JP2769121B2 - Lubricating oil for compression refrigerators - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel lubricating oil for a compression refrigerator. More specifically, the present invention particularly relates to 1,1,1,2-tetrafluoroethane (hereinafter referred to as fluorocarbon) which can be an alternative to dichlorodifluoromethane (hereinafter referred to as fluorocarbon 12) as a refrigerant which is a problem due to environmental pollution. 134a) and a lubricating oil for compression refrigerators containing a polyoxyalkylene glycol derivative as a main component and having excellent lubrication performance.

[0002]

2. Description of the Related Art A compression type refrigerator generally comprises a compressor, a condenser, an expansion valve, and an evaporator, and has a structure in which a liquid mixture of a refrigerant and lubricating oil circulates in this closed system. In such a compression refrigerator, although it depends on the type of the device, generally, the temperature inside the compressor is increased to 50 ° C. or more.
Since the temperature in the cooler is about −40 ° C., it is necessary that the refrigerant and the lubricating oil circulate in this system without phase separation usually at a temperature in the range of −40 to + 50 ° C. If phase separation occurs, the life and efficiency of the apparatus are significantly adversely affected. For example, if phase separation occurs between the refrigerant and the lubricating oil in the compressor part, the moving parts will be poorly lubricated, causing seizure, etc., significantly shortening the life of the device, and if phase separation occurs in the evaporator. In addition, the presence of a high-viscosity lubricating oil causes a decrease in heat exchange efficiency.

[0003] Further, since lubricating oil for refrigerators is used for lubricating the movable parts of the refrigerator, lubrication performance is naturally important. Particularly, since the temperature inside the compressor becomes high, the oil film necessary for lubrication is retained. It is required to have an acceptable viscosity. This required viscosity depends on the type of compressor used,
The viscosity (kinematic viscosity) of the lubricating oil before mixing with the refrigerant is preferably in the range of 2 to 50 centistokes at a temperature of 100 ° C., although it varies depending on the use conditions and the like. If the viscosity is lower than the above-mentioned value, the oil film becomes thin and lubrication failure is likely to occur, and if the viscosity is higher, the efficiency of heat exchange decreases. Further, since lubricating oil for refrigerators is circulated and used in a wide temperature range from high temperature to low temperature, it is preferable that its viscosity index is high.
The above viscosity index is required, and further, as another performance, low hygroscopicity for preventing blockage of the expansion valve due to icing is required.

Conventionally, Freon 12 has been widely used as a refrigerant for compression refrigerators, and various mineral oils and synthetic oils satisfying the above-mentioned required characteristics have been used as lubricating oils.
However, since Freon 12 may cause environmental pollution such as destruction of the ozone layer, its regulations have recently become stricter worldwide, and as a result, Freon 134a has been attracting attention as a new refrigerant. Was. This fluorocarbon 134a is preferable as a refrigerant for a compression-type refrigerator, in that the fluorocarbon 134a is less likely to destroy the ozone layer and can be replaced with fluorocarbon 12 without substantially changing the structure of the conventional refrigerator. .

If the above-mentioned Freon 134a is employed as the refrigerant of the compression type refrigerator instead of Freon 12, the lubricating oil naturally has excellent compatibility with Freon 134a and satisfies the above-mentioned required performance. Although excellent lubrication performance is required, the lubricating oil used with the conventional Freon 12 has poor compatibility with Freon 134a, so a new lubricating oil suitable for Freon 134a is required. In this case, particularly in the case of air conditioners for automobiles, it is demanded that the structure of the device is hardly changed when substituting for chlorofluorocarbon, and for lubricating oil, it is not desirable to greatly change the structure of the current device. Therefore, a lubricating oil having extremely good compatibility with Freon 134a is required.

As lubricating oils compatible with Freon 134a, for example, Ulcon LB-165 and Ulcon LB-525 (both manufactured by Union Carbide, trade names) made of polyalkylene glycol are known. Is reported to be compatible with Freon 134a at a low temperature of at least −50 ° C. in all composition ratios. ["Research Disclosure (Resear
ch Disclosure) No. 17463 (October 1978
Month)〕.

However, these lubricating oils are polyalkylene glycol derivatives in which one end of polypropylene glycol has a hydroxyl group and the other end has an n-butyl ether bond, and has a relatively good phase with Freon 134a on the low temperature side. Although it has solubility, the compatibility is not sufficient on the high temperature side. For example, the Urcon LB-525 is
It is also known that phase separation occurs at room temperature with Freon 134a (U.S. Pat. No. 4,755,316).

On the other hand, a polyglycol having at least two hydroxyl groups in one molecule has been proposed as having good compatibility with Freon 134a (US Pat.
755,316). However, this polyglycol does not always have sufficient compatibility, and has a disadvantage that the number of hydroxyl groups in one molecule is so large that an increase in hygroscopicity and a decrease in viscosity index cannot be avoided. Increased hygroscopicity leads to an increase in the amount of dissolved water in the mixture of refrigerant and lubricating oil, which can cause the expansion valve to become clogged with ice, and a decrease in viscosity index can result in lower evaporator temperatures. May cause an increase in the viscosity, and may decrease the heat exchange efficiency. It is known that when a mixture of polyglycol and CFC is heated from a low temperature to a high temperature, the mixture that has been phase-separated generally exhibits a temperature dependency such that the mixture is once dissolved and phase-separated.

On the other hand, it has been proposed to use Freon 134a and a compound capable of dissolving Freon 134a in an absorption refrigerator (Japanese Patent Application Laid-Open No. 56-79175). The mechanism is completely different from that of the compression type refrigerator, which is the subject, and the tetraethylene glycol dimethyl ether described in the examples is not suitable as a lubricating oil for the compression type refrigerator because of its extremely low viscosity. As described above, a lubricating oil for a compression type refrigerator having sufficiently good compatibility with Freon 134a and excellent lubricating performance has not yet been found, and its development is strongly desired. Was.

[0010]

SUMMARY OF THE INVENTION The present invention satisfies such a demand and, in particular, has good compatibility with Freon 134a which can substitute for Freon 12 of the refrigerant which is a problem in environmental pollution over the entire operating temperature range. In addition, it is an object of the present invention to provide a method for efficiently producing a lubricating oil for a compression type refrigerator having excellent lubrication performance.

[0011]

Means for Solving the Problems The present inventors have developed Freon 1
As a result of intensive studies to develop a lubricating oil for compression refrigerators, which has both excellent compatibility with 34a and excellent lubrication performance,
It has been found that those having a polyoxyalkylene glycol derivative having a specific structure as a main component can be suitable for the above purpose. The present invention has been completed based on such findings. That is, the present invention provides a compound represented by the general formula (I):

[0012]

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(Wherein R ¹ represents an alkyl group having 1 to 10 carbon atoms, an acyl group or an aliphatic hydrocarbon group having 2 to 6 bonding sites, and R ² represents an alkylene group having 2 to 4 carbon atoms. R ³ represents an alkyl group or an acyl group having 1 to 10 carbon atoms, n represents an integer of 1 to 6, and m represents m × n.
Is a number such that the average value is 6 to 80. However, at least one of R ¹ and R ³ represents an acyl group. 1,1,1,2-tetrafluorofluoroethylene, characterized by comprising a polyoxyalkylene glycol derivative represented by the following formula:
Ethane is to provide a lubricating oil for compression type refrigerator to be used as a refrigerant.

Hereinafter, the present invention will be described in detail. The lubricating oil of the present invention contains a polyoxyalkylene glycol derivative represented by the above general formula (I) as a main component. In the formula, R ¹ represents an alkyl group having 1 to 10 carbon atoms, an acyl group or an aliphatic hydrocarbon group having 2 to 6 bonding sites; R ² represents an alkylene group having 2 to 4 carbon atoms; ³ represents an alkyl group or an acyl group having 1 to 10 carbon atoms. However, at least one of R ¹ and R ³ represents an acyl group. Further, n is an integer of 1 to 6, and m is an average value of m × n of 6
It is a number that becomes ８０80.

The alkyl group may be linear, branched or cyclic. Specific examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, various butyl groups, various pentyl groups, various hexyl groups, various heptyl groups, various octyl groups, various nonyl groups,
Examples include various decyl groups, cyclopentyl groups, and cyclohexyl groups. The alkyl group has 1 carbon atom
If it exceeds 0, the compatibility with Freon 134a decreases, and phase separation occurs. The preferred alkyl group has 1 to 6 carbon atoms. The alkyl group of the acyl group may be linear, branched, or cyclic. Specific examples of the alkyl group portion of the acyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, various butyl groups, various pentyl groups, various hexyl groups, various heptyl groups, various octyl groups, and various nonyl groups. , Cyclopentyl group, cyclohexyl group and the like. If the acyl group has more than 10 carbon atoms, the compatibility with Freon 134a will be reduced, and phase separation will occur. Preferred acyl groups have 2 to 6 carbon atoms.

The R ¹ and R ³ may be the same or different. Further, when n is 2 or more, a plurality of R ^{3 in} one molecule may be the same or different. When R ¹ is an aliphatic hydrocarbon group having 1 to 10 carbon atoms having 2 to 6 bonding sites, the aliphatic hydrocarbon group may be in a chain form or in a cyclic form. Is also good. Examples of the aliphatic hydrocarbon group having two bonding sites include an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, a heptylene group, an octylene group, a nonylene group, a decylene group, a cyclopentylene group, and a cyclohexylene group. And the like. Examples of the aliphatic hydrocarbon group having 3 to 6 binding sites include trimethylolpropane, glycerin, pentaerythritol, sorbitol, 1,2,3
And a residue obtained by removing a hydroxyl group from a polyhydric alcohol such as -trihydroxycyclohexane, 1,3,5-trihydroxycyclohexane. If the aliphatic hydrocarbon group has more than 10 carbon atoms, the compatibility with Freon 134a will be reduced, and phase separation will occur. The preferred number of carbon atoms is 2 to 6.

R ² in the general formula (I) has 2 to 4 carbon atoms.
And the oxyalkylene group of the repeating unit includes an oxyethylene group, an oxypropylene group, and an oxybutylene group. The oxyalkylene groups in one molecule may be the same or may contain two or more oxyalkylene groups, but those containing at least oxypropylene units in one molecule are preferable,
Particularly, those containing 50 mol% or more of oxypropylene units in the oxyalkylene unit are preferable.

In the general formula (I), n is an integer of 1 to 6, and is determined according to the number of R ¹ binding sites. For example, R
^{When 1} is an alkyl group or an acyl group, n is 1 and R ¹
Is an aliphatic hydrocarbon group having 2, 3, 4, 5, and 6 bonding sites, n is 2, 3, 4, 5, and 6, respectively. Further, m is a number such that the average value of m × n is 6 to 80. If the average value of m × n is out of the above range, the object of the present invention cannot be sufficiently achieved.

The polyoxyalkylene glycol derivative represented by the general formula (I) used in the lubricating oil of the present invention can be produced by the following various methods. Method (A): An alkylene oxide having 2 to 4 carbon atoms such as ethylene oxide or propylene oxide is polymerized using water or an alkali hydroxide as an initiator to obtain a compound represented by the general formula (II):

[0020]

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(Wherein p is an average number of 6 to 80, and R ² has the same meaning as described above), and a polyoxyalkylene glycol having a hydroxyl group at both terminals is obtained. By esterifying both of the hydroxyl groups of the product, or by etherifying one of the hydroxyl groups and esterifying the other, the general formula (III)

[0022]

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(Wherein R ³ and R ^{4 each} have 1 to 10 carbon atoms)
Which may be the same or different from each other (provided that
At least one of R ³ and R ⁴ is an acyl group. ). R ² and p have the same meaning as described above.
A polyoxyalkylene glycol derivative represented by the following formula is obtained.

Method (B): Using a monohydric alcohol having 1 to 10 carbon atoms or an alkali metal salt thereof as an initiator, an alkylene oxide having 2 to 4 carbon atoms is polymerized to obtain a compound represented by the general formula (IV):

[0025]

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(Wherein R ⁵ is an alkyl group having 1 to 10 carbon atoms, R ² and p have the same meaning as described above). After obtaining a polyoxyalkylene glycol monoalkyl ether having a hydroxyl group at the end, the hydroxyl group is esterified to obtain a compound represented by the general formula (V):

[0027]

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(Wherein R ² , R ⁵ and p have the same meanings as described above. In this case, R ³ represents an acyl group having 1 to 10 carbon atoms.) A derivative is obtained.

Method (C): A divalent to hexavalent polyhydric alcohol having 1 to 10 carbon atoms or an alkali metal salt is used as an initiator to polymerize an alkylene oxide having 2 to 4 carbon atoms.
General formula (VI)

[0030]

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(Wherein R ⁶ is an aliphatic hydrocarbon group having 1 to 10 carbon atoms having 2 to ⁶ bonding sites, r is an integer of 2 to 6,
q is a number such that the average of q × r is 6 to 80, and R ² has the same meaning as described above), to obtain a polyoxyalkylene glycol derivative having a hydroxyl group at a terminal represented by the following formula. By esterification, or by performing esterification and etherification of this hydroxyl group,
General formula (VII)

[0032]

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[0033] (R ^2, R ^6, q and r in the formulas have the same meanings as defined above. In addition, R ³ represents an alkyl group or an acyl group having 1 to 10 carbon atoms. However, at least one R ³ One represents an acyl group having 1 to 10 carbon atoms.).

In these production methods, in order to esterify the hydroxyl group of the polyoxyalkylene glycol having a hydroxyl group at a terminal or a derivative thereof, usually an aliphatic carboxylic acid having 1 to 10 carbon atoms or an acid thereof is used. A method of reacting a reactive derivative such as an anhydride, an acid halide or an ester, or a method of converting the hydroxyl group of the polyoxyalkylene glycol or a derivative thereof into a sulfonic acid ester or a halide, and then adding the carboxylic acid or a salt thereof. And the like.

Specific examples of the carboxylic acid include formic acid,
Examples include acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid, capric acid, and cyclohexanecarboxylic acid. Further, when esterification using the carboxylic acid or acid anhydride, or using an ester of the carboxylic acid,
In the case of performing esterification by transesterification, an acid catalyst such as sulfuric acid or p-toluenesulfonic acid is generally used.On the other hand, when esterification is performed using an acid halide,
Usually, amines are used as the dehydrohalogenating agent.

On the other hand, in order to etherify the hydroxyl group of a polyoxyalkylene glycol having a hydroxyl group at a terminal or a derivative thereof, an alkali metal such as sodium metal or an alkali metal salt of a lower alcohol such as sodium methoxide is usually added. To obtain an alkali metal salt of the polyoxyalkylene glycol or a derivative thereof, and then reacting it with an alkyl halide having 1 to 10 carbon atoms, a sulfate or a sulfonate, or A method of converting a hydroxyl group of oxyalkylene glycol or a derivative thereof into a sulfonic acid ester or a halide, and then reacting the sulfonic acid ester or a halide with an aliphatic alcohol having 1 to 10 carbon atoms or an alkali metal salt thereof is usually used.

In the polyoxyalkylene glycol derivative of the present invention thus obtained, the bonding mode of the oxyalkylene unit is usually head-to-tail in the case of an oxypropylene unit or an oxybutylene unit. A small amount of tail-to-tail binding may also be included. The lubricating oil of the present invention contains the polyoxyalkylene glycol derivative represented by the general formula (I) thus obtained as a main component, and the polyoxyalkylene glycol derivative is used alone. Or two or more of them may be used in combination. In addition, the lubricating oil may contain, in addition to the polyoxyalkylene glycol derivative represented by the general formula (I), a polyoxyalkylene glycol derivative having a hydroxyl group at a terminal, wherein the content of the hydroxyl group is 30 mol% based on all terminals. As long as the ratio is as follows, it can be suitably used even if it is contained. When the content of the hydroxyl group exceeds 30 mol%, the hygroscopicity increases, and the viscosity index decreases, which is not preferable. The purpose of the present invention cannot be achieved with a polyoxyalkylene glycol derivative in which R ¹ and R ³ in the general formula (I) are aromatic, although the reason is not clear.

The lubricating oil of the present invention has a viscosity at 100 ° C. of 2 to maintain the oil film thickness required for lubrication.
It is desirably in the range of ~ 50 centistokes, preferably 5-30 centistokes. The lubricating oil of the present invention includes various additives conventionally used in lubricating oils,
For example, load-bearing additives, chlorine scavengers, antioxidants, metal deactivators, defoamers, detergents / dispersants, viscosity index improvers, oil agents, anti-wear additives, extreme pressure agents, rust inhibitors, corrosion Inhibitors, pour point depressants and the like can be added as desired.

Examples of the load-bearing additives include monosulfides, polysulfides, sulfoxides, sulfones, thiosulfinates, sulfurized oils and fats, thiocarbonates, thiophenes, thiazoles, methanesulfonic acid esters and the like. Organic sulfur compounds, phosphoric acid esters such as phosphoric acid monoesters, phosphoric acid diesters, phosphoric acid triesters (tricresyl phosphate), phosphorous acid monoesters, phosphorous acid diesters , Phosphite esters such as phosphite triesters, thiophosphate esters such as thiophosphate triesters, higher fatty acids, hydroxyaryl fatty acids, carboxylic acid-containing polyhydric alcohol esters, metal soaps Fatty acid type, polyhydric alcohol esters, acrylic acid Fatty acid ester-based compounds such as ters, organic chlorine-based compounds such as chlorinated hydrocarbons and chlorinated carboxylic acid derivatives, fluorinated aliphatic carboxylic acids, fluorinated ethylene resins, fluorinated alkylpolysiloxanes, fluorinated Organic fluorine compounds such as graphite, alcohol compounds such as higher alcohols, naphthenates (lead naphthenate), fatty acid salts (lead fatty acid), thiophosphates (zinc dialkyldithiophosphate), thiocarbamates, organic Molybdenum compounds, organotin compounds, organogermanium compounds, metal compounds such as borates, etc. As the chlorine scavenger, glycidyl ether group-containing compounds, epoxidized fatty acid monoesters, epoxidized oils and fats, epoxycycloalkyl groups Phenols (2, -Ditert-butyl-p-cresol), aromatic amines (α-naphthylamine), benzotriazole derivatives as metal deactivators, silicone oil (dimethylpolysiloxane) as polyfoaming agents, polymethacrylates, Examples of the detergent and dispersant include sulfonates, phenates, and succinimides, and examples of the viscosity index improver include polymethacrylate, polyisobutylene, an ethylene-propylene copolymer, and a hydrogenated styrene-diene copolymer.

The lubricating oil of the present invention is excellent in compatibility with a refrigerant and lubricating performance and is used for a compression refrigerator. However, unlike a conventional lubricating oil, it has good compatibility with Freon 134a. It is suitable for a compression refrigerator using Freon 134a as a refrigerant. For the purpose of improving the compatibility with the refrigerant, it can be mixed with other lubricating oils for compression refrigerators and used.

[0041]

Next, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples. Production Example 1 In a 200 ml three-neck glass flask equipped with a stirrer and a dropping funnel, Unilube MB-11 (polyoxypropylene glycol mono n manufactured by NOF Corporation) was placed.
-Butyl ether, average molecular weight 1000), 50 g of pyridine, 9.5 g (0.12 mol) of pyridine and 100 ml of ethyl ether were added thereto, and acetyl chloride 9.
4 g (0.12 mol) was added from the dropping funnel over 30 minutes. After heating and refluxing for 2 hours, the mixture was cooled to room temperature, and then the reaction mixture was transferred to a separating funnel.
Washed 5 times using milliliters. After the ether was distilled off, the residue was dried at 100 ° C. for 1 hour under reduced pressure of a vacuum pump to obtain 49.0 g of the desired acetate ester of Unilube MB-11.
I got

Production Example 2 In a 300-ml glass three-necked flask equipped with a stirrer and a distillation head, 75 g of Unilube MB-11 manufactured by NOF Corporation and 50 ml of toluene were added, and about 20 ml of toluene was heated and stirred. Was distilled off to remove water. Next, after removing the distillation head, attaching a condenser and a dropping funnel, 11.9 g of pyridine was obtained.
(0.15 mol) and 50 ml of toluene.
While stirring at room temperature, 16.0 g (0.15 mol) of n-butyryl chloride was added from the dropping funnel over 30 minutes. After heating and refluxing for 4 hours, the mixture was cooled to room temperature, and then the reaction mixture was transferred to a separating funnel and washed five times with 50 ml of a saturated saline solution. After the toluene was distilled off, the residue was dried under reduced pressure of a vacuum pump at 100 ° C. for 1 hour to obtain 70.5 g of the desired n-butyric ester of Unilube MB-11.

Production Example 3 16.0 g of isobutyryl chloride instead of n-butyryl chloride
(0.15 mol), except that isobutyric acid ester 7 of Unilube MB-11 was used.
4 g were obtained.

Reference Example 1 In a glass 200 ml three-necked flask equipped with a stirrer and a dropping funnel, 50 g of Unilube MB-11 manufactured by NOF Corporation and 7.9 g of potassium hydroxide (0.14 g) were added.
Mol) and 80 ml of toluene, and 15.2 g (0.12 mol) of benzyl chloride was added from a dropping funnel over 30 minutes while stirring and heating under reflux with toluene. After heating and refluxing for 4 hours, the reaction mixture was cooled to room temperature, then transferred to a separating funnel, and washed 5 times with 50 ml of a saturated saline solution. After the toluene was distilled off, the residue was dried at 100 ° C. for 1 hour under reduced pressure of a vacuum pump (0.1 mmHg) to obtain 49.0 g of benzyl ether of Unilube MB-11.
I got

Examples 1 to 3 and Comparative Examples 1 and 2 The compatibility of the compounds obtained in Production Examples 1 to 3 and Reference Example 1 and the starting polyglycol of Production Example 1 were measured. A predetermined amount of a sample is added to a pressure-resistant glass ampule so as to be 10% by weight and 20% by weight with respect to Freon 134a (1,1,1,2-tetrafluoroethane), and this is connected to a vacuum pipe and Freon 134a gas pipe. did. After the ampoule was degassed in vacuum at room temperature, it was cooled with liquid nitrogen, and a predetermined amount of Freon 134a was collected. Next, the ampoule was sealed, the temperature was raised from -40 ° C in a thermostat, and the temperature at which phase separation started was measured. The higher the phase separation temperature, the better. The results are shown in Table 1.

[0046]

[Table 1]

[0047]

[Table 2]

[0048]

[Table 3]

[0049]

The lubricating oil for a compression refrigerator according to the present invention has a structure in which hydroxyl groups at both ends of polyoxyalkylene glycol are esterified, or a hydroxyl group at one end is etherified and another hydroxyl group at one end is esterified. The main component is a polyoxyalkylene glycol derivative having a generalized structure, and its compatibility with Freon 134a, which has attracted attention as a substitute for Freon 12, which has become a problem particularly due to environmental pollution, is determined at all operating temperatures. It has good lubrication performance as well as good lubrication performance over the range.
It is very suitable as a lubricating oil for a compression refrigerator using 4a. Further, the polyoxyalkylene glycol derivative can be used by being mixed with another lubricating oil for a compression type refrigerator for the purpose of improving the compatibility with the refrigerant.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-55-58298 (JP, A) JP-A-59-21632 (JP, A) JP-A-61-281199 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) C10M 107/34 C09K 5/04 C10M 105/18 C10N 30:00 C10N 40:30

Claims (1)

(57) [Claims] 1. A compound of the general formula (I) (In the formula, R ¹ represents an alkyl group having 1 to 10 carbon atoms, an acyl group or an aliphatic hydrocarbon group having 2 to 6 bonding sites; R ² represents an alkylene group having 2 to 4 carbon atoms; ³ represents an alkyl group or an acyl group having 1 to 10 carbon atoms, n represents an integer of 1 to 6, and m represents an average value of m × n of 6
It is a number that becomes ８０80. However, at least one of R ¹ and R ³ represents an acyl group. ) Characterized by containing a polyoxyalkylene glycol derivative represented by
1,1,1,2-tetrafluoroethane as a refrigerant
Lubricating oil for compression type refrigerator to be used as.