Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Organic oxygen compound
Reexamination Certificate
1999-09-21
2001-05-29
Howard, Jacqueline V. (Department: 1764)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Organic oxygen compound
C252S068000
Reexamination Certificate
active
06239086
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to refrigerating machine oils, more particularly to such a refrigerating machine oil suitable for a refrigerating machine using ammonia as a refrigerant.
2. Description of the Prior Art
Due to the recent issues concerning with the ozone shield depletion, conventional refrigerants for refrigerating machine such as CFC (chlorofluorocarbon) and HCFC (hydrochlorofluorocarbon) have been targeted for regulation. In place of these refrigerants, HFC (hydrofluorocarbon) has been used as such a refrigerant. However, since the HFC refrigerant also has a problem that it is high in Global Warming Potential (GWP), it has been considered to use refrigerants containing natural materials as alternative refrigerants for the fluorocarbon type refrigerants.
Conventionally, ammonia has been used as a refrigerant for the industrial use, and mineral oils have been used as refrigerating machine oils for use with an ammonia refrigerant. However, due to inmiscibility of ammonia with mineral oils, it is rather difficult for the oil pumped out from a compressor to return to the compressor through the refrigerating cycle, resulting in poor lubricity in the compressor and the reduction of efficiency of heat exchange. Under these circumstances, the development and research of a refrigerating machine oil miscible with ammonia has been progressed.
When ammonia is used as a refrigerant, water possibly enters into a refrigerating cycle due to the hygroscopicity of ammonia itself which is extremely high, compared with fluorocarbon type refrigerants. When a refrigerating machine oil containing a mineral oil is used, the water entering into a refrigerating cycle creates a problem that the water separated from the oil freezes and closes the line of the refrigerating cycle, which adversely affect the stability of the refrigerant and oil and of the pipings of the system. Therefore, a refrigerating machine oil for use with an ammonia refrigerant is required to be stable in the presence of water.
A study has been placed on a PAG (polyalkylene glycol) compound as disclosed in Japanese Patent Laid-Open Publication No. 5-009483 to use as a refrigerant which is miscible with ammonia. An oxyethylene oxypropylene copolymer has been regarded as being superior in miscibility and fluidity at low temperatures.
However, the use of PAG containing an oxyethylene group in its molecule poses a problem in terms of stability when water and oxygen enter into a refrigerating cycle. For the foregoing reasons, it has not been accomplished to develop a refrigerating machine oil for use with an ammonia refrigerant which has satisfyingly required properties such as lubricity, miscibility with a refrigerant, fluidity at low temperatures and stability, in a well-balanced manner.
In view of the foregoing, it is an object of the present invention to provide a refrigerating machine oil which can meet all of the requirements such as lubricity, miscibility with a refrigerant, fluidity at low temperatures and stability, in a well-balanced manner when used with an ammonia refrigerant.
SUMMARY OF THE INVENTION
An extensive research and investigation found that it is made possible to obtain a refrigerating machine oil which is improved in stability and has capabilities such as lubricity and miscibility with a refrigerant in a well balanced manner by using specific types of PAG monoethers which have been recognized as being defective in terms of stability, as a base oil.
According to the present invention, there is provided a refrigerating machine oil for use with an ammonia refrigerant which comprises a polypropylene glycol monoether represented by the formula
wherein R is an alkyl group having 1 to 10 carbon atoms and n is an integer to be selected such that the number-average molecular weight of the oil becomes 500 to 5,000.
DETAILED DESCRIPTION OF THE INVENTION
The refrigerating machine oil according to the present invention comprises a polypropylene glycol monoether represented by the formula
In formula (1), R is an alkyl group having 1 to 10 carbon atoms which may be of straight- or branched-chain type. Specific examples of such alkyl groups are methyl, ethyl, straight or branched propyl, straight or branched butyl, straight or branched pentyl, straight or branched hexyl, straight or branched octyl, straight or branched nonyl and straight or branched decyl groups. Among these groups, preferred are methyl, ethyl, straight or branched propyl and straight or branched butyl groups in view of miscibility and fluidity at low temperatures. In view of lubricity, more preferred are straight or branched alkyl group having 6 to 10 carbon atoms and further more preferred are those having 8 to 10 carbon atoms. Alkyl groups having more than 10 carbon atoms are not preferred in view of miscibility and fluidity at low temperatures.
In formula (1), n represents an integer to be selected such that the number-average molecular weight of the oil becomes 500 to 5,000. In view of improving the sealing capability of a compressor, the number-average molecular weight is preferably more than 600. Furthermore, in view of miscibility with a refrigerant, the number-average molecular weight is preferably less than 3,000, more preferably less than 1,500.
The polypropylene glycol monoether used in the present invention has a pour point of preferably less than −10° C., more preferably −20 to −50° C. in view of less possibility that the resulting refrigerating machine oil reduced in fluidity in a refrigerating cycle.
Preferred polypropylene glycol monoethers are those having a kinematic viscosity at 100° C. of less than 2 mm
2
/s in view of the capability of maintaining the sealing of a compressor. More preferred are those having a kinematic viscosity at 100° C. of less than 2 mm
2
/s in view of miscibility with ammonia.
The ratio (Mw/Mn) of weight average molecular weight (Mw) to the number-average molecular weight (Mn) is preferably within the range of 1.00 to 1.20 in view of improving miscibility with ammonia.
When a consideration given to the necessity of decreasing the amount of moisture entering into a refrigerating system to the utmost, the water content of the polypropylene glycol monoester used in the invention is less than 500 ppm, preferably less than 200 ppm, more preferably less than 100 ppm. Polyglycol-based oils are generally high in hygroscopicity and the PAG monoethers of the present invention are higher in hygroscopicity, compared with diehters. Therefore, it is necessary to pay meticulous attention to the moisture content of the oil to be introduced into a refrigerating system. However, on the other hand, due to higher hygroscopicity of ammonia than fluorocarbonaceous refrigerants such as HFC (hydrofluorocarbon), the moisture entering into a refrigerating system upon the introduction of the refrigerant thereto tends to cause e a problem. If a PAG monoethers having high hygroscopicity coexists with a refrigerant in a refrigerating system, it can prevent the moisture entering therein from liberating by capturing it into the molecules, thereby avoiding harmful influences caused by the deterioration of the refrigerant and the pipings in the system and the freezing of the moisture.
The content of the polypropylene glycol monoether in the refrigerating machine oil of the present invention is not particularly limited, but is preferably more than 50 mass percent, more preferably more than 70 mass percent, further more preferably more than 80 mass percent, most preferably more than 90 mass percent, based on the total mass of the oil, because the resulting oil can be imparted with various superior characteristics such as lubricity, miscibility with a refrigerant, thermal and chemical stability and electric insulation.
A refrigerating machine oil according to the present invention comprises the above mentioned polypropylene glycol monoether but may further comprise a hydrocarbon base oil such as mineral oils, olefin polymers, naphthalene compounds and alkylbenzene oils and oxyg
Hirano Hiroyuki
Shimomura Yuji
Suda Satoshi
Akin Gump Strauss Hauer & Feld L.L.P.
Howard Jacqueline V.
Nippon Mitsubishi Oil Corporation
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