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Plate smearing (scumming) can occur when
printing is stopped then restarted after steps of some
sort have been implemented (stoppage scumming). The
cause of this is that the plate surface (non imaged
areas) dries and becomes sensitized during the stoppage.
- Compared to ordinary papers, YUPO®
is sensitive to plate smearing and has a tendency
to be affected by scumming.
- Inks designed for YUPO® and UV
inks tend to emulsify easily and plate scumming
tends to occur particularly with magenta, thus
requiring rigorous control of dampening water.
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| (1) |
During a print stoppage, be sure to gum
up the plates to protect them (and be sure
the gum is sufficiently dry). |
| (2) |
Carry out paper dust washing on the blanket
only and do not touch the plate surfaces. |
| (3) |
Change the dampening water to a "gum
etch" or add 0.1% (200cc/20L) of gum
arabic. |
| (4) |
If you have treated a sensitized spot
with an erasing pen, always be sure to protect
this with gum. |
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