PRINTED FEATURES FIELD OF THE INVENTION

This invention relates to a method and apparatus for assisting in accurate registration of embossed features and printed features in documents and tokens. DEFINITIONS

Security Document

As used herein the term security document includes all types of documents and tokens of value and identification documents including, but not limited to the following: items of currency such as banknotes and coins, credit cards, cheques, passports, identity cards, securities and share certificates, driver's licenses, deeds of title, travel documents such as airline and train tickets, entrance cards and tickets, birth, death and marriage certificates, and academic transcripts.

The invention is particularly, but not exclusively, applicable to security documents such as banknotes or identification documents such as identity cards or passports formed from a substrate to which one or more layers of printing are applied.

Substrate

As used herein, the term substrate refers to the base material from which the security document or token is formed. The base material may be paper or other fibrous material such as cellulose; a plastic or polymeric material including but not limited to polypropylene (PP), polyethylene (PE), polycarbonate (PC), polyvinyl chloride (PVC), polyethylene terephthalate (PET); or a composite material of two or more materials, such as a laminate of paper and at least one plastic material, or of two or more polymeric materials.

The use of plastic or polymeric materials in the manufacture of security documents pioneered in Australia has been very successful because polymeric banknotes are more durable than their paper counterparts and can also incorporate new security devices and features. One particularly successful security feature in polymeric banknotes produced for Australia and other countries has been a transparent area or "window". Transparent Windows and Half Windows

As used herein the term window refers to a transparent or translucent area in the security document compared to the substantially opaque region to which printing is applied. The window may be fully transparent so that it allows the transmission of light substantially unaffected, or it may be partly transparent or translucent partially allowing the transmission of light but without allowing objects to be seen clearly through the window area.

A window area may be formed in a polymeric security document which has at least one layer of transparent polymeric material and one or more opacifying layers applied to at least one side of a transparent polymeric substrate, by omitting least one opacifying layer in the region forming the window area. If opacifying layers are applied to both sides of a transparent substrate a fully transparent window may be formed by omitting the opacifying layers on both sides of the transparent substrate in the window area. A partly transparent or translucent area, hereinafter referred to as a "half- window", may be formed in a polymeric security document which has opacifying layers on both sides by omitting the opacifying layers on one side only of the security document in the window area so that the "half-window" is not fully transparent, but allows some light to pass through without allowing objects to be viewed clearly through the half-window.

Alternatively, it is possible for the substrates to be formed from an substantially opaque material, such as paper or fibrous material, with an insert of transparent plastics material inserted into a cut-out, or recess in the paper or fibrous substrate to form a transparent window or a translucent half-window area. Opacifying layers

One or more opacifying layers may be applied to a transparent substrate to increase the opacity of the security document. An opacifying layer is such that

L _τ < L _{0 ,} where L ₀ is the amount of light incident on the document, and L _τ is the amount of light transmitted through the document. An opacifying layer may comprise any one or more of a variety of opacifying coatings. For example, the opacifying coatings may comprise a pigment, such as titanium dioxide, dispersed within a binder or carrier of heat-activated cross-linkable polymeric material. Alternatively, a substrate of transparent plastic material could be sandwiched between opacifying layers of paper or other partially or substantially opaque material to which indicia may be subsequently printed or otherwise applied. Security Device or Feature

As used herein the term security device or feature includes any one of a large number of security devices, elements or features intended to protect the security document or token from counterfeiting, copying, alteration or tampering. Security devices or features may be provided in or on the substrate of the security document or in or on one or more layers applied to the base substrate, and may take a wide variety of forms, such as security threads embedded in layers of the security document; security inks such as fluorescent, luminescent and phosphorescent inks, metallic inks, iridescent inks, photochromic, thermochromic, hydrochromic or piezochromic inks; printed and embossed features, including relief structures; interference layers; liquid crystal devices; lenses and lenticular structures; optically variable devices (OVDs) such as diffractive devices including diffraction gratings, holograms and diffractive optical elements (DOEs). Diffractive Optical Elements (DOEs)

As used herein, the term diffractive optical element refers to a numerical- type diffractive optical element (DOE). Numerical-type diffractive optical elements (DOEs) rely on the mapping of complex data that reconstruct in the far field (or reconstruction plane) a two-dimensional intensity pattern. Thus, when substantially collimated light, e.g. from a point light source or a laser, is incident upon the DOE, an interference pattern is generated that produces a projected image in the reconstruction plane that is visible when a suitable viewing surface is located in the reconstruction plane, or when the DOE is viewed in transmission at the reconstruction plane. The transformation between the two planes can be approximated by a fast Fourier transform (FFT). Thus, complex data including amplitude and phase information has to be physically encoded in the micro- structure of the DOE. This DOE data can be calculated by performing an inverse FFT transformation of the desired reconstruction (i.e. the desired intensity pattern in the far field).

DOEs are sometimes referred to as computer-generated holograms, but they differ from other types of holograms, such as rainbow holograms, Fresnel holograms and volume reflection holograms. BACKGROUND OF THE INVENTION

A window formed in a security document is particularly suited for incorporating a security device, such as a diffraction grating or hologram. The usual method of incorporating a diffraction grating or hologram in a security documents is to emboss the required diffractive relief structure onto a transfer foil of metallic material, and to transfer the foil bearing the diffractive structure on to the required area of the security documents in a hot stamping operation. This is a relatively expensive process which is not particularly suitable for the mass production of security documents such as bank notes or the like. Another method of producing diffractive structures in security documents is disclosed in our International Patent Application No. WO01/00418 in which an optically diffractive structure is formed by irradiation of an area of the substrate by laser ablation. Whilst such a laser ablation process can reduce the cost of providing diffractive structures in bank notes or the like, the process still involves the use of relatively expensive laser equipment.

Further, many security documents, such as banknotes, have several different security features in different areas of the note. This can be confusing for the public, but is a necessity imposed by applying security features by different methods which requires relatively large tolerances, typically of at least 1.5-2.0 mm so that the features stand by themselves. It is therefore desirable to provide a process for forming multiple security features in a single area that does not require large tolerances and which is difficult to replicate.

In our International Patent Application WO2008/031 170 there is described a security document and method of manufacture in which a radiation curable ink is applied to a substrate in a window or half window area and the ink is embossed and cured with radiation to form a relief structure, such as a diffractive structure or a lens structure.

The method disclosed in WO2008/031 170 is particularly suitable for forming microscopic relief structures, in particular diffractive structures such as diffractive optical elements (DOEs) and holograms, and microlens structures. However, when clear transparent or translucent embossable ink is used, difficulties can arise in accurately registering the position of the embossed relief structure with the area of transparent ink and/or with other printed features on the security document, for example, when the embossed relief structure is provided in a window of half window and/or when an embossed microlens structure is provided in combination with microimages.

One proposal has been to use a digital signal to hold the relative roll positions of printing and embossing stations in register independently of the printed image. However, this has an impact on tension at the embossing head and can adversely affect the print quality.

It is therefore desirable to provide a method and apparatus for assisting in accurate registration of an embossed feature provided by embossing an embossable ink on a document. SUMMARY OF THE INVENTION

According to one aspect of the invention, there is provided a method of registration for an embossed security feature on a security document, including: providing a substrate; applying an embossable ink to an area of the substrate at a first printing station; embossing at least part of said area of the embossable ink with embossing means at an embossing station to form the embossed security feature; wherein the method further includes: printing a registration region of embossable ink on the substrate at the first printing station; embossing at least part of said registration region to form a detectable registration key; detecting the position of the registration key; comparing the position of the registration key with at least one registration mark provided at least partly by a printing means; and adjusting the position of the printing means relative to the embossing means in response to said comparison of the positions of the registration key and the registration mark. According to another aspect of the invention, there is provided apparatus for registration of an embossed security feature on a document including: a first printing station for applying an embossable ink to an area of a substrate; an embossing station having embossing means for embossing at least part of the area of the embossable ink to form the embossed security feature; wherein the first printing station is arranged to print a registration region of embossable ink on the substrate, and the embossing means is arranged to emboss at least part of the registration region to form a registration key; printing means for applying an at least partly printed registration mark to the substrate; detecting means for detecting the position of the registration key and for detecting the position of the registration mark; comparing means for comparing the relative positions of the registration key and the registration mark; and adjusting means for adjusting the position of the printing means relative to the embossing means if the registration key and the registration mark are not in register. In a particularly preferred embodiment, the registration mark is printed by printing means in the embossable ink at the first printing station, and the position of the printing means at the first printing station is adjustable relative to the embossing means at the embossing station in response to the comparison between the relative positions of the registration key and registration mark. Preferably the position of the printing station is adjusted relative to the embossing station if the distance between the positions of the registration key and registration mark is not equal to a predetermined distance. The predetermined distance may be zero or non-zero.

In a particularly preferred embodiment, the position of the embossing means is fixed and the position of the printing means is adjustable. In this manner, the relative positions of the embossing means and printing means are adjustable without affecting the tension at the embossing means.

Preferably, at least one of the registration key and the registration mark is printed and embossed. It is preferable for the registration key to be printed and embossed, but it may also be unembossed and surrounded by a printed embossed area.

Preferably, an elongate or enlarged zone larger than the registration mark printed in embossable ink is embossed over the registration mark to form a printed, embossed registration mark. The printed, embossed registration key and registration mark are more readily detectable than unembossed, printed registration marks, particularly if a substantially transparent or translucent embossable ink is used. Also, embossing an elongate or enlarged zone over the printed registration mark helps to ensure that a detectable embossed registration mark is produced. Similarly, if the registration region is an elongate or enlarged region printed in the embossable ink larger than the registration key, this also helps to ensure a detectable registration key is produced.

In a further aspect, the present invention provides a method of registration for an embossed security feature on a security document, including: providing a substrate; applying an embossable ink to an area of the substrate at a first printing station; and applying embossing means to the whole of said area of the substrate to form the embossed security feature.

In a yet further aspect, there is provided an apparatus for registration for an embossed security feature on a security document, including: a first printing station for applying an embossable ink to an area of a substrate; and an embossing means for embossing the whole of said area of the substrate to form the embossed security feature.

The embossing means may include a plurality of embossing elements in a repeating pattern, one or more of the embossing elements being applied to said area of the substrate to form the embossed security feature. The repeating pattern may extend over a substantial portion, or all, of a surface of the embossing means. A registration region of embossable ink may be printed on the substrate at the first printing station. One or more of the embossing elements may also be applied to the registration region to form a detectable registration key.

In these aspects, the invention has the advantage that the area of embossable ink and the embossed security feature are automatically in register, without requiring the additional step of aligning the first printing station and the embossing means. If a registration region is embossed to form a detectable registration key, then any further features to be applied to the substrate by further printing or embossing stations can be registered with the detectable registration key.

The present invention is particularly advantageous when a substantially transparent or translucent embossable ink is used because a registration mark or other area printed with such an ink is difficult to detect by optical means and therefore register. Further, when such a registration mark is embossed, the embossed mark is easier to detect by optical means. The elongate or enlarged region printed with the embossable ink adjacent to the printed registration mark, with said region being embossed with a registration key and an elongate or enlarged zone embossed over the registration mark, enables relatively small registration marks and registration keys to be used for more accurate control of the process for forming the embossed security element. It will, however, be appreciated that the invention is equally applicable to a process in which an opaque or reflective embossable ink is embossed to form a security device that is to be viewed in reflection.

Embossable Radiation Curable Ink

Preferably, the embossable ink used is an embossable radiation curable ink. This term as used herein refers to any ink, lacquer or other coating which may be applied to the substrate in a printing process, and which can be embossed while soft to form a relief structure and cured by radiation to fix the embossed relief structure. The curing process may take place either after embossing or at substantially the same time as the embossing step, via curing means at the embossing station. The radiation curable ink is preferably curable by ultraviolet (UV) radiation. Alternatively, the radiation curable ink may be cured by other forms of radiation, such as electron beams or X-rays.

The radiation curable ink is preferably a transparent or translucent ink formed from a clear resin material. Such a transparent or translucent ink is particularly suitable for printing light-transmissive security elements such as numerical-type DOEs and lens structures. In one particularly preferred embodiment, the transparent or translucent ink preferably comprises an acrylic based LJV curable clear embossable lacquer or coating. Such UV curable lacquers can be obtained from various manufacturers, including Kingfisher Ink Limited, product ultraviolet type UVF-203 or similar. Alternatively, the radiation curable embossable coatings may be based on other compounds, eg nitro-cellulose. The radiation curable inks and lacquers used in the invention have been found to be particularly suitable for embossing microstructures, including diffractive structures such as DOEs, diffraction gratings and holograms, and microlenses and lens arrays. However, they may also be embossed with larger relief structures, such as non-diffractive optically variable devices. The ink is preferably embossed and cured by ultraviolet (UV) radiation at substantially the same time. In a particularly preferred embodiment, the radiation curable ink is applied and embossed at substantially the same time in a Gravure printing process.

Preferably, in order to be suitable for Gravure printing, the radiation curable ink has a viscosity falling substantially in the range from about 20 to about 175 centipoise, and more preferably from about 30 to about 150 centipoise. The viscosity may be determined by measuring the time to drain the lacquer from a Zahn Cup #2. A sample which drains in 20 seconds has a viscosity of 30 centipoise, and a sample which drains in 63 seconds has a viscosity of 150 centipoise.

With some polymeric substrates, it may be necessary to apply an intermediate layer to the substrate before the radiation curable ink is applied to improve the adhesion of the embossed structure formed by the ink to the substrate. The intermediate layer preferably comprises a primer layer, and more preferably the primer layer includes a polyethylene imine. The primer layer may also include a cross-linker, for example a multi-functional isocyanate. Examples of other primers suitable for use in the 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 acetyl acetone; melamines; and carbodi-imides. The type of primer may vary for different substrates and embossed ink structures. Preferably, a primer is selected which does not substantially affect the optical properties of the embossed ink structure.

In another possible embodiment the radiation curable ink may include metallic particles to form a metallic ink composition which is both printable and embossable. Such a metallic ink composition may be used to print a reflective security element, such as a diffraction grating or hologram. Alternatively, a transparent ink, e.g. formed from a clear resin, may be applied on one side of the substrate, with or without an intermediate primer layer, the transparent ink then being embossed and cured with radiation and a metallic ink composition subsequently applied to the embossed transparent ink in a printing process, if it is desired to form a reflective security element as part of the security device.

It is also possible for the metallic ink composition to be applied in a layer which is sufficiently thin to allow the transmission of light. When a metallic ink is used, it preferably comprises a composition including metal pigment particles and a binder. The metal pigment particles are preferably selected from the group comprising: aluminium, gold, silver, platinum, copper, metal alloy, stainless steel, nichrome and brass. The metallic ink preferably has a low binder content and a high pigment to binder ratio. Examples of metallic ink compositions suitable for use in the present invention are described in WO2005/049745 of Wolstenholme International Limited, which describes coating compositions suitable for use in coating a diffraction grating comprising metal pigment particles and a binder, wherein the ratio of pigment to binder is sufficiently high as to permit the alignment of the pigment particles to the contours of the diffraction grating. Suitable binders may comprise any one or more selected from the group comprising nitrocellulose, ethyl cellulose, cellulose acetate, cellulose acetate propionate (CAP), cellulose acetate butyrate (CAB), alcohol soluble propionate (ASP), vinyl chloride, vinyl acetate co-polymers, vinyl acetate, vinyl, acrylic, polyurethane, polyamide, rosin ester, hydrocarbon, aldehyde, ketone, urethane, polyethyleneterephthalate, terpene phenol, polyolefin, silicone, cellulose, polyamide and rosin ester resins. In one particularly preferred metallic ink composition, the binder comprises nitro cellulose and polyurethane. The pigment to binder ratio preferably falls substantially within the range from about 5:1 to about 0.5:1 by weight, and more preferably falls substantially within the range from about 4:1 to about 1 :1 by weight.

The metal pigment content by weight of the composition is preferably less than about 10%, and more preferably less than about 6%. In particularly preferred embodiments, the pigment content by weight of the composition falls substantially in the range from about 0.2% to about 6%, and more preferably from about 0.2% to about 2%.

The average particle diameter may be in the range from about 2μm to about 20μm, preferably in the range from about 5μm to about 20μm, and more preferably in the range from about 8μm to about 15μm.

The thickness of the pigment particles is preferably less than about 100nm and more preferably less than about 50nm. In one embodiment, the thickness of the pigment particles falls substantially within the range from 10-50nm. In another embodiment, the thickness of the pigment particles falls substantially within the range from 5-35nm, and in another embodiment the average thickness of the pigment particles falls substantially within the range from 5-18nm.

The substrate is preferably formed from at least one layer of transparent polymeric material with at least one opacifying layer applied to at least one side of the transparent polymeric substrate, with at least one opacifying layer omitted in the region forming the window or half-window area.

Alternatively, it is possible for the substrate to be formed from an at least partly opaque material, such as paper or fibrous material with an insert of transparent plastics material inserted into a cut-out, or recess in the paper or fibrous substrate to form the window or half-window area.

The method and apparatus of the invention may include one or more stations for applying windows, half-windows and/or other printed features to the substrate, and the embossed registration mark and registration key may be used to assist in registering such features with the embossed security feature. For example, a second printing station may include printing means for applying print to the substrate, said print including a printed registration mark, and the position of the printing means at the second printing station is adjustable relative to the embossing means at the embossing station in response to a comparison between the relative positions of the registration key and the printed registration mark. Preferably, the position of the embossing means is fixed and the position of the printing means at the second printing station is adjustable.

Alternatively, or additionally, at least one opacifying station may be provided which has opacifying means for applying at least one opacifying layer to at least one side of a transparent substrate, and the position of the opacifying means at the opacifying station is adjustable relative to the embossing means at the embossing station in response to a comparison of the position of the registration key relative to a registration mark applied at the opacifying station. In one preferred embodiment, opacifying layers are applied to opposite sides of the substrate with the opacifying layers on both sides of the substrate omitted in one region to form a transparent window in the security document. In another embodiment, at least one opacifying layer is applied to one side of the transparent substrate to completely cover said one side, and at least one opacifying layer is applied to the opposite side of the substrate, except in a region which forms the half-window area. In each of these embodiments, the opacifying station may include means for applying an opaque printed registration mark, with detecting means provided for detecting relative positions of the opaque printed registration mark and an embossed registration mark and/or registration key produced in the manner described above. Such an arrangement enables accurate control of the location of an embossed security device within a window or half-window, eg by adjusting the position of the opacifying means relative to the embossing means. Preferably, the position of the embossing means is fixed, and the position of the opacifying means is adjustable relative to the embossing means.

In one particularly preferred embodiment, the security device formed by the embossed metallic ink includes a diffractive structure, such as a DOE, or a holographic structure. In another embodiment, the security device formed by the embossed ink may include a lens structure. There is also the possibility of the integration of other security elements having a relief structure, such as non- diffractive optically variable devices, formed from an embossed transparent or metallic ink into a window or half-window area. In one particular embodiment, the security device may be a transmissive device, such as a transmission DOE which produces a projected image in the remote reconstruction plane when viewed in transmission with collimated light from a point light source or a laser. Such a transmission DOE may be formed from a clear or transparent embossable UV curable ink. In another embodiment, when a metallic ink is used, the embodiment metallic ink applied to the transparent region of the substrate may be sufficiently thin to allow the transmission of light to enable a transmission DOE to be formed.

In the case of a half-window in which the transparent region is covered on one side by at least one opacifying layer, a security device formed from an embossed metallic ink may be a reflective device which is only visible in the half- window from the opposite side of the substrate, which is not covered by an opacifying layer in the half-window area.

It is also possible for the opacifying layer, which covers the half-window area on one side of the substrates, to allow the partial transmission of light so that the security device formed by the embossed ink is partially visible in transmission from the side, which is covered by the opacifying layer in the half-window area.

In a particularly preferred embodiment, the security device formed by the embossed radiation curable ink is a composite security device containing two or more different security elements.

In one embodiment, the composite security device may include two or more different diffractive relief structures, e.g. selected from a diffraction grating, a hologram and a numerical-type diffractive optical element.

In another embodiment, the composite security device may include an optically diffractive relief structure forming one security element, and a non- diffractive relief structure forming another security element. The other security elements may be an optically variable non-diffractive relief structure or a relief structure forming a lens or lenticular array.

In a particularly preferred embodiment, the security device formed from the embossed ink may include a verification means for verifying another security feature provided on the document or device. In the case of a composite security device, the device may include an inspectable security elements and a verification means for verifying another security element on the document. The verification means preferably includes at least one lens. For example, the ink may be embossed with a relief structure forming a Fresnel lens or a magnifying lens, which can be used to verify an area of micro printing when the lens is superimposed over the security feature. Alternatively, the ink may be embossed with a lenticular array or an array of micro lenses, which can be used to verify a security feature in the form of an array of micro images, the array of micro images preferably being in register with the array of micro lenses, when the lenticular array or array of micro lenses is superimposed over the security feature.

In an alternative embodiment, the ink may be embossed with a diffractive relief structure, in the form of a diffractive filter or a holographic filter as a verification means. Such a filter may be used to verify a security feature in the form of an image which exhibits colour changing effects or a latent image, which becomes visible when the diffractive filter or holographic filter is superimposed over the security feature. In the case of a half-window the security feature may be provided on the opposite side of the substrate from the verification means and in register with the verification means, so that the verification means is permanently superimposed over the security feature.

In the case of a flexible security document, such as a bank note or the like, which is foldable, if the verification means is provided in a full window area, the security feature may be provided on another part of the document which is laterally spaced from the verification means, whereby the security feature is only verifiable when the verification means is superimposed over the security feature, e.g. by folding. The method and apparatus of the invention may assist in accurate registration of each of the combinations of security features mentioned above.

BRIEF DESCRIPTION OF THE DRAWINGS

Some preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic section through a security document with an integrated security device in the form of an embossed ink in a window area; Figure 2 is a schematic section through a modified security document with an integrated security device formed from an embossed ink in a half-window area;

Figure 3 is a schematic section through a security document with an integrated composite security device including an array of lenses and a diffractive security element in a half-window;

Figure 4 is a schematic view of apparatus for registration control of the printing and embossing of security features in a security document;

Figures 5, 6(a) and 6(b) are schematic views of registration keys and registration marks applied to a security document by the apparatus of Figure 4;

Figure 7 is a plan view of a foldable self-verifying security document with an integrated composite security device including a lens structure in a window for verifying a security element at another part of the document;

Figure 8 is a view of the document of Figure 7 folded for verification; Figure 9 is a plan view of a foldable security document with an integrated composite security device incorporating a filter for verifying a security element at another part of the document;

Figure 10 is a view of the document of Figure 9 folded for verification; and

Figures 1 1 (a) and 1 1 (b) are schematic views of registration keys and registration marks applied to a security document by an alternative printing and embossing apparatus.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to Figure 1 there is shown a security document 10 comprising a substrate 1 1 of transparent plastic materials having a first or upper side 12 and a second or lower side 13. The transparent substrate is preferably formed from a transparent polymeric material such as a laminated structure of two or more layers of bi-axially oriented polypropylene. It will, however, be appreciated that other transparent or translucent polymeric substrates may be used in the present invention such as polyethylene and polyethyleneterephthalate (PET). Opacifying layers 14 and 15 are applied respectively to the first and second sides 12 and 13 of the transparent substrate 11 with the opacifying layers 14 and 15 omitted in one region of the substrates to form a window area 16 in which a security device 17 is provided. The security device 17 is formed from an embossable ink composition 18 applied on one side 13 of the substrate within the window area, and the ink composition 18 is embossed with a relief structure 19 to form the security device 17. In a preferred method of manufacturing the security document of Figure 1 , the ink composition, which preferably comprises a UV-curable transparent ink, is printed onto the side 13 of the transparent plastics substrate 1 1 and is embossed while soft and cured with UV radiation simultaneously before the opacifying layers 13 and 14 are applied to the substrate 11 . Alternatively, the ink composition may comprise a UV-curable, embossable metallic ink composition, e.g. of the type manufactured by Wolstenholme International Limited. Such a metallic ink composition may be used when it is required to produce a reflective security device such as a reflective diffraction grating or hologram.

In some applications, an intermediate primer layer (not shown) may be applied to the surface 13 of the transparent substrate 11 before the embossable ink composition 18 is applied to improve the adhesion of the resulting embossed security device to the substrate.

In an alternative method, the opacifying layers 14 and 15 could first be applied to the opposite sides 12 and 13 of the substrate 1 1 with the ink composition 18 being printed on the window area 16 of the substrate 1 1 and then embossed and cured with UV radiation.

The opacifying layers 14 and 15 may comprise any one or more of a variety of opacifying coatings. For example, the opacifying coatings may comprise a pigment, such as titanium dioxide, dispersed within a binder or carrier of heat-activated cross-linkable polymeric material. Alternatively, the substrate 1 1 of transparent plastic material could be sandwiched between opacifying layers of paper to which indicia may be subsequently printed or otherwise applied. It is also possible for the security documents to be formed from a paper or fibrous substrate which has an area cut-out with a transparent plastics insert inserted into the cut-out area to form a transparent window to which the ink composition is applied and embossed to form the security device 17.

The security device 17 formed from the embossed ink composition 18 may include one or more of a variety of relief structures to form different security elements, including diffractive structures such as diffraction gratings, holograms and numerical-type diffractive optical elements (DOEs). Alternatively or additionally, the security device 17 may include other relief structures such as lens structures and optically variable non-diffractive relief structures. In a particularly preferred embodiment, the security device 17 includes a multilayer diffractive optical element (DOE). The method of embossing a radiation curable ink or lacquer when soft and curing the ink or lacquer of the invention enables multi-layer DOEs and non-centro-symmetric DOEs to be formed by embossing. A multi-level DOE is a diffractive optical element with a discrete number of phase levels wherein the number is an integer greater than one. The discrete phase levels of the binary DOE may be formed by embossing each level to a different surface relief depth.

Multiple phase levels each having a discrete surface relief depth may provide multi-bit storage of data. At least some of the phase levels may generate a projected visual image which is visible in a reconstruction plane when the multilevel DOE is illuminated with collimated light, such as from a laser, an LED or other point light source. It is also possible for at least some phase levels to store encrypted data. A multi-layer DOE enables the DOE to store more information and to be provided over a larger area, thereby providing stronger, brighter and more effective DOEs which may also generate animated or moving images. Further, multi-level DOEs which have more than two phase levels may be asymmetrical or symmetrical, whereas single phase and binary DOEs are limited to symmetrical DOEs.

Figure 2 shows a modified security document 20 which is similar to the security document of Figure 1 , and corresponding reference numerals have been applied to corresponding parts. Figure 2 differs from Figure 1 in that the opacifying layer 15 is applied to cover the side 13 of the transparent substrate completely in the area of an embossed metallic ink 18, but the opacifying layer 14 on the opposite side 12 of the substrate 1 1 is omitted in the area of the embossed metallic ink 18 to form a half-window area 26.

The security device 27 formed from the embossed metallic ink 18 in Figure 2 preferably includes at least one reflective security element which is visible from one side of the security document, i.e. the side corresponding to the side 12 of the substrate 1 1 to which the opacifying layer 14 is only partially applied. The security device 27 may be either completely invisible or partially visible from the opposite side of the substrate, depending upon the thickness and opacity of the opacifying layer 15 which is applied to the opposite side 13 of the substrate 1 1 . The security document 20 may be manufactured by first printing the UV curable metallic ink 18 on the transparent substrate 1 1 in the region which is to become the half-window 26, then embossing and curing the metallic ink 18 simultaneously to form the embossed relief structure 19, and then applying the opacifying layers 14 and 15 to the substrate 1 1. Alternatively, a UV curable transparent ink may be printed on one side of the transparent substrate in the half-window region, embossed and simultaneously cured and then a metallic ink composition may be applied to the embossed transparent ink before the opacifying layer 15 is applied. As shown in Figure 2, these methods have the advantage that the embossed relief structure 19 of the metallic ink 18 is protected by the opacifying layer 15 which completely covers the metallic ink 18. However, in an alternative method the metallic ink could be applied to the opposite surface 12 of the transparent substrate 1 1 in the half-window area either before, during or after the application of the opacifying layer 14. In this case, it may be necessary to apply a protective coating, such as a transparent gloss varnish over the security device formed from the embossed metallic ink.

Figure 3 shows another embodiment of a security document 50 in accordance with the invention which is similar to the document 20 of Figure 2 and corresponding reference numerals have been applied to corresponding parts. The security document 50 differs from that of Figure 2 in that a security device 57 formed by the embossed ink 18 is a composite security device containing two different security elements 51 and 52.

Figure 3 also differs from Figure 2 in that additional layers 34 and 35 are applied to the opacifying layers 14 and 15. The layers 34 and 35 may be additional opacifying layers, e.g. pigmented coatings containing titanium dioxide when it is desired to increase the opacity of the security document except in the half-window area 56. Alternatively, the additional layers 34 and 35 may be layers of printed indicia. The security document 50 also differs from that of Figure 2 in that the composite security device 57 is provided on the same side of the transparent substrate 1 1 as the half-window 56, with a further security element 58 provided on the opposite side 13 of the transparent substrate 1 1 which is completely covered by the opacifying layers 15 and 35 in the half-window area.

The further security element 58 is preferably in the form of an element which interacts with at least one of the first and second security devices 51 and 52 of the composite security device 57. In one embodiment the first security element 51 may comprise a reflective diffractive structure, such as a DOE or hologram, and the second security element 52 may comprise a lens structure with the further security element 58 comprising a security feature which can be verified, inspected or enhanced by the lens structure 52. For example, the further security element 58 may comprise an area of micro printing, with the second security element comprising a Fresnel lens or a magnifying lens for magnifying a viewing the micro printing. Alternatively, the second security element 52 may comprise a lenticular array, such as an array of microlenses 53 with the second security element comprising an array of micro-images 59 in register with the micro lenses such that the micro-images 59 can be viewed through the lenticular array 52. The micro-images 59 may be formed by a variety of different methods. The micro images 59 could be printed onto the surface 13 of the transparent substrate; or they could be markings formed with a laser, eg by laser blackening, laser colouration or ablation.

The micro-images 59 may be clear, coloured or black, or a combination of the above. The combination of microlenses 53 and micro-images 59 may produce a magnified image of the individual micro-images by a process known as Moire magnification. It is also possible for the combination of microlenses 53 and microimages 59 to produce moving or floating images.

In another possible embodiment, the micro-images 59 may be replaced by a hologram structure 58, such as an embossed reflective rainbow hologram, which in combination with the array of microlenses 53, can produce some interesting optical effects.

The printing and embossing apparatus 100 shown schematically in Figure 4 includes supply unit 102 for supplying a sheet-like substrate 101 to various printing and embossing stations, including an opacifying station 104, a first printing station 106, an embossing station 1 10, and a second printing station 1 14.

The substrate 101 is preferably made of a substantially transparent polymeric material and may be continuously supplied to the opacifying station 104 from a roll 103 of the material at the supply unit 102. The opacifying station 104 includes opacifying means for applying at least one opacifying layer to at least one side of the substrate 101 . The opacifying means is preferably in the form of a printing unit, eg one or more Gravure printing cylinders 105 for applying one or more opacifying coatings of ink to one or both sides of the substrate. However, it is possible the opacifying station 104 could include opacifying means in the form of a laminating unit for applying one or more sheet-like layers of at least partly opaque material, such as paper or other fibrous material to at least one side of the transparent substrate.

Preferably, the opacifying means 105 at the opacifying station 104 is arranged to omit at least one opacifying layer on one or both sides of the substrate in at least one region to form a window or half-window area.

The first printing station 106 includes printing means 107, 108 for applying an embossable radiation-curable ink to the substrate 101 . The printing means may comprise at least one printing cylinder 107, eg a Gravure printing cylinder, with the opacified transparent substrate fed between the printing cylinder 107 and a corresponding cylinder or roller 108 on the opposite side of the substrate.

The printing means 107, 108 is arranged to apply the radiation curable ink to a first area 120 of the substrate on which an embossed security element is to be embossed at the embossing station. The printing means 107, 108 is also arranged to apply an elongate or enlarged registration region 121 and a registration mark 122 to the substrate 101 , both said region 121 and said mark 122 being printed in the embossable radiation curable ink.

The embossing station 1 10 includes embossing means preferably in the form of a plate cylinder 1 1 1 and impression cylinder 1 12. The embossing means 1 1 1 , 1 12 includes embossing portions arranged to emboss different areas of the substrate as it passes through the nip between the plate and impression cylinders 1 1 1 , 1 12. A first embossing portion is arranged to emboss the first area 120 of the substrate 101 to which the embossable radiation curable ink is applied to form the embossed security element 123. A second embossing portion is arranged to emboss the registration region 121 to form a printed, embossed registration key 124, and a third embossing portion is arranged to emboss a zone 126 over the printed registration mark 122 to form a printed, embossed registration mark 128. As illustrated by Figure 5, the second embossing portion is wedge-shaped, and is smaller than the elongate or enlarged registration region 121 printed at the first printing station 106. Conversely, the embossed zone 126 is an elongate or enlarged zone larger than the printed registration mark 122 which in a preferred embodiment is also wedge-shaped. Therefore the printed and embossed registration key 124 and the printed, embossed registration mark 128 are both wedge-shaped and smaller than the respective elongate or enlarged registration region 120 and registration zone 126.

The relatively small, wedge-shaped registration key 124 and registration mark 128 enable more accurate registration control to enable the embossed security feature 123 to be accurately located in relation to the first area 120 of radiation curable ink and also in relation to other features on the document. It will, however, be appreciated that shapes of registration keys and registration marks other than or in addition to wedge shapes, for example bars or dots or a combination thereof, may be used. The embossing station 1 10 may also include radiation curing means 1 13 for curing the embossable, radiation curable ink substantially simultaneously or almost immediately after the ink has been embossed to form the embossed security element and the printed, embossed registration key 124 and registration mark 128. Alternatively, a separate curing station may be provided. The radiation curing means preferably comprises an ultraviolet (UV) curing unit for curing a UV curable ink, but other types of curing units, eg X-ray or electron beam (EB) curing units may be used for X-ray or EB radiation curable inks.

The second printing station 1 14 includes printing means for applying printed features to the substrate. The printed means preferably includes a printing cylinder 1 16 such as a Gravure, offset or intaglio cylinder, and may be used to apply a wide variety of printed features to the substrate. For instance, the printing cylinder 1 16 at the second printing station 1 14 may be used to apply printed security features in register with, adjacent to or surrounding the embossed security element. One example of a printed security feature could include a printed metallic ink applied over the embossed security device 123. Another example of a printed security feature applied at the second printing station 114 is an area of microprinting which can be viewed or inspected when overlaid by a microlens array. In one preferred embodiment, the printing means at the second printing station 1 14 is also arranged to apply a printed registration mark 130 to the substrate, so that the position of the registration mark 130 can be compared with the position of the embossed registration key 124 to determine whether the printed features applied by the second printing station 1 14 are in the correct position relative to the embossed security features.

The apparatus in accordance with the invention also includes first and second registration stations 131 , 132. Each registration station 131 , 132 includes a respective detector for detecting the positions of the respective registration mark 128,130 relative to the embossed registration key 124, and a comparator for comparing the relative positions of the registration mark 128 or 130 relative to the registration key 124. The apparatus also includes a control means 140 in the form of a central processor unit (CPU) for adjusting the relative positions of the printing means 107 and 1 16 of the first and second printing stations 106, 1 14 relative to the embossing means at the embossing station 1 10. In operation of the apparatus, the transparent substrate 101 is supplied from the supply unit 102 through the opacifying station 104 where at least one opacifying layer is applied to at least one side of the substrate 101 . The at least partly opacified substrate 101 is then fed through the first printing station 106 where the embossable radiation curable ink is applied to the first area 120 which is to be embossed to form the embossed security element. The first printing station 106 also applies the embossable radiation curable ink to the substrate to form the registration region 121 and the registration mark 122.

The substrate 101 is then fed through the embossing station 1 10 where the first area 120 of the substrate is embossed to form the embossed security element 123 and the registration region 121 and the zone 126 over the registration mark 122 are also embossed to form the printed and embossed registration key 124 and registration mark 128. The radiation curable ink is then cured by radiation, preferably at the embossing station 1 10 to fix the embossed structures 123, 124 and 128.

The substrate bearing the embossed structures is then fed through the first registration station 131 where the relative positions of the embossed registration key 124 and embossed registration mark 128 are detected and compared. If the registration key 124 and registration mark 128 are not in register, the registration station 131 sends a misregistration signal to the CPU 140 which then sends a control signal to the first printing station 106 to adjust the position of the printing means 107, 108 relative to the embossing means 1 1 1 at the embossing station 1 10. For example, in Figure 5, the embossed registration key 124 is shown behind the embossed registration mark 128, and the printing 120 and embossing 123 in security element 150 are misregistered. The printing means is therefore adjusted to move the position of the printed registration mark 122 rearwardly so that the embossed registration mark is moved to position 128' shown in Figure 5(a). In the case of a printing cylinder 107 at the printing station 106, this may be achieved by advancing the rotational position of the cylinder 107 relative to the substrate 101. This method helps to ensure that a subsequent embossed area of the substrate which is embossed to form the security feature 123' is in register with a subsequent printed area 120' in the printed embossed security element 150'.

After the substrate passes through the first registration station 131 it is fed through the second printing station 1 14 where further printed features are applied to the substrate. It is also desirable for the position of such printed features to be accurately located relative to the embossed security feature. For this purpose, the position of the printed registration mark 130 applied by the second printing station 1 14 relative to the registration key 128 is detected at the second registration station 132. If the printed registration mark 130 is not in register with the registration key 128, the registration station 132 sends a signal to the CPU 140 which, in turn sends a control signal to the second printing station 1 14 to adjust the position of the printing means 1 16 at the second printing station 1 14 relative to the embossing means 1 1 1 at the embossing station 1 10. For example, if the printed registration mark 130 is in front of the embossed, printed registration key 124, the position of the printing cylinder 116 is adjusted backwards so that subsequent registration marks 130 are in register with the registration key 124.

The apparatus 100 may also include further printing stations (not shown) for applying further printed features and registration marks 134, 136 to the substrate 101 , and further registration stations with detectors (not shown) may be provided for detecting the positions of those registration marks 134, 136 relative to the position of the embossed, printed registration key 124 to enable adjustment of the printing means at the further printing stations relative to the embossing means 1 1 1 . In the case where the embossed security element is provided in a window or half-window area formed by the opacifying station 104 omitting the opacifying layer or layers in a region on at least one side of the substrate 101 , the opacifying station 104 may also include means for applying a registration mark to the substrate 101 , with the detector at the first registration station 131 or another detector arranged to detect the position of said registration mark relative to the position of the embossed registration key 124. The position of the opacifying means 105 at the opacifying station 104 may then be adjusted by the control means 140 in response to signals from the first registration station 131 or other detector to ensure the position of the embossed security element 123 is accurately in register within the window or half-window area.

It is also possible for an opacifying station to be located after the embossing station, with this opacifying station applying at least one opacifying layer to at least one side of the substrate except in the area of the embossed security element 123 to form a window or half-window. This opacifying station may also apply a printed registration mark which is used to adjust the position of the opacifying means to ensure accurate registration with the security element in the aforesaid manner.

Referring now to Figure 6(a), there is shown a schematic of an alternative method of registration according to another embodiment of the invention. Instead of a pair of strips on the substrate, a single strip is used to detect misregistration. A strip 160 is printed in an embossable radiation curable ink to form a first region 161 and a second relatively small wedge-shaped region 162. The strip is then embossed at embossing station 1 10 with the pattern shown at 164 and 166. In this embodiment the registration key 166 is 'reversed out' of the embossing shim so that the region 164 is embossed but the blank regions 166 are not. This results in embossed printed registration mark 128 and unembossed printed registration key 168. The contrast between each of registration mark 128 and registration key

168 and the embossed background aids in detection of their relative positions. Misregistration is detected by comparing the actual separation S' to the predetermined separation S required for registration of printed area 120 to embossed security feature 123. If S' differs from S by an amount dS, then the position of printing cylinder 106 is adjusted by dS so that the registration mark 128' is at the correct position for security element 150' to be formed with the printed area 120' and the embossed security feature 123' being in register.

Further printed features and registration marks (not shown) may be provided as in the embodiment described with reference to Figures 4 and 5(a). Similarly, in Figure 6(b) there is shown a further variation in which the registration key 176 and a strip 174 are embossed, but blank area 175 is not. This results in formation of embossed printed registration key 178 and embossed printed registration mark 128, which can be brought into register in the same manner as in the embodiment of Figure 5(b), so that the printed area 120' and the embossed security feature 123' are in register in the security element 150'.

The registration key 168, 178 may be formed by a plurality of marks, e.g. a wedge-shaped mark and a series of bars or stripes as shown in Figures 5(b) and 5(c), which may assist in detection of the registration key.

In certain situations it may be desirable to emboss a repeating pattern of elements into the embossable radiation curable ink, for example an array of substantially identical microlenses or a lenticular array to view an array of microimages 59 as described above. In such cases it is advantageous to employ an alternative embossing station 210, 310 as depicted for example in Figures 1 1 (a) and 1 1 (b). In Figure 1 1 (a), the impression cylinder of embossing station 210 comprises an array 225 of substantially identical elements. Each element has a (concave) shape which is the inverse of the shape of a microlens, so that when the impression cylinder is applied to the embossable ink regions 120, 222 and the ink is cured, a plurality of microlenses is formed in each of the regions 223 and 224. Because the embossing elements are repeated over the whole cylinder, and each element is much smaller than the region 120, the embossed security feature in the form of microlens array 223 is automatically in register with the ink region 120, by way of contrast with embossed security feature 123 which is initially misaligned with the region 120 in Figure 5 (a). Printed embossed region 224 forms a registration key which may be used to align security feature 223 with other features on the security document by comparison of the position of the registration key 224 relative to one or more registration marks 130, 134, 136 printed at one or more subsequent printing stations 1 14.

Figure 11 (b) is a variation of Figure 1 1 (a) in which inverse lenticular shapes 325 cover the entire surface of the impression cylinder of embossing station 310. When the impression cylinder is applied to the substrate, and the embossed ink regions are cured, lenticular lens array 323 and registration key 324 are formed in similar fashion to microlens array 223 and registration key 224 of Figure 1 1 (a).

Registration of subsequently applied features may be accomplished by comparing the positions of registration marks 130, 134, 136 to registration keys 224, 324 by analogy to the cases described with reference to Figures 5, 6(a) and 6(b).

A particular advantage of the embodiments depicted in Figures 1 1 (a) and 1 1 (b) is that the same impression cylinder (shim) can be used regardless of the exact placement of the ink region 120, thus obviating the need to create a new impression cylinder or recombined shim when it is desired to place the security document 223, 323 elsewhere on the security document.

It is of course possible to configure the embossing stations 210, 310 so that not all of the impression cylinder surface is covered with embossing elements, should this be desirable.

Whilst the method and apparatus of the present invention may be used for registration of embossed features on metallic or other substantially opaque inks, they are particularly applicable for registration of security features embossed on substantially transparent or translucent inks, because an unembossed registration mark printed in such a transparent or translucent ink would be very difficult to detect. It is therefore preferable that the detectors at the registration stations 131 , 132 are those of the type suitable for detecting a registration key 124 embossed on a region printed in a transparent or translucent ink. For this purpose, the embossed registration key 124 and registration mark 128 may be diffractive embossings with the detectors being optical devices for detecting such diffractive embossings. A preferred method of detection is to rely on the contrast between the registration key and its background, and similarly on the contrast between the registration mark and its background, at a particular wavelength or range of wavelengths, in order to detect the relative positions of the registration key and registration mark.

The method and apparatus of the present invention provide various advantages, including improved control of registration of embossed security features on areas of embossable radiation curable inks, and/or relative to the position of windows or half windows in opacified layers, and/or to the position of other printed security features. Further, if the position of the embossing means 1 1 1 at the embossing station 1 10 is fixed, and the positions of the printing means 107, 108; 1 16 and/or opacifying means 105 at the printing stations 106, 1 14 and/or opacifying station 104 are movable, this provides improved control of tension of the embossing means 1 1 1. Each of the above can lead to a higher quality of finished product and reduction of waste.

Figures 7 and 8 show a rectangular security document in the form of a bank note having side edges 61 and end edges 62. The bank note 60 comprises a flexible sheet which can be folded, e.g. about a central fold line 63 extending parallel to the end edges 62 as shown in Figure 8. The upper surface 64 and the lower surface 74 of the bank note 60 are printed with indicia 65. The bank note 60 has a transparent window 66 in which a composite security device 67 is integrated. The window 66 and the composite security device 67 are preferably formed in the same manner as described with reference to Figures 1 to 4. The composite security device 67 includes a first security element 71 in the form of a diffractive structure, such as a DOE, and a second security element 72 in the form of a lens structure. The bank note 60 also has a further security feature 68 in the form of an area of micro printing 69 provided at a region of the bank note which is laterally spaced from the composite security device. The arrangement of the composite security device 67 and the further security feature 68 is such that when the bank note is folded about the central fold line so that the composite security device is superimposed over the security feature 68, the micro printing 69 is magnified by the lens structure 72 and becomes visible so that the authenticity of the bank note can be verified.

Figures 9 and 10 show another self-verifying bank note 80 which is similar to the bank note 60 of Figures 7 and 8 and corresponding reference numerals have been applied to corresponding parts. The bank note 80 differs from that of Figures 7 and 8 in the form of the composite security device 87 and the further security feature 88. The first security element 91 of the composite security device 87 is in the form of an inspectable relief structure, preferably in the form of a diffractive structure such as a DOE or a hologram, and the second security element 92 of the composite security device is in the form of a filter, preferably a diffractive or holographic filter. The further security feature 88 preferably comprises a dichroic feature, eg an image printed from metameric inks. Dichroic features and metameric inks have the unique property of appearing to change colour when viewed in different lighting conditions or in different spectral environments. For example, two inks with different metameric properties may appear to be an identical colour when viewed in a particular white light environment, e.g. daylight, but when viewed in different lighting conditions, e.g. in filtered light, the two inks will appear to have different reflective colours so that one ink appears in a colour distinguishable from the other.

As in Figures 7 and 8, the composite security device 87 and the further security feature 88 are located at laterally spaced locations on the bank note and are arranged so that when the bank note 80 is folded about the central fold line 63, the composite security device 87 is superimposed over the further security feature 88, and the colour changing properties of the further security feature become apparent when the printed image 89 is viewed through the second security element in the form of the filter 92. As shown in Figures 9 and 10, the image 89 printed with metameric inks may be a permanent image which appears a single colour when viewed in ambient light, with part of the image 99 appearing a different colour from the remainder of the image 98 when the filter of the composite security device is superimposed over the further security feature 88. Alternatively, it is possible for the further security feature 88 to be a latent image which becomes visible when viewed through the filter of the second security element 92 when the bank note 80 is folded to superimpose the composite security device 87 over the further security feature 88. Although it may be possible for the second security element 92 of the composite security device to be in the form of a colour-tinted filter, preferably the second security element comprises a holographic or diffractive filter which can provide a clearer or sharper image when verifying the image 89 of the further security feature 88. The use of an embossable ink which can be embossed with diffractive structures to form the composite security device 87 particularly lends itself to the integration of the composite security device 87 into the window area 66 of the security document of Figures 9 and 10. Also, it is possible to locate different security elements closer together in the composite security device than when other methods of forming security devices are used. For instance, separations of less than 0.3 mm and as low as 0.1 mm have been achieved between the different security elements of the composite security device. Further, the embodiments of Figures 7 and 8, and Figures 9 and 10 provide the advantage of a composite security device having a first security element which can be readily inspected, such as a DOE or hologram, and a second security element in the form of a verification means which can be used to verify another security feature at a laterally spaced location on the bank note.

The apparatus for embossing the UV curable ink to form the embossed structure may include a shim or a seamless roller. The shim or roller may be manufactured from any suitable material, such as nickel or polyester.

Preferably, the nickel shims are produced via a nickel sulphamate electroplating process. The surface of a photoresist glass plate holding a microscopic structure used to form a DOE or array of microlenses may be vacuum metallised or sprayed with pure silver. The plate may then be placed in a nickel sulphamate solution and over a period of time molecules of nickel are deposited on the surface of the silver-coated photoresist, resulting in a master copy. Subsequent copies may be used in transferring the image for reproduction, or transferring to ultraviolet polyester shims or to make a seamless roller. Polyester shims may be made by coating polyester with an ultraviolet curable lacquer and contact copying the master image and curing the transferred image by means of ultraviolet light.

Seamless cylinders may be made using a metallised transfer film with a sub-microscopic diffractive pattern or a microscopic lens pattern for microlenses thereon, which may be fixed and transferred to a cylinder coated with an adhesive. The metallised transfer film may be glued to the roller via a nip. The adhesive may then cured, preferably by heat. Once cured the transfer film is removed leaving the metallised layer with the sub-microscopic or microscopic pattern on the surface of the cylinder ie the roller. This is repeated until the cylinder is completely covered. This cylinder then may be placed in a casting tube and cast with silicone to make a mould. The sub-microscopic or microscopic pattern may be moulded to the inside surface of the silicone.

Once the silicone is cured the mould is removed and placed in a second casting tube. A casting roller may then be placed in the mould and cast with a hard resin, preferably cured with heat. Once cured the roller can be removed from the mould, where the pattern in the inside surface of the silicone has transferred to the outside surface of the resin cylinder and is ready for use, to transfer the sub-microscopic diffractive pattern or lens pattern on the surface of the cylinder into the surface of a printed ultraviolet curable lacquer on the first surface of a substrate.

In another embodiment a cylinder is coated with ultraviolet curable resin, placing a clear transfer film with a sub-microscopic diffractive pattern or a lens pattern to the surface of the ultraviolet resin via a nip and cured with ultraviolet light. The cylinder can then be subsequently cast, as described above and used to directly transfer the pattern into the surface of a printed ultraviolet cured lacquer on the first surface of a substrate.

The upper surface of the substrate may be printed with the embossable UV curable ink in discrete register with the window or half-window area, so that other subsequent printing can take place on non-registered areas as images/patterns outside the window or half-window area. The substrate may then pass through a nip roller to a cylinder carrying a sub-microscopic diffractive pattern or a lens pattern or image in the form of a nickel or polyester shim affixed to the surface of a cylinder. In a preferred embodiment the patterns are held on a seamless cylinder so that the accuracy of the transfer can be improved. The sub-microscopic diffractive pattern or lens pattern may then be transferred from the shim or seamless roller into the surface of the exposed ultraviolet curable lacquer by means of bringing the surface of the shim or seamless roller into contact with the surface of the exposed ultraviolet curable lacquer. An ultraviolet light source may be exposed through the upper surface of the filmic substrate and instantly cures the lacquer by exposure to ultraviolet light. The ultraviolet light sources may be lamps in the range of 200 watts to 450 watts disposed inside the cylinder, curing through the printed ultraviolet lacquer and fixing the transferred sub-microscopic diffractive pattern or lens pattern.

The method described above in which embossed relief structure security devices are formed by printing a transparent radiation curable ink onto a sheet, embossing the ink while still soft and simultaneously curing the ink with radiation, allows multiple security features to be formed in a sheet of banknotes or other security documents in which the security features are more accurately in register with the window or half-window areas of the individual documents of the sheet compared to other methods of applying embossed security devices such as diffraction gratings or holograms by transferring the security devices from a transfer sheet onto the security documents. More particularly, in the present invention, the method and apparatus for registration control enables very accurate location of the embossed security device relative to a window or half- window and/or other security features on the document

It will be appreciated that various modifications and alterations may be made to the embodiments of the present invention described above without departing from the scope and sprit of the present invention. For example, whilst the embodiments of Figures 7 to 10 have been described with particular reference to a security document in the form of a bank note, it will be appreciated that the various aspects and embodiments of the invention have application to other types of security and identification documents including, but not limited to the following: credit cards, cheques, passports, identity cards, securities and share certificates, driver's licenses, deeds of title, travel documents such as airline and train tickets, entrance cards and tickets, birth, death and marriage certificates, and academic transcripts.