WO2003101755A1

WO2003101755A1 - Authentication means

Info

Publication number: WO2003101755A1
Application number: PCT/EP2003/005559
Authority: WO
Inventors: Christopher Regan
Original assignee: Ucb, S.A.
Priority date: 2002-05-31
Filing date: 2003-05-27
Publication date: 2003-12-11
Also published as: AU2003237695A1; GB0212638D0

Abstract

There is disclosed an article for authentication (e.g. security document or sheet made from a transparent polymeric film such as biaxially oriented polypropylene (BOPP)) which comprises a first luminescent material in first region (201) (e.g. an optionally patterned coating of a pigment of a rare earth complex) and a second luminescent material in a second region (207) (e.g. 2,5-thiopheneduiylbis(5-tert-butyl-1,3-benzoaxole - Uvitex B from CIBA optionally incorporated at 2 x 10-3 % w/w through the core layer (205) of the polymer film). The second region contains a transparent window (207), the rest of the article is optionally opacified. The article can be folded over itself so the window (207) overlaps with at least part of the first region. The two materials luminesce at different visible wavelengths when excited (e.g. the coating fluoresces red/orange when excited with UV-C at 254 nm whereas the window fluoresces blue when excited with UV-A at 365 nm). However when the article is folded so the first region (201) is viewed through the transparent window (207) and is then excited (e.g. illuminated with broad spectrum UV) the combined luminescence of both materials is seen as a colour change (e.g. fluorescent purple / green) which may be used to authenticate the article.

Description

AUTHENTICATION MEANS

The present invention relates to security features used to authenticate an article such as a security document comprising a transparent substrate for example a polymer film.

It is well known that additives which have a distinct non-visible spectral signature can be incorporated into polymer articles at the time of their manufacture to provide a means of authentication of the article.

For example a luminescent additive can be incorporated into a polymer film at the time of manufacture so the film will luminescence under an ultra-violet light source to identify the film. However incorporating such additives into the film can cause problems as the additive can migrate to the film surface causing blooming. This can adversely effect the surface properties of the film such as its reception to coating and/or its printability.

Furthermore using a single additive in the film can be more readily detected by a counterfeiter and may be mimicked by coating or overprinting the film. Other more sophisticated means exist to deter counterfeiting but these can require expensive equipment or training to detect and are not readily apparent to the causal user.

Therefore in practise most known commercially available polymeric film used in security documents is optically UV dull, which means that when an ultra-violet light source is passed over the surface of the film it is not excited by the light and does not depict a luminescent glow.

Various prior art documents describe security substrates to which UV fluorescent materials have been added.

GB 2,300,596 (Portals Ltd) describes a fluorescent security feature in a transparent film (whether in a coating or in the film substrate) which consists of two materials which fluoresce under UV light at different wavelengths. The materials are located in different layers with a UV absorber positioned between these layers. The film is designed to have a different appearance in UV transmitted and reflected light and also exhibits a different appearance depending on which film surface is viewed. This teaches away from the present invention where a window on the film contains UV fluorescent material, and this window is used to view another UV fluorescent security feature positioned in another region of the film so the fluorescent colours combine. The intermediate layer of UV absorber described in '596 would block any such combination or interaction between two UV-fluorescent layers and indeed is designed to do so. Examples of films described in this document are shown schematically in Figures 11 , 12 and 13 herein.

EP 0775589 (Agfa-Gevaert) (= US 5,733,352) describes a laminated transparent security substrate having a single fluorescent dye incorporated into an information layer sandwiched between the laminate layers. The dye fluoresces when irradiated with light of wavelength between 200 nm and 1000 nm to provide a readily verifiable effect of light piping from the edge of the film when the film is irradiated. This document requires that the dye must be located within a laminate sandwich and away from the substrate edge (e.g. see Example 1 , page 9, line 26) to create the best light piping effect. Using two different UV absorbers is not suggested. A laminate structure also teaches away from using more flexible non laminated substrates and thus from self-authentication using a window. Examples of films described in this document are shown schematically in Figures 14 and 15 herein.

DE 4114732 -A (Bayer) describes a security mark made from an intimate mixture of two fluorescent materials (one material with an excitation radiation of short wavelength UV the other material excited by X-rays). The mixture is added as a coating to a security substrate (mainly paper is envisaged). This coating provides a unique spectra for covert authentication of the substrate when viewed under selected radiation. As the two materials are mixed together this teaches away from using two UV-fluorescent materials located in different regions of the substrate to create a new effect when the regions are overlapped. Examples of films described in this document are shown schematically in Figures 16, 17 and 18 herein.

There is no suggestion in these prior art documents that suitable regions of a film might be folded to overlap so that fluorescent radiation emitted from a material in one region of the film might combine with and/or be used to excite fluorescence in another material in another region of the film to create a different appearance in the overlapping region. Indeed the prior art films either require the film to contain intermediate UV absorbing layers, use less-flexible laminated substrates which are thus difficult to bend to create overlapping regions and/or use mixtures of absorbers which could not be separately added to different regions of the film.

Yet the applicant has discovered adding a luminescent additive to a film (whether in a inner layer or in a coating) in an region positioned near the film edge becomes even more dramatic under illumination with the exciting radiation, as the edges of the film, show a "glow" due to total internal reflection of the luminesced light within the film in much the same way as the fibre optic phenomenon. The applicant has also found that if the film has been opacified (e.g. to provide a printable surface) this edge effect tends to be-revealed within the clear window areas of the design which have been left non-opaque rather at the edges near where the film surface has been opacified.

Various prior art documents describe the use of transparent windows as a security feature.

WO 83/00659 (Securency) (= US 4536016) describes an opacified transparent film which can be used as security substrate having a transparent window therein. The window optionally contains an optical variable device such as a Moire pattern or diffraction grating added to the window using a transfer foil.

EP 0388090 (De La Rue) describes a sheet with a transparent window as a security device made for example by partially over printing a transparent substrate. The window is used so features printed on the reverse side of the sheet can be seen in register through the window as means to deter counterfeiting and copying.

Neither of these documents suggest that two or more different luminescent materials might be viewed in combination through a transparent window. Perceived problems with register of an image would deter folding over such windows as means to self-verify other locations on the film.

Use of a window as a self verifying device for other regions of a security product has been described. For example WO 98/15418 (Securency) (= EP 0930979, US ,6273,473 & US 6,062,604) describes a self verifying security document in which a transparent window on a security document is used to verify a security feature located on another part of the document. WO 00/41159 (UCB) describes a self-verifying label or article which contains a window used to authenticate a differently located security feature.

However these documents teach that it is undesirable to use UV fluorescent materials as a means of verification as they require illumination by external sources of UV radiation. Instead the windows described in these prior art documents use inherent devices on the film (such as Moire pattern or diffraction gratings) to produce an overt effect which can be easily verified by the end user.

In contrast the present invention may also encompass semi- overt and/or covert features where it would be acceptable to use additional equipment to authenticated the film if necessary. It is not a disadvantage for the security device of the present invention to be hidden from a casual user as the feature may then also remain undisclosed to a counterfeiter (and so not be so readily coped).

It is an object of the invention to provide an improved security feature for use in aiding the authentication of an article. The term "article" as used herein includes security documents.

Therefore broadly in accordance with the present invention there is provided an article comprising a first region having a first colorant and transparent second region having a second colorant, where the respective first and second colorants luminesce at different visible wavelengths when excited by excitation means, and where the first and second regions can be overlapped to with one another by manipulation of the article and/or document to form an overlap region between the first and second regions such that when the article is excited, the combined luminescence of both the first and the second colorants is seen through that part of transparent second region which defines the overlap region.

A further embodiment of the present invention provides an article comprising a first portion and transparent second portion comprising respectively first and second colorants which fluoresce at different visible wavelengths when irradiated by exciting radiation at separate (preferably non-visible, more preferably UV) wavelengths, the first and second portions being capable of being brought to register with on another by manipulation of the article or document such that when the first portion is irradiated with the exciting radiation through the transparent second portion, the combined fluorescence of both the first and second colorants can be observed through the transparent second portion.

Another embodiment of the present invention provides a method for authenticating an article comprising a first region having a first colorant and transparent second region having a second colorant, where the respective first and second colorants luminesce at different visible wavelengths when excited by excitation means, the method comprising the steps of:

(a) overlapping at least a part of the first and second regions with one another by manipulating the article and/or document to form an overlap region between said first and second regions

(b) exciting said first and second colorant so they both luminesce; and

(c) observing the combined luminescence of both said first and said second colorants through that part of the transparent second region which is defined by the overlap region to authenticate said article and/or document.

Yet another embodiment of the present invention provides a method of authenticating a product comprising the steps of: (a) positioning into register a first and second portion of an article comprising respectively a first and second colorants which fluoresce at different visible wavelengths when irradiated as different non-visible wavelengths;

(b) irradiating the first portion through a transparent second portion to cause both portions to fluoresce; and

(c) observing the combined fluorescence spectrum through the transparent second portion.

Preferably the excitation means comprises exciting radiation, more preferably at separate wavelengths for each colorant. Most preferably the wavelength of each exciting radiation is non-visible, such as UV radiation for example of wavelength 254 nm and/or 365 nm.

Conveniently the exciting radiation for the first colorant may substantially passes through the transparent second region. More conveniently the same source of radiation (but not necessarily the same wavelength) provides the exciting radiation for both the first and the second colorants. Most conveniently both the first and second colorants are excited substantially simultaneously throughout the overlap region.

Alternatively the first colorant throughout the overlap region is excited by the luminescent radiation emitted from the excited second colorant after said radiation passes through the transparent second region.

The term luminescence as used herein denotes any emission of visual radiation from an electronically excited state of a material. Luminescence thus encompasses (among other things) both fluorescence and phosphorescence. An example of fluorescence is where the excited state is an unstable singlet from which radiative decay to the ground state occurs very rapidly through an allowed transition. Delayed fluorescence via other routes (such as E-type, P-type and/or recombination fluorescence) may also be possible. An example of phosphorescence is where the excited state is a more stable triplet from which radiative decay to the ground state occurs less rapidly via an intermediate species as the direct radiative path is a forbidden transition.

The excited state which luminesces may be formed by any suitable means, most usually by excitation with any suitable radiation, such as high energy invisible UV (photo-luminescence), X-rays (radio-luminescence), electrons (cathodo-luminescence); infra-red radiation (up-conversion); and/or any suitable combinations thereof. However any convenient excitation means may be used to obtain a population of excited state. A non exhaustive list of some non-radiative excitation methods includes any of the following and any suitable combinations thereof: chemical reaction (chemi-luminescence - such as peroxide decomposition, singlet oxygen, ion radical and/or electron transfer [e.g. electrochemi-luminescence]); biological process(es) (bio-luminescence); strong electric field (electro-luminescence); and/or stress (tribo-luminescence).

The preferred mode(s) of luminescence used in the present invention are fluorescence and/or phosphorescence, more preferably that induced by irradiating with exciting radiation, most preferably by radiation within the UV region.

Preferably the excitation means is non-destructive of the article and/or document which incorporates the luminescent material(s). For example methods to produce luminescence which require sampling of material, use of highly reactive species, excessive heating, and/or irradiation at excessively high flux densities and/or energies are not generally preferred.

As used herein the term visible radiation or visible light denotes electromagnetic radiation having a wavelength from about 350 nm to about 750 nm. As used herein the term ultra-violet (UV) radiation (or UV light) denotes electromagnetic radiation having a wavelength from about 100 nm to about 400 nm. UV-radiation includes the sub regions of UV-A (320 nm to 400 nm), UV-B (290 nm to 320nm) and UV-C (100 nm to 290 nm). It can be seen there is a slight overlap between the visible and UV-A regions of the electromagnetic spectrum. As the context dictates the terms UV-A, UV-B and UV-C are also used herein to denote that a specific wavelength of UV radiation falls within these regions as well as denoting the regions themselves.

The UV in normal sunlight is mostly UV-A with some UV-B and little or no UV-C. Radiation at smaller UV wavelengths is partially (UV-B) and almost completely (UV-C) absorbed by ozone present in the upper atmosphere. Therefore although sunlight alone may be sufficient to produce luminescence, depending on the luminescent material there may also be a need for additional artificial source(s) of UV light to excite strong luminescence (i.e. that which is easily visible in daylight). The UV source which excites luminescence can emit a broad spectrum of wavelengths including those wavelengths desired, or can be tuned to emit only those wavelength(s) which are required to excite the selected luminescent materials(s). Wavelengths of 365 nm (UV-A) and 254 nm (UV-C) are those typically used to detect counterfeiting as they are present in conventional UV lamps.

One embodiment of the present invention comprises the selection of first and second colorants which each luminesce at different visible wavelengths when irradiated by non visible radiation (preferably UV). The exciting wavelength(s) for each colorant are substantially different. The first colorant may be applied onto an opacified region of the surface of a polymeric film. The second colorant may be incorporated throughout the whole film, throughout a selected transparent region thereof and/or coated and/or printed on top of a transparent region of the film in which case the film need not be impregnated.

As used herein, unless the context indicates otherwise, the term transparent means transparent both to the visible light emitted and to the source of excitation radiation where used (such as UV).

With reference to Figure 1 to 3 (and by analogy to the other figures), in the first embodiment the first colorant may be selected so it emits visible light when irradiated at a first wavelength (preferably in the UV) which is neither absorbed by the film nor by the second colorant. Optionally the first colorant may be opaque to the wavelength(s) which cause the second colorant to luminesce. A first region of the film may be printed or coated on one side with the first colorant (1). A second region of the film disposed from the first region may comprise a transparent window (7) in the film which may expose the film impregnated with the second colorant and/or may be a overprinted with the second colorant on the same or opposite side of the film (5) to the first colorant (more preferably the opposite side). The transparent window may be formed by a gap in an opacifying coating (3) or treatment on one side of the film surface.

In the figures arrow A denotes for broad spectrum radiation which excites both colorants and A1 + A2 for those wavelengths which separately excite the first and second colorants respectively. Arrow B denotes luminescence from the first colorant and arrow C from the second colorant. Crossed arrows indicate no luminescence occurs due to the absence of the relevant colorant or the blocking of the exciting radiation to that region.

When the film is irradiated with exciting radiation (arrows A or (A1 + A2)) the first and second colorants luminesce at their different visible wavelengths (respectively arrows B and C) to give a marks of different colour in the first region (1) and transparent window (7) respectively.

However when the film is folded to view the first region (1) through the transparent window (7) the colorants overlap through the window. The window may be illuminated from the side opposite the first region (1) with the non-visible exciting radiation (arrow A) to excite both the first and second colorants (e.g. broad spectrum UV) to view a new "UV feature". The film window (7) does not block excitation or luminescence of the first colorant. The second colorant is excited at different wavelengths from the first colorant. This has been found to be important as if the excitation wavelengths of the two colorants are found to be substantially the same, attenuation of radiation due to absorption by the second colorant as the radiation passes through the window means the first colorant does not luminesce or only does so weakly. The applicant tried using two colorants which were excited by the same UV region but in that case the impregnated film also absorbed the UV so the (yellow) colorant underneath the window was dull and did not luminesce.

The second colorant has also been selected so it is transparent to the luminescence from the first colorant. Thus on irradiation (indicated by arrows A in the Figures) both the first and second colorants can be seen to luminesce at visible wavelengths through the window to a new coloured luminescent feature additive of the luminescent colour of the two colorants.

The combined colour seen through the window can be more sensitive to the precise luminescence spectrum of each colorant making it more difficult for a counterfeiter to match the feature. If the second colorant is incorporated into the film directly then the edge effect and luminescence from other parts of the film make it more difficult to reproduce this feature.

The new additive luminescence feature can be made one way as for example if the folded film is viewed or / irradiated from the other film surface on the other side of the fold from the transparent window the first colorant and/or it's underlying opaque coat can be selected to block the exciting radiation from the window and/or the luminescence from the second colorant so no colour change can be seen though the transparent window from that side. This feature is thus a non-visible (UV) one-way security feature as it seen from only one side when the film is folded over.

If a counterfeiter separately detects the presence of both the first and second colorants and prints luminescent colorants onto the film to mimic the individual features of each colorant he is unlikely to appreciate the need to match their spectral properties to produce the above one way and additive UV feature through the window. Even if the effect was understood it would be very difficult to analyse and detect in the label the colorants with the correct spectra which would be required to reproduce exactly the same additive colour seen through the window. This is especially true if the second colorant is incorporated into the bulk film rather than overprinted on the window.

To exhibit the edge glow effect it is preferred that the second region is positioned near to or adjacent the edge of the sheet. Of course this feature could be use independently of the first colorant and is a further aspect of the present invention. Various alternative arrangements of a sheet according to the invention are shown in the Figures herein including the one-way effect of the feature seen on folding.

Colorants which are suitable for use in the present invention are any with the required luminescent properties which are available from colorant manufacturers. The term 'colorant' as used herein also includes materials which are uncoloured in their unexcited ground state and which only emit coloured light when they are excited. This is indeed advantageous as the presence of colorant can be hidden to the causal user. It will be appreciated that for colorants to be incorporated into a polymer film they must be compatible with the polymer (for example by being, chemically similar). As used herein the term 'colorant' encompasses both of the terms 'dye' and 'pigment'. Dyes are usually at least partially soluble in the medium to which they are added and are often small organic molecules which are more unstable. Pigments are usually substantially insoluble in the medium to which they are added and are often inorganic crystalline materials or large organic molecules, which are more stable so their colour tends to fade less over time. However unless the context dictates otherwise, the terms 'colorant', 'dye' and 'pigment' can be considered interchangeable as used herein.

UV luminescent materials, which may be used in the present invention as either the first and/or second materials may comprise: any known and future optical brighteners and/or phosphorescent or fluorescent whitening agents which for example may absorb non-visible UV radiation to luminesce in the visible spectrum.

Some specific examples of fluorescent, phosphorescent and/or luminescent materials suitable for use in the present invention are described in the Kirk Othmer Encyclopaedia of Chemical Technology 4^th edition (published 1994): in Volume 11 , pages 227 to 241 under the entry headed "Fluorescent Whitening Agents" and in Volume 15, pages 518 to 607 under the entry headed "Luminescent Materials" especially the sub-entries on pages 562 to 584 entitled "Phosphors" and pages 584 to 607 entitled "Luminescent Materials (Fluorescent)". Each of these documents are incorporated herein by reference.

A non-exhaustive list of suitable commercially available materials which fluoresce when excited with UV comprises (known by the following chemical and/or trade names): stilbene derivatives; styryl derivatives of benzene and biphenyl; pyrazolines; bis(benzoxazol-2-yl) derivatives (such as 2'-[2-benzathiazoyl]-6-phosphate-benzathiazole which is available commercially under the trade mark AttoPhos® to detect alkaline phosphatase); benzoxadiazoles (such as nitrobenzoxadiazole (NBD)); coumarins (such as 7-amino-4- methylcoumarin); carbostyrils; naphthalimides; acylamino derivatives of diaminodibenzothiophene disulphonic acid dioxides; pyrene derivatives of triazines; quaternized pyridotriazoles; rhodamines and derivatives thereof (such as tetramethyl rhodamine, rhodamine X and/or PicoGreen®) benzothioxanthenes; benzoxanthenes; organic dyes with n → π^* and/or donor-acceptor chromogens; cyanines, acrylic polyenes; cyclic polyenes (such as those dyes available commercially under the names Thermoplast Brilliant Yellow 10G and/or Lumogen L Red Orange); fluoresceins; fluorescamines, eoisns, erythrosins; hydrazinocarbonyl)amino derivatives of isoquinoline disulfonic acids and salts thereof (such as 1 H-Benz[de]isoquinoline-5,8-disulfonic acid, 6-amino-2- [(hydrazinocarbonyl)amino]-2, 3-dihydro-1 ,3-dioxo dilithium salt, which is also known as Lucifer Yellow); ethidium bromide (2,7,-diamino-10-ethyl-9-phenyl-phenanthridium bromide); acridine orange; SYBR® DNA stains (such as SYBR® Gold, Green I and/or Green II), SYPRO® protein stains such as (SYPRO® Orange, and/or Red), ATTOTAG (such as Nano Orange), RiboGreen®; OHGreen®, Gelstar®, VistaGreen, fluorescent proteins (such as Enhanced Green / Yellow / Blue Fluorescent Protein respectively EGFP, EYFP or EBFP), 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene derivatives (such as those available commercially under the trade mark BODIPY®); bisbenzimide: blue (also known as Hoescht 33258); lanathanide chelates; porphyrins; metalloporphyrins; and/or any suitable salts, esters, derivatives, mixtures and/or combinations of any of the aforegoing.

Readily available sources of fluorescent materials comprise any material (including those already listed herein) which are known in the art as fluorescent labels and/or stains for biological systems. Other suitable luminescent materials suitable for use in the present invention will be well known to those skilled in the art.

Examples of suitable commercially available materials which phosphoresce when excited with UV comprise: rare earth phosphors and/or calcium, strontium and/or barium halophosphate phosphors optionally activated with sensitiser ions to provide a route for the triplet state to undergo radiative decay and/or any suitable mixtures and/or combinations thereof.

Preferred luminescent (fluorescent and/or phosphorescent) materials which may be used in the present invention comprise any of the following: benzoxadiazoles and derivatives such as: 2'-[2-benzathiazoyl]-6-phosphate-benzathiazole (AttoPhos®); nitrobenzoxadiazole (NBD);

2,5-di(5-(2-methylprop-2-yl)-1 ,3-benzoxazolyl) thiophene which is available commercially from Ciba Speciality Chemicals under the trade mark Uvitex® OB ; coumarins such as:

40, where X denotes any suitable counter

coumarin 4-(carboxy succinimidyl) ester, Alexa Fluor 350® carboxy succinimidyl ester,

coumarin maleimide,

coumarin hydrazine

umarin isothiocyanate; e donor acceptor chromogens such as:

CI Solvent Yellow 44,

CI Solvent Yellow 43; fluoresceins and derivatives thereof, such as:

and suitable salts thereof such as the di-sodium salt, inimidyl ester,

such as:

rhodamine B (and any other suitable salts thereof)

rhodamine 6G or F5G (and any other suitable salts thereof)

rhodamine green 5 / 6-carboxy succinimidyl ester hydrochloride (and any other suitable salts thereof),

Alexa Fluor 488 ® 5 / 6-carboxy succinimidyl ester di-lithium salt (and any other suitable salts thereof),

etra-N-methyl rhodamine 5 / 6-isothiocyanate,

rhodamine 101 (and any other suitable salts thereof),

4,4-difluoro-4-bora-3a,4a-diaza-s-indacene derivatives such as:

6-((4,4-difluoro-5,7-dimethyl-4-bora-3a,4a- diaza-s-indacene-3-propionyl)amino)hexanoic acid, succinimidyl ester (available commercially under the trade mark BODIPY® FL-X, SE)

6-(((4,4-difluoro-5-(2-thienyl)-4- bora-3a,4a-diaza-s-indacene-3-yl)phenoxy)acetyl)amino)hexanoic acid, succinimidyl ester (available commercially under the trade mark BODIPY® TR-X, SE) other molecules which comprise cyanine chromogens, such as:

Basic Red 12 and any other suitable salts thereof,

other fluorophors such as:

Brilliant Yellow 10 G;

lanthanide chelates such as:

Tb Na

M may be for example a metal capable of forming a porporphyin complex such as Pd or Pt; any of inorganic phosphorescent materials such as calcium halophosphates phosphors activated with Sb³⁺ and/or Mn²⁺ sensitiser ions; rare earth phosphors such as: Y₂O₂ and/or Y₂O₂S with Eu³⁺ ions; CeMgAlnOig with Tb³⁺; LaPO₄ with Ce³⁺ and/or Tb³ ; LnMgB₅Oι₀ with Ce³⁺ and/or Tb³ (where Ln denotes any lanthanide, preferably Gd); BaMg₂ALι₆O₂₇ with Eu²⁺; Sr₅.χ-yBaχCa_y(PO₄)₃CI with Eu²⁺ (where y <1); BaSi₂O₅ with Pb²⁺; Sr₄B₄O₇ with Eu²⁺; SrAI₁₄O₂₅ with Eu²⁺; Sr₆P₅BO₂₀ with Eu²⁺; BaAI₈O₁₃ with Eu²⁺; YAG with Ce³⁺; BaMg₂AI₁₆O₂₇ with Eu²⁺ and/or Mn²⁺; Zn₂SiO₄ with Mn²⁺; and/or any suitable salts, esters, derivatives, mixtures and/or combinations of any of the aforegoing. Certain of the aforementioned luminescent materials may act as probes and only luminesce when bound to a target molecule or class of molecules (such as DNA). Where necessary such target molecules can also be added to an article authenticated according to the present invention. This is a further optional feature of the invention as for example an otherwise undetectable (i.e. colourless, at very low concentration) target molecule can be incorporated into the body of a security film which can then be overprinted with a highly sensitive and/or selective probe which fluoresces under UV when bound to the target. If a counterfeiter prints the incorrect film (i.e. doped with no target molecule or the wrong target molecule) no fluorescence will be seen under UV even if the correct probe was used. This aspect of the invention can optionally be used in combination with the taggants (such as informational molecules e.g. DNA) used as described in the applicant's patent application WO03/030129.

A specific example of a second colorant which may be used when the polymer film is a polyolefin such as BOPP is the dye which fluoresces blue when excited at 365 nm (UV-A), which is available commercially from Ciba under the trade mark Uvitex® OB (structure given previously).

Colorants which luminesce when excited at 280 nm (UV-C) include phosphorescent rare earth complexes for example those available from Honeywell under the trade mark Lumilux® and these could be used as the first colorant especially in combination with a second colorant of Uvitex® OB.

Colorants which luminesce at two wavelengths when excited at 330 nm (UV-A) and at 270 nm (UV-C) (dual wavelength) include mixtures of two or more luminescent materials for example the pigment composition comprising a mixture of two phosphor complexes Y₂O₂S:Eu and Zn₂SiO₄:Mn which phosphoresce respectively pink (525 nm) and yellow / green (625 nm). This composition is available commercially from Honeywell under the trade name Lumilux® CD-R/G I. Such mixtures can be used as either the first or second colorant herein.

It has been found that 0.01% (1 x 10^'2 %) of colorant in the core polymer of the film leads to migration into the surface layers and blooming which is undesirable.

The applicant has found that at a weight concentration of colorant (Uvitex OB) of 0.002 % (2 x 10^"3 %) in the core polymer of an otherwise conventional BOPP film no colorant can be detected at the surface layers using secondary ion mass spectrometry (SIMS) hence no significant migration or blooming occurs. So if the second colorant is added to the film it is at a weight concentration of no more than 0.005% (5 x 10^-3 %), preferably from about 0.001 % (1 x 10^-3 %) to about 0.003 % (3 x 10^"3

%)

Of course as well as folding a sheet the authentication means described herein can use any other means to bring the first and second colorants into register as described for example a sheet can be bent, folded and/or twisted. Differently shaped articles (e.g.3D articles such as bottles) may be shaped, be deformable and/or have removable parts which can also bring the first and second colorants into register with one so they can be illuminated with exciting radiation.

Preferably the security feature of the present invention may be incorporated directly into a suitable article and/or document or may be attached thereto (e.g. in a permanent or tamper evident manner) and/or is otherwise associated therewith as part of a security and/or authentication means. As used herein the term article includes but is not limited to printed matter such as documents.

Suitable articles which may be authenticated as described herein may comprise an integral part of a larger article and/or product (e.g. a high value article whose authenticity it is desired to check). Alternatively the article may comprise for example a label and/or tag which is designed to be or attached to another article and/or for example comprise the packaging associated with another article.

An article of the present invention (in which the article and/or product to which the security article is attached, of which it is an integral part and/or with which it is associated), may preferably be one which would otherwise be susceptible to counterfeiting due to the high value, prestige and/or other importance associated with the article and/or product and/or where authentication of a genuine article and/or product is desired.

Preferably an article of the present invention comprises a security document such as one or more of; security tag, label, packaging, brand, trademark, logo, currency note, cheque, share certificate, bond, stamp, passport, official document, ticket, security pass and the like.

More preferably an article of the present invention is associated with, attached to and/or comprises an article selected from at least one of the group consisting of: antique objects; audio and/or visual goods for example blank and/or pre-recorded media in any format (e.g. compact disks, audio tapes and/or video tapes); chemical products for example pesticides, cleaning products, washing powders and/or detergents; tobacco products for example cigarettes, cigars, and/or tobacco goods; clothing articles for example leather articles; soft and/or alcoholic beverages for example wines or spirits; entertainment goods for example toys and/or computer games; foodstuffs for example tea, coffee, meats, fish, caviar and/or delicatessen produce, electrical and electronics parts for example computers and/or spare parts therefor, electronic objects and/or computer software, high technology machines and/or equipment; jewellery for example watches; leisure items for example binoculars and/or telescopes; perfumes and/or cosmetics for example shampoos, soaps, perfumes, deodorants, body lotions, creams, toothbrushes, toothpastes, razors and/or razor blades; products related to or for the treatment, diagnosis, therapy and/or prophylaxis of humans and/or animals, for example dental, medical and/or surgical equipment, blood transfusion pouches, medical infusion pouches, packaging for donated organs, osmotics bags, personal health equipment (e.g. optical glasses and/or sunglasses) and/or pharmaceutical products (e.g. in any suitable form for application for example pills, tablets, syrups and/or lotions); military equipment for example guns, gun sights, ammunition, rockets, military clothing, foodstuffs, gas-masks, mines, grenades and/or ordinance; photographic industry goods for example cameras and/or pellicles; scientific instruments and spare parts therefor, for example microscopes, chromatographic apparatus, spectrometric and/or nuclear magnetic resonance apparatus; machinery and spare parts for the transport industry for example parts for automotive, aerospace and/or aeronautical industry goods, cars, lorries/trucks, motorcycles, space vehicles, rocket ships, vehicle's windscreen stickers, tax discs, trains, coaches and buses, aeroplanes, tubes, trams, helicopters, deep sea exploration equipment, submarines, ships, boats, liners and/or merchant vessels; travel goods for example luggage; security goods, for example currency (such as bank-notes), cheques, share certificates, stamps and/or official documents; sports articles for example sport shoes, tennis rackets, squash rackets and/or equipment for fishing, golf, climbing, skiing, shooting sailing, and/or scuba or other deep-sea diving; any other articles which are safety critical and/or where the failure of which would be critical and where authentication of a genuine and/or correctly prepared article is essential; any article which has utility in one or more of the uses to which the aforementioned articles may be used, any other instructional, recordal and/or promotional material associated with the article and/or related activities such as instruction manuals, guarantees, warranties, guides, log-books, records and the like; and/or any other article which is suitable for attachment to (e.g. as a security label and/or tag) and/or association with (e.g. comprising the packaging) to any of the aforementioned articles.

An article made using the authentication means as described herein may comprise any other compatible security and/or authentication means in any compatible combination comprises, optionally in corresponding patterns the article: such as any of Moire inducing pattern, optical lens, Fresnel lens, multiple micro-lens, lenticular lens, distorting lens, metameric ink, micro-printing and polarising filter.

A further aspect of the invention broadly comprises a method of manufacturing a comprising the step of: applying an article (for example a security document) as described herein to the product as an integral part of the product, by attaching the article to the product and/or by associating the article with the product.

Another aspect of the invention broadly comprises a method of authenticating a product comprising the steps of:

(a) positioning into register a first and second portion of an article comprising respectively a first and second colorants which luminesce at different visible wavelengths when irradiated as different non-visible wavelengths (b) irradiating the first portion through a transparent second portion to cause both portions to luminesce; and

(c) observing the combined luminescence spectrum through the transparent second portion.

Still other aspects of the invention broadly comprise:

Use of a product, article, security document and/or authentication means as described herein to provide a means of authentication.

A product authenticated by an article, security document and/or authentication means as described herein.

Preferred articles of the invention comprise a self supporting sheet like substrate which incorporate a transparent or translucent window suitable for use with the authentication feature as described herein.

Sheets which may be used to make the authentication device of the present invention comprise membranes, films, layers, laminates, webs, vellums, pellicles, skins, matrices, mats, veils, weaves, coatings, additives, impregnates, composites, and similar terms, mixtures and/or combinations thereof whether synthetic or natural and such sheets may be suitable for the uses described herein, for example to form (in whole or in part) packaging, labels and/or documents which may have need of a security and/or tracking feature.

Suitable materials from which to make sheets with the authentication device described herein comprise thermoplastic polymers such as BOPP and/or biopolymers such as cellulose or polylactic acid. Other suitable sheet materials suitable to form the authentication device described herein are well known to those skilled in the art. A non- exhaustive list of such materials is given in the applicant's patent application WO02/40579 for a film coated with a nanostarch coating as an oxygen barrier (especially the section from page 14, lines 1 to 24) and this document is incorporated herein by reference.

Other features of suitable polyolefin (e.g. BOPP) polymer films are also described in WO02/40579 (page 14, line 25 to page 18, line 27). Additives suitable for use in polyolefin films are described in WO02/40579 (page 18, line 29 to page 21 , line 37)

Suitable biopolymeric films for use in the present invention comprise cellulose and/or polylactic acid films. Other suitable biopolymers and preferred features thereof are described in the applicant's patent application WO 02/074874 for a wet glue label, (especially the section from page 5, line 33 to page 8, line 6) and this document is incorporated herein by reference.

Suitable uses of such sheets include as documents, synthetic paper, labels, graphic art displays, print receptive substrates (e.g. using conventional printing methods such as screen, flexographic, gravure, offset etc and/or digital printing methods such as ink-jet printing, thermal image transfer and/or electrorepography), food packaging, lidding, overwrap, stretch wrap, shrink wrap and/or for tamper evidence. The films may be supplied in any suitable form e.g. as roll stock and/or sheets.

Preferred sheets for use herein are which may be optionally coated, metallised, opacified or otherwise conventionally treated at least over part of the surface thereof so that a transparent region remains thereon.

Further and/or alternative aspects and features of the present invention are described in the claims if not already described herein.

It is appreciated that certain features of the invention, which are for clarity described in the context of separate embodiments may also be provided in combination in a single embodiment. Conversely various features of the invention, which are for brevity, described in the context of a single embodiment, may also be provided separately and/or in any suitable sub-combination.

The term "comprising" as used herein will be understood to mean that the list following is non-exhaustive and may or may not include any other additional suitable items, for example one or more further feature(s), component(s), ingredient(s) and/or substituent(s) as appropriate.

Further and/or alternative features and aspects of the present invention are described in the claims.

Embodiments of films according to the present invention will now be described by way of example with reference to the accompanying drawings. Features in each drawing are given number labels with the numbering in each drawing starting at the next hundred (i.e. 1 , 101 , 201 etc). Similar and/or analogous features in each drawing are labelled by numbers separated by an whole number multiple of one hundred (e.g. features 5, 105 and 205 each refer to the base film in Figures 1 to 3, Figures 4 to 6 and Figures 7 to 8 respectively).

Figure 1 is a sectional view through part of a film of the present invention comprising a first exemplary embodiment of a security device of the invention where a region (101 ) of a first luminescent colorant (B) is printed is printed on top of the opaque coating (103). The core film (105) is impregnated with a second luminescent colorant (C). Figure 2 and 3 show the film of Figure 1 folded over itself with alternate surfaces adjacent in each Figure and illuminated with broad spectrum UV (A). Folded either way the film appearance viewed through the window (103) without the coating (103) is different from the rest of the film.

Figure 4 is a sectional view through part of a film of the present invention comprising a second exemplary embodiment of a security device of the invention where the region (101) of the first luminescent colorant (B) is printed on the other side of the film to the opaque coating (103).

Figure 5 and 6 show the film of Figure 4 folded over itself with alternate surfaces adjacent in each Figure and illuminated with broad spectrum UV (A). Folded one way (Figure 5) the film appearance viewed through the window (103) is the same as the rest of the film as the opaque coat (103) blocks excitation of the colorants. Folded the other way (in Figure 6) the film appearance viewed through the window (107) is different from the rest of the film.

Figure 7 is a sectional view through part of a film of the present invention comprising a third exemplary embodiment of a security device of the invention similar to the film in Figure 4 where the first region (201) and the core film layer (205) luminesce when irradiated at different UV wavelengths. Figure 8 to 10 show the film of Figure 7 folded over itself and illuminated with UV at a wavelength to cause respectively in Figure 8 the first area (201), in Figure 9 the core film layer (205) and in Figure 10 both of them to luminesce.. In each case the film appearance viewed through the window (207) is different from the rest of the film.

Figure 11 is a sectional view through part of a prior art film (such as described in GB 2,300,956) comprising two UV fluorescent materials in different layers (301 , 305) with a UV opaque layer (303) there between.

Figure 12 to 13 show the film of Figure 11 folded over itself with alternate surfaces adjacent in each Figure and illuminated with broad spectrum UV (A). It can been that the both colorants (B and C) cannot fluoresce simultaneously as the UV radiation (A) does not pass through the opaque layer (303).

Figure 14 is a sectional view through part of a prior art film (such as described in EP 0775589) comprising a UV fluorescent layer (401) sandwiched between two transparent layers.

Figure 15 shows that the when the film is illuminated with broad spectrum UV (A) the fluorescent layer emits light of only one colour (B) irrespective of whether of not the film is folded over itself.

Figure 16 is a sectional view through part of a prior art film (such as described in DE

4114732) coated with a mixture two UV fluorescent materials (501 , 505). The film is transparent to UV but there is no separate transparent window in the film.

Figures 17 and 18 show the film of Figure 16 folded over itself with alternate surfaces adjacent in each Figure and illuminated with broad spectrum UV (A). It can been that the both colorants (B and C) in the coating fluoresce simultaneously to give the coating a uniform appearance.

There are no transparent windows in the prior art films shown in Figures 11 to 18 so there is no difference when the film is folded over itself to the fluorescent colours seen under UV. Given the construction of these films it would not be ease to introduce separate transparent windows and they would make no difference to the fluorescence seen.

In contrast to these prior art films, those of the present invention emit different colours when an overlapping region of the film is viewed under UV light thorough the transparent window as compared to a non-overlapping region of the film. Example 1

A conventional stiffened BOPP three layer film of thickeness 90 microns was produced by coextrusion in the well know bubble process comprising a core polymer layer of BOPP and other surface polymer layers for easier of printablity and further coating and surface treatment. An additive Uvitex OB (described herein) which luminesces in blue after irradiation at 365 nm was added to the core polypropylene polymer before extrusion and orientation at a concentration of 0.002% (2 x 10^"3 %).

The resulted film was opacified by use of a conventional coating apart from a transparent window near one edge. A rare earth complex pigment which luminesces red / orange on irradiation at 254 nm was printed onto the film in a first region sufficiently spaced from the window so the window can be folded over that region.

On irradiation of the flat film with an artificial UV source at wavelengths of 254 nm and 365 nm the first region was seen to luminesce orange red and the transparent window luminesced blue. In addition a blue glow was seen from the film edge near the window due to total internal reflection of the luminescence within the film.

The film was folded so the window overlapped the first region and UV irradiated (254 nm and 365 nm) through the window. A purple / green luminescence was seen through the window as well as blue glow from the film edge near the window.

Claims

1 An article comprising a first region having a first colorant and transparent second region having a second colorant, where the respective first and second colorants luminesce at different visible wavelengths when excited by excitation means, the first and second regions being capable of being brought to register with one another by manipulation of the article and/or document to form an overlap region between the first and second regions such that when the first colorant is excited, the combined luminescence of both the first and the second colorants is seen through that part of transparent second region which defines the overlap region .

2 An article according to the preceding claim in which the second colorant is incorporated into the material from which the article is made.

3 An article according to any preceding claim, in which comprises a polymeric security film.

4 An article according to the immediately preceding claim, where the polymer film comprises polypropylene, cellulose and/or polylactic acid.

5 An article according to any preceding claim where the concentration of second colorant is less than about 5 x 10^"3 % by weight.

6 An article according to any preceding claim, where the first and second regions are located on a substantially planar and/or sheet-like region.

7 An article according to the immediately preceding claim, where the second region is positioned adjacent the edge of the sheet.

8 An article according to any preceding claim, which comprises a security document.

9 An article substantially as described herein with reference to the Example and

Figures herein.

10 A method for authenticating an article comprising a first region having a first colorant and transparent second region having a second colorant, where the respective first and second colorants luminesce at different visible wavelengths when excited by excitation means, the method comprising the steps of: (a) overlapping at least a part of the first and second regions with one another by manipulating the article to form an overlap region between said first and second regions

(b) exciting said first and second colorant with the exciting means; and

(c) observing the resultant luminescence through that part of transparent second region which is defined by the overlap region to authenticate said article and/or document.

11. A method as claimed in the immediately preceding claim, where the excitation means comprises exciting radiation.

12. A method as claimed in the immediately preceding claim, where the exciting radiation comprises separate wavelengths which excite each colorant.

13. A method as claimed in the immediately preceding claim, where the exciting radiation is non-visible.

14. A method as claimed in the immediately preceding claim, where the exciting radiation is UV radiation.

15. A method as claimed in the immediately preceding claim, where the UV radiation comprises wavelengths of 254 nm and/or 365 nm.