GB2250473A - Security articles - Google Patents

Abstract

A security article, such as a bank note or credit card, oomprises one or more elongate security elements partially or wholly embedded therein or affixed to the surface of said article, said elements comprising a transparent or translucent substrate (1), one or more opaque layers (2) having transparent or translucent portions (3) in the form of a pattern, design. indicia or the like, and one or more layers (5) of low optical density having the same surface appearance as said opaque layer when viewed in reflected light, such that when the article is viewed in reflected light the said transparent or translucent portions (3) closely resemble the opaque portions of the opaque layer (2) when the article is viewed in transmitted light the said transparent or translucent portions are readily discernable to the viewer. <IMAGE>

Description

8ECURITY ARTICLES This invention relates to security articles such as those produced from security paper, for example bank notes, traveller's cheques, bonds, tickets, and security documents, and also such security articles as credit, charge and identity cards.

Where used herein, the term "security paper" is to be understood to include sheets formed wholly, or partially, from natural fibres and/or synthetic fibres, or from wet or dry laminations of sheets formed from such fibres, or non-fibrous plastic sheets.

The use of strips, threads, ribbons or other forms of elongate security element in bank notes and other security documents, in the form of a metal strip or a strip of transparent film provided with a reflective metal layer is well known. The principle of use of such threads when embedded in security paper is that the thread cannot readily be seen in reflected light but is clearly visible when the security article is viewed in transmitted light.

However, there is a continual demand for more sophisticated security devices as counterfeiters become more able to simulate security articles with advances in technology in such fields as, for example, photocopying, printing, and hot foil stamping techniques.

In GB 2 213 098 there is described and claimed a security paper comprising opposed surfaces for the provision of printing to identify a document formed from the paper, and positioned at least partially between the two surfaces of the paper a security strip or thread which provides a continous metal path along the length of said strip or thread, wherein the said strip has a metal coverage between 50% and 90% of its area and the metal-free portion of the strip provides a pattern, design, indicia or the like.The security article described in GB 2 213 098 provides a considerable advantage over previous security devices in that it is more difficult for a counterfeiter to simulate the effect of a security strip which is not metallised over the whole of its area, because a simple drawn or printed line can be clearly seen not to be the genuine strip, and printing to simulate a security strip cannot adequately simulate the effect when the security article is examined in both transmitted and reflected light. However, it is desirable from the point of view of increasing security and reducing further risk of counterfeiting to produce a security article which has as different appearance as possible when viewed respectively in reflected and transmitted light, and is as difficult as possible to simulate.

According to the present invention there is provided a security article comprising one or more elongate security elements partially or wholly embedded therein or affixed to one surface of said article, said elements comprising a transparent or translucent substrate, one or more opaque layers having transparent or translucent portions in the form of a pattern, design, indicia, or the like, and one or more layers of low optical density having the same surface appearance as said opaque layer when viewed in reflected light, such that when the article is viewed in reflected light the said transparent or translucent portions closely resemble the opaque portions of the opaque layer but when the article is viewed in transmitted light the said transparent or translucent portions are readily discernable to the viewer.

Preferably the said opaque layer having transparent portions, is in the form of a partial metal film on the substrate, produced as described in GB 2 213 098. However, the effect produced in the security articles of the invention can also be obtained by using non-metallic coatings produced, for example, by printing techniques.Thus an opaque coating is applied to a substrate in a particular pattern. (By the term "opaque coating" it is to be understood that when the security element is incorporated into a security article as described herein, the coated regions of the substrate transmit significantly less light when viewed with the naked eye in comparison to those regions of the substrate not coated and in comparison with the regions of the security article adjacent to the security element.) A transparent or translucent coating of the same colour is then applied, either superposed over the opaque coating or on the reverse side of the substrate. The transparent coating can be applied uniformly all over the relevant side of the security element or only in register with the blank regions of the opaque coating.

However, as stated above, the preferred layers for use in the security element are metallic. In one form of this aspect of the invention a layer of metal of a low optical density is deposited over a selectively metallised film to produce a security strip such that when the strip is viewed in reflected light it has the appearance of a uniformly metallised strip but when the strip is viewed in transmitted light, a pattern or set of characters is revealed.

The low optical density layer must be sufficiently thick to provide a high level of reflectivity but, on the other hand, must be sufficiently thin to allow a visually detectable portion of light which is incident upon it to be transmitted through it.

Preferably the partially transparent or translucent i.e. low optical density layer, whether metallic or non-metallic, has an optical density of 0.1 to 1.2 and more preferably 0.3 to 0.9. Where appropriate, two or more thin transparent or translucent layers may be used within the thread structure in place of a single layer of low optical density, the combined optical density preferably being in the range as stated above.

The preferred metal for both the opaque and low optical density layers is vacuum deposited aluminium, but other metals, for example nickel, gold, copper, and cobalt:nickel alloys may be used for one or both layers. Instead of vacuum deposition other techniques such as electroplating may be used to deposit the layers.

It will be seen that in essence the idea behind the present invention is that the low optical density layer is used to, in effect, camouflage the transparent or translucent regions in the opaque layer so that the security element appears uniform in reflected light but the blank, i.e. transparent or translucent, regions are visually detectable in transmitted light.

As described in GB 2 213 098 the transparent or translucent blank portions of the opaque layer preferably provide characters or symbols of a language, such as letters of the English alphabet.

Alternatively or additionally there can be provided a wide variety of patterns or designs. Examples are shown in Figures 7 to 14 of the accompanying drawings, as described hereafter.

It is also preferred that when the opaque layer comprises a metal the metal coverage is between 50% and 90% of the area of one side of the security element.

It is preferred that the opaque layer provides a continuous metal path along the length of the security element so that a continuous electrically conductive path is provided in order that, when the security element is present in a bank note, for example, or other security document, it can be detected using conventional metal thread detection equipment on, for example, a used note sorting machine. Additionally, the distribution of metal can be determined by electrical, optical, or other means using a detector and then compared with a reference, thus giving an additional alternative technique for authentication of a genuine document containing the security element.The continuous metal path may, for example, be at one or both edges of the strip or thread, or it may be intermediate the edges or may vary along the length of the strip from the edge to some intermediate location or locations.

The strip or thread may also have parallel sides or one or both sides may have a regular or irregular non-linear configuration (as shown in the accompanying Figure 14 of the drawings).

Additionally, the strip may have an opaque metal layer on both sides of a plastic substrate i.e. the strip has two opaque layers, provided that transparent or translucent regions of each opaque layer overlap so that light can be transmitted through the strip in the overlap regions.

As described above it is preferred that the material of the opaque layer, preferably a metal, occupies between 50 and 90% of the area of one side of the strip but the lower limit is preferably 55% or 60% and the upper limit is preferably 85%.

In the particularly desired embodiments of the security articles of the invention the security strip is located within a watermark or is exposed by being placed within a window or aperture of the paper where no or virtually no paper fibres are present in the strip.

Either or both sides of the security strip or thread may comprise a layer containing a dye or luminescent material, which may be the same or different when the layer is present on both sides of the strip or thread.

In another aspect of the invention the security strip or thread may comprise a plastic substrate with metal on one side thereof and a dye or luminescent material present in the substrate or on the surface of the substrate. Also, the strip or thread may comprise a plastic substrate with metal on one side and a dye or luminescent material in a coating on the surface of the metal Furthermore, the strip or thread may comprise a plastic substrate with metal on one side and a dichroic layer on at least one side of the strip or thread.

The use of a pattern, characters, indicia, etc.

in the security thread significantly enhances the security of the thread when the security article has windows or apertures through which the thread is directly visible. Such windows or apertures may be provided by means known in the art, such as those disclosed in EP 0059056. Alternatively the strip or thread may be embedded between two layers of fibre formed separately on a paper machine and subsequently brought together to form a single sheet whereby at least one of the plies contains a sequence of holes formed by a watermarking or other process such that these holes, which contain no or virtually no fibre, are at least partially located over the strip or thread thus exposing it. If the holes are formed in one layer of fibre only, the security strip or thread will be exposed, or windowed, on one surface only of the final security article.On the other hand, if the holes are present in both fibre layers but in different locations, the strip or thread will be exposed, or windowed, on both sides of the final sheet in different locations. Likewise it will be seen that if the holes are present in both fibre layers such that they are at least partially in register with each other and the strip or thread, then the strip or thread will be simultaneously exposed on both sides of the article to form an aperture.

As explained above, the security element itself may be of uniform width or may vary in width as in the case of certain known security threads. For threads of uniform width, the thread widths may range typically from 0.5 mm to 2.0 mm, with character or indicia heights (i.e. the dimension across the width of the thread) in the range 0.3 mm to 1.5 mm.

However wider strips or threads may be used, for example 3 mm or more, depending on the procedure used to incorporate the strip or thread into the security article. The strips or threads may be formed from transparent colourless plastic film with partial demetallisation providing the pattern, the design, indicia, or the like, as explained above, and this film can then be slit to provide strips or threads of appropriate width, for example about 1.2 mm.

Where the opaque and/or highlight areas of the strip used in the present invention are coloured or provided with a luminescent coating according to one of the methods already described, then by providing a suitable lumination and detection system the coloured opaque material and/or the highlight areas may be compared with a reference, thus providing a further technique for authentication of a genuine document containing the strip or thread.

The invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a longitudinal section of a security element in accord with the prior art.

Figures 2 to 6 are longitudinal sections of security elements in accord with this invention; and Figures 7 to 14 are examples of the configurations of opaque layers which can be used in the invention.

Example 1 Referring to Figure 1, a web of 12 micron thick colourless polyester 1 e.g. Emblet 1200, is uniformly coated on one side with a vacuum deposited opaque layer of aluminium of an optical density 2.0-2.5.

The film is then printed in selected regions with a suitable resist 4 which is cured and hardened by the action of heat and/or UV light as appropriate. A spray of 5% sodium hydroxide solution at 600C is then applied to the metallised side of the web so that the aluminium is dissolved in those regions not protected by the overlying resist. The web is then rinsed and dried. An acid etchant may be used instead of caustic soda in which case an acidresistant resist must be used. This resist-and-etch technique for selectively demetallising a metallised film is well known and is described for example in US 4 398 994, US 4 652 015, GB 2 213 098. The resist may be printed as a series of bars e.g. running horizontally or diagonally across the web, as alphabetical characters or as a geometric pattern.

Examples of this are shown in Figures 7 to 14. The opaque aluminium is now present in selected regions 2 on one side of the substrate 1 which which have an overlying layer of resist 4. Light may be transmitted through the regions 3 between the metallised regions 2. This structure is in accord with that produced as described in GB 2 213 098.

Other known techniques may be used to produce the selectively metallised web.

A second layer of aluminium of an optical density 0.5 is then vacuum deposited over the metallised side of the web. This forms a thin layer 5 which is superposed on the resist 4 over the opaque metal 2 and is present on the substrate at regions 3 between the opaque metal regions 2, as shown in Figure 2.

The web is then coated on both sides with a protective lacquer (not shown in the drawings), slit to security thread with a width in the range 0.5-2.0 mm (preferably 1.2 mm) and run into paper as an embedded security thread. When viewed in reflected light, the thread has a similar appearance to a simple uniformly metallised security thread and is virtually invisible (the regions 3 between the opaque regions 2 may be a little darker and less reflective than regions 2 but this difference will only be apparent on very careful inspection). However, when viewed in transmitted light, the regions 3 between the opaque metal regions 2 transmit a visually detectable amount of light and hence the pattern, characters, code or the like of regions 3 is apparent to the eye.

Thus the security offered by the thread described in GB 2 213 098 is further enhanced since a counterfeiter has to simulate both the reflected light appearance of the simple uniformly metallised thread and the transmitted light appearance of the thread described in GB 2 213 098.

Example 2 The procedure of this Example is the same as in Example 1, except that the low optical density aluminium layer 5 is deposited over the reverse side of the substrate to the opaque metal regions 2, as shown in Figure 3. The optical effects obtained are the same as in Example 1.

Example 3 The procedure in this Example is the same as in Example 2, except that a yellow dyed transparent lacquer is applied over both sides of the web before it is slit to thread dimensions and run into paper.

When viewed in reflected light on either side of the paper, the thread appears as a uniform yellow strip. When viewed in transmitted light, the regions 3 are seen as yellow surrounded by the dark, opaque regions 2. Therefore, the thread presents a different coloured effect according to the viewing conditions, and a counterfeiter must attempt to simulate both.

Example 4 In this Example the procedure is also the same as in Example 2, except that prior to slitting to thread width, the web is coated on both sides with a suitable adhesive. After slitting, the thread is run into paper such that it is exposed in windows according to the technique described in EP 0 059 056.

When the paper is viewed in reflected light on the appropriate side, the thread has a more or less uniform bright shiny appearance in the exposed window regions; the regions 3 between the opaque regions 2 may be marginally darker and less reflective than regions 2 but this will only be apparent on very close visual inspection, e.g. with a lens. The appearance in the bridge regions between the windows is as described for embedded thread in Example 1. On the reverse side of the paper, the thread has the appearance of a uniformly metallised thread as described in Example 1.

When the paper is viewed in transmitted light, the regions 3 between the opaque regions 2 transmit light and are detectable. Preferably, these regions 3 are in the form of alphabetical characters as shown in Figures 7 to 10. Regions 3 will appear brighter in those portions of paper where the thread is exposed in a window since there is reduced fibre coverage of the thread and thus reduced absorption and scattering of light.

A counterfeiter's difficulty in simulating the thread described in GB 2 213 098 is now even more difficult. Attempts to simulate the windowed regions of the thread by hot foil stamping of a metallic material in the appropriate pattern will be inadequate since the regions 3 will be apparent in reflected and transmitted light whereas for a security element in accord with the present invention, they are only apparent in transmitted light.

Example 5 The procedure in this Example is the same as in Example 2, except that the opaque regions 2 are made from a 0.9 micron thick layer of sputter deposited cobalt:nickel alloy in the ratio 85:15, by weight.

This alloy is demetallised using an etchant of 1.ON nitric acid at 200C.

Apart from the visual effects described in Example 2, the thread for this example is machine readable by virtue of its magnetic content.

Optionally, the low optical density aluminium layer 5 is replaced by a layer of vacuum deposited cobalt:nickel of optical density 0.5 to more closely match the appearance of the opaque regions 2.

Examnle 6 In this Example the procedure is as in Example 5, except that the opaque regions 2 are formed by firstly vacuum depositing an opaque layer of aluminium of optical density 2.0, then sputtering a 0.9 micron thick layer of cobalt:nickel alloy in the ratio 85%:15% onto the aluminium, thereafter applying a further aluminium layer of optical density 2.0 to the surface of the cobalt:nickel alloy, and finally demetallising in three stages where no resist has been printed using a solution of 0.0SN cupric chloride in 0.1N hydrochloric acid at 200C to remove the top aluminium layer, a solution of 1.ON nitric acid at 200C to remove the cobalt:nickel layer, and 0.08N cupric chloride in 0.1N hydrochloride acid at 200C to remove the bottom aluminium layer.This three stage process enables weaker etchants and lower temperatures to be employed than would be the case if a single etchant is used, thus saving on material and energy costs and reducing safety hazards. Also, there is less tendency for unwanted sideways etching into a layer already partly removed, thus improving character definition.

However, a single etchant for all three layers e.g.

2N sulphuric acid at 800C is a further option.

The advantage of this structure over that of Example 5 is that the opaque aluminium layers make the regions 2 more bright and shiny than is the case where regions 2 are formed from cobalt:nickel alone.

Example 7 The procedure on this Example is the same as in Example 4, except that vacuum deposited copper is used to provide the opaque regions 2 and low optical density regions 5.

Example 8 Referring to Figure 4, a resist layer 4 over the opaque metal regions 2 contains a suitable dye or pigment (as described in GB 2 213 098 and US 4 398 994). A further layer 6 beneath the opaque metal regions also contains a dye or pigment. A means for producing such coloured layers 4 and 6 above and below the opaque metal regions 2 is described in US 4 941 687.

An aluminium layer of optical density about 0.5 is then vacuum deposited on the opposite side of the polyester support layer 1 to the opaque metal regions 2. By choosing an appropriate colour for the dye or pigment added to layers 4 and 6, any small differences in reflected light appearance between the regions 3, between the opaque metal regions 2 and said regions 2 are reduced N eliminated so that the thread in paper has a completely uniform appearance when viewed in reflected light. The layer 5 is sufficiently thin to transmit a visually detectable amount of light as described in the previous Examples.

In a variation, layer 5 is deposited on the same side of the support layer 1 as the opaque metal region 2.

Example 9 A web of 12 micron polyester (e.g. ICI Melinex 813) is printed with a high reflectivity metallic ink (e.g. "Metasheen" from Johnson and Bloy Ltd., Crawley, Sussex, England) to produce an effect similar to that derived from a demetallised vacuum deposited aluminium layer. The web is then further processed as described in Example 1.

Example 10 A web of colourless transparent 12 micron polyester (e.g. ICI Melinex 813) is printed in a characteristic pattern such as shown in Figures 7 to 10, with an opaque, e.g. a non-metallic, ink. The web is then given a uniform coating on the reverse side of a transparent or translucent coating of the same colour as the opaque ink; optionally, this transparent coating is applied uniformly over the side of the web with the opaque coating, or locally on one or both sides of the web in register with the blank non-printed regions of the opaque coating. A clear protective coat is then applied to both sides, the web slit to thread dimensions and run into paper as an embedded thread.

In reflected light, the thread has a uniform colour when viewed from either side of the paper. In transmitted light, the regions not printed with the opaque ink are visually detectable as a coloured pattern.

Either or both of the opaque and transparent/ translucent coatings may contain a luminescent substance.

Example 11 A security thread is formed as described in Example 2. However, instead of being incorporated into paper, the thread is placed between two sheets of transparent or translucent plastic which, after further printing and processing, is formed into an identity or credit card.

Example 12 A web of film is prepared as described in Example 2. Prior to slitting to thread dimensions, the web is coated with an adhesive on the side of the substrate 1 coated with the partially transparent metal layer 5. After slitting to a width of 5 mm, the thread is laminated using the said adhesive to the surface of a paper or plastic sheet which, after printing or processing, is formed into an identity card.

Example 13 Referring to Figure 5, a web of 12 micron thick polyester 1A incorporating a green dye is coated with an opaque layer of vacuum deposited aluminium of an optical density 2.0. A caustic-resistant resist 4A is then printed over the metal in the form of bars 3.0 mm wide spaced 3.0 mm apart parallel to the transverse direction of the web. The web is then etched with 5% sodium hydroxide solution at 600C as previously described to produce bars of opaque metal 2A. After rinsing and drying, a layer of aluminium of optical density 0.3 is vacuum deposited over the side of the film 1 containing the opaque bars 2A to produce regions 5A as previously described.

The web is then laminated to a similar web such that the opaque metal bars 2A and 2B are in longitudinal register and on the outside of the laminate. The laminated web is then given a clear protective coating on each surface (not shown in Figure 5), slit to 1.6 mm width and run into paper as an embedded thread.

When viewed in reflected light from either side, the thread has the appearance of a uniformly metallised thread. In transmitted light, the two layers 5A and 5B have a combined optical density of 0.6 and still transmitted a visually detectable amount of light; hence regions 3 are observed as green bars surrounded in the longitudinal direction by opaque dark bars 2.

Example 14 With reference to Figure 6, a web 1A of 12 micron polyester dyed green is provided with regions 2A, 3A, 4A and 5A as described for Example 13. The web is then laminated to a similar web with the opaque metal bars 2 in longitudinal register, with the regions 2, 3, 4 and 5 on the inside of the laminate. The laminated web was coated with a suitable adhesive on both external surfaces, slit to 1.2 mm width and run into paper according to the technique described in EP 0 059 056.

When viewed in reflected light, in the windowed regions of the paper, the thread had a uniformly reflective green appearance. In the bridges between the windows and on the non-windowed side of the paper, the thread appeared as a uniform green strip.

When viewed in transmitted light, the regions 3 appeared as green bars surrounded in the longitudinal regions by opaque dark bars.

In all security elements described in this specification, additional adhesive and protective coatings not shown in the figures may be applied.

All adhesives and protective coatings, and the support layers, may contain dyes and/or pigments to provide colour and/or luminescent effects, as described in GB 2 213 098.

Claims (15)

CLAIMS:

1. A security article comprising one or more elongate security elements partially or wholly embedded therein or affixed to one surface of said article, said elements comprising a transparent or translucent substrate, one or more opaque layers having transparent or translucent portions in the form of a pattern, design, indicia or the like, and one or more layers of low optical density having the same surface appearance as said opaque layer when viewed in reflected light, such that when the article is viewed in reflected light the said transparent or translucent portions closely resemble the opaque portions of the opaque layer but when the article is viewed in transmitted light the said transparent or translucent portions are readily discernable to the viewer.

2. A security article as claimed in claim 1 wherein the said opaque layer and said layer of low optical density are both non-metallic coatings having the same colour as each other.

3. A security article as claimed in claim 1 wherein the said opaque layer and said layer of low optical density are metallic.

4. A security article as claimed in claim 3 wherein a layer of metal of low optical density is deposited over a selectively metallised film on the substrate.

5. A security article as claimed in any one of the preceding claims wherein the layer of low optical density has an optical density of 0.1 to 1.2.

6. A security article as claimed in claim 5 wherein. the layer of low optical density has an optical density of 0.3 to 0.9.

7. A security article as claimed in any one of the preceding claims comprising two or more thin layers of low optical density having a combined optical density in the range of 0.1 to 1.2.

8. A security article as claimed in any one of claims 3 to 7 wherein both the opaque and the low optical density layers comprise vacuum deposited aluminium.

9. A security article as claimed in any one of claims 3 to 8 wherein the metal coverage in the opaque layer is between 50% and 90% of the area of one side of the strip.

10. A security article as claimed in any one of claims 3 to 9 having an opaque metal layer on both sides of the substrate said layers having transparent or translucent regions which overlap.

11. A security article as claimed in any one of the preceding claims wherein the security element is exposed by being located within a window or aperture in the substrate.

12. A security article as claimed in claim 1 substantially as hereinbefore described in any one of the Examples.

13. A security article as claimed in any one of the preceding claims which is in the form of a bank note.

14. A security article as claimed in any one of claims 1 to 12 which is in the form of a credit, charge or identity card.

15. A security article as claimed in any one of claims 1 to 12 which is in the form of a paper or plastic ticket or coupon.