What influence does the dye have on ink receptivity and printing?
The dye improves receptivity, because it contains fatty cod liver oil (Coatax).
Should water be added to the dye solution? What does this change? What is recommended?
Water changes the surface tension of the dye, which can lead to a more intensive and more homogenous dyeing of the plate. However, this causes quite strong foaming of the dye liquid. This problem can be remediated with anti-foaming additives. These agents usually contain silicone, which can however have a negative effect on the printing ink receptivity of the plate.
What is the precise chemical/physical effect of pretreatment?
The molecular chains, namely the connection between the silicone layer and the printing layer, are cracked.
What is the influence of water hardness on the plate processor and development?
If the water is too soft (under 5 °dH), then development deteriorates and a lubricating effect occurs. In the case of very hard water and if calcium deposits have been formed, then the machine should be decalcified with a vinegar solution at regular intervals. Reverse osmosis is not recommended, since salt crystals that remain in the water could lead to scratch problems.
How can the quality of the chemicals be determined? Are measuring wedges / testing strips / testing fluids available?
A testing kit is available for a quality assessment, however its use is highly complicated. The safest measure is to exchange the pre-treatment after 5,000 squaremetres or 10,000 plates. The costs of such a procedure are limited. The shelf life lies at approximately 8,000 squaremetres. If this limit is reached then a "loss of dots" will be experienced. A production error due to the plate not getting completely developed will occur. It is therefore recommended that you maintain a safety interval! The pre-treatment solution can be regenerated with the help of diglycolamine, but this is not recommended in terms of process reliability.
When is it absolutely necessary to change the chemicals?
The performance of the pre-treatment agent is not decreased through a slow, inconspicuous process; this happens very suddenly from one plate to the next. Often this is the case after longer pauses in processing.
What happens when the pre-treatment agent comes in contact with water?
The pre-treatment chemicals age more quickly when they come in contact with water. Minor quantities are unimportant. In the event of more than 20 % however, the quality of development declines (loss of dots). Contact with water should be avoided as a matter of principle.