Methods of developing photopolymerizable compositions containing an 0-nitroaromatic compound as photoinhibitor

Method of making a positive polymeric image on a substrate which comprises

• (1) coating the substrate with the photopolymerizable coating composition in which the photopolymerizable and photosensitive components consist essentially of
• (a) normally nongaseous, ethylenically unsaturated compound selected from the group consisting of unsaturated esters of polyols, unsaturated amides, vinyl esters and unsaturated aldehydes capable of addition polymerization by free-radical initiated chain propagation,
• (b) 0.004 to 0.7 part by weight, per part of component (a), of nitroaromatic compound of the formula ##STR22## wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4, alike or different, are H, OH, halogen, NO.sub.2, CN, alkyl of 1 to 18 carbons, alkoxy in which the alkyl is of 1 to 18 carbons, acyloxy of 2-7 carbons, aryl of 6 to 18 carbons, benzyl, halogen-substituted phenyl, polyether of 2 to 18 carbons and 2 to 10 oxygens, dialkylamino in which each alkyl is of 1 to 18 carbons, thioalkyl in which the alkyl is of 1 to 18 carbons, or thioaryl in which the aryl is of 6 to 18 carbons, R.sup.2 and R.sup.3, taken together, are --OCH.sub.2 O-- or --O--CH.sub.2 CH.sub.2 O--.sub.q in which q is an integer from 1 to 5, or any two of R.sup.1, R.sup.2, R.sup.3 and R.sup.4, taken together, are the residue of a second benzene ring fused onto the benzene nucleus, with the proviso that not more than one of R.sup.1, R.sup.2, R.sup.3 and R.sup.4 is OH or NO.sub.2,
• R.sup.5 is H, alkyl of 1 to 18 carbons, halogen, phenyl, or alkoxy in which the alkyl is of 1 to 18 carbons,
• R.sup.6 is H, OH, alkyl of 1 to 18 carbons, phenyl, alkoxy in which the alkyl is of 1 to 18 carbons, or aryloxy of 6 to 18 carbons unsubstituted or substituted with halogen, alkyl of 1 to 6 carbons, or alkoxy of 1 to 6 carbons, with the proviso that only one of R.sup.5 and R.sup.6 is H, or
• R.sup.5 and R.sup.6 taken together are .dbd.O, .dbd.CH.sub.2, --O--CH.sub.2 --, .dbd.NC.sub.6 H.sub.5, .dbd.NC.sub.6 H.sub.4 N(alkyl).sub.2 in which each alkyl is of 1 to 18 carbons, --O--C.sub.2 H.sub.4 --O--, .dbd.N(alkyl) in which the alkyl is of 1 to 6 carbons, ##STR23## in which the hydrocarbylene group is of 1 to 18 carbons, or ##STR24## in which R.sup.8 and R.sup.9, alike or different, are H or alkyl of 1 to 4 carbons, and R.sup.7 and R.sup.10, alike or different, are --CN, --COR.sup.11 in which R.sup.11 is alkyl of 1 to 5 carbons, or --COOR.sup.12 in which R.sup.12 is alkyl of 1 to 6 carbons which may be interrupted by an oxygen atom, alkenyl of 2 to 5 carbons, or alkynyl of 2 to 5 carbons, or R.sup.7 and R.sup.8 together, or R.sup.9 and R.sup.10 together, complete a 6-membered carbocyclic ring containing a keto group, and
• (c) 0.001 to 10 parts by weight, per part of component (a), of an organic, radiation-sensitive, free-radical generating system, activatable by actinic radiation that does not significantly rearrange the nitroaromatic compound to an inhibitor of free-radical polymerization,
• (2) imagewise exposing a portion of the photopolymerizable coating through an image-bearing transparency to radiation at least 20% of which has a wavelength of 200 to 380 nm, thereby rearranging at least some of the nitroaromatic compound to polymerization inhibiting nitroso-aromatic compound, and
• (3) subjecting the coating to a second exposure whereby a greater portion of the coating, including the portion exposed during the imagewise exposure, is exposed to radiation substantially limited to wavelengths greater than 380 nm, whereby a positive polymeric image is formed in the areas exposed during the second exposure but not exposed during the imagewise exposure.