Plates, printing

Letterpress. This is the oldest printing process stiU in use. It continues to be replaced by newer printing processes. Printing is conducted from a raised image area of the printing plate. Inks in the printing process are transferred directly from a raised area to a substrate. The printing plates contain a thick layer of photopolymer (often a mixture with polymer such as poly(vinyl alcohol) deposited over a plastic or aluminum base. 

Printing is conducted with a printing plate similar to letterpress. However, the chemistry of the photopolymer is somewhat different in order to... 

Electronic Film Output. Imagesetters are precision electromechanical devices that image monochromatic color separations onto photographic film or paper. Each separation is used to expose a printing plate for a single ink color (4). 

Fig. 15. Flexographic printing station, where the fountain pan suppHes ink to the mbber fountain roU, which in turn suppHes ink to the anilox roU. The doctor blade removes excess ink from the surface of the anilox roU so that it transfers a uniform layer of ink to the printing plate. The printing plate then...

Flexographic Printing Plates. There are three primary types of flexographic printing plates molded mbber, soHd-sheet photopolymer, and hquid photopolymer. 

Proofing materials have many of the same sources of variability as film, plus the added problem of registering, ie, accurately overlaying, the different colored layers. The printing plate must be exposed precisely to hold all that is discernible in the films. The accuracy of the exposure is critical because the plate must retain all the information contained in the films for faithful reproduction on the press. 

The polymer may be regarded in these applications as a form of photoresistor (see Chapter 14) and is now finding other applications in this area. It has been used in holography and in the manufacture of printing plates whilst it has also been suggested for use in solar cells and for measuring photoelectric resistance. 

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