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EP-3684627-B1 - DISC-SHAPED PIGMENT, PRINTING INK, SECURITY ELEMENT AND METHOD OF PRODUCTION

EP3684627B1EP 3684627 B1EP3684627 B1EP 3684627B1EP-3684627-B1

Inventors

  • FUHSE, CHRISTIAN
  • RAHM, MICHAEL
  • HEIM, MANFRED
  • RENNER, PATRICK
  • SCHIFFMANN, PETER
  • MENGEL, CHRISTOPH

Dates

Publication Date
20260513
Application Date
20180919

Claims (11)

  1. A platelet-shaped pigment (33, 37) having a layered structure comprising, in order, the following layers: - optionally, a carrier substrate; - a transparent embossing lacquer layer (36, 38) with an embossed relief structure; - a reflection-enhancing coating (35, 40) following the relief structure and forming a reflective microstructure, wherein the reflective microstructure is in the form of a mosaic comprising a plurality of reflective mosaic elements, and the reflective mosaic elements reflect the incident light, with respect to the plane of the wafer, not in the direction of specular reflection but in a spatial direction deviating therefrom, and each has a lateral dimension 1 greater than 2 µm, characterized in that the reflection-enhancing coating is a metallization covered by a translucent color layer (34, 39), and the embossing lacquer layer (36, 38) is colored in a shade identical to the shade of the translucent color layer (34, 39).
  2. A platelet-shaped pigment according to claim 1, wherein the lateral dimension 1 satisfies the following relationship: 4 µm < 1 < 25 µm, more preferably the relationship 4 µm < 1 < 20 µm, even more preferably the relationship 4 µm < 1 ≤ 10 µm, and particularly preferably the relationship 6 µm < 1 ≤ 10 µm.
  3. A platelet-shaped pigment according to claim 1 or 2, wherein the reflective microstructure consists of basic elements selected from the group consisting of saw teeth or wedges, cones, truncated cones, pyramids, and truncated pyramids.
  4. A platelet-shaped pigment according to any one of claims 1 to 3, wherein the pigment additionally comprises a magnetic layer.
  5. Printing ink comprising platelet-shaped pigments according to any one of claims 1 to 4.
  6. Printing ink according to claim 5, wherein the printing ink is a screen printing ink, flexographic ink, or gravure ink.
  7. Printing ink according to claim 5 or 6, wherein the printing ink comprises two or more types of pigments that differ in terms of color impression.
  8. Printing ink according to claim 7, wherein the printing ink comprises two types of pigments, the first type of pigment being based on platelet-shaped pigments according to any one of claims 1 to 4 and the second type of pigment being based on conventional platelet-shaped metallic pigments with a flat reflective layer.
  9. A security feature for securing valuable documents, in particular banknotes, comprising platelet-shaped pigments according to any one of claims 1 to 4 or obtainable by using an ink according to any one of claims 5 to 8.
  10. A method for producing a platelet-shaped pigment (33, 37) according to any one of claims 1 to 4, comprising a) providing a carrier substrate, e.g., a carrier film; b) applying an embossing lacquer (36, 38) to the carrier substrate; c) embossing a relief structure into the embossing lacquer (36, 38); d) providing the relief structure with a reflection-enhancing coating (35, 40) that follows the relief structure and forms a reflective microstructure, wherein the reflective microstructure is in the form of a mosaic comprising a plurality of reflective mosaic elements, and the reflective mosaic elements reflect the incident light, with respect to the plane of the wafer, not in the direction of the specular reflection but in a spatial direction deviating therefrom, and each has a lateral dimension 1 greater than 2 µm, wherein the reflection-enhancing coating is a metallization covered by a translucent color layer (34, 39), and the embossing lacquer layer (36, 38) is colored in a shade identical to the shade of the translucent color layer (34, 39); e) the step of further processing and comminuting the resulting layer structure into individual platelet-shaped pigments (33, 37).
  11. The method according to claim 10, wherein, in step e), prior to comminuting the resulting layer structure into individual platelet-shaped pigments, the carrier substrate is first detached from the coated embossing lacquer.

Description

The invention relates to a platelet-shaped pigment, a method for producing the same, a printing ink containing the platelet-shaped pigment and a safety element based on the platelet-shaped pigment according to the invention. In the prior art, screen printing inks exhibiting a color-changing effect are known, for example. In banknote production, optically variable ink (OVI) has been used for many years, in which platelet-shaped pigments are coated on both sides with an interference layer structure. This interference layer structure, in particular a three-layer reflector/dielectric/absorber structure, conveys a different color impression to the viewer depending on the viewing angle. Such interference layer structures are usually produced by vacuum evaporation, which is technically demanding and expensive. Typically, such color-changing effects cannot be achieved with arbitrary colors. When the object being viewed is tilted from a perpendicular viewing angle, the reflection spectrum shifts into the shorter wavelength range, so that, for example, a color change can occur from the reddish wavelength range through the yellow wavelength range to the green wavelength range, but not vice versa. It is still hardly feasible to reverse the color change effect towards a resulting colorless or white appearance. Furthermore, first-order interference pigments are known that are based on natural mica or on aluminum oxide flakes, borosilicate flakes, or silicon dioxide flakes and are coated with titanium dioxide and/or metal oxide using a wet chemical process. Printing inks based on interference pigments that only have a titanium dioxide coating are transparent and are virtually invisible when printed on white substrates, while the interference color becomes visible at an angle. The interference color depends on the titanium dioxide coating. Depending on the thickness, the hue changes from yellow through red to blue. Such pigments are offered, for example, by Merck under the brand name Iriodin. In contrast, interference pigments with an iron oxide coating are visually perceptible and, depending on the coating thickness, already show a bronze or red color impression when viewed from above on a white background. In the EP 1 560 884 B1 The production of diffractive pigments is described. The WO 2005/017048 A2 describes pigment flakes that may be embossed with a grid pattern. In the EP 1 760 118 A2 It describes how diffractive pigments can be aligned in a magnetic or electric field. In a further development according to the EP 1 806 238 B1 These pigments can also be used to create metameric features or ambiguous images. Another manufacturing process for pigments that have an embossed pattern is found in the WO 2009/010377 A2 described. The EP 1 760 118 A2 describes orientable diffractive pigment particles with a material forming a diffraction lattice, wherein the material enables the orientation of the pigment particle in the presence of an applied electric field. The EP 0 643 745 A1 describes a process for producing embossed, finely dispersed shiny metallic particles, comprising creating an embossed release surface on at least one side of a support layer, applying a metal film to the release surface so that the metal film follows the embossed surface, dissolving the release surface, removing the metal film from the support layer, and breaking the thin metal film into embossed particles with a mean diameter between 25 and 50 micrometers. Based on the prior art cited above, the invention aims to provide improved pigments and pigment colors that overcome the problems of high costs and the previously common limitations with regard to the color palette. The invention is particularly applicable to the use of pigments as a security feature in the field of valuable documents, but is not limited to this. The color-shifting coatings according to the invention can also be used alternatively and/or additionally for decorative purposes, e.g., as a printed decorative element on printed products or as a color-shifting coating in the field of automobiles, smartphones, or the like. The problem is solved by the combination of features defined in the main claim. Further developments of the invention are the subject of the dependent claims. Summary of the invention 1. (First aspect of the invention) Platelet-shaped pigment with a layer structure comprising the following layers in sequence: optionally a carrier substrate; a transparent embossed varnish layer with an embossed relief structure; a reflection-enhancing coating following the relief structure, forming a reflective microstructure, wherein the reflective microstructure is in the form of a mosaic of a multitude of reflective mosaic elements and the reflective mosaic elements reflect the incident light with reference to the plane of the plate not in the direction of the specular reflection, but in a spatial direction deviating from it and each have a lateral dimension 1 that is greater than