Lithographic imaging with printing members having multiphase laser-responsive layers

#The present invention relates to printing apparatus and methods, and more particularly to imaging of lithographic printing-plate constructions on- or off-press using controlled laser output.

#In offset lithography, a printable image is present on a printing member as a pattern of ink-accepting (oleophilic) and ink-rejecting (oleophobic) surface areas. Once applied to these areas, ink can be efficiently transferred to a recording medium in the imagewise pattern with substantial fidelity. Dry printing systems utilize printing members whose ink-repellent portions are sufficiently phobic to ink as to permit its direct application. Ink applied uniformly to the printing member is transferred to the recording medium only in the imagewise pattern. Typically, the printing member first makes contact with a compliant intermediate surface called a blanket cylinder which, in turn, applies the image to the paper or other recording medium. In typical sheet-fed press systems, the recording medium is pinned to an impression cylinder, which brings it into contact with the blanket cylinder.

#In a wet lithographic system, the non-image areas are hydrophilic, and the necessary ink-repellency is provided by an initial application of a dampening fluid to the plate prior to inking. The dampening fluid prevents ink from adhering to the non-image areas, but does not affect the oleophilic character of the image areas.

#The above-discussed and other features and advantages of the present invention will be further appreciated and understood by those skilled in the art from the following detailed description and drawings. The drawings are not necessarily drawn to scale, and like reference numerals refer to the same parts throughout the different views.

#FIGS. 1, 2 and 3 are enlarged sectional views of prior-art printing members.

#FIG. 4A is an enlarged sectional view of a lithographic printing member having a metal substrate.

#With reference to FIG. 4A, a representative embodiment of a lithographic printing member in accordance herewith includes a metal substrate layer 401, and a radiation-absorptive multiphase layer 404. FIG. 4B illustrates an alternative embodiment that includes a polymer substrate 402 and a radiation-absorptive multiphase layer 404. The multiphase layer 404 comprises a polymer-rich phase 406 and an inorganic-rich phase including 408 and 410. In one embodiment as illustrated in FIG. 4A, the multiphase layer 404 comprises an inorganic-rich interfacial layer 410 at the interface with the metal substrate.

#1. Substrate 401, 402

#The primary functions of substrate 401, 402 are to serve as a dimensionally stable mechanical support, and to provide different affinity characteristics for ink and/or a fluid to which ink will not adhere. Suitable metals for substrate 401 include, but are not limited to, aluminum, copper, steel, and chromium. Preferred thicknesses range from 0.004 to 0.02 inch, with thicknesses in the range 0.005 to 0.012 inch being particularly preferred.