Lubricant for refrigerators using ammonia refrigerant

Details Lubricant for refrigerators using ammonia refrigerant Lubricant for refrigerators using ammonia refrigerant

2000-03-20

2002-01-01

Keys, Rosalynd (Department: 1621)

Solid anti-friction devices, materials therefor, lubricant or se

Lubricants or separants for moving solid surfaces and...

Organic oxygen compound

C508S583000, C252S068000, C568S606000, C568S608000, C568S613000

Reexamination Certificate

active

06335311

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a lubricant for refrigerators using ammonia refrigerant.
2. Description of the Related Art
Traditionally, compression type refrigerating machines comprise a compressor, a condenser, an expansion mechanism (such as expansion valves) and an evaporator, and chlorine-containing fluorinated hydrocarbons (fluorine compounds) such as trichlorofluoromethane (R11), dichlorodifluoromethane (R12) and chlorodifluoromethane (R22) have been used as refrigerants for a long time. These fluorine compounds have caused the global environmental problem of ozone layer depletion, and so use thereof is restricted, and these compounds have been replaced by chlorine-free fluorine compounds such as difluoromethane (R32), tetrafluoromethane (R134 or R134a) and difluoroethane (R152 or R152a). It has been pointed out, however, that it is very likely that these chlorine-free fluorine compounds also contribute to global warming and are likely to cause environmental problems in the long term.
Accordingly, attention has recently been directed to hydrocarbons and ammonia as refrigerants which would not cause these environmental problems. These refrigerants are superior to the fluorine compounds in terms of compatibility and safety with respect to the global environment and the human body. Moreover, these compounds have been tested over time, although they are not often used as refrigerants.
Heretofore, ammonia has been used only in refrigerators equipped with an oil circulation apparatus at the outlet of the compressor, which separates and collects oil and returns the oil to the inlet of the compressor, because ammonia is not compatible with mineral oils, alkylbenzenes and the like which are refrigerator oils. Also, when such oil circulation apparatus does not function properly, the refrigerator oils are drawn into the refrigeration cycle and cause a shortage of lubricant oil in the compressor, which may result in seizure due to insufficient lubrication at sliding sections and significant reduction in equipment life. Furthermore, since the evaporator is cold, highly viscous refrigerator oils brought in the refrigeration cycle remain in the evaporator and may thereby decrease heat transfer efficiency. Therefore, refrigerators using ammonia have only been used in relatively large industrial devices which receive regular maintenance.
In view of the above-mentioned environmental problems, however, the merits of ammonia refrigerants have been reevaluated. In view of this, refrigerator oils which are compatible with ammonia refrigerant and do not require an oil circulation apparatus, as in the case of fluorine refrigerants, have been proposed. For example, EP Publication No.0490810 discloses lubricants comprising polyalkylene glycols which are copolymers of ethylene oxide (EO) and propylene oxide (PO), wherein EO/PO is 4/1. EP Publication No.585934 discloses lubricants comprising mono- or difunctional polyalkylene glycols, wherein EO/PO is 2/1-1/2. DE Patent Publication No.4404804 discloses polyether-based lubricants represented by the general formula RO-(EO)
x
—(PO)
y
—H (wherein R is an alkyl group of 1-8 carbon atoms; and x and y are each a number from 5 to 55). Furthermore, EP Publication No.699737 discloses lubricants represented by the general formula Z{—O(CH
2
CH(R
1
)O)
n
—(CH
2
CH(R
1
)O)
m}
p
—H (wherein Z has 6 or more carbon atoms in the case of an aryl group and 10 or more carbon atoms in the case of an alkyl group; R
1
is H, a methyl group or an ethyl group; n is 0 or a positive number; m is a positive number; and p is a number corresponding to the valence of Z).
Moreover, Japanese Patent Laid-Open No. 5-9483 and WO Publication 94/12594 disclose refrigerator oils comprising polyalkylene glycol diethers which are superior in compatibility with ammonia and have superior stability.
When using the above-mentioned polyalkylene glycol-based compounds as refrigerant oils for a refrigerator with ammonia refrigerant, it has been pointed out that multifunctional polyalkylene glycols having two hydroxyl groups have problems associated with their stability and hygroscopicity. Another problem is that the above-mentioned polyalkylene glycol diethers are less compatible with ammonia than are the polyalkylene glycols having hydroxyl groups, and they are not compatible depending on the structure. Furthermore, the polyalkylene glycol diethers are blocked at the molecular terminal with alkyl groups and have a shortcoming in that this terminal blocking complicates the manufacturing process.
Therefore, it is an object of the present invention to provide a refrigerant oil for refrigerators using ammonia as a refrigerant, which is superior in compatibility with ammonia, lubrication properties, and stability.
SUMMARY OF THE INVENTION
Accordingly, the present invention is a lubricant for a refrigerator using ammonia refrigerant, comprising any one or more of polyethers selected from the group consisting of a polyether represented by the following general formula (1)
X—{—O—(AO)
n
—H}
p
  (1)
(wherein X represents a residue of a monool or polyol from which a hydroxyl group is eliminated; (AO)
n
represents a polyoxyalkylene group formed by copolymerization of ethylene oxide and an alkylene oxide having 3 or more carbon atoms; n is 2 or more; and p is a valence of X) and having 50% or more of secondary hydroxyl groups among the hydroxyl groups located at the terminal of the structure based on the total hydroxyl groups, or a polyether represented by the following general formula (2)
X—{—O—(AO
1
)
a
—(AO
2
)
b
—H}
p
  (2)
(wherein x represents a residue of a monool or polyol from which a hydroxyl group is eliminated; (AO
1
)
a
represents a polyoxyalkylene group composed of copolymerization of ethylene oxide and propylene oxide or butylene oxide; AO
2
represents an oxyalkylene group having 3 or more carbon atoms; a is 2 or more; b is 1 or more; and p is a valence of X).
DETAILED DESCRIPTION OF THE INVENTION
In the general formula (1) or formula (2), X represents a residue of a monool or polyol from which a hydroxyl group is eliminated. The monool includes, for example, alcohols such as methanol, ethanol, propanol, 2-propanol, butanol, 2-butanol, pentanol, 2-pentanol, 3-pentanol, isopentyl alcohol, 2-methyl-4-pentanol, hexanol, secondary hexanol, isohexanol, heptanol, secondary heptanol, octanol, 2-ethylhexanol, secondary octanol, isooctanol, nonanol, secondary nonanol, 1-decanol, isodecyl alcohol, secondary decanol, undecanol, secondary undecanol, 2-methyldecananol, lauryl alcohol, secondary dodecanol, 1-tridecanol, isotridecyl alcohol, secondary tridecanol, myristyl alcohol, secondary tetradecanol, pentadecanol, secondary pentadecanol, cetyl alcohol, palmityl alcohol, secondary hexadecanol, heptadecanol, secondary heptadecanol, stearyl alcohol, isostearyl alcohol, secondary octadecyl alcohol, oleyl alcohol, behenyl alcohol, eicosanol, docosaol, tetracosanol, hexacosanol, octacosanol, myricyl alcohol, laccerol, tetratriacontanol, allyl alcohol, cyclopentanol, cyclohexanol, 2-butyloctanol, 2-butyldecanol, 2-hexyloctanol, 2-hexyldecanol, 2-hexyldodecanol, 2-octyldecanol, 2-octyldodecanol, 2-octyltetradecanol, 2-decyldodecanol, 2-decyltetradecanol, 2-decylhexadecanol, 2-dodecyltetradecanol, 2-dodecylhexadecanol, 2-dodecyloctadecanol, 2-tetradecyloctadecanol, 2-tetradecyleicosanol, 2-hexadecyloctadecanol and 2-hexadecyleicosanol; and phenols such as phenol, cresol, ethylphenol, tert-butylphenol, hexylphenol, octylphenol, nonylphenol, decylphenol, undecylphenol, dodecylphenol, tridecylphenol, tetradecylphenol, phenylphenol, benzylphenol, styrenated phenol, and p-cumylphenol.
The polyol includes, for example, diols such as ethylene glycol, propylene glycol, 1,4-butanediol, 1,2-butanediol, neopentylglycol, 1,6-hexandiol, 1,2-octanediol, 1,8-octanediol, isopreneglycol, 3-methyl-1,5-pentanediol, sorbite, catechol, resorcine, hydroquinone, bisphenol A, bisphenol F, hydrogenated bisphenol A, hydrogenated

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