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FLEXO Magazine : February 2009
TECHNOLOGIES & TECHNIQUES You should not be adding anything to a system that it is not losing. the system, but if anything, raising it a bit. There are some ink systems out there that are less pH sensitive, but most are very dependent. Some people don't like to have ammonia in the pressroom. If you have a very light color, are experiencing some takeoff, and you use 10 percent ammonia in water, that 10 percent gas is going to evaporate and leave behind just water. If this contin- ues to happen over the course of the day, you are going to end up with a weak, thick ink. That's why some of these solutions are being used, because they are more stable. The acid stays with the water. If you go back in history a little bit, all this derived from S.E. Johnson and its floor wax technology. At that time, it was something you put on the floor with a water solution. But once it dries, you can take soap and water and wash all you want, it will stay there. As soon as you grab some- thing like ammonia that has a high pH, it will strip the acrylic be- cause they are soluble in amines. In some cases, am- monia is the best thing to use because it's the fastest and you may be trying to maximize your press speed. As far as longevity and long runs, it's not the best. For that, you want to use DMEA (Dimethylethanolamine). That's what many people use today. Ink companies will differ on their percentages, but it's usually a solution of about 20 percent DMEA and 80 percent water. It does not dry as fast as ammonia, and so it is not suitable for high speeds. It's comparable to water in terms of flashing off. NEED FOR SPEED Let's say your pH drops to 8.8 and you want to get it up to 9.4, this will also affect your viscosity. In this case, the acrylic resin is - entering a solid state, which will affect the fluid speed. The vis- cosity is directly related to pH. Once the pH is in line, then you add some pH -compatible fluid to increase the viscosity. Some additives will contain a certain percentage of pigments in it, but I don't advise using those. Viscosity and pH change because wa- ter and other chemicals disperse, but the pigments do not. You should not be adding anything to a system that it is not losing. Now, as you add this chemical, the amount of total pigment sol- ids in the formulation is increasing. Eventually, this is going to weaken the color, because you are extending the ink. Once you have color stable, it's important to continually monitor and adjust before dot gain and darkening or lightening starts. If you tighten that cycle you will minimize the amount of fluctuation that you have. The amount of frequency will depend on the amount of heat the press generates. Some inks are, what we like to call, stupid inks, which means you have to adjust them more frequently. Ideally, you should run it through a completely enclosed system. Unfortunately, we don't know any printer/converter that is running a com- pletely airtight system. Even those with en- closed doctor blade systems have open ink buckets, or an ink pan with no cover. Wide web presses tend to have the tightest systems. N ow that you are on press, you need to adjust the speed of the press to coordinate with the speed of the ink and vice versa. If you have a stripping matrix that slows the press down, you may need to add propylene glycol to slow the press down. Be careful, though: Even though that does not affect the pH, it can affect the color because you are extending it out. In that case, you may have to come in with a slightly stronger ink. FEBRUARY 2009 www.flexography.org FLEXO
Sustainable Winter 2009