METHOD FOR PRODUCING A COOLING OIL AND LUBRICING A COMPRESSOR, AND COMPRESSOR AND ITS USE FOR A COOLING SYSTEM

Abstract

Method for producing a cooling oil and lubricating a compressor, the method comprising: a selection step of choosing a lubricating reagent that has a decomposition start temperature in a temperature range of 70 °C to 90 °C, as an additive that improves lubricating properties, if the decomposition start temperature is defined as a temperature at which a thermogravimetric change of 0.675% to 0.825% is observed; and a mixing step of mixing the selected lubricating reagent in an amount of 1 to 5 wt% with a base oil that has an ester bond in its molecular structure, and supplying the produced cooling oil to a compressor, wherein the compressor (1) comprises: an Oldham joint (23) comprising a projecting key (23A) and made of iron or an aluminium alloy; and an element (21) which is provided with a keyway (21A) into which the key (23A) is inserted and which is made of a material other than a material of the Oldham joint, wherein the element (21) consists of an aluminium alloy or iron.

Description

TECHNICAL AREA

[0001] The present invention relates to a method for producing a cooling oil and lubricating a compressor, and to a compressor and its use for a cooling system. STATE OF THE ART

[0002] A refrigeration unit contains at least one compressor, one condenser, one expansion valve, and one evaporator. In a refrigeration unit, the components are connected to each other in a closed circuit via refrigerant pipes, and a structure is used in which a mixed fluid, in which a refrigerant and a cooling oil are compatible, circulates in a closed system.

[0003] As part of countermeasures against global warming, it was essential to reduce the global warming potential (GWP) of refrigerants, and the transition to fluorocarbon (HFC) replacement refrigerants has long been complete. R410A, R32, and similar refrigerants are known as HFC refrigerants. The GWP of R32 is about one-third that of R410A.

[0004] It is assumed that HFC refrigerants are used under higher pressure than previously used chlorofluorocarbon (CFC) refrigerants or refrigerants made from partially halogenated chlorofluorocarbons (HCFCs). The pressure load in the compressor of the refrigeration unit using HFC refrigerants is high.

[0005] The cooling oil is responsible for lubricating the compressor. As described in JP 2013-108033 A, the cooling oil contains a base oil and a lubricant.

[0006] JP 2000-129275 A and JP 2017-089982 A describe cooling systems with Oldham couplings that are operated with a lubricant. According to JP 2017-089982 A, the lubricant is a polyol ester base oil to which triphenyl phosphate is added as an additive, and according to JP 2000-129275 A, it is a polyalkylene glycol with 0.05 to 5.0 wt% of a phosphorus compound.

[0007] A refrigeration oil composition according to DE 692 05 254 T2 is produced by adding 0.01 to 0.30 wt.% of a phenolic antioxidant, 0.01 to 0.30 wt.% of an amine with a melting point of -15 °C or below and a boiling point of 100 °C or above, and 0.10 to 1.0 wt.% of a phosphoric acid triester to a polyol ester base oil composed of a polyhydric alcohol and a fatty acid.

[0008] DE 691 01 680 T2 shows a phosphate compound such as tributyl phosphate as an additive to a lubricating oil with polyester base oil. BRIEF DESCRIPTION OF THE INVENTION Technical Problem

[0009] One type of compressor is the scroll compressor, which contains a fixed screw and a rotating screw. The scroll compressor incorporates an Oldham joint that allows the rotating screw to rotate while preventing it from rotating. The Oldham joint slides back and forth along a groove as the rotating screw moves.

[0010] When using HFC refrigerant in a cooling system under high load, reducing wear on the Oldham compound during low-speed operation is a concern. Specifically, an oil film is unlikely to form at low speeds, and lubrication is severely compromised. Furthermore, the low oil viscosity at high temperatures deteriorates the lubricating properties, which is problematic.

[0011] The present invention was developed in view of such circumstances, and one object of the present invention is to provide a cooling oil and a method for producing the same which are able to improve the wear resistance of an Oldham compound compared to the current level during high oil temperature and low-speed operation. Solution to the problem

[0012] The invention is defined in the claims. To solve the above problems, a method and a compressor and its use in a cooling system according to the present invention employ the following means.

[0013] According to one aspect of the present disclosure, the method of claim 1 is provided.

[0014] The additive that improves the lubricating properties decomposes upon heat, and its weight changes (decreases). Following careful investigations, the inventors defined the decomposition start temperature as a temperature at which the thermogravimetric analysis shows a decrease of 0.675% to 0.825%, preferably 0.7125% to 0.7875%, and more preferably 0.75% from an initial state. They selected the lubricating reagent based on this decomposition start temperature.

[0015] When a tribofilm forms on an Oldham compound, the change in thermogravimetric analysis (TGRA) is approximately 0.75% ± 10%. The rate of change in TGRA is obtained from a TGRA analysis graph. If the change in TGRA is too small (for example, 0.3%), it is difficult to determine the inflection point. If the change in TGRA is too large, there is a high probability that the lubricating reagent, which does not improve wear resistance, is included in the options.

[0016] According to the inventors' studies, the oil temperature during high-temperature, low-speed operation, where wear was pronounced, was between 70°C and 90°C, and the temperature of a sliding section of the Oldham compound was higher than 90°C. The lubricating reagent, which begins to decompose in this temperature range (70°C to 90°C), can function as a high-pressure lubricant or an anti-wear agent in the Oldham compound during high-temperature, low-speed operation. If the decomposition initiation temperature is too low, problems may arise regarding the chemical stability of the lubricating reagent, such as its oxidation stability. If the decomposition initiation temperature is too high, it is unlikely that a tribofilm will form on any surface of the Oldham compound during low-speed operation, and adequate lubrication performance will not be demonstrated.

[0017] In one aspect of the disclosure, the selection step may include a step of selecting a high-temperature lubricating reagent, which has a decomposition start temperature in a temperature range above 90 °C, from among the additives that improve the lubricating properties. The mixing step may include a step of mixing the selected high-temperature lubricating reagent with the base oil.

[0018] The cooling oil, which can exhibit lubricating performance over a wide temperature range, can be obtained by further mixing with the high-temperature lubricating reagent, which begins to decompose (form a tribofilm) at a higher temperature than the lubricating reagent.

[0019] According to one aspect of the present disclosure, the compressor of claim 3 is provided.

[0020] Since the Oldham joint and the keyway are made of different materials, sticking caused by the same material during sliding can be prevented.

[0021] According to one aspect of the present disclosure, the compressor is used for a cooling system. Advantageous effects of the invention

[0022] The wear resistance of the Oldham joint during operation at high oil temperature and low speed is improved by means of a cooling oil produced by selecting the appropriate lubricating reagent for the operating environment based on its decomposition start temperature, mixing the lubricating reagent, and feeding the resulting cooling oil to a compressor. This reduces the amount of wear in the Oldham joint section. BRIEF DESCRIPTION OF THE DRAWINGS Fig.Figure 1 is a sectional view showing a scroll compressor according to a first embodiment. Fig. 2 is a top view showing an Oldham joint and an upper bearing made of Fig. 1 shows. Fig. 3 is a sectional view taken at the position of a keyway of the Oldham joint. Fig. 2 is cut. Fig. Figure 4 is a block diagram of a cooling system. Fig. Figure 5 is a diagram of a thermogravimetric analysis of reagent A for reference. Fig. Figure 6 is a diagram of a thermogravimetric analysis of reagent B for reference. Fig. Figure 7 is a diagram of a thermogravimetric analysis of reagent C. Fig. Figure 8 is a diagram showing the relationship of wear depth in relation to a refrigerant and a cooling oil. Fig.Figure 9 is a diagram showing the relationship between the amount of TBP added and the wear depth. DESCRIPTION OF EXECUTION FORMS

[0023] Below, an embodiment of a method for producing a cooling oil and lubricating a compressor, the compressor and its use for a cooling system according to the present disclosure are described. [First embodiment]

[0024] The production of a cooling oil according to the present embodiment involves a selection step of selecting a lubricating reagent and a mixing step of mixing the selected lubricating reagent with a base oil. (Selection step)

[0025] In the selection step, a lubricating reagent that has a decomposition start temperature in a temperature range of 70 °C to 90 °C is selected as an additive for a cooling oil that improves the lubricating properties.

[0026] The decomposition initiation temperature is the temperature at which the weight of the lubricating reagent begins to change (decrease) due to heat. The decomposition initiation temperature of the lubricating reagent can be obtained by thermogravimetric analysis. In thermogravimetric analysis, the temperature of reactions, such as oxidation and decomposition, is determined by changing the temperature of a sample and a reference substance in the same way and measuring the electrical energy required for the change. Thermogravimetric analysis can be performed using a differential thermoanalyzer (DTA). If the decomposition initiation temperature of the reagent is published in a catalog or similar document, it can be used.

[0027] In the present embodiment, a temperature at which the amount of the weight change (decrease) of the lubricating reagent compared to an initial state is 0.675% to 0.825%, preferably 0.7125% to 0.7875% and more preferably 0.75%, is defined as the "decomposition start temperature". (Mixing step)

[0028] In the mixing step, the lubricating reagent is mixed with the base oil in an amount of 1 to 5 wt.%, and preferably 1 to 3 wt.%. A mixture of the lubricating reagent and the base oil is a cooling oil. Known base oils include polyol esters (POE), polyvinyl ethers (PVE), polyalkylene glycol (PAG), mineral oil, or the like. According to the invention, the base oil has an ester bond in its molecular structure.

[0029] Furthermore, an additive or similar substance that improves thermal stability can be added during the mixing step. (Application on compressor)

[0030] The cooling oil produced according to the embodiment is suitable for use in a scroll compressor with an Oldham connection and is supplied to it.

[0031] According to the invention, the material of the Oldham compound is iron or an aluminum alloy.

[0032] Fig. Figure 1 is a section view of the scroll compressor.

[0033] A scroll compressor (a scroll fluid machine) 1 is provided in a refrigerant circuit (cooling system) of an air conditioning device and compresses a gaseous refrigerant supplied from an evaporator to supply the gaseous refrigerant at high pressure to a condenser. As in Fig. As shown in Figure 1, the scroll compressor 1 contains a fixed screw 3 and a rotating screw 4 which rotates in relation to the fixed screw 3, in a housing 2.

[0034] The fixed screw 3 is attached to the housing 2 via an upper bearing 21 and contains a wall body 33 with a helical shape, which is erected on an end plate 31. The rotating screw 4 contains a wall body 43 with a helical shape, which is erected on an end plate 41. The wall body 33 of the fixed screw 3 and the wall body 43 of the rotating screw 4 have essentially the same shape. The rotating screw 4 is rotated 180° relative to the fixed screw 3 to cause the wall bodies 33 and 43 to interlock, thus forming several sealed compression chambers R1.

[0035] The rotating screw 4 undergoes a rotational movement relative to the fixed screw 3 in a state in which the rotation of the rotating screw 4 is limited by an Oldham connection 23.

[0036] The rotating worm 4 is turned by a motor 6, which drives the rotating worm 4. A rotating shaft 5, which is turned by the motor 6, is connected to the rotating worm 4 via a crank pin 27. The crank pin 27 is eccentrically positioned with respect to a central axis of the rotating shaft 5. The crank pin 27 is rotatably connected to a hub formed on a rear side (lower surface in the drawing) of the end plate 41 of the rotating worm 4 via a drive bushing and a drive bearing 52. The rotating shaft 5 is rotatably supported by the upper bearing 21 and a lower bearing 24, which is attached to the housing 2.

[0037] A storage area 26, in which the cooling oil (the lubricant O) is stored, is provided in a lower section of the housing 2. The lubricant O is pumped through an oil supply path 53 within the rotating shaft 5 by a pump 54, which is provided at a lower end of the rotating shaft 5, and is supplied to sliding sections of the lower bearing 24, the upper bearing 21, the drive bearing 52, which is provided around the crankpin 27, the circulating worm 4, the Oldham connection 23 and the like.

[0038] The housing 2 is equipped with a suction pipe 28, which draws in the gaseous refrigerant at low pressure, and a discharge pipe 29, which discharges the compressed gaseous refrigerant at high pressure. The suction pipe 28 and the discharge pipe 29 are connected to the refrigerant circuit of the air conditioning system (not shown).

[0039] The scroll compressor 1 described above works as follows.

[0040] When a drive current is supplied to a stator 61 of the motor 6 from a power supply not shown, a rotor 62 of the motor 6 rotates and a drive force is output to the rotating shaft 5.

[0041] When the rotating shaft 5 rotates, the driving force is transmitted to the rotating worm 4 via the crank pin 27, which is positioned at an upper end of the rotating shaft 5 such that it is radially eccentric to the central axis of the rotating shaft 5 in an outward direction (eccentric direction). Accordingly, the rotating worm 4 rotates relative to the stationary worm 3, while its rotation is prevented by the action of the Oldham connection 23.

[0042] The refrigerant flowing in from the suction pipe 28 is drawn in between the rotating screw 4 and the stationary screw 3 by the rotation of the rotating screw 4. Then, as the rotating screw 4 rotates, the volume of the compression chambers R1 between the rotating screw 4 and the stationary screw 3 decreases, thus compressing the refrigerant in the compression chambers R1.

[0043] The compressed refrigerant is discharged through the discharge pipe 29 via a discharge port 32 of the fixed screw 3 and a discharge port 38 of a discharge cover 37 into the refrigerant circuit. A multi-port 32A is formed in the fixed screw 3, and this multi-port 32A is equipped with a reed valve 36, which is attached to the end plate 31 of the fixed screw 3 by means of a holder 35. The discharge port 38 of the discharge cover 37 is also equipped with a reed valve 37B, which is attached to the discharge cover 37 by means of a holder 37A. When the pressure of the compressed refrigerant reaches a predetermined value, the refrigerant, which presses on and opens the reed valves 36 and 37B, is discharged to a condenser side of the refrigerant circuit.

[0044] The Fig. 2 and Fig. Figure 3 shows the Oldham connection 23, which is in Fig.Figure 1 shows the Oldham connection 23, which is planned for the upper bearing 21. As shown in Fig. As shown in Figure 1, the Oldham connection 23 is provided on a rear surface side of the end plate 41 of the circumferential screw 4.

[0045] As in Fig. As shown in Figure 2, the Oldham connection 23 has a substantially ring-shaped form in plan view. In plan view, as shown in Figure 2, the Oldham connection 23 has a substantially ring-shaped form. Fig. As shown in Figure 2, downward-projecting keyways 23A (side of the upper bearing 21) are provided on both the right and left sides, at the 3 o'clock and 9 o'clock positions. In the case of a top view, as shown in Figure 2, the keyways are located on the right and left sides, at the 3 o'clock and 9 o'clock positions. Fig.As shown in Figure 2, upwardly projecting keys 23B (side of the orbiting worm 4) are provided on both the top and bottom surfaces, at the 6 o'clock and 12 o'clock positions. Specifically, one direction in which two keys 23A are provided and one direction in which two keys 23B are provided are perpendicular to each other. As shown in Fig. As shown in Figure 3, each of the downward-projecting keys 23A is inserted into a keyway 21A formed in the upper bearing 21. Each of the upward-projecting keys 23B, although not shown, is inserted into a keyway formed in the end plate 41 of the rotating worm 4.

[0046] The upper bearing 21 and the worm gear 4 can be made of a different material than the Oldham joint 23. If the material of the Oldham joint 23 is iron, the material of the keyways formed in the upper bearing 21 and the worm gear 4 is aluminum. If the material of the Oldham joint 23 is aluminum, the material of the keyways formed in the upper bearing 21 and the worm gear 4 is iron.

[0047] Fig. Figure 4 is a block diagram of the cooling system, which includes the scroll compressor 1. As shown in Fig. As shown in Figure 4, the cooling system includes, for example, the scroll compressor 1, a condenser 12, an expansion valve 13 and an evaporator 14. These components are connected to each other via pipes 15a to 15d, which allow the refrigerant flow to transfer the refrigerant.

[0048] In the refrigeration system, the condenser 12 condenses and liquefies the high-temperature, high-pressure refrigerant gas to dissipate heat. The expansion valve 13 adiabatically expands the high-temperature, high-pressure liquid refrigerant that has passed through the condenser 12 to reduce the pressure. The evaporator 14 evaporates the low-temperature, low-pressure liquid refrigerant that has passed through the expansion valve 13 to absorb heat. Finally, the scroll 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 scroll compressor 1 is then fed to the condenser 12.The heat transfer from the evaporator 14 to the condenser 12 can be realized and indoor air conditioning (heating and cooling) is possible by circulating the refrigerant as a heat transfer medium in such a way in the closed system.

[0049] The cooling oil supplied to the scroll compressor 1 circulates in the cooling system, which contains the evaporator 14, the expansion valve 13, and the condenser, in a state where the cooling oil is mixed with the refrigerant, and returns to the compressor. The cooling oil in the cooling system remains in a sealed state with the refrigerant for the duration of the cooling system's operation, requiring almost no replacement.

[0050] In the actual machine environment, the temperature of the cooling oil near the Oldham joint 23 during high-temperature, low-speed operation is 80 °C ± 10 °C. The lubricating reagent, with a decomposition start temperature in the temperature range of 70 °C to 90 °C, forms a low-shear tribofilm on a sliding surface of the Oldham joint during low-speed operation to reduce the coefficient of friction of the sliding section. Consequently, the lubricating reagent, with its decomposition start temperature in the temperature range of 70 °C to 90 °C, has the effect of reducing the amount of wear. [Second embodiment]

[0051] In the present embodiment, the selection step may further include a step of selecting a high-temperature lubricating reagent. The mixing step may further include a step of mixing the selected high-temperature lubricating reagent with the base oil.

[0052] The high-temperature lubricating reagent is one or more additives with a decomposition start temperature in a temperature range of more than 90 °C selected from additives that act as high-pressure agents or lubricating reagents.

[0053] The high-temperature lubricating reagent in an amount of 0.1 to 5 wt.% and preferably 0.1 to 3 wt.% is mixed with the base oil. [Test](Selection of the lubricating reagent)

[0054] The decomposition start temperatures of the following reagents A to C were obtained by thermogravimetric analysis. A: Triphenyl phosphate (TPP) B: Ethyldiethylphosphonoacetate (JC-224) C: Tributyl phosphate (TBP)

[0055] The results are in the Fig. 5, Fig. 6 to Fig. 7 and Table 1 shown.

[0056] Fig. Figure 5 is a diagram showing a change in the thermogravimetric analysis of reagent A (TPP). Fig. Figure 6 is a diagram showing a change in the thermogravimetric analysis of reagent B (JC-224). Fig. Figure 7 is a diagram showing a change in the thermogravimetric analysis of reagent C (TBP). In the Fig. 5, Fig. 6 to Fig. 7 is the horizontal axis time (minutes), the left vertical axis is a change in thermogravimetry (%) and the right vertical axis is temperature (°C).

[0057] Table 1 shows the temperatures obtained from the thermogravimetric data following a 0.75% change in thermogravimetric analysis. Fig. 5, Fig. 6 and Fig. 7 taken from and described as the decomposition start temperatures. [Table 1] reagent Decomposition start temperature (°C) Decomposition temperature (°C) Acid number (mgK OH / g) Pour point or melting point (°C) A 190 300 0.03 or less 47 to 53 (solid) B 165 225 0.03 or less liquid C 80 210 0.07 or less liquid

[0058] According to Table 1, reagents A, B, and C exhibited low acid numbers. The difference between the decomposition temperatures of reagents B and C was only a few degrees Celsius, but the difference in the decomposition start temperature was approximately 85 °C. (Wear resistance)

[0059] Wear resistance was investigated by sliding a fixed part and a rotating part according to JIS K7218 using a ring-on-disc friction test device in a refrigerant atmosphere.

[0060] The stationary part was made of ADC12, an Al-Si-Cu alloy, and its surface was coated with hard aluminite. The rotating part was made of cast iron with lamellar graphite (FC200).

[0061] In the actual machine, wear of the Oldham joint is observed at high oil temperature and low speed. The test conditions were set according to the operating conditions of the actual machine.

[0062] Table 2 shows the test conditions, of which tests 1 and 3 are given for reference and test 2 is given to illustrate the invention. [Table 2] Object Test 1 Test 2 Test 3 Refrigerant R410A* 1 R32* 2 Lubrication environment POE Oil No. 1 Oil Bath POE Oil No. 2 Oil Bath Additive - TBP0 to 5 wt.% JC-2245 wt.% load 950 N speed 2000 rpm Test period 4,5 h Test start oil temperature 86 °C Pressure 1.05 MPaG *1: Refrigerant in which R32 and R125 (pentafluoroethane) are mixed in equal amounts *2: Difluoromethane

[0063] The results are in the Fig. 8 and Fig. 9 shown. Fig. Figure 8 is a diagram showing the relationship between wear depth and the refrigerant and cooling oil. Fig. Figure 9 is a diagram showing the relationship between the amount of TBP added and the wear depth of the solid part during Test 3. In the diagram, the horizontal axis represents the amount of TBP added (wt%) and the vertical axis represents the wear depth (µm) of the solid part.

[0064] According to Fig. 8. The wear depth of the TBP (with 1 wt% and 5 wt% added) in Test 2 was approximately 3 µm and was the lowest compared to Tests 1 and 3. Regarding the amount of wear in Test 3, where JC-224 was added, the amount of wear was less than in Test 2, where TBP was not added, but greater than in Test 1, which used refrigerant R410A.

[0065] According to Fig.In Test 2, where TBP was added, the effect of improved wear resistance was observed when the added amount of TBP was set to 1% or more. In a test where 1 to 5 wt% TBP was added, the wear depth of the solid part was approximately 2.5 µm to 3.2 µm. Meanwhile, in tests where 0.75 wt% and 0.25 wt% TBP were added, the wear depths of the solid parts were 20 µm and 19 µm, respectively. Based on the above results, it was confirmed that the wear resistance was significantly improved by adding 1 wt% or more of TBP.

[0066] Furthermore, according to Fig.In test 3, where JC-224 was added, the wear depth of the solid part was 55 µm. In test 1, where refrigerant R410A was used and no additive was added, the wear depth of the solid part was 43 µm, and no effect of improved wear resistance was observed with an oil to which 5 wt% of JC-224 was added.

[0067] Both JC-224 and TBP are phosphorus compounds, but they have different decomposition initiation temperatures. The decomposition initiation temperature of TBP is equal to or lower than the test start oil temperature of this test. Therefore, TBP is expected to decompose during the test to form a tribofilm, while JC-224, with a decomposition initiation temperature approximately 85°C higher than the test start oil temperature of this test, is not expected to form a tribofilm. REFERENCE MARK LIST 1 Scroll compressor (scroll fluid machine) 2 cases 3 fixed snail 4 rotating screws 12 Capacitor 13 Expansion valve 14 evaporators 15a to 15d pipe 21 upper bearings 21A Keyway 23 Oldham connection 23A Keyway 23B Keyway 24 lower bearings 26 Memory area 27 crank pins 28 Intake manifold 29 Delivery pipe 31 End plate 32, 38 Delivery connection 32A multiple connection 33 wall bodies 35 holders 36 reed valve 37 Delivery Coverage 37A Holder 37B Reed valve 41 End plate 43 wall bodies 52 drive bearings R1 Compression chamber

Claims

[1] Method for producing a cooling oil and lubricating a compressor, the method comprising: a selection step of choosing a lubricating reagent that has a decomposition start temperature in a temperature range of 70 °C to 90 °C, as an additive that improves lubricating properties, if the decomposition start temperature is defined as a temperature at which a thermogravimetric change is from 0.675% to 0.825%; and a mixing step of mixing the selected lubricating reagent in an amount of 1 to 5 wt% with a base oil that has an ester bond in its molecular structure, and supplying the produced cooling oil to a compressor, wherein the compressor (1) comprises: an Oldham joint (23) comprising a projecting key (23A) and made of iron or an aluminium alloy; and an element (21) which is provided with a keyway (21A) into which the key (23A) is inserted and which is made of a material other than a material of the Oldham joint, wherein the element (21) consists of an aluminium alloy or iron. [2] Method according to claim 1, wherein the selection step includes a step of selecting a high-temperature lubricating reagent that exhibits a decomposition start temperature in a temperature range of more than 90 °C from the additives that improve the lubricating properties, and The mixing step includes a step of mixing the selected high-temperature lubricating reagent with the base oil. [3] Compressor (1) to which a cooling oil produced by a production process is supplied, the compressor (1) comprising: an Oldham joint (23) comprising a projecting key (23A) and made of iron or an aluminium alloy; and an element (21) which is provided with a keyway (21A) into which the key (23A) is inserted and which is made of a material other than a material of the Oldham joint, wherein the element (21) consists of an aluminium alloy or iron, and the production process includes: a selection step of choosing a lubricating reagent that has a decomposition start temperature in a temperature range of 70 °C to 90 °C, as an additive that improves lubricating properties, if the decomposition start temperature is defined as a temperature at which a thermogravimetric change is from 0.675% to 0.825%; and a mixing step of mixing the selected lubricating reagent in an amount of 1 to 5 wt.% with a base oil that has an ester bond in the molecular structure. [4] Use of the compressor (1) according to claim 3 for a cooling system.

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