Vapor degreasing and solvent cleaning with fluorocarbon based solvents have found widespread use in industry for the degreasing and otherwise cleaning of solid surfaces, especially intricate parts and difficult to remove soils.
In its simplest form, vapor degreasing or solvent cleaning consists of exposing a room temperature object to be cleaned to the vapors of a boiling solvent. Vapors condensing on the object provide clean distilled solvent to wash away grease or other contamination. Final evaporation of solvent from the object leaves behind no residue as would be the case where the object is simply washed in liquid solvent.
For difficult to remove soils where elevated temperature is necessary to improve the cleaning action of the solvent, or for large volume assembly line operations where the cleaning of metal parts and assemblies must be done efficiently and quickly, the conventional operation of a vapor degreaser consists of immersing the part to be cleaned in a sump of boiling solvent which removes the bulk of the soil, thereafter immersing the part in a sump containing freshly distilled solvent near room temperature, and finally exposing the part to solvent vapors over the boiling sump which condense on the cleaned Part. In addition, the part can also be sprayed with distilled solvent before final rinsing.
Vapor degreasers suitable in the above-described operations are well known in the art. For example, Sherliker et al. in U.S. Pat. No. 3,085,918 disclose such suitable vapor degreasers comprising a boiling sump, a clean sump, a water separator, and other ancillary equipment.
Cold cleaning is another application where a number of solvents are used. In most cold cleaning applications, the soiled part is either immersed in the fluid or wiped with rags or similar objects soaked in solvents and allowed to air dry.
Fluorocarbon solvents, such as dichlorotrifluoroethane, have attained widespread use in recent years as effective, nontoxic, and nonflammable agents useful in degreasing applications and other solvent cleaning applications. Dichlorotrifluoroethane has been found to have satisfactory solvent power for greases, oils, waxes and the like. It has therefore found widespread use for cleaning electric motors, compressors, heavy metal parts, delicate precision metal parts, printed circuit boards, gyroscopes, guidance systems, aerospace and missile hardware, aluminum parts and the like.
The art is continually seeking new hydrochlorofluorocarbon solvents which offer alternatives for new and special applications for vapor degreasing and other cleaning applications. Solvents which are based on hydrochlorofluorocarbons are considered to be stratospherically safe substitutes for presently used fully halogenated chlorofluorocarbons. The latter are suspected of causing environmental problems in connection with the earth's protective ozone layer. Mathematical models have substantiated that hydrochlorofluorocarbons, such as dichlorotrifluoroethane, will not adversely affect atmospheric chemistry, being negligible contributors to ozone depletion and to green-house global warming in comparison to the fully halogenated species.
Hydrochlorofluorocarbons such as dichlorotrifluoroethane hydrolyze to form hydrogen chloride. While dichlorotrifluoroethane is useful as a cleaning solvent, the dichlorotrifluoroethane should be stabilized against possible changes during storage and use. When metallic materials are present such as occurs in many cleaning applications, the problem is worsened because the metal acts as a catalyst and causes the hydrolysis of dichlorotrifluoroethane to increase exponentially. Because metallic materials such as Al-2024 which is an aluminum based alloy having about 4.5% copper, copper, cold rolled steel, galvanized steel, stainless steel, and zinc are commonly used in cleaning apparatus, the hydrolysis problem is common. Also, ultraviolet light decomposes hydrochlorofluorocarbons such as dichlorotrifluoroethane.
In addition to hydrochlorofluorocarbons such as dichlorotrifluoroethane reacting with water to form acids such as hydrogen chloride and hydrogen fluoride, dichlorotrifluoroethane also reacts with alcoholic hydroxyl groups to form aldehydes and ketones. Known stabilizers for compositions of 1,1-dichloro-2,2,2-trifluoroethane and alcohol include: epoxy compounds as taught by Kokai Patent Publication No. 56,630 published Mar. 3, 1989; combinations of styrene and epoxy compounds as taught by Kokai Patent Publication No. 56,631 published Mar. 3, 1989; combinations of styrene compounds and phenols as taught by Kokai Patent Publication No. 56,632 published Mar. 3, 1989; combinations of epoxy and styrene compounds and phenols as taught by Kokai Patent Publication No. 128,943 published May 22, 1989; hydrocarbons containing nitro groups as taught by Kokai Patent Publication No. 128,944 published May 22, 1989; combinations of hydrocarbons containing nitro groups and epoxy compounds as taught by Kokai Patent Publication No. 128,945 published May 22, 1989; and phenols as taught by Kokai Patent Publication No. 265,042 published Oct. 23, 1989. Kokai Patent Publication No. 139,539 teaches 1,2-dichloro-1,1,2-trifluoroethane based azeotropic compositions which are stabilized with at least one of nitro compounds, phenols, amines, ethers, amylenes, esters, organic phosphites, epoxides, furans, alcohols, ketones, and triazoles.
Because dichlorotrifluoroethane may be used alone as a solvent, it would be advantageous to have a stabilized dichlorotrifluoroethane system which undergoes substantially no hydrolysis. This ideal stabilized dichlorotrifluoroethane system could then be used in commercial cleaning applications wherein a solvent is typically exposed to water, metallic materials, and ultraviolet light.
USPTO Backgrounds
USPTO Backgrounds