NZ780551A - Laser marked optically variable device - Google Patents

Abstract

security device for security documents provides an angle-dependent Moiré effect. A security device for a security document and method for making the security device are provided. At least two interlaced laser engraved images form an angle dependent parallax effect. First and second images are laser engraved at a substrate of the security document. To render the security device more difficult to copy, a colour changing effect or a nonreciprocal transmission effect may be achieved by adding a coloured (absorptive or emissive) layer between or within non-laser engravable layers situated between the laser engravable layers, and/or by adding a patterned phase diffraction grating situated between the laser engravable layers. ser engraved at a substrate of the security document. To render the security device more difficult to copy, a colour changing effect or a nonreciprocal transmission effect may be achieved by adding a coloured (absorptive or emissive) layer between or within non-laser engravable layers situated between the laser engravable layers, and/or by adding a patterned phase diffraction grating situated between the laser engravable layers.

Description

Laser Marked Optically Variable Device This application claims ty from Canadian patent application 381, filed 24 September 2020, the entire content of which is incorporated by reference.

Field The invention relates generally to security documents such as identification documents and particularly to a security device for ty documents, the security device comprising interlaced images producing an angle-dependent Moiré effect with an additional colour functional layer.

Background Counterfeits in security documents are quite prevalent due to the demand of fake ID for various purposes including underage drinking, access to als with age restriction, and illegal activities such as financial frauds and unauthorized travels.

The recent advancement in digital printing technologies poses a challenge. The resolution of off-the-shelf inkjet and dye sub printers, availability of papers and polymers that accept uality print, and access to all the materials and knowledge through smart phones make counterfeiters’ work more efficient. This advancement in printing technologies and communication produces a challenging ion for security printers.

To fight counterfeiters, it is useful to include security es that can be identified without the use of an aid, such as a hologram, kinegram, optically variable ink, etc.

Unfortunately, low grade holograms and optically variable ink can be purchased online, to which counterfeiters have easy access. To fight the modern counterfeiters, it is important to produce security features that can only be produced h the manufacturing process that is used for card production. This may not be a roof method, but it will serve as a challenge for rfeiters.

EP0353974A2 discloses the use of a parallax effect (angle dependent Moiré phenomenon) to obtain an optical system on a transparent/translucent film. The metallic image lines and screen (grid) interleaved lines are applied by chemical deposition, vacuum deposition, by printing with metallic ink or by chemical or laser demetallization.

The feature will be costly due to ization and the need for registration between two images. Personalization is difficult to achieve with this technique as the metallization is done in sheet/web form.

US6494491B1 discloses a similar optical effect obtained using the printing of at least two image patterns at a ted distance from each other by means of a transparent layer of material. The feature changes from light to dark due to Moiré effect raised by the overlapping patterns. The overlapping patterns are printed simultaneously or on two ent layers and ted er. This que would not allow for personalization of the feature.

In US4766026A, the parallax effect is obtained by laser ing an image through a transparent layer. The polymer layers, which blacken at different intensity values, are used to achieve this feature. A disadvantage of this is that the synthetic material used will have different grey value due to varying laser sensitivity. A higher laser sensitivity means the darker the film. This will produce a card with different grey on either side.

The cost of material with varying laser sensitivities is high and would add more cost to the security device.

In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for sing the features of the invention. Unless specifically stated otherwise, reference to such external documents or such sources of information is not to be construed as an admission that such documents or such sources of ation, in any jurisdiction, are prior art or form part of the common general knowledge in the art.

Disclosed herein is a security device for a security document comprising at least two interlaced laser ed images forming an angle dependent parallax effect wherein each image is laser engraved at a substrate of the security document, the substrate comprising at least one non-laser-engravable layer within or between laser engravable layers.

The present invention makes use of an angle-dependent Moiré phenomenon to provide a security device for fication documents. Moiré patterns are made up of twodimensional images that result from the interference of two overlapping patterns. In the present invention, the overlapping patterns are laser engraved on identification documents, which would allow for personalization. By displacing two immediately adjacent patterns by tilt, the Moiré interference pattern also changes, leading to the known, changing dark image effect.

Disclosed herein is an improvement to a laser engraved dependent Moiré effect achieved by adding absorptive and/or emissive lines to at least one ser engravable layer between the two eaved laser engraved layers. Two variations are disclosed: 1. Adding absorptive colour lines in registration with the laser engraved images on the face and back side of the card. 2. Adding emissive lines such as luminescent or fluorescent lines in registration with the laser engraved images on the face and back side of the card.

Also disclosed herein is an improvement to a laser ed angle-dependent Moiré effect, namely a nonreciprocal transmission window, achieved by adding a patterned phase diffraction grating between the two laser engraved layers.

The term ‘comprising’ as used in this specification and claims means ‘consisting at least in part of’. When interpreting statements in this specification and claims which e the term ‘comprising’, other features besides the es prefaced by this term in each statement can also be present. Related terms such as ‘comprise’ and ‘comprised’ are to be interpreted in a similar manner.

Brief Description of the Drawings Figure 1 illustrates a security document card construction for ing laser engraved Moiré .

Figure 2 illustrates two images used to obtain laser engraved Moiré effect in a transparent region of a security document.

Figure 3 illustrates a security nt card construction and the laser ing specification of the Moiré effect in a transparent region of the card.

Figure 4 illustrates a security document card construction for obtaining a laser engraved Moiré effect with a colour changing .

Figure 5 rates a security document card construction, the laser engraved Moiré effect in a transparent region of the card, with absorptive and/or emissive lines for the creation of a colour changing effect.

Figure 6 illustrates a side view of a nonreciprocal transmission window in a security document card.

Figure 7 illustrates a top view of a nonreciprocal transmission window in a security document card.

Figure 8 illustrates a UV imprint lithography process for replicating small micro scale patterns.

Figure 9 illustrates a possible method for manufacturing a diffractive l element.

Figure 10 illustrates an exemplary embodiment of a non-reciprocal transmission window in a polycarbonate data page.

Detailed Description The optically variable devices disclosed herein make use of an angle ent Moiré phenomenon to obtain a security feature for security documents. Moiré patterns are made up of two-dimensional images that result from the interference of two overlapping patterns. By cing two ately adjacent patterns by tilt, the Moiré interference pattern also changes, g to a changing light-dark image effect. As disclosed herein, the overlapping patterns are laser engraved on the security documents, and a further functional layer is included between the laser engraved layers.

As disclosed herein, no layering of metals with high optical density is necessary in order to create the Moiré interference pattern. Since the laser engraving is the last process, personalization is possible.

Further as disclosed herein, laser receptive film (or laser engravable layers) with at least one non-laser receptive film (non-laser engravable layer) in the middle or in between is used to achieve the result. The at least one non-laser receptive film will ce the adjacent pattern to its ess and allows for the angle-dependent Moiré effect.

As used herein, the term "absorptive" refers to the property of pigments and dyes to selectively absorb certain wavelengths from the visible spectrum while reflecting others from the same spectrum. Absorptive colour in a security feature appears under normal illumination.

As used herein, the term "emissive" refers to the property of ts and dyes to respond by emitting a fluorescent or phosphorescent light in the visible spectrum when exposed to UV illumination. Thus, emissive colour in a security feature appears under UV illumination.

To make the security feature more difficult to copy, an additional element may be added to the at least one non-laser engravable film or layer situated between the laser able layers.

In an embodiment, an absorptive/passive colour layer (pigments/dyes) or emissive/active colour layer (luminescence effect) may be added between the two laser engraved layers to provide a colour ng effect instead of light-dark image effect.

In an embodiment, the additional element may consist in a patterned phase diffraction grating. The ction grating may be transparent under incoherent illumination in the visible spectrum. In this case the effect it is no longer solely a Moiré enon - the incoming lly coherent light is steered by diffraction on the phase grating regions and it may be designed to create a colour, non-reciprocal image when the window is viewed face-up versus bottom-up. This embodiment of the invention relies on the asymmetric positioning of the diffraction grating layer between the two laser marked Moiré screens, i.e. as close as possible to the top one and as far as possible from the bottom one. Such a uration , in the situation of the top illumination – bottom observation, the necessary optical path for the diffracted beam to deflect and outcouple through the gs of the bottom Moiré screen that are darkened at that particular angle of observation. The result is an angular variable colour image superposed over the black and white Moiré pattern. In the reverse illumination-observation configuration this diffraction image will ear, only the reciprocal Moiré pattern ing visible.

In Figure 1, the card construction for laser engraved Moiré effect is shown. In this embodiment, a 205µm non-laser engravable layer is used between the laser engravable layers to achieve the effect. In an ment, the laser engravable layers and nonlaser engravable layers may be polycarbonate (for example, laser engravable and nonlaser able forms of polycarbonate are available from ro). Other laser engravable (LE) and non-laser engravable (NLE) materials are possible as well, such as PET and PVC. The thickness of the NLE layer can be between 50 to 400µm, preferably between 150 to 300µm.

The angle dependent Moiré effect (parallax) may be partially or ly in a transparent region of the card. The transparent region of the card is produced by leaving a knockout on the white (opaque) layer. During lamination, the clear layer will fuse into the knockout region and form a transparent window region where the parallax feature will be laser engraved.

To achieve the parallax feature, the card construction is very important. The uction must have a laser able layer on each side of the card and at least one ser engravable layer in the middle. This at least one non-laser engravable layer would allow for a series of laser engraved lines at a distance. The separation allows for angle dependent Moiré effect.

To achieve the Moiré effect, two interlaced images (image a1 and a2 as shown in figure 2) must be laser engraved; one at the face side of the nt and other at the back side; at least partially over the transparent region. The image a1, shown in figure 2, is called the grid line. On a laser engraved window, these lines create a path for light to transmit though. The image line "image a2", which carries the data, allows or blocks the light travels though the "image a1" depends on the phase shift. The image a2 shows one data (JAN 70) embedded within. Additional data may be added. Image a1 is called a screen image with a series of parallel lines. Image a2 contains a series of parallel lines, which carries phase shifted lines with personal data.

Both images discussed in figure 2 are laser engraved on the card. As discussed, the "image a1" gets laser engraved on side one and "image 2" laser ed on side 2.

During laser engraving, the density of the laser beam will be high at the surface (first side) of the card leading to darker marking. As the laser beam travels down the card, the density will be dropped due to absorption, and the marking intensity will decrease.

This leads to r laser engraving further down in the card at the second side (shown in faded line in figure 3). A similar process happens during laser engraving of the second image (image a2) at the second side of the card. During engraving, the nonlaser engravable layer will not be affected. The darker image of "image a1" at the first side and darker image of "image a2" at the second side will be ted by the thickness of the at least one non-laser engravable layer as shown in figure 3. This separation allows for angle-dependent Moiré effect and leads to the light-dark image effect.

It is possible to create an angle dependent Moiré effect that overlaps transparent and opaque regions of the card. Having a middle colour/absorptive (passive) and/or emissive e) layer would enhance the feature and make it ult to counterfeit. To add a colour and/or emissive layer to the angle dependent Moiré effect, a printed layer must be ed between the two sets of laser engraved lines. The print has to be in series of lines and has to match the frequency of the laser engraved lines (i.e. the lines must be in tight registration with the laser engraved lines). Lithography, flexography, gravure, Intaglio, Silkscreen, , digital press, and toner printing can be used to e this.

Figure 4 shows a way of inserting an tive/emissive layer within a document. As shown in Figure 1, the construction of the card has a 205µm non-laser engravable layer in the middle (although anywhere from 50-400µm is le). To insert the absorptive/emissive layer, it is possible to use two thinner non-laser engravable layers, for example one 100µm thick and one 125µm thick, with the absorptive or emissive colour layer applied to one of the non-laser engravable layers and being situated between or within the non-laser engravable layer(s). As illustrated in Figure 4, the absorptive and/or emissive print lines are located at the bottom of the 125µm NLE layer.

Figure 5 illustrates a document with laser engraved Moiré effect in the transparentwindow region. The absorptive and/or emissive lines are placed between the non-laser engravable . Emissive lines can be also used which may either be arent or . The emissive lines will be viewed using ultraviolet light and/or infrared light.

As illustrated in Figures 6 and 7, to achieve non-reciprocal transmission, a patterned phase diffraction grating layer may be ed n the laser engravable layers. In this case the effect is no longer uniquely rooted on the Moiré effect, the incoming partially nt light is steered by diffraction on the phase grating regions and it may be designed to create a colour, non-reciprocal image when the window is viewed from one side, such as face-up versus bottom-up.

In this embodiment, the Moiré pattern obtained by laser marking the top and the bottom laser engravable layers, combined with the patterned phase diffraction g layer, s the appearance of a colour image when the illumination is made from a first side, such as the top side of the card, and the viewing is made from a second side, such as the bottom side at or close to the normal incidence. This effect is due to the diffraction that steers part of the incoming light toward the apertures of the bottom layer that are otherwise masked at normal incidence – in Moiré terms, there is a d image superposed on a black Moiré fringe. In inverse viewing condition the diffraction appears but does not have sufficient optical space to develop and outcouple through the top apertures, and accordingly the Moiré fringe remains dark.

The apertures can be holes on the opaque layer or voids left during laser engraving ked area) over the transparent window. The term "aperture" should be interpreted in the optical transparency sense and not strictly as a cut-out in the opaque layer.

The diffraction grating may be created by, for e, UV imprint lithography. It is a simple lithography process with low cost, high throughput and high resolution. It creates patterns by mechanical deformation of imprint resist or varnish and subsequent processes. The imprint resist is typically a monomer or polymer formulation that is cured by heat or UV light during the imprinting. Adhesion between the resist and the template is controlled to allow proper release.

Figure 8 illustrates the steps in the process.

The polycarbonate insert is a carrier for the UV cured image. The UV cured image may then be incorporated into polycarbonate security documents that contain a transparent window feature, for example to be combined with or placed between laser engraved layers, as bed herein.

Figure 9 illustrates a method for production of a polycarbonate layer comprising the diffractive l t in a transparent window, according to one embodiment.

Reels of polycarbonate can be mounted on commercially available equipment (i.e.

Melzer lamination line) equipped with a punch mechanism that allows the polycarbonate opaque core material to be d with a void area, then the transparent insert carrying the UV cured embossed diffractive optical element (DOE) is punched from a separate reel, and d into the void usly created in the core material.

A plug insert method used in manufacturing is expected to be very efficient.

Alternatively, a method may be used which also uses the same punch method r), but the inlay manufacturing machine (combo machine, parts from lly variable device (OVD) Kinegram, Melzer, and Durrer) incorporates a pick & place robot that affixes the "plug" carrying the DOE image onto a carrier sheet, in register with voids cut out (windows) in the opaque core sheet. The inlay is then collated with other sheets that make up the document construction, and laminated on a hot press laminator (Burkle), using heat and pressure over a period of time. A typical heat g for the plates is in the 185 -190° C range. The pressure may vary from 20 to 240 bar, time may vary from 50 to 90 minutes, including startup heating time and cooling back to room temperature.

In an embodiment illustrated in Figure 10, a cross-section of a non-reciprocal transmission window in a polycarbonate data page may comprise the following layers: Legend: 1 – opaque rbonate layer with perforated apertures, diameter of 50µm 2 – polycarbonate or compatible layer with phase diffraction layer 3 – clear polycarbonate layer, optical open space role 4 – re print on the bottom of the 3rd layer As discussed above, the non-reciprocal transmission window may be placed between laser engraved layers to create a colour, non-reciprocal image.

The us detailed description has been provided for the purposes of illustration and description. Thus, although there have been described particular embodiments of the present invention, it is not intended that such references be construed as limitations upon the scope of this invention except as set forth in the following claims.

We

Claims (20)

claim:

1. A security device for a ty document comprising at least two interlaced laser engraved images forming an angle dependent parallax effect wherein first and second images are laser engraved at a surface of a substrate of the ty document, and the security device comprises a colour image on or within at least one ser-engravable layer situated between laser engravable layers.

2. A security device as claimed in claim 1, wherein the colour image is in registration with the laser engraved images.

3. A security device as claimed in claim 1 or 2, wherein the first image is engraved on a front surface of the substrate and the second image is engraved on a back e of the ate.

4. A security device as claimed in any one of claims 1-3, comprising at least two non-laser engravable layers, wherein the colour image is situated between the at least two non-laser engravable layers.

5. A security device as d in any one of claims 1-4, wherein the colour image is a e colour image or an absorptive colour image.

6. A security device as claimed in any one of claims 1-4, wherein the colour image is an active colour image or an emissive colour image.

7. A security device for a security document comprising at least two interlaced laser engraved images forming an angle dependent parallax effect wherein first and second images are laser engraved at a surface of a substrate of the security document, and the security device comprises a diffraction grating between laser able layers.

8. A security device as claimed in claim 7, wherein the first image is engraved on a front surface of the substrate and the second image is engraved on a back surface of the substrate.

9. A ty device as claimed in claim 7 or 8, r comprising at least one aperture on a front side of the substrate and at least one re on a back side of the substrate.

10. A security device as claimed in any one of claims 7-9, wherein the diffraction grating is situated closer to a first side of the substrate than to a second side of the substrate.

11. A ty device as claimed in any one of claims 7-10, wherein the at least one aperture is an optically transparent portion of the substrate.

12. A security device as claimed in any one of claims 7-10, wherein the at least one aperture is a hole or gap in an outer layer of the substrate.

13. A security device as claimed in any one of claims 7-12, wherein the diffraction grating is situated in a transparent window portion of a ty document.

14. A method for making a security device for a security document comprising at least two interlaced laser engraved images forming an angle ent parallax effect wherein first image and second images are laser ed on a substrate of the security document, and the security device comprises a colour image on or within the at least one non-laser-engravable layer situated between laser engravable layers.

15. A method for making a security device for a security document comprising at least two interlaced laser engraved images forming an angle dependent parallax effect wherein first image and second images are laser engraved on a substrate of the security document, and the substrate comprises a diffraction grating n laser engravable layers.

16. A security document comprising a security device according to any one of claims 1-13.

17. A security document comprising a security device made by the method of claim 14 or 15.

18. A security device as claimed in claim 1, substantially as herein described with reference to any embodiment disclosed.

19. A method for making a security device for a security document as claimed in claim 14 or 15, substantially as herein bed with reference to any embodiment sed.

20. A security document as claimed in claim 16 or 17, substantially as herein described with reference to any embodiment disclosed.