A method for making a lithographic printing plate precursor

Abstract

A method for making a lithographic printing plate precursor is disclosed comprising the steps of a. providing a lithographic printing plate precursor including a support having a hydrophilic surface or which is provided with a hydrophilic layer, a photopolymerizable coating comprising a photopolymerizable composition, and an overcoat layer comprising a water soluble low molecular weight acid, wherein said overcoat layer has a surface pH-value ranging between 1 to 6; b. image -wise exposing the precursor; c. optionally heating the exposed precursor; d. processing the obtained precursor by applying a gum solution and optionally brushing the precursor, and / or by mounting the precursor on a plate cylinder of a lithographic printing press and rotating the plate cylinder while feeding dampeningliquid and / or ink to the coating. The printing plate obtained after imaging and processing in an off- press configuration with a gum solution or in an on-press configuration with fountain solution andink shows an improved roll- up performance in the start-up of a printing process on a printing press.

Description

field of invention [0001] The present invention relates to a method of making a lithographic printing plate precursor with a photopolymerizable coating by image-wise exposing the precursor and developing with a gum solution in an off-machine configuration or with a fountain solution in an on-machine configuration and ink development to carry out. Background of the invention [0002] In lithography, so-called printing masters, such as printing plates, are mounted on printing press cylinders. A master bears a lithographic image on its surface to which a print is made by applying ink to the image, followed by transfer of the ink from the master to a printing substrate, usually paper. In conventional so-called "wet" lithography, ink is supplied with an aqueous dampening solution (also called dampening liquid) to areas composed of oleophilic (or hydrophobic, ie accept ink but repel water) and hydrophilic (or hydrophobic) areas. A lithographic image composed of areas that accept...

AI Technical Summary

Problems solved by technology

[0011] One problem associated with prior art lithographic printing plate precursors which are developed on-press with fountain solution and ink after image-wise exposure or developed and gummed in a single step by using a gumming solution is the rolling ink ( roll-up) Insufficient performance

This means that the ink receptivity in the printed area (i.e. the exposed area) is too poor during the start of the printing process, resulting in too low ink absorption in the printed area and too low optical density on the first number of sheets

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