Method for preparing a 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 disposed above a layer of a photopolymerizable composition in the photosensitive element, wherein the photopolymerizable composition comprises a binder, an ethylenically unsaturated compound and a photoinitiator;
• (b) imagewise exposing the photopolymerizable layer to actinic radiation through the in-situ mask in an environment having an inert gas and a concentration of oxygen between 50,000 ppm and 2000 ppm, forming at least a polymerized portion and at least an unpolymerized portion;
• (c) treating by heating the photosensitive element of step b) to a temperature sufficient to cause the unpolymerized portion to melt, flow, or soften, and,
• (d) removing the unpolymerized portion that melt, flow, or soften to form the relief printing form having a plurality of raised surface elements made of the polymerized portion, each raised surface element having a print surface area,
• wherein the in-situ mask includes actinic radiation opaque areas and open areas, and in one or more of the open areas that produce image areas comprising halftone dot image areas and in one or more of the open areas that produce image areas comprising solid image areas, comprises a microcell pattern comprising a plurality of features in which each feature has dimension between 5 and 30 microns that is opaque to actinic radiation, and
• wherein after the removing step, the print surface area of one or more of the raised surface elements that form halftone dot image areas have the microcell pattern induced therein, and the print surface area of one or more of the raised surface elements that form the solid image areas have the microcell pattern induced therein.