WO2018069216A1

WO2018069216A1 - Method for producing a security element

Info

Publication number: WO2018069216A1
Application number: PCT/EP2017/075621
Authority: WO
Inventors: Pierre Sarrazin
Original assignee: Oberthur Fiduciaire
Priority date: 2016-10-10
Filing date: 2017-10-09
Publication date: 2018-04-19
Also published as: RU2741481C2; CN109843597B; EP3523136B1; RU2019107329A; KR20190067173A; RU2019107329A3; FR3057205A1; CN109843597A; EP3523136A1; FR3057205B1

Abstract

The invention relates to a method for producing a security element comprising a support made from oriented plastic and at least one layer of liquid crystals borne and oriented by the support, an adhesion primer being deposited before or after the support is stretched in at least one direction, said stretching bringing the support to the oriented state and the liquid crystals being deposited by means of printing on the adhesion primer.

Description

METHOD FOR MANUFACTURING A SECURITY ELEMENT

The present invention relates to security elements for secure documents, and their manufacturing processes.

The invention relates more particularly to safety elements carrying liquid crystals.

Liquid crystals, especially cholesteric crystals, are widely used in safety elements for their goniochromatic properties. In order to improve the visibility of the color change effect with the viewing angle, they are usually arranged in front of a dark background, especially black.

In addition, the security elements tape, still called security son, are very often incorporated into secure documents such as bank notes.

These security elements conventionally comprise a substrate made of a thermoplastic material, for example PET, which can be metallized and provided with zones demetallized in the form of patterns appearing in transmitted light.

There is interest in providing these security elements with liquid crystals to enhance security by creating optical effects visible to the naked eye.

Removal of liquid crystals, however, faces multiple problems, which are solved at present only through complex processes to implement, costly and imposing certain limitations in terms of layout.

Thus, it is known to apply the liquid crystals in the form of a solid surface by a transfer method, with the disadvantage of limiting the possibilities on the artistic level, and to impose the presence of liquid crystals in the demetallized zones. This confers a coloration in transmitted light which is unattractive, and the presence of liquid crystals in the demetallized zones increases the cost of security without bringing a significant gain in terms of security or on the artistic level.

The transfer process generates a loss of material and lamination steps, which complicate the manufacture.

EP 1 744 904 discloses a substrate consisting of a bi-oriented PET film coated with oriented liquid crystals. This type of structure does not offer complete satisfaction in terms of adhesion to the substrate.

US 2003189684 describes various methods for the orientation of liquid crystals. US20070216518 discloses multilayer liquid crystal structures. The superposition of liquid crystals makes the structures expensive, by increasing the amount of liquid crystal to be used. Manufacturing by a transfer method is preferred.

EP2073 986 also describes structures with liquid crystal overlay.

JP 2009-98568 discloses a security element having an oriented plastic film which can be biaxially stretched and can carry liquid crystals.

GB 2527 763 discloses a sheet having an oriented polymeric film and capable of containing liquid crystals as well as an adhesive layer.

WO 2008/116796 relates to a security document comprising a plurality of polymeric films including a non-transparent film undergoing axial stretching. Adhesive layers can be applied to this film by printing. Moreover, this film may comprise liquid crystals.

There is a need to further improve the liquid crystal security elements and their manufacturing processes, in particular to have security elements in which the liquid crystals adhere well to the substrate, are used fully and in a manner allowing a great richness of optical effects.

The invention aims to meet this need, and it achieves this through a method of manufacturing a security element comprising an oriented plastic support and at least one layer of liquid crystal carried and oriented by the support, a primary adhesion being deposited before or after stretching the support at least in one direction, said stretching to bring the support in the oriented state and the liquid crystals being deposited by printing on the adhesion primer.

By "adhesion primer" it is necessary to understand any layer that favors adhesion. Thus this expression must not be understood in a limiting way.

Thanks to the invention, the adhesion of liquid crystals is improved and the deposition of liquid crystals by printing offers multiple possibilities in terms of aesthetics and optical effects obtained.

The application of the liquid crystals can be carried out in arbitrary patterns, on well-defined areas, offering great flexibility in the arrangement different means of security within the element. It is possible to obtain a greater diversity of effects of color changes, without penalizing, if necessary, the transparency of the openings of a Cleartext.

The invention makes it possible to prevent deposition of the liquid crystals by transfer, which facilitates the implementation of the method.

Preferably, the adhesion primer is deposited before a step of stretching the support.

More preferably, the support is oriented in one direction, then the primary is deposited, and the support is then stretched in another direction.

Applying the primer before stretching the support allows the primer to accompany the stretching of the support and thus further improves the orientation of the liquid crystals.

The support preferably comprises PET, but other materials are usable.

The primer may require crosslinking before application of the liquid crystals, especially when it comprises monomers. The method may thus comprise a step of crosslinking the adhesion primer, preferably after stretching the support.

The adhesion primer may comprise a polyolefin (or polyalkene), preferably polyethylene, polyurethane, polyester, polyether, polycarbonate, polyacrylic or a copolymer thereof, and preferably comprise a polyacrylic.

The adhesion primer may comprise, in particular before its deposition, at least one olefin (or alkene), urethane, ester, ether, carbonate or acrylic monomer, preferably acrylic monomer.

The application of the primer can be carried out by any means, including printing, coating, spraying or co-extrusion.

Printing liquid crystals can be done by any means and preferably by screen printing, gravure or flexography. The liquid crystals are deposited after stretching the support.

The method may comprise printing on the adhesion primer two different inks, at least one of which comprises the liquid crystals, the better of which both comprise liquid crystals, the liquid crystals being preferably cholesteric. These two inks can be deposited without overlapping; the quantity deposited is thus limited to the quantity just needed.

The effect of reflection diffusion fog ("Haze of reflection" hereinafter "Haze") of the cholesteric liquid crystal layer may be less than that of a reference security element without the adhesion primer layer . The reflective diffusion veil is responsible for a milky appearance, associated with low intensity light scattering next to the main reflection, which corresponds to reflection in the specular direction. The measurement can be performed according to ASTM D4039-09 (reapproved 2015) or ISO 13803: 2014. This allows visibility over a wider angular range of the goniochromatic effect and hence masking of the background over a wider angular range.

A dark background may be provided under the liquid crystal layer, in particular on the opposite side of the support. Alternatively, the dark background may be provided on the liquid crystal layer, including the same side of the support. This dark background can be obtained by printing a dye, or a pigment (absorbent or interferential). As a variant, the dark background is obtained by metallization, in particular under vacuum or electrochemically or by any other technique for depositing a metal, a metal oxide or a metal oxide salt. The dark background may also be carried by an additional support, preferably comprising PET, fixed to the support by any appropriate means, in particular by lamination by means of an adhesive. If necessary, the additional support is preferably attached to the support on the side of the liquid crystal layer.

Preferably, the dark background is superimposed at least partially on the liquid crystal layer.

The dark background is preferably arranged in a manner marked with respect to the printing of the liquid crystals; in particular, the dark background can be superimposed exactly on the liquid crystals.

The dark background can be achieved before or after the application of the liquid crystal.

The dark background may have a transmission rate of less than 80%, and is preferably opaque.

The adhesion primer is preferably transparent. The invention further relates, in another of its aspects, to a security element for secure document, in particular obtained by means of a method according to the invention as dein ini above, comprising:

at. a thermoplastic support stretched,

b. an adhesion primer on the surface of the support,

vs. at least one layer of liquid crystals, especially cholesteric, deposited by printing on the adhesion primer.

The security element may comprise an impression of at least two liquid crystal inks, preferably without overlapping between them.

The adhesion of the liquid crystal layer to the support measured according to the Tesa test described below is preferably equal to 2.

Preferably, the liquid crystal layer is in the form of patterns, in particular alphanumeric.

The invention also relates to a method for authenticating a security element according to the invention, comprising observing the element so as to determine whether a goniochromatic effect is observed for incidences greater than or equal to 70 ° and the step of generating authenticity information based at least on this observation.

The authentication method may include observing the element through a polarizing filter to highlight the orientation of the support and the adhesion primer and the step of generating information about the authenticity on the basis at least of this observation.

The invention will be better understood on reading the following description, non-limiting examples of implementation thereof, and on examining the appended drawing, in which:

FIG. 1 represents a view from above of a security element according to the invention,

FIG. 2 is a longitudinal section along Π-Π of FIG. 1,

FIG. 3 represents a detail of embodiment of the element,

FIG. 4 is a view similar to FIG. 1 of an alternative embodiment,

FIG. 5 is a longitudinal section of the element of FIG. 4, FIG. 6 is a view similar to FIG. 3 of an alternative embodiment of the element,

FIG. 7 illustrates various steps of an exemplary method according to the invention,

FIG. 8 represents an example of a secure article incorporating a secure element according to the invention, and

- Figure 9 is a diagram illustrating the measurement of the "Haze" described below. In the drawing, the real proportions have not always been respected for the sake of clarity.

FIGS. 1 to 3 show a security element 10 according to the invention, comprising a support 11, a primer 12 and a liquid crystal layer 13 deposited by printing on the primer 12.

The layer 13 is formed by two impressions 13a, 13b without overlapping them, of different colors. In the example of Figures 1 to 3, the prints 13a and 13b together do not cover the entire surface of the face 1a of the support. There thus remains around the prints of the zones 14 that can be used by other security means, such as for example a layer, in particular an ink, fluorescent or opaque.

In the example of Figures 4 to 6, the prints 13a and 13b together cover the entire face 1a of the support.

In order to improve the visibility of the liquid crystal, the prints are advantageously carried out in superposition with an opaque background, preferably dark or reflecting, for example black.

By way of example, FIG. 6 shows the presence of a dark background in the form of an opaque layer 15 on the support 11, on the opposite side to the layer 13 of liquid crystals. The opaque layer 15 is for example an impression of a black ink or a metallization.

The embodiment of the layer 15 is carried out for example after deposition of the liquid crystal layer 13.

According to an alternative embodiment of FIG. 6, the opaque layer 15 is present on the layer 13 of liquid crystals on the same side of the support. The observation of the security element is then from the side of the support opposite the layer 13 of liquid crystal.

Support

The support is made of a stretchable thermoplastic material.

Preferably, the support is made of PET, polypropylene or polyethylene.

In order to improve the durability of the security element, an additional support, preferably comprising PET, is fixed to the support by any appropriate means, in particular by lamination by means of an adhesive.

The additional support is preferably attached to the support on the side of the liquid crystal layer. In a variant for improving the cohesion of the sandwich thus formed, the liquid crystal layer is preferably in the form of patterns, and covers for example less than 50% of the surface of the support. The adhesion between the support and the additional support is thus reinforced.

Liquid crystals

Preferably, the liquid crystals are cholesteric liquid crystals

(CLC). Alternatively, the liquid crystals are nematic liquid crystals.

Many liquid crystal inks currently exist on the market and can be used. The ink can be a mixture of cholesteric and nematic liquid crystals, in a ratio chosen according to the desired color variation.

Primary membership

The adhesion primer increases the adhesion of the liquid crystals to the support without preventing the support from participating by its intrinsic structure in the orientation of the liquid crystals.

The adhesion primer comprises one or more polymers.

The primer can be applied in the form of monomers, especially olefin

(or alkene), urethane, ester, ether, carbonate or acrylic, preferably acrylic, on the support and this application is then followed by crosslinking, for example by exposure to UV radiation.

Preferably, the chemical nature of the primer is chosen to have the best affinity with the liquid crystal ink used. Thus, since many liquid crystal inks are based on acrylate monomers, it is preferred to use a primer based on acrylate monomers as well. The amount of primer that is deposited is chosen so that the thickness of the deposit remains low enough that the structure of the underlying support remains active vis-à-vis the orientation of the liquid crystal.

The thickness of the primer is thus preferably less than 1000 nm, more preferably 100 nm.

Orienting the support with the primary already present on it can be used to orient the primary and thus allow a greater removal of primer.

Other means of securing

The security element may comprise, in addition to the liquid crystals, any other security means selected from those of first, second or third levels.

It can be:

- patterns appearing in transmitted light and formed by metallization and / or demetallization,

dyes, luminescent pigments, interferential pigments, in particular in printed form or mixed with at least one constituent layer of the security element,

- Photochromic or thermochromic compounds, dyes and / or pigments, in particular in printed form or mixed with at least one constituent layer of the security element,

ultraviolet (UV) absorber, especially in the form coated or mixed with at least one constituent layer of the security element,

multilayer interference structure

a refractive, birefringent or polarizing layer,

a diff action structure,

means producing a "moiré effect", such an effect being able for example to reveal a pattern produced by the superimposition of two security means, for example by bringing lines of two security means closer together,

- a colored filter.

- an automatically readable security having specific and measurable luminescence characteristics (eg fluorescence, phosphorescence), light absorption (eg ultraviolet, visible or infrared), Raman activity, magnetism, micro interaction wave, X-ray interaction or electrical conductivity. Security element

The security element according to the invention is advantageously a security thread, a foil, a patch or a variable data protection film. It may still be a card or a film of protection or inviolability.

In the case of a security element consisting of a security thread, it can be integrated in windows to a security paper such as a banknote 30, as shown in Figure 8. The security element then extends from one edge 31 to the other 32 of the document.

When the security element is in wire form, its width is for example between 1 and 10 mm and its thickness between 10 and 100 μηι.

In the case of a foil, the security element is applied by transfer to the surface of a paper, a film or a card for example.

By "patch" is meant a film that does not cover the entire surface of the underlying substrate.

Manufacturing process

According to the invention, the method comprises, as illustrated in Figure 7, a step 21 for producing a plastic film, for example by extrusion. This film can be monolayer or multilayer.

It undergoes at least one stretching step 22, which allows it to be oriented in a first direction. This is for example a first stretch in the longitudinal direction (still called direction).

Then, the adhesion primer is applied to a step 23, then the film is stretched again, in a direction different from the first, for example in the transverse direction (also called cross direction), in a step 24.

Finally, the liquid crystals are deposited by printing in step 25 on the film thus stretched and coated with the adhesion primer.

The orientation of the liquid crystals is during the evaporation of the solvent present in the ink used. This evaporation is preferably done by "airborne" drying (air flow in English), preferably horizontally to promote the orientation of the liquid crystals. Preferably, the ink is crosslinkable under UV, and the crosslinking which follows the removal of the ink makes it possible to definitively fix this orientation. The printing is preferably carried out with a plurality of liquid crystal inks, which are preferably deposited without overlapping them. Inks can be deposited as flat or patterned. "Pattern" designates any pattern recognizable to the naked eye in particular, such as for example one or more alphanumeric characters, or the image of a subject such as a character, animal, object, landscape, plant or monument. It may be a halftone halftone pattern, preferably appearing in 3D due to a shading effect obtained by halftone reproduction of the pattern, which may be a repetitive pattern arranged in a given direction, in a pattern or preferably in a checker pattern.

The printing can be done by flexography, screen printing or gravure, among other printing techniques that can be used.

In a variant of the process, the film undergoes a double stretch in the forward and through directions after removal of the adhesion primer. This removal preferably takes place after a first stretch in the direction.

We can thus have the following sequence:

- stretching direction,

- removal of the primary,

- stretching through,

- stretching direction walk.

Authentication method

The authentication of a security element according to the invention can be carried out by observing the element so as to determine whether a goniochromatic effect is observed for incidences greater than or equal to 70 °, this effect being related to the presence of liquid crystal.

It is then possible to generate information regarding authenticity based at least on this observation.

The authentication may include observing the element through a polarizing filter to highlight the orientation of the support and the adhesion primer and the step of generating authenticity information about the basis at least of this observation.

The bi-orientation of the support can be verified by analyzing the birefringence of the film in a conventional manner. A linear polarizer, such as a filter to be placed on the security element, can be used, which is rotated through 90 ° to determine whether a darker aspect is shifted to a lighter aspect when rotating. Examples

The "Tesa" test mentioned hereinafter is an adhesion test of a layer deposited on a substrate, in which an adhesive tape is applied to the layer whose cohesion and adhesion to the substrate is to be measured.

A score of 0 to 2 is obtained according to the proportion of the layer tested which remains attached to the ribbon after its withdrawal:

- 0 denotes a total adhesion to the tape so no adhesion to the substrate of the tested layer

1 denotes a partial attachment to the ribbon and

- 2 denotes an absence of hanging tape so a better adhesion to the substrate of the tested layer.

Examples 1 to 3 (comparative ')

Several PET films are printed with a liquid crystal ink formulated with a mixture of three products, namely:

cholesteric liquid crystal: 5.29 g

nematic liquid crystals: 3.11 g

photoinitiator: 1.6 g

The mixture constitutes an ink with an acrylic base, comprising cholesteric and nematic liquid crystals.

The ratio chosen between the cholesteric and nematic liquid crystals gives the color; here we get a change from blue to green-yellow with the angle of observation.

The deposition of the liquid crystals takes place at a thickness of 3 microns, at the coating bar.

Drying under hot air blown to align the liquid crystal The ink is subjected to UV crosslinking.

Liquid crystals are observed in front of a dark background.

Chemical attack: treatment with an acidic solution creating a surface micro-roughness

** Goniochromatic effect: the observed parameters are: clear observation of the two colors, brightness of the colors and angle of the change of color.

Plasma treatment does not offer optimal adhesion but the alignment of the liquid crystals is correct.

The PET film treated by etching allows to have excellent adhesion but the optical effect is degraded.

Examples 4 (comparative) and 5 to 7 (according to the invention)

The deposition of the liquid crystals is carried out as in Examples 1 to 3 by means of a commercially available liquid crystal ink.

*** Offline: The application occurs after the stretching steps of the PET film. Online: The application takes place during the manufacture of the film between at least two stretching steps of the PET film.

The goniochromatic effect is surprisingly preserved for Examples 5 to 7, despite the presence of an intermediate primer layer between the biaxially oriented PET support which permits alignment and the liquid crystal layer.

The alignment of the liquid crystals is modified by the presence of the adhesion primer. The modification of this alignment makes it possible to increase the visibility of the color change effect, and to confer on the liquid crystal layer a translucency which makes it possible to limit the visibility of the black background.

The degree of translucency can be determined by the reflection "Haze" measurement according to ASTM D4039-09 and ISO13803. This is a measure of the veil, ie milky opalescence, a glossy or transparent top coating.

On quality surfaces (class A), we expect a picture with a clear and bright appearance. Microstructures can cause a milky appearance. This effect is called diffusion veil or "Haze". If microscopic and fine defects are present on a very bright surface, this leads to a diffusion of light of low intensity next to the main reflection. The preponderant part is reflected in the specular direction, the surface thus appears very bright and with an image rendering, but it is covered with a milky and cloudy veil.

The "haze" of the liquid crystal layer on a support according to the invention may be less than that of the liquid crystal layer on an untreated PET, which causes much less gloss than for the supported liquid crystal layer. standard. In addition, the reduction of the "Haze" increases the light diffusion of the liquid crystal layer and thus allows the observation of the goniochromatic effect over a larger range of angles. Thus, surprisingly, at "grazing" angles, the goniochromatic effect is maintained with a support according to the invention, whereas with a standard support, the liquid crystals are no longer visible and the dark background is observed, which is not desirable.

The "Haze", measured according to the ISO 13803: 2014 standard, of the films (1) and (6) is respectively 274 and 79. Such a measurement is illustrated in FIG. 9 on which the support to be measured 91 is illuminated according to a angle which is for example 20 ° for the above standard). The measurement of the "Haze" is done by means of the sensors 92 and corresponds to the intensity of the light rays 93, as opposed to the brightness which corresponds to the intensity of the specular ray 94 (angle -a).

In order to quantify the increase in the angular range of the goniochromatic effect, the maximum intensity in the wavelength range 400 - 700nm ("Intensity" in the table below) was measured at different angles of observation for illumination at an angle of 50 °, on samples (1) and (6). All the intensity measurements indicated in the table below are given in arbitrary unit corresponding to a given calibration, in particular the intensities of the samples (1) and (6) were measured with the same calibration.

It is noted that for grazing angles of observation, for example 10 °, 20 °, 70 ° and 80 °, the intensity of the sample 6 is greater than that of the sample 1, which indicates the visibility on a sample. wider angular range of the goniochromatic effect of the sample 6.

Claims

A method of manufacturing a security element comprising a support (11) of oriented plastic material and at least one layer of liquid crystal (13) carried and oriented by the support, an adhesion primer (12) being deposited before or after the stretching of the support at least in one direction, said stretching to bring the support in the oriented state and the liquid crystals being deposited by printing on this adhesion primer.

2. Method according to claim 1, the adhesion primer (12) being deposited before a step of stretching the support (11).

3. Method according to claim 1 or 2, the support comprising PET.

4. Method according to any one of claims 1 to 3, said method further comprising a step of crosslinking the adhesion primer, preferably after said stretching of the support.

5. Method according to any one of claims 1 to 4, the adhesion primer comprising a polyolefin, a polyurethane, polyester, polyether, polycarbonate, polyacrylic or a copolymer thereof.

6. The method of claim 5, the adhesion primer comprising a polyacrylic.

7. The method of claim 4, the adhesion primer comprising, in particular before its deposition, at least one urethane monomer, ester, ether, carbonate or acrylic.

8. Process according to any one of the preceding claims, the printing of the liquid crystals being carried out by screen printing, gravure printing or flexography.

9. Method according to any one of the preceding claims, the liquid crystals being deposited after stretching of the support.

10. A method according to any one of the preceding claims, comprising printing on the adhesion primer two different inks, at least one of which comprises cholesteric liquid crystals, the better both comprise cholesteric liquid crystals.

11. A method according to any one of the preceding claims, the diffusion fog effect of the cholesteric liquid crystal layer being lower than that of a reference security element without the adhesion primer layer.

The method of any one of the preceding claims, having a dark background under the liquid crystal layer.

13. Method according to any one of the preceding claims, the adhesion primer being transparent.

Security element (10) for secure document, in particular obtained by means of a method according to any one of the preceding claims, comprising:

at. a support (11) of stretched thermoplastic material,

b. an adhesion primer (12) on the surface of the support,

vs. at least one layer (13) of liquid crystal deposited by printing on the adhesion primer.

15. Security element according to claim 14, comprising an impression of at least two liquid crystal inks, preferably without superposition between them.

16. Security element according to claim 14 or 15, the adhesion of the liquid crystal layer on the support measured according to the Tesa test being equal to 2.

17. Security element according to any one of claims 14 to 16, the cholesteric liquid crystal layer being in the form of a pattern, in particular alphanumeric.

18. Security element according to any one of claims 14 to 17, further comprising a dark background.

19. A method of authenticating a security element according to any one of claims 14 to 18, comprising observing the element so as to determine whether a goniochromatic effect is observed for incidences greater than or equal to 70 ° and the step of generating authenticity information based at least on this observation.

20. A method of authenticating a security element according to any one of claims 14 to 18, comprising observing the element through a polarizing filter in order to highlight the orientation of the support and of the adhesion primer and the step of generating authenticity information based at least on this observation.