METHOD FOR MAKING PRINTING PLATE BY INKJET DEPOSITION ON POSITIVE-WORKING MEDIA

摘要

An inkjet method is used to make a negative working offset lithographic printing master by imagewise application of liquid inkjet droplets that form a mask on a layer of positive-working radiation imageable material pre-coated on a hydrophilic lithographic base. The masked layer is then subjected to a developer and developed. After development, only the masked areas of the positive working imageable material remain. Since this material is hydrophobic the resulting imaged layer on the hydrophilic lithographic base may be employed as a wet offset lithographic master. Since the image that is printed by the printing master coincides directly with the image printed by the inkjetting process on the imageable material, the method is inherently negative-working. By the method of the present invention positive-working radiation imageable media is therefore employed to make a negative-working printing master. The combination of positive working radiation-imageable medium and masking fluid of this invention may be used in the fully on-press fabrication of a negative working lithographic master, which may optionally may also be made on a re-usable base.