Cleaning and liquid contact with solids – Processes – Including regeneration – purification – recovery or separation...
Reexamination Certificate
2001-12-07
2004-11-02
Markoff, Alexander (Department: 1746)
Cleaning and liquid contact with solids
Processes
Including regeneration, purification, recovery or separation...
C134S034000, C134S042000
Reexamination Certificate
active
06811616
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method for the liquid cleaning of objects.
In practice, cleaning objectives are encountered at very different locations, be it for the liquid cleaning of objects of metal, glass, ceramic, plastic or composite materials, to remove contaminations for the reuse of the objects in a clean state, for example in hospitals or domestic use, be it for the cleaning of objects within manufacturing processes in which the processing technique such as lacquering, soldering, welding, etc., requires clean surfaces, or be it for the cleaning of textiles, just to name a few examples. In this connection, very different contaminations must be removed, for example inorganic dirt such as pigments or dirt containing ionic salts that are easily removed with water, organic dirt in the form of residues from charging, lubrication, lapping and polishing paste, soldering paste, adhesives, etc., as well as various combinations of the types of dirt mentioned by way of example.
For respective types of dirts various solvents are provided that dissolve the respective dirt particularly well, whereby such solvents are not only expensive, but frequently also have a poor compatibility with the environment, so that one must use them as sparingly as possible. DE 199 08 434 A1 discloses a method for the liquid cleaning of objects according to which the objects that are to be cleaned are brought into intense contact with a cleaning liquid that has an organic solvent having good solubility characteristics for the dirt that is to be removed, and is present in the form of an emulsion of the type solvent in water. With such an aqueous emulsion, despite relatively small concentrations of the solvent organic dirt, as well as inorganic dirt due to the water content, can be effectively removed. Removed dirt is to be deposited on the surface of the cleaning liquid from where it is removed, so that the cleaning liquid, i.e. the solvent contained therein, need be only slightly topped off.
The object of the present invention is to provide a method for the liquid cleaning of objects with which excellent cleaning effects are achieved and with which the quantity of required solvent or solvents or organic components is further reduced.
SUMMARY OF THE INVENTION
This object is realized with the features of the main claim.
The invention utilizes the recognition known from the aforementioned DE 199 08 434 A1 that cleaning liquids having at least two components, which are adapted to the respective contamination, clean particularly efficiently if the two components, under certain first conditions, for example under certain pressure and temperature conditions, form a solubility gap in the concentrations that are present.
For the purposes of definition, in the following “mixture” means a system comprising two or more types of molecules, the chemical and physical characteristics of which are spatially constant (homogeneous system). A solution is a mixture with which one material or one type of molecule is present in excess. Two liquids form a solubility gap if they cannot be mixed together without limitation; one then obtains two liquid phases in which the components of the liquid are present in a varying composition, for example, the one component extensively in the one phase and the other component extensively in the other phase. A solubility gap can be observed in that the clear liquid becomes turbid with a change in temperature, i.e. forms an emulsion, that is an indication of the phase separation. However, the turbidity or emulsion is not a necessary indication for a solubility gap; there are so-called micro emulsions in which the two phases are finely distributed such that the liquid continues to be optically clear.
Due to phenomena that up to now are not fully understood, in general a liquid that is composed of two components and is in the state of a solubility gap has a better cleaning capacity than do the two individual components if they are used in a pure state or in a highly concentrated state one after the other. Perhaps the excellent cleaning effect of liquids that are present in a solubility gap is brought about by interaction at the interfaces between the two phases, and possibly additionally by mechanical effects due to the droplets that are frequently held in distinct movement via ultrasound or a stirring mechanism. The use of the liquid in the state of the solubility gap thus enables an advantageous cleaning not only with regard to its cleaning effect but also with regard to the duration and with regard to the quantities of individual components that are required.
So that the cleaning liquid can remain in use as long as possible, it must be freed from the contaminations that it has received. Pursuant to the invention, this takes place in that the cleaning liquid is brought out of the state of the solubility gap into the state of a true mixture, i.e. a homogeneous state. From this homogeneous liquid the contaminations can be removed, depending on the nature thereof, via a filter (especially inorganic pigment-containing contaminations), or in that the contaminations, as a consequence of their densities that are different from the liquid, accumulate at the base or on the surface of the liquid, from where they are withdrawn (especially fatty contaminations). If a filtration or a separation of the liquid is, in contrast, to be effected in the state of the solubility gap, in so doing also a large percentage of at least that component is separated off that ties up or captures a respective contamination or binds it to its contact surface.
On the whole, as a result of the planned conversion of the cleaning liquid on the one hand into the state of the solubility gap for the cleaning, and on the other hand into the state of the true mixture for the separation of the contaminations, an efficient method is provided for the liquid cleaning of objects, which method, with an extensive ability to recycle the cleaning liquid (separation of contaminations), enables an effective cleaning of very different types of objects. It is to be understood that the composition of the cleaning liquid is adapted to the respective cleaning problem, whereby it is merely mandatory to select such components that under first designated conditions form a solubility gap, and under second designated conditions mix with one another.
In another aspect of the present teachings, the cleaning liquid preferably comprises water and an organic component, which provides the advantage that not only inorganic but also organic dirt can be dissolved, whereby the organic component can frequently be present in a relatively low concentration and yet deans as if it were present in a higher concentration.
A very good cleaning effect for a wide variety of types of contamination is achieved when the organic components include molecules having lipophilic and hydrophilic groups that can form a solubility gap with water.
In another aspect, the cleaning liquid is preferably in the state of a two-phase system under the second designated conditions, in which organic-rich droplets are dispersed in a continuous aqueous phase. In this case, a cleaning method is provided according to which the cleaning liquid comprises predominantly water.
The present methods can be carried out in a particularly straightforward manner if the state of the solubility gap changes to the state of the homogeneous mixture by merely altering the temperature. Other possibilities for converting the two states into one another comprise a change in pressure, a particularly intensive agitation, e.g. by means of ultrasound, by introduced contaminations that lead to a shifting of an equilibrium or to an unstable state suddenly changing over into a stable one, etc.
It is particularly advantageous if the first designated condition includes a temperature that is higher than the temperature of the second designated condition, since the cleaning effect is generally better at a higher temperature than at a lower temperature.
In another aspect, the homogenous mixture subjected
Becker R W
Markoff Alexander
O. K. Wack
R W Becker & Associates
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