Process for spray-painting with aqueous paints

Details Process for spray-painting with aqueous paints Process for spray-painting with aqueous paints

1996-02-12

1997-08-19

Dudash, Diana

Coating processes

With post-treatment of coating or coating material

Coating material recirculation or regeneration

4273884, 427409, 427421, B05D 102, B05D 714, B05D 300

Patent

active

056586167

DESCRIPTION:

BRIEF SUMMARY
The invention relates to a process for spray-painting with aqueous paints, in which two or more aqueous paints with different hues or colors are processed in a single coating unit and the paint which has not gone onto the substrate to be painted (overspray) is washed out of the exhaust air from the coating unit and washed off the parts of the coating unit which come into contact with overspray, using water, and the water in which overspray has accumulated is concentrated and is recycled as recovered aqueous paint, if desired after admixing with newly supplied paint (fresh paint), to the coating operation.
In spray-painting with aqueous paints the paint which has not gone onto the substrate to be painted (overspray) is washed out of the exhaust air from the coating unit and washed off the parts of the coating unit which come into contact with overspray, using water. In this process water in which overspray has accumulated is obtained, and has to be disposed of. For this purpose the overspray is precipitated from the water in which overspray has accumulated. This results in a paint sludge, which can only be reprocessed to give other products to a limited extent and which in many cases has to be disposed of as waste.
Alternative proposals for recovering the overspray from water in which overspray has accumulated include processes in which the water in which overspray has accumulated is concentrated until the solids concentration of the aqueous paint originally employed is reached again. The recovered aqueous paint obtained in this way can be recycled, directly or after admixing with newly supplied paint (fresh paint), to the coating operation (cf. for example Journal fur Oberflaachentechnik (JOT), 1992, issue 10, pp. 32 to 38).
This process is well suited when one paint in one color is processed over relatively long periods of time. However, in practice--especially when finishing car bodies--a frequent change in the colors of the paints employed is necessary. The recovered paint then has a mixed color which varies, in some cases continuously, depending on the color and quantity of the processed paints. Hitherto, paints of mixed color recovered from units in which paints with different colors are processed have been employed for painting those regions of the substrates to be coated which are generally out of sight. This solution to the problem is unsatisfactory because, in general--if at all [sic]--it is not possible to use all of the quantity of recovered paint obtained in a coating unit in this way. The remaining quantity of recovered paint must then, disadvantageously, either be processed in other coating units, as described in Journal fur Oberflachentechnik (JOT), 1993, issue 3, on pages 27, 30 and 31 depigmented by microfiltration or even disposed of as unusable waste. In the Journal fur Oberflachentechnik (JOT), 1993, issue 3, pages 26 to 32 it is proposed, moreover, to extend coating units in which the color of the paints processed undergoes frequent changes by the installation of additional working tanks, tanks for retained material and pumps, in order to enable the separate processing of the overspray from the different paints. This solution to the problem, however, has the disadvantages that it is associated with additional costs, and, moreover, that it requires the coating unit to be cleaned before each change of color.
The object of the present invention consists in the provision of a process for spray-painting, of the type described above, in which the disadvantages of the prior art are eliminated or reduced.
It has been possible, surprisingly, to achieve this object by a process for spray-painting, of the type described above, which is characterized in that unit are selected such that some of the substrates to be painted in the coating unit can be painted using a mixture of the aqueous paints with different hues or colors ("mixed paint") which are to be processed in the coating unit, and the coating unit are selected such that the total amount of aqueous paints of different hues or colors process

REFERENCES:
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patent: 4044175 (1977-08-01), Coxon et al.
patent: 4607592 (1986-08-01), Richter
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patent: 5223306 (1993-06-01), Bartow
patent: 5453301 (1995-09-01), Saatweber et al.
Dr. Hans Sutter, "Wasserlackrecycling bei der Spritzlackierung Teil 1", JOT 1992, pp. 1-4 (no month available).
Dr. Hans Sutter, "Wasserlackrecycling bei der Spritzlackierung Teil 2", JOT 1993, pp. 1-5 (no month available).
Johann Halbartschlager, "Neuester stand beim Wasserlack-Recycling" JOT 1993, pp. 1-4 (no month available).

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