Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Organic -co- compound
Reexamination Certificate
2002-07-12
2004-08-10
McAvoy, Ellen M (Department: 1764)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Organic -co- compound
C252S068000
Reexamination Certificate
active
06774093
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to synthetic ester lubricant base stocks, and more particularly to high molecular weight synthetic ester lubricant base stocks formed from neopentylpolyols and monocarboxylic acids or mixtures of monocarboxylic acids suitable for use in industrial refrigeration systems.
It is well known that chlorofluorocarbons previously utilized as propellants in aerosols and as refrigeration fluids are no longer used due to the adverse impact on the earth's ozone layer. Efforts to eliminate the use of chlorofluorocarbons has led to the development of alternative fluids that are highly or fully fluorinated hydrocarbons.
Working refrigeration fluids generally include a minor amount of lubricant. Typically, the refrigeration fluids include between about 5 to 15 or 20 parts by weight of lubricant with the balance being the fluorocarbon. In chlorofluorocarbon systems, lubricants have been mineral oils which are fully miscible with the chlorofluorocarbons. However, such lubricants are not miscible with the highly or fully fluorinated hydrocarbons such as 1,1,1,2-tetrafluoroethane, commonly known as HFC-134a. Other chlorine-free fluorocarbons include a hydrofluorocarbon (HFC) having 1 to 3 carbon atoms and preferably 1 to 2 carbon atoms, for example, difluoromethane (HFC-32), trifluoromethane (HFC-23), pentafluoroethane (HFC-125), 1,1,2,2-tetrafluoroethane (HFC-134), 1,1,1-trifluoroethane (HFC-143a), 1,1-difluoroethane (HFC-152a) or a mixture of two or more kinds of these HFCs.
It has been found that certain carboxylic esters of polyhydroxy compounds are fully miscible with the highly or fully fluorinated fluids. An early publication describing such lubricants is European Patent EP 0 422 185 B1. Lubricants of the type disclosed are low viscosity fluids of the type utilized in home window air conditioning units and automotive air conditioning units. The lubricants are prepared by the condensation of pentaerythritol and monocarboxylic acids containing between about 6 to 8 carbon atoms. This generally produces an ester having a viscosity at 40° C. of between about 17.5 to about 52.0 cSt. Such lubricants are also disclosed in U.S. Pat. No. 5,964,581.
Larger industrial refrigeration units of the type utilized in building and factory cooling units call for refrigeration fluids including lubricants having significantly higher viscosity in the ISO 100 to 350 range (100 to 350 centistokes at 40° C.). Typically such higher viscosity lubricants would be formed from dipentaerythritol and higher molecular weight carboxylic acids. This would include lubricant base stocks having a viscosity between about 68 to 400 cSt at 40° C. Alternatively, dicarboxylic acids can be utilized along with the monocarboxylic acids to form complex esters when reacted with a polyol, however these esters tend to be less stable than polyol esters of monocarboxylic acid alone. Production of higher viscosity lubricants is generally not possible from a monopentaerythritol starting material. It is preferable to use monopentaerythritol, however, because the cost of monopentaerythritol is much lower than the cost of dipentaerythritol.
Accordingly, it is desirable to provide a synthetic ester lubricant base stock having a viscosity between about ISO 68 to 400 based on condensation of monopentaerythritol and monocarboxylic acids.
SUMMARY OF THE INVENTION
Generally speaking, in accordance with the invention, high viscosity synthetic ester lubricant base stocks based on polyneopentylpolyol esters suitable for use with high-fluorine containing refrigeration fluids are provided. The polyneopentylpolyol esters are formed by reacting a neopentylpolyol having less than 10 carbon atoms with at least one monocarboxylic acid selected from the group of linear acids having from 4 to 10 carbon atoms, and branched chain acids having from 5 to 10 carbon atoms. The neopentylpolygls include pentaerythritol, trimethylolpropane, trimethylolethane, neopentyl glycol and the like. A preferred acid is a mixture of a linear acid and a branched acid in a mole ratio of between 5:1 to 1:5, preferably between about 1:1 to 1:3 and most preferably between 1:3 to 1:4.
The polyol and acid are first reacted in the presence of an excess of hydroxyl groups to form a partial polyneopentylpolyol ester of desired viscosity. Then an excess of monocarboxylic acid or acid mixture is added to the reaction mixture and the esterification reaction is continued to yield an ester having a viscosity in the range of 68 to 400 cSt at 40° C.
Optionally, finished esters can be prepared to a higher viscosity than desired. These can then be blended with a lower viscosity neopentylpolyol ester to achieve the desired target viscosity. Significant economic benefits are realized by this approach to building viscosity in the ISO range of between about 68 to 400. The base stocks are then blended with a refrigerant lubricant additive package to form the lubricant. The additive packages are well known in the art and include antioxidants, anti-wear agents, metal pacifiers, friction modifiers and the like.
In a preferred embodiment of the invention, the starting polyol is pentaerythritol and the acid is a mixture of valeric acid (C
5
acid) and 3,5,5-trimethylhexanoic acid (isoC
9
acid). It has been found that these esters are particularly suitable for use in synthetic refrigeration fluids as they provide good miscibility with highly or fully fluorinated refrigeration fluids over a broad temperature range.
Accordingly, it is an object of the invention to provide a high viscosity synthetic ester base stock having satisfactory miscibility with refrigeration fluids.
Another object of the invention is to provide an improved high viscosity synthetic ester base stock formed from a neopentylpolyol at reduced costs.
A further object of the invention is to provide a high molecular weight synthetic ester base stock having a high ISO grade in the range of about 68 to 400 based on a neopentylpolyol.
Yet another object of the invention is to provide a method for preparing a high viscosity synthetic ester base stock from a neopentylpolyol and an acid or acid mixture consisting of monocarboxylic acids.
Yet a further object of the invention is to provide a high viscosity synthetic ester base stock formed from monopentaerythritol and an acid mixture of valeric acid and isoC
9
acid.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification. The invention accordingly comprises a composition of matter possessing the characteristics, properties and the relation of components which will be exemplified in the compositions hereinafter described, and the scope of the invention will be indicated in the claims.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The high viscosity synthetic ester lubricant base stocks prepared in accordance with the invention are esters or blends of esters of certain polyneopentylpolyols. These esters provide good miscibility with highly or fully fluorinated refrigeration working fluids and are obtained at significant economic benefit.
In the preferred embodiments of the invention, the base stock is a blend of esters which form the reaction product of a two step process. In the initial step a neopentylpolyol having less than 10 carbon atoms and preferably from 5 to 8 carbon atoms is reacted with an acid or acid mixture of linear C
4
-C
10
acid and/or branched C
5
-C
10
acid in the presence of an excess of hydroxyl groups to carboxyl groups in the presence of an acid catalyst to form a partial polyneopentylpolyol ester mixture. When the anticipated water of reaction has been removed from the reaction vessel to yield a product of desired viscosity, the resulting partial polyneopentylpolyol ester is then reacted with an excess of an acid or acid mixture that can vary or be the same acid or acid mixture used in the initial step to yield the high viscosity ester product.
The neopentylpolyol utilized to prepare compositions in accordance with the invention preferably is at least one neo
Carr Dale D.
McHenry Michael A.
Styer Jeremy P.
Hatco Corporation
McAvoy Ellen M
Reed Smith LLP
Wolfson Michael I.
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