METHOD FOR MANUFACTURING A MULTILAYER DATA MEDIUM WITH REFLECTING METALLISED INSCRIPTIONS

Abstract

Disclosed is a method for manufacturing a multilayer data medium having reflecting metallised inscriptions (23) visible from at least one outer surface (11). A basic pattern (24) is imprinted onto a transparent impression layer (21), the pattern being selected so as to be able to receive the inscriptions (23), to be transparent and to have a surface tension of more than 40 dynes/cm and a smooth surface condition with specular reflection of more than 50% measured according to the ISO 2813 standard at an angle of 60, and no glass-transition temperature in the rolling temperature range; then the inscriptions (23) are imprinted in contact with the basic pattern (24), and then hot rolling under pressure of a stack including the impression layer (21) is carried out.

Claims

1. Method of manufacturing a multilayer data medium (10) by hot rolling under pressure of a stack of a plurality of superimposed layers comprising at least one layer of at least one thermoplastic material, said multilayer data medium having inscriptions, named reflecting metallised inscriptions (23), having a metallic appearance, being at least partially reflective and visible from at least one outer surface (11) of said multilayer data medium (10), said hot rolling being effected in a temperature range, named rolling temperature range, wherein: one surface, named impression surface (22), of at least one transparent layer, named impression layer (21), of said stack is imprinted with a varnish composition in a pattern, named the basic pattern (24), selected to be able to receive said reflecting metallised inscriptions (23), said varnish composition being selected in orderafter curingto be transparent and to have: a surface tension of more than 40 dynes/cm and a smooth surface condition with specular reflection of more than 50% measured according to the ISO 2813 standard at an angle of 60, no glass-transition temperature in the rolling temperature range, said reflecting metallised inscriptions (23) are imprinted in contact with said basic pattern (24) of said impression layer with a composition of metallised ink comprising a curable binder incorporating discrete particles, named the reflecting metallised particles, in the general form of platelets dispersed in the curable binder having a grain size selected to form pigments having a metallic, at least partially reflecting, appearance, then said stack is formed, comprising said impression layer (21), said impression surface (22) being opposite to said outer surface (11) and having said reflecting metallised inscriptions (23) applied thereto in contact with another adjacent layer (19) of the stack, then this stack is hot rolled under pressure.

2. Method according to claim 1, wherein at least a part of said reflecting metallised inscriptions (23) is imprinted with a mark width less than 500 m.

3. Method according to claim 1, wherein an impression layer (21) is used, being of a material selected from the group of transparent thermoplastic materials and transparent synthetic papers.

4. Method according to claim 1, wherein an impression layer (21) is used, being of a material selected from the group of transparent polycarbonates, transparent polyesters and transparent PVC.

5. Method according to claim 1, wherein said basic pattern (24) is imprinted using a varnish composition selected from the group of ultraviolet-curing transparent acrylic varnishes and volatile solvent-based transparent varnishes containing acrylic binders and at least one curing agent.

6. Method according to claim 1, wherein a metallised ink composition is used, comprising reflecting metallised particles selected from vacuum-metallised pigments and reflecting metallised particles.

7. Method according to claim 1, wherein a metallised ink composition is used, comprising reflecting metallised particles having an average grain size between 8 m and 11 m.

8. Method according to claim 1, wherein reflecting metallised inscriptions (23) are imprinted on the basic pattern (24) with a peripheral overhang (26) of the basic pattern (24) with respect to the reflecting metallised inscriptions (23).

9. Multilayer data medium comprising a plurality of layers superimposed by hot rolling under pressure, comprising at least one layer of at least one thermoplastic material, said multilayer data medium having inscriptions, named reflecting metallised inscriptions (23), having a metallic appearance, being at least partially reflective and visible from at least one outer surface (11) of the multilayer data medium (10): wherein said reflecting metallised inscriptions (23): are formed of an imprinted metallised ink comprising a cured binder incorporating discrete particles, named reflecting metallised particles, generally in the form of platelets dispersed in the binder with a grain size forming pigments having a metallic, at least partially reflecting, appearance, are imprinted in contact with a basic pattern (24) imprinted on a transparent layer, named impression layer (21), said basic pattern (24) being formed of a transparent varnish having: a surface tension of more than 40 dynes/cm and a smooth surface condition with specular reflection of more than 50% measured according to the ISO 2813 standard at an angle of 60, no glass-transition temperature lower than 200 C.

10. Medium according to claim 9, wherein at least a part of said reflecting metallised inscriptions (23) has a mark width less than 500 m.

11. Medium according to claim 9, wherein at least a part of said reflecting metallised inscriptions (23) has a mark width less than 200 m.

12. Medium according to claim 9, wherein said impression layer (21) is of a material selected from the group of transparent thermoplastic materials and transparent synthetic papers.

13. Medium according to claim 9, wherein said impression layer (21) is of a material selected from the group of transparent polycarbonates, transparent polyesters and transparent PVC.

14. Medium according to claim 9, wherein layers (12, 19, 20, 21) are formed of at least one material selected from the group of thermoplastic materials and synthetic papers.

15. Official document comprising a data medium according to claim 9, of which at least one outer surface (11) has reflecting metallised inscriptions (23).

16. Method according to claim 2, wherein an impression layer (21) is used, being of a material selected from the group of transparent thermoplastic materials and transparent synthetic papers.

17. Method according to claim 2, wherein an impression layer (21) is used, being of a material selected from the group of transparent polycarbonates, transparent polyesters and transparent PVC.

18. Method according to claim 3, wherein an impression layer (21) is used, being of a material selected from the group of transparent polycarbonates, transparent polyesters and transparent PVC.

19. Method according to claim 2, wherein said basic pattern (24) is imprinted using a varnish composition selected from the group of ultraviolet-curing transparent acrylic varnishes and volatile solvent-based transparent varnishes containing acrylic binders and at least one curing agent.

20. Method according to claim 3, wherein said basic pattern (24) is imprinted using a varnish composition selected from the group of ultraviolet-curing transparent acrylic varnishes and volatile solvent-based transparent varnishes containing acrylic binders and at least one curing agent.

Description

[0041] Other aims, features and advantages of the invention will become clear upon reading the following description of different embodiments of the invention given in a non-limiting manner and referring to the attached figures in which:

[0042] FIGS. 1a and 1b are schematic cross-sectional views of an impression layer of a multilayer data medium in accordance with the invention, respectively at the end of two steps of imprinting a basic pattern and reflecting metallised inscriptions, of a method in accordance with the invention,

[0043] FIG. 2 is a schematic cross-sectional view of a multilayer data medium in accordance with the invention at the end of the hot rolling under pressure step of a method in accordance with the invention,

[0044] FIG. 3 is a schematic top view of an example of a data medium in accordance with the invention.

[0045] In the figures, for the sake of illustration, the relative scales and dimensions have not been respected. In particular, the thicknesses are shown in an exaggerated fashion.

[0046] FIG. 2 shows an example of a data medium 10 in accordance with the invention at the end of a hot rolling under pressure step and ready for use, being suitable for undergoing personalising laser marking in order to obtain an official document in accordance with the invention. This data medium 10 is formed of a stack of a plurality of layers superimposed one on another and having been subjected to hot rolling under pressure. The majority of the layers are preferably formed of a thermoplastic material, in particular selected from among polycarbonates, PVCs, polyesters (polyethylene terephthalate PET, polyethylene terephthalate glycol PETG), and co-extruded films of polyester and polycarbonate (PEC). In some advantageous embodiments, in particular for applications of the bank card, identity card or transport card type, the data medium 10 is formed of a plurality of polycarbonate layers. There is nothing to prevent the data medium incorporating layers of different materials, including layers of a material other than a thermoplastic material, e.g. paper, more particularly synthetic paper. The total number of layers making up a data medium 10 in accordance with the invention is of no significance within the scope of the present invention.

[0047] The data medium 10 is in the general form of a sheet or card and thus has two opposing outer planar main surfaces and a relatively small thickness. Throughout the following, only a main surface, named the outer surface 11, is described and has the features of the invention, it being understood that the other outer, main surface can equally have the same features or, in contrast, can have other features. Consequently, it is assumed throughout the following that the surface opposite the outer surface 11 in question is an outer main surface of a base 12 illustrated in cross-section in FIG. 2, without this implying any limitation whatsoever, such a base 12 possibly not being present and/or itself being formed of a layer or a plurality of layers of various thicknesses, not described in this description.

[0048] In particular, the base 12 can be formed of at least one layer of thermoplastic material selected from among polycarbonates, PVCs, polyesters (polyethylene terephthalate PET, polyethylene terephthalate glycol PETG), co-extruded films of polyester and polycarbonate (PEC), synthetic papers (in particular selected from among the paper sold under the trade mark Teslin by the company PPG, Monroeville, USA, the paper sold under the trade mark Neobond by the company Neenah Lahnstein, Lahnstein, Germany, and the paper sold under the trade mark Polyart by the company Arjobex, Boulogne, France). Other examples are possible.

[0049] The outer surface 11 of the data medium 10 has different markings representing information (common details) and/or constituting security markings intended to reinforce resistance to attempted forgery and/or to prevent reproduction by optical reading. The data medium 10 comprises in particular reflecting metallised inscriptions 23, i.e. in the example illustrated in FIG. 3, marking 23a in the form of guilloch, and marking 23b in the form of a compass dial. Of course, numerous other examples are possible.

[0050] In the embodiment illustrated in FIG. 2, the data medium 10 comprises, starting from the base 12: [0051] a basic layer 19 which can be formed e.g. by an opaque white block (contrasting with all the coloured, dark or black inscriptions optically superimposed on this basic layer on the side of the outer surface 11), [0052] a laser-marked sub-layer 20 sensitive to marking laser radiation, in particular infrared laser radiation, e.g. at 1064 nm, so as to permit the production of personalising marking in at least a part of the thickness of this laser-marked sub-layer 20 under the effect of this laser radiation applied from the outer surface 11, [0053] a transparent impression layer 21 placed overlapping and in contact with the whole of the surface of the laser-marked sub-layer 20. The outer surface 11 is formed by the impression layer 21.

[0054] The multilayer data medium 10 is manufactured by hot rolling under pressure of a stack of these different layers, the features of this lamination step being selected depending on the nature and features of the different constituent layers of the stack. For example, in the case where the different layers are formed of polycarbonate, the hot rolling under pressure can be effected in a rolling press under the following conditions: [0055] 1 min. rising to 180 C. [0056] 12 min. at 180 C. under 30 N/cm.sup.2 [0057] 5 min. at 180 C. under 150 N/cm.sup.2 [0058] cooling to 26 C. for 17.5 min. under 180 N/cm.sup.2.

[0059] Thus, this hot rolling under pressure has a rolling temperature range between 20 C. and 180 C. Of course, numerous other values and conditions for hot rolling under pressure are possible.

[0060] The laser-marked sub-layer 20 can extend in the form of a continuous block of colour in the format of the outer surface 11 (except for possible peripheral shrinkage); or, in contrast, it can be applied in the form of a plurality of distinct, separate portions, at least facing locations intended to receive laser marking, or only facing these locations. It can be formed of a thickness of a varnish imprinted with an ink composition incorporating a marking agent sensitive to the laser radiation and/or be selected from among the films sold in a state ready to be laser-marked, e.g. a film sold under the name Makrofol ID 6-2 laserable by the company Bayer Materials Science, Leverkusen, Germany.

[0061] The reflecting metallised inscriptions 23 are produced by imprinting on a transparent basic pattern 24 which is itself imprinted on the impression layer 21 incorporated into a stack of layers used to form the multilayer data medium 10 by hot rolling under pressure.

[0062] The impression layer 21 can be formed e.g. by a transparent thermoplastic material, in particular selected from among polycarbonates, PVCs, polyesters (polyethylene terephthalate PET, polyethylene terephthalate glycol PETG), and co-extruded films of polyester and polycarbonate (PEC). The same is true of the various other constituent layers of the multilayer data medium 10.

[0063] The method of manufacturing the data medium 10 of FIG. 2 comprises the following successive steps.

[0064] In the first step shown in FIG. 1a, a transparent basic pattern 24 is imprinted on one surface, named the impression surface 22, of the two surfaces of the impression layer 21, with shapes and dimensions selected to be able to receive all the reflecting metallised inscriptions 23.

[0065] In a preferred manner, and taking account of the fact that the basic pattern 24 must have a peripheral overhang 26 around the reflecting metallised inscriptions 23, these inscriptions being able to be produced in the form of narrow lines, in particular micro-printing, the basic pattern 24 is preferably imprinted in the form of at least one block of colour in the format of an enclosing contour for each surface zone comprising reflecting metallised inscriptions 23. For example, when the reflecting metallised inscriptions 23 are guilloch patterns, the transparent basic pattern 24 is imprinted in the format of the enclosing contour of these guilloch patterns with a peripheral overhang 26 around this enclosing contour.

[0066] The basic pattern 24 is imprinted with a varnish composition permitting a transparent varnish finishing layer to be formed, having an extremely smooth surface 25 with high surface tension, i.e. free of surface flaws (such as an orange peel effect, fish eyes or pin holes) and adapted to have a surface tension of more than 40 dynes/cm and a smooth surface condition with specular reflection of more than 50% measured according to the ISO 2813 standard at an angle of 60.

[0067] Furthermore, a varnish composition is selected which is free, after curing, of any glass-transition detectable by differential thermal analysis in said rolling temperature range.

[0068] In order to do this, it is possible to use an ultraviolet-drying varnish composition or acrylic solvent-based varnish composition, having more than 90% transparency and being very glossy, e.g. such as that sold under the name UVLG6 by the company Marabu (www.marabu-druckfarben.de). Other examples are possible since the varnish composition can be imprinted on the impression surface 22 of the impression layer 21, it is transparent, it has the surface condition mentioned above and no glass-transition temperature which can be detected in the rolling temperature range.

[0069] This layer of transparent varnish forming the basic pattern 24 can be tinted and/or cover a layer of tinted varnish previously produced (not shown in the figures), permitting the metallic effect obtained to be modified. In order to do this, it is possible to use an ultraviolet-drying transparent varnish composition such as mentioned above, in which 1% to 25% of an ultraviolet-drying ink, e.g. a yellow coloured ink or one such as sold by the company Tiflex (Poncin, France) under the reference 3*5559 is added. Of course, numerous other examples are possible.

[0070] In the second step, illustrated in FIG. 1b, the reflecting metallised inscriptions 23 are imprinted on the smooth surface 25 of the basic pattern 24. In order to do this, e.g. a composition of reflecting metallised ink as indicated e.g. by WO 2010/125316 or U.S. Pat. No. 8,526,086 is used. Thus a reflecting metallised ink composition is used, comprising a filler of reflecting metallised particles having a reflecting metallic appearance, dispersed in a curable binding composition which can be formed of a traditional transparent imprinting ink, e.g. a transparent solvent-based ink composition sold by the company Mistral Graphic (Carcassonne, France). The reflecting metallised ink layer is imprinted like a traditional ink layer, on the surface 25 of the varnish layer forming the pattern 24 from low to high surface tension and having a very smooth surface, in particular a surface tension of more than 40 dynes/cm and a smooth surface condition with specular reflection of more than 50% measured according to the ISO 2813 standard at an angle of 60.

[0071] Said filler of reflecting metallised particles can incorporate particles generally in the form of platelets, e.g. in the form of petals, chips or shards, which have themselves previously been manufactured by vacuum metallisation. Such particles can be obtained by vacuum sublimation and metallic aluminium vaporisation on a medium such as a polyester film, the fine aluminium layer obtained then being detached from the medium then ground to the desired grain size, in particular between 8 m and 11 m, with a thickness of the order of 300 Angstroms corresponding to that of the deposited aluminium layer.

[0072] As a variation, or in combination, the metallised particle filler can incorporate metallised particles selected from among the composition of metallised pigments sold under the name Xymara Metasheen by the company Ciba (Basel, Switzerland), and the composition of metallised pigments sold under the name StarBrite by the company Silberline (Leven, United Kingdom).

[0073] These reflecting metallised particles are used in sufficient quantity in the imprinting composition to obtain, depending on the imprinting process used, the desired reflecting effect after imprinting and curing. For example, in the case of screen printing, the quantity of metallised filler particles in the imprinting composition is between (proportions by volume) 5% and 15%, in particular of the order of 10%.

[0074] Such a layer of metallised ink is reflective and opaque and can as such have properties similar to those of vacuum deposition of metal. For example, it makes it possible to increase by the order of 80% the optical reflecting power of visible light of the film. However, it should be noted that the invention makes it possible to precisely adjust the reflection and opacity properties of this reflecting metallised ink layer according to different values depending on the application. By decreasing the quantity of the metallised particle filler, the reflectivity and opacity of the reflecting metallised inscriptions 23 is decreased. In contrast, by increasing the quantity of this filler, the reflectivity and opacity are increased.

[0075] In order to obtain a coloured mirror effect in the reflecting metallised inscriptions 23 it is possible to use an imprinting composition comprising a cured binder incorporating at least one dye which is soluble in organic solvents such as those sold by CIBA (Basel, Switzerland) under the name Ciba OROSOL.

[0076] A silver mirror effect is obtained without addition of dyes to the imprinting composition comprising the reflecting metallised particles. In order to obtain a golden appearance, yellow-orange-tinted dyes are used; in order to obtain a chrome-like appearance, blue-tinted dyes are used; in order to obtain a nickel-like appearance, green-tinted dyes are used; and in order to obtain a copper-like appearance, red-orange-tinted dyes are used.

[0077] Furthermore, the reflecting metallised particles have average dimensions suitable for permitting imprinting according to the chosen imprinting method with the precision and quality required. In an advantageous manner, the metallised particles have an average grain size between 8 m and 11 m with, in the case of platelets, a thickness of the order of 300 Angstroms.

[0078] Moreover, it is noted that the imprinting of a layer of reflecting metallised ink comprising a filler of reflecting metallised particles in the general form of platelets on the surface 25 of the basic pattern 24 which is very smooth and has high surface tension causes, in spite of the very small dimensions of these reflecting metallised particles, the spontaneous coating of the different particles in parallel with the surface, considerably increasing the reflecting effect obtained. In this way, for the same optical effect, it is possible to reduce the filler quantity of metallised particles, which facilitates the operations involving the imprinting of the reflecting metallised inscriptions 23.

[0079] The reflecting metallised inscriptions 23 can be produced at least in part with a very high level of fineness, in particular with a mark width less than 500 mpreferably less than 200 me.g. of the order of 100 m to 150 m.

[0080] Furthermore, as indicated above, the reflecting metallised inscriptions 23 are imprinted with the provision of a peripheral overhang 26 of the basic pattern 24 around the reflecting metallised inscriptions 23, i.e. preferably around an enclosing contour thereof. This peripheral overhang 26 is e.g. between 0.5 mm and 3 mm, in particular of the order of 2 mm.

[0081] The imprinting of the basic pattern 24 and that of the reflecting metallised inscriptions 23 can be effected by any imprinting technique, e.g. one selected from screen printing, photogravure, flexography, offset printing or the like.

[0082] At the end of this second imprinting step, a layer formed by the transparent impression layer 21 is obtained, bearing the basic pattern 24 and the reflecting metallised inscriptions 23 as shown in FIG. 1b. This layer can be used in a stack subjected to hot rolling under pressure to form the multilayer data medium 10, in the manner of any other layer of this stack.

[0083] In the example illustrated in FIG. 2, the different layers 12, 19, 20 and 21 are stacked one on another with the laser-marked sub-layer 20 interposed between the basic layer 19 and the impression layer 21, and are hot rolled under pressure in a rolling press, the total thickness of the stack decreasing by about 10%, to obtain the multilayer data medium 10 as shown in FIG. 2, ready for use in order to undergo personalising marking by laser radiation.

[0084] It is noted that the reflecting metallised inscriptions 23 are visible, as seen from the outer surface 11 through the thickness of the transparent impression layer 21 and through the transparent basic pattern 24, with a very pleasing reflecting and metallised effect.

[0085] The invention makes it possible in particular to forgo any vacuum metallisation step, and the impression layer 21 can be any thermoplastic material covering layer of a multilayer data medium 10 without itself having to have specific surface features (surface tension, surface condition . . . ). It will suffice for the impression layer 21 to permit imprinting of the basic pattern 24 with transparent varnish.

EXAMPLE 1

[0086] On one of the surfaces of two sheets of polycarbonate, 100 m in thickness, of the trade mark Makrofol ID 6-2 sold by the company Bayer Materials, Leverkusen, Germany, a basic pattern 24 is imprinted using a transparent varnish sold under the reference UVLG6 by the company MARABU (France) in the format of the enclosing contour of the reflecting metallised inscriptions 23 to be produced in accordance with FIG. 3, with a peripheral overhang (not shown in FIG. 3, the varnish being transparent) of 2 mm of the basic pattern 24 all around this enclosing contour. The layer of varnish of the basic pattern 24 is imprinted with a screen printing screen produced from a fabric with a mesh size of 150 threads/cm, the threads having a diameter of 34 m.

[0087] A glass-transition temperature measurement by differential thermal analysis does not permit a glass-transition temperature of the basic pattern 24 thus formed to be detected after curing thereof.

[0088] After curing of the basic pattern 24, the reflecting metallised inscriptions 23 are imprinted with a reflecting metallised ink composition sold under the reference 3Y2656 by the company Tiflex (Poncin, France). In order also to obtain a coloured reflecting metallised effect, 2% to 10% of dye are added to this reflecting metallised ink composition.

[0089] The reflecting metallised inscriptions 23 are imprinted with a screen printing screen made of a fabric of which the mesh size comprises 120 threads/cm, the threads being of a diameter of 34 m. The guilloch 23a is formed by lines having a width between 100 m and 150 m.

[0090] It should be noted that the metallised inscriptions 23 thus imprinted are reflective, seen by transparency from the side of the surface of the polycarbonate sheets which is opposite to the impression surface 22 but that the free surfaces thereof seen from the same side as the impression surface 22 are not reflective.

[0091] The imprinted polycarbonate sheets are associated with three other polycarbonate sheets interposed between the imprinted polycarbonate sheets so as to form a stack, the imprinted surfaces being placed in contact with the underlying sheets of the stack, i.e. not constituting outer surfaces thereof. The five polycarbonate sheets forming, with the two imprinted sheets, said stack are successively the following: a sheet of 200 m white polycarbonate, a sheet of 200 m white polycarbonate; a sheet of 200 m white polycarbonate.

[0092] The sheet assembly forming this stack is rolled in a rolling press under the following conditions: [0093] 1 min. rising to 180 C. [0094] 12 min. at 180 C. under 30 N/cm.sup.2 [0095] 5 min. at 180 C. under 150 N/cm.sup.2 [0096] cooling to 26 C. for 17.5 min. under 180 N/cm.sup.2.

[0097] A multilayer data medium 10 is obtained in the form of a card, the total thickness of which is equal to the sum of the thicknesses of the polycarbonate sheets used, decreased by about 10%.

[0098] It is noted that the reflecting metallised inscriptions 23 retain their metallised and reflecting appearance as seen from the side of the outer surface 11 of the multilayer data medium 10 and that their fineness is in no way adversely affected by the hot rolling under pressure. No smudging or other deformation is perceived.

COMPARATIVE EXAMPLE 2

[0099] The same method as in example 1 above is carried out, replacing the varnish composition forming the basic pattern 24 with a varnish composition sold under the name Ultraflex by the company Marabu (France, www.marabu.com). After curing, this varnish has a surface condition suitable for receiving the reflecting metallised inscriptions but a glass-transition temperature Tg between 20 C. and 60 C., detectable by differential thermal analysis.

[0100] After hot rolling under pressure of the different constituent layers of the stack, it is noted that the multilayer data medium obtained has reflecting metallised inscriptions but with deformation and thickening of the lines.

COMPARATIVE EXAMPLE 3

[0101] The same method as in example 1 above is carried out, replacing the varnish composition forming the basic pattern 24 with a varnish composition sold under the name Marastar SR by the company Marabu (France, www.marabu.com). After curing, this glossy varnish has a surface condition suitable for receiving the reflecting metallised inscriptions but a glass-transition temperature Tg between 55 C. and 65 C., detectable by differential thermal analysis.

[0102] After hot rolling under pressure of the different constituent layers of the stack, it is noted that the multilayer data medium obtained has reflecting metallised inscriptions but with deformation and thickening of the lines.

COMPARATIVE EXAMPLE 4

[0103] The same method as in example 1 above is carried out but without using the basic pattern 24, the reflecting metallised inscriptions 23 being directly imprinted on sheets of a polycarbonate film such as that sold under the name Makrofol ID1-4 by the company Bayer MaterialScience (Leverkusen, Germany). These polycarbonate sheets have a smooth surface with specular reflection of more than 98% measured according to the ISO 2813 standard at an angle of 60 and a surface tension of more than 40 dynes/cm.

[0104] After imprinting and curing the reflecting metallised inscriptions on these polycarbonate sheets with the same composition of reflecting metallised ink as in example 1 and incorporation thereof into the stack then hot rolling under pressure of the different constituent layers of the stack, it is noted that the metallised inscriptions have lost their reflecting effect.

[0105] It goes without saying that the invention can cover numerous variant embodiments and applications other than those described above and illustrated in the figures. In particular, the reflecting metallised inscriptions 23 can be used in different forms and in different applications including to produce holographic patterns.