JP3214811B2 - Composition for working fluid of refrigerator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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).
The present invention relates to a composition for a working fluid of a compression refrigerator using a mixed hydrofluorocarbon composed of 25) or a mixed hydrofluorocarbon composed of difluoromethane (HFC32) and pentafluoroethane (HFC125) as a refrigerant.

[0002]

2. Description of the Related Art As a refrigerant for a room air conditioner or a package air conditioner, 1,1,1,1 is used.
Candidates include a mixed hydrofluorocarbon composed of 2-tetrafluoroethane (HFC134a), difluoromethane (HFC32) and pentafluoroethane (HFC125) or a mixed hydrofluorocarbon composed of difluoromethane (HFC32) and pentafluoroethane (HFC125). I have. These mixed hydrofluorocarbons are preferable from the viewpoint of refrigerating capacity, but because of the high polarity of difluoromethane (HFC32), 1,1,1,2-tetrafluoroethane (HFC1) is preferred.
There is a problem that it is not compatible at low temperature with an ester used in a 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%.
If the content is 5% by weight or more, the compatibility is significantly reduced. Also,
1,1,1,2-tetrafluoroethane (HFC134
Compared to the case where only a) is used, these mixed refrigerants contain difluoromethane (HFC32) having a high vapor pressure, so that the pressure in the compressor becomes high. When using an ester as the base oil, when used under high pressure, frictional heat is generated on the sliding surface due to operation under high pressure, and the refrigerating machine oil used is exposed to severe thermal conditions. May cause thermal decomposition to generate a carboxylic acid, and further react with a metal to generate a metal carboxylate, which may block the capillary tube.
Therefore, it is required to have thermal stability in a refrigerant atmosphere in which oxygen does not exist and in the presence of a metal, and not to wear metal. In particular, thermal stability at a high temperature of about 250 ° C. is important.

[0003] JP-A-5-239480 and JP-A-6-17073 disclose difluoromethane (HFC).
32), the compatibility of hydrofluorocarbons and esters, including 1,1,1,2-tetrafluoroethane (HFC134a), difluoromethane (HFC32) and pentafluoroethane (HFC1).
There is no description of a mixed hydrofluorocarbon composed of 25) or a mixed hydrofluorocarbon composed of difluoromethane (HFC32) and pentafluoroethane (HFC125), and no mention is made of esters that can be used with these mixed hydrofluorocarbons.

Japanese Patent Application Laid-Open No. 6-184575 discloses the compatibility of a mixed hydrofluorocarbon composed of 40% by weight of difluoromethane (HFC32) and 60% by weight of pentafluoroethane (HFC125) with an ester. Difluoromethane (HFC32)
No mention is made of the compatibility with mixed hydrofluorocarbons having a ratio of 45% by weight or more. Moreover, the above three publications all disclose 1,1,1,2-tetrafluoroethane (HFC134a) and difluoromethane (HFC134a).
FC32) and pentafluoroethane (HFC125)
Mixed hydrofluorocarbon or difluoromethane (HFC32) and pentafluoroethane (H
No mention is made of the thermal stability of a refrigerator working fluid composition using a mixed hydrofluorocarbon comprising FC125).

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide 1,1,1,2,1 by containing a specific ester.
-Tetrafluoroethane (HFC134a), difluoromethane (HFC32) and pentafluoroethane (HFC134a)
FC125), and has excellent compatibility with mixed hydrofluorocarbons composed of difluoromethane (HFC32) and pentafluoroethane (HFC125), and exhibits thermal stability even at a high temperature of about 250 ° C. An object of the present invention is to provide a composition for a working fluid of a refrigerator having excellent wear properties.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, a composition for a working fluid of a refrigerator containing a specific ester and a mixed hydrofluorocarbon has solved the above-mentioned problems. The inventors have found that the present invention can be performed, and have completed the present invention.

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

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The present invention relates to a refrigerator oil comprising pentaerythritol and 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; ,
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. It is also preferable because the resulting ester is superior in electric insulation to neopentyl polyol such as trimethylolpropane, neopentylglycol, ditrimethylolpropane, dipentaerythritol and the like. Further, since it is a tetrahydric alcohol, the obtained ester has a viscosity suitable for a refrigerator working fluid for a room air conditioner or a package air conditioner, or for a rotary compressor or a scroll compressor.

[0010] The pentaerythritol used here is a commercially available high-purity product having a purity of 90%.
If it is at least 95% by weight, preferably at least 95% by weight, even if pentaerythritol dimer, trimer or the like is contained as an impurity, it can be used because it does not affect the effect of the present invention. As the ester in the present invention, pentaerythritol is used as the alcohol component.However, other alcohols are used as long as the viscosity of the obtained ester, the compatibility with the mixed hydrofluorocarbon and the thermal stability of the working fluid of the refrigerator are not affected. You may use together. In this 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 alcohol amount.

In the ester of the present invention, a branched fatty acid having 7 carbon atoms and a branched fatty acid having 9 carbon atoms are used as the fatty acid component. The branched fatty acid having 7 carbon atoms includes 3-methylhexanoic acid, 5-methylhexanoic acid, As the branched fatty acid of Formula 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 with 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 properties, and a viscosity index. High viscosity characteristics. Also, as compared with straight-chain fatty acids, it has excellent compatibility with mixed hydrofluorocarbons and excellent heat stability.

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

In the present invention, 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 is preferably 70% or less from the viewpoint of abrasion resistance of the resulting ester. It is more preferably at most 60%, particularly preferably at most 55%. Further, from the viewpoint of energy saving, compatibility with mixed hydrofluorocarbon 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, and 30% or more.
% Is particularly preferable. The suitable range of the ratio of the number of acyl groups derived from 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 the hydrolysis resistance and thermal stability of the obtained ester, the composition ratio of 3-methylhexanoic acid and 5-methylhexanoic acid / 3,5,5-trimethylhexanoic acid is 2/98 weight ratio. It is preferably at least 10
/ 90 weight ratio or more, more preferably 30/90
It is particularly preferred that the ratio be at least 70% by weight. Further, from the viewpoint of the viscosity index of the obtained ester, it is preferably at most 98/2 weight ratio, more preferably at most 90/10 weight ratio, particularly preferably at most 70/30 weight ratio. The suitable range of the composition ratio of 3-methylhexanoic acid and 5-methylhexanoic acid / 3,5,5-trimethylhexanoic acid is appropriately determined from the above viewpoint, and is not particularly limited. 2 weight ratio, preferably 10/90 to 90/10 weight ratio, 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 determined by the abrasion resistance of the resulting ester. From the viewpoints of energy saving, compatibility with the mixed hydrofluorocarbon, 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 of only 3-methylhexanoic acid, 5-methylhexanoic acid and 3,5,5-trimethylhexanoic acid as a fatty acid component. May be used. In this case, from the viewpoint of compatibility with the mixed hydrofluorocarbon 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 preferred. From the viewpoint of compatibility with the mixed hydrofluorocarbon, 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%.
It is preferably 0% or less, more preferably 20% or less, and 1% or less.
0% or less is particularly preferred. Similarly, from the viewpoint of compatibility with the mixed hydrofluorocarbon, the ratio of the number of acyl groups in which the total number of carbon atoms of the branched chain present at the α-position of the carbonyl group to the total number of acyl groups in the ester is 2 or more is particularly small. Is more preferable, 20% or less is preferable, and 10%
The following is further preferable, and 5% or less is particularly preferable.

The ester in the present invention can be obtained by ordinary esterification or transesterification without a solvent or in the presence of a catalyst using no solvent.

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

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

The refrigerating machine oil containing ester as a base oil in the present invention includes 1,1,1,2-tetrafluoroethane (H
FC134a), a mixed hydrofluorocarbon comprising difluoromethane (HFC32) and pentafluoroethane (HFC125) or difluoromethane (HF)
C32) and pentafluoroethane (HFC125) as long as the compatibility with the mixed hydrofluorocarbon is not impaired, as long as it does not impair the compatibility, a commonly used antioxidant, extreme pressure agent, oiliness improver, defoamer, detergent / dispersant, rust prevention Various lubricating oil additives such as an emulsifier, a demulsifier, a viscosity index adjuster, a metal deactivator, and a pour point depressant can be used.

The 1,1,1,2-tetrafluoroethane (HFC134a), difluoromethane (HFC32) and pentafluoroethane (HFC1) used in the present invention.
25, from the viewpoint of refrigeration efficiency and safety, 1,1,1,2-
Tetrafluoroethane (HFC134a) is 10 to 80
% By weight, more preferably 20 to 70% by weight. 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 mixing ratios is 1,1,1,2-tetrafluoroethane (HFC134a) 52% by weight, difluoromethane (HFC32) 23% by weight, and pentafluoroethane (HFC125) 25% by weight.

The difluoromethane (H
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 from 30 to 55% by weight, and from 40 to 55% by weight.
% By weight is more preferred. One of the most preferable mixing ratios is difluoromethane (HFC32) 50% by weight,
50% by weight of pentafluoroethane (HFC125).

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

In the composition for a working fluid of a refrigerator 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, which by no means limit the present invention.

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 dehydrating tube equipped with a condenser. 151.4 g (1.16 mol) of 3,5-methylhexanoic acid (= 68/32 weight ratio) and 3,5,5-
185.0 g (1.17 mol) of trimethylhexanoic acid was added, and a normal pressure reaction was performed at 240 ° C. for 3 hours under a nitrogen stream. Thereafter, a reduced pressure reaction was performed at 400 Torr for 5 hours. After completion of the reaction, unreacted fatty acids were 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 described above was carried out to obtain esters BF used for the product of the present invention and esters al used for 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 Production Examples were measured. As a result, as shown in Tables 1 and 2, 40 ° C. of a, b, d, and f used for comparative products
The kinematic viscosity was not in a range suitable for a refrigerator oil for a room air conditioner or a package air conditioner.

[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 product of the present invention obtained in the production example and the ester c used in the comparative product,
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 in electrical insulation to the comparative product.

[0031]

[Table 3]

Test Example 3 Esters A to F used in the product of the present invention obtained in Production Examples or esters b, e, h, i, k, l used in the comparative product and 1,1,1,2-tetrafluoroethane (HFC134
a), a mixed hydrofluorocarbon composed of difluoromethane (HFC32) and pentafluoroethane (HFC125) or a mixed hydrofluorocarbon composed of difluoromethane (HFC32) and pentafluoroethane (HFC125) was examined. Esters A to F or esters b, e, h, i, k, l and 1,
1,1,2-tetrafluoroethane (HFC134
a) A low-temperature two-phase separation temperature of 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 more excellent in compatibility than the comparative product. As shown in Table 7, difluoromethane (HFC32) / pentafluoroethane (HFC12)
5) Although there is a good compatibility with the mixed hydrofluorocarbon having a weight ratio of 40/60, as shown in Tables 5 and 6, difluoromethane (HFC32) having a preferable composition from the viewpoint of refrigeration efficiency is 45%. None of the comparative products was satisfactory in terms of compatibility with the mixed hydrofluorocarbon of not less than% by weight. In contrast, as can be seen from Tables 6 and 7, the product of the present invention exhibited excellent compatibility 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 Ester A to F used in the product of the present invention obtained in Production Example or esters d, f, g, j to l used in the comparative product and 1,
1,1,2-tetrafluoroethane (HFC134
a) In order to examine the thermal stability of a mixed hydrofluorocarbon composed of difluoromethane (HFC32) and pentafluoroethane (HFC125) or a mixed hydrofluorocarbon composed of difluoromethane (HFC32) and pentafluoroethane (HFC125), the following conditions were used. A shield tube test was performed. A water concentration of 10 ppm or less and an acid value of 0.01 mg KOH /
g 10 g of the esters A to F and the esters d, f, g, j to l shown in Tables 8 and 9 are combined with 1,1,1,2-tetrafluoroethane (HFC134a), difluoromethane (HFC32) and pentane. Fluoroethane (HFC12
5) A mixed hydrofluorocarbon composed of 5) or 5 g of a mixed hydrofluorocarbon composed of difluoromethane (HFC32) and pentafluoroethane (HFC125), and 1.6 mm in diameter and 150 mm in length as a catalyst
Copper, iron and aluminum are added to the glass tube and sealed,
It was sealed in a stainless steel autoclave. 250
After testing at ℃ for 3 days, the color 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 to the comparative product in thermal stability.

[0038]

[Table 8]

[0039]

[Table 9]

Test Example 5 Ester A, 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
The FLEX test was used to examine 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). . Ester 10
0 ml was heated to 80 ° C., and 1,1,1,2-tetrafluoroethane (HFC134a) and difluoromethane (H
FC32) and pentafluoroethane (HFC125)
Mixed hydrofluorocarbon or difluoromethane (HFC32) and pentafluoroethane (H
The mixture was operated for 4 hours under a load of 150 lb under a flow of a mixed hydrofluorocarbon composed of FC125) (10 liters / hour), and the abrasion loss of the V block and the pins after the operation was measured. As a result, as shown in Table 10, the product of the present invention was superior to the comparative product in abrasion resistance.

[0041]

[Table 10]

[0042]

Industrial Applicability The composition for a working fluid of a refrigerator according to the present invention is excellent in compatibility, heat stability and abrasion resistance as compared with the conventional composition.

Continuation of the front page (56) References JP-A-6-17073 (JP, A) JP-A-6-184575 (JP, A) JP-A-5-239480 (JP, A) JP-A-5-209171 (JP) JP-A-6-330061 (JP, A) JP-A-3-217493 (JP, A) JP-A-8-503975 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB Name) C10M 105/34 C09K 5/04 C10N 40:30

Claims (6)

(57) [Claims] 1. A method according to claim 1, wherein the pentaerythritol comprises at least 3
-Methylhexanoic acid, 5-methylhexanoic acid and 3,
Refrigerating machine oil based on an ester obtained from a fatty acid component containing 5,5-trimethylhexanoic acid, and 1,1,1,
Refrigerator operation containing a mixed hydrofluorocarbon composed of 2-tetrafluoroethane (HFC134a), difluoromethane (HFC32) and pentafluoroethane (HFC125) or a mixed hydrofluorocarbon composed of difluoromethane (HFC32) and pentafluoroethane (HFC125) Fluid composition. 2. The composition according to claim 1, wherein the composition ratio of 3-methylhexanoic acid / 5-methylhexanoic acid is 5/95 to 95/5 by weight. 3. The method according to claim 1, wherein 3- is based on the total number of acyl groups in the ester.
The composition 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 a working fluid of a refrigerator according to any one of claims 1 to 3, wherein the ester is a base oil wherein the ratio of the number of acyl groups having a branched chain to the total number of acyl groups in the ester is 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 a refrigerator working fluid according to any one of claims 1 to 4, wherein the following ester is used as a base oil. 6. An ester 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 to the total number of acyl groups in the ester is 2 or more to 20% or less to the total number of acyl groups in the ester is 20% or less. 6. The composition for a working fluid of a refrigerator according to any one of 1 to 5.