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FLEXO Magazine : October 2009
and Carbon Density (Mask) Specifications for Digitally Imaged Photopolymer Plates What happens: FIRST says, The black carbon mask should have a density greater than 3.0, a uniform consisten- cy of coating, and be free of visual defects (such as pinholes, scratches, abrasions, and smudges). After ablation, the carbon black opening "stain level" should have a density of 0.06 or less on a transmission densitometer. TEST says, This section of FIRST 4.0 contains a comprehensive description of the important imaging char- acteristics of a digitally imaged photopolymer plate. The carbon mask takes the place of a film negative and has the same important job of selectively blocking and allowing UV light to expose the plate during the main exposure. Any defect or problem with the carbon mask or the ablated areas will translate into defects on the finished plate. For example, if the carbon mask itself is not dense (opaque) enough, UV light may penetrate the mask and begin to polymerize the photopolymer. Conversely, if the ablated (clear) areas are not "open" enough (have low enough transmission density), UV light will be blocked to an extent affecting the image areas of the plate. Another problem that can occur is "laser banding." Due to improper laser focus and/or power, small bands are imaged onto the plate by either leaving narrow streaks of carbon or over-ablating the plate. This can result in streaks in the image areas. It is more noticeable in printed solids where small, narrow lines of missing ink can appear leading to problems achieving solid ink density and other potential defects. For more information, see Section 17.3.1 (page 136) of FIRST 4.0. The Keys to Flexographic Excellence What is FIRST The intention of FIRST is to provide all participants in the flexographic reproduction process with a common set of guidelines, tutorials and data that can be used as communication and production tools. The aim of FIRST is to create a common set of specifications and commu- nication protocols for the industry. This platform should establish common communication and identify the responsibility of the provider(s). To order FIRST, call 631-737-6020 or visit www.ftastore.com. What is TEST TEST is the educational arm of the Flexographic Technical Association. The aim of TEST is to align all of the training materials available through the FTA with the guidelines, tutorials and data identified in FIRST. TEST is focused on implementing new learning methodologies to reach out to a larger portion of the FTA membership. For more information on TEST, visit www.flexography.org.
Sustainable Fall 2009