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FLEXO Magazine : November 2011
Total Ink Dynamics for Print Process Improvement Condition, Clean, Circulate & Control By Craig Shields & Ed Dedman “T otal Ink Dynamics” is an approach to flexo- graphic printing which focuses on controlling variables related to the “ wet end” of the press— those areas and components which directly contact the inks and coatings used every day. For a minimal outlay of cash and a bit of discipline, the quality of flexographic printing can be increased, resulting in happier customers and im- proved run-to-run consistency. Anyone who has ever bought a diamond ring quickly learned the “Four C’s” of diamond selection—cut, color, clarity, and carat. These four easily-recalled categories allow potential buyers to put some framework around their acquisi- tion. Likewise, there are four C’s of Total Ink Dynamics: condi- tion, clean, circulate, and control. Following these “Four C’s ” gives the flexo printer a framework for improved print quality and an edge against the competition. WHY IT MATTERS No one in this industry needs to be told that printers are under increased pressure. Rapidly rising raw material costs, combined with limited pricing power, have led to a continuing erosion of margins. Purchasers of narrow web printed products have begun to examine alternatives in light of the importance of consistent branding and the decreasing premium for going digital, while wide web-produced packaging is being redesigned to mini- mize styles and sizes, allowing consumer product companies (CPCs) to maximize their purchasing power. Controlling the Total Ink Dynamics of your press via proper application of the “Four C’s ” is part of the answer. Other as- pects of efficiency, such as quick changeovers, minimal web waste during setup and registration, and effective purchasing practices, are also crucial. However, Total Ink Dynamics pro- vides a high return on your investment of both cash and time. FOUR CS To begin, let’s review what we mean by these four catego- ries of Total Ink Dynamics: • Condition: Conditioning the ink refers to controlling its rheology. UV-curable, water- and solvent-based inks are thixotropic fluids. That means that their viscosity goes down as you stir them. • Clean: Cleaning the ink refers to physically removing unwanted debris. Typically, this is one of three types: dried ink flakes, metal shavings (usually from the doctor blade or central supplies for solvent and makeup fluid), and foreign debris. • Circulate: Circulating the ink refers to moving it from bucket to deck and back. Typically, this is accomplished by using a pump and a gravity return, though some ap- plications involve pumping in both directions. • Control: Controlling the ink refers to maintaining the various characteristics of the ink as recommended by the supplier especially pH, temperature, and viscosity. CONDITIONING Failure to properly condition ink has three major effects. 1. First, the viscosity reads too high for the pigment load. Failing to condition the ink before adjusting viscosity will lead to over-thinning the ink and a too-low pigment load, potentially throwing the printed color off. 2. Second, if the ink is not properly conditioned, movement in and out of the anilox cells will be affected, resulting in sub-optimal ink transfer to the printing plate. 3. Third, an insufficiently conditioned ink that is improperly thinned to compensate will have different surface tension characteristics than properly conditioned ink. As surface tension is integral to dot structure, poor conditioning can lead to reduced dot coherence and such outcomes as muddy printing. Conditioning is usually done in one of three ways. Most crudely, a shaker or mix- er in the ink room can be used; however, the effect is transitory. Some centrifugal pumps provide conditioning inherent in their design, typically through bypass mechanisms. Finally, some printers use secondary mixers press-side, usually pneumatic for easy speed adjustment. CLEANING Cleaning is essential for several reasons. 1. First, contaminants can damage expensive and fragile anilox rolls. Debris caught be- tween the anilox and the doctor blade can score the anilox, creating grooves in the ceramic surface. Typically, this shows up Centrifugal (right and peristaltic ink pumps rank among mainstream choices for ink circulating systems. www.flexography.org novEmBEr 2011 FLEXO 37 FLX_November11.indd 37 11/8/11 3:54 PM