A soluble, light-sensitive, organic substance that undergoes polymerization when exposed to light. A photopolymer coating is applied to several types of printing plates used in offset lithography. Commonly used photopolymers are esters of cinnamic acid (produced by reacting cinnamic acid—denoted C9H8O2 and derived from cinnamon—with an alcohol, resulting in the release of a molecule of water). When light comes into contact with these molecules, they form large chain molecules. (See Polymerization.) The advantages of photopolymer plates are their high abrasion resistence and durability, as well as their ability to resist temperature and humidity changes. Thermal curing of photopolymers after plate processing enhances their durability, and results in the ability to use such plates for print runs in excess of 1,000,000 impressions. (See Photopolymer Plate and Plate: Offset Lithography.)

Photopolymer emulsions are also used as resist coatings for use in the chemical etching of image-carrying gravure cylinder. See Gravure Etching: Direct-Transfer Process.

Photopolymers are also widely used in the exposing of printing plates used in flexography. See Plates: Flexoography.

Photopolymers are also used as emulsions in photostencils used in screen printing. See Photostencil.

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