JP7604292B2 - Polymer additive, lubricating oil composition and working fluid composition for refrigeration - Google Patents

Description

The present invention relates to a polymer additive, a lubricating oil composition, and a working fluid composition for a refrigeration machine.

In industrial machinery that has mechanical elements such as hydraulic machinery, compression machinery, turbines, gear elements, and bearings, lubricating oils are used to improve the lubrication between components. For example, compressors in refrigeration units such as refrigerators and air conditioners are filled with refrigeration lubricating oil (refrigeration oil) to lubricate the sliding components.

Generally, lubricating oils contain base oils and additives that are blended according to the desired characteristics. Mineral oils or synthetic oils are used as base oils. In recent years, ester-based base oils have been attracting attention as base oils for lubricating oils used in special environments such as refrigeration oils, due to their low volatility, high polarity, and excellent heat transfer properties. For example, Patent Document 1 below discloses a refrigeration oil that contains a specific ester-based base oil and various additives.

Patent No. 6545337

However, because ester base oils are more polar than mineral oils, it is difficult to obtain the effects of additives compared to when mineral oils are used, and in particular, it tends to be difficult to obtain the improved wear resistance provided by phosphorus-based additives such as tricresyl phosphate (TCP), which have traditionally been used.

The main objective of the present invention is to provide an additive for lubricating oils that is effective in improving the wear resistance of lubricating oils that contain ester-based base oils.

After extensive research, the inventors discovered that polymerizing the additive makes it easier for the additive to be adsorbed onto metal surfaces and makes the additive more compatible with ester-based base oils, thus completing the present invention.

［式（１）中、Ｒ^１及びＲ^２は、それぞれ独立して、水素原子又は１価の炭化水素基を表し、Ｘは２価の炭化水素基を表す。］ One aspect of the present invention relates to an additive for a lubricating oil containing an ester-based base oil, the polymer additive containing a phosphate ester methacrylate represented by the following formula (1) as a monomer unit.

[In formula (1), R ¹ and R ² each independently represent a hydrogen atom or a monovalent hydrocarbon group, and X represents a divalent hydrocarbon group.]

The polymer additive of the above aspect can improve the wear resistance of lubricating oils containing ester-based base oils even in small amounts. In addition, while using a large amount of phosphorus-based additives such as TCP to achieve the effect of improving wear resistance is likely to cause problems such as reduced thermal stability, the polymer additive of the above aspect does not need to be used in large amounts, so there is a tendency for superior thermal stability to be obtained compared to the use of phosphorus-based additives such as TCP. Therefore, for example, when the polymer additive of the above aspect is used in refrigeration oil, there is also the advantage that sludge is less likely to be generated.

The weight average molecular weight of the polymer additive in the above aspect may be 3,000 to 20,000. In this case, the effect of improving abrasion resistance tends to be more excellent.

The content of the phosphate ester methacrylate as a monomer unit in the polymer additive of the above aspect may be 0.1 to 90 mass % based on the total mass of the polymer additive. In this case, the effect of improving abrasion resistance tends to be more excellent.

［式（２）中、Ｒ^３は、炭素数が１～３６のアルキル基を表し、Ｒ^４は、水素原子又はメチル基を表す。］ The polymer additive of the above aspect may further contain, as a monomer unit, an alkyl (meth)acrylate represented by the following formula (2): In this case, there is a tendency for the effect of improving abrasion resistance to be more excellent.

[In formula (2), R ³ represents an alkyl group having 1 to 36 carbon atoms, and R ⁴ represents a hydrogen atom or a methyl group.]

Another aspect of the present invention relates to a lubricating oil composition containing an ester-based base oil and the polymer additive of the above aspect.

The content of the polymer additive in the lubricating oil composition of the above aspect may be 0.1 to 10 mass % based on the total mass of the lubricating oil composition. In this case, better wear resistance and better thermal stability tend to be obtained.

The phosphorus content in the lubricating oil composition of the above aspect may be 150 ppm by mass or more based on the total mass of the lubricating oil composition. In this case, better wear resistance tends to be obtained.

The lubricating oil composition of the above aspect may be used as a refrigeration oil.

Another aspect of the present invention relates to a working fluid composition for a refrigeration machine, which contains a refrigerant and the lubricating oil composition of the above aspect.

The present invention provides an additive for lubricating oils that is highly effective in improving the wear resistance of lubricating oils that contain ester-based base oils.

The following describes preferred embodiments of the present invention. However, the present invention is not limited to the following embodiments.

［式（１）中、Ｒ^１及びＲ^２は、それぞれ独立して、水素原子又は１価の炭化水素基を表し、Ｘは、２価の炭化水素基を表す。］

［式（１ａ）中のＲ^１、Ｒ^２及びＸは、それぞれ式（１）中のＲ^１、Ｒ^２及びＸと同義である。式（１ａ）中の＊は、他のモノマー単位への結合手を表す。］ <Polymer Additives>
The polymer additive of one embodiment is an additive for a lubricating oil (e.g., a refrigerating machine oil) containing an ester-based base oil. The polymer additive contains a phosphate ester methacrylate represented by the following formula (1) as a monomer unit. In other words, the polymer additive contains a monomer unit represented by the following formula (1a).

[In formula (1), R ¹ and R ² each independently represent a hydrogen atom or a monovalent hydrocarbon group, and X represents a divalent hydrocarbon group.]

[R ¹ , R ² and X in formula (1a) are defined the same as R ¹ , R ² and X in formula (1), respectively. * in formula (1a) represents a bond to another monomer unit.]

R ¹ and R ² may be the same or different. The hydrocarbon group is, for example, an alkyl group or an aryl group. The alkyl group may be linear, branched, or cyclic. The number of carbon atoms in the alkyl group may be, for example, 1 to 8. The aryl group is, for example, a phenyl group. From the viewpoint of further enhancing the effect of improving the abrasion resistance, it is preferable that at least one of R ¹ and R ² is a phenyl group, and it is more preferable that both are phenyl groups.

The hydrocarbon group represented by X may be linear, branched, or have a cyclic structure. The number of carbon atoms in the hydrocarbon group may be, for example, 2 to 18. The hydrocarbon group may be, for example, an alkylene group (alkanediyl group). Examples of the alkylene group include an ethylene group, a propylene group, a butylene group, and a hexylene group. From the viewpoint of further enhancing the effect of improving abrasion resistance, X is preferably an alkylene group having 2 to 4 carbon atoms.

Specific examples of the phosphate ester methacrylate represented by the above formula (1) include mono(2-hydroxyethyl methacrylate) diphenyl phosphate, di(2-hydroxyethyl methacrylate) monophenyl phosphate, mono(2-hydroxyethyl methacrylate) phosphate, mono(2-hydroxyethyl methacrylate) di-t-butyl phosphate, etc. Among these, when the polymer additive contains mono(2-hydroxyethyl methacrylate) diphenyl phosphate as a monomer unit, it tends to have a better effect of improving wear resistance.

The polymer additive may contain one or more types of phosphate ester methacrylate represented by the above formula (1) as a monomer unit.

The content of the phosphate ester methacrylate represented by the above formula (1) as a monomer unit (the content of the monomer unit represented by the above formula (1a)) is preferably 0.1% by mass or more, more preferably 1% by mass or more, even more preferably 10% by mass or more, and particularly preferably 15% by mass or more, based on the total mass of the polymer additive, from the viewpoint of improving the effect of improving wear resistance and solubility and stability in the ester base oil. The content of the phosphate ester methacrylate represented by the above formula (1) as a monomer unit is preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 70% by mass or less, based on the total mass of the polymer additive, from the viewpoint of improving the compatibility with the ester base oil and thereby further improving the effect of improving wear resistance. From these viewpoints, the content of the phosphate ester methacrylate represented by the above formula (1) as a monomer unit may be 0.1 to 90% by mass, 1 to 80% by mass, 10 to 70% by mass, or 15 to 70% by mass, based on the total mass of the polymer additive. The content of the phosphate ester methacrylate represented by the above formula (1) as a monomer unit may be 1 to 10 mass%, 10 to 15 mass%, 1 to 60 mass%, 5 to 55 mass%, or 10 to 50 mass% based on the total mass of the polymer additive.

The polymer additive may further contain, as a monomer unit, a monomer polymerizable with the phosphate ester methacrylate represented by the above formula (1). That is, the polymer additive may be a copolymer of the phosphate ester methacrylate represented by the above formula (1) and a monomer polymerizable with the phosphate ester methacrylate. The copolymer may be a block copolymer or a random copolymer.

Examples of monomers polymerizable with the phosphate ester methacrylate represented by the above formula (1) include alkyl (meth)acrylates. Here, (meth)acrylate means at least one of an acrylate and the corresponding methacrylate.

［式（２）中、Ｒ^３は、炭素数が１～３６のアルキル基を表し、Ｒ^４は、水素原子又はメチル基を表す。］ From the viewpoint of enhancing the effect of improving wear resistance by increasing compatibility with the ester-based base oil, it is preferable that the polymer additive further contains an alkyl (meth)acrylate represented by the following formula (2) as a monomer unit.

[In formula (2), R ³ represents an alkyl group having 1 to 36 carbon atoms, and R ⁴ represents a hydrogen atom or a methyl group.]

The alkyl group represented by ^R3 may be linear or branched, but is preferably linear from the viewpoint of improving compatibility with the ester-based base oil. When the alkyl group is linear, the number of carbon atoms in the alkyl group may be 18 or less. From the viewpoint of improving the adsorptivity to the metal surface, the number of carbon atoms in the alkyl group is preferably 1 to 10, and more preferably 1 to 6. Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group, a pentyl group, an isopentyl group, a neopentyl group, a hexyl group, and an isohexyl group.

The polymer additive may contain two or more types of alkyl (meth)acrylate as monomer units. At least one of the two or more types of alkyl (meth)acrylate contained in the polymer additive as monomer units is preferably methyl (meth)acrylate from the viewpoint of improving the adsorption to the metal surface in the ester-based base oil. From the viewpoint of improving the compatibility with the ester-based base oil, it is preferable that the polymer additive contains, as monomer units, methyl (meth)acrylate and at least one alkyl (meth)acrylate selected from the group consisting of ethyl (meth)acrylate, n-propyl (meth)acrylate, and n-butyl (meth)acrylate.

From the viewpoint of improving solubility in ester-based base oils, the content of methyl (meth)acrylate as a monomer unit is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more, based on the total mass of the polymer additive. From the viewpoint of improving wear resistance, the content of methyl (meth)acrylate as a monomer unit is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 80% by mass or less, based on the total mass of the polymer additive. From these viewpoints, the content of methyl (meth)acrylate as a monomer unit may be 5 to 95% by mass, 10 to 90% by mass, or 20 to 80% by mass, based on the total mass of the polymer additive.

The content of the alkyl (meth)acrylate as a monomer unit is preferably 40% by mass or more, more preferably 45% by mass or more, and even more preferably 50% by mass or more, based on the total mass of the polymer additive, from the viewpoint of improving compatibility with the ester-based base oil. The content of the alkyl (meth)acrylate as a monomer unit is preferably 99% by mass or less, more preferably 95% by mass or less, and even more preferably 90% by mass or less, based on the total mass of the polymer additive, from the viewpoint of improving wear resistance. From these viewpoints, the content of the alkyl (meth)acrylate as a monomer unit may be 40 to 99% by mass, 45 to 95% by mass, or 50 to 90% by mass, based on the total mass of the polymer additive. The content of the alkyl (meth)acrylate as a monomer unit may be 10 to 99.9% by mass, 20 to 99% by mass, 30 to 90% by mass, 30 to 85% by mass, 90 to 99% by mass, or 85 to 90% by mass, based on the total mass of the polymer additive.

If it is desired to reduce the effect of the polymer additive on physical properties such as viscosity, it is possible to do so by decreasing the weight average molecular weight of the polymer additive, and if it is desired to improve the viscosity-temperature characteristics of the polymer additive, it is possible to do so by increasing the weight average molecular weight of the polymer additive. From the viewpoint of improving thermal stability, the weight average molecular weight of the polymer additive is preferably 3,000 or more, more preferably 5,000 or more, and even more preferably 7,000 or more. From the viewpoint of suppressing viscosity increase, the weight average molecular weight of the polymer additive is preferably 20,000 or less, more preferably 18,000 or less, and even more preferably 15,000 or less. From these viewpoints, the weight average molecular weight of the polymer additive may be 3,000 to 20,000, 5,000 to 18,000, or 7,000 to 15,000. Here, the weight average molecular weight of the polymer additive is a standard polystyrene equivalent value measured by gel permeation chromatography.

The polymer additive described above can be obtained, for example, by polymerizing the phosphate ester methacrylate represented by the above formula (1) alone, or by polymerizing (copolymerizing) the phosphate ester methacrylate and a compound polymerizable with the phosphate ester methacrylate. The polymerization may be performed, for example, by applying light or heat in the presence of a polymerization initiator (e.g., a radical polymerization initiator). That is, the polymerization initiator may be a photopolymerization initiator or a thermal polymerization initiator. The amount of the monomer components and the polymerization conditions may be set in view of the composition and physical properties (e.g., weight average molecular weight) of the desired polymer additive.

<Lubricating Oil Composition>
A lubricating oil composition in one embodiment contains an ester-based base oil and the polymer additive of the above embodiment.

The content of the polymer additive is preferably 0.1 mass% or more, more preferably 0.5 mass% or more, even more preferably 0.8 mass% or more, and particularly preferably 1 mass% or more, based on the total mass of the lubricating oil composition, from the viewpoint of obtaining better wear resistance. The content of the polymer additive is preferably 10 mass% or less, more preferably 8 mass% or less, even more preferably 6 mass% or less, and particularly preferably 4 mass% or less, based on the total mass of the lubricating oil composition, from the viewpoint of reducing the effect on the physical properties of the lubricating oil composition and obtaining better thermal stability. From these viewpoints, the content of the polymer additive may be 0.1 to 10 mass%, 0.5 to 8 mass%, 0.8 to 6 mass%, or 1 to 4 mass%, based on the total mass of the lubricating oil composition.

Examples of ester-based base oils include monoesters, polyol esters, aromatic esters, dibasic acid esters, complex esters, carbonate esters, and mixtures thereof. Among these, polyol esters, complex esters, and mixtures thereof are preferably used.

The polyol ester is an ester of a polyhydric alcohol and a fatty acid. The fatty acid may be either a saturated fatty acid or an unsaturated fatty acid. The number of carbon atoms in the fatty acid is preferably 4 to 20, more preferably 4 to 18, even more preferably 4 to 9, and particularly preferably 5 to 9. The polyol ester may be a partial ester in which some of the hydroxyl groups of the polyhydric alcohol remain as hydroxyl groups without being esterified, a complete ester in which all of the hydroxyl groups are esterified, or a mixture of a partial ester and a complete ester. The hydroxyl value of the polyol ester is preferably 10 mgKOH/g or less, more preferably 5 mgKOH/g or less, and even more preferably 3 mgKOH/g or less. The hydroxyl value in the present invention means a hydroxyl value measured in accordance with JIS K0070:1992.

Among the fatty acids constituting the polyol ester, the proportion of fatty acids having 4 to 20 carbon atoms is preferably 20 to 100 mol%, more preferably 50 to 100 mol%, even more preferably 70 to 100 mol%, and particularly preferably 90 to 100 mol%.

Specific examples of fatty acids having 4 to 20 carbon atoms include butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, nonadecanoic acid, icosanoic acid, and oleic acid. These fatty acids may be linear or branched. More specifically, fatty acids having branches at the α-position and/or β-position are preferred, and 2-methylpropanoic acid, 2-methylbutanoic acid, 2-methylpentanoic acid, 2-methylhexanoic acid, 2-ethylpentanoic acid, 2-methylheptanoic acid, 2-ethylhexanoic acid, 3,5,5-trimethylhexanoic acid, and 2-ethylhexadecanoic acid are more preferred, with 2-methylpropanoic acid, 2-ethylhexanoic acid, and 3,5,5-trimethylhexanoic acid being even more preferred. The fatty acid having 4 to 20 carbon atoms may be one type or two or more types.

The fatty acid may contain a fatty acid other than fatty acids having 4 to 20 carbon atoms. Examples of fatty acids other than fatty acids having 4 to 20 carbon atoms may be fatty acids having 21 to 24 carbon atoms. Specific examples include henicoic acid, docosanoic acid, tricosanoic acid, and tetracosanoic acid. These fatty acids may be linear or branched.

As the polyhydric alcohol constituting the polyol ester, a polyhydric alcohol having 2 to 6 hydroxyl groups is preferably used. The number of carbon atoms of the polyhydric alcohol is preferably 4 to 12, more preferably 5 to 10. Specifically, hindered alcohols such as neopentyl glycol, trimethylolethane, trimethylolpropane, trimethylolbutane, di-(trimethylolpropane), tri-(trimethylolpropane), pentaerythritol, and dipentaerythritol are preferred. When the lubricating oil composition is used as a refrigeration oil, pentaerythritol or a mixed ester of pentaerythritol and dipentaerythritol is more preferred because of its excellent compatibility with the refrigerant and hydrolysis stability.

The complex ester is, for example, an ester synthesized by the following method (a) or (b).
(a) A method in which the molar ratio of a polyhydric alcohol to a polybasic acid is adjusted to synthesize an ester intermediate in which some of the carboxyl groups of the polybasic acid remain unesterified, and then the remaining carboxyl groups are esterified with a monohydric alcohol. (b) A method in which the molar ratio of a polyhydric alcohol to a polybasic acid is adjusted to synthesize an ester intermediate in which some of the hydroxyl groups of the polyhydric alcohol remain unesterified, and then the remaining hydroxyl groups are esterified with a monobasic fatty acid.

The complex ester obtained by the above method (a) is less likely to produce a relatively strong acid when hydrolyzed during use as a refrigeration oil, and tends to be more stable than the complex ester obtained by the above method (b). In this embodiment, the complex ester obtained by the above method (a), which is more stable, is preferred.

The complex ester is preferably an ester synthesized from at least one selected from polyhydric alcohols having 2 to 4 hydroxyl groups, at least one selected from polybasic acids having 6 to 12 carbon atoms, and at least one selected from monohydric alcohols having 4 to 18 carbon atoms and monobasic fatty acids having 2 to 12 carbon atoms.

Examples of polyhydric alcohols having 2 to 4 hydroxyl groups include neopentyl glycol, trimethylolpropane, and pentaerythritol. As polyhydric alcohols having 2 to 4 hydroxyl groups, neopentyl glycol and trimethylolpropane are preferred from the viewpoint of ensuring a suitable viscosity and obtaining good low-temperature characteristics when the complex ester is used as the base oil, and neopentyl glycol is more preferred from the viewpoint of being able to adjust the viscosity over a wide range.

From the viewpoint of excellent lubricity, it is preferable that the polyhydric alcohol constituting the complex ester further contains a dihydric alcohol having 2 to 10 carbon atoms other than neopentyl glycol in addition to the polyhydric alcohol having 2 to 4 hydroxyl groups. Examples of dihydric alcohols having 2 to 10 carbon atoms other than neopentyl glycol include ethylene glycol, propanediol, butanediol, pentanediol, hexanediol, 2-methyl-1,3-propanediol, 3-methyl-1,5-pentanediol, and 2,2-diethyl-1,3-pentanediol. Of these, butanediol is preferred from the viewpoint of excellent lubricating base oil properties. Examples of butanediol include 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, and 2,3-butanediol. Of these, 1,3-butanediol and 1,4-butanediol are more preferred from the viewpoint of obtaining good properties. The amount of the dihydric alcohol having 2 to 10 carbon atoms other than neopentyl glycol is preferably 1.2 moles or less, more preferably 0.8 moles or less, and even more preferably 0.4 moles or less per mole of the polyhydric alcohol having 2 to 4 hydroxyl groups.

Examples of polybasic acids having 6 to 12 carbon atoms include adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, and trimellitic acid. Among these, adipic acid and sebacic acid are preferred, and adipic acid is more preferred, from the viewpoint of excellent balance of properties of the synthesized ester and easy availability. The amount of polybasic acid having 6 to 12 carbon atoms is preferably 0.4 mol to 4 mol, more preferably 0.5 mol to 3 mol, and even more preferably 0.6 mol to 2.5 mol per mol of polyhydric alcohol having 2 to 4 hydroxyl groups.

Examples of monohydric alcohols having 4 to 18 carbon atoms include aliphatic alcohols such as butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, dodecanol, and oleyl alcohol. These monohydric alcohols may be linear or branched. From the viewpoint of balance of properties, the monohydric alcohol having 4 to 18 carbon atoms is preferably a monohydric alcohol having 6 to 10 carbon atoms, and more preferably a monohydric alcohol having 8 to 10 carbon atoms. Among these, 2-ethylhexanol and 3,5,5-trimethylhexanol are more preferable from the viewpoint of improving the low-temperature properties of the synthesized complex ester.

Examples of monobasic fatty acids having 2 to 12 carbon atoms include ethanoic acid, propanoic acid, butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, and dodecanoic acid. These monobasic fatty acids may be linear or branched. The monobasic fatty acids having 2 to 12 carbon atoms are preferably monobasic fatty acids having 8 to 10 carbon atoms, and among these, 2-ethylhexanoic acid and 3,5,5-trimethylhexanoic acid are more preferable from the viewpoint of low-temperature properties.

The solubility parameter (SP value) of the ester base oil is usually 10.0 or less. The SP value of the ester base oil may be 8.5 to 10.0, or 9.0 to 9.8. The SP value is a value calculated by the method described in the Fedors method (Polymer Engineering and Science, February, 1974, Vol. 14, No. 2, pp. 147-154). When the ester base oil contains multiple monomer units, the SP value of each monomer constituting the ester base oil is calculated by the above method, and the SP values of each monomer are averaged based on the molar fraction of the monomer unit to obtain the SP value of the ester base oil.

From the viewpoint of being easily applied to a working fluid for a refrigeration oil, the content of the ester-based base oil is preferably 90% by mass or more, more preferably 93% by mass or more, and even more preferably 95% by mass or more, based on the total mass of the lubricating oil composition. From the viewpoint of improving wear resistance, the content of the ester-based base oil is preferably 99.9% by mass or less, more preferably 99.7% by mass or less, and even more preferably 99.5% by mass or less, based on the total mass of the lubricating oil composition. From these viewpoints, the content of the ester-based base oil may be 90 to 99.9% by mass, 93 to 99.7% by mass, or 95 to 99.5% by mass, based on the total mass of the lubricating oil composition. The content of the ester-based base oil may be 99.2% by mass or less, or 99.0% by mass or less, based on the total mass of the lubricating oil composition.

The lubricating oil composition may further contain other components in addition to the above components. For example, the lubricating oil composition may further contain a base oil other than the above ester-based base oil, as long as the effect of the present invention is not impaired. Examples of such base oils include known mineral oils or synthetic oils (excluding the above ester-based base oils).

Examples of mineral oils include paraffinic and naphthenic mineral oils, which are obtained by refining the lubricating oil fraction obtained by atmospheric and reduced pressure distillation of crude oil through a single or suitable combination of two or more refining processes such as solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, hydrorefining, sulfuric acid washing, and clay treatment, and paraffinic mineral oils are particularly preferred. These mineral oils may be used alone or in any combination of two or more types in any ratio.

Synthetic oils other than ester-based base oils include ethers, carbonates, ketones, silicones, polysiloxanes, etc., and it is preferable to use ether-based base oils. Examples of ether-based base oils include polyvinyl ethers, polyalkylene glycols, polyphenyl ethers, perfluoroethers, and mixtures thereof.

When the base oil contains a base oil other than an ester-based base oil, the content of the ester-based base oil may be, for example, 50% by mass or more, 70% by mass or more, 90% by mass or more, or 95% by mass or more based on the total amount of the base oil. The content of the ester-based base oil may be, for example, less than 100% by mass based on the total amount of the base oil.

The lubricating oil composition may further contain additives such as antioxidants, acid scavengers, extreme pressure agents, oiliness agents, antifoaming agents, metal deactivators, antiwear agents other than the above polymer additives, viscosity index improvers, pour point depressants, detergent dispersants, etc. The total content of these additives is not particularly limited, but may be 10 mass % or less or 5 mass % or less based on the total mass of the lubricating oil composition.

From the viewpoint of obtaining better wear resistance, the phosphorus content in the lubricating oil composition is preferably 150 ppm by mass or more, more preferably 170 ppm by mass or more, and even more preferably 200 ppm by mass or more, based on the total mass of the lubricating oil composition. From the viewpoint of thermal stability, the phosphorus content in the lubricating oil composition is preferably 2000 ppm by mass or less, more preferably 1500 ppm by mass or less, and even more preferably 1000 ppm by mass or less, based on the total mass of the lubricating oil composition. From these viewpoints, the phosphorus content in the lubricating oil composition is, for example, 150 to 2000 ppm by mass, 170 to 1500 ppm by mass, or 170 to 1500 ppm by mass. Here, the phosphorus content is an elemental equivalent value measured by ICP elemental analysis.

The kinetic viscosity of the lubricating oil composition at 40°C may be preferably 3 ^mm2 /s or more, more preferably 4 ^mm2 /s or more, and even more preferably 5 ^mm2 /s or more. The kinetic viscosity of the lubricating oil composition at 40°C may be preferably 500 ^mm2 /s or less, more preferably 400 ^mm2 /s or less, and even more preferably 300 ^mm2 /s or less. The kinetic viscosity of the lubricating oil composition at 100°C may be preferably 1 ^mm2 /s or more, more preferably 2 ^mm2 /s or more. The kinetic viscosity of the lubricating oil composition at 100°C may be preferably 100 ^mm2 /s or less, and more preferably 50 ^mm2 /s or less. The kinetic viscosity in the present invention means the kinetic viscosity measured in accordance with JIS K2283:2000.

The lubricating oil composition described above is suitable for use as a refrigeration oil. Refrigeration oil is usually present in the form of a refrigeration working fluid composition mixed with a refrigerant in a refrigerator equipped with a refrigerant circulation system having a compressor, a condenser, an expansion mechanism, and an evaporator.

<Working fluid composition for refrigerator>
A working fluid composition for a refrigeration machine according to one embodiment includes a refrigerant and a refrigeration oil. The refrigeration oil is the lubricating oil composition according to the above embodiment.

The content of refrigeration oil in the working fluid composition for a refrigeration machine may be 1 to 500 parts by mass, or 2 to 400 parts by mass, per 100 parts by mass of refrigerant.

Examples of refrigerants include saturated fluorohydrocarbon refrigerants, unsaturated fluorohydrocarbon refrigerants, hydrocarbon refrigerants, fluorine-containing ether refrigerants such as perfluoroethers, bis(trifluoromethyl)sulfide refrigerants, trifluoroiodomethane refrigerants, and natural refrigerants such as ammonia and carbon dioxide.

The saturated fluorohydrocarbon refrigerant is preferably a saturated fluorohydrocarbon having 1 to 3 carbon atoms, more preferably 1 to 2. Specific examples of the saturated fluorohydrocarbon refrigerant include difluoromethane (R32), trifluoromethane (R23), pentafluoroethane (R125), 1,1,2,2-tetrafluoroethane (R134), 1,1,1,2-tetrafluoroethane (R134a), 1,1,1-trifluoroethane (R143a), 1,1-difluoroethane (R152a), fluoroethane (R161), and 1,1 , 1,2,3,3,3-heptafluoropropane (R227ea), 1,1,1,2,3,3-hexafluoropropane (R236ea), 1,1,1,3,3,3-hexafluoropropane (R236fa), 1,1,1,3,3-pentafluoropropane (R245fa), and 1,1,1,3,3-pentafluorobutane (R365mfc), or a mixture of two or more of these.

The saturated fluorohydrocarbon refrigerant is selected appropriately from the above depending on the application and required performance. Examples of saturated fluorohydrocarbon refrigerants include R32 alone; R23 alone; R134a alone; R125 alone; a mixture of R134a/R32 = 60-80% by mass/40-20% by mass; a mixture of R32/R125 = 40-70% by mass/60-30% by mass; a mixture of R125/R143a = 40-60% by mass/60-40% by mass; a mixture of R134a/R32/R125 = 60% by mass/30% by mass/10% by mass; a mixture of R134a/R32/R125 = 40-70% by mass/15-35% by mass/5-40% by mass; a mixture of R125/R134a/R143a = 35-55% by mass/1-15% by mass/40-60% by mass, and the like. More specifically, the saturated fluorohydrocarbon refrigerant may be a mixture of R134a/R32=70/30% by mass; a mixture of R32/R125=60/40% by mass; a mixture of R32/R125=50/50% by mass (R410A); a mixture of R32/R125=45/55% by mass (R410B); or a mixture of R125/R143a=50/50% by mass (R507C). ; A mixture of R32/R125/R134a = 30/10/60% by mass; A mixture of R32/R125/R134a = 23/25/52% by mass (R407C); A mixture of R32/R125/R134a = 25/15/60% by mass (R407E); A mixture of R125/R134a/R143a = 44/4/52% by mass (R404A), etc.

The unsaturated fluorohydrocarbon (HFO) refrigerant is preferably an unsaturated fluorohydrocarbon having 2 to 3 carbon atoms, more preferably a fluoropropene, and even more preferably a fluoropropene having 3 to 5 fluorines. The unsaturated fluorohydrocarbon refrigerant is preferably one or a mixture of two or more of 1,2,3,3,3-pentafluoropropene (HFO-1225ye), 1,3,3,3-tetrafluoropropene (HFO-1234ze), 2,3,3,3-tetrafluoropropene (HFO-1234yf), 1,2,3,3-tetrafluoropropene (HFO-1234ye), and 3,3,3-trifluoropropene (HFO-1243zf). From the viewpoint of refrigerant properties, the unsaturated fluorohydrocarbon refrigerant is preferably one or more selected from HFO-1225ye, HFO-1234ze, and HFO-1234yf. The unsaturated fluorohydrocarbon refrigerant may be fluoroethylene, and is preferably 1,1,2,3-trifluoroethylene.

The hydrocarbon refrigerant is preferably a hydrocarbon having 1 to 5 carbon atoms, more preferably a hydrocarbon having 2 to 4 carbon atoms. Specific examples of the hydrocarbon include methane, ethylene, ethane, propylene, propane (R290), cyclopropane, normal butane, isobutane, cyclobutane, methylcyclopropane, 2-methylbutane, normal pentane, or a mixture of two or more of these. Of these, the hydrocarbon refrigerant is preferably a hydrocarbon refrigerant that is gaseous at 25°C and 1 atmospheric pressure, more preferably propane, normal butane, isobutane, 2-methylbutane, or a mixture of these.

When the lubricating oil composition is used as a refrigeration oil, the lubricating oil composition and the working fluid composition for a refrigeration machine according to this embodiment are suitable for use in air conditioners having reciprocating or rotary hermetic compressors, refrigerators, open or hermetic car air conditioners, dehumidifiers, water heaters, freezers, refrigerated and frozen warehouses, vending machines, showcases, refrigeration machines in chemical plants, and refrigeration machines having centrifugal compressors.

The present invention will be described in more detail below using examples and comparative examples, but the present invention is not limited to the following examples.

<Synthesis Examples 1 to 3: Preparation of polymer additive-containing liquid>
As a solvent, an ester-based base oil, Ester-1 (an ester-based base oil in which the alcohol is pentaerythritol and the fatty acid is isobutanoic acid and isononanoic acid (isobutanoic acid: isononanoic acid = 40: 60 [mass ratio]), SP value = 9.1) was used, and methyl methacrylate (MMA), n-butyl methacrylate (n-BuMA), and a compound represented by the following formula (A) (mono (2-hydroxyethyl methacrylate) diphenyl phosphate, HEMDPP) were polymerized by random copolymerization to obtain a polymer additive-containing liquid A (polymer additive concentration: 37.8 mass%) containing a polymer additive A, a polymer additive-containing liquid B (polymer additive concentration: 38.2 mass%) containing a polymer additive B, and a polymer additive-containing liquid C (polymer additive concentration: 40.4 mass%) containing a polymer additive C. Each monomer component was blended so that the content as a monomer unit in the polymer additive was the amount shown in Table 1. The amount shown in Table 1 is based on the total mass of the polymer additive.

The weight average molecular weights of the resulting polymer additives A to C were measured using gel permeation chromatography. The weight average molecular weight of polymer additive A was 5,400, the weight average molecular weight of polymer additive B was 9,980, and the weight average molecular weight of polymer additive C was 18,900. All weight average molecular weights are expressed in terms of standard polystyrene.

<Examples 1 to 3 and Comparative Examples 1 to 2>
(Preparation of Lubricating Oil Composition)
The ester-based base oil Ester-1 and the polymer additive-containing liquids A to C prepared above or tricresyl phosphate (tricresyl phosphate, manufactured by Tokyo Chemical Industry Co., Ltd.) were mixed in the amounts shown in Table 2 to obtain the lubricating oil compositions of Examples 1 to 3 and Comparative Examples 1 and 2. The amounts shown in Table 2 are based on the total mass of the lubricating oil composition (the total amount of the blended components).

(Measurement of Kinematic Viscosity and Viscosity Index)
The kinematic viscosity and viscosity index of each lubricating oil composition were measured at 40° C. and 100° C. in accordance with JIS K2283:2000. The results are shown in Table 2.

(Phosphorus content measurement)
The phosphorus content in the lubricating oil composition was measured by ICP elemental analysis, and the results are shown in Table 2.

(Wear resistance evaluation test)
Abrasion resistance was evaluated by a high-speed four-ball test in accordance with ASTM D4172-94. Using SUJ2 as the hard ball, the test was performed under the conditions of 20 mL of test oil, 80°C test temperature, 1200 rpm rotation speed, 294 N load, and 30 minutes test time, and the wear scar diameter (mm) of the hard ball was measured. The results are shown in Table 2. The smaller the wear scar diameter, the better the wear resistance.

(Sludge resistance evaluation test)
Sludge resistance was evaluated by a test method conforming to JIS K2211, Appendix 2. The refrigerant used was highly stable HFC-134a, and the catalysts used were iron, copper, and aluminum. 1 g each of the refrigerant and the lubricating oil composition was used. The test was performed by sealing the refrigerant, the lubricating oil composition, and the catalyst in a glass tube and keeping them in a thermostatic chamber at 200°C for 10 days. The evaluation was performed based on the presence or absence of insoluble matter (sludge) generated at the bottom of the glass tube after the test. The results are shown in Table 2. It was determined that the thermal stability was high when no sludge was generated.

<Comparative Example 3>
The 40° C. kinematic viscosity, 100° C. kinematic viscosity, viscosity index, and phosphorus content of Ester-1, an ester-based base oil, were measured, and an anti-wear evaluation test was also carried out in the same manner as in Example 1. The results are shown in Table 2.

Claims (7)

1. A polymeric additive for a lubricating oil comprising an ester-based base oil, comprising:
The polymerizable composition includes, as monomer units, a phosphate ester methacrylate represented by the following formula (1) and an alkyl (meth)acrylate represented by the following formula (2) :
The content of the phosphate ester methacrylate as a monomer unit is 5 to 55% by mass based on the total mass of the polymer additive;
A polymer additive, the content of the alkyl (meth)acrylate as a monomer unit being 45 to 95 mass% based on the total mass of the polymer additive (excluding the case where the polymer additive contains a compound represented by the following formula (3) as a monomer unit).

[In formula (1), R ¹ and R ² each independently represent a hydrogen atom or a monovalent hydrocarbon group, at least one of R ¹ and R ² is a phenyl group, and X represents an alkylene group having 2 to 4 carbon atoms .]

[In formula (2), R ³ represents an alkyl group having 1 to 36 carbon atoms, and R ⁴ represents a hydrogen atom or a methyl group.]

[In formula (3), R ⁵ represents a hydrogen atom or a methyl group, -Y- represents -O- or -NH-, R ⁶ represents a linear or branched alkylene group having 2 to 4 carbon atoms, R ⁷ represents a branched alkyl group having 32 to 44 carbon atoms, and p is an integer of 0 to 20. When p is 2 or more, multiple R ^6s may be the same or different. The (R ⁶ O)p portion may be a random bond or a block bond.] The polymer additive according to claim 1, having a weight average molecular weight of 3,000 to 20,000. A lubricating oil composition comprising an ester-based base oil and the polymer additive according to claim 1 or 2. 4. The lubricating oil composition according to claim 3 , wherein the content of the polymer additive is 0.1 to 10 mass %, based on the total mass of the lubricating oil composition. 5. The lubricating oil composition according to claim 3 , having a phosphorus content of 150 ppm by mass or more, based on the total mass of the lubricating oil composition. The lubricating oil composition according to any one of claims 3 to 5 , which is used as a refrigeration oil. A working fluid composition for a refrigerating machine, comprising a refrigerant and the lubricating oil composition according to any one of claims 3 to 5 .