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FLEXO Magazine : June 2014
as is usually the case, this practice will cause the printing ink to be pressed deeper into the reverses than the substrate. This will cause an agglomeration of the printing ink in the reverses and will eventually lead to ink bridging. Again, this will cause the press operator to stop the press and clean the printing plates. PURSUING PLANOFLEX At the DFTA Technology Center, we were able to verify these con- siderations and observed longer term clean printing if we set up the impression engagement of the anilox roller to the printing plate more mildly than the engagement of the printing plate to the substrate. However, we also had to vary press speed in search of an operating window that would avoid vibrations and the resulting streaks. In the end, we developed a new practice that may ease our lives considerably and has done so a number of times already. This new practice is called DFTA Planoflex. Using the aforementioned rule of thumb for clean printing free of ink bridging and filling in, you start to recognize that the differen- tiation between the printing and the nonprinting areas will already be achieved during the inking process, in that the anilox roller only touches the raised relief elements and therefore inks them up. It is only these elements that transfer ink to the substrate. This is already a not so trivial fact of letterpress printing. We all seem to learn during our professional education that it is in the contact between the printing plate and the substrate where this differentia- tion happens. Conventional thinking says that is why we need raised image elements that only get in contact with the substrate. Left alone, this “new” cognition about the differentiation between printing and nonprinting elements may not contain too much potential for im- proving the flexo printing process. However, if one continues the line of thought started here, a powerful conclusion is reached. Encouraged by the successes we had with our impression engagement signal element DFTA KE 2.0, which executes the aforementioned principle, we lifted the entire nonprinting area of the printing plate— usually called floor—to such a high level that it contacts the substrate in the nip between the printing plate and the substrate. In other words, we have full contact between the printing plate and the sub- strate—or vice versa, as the relief depth is lowered such that the entire floor touches the substrate. Usually, we work with only about 120-μm. of relief depth on our printing plates while using approximately 150-μm. of impression engagement from the plate to the substrate and an impression engagement of only about 70-μm. between the anilox roller and the printing plate. The relief depth therefore comes in between the two impression engagement settings (our reference for these figures is always the so called “kiss print” setting). Due to the full contact between the printing plate and the substrate, we get a very harmonic unrolling, because the hardly detectable relief elements (raised by only a little more than the width of a human hair) do not cause any disruptions. Vibrations and the streaks in the print design, that the relief elements tend to cause, have now lost their JUNE 2014 | FLEXO 85 See what we’ve engineered at rotoflex.com LEADERS BY DESIGN The experience of over 7,000 installations has taught us that precision engineering and true partnership keep you moving forward. And that’s how you become a leader: by design. PERFORMANCE. PRECISION. PRODUCTIVITY. IT’S ROTOFLEX. RF_Ad_2013_3.375x9.5.indd 1 5/12/14 9:29 AM