Coating processes – With post-treatment of coating or coating material – Heating or drying
Patent
1982-09-27
1984-05-15
Beck, Shrive P.
Coating processes
With post-treatment of coating or coating material
Heating or drying
427424, 98115SB, 118663, 118DIG7, B05D 102
Patent
active
044488122
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a spray coating process using spray tools located in a closed spraying cabin, in which process the solvent-rich atmosphere is drawn off and, in considerable proportion, re-discharged into the spraying zone, and to an arrangement for carrying out such a process.
In coating individual components, such as, for example, automotive bodies, metal housings and the like, attempts are made, on the one hand, to increase further the quality of the coating film, while, on the other hand, efforts can be seen to lower the consumption of materials and energy. Raw material consumption is intended to be reduced, and, at the same time, the resulting emissions are intended to be reduced. To satisfy these different requirements, the particular coating processes and finish systems have been considerably further developed, and, for example, the two-component finishes, which are frequently used these days, satisfy the quality requirements and the energy-saving measures, but these finishes give rise to processing problems in respect of metering and safety at work aspects.
The proportion of returned air can be up to 100% when the spray guns are not operating. If the spray guns are in action, the proportion of returned air is lower. According to the prior art, for subdividing the exit air stream a mixing device comprising a deflection plate, an activator and a control system is provided. The prior art literature further states that the control device can be so adjusted that, in the work space, a maximum solvent concentration in the ambient air is not exceeded. In the known process, there is thus no recovery of the solvent, but more or less exit air from the spraying cabin is returned to the spraying cabin as a function of the solvent concentration.
The object of the invention is therefore to reduce the problems arising on using solvent-containing finishes and to propose a spray coating process in which, while the quality standard remains as high as before, the problems of metering, recovery of the materials, safety at work and environmental protection conditions are improved.
This object on which the invention is based starts from the consideration that it must be possible to maintain, in the actual spraying zone of a spray coating process, an inert gas atmosphere which, when enriched to a certain proportion by volume with solvents in the form of vapors, can be drawn off, the solvents then being removed from the inert gas atmosphere and the essentially solvent-free inert gas atmosphere being drawn off or returned into the cycle.
The inventive proposal is based on the consideration that when using an inert gas atmosphere not posing an explosive hazard the solvent fraction of the atmosphere can be considerably increased and that handling this mixture containing inert gas and solvent is possible without hazard, so that such a mixture can be processed in any conceivable treatment process without explosion protection measures and devices being necessary.
Solvents are added in coating technology as auxiliaries and they serve to improve atomization and to obtain certain properties of the wet finish film. When the finish has been applied, these solvents have fulfilled their task and are at present removed, while, according to the invention, it is now proposed that the solvents are concentrated, the fact that spraying zones will be fully automated in the future also supporting this consideration.
The most inexpensive inert gas available is fume gas, which is obtained on heating the spraying zone and generally the coating plant and to carry out the drying processes. In the dried and desulfurized state, it is alternately enriched with and stripped of solvent, so that continuous circulation of this inert gas is possible. In the spraying zone, the finish is applied at an elevated temperature which, in turn, is also possible since due to the ambient inert gas atmosphere such high temperatures are feasible without possible explosion hazards arising. At the same time, the higher temperature of the inert gas atmosphere effe
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patent: 4313369 (1982-02-01), Tsuruta
patent: 4344381 (1982-08-01), Ostrowski
BASF Farben & Fasern A.G.
Beck Shrive P.
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