Security document including an optical security feature

Abstract

A security document, including: a polymer substrate; at least one print layer disposed on one or both sides of the polymer substrate; and a security feature including an image area embodied within the polymer substrate and at least partially covered by the at least one print layer, wherein the security feature is an optical security feature formed in the image area.

Claims

1. A security document, including: an opaque polymer substrate having particles disposed therein configured to react to a designated wavelength of light from a light source, wherein the polymer substrate is opaque before reacting to the designated wavelength of light; at least one print layer, the print layer being substantially opaque when viewed in reflection, disposed on one or both sides of the opaque polymer substrate; and a security feature including an image area embodied within the opaque polymer substrate and at least partially covered by the at least one print layer, wherein the security feature is an optical security feature which includes markings formed from exposure of the particles to the designated wavelength of light in the image area, wherein the particles absorb energy and vaporize the polymer substrate adjacent the particles, wherein the markings absorb light to create a dark color and are discernible when illuminated by light and viewed in transmission of said light through the security feature.

2. A security document according to claim 1, wherein the image area is completely covered by the at least one print layer disposed on one or both sides of the polymer substrate.

3. A security document according to claim 2, wherein the at least one print layer includes a printed image overlying at least part of the optical security feature.

4. A security document according to claim 3, wherein the optical security feature is derived from the printed image such that the printed image wholly overlies the optical security feature.

5. A security document according to claim 3, wherein the optical security feature differs from the printed image such that the printed image does not wholly overlie the optical security feature.

6. A security document according to claim 1, wherein the particles react to the designated wavelength of light by absorbing energy from the designated wavelength of light and vaporising the polymer substrate adjacent the particles to form bubbles in the polymer substrate.

7. A security document according to claim 6, wherein the bubbles scatter light or the markings absorb light to create the dark color of the optical security feature when the optical security feature is viewed in transmission of the light through the security feature.

8. A security document according to claim 1, wherein the markings absorb light to create the dark color of the optical security feature when the optical security feature is viewed in direct reflection of the light from the optical security feature.

9. A method of manufacturing a security feature for a security document, the method including: irradiating an image area embodied within an opaque polymer substrate of a security document with a designated wavelength of light produced from a light source; the opaque polymer substrate having particles disposed therein reacting to the designated wavelength of light to form an optical security feature in the image area, wherein the optical security feature includes markings formed from exposure of the particles to the designated wavelength of light in the image area, wherein the particles absorb energy and vaporize the polymer substrate adjacent the particles; and at least partially covering the image area with at least one print layer, the print layer being substantially opaque when viewed in reflection and being disposed on one or both sides of the polymer substrate, wherein the markings absorb light to create a dark color, which is discernible when illuminated by light and viewed in transmission of said light.

10. A method according to claim 9, further including: irradiating an image mask provided between the light source and the polymer substrate of the security document with the designated wavelength of light produced from the light source, wherein the image mask includes an image area corresponding to the optical security feature formed from a first material and a complementary area to the image area formed from a second material.

11. A method according to claim 10, wherein the first material is transmissive to the designated wavelength of light produced from the light source and the second material is not transmissive to the designated wavelength of light.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) Embodiments of the invention will now be described with reference to the accompanying drawings. It is to be understood that the embodiments are given by way of illustration only and the invention is not limited by this illustration. In the drawings:

(2) FIG. 1 is a sectional view of a security document according to an embodiment of the present invention;

(3) FIG. 2 is a top view of the security document of FIG. 1 showing a security feature viewed in transmission according to an embodiment of the present invention;

(4) FIG. 3 is a top view of the security document of FIG. 1 viewed in reflection according to an embodiment of the present invention;

(5) FIG. 4 is a schematic representation of part of an apparatus for use in manufacturing a security feature according to an embodiment of the present invention;

(6) FIG. 5 is a further sectional view of a security document according to an embodiment of the present invention;

(7) FIG. 6 is a flowchart showing a method of manufacturing a security feature for a security document according to an embodiment of the present invention;

(8) FIGS. 7A and 7B are representations of an optical security feature and a printed image according to another embodiment of the present invention;

(9) FIGS. 8A, 8B and 8C are representations of an optical security feature, a printed image and the optical security feature with overlaid printed image according to another embodiment of the present invention.

DETAILED DESCRIPTION

(10) Referring to FIG. 1, there is shown an embodiment of a security document 10 including a polymer substrate 12, a first print layer 16 disposed on one side of the polymer substrate 12, and a second print layer 18 disposed on the opposed side of the polymer substrate 12. In the embodiment, the polymer substrate 12 is a transparent substrate of the security document 10 made from a transparent polymer and the security document 10 is a polymer based bank note. The polymer substrate 12 will hereinafter be referred to as a transparent substrate 12 and the security document 10 will hereinafter be referred to as a polymer based bank note 10. In the embodiment, the first 16 and second 18 print layers are opacifying layers disposed on the transparent substrate 12. The first 16 and second 18 print layers will hereinafter be referred to as first opacifying layer 16 and second opacifying layer 18.

(11) The bank note 10 shown in the Figures includes a security feature 14 including an image area 15 embodied within the transparent substrate 12 and at least partially covered by the first and second opacifying layers 16 18. It can be seen from the cross-sectional view in the embodiment shown in the Figures, the image area 15 is embodied wholly within the transparent substrate 12 and is completely covered by both the first and second opacifying layers 16 18 disposed on both sides of the transparent substrate 12.

(12) The security feature 14 in the Figures is an optical security feature 17 in the form of a shadow image formed in the image area 15 which is discernible when illuminated by light and when viewed in transmission of the light though the security feature 14. The optical security feature 17 will hereinafter be referred to as shadow image 17. The shadow image 17 is shown in FIG. 2 as the text “SHADOW”, and FIG. 2 represents the bank note 10 being viewed in transmission. That is, the shadow image 17 can be discerned when the bank note 10 is placed between the viewer and the source of the light. In FIG. 3, on the other hand, the text “SHADOW” is not discernible as FIG. 3 represents the bank note 10 being illuminated and viewed in reflection of the light. As mentioned, the security feature 14 is thus covert and intended to be hidden to a viewer when viewed in reflected light to enhance its effectiveness as a security feature.

(13) FIGS. 2 and 3 also show first and second image elements 20 22 applied to the bank note 10. It will be appreciated that these image elements 20 22 are normally found on bank notes, such as the first element 20 being a “star” and the second image element 22 being a denomination (e.g. “$50”). In the embodiment, these image elements 20 22 are formed in design layers applied to the first opacifying layer 16 These image elements are applied with an ink having a colour that is different from the colour of the first 16 or second opacifying layers 18 to provide visual design elements of the bank note 10. Additional image element layers could also be applied, on top of the first and second opacifying layers 16 18, using for example invisible inks, such as UV fluorescing or IR absorbing inks. Such images are machine readable images invisible to a viewer, but can be revealed using appropriate light sources and viewing equipment.

(14) FIG. 5 shows an embodiment of a bank note 10 with multiple opacifying layers. The bank note 10 shown in FIG. 5 has the above mentioned security feature 14 in the image area 15 embodied within the transparent substrate 12. It can be seen from this Figure that the shadow image 17 includes first and second shadow image portions 17A 17B formed in the image area 15 that extend throughout the thickness of the transparent substrate 12. By opacifying the transparent substrate 12 throughout the entire thickness of the substrate, the shadow image 17 is more durable and is more difficult to counterfeit and to be rubbed off. Further, as the transparent substrate 12 is opacified throughout the entire thickness of the substrate, the shadow image 17 is more visible when viewed in transmission. In this embodiment also, the image area 15 of the bank note 10 is completely covered by two first opacifying layers 16 24 and two second opacifying layers 18 26.

(15) As mentioned above, to form the shadow image 17, the transparent substrate 12, in one embodiment, is doped with particles that are configured to react to a designated wavelength of light from a light source to opacify the transparent substrate 12 adjacent these particles. That is, for example, a pigment, such as the above mentioned LS800 is embodied into the transparent substrate 12 which is doped with these particles. These particles react to the designated wavelength of light by absorbing energy from the designated wavelength and then by vaporising the transparent substrate 12 adjacent the particles to form bubbles in the transparent layer. Also, as mentioned, these bubbles scatter light to create a white appearance of the shadow image 17 if the shadow image 17 was viewed in direct reflection without being covered by the first 16 or second 18 opacifying layers. As the first 16 and second 18 opacifying layers, typically a white layer, at least partially cover the shadow image 17, the shadow image 17 is not readily discernible by the viewer when viewed in reflection of light from the security feature. Further, the scattered light also creates a dark appearance of the shadow image 17 when viewed in transmission of light that is discernible to the viewer. It will be appreciated by those persons skilled in the art that the light is white light from a light source such as the sun or electric lighting.

(16) An embodiment of an apparatus 30 configured to manufacture a security feature 14 for a security document 10—in particular, a security feature for the above described bank note 10—is shown in FIG. 4. The apparatus 30 includes a laser (not shown) configured to irradiate the image area 15 in the transparent substrate 12 of the bank note 10 with a designated wavelength of light. In the example where the LS800 pigment is used, the light source is a CO2 laser having a designed wavelength of 9.4 μm or 10.6 μm. The laser beam is shown as arrow A and is first applied to an image mask 32 provided between the laser and the transparent substrate 12 of the bank note 10.

(17) The image mask 32 shown in FIG. 4 includes an image area 36 corresponding to a desired shadow image that is formed from a first material. The first material is a material that is transmissive to the designated wavelength of light produced from the laser. The image mask 32 also includes a complementary area 34 to the image area 36 that is formed from a second material that is not transmissive to the designated wavelength of light. That is, the second material absorbs and dissipates the laser energy used for opacifying (e.g. marking) the transparent substrate 12 in the image area 15 but without itself being damaged. In an example, the first material is simply air and thus the image mask 32 is a negative of the image corresponding to a desired shadow image made of the second material. Here, the shadow image 17 formed on the transparent substrate 12 shown in FIG. 4 is an image of a person's head, and the image mask 32 is a negative of the image of the person's head formed out of the second material.

(18) In another embodiment, the shadow image is made by directly writing an image on the transparent substrate 12 using a scanning laser system (not shown). It will be appreciated that this embodiment may be of particular interest when the security document is not a bank note, for example when the security document is an ID card. Turning back to the embodiment in FIG. 4, the image mask 32 enables the shadow image 17 to be formed quicker and it will be appreciated that speed is required for manufacturing bank notes.

(19) The apparatus 30 for manufacturing the security feature 14 also includes a demagnification optic 38 to reduce the size of the shadow image 17 to be formed on the transparent substrate 12 to a desired size and to ensure the laser energy density in the image area is sufficiently high to form bubbles in the transparent substrate 12. In use of the apparatus 30, the laser irradiates the image area 15 embodied within the transparent substrate 12 via the image mask 32 and the demagnification optic 38. The transparent substrate 12 has particles disposed therein that react to the designated wavelength of light of the laser to opacify the transparent substrate 12 adjacent the particles to form the shadow image 17 in the form of the person's head in the image area 15.

(20) To then complete the security feature 14, the bank note 10 is transported to another apparatus (not shown) for at least partially covering 46 of the image area 15 with at least one opacifying layer 16 18 on one or both sides of the transparent substrate 12. The shadow image 17 created directly in the image area 15 can thus be completely covered by the opacifying layers 16 18 applied on top on both sides, on one side (½ window), or a combination thereof. In any event, the security feature 14 is thus a shadow image 17 as above which is discernible when illuminated by light and when viewed in transmission. The size and density of the formed shadow image 17 is related to the thickness of the transparent substrate 12 containing the pigment, the amount of pigment contained within the transparent substrate 12 and the influence of the laser applied (energy per unit area).

(21) For example, the transparent substrate 12 is optically clear polymer film manufactured by Innovia Films Wigton which is doped with finely dispersed particles having high absorbance to a specific laser irradiation wavelength. A single pulse of laser irradiation having the designated wavelength is directed through the image mask 32 and the demagnification optic 38—forming a mask projection optical system—onto the doped polymer film 12 effecting localised heating and bubble formation to thereby spatially opacify the film 12 in correspondence with regions 36 of the image mask 32 that are optically transmissive to the designated wavelength of laser radiation. The image 32 mask transmissive regions 36 are in correspondence with a desired spatial distribution of tonality in the shadow image 17 and the mask transmissive regions 36 are in correspondence with mask design rules defining the relationship between spatial distribution of opacity in the film 12 and spatial distribution of tonality in the shadow image 17.

(22) Referring now to FIG. 6, there is shown a summary of a method 40 of manufacturing a security feature for a security document, the method including: irradiating 42 an image area embodied within a polymer substrate of a security document with a designated wavelength of light produced from a light source; the polymer substrate having particles disposed therein reacting 44 to the designated wavelength of light to mark or opacify the polymer substrate adjacent the particles to form an optical security feature in the image area; and at least partially covering 46 the image area with at least one print layer disposed on one or both sides of the polymer substrate, thereby forming the security feature as the optical security feature in the image area which is discernible when illuminated by light and when viewed in transmission of the light though the security feature.

(23) Further aspects of the method 40 will be apparent from the above description of the bank note 10. A person skilled in the art will also appreciate that at least parts of the method 40 could be embodied in program code for implementation on a microprocessor of the apparatus 30. The program code could be supplied in a number of ways, such as on a memory of the apparatus 30 or in data communication with the microprocessor.

(24) In another embodiment of the invention, with reference to FIGS. 7A and 7B, the security document is a polymer based bank note and the polymer substrate is an opaque substrate made from a white polymer. In this embodiment, the print layer includes a printed image wholly overlying the optical security feature.

(25) FIG. 7A shows an optical security feature 50 derived from a corresponding printed image 52 (shown in FIG. 7B). The printed image 52 is a gravure banknote design element, in this example a portrait that is printed in a dark colour. The optical security feature 50 is designed such that it is smaller in extent than the printed image 52 by at least an amount taking into account a registration tolerance, such that the optical security feature 50 is completely covered by the printed image 52 in the final security document.

(26) Similarly to the transparent substrate example, the polymer substrate in this embodiment has particles disposed therein configured to react to a designated wavelength of light by absorbing energy and vaporising the polymer substrate adjacent the particles to form markings in the polymer substrate. The markings in this case absorb light to create a dark appearance of the optical security feature when the optical security feature is viewed in direct reflection of light from the security feature. That is, the markings would create a dark appearance of the optical security feature if it was viewed directly without the print layer covering it. For example, the optical security feature may appear dark black or dark blue.

(27) In this embodiment, the printed image 52 effectively camouflages the optical security feature 50 when viewed in direct reflection of light such that the optical security feature 50 is hidden from view. When the security document is viewed in transmitted light, the optical security feature may or may not be visible. There may be a contrast between the printed image 52 and security feature 50 due to transmitted light being absorbed by the markings of the optical security feature 50. However, it is possible that no shadow image is produced. In either case, the optical security feature 50 produces an indelible image in the substrate that survives after the printed image 52 has worn off.

(28) FIGS. 8A-8C illustrate another embodiment of the invention involving a white polymer substrate. In this embodiment, an optical security feature 54, shown in FIG. 8A, is a dithered binary image of a portrait and the printed image 56, shown in FIG. 8B, is a repeating pattern of straight and curved lines. In the final security document, the printed image 56 overlies part of the optical security feature 54 as shown in FIG. 8C.

(29) In this embodiment, the optical security feature 54 differs from the printed image 56 such that the printed image does not wholly overlie the optical security feature. However, the printed image 56 effectively camouflages the optical security feature 54 when viewed in direct reflection of light, as the optical security feature 54 appears faint and difficult to discern. The optical security feature 54, however, is visible in transmitted light, as the markings of the optical security feature 54 absorb enough transmitted light to produce an image with adequate contrast when viewed in transmission. The end result could be considered as a type of shadow image.

(30) It will be appreciated that the method and apparatus described above for manufacturing an optical security feature in a transparent substrate using a laser and laser marking additives or pigments may also be used to manufacture a security feature in an opaque substrate. The difference in the process between the two substrates being that in the transparent substrate the laser markings appear white, whereas in the opaque substrate the laser markings appear dark.

(31) While the invention has been described in conjunction with a limited number of embodiments, it will be appreciated by those skilled in the art that many alternative, modifications and variations in light of the foregoing description are possible. Accordingly, the present invention is intended to embrace all such alternative, modifications and variations as may fall within the spirit and scope of the invention as disclosed.

(32) Any reference herein to a patent document or other matter which is given as prior art is not to be taken as an admission that that document or matter was known or that the information it contains was part of the common general knowledge as at the priority date of any of the claims.

(33) The present application may be used as a basis or priority in respect of one or more future applications and the claims of any such future application may be directed to any one feature or combination of features that are described in the present application. Any such future application may include one or more of the following claims, which are given by way of example and are non-limiting in regard to what may be claimed in any future application.