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pH ValueThe degree of acidity of alkalinity measured on a scale from 0 to 7 is acid; from 7 to 14 is alkaline, and 7 is neutral. Numerous instruments are available for measuring the pH value.
PhotopolymersGeneric name for a mixture of materials that can change physical properties (usually harden) on exposure to ultraviolet or visible light.
PigmentInsoluble fine solid particle matter used to give color, transparency or opacity to inks, paints and plastics.
Pin registerThe use of accurately positioned holes and special pins on copy, film, plates, and presses to insure proper register or fit of colors.
Plate cylinderThe cylinder of a press on which the plate is mounted. There are two types of plate cylinder, the Integral, with the shaft a permanent part of the body, and the Demountable, in which the shaft is removable to receive a multiplicity of bodies of varying diameters, and in some cases face widths.
Plate, FlexographicThe image carrier used in Flexographic printing. Flexographic printing is a modern version of the original relief printing process – letterpress. On a flexo plate, the image area is raised above the floor of the plate. Ink is applied to the surface of the plate through an anilox ink metering system, and then is directly transferred to the printed substrate.
Plate on sleeveIn a plate on sleeve workflow. Raw photopolymer is mounted onto a printing sleeve prior to imaging, exposing and processing. In this manner, the plates are imaged in position and the print form is ready for immediate loading onto a flexo press as soon as processing is completed. See continuous print sleeve.
PolyesterSupport backing of the plate structure which provides the plate's mechanical strength and dimensional stability. A layer of photopolymer is anchored to this backing.
PolymerA compound reaction in which the molecules of a monomer are linked together to form large molecules whose weight is a multiple of that of the original substance.
Post exposureUV light exposure of a dried and light finished plate to complete polymerization and attain maximum durability.
Printing, FlexographicThe method of direct rotary printing using resilient, raised image printing plates, affixable to plate cylinders of various repeat lengths, inked by a roll or doctor-blade-wiped metering roll, carrying fluid or paste type inks to virtually any substrate.
Process colorHalftone color printing created by the color separation process whereby a piece of copy is broken down to the primary colors - yellow, cyan, magenta plus black - to produce individual halftones. These are recombined at the press to produce the complete range of colors of the original.
ProcessingUnpolymerized photopolymer material is removed to produce a relief printing plate. A washout solution and brushing action removes the unpolymerized photopolymer which dissolves in the washout solution.
Process inksA set of transparent inks for high reproduction illustrations by halftone color separation process. Colors are yellow, magenta, cyan with or without black.
Process printingThe printing from a series of two or more halftone plates to produce intermediate colors and shades.
ProofA prototype of the printed job that is made from plate, film, or electronic data. Used for in-house quality control and/or for customer inspection and approval.
Proofing equipmentDevice for obtaining proofs for register and impression, off the press.