Positive-working, infrared-sensitive lithographic printing plate and method of imaging

摘要

A positive-working, infrared imageable coating and a lithographic printing plate or other element with the coating are described. The coating is a phenolic resin containing an o-diazonaphthoquinone derivative which couples or reacts with the resin to partially insolubilize the coating and an infrared absorbing dye or pigment which further insolubilizes the coating and which renders the coating imageable by infrared radiation. The coating contains only that quantity of infrared radiation absorber necessary to be imageable and only that small quantity of o-diazonaphthoquinone derivative necessary to supplement the insolubilizing function of the absorber. Specifically, the absorber is from 1 to 10 weight percent of the total dry weight of the coating and the dry weight ratio of the absorber to the diazonaphthoquinone moiety is greater than 1:5 and preferably 1:2 or greater. By replacing a portion of expensive dye with some less expensive o-diazonaphthoquinone derivative to obtain the necessary degree of insolubility, the cost of the coating is greatly reduced.