Compositions – Vaporization – or expansion – refrigeration or heat or energy... – With lubricants – or warning – stabilizing or anti-corrosion...
Reexamination Certificate
1997-02-04
2001-07-17
Ogden, Necholus (Department: 1751)
Compositions
Vaporization, or expansion, refrigeration or heat or energy...
With lubricants, or warning, stabilizing or anti-corrosion...
C252S067000, C508S579000, C508S580000
Reexamination Certificate
active
06261474
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a lubricating oil for compression-type refrigerators. More particularly, the present invention relates to a lubricating oil for compression-type refrigerators using a hydrofluorocarbon refrigerant containing pentafluoroethane which lubricating oil comprises a polyvinyl ether compound, shows an excellent compatibility with hydrofluorocarbon refrigerants containing pentafluoroethane which can replace chlorofluorocarbons causing environmental pollution, has a volume intrinsic resistance of 10
12
&OHgr;cm or more at 80° C., and exhibits excellent stability and lubricating property.
PRIOR ART OF THE INVENTION
In general, compression-type refrigerators are constituted at least with a compressor, a condenser, an expansion mechanism (such as an expansion valve and a capillary tube), an evaporator, and a drier and has a structure in which a mixed fluid of a refrigerant and a lubricating oil is circulated in the closed system. Temperature is high in the compressor and low in the refrigerating chamber generally in the compression-type refrigerator though the conditions may be different depending on the type of machinery, and it is generally required that the refrigerant and the lubricating oil be circulated in the system without causing phase separation in the wide range of temperature. A mixture of a refrigerant and a lubricating oil generally has regions of phase separation at the low temperature side and at the high temperature side. The highest temperature in the region of phase separation at the low temperature side is preferably −10° C. or lower, more preferably −20° C. or lower. The lowest temperature in the region of phase separation at the high temperature side is preferably 30° C. or higher, more preferably 40° C. or higher. When phase separation occurs during the operation of the refrigerator, life and efficiency of the apparatus are adversely affected to a great extent. For example, when phase separation of the refrigerant and the lubricating oil occurs in the part of the compressor, lubrication of the moving parts is deteriorated, and seizure occurs to cause decrease in the life of the apparatus to a great extent. When the phase separation occurs in the evaporator, efficiency of heat exchange is decreased because of the presence of lubricating oil of high viscosity.
Because the lubricating oil for refrigerators is used for the purpose of lubricating moving parts in refrigerators, the lubricating property is naturally important. Particularly, because the temperature in the compressor is high, the viscosity which can hold the oil film necessary for the lubrication is important. The required viscosity is different depending on the type of the compressor used and working conditions, and it is generally preferred that the viscosity (kinematic viscosity) of the lubricating oil before mixing with a refrigerant is 5 to 200 cSt, more preferably 5 to 100 cSt, at 40° C. When the viscosity is lower than this range, the oil film becomes thin to cause insufficient lubrication. When the viscosity is higher than this range, efficiency of the heat exchange is decreased.
Electric refrigerators and air conditioners have a motor and a compressor integrally built into a single body, and the lubricating oil for them is required to have a high degree of electric insulating property. In general, a volume intrinsic resistance of 10
12
&OHgr;cm or more at 80° C. is required. When the resistance is lower than this value, possibility of leak of electricity arises. Moreover, high stability is required for a lubricating oil. For example, when organic acids are formed by hydrolysis or the like, corrosion and wear of the apparatus tend to take place although degree of the corrosion and the wear depends on the amount of the organic acids.
As the refrigerant for compression-type refrigerators, particularly for air conditioners, mainly chlorodifluoromethane (hereinafter referred to as R22) or a mixture of chlorodifluoromethane and chloropentafluoroethane in a ratio by weight of 48.8 and 51.2 (hereinafter referred to as R502) has heretofore been used. As the lubricating oil, various types of mineral oils and synthetic oils satisfying the required properties described above have been used. However, R22 and R502 are more rigorously restricted world-wide because there is the possibility that they cause environmental pollution such as the ozonosphere destruction. By this reason, hydrofluorocarbons represented by 1,1,1,2-tetrafluoroethane, difluoromethane, pentafluoroethane, and 1,1,1-trifluoroethane (hereinafter referred to as R134a, R32, R125, and R143a, respectively) are attracting attention as the novel types of the refrigerant. The hydrofluorocarbons, particularly R134a, R32, R125, and R143a, are preferred as the refrigerant for compression-type refrigerators because they have little possibility of causing the ozonosphere destruction. However, the above hydrofluorocarbon causes a problem when it is used singly. For example, it is reported in “Energy Shigen (Energy and Resources)” Volume 16, Number 5, Page 474 that (1) when R134a is applied to an air conditioner to replace R22, the pressure in operation is lower, and the ability is decreased by about 40% and the efficiency is decreased by about 5% from those obtained by using R22; (2) R32 shows a higher efficiency but a higher pressure in operation than those obtained by using R22 and is slightly combustible; and (3) R125 has a lower critical pressure to cause decrease in the efficiency although it is not combustible. R143a has the problem of combustibility like R32.
It is desirable that a refrigerant for compression-type refrigerators can be used without change in the structure of the currently used refrigerator. However, the above mixed hydrofluorocarbon refrigerants must be used actually because of the problems described above. More specifically, it is desirable in view of the efficiency that R32 and R143a which are combustible are used to replace R22 and R502 which are currently used, and R125 or R134a is mixed to R32 or R143a to provide the incombustibility. It is described in The International Symposium on R22 & R502 Alternative Refrigerants, 1994, Page 166 that a mixture of R32 and R134a is combustible when the content of R32 is 56% by weight or more. In view of the incombustibility, a refrigerant containing 45% by weight or more of an incombustibile hydrofluorocarbon such as R125 and R134a is desirable although the content may be different depending on the composition of the refrigerant.
On the other hand, a refrigerant is used under various conditions in a refrigeration system, and it is not desirable that the composition of the refrigerant containing hydrofluorocarbons is different to a great extent in various parts of a refrigeration system. The refrigerant is in the gaseous state as well as in the liquid states in one refrigeration system. Therefore, when boiling points of hydrofluorocarbons used as a mixture are different to a great degree, there is the possibility that the composition of the mixed refrigerant is different to a great extent in various parts of the refrigeration system because of the above reason.
Boiling points of R32, R143a, R125, and R134a are −51.7° C., −47.4° C., −48.5° C., and −26.3° C., respectively. Using R134a in a mixed hydrofluorocarbon refrigerant must be made carefully in view of the above consideration. Therefore, when R125 is used in a mixed refrigerant, it is preferred that the content of R125 is 20 to 80% by weight, more preferably 40 to 70% by weight. When the content is less than 20% by weight, a refrigerant having a different boiling point such as R134a must be used in a larger amount in order to provide the obtained mixed refrigerant with the incombustibility, and the content is not preferable by the above reason. When the content of R125 is more than 80% by weight, the efficiency is decreased, and the content is not preferable, either.
From the reasons described above, a mixture of R32, R125, and R134a in a ratio by we
Egawa Tatsuya
Handa Toyokazu
Kaneko Masato
Mogami Kenji
Nagao Satoshi
Idemitsu Kosan Co. Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ogden Necholus
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