Compositions – Vaporization – or expansion – refrigeration or heat or energy... – With lubricants – or warning – stabilizing or anti-corrosion...
Reexamination Certificate
1998-10-19
2002-06-18
Einsmann, Margaret (Department: 1751)
Compositions
Vaporization, or expansion, refrigeration or heat or energy...
With lubricants, or warning, stabilizing or anti-corrosion...
C252S067000
Reexamination Certificate
active
06406642
ABSTRACT:
TECHNICAL FIELD TO WHICH THE INVENTION BELONGS
The present invention relates to a lubricating oil for refrigerator which is used for e.g. a compression type refrigerator such as an air conditioning system or an electric refrigerator. Particularly, it relates to a lubricating oil for refrigerator comprising a polyether which is excellent in compatibility with a hydrofluorocarbon type refrigerant (hereinafter referred to as a HFC type refrigerant) such as 1,1,1,2-tetrafluoroethane (hereinafter referred to as HFC-134a) difluoromethane (hereinafter referred to as HFC-32) or pentafluoroethane (hereinafter referred to as HFC-125).
PRIOR ART
Heretofore, dichlorodifluoromethane (hereinafter referred to as CFC-12) has been mainly used as a refrigerant for a refrigerator for car air conditioning or cold storage, and chlorodifluoromethane (hereinafter referred to as HCFC-22) has been mainly used as a refrigerant for a refrigerator for room air conditioning. However, with a view to protecting the ozone layer, a HFC type refrigerant such as HFC-134a, HFC-32 or HFC-125, has been developed as a refrigerant which can be substituted for a chlorine-containing refrigerant such as CFC-12 or HCFC-22.
As compared with CFC-12 or CFC-22, the HFC type refrigerant has a high polarity and shows no substantial compatibility with a lubricating oil such as an alkylbenzene or a naphthene type mineral oil which has been commonly used as a refrigerating machine oil. Thus, it tends to lead to double layer separation within the practical temperature range of the refrigerator. Once double layer separation takes place, oil return tends to be poor, which cases various serious problems such that the lubricating oil deposits on the inner wall of an heat exchanger, whereby the heat exchange rate tends to be poor, or lubrication failure or foaming at the start up occurs. Therefore, conventional refrigerating machine oils can not be used as refrigerating machine oils in such a new refrigerant atmosphere.
As refrigerating machine oils which can be used together with a HFC type refrigerant such as HFC-134a, polyether type oils (e.g. JP-B-4-78674, JP-A-1-259095, JP-A-2-102296 and JP-A-3-109492), polyether type oils (JP-A-3-502472, JP-A-3-505602, JP-A-3-88892, JP-3-217494, JP-A-5-25484 and JP-A-5-179268) and carbonate type oils (e.g. JP-A-3-217495, JP-A-4-18490, JP-A-4-63893, JP-A-5-32588, JP-A-5-32992, JP-A-5-186784 and JP-A-6-87791) have been proposed.
Problems to be Solved by the Invention
These refrigerating machine oils heretofore proposed have a high polarity as compared with an alkylbenzene or a naphthene type mineral oil and accordingly certainly have good compatibility with a HFC-type refrigerant such as HFC-134a. However, as compared with conventional working fluids of CFC-12/mineral oil type and CFC-22/mineral oil type, both the refrigerant and the refrigerating machine oil tend to have a high polarity and tend to contain water.
Accordingly, these refrigerating machine oils have drawbacks that the thermal stability in the co-existence of a HFC type refrigerant such as HFC-134a is poor, and they tend to hydrolyze e.g. a polyethyleneterephthalate film as a coating material of a coil for a motor for compressor. Especially the polyester type oils have a problem that they themselves undergo hydrolysis to form a carboxylic acid, and this carboxylic acid corrode a metal, thus reading to metal erosion. Whereas, the carbonate type oils have a problem that by the hydrolysis, non-condensable carbon dioxide will form.
Further, since a compressor motor is built in the compressor, good electrical insulation is required. However, with the polyether type lubricating oils which are excellent in that they do not undergo hydrolysis, the volume resistivity used to be about 10
11
&OHgr;/cm, and it can hardly be said that they have good electrical insulation properties.
Whereas, polyether type oils having low hygroscopic properties and good electrical insulation properties, have been proposed in JP-A-4-19295, JP-A-4-39394, JP-4-130188 and JP-A-6-330062. However, such polyether type oils did not fully satisfy all of the properties such as the compatibility with a HFC type refrigerant, low hygroscopic properties and high electrical insulation properties.
It is the object of the present invention to provide a refrigerating machine oil which exhibits good compatibility with a HFC type refrigerant within a wide temperature range and which is excellent in the electrical insulation properties, the lubricating properties, the low hygroscopic properties, durability, etc., and a composition for refrigerator comprising such an oil and a HFC type refrigerant.
Means to Solve the Problem
The present inventors have paid an attention to a polyoxyalkyleneglycol which has no problem of hydrolysis and have conducted a study earnestly to overcome above mentioned drawbacks of a polyoxyalkylene glycol oil, and they have found that a polyoxyalkylene glycol derivative having a certain structure is excellent in compatibility with a HFC type refrigerant and has a high volume resistivity of at least 10
12
&OHgr;/cm and have arrived at the present invention.
The present invention is a lubricating oil for refrigerator comprising a polyether represented by the following general formula (1):
R
1
−[X—OR
4
]
s
(1)
wherein R
1
is a s-valent group having an aromatic nucleus, X is a bivalent group comprising average q —OR
2
— and average r —OR
3
—, R
2
is an ethylene group which may have a methyl group or an ethyl group, R
3
is an ethylene group having an alkoxymethyl group wherein the carbon number of the alkoxy group is from 1 to 4, R
4
is a C
1-10
alkyl group, s is an integer of from 1 to 6, q is from 0 to 6, and r is at least 0.5, provided that (q+r)×s is a number of from 3 to 80.
R
1
of the polyether represented by the general formula (1) in the present invention, is a s-valent group having an aromatic nucleus. s is an integer of from 1 to 6, and s is preferably an integer of from 1 to 2 from the availability of raw material. As a monovalent group having an aromatic nucleus, an aryl group or an aralkyl group, may, for example, be mentioned.
The aryl group is a residue having one hydrogen atom directly bonded to an aromatic nucleus removed from an aromatic hydrocarbon, and it may, for example, be a phenyl group, a biphenyl group or a naphthyl group, or such a group having an alkyl moiety. The aralkyl group is one having a hydrogen atom of an alkyl group substituted by an aryl group, and in other words, it is one having an aryl group bonded to one of the bonds of an alkylene group.
As a 2 to 6 valent group having an aromatic nucleus, a residue having from 1 to 5 hydrogen atoms removed from an aryl group or an aralkyl group, or a group having a hydroxyl group removed from a bisphenol such as bisphenol A, bisphenol F or bisphenol S, may, for example, be mentioned.
The above mentioned from 1 to 5 hydrogen atoms removed from an aryl group or an aralkyl group, may be either hydrogen atoms directly bonded to the aromatic nucleus or hydrogen atoms bonded to an alkyl moiety or an alkylene moiety directly bonded to the aromatic nucleus, or both of them.
Preferred R
1
is a monovalent group having an aromatic nucleus, particularly an aryl group, more preferably a phenyl group or a naphthyl group having an alkyl moiety.
The alkyl moiety of the phenyl group or the naphthyl group having an alkyl moiety may be straight chain, branched chain or cyclic. As the phenyl group or the naphthyl group having an alkyl moiety, the following groups are preferred:
A methylphenyl group, an ethylphenyl group, a propylphenyl group, a butylphenyl group, a pentylphenyl group, a hexylphenyl group, a heptylphenyl group, an octylphenyl group, a nonylphenyl group, a decylphenyl group, a dodecylphenyl group, a dimethylphenyl group, a diethylphenyl group, a dipropylphenyl group, a dibutylphenyl group, a dipentylphenyl group, a dihexylphenyl group, a diheptylphenyl group, a dioctylphenyl group, a dinonylphenyl group, a didecylphenyl group, a didodecylphenyl
En-na Gen-ichirou
Fukuda Hiroki
Ohtsuka Yoshihiro
Asahi Glass Company Ltd.
Einsmann Margaret
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