Photochromic system and layers produced therewith

DETAILED DESCRIPTION We claim: 1.
A photochromic composition containing an oxidizable leuco dye and a photochemically activated initiator which converts the leuco dye to the dye, wherein the initiator is a compound of the formula (I) or (II) ##STR12## where R.
sup.
1, R.
sup.
2, R.
sup.
3 and R.
sup.
4 are identical or different and are each hydrogen, alkyl, alkoxy, halogen or amino, R.
sup.
5 is hydrogen, alkyl, aralkyl, alkylsulfonyl, arylsulfonyl, dialkoxyphosphoryl, dialkylphosphoryl, diarylphosphoryl or a carbonyl radical ##STR13## and R.
sup.
6 is alkyl, alkoxy, phenyl or dialkylamino.
2.
A photochromic layer which contains a photochromic composition and one or more film-forming polymers, wherein the said photochromic layer contains the photochromic composition defined in claim 1.
3.
A process for the production of a lithographic layer for photoresist, offset printing, letter press printing or gravure printing or for etching glass or aluminum, wherein a photochromic layer as defined in claim 2 is subjected to actinic light through an image-bearing transparency, whereby the photochromic layer provides good color contrast between the exposed and unexposed image areas.




Description:
The present invention relates to a novel photochromic system, photochromic layers produced therewith, and their use for the production of recording materials, in particular for lithographic layers and for other printing processes.
Image-forming compositions and processes play an important role in the use of recording materials, for example in the production of relief printing plates, lithographic printing plates, printed circuits etc.
For these applications, these recording materials are exposed imagewise to actinic light while they are in contact with an image-bearing transparency.
Exposure is usually carried out by contact exposure or by the reflex copy process.
After exposure, recording materials of this type are developed, for example, by washing out with solvents, dusting on pigments or making use of the different adhesion of exposed and unexposed parts of the layer