Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Organic -co- compound
Reexamination Certificate
1999-11-03
2001-10-23
Howard, Jacqueline V. (Department: 1764)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Organic -co- compound
C508S579000, C252S068000
Reexamination Certificate
active
06306803
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a refrigerator oil for carbon dioxide (CO
2
) refrigerant, and to a method of using it for lubrication. The refrigerator oil can be used in compression refrigerators with carbon dioxide refrigerant therein, especially in refrigerating or heating-cooling equipment such as car air conditioners, refrigerators, freezers, air conditioners, heat pumps, compression refrigeration cycles equipped with oil separator and/or hot gas line, etc.
2. Description of the Related Art
In general, a compression refrigeration cycle for refrigerators, for example, that for compression refrigerators comprising a compressor, a condenser, an expansion valve and an evaporator is of a closed system in which is circulated a mixed liquid comprising a refrigerant and a lubricating oil. In compression refrigerators of that type, in general, chlorofluorocarbons such as dichlorodifluoromethane (R-12) and chlorodifluoromethane (R-22) have heretofore been used as refrigerants. Various types of lubricating oils have been produced and used together with such refrigerants. However, when released in air, these Flon compounds that have heretofore been used as refrigerants will bring about environmental pollution, as destroying the ozone layer existing in the stratosphere. Therefore, their use is being severely controlled in all the world. Given the situation, new refrigerants, hydrofluorocarbons and fluorocarbons such as typically 1,1,1,2-tetrafluoroethane (R-134) have become specifically noted. Hydrofluorocarbons and fluorocarbons will not destroy the ozone layer. However, as their life in air is long, they will cause global warming. Therefore, the recent tendency in the art is toward using refrigerants from natural resources that are free from the problem.
Above all, carbon dioxide is excellent as it is harmless to the environment and is safe to human beings. In addition, it has the advantages of anywhere easy availability and extremely low costs with no necessity for recovery. For these reasons, carbon dioxide has been much used as the refrigerant for refrigerators.
Unexpectedly, however, using such carbon dioxide as a refrigerant is often problematic in that the system with carbon dioxide therein requires higher jetting pressure and has higher temperature, as compared with that where is used R-134a or the like, with the result that the refrigerator oil in the system is exposed to carbon dioxide of being in a supercritical condition. Therefore, when such a carbon dioxide refrigerant is combined with ordinary refrigerator lubricating oil, the lubricating oil could not exhibit good lubricity and its ability to improve the abrasion resistance of machine parts is often poor. In addition, the stability of the lubricating oil is worsened, and stably using it for a long period of time is impossible.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the viewpoints noted above, and its object is to provide a refrigerator oil, which exhibits good lubricity and can be stably used for a long period of time even in a refrigeration cycle where is used a refrigerant that comprises, as the essential component, carbon dioxide of being in a supercritical condition at high temperature and under high pressure. The invention is also to provide a refrigerator oil capable of exhibiting good lubricity and good sealability and capable of being stably used for a long period of time even in a compression refrigeration cycle where is used a refrigerant comprising carbon dioxide as the essential component, and further to provide a method of using the refrigerator oil for lubrication.
We, the present inventors have assiduously studied and, as a result, have found that the object of the invention can be effectively attained by using a lubricating oil comprising a specific base oil and an additive thereto. Unexpectedly, in addition, we have further found that, when a mixture of a polyoxyalkylene glycol and a polyvinyl ether is used as the base oil for refrigerator oil, then the compatibility of the polyoxyalkylene glycol with carbon dioxide refrigerant is enhanced, and that, when a specific additive is added to the refrigerator oil comprising the base oil of that type, then the refrigerator oil is well stable and can exhibit good lubricity even in a carbon dioxide atmosphere of being in a supercritical condition while it maintains good compatibility with carbon dioxide refrigerant. On the basis of these findings, the inventors have completed the present invention.
Specifically, the invention provides the following:
1. A refrigerator oil for carbon dioxide refrigerant, which comprises a base oil comprising an oxygen-containing organic compound as the essential component and having a kinematic viscosity at 100° C. of from 5 to 50 mm
2
/sec and a viscosity index of at least 60.
2. The refrigerator oil of above 1, which further contains a metal salt of a carboxylic acid.
3. The refrigerator oil of above 2, wherein the metal salt of a carboxylic acid is an alkali metal salt of a carboxylic acid having from 3 to 60 carbon atoms.
4. The refrigerator oil of above 1, wherein the oxygen-containing organic compound is at least one selected from polyoxyalkylene glycols, polyvinyl ethers, polyesters and carbonates.
5. The refrigerator oil of above 1, wherein the oxygen-containing organic compound is a compound of a general formula (I) or a compound comprising structural units of a general formula (V):
R
1
—[(OR
2
)
m
—OR
3
]
n
(I)
where R
1
represents a hydrogen atom, an alkyl group having from 1 to 10 carbon atoms, an acyl group having from 2 to 10 carbon atoms, or an aliphatic hydrocarbon group having from 2 to 6 bonding sites and having from 1 to 10 carbon atoms; R
2
represents an alkylene group having from 2 to 4 carbon atoms; R
3
represents a hydrogen atom, an alkyl group having from 1 to 10 carbon atoms, or an acyl group having from 2 to 10 carbon atom; n represents an integer of from 1 to 6; and m represents a number to give a mean value of m×x falling between 6 and 80;
where R
16
, R
17
and R
18
each represent a hydrogen atom, or a hydrocarbon group having from 1 to 8 carbon atoms, and they may be the same or different; R
19
represents a divalent hydrocarbon group having from 1 to 10 carbon atoms; R
20
represents a hydrocarbon group having from 1 to 20 carbon atoms; k represents a number of from 0 to 10 on average; R
16
to R
20
may be the same or different in different structural units; and plural R
19
O's, if any, may be the same or different.
6. The refrigerator oil of above 1, wherein the oxygen-containing organic compound is {circle around (1)} a polyalcohol ester, or {circle around (2)} a polycarboxylate.
7. The refrigerator oil of above 1, which further contains a phosphorus-containing extreme pressure agent.
8. The refrigerator oil of above 1, which further contains an acid scavenger.
9. The refrigerator oil of above 1, wherein the oxygen-containing organic compound which further contains a phenolic antioxidant.
10. The refrigerator oil of above 1, wherein the base oil is a mixture of a polyoxyalkylene glycol and a polyvinyl ether.
11. The refrigerator oil of above 10, wherein the ratio of the polyoxyalkylene glycol to the polyvinyl ether falls between 40/60 and 99.9/0.1 by weight.
12. The refrigerator oil of above 11, wherein the polyoxyalkylene glycol is a compound of a general formula (I):
R
1
—[(OR
2
)
m
—OR
3
]
n
(I)
where R
1
represents a hydrogen atom, an alkyl group having from 1 to 10 carbon atoms, an acyl group having from 2 to 10 carbon atoms, or an aliphatic hydrocarbon group having from 2 to 6 bonding sites and having from 1 to 10 carbon atoms; R
2
represents an alkylene group having from 2 to 4 carbon atoms; R
3
represents a hydrogen atom, an alkyl group having from 1 to 10 carbon atoms, or an acyl group having from 2 to 10 carbon atom; n represents an integer of from 1 to 6; and m represents a number to give a mean value of m×x falling betw
Howard Jacqueline V.
Idemitsu Kosan Co. Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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