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FLEXO Magazine : June 2013
anilox roll feasible for a job, will help to ensure that the print produced stays clean through a run. It is critical that house- keeping capabilities are considered to insure optimal print results from clean and well maintained engravings. If it is difficult to clean and maintain the anilox rolls, discuss moving to a lower line count to make roll maintenance easier. If the anilox roll is easily cleaned, either on press or in a cleaning system, then fine line counts are possible but cleanli- ness should be confirmed with the anilox and ink suppliers to maximize press uptime. For traditional 60 degree engravings—currently, the most common now in use—400 lpi has 184,000 cells/in2, 600 lpi has 414,000 cell/in2, 1,000 lpi has 1,150,000 cells/in2. This can impact cleaning and release in traditional closed structure engravings. While in North America, we use lpi (lines per inch); the rest of the world uses lpcm (lines per centimeter). The conversion is: lpcm x 2.54 = lpi. ANILOX ROLL MANUFACTURING Thermal spray coatings reduce the harmful effects of abra- sion, wear and extreme heat on metal parts. For the printing industry, anilox and coater rolls are generally manufactured through the following processes. 1. A new roll base or used anilox roll set for refurbishing is inspected for condition 2. Dimensions are measured, prior to applying any form of surface coating 3. Existing rolls are stripped of used ceramic or chrome 4. Grit blasting prepares the raw roll and then Chrome Oxide plasma spray is applied 5. The surface is diamond ground and lapped to blueprint dimensions and anilox roll processing specifications 6. The required pattern is then laser engraved to specified pattern, screen and volume counts 7. Post engraving, a superfinishing is done to remove any high spots and minimize engraving wear in and blade wear 8. The anilox roll engraving is measured and inspected; then certified. At Praxair Surface Technologies, the composition of the coating is 99 percent pure Chromium Oxide. Using Praxair’s proprietary LC-4 Chrome Oxide, the coating is measured against internal standards and industry approved methods in the Praxair plant and its technology metalurgical labs to the following specifications: • Hardness (per ASTM E99-72, 384-73) measures an aver- age of 1300 Vickers • Bond Strength (per ASTM C633) is a 5,000 psi minimum tensile bond strength • Coating Porosity (per ASTM B276-54): is <less than 3% and typical analysis is < less than 2%. Quality control of coating is critical to the roll life and en- graving integrity and uniformity. OPEN STRUCTURES FOR SPECIAL EFFECTS For over a decade, Praxair has been producing open cell structured engravings for printing with REV and ART engrav- ings that have been updated in its open structure NovalineTM engravings. Anilox rolls of 2013 can deliver higher ink densities at finer line screens and are easier to maintain. Precise and digital control of the cell shape ensures unsurpassed repeatability and reproducibility of all engravings. Ink release has been im- proved, cell cleaning enhanced and the probability of ghost- ing reduced. Also, smoother and uniform walls are ensuring optimal contact with doctor blades, thus reducing probability of score lines. In recent years, flexographic print jobs and offset coaters utilizing raise UV, soft touch metallic and embossing technolo- gies have become far from uncommon. When it comes to the function and performance of the anilox roll, production 50 FLEXO June 2013 www.flexography.org C:\Documents and Settings\idyewlc1\My Documents\marketing communications\printing\Layout Files\P10341_novaline_series_datasheet.indd April 16, 2010 1:35 PM page 1 NovalineTM Series Laser Engravings for Anilox Rolls. Digital precision engravings for demanding flexo printing applications. New!NovalineTMSeries Novaline engravings are a new series of open-cell engravings that build upon Praxair’s open- structure engraving breakthrough with the introduction of our ARTTM and REVTM engravings more than 10 years ago. The Novaline Series of engravings utilize the latest laser technology where the laser beam is deflected and modulated at high speed to create a digital description of each cell. Novaline Advantages • Precise and digital control of the cell shape ensure unsurpassed repeatability and reproducibility of all engravings • Smooth cell surface produces better ink transfer from cell and improved cleaning • Increased wear resistance due to re-melt effect of ceramic • Smoother and more regular side walls ensure optimal contact with doctor blades thus reducing probability of score lines • Much higher opening-to-depth ratio compared to conventional 60-degree engravings • Improved ink release / cell cleaning and reduced probability of ghosting effects • Maximum achievable volumes increased by 20% to 40% for a given screen count depending on Novaline Series engraving • Allows for an increased anilox line count for a given volume transferred on the substrate improving print resolution without compromising print quality Multipurpose applications High-quality applications Flexible Packaging Paper Packaging Corrugated Labels Offset, Varnish NovaTM Silver Engraving NovaTM Gold Engraving ARTTM Gold Engraving UVTM Gold Engraving ARTTM Gold Engraving UVTM Gold Engraving Open Structure engravings Development of engraving Technology Metallurgical Lab and Sample