Method of manufacturing a security element having microimaged elements

Abstract

The invention relates to a method for producing a security element for security paper, value documents or the like, which has a carrier, which on its upper side has microimaging elements and on its lower side has structures, which together with the microimaging elements in front of the upper side of the carrier image a pattern, wherein the position of the pattern depends on the viewing angle. According to the invention first a semi-transparent or transparent carrier (1) is provided, which has an upper side and a lower side. A first embossing layer (2) is applied to the upper side of the carrier and a plurality of microimaging elements (3) is introduced into the side of the first embossing layer facing away from the carrier. A second embossing layer (4) is applied to the lower side of the carrier and a plurality of embossing structures (5) is introduced into the side of the second embossing layer facing away from the carrier. The second embossing layer is at least almost flat between the embossing structures. Subsequently a metal layer (7) is applied uniformly to the side of the second embossing layer facing away from the carrier. Subsequently the metal layer is removed from the embossing structures by an etching process. In this case the metal layer remains in the regions of the second embossing layer which are at least almost flat between the embossing structures. Subsequently a color layer (8) can be applied to the metal layer and the regions with embossing structures.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing an anti-counterfeiting element for security paper, valuable documents or the like, the anti-counterfeiting element having a carrier having a micro-imaging element on its upper side and a structure on its lower side, the structure together with the micro-imaging element imaging a pattern (German: Motiv) on the upper front of the carrier, wherein the position of the pattern depends on the viewing angle. Background Technology

[0002] This layout is known from existing technologies, such as those described in patent documents EP 3580067 A1, EP 1695121 B1, EP1893074 B2, EP 2493698 B1, EP 1846253 B1, or EP 2049345 B1, and is known, for example, as products of Crane Corporation under the trademarks “Motion,” “Rapid,” and “Surface,” products of De La Rue Corporation under the brand name “Active,” or products of Kurz Corporation under the brand name “zero.zero.” However, the manufacturing methods for these products are held by only a very few companies and are costly and complex. For example, the manufacturing of products “Motion” and “Rapid” requires a so-called “color-filling method” to insert colored designs or patterns into these products. Summary of the Invention

[0003] Therefore, the technical problem to be solved by the present invention is to improve this anti-counterfeiting element in order to eliminate the shortcomings of the prior art and further enhance anti-counterfeiting protection.

[0004] This technical problem is solved by a method according to the present invention for manufacturing anti-counterfeiting elements for security paper and valuable documents. Further designs of the invention are given in the specification.

[0005] According to the present invention, a translucent or transparent carrier having an upper side and a lower side is first provided in method step [1.1]. In method step [1.2], a first imprint layer is applied to the upper side of the carrier, and in method step [1.3], a plurality of microimaging elements are introduced into the side of the first imprint layer opposite to the carrier. In method step [1.4], a second imprint layer is applied to the lower side of the carrier, and in method step [1.5], a plurality of imprint structures are applied to the side of the second imprint layer opposite to the carrier. The second imprint layer is at least nearly flat between the imprint structures. Therefore, the side of the second imprint layer opposite to the carrier has a surface that is at least nearly flat, into which the imprint structures are introduced, for example, by an imprinting method known in the prior art. Here, in addition to individual imprint layers, multiple layers of varnish can also be stacked, and the structures are then imprinted into these varnishes. Using multiple embossed paint layers offers advantages in several aspects, including adhesion to the carrier, paint layer orientation (German: Verlauf), uniformity, imprintability, improved shape fidelity of the embossed structure, enhanced flow stability, and avoidance of contamination tendencies. The embossed structure, together with the micro-imaging element, forms a layout that images a pattern on the upper front of the carrier, the position of which depends on the viewing angle. Subsequently, in method step [1.7], a metal layer is applied uniformly to the side of the second embossed layer facing away from the carrier. In a subsequent method step [1.8], the metal layer is removed from the embossed structure by an etching process. In this case, the metal layer remains in the area of ​​the second embossed layer that is at least almost flat between the embossed structures. For an observer viewing the anti-counterfeiting element from above, a pattern of light and dark contrast is produced through the metal coating and through the embossed structure or the voids formed therein in the metal coating.

[0006] According to a preferred embodiment, in a subsequent method step [1.9], at least one color layer is applied at least partially, preferably entirely, to the embossed structure and the second embossed layer in an area at least nearly flat between the embossed structures. Here, at least one color layer is visible to an observer viewing the anti-counterfeiting element from above through the gaps thus formed by the embossed structure or the metallic coating, thereby allowing the anti-counterfeiting element to display a monochrome or multicolor pattern.

[0007] As is known in the prior art, the etching process uses a NaOH solution of a defined concentration at a defined temperature. The etching process is then typically stopped by neutralization, followed by rinsing and drying of the substrate. These latter two steps prevent the slow progression of the etching process in the finished or semi-finished product. It is important for etching to expose the substrate to the etching solution for a very defined time, chosen just enough for the metal layer to largely disappear from the imprinted structure or become transparent through a chemical reaction, while conversely, the metal layer remains substantially opaque in adjacent, at least nearly flat, areas. The metal layer is typically composed of aluminum, which is etched using the described process. Alternatively, phosphoric acid can also be used for the etching process.

[0008] Alternatively, photoresist can be coated onto a metal layer for alternative, well-defined etching processes. These photoresists can be designed to undergo a chemical change upon exposure, making them soluble in etching alkalis and releasing the metal layer for the etching process. However, photoresists can also have the opposite properties. In this case, the photoresist is first chemically cross-linked upon exposure, giving it a protective effect against etching alkalis.

[0009] When exposing a carrier with microstructures imprinted on both sides from above, the exposure can be selectively chosen such that the photoresist already coated on the metal layer is chemically altered in the areas of the imprinted structure, so that in subsequent etching steps, the photoresist is removed only in the areas with the metal layer. The advantage of this etching process using photoresist is that it generally allows for better selection between areas with imprinted structures and at least nearly flat areas, and is therefore less prone to error.

[0010] According to the present invention, the surface of the second embossed layer in the embossed structure region is enlarged due to the embossed structure, because the surface of the second embossed layer becomes uneven or roughened by the embossed structure. Therefore, the surface of the embossed layer relative to the projection of the embossed layer perpendicular to the (unembossed) embossed layer is increased by, for example, 1 mm. 2The surface area of ​​the imprinted layer per unit area is preferably at least 20% larger in the region of the imprinted structure than in the at least nearly flat region between the imprinted structures. When the metal layer is applied to the second imprinted layer, particularly preferably by surface vacuum evaporation (PVD or CVD), electroplating, atmospheric plasma, or printing, wherein the printing apparatus moves uniformly on the surface of the second imprinted layer, the metal layer material applied to the imprinted structure is less than that in the at least nearly flat region between the imprinted structures due to the increased actual surface area of ​​the imprinted structure. Therefore, the thickness of the metal layer in the at least nearly flat region between the imprinted structures is greater than its thickness in the region of the imprinted structure. Thus, during etching, the thinner metal layer on the imprinted structure is almost or completely removed, while the thicker metal layer in the at least nearly flat region between the imprinted structures remains. During etching, the thickness of the metal layer in the at least nearly flat region between the imprinted structures may be slightly reduced, but a continuous metal layer is retained in these regions.

[0011] Therefore, the imprinted structure results in a reduction in the effective thickness of the metal layer applied there compared to the surrounding area.

[0012] According to the invention, the fact that the second imprinted layer is "at least nearly flat" in the region between the imprinted structures does not mean that there are no imprinted structures in the "at least nearly flat" region. Rather, other imprinted structures can be arranged in these regions, but these imprinted structures only allow for such a small increase in the surface area of ​​the imprinted layer that a continuous metal layer remains there after the etching process. For example, in addition to the imprinted structures that enable etch-demetallization at their locations, smaller imprinted structures can be locally introduced into the second imprinted layer in the at least nearly flat region between the imprinted structures, and these smaller imprinted structures do not cause the metal layer to be etched away. In this way, additional color micro-images for lens effects can be integrated, for example, through nanostructures.

[0013] Therefore, other imprint structures only need to be such that their impact on surface height is significantly less than that of imprint structures capable of etch-demetallization at their location. This is exemplified by holograms with typical heights from 100 nm to 500 nm or micromirrors with heights less than 2 µm. In particular, additional imprint structures only allow for an increase of less than 20% in the surface area of ​​the second imprint layer relative to the area of ​​the imprint structure capable of etch-demetallization at its location.

[0014] According to a preferred embodiment, the imprinted structure has a height or depth of at least 2µm to 3µm. If the imprinted structure is introduced into the second imprint layer through a high-pressure imprinting process where the structure to be imprinted protrudes from the imprinting tool, the imprinted structure constitutes a recess in the second imprint layer. Conversely, if the imprinted structure is introduced into the second imprint layer through a low-pressure imprinting process where the structure to be imprinted extends into the imprinting tool, the imprinted structure constitutes a raised portion in the second imprint layer.

[0015] According to another preferred embodiment, after method step [1.9], an additional metal layer is applied to the side of the at least one color layer opposite to the carrier. This at least one color layer typically consists of a varnished color, the brilliance, luminance, color saturation, and / or contrast of which are enhanced by applying the additional metal layer located behind it along the viewing direction.

[0016] The one or more color layers can form a macroscopic multicolor pattern that appears only under predefined viewing conditions.

[0017] A particularly preferred embodiment also allows for the alternating appearance of two or more colored patterns under different viewing conditions. This is achieved by coating photosensitive colors beneath the etched metal, which change color, for example, through laser exposure from a defined angle of incidence.

[0018] In addition, other anti-counterfeiting features, such as a magnetic layer, can be hidden behind these additional metal layers. These anti-counterfeiting features cannot be detected by counterfeiters optically.

[0019] According to another preferred embodiment, the micro-imaging element is composed of a focusing element, such as a lens or a concave mirror, and the imprinted structure is at least partially arranged within the focal plane of the micro-imaging element. The focusing element may also be designed without surface topography, in that the focusing element is made of a material with a refractive index of n1, which preferably differs from the refractive index n2 of the substrate surrounding and embedding the focusing element by at least 0.3.

[0020] According to another preferred embodiment, the first and second imprint layers are each composed of imprinting ink, which is printed on a carrier.

[0021] The carrier is particularly preferably made of a plastic film, such as polyethylene terephthalate (PET).

[0022] In this invention, translucency refers to an object, such as a substrate or plastic film, that allows incident light to pass through at a certain percentage. If light is incident on one side of the object, a certain percentage of the light is allowed to pass through to the other side of the object and exit from there again. The greater the percentage of transmitted light relative to the incident light, the higher the translucency of the object. If this percentage is at least 90%, that is, the object allows incident light to pass through with almost no attenuation, like a window, then the object is said to be transparent. Conversely, if an object allows less than 10%, and preferably about 0%, of incident light to pass through, that is, the proportion of transmitted light relative to the incident light is small or close to or equal to zero, then the object is said to be opaque or non-transparent.

[0023] Valuable documents, especially banknotes, stocks, bonds, certificates, vouchers, checks, and high-quality admission tickets, can use anti-counterfeiting elements manufactured by the method according to the present invention. They can also be other papers with a risk of counterfeiting, such as passports and other identity documents, as well as cards such as credit cards or debit cards, whose card bodies have at least one layer of anti-counterfeiting paper. Furthermore, they can also be anti-counterfeiting elements for products, such as labels, seals, packaging, folding boxes, packaging inserts, etc.

[0024] The simplified name "valuable documents" encompasses all the aforementioned materials, documents, and product anti-counterfeiting measures.

[0025] The terms "upper side" or "lower side" of a carrier are relative and can also be referred to as "the one side" and "the opposite side." Here, "upper side" refers to the side of the carrier facing the observer of the anti-counterfeiting element. These two sides constitute the main part of the total surface of the carrier. These terms explicitly exclude the side surfaces of the carrier, which are extremely small when the carrier thickness is only a fraction of a millimeter and are usually not equipped with or cannot be equipped with anti-counterfeiting elements or coatings.

[0026] In this invention, a pattern is a visually perceptible representation designed in graphic form. It can, for example, be an alphanumeric string consisting of numbers and / or letters, a graphic map, an image, text, or other characters. This information is particularly preferably composed of positive and / or negative patterns. Here, in the case of a positive pattern, the pattern element itself is applied to the substrate; conversely, in the case of a negative pattern, the area surrounding the pattern element is applied to the substrate. A positive pattern is, for example, letters printed in dark on a light-colored substrate. A negative pattern is, for example, a surface applied in dark to a light-colored substrate, within which there are unprinted areas in the form of letters.

[0027] Of course, the features mentioned above and those to be described below can be used not only in the given combinations but also in other combinations, as long as they do not depart from the scope of protection of this invention as covered by the claims. Attached Figure Description

[0028] The advantages of the present invention will be explained with reference to the following embodiments and supplementary drawings. These embodiments represent preferred implementations, but the invention should not be limited thereto. Furthermore, for better understanding, the illustrations in the drawings are highly schematic and do not reflect the actual situation. In particular, the scale shown in the drawings does not conform to the actual situation and is only used to improve visual appeal. Moreover, for better understanding, the implementations described in the following embodiments are reduced to the main core information. Much more complex drawings or images may be used in actual implementations.

[0029] Detailed illustration: Figure 1 illustrates a method for manufacturing anti-counterfeiting elements according to the present invention, and in this case... Figures 1a to 1b The individual, sequential method steps are shown in the diagram; Figure 2 An embodiment of an anti-counterfeiting element manufactured by the method according to the present invention is shown; Figure 3 Another embodiment of an anti-counterfeiting element manufactured by the method according to the invention is shown. Detailed Implementation

[0030] Figure 1 schematically illustrates a method for manufacturing anti-counterfeiting elements according to the present invention. In this case, Figure 1a A translucent carrier 1 is shown, having an upper side O and a lower side U. A first imprint layer 2 is applied to the upper side of the carrier 1, and a plurality of microlens-like micro-imaging elements 3 are introduced in the side of the first imprint layer 2 facing away from the carrier 1. A second imprint layer 4 is applied to the lower side of the carrier 1, and a plurality of imprint structures 5 are introduced in the side of the second imprint layer 4 facing away from the carrier 1. The second imprint layer 4 is at least nearly flat in the region 6 between the imprint structures 5. Therefore, the side of the second imprint layer 4 facing away from the carrier 1 has a surface that is at least nearly flat, and the imprint structures are introduced into this surface, for example, by an imprinting method known in the art.

[0031] exist Figure 1b In this process, the metal layer 7 has been applied to the side of the second imprint layer 4 facing away from the carrier 1, and the metal layer has been removed from the imprint structure 5 by an etching process. Therefore, the metal layer 7 only remains in the region 6 of the second imprint layer 4 that is at least almost flat between each imprint structure 5.

[0032] exist Figure 1c In this case, color layer 8 has been applied to metal layer 7 and area 6. In this case, the anti-counterfeiting element displays a monochrome pattern.

[0033] Alternative sites, based on Figure 1d Alternatively, two color layers 9 and 10 can be applied to the metal layer 7. In this case, the anti-counterfeiting element displays a two-color pattern.

[0034] Figure 2 An embodiment of an anti-counterfeiting element manufactured by the method according to the invention is shown, wherein, in Figure 1d Another metal layer 11 is applied over the entire surface of the metal layer 7.

[0035] The additional metal layer 11 enhances the gloss, brightness, color saturation, and / or contrast of color layers 9 and 10. Furthermore, additional anti-counterfeiting features, such as a magnetic layer 13, can be hidden behind the additional metal layer 11; these features are optically undetectable by counterfeiters.

[0036] Figure 3 Another embodiment of an anti-counterfeiting element manufactured by the method according to the invention is shown. In this case, the micro-imaging element is not composed of exposed lenses that can be easily imitated by counterfeiters. Instead, the micro-imaging element is composed of lenses 12 made of a high-refractive-index material, which are fully embedded in an embossed layer 2 made of a low-refractive-index medium.

Claims

1. A method for manufacturing anti-counterfeiting elements for security paper and valuable documents, wherein, [1.1] A translucent or transparent carrier (1) is provided, the carrier having an upper side and a lower side; [1.2] The first imprint layer (2) is applied to the upper side of the carrier (1); [1.3] Multiple micro-imaging elements are introduced into the side of the first imprint layer (2) opposite to the carrier (1); [1.4] The second imprint layer (4) is applied to the underside of the carrier (1); [1.5] A plurality of embossed structures (5) are introduced into the side of the second embossed layer (4) opposite to the carrier (1), wherein the second embossed layer (4) is at least nearly flat between the embossed structures (5); [1.6] wherein the imprint structure (5) together with the microimaging element forms an image pattern on the front of the upper side of the carrier (1), wherein the position of the pattern depends on the viewing angle; [1.7] Apply the metal layer (7) all over the side of the second imprint layer (4) away from the carrier (1); Its features are, [1.8] The metal layer (7) is removed from the imprinted structure (5) by an etching process, and the metal layer remains in the second imprinted layer (4) in a region (6) that is at least almost flat between each imprinted structure (5), wherein the imprinted structure (5) is arranged directly below the micro-imaging element, wherein selective exposure is performed on a carrier with microstructures imprinted on both sides, causing the photoresist coated on the metal layer to undergo a chemical change in the region of the imprinted structure, so that only the photoresist in the region with the metal layer is removed in the subsequent etching step; wherein, in another step [1.9], at least one color layer (8, 9, 10) is applied to the imprinted structure (5) and the region (6); wherein, an additional metal layer (11) is applied to the opposite side of the at least one color layer (8, 9, 10). On the other side of the carrier (1), wherein, behind the other metal layer (11), there is a hidden anti-counterfeiting feature that is optically undetectable by counterfeiters, wherein the embossed structure (5) has a height or depth of at least 2µm, and relative to the unit area of ​​the surface of the second embossed layer (4) in a projection perpendicular to the second embossed layer (4), the surface of the second embossed layer (4) is increased by at least 20% in the region of the embossed structure (5) than the at least almost flat region between the embossed structures (5), thereby reducing the effective layer thickness of the metal layer in the region of the embossed structure (5) relative to the metal layer thickness in the region (6) when the metal layer (7) is applied, and during the etching process, the thinner metal layer on the embossed structure (5) is removed, while the thicker metal layer on the region (6) remains as a continuous metal layer; In addition to the imprinted structure (5) that can achieve etching demetallization at the position of the imprinted structure, a smaller additional imprinted structure is introduced locally into the second imprinted layer (4) in the region (6). The smaller additional imprinted structure does not cause the metal layer (7) to be etched away, and a continuous metal layer is still retained in the region (6) after the etching process. The smaller additional imprinted structure is a nanostructure for lens effect, a hologram with a height of 100nm to 500nm, or a micromirror with a height of less than 2µm. Furthermore, the micro-imaging element is not composed of an exposed lens, but rather of a lens made of a high-refractive-index material, which is fully embedded in a first imprint layer (2) made of a low-refractive-index medium.

2. The method according to claim 1, characterized in that, The micro-imaging element is composed of a focusing element, and the imprint structure (5) is at least partially arranged within the focal plane of the micro-imaging element.

3. The method according to claim 1 or 2, characterized in that, The first embossing layer (2) and the second embossing layer (4) are respectively composed of embossing paint, which is printed on the carrier (1).

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