The present invention relates to methods of forming security devices and to security devices formed thereby. In particular, although not exclusively, the invention relates to security devices which may be provided on security documents or tokens such as banknotes, cheques, travellers cheques, credit cards, identification cards, passports, stock and share certificates, tickets and the like, and is particularly concerned with providing a security device for security documents which is readily discernible only at certain viewing angles and which is difficult to copy or counterfeit.
The use of transitory embossed images as security devices in security documents has been previously proposed. For example, U.S. Pat. No. 5,199,744 discloses a security device formed by embossing a substrate with a transitory image in association with an embossed non-transitory linear area which is visible from substantially all viewing angles. The transitory image may be a transient image which is one that can be seen when viewing the substrate normally but not when the substrate is viewed off normal, or a latent image which is one that cannot be seen when viewing the substrate normally but which can be seen when the substrate is viewed from certain off normal angles. In U.S. Pat. No. 5,199,744, the surface to be embossed may be specularly reflecting, such as provided by a metallic ink. Also, the security device of U.S. Pat. No. 5,199,744 requires the embossed non-transitory linear area to circumscribe or define an identifiable portion of the design element.
Although U.S. Pat. No. 5,199,744 provides a transitory embossed security device which has some unusual visual effects, it is an object of this invention to achieve more striking visual effects.
In a more preferred form of the invention, the sheet may include a transparent substrate with one or more opacifying layers applied to at least the first side except in the region of said portion of the transparent substrate, to form a window on the first side of the sheet. An appropriate substrate is a laminated film of biaxially oriented polymeric material, such as disclosed in Australian patent no 558476 (or U.S. Pat. No. 4,536,016). Instead of applying the opacifying layers to the substrate, means may be provided to selectively opacify regions within the substrate. A polymer substrate is preferred because of the smoother surface in comparison to paper.
Alternatively, transparent polymeric card materials such as polycarbonate or polyvinylchloride (PVC) may be used as the substrate. The reflective layer may be applied to one side or embedded into the transparent polymeric substrate.
The second, reverse, side of the sheet may also be at least partly opacified, particularly in the case where a transparent substrate is used. The second side may be opacified except in the region of said portion of the transparent substrate to form a window on the second side of the sheet in register with the window formed on the first side of the sheet. Alternatively, the opacification on the second side may form a complete covering to cover the reflective layer so that the window on the first side forms “a half window”. The opacification may take place before or after the step of blind embossing. Opacification on the second side results in the reflective layer being embedded between the at least one opacifying layer and the transparent layer, protecting the reflective layer against chemical and physical attack.
The embossed transitory image may be provided wholly within the window or “half window”. Alternatively, the embossed transitory image may extend over at least part of the window and over part of an opaque region adjacent to or surrounding the window.
In an alternative form of the invention, the substantially transparent or translucent layer may be formed by means of a coating applied to a substrate. The substrate may constitute the reflective layer, for example a layer of foil. Alternatively, the coating may be applied to a separate substrate layer, in which case the coating is applied over the reflective layer to sandwich the reflective layer between the coating and the substrate.
A suitable coating may comprise UV curable gloss overcoat varnish which could be printed using offset or gravure printing. Preferably such coatings should have a relatively high reflectance of at least 70 gloss units and have a suitable adhesion to the reflective layer. Opacifying inks may be applied over the coating to create a window on the first side of the sheet.
A substrate per se is not necessarily essential to the present invention. A bonded transparent layer and reflective layer may together be of sufficient strength to undergo the embossing process. For example, the sheet may simply comprise a transparent layer in the form of a film of transparent material bonded to a layer of foil. Alternatively, the metal reflective layer may be sputtered onto the transparent layer.
Irrespective of the medium used to create the substantially transparent or translucent layer, preferably it is has a glossy surface, the reflection from which enhances the effect created by the embossing in the reflective surface of the reflective layer. The transparent layer preferably has a gloss value of at least 75, and more preferably falling substantially within the range from about 80 to about 90. These values are measured using a Gardener micro-tri-gloss meter at an angle of 45°.
An additional benefit of the substantially transparent or translucent layer is that it provides a protective coating over the reflective layer against chemical or physical attack.
The reflective layer is preferably also highly reflective. The reflective layer preferably has a gloss value of at least 60 units, as measured with a Gardener micro-tri-gloss meter at an angle of 45° As mentioned above, the reflective layer may be comprised of a reflective material such as metal foil applied to a substrate.
Alternatively, the reflective layer may be formed by printing with reflective ink. A preferred printing method is the gravure printing process which can achieve a layer of ink of two-three microns in thickness (dry weight). Where the security device is formed on a larger document such as bank note, the printing of the reflective layer by the gravure process may be conducted when other parts of the security document are being printed. The reflective layer can also be printed with the silk screen process.
The reflective layer may comprise metallic material applied to a substrate such as by sputtering or a vapour deposition process. Alternatively, the substrate itself could be made of a suitable material such as a foil.
The extent of the reflective layer is preferably sufficient to contain the whole of the embossed image. Where the security device is incorporated into a security document or article, the reflective layer may constitute a patch or a specific region on the document or article. The reflective layer is preferably continuous within the patch or region.
The reflective ink may comprise a metallic ink which is highly reflective, such as a silver or gold metallic ink, or a nacreous or pearlescent pigment such as iriodin. Iriodin is a Registered Trade Mark of Merck KGaA.
The reflective ink may be of the type comprising an optically variable pigment. The term optically variable pigment as used herein refers to a coating composition, such as an ink, which provides a colour shift between two distinct colours with the colour shift being dependent upon the viewing angle. An example of such an optically variable ink (OVI) is described in EP 0,984,043 of SICPA Holding SA, and OVI is a Registered Trade Mark of SICPA Holding SA.
One example of an optically variable pigment is a green/blue OVI which appears green when viewed in reflection at viewing angles around the normal to the substrate, and which appears blue when viewed at acute angles to the plane of the substrate. Another example of an optically variable coating is one which changes colour from gold when viewed at normal incidence, to green when viewed obliquely.
Combinations of various reflective inks may be used to make up the reflective layer. For example, a secondary image may be created within the reflective layer using two different types of reflective inks.
The blind embossing may be conducted by a stamping operation. Preferably, the blind embossing may be conducted by the process of intaglio printing, except without ink. This enables a deeper emboss to be achieved than can be achieved with ink. Where the security device is incorporated into a larger document or article such as a bank note, the blind embossing operation may use the same intaglio printing plate to emboss the security device as is used to print other portions of the document or article, except that the blind embossing is carried out by un-inked portions of the plate. The printing and embossing could occur in line on a continuous web based process as used in the bank note production and labels industry.
The embossed image may comprise a set of lines or dots.
It has also been discovered that unusual visual effects can be obtained when the transitory embossed image includes a first set of embossed lines or dots extending in one direction, and a second set of embossed lines or dots extending in a different direction. The first set of embossed lines or dots may form a first part or a background of the transitory embossed image and the second set of embossed lines or dots may form a second part of the transitory embossed image, eg indicia, such as numbers and/or lettering, or a picture. In one preferred embodiment, the second set of embossed lines or dots extends substantially perpendicularly to the first set of embossed lines or dots.
Alternatively, the pattern of the embossing may include indicia such as letters or numbers. Alternatively, the embossing pattern may comprise a device such as a logo or a crest. In such a pattern, the embossed image may be formed against a plain non-embossed background.
In accordance with a further aspect of the invention, there is provided a method of forming a security device including: providing a sheet including a reflective layer; and blind embossing the sheet in the region of the reflective layer to form a transitory embossed image; wherein the transitory embossed image comprises a first embossing having a predetermined feature and a second embossing of smaller dimensions formed on said predetermined feature of said first embossing, said first embossing being formed to hide and reveal said second embossing at predetermined viewing angles.
Preferably, the sheet includes a substrate and is embossed through the substrate layer and onto the reflective layer. The substrate preferably includes a transparent or translucent layer, and the arrangement of the layers may be such that the reflective layer is visible through the transparent or translucent layer. However, the arrangement may be such that the transparent or translucent layer is disposed behind the reflective layer, relative to the viewing direction.
The first embossing may comprise a set of spaced first features having sides and the second embossing is formed on the sides of the first features. For example, the first embossing may comprise a set of spaced lines or grooves. These lines or grooves may be parallel.
The second embossing preferably comprises a first set of image embossings disposed on corresponding first sides of the first features and a second set of image embossings disposed on corresponding second sides of the first features to form a first image corresponding to the first set of image embossings at a viewing angle facing the first sides and to form a second image corresponding to the second set of image embossings at a viewing angle facing the second sides.
The first image may be different to the second image.
Alternatively, the first embossing may comprise a set of spaced first features having sides with lower portions of the first embossing being disposed between the spaced first features, the second embossing being formed between the first features on the lower portions. In other words, the second embossing may be formed in the troughs of a set of raised lines.
Any of the features described in connection with any of the foregoing aspects of the invention may be incorporated into the aspect above.
In accordance with still a further aspect of the invention, there is provided, a security device comprising: a sheet including a reflective layer in the region of the reflective layer, and a blind embossed transitory image formed in the sheet, wherein the transitory embossed image comprises a first embossing having a predetermined feature and a second embossing of smaller dimensions formed on said predetermined feature of said first embossing, said first embossing being formed to hide and reveal said second embossing at predetermined viewing angles.
Any of the features described in connection with any of the foregoing aspects of the invention may be incorporated into the aspect above.
In accordance with a still further aspect of the invention, there is provided a method of forming a security device including: providing a substantially transparent or translucent layer; blind embossing the substantially transparent or translucent layer through the transparent or translucent layer to produce an embossment in the layer; applying a reflective layer to the substantially transparent or translucent layer at least in part register with the embossment, wherein the transitory embossed image comprises a first embossing having a predetermined feature and a second embossing of smaller dimensions formed on said predetermined feature of said first embossing, said first embossing being formed to hide and reveal said second embossing at predetermined viewing angles.
Any of the features described in connection with any of the foregoing aspects of the invention may be incorporated into the aspect above.
According to another aspect of the invention there is provided a security document or device comprising a substrate, a layer of optically variable pigment applied to an area of the substrate, and an embossed transitory image formed by an embossing in the area of optically variable pigment, wherein the embossed transitory image includes a first set of lines or dots extending in one direction and a second set of lines or dots extending in a different direction.
The term optically variable pigment as used herein refers to a coating composition, such as an ink, which provides a colour shift between two distinct colours with the colour shift being dependent upon the viewing angle. An example of such an optically variable ink (OVI) is described in EP 0,984,043 of SICPA Holding SA, and OVI is a Registered Trade Mark of SICPA Holding SA.
One example of an optically variable pigment is a green/blue OVI which appears green when viewed in reflection at viewing angles around the normal to the substrate, and which appears blue when viewed at acute angles to the plane of the substrate. Another example of an optically variable coating is one which changes colour from gold when viewed at normal incidence, to green when viewed obliquely.
While the optically variable pigment and the embossed transitory image may be provided on an opaque substrate, the optically variable pigment and the embossed transitory image are preferably applied at least partly in a transparent or translucent window of the substrate. The substrate may be formed from a transparent plastics material to which at least one opacifying coating has been applied, except in the region of the transparent window. Alternatively, a transparent plastics substrate could be inserted as a window in a security document formed from paper or other material.
According to another aspect of the invention there is provided a method of forming an optically variable transitory embossed image for a security document or device comprising the steps of applying an optically variable pigment over an area of a substrate, and embossing said area of the substrate to form an embossed transitory image, wherein the embossed transitory image includes a first set of lines or dots extending in one direction and a second set of lines or dots extending in a different direction.
In a particularly preferred embodiment, the optically variable pigment and the embossed transitory image are applied over at least part of a transparent window and over part of an opaque region surrounding the transparent window.
In another preferred embodiment, the optically variable pigment is applied to one side of the substrate and the embossing step is performed by embossing the opposite side of the substrate.
Surprisingly, it has been found that for a transitory image formed from a set of embossed lines or dots on an unembossed area of optically variable pigment, the part of the image formed by the embossed lines appears substantially the same colour as the unembossed area of the optically variable pigment when viewed in reflection at typical oblique viewing angles (say 30° from normal) to form a latent image but as the viewing angle changes to more oblique viewing angles, although the colour of the optically variable pigment changes (eg from green to blue), the part of the transitory image formed by embossed lines extending perpendicularly to the viewing direction does not change colour (eg stays green) and so differs from the changed colour of optically variable pigment at oblique viewing angles to reveal the latent image at that angle. The transitory embossed image is preferably substantially hidden when viewed in light transmitted through the substrate.
It has also been discovered that unusual visual effects are obtained when the transitory embossed image includes a first set of embossed lines or dots extending in one direction, and a second set of embossed lines or dots extending in a different direction as per the claimed invention. The first set of embossed lines or dots may form a first part or a background of the transitory embossed image and the second set of embossed lines or dots may form a second part of the transitory embossed image, eg indicia, such as numbers and/or lettering, or a picture. In one preferred embodiment, the second set of embossed lines or dots extends substantially perpendicularly to the first set of embossed lines or dots.
Further, different unusual colour effects provided by the transitory embossed image can be observed when the image is viewed in reflection through rotations in different planes perpendicular to the substrate and also through a rotation in a plane substantially parallel to the substrate, with different parts of the image appearing either the same colour or a different colour as the optically variable pigment at different viewing angles, so that different parts of the transitory embossed image appear to switch on and off in different colours at different viewing angles.
In accordance with yet another aspect of the present invention, there is provided a security document or device comprising a substrate, a layer of optically variable or reflective coating applied to an area of the substrate, and an embossed transitory image formed by embossing in the area of the optically variable or reflective coating, wherein the security document is formed with a transparent window and the embossed transitory image is at least partly disposed in the transparent window.
Any of the features described above in connection with the previous aspects of the invention may be incorporated into the above aspect of the invention.
The present invention will now be described in more detail, by way of example only, with reference to the accompanying drawings in which:
FIGS. 1 to 5 show a rectangular security document 1, such as banknote, having a transparent window 2 in which is provided a security device 3 in the form of a transitory embossed image. The remaining region 4 of the security document is substantially opaque. The opaque region 4 is printed with indicia.
As shown in
The opacifying layers 14 preferably comprise a coating of a substantially opaque ink applied to opposite surfaces of the substrate 10, although it will be appreciated that other opacifying layers may be used. For example, a transparent plastics substrate may be sandwiched between layers of substantially opaque paper or plastics material.
Referring more particularly to
The reflective layer 11 may be comprised of metallic ink 11. Two suitable systems (silver and gold) are described below.
The formulations and gravure engraving specifications are as follows:
Gold coloured reflective patch,
The cylinder configuration used for these pigments is:
Alternatively, an optically variable pigment may be used in the present invention instead of metallic ink. The optically variable pigment may comprise a nacreous or pearlescent pigment, such as iriodin. Another preferred type provides a colour shift between two distinct colours with the colour shift being dependent upon viewing angle. Such optically variable inks may be made by producing an optically variable thin film structure using layers of metallic or high refractive materials (eg certain metal oxides or metal sulphides) and dielectric materials, grinding the film into micro flakes and adding the flakes to an appropriate ink medium. Another method for the production of an optically variable pigment which incorporates a totally reflecting layer made by physical vapour deposition from aluminium alloy is disclosed in EP0984043 of SICPA Holding SA.
As shown in
When the document is viewed at angles outside the range of angles or “window” of high reflection, e.g. at an oblique angle β as shown in
The transitory effects exhibited by the embossed image forming the security device 3 of
At certain angles between the viewing angles within the window of high reflection of
When the oblique viewing angle changes from the oblique angle of
The changing patterns of bright and dull as the security document is moved through different angles create a visual effect which cannot be reproduced by normal photocopying machines. Thus, the visual effect serves as a useful security feature easily distinguishable/recognisable by the general public. Other enhanced visual effects can be achieved through the use of optically variable pigment as will be described with reference to FIGS. 13 to 19, and also through the use of macro and micro embossings as will be described with reference to FIGS. 20 to 27.
In a preferred method of manufacturing a security document or a security device such as described with reference to FIGS. 1 to 7, the layer of reflective ink or optically variable pigment 11 is applied to one side of the substrate 10 in the area where the security device 3 is to be located in a printing operation, e.g. by silk screen printing, offset or gravure printing. Then, the opacifying layers 14 are applied to opposite surfaces of the transparent substrate 10 eg by printing over region 4 of the substrate. This step could also be done after the step of creating the embossment. The area of the substrate 10 containing the layer of reflective ink or optically variable pigment 11 is embossed, engraved or otherwise deformed to form the transitory embossed image.
As shown in
In the embodiment described in connection with FIGS. 1 to 5, the transitory image may be formed by embossed lines formed in the substrate, the lines having a predetermined height H and a predetermined spacing S. The height H may vary from a minimum of about 5 microns to a maximum corresponding to the maximum embossable height of the substrate. The spacing S depends on the height and the ratio S:H is typically from about 6:1 to 2:1. The embossed lines are therefore macro embossings, in contrast to lines of a diffraction grating or hologram which typically have a height and spacing of at least an order of magnitude smaller.
Either one or preferably both of the silver image 42 and the gold background may be embossed with lines or dots in the same manner described with reference to FIGS. 1 to 11 to form a transitory embossed image. For example, the silver image 42 may be embossed with lines extending parallel to the longitudinal axis of the elliptical security device 40 and the gold background 44 may be embossed with lines extending transversely to the longitudinal axis of the security device 40. It will be appreciated that the different parts of the security device, i.e. the silver moon 42 and the gold background 44 appear brighter or duller as the security device 40 is viewed in reflection at different angles either within the range of angles or “window” of high reflection, or at oblique angles outside the window of high reflection. Also, different parts of the image appear brighter or duller and appear to switch on and off as the security device 40 is viewed from different viewing angles parallel or perpendicular to the longitudinal or transverse lines of the embossed transitory image.
It will be apparent from the description above that the present invention provides a security device which has some unusual visual effects. A security document incorporating such a security device is also difficult for counterfeiters to reproduce. It would not be possible to reproduce the effects of the transitory embossed image by colour photocopying, and a counterfeiter would require access not only to an appropriate transparent polymeric substrate, but also the specific reflective ink used by the document printing authority and appropriate embossing apparatus in order to produce a counterfeit document.
It will also be appreciated that various modifications and alterations may be made to the embodiments described above without departing from the scope and spirit of the present invention. For example, the transitory embossed image may be formed by at least one set of embossed dots, which extend in lines substantially parallel to other lines of dots in the set. Also, the area of reflective ink may extend outside the area which is embossed with the lines or dots. Further, the area of reflective ink and the embossed transitory image may extend over part of the transparent windows 2 and over part of the opaque region 4 surrounding or adjacent to the window 2. Preferably, the embossed image is formed by at least two sets of embossed lines or dots extending at different angles to one another. It will also be appreciated that more than two sets of embossed lines or dots may be provided to form a more complex transitory embossed image with different parts of the image appearing at different oblique angles.
FIGS. 13 to 17 show a rectangular security document 1a, such as banknote, which is provided with a transparent window 2a and a security device 3a in the form of an optically variable transitory embossed image. The remaining region 4a of the document 1a outside the transparent window 3a is substantially opaque. The opaque region 4a is printed with indicia. The optically variable transitory embossed image forming the security device 3a preferably overlaps part of the transparent window 2a and part of the surrounding opaque region 4a.
As shown in
The opacifying layer 14a preferably comprises a coating of a substantially opaque ink applied to opposite surfaces of the substrate 10a, although it will be appreciated that other opacifying layers may be used. For example, a transparent plastics substrate may be sandwiched between layers of substantially opaque paper or plastics material.
Referring more particularly to
The optically variable pigment used is preferably a coating composition in the form of an optically variable ink, which provides a colour shift between two distinct colours with the colour shift being dependent upon viewing angle. Such optically variable inks may be made by producing an optically variable thin film structure using layers of metallic or high refractive materials (eg certain metal oxides or metal sulphides) and dielectric materials, grinding the film into micro flakes and adding the flakes to an appropriate ink medium. Another method for the production of an optically variable pigment which incorporates a totally reflecting layer made by physical vapour deposition from aluminium alloy is disclosed in EP0984043 of SICPA Holding SA. These type of optically variable pigments and inks are distinguished from metallic inks and coatings which have a reflecting metallic appearance and from optically variable inks of the pearl lustre type which present a conspicuous pearl lustre effect in reflection, while in transmission the substrate takes an unmistakable complementary hue. In such optically variable inks of the pearl lustre type, the colour shift with the angle of observation is small.
The unusual colour effects exhibited by the embossed transitory image forming the security device 3a of
When the oblique viewing angle changes from the oblique angle of
Also, as the viewing angle increases towards the perpendicular through a rotation in a plane substantially perpendicular to the substrate and to the direction of the transverse lines of the first set of embossed lines 15a, the latent image becomes substantially hidden again because the parts of the image formed by the first and second sets of embossed lines 15a and 16a appear the same colour λ1.
As shown in FIGS. 13 to 18, the optically variable transitory embossed image 13a forming the security device 3a overlaps the transparent window 2a and the opaque region 4a of the security document 1a. This also creates an unusual optical effect in that the colour changing effects of the portion of the transitory embossed image provided in the area of the transparent window 2a are visible in reflected light from both sides of the security document, whereas the colour changing effects of the portion of the transitory embossed image provided on the opaque region 4a are only visible in reflected light from one side of the security document 1a, that is the side on which the layer of optically variable pigment 11a has been applied.
A further unusual visual effect is observed when the portion of the transitory embossed image 13a in the area of the transparent window 2a is observed in transmitted light. When an optically variable ink (OVI) of the kind produced by SICPA Holding SA is applied to a transparent substrate, the striking colour changing effects seen in reflected light are not observable in transmitted light instead the OVI can appear as a dull grey colour in transmitted light irrespective of the viewing angle, and the portion of the transitory embossed image provided on the OVI in the area of the transparent window is substantially invisible when observed in transmitted light, once again forming a latent image which is only observable at certain angles in reflected light.
While FIGS. 13 to 18 show the transitory embossed image 3a overlapping the transparent window 2a and the opaque region 4a, it will, however, be appreciated that the transitory embossed image in accordance with the invention could be provided solely within a transparent window 2a of the security document 1a, solely on the opaque region 4a, or even on a completely opaque substrate or security document. The transitory embossed image could also be provided in a “half window”, such as illustrated in
The security device 3a of
In a preferred method of manufacturing a security document or a security device such as described with reference to FIGS. 13 to 19, the opacifying layers 14a are applied to opposite surfaces of the transparent substrate 10a, eg by printing, over region 4a of the substrate 10a to form the transparent window 2a, the layer of optically variable pigment 11a is then applied to one side of the substrate 10a in the area where the security device 3a is to be located in a printing operation eg by silk screen printing, offset or gravure printing, and finally the area of the substrate 10a containing the layer of optically variable pigment 11a is embossed, engraved or otherwise deformed to form the sets of embossed lines 15a and 16a to form the optically variable transitory embossed image. The embossing step may be performed by applying pressure to at least one side of the substrate in a stamping operation or in an intaglio printing operation in which raised printed lines are applied to at least one side of the substrate 10a in the opaque region 4a. Preferably, the embossing step is performed on the opposite side of the substrate 10a to the side on which the layer of optically variable ink 11a is applied to reduce the likelihood of the ink layer 11a cracking.
In a simple embodiment the transitory image may be formed by embossed lines formed in the substrate, the lines having a predetermined height H and a predetermined spacing S. The H may vary from a minimum of about 5 microns to a maximum corresponding to the maximum embossable height of the substrate. The spacing S depends on the height and the ratio S:H is typically from about 6:1 to 2:1.
It will be apparent from the description above that the embodiments described above using an optically variable ink provide a security device which has some unusual visual effects. A security document incorporating such a security device is also difficult for counterfeiters to reproduce. It would not be possible to produce the effects of the optically variable transitory embossed image by colour photocopying, and a counterfeiter would require access not only to an appropriate transparent polymeric substrate, but also the specific optically variable ink used by the document printing authority and appropriate embossing apparatus in order to produce a counterfeit document.
It will also be appreciated that various modifications and alterations may be made to the embodiments described above without departing from the scope and spirit of the present invention. For example, the transitory embossed image may be formed by at least one set of embossed dots, which extend in lines substantially parallel to other lines of dots in the set. Also, the area of optically variable pigment may extend outside the area which is embossed with the lines or dots. In this case, a single set of embossed lines or dots may be provided, with the image formed by the set of embossed lines or dots appearing a different colour to the surrounding area of optically variable ink when viewed in reflection at an oblique angle in a plane perpendicular to the direction of the embossed lines or dots; the image appearing the same colour as the background of optically variable ink when viewed in reflection at an oblique angle in a plane parallel to the direction of the embossed lines or dots. Preferably, however, the embossed image is formed by at least two sets of embossed lines or dots extending at different angles to one another. It will also be appreciated that more than two sets of embossed lines or dots may be provided to form a more complex transitory embossed image with different parts of the image appearing at different oblique angles. It is also envisaged that the unusual visual effects of the present invention could be obtained by directly printing a transitory embossed image using an optically variable ink during the intaglio process.
FIGS. 20 to 23 indicate three further modified forms of a security device 41, 42, 43 respectively which may be incorporated into a security document or security article. In each embodiment, the security document or article is comprised of a transparent substrate in the form of a transparent polymer film 44. In the first form of the security device 41 shown in
In the second form of the security device 42, the reflective metallic ink 47 is instead applied to the first side of the substrate 44. The embossment 48 is applied from a side of the substrate 44 bearing the reflective metallic ink. A coating may be applied over the reflective metallic ink 47 below embossment 48.
In the third alternative form of the device 43 shown in
In each of the devices 41, 42, 43 described briefly above, the embossment is in the form of macro embossments 52, 53 whereby micro embossments 54A, 54B are formed on portions of the macro embossments 52, 53.
Referring to
In the embodiments of FIGS. 20 to 22, the micro embossments are formed so as to bear two different images at different viewing angles. As can be seen from
Additionally, as illustrated in
In the embodiment of
FIGS. 20 to 25 exhibit a particular effect, with varying degrees of effectiveness. The reflections from the reflective metallic ink layer 47 and the transparent substrate 44 create reflections such that the first micro image, then the second micro image can be seen from viewing directions facing the first walls 55, by switching through different viewing angles relative to the plane of the sheet. Similarly, the second micro image, then the first micro image can also be viewed from viewing angles facing the second corresponding walls 56, by switching through different viewing angles relative to the plane of the sheet. The security device 41 provided in a “half window” or shown in
The macro and micro embossing may be created by the process of hot stamping or embossing through an inkless intaglio process, otherwise known as blind embossing. The stamping plate or intaglio plate may be derived from a metal plate created in the following fashion shown in
In the above process, both the micro-mask 120 and the micro-mask 130 consist of elongated images. The extent of the elongation is predetermined by the preferred viewing angle. The preferred viewing angle has been set at about 300 to the document.
Elongation Ratio: x/y=1/sin (gamma)
x=elongated length of image on substrate
y=image viewing height
With an optimum viewing angle of 30°, the extent of elongation is 2:1. For example, if an image has a viewing height of 15 mm. then the image created by the micro-mask will be 30 mm long on the substrate. The image is only to be elongated in the vertical viewing direction.
Following the above processes, the intaglio plate for achieving the macro and micro-embossing may be made by the following steps:
The embossing process is a continuous process whereby the substrate to be embossed is passed through two rolling cylinders under high pressure. The embossed intaglio plate covers one of the two cylinders, the other cylinder is the impression cylinder. During the process, the substrate is forced into etchings of the plate by the impression cylinder. The substrate plastically deforms into the shape of the etchings. When the substrate exists the rolling cylinders, the macro-emboss reflexes partially back into shape, due to the nature of the material. The embossing on the substrate remains intact. However, the height of the embossing does not equal the height of the etching on the plate, a typical ratio is about 1:5. For this reasons the maximum foreseeable final emboss on the relaxed substrate is about 35-40 μm.
The intaglio process has some restriction as to the temperature range within which the process may be used. The process of hot stamping may be used at higher temperatures.
It will be appreciated from the foregoing that the intaglio printing plate created is a negative printing plate having recessed engravings to create the embossments. For a hot stamping process, it is proposed to use stamping tools having raised engravings. Instead of a series of grooves to form the macro embossments as in the intaglio plate, the hot stamping plate may comprise a series of raised lines. The micro embossments can therefore be formed on the sides of the raised lines. It is also possible for the micro-embossings on the macro-embossings to be formed in a laser engraving process.
The above process may be used to form micro-embossings 241,243 on a macro-embossed structure 210 in a metallic layer of a security device or security document. More preferably the process is used to form a metal intaglio printing plate for achieving macro- and micro-embossings in an intaglio printing process in a similar manner to that described above.
It will be apparent that the embodiments described above which have micro-embossings formed or macro-embossings on a reflective background provide a security device which has unusual visual effects. A security document incorporating such a security device is also difficult for counterfeiters to reproduce. It would not be possible to produce the effects of the transitory embossed micro images by colour photocopying, and a counterfeiter would require access not only to an appropriate transparent polymeric substrate, but also the specific reflective ink used by the document printing authority and appropriate micro-embossing apparatus in order to produce a counterfeit document.
It will also be appreciated that various modifications and alterations may be made to the embodiments described above without departing from the scope and spirit of the present invention. For example, the macro-embossings of the transitory embossed image may be formed by at least one set of embossed dots, which extend in lines substantially parallel to other lines of dots in the set. Also, the area of reflective ink may extend outside the area which is embossed with the lines or dots. Further the transitory embossed image may extend outside the window or half window into the opaque area surrounding the half window. Also, the transitory embossed image with micro embossings on macro-embossings may be provided on a background of optically variable ink instead of metallic ink.
Number | Date | Country | Kind |
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2002951870 | Oct 2002 | AU | national |
2003903687 | Jul 2003 | AU | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/AU03/01316 | 10/7/2003 | WO | 10/5/2005 |