UV inks are much more sensitive to dampening solution than conventional inks are and the trick is more about finding the best combination of ink brand/etch brand/amount of alcohol sub than it is worrying about a 1 or 2 mm difference on some of your roller stripe settings (though I will always prefer segregated over integrated). The roller settings matter just like they always do, of course, but the trouble with your ink settling down and the color spiking you’re experiencing (guessing on startups and throughout shorter runs) is probably not so much from rollers as it is about UV ink being made different, and the photopolymers that are in it can inherently make it more difficult to create a stable emulsification.
I see two possible issue here. One is about the fundamental cause of ink water balance, print density variation. From my work on the subject, I have found that the cause is related to the inconsistency of the ink transfer by the ductor roller. Your comment about water getting up to the fountain ball highlights the problem of ink transfer at the ductor. I have done tests where ink is fed into a roller train in a way that is not affected by any amount of water on the roller train and this resulted in consistent print density. These tests were done with EB, UV and conventional inks.
well, we try to run the water speed as low as possible, that helps. We Integrate our magenta unit it seems to help that particular color. All our scum lines are nice. Just a side note, the pressman that works opposite me puts in a lot of Isopropyl alcohol in our water tank almost every day, along with the alcohol substitute. I don't think that's doing us any favors.
also in UV printing)Dear Joe, Do you have any practical experience with Heidelberg LotoTec rollers? We are currently using Westland MIX hybrid rollers and are printing on plastic and paper substrates. However, we are experiencing significant dot gain, particularly when running UV jobs. Based on your experience, would switching to LotoTec Hybrid rollers help reduce dot gain and improve print stability on plastic substrates? ThanksThis is what I can tell you regarding my daily experiences at work as a printing instructor
Not all water is the same
Many printing companies draw water for dampening solution production from the drinking water supply without knowing exactly what it contains and how it affects the printing process. This can result in quality losses or printing problems, the actual cause of which often remains unknown. Targeted water treatment can remove many disruptive factors from the water.
Consistent water quality
Targeted water treatment forms the basis for optimal conditions. Water quality is much more important in alcohol-free and reduced-alcohol printing than in conventional offset printing with IPA. If the water hardness is too low or too high, this is immediately noticeable in the print result: if the water is too soft, the printing process tends to emulsify; if the water is too hard,
it can cause the ink rollers to run dry due to lime deposits. Therefore, a constant, suitable water quality must be ensured.
If this water hardness is not achieved or if the water quality fluctuates, the water should be treated by means of a hardening
or reverse osmosis system before it is fed into the machine as a dampening solution.
Along with print chemicals that affect the roller directly, external factors such as UV light, fountain additive, solvent and room
temperature may result in premature ageing of the rubber.
on UV printing, the service-life oft he rollers is as a rule shorter.
long service life of the rollers can only be achieved with proper handling and maintenance.
Print quality starts with the interaction of the inking and dampening system: Consistently good results assume a stable ink-water balance. Precise adjustment ensures thin and equal distribution of the dampening agent film on the printing plate.
A responsible printer checks the adjustments every three months and adjusts in line with the operating manual.
What I see time and again in my practical experience is that many printers follow the rule: “The more alcohol I add, the better it is.” We all know that this is wrong.
Have you had the press fingerprinted with both conventional and UV inks? Or have you at least checked your gain measurement in the shadow, mid-tone, and highlight patches? Depending on the press and software, this may be achievable with option settings on your screen, and can be checked with any sheet scanned at the console.
