Refrigeration oil and working fluid composition for refrigerator

Abstract

To provide a refrigeration oil having excellent low-friction properties even in a lubrication region where a sliding speed is relatively high.SOLUTION: One aspect of the present invention provides a refrigeration oil comprising a lubricant base oil and a polymer containing an unsaturated carboxylic ester as a monomer unit. The unsaturated carboxylic ester includes an ester of an unsaturated carboxylic acid and an alcohol having a hydrocarbon group represented by the following general formula (1). In the formula (1), x represents an integer of 5 to 18, and y represents an integer of 3 to 18.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a refrigerating machine oil and a working fluid composition for a refrigerating machine. [Background technology]

[0002] A freezing machine such as a refrigerator is equipped with a refrigerant circulation system that has a compressor, a condenser, an expansion mechanism (expansion valve, capillary), an evaporator, etc., and heat exchange occurs as the refrigerant circulates within this refrigerant circulation system.

[0003] Refrigeration compressors include rotary compressors and piston-crank compressors. For example, in a piston-crank compressor, the rotational motion of a motor is converted into reciprocating motion by a connecting rod, and the refrigerant is compressed by reciprocating motion of a piston connected to the connecting rod. Refrigeration oil is sealed inside the compressor together with the refrigerant and lubricates sliding members such as the connecting rod and piston. For example, Patent Document 1 listed below discloses such a refrigeration oil that contains a relatively low-viscosity mineral oil and a specific copolymer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-83920 Summary of the Invention [Problem to be solved by the invention]

[0005] Although reducing the viscosity of conventional refrigeration oils is effective to some extent in reducing friction in the hydrodynamic lubrication region, in the low sliding speed region such as the elastohydrodynamic lubrication region, the mixed lubrication region, or the boundary lubrication region, the metal-to-metal contact opportunities increase, and friction tends to increase. Also, for example, the above-mentioned conventional refrigeration oils are expected to be effective to some extent in reducing friction in the boundary lubrication region where the friction coefficient is high, but are not necessarily sufficient to improve the efficiency of the compressor. In particular, in the lubrication region (elastohydrodynamic lubrication region or mixed lubrication region) where the friction coefficient begins to increase rapidly with the decrease in sliding speed, which is the focus of the present inventors, the effect of reducing friction cannot be fully obtained, and there is still room for improvement in this respect.

[0006] The present invention has been made in view of the above circumstances, and has as its object to provide a refrigeration oil that has excellent low friction characteristics even in the lubrication range where the sliding speed is relatively high, as described above. [Means for solving the problem]

[0007] One aspect of the present invention provides a refrigerating machine oil comprising a lubricating base oil and a polymer including an unsaturated carboxylic acid ester as a monomer unit, wherein the unsaturated carboxylic acid ester comprises an ester of an unsaturated carboxylic acid and an alcohol having a hydrocarbon group represented by the following general formula (1): [ka] In formula (1), x represents an integer of 5 to 18, and y represents an integer of 3 to 18.

[0008] The unsaturated carboxylic acid ester may further include an ester of an unsaturated carboxylic acid and an alcohol having an alkyl group other than the hydrocarbon group represented by general formula (1).

[0009] The lubricating base oil has a kinematic viscosity of 6mm at 40°C. 2 In this case, the lubricating base oil may comprise a first hydrocarbon-based base oil and a lubricating base oil having a kinematic viscosity of 6 mm / s at 40°C.2 The kinematic viscosity of the mixed base oil at 40°C may be (A) and the kinematic viscosity of the first hydrocarbon base oil at 40°C may be (B), and the ratio (A) / (B) may be greater than 1 and not greater than 1.5.

[0010] The content of the polymer may be 5% by mass or less based on the total amount of the refrigerating machine oil.

[0011] The kinematic viscosity of refrigeration oil at 40°C is 6mm 2 / s or less.

[0012] The refrigeration oil may be used in conjunction with a hydrocarbon refrigerant.

[0013] Another aspect of the present invention provides a working fluid composition for a refrigerating machine, comprising the refrigerating machine oil and a refrigerant. The refrigerant may include a hydrocarbon refrigerant. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a refrigeration oil that has excellent low friction characteristics, especially in a lubrication range where the sliding speed is relatively high. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 shows total ion chromatograms of copolymer 1 (upper row) and copolymer 2 (lower row) in an example. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, embodiments of the present invention will be described in detail.

[0017] The refrigerator oil according to this embodiment contains a lubricating base oil and a polymer containing an unsaturated carboxylic acid ester as a monomer unit.

[0018] The lubricating base oil may be any of mineral oil, synthetic oil, or a mixture of both, but preferably contains mineral oil from the viewpoint of achieving better friction characteristics. When the lubricating base oil contains mineral oil, the lubricating base oil may consist solely of mineral oil (i.e., the mineral oil content is 100% by mass based on the total amount of the lubricating base oil), or may further contain base oil components other than mineral oil. When further containing base oil components other than mineral oil, the mineral oil content may be 50% by mass or more, 70% by mass or more, or 90% by mass or more based on the total amount of the lubricating base oil.

[0019] Examples of mineral oils include paraffinic mineral oils and naphthenic mineral oils, which are obtained by refining lubricating oil fractions obtained by atmospheric distillation and vacuum distillation of crude oil through a 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.

[0020] %C of mineral oil P and %C N Ratio (%C P / %C N ) may be, for example, 0.2 or more, preferably 0.5 or more, more preferably 1 or more, and even more preferably 1.1 or more.

[0021] %C of Paraffinic Mineral Oil P and %C N Ratio (%C P / %C N ) is preferably greater than 1, more preferably 1.1 or greater, and even more preferably 1.5 or greater. P / %C N When %C is greater than 1, the flash point (COC) is improved (for example, 100°C or higher, preferably 120°C or higher), and a refrigerating machine oil with better friction characteristics can be obtained. P and %C NThe values ​​indicated are those measured by the method (NdM ring analysis) in accordance with ASTM D3238-95 (2010). The flash point (COC) indicates the flash point measured by the Cleveland open flame method in accordance with JIS K 2265-4 (2007).

[0022] Examples of synthetic oils include synthetic hydrocarbon oils, oxygenated oils, etc. Examples of synthetic hydrocarbon oils include alkylbenzene, alkylnaphthalene, polyα-olefin (PAO), polybutene, ethylene-α-olefin copolymer, etc.

[0023] Examples of oxygen-containing oils include esters, ethers, carbonates, ketones, silicones, and polysiloxanes. The term "ester" as used herein does not include the copolymers. Examples of esters include monoesters, polyol esters, aromatic esters, dibasic acid esters, complex esters, carbonate esters, and mixtures thereof. Among these, it is preferable to use a monoester of a monohydric aliphatic alcohol and a monohydric fatty acid, and, if necessary, it is desirable to use a mixture of the monoester with a polyol ester of a dihydric to hexahydric alcohol and a monohydric fatty acid.

[0024] Examples of monohydric aliphatic alcohols constituting such esters include monohydric aliphatic alcohols having 1 to 20 carbon atoms, preferably 4 to 18, and more preferably 4 to 12. Examples of monohydric fatty acids constituting such esters include monohydric fatty acids having 1 to 20 carbon atoms, preferably 4 to 18, and more preferably 4 to 12. Examples of dihydric to hexahydric alcohols constituting such esters include neopentyl glycol, trimethylolpropane, pentaerythritol, dipentaerythritol, etc. Examples of ethers include polyvinyl ethers, polyalkylene glycols, polyphenyl ethers, perfluoroethers, and mixtures thereof.

[0025] The lubricating base oil may contain a hydrocarbon-based base oil, such as a mineral hydrocarbon oil, a synthetic hydrocarbon oil, or a mixture thereof.

[0026] The mineral hydrocarbon oil may be a paraffinic mineral oil, a naphthenic mineral oil, or the like, which is obtained by refining a lubricating oil fraction obtained by atmospheric distillation and vacuum distillation of a paraffinic, naphthenic, or other crude oil through methods such as solvent deasphalting, solvent refining, hydrorefining, hydrocracking, solvent dewaxing, hydrodewaxing, clay treatment, or sulfuric acid washing. These refining methods may be used alone or in combination of two or more. Examples of synthetic hydrocarbon oils include alkylbenzenes, alkylnaphthalenes, polyα-olefins (PAOs), polybutenes, and ethylene-α-olefin copolymers.

[0027] If the lubricating base oil contains hydrocarbon base oil, the kinematic viscosity at 40°C is 6mm 2 / s (hereinafter also referred to as "first hydrocarbon base oil"). When the lubricating base oil contains the first hydrocarbon base oil, the friction coefficient can be more effectively reduced.

[0028] From this viewpoint, the kinematic viscosity of the first hydrocarbon base oil at 40°C is 5mm 2 / s or less is more preferable, and 4 mm 2 The lower limit of the kinematic viscosity at 40°C of the first hydrocarbon base oil is not particularly limited, but may be, for example, 0 mm 2 / s, preferably 0.5 mm 2 / s or more, preferably 1 mm 2 / s or more, more preferably 1.5 mm 2 The kinematic viscosity in this specification means the kinematic viscosity measured in accordance with JIS K2283:2000.

[0029] When the lubricating base oil contains the first hydrocarbon-based base oil, in addition to the first hydrocarbon-based base oil, 2It is preferable that the lubricating base oil further contains a hydrocarbon base oil having a viscosity of 1 / 2 kJ / s or more (hereinafter, sometimes referred to as a "second hydrocarbon base oil"). That is, the lubricating base oil may be a mixed base oil of the first hydrocarbon base oil and the second hydrocarbon base oil. When the lubricating base oil contains the second hydrocarbon base oil in addition to the first hydrocarbon base oil, the friction coefficient can be more effectively reduced.

[0030] From this viewpoint, the kinematic viscosity of the second hydrocarbon base oil at 40°C is 8mm 2 / s or more is more preferable, and 10 mm 2 / s or more is more preferable, and 50 mm 2 / s or more is particularly preferable, and 90 mm 2 The upper limit of the kinematic viscosity at 40°C of the second hydrocarbon base oil is not particularly limited, but is preferably 1000 mm 2 / s or less, preferably 500 mm 2 / s or less.

[0031] When the lubricating base oil is a mixed base oil of the first hydrocarbon base oil and the second hydrocarbon base oil, where (A) is the kinematic viscosity of the mixed base oil at 40°C and (B) is the kinematic viscosity of the first hydrocarbon base oil at 40°C, it is preferable that (A) / (B) is 1.5 or less. When (A) / (B) is 1.5 or less, the friction coefficient can be more effectively reduced. From this perspective, (A) / (B) is more preferably 1.4 or less, and even more preferably 1.3 or less. The lower limit of (A) / (B) is not particularly limited, but it is usually greater than 1, for example, 1.1 or more. Note that when a plurality of base oil components corresponding to the first hydrocarbon base oil or the second hydrocarbon base oil are contained, the above (A) refers to the kinematic viscosity of the mixed base oil containing all of the base oil components corresponding to the first hydrocarbon base oil or the second hydrocarbon base oil. In addition, when multiple base oil components corresponding to the first hydrocarbon base oil are contained, the above (B) means the kinematic viscosity of the mixed base oil containing all of the base oil components corresponding to the first hydrocarbon base oil.

[0032] The content of the first hydrocarbon base oil may be 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, or 95% by mass or more, based on the total amount of the first hydrocarbon base oil and the second hydrocarbon base oil (i.e., the total amount of the mixed base oil; the same applies below). The upper limit of the content of the first hydrocarbon base oil is not particularly limited, but may be, for example, less than 100% by mass or 99.9% by mass or less, 99.5% by mass or less, or 99% by mass or less, based on the total amount of the first hydrocarbon base oil and the second hydrocarbon base oil.

[0033] The content of the first hydrocarbon base oil may be 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, or 85% by mass or more, based on the total amount of the refrigerating machine oil. The upper limit of the content of the first hydrocarbon base oil is not particularly limited, but may be, for example, 98% by mass or less, 95% by mass or less, or 90% by mass or less, based on the total amount of the refrigerating machine oil.

[0034] The content of the second hydrocarbon base oil may be 0.1% by mass or more, 0.5% by mass or more, or 1% by mass or more, based on the total amount of the first hydrocarbon base oil and the second hydrocarbon base oil. The upper limit of the content of the second hydrocarbon base oil may be, for example, 50% by mass or less, 40% by mass or less, 30% by mass or less, 20% by mass or less, 10% by mass or less, or 5% by mass or less, based on the total amount of the first hydrocarbon base oil and the second hydrocarbon base oil.

[0035] The content of the second hydrocarbon base oil may be 0.1% by mass or more, 0.5% by mass or more, 1% by mass or more, or 3% by mass or more, based on the total amount of the refrigerating machine oil. The upper limit of the content of the second hydrocarbon base oil is not particularly limited, but may be, for example, 50% by mass or less, 40% by mass or less, 30% by mass or less, 20% by mass or less, 10% by mass or less, or 5% by mass or less, based on the total amount of the refrigerating machine oil.

[0036] The total content of the first hydrocarbon base oil and the second hydrocarbon base oil is, for example, 50 mass% or more, based on the total amount of the lubricating base oil, and may be 60 mass% or more, 70 mass% or more, 80 mass% or more, 90 mass% or more, or 100 mass%.

[0037] The total content of the first hydrocarbon base oil and the second hydrocarbon base oil may be 50 mass% or more, 60 mass% or more, 70 mass% or more, 80 mass% or more, or 90 mass% or more, based on the total amount of the refrigerating machine oil.

[0038] The kinematic viscosity of the lubricating base oil at 40°C is preferably 20mm from the viewpoint of more effectively reducing the friction coefficient. 2 / s or less, and more preferably 10 mm 2 / s or less, and more preferably 6 mm 2 / s or less, and more preferably 4 mm 2 / s or less, and particularly preferably 3.5 mm 2 The lower limit of the kinematic viscosity of the lubricating base oil at 40°C is not particularly limited, but for example, it is 0.5 mm 2 / s or more, preferably 1 mm 2 / s or more, more preferably 1.5 mm 2 / s or more.

[0039] The kinematic viscosity of the lubricating base oil at 100°C is preferably 0.5 mm 2 / s or more, preferably 0.8 mm 2 / s or more, more preferably 1 mm 2 The kinematic viscosity of the lubricating base oil at 100°C is preferably 10 mm / s or more. 2 / s or less, preferably 5 mm 2 / s or less, more preferably 3 mm 2 / s or less, particularly preferably 2 mm 2 / s or less or 1.5 mm 2 / s or less.

[0040] The content of the lubricating base oil may be 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more, based on the total amount of the refrigerating machine oil, and may be 99.9% by mass or less, 99.5% by mass or less, or 99% by mass or less.

[0041] The polymer contained in the refrigerating machine oil according to this embodiment contains an unsaturated carboxylic acid ester as a monomer unit. The unsaturated carboxylic acid ester contains an ester (Eg) of an unsaturated carboxylic acid (a carboxylic acid having a polymerizable unsaturated bond) and an alcohol having a hydrocarbon group (branched alkyl group) represented by the following general formula (1): [ka] In formula (1), x represents an integer of 5 to 18, and y represents an integer of 3 to 18.

[0042] The polymer is not particularly limited as long as it contains the above-mentioned Eg as a monomer unit, and may further contain other monomers. The other monomers may be unsaturated carboxylic acid esters other than the above-mentioned Eg, or may be monomers other than unsaturated carboxylic acid esters (monomers copolymerizable with unsaturated carboxylic acid esters). Examples of unsaturated carboxylic acid esters other than the above-mentioned Eg include esters (Es) of unsaturated carboxylic acids and alcohols having a linear alkyl group, and esters (Eb, excluding the above-mentioned Eg) of unsaturated carboxylic acids and alcohols having a branched alkyl group.

[0043] The unsaturated carboxylic acid constituting Eg has at least one polymerizable unsaturated bond (polymerizable carbon-carbon double bond) and at least one carboxyl group. For example, it may be an unsaturated monocarboxylic acid having one polymerizable unsaturated bond and one carboxyl group, or an unsaturated dicarboxylic acid having one polymerizable unsaturated bond and two carboxyl groups. Examples of unsaturated monocarboxylic acids include acrylic acid, methacrylic acid, and crotonic acid. Examples of unsaturated dicarboxylic acids include maleic acid, fumaric acid, citraconic acid, mesaconic acid, and itaconic acid. The unsaturated carboxylic acid is preferably acrylic acid or methacrylic acid (hereinafter, collectively referred to as "(meth)acrylic acid"), or maleic acid, and more preferably (meth)acrylic acid.

[0044] The alcohol constituting Eg is preferably an alcohol represented by the following formula (2). [ka] In formula (2), x and y have the same meanings as x and y in formula (1), respectively.

[0045] In the above formulas (1) and (2), x is preferably an integer of 9 to 17, more preferably an integer of 10 to 14. y is preferably an integer of 7 to 15, more preferably an integer of 7 to 12. xy may be, for example, from 2 to 15, preferably 10 or less, more preferably 6 or less, and most preferably 2.

[0046] Examples of such alcohols include β-branched alcohols (so-called Guerbet alcohols) synthesized by the Guerbet reaction, which dimerizes a raw material alcohol. The Guerbet alcohol may be, for example, a Guerbet alcohol having 12 to 40 carbon atoms, preferably 12 to 36 carbon atoms (specifically, 12, 14, 16, 18, 20, 24, 28, 32, or 36 carbon atoms), and more preferably 20 to 36 carbon atoms (20, 24, 28, 32, or 36 carbon atoms).

[0047] Specific examples of such Guerbet alcohols include 2-butyloctanol (x=5, y=3), 2-hexyldecanol (x=7, y=5), 2-octyldodecanol (x=9, y=7), 2-decyltetradecanol (x=11, y=9), 2-dodecylhexadecanol (x=13, y=11), 2-tetradecyloctadecanol (x=15, y=13), and 2-hexadecyl eicosanol (x=17, y=15). Guerbet alcohols may be produced by known methods (e.g., the production methods described in JP 2015-13815 A and Patent Documents 1 and 2 described therein).

[0048] Examples of the unsaturated carboxylic acid constituting Es include unsaturated monocarboxylic acids such as (meth)acrylic acid and crotonic acid, and unsaturated dicarboxylic acids such as maleic acid, fumaric acid, citraconic acid, mesaconic acid, and itaconic acid. The unsaturated carboxylic acid is preferably (meth)acrylic acid or maleic acid, and more preferably (meth)acrylic acid.

[0049] The alcohol constituting Es is an aliphatic alcohol having a straight-chain alkyl group having 1 to 40 carbon atoms, preferably 1 to 30 carbon atoms, and more preferably 1 to 18 carbon atoms. Examples of these straight-chain aliphatic alcohols include methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, undecanol, dodecanol, tridecanol, tetradecanol, pentadecanol, hexadecanol, heptadecanol, and octadecanol.

[0050] Examples of the unsaturated carboxylic acid constituting Eb include unsaturated monocarboxylic acids such as (meth)acrylic acid and crotonic acid, and unsaturated dicarboxylic acids such as maleic acid, fumaric acid, citraconic acid, mesaconic acid, and itaconic acid. The unsaturated carboxylic acid is preferably (meth)acrylic acid or maleic acid, and more preferably (meth)acrylic acid.

[0051] The alcohol constituting Eb is an aliphatic alcohol having a branched alkyl group (excluding the branched alkyl group represented by the above formula (1)) having 3 to 40 carbon atoms, preferably 4 to 30 carbon atoms, and more preferably 6 to 18 carbon atoms. Examples of the alcohol include 2-propanol, 2-methylpropanol, 2-methylbutanol, 2-methylpentanol, 2-methylhexanol, 2-methylheptanol, 2-ethylhexanol, 2-methyloctanol, and 3,5,5-trimethylhexanol.

[0052] The other monomer (monomer copolymerizable with the unsaturated carboxylic acid ester) besides the unsaturated carboxylic acid ester is not particularly limited, and examples thereof include the unsaturated carboxylic acids or anhydrides thereof exemplified as the unsaturated carboxylic acids constituting the unsaturated carboxylic acid esters described above, and unsaturated hydrocarbon compounds having a polymerizable unsaturated bond. The unsaturated hydrocarbon may be, for example, an unsaturated hydrocarbon compound having 2 to 20 carbon atoms, and preferably an α-olefin or styrene having 2 to 20 carbon atoms. Specific examples of the α-olefin include propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene, and 1-eicosene.

[0053] The polymer contained in the refrigerating machine oil according to the present embodiment is a (co)polymer containing the Eg as a monomer unit. In order to obtain a good balance of basic performances such as a viscosity index improving effect and a pour point lowering effect, in one embodiment, the polymer is preferably a copolymer containing the Eg and the Es as monomer units, and may further contain the Eb as a monomer unit.

[0054] The content of Eg in such a copolymer is preferably 1 mol% or more, more preferably 3 mol% or more, even more preferably 6 mol% or more, particularly preferably 8 mol% or more, based on all monomer units constituting the copolymer, and is preferably 90 mol% or less, more preferably 50 mol% or less, even more preferably 30 mol% or less, particularly preferably 20 mol% or less or 15 mol% or less.

[0055] The content of Es in the copolymer is, based on all monomer units constituting the copolymer, preferably 10 mol% or more, more preferably 50 mol% or more, even more preferably 70 mol% or more, particularly preferably 80 mol% or more or 85 mol% or more, and is preferably 99 mol% or less, more preferably 97 mol% or less, even more preferably 94 mol% or less, particularly preferably 92 mol% or less.

[0056] The proportion of Es (Es-1) in which the linear alkyl group in the alcohol constituting Es is a linear alkyl group having 1 to 4 carbon atoms is preferably 5 mol% or more, more preferably 10 mol% or more, and even more preferably 14 mol% or more, based on all monomer units constituting the copolymer, and is preferably 95 mol% or less, more preferably 85 mol% or less, and even more preferably 80 mol% or less. Examples of Es-1 include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, and butyl (meth)acrylate. Es-1 is preferably methyl (meth)acrylate, and particularly preferably methyl methacrylate.

[0057] The proportion of Es (Es-2) in which the linear alkyl group in the alcohol constituting Es is a linear alkyl group having 5 to 19 carbon atoms is preferably 5 mol% or more, more preferably 10 mol% or more, and even more preferably 14 mol% or more, based on all monomer units constituting the copolymer, and is preferably 95 mol% or less, more preferably 85 mol% or less, and even more preferably 80 mol% or less. Es-2 is preferably a linear alkyl (meth)acrylate having 8 to 18 carbon atoms, specific examples of which include octyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, and octadecyl (meth)acrylate, and more preferably a linear alkyl (meth)acrylate having 12 to 18 carbon atoms.

[0058] The polymer contained in the refrigerating machine oil according to this embodiment is preferably a copolymer containing the Eg, Es-1, and Es-2 as monomer units. In this case, when the total of the Eg, Es-1, and Es-2 is taken as 100 mol%, the proportion of Eg may be 1 mol% or more, 3 mol% or more, 5 mol% or more, or 8 mol% or more, and may be 90 mol% or less, 50 mol% or less, 30 mol% or less, or 20 mol% or less. Furthermore, when the total of the Eg, Es-1, and Es-2 is taken as 100 mol%, the proportion of Es-1 may be 10 mol% or more, 30 mol% or more, 40 mol% or more, or 60 mol% or more, and may be 90 mol% or less, 80 mol% or less, or 75 mol% or less. Furthermore, when the total of Eg, Es-1, and Es-2 is taken as 100 mol%, the proportion of Es-2 may be 1 mol% or more, 5 mol% or more, 10 mol% or more, or 15 mol% or more, or 50 mol% or less, 40 mol% or less, 30 mol% or less, or 25 mol% or less. Furthermore, the total proportion of Eg, Es-1, and Es-2 may be 80 mol% or more, 85 mol% or more, or 90 mol% or more based on all monomer units constituting the copolymer.

[0059] The polymer contained in the refrigerating machine oil according to this embodiment is a (co)polymer containing the Eg as a monomer unit, but since basic performances such as viscosity index improving effect and pour point depressing effect are also obtained in a well-balanced manner, in one embodiment, the polymer may further contain another monomer other than the unsaturated carboxylic acid ester described above, such as an α-olefin, as a monomer unit. In this case, the molar ratio of the total of the Eg, Es, and Eb to the other monomer (α-olefin) is not particularly limited, but may be preferably 1 / 9 or more, more preferably 3 / 7 or more, and is preferably 9 / 1, more preferably 7 / 3 or less.

[0060] The weight average molecular weight (Mw) of the polymer is preferably 400 or more, more preferably 1000 or more, even more preferably 2000 or more, and particularly preferably 3000 or more, and may be 5000 or more, 8000 or more, 10000 or more, 12000 or more, 14000 or more, or 15000 or more, and is preferably 10000000 or less, more preferably 100000 or less, even more preferably 50000 or less, and particularly preferably 30000 or less, and may be 25000 or less or 20000 or less.

[0061] The number average molecular weight (Mn) of the polymer is preferably 300 or more, more preferably 1000 or more, even more preferably 1500 or more, and particularly preferably 3000 or more, and may be 4000 or more, 5000 or more, 6000 or more, 7000 or more, 8000 or more, or 9000 or more, and may be preferably 500,000 or less, more preferably 50,000 or less, even more preferably 30,000 or less, and may be 20,000 or less or 15,000 or less.

[0062] The Mw / Mn of the polymer is preferably 1.2 or more, more preferably 1.5 or more, even more preferably 1.7 or more, particularly preferably 2 or more, and is preferably 5 or less, more preferably 3.5 or less, even more preferably 3 or less, and may be 2.5 or less or 2 or less. 2 is fine.

[0063] In this specification, the terms "weight average molecular weight (Mw)" and "number average molecular weight (Mn)" refer to the weight average molecular weight and number average molecular weight, respectively, calculated in terms of polystyrene, determined by gel permeation chromatography (GPC) using a Waters APC XT column as the column and tetrahydrofuran as the mobile phase (standard substance: polystyrene).

[0064] The polymer according to the present embodiment may be added as a polymer additive to a refrigerating machine oil. The polymer additive may further contain other components other than the polymer, such as a diluent oil, in addition to the polymer. When the polymer additive contains other components, the number average molecular weight (Mn) and weight average molecular weight (Mw) of the polymer are measured after excluding the other components.

[0065] The content of the polymer is not particularly limited, but from the viewpoint of further improving the friction properties of the refrigerating machine oil, it is preferably 0.1 mass% or more, more preferably 0.5 mass% or more, and even more preferably 0.8 mass% or more, based on the total amount of the refrigerating machine oil; and from the viewpoint of suppressing the viscosity of the refrigerating machine oil and achieving a lower friction coefficient even in a region where the sliding speed is relatively high, it is preferably 5 mass% or less, more preferably 2 mass% or less, even more preferably less than 2 mass%, particularly preferably 1 mass% or less, and may be less than 1 mass%.

[0066] The refrigerating machine oil according to this embodiment may further contain additives other than the above-mentioned components. Examples of additives include antioxidants, acid scavengers, extreme pressure agents, metal deactivators, antiwear agents, pour point depressants, detergent dispersants, etc. The content of these additives may be 10% by mass or less or 5% by mass or less based on the total amount of the refrigerating machine oil, unless otherwise specified below.

[0067] Examples of antioxidants include phenol-based antioxidants and amine-based antioxidants. Examples of phenol-based antioxidants include 2,6-di-tert.-butyl-p-cresol (DBPC), 2,6-di-tert.-butyl-phenol, and 4,4'-methylenebis(2,6-di-tert.-butyl-phenol). Examples of amine-based antioxidants include phenyl-α-naphthylamines and dialkylated diphenylamines. These antioxidants can be used alone or in combination of two or more. The content of the antioxidant is, for example, 0.01 to 5 mass%, preferably 0.1 to 3 mass%, based on the total amount of the refrigerating machine oil.

[0068] Examples of the acid scavenger include epoxy compounds (epoxy acid scavengers). Examples of the epoxy compounds include glycidyl ether type epoxy compounds, glycidyl ester type epoxy compounds, aryl oxirane compounds, alkyl oxirane compounds, alicyclic epoxy compounds, epoxidized fatty acid monoesters, and epoxidized vegetable oils. These acid scavengers can be used alone or in combination of two or more. The content of the acid scavenger is, for example, 0.01 to 5 mass %, preferably 0.1 to 3 mass %, based on the total amount of the refrigerating machine oil.

[0069] Examples of extreme pressure agents include phosphorus-based extreme pressure agents. Examples of phosphorus-based extreme pressure agents include phosphate esters, acidic phosphate esters, amine salts of acidic phosphate esters, chlorinated phosphate esters, phosphites, and phosphorothioates. The phosphate esters are preferably triphenyl phosphate (TPP), tricresyl phosphate (TCP), or triphenyl phosphorothioate (TPPT). These extreme pressure agents can be used alone or in combination of two or more. The content of the extreme pressure agent is, for example, 0.01 to 5 mass%, preferably 0.1 to 3 mass%, based on the total amount of the refrigerating machine oil.

[0070] The kinematic viscosity of the refrigerating oil at 40°C is preferably 6 mm from the viewpoint of more effectively reducing the friction coefficient. 2 / s or less, preferably 5 mm 2 / s or less, more preferably 4 mm 2 The lower limit of the kinematic viscosity of the refrigerating oil at 40°C is not particularly limited, but for example, 2 / s or more or 2 mm 2 / s or more.

[0071] The kinematic viscosity of the refrigerating oil at 100°C is preferably 0.5 mm 2 / s or more, preferably 0.8 mm 2 / s or more, more preferably 1 mm 2 The kinematic viscosity of the refrigerating machine oil at 100°C is preferably 10 mm / s or more. 2 / s or less, preferably 5 mm 2 / s or less, more preferably 3 mm 2 / s or less, particularly preferably 2 mm 2 / s or less.

[0072] The viscosity index of the refrigerating machine oil may be -50 or more, preferably 0 or more, more preferably 50 or more, and may be 200 or less. In this specification, the viscosity index means a viscosity index measured in accordance with JIS K2283:2000.

[0073] The pour point of the refrigerating machine oil may be preferably −10° C. or lower, more preferably −20° C. or lower. In this specification, the pour point refers to the pour point measured in accordance with JIS K2269:1987.

[0074] The volume resistivity of the refrigerating machine oil is preferably 1.0 x 10 9 Ω·m or more, preferably 1.0×10 10 Ω·m or more, more preferably 1.0×10 11 The volume resistivity in this specification means the volume resistivity at 25°C measured in accordance with JIS C2101:1999.

[0075] The water content of the refrigerating machine oil may be preferably 200 ppm or less, more preferably 100 ppm or less, and even more preferably 50 ppm or less, based on the total amount of the refrigerating machine oil. In this specification, the water content means the water content measured in accordance with JIS K2275-2 or 3 (Karl Fischer volumetric titration method or coulometric titration method).

[0076] The acid value of the refrigerating machine oil may be preferably 1.0 mgKOH / g or less, more preferably 0.1 mgKOH / g or less. The hydroxyl value of the refrigerating machine oil is, for example, 10 mgKOH / g or less, preferably 5 mgKOH / g or less, more preferably 2 mgKOH / g or less. The acid value in this specification means the acid value measured in accordance with JIS K2501:2003. The hydroxyl value in this specification means the hydroxyl value measured in accordance with JIS K0070:1992.

[0077] The ash content of the refrigerating machine oil may be preferably 100 ppm or less, more preferably 50 ppm or less. In this specification, the ash content refers to the ash content measured in accordance with JIS K2272:1998.

[0078] The refrigerating machine oil according to this embodiment is typically present in the form of a working fluid composition for a refrigerating machine mixed with a refrigerant in a refrigerating machine equipped with a refrigerant circulation system having a compressor, a condenser, an expansion mechanism, and an evaporator, and lubricates, for example, sliding members in the compressor. That is, another embodiment of the present invention is a working fluid composition for a refrigerating machine containing the above-mentioned refrigerating machine oil and a refrigerant. The content of the refrigerating machine oil in the working fluid composition for a refrigerating machine may be 1 to 500 parts by mass, or 2 to 400 parts by mass, per 100 parts by mass of the refrigerant.

[0079] Examples of refrigerants include hydrocarbon refrigerants, saturated fluorohydrocarbon refrigerants, unsaturated fluorohydrocarbon refrigerants, fluorinated ether refrigerants such as perfluoroethers, bis(trifluoromethyl)sulfide refrigerants, trifluoroiodomethane refrigerants, and natural refrigerants such as ammonia and carbon dioxide. In particular, the refrigerating machine oil according to this embodiment is preferably used together with a hydrocarbon refrigerant. In other words, the working fluid composition for a refrigerating machine preferably contains a refrigerating machine oil and a hydrocarbon refrigerant.

[0080] 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 hydrocarbons include methane, ethylene, ethane, propylene, propane (R290), cyclopropane, normal butane, isobutane (R600a), cyclobutane, methylcyclopropane, 2-methylbutane, normal pentane, and mixtures 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, and more preferably propane, normal butane, isobutane, 2-methylbutane, or a mixture of these.

[0081] The saturated fluorohydrocarbon refrigerant is preferably a saturated fluorohydrocarbon refrigerant having 1 to 3 carbon atoms, more preferably 1 to 2. Specific examples of saturated fluorohydrocarbon refrigerants 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, Examples include 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 thereof.

[0082] The saturated fluorohydrocarbon refrigerant is appropriately selected 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 to 80 mass% / 40 to 20 mass%, a mixture of R32 / R125 = 40 to 70 mass% / 60 to 30 mass%, a mixture of R125 / R143a = 40 to 60 mass% / 60 to 40 mass%, a mixture of R134a / R32 / R125 = 60 mass% / 30 mass% / 10 mass%, a mixture of R134a / R32 / R125 = 40 to 70 mass% / 15 to 35 mass% / 5 to 40 mass%, and a mixture of R125 / R134a / R143a = 35 to 55 mass% / 1 to 15 mass% / 40 to 60 mass%, etc. More specifically, saturated fluorohydrocarbon refrigerants include a mixture of R134a / R32=70 / 30 mass%, a mixture of R32 / R125=60 / 40 mass%, a mixture of R32 / R125=50 / 50 mass% (R410A), a mixture of R32 / R125=45 / 55 mass% (R410B), and a mixture of R125 / R143a=50 / 50 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.

[0083] 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 fluorine atoms. 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 physical 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 a fluoroethylene having 1 to 3 fluorine atoms, and is preferably 1,1,2,3-trifluoroethylene. [Example]

[0084] The present invention will be described in more detail below based on examples, but the present invention is not limited to the following examples.

[0085] [Lubricant base oil] Base oils 1 to 3 shown below were prepared and mixed so that the contents of base oil 1, base oil 2, and base oil 3 were 50 parts by mass, 43 parts by mass, and 7 parts by mass, respectively, as shown in Table 1, to obtain a mixed base oil. Base oil 1: Mineral oil (kinematic viscosity at 40°C: 3.4 mm 2 / s) Base oil 2: Mineral oil (kinematic viscosity at 40°C: 2.4 mm 2 / s) Base oil 3: Mineral oil (kinematic viscosity at 40°C: 100 mm 2 / s) Base oil 1 and base oil 2 correspond to the first hydrocarbon-based base oil described above, and base oil 3 corresponds to the second hydrocarbon-based base oil described above.

[0086] The kinematic viscosity (A) [mm 2 / s], kinematic viscosity (B) [mm 2 / s] and the values ​​of (A) / (B) are shown in Table 1 below. [Table 1]

[0087] [Refrigerating machine oil] In the examples and comparative examples, refrigerating machine oils having the compositions (mass % based on the total amount of refrigerating machine oil) shown in Table 2 were prepared using the lubricating base oil (mixed base oil) and the copolymers and phosphorus-based extreme pressure agents shown below as additives.

[0088] Copolymer 1: A copolymer of a monomer mixture containing methyl methacrylate (C1, 70 mol%), long-chain linear alkyl methacrylates (n-dodecyl methacrylate (C12), n-tridecyl methacrylate (C13), n-tetradecyl methacrylate (C14), n-hexadecyl methacrylate (C16), n-octadecyl methacrylate (C18)) (total 19 mol%), and 2-decyl-tetradecyl methacrylate (C24, 11 mol%) as the main components (Mn = 10,500, Mw = 18,000, Mw / Mn = 1.7). In addition, 2-decyl-tetradecyl methacrylate has a hydrocarbon group in which, in formula (1), x = 11 and y = 9. In addition, the content of the above main component was 90 mol % or more based on the total amount of the monomer mixture.

[0089] Copolymer 2: A copolymer of a monomer mixture containing, as main components, methyl methacrylate (C1, 49 mol%), long-chain linear alkyl methacrylates (n-dodecyl methacrylate (C12), n-tridecyl methacrylate (C13), n-tetradecyl methacrylate (C14), n-pentadecyl methacrylate (C15), n-hexadecyl methacrylate (C16), n-octadecyl methacrylate (C18)) (43 mol% in total), and branched alkyl methacrylates having a branched alkyl group having less than 20 carbon atoms other than the hydrocarbon group represented by formula (1) (8 mol% in total) (Mn=9300, Mw=16000, Mw / Mn=1.7) The content of the above main component was 90 mol % or more based on the total amount of the monomer mixture.

[0090] The structures of the monomers constituting the copolymers 1 and 2 were determined by pyrolysis GC / MS, IR, and 13 This was confirmed by C-NMR analysis. In pyrolysis GC / MS, the pyrolysis product (500°C) of the rubber membrane dialysis residue was analyzed using an Agilent 7890B and a JEOL JMS-T200GC (column: ZB-5HT and deactivated fused silica, split ratio: 100:1, heating conditions: 40°C to 400°C, 10°C / min). As an example of the analytical results, the total ion chromatogram (ionization method: EI) is shown in Figure 1. The upper panel of Figure 1 is the total ion chromatogram for copolymer 1, and the lower panel is the total ion chromatogram for copolymer 2. Symbols such as C1 and C12 in Figure 1 correspond to the symbols C1, C12, etc. attached to the monomers in the above description of copolymers 1 and 2 (meaning that the peaks are derived from the monomers to which the symbols are attached). For linear alkyl methacrylate and 2-decyl-tetradecyl methacrylate, this was also confirmed by comparison with the above analytical results using (co)polymers of known monomers.

[0091] Phosphorus-based extreme pressure agent: A mixture of tricresyl phosphate (TCP) and triphenyl phosphorothionate (TPPT)

[0092] [Evaluation of friction characteristics] In order to evaluate the friction characteristics of each of the refrigeration oils of the Examples and Comparative Examples, the following tests were carried out. Using an MTM (Mini Traction Machine) tester (manufactured by PCS Instruments), the friction coefficient (μ) was measured in each lubrication region under the following conditions. The results are shown in Table 2. The smaller the friction coefficient, the better the friction characteristics. Balls and discs: Standard test pieces (AISI 52100 standard) Test temperature: 40℃ Sliding speed: 0.0006 to 0.9 m / s (partial excerpt) Load: 10N Slip rate: 30% The sliding speed is |U D -U B |[m / s] value was used. Here, U D is the speed of the disk at the sliding part [m / s], and U B is the ball speed at the sliding part [m / s].

[0093] [Table 2]

Claims

1. a lubricating base oil; a polymer containing an unsaturated carboxylic acid ester as a monomer unit, The unsaturated carboxylic acid ester includes an ester Eg of an unsaturated carboxylic acid and an alcohol having a hydrocarbon group represented by the following general formula (1), and an ester Es of an unsaturated carboxylic acid and an aliphatic alcohol having a linear alkyl group having 1 to 18 carbon atoms: Dynamic viscosity at 40°C is 6mm ２ / s or less and used with a refrigerant consisting solely of a hydrocarbon refrigerant. 【Chemical 1】 (In formula (1), x represents an integer of 5 to 18, and y represents an integer of 3 to 18.)

2. The lubricating base oil has a kinematic viscosity of 6 mm at 40°C. ２ The refrigerator oil according to claim 1, comprising a first hydrocarbon-based base oil having a viscosity of less than 1000 kJ / s.

3. The lubricating base oil is a mixture of the first hydrocarbon base oil and a kinematic viscosity at 40°C of 6 mm ２ / s or more of a mixed base oil with a second hydrocarbon-based base oil, and 3. The refrigerating machine oil according to claim 2, wherein, when the kinematic viscosity of the mixed base oil at 40°C is (A) and the kinematic viscosity of the first hydrocarbon base oil at 40°C is (B), the ratio (A) / (B) is greater than 1 and not greater than 1.

5.

4. The refrigerating machine oil according to any one of claims 1 to 3, wherein the content of the polymer is 5 mass% or less based on the total amount of the refrigerating machine oil.

5. The refrigerating machine oil according to any one of claims 1 to 4, and a refrigerant consisting solely of a hydrocarbon refrigerant.

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