Cleaning, storage and reuse of photopolymer printing plates.
Printing plates cleaning.
1. Printing plates are cleaned from ink by a solvent compatible with the plate material after the printing equipment operation was stopped. Cleaning can be carried out at regular intervals during printing or after printing was completed, before dismantling the printing plates. Do not allow the ink to get dry on a printing plate, since even small ink residues when dried on the surface can cause the plate cracking.
2. When cleaning the printing form located on a printing cylinder, it is necessary to avoid the ingress of alcohol between the mounting tape and the shaft surface to prevent a decrease in the adhesive properties of the tape.
3. It is necessary to treat printing plates with a cleaning agent after they were removed from a printing cylinder, and then thoroughly clean the plates with a lint free cloth or a soft brush with a natural pile, without undue force. Do not use rags, sponges or other aggressive tools for cleaning to avoid plate damage.
4. After cleaning and before stacking, printing plates should be washed with a pure solvent. Then carefully collect excess liquid from the surface and leave the plates to get dry in the open air at room temperature for at least 30 minutes. You can also purge screened areas and inversion parts of the printing plates with compressed air to remove solvent residue. After complete drying, the printing plates can be stored.
5. Kerosene, toluene, benzine or ketone cannot be used to clean printing plates. Never use pure ethyl acetate. Only ethanol or mixtures such as ethyl alcohol/ethyl acetate 85:15 are suitable for cleaning.
Storage and reuse of photopolymer printing plates.
1. The cleaned printing plates should not be exposed to sunlight during storage. The processed printing plates must be stored at min. 60% relative humidity and 20°–22°C, so that they do not dry out and become brittle.
2. The printing plates react to white and UV-light, so windows and lamps in workshops and storage rooms should be covered with an air and UV-light protecting foil (e.g. black foil). The printing plates should be stored in light-protective plastic bags or cardboard boxes to prevent absorption of additional moisture or drying out, as well as exposure to UV-light. If plates are stacked, put a cardboard interlayer between each plate to prevent them from sticking to each other.
3. In case the printing plates are placed on a printing cylinder for storage, make sure that they are protected from air and UV-light with the appropriate material wrapped around the cylinder - it is advisable to use a black plastic foil.
4. The freshly processed printing plates usually become thinner over a certain time (approx. three months). As the shrinkage characteristics of all plates in one set are the same, in case they made at the same time and are from the same batch, the plates can be reused for printing without any problems. But this is not the case if one plate of a set has to be re-made. The new plate is then thicker than the other plates. Then the entire set of plates should be made in order to avoid problems with the impression.
If this is closely monitored, the printing plates can be reused without any problems. There are no other restrictions as long as the printing, ink, cleaning and storage conditions of the plates are correct.