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FLEXO Magazine : April 2009
TECHNOLOGIES & TECHNIQUES PROCESS CONSISTENCY One of the defi ciencies frequently attributed to fl exo is the lack of consistency from run to run and job to job. Impression setting is one of the most important missing links in the process standardization chain. With manual procedures, the quality of impression setting is dependent on the perception of the eye and the expertise of the printer. With automatic optical systems, the human eye is replaced by a camera. However, the process remains essentially the same: it is a matter of viewing the print and then making corrections, viewing again and correcting again. This has to be repeated until, after a lot of time and eff ort, the print is fi nally set. Graphic positioning systems provide for greater print consis- tency in a number of ways, including: 1. The register and impression setting is consistent irrespec- tive of operator and ambient conditions. 2. The system works independent of the ink or coating color ensuring that an optical image or color doesn’t aff ect the impression adjustment and even coatings that are normally diffi cult to see or detect can be set correctly 3. The system works on any substrate, including metallized fi lms, and foils, with paperboard to be added. Since it is not an optical system, correct impression and register is ensured. 4. Print data remains with the sleeve until such time as the plates may be re-mounted or rescanned, so impression stays consistent, even when moved between presses. 5. The system provides the correct impression setting inde- pendent of diff ering drying characteristics of inks at various speeds. One major problem facing all producers of fl exible packaging that use solvent based inks is that of correct dry- ing. Modern fast drying inks do not start to dry correctly RFID chips imbedded in the sleeves allow the graphic positioning system to set register and impression based on a topographical profi le of the plate and sleeve. until a reasonable production speed is achieved. Only then is the dwell time of the ink on the plate short enough to prevent the ink from drying prematurely. At the lower machine speeds used for impression setting, the dwell time between the application of the ink to the plate and its transfer onto the substrate is far too long. This leads to premature evaporation of the solvent and the retention of the ink to the plate, rather than the substrate, as well as an unsatisfactory, prob- lematic ink transfer. Even the most experienced printers often fail to recognize that the cause of the poor print results is premature drying of inks rather than insuffi cient impression. As a matter of fact, with increased impression, the quality of the graphics ap- pears to improve. While the problem may seem to be eliminated, the measures taken actually were the wrong ones. In most cases, actions based on the initial false assumption (that the problem was insuffi cient impression) lead to highly over-impressed set- tings throughout the printrun. Conventional optical systems do not help overcome this di- lemma. In fact, no optical system can overcome this without gen- erating large amounts of waste. While adjusting the settings at higher speeds eliminates the problem of premature drying, it also considerably increases waste production. With graphic positioning technology, the print adjustments are known before the job enters the press. That means that the machine can be accelerated to production speed immediately after the fi rst kiss contact. The result is waste reduced to zero and the drying issue is completely avoided. One more advan- tage over conventional systems is that this also works on coat- ings or lacquers, which have no contrast with the background substrate, without any restrictions. Since there is no chance for over impression and the sub- sequent damage to plates and cushion back, plate life is sig- nifi cantly extended. The system can also track anilox rolls. Operators know exactly the location of each roll along with its specifi cation in advance of a print job, thus reducing the possibility of mix ups that generate waste and downtime. To summarize, be- fore introduction of the graphic positioning sys- tem, reproducibility was virtually impossible. This technology addresses all the variables that tradi- tionally inhibit consistent fl exo printing, including those infl uenced by day and night shift; time of the year; ink variations and the interval between repeat orders. 22 FLEXO APRIL 2009 www. f le xography. org