Method of making lithographic printing plates

Abstract

A method for preparing a lithographic printing plate is provided which comprises the steps of providing a lithographic printing plate precursor comprising (i) a support having a hydrophilic surface or which is provided with a hydrophilic layer, (ii) on said support, a coating comprising an image recording layer, said layer comprising hydrophobic thermoplastic polymer particles, having an average particle size between 40 nm and 63 nm and a hydrophilic binder, said coating further comprising a pigment, present in said image recording layer or in an additional layer of said coating, image-wise exposing said coating, thereby inducing coalescence of the thermoplastic polymer particles at the exposed areas of the image recording layer, developing the precursor by applying a gum solution to the coating, thereby removing the non-exposed areas of the image recording layer from the support, and optionally, baking the developed precursor, wherein the hydrophobic thermoplastic polymer particles have an average particle size between 40 nm and 63 nm, wherein the amount of the hydrophobic thermoplastic polymer particles is more than 70 % and less than 85 % by weight, relative to the image recording layer, and wherein said pigment has a hydrophilic surface and provides a visible image after image-wise exposing and developing with the gum solution. The lithographic printing plate precursor, used in the above method, has an improved sensitivity, and the obtained lithographic printing plates exhibit an excellent clean-out, no toning and a high printing run length.

Description

field of invention [0001] The present invention relates to a method of making lithographic printing plates by which a printing plate precursor having improved sensitivity is image-wise exposed and developed with a gum solution. Background of the invention [0002] In lithographic printing, so-called printing masters, such as printing plates, are mounted on the cylinders of a printing press. A master has a lithographic image on its surface, ink is applied to the image, and the ink is then transferred from the master to a receiving material, typically paper, to produce a copy. In conventional so-called "wet" lithography, ink and an aqueous dampening solution (also called dampening solution) are supplied to a lithographic image consisting of oleophilic (or hydrophobic, i.e. accepts ink and repels water) regions and hydrophilic ( Or oleophobic (accept water, repel ink) area. In so-called "dry offset printing", where the lithographic image consists of ink-accepting areas and in...

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