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FLEXO Magazine : June 2011
Technologies & Techniques doctor blade. Made improperly, without the channel, the cell shape offers no benefits and may create issues of blade chat- ter as two walls are parallel to the doctor blade. Then and now; The 30-degree hexagonal cell shape of- fers an opportunity to apply a smoother lay down of all inks, including: white, metalics, fluorescents, pearlescents and varnishes. With better visual and measured densities, opaci- ties and Pantone color matches 30-degree hexagonal cell shapes work well with water, solvent and UV ink systems and coatings. In fact, for volumes above process and combination requirements, there is no reason not to specify a 30-degree hexagonal shaped cell for improved solid coverage. At this ink film thickness, we are not concerned about dot gain and print contrast. Made properly, this cell shape cleans up well at the end of pressruns when inks are wet. CHANNELED Capitalizing on available software, anilox roll manufac- turers continue to manipulate the laser beam into different engraved cell shapes and patterns to include a variety of geo- metric cell shapes and mutations--with and without channels. The ability to laser engrave designed cell shapes is as easy as loading an artwork file. A visit to a laser manufacturer’s web site demonstrates the cell shapes capable of being engraved by anyone with standard software. Elongated slots and hexagonal patterns, reverse quad configurations and various channeled sur- faces have been introduced as alternatives to traditional cell shapes, primarily with improved flow and transfer being the goal(s). Increased volumes are also possible at higher screen counts, providing opportunities for more controlled transfer of thicker ink films. Example: 7.5 BCM volume engraved at 250 line count, 60-de- gree hex is now possible at up to 450 line count with an elon- gated hex. The difference goes well beyond the 200 cells per linear inch. In a square inch we have gone from 62,500 cells/ square inch (250 cell count) to 202,500 cells/square inch (450 cell count) controlling the same volume / ink film thickness to minimize or eliminate pinholes and striations in solid coverage. Volume is the most important specification of your anilox rolls, regardless of application. Too little and you do not achieve desired color or coating weight. Too much and you print dirty, suffer poor surface finish or cannot dry the applied material. In today ’s laser-engraving world, you can achieve volume at a plethora of cell counts, some dating back to the early days of laser application. It is not as important as volume, or in some cases, the cell shape of the engraving. Dot dipping is a paradigm created to sell higher line count anilox rolls. Is it possible? Of course it is, if your plate consists of only 1-percent dots with no support from other graphic ele- ments. But all production plates I have seen combine process dots, throughout the tonal range, with text, line work, solid coverage and even bearer bars to support image areas. Run- ning targets provide a tool to see and measure impression settings. Dot gain is primarily a function of ink film thickness. Which cell shape is right for you? As discussed, for the application of process and Pantone colors, the 60-degree hexagonal cell shape is preferred for the ultimate control of the desired ink film, as well as for the highest quality print at volumes typically used for process and combination work. At volumes and ink film thicknesses for solids and com- binations, the use of a 30-degree hexagonal cell shape with a channel, will allow inks of all types and coatings to flow underneath the doctor blade, thereby facilitating a smoother lay down for improved density, opacity and solid coverage. Results will vary from market to market, depending on all of the elements of the process working together. Being a process, all elements must be optimized for the application at hand. The combination of anilox roll, ink/coating, printing plate/tint screen, mounting tape, doctor blade(s), and sub- strate will mean success or failure, progress or setback. With so many cell patterns and channels available, I would encourage printers and suppliers to ask questions, investigate opportunities for research and development and then conduct their own testing. A banded roll perhaps, when appropriate. Remember that when a change is made to an element of the process, attention may need to be given to the elements with which it works to optimize print quality and process efficiency. n About the Author: Dan Foy is technical service and support specialist for ARC International, based out of Charlotte, NC. With 16 years experience in the anilox roll industry, Dan draws from experience in production, technical service, and technical sales to offer proactive solutions to; anilox roll specifications, coating applications, testing, inventory management and training. Dan has shared his experience with students, faculty, printers, co -suppliers and print buyers through technical presentations at national/regional industry forums, sales meetings and in-plant seminars. With several technical articles published in industry trade publications his message has reached the Flexo printing industry in the US and abroad. L-R: 40-degree channel, elongated hexagon, serpentine channel, straight channel, trihelical, 30-degree hexagon without channel and 45-degree quad shaped cell patterns. The difference between F&K and other presses is the amount of waste we don’t generate during set-ups. Bobst Group North America, Inc. 146 Harrison Avenue, Roseland, NJ 07068 -1294 Tel: 888-226-8800 Establishing press settings & registration on a conventional flexo press is done while running. This wastes substrate, ink, energy and, just as importantly, time. Given that each and every job change requires a set-up, multiply that waste by how many changes you make in a day, in a week, in a year and the losses are staggering. F&K flexo presses cut that waste. In fact with our smart GPSTM system of setting register and impression settings before the cylinders are even put on the press, waste can be cut by 90% or more. Our presses are also designed for modern plants where space is at a premium and efficiency is a primary concern. For example, our face-to-face design option enables both the unwind & rewind to be accessed and monitored from one central position. The highly efficient web path also minimizes the height requirement. Exceptional performance and features for a remarkably reasonable price. Every aspect of an F&K press is state-of-the-art, except the price. We’ve addressed operator and maintenance accessibility, operate at high speeds and work with a wide range of substrates to give you more flexibility and maximimum potential. It’s premium F&K performance and quality at a highly competitive price. Talk F&K with your Bobst representative and learn more about staying competitive by reducing waste, maximizing run-time and using technology to stay ahead. We offer about 45 feet of run-out per set-up —vs— What did you say you’re wasting now? Bobst-F&K-smartGPS_Layout 1 4/27/11 10:41 AM Page 1 52 FLeXO June 2011 www.flexography.org Which cell shape is right for you? As discussed, for the application of process and pantone colors, the 60° hexagonal cell shape is preferred for the ultimate control of the desired ink film for the highest quality print at volumes typically used for process and combination work. At volumes and ink film thicknesses for solids and combinations the use of a 30° hexagonal cell shape with a channel will allow inks of all types and coatings to flow underneath the doctor blade facilitating a smoother lay down for improved density, opacity and solid coverage. Results will vary from market to market depending on all of the elements of the process working together. Being a process, all elements must be optimized for the application at hand. The combination of anilox, ink/coating, printing plate/tint screen, mounting tape, doctor blade(s), and substrate will mean success or failure, progress or set back. With so many cell patterns and channels available, I would encourage printers and suppliers to ask questions, investigate opportunities for research and development and then conduct their own testing. A banded roll perhaps, when appropriate. Remember that when a change is made to an element of the process, attention may need to be given to the elements with which it works to optimize print quality and process efficiency. From left to right: 40° Channel, Elongated Hex, Serpentine Channel, Straight Channel, Trihelical, 30° Hex Without Channel, 45° Quad shaped cell patterns.
Sustainable Spring 2011