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Summary:
DuPont pioneered the technology of dry process, peel-apart development in photopolymer imaging films in the 1960's with the introduction of CroluxTM, a black architectural drafting film. Since then, several other graphic arts and electronic products; notable, negative CromalinTM and CromacheckTM, have emerged from development using peel-apart technology, in which distinct, inherent advantages over wet processed systems have steadily gained customer interest. Peel apart processing is simple, fast and dry requiring no wet processing chemicals, no expensive investment in processing equipment and not costs associated with spent developer disposal. A peel apart film requires a minimum of 3 layers for operation; a peelable coversheet (usually a PET film), an image forming photopolymer layer and a supportive bottom layer. The peel development, following an imagewise exposure to actinic radiation, creates positive or negative readouts, depending upon adhesional and rheological changes taking place in the photopolymer layer as a result of the photochemical reactions. Peel apart processing is simple, fast and dry requiring no wet processing chemicals, no expensive investment in processing equipment and not costs associated with spent developer disposal. A peel apart film requires a minimum of 3 layers for operation; a peelable coversheet (usually a PET film), an image forming photopolymer layer and a supportive bottom layer. The peel development, following an imagewise exposure to actinic radiation, creates positive or negative readouts, depending upon adhesional and rheological changes taking place in the photopolymer layer as a result of the photochemical reactions. Considerable effort has been expended in understanding the peel-apart mechanism by using negative imaging films. A viscoelastic model, showing the postulated mechanism, will be presented for the peel-apart image development based upon: quantitatively measuring the peel force while varying physical-mechanical factors; such as peel rate, peel angle, peel temperature and coversheet thickness, correlating the observed peel force to the effective adhesivestrength using fundamental concepts in rheology and adhesion, and considering other factors affecting image resolution in terms of the effective adhesive strength. Examples, depicting both the positive and negative modes of peel separation relying upon structural and compositional changes, will be discussed.