CN107709033B

CN107709033B - Security element and method for producing a security element

Info

Publication number: CN107709033B
Application number: CN201680023152.0A
Authority: CN
Inventors: K·舒尔特-维京; S·博格斯穆勒; S·诺艾特
Original assignee: Tisas Cribos Co Ltd
Current assignee: Tisas Cribos Co Ltd
Priority date: 2015-04-22
Filing date: 2016-04-22
Publication date: 2019-12-10
Anticipated expiration: 2036-04-22
Also published as: WO2016170132A1; CN107709033A; DE102015207268A1

Abstract

The invention relates to a security element (10) having an optical security feature introduced by means of laser etching, comprising a transparent polymer film (11) and a colorant layer (14) applied directly or indirectly to the polymer film, characterized in that the colorant layer comprises a metallic pigment (12).

Description

Security element and method for producing a security element

Technical Field

The invention relates to a security element with an optical security feature introduced by means of laser etching, comprising a transparent polymer film and a colorant layer applied directly or indirectly to the polymer film.

Background

Security elements having a transparent film as carrier material are known. They are often used for security or protection against forgery in the form of adhesive labels with embossed holograms, dynamic images (kinegrams), or other optically variable elements.

In many cases, the film is provided with an embossed structure (relief structure) for this purpose by means of a finely structured embossing tool, or for a thin layer of colorant applied to the film. By means of a subsequent metallization step thereto, the structure can be observed in reflection as a phase modulation structure. It is also possible to metallize the film, or the film with a suitable lacquer layer, first and then to emboss it. This also results in a phase modulation structure that can be observed in reflection.

In many cases, the metallization step is performed by vacuum deposition or by a sputtering process. The resulting metallization is therefore full-surface. However, partial metallization can also be performed as follows: for example, a partial release layer imprint is first performed on the film. After subsequent vapor deposition thereof, the release layer, and thus the metallization, may be partially removed.

In addition to embossing methods for producing optical security elements, and/or optical variable elements, laser etching methods are also known. By means of a focused pulsed laser beam, the film provided with the metallization is processed in this case such that the focused laser radiation produces a local, microscopic demetallization in the metallization layer. Many such demetallised spots give the desired optically variable structure, arranged in a pre-calculated distribution.

For example, the demetallized spots may be arranged in the X and Y directions on an orthogonal grid. The diameter of the demetallization spot resulting from the etching step depends in this case essentially on the intensity distribution of the laser in the focal region and on the introduced energy of the laser pulse, but also on the layer thickness of the metallization. It is desirable that the diameter of the demetallised dots be of the same size as the grid spacing of the orthogonal grid.

Tobias Kresse in "Realisierung einesVolumendaten-speichers[Implementation of a cylindrical volume data store]The experiments described in "", discovery, University of Heidelberg, 2005, show the dependence of the layer thickness of the metallization and the optical absorption of light in the visible range resulting therefrom. As the layer thickness increases, the absorption also increases, which then passes through a maximum at the so-called percolation point, and then again as the layer thickness increasesplus and minus. Thus, for example, for aluminum, a maximum absorption value of about 20% to 25% is achieved. This absorption used during the etching process briefly heats the metal layer during the laser pulse. Thus "demetallization sites" appear. If the layer thickness with the largest absorption is chosen, a stable etching process with the desired uniform large diameter of the demetallised spots is likely to occur, since a change in the thickness of the metallisation layer produces only a small change in absorption. It also results that a low, and thus efficient, laser power generating structure can be used, since a high absorption is provided. However, it has proven to be disadvantageous that a layer thickness with the greatest absorption leads to a reflection of only about 50%. Such vapor deposition is generally not reflective, but rather grayish and reduces the clarity of the incorporated security features.

EP 2005425B 1 discloses a holographic storage material having: a polymer film; a first metal layer applied over the polymer film, having a relatively low layer thickness, and being in the maximum absorption range to achieve high absorption; followed by a second non-metal layer; then a third metal layer, the layer thickness of which is greater than the first layer. Thus a structure is produced which exhibits both high absorption (resulting from the first layer) and high reflection and optical density (resulting from the third layer). It is decisive for the properties of the three-layer structure that the two metal layers are electrically separated from one another by the second layer. The conductivity properties of the first and third layers substantially determine their respective optical properties. In this way, an etchable exposed material can be produced which has an absorption which is stable with respect to layer thickness variations and is also high, thus enabling the etching process to be stable and efficient, and which furthermore has a high reflection, which makes the introduced structure clearly visible later on in use. In this method, a complicated and therefore expensive method of producing three thin layers by vapor deposition and sputtering is disadvantageous.

Disclosure of Invention

The invention is based on the following objectives: a security element is provided which has a combination of high absorption, high reflection, high process stability, and simple manufacturing possibilities.

The invention achieves this object with the features of the independent claims. The security element according to the invention comprises a transparent film and a colorant layer comprising a metallic pigment applied thereto. The present inventors have recognized that the optical absorption of such a colorant layer remains constant when the variation in the colorant layer thickness is large. Important for the absorption is: a single metallic pigment present in the colorant layer in an electrically insulated manner from adjacent pigments. Thus, the optical properties are determined by the layer thickness of the single pigment.

With the metallic pigment colorants according to the invention, optical properties can be achieved which have an almost uniform absorption for the etching process when the colorant layer thickness is significantly changed. Furthermore, the colorant with metallic pigment may have high absorption. This results in a high process stability of the etching process, for example with respect to changes in the laser power or to changes in the focusing position relative to the absorber layer and with intensity distribution in the absorber layer. Furthermore, the necessary laser power is relatively low. The energy introduced into the pigment and/or pigment layer via absorption generates metal displacements, thus creating "demetallization sites". It has been shown that films with metallic pigment application rates of about OD 0.5 optical density up to about OD 1.5 optical density can be successfully exposed using equal laser pulse powers.

The pigment layer preferably comprises metallic pigments having a relatively large average diameter of at least 1 μm, and in some embodiments, preferably at least 2 μm, or at least 5 μm, or at least 10 μm. For certain printing processes (e.g. inkjet printing) it may be advantageous for the average diameter to be at most 50 μm, more preferably at most 30 μm, still more preferably at most 20 μm or 15 μm. The metallic pigment is preferably in the shape of a disk whose thickness is smaller than the diameter.

The average thickness is from 10nm to 200nm, preferably from 10nm to 150 nm. The diameter of the metallic pigment is preferably within a narrow range around the average diameter. Advantageously, less than 10% of the metallic pigments have an average diameter less than half the average diameter of all the pigments, and/or less than 10% of the metallic pigments have an average diameter greater than twice the average diameter of all the pigments.

The colorant layer may be arranged directly (i.e., immediately) on the film. Alternatively, one or more other layers may be positioned between the film and the stain layer (e.g., adhesion promoter and/or paint layer).

The advantageous embossing of the film allows the pigments to have the following arrangement: the pigment is mostly or even almost completely parallel with respect to the membrane surface. A high optical quality mirror layer with only minor scattering is obtained. Via the printing step, it is possible to produce a colorant layer comprising a plurality of pigments which are arranged on top of one another and predominantly or almost completely parallel to one another. However, the pigments advantageously do not contact each other and are therefore advantageously arranged electrically insulated from each other.

Advantageously for the introduction of the optical security feature, the metallization in the layer system according to the invention can be designed in a simple manner batch-wise or separately at the layer level. Embossing in the form of non-full surfaces can be used, which is carried out via classical printing methods, such as screen printing or gravure printing. However, it is possible to use inks with metallic pigments suitable for inkjet processes, which enable the production of layer systems that can be used for etching processes. There is advantageously a correlation between the informational article of the embossed indicia visible to the human eye and the optical security feature incorporated at least in part therein.

In one embodiment, the layer structure made from the film and the colorant layer can be etched and then further processed without further intermediate steps. In an alternative embodiment, the layer structure can first be provided with one or more further layers, for example a layer of a coloured colour or an adhesive layer, optionally with a liner or a hot-melt adhesive or other layer, before the etching process is carried out. It is also possible to color the metallic pigment color layer by adding suitable colorants, thus obtaining a safety feature of a non-ferrous gloss. Although micro-demetallization typically occurs during the etching process, the process parameters may produce refractive index changes in the film or form a relief in such a layer structure and thus represent not an optical amplitude modulation structure but an optical phase modulation structure.

The colorant layer can also be micro-ablated if it is in air in one embodiment, i.e., not covered by another layer (e.g., an adhesive layer).

Drawings

the invention will be explained below on the basis of preferred embodiments with reference to the drawings. In the attached drawings

Fig. 1 shows a schematic view of the layer structure of a security element according to the invention;

FIG. 2 shows a schematic representation of a metallic pigment in an advantageous embodiment; and

Fig. 3 shows a schematic representation of the layer structure of a security element according to the invention in a further embodiment.

Detailed Description

The security element 10 is, for example, a label for a product or packaging which is used for anti-counterfeit protection purposes. To produce the security element 10, a transparent polymer film 11 made of plastic is first provided, which represents a major part of the thickness of the security element 10 and serves as a substrate and/or carrier film. Polymer film 11 is then imprinted with stain 13 containing metallic pigment 12 (particularly aluminum pigment), and/or paint by means of digital printing, to produce a color or paint layer 14 containing metallic pigment 12. The metallic pigment 12 forms the largest portion of the additive in the color layer 14. The layer thicknesses are not shown to scale in fig. 1, but rather the thickness of the film 11 relative to the thickness of the colorant layer 14 is significantly greater than that shown in fig. 1. The metallic pigment 12 is such that an optically perceivable reflective color layer 14 is formed.

For example, in fig. 2, aluminum pigment 12 is shown enlarged. The average diameter D of the metal pigment 12 is the diameter of a circle having an area equal to that of the metal pigment 12 when viewed in a plan view. The metal particles 12 have the shape of flat discs.

The metallic pigments 12 are advantageously arranged predominantly approximately parallel to one another and to the layer extent in the color layer 14.

In a subsequent step, an optical security feature is introduced into the colorant layer 14 by means of laser etching. The security feature may contain personalization information to make the security feature as counterfeit-proof as possible. This may include, for example, holograms, in particular phase holograms and/or amplitude holograms. However, other optically recognizable structures may also be introduced. Diffractive and/or non-diffractive microstructures are formed in the colorant layer 14 by laser etching processing. More precisely, the metallized film is processed by means of a focused pulsed laser beam, so that the focused laser radiation produces a local, microscopic demetallization (laser-induced material displacement and/or ablation) in the metallized layer 14. Many such demetallised spots give the desired optically variable structure, arranged in a pre-calculated distribution. For example, the demetallized spots may be arranged in the X and Y directions on an orthogonal grid.

In the embodiment according to fig. 3, in addition to the layer structure shown in fig. 1, an adhesive layer 15 is also provided, which is applied in particular to the side of the color layer 14 facing away from the film 11. For example, the security element 10 is embossed here as an adhesive label. Adhesive layer 15 may be attached to a substrate or release liner (not shown). In this embodiment, either before or after application of the adhesive layer 15 and/or other layers, a photolithographic process may be performed.

Claims

1. Security element (10) with an optical security feature introduced by means of laser etching, comprising a transparent polymer film (11) and a colour layer (14) applied directly or indirectly to the film, characterized in that the colour layer comprises a metallic pigment (12) and the optical security feature is introduced into the colour layer (22) by means of laser etching and the metallic pigment (12) is formed in the shape of a disc with a thickness D and is predominantly aligned parallel to one another, wherein the thickness D is smaller than the diameter D, the metallic pigments (12) in the colour layer (14) are predominantly or substantially completely electrically insulated from one another, the average thickness D of the metallic pigments (12) is 10 to 200nm, and the metallic pigments (12) are predominantly or even almost completely parallel with respect to the surface of the polymer film (11).

2. A security element as claimed in claim 1, characterized in that said metallic pigment (12) comprises an aluminium pigment.

3. Security element according to any of the preceding claims, characterized in that the average diameter D of the metallic pigments (12) is at least 1 μm.

4. Method of manufacturing a security element (10), comprising the steps of: providing a transparent polymer film (11), applying a colour layer (14) directly or indirectly to the polymer film (11), and introducing an optical security feature by means of laser etching, characterized in that a colour comprising metallic pigments (12) is used for the colour layer (14), and the metallic pigments (12) are formed in the shape of discs having a thickness D and are arranged predominantly parallel with respect to one another, wherein the thickness D is smaller than the diameter D, the metallic pigments (12) in the colour layer (14) are arranged predominantly or substantially completely electrically insulated from one another, the average thickness D of the metallic pigments (12) is from 10nm to 200nm, and the metallic pigments (12) are predominantly or even almost completely parallel with respect to the surface of the polymer film (11).

5. A method as claimed in claim 4, characterized in that the colorant comprising metallic pigments is printed onto the polymer film (11).