Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
  • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
  • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
  • B42D25/30—Identification or security features, e.g. for preventing forgery
  • B42D25/328—Diffraction gratings; Holograms
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
  • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
  • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
  • B42D25/40—Manufacture
  • B42D25/405—Marking
  • B42D25/43—Marking by removal of material
  • B42D25/445—Marking by removal of material using chemical means, e.g. etching
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
  • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
  • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
  • B42D25/30—Identification or security features, e.g. for preventing forgery
  • B42D25/324—Reliefs
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
  • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
  • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
  • B42D25/30—Identification or security features, e.g. for preventing forgery
  • B42D25/351—Translucent or partly translucent parts, e.g. windows
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
  • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
  • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
  • B42D25/30—Identification or security features, e.g. for preventing forgery
  • B42D25/36—Identification or security features, e.g. for preventing forgery comprising special materials
  • B42D25/373—Metallic materials
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
  • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
  • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
  • B42D25/40—Manufacture
  • B42D25/405—Marking
  • B42D25/425—Marking by deformation, e.g. embossing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
  • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
  • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
  • B42D25/40—Manufacture
  • B42D25/45—Associating two or more layers

Definitions

• This invention relates to security devices, suitable for establishing the authenticity of objects of value, particularly security documents, and their methods of manufacture.
• the invention relates to security devices incorporating optically variable effect generating relief structures such as holograms and diffraction gratings.
• Optically variable effect generating relief structures such as holograms and diffraction gratings have been used widely over the last few years to impart security to documents of value such as banknotes, credit cards, passports and the like.
• the structure is provided on a transfer foil and then hot stamped from the transfer foil onto the final document substrate.
• An early example of this approach is described in US-A-4728377. More recently, such structures have been used in combination with transparent window features formed in the document substrate to allow the optically variable effect to be viewed through the document.
• the window may take the form of an aperture through one or more layers of the document substrate or may comprise an optically transparent region of the document substrate.
• An example of an optically variable effect generating relief structure located in a window region formed as an aperture in a document is given in CA-C-2163528.
• An example of an optically variable effect generating relief structure located in a window region formed as a transparent region of a document is given in WO-A-2008/031 170.
• Placing a security device in a window has the advantage that the device can be viewed from both sides of the document. As such it is desirable that a secure visual effect is exhibited by both sides of the security device, in order to increase the difficulty of counterfeiting. Examples of devices in which both sides exhibit a secure effect are disclosed in CA-C-2163528, US-A-2005/0104364, US-A- 2007/01 14787, CA-A-2717775, CA-A-261 1 195, EP1972462 and US2003/0175545. However, there is an ever-present need to improve the security level of such devices in order to stay ahead of would-be counterfeiters.
• a method of manufacturing a security device comprising:
• the manufactured device appears to present two different secure visual effects (one visible from each side of the device), in exact register with one another.
• the appearance of the optically variable effect is dictated by the appearance of the formable material, which in preferred embodiments, comprises an optically effective substance (such as a colour tinted embossable lacquer) as will be explained in more detail below.
• the appearance of the optically variable effect appears different, being due to the reflection enhancing material.
• the high degree of registration is achieved by using a pattern defining substance which impedes retention of subsequently applied layers to define those parts of the layered device in which the formable material and any overlaying reflection enhancing material will be retained. It is therefore preferable that the pattern defining substance is applied in register with the relief structure formed in step (d). Moreover, the use of a pattern defining substance in this way has the benefit that each of the steps defining the end locations of the formable material and reflection enhancing material can be performed using similar or the same type of application techniques (e.g. printing or coating) and hence all can be performed in a continuous, in-line process. This further enhances the achievable registration and simplifies the manufacturing process.
• the pattern defining substance could operate according to various different mechanisms, including inhibiting adhesion of the reflection enhancing material to the substrate and/or obstructing deposition of the reflection enhancing material onto the substrate in the first place.
• the pattern defining substance may repel the formable material such that no deposition of the reflection enhancing material occurs in the areas to which the pattern defining substance has been applied. In other cases, there may be some deposition of the formable material in these areas.
• the reflection enhancing material is a metal or alloy, or a material with a refractive index which differs from that of the formable material by at least 0.3, more preferably 0.5 (known as "high refractive index (HRI)” materials).
• suitable metals or alloys include aluminium, copper, nickel, chrome, aluminium-copper allows, silver, gold, etc.
• HRI high refractive index
• suitable HRI materials include zirconium dioxide and zinc sulphide and titanium dioxide.
• the sequence of steps therefore may be (d), (e), (f) or (e), (f), (d) as will be explained in more detail with reference to the examples described below.
• the removing step may be achieved by using a liquid (e.g. a solvent such as water) or gaseous (e.g. air jet) substance).
• a liquid e.g. a solvent such as water
• gaseous e.g. air jet
• the liquid preferably the liquid has the capacity to dissolve the pattern defining substance (e.g. the mask is soluble within the washing liquid) and the formable material is permeable to the washing liquid to enable the washing liquid to reach the pattern defining substance.
• the pattern defining substance comprises a soluble mask, such as soluble ink (comprised of an appropriate binder and pigment combination), which does not adhere strongly to the substrate or can be dissolved by application of a solvent (aqueous or otherwise), thereby impeding adhesion of the reflection enhancing material applied thereto to the substrate.
• a washing step may be required and the formable material should enable the solvent to reach the pattern defining substance.
• a suitable soluble mask in the form of a heavily pigmented ink are described in WO-A-9913157.
• the soluble mask is configured such that, when coated with a thin deposited layer of formable material (e.g.
• the pattern defining substance creates small holes or discontinuities in the overlaid lacquer and metal film by virtue of the fact that the lacquer and metal film is not thick enough to continuously over coat the pigment grains in the mask.
• a suitable solvent preferably water
• the solvent enters through these holes, dissolving the pigment such that the overlying metal layer disbands.
• the pigment grain dimensions are preferably greater than the thickness of the lacquer and metal film.
• preferred pigment grain sizes may be in the range of greater than or equal to about 100 nm, and less than 500 nm.
• the formable layer comprises one or more optically effective substances such as a UV-responsive substance or a visible colorant for example.
• the one or more optically effective substance(s) impart a coloured tint to the formable material, which colour is visible under illumination at visible wavelengths. In this way the two different appearances of the device can be checked for without the need for any special illumination.
• colour used herein should be taken to encompass optical effects which are invisible under ambient illumination conditions (i.e. visible illumination wavelengths), and become apparent only under illumination at specific non-visible wavelengths such as UV or IR, as well as colours which are visible in visible light.
• colour encompasses all hues and tones which are visible, including black, grey and silver as well as chromacities such as red, blue, green etc.
• at least partially translucent or transparent indicate that the material in question is substantially clear, with low optical scattering - i.e. items on one side of the material can be seen through it, from the other - but not necessarily colourless. For instance, an at least partially translucent or transparent material may carry a coloured tint.
• the formable material may be at least visually semi-transparent (i.e. transmits wavelengths in the visible range),
• the term "formable” means that any forming technique could be used to provide the relief in the formable material.
• the optically variable effect generating relief structure is formed in the surface of the formable material by embossing or cast-curing, preferably UV cast-curing.
• the formable material may be an embossable or curable material.
• the formable material forms a thin film or a patterned screen as will be explained in more detail below.
• the formable material comprises a thermoplastic polymer, such as an embossing lacquer carried thereon.
• the relief structure may be formed in the surface of the thermoplastic by conventional embossing techniques using heat and pressure, for example.
• the formable material may comprise a curable polymer, preferably a UV-curable polymer.
• the relief could be cast-cured into a coating of UV-curable resin.
• the formable material could comprise a curable thermoplastic polymer (i.e. a thermoplastic polymer with a curing agent added) such that, after embossing, the relief can be fixed by curing.
• the application of radiation can generally be more accurately controlled than that of heat, e.g. through the use of appropriately directed radiation sources and/or masks.
• the first layer may also comprise a formable material such as a thermoplastic polymer, for instance forming part of a substrate web of e.g. polyester, or which may act as a support for the security device as a whole or even for a security document of which the security device will ultimately form part.
• a formable material such as a thermoplastic polymer, for instance forming part of a substrate web of e.g. polyester, or which may act as a support for the security device as a whole or even for a security document of which the security device will ultimately form part.
• the formable material forms a layer with a thickness of between 0.5 and 5 microns, more preferably between 0.5 and 2 microns.
• the relief structure will optionally be present in the first layer underlying the e.g. colour tinted formable material, the two layers being formed simultaneously.
• the layer of formable material is usually thin, for example 0.5-1 micron in order to ensure it is permeable such that the solvent can penetrate it.
• the advantage of additionally forming the relief structure in the underlying first layer is that deeper relief structures can be used such as those with a depth of greater than 1 micron.
• Preferably formable layers are embossed with a die carrying the relief structure, wherein the die advantageously forms part of an embossing roller.
• the embossing roller may preferably carry the relief structure in the form of a repeating pattern. The repeat periodicity is preferably matched to that of the document repeat length and/or width.
• the formable material comprises one or more optically effective substance(s) which are visible only under illumination at selected wavelengths outside the visible spectrum, preferably ultraviolet or infrared wavelengths. This provides for a more covert security feature which can be checked by eye or by machine.
• the formable material comprises one or more optically effective substance(s) which undergo a change in appearance in response to changes in one or more of temperature, pressure, strain or electrical potential.
• thermochromic, piezochromic or electrochromic substances could be used. In each case the varying appearance of the substance may be visible within or outside the visible spectrum, and may change from one to the other.
• the optically effective substance(s) comprise dyes and/or pigments. Dyes are preferred in order to preserve the optical clarity of the layer(s).
• the optically effective substance(s) could be provided uniformly across the formable material. However in some embodiments the complexity of the security device may be further enhanced by arranging one or more of the substances to appear as a pattern.
• the formable material may be a printed layer, preferably formed by gravure printing, flexographic printing or slotted die printing.
• the formable material can be laid down in any desirable form through control of the printing apparatus using well-known printing techniques. Gravure printing is most preferred due to the high resolution that is achievable. Printing techniques enable precise control of the shape or pattern in which the formable material is laid down.
• the formable material could be applied by coating, deposition or transfer techniques.
• the lateral extent of the retained formable material and that of the reflection enhancing layer defines a secure or decorative shape or pattern, preferably a fine line pattern, or an item of information, preferably a number, letter, alphanumerical text, a symbol or a graphic.
• the formable material is registered to the relief structure.
• the location of the formable material is defined by the pattern defining layer being registered to the relief structure. It will be appreciated however that they do not have to be directly superimposed and there could be regions of the formable material without a relief. That is, the pattern defining substance has been laid down in register with the relief structure having the result that the two items will be in substantially the same relative position to one another on each security device made to the same design (e.g. a series of such devices). This increases the difficulty of counterfeiting since a document displaying a different alignment between the optically variable effect and the lateral extent of the reflection enhancing layer and formable material (which will be the same) will be readily distinguished from genuine devices.
• the formable material and the reflection enhancing layer could define any shape or pattern and in preferred examples the reflection enhancing layer (and the second transparent layer, since this will have the same lateral extent) includes at least two laterally offset regions which are visibly discontinuous. This increases the complexity of the device and hence the difficulty of forgery.
• the reflection enhancing layer is substantially opaque such that the formable material cannot be seen therethrough.
• the reflection enhancing layer may be semi-transparent, achieved for example through the use of an extremely thin layer of reflection enhancing material.
• the formable material may be apparent through the reflection enhancing material when the device is viewed in transmitted light.
• the formable material should be substantially hidden by the reflection enhancing material when the device is viewed in reflection through the first transparent layer.
• the apparent colour of the security device viewed from one side may be different depending on whether the device is being viewed in reflected or transmitted light.
• the light reflected by the reflection enhancing layer dominates the appearance of the device and effectively conceals the colour of the formable material behind it such that the device appears to have the colour of the reflection enhancing layer.
• the colour of the formable material When viewed in transmission from the same side, the colour of the formable material will be visible through the reflection enhancing layer, thereby appearing to change the colour of the device.
• the formable material may be applied as a continuous layer in each region of the shape or pattern to be defined.
• the formable material must be permeable to the solvent.
• the formable material may comprise a screened working of discontinuous elements.
• the screen elements would be too small to be individually discerned by the naked eye.
• the reflection enhancing material would by definition be arranged according to the same screen. In this way the optically variable effect may appear semi-transparent from both sides of the device, in reflection and/or transmission. However it should be noted that this configuration will not lead to the additional colour effect described above unless the reflection enhancing layer is also formed sufficiently thinly so as to be intrinsically semi-transparent.
• the reflection enhancing layer is applied in a continuous layer over the relief structure.
• the reflection enhancing layer could be applied in a patterned manner e.g. through the use of a repellent coating applied to selected regions of the relief before application of the reflection enhancing material.
• the reflection enhancing layer may thus be defined by the pattern defining layer which can be patterned in the region of the relief.
• the deposition of the reflection enhancing material can be achieved using any appropriate deposition technique but generally a non-selective deposition technique will be preferred for simplicity. That is, the technique will result in the deposition of a contiguous layer of the reflection enhancing material across the entire area of the substrate which is exposed to the deposition process. In many cases, this will be the entire first surface of the substrate (although this is not essential).
• the reflection enhancing material is deposited by vacuum deposition, suitable techniques including electron beam vapour deposition, vapour deposition from a resistively heated source (e.g. a boat source), pulsed laser vapour deposition, evaporative vapour deposition and sputtering, as well as chemical vapour deposition methods.
• a resistively heated source e.g. a boat source
• pulsed laser vapour deposition e.g. a laser vapour deposition
• evaporative vapour deposition e.g. a boat source
• sputtering e.g. a chemical vapour deposition methods.
• Evaporative vapour deposition techniques from resistively heated or electron beam sources are generally preferred.
• the reflection enhancing layer comprises one or more metals or alloys thereof, preferably copper, aluminium, nickel, chrome or any alloys thereof (e.g. nickel-chrome alloys).
• Metal reflective layers preferably laid down by vacuum deposition (encompassing sputtering, resistive boat evaporation or electron beam evaporation for example), or by chemical vapour deposition, achieve highly specular reflection and hence a very bright replay of the optically variable effect.
• the reflection enhancing layer could comprise any of:
• the reflection enhancing layer follows the contour of the relief structure and preferably has a thickness less than the profile depth of the relief structure.
• typical diffractive relief structures such as holograms may have profile depths of the order of 50 to 500 nm, more often between 80 and 150 nm.
• the reflection enhancing layer preferably has a thickness between 5 and 100 nm.
• a layer of aluminium having a thickness of around 10 to 30 nm is suitable for providing a virtually fully opaque reflective layer.
• the optically variable effect generating relief structure comprises a diffractive device which comprises a structure operating in either the first order of diffraction or zero order diffraction, and which would be categorised as a form of form of DOVID (diffractive optically variable image device) as described in Optical Document Security, 2 nd edition by Van Renesse and includes spatial domain oriented structures, graphical domain oriented structures, pixel domain oriented structures, track oriented structures, vector oriented structures and time domain oriented structures. Examples include a 3D hologram, a KinegramTM or an Exelgram.
• DOVID diffractive optically variable image device
• the optically variable effect generating relief structure may comprise a non-diffractive micro-optical structure such as 1 D and 2D periodic faceted reflective structures (i.e. forms of micro-mirrors).
• Non-diffractive optical structures typically are of much larger dimensions to those mentioned above in relation to holographic devices, with profile depths of between 2 and 50 microns.
• Examples of faceted reflective structures suitable for the current invention include, but are not limited to, a series of parallel linear prisms with planar facets arranged to form a grooved surface, a ruled array of tetrahedra, an array of square pyramids, an array of corner-cube structures, and an array of hexagonal- faced corner-cubes.
• a second preferred type of micro-optical structure is one which functions as a microlens including those that refract light at a suitably curved surface of a homogenous material such as plano-convex lenslets, double convex lenslets, plano-concave lenslets, and double concave lenslets.
• Other suitable micro-optical structures include geometric shapes based on domes, hemispheres, hexagons, squares, cones, stepped structures, cubes, sawtooth structures, faceted structures or combinations thereof.
• step (d) further comprising forming the surface of the first layer in at least one fourth region separate from and optionally adjacent to the at least one third region such that it follows the contours of a second optically effect generating relief structure.
• the reflection enhancing material is preferably also applied over the at least one fourth region. This increases the complexity of the security device with a correspondingly increased degree of security.
• the method further comprising the steps of:
• a third layer which is at least partially translucent or transparent, wherein the third layer comprises one or more optically effective substances which impart a coloured tint to the third layer, which colour is preferably different from the colour of the formable material, and preferably, washing the device to remove any residual reflection enhancing material in areas in which the second layer was not applied.
• a first colour dictated by the colour of the formable material
• the same device may present a second, different colour (dictated by the colour of the third transparent layer), in register with a metallic region.
• the method further comprising the steps of:
• a fourth layer comprising a thermoplastic polymer or a curable polymer, preferably a UV-curable polymer, the fourth layer being at least partially translucent or transparent;
• a fifth layer which is at least a partially translucent or transparent, wherein the fifth layer comprises one or more optically effective substances which impart a coloured tint to the fifth transparent layer, which colour is preferably different from the colour of the formable material, and preferably, removing any residual reflection enhancing material overlaying the fifth layer in areas not covered by the fifth layer.
• Such methods also result in devices which on one side may display a first colour (dictated by the colour of the formable material) in register with a metallic region.
• the same device may present a second, different colour (dictated by the colour of the fifth transparent layer), in register with a metallic region.
• the first layer may take a number of forms depending in part on how the security device is to be incorporated or applied to an object of value.
• the first layer forms an integral part of a substrate, preferably a security document substrate or a security article substrate. If the device is to be formed independently of the security document or other object of value to which it is to be applied, the device preferably further comprises one or more transparent adhesive layers. These may form the outermost layer of the device on either or both sides.
• the security device is formed as a security article
• the security article including the device may be incorporated into or applied to a security document by any conventional technique, such as hot stamping, cold adhesion, laminating, incorporation into paper-making process, etc.
• the security device is preferably arranged to overlap at least partially and preferably fully with a window region of the document which may have a paper or polymer substrate, e.g. an aperture or a transparent portion, which may be formed before or after incorporation of the security device.
• a transferrable structure such as a security thread, transfer foil, or patch may include a carrier releasably attached to the security device.
• Figure 1 is a schematic cross-section of a security article equipped with a security device according to the invention
• Figure 2 is a schematic cross-section of a security article incorporating another security device according to the invention
• Figure 3 is a plan view of the security article of Figure 1 ;
• Figure 4 is a flowchart indicating selected steps of a method for manufacture of a security device according to the invention.
• FIGS. 5a to 5g schematically depict components of a security device at various stages of manufacture
• Figures 6a to 6d schematically depict components of a further security device at various stages of manufacture, the device comprising a colour tinted layer applied as a patterned screen;
• Figures 7a to 7d schematically depict components of a further security device at various stages of manufacture, wherein the steps of forming the relief structure and applying the reflection enhancing material are reversed compared to the method of Figures 5a to 5g;
• FIGS. 8a to 8j schematically depict components of a further security device at various stages of manufacture
• FIGS. 9a to 9k schematically depict components of a further security device at various stages of manufacture
• Figure 10 is a plan view of a security article comprising at least two holograms formed by including relief structures in at least two adjacent regions, according to Figures8j, or 9k for example;
• Figures 1 1 a and 11 b depict an exemplary security document in accordance with the present invention, Figure 1 1 b showing a cross-section along the line XX' in Figure 1 1 a;
• Figures 12a and 12b depict a further exemplary security document incorporating a security device in accordance with the present invention, Figure 12b being a cross-section along line XX' in Figure 12a;
• Figures 13a, 13b and 13c depict a further exemplary security document incorporating a security device in accordance with the present invention, Figures 13b and 13c depicting alternative cross-sections of the security document taken along line XX' in Figure 13a. Description of Embodiments
• the present description will focus on security documents provided with integral security devices having optically variable effect generating relief structures which give rise to diffractive optical effects, such as holograms or diffraction gratings.
• the relief structure may be a non-holographic micro-optical structure, such as a prismatic structure.
• prismatic structures suitable for the security devices of the sort presently disclosed include, but are not limited to, a series of parallel linear prisms with planar facets arranged to form a grooved surface, a ruled array of tetrahedral, an array of square pyramids, an array of corner cube structures, and an array of hexagonal faced corner cubes.
• micro-optical structure is one which functions as a micro lens, including those that refract light at a suitably curved surface of a homogeneous material such as plano-convex lenslets, double-convex lenslets, plano-concave lenslets and double-concave lenslets.
• suitable micro-optical structures include geometric shapes based on domes, hemispheres, hexagons, squares, cones, stepped-structures, cubes or combinations thereof.
• Figure 1 shows a security article 1 such as a transfer foil, security thread, patch, or similar which includes a security device 10 carried on a support layer 2a (here the lower surface, facing observer B).
• the support layer 2a acts as a release sheet or strip from which the device 10 is detached upon application to a security document, in which case the support layer 2a can take any convenient form such as a (opaque, translucent or transparent) polymer or paper web.
• the support layer 2a may be transferred with the security device onto the security document for example when the security device is applied over an aperture in the security document substrate.
• the support layer 2a may for example be an integral part of a security document, e.g. a polymer banknote substrate, or a layer of an identity card. If the support layer 2a is to remain in situ when the device is put in circulation, the support layer 2a should be transparent at least in regions at which the security devices are to be formed.
• the substrate could however be opaque in other regions, e.g. carrying one or more opacifying layers 15 defining window regions 1 1 in which the devices are to be formed, as illustrated in Figure 3 for example.
• a release layer may be provided between the support layer 2a and security device 10 to assist in the detachment of the security device 10 from the support layer 2a upon application of the device 10 to a security document.
• the release layer may comprise a release coat such as a layer of wax or similarapplied to the support layer 2a prior to the application of the other functional layers.
• the security device 10 comprises an at least partially translucent or transparent substrate 2b, such as a polymer film and a coloured tinted layer 3 which is a formable material, such as an embossable lacquer.
• a holographic (or other optically variable) relief structure 4 is formed solely in the colour tinted layer 3 disposed on the substrate 2b across a region F ⁇ .
• the support layer 2a may also be formable and comprise for example a thermoplastic layer such as polyesterpolyethylene teraphthalate (PET), polyethylene, polyamide, polycarbonate, poly(vinylchloride) (PVC), poly(vinylidenechloride) (PVdC), polymethylmethacrylate (PMMA), polyethylene naphthalate (PEN), polystyrene, or polysulphone; or an embossing lacquer layer, such as a PMMA-based resin.
• PET polyesterpolyethylene teraphthalate
• PVC poly(vinylchloride)
• PVdC poly(vinylidenechloride)
• PMMA polymethylmethacrylate
• PEN polyethylene naphthalate
• PEN polystyrene
• polysulphone or an
• the device requires at least one formable layer (2a or 2b) which is not subsequently released as will be explained below in more detail.
• a single formable support layer e.g. 2a
• an additional formable layer e.g. 2b
• forming the relief in the underlying substrate 2b (or support layer 2a) is dependent on the thickness of the colour tinted layer 3.
• the colour tinted layer 3 (and optionally the substrate 2b, as shown in Figure 2) can be formed of any suitable material in which a relief structure 4 can be formed, for example a conventional embossing lacquer such as a thermoplastic polymer or a radiation curable resin.
• the colour tinted layer 3 includes a colorant such as a suitable dye which imparts a tint to the layer 3.
• the tint may or may not be visible to the human eye under illumination at visible wavelengths.
• the colorant could be invisible unless irradiated with selected wavelengths outside the visible spectrum, such as UV or IR, and could be phosphorescent, fluorescent or luminescent.
• the colorant is visible under ambient lighting conditions in order that the colour effect is readily apparent without the need for specialist equipment.
• the relief structure 4 is formed into the colour tinted layer 3 in Figure 1 (as well as in the substrate 2b in Figure 2, depending on the thickness of the colour tinted layer) using an appropriate conventional technique such as embossing under the combined action of heat and pressure, or cast curing, in which the colour tinted layer 3 is coated as a relatively fluid resin onto the support layer 2a and a shaped die applied to the fluid resin having the desired relief shape.
• the resin flows to accommodate the die thereby taking on the desired relief shape and is simultaneously or subsequently hardened, e.g. by curing with radiation such as UV.
• the colour tinted layer 3 typically comprises a single homogenous film of resin.
• a formable substrate 2b may comprise multiple layers including at least a protective coating layer (commonly termed a "scuff layer) which will cover the hologram in use and an embossing layer which is usually of a material which is mechanically softer and/or of lower glass transition temperature than the protective layer.
• a formable substrate 2b is between 1 and 5 microns thick, preferably between 1 and 3 microns thick.
• the colour tinted layer 3 carries a reflection enhancing material 5 such as a metal film (e.g. aluminium or copper).
• the colour tinted layer 3 has been formed so as to follow the contours of surface relief 4 defining an optically variable effect generating structure such as a hologram or diffraction grating (as discussed further above), and the reflection enhancing material 5 follows the contours of the relief.
• an optically variable effect generating structure such as a hologram or diffraction grating (as discussed further above)
• the reflection enhancing material 5 follows the contours of the relief.
• the position tolerance of the colour tinted layer 3 and reflection enhancing material 5 and any other layers may be as low as +/- 100 to 200 microns or exceptionally less from one document to the next.
• the reflection enhancing material may be covered with a protective coating (not shown) which may optionally contain a security substance (e.g. a fluorescent, luminescent or phosphorescent material).
• a security substance e.g. a fluorescent, luminescent or phosphorescent material.
• the security device 10 is visible from both sides of the security article 1 as illustrated by observers A and B.
• Figure 3 shows a plan view of the security document of Figure 1 as viewed by observer B.
• the document 1 has a window 1 1 inside which the security device 10 extends across the region R 3 which here has the form of a sun-shaped symbol.
• the region R 3 may define an alternative indicia such as a letter, number or graphic, and the region R 3 could extend to cover the whole window 1 1 (although this is less preferred).
• the sun-shaped symbol has a metallic appearance, which is dictated by the reflection enhancing material 5.
• observer A sees the same optically variable effect although the content of the hologram will appear reversed (i.e. a mirror image of that seen from the position of observer B) due to the fact that the reverse side of relief 4 is being viewed.
• the colour of the optically variable effect and the device as a whole will appear different from that seen from position B since it will be determined by the colour tinted layer 3 (which is at least semi-transparent) in combination with the reflection enhancing layer 5.i.e a coloured metallic appearance will be observed from position A where the colour is determined by the tint in the formable material.
• Figure 4 is a flowchart depicting selected steps of the method.
• Figures 5a to 5g depict a security device made according to the described method, at various stages of production for cross reference with Figure 4.
• a pattern defining substance 6 is applied to a first surface of a first transparent layer, in this case represented by an embossable substrate 2b on a transparent carrier 2a as shown in Figures 5a and 5b.
• the pattern defining substance 6 is laid down across areas of the substrate in which the colour tinted layer 3 is ultimately not desired, in this case outside of region F ⁇ as shown in Figure 5b.
• the pattern defining substance 6 can comprise any material which impedes adhesion of the colour tinted layer 3 (typically an embossable resin lacquer) to the underlying substrate 2b (and any overlying layers such as a reflection enhancing material 5 in this example).
• the pattern defining substance 6 comprises a soluble mask, such as soluble ink.
• soluble ink is heavily pigmented ink as disclosed in WO- A-99-13157.
• Mechanisms by which soluble masks operate vary but in one example, the pigment grains in the mask are sufficiently large that when a layer of metal or other reflection enhancing material is deposited on top of the ink, holes are formed through the deposited layer. As such, during subsequent washing with a solvent such as water, the fluid can pass through the deposited layer, reaching and dissolving the pigment. This leads to detachment of the colour tinted layer 3 from the substrate in the regions where the soluble mask is present. Further examples of suitable soluble masks are given in US-A- 5142383, US-A-3935334 and EP-A-1023499.
• step S102 colour tinted material 3 is deposited onto the first surface 2a of the substrate 2 to form a layer of colour tinted material 3 which extends over the window F ⁇ defined by the pattern defining substance 6 and neighbouring regions of the substrate, including portions covered by pattern defining substance 6 as shown in Figure 5c.
• the colour tinted layer 3 is applied in region R 2, which second overlaps at least in part the first region in order that the colour tinted layer 3 can be deposited onto and strongly bond to at least part of the substrate 2b.
• the overlapping portions of the first and second regions R 2 define a third region R 3 in which ultimately the formed relief structure 4 is present.
• the third region R 3 in which the relief structure is formed may be coincident with the first region RL but this is not essential.
• the colour tinted layer 3 should be permeable to the solvent.
• the colour tinted layer 3 may be applied as a continuous coating layer as shown in Figure 5b or may be printed in distinct regions.
• the colour tinted material is applied in a patterned screen 30.
• the region of the substrate 2b onto which colour tinted layer 3 is applied i.e. the overlapping parts of regions Ri and R 2 , termed the third region, R 3 ) exhibits the desired optically variable effect.
• an optically variable effect generating relief structure 4 is formed in the surface of the colour tinted layer 3 as shown in Figure 5d.
• the relief structure 4 may additionally be formed into the underlying formable substrate 2b depending on the thickness of the colour tinted layer 3 (an example of which was shown in Figure 2).
• the relief structure 4 may be formed through a conventional embossing process, e.g. involving forming the surface relief 4 (by impressing a cylindrical image forming die (e.g. an embossing roller) into a thermoplastic layer 3 through the combined action of heat and pressure.
• the colour tinted layer 3 could be an embossable lacquer or a cast cure resin.
• the layer 3 may be applied as a viscous liquid coating or film of monomer which is contacted by an image forming die or roller.
• the surface relief 4 is cast into the film by the simultaneous or near simultaneous exposure of the layer 3 to radiation (e.g. UV radiation), causing polymerisation.
• the surface relief 4 is thus set into the layer 3.
• UV curable polymers employing free radical or cationic UV polymerisation are suitable for the UV casting process.
• free radical systems include photo-crosslinkable acrylate-methacrylate or aromatic vinyl oligomeric resins.
• cationic systems include cycloaliphatic epoxides.
• Hybrid polymer systems can also be employed combining both free radical and cationic UV polymerization.
• the colour tinted layer 3 has a relatively low glass transition or softening temperature, e.g. biaxially orientated polypropylene (BOPP) which softens at temperatures around 85°C. Structures embossed into such materials may be vulnerable to damage should the device encounter high temperatures during circulation.
• BOPP biaxially orientated polypropylene
• a reflection enhancing material is applied to the relief 4 to form a reflection enhancing layer 5 (Figure 5e).
• the reflection enhancing layer 5 conforms to the surface relief 4 and this is replicated in the reflection enhancing layer's opposite side, thus rendering the optically variable effect visible from both sides of the device (layer 3 being transparent or semi-transparent).
• the thickness ti of the reflection enhancing layer 5 is preferably less, more preferably substantially less, than the profile depth d of the relief profile 4.
• the relief 4 may have a profile depth d of between 50 and 500 nm, whilst the reflective layer 5 may have a thickness of between 10 and 100 nm, preferably 10 to 30 nm.
• the thickness of the reflection enhancing layer may be kept very thin, e.g. 5 to 10 nm, in order to render it semi-transparent. This provides for the possibility of a further colour effect whereby the apparent colour of the device changes when viewed from the same side in reflected as compared to transmitted light.
• steps S103 forming the relief structure
• S104 applying the reflection enhancing material
• the colour tinted layer 3 may be embossed prior to or after depositing the reflection enhancing material 5.
• the reflection enhancing layer 5 is preferably a metal layer formed of one or more metals and/or alloys, e.g. aluminium, copper, nickel and/or chrome (or any alloy thereof). If desired, two or more metals or alloys could be laid down in a pattern of different regions to collectively form the layer 5, as described in EP-A-1294576.
• the reflection enhancing material could comprise an optical interference thin film structure, a layer containing metallic particles, optically variable particles or optically variable magnetic particles, a photonic crystal layer, or a liquid crystal layer. Materials of this sort not only provide the requisite reflective properties but may impart an additional optical effect to the device, e.g. exhibiting different colours depending on the angle of view.
• the reflection enhancing layer could comprise a multilayer structure of alternating high and low refractive index dielectric layers resulting in an optical interference structure which exhibits different colours when viewed in reflection as compared with when viewed in transmission.
• the reflection enhancing material(s) could be laid down by any appropriate technique but vacuum deposition is preferred. It should be noted that whilst typically the reflection enhancing layer 5 will be applied directly to the first colour tinted layer 3 and therefore will be in contact with the surface of the element in which the relief structure 4 is formed, the reflection enhancing layer 5 could be spaced from that element by an intermediate transparent layer or the like, provided that the intermediate layer is sufficiently thin so that the reflection enhancing layer again follows the surface relief contour. Depending on the nature of pattern defining substance 6, the colour tinted layer 3 (and any overlaying reflection enhancing material 5) may not settle on the pattern defining substance 6.
• a removal step such as washing step S105 (and Figure 5f) may be performed.
• a liquid e.g. water
• a gaseous substance such as an air jet.
• a mechanical action such as vibration may be used as the removal step.
• the liquid preferably the liquid has the capacity to dissolve the pattern defining substance (e.g. the soluble mask is soluble within the washing liquid) and the colour tinted layer 3 is permeable to the liquid to allow it to reach the pattern defining substance 6 underneath it.
• Figures 6a to 6d schematically depict a variation of a method according to the invention wherein a security device 10' is formed using the same technique as described above, except a patterned screen of colour tinted material 30 is applied instead of a continuous layer 3 as described with reference to Figures 5c to 5g above.
• a screen 30 enhances permeability of the colour tinted layer.
• the method steps of Figures 6a to 6d is the same as that described with the Figures 5a to 5g, the detailed description of which is not repeated here.
• the patterned screen of colour tinted material 30 in this example is a thin screen of colour tinted material with a typical thickness of 0.5 to 5 microns, preferably 0.5 to 2 microns.
• the width of the lines or the diameter of the dots forming the screen 30 are preferably in the range 20-200 microns and the spaces between the dots or lines are also in the range 20-200 microns. Accordingly, the dimensions of the screen 30 are such that it is not readily observable with the naked eye.
• the reflection enhancing material 50 is applied over the screen 30 in a similar manner as indicated above.
• Figures 7a to 7d schematically depict components of a further security device 10" at various stages of manufacture, wherein the steps of forming the relief structure (S103) and applying the reflection enhancing material (S104) are reversed compared to the method of Figures 5a to 5g described above.
• the relief structures 4, 40 are formed at the same stage (depicted by Figure 7d), for example with a die carrying the relief structure, wherein the die advantageously forms part of an embossing roller.
• the device as shown in Figure 7d is not preferrable as there is no reflection enhancing layer associated with relief structure 40 therefore the optically variable effect generated by the relief structure will not be readily apparent.
• a further metallised layer may be added to 40 as a later step or the same process may be applied, as shown in Figures 8a-8g, so that both relief structures have a metallised layer.
• Figures 8a to 8j schematically depict components of a further security device 10"' at various stages of manufacture.
• Figures 8a to 8c respectively illustrate the same method steps as Figures 5a to 5c described above.
• the substrate 2b is a formable (e.g. embossable) layer as described above.
• Figure 8d in addition to forming a relief structure 41 in region comprising the colour tinted layer 3, at least a further relief structure 42 is formed in an adjacent region R 5 not comprising the colour tinted layer.
• the relief structures 41 , 42 are formed at the same stage (depicted by Figure 8d), for example by embossing structures 41 and 42 simultaneously.
• structures 41 and 42 are embossed with a die carrying the relief structure, wherein the die advantageously forms part of an embossing roller.
• a reflection enhancing layer 52 such as a metal is applied, preferably by vacuum metallisation (as described above with reference to S104 of Figure 4 for example).
• the reflection enhancing layer 52 respectively conforms to the relief structures 41 and 42.
• the metallisation covers the full area of the device 10"'.
• the layer 22 may in practice be formed of multiple layers laminated to one another, and this applies to all "layers" mentioned throughout this disclosure.
• the second layer 22 is a clear alkali resistant mask printed in register with the coloured lacquer 3 (with a register tolerance achievable by normal printing techniques i.e. +/- 100 microns).
• the thickness of the second transparent layer 22 is 0.5-5 microns and preferably 1 -2 microns.
• the material forming layer 22 is suitable for acting as a etch resist, with the layer 22 protecting the reflection enhancing layer 52 during a subsequent etching step shown in Figure 8j, in which those regions of the reflection enhancing layer 52 which are not covered by the third layer 24 are removed.
• a third layer 24 which is at least partially translucent or transparent is applied over the reflection enhancing layer 23 across a region R 5 (right hand side of the device).
• the third layer 24 is preferably laid down in the form of a decorative or secure shape or pattern, such as letters, numbers, symbols or other indicia, or a shape or fine line pattern.
• the shape or pattern includes at least two visibly discontinuous regions - i.e. areas of the pattern which are sufficiently large and spaced by a sufficient distance that they can be individually distinguished by the naked eye. This increases the complexity and visual impact of the design.
• the third layer 24 can be applied in a contiguous, all-over layer, or could be applied as a screened working - that is, an array of spaced screen elements.
• the dimensions of such a screen are typically sufficiently small that the elements cannot be individually distinguished by the naked eye, and the region appears as if the layer is continuous. Nonetheless, this can be used to make the device semi-transparent since light can be transmitted through the screen.
• Similar materials may be used for layers 22 and 24, for example they may be both etch resists.
• Layer 22 in region R1 may be colour tinted but preferably it is not to contrast with the colour of layer 24 region R5. As shown in Figures 8h-8j, layers 22 and 24 do not follow the relief structure at the outermost surface i.e. the outer surface is flat.
• the material is preferably laid down using a printing technique such as gravure printing.
• a printing technique such as gravure printing.
• other application techniques such as coating, deposition or transfer methods could be used as appropriate.
• the third layer 24 includes an optically effective substance such as a colorant typically in the form of a dye or pigment (a dye is preferred in order to preserve the optical clarity of the layer).
• a colorant typically in the form of a dye or pigment (a dye is preferred in order to preserve the optical clarity of the layer).
• a colorant typically in the form of a dye or pigment (a dye is preferred in order to preserve the optical clarity of the layer).
• Various different types of colorant may be used which may or may not be visible to the human eye under normal illumination conditions.
• the colorant could be visible or detectable only under selected non-visible radiation wavelength such as ultraviolet or infrared.
• the colorant is visible under ambient white light and imparts a coloured tint to the layer 24, e.g. red, blue, green etc.
• a multi-coloured arrangement of transparent materials containing different colorants could be used to form the layer 24.
• one half of the layer 24 may appear red, whilst the other laterally offset half may appear blue, resulting in a visible pattern.
• the entire layer 24 may have the same visible colour, with selected portions thereof additionally carrying a UV or IR active substance.
• the different colours could be arranged in any desired pattern, e.g. defining indicia, or different colours could be used to highlight different regions of the optically variable area. Some individual areas of layer 24 could contain no optically effective substance.
• Patterned arrangements such as this can be achieved by laying down two or more transparent materials, at least one containing an optically effective substance, in registration with one another in accordance with the desired design, e.g. by printing.
• Any of the optically effective substances may if desired be responsive to non- optical stimuli such as temperature, pressure, strain, electrical potential or any combination thereof.
• the substance could be thermochromic, piezochromic or electrochromic, undergoing a change in appearance as the relevant parameter changes.
• the optically effective substance may only be visible or detectable under certain stimulus conditions (e.g. within a certain temperature range).
• the colorant or other optically effective substance is dispersed within a clear material to make up layer 24, such as a polymeric binder or resin.
• a clear material to make up layer 24 such as a polymeric binder or resin.
• Suitable examples include vinyl resins such as UCARTM VMCA Solution Vinyl Resin or UCARTM VCMH Solution Vinyl Resin, both of which are supplied by The Dow Chemical Company and which are carboxy-functional terpolymers comprised of vinyl chloride, vinyl acetate and maleic acid.
• the material forming layer 24 is suitable for acting as a etch resist, with the layer 24 protecting the reflection enhancing layer 52 during a subsequent etching step shown in Figure 8j, in which those regions of the reflection enhancing layer 52 which are not covered by the third layer 24 are removed.
• the reflection enhancing layer 52 is a metal
• this removal step is achieved by immersing the structure in an etchant solution which dissolves or otherwise removes the uncovered metal.
• an etchant solution which dissolves or otherwise removes the uncovered metal.
• sodium hydroxide can be used as the etchant.
• an acidic etchant is typically used, such as (i) a mixture of Hydrochloric acid 50%v and Ferric chloride (40 Baume) 50%v, at room temperature; or (ii) a mixture of Sulphuric acid (66 Baume) 5-10%v and Ferrous sulphate 10Og/litre, at 40 to 60 degrees C.
• Other etchants may also be used such as nitric acid but generally the above systems are the most convenient to work with.
• the third transparent layer 24 preferably has a thickness of t z the order of 0.5 to 5 microns, more preferably 1 to 2 microns. However, the thickness required will depend on the selected materials and etchant. Other techniques such as laser ablation or (reactive) ion etching could be used to remove the uncovered material of the reflection enhancing layer 52 and these may be particularly preferred where the layer is not solely a metal or alloy layer, such as metallic ink or an interference layer structure as mentioned above.
• the second transparent layer would still be used to define the bounds of the area in which the layer is removed.
• the reflection enhancing layer 52 is an interference thin film structure (e.g. metal/dielectric/metal)
• etching techniques may be used for removal in the same manner as a metal reflective layer. In this case, not all the layers of the interference thin film structure may be removed by the etching.
• This further increases the security of the device since such an effect is difficult to reproduce by counterfeiters.
• Figures 9a to 9k depicts an alternative method to the method of Figures 8a to 8j described above for producing a device 10"" with optical effects displayed in front and back colours in register with opposing metallic regions.
• the steps of Figures 9a, 9b, 9c respectively correspond to those of steps 5a, 5b, 5c and 8a,8b,8c described above.
• the method depicted in Figures 9a to 9k differs from the method of Figures 8a to 8j in that the first and second relief structures 43, 44 (on the left and right hand side of the device respectively) are formed in separate relief forming stages, in Figures 9d and 9h, respectively.
• the second relief structure 42 is formed into layer 2b and a third layer 24, typically an alkali resist layer, is subsequently applied and serves to protect the reflection enhancing material 52 from being removed (e.g. etched) by a second removal step (i.e. demetallisation) as described with reference to Figure 8j.
• the second layer 22' (which is at least partially translucent or transparent) is applied throughout all regions of the device 10"'.
• layer 22' is a thermoformable layer (rather than an alkali resist layer as described with reference to Figures 8h to 8j above).
• the thermoformable layer 22' can be formed with a second relief structure 44 ( Figure 9h) at temperature and pressure sufficiently below that of the coloured tinted layer 3, that the relief 43 previously formed into the coloured tinted layer 3 is not degraded.
• a post cure process applied ( Figure 9h) to either the coloured tinted layer 3 after forming the second relief structure 44 the thus elevating its softening temperature to a value where it is not impacted by the first forming of the relief structure 43 (i.e. first embossing phase in Figure 9e).
• a post cure process may be applied after forming the second relief structure 44 (i.e. the embossing of the layer 22') such that in its pre cure phase it has a much lower softening temperature than the colour tinted layer 3 and can be 'soft embossed' and then cured to a more durable state.
• a UV curable layer 22' may be applied as a viscous liquid coating or film of monomer which is contacted by an image forming die or roller.
• the surface relief is cast into the film by the simultaneous or near simultaneous exposure of the layer 22' to radiation (e.g. UV radiation), causing polymerisation.
• UV curable polymers employing free radical or cationic UV polymerisation are suitable for the UV casting process.
• free radical systems include photo-crosslinkable acrylate-methacrylate or aromatic vinyl oligomeric resins.
• cationic systems include cycloaliphatic epoxides.
• Hybrid polymer systems can also be employed combining both free radical and cationic UV polymerization.
• a second reflection enhancing layer 5 is applied, preferably by vacuum metallisation as described above. It will be appreciated that the second reflection enhancing layer 5 may comprise a metal which is may different than the metal applied in the previous step metallisation step (of Figure 9e). The second reflection enhancing layer 5 follows the relief structure 44 and is typically 10-30 nm thick.
• a further layer 26 which is transparent or semi-transparent is applied to protect the reflection enhancing layer 53 above relief structure 44.
• layer 26 is suitable for acting as an etch resist, protecting the second reflection enhancing layer 5 (applied in the step of Figure 9i) during a subsequent etching step shown in Figure 9k, in which those regions of the reflection enhancing layer 5 which are not covered by layer 26 are removed.
• layer 26 is tinted with a colour different to the colour of the formable material applied previously (in the step of Figure 9c) so that the device advantageously displays different colours on the left hand side of the device compared to the right hand side.
• FIG. 10 is a plan view of a security article V comprising at least two holograms formed by including relief structures in at least two regions, according to Figures 8j or 9k described above.
• the device has an additional region R 4 or R 5 as referred to above according to Figures 8j or 9k which appear metallic silver (due to the Al layer) from viewpoint A and purple, for example, from viewpoint B.
• Numeral 50 indicates a region where there is no metal is formed by patterning of the metallisation layer in region R 4 or R 5 .
• a pattern defining substance 6 may be applied in the shape indicated by shape 50 in the middle of region R 4 .
• shape 50 may be achieve by patterning the coloured resist layer 26 in region R 5 .
• Figures 1 1 , 12 and 13 depict examples of security documents in which security devices of the sorts described above have been incorporated.
• Figure 1 1 1 shows a first exemplary security document, here a banknote 140, in (a) plan view and (b) cross-section along line XX'.
• the banknote 140 is a polymer banknote, comprising an internal transparent polymer substrate 142 which is coated on each side with opacifying layers 143a and 143b in a conventional manner.
• the opacifying layers may be provided on one side of the substrate 142 only.
• the opacifying layers 143a and 143b are omitted in a region of the document so as to define a window 141 , here having a square shape.
• a security device 120 within the window region 141 is located within the window region 141 in accordance with any of the embodiments discussed above.
• the outer perimeter of the device 120 is denoted by the dashed circular line surrounding the "sun shaped" optically variable effect region.
• the security device 120 may be formed integrally in the banknote 140 with the relief structure 122 being formed directly in the surface of transparent substrate 142.
• the security device 120 may have been formed separately as a security article such as a transfer patch or label.
• the security device 120 may be affixed to the transparent substrate 142 inside the window region 141 by means of the transparent adhesive 125.
• Application may be achieved by a hot or cold transfer method e.g. hot stamping.
• a similar construction could be achieved using a paper/plastic composite banknote in which the opacifying layers 143a and 143b are replaced by paper layers laminated (with or without adhesive) to an internal transparent polymer layer 142.
• the paper layers may be omitted from the window region from the outset, or the paper could be removed locally after lamination.
• the order of the layers may be reversed with a (windowed) paper layer on the inside and transparent polymer layers on the outside.
• the banknote 140 is of conventional construction having a substrate 144 formed for example of paper or other relatively opaque or translucent material.
• the window region 41 is formed as an aperture through the substrate 144.
• the security device 120 is applied as a patch overlapping the edges of window 141 utilising transparent adhesive 125 to join the security article to the document substrate 144.
• the application of the security device and document could be achieved using various methods including hot stamping.
• Figure 13 depicts a third example of a security document, again a banknote 140, to which a security article 150 in the form of a security thread or security strip has been applied. Three security devices 20 each carried on the strip 150 are revealed through windows 141 , arranged in a line on the document 140.
• Figure 13b depicts the security thread or strip 150 incorporated within the security document 140.
• the security thread or strip 50 may be incorporated within the substrate's structure during the paper making process using well known techniques.
• the paper may be removed locally after completion of the paper making process, e.g. by abrasion.
• the paper making process could be designed so as to omit paper in the desired window regions.
• Figure 13c shows an alternative arrangement in which the security thread or strip 150 carrying the security device 120 is applied to one side of document substrate 145, e.g. using adhesive.
• the windows 141 are formed by provision of apertures in the substrate 145, which may exist prior to the application of strip 150 or be formed afterwards, again for example by abrasion.
• security documents of the sorts discussed above are known and could be used.
• the above described device structures could be formed directly on other types of security document including identification cards, driving licenses, bankcards and other laminate structures, in which case the security device may be incorporated directly within the multilayer structure of the document.

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