Security paper

1. Security paper comprising a security zone for providing protection against mechanical falsification, said security zone extending over a portion only of the security paper and comprising a set of cells formed by indentations in the paper and interconnected by indented link portions, the thickness of the paper being substantially uniform throughout an area of said security zone that is complementary to the cells and to the link portions.

2. Paper according to claim 1 , wherein the security zone comprises 1 to 20 cells per cm 2 .

3. Paper according to claim 1 , wherein the area occupied by the cells and the link portions constitutes at least 50% of the total area of the security zone.

4. Paper according to claim 1 , wherein the depth of the cells lies in the range 50% to 90% of the maximum thickness of the paper around the cells in the security zone.

5. Paper according to claim 1 , wherein the cells are of substantially the same depth with each other.

6. Paper according to claim 1 , wherein the cells are distributed in a regular array.

7. Paper according to claim 1 , wherein the cells and the link portions constitute pale zones in the paper when observed in transmitted light prior to printing, said pale zones being outlined by dark zones.

8. Paper according to claim 7 , wherein the pale zones and the dark zones define a half-tone image.

9. Paper according to claim 8 , wherein the half-tone image presents a screen of spots constituted by lines.

10. Paper according to claim 7 , wherein the pale zones are not disjoint.

11. Paper according to claim 1 wherein the security zone is printed so that the ink is deposited in bottoms of the cells.

12. Paper according to claim 11 , wherein the printing is laser printing.

13. Paper according to claim 1 , wherein the security zone comprises 2 to 10 cells per cm 2 .

14. Paper according to claim 1 , wherein the depth of the cells lies in the range of 70% to 80% of the maximum thickness of the paper around the cells in the security zone.

15. Paper according to claim 1 , comprising a single layer of paper.

16. A method of making a sheet of paper having a security zone for providing protection against mechanical falsification and extending over a portion only of the security paper, comprising providing a wire for use during a wet stage of paper-making with a set of masks configured for creating a set of cells formed in the thickness of the paper in a zone of the paper that lies in register with the masks while the paper is being made, and link portions interconnecting the cells.

17. Security paper comprising a security zone for providing protection against mechanical falsification, said security zone extending over a portion only of the security paper and comprising a set of cells formed by indentations in the paper, the cells being distributed in a regular bidimensional array.

18. Paper according to claim 17 , wherein the cells are interconnected by indented link portions.

19. Paper according to claim 18 , wherein the thickness of the paper is substantially uniform throughout an area of the security zone that is complementary to the cells and to the link portions.

20. Paper according to claim 18 , wherein the cells and link portions constitute pale zones in the paper when observed in transmitted light prior to printing, said pale zones being outlined by dark zones.

21. Paper according to claim 20 , wherein the pale zones and the dark zones define a half-tone image.

22. Paper according to claim 21 wherein the half-tone image presents a screen of spots constituted by lines.

23. Paper according to claim 20 , wherein the pale zones are not disjoint.

24. Paper according to claim 17 , wherein the security zone comprises 1 to 20 cells per cm 2 .

25. Paper according to claim 17 , comprising a single layer of paper.

26. Security paper comprising a security zone for providing protection against mechanical falsification, said security zone extending over a portion only of the security paper and comprising a set of cells formed by indentations in the paper, the security zone being printed so that ink is deposited in bottoms of the cells.

27. Paper according to claim 26 , wherein the cells are interconnected by indented link portions.

28. Paper according to claim 27 , wherein the thickness of the paper is substantially uniform throughout an area of the security zone that is complementary to the cells and to the link portions.

29. Paper according to claim 26 , wherein the printing is laser printing.

30. Paper according to claim 26 , comprising a single layer of paper.

31. A method of making a sheet of paper having a security zone for providing protection against mechanical falsification and extending over a portion only of the security paper, comprising providing a wire for use during a wet stage of paper-making with a set of masks configured for creating a set of cells formed in the thickness of the paper in a zone of the paper that lies in register with the masks while the paper is being made, the set of cells being distributed in a bidimensional regular array.

32. A method of making a sheet of paper having a security zone for providing protection against mechanical falsification and extending over a portion only of the security paper, comprising providing a wire for use during a wet stage of paper-making with a set of masks configured for creating a set of cells formed in the thickness of the paper in a zone of the paper that lies in register with the masks while the paper is being made, the method further comprising the step consisting in printing the security zone so that the ink is deposited in bottoms of the cells.