WO2018191827A1

WO2018191827A1 - Security document having a window and a refractive structure

Info

Publication number: WO2018191827A1
Application number: PCT/CH2017/000035
Authority: WO
Inventors: Sylvain Chosson
Original assignee: Orell Füssli Sicherheitsdruck Ag
Priority date: 2017-04-18
Filing date: 2017-04-18
Publication date: 2018-10-25
Also published as: PL3571062T3; EP3571062B1; EP3571062A1

Abstract

The security document comprises a window (6) with an invisible, printed refractive, non-diffractive structure (7) printed thereon. In addition, it can carry a visible printed image (8). When the window is viewed against a dark background, the structure becomes visible and thereby allows testing the document's authenticity.

Description

Security document having a window and a refractive struc- ture

Technical Field

The invention relates to a security document, such as a banknote or an identification document, having a window and a structure printed onto the window.

The invention also relates to a method for manufacturing such a document and to a method for testing the authenticity of the document.

Background Art

Security documents comprising a substrate and a window within the substrate have been known.

Further, it has been known to place opaque structures on the window, such as e.g. offset and intag- lio ink structures of visible ink.

Disclosure of the Invention

The problem to be solved by the present in- vention is to enhance the security for documents of this type.

This problem is solved by a security document according to the independent claim.

Hence, the security document comprises:

- A substrate: The substrate is the carrier of the security document. It can e.g. be of plastics or a laminated structure of plastic and non-plastic layers.

- A window arranged in the substrate: This is a region of the substrate that is transparent. It can e.g. be formed by a transparent plastic layer. A defini- tion of the term "window" is provided in the section "Definitions" below. - A transparent refractive structure printed onto the window: This is a refractive structure printed with a transparent ink. The terms "refractive structure" and "transparent structure" are again defined below.

Typically, when viewing such a window on a light background or in transmission against a light source, such that the light source is visible through the window, the refractive structure is not visible or hardly visible.

However, when viewing the window against a darkish background, with the light source being off-axis to the viewing axis, the structure becomes visible or more apparent and thus provides an easy-to-verify secu- rity feature.

Since the structure is refractive, and not diffractive, it does not need a high spatial resolution and can therefore be applied using conventional security printing techniques.

The invention also relates to a method for testing the authenticity of such a security document. It comprises the step of visually checking for the presence of the refractive structure.

Advantageously, for testing the document's authenticity, the following steps are carried out:

- Viewing said window along a viewing axis from a first side of said document while a light source is arranged on a second side of said document off said viewing axis and not visible through said window: In other words, the viewing axis does not intersect with the light source, and the light source is at a sufficient distance therefrom in order to not be directly visible through the window. In that case, in the regions where the light is not refracted by the structure, the window is comparatively dark, which makes it easy to detect the refracted light. - Checking for light from said light source refracted by said structure: Such light is indicative of the presence of the refractive structure.

In a further advantageous embodiment, the structure represents a first motif, such as a portrait, writing or a geometrical figure, while the document com- prises an image printed in visible ink showing a second motif. The two motifs can be used to interact in various ways in order to render the testing of the document eas- ier.

For example, the first and the second motif can be equal, i.e. the can both show the same thing, such as the same portrait or the same writing. This makes it possible to compare the two.

In another example, the first and the second motif can be adjacent to each other or overlapping each other. This allows the user to e.g. check the two motives for their mutual register or for a third motif that they generate under conditions where they are both visible.

For example, the first and second motif can form a first edge and a second edge, respectively. These edges can be placed to be contiguous, i.e. they are on the same line (or curve) and at least one of the edges continues where the other ends. This makes it particu- larly easy to test the register of the two motifs.

In another example, the first and the second motif can form a first and a second periodic pattern, re- spectively. The two patterns have periodicities that dif- fer in a range of 1% to 20%, in particular of 2% to 10%, which gives rise to a visually perceptive interference (moire-) effect between the two.

In yet another embodiment, the structure can comprise a luminescent dye, which provides a further way to test the document's authenticity while allowing the structure to remain transparent.

The invention also relates to a method for manufacturing this document. This method comprises the step of printing the refractive structure onto the win- dow. In particular, offset printing, intaglio printing, screen-printing or inkjet printing can be used for apply^¬ ing the structure.

The security document is advantageously a banknote or an identification document, such as a pass- port.

Brief Description of the Drawings

The invention will be better understood and objects other than those set forth above will become ap- parent when consideration is given to the following de- tailed description thereof. This description makes refer- ence to the annexed drawings, wherein:

Fig. 1 is an example of a security document, Fig. 2 is a sectional view of the window of the security document in a first example (A) and a second example (B) ,

Fig. 3 illustrates a first viewing geometry

A,

Fig. 4 illustrates a second viewing geometry B,

Fig. 5 shows a first example of the security element,

Fig. 6 shows a second example of the security element,

Fig. 7 shows a third example of the security element,

Fig. 8 shows a fourth example of the security element,

Fig. 9 shows a fifth example of the security element,

Fig. 10 is an example where the transparent refractive structure comprises a halftone image, and

Fig. 11 is an identification document. Modes for Carrying Out the Invention

Definitions :

Refraction" is understood to designate the change of direction of light passing through media having different refractive indices. Advantageously, refraction is understood to include processes where light is re- fracted on structures having sizes larger than 2 μιπ, and/or where light is scattered on finer, but non-peri- odic structures. Processes including diffraction (defini- tion see below) are not understood to be refraction, though. In other words, "refraction" is understood as a "non-diffractive refraction".

A "refractive structure" is a structure that changes the direction of light due to refraction, i.e. it is understood as a "non-diffractive, refractive struc- ture" .

Diffraction" and "diffractive" are under- stood to designate a coherent scattering effect of light passing through a periodic structure of varying refrac- tive index when the structure is periodic and has a peri- odicity between a few tenth of the wavelength of the light and a few times the wavelength of the light. In particular, holographic effects and scattering of light at diffractive gratings are understood to be diffraction processes. In the present context, diffraction is not un- derstood as a refractive process.

A "window" in a security document is under- stood to designate a region of the security document hav- ing, for perpendicularly incident light, a wavelength-av- eraged transparency of at least 50%, in particular of at least 80% for visible light. In other words, the wave- length-normalized integral

(1)

of the transmission t( λ) of the window (integrated over all directions of transmitted light) over the wavelength range λ_min = 400 to λ_max — 700 nra is at least 0.5, in particular at least 0.8.

A refractive structure is considered to be "transparent" if it has a wavelength-averaged transpar- ency of at least 50%, in particular of at least 80%, again in the sense of above equation (1) .

"Macroscopic" is used to the describe fea- tures with a sufficiently large size to make them visible to the naked eye. Advantageously, such features have a size of at least 100 μm, in particular of at least 1 mm.

Basic design:

Fig. 1 shows a banknote as an example for a security document 1. It comprises a substrate 2, which can e.g. be a paper substrate (where "paper" is to in- clude cotton-based paper) , a plastic substrate or a lami- nate of plastic and paper layers.

Substrate 2 carries various printed insignia, such as a denomination 3, printed security features 4, and a unique serial number 5.

Further, substrate 2 comprises one or more windows 6.

Advantageously, substrate 2 is non-transpar- ent outside the window (s) 6.

A transparent, refractive structure is printed onto window 7.

Instead of being a banknote, security docu- ment 1 can e.g. an identification document, such as a passport or an ID card, or it can e.g. be a credit card, a check, a coupon, a brand certificate, or any other type of document that should be hard to copy.

Fig. 2 shows an enlarged sectional view through window 6. In this example, window 6 carries not only the transparent refractive structure 7 printed thereon, but also an image 8 printed with visible ink.

Transparent refractive structure 7 can be of an invisible ink, such as a lacquer, a primer, a lumines- cent ink or any other type of ink that is transparent in the visual spectral range of 400 - 700 nm.

Advantageously, transparent refractive struc- ture 7 is of a material different from window 6 such that it can be optimized for printing.

Image 8 is advantageously also a printed structure, but it consists of visible ink, i.e. an ink that is visible at least in part of the spectral range of 400 - 700 nm. Image 8 can be printed either on the same side as image 7 (as shown in image (A) of Fig. 2) but also on the other side in register (as shown in image (B) of Fig. 2) .

Window 6 with its transparent, refractive structure 7 and, optionally, its visible image 8, forms a security element of document 1.

The function of the security element is now illustrated with reference to Figs. 3 and 4.

Figs. 3 and 4 show a user 10 viewing window 6 along a viewing axis 12.

In the viewing geometry A of Fig. 3, a light source 14 (or a bright background) is arranged on or close to viewing axis 12 but on a side of document 1 op- posite to user 10 such that it is visible for user 10 through window 6.

Most of the light from light source 14 passes window 6 without being affected by transparent refractive structure 7, which is illustrated by the fat arrow 16. A small amount of the light (e.g. in the order of a few percent) is refracted by structure 7 into off-axis direc- tions and will not enter the user's eye. However, since the percentage of refracted light is small, there is a very weak contrast between regions where structure 7 causes weak scattering as compared to regions where structure 7 causes strong scattering. Thus, structure 7 is mostly or completely invisible to user 10 in viewing geometry A.

In the viewing geometry B of Fig. 4, light source 14 is still located on the side of security docu- ment 1 that is opposite to user 10, but it is positioned at such a distance away from viewing axis 12 that it is not directly visible for user 10 in window 6. In other words, the light 16 passing through structure 7 without being strongly refracted does not enter the user's eye. Only a small percentage of the light will be refracted (as shown under 18) in a direction where it can enter the user's eye.

In this case, however, the contrast between strongly and weakly refractive regions of structure 7 can be much larger. This is particularly true if the user places security document 1 such that the background visi- ble through window 6 is much darker than light source 14.

Therefore, in the viewing geometry B, struc- ture 7 becomes visible.

Hence, in order to check security document 1 for authenticity, a user can check for the presence of the refractive structure by using his naked eyes.

Advantageously, the user views the window along viewing axis 12 from a first side of document 1 while light source 14 is arranged off (i.e. away from) viewing axis 12 such that it is not visible through the window. He can then check for the presence of light from light source 14 that has been refracted from structure 7 .

Advantageously, the viewing step is carried out such that the background visible through window 7 is much darker (in particular at least ten times darker) than light source 14.

Refractive structure 7 should refract enough light for it to become visible in viewing geometry B. Even more advantageously, though, it should not refract too much light to prevent it from becoming visible in viewing geometry A.

Hence, advantageously, structure 7 illumi- nated by a white light beam perpendicular to the surface of window 6 refracts at least 1%, in particular at least 5%, of the transmitted light into directions that have an angle of less than 80° to the window's surface (i.e. into off-axis directions) . This allows the structure to be seen in situations where the light source is not visible in the window.

Also advantageously, though, the structure 7 illuminated by a white light beam perpendicular to the window's surface refracts no more than 20%, in particular no more than 10%, of the transmitted light into direc- tions that have an angle of less than 80° to the window's surface. This prevents the structure from being easily seen in viewing geometry A.

One or both of the conditions in the above to paragraphs should advantageously hold for any macroscopic diameter of the light beam.

In the following, various examples of the se- curity element are described with reference to Figs. 5 - 9. Each of these figures shows four images. From left to right, these are:

- "visible": A representation of the visible image printed on window 6.

- "invisible": A representation of transpar- ent refractive structure 7. In this case, the dark areas represent regions where the refraction caused by struc- ture 7 is low, i.e. where structure 7 is less dense, ho- mogenous, or absent, while the bright areas represent re- gions where the refraction caused by structure 7 is high, i.e. where structure is denser and inhomogeneous .

- "A": the image the user sees in viewing ge- ometry A (Fig. 3) .

- "B": the image the user sees in viewing ge- ometry B (Fig. 4) . First example:

In the first embodiment of Fig. 5, the secu- rity element comprises no visible image 8, and structure 7 represents a portrait 20.

Under viewing geometry A, portrait 20 is nearly or completely invisible, and window 6 appears to be transparent.

Under viewing geometry B, portrait 20 becomes visible as shown.

Second example:

In the second example of Fig. 6, the security element comprises a visible image showing a portrait 22, and structure 7 also represents a portrait 20, advanta- geously the same portrait.

Under viewing geometry A, portrait 20 is nearly or completely invisible. However, portrait 22 is visible.

Under viewing geometry B, both portraits are visible.

In this example, the motifs represented by structure 7 as well as by the visible printed image 8 are equal. The user can compare them in viewing geometry B when checking the document for authenticity.

Third example:

In the third example of Fig. 7, the visible printed image shows a part 24 of a portrait, and struc- ture 7 represents a complementary part 26 of the same portrait .

Under viewing geometry A, only part 24 is visible.

Under viewing geometry B, both parts 24, 26 are visible and complement each other to represent the full portrait. In more general terms, the first motif 26 represented by structure 7 and the second motif 24 repre- sented by visible image 8 are complementary parts of a common motif.

Forth example:

In the fourth example of Fig. 8, the first motif 30 represented by structure 7 is a first set of lines, while the second motif 32 represented by the visi- ble printed image 8 is a second set of lines.

In viewing geometry A, only second motif 32 is visible.

In viewing geometry B, both motives 30, 32 are visible and generate continuous lines extending through both motives.

In more general terms, the motif 30 has a first edge and the second motif 32 has a second edge (in this case the edges of the lines), wherein said first and second edges are contiguous.

Fifth example:

In this example, the first motif formed by structure 7 forms a first periodic pattern 34. The second motif formed by printed image 8 forms a second periodic pattern 36. The two periodic patterns differ slightly in their periodicities.

In viewing geometry A, only the second peri- odic pattern 36 is visible.

In viewing geometry B, both periodic patterns 34, 36 are visible. Since their periodicities differ only slightly, a Moire effect becomes visible.

Advantageously, the direction of the two pe- riodic patterns differ by less than 10°, in particular by less than 5°.

Halftone rendering: As mentioned, the refraction of structure 7 is strong in those regions where it is highly homogeneous while it is weak in those regions where it is weakly ho- mogeneous .

Hence, in a region that is to appear bright in viewing geometry B, structure 7 needs to be highly in- homogeneous in order to cause strong refraction. In a re- gion that is to appear dark, structure 7 should be weakly inhomogeneous and, advantageously, mostly absent.

This is illustrated in Fig. 10, which shows the desired appearance (when viewed in viewing geometry B) under reference number 40. In this case, desired ap- pearance 40 is a grayscale run from bright (top) to dark (bottom) . Image 42 shows a possible design of structure 7 to achieve this effect (with the black parts showing where the invisible ink of structure 7 has been applied) .

As can be seen, in the dark regions of de- sired appearance 40, there is only a small amount of structure 7, while in the bright parts of desired appear- ance 40 there is a larger, non-homogeneously distributed amount of structure 7. This can e.g. implemented as a halftone image 42 as shown.

Individualized security documents:

Structure 7 can be unique to the security document, i.e. it can differ between different security documents .

As an example, Fig. 11 shows a document of identification 50, which carries the bearer's portrait 52 in visible ink. In addition, structure 7 also represents the bearer's portrait in window 6.

Alternatively, structure 7 can represent some other unique feature of the security document. For exam- ple, if the document has a serial number (such as the se- rial number of a banknote) , it can be a motif derived from this serial number, such as a numeric of alphanu- meric representing the serial number. Method of manufacture:

In order to manufacture security document 1, structure 7 is applied to window 6 using invisible ink, i.e. ink that is transparent.

Any printing process can be used for applying structure 7.

Advantageously, structure 7 is applied by offset printing, intaglio printing, screen-printing or inkjet printing.

Using inkjet printing is particularly advan- tageous for individualized security documents where structure 7 should be unique to the security document .

Printed image 8 can be printed prior or after applying structure 7.

Printed image 8 can be on the same side of the window 6 as structure 7 or its opposite side.

Notes :

Transparent, refractive structure 7 is advan- tageously macroscopically inhomogeneous, i.e. it com- prises inhomogeneities that is visible by the naked human eye, which makes the security feature easy to observe.

In a preferred embodiment, transparent re- fractive structure 7 does not cover all of window 6 but leaves macroscopic regions non-covered, which also makes the feature easier to observe.

As mentioned, structure 7 can comprise a lu- minescent dye, which allows checking for its presence by yet a further method, thereby providing a redundancy of the security check.

Advantageously, structure 7 comprises a dye that emits visible light when being exposed to UV radia- tion. An example of a suitable ink is e.g. the ink 990660 (red-luminescent) by Sicpa S.A., Prilly, Switzerland. While there are shown and described presently preferred embodiments of the invention, it is to be dis- tinctly understood that the invention is not limited thereto but may be otherwise variously embodied and prac- ticed within the scope of the following claims.

Claims

1. A security document comprising a substrate ( 1) ,

a window (6) arranged in said substrate (1) , and

a transparent refractive structure ( 7 )

printed onto said window (6) .

2. The document of claim 1 wherein said structure ( 7 ) represents a first motif, and wherein said document further comprises an image (8) printed in visi- ble ink showing a second motif.

3. The document of claim 2 wherein said first and said second motives are equal.

4. The document of any of the claims 2 or 3 wherein said first and said second motives are adjacent to each other or overlapping each other.

5. The document of claim 4 wherein said first motif has a first edge and said second motif has a second edge, wherein said first and second edges are contiguous.

6. The document of any of the claims 2 to 5 wherein said first motif and said second motif form a first and a second periodic pattern (34, 36), respec- tively, wherein the first and second periodic patterns (34, 36) have periodicities that differ in a range of 1% to 20%, in particular of 2% to 10%.

7. The document of any of the preceding claims wherein said structure ( 7 ) comprises a luminescent dye, in particular a dye emitting visible light under UV- irradiation .

8. The document of any of the preceding claims wherein said structure (7) comprises a halftone image (42) .

9. The document of any of the preceding claims wherein said structure (7) is macroscopically in- homogeneous .

10. The document of any of the preceding claims wherein macroscopic regions of said window (6) are non-covered by said structure (7) .

11. The document of any of the preceding claims wherein said structure (7) is unique to the docu- ment .

12. The document of any of the preceding claims wherein said structure (7) is of an invisible ink.

13. The document of any of the preceding claims wherein said document is an identification docu- ment (50) and said structure (7) represents a portrait of a bearer of said identification document.

14. The document of any of the claims 1 to 12 wherein said document is a banknote.

15. A method for manufacturing the security document of any of the preceding claims comprising the step of printing said refractive structure (7) onto said window (6) using invisible ink.

16. The method of claim 15 wherein said re- fractive structure (7) is printed by one of offset print- ing, intaglio printing, screen-printing, and inkjet printing.

17. A method for testing the authenticity of the security document (1) of any of the claims 1 to 14 comprising the step of visually checking for the presence of said refractive structure (7) .

18. The method of claim 17 comprising the steps of

viewing said window (6) along a viewing axis (12) from a first side of said document while a light source (14) is arranged on a second side of said document (1) off said viewing axis (12) and not visible through said window (6) and

checking for light from said light source (14) refracted by said structure (7) .