Refrigerant oil, working fluid composition, and method for reducing friction coefficient of sliding part

Abstract

A refrigerant oil containing an alkylbenzene and a hydrocarbon oil other than the alkylbenzene that has a refractive index at 20°C of 1.445 or less.

Description

Refrigerating machine oil, working fluid composition, and method for reducing the coefficient of friction of sliding parts

[0001] The present disclosure relates to a refrigeration oil, a working fluid composition, and a method for reducing the coefficient of friction of a sliding part.

[0002] Refrigeration machines such as freezers, refrigerators, air conditioners (such as car air conditioners and room air conditioners), and water heaters are equipped with compressors that circulate refrigerants through a refrigeration cycle. The compressors are filled with refrigeration oil to lubricate the sliding parts.

[0003] Various types of base oils are known as the main component of refrigeration oils, and an appropriate base oil is selected depending on the desired properties. For example, Patent Document 1 discloses a lubricant composition for use in a refrigerator operating with a refrigerant consisting of at least one component of the HC (hydrocarbon) group, the lubricant composition comprising an alkylbenzene oil containing at least 90 wt % of linear alkylbenzene selected from the group of linear alkyls having paraffin side chains of 10 to 13 carbon atoms, having an average molecular weight of 239 to 244 g / Mol, and having a viscosity of between 4.0 cSt and 5.0 cSt at a temperature of 40°C.

[0004] Patent No. 5683068

[0005] According to the investigations conducted by the present inventors, the refrigeration oil containing alkylbenzene as disclosed in Patent Document 1 does not necessarily have a sufficiently low friction property, and there is room for improvement.

[0006] Therefore, one aspect of the present invention aims to effectively reduce the coefficient of friction of sliding parts by using a refrigerating machine oil containing alkylbenzene.

[0007] The present inventors have investigated a method for reducing the coefficient of friction of sliding parts by mixing an alkylbenzene with a hydrocarbon oil other than alkylbenzene, and have found that by mixing a hydrocarbon oil having a specific refractive index, the coefficient of friction of sliding parts can be reduced effectively (additively or synergistically) compared to when alkylbenzene is used alone. The present invention includes the following aspects.

[0008] [1] A refrigerating machine oil containing an alkylbenzene and a hydrocarbon oil other than alkylbenzene, the hydrocarbon oil having a refractive index of 1.445 or less at 20°C. [2] The refrigerating machine oil according to [1], wherein the refractive index (n20) at 20°C and the kinematic viscosity (KV100) at 100°C of the hydrocarbon oil satisfy the following formula: 1.420≦n20−0.002×KV100≦1.445. [3] The refrigerating machine oil according to [1], wherein the kinematic viscosity at 40°C of the refrigerating machine oil is 5mm ２ [4] A working fluid composition comprising the refrigerating machine oil according to any one of [1] to [3] and a refrigerant. [5] A method for reducing the coefficient of friction of a sliding part by using a refrigerating machine oil containing an alkylbenzene, the method comprising mixing, with the alkylbenzene, a hydrocarbon oil other than alkylbenzene, the hydrocarbon oil having a refractive index at 20°C of 1.445 or less.

[0009] According to one aspect of the present invention, the coefficient of friction of sliding parts can be effectively reduced by using a refrigerating machine oil containing an alkylbenzene.

[0010] An embodiment of the present invention is a refrigeration oil containing an alkylbenzene and a hydrocarbon oil other than an alkylbenzene, the hydrocarbon oil having a refractive index of 1.445 or less at 20°C (hereinafter simply referred to as "hydrocarbon oil").

[0011] The alkylbenzene may be a linear alkylbenzene or a branched alkylbenzene. The linear alkylbenzene is an alkylbenzene in which a linear alkylating agent is bonded to the benzene ring. The linear alkyl group may be bonded to the benzene ring at any position of the alkyl group. The branched alkylbenzene is an alkylbenzene in which a branched alkylating agent is bonded to the benzene ring. The branched alkyl group may be bonded to the benzene ring at any position of the alkyl group.

[0012] The alkylbenzene is preferably a linear alkylbenzene, from the viewpoint that the viscosity of the refrigerating machine oil is likely to be low and that the effect of reducing the friction coefficient by blending a hydrocarbon oil other than alkylbenzene is likely to be obtained. The linear alkylbenzene may be a compound represented by the following formula (1): In the formula, m and n are each independently an integer of 0 to 12, and are integers that satisfy the relationship m+n=7 to 12.

[0013] m and n are each independently an integer of preferably 1 to 11, 1 to 10, 1 to 9, 1 to 8, 1 to 7, or 1 to 6, and may be an integer that satisfies m+n=8 to 12 or 9 to 12.

[0014] The alkylbenzene may be a mixture of two or more types of linear alkylbenzenes represented by formula (1). The alkylbenzene may contain two or more types of linear alkylbenzenes in which m and n in formula (1) are each independently integers of 1 to 6 and m + n = 9 to 12, and preferably contains two or more types of linear alkylbenzenes as the main component. The total content of the two or more types of linear alkylbenzenes is preferably 40% by mass or more, 50% by mass or more, 60% 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 alkylbenzene.

[0015] The average molecular weight of the alkylbenzene (preferably linear alkylbenzene) may be 180 or more, 200 or more, 230 or more, and may be 280 or less, 260 or less, or 250 or less.

[0016] The kinematic viscosity of the alkylbenzene (preferably linear alkylbenzene) at 40°C is 10 mm ２ / s or less, 5mm ２ / s or less, 4.8mm ２ / s or less, 4.6mm ２ / s or less, or 4.5 mm ２ / s or less, and ２ / s or more, 2mm ２ / s or more, 3mm ２ / s or more, or 4 mm ２The kinematic viscosity of the alkylbenzene (preferably linear alkylbenzene) at 100°C may be 0.5 mm / s or more. ２ / s or more, 1mm ２ / s or more, 1.2mm ２ / s or more, or 1.3 mm ２ / s or more, and ２ / s or less, 3mm ２ / s or less, 2mm ２ / s or less, 1.8mm ２ / s or less, 1.7mm ２ / s or less, or 1.6 mm ２ The kinematic viscosity in this specification means a kinematic viscosity measured in accordance with JIS K2283:2000.

[0017] The refractive index of the alkylbenzene (preferably linear alkylbenzene) at 20°C may be 1.470 or more, or 1.480 or more, and may be 1.500 or less, 1.495 or less, or 1.490 or less. The refractive index in this specification means the refractive index measured in accordance with JIS K0062:1992.

[0018] The content of alkylbenzene (preferably linear alkylbenzene) may be 10% by mass or more, 20% by mass or more, 30% by mass or more, or 40% by mass or more, based on the total amount of the refrigerating machine oil, and may be 90% by mass or less, less than 90% by mass, 85% by mass or less, 80% by mass or less, 70% by mass or less, or 60% by mass or less.

[0019] The method for producing alkylbenzene is not particularly limited and may be any method. For example, alkylbenzene can be produced by contacting an aromatic compound with an alkylating agent in the presence of a catalyst. Specific examples of aromatic compounds that can be used as raw materials include benzene, toluene, xylene, ethylbenzene, methylethylbenzene, diethylbenzene, and mixtures thereof.

[0020] Examples of linear alkylating agents for obtaining linear alkylbenzene include linear paraffins or olefin compounds having 8 to 40 carbon atoms, such as linear paraffins separated from petroleum fractions such as kerosene and light oil, linear olefins obtained by catalytic olefination of linear paraffins, and linear olefins obtained by polymerizing ethylene. Examples of branched alkylating agents for obtaining branched alkylbenzene include branched olefins having 6 to 40 carbon atoms obtained by polymerization of lower monoolefins such as ethylene, propylene, butene, and isobutylene; branched olefins having 6 to 40 carbon atoms obtained by thermal cracking of wax, heavy oil, petroleum fractions, polyethylene, polypropylene, and the like, and mixtures thereof, with propylene oligomers being preferred.

[0021] Examples of alkylation catalysts that can be used in the alkylation include known catalysts such as Friedel-Crafts catalysts such as aluminum chloride and zinc chloride; and acidic catalysts such as sulfuric acid, phosphoric acid, tungstosilicic acid, hydrofluoric acid, and activated clay.

[0022] When a linear alkylbenzene represented by formula (1) is used, the linear alkylbenzene represented by formula (1) may be separated from the alkylated aromatic compound obtained as described above and used, or it is preferable to produce the linear alkylbenzene by directly alkylating benzene using a linear olefin such as a linear paraffin, a linear chlorinated paraffin, or an α-olefin as the alkylating agent. Linear alkylbenzenes in which m+n=9 to 12 in formula (1) using a linear alkylating agent having 10 to 13 carbon atoms are available as industrially produced products and are preferred from the viewpoint of economy.

[0023] The hydrocarbon oil other than alkylbenzene has a refractive index of 1.445 or less at 20°C. In one embodiment, the hydrocarbon oil has a lower refractive index than the alkylbenzene, so the two can also be distinguished based on the refractive index. From the viewpoint of further reducing the coefficient of friction, the refractive index of the hydrocarbon oil at 20°C may be preferably 1.444 or less or 1.443 or less, and more preferably 1.442 or less, 1.441 or less, 1.440 or less, or 1.439 or less. The refractive index of the hydrocarbon oil at 20°C may be 1.420 or more, 1.425 or more, 1.430 or more, 1.432 or more, or 1.435 or more.

[0024] The hydrocarbon oil may be appropriately selected from hydrocarbon oils having the above refractive index. Examples of the hydrocarbon oil include mineral hydrocarbon oils and synthetic hydrocarbon oils. The hydrocarbon oils may be used alone or in combination of two or more.

[0025] Examples of mineral hydrocarbon oils include normal paraffinic, isoparaffinic, or naphthenic hydrocarbon oils (refined mineral oils) that are obtained by using crude oil or its distillation residue as a raw material and refining it through an appropriate combination of conventional petroleum refining processes (solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, hydrorefining, sulfuric acid washing, clay treatment, distillation, etc.).

[0026] Examples of synthetic hydrocarbon oils include poly-α-olefins or hydrogenated products thereof, olefins such as α-olefins, isoparaffins, etc. The synthetic hydrocarbon oil is preferably α-olefins or isoparaffins.

[0027] The number of carbon atoms in the olefin may be 12 or more, 13 or more, or 14 or more, and may be 30 or less, 25 or less, or 20 or less. The olefin is preferably a linear olefin such as an α-olefin. The isoparaffin may be, for example, a component containing normal paraffin obtained by a dewaxing step in a petroleum refining process or Fischer-Tropsch synthesis, or an isoparaffin obtained by refining a polymer of an olefin such as ethylene, propylene, butylene, or diisobutylene through an appropriate combination of hydrocracking, hydroisomerization, hydrodewaxing, hydrorefining, distillation, and the like.

[0028] From the viewpoint of further reducing the friction coefficient, the hydrocarbon oil may preferably contain at least one hydrocarbon oil selected from the group consisting of normal paraffin-based, olefin-based, and isoparaffin-based hydrocarbon oils, and more preferably may contain at least one hydrocarbon oil selected from the group consisting of linear olefin-based oils such as α-olefins, and isoparaffin-based hydrocarbon oils.

[0029] The kinematic viscosity of hydrocarbon oil at 40°C is 1 mm ２ / s or more, 1.5mm ２ / s or more, or 2 mm ２ / s or more, and ２ / s or less, 4mm ２ / s or less or 3mm ２ The kinematic viscosity of the hydrocarbon oil at 100°C may be 0.5 mm / s or less. ２ / s or more, 0.7mm ２ / s or more, or 0.9 mm ２ / s or more, and ２ / s or less, 1.5mm ２ / s or less, or 1.2 mm ２ / s or less.

[0030] The refractive index (n20) at 20°C and the kinematic viscosity (KV100) at 100°C of the hydrocarbon oil preferably satisfy the following formula: 1.420≦n20−0.002×KV100≦1.445. Hereinafter, the value of “n20−0.002×KV100” in the center of the above formula will also be referred to as the N value.

[0031] The lower limit of the N value in the above formula may be 1.421, 1.422, 1.423, 1.424, 1.425, 1.426, or 1.427. The upper limit of the N value in the above formula may be 1.444, 1.443, 1.442, 1.441, 1.440, 1.439, 1.438, or 1.437.

[0032] %C of hydrocarbon oil Ａ (Percentage of aromatic carbons) may be 5 or less, 3 or less, 2 or less, 1 or less, or 0.5 or less. Ｎ (percentage of naphthenic carbons) may be 50 or less, 30 or less, 20 or less, less than 20, 15 or less, 10 or less, or 5 or less. Ｐ (percentage of paraffinic carbon) may be 50 or more, 70 or more, 80 or more, 90 or more, or 95 or more, and may be 100 or less, 95 or less, or 80 or less. Ａ , %C Ｎ , and %C Ｐ The total is 100.

[0033] Hydrocarbon oil R Ａ (average number of aromatic rings per molecule) may be 0.5 or less, 0.2 or less, 0.1 or less, or 0.05 or less, or may be 0.00, or may be 0.00 or more. Ｎ (average number of naphthenic rings per molecule) may be 0.8 or less, 0.5 or less, 0.2 or less, or 0.1 or less, or may be 0.00 or more. Ｔ (Average total number of rings per molecule = R Ｎ +R Ａ ) may be 0.8 or less, 0.5 or less, 0.2 or less, or 0.1 or less, may be 0.00, or may be 0.00 or more.

[0034] %C in this specification Ａ , %C Ｎ , %C Ｐ , R Ａ , R Ｎ and R Ｔmeans a value calculated in accordance with ASTM D3238-17a (2017), "Standard Test Method for Calculation of Carbon Distribution and Structural Group Analysis of Petroleum Oils by the ndM Method." However, if the average molecular weight of the target hydrocarbon oil is 250 or greater, the average molecular weight calculated in accordance with ASTM D2502 or 2503 may be used. However, if the average molecular weight of the hydrocarbon oil is less than 250, this value may not necessarily be accurate. Therefore, particularly when the average molecular weight of the hydrocarbon oil is less than 250, the molecular weight should be experimentally determined based on the description in Section "3. Summary of Test Method" of the test method, and the calculated average molecular weight should be used. In this case, the average molecular weight should be calculated from the carbon number distribution (area %) by gas chromatography (standard sample: n-paraffin). The average molecular weight of the hydrocarbon oil is preferably 430 or less, 350 or less, 300 or less, 250 or less, less than 250, or 220 or less from the viewpoint of imparting even lower friction, and is preferably 140 or more, 150 or more, 160 or more, or 180 or more from the viewpoint of reducing volatility and maintaining the flash point. P , %C Ａ and %C Ｎ If any of the calculated values ​​is negative, that value shall be regarded as 0, and the remaining calculated values ​​shall be corrected with the ratio remaining as it is, with the total being 100. Of the hydrocarbon oils mentioned above, olefins or hydrocarbon oils containing olefins are not subject to this test method, and the values ​​may not necessarily be accurate. Therefore, when the influence of olefins cannot be ignored, the values ​​shall be used as reference values.

[0035] The content of the hydrocarbon oil may be 10% by mass or more, more than 10% by mass, 15% by mass or more, 20% by mass or more, 30% by mass or more, or 40% by mass or more, based on the total amount of the refrigerating machine oil, and may be 90% by mass or less, 80% by mass or less, 70% by mass or less, or 60% by mass or less.

[0036] The total content of alkylbenzene and hydrocarbon 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% by mass or less.

[0037] In the refrigeration oil described above, by mixing a hydrocarbon oil other than the alkylbenzene with the alkylbenzene, the friction coefficient can be reduced compared to when the alkylbenzene is used alone. That is, one embodiment of the present invention can also be said to be a method for reducing the friction coefficient of a sliding part using a refrigeration oil containing an alkylbenzene, in which the friction coefficient of the sliding part is reduced by mixing a hydrocarbon oil other than an alkylbenzene, the hydrocarbon oil having a refractive index at 20°C of 1.445 or less, with the alkylbenzene. The sliding part is a sliding part in a refrigerator, and may be a sliding part in a compressor of the refrigerator.

[0038] Furthermore, one embodiment of the present invention can also be said to be a method for producing a refrigeration oil that uses a refrigeration oil containing an alkylbenzene to reduce the coefficient of friction of a sliding part, the method comprising a step of mixing a hydrocarbon oil other than an alkylbenzene, the hydrocarbon oil having a refractive index at 20°C of 1.445 or less, with the alkylbenzene.

[0039] From the viewpoint of improving wear resistance, the refrigerating machine oil may further contain an antiwear agent (also called an extreme pressure agent) as an additive. Examples of the antiwear agent include phosphorus-containing antiwear agents. Examples of the phosphorus-containing antiwear agent include phosphate esters, thiophosphate esters, acidic phosphate esters, amine salts of acidic phosphate esters, chlorinated phosphate esters, phosphites, amine salts of phosphites, phosphonate esters, and amine salts of phosphonate esters. The phosphorus-containing antiwear agent is preferably one or more selected from phosphate esters and thiophosphate esters.

[0040] Examples of phosphate esters include trialkyl phosphate, trialkenyl phosphate, and triaryl phosphate. Examples of trialkyl phosphates include tributyl phosphate, tripentyl phosphate, trihexyl phosphate, triheptyl phosphate, trioctyl phosphate, trinonyl phosphate, tridecyl phosphate, triundecyl phosphate, tridodecyl phosphate, tritridecyl phosphate, tritetradecyl phosphate, tripentadecyl phosphate, trihexadecyl phosphate, triheptadecyl phosphate, and trioctadecyl phosphate. Examples of trialkenyl phosphates include trioleyl phosphate. Examples of triaryl phosphates include triphenyl phosphate, tricresyl phosphate, tri(ethylphenyl)phosphate, tri(butylphenyl)phosphate, trixylenyl phosphate, cresyl diphenyl phosphate, and xylenyl diphenyl phosphate. The phosphoric acid ester is preferably a triaryl phosphate, more preferably selected from triphenyl phosphate and tricresyl phosphate, and even more preferably tricresyl phosphate.

[0041] Examples of thiophosphate esters include trialkyl phosphorothionate, trialkenyl phosphorothionate, and triaryl phosphorothionate. Examples of trialkyl phosphorothionates include tributyl phosphorothionate, tripentyl phosphorothionate, trihexyl phosphorothionate, triheptyl phosphorothionate, trioctyl phosphorothionate, trinonyl phosphorothionate, tridecyl phosphorothionate, triundecyl phosphorothionate, tridodecyl phosphorothionate, tritridecyl phosphorothionate, tritetradecyl phosphorothionate, tripentadecyl phosphorothionate, trihexadecyl phosphorothionate, triheptadecyl phosphorothionate, and trioctadecyl phosphorothionate. Examples of trialkenyl phosphorothionates include trioleyl phosphorothionate. Examples of triaryl phosphorothioates include triphenyl phosphorothioate, tricresyl phosphorothioate, trixylenyl phosphorothioate, cresyl diphenyl phosphorothioate, and xylenyl diphenyl phosphorothioate. The thiophosphate ester is preferably triphenyl phosphorothioate.

[0042] Examples of acidic phosphate esters include monobutyl acid phosphate, monopentyl acid phosphate, monohexyl acid phosphate, monoheptyl acid phosphate, monooctyl acid phosphate, monononyl acid phosphate, monodecyl acid phosphate, monoundecyl acid phosphate, monododecyl acid phosphate, monotridecyl acid phosphate, monotetradecyl acid phosphate, monopentadecyl acid phosphate, monohexadecyl acid phosphate, monoheptadecyl acid phosphate, and monooctadecyl acid phosphate. , monooleyl acid phosphate, dibutyl acid phosphate, dipentyl acid phosphate, dihexyl acid phosphate, diheptyl acid phosphate, dioctyl acid phosphate, dinonyl acid phosphate, didecyl acid phosphate, diundecyl acid phosphate, didodecyl acid phosphate, ditridecyl acid phosphate, ditetradecyl acid phosphate, dipentadecyl acid phosphate, dihexadecyl acid phosphate, diheptadecyl acid phosphate, dioctadecyl acid phosphate, and dioleyl acid phosphate.

[0043] Examples of the phosphite ester include dibutyl phosphite, dipentyl phosphite, dihexyl phosphite, diheptyl phosphite, dioctyl phosphite, dinonyl phosphite, didecyl phosphite, diundecyl phosphite, didodecyl phosphite, dioleyl phosphite, diphenyl phosphite, dicresyl phosphite, tributyl phosphite, tripentyl phosphite, trihexyl phosphite, triheptyl phosphite, trioctyl phosphite, trinonyl phosphite, tridecyl phosphite, triundecyl phosphite, tridodecyl phosphite, trioleyl phosphite, triphenyl phosphite, and tricresyl phosphite.

[0044] Examples of the phosphonate ester include dialkyl phosphonoacetic acid, dialkyl hydroxymethyl phosphonate, dialkyl hydroxyethyl phosphonate, dialkyl hydroxyundecyl phosphonate, etc. The alkyl group in these phosphonate esters may be a linear or branched alkyl group having 1 to 20 carbon atoms.

[0045] The amines constituting the amine salts are exemplified by alkyl or alkenyl amines having 4 to 20 carbon atoms.

[0046] The content of the anti-wear agent (preferably a phosphorus-containing anti-wear agent) may be 0.1 mass % or more, 0.5 mass % or more, or 1 mass % or more, and may be 5 mass % or more, 4 mass % or less, or 3 mass % or less, based on the total amount of the refrigerating machine oil.

[0047] The refrigerating machine oil may further contain other additives, such as antioxidants, acid scavengers, metal deactivators, pour point depressants, detergent dispersants, and antifoaming agents. The total content of the other additives may be 10% by mass or less or 5% by mass or less, based on the total amount of the refrigerating machine oil.

[0048] The kinematic viscosity of refrigerating machine oil at 40°C is 1 mm ２ / s or more, 1.5mm ２ / s or more, or 2 mm ２ / s or more, and ２ / s or less, 15mm ２ / s or less, 10mm ２ / s or less, 7mm ２ / s or less, 5mm ２ / s or less or 4mm ２ / s or less.

[0049] The kinematic viscosity of the refrigerating oil at 100°C is 0.5 mm ２ / s or more, 0.8mm ２ / s or more, or 1 mm ２ / s or more, and ２ / s or less, 5mm ２ / s or less, 3mm ２ / s or less, 2mm ２ / s or less, or 1.5 mm ２ / s or less.

[0050] The refractive index of the refrigerating machine oil at 20° C. may be 1.445 or more, 1.450 or more, or 1.455 or more, and may be 1.480 or less, 1.470 or less, or 1.465 or less. When such a refrigerating machine oil is used, the coefficient of friction of the sliding parts tends to be lower than when a mineral oil-based refrigerating machine oil having a refractive index within this range but not containing alkylbenzene is used.

[0051] The refractive index (n20) at 20°C and the kinematic viscosity (KV100) at 100°C of the refrigerating machine oil preferably satisfy the following formula: 1.430≦n20−0.002×KV100≦1.464. Hereinafter, the value of "n20−0.002×KV100" in the center of the above formula will also be referred to as the Nr value.

[0052] The lower limit of the Nr value in the above formula may be 1.430, 1.435, 1.440, or 1.445. The upper limit of the Nr value in the above formula may be 1.464, 1.462, 1.460, 1.459, or 1.458.

[0053] The pour point of the refrigerating machine oil may be 10° C. or lower, 0° C. or lower, −10° C. or lower, −20° C. or lower, −30° C. or lower, or −40° C. or lower. The pour point in this specification means the pour point measured in accordance with JIS K2269:1987.

[0054] The density of the refrigerating machine oil is, for example, 0.790 g / cm ３ Above, 0.800g / cm ３ or more, or 0.810 g / cm ３ or more, and ３ Below, 0.840g / cm ３ or less, or 0.835 g / cm ３ The density in this specification means the density at 15°C measured in accordance with the "oscillating method" described in JIS K2249-1:2011.

[0055] The refrigerating machine oil may be present in the form of a 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. That is, 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 in the working fluid composition 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.

[0056] Examples of the refrigerant include hydrocarbons, saturated fluorohydrocarbons, unsaturated fluorohydrocarbons, fluorine-containing ethers such as perfluoroethers, bis(trifluoromethyl)sulfide, trifluoroiodomethane, ammonia, and carbon dioxide.

[0057] The refrigerant preferably contains a hydrocarbon. 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. The refrigerant may consist solely of hydrocarbons.

[0058] The hydrocarbon is preferably a hydrocarbon having 1 to 5 carbon atoms, more preferably a hydrocarbon having 2 to 4 carbon atoms. Examples of the hydrocarbon include methane, ethylene, ethane, propylene, propane (R290), cyclopropane, normal butane, isobutane (R600a), cyclobutane, methylcyclopropane, 2-methylbutane, normal pentane, and mixtures of two or more thereof. The hydrocarbon is preferably a hydrocarbon that is gaseous at 25°C and 1 atmospheric pressure, and more preferably propane, normal butane, isobutane, 2-methylbutane, or a mixture thereof.

[0059] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0060] In the examples and comparative examples, alkylbenzene (a mixture of linear alkylbenzenes in which m and n in formula (1) are each independently an integer of 1 to 6 and m + n = 9 to 12, average molecular weight: 242, kinematic viscosity at 40°C: 4.24 mm ２ / s, 100℃ kinematic viscosity: 1.42mm２ / s, refractive index: 1.483, N value: 1.480) and the following hydrocarbon oils 1 to 5, with kinematic viscosities at 40°C and 100°C of approximately 1.2 mm ２ / s and about 3 mm ２ / s.

[0061] (Hydrocarbon Oil) Hydrocarbon Oil 1: A mineral hydrocarbon oil (refractive index (20°C): 1.451, kinematic viscosity at 40°C: 2.39 mm) obtained by hydrotreating and fractionating a hydrocracked light oil containing a vacuum distillation residue as a raw material. ２ / s, 100℃ kinematic viscosity: 1.02mm ２ / s, N value: 1.449, average molecular weight: 201, % C Ｐ : 57.9, % C Ｎ : 42.1, % C Ａ : 0, R Ｎ : 1.06, R Ａ : 0.00, R Ｔ Hydrocarbon oil 2: A mineral hydrocarbon oil (refractive index (20°C): 1.443, kinematic viscosity at 40°C: 2.39 mmHg) obtained by hydrotreating and fractionating a hydrocracked light oil containing a vacuum distillation residual oil. ２ / s, 100℃ kinematic viscosity: 1.04mm ２ / s, N value: 1.441, average molecular weight: 204, % C Ｐ : 75.8,% C Ｎ : 23.7, % C Ａ : 0.5, R Ｎ : 0.61, R Ａ : 0.02, R Ｔ Hydrocarbon oil 3: A normal paraffinic hydrocarbon oil (refractive index (20°C): 1.429, kinematic viscosity at 40°C: 2.09 mm) obtained by adsorption separation using a molecular sieve from a kerosene fraction obtained by hydrodesulfurizing a crude oil atmospheric distillate. ２ / s, 100℃ kinematic viscosity: 0.97mm ２ / s, N value: 1.427, average molecular weight: 201, % C Ｐ : 99.7,% C Ｎ : 0, % C Ａ : 0.3, R Ｎ : 0.00, R Ａ : 0.01, R Ｔ: 0.01) Hydrocarbon oil 4: Mixture of 1-tetradecene (reagent) and 1-hexadecene (reagent) (mass ratio 50:50) (refractive index (20 ° C): 1.439, kinematic viscosity at 40 ° C: 2.21 mm ２ / s, 100℃ kinematic viscosity: 1.01mm ２ / s, N value: 1.437, average molecular weight: 210, % C Ｐ , %C Ｎ , %C Ａ , R Ａ and R Ｎ Hydrocarbon oil 5: isoparaffin obtained by hydrocracking / isomerization / refining a paraffin component synthesized from carbon monoxide and hydrogen by the Fischer-Tropsch reaction, followed by fractional distillation (refractive index (20°C): 1.432, kinematic viscosity at 40°C: 2.16 mm ２ / s, 100℃ kinematic viscosity: 0.96mm ２ / s, N value: 1.430, average molecular weight: 204, % C Ｐ : 97.2, % C Ｎ : 2.6, % C Ａ : 0.2, R Ｎ : 0.07, R Ａ : 0.01, R Ｔ : 0.08)

[0062] The above alkylbenzene and hydrocarbon oils 1 to 5 were each mixed with 1.5% by mass of tricresyl phosphate, and the friction coefficients were measured according to the following procedure. The results are shown in Table 1.

[0063] (Measurement of Friction Coefficient) Using an MTM (Mini Traction Machine) testing machine (manufactured by PCS Instruments), the friction coefficient (μ) was measured under the following conditions. The results are shown in Tables 1 and 2. The smaller the friction coefficient, the better the friction characteristics. Ball and disc: Standard test piece (AISI 52100 standard) Test temperature: 40°C Sliding speed: 0.3 to 0.9 m / s (partial excerpt) Load: 10 N Sliding ratio: 30% The sliding speed was measured using |U Ｄ -U Ｂ The value of |(m / s) was used. Ｄ is the speed of the disk at the sliding part (m / s), and U Ｂis the ball speed at the sliding part (m / s).

[0064]

[0065] Subsequently, the above alkylbenzenes and hydrocarbon oils 1 to 5 were used to prepare base oils having the compositions (mass % based on the total amount of base oil) shown in Table 2. 1.5 mass % of tricresyl phosphate was blended with each of the obtained base oils to obtain each of the refrigerating machine oils of the Examples and Comparative Examples. The friction coefficients of each of the obtained refrigerating machine oils were measured using the procedure described above. From the friction coefficients (μ) when each of the measured refrigerating machine oils was used, the friction coefficients (μ) when the alkylbenzenes shown in Table 1 were used were calculated. ０ ) minus the value (μ-μ ０ ) was calculated, and the effect of reducing the friction coefficient was evaluated based on this value. ０ ) is a negative value, it means that the friction coefficient when using a refrigeration oil containing alkylbenzene and hydrocarbon oil is reduced compared to the friction coefficient when using alkylbenzene alone, and the larger the absolute value of the negative value, the greater the effect of reducing the friction coefficient. The results are shown in Table 2.

[0066]

[0067] The Nr values ​​of the refrigeration oils of Comparative Example 1 and Examples 1 to 4 are as follows: Comparative Example 1: 1.4656 Example 1: 1.4596 Example 2: 1.4526 Example 3: 1.4576 Example 4: 1.4556

[0068] As can be seen from Table 2, when alkylbenzene was mixed with hydrocarbon oil 1 having a refractive index of more than 1.445 at 20°C (Comparative Example 1), almost no effect of reducing the friction coefficient was obtained, whereas when hydrocarbon oils 2 to 5 having a refractive index of 1.445 or less at 20°C were mixed with alkylbenzene (Examples 1 to 4), a significant effect of reducing the friction coefficient was obtained. In particular, in Examples 2 and 3, a significant effect of reducing the friction coefficient (synergistic effect) was observed compared to alkylbenzene alone, hydrocarbon oil 2 alone, or hydrocarbon oil 3 alone.

[0069] Furthermore, when the mass ratio of the alkylbenzene (straight-chain alkylbenzene) to the hydrocarbon oils 2 to 5 is changed to 15 / 85, 30 / 70, 70 / 30, and 85 / 15, additive or synergistic friction-reducing effects are observed compared to the alkylbenzene alone or the hydrocarbon oils 2 to 5 alone.

[0070] Furthermore, when a branched alkylbenzene (having a branched alkyl group having 9, 12, or 15 carbon atoms derived from a propylene oligomer) is used instead of the linear alkylbenzene, the coefficient of friction of the sliding part tends to be higher than when a linear alkylbenzene is used, but by mixing hydrocarbon oils 2 to 5, the coefficient of friction of the sliding part can be reduced.

Claims

1. A refrigeration oil containing an alkylbenzene and a hydrocarbon oil other than the alkylbenzene, the hydrocarbon oil having a refractive index of 1.445 or less at 20°C.

2. The refrigeration oil according to claim 1, wherein the refractive index (n20) at 20° C. and the kinematic viscosity (KV100) at 100° C. of the hydrocarbon oil satisfy the following formula: 1.420≦n20−0.002×KV100≦1.

445.

3. The kinetic viscosity of the refrigeration oil at 40°C is 5 mm ２ The refrigeration oil according to claim 1, wherein the refrigeration oil has a viscosity of 1000:1 or less.

4. A working fluid composition comprising the refrigerating machine oil according to any one of claims 1 to 3 and a refrigerant.

5. A method for reducing the coefficient of friction of sliding parts by using a refrigeration oil containing an alkylbenzene, comprising mixing a hydrocarbon oil other than the alkylbenzene, the hydrocarbon oil having a refractive index of 1.445 or less at 20°C, with the alkylbenzene to reduce the coefficient of friction.

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