How-to for “ghost” busters
During printing, “ghosting” occurs when printing form elements other than the desired positive or negative ones duplicate themselves onto the printed surface. These “stencils” or “ghost images” can emerge from repeated passes of the ink form roller over the plate cylinder, and from a reduction or accumulation of ink. Hard-used or poorly adjusted ink rollers facilitate ghosting, and the tendency toward ghosting increases with weak pigment inks. An optimal balance between ink and dampening solution helps prevent ghosting, since too much water negatively influences printing outcomes. To avoid ghosting, use the following remedies:
• When maintaining rollers, only use the appropriate cleansing agents. A weekly application of wash paste removes lime deposits and will regenerate the rollers.
• Adjust the rollers in accordance with the instruction manual. Inspect the adjustment regularly.
• Change used rollers: the rubber surface of older rollers will become glossy and over-smooth. At the same time, as their hardness increases, the edges bulge out in a trumpet shape. More pronounced abrasion becomes evident.
• Adjust for maximum lateral reciprocation.
• Adjust reciprocation of the ink form rollers.
• Shift the engaging point of the lateral reciprocation.
• Reduce the quantity of dampening solution being used.
• Employ high-pigment inks.