Refrigerating machine oil and refrigerating device

Abstract

The purpose of the invention is both to suppress viscous resistance loss at compressor start (normal temperature) and improve oil film load performance during operation (high temperature) in a refrigerating machine oil and a refrigerating device. A refrigerating machine oil according to the present disclosure is for a refrigerating device in which propane is sealed therein as a refrigerant, said refrigerating machine oil containing an ester-based oil having a viscosity grade of ISO VG32 or less, and a viscosity index improver containing a polymethacrylic acid ester having a C1-18 alkyl substituent, the concentration of the polymethacrylic acid ester being from 0.6 to 6 wt%.

Description

Refrigerating machine oil and refrigeration equipment

[0001] The present disclosure relates to a refrigeration oil and a refrigeration device.

[0002] A refrigeration system is composed of at least a compressor, a condenser, an expansion valve, and an evaporator. Each component is connected to the other in a closed circuit by refrigerant piping. A refrigeration system is designed so that a mixture of refrigerant and refrigerating machine oil circulates within a sealed system.

[0003] When a new refrigerant is adopted, a compressor compatible with the new refrigerant must be developed. In compressor development, it is urgent to reduce wear loss and improve wear resistance in sliding parts, and it is necessary to select the appropriate refrigeration oil and oil additives for each refrigerant.

[0004] Patent Document 1 discloses an invention in which an anti-wear agent (TBP) is added to refrigerating machine oil to suppress wear of sliding parts even when the oil film load capacity is reduced due to high temperatures.

[0005] Japanese Patent Application Laid-Open No. 2020-158566

[0006] R290 is a natural refrigerant with a very low GWP. However, R290 is highly soluble in refrigeration oil. Therefore, in refrigeration systems that use R290 as a refrigerant, there is concern that abnormal wear of sliding parts may occur due to a decrease in the viscosity of the refrigeration oil.

[0007] This can be suppressed by increasing the viscosity grade of the base oil used in the refrigeration oil. However, increasing the viscosity grade of the base oil increases the kinematic viscosity of the refrigeration oil when the compressor of the refrigeration system starts up, which creates the problem of increasing friction loss due to viscous resistance.

[0008] When R290 is used as the refrigerant, there is a concern that the anti-wear effect may be insufficient simply by adding the anti-wear agent described in Patent Document 1 to the refrigerating machine oil.

[0009] The present disclosure has been made in consideration of the above circumstances, and aims to achieve, in a refrigeration oil and a refrigeration device, both suppression of viscous resistance loss during compressor startup (room temperature) and improvement of oil film load capacity during operation (high temperature).

[0010] In order to solve the above problems, the refrigeration oil and the refrigeration device of the present disclosure employ the following measures.

[0011] The present disclosure provides a refrigeration oil for a refrigeration system in which propane is sealed as a refrigerant, the refrigeration oil comprising an ester-based base oil having a viscosity grade of ISO VG32 or less and a viscosity index improver including a polymethacrylic acid ester having an alkyl substituent having 1 to 18 carbon atoms, wherein the concentration of the polymethacrylic acid ester is 0.6 wt % or more and 6 wt % or less.

[0012] The present disclosure provides a refrigeration system in which a refrigerant circulation circuit is configured, in which a compressor, a condenser, an expansion valve, and an evaporator are connected by a main pipe to circulate a refrigerant, wherein the compressor is provided with a refrigeration oil supply mechanism that supplies refrigeration oil to sliding parts, the refrigeration oil contained in the refrigeration oil supply mechanism contains an ester-based base oil having a viscosity grade of ISO VG32 or less, and a viscosity index improver containing a polymethacrylic acid ester having an alkyl substituent having 1 to 18 carbon atoms, the concentration of the polymethacrylic acid ester being 0.6 wt % or more and 6 wt % or less, and propane is sealed in the refrigerant circulation circuit as a refrigerant.

[0013] According to the present disclosure, by incorporating a viscosity index improver containing a polymethacrylic acid ester having an alkyl substituent having 1 to 18 carbon atoms into an ester-based base oil, it is possible to realize a refrigeration oil and a refrigeration device equipped with the same that can simultaneously suppress viscous resistance loss during compressor startup (at room temperature) and improve oil film load capacity during operation (at high temperature).

[0014] FIG. 1 is a block diagram of a refrigeration system. FIG. 2 is a longitudinal sectional view showing a scroll compressor. FIG. 3 is a longitudinal sectional view taken at the position of the Oldham link key of FIG. 3. FIG. 4 is an evaluation diagram of a viscosity index improver. FIG. 5 is a diagram showing the two-phase separation temperature of a mixture of a refrigerant and a refrigerating machine oil containing a viscosity index improver. FIG. 6 is a graph summarizing the effect of a viscosity index improver on a base oil.

[0015] Hereinafter, an embodiment of a refrigeration oil and a refrigeration device according to the present disclosure will be described with reference to the drawings.

[0016] (Refrigerating machine oil) The refrigerating machine oil contains a base oil and a viscosity index improver. The refrigerating machine oil may contain an anti-wear agent. The refrigerating machine oil may contain an oiliness agent, an extreme pressure agent, an antioxidant, an acid scavenger, an antifoaming agent, a leak detection agent, etc. The pour point of the refrigerating machine oil is -45°C or lower.

[0017] The base oil is an ester-based synthetic lubricating oil (ester-based base oil). The ester-based base oil may be, for example, polyol ester, polyvinyl ether, polyalkylene glycol, alkyl benzene, mineral oil, etc. The viscosity grade of the base oil is ISO VG32 or less. The viscosity grade of the base oil is preferably ISO VG22 or more.

[0018] Viscosity grade is a viscosity grade of lubricating oils defined by ISO (International Organization for Standardization). The higher the viscosity grade number, the higher the viscosity. Each number at the end of the viscosity grade defines a kinematic viscosity range, and this number represents the kinematic viscosity (mm ２ / s). The kinematic viscosity range of ISO VG32 at 40°C is 28.8 mm ２ / s or more 35.2mm ２ / s or less. The kinematic viscosity range of ISO VG22 at 40°C is 19.8 mm ２ / s or more 24.2mm ２ / s or less.

[0019] Viscosity index improvers have the effect of reducing the viscosity change of base oils that occurs with temperature changes. Viscosity index improvers have a structural unit represented by formula (I). In formula (I), R is an alkyl substituent having 1 to 18 carbon atoms.

[0020] The viscosity index improver contains polymethacrylic acid ester (PMA). The molecular weight of the polymethacrylic acid ester is 35,000 or less, preferably about 30,000. In the viscosity index improver, the PMA may be diluted with a solvent. Mineral oil is a suitable solvent. The PMA:solvent ratio may be 60:40 (weight ratio). The viscosity index improver may be, for example, Aclub A-1061 manufactured by Sanyo Chemical Industries, Ltd.

[0021] The concentration of polymethacrylate ester in the refrigeration oil is 0.6 wt% or more and 6 wt% or less. When a base oil with a viscosity grade of ISO VG32 is used, the concentration of polymethacrylate ester should be 0.6 wt% or more and 3 wt% or less. When a base oil with a viscosity grade of ISO VG22 is used, the concentration of polymethacrylate ester should be 3 wt% or more and 6 wt% or less.

[0022] The viscosity index (VI) can be improved by blending a viscosity index improver containing a polymethacrylic acid ester into the base oil. The "viscosity index" is a numerical value that indicates the degree of viscosity change due to temperature. It is expressed as an index based on the kinematic viscosity at 40°C and 100°C relative to a standard oil, and the higher the viscosity index, the smaller the viscosity change. The viscosity index at 40°C of a refrigeration oil using an ISO VG32 base oil is preferably 186±10% to 206±10%. The viscosity index at 40°C of a refrigeration oil using an ISO VG22 base oil is preferably 167±10% to 184±10%. The viscosity index is measured in accordance with JIS K2283:2000.

[0023] Generally, the viscosity of a base oil decreases as the temperature increases. By improving the viscosity index of a refrigeration oil, the difference in fluid viscous resistance between startup and operation can be reduced. Even with the same viscosity grade, a higher viscosity index increases the oil film load capacity in high temperature ranges. This allows for startup at low viscosity. Even if the viscosity grade of the base oil is lowered, by adding a viscosity index improver containing polymethacrylate ester, the oil film load capacity in high temperature ranges will be higher than that of a refrigeration oil that does not contain a viscosity index improver containing polymethacrylate ester.

[0024] The anti-wear agent is tributyl phosphate (TBP). The concentration of the anti-wear agent in the refrigerating machine oil is 1 wt% or more and 5 wt% or less, preferably 1 wt% or more and 3 wt% or less. By adding 1 wt% or more of TBP, the anti-wear properties of the refrigerating machine oil are significantly improved. If the TBP concentration is 1 wt% or more, the anti-wear properties do not change significantly even if the concentration is increased thereafter. Therefore, the upper limit of the TBP concentration should be 5 wt% or less, preferably 3 wt% or less.

[0025] The refrigeration oil according to this embodiment is suitable for use in a refrigeration system that uses propane (R290 refrigerant) as a refrigerant. The refrigeration oil becomes contaminated with the refrigeration oil during operation of the refrigeration system. The refrigeration oil according to this embodiment is compatible with the R290 refrigerant within the operating temperature range of the refrigeration system.

[0026] (Refrigeration Device) The refrigeration oil according to the present embodiment is suitable for use in, for example, home room air conditioners, commercial air conditioners, chillers, car air conditioners, refrigerated / freezer showcases, hot water heat pumps, etc. Fig. 1 shows a block diagram of a refrigeration device that uses the refrigeration oil according to the present embodiment.

[0027] 1 includes a refrigerant circulation circuit having a compressor 1, a condenser 12, an expansion valve 13, and an evaporator 14. The refrigerant circulation circuit is a closed circuit in which the compressor 1, the condenser 12, the expansion valve 13, and the evaporator 14 are connected via pipes 15a to 15d that circulate and transport the refrigerant.

[0028] The refrigerant circuit is filled with a refrigerant, such as propane (R290). The amount of refrigerant charged in the refrigeration system is 300 g or more, preferably 500 g or more.

[0029] The compressor is supplied with refrigeration oil, which includes an ester-based base oil having a viscosity grade of ISO VG32 or lower and a viscosity index improver including a polymethacrylic acid ester having an alkyl substituent having 1 to 18 carbon atoms, and the concentration of the polymethacrylic acid ester is selected from those having a concentration of 0.6 wt % or higher and 6 wt % or lower.

[0030] In the refrigeration system, the condenser 12 condenses and liquefies the high-temperature, high-pressure refrigerant gas to release heat, the expansion valve 13 adiabatically expands and reduces the pressure of the high-temperature, high-pressure liquid refrigerant that has passed through the condenser 12, the evaporator 14 absorbs heat by evaporating and vaporizing the low-temperature, low-pressure liquid refrigerant that has passed through the expansion valve 13, and the compressor 1 adiabatically compresses the low-temperature, low-pressure refrigerant gas that has passed through the evaporator 14. The high-temperature, high-pressure refrigerant gas that has passed through the compressor 1 is supplied to the condenser 12. By circulating the refrigerant as a heat transfer medium in this closed system, heat is transferred from the evaporator 14 to the condenser 12.

[0031] The refrigerating machine oil supplied to the compressor 1 circulates mixed with the refrigerant through a refrigerant circulation circuit including the evaporator 14, expansion valve 13, and condenser 12, and returns to the compressor 1. The refrigerating machine oil supplied to the refrigeration system is sealed together with the refrigerant within the system, and is used without being replaced while the refrigeration system is in use.

[0032] (Compressor) The compressor 1 of the refrigeration system may be a scroll compressor or a rotary compressor. The refrigeration oil according to this embodiment is particularly suitable for use in a scroll compressor equipped with an Oldham link.

[0033] FIG. 2 is a vertical cross-sectional view of a scroll compressor to which refrigerating machine oil is applied.

[0034] A scroll compressor (scroll fluid machine) 1 includes a fixed scroll 3 and an orbiting scroll 4 that revolves around the fixed scroll 3 within a housing 2 .

[0035] The fixed scroll 3 is fixed to the housing 2 via the upper bearing 21, and includes a scroll-shaped wall body 33 standing on an end plate 31. The orbiting scroll 4 includes a scroll-shaped wall body 43 standing on an end plate 41. The wall body 33 of the fixed scroll 3 and the wall body 43 of the orbiting scroll 4 have substantially the same shape. By rotating the orbiting scroll 4 180° relative to the fixed scroll 3 and engaging the walls 33, 43 with each other, a plurality of sealed compression spaces R1 are formed.

[0036] The orbiting scroll 4 is adapted to make an orbital motion relative to the fixed scroll 3 while its rotation is restricted by the Oldham link 23 .

[0037] The orbiting scroll 4 is rotated by a driving motor 6. The rotary shaft 5 rotated by the motor 6 is connected to the orbiting scroll 4 via a crank pin 27. The crank pin 27 is provided eccentrically with respect to the central axis of the rotary shaft 5. The crank pin 27 is rotatably connected to a boss formed on the back surface (the lower surface in the drawing) of the end plate 41 of the orbiting scroll 4 via a drive bushing and a drive bearing 52. The rotary shaft 5 is rotatably supported by an upper bearing 21 and a lower bearing 24 fixed to the housing 2.

[0038] A storage area 26 for storing refrigerating machine oil is provided in the lower part of the housing 2. The refrigerating machine oil is pumped up through an oil supply path 53 inside the rotating shaft 5 by a pump 54 provided at the lower end of the rotating shaft 5, and is supplied to sliding parts such as the lower bearing 24, the upper bearing 21, a drive bearing 52 provided around the crank pin 27, the orbiting scroll 4, and the Oldham link 23. In this embodiment, the storage area 26, the pump 54, and the oil supply path 53 are collectively referred to as a refrigerating machine oil supply mechanism.

[0039] The housing 2 is provided with a suction pipe 28 that draws in low-pressure gas refrigerant and a discharge pipe 29 that discharges compressed high-pressure gas refrigerant. The suction pipe 28 and the discharge pipe 29 are connected to a refrigerant circulation circuit of a refrigeration device (not shown).

[0040] The scroll compressor 1 operates as follows: When a driving current is supplied to the stator 61 of the motor 6 from a power source (not shown), the rotor 62 of the motor 6 rotates, and a driving force is output to the rotary shaft 5. When the rotary shaft 5 rotates, the driving force is transmitted to the orbiting scroll 4 via a crank pin 27 that is provided at the upper end of the rotary shaft 5 eccentrically in one direction (eccentric direction) radially outward from the central axis of the rotary shaft 5. As a result, the orbiting scroll 4 revolves around the fixed scroll 3 while being prevented from rotating on its own axis by the action of the Oldham link 23.

[0041] As the orbiting scroll 4 orbits, the refrigerant that has flowed in from the suction pipe 28 is sucked into the space between the orbiting scroll 4 and the fixed scroll 3. As the orbiting scroll 4 orbits, the volume of the compression space R1 between the orbiting scroll 4 and the fixed scroll 3 decreases, and the refrigerant is compressed in the compression space R1.

[0042] The compressed refrigerant passes through the discharge port 32 of the fixed scroll 3 and the discharge port 38 of the discharge cover 37, and is discharged into the refrigerant circulation circuit through the discharge piping 29. A multi-port 32A is formed in the fixed scroll 3, and a reed valve 36 is provided in the multi-port 32A, which is attached to the end plate 31 of the fixed scroll 3 via a retainer 35. A reed valve 37B is also provided in the discharge port 38 of the discharge cover 37, which is attached to the discharge cover 37 via a retainer 37A. When the pressure of the compressed refrigerant reaches a predetermined value, the refrigerant pushes open the reed valves 36, 37B and is discharged to the condenser side of the refrigerant circulation circuit.

[0043] Fig. 3 shows the Oldham link 23 shown in Fig. 2. The Oldham link 23 is provided above the upper bearing 21. As shown in Fig. 2, the Oldham link 23 is provided on the back surface side of the end plate 41 of the orbiting scroll 4.

[0044] As shown in FIG. 3 , the Oldham link 23 has a generally ring-shaped configuration in plan view. In plan view as shown in FIG. 3 , keys 23A protruding downward (toward the upper bearing 21) are provided on both the left and right sides, i.e., at the 3 o'clock and 9 o'clock positions. Also, in plan view as shown in FIG. 3 , keys 23B protruding upward (toward the orbiting scroll 4) are provided on both the top and bottom sides, i.e., at the 6 o'clock and 12 o'clock positions. That is, the direction in which the two keys 23A are provided is perpendicular to the direction in which the two keys 23B are provided. Each downward-protruding key 23A is inserted into a key groove 21A formed in the upper bearing 21, as shown in FIG. 4 . Each upward-protruding key 23B is inserted into a key groove formed in an end plate 41 of the orbiting scroll 4, not shown.

[0045] The upper bearing 21 and the orbiting scroll 4 are preferably made of a material different from that of the Oldham link 23. When the material of the Oldham link 23 is iron, the material of the keyways formed in the upper bearing 21 and the orbiting scroll 4 is preferably aluminum. When the material of the Oldham link 23 is aluminum, the material of the keyways formed in the upper bearing 21 and the orbiting scroll 4 is preferably iron.

[0046] (Compatibility with R290 Refrigerant) The two-phase separation temperature was measured in accordance with "Test method for compatibility with refrigerants" in JIS K2211:2009 "Refrigerating machine oil."

[0047] First, the compatibility of the viscosity index improver alone with the refrigerant was confirmed. R290 was used as the refrigerant. The viscosity index improver used was a fluid in which polymethacrylate ester (PMA) was diluted with diluent oil. The formulations of PMA and diluent oil are shown in Table 1, Nos. 1 to 3 (Sanyo Chemical Co., Ltd.). PMA has a structural unit represented by formula (I) above and has an alkyl substituent with 1 to 18 carbon atoms.

[0048] Figure 5 shows the evaluation results of viscosity index improvers. The figure shows the two-phase separation temperature for a mixture of viscosity index improver and refrigerant in a 10:50 weight ratio. Viscosity index improver No. 2 separated from R290 refrigerant across the entire temperature range. On the other hand, No. 1 did not separate at temperatures below 32°C. No. 3 did not separate at temperatures above -26°C. The discharge temperature of a refrigeration system compressor reaches 120°C. Therefore, it is necessary for the viscosity index improver not to separate at high temperatures. It is sufficient that it not separate at low temperatures at outside air temperatures. For these reasons, viscosity index improver No. 3 is suitable for use in refrigeration system compressors.

[0049] Next, the compatibility of refrigerant with a viscosity index improver-containing refrigerant oil was examined. The viscosity index improver used was No. 3 listed in Table 1 above. A polyol ester (viscosity grade ISO VG32) was used as the base oil. The concentration of the viscosity index improver in the refrigerant oil was 5 wt %.

[0050] Figure 6 shows the two-phase separation temperature for mixtures of refrigerant and refrigerant containing viscosity index improver. The leftmost column in Figure 6 displays the results for No. 3 in Figure 5 for reference. In the mixtures shown in Figure 6, the refrigerant oil (containing viscosity index improver No. 3) and refrigerant ratios range from 10:90 to 40:60 (by weight). The curves superimposed on the bar graph in Figure 6 represent the two-phase separation temperature curve (a) for a mixture of VG32 polyol ester (VG32_POE) and R410, which are used in conventional refrigerant oils. The dashed-dotted line below the bar graph in Figure 6 represents the lower limit (b) of the compatibility range for a mixture of VG46 polyol ester (VG46_POE) and R290, which are used in conventional refrigerant oils. VG32_POE is a refrigerant oil for R410A, etc. VG46_POE is a candidate refrigerant oil for propane.

[0051] The compatibility characteristics of refrigerating machine oils containing viscosity index improver No. 3 with the refrigerant were good. The lower limit of the compatibility range (lower temperature two-phase separation temperature) of refrigerating machine oils containing viscosity index improver No. 3 was approximately 10 to 15°C wider than when No. 3 was mixed alone with R290 refrigerant. It is expected that increasing the concentration of viscosity index improver will tend to narrow the compatibility range. The mixing ratio of refrigerating machine oil to refrigerant had almost no effect on the two-phase separation temperature.

[0052] It was confirmed that a mixture of refrigerating machine oil containing viscosity index improver No. 3 and R290 refrigerant has a wider compatibility range (see the two-phase separation temperature curve (a) in Figure 6) than a mixture of refrigerating machine oil and refrigerant used in conventional refrigeration systems, and that the same compatibility characteristics can be maintained (see the lower limit (b) of the compatibility range in Figure 6). From the above, it was confirmed that a mixture of refrigerating machine oil containing viscosity index improver No. 3 and R290 refrigerant can be used within the operating temperature range of conventional refrigeration systems.

[0053] (Concentration of Viscosity Index Improver) For refrigerating machine oils containing viscosity index improvers in ester-based base oils of different viscosity grades, the kinematic viscosities at 40°C and 100°C were measured, and the viscosity index (VI) was calculated from the results.

[0054] Table 2 shows the test conditions and results. For reference, Table 2 also lists the acid number, kinematic viscosity, and viscosity index (VI) of base oils of different viscosity grades. No. 3 in Table 1 above was used as the viscosity index improver. Samples No. 3 to 6 of the refrigeration oil contained tributyl phosphate (TBP) as an anti-wear agent.

[0055]

[0056] The viscosity index improver (No. 3 in Table 1) did not impair the properties of the refrigerating machine oil when added to the ester-based base oil.

[0057] The base oils (samples No. 1, 2, 7, and 8) to which no viscosity index improver was added exhibited higher viscosity indexes as the viscosity grade increased. By adding a viscosity index improver to a base oil with a viscosity grade of ISO VG32, the viscosity index of the refrigeration oil improved. The viscosity index also increased as the concentration of the viscosity index improver increased. By adding 5 wt% of viscosity index improver (3 wt% PMA), the viscosity index increased by approximately 10% compared to the base oil before addition. This was approximately 5% higher than the viscosity index of ISO VG46.

[0058] As the viscosity index improver concentration increased, the kinematic viscosities at 40°C and 100°C increased. Sample No. 5, which had a viscosity index improver concentration of 10 wt% (PMA 6 wt%), had kinematic viscosities at 40°C and 100°C close to those of ISO VG46, despite using an ISO VG32 base oil. The kinematic viscosity at 40°C was lower than that of ISO VG46 base oil up to a viscosity index improver concentration of 10 wt% (PMA 6 wt%).

[0059] According to the above results, by adding a viscosity index improver, the viscosity index of a refrigeration oil using a base oil with a viscosity grade of ISO VG32 was able to be made equal to or better than that of ISO VG46. Refrigeration oil (Sample No. 5) containing 10 wt% (6 wt% PMA) of viscosity index improver or less was able to start at a kinematic viscosity lower than ISO VG46, and during operation, exhibited a kinematic viscosity equivalent to ISO VG46. Refrigeration oil (Sample No. 4) containing 5 wt% (3 wt% PMA) of viscosity index improver was able to start at a kinematic viscosity approximately 25% lower than ISO VG46, and was able to operate at a kinematic viscosity approximately 20% higher than before the addition of the viscosity index improver.

[0060] Figure 7 shows a graph summarizing the effect of viscosity index improvers on base oil. In this figure, the horizontal axis represents the viscosity index improver concentration (wt%) and the vertical axis represents the 40°C kinematic viscosity (mm ２ 7 is the viscosity index (VI) of the oil. The viscosity index improver concentrations in FIG. 7 assume the use of viscosity index improver No. 3 in Table 1.

[0061] As the viscosity index improver concentration increases, the kinematic viscosity and viscosity index at 40°C improve approximately linearly. If the viscosity index improver concentration is 10 wt% or less (6 wt% PMA), the kinematic viscosity at low temperatures (40°C) will not become too high. For base oils with a viscosity grade of ISO VG32, a viscosity index improver concentration of 1 to 5 wt% (0.6 to 3 wt% PMA) can reliably achieve a 40°C kinematic viscosity lower than ISO VG46. For base oils with a viscosity grade of ISO VG22, a viscosity index improver concentration of 5 to 10 wt% (3 to 6 wt% PMA) can still achieve a 40°C kinematic viscosity lower than ISO VG46.

[0062] <Additional Notes> The refrigeration oil and the refrigeration device described in the above-described embodiment can be understood, for example, as follows.

[0063] A refrigeration oil according to a first aspect of the present disclosure is a refrigeration oil for a refrigeration unit in which propane is sealed as a refrigerant, and includes an ester-based base oil having a viscosity grade of ISO VG32 or less, and a viscosity index improver including a polymethacrylic acid ester having an alkyl substituent having 1 to 18 carbon atoms, and the concentration of the polymethacrylic acid ester is 0.6 wt % or more and 6 wt % or less.

[0064] According to the present disclosure, the viscosity index can be improved by adding the polymethacrylic acid ester to an ester-based base oil. This allows the kinematic viscosity to be maintained at high temperatures even when a base oil with a low viscosity grade is used. The use of a base oil with a low viscosity grade reduces frictional resistance at room temperature. Because the kinematic viscosity can be maintained at high temperatures, the oil film load capacity during operation (at high temperatures) is improved compared to base oils without the addition of polymethacrylic acid ester.

[0065] When using ISO VG32 ester base oil, the concentration of polymethacrylate ester should be 0.6 wt% or more and 3 wt% or less, which allows the kinematic viscosity at startup to be lower than that of ISO VG46 base oil, while still ensuring a kinematic viscosity equal to or higher than that of ISO VG46 during operation.

[0066] The refrigerating machine oil according to the second aspect of the present disclosure may be the refrigerating machine oil of the first aspect, further comprising tributyl phosphate as an anti-wear agent, and the concentration of the anti-wear agent may be 1 wt % or more and 5 wt % or less.

[0067] By adding 1 wt % or more of TBP, the wear resistance of the refrigerating machine oil is significantly improved.

[0068] A refrigeration device according to a third aspect of the present disclosure is a refrigeration device including a compressor (1), a condenser (12), an expansion valve (13), and an evaporator (14) connected by main pipes (15a to 15d) to form a refrigerant circulation circuit that circulates a refrigerant, wherein the compressor includes a refrigeration oil supply mechanism (26, 54, 53) that supplies refrigeration oil to sliding parts (24, 21, 52, 4, 23), the refrigeration oil contained in the refrigeration oil supply mechanism includes an ester-based base oil having a viscosity grade of ISO VG32 or less and a viscosity index improver including a polymethacrylic acid ester having an alkyl substituent having 1 to 18 carbon atoms, the concentration of the polymethacrylic acid ester being 0.6 wt % or more and 6 wt % or less, and propane is sealed in the refrigerant circulation circuit as a refrigerant.

[0069] A refrigeration device according to a fourth aspect of the present disclosure is the refrigeration device of the third aspect, wherein the amount of the refrigerant charged is 300 g or more.

[0070] A refrigeration apparatus according to a fifth aspect of the present disclosure is the refrigeration apparatus of the third or fourth aspect, wherein the compressor is a scroll compressor equipped with an Oldham link (23) as an anti-rotation mechanism.

[0071] REFERENCE SIGNS LIST 1 Compressor (scroll compressor, scroll fluid machine) 2 Housing 3 Fixed scroll 4 Orbiting scroll 12 Condenser 13 Expansion valve 14 Evaporator 15a, 15b, 15c, 15d Piping 21 Upper bearing 21A Keyway 23 Oldham link 23A Key 23B Key 24 Lower bearing 26 Storage area 27 Crank pin 28 Suction pipe 29 Discharge pipe 31 End plate 32, 38 Discharge port 32A Multi-port 33 Wall 35 Retainer 36 Reed valve 37 Discharge cover 37A Retainer 37B Reed valve 41 End plate 43 Wall 52 Drive bearing R1 Compression space

Claims

1. A refrigeration oil for a refrigeration unit containing propane as a refrigerant, comprising: an ester-based base oil having a viscosity grade of ISO VG32 or less; and a viscosity index improver containing a polymethacrylic acid ester having an alkyl substituent having 1 to 18 carbon atoms, wherein the concentration of the polymethacrylic acid ester is 0.6 wt% or more and 6 wt% or less.

2. The refrigeration oil according to claim 1, further comprising tributyl phosphate as an anti-wear agent, the concentration of the anti-wear agent being 1 wt % or more and 5 wt % or less.

3. A refrigeration system in which a compressor, a condenser, an expansion valve, and an evaporator are connected by a main pipe to form a refrigerant circulation circuit for circulating a refrigerant, wherein the compressor is equipped with a refrigeration oil supply mechanism that supplies refrigeration oil to sliding parts, the refrigeration oil contained in the refrigeration oil supply mechanism contains an ester-based base oil having a viscosity grade of ISO VG32 or less and a viscosity index improver containing a polymethacrylic acid ester having an alkyl substituent having 1 to 18 carbon atoms, the concentration of the polymethacrylic acid ester being 0.6 wt% or more and 6 wt% or less, and propane is sealed in the refrigerant circulation circuit as the refrigerant.

4. The refrigeration device according to claim 3, wherein the amount of the refrigerant charged is 300 g or more.

5. A refrigeration system according to claim 3, wherein the compressor is a scroll compressor equipped with an Oldham link as a rotation prevention mechanism.

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