GB2338679A - Substrates for security documents - Google Patents

Abstract

A substrate for producing security documents such as banknotes, cheques, passports and the like which are required to provide a high degree of security against imitation comprises a plurality of layers (14, 15) of transparent biaxially oriented polymeric film laminated together, in which at least one of which layers of polymeric film is partially metallised to provide a metallic layer having some opaque metal areas (18) and some non-metallised areas (19) providing transparent regions such that the metallic layer provides opacity and visually recognisable identifying indicia, in which the metallic layer is wholly encapsulated between the layers of the polymeric film. The metallic layer may have a translucent coloured coating on one or both sides. The substrate may comprise a magnetic material or at least one internally printed layer where the link may be coloured and translucent or opaque and be luminescent between the polymeric layers.

Description

1 - 1 IMPROVEMENTS IN SECURITY DOCUMENTS AND SUBSTRATES THEREFOR 2338679

The invention relates to improved security documents such as banknotes, cheques, passports and the like which are required to provide a high degree of security against imitation and a substrate for producing such security documents.

Such documents are traditionally made from security paper, that is paper having good durability and a high resistance to crumpling and tearing. However, such documents are still prone to damage through water, cutting and eventual wear. Furthermore such security documents are vulnerable to forgery.

To prevent counterfeiting it is widely known to use in traditional banknotes and security documents, security devices such as security threads or strips which are made from a transparent polyester film provided with a wholly or partially reflective metallised layer. The threads are wholly or partially embedded within the paper and provide a high degree of security against counterfeiting. However, the paper itself is still subject to a degree of wear and damage.

This problem has been addressed in International Patent Application W083/00659 which describes a plastic banknote. This banknote is made up from one or more films of transparent biaxially oriented polymers which are coated with layers of relatively opaque printing ink and heat activated adhesive material. An optically variable security device such as a diffraction grating is adhered to the substrate in a window left in the opaque layer. The substrate is then printed with identifying indicia and covered on both sides by further layers of polymer material. Most counterfeiters do not have access to equipment for making such materials and plastic banknotes are 0 2 damage and wear resistant. It should be noted that whilst biaxially oriented polymer films such as those described in W083/00659 have excellent resistance to tear initiation (i.e. edge tear resistance) they have poor resistance to tear propagation (i.e. internal tear resistance) when compared to paper.

It is an object of the present invention to provide improved security documents and substrates therefor made from a polymeric material to address the problems of counterfeitability.

According to the invention there is therefore provided a substrate for security documents and the like comprising a plurality of layers of transparent biaxially oriented polymeric film laminated together, in which at least one of which layers of polymeric film is partially metallised to provide a metallic layer having some opaque metal areas and some nonmetallised areas providing transparent regions such that the metallic layer provides opacity and visually recognisable identifying indicia, in which the metallic layer is wholly encapsulated between the layers of the polymeric film.

The metallic layer preferably has a translucent coloured coating on one or both sides.

Preferably the metallic layer provides an electrically conductive path along the width or length of the substrate.

A magnetic material may be provided between the polymeric layers.

At least one internally printed layer may be provided between the polymeric layers.

The ink may be coloured and translucent or opaque.

The ink may be luminescent.

Preferably the thicknesses of at least two of the polymeric layers are different.

The invention also provides a security document 0 3 - made from the substrate.

Additional indicia may be printed on the external surfaces of said document.

Additional indicia are preferably printed on the internal surfaces of one or more of the polymeric layers.

Additional indicia are preferably printed on the external surfaces of the substrate and the internal surfaces of one or more of the polymeric layers.

The invention will now be illustrated by the following examples with reference to the accompanying drawings, in which:- Figs. 1 and 3 are plan views of alternative samples of security documents according to the present invention; and Figs. 2 and 4 are a longitudinal cross- sectional side elevations of a substrate for a security document according to the present invention.

In all of the examples described below the substrate comprises a laminate of two or more biaxially oriented polymeric layers laminated together one or more of which is partially metallised to provide a partial layer of metal sandwiched between the polymeric layers. The substrate can be used to produce security documents such as banknotes and the like without the need to apply opaque coatings for opacity.

The metal layer(s) is preferably a metallic thin film applied to one or both surfaces of one or more of the polymer layers, for instance a vacuum deposited aluminium film.

The polymeric layers are preferably laminated together with a layer of a suitable adhesive, such as a cross linking adhesive. Alternatively a thermally 0 4 is activated adhesive may be used.

The polymeric layers are films of polyethylene or polypropylene or another suitable material and are transparent. The substrate may also include additional security features, such as printed indicia, security devices and so on sandwiched between the polymeric layers. The outermost polymeric layers protect these features from damage or removal.

Example 1

Referring to Fig. 2, one embodiment of the substrate 11 comprises two polymeric layers 14, 15, laminated together with a layer of adhesive 16. Layer 14 is a transparent film which has been partially metallised. The film 14 is metallised with a layer of, say, vacuum deposited aluminium, although another metal such as cobalt or sputtered nickel/iron may be used. The metallised layer 14 may be an SHM (') film from Hoechst Trespaphan which is available in various thicknesses, which is selectively demetallised to leave regions of opaque metal 18 and clear regions 19, which regions 18, 19 form embedded identifying indicia 13. The embedded indicia 13 may be of a positive nature, i.e. the indicia 13 formed by the metallic regions 18, or negative in which the indicia 13 are formed by the clear regions 19. The indicia 13 may be in the form of alphanumeric text, a pattern, or any other appropriate form, some examples of which are shown in Fig. 1. The indicia 13 may incorporate clear windows which eliminates the need to selectively coat the surfaces of the substrate 11.

Layer 15 is also a transparent film, which is not metallised, such an GND (') film also from Hoechst Trespaphan which is also available in various thicknesses.

The layers 14, 15 are laminated together with the metallic layer located between the transparent layers 0 is 14, 15 so that it is wholly encapsulated within the substrate 11. As the layers 14, 15 are transparent, the indicia 13 formed by the metallic layer can be seen from both sides of the substrate 11 and renders the substrate 11 opaque in the regions 18, whilst it is transparent in the regions 19. The substrate 11, when viewed from either side in reflected light, will have a bright shiny metallic appearance in the metallised regions 18 and will be transparent in the clear regions 19. This contrasting visual effect is enhanced when the substrate 11 is viewed in transmitted light.

The substrate 11 incorporating embedded indicia 13 may then be subsequently printed with superficial indicia 12.

The superficial indicia maybe printed in a translucent medium to provide a coloured metallic appearance, similar to coloured metallic foils (hot stamped or otherwise applied) and of enhanced reflective appearance to surface applied metallic inks.

The metal component of such metallic identifying indicia is protected from chemical attack and abrasion by virtue of its being embedded within the substrate and the indicia is thus of superior durability to conventional surface applied aluminium flake based metallic inks or surface coatings. Such a metal layer furthermore provides increased opacity compared with transparent films having opaque surface coatings, for situations where further indicia are to be printed over the metal layer. It also reduces or eliminates the need for separate surface coatings for the purpose of providing opacity on which identifying indicia is to be printed. Such coatings, where applied, need only be of low intrinsic opacity, sufficient for decorative or aesthetic effects.

A significant advantage of this substrate 11 is 0 that, where suitable unbalanced biaxially oriented films are used as layers 14, 15, when it is viewed through a polarising filter, the substrate 1:1 provides a coloured effect in the metal regions 18, due to the birefringence effect of the polymeric films, and the specular reflection from the metal layer which enhances the difference between the metallised 18 and unmetallised 19 regions.

The pattern forming the embedded indicia 13 may be a screen pattern which gives variable opacity, for example a continuous change in opacity by making the screen ruling or dot size progressively smaller or larger.

The demetallisation of large areas of the metallised layer 14 may also be used to provide a pseudo watermark effect with very high resolution, similar to that achieved by intaglio printing.

Such selective demetallisation provides a high quality image with good resolution.

For the demetallisation process, any suitable methods may be used, such as direct etching or indirect etching using a resist. Where the indirect resist and etch method is used, coloured resist materials may be employed which leaves a layer of translucent coloured material on the metallised regions 18 resulting in indicia 13 having a good coloured metal effect.

Alternatively a selective metallisation process may be used or the metal regions 18 may be created by printing with a high reflectivity metallic ink.

A further alternative would be to image the metallic layer by laser cutting or ablation of the metal either as an intermediate step in the construction of the substrate, or subsequent to its assembly. This would be particularly useful for metal other than aluminium, e.g. stainless steel.

In all these embodiments, it should be recognised 0 7 that the use of a partially metallised layer can provide indicia in much finer detail than can be provided by most printing techniques. in the aforementioned example, where there is a continuous metal path either along the length or width of the substrate, this provides an electrically conductive path which can be used for authentication using appropriate machine readers.

In some applications, it may be advantageous for the metallic layer or layers to be partially or wholly obscured as in the following examples 2 to 6.

Examnle 2 The aforementioned example may be modified by overprinting with a translucent coloured ink to give a coloured metallic effect. The translucent coloured ink may be applied directly to the metal layer 18 or the polymer layer 15 before the polymeric layers 14, 15 are laminated together. Alternatively the adhesive 16 may be coloured.

Example 3

In this example, a coating is used which is partially opaque so that in transmitted light a partially metallised layer 14 such as that shown in Fig. 2 can be seen as a shadow/light image.

ExamiDle 4 In this example, as illustrated in Fig. 3, an opaque or partially opaque coating 15 or coatings is/are applied to one or both of the external surface of the substrate 11 leaving one or more areas 25 uncoated which form windows in which some of the metal indicia 13 as described in example 1 can be seen clearly in reflected light. Such a coating need not contain a high proportion of opacifying pigment and is 0 8 used purely for aesthetic and decorative reasons, or as a background for printing on.

Example 5

The security of documents produced from substrates according to the present invention may be further enhanced by the provision of additional embedded indicia 13 formed by printing 26 on the inner surface (s) of one or more of the layers 14, 15 before laminating to be visible over or through the metal layer 18. The printing 26 may be provided by black, white or other coloured, translucent or opaque, inks or inks containing luminescent materials which are invisible until activated by appropriate heat or light is sources, such luminescence to include fluorescence, phosphorescence and excitation by UV, IR, visible light and other radiation as appropriate. In the example shown in Fig. 4, polymeric layer 14 is partially demetallised, having metal regions 18. A fluorescent ink layer 26 is printed over the layer before lamination. Thus when the substrate 11 is viewed from the direction of arrow A, when viewed under an ultraviolet light source the substrate 11 will fluoresce in the demetallised regions 19.

Example 6

The embodiments of any of the aforementioned examples may be directly embossed with a latent image line or dot patterns in other indicia on an intaglio press without using special embossing dies. Such embossings are well known for imparting visual and tactile authentication and recognition.

Additional security can be obtained by embossing directly with a holographic or other diffractive pattern shim on an intaglio press or in a hot stamping press. Embossing into metallised areas provides a 0 9 reflective, optically variable image which cannot be removed and used on a counterfeit or replica document. Embossing into a demetallised, transparent area can provide subtle optically variable images.

It should be understood that although many of the examples above have been described with reference to two polymeric layers 14,15 only, the substrate 11 may comprise a laminate of more than two such layers each having the same or different features described in the examples.

is 1,1 kl-,/ - 10

Claims (14)

CLAIMS:

1. A substrate for security documents and the like comprising a plurality of layers of transparent biaxially oriented polymeric film laminated together, in which at least one of which layers of polymeric film is partially metallised to provide a metallic layer having some opaque metal areas and some nonmetallised areas providing transparent regions such that the metallic layer provides opacity and visually recognisable identifying indicia, in which the metallic layer is wholly encapsulated between the layers of the polymeric film.

2. A substrate as claimed in claim 1 in which the metallic layer has a translucent coloured coating on one or both sides.

3.

A substrate as claimed in any one of the preceding claims in which the metallic layer provides an electrically conductive path along the width or length of the substrate.

4.

A substrate as claimed in any one of the preceding claims further comprising a magnetic material between the polymeric layers.

5. A substrate as claimed in any one of the preceding claims further comprising at least one internally printed layer between the polymeric layers.

6. A substrate as claimed in claim 5 in which the ink is coloured and translucent or opaque.

7. A substrate as claimed in claim 6 in which the ink is luminescent.

1- ' 1 - 11

8. A substrate as claimed in any one of the preceding claims in which the thicknesses of at least two of the polymeric layers are different.

9. A security document made from a substrate as claimed in any one of the preceding claims.

10. A security document as claimed in claim 9 on the external surfaces of which are printed additional indicia.

11. A security document as claimed in claim 9 or claim 10 in which additional indicia are printed on the internal surfaces of one or more of the polymeric is layers.

12. A security document as claimed in any one of claims 9 to 11 in which additional indicia are printed on the external surfaces of the substrate and the internal surfaces of one or more of the polymeric layers.

13. A substrate substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

14. A security document substantially as hereinbefore described with reference to and as shown in the accompanying drawings.