Refrigerating machine oil and refrigeration equipment

Abstract

The objective of the present invention is to achieve both suppression of viscous resistance loss during compressor start-up (normal temperature) and improvement of oil film load capacity during operation (high temperature) in refrigeration oil and refrigeration equipment. [Solution] The refrigeration oil disclosed herein is for use in a refrigeration unit in which propane is filled as a refrigerant, and 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 0.6 wt% or more and 6 wt% or less.

Description

[Technical field]

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

[0002] A refrigeration system is composed of at least a compressor, a condenser, an expansion valve, and an evaporator. Each component of the refrigeration system is connected to each other as a closed circuit by refrigerant piping, and a mixture of a refrigerant and a refrigerating machine oil circulates in the closed 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 of 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 refrigeration oil to suppress wear of sliding parts even when the oil film load capacity is reduced due to high temperatures. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2020-158566 A Summary of the Invention [Problem to be solved by the invention]

[0006] R290 is a natural refrigerant with a very low GWP. On the other hand, R290 is highly soluble in refrigeration oil. Therefore, in refrigeration equipment that uses R290 as a refrigerant, there is concern that abnormal wear of sliding parts will 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, but increasing the viscosity grade of the base oil increases the kinetic viscosity of the refrigeration oil when the compressor of the refrigeration device starts up, which creates a problem of increased 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 refrigeration 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, a balance between suppression of viscous resistance loss during compressor startup (room temperature) and improvement of oil film load capacity during operation (high temperature). [Means for solving the problem]

[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 device in which propane is sealed as a refrigerant, the refrigeration oil comprising an ester 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, the concentration of the polymethacrylic acid ester being 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 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 is 0.6 wt% or more and 6 wt% or less, and propane is sealed in the refrigerant circulation circuit as a refrigerant. Effect of the Invention

[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 (room temperature) and improve oil film load capacity during operation (high temperature). [Brief description of the drawings]

[0014] [Figure 1] FIG. 2 is a block diagram of a refrigeration device. [Diagram 2] FIG. 2 is a vertical cross-sectional view showing a scroll compressor. [Diagram 3] FIG. 3 is a plan view showing the Oldham link and the upper bearing of FIG. 2. [Figure 4] FIG. 4 is a longitudinal sectional view taken at the position of a key of the Oldham link in FIG. 3. [Diagram 5] FIG. 2 is an evaluation chart of a viscosity index improver. [Figure 6] FIG. 2 is a diagram showing the two-phase separation temperature of a mixture of a refrigerating machine oil containing a viscosity index improver and a refrigerant. [Figure 7] 1 is a graph summarizing the effect of a viscosity index improver on a base oil. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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 refrigeration oil contains a base oil and a viscosity index improver. The refrigeration oil may contain an anti-wear agent. The refrigeration 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 refrigeration oil is -45°C or lower.

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

[0018] Viscosity grade is a classification of the viscosity of lubricants as defined by ISO. 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 the number indicates the kinematic viscosity (mm 2 / s) at 40°C. The kinematic viscosity range of ISO VG32 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 change in viscosity of base oil that occurs with temperature changes. The viscosity index improver has a structural unit represented by formula (I). [ka] In formula (I), R is an alkyl substituent having 1 to 18 carbon atoms.

[0020] The viscosity index improver includes 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 suitable as the solvent. The ratio of PMA to solvent may be 60:40 (weight ratio). The viscosity index improver may be, for example, Aclube A-1061 manufactured by Sanyo Chemical Industries, Ltd.

[0021] The concentration of polymethacrylate ester in the refrigeration oil is 0.6wt% or more and 6wt% or less. When using a base oil of viscosity grade ISO VG32, the concentration of polymethacrylate ester should be 0.6wt% or more and 3wt% or less. When using a base oil of viscosity grade ISO VG22, the concentration of polymethacrylate ester should be 3wt% or more and 6wt% 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 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 and a standard oil as a reference, 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 above viscosity index means a viscosity index measured in accordance with JIS K2283:2000.

[0023] In general, 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 start-up and operation can be reduced. Even with the same viscosity grade, a higher viscosity index increases the oil film load capacity in the high temperature range. Thus, startup at a low viscosity is achieved. Even if the viscosity grade of the base oil is lowered, the oil film load capacity in the high temperature range is higher by including a viscosity index improver containing a polymethacrylic acid ester than a refrigeration oil that does not contain a viscosity index improver containing a polymethacrylic acid ester.

[0024] The anti-wear agent is tributyl phosphate (TBP). The concentration of the anti-wear agent in the refrigeration oil is 1 wt% or more and 5 wt% or less, preferably 1 wt% or more and 3 wt% or less. By including 1 wt% or more of TBP, the anti-wear properties of the refrigeration 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 is set to 5 wt% or less, preferably 3 wt% or less.

[0025] The refrigeration oil according to the present embodiment is suitable for use in a refrigeration device in which propane (R290 refrigerant) is sealed as a refrigerant. The refrigeration oil is mixed with the refrigerant during operation of the refrigeration device. The refrigeration oil according to the present embodiment is compatible with the R290 refrigerant within the operating temperature range of the refrigeration device.

[0026] (Refrigeration equipment) The refrigerating machine 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, heat pumps for hot water supply, etc. Fig. 1 illustrates a block diagram of a refrigeration device that uses the refrigerating machine 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 circulation circuit is filled with a refrigerant. The refrigerant is propane (R290). The amount of the refrigerant charged in the refrigeration device is 300 g or more, and preferably 500 g or more.

[0029] The compressor is supplied with refrigeration oil, which 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, and the concentration of the polymethacrylic acid ester is selected from those having a concentration of 0.6 wt% or more and 6 wt% or less.

[0030] In the refrigeration system, the condenser 12 condenses / liquefies the high-temperature, high-pressure refrigerant gas to release heat, the expansion valve 13 adiabatically expands the high-temperature, high-pressure liquid refrigerant that has passed through the condenser 12 to reduce its pressure, the evaporator 14 evaporates / vaporizes the low-temperature, low-pressure liquid refrigerant that has passed through the expansion valve 13 to absorb heat, 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 refrigeration oil supplied to the compressor 1 mixes with the refrigerant and travels through a refrigerant circulation circuit including the evaporator 14, the expansion valve 13, and the condenser, before returning to the compressor. The refrigeration 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 of the refrigeration system may be a scroll compressor or a rotary compressor. The refrigeration oil according to the present embodiment is particularly suitable for use in a scroll compressor equipped with an Oldham link.

[0033] FIG. 2 is a vertical sectional view of a scroll compressor to which refrigeration oil is applied.

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

[0035] The fixed scroll 3 is fixed to the housing 2 via the upper bearing 21, and has a scroll-shaped wall body 33 standing on an end plate 31. The orbiting scroll 4 has 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 approximately the same shape. The orbiting scroll 4 is rotated 180° relative to the fixed scroll 3 to mesh the walls 33, 43 with each other, thereby forming a plurality of sealed compression spaces R1.

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

[0037] The orbiting scroll 4 is rotated by a driving motor 6. A rotating 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 rotating shaft 5. The crank pin 27 is rotatably connected to a boss formed on the back surface (the lower surface in the figure) of an end plate 41 of the orbiting scroll 4 via a drive bush and a drive bearing 52. The rotating 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 refrigeration oil is provided at the bottom of the housing 2. The refrigeration 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 refrigeration oil supply mechanism.

[0039] A suction pipe 28 that draws in low-pressure gas refrigerant and a discharge pipe 29 that discharges compressed high-pressure gas refrigerant are provided in the housing 2. 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 rotating shaft 5 rotates, a driving force is transmitted to the orbiting scroll 4 via a crank pin 27 that is provided at the upper end of the rotating shaft 5 eccentrically in one radially outward direction (eccentric direction) from the central axis of the rotating 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 to the refrigerant circulation circuit through the discharge piping 29. The fixed scroll 3 is formed with a multi-port 32A, and the multi-port 32A is provided with a reed valve 36 attached to the end plate 31 of the fixed scroll 3 via a retainer 35. The discharge port 38 of the discharge cover 37 is also provided with a reed valve 37B 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 side of the end plate 41 of the orbiting scroll 4.

[0044] As shown in FIG. 3, the Oldham link 23 is generally ring-shaped when viewed from above. When viewed from above as 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. When viewed from above as 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 and the direction in which the two keys 23B are provided are provided so as to be perpendicular to each other. Each of the keys 23A protruding downward is inserted into a key groove 21A formed in the upper bearing 21 as shown in FIG. Each of the keys 23B protruding upward 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 key grooves 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 key grooves 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 the "Test method for compatibility with refrigerants" in JIS K2211:2009 "Refrigerating machine oils."

[0047] The refrigerant used was R290. The viscosity index improver used was a fluid in which polymethacrylate ester (PMA) was diluted with diluent oil. The blending ratio of PMA and diluent oil is as shown in Table 1, No. 1 to 3 (Sanyo Chemical Industries, Ltd.). The base oil used was polyol ester (viscosity grade ISO VG32). PMA has a structural unit represented by the above formula (I) and has an alkyl substituent with 1 to 18 carbon atoms. The concentration of the viscosity index improver in the refrigeration oil was 5 wt%. [Table 1]

[0048] The evaluation results of the viscosity index improver are shown in Figure 5. The figure shows the two-phase separation temperature of a mixture of viscosity index improver and refrigerant in a weight ratio of 10:50.

[0049] FIG. 6 shows the two-phase separation temperature of a mixture of refrigerant and refrigerant containing a viscosity index improver. In the mixture shown in the figure, the ratio of refrigerant (containing viscosity index improver No. 3) to refrigerant is 10:90 to 40:60 (weight ratio). In the figure, the curve superimposed on the bar graph is the two-phase separation temperature curve (a) of a mixture of VG32 polyol ester (VG32_POE) and R410 used in conventional refrigerant oil. In the figure, the two-dot chain line shown below the bar graph is the lower limit (b) of the compatibility region of a mixture of VG46 polyol ester (VG46_POE) and R290 used in conventional refrigerant oil. VG32_POE is a refrigerant oil for R410A, etc. VG46_POE is a candidate refrigerant oil for propane.

[0050] Viscosity index improver No. 2 separated from the R290 refrigerant over the entire 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 refrigeration system compressors rises to 120°C. For this reason, it is required that the viscosity index improver does not separate on the high temperature side. On the low temperature side, it is sufficient that it does not separate at the outside air temperature. For this reason, viscosity index improver No. 3 is suitable for use in refrigeration system compressors.

[0051] The compatibility characteristics of the refrigerating machine oil containing viscosity index improver No. 3 and the refrigerant were good. The lower limit of the compatibility region (lower temperature side two-phase separation temperature) of the refrigerating machine oil containing viscosity index improver No. 3 was expanded by about 10 to 15°C compared to when No. 3 alone was mixed with R290 refrigerant. It is expected that the compatibility region will tend to narrow as the concentration of the viscosity index improver is increased. The mixing ratio of the refrigerating machine oil to the refrigerant had almost no effect on the two-phase separation temperature.

[0052] It was confirmed that the mixture of refrigeration 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 the mixture of refrigeration oil and refrigerant used in conventional refrigeration equipment, and also maintains the same compatibility characteristics (see the lower limit of the compatibility range (b) in Figure 6). From the above, it was confirmed that the mixture of refrigeration oil containing viscosity index improver No. 3 and R290 refrigerant can be used within the operating temperature range of conventional refrigeration equipment.

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

[0054] Table 2 shows the test conditions and the results. For reference, Table 2 also lists the acid value, kinematic viscosity, and viscosity index (VI) of base oils with 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] [Table 2]

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

[0057] For base oils without added viscosity index improver (samples No. 1, 2, 7, and 8), the higher the viscosity grade, the higher the viscosity index was. By adding a viscosity index improver to a base oil with a viscosity grade of ISO VG32, the viscosity index of the refrigeration oil was improved. The viscosity index also increased as the concentration of the viscosity index improver increased. By adding 5 wt% viscosity index improver (PMA 3 wt%), the viscosity index was approximately 10% higher than the base oil before addition. This was approximately 5% higher than the viscosity index of ISO VG46.

[0058] As the concentration of the viscosity index improver increased, the kinematic viscosity at 40°C and 100°C increased. In sample No. 5, which had a viscosity index improver concentration of 10 wt% (PMA 6 wt%), the kinematic viscosity at 40°C and 100°C was close to that of ISO VG46, even though ISO VG32 base oil was used. The kinematic viscosity at 40°C was lower than that of ISO VG46 base oil up to the 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 can be made equal to or higher than that of ISO VG46. Refrigeration oil containing 10 wt% (PMA 6 wt%) or less of viscosity index improver (sample No. 5) can start up at a lower kinetic viscosity than ISO VG46, and during operation, it shows a kinetic viscosity equal to that of ISO VG46. Refrigeration oil containing 5 wt% (PMA 3 wt%) of viscosity index improver (sample No. 4) can start up at a kinetic viscosity about 25% lower than ISO VG46, and can operate at a kinetic viscosity about 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 the figure, the horizontal axis shows the viscosity index improver concentration (wt%), and the vertical axis shows the 40°C kinematic viscosity (mm 2 / s) or viscosity index (VI). The viscosity index improver concentrations in Figure 7 assume the use of viscosity index improver No. 3 in Table 1.

[0061] As the concentration of the viscosity index improver increases, the kinematic viscosity and viscosity index at 40°C improve almost linearly. If the concentration of the viscosity index improver is 10wt% or less (PMA 6wt%), the kinematic viscosity at low temperatures (40°C) will not become too high. If the viscosity grade of the base oil is ISO VG32, the 40°C kinematic viscosity can be reliably made lower than ISO VG46 by setting the concentration of the viscosity index improver to 1-5wt% (PMA 0.6-3wt%). If the viscosity grade of the base oil is ISO VG22, the 40°C kinematic viscosity can be made lower than ISO VG46 even if the concentration of the viscosity index improver is 5-10wt% (PMA 3-6wt%).

[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 for a refrigeration device in which propane is filled as a refrigerant, and includes an ester 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 a 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 kinetic viscosity to be maintained in the high temperature range even when a base oil with a low viscosity grade is used. The use of a base oil with a low viscosity grade allows the friction resistance at room temperature to be reduced. Since the kinetic viscosity can be maintained in the high temperature range, the oil film load capacity during operation (high temperature) is improved compared to a base oil without the addition of a 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 kinetic viscosity at start-up to be lower than that of ISO VG46 base oil, while still ensuring a kinetic viscosity equal to or higher than that of ISO VG46 during operation.

[0066] The refrigeration oil according to the second aspect of the present disclosure may be 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 incorporating 1 wt % or more of TBP, the wear resistance of the refrigeration oil is significantly improved.

[0068] A refrigeration device according to a third aspect of the present disclosure is a refrigeration device in which a refrigerant circulation circuit is configured in which a compressor (1), a condenser (12), an expansion valve (13), and an evaporator (14) are connected by main pipes (15a-15d) to circulate a refrigerant, 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 fourth aspect of the present disclosure relates to a refrigeration device in accordance with 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 according to the third or fourth aspect, wherein the compressor is a scroll compressor including an Oldham link (23) as an anti-rotation mechanism. [Explanation of symbols]

[0071] 1 Compressor (scroll compressor, scroll fluid machine) 2. Housing 3 Fixed Scroll 4 Swivel Scroll 12 Condenser 13 Expansion valve 14 Evaporator 15a~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 piping 29 Discharge piping 31 End plate 32,38 Discharge port 32A Multiport 33 Wall 35 Retainer 36 Reed valve 37 Discharge cover 37A Retainer 37B Reed valve 41 End plate 43 Wall 52 Drive bearing R1 Compressed Space

Claims

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

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

3. A refrigeration apparatus including a refrigerant circulation circuit in which a compressor, a condenser, an expansion valve, and an evaporator are connected by a main pipe to circulate a refrigerant, The compressor includes a refrigeration oil supply mechanism for supplying refrigeration oil to a sliding portion, 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, and a concentration of the polymethacrylic acid ester is 0.6 wt % or more and 6 wt % or less, The refrigeration apparatus, wherein propane is sealed as the refrigerant in the refrigerant circulation circuit.

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

5. 4. The refrigeration system according to claim 3, wherein the compressor is a scroll compressor having an Oldham link as an anti-rotation mechanism.

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