Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
2002-06-18
2003-04-08
Schilling, Richard L. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S204000, C430S271100, C430S278100, C430S302000, C430S616000, C430S935000
Reexamination Certificate
active
06544719
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of making a heat-mode lithographic printing plate precursor comprising a hydrophilic base and a hydrophobic silver metal layer provided on said base. The invention also relates to the method of heat-mode exposure of such a precursor, thereby causing ablation of the silver metal at exposed areas. The silver metal is obtained by the silver salt diffusion transfer reversal process.
BACKGROUND OF THE INVENTION
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 (so-called ‘wet’) 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.
Printing masters are generally obtained by the so-called computer-to-film method wherein various pre-press steps such as typeface selection, scanning, color separation, screening, trapping, layout and imposition are accomplished digitally and each color selection is transferred to graphic arts film using an image-setter. After processing, the film can be used as a mask for the exposure of an imaging material called plate precursor and after plate processing, a printing plate is obtained which can be used as a master.
In recent years the so-called computer-to-plate method has gained a lot of interest. This method, also called direct-to-plate method, bypasses the creation of film because the digital document is transferred directly to a plate precursor by means of a so-called plate-setter. A lithographic printing plate precursor that is highly suitable for computer-to-plate imaging is the so-called Lithostar™ material, available from Agfa-Gevaert. Lithostar™ is a silver salt diffusion transfer reversal (DTR) material comprising, in the order given, a grained and anodized aluminum base, an image receiving layer comprising physical development nuclei, an intermediate layer and a silver halide emulsion layer. After image-wise exposure of the silver halide emulsion layer, the material is processed with a DTR developer which comprises silver halide solvent(s). The exposed silver halide is reduced by the developer so as to form chemically-developed silver metal in the emulsion layer. The non-exposed silver halide dissolves in the developer, diffuses to the physical development nuclei and is there reduced to form a silver metal deposit on the aluminum base. Subsequently the silver halide emulsion layer and any other optional hydrophilic layers are removed, the silver metal is hydrophobized, neutralized and finally gummed. Such DTR materials offer the benefits of high sensitivity and the capability of spectral sensitization to the complete visible wavelength range from violet to red light. The principles of the DTR process have been described e.g. in U.S. Pat. No. 2,352,014 and in the book “Photographic Silver Halide Diffusion Processes” by André Rott and Edith Weyde—The Focal Press—London and New York, (1972).
So-called thermal or heat-mode printing plate precursors are also widely used in computer-to-plate workflow, i.e. materials of which the imaging mechanism can be triggered by heat or exposure to infrared light. Also image-recording materials which require no processing or may be processed with plain water, ink or fountain are another major trend in plate making. Typical heat-mode materials which require no wet processing are based on ablation, such as the plate materials described in EP-A 580 393 and 580 394. EP-A 609 941 describes a heat-mode lithographic printing plate precursor comprising an ablative silver metal layer that is obtained by means of the DTR process. According to that method, a similar material as the above described Lithostar™ is processed by the plate manufacturer without exposure, so that a uniform hydrophobic silver metal layer is obtained on the grained and anodized aluminum support. That material can then be image-wise exposed in heat-mode by the end-user, thereby ablating the silver metal and revealing the hydrophilic surface of the support at exposed areas. Further improvements of this material and method have been described in EP-A 628 409; EP-A 816 071; WO98/055307; WO98/055307; WO98/055308; WO98/055309; WO98/055310; WO98/055311; WO98/055330; WO98/055331; WO98/055332; EP-A 934 824; EP-A 934 823; U.S. Pat. No. 5,916,734; U.S. Pat. No. 6,132,938; EP-A 1 106 349; and EP-A 1 106 382.
JP-A 2000-206678 describes a similar method for making a heat-mode lithographic printing plate precursor comprising an ablative silver metal layer that is obtained by means of the DTR process. First, an aluminum support which is provided with physical development nuclei is coated with a silver halide emulsion layer. Before the silver emulsion layer is completely dried, a DTR development solution is applied in a second coating step on the silver halide emulsion layer. The emulsion layer is then washed off and finally, the silver metal is hydrophobized and neutralized. A problem associated with this method is the requirement of two coating steps: in view of the high coating speed used during manufacturing of such materials, the required length of the coating alley makes this method very expensive and impractical. An alternative method wherein the developer is mixed with or injected into the coating liquid of the emulsion layer just before coating does not provide a solution for this problem because the development of the silver halide occurs very fast and the silver metal that is thereby formed, induces coating defects.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method, which is cost efficient and provides a good coating quality, for making a heat-mode lithographic printing plate precursor containing an ablative silver metal phase as image-recording layer. This object preferably is achieved by the characterizing features of the present invention. Advantageous embodiments and further developments of the solution will be apparent from the description of the invention provided herein. It has been found that a DTR development solution can be coated as a second layer simultaneously with the silver halide emulsion layer without causing coating defects. Since the development solution makes contact with the wet emulsion layer as soon as it is coated, the chemicals in the developer diffuse immediately into the emulsion layer and physical development of the silver halide occurs very rapidly.
Specific features for preferred embodiments of the invention are set out in the dependent claims. Further advantages and embodiments of the present invention will become apparent from the following description.
DETAILED DESCRIPTION OF THE INVENTION
According to the method of the present invention, a silver halide emulsion layer and a solution, which induces silver salt diffusion transfer reversal development of the silver halide, are coated simultaneously on a hydrophilic base that is provided with physical development nuclei. Hereinafter, said solution which induces silver salt diffusion transfer reversal development of the silver halide shall be referred to briefly as “DTR development solution” or “DTR developer”. Since the silver halide emulsion layer is not exposed to light, all the silver is dissolved by the DTR developer and deposited on the hydrophilic base to form a uniform layer. In a subsequent wash-off step the emulsion layer is removed from the silver metal and the material may then be dried, cut and shipped to the end-user. The hydrophobic character of the surface of the silver metal layer is preferably enhanced by applying a hydrophobizing agent thereto, either from the DTR developer or in a separate top coat
Coppens Paul
Vervloet Ludo
Agfa-Gevaert
Leydig , Voit & Mayer, Ltd.
Schilling Richard L.
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