WO2015085439A1

WO2015085439A1 - Security document with invisible marking

Info

Publication number: WO2015085439A1
Application number: PCT/CH2013/000217
Authority: WO
Inventors: Martin Eichenberger; Dieter Sauter
Original assignee: Orell Füssli Sicherheitsdruck Ag
Priority date: 2013-12-09
Filing date: 2013-12-09
Publication date: 2015-06-18
Also published as: EP3079915A1

Abstract

The security document comprises a substrate (1) carrying visible printed insignia (2 - 5) thereon. A first transparent coating (6) and a second transparent coating (7) are applied on top of the printed insignia (2 - 5). The first transparent coating (6) carries a plurality of surface structures (8), which are invisible to the unaided eye but may be read out by a suitable detection device. The second transparent coating (7) is arranged below the first transparent coating (6) and acts as a barrier preventing the first coating (6), during manufacture, to seep into the underlying structures. Inkjet printing is used for the application of the first transparent coating (6).

Description

Security document with invisible marking

Technical Field

The invention relates to a security document having a transparent coating carrying a plurality of sur^¬ face structures of small size as well as to methods for manufacturing such a security document. The invention also relates to a set of such security documents.

Background Art WO 2009/056571 describes a method and device for detecting irregularities in surfaces and their appli^¬ cation to a secure tracking system. The irregularities can form a substantially invisible marking.

US 2013/0301035 describes a method for scan- ning surface structures of a security document in order to identify it.

US 2008/0149820 describes a method for providing a security document with an invisible marking. The marking is formed by applying a layer of a transpar- ent material to a substrate, which layer comprises small surface structures of increased or decreased thickness that are invisible to the human observer but that can be detected optically by means of a suitable detection apparatus .

Disclosure of the Invention

In a first aspect of the invention, the problem to be solved by the present invention is to provide a security document of this type that has improved relia- bility, as well as a method for manufacturing such a security document .

This problem is solved by the method and security document according to the first two independent claims .

Accordingly, the method according to the invention comprises the following steps:

- Providing a flexible substrate. The flexi^¬ ble substrate can e.g. be a substrate of paper, such as cotton-based paper, or plastics, or a combination there- of .

- Printing visible insignia on said substrate: Such visible insignia comprise e.g. regular printed signs, patterns, characters or other subjects using conventional printing techniques, such as offset print, intaglio print or screen print. Regular inks and/or various types of security inks can be used.

- Applying a first transparent coating to the document above at least part of said insignia and forming a plurality of surface structures in said first transpar- ent coating: This first transparent coating carries surface structures that are basically invisible to the unaided eye but can be detected using the means described in US 2008/0149820. The lateral size of the surface structures is between 5 and 1000 μπι, in particular be- tween 10 and 500 pm.

According to the invention, the method further comprises the following steps: - Applying a second transparent coating, prior to applying said first transparent coating, to the document: This second transparent coating acts as a barrier between the first transparent coating and the substrate, thereby preventing, during the manufacturing process, the still liquid first transparent coating from seeping into the substrate. This avoids a degradation of the surface structures due to such seeping effects.

- Hardening said second transparent coating at least partially before applying said first transparent coating: The term "hardening" is to be understood as a drying and/or cross-polymerization process that increases the stability of the second coating. By at least partially hardening the second coating before applying the first coating, the second coating can act as the barrier mentioned in the preceding paragraph.

The first transparent coating is arranged such that it covers at least part of the second transpar^¬ ent coating, thus that it can profit from the barrier function of the latter.

Advantageously, the first transparent coating is applied by means of inkjet printing, which provides an economical printing method well suited to manufacture the surface structures of the first coating.

In yet another embodiment, the invention com^¬ prises the step of determining a unique identifier for each document and encoding this identifier in said surface structure. Using this technique for manufacturing a plurality of security documents allows to distinguish the individual documents by their surface structure. This is best combined with using inkjet printing for the first coating because this printing technique is well suited for generating individualized surface structures.

The unique identifier can also be encoded in the visible insignia, e.g. as a bank note serial number. This allows a cross-check between the insignia and the surface structure for verifying the validity of the document .

In another embodiment, the method comprises the step of intaglio printing the document prior to ap- plying the first coating. During intaglio printing, engraved printing plates are pressed against the document, which allows to flatten inherent microscopic irregularities of the surface of the substrate. Thus, when applying the first coating afterwards, the surface structures are easier to detect.

For the reasons above, the invention also re^¬ lates to a security document comprising a flexible substrate carrying printed, visible insignia. The document further comprises a first transparent coating arranged above at least part of the insignia, wherein this first transparent coating carries a plurality of surface structures having a lateral size between 5 and 1000 μιη, in particular between 10 and 500 m. A second transparent coating is arranged somewhere between the first transpar- ent coating and the substrate. The first transparent coating covers at least part of the second transparent coating, such that the second transparent coating can form a barrier as described above.

In a second aspect of the invention, the problem to be solved is to provide a method for manufacturing invisible markings of the type described in US 2008/0149820.

This problem is solved by the method of claim 18. Accordingly, in this second aspect, a first transpar- ent coating is applied to the document and a plurality of surface structures are formed in said first transparent coating. As above, the structures have a lateral size between 5 and 1000 μπ\, in particular between 10 and 500 ym. The method is characterized by using inkjet printing for applying the first transparent coating. It has been found that inkjet printing is well suited for forming structures of this size. The method of the second aspect of the inven^¬ tion can be used in combination with or separately from the method of the first aspect of the invention. In other words, the method of the second aspect of the invention can be combined with the application of a second transparent coating as described above, or it may also be used without a second transparent coating.

It will be clear to the skilled person that the various optional features of the first aspect of the invention can also be used in context with the second aspect of the invention, and vice versa.

Other advantageous embodiments are listed in the dependent claims as well as in the description below.

Brief Description of the Drawings

The invention will be better understood and objects other than those set forth above will become ap- parent from the following detailed description thereof.

Such description makes reference to the annexed drawings, wherein :

Fig. 1 shows a view of a security document, Fig. 2 is a sectional view along line II-II of Fig. 1 (not to scale),

Fig. 3 is a sectional view along line II-II of Fig. 1 for a second aspect of the present technology (not to scale) ,

Fig. 4 is an embodiment where the surface structures extend over an area covering the whole securi^¬ ty document,

Fig. 5 shows a set of different security doc^¬ uments having different surface structures,

Fig. 6 illustrates different locations for positioning the surface structures,

Fig. 7 shows an embodiment where surface structures are applied to both sides of the document. Modes for Carrying Out the Invention

Definitions :

The term "document" relates to a sheet-like flexible object carrying printed information on at least one of its surfaces.

The terms "lateral" and "laterally" refer to all directions extending parallel to a surface of the security document.

Terms of the type "above", "below", "top" and "bottom" are understood in respect to a center plane of the substrate, which center plane extends parallel to the surfaces of the document. Any object A closer to the center plane than an object B is below object B and object B is on top of object A.

A coating is "transparent" or "translucent" if it transmits at least 80% of all light in the visible spectrum .

A "flexible" substrate or document is a substrate or document that can reversibly be bent to a curvature of 10 mm or less.

Embodiments :

A first embodiment of the invention is illus- trated in Figs. 1 and 2. These figures show a security document in the form of a banknote.

The shown security document comprises a flexible substrate 1 of paper (conventional paper or cotton- based paper) and/or plastics, onto which visible insig- nia, for example security designs 2, illustrations 3, indications of value 4 and a serial number 5, are printed in known manner. In addition the document comprises a first transparent coating 6 and a second transparent coating 7.

First transparent coating 6 is substantially invisible to the unaided eye, but for clarity it is shown in Fig. 1. It comprises a plurality of surface structures 8 formed e.g. by a plurality of bumps and/or recesses arranged thereon. The pattern formed by surface structures 8 is predetermined in the sense that it does not depend on random surface structures of substrate 1. This pattern may, however, be superimposed by a random structures caused by the surface roughness of substrate 1.

As described in US 2008/0149820, this type of structure can be detected and be used for document authentication, e.g. by recording the specular reflection of light impinging thereon and then processing the recorded image using correlation techniques.

As mentioned, the lateral size L of the sur^¬ face structures 8 is between 5 and 1000 ym, in particular between 10 and 500 μιτι, such that they can be detected easily by means of a suitable detection apparatus e.g. using specular reflection.

First transparent coating 6 typically extends only over part of the surface of the security document, which allows a quicker application thereof.

Second transparent coating 7 is arranged below first transparent coating 6, i.e. it extends through a region between first transparent coating 6 and substrate 1.

Second transparent coating 7 advantageously acts as a protective layer for the whole document and therefore can extend over the whole length and width of substrate 1, and it may be spared at locations that do not need protecting, e.g. at the location of patches (such as diffractive patches) and/or windows of the security document. In the embodiment of Fig. 2, second transparent coating 7 covers the visible printed insignia 2, 3, 4, thereby protecting them from the environment.

The visible printed insignia 2, 3, 4 can e.g. comprise an offset print layer 10, which e.g. forms a background pattern for the security document as well as part of the objects represented thereon. Further, the visible printed insignia can at least partially be formed by an intaglio print layer 11. Other types of print lay- ers, such as a screen print layer, can be present as well .

As can be seen on Fig. 2, the first and sec^¬ ond transparent coatings 6, 7 are arranged at least on a first side 12 of substrate 1. They may, however, also be applied to both sides. Alternatively, for example and as shown in Fig. 2, the second, opposite side 13 may only carry a printed layer 14 and a single transparent coating 15, the latter acting as protection for printed layer 14. Method of manufacture:

In the following, we describe an advantageous method for manufacturing such a document.

This method starts from a substrate 1, e.g. in the form of a sheet carrying several such substrates side by side, which will be cut apart after completion of the following steps.

In a first, optional step, a primer may be applied to both sides of substrate 1. This step is known to the skilled person and prepares substrate 1 for the following printing steps.

Following this, the printed layers can be applied, e.g. first starting with offset print layer 10, followed by intaglio printer layer 11 and/or any further conventional printing layers. Before, between or after these printing steps, security patches, such as diffrac- tive patches, can be applied to the security document. Now, second transparent coating 7 is applied, in particular using flexoprint. Advantageously, a resin is used for this step, and second transparent coating 7 is cross-polymerized after its application using UV radi- ation. Hardening second transparent coating 7 by means of UV irradiation leads to a very tight layer that cannot be dissolved or penetrated during the following application of first transparent coating 6.

In order to form a tight barrier without un- necessarily stiffening the security document, the applied amount of second transparent coating 7 is advantageously between 1 and 2 g/m^, in particular 1.7 g/m^.

After applying second transparent coating 7, first transparent coating 6 is formed on top of it. Ad- vantageously , the first and second transparent coatings

6, 7 are applied adjacent to each other, i.e. with no intermediate layer between them, such that a good adhesion is achieved. Advantageously, first transparent coating 6 advantageously has a thickness between 1 and 3 μπι.

As mentioned above, first transparent coating

6 is best applied by means of ink jet printing, such that the surface structures 8 can be customized during printing, e.g. depending on the serial number 5 of the document it is applied to. Alternatively, first transparent coating 6 can e.g. be applied using screen printing or intaglio printing techniques, which both also allow to form the surface structures 8.

While first transparent coating 6 is in its unhardened state, immediately after its application to the security document, second transparent coating 7 acts, as mentioned, as a barrier that prevents first transpar^¬ ent coating from seeping into the underlying layers.

Thus, a degradation of the surface structures 8 at this step is avoided.

After application, first transparent coating

6 is advantageously again hardened using UV irradiation in order to "freeze" surface structures 8 quickly. Both, first as well as second transparent coating 6, 7 can be made using a UV-hardening lacquer or varnish. A suitable composition is e.g. a UV polymeriza- ble resin, such as type 889376 flexo printing varnish du- al cure by Sicpa, which combines thermo drying and UV polymeri zation .

In order to obtain a well-structured first transparent coating 6, the UV radiation should be applied quickly after, or even during, the application of the polymerizable resin in order to prevent the applied structures from completely flowing into each other before they harden. Hence, in a particularly advantageous embodiment, the document is irradiated with UV radiation while applying the first transparent coating. This can e.g. be achieved by combining the inkjet printing head with a UV light source which irradiates the region where the ink hits the document.

In a particularly advantageous embodiment, if two transparent coatings 6, 7 are used, the glossiness of first and second transparent coatings 6, 7 differ because such a difference in glossiness makes the structure easier to detect. A particularly good contrast is observed if second transparent coating 7 is more matte than first transparent coating 6.

As mentioned above, a unique identifier can be attributed to each document. This identifier can also be encoded in the visible insignia 2 - 5, in particular in human-readable form, e.g. as a serial number 5. The identifier is also encoded in surface structures 8, e.g. by omitting or emphasizing an identifier-dependent pattern of the bumps formed therein.

When verifying the authenticity of the document, the pattern formed by the surface structures 8 is compared to the serial number 5 of the security document. Only if the information encoded in the pattern of the surface structures 8 matches the serial number 5, the document is considered to be authentic. In the embodiments described so far, the security document comprises a first and a second transparent coating 6, 7. It must be noted, though, that the second aspect of the invention, which relates to inkjet printing the fine structures, the second transparent coating 7 is optional. A document of this type is shown in Fig. 3. As can be seen, first transparent coating 6 of this embodiment is directly applied to offset print layer 10 or any other part of the document, without underlying second transparent coating 7.

Further embodiments:

In the embodiment of Fig. 1, the surface structures 8 extend over an area 20 that covers only a small part of the security document. However, the surface structures 8 may also cover an area 20 extending over substantially the whole substrate, as shown in the embod^¬ iment of Fig. 4. In this context, the "area covered by the surface structures 8" is to be understood as the con- vex hull of the surface structures, see e.g. Fig. 4. In the embodiment of Fig. 4, the area 20 covers at least 70% of one surface of the security document.

Advantageously, however, the area 20 covers only a smaller part of the security document, such as shown in Fig. 1, which makes it easier to hide the surface structures and which reduces the visual impact of the surface structures. Hence, advantageously, area 20 covers no more than 30% of one surface of the security document .

As mentioned above, a unique identifier of each security document, such as the serial number of a banknote, can be encoded in the surface structures 8. To do so, the pattern formed by the surface structures 8 is a function of the information to be encoded. For example, the positions and/or sizes of bumps or recesses formed by the surface structures 8 can be calculated as a function of the data to be encoded. Fig. 5 shows another scheme for encoding data in the surface structures 8. In this embodiment, the data encoded in the surface structures 8 is not a unique identifier, but rather it designates a banknote denomination. To encode this information, two areas 21, 22 of the banknotes are provided for receiving the surface structures 8. For the denomination 50, the surface structure is ar^¬ ranged in both areas 21, 22, for the denomination 100 only in first area 21, for the denomination 200 only in second area. The denomination 1000 again contains surface structures in both areas 21, 22, but of a different design as compared to the denomination 50.

In more general terms, the invention also relates to a set of security documents of the present invention .

The set of security documents can comprise banknotes of different denominations, wherein the surface structures 8 of banknotes of the same denomination are equal but the surface structures 8 of banknotes of dif^¬ ferent denominations and/or different serial numbers differ. For example, the location of the structures 8 on the banknote can be a function of the denomination and/or of the serial number.

Alternatively or in addition thereto, each of the security documents of the set can comprise at least two distinct areas 21, 22, wherein

- in a first subset of said security documents said surface structures are arranged in said first and not in said second area, and wherein

- in a second subset of said security documents said surface structures are at least arranged in said second area.

Further, the surface structures 8 can encode several sets of data using different encodings. For example, one part of the surface structures 8 can encode the serial number using a first encoding scheme, while another part of the surface structures 8 can encode the denom- ination or country of issue using a second encoding scheme .

Fig. 6 illustrates another aspect of present technique. Here, the different areas 21, 22 are coloured differently, e.g. by using different inks or inks densities in the underlying offset print layer 10. Hence, in this aspect the two distinct areas 21, 22 have different colour. In this context, the term "different colour" refers to differences in at least one of the parameters hue, saturation and brightness (value), i.e. a dark grey is e.g. considered to be a different colour from a light grey.

Fig. 7 shows a further embodiment where the surface structures 8 is applied to both sides of the document, i.e. to first side 12 as well as second side 13. This e.g. allows an automatic detection device to distinguish between the first and second sides using the surface structures alone. Advantageously, the surface structures 8 on the first and the second side differ, i.e. they have different shapes, sizes and/or distributions.

Notes :

In the embodiment shown above, the first and second transparent coatings 6, 7 are both applied after printing the visible insignia 2 - 5, thus that the visible insignia are protected by the transparent coatings.

Alternatively, at least some or all of the visible insignia may be applied over the first and second transparent coatings and/or between them.

In summary, in the described embodiment, the security document comprises a substrate 1 carrying visible printed insignia 2 - 5 thereon. A first transparent coating 6 and a second transparent coating 7 are applied on top of the printed insignia 2 - 5. The first transparent coating 6 carries a plurality of surface structures 8, which are invisible to the unaided eye but may be read out by a suitable detection device. The second transparent coating 7 is arranged below the first transparent coating 6 and acts as a barrier preventing the first coating 6 from seeping, during manufacture, into the underlying structures.

First transparent coating 6 can be continuous (as shown in Figs. 2 and 3) or non-continuous. In the latter case, for example, first transparent coating 6 can consist of individual, mutually separated bumps forming the surface structure 8.

Typically, the surface structures 8 are correlated with at least one printed information on the security document. For example, it has been mentioned that the surface structures 8 encode a unique identifier, such as the serial number, or they can encode the denomination of a banknote. Hence, the position, size and/or distribution of the surface structures is advantageously a function of at least one information printed with ink on the security document. In this case, a verification method can e.g. comprise the step of comparing the printed information with the information encoded in the surface structure .

While there are shown and described presently preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims.

Claims

1. A method for manufacturing a security document comprising the steps of,

providing a flexible substrate (1), printing visible insignia (2 - 5) on said substrate ( 1 ) ,

applying a first transparent coating (6) to said document above at least part of said insignia (2 - 5) and forming a plurality of surface structures (8) in said first transparent coating (6), which surface structures (8) have a lateral size (L) between 5 and 1000 μΐΐΐ, in particular between 10 and 500 μτη,

wherein said method further comprises the steps of

applying a second transparent coating (7), prior to applying said first transparent coating (6), to said document and

hardening said second transparent coating (7) at least partially before applying said first transparent coating ( 6 ) ,

wherein said first transparent coating (6) covers at least part of said second transparent coating (7) .

2. The method of claim 1 wherein said first transparent coating (6) is applied by means of inkjet printing .

3. The method of any of the preceding claims comprising the step of determining, for each document, a unique identifier and encoding said identifier in said surface structures (8) .

4. The method of claim 3 further comprising the step of encoding said identifier in said visible insignia (2 - 5), in particular in human-readable form.

5. The method of any of the preceding claims comprising the step intaglio printing said document prior to applying said first transparent coating (6).

6. The method of any of the preceding claims wherein said first and/or second transparent coating (6, 7) are hardened using UV radiation.

7. The method of any of the preceding claims wherein said first and said second transparent coating (6, 7) are applied adjacent to each other.

8. The method of any of the preceding claims wherein said second transparent coating (7) extends over a whole width and length of a side of said substrate (1) and/or wherein said first transparent coating (6) extends only over part of a surface of said security document.

9. The method of any of the preceding claims wherein said first and said second transparent coatings (6, 7) are applied after printing said visible insignia (2 - 5) .

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

printed, visible insignia (2 - 5) arranged on said substrate (1),

a first transparent coating (6) arranged above at least part of said insignia (2 - 5), wherein said first transparent coating (6) carries a plurality of surface structures (8) having a lateral size (L) between 5 and 1000 μιη, in particular between 10 and 500 μπι,

wherein said security document further comprises

a second transparent coating (7) arranged between said first transparent coating (6) and said substrate ( 1 ) ,

11. The security document of claim 10 wherein said first and said second transparent coatings (6, 7) are located adjacent to each other.

12. The security document of any of the claims 10 or 11 wherein said second transparent coating (7) extends over a whole width and length of a side of said substrate (1) and/or wherein said first transparent coating (6) extends only over part of a surface of said security document.

13. The security document of any of the claims 10 to 12 further comprising an intaglio print lay er (11) located below said first transparent coating (6)

14. The security document of any of the claims 10 to 13 further comprising an offset print layer (10) located below said first transparent coating (6).

15. The security document of any of the claims 10 to 14 wherein said second transparent coating (7) covers said printed, visible insignia (2 - 5).

16. The security document of any of the claims 10 to 15 wherein said first and said second coating (6, 7) have different glossiness.

17. The security document of any of the claims 10 to 16 wherein said second transparent coating (7) is more matte than said first transparent coating (6) .

18. The security document of any of the claims 10 to 17 wherein said surface structures (8) extend over an area (20) covering at least 70% of one surface of said security document.

19. The security document of any of the claims 10 to 17 wherein said surface structures (8) extend over an area (20) covering no more than 30% of one surface of said security document.

20. The security document of any of the preceding claims wherein a position, size and/or distribu^¬ tion of the surface structures (8) is a function of at least one information printed on the security document.

21. The security document of any of the preceding claims having a first and a second side (12, 13) and carrying surface structures on said first side (12) as well as on said second side (13), and in particular wherein said surface structures on said first side (12) and said second side (13) have different shapes, sizes and/or distributions.

22. A method for manufacturing a security document, in particular of any of the claims 1 to 9, comprising the steps of,

providing a flexible substrate (1), applying a first transparent coating (6) to said document and forming a plurality of surface structures (8) in said first transparent coating (6), which surface structures (8) have a lateral size (L) between 5 and 1000 μπι, in particular between 10 and 500 ym,

wherein said first transparent coating (6) is applied by means of inkjet printing.

23. The method of claim 22 further comprising the step of hardening said first transparent coating (6) by means of UV radiation after applying said first transparent coating (6) to said document.

24. The method of claim 23 comprising the step of irradiating said document with said UV radiation while applying said first transparent coating (6).

25. The method of any of the preceding claims comprising the step of determining, for each document, a unique identifier and encoding said identifier in said surface structures (8).

26. The method of any of the preceding claims comprising the steps of

printing visible insignia (2 - 5) on said substrate ( 1 ) ,

applying said first transparent coating over at least part of said visible insignia (2 - 5) .

27. The method of any of the preceding claims comprising the step intaglio printing said document prior to applying said first transparent coating (6).

28. A set of security documents of any of the claims 10 to 21.

29. The set of claim 28 comprising banknotes of different denominations, wherein the surface struc- tures (8) of banknotes of the same denomination are equal but the surface structures (8) of banknotes of different denominations differ.

30. The set of any of the claims 28 or 29, wherein each of the security documents of the set comprises at least two distinct areas (21, 22), wherein in a first subset of said security documents said surface structures (8) are arranged in said first (21) and not in said second (22) area, and wherein in a second subset of said security documents said surface structures (8) are at least arranged in said second area (22).

31. The set of claim 30 wherein the at least two different areas (21, 22) have different colour.