JP2002180075A - Refrigeration oil for carbon dioxide refrigerant and fluid composition for refrigeration - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sufficiently wide composition range showing compatibility when mixed with a carbon dioxide refrigerant under a low temperature condition, and excellent in lubricity and stability. Provided are a refrigerating machine oil for a carbon dioxide refrigerant that can sufficiently prevent poor lubrication of a refrigerant compressor when used and can obtain a sufficiently high heat exchange rate, and a fluid composition for a refrigerating machine using the same. thing. SOLUTION: The following general formula (1): The following general formula (1): R ¹ — (OR ² ) _n —OH (1) wherein R ¹ is a hydrogen atom, an alkyl group having 1 to 2 carbon atoms or Represents an acyl group having 2 to 3 carbon atoms, and R ² represents 2 to 3 carbon atoms.
4 represents an alkylene group, and n has a number average molecular weight of 500 to
Refrigeration oil for carbon dioxide refrigerant, characterized by containing a polyalkylene glycol represented by the following formula:

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION Due to the problem of depletion of the ozone layer in recent years, CF conventionally used as a refrigerant for refrigeration equipment
C (chlorofluorocarbon) and HCFC (hydrochlorofluorocarbon) are subject to regulation, and HFC (hydrofluorocarbon) is being used as a refrigerant instead. However, such HFC refrigerants also have problems such as high global warming ability. Therefore, the use of natural refrigerants such as carbon dioxide, ammonia, and hydrocarbons as alternative refrigerants instead of these chlorofluorocarbon refrigerants is being studied.

Among them, carbon dioxide (CO ₂ ) is harmless to the environment and is excellent in safety, and it has been used as a refrigerant for refrigerators and the like, although it has not been mainstream so far. In recent years, its application as a refrigerant for a car air conditioner, a room air conditioner, or a hot water supply heat pump using an open type compressor or a closed type electric compressor has been studied.

As a base material of a refrigerating machine oil for a carbon dioxide refrigerant, use of a polyalkylene glycol (PAG) as disclosed in, for example, JP-A-10-46169 has been studied.

[0004]

By the way, refrigeration equipment generally has a refrigerant circulation system composed of a refrigerant compressor, a gas cooler, an expansion mechanism, an evaporator, and the like. In addition to lubricity for lubricating the refrigerant compressor, the refrigerating machine oil used in the compressor has a flow path (circulation path) when discharged together with the refrigerant from the refrigerant compressor.
The refrigerant compatibility and low-temperature fluidity to ensure the property of returning to the refrigerant compressor through the passage (hereinafter referred to as "oil returnability"), and stability to various substances such as a wide range of temperature changes and refrigerant are required. You. In particular, due to the mechanism of the refrigerant compressor, the phenomenon that refrigeration oil is discharged from the refrigerant compressor to the flow path is inevitable, and controls the composition of the mixture of refrigerant and refrigeration oil at a predetermined position in the refrigerant circulation system. Since it is very difficult, it is desirable to use a refrigerating machine oil that exhibits refrigerant compatibility at a wide range of temperature and composition.

[0005] However, conventional refrigerating machine oil for carbon dioxide refrigerant has a certain degree of compatibility under relatively high temperature conditions, but does not always have sufficient compatibility, such as a narrow composition range showing compatibility under low temperature conditions. When such a refrigerating machine oil is used for the refrigerating machine, the refrigerating machine oil is contained in a portion where one of the carbon dioxide refrigerant and the refrigerating machine oil has a high ratio and a low temperature, such as an expansion mechanism or an evaporator in the refrigerant circulation system. As a result, the amount of refrigerating machine oil in the refrigerant compressor is reduced, and poor lubrication is likely to occur, and heat exchange in the evaporator is more likely to be hindered by the refrigerating machine oil. In such refrigerating machine oil, PAG
Can be reduced in viscosity to improve the oil return property, but in that case, the lubricating property inherent in the refrigerating machine oil becomes insufficient, and this does not solve the fundamental problem.

The present invention has been made in view of the above-mentioned problems of the prior art, and has a sufficiently wide composition range showing compatibility when mixed with a carbon dioxide refrigerant under a low temperature condition, and has lubricity and stability. Refrigeration oil for carbon dioxide refrigerant, which sufficiently prevents poor lubrication of the refrigerant compressor and can obtain a sufficiently high heat exchange rate when used in a refrigerator for carbon dioxide refrigerant; and An object of the present invention is to provide a fluid composition for a refrigerator using the same.

[0007]

Means for Solving the Problems The present inventors have made intensive studies to achieve the above object, and as a result, when the polyalkylene glycol having a specific structure is contained in refrigerating machine oil, the above object has been solved. The inventors have found that the present invention has been completed.

That is, the refrigerating machine oil for carbon dioxide refrigerant of the present invention has the following general formula (1): R ^1- (OR ² ) _n -OH (1) wherein R ¹ is a hydrogen atom and has 1 to 1 carbon atoms. 2 represents an alkyl group or an acyl group having 2 to 3 carbon atoms, and R ² represents 2 to 3 carbon atoms.
4 represents an alkylene group, and n represents a number average molecular weight of 500 of the polyalkylene glycol represented by the general formula (1).
A polyalkylene glycol represented by an integer of up to 3000].

The fluid composition for a refrigerator according to the present invention is characterized by containing the refrigerant oil for a carbon dioxide refrigerant of the present invention and a carbon dioxide refrigerant.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

The refrigeration oil for carbon dioxide refrigerant of the present invention has the following general formula (1): R ^1- (OR ² ) _n -OH (1) wherein R ¹ is a hydrogen atom, Represents an alkyl group or an acyl group having 2 to 3 carbon atoms, and R ² represents 2 to 3 carbon atoms.
4 represents an alkylene group, and n represents a number average molecular weight of 500 of the polyalkylene glycol represented by the general formula (1).
A polyalkylene glycol represented by an integer of ~ 3000], and a composition range that shows compatibility when mixed with a carbon dioxide refrigerant under low-temperature conditions is sufficient. Wide and excellent in lubricity and stability. By using the carbon dioxide refrigerant refrigerating machine oil of the present invention for a carbon dioxide refrigerant refrigerating machine, it is possible to sufficiently prevent poor lubrication of the refrigerant compressor and to obtain a sufficiently high heat exchange rate.

As shown in FIG. 1, the refrigeration / air-conditioning apparatus has a refrigerant circulation system in which a refrigerant compressor 1, a gas cooler 2, an expansion mechanism 3 (capillary, expansion valve, etc.), and an evaporator 4 are sequentially connected by a flow path 5. Generally, in such a refrigerant circulation system, first, the refrigerant compressor 1
The high-temperature (usually 70 to 120 ° C) refrigerant discharged into the
The gas cooler 2 turns the fluid into a high-density fluid (such as a supercritical fluid). Subsequently, the refrigerant is liquefied by passing through the narrow flow path of the expansion mechanism 3, and is further vaporized by the evaporator 4 to a low temperature (normally −40 to 0 ° C.).

Here, a mixed state of a mixture of carbon dioxide refrigerant and refrigerating machine oil (hereinafter, simply referred to as a “mixture”) circulating in the refrigerant circulation system will be described with reference to FIG. FIG. 2 is a graph showing an example of the correlation between the concentration of the refrigerating machine oil in the mixture and the separation temperature. The two curves in FIG. 2 show the lower limit value of the temperature at which the refrigerant and the refrigerating machine oil show compatibility at a predetermined composition, the solid line is the refrigerating machine oil for carbon dioxide refrigerant of the present invention, and the dashed line is the conventional one. This is for refrigerant oil for carbon dioxide refrigerant. The upper side of the curve is the compatible region, and the lower side is the incompatible region. FIG.
Points a to d in the graph show the relationship between the concentration of the refrigerating machine oil in the mixture and the temperature at the points a to d in the flow path in FIG. 1, respectively.

In the refrigerant compressor 1 shown in FIG. 1, a small amount of carbon dioxide refrigerant and a large amount of refrigerating machine oil coexist under high temperature conditions (usually 70 to 120 ° C.). The refrigerant discharged from the refrigerant compressor 1 to the flow path 5 is in a gaseous state and has a small amount (usually 1 to 1).
(0%) of refrigeration oil as a mist, and a small amount of refrigerant is dissolved in this mist-like refrigeration oil (point a in FIG. 2). Next, in the gas cooler 2, the gaseous refrigerant is compressed into a high-density fluid, and a relatively large amount of refrigerant and a small amount of refrigerating machine oil coexist under a relatively high temperature (usually around 50 to 70 ° C). (Point b in FIG. 2). Further, a mixture of a large amount of the refrigerant and a small amount of the refrigerating machine oil is sequentially sent to the expansion mechanism 3 and the evaporator 4 and rapidly cooled (usually at -40 to 0 ° C.).
(Points c and d in FIG. 2), and the refrigerant is returned to the refrigerant compressor 1 again.

In such a refrigeration cycle, it is desirable that a large amount of refrigerant and a small amount of refrigerating machine oil be in a compatible state over the entire temperature range (for example, -40 to 70 ° C.) in the system. According to the study of, for example, point a in FIG.
Under high temperature conditions such as between -b, even if the refrigerant and the refrigerating machine oil are not in a compatible state, the viscosity of the refrigerating machine oil is reduced and the fluidity is improved, and the refrigerating machine oil separated by the flow of the refrigerant flows together. Therefore, even in the case of conventional refrigerating machine oil for carbon dioxide refrigerant, the oil return property does not often cause a problem. However, as shown in FIG. 2, most or all of the process under a low temperature condition (between points cd in FIG. 2) in which a mixture of the refrigerant and the refrigerating machine oil is sent to the evaporator 4 via the expansion mechanism 3. Is performed in the incompatible region (region below the broken line), the refrigerating machine oil, which has a high viscosity under low temperature conditions and cannot be caused to flow by the flow of the refrigerant, stagnates, and as a result, the refrigerant compressor Poor lubrication and hindrance to heat exchange in the evaporator are likely to occur.

On the other hand, the refrigerating machine oil for carbon dioxide refrigerant of the present invention has a sufficiently wide composition range showing compatibility when mixed with the carbon dioxide refrigerant under a low temperature condition. The ratio of the portion performed in the compatible region (region above the solid line) in the process between d and d can be sufficiently increased. Usually, even when the refrigerant and the refrigerating machine oil are in a phase separated state, a predetermined amount of the refrigerant dissolves in the refrigerating machine oil and the viscosity of the refrigerating machine oil decreases. The saturation solubility of carbon dioxide under is high enough,
Since the viscosity of the refrigerating machine oil is sufficiently reduced due to the dissolution of the refrigerant, even when a part of the process between the points c and d in FIG. 2 is performed in the incompatible region, the oil return is sufficiently high. Character can be obtained. Therefore, it is possible to sufficiently prevent the refrigerating machine oil from remaining in the expansion mechanism and the evaporator, and the resulting poor lubrication of the refrigerant compressor and hindrance to heat exchange in the evaporator.

JP-A-10-46169 discloses a refrigerating machine oil for carbon dioxide refrigerant containing a polyalkylene glycol, and discloses that such refrigerating machine oil dissolves a predetermined amount of carbon dioxide refrigerant. However, the publication does not disclose temperature conditions for dissolving a carbon dioxide refrigerant in refrigerating machine oil. According to the study of the present inventors based on the correlation between the saturated vapor pressure and the dissolved amount of the carbon dioxide refrigerant,
The measurement result of the dissolved amount of the carbon dioxide refrigerant described in the publication is based on a temperature condition of 15 ° C. or higher. As will be described later, the above-mentioned conventional refrigerating machine oil has a narrow composition range showing compatibility under low-temperature conditions, and also has a small viscosity lowering effect due to dissolution of a refrigerant in an incompatible region. It is very difficult to prevent poor lubrication of the refrigerant compressor and hindrance of heat exchange in the evaporator by using the above method.

The polyalkylene glycol used in the present invention has a structure represented by the above general formula (1), wherein R ¹ in the formula (1) is a hydrogen atom, an alkyl group having 1 to 2 carbon atoms or Represents an acyl group having 2 to 3 carbon atoms. The alkyl group or acyl as R ¹ may be linear or branched, and specific examples include a methyl group, an ethyl group, an acetyl group, and an ethanoyl group. . Among these atoms or groups represented by R ¹ , a hydrogen atom, a methyl group or an acetyl group is preferred from the viewpoint of compatibility with a carbon dioxide refrigerant. When R ¹ is an alkyl group having more than 2 carbon atoms or an acyl group having more than 3 carbon atoms, the composition range showing compatibility with a carbon dioxide refrigerant under low-temperature conditions is narrowed, and Poor lubrication and heat exchange in the evaporator are likely to occur.

In the general formula (1), R ² represents an alkylene group having 2 to 4 carbon atoms. As such an alkylene group, specifically, for example, an ethylene group (—CH ₂ C
H ₂ —), a propylene group (—CH (CH ₃ ) CH ₂ —),
Trimethylene group _{(-CH 2 CH 2 CH 2 -} ), butylene _{(-CH (CH 2 CH 3)} CH 2 -), tetramethylene _{(-CH 2 CH 2 CH 2 CH} 2 -) and the like. Among these alkylene groups, an ethylene group, a propylene group, a butylene group, and a tetramethylene group are preferable.

Further, in the above general formula (1), n is OR ²
Number of repeating oxyalkylene groups represented by (degree of polymerization)
Wherein the number average molecular weight of the polyalkylene glycol represented by the formula (1) is 500 to 3,000, preferably 600 to 2,000, and more preferably 600 to 15.
00 and n is an integer such that the number average molecular weight of the polyalkylene glycol satisfies the above condition. If the number average molecular weight is less than the above upper limit, the lubricity in the coexistence of a carbon dioxide refrigerant tends to be insufficient. On the other hand, if the number average molecular weight exceeds the upper limit, the composition range showing compatibility with carbon dioxide refrigerant under low temperature conditions becomes narrower,
Poor lubrication of the refrigerant compressor and inhibition of heat exchange in the evaporator are likely to occur. In the polyalkylene glycol, the ratio ( _Mw / _Mn ) of the weight average molecular weight ( _Mw ) to the number average molecular weight ( _Mn ) is preferably 1.00 to 1.20. When M _w / M _n exceeds 1.20, the compatibility between the carbon dioxide refrigerant and the refrigerating machine oil tends to be insufficient.

Further, in the polyalkylene glycol represented by the above general formula (1), the proportion of the ethylene group in the alkylene group represented by R ² is preferably 80 mol% or less, more preferably 60 mol%. %, More preferably 50 mol% or less, particularly preferably 40 mol% or less.
When the proportion of the ethylene group in the alkylene group represented by R ² exceeds 80 mol%, the refrigerating machine oil tends to be solid at room temperature or its pour point tends to be high.

The kinematic viscosity at 100 ° C. of polyalkylene glycol represented by the above general formula (1) is preferably 5 to 20 mm ² / s, more preferably 6~18mm ² /
s, more preferably 7 to 16 mm ² / s, even more preferably 8 to 15 mm ² / s, and most preferably 10 to 10 mm ² / s.
15 mm ² / s. Kinematic viscosity at 100 ° C is 5m
If it is less than m ² / s, the lubricity in the presence of carbon dioxide tends to be insufficient. On the other hand, if the kinematic viscosity at 100 ° C. exceeds 20 mm ² / s, the composition range showing compatibility with the carbon dioxide refrigerant under low-temperature conditions becomes narrow, resulting in poor lubrication of the refrigerant compressor and inhibition of heat exchange in the evaporator. Is more likely to occur. In addition, 4 of the polyalkylene glycol
The kinematic viscosity at 0 ° C. is preferably 10 to 200 mm ²
/ S, more preferably from 20 to 150 mm ² / s.
If the kinematic viscosity at 40 ° C. is less than 10 mm ² / s, the lubricity and the hermeticity of the compressor tend to decrease.
If it exceeds 00 mm ² / s, the composition range showing compatibility with carbon dioxide refrigerant under low temperature conditions becomes narrow, and poor lubrication of the refrigerant compressor and inhibition of heat exchange in the evaporator tend to occur.

The pour point of the polyalkylene glycol represented by the general formula (1) is preferably -10 ° C or lower, more preferably -20 to -50 ° C. When a polyalkylene glycol having a pour point exceeding −10 ° C. is used, the refrigerating machine oil tends to be easily solidified in a refrigerating cycle at a low temperature.

The polyalkylene glycol according to the present invention can be synthesized by a conventionally known method ("Alkylene oxide polymer", Mitsuta Shibata et al., Kaibundo, issued November 20, 1990, etc.), for example, an alcohol (R ¹ -OH; R ¹ is the general formula (1) by addition polymerization of more than one alkylene oxide to a representative) same definition as R ¹ in the general formula ( The polyalkylene glycol represented by 1) is obtained. Here, when two or more different alkylene oxides are used in the production process of the polyalkylene glycol, the obtained polyalkylene glycol may be any of a random copolymer and a block copolymer. A block copolymer is preferred because it tends to be excellent in stability, and a random copolymer is preferred because it tends to be more excellent in low-temperature fluidity.

In the production of the polyalkylene glycol represented by the above general formula (1), an alkylene oxide such as propylene oxide causes a side reaction in the production process and causes an unsaturated group such as an allyl group in the molecule. May be formed. When unsaturated groups are formed in the polyalkylene glycol molecule, the thermal stability of the polyalkylene glycol itself decreases, a polymer is formed to form sludge, or the antioxidant (antioxidant) decreases. A phenomenon such as the formation of peroxide is likely to occur. In particular, when a peroxide is generated, it is decomposed to generate a compound having a carbonyl group, and the compound having a carbonyl group reacts with a carbon dioxide refrigerant to generate an acid amide, which tends to cause clogging of the capillary.

Therefore, as the polyalkylene glycol according to the present invention, those having a low degree of unsaturation derived from unsaturated groups and the like are preferable, and specifically 0.04 meq / g.
Or less, more preferably 0.03 meq / g or less, and most preferably 0.02 meq / g or less. The peroxide value is 10.0 m
eq / kg or less, preferably 5.0 meq /
kg or less, more preferably 1.0 meq / k.
g is most preferred. Further, the carbonyl value is preferably not more than 100 ppm by weight,
Weight ppm or less, more preferably 20 weight p
pm or less.

The degree of unsaturation, peroxide value and carbonyl value according to the present invention refer to the values measured by the standard oil and fat analysis test established by the Japan Oil Chemists' Society. That is, the degree of unsaturation according to the present invention means that the whisper solution (I
Cl-acetic acid solution), leave in the dark,
The excess ICL is reduced to iodine, the iodine content is titrated with sodium thiosulfate to calculate the iodine value, and this iodine value is converted to a vinyl equivalent (meq / g); a peroxide value according to the present invention. The term refers to a value (meq / kg) obtained by adding potassium iodide to a sample, titrating the free iodine generated with sodium thiosulfate, and converting the free iodine to the number of milliequivalents per 1 kg of the sample; Such a carbonyl value means that a sample is treated with 2,4-dinitrophenylhydrazine to produce a chromogenic quinoid ion, and the absorbance at 480 nm of the sample is measured.
It is a value (ppm by weight) converted to the amount of carbonyl based on a calibration curve previously determined using cinnamaldehyde as a standard substance.

In the present invention, in order to obtain a polyalkylene glycol having a low degree of unsaturation, a low peroxide value and a low carbonyl value, the reaction temperature when reacting propylene oxide is 120 ° C. or lower (more preferably 110 ° C. or lower).
It is preferable that If an alkaline catalyst is used in the production, an inorganic adsorbent such as activated carbon, activated clay, bentonite, dolomite, or aluminosilicate may be used to remove the alkali catalyst.
The degree of unsaturation can be reduced. In addition, when producing or using the polyalkylene glycol, contact with oxygen can be avoided as much as possible, and an increase in peroxide value or carbonyl value can be prevented by adding an antioxidant.

The refrigerating machine oil for a carbon dioxide refrigerant of the present invention contains the polyalkylene glycol having the above-described structure. Even when the polyalkylene glycol alone is used alone, it has low-temperature fluidity and lubricity. And have sufficiently high stability, and have excellent properties such as having a sufficiently wide compatibility region with respect to carbon dioxide refrigerant, but may be added with other base oils and additives described below as necessary. Good. Incidentally, the content of the polyalkylene glycol in the refrigerator oil for carbon dioxide refrigerant of the present invention,
It is not particularly limited as long as the above excellent properties are not impaired, but is preferably 50% by mass or more, more preferably 70% by mass or more, and more preferably 80% by mass or more based on the total amount of the refrigerating machine oil. Preferably 90
It is particularly preferred that the content be at least 10% by mass. When the content of the polyalkylene glycol represented by the general formula (1) is less than 50% by mass, one of various performances such as lubricating oil of a refrigerating machine oil, compatibility with a refrigerant, and thermal and chemical stability is reduced. It tends to be insufficient.

In the refrigerating machine oil for carbon dioxide refrigerant of the present invention, examples of the base oil usable together with the above-mentioned polyalkylene glycol include mineral base oils, olefin polymers, naphthalene compounds, and hydrocarbon base oils such as alkylbenzenes. Esters, ketones, polyphenyl ethers,
Silicone, polysiloxane, perfluoroether,
Oxygen-containing synthetic oils such as polyvinyl ethers and polyglycols other than the polyalkylene glycols according to the present invention, and the like. As the oxygen-containing synthetic oil, among the above, polyvinyl ether and / or polyglycol other than the polyalkylene glycol according to the present invention are preferably used.

As described above, the refrigerating machine oil for carbon dioxide refrigerant of the present invention contains the above-mentioned polyalkylene glycol and, if necessary, a hydrocarbon-based oil and / or a synthetic oil containing oxygen. These are used as base oils. Although the refrigerating machine oil for carbon dioxide refrigerant of the present invention can be suitably used even if no additive is added, various additives described later can be blended and used as needed.

In order to further improve the wear resistance and load bearing capacity of the refrigerator oil of the present invention, phosphate esters, acidic phosphate esters, amine salts of acidic phosphate esters, chlorinated phosphate esters, phosphite esters And at least one phosphorus compound selected from the group consisting of phosphorothionates. These phosphorus compounds are esters of phosphoric acid, phosphorous acid, or thiophosphoric acid with alkanol or polyether-type alcohols or derivatives thereof.

Specifically, for example, phosphate esters include tributyl phosphate, tripentyl phosphate, trihexyl phosphate, triheptyl phosphate, trioctyl phosphate, trinonyl phosphate, tridecyl phosphate, triundecyl phosphate, and tridodecyl phosphate. , Tritridecyl phosphate, tritetradecyl phosphate, tripentadecyl phosphate, trihexadecyl phosphate, triheptadecyl phosphate, trioctadecyl phosphate, trioleyl phosphate, triphenyl phosphate, tricresyl phosphate, trixylenyl phosphate, cresyl diphenyl Phosphates, xylenyl diphenyl phosphate, etc .; Monobutyl acid phosphate, monopentyl acid phosphate, monohexyl acid phosphate, monoheptyl acid phosphate, monooctyl acid phosphate, monononyl acid phosphate, monodecyl acid phosphate, monoundecyl acid phosphate, monododecyl acid phosphate, monotridecyl acid Phosphate, monotetradecyl acid phosphate, monopentadecyl acid phosphate, monohexadecyl acid phosphate, monoheptadecyl acid phosphate, monooctadecyl acid phosphate,
Monooleyl acid phosphate, dibutyl acid phosphate, dipentyl acid phosphate, dihexyl acid phosphate, diheptyl acid phosphate, dioctyl acid phosphate, dinonyl acid phosphate, didecyl acid phosphate, diundecyl acid phosphate, didodecyl acid, didodecyl acid acid , Ditetradecyl acid phosphate, dipentadecyl acid phosphate, dihexadecyl acid phosphate, diheptadecyl acid phosphate, dioctadecyl acid phosphate, dioleyl acid phosphate, etc .; Acid esters of methylamine, ethylamine, , Butylamine, pentylamine, hexylamine, octylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine, dihexylamine, diheptylamine, dioctylamine, trimethylamine, triethylamine, tripropylamine,
Salts with amines such as tributylamine, tripentylamine, trihexylamine, triheptylamine, trioctylamine and the like; chlorinated phosphates include tris-dichloropropyl phosphate, tris-chloroethyl phosphate, and tris-chlorophenyl phosphate , Polyoxyalkylene bis [di (chloroalkyl)] phosphate and the like;
Dibutyl phosphite, dipentyl phosphite, dihexyl phosphite, diheptyl phosphite, dioctyl phosphite, dinonyl phosphite, didecyl phosphite, diundecyl phosphite, didodecyl phosphite, dioleyl phosphite, diphenyl phosphite, Dicresyl phosphite, tributyl phosphite, tripentyl phosphite, trihexyl phosphite, triheptyl phosphite, trioctyl phosphite, trinonyl phosphite, tridecyl phosphite, triundecyl phosphite, tridodecyl phosphite, Trioleyl phosphite, triphenyl phosphite, tricresyl phosphite, etc .; Methylphosphorothionate, trihexyl phosphorothionate, triheptyl phosphorothionate, trioctyl phosphorothionate, trinonyl phosphorothionate, tridecyl phosphorothionate, triundecyl phosphorothionate, Tridodecyl phosphorothionate, tritridecyl phosphorothionate, tritetradecyl phosphorothionate, tripentadecyl phosphorothionate, trihexadecyl phosphorothionate, triheptadecyl phosphorothionate, trioctadecyl phosphorothionate Thionate, trioleyl phosphorothionate, triphenyl phosphorothionate, tricresyl phosphorothionate, trixylenyl phosphorothionate, Residyl diphenyl phosphorothionate, xylenyl diphenyl phosphorothionate, tris (n-propylphenyl) phosphorothionate, tris (isopropylphenyl) phosphorothionate, tris (n-butylphenyl) phosphorothionate , Tris (isobutylphenyl) phosphorothionate, tris (s-butylphenyl) phosphorothionate, tris (t-butylphenyl) phosphorothionate and the like.

When these phosphorus compounds are blended with the refrigerating machine oil for carbon dioxide refrigerant of the present invention, the blending amount is not particularly limited, but is usually based on the total amount of the refrigerating machine oil (based on the total amount of the base oil and all the blended additives). And its content is 0.01 to 10.0
It is desirable to add the phosphorus compound in such an amount that the amount becomes 0.02 to 5.0% by mass, more preferably 0.02 to 5.0% by mass.

Further, in the refrigerating machine oil for carbon dioxide refrigerant of the present invention, in order to further improve the heat / hydrolysis stability, (1) phenylglycidyl ether type epoxy compound (2) alkyl glycidyl ether type epoxy compound (3) ) Glycidyl ester type epoxy compound (4) Allyl oxirane compound (5) Alkyl oxirane compound (6) Alicyclic epoxy compound (7) Epoxidized fatty acid monoester (8) Epoxidized vegetable oil At least one kind selected from the group consisting of It is preferable to mix an epoxy compound.

(1) Specific examples of the phenylglycidyl ether type epoxy compound include phenylglycidyl ether and alkylphenylglycidyl ether. The alkylphenyl glycidyl ether referred to herein includes those having 1 to 3 alkyl groups having 1 to 13 carbon atoms, among which those having one alkyl group having 4 to 10 carbon atoms, for example, n-butylphenyl glycidyl Ether, i-butylphenyl glycidyl ether, sec-butylphenyl glycidyl ether, te
Preferred examples include rt-butylphenylglycidyl ether, pentylphenylglycidylether, hexylphenylglycidylether, heptylphenylglycidylether, octylphenylglycidylether, nonylphenylglycidylether, and decylphenylglycidylether.

(2) Specific examples of the alkyl glycidyl ether type epoxy compound include decyl glycidyl ether, undecyl glycidyl ether, dodecyl glycidyl ether, tridecyl glycidyl ether, tetradecyl glycidyl ether, 2-ethylhexyl glycidyl ether, neoethyl Pentyl glycol diglycidyl ether, trimethylolpropane triglycidyl ether, pentaerythritol tetraglycidyl ether, 1,6-hexanediol diglycidyl ether,
Examples thereof include sorbitol polyglycidyl ether, polyalkylene glycol monoglycidyl ether, and polyalkylene glycol diglycidyl ether.

(3) Specific examples of the glycidyl ester type epoxy compound include the following general formula (2):

[0039]

Embedded image (In the formula (2), R represents a hydrocarbon group having 1 to 18 carbon atoms).

In the above formula (2), R represents a hydrocarbon group having 1 to 18 carbon atoms, such as an alkyl group having 1 to 18 carbon atoms and an alkenyl having 2 to 18 carbon atoms. Group, cycloalkyl group having 5 to 7 carbon atoms, 6 to 1 carbon atoms
An alkylcycloalkyl group having 8 carbon atoms, an aryl group having 6 to 10 carbon atoms, an alkylaryl group having 7 to 18 carbon atoms, and an arylalkyl group having 7 to 18 carbon atoms. Among them, alkyl groups having 5 to 15 carbon atoms, 2 to 15 carbon atoms
And an alkylphenyl group having an alkyl group having 1 to 4 carbon atoms.

Among the glycidyl ester type epoxy compounds, preferred are, for example, glycidyl-2,2-dimethyloctanoate, glycidyl benzoate, glycidyl-tert-butyl benzoate, glycidyl acrylate, glycidyl methacrylate and the like. Can be illustrated.

(4) As the allyloxirane compound,
Specifically, 1,2-epoxystyrene, alkyl-
Examples thereof include 1,2-epoxystyrene.

(5) Specific examples of the alkyloxirane compound include 1,2-epoxybutane, 1,2-epoxypentane, 1,2-epoxyhexane, and 1,2-epoxyhexane.
Epoxy heptane, 1,2-epoxyoctane, 1,2
-Epoxynonane, 1,2-epoxydecane, 1,2-
Epoxy undecane, 1,2-epoxide decan, 1,
2-epoxytridecane, 1,2-epoxytetradecane, 1,2-epoxypentadecane, 1,2-epoxyhexadecane, 1,2-epoxyheptadecane, 1,
Examples thereof include 1,2-epoxyoctadecane, 2-epoxynonadecane, and 1,2-epoxyicosane.

(6) As the alicyclic epoxy compound, the following general formula (3):

[0045]

Embedded image Compounds in which the carbon atom constituting the epoxy group directly constitutes an alicyclic ring, such as the compound represented by

Specific examples of the alicyclic epoxy compound include 1,2-epoxycyclohexane and 1,2-epoxycyclohexane.
Epoxycyclopentane, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, bis (3,4-epoxycyclohexylmethyl) adipate, exo-2,3-epoxynorbornane, bis (3,4-epoxy- 6-methylcyclohexylmethyl) adipate, 2- (7-oxabicyclo [4.1.0] hept-3-yl) -spiro (1,3-
Dioxane-5,3 '-[7] oxabicyclo [4.
1.0] heptane, 4- (1′-methylepoxyethyl) -1,2-epoxy-2-methylcyclohexane,
4-epoxyethyl-1,2-epoxycyclohexane and the like can be exemplified.

(7) Specific examples of the epoxidized fatty acid monoester include epoxidized C12 to C20.
And esters of fatty acids with alcohols or phenols having 1 to 8 carbon atoms and alkylphenols. In particular, butyl, hexyl, benzyl, cyclohexyl, methoxyethyl, octyl, epoxy stearic acid,
Phenyl and butylphenyl esters are preferably used.

(8) Specific examples of the epoxidized vegetable oil include epoxy compounds of vegetable oils such as soybean oil, linseed oil, and cottonseed oil.

Among these epoxy compounds, the thermal and hydrolytic stability can be further improved.
Phenyl glycidyl ether type epoxy compounds, glycidyl ester type epoxy compounds, alicyclic epoxy compounds, and epoxidized fatty acid monoesters are preferred, and glycidyl ester type epoxy compounds and alicyclic epoxy compounds are more preferred.

When these epoxy compounds are blended with the refrigerating machine oil for carbon dioxide refrigerant of the present invention, the blending amount is not particularly limited, but is usually based on the total amount of the refrigerating machine oil (based on the total amount of the base oil and all the blended additives) And its content is 0.1 to 5.0
It is desirable to mix the epoxy compound in such an amount that the amount becomes 0.2% by mass, more preferably 0.2 to 2.0% by mass.

Of course, two or more of the above phosphorus compounds and epoxy compounds may be used in combination.

Further, in the refrigerating machine oil for carbon dioxide refrigerant of the present invention, conventionally known additives for refrigerating machine oil, for example, di-te
Phenolic antioxidants such as rt-butyl-p-cresol and bisphenol A; amine antioxidants such as phenyl-α-naphthylamine, N, N-di (2-naphthyl) -p-phenylenediamine; dithiophosphoric acid Anti-wear agents such as zinc, extreme pressure agents such as chlorinated paraffins and sulfur compounds, oil agents such as fatty acids, defoamers such as silicones, metal deactivators such as benzotriazole, viscosity index improvers, pour points Additives such as a depressant and a cleaning dispersant may be used alone or in combination of several kinds. The total blended amount of these additives is not particularly limited, but is preferably 10% by mass or less, more preferably 5% by mass or less based on the total amount of the refrigerating machine oil (based on the total amount of the base oil and all the blended additives).

The kinematic viscosity of the refrigerating machine oil for carbon dioxide refrigerant of the present invention is not particularly limited.
２００200 mm ² / s, preferably 20-15
More preferably, it is 0 mm ² / s. Tend to have kinematic viscosity at 40 ° C. decreases the sealing property of the lubricating property and the compressor is less than 10 mm ² / s, also, 200 mm ² /
If the ratio exceeds s, the compatibility tends to be insufficient when the ratio of the refrigerating machine oil to the carbon dioxide refrigerant is high or when the ratio is low. The kinematic viscosity at 100 ° C. of the refrigerating machine oil for carbon dioxide refrigerant of the present invention is 5 to 20.
It is preferably mm ² / s, more preferably 6~18mm ² / s. Kinematic viscosity at 100 ° C is 5
If it is less than mm ² / s, the lubricity and the hermeticity of the compressor tend to decrease, and if it exceeds 20 mm ² / s, the ratio of refrigeration oil to carbon dioxide refrigerant is high or the ratio is low. In some cases, the compatibility tends to be insufficient.

In the refrigerant circulation system, it is usually necessary to minimize the amount of water mixed in the system. In this respect, the water content of the refrigerating machine oil for carbon dioxide refrigerant of the present invention is 500 ppm or less. Preferably, 20
More preferably 0 ppm or less, 100 ppm
It is more preferred that: In general, since polyalkylene glycol has relatively high hygroscopicity, it is preferable to pay close attention to the water content when introducing the refrigerant oil for carbon dioxide refrigerant of the present invention into the refrigerant circulation system. However, on the other hand, when polyalkylene glycol having high hygroscopicity coexists, the mixed water is trapped in the molecules of the polyalkylene glycol and is not released, so that the effect of preventing adverse effects such as deterioration of the refrigerant and piping and freezing is obtained. Can be

The refrigerating machine oil for a carbon dioxide refrigerant having the above-described structure is used as a fluid composition mixed with a carbon dioxide refrigerant in a carbon dioxide refrigerant refrigerator. That is, the refrigerating machine fluid composition of the present invention contains the refrigerating machine oil for carbon dioxide refrigerant of the present invention and a carbon dioxide refrigerant. Here, the mixing ratio of the refrigerating machine oil and the refrigerant in the refrigerating machine fluid composition of the present invention is not particularly limited, but the refrigerating machine oil is preferably 1 to 500 parts by weight, more preferably 2 to 500 parts by weight, based on 100 parts by weight of the refrigerant. 400 parts by weight.

The fluid composition for a refrigerator of the present invention contains a carbon dioxide refrigerant as described above, but further contains other refrigerants such as hydrofluorocarbon (HFC), hydrocarbon, and ammonia. You may.

Here, examples of the hydrofluorocarbon refrigerant according to the present invention include hydrofluorocarbons having 1 to 3 carbon atoms, preferably 1 to 2 carbon atoms. Specifically, for example, difluoromethane (HFC-32),
Trifluoromethane (HFC-23), pentafluoroethane (HFC-125), 1,1,2,2-tetrafluoroethane (HFC-134), 1,1,1,2-tetrafluoroethane (HFC-134a) , 1,1,1
-Trifluoroethane (HFC-143a), 1,1-
Examples include difluoroethane (HFC-152a), or a mixture of two or more thereof. These refrigerants are appropriately selected depending on the application and required performance.
C-32 alone; HFC-23 alone; HFC-134a alone; HFC-125 alone; HFC-134a / HFC-
32 = mixture of 60-80% by mass / 40-20% by mass;
HFC-32 / HFC-125 = 40 to 70% by mass / 6
0 to 30% by mass of a mixture; HFC-125 / HFC-1
43a = a mixture of 40 to 60% by mass / 60 to 40% by mass; HFC-134a / HFC-32 / HFC-125
= 60% by weight / 30% by weight / 10% by weight mixture; HF
C-134a / HFC-32 / HFC-125 = 40 ~
70% by mass / 15 to 35% by mass / 5 to 40% by mass of a mixture; HFC-125 / HFC-134a / HFC-14
3a = 35 to 55% by mass / 1 to 15% by mass / 40 to 60%
A preferable example is a mixture by mass%. More specifically, HFC-134a / HFC-32 = 7
0/30% by weight mixture; HFC-32 / HFC-12
5 = mixture of 60/40% by mass; HFC-32 / HFC
-125 = 50/50% by weight mixture (R410A);
HFC-32 / HFC-125 = 45/55% by weight mixture (R410B); HFC-125 / HFC-143
a = 50/50% by weight mixture (R507C); HFC
-32 / HFC-125 / HFC-134a = 30/1
0/60% by weight mixture; HFC-32 / HFC-12
5 / HFC-134a = 23/25/52% by weight of a mixture (R407C); HFC-32 / HFC-125 / H
FC-134a = mixture of 25/15/60% by mass (R
407E); HFC-125 / HFC-134a / HF
C-143a = 44/4/52% by mass of a mixture (R40
4A) and the like.

As the hydrocarbon refrigerant according to the present invention, a gaseous refrigerant at 25 ° C. and 1 atm is preferably used. Specifically, it has 1 to 5 carbon atoms, preferably 1 to 5 carbon atoms.
4, alkanes, cycloalkanes, alkenes or mixtures thereof. Specifically, for example, methane, ethylene, ethane, propylene, propane, cyclopropane,
Butane, isobutane, cyclobutane, methylcyclopropane or a mixture of two or more thereof. Among these, propane, butane, isobutane or a mixture of two or more thereof is preferred.

The mixing ratio of carbon dioxide to hydrofluorocarbon and / or hydrocarbon is not particularly limited. However, the total amount of hydrofluorocarbon and hydrocarbon is preferably 1 to 200 parts by weight per 100 parts by weight of carbon dioxide. Parts, more preferably 10 to 100 parts by weight.

The refrigerating machine oil for a carbon dioxide refrigerant and the fluid composition for a refrigerating machine of the present invention sufficiently satisfy all the required properties such as lubricity, refrigerant compatibility, low-temperature fluidity and stability in a well-balanced manner. It can be suitably used for refrigeration equipment or heat pumps having a reciprocating or rotary open or closed type compressor. As the refrigeration equipment, more specifically, an air conditioner for an automobile, a dehumidifier,
Refrigerators, refrigerated warehouses, vending machines, showcases, cooling equipment for chemical plants, etc., residential air conditioners, hot water supply heat pumps, and the like.

[0061]

EXAMPLES The present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to the following examples.

Examples 1 to 8, Comparative Examples 1 to 3 In Examples 1 to 8 and Comparative Examples 1 to 3, sample oils were prepared using the following base oils 1 to 11. Table 1 shows the kinematic viscosity, pour point and total acid value of the obtained sample oil. In addition,
In the following formulas (4) to (14), EO represents an oxyethylene group, PO represents an oxypropylene group, Me represents a methyl group, and Ac represents an acetyl group. Also,-(EO,
PO) _n- represents a polyoxyalkylene group formed by random copolymerization of ethylene oxide and propylene oxide.

Base oil 1 Me—O— (PO) _n —H (4) [Number average molecular weight: 1200, ratio (M _w / M _n ) between weight average molecular weight (M _w ) and number average molecular weight (M _n ) ): 1.1, ratio of oxyethylene groups to all oxyalkylene groups: 0 mol%] Base oil 2 : Me-O- (EO, PO) _n -H (5) [number average molecular weight: 1200, weight] Ratio of average molecular weight ( _Mw ) to number average molecular weight ( _Mn ) ( _Mw / _Mn ): 1.1, ratio of oxyethylene groups to all oxyalkylene groups: 10 mol%] Base oil 3 : _{Me-O- (PO) n -H} (6) [ number average molecular weight: 1500, weight average molecular weight (M _w) and number average molecular weight (M _n) and the ratio of _{(M w / M n):} 1.1, Ratio of oxyethylene groups in all oxyalkylene groups: 0 mol%] Base oil 4 : Me-O- (EO, P O) _n -H (7) [number average molecular weight: 1500, weight average molecular weight (M _w) and number average molecular weight (M _n) and the ratio of _{(M w / M n):} 1.1, all the oxyalkylene group Base oil 5 : Me-O- (PO) _n- H (8) [Number average molecular weight: 1800, weight average molecular weight ( _Mw ) and number average molecular weight ( _Mn) ( _Mw / _Mn ): 1.1, ratio of oxyethylene groups to all oxyalkylene groups: 0 mol%] Base oil 6 : Me-O- (EO, PO) _n- H ( 9) [number average molecular weight: 1800, weight average molecular weight (M _w) and number average molecular weight (M _n) and the ratio of _{(M w / M n):} 1.1, of oxyethylene groups occupied in all the oxyalkylene groups ratio: 40 mol% base oil 7: Ac-O- (PO) n -H (10) [ number average molecular weight: 000, weight average molecular weight (M _w) and number average molecular weight ratio (M _w / M _n) of the (M _n): 1.1, the ratio of oxyethylene groups occupied in all the oxyalkylene groups: 0 mol% based on Oil 8 : HO- (PO) _n -H (11) [Number average molecular weight: 1200, ratio of weight average molecular weight (M _w ) to number average molecular weight (M _n ) (M _w / M _n ): 1.1 And the ratio of oxyethylene groups to all oxyalkylene groups: 0 mol%] Base oil 9 : Me—O— (PO) _n —H (12) [Number average molecular weight: 400, weight average molecular weight (M _w ) Ratio to number average molecular weight ( _Mn ) ( _Mw / _Mn ): 1.1, ratio of oxyethylene groups in all oxyalkylene groups: 0 mol%] Base oil 10 : Me-O- (PO) _n- H (13) [Number average molecular weight: 2300, weight average molecular weight (M _w ) and number average molecular weight (M _n) and the ratio of _{(M w / M n):} 1.1, the ratio of oxyethylene groups occupied in all the oxyalkylene groups: 0 mol%] Base Oil 11: Bu-O- (PO) n -H (14) number-average molecular weight: 2700, weight average molecular weight (M _w) and number average molecular weight (M _n) ratio of _{(M w / M n):} 1.1, oxyethylene groups occupied in all the oxyalkylene groups Of 0 mol%].

Next, the following tests were conducted using the sample oils of Examples 1 to 8 and Comparative Examples 1 to 3.

(Compatibility test with refrigerant 1) Internal volume 10 ml
The carbon dioxide refrigerant and the sample oil were sealed so as to have a total amount of 5 g in a pressure-resistant glass container of No. 5, and the state of the mixture (compatible or separated) when cooled to −30 ° C. was visually observed. This test was started at a refrigerator oil concentration of 1% by weight (carbon dioxide refrigerant: 4.95 g, sample oil 0.05 g), and the total amount of the carbon dioxide refrigerant and the sample oil was kept constant (5.00 g). Starting from a gradually increasing ratio or a refrigerator oil concentration of 90% by mass (carbon dioxide refrigerant: 0.50 g, sample oil 4.50 g), the total amount of carbon dioxide refrigerant and sample oil is constant (5.000 g) ), The ratio of the carbon dioxide refrigerant was gradually increased, and the composition range in which the mixture of the carbon dioxide refrigerant and the sample oil was in a separated state was determined. Table 1 shows the obtained results. In Table 1, “compatible” indicates that the mixture was not separated even when the mixing ratio of the carbon dioxide refrigerant and the sample oil was changed, and “<” in the lower limit of the composition range.
"1" indicates that the sample oil had already been separated at a concentration of 1% by weight.

(Compatibility test 2 with refrigerant) Using the refrigerant solubility measuring device shown in FIG. 3, the solubility of the carbon dioxide refrigerant in the sample oil under the condition that the mixture of the carbon dioxide refrigerant and the sample oil is separated Was measured.

The apparatus shown in FIG. 3 controls a pressure vessel 305 (made of stainless steel, internal volume: 200 ml) having a viscometer 301, a pressure gauge 302, a thermocouple 303 and a stirrer 304, and a temperature inside the pressure vessel 305. Thermostat 306 for
And the pressure vessel 3 via a flow path 307.
05 and a sampling cylinder 308 connected thereto. The sampling cylinder 308 and the flow path 307 are detachable, and the weight of the sampling cylinder 308 is measured after vacuum degassing or after weighing a mixture of carbon dioxide refrigerant and sample oil. It is possible to do. In addition, thermocouple 303 and thermostat 3
Numerals 06 are electrically connected to temperature control means (not shown), and a data signal relating to the temperature of the sample oil (or a mixture of carbon dioxide refrigerant and sample oil) is sent from the thermocouple 303 to the temperature control means. At the same time, a control signal is sent from the temperature control means to the thermostatic bath 306, so that the temperature of the sample oil or the mixture can be controlled. Further, the viscometer 301 is electrically connected to an information processing device (not shown), and measurement data regarding the viscosity of the liquid in the pressure vessel 305 is sent from the viscometer 301 to the information processing device.
It is possible to measure viscosity under predetermined conditions.

In this test, first, the pressure vessel 305
After putting 30 g of sample oil in the container and degassing the inside of the container under vacuum, 70 g of carbon dioxide refrigerant is introduced, and the mixture of the carbon dioxide refrigerant and the sample oil is stirred at −30 ° C.
Hold for hours. Thereafter, the stirring was stopped and the mixture was allowed to stand until the carbon dioxide refrigerant and the sample oil were separated into two layers. Next, after the inside of the sampling cylinder 308 is evacuated to vacuum and its mass W ₁ is measured, it is connected to the channel 307 and the sample oil layer is sampled by utilizing the pressure difference between the pressure vessel 305 and the sampling cylinder 308. It was collected in a cylinder 308.

The mass W ₂ (sum of the mass of the sample oil in which the refrigerant is dissolved and the mass of the sampling cylinder 308) of the sampling cylinder 308 after the above sampling is performed.
After removing the carbon dioxide refrigerant dissolved in the sample oil by opening the valve and heating while vacuum degassing, the weight W ₃ (sum of the mass of the sample oil and the sampling cylinder 308) is measured. Was measured.

Using the measured values thus obtained, the following formula: (solubility of carbon dioxide refrigerant [% by mass]) = [(W ₂ −
W ₃ ) / (W ₃ −W ₁ )] × 100 was used to determine the solubility of the carbon dioxide refrigerant in each sample oil. Table 1 shows the obtained results.

(Compatibility test 3 with refrigerant) JIS K 2
In accordance with "Method for testing compatibility with refrigerant" of 211 "Refrigeration oil", a temperature range showing compatibility when a carbon dioxide refrigerant and a sample oil were mixed with a predetermined composition was measured. Table 1 shows the obtained results. The composition in this test was such that the sample oil concentration was 50% by weight (carbon dioxide refrigerant: 1.5 g, sample oil: 1.5 g) and 60% by weight (carbon dioxide refrigerant: 1.
2g, sample oil 1.8g), the measurement temperature is -55-
Performed at 30 ° C. In Table 1, “<−55” in the lower limit of the temperature range showing compatibility indicates that no phase separation was observed even when cooled to −55 ° C., and the upper limit of the temperature range showing compatibility was shown. Among the values, “> 30” indicates that no phase separation was observed even after heating to 30 ° C., and “<−55 to
> 30 "indicates that no phase separation was observed at any temperature within the measurement temperature range.

(Stability Test in Refrigerant Atmosphere) In an autoclave, 50 g of each sample oil, 10 g of carbon dioxide refrigerant, and a catalyst (iron wire, aluminum wire of 1.6 mmφ × 50 mm,
After enclosing (3 copper wires each), the mixture was heated to 175 ° C. and kept for 2 weeks. Thereafter, carbon dioxide was removed from the sample oil, the appearance of the sample oil and the appearance of the catalyst were observed, and the total acid value of the sample oil was measured. Table 1 shows the obtained results.

(Lubricity test) According to ASTM D 3233, 10 g / h of a carbon dioxide refrigerant was added to 60 g of a sample oil.
After a break-in operation was performed under a condition of a sample oil temperature of 50 ° C. under a load of 250 lb for 5 minutes while blowing at a flow rate of, the seizure load was measured. Table 1 shows the obtained results.

[0074]

[Table 1] As is clear from the results shown in Table 1, the sample oils of Examples 1 to 8, which are the refrigerating machine oils for carbon dioxide refrigerant of the present invention, regardless of whether the ratio to the carbon dioxide refrigerant is high or low. Shows sufficiently high compatibility, and even when carbon dioxide refrigerant and sample oil are separated into two layers,
It was confirmed that a sufficient amount of the carbon dioxide refrigerant was dissolved in the sample oil. Furthermore, the sample oils of Examples 1 to 8 were excellent in all of the properties of lubricity, low-temperature fluidity and stability in a well-balanced manner.

On the other hand, in the case of the sample oils of Comparative Examples 1 to 3 using the polyalkylene glycol compound other than the polyalkylene glycol according to the present invention, when used together with the carbon dioxide refrigerant, the refrigerant compatibility and lubricity were low. One of them was inadequate.

[0076]

As described above, the refrigerating machine oil for carbon dioxide refrigerant of the present invention has a sufficiently wide composition range showing compatibility when mixed with carbon dioxide refrigerant under low temperature conditions, and has lubricity and stability. Therefore, when the refrigerating machine oil and the refrigerating machine fluid composition using the same are used for a carbon dioxide refrigerant refrigerating machine, the lubrication failure of the refrigerant compressor is sufficiently prevented and the heat exchange rate is sufficiently high. Can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating an example of a refrigerant circulation system.

FIG. 2 is a graph showing a correlation between a refrigerating machine oil concentration in a refrigerant / refrigerating machine oil mixture and a phase separation temperature of the mixture.

FIG. 3 is a schematic configuration diagram showing a refrigerant solubility measuring device used in Examples.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Refrigerant compressor, 2 ... Gas cooler, 3 ... Expansion mechanism, 4
.. Evaporator, 5 flow path, 301 viscosity meter, 302 pressure gauge, 303 thermocouple, 304 stirrer, 305 pressure vessel, 306 constant temperature bath, 307 flow path, 308 sampling cylinder.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) C10N 20:04 C10N 20:04 30:00 30:00 Z 30:08 30:08 40:30 40:30

Claims (3)

[Claims] 1. The following general formula (1): The following general formula (1): R ¹ — (OR ² ) _n —OH (1) wherein R ¹ is a hydrogen atom, an alkyl group having 1 to 2 carbon atoms. Or an acyl group having 2 to 3 carbon atoms, and R ² represents 2 to 3 carbon atoms.
4 represents an alkylene group, and n represents a number average molecular weight of 500 of the polyalkylene glycol represented by the general formula (1).
Refrigerator oil for carbon dioxide refrigerant, which comprises a polyalkylene glycol represented by the following formula: 2. The polyalkylene glycol of 100
Kinematic viscosity at ℃ is characterized in that it is a 5 to 20 mm ² / s, carbon dioxide refrigerant refrigerating machine oil according to claim 1. 3. A fluid composition for a refrigerator comprising the refrigerating machine oil for a carbon dioxide refrigerant according to claim 1 or 2 and a carbon dioxide refrigerant.