Claims
- 1. A method of modifying the structure of a lithographic plate having at least one highly electroconductive surface that is to be imaged with a spark-discharge recording apparatus so as to control overburn caused thereby, comprising the steps of introducing an electroconductive sheet immediately beneath the at least one surface to be imaged, and selecting the volume resistivity of said conductive sheet to be at least 0.5 ohm-cm.
- 2. The method of claim 1 wherein the volume resistivity of said conductive sheet is no greater than 1000 ohm-cm.
- 3. A method of imaging a lithographic plate having a printing surface including a thin metal layer and a substrate, comprising the steps of:
- a. mounting the plate to the plate cylinder of a lithographic press having at least one plate cylinder, a corresponding number of blanket cylinders and an impression cylinder;
- b. exposing the printing surface to spark discharges between the plate and an electrode spaced close to the printing surface produced in response to picture signals representing an image, the spark discharges producing sufficient heat to remove the thin metal layer from the substrate at the points thereof exposed to the spark discharges;
- c. moving the electrode and the plate relatively to effect a scan of the printing surface;
- d. controlling the spark discharges to the plate in accordance with picture signals so that they occur at selected times in the scan; and
- e. dissipating excess spark energy over that which is required to create image points having desired diameters, thereby forming an array of the image points on the printing surface that corresponds to the picture represented by the picture signals.
- 4. A method of imaging a lithographic plate having a printing surface including a thin metal layer and a substrate, comprising the steps of:
- a. exposing the printing surface to spark discharges between the plate and an electrode spaced close to the printing surface produced in response to picture signals representing an image, the spark discharges producing sufficient heat to remove the thin metal layer from the substrate at the points thereof exposed to the spark discharges;
- b. moving the electrode and the plate relatively to effect a scan of the printing surface;
- c. controlling the spark discharges to the plate in accordance with picture signals so that they occur at selected times in the scan; and
- d. dissipating excess spark energy over that which is required to create image points having desired diameters, thereby forming an array of the image points on the printing surface that corresponds to the picture represented by the picture signals.
- 5. An apparatus for producing a lithographic plate comprising:
- a. a lithographic plate bank having a printing surface including a thin metal layer and a substrate;
- b. a lithographic press having at least one plate cylinder to which the plate blank is mounted, a corresponding number of blanket cylinders and an impression cylinder;
- b. an electrode spaced close to the printing surface for producing spark discharges in response to picture signals representing an image, the spark discharges creating sufficient heat to remove the thin metal layer from the substrate at the points thereof exposed to the spark discharges;
- c. means for moving the electrode and the plate bank relatively to effect a scan of the printing surface;
- d. means for controlling the spark discharges to the plate bank in accordance with picture signals so that they occur at selected times in the scan; and
- e. means for dissipating excess spark energy over that which is required to create image points having desired diameters, thereby forming an array of the image points on the printing surface that corresponds to the picture represented by the picture signals.
- 6. An apparatus for producing a lithographic plate comprising:
- a. a lithographic plate bank having a printing surface including a thin metal layer and a substrate;
- b. an electrode spaced close to the printing surface for producing spark discharges in response to picture signals representing an image, the spark discharges creating sufficient heat to remove the thin metal layer from the substrate at the points thereof exposed to the spark discharges;
- c. means for moving the electrode and the plate bank relatively to effect a scan of the printing surface;
- d. means for controlling the spark discharges to the plate bank in accordance with picture signals so that they occur at selected times in the scan; and
- e. means for dissipating excess spark energy over that which is required to create image points having desired diameters, thereby forming an array of the image points on the printing surface that corresponds to the picture represented by the picture signals.
- 7. A lithographic plate having at least one surface alterable by spark discharges to the plate to thereby change the affinity of said at least one surface for at least one of the group consisting of water and ink, wherein said plate comprises a highly electroconductive thin metal layer and an electroconductive sheet thereunder, whose volume resistivity is at least 0.5 ohm-cm.
- 8. The plate of claim 7 wherein the volume resistivity of the conductive sheet is no greater than 1000 ohm-cm.
- 9. The plate of claim 7 wherein said metal layer is selected from the group consisting of aluminum and copper.
- 10. The plate of claim 9 wherein the volume resistivity of the conductive sheet is no greater than 1000 ohm-cm.
- 11. The plate of claim 7 wherein the surface is altered by removal of the thin metal layer by the spark discharges at each image point.
- 12. The plate of claim 11 further comprising a layer of silicone or a fluoropolymer overlying the thin metal layer.
- 13. The plate of claim 7 wherein the surface is altered by removal of the thin metal layer by the spark discharges.
- 14. The plate of claim 13 further comprising a layer of silicone or a fluoropolymer overlying the thin metal layer.
Parent Case Info
This application is a continuation of Ser. No. 410,295 filed 9-21-89, now abandoned, which is a continuation-in-part of Ser. No. 07/234,475 now U.S. Pat. No. 4,911,075.
US Referenced Citations (11)
Foreign Referenced Citations (4)
Number |
Date |
Country |
130028 |
Jan 1985 |
EPX |
0200488 |
Dec 1986 |
EPX |
938220 |
Mar 1948 |
FRX |
458074 |
Aug 1968 |
SEX |
Non-Patent Literature Citations (1)
Entry |
Hartsuch, Paul J.; Ph.D., Chemistry for the Graphic Art, Graphic Art Techical Foundation; 1979, pp. 165-173. |
Continuations (1)
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Number |
Date |
Country |
Parent |
410295 |
Sep 1989 |
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Continuation in Parts (1)
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Number |
Date |
Country |
Parent |
234475 |
Aug 1988 |
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