JPH09302370A - Composition for refrigerator working fluid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composition for a refrigerator working fluid having more excellent miscibility than a usual composition, and excellent in heat stability and wear resistance. SOLUTION: This composition contains a refrigerator oil containing an ester obtained from pentaerythritol with an aliphatic acid component containing at least 3-methylhexanoic acid, 5-methylhexanoic acid and 3,5,5-trimethylhexanoic acid as a base oil and a mixed hydrofluorocarbon composed of 1,1,1,2- tetrafluoroethane (HFC134a), difluoromethane (HFC32) and pentafluoroethane (HFC125) or a mixed hydrofluorocarbon composed of difluoromethane (HFC32) and pentafluoroethane (HFC125).

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a composition for a working fluid of a refrigerator, and more particularly, to 1,1,1,2-tetrafluoroethane (HFC134a), difluoromethane (HFC32) and pentafluoroethane (HFC1).
25) A composition for a working fluid of a compression refrigerator using a mixed hydrofluorocarbon consisting of 25) or a mixed hydrofluorocarbon consisting of difluoromethane (HFC32) and pentafluoroethane (HFC125) as a refrigerant.

[0002]

2. Description of the Related Art As a refrigerant for room air conditioners and package air conditioners 1, 1, 1,
2-tetrafluoroethane (HFC134a), difluoromethane (HFC32) and pentafluoroethane (HFC125) mixed hydrofluorocarbons or difluoromethane (HFC32) and pentafluoroethane (HFC125) mixed hydrofluorocarbons are listed as candidates. There is. These mixed hydrofluorocarbons are preferable from the viewpoint of refrigerating capacity, but since difluoromethane (HFC32) has high polarity, 1,1,1,2-tetrafluoroethane (HFC1) is used.
There is a problem that it is not compatible at low temperature with the ester used in the compression refrigerator using only 34a) as a refrigerant. This problem is remarkable when a mixed hydrofluorocarbon composed of difluoromethane (HFC32) and pentafluoroethane (HFC125) is used as a refrigerant, and particularly when the ratio of difluoromethane (HFC32) is 4%.
When it is 5% by weight or more, the compatibility remarkably decreases. Also,
1,1,1,2-tetrafluoroethane (HFC134
Compared to the case where only a) is used, these mixed refrigerants contain difluoromethane (HFC32) with a high vapor pressure, so that the pressure inside the compressor becomes high. Especially, it is used for a room air conditioner or a package air conditioner, or a rotary compressor. When used for a scroll compressor or a scroll type compressor, frictional heat is generated on the sliding surface due to operation under high pressure, and the refrigerating machine oil used is exposed to thermally severe conditions. May cause thermal decomposition, generate carboxylic acid, and further react with a metal to generate a carboxylic acid metal salt, which may block the capillary tube.
Therefore, thermal stability in a refrigerant atmosphere in which oxygen does not exist and in the presence of a metal is required, and it is also required that the metal is not abraded. In particular, thermal stability at a high temperature of about 250 ° C. is important.

JP-A-5-239480 and JP-A-6-17073 disclose difluoromethane (HFC).
32), the compatibility between hydrofluorocarbons and esters is described, but 1,1,1,2-tetrafluoroethane (HFC134a), difluoromethane (HFC32) and pentafluoroethane (HFC1).
There is no mention of mixed hydrofluorocarbons consisting of 25) or mixed hydrofluorocarbons consisting of difluoromethane (HFC32) and pentafluoroethane (HFC125), and no mention is made of the esters which can be used with these mixed hydrofluorocarbons.

Further, Japanese Patent Laid-Open No. 6-184575 discloses compatibility of ester with mixed hydrofluorocarbon composed of 40% by weight of difluoromethane (HFC32) and 60% by weight of pentafluoroethane (HFC125). Difluoromethane (HFC32)
No mention is made of the compatibility with mixed hydrofluorocarbons whose proportion is 45% by weight or more. Moreover, all of the above three publications are 1,1,1,2-tetrafluoroethane (HFC134a) and difluoromethane (H
FC32) and pentafluoroethane (HFC125)
Mixed hydrofluorocarbons or difluoromethane (HFC32) and pentafluoroethane (H
No mention is made of the thermal stability of compositions for refrigerator working fluids using mixed hydrofluorocarbons consisting of FC125).

[0005]

The object of the present invention is to provide 1,1,1,2 by incorporating a specific ester.
-Tetrafluoroethane (HFC134a), difluoromethane (HFC32) and pentafluoroethane (H
FC125) has excellent compatibility with mixed hydrofluorocarbons composed of FC125) or mixed hydrofluorocarbons composed of difluoromethane (HFC32) and pentafluoroethane (HFC125), and exhibits thermal stability even at a high temperature of about 250 ° C. It is intended to provide a composition for a working fluid of a refrigerator, which is excellent in wear resistance.

[0006]

As a result of intensive studies to solve the above problems, the present inventor has found that a composition for a working fluid of a refrigerator containing a specific ester and mixed hydrofluorocarbon solves the above problems. They have found that they can do so and have completed the present invention.

That is, the gist of the present invention is (1) pentaerythritol and at least 3-methylhexanoic acid, 5
-Refrigerating machine oil containing an ester obtained from a fatty acid component containing methylhexanoic acid and 3,5,5-trimethylhexanoic acid as a base oil, 1,1,1,2-tetrafluoroethane (HFC134a), difluoromethane (HFC32) )
And a mixed hydrofluorocarbon consisting of and pentafluoroethane (HFC125) or difluoromethane (HFC32) and pentafluoroethane (HFC12)
A composition for a working fluid of a refrigerator containing a mixed hydrofluorocarbon consisting of 5), and (2) a composition ratio of 3-methylhexanoic acid / 5-methylhexanoic acid of 5/95 to 95.
The composition for a working fluid of a refrigerator according to (1), which has a / 5 weight ratio, (3) 3-based on the total number of acyl groups in the ester.
The composition for refrigerator working fluid according to (1) or (2) above, wherein the ratio of the number of acyl groups derived from methylhexanoic acid and 5-methylhexanoic acid is 10 to 70%, and (4) the total number of acyl groups in the ester. The ester having a ratio of the number of acyl groups having a branched chain to 80% or more as a base oil (1)
A composition for working fluid of a refrigerator according to any one of (3) to (3),
(5) The refrigerator according to any one of (1) to (4), wherein the ester is a base oil in which the ratio of the number of acyl groups having a branched chain at the α-position of the carbonyl group to the total number of acyl groups in the ester is 30% or less. Working fluid composition, and (6) An ester group having a ratio of the number of acyl groups in which the total number of carbon atoms of the branched chain existing at the α-position of the carbonyl group is 2 or more to the total number of acyl groups in the ester is 20% or less The oil (1)
(5) The composition for a working fluid of a refrigerator according to any one of (5).

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The present invention relates to a pentaerythritol, a refrigerating machine oil having an ester obtained from a fatty acid component containing at least 3-methylhexanoic acid, 5-methylhexanoic acid and 3,5,5-trimethylhexanoic acid as a base oil, and 1,1. ，
Refrigeration containing a mixed hydrofluorocarbon composed of 1,2-tetrafluoroethane (HFC134a), difluoromethane (HFC32) and pentafluoroethane (HFC125) or a mixed hydrofluorocarbon composed of difluoromethane (HFC32) and pentafluoroethane (HFC125) It is a composition for machine working fluid.

The ester in the present invention uses pentaerythritol as an alcohol component. Since pentaerythritol is a neopentyl polyol, it has better heat resistance than other polyhydric alcohols. Further, compared with neopentyl polyols such as trimethylol propane, neopentyl glycol, ditrimethylol propane, and dipentaerythritol, it is preferable because the obtained ester has excellent electric insulation. Further, since it is a tetrahydric alcohol, the obtained ester has a viscosity suitable for a refrigerator working fluid for room air conditioners, package air conditioners, rotary type compressors and scroll type compressors.

The pentaerythritol used here is a commercially available high-purity product and has a purity of 90.
As long as it is contained in an amount of not less than 95% by weight, preferably not less than pentaerythritol such as a dimer or trimer of pentaerythritol, it can be used because the effect of the present invention is not affected. In the ester of the present invention, pentaerythritol is used as the alcohol component, but other alcohols may be used within a range that does not affect the viscosity of the obtained ester, the compatibility with the mixed hydrofluorocarbon, and the thermal stability of the working fluid of the refrigerator. You may use together. In that case, the amount of pentaerythritol used is preferably 50% by weight or more, more preferably 70% by weight or more, and particularly preferably 90% by weight or more, based on the total amount of alcohol.

The ester in the present invention uses a branched fatty acid having 7 carbon atoms and a branched fatty acid having 9 carbon atoms as a fatty acid component, and as the branched fatty acid having 7 carbon atoms, 3-methylhexanoic acid, 5-methylhexanoic acid and carbon are used. As the branched fatty acid of the number 9, 3,5,5-trimethylhexanoic acid is used. Since these branched fatty acids have a branch at the 3- or 5-position, 2-ethylhexanoic acid, 2-ethylpentanoic acid,
Compared to branched fatty acids having a branch at the 2-position such as 2-methylhexanoic acid and 2-ethylbutanoic acid, the resulting ester has excellent compatibility with mixed hydrofluorocarbons, a low melting point, excellent low temperature characteristics, and a viscosity index. It has high viscosity properties. Further, even when compared with linear fatty acids, they have excellent compatibility with mixed hydrofluorocarbons and excellent thermal stability.

From the viewpoint of hydrolysis resistance and thermal stability of the obtained ester, the composition ratio of 3-methylhexanoic acid / 5-methylhexanoic acid is preferably 5/95 weight ratio or more, and 15/85 weight%. The ratio is more preferably the ratio or more, and particularly preferably the ratio 30/70 or more. Also, from the viewpoint of the viscosity index of the obtained ester, 95
/ 5 weight ratio or less is preferable, 90/10 weight ratio or less is more preferable, and 85/15 weight ratio or less is particularly preferable. The suitable range of the composition ratio of such 3-methylhexanoic acid / 5-methylhexanoic acid is appropriately determined from the above viewpoints and is not particularly limited, but is 5/95 to 95/5 weight ratio, preferably 15/85.
To 90/10 weight ratio, more preferably 30/70 to 8
5/15 weight ratio.

The ratio of the number of acyl groups derived from 3-methylhexanoic acid and 5-methylhexanoic acid to the total number of acyl groups in the ester in the present invention is preferably 70% or less from the viewpoint of the abrasion resistance of the obtained ester. 60% or less is more preferable, and 55% or less is particularly preferable. Further, from the viewpoint of energy saving, compatibility with mixed hydrofluorocarbons, and viscosity index, 3-methylhexanoic acid and 5
-The ratio of the number of acyl groups derived from methylhexanoic acid is 10
% Or more, more preferably 20% or more, 30
% Or more is particularly preferable. The suitable range of the ratio of the number of acyl groups derived from such 3-methylhexanoic acid and 5-methylhexanoic acid is appropriately determined from the above viewpoint and is not particularly limited, but is 10 to 70%, preferably 20 to 60%. More preferably, it is 30 to 55%.

From the viewpoint of hydrolysis resistance and thermal stability of the resulting ester, the composition ratio of 3-methylhexanoic acid and 5-methylhexanoic acid / 3,5,5-trimethylhexanoic acid is 2/98 weight ratio. It is preferable that it is 10 or more.
The ratio is more preferably 90/90 or more, more preferably 30 /
It is particularly preferable that the ratio is 70% by weight or more. Further, from the viewpoint of the viscosity index of the obtained ester, it is preferably 98/2 weight ratio or less, more preferably 90/10 weight ratio or less, and particularly preferably 70/30 weight ratio or less. The suitable range of the composition ratio of such 3-methylhexanoic acid and 5-methylhexanoic acid / 3,5,5-trimethylhexanoic acid is appropriately determined from the above viewpoint and is not particularly limited, but is 2/98 to 98 / 2 weight ratio, preferably 10/90 to 90/10 weight ratio, and more preferably 30/70 to 70/30 weight ratio.

In the present invention, the ratio of the number of acyl groups derived from 3-methylhexanoic acid, 5-methylhexanoic acid and 3,5,5-trimethylhexanoic acid to the total number of acyl groups in the ester is the abrasion resistance of the resulting ester. From the viewpoints of energy saving, compatibility with mixed hydrofluorocarbons, and thermal stability, 50% or more is preferable, 70% or more is more preferable, and 80% or more is particularly preferable.

The ester in the present invention is preferably an ester consisting only of 3-methylhexanoic acid, 5-methylhexanoic acid and 3,5,5-trimethylhexanoic acid as a fatty acid component, but if desired, other fatty acids may be used in combination. You may use. At that time, from the viewpoint of compatibility with mixed hydrofluorocarbons and thermal stability, the ratio of the number of acyl groups having a branched chain to the total number of acyl groups in the ester is preferably 80% or more, more preferably 90% or more, and 95% or more. Is particularly preferable. From the viewpoint of compatibility with mixed hydrofluorocarbons, the ratio of the number of acyl groups having a branched chain at the α-position of the carbonyl group to the total number of acyl groups in the ester is 3
0% or less is preferable, 20% or less is more preferable, and 1
0% or less is particularly preferable. Similarly, from the viewpoint of compatibility with mixed hydrofluorocarbons, the ratio of the number of acyl groups in which the total number of carbon atoms in the α-position of the carbonyl group to the total number of acyl groups in the ester is 2 or more is particularly small. 20% or less is preferable, and 10% is preferable.
The following is more preferable, and 5% or less is particularly preferable.

The ester in the present invention can be obtained by a normal esterification reaction or transesterification in the absence of a catalyst or in the presence of a catalyst, without using a solvent.

The ester of the present invention has a kinematic viscosity of 4 at 40 ° C. from the viewpoint of energy saving and abrasion resistance.
The range of 0 to 100 mm ² / s is preferable, and 50 to 85 m
The range of m ² / s is more preferable. When the ester of the present invention is used for a composition for a room air conditioner, a package air conditioner, or a refrigerator working fluid for a rotary compressor or a scroll compressor, the range of 50 to 85 mm ² / s is particularly preferable. Moreover, the kinematic viscosity at 100 ° C. is preferably in the range of 1 to ²⁰ mm ² / s, more preferably in the range of 1 to 10 mm ² / s, from the viewpoint of energy saving and abrasion resistance. The viscosity index is 8 from the viewpoint of energy saving.
0 or more is preferable, 90 or more is more preferable, and 95 or more is further preferable.

The refrigerating machine oil containing an ester as a base oil in the present invention includes 1,1,1,2-tetrafluoroethane (H
FC134a), difluoromethane (HFC32) and pentafluoroethane (HFC125) mixed hydrofluorocarbon or difluoromethane (HF)
C32) and pentafluoroethane (HFC125) as long as the compatibility with the mixed hydrofluorocarbon is not impaired, mineral oil, poly α-olefins, alkylbenzenes, esters and polyethers other than the above, perfluoroethers, phosphates, etc. May be mixed.
The ester in the present invention is used as a base oil and occupies 50% or more, preferably 80% or more of the lubricating oil blended in the refrigerating machine oil.

Refrigerating machine oil containing an ester as a base oil in the present invention includes 1,1,1,2-tetrafluoroethane (H
FC134a), difluoromethane (HFC32) and pentafluoroethane (HFC125) mixed hydrofluorocarbon or difluoromethane (HF)
C32) and pentafluoroethane (HFC125) as long as the compatibility with the mixed hydrofluorocarbon is not impaired, usually used antioxidants, extreme pressure agents, oiliness improvers, defoamers, detergent dispersants, rust preventives Various lubricating oil additives such as agents, demulsifiers, viscosity index modifiers, metal deactivators, pour point depressants and the like can be added and used.

1,1,1,2-Tetrafluoroethane (HFC134a), difluoromethane (HFC32) and pentafluoroethane (HFC1) used in the present invention.
From the viewpoint of refrigeration efficiency and safety, the mixing ratio of the mixed hydrofluorocarbon consisting of 25 is 1,1,1,2-
Tetrafluoroethane (HFC134a) is 10-80
Weight% is preferable, and 20 to 70 weight% is more preferable. Difluoromethane (HFC32) is 5 to 40% by weight
Is preferred, and 10 to 30% by weight is more preferred. Pentafluoroethane (HFC125) is preferably 5 to 80% by weight, more preferably 10 to 70% by weight. One of the most preferable mixing ratios is 52% by weight of 1,1,1,2-tetrafluoroethane (HFC134a), 23% by weight of difluoromethane (HFC32), and 25% by weight of pentafluoroethane (HFC125).

Difluoromethane (H used in the present invention
FC32) and pentafluoroethane (HFC125)
The mixing ratio of the mixed hydrofluorocarbon consisting of
From the viewpoint of refrigeration efficiency and safety, difluoromethane (H
FC32) is preferably 45 to 70% by weight and 45 to 60% by weight.
% By weight is more preferred. Pentafluoroethane (HF
C125) is preferably 30 to 55% by weight, and 40 to 55
% By weight is more preferred. As one of the most preferable mixing ratios, 50% by weight of difluoromethane (HFC32),
50% by weight of pentafluoroethane (HFC125) may be mentioned.

Refrigerating machine oil containing an ester as a base oil in the present invention and 1,1,1,2-tetrafluoroethane (HF)
C134a), difluoromethane (HFC32) and pentafluoroethane (HFC125) mixed hydrofluorocarbon or difluoromethane (HFC)
32) and a composition for a working fluid of a refrigerator containing a mixed hydrofluorocarbon composed of pentafluoroethane (HFC125), the blending ratio thereof being mixed hydrofluorocarbon / refrigerating machine oil = 20/1 to 1/1
The weight ratio is 0, preferably 10/1 to 1/5, and particularly preferably 5/1 to 1/5.

In the refrigerator working fluid composition of the present invention thus obtained, the two-phase separation temperature is desirably low, preferably 10 ° C. or lower, more preferably 0 ° C. or lower, and particularly preferably −10 ° C. or lower. preferable.

[0025]

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

Production Example 1 72.5 g (0.53 mol) of pentaerythritol and 3-methylhexanoic acid were placed in a 1-liter four-necked flask equipped with a stirrer, a thermometer, a nitrogen blowing tube and a dehydration tube equipped with a condenser. / 5-methylhexanoic acid (= 68/32 weight ratio) 151.4 g (1.16 mol) and 3,5,5-
185.0 g (1.17 mol) of trimethylhexanoic acid was added, and the reaction was carried out at 240 ° C. under atmospheric pressure for 3 hours under atmospheric pressure. Then, the reduced pressure reaction was carried out at 400 Torr for 5 hours. After completion of the reaction, unreacted fatty acid was removed under reduced pressure to obtain ester A used in the product of the present invention. The obtained ester A was partially hydrolyzed, and the acid composition was examined by gas chromatography analysis. As a result, the acid composition was as shown in Table 1. Further, the same reaction as above was carried out to obtain the esters B to F used in the products of the present invention and the esters a to l used in the comparative products having the acid compositions shown in Tables 1 and 2.

Test Example 1 The kinematic viscosity at 40 ° C. and 100 ° C. and the viscosity index (JIS K-2283) of the ester used in the product of the present invention and the ester used in the comparative product obtained in the Production Example were measured. As a result, as shown in Tables 1 and 2, a, b, d, and f used at 40 ° C.
The kinematic viscosity was not within the preferred range for refrigerator oils for room air conditioners and package air conditioners.

[0028]

[Table 1]

[0029]

[Table 2]

Test Example 2 In order to examine the electrical insulation properties of the esters A and B used in the products of the present invention and the ester c used in the comparative products obtained in the production example,
The volume resistivity at 25 ° C. was measured according to JIS C-2101. As a result, as shown in Table 3, the product of the present invention was superior to the comparative product in electrical insulation.

[0031]

[Table 3]

Test Example 3 Esters A to F used in the products of the present invention obtained in Production Examples or esters b, e, h, i, k, l and 1,1,1,2-tetrafluoroethane used in comparative products. (HFC134
The compatibility with a), a mixed hydrofluorocarbon composed of difluoromethane (HFC32) and pentafluoroethane (HFC125) or a mixed hydrofluorocarbon composed of difluoromethane (HFC32) and pentafluoroethane (HFC125) was investigated. Ester A to F or ester b, e, h, i, k, l and 1,
1,1,2-Tetrafluoroethane (HFC134
The low temperature two-phase separation temperature of a), a mixed hydrofluorocarbon composed of difluoromethane (HFC32) and pentafluoroethane (HFC125) or a mixed hydrofluorocarbon composed of difluoromethane (HFC32) and pentafluoroethane (HFC125) was measured. As a result, as shown in Tables 4 to 7, the product of the present invention was superior in compatibility to the comparative product. Further, as shown in Table 7, in the ester used for the comparative product, difluoromethane (HFC32) / pentafluoroethane (HFC12)
5) = 40/60 There is a good compatibility with a mixed hydrofluorocarbon having a weight ratio, but as shown in Tables 5 and 6, difluoromethane (HFC32), which is a preferable composition from the viewpoint of refrigeration efficiency, is 45 None of the comparative products satisfied the compatibility with the mixed hydrofluorocarbon in an amount of not less than wt%. On the other hand, as can be seen from Tables 6 and 7, the products of the present invention showed excellent compatibility regardless of whether difluoromethane (HFC32) was 40% by weight or 45% by weight.

[0033]

[Table 4]

[0034]

[Table 5]

[0035]

[Table 6]

[0036]

[Table 7]

Test Example 4 Esters A to F used in the products of the present invention or esters d, f, g, j to 1 used in the comparative products obtained in Production Examples and 1,
1,1,2-Tetrafluoroethane (HFC134
In order to investigate the thermal stability of a), a mixed hydrofluorocarbon composed of difluoromethane (HFC32) and pentafluoroethane (HFC125) or a mixed hydrofluorocarbon composed of difluoromethane (HFC32) and pentafluoroethane (HFC125), the following conditions are examined. The shield tube test was conducted at. Water content of 10ppm or less, acid value of 0.01mgKOH /
g 10 g of ester A to F and ester d, f, g and j to l shown in Tables 8 and 9 below and 1,1,1,2-tetrafluoroethane (HFC134a), difluoromethane (HFC32) and penta. Fluoroethane (HFC12
5 g of mixed hydrofluorocarbon composed of 5) or 5 g of mixed hydrofluorocarbon composed of difluoromethane (HFC32) and pentafluoroethane (HFC125) and a catalyst having a diameter of 1.6 mm and a length of 150 mm
Add copper, iron and aluminum to a glass tube and seal it.
It was placed in a stainless steel autoclave and sealed. 250
After testing at ℃ for 3 days, the hue of the product of the present invention (JIS K-258
0), acid value (JIS K-2501) and the presence or absence of precipitates were examined.
As a result, as shown in Tables 8 and 9, the product of the present invention was superior in heat stability to the comparative product.

[0038]

[Table 8]

[0039]

[Table 9]

Test Example 5 Esters A and B used in the product of the present invention obtained in Production Example or ester a used in the comparative product and 1,1,1,2-tetrafluoroethane (HFC134a), difluoromethane (HFC32) and Pentafluoroethane (HFC12
In order to investigate the wear resistance of a composition for a working fluid of a refrigerator containing a mixed hydrofluorocarbon composed of 5) or a mixed hydrofluorocarbon composed of difluoromethane (HFC32) and pentafluoroethane (HFC125), a FALEX test was carried out. . Ester 10
0 ml was heated to 80 ° C., 1,1,1,2-tetrafluoroethane (HFC134a), difluoromethane (H
FC32) and pentafluoroethane (HFC125)
Mixed hydrofluorocarbons or difluoromethane (HFC32) and pentafluoroethane (H
FC125) was run under a flow of mixed hydrofluorocarbon (10 liters / hour) under a load of 150 lbs for 4 hours, and the abrasion amount of V block and pin after the operation was measured. As a result, as shown in Table 10, the product of the present invention was superior in wear resistance to the comparative product.

[0041]

[Table 10]

[0042]

The composition for a working fluid of a refrigerator of the present invention is more excellent in compatibility, heat stability and abrasion resistance than conventional compositions.

Claims (6)

[Claims] 1. Pentaerythritol and at least 3
-Methylhexanoic acid, 5-methylhexanoic acid and 3,
Refrigerating machine oil having an ester obtained from a fatty acid component containing 5,5-trimethylhexanoic acid as a base oil;
2-Tetrafluoroethane (HFC134a), difluoromethane (HFC32) and pentafluoroethane (HFC125) mixed hydrofluorocarbon or refrigerator operation containing difluoromethane (HFC32) and pentafluoroethane (HFC125) mixed hydrofluorocarbon Fluid composition. 2. The composition for refrigerator working fluid according to claim 1, wherein the composition ratio of 3-methylhexanoic acid / 5-methylhexanoic acid is 5/95 to 95/5 by weight. 3. 3-based on the total number of acyl groups in the ester
The composition for refrigerator working fluid according to claim 1 or 2, wherein the ratio of the number of acyl groups derived from methylhexanoic acid and 5-methylhexanoic acid is 10 to 70%. 4. The composition for refrigerator working fluid according to claim 1, wherein the ester is a base oil having a ratio of the number of acyl groups having a branched chain to the total number of acyl groups in the ester of 80% or more. 5. The ratio of the number of acyl groups having a branched chain at the α-position of the carbonyl group to the total number of acyl groups in the ester is 30%.
The composition for refrigerator working fluid according to claim 1, wherein the following ester is used as a base oil. 6. The base oil is an ester having a ratio of the number of acyl groups having a total of 2 or more carbon atoms in the branched chain existing at the α-position of the carbonyl group to the total number of acyl groups in the ester of 20% or less. The composition for refrigerator working fluid according to any one of 1 to 5.