JPH1046170A - Working fluid composition for refrigerator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a working fluid compsn. for refrigerators which is excellent in the thermal stability and hydrolysis stability of a base oil by incorporating a refrigerator oil contg. a specific ester as the base oil and a hydrofluorocarbon component contg. difluoromethane into the same. SOLUTION: This compsn. contains a refrigerator oil contg. an ester base oil obtd. from a 2-10C di-to hexahydric alcohol, a 2-10C linear and/or branched monocarboxylic acid or its deriv., and a dibasic acid having an arom. ring or its anhydride and a hydrofluorocarbon component contg. difluoromethane (HFC-320. The compsn. suits best to rotary-type. scroll-type, and screw-type compressors wherein sliding condition is severe and frictional heat is easily generated. Therefore. the compsn. is suitable for the use in compressors of room air conditioners, package air conditioners, industrial refrigerators, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a refrigerator working fluid having excellent compatibility with hydrofluorocarbons containing difluoromethane (HFC32) and excellent insulation properties, and particularly excellent heat stability and hydrolysis stability of ester base oils. For the composition for use, specifically, a di- to hexa-hydric alcohol having 2 to 10 carbon atoms, (1) a linear and / or branched monocarboxylic acid having 2 to 10 carbon atoms, or a derivative thereof, and (2) Thermal stability of an ester base oil comprising a refrigerating machine oil containing an ester base oil obtained from a dibasic acid having an aromatic ring or an anhydride thereof, and a hydrofluorocarbon containing difluoromethane (HFC32); The present invention relates to a composition for a working fluid of a refrigerator having excellent hydrolysis stability.

[0002]

2. Description of the Related Art The use of dichlorodifluoromethane (CFC12) used in refrigerators and car coolers was banned in 1995 to protect the ozone layer. Subsequently, regulations on the use of chlorodifluoromethane (HCFC22) used in room air conditioners, package air conditioners, industrial refrigerators, and the like have begun. Therefore, this dichlorofluoromethane (CFC1
2) As an alternative to chlorodifluoromethane (HCFC22), hydrofluorocarbons that do not destroy the ozone layer, such as 1,1,1,2-tetrafluoroethane (HFC134a) and difluoromethane (HFC32)
And pentafluoroethane (HFC125) have been developed.

Since these hydrofluorocarbons have a higher polarity than dichlorofluoromethane (CFC12) or chlorodifluoromethane (HCFC22), naphthenic mineral oils and poly-α-olefins which have been conventionally used as refrigerating machine oils have been used. When a lubricating oil such as an alkylbenzene is used, the compatibility between the lubricating oil and the hydrofluorocarbon is poor, and two-phase separation occurs at a low temperature. When two-phase separation occurs, oil return deteriorates, a thick oil film adheres near the condenser or evaporator as a heat exchanger, hinders heat transfer, and other important defects such as poor lubrication and foaming at startup. Cause. Therefore, conventional refrigerating machine oil cannot be used as refrigerating machine oil in the presence of these new refrigerants.

Accordingly, at present, base oils such as polyalkylene glycols, esters, carbonates and the like which are compatible with the above-mentioned hydrofluorocarbons are used for refrigerating machine oils. In fact, refrigerators contain ester base oil as refrigerator oil,
1,1,1,2-Tetrafluoroethane (HFC134a) is used as the hydrofluorocarbon. Ester base oils are also evaluated as refrigerating machine oils for room air conditioners, package air conditioners, industrial refrigerators, and the like.

However, conventional chlorodifluoromethane (HCFC22) such as a room air conditioner, a package air conditioner, and an industrial refrigerator are used.
In the field where has been used, hydrofluorocarbons containing difluoromethane (HFC32) have been evaluated as hydrofluorocarbons from the viewpoint of refrigeration efficiency. However, when difluoromethane (HFC32) is used, the compatibility with the ester base oil becomes worse as compared with 1,1,1,2-tetrafluoroethane (HFC134a), and two-phase separation occurs at a low temperature. In particular, difluoromethane (HFC32) and pentafluoroethane (HFC125)
32) is remarkable when the content is 45% by weight or more. When two-phase separation occurs, oil return deteriorates as described above, and a thick oil film adheres near the condenser or evaporator as a heat exchanger, hinders heat transfer, and causes poor lubrication and foaming at startup. Difluoromethane (H
A composition for a refrigerator working fluid having good compatibility with hydrofluorocarbons containing FC32), particularly a composition for a refrigerator working fluid compatible at −20 ° C. or lower is required for industrial refrigerators and the like.

Further, the use of difluoromethane (HFC32) increases the pressure in the compressor, and the sliding conditions become severe, so that frictional heat is generated, and 1,1,1,2-tetrafluoroethane (HFC134a) is produced. Thermal decomposition of the ester base oil, which did not occur in the refrigerator used, has occurred. The acid generated by the thermal decomposition of the ester base oil corrodes the metal of the compressor to cause a failure and a problem of blocking the capillary tube. Furthermore, in contrast to reciprocating compressors used in refrigerators, room air conditioners, package air conditioners, industrial refrigerators, etc. mainly use rotary, scroll and screw compressors. Since the lubricating conditions of the compressor are more severe than that of the reciprocating compressor, frictional heat is generated, and thermal decomposition of the ester base oil, which has not occurred in the refrigerator using the reciprocating compressor, has occurred.
In particular, thermal stability at a high temperature of about 250 ° C. is important.

In addition, ester base oils are hydrolyzed by the incorporation of moisture, and the above-mentioned problems may occur due to the generated acid. Especially difluoromethane (HFC32)
In the presence of a hydrofluorocarbon containing, or in the use of a rotary, scroll, or screw compressor, frictional heat is generated, which may cause a problem of promoting hydrolysis of the ester base oil. Therefore, in the presence of a hydrofluorocarbon containing difluoromethane (HFC32) or in the use of a rotary, scroll, or screw compressor, difluoromethane (HFC3) is used.
There is a demand for a composition for a working fluid of a refrigerator, which has good compatibility with the hydrofluorocarbon containing 2) and is excellent in heat stability and hydrolysis stability of the ester base oil.

[0008] JP-A-5-17789, JP-A-5-17989
32985, JP-A-5-239480, JP-A-6-9978 and JP-A-6-17073 disclose refrigeration comprising a refrigerating machine oil containing an ester as a base oil and a hydrofluorocarbon containing difluoromethane (HFC32). Although a composition for a working fluid is disclosed, the thermal stability and hydrolysis at high temperatures in the presence of a hydrofluorocarbon containing difluoromethane (HFC32) and in the use of a rotary, scroll, or screw compressor are disclosed. No mention is made of stability. Tokiohei 8
JP-A-502769 discloses a composition for a working fluid of a refrigerator comprising a refrigerator oil containing ester as a base oil and difluoromethane (HFC32), and a screw type compressor test is described in Examples. No mention is made of heat stability and hydrolysis stability at high temperatures.

Japanese Unexamined Patent Publication (Kokai) No. 6-184575 discloses a refrigerator oil based on an ester obtained from an alcohol, a fatty acid and a dibasic acid, difluoromethane (HFC32) and 1,1,1,2-tetrafluoroethane. (HFC13
4a) and / or pentafluoroethane (HFC12
A composition for a working fluid of a refrigerator comprising 5) is disclosed, but difluoromethane (HFC32) and 1,1,1,
Since it aims at improving the compatibility with 2-tetrafluoroethane (HFC134a) and difluoromethane (HFC32) and / or pentafluoroethane (HFC125), heat stability and hydrolysis stability at high temperatures are all Did not mention.

[0010]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a refrigeration having good compatibility with hydrofluorocarbons containing difluoromethane (HFC32) and excellent heat stability and hydrolysis stability of an ester base oil. An object of the present invention is to provide a composition for a working fluid.

[0011]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above problems, and as a result, have found that a refrigerating machine oil containing a specific ester as a base oil and difluoromethane (HFC3
The present inventors have found that a composition for a working fluid of a refrigerator containing a hydrofluorocarbon containing 2) can solve the above problems, and have completed the present invention.

That is, the gist of the present invention is: [1] a di- to hexa-hydric alcohol having 2 to 10 carbon atoms, and (1) a straight-chain and / or branched-chain monocarboxylic acid having 2 to 10 carbon atoms, or A refrigerating machine oil containing an ester base oil obtained from the derivative thereof, and (2) a dibasic acid having an aromatic ring and / or an anhydride thereof; and a hydrofluorocarbon containing difluoromethane (HFC32). A composition for a working fluid of a refrigerator, wherein the ester base oil provides the following thermal stability: Thermal stability: (a) a water concentration of 10 ppm or less and an acid value of 0.01 mgKOH / g. Ester base oil 1 prepared below
(B) 2.5 g of difluoromethane (HFC32) and 2.5 g of pentafluoroethane (HFC125), or 1.15 g of difluoromethane (HFC32), 1.25 g of pentafluoroethane (HFC125) and 1,1,
1,2-tetrafluoroethane (HFC134a)
And (c) an iron piece having a diameter of 1.6 mmφ and a length of 150 mm as a catalyst was added to a glass tube, sealed, and left at 250 ° C. for 3 days, the acid value of the ester base oil increased by 4. 0mgK
OH / g or less. [2] The dibasic acid having an aromatic ring has 8 to 1 carbon atoms.
The composition for a working fluid of a refrigerator according to the above [1], wherein the composition is a dibasic acid of 2.

[3] The composition according to [2], wherein the dibasic acid having 8 to 12 carbon atoms is one or more acids selected from the group consisting of phthalic acid, isophthalic acid, and terephthalic acid. [4] Hydrofluorocarbon (H) containing 30% by volume of ester base oil and difluoromethane (HFC32)
Under the condition that FC32 is 70% by volume (50% by weight in hydrofluorocarbon), the low temperature two-phase separation temperature is -2.
The composition for a refrigerator working fluid according to any one of the above [1] to [3], which is 0 ° C or lower, [5] The above [1] to [4], wherein the ester base oil provides the following hydrolysis stability. The composition for a working fluid of a refrigerator according to any one of the above, Hydrolysis stability: 10 g of an ester base oil having a water concentration adjusted to 3000 ppm or less, an acid value adjusted to 0.01 mgKOH / g or less, 2.5 g of difluoromethane (HFC32) and A composition comprising 2.5 g of pentafluoroethane (HFC125), and a catalyst having a diameter of 1.6 mmφ and a length of 1
When an iron piece of 50 mm is added to a glass tube and sealed and left at 175 ° C. for 14 days, the acid value increase of the ester base oil is 4.0 mgKOH / g or less. It is about.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The composition for a working fluid of a refrigerator according to the present invention comprises a divalent to hexavalent alcohol having 2 to 10 carbon atoms, and (1) a linear and / or branched monocarboxylic acid having 2 to 10 carbon atoms, or a derivative thereof. And (2) a refrigerating machine oil containing an ester base oil obtained from a dibasic acid having an aromatic ring and / or an anhydride thereof, and a hydrofluorocarbon containing difluoromethane (HFC32). Features.

1. About Ester Base Oil Ester base oil in the present invention is defined as having 2 to 10 carbon atoms.
Of a di- to hexahydric alcohol (component-1) and
An ester obtained from 10 straight-chain and / or branched-chain monocarboxylic acids or derivatives thereof (component-2), and dibasic acids having an aromatic ring and / or anhydrides thereof (component-3). That is, the ester base oil in the present invention is obtained from a mixture of the alcohol of the component-1, the acid of the component-2, and the acid of the component-3.

Component-1 The alcohol of component-1 has a valence of 2 to 6, preferably 2 to 4, and more preferably 2. The valence is preferably 2 or more from the viewpoint of having an appropriate viscosity, and is preferably 6 or less from the viewpoint of avoiding unnecessary viscosity and compatibility with the hydrofluorocarbon. The number of carbon atoms is 2 to 10, preferably 5 to 10, and more preferably 5 to 6. The number of carbon atoms is preferably 2 or more from the viewpoint of having an appropriate viscosity, and is preferably 10 or less from the viewpoint of avoiding unnecessary viscosity and compatibility with the hydrofluorocarbon. Further, it is preferable not to contain unsaturated bonds from the viewpoint of thermal stability.

Specific examples of the alcohol of the component-1 include:
Hindered alcohols such as neopentyl glycol, trimethylolethane, trimethylolpropane, pentaerythritol, ditrimethylolpropane and dipentaerythritol, and ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,3-propanediol, Alcohols such as 1,4-butanediol, 1,6-hexanediol, glycerin, diglycerin, triglycerin, sorbitol, and mannitol. Among these, hindered alcohol is particularly excellent from the viewpoint of thermal stability.

Regarding Component-2 The monocarboxylic acid of Component-2 has 2 to 10, preferably 5 to 9, and more preferably 7 to 9 carbon atoms. The number of carbon atoms is preferably 2 or more from the viewpoint of suppressing corrosiveness to metals, and is preferably 10 or less from the viewpoint of compatibility with hydrofluorocarbons. From the viewpoint of compatibility with the hydrofluorocarbon and hydrolysis stability, a branched-chain monocarboxylic acid is more preferable than a straight-chain monocarboxylic acid. On the other hand, from the viewpoint of lubricity, straight-chain monocarboxylic acids are more preferable than branched-chain monocarboxylic acids. From the viewpoint of the thermal stability and hydrolysis stability of the ester base oil, the proportion of the branched-chain monocarboxylic acid to the straight-chain monocarboxylic acid is preferably such that the proportion of the branched-chain monocarboxylic acid in all the monocarboxylic acids is 50 mol% or more. It is preferably at least 60 mol%, more preferably at least 70 mol%, particularly preferably at least 80 mol%. In the present invention, a suitable material is selected according to the mode of use as the composition for the working fluid of the refrigerator. Further, it is more preferable not to contain an unsaturated bond from the viewpoint of thermal stability.

Specific examples of the monocarboxylic acid of the component-2 include capric acid, valeric acid, isovaleric acid, 2-methylbutyric acid, caproic acid, enanthic acid, 2-ethylpentanoic acid, 2-methylhexanoic acid, caprylic acid , 2-ethylhexanoic acid, pelargonic acid, 3,5,5-trimethylhexanoic acid, and the like. Further, specific examples of the monocarboxylic acid derivative of Component-2 include methyl esters, ethyl esters, and acid anhydrides of these monocarboxylic acids.

Regarding Component-3 The dibasic acid having an aromatic ring of Component-3 is not particularly limited, but has 8 carbon atoms from the viewpoint of compatibility with hydrofluorocarbons including difluoromethane (HFC32). To 12 are preferable, and the number of carbon atoms is 8 to
Those having 10 carbon atoms are more preferable, and those having 8 carbon atoms are particularly preferable. As a specific example of such a dibasic acid having 8 to 12 carbon atoms, from the viewpoint of thermal stability of the ester base oil,
Phthalic acid, isophthalic acid and terephthalic acid are preferred. Further, phthalic acid is more preferred from the viewpoint of availability and low-temperature fluidity. It is more preferable to use these anhydrides in the production of the ester, because the reactivity increases.

The amount of the dibasic acid having an aromatic ring of the component-3 is preferably selected from the viewpoints of proper viscosity and compatibility with the hydrofluorocarbon containing difluoromethane (HFC32). Alcohol 1
It is preferably 0.1 to 0.6 mol with respect to mol,
More preferably, it is 0.2 to 0.5 mol. The amount of the monocarboxylic acid used as the component-2 depends on the acid value of the component-2 used and the component used from the viewpoint of having an appropriate viscosity and compatibility with the hydrofluorocarbon containing difluoromethane (HFC32). The amount of the acid value of the dibasic acid having an aromatic ring of -3 is preferably 0.7 to 1.5 times the hydroxyl value of the alcohol of the component-1 used, and more preferably 0.8 to 1.5 times. The amount is 1.2 times equivalent, particularly preferably 0.9 to 1.1 times equivalent.

Specific examples of such an ester include phthalic acid / 2-methylhexanoic acid mixed acid ester of neopentyl glycol and phthalic acid / 2-methylhexanoic acid of neopentyl glycol.
-Ethylhexanoic acid mixed acid ester, neopentyl glycol phthalic acid / 3,5,5-trimethylhexanoic acid mixed acid ester, neopentyl glycol phthalic acid /
2-methylhexanoic acid / 3,5,5-trimethylhexanoic acid mixed acid ester, neopentyl glycol phthalic acid / 2-ethylhexanoic acid / 3,5,5-trimethylhexanoic acid mixed acid ester, neopentyl glycol phthalate Acid / caproic acid / 2-ethylhexanoic acid mixed acid ester, neopentyl glycol phthalic acid / valeric acid / 3,5,5-trimethylhexanoic acid mixed acid ester,
Neopentyl glycol mixed acid ester of isophthalic acid / 2-methylhexanoic acid, neopentyl glycol mixed acid ester of isophthalic acid / 2-ethylhexanoic acid, neopentyl glycol mixed acid ester of terephthalic acid / 2-methylhexanoic acid, neopentyl Glycol terephthalic acid / 3,5,5-trimethylhexanoic acid mixed acid ester, trimethylolpropane phthalic acid / 2-methylhexanoic acid mixed acid ester, trimethylolpropane phthalic acid / caproic acid mixed acid ester, trimethylolpropane Phthalic acid / isovaleric acid mixed acid ester of trimethylolpropane, isophthalic acid / caproic acid mixed acid ester of trimethylolpropane, isophthalic acid / 2-methylhexanoic acid mixed acid ester of trimethylolpropane, and trimethylolpropane mixed acid ester Phthalic acid / 2-methylhexanoic acid mixed acid ester, pentaerythritol phthalic acid / valeric acid mixed acid ester, pentaerythritol phthalic acid / isovaleric acid mixed acid ester, pentaerythritol isophthalic acid / isovaleric acid mixed acid ester, pentaerythritol And terephthalic acid / valeric acid mixed acid esters.

In the present invention, two or more esters may be used as a mixture as the ester base oil. In the present invention, the ester base oil is composed of the alcohol 1
A known esterification reaction usually performed from at least one kind, at least one kind of a monocarboxylic acid or a derivative thereof of Component-2, and at least one kind of a dibasic acid having an aromatic ring or an anhydride thereof of Component-3. Or by a transesterification reaction.

The acid value of the ester base oil obtained as described above, which is used in the present invention, is not particularly limited, but the corrosion of the metal material, the decrease in wear resistance, the decrease in thermal stability, and the decrease in electrical insulation 1mgK from the viewpoint of suppressing the decrease
OH / g or less is preferable, 0.2 mgKOH / g or less is more preferable, 0.1 mgKOH / g or less is further preferable, and 0.05 mgKOH / g or less is particularly preferable. The hydroxyl value of the ester base oil in the present invention is 50 mg from the viewpoint of storage stability at room temperature because the ester base oil has a hygroscopic property, heat stability, and particularly a possibility of solid precipitation at room temperature.
KOH / g or less is preferable, 30 mgKOH / g or less is more preferable, 20 mgKOH / g or less is further preferable, and 10 mgKOH / g or less is used.
The following is particularly preferred, and 5 mgKOH / g or less is most preferred.

The iodine value (Img / 100 g) of the ester base oil in the present invention is not particularly limited, but is preferably 10 or less, more preferably 5 or less, further preferably 3 or less from the viewpoint of the thermal oxidation stability of the obtained refrigerating machine oil. Preferably 1
The following are particularly preferred. The two-phase separation temperature of the ester base oil at a low temperature with the hydrofluorocarbon in the present invention is not particularly limited, but is preferably 10 ° C or lower, more preferably 0 ° C or lower, further preferably -10 ° C or lower, and -20 ° C.
The following is particularly preferred, and the temperature is most preferably -30 ° C or less. The kinematic viscosity at 40 ° C. of the ester base oil in the present invention is not particularly limited, but is preferably in the range of 10 to 400 mm ² / s, from the viewpoint of energy saving and abrasion resistance, and 32 to ³ mm.
The range of 00 mm ² / s is more preferable, and 46 to 100 mm ² / s
Is more preferable, and the range of 56 to 75 mm ² / s is particularly preferable. Further, the viscosity index is preferably 80 or more, more preferably 90 or more, and 9
5 or more is more preferable.

In the present invention, the ester base oil may be used as it is as the refrigerating machine oil, but the refrigerating machine oil may contain other components in addition to the ester base oil. That is, in the refrigerating machine oil containing the ester base oil in the present invention, as long as the compatibility with the hydrofluorocarbon containing difluoromethane (HFC32) is not impaired,
Mineral oils, poly-α-olefins, alkylbenzenes, esters other than those described above, polyethers, perfluoroethers, phosphate esters and the like may be contained. The ester used in the present invention is used as a base oil, and preferably accounts for 50% by weight or more, more preferably 80% by weight or more, of the oil components blended in the refrigerator oil. In the refrigerating machine oil having an ester as a base oil in the present invention, an antioxidant, an extreme pressure agent, an oiliness improver, and an oil improver which are generally used are used as long as compatibility with a hydrofluorocarbon containing difluoromethane (HFC32) is not impaired. Various lubricating oil additives such as a foaming agent, a detergent / dispersant, a rust inhibitor, a demulsifier, a viscosity index adjuster, a metal deactivator, and a pour point depressant can be used.

2. About hydrofluorocarbon The hydrofluorocarbon used in the present invention contains at least difluoromethane (HFC32). That is, difluoromethane (HFC32) may be used alone, or another hydrofluorocarbon may be mixed with difluoromethane (HFC32). As other hydrofluorocarbons, specifically, 1,1-difluoroethane (HFC152a), 1,1,1-trifluoroethane (HFC143a), 1,1,1,1,2-
Tetrafluoroethane (HFC134a), 1, 1,
Examples thereof include 2,2-tetrafluoroethane (HFC134) and pentafluoroethane (HFC125). Preferred mixed hydrofluorocarbons include 1,
1,1,2-tetrafluoroethane (HFC134a)
/ Difluoromethane (HFC32) / tetrafluoroethane (HFC125) combination or difluoromethane (HFC32) / pentafluoroethane (HFC1
25) and the like.

Further, 1,1,1,2-tetrafluoroethane (HFC134a) / difluoromethane (HFC3
The mixing ratio of 2) / pentafluoroethane (HFC125) is 1,1,1,2 from the viewpoint of refrigeration efficiency and safety.
-10 to 8 of tetrafluoroethane (HFC134a)
0% by weight is preferable, and 20 to 70% by weight is more preferable. Difluoromethane (HFC32) is 5 to 40% by weight
Is preferable, and 10 to 30% by weight is more preferable. Pentafluoroethane (HFC125) is preferably from 5 to 80% by weight, more preferably from 10 to 70% by weight. One of the most preferable compounding ratios is 52% by weight of 1,1,1,2-tetrafluoroethane (HFC134a) / 23% by weight of difluoromethane (HFC32) / 25% by weight of pentafluoroethane (HFC125). The mixing ratio of difluoromethane (HFC32) / pentafluoroethane (HFC125) is 20 to 7 for difluoromethane (HFC32) from the viewpoint of refrigeration efficiency and safety.
It is preferably 0% by weight, more preferably 40 to 60% by weight. Pentafluoroethane (HFC125) is 30 to 8
It is preferably 0% by weight, more preferably 40 to 60% by weight. One of the most preferable mixing ratios is 50% by weight of difluoromethane (HFC32) / 50% by weight of pentafluoroethane (HFC125).

3. Regarding the composition for a working fluid of a refrigerator The composition for a working fluid of a refrigerator of the present invention comprises a refrigerator oil containing an ester base oil as described above and difluoromethane (H
It comprises a hydrofluorocarbon containing FC32). Further, the composition for a working fluid of a refrigerator of the present invention is excellent in heat stability and hydrolysis stability of an ester base oil. The composition for a working fluid of a refrigerator according to the present invention, which is excellent in heat stability and hydrolysis stability of an ester base oil, is a rotary type, a scroll type, and a screw type compressor in which sliding conditions are strict and frictional heat is easily generated. Ideal for
It is suitable for use in compressors such as room air conditioners, package air conditioners, and industrial refrigerators.

In the composition for a working fluid of a refrigerator according to the present invention, which is excellent in thermal stability and hydrolysis stability of the ester base oil, the hydrodynamic fluid containing the above-mentioned ester-based refrigerator oil and difluoromethane (HFC32). The mixing ratio of the fluorocarbon is not particularly limited, but preferably, hydrofluorocarbon / refrigeration oil containing difluoromethane (HFC32) / 20/1 to 1/10 (weight ratio), more preferably 10/1 to 1/5 (weight ratio) ), Particularly preferably 5/1 to 1/5 (weight ratio). From the viewpoint of obtaining a sufficient refrigerating capacity, the mixing ratio is preferably higher than 1/10 in the ratio of hydrofluorocarbon containing difluoromethane (HFC32), and from the viewpoint of making the viscosity of the composition for a working fluid of a refrigerator suitable, Preferably, the ratio of the refrigerating machine oil is higher than 20/1.

The composition for a working fluid of a refrigerator according to the present invention has excellent heat stability of an ester base oil. Here, "excellent in thermal stability" means that the acid value increase value of the ester base oil is preferably 4.0 mg KO according to the thermal stability test shown below.
H / g or less, more preferably 3.0 mgKOH / g or less, further preferably 2.0 mgKOH / g or less, particularly preferably 1.0 mgKOH / g or less. This increase in acid value is due to the acid generated by the thermal decomposition of the ester base oil. Regarding the increase in acid value,
From the viewpoint of preventing corrosion of the compressor, the content is preferably 4.0 mgKOH / g or less. Such a composition for a refrigerator working fluid having excellent heat stability of an ester base oil is provided by the heat stability of the ester base oil described above.

In the thermal stability test, the water concentration was 10 ppm.
And 10 g of an ester base oil whose acid value has been adjusted to 0.01 mg KOH / g or less, and difluoromethane (HFC3
2) 2.5 g and pentafluoroethane (HFC12
5) 2.5 g or difluoromethane (HFC32)
1.15 g, pentafluoroethane (HFC125)
A composition for a working fluid of a refrigerator composed of 1.25 g and 2.6 g of 1,1,1,2-tetrafluoroethane (HFC134a) was prepared, and this was used as a catalyst and had a diameter of 1.6 m.
This is a test in which the sample is put in a glass container together with an iron piece having a diameter of mφ and a length of 150 mm, sealed, and left at 250 ° C. for 3 days. After the test, the acid value of the composition is measured, and the increase value is determined. The acid value is measured according to JIS K-2501. This thermal stability test corresponds to an evaluation when the composition for a working fluid of a refrigerator is used for a room air conditioner, a package air conditioner, or an industrial refrigerator.

Further, the composition for a working fluid of a refrigerator according to the present invention is excellent in hydrolytic stability of an ester base oil. Here, “excellent in hydrolytic stability” means that the acid value increase value of the ester base oil is preferably 4.0 mgKOH / g or less, more preferably 3.0 mg, according to the test described below.
KOH / g or less, more preferably 2.0 mg KOH / g
g, particularly preferably 1.0 mg KOH / g or less. This increase in acid value is due to the acid generated by hydrolysis of the ester base oil. Regarding the increase in acid value, from the viewpoint of preventing corrosion of the compressor, 4.0 mgK
OH / g or less is preferred. Such a composition for a working fluid of a refrigerator having excellent hydrolysis stability of the ester base oil is provided by the hydrolysis stability of the ester base oil described above.

The test for evaluating the hydrolytic stability includes:
Water concentration is less than 3000ppm, acid value is 0.01mgK
A composition for a refrigerator working fluid, which is a mixture of 10 g of an ester base oil adjusted to OH / g or less, 2.5 g of difluoromethane (HFC32) and 2.5 g of pentafluoroethane (HFC125), was prepared. In this test, a catalyst was added to a glass container together with an iron piece having a diameter of 1.6 mmφ and a length of 150 mm in a glass container, and the tube was left at 175 ° C for 14 days. After the test, the acid value of the composition is measured, and the increase value is determined. The acid value is measured according to JIS K-2501.

The composition for a working fluid of a refrigerator according to the present invention is excellent in compatibility between hydrofluorocarbon and refrigerator oil, particularly at low temperatures. In particular,
30% by volume of ester base oil, difluoromethane (HFC
32) containing 70% by volume of a hydrofluorocarbon (HFC32 is 50% by weight in the hydrofluorocarbon).
, The low-temperature two-phase separation temperature is preferably -20 ° C or lower, more preferably the temperature is -30 ° C.
The temperature is particularly preferably −40 ° C.

The following additives may be appropriately added to the refrigerator working fluid composition of the present invention, which is excellent in heat stability and hydrolysis stability of the ester base oil. (I) An additive for removing water may be added to the composition for a refrigerator working fluid of the present invention, which is excellent in heat stability and hydrolysis stability of an ester base oil. Examples of the additive for removing water include compounds having an epoxy group, and additives such as orthoester, acetal (ketal), and carbodiimide.

(Ii) The composition for a working fluid of a refrigerator according to the present invention, which is excellent in heat stability and hydrolysis stability of an ester base oil, has a radical trapping function for improving heat stability. A phenolic compound or a metal deactivator having chelating ability may be added.

The composition for a working fluid of a refrigerator according to the present invention, which is excellent in heat stability and hydrolysis stability of an ester base oil, is characterized in that the ester base oil has a steric hindrance due to an aromatic ring of the ester base oil, and the ester base oil has a metal surface. It is considered that it is difficult to be adsorbed, so that thermal decomposition of the ester base oil occurring on the metal surface is suppressed.
It is also considered that the ester bond is hardly affected by moisture due to steric hindrance caused by the aromatic ring of the ester base oil, and the hydrolysis of the ester base oil is suppressed.

[0039]

The present invention will be described in more detail with reference to the following production examples and test examples, but the present invention is not limited to the following test examples.

Production Example In a 2-liter four-necked flask equipped with a stirrer, a thermometer, a nitrogen blowing tube and a dehydrating tube equipped with a condenser, 300.0 g (2.9 mol) of neopentyl glycol, 2-
494.7 g of ethylhexanoic acid (1.20 times the mol used of neopentyl glycol) and 161.0 g of phthalic anhydride (mol used of neopentyl glycol)
[(Total acid value of monocarboxylic acid and dibasic acid) / (hydroxyl value of alcohol) =
1.0], and a normal pressure reaction was performed at 240 ° C. for 1 hour under a nitrogen stream. Thereafter, a reduced pressure reaction was performed at 400 Torr for 20 hours,
An ester base oil A used in the present invention was obtained. Further, the same reaction as described above was carried out to obtain ester base oils BF shown in Tables 1 and 2 and ester base oils ad used for comparative products. The hydrofluorocarbon containing difluoromethane (HFC32) used in the test example is shown. Hydrofluorocarbon 1: HFC134a / HFC32 / HFC125
(52/23/25 wt%) Hydrofluorocarbon 2: HFC32 / HFC125 (50/50 wt%)

Test Example 1 The kinematic viscosity at 40 ° C. (JIS) of the ester base oil obtained in Production Example
K-2283), 50% by weight of difluoromethane (HFC32)
/ Pentafluoroethane (HFC125) compatibility with 50% by weight and volume resistivity at 25 ° C. (based on JIS C-2101). The results are shown in Tables 1 and 2. The product of the present invention has excellent volume resistivity and good compatibility with hydrofluorocarbons containing difluoromethane (HFC32), but the comparative product a is used for room air conditioners, package air conditioners and industrial refrigerators. And the comparative products b to c were inferior in compatibility with the hydrofluorocarbon containing difluoromethane (HFC32) to the product of the present invention.

Test Example 2 In order to examine the thermal stability of an ester base oil in a refrigerator working fluid composition containing the ester base oil obtained in the production example and a hydrofluorocarbon containing difluoromethane (HFC32), The shield tube test was performed under the conditions shown in the following.

10 g of the ester base oil shown in Tables 1 and 2 in which the water concentration was adjusted to 10 ppm or less and the acid value to 0.01 mg KOH / g or less, and hydrofluorocarbon 1 (5
g) or a composition for a working fluid of a refrigerator comprising hydrofluorocarbon 2 (5 g), and a catalyst having a diameter of 1.6.
An iron piece having a diameter of 150 mm and a length of 150 mm was added to a glass tube and sealed. This glass tube was placed in a stainless steel autoclave and tested at 250 ° C. for 3 days, after which the acid value increase of the ester base oil was examined. As a result, the product of the present invention shown in Table 3
In the presence of difluoromethane (HFC32), the acid value rise was smaller than that of the comparative product, and the ester base oil was excellent in thermal stability.

As shown in the reference example of Table 4, 1,1,1,1,
Method for testing thermal stability for refrigerator applications using 2-tetrafluoroethane (HFC134a) (1,1,1,2)
In the presence of 2-tetrafluoroethane (HFC134a)
Test at 175 ° C. for 14 days. Other conditions are the same as the above shield tube test. ), Thermal decomposition of the ester base oil did not occur, but difluoromethane (HFC3
Method for testing the thermal stability of room air conditioners, packaged air conditioners and industrial refrigerators using hydrofluorocarbons containing 2) (Test at 250 ° C for 3 days in the presence of hydrofluorocarbons containing difluoromethane (HFC32)) )
As shown in Table 3, the product of the present invention was superior to the comparative product in the thermal stability of the ester base oil.

Test Example 3 In order to examine the hydrolysis of the ester base oil in a refrigerator working fluid composition containing the ester base oil obtained in the production example and a hydrofluorocarbon containing difluoromethane (HFC32), A shield tube test was performed under the conditions shown.

10 g of the ester base oil shown in Tables 1 and 2 in which the water concentration was adjusted to 3000 ppm or less and the acid value was adjusted to 0.01 mg KOH / g or less, and difluoromethane (HFC3
2) 2.5 g and pentafluoroethane (HFC12
5) A composition for working fluid of a refrigerator consisting of 2.5 g and an iron piece having a diameter of 1.6 mmφ and a length of 150 mm as a catalyst were added to a glass tube and sealed. This glass tube was placed in a stainless steel autoclave and tested at 175 ° C. for 14 days, after which the acid value increase of the ester base oil was examined. As a result, the product of the present invention shown in Table 5 was obtained from difluoromethane (HFC3
In the presence of 2), the increase in the acid value was smaller than that of the comparative product, and the hydrolysis stability of the ester base oil was excellent.

[0047]

[Table 1]

[0048]

[Table 2]

[0049]

[Table 3]

[0050]

[Table 4]

[0051]

[Table 5]

[0052]

According to the present invention, difluoromethane (HF)
It has become possible to provide a composition for a working fluid of a refrigerator, which has good compatibility with hydrofluorocarbons containing C32) and is excellent in heat stability and hydrolysis stability of an ester base oil.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location C10N 40:30

Claims (5)

[Claims] 1. A divalent to hexavalent alcohol having 2 to 10 carbon atoms, (1) a linear and / or branched monocarboxylic acid having 2 to 10 carbon atoms, or a derivative thereof, and (2) an aromatic ring. A refrigerating machine oil containing an ester base oil obtained from a dibasic acid and / or an anhydride thereof, and a hydrofluorocarbon containing difluoromethane (HFC32), wherein the ester base oil has the following heat A composition for a working fluid of a refrigerator, which provides stability. Thermal stability: (a) Ester base oil 1 whose water concentration is adjusted to 10 ppm or less and acid value is adjusted to 0.01 mgKOH / g or less
(B) 2.5 g of difluoromethane (HFC32) and 2.5 g of pentafluoroethane (HFC125), or 1.15 g of difluoromethane (HFC32), 1.25 g of pentafluoroethane (HFC125) and 1,1,
1,2-tetrafluoroethane (HFC134a)
And (c) an iron piece having a diameter of 1.6 mmφ and a length of 150 mm as a catalyst was added to a glass tube, sealed, and left at 250 ° C. for 3 days, the acid value of the ester base oil increased by 4. 0mgK
OH / g or less. 2. A dibasic acid having an aromatic ring having 8 carbon atoms.
The composition for a working fluid of a refrigerator according to claim 1, which is a dibasic acid of (1) to (12). 3. The composition according to claim 2, wherein the dibasic acid having 8 to 12 carbon atoms is one or more acids selected from the group consisting of phthalic acid, isophthalic acid and terephthalic acid. 4. A low-temperature two-phase separation temperature of -20 ° C. under the conditions of 30% by volume of ester base oil and 70% by volume of hydrofluorocarbon containing difluoromethane (HFC32) (HFC32 is 50% by weight in hydrofluorocarbon). The composition for a refrigerator working fluid according to any one of claims 1 to 3, which is: 5. The composition for a working fluid of a refrigerator according to claim 1, wherein the ester base oil provides the following hydrolysis stability. Hydrolysis stability: a composition comprising 10 g of an ester base oil having a water concentration of 3000 ppm or less and an acid value of 0.01 mg KOH / g or less, 2.5 g of difluoromethane (HFC32) and 2.5 g of pentafluoroethane (HFC125). , And 1.6 mm in diameter and 1 length as a catalyst
When an iron piece of 50 mm is added to a glass tube and sealed and left at 175 ° C. for 14 days, the acid value increase of the ester base oil is 4.0 mgKOH / g or less.