Offset printing: Dampening water
Adjusting the dampening water
The key to offset printing with YUPO is to control the amount of dampening water.
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.
YUPO is a film and does not absorb water. Therefore, if the same amount of dampening 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 dampening 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 dampening 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 excess emulsification. The water in the over-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.
Preventive measures
- It is essential to use the appropriate amount of dampening water with YUPO. Consult with your dampening water (etchant) manufacturer.
- 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.
- Installation of solid band (solid patch)
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.
Dampening water (etchant)
Add a specific amount of solution, following the manufacturer's 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.
- Etching Solution Type
- We recommend using a type that suppresses emulsification of the ink.
This will make it easier to avoid problems due to over-emulsification of the ink.
Alcohol (IPA)
If it is possible to add alcohol (IPA) to your dampening water, it will be easier to limit the amount of water on the plate surface.
When using an alcohol substitute, follow the manufacturer's instructions.
When using alcohol, excessive dampening water will promote emulsification of the ink, so be sure to restrict it severely.