Multilayer Body and Method for Producing a Security Element

Abstract

A multilayer body ( 1, 2, 3 ) and a method for producing a security element are described. The multilayer body has a metal layer ( 21 ). An optically active surface relief is molded at least in areas in a first surface of the metal layer ( 21 ) facing the upper side of the multilayer body or forming the upper side of the multilayer body and/or in a second surface of the metal layer ( 21 ) facing the underside of the multilayer body or forming the underside of the multilayer body. In at least one first area ( 31 to 39 ) of the multilayer body the surface relief is formed by a first relief structure ( 61 ). In at least one direction ( 617 ) determined by an allocated azimuth angle, the first relief structure ( 61 ) has a sequence of elevations ( 612 ) and depressions ( 614 ), the elevations ( 612 ) of which follow on from each other with a period P which is smaller than a wavelength of visible light, wherein the minima of the depressions ( 614 ) lie on a base surface and the first relief structure ( 61 ) has a relief depth t which is determined by the spacing of the maxima of the elevations ( 612 ) of the first relief structure ( 61 ) from the base surface in a direction perpendicular to the base surface. The profile shape and/or the relief depth t of the first relief structure ( 61 ) is chosen such that the colored appearance of the light ( 52, 53 ) incident on the first area ( 31 to 39 ) at least at a first angle of incidence and directly reflected by the metal layer ( 21 ) in the first area or directly transmitted through the metal layer is modified, in particular is modified by plasmon resonance of the metal layer with the incident light.

1 . A multilayer body, in particular security element for security documents, with an upper side and an underside, wherein the multilayer body has a metal layer, wherein in a first surface of the metal layer facing the upper side of the multilayer body or forming the upper side of the multilayer body and/or in a second surface of the metal layer facing the underside of the multilayer body or forming the underside of the multilayer body an optically active surface relief is molded at least in areas, wherein in at least one first area of the multilayer body the surface relief is formed by a first relief structure which, in at least one direction determined by an allocated azimuth angle, has a sequence of elevations and depressions, the elevations of which follow on from each other with a period P which is smaller than a wavelength of visible light, wherein the minima of the depressions lie on a base surface and the first relief structure has a relief depth t which is determined by the spacing of the maxima of the elevations of the first relief structure from the base surface in a direction perpendicular to the base surface, and wherein the profile shape and/or the relief depth t of the first relief structure is chosen such that the colored appearance of the light incident on the first area at least at one first angle of incidence and reflected directly by the metal layer in the first area or transmitted directly through the metal layer is modified, by plasmon resonance of the metal layer with the incident light. 
     
     
         2 . A multilayer body according to  claim 1 , wherein the profile shape and/or the relief depth t of the first relief structure is chosen such that the metal layer, in the case of direct reflection for the light incident at the first angle of incidence, in the first area, in a first spectral range visible to the human eye with a width of at least 50 nm, has a reflectance of less than 10%, and in a second spectral range visible to the human eye with a width of 20 nm to 150 nm, has a reflectance that is at least 4 times higher, relative to the average value of the reflectance in the first spectral range. 
     
     
         3 . A multilayer body according to  claim 1 , wherein the profile shape and/or the relief depth t of the first relief structure is chosen such that at a second angle of incidence different from the first angle of incidence the colored appearance of the light reflected directly by the metal layer in the first partial area or transmitted directly through the metal layer is modified differently wherein different colors appear at these angles of incidence in the case of reflected light observation and in the case of transmitted light observation. 
     
     
         4 . A multilayer body according to  claim 1 , wherein the first relief structure has a profile shape that is asymmetrical in relation to a specular reflection at the base surface. 
     
     
         5 . A multilayer body according to  claim 1 , wherein the width of the elevations or depressions of the first relief structure, relative to a distance of t/2 from the base surface, is at least 0.6×P, or at most 0.3×P. 
     
     
         6 . A multilayer body according to  claim 1 , wherein the edge steepness of the first relief structure, relative to a distance t/2 from the base surface, is between 70° and 85°. 
     
     
         7 . A multilayer body according to  claim 1 , wherein the edge steepness of the first relief structure, relative to each distance between t/4 and ¾ t from the base surface, is between 50° and 85°. 
     
     
         8 . A multilayer body according to  claim 1 , wherein the edge steepness of the first relief structure, relative to each distance between 0 and t/4 and/or between t×¾ from the base surface, is between 0° and 40°. 
     
     
         9 . A multilayer body according to  claim 1 , wherein the layer thickness d of the metal layer in the area of the edges of the first relief structure, relative to a distance of t/2 from the base surface, is reduced by at least 30%, compared with the thickness of the metal layer in the area of the maxima of the elevations and/or the minima of the depressions. 
     
     
         10 . A multilayer body according to  claim 1 , wherein the period P of the first relief structure is between 250 nm and 450 nm. 
     
     
         11 . A multilayer body according to  claim 1 , wherein the relief depth t of the first relief structure is between 100 nm and 400 nm. 
     
     
         12 . A multilayer body according to  claim 1 , wherein in the first area, the metal layer has a layer thickness of between 10 nm and 100 nm. 
     
     
         13 . A multilayer body according to  claim 1 , wherein in the first area, the metal layer has a layer thickness d which corresponds to an optical depth of between 0.7 and 2.3. 
     
     
         14 . A multilayer body according to  claim 1 , wherein the first relief structure is a cross grating which has a sequence of elevations and depressions in two directions. 
     
     
         15 . A multilayer body according to  claim 1 , wherein the surface relief in one or more second areas and/or further areas is formed by a second and/or further relief structure(s) which is or are selected from the group: diffractive relief structure, holographic relief structure, mirror surface, mat structure, macrostructure, lens, grid of microlenses. 
     
     
         16 . A multilayer body according to  claim 15 , wherein the at least one first area and the at least one second area are formed by a plurality of partial areas, wherein the partial areas of the first area and the partial areas of the second area are interleaved. 
     
     
         17 . A multilayer body according to  claim 15 , wherein the at least one second area is formed by a plurality of partial areas separated from each other, and the first area surrounds these partial areas of the background area. 
     
     
         18 . A multilayer body according to  claim 1 , wherein the first area or at least one of the first areas has a patterned shaping and has a shaping which contains an item of information which can only be made visible using an aid, and is molded in the form of a nanotext or a moire pattern. 
     
     
         19 . A multilayer body according to  claim 1 , wherein the first area or at least one of the first areas comprises one or more first zones in which one or more of the parameters of the first relief structure selected from the group: period P, azimuth angle, relief depth t, base surface area and profile shape, differ from the corresponding parameters of the first relief structure in one or more second zones and/or one or more further zones of the first area. 
     
     
         20 . A multilayer body according to  claim 19 , wherein the one or more first and second zones are molded to form a motif, wherein the first zones form a foreground area of the motif and the second zones form a background area of the motif, or wherein the one or more first zones are molded to form a first motif and the one or more second zones are molded to form a second motif. 
     
     
         21 . A multilayer Multilayer body according to  claim 19 , wherein the first, second and/or further zones in each case have at least one lateral dimension of less than 150 μm, and wherein the first, second and/or third zones are interleaved. 
     
     
         22 . A multilayer body according to  claim 19 , wherein the first zones are arranged to represent a first motif and the second zones are arranged to represent a second motif, or wherein the first and the second zones are arranged to generate a multicolored representation or to generate mixed colors by means of additive color mixing. 
     
     
         23 . A multilayer body according to  claim 1 , wherein in the first area or in at least one of the first areas the base surface of the first relief structure is formed by a mat structure. 
     
     
         24 . A multilayer body according to  claim 1 , wherein in the first area or in at least one of the first areas, the period P of the first relief structure is varied in areas, by up to 10%. 
     
     
         25 . A multilayer body according to  claim 1 , wherein in the first area or in at least one of the first areas the azimuth angle of the first relief structure is varied in areas. 
     
     
         26 . A multilayer body according to  claim 1 , wherein the first area or at least one of the first areas has a plurality of partial areas, wherein each of the partial areas has a minimum dimension of more than 3 μm and a maximum dimension of less than 300 μm, wherein one or more of the parameters selected from the group: shape of the partial area, area size of the partial area, position of the center of area of the partial area, inclination angle of the base surface of the first relief structure relative to a base plane, angle of rotation of the base surface of the first relief structure about an axis perpendicular to the base plane, azimuth angle of the first relief structure, period P of the relief structure, is varied pseudorandomly, for each of the partial areas, within a variation range predefined in each case for the first area. 
     
     
         27 . A multilayer body according to  claim 1 , wherein the first area or at least one of the first areas has a plurality of partial areas, and wherein the parameters of the first relief structure in each of the partial areas is chosen according to a relief structure selected from a set of predefined relief structures pseudorandomly for the respective partial area. 
     
     
         28 . A multilayer body according to  claim 1 , wherein in the first area or in at least one of the first areas the multilayer body has dyes and/or luminescent substances which are arranged less than 1 μm, away from the first surface and/or the second surface of the metal layer. 
     
     
         29 . A multilayer body according to  claim 1 , wherein the multilayer body has at least one first layer bordering the first surface of the metal layer and/or one second layer bordering the second surface of the metal layer, which second layer has dyes and/or luminescent substances, wherein the first and/or second layer covers the first surface or the second surface of the metal layer in areas or over the whole surface in the first area or in at least one of the first areas in which the first relief structure is molded into the first or second surface. 
     
     
         30 . A multilayer body according to  claim 29 , wherein the first layer and/or the second layer is applied to the first surface or second surface of the metal layer only in the first area, or the first layer and/or the second layer is applied to the first or second surface of the metal layer only in areas of the first surface or second surface in which the first relief structure is molded into the first surface or second surface. 
     
     
         31 . A multilayer body according to  claim 29 , wherein the first layer and/or the second layer has a layer thickness of between 50 nm and 1 μm. 
     
     
         32 . A multilayer body according to  claim 29 , wherein the concentration of the dyes or luminescent substances in the area of the first and/or second layer less than 500 nm, away from the first or second surface of the metal layer is higher than in the remaining area of the first or second layer. 
     
     
         33 . A multilayer body according to  claim 29 , wherein the first layer and/or the second layer is a replication varnish layer, a layer arranged between a replication varnish layer and the metal layer, or a protective varnish layer. 
     
     
         34 . A multilayer body according to  claim 28 , wherein the dye and/or luminescent substance is a soluble dye or luminescent substance which is dissolved in the binder of the first layer or of the second layer. 
     
     
         35 . A multilayer body according to  claim 29 , wherein the first layer and/or the second layer has a transmittance of at least 70%, preferably of at least 90%, in the wavelength range visible to the human eye. 
     
     
         36 . A multilayer body according to  claim 29 , wherein the concentration of the dye and/or luminescent substances in the first layer and/or in the second layer is chosen such that the optical action thereof in a second area in which the surface relief is formed by a mirror surface, a diffractive structure, a macrostructure or a mat structure is not visible to the human observer at an observation distance of more than 30 cm and under an illumination with an illuminance of less than 10,000 LUX. 
     
     
         37 . A multilayer body according to  claim 29 , wherein the percentage by weight of the dye and/or of the luminescent substance in the dry weight of the first and/or second layer is between 0.5% and 10%. 
     
     
         38 . A multilayer body according to  claim 29 , wherein the color of the dye and/or luminescent substance of the first and/or second layer is chosen such that its color, or its color when excited, corresponds to the color generated by the first relief structure for a particular angle of incidence of the incident light in direct reflection or transmission or differs from these colors. 
     
     
         39 . A multilayer body according to  claim 29 , wherein two or more first layers and/or two or more second layers are provided, the dyes or luminescent substances of which are chosen such that the color of the dyes or luminescent substances of the first layer and/or of the second layer mutually differ, and wherein the first area or at least one of the first areas has a first partial area which is covered with one of the first and/or second layers and has a second partial area which is covered with another of the first and/or second layers. 
     
     
         40 . A multilayer body according to  claim 1 , wherein the multilayer body is a transfer film, a laminating film or a security thread. 
     
     
         41 . A multilayer body according to  claim 1 , wherein the multilayer body is a security element of a banknote or an ID document. 
     
     
         42 . A multilayer body according to  claim 1 , wherein the multilayer body is a banknote, a card or an ID document. 
     
     
         43 . A method for producing a security element comprising:
 manufacturing a multilayer body comprising a metal layer with an optically active surface relief molded into a first surface and/or a second surface opposite the first surface, wherein in at least one first area of the multilayer body the surface relief is formed by a first relief structure which, in at least one direction determined by an allocated azimuth angle, has a sequence of elevations and depressions, the elevations of which follow on from each other with a period P which is smaller than a wavelength of visible light, wherein the minima of the depressions define a base surface and the first relief structure has a relief depth t which is determined by the spacing of the maxima of the elevations of the relief structure from the base surface in a direction perpendicular to the base surface, and wherein the profile shape and/or the relief depth t of the first relief structure is chosen such that the colored appearance of the light incident on the first area at least at one first angle of incidence and reflected directly by the metal layer in the first area or transmitted directly through the metal layer is modified by plasmon resonance of the metal layer with the incident light.   
     
     
         44 . A method according to  claim 43 , wherein the multilayer body is formed as a transfer film, and wherein, by means of an embossing stamp formed patterned, a partial area of the multilayer body molded correspondingly patterned is stamped onto a substrate. 
     
     
         45 . A method according to  claim 44 , wherein the surface of the substrate onto which the multilayer body is stamped has a coarse structure or a mat structure, and wherein the stamping pressure is chosen such that the base surface of the first relief structure is deformed according to the coarse structure or mat structure during the stamping. 
     
     
         46 . A method according to  claim 43 , wherein a blind embossing die with a coarse structure molded in the embossing surface is pressed onto the multilayer body, and wherein the stamping pressure is chosen such that the base surface of the first relief structure is deformed according to the coarse structure of the blind embossing die.