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
Apreferred 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
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
5 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
10 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
15 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
20 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.
25 ("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
30 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
35 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
40 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
45 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
5Q 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
55 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
60 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
65 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