Mist-like stain around the image. This tends to happen when thixotropic ink is printed in low viscosity.
The problem that may happen when multi-layers are printed with UV ink. When multi-colors are printed, the substrate passes UV curing machine many times. The colors earlier cured are over-cured for this reason and the adhesion of the next color is spoiled. That means poor inter-coat adhesion. The problem tends to happen to the UV curing machine with air-cooling system which enerates more heat. As the ink film becomes thick due to multi-layer printing, flexibility of the ink film becomes poor, which may lead to the peeling of the ink off the substrate. The solutions to this problem are :
1) to choose the ink with good multi-layer printability,
2) to change curing conditions; to control the heat, to increase UV irradiation for the colors that are printed later.