GB2438384A

GB2438384A - Forming a customisable security device having a customising layer on a liquid crystal film.

Info

Publication number: GB2438384A
Application number: GB0610540A
Authority: GB
Inventors: Lawrence George Commander; Adam Jeacock; Carole Lesley Foster
Original assignee: De la Rue International Ltd
Current assignee: De la Rue International Ltd
Priority date: 2006-05-26
Filing date: 2006-05-26
Publication date: 2007-11-28
Anticipated expiration: 2026-05-26
Also published as: GB2438384B; GB0610540D0; WO2007138255A1; EP2069148A1

Abstract

Forming security devices on substrates that can be used in varying shapes and sizes for various authenticating or security applications, particularly an optically variable security device utilising liquid crystal films. The method of forming a customisable security device 10 comprises the steps of applying a liquid crystal film 11 to a base substrate 16, applying an at least partially absorbing layer 12 to at least a part of one side of the liquid crystal film 11, and applying a customising layer 13 to at least a part of an opposite side of the liquid crystal film in selected regions. The customising layer modifies the appearance of the liquid crystal film such that contrasting regions are provided between those regions B covered by the customising layer and those A not covered by the customising layer, and the customising layer is applied after application of the security device to the substrate. The customising layer may be a scattering layer in the form of a matt varnish or lacquer. This modifies the appearance of the colour shifting liquid crystal film.

Description

I

IMPROVEMENTS IN FORMING SECURITY DEVICES

The present invention relates to improvements in forming security devices on substrates that can be used in varying shapes and sizes for various authenticating or security applications, particularly an optically variable security device 10 utilising liquid crystal films.

The increasing popularity of colour photocopiers and other imaging systems, and the improving technical quality of colour photocopies, has led to an increase in the counterfeiting of bank notes, passports, fiscal stamps, authentication labels and identification cards etc. There is, therefore, a need to add additional authenticating or security features to existing features.

Steps have already been taken to introduce optically variable features into such documentation that cannot be reproduced by a photocopier. There is also a demand to introduce features which are discernible by the naked eye but which are "invisible" to, or viewed differently, by a photocopier. Since a photocopying process typically involves scattering high energy light off an original document containihg the image to be copied, one solution would be to incorporate one or more features into the document which have a different perception in reflected and transmitted light, an example being watermarks and enhancements thereof.

It is known that certain liquid crystal materials exhibit a difference in colour when viewed in transmission and reflection as well as an angularly dependent coloured reflection. Liquid crystal materials have been incorporated into documents, identification cards and other security elements with a view to creating distinctive optical characteristics. EP-A-0435029 is concerned with a data carrier, such as an identification card, which comprises liquid crystal polymer layer or film in the data carrier. The liquid crystal polymer is in solid form at room temperature and is typically within a laminate structure. The intention is that the liquid crystal layer, which is applied to a black background, will demonstrate a high degree of colour purity in the reflected spectrum for all viewing angles. Automatic testing for verification of authenticity is described using the wavelength and polarization properties of the reflected light in a single combined measurement. This has the disadvantage of being optically complex using a single absolute reflective measurement requiring a

uniform liquid crystal area on a black background.

AU-A-488,652 is also concerned with preventing counterfeit copies by introducing a distinctive optically-variable feature into a security element. This patent discloses the use of a liquid crystal "ink" laminated between two layers of plastic sheet. The liquid crystal is coated onto a black background so that only the reflected wavelengths of light are seen as a colour.

The patent specification is primarily concerned with thermochromic liquid crystal materials, which have the characteristic of changing colour with variation in temperature.

Cholesteric liquid crystals have certain unique properties in the chiral nematic phase. It is the chiral nematic phase which produces an angularly dependent coloured reflection and a difference in colour when viewed in either transmission or reflection. Cholesteric liquid crystals form a helical structure which reflects circularly polarised light over a narrow band of wavelengths. The wavelength is a function of the pitch of the helical structure which is formed by alignment within the liquid crystal material. An example of such a structure is depicted in Figure 1 with the cholesteric helical axis in the direction of the arrow X. The reflection wavelength can be tuned by appropriate choice of chemical composition of the liquid crystal. The materials can be chosen to be temperature sensitive or insensitive. Both handednesses of circularly polarised light can be reflected by choice of the correct materials and thus high reflectivities at specific wavelengths can be achieved with double layers of liquid crystals. The wavelength of reflected light is also dependent on the angle of incidence, which results in a colour change perceived by the viewer as the device 10 is tilted (Figure 2) On a dark background, only the reflective effect is observed, since little light is being transmitted from

behind. When the dark background is removed or not

present and the device 10 is viewed in transmission, the intensity of the transmitted colour saturates the reflective colour. Of the light which is not reflected, a small proportion is absorbed and the remainder is transmitted through the liquid crystal material. When correctly configured there is a dramatic change between the transmitted colour in the direction of arrow Y and reflected colour in the direction of arrow Z (Figure 3) The region on either side of the liquid crystal layer in Figure 3 is a transparent polymer or glass. To achieve this effect, the area of the substrate which is occupied by the liquid crystal must be transparent or translucent.

The transmitted and reflected colours are complementary, for example, a green reflected colour produces a magenta transmitted colour.

Liquid crystal materials can be incorporated into security device 10 either as a non-pigmented coating applied as a uniform film, as for example in WO-A- 03061980, or in the form of an ink as a liquid crystal pigment in an organic binder, as for example in EP-A- 1156934. The advantage of a liquid crystal ink is that it can be applied using conventional printing processes and it is therefore relatively straightforward to apply the liquid crystal material in the form of a design. However the colour purity, brightness and sharpness of the observed colour and colour-shift are significantly degraded for a pigmented liquid crystal ink compared to a liquid crystal film. This degradation is due to the variability in alignment of the cholesteric helical axis between the individual liquid crystal pigments compared to the uniform alignment of the liquid crystal film.

A disadvantage with the use of liquid crystal films in the security devices described in the prior art is that the production route requires several steps, such as coating the liquid crystal polymer on a carrier substrate, and then transferring the formed liquid crystal polymer film from the carrier substrate to the substrate of the security device. It is neither straightforward nor cost-effective to customise the base liquid crystal film for each security application.

In the prior art the visual appearance of multilayer security devices utilising liquid crystal films has been customised by the incorporation of additional layers prior to the device being applied to the substrate. For example, in EP-A-0435029 the security device is customised by applying a black printed image under the liquid crystal layer, or by locally varying the colour of the absorbing layer under the liquid crystal film. In WO-A-03061980 the liquid crystal security thread is customised by the introduction of demetallised characters using a dark resist. WO-A-0306l980 discloses a method for manufacturing a security substrate, which combines the use of demetallised indicia with the colourshift effect of liquid crystal materials.

In order to be effective against counterfeiting, the security device is preferably linked to the document it is protecting by content and registration to the designs and identifying information provided on the document.

The problem with the prior art methods of customising the security device 10 prior to application is that it is difficult to provide the registrational link between the design on the security device and the design on the document without using complex equipment. It is particularly difficult to incorporate security threads or stripes, which run as a continuous strip either in or on the document, in register. Currently it is therefore common to provide security threads or stripes based on liquid crystal films with repeating patterns or features along their length in order to avoid the need to register the device to the paper substrate in the machine direction during paper production.

The present invention overcomes the problems of the prior art by enabling the liquid crystal film of the security device to be customised either during, or after, the security device has been formed on the substrate.

The present invention therefore provides a method of forming a customisable security device, comprising the steps of applying a liquid crystal film to a base substrate, applying an at least partially absorbing layer to at least a part of one side of the liquid crystal film, and applying a custornising layer to at least a part of an opposite side of the liquid crystal film to the absorbing layer in selected regions to modify the appearance of the liquid crystal film such that contrasting regions are provided between those regions covered by the customising layer and those not covered by the customising layer, wherein the customising layer is applied after application of the security device to the substrate.

The invention also provides a method of forming a customisable security device, comprising the steps of applying a liquid crystal film to a base substrate, applying an at least partially absorbing layer to at least a part of one side of the liquid crystal film, further including the step of applying a customising layer which modifies the appearance of at least a part of the liquid crystal film in selected regions such that contrasting regions are provided between those regions with the customising layer and those without the customising layer, wherein the customising layer is applied during application of the security device to the substrate.

The security device formed by either of the methods of the present invention benefits from the excellent optical properties of a liquid crystal film, whilst retaining the design flexibility of a pigmented ink. The integration of the customisation measures for both the liquid crystal film and the substrate or document means that a large number of security devices can be produced from the same liquid crystal film. This enables the liquid crystal film to be produced in advance, and later customised and/or finished in the subsequent method steps. This results in economic advantages due to the industrial scale production of non-customised liquid crystal film.

The invention will now be described, by way of example only, with reference to, and as shown in the accompanying drawings in which:-Figure 1 depicts chiral nematic alignment of a cholesteric liquid crystal material; Figure 2 shows how the reflection from a cholesteric liquid crystal material varies with the angle of incidence; Figure 3 depicts the transmission and reflection of light incident on a liquid crystal material; Figure 4 is a cross-sectional end elevation of a security device prior to application of a customisation layer on a transfer substrate prior to application to a base substrate; Figure 5 is a plan view of a security device with the customisation layer and applied to a base substrate according to the present invention; Figure 6 is a cross-sectional end elevation of the security device of Figure 5 after application to a base substrate, taken on the line V-V on Figure 6; Figures 7 and 9 are a plan views of an alternative security device; Figures 8 and 10 are cross-sectional end elevations of the security devices of Figures 7 and 9 respectively, taken on the lines Vu-Vu and IX-IX respectively; Figures 11 to 18 are plan views of further alternative security devices applied to a substrate; Figure 19 is a plan view of yet a further alternative security device; Figure 20 is a plan view of two alternative security devices applied to a single substrate; Figures 21 and 22 are a plan view and a cross-sectional end elevation of an alternative embodiment of the security device applied to a substrate the crosssection being taken on the line XXII-XXII; and Figure 23 is a cross-sectional end elevation of a further alternative security device.

Referring to Figs. 4 to 6, a security device 10 formed in accordance with the present invention for protecting a document of value made from a security substrate 16 comprises a liquid crystal film 11, an absorbing layer 12 and a customisation layer 13 which is applied during or after the security device has been transferred to the security substrate 16.

The device 10 may be applied to or incorporated into security substrates 16 or secure documents in any of the conventional methods known in the prior art, for example as a patch, foil, stripe, strip or thread. The liquid crystal film 11 may be arranged either wholly on the surface of the document, as in the case of a stripe or patch, or may be visible only partly on the surface of the document in the form of a windowed security thread.

Security threads are now present in many of the world's currencies as well as vouchers, passports, travellers' cheques, identity cards, authentication labels, postal stamps and other documents. In many cases the thread is provided in a partially embedded or windowed fashion where the thread appears to weave in and out of the paper. Methods for producing paper with so-called windowed threads can be found in EP-A-0059056 and EP-A-0860298.

In one embodiment, the device 10 may be incorporated into a document such that regions of the device 10 are viewable from the both sides of the document. Methods for incorporating a security device 10 such that it is viewable from both sides of the document are described in EP-A-1l41480 and WO-A-03054297. In the method described in EP-A-ll4l480, one side of the device 10 is wholly exposed at one surface of the document in which it is partially embedded, and partially exposed in windows at the other surface of the substrate.

In the case of a stripe or patch, the liquid crystal film 11 may be coated onto a carrier substrate 14 and transferred to the security substrate 16 in a subsequent working step. The device 10 can be applied to the security substrate 16 using an adhesive layer 15. The adhesive layer 15 is applied either to the liquid crystal film 11, or the surface of the security substrate 16 to which the device 10 is to be applied. After transfer, the carrier substrate 14 may be removed, leaving the security device 10 as the exposed layer. Alternatively the carrier layer 14 can remain as part of the structure acting as an outer protective layer.

Following the application of the security device 10, the security substrate 16 undergoes further standard security printing processes to create a secure document, including one or all of the following; wet or dry lithographic printing, intaglio printing, letterpress printing, flexographic printing, screen printing, and/or gravure printing. In one aspect of the present invention, customisation of the liquid crystal film 11 takes place at the same time, and preferably using the same equipment, as the standard security printing processes.

In the following examples the security device 10 is applied to the secure substrate 16 as a stripe, but in each case, unless stated, the method of customisation is equally applicable to patches, windowed security threads and partially elongate elements that are viewable from either side of the document.

Figure 4 is a cross-sectional view of a security device 10 prior to application of a customisation layer, the device 10 being suitable for application to a security substrate 16 as a stripe. The device 10 is formed on a carrier substrate 14, which may be coated with an optional release layer 17, onto which is applied a liquid crystal material forming a uniform liquid crystal film 11. The liquid crystal film 11 can be formed on the carrier layer 14 by coating a polymeric liquid crystal material and then curing to form a film or by transferring or laminating an already formed liquid crystal film 11 onto the carrier substrate 14. An absorbing layer 12 is then printed over the liquid crystal film 11. An adhesive layer 15 is applied to the absorbing layer 12 and the device 10 is ready to be transferred to a security substrate 16, such as a banknote.

In one embodiment of the invention, as shown in Figs. 5 and 6, the customisation of the security device is achieved by applying a customisation layer which is a scattering layer 13, in the form of a design, to the exposed liquid crystal film 11. In a preferred embodiment the scattering layer 13 takes the form of a matt varnish or lacquer which-can be applied using one of the standard security printing processes. In this context a matt varnish or lacquer is one that reduces the gloss of the liquid crystal film 11 by scattering the light reflected from the liquid crystal film 11. One preferred example of a matt varnish is a suspension of fine particles in an organic resin which migrate to the surface of the varnish or lacquer when it is applied to the liquid crystal film 11. The surface particles scatter the light as it passes through the varnish resulting in a matt appearance. In an alternative solution the fine particles can be replaced by organic waxes. As a further alternative, the scattering layer 13 can be generated by embossing a matt structure into the surface of a liquid crystal film.

Suitable embossed matt structures are described in W0-A- 9719821. The scattering layer modifies the colourshifting properties of the liquid crystal film 11 such that two contrasting optically variable regions can be defined as follows: Region A -Liquid crystal film 11 over absorbing layer 12. In this region the reflective colourshift of the liquid crystal film 11 is observed i.e. the wavelength of reflected light is dependent on the angle of incidence, which results in a colour change perceived by the viewer as the device 10 is tilted, for example red to green as the device 10 is tilted away from the normal.

Region B -Light scattering layer 13 above Region A. In this Region, the scattering layer 13 modifies the appearance of the colourshifting liquid crystal film 11.

The liquid crystal film 11 has a uniform surface which exhibits negligible scattering of light and, for the situation where there is directed white light illumination from a distant light source, the incident light undergoes specular reflection and a high gloss surface is observed the colour of which is dependent on the angle of the viewing direction relative to the substrate. The scattering layer 13 modifies the surface of the liquid crystal film 11 such that the reflection is now more diffuse reducing the glare of the liquid crystal film 11 and increasing the angular range over which the respective colours of the security device 10 are easily viewable to the authenticator.

In two further embodiments shown in Figs. 7 and 8, and 9 and 10 respectively, the absorbing layer 12 is applied in the form of a design and by combining with the scattering layer 13 enables the creation of two further optically variable regions that can be defined as follows: Region C -Liquid crystal over transparent adhesive and base substrate 16, for example paper or an opaque polymeric coating on a transparent polymeric substrate.

Where the absorbing layer 12 is absent, the intensity of the transmitted colour through the liquid crystal film 11 saturates the reflective colour. The transmitted and reflected colours are complementary, for example, a red to green colourshift in reflection is seen as a cyan to magenta colourshift in transmission. Therefore in Region C the light transmitted through the liquid crystal film 11 is observed against a predominantly white background of the substrate 16 and gives the substrate 16 a noticeable tint of colour which exhibits a complementary colour shift to Region A. Region D -Light scattering layer applied over Region C -The scattering layer 13 effectively negates the colourshifting effect of the liquid crystal film 11 over transparent adhesive 15 and the substrate 16.

Whilst the use of a black, or very dark, substantially totally absorbing layer 12 may give rise to the most strong colourshift effects, other effects may be generated by the use of a partially absorbing layer 12 of other colour or a combination of colours, giving rise to differing apparent colourshift colours. The use of partially absorbing layers 12 of different colours enables the number of optically variable regions A, B, C, D to be increased further. The absorbing layer 12 of the present invention may comprise a pigmented ink or coating or alternatively a non-pigmented absorbing dark dye can be used.

The use of these different optically variable regions will now be described further by use of the

examples below.

Referring back to Figs. 5 and 6 which illustrate the security device 10 transferred to a plain, substantially white security substrate 16. The scattering layer 13 in the form of a matt varnish is applied after transfer in the form of a design which cooperates with the liquid crystal film 11 to form optically variable regions A and B. In region A the liquid crystal film 11 lies over the absorbing layer 12 defining the background, and in region B scattering layer 13 lies over the liquid crystal film 11, which already lies over the absorbing layer 12, defining the dollar symbol. For the purpose of this example the liquid crystal film 11 exhibits a red-green colourshift when viewed in reflection over a dark absorbing layer 12. However the invention is not limited to this colourshift and any colourshifting liquid crystal film 11 can be used.

On viewing the security device 10 under ambient lighting conditions and from normal incidence (viewing direction a in Fig. 6) the background region A and region B both appear red due to the reflected light of the liquid crystal film 11. However, at normal incidence the intensity of the specular reflection from region A is less than the intensity of the diffuse reflection from region B, and therefore region B appears lighter than region A and the two regions are visually distinct.

On changing the viewing direction from normal incidence (viewing from cx through 13 to y), the reflected light of the liquid crystal film 11, present in regions A and B, switches from red to green. The matt varnish of the scattering layer 13 in region B scatters the reflected light and increases the angular range at which the green colour is observed and therefore the switch from red to green occurs closer to normal incidence for region B compared to region A. With reference to Fig. 6, region B will switch from red to green at viewing direction 13 and region A will switch from red to green at viewing direction y.

The customised security device 10 in Figs. 5 and 6 comprises two colourshifting regions which are clearly distinct from each other. In addition to this, the optically variable nature of the security device 10 is further enhanced by the difference in gloss between regions A and B. As the angle of view is changed, the intensity of the diffuse reflected light in region B remains constant but the intensity of the specular reflection from region A varies such that it is either equal to, less than or greater than the intensity of the diffuse reflection from region B. The angular range at which these conditions occur depends on the lighting conditions but on tilting the sample in ambient conditions an angle of view can be located such that the intensity of regions A and B are the same and therefore indistinguishable and where the intensity of region A is greater than region B nd vice-versa. Therefore on tilting the device 10 shown in Figs. 5 and 6, the dollar symbol will appear to come in and out of view depending on the degree of specular reflection from the background liquid crystal film 11.

The designs generated by the customisation are preferably in the form of images such as patterns, symbols and alphanumeric characters and combinations thereof. The designs can be defined by patterns comprising solid or discontinuous regions which may include for example line patterns, fine filigree line patterns, dot structures and geometric patterns.

Possible characters include those from non-Roman scripts of which examples include but are not limited to, Chinese, Japanese, Sanskrit and Arabic.

Figs. 7 and 8 illustrate an alternative embodiment of a security device 10 to that shown in Figs. 5 and 6, except that, in this example, the dark absorbing layer 12 is in the form of a design and cooperates with the liquid crystal film 11 and the matt varnish of the scattering layer 13 to form an additional optically variable region C. The dark absorbing layer 12 is omitted from certain regions such that in region C the liquid crystal film 11 is over the transparent adhesive 15 and the base substrate 16 defining the repeating pattern of the word "STRIPE".

Region C, when viewed from normal incidence, appears as the substrate 16 tinted cyan by the transmitted light of the liquid crystal film 11. On changing the viewing direction from normal incidence (viewing from a through 13 to y) the transmitted light, present in region C, switches from cyan to magenta. The colours present in region C, resulting from the light transmitted through the liquid crystal film 11, are the complementary colours to the reflected light colours observed in region A. The customised security device 10 of Figs. 7 and B comprises three colourshifting regions A, B and C, which are clearly distinct from each other. In addition to this, the optically variable nature of the device 10 is further enhanced by the difference in gloss between regions A and C as described with reference to Figs. 5 and 6. In addition, for the viewing direction where the specular reflection is at its most intense the glare from region A saturates the localised areas of the tinted substrate in region C, resulting in the designs defined by regions C being hidden from view. For this to be most effective it is preferable that the individual design e1ement, for region C, for e.g. alphanumeric characters, have an area of less than 30mm2.

In summary the device 10 shown in Figs. 7 and 8

comprises three viewing regions A,B,C which exhibit contrasting colourshifts and, in addition, two of the regions B,C are substantially invisible at certain angles of view resulting in a device 10 which is striking and memorable to the general public but very complex for a potential counterfeiter to try to reproduce.

Figs. 9 and 10 illustrate a further embodiment of the invention in which the security device 10 is customised by the localised application of a matt varnish which forms the scattering layer 13. The dark absorbing layer 12 and the matt varnish are applied in the form of designs and cooperate with the liquid crystal film 11 to form optically variable regions A, B and C as described with reference to Figs. 7 and 8. In this embodiment, a further region D is formed where the matt varnish is applied over sections of the liquid crystal film 12 that is just over the transparent adhesive 15 and the base substrate 16, defining a box around the word "STRIPE".

The matt varnish effectively negates the colourshifting effect of the liquid crystal film 11 over the transparent adhesive 15 and the base substrate 16 and the colour of the substrate 16, preferably substantially white, will be visible in this region D irrespective of viewing direction. Therefore, on tilting the device 10 shown in Figs. 9 and 10 the word "STRIPE" (region C) will switch from a cyan tinted substrate colour to a magenta tinted substrate colour, while the surrounding box (region D) will have the colour of the untinted substrate 16.

The switch from cyan to magenta is not instantaneous and the colours are difficult to see with the naked eye close to the switching angle and therefore for angles of view close to the switching angle regions C and D are indistinguishable. Viewing at normal incidence, the word "STRIPE"appears cyan, and then on tilting away from the normal incidence disappears into the white background of the box, before reappearing on further tilting but now in the colour magenta.

One of the advantages of the present invention is that it enables the customised regions of the liquid crystal film 11 to be easily registered to the adjacent security features on the substrate 16. The matt varnish of the scattering layer 13 can be applied at the same time as the traditional security printing on the substrate 16 using any of the standard security printing processes including one or all of the following; wet or dry lithographic printing, intaglio printing, letterpress printing, flexographic printing, screen printing, and/or gravure printing. For example the matt varnish can replace one of the colours on a litho or intaglio printing press or be printed using an additional unit on a gravure or flexographic printing press. The fact that the varnish is applied during the same printing process as the surrounding substrate 16 printing means that the tight registrational tolerances, which are standard between different colours on the substrate 16, can be achieved between the customised images on the applied security device 10 and the traditional security printing on the substrate 16.

Fig. 11 shows an example where the customised image is registered to a security feature 17, in the form of printing, on the security substrate 16. As before, a matt varnish is applied to form the scattering layer 13 in the form of a design and cooperates with the liquid crystal film 11 to form optically variable regions A and B as defined previously. In this example the matt varnish is applied during the lithographic printing of the substrate 16 and forms optically variable region B in the form of the letter "L" which is registered to the letters "D" and "R" printed on the substrate 16 on either side of the security device 10 to form the identifying information "DLR". In a preferred embodiment the letters D and R can be printed in one of the colours of the liquid crystal film 11 to further increase the link between the security device 10 and the substrate 16.

The example shown in Fig. 11 does not require the original security device 10 to be transferred to the security substrate 16 in register with any security features 17. However if the security device 10 comprises a patterned absorbing layer 12 in order to create optically variable regions C and/or D, then it may be beneficial to register the designs defined by regions C and D with the adjacent security features 17 on the substrate 16. One method of achieving this is to register the application of the original security device 10 such that the same region of the patterned absorbing layer 12 appears on every document formed from the substrate 16.

The method for doing this will depend on the chosen method of incorporation into the substrate 16 for the liquid crystal film 11, for example as a thread, stripe or patch etc. One possible thread registration system, described in GB-A-235959, monitors the location of a control feature on a security element as it is being unwound and fed into the papermaking machine and a control feature on the substrate as it is formed. The system uses these position indicators to control the tension of the security element and rate of its embedment, so that the control features of the security element and substrate are in register.

The incorporation of a patch or stripe in register can be done using known registration systems to ensure that the device 10 is correctly placed on the substrate 16. An alternative method for registering the designs defined by regions C and D with the adjacent security features 17 on the substrate 16 is to apply the absorbing layer 12 to the substrate 16 prior to the application of the liquid crystal film 11. In the case of a surface applied stripe, this would remove the requirement for registration in the machine direction and therefore only require the rather more straightforward requirement of registration in the cross-direction.

Fig. 12 shows one example where the customised images defined by optically variable regions A, B, C, and D are registered to the traditional printing 18 on the security document. The matt varnish, which forms the scattering layer 13, is applied in the form of a design and cooperates with the liquid crystal film 11 and the patterned absorbing layer 12 to form optically variable regions A, B, C and D as defined previously. The dark absorbing layer 12 is applied in blocks along the device defining regions A and C. The matt varnish is applied during the lithographic printing of the substrate 16 and forms optically variable regions B and D. Region B is formed within region A in the form of the letters "TRIP", which is registered to the letters "S" and "E" printed on either side of the security device 10 to form the word "STRIPE". Region D is formed within Region C in the form of the letters "TRIP" which is registered to the letters "S" and "E" printed on either side of the security device to form the word "STRIPE". In addition to the different colourshifting effects exhibited by regions A, B and C, the letters "TRIP" will disappear and reappear from view on tilting for reasons described with reference to Figs. 5 and 6 (Region B) and Figs. 9 and 10 (Region D).

A security device 10 of the type shown in Fig. 12 exhibits three anti-counterfeit aspects; multiple contrasting colourshifting regions, the disappearance and reappearance of an identifying image on tilting, and a registrational link between the images on the applied device 10 and the traditional printed images 18 on the adjacent regions of the substrate 16.

Figs. 13a and 13b shows one example where the customised images defined by optically variable regions A, B and C are registered to printing 18 on the security substrate 16. The scattering layer 13 is applied by a screen printing process to both the substrate 16 and the device 10 such that it forms a continuous pattern across the interface. In this example, the scattering layer 13 contains a fluorescent material such that a visible colour is observed when viewed under UV illumination. The pattern of the varnish over the liquid crystal film 11 defines region B. In addition the dark absorbing layer 12 is omitted from certain regions such that in region C the liquid crystal film 11 is over the plain substrate 13 defining the image of a star. Region A is the background. The security device 10 is applied in register to the substrate 16 such that the stars always fall in the same position on each document formed from the substrate 16 and the varnish is then applied to form a complementary design. On viewing the substrate 16 in normal illumination (Fig. 13a) three different colourshifting regions, A, B and C will be observed on the liquid crystal film. When the substrate 16 is then viewed under TJV illumination (Fig. 13b)a continuous visible pattern will be observed to continue uninterrupted across the substrate 16 and the liquid crystal film in perfect registration, thereby providing a clear link between the liquid crystal film and the substrate 16 it is protecting.

In a further embodiment of the present invention, the customisation of the security device 10 occurs by applying printed information after the liquid crystal film 11 has been applied to the substrate 16. The liquid crystal film 11 may be printed with images using any of the conventional printing processes such as intaglio, gravure, ink jet, offset lithography, screen, dye diffusion and flexography. The print may be applied as a single print working in a single colour or as multiple print workings in multiple colours.

In a preferred embodiment the images are printed partly on the substrate 16 and partly on the liquid crystal film 11 such that the design continues uninterrupted between the two surfaces. In a further embodiment, one of the colours of the printed images matches one of the switching colours of the liquid crystal film 11. For example if the liquid crystal film 11 switches from red to green on tilting the substrate 16 away from normal incidence, then any red printed information will be substantially invisible at normal incidence but becomes visible as the sample is tilted as the static red of the printed information contrasts with the green of the optically variable liquid crystal film 11. In this manner a latent image security feature can be created.

Fig. 14 illustrates another example of the present invention. A red identifying image is printed such that a part 19a is on the substrate 16 and another part l9b is on the liquid crystal film 11. on viewing the substrate 16 at normal incidence (Fig. 14a) the liquid crystal film 11 appears red and saturates the printed information 19b on the film 11 such that only the printed information 19a on the substrate 16 is visible. On tilting the substrate 16, the liquid crystal film 11 switches from red to green revealing the printed information 19b on the liquid crystal film 11 and forming a complete image with the printed information 19a on the substrate (Figure 14b) One of the drawbacks of using liquid crystal films 11 to generate colourshifting images is that it is very difficult to transfer small regions of liquid crystal film 11 onto the substrate 16. It is therefore very difficult to generate high-resolution line patterns which are commonly observed on banknotes and referred to as filigreeline structures. The customisation of the liquid crystal film 11 after application to the substrate 16 can be used to provide high-resolution structures which exhibit a pure well-defined colourshift. This can be achieved by printing a design comprising a fine line spacing with a substantially opaque ink over the liquid crystal film 11. The liquid crystal film 11 will be visible between the spacings of the opaque lines and therefore give the appearance of a fine-line colourshifting structure. Preferably the opaque ink will have substantially the same visible appearance as the main substrate 16, such that, to the viewer, the liquid crystal material 11 appears to be present in the form of a highresolution image. An example of a typical fine line structure is shown in Fig. 15 in which a design comprising a high resolution line structure 20 has been applied over the liquid crystal film 11 using a substantially opaque ink, such that the liquid crystal film 11 is present within the line spacings. Preferably the design would be printed using lithograpahic or intaglio printing. An added advantage of using intaglio printing is that the design will exhibit a raised surface which can be identified by touch.

In the example shown in Fig. 16 a design 20b with a fine line spacing is applied onto a liquid crystal film 11 using an ink which has substantially the same colour as the substrate 16 to which the liquid crystal film 11 is applied to give the appearance of a high-resolution colourshifting line structure. In addition the design is extended into the adjacent substrate regions using a different coloured ink such that the lines of the extended design 20a are registered to the fine colourshifting lines 20b of the liquid crystal film 11.

The use of an opaque ink, substantially the same colour as the substrate 16, to cover part of the liquid crystal film 11 such that the exposed areas form a design, enables the liquid crystal film 11 to be used as a component in a wide range of security features. One particular example is a security device described in WO-A-20050470l3. WO-A2005047013 describes a security device for securing a document e.g. a banknote, which has a camouflage pattern formed over an image, which renders the image invisible when viewed under reflected light but visible when viewed under transmission light. The image is defined by two regions; a background region and a discontinuous pattern.

Fig. 17 illustrates an example where the colourshifting liquid crystal film 11 is customised to create a security feature as described in WO-A-2005047013. A liquid crystal security device 10, comprising a liquid crystal film and a dark absorbing layer, is formed on a carrier layer. The dark absorbing

layer 12 comprises a solid background region and a

discontinuous pattern 21 defines the numeral 50. The security device 10 is then transferred to a plain substantially white banknote paper substrate 16 as described above. Figure 17a shows the liquid crystal film 11 as applied to the document. In reflected light the discontinuous pattern 21 defining the numeral 50 and the solid background region are visible as a colourshifting liquid crystal film 11. The film is then custornised by printing an image 22 over the liquid crystal film in a colour substantially the same as the colour of the substrate. The camouflage pattern 22 is then defined by the liquid crystal film 11 visible in the unprinted areas between the printed lines (Fig. 17b). In reflected light, the viewer observes the camouflage pattern 22, as shown in Fig. l7b, which exhibits an optically variable effect on tilting the substrate 16. In transmitted light the numeral 50 becomes clearly visible due to the high contrast between the discontinuous pattern 21 and the other regions.

As an alternative to the printing of ordinary coloured inks, it is also possible to print functional inks. By functional inks we mean inks that react to an external stimulus. Inks of this type include but are not limited to fluorescent, phosphorescent, infrared absorbing, thermochromic, photochromic, magnetic, electrochromjc conductive and piezochromic.

As well as functional inks, it is also possible to print onto the liquid crystal film 11 with other optical effect inks. Optical effect inks include OVI and Oasis marketed by Sicpa. Other optical inks include inks containing iridescent, iriodine, pearlescent, liquid crystal and metal-based pigments.

In a further embodiment, the customisatjon of the security device 10 occurs by embossing the liquid crystal film 11 with non-diffractive line structures. Non-diffractive line structures are structures which produce an optically variable effect when the angle of incidence light varies, but in which this effect is not caused by interference or diffraction. Security devices based on non-diffractive line structures are known in the prior art for example WO-A-9002658 describes a security device in which one or more transitory images are embossed into a reflective surface. WO-A-9820382 discloses a further security device in which a group of elemental areas in which lines extend at different angles from each other form respective image pixels. US-A-1996539 discloses a decorative device in which a relief structure is formed in a surface and has an optically variable effect. WO-A- 2005080089 discloses a security device which has segments defined by line structures in a reflective portion of a substrate, which cause incident light to be reflected non-diffractively as the angle of incidence changes.

The embossing of non-diffractive line structures into liquid crystal films is particularly advantageous because the facets generated by the embossing result in a change in the angle of incidence of the incoming light, generating facets of differing colours due to the fact that the colour of the liquid crystal film 11 is dependent on the angle of view. The use of a non-diffractive line structure with a liquid crystal film 11 has two secure aspects; firstly the optically variable feature generated by the line structure and secondly localised regions exhibiting different colourshifts from

the background film 11.

The embossed line structures can take any convenient form including straight (rectilinear) or curved such as full or partial arcs of a circle or sections of a sinusoidal wave. The lines may be continuous or discontinuous and, for example, formed of dashes, dots or other shapes. By other shapes we mean the dots or dashes could have a graphical form. The line widths are typically in the range 10-500 microns, preferably 50-300 microns. Preferably, the individual lines are barely visible to the naked eye, the main visual impression being given by an array of multiple lines. The lines can define any shape or form, for example square, triangle, hexagon, star, flower or indicia such as a letter or number.

The embossed line structures are preferably formed by applying an embossing plate to the liquid crystal film 11 under heat and pressure. Preferably the embossing process takes place during the intaglio printing process and is carried out using an intaglio plate having recesses defining the line structures. Preferably the liquid crystal film 11 is blind embossed, i.e. the recesses are not filled with ink. However it is also possible that some of the recesses defining the embossed structure may be filled with ink and others left unfilled. Further intaglio printing or blind embossing may be carried out on regions of the substrate 16 adjacent to the liquid crystal film 11 using the same intaglio plate so as to achieve precise registration between the different regions.

Fig. 18 shows an example of a security substrate 16 comprising a liquid crystal film 11 which has been customised by embossing the film 11 after it has been applied to the base substrate 16. In this example a red-green colourshiftirig liquid crystal film 11 is used, i.e. the film 11 appears red at normal incidence and shifts to green as the sample is tilted away such that the angle of view is away from normal incidence. The embossed line structures 23, farmed by a respective set of substantially parallel raised lines, define the numeral "5". When viewed at normal incidence, both the embossed and non-embossed regions appear red.

On tilting the substrate 16 away from normal incidence, and viewing along viewing direction Y such that the lines extend at 900 to the incident light direction, the numeral "5" switches almost instantaneously from red to a predominantly green colour due to the dominant reflected light arising from the edges of the raised lines. In contrast, the non-embossed region switches from red to green at a greater angle of incidence relative to the flat substrate. The difference in the viewing angle at which the colour switch occurs arises because when viewed normally to the substrate the effective angle of incidence for light incident on the edge regions is greater than the angle of incidence for light incident on flat non-embossed regions. If the device 10 is rotated by 90 , such that it is viewed along viewing direction X parallel to the direction of the embossed lines, then on tilting the substrate 16 both the embossed and no-embossed regions switch from red to green at substantially the same viewing angle because very little light is reflected by the edge of the lines.

If the embossed lines are such that a significant portion of the edge region extends at angle of approximately 45 to the base substrate 16, then on tilting the substrate 16 away from normal incidence, and viewing perpendicularly to the direction of the lines, an almost Lnstantaneous switch from red to a predominantly green colour will occur as described previously. However on tilting the substrate 16 further, the angle of incidence for the light incident on the edge regions will move closer to normal incidence resulting in a switch back to red, effectively exhibiting a reverse colourshift.

One example of a non-diffractive line structure 23 suitable for embossing into a liquid crystal film 11 is described in WO-A-2005080089 WO-A-2005080089 describes a security device 10 comprising a substrate 16 having a reflective portion, which is provided with a raised line structure 23, the line structure 23 defining a plurality of segments, each segment being formed by a respective set of substantially parallel raised lines. The lines of at least three segments extend in different directions, wherein each segment causes incident light to be reflected non-diffractively in a variable manner as the angle of incidence changes. Thus, as the substrate 16 is tilted relative to the incident light and angle of view it will exhibit optically variable effects. The invention provides a security device 10 which presents a moving effect viewable across a wide range of angles. It is simple to authenticate yet difficult to counterfeit.

If the reflective portion of the device 10 in WO-A- 2005080089 comprises a liquid crystal film 11, then the different segments will exhibit regions of different colour and exhibit different colourshifts on tilting the device 10. Fig. 19 shows an example of such a device 10 where a red-green colourshifting liquid crystal film 11 is customised by embossing segments P, Q, R and S. When viewed at normal incidence all the segments P, Q, R, S and the non-embossed region appear red irrespective of the line direction within the segment P, Q, R, S. On tilting the device 10 away from normal incidence (relative to the flat substrate), and viewing along viewing direction X, the segments P, where the lines extend at 90 to the incident light direction, switch almost instantaneously to green due to the dominant reflected light arising from the edges of the raised lines. In contrast segment Q, where the lines extend parallel to the incident light direction, switches from red to green at a greater angle of incidence (relative to the flat substrate) than segment P and similar to the switch angle of the non-embossed because very little light is reflected by the edge of the lines. Segments R and S, with line orientations between these two directions, will switch from red to green at angles of incidence in-between these two extremes generating a device 10 with variable colourshfiting regions.

If the device 10 is rotated by 900 such that it is viewed along viewing direction Y, then angles of incidence at which the colourshift occurs in segments P and Q when viewed along viewing direction X will be reversed. In addition to the different colour-shifting regions, the device 10 will also display the otica11y variable effects as defined in WO-A-2005080089. When viewed along viewing direction X, segments P appear bright because the lines in these segments P extend at or near 90 to the incident light direction. When the device 10 is rotated so that the incident light direction is in viewing direction Y, segments Q appear bright. For viewing directions in between these two extremes some of the segments appear bright, while the remaining segments appear dark. Again, this brightness depends upon how close the lines defining the segment extend at 90 to the incident light direction. This provides a security device which presents a moving effect viewable across a wide range of angles.

Fig. 20 shows two examples where a liquid crystal film 11, in the form of a stripe, has been embossed post application to a substrate 16, such that the design of the emboss links in to other images on the liquid crystal film 11 and/or the substrate 16. On the left hand side of the substrate 16 shown in Fig.20 a blind embossing 24 of the liquid crystal film 11 during the intaglio printing forms the letters "TRIP" and this is registered to the letters "5" and "E" printed on either side of the film 11 during the same intaglio printing process to form the On the right hand side of the substrate 16 shown in Fig.20, the numeral "5" is formed within the liquid crystal film 11 by omitting the dark absorbing layer 12 and the numeral "0" is formed by a blind embossing 24 of the liquid crystal film 11 during the intaglio printing process. In addition a "$" symbol 18 is printed during the same intaglio printing process. The incorporation of the security device 10 and the subsequent intaglio printing process are controlled such that the "5", "0" and "$1' combine to display the denomination of the banknote "$50".

In a further embodiment the customisation of the security device 10 occurs during the transfer of the device lO to the substrate 16. This customisation method is applicable to surface applied stripes and patches. It is known, see for example US-A-5817205, to apply an adhesive or primer layer to a paper substrate during the transfer process of a stripe in a continuous in-line process by installing an in-line coating unit, such as a screen coater, prior to the stripe transfer unit. In the present invention, an in-line coating unit can be used to apply a layer to the base substrate 16, which is brought into contact with the liquid crystal film during the transfer of the device to the substrate and subsequently customises the applied security device 10.

The in-line coating unit prior to the transfer unit can be used to simply apply a single dark absorbing layer to the substrate 16 rather than applying the absorbing layer 12 to the liquid crystal film 11 prior to the transfer to the substrate 16 as described with reference to Figure 4. As indicated in previous examples the dark absorbing layer 12 can be patterned to generate designs within the liquid crystal film 11. The dark absorbing layer 12 can also be applied such that it extends outside the region covered by the liquid crystal film 11 and is visible as a printed layer on the substrate 16. This enables precise registration between the printed layer and the patterned liquid crystal film 11.

In another preferred embodiment, an in-line coating unit can be used to apply a second absorbing layer. The most efficient colour for the absorbing layer is black because it absorbs all wavelengths transmitted through the liquid crystal film 11 and the reflected light is solely a function of the pitch of the helical structure of the liquid crystal material. It is possible, however, to use other colours as an absorbing layer behind the film 11. These will act as colour filters reflecting some wavelengths of the transmitted component back through the liquid crystal film 11. The result is a modification of the observed colour shift, and therefore the use of differently coloured absorbing layers under one liquid crystal film enables designs to be generated exhibiting different colourshifts.

Fig. 21 illustrates an example where a security device 10 in the form of a stripe is customised during its transfer to the main substrate 16. A security device 10, comprising a liquid crystal film 11 and a first dark absorbing layer 12, is formed on a carrier layer 14. The first dark absorbing layer 12 is omitted in certain regions 25 to generate a pattern. The security device 10 is transferred to a plain substantially white banknote paper substrate 16 using a conventional foil stripe transfer machine, for example the MTL-840/S as supplied by Leonhard Kurz GmbH and Co. An in-line coating unit, positioned immediately prior to the foil transfer unit, is used to apply a second absorbing layer 26, of a different colour to the first dark absorbing layer 12, uniformly over the substrate 16 in the area to which the security device 10 is to be applied. Fig. 21 shows the cross-sectional view of the customised device 10 on the substrate 16. It can be seen that in region E the liquid crystal film 11 is visualised through the first dark absorbing layer 12 and in regions F, where the first dark absorbing layer 12 is omitted, the liquid crystal film 11 is visualised against the second differently coloured absorbing layer 26. Fig. 22 is the plan view of the customised device 10 on the substrate 16 and shows that region E, liquid crystal 11 visualised against first dark absorbing layer 12, defines the background and region F, liquid crystal 11 against second absorbing layer 26, defines the images, in this example a series of "$" symbols.

In the example shown in Figs. 21 and 22 the second absorbing layer 26 applied by the in-line coating unit is not registered to the applied security device 10 and its effect is observed through the omitted regions of the first dark absorbing layer 12. In a further example illustrated in Fig. 23, the second absorbing layer 26 is registered to the first absorbing layer 12 such that in region G the liquid crystal film 11 isvisualised against the substantially white substrate 16 enabling the generation of three distinct colourshifting regions. Fig. 23 also shows that the second absorbing layer 26 can be applied such that it extends outside the region covered by the liquid crystal film 11 and is visible as a printed layer 27 on the substrate 16. This enables precise registration between the printed layer 27 and the patterned liquid crystal film 22, thereby providing a clear link between the liquid crystal film 22 and the substrate/document it is protecting.

By selection of appropriate colours for the second absorbing layer 26 the designs defined by the region F can be visible at certain angles of view and invisible at others. For example the liquid crystal film 11 transmits all wavelengths except red at normal incidence and the first absorbing layer 12 is black and the second absorbing layer 26, defining the designs in region F, is red. Then, at normal incidence, the designs are invisible with the device 10 appearing a uniform red colour, but on tilting a different colourshift is observed for the liquid crystal regions in regions E compared to region F and therefore the designs are revealed.

Additional in-line coating units can be used to apply multiple absorbing layers of different colours or additional registered printed layers extending beyond the liquid crystal film 11. The chemistry of the absorbing layers, applied by the in-line coating units, can be chosen such that they additionally act as a primer or adhesive layer and increases the adherence of the security device 10 to the base substrate 16.

The layer(s) applied by the in-line coating unit can contain functional components that react to an external stimulus. Components of this type include, but are not limited to, fluorescent, phosphorescent, infrared absorbing, thermochromic, photochromic, magnetic, electrochromic, conductive and piezochromic.

The customisation layers applied to the liquid crystal device 10 by the in-line coating unit during the transfer of the device 10 to the main substrate 16 can subsequently be correlated and registered to images and designs generated by further standard security printing processes. In addition the device 10, customised during application to the substrate 16, can be further customised after application to the substrate 16 using the methods described with reference to Figs. 5-17 and the designs formed by both customisation steps can be registered to each other.

Claims

CLAIMS: 1. A method of forming a customisable security device,

comprising the steps of applying a liquid crystal film to a base substrate, applying an at least partially absorbing layer to at least a part of one side of the liquid crystal film, and applying a customising layer to at least a part of an opposite side of the liquid crystal film in selected regions which modifies the appearance of the liquid crystal film such that contrasting regions are provided between those regions covered by the customising layer and those not covered by the customising layer, wherein the customising layer is applied after application of the security device to the substrate.

2. A method of forming a customisable security device, comprising the steps of applying a liquid crystal film to a base substrate, applying an at least partially absorbing layer to at least a part of one side of the liquid crystal film, further including the step of applying a customising layer which modifies the appearance of at least a part of the liquid crystal film in selected regions such that contrasting regions are provided between those regions with the customising layer and those without the customising layer, wherein the customising layer is applied during application of the security device to the substrate.

3. A method of forming a customisable security device as claimed in claim 2 in which the customising layer is applied to the whole the liquid crystal film.

4. A method of forming a customisable security device as claimed in claim 2 in which the customising layer is applied to at least a part of the substrate wherein the customising layer is brought into contact with the liquid crystal film during application of the security device to the substrate.

5. A method of forming a customisable security device as claimed in any one of claims 2 to 4 in which the customising layer comprises a second absorbing layer on the same side of the liquid crystal film to the first absorbing layer.

6. A method of forming a customisable security device as claimed in claim 5 in which the first and second absorbing layers are applied in register with each other.

7. A method of forming a customisable security device as claimed in claim 5 or claim 6 in which the second absorbing layer is a partially absorbing layer.

8. A method of forming a customisable security device as claimed in any one of the preceding claims in which some or all of the contrasting regions are optically variable.

9. A method of forming a customisable security device as claimed in any one of the preceding claims in which the customising layer modifies the colour shifting properties of the liquid crystal film.

10. A method of forming a customisable security device as claimed in any one of the preceding claims in which the customising layer is a light scattering layer.

11. A method of forming a customisable security device as claimed in claim 8 in which the light scattering layer is a matt varnish or lacquer.

12. A method of forming a customisable security device as claimed in claim 8 in which the light scattering layer is an embossed matt structure.

13. A method of forming a customisable security device as claimed in any one of claims 1 to 8 in which the customisii-ig layer comprises an optically variable device.

14. A method of forming a customisable security device as claimed in claim 13 in which the optically variable device is printed with an optically variable ink.

15. A method of forming a customisable security device as claimed in claim 14 in which the optically variable ink contains an iridescent, iriodine, pearlescent, liquid crystal and/or a metal based pigment.

16. A method of forming a customisable security device as claimed in claim 13 in which the optically variable device comprises a non-diffractive line structure.

17. A method of forming a customisable security device as claimed in claim 16 in which the non-diffractive line structure is formed by embossing the liquid crystal film.

18. A method of forming a customisable security device as claimed in claim 16 or claim 17 in which the line structure is formed by a set of substantially parallel raised lines.

19. A method of forming a customisable security device as claimed in claim 16 or claim 17 in which the line structure defines a plurality of segments, each segment being formed by a respective set of substantially parallel raised lines, the lines of at least two segments extending in different directions, thereby providing at least three optically variable regions.

20. A method of forming a customisable security device as claimed in any one of the preceding claims in which the absorbing layer is applied in the form of a design having blank areas in which the layer is not present.

21. A method of forming a customisable security device as claimed in any one of the preceding claims in which the customising layer is applied such that it partially overlaps the absorbing layer leaving some regions of the absorbing layer not overlapped by the customising layer to provide at least three optically variable regions.

22. A method of forming a customisable security device as claimed in claim 21 as dependent on any of claims 11 to 13 in which the customising layer is applied such that some regions of the customising layer overlap with the blank areas in the absorbing layer, thereby negating the optically variable effect of the liquid crystal film.

23. A method of forming a customisable security device as claimed in any one of the preceding claims in which the customising layer is printed in the form of indicia.

24. A method of forming a customisable security device as claimed in claim 23 in which the indicia are printed in a single colour.

25. A method of forming a customisable security device as claimed in claim 23 in which the indicia are printed in multiple colours.

26. A method of forming a customisable security device as claimed in any one of the preceding claims in which customising layer is of substantially the same colour as the substrate.

27. A method of forming a customisable security device as claimed in any one of claims 23 to 26 in which the customising layer is printed with a functional ink which reacts to an external stimulus.

28. A method of forming a customisable security device as claimed in claim 27 in which the ink of the customising layer includes one or more of fluorescent, phosphorescent, infrared absorbing, thermochromic, photochromic, magnetic, electrochromic, conductive and/or piezometric characteristics.

29. A method of forming a customisable security device as claimed in any one of the preceding claims comprising the step of applying multiple absorbing layers of different absorption characteristics.

30. A method of forming a customisable security device as claimed in any one of the preceding claims in which the security device is applied to the substrate as a stripe, patch, a windowed or a non-windowed security thread.

31. A method of forming a customisable security device as claimed in any one of the preceding claims in which the absorbing layer is applied by coating the substrate during application of the security device.

32. A method of forming a customisable security device as claimed in any one of claims 23 to 31 in which the printed customising layer also forms printing on the substrate.

33. A method of forming a customisable security device as claimed in any one of the preceding claims in which the step of applying the customising layer is carried out simultaneously with printing the substrate.

34. A method of forming a customisable security device as claimed in any one of the preceding claims in which a single printing process is used to apply the customising layer.

35. A method of forming a customisable security device as claimed in any one of claims 1 to 33 in which multiple prints processes are used to apply the customising layer.

36. A method of forming a customisable security device as claimed in any one of the preceding claims in which the absorbing layer is a substantially totally absorbing layer.

37. A method of forming a customisable security device as claimed in ny one of the preceding claims wherein the customising layer creates at least one design, said at least one design being a pattern, symbol, alphanumeric or a combination of thereof.

38. A method of forming a customisable security device as claimed in any one of the preceding claims wherein the customising layer and absorbing layer are positioned relative to each other such that the combination of the contrasting regions creates at least one design, said at least one design being a pattern, symbol, alphanumeric or a combination of thereof.

39. A method of forming a customisable security device as claimed in claim 37 or claim 38 in which the at least one design has a plurality of solid regions.

40. A method of formihg a customisable security device as claimed in claim 37 or claim 38 in which at least one design has a plurality discontinuous regions.

41. A method of forming a customisable security device as claimed in claim 37 or claim 38 in which the patterns include line patterns, fine filigree line patterns, dot structures and/or geometric patterns.

42. A method of forming a customisable security device as claimed in any one of claims 37 to 41 in which the designs are formed in register with security features of the substrate.

43. A method of forming a customisable security device as claimed in any one of claims 37 to 42 in which the designs are formed in register with printed features on the substrate.

44. A method as claimed in any one of the preceding claims in which the absorbing layer is applied after the liquid crystal film is applied to the substrate.

45. A method as claimed in any one of the preceding claims in which the absorbing layer is applied before the liquid crystal film is applied to the substrate.

46. A security device formed by the method as claimed in any one of the preceding claims.

47. A security substrate comprising a security device formed on a base substrate by the method as claimed in any one of claims 1 to 45.

48. A security document made from the security substrate of claim 45 comprising a voucher, fiscal stamp, authentication label, passport, cheque, certificate, identity card, banknote or the like.

49. A method of forming a security device substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

50. A security device substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

711656, TAB, TAB