Waterborne Coatings in Summer Weather

Q. I run the painting operations at a plant in the Southern U.S. I am inquiring if there is a general rule of thumb on applying waterbased coatings in the Summer. We are applying a waterbased coating with a robot. The parts first pass through an IR heater set for 650°F, so the parts are “warm” when reaching the paint application area. The issues we see are more drips, runs and sags in the Summer. After doing studies, we can not pin down if it is more relative humidity related, or dew point.
Are there any ranges the industry uses when selecting environmentally controlled booths? We have an open booth system now, but if there are “norms” in the industry, I may be able to justify the cost of the needed investment. L. M.

A. It is well known that waterborne paints tend to run and sag more readily than solvent borne paints. In the old days, we accommodated seasonal changes by solvent changes. The introduction and use of waterborne paints has denied us that luxury. Unlike solventborne paints, whose viscosity increases because their solvents evaporate during spray application, waterborne paints do not increase in viscosity because of water’s slow evaporation rate. Simply stated, the problems are magnified during the Summer especially during periods of high humidity. It is beyond the scope of this column to go into the physical phenomena involved.

If this is really a problem for you and it sounds like it is, I suggest you install an enclosed spray booth having humidity and temperature controlled makeup air. Suppliers of these booth are listed in the 2006 Products Finishing Directory and Technology Guide.