 1 to 30 carbon atoms represented by the formula (I) include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, a nonadecyl group, an icosyl group, a heneicosyl group, a docosyl group, a tricosyl group, a tetracosyl group, a pentacosyl group, a hexacosyl group, a heptacosyl group, an octacosyl group, a nonacosyl group, and a triacontyl group. ２ Since the linear or branched alkyl group represented by the formula (I) has 1 to 30 carbon atoms, the lubricating oil composition of the present disclosure has excellent friction reducing properties in the presence of seawater, and precipitation of the polyalkyl(meth)acrylate (B) at low temperatures is suppressed. ２ The number of carbon atoms in the linear or branched alkyl group represented by the formula (I) is preferably 12 or more in order to improve the friction reducing property in the presence of seawater, and is preferably 22 or less in order to suppress precipitation of the (B) polyalkyl(meth)acrylate at low temperatures.

[0037] The weight-average molecular weight of the (B) polyalkyl (meth)acrylate is 20,000 to 800,000. If the weight-average molecular weight is less than 20,000, sufficient friction reduction may not be achieved in the presence of seawater. On the other hand, if the weight-average molecular weight is greater than 800,000, the solubility in the (A) ester compound, which is the base oil, decreases, and the (B) polyalkyl (meth)acrylate may precipitate at low temperatures when added to the (A) ester compound, and sufficient friction reduction may not be achieved in the presence of seawater. From these viewpoints, the weight-average molecular weight of the (B) polyalkyl (meth)acrylate is preferably 30,000 to 775,000, more preferably 50,000 to 750,000, even more preferably 80,000 to 700,000, and particularly preferably 80,000 to 400,000.

[0038] The weight average molecular weight in this disclosure is a value measured using gel permeation chromatography (GPC) under the following conditions and calculated in terms of polystyrene. <Measurement conditions> Apparatus: HLC-8320 manufactured by Tosoh Corporation Column: LF-804 manufactured by Shodex Standard material: Polystyrene Eluent: THF (tetrahydrofuran) Flow rate: 1.0 ml / min Temperature: 40°C Detector: RI (differential refractive index detector)

[0039] <(C) Acidic Phosphate Amine Salt> The lubricating oil composition of the present disclosure contains (C) an acidic phosphate amine salt represented by the following general formula (1) (sometimes referred to as "(C) acidic phosphate amine salt" in the present disclosure). In the lubricating oil composition of the present disclosure, the (C) acidic phosphate amine salt is used as an extreme pressure agent.

[0040] (In general formula (1), n ​​is an integer of 1 or 2, R' is a linear alkyl group having 4 to 6 carbon atoms, and R'' is a hydrogen atom or an alkyl group having 11 to 14 carbon atoms.)

[0041] In the above general formula (1), n ​​is an integer of 1 or 2. That is, the (C) acidic phosphate amine salt used in the present disclosure has one or two hydroxyl groups per molecule. When there is one hydroxyl group in one molecule, there are two -OR' groups, and when there are two hydroxyl groups, there is one -OR' group. The lubricating oil composition of the present disclosure can contain, as the (C) acidic phosphate amine salt, one acidic phosphate amine salt represented by the above general formula (1) alone or in combination of two or more types. The lubricating oil composition of the present disclosure contains at least either an acidic phosphate amine salt represented by the above general formula (1) in which n is 1, or an acidic phosphate amine salt represented by the above general formula (1) in which n is 2. However, from the viewpoint of improving the lubricity (extreme pressure properties) of the lubricating oil composition of the present disclosure, it is preferable to contain both an acidic phosphate amine salt represented by the above general formula (1) in which n is 1 and an acidic phosphate amine salt represented by the above general formula (1) in which n is 2.

[0042] In the above general formula (1), R' is a linear alkyl group having 4 to 6 carbon atoms. If the number of carbon atoms in R' is outside the range of 4 to 6, the lubricating oil composition may have insufficient lubricity (extreme pressure properties). From the viewpoint of lubricity (extreme pressure properties), R' is most preferably a linear alkyl group having 6 carbon atoms (i.e., a hexyl group). Therefore, (C) the acidic phosphate amine salt is preferably at least one selected from the group consisting of amine salts of monohexyl phosphate and amine salts of dihexyl phosphate, and it is more preferable to use both of these in combination.

[0043] In the above general formula (1), R" is a hydrogen atom or an alkyl group having 11 to 14 carbon atoms. The alkyl group is preferably a linear or branched alkyl group. From the viewpoint of improving the lubricating properties (extreme pressure properties) of the lubricating oil composition of the present disclosure, NR" in the above general formula (1) ３Preferably, at least one of the three R"s is a linear or branched alkyl group having 11 to 14 carbon atoms; more preferably, one or two of the three R"s are linear or branched alkyl groups having 11 to 14 carbon atoms and the remaining is a hydrogen atom; and even more preferably, two of the three R"s are linear or branched alkyl groups having 11 to 14 carbon atoms and one is a hydrogen atom. If the alkyl group in R" has 10 or fewer carbon atoms, the solubility of (C) acidic phosphate amine salt in (A) ester compound decreases, which may result in precipitation of (C) acidic phosphate amine salt at low temperatures. On the other hand, if the alkyl group in R" has 15 or more carbon atoms, the extreme-pressure performance of the lubricating oil composition may be insufficient. From this viewpoint, the alkyl group in R" more preferably has 12 to 13 carbon atoms.

[0044] <Composition of Lubricating Oil Composition> The lubricating oil composition of the present disclosure contains 0.1 to 10.0 parts by mass of (B) polyalkyl(meth)acrylate and 0.1 to 1.5 parts by mass of (C) acidic phosphate amine salt per 100 parts by mass of (A) ester compound. The lubricating oil composition of the present disclosure contains the (A) ester compound as a base oil and the (B) polyalkyl(meth)acrylate and (C) acidic phosphate amine salt as additives in the above-mentioned specific ratios, thereby achieving excellent friction-reducing properties even in the presence of seawater due to the synergistic effect of these additives. As shown in Comparative Examples 1, 2, and 6 described below, excellent friction-reducing properties in the presence of seawater are not exhibited when at least one of the (A) ester compound, (B) polyalkyl(meth)acrylate, and (C) acidic phosphate amine salt is not present. Furthermore, when the content of the (B) polyalkyl(meth)acrylate is less than 0.1 parts by mass or more than 10.0 parts by mass per 100 parts by mass of the (A) ester compound, excellent friction reduction properties are not exhibited in the presence of seawater. When the content of the (B) polyalkyl(meth)acrylate exceeds 10.0 parts by mass per 100 parts by mass of the (A) ester compound, the biodegradability of the lubricating oil composition may be further deteriorated, and the (B) polyalkyl(meth)acrylate may precipitate at low temperatures, resulting in insufficient lubricity (extreme pressure properties) and friction reduction properties. From these viewpoints, the content of the (B) polyalkyl(meth)acrylate is preferably 0.30 to 8.00 parts by mass, more preferably 0.45 to 6.00 parts by mass, and even more preferably 0.60 to 5.00 parts by mass per 100 parts by mass of the (A) ester compound. Furthermore, when the content of the (C) acidic phosphate amine salt per 100 parts by mass of the (A) ester compound is less than 0.1 parts by mass, excellent friction reduction properties are not exhibited in the presence of seawater. When the content of the (C) acidic phosphate amine salt per 100 parts by mass of the (A) ester compound is less than 0.1 parts by mass, lubricity (extreme pressure properties) or friction reduction properties may be insufficient. When the content of the (C) acidic phosphate amine salt per 100 parts by mass of the (A) ester compound is more than 1.5 parts by mass, demulsibility may be impaired.From this viewpoint, the content of (C) acidic phosphoric acid ester amine salt is preferably 0.2 to 1.25 parts by mass, and more preferably 0.3 to 1.00 parts by mass, per 100 parts by mass of (A) ester compound.

[0045] In addition to the above-described (A) ester compound, (B) polyalkyl(meth)acrylate, and (C) acidic phosphate amine salt, the lubricating oil composition of the present disclosure may contain known lubricating oil additives, as needed, in amounts that do not impair the objectives of the present disclosure, in order to further enhance the performance of the lubricating oil composition. Examples of such additives include antioxidants, metal deactivators, rust inhibitors, antifoaming agents, pour point depressants, and viscosity index improvers. These additives may be used alone or in combination of two or more.

[0046] Examples of antioxidants include amine-based antioxidants, phenol-based antioxidants, organometallic compound-based antioxidants, sulfur-based antioxidants, and phosphorus-based antioxidants. Examples of amine-based antioxidants include phenyl-α-naphthylamine, phenyl-β-naphthylamine, alkylphenyl-α-naphthylamine, alkylphenyl-β-naphthylamine, bis(alkylphenyl)amine, phenothiazine, monooctydiphenylamine, 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, 2,2,4-trimethyl-1,2-dihydroquinoline or polymers thereof, 6-methoxy-2,2,4-trimethyl-1,2-dihydroquinoline or polymers thereof, and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline or polymers thereof. It is preferable to use one or a combination of two or more selected from this group. Among these, phenyl-α-naphthylamine, phenyl-β-naphthylamine, alkylphenyl-α-naphthylamine, alkylphenyl-β-naphthylamine, bis(alkylphenyl)amine, monooctydiphenylamine, and 4,4'-bis(α,α-dimethylbenzyl)diphenylamine are more preferred, and phenyl-α-naphthylamine, phenyl-β-naphthylamine, alkylphenyl-α-naphthylamine, alkylphenyl-β-naphthylamine, and bis(alkylphenyl)amine are even more preferred. Examples of phenolic antioxidants include 2,6-di-t-butyl-paracresol, 4,4-methylenebis(2,6-di-t-butylphenol), 4,4-thiobis(2-methyl-6-t-butylphenol), 4,4-bis(2,6-di-t-butylphenol), and pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. It is preferable to use one or a combination of two or more selected from this group. Furthermore, phenolic antioxidants with a high molecular weight are preferred because they are less likely to accumulate in aquatic organisms. From this perspective, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] is particularly preferred as the phenolic antioxidant.Examples of organometallic compound-based antioxidants include zinc dialkyldithiophosphate. Examples of sulfur-based antioxidants include dilauryl-3,3'-thiodipropionate. Examples of phosphorus-based antioxidants include triethyl phosphite. These antioxidants can be used alone or in combination of two or more. From the viewpoint of improving the oxidation stability of the lubricating oil composition of the present disclosure, it is more preferable to use a mixture of two or more antioxidants, and it is even more preferable to use a mixture of an amine-based antioxidant and a phenol-based antioxidant. When the lubricating oil composition of the present disclosure contains an antioxidant, the content of the antioxidant is preferably 0.3 to 2.0 parts by mass, more preferably 0.5 to 1.5 parts by mass, and even more preferably 0.6 to 1.0 part by mass, per 100 parts by mass of the (A) ester compound.

[0047] Examples of metal deactivators include benzotriazole and its derivatives, and alkenyl succinate esters. These metal deactivators can be used alone or in combination of two or more. When the lubricating oil composition of the present disclosure contains a metal deactivator, the content of the metal deactivator is preferably 0.001 to 0.1 parts by mass, more preferably 0.002 to 0.08 parts by mass, and even more preferably 0.003 to 0.06 parts by mass, per 100 parts by mass of the ester compound (A).

[0048] Examples of rust inhibitors include alkenyl succinic acid and its derivatives, imidazoline derivatives such as carboxyimidazoline, oleoyl sarcosine, and alkylphenoxyacetic acid. These rust inhibitors can be used alone or in combination of two or more. In the present disclosure, alkenyl succinic acid and its derivatives are preferably used because they can impart high rust prevention properties. Examples of the antifoaming agent include silicone compounds.

[0049] <Characteristics of Lubricating Oil Composition> The kinematic viscosity at 40°C of the lubricating oil composition of the present disclosure is 65 mm ２ / s or more, and from the viewpoint of suppressing high viscosity and suppressing deterioration of fuel efficiency of the equipment, ２ From this perspective, the kinematic viscosity at 40°C of the lubricating oil composition of the present disclosure is more preferably 75 to 350 mm ２ / s, and more preferably 80 to 300 mm ２ / s.

[0050] The kinematic viscosity at 100°C of the lubricating oil composition of the present disclosure is 12 mm ２ / s or more, and from the viewpoint of suppressing high viscosity and suppressing deterioration of fuel efficiency of the equipment, ２ From this perspective, the kinematic viscosity at 100°C of the lubricating oil composition of the present disclosure is more preferably 13 to 60 mm / s. ２ / s, and more preferably 14 to 50 mm ２ / s.

[0051] From the viewpoint of suppressing viscosity changes due to temperature changes, the lubricating oil composition of the present disclosure preferably has a viscosity index of at least 100, more preferably at least 130, and even more preferably at least 150. There is no particular upper limit to the viscosity index of the lubricating oil composition of the present disclosure, but it is usually 350 or less.

[0052] The lubricating oil composition of the present disclosure has excellent biodegradability, and therefore the degree of biodegradation measured in accordance with OECD 301C (modified MITI test method) is preferably 60% or more, more preferably 70% or more.

[0053] The lubricating oil composition of the present disclosure has excellent lubricity (extreme pressure properties), and therefore has a maximum non-seizure load measured by the Shell four-ball load capacity test in accordance with ASTM D2783 of preferably 100 kgf or more, more preferably 160 kgf or more.

[0054] The lubricating oil composition of the present disclosure has excellent demulsibility properties, and when a demulsibility test is carried out in accordance with JIS K 2520 on a mixture of 40 mL of the lubricating oil composition and 40 mL of water, the time until the emulsion layer becomes 3 mL or less is preferably less than 60 minutes, more preferably less than 30 minutes.

[0055] The lubricating oil composition of the present disclosure has excellent friction-reducing properties, and therefore the friction coefficient measured by a cylinder-on-disk friction test is preferably less than 0.050, more preferably less than 0.040. Furthermore, the lubricating oil composition of the present disclosure has excellent friction-reducing properties even in the presence of seawater, and therefore the friction coefficient of a seawater-containing lubricating oil composition obtained by adding 1 mass % of artificial seawater to the lubricating oil composition of the present disclosure is also preferably less than 0.050, more preferably less than 0.040.

[0056] <Method for Producing Lubricating Oil Composition> The method for producing the lubricating oil composition of the present disclosure is not particularly limited. For example, the lubricating oil composition can be produced by adding a predetermined amount of (B) polyalkyl(meth)acrylate and (C) acidic phosphate amine salt to the above-mentioned (A) ester compound, and further adding the various additives described above, as necessary. The method for adding and mixing each material is not particularly limited, and various methods can be used. The order of addition is also not particularly limited. For example, a method may be used in which (B) polyalkyl(meth)acrylate, (C) acidic phosphate amine salt, and other additives are directly added to the (A) ester compound, and then heated and mixed. Alternatively, a method may be used in which high-concentration solutions of the (B) polyalkyl(meth)acrylate, (C) acidic phosphate amine salt, and other additives are prepared in advance, and these high-concentration solutions are mixed with the (A) ester compound.

[0057] <Uses of Lubricating Oil Composition> The uses of the lubricating oil composition of the present disclosure are not particularly limited, but it can be suitably used as a bearing oil, hydraulic oil, gear oil, etc., and in particular as a stern tube bearing oil or thruster oil used in marine areas.

[0058] The present disclosure will be described in more detail below with reference to examples and comparative examples. Note that percentages are by mass unless otherwise specified. Hereinafter, the acid value and hydroxyl value were measured according to JIS K 0070. The kinematic viscosity at 40°C, the kinematic viscosity at 100°C, and the viscosity index were measured according to JIS K 2283. The flash point was measured using a Cleveland open cup (COC) according to JIS K 2565.

[0059] Synthesis of Ester Compounds Synthesis Example 1 A 3 L four-neck flask equipped with a thermometer, a nitrogen inlet tube, a stirrer, and a condenser was charged with (a) 285 g (2.09 mol) of pentaerythritol, (c) 88 g (0.60 mol) of adipic acid, (b) linear fatty acids having 14 to 20 carbon atoms (myristic acid (C14, saturated): 2.0 mass%, myristoleic acid (C14, unsaturated): 1.4 mass%, pentadecenoic acid (C15, unsaturated): 0.2 mass%, palmitic acid (C16, saturated): 4.2 mass%, palmitoleic acid (C16, saturated): 0.2 mass%, and 2.0 g (0.60 mol) of adipic acid. 1728 g (6.21 mol) of oleic acid (C16, unsaturated): 7.0% by mass, heptadecenoic acid (C17, unsaturated): 1.6% by mass, stearic acid (C18, saturated): 1.2% by mass, oleic acid (C18, unsaturated): 73.8% by mass, linoleic acid (C18, unsaturated): 6.7% by mass, linolenic acid (C18, unsaturated): 1.8% by mass, and arachidic acid (C20, saturated): 0.1% by mass was added and reacted at normal pressure under a nitrogen stream at 240 ° C. while distilling off the reaction water. After cooling the reaction product, 0.5% by mass of activated clay was added to the reaction product to adsorb it, and the adsorbent was removed by filtration to obtain ester compound A1.

[0060] Synthesis Examples 2 and 3 Ester compound A2 and ester compound A'1 were obtained in the same manner as in Synthesis Example 1, except that the amounts of (a) pentaerythritol, (b) linear fatty acid, and (c) adipic acid added were changed according to Table 1.

[0061] Regarding the ester compounds A1, A2 and A'1 obtained above, １H NMR was used to measure (a) the mole percentage of components derived from pentaerythritol, (b) the mole percentage of components derived from straight chain fatty acids, and (c) the mole percentage of components derived from adipic acid. The mole percentages of each component are shown in Table 1.

[0062] Furthermore, the acid value, hydroxyl value, kinematic viscosity at 40° C., kinematic viscosity at 100° C., viscosity index, and flash point of the ester compounds A1, A2, and A′1 obtained above were measured. The measurement results are shown in Table 1.

[0063]

[0064] [Preparation of Lubricating Oil Compositions] (Examples 1 to 7 and Comparative Examples 1 to 6) In a 3 L four-neck flask equipped with a thermometer, a nitrogen inlet tube, a stirrer, and a condenser, polyalkyl (meth)acrylate, acidic phosphate ester amine salt, and metal deactivator were added as additives to an ester compound serving as a base oil according to Table 2 or Table 3, and the mixture was stirred and mixed at 120°C for 2 hours to prepare the lubricating oil compositions of Examples 1 to 7 and Comparative Examples 1 to 6. The ester compound used was the ester compound A1, A2, or A'1 obtained above, and the following additives were used. <Polyalkyl (meth)acrylate> B1: Non-dispersant polyalkyl methacrylate having an alkyl group having 12 to 22 carbon atoms on the side chain, weight average molecular weight 360,000, manufactured by Evonik, trade name "VISCOPLEX (registered trademark) 10-950" B2: Non-dispersant polyalkyl methacrylate having an alkyl group having 12 to 22 carbon atoms on the side chain, weight average molecular weight 59,000, manufactured by Sanyo Chemical Industries, Ltd., trade name "Acluv (registered trademark) 146" B'1: Dispersant polyalkyl methacrylate having an alkyl group having 1 to 14 carbon atoms on the side chain, weight average molecular weight 33,000, manufactured by Evonik, trade name "VISCOPLEX (registered trademark) 0-777" <Acidic phosphate ester amine salt> C1: C11 to C14 branched alkylamine salt of mono- or dihexyl phosphate (NR" in the above general formula (1) ３wherein two of the three R's are C11-C14 branched alkyl groups and one is a hydrogen atom), BASF, trade name "IRGALUBE (registered trademark) 349" <Metal deactivator> Benzotriazole derivative, BASF, trade name "IRGAMET (registered trademark) 39"

[0065] [Physical Properties of Lubricating Oil Composition] The kinematic viscosity at 40° C., kinematic viscosity at 100° C., and viscosity index of the lubricating oil composition were measured. The measurement results are shown in Tables 2 and 3.

[0066] [Performance Evaluation of Lubricating Oil Compositions] (Biodegradability) A biodegradability test was carried out on the lubricating oil compositions in accordance with OECD 301C (modified MITI test method). The Ecomark Office of the Japan Environment Association, a public interest incorporated foundation, sets a biodegradability standard of 60% or more for biodegradable lubricating oils. In this test, the biodegradability of the lubricating oil compositions was evaluated as "◎" when the biodegradability was 70% or more but less than 70%, "◯" when it was 60% or more but less than 70%, and "×" when it was less than 60%. The evaluation results are shown in Tables 2 and 3.

[0067] (Destabilization) The lubricating oil composition was subjected to a demulsification test in accordance with JIS K 2520. Specifically, 40 mL of the lubricating oil composition and 40 mL of water were placed in a test tube, kept at 82°C ± 1°C, and stirred with a stirring plate at 1,500 revolutions per minute. The volumes (mL) of the oil layer, water layer, and emulsified layer were measured every 5 minutes, and the test was terminated when the emulsified layer became 3 mL or less. The shorter the time required for the emulsified layer to decrease, the better the demulsification properties of the lubricating oil composition. In this test, the demulsification properties of the lubricating oil composition were evaluated as follows: "◎" indicates that the time it took for the emulsified layer to become 3 mL or less was less than 30 minutes; "○" indicates that the time taken for the emulsified layer to become 3 mL or less was 30 minutes or more but less than 60 minutes. "X" indicates that the time taken for the emulsified layer to become 3 mL or less was 60 minutes or more, or that the emulsified layer did not become 3 mL or less even after 60 minutes. The evaluation results are shown in Tables 2 and 3.

[0068] (Lubricity (Extreme Pressure)) The lubricating oil compositions were subjected to a Shell four-ball load-bearing capacity test using a high-speed Shell four-ball tester in accordance with ASTM D2783 to measure the maximum non-seizure load. The test conditions were 10 mL of lubricating oil composition, a test temperature of 25°C, a rotation speed of 1800 rpm, and a measurement time of 10 seconds. The higher the maximum non-seizure load, the more excellent the lubrication performance (extreme pressure performance) of the lubricating oil composition. In this test, the lubricating oil composition's lubricating performance (extreme pressure) was evaluated as "◎" when the maximum non-seizure load was 160 kgf or more, "◯" when it was 100 kgf or more but less than 160 kgf, and "×" when it was less than 100 kgf. The maximum non-seizure loads are shown in Tables 2 and 3 together with the evaluation results.

[0069] (Friction Reducing Properties) The lubricating oil compositions were subjected to a friction test using a multi-function friction and wear tester (UMT-TribolaB, manufactured by BRUKER) to evaluate their friction reducing properties. The friction test was performed using a cylinder-on-disc, with the cylinder positioned at a radius of 20 mm from the center of the disc. A cylinder made of SUJ-2 with an outer diameter of 10 mm and a length of 14 mm and a disc made of SUJ-2 with an outer diameter of 70 mm and a width of 6.6 mm were used. The test conditions were a test temperature of 25°C, a load of 20 N, a rotation speed of 300 rpm, and a measurement time of 30 seconds, and the coefficient of friction between the cylinder and the disc was measured. Five measurements were performed, and the average value calculated from the results was used for evaluation. The lower the friction coefficient, the better the lubricating oil composition's friction reducing properties. In this test, the friction reducing ability of the lubricating oil composition was evaluated by rating a friction coefficient of less than 0.040 as "◎", a coefficient of friction of 0.040 to 0.049 as "◯", and a coefficient of friction of 0.050 or more as "×". The evaluation results and the average values ​​of the friction coefficients are shown in Tables 2 and 3.

[0070] (Friction-reducing ability in the presence of seawater) The lubricating oil compositions prepared in each Example and Comparative Example were each added with 1% by mass of artificial seawater to prepare seawater-containing lubricating oil compositions, and the friction-reducing ability of the lubricating oil compositions in the presence of seawater was evaluated in the same manner as above. The artificial seawater was prepared in accordance with ASTM D1141.

[0071]

[0072]

[0073] As shown in Table 2, the lubricating oil compositions of Examples 1 to 7 were lubricating oil compositions according to the present disclosure, containing 100 parts by mass of the above-described (A) ester compound, 0.1 to 10.0 parts by mass of (B) polyalkyl(meth)acrylate, and 0.1 to 1.5 parts by mass of (C) acidic phosphate amine salt. These compositions were excellent in biodegradability, lubricity (extreme pressure properties), demulsibility, and friction-reducing properties, even in the presence of seawater. On the other hand, as shown in Table 3, the lubricating oil composition of Comparative Example 1 did not contain the above-described (A) ester compound, but contained ester compound A'1 as the base oil. Ester compound A'1 had a molar percentage of (a) pentaerythritol-derived components exceeding 30 mol% and a hydroxyl value exceeding 100 mgKOH / g, and therefore the lubricating oil composition of Comparative Example 1 exhibited insufficient demulsibility and friction-reducing properties in the presence of seawater. The lubricating oil composition of Comparative Example 2 did not contain the above-mentioned (B) polyalkyl (meth)acrylate as a viscosity modifier, but contained a dispersant polyalkyl methacrylate B'1, and therefore exhibited insufficient friction-reducing properties in the presence of seawater. The lubricating oil composition of Comparative Example 3 contained the above-mentioned (B) polyalkyl (meth)acrylate, non-dispersant polyalkyl methacrylate B1, as a viscosity modifier, but the content was low, and therefore the friction-reducing properties in the presence of seawater were insufficient. The lubricating oil composition of Comparative Example 4 contained the above-mentioned (B) polyalkyl (meth)acrylate, non-dispersant polyalkyl methacrylate B1, as a viscosity modifier, but the content was high, and therefore the biodegradability, lubricity (extreme pressure properties), and friction-reducing properties were insufficient, and the friction-reducing properties in the presence of seawater were also insufficient. The lubricating oil composition of Comparative Example 5 contained the C11-C14 branched alkylamine salt C1 of mono- and dihexyl phosphate, which is the above-mentioned (C) acidic phosphate amine salt, but the content was too high, so the demulsibility was insufficient.The lubricating oil composition of Comparative Example 6 did not contain the above-mentioned (C) acidic phosphate amine salt, so the lubricating oil composition was insufficient in lubricity (extreme pressure properties) and friction-reducing properties in the presence of seawater.

[0074] The biodegradable lubricating oil composition of the present disclosure has excellent biodegradability, lubricity (extreme pressure properties), demulsibility, and friction-reducing properties, and also has excellent friction-reducing properties even in the presence of seawater. Therefore, the biodegradable lubricating oil composition of the present disclosure can be suitably used as bearing oil, hydraulic oil, gear oil, etc., and particularly as stern tube bearing oil and thruster oil used in marine areas.

Claims

1. A biodegradable lubricating oil composition comprising, per 100 parts by mass of the following (A) ester compound, 0.1 to 10.0 parts by mass of the following (B) polyalkyl(meth)acrylate and 0.1 to 1.5 parts by mass of the following (C) acidic phosphoric acid ester amine salt. (A): an ester compound of (a) pentaerythritol, (b) a straight-chain fatty acid having 14 to 22 carbon atoms, and (c) adipic acid, wherein the molar percentage of the component derived from the pentaerythritol (a) is 20 to 30 mol %, the molar percentage of the component derived from the straight-chain fatty acid having 14 to 22 carbon atoms (b) is 55 to 79 mol %, and the molar percentage of the component derived from the adipic acid (c) is 1 to 15 mol %, the molar ratio of the component derived from the adipic acid (c) to the component derived from the straight-chain fatty acid having 14 to 22 carbon atoms (b) is 0.02 to 0.25, and the hydroxyl value is 10 to 100 mgKOH / g; (B): a non-dispersed polyalkyl(meth)acrylate having a weight-average molecular weight of 20,000 to 800,000; and (C): an acidic phosphate amine salt represented by the following general formula (1): (In general formula (1), n is an integer of 1 or 2, R' is a linear alkyl group having 4 to 6 carbon atoms, and R'' is a hydrogen atom or an alkyl group having 11 to 14 carbon atoms.)

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