WO2004087430A1 - Authentication means - Google Patents

Abstract

There is described a two part means of authenticating a polymeric film where the film contains one component a colourless additive and/or modification of the polymer which will react with the other component applied to the film by a suitable means (such as a pen) to form a visible colour change and thus authenticate the film. Suitable components include colourless benzene diammonium salts and anilines which react to form azo dyes; polyethylenimine (= PEI or mica) which fixes Eosin red stain applied to the film, (the colourless component incorporated onto the film surface by wash coating); particles to modify the film properties at the surface (such as silica particles can be treated with pH sensitive dyes such as crystal violet lactone); penetrating inks which penetrate a modified non-surface layer (e.g. containing nano-clay); and/or an encapsulated component which is released when pressure is applied to the film in use (e.g. on a package) to react with other component (e.g. in the film or wrapped package) to form a colour change. Films of the invention may be used in for example security documents and/or packaging (such as overwrap for tobacco products).

Description

Authentication means

The present invention relates to security features used to authenticate an article and methods of authenticating articles. It is particularly applicable to articles such as security documents, identity documents or value documents but is also applicable to other tokens or articles requiring verification of authentication, such as entrance documents and tickets. The articles or documents which are to be authenticated preferably comprise a polymeric film substrate with a security feature. Desirable security features are not readily apparent to a potential counterfeiter or if identified cannot be readily reproduced by other means.

There are various known methods of forming colour in situ on a substrate which could be used to verify documents during use.

Colour images can be formed on a substrate by reacting diazonium salts with couplers such as phenols or amines to produce coloured derivatives in alkaline media. Coating substrates with a light-sensitive diazonium salt and a coupler has been used as a simple method of forming an image or copy. A transparent original is placed between a UV source and the treated substrate, and the diazonium salts photolyse beneath the areas of image which are transparent. The photolysed salts can no longer subsequently react with coupler to form colour. The exposed substrate is treated with an alkaline activator to develop the colour in those areas where the diazonium salts have not been photolysed to give a direct positive azodye image of the original . There are various different ways by which the diazonium coupling reaction can be used to produce coloured images on a pre exposed colourless substrate by subsequent treatment in situ. The dry process uses the diazonium salt, coupler and an acid stabilizer to prevent premature colour formation and after UV exposure the image is developed by treating the substrate with alkali In the semi dry process a coating of the diazonium salt and the stabilizer is treated after exposure to a neutral or alkaline aqueous solution of the coupler which immediately forms colour in the nonexposed areas. In the thermal process the coating is the diazonium salt, the coupler and a compound that releases alkali when heated and an image is developed when the substrate is heated after exposure. In the pressure sensitive process the coating is a diazonium salt, coupler and acid stabilizer and an extremely thin layer of an alkali is applied by pressure to the exposed coating to develop the colour image.

Vesicular photography another known method which uses photolysis of a substrate coated with light sensitive compounds in a polymer matrix to form an image. In this case this photolysis liberates a gas which forms microscopic bubbles or vesicles and the image is developed by subsequent heating. The vesicles have a refractive index different from the surrounding medium so the incident light scatters or diffuses to form an image. When viewed with reflected light an irradiated, transparent film appears white on the image areas and black on the non imaged areas. When viewed with transmitted light the imaged areas appear as dark spots. Suitable materials for vesicular photography include diazonium salts or azides which form nitrogen gas on photolysis. The nitrogen gas formed on the exposed parts of the light sensitive coating is immobilized in the polymeric matrix and can expand into microscopic cavities when the system is briefly heated. Other photosensitive systems that can be used in vesicular photography include photochemically formed acids in matrices containing salts which will react with acid to form gases (e.g. NaHC0₃) and photochemical depolymerization to form gaseous monomers which can expand to form vesicles in the matrix. Vesicular photography forms an irreversible image.

Images forming from diazonium salts by conventional means (e.g. using a coupler or vesicular photography) are irreversible. It is desirable to provide a latent authenticity marking which is detectable for a period of time and which can disappear until it is required to be detected at another time. It can be difficult to readily diazonium salts in suitable polymeric substrates without adversely effecting other desirable properties of the substrate.

There are other methods which have also been proposed to provide latent images in security documents so that a normally invisible image becomes coloured when a colourless developer is applied thereto.

US 5130290 discloses a water sensitive colour sheet comprising a substrate and a water- sensitive colouring layer containing a colourless basic dye, a colour developing material capable of forming a colour on contact with the dye, a desensitizer and a binder. The desensitizer inhibits the colour forming reaction between the basic dye and the colour developing material in the absence of water in the water sensitive layer. When water is applied, coloured images are formed by the colour forming reaction between the basic dye and the colour developing material. In one embodiment, a porous substrate is used and the coloured images are irreversibly left on the substrate after evaporation of water. In another embodiment, a water-repellent substrate is used and the coloured images formed by water applied are allowed to disappear after evaporation of the water. This embodiment thus provides a method in which a latent coloured image which is detectable for a period of time but disappears after evaporation of the water applied. However, US 5130290 requires the basic dye, the colour developer and a desensitizer to be incorporated into the water-sensitive colouring layer. Further, there are many basic colourless dyes that form a colour with the application of water and so a security document made from the water-sensitive colouring sheet of US 5130290 would be relatively easy to counterfeit. Also, such a document may be coloured unintentionally if it is exposed to an environment where water is prevalent, e.g. an atmosphere of high humidity.

US 5290068 discloses a method and system for securing a document against counterfeiting, photocopying and facsimile transmission in which one of a colourless colour-former and a colourless colour developer pair is applied to an area of a substrate having a background colour and the other of the colour developer and colour-former pair is applied the area to change the colour of the background. Information may be printed in the selected area in a substantially black colour which is different from the colour produced when the colour developer and colour former react when mixed over wavelengths for the human eye, but the same colour over the wavelengths of a facsimile or photocopier machine. Thus the information will be readable by a human, but will be indistinguishable by a photocopier or facsimile machine to protect against unauthorised verification by facsimile or photocopying. In US 5290068 the colour former may be applied to the substrate by printing, and the colour developer may be applied by an applicator, such as a marker pen. However, the process described is not reversible..

US 5595590 describes a method for authenticating a document or article where a leuco dye and an activator are applied to the surface of the document or article and a colour change is induced by frictional heating caused by rubbing the surface.

WO 00/05076 (Acordis Acetate) discloses a process for testing the authenticity of packaged goods in which a colourless latent dye-stuff is dispersed in a plastics film used for packaging. A colour-developing chemical can be applied to the film, e.g. by using a marker pen, to develop the colour of the latent dye-stuff to form a marking for authentication of the packaged goods. The process is reversible, but requires application of a second chemical for reversing the reaction to make the marking disappear.

It is therefore desirable to provide an optional method of verifying documents in which a latent colour image or mark can be made to appear visible in a reversible process with a simple method which can be readily be used at the point of use of the article or document to be authenticated and where some or all of the disadvantages of the prior art are alleviated.

It is also desirable to provide a security document or token, a latent authenticity marking and a colour developer which can be verified with such a method.

It is an further preferred object of the invention to provide a covert means to authenticate a polymeric film.

It is useful when an article or document is being used to be able to authenticate the article or document in situ. The present invention optionally provides means to do so for example by a retailer or customer at the point of sale. The authentication means may be covert i.e. the presence of the security feature is not readily apparent to a potential counterfeiter. It is also a preferred object of the invention that the means used to authenticate the article is fairly simple and useful without expensive equipment.

Broadly in accordance with one aspect of the invention there is provided a substrate comprising a latent authentication means which can reversibly interact with a further specific means matched with the latent authentication means to provide when the specific means is applied thereto a (optionally temporary) change in the substrate corresponding to latent authentication means the change being directly perceivable by a person wishing to authenticate the substrate.

In accordance with a further aspect of the invention there is provided a method for authenticating a substrate comprising a latent authentication means, the method comprising the steps of: applying to the substrate a specific means matched with the latent authentication means to reversibly interact to provide a (optionally temporary) change in the substrate corresponding latent authentication means; perceiving the change to confirm that the substrate is authenticate.

Optionally the method comprises forming a reversible colour change for verifying an article

Preferably the latent authentication means is located substantially at the surface of the substrate, more preferably the latent authentication means comprises a substantially colourless additive in and/or modification to a surface layer of the substrate and/or a colourless colour-forming dye in at least one area of the substrate. Preferably the specific means is matched to the latent authentication means more preferably comprises an optionally colourless component which can reversibly react with the latent authentication means to provide substantially immediately a detectable change in the substrate, most preferably the detectable change is a colour change. Optionally the specific means comprises a volatile colour developer which reacts with the colour-forming dye to form a coloured mark corresponding to the latent authenticity mark;

Optionally the further component is applied from a suitable medium (more optionally a pen) to provide the directly perceivable change in the substrate. More optionally the reaction between the volatile colour developer and colour-forming dye is reversible upon evaporation of the volatile colour developer so that the coloured mark is temporarily visible for a period of time until the volatile colour developer evaporates whereupon the coloured mark disappears.

According to one further aspect of the invention, there is provided a polymeric film suitable for use as a substrate to provide improved authentication, the film comprising therein (preferably as part of a surface layer) a substantially colourless additive and/or modification to the outer polymer layer which can react with a further component (which may or may not be coloured) applied from a suitable medium (e.g. a pen) to provide a detectable change (preferably visible colour) on the film.

According to another further aspect of the invention, there is provided a colour forming method for verification of an article comprising: applying a colourless colour-forming dye to at least an area of the article to form a latent authenticity mark; separately applying a volatile colour developer to the area of the article bearing the latent authenticity mark wherein the colour developer reacts with the colour-forming dye to form a coloured mark corresponding to the latent authenticity mark; wherein the reaction between the volatile colour developer and colour-forming dye is reversible upon evaporation of the volatile colour developer so that the coloured mark is temporarily visible for a period of time until the volatile colour developer evaporates whereupon the coloured mark disappears.

In the method of the invention, the colour-forming dye may be permanently applied to the substrate, e.g. by printing or by incorporating the dye in the substrate, and the volatile colour developer may be applied to the substrate by means of an applicator, such as a marker pen, containing the volatile colour developer. Preferably, the colour forming method is repeatable, so that when the coloured authenticity marking disappears upon evaporation of the volatile colour developer, a further application of the volatile colour developer causes the latent authenticity marking to reappear.

According to another aspect of the invention, there is provided an article comprising a substrate and a latent authenticity mark permanently applied to at least an area of the article, wherein the latent authenticity mark comprises a colourless colour-forming dye that is normally invisible but which is able to react with a volatile colour developer applied separately to the substrate in a reversible reaction to form a coloured authenticity mark which is temporarily visible for a period of time until the colour developer evaporates, whereupon the coloured authenticity mark disappears.

According to a further aspect of the invention, there is provided a colour developer for use in a colour forming method of document verification, wherein the colour developer comprises a volatile liquid containing an acid or base which reacts in a reversible reaction with a colourless colour-forming dye applied on a substrate to form a coloured authenticity mark which is temporarily visible for a period of time until the colour developer evaporates, whereupon the coloured authenticity mark disappears.

It is preferred that of the latent authentication means and the specific means used to authenticate the more complicated component of the two (e.g. dye etc) which are more difficult to reverse engineer are incorporated into the article as the latent authentication means and therefore more inaccessible to any counterfeiter trying to mimic the effect.

The latent authenticity mark is preferably a coating containing a dye which is colourless under ambient conditions, but which develops colour on contact with an acid or base. Preferably, the colour-forming dye is a colourless leuco dye which can be colour activated by a colour developer containing an acid.

The latent authentication means preferably forms part of a polymeric substrate and the substrate may form part of the article (e.g. when the article is a security document) and/or may be associated with another article (e.g. the film may comprise a label or packaging for an associated article).

The substrate may comprise a transparent plastics substrate, preferably a polymeric sheet, and more preferably a biaxially oriented polymeric film, such as described in WO 83/00659. Advantageously at least one opacifying layer or coating is applied to the transparent substrate to form at least one opaque area which is of a different colour. The at least one opacifying layer or coating may be formed from an opacifying pigment coaling, such as described in WO 83/00659, which contains a major portion of pigment in a minor proportion of cross-linked polymeric binder.

In one embodiment of the invention the substrate used is biaxially oriented polypropylene (BOPP) films. The BOPP films may be prepared with substantially balanced physical properties, for example as can be produced using substantially equal machine direction and transverse direction stretch ratios or can be unbalanced where the film is significantly more oriented in one direction (MD or TD). Sequential stretching can be used, in which heated rollers effect stretching of the film in the machine direction and a stenter oven is thereafter used to effect stretching in the transverse direction or simultaneous stretching, for example using the so-called double bubble process or a simultaneous draw stenter. The machine direction and transverse direction stretch ratios are preferably in the range of from 4:1 to 10:1 , and more preferably from 6:1 to 8:1.

The films used in accordance with the present invention can be of a variety of thicknesses according to the requirements of the packages which are to be produced. For example they can be from about 10 to about 120 microns thick, and preferably from about 14 to about 40 microns thick.

The latent authentication means and the specific means may be provided by one or more of the following systems: two component which react to form the detectable authentication mark, materials which exhibit ionochromism, solvatochromism, redox reactions,

In one embodiment of the invention these is provided a two component system involving at least one colourless component incorporated in the film preferably as part of a surface wash coat and the other component (which may or may not be coloured) is incorporated in to a suitable medium for application on to the film surface. Once the two components come in to contact, they react to form a highly coloured dye. The two component system can be used in the present invention with a number of different chemistries, to give number of colour options. There are many other organic and inorganic systems that could be used, for example metal complexes, components of azo dyes. For example the following system can be used:

benzene diamonium bisulphate N;N di ethylaniline colourless colourless

p-(dimethylamino)azobenzene Yellow crystals The reaction can be reversed by photolysis of the azo dye so formed.

Ionochromism is the phenomena of the colour change associated with the interaction of compounds or materials with an ionic species. Common ionic species that are often associated with this colour change are metal ions, onium ions (such as Ammonium or Phosphonium salts), or the solvated hydrogen ion (pH sensitive). Examples of some ionochromic materials which are suitable for use in the present invention are given below as representatives of classes or types of materials which can be used.

Phenolphthalein (3,3-bis(4-hydroxyphenyl)-1 (3H)-isobenzofuranore) changes from colourless to pink when caustic soda is added. If the pH of the coating and the applicator are suitable balanced, a reversible colour change can be achieved, for example if the caustic is in excess, then the coating will stay pink. An X90 copolymer coating which starts as a neutral solution, pH 7 can be used with phenolphthalein to achieve reversible colour change. Phenolphthalein is water soluble and if for example an applicator (e.g. a pen) of caustic soda is swiped on the film to create the colour change it may picks up the phenolphthalein and the applicator tip may be coloured, which could produce a false positive when used for further authentification. Therefore for optimum effect migration of the phenolphthalein should be minimised by for example encapsulation in suitable partciles, such as silica particles.. Nano sized particles are preferred as the encapsulation medium to reduce haze of the film. This is a general optional for all latent authenication means which soluble in the specific means which is used to general the authentication mark. Toluidine Blue is denoted by the following

and changes colour (from blue to pink) in response to the polarity of the solvent present, i.e. the ionic nature of its environment. Toluidine Blue can be incorporated into a coating so that on changing the ionic balance at the surface of the substrate the Toluidene Blue will reversibly change from purple to pink. No colour change was observed in the presence of HCl, but substrates incorporating Toluidine Blue turned pink with NaOH.. In the presence of water (even mositure) a rerverisble colour change is observed in the substrates from blue to pink (e.g. on BOPP film incorporating Toluidine Blue) as once the water evaporates the substrate returns back to blue. No colour change was observed with Toluidine Blue in the presence of HCl, but a pink colour change was observed with NaOH. As Toluidine Blue is water soluble it is preferred to encapsulate the dye in a suitable material to minimise migration from the film.

Solvatochromism is the phenomena of colour change when a compound is dissolved in different solvents. An example of a solvatochromic compound is:

Reichardt's dye; 2,6-diphenyl-4-(2,4,6- tripheynylpyidinio)phenolate. The colour of Reichardt's dye depends upon the polarity of the solvent it is dissolved in. For example in methanol Reichardt's dye appears green- blue; in ethanol blue-violet; in 2-propanol red-violet; in acetone orange; and in mixtures of acetone with water as the amount of water added increases, the color of the mixture changes from blue-violet to violet to red-violet to red and then orange.

Vat dyes are an example of a redox system as a vat dye will change colour when it is converted into its leuco form by reducing it with a reducing agent. The leuco form is unstable in air, and it will be quickly oxidised back to its original form by oxygen. An example of a suitable reducing agent is ascorbic acid. L ascorbic acid is Vitamin C, the enolic form of 3-oxo-L-gulofuranolactone

Ascorbic acid is a reasonably strong reducing agent, and very effective at reducing indophenol dye. Another suitable redox dye which can be used in the present invention is Variamine which denotes Variamine Blue B hydrochloride ( = N-(4-methoxyphenyl)-1 ,4- phenylenediamine, hydrochloride). Variamine can be reversibly oxidised from colourless to blue.

reduced form (colourless) oxidised form (blue)

Leuco dye colour formers are colourless organic molecules which develop intense colouration in the presence of acid, as shown. The acid compound interferes with the lactone ring causing the dye to form a coloured species. The most commonly used colour is black, although many other colours are available. One example is crystal violet lactone, shown below.

Colourless Coloured, intense

Colour forming reaction for crystal violet lactone

Another example of a leuco dye is Methyl Orange:

Yellow Red

Colour forming reaction for methyl orange

Leuco dye powders usually have an average particle size below 5 microns and can generally withstand temperatures up to 240"C subject to specific time and shear. There are many types of leuco dyes such as spiropyran leuco dyes, leuco quinine dyes, leuco triarylamines, phthalide type and Fluron dyes to name a few.

The coating preferably contains an amount of well dispersed latent authentication means (such as a leuco dye) falling substantially within the range from about 0.01% to about 0.5% of the dye by weight of the coating.

The colour developer is preferably a volatile acidic colour developer, for example, acetic acid. The colour developer may contain a solvent in addition to the acid which reacts with the colour-forming dye. For example, a heavily diluted strong acid, such as hydrochloric acid or sulphuric acid could be used as the colour developer, though weaker acids, such as acetic acid or benzoic acid are more suitable for use in an applicator such as a marker pen.

The acid should be chosen such that the boiling point is relatively low so that the solution can evaporate rapidly from a printed surface. In the case of acetic acid this is 118°C. As acetic acid has a strong odour the solution can be diluted to reduce the odour particularly with solvents such as R-acetates as they have a sweet fruit odour. The minimum concentration of the acid solution is preferably at least 20% and the pH should preferably be below 3. When using acid based marker pens the mechanical parts of the pens should be non-metallic and preferably plastic. The solvent used to reduce the concentration of the acid should be chosen such that it has the correct surface tension for wetting the printed area of the substrate and is not intrusive of the printed surface. The preferred surface tension of the marking liquid should be below 35 dynes. The surface tension of a water based solution could be lowered to the appropriate levels by adding a surfactant.

Preferably, an organic solvent, such as an alcohol or acetate is used to dilute the acidic colour developer. In one embodiment, acetic acid or benzoic acid is diluted with ethanol to form the volatile colour developer. Ethanol is particularly preferred because it does not attack the substrate or printing on the substrate.

The strength of the acid, the volatility of the solvent and the relative concentrations of the acid and solvent may be varied for different applications and to provide different time periods within which the latent authenticity marking is visible from when the colour developer is applied to when the colour developer evaporates. In one preferred embodiment, using acetic acid or benzoic acid as the colour developer and a solvent such as ethanol, the concentration of acid to solvent is preferably at least 20%, and more preferably at least 50%.

Various application methods can be used to mix the two components to cause the authentication colour change such as wash coating, functionalisation (e.g. incorporating functionalised particles and/or polymers) penetrating inks and/or an encapsulated component within the film which is released when pressure is applied to the film (e.g. by scratching).

The method can be applied to any suitable film substrate such as for example thermoplastic and/or biopolymeric films for example polyolefinic (e.g. BOPP), polyester and/or cellulose films.

The idea of two component verification systems is to create an invisible, easy to authenticate security marker by for example using a pair of molecules, one added to the film and the other incorporated into a pen. When the pen is swiped across the film the two components come in contact, and react to form a highly coloured dye.

The additive can be applied to a film such as BOPP by wash coating the cast tube as the film is produced. This will cover the outside of the film with a molecule with the necessary functionality to impart a colour change when the second component is applied by a suitable applicator.

In an alternative embodiment the film polymer can also be modified. If a polymer is modified to include the necessary functionality that is required to give the colour change, then it can be simply co-extruded with the outer coat polymer. In yet another embodiment of the invention modified particles can be incorporated to film preferably in the outer layer. For example silica particles can be added to the outer extrusion layer of the film using a similar principle to polymer modification route. Dyes sensitive to pH or other changes at the film surface due to the surface may react with the treated film (e.g. crystal violet lactone). Nano clays could be modified and added to the bulk of the polypropylene, with the second component of this system being an ink that has the ability to penetrate through the surface layer of the film.

In a still other embodiment of the invention an encapsulated component within the film may be released when pressure is applied to the film to react with a further component which for example is located in the article and/or packaging (e.g. in the print on a box or carton) which is wrapped in said film. On intimate contact no reaction is seen but once pressure is applied to the overwrap by the user, the capsules rupture and the two components react to form a highly coloured dye. This method can be applied to any substrate such as PET, BOPP or cellulose films. Preferably the reaction is reversible so optionally the colour can fade or disappear after the pressure is released.

The latent authenticity marking formed by the colourless colour-forming dye may be printed on the at least one opacifying layer or coating which forms a background of a different colour to the colour produced when the colour-forming dye and colour developer react. Alternatively, the at least one opacifying layer or coating, or the uppermost opacifying layer or coating when two or more are provided, may include the colour-forming dye dispersed in the coating. Thus, it is possible for the complete surface area of the substrate to incorporate the colour-forming dye, so that the colour developer can be applied to any part of the surface of the security document for document verification. This has the advantage over security documents with latent authenticity markings provided in specific areas, which require the person performing verification by means of a marker pen containing the colour developer to have knowledge of the specific area where the colour- forming dye has been applied. Of course, the latent authenticity marking formed by the colour-forming dye may be applied to a specific area or specific areas of the security document, for instance when the colourless colour-forming dye is applied by printing to the substrate.

The at least one opacifying layer or coating may be applied to the transparent plastics substrate in such a manner as to leave a region of the substrate which is uncovered by the opacifying layer or coating to form a transparent region or window. In another embodiment, the colourless colour forming dye is preferably dispersed in a clear or transparent ink or varnish, such as a transparent matt resin varnish. The transparent ink or varnish containing the colour-forming dye may be applied to an opaque area of the substrate, to a transparent region or window, or even to an area which overlaps a transparent region or window and an opaque area adjacent to or surrounding the transparent region or window.

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 documents and/or analogous goods or articles, more preferably one or more security, value, identity and/or entrance document(s) and/or analogous goods or articles. A non-exhaustive list of such documents comprises one or more: aeroplane ticket, bank note, bond, brand, bus ticket, certificate, charge card, cheque, concert ticket, credit card, currency, drivers' licence, identity card, label, logo, lottery ticket, official document, other ticket, packaging, passport, postage stamp, rail ticket, security pass, security tag, share, theatre ticket, ticket to amusement parks and specific rides, trademark, travellers cheque and/or visa. As used herein, the term document encompasses all of these and similar types of documents. In another preferred embodiment a film of the invention may package, wrap, be associated with, attached to and/or comprise an article selected from for example any of the following non-exhaustive list: alcoholic and/or soft beverages for example wines or spirits; 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; documents as described herein 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 ordnance; 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; sports articles for example sport shoes, tennis rackets, squash rackets and/or equipment for fishing, golf, climbing, skiing, shooting 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 with the article 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 and/or security document as described herein to the product as an integral part of the product, by attaching or associating 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) incorporating a colourless reactive additive into the film and/or functionalising the film polymer so the additive or polymer will react with a second component to cause a visible colour change.

(b) applying to the film in use the second component to cause a visual colour change on the film surface to authenticate the film.

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. 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.

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

Figure 1 is a plan view of a security document incorporating a latent authenticity marking in accordance with the invention; Figure 2 is a plan view of the security document of Figure 1 showing the authenticity marking made visible by the application of a colour developer;

Figure 3 is a schematic view of the security document of Figures 1 and 2 showing the latent authenticity marking viewed in reflection;

Figure 4 is a schematic view of the security document of Figures 1 and 2 showing the latent authenticity marking viewed in transmission;

Figure 5 is a sectional view through a polymeric banknote showing different layers in which a latent authenticity marking can be provided.

The preferred embodiments below are described with particular reference to a security document in the form of a banknote. It will, however, be appreciated that the present invention is applicable to other types of articles or documents as listed herein.

Figures 1 and 2 show a security document 10, in the form of a banknote, incorporating a latent authenticity marking 12 in accordance with the invention. The security document 10 has an opaque area 16 and a transparent region or window 18. Indicia 14 may be printed on the opaque area 16. The latent authenticity marking 12 comprises an area of the document printed with a colourless colour-forming dye which is normally invisible as illustrated schematically by Figure 1 , but which reacts with a volatile colour developer, e.g. applied by a marker pen 20 to form a coloured marking 12 (Figure 2) that is temporarily visible as illustrated by Figure 2 for a period of time until the volatile colour developer evaporates whereupon the coloured marking disappears.

As shown in Figures 1 and 2, the latent authenticity marking 12 comprises an image which is printed on an area of the document which overlaps the transparent window 18 and the adjacent or surrounding opaque area 16. It will, however, be appreciated that the latent authenticity marking may be provided solely on the opaque area 16 or solely on the transparent window 18.

When the latent authenticity marking 12 overlaps the transparent window 18 and the adjacent or surrounding area 16, different visual effects may be observed depending upon whether the security document 10 is observed in reflection or transmission as shown in Figures 3 and 4.

For example, when the colour developer is applied, the latent authenticity marking 12 may appear in a first colour or shade having a first wavelength λt when viewed in reflection (Figure 3) and the marking 12 may appear in a second colour or shade having a second wavelength λ₂ when viewed in transmission (Figure 4). This colour shift may be due to the amount of light transmitted through the image.

Figure 5 shows a sectional view of a polymeric banknote suitable for incorporating a latent authenticity marking in accordance with the invention. The banknote comprises a transparent polymeric film or substrate 22, and a plurality of layers of an opacifying ink or pigment coating 23, 24 applied to each surface of the transparent substrate 22 except in a region forming the transparent window 18. The substrate 22 is preferably a laminated biaxially oriented polymeric film of the type disclosed in WO 83/00659, though other polymeric substrates may be used. The layers 23, 24 may be formed from an opacifying pigment coating, such as described in WO 83/00659.

As shown in Figure 5, different forms of printing may be provided on the upper opacifying layer 24, e.g. a first printed layer 26 which may be formed by an offset, ink jet, screen or gravure printing process; intaglio printed areas 28; and alphanumeric printing 30 produced by a letterpress. The transparent window 18 contains a security device in the form of an embossing 32 which may be produced in an intaglio process. Alternatively, the transparent window may contain other types of security devices, for example, optically variable devices such as diffraction gratings or holograms, optical or polarising filters, or interference features such as lines or dots designed to produce moire effects.

The security document of Figure 5 also incorporates a clear UV protective overcoat 34 which is preferably formed from a transparent matt resin varnish over the opaque areas 16 containing the printing 26, 28 and 30, and optionally over the transparent window 18.

A latent authenticity marking 12 such as that of Figures 1 to 4 may be provided in the security document of Figure 5 in a variety of ways.

The latent authenticity marking 12 may be provided by printing an area overlapping the layers 23, 24 of opacifying coating and the transparent window 18 with a transparent coating 36 containing a well dispersed colourless colour-forming dye. The transparent coating 36 may be formed by the transparent matt resin varnish overcoat 34, although other transparent coating materials for containing the colour-forming dye may be used. The colour-forming dye preferably comprises a leuco dye, such as crystal violet lactone, which is normally colourless, but which reacts with an acidic colour developer to produce an intense dark violet colouration. It will, however, be appreciated that other acid/base colour-forming dyes which react with a volatile acidic or basic colour developer in a reaction which is reversible when the developer evaporates may be used.

The colour developer used to react with the colour-forming dye is preferably a volatile acidic colour developer, such as acetic acid or benzoic acid. The acid is preferably mixed with a volatile solvent having a volatility chosen to optimise the time during which the acid remains in contact with the latent authenticity marking 12.

The transparent coating 36 containing the colour-forming dye may be applied by a gravure printing process, or alternatively by using a flexo or offset printing technique. Preferably, there is minimal background printing in the area containing the latent authenticity marking12 in order to improve the visibility of the coloured image produced when the colour developer is applied.

In a modified embodiment, a transparent coating containing the colour-forming dye may be applied over the entire surface of the security document. This enables a person to use a marker pen anywhere on the surface of the security document to apply the colour developer to form a general coloured authenticity marking without the person requiring knowledge of the particular location of a latent image. It will also be appreciated that a plurality of latent authenticity markings may be provided, and the latent authenticity marking or markings may be provided on either side or on both sides of the security document.

In an alternative embodiment, not shown, the colour-forming dye may be incorporated in at least one, and preferably the uppermost layer 24, of the layers 23, 24 of opacifying pigment coating. In this case, one or more areas of the opacifying layer 24 may be exposed by the absence of printing to provide an area containing a latent authenticity marking contaclable by the colour developer.

In a further embodiment, the colour-forming dye could be added to the layers of the co- extruded biaxially oriented polymeric film 22 during manufacture. In this case, the latent authenticity marking 12 may only become visible in the transparent region or window 18 which is not covered by the opacifying layers 23, 24 and/or the areas of printing 26, 28, 30.

In another embodiment, the colourless colour-forming dye could be added to a transparent intaglio printing ink and arranged to produce a coloured image upon application of a colour developer. This embodiment may be suitable for application to passports which are not used as frequently as banknotes, and therefore soiling and UV protection are not significant concerns.

In another possible embodiment, a permanently visible image may be printed in the transparent region or window 18, for example using a matt resin white ink. The colourless colour-forming dye could be added to such an ink whereby application of the colour developer over the permanently visible printed image causes the white image to change colour.

Further embodiments of latent authenticity markings in accordance with the invention are envisaged, including multiple coloured images formed by applying two or more different colour-forming dyes to the substrate, or formed by using colour formers which generate the four colours used in the four colour printing process.

Other aspects of the invention, embodiments thereof and preferred features thereof are described in the claims herein.

It will also be appreciated that various modifications and alterations may be made to the preferred embodiments described above without departing from the scope and spirit of the invention.

Ingredients

For convenience the following ingredients are referred to herein by their various registered and unregistered trademarks, trade names, trade designations and/or other non systematic names as follows:

"7216" denotes the polypropylene / butylene / ethylene random terpolymer available commercially from Basell under the trade designation Adsyl® 7216. "107" denotes another polypropylene / butylene / ethylene random terpolymer available commercially from Mitsui Chemicals America Inc under the trade designation Tafmer® XR

107 SI.

The Tafmer® and Adsyl® grades used had different proportions of the three monomers.

Polymin P® denotes an aqueous, cationic solution of pure polyethylenimine (=PEI), at the specified concentrations, and is available commercially from BASF.

Fluroad (TM) denotes the fluorosurfactant available commercially from 3M.

"Eosin" denotes the conventional bright red stain d id Red 87

or tetrabromofluorescein with a structure of

which is available commercially from for example Abbey Colour. "1290" denotes an ammonia neutralised ethylene acrylic acid (EAA) copolymer available commercially from Paramelt under the trade mark Aquaseal®1290.

Paraloid® denotes a polymethyl methacrylate available commercially from Rohm & Haas.

"WB1240" denotes a proprietary acrylic copolymer available commercially from UCB

Surface Specialties under the trade mark Ucecryl® WB1240 "XK90" denotes a proprietary imine functionalised methyl methacrylate / butyl methacrylate copolymer dispersion (45 % by weight in water) available commercially from Avecia

NeoResins under the trade designation NeoCryl XK90.

"R610" denotes a proprietary polyurethane copolymer available commercially from Avecia

NeoResins under the trade designation Neorez R610. "Irganox 1010" denotes the UV absorber

Tetrakis[methylene(3,5-di-t-butyl-4-hydroxyhydrocinnamate)]methane available commercially from Avecia NeoResins under the trade designation Irganox 1010.

"500LS" denotes the precipitated silica available commercially from Degussa under the trade mark Sipernat®500LS.

"TS100" denotes the precipitated silica available commercially from Degussa under the trade mark Acematt®TS100.

"Hydrex®" denotes the precipitated synthetic sodium magnesium alumino filler available commercially from Huber under the trade mark Hydrex®. "EN1020" denotes a vinyl acetate / ethylene copolymer dispersion available commercially from Air Products under the trade designation Airflex EN1020.

"CEF19" denotes a vinyl acetate / ethylene / vinyl chloride terpolymer dispersion available commercially from Air Products under the trade designation Airflex CEF19.

"EPN865" denotes a vinyl acetate / ethylene copolymer dispersion available commercially from Air Products under the trade designation Airflex EPN865.

Various otherwise conventional films were modified according to the present invention to be authenticated as described herein. The films comprise mulilayer BOPP films available from UCB Surface Specialties under the trade designations "RC" & "RK" (both coated packaging films); "WGS92" (a coated label film) and "C50" & "WG90" (both coextruded label films). Uncoated monolayer films were also used such as BOPP (biaxially oriented polyproylene) and PET (Polyethylene terephthalate) films.

Unless otherwise indicated or the context clearly suggests differently as used herein

"indophenolate" denotes sodium 2,6 -dichloroindophenolate.

Examples 1 to 6 (PEI)

A conventional aqueous solution of polyethylene imine (PEI) primer (1% solids) was coated onto a conventional 50 micron BOPP base film using a number 1 k-bar. The primer was then diluted and film samples were coated similarly at a wide range of PEI concentrations. The blocking properties of each film was assessed to determine the effect of solids concentration. Two sheets of the film with the treated surfaces were pressed together at the given temperature and time or pressure. The result is the force required in grams to separate the two films. Eosin stain was added to each film and the colour of the film was also assessed. The colour density was rated on a scale of 0 to 10 with 0 being not visible and 10 being the colour obtained with the conventional 1 % PEI solution. Table 1

Ex PEI 38°C for 60°C for Pressure Colour

% w/w 3 hours / g 1 hour / g 3 tonnes /g density

1 1.00% 0 30 0 10

2 0.75% 0 20 0 8.5

3 0.50% 0 10 0 7

4 0.25% 0 5 0 5.5

5 0.10% 0 0 0 3.5

6 0.05% 0 0 0 2

When the PEI was coated onto the film, as the concentration was reduced to 0.10%, there was noticeable reticulation around the edges of the sample. When 0.01% primer was tried, all of the coating reticulated making it impossible to test.

Without wishing to be bound by any mechanism it is believed that the primer only blocks at high temperature and the lower the solids, the lower the amount of blocking in the sample. The colour was suitable to provide authentication at PEI concentrations as low as 0.05% as long as the film was viewed against a white background.

Examples 7 to 10 (wash coat)

A conventional BOPP film was prepared by the well known double bubble process. On a production scale film the wash coat would be applied to the outer surface of the cast tube just before it is blown into the bubble in the following manner, although for convenience the examples herein were prepared on a smaller scale in the laboratory. The wash coat formulation is fed from a suitable reservoir by a peristaltic pump to an annular sponge which surrounds and just wipes the surface of the cast tube and is located just above the heaters which heat the tube neck to 160°C prior to bubble formation. The flow rate of the pump determines the initial thickness of the applied wash coat which thins as the film bubble expands to form an even homogenous surface layer on the final film . To prevent reticulation of the wash coat the coat must be matched to the surface tension of the polymer. As can be seen from the results it is preferred that the outer layer of the cast tube is pure PP homo-polymer for good wash coat adhesion, although this depends on the wash coat selected.

Preparation Adsyl®7216 and Tafmer®107 polymers were used to made laboratory samples of wash coated then oriented film as follows. Plaques of the polymer were heated to 55°C in an oven for 20 minutes. They were then placed in a bath of the wash coat (5% or 10% aqueous solutions of Polymin P® to which 0.13% w/w of Fluroad® had been added) for approximately 2 seconds. The excess coating was removed by smoothing it over with a soft rubber strip, before drying the sample with a hairdryer. The plaques were then stretched on a laboratory long stretcher. Eosin® red stain was applied to the resultant film and the amount of stain remaining fixed to the film was observed. Table 2 Ex Film Polymer Wash coat Stain Intensity

7 7216 5% Polymin P 1

8 7216 10% Polymin P 9

9 107 5% Polymin P 2

10 107 10% Polymin P 3

Examples 9 and 10 were streaky after orientation due to reticulation of the wash coat on the surface. Examples 7 and 8 were clear, and after testing with the Eosin, only slight defects in the coating were seen.

Example 8 comprising a wash coat of 10% Polymin P (PEI) wash coat on Adsyl®7216 polymer (polyproylene) is the sample which provided the strongest colour change and thus would be an especially good means of authenticating film.

Example 11 (Silica particles)

Nano sized silica particles (such the hydrophillic fumed silica available commercially from

Degussa under the trade mark Aerosil® 300) were incorporated into standard homopolymer polypropylene at 10% w/w. Plaques were formed from the resulting masterbatch, and these were treated with a 1% solution of the known organic colorant crystal violet lactone dispersed in toluene. Areas of the plaque that were exposed to the xylene solution changed to a deep blue colour as the colorant is sensitive to the presence of the silica particles in the film. No colour change was observed when plaques of standard polypropylene (with no silica added) were treated with the crystal violet lactone solution as there were no silica particles in the film to effect the dye as it was applied. In the following examples use the two components that are generally used to create an azo dye. One is added to the film (naphthol) and the other into a pen (the diazonium salt):

Examples Comp A and Example 12 Two further examples of film were prepared one coated with a control coating (Comp A)and the other with a coating comprising naphthol (Example 12).

Comp A

The coating for the control sample consisting of EN 1020, TS100, Foam master and water was made up in an 800 gram portion. R610 primer and the control coating were then applied to WG90 film using the RK coater. The coated film had a slight ribbed effect and so a second control sample was made up with the addition of iso propyl alcohol to increase wetting. The head pressure of the gravure was also increased. Another coating was made up of the same components as the control and the Naphthol coupler. This too was applied to R610 primed WG90 film on the RK coater. Both film samples were wiped with 2% caustic and then 2% Variamine solution.

Coating Coatweights Comments

Comp A (Control) 6.38g/m² No change when wiped with caustic and Variamine.

Ex 12 (Naphthol) 5.54g/m² Turned blue when wiped with caustic and

Variamine.

The IPA increased wetting of the coating and made it easier to apply. This, along with increasing the head pressure of the gravure, gave the coating a smoother finish. As can be seen from the results the coating containing the Naphthol turned blue when combined with the caustic and Variamine. The control coating did change colour, which shows that all 3 components are needed to produce an azo dye. Weaker Variamine solutions were also tested out on the coating and a 0.125% solution still gave a significant colour change.

Examples Comp B and Examples 13 to 16

Further film examples were produced; one coated with a control coating (Comp B), others with a coated with naphthol at various concentrations (Examples 13 and 14) and others coated with a mixture of naphthol and caustic soda at various concentrations (Examples 15 to 16). The control film (Comp B) was prepared by using the conventional coater to apply a functionalised copolymer (XK90 from Avecia) at 45% solids to a BOPP film (C50 from UCB). A coated film of the invention was prepared in an analogous manner from a coating of the XK90 and 2% naphthol at 45% solids (Example 13) . The coating of Example 13 was viscous so a second coated film of the invention was prepared by diluting the coating to 22.5% solids (Example 14). A further solution of 45% solids was prepared comprising XK90, 2% Naphthol and 2% caustic and used to make another coated film of the invention (Example 15). This again was viscous when coated onto the film and so a further coated film of the invention was prepared from a more dilute coating of 22.5% solids (Example 16). The coat weights for each example are given below.

Coatinα % Solids Coat weight

Comp B (XK90I) 45 4.92 g/m²

Ex 13 (XK90, 2% Naphthol) 45 3.68 g/m²

Ex 14 (XK90, 2% Naphthol) 22.5 2.47 g/m²

Ex 15 (XK90, 2% Naphthol, 2% caustic) 45 3.55 g/m²

Ex 16 (XK90, 2% Naphthol, 2% caustic) 22.5 1.26 g/m²

Comp B was too thick and uneven

Ex 13 Turned dark blue when wiped with caustic and Variamine. Colour reasonably evenly spread. Ex 14 Turned blue when wiped with caustic and Variamine. Colour reasonably evenly spread.

Ex 15 Mixture turned bright yellow. Coating had slight yellow tint. Turned dark blue when wiped with Variamine. Colour more evenly spread with caustic in coating. Ex 16 Mixture turned bright yellow. Coating had slight yellow tint. Turned blue when wiped with Variamine. Colour more evenly spread with caustic in coating.

Examples 14a and 14b made with a coating solution containing naphthol and caustic soda turned bright yellow when mixed together. Without wishing to be bound by any mechanism it is believed that the caustic may reacted with the naphthol and the reaction product may then dissolve into the XK90 polymer. In Examples 13a and 13b the Naphthol by itself dispersed in the binder to give the coating a brown tint. Compared to the control Comp B, the coatings of Examples 13a, 13b, 14a & 14bd all turned deep blue when wiped with the Variamine solution. The colour change with Variamine appeared more evenly distributed and slightly more intense in Examples 14a & 14b where the coating containing the caustic soda. The coatings (Examples 13b & 14b) applied at a lower solids (22.5%) coated more easily onto the film with a satisfactory though lighter colour change with Variamine compared the Examples (13a & 14a) applied at higher (45%) solids.. Example 15 to 28 (Ascorbic acid)

Ascorbic acid was included in the coating of a conventional coated BOPP packaging film from UCB (that sold under the trade name RC) at a weight of 5%. A very good reaction was recorded with indophenol, but the addition of the ascorbic acid caused a reduction in heat seal performance, so <5% of ascorbic acid (for example 2.5%) is preferred. Adding 1290 to the formulation improved the heat seal performances.

It was found that a coating formulation comprising 2.5% ascorbic acid in WB1240 with 8.5% carnauba wax, and 1 % Paraloid is suitable and Examples 16 to 18 were prepared with additional and respectively 5%, 10% and 20% of "Aquaseal 1290" and tested as follows

Example 16 Example 1 Exami Die 18

Heat Seal (107°C M/M) 150 96 44

Slips (3 point test) 2.34 High High

Haze 8.1 7.4 5.9

Example 19 was prepared as Example 16 with the ascorbic acid reduced from 2.5% to 2% and tested as follows.

Example 19

Heat Seals 252 Slips 2.17

Haze 7.3

Initially when Example 19 was prepared the film was hazy as ascorbic acid causes the

Aquaseal polymer to precipitate. To prevent this, the ascorbic acid and Aquaseal were added together and mixed thoroughly to get the polymer back into solution. This pre- mixture was then added to the other components, which were also pre-mixed. This reducing the haze value to 3, while keeping the other results the same. Further examples were prepared Example Level of Level of Level of

Ascorbic Acid Aquaseal 1290 Indophenolate

20 0 0 0 21 0 5 0

22 2 5 0 23 1.5 3 0 24 2.5 3 0 25 1.5 7 0

26 2.5 7 0 27 2 5 0.5 28 2 5 0 All samples contain 8.5% Carnauba, 0.5% Paraloid in WB1240.

Coatings were made up in two separate parts. The water, ascorbic acid and Aquaseal were added together and mixed. It was observed that the Aquaseal polymer was dropping out in the acid, but if a high enough level of aquaseal was added, the polymer would re- disperse. The WB1240, Carnauba wax and Paraloid mixed separately before the other part was added to it. In Example 28, to try to combat this problem, the ascorbic acid solution was neutralised using ammonia. No drop out was observed!

Immediately after the coat had been applied to the film Examples 22 to 26 were initially tested with blue indophenolate dye and all these Examples reduced the blue dye well as the colour rapidly disappeared. Examples 22 to 26 were re-tested , after accelerated ageing in a 50°C oven for 1 day, then 3 further days at room temp and the time taken for the indophenolate colour to disappear were noted:

Examples 22 23 24 25 26

After ageing Not fully reduced 60secs 25secs Not fully reduced 10secs

Example 22 was found to be a satisfactory film for use in applications such as overwrap. The ascorbic acid is oxidised over a period of time and will not reduce the dye so preferably the ascorbic acid should be stabilised to minimise this degradation.

The anti-oxidants available commercially from Ciba under the trade designation Irganox are used as antioxidants in polypropylene. Only the Irganox 1010 is water dispersible so a coating was produced and drawn down. The Irganox 1010 in the coating was visible as large particles, and did not disperse particularly satisfactorily. When the dye was added to the coating, it turned from blue to pink over a long period after the dye had been rubbed into the film.

Oxidising a dye in the film can creates a strong visual effect but the colour change may be irreversible. For example sodium persulfate oxidising agent can be used to react with the indophenol dye in the film to turns the dye from blue to pink. No problems were encountered in the degradation over time and a larger amount of the oxidising agent in the film created better results. A similar trend can be observed to ascorbic acid, but a stronger concentration of indophenol was used to create a strong pink mark on the film. It is preferred that the concentration of sodium persulfate in the film is about 5% by weight. Preferably the concentration of indophenol dye applied to the film is a solution of at least about 0.5% by weight.

Reactions Involving Indicators and pH changes

Ex Additive in Film Reaction with Acid Reaction with Base

27 1% Toluidene Blue: in RC No Change Turned Pink (coating comes off) 28 1 % Toluidene Blue: in XK90 No Change Turned Pink

29 1 % Crystal Violet Lactone No Change Turned Pink in XK90 In Example 27 on "RC" uncoated BOPP film the coating could be removed with NaOH, and in Examples 28 and 27 using BOPP film coated with XK90 copolymer the coating could be removed with HCl.

Example 30

As the coating of the RC film may degrades in the presence of NaOH, an acid indicator such a methyl orange was put into the coating, and citric acid used to induce the change in pH. Methyl orange was used in the film, but the coating was a yellow colour. When citric acid was added, the methyl orange went pink, and migrated out of the film. The results were very much the same as those for phenolphthalein.

Example 31

1 , 9 Diphenyl-1 ,3,6,8-nonatetraen-5-one: A colour change can be observed with this compound in the presence of a hydrogen halide. To disperse this compound in the coating, as it is very insoluble in water,. It was adsorbed onto silica particles which were the dispersed in the coating. Various concentrations of HCl were placed on the surface of the film, and the reaction observed as no reaction took place in the presence of water, the HCl was mixed with acetone. A colour change was observed at a 1 :1 mixture of HCl and acetone by weight. This is a solvatochromic compound and different solvents would have different effects and therefore produce different colours. Solvents should be selected which both produce a visible colour change in the film and also do not damage the film or coating

Other coated film

EAA coatings are known to have desirable properties such as good seal properties. A BOPP film coated with EEA were also used in a method of the present invention.

Example Coating formulation (% w/w) Ex 32 EAA + 10% Carnauba Wax + 2.5% Ascorbic acid

Ex 33 EAA + 10% Carnauba Wax + 2% Napthol

Ex 34 EAA + 10% Carnauba Wax + 2% Napthol + 2% Caustic

Ex 35 EAA + 10% Carnauba Wax + 1 % Phenolphthalein

Ex 36 Ex 32 + 35% WB1240 Ex 37 Ex 33 + 35% WB1240

Ex 38 Ex 34 + 35% WB1240

Ex 39 Ex 35 + 35% WB1240 Examples 35 and 39 produced a good colour change

Further samples were prepared and tested with varying amounts of Paraloid and

Carnauba wax.

Ex 40 8.5% Carnauba Wax, 2% Paraloid

Ex 41 8.5% Carnauba Wax, 1.5% Paraloid

Ex 42 7.5% Carnauba Wax, 2% Paraloid

Ex 43 7.5% Carnauba Wax, 1.5% Paraloid

All trial coatings were produced at 1 g/m².

Two Component Verification Systems

The 2 components to be used in these examples were the diazonium salt, Variamine Blue and Naphthol AS coupler, one of which will be incorporated into a topcoat and the other into a pen. When combined an azo dye was produced and a colour change occurred. The azo dye will photodegrade to produce a temporary mark.

Many different coatings were made up using various binders and fillers and different concentrations of the diazonium salt and coupler were used. These were drawn down onto various types of film e.g. BOPP, PET, C50, WG90 and WGS92.

Firstly the diazonium salt alone was placed in various binders, coated onto OPP film and exposed to UV radiation, using the UV curer, to determine the effect on the salt. Some of the coatings turned slightly hazy however the change was not very significant. Also, the diazonium salt did not incorporate well into the binder and showed signs of degrading.

The next step was to combine the diazonium salt with the coupler in order to produce an azo dye. Various fillers, 500LS, TS100, Hydrex and Calcium Carbonate were added to EN1020 binder along with the coupler and diazonium salt. When mixed the coatings became extremely viscous and were unable to be used. The TS100 proved to be the best silica and so coatings were made up consisting of this, the EN 1020 binder and the Naphthol coupler. Some Variamine was dissolved in water and wiped over the film however no change occurred. The film was then wiped with both Caustic and Variamine solutions resulting in the treated area turning a deep blue colour. This proved that an alkaline environment and hence a 3 component system is needed to produce an azo dye.

As all 3 components were applied separately in order for the colour change to occur, more tests were carried out to see if 2 of them could be combined. The most reasonable option was to incorporate 2 into the coating and as discovered previously, the diazonium salt and the coupler were not compatible. The only other option was to incorporate the coupler and the caustic into the coating. The components were placed in various binders, XK90, CEF19 and EPN865 and coated onto clear film. Once dry, they were all wiped with the Variamine solution. The only colour change occurred with the XK90 binder suggesting that it was the only one that allowed the Variamine to penetrate through it. The coating turned bright yellow when mixed which was probably due to a reaction occurring between the Caustic and Naphthol, however once dry it appeared only a very faint yellow tint was observed. The colour change when wiped with the Variamine was also more intense and more evenly distributed than when the Naphthol AS alone was incorporated into the film

Two trials were carried out on the RK coater in order to produce larger quantities of the coated films for further investigations. In the first trial the EN 1020 and 3% Naphthol coating was coated onto mica primed WG90 film. A control coating without the Naphthol was also made up. In the second trial unprimed C50 film was coated with XK90 containing 2% Naphthol AS, as well as XK90 with 2% Naphthol AS and 2% Caustic. Samples were made from coating s containing 45% and 22.5% solids. A control coating of just XK90 was also applied to the film.

Various tests have been carried out on the coated films with Variamine in order to see how they are affected by different conditions. Samples of each of the 3 trial films (EN1020 with 3% Naphthol, XK90 with Naphthol and the XK90 with Naphthol and Caustic) were cut and placed in the QUV. Every 24 hours over a period of 96 hours a sample of each film was removed and wiped with Variamine (as well as Caustic - if required). After 24 hours there was no apparent colour change with the Naphthol containing XK90 coated films when treated with Variamine. This suggests that something in the coating had been affected by the UV radiation. More samples of these films were then placed in the QUV and tested every 15 minutes. After 30 minutes there was no sign of a colour change showing that it only takes a short while for a change in the coating to occur. The white WG90 film however still showed a colour change after 96 hours when wiped with the Variamine and Caustic. This suggests that there is something within the film or coating that does not affect or inhibit any of the components needed for the azo dye to be produced.

As the temperature of the QUV was reasonably high, around 55°C, samples of the film were placed in the oven at 86°C to check that temperature was not the cause of the change in the coating. After 1 hour a colour change still occurred when the film was tested which ruled the temperature factor out.

In order to test the stability of the Variamine a sample of 0.5% solution was placed in the oven, set at 50°C, and every hour for 7 hours was tested on the film. These samples will be analysed using the Macbeth.

Various other tests, wide angle haze, narrow angle haze, gloss, wet/dry/alcohol rub resistance, coefficient of friction, block resistance and printability were also carried out, some of which again need to be analysed.

Diazonium salts and couplers were incorporated into various coating mixtures to form azo dyes.. The coating (50g) was prepared by mixing EN1020, IPA, water, Foam master, 3% Naphthol and Calcium Carbonate in suitable proportions . This coating was applied to the following BOPP films (denoted by product codes see above) Corresponding control examples (respectively Ex 47 to 49) were also prepared where the same films were coated with a control coating that did not contain the Naphthol coupler. Once dry, sections of the films were dipped in solutions of 2% caustic then 2% Variamine.

Calcium Carbonate filler;

Two further coatings and corresponding controls, were made up in 25 gram portions, each containing EN1020, 3% Naphthol, IPA, water, Foam master and either TS100, or 500LS. Each coating was applied to WG90 film, primed with R610 and WGS92 film. Once the coatings were dry they were wiped with the 2% caustic solution then the 2% Variamine solution.

As shown in the results, the control coatings did not change colour when wiped with the caustic and the Variamine. This shows that all three components, caustic, Variamine and Naphthol are needed for the colour change to occur.

More Diazonium salts

Diazonium salt were combined with a coupler to produce azo dyes by incorporating the salts into various coating formulations which produce clear coating son a BOPP film Three coatings consisting of 1% Naphthol and either XK-90, CEF19 or EPN865 were made up and applied to primed C50 film. Mica primer was used with the XK-90 coating and R610 with the CEF19 and the EPN865 coatings. Once dry the films were wiped with 2% caustic then 0.125% Variamine. 0.5% Variamine was also tested.

Two more examples of XK90 were prepared, both consisted of XK-90 and 2% Naphthol and one also containing 5% Bindzil CAT 220, a modified nano silica. These coatings were applied to un-primed C50 film and then wiped with caustic and Variamine.

A two component system, was prepared a coating consisting of XK-90, 2% Naphthol and 0.5% caustic was made up and applied to C50 film. Once dry it was wiped with 0.5% Variamine solution. The same coating was made up but this time the caustic was increased to 2%.

Results

The XK-90 binder showed a colour change and increasing the Naphthol to concentration to 2% by weight increased the intensity of the colour produced, as did increasing the Variamine to 0.5%. The coatings containing the caustic changed blue when wiped with the Variamine solution. Increasing the caustic increased the intensity of the colour produced. Incorporating the caustic and Naphthol into the coating shows that a two component system is possible.

Claims

Claims

1 A method of authenticating a polymeric film comprising the steps of:

(a) incorporating (as a latent authentication means) a colourless reactive additive into the film and/or functionalising the film polymer so the additive or polymer will react with a second component to cause a visible colour change.

(b) applying to the film in use (as a specific means) a second component to cause a visual colour change on the film surface to authenticate the film.

2. A method for authenticating a substrate comprising a latent authentication means, the method comprising the steps of: a) applying to the substrate a specific means matched with the latent authentication means to reversibly interact to provide a (optionally temporary) change in the substrate corresponding latent authentication means; b) detecting and/or perceiving the change to confirm that the substrate is authenticate.

3. A method as claimed in either preceding claim, in which the article is authenticated by forming a reversible colour change thereon

4. A method as claimed in any preceding claim, where the latent authentication means is located substantially at the surface of the substrate.

5. A method as claimed in any preceding claim, where the latent authentication means comprises a substantially colourless additive in and/or modification to a surface layer of the substrate and/or comprises a colourless colour-forming dye in at least one area of the substrate.

6. A method as claimed in any preceding claim, where the specific means is matched to the latent authentication means so that the change in the article will not occur with other latent authentication means.

7. A method as claimed in any preceding claim, where the specific means comprises an optionally colourless component which can reversibly react with the latent authentication means to provide substantially immediately a detectable change in the substrate,

8. A method as claimed in any preceding claim, where the change in step b) is a colour change.

9. A method as claimed in any preceding claim, where the specific means comprises a volatile colour developer and the latent authentication means comprises a colour- forming dye which reacts with developer to form a coloured mark corresponding to the latent authenticity mark;

10. A method as claimed in any preceding claim, where the specific means is applied from a suitable medium and/or applicator, optionally a pen, to provide the change

11. A method as claimed in any preceding claim, where the reaction between the latent authentication means and the specific means is reversible upon evaporation of the specific means so that the change is temporarily visible for a period of time until the volatile specific means evaporates whereupon the change disappears.

12. A method as claimed in any preceding claim, where the reaction between the latent authentication means and the specific means is reversible and repeatable after the temporary change disappears.

13 A colour forming method for verification of an article comprising: applying a colourless colour-forming dye to at least an area of the article to form a latent authenticity mark; separately applying a volatile colour developer to the area of the article bearing the latent authenticity mark wherein the colour developer reacts with the colour-forming dye to form a coloured mark corresponding to the latent authenticity mark; wherein the reaction between the volatile colour developer and colour-forming dye is reversible upon evaporation of the volatile colour developer so that the coloured mark is temporarily visible for a period of time until the volatile colour developer evaporates whereupon the coloured mark disappears.

14 An article capable of being authenticated by a method as claimed in any preceding claim.

15 A polymeric film suitable for use as a substrate to provide improved authentication, the film comprising therein, optionally as part of a surface layer, a substantially colourless additive and/or modification to the outer polymer layer which can react with a further optionally coloured component applied from a suitable medium and/or applicator to provide a detectable change optionally a visible colour on the substrate.

16. A substrate comprising a latent authentication means which can reversibly interact with a further specific means matched with the latent authentication means to provide when the specific means is applied thereto a (optionally temporary) change in the substrate corresponding to latent authentication means the change being directly perceivable by a person wishing to authenticate the substrate.

17 An article comprising a substrate and a latent authenticity mark permanently applied to at least an area of the article, wherein the latent authenticity mark comprises a colourless colour-forming dye that is normally invisible but which is able to react with a volatile colour developer applied separately to the substrate in a eversible reaction to form a coloured authenticity mark which is temporarily visible for a period of time until the colour developer evaporates, whereupon the coloured authenticity mark disappears.

18 A polymeric substrate film as claimed in any of claims 14 to 17 which comprises a surface coat comprising (a) a colourless benzene diammonium salt or aniline; (b) polyethylene imine (=PEI); and/or (c) silica particles .

19 An article as claimed in any of claims 14 to 18, which is selected from documents and/or analogous goods or articles, optionally one or more security, value, identity and/or entrance document(s) and/or analogous goods or articles.

20. An article as claimed in claim 19 which is selected from one or more: aeroplane ticket, bank note, bond, brand, bus ticket, certificate, charge card, cheque, concert ticket, credit card, currency, drivers' licence, identity card, label, logo, lottery ticket, official document, overwrap film , packaging (optionally for tobacco products), passport, postage stamp, rail ticket, security pass, security tag, share, theatre ticket, ticket to amusement parks and specific rides, trademark, travellers cheque and/or visa.

21. A colour developer for use in a colour forming method of document verification, wherein the colour developer comprises a volatile liquid comprising an acid or base and/or a reducing agent or oxidisng agent where the developer is capable of reacting in a reversible reaction with a colourless colour-forming dye applied on a substrate to form a coloured authenticity mark which is temporarily visible for a period of time until the colour developer evaporates, whereupon the coloured authenticity mark disappears.