PLATE-SHAPED PIGMENT, PRINTING INK, SAFETY ELEMENT AND MANUFACTURING PROCESS

Description

[0001] 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.

[0002] 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. The 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 short-wavelength range, so that, for example...Starting from the reddish wavelength range, a color change can occur, progressing through the yellow wavelength range to the green wavelength range, but not vice versa. Furthermore, it is virtually impossible to reverse the color change effect to a resulting colorless or white appearance.

[0003] 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.

[0004] 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.

[0005] EP 1 560 884 B1 describes the production of diffractive pigments.

[0006] WO 2005 / 017048 A2 describes pigment flakes which may be embossed with a grid pattern.

[0007] EP 1 760 118 A2 describes how diffractive pigments can be aligned in a magnetic or electric field. In a further development according to EP 1 806 238 B1, metameric features or reversible images can also be generated using these pigments.

[0008] Another manufacturing process for pigments that have an embossed pattern is described in WO 2009 / 010377 A2.

[0009] EP 1 760 118 A2 describes orientable diffractive pigment particles with a material forming a diffraction grating, wherein the material enables the orientation of the pigment particle in the presence of an applied electric field.

[0010] EP 0 643 745 A1 describes a method 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.

[0011] 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.

[0012] 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.

[0013] 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

[0014] 1. (First aspect of the invention) Platelet-shaped pigment with a layered 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 and forming a reflective microstructure, wherein the reflective microstructure is in the form of a mosaic consisting of a plurality of reflective mosaic elements, and the reflective mosaic elements reflect the incident light with respect to the plane of the platelet not in the direction of the specular reflection, but in a spatial direction deviating from it, and each has a lateral dimension 1,which is larger than 2 µm, wherein the reflection-enhancing coating is a metallization covered by a translucent color layer, and the embossing lacquer layer is tinted in a shade identical to the shade of the translucent color layer.

[0015] The embossed lacquer layer on the side opposite the relief structure can additionally have a flat metallized surface and optionally another translucent color layer, wherein the color of the translucent color layer and the color of the optional further translucent color layer are preferably different colors, e.g. red and green.

[0016] The pigment dimension or pigment width is preferably 2 to 4 times, more preferably 2.5 to 3.5 times, and particularly preferably 3 times, larger than the lateral dimension 1 of the reflective mosaic elements.

[0017] Furthermore, it is preferred that the lateral dimension 1 of the reflective mosaic elements each satisfy the following relationship 2 µm < 1 < 25 µm, in particular preferably the following relationship 2 µm < 1 < 20 µm.

[0018] According to a preferred variant, the reflective microstructure in the form of a mosaic made up of a large number of reflective mosaic elements is such that 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 exactly one spatial direction different from it.

[0019] According to another preferred variant, the reflective microstructure, in the form of a mosaic composed of numerous reflective mosaic elements, is configured such that the reflective mosaic elements reflect the incident light, with respect to the plane of the plate, not in the direction of the specular reflection, but in a plurality of different spatial directions or areas. The plurality of different spatial directions or areas can, in particular, be 2, 3, 4, 5, or 6.

[0020] The reflection-enhancing coating can be, in particular, a continuous or a discontinuous, i.e., interrupted, coating. A continuous (or full-surface) reflection-enhancing coating is preferred due to its simpler production, e.g., by full-surface vapor deposition of a metallization. A discontinuous coating can be obtained, for example, by oblique vapor deposition of a metallization.

[0021] 2. (Preferred embodiment) Platelet-shaped pigment according to claim 2.

[0022] 3. (Preferred embodiment) Platelet-shaped pigment according to claim 3.

[0023] In particular, if the basic element of the reflective microstructure is a wedge or sawtooth, the basic element of the reflective microstructure is equivalent to the reflective mosaic element of the reflective microstructure. In particular, if the basic element of the reflective microstructure is an element chosen from the group consisting of cones, truncated cones, pyramids, and truncated pyramids, the basic element comprises two mosaic elements.

[0024] 4. (Preferred embodiment) Platelet-shaped pigment according to claim 4.

[0025] 5. (Second aspect of the invention) Printing ink according to one of claims 5 to 8.

[0026] The planar reflective layer is, in particular, a metallic reflective layer.

[0027] According to a particular variant, the conventional platelet-shaped metallic pigment can have a flat reflective layer, which has a translucent color layer on both its upper and lower surfaces. The translucent color layers preferably have the same hue.

[0028] 9. (Third aspect of the invention) Security element according to claim 9 for securing valuable documents, in particular banknotes.

[0029] 10. (Fourth aspect of the invention) Method according to claim 10 for producing a platelet-shaped pigment.

[0030] 11. (Preferred embodiment) Method according to claim 11.

[0031] Detailed description of preferred embodiments The subject matter of the present invention is in particular: a) Plate-shaped pigments provided with a relief structure such that incident light is reflected in a different direction compared to pigments with a flat, reflective surface or interface. b) Plate-shaped pigments in which the relief structure is additionally provided with a reflection-enhancing coating, namely a metallization. c) Plate-shaped pigments in which the reflection-enhancing coating is additionally colored and / or a colored impression is created by means of a translucent ink applied at least on one side. d) A printing ink, in particular a screen printing ink, containing one or more types of the above-mentioned pigments. e) A screen printing ink in which the pigments according to the invention are present in a translucent, colored matrix or in a translucent, colored binder.f) A printing or coating process for producing color-shifting layers, in which at least one color layer is obtained by printing or coating using one or more of the pigments described above. g) A security feature obtainable by printing using the printing ink according to the invention. h) A decorated object obtainable by printing or coating with the printing ink according to the invention. i) A security feature obtainable by printing using the printing ink according to the invention, wherein the security feature arranged on the document substrate (in particular a paper substrate) additionally features partial embossing or debossing, such that the relief structures of the pigments according to the invention are leveled out or significantly reduced in the area of ​​embossing, or replaced by a different relief structure. The partial embossing can, for example,This can be done using a numerical printing unit or an intaglio printing plate with defined engravings.

[0032] Further embodiments and advantages of the invention are explained below with reference to the figures, in the representation of which a scale and proportion-accurate reproduction has been omitted in order to increase clarity.

[0033] They show: Fig. 1 shows light reflection from a flat surface; Fig. 2 shows light reflection from reflective pigment platelets, wherein Fig. 2 (i) a detailed view showing slightly tilted plates within the paint layer and Fig. 2(ii) describes the resulting macroscopic widening of a reflected light beam; Fig. 3 a pigment platelet with a relief structure that leads to a direction of light reflection that deviates from the macroscopic surface normal of the pigment platelet; Fig. 4 the light reflection from paint with conventional pigment platelets in region A and from paints according to the invention in region B; Fig. 5 a pigment according to a comparative example; Fig. 6 the light reflection on the top and bottom of a pigment platelet according to another comparative example; Fig. 7 the production of a color-reflecting pigment by means of colored metallization ( Figure 7 , above) according to a comparative example, and the production of a color-reflecting pigment according to the invention by means of glazing colored layers ( Figure 7, below); Fig. 8 two different types of pigment that reflect incident light in different directions and with different colors; Fig. 9 the effect of a printing ink that combines the two types of pigment. Figure 8 in the form of a mixture; Fig. 10 contains a combination pigment which, depending on its orientation (i.e., the relief structure faces the object to be printed ( Figure 10 , right) or the relief structure points away from the object to be printed ( Figure 10 , left)) the light is reflected in different colors in different directions; Fig. 11 further embodiment variants for the microstructure elements; Fig. 12 in a highly idealized graphical form the production of pigments according to the invention; Fig. 13 a supplementary representation for determining the angle of reflection; Fig. 14 a further embodiment variant.

[0034] In the description, the abbreviations "LB" (stands for solvent-based binder), "WB" (stands for water-based binder) and "UV" (stands for UV-drying or UV-curing binder) are used, particularly in connection with printing inks.

[0035] Printing inks with platelet-shaped metal pigments are known in the prior art. Such pigments reflect incident light 2 essentially by specular reflection, i.e., the light reflection occurs such that the angles of incidence and reflection with respect to the surface normal (in the Figure 1 (shown in dashed lines) are the same. Figure 1 shows the light reflection 3 on a flat surface 1.

[0036] A printing ink according to the invention contains a plurality of the pigments according to the invention. When the ink is printed onto a (paper) substrate, the pigments align themselves substantially parallel to the substrate surface. Incident light is then no longer reflected precisely in a specific direction, but rather within a certain angular range Ω. The width of the angular range Ω depends on how far the actual orientation of the pigments deviates from an orientation perfectly parallel to the substrate surface. Figure 2 illustrates the light reflection 8 of the incident light 7 on reflecting pigment plates. Figure 2 (i) shows a detailed view with slightly tilted plates 4 within the ink layer 5 located on a substrate 6, e.g. a paper substrate. Figure 2 (ii) describes the resulting macroscopic expansion of a reflected light ray. In the Figure 2 (i)The dashed lines symbolize the surface normal of the pigment platelet, the dotted arrows symbolize the incident light, and the solid arrows symbolize the reflected light.

[0037] A pigment platelet according to the invention has a relief structure such that light incident from at least one side is not reflected in the direction of the specular reflection with respect to the plane of the platelet, but is reflected at a different angle or within a different angular range. This can be achieved in particular by using a sawtooth-shaped relief structure with regularly or irregularly arranged microfacets or micromirrors. In this case, incident light is reflected in the direction of the specular reflection only with respect to the surface of the individual microfacets, which deviates from the macroscopic surface normal of the pigment platelet. Figure 3Figure 1 shows a pigment plate 9 according to the invention with a relief structure which (in the case of light incident perpendicularly on the pigment plate) leads to a direction of light reflection 11 of the incident light 10 that deviates from the macroscopic surface normal of the pigment plate.

[0038] Figure 4Figure 12 shows the light reflection in region A for a color 12 with conventional pigment platelets and in region B for a color 13 according to the invention. Reference number 14 denotes the substrate, e.g., a paper substrate. When a color 12 is printed with conventional, flat pigments in region A, the pigments (assuming perfect alignment parallel to the substrate surface) reflect incident light 15 in one direction "R1". A printing ink 13 with the pigments according to the invention in region B reflects the incident light 16 in a different direction, specifically in other directions "R2". Normally, the pigment platelets according to the invention are indeed aligned parallel to the surface, but within this plane they can be arranged arbitrarily with respect to rotation.The light reflected from these pigment platelets is therefore not reflected in a single direction, but in many directions "R2", all of which lie along a cone arranged around the direction "R1". The opening angle of the cone, i.e., the deviation from the reflection direction of conventional pigment platelets or metallic silver paints, results from the inclination of the reflecting facets to the macroscopic surface of the pigment platelet.

[0039] In summary, when using the pigment platelets according to the invention, the incident light is reflected in different directions than when using conventional pigment platelets with flat reflective surfaces. This applies even if the pigments are not aligned exactly parallel to the substrate, but deviate by a slight angle of a few degrees. In this case, the reflection direction "R1" becomes a correspondingly larger angular range, and the cone of the direction "R2" increases. To ensure that the light reflected in region A and region B can be clearly separated, the inclination of the facets to the pigment plane is advantageously chosen to be greater than the variation in pigment orientation that occurs during the printing of the pigment ink.

[0040] To reduce the loss of reflected light, a symmetrical relief structure is advantageous because, in this case, the incident light is reflected at two angles, not just one. Relief structures that reflect the incident light at more than two angles are particularly advantageous. This is demonstrated by the Figure 11This is shown, for example, in the case of cones 17, truncated cones, pyramids, and truncated pyramids as the basic element. In the case of a pyramid, for example, a square pyramid 18, a rectangular pyramid 19, a triangular pyramid 20, or a hexagonal pyramid 21 may be present. It is advantageous if the flank angle of the individual relief structure basic elements is uniform within the pigment. In a printing ink, pigments can be present in a uniform form, but printing inks based on a mixture of several different pigments that differ in color and / or flank angle can also be used.

[0041] The pigment platelets according to the invention advantageously have an embossed relief structure and a reflection-enhancing or reflective coating, namely a metallization such as aluminium. Figure 5Figure 22 shows a pigment 22 according to an example not covered by the scope of the appended claims, with an embossing varnish 23 having a relief structure and a discontinuous or interrupted metallization 24. The relief structure consists of saw teeth, with a metallization present on the longer side of each saw tooth (in the Figure 5 (represented by a thickened line). Such metallization can be achieved, for example, by oblique vapor deposition. Alternatively, the metallization could also be applied across the entire sawtooth relief.

[0042] A preferred manufacturing process for the pigment includes the following steps: the application of an embossing varnish to a carrier film; the embossing of a relief structure into the embossing varnish; the step of metallizing the relief structure; the further processing of the resulting layer structure into individual pigments.

[0043] In the step of further processing the resulting layer structure into individual pigments, the metallized embossing lacquer can be peeled from the carrier film and ground into pigments of a suitable size. Optionally, a release layer, such as a release lacquer layer, can be applied between the carrier film and the embossing lacquer to facilitate separation. Furthermore, it can be advantageous to apply a protective lacquer to the metallization.

[0044] Preferred methods for treatment directly during the PVD process, or at least before removal from the carrier film, and thus before actual pigment production ("particle sizing"), are in particular: 1. A sol-gel coating prior to stripping via dip-coating, spin-coating, spray-coating, inkjet printing, pad-coating, microdrop coating, gravure printing, flexographic printing, screen printing, or a sol-gel bath with alkoxysilanes. 2. Physical vapor deposition (PVD process) with SiO₂ and / or Al₂O₃ and / or ZnS and / or TiO₂, so that the corrosion-sensitive metal pigment (especially aluminum) is embedded or protected in a sandwich structure (e.g., SiO₂ / Al / SiO₂), followed optionally by a coating according to paragraph 1 above (e.g., for a leafing pigment). 3. Chemical vapor deposition (CVD process) or plasma-enhanced chemical vapor deposition. 4. Plasma-chemical vapor deposition (or plasma coating) with, for example, fluorocarbon polymers, plasma deposition of glassy, ​​thin films based on organosilicon monomers, for example, hexamethyldisiloxane (HMDSO), or tetraethoxysilane.

[0045] Furthermore, it can be advantageous to phosphate the pigment to protect it from corrosion.

[0046] To avoid damaging the pigments when they are incorporated into a printing ink binder, the pigments are preferably dispersed gently, e.g. by means of an open three-roll mill, or mixed in, e.g. by means of a propeller stirrer as a tool.

[0047] Suitable binder matrices include, for example, solvent-based, water-based, dual-cured UV-curing binders (WB / UV or LB / UV), and UV-curing binders for gravure, flexographic, and screen printing. The pigment is present in the printing ink in a suitable concentration, for example, between 2% and 20% by weight. The orientation of the pigments can be positively influenced by the use of additives and / or by a low viscosity of the overall ink. With UV-curing inks, it is advantageous to apply the ink at a slightly elevated temperature (e.g., 30°C instead of 20°C) because the increased temperature reduces the viscosity.

[0048] Example of a UV flexographic printing ink and a screen printing ink (radical, leafing pigments): Pigment preparation (leafing):

[0049] The pigment is present, for example, as a 50% dispersion in liquid photoinitiator or reactive diluent. Such a paste is obtained by rewetting or rewetting from organic solvent after the prior addition of dissolved octylphosphonic acid, laurylphosphonic acid, or mono- / diphosphoric stearyl esters (note: the term "rewetting" comes from surfactant chemistry and describes the adsorption of a surfactant-like substance (e.g., a long-chain phosphoric or phosphonic acid) to the surface of a pigment; this changes the surface tension of the pigment, e.g., from polar to nonpolar; the solvent serves only as a reaction medium and is removed, so that the pigment preparation becomes a paste). Pigment preparation (leafing): 4-7% Monomer / reactive diluents: 30-40% Prepolymers / oligomers: 40-60% Defoamers: 0-1% Wetting agents: 0-1% Waxes: 0-3% Stabilizers (HALS, antioxidants): 0.5-3% Photoinitiators: 4-15% Coinitiators (e.g., amine synergist, ITX, benzophenone): 0-4% Examples of initiators:

[0050] Benzoyl phosphine oxides, amino ketones, hydroxy ketones, benzil ketals Examples of monomers / reactive diluents:

[0051] PEA 2-Phenoxyethyl acrylate HDDA Hexanediol diacrylate TPGDA Tripropylene glycol diacrylate TMPTA Trimethylolpropane triacrylate TMP(EO) X TA Ethoxyliertes Trimethylolpropane triacrylate GPTA Propoxyliertes Glycerin triacrylate POKE Pentaerythritol triacrylate DiTMPTTA Ditrimethylolpropane tetraacrylate DiPEPA Dipentaerythritol pentaacrylate DPHA Dipentaerythritol hexaacrylate DVE-3 Triethylene glycol divinyl ether Examples of oligomers:

[0052] Highly structured (prepolymerized) epoxy acrylates, urethane acrylates, polyester acrylates, polyether acrylates, inert resins UV gravure printing:

[0053] The color formulation should preferably contain higher proportions of very low-viscosity reactive diluents such as DVE-3 or HDDA and fewer / lower-viscosity prepolymer components; processing at higher temperatures up to 40°C is advantageous. UV offset:

[0054] The color formulation contains highly viscous / highly structured, (for wet offset) less hydrophilic monomers as well as a relatively high prepolymer content. UV-cationic components (leafing pigments):

[0055] Prepolymers: Bisphenol-A diglycidyl ether, Epoxy Novolac, Dentrimers, Reactive diluents: Epoxides, Divinyl ethers, Polyols, Oxetanes, Photoinitiators: Sulfonium salts and Iodonium salts. Components of wet / dry offset and letterpress printing:

[0056] e.g. modified rosin resins, hydrocarbon resins, alkyd resins, unsaturated vegetable oils, animal oils and / or solvents such as mineral oils and fatty acid esters; Co / Mn catalyst and, if necessary, auxiliaries. Components of solvent-based printing inks (non-leafing pigments):

[0057] e.g. cellulose, especially nitrocellulose resins; vinyl polymers, especially polyvinyl butyral, possibly polyamides; solvents: alcohols, ketones, esters, hydrocarbons; possibly auxiliaries.

[0058] For solvent-based printing inks, the pigment content is preferably chosen to be as high as possible, e.g., more than 30% solids content. The pigment / binder ratio is preferably about 1:2 or higher. The pigment content should generally be chosen high enough to just meet the requirements for the printing ink, e.g., abrasion resistance, adhesion, and overpressure. Conversely, the total solids content in the printing ink should be chosen to be as low as possible, preferably less than 10% of the total ink volume. Dilution can be achieved, for example, by using solvents. Components of aqueous printing inks (non-leafing pigments):

[0059] Acrylates, maleates, polyesters, polyurethanes, water, isopropanol, ethanol, possibly auxiliaries, in particular defoamers, wetting additives, dispersing agents and pigment stabilizers.

[0060] Aqueous UV: Supplemented with acrylate dispersions and photoinitiator.

[0061] In the case of using a transparent embossing varnish, light incident from both sides can be reflected in directions that deviate from the specular reflection according to the macroscopic surface normal of the plate (see Figure 6). Figure 6 Figure 1 shows the light reflection 26 of incident light 25 on the top surface and light reflection 28 of incident light 27 on the underside of a pigment platelet 29 according to the invention in a further embodiment. The relief structure consists of saw teeth, with a metallization present on the longer side of each saw tooth (in the Figure 6(represented by a thickened line). Such metallization can be achieved, for example, by oblique vapor deposition. Alternatively, the metallization could also be applied across the entire surface of the sawtooth relief.

[0062] Metallization and embossing on one pigment side are therefore entirely sufficient if a embossing varnish is used, which is preferably at least transparent in the visible spectrum, to achieve the desired effect on both the top and bottom surfaces. It is therefore irrelevant whether the pigment, after printing the pigment ink onto the object to be printed, faces the object with its top or bottom surface.

[0063] According to another preferred embodiment, the pigments do not reflect incident white light as white, but as colored light. For example, if a gold or copper metallization is used instead of an aluminum metallization, the reflected light will be gold or copper-colored, respectively. Instead of gold, a more cost-effective, gold-colored alloy can be chosen, such as an aluminum-copper alloy. Furthermore, the color palette can be expanded by vapor deposition of a multilayer system. For example, a thin silicon layer on an aluminum metallization can make it appear gold or blue. In particular, such a silicon layer can be vapor deposition on both sides of an aluminum layer. That is, the embossing lacquer would be coated with a silicon / aluminum / silicon multilayer system. Such multilayer systems are known in the prior art; see, for example, WO 2016 / 188619 A1.

[0064] Alternatively, instead of a colored metallization, a translucent (i.e., without diffusing or opaque colorants, e.g., in the form of undissolved dyes or pigments) color can be used. For example, to achieve a green color effect, a green-tinted embossing varnish could be used, and if necessary, an additional translucent green color layer could be applied over the metallization. Figure 7 a) Figure 30 illustrates the production of color-reflective pigments by means of a colored metallization 31, in this example a copper metallization. Reference number 32 designates an embossing lacquer with an embossed relief structure. The relief structure consists of saw teeth, with a metallization present on the longer side of each saw tooth (in the Figure 7 a)(represented by a thickened line). Such metallization can be achieved, for example, by oblique vapor deposition. Alternatively, the metallization could also be applied across the entire surface of the sawtooth relief. Figure 7b) Figure 36 illustrates the production of color-reflective pigments 33 according to the invention by means of translucent colored layers 34 and 36. Reference number 36 designates a green-colored embossing varnish with an embossed relief structure. Reference number 34 designates a green topcoat. The relief structure consists of saw teeth, with a metallization 35 present on the longer side of each saw tooth (in the Figure 7b) (represented by a thickened line). Such metallization can be achieved, for example, by oblique vapor deposition. Alternatively, the metallization could also be applied across the entire surface of the sawtooth relief.

[0065] With reference to Figure 14This paragraph explains a further, alternative execution variant. Layer 36 is an uncolored, transparent embossing varnish. Layer 35 is a metallization, and layer 34 is a translucent color layer. Layer 34' is a further translucent color layer located beneath the embossing varnish layer 36, which preferably has the same color as layer 34. This ensures that, regardless of the pigments' position, the macroscopic color of the pigments does not change, and that no mixed color occurs from differently colored pigment sides. The further translucent color layer 34' can be applied before or after the embossing.

[0066] Basically, instead of a colored embossing varnish, a colorless embossing varnish can be used with a translucent colored layer underneath, which is applied before the embossing varnish. Alternatively, further transparent layers can be placed between the embossing varnish layer and the translucent colored layer.

[0067] Furthermore, it is possible to embed colorless pigments in a colored binder or to coat a printing ink according to the invention with a further translucent color layer in order to obtain a desired color effect. In the case of a transparent (paper) substrate to be printed, a corresponding translucent color layer could also be printed before the printing ink containing the pigments according to the invention in order to achieve a color effect.

[0068] Color-changing effects can be achieved by combining pigments of different colors and facet inclinations according to the invention. This makes it possible, for example, to flexibly produce almost any shade from pigment mixtures or color mixtures of monopigmented base colors from a basic pigment palette (such as yellow, magenta, and cyan, optionally with the addition of orange and / or green), according to customer requirements. The facet inclination (or relief structure) is preferably the same. In the simplest case, one type of pigment has no inclination at all, i.e., it is merely a colored pigment with a flat reflective layer. According to the [reference to the invention], Figure 8 In the illustrated embodiment, green pigments 37 ( Figure 8 , left), which have a relief structure, as a first type of pigment in combination with red pigments 41 ( Figure 8(right) with a flat reflective layer as a second type of pigment. In the case of the first type of pigment, incident light is reflected green in a first direction "RG", while in the case of the second type of pigment, incident light is reflected red in the direction "RR". The green pigment 37 contains a green-colored embossing varnish 38 with an embossed relief structure. Reference number 39 refers to a green transparent varnish (or topcoat) which is arranged above the embossing varnish. The relief structure consists of saw teeth, with a metallization 40 present on the longer side of each saw tooth (in the Figure 8 (represented by a thickened line). Such metallization can be achieved, for example, by oblique vapor deposition of a metallization.

[0069] When pigments are provided with discontinuous metallization, these pigments exhibit maximum transparency or minimum reflectivity at an angular position such as the "sawtooth" 35 (acute angle) due to the lack of metallization on the perpendicularly arranged flank. This results in a further colored printing layer arranged below the printing ink based on the pigments according to the invention being particularly easy to see at this angular position, or, in the case of application on a transparent substrate, maximum light transmittance being detectable.

[0070] In another variant, a first metallic layer is deposited discontinuously, a second metallic layer of a different color is deposited continuously, and a third metallic layer in the same color as the first metallic layer is deposited discontinuously again, so that under an angle such as the sawtooth 35, a different color can be seen in the reflection.

[0071] Alternatively, the metallization could also be present across the entire surface of the sawtooth relief. The red pigment 41 ( Figure 8 , right) is based on a flat metallization 42, which has a red translucent color layer 43 on the top side and a red translucent color layer 44 on the bottom side.

[0072] Figure 9 shows the available area with angle-dependent color impression, (i) when the two in the Figure 8The pigment types 37 and 41 shown are mixed to form a single printing ink and printed onto an object to be printed, or (ii) a first ink layer is printed onto an object to be printed using only one pigment type, followed by a second ink layer printed onto the first ink layer using only the other pigment type, or (iii) nested first and second printing areas are printed onto an object to be printed, the first printing area being produced using only one pigment type and the second printing area being produced using only the other pigment type. Accordingly, the effect of the two pigment types of Figure 8The ink contains a mixed color. Part of the incident light is reflected green in the direction "RG," and another part is reflected red in the direction "RR." A viewer sees a red color from the direction "RR" and a green color from the direction "RG." The green pigments in the combination reflect incident light green in the direction "RG," while the red pigments reflect the light red in the direction "RR." Thus, the surface appears green to a viewer from the direction "RG" and red from the direction "RR." This results in a printing ink with a direction-dependent color impression.

[0073] Depending on the choice of pigment types to be used, possibly in combination with a colored binder and / or a glazing color, virtually any color impressions and color changes can be achieved.

[0074] Instead of using two types of pigment (e.g., those in the Figure 8The combination of pigments 37 and 41 shown can alternatively be achieved using only one type of pigment, provided that the pigments have different reflection colors and directions on their top and bottom surfaces. For example, a pigment shown in the Figure 10 The pigment 45 shown can be used with the following layer structure: first translucent color layer 46, e.g. red; flat, metallized surface 47; embossing varnish 48, which has a relief structure embossed into the varnish; a second metallization 49, the surface texture of which follows the relief structure embossed into the varnish (the relief structure consists of saw teeth, with a metallization 49 present on the longer side of each saw tooth (represented in the figure by a thickened line; such a metallization can be achieved, for example, by oblique vapor deposition; alternatively, the metallization could also be present over the entire surface of the saw tooth relief); second translucent color layer 50, e.g. green.

[0075] A pigment with the layered structure described in the preceding paragraph thus combines, on its upper surface and on its lower surface, the effects of the components described in the previous paragraph. Figure 8The pigment types shown on the left and right. Assuming that such "combination pigments" are applied with an equal probability to the object being printed, with their red side on one side and their green side on the other, the result is practically the same as with a 50 / 50 mixture of the pigment types shown. Figure 8 .

[0076] Figure 10 shows a combination pigment described above, which, depending on its orientation (i.e., the relief structure faces the object to be printed ( Figure 10 , right) or the relief structure points away from the object to be printed ( Figure 10 , left)) the light is reflected in different colors in different directions.

[0077] With reference to the in the Figure 10Regarding the depicted version, it should be noted that, according to a variant (not shown in the drawing), instead of two color layers, only one color layer and, for example, a colored metallization in the pigment may be present. With reference to the Figure 10 For example, a yellow color layer 46 would be unnecessary if the metallization 47 is gold-colored. The same applies to layers 49 and 50.

[0078] In principle, instead of using two types of pigment in combination, three or more types of pigment can also be used in combination, with the pigment types differing in terms of their tendency to create faceted relief structures and / or in terms of their color appearance. This also makes more complex variations with multiple color changes, e.g., green-to-red-to-blue or the like, possible.

[0079] The pigments according to the invention can advantageously have an additional magnetic layer. In this way, pigments are available that can be aligned by the use of magnetic fields. In this way, a variety of dynamic motion effects and color effects can be achieved. For example, if the pigments in the Figure 8 The green and red pigments shown, each coated with a magnetic layer, can exhibit red-green movement effects after being printed onto an object and aligned in a magnetic field. Similar movement effects are known in the prior art, for example, in connection with commercially available OVMI inks; see, among others, the security feature Sicpa SPARK®.

[0080] According to a further embodiment, the magnetic layer of the pigment according to the invention can be structured. The structuring of the magnetic layer can be achieved, in particular, by embossing. Here, too, the structuring can be carried out by oblique (vacuum) vapor deposition. The embossed area can then be coated with a magnetic material; alternatively, the embossing can also take place after the coating. Suitable materials include, for example, layers containing Fe, Ni, and / or Co. Typical layer thicknesses are, for example, in the range of 50 nm to 500 nm, preferably in the range of 50 nm to 300 nm. In this way, it is possible to prevent the pigments from rotating arbitrarily in the substrate plane, i.e., about their normal vector; rather, a suitable structuring allows magnetic anisotropy in the plane of the pigments to be achieved. By means of a strip-shaped structuring of the magnetic layer (e.g.,A line lattice with a preferred lattice period in the range of 100 nm to 5 micrometers, more preferably 100 nm to 1000 nm, and a preferred depth of 50 nm to 0.5 micrometers, more preferably 100 nm to 300 nm, can be achieved, for example, by rotating the pigments about their normal vector such that the lines of the magnetic structuring are oriented parallel to the magnetic field. In an external magnetic field, such pigments will thus preferably align themselves so that the pigment plane lies parallel to the field lines and the pigment is rotated about its normal vector such that the lattice lines also run parallel to the magnetic field lines. Alternatively, instead of generating magnetic anisotropy in the pigment plane by means of embossed structures, magnetic anisotropy can also be achieved by making the platelet-shaped pigments not circular or essentially as wide as they are long, but elliptical or...They generally have an elongated shape. Elongated plates preferentially align themselves in an external magnetic field such that the plane of the plates lies parallel to the field lines and the long axis points in the direction of the field lines.

[0081] When using a magnetic lattice structure to introduce magnetic anisotropy, it must be considered that, in addition to this magnetic effect, the magnetic lattice structure also causes a visually perceptible optical effect, which is determined by the lattice parameters, and primarily by the period. If the lattice period is approximately in the range of the wavelength of visible light, diffractive effects, typical of embossed holograms, occur predominantly. At smaller periods in the sub-wavelength range, plasmon and resonance effects can be observed, leading to color changes in specular reflections. When using color-shifting coatings (e.g., with a reflector / dielectric / absorber multilayer structure), their color effect can also be altered.

[0082] The magnetically anisotropic coating can be applied in addition to the reflective relief structure. In this case, two embossing patterns are useful. For example, the pigments could be in the Figure 10In addition to the reflective relief structure, i.e., in addition to the micromirror layer, a grid-structured magnetic layer can be incorporated instead of the additional flat metal layer. This would result in the optical appearance of the pigments being modified by the optical effect of the grid. The orientation of the grid lines relative to the orientation of the micromirrors can be selected during the manufacturing process. Using an external magnetic field, the desired orientation of the micromirrors can then be achieved via the anisotropy of the grid lines. For example, the magnetic grid structures are arranged in the plane spanned by the normal vector of the micromirrors and the normal vector of the pigment. From the cone of reflection directions of the pigments described above, only two directions on this cone are ultimately selected. In this way, for example...Print patterns are now possible in which red and green areas are much better separated from each other.

[0083] In one variant, the micromirror structures required for the micromirror effect are superimposed on the lattice structures necessary for generating magnetic anisotropy. In this case as well, the optical effect of the pigments is modified by the presence of the magnetic structures.

[0084] To achieve the best possible results when printing with the pigments according to the invention, it is advantageous to use low-viscosity binder systems that allow for good pigment orientation. Furthermore, it is preferred to use printing processes that allow the processing or application of large, flat pigments; therefore, screen printing, flexographic printing, and gravure printing are particularly preferred.

[0085] The pigments according to the invention can also be used to produce a security element for protecting valuable documents, especially banknotes. According to a preferred embodiment, a color change from a first to a second color is generated when the valuable document is tilted. According to a specific embodiment, one of the two colors can be achromatic or non-colored (especially white), which can be achieved, for example, with colorless metallized pigments.

[0086] Furthermore, it is possible to print a printing ink containing the pigments according to the invention over a dark background, e.g., a black surface. In this case, the surface appears dark, particularly black (i.e., outside the angle of reflection), from some viewing angles, and colored from other viewing angles, providing a particularly noticeable contrast. The background print can be in the form of a pattern or in the form of characters, such as a numerical value.

[0087] In principle, with regard to the optical effect obtained, it is advantageous if the pigments according to the invention are arranged as parallel as possible to the surface of the object to be printed. Optimal alignment parallel to the substrate can be achieved, for example, in the case of rough substrates, by printing a suitable primer that reduces surface roughness.

[0088] The effect according to the invention is enhanced if reference fields for a top view are present in the immediate vicinity of the print based on the pigments according to the invention, or if illumination is carried out using a diffuse light source, and / or when viewed with a directed light at the flank angle of the relief structure (reflection).

[0089] Furthermore, the effect according to the invention can be enhanced by arranging a first printing field based on a first type of pigment with a first coloring and a first flank angle in the immediate vicinity of a second printing field based on a second type of pigment with a coloring and a second flank angle, so that ideally hidden information is only revealed when the illumination angle is changed.

[0090] Furthermore, it is possible to emboss a print based on the pigments according to the invention, at least in partial areas, after application by means of an embossing tool or a printing plate, preferably by means of a steel engraving plate, so that the relief structure of the pigments is at least significantly reduced or superimposed with another relief structure, resulting in a different color impression in the embossed area than in the area outside the embossed area. This effect is observed when illuminated with directed light at the flank angle of the relief structure.

[0091] In another variant, a portion of the print based on the pigments according to the invention is marked using an Nd:YAG laser, so that only the reflective layer of the pigment is removed, while the coloration is retained. In this case, the marked area shows no directional reflection at the flank angle of the relief structure.

[0092] In another variant, a printing ink based on an undyed pigment according to the invention is applied to a transparent (paper) substrate area. Subsequently, the first side of the substrate is colored with a different translucent color than the second side of the substrate area. As a result, different colors appear when viewed from above with diffuse light, while a similar color impression is shown when viewed with directed light at the angle of the relief structure.

[0093] The pigments according to the invention preferably have a width or pigment dimension in the range of 10 µm to 60 µm. The thickness of the pigments according to the invention is preferably less than 5 µm. More preferably, the pigments according to the invention have a width (D50) in the range of 5 µm to 30 µm, in particular a width (D10 - D90) in the range of 3 µm to 50 µm. Particularly preferably, the pigments according to the invention have a width (D50) in the range of 10 µm to 20 µm, in particular a width (D10 - D90) in the range of 5 µm to 35 µm.

[0094] It is preferred that the relief structure of the pigment according to the invention consists of regular sawtooth grids or micromirror arrangements. The facets of the relief structure have a preferred embossing depth of less than 10 µm, more preferably less than 5 µm, and particularly preferably less than 3 µm. The width of the facets of the relief structure is preferably less than 20 µm and particularly preferably less than or equal to 10 µm. The width of the facets of the relief structure is also referred to in this description as the lateral dimension 1. To avoid diffraction effects, the facets of the relief structure have a preferred dimension (or the sawtooth grids have a preferred period) of more than 2 µm, more preferably more than 4 µm, and particularly preferably more than 6 µm.

[0095] It is preferred that the inclination angle of the reflecting facets of the relief structures lies in a range of 3° to 60°, with the range of 10° to 30° being particularly preferred.

[0096] The embossing varnish is preferably a UV embossing varnish. However, thermoplastic embossing varnishes can also be used.

[0097] The printing inks containing the pigments according to the invention are preferably screen printing inks, flexographic printing inks, or gravure printing inks. However, it is also possible to produce and use other coatings, e.g., automotive coatings.

[0098] In the case of automotive or industrial coatings, spray coating (mostly water-based coatings), dip coating (mostly water-based coatings), and / or powder coating (especially electrostatic coating) are preferred. Since good plane-parallel orientation of the pigments is advantageous for a very good optical effect, powder coating would be less preferred.

[0099] The printing inks with the pigments according to the invention are preferably based on organic solvents, water, oils, or reactive diluents and can form a film via actinic radiation, repellency, and / or evaporation. They can be one-component, two-component, and / or DualCure.

[0100] The colors containing the pigments according to the invention are preferably printed by screen printing. If the pigments have an additional magnetic layer, a magnetic field can also be applied.

[0101] The reflective facets of the relief structures of the pigments according to the invention need not all be uniformly oriented. It is also possible that the facets have only the same, or at least similar, inclination angles, but different azimuth angles. It is irrelevant whether a pigment is deposited on the printing substrate in a state rotated in the substrate plane or whether the facets of the pigment are rotated from the outset.

[0102] Accordingly, pyramidal structures can be used instead of sawtooth grids for the relief structure facets. Furthermore, good effects can also be achieved with conical structures. Sawtooth grids, pyramidal structures, or conical structures are preferred for the relief structure facet arrangements because the angle of inclination relative to the macroscopic pigment substrate plane can be particularly advantageously adjusted. In the case of pyramidal and conical structures, the lateral dimension 1, i.e., the width of the relief structure facets, is equal to half the diameter of the base of the respective structure.

[0103] Furthermore, it is advantageous to choose the aspect ratio of the pigments (i.e., the thickness to the length) as large as possible, in particular at least 1:3, in order to achieve an alignment of the pigments that is as parallel as possible to the (paper) substrate, depending on the rheology of the binder of the printing ink.

[0104] Figure 12In a highly simplified form, this shows an example of the production of the pigments according to the invention. Reference number 51 shows a top view of a web-shaped material 51 comprising a carrier film with an embossing varnish applied to it. The embossing varnish has an embossed and metallized relief structure. In further processing, the web-shaped material 51 is comminuted into individual pigments 52, e.g., by grinding (the individual pigments 52 are shown in a highly idealized form as regular rectangles). Before comminuting the web-shaped material 51 into individual pigments 52, the metallized embossing varnish can optionally be peeled off the carrier film.

[0105] Each pigment 51 contains a plurality of reflective micromirrors or microfacets 53, 54. The micromirrors are characterized by the parameters size, outline shape, relief shape, reflectance, and spatial orientation, and reflect incident light into a specific spatial area according to the specifications of this parameter set. Optically variable safety elements with such a microstructure are known from WO 2007 / 079851 A1 and WO 2011 / 066991 A2.

[0106] For example, micromirrors 53 and 54 of the Fig. 12 Each has a square base area A, thus a square outline, and a lateral dimension of 15 x 15 µm². Furthermore, the micromirrors have a simple relief shape with a single, flat reflective surface 55, which forms a specific angle of inclination α with the surface of the pigment.

[0107] In the case of the micromirror 53 (which, when viewed from the side, has the shape of a sawtooth or wedge), the reflective surface 55 has an inclination angle of α = 30° to the surface of the pigment. With a lateral extent of 1 = 15 µm, this inclination angle results in a structure height h of h = 1*tan(α) = 8.7 µm for the micromirror 53. In the case of the second micromirror 54, the reflective surface 55 is not inclined to the surface of the pigment (expressed by an inclination angle α = 0°). The following is mentioned only as an addendum:

[0108] Determining the reflection angle using special sensors (e.g., a handheld testing device) can serve as a authentication feature. For example, the print sample is illuminated at a defined angle (relative to the sample's position), and the angle corresponding to the reflection maximum of the reflected light is determined. From this, the angular deviation, and thus the angle of the sawtooth pattern 35, can be determined. This angle is characteristic of the pigment's relief structure. Figure 13 The angles α are denoted as follows: α = angle of incidence relative to the substrate; β = expected angle of reflection at total internal reflection relative to the substrate; γ = measured angle of reflection relative to the substrate; δ = angle of the wedge structure relative to the substrate.

Claims

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.