Abstract:
The invention relates to improvements in security features in paper and other substrates and in particular to an activatable feature to warn of tampering. The invention further relates to a security feature for a security document comprising at least one activatable layer and at least one visually apparent masking layer, said at least one activatable layer comprising a composition which is generally non-mobile but which becomes mobile when wetted with a liquid, said composition further including at least one detectable component, in which under dry conditions said at least one masking layer wholly covers the activatable layer and renders it non-detectable.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to improvements in security features in paper and other substrates, and in particular to an activatable feature to warn of tampering. 
     Documents of value and means of identification, such as banknotes, passports, identification cards and the like, are vulnerable to copying or counterfeiting. The increasing popularity of colour photocopiers and other imaging systems, and the improving technical quality of colour photocopiers, has led to an increase in the counterfeiting of such documentation. There is, therefore, a need to improve the security features of such documentation, or paper, to add additional security features or to enhance the perceptions and resistance to simulation of existing features. Steps have already been taken to introduce optically variable features into such documentation which cannot be reproduced by a photocopier. Furthermore, features are now available which are discernible by the naked eye, but invisible to, or viewed differently by, a photocopier. Known examples of such security features include watermarks, embedded and windowed security threads, fluorescent pigments and the like. 
     However, in addition to attempting to reproduce security features, counterfeiters also endeavour to tamper with or remove information or print or other security indicators associated with documents by immersing the document in water or a solvent. 
     It is therefore an object of the present invention to provide an improved security feature for a security document which services as an indicator of tampering of the document. 
     SUMMARY OF THE INVENTION 
     According to the invention there is provided a security feature for a security document comprising at least one activatable layer and at least one visually apparent masking layer, the at least one activatable layer comprising a composition which is generally nonmobile but which becomes mobile when wetted with a liquid, the composition further including at least one detectable component, in which under dry conditions the at least one masking layer wholly covers the activatable layer and renders it nondetectable. 
     A security feature as claimed in claim  1  in which the composition becomes mobile when wetted with an aqueous liquid. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred embodiment of the present invention will now be described in detail, by way of example only, with references to the accompanying drawing in which: 
     FIG. 1 is a plan view of a security document including the security feature of the present invention; 
     FIGS. 2 and 3 are cross sectional side elevations of a security element or thread comprising the security feature of FIG. 1; 
     FIG. 4 is a schematic view of a holographic label including the security feature of the present invention; and 
     FIG. 5 is a plan view of security document including the security feature of the present invention having a UV element. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1 there is illustrated a typical security document, such as a banknote, identification card, cheque, certificate, etc., which includes the security feature of the present invention in the form of a windowed security thread or element  11 . The security element  11  is preferably made from a transparent colourless polyester film which is flexible and water-impermeable and which is provided with a layer of metal on one side thereof. Commonly used films for security elements  11  are vacuum deposited with aluminium or another suitable metal. The film is slit to form a number of individual security elements having a width typically of at least 0.5 mm and preferably at least 2 mm. However, the size is not relevant to the present invention. The security element  11  is inserted into a sheet of paper by one of a number of known methods. One of the most commonly used methods is using a cylinder mould paper machine, for example by the method disclosed in EP-A-0,059,056. In the resulting security paper the security element  11  is exposed on one side of the sheet at intervals along the length of the element  11 , the region of exposure being referred to as a window  12 . Bridges  13  are formed from paper fibres between the windows  12  to wholly embed the element  11  in those regions. 
     In the present invention, the security element  11 , as illustrated in FIG. 2, comprises the polyester film substrate  16 , on an upper side of which is located a metal layer  17 . (“Upper” being defined as being nearer to the surface  15  which is exposed in the window  12 ). A further “activatable” layer  18 , which comprises a composition containing an activatable component is provided on an opposite “lower” side to the metal layer  17 . The activatable component is one generally non-mobile, under normal conditions, but: which is soluble in a liquid such as a solvent to become mobile. The composition also includes a colourant. 
     In a security document  10  made from security paper containing the security feature according to the present invention, under normal conditions the security element  11  will be seen in reflected light in the windows  12  as bright shiny metallic blocks. The metal layer  17 , however, wholly masks the activatable layer  18  so that it cannot be seen in the windows  12 , so that the document  10  looks like a typical window thread document in both reflection and transmission. 
     However, if a counterfeiter were to attempt to tamper with the document  10  by immersing it in a liquid with the aim of removing the thread, printed information, or any other security features on the document  10 , the activatable component which holds the colourant in place will become mobile in the solvent, allowing it to leach out into the surrounding paper to provide a highly visible frame or halo  19  stained with the colourant surrounding the windows  12 . The activatable layer  18  is therefore no longer masked and is now clearly visible to the naked eye. 
     In an alternative embodiment of the feature described above, the security element  11  may have the construction shown in FIG.  3 . In this security element  11 , the transparent polyester film  16  has the activatable component layer  18  applied to its upper surface. A metal layer  17  is applied over the top of the activatable component layer  18 . Since the polyester film  16  and the metal layer  17  are water impermeable, the solvent to activate layer  18  enters through the sides of the thread  20 . 
     The metal layer  17  thus acts as a visible or dominant component the function of which is to mask an activatable component. The metal layer  17  may, therefore, in other embodiments of the present invention, be replaced by other layer, patches all of which serve these functions. The masking layer may be optically variable, such as irridescent or pearlescent coating, a UV dull or inhibiting substance such as a coating containing titanium dioxide or hindered phenol or an opaque coloured strip or layer. 
     In other embodiments of the present invention, the nature of the security feature may be something other than a security element  11 . For example, it may be a hologram applied to the security paper overlying a patch of an activatable component to thereby mask the activatable component in normal conditions. 
     In another example the masking, or dominant, component may consist of a coating strip of opaque ink applied over a similar strip of the activatable component, or alternatively an OVI. 
     In yet another embodiment of the invention the dominant masking component is provided by a label applied to a paper or other substrate, and the activatable component is incorporated into the adhesive. When the security document bearing this embodiment of the invention is immersed in a solvent designed to dissolve adhesive, the activatable component becomes mobile and the colourant leaches out into and/or around the label. 
     Where the masking component itself is made from paper or another permeable substrate, the security document itself can be made of an impermeable substrate such as plastic. In this situation the water or solvent is able to permeate the masking layer to reach the activatable component. 
     A further embodiment of the invention may comprise a combination print, such as flexographic or screen printing. 
     In the first mentioned example the activatable component is described as including a colourant which on leaching out into the area around the thread  11  becomes visible to the naked eye. What is important, however, is that an element of the activatable component is clearly detectable whether by eye, under normal light, under UV light or IR light or with another type of machine or detector. 
     The composition may therefore alternatively contain a fluorescent substance which is invisible to the naked eye and is initially masked by an ultraviolet dull coating, instead of a layer of metal. After activation the frames  19  of the fluorescence will be clearly discernible from the windowed side of the document  10  when examined under ultraviolet light, although to the naked eye it will not be visible. On the reverse side of the document  10 , a long strip of fluorescence can be clearly detected. 
     Other detectable components may alternatively include a non-bleachable dye, polar/non-polar or a pH sensitive component. 
     The security feature may include a plurality of activatable component features which may include different components which are activated by different liquids, e.g. one water soluble component, one solvent soluble component etc. 
     The security feature may also include a plurality of masking features being the same or different. 
     Some specific examples of the present invention will e described below. 
     EXAMPLE 1 
     In this example a stripe is applied to a paper substrate using a gravure coater. The stripe is formed from a composition which includes an optically variable ink that has been doped with a mixture of UV fluorescent water soluble component plus an ultraviolet inhibitor, such as a hindered phenol. Under normal conditions, this stripe is visible as an optically variable image in normal light and is UV dull in UV fluorescent light. 
     Immersing a document made from such paper in water or an aqueous eradicator causes the water mobile component to move. After activation, under normal light the strip remains optically variable. However under UV fluorescent light the strip is UV dull with a fluorescent halo appearing around the strip. When the document is turned over the back of the strip is distinctively UV fluorescent. 
     EXAMPLE 2 
     In this example, the document is readable using fluorescent bar code sorter. This involves detecting a preprinted fluorescent bar code which sorts the documents into denominations. Following activation, an additional fluorescent strip is produced which would cause the document to be rejected, thus providing machine detection of potentially tampered documents. 
     EXAMPLE 3 
     As shown in FIG. 4, holographic label ( 21 ) is manufactured by a conventional embossing process. When the adhesive is applied to the back of the foil it is applied over a printed mesh of mobile component ( 22 ) such as a solvent soluble dye stuff. Thus the adhesion to the foil to the receptive substrate is not effected. On the immersion of the document in a solvent or water, the mobile component bleeds into the surrounding fibres creating a halo around the holographic label. 
     EXAMPLE 4 
     An ink is prepared containing a mixture of a UV dull chemical, such as a hindered phenolic or titanium dioxide and a UV fluorescent product such as Uvitex (trade mark). This ink is printed by a variety of techniques such as flexography, gravure or litho onto a UV dull paper, as shown in FIG.  5 . The print will be a message, such as “void”. Before immersion the document is viewed under UV light and found to be dull with no message showing, as shown on the left hand side of FIG.  5 . On immersion in water or a solvent the fluorescent components separates from the print producing the word “void” in hollow letters, as shown on the right hand side of FIG.  5 .