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FLEXO Magazine : November 2011
QUICKCHANGEINFLEXOPRINTING UTECO CONVERTING SPA • I 37030 COLOGNOLA AI COLLI (VR) • PH.: +39 045 6174555 • FAX: +39 045 6150855 © GENETIC INNOVATION And a new innovation is coming... Leading edge innovation in flexographic printing • Print configurations: 6 - 8 - 10 color • Max. print speed: 1300 fpm (opt. 1460 fpm) • Printing widths: 48” to 60” • Print repeat range: 13” to 32” • Fully equipped state of the art machine • Reduced make ready and maintenance times • Quick and simple sleeve changeover UTECO NORTH AMERICA 3400 TOWN POINT DRIVE • SUITE 160 KENNESAW, GA 30144 • PH. (770) 427-4100 • FAX (770) 427-4872 firstname.lastname@example.org • www.uteco.com HIGH PROFITABILITY FLEXO A03/11HP-RANGE email@example.com • www.uteco.com QUICKCHANGEINFLEXOPRINTING And a new innovation is coming... • Quick and simple sleeve changeover KENNESAW, GA 30144 • PH. (770) 427-4100 • FAX (770) 427-4872 www.uteco.com • P2P®: dynamic adjustment system controls printing pressures • PCT®: Press Control during Transition • PTC®: Predictable Torque Control • SprintWash®: new automatic washup system • FlexoSmartPackQC®: Uteco engineering platform for improved performance and profitability in quick change flexographic printing • ShopWare® Production Management, Control & Monitoring: easy machine-operator interface to manage high-productivity • LogiPack®: automatic handling of reels and cores as lines or floods in the print along the axis of the web and requires an expensive repair of the roll. 2. Second, the debris can plug both the cells of an anilox and the plate itself. In the former case, the likely symp- tom is starvation, while in the latter it is dirty printing, often referred to as bridging. For most applications, a two-stage filtration process is essential. A mesh-style cartridge removes solid particulates, while a magnet removes metallic waste. Most manufacturers offer a variety of options in both categories. Cartridges are specified by the size of contaminant they can pass. Manufac- turers offer a mainstream range from 590 micron (or 30 mesh) to 99 micron (or 150 mesh). Some specialty applications demand down to 58 micron (250 mesh). The general rule of thumb is that dirty environments, such as corrugated, require the largest micron size, process print- ing requires a medium micron size, and varnishes, coatings, and adhesives require the smallest. Likewise, there are typically two choices of magnets for sepa- rating the metallic waste. At the low end are perma- nent “crown” magnets. These have moderate pull- ing power but are lower cost. Most manufac- turers also offer an option for rare earth magnets; these powerful magnets are considered the best choice when steel doctor blades are in use. CIRCULATING Cutting out this “C ” by simply pouring the ink into a tray is one shortcut that some printers take. While this can be justi- fied for some short runs, if strict care is taken, there are risks. 1. First, the circulating system usually acts to condition the ink, as mentioned previously. 2. Second, circulating the ink helps to stop settling and dead zones. Ink that is not circulated tends to settle, resulting in both viscosity changes and the problems mentioned in the discussion on conditioning above but also color changes. One of the authors distinctly remembers seeing a narrow web press where eight decks had circulating systems and one did not. On the eight decks, colors were consistent across the anilox roll. However, on the one uncirculated deck, the blue ink changed from dark blue at the center to a royal blue at the edge of the roll, simply because of the difference in mixing caused by the edges of the anilox. There are three mainstream choices for circulating systems on flexo presses: centrifugal, diaphragm, and peristaltic. • Diaphragm pumps usually offer a low purchase cost, but they create a high degree of pulsation, due to the on-off action of their pumping method. • Centrifugal pumps are also relatively inexpensive. Some offer some sort of conditioning for the ink, usually by bypassing part of the flow out of the volute of the pump. • Peristaltic pumps offer faster changeover, since the ink is contained within a tube, and changeovers can be made even faster with quick-swap pump heads available from many manufacturers. Additionally, peristaltic pumps are usually reversible, shortening cleanup time by return- ing excess ink to the ink bucket. Given their self-priming nature, they can be located almost anywhere on press. CONTROLLING Today ’s flexo inks are designed and formulated to achieve the correct color at the correct film thickness and at a specific viscosity, pH, and temperature. For UV-curable inks, that vis- cosity is controlled by the aforementioned conditioning, as many of these inks are still somewhat thixotropic. Once stirred and returned to a fluid state, UV-curable inks are very stable, so long as they are kept agitated. It is recommended to keep the pan or reservoir covered, to prevent ambient light from beginning the photoinitiation process, which can also lead to thickening and increased viscosity. For water-based inks, it is crucial to maintain the pH at the correct level. Too high a pH can cause pigment burnout and artificially reduced viscosity, and if the pH is too low, the ink will increase in viscosity and print poorly. Too often, operators will add reducer to lower the viscosity, when they should instead adjust the pH first. For solvent-based inks, it is again important to maintain them at the recommended running viscosity, in order to prevent premature drying and poor print quality. It should be noted that every solvent-based ink formulation has a specific solvent chemistry, and only recommended solvents should be used to adjust viscosity. Cross-contamination with the wrong solvent can have extremely negative results. Temperature is also a crucial issue, especially for water- and solvent-based inks for several reasons, though there is also a concern that heat affects UV ink by helping to initiate the curing process. 1. First, a higher ink temperature results in excess evaporation of reducer or solvent, which needs to be replaced, increasing both the raw material and, poten- tially, environmental costs for the printer. 2. Second, ink thins with increasing temperature. This gives rise to an artificially low viscosity reading. If the viscos- ity is thinned with heat, less reducer or solvent is added by the automatic viscosity control or the operator. The outcome of this is printing with insufficiently diluted ink, increasing consumption and adversely affecting both dot Latest circulating technologies are reflected in this double peristaltic pump with quick- change heads and remote control. 38 FLEXO november 2011 www.flexography.org FLX_November11.indd 38 11/8/11 3:54 PM