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FLEXO Magazine : July 2014
result in the smoothest ink laydown and increased opacity—within one pass, at high production speed, using commonly available, solvent based white ink.” Finding a way to improve white ink performance without altering existing formulations, slowing press speed or increasing ink usage was a key requirement of our research. We know that printers face con- tinued increases to the cost of titanium dioxide, the main component of white ink, so anything we could do to positively impact their profit margin was mission critical. Building The White Ink Matrix In order to run an efficient and comprehensive experiment, the team designed a print layout that encompassed 270 combinations of plate durometers, micro pattern frequencies, print surface texture and mounting tape densities, all to be combined with different volumes and LPIs of aniloxes. The test plate was eventually printed at several locations, each time on a web press more than 50-in. wide. The exper- iment used four printing decks, three different aniloxes, and multiple sleeves. A common white ink formulation on each print station was set and maintained at exactly the same viscosity— one that is typical for high volume production speed. Polyethylene film was chosen for the test as one of the most common materials used in wide web flexo printing. In addition, process cyan swatches were overprinted in order to observe additional ink laydown effects. All plates were carefully coded, photographed and measured before and after the test. "The plate surface treatments and micro pattern frequencies we chose were based on current flexo general practices, as well as some new concepts developed by our team," explains CSW’s Senior Image Engineer Brian Moore. "White ink typically does not level out well or lay down smoothly, which causes pinholing defects—also referred to by printers as mottling. By observing and measuring the behavior of white ink in relationship to the contractive tendency of various sub- strates, we developed a plate surface treatment that worked perfectly in conjunction with MacDermid’s new photopolymer material.” The test was run at production speed, more than 1,500 fpm, using solvent based ink formulated with titanium dioxide pigment. Results were measured with spectrophotometers and opacitometers at four different locations, including the printer, CSW, MacDermid and the ink company, and recorded in a spreadsheet for comparison and analysis. In order to better evaluate the effects of various plate treatments and eliminate any sources of variation, certain elements of this experiment were further repeated at different print locations, at even higher pro- duction speeds and at more than one million impressions. “ This addi- tional data set strengthened the experiment's validity,” notes Moore. Forum Presentation In April, test results—the matrix—were presented during FTA’s An- nual Forum in Baltimore. Commercial samples of flexible packaging printed in both Europe and the U.S . reveal the universal challenge of achieving optimal white ink laydown. Thirty-eight different products JULY 2014 | FLEXO 53