The Recycling of Waterborne Paint Overspray
out of Water Wash Spray Booth
Did you ask yourselve, how to recover the paint overspray? How to work without disposal?
In todays way of thinking about environment protection the following priority has assembled:
1. Avoidance 2. Utilisation 3. Disposal.
.
Ever raising costs for disposals and an increasing flow of legal limitations and regulations forced us concentrating our efforts in research and developement of waterborne paints including recycling methods of their waste.
There are two ways of recycling, we have know- how about.
The first type is the direct recycling of waterborne paint overspray out of water wash spray booth:
For this we discovered an old known method for electrocoating again: Ultrafiltration, which is the separation of little and big molecules by means of a semipermeable membrane (picture 1).
In course of time the paint concentration grows in the wash water of the spray booth. So we get a highly dilluted paint in the water. We pump this mixture in charges to our Ultrafiltration plant and let it circulate there till the paint concentration is equal to the original spraying concentration or viscosity (picture 2).
The knowledge about the pump type, layout of the units and the membrane type is essential for the successfull application of this method (picture 3).
Thermocuring paints which are soluble in water are predestinated for this method. Especially paints based on alkyd-melamine resines are very often used for paints to recycle.
A simple scetch shows the principle of this method (picture 4).
If you use a single shade you can take the recycled paint as finish.
If the paint is applicated in numerous shades the recycled paint has the according mix shade. It can be used as primer.
The second type is the indirect recycling or recycling of waterborne paints sludge.
In course of time the paint concentration grows in the wash water of the spray booth. So we get a highly dilluted paint in the water. The paint particles must be detackified to avoid soiling of the system components as pumps, pipes, tanks and the water wall of the spray booth. For this reason we use physical working adsorbative coagulating agents. These are anorganic silicates (clay, argillaceous earth) and work in neutral or weak alcalic pH-range. Depositing to the paint parts they cover the resin and so the tackling is eliminated.
When the paint concentration is about 2%, the wash water is pumped to a separate tank (for flocculation). After dosing the needed amount of the flocculant and stirring well, the mixture is led to a filtering unit. The paint sludge is separated from the water. The water can be used again as wash water. The sludge is now in the filter bags. With a suitable typ of press the remaining water is squeezed out of the sludge.
Also other separating methods as filterpresses or centrifuges can be used.
Today we can use sludge containing maximally 20% water in divers waterborne paint formulations at about 30% addition.
1. waterborne primer:
If the sludge consists thermocuring paints, the primer must be stoved, in other cases, it is air drying.
2. waterborne antinoise paint
This product is air drying. The drying time can be shortened by curing at a temperature of about 80°C at last 30 minutes after application.
