IN LINE MANUFACTURING OF DOCUMENTS WITH SECURITY ELEMENTS

Abstract

A method and apparatus for in-line manufacture of a security document with a structured security element is provided in which a continuous web of document substrate is fed through a series of processing stations. The processing stations include a station for forming a structured security element in a radiation sensitive coating applied to the document substrate, and at least one station for applying at least one additional layer to the document substrate excluding the security element area. In a security document manufactured with the method or apparatus, the additional layer or layers have a combined thickness which is preferably substantially equal to the height of the structured security element or which differs from the height of the structured security element by a predetermined amount.

Claims

1. A method of manufacturing a security document with a structured security element, the method comprising: (a) providing a document substrate having a first surface on one side and a second surface on the opposite side; (b) applying a radiation sensitive coating to a security element area on the first surface of the document substrate; (c) forming a structured security element in the radiation sensitive coating, the security element having a structure extending to a height from the first surface; (d) applying one or more additional layers to the first surface of the substrate, excluding the security element area; (e) wherein the one or more additional layers have a combined thickness which differs from the height of the security element structure by less than 50% of the height of the security element structure and/or by less than 10 m.

2. A method according to claim 1, wherein the combined thickness of the additional layer or layers is substantially equal to the height of the security element structure or wherein the combined thickness of the additional layer or layers differs from the height of the security element structure by less than 20%, more preferably less than 15%, and even more preferably less than 10% of the height of the security element structure, or wherein the combined thickness of the additional layer or layers differs from the height of the security element structure by less than 5 m.

3. A method according to claim 1, further including: providing the document substrate as a continuous web; and feeding the web through a series of processing stations in a machine direction for application of the radiation sensitive coating, for forming the security element structure in the radiation sensitive coating; and for application of the one or more additional layers such that the continuous web with the security element and the additional layers is collected downstream of the roller assemblies in a substantially cylindrical roll.

4. A method according to claim 1, wherein the radiation sensitive coating is applied by a printing process, such as flexographic printing, gravure printing, intaglio printing or silkscreen printing.

5. A method according to claim 1, wherein the radiation sensitive coating is an embossable, curable coating which is embossed and cured to form a security element with a relief structure, and preferably the embossable, curable coating is a radiation-curable coating, more preferably a UV-curable coating.

6. A method according to claim 5, wherein the security element is an optically variable device (OVD) selected from a lens or other focusing structure, an array of focusing elements and/or a diffractive structure.

7. A method according to claim 1, wherein the radiation sensitive coating is a photo-sensitive coating, such as a photo-polymer, which is irradiated with radiation of a suitable range of wavelengths to form the security element structure, and preferably the security element structure is a volume hologram, a polarising device and/or a liquid crystal device.

8. A method according to claim 1, wherein the first surface of the document substrate is subjected to an adhesion promoting process prior to the application of the radiation sensitive coating, and preferably by applying an adhesion promoting layer or a primer layer to the first surface of the document substrate prior to the application of the radiation sensitive coating.

9. A method according to claim 1, wherein a protective coating is applied to the security element structure.

10. Apparatus for manufacturing a security document with a structured security element comprising a series of processing stations including: a substrate feeding station for feeding a continuous web of document substrate having a first surface on one side and a second surface on the opposite side; a station for applying a radiation sensitive coating to a security element area on the first surface of the document substrate; a security element forming station for forming a structured security element in the radiation sensitive coating, the security element comprising a structure extending to a height from the first surface; a station for applying one or more additional layers to the first surface of the substrate, excluding the security element area, wherein the one or more additional layers have a combined thickness which differs from the height of the security element structure by less than 50% of the height of the security element structure and/or by less than 10 m.

11. Apparatus according to claim 10, wherein the radiation sensitive coating is an embossable, curable coating and the security element forming station includes an embossing station for embossing the radiation sensitive coating to form security element having a relief structure, such as a lens or other focusing structure, an array of focusing elements and/or a diffractive structure, and the security element forming station includes a curing station for curing the embossed radiation sensitive coating.

12. Apparatus according to claim 10, wherein the radiation sensitive coating is a photo-sensitive coating, such as a photo-polymer, and the security element forming station includes means for irradiating the radiation sensitive coating with patterned radiation.

13. Apparatus according to claim 10 further including an adhesion promoting station for subjecting the substrate to an adhesion promoting process prior to the application of the radiation sensitive coating, and preferably the adhesion promoting station includes means for applying an adhesion promoting layer or a primer layer to the first surface of the substrate prior to the application of the radiation sensitive coating.

14. Apparatus according to claim 10 further including a coating applying station for applying a protective coating to the security element structure.

15. Apparatus according to claim 10, wherein one or more of the processing stations in the apparatus includes a roller assembly.

16. A security document comprising: a document substrate having a first surface and a second surface; a structured security element positioned on a security element area of the first surface, the security element having a structure that extends to a height from the first surface; and one or more additional layers on the first surface of the document substrate excluding the security element area; wherein the one or more additional layers have a combined thickness which differs from the height of the security element structure by less than 50% of the height of the security element structure and/or by less than 10 m.

17. A security document according to claim 16, wherein the combined thickness of the additional layer or layers is substantially equal to the height of the security element structure, or wherein the combined thickness of the additional layer or layers differs from the height of the security element structure by less than 20%, more preferably less than 15%, and even more preferably less than 10% of the height of the security element structure, or wherein the combined thickness of the additional layer or layers differs from the height of the security element by less than 5 m.

18. A security document according to claim 16, wherein the security element structure comprises at least one focusing element, and the at least one focusing element is selected from: an array of microlenses, diffractive lenses, Fresnel lenses and zone plates; or an array of cylindrical or part cylindrical lenses; or a microlens array in which the lens structure are spherical, part-spherical or aspherical microlenses.

19. A security document according to claim 16, wherein the security element comprises a diffractive structure, such as a diffraction grating, a hologram or a volume hologram, or wherein the security element comprises a polarising device and/or a liquid crystal device.

20. A security document according to claim 16, or claim 17 wherein the document substrate is formed from a transparent or translucent polymeric material, such as biaxially oriented polypropylene, and wherein the additional layer or layers applied to the first surface of the substrate are opacifying layers which are omitted in the security element area to form a window of half window area that contains the security element, the opacifying layers comprising opacifying coatings of ink which are applied in a printing process, or layers of a substantially opaque material, such as paper or opaque plastics material that is laminated or otherwise secured to the substrate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0066] The invention will now be described by way of example only with reference to the accompanying drawings, in which:

[0067] FIG. 1 is a schematic representation of apparatus for in line manufacturing of a security document with a security element structure;

[0068] FIG. 2 is a schematic cross-section of a security document with a security element structure in the form of a lens-based security device;

[0069] FIG. 3 is a schematic cross-section of a security document with a security element structure in the form of a volume hologram; and

[0070] FIG. 4 is a schematic cross section of a modified security document with a security element structure in the form of a volume hologram.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0071] Referring to FIG. 1, apparatus 27 for in line manufacture of the security documents is schematically shown. A continuous web of translucent or transparent material such as polypropylene, PET or the like is subject to an adhesion promoting process at a first processing station 2 including a roller assembly. Suitable adhesion promoting processes are flame treatment, corona discharge treatment, plasma treatment or similar. The adhesion promoting process raises the surface energy of the security document substrate 1 such that the energy of a first surface 11 (see FIG. 2) is more than 5 and preferably more than 10 dynes greater than that of an adhesion promoting layer that is next applied to the first surface 11 of the document substrate 1.

[0072] An adhesion promoting layer 28 is applied at a second processing station 3 including a roller assembly. A suitable adhesion promoting layer is one specifically adapted for the promotion of adhesion of UV curable coatings to polymeric surfaces. The adhesion promoting layer may have a UV curing layer, a solvent-based layer, a water-based layer or any combination of these. Preferably, the adhesion promoting layer has a primer layer that typically includes a polyethylene ionine. The primer layer may also include a cross linker, for example a multifunctional isocyanate. Examples of suitable primers for use with the present invention include: hydroxyl terminated polymers; hydroxyl terminated polyester based co-polymers; cross-lined or uncross-linked hydroxylated acrylates; polyurethanes; and UV curing anionic or cationic acrylates. Examples of suitable cross-linkers include: isocyanates; polyaziridines; zirconium complexes; aluminium acetylacetone; melamines; and carbodi-imides.

[0073] The type of primer is selected to best suit the radiation sensitive coating for forming the security element. The selected primer should not substantially affect the optical properties of the security element 17; 37 (FIGS. 2 and 3) that is eventually formed.

[0074] At a third processing station 4, which also includes a roller assembly, the radiation sensitive coating, is applied to the dried surface of the adhesion promoting layer 28. The radiation sensitive coating can be applied via flexographic printing, gravure printing or a silk screen printing process.

[0075] The radiation sensitive coating is only applied to the security element area 22 (see FIGS. 2 and 3) on the first surface 11 where the OVD 16 is to be positioned. The security element area 22 can take the form of a stripe, a discrete patch in the form of a simple geometric shape or in the form of a more complex graphical design.

[0076] While the radiation sensitive coating is still liquid, it is processed to form the security element structures 17; 37 (shown in FIGS. 2 and 3) at a fourth processing station 5.

[0077] In one embodiment, processing station 5 includes an embossing roller 6. Embossing roller 6 has a cylindrical embossing surface 23 for embossing an security element structure, such as a lens structure 17 (FIG. 2) into a radiation sensitive coating in the form of a UV curable ink. The cylindrical embossing surface 23 has surface relief formations corresponding to the shape of the security element structure to be formed. In one embodiment, the surface relief formations can orient microlenses 17 in the machine direction, transverse to the machine direction, or in multiple directions at any angle to the machine direction. The microlenses 17 may be cylindrical, part-cylindrical, spherical, part-spherical, aspherical or an alternative design, or indeed a combination of various types of microlens structures. Alternatively, the cylindrical embossing surface 23 of the embossing roller 6 may have surface relief formations for embossing a diffractive structure, or other embossed OVD structure, into the UV curable ink.

[0078] The cylindrical embossing surface 23 of the embossing roller 6 may have a repeating pattern of surface relief formations or the relief structure formations may be localised to individual shapes corresponding to the shape of the security element area 22 on the document substrate 1. The embossing roller 6 may have the surface relief formations formed by a diamond stylus of appropriate cross section, or the surface relief formations may be provided by at least one metal shim provided on the embossing roller 6. The at least one metal shim may be attached via adhesive tape, magnetic tape, clamps or other appropriate mounting techniques.

[0079] The UV curable ink on the substrate is brought into intimate contact with the cylindrical embossing surface 23 of the embossing roller 6 by a UV roller 24 at processing station 5 such that the liquid UV curable ink flows into the surface relief formations of the cylindrical embossing surface 23. At this stage, the UV curable ink is exposed to UV radiation transmitted though the substrate layer 1. The UV radiation may be transmitted through the surface of the UV roller 24. The UV roller 24 preferably has internal UV lamps and a roller surface that is UV transparent in at least some areas.

[0080] By careful selection of the UV curable materials and/or the radiation source it is possible to create the security element structure at a later stage of the in line manufacturing process. The radiation intensity must be sufficient to penetrate all layers between the UV curable ink and the radiation source. For example, it is possible to use E-beam curing or metal doped microwave discharge lamps as the radiation source. Alternatively, the UV curable ink may include a photo initiator that is tuned to absorb the emissions from an appropriate light source.

[0081] The UV cylinder 24 and the embossing cylinder 6 may use a registration device to accurately register the radiation sensitive coating with the security element area 22 on the document substrate 1. A suitable method for accurate registration of the embossing cylinder with the radiation sensitive coating in the designated security element area 22 on the substrate 1 is described in greater detail in WO 2008/031170 to the present applicant.

[0082] With the security element structure 17 applied to the document substrate 1, one or more additional layers are applied at a downstream processing station including further roller assemblies 25 and 26. The additional layers may be clear or pigmented coatings and applied as a partial coating, as a contiguous coating or a combination of both. In one preferred method, the additional layers are opacifying layers which are applied to one or both surfaces of the substrate 1 except in the region of the security element structure.

[0083] FIG. 2 schematically shows a security document 10 formed with an embossed security element structure 17 in the form of a lens structure having an array of microlenses manufactured in accordance with the method of the invention. The security document comprises a transparent substrate of polymeric material, preferably biaxially oriented polypropylene (BOPP), having a first surface 11 and a second surface 12. Opacifying layers 13, 14 and 15 are applied to the first surface having a combined total thickness T. The opacifying layers are omitted in a window area 16 where the security element structure 17 is applied to the first surface 11. The microlenses of the embossed security element structure 17 have a height H.

[0084] In a preferred embodiment, the combined thickness T of the opacifying layers 13, 14 and 15 is preferably substantially equal to the height H of the security element structure 17. Where there is any difference between the height H of the embossed security element structure 17 and the combined thickness T of the opacifying layers 13, 14 and 15, the difference is less than 50%, preferably less than 20%, more preferably less than 15%, and even more preferably less than 10% of the height of the security element structure. The difference is preferably less than 10 m. In a particularly preferred embodiment, the difference is less than 5 m.

[0085] As shown in FIG. 2, opacifying layers 20, 21 applied to the second surface 12 on the opposite side of the substrate 1 are omitted in a window area 19. The window area 19 substantially coincides with the window area 16 on the first surface. The window area 19 shown in FIG. 2 is smaller than the window area 16, though it will be appreciated that the relative sizes and locations of the window areas 16 and 19 may be changed. In one preferred embodiment, the window areas are of the same size.

[0086] A printed layer 18 may be applied to the second surface 12 on the opposite side of the substrate in the window area 19. The printed layer 19 may form an image or images viewable through the security element structure 17. When the embossed security element structure is an array of microlenses, the printed area 19 may include a corresponding array of microimages.

[0087] In an alternative embodiment, the radiation sensitive coating may be a photosensitive polymer, with a radiation source provided at the processing station 5 for irradiating the radiation sensitive coating with patterned radiation to form an security element structure 37 (see FIG. 3) in the radiation sensitive coating. In this case, the security element structure may comprise a volume hologram, a polarising device or a liquid crystal device.

[0088] FIG. 3 shows a security document 30 comprising a transparent polymeric substrate 1 with a security element structure 37, such as a volume hologram, a polarising device or a liquid crystal device, formed in a radiation sensitive coating 31 applied to the first surface 11 of the substrate. An optional protective coating 35 is applied over the security element structure 37. The security element structure 37, including the optional protective coating 31, has a height H, which may typically range from about 10 m to about 30 m. At least one opacifying layer 32 is applied to the first surface 11 except in a window area 36 where the radiation sensitive coating 31 forming the security element 37 is applied to the first surface 11. Although only one opacifying layer 32 is shown in FIG. 3, it will be appreciated that two or more opacifying layers may be applied to the first surface as described with reference to FIG. 2. The at least one opacifying layer 32 has a thickness T.

[0089] In a preferred embodiment, the thickness T of the opacifying layer(s) 32 is preferably substantially equal to the height H of the security element structure 37 including any protective coating 35. Where there is any difference between the height H of the security element structure 37 and the thickness T of the opacifying layer(s) 32, the difference is less than 50%, preferably less than 20%, more preferably less than 15%, and even more preferably less than 10% of the height of the security element structure. The difference is preferably less than 10 m. In a particularly preferred embodiment, the difference is less than 5 m.

[0090] As shown in FIG. 3, at least one opacifying layer 34 is applied to the second surface 12 on the opposite side of the substrate 1 to completely cover the second surface 12 so that the security element structure is provided in a half-window.

[0091] FIG. 4 shows a modified embodiment similar to that of FIG. 3 and corresponding reference numerals have been applied to corresponding parts. The embodiment of FIG. 4 differs from that of FIG. 3 in that the at least one opacifying layer 34 is omitted in a window area 39. The window area 39 substantially coincides with the window area 36 on the first surface. The window area 39 shown in FIG. 4 is the same size as the window area 16, though it will be appreciated that the relative sizes and locations of the window areas 16 and 19 may be changed.

[0092] Keeping any difference between the combined thickness T of the one or more additional layers 13, 14, 15; 32 and the height H of the security element structure to less than 50%, preferably less than 20%, more preferably less than 15%, and even more preferably less than 10%, of H, and less than 10 m, more preferably less than 5 m, substantially reduces the localised thickness increase of the security element structure, and allows the continuous web of documents 10 to be wound onto a collection roller. Collecting the documents 10 in a substantially cylindrical roll avoids the pressure blocking and other web tension problems normally associated with the in line manufacture of documents authenticated with security element structures such as lens-based devices and volume holgrams. Similarly, security documents according to the invention can form a stack of separate sheets and maintain a substantially flat profile. This makes sheet feed systems less problematic and avoids the need to rotate equal portions of the stack by 180.

[0093] Workers in this field will appreciate that localised thickness decreases, or recesses, in the document do not present the same drawbacks as an area of increased thickness or height. As shown in FIGS. 2 and 4, the corresponding region 19; 39 opposite the security element structure 16 has a window area 39 formed by the opacifying layer(s) 20, 21; 34 being omitted in the region of the security element structure. This window area 39 is relatively small compared to the overall security document. Stacking documents with localised recesses will not result in wedge-shaped stacks; merely small voids within the stack that are inconsequential in sheet feed systems or in line manufacturing processes. In addition, security documents manufactured in accordance with the invention also allow for more efficient stacking of the finished security documents in cash machines and cash processing machines with less need for manual intervention.

[0094] A skilled addressee will readily recognise many variations and modifications to the described embodiments, which do not depart from the spirit and scope of the broad inventive concept.