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Positive-working lithographic printing plate precursor

a lithographic printing plate and positive-working technology, applied in the field of heat-sensitive positive-working lithographic printing plate precursors, can solve the problem of limited shelf life of coatings, and achieve the effects of improving material shelf life, low surface roughness, and improving shelf li

Inactive Publication Date: 2005-11-24
AGFA GEVAERT AG
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0005] It is an aspect of the present invention to provide a positive-working thermal lithographic printing plate precursor with improved shelf life. This object is realized by the material of claim 1, having the characterizing feature that a low surface roughness of the grained and anodized aluminum support unexpectedly provides an improved shelf life of the material. Specific embodiments of the invention are defined in the dependent claims.

Problems solved by technology

A specific problem associated with thermal plate precursors is the limited shelf life of the coating.

Method used

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  • Positive-working lithographic printing plate precursor

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Preparation of Lithographic Support 1 (Comparative Example)

[0027] A 0.30 mm thick aluminum foil was degreased by immersing the foil in an aqueous solution containing 40 g / l of sodium hydroxide at 60° C. for 8 seconds and rinsed with demineralized water for 2 seconds. The foil was then electrochemically grained using an alternating current in an aqueous solution containing 12 g / l of hydrochloric acid and 38 g / l of aluminum sulphate (18 hydrate) at a temperature of 33° C. and a current density of 130 A / dm2 to form a surface topography with an average center-line roughness Ra of 0.5 μm. After rinsing with demineralized water for 2 seconds, the aluminum foil was then etched with an aqueous solution containing 155 g / l of sulfuric acid at 70° C. for 4 seconds and rinsed with demineralized water at 25° C. for 2 seconds. The foil was subsequently subjected to anodic oxidation in an aqueous solution containing 155 g / l of sulfuric acid at a temperature of 45° C., at a current density of 22 A...

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Abstract

A positive-working lithographic printing plate precursor is disclosed which comprises (i) a grained and anodized aluminum support having a hydrophilic surface and (ii) a heat-sensitive oleophilic coating provided on the hydrophilic surface, wherein said coating is capable of dissolving in an aqueous alkaline developer at a higher dissolution rate in areas of said coating which are exposed to heat or infrared light than in unexposed areas, characterized in that the hydrophilic surface has a surface roughness, expressed as arithmetical mean center-line roughness Ra, which is less than 0.40 μm. The use of a low surface roughness as defined above provides an improved shelf life of the coating.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a heat-sensitive positive-working lithographic printing plate precursor that requires aqueous alkaline processing. BACKGROUND OF THE INVENTION [0002] Lithographic printing presses use a so-called printing master such as a printing plate which is mounted on a cylinder of the printing press. The master carries a lithographic image on its surface and a print is obtained by applying ink to said image and then transferring the ink from the master onto a receiver material, which is typically paper. In conventional lithographic printing, ink as well as an aqueous fountain solution (also called dampening liquid) are supplied to the lithographic image which consists of oleophilic (or hydrophobic, i.e. ink-accepting, water-repelling) areas as well as hydrophilic (or oleophobic, i.e. water-accepting, ink-repelling) areas. In so-called driographic printing, the lithographic image consists of ink-accepting and ink-adhesive (ink-repel...

Claims

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Application Information

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IPC IPC(8): B24B5/04B41N3/03
CPCB41N3/034
Inventor VAN DAMME, MARCVERMEERSCH, JOAN
Owner AGFA GEVAERT AG