Press room problems and solutions – Series 1 – Ghosting

Posted: September 27, 2012 in Color, Density, ghosting, ISO Press standardisation, issues in press room
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A host of factors affect the quality of your printed products: in addition to the machine itself, there are the printing stock and inks, as well as external factors such as atmospheric humidity, and room temperature. Often, when problems arise in the pressroom, the root cause is not immediately apparent. Frequently, it takes time to filter out the underlying cause from among the many possible variables.

This series of blog with Professional Tips offers advice on tips in the most common problem cases. This handy guide should not be missing from any pressroom.

Ghosting:

By ghosting, one understands a circumstance where printing form elements other than the desired positive or negative ones duplicate themselves onto the printed surface. These “stencils” or “ghost images” emerge from repeated passes of the ink form roller over the plate cylinder, and from a reduction or accumulation of ink. Used (hard) 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.

remedy

• 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 distribution

• Adjust reciprocation of the ink form rollers

• Shift the engaging point of the lateral distribution

• Reduce the quantity of dampening solution being used (smearing limit)

• Employ high pigment inks

• Turn on the vario

• Turn the printing form (prepress)

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