JPH03200895A - Refrigerator oil for use in chlorine-free fluorocarbon refrigerant - Google Patents

Abstract

PURPOSE:To provide a lubricating oil for use in a chlorine-free fluorocarbon refrigerant, wherein good compatibility with the chlorine-free fluorocarbon and good electrical insulating properties are achieved, by compounding a pentaerythritol ester having a specific structure as the principal component. CONSTITUTION:A refrigerator oil for use in a chlorine-free fluorocarbon refrigerant consists mainly of a pentaerythritol ester shown by the formula (where R1 to R4 are the same or different 3-11C and preferably 3-7C linear chain alkyls, 3-15C and preferably 4-11C branched alkyls and 6-12C and preferably 6-8C cycloalkyls; the linear chain alkyl groups should amount to 60% or less and preferably 50% or less of the total alkyl groups; and (n) is 1 to 3) (e.g. tetraester of pentaerythritol with 2-ethylhexanoic acid). The refrigerator oil has good compatibility with chlorine-free fluorocarbon such as HFC-134a and has good wear resistance and nonhygroscopic properties.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a refrigerating machine oil for non-chlorinated fluorocarbon refrigerant, and more specifically, the present invention relates to a refrigerating machine oil for non-chlorinated fluorocarbon refrigerant, and more specifically, a refrigerating machine oil having a specific structure and having excellent performance. This relates to refrigeration oil for non-chlorinated fluorocarbon refrigerants.

[Prior art and problems to be solved by the invention] Conventionally, refrigerating machine oil has a kinematic viscosity of 1 at 40"C.
Generally used are naphthenic mineral oils of 0 to 200 cSt, paraffinic mineral oils, alkylbenzenes, polyglycol oils, ester oils, mixtures thereof, or mixtures of these various base oils with additives.

On the other hand, as a fluorocarbon refrigerant used in refrigerators, CF
C-11SCFC-12, CFC-113, HCFC-
22 etc. are used.

Among these fluorocarbon refrigerants, CF C'-IL CF
CFCs, which are hydrocarbons such as C-12, CF, and C-113, in which all the hydrogen is replaced with halogens including chlorine, are subject to regulations because they lead to ozone layer destruction. Therefore, non-chlorinated fluorocarbons such as RF C-134a and RF C-152a are being used as substitutes for CFCs.
In particular, RFC-184a is based on CFC-12, which has traditionally been used in many refrigerators such as household refrigerators and air conditioners.
It has similar thermodynamic properties and is a promising alternative refrigerant.

Although refrigerating machine oil has various performance requirements, compatibility with refrigerant is extremely important from the viewpoint of lubricity and system efficiency of the refrigerating machine. However, refrigeration oils based on naphthenic mineral oils, paraffinic mineral oils, alkylbenzenes, and conventionally known ester oils are classified as RF C-13.
Since it has almost no compatibility with non-chlorinated fluorocarbons such as 4a, when used in combination with RFC-134a, two-layer separation occurs at room temperature, impairing oil return, which is the most important property in a refrigeration system, and reducing refrigeration efficiency. This causes various problems in practical use, such as a decrease in lubricity or poor lubricity, such as seizure of the compressor, making it unusable. Polyglycols are also known as refrigerating machine oils having a high viscosity index;
It is described in Japanese Patent Application Laid-Open No. 57-51795, etc. However, the polyglycol oils specifically disclosed in these prior art still contain HF C-134a.
The same problem as above occurs because the compatibility with the compound is not sufficient, and it cannot be used practically.

Also, in U.S. Patent No. 4,755.316, RFC-1
A polyglycol-based refrigerating machine oil that is compatible with No. 34a is disclosed. Additionally, the present inventors have previously developed a polyglycol-based refrigerating machine oil that has significantly better compatibility with RFC-134a than conventionally known refrigerating machine oils, and have already filed an application for the same (Unexamined Patent Publication No. -256594 Publication, 1-27
1491, etc.). However, it has been found that polyglycol oils have the problems of high water solubility and poor electrical insulation.

On the other hand, refrigeration oil used in compressors such as home refrigerators is required to have high electrical insulation properties.Among the known refrigeration oils, those with the highest insulating properties are alkylbenzene and mineral oil. Alkylbenzene and mineral oil have almost no compatibility with non-chlorinated fluorocarbons such as RF C-134a. Therefore, a refrigerating machine oil that has both high compatibility with non-chlorinated fluorocarbons such as RF C-134a and high insulation properties has not yet appeared.

As a result of repeated research to develop a refrigerating machine oil that can meet the above requirements, the present inventors discovered that an ester with a specific structure
Excellent compatibility with non-chlorinated fluorocarbons such as C-134a,
They have also discovered that it has high electrical insulation properties and even better lubrication properties, leading to the completion of the present invention.

The present invention provides R
The object of the present invention is to provide a lubricating oil for a non-chlorinated fluorocarbon refrigerant that has excellent compatibility with non-chlorinated fluorocarbons such as FC-134a and has high electrical insulation properties.

[Means for Solving the Problems] That is, the present invention provides the following: a straight chain alkyl group having 3 to 11 carbon atoms, a straight chain alkyl group having 3 to 11 carbon atoms;
5 branched alkyl groups and cycloalkyl groups having 8 to 12 carbon atoms, the proportion of straight chain alkyl groups is 60% or less of the total alkyl groups, and n is 1.
[indicates an integer from 3 to 3] ] A refrigerating machine oil for a non-chlorine-based fluorocarbon refrigerant is provided, which is characterized by containing a pentaerythritol ester represented by the following as a main component.

Hereinafter, the content of the present invention will be explained in more detail.

The refrigerating machine oil of the present invention has a pentaerythritol ester represented by the symbol - as a main component. In the above formula, R1-R4 may be the same or different and each has 3 to 11 carbon atoms, preferably 3
~7 straight chain alkyl group, 3 to 15 carbon atoms, preferably 4
-11 branched alkyl groups, and cycloalkyl groups having 6 to 12 carbon atoms, preferably B to 8 carbon atoms.

In addition, the cycloalkyl group as used in the present invention also includes an alkylcycloalkyl group. In addition, the proportion of straight chain alkyl groups is 60% or less, preferably 50% or less, based on the total alkyl groups.
% or less. Furthermore, n has shown the integer of 1-3. That is, the above formula shows monopentaerythritol ester, dipentaerythritol ester, and tripentaerythritol ester. If a pentaerythritol ester that does not meet the above conditions is used as the main component, it is not preferable because it has poor compatibility with non-chlorinated chlorofluorocarbons.

R1-R4 are specifically, for example, n-propyl group, n-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, n-nonyl group, n-
-decyl group, n-undecyl group, 1so~propyl group,
1so-butyl group, 15o-pentyl group, 1so-hexyl group, 1so-heptyl group, 1so-octyl group, 1
so-nonyl group, 1so-decyl group, 1so-undecyl group, 1so-dodecyl group, 1so-tridecyl group, 1
so-tetradecyl group, 1so-pentadecyl group, cyclohexyl group, cycloheptyl group, cyclooctyl group,
Examples thereof include a cyclononyl group, a cyclodecyl group, a cycloundecyl group, a cyclododecyl group, a methylcyclohexyl group, an ethylcyclohexyl group, a propylcyclohexyl group, a butylcyclohexyl group, a pentylcyclohexyl group, and a hexylcyclohexyl group.

The pentaerythritol ester used in the present invention is
An ester of pentaerythritol, dipentaerythritol or tripentaerythritol with a monocarboxylic acid, usually containing pentaerythritol, dipentaerythritol or tripentaerythritol, or a mixture thereof, and an alkyl group as described above. It can be obtained by reacting one, one species, or a mixture of two or more carboxylic acids. The obtained product may be purified to remove by-products and unreacted substances, but small amounts of by-products and unreacted substances may be removed as long as they do not adversely affect the excellent performance of the refrigeration oil of the present invention. , there is no problem even if it exists.

As the pentaerythritol ester used in the present invention, any compound having the structure shown in the above formula can be used, but the kinematic viscosity is 2 to 150 cst at 100°C, preferably 5 to 100 cst.
It is desirable that it be t.

The refrigerating machine oil of the present invention may use the above pentaerythritol ester alone, but may also be used in combination with other refrigerating machine oil base oils as required. Preferred base oils include the following.

General formula % Formula % [In the formula, R5 and R6 represent hydrogen or an alkyl group having 1 to 18 carbon atoms, R7 represents an alkylene group having 2 to 4 carbon atoms, and a represents an integer of 5 to 70] The represented polyoxyalkylene glycol or its ether.

General formula % Formula % [In the formula, R8-R10 represents hydrogen or an alkyl group having 1-18 carbon atoms, R0-R13 represents an alkylene group having 2-4 carbon atoms, and b-d is an integer of 5-7. Polyoxyalkylene glycol glycerol ether represented by:

The group represented by the general formula % formula %, Y represents age or represents, R14 and R2゜ are alkylene groups having 1 to 8 carbon atoms, RIg and R17 are alkylene groups having 2 to 1B carbon atoms, and R16 and R21 are alkylene groups having 2 to 1B carbon atoms. 1 to 15 alkyl groups, RIs and R19 each represent an alkyl group having 1 to 14 carbon atoms, e and f represent 0 or the number of l, and n represents an integer of 0 to 30, respectively] ester.

- Monana [wherein R2□ to R2□ represent an alkyl group having 3 to 15 carbon atoms, R28 represents a divalent hydrocarbon group having 1 to 8 carbon atoms,
In addition, h represents an integer of 1 to 5] pentaerythritol dicarboxylic acid ester.

These oils may be used alone or in combination. Note that oils such as paraffinic and naphthenic mineral oils, polyα-olefins, and alkylbenzenes may also be mixed, but in this case, the compatibility with non-chlorinated chlorofluorocarbon solvents decreases.

The blending amount of these base oils is not particularly limited as long as it does not impair the excellent performance of the refrigerating machine oil of the present invention, but the proportion of pentaerythritol ester is usually 50% by weight based on the total amount of the refrigerating machine oil. %, preferably 70% or more by weight.

In the refrigeration oil composition of the present invention, in order to further improve its wear resistance and load carrying capacity, phosphoric acid esters, acidic phosphoric esters, amine salts of acidic phosphoric esters, chlorinated phosphoric esters and phosphorous esters are used. At least one phosphorus compound selected from the group consisting of esters can be blended. These phosphorus compounds are esters of phosphoric acid or phosphorus with alkanols, polyether-type alcohols, or derivatives thereof. Specifically, examples of the phosphoric acid ester include tributyl phosphate, triphenyl phosphate, tricresyl phosphate, and the like. Examples of the acidic phosphoric acid ester include ditetradecyl and phosphate, dipentadecyl acid phosphate, dihexadecyl acid phosphate, dipentadecyl acid phosphate, dioctadecyl acid phosphate, and the like. Examples of the amine salts of acidic phosphoric esters include methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, heptylamine, octylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, Examples include salts with amines such as dibentylamine, diethylamine, diethylamine, dioctylamine, trimethylamine, triethylamine, tripropylamine, tributylamine, tripentylamine, trihexylamine, trihebutylamine ζ°trioctylamine, and the like. Examples of the chlorinated phosphate ester include tris dichloropropyl phosphate, tris chloroethyl phosphate, polyoxyalkylene bis[di(chloroalkyl)] phosphate, tris chlorophenyl phosphate, and the like. Phosphite esters include dibutyl phosphite, tributyl phosphite, dioctyl phosphite, tripentyl phosphite, didecyl phosphite, trihexyl phosphite, dioctyl phosphite, trihebutyl phosphite, dioctyl phosphite, and trihexyl phosphite. Octyl phosphite, dinonyl phosphite, didecyl phosphite, dioctyl phosphite, triundecyl phosphite, didodecyl phosphite, tridodecyl phosphite, diphenyl phosphite, triphenyl phosphite, didecyl phosphite, tricle Examples include dilphosphite.

Mixtures of these can also be used. When blending these phosphorus compounds, the amount is 0, 1 to 5.
It is desirable to contain it in a proportion of 0% by weight, preferably 0.2 to 2.0% by weight.

Furthermore, in order to further improve the stability of the refrigeration oil of the present invention, at least IFJ selected from the group consisting of phenyl glycidyl ether type epoxy compounds, glycidyl ester type epoxy compounds, epoxidized fatty acid monoesters, and epoxidized vegetable oils is added. An epoxy compound can be blended. Examples of the phenylglycidyl ether type epoxy compound mentioned here include phenylglycidyl ether and alkylphenylglycidyl ether. The alkyl phenyl glycidyl ether herein refers to an alkyl group having 1 to 13 carbon atoms.
Among them, those having one alkyl group having 4 to 10 carbon atoms, such as butylphenyl glycidyl ether, pentylphenyl glycidyl ether, hexylphenyl glycidyl ether, heptylphenyl glycidyl ether, octylphenyl glycidyl ether, nonylphenyl Glycidyl ether and daisylphenyl glycidyl ether are preferred. Examples of the glycidyl ester type epoxy compound include phenyl glycidyl ester, alkyl glycidyl ester, alkenyl glycidyl ester, etc., and preferred ones include glycidyl benzoate, glycidyl acrylate,
Examples include glycidyl methacrylate.

Examples of epoxidized fatty acid monoesters include esters of epoxidized fatty acids having 12 to 20 carbon atoms and alcohols, phenols, and alkylphenols having 1 to B carbon atoms. In particular, butyl, hexyl, benzyl, cyclohexyl, methoxyethyl, octyl, phenyl and butylphenyl esters of epoxystearic acid are preferably used.

Examples of epoxidized vegetable oils include epoxy compounds of vegetable oils such as soybean oil, linseed oil, and cottonseed oil.

Among these epoxy compounds, preferred are phenyl glycidyl ether type epoxy compounds and epoxidized fatty acid monoesters.

Among these, phenylglycidyl ether type epoxy compounds are more preferred, and phenylglycidyl ether, butylphenylglycidyl ether and mixtures thereof are particularly preferred.

When blending these epoxy compounds, the amount is 0.1 to 5.0% by weight, preferably 0.2 to 26% by weight based on the total amount of refrigerating machine oil.
It is desirable to contain it in a proportion of 0% by weight.

Moreover, it goes without saying that the above-mentioned phosphorus compound and epoxy compound may be used in combination.

Furthermore, in order to further improve the performance of the refrigerating machine oil in the present invention, conventionally known refrigerating machine oil additives may be added, for example, phenolic additives such as di-tert-butyl-p-cresol, bisphenol A, phenyl -α-naphthylamine, N,N-di(2-naphthyl)
-Amine-based antioxidants such as p-phenylenediamine,
Anti-wear agents such as zinc dithiophosphate, chlorinated paraffin,
Additives such as extreme pressure agents such as sulfur compounds, oily agents such as fatty acids, antifoaming agents such as seeso-cone type, and metal deactivators such as benzotriazole may be added singly or in combination. It is possible. The total amount of these additives is usually 10% by weight or less, preferably 5% by weight or less, based on the total amount of refrigerating machine oil.

The refrigerating machine oil containing pentaerythritol ester as a main component of the present invention only needs to have a kinematic viscosity and pour point that are normally used as refrigerating machine oil, but in order to prevent the refrigerating machine oil from solidifying at low temperatures, has a pour point of 110°C or less,
The temperature is preferably -20°C to -80°C.

In addition, in order to maintain a tight seal with the compressor, the kinematic viscosity at 100°C is desirably 2 CSt or more, preferably 3 cSt or more. Considering the fluidity at low temperatures and the efficiency of heat exchange in the vaporizer, is 15
It is desirable that it be 0 cSt or less, preferably 100 cSt or less.

The refrigerating machine oil of the present invention has significantly better compatibility with non-chlorinated fluorocarbons than conventionally known refrigerating machine oils. Specific examples of non-chlorinated chlorofluorocarbons include -1.1.2°2-tetrafluoroethane (RFC-134).

1.1.2-tetrafluoroethane (RF C-184
a), 1,1-difluoroethane (RFC-152g)
, trifluoromethane (RFC-23), etc., but the preferred one is RF C-134a.

Furthermore, the refrigerating machine oil of the present invention not only has high compatibility with non-chlorinated fluorocarbons and high electrical insulation properties, but is also an excellent refrigerating machine oil with high lubricity and low hygroscopicity.

The refrigeration oil of the present invention can be used in air conditioners with reciprocating or rotary compressors, dehumidifiers, refrigerators, freezers, frozen and refrigerated warehouses,
It can be particularly preferably used for cooling devices such as vending machines, showcases, and chemical plants, but it can also be preferably used for those having centrifugal compressors.

[Example] Hereinafter, the content of the present invention will be explained in more detail with reference to Examples and Comparative Examples.

Examples 1 to 7 and Comparative Examples 1 to 6 The refrigerators (oil) used in the Examples and Comparative Examples are shown below.

Example 1: Tetraester of pentaerythritol (1of) and 2-ethylhexanoic acid (4soJ).

Example 3: Tetraesters of pentaerythritol (1soJ) and 2-ethylhexanoic acid (2soj) and 3,5.5-trimethylhexanoic acid (2maroJ).

Example 4 Nidipentaerythritol (1soJ) and n-
Hexaester of hexanoic acid (8soJ) and 2,4-dimethylbencunic acid (3■oj).

Example 5 Nidipentaerythritol (1soJ), 8.
5.5-) Hexaester of trimethylhexanoic acid (B■oJ).

Example 2: Pentaerythritol (1soJ) and 3.5
．． Tetraester of 5-trimethylhexanoic acid (4soJ).

Example 6: 50 parts by weight of the ester of Example 1, Example 5
A mixture of 50 parts by weight of esters.

Example 7: 30 parts by weight of the ester of Example 2, Example 5
and the following tripentaerythritol (1a+oj), 3-methylbutanoic acid (4
a+oj) and 3-methylpentanoic acid (4-oJ)
A mixture of 30 parts by weight of octaester.

Comparative Example 1: Naphthenic mineral oil (1 viscosity at 100°C; 5.2
cst).

Comparative Example 2: Branched alkylbenzene (kinematic viscosity at 100°C; 5.Ocst).

Comparative Example 3: Polyoxypropylene glycol monobutyl ether (kinematic viscosity at 100°C: 5.4CSt).

Comparative Example 4: Polyoxypropylene glycol dimethyl ether (kinematic viscosity at 100°C; 9.5 cst).

Comparative Example 5: Tetraester of pentaerythritol (1soJ) and n-nonanoic acid (4soJ).

Comparative Example 6: Tetraester of pentaerythritol (lsoJ) and coconut oil.

In order to evaluate the performance of the base oils of the refrigerating machine oils of Examples 1 to 7 related to the present invention, the solubility with RF C-184a, insulation properties, and Falex abrasion test were evaluated.

For comparison, Table 1 also lists the test results of mineral oil, alkylbenzene, polypropylene glycol monoalkyl ether, and polypropylene glycol dialkyl ether, which have been conventionally used as refrigerating machine oil.

(Solubility with RF C-134a) 0.2 g of the sample oils of Examples and Comparative Examples were collected in a glass tube with an inner diameter of 8 ms and a length of 220J111, and the refrigerant (R
FC-134a) Collect 1.8g and seal it in a glass tube. This glass tube is placed in a low-temperature bath or high-temperature bath at a predetermined temperature, and it is observed whether the refrigerant and sample oil are mutually dissolved, separated, or cloudy.

(Insulating properties) The volume resistivity of the sample oil at 25° C. was measured in accordance with JISC2101.

(FALEX wear test) Based on ASTM 02670, sample oil temperature 10
After a 1-minute break-in operation at 0° C. and a load of 1507b, the test journal was operated for 2 hours under a load of 2501b, and the amount of wear on the test journal was measured.

(Hygroscopicity) Take 30g of sample oil in a 300m beaker and heat at 60℃ for 30 minutes.
% humidity for 7 days, the water content was measured by Karl Fischer method.

As shown in Examples 1 to 7 in Table 1, the refrigerating machine oil according to the present invention has a higher RF C-1 than Comparative Examples 1 to 2 and 5 to 6.
The refrigerant solubility for 34a is very good.

If all the alkyl groups on the acid side are linear as in Comparative Example 5, the solubility is poor. Furthermore, the tetraester of pentaerythritol and natural oil, which has been conventionally used in lubricating oils, refrigerating machine oils, etc., as shown in Comparative Example 6, has poor solubility in refrigerants.

As shown in Comparative Examples 3 and 4, although polyalkylene glycol has excellent refrigerant solubility, it has poor insulation properties and cannot be used in hermetic compressors.

In addition, the alkylene glycols shown in Comparative Examples 3 and 4 are
The moisture absorption amount is 5 to IO times that of Examples 1 to 7, and it is inferior to each Example in terms of electrical insulation, ice choke, abrasion resistance, stability, etc.

In addition, in the wear test by Falex, Example 1
It can be seen that Comparative Examples 3 to 7 are equivalent to or higher than Comparative Examples 3 to 4.

[Effects of the Invention] As is clear from the above explanation and examples, the refrigerating machine oil of the present invention is suitable for use in refrigerators for hydrogen-containing fluorocarbons, and has excellent electrical insulation properties, which are essential for close-contact type compressors. It is a refrigerating machine oil with excellent wear resistance and non-hygroscopicity.

Claims (1)

[Claims] 1. General formula ▲ Numerical formula, chemical formula, table, etc. ▼ [In the formula, R_1 to R_4 may be the same or different, and each represents a straight-chain alkyl group having 3 to 11 carbon atoms, a carbon number 3
It represents a group selected from the group consisting of ~15 branched alkyl groups and cycloalkyl groups having 6 to 12 carbon atoms, and the proportion of straight chain alkyl groups is 60% or less of the total alkyl groups,
Further, n represents an integer of 1 to 3.] Refrigerating machine oil for non-chlorine-based fluorocarbon refrigerant, characterized in that the main component is a pentaerythritol ester represented by the following. 2. Refrigerating machine oil for non-chlorinated fluorocarbon refrigerant according to claim 1, which uses the pentaerythritol ester as a base oil. 3. (I) The above pentaerythritol ester, and (II) General formula ▲ Numerical formula, chemical formula, table, etc. ▼ [In the formula, R_5 and R_6 are hydrogen or 1 to 1 carbon atoms]
8 alkyl group, R_7 represents an alkylene group having 2 to 4 carbon atoms, and a represents an integer of 5 to 70] Polyoxyalkylene glycol or its ether represented by the general formula ▲ Numerical formula, chemical formula, table etc. ▼ [In the formula, R_8 to R_1_0 are hydrogen or carbon number 1 to 1
8 alkyl group, R_1_1 to R_1_3 represent an alkylene group having 2 to 4 carbon atoms, and b to d represent an integer of 5 to 7] Polyoxyalkylene glycol glycerol ether represented by the general formula ▲ Numerical formula, There are chemical formulas, tables, etc. ▼ [In the formula, X is -OR_1_6 or ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ The group represented by There are tables etc. The groups represented by ▼ are shown respectively, and R_1_4 and R_2_0 have 1 to 8 carbon atoms.
R_1_5 and R_1_7 are alkylene groups having 2 to 16 carbon atoms, R_1_6 and R_2_1
is an alkyl group having 1 to 15 carbon atoms, R_1_8 and R_
1_9 each represents an alkyl group having 1 to 14 carbon atoms,
In addition, e and f represent the numbers 0 or 1, and n represents an integer from 0 to 30.] General formula ▲ Numerical formula, chemical formula, table, etc. ▼ [In the formula, R_2_2 to R_2_8 are carbon From the group consisting of a pentaerythritol dicarboxylic acid ester represented by an alkyl group of 3 to 15, R_2_9 represents a divalent hydrocarbon group having 1 to 8 carbon atoms, and h represents an integer of 1 to 5. The refrigerating machine oil for a non-chlorinated fluorocarbon refrigerant according to claim 1, wherein the base oil is a mixed oil of at least one selected oil. 4. (I) The refrigerating machine oil for a non-chlorinated fluorocarbon refrigerant according to claim 3, wherein the pentaerythritol ester is blended in an amount exceeding 50% by weight based on the refrigerating machine oil. 5. At least one phosphorus compound selected from the group consisting of phosphoric acid esters, acidic phosphoric esters, amine salts of acidic phosphoric esters, chlorinated phosphoric esters, and phosphorous esters, based on the total amount of refrigerating machine oil. ~5.0% by weight
The refrigerating machine oil for non-chlorinated fluorocarbon refrigerant according to any one of claims 1 to 4, which contains as an essential component. 6. 0.1 to 5.0 weight of at least one epoxy compound selected from the group consisting of phenyl glycidyl ether type epoxy compounds, glycidyl ester type epoxy compounds, epoxidized fatty acid monoesters, and epoxidized vegetable oils, based on the total amount of refrigerating machine oil. % as an essential component.