Method for producing tamper-proof identification elements

The invention relates to a method for the production of counterfeit-proof identification features which have a color shift effect caused by metallic clusters which are separated from a mirror layer by a defined transparent layer.

Out <patcit id="pcit0001" dnum="WO0218155A"><text>WO 02/18155</text></patcit> A method is known for the counterfeit-proof marking of objects, wherein the object is applied with a marking consisting of a first layer reflecting electromagnetic waves to the one inertial layer, which is permeable to electromagnetic waves, with a defined thickness, whereupon this inert layer is formed from metallic clusters Third layer. <patcit id="pcit0002" dnum="WO0153113A"><text>WO 01/53113</text></patcit> Describes optically variable security elements which have an angle-dependent color shifting effect, the construction consisting essentially of a reflector layer, a dielectric layer and an absorber layer. <patcit id="pcit0003" dnum="WO02051646A"><text>WO 02/051646 A</text></patcit>) Describes a decorative film which is constructed as a layer composite and has a transparent base film, a transparent cover layer and a transparent dielectric transparent layer arranged therebetween. A metal layer is arranged at least partially between the dielectric layer and the cover layer.

The object of the invention is to provide a method for the production of counterfeit-proof identification features on flexible materials, wherein the counterfeiting security is provided by a visible color change under different viewing angles (tilting effect), which is also to be machine-readable. The production process is to be unambiguously coded in the machine-read spectrum.

The invention relates to a method for the production of counterfeit-proof identification features consisting of at least one electromagnetic wave reflecting layer, an optically transparent spacer layer and a layer formed by metallic clusters.

The further essential features of the invention are defined in independent claims 1 to 3.

Suitable carrier substrates are preferably flexible plastic films, for example of PI, PP, MOPP, PE, PPS, PEEK, PEK, PEI, PSU, PAEK, LCP, PEN, PBT, PET, PA, PC, COC, POM, ABS, PVC . The carrier films preferably have a thickness of 5 to 700 μm, preferably 8 to 200 μm, particularly preferably 12 to 50 μm. Furthermore, metal foils, for example Al-, Cu-, Sn-, Ni, Fe or stainless steel films with a thickness of 5-200 μm, preferably 10-80 μm, particularly preferably 20-50 μm, can also be used as carrier substrate. The films can also be surface-treated, coated or laminated, for example with plastics, or lacquered. In addition, carrier-free substrates, such as cellulose-free or cellulose-containing paper, thermo-activatable paper or composites with paper, for example composites with plastics having a basis weight of 20-500 g / m.sup.2², Preferably 40-200 g / m², be used.

An electromagnetic wave reflecting layer is applied to the carrier substrate. This layer can preferably consist of metals such as aluminum, gold, chromium, silver, copper, tin, platinum, nickel and their alloys, for example nickel / chromium, copper / aluminum and the like.

The electromagnetic wave reflective layer can be applied all over the surface or partially by known methods such as spraying, evaporation, sputtering, printing (gravure, flexographic, screen printing, digital printing), varnishing, roll coating and the like.

For partial application, a process using a soluble ink coating is particularly suitable for producing the partial metallization. In a first step, a layer which is soluble in a solvent is applied to the carrier substrate, in a second step this layer is optionally treated by means of an inline plasma, corona or flame process, and in a third step a layer of the metal or the metal to be patterned Metal alloy, whereupon, in a fourth step, the paint application is removed by means of a solvent, optionally combined with a mechanical action. The soluble paint application can take place over the entire surface or in part, and the metal or the metal alloy is applied over the entire surface or partially.

The application of the ink application can be carried out by any desired method, for example by intaglio printing, flexographic printing, screen printing, digital printing and the like. The color or lacquer used is soluble in a solvent, preferably in water, but it is also possible to use a color which is soluble in any solvent, for example in alcohol, esters and the like. The paint or lacquer may be conventional compositions based on natural or artificial macromolecules. The soluble color may be pigmented or non-pigmented. All known pigments can be used as pigments. Particularly suitable are TiO₂, ZnS, kaolin and the like.

Subsequently, the printed carrier substrate is optionally treated by means of an in-line plasma (low-pressure or atmospheric plasma), corona or flame process. By energetic plasma, for example Ar- or Ar / O₂The surface of toning residues of the printing inks is cleaned.

At the same time, the surface is activated. At the same time, terminal polar groups are generated on the surface. Thereby, the adhesion of metals and the like on the surface is improved.

If appropriate, a thin metal or metal oxide layer can be applied as an adhesion promoter, for example by sputtering or evaporation, simultaneously with the application of the plasma or corona or flame treatment or subsequently. Cr, Al, Ag, Ti, Cu, TiO are particularly suitable₂, Si oxides or chromium oxides. This adhesion-promoting layer generally has a thickness of 0.1 nm-5 nm, preferably 0.2 nm-2 nm, particularly preferably 0.2 nm to 1 nm.

This further improves the adhesion of the metal or metal alloy layer which is partially or completely exposed to electromagnetic waves.

A partial electromagnetic wave reflecting layer can, however, also be produced by a customary known etching method.

The thickness of the electromagnetic wave reflecting layer is preferably about 10-50 nm, but higher or lower layer thicknesses are also possible. If metal foils are used as carrier substrates, the carrier substrate itself can already form the electromagnetic waves reflecting layer. Preferably, the reflection of this layer for electromagnetic waves, in particular as a function of the thickness of the layer or of the metal foil used, is -100%.

The subsequent polymeric layer or the polymer layers can also be applied over the entire surface or partially. The polymeric layers consist, for example, of color or lacquer systems based on nitrocellulose, epoxy, polyester, rosin, acrylate, alkyd, melamine, PVA, PVC, isocyanate or urethane systems.

This polymeric layer essentially serves as a transparent spacer layer, but may be absorbing in a certain spectral range depending on the composition. If desired, this absorbing property can also be enhanced by the admixture of a suitable chromophore. By selecting different chromophores, a suitable spectral range can be selected. As a result, in addition to the tilting effect, the polymer layer can also be designed to be machine-readable. For example, in the blue spectral range (in the region of about 400 nm) a yellow AZO dye, for example anilides; Rodural, eosin, can be used. The dye also changes the spectrum of the label in a characteristic manner.

This polymeric layer can exhibit dewetting effects, depending on the quality of the adhesion on the carrier web or an underlying layer, which leads to a characteristic, macroscopic lateral structuring. This structuring can be specifically modified, for example, by modification of the surface energy of the layers, for example by plasma treatment, corona treatment, electron beam treatment, ion beam treatment or laser modification. Furthermore, it is possible to apply an adhesion-promoting layer with a different surface energy.

The polymeric layer has a defined thickness, preferably 10 nm to 3 μm, particularly preferably 100-1000 nm. If a plurality of polymeric layers are applied, these may each have different thicknesses.

The polymeric layer is applied by coating, varnishing, casting, spraying, printing (screen printing, rotogravure printing, or digital printing) or roller coating processes.

The polymeric layer is applied in a process which allows the application of very homogeneous layer thicknesses over large areas. A homogeneous layer thickness is therefore necessary in order to ensure a uniform coloration in the finished product. The tolerances are not more than ± 5%, preferably ≤ ± 2%.

A printing process is particularly suitable, wherein the ink or varnish is applied from a temperature-controlled varnish tray to the printing cylinder via an immersion cylinder and a transfer roller, essentially only the depressions of the printing cylinder being filled with the ink or the varnish. By means of a doctor blade, excess paint or lacquer is stripped off and, if necessary, dried further by means of a blow bar.

A layer formed from metallic clusters is then applied to the polymeric layer. The metallic clusters can be, for example, aluminum, gold, palladium, platinum, chromium, silver, copper, nickel and the like or their alloys, for example Au / Pd or Cr / Ni. This cluster layer is applied by sputtering (for example ion beam or magnetron) or evaporation (electron beam) from a solution or by adsorption.

During the production of the cluster layer in vacuum processes, the growth of the clusters and thus their shape as well as the optical properties can advantageously be influenced by adjusting the surface energy or the roughness of the underlying layer. This changes the spectra in a characteristic manner. This can be effected, for example, by thermal treatment in the coating process or by preheating the substrate. For example, the shape and thus the optical properties of the clusters can be influenced by adjusting the surface energy or the condensation coefficient of the metal on the underlying layer. These parameters can be carried out, for example, by treating the surface with oxidizing liquids, for example with Na hypochlorite or in a PVD or CVD process.

The cluster layer is preferably applied by means of sputtering. The characteristics of the layer, in particular the density and the structure, are set above all by the power density, the gas quantity used and its composition, the temperature of the substrate and the web speed.

When applied from the solution by means of a nasemic method, the clusters are prepared in solution in a first step, the clusters are then derivatized, concentrated and applied directly to the polymer surface.

For the application by means of printing techniques, small amounts of an inert polymer, for example PVA, polymethylmethacrylate, nitrocellulose, polyester or urethane systems, are admixed after the concentration of the clusters. The mixture can then be applied to the polymer layer by means of a printing process, for example screening, flexographic or, preferably, gravure printing.

The thickness of the cluster layer is preferably 2-20 nm, particularly preferably 3-10 nm.

In addition, a protective layer can be applied thereover using vacuum or printing techniques.

In a preferred embodiment, the polymer layer is selectively structured by modifying the surface energy. The structures then appear very contrasting due to the color effect due to the subsequently applied cluster layer, which makes them easily recognizable for the eye. Therefore, an additional counterfeit-proof feature is produced by such structuring.

Furthermore, this structuring can be converted by fingerprint algorithms into one-to-one codes, which can then be read out by machine. In this way, a structuring can be assigned to a defined numerical value, wherein markings with the same manufacturing parameters, ie with the same color effect, can be customized.

For application in particular as a safety feature, the individual layer combinations can also be applied to separate substrates. For example, the electromagnetic wave reflective layer and the polymeric spacer layer can be applied to a first substrate, which can be applied, for example, to a value document or inserted into this value document. The cluster layer, which is optionally provided with an adhesive layer, can then be applied to a further substrate. By combining the two coated substrates, the characteristic color effect then appears according to the key / lock principle.

The carrier substrate may also already have one or more functional and / or decorative layers. Various compositions can be used as such paint or varnish layers. The composition of the individual layers can vary, in particular according to their task, depending on whether the individual layers are intended exclusively for decorative purposes or are to be a functional layer, or whether the layer is to be both a decorative layer and a functional layer.

The layers to be printed may be pigmented or non-pigmented. As pigments, all known pigments such as, for example, titanium dioxide, zinc sulfide, kaolin, ATO, FTO, ITO, aluminum, chromium and silicon oxides as well as colored pigments can be used. Solvent-containing lacquer systems as well as systems without solvents can be used. Suitable binders are various natural or synthetic binders.

The functional layers may, for example, have certain electrical, magnetic, special chemical, physical and also optical properties.

For setting electrical properties, for example conductivity, for example, graphite, carbon black, conductive organic or inorganic polymers. Metal pigments (for example copper, aluminum, silver, gold, iron, chromium lead and the like), metal alloys such as copper-zinc or copper-aluminum or their sulfides or oxides, or else amorphous or crystalline ceramic pigments such as ITO and the like. Furthermore, doped or non-doped semiconductors such as, for example, silicon, germanium or ionic conductors such as amorphous or crystalline metal oxides or metal sulfides can also be used as additives. In addition, to adjust the electrical properties of the layer, polar or partially polar compounds,

To adjust the magnetic properties, paramagnetic, diamagnetic and also ferromagnetic materials such as iron, nickel and cobalt or their compounds or salts (for example, oxides or sulfides) can be used.

The optical properties of the layer can be influenced by visible dyes or pigments, luminescent dyes or pigments which fluoresce or phosphoresize in the visible, UV or IR range, effect pigments, such as liquid crystals, pearl luster, bronzes and / or heat-sensitive Colors or pigments. These can be used in all possible combinations. In addition, phosphorescent pigments can also be used alone or in combination with other dyes and / or pigments.

Various properties can also be combined by adding various abovementioned additives. Thus, it is possible to use colored and / or conductive magnetic pigments. All the above-mentioned conductive additives can be used. All known soluble and non-soluble dyes or pigments can be used for dyeing magnetic pigments. Thus, for example, a brown magnetic color can be adjusted metallic, eg, silvery, by the addition of metals in their color.

Insulator layers can also be applied, for example. Examples of suitable isolators are organic substances and their derivatives and compounds, for example color and lacquer systems, for example epoxy, polyester, rosin, acrylate, alkyd, melamine, PVA, PVC, isocyanate, urethane systems, which are radiation-curing For example by heat or UV radiation.

These layers can be applied by known methods, for example by vapor deposition, sputtering, printing (for example, deep, flexographic, screen, digital printing and the like), spraying, electroplating, roller coating processes and the like. The thickness of the functional layer is 0.001 to 50 μm, preferably 0.1 to 20 μm.

By repeating one or more described process steps once or several times, multilayer constructions can be produced which have different properties in the superimposed layers. It is thereby possible to manufacture superstructures, for example, for safety elements with a plurality of precise properties of authenticity by combining different properties of the individual layers, for example layers with different conductivity, magnetisability, optical properties, absorption behavior and the like.

The layers can in each case already be present or applied to the substrate over the full area or partially.

In this case, the process steps can be repeated as often as desired, it being possible, for example, to dispense with the application of the ink in the case of a full-surface application of a functional layer.

However, other layers can also be applied, for example, in known direct metallization processes or in metallization processes with etching partial metal layers or in known multi-color printing processes.

If desired, the coated film thus produced can also be protected by a protective lacquer layer or further refined, for example, by laminating or the like.

If desired, the product can be applied to the corresponding carrier material with a sealable adhesive, for example a hot or cold seal adhesive, or, for example, in the paper manufacture for safety papers, can be embedded in the paper by conventional methods.

These sealing adhesives can be provided with visible or fluorescence-absorbing features which are visible in the UV-light, fluorescent, phosphorescent or laser-absorbing and IR-radiation-absorbing features for increasing the counterfeiting security. These features can also be present in the form of patterns or signs or color effects, in principle any number of colors, preferably 1 to 10 colors or color blends, being possible.

The carrier substrate can be removed or left on the product when applied on one side after application. In this case, the carrier film can optionally be equipped on the non-coated side, for example, scratch-resistant, antistatic and the like. The same applies to a possible lacquer layer on the carrier substrate.

Furthermore, the layer structure can be set to be transferable or non-transferable, optionally with a transfer lacquer layer, which can optionally have a diffraction structure, for example a hologram structure.

The structure according to the invention can also be applied inversely to the carrier material, wherein a layer is formed on a carrier substrate from metallic clusters which are produced by means of a vacuum technique or from solvent-based systems and subsequently one or more partial and / or full-area polymeric layers of defined thickness are applied And a partial or full-area electromagnetic waves reflecting layer is applied thereon to the spacer layer.

In the <figref idrefs="f0001 f0002 f0003 f0004">Figs</figref> Examples of safety features according to the invention are shown. 1 is the carrier substrate, 2 the electromagnetic wave reflecting first layer, 3 the transparent layer, 4 the layer composed of metallic clusters, 5 an optically transparent substrate, 6 an adhesive layer.<ul><li><figref idrefs="f0001">FIG</figref> 10 shows a schematic cross-sectional view of a first permanently visible marking on a carrier substrate,</li><li><figref idrefs="f0001">FIG</figref> A schematic cross-sectional view of a non-permanently visible first marking on a carrier substrate and a</li><li>For visualization, a second carrier substrate,</li><li><figref idrefs="f0002">FIG</figref> A schematic cross-sectional view of a permanently visible first laminate or adhesive label,</li><li><figref idrefs="f0002">FIG</figref> 12 is a schematic cross-sectional view of another permanently visible second laminate or adhesive label.</li><li><figref idrefs="f0003">FIG</figref> A schematic cross-sectional view of a non-permanently visible first laminate or adhesive label and a</li><li>Which is suitable for visualization.</li><li><figref idrefs="f0004">FIG</figref> A large-scale continuously coated counterfeit-proofed carrier substrate, which is partially wound on rollers</li></ul>

In the cases shown in FIGS <figref idrefs="f0001 f0002 f0003">FIGS. 1 to 5</figref> An electromagnetic wave reflecting first layer is denoted by (2). This may be a thin layer of eg aluminum. However, the first layer (2) can also be a layer formed from metallic clusters which is applied to a carrier (1). The carrier (1) can be the carrier substrate to be marked. The inert spacer layer is indicated by (3). The metallic clusters (4) are expediently made, for example, from copper. In the <figref idrefs="f0002 f0003">FIGS. 3 to 5</figref> The adhesive or laminating layer provided for further processing of the counterfeit-proofed carrier substrate is designated by (6). The change in the reflected light which produces the characteristic color spectrum in comparison to the incident light is visualized in an arrow in these two figures by means of the gray scale sequence.

In the cases shown in FIGS <figref idrefs="f0001">FIG</figref> and <figref idrefs="f0002">3</figref> , A third layer (4) made of metallic clusters is applied to the second layer (3). The second layer (3) is applied to a mirror layer (2). Furthermore,<figref idrefs="f0001">FIG</figref> and <figref idrefs="f0002">3</figref> The mirror layer is applied to a carrier substrate (1).

In the <figref idrefs="f0002">FIG</figref> The third layer (4), then the second layer (3), then the mirror layer (2) and finally the adhesive or laminating layer (6), are first applied to a carrier substrate (1).

In the case of the <figref idrefs="f0001">FIG</figref> and <figref idrefs="f0003">5</figref> , Only the optically transparent second layer (3) is applied to the electromagnetically reflecting first layer (2) and this is applied to a carrier substrate (1). The marking is initially not visible. The markings are only visible when they are brought into contact with a substrate (5) on the surface of which the third layer (4) formed from metallic clusters is applied. A color effect, which is observable by the substrate (5), is then produced. The carrier substrate (5) is conveniently made of a transparent material, for example of plastic, such as polyethylene terephthalate, polycarbonate, polyurethane, polyethylene, polypropylene, polyacrylate, polyvinyl chloride, polyepoxide.

The function of the marking is as follows: <ul><li>When irradiating light from a light source, such as a light bulb, a laser, a fluorescent tube, a halogen lamp, in particular a xenon lamp, to one of the light sources shown in FIG <figref idrefs="f0001">FIG</figref>, <figref idrefs="f0002">3 and 4</figref> , This light is reflected on the first layer (2). An interaction of the reflected light with the third layer (4) formed from the metallic clusters absorbs part of the irradiated light. The reflected light has a characteristic spectrum dependent on several parameters, such as the optical constants of the layer structure. The marking appears colored. The coloring serves as a counterfeit proof for the authenticity of the marking. The color impression thus obtained is angle-dependent and can be identified both with the naked eye and with a reading device, preferably a spectrophotometer, operating in the reflection mode. Such a photometer can, for example, detect the coloration of the surfaces from two different angles.</li></ul>

With regard to the parameters to be observed for the generation of the interactions, <patcit id="pcit0004" dnum="US5611998A"><text>US 5,611,998</text></patcit>, the <patcit id="pcit0005" dnum="WO9848275A"><text>WO 98/48275</text></patcit> As well as the <patcit id="pcit0006" dnum="WO9947702A"><text>WO 99/47702</text></patcit> and <patcit id="pcit0007" dnum="WO0218155A"><text>WO 02/18155</text></patcit> Respectively.

The coated carrier materials produced according to the invention can be used as safety features in data carriers, value documents, labels, labels, seals, in packagings, textiles and the like.

Examples:

Example 1:

Preparation of the cluster layer by means of nasemic method:

A) Synthesis of 14 nm gold clusters

100 ml of aqua distilled are heated to boiling in a 250 ml flask. With strong stirring, first 4 ml of 1% tri sodium citrate in aqua distilled and then 1 ml of 1% tetrafluoro-gallic acid are added in anhydrous. Within 5 min, the color of the reaction mixture changes from almost colorless over dark violet to cherry red. The heat supply is then stopped and the batch is stirred further for about 10 minutes. The analysis of the resulting sol with the transmission electron microscope shows spherical particles with an average diameter of 14 nm. The size distribution of the clusters is narrow (cv &lt;20%). The wavelength maximum of the optical absorption is 518 nm.

B) Derivation of gold clusters:

To 100 ml of gold sol, according to the above synthesis, 1 ml of a 1% solution of BSA (bovine serum albumin) is added in vigorous agitation with vigorous stirring. The solution turns slightly from cherry red to a darker red. The maximum of optical absorption is retained. The absorption in the wavelength range of 550 nm and higher increases. In the transmission electron microscope, defined distances between the particles can be seen.

C) Attachment of the gold clusters on a surface of nitrocellulose:

The sol (almost pH neutral, hardly salt) is buffered by the addition of 5 ml of 1 M sodium carbonate solution (pH 9.6). Only sufficiently protected clusters remain in solution and do not precipitate. The sol can be concentrated by centrifugation or binds directly after application to the nitrocellulose-coated surface. If the nitrocellulose layer thickness is suitably selected, strong surface colorations are formed after the excess water has dried.

Example 2:

Production of the cluster layer by means of printing techniques

After the concentration, small amounts (eg 5%) of a neutral polymer (eg PVA) are added to the sol by a factor of 10. This makes it possible to print with conventional gravure cylinders. The colloids dry randomly oriented with the polymer in a very thin layer. Characteristic colors are observed as in Example 1c).

Example 3:

Preparation of the cluster layer by means of a vacuum technique

Under high vacuum conditions (basic pressure p &lt;1x10^-3 Mbar), a Cu layer with a thickness of 4 nm is sputtered onto a web-shaped carrier substrate which is already provided with a mirror layer and a nitrocellulose layer as a transparent spacer layer.

The sputtering is carried out by means of a magnetron plasma source with a power of 20W / cm² At 25 ° C using Ar with a partial pressure of 5 × 10^-3 Mbar as process gas. The speed of the web is 0.5 m / s. Under these conditions, the Cu layer exhibits marked island growth. The islands with a mean diameter of a few nm correspond to the clusters in the nasemic process. Significantly different characteristic color spectra are observed.