Apparatus and method for preparing relief printing form

A method for preparing a relief printing form from a photosensitive element, comprising the steps of:

• a) forming an in-situ mask adjacent to a photopolymerizable layer in the photosensitive element, wherein the photopolymerizable layer comprises a binder, an ethylenically unsaturated compound and a photoinitiator;
• b) enclosing the photosensitive element in a closed exposure chamber;
• c) controlling the oxygen concentration within the closed exposure chamber to provide an environment within the closed exposure chamber having a concentration of oxygen less than atmospheric but greater than an environment that is completely free of oxygen or greater than an environment composed completely of an inert gas;
• and
• d) exposing the photosensitive element to actinic radiation through the in-situ mask.