Claims
- 1. Printing apparatus comprising:
- a. a plate cylinder and a printing plate having a printing surface and including an oleophobic layer, a metal layer underlying said oleophobic layer, and an oleophilic layer underlying said metal layer;
- b. a discharge source;
- c. means for mounting said plate to the plate cylinder;
- d. means for exposing the printing surface to discharges between said plate and said discharge source spaced close to said printing surface, said discharge being of sufficient strength to remove said oleophobic and metal layers and expose said oleophilic layer at selected points on the plate;
- e. means for moving the discharge source and plate cylinder relatively to effect a scan of the printing surface by the discharge source; and
- f. means for controlling the discharges in accordance with electronic signals representing an image so that they occur at selected times in the scan, thereby directly producing on the plate an array of image spots which can be inked to make copies of the image represented by the electronic signals.
- 2. The apparatus defined in claim 1 wherein the discharge source is an electrode that produces spark discharges, said discharges carrying current of at least 0.1 amp.
- 3. The apparatus defined in claim 1 wherein the discharge source is an electrode that produces spark discharges having potentials that exceed 2000 volts.
- 4. The apparatus defined in claim 3 wherein the potential is established by applying a positive voltage to the electrode relative to the plate.
- 5. The apparatus defined in claim 3 wherein the potential is established by applying a negative voltage to the electrode relative to the plate.
- 6. The apparatus defined in claim 1 wherein the discharge source is an electrode that produces spark discharges having potentials sufficient to cause substantially straight-line travel of said discharges from said electrode to said printing surface.
- 7. The apparatus defined in claim 1 and further comprising means for varying a characteristic selected from the group consisting of voltage, current, time duration and number of said discharges for varying the sizes of the spots produced by said discharges.
- 8. Apparatus for imaging a lithographic plate, said apparatus comprising:
- a. a lithographic plate having a printing surface and including an oleophobic layer, a metal layer underlying said oleophobic layer, and an oleophilic layer underlying said metal layer, and means for supporting said lithographic plate;
- b. at least one spark-discharge source, each of which includes an electrode;
- c. means for positioning the source close to the printing surface; and
- d. means for delivering high-voltage pulses in excess of 2000 volts to each electrode to produce spark discharged substantially perpendicular to the printing surface without contacting the printing surface with the spark-discharge source, said discharges being of sufficient strength to remove said oleophobic and metal layers at the selected points, thereby exposing said oleophilic layer.
- 9. The apparatus defined in claim 8 wherein the spark discharges carry current of at least 0.1 amp.
- 10. The apparatus defined in claim 8 wherein the potential is established by applying a positive voltage to the electrode relative to the plate.
- 11. The apparatus defined in claim 8 wherein the potential is established by applying a negative voltage to the electrode relative to the plate.
- 12. The apparatus defined in claim 8 wherein the potential of the spark discharge is sufficient to cause substantially straight-line travel of said spark from said electrode to said printing surface.
- 13. The apparatus defined in claim 8 and further comprising means for varying a characteristic selected from the group consisting of voltage, current, time duration and number of said spark discharges for varying the sizes of the spots produced by said discharges.
- 14. A method of imaging on a press including a plate cylinder, said method comprising the steps of:
- a. providing a printing plate having a printing surface and comprising an oleophobic layer, a metal layer underlying said oleophobic layer, and an oleophilic layer underlying said metal layer;
- b. mounting said plate to the plate cylinder;
- c. without contacting said printing surface, exposing the printing surface to discharges between said plate and a discharge source spaced close to said printing surface at selected points thereon to remove said oleophobic and metal layers and expose said oleophilic layer at the selected points on the plate;
- d. moving the discharge source and the plate cylinder relatively to effect a scan of the printing surface by the discharge source; and
- e. controlling the discharges in accordance with electronic signals representing an image so that they occur at selected times in the scan, thereby directly producing on the plate an array of image spots which can be inked to make copies of the image represented by the electronic signals.
- 15. The method defined in claim 14 wherein the discharge source is an electrode that produces spark discharges, said discharges carrying current of at least 0.1 amp.
- 16. The method defined in claim 14 wherein the discharge source is an electrode that produces spark discharges having potentials that exceed 2000 volts.
- 17. The method defined in claim 16 wherein the potential is established by applying a positive voltage to the electrode relative to the plate.
- 18. The method defined in claim 16 wherein the potential is established by applying a negative voltage to the electrode relative to the plate.
- 19. The method defined in claim 14 wherein the discharge source is an electrode that produces spark discharges having potentials sufficient to cause substantially straight-line travel of said discharges from said electrode to said printing surface.
- 20. The method defined in claim 14 and further comprising the step of varying a characteristic selected from the group consisting of voltage, current, time duration and number of said discharges for varying the sizes of the spots produced by said discharges.
- 21. A method of imaging a printing plate, said method comprising the steps of:
- a. providing a printing plate having a printing surface and comprising an oleophobic layer, a metal layer underlying said oleophobic layer, and an oleophilic layer underlying said metal layer;
- b. spacing from the printing surface at least one spark discharge source, each of which includes a writing head comprising an electrode, each writing head being oriented opposite the printing surface; and
- c. delivering high-voltage pulses in excess of 2000 volts to each electrode to produce spark discharges substantially perpendicular to the printing surface without contacting the printing surface with the writing head, said discharges being of sufficient strength to remove said oleophobic and metal layers at selected points, thereby exposing said oleophilic layer at such points.
- 22. The method defined in claim 21 wherein the spark discharges carry current of at least 0.1 amp.
- 23. The method defined in claim 21 wherein the potential difference is established by applying a positive voltage to the electrode relative to the plate.
- 24. The method defined in claim 21 wherein the potential difference is established by applying a negative voltage to the electrode relative to the plate.
- 25. The method defined in claim 21 wherein the potential difference is sufficient to cause substantially straight-line travel of said spark discharge from said writing head to said printing surface.
- 26. The method defined in claim 21 and including the additional step of varying a characteristic selected from the group consisting of voltage, current, time duration and number of said discharges for varying the amount of the oleophobic and metal layers removed by said discharges.
Parent Case Info
This is a division of U.S. Ser. No. 07/639,254, filed Jan. 9, 1991 now U.S. Pat. No. 5,163,368, which is itself a continuation-in-part of U.S. Ser. No. 07/413,172 filed Sep. 27, 1989, now U.S. Pat. No. 5,005,479 (the entire contents of which are hereby incorporated by reference), itself a continuation-in-part of U.S. Ser. No. 07/234,475 filed Aug. 19, 1988, now U.S. Pat. No. 4,911,075.
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Divisions (1)
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Number |
Date |
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Parent |
639254 |
Jan 1991 |
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Continuation in Parts (2)
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Number |
Date |
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Parent |
413172 |
Sep 1989 |
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Parent |
234475 |
Aug 1988 |
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