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A type of digitally imaged printing plate used for the flexographic printing process. Digital imaging of flexographic plates is a multiple step process, but it requires fewer steps than conventional flexographic platemaking. The process begins with the placement of the plate material on an external drum where it is held in place by a vacuum or double-stick tape. The process of imaging the plate on the external drum is known as imaging in the round. A flexographic plate for CTP (computer-to-plate) systems consists of a photopolymer layer topped by a black masking layer. As the imaging drum rotates, a laser head creates the image on the plate by ablating portions of the black masking layer to reveal corresponding areas on the photopolymer layer. Only a light coating of ash is formed from the imaging process, which is removed with a debris extractor built into the system. This is followed by a simple water wash and a short drying period. Many flexographic digital platesetters use infrared lasers that operate at 830 nm or 1064 nm wavelengths. Flexographic platesetters for CTP require more power than offset CTP thermal units because the lasers must be able to ablate unwanted areas of the plate material in order to provide proper imaging. The plate material must be strong enough to withstand the extremes placed upon it during the printing process, but must also allow the lasers to erode the material easily during the imaging process.
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