Cleaning and liquid contact with solids – Processes – Using sequentially applied treating agents
Patent
1996-02-28
1997-11-25
Warden, Jill
Cleaning and liquid contact with solids
Processes
Using sequentially applied treating agents
134 31, B08B 300, B08B 500
Patent
active
056907516
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the cleaning of one or more articles in the vapor phase of an organic solvent. This cleaning method is generally known as "vapor degreasing" and is often used for degreasing articles, such as metals, glass or plastic, etc.. In vapor degreasing processes the article to be cleaned is placed in a zone of solvent vapor. The surface of the article has a lower temperature than the solvent vapor. The vapor condenses on the article and subjects its surface to a solvent-flushing action as it flows downward. The liquid drops are collected and revaporized. Thus, the surface of the article is continually rinsed with distilled solvent until at least the surface of the article has the same temperature as the solvent vapor and condensation ceases. Very effective cleaning of the surface of the article is achieved. Typically halogenated solvents, such as perchloroethylene, trichloroethylene, 1,1,1 -trichloroethane or methylene chloride are used. However, for environmental reasons the use of halogenated solvents becomes less and less desirable in spite of their many good properties, such as excellent cleaning efficiency, non-flammability etc.. Much research is being spent on the replacement of chlorinated solvents by environmentally more friendly solvents. However, the utility of other solvents is limited because many halogen-free solvents have a flash point and, accordingly, are a substantial explosion and fire hazard.
Accordingly, one object of the present invention is to provide an efficient process for cleaning articles wherein halogen-free solvents can be used but wherein a substantial explosion hazard can be avoided. Another object of the present invention is to provide such a cleaning process wherein a substantial explosion hazard can be avoided by other means than expensive explosion proof installations or the use of inert gases.
It has been found that a substantial explosion hazard can be avoided when a vapor phase cleaning is conducted in an apparatus wherein an absolute pressure of 200 mbar or less is maintained.
EP-A-0,381,887 describes a process, wherein freon or trichloroethylene is used as a solvent. A decreased pressure is recommended in the cleaning tank, such that no solvent vapor is released from the cleaning tank. However, the use of halogenated solvents is undesirable for the above-mentioned reasons.
WO-A-93/08933 relates to a process wherein an object to be cleaned is placed in a chamber and the chamber is evacuated in order to remove air and other non-condensible gases, before a solvent is introduced to the chamber. The chamber is evacuated in order to prevent that solvent is mixed with air and has to be separated from air at a later stage. The vacuum pump is then shut off. When solvent is introduced into the chamber, the pressure in the chamber increases. Aldehydes, alcohols, amines, ketones and aromatic solvents are mentioned in addition to halogenated solvents. However, it is not indicated how to avoid an explosion hazard when such solvents are used.
Accordingly, one aspect of the present invention is a process for cleaning one or more articles in the vapor phase of an organic solvent, which process is characterized in that solvent vapor is fed into a cleaning chamber wherein an absolute pressure of 200 mbar or less is maintained and the cleaning is conducted at a temperature at or above the flash point of the organic solvent.
Another aspect of the present invention is an apparatus for conducting the process of the present invention which comprises a cleaning chamber, an evaporator and a vacuum pump.
BRIEF DESCRIPTION OF THE DRAWINGS
The sole FIGURE is a schematic illustration of a preferred embodiment of the apparatus of the invention.
It has been found that according to the process of the present invention one or more articles can be safely cleaned in the vapor phase of an organic solvent, even when the cleaning is conducted at a temperature at or above the flash point of the organic solvent. For the sake of convenience, the following description relates to the
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Adams Hans-Norbert
Baggenstoss Werner
Hosel Peter
Muller Wolfgang
EMO Oberflachentechnik GmbH
Markoff Alexander
The Dow Chemical Company
Warden Jill
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