Photopolymer Printing Plate

a letterpress printing plate, the printing elements of which are produced as a result of the action of light on a composite photopolymer material. The photopolymer material may be a solid or a liquid that becomes insoluble in its usual solvent when subjected to strong light; liquid materials become solid, and solid materials undergo further polymerization. In addition to the primary polymer (polyamide and acrylate resins, esters of cellulose, and polyurethane resins), the materials also contain small amounts of a photopolymerization catalyst, such as benzoin. Photopolymer printing plates made from solid materials first appeared in the late 1950’s in the USA; plates made from liquid materials appeared several years later in Japan.

In the production of printing plates from solid photopolymer materials, a layer of the material 0.4–0.5 mm thick is applied to thin sheets of aluminum or steel. After exposure of the negative, the nonpolymerized layer in the blank sections is washed away, and the plate is dried. In the production of plates from liquid photopolymer materials, the negative is placed in a special device, such as a tray made of transparent, colorless glass; it is then covered with a thin, colorless, transparent film, and the liquid photopolymer material is poured on top. The tray is then exposed from both sides; solid, polymerized printing elements are produced on the negative side, and the plate support on the opposite side. A stream of solvent is used to wash away the nonpolymerized material from the blank sections, and the final plate is dried.

Photopolymer printing plates (often called full-size wraparound plates) are used to print magazines and books, including those with illustrations. They are simple to manufacture, lightweight, and capable of providing runs up to 1 million impressions. They also permit wide use of phototypesetting techniques, and they do not require large expenditures of time for preparatory operations during printing.