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Dampening Water |
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Using the Right Quantity
of Dampening Water |
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While printing on YUPO®,
in order to prevent problems with incomplete drying,
use as little water on the plate as possible, waiting
until the last moment before the plate becomes stained.
Adjust the water temperature under the same printing
conditions as you would for coated paper.
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The key to offset printing with YUPO®
is to control the amount of dampening water.
YUPO® is a plastic film and
does not absorb water. Therefore, if the
same amount of water is used as with conventional
paper printing, excess water will collect
on the surface of the YUPO®
as well as the surface of the printing plate.
When printing with YUPO®,
it is necessary to restrict the amount of
water used more so than with conventional
paper.
If the amount of water fed to the plate
exceeds the ideal amount even by a small
margin, the two following problems will
emerge: |
| (1) |
Poor ink transfer (for multi-color presses)
There will be too much water in the cylinder
before the generating cylinder(either
the first or second cylinder), and
water will remain on the YUPO®,
causing ink from later cylinders not to
adhere properly. |
| (2) |
Delayed ink drying
Since YUPO® does not absorb
water, the ink on the rollers will absorb
the excess water instead, causing emulsification.
The water in the emulsified ink will take
a long time to evaporate, and will prevent
the proper functioning of the dryer during
this time, causing significant delays in
the ink-drying process. Furthermore, set-off
may commonly occur, and ink adherence and
ink film strength will also be compromised. |
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| Countermeasures |
| (1) |
It is essential to use the appropriate
amount of dampening water with YUPO®.
Consult with your dampening water manufacturer.
In particular, the use of dampening water
with glycerin added is highly dangerous. |
| (2) |
Use as little water as possible. In particular,
it is important to use less water in the
first and second cylinders as you would
with conventional paper. The target amount
of water restriction should be to add water
just as the smaller letters in the printing
area begin to bleed into one another or
just to the point where the gripper side
appears to be on the verge of getting stained. |
| (3) |
Solid pattern impression
The problems described in (2) above are
particularly likely to emerge with print
jobs featuring only characters and lines,
with no solid patterns. In that case, allowing
for a solid belt impression to be made in
the margins, will allow for the ink on the
rollers to be refreshed, reducing the risk
of emulsification. |
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Add a specific amount of solution, in
following the manufacturer instructions. Also, since
the Ph and conductivity values will vary according to
the base water used, consult with your etching solution
manufacturer to determine the appropriate amount of
etching solution to add. |
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If it is possible to add alcohol to your
dampening water, it will be easier to limit the amount
of water on the plate surface. |
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