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printech, December, 2002
Re: Differences Between Flexo & Offset Printing

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From: Gary Jones ( gjonesprinting@aol.com )
Date: Sun, 8 Dec 2002 23:05:45

Here are brief descriptions of the two printing processes:

The lithographic printing process is a planographic technique where the image and nonimage areas are, for all practical purposes, in the same geometric plane. The image area of a plate is made of a material having an ink-receptive oleophilic surface, while the nonimage area is made of a water-receptive, or hydrophilic, material. In printing, a thin film of aqueous solution (fountain, or dampening, solution) is applied to the plate and wets the nonimage area. Then ink is applied to the plate.

The flexographic printing process is a relief technique where the image area is raised relative to the nonimage area. Flexographic printing uses flexible plates with raised images to transfer fluid inks to a substrate. The plates are typically plastic or rubber or some other flexible material and the image is attached to a roller or cylinder. Four rollers are used to transfer a single ink to the substrate. The first roller transfers ink from an ink fountain to an engraved roller, known as an anilox roller.

For more information, there are two EPA documents that contain printing process descriptions. There is a link on PNEAC's web page at http://www.pneac.org/sheets/all/index.cfm to EPA's Printing Industry and Use Cluster Profile that has great process descriptions. Also, there is another publication called Profile of the Printing Industry (EPA 310-R-95-014) that has process descriptions. It can be obtained from EPA at http://es.epa.gov/oeca/sector/index.html

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