Volume Holograms for Security Documents

1 .- 30 . (canceled)

31 . A method for producing a security document comprising a volume hologram, including the steps of:

a) applying an optically sensitive material onto a first surface of a substrate in a first region of the first surface; and

b) irradiating the optically sensitive material with patterned radiation configured for recording a volume hologram within the optically sensitive material.

32 . A method as claimed in claim 31 , where the optically sensitive material is applied using a printing and/or embossing process.

33 . A method as claimed in claim 31 , including the further step of applying a protective coating to an outwards facing surface of the optically sensitive material.

34 . A method as claimed in claim 33 , wherein the protective coating is applied after the irradiation of the optically sensitive material with patterned light.

35 . A method as claimed in claim 31 , wherein the substrate is formed from a polymeric material, preferably biaxially oriented polypropylene.

36 . A method as claimed in claim 31 , wherein the optically sensitive material is a printable photopolymer.

37 . A method as claimed in claim 31 , wherein once applied, the optically sensitive material includes a substantially flat outward facing surface.

38 . A method as claimed in claim 31 , wherein once applied, the optically sensitive material includes a non-flat outward facing surface, such that the optical sensitive material provides a further optical effect in addition to providing a volume hologram.

39 . A method as claimed in claim 38 , wherein the outward facing surface is shaped as an arrangement of microlenses or is shaped as a diffraction grating.

40 . A method as claimed in claim 31 , wherein the thickness of the optically sensitive material is not greater than 20 microns, preferably not greater than 10 microns.

41 . A method as claimed in claim 40 , wherein the minimum thickness of the optically sensitive material is sufficient to record a volume hologram.

42 . A method as claimed in claim 31 , including the step of: applying a first opacifying layer to the first surface, the first opacifying layer being omitted in a first window region, wherein the optically sensitive material is located within the first window region.

43 . A method as claimed in claim 42 , wherein the first opacifying layer and the optically sensitive material are applied in registration, such that the first window region is registered with the optically sensitive material.

44 . A method as claimed in claim 42 , including the step of applying a second opacifying layer to a second surface of the substrate.

45 . A method as claimed in claim 44 , wherein the second opacifying layer is configured to partially or entirely cover the optically sensitive material, such that where the second opacifying layer covers the optically sensitive material, the volume hologram is only visible from the first surface.

46 . A method as claimed in claim 44 , wherein the second opacifying layer is omitted in a second window region, wherein the optically sensitive material is visible through the second window region of the second opacifying layer.

47 . A method as claimed in claim 42 , wherein the, or each, opacifying layer is applied after the irradiation with patterned radiation.

48 . A method as claimed in claim 31 , wherein the substrate includes a primer layer, such that the optically sensitive material is applied directly to the primer layer.

49 . A method as claimed in claim 48 , wherein the primer includes a polyethylene imine.

50 . A method as claimed in claim 31 , wherein patterned radiation is provided by one or more lasers.

51 . A method as claimed in claim 50 , wherein the patterned radiation is created at least in part through reflection of laser radiation of an object.

52 . A method as claimed in claim 50 , wherein the patterned radiation is created at least in part through the provision of a master hologram.

53 . A method as claimed in claim 31 , wherein the patterned radiation includes wavelengths selected from one or more of the visible spectrum, infra-red spectrum, and ultra-violet spectrum.

54 . A security document including a substrate having a first opacifying layer applied to a first surface, the first opacifying layer including a first window region in which a volume hologram is located, said volume hologram formed from an optically sensitive material applied to the first surface.

55 . A security document as claimed in claim 54 , wherein the substrate includes a primer layer, and wherein the optically sensitive material is applied directly to the primer layer.

56 . A security document as claimed in claim 54 , wherein the substrate has a second opacifying layer applied to a second side.

57 . A security document as claimed in claim 56 , wherein the second layer partially or entirely covers the volume hologram.

58 . A security document as claimed in claim 66 , wherein the second layer includes a second window region substantially in register with the first window region in which the volume hologram is located, such that the volume hologram is located in a full window of the security document.

59 . A security document produced by the method of claim 31 .

60 . A security document as claimed in claim 54 , wherein the security document is a banknote.