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FLEXO Magazine : March 2011
Technologies & Techniques in use. This is the time to conduct an anilox roll audit on the entire inventory. Short of proofing each and every anilox roll (which consumes considerable press time, ink and other materi- als), an audit will document the current volumes of each and every anilox roll on hand. Consistent anilox roll performance comes down to cell quality, consistency and volume—all traits that are best evaluated with an audit. If the anilox rolls are stamped correctly, the original volumes will be apparent, and an audit will provide wear indications through pictures and current anilox specifications. Further examination will expose cleaning issues that will af- fect your ability to match color and printability. The audit itself is useful because it gives you both a visual and a numerical analysis of the condition of the anilox cells; you will know why the volume is what it is, as well as anything that might affect it, be it wear or cleanliness. Once identified, the issues can be addressed. Always review the audit’s result with your anilox roll suppli- er’s technical service agent and your ink representative to get their insights on how the inventory compares to the banded roll results. If you find yourself compromising your anilox roll selection—for example, saying “Close enough,” or “We have two, but we really need four”— you will have the same color matching and print problems as before, which means that you essentially wasted your time trying to optimize. Only in limited cases can you consider a compromise. Take a look at the anilox roll inventory examples in Table 2. Only “B” is workable, as it most closely resembles the target without compromise. “A” is flawed in deposit efficiency and dot support with the lower cell count component and “C ” is flawed, in one case with a weak volume and in the other case with too strong a volume. Compromise often means a sacrifice of print quality, color and consistency in flexo, so it is important to have anilox rolls of the right cell count and volume. Anilox rolls that have the same volumes but different cell counts will have a different deposit efficiency. In printing screens you may lack proper plate dot support. Streamline the inventory by removing worn anilox rolls and then by setting aside any considered obsolete. What remains will be your viable inventory. Keep in mind that every anilox roll has a single volume, not multiple volumes. What you put in is what you get out. Don’t be confused by claims that anilox rolls may be manipulated and transfer different film thicknesses with one volume. The only way to get different percentages in solids in the dry ink film thickness is to change viscosity or volume drastically, which takes the ink completely out of optimization. Once you have optimized ink release, you will have to maintain consistency in ink delivery. You can keep the volume cur- rent and forge an ability to guarantee it by inspection: The ability to examine anilox rolls and verify cell conditions of cleanliness and wear at the microscopic level is crucial. There are a couple of methods for doing so, including the aforementioned periodic audits over time and visual/scope inspection. Audits give you a long-term view of the inventory, but for frequent checks, it is best to use a microscope, preferably one that is illuminated through the viewing area because side shadows can make discernment difficult. You can purchase microscopes that measure volume and provide results in the same fashion as the anilox roll supplier. But my advice is to start simple, then determine if you need more information to make the proper decisions on anilox roll condition, before going to press. Table 2. Anilox Inventory A Target: 800 2.2 , need four aniloxes (3) 800 2.2 BCM Good for process (1) 500 2.2 BCM Different deposit efficiency, less dot support Anilox Inventory B Target: 800 2.2 , need four aniloxes (2) 900 2.2 BCM Workable in most situations (2) 800 2.2 BCM Good for process Anilox Inventory C Target: 800 2.2 , need four aniloxes (2) 800 1.8 BCM Too weak, struggle to get color (2) 700 2.5 BCM Too strong, wasted ink thickness after extension PeRIODIC MaINTeNaNCe Once the inspection is complete, you will be ready to examine the anilox roll cleaning process. Anilox cleaning can be the greatest asset to optimized ink films. First-hand experi- ink film is kept consistent with effective anilox cleaning. 42 FLeXO march 2011 www.flexography.org FLX_March11.indd 42 3/18/11 1:33 PM