Paint Color Shift

Q. I am the painting supervisor at our plant. We make electrical control panel boards and boxes. We paint them in a dip tank filled with solvent based baking enamel. To comply with fire safety regulation, the dip tank is connected to a large underground safety dump tank by a large pipe and automatic discharge valve. We recently noticed our paint use was increasing, so we checked the dump tank and found it full of paint because the discharge valve was leaking. We have no clue as to how long it was leaking. We pumped the paint into drums and started adding it to the dip tank. Solvent was added to adjust the viscosity. Now we are having trouble with color shifting and hiding of the painted parts. One of the painters thinks the problem is caused by using the recovered paint. S. G.

A.Your painter is probably correct. The color shift and loss of hiding power could be due to the condition of the paint you recovered from the safety dip tank. Two possible causes are: 1) The paint leaked into the safety dump tank over a long period of time where it polymerized and increased in viscosity and required excess solvent to adjust its viscosity when added to the dip tank or 2) The paint in the safety dump tank was not agitated, causing the pigment to settle and resulting in a variation in pigment volume concentration (PVC) and % solids from the top to bottom. In both the aforementioned cases, the composition of the recovered paint has changed. Furthermore, the PVC and % solids of the recovered paint probably varies from drum to drum. Adding recovered paint and the additional solvent to the dip tank changed the composition of the entire batch resulting in a color shift and poor hiding.

You should ask your supplier if he can rework the recovered paint. If the paint can’t be reworked, you should discard it, and then your color shift and hiding problems will magically disappear