Method of manufacturing an engraved plate

1. A method of engraving a plate for intaglio printing of sheets carrying a pattern of rows and columns of security papers, comprising the steps of

generating on a computer at least one original depth-map consisting of a three-dimensional raster image of at least a part of one of said security papers;

generating a master depth-map of the plate to be engraved, which master depth-map consists of three-dimensional pixel data and provides for multiple repetitions on the plate of said at least one original depth-map according to a pattern of rows and columns corresponding to the security papers to be printed on said sheets of security papers, wherein said master depth-map is generated by taking into account information necessary for compensating for sheet distortion created during the intaglio printing process; and

controlling a computer-controlled engraving tool to engrave the plate according to the three-dimensional pixel data of said master depth-map, whereby the plate is engraved pixel by pixel by performing a plurality of elementary three-dimensional engraving steps each corresponding to a pixel of said three-dimensional pixel data.

2. The method as claimed in claim 1 , wherein said three-dimensional raster image is generated by processing at least one three-dimensional element selected from:

a) three-dimensional line patterns

b) three-dimensional raster patterns

c) three-dimensional elements composed of flat areas

d) three-dimensional scans of low relief

and combinations thereof.

3. The method as claimed in claim 2 , wherein said three-dimensional elements include lines and wherein a depth of said lines is selected to have a determined profile for each line or for any group of lines.

4. The method as claimed in claim 3 , wherein said line profile is selected from the group comprising V-shaped, U-shaped and square-shaped profiles.

5. The method according to claim 1 , wherein generation of said original depth-map includes generation of three-dimensional elements of different types and assembly of said three-dimensional elements into one or more computer files.

6. The method according to claim 1 , wherein said master depth-map is generated in-flight during engraving.

7. The method according to claim 1 , wherein said plate is a precursor of an intaglio printing plate.

8. The method according to claim 7 , wherein said plate is a polymer plate.

9. The method according to claim 8 , wherein said plate serves as precursor of a nickel-alto plate.

10. The method according to claim 8 , wherein said polymer plate is constituted of a layered structure comprising a polymer layer which is engraved, an adhesive layer, and a metallic base plate.

11. The method according to claim 10 , wherein said polymer layer is a polyimide containing dispersed carbon black.

12. The method according to claim 1 , wherein said engraving tool is a laser engraving machine.

13. The method according to claim 1 , wherein said engraving tool is an excimer laser or a YAG-laser.

14. The method according to claim 1 , wherein a resolution of said three-dimensional raster image is of 8000 dpi.

15. A method of engraving a plate for intaglio printing of sheets carrying a pattern of rows and columns of security papers, comprising the steps of

generating on a computer at least one original depth-map consisting of a three-dimensional raster image of at least a part of one of said security papers;

generating a master depth-map of the plate to be engraved, which master depth-map consists of three-dimensional pixel data and provides for multiple repetitions on the plate of said at least one original depth-map according to a pattern of rows and columns corresponding to the security papers to be printed on said sheets of security papers; and

controlling a computer-controlled engraving tool to engrave the plate according to the three-dimensional pixel data of said master depth-map, whereby the plate is engraved pixel by pixel by performing a plurality of elementary three-dimensional engraving steps each corresponding to a pixel of said three-dimensional pixel data.

16. A method of producing an intaglio printing plate for intaglio printing of sheets carrying a pattern of rows and columns of security papers, comprising the steps of

generating on a computer at least one original depth-map consisting of a three-dimensional raster image of at least a part of one of said security papers;

generating a master depth-map of a precursor plate to be engraved, which master depth-map consists of three-dimensional pixel data and provides for multiple repetitions on the precursor plate of said at least one original depth-map according to a pattern of rows and columns corresponding to the security papers to be printed on said sheets of security papers;

controlling a computer-controlled engraving tool to engrave the precursor plate according to the three-dimensional pixel data of said master depth-map, whereby the precursor plate is engraved pixel by pixel by performing a plurality of elementary three-dimensional engraving steps each corresponding to a pixel of said three-dimensional pixel data; and

producing an intaglio printing plate from said precursor plate.

17. The method according to claim 16 , wherein said precursor plate is a polymer plate.

18. The method according to claim 16 , wherein said precursor plate serves as precursor of a nickel-alto plate.

19. The method according to claim 17 , wherein said polymer plate is constituted of a layered structure comprising a polymer layer which is engraved, an adhesive layer, and a metallic base plate.

20. The method according to claim 19 , wherein said polymer layer is a polyimide containing dispersed carbon black.

21. A method of engraving a plate for intaglio printing of sheets carrying a pattern of rows and columns of security papers, comprising the steps of

generating on a computer at least one original depth-map consisting of a three-dimensional raster image of at least a part of one of said security papers;

generating a master depth-map of the plate to be engraved, which master depth-map consists of three-dimensional pixel data and provides for multiple repetitions on the plate of said at least one original depth-map according to a pattern of rows and columns corresponding to the security papers to be printed on said sheets of security papers; and

controlling a computer-controlled laser engraving tool to engrave the plate according to the three-dimensional pixel data of said master depth-map, whereby the plate is laser-engraved pixel by pixel by performing a plurality of elementary three-dimensional engraving steps each corresponding to a pixel of said three-dimensional pixel data.

22. The method according to claim 21 , wherein said laser engraving tool is an excimer laser or a YAG-laser.