JPH1046169A - Lubricating oil composition for refrigerator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a lubricating oil compsn. which has high lubricating and sealing properties in an atmosphere of CO2 as a refrigerant by compounding a refrigerant mainly comprising CO2 with a base oil comprising a polyoxyalkylene glycol or a polyvinyl ether. SOLUTION: This compsn. contains a refrigerant mainly comprising CO2 and a base oil comprising at least either a polyoxyalkylene glycol or a polyvinyl ether and having a kinematic viscosity of 5 cSt or higher at 100 deg.C and is esp. suitable for a compression refrigeration cycle of a compression refrigerator. Esp. remarkable effects are achieved when the compsn. is applied to a compression refrigeration cycle having an oil separator and/or a hot gas line.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a lubricating oil composition for a refrigerator, and more particularly, to a lubricating oil composition for a refrigerator using a refrigerant containing CO ₂ as a main component.

[0002]

2. Description of the Related Art Conventionally, refrigerators such as compressors, condensers,
In a compression refrigeration cycle including an expansion valve and an evaporator, a fluorocarbon-based fluorocarbon compound such as dichlorodifluoromethane (R-12) or chlorodifluoromethane (R-22) is used as a refrigerant, and Many lubricating oils have been produced and used in combination therewith. However,
It has been feared that this fluorocarbon compound, which has been conventionally used as a refrigerant, may destroy the ozone layer and cause environmental pollution when released into the atmosphere. Recently, from the viewpoint of environmental pollution countermeasures, 1,1,
The development of fluorohydrocarbons (or chlorofluorohydrocarbons) such as 1,2-tetrafluoroethane (R-134a) has been promoted, and there is already little risk of environmental pollution including R-134a, and the above-mentioned required characteristics A variety of so-called alternative CFCs that can satisfy the requirements have come to market. However, such fluorinated hydrocarbons (or chlorinated fluorinated hydrocarbons) also have problems such as high global warming ability. In recent years, use of natural refrigerants free from such problems has been considered. . On the other hand, carbon dioxide gas is harmless to the environment and is excellent in terms of safety for humans.In addition, the pressure is close to the economically optimal level, the pressure ratio is very small compared to conventional refrigerants, It has the advantages of excellent compatibility with ordinary oil and structural materials of machinery, easy availability everywhere, no need for recovery, and very low cost. It has been commonly used. However, when such a carbon dioxide gas is used as a refrigerant of a refrigerator, lubricating with a lubricating oil generally used conventionally as a lubricating oil for a refrigerator results in poor lubrication and insufficient wear resistance. This results in poor stability and the like. Further, in the system using carbon dioxide gas, the discharge pressure is higher than in the system using R-134a or the like, and as a result, the viscosity of the lubricating oil is reduced, and the sealing performance of the system is deteriorated.

[0003]

SUMMARY OF THE INVENTION The present invention
It was achieved under the circumstances and the CO
_TwoUnder lubrication performance, high lubrication performance and sealability
It is intended to provide a lubricating oil composition.

[0004]

The present inventors have conducted intensive studies to develop a lubricating oil composition for a refrigerator having the above-mentioned preferable properties, and as a result, a specific type of lubricating oil having specific properties has been obtained. It has been found that the object can be achieved by using a lubricating oil composition comprising The present invention has been completed based on such findings. That is, the present invention
(A) a refrigerant mainly composed of CO ₂ and (B) a base oil comprising at least one selected from polyoxyalkylene glycols and polyvinyl ethers and having a kinematic viscosity at 100 ° C. of 5 cSt or more. And a lubricating oil composition for a refrigerator.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The lubricating oil composition for a refrigerator according to the present invention comprises (A) a refrigerant mainly composed of CO ₂ , and (B) at least one selected from polyoxyalkylene glycol and polyvinyl ether; A base oil having a kinematic viscosity at 100 ° C. of 5 cSt or more. (A) used in the present invention
As the refrigerant mainly containing CO ₂ as a component, in addition to the case where CO ₂ is used as it is, it is used as a hydrocarbon, R-13.
A mixture of a hydrocarbon such as 4a (or a fluorinated chlorohydrocarbon) and a refrigerant such as ether can also be used. Further, as the base oil of the component (B), one composed of at least one selected from polyoxyalkylene glycol and polyvinyl ether is used.

The polyoxyalkylene glycol used is, for example, a compound represented by the following general formula (I): R ¹ -[(OR ² ) _m -OR ³ ] _n (I) wherein R ¹ is hydrogen An atom, an alkyl group having 1 to 10 carbon atoms, an acyl group having 2 to 10 carbon atoms or an aliphatic hydrocarbon group having 1 to 10 carbon atoms having 2 to 6 bonding portions, and R ² is an alkylene having 2 to 4 carbon atoms Group, R ³ is a hydrogen atom, having 1 to 1 carbon atoms
0 alkyl group or acyl group having 2 to 10 carbon atoms, n is 1
And m is a number such that the average value of m × n is 6 to 80. )). In the general formula (I), the alkyl group for R ¹ and R ³ may be any of 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, and various decyl groups. , Cyclopentyl group,
Examples include a cyclohexyl group. If the carbon number of the alkyl group exceeds 10, the compatibility with the refrigerant is reduced, and phase separation may occur. The preferred alkyl group has 1 to 6 carbon atoms.

Further, R¹, R^ThreeA of the acyl group in
The alkyl group moiety may be linear, branched, or cyclic.
You may. Specific examples of the alkyl group portion of the acyl group
Is a group having 1 to 9 carbon atoms mentioned as a specific example of the alkyl group.
Various groups can be similarly mentioned. The acyl group
If the carbon number exceeds 10, the compatibility with the refrigerant decreases,
Separation may occur. A preferred acyl group has 2 carbon atoms.
~ 6. R¹And R^ThreeIs an alkyl group or
When it is an acyl group, R¹And R ^ThreeAre the same
Good or different. N is 2 or more
In the case above, multiple Rs in one molecule^ThreeMay be the same
And may be different.

R ¹ has ¹ to 2 carbon atoms having 2 to 6 bonding sites
In the case of an aliphatic hydrocarbon group of 10 to 10, the aliphatic hydrocarbon group may be a chain-like one or a cyclic one. 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-trihydroxycyclohexane; 1,3,5-trihydroxycyclohexane and the like. And the residue obtained by removing the hydroxyl group from the polyhydric alcohol. If the aliphatic hydrocarbon group has more than 10 carbon atoms, the compatibility with the refrigerant may be reduced, and phase separation may occur. The preferred number of carbon atoms is 2 to 6. In the present invention, at least one of R ¹ and R ³ is preferably an alkyl group, particularly an alkyl group having 1 to 3 carbon atoms, and particularly preferably a methyl group from the viewpoint of viscosity characteristics. Further, for the same reason as described above, R ¹ and R
It is preferred that both of ³ are alkyl groups, especially methyl groups.

In the general formula (I), R ² 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. Particularly, a copolymer containing an oxyethylene group (EO) and an oxypropylene group (PO) is preferable. In such a case, a seizure load,
From the viewpoint of viscosity characteristics, the value of EO / (PO + EO) is 0.1 to 0.1.
8, and from the viewpoint of hygroscopicity, the value of EO / (PO + EO) is preferably in the range of 0.3 to 0.6.

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
Becomes 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 polyalkylene glycol represented by the general formula (I) includes a polyalkylene glycol having a hydroxyl group at a terminal, and the content of the hydroxyl group is 50 mol% or less based on all terminal groups. If it is contained in a suitable ratio, it can be suitably used even if it is contained. If the content of the hydroxyl group exceeds 50 mol%, the hygroscopicity increases and the viscosity index decreases, which is not preferable. As such a polyalkylene glycol, a general formula

[0011]

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Wherein x is a number from 6 to 80, a polyoxypropylene glycol dimethyl ether represented by the general formula:

[0013]

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(Where a and b are each 1 or more,
In addition, the numbers indicate a total of 6 to 80. The polyoxyethylene polyoxypropylene glycol dimethyl ether represented by the general formula (1) is preferred in terms of economy and effect, and

[0015]

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(Where x represents a number of 6 to 80), polyoxypropylene glycol monobutyl ether, and polyoxypropylene glycol diacetate are preferred from the viewpoint of economy and the like. As the polyalkylene glycol represented by the general formula (I), any of those described in detail in JP-A-2-305893 can be used. In the present invention, as the polyoxyalkylene glycol,
General formula (II)

[0017]

Embedded image [R ^{4 to} R ⁷ are each hydrogen, a monovalent hydrocarbon group having 1 to 10 carbon atoms or a general formula (III)

[0018]

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(R ⁸ and R ⁹ each represent hydrogen, carbon number 1
A monovalent hydrocarbon group of 10 to 10 or an alkoxyalkyl group of 2 to 20 carbon atoms, wherein R ¹⁰ is an alkylene group of 2 to 5 carbon atoms, or a substituted alkylene group of 2 to 5 carbon atoms having an alkyl group as a substituent Or a substituted alkylene group having a total of 4 to 10 carbon atoms having an alkoxyalkyl group as a substituent, n is an integer of 0 to 20, and R ¹¹ is a monovalent hydrocarbon of 1 to 10 carbon atoms. ) Wherein at least one of R ^{4 to} R ⁷ is a group represented by the general formula (III)]. be able to. Here, in the formula, R ^{4 to} R ⁷ are each hydrogen and have 1 to 10 carbon atoms.
A monovalent hydrocarbon group or a group represented by the above general formula (III). As the monovalent hydrocarbon group having 1 to 10 carbon atoms, a monovalent hydrocarbon group having 6 or less carbon atoms is preferably used. Most preferably, an alkyl group having 3 or less carbon atoms is optimal.

In the general formula (III), R ⁸ and R
Reference numeral ⁹ represents hydrogen, a monovalent hydrocarbon group having 1 to 10 carbon atoms or an alkoxyalkyl group having 2 to 20 carbon atoms, and among these, an alkyl group having 3 or less carbon atoms or an alkoxyalkyl having 6 or less carbon atoms. Groups are preferred. R ¹⁰ represents an alkylene group having 2 to 5 carbon atoms, a substituted alkylene group having 2 to 5 carbon atoms having an alkyl group as a substituent or a substituted alkylene group having 4 to 10 carbon atoms having an alkoxyalkyl group as a substituent. Is preferably an ethylene group having 6 or less carbon atoms and a substituted ethylene group. R ¹¹ has 1 carbon atom
And a monovalent hydrocarbon group of 10 to 10, of which a hydrocarbon group having 6 or less carbon atoms is preferable, and a hydrocarbon group having 3 or less carbon atoms is particularly preferable. In addition, at least one of R ^{4 to} R ⁷ in the general formula (II) is a group represented by the general formula (III). In particular, one of R ⁴ and R ⁶ is a group represented by the general formula (III), and the other one of R ⁴ and R ⁶ and R ⁵ and R ⁷ are each hydrogen or a group having 1 to 10 carbon atoms. It is preferably a valent hydrocarbon group.

The above polyoxyalkylene glycol derivative contains at least one structural unit represented by the general formula (II). More specifically, the polyoxyalkylene glycol derivative has a single polymer consisting of the structural unit represented by the general formula (II). A copolymer comprising two or more different structural units contained in the general formula (II), and a structural unit of the general formula (II) and another structural unit, for example, a general formula
(IV)

[0022]

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[R ^{12 to} R ¹⁵ are each hydrogen or carbon 1
And represents an alkyl group of 1 to 3. And the copolymers comprising the structural units represented by the following general formulas: A preferred example of the homopolymer has 1 to 200 structural units A represented by the general formula (II), and has a hydroxyl group, an acyloxy group having 1 to 10 carbon atoms, and an end group having 1 to 10 carbon atoms, respectively.
And those comprising an alkoxy group or an aryloxy group. On the other hand, preferred examples of the copolymer include two types of structural units A and B represented by the general formula (II) each having 1
Or 200 to 200 or 1 to 200 structural units A represented by the general formula (II) and 1 to 200 structural units C represented by the general formula (III), and each of the terminal groups has a hydroxyl group. , An acyloxy group having 1 to 10 carbon atoms, 1 carbon atom
And 10 to 10 alkoxy groups or aryloxy groups. These copolymers are obtained by alternating copolymerization of a structural unit A and a structural unit B (or a structural unit C), random copolymerization, a block copolymer or a graft in which the structural unit B is graft-bonded to the main chain of the structural unit A. There are various things such as copolymers. As the polyvinyl ether used as the base oil as the component (B), for example, the general formula (V)

[0024]

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(Wherein, R ¹⁶ , R ¹⁷ and R ¹⁸ each represent a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms, which may be the same or different, and R ¹⁹ has 1 carbon atom.
A divalent hydrocarbon group having 10 to 10 carbon atoms or a divalent ether-bonded oxygen-containing hydrocarbon group having 2 to ²⁰ carbon atoms, and R ²⁰ has 1 to 2 carbon atoms.
0 represents a hydrocarbon group, k represents a number having an average value of 0 to 10, R ^{16 to} R ²⁰ may be the same or different for each structural unit, and when there are a plurality of R ¹⁹ Os In
A plurality of R ¹⁹ Os may be the same or different. A) a polyvinyl ether-based compound having a structural unit represented by the formula: Further, the structural unit represented by the general formula (V) and the general formula (VI)

[0026]

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Where R^{twenty one}~ R^{twenty four}Is a hydrogen atom
Or a hydrocarbon group having 1 to 20 carbon atoms,
May be the same or different.^{twenty one}~ R^{twenty four}Ha
It may be the same or different for each unit
No. Or a block having a structural unit represented by)
Polyvinyl ether compounds consisting of dam copolymers are also used.
Can be used. R in the above general formula (V)¹⁶,
R¹⁷And R¹⁸Each represents a hydrogen atom or a carbon number of 1 to 8,
Preferably they represent 1 to 4 hydrocarbon groups, each of which
They may be the same or different. Here, the hydrocarbon group is
Specifically, methyl, ethyl, n-propyl, iso-
Propyl group, n-butyl group, isobutyl group, sec-butyl
Tyl group, tert-butyl group, various pentyl groups, various
Alkyl of xyl group, various heptyl groups, various octyl groups
Group, cyclopentyl group, cyclohexyl group, various methyl
Cyclohexyl group, various ethylcyclohexyl groups, various
Cycloalkyl groups such as dimethylcyclohexyl,
Phenyl group, various methylphenyl groups, various ethylphenyl
Groups, aryl groups of various dimethylphenyl groups, benzyl
Groups, various phenylethyl groups, various methylbenzyl groups
Represents a reel alkyl group. Note that these R ¹⁶, R¹⁷,
R¹⁸Is particularly preferably a hydrogen atom.

On the other hand, R ¹⁹ in the general formula (V) has 1 carbon atom.
A divalent hydrocarbon group having 10 to 10, preferably 2 to 10 or a divalent ether-bonded oxygen-containing hydrocarbon group having 2 to 20 carbon atoms, wherein a divalent hydrocarbon group having 1 to 10 carbon atoms Specifically, methylene group; ethylene group; phenylethylene group; 1,2-propylene group; 2-phenyl-1,2
-Propylene group; 1,3-propylene group; various butylene groups; various pentylene groups; various hexylene groups; various heptylene groups; various octylene groups; various nonylene groups; divalent aliphatic groups of various decylene groups; cyclohexane; methylcyclohexane Alicyclic groups having two binding sites to an alicyclic hydrocarbon such as ethylcyclohexane; dimethylcyclohexane; propylcyclohexane; various phenylene groups; various methylphenylene groups; various ethylphenylene groups; various dimethylphenylene groups; various naphthylene Aromatic hydrocarbon group such as a group, toluene; xylene; an alkyl aromatic group having a monovalent bonding site in each of an alkyl group portion and an aromatic portion of an alkyl aromatic hydrocarbon such as ethylbenzene, xylene; diethylbenzene, etc. Polyalkyl aromatic carbonization It is an alkyl aromatic group having a bonding site in the alkyl group moiety of the unit. Of these, aliphatic groups having 2 to 4 carbon atoms are particularly preferred.

Specific examples of the divalent ether-bonded oxygen-containing hydrocarbon group having 2 to 20 carbon atoms include a methoxymethylene group; a methoxyethylene group; a methoxymethylethylene group; a 1,1-bismethoxymethylethylene group; 1,2-
Bismethoxymethylethylene group; ethoxymethylethylene group; (2-methoxyethoxy) methylethylene group;
A (1-methyl-2-methoxy) methylethylene group can be preferably exemplified. Here, k in the general formula (V) indicates the number of repetitions of R ¹⁹ O, and the average value thereof is 0 to
It is a number in the range of 10, preferably 0-5. When the R ¹⁹ O is plural, plural R ¹⁹ O may be the same or different.

Further, R ²⁰ in the general formula (V) represents a hydrocarbon group having 1 to ²⁰ carbon atoms, preferably 1 to 10 carbon atoms, specifically, a methyl group, an ethyl group, n-propyl group, isopropyl group, n-butyl group,
Isobutyl group, sec-butyl group, tert-butyl group, various pentyl groups, various hexyl groups, various heptyl groups, various octyl groups, various nonyl groups, various decyl alkyl groups, cyclopentyl groups, cyclohexyl groups, various methylcyclohexyl groups , Various ethylcyclohexyl groups, various propylcyclohexyl groups, various cycloalkyl groups such as dimethylcyclohexyl groups, phenyl groups, various methylphenyl groups, various ethylphenyl groups, various dimethylphenyl groups, various propylphenyl groups, various trimethylphenyl groups, various Aryl groups such as butylphenyl group and various naphthyl groups, benzyl group, various phenylethyl groups, various methylbenzyl groups, various phenylpropyl groups,
And the arylalkyl groups of various phenylbutyl groups. Note that R ^{16 to} R ²⁰ may be the same or different for each structural unit.

The polyvinyl ether compound (1) represented by the general formula (V) has a carbon / oxygen molar ratio of 4.2.
Those in the range of ~ 7.0 are preferred. This molar ratio is 4.2
If it is less than 7, the hygroscopicity is high, and if it exceeds 7.0, the compatibility with the refrigerant may decrease. In the general formula (VI), R ^{21 to} R ²⁴ each represent a hydrogen atom or a carbon atom
Shows 20 hydrocarbon groups, which may be the same or different. Examples of the hydrocarbon group having 1 to 20 carbon atoms may include the same as those exemplified in the description of R ²⁰ in formula (V). R ^{21 to} R ²⁴ may be the same or different for each structural unit.

The polyvinyl ether compound (2) comprising a block or random copolymer having the structural unit represented by the general formula (V) and the structural unit represented by the general formula (VI) has a carbon / carbon Those having an oxygen molar ratio in the range of 4.2 to 7.0 are preferably used. If the molar ratio is less than 4.2, the hygroscopicity is high, and if it exceeds 7.0, the compatibility with the refrigerant may be reduced. Furthermore, in the present invention, a mixture of the polyvinyl ether compound (1) and the polyvinyl ether compound (2) can also be used. The polyvinyl ether compounds (1) and (2) used in the present invention are obtained by polymerizing the corresponding vinyl ether monomers and copolymerizing the corresponding hydrocarbon monomers having an olefinic double bond with the corresponding vinyl ether monomers. Can be manufactured. As the polyvinyl ether compound used in the present invention,
Those having the following terminal structure, that is, one terminal of which has the general formula (VII) or (VIII)

[0033]

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[0034] (wherein, R ^25, R ²⁶ and R ²⁷ each represent a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms, R ^25,
R ²⁶ and R ²⁷ may be the same or different,
R ³⁰ , R ³¹ , R ³² and R ³³ each represent a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms, and R ³⁰ , R ³¹ , R ³² and R ³³ may be the same or different. . R ²⁸ is a divalent hydrocarbon group having 1 to 10 carbon atoms or 2 to 20 carbon atoms.
Wherein R ²⁹ is a hydrocarbon group having 1 to 20 carbon atoms, p is a number having an average value of 0 to 10, and when there are a plurality of R ²⁸ O, of R ²⁸ O may be the same or different. ) And the remaining terminal is represented by the general formula (IX) or (X)

[0035]

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[0036] (wherein, R ^34, R ³⁵ and R ³⁶ each represent a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms, R ^34,
R ³⁵ and R ³⁶ may be the same or different,
R ³⁹ , R ⁴⁰ , R ⁴¹ and R ⁴² each represent a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms, and R ³⁹ , R ⁴⁰ , R ⁴¹ and R ⁴² may be the same or different. . R ³⁷ is a divalent hydrocarbon group having 1 to 10 carbon atoms or 2 to 20 carbon atoms;
R ³⁸ is a hydrocarbon group having 1 to 20 carbon atoms, q is a number having an average value of 0 to 10, and when there are a plurality of R ³⁷ O, R ³⁷ O may be the same or different. ) And one end thereof is represented by the above general formula (VII) or (VIII), and the other end is represented by the general formula (XI)

[0037]

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(Wherein R⁴³, R⁴⁴And R⁴⁵Respectively
A hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms,
They may be the same or different. )
Those having a structure are preferred. Such polyvinyl alcohol
Among the compounds based on ether, the following compounds are particularly preferred in the present invention.
In this case, it is preferable. (1) One terminal is represented by the general formula (VII) or (VIII).
And the remaining terminal is represented by the general formula (IX) or (X).
Having a structure represented by the general formula (V)¹⁶, R ¹⁷as well as
R¹⁸Are both hydrogen atoms, k is a number from 0 to 4, R¹⁹Has 2 carbon atoms
To 4 divalent hydrocarbon groups and R²⁰Is charcoal having 1 to 20 carbon atoms
What is a hydride group. (2) having only the structural unit represented by the general formula (V)
Wherein one end is represented by the general formula (VII),
And the remaining terminal has a structure represented by the general formula (IX),
R in the general formula (V)¹⁶, R¹⁷And R¹⁸Are both hydrogen sources
Child, k is a number from 0 to 4, R¹⁹Is a divalent carbon having 2 to 4 carbon atoms
Hydrogen group and R²⁰Is a hydrocarbon group having 1 to 20 carbon atoms
of.

(3) The one terminal is represented by the general formula (VII) or
(VIII), and the remaining terminal is represented by the general formula (XI).
Having a structure represented by the general formula (V)¹⁶, R¹⁷as well as
R¹⁸Are both hydrogen atoms, k is a number from 0 to 4, R¹⁹Has 2 carbon atoms
To 4 divalent hydrocarbon groups and R ²⁰Is charcoal having 1 to 20 carbon atoms
What is a hydride group. (4) having only the structural unit represented by the general formula (V)
Wherein one terminal is represented by the general formula (VII),
And the remaining terminal has a structure represented by the general formula (X),
R in the general formula (V)¹⁶, R¹⁷And R¹⁸Are both hydrogen sources
Child, k is a number from 0 to 4, R¹⁹Is a divalent carbon having 2 to 4 carbon atoms
Hydrogen group and R²⁰Is a divalent hydrocarbon group having 1 to 20 carbon atoms and
And R²⁰Is a hydrocarbon group having 1 to 20 carbon atoms. Also
In the present invention, the structural unit represented by the general formula (V)
One end of which is represented by the general formula (VII),
The remaining terminal is the general formula (XII)

[0040]

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[0041] (wherein, R ^46, R ⁴⁷ and R ⁴⁸ each represent a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms, they may be different even identical to each other, R ⁴⁹ And R ⁵¹ each represent a divalent hydrocarbon group having 2 to 10 carbon atoms, which may be the same or different, and R ⁵⁰ and R ⁵² each represent a hydrocarbon group having 1 to 10 carbon atoms. And they may be the same or different from each other, c and d each represent a number having an average value of 0 to 10, they may be the same or different from each other, and it is more R ⁴⁹ O if there are R ⁴⁹ O may be the same or different and when there are a plurality of R ⁵¹ O is a plurality of R ⁵¹ O are independently identical or different And a polyvinyl ether compound having a structure represented by the following formula: It is possible to use. Further, in the present invention, the compound represented by the general formula (XIII) or (XIV)

[0042]

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(Wherein, R ⁵³ represents a hydrocarbon group having 1 to 8 carbon atoms), the weight average molecular weight is 300 to 5,000, and one terminal is generally Formula (XV) or (XVI)

[0044]

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(Wherein, R ⁵⁴ represents an alkyl group having 1 to 3 carbon atoms, and R ⁵⁵ represents a hydrocarbon group having 1 to 8 carbon atoms). A polyvinyl ether compound composed of a polymer can also be used. The above-mentioned polyvinyl ether is described in detail in JP-A-6-128578 or Japanese Patent Application Nos. 5-125649, 5-125650 and 5-303736. Any of these can be used.

The kinematic viscosity at 100 ° C. of the base oil (B) is 5 cSt or more. This viscosity is 5 cS
If it is smaller than t, the sealing performance is poor and the lubricating performance is undesirably reduced. From such a viewpoint, the viscosity range is more preferably 10 cSt or more, particularly preferably 10 to 500 cSt. In the present invention, the amounts of the CO ₂ refrigerant (A) and the base oil (B) are as follows.
99/1 to 10/9 by weight ratio of component (A) / component (B)
It is preferably in the range of 0. When the amount of the component (A) is less than the above range, the refrigerating capacity is reduced. From such a viewpoint, the weight ratio of the component (A) / the component (B) is more preferably in the range of 95/5 to 30/70.

The refrigerator oil composition of the present invention may contain, if necessary, various known additives such as phosphates such as tricresyl phosphate (TCP) and phosphites such as trisnonylphenyl phosphite. Pressure agent;
Stabilizers such as phenolic antioxidants, amine antioxidants, and epoxy compounds such as phenylglycidyl ether, cyclohexene oxide, and epoxidized soybean oil; copper deactivators such as benzotriazole and benzotriazole derivatives; silicone oil And a defoaming agent such as fluorinated silicone oil. Furthermore,
Load-bearing additives, chlorine scavengers, detergents / dispersants, viscosity index improvers, oil agents, rust inhibitors, corrosion inhibitors, pour point depressants and the like can be added as desired. These additives are usually contained in the composition of the present invention in an amount of 0.01 to 10% by weight. Although the lubricating oil composition of the present invention can be used for various refrigerators, it can be particularly preferably applied to a compression refrigeration cycle of a compression refrigerator. In particular, the lubricating oil composition of the present invention exerts its effects effectively when applied to, for example, a compression refrigeration cycle having an oil separator and / or a hot gas line as shown in each of FIGS. Things.

[0048]

EXAMPLES Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. The properties and performance of the lubricating oil composition were determined according to the following methods. (1) Solubility Carbon dioxide gas is blown into 100 g of oil under a pressurized condition of 50 kg / cm ² , and the dissolved amount of carbon dioxide gas in the oil (% by weight)
Was measured. (2) Shield tube test The catalyst Fe / Cu / Al was put in a glass tube, and a sample was filled at a ratio of carbon dioxide / oil / water = 0.5 g / 4 g / 0.02 g and sealed. After maintaining at 175 ° C. for 10 days, oil appearance, catalyst appearance, total acid value, and presence or absence of sludge were evaluated. (3) Hygroscopicity test 10 g of oil at 85% RH. H. The amount of moisture absorption (% by weight) after standing at (30 ° C.) for 120 hours was determined. (4) Falex baking test Using a Falex testing machine, the pin / block material was AI
SIC1137 / SAE3135. The pin / block was set, 200 g of the sample oil was put into the test container, and carbon dioxide gas was blown at 5 liter / h.
The seizure load was measured at 50 rpm at an oil temperature of 50 rpm.

Examples 1 to 11 and Comparative Examples 1 to 4 Each of the base oils having the properties shown in Table 1 was subjected to each of the tests described above and evaluated. The results are shown in Table 2.

[0050]

[Table 1]

[0051]

[Table 2]

[0052]

According to the present invention, it is possible to provide a lubricating oil composition for a refrigerator having excellent lubricating performance and high sealability in a CO ₂ atmosphere as a refrigerant.

[Brief description of the drawings]

FIG. 1 is a flowchart showing an example of a compression refrigeration cycle having an oil separator and a hot gas line.

FIG. 2 is a flowchart showing an example of a compression refrigeration cycle having an oil separator.

FIG. 3 is a flowchart showing an example of a compression refrigeration cycle having a hot gas line.

FIG. 4 is a flowchart of a compression refrigeration cycle.

[Explanation of symbols]

 1: Compressor 2: Condenser 3: Expansion valve 4: Evaporator 5: Oil separator 6: Hot gas line 7: Valve for hot gas line

Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location C10N 30:06 40:30

Claims (5)

[Claims] 1. A refrigerant comprising (A) a refrigerant mainly composed of CO ₂ and (B) at least one selected from polyoxyalkylene glycols and polyvinyl ethers.
A lubricating oil composition for refrigerators, comprising: a base oil having a kinematic viscosity at 5 ° C. of 5 cSt or more. 2. The lubricating oil composition for a refrigerator according to claim 1, wherein the base oil as the component (B) is a polyoxyalkylene glycol. 3. The lubricating oil composition for a refrigerator according to claim 2, wherein at least one terminal group of the polyoxyalkylene glycol is an alkyl group. 4. The lubricating oil composition for a refrigerator according to claim 3, wherein both terminal groups of the polyoxyalkylene glycol are alkyl groups. 5. The lubricating oil composition for a refrigerator according to claim 1, wherein the kinematic viscosity at 100 ° C. of the base oil (B) is 10 cSt or more.