Refrigerating machine oil and working fluid composition

Abstract

A refrigerating machine oil according to the present invention contains a compound represented by formula (1) as a base oil, the surface tension of the compound represented by formula (1) at 25°C being at least 31 mN / m. (In the formula, R1 and R2 are each independently a hydrogen atom or an alkyl group, R3 is an ethylene group or a propylene group, and m is an integer that is equal to or greater than 2.)

Description

Refrigerating machine oil and working fluid composition

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

[0002] Refrigerating machine oils used to lubricate sliding parts in refrigerating machines such as refrigerators and air conditioners are sometimes used together with refrigerants that are highly soluble in the refrigerating machine oil (e.g., hydrocarbon refrigerants). In this case, the viscosity of the refrigerating machine oil decreases as the refrigerant dissolves, making it difficult to maintain an oil film of the refrigerating machine oil on the sliding parts, which tends to result in stricter lubrication conditions (see, for example, Patent Document 1).

[0003] JP 2016-33222 A

[0004] Under the above-mentioned severe lubrication conditions, refrigeration oils are required to have anti-seizure properties to prevent sliding members from seizing together. Therefore, one aspect of the present invention aims to provide a refrigeration oil with excellent anti-seizure properties.

[0005] The present inventors have found that when a polyalkylene glycol compound is used as the base oil of a refrigerating machine oil, the refrigerating machine oil has excellent seizure resistance if the surface tension of the refrigerating machine oil is within a specific range.

[0006] The present invention includes the following aspects: [1] A refrigerating machine oil containing a compound represented by the following formula (1) as a base oil, [In the formula, R １ and R ２ are each independently a hydrogen atom or an alkyl group, and R ３is an ethylene group or a propylene group, and m is an integer of 2 or more.] A refrigerating machine oil in which the surface tension of the compound represented by formula (1) at 25°C is 31 mN / m or more. [2] A refrigerating machine oil according to [1], in which the proportion of terminal hydroxyl groups to all terminal groups of the compound represented by formula (1) is 20 mol % or more. [3] A refrigerating machine oil according to [1] or [2], in which the molar ratio of ethylene groups / propylene groups in the compound represented by formula (1) is 55 / 45 or more. [4] A refrigerating machine oil according to any one of [1] to [3], in which the refractive index of the compound represented by formula (1) at 20°C is 1.4480 or more. [5] A refrigerating machine oil according to any one of [1] to [4], further containing a phosphorus-based antiwear agent and having a surface tension of 35 mN / m or more and 41 mN / m or less. [6] A refrigerating machine oil according to [5], in which the content of the phosphorus-based antiwear agent is 0.1 mass % or more based on the total amount of the refrigerating machine oil. [7] The refrigerating machine oil according to any one of [1] to [6], which is used together with a refrigerant consisting solely of hydrocarbons. [8] A working fluid composition containing the refrigerating machine oil according to any one of [1] to [7] and a refrigerant. [9] The working fluid composition according to [8], wherein the refrigerant consists solely of hydrocarbons.

[0007] According to one aspect of the present invention, a refrigerating machine oil having excellent anti-seizure properties can be provided. According to another aspect of the present invention, the refrigerating machine oil can also have excellent load-bearing performance.

[0008] One embodiment of the present invention is a refrigeration oil containing a compound represented by the following formula (1) (hereinafter also referred to as a "PAG compound") as a base oil. In the formula, R １ and R ２ are each independently a hydrogen atom or an alkyl group, and R ３ is an ethylene group or a propylene group, and m is an integer of 2 or more.

[0009] R １ and R ２The alkyl group represented by the formula (I) may be linear or branched. The number of carbon atoms in the alkyl group may be 1 or more, 2 or more, or 3 or more, and may be 16 or less, 12 or less, 8 or less, or 5 or less, or may be 4. The alkyl group may preferably be an n-butyl group.

[0010] From the viewpoint of further improving the seizure resistance, the PAG compound is preferably R １ and R ２ a compound in which one of the groups is a hydrogen atom and the other is an alkyl group (a PAG compound having a hydroxyl group at one end), and １ and R ２ and (b) are hydrogen atoms (PAG compounds having hydroxyl groups at both ends).

[0011] The ratio of terminal hydroxyl groups to all terminal groups of a PAG compound (R １ and R ２ R for all of １ , R ２ are hydrogen atoms) may be preferably 5 mol% or more, 10 mol% or more, 20 mol% or more, 30 mol% or more, 40 mol% or more, 50 mol% or more, 60 mol% or more, 70 mol% or more, 80 mol% or more, 90 mol% or more, or may even be 100 mol% from the viewpoint of further improving the seizure resistance.

[0012] The ratio of terminal hydroxyl groups to all terminal groups of the PAG compound is １３ It is determined by C-NMR measurement. Specifically, the ratio is １３ From the spectrum obtained by C-NMR measurement, a peak derived from the carbon constituting the hydrocarbon group having a terminal hydroxyl group and a peak derived from the carbon constituting the terminal hydrocarbon group (such as an alkyl group) can be identified, and the integral value of each peak can be used to appropriately determine the molecular weight.

[0013] In one molecule of a PAG compound, R ３ is an ethylene group, and R ３is a propylene group. That is, the PAG compound preferably contains both ethylene oxide units (EO units) and propylene oxide units (PO units). In this case, the PAG compound may be a random copolymer or a block copolymer.

[0014] The molar ratio of ethylene groups to propylene groups (EO units to PO units) in the PAG compound (hereinafter also referred to as "EO / PO ratio") may be 0 / 100 or more, 5 / 95 or more, 10 / 90 or more, 20 / 80 or more, 30 / 70 or more, 40 / 60 or more, or 50 / 50 or more, and from the viewpoint of further improving seizure resistance, may be preferably 55 / 45 or more, 60 / 40 or more, or 62 / 38 or more. The EO / PO ratio may be 95 / 5 or less, 92 / 8 or less, 90 / 10 or less, 80 / 20 or less, 70 / 30 or less, or 65 / 35 or less.

[0015] The EO / PO ratio in the PAG-based compound is １３ Specifically, the EO / PO ratio is determined by C-NMR measurement. １３ From the spectrum obtained by C-NMR measurement, peaks derived from carbons constituting EO units and peaks derived from carbons constituting PO units can be identified, and the amount of each peak can be appropriately determined using information on EO units and PO units and the integral values ​​of each peak.

[0016] In formula (1), m may be 2 or more, 5 or more, 10 or more, or 15 or more, and may be 40 or less, 35 or less, 30 or less, or 25 or less. The PAG compound may be a mixture of multiple types of PAG compounds each having a different m value. The average value of m may be 2 or more, 5 or more, 10 or more, or 15 or more, and may be 40 or less, 35 or less, 30 or less, or 25 or less.

[0017] The kinematic viscosity of the PAG compound at 40°C is 15 mm ２ / s or more, 20mm ２ / s or more, 30mm ２ / s or more, 40mm ２ / s or more, or 50 mm ２ / s or more, and２ / s or less, 300mm ２ / s or less, 200mm ２ / s or less, 100mm ２ / s or less, 80mm ２ / s or less, or 60 mm ２ The kinematic viscosity of the PAG compound at 100°C may be 1 mm / s or less. ２ / s or more, 3mm ２ / s or more, 5mm ２ / s or more, or 8 mm ２ / s or more, and ２ / s or less, 60mm ２ / s or less, 40mm ２ / s or less, 30mm ２ / s or less, 20mm ２ / s or less, or 16 mm ２ / s or less.

[0018] The viscosity index of the PAG compound may be 100 or more, 120 or more, 140 or more, or 160 or more, and may be 270 or less, 250 or less, or 230 or less. The kinematic viscosity and viscosity index in this specification refer to the kinematic viscosity and viscosity index measured in accordance with JIS K2283:2000.

[0019] The content of the PAG compound 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.

[0020] The refrigeration oil may further contain other base oils. Examples of the other base oils include mineral oils and synthetic oils. The mineral oils may be paraffinic mineral oils, naphthenic mineral oils, etc. Examples of the synthetic oils include synthetic hydrocarbon oils such as poly-α-olefins and alkylbenzenes, and oxygenated oils such as polyalkylene glycol compounds other than the above-mentioned PAG compounds, esters, and polyvinyl ethers.

[0021] The refrigerating machine oil may further contain additives. Examples of the additives include antioxidants, antiwear agents, acid scavengers, oxygen scavengers, extreme pressure agents, oiliness agents, antifoaming agents, metal deactivators, viscosity index improvers, pour point depressants, and detergent dispersants. The content of the additives may be 0.1% by mass or more or 1% by mass or more, and 10% by mass or less or 5% by mass or less, based on the total amount of the refrigerating machine oil.

[0022] From the viewpoint of further improving seizure resistance, the refrigerating machine oil preferably further contains an anti-wear agent, more preferably a phosphorus-based anti-wear agent. Examples of phosphorus-based anti-wear agents include phosphate esters, thiophosphate esters, acidic phosphate esters, amine salts of acidic phosphate esters, chlorinated phosphate esters, and phosphites. Examples of phosphate esters include triaryl phosphates such as tricresyl phosphate (TCP), triphenyl phosphate (TPP), and alkylated triphenyl phosphates (e.g., propylated triphenyl phosphate, butylated triphenyl phosphate), and trialkyl phosphates. Examples of thiophosphate esters include triphenylphosphorothionate (TPPT). Examples of phosphites include monohydrocarbyl (hydrogen) phosphites, dihydrocarbyl (hydrogen) phosphites, and trihydrocarbyl phosphites. The content of the phosphorus-based antiwear agent may be, for example, 0.01 mass % or more, 0.1 mass % or more, 0.3 mass % or more, or 0.5 mass % or more, and may be 5 mass % or less, 3 mass % or less, 2 mass % or less, or 1 mass % or less, based on the total amount of the refrigerating machine oil.

[0023] The refrigerating machine oil preferably further contains an antioxidant. Examples of the antioxidant include phenol-based antioxidants. Examples of the phenol-based antioxidant 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). The content of the antioxidant may be 0.01% by mass or more or 0.1% by mass or more, and may be 5% by mass or less, 3% by mass or less, or 1% by mass or less, based on the total amount of the refrigerating machine oil.

[0024] The refrigerating machine oil preferably further contains an acid scavenger. Examples of the acid scavenger include epoxy-based acid scavengers. Examples of epoxy-based acid scavengers include glycidyl ether-based acid scavengers having a hydrocarbon group with 6 to 18 carbon atoms, such as 2-ethylhexyl glycidyl ether and 4-tert-butylphenyl glycidyl ether; glycidyl ester-based acid scavengers having a hydrocarbon group with 6 to 18 carbon atoms, such as glycidyl neodecanoate; α-olefin oxide-based acid scavengers having 6 to 18 carbon atoms, such as 1,2-epoxydodecane and 1,2-epoxytetradecane; and alicyclic epoxy-based acid scavengers. The content of the acid scavenger may be 0.01% by mass or more or 0.1% by mass or more, and may be 5% by mass or less, 3% by mass or less, or 1% by mass or less, based on the total amount of the refrigerating machine oil.

[0025] The PAG compound or refrigerating machine oil described above has a surface tension of 31 mN / m or more at 25°C. This improves the seizure resistance of the refrigerating machine oil. In one embodiment, the load-bearing performance of the refrigerating machine oil may also be improved. From the viewpoint of further improving the seizure resistance, the surface tension of the PAG compound or refrigerating machine oil at 25°C may be preferably 31.5 mN / m or more, 32 mN / m or more, 32.5 mN / m or more, 33 mN / m or more, 33.5 mN / m or more, or 34 mN / m or more. In the case where the refrigerating machine oil further contains a phosphorus-based wear inhibitor, from the viewpoint of particularly significantly obtaining the effect of improving the load-bearing performance by adding the phosphorus-based wear inhibitor, the surface tension may more preferably be 34.5 mN / m or more or 35 mN / m or more.

[0026] The surface tension of the PAG compound or refrigerating machine oil at 25°C may be 50 mN / m or less, 48 ​​mN / m or less, 46 mN / m or less, or 44 mN / m or less. When the refrigerating machine oil further contains a phosphorus-based antiwear agent, from the viewpoint of obtaining a particularly significant effect of improving load-bearing performance by adding the phosphorus-based antiwear agent, the surface tension may be preferably 43 mN / m or less, 42 mN / m or less, 41 mN / m or less, or 40 mN / m or less. In this specification, the surface tension is the surface tension at 25°C measured in accordance with JIS K2241:2017, except that the PAG compound or refrigerating machine oil is used undiluted when measuring the surface tension.

[0027] The PAG compound or refrigerating machine oil preferably has a refractive index of 1.4480 or more at 20°C. This further improves the seizure resistance of the refrigerating machine oil and can also improve the load-bearing performance. The refractive index of the PAG compound or refrigerating machine oil at 20°C may be 1.4500 or more, 1.4520 or more, 1.4540 or more, 1.4560 or more, or 1.4600 or more, and may be 1.4700 or less, 1.4620 or less, or 1.4570 or less.

[0028] The PAG compound or refrigerating machine oil having the above surface tension (and further refractive index) can be adjusted, for example, by adjusting the terminal hydroxyl groups or EO units in the PAG compound. Specifically, the surface tension (and further refractive index) can be increased by increasing the proportion of terminal hydroxyl groups or EO units in the PAG compound.

[0029] The kinematic viscosity of the refrigerating oil at 40°C is 15 mm ２ / s or more, 20mm ２ / s or more, 30mm ２ / s or more, 40mm ２ / s or more, or 50 mm ２ / s or more, and ２ / s or less, 300mm ２ / s or less, 200mm ２ / s or less, 100mm ２ / s or less, 80mm ２ / s or less, or 60 mm ２The kinematic viscosity of the refrigerating machine oil at 100°C may be 1 mm / s or less. ２ / s or more, 3mm ２ / s or more, or 5 mm ２ / s or more, and ２ / s or less, 60mm ２ / s or less, 40mm ２ / s or less, 30mm ２ / s or less, 20mm ２ / s or less, or 16 mm ２ The viscosity index of the refrigerating machine oil may be 100 or more, 120 or more, 140 or more, or 160 or more, and may be 270 or less, 250 or less, or 230 or less.

[0030] The refrigerating machine oil is used together with a refrigerant in a refrigerator. Another embodiment of the present invention is a working fluid composition containing the above-mentioned refrigerating machine oil and a refrigerant. The content of the refrigerating machine oil may be 1 part by mass or more or 2 parts by mass or more, and may be 500 parts by mass or less or 400 parts by mass or less, per 100 parts by mass of the refrigerant.

[0031] The refrigerant preferably contains a hydrocarbon. The hydrocarbon is preferably a hydrocarbon having 1 to 5 carbon atoms, more preferably a hydrocarbon having 2 to 4 carbon atoms. Examples of hydrocarbons include methane, ethylene, ethane, propylene, propane (R290), cyclopropane, normal butane, isobutane (R600a), cyclobutane, methylcyclopropane, 2-methylbutane, and normal pentane. The refrigerant may contain only one of these hydrocarbons, or may contain two or more of them. The refrigerant preferably contains a hydrocarbon that is gaseous at 25°C and 1 atmosphere, and more preferably contains at least one selected from the group consisting of propane, normal butane, isobutane, and 2-methylbutane.

[0032] The refrigerant may consist solely of hydrocarbons, or may contain hydrocarbons and other refrigerants, such as saturated fluorohydrocarbons, unsaturated fluorohydrocarbons, fluorinated ethers such as perfluoroethers, bis(trifluoromethyl)sulfide, trifluoroiodomethane, ammonia, and carbon dioxide.

[0033] The hydrocarbon content may be 50 mass % or more, 60 mass % or more, 70 mass % or more, 80 mass % or more, 90 mass % or more, or 95 mass % or more based on the total amount of the refrigerant.

[0034] Examples of the refrigeration machine include refrigeration devices, air conditioners, etc. Examples of the refrigeration device include refrigerators, refrigerated and frozen warehouses, vending machines, cooling devices in chemical plants, etc. Examples of the air conditioner include automotive air conditioners, residential air conditioners, packaged air conditioners, dehumidifiers, etc.

[0035] As explained above, by using the PAG compound as a base oil, it is possible to improve seizure resistance. That is, another embodiment of the present invention can be said to be a refrigerating machine oil containing the PAG compound as a base oil and having improved seizure resistance. Furthermore, in one embodiment, it is possible to improve load-bearing performance by using the PAG compound as a base oil. That is, another embodiment of the present invention can be said to be a refrigerating machine oil containing the PAG compound as a base oil and having improved load-bearing performance. Another embodiment of the present invention can be said to be a refrigerating machine oil containing the PAG compound as a base oil and further containing a phosphorus-based wear inhibitor and having improved seizure resistance and load-bearing performance.

[0036] Another embodiment of the present invention can also be described as a method for improving the seizure resistance of a refrigerating oil, comprising the step of selecting the PAG compound as a base oil of the refrigerating oil based on the relationship between the surface tension of the PAG compound at 25°C and the seizure resistance of the refrigerating oil. Another embodiment of the present invention can also be described as a method for improving the load-bearing performance of a refrigerating oil, comprising the step of selecting the PAG compound as a base oil of the refrigerating oil based on the relationship between the surface tension of the PAG compound at 25°C and the load-bearing performance of the refrigerating oil. Another embodiment of the present invention can also be described as a method for improving the seizure resistance and load-bearing performance of a refrigerating oil, comprising the steps of selecting the PAG compound as a base oil of the refrigerating oil based on the relationship between the surface tension of the PAG compound at 25°C and the seizure resistance of the refrigerating oil and the effect of improving the load-bearing performance by adding a phosphorus-based wear inhibitor, and blending a phosphorus-based wear inhibitor with the selected base oil (PAG compound).

[0037] Another embodiment of the present invention can be said to be a method for producing a refrigerating oil, comprising the steps of selecting a PAG compound as a base oil for the refrigerating oil based on the relationship between the surface tension of the PAG compound at 25°C and the seizure resistance of the refrigerating oil, and preparing a refrigerating oil containing the selected PAG compound as a base oil.Another embodiment of the present invention can be said to be a method for producing a refrigerating oil, comprising the steps of selecting a PAG compound as a base oil for the refrigerating oil based on the relationship between the surface tension of the PAG compound at 25°C and the load-bearing performance of the refrigerating oil, and preparing a refrigerating oil containing the selected PAG compound as a base oil. Another embodiment of the present invention can also be described as a method for producing a refrigerating machine oil, comprising: a step of selecting a PAG compound as a base oil for the refrigerating machine oil based on the relationship between the surface tension of the PAG compound at 25°C, the seizure resistance of the refrigerating machine oil, and the effect of improving load-bearing performance by adding a phosphorus-based anti-wear agent; and a step of blending the phosphorus-based anti-wear agent with the selected base oil (PAG compound) to prepare the refrigerating machine oil.

[0038] The present invention will be described in more detail below based on examples, but the present invention is not limited to the following examples.

[0039] The following PAG compounds 1 to 8 were used as base oils to prepare refrigerating machine oils for Examples and Comparative Examples.

[0040] PAG compound 1: In the above formula (1), R １ and R ２ is a hydrogen atom (ratio of terminal hydroxyl groups to all terminal groups: 100 mol%), R ３ is an ethylene group or a propylene group (EO / PO ratio: 62 / 38) (kinematic viscosity at 40°C: 88.37 mm ２ / s, 100℃ Kinematic viscosity: 15.65mm ２ / s, viscosity index: 189)

[0041] PAG compound 2: In the above formula (1), R １ and R ２ is a hydrogen atom or an n-butyl group (ratio of terminal hydroxyl groups to all terminal groups: 31 mol%), R ３ is an ethylene group or a propylene group (EO / PO ratio: 60 / 40) (kinematic viscosity at 40°C: 45.6 mm ２ / s, 100℃ kinematic viscosity: 9.72mm ２ / s, viscosity index: 206)

[0042] PAG compound 3: In the above formula (1), R １ and R ２ is a hydrogen atom (ratio of terminal hydroxyl groups to all terminal groups: 100 mol%), R ３ is an ethylene group or a propylene group (EO / PO ratio: 92 / 8) (kinematic viscosity at 40°C: 56.1 mm ２ / s, 100℃ kinematic viscosity: 9.60mm ２ / s, viscosity index: 156)

[0043] PAG compound 4: In the above formula (1), R １ and R ２ is a hydrogen atom (ratio of terminal hydroxyl groups to all terminal groups: 100 mol%), R ３ is a propylene group (EO / PO ratio: 0 / 100) (kinematic viscosity at 40°C: 64.1 mm ２ / s, 100℃ kinematic viscosity: 10.14mm ２ / s, viscosity index: 144)

[0044] PAG compound 5: In the above formula (1), R １ and R ２ is a hydrogen atom or an n-butyl group (ratio of terminal hydroxyl groups to all terminal groups: 32 mol%), R ３ is an ethylene group or a propylene group (EO / PO ratio: 27 / 73) (kinematic viscosity at 40°C: 33.3 mm ２ / s, 100℃ kinematic viscosity: 7.55mm ２ / s, viscosity index: 205)

[0045] PAG compound 6: In the above formula (1), R １ and R ２ is a hydrogen atom or an n-butyl group (ratio of terminal hydroxyl groups to all terminal groups: 37 mol%), R ３ is an ethylene group or a propylene group (EO / PO ratio: 51 / 49) (kinematic viscosity at 40°C: 51.6 mm ２ / s, 100℃ kinematic viscosity: 11.1mm ２ / s, viscosity index: 214)

[0046] PAG compound 7: In the above formula (1), R １ and R ２ is a methyl group (ratio of terminal hydroxyl groups to all terminal groups: 0 mol%), R ３ is an ethylene group or a propylene group (EO / PO ratio: 24 / 76) (kinematic viscosity at 40°C: 45.7 mm ２ / s, 100℃ kinematic viscosity: 10.4mm ２ / s, viscosity index: 226)

[0047] PAG compound 8: In the above formula (1), R １ and R ２ is a hydrogen atom, a methyl group, or an n-butyl group (ratio of terminal hydroxyl groups to all terminal groups: 5 mol%), R ３ is a propylene group (EO / PO ratio: 0 / 100) (kinematic viscosity at 40°C: 43.8 mm ２ / s, 100℃ kinematic viscosity: 9.86mm ２ / s, viscosity index: 220)

[0048] (Evaluation of Anti-Seizure Property) For each refrigeration oil using each of the PAG compounds 1 to 8, anti-seizure property was evaluated by the FALEX Pin / Vee-Block test. Specifically, using an ASTM standard specimen, a break-in operation was performed for 5 minutes at room temperature in an air atmosphere at a rotation speed of 290 rpm and a load of 300 lbf, and then the load was gradually applied, and the load at which seizure occurred was recorded as the seizure load (lbf). A larger seizure load means better anti-seizure property. The results are shown in Table 1.

[0049]

[0050] (Evaluation of Load-Carrying Capacity) Refrigerating machine oils consisting of PAG compound 1, PAG compound 2, PAG compound 3, or PAG compound 6, and refrigerating machine oils each containing 1.0 mass% of a phosphorus-based anti-wear agent (TCP) were prepared. For each refrigerating machine oil before and after the addition of TCP, the maximum non-seizure load (LNSL) and load-wear index (LWI) at 1800 rpm were measured using a high-speed four-ball tester in accordance with ASTM D2596. The higher the LNSL and LWI values, the better the load-carrying capacity. The ratios of LNSL and LWI before and after the addition of TCP are shown in Table 2. If the ratio of LNSL to LWI before and after the addition of TCP is less than 1, this means that the load-bearing performance is deteriorated due to the interaction between the PAG compound and the phosphorus-based wear inhibitor (TCP). Therefore, it is desirable that this ratio be 1 or more or exceed 1.

[0051]

[0052] The above-described effect of adding the phosphorus-based antiwear agent can also be obtained when TCP is changed to triphenyl phosphate, propylated triphenyl phosphate, or butylated triphenyl phosphate, and when the content of the phosphorus-based antiwear agent is changed to 0.5 to 3 mass%.

Claims

1. A refrigeration oil containing a compound represented by the following formula (1) as a base oil, [In the formula, R １ and R ２ are each independently a hydrogen atom or an alkyl group, and R ３ is an ethylene group or a propylene group, and m is an integer of 2 or more.] A refrigerating machine oil, wherein the compound represented by formula (1) has a surface tension at 25°C of 31 mN / m or more.

2. The refrigerating machine oil according to claim 1, wherein the proportion of terminal hydroxyl groups to all terminal groups of the compound represented by formula (1) is 20 mol % or more.

3. The refrigerating machine oil according to claim 1, wherein the molar ratio of the ethylene group to the propylene group in the compound represented by formula (1) is 55 / 45 or more.

4. The refrigerating machine oil according to claim 1, wherein the refractive index of the compound represented by formula (1) at 20°C is 1.4480 or more.

5. The refrigeration oil according to claim 1, further comprising a phosphorus-based anti-wear agent, and the surface tension is 35 mN / m or more and 41 mN / m or less.

6. The refrigerating machine oil according to claim 5, wherein the content of the phosphorus-based anti-wear agent is 0.1 mass % or more based on the total amount of the refrigerating machine oil.

7. The refrigeration oil according to any one of claims 1 to 6, which is used together with a refrigerant consisting solely of hydrocarbons.

8. A working fluid composition comprising the refrigerating machine oil according to any one of claims 1 to 6 and a refrigerant.

9. The working fluid composition of claim 8, wherein the refrigerant consists solely of hydrocarbons.

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