Security document with transparent window formed in substrate

Abstract

A security document (02) with a transparent window (04) formed in a substrate (26), the security document (02) comprises a micro-optical structure (03) consisting of a number of micro-lenses (11), on the other side of the substrate (26) opposite to the side facing the micro-optical structure (03), at least one printed image (27) is arranged at least in the area of ​​the transparent window (04), the printed image (27) having a number of image elements (28a-28j) in a dot- or line-shaped halftone screen, the pixel size (38) or line width (38) of the image elements (28a-28j) being smaller than the lens width (18) of the micro-lenses (11) arranged in the micro-optical structure (03), and on the other side of the substrate (26) opposite to the side facing the micro-optical structure (03), the printed image (27) is arranged at least in the area of ​​the transparent window (04), the pixel size (38) or line width (38) of the image elements (28a-28j) being smaller than the lens width (18) of the micro-lenses (11) arranged in the micro-optical structure (03), and on the other side of the substrate (26) opposite to the side facing the micro-optical structure (03), the printed image (27) has a number of image elements (28a-28j) in a dot- or line-shaped halftone screen, the pixel size (38) or line width (38) of the image elements (28a-28j) being smaller than the lens width (18) of the micro-lenses (11) arranged in the micro-optical structure (03), respectively. A layer (39) is arranged on at least a portion of the printed image (27) on the opposite side, the layer (39) being produced by inkjet printing and being transparent to electromagnetic radiation having a wavelength in the range of 380 nm to 780 nm, the degree of transparency for said electromagnetic radiation being in the range of 10% to 90%, the transparency being graded over the two-dimensional extent of the layer (39) covering the printed image (27), so that at least one portion of the layer (39) or some portions of the layer (39) have a degree of transparency different from other portions of the layer (39). The layer (39) may be provided with a second printed image (41), which may be visible after folding.

Description

[Technical field]

[0001] The present invention relates to a security document comprising a transparent window formed in a substrate as claimed in claim 1.

[0002] A method for producing an image element array for an optically variable security device is known from WO 2017 / 081447, comprising the steps of: a) providing a production tool with a surface pattern of a plurality of ink absorbing elements spaced apart from one another by non-ink absorbing areas and defining image elements of a desired image element array; b) applying a first multi-coloured image formed from a plurality of printing inks only to the ink absorbing elements of the surface pattern and not to the areas between; c) transferring only those parts of the first multi-coloured image that correspond to the image elements of the desired image element array from the production tool to the substrate by contacting the plurality of printing inks on the surface pattern with a substrate or a transfer unit which then contacts the substrate, thereby forming an image element array on the substrate; and d) the surface pattern of the production tool is arranged such that the image elements of the desired image element array are transferred from the substrate to the substrate by contacting the plurality of printing inks on the surface pattern with a substrate or a transfer unit which then contacts the substrate. The ink absorbing elements defining the image elements of the image element array are configured to be periodic in at least one direction within at least a first area of ​​the image element array, such that when an observation element array with a corresponding periodicity is overlaid on the image element array, each observation element in the first area of ​​the image element array redirects light from each image element, or from each intermediate space between the image elements, in response to the observation angle, such that the observation element array in the first area redirects light from the array of image elements, or from the intermediate spaces therebetween, in response to the observation angle, such that as the observation angle changes, a first image is displayed in a first region of observation angles and is not displayed in a second region of observation angles by the image elements combined across the first area of ​​the image element array. Based on US20180196980 A1, a security substrate is known, which comprises a polymer substrate with a first and a second surface, an arrangement of focusing elements in the form of a surface relief over a first region of the polymer substrate, the surface relief being defined in a surface of a transparent base layer, the transparent base layer comprising a polymer substrate or a layer arranged thereon, and an optical adaptation layer arranged on the transparent base layer over a second region of the polymer substrate, the second region surrounding at least the first region, the optical adaptation layer comprising a profile that is not effective for focusing visible light, located opposite the first surface in contact with the surface relief of the transparent base layer. and a second surface including a first transparent material extending over a first lower region of the arrangement of focusing elements, the first lower region including the entire first region or only a portion of the first region, the first transparent material having a different refractive index than the transparent base layer, the focusing elements in the first lower region of the arrangement being functional focusing elements, and comprising at least one first masking layer including a reflective and / or non-transparent material configured over the optical matching layer and a third region of the polymer substrate, the third region defining at least one gap in the first masking layer, the gap surrounding at least a portion of the first lower region such that the functional focusing elements of the arrangement are revealed by the at least one gap.

[0003] From the translation of DE 112009002538 A1 an apparatus for registering security features to be embossed on a document in precise register is known which comprises: a) a first printing station for applying an embossable printing ink to a predefined area of ​​a substrate; b) an embossing station with embossing means for embossing at least a part of the area of ​​the embossable printing ink while forming an embossed security feature, the first printing station being arranged to print registration areas of the embossable printing ink onto the substrate and the embossing means being arranged to emboss at least a part of the registration area while forming a registration key; c) printing means for applying at least partially printed registration marks onto the substrate; d) identification means for identifying the position of the registration key and for identifying the position of the registration mark; e) comparison means for comparing the relative positions of the registration keys and the registration marks when the registration keys and the registration marks are not oriented in precise register and adjustment means for adjusting the position of the printing means relative to the embossing means.

[0004] According to US20190232708 A1, a security device is known, comprising an arrangement of focusing elements with a regular periodicity in at least one first direction, each focusing element having an optical footprint with different portions directed towards the observer depending on the observation angle, and an arrangement of image elements with a regular periodicity in at least the first direction and superimposed on the arrangement of focusing structures, the image elements representing portions of at least two respective images, at least one image element of each image being located within the optical footprint of the respective focusing structure, the security device surrounding a first region and a second region laterally offset from the first region, the image elements in the first region being shifted in at least a first direction in the laterally direction relative to the image elements in the second region, such that at a first observation angle, the image elements are directed towards the observer depending on the observation angle, and the image elements are directed towards the observer depending on the observation angle, the image elements being ... In a first region of the device, the focusing structure conveys image elements corresponding to the first image to the observer, such that the first image is displayed across the first region of the device, and at the same time, in a second region of the device, the focusing structure conveys image elements corresponding to the second image to the observer, such that the second image is displayed across the second region of the device, and in the case of a second observation angle, the first image is displayed across the second region of the device, such that the second image is displayed across the first region of the device, and at the same time, the first image is displayed across the second region of the device, and the security device further includes a color filter located in an insert between the image elements and the observer, the color filter overlaying at least a portion of the arrangement of focusing elements and the arrangement of image elements, and the color filter has a first color in the first region of the device and another color in the second region of the device, such that the coloring of the first and second images in the first and second regions of the device, respectively, is different.

[0005] From EP 2 493 700 A a method for producing a security device is known, which comprises the steps of: preparing an arrangement of lenticular focusing elements on one side of a transparent substrate; and preparing an arrangement of corresponding sets of image strips on the other side of the transparent substrate, the image strips and the lenticular focusing elements defining a lenticular device, whereby in different observation directions, each corresponding set of image strips is observed through each lenticular focusing element.

[0006] The security document known from WO 2011 / 107783 comprises a document substrate with at least two transparent or clear windows spaced apart from one another, and a device having a transparent substrate, the transparent substrate supporting i) a uniform arrangement of microfocusing elements defining a focal plane at a first surface thereof, ii) a corresponding first arrangement of microimage elements of a first color located in a plane substantially coinciding with the focal plane of the focusing elements, and iii) a corresponding second arrangement of microimage elements of a color different from the first color located in a plane substantially coinciding with the focal plane of the focusing elements, the pitch of the microfocusing elements and the first and second arrangements of microimage elements and their relative positions being determined by the cooperation of the arrangement of microfocusing elements with the first and second arrangements of microimage elements A magnified version of each of the micro-image elements in each arrangement is generated based on the Moire effect, at least one section of the first arrangement of the micro-image elements does not overlap with the second arrangement and at least one section of the second arrangement of the micro-image elements does not overlap with the first arrangement, the device is incorporated into a document substrate or is adapted to be aligned with at least two windows, the device is registered with respect to the document substrate such that a magnified version of the first micro-image element arrangement is viewable through a first of the two windows and a magnified version of the second micro-image element arrangement is viewable through a second of the two windows, and the transition between the two micro-image element arrangements is obscured by the document substrate between the two windows.

[0007] From the translation of DE 112010000957, a lens array for imaging a plurality of image elements in an object plane is known, which lens array comprises a plurality of microlenses arranged and formed on opposite sides of a transparent or semi-transparent material with image elements on one side, the lens array having a gauge thickness corresponding to the distance from the apex of each microlens to the object plane, each microlens having a set of lens parameters, the gauge thickness and / or at least one lens parameter being optimized such that each microlens has a focal size in the object plane that is substantially equal to the size of the image elements in the object plane or that differs from the size of the image elements by a predefined dimension. In this case, the gauge thickness of the lens array is preferably smaller than the focal length of all the microlenses. The image elements can, for example, have the shape of points or lines. The lens array described in the translation of German Patent Invention No. 112010000957 is formed in such a way that within the cone or angular range of light incident on the microlens towards the image element, only a single image element of the image elements arranged side by side is always arranged in a cross section parallel to the main plane of the microlens, so that an observer viewing the printed image at a particular viewing angle can always perceive only a single frame at a particular time.

[0008] The problem underlying the present invention is to provide a security document with a transparent window formed in a substrate.

[0009] This problem is solved by a security document having the features of claim 1. The dependent claims indicate advantageous configurations and / or refinements of the solution found.

[0010] One embodiment is shown in the drawings. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 shows a security document equipped with a security element having an optical imaging structure. [Diagram 2] A greatly enlarged cross-sectional view of an arrangement having at least one printed image and a single plano-convex microlens incorporated within the optical imaging structure and having light incident from a first observation angle. [Diagram 3] FIG. 3 shows the arrangement shown in FIG. 2 with light incident from a second observation angle. [Figure 4] FIG. 1 shows a security document with self-authentication means. [Diagram 5] FIG. 1 illustrates a security document with a contrast enhancing back side. [Figure 6] FIG. 2 shows a security document with a contrast enhancing back side and a self-authentication means. [Figure 7] FIG. 7 is a simplified schematic diagram of a printing press for producing security documents, particularly as shown in FIG. 5 or FIG. 6.

[0012] In optics, the term "lens" refers to a light-transmissive component with at least one light-refractive surface arranged in the light path. Here, the term light refers to that portion of electromagnetic radiation that is visible to the human eye. In the electromagnetic spectrum, the light range includes wavelengths from approximately 380 nm (violet) to 780 nm (red). In the following, focusing lenses, i.e. lenses that focus the incident light, are taken as the basis, in particular lenses that are designed plano-convex. Preferred design forms are, on the one hand, rotationally symmetric lenses with a spherical or aspherical design, and, on the other hand, axially symmetric lenses with a rod-shaped design, whose axes of symmetry and the optical axis respectively run coincidently. That is to say, the optical axis is a straight line that usually runs through the center of curvature of the convex lens surface. In the case of a flat lens surface, the optical axis is perpendicular to this lens surface. The curvature of a light-refractive, for example convex, surface is indicated by its radius of curvature, which has its origin on the optical axis. A flat lens surface is defined by an infinitely large radius of curvature.

[0013] Rod-shaped lenses are formed in the shape of their respective rod lengths like two equally divided straight or elliptical cylinders, the respective axes of symmetry of such lenses running perpendicular to the respective rod lengths. In the case of spherically shaped lenses, the light-refractive surface is formed as a part of the surface of a sphere, i.e., for example in the form of a spherical cap. Aspherically shaped lenses have at least one light-refractive surface that differs from a spherical or flat shape. The shape of a rotationally symmetrical aspherical surface is usually shown as a conic section (circle, ellipse, parabola, hyperbola) plus correction polynomials for higher-order deformations.

[0014] A lens has two surfaces that intersect the light path, the so-called envelope surfaces, and the light enters a focusing lens, which is formed plano-convex in terms of the light beam definition, at a convexly curved envelope surface in each case, and exits from this lens at its flat envelope surface. These envelope surfaces are each interfaces between different media through which the light propagates. One of these media is formed by the substance, i.e. the material of the lens. At least one other medium is the space, usually filled with air, in which the lens is located. At least two of the media arranged in the light path differ from each other in at least their respective optical material properties, so that the light is refracted at the interface between these mutually bordering media. This means that at least one of the envelope surfaces of each lens, in particular at the curved envelope surface of the lens, refraction of light occurs. The optical material properties associated with the refraction of light are represented by the respective refractive indices of the media. The refractive index is a dimensionless physical quantity that indicates the rate at which the wavelength and phase velocity of light in a medium are reduced compared to that in a vacuum. Of two media with different refractive indices that form a common interface, the one with the higher refractive index is optically called the higher refractive index. The Abbe number, also called the inverse dispersion, is a dimensionless quantity that characterizes the optical dispersion properties of a lens and indicates how significantly the refractive index of a lens varies with the wavelength of light. The properties of a lens that can form an optical image of an object viewed through the lens depend on the refractive index of the material of each lens and the shape of the lens envelope that forms the interface between the different media.

[0015] The planes arranged in this component perpendicular to the axis of symmetry of the lens are called the principal planes of the lens. In the case of thin lenses, whose maximum extension along the axis of symmetry, i.e. the thickness of the lens, is considered to be much smaller than the radius of curvature of its convex envelope, the radius of curvature of the convex envelope being, for example, at least five times larger than this thickness, it is usually sufficient to assume only a single principal plane in the evaluation of the properties of the lens, since this radius is, for example, at least five times larger than this thickness. In the case of plano-convex lenses, this principal plane coincides with the flat lens surface. The focal length of a lens is the distance between the principal plane of the lens and its focus, which means the intersection point of several rays of light which enter the lens parallel to one another and are focused by this lens. In this case, the rays of light which enter the lens parallel to one another do not necessarily enter parallel to the optical axis of the lens, but at an arbitrary, in particular acute, angle of incidence to the principal plane of the lens. The planes arranged perpendicular to the optical axis in the focus are called focus or focal planes.

[0016] The envelope surface of the lens used for light incidence has two boundary points, located on opposite sides of the optical axis and defining the envelope surface, for example located in the main plane of the lens, the distance between these two boundary points determines the width of the lens (=lens width). The aperture or aperture width of the lens represents the open aperture of the lens through which light rays can be received without hindrance or its diameter, and corresponds at most to the lens width. The point located at the intersection of the optical axis and the envelope surface used for light incidence of the lens is called the apex. The apex is located in the envelope surface used for light incidence farthest from the focal point of the lens.

[0017] A rotationally symmetrical, spherically or aspherically shaped lens focuses the incoming light into a cone or cone whose base diameter corresponds at most to the lens width and whose height extending perpendicularly to the base corresponds to the focal length of the lens. An axially symmetrical, rod-shaped lens focuses the incoming light within an acute angular range, the origin of which is located at the focal point of the lens. The numerical aperture describes the lens's ability to focus light. It determines the smallest size of the light spot that can be formed at the focal point and is therefore an important value that limits the resolution.

[0018] A plurality of rotationally symmetrical, spherically or aspherically shaped lenses, arranged in a preferably uniform grid of square or hexagonal grid cells, in particular without gaps and without overlap, form a lens group, also called a lens array. A plurality of axially symmetrical, rod-shaped lenses, arranged in a row perpendicular to their rod length, also preferably without gaps and without overlap, form a lens mesh screen, also called a lenticular. The lenses arranged in a grid-shaped lens group and / or in a lens mesh screen form an optical imaging structure in each of their combined groups in the form of a geometric figure extending over a flat or curved surface. The surface of the optical imaging structure may have any contour, for example a rectangular, circular, elliptical or polygonal contour. In geometry, a geometric figure is understood to consist of a set of points. For the optical imaging structure, a lens is arranged in each case per at least a subset of the points forming the geometric figure.

[0019] In the optical imaging structure, only one or more respective lattice-shaped lens groups or only one or more respective lenses arranged in a lens mesh screen may be arranged, or both lens arrays may be arranged together with other lens arrays, so that in the same optical imaging structure, both lattice-shaped lens groups and lenses arranged in a lens mesh screen are arranged. The lens mesh screens formed in the optical imaging structure may have, for example, different orientations, the orientation of each of the lens mesh screens being determined by the respective directions of the lengths of the lenses involved in the structure of the lens mesh screen.

[0020] A microlens is a miniaturized form of a conventional lens. The term microlens here means a lens whose lens width is less than 100 μm, preferably in the range of 20 μm to 65 μm. A microlens has for example a focal length of less than 100 μm, preferably at most 95 μm. Microlenses can nowadays be produced industrially. Microlenses made of plastic or resin can be produced for example using (injection) casting or (injection) embossing or printing methods. Optical imaging structures made of microlenses are also called micro-optical structures.

[0021] In particular, when an optical imaging structure formed from microlenses is arranged or arranged in combination with a printed image, preferably formed in a planar manner, for example by applying or being applied to a substrate carrying the printed image, various effects can be generated for the observer who views the printed image through the optical imaging structure. That is, an arrangement consisting of at least one printed image and at least one optical imaging structure can generate, for example, so-called flip or oscillating images (flip) and / or stereoscopic, i.e. three-dimensional effects and / or morphing effects and / or zoom effects and / or animations. These effects are perceptible to the observer without optical aids when the observer alternately views the printed image at different viewing angles. The perceived image that is shown to the observer by different viewing angles is also called a lenticular image.

[0022] The usually planar printed image is preferably formed on a substrate, preferably two-dimensionally formed, for example in an industrial production process, preferably by a printing machine. The substrate is formed, for example, as a web or a printing sheet of the material to be printed. The printed image is applied to the substrate, for example with a dot-like or line-like mesh screen. The printed image thus consists, for example, of a plurality, in particular a large number of pixels and / or lines. In this case, the pixel size or line width is in the range of less than 100 μm, preferably less than 50 μm, in particular less than 20 μm, for example in the range of about 5 μm to 10 μm. In the following, it is assumed that the pixel size of the pixels and / or line width of the lines each participating in the formation of the printed image used together with the optical imaging structure are, for example, respectively, at most equal in size to the respective lens width of the lenses participating in the construction of the optical imaging structure, preferably less than half the size.

[0023] In optics, the ability to distinguish fine structures, i.e. the minimum distance that for example two pixels or two lines must have from each other to be able to perceive them as separate pixels or lines, is called resolution. The resolution of the human eye varies from person to person. At a distance of 25 cm, an emmetropic adult can still distinguish structures that are mostly 150 μm apart. This corresponds to a visual angle of about 2 arc minutes, which is called the angular resolution. At low contrasts, the visual acuity of the human eye is significantly reduced, and in this case visual acuity represents the reciprocal of the resolution. Thus, the lens width of a microlens is generally smaller than the resolution of the emmetropic adult's eye.

[0024] To produce a coloured printed image, a substrate is printed or has been printed with a number of printing inks, for example red, green, blue and possibly black printing inks, which are called primary colours. A printed image usually consists of an arrangement of a number of small-area picture elements arranged at different positions on the printed image, each of which preferably has a number of pixels or lines and usually extends over a length of less than 100 μm. Each picture element or a group of adjacent picture elements forms an object to be observed, for example through a lens. The individual picture elements are arranged in a printed image so as to form a printed motif, which usually determines the information content of the printed image. Individual picture elements used with microlenses usually cannot be perceived in their entirety by the naked human eye due to their limited, usually insufficient, resolution. The colour impression of a printed image or at least of a part of this printed image perceived by a person is caused by additive colour mixing, which takes place in the eye and brain of the observer, of the pixels and / or lines printed in the picture element with different printing inks. The superposition of each two primary colours produces colour impressions of yellow, cyan and magenta, which are called secondary colours. The superposition of all three primary colors produces a white color impression. The color registration, i.e. the match retention, i.e. the match accuracy, of the pixels and / or lines of the different printing inks arranged relative to one another is less than 20 μm, preferably less than 10 μm, in particular in the range of about 5 μm, in the embodiments of the invention considered here.

[0025] The optical imaging structures provided in connection with the embodiments of the invention considered here are preferably arranged as a combination of pixels and / or lines of several different printing inks. The printing image is preferably formed as or produced by the superposition of several partial printing images, each of which, or preferably each of which, has been or is printed with a different printing ink. In this case, the superposition may be produced or be produced by successive superimposed printing on the substrate or preferably by collecting the partial printing images on a printing member, for example on a cylinder, and transferring them simultaneously to the substrate. The partial printing images themselves each consist of pixels and / or lines, the pixel size of these pixels and / or the thickness of the lines being each in the micrometer range, for example in the range of less than 20 μm. In the case of an observer observing the printing image, in the perception of this observer, the several partial printing images participating in this printing image are superimposed to form an overall impression, for example of one color.

[0026] The arrangement of at least one printed image and at least one optical imaging structure allows an observer observing the printed image to perceive a number of different individual images at various viewing angles, where successive individual images in the observer's perception produce a flip or oscillating image and / or a stereoscopic, i.e. three-dimensional effect and / or a morphing effect and / or a zoom effect and / or an animation. Each of these individual images is also called a frame. The individual images perceivable by the observer at each given viewing angle arise at each position of the microlens on the basis of a selection determined by the optical imaging structure from a set of partial printed images perceivable on the basis of at least one image element present there or on the basis of a number of image elements present there, and the overall color impression for a position of the printed image is produced by the superposition of all perceivable partial printed images present at this position. The optical imaging structure arranged in combination with the printed image is therefore an optical masking of the partial printed images participating in said printed image, which are arranged to overlap with the surface of the optical imaging structure.

[0027] In order to realize, for example, more complex and / or more detailed animations, by making several frames simultaneously perceptible to an observer observing the printed image at a particular observation angle in each case, an arrangement is used, for example, with a printed image and an optical imaging structure consisting of several plano-convex microlenses, in which several, preferably four or more, in particular 5 to 10, image elements are arranged side by side under at least one microlens of the optical imaging structure, which image elements are arranged in a cross section parallel to the main plane of the microlens between the extension of the lens width of the microlens and its focus, which cross section is arranged in each case so as to intersect a cone or angular range of light passing through the lens width of the microlens and incident on the image elements arranged side by side, and in the cross section inside the cone or angular range several different image elements are arranged side by side at the same time.

[0028] This results in an arrangement having a printed image and an optical imaging structure consisting of a number of plano-convex microlenses, each of which has a lens width along the printed image, preferably less than 100 μm, and the printed image has a large number of image elements, and a number of image elements each arranged under at least one microlens of the optical imaging structure are arranged side by side along the lens width and each extend in the direction of the lens width over a length that is smaller than the lens width, and between the extension of the lens width of the microlens and its focus, in a cross section that is parallel to the main plane of the microlens within the cone or angular range of light that passes through the lens width of the microlens and is incident on the image elements arranged side by side, a number of image elements, preferably at least three, in particular four or more, which are each different from one another, are arranged side by side. This arrangement allows an observer looking at the printed image to perceive multiple frames simultaneously, each at a given viewing angle, thereby resulting in complex and / or detailed animations as well as smooth color transitions in the case of image elements formed in corresponding colors and / or smooth frame transitions in the case of different printing motifs formed from multiple image elements.

[0029] The substrate is, for example, a fiber-containing printing material, in particular paper, or a film, preferably a polymer film. The substrate may be made opaque or transparent. The substrate may be made monolayer or multilayer, in particular partially multilayer. The different layers of the multilayer substrate may be made of different materials, for example one layer may be made of paper and another layer may be made of a polymer film. The substrate or at least one layer of this substrate each has a given material thickness, i.e. for example less than 100 μm, preferably less than 50 μm, in particular about 25 μm. The printed image formed on the substrate has, for example, a layer thickness of less than 10 μm, preferably less than 5 μm, in particular in the range of 1 μm to 2 μm. The substrate may be printed on one or both sides.

[0030] In a preferred embodiment of the invention, the arrangement of the printed image and the optical imaging structure is a component of a security element or document, in particular a security document. These documents include, for example, banknotes, credit cards, cheques, securities, stock certificates, passports, identity cards, driver's licenses, ownership certificates, travel documents such as airline or rail tickets, admission tickets, research materials, and other official or government documents such as birth, death or marriage certificates. This list is merely exemplary and not complete, but is preferably banknotes.

[0031] 1 shows by way of example a document 02, in particular a security document 02, on which or in which at least one security element 01 is arranged. The document 02 and / or the security element 01 has at least one optical imaging structure 03 over a partial or full surface, each optical imaging structure 03 being preferably designed as a micro-optical structure 03 formed from a number of microlenses 11. The optical imaging structure 03 is arranged, for example, such that it at least partially covers a printed image 27 formed or applied to the document 02.

[0032] FIG. 2 exemplarily shows, in a greatly enlarged cross-sectional view, an arrangement with a single plano-convex microlens 11 integrated into a group of microlenses 11 or into a mesh screen, in particular as part of the security element 01 or document 02 shown in FIG. 1. The microlens 11 has an axis of symmetry 12, which at the same time also forms the optical axis 12 of the microlens 11. The microlens 11 can be rotationally symmetrically spherical or aspherically shaped or, for example, axially symmetrically rod-shaped, in which case the axis of symmetry 12 runs perpendicular to the rod length. The microlens 11 is produced, for example, from a transparent plastic or resin by injection or casting or embossing or printing techniques. The microlens 11 has a convex envelope surface 13 for light incidence, into which a bundle of, for example, parallel light rays 14 enters. The microlens 11 has two boundary points 16;17 that define the convex envelope 13, located on opposite sides of the optical axis 12 that runs through the vertex 37 of the convex envelope 13, the distance between these two boundary points 16;17 determining the width of the microlens 11, called the lens width 18. The lens width 18 of a microlens 11 is less than 100 μm. The two boundary points 16;17 of the convex envelope 13 lie in a plane, also called the main plane 19 of the microlens 11, that is arranged perpendicular to the optical axis 12 of the microlens 11. In the embodiment shown in FIG. 2, the main plane 19 forms a flat envelope 21 of the microlens 11. The distance between the main plane 19 of the microlens 11 and its focus 23 forms the focal length 22 of the microlens 11, which is in particular the intersection of multiple light rays 14 that are incident parallel to each other on the microlens 11 and are focused. The focal length 22 of one microlens 11 is less than 100 μm. The plane at the focus 23 that is arranged perpendicular to the optical axis 12 is called the focal plane 24.

[0033] In the embodiment shown in FIG. 2, the microlenses 11 are part of a lens array or lens mesh screen in which a multiplicity of microlenses 11 are arranged, preferably without gaps and without overlap, respectively, in a given area of ​​arbitrary contour. The lens array or lens mesh screen is arranged on a substrate 26, which is formed, for example, as a printable material containing fibers and having a transparent window, in particular as paper, or as a film, preferably as a transparent polymer film. The substrate 26 has a material thickness 29 or thickness 29, for example, of less than 100 μm, preferably less than 50 μm, in particular about 25 μm. The substrate 26 is preferably part of a security element 01 or a document 02, in particular a security document 02. The substrate 26 is formed transparent, at least in the area covered by the flat envelope surface 21 of each microlens 11.

[0034] 2, a printed image 27 with a small layer thickness 36, for example less than 10 μm, is applied to the rear side of the substrate 26, i.e. on the side of the substrate 26 facing away from the microlens 11, which printed image 27 has a large number of individual image elements 28, each different from one another. These individual image elements 28 are formed with an extremely small area and extend parallel to the lens width 18 over a few micrometers, for example up to 10 μm. It is thus possible to arrange a number of such image elements 28a-28j, for example side-by-side, in the area covered by the flat envelope surface 21 of the microlens 11. At least one of these image elements 28a-28j preferably has pixels and / or lines printed with different printing inks, in particular depending on the number of adjacently arranged image elements 28a-28j, the pixel size 38 of each of the pixels of the image elements 28a-28j and / or the line thickness 38 of the image elements 28a-28j being in the range of a few micrometers, preferably in the range of less than 20 μm. The printed image 27 preferably consists of an overprint or of a superposition of several partial printed images, each printed with different printing inks. The image elements 28a-28j arranged in the area covered by the flat envelope surface 21 of the microlens 11, i.e. below said microlens 11, in particular adjacent to each other, preferably belong to different printing motifs.

[0035] The image elements 28a-28j, which are arranged below the microlens 11, for example adjacent to each other, are advantageously arranged closer to the microlens 11 than the focus 23 of the microlens 11. Preferably, these image elements 28a-28j are arranged between the microlens 11 and its focus 23 in a cross section 31 which lies parallel to the main plane 19 of the microlens 11, the cross section 31 being arranged in each case to intersect a cone 32 or an angular range 32 of light which passes through the lens width 18 of the microlens 11 towards the image elements 28a-28j, for example adjacent to each other, and within the cross section 31 inside the cone 32 or angular range 32, preferably several of the image elements 28a-28j are arranged side by side at the same time. In the embodiment shown in Fig. 2, for example five image elements 28c-28g are arranged side by side inside the cone 32 or angle range 32 at the same time, whereas the other image elements 28a, 28b and 28h-28j arranged in the area covered by the flat envelope surface 21 of the microlens 11 are not perceptible to the observer looking at the printed image 27 at a first observation angle 33, for example an acute one, corresponding to the incident light ray 14. If for the observer looking at the printed image 27 the observation angle is changed to a second observation angle 34, for example an obtuse one, different from the first observation angle 33, the image elements 28a-28j perceptible by the observer also change. This is shown in Fig. 3, which has the same arrangement with the printed image 27 and the optical imaging structure 03, which consists of a number of plano-convex microlenses 11 as in Fig. 2. Based on a second observation angle 34 different from the first observation angle 33, in the embodiment shown in Figure 3, only image elements 28d-28h are perceptible to an observer observing the printed image 27, whereas the other image elements are imperceptible.

[0036] As explained, the image elements 28a-28j arranged in the area covered by the flat envelope surface 21 of the individual microlenses 11 shown in Figs. 2 and 3 are preferably formed by pixels and / or lines printed with different printing inks. Typically, the pixel size 38 of the pixels and / or the line width 38 of the lines are significantly smaller than the lens width 18 of the microlenses 11, preferably within the range of a few micrometers, in particular within the range of less than 20 μm. In particular, in order to form a machine-readable printed image 27 including these image elements 28a-28j, at least one of these image elements 28a-28j has pixels and / or lines for which a special printing fluid, in particular an ink, is used for printing, which printing fluid differs in its optical properties from common printing fluids, in particular common printing inks or inks. These special printing fluids are, for example, inks that are invisible to the naked human eye of a normal-sighted observer without excitation lying outside the electromagnetic spectrum visible to the human eye, in particular inks that absorb infrared radiation, or inks that reflect infrared radiation, or inks that convert infrared radiation to visible radiation, or inks that fluoresce under ultraviolet radiation, or magnetic inks. These inks, which are invisible, in particular under daylight conditions, can, upon appropriate excitation, become perceptible in various shades, for example in the blue, green or red color range, just like other printing inks. This excitation is preferably electromagnetic or magnetic.

[0037] The term ink is used herein to mean an intensely colored liquid, consisting of dyes dissolved or dispersed in water or another solvent, which is free of binder or, in the case of inks formulated as India ink, contains small amounts of binder. Dyes are color-imparting substances, such as pigments and dyes, which may be inorganic or organic, naturally or artificially produced. In contrast, a printing ink is a mixture containing dyes, which is transferred to a substrate, i.e. a printed material, via a printing plate. Printing inks contain inorganic and organic pigments, such as titanium dioxide as a white pigment or carbon black as a black pigment, as well as a binder that encases the pigments. Both conventional printing inks and inks, including inks that are invisible to the human eye under daylight conditions, may be encompassed by the term printing fluid.

[0038] The above-mentioned special inks sensitive to infrared (IR) are used, for example, in connection with electromagnetic radiation in the near infrared range (NIR), preferably with radiation having a wavelength in the range 780 nm to 2000 nm, in particular in the range 780 nm to 1200 nm. Ink sensitive to infrared (IR; NIR) contains, for example, inorganic, usually pigment-like luminophores which emit radiation in the visible spectral range and / or in the infrared range (NIR) after energy absorption. Ink converting infrared to visible contains so-called anti-Stokes pigments.

[0039] Ultraviolet light, abbreviated UV or UV rays, is electromagnetic radiation that is invisible to the human eye and has a shorter wavelength than visible light. The ultraviolet spectrum, according to a widely accepted classification, includes wavelengths from 100 nm to 380 nm, that is, wavelengths ranging from the shortwave region to the border of visible light. UV-fluorescent inks contain fluorescent pigments that emit strong light when exposed to ultraviolet light, and sometimes utilize the ultraviolet light of daylight.

[0040] By magnetic ink is meant in particular ink mixed with iron oxide particles, which can be magnetized by a magnetic field external to the arrangement comprising substrate 26 and optical imaging structure 30 and different from the Earth's magnetic field, and can thus be magneto-optically analyzed and read out.

[0041] An advantageous arrangement with respect to machine readability, with a printed image 27 applied to a substrate 26 and an optical imaging structure 03 covering at least a part of the printed image 27, is that the optical imaging structure 03 comprises a group or mesh screen of a plurality of plano-convex microlenses 11, the flat envelope surface 21 of the microlenses 11 facing the substrate 26, and the printed image 27 arranged on the substrate 26 preferably has at least one image element 28a-28j arranged on its side facing the optical imaging structure 03 and with at least one pixel and / or line, which pixels and / or lines are formed by a printing technique with a printing fluid, which is intended to be visible to the human eye only upon excitation by light outside the electromagnetic spectrum visible to the human eye. The printing fluid is preferably formed as an ink that absorbs infrared light, or an ink that reflects infrared light, or an ink that converts infrared light to visible light, or an ink that fluoresces under ultraviolet light, or a magnetic ink. The at least one image element 28a-28j of the machine-readable printed image 27 is thus a component integrated into the arrangement, for example in a security element 01 or in a document 02, in particular in a security document 02. The excitation light of the printing fluid, which is located outside the electromagnetic spectrum visible to the human eye, is directed, with respect to the optical imaging structure 03 covering at least a part of the printed image 27, either on the front side, i.e. towards the respective convex envelope surfaces 13 of the microlenses 11, if the optical imaging structure 03 is designed to act through the optical imaging structure 03, or on the back side, i.e. towards the substrate side or towards the respective flat envelope surfaces 21 of the microlenses 11, if the optical imaging structure 03 is designed to block the excitation light.

[0042] If it is assumed that a printing fluid that is visible to the human eye only based on excitation light that is outside the electromagnetic spectrum visible to the human eye should not interact with the microlenses 11 of the optical imaging structure 03, in such an arrangement, the pixel size 38 of the pixels and / or the line thickness 38 of the lines are formed, for example, larger than the lens width 18 of the microlenses 11.

[0043] It may further be envisaged that in said arrangement of substrate 26 and optical imaging structure 03, at a number of individual locations in the group of optical imaging structures 03 with a number of plano-convex microlenses 11 or in the mesh screen of each optical imaging structure 03 with a number of plano-convex microlenses 11, each microlens 11 remains unformed, and at said missing places at least one image element 28a-28j of printed image 27 with at least one pixel and / or line is arranged, said pixel and / or said line being formed by printing techniques with a printing fluid that is visible to the human eye only on the basis of excitation light that is located outside the electromagnetic spectrum visible to the human eye. Thus, a printing fluid that is invisible to the human eye under normal conditions is applied or arranged or is applied or arranged at selected missing places in each optical imaging structure 03.

[0044] As mentioned above, the arrangement consisting of the substrate 26 and the optical imaging structure 03 can have a printed image 27, which allows an orthoscopic observer, observing the printed image 27 with the naked eye through the optical imaging structure 03, to perceive a number of different individual images at various viewing angles, where successive individual images in the observer's perception produce a switching or oscillating image (flip) and / or a stereoscopic, i.e. three-dimensional effect and / or a morphing effect and / or a zoom effect and / or an animation. These different individual images are also called frames. These above-mentioned effects are each based on a number of partial printed images, from which at least one said printed image 27 is synthesized. To form an arrangement consisting of the substrate 26 and the optical imaging structure 03 with at least one machine-readable printed image 27, it is assumed that the said printed image 27 comprises a number of partial printed images, at least in the area covered by the optical imaging structure 03. At least one of these partial printed images has an image element 28a-28j with at least one pixel and / or line, which pixel and / or line is formed by a printing technique with a printing fluid that is visible to the human eye only on the basis of excitation light that is located outside the electromagnetic spectrum visible to the human eye. In an alternative or additional configuration, it may be provided that at least one image element 28a-28j of at least one partial printed image of the printed image 27 that includes a plurality of partial printed images to be formed in a machine-readable form is formed by a mixture, which mixture includes a printing fluid that is visible to the human eye, in particular under daylight conditions, and a printing fluid that is visible to the human eye only on the basis of excitation light that is located outside the electromagnetic spectrum visible to the human eye.

[0045] Furthermore, in order to form an arrangement with at least one machine-readable printed image 27, it may be assumed that in an arrangement having a substrate 26 having a printed image 27 and a structure 03 for optically imaging this printed image 27, in a first area covered by the optical imaging structure 03, the image elements 28a-28j of the printed image 27 arranged thereon are each formed by a printing fluid that is visible to the human eye, in particular under daylight conditions, and in a second area covered by the optical imaging structure 03, the image elements 28a-28j of the printed image 27 arranged thereon are each formed by a printing fluid that is visible to the human eye only based on excitation light that is located outside the electromagnetic spectrum visible to the human eye.

[0046] What may be described below may be assumed without taking into account the type of printing fluid used for each configuration of the substrate 26 and / or each configuration of the optical imaging structure 03 formed on the substrate 26 and / or for forming the at least one printed image 27, in particular whether a printing fluid visible to the human eye under daylight conditions is used, or whether a printing fluid visible to the human eye only based on excitation light that is outside the electromagnetic spectrum visible to the human eye is used, or whether two types of printing fluids as mentioned above are used together for the creation of the same printed image 27 to form a security element 01 or a confidential document 02.

[0047] 4 shows an exemplary security document 02, for example a banknote, whose substrate 26 consists, for example, of a fiber-containing printable material, in particular paper, and has at least one transparent window 04. Alternatively, the substrate 26 of the security document 02 can also be a film, preferably a transparent polymer film or a film with a transparent window 04. On one side of the security document 02, at least in the region of the transparent window 04, a micro-optical structure 03 is arranged, which partially or completely covers the window 04. The micro-optical structure 03 is formed as a lens array or as a lenticular, each of which consists of a number of plano-convex micro-lenses 11. In the case of a lens array, the micro-lenses 11 are formed rotationally symmetrically spherically or aspherically, and in the case of a lenticular, for example, axially symmetrically rod-shaped. On the other side of the security document 02, spaced outward from the area of ​​the transparent window 04, i.e. on the side of the security document 02 that does not have the above-mentioned lens array or lenticulars, a printed image 27 is formed or applied, which may be formed with a printing fluid that is visible to the human eye, in particular under daylight conditions, or may be formed with a printing fluid that is visible to the human eye only on the basis of excitation light that is located outside the electromagnetic spectrum visible to the human eye. The printed image 27 may contain information that is directly recognizable to a human being or may be formed only machine-readable. The printed image 27 is applied to the substrate 26 with, for example, a dot- or line-shaped halftone screen consisting of image elements 28a-28j, and is preferably produced by an industrial printing process, for example by offset printing. The pixel size 38 or line width 38 of the image elements 28a-28j of the printed image 27 applied to the substrate 26 is made smaller than the lens width 18 of the microlenses 11 arranged in the lens array or lenticular, and is therefore significantly less than 100 μm, and preferably about 20 μm or less.If a window 04 partially or completely covered by a micro-optical structure 03 in this substrate 26 of a security document 02 also has on its back side, i.e. on the side of the substrate 26 of the security document 02 opposite to the side facing the micro-optical structure 03, a further printed image 27, preferably also produced by an offset printing method, arranged in the area of ​​the transparent window 04 has at least one non-printed surface, i.e. a cutout 06, in the area covered by the micro-optical structure 03, so that said cutout 06 in the further printed image 27 arranged in the area of ​​the window 04 partially exposes the micro-optical structure 03 applied to the substrate 26 of this security document 02 and opens up the field of view for the respective flat envelope surfaces 21 of the plano-convex microlenses 11 arranged in the micro-optical structure 03 through the transparent window 04.

[0048] The method for authenticating a security document 02 having a micro-optical structure 03 is characterized in that the substrate 26 of the security document 02 is folded (as suggested by the arrow in FIG. 4 ) at a fold line 07, preferably transverse to the security document 02, so that a printed image 27 formed or applied spaced outward from the area of ​​the transparent window 04 can be superimposed or at least superimposed with a micro-optical structure 03 applied on the other side of the substrate 26 of the security document 02 or at least with one of the cut-outs 06 partially exposing the micro-optical structure 03 in the printed image 27 arranged in the area of ​​the window 04. The substrate 26 of the security document 02 can be folded, for example approximately in half (as suggested in FIG. 4 ), so that the folded part of the substrate 26 having the printed image 27 spaced outward from the area of ​​the transparent window 04 rests or at least can be rested on the other part of the substrate 26 having the transparent window 04 and the micro-optical structure 03. By folding the substrate 26 of the security document 02, the printed image 27, which is deposited spaced outward from the area of ​​the transparent window 04, is placed within the transparent window 04 of the substrate 26 of the security document 02 on the flat envelope surfaces 21 of each of the plano-convex microlenses 11 arranged in the micro-optical structure 03.

[0049] Optionally, by performing a relative movement between the micro-optical structure 03 and a printed image 27 formed or applied on the micro-optical structure 03 and spaced outward from the area of ​​the transparent window 04, or by performing a tilting movement of the entire security document 02 folded at the fold line 07, the printed image 27 or at least the information contained in the printed image 27 becomes visible or discernible upon observation directed towards the printed image 27 through the micro-optical structure 03 from the direction of the convex envelope surface 13, as exemplarily shown in FIG. 4 , preferably by a human-readable "&" symbol.

[0050] The advantage of the solution found is that the security document 20 can be authenticated without the use of external means, i.e. the proposed method allows the self-authentication of the security document 02 based only on its own means. The authentication proposed here can therefore be performed anywhere and at any time to prove that the security document 02 is an original, in particular a genuine banknote.

[0051] It has been found that, in the region of the transparent window 04, on the back side of the substrate 26, i.e. on the side of this substrate 26 opposite to the side facing the micro-optical structure 03, a printed image 27 created with a printing fluid normally visible to the human eye under daylight conditions, is sometimes not sufficiently well distinguishable upon observation directed towards the printed image 27 through the micro-optical structure 03 from the direction of the convex envelope surface 13, particularly under low light conditions, for example twilight light conditions.

[0052] In order to improve the discernibility of such a printed image 27, in particular for the human eye, it is proposed to overprint the printed image 27 produced on the rear side of the substrate 26 in the region of the transparent window 04 with a printing fluid having a lighter shade than the shade of the printing fluid used to produce the printed image 27. If the printed image 27 applied to the rear side of the substrate 26 in the region of the transparent window 04 is produced from a number of printing fluids of different shades, a printing fluid having a lighter shade than the lightest shade of the printing fluid used to produce the printed image 27 is used for overprinting the printed image 27 produced in this way. Advantageously, the printed image 27 applied to the rear side of the substrate 26 in the region of the transparent window 04 is at least partially overprinted with a layer 39 of white ink. This layer 39 forms an areal spreading covering layer of light, in particular white ink, on the printed image 27 applied to the rear side of the substrate 26 in the region of the transparent window 04. In this case, the coating layer may be made opaque, i.e. non-transparent to electromagnetic radiation having a wavelength in the range of about 380 nm (violet) to 780 nm (red), i.e. opaque, or partially transparent to electromagnetic radiation having a wavelength in the range of about 380 nm (violet) to 780 nm (red). The partial transparency may be made to vary stepwise over the two-dimensional surface area of ​​the coating layer, so that some parts of the coating layer are more transparent than other parts of the coating layer. The degree of transparency may preferably be in the range of 10% to 90% for incident light.

[0053] Thus, a security document 02 is obtained with a transparent window 04 formed in a substrate 26 (as exemplarily shown in FIG. 5), on one side of which, at least in the region of the transparent window 04, a micro-optical structure 03 consisting of a number of microlenses 11 is arranged, and on the other side of the substrate 26, opposite to the side facing the micro-optical structure 03, at least one printed image 27 is arranged. The printed image 27 comprises a number of image elements 28a-28j in a dot- or line-shaped halftone screen, which are formed in a color tone different from white. The pixel size 38 or line width 38 of these image elements 28a-28j is formed smaller than the lens width 18 of the microlenses 11 arranged in the micro-optical structure 03, respectively. For contrast enhancement, it is assumed here that a layer 39 is arranged on at least a part of the surface of the printed image 27 opposite the side facing the micro-optical structure 03, i.e. on a part of the printed image 27, which is spread over the printed image 27 and has a lighter color tone than the at least one color tone different from white that constitutes the printed image 27. Preferably, the layer 39 is formed in a white color tone. As mentioned above, the layer 39 covering the printed image 27 is formed opaque to electromagnetic radiation having a wavelength in the range of 380 nm to 780 nm, or the layer 39 can be formed transparent to electromagnetic radiation having a wavelength in the range of 380 nm to 780 nm, the degree of transparency to this electromagnetic radiation being, for example, in the range of 10% to 90%. Furthermore, the transparency across the two-dimensional extent of the layer 39 covering the printed image 27 may be made to vary in a graduated manner, such that some portions of the layer 39 are made to have a different degree of transparency than other portions of the layer 39. This allows certain image elements 28a-28j of the printed image 27 to be highlighted based on their improved distinctiveness to the human eye, while other image elements 28a-28j of the printed image 27 remain intentionally made less distinctive.In a preferred configuration, the layer 39 covering the printed image 27 is produced by inkjet printing or offset printing or screen printing, whereas the printed image 27 arranged on the other side of the substrate 26 opposite the side facing the micro-optical structure 03 is produced by offset printing.

[0054] By overprinting the printed image 27 applied to the back of the substrate 26 in the region of the transparent window 04, an increased contrast is achieved between the image elements 28a-28j contained in the printed image 27, i.e. between the pixels and / or lines of the printed image 27 and the respective direct outer edges of the image elements 28a-28. Contrast generally means the difference in brightness between adjacent light and dark areas in an image. By overprinting the printed image 27 applied to the back of the substrate 26 in the region of the transparent window 04 with a layer 39 of light, in particular white, ink, an increased contrast is achieved for a number of, preferably most and in particular all, image elements 28a-28j of the printed image 27 in an observation directed towards the printed image 27 through the micro-optical structure 03 from the direction of the convex envelope 13, so that the printed image 27 or at least the information contained in the printed image 27 is or can be better distinguished by the human eye, in particular also under weak light conditions, for example under twilight light conditions.

[0055] In one particularly advantageous configuration of the present invention, a security document 20 is provided with a contrast-enhancing layer 39 on the rear side of the substrate 26, together with a self-authentication means, as exemplarily shown in cross-section in FIG. 6 and described below.

[0056] 6 shows a security document 02 with a transparent window 04 formed in a substrate 26 as exemplarily shown in FIG. 5, on one side of which, at least in the region of the transparent window 04, a micro-optical structure 03 consisting of a number of microlenses 11 is arranged, and on the other side of the substrate 26, opposite to the side facing the micro-optical structure 03, a first printed image 27 is arranged. In this embodiment, too, the first printed image 27 has a number of image elements 28a-28j in a dot- or line-shaped halftone screen, which are preferably formed in a color tone different from white. The pixel size 38 or line width 38 of these image elements 28a-28j is formed smaller than the lens width 18 of the microlenses 11 arranged in the micro-optical structure 03. Here too, for contrast enhancement, it is assumed that a layer 39 is arranged on at least a partial surface or part of the first printed image 27 on the side opposite the side facing the micro-optical structure 03, the layer 39 being preferably of a lighter color tone than at least one color tone different from white that constitutes the first printed image 27.

[0057] The security document 20 proposed on the basis of Fig. 6 differs from the embodiment shown in Fig. 5 in that a second, i.e. another, preferably also produced by offset printing method, printed image 41 is arranged on the layer 39 covering a part of the first printed image 27 on the side opposite to the side facing the micro-optical structure 03. This second printed image 41 is arranged on the layer 39 covering a part of the first printed image 27 in such a way that, after folding has been carried out at a fold line 07, preferably transverse to the security document 02, as indicated by the arrow in Fig. 6, this second printed image 41 is superimposed or at least superimposable with the micro-optical structure 03 applied on the other side of the substrate 26 of this security document 02 (as exemplarily shown in Fig. 4), so that this second printed image 41 or at least one piece of information contained in the second printed image 41 is visible and / or recognizable or becomes visible and / or recognizable when observed from the direction of the side of the micro-optical structure 03. The fold line 07 along which the substrate 26 of the security document 02 is folded is preferably located outside the layer 39 covering a portion of the first printed image 27, i.e. spaced apart from this layer 39. The fold line 07 is preferably located in a portion of the first printed image 27 that is not covered by the layer 39 arranged on the first printed image 27.

[0058] Even in the embodiment of the present invention shown in Figure 6, it may be assumed that the image elements 28a to 28j of the first printed image 27 are formed in a color tone different from white, and the layer 39 covering a portion of the first printed image 27 is made of a color tone lighter than at least one color tone different from white that constitutes the first printed image 27.

[0059] Moreover, the embodiment of the invention shown in FIG. 6 may also have at least some of the features already described in relation to FIGS. 1 and 5, in any technically significant combination.

[0060] With reference to FIG. 7, it will now be further explained how a security document 02, in particular according to the embodiment shown in FIG. 5 or 6, can be produced. As already explained, the layer 39, in particular the contrast-enhancing layer, which covers the printed image 27, is produced in a preferred configuration by inkjet printing, but can also be produced by offset or screen printing, whereas the printed image 27, arranged on the side of the substrate 26 opposite the side facing the micro-optical structure 03, is produced by offset printing. The printed image 27 consists of a number of image elements 28a-28j printed with at least two different printing inks, which image elements 28a-28j themselves form pixels and / or lines. The pixel size 38 or line width 38 is preferably in the range of less than 20 μm, for example in the range of about 5 μm to 10 μm. The accuracy of the color registration, i.e. the positioning relative to one another, of the image elements 28a-28j printed with the different printing inks is, in the example considered here, respectively less than 20 μm, preferably less than 10 μm, in particular in the range of about 5 μm.

[0061] The production of the print image 27 with the above-mentioned color registration takes place, for example, in a printing press configured as a rotary printing machine, in particular in a printing press used for printing securities, in which the substrate 26, for example configured as a web or print sheet of printable material, is guided over a cylinder configured, for example, as an impression cylinder 42, the printing inks which contribute to the print image 27 being applied to the substrate 26 by successive superimposed printing, or in a preferred embodiment, a plurality of printing inks which contribute to the print image 27 are collected, for example, on a transfer cylinder 43 and fed from there together to the substrate 26 which is guided by the impression cylinder 42. The substrate 26 is configured as a web of printable material, for example in the form of a polymer film, or as a print sheet made of paper.

[0062] At least two plate cylinders 44 are applied or at least can be applied around the transfer cylinder 43, each of which transfers one of the printing inks responsible for the print image 27 to the transfer cylinder 43. The respective directions of rotation of the impression cylinder 42, the transfer cylinder 43 and the plate cylinder 44 are indicated by respective rotation arrows in FIG. 7. It is known to those skilled in the art that an inking unit (not shown in FIG. 7) is assigned to each plate cylinder 44. In a preferred arrangement, the printing inks transferred from the plate cylinders 44 applied to the transfer cylinder 43 are of different shades.

[0063] Downstream of the transfer point, where the transfer cylinder 43 prints the printing ink collected thereon onto the substrate 26 guided by the impression cylinder 42 to produce the printed image 27, a printing device is provided on the same side of the substrate 26 facing the printed image 27 produced at the transfer point, which prints at least partially over the printed image 27 with a layer 39 of light-toned, preferably white, ink. The printing device is preferably formed as at least one inkjet printhead 46. In a preferred embodiment, the ink tones printed by the inkjet printhead 46 are lighter than the respective tones of the printing ink applied from the transfer cylinder 43 to the substrate 26.

[0064] The printing press is preferably also provided with an embossing device 47, by means of which the micro-optical structure 03 consisting of the microlenses 11 is produced on the substrate 26. The embossing device 47 can therefore be arranged upstream of the impression cylinder 42 in the printing press. In one particularly advantageous embodiment, however, the impression cylinder 42 has the embossing device 47 on its periphery, by means of which the micro-optical structure 03 consisting of the microlenses 11 is produced and is placed on the substrate 26 guided by the impression cylinder 42 during its rotation. The microlenses 11, for example made of plastic or resin, have a lens width 18 of, for example, less than 100 μm, preferably between 20 μm and 65 μm.

[0065] This results in a printing machine for producing security documents 02, which comprises an impression cylinder 42 for guiding the substrate 26 of the security document 02 and a transfer cylinder 43 for printing a print image 27 onto the substrate 26 in cooperation with the impression cylinder 42 at a transfer point. The substrate 26 of the security document 02 has at least one transparent window 04, and at least in the region of said transparent window 04 on one side of the substrate 26, a micro-optical structure 03 consisting of a number of microlenses 11 is provided. The impression cylinder 42 and the transfer cylinder 43 are arranged in a cooperative manner, so that during the printing process, at least in the region of said transparent window 04, a micro-optical structure 03 consisting of a number of microlenses 11 is arranged on one side of the substrate 26, and at least in the region of the transparent window 04, at least one print image 27 is arranged on the other side of the substrate 26, opposite to the side facing the micro-optical structure 03, at least in the region of the transparent window 04. This arrangement of the micro-optical structure 03 consisting of a plurality of microlenses 11 formed by the embossing device 47 and at least one printed image 27 formed in the area of ​​the transparent window 04 by the impression cylinder 42 and the transfer cylinder 43 may be generated simultaneously at the above-mentioned transfer points or at different points around the impression cylinder 42 with a time lag.

[0066] The printing press is further provided with a printing device, which applies a layer 39 spread over at least a part of the printed image 27 on the side opposite to the side facing the micro-optical structure 03, so as to cover the printed image 27. The printing device is arranged downstream of a transfer point, where a transfer cylinder 43 prints the printed image 27 on the substrate 26 guided by the impression cylinder 42, on the same side of the substrate 26 facing the printed image 27 produced at the transfer point, and is formed in the present invention as at least one inkjet printhead 46. In its preferred configuration, the printed image 27 has a number of differently colored image elements 28a-28j in a dot- or line-shaped halftone screen, each of which is formed in a shade different from white, and the layer 39 formed by the at least one inkjet printhead 46 is of a shade lighter than the shade different from white constituting the printed image 27.

[0067] Advantageously, in order to maintain a high register accuracy, the impression cylinder 42 has an embossing device 47 on its periphery, which forms a micro-optical structure 03 consisting of a number of micro-lenses 11 and is arranged in such a way that during the rotation of the impression cylinder 42, i.e. during the printing process, the embossing device 47 forms the micro-optical structure 03 consisting of a number of micro-lenses 11 on the substrate 26 guided by the impression cylinder 42. In this case, the pixel size 38 or the line width 38 of the image elements 28a-28j of the printed image 27 is preferably made smaller than the lens width 18 of the micro-lenses 11 arranged in the micro-optical structure 03, respectively.

[0068] In one preferred configuration of the printing press, at least two plate cylinders 44 are provided which are applied or at least can be applied around the transfer cylinder 43, each of which transfers one of the printing inks involved in the print image 27 to the transfer cylinder 43, which collects these different color printing inks, which are transferred together to the substrate 26 guided by the impression cylinder 42. [Explanation of symbols]

[0069] 01 Security element 02 Confidential Documents 03 Optical imaging structure, micro-optical structure 04 Window 05 - 06 Notch 07 Folding line 08 - 09 - 10 - 11 Microlenses 12 Axis of symmetry, optical axis 13 Convex Envelope 14 rays 15 - 16 Boundary points 17 Boundary Points 18 Lens width 19 Main plane 20 - 21 Flat Envelope 22 focal length 23. Focus 24 focal plane twenty five - 26 Base material 27 Printed Images 28 Image elements (28a-28j) 29 Material thickness, thickness 30 - 31 Section 32 Cone, Angle Range 33 First Observation Angle 34 Second Observation Angle 35 - 36 Layer Thickness 37 Vertex 38 Pixel size, lens thickness 39 layers 40 - 41 Printed Images 42 impression cylinder 43 Teleportation Torso 44 Print cylinder 45 - 46 Inkjet Print Head 47 Embossing device

Claims

1. A security document (02) with a transparent window (04) formed in a substrate (26), in which a micro-optical structure (03) consisting of a number of micro-lenses (11) is arranged on one side of the substrate (26) at least in the region of the transparent window (04), and on the other side of the substrate (26) opposite to the side facing the micro-optical structure (03), at least one printed image (27) is arranged at least in the region of the transparent window (04), the printed image (27) having a number of image elements (28a-28j) in a dot-like or line-like halftone screen. The pixel size (38) or line width (38) of the image elements (28a to 28j) is formed smaller than the lens width (18) of the microlens (11) arranged in the micro-optical structure (03), and a layer (39) spread over the surface so as to cover the printed image (27) is arranged on at least a part of the printed image (27) on the side opposite to the side facing the micro-optical structure (03), and the layer (39) covering the printed image (27) is The layer (39) is made transparent to electromagnetic radiation having a wavelength in the range of 380 nm to 780 nm, the degree of transparency with respect to said electromagnetic radiation being in the range of 10% to 90%, said transparency being made to vary stepwise over the two-dimensional surface extent of the layer (39) covering the printed image (27), so that at least one place of the layer (39) or some places of the layer (39) are made with a degree of transparency different from other places of the layer (39), and a second printed image (27) is formed on the side of the layer (39) covering a part of the first printed image (27) opposite to the side facing the micro-optical structure (03). a second printed image (41) is arranged on the layer (39) covering a portion of the first printed image (27) in such a way that the second printed image (41) can be superimposed on the micro-optical structure (03) applied to the other side of the substrate (26) of the security document (02) after folding at the fold line (07), and the superimposition makes the second printed image (41) or at least one piece of information contained in the second printed image (41) visible and / or identifiable when observed from the direction of the micro-optical structure (03).

2. The confidential document (02) according to claim 1, characterized in that the image elements (28a to 28j) of the printed image (27) are formed in a color tone different from white, and the layer (39) covering the printed image (27) is made of a color tone lighter than at least one color tone different from white that constitutes the printed image (27).

3. 3. The security document (02) according to claim 1 or 2, characterized in that said layer (39) is made in a white color tone.

4. 3. The security document (02) according to claim 1 or 2, characterized in that the printed image (27) arranged on the side of the substrate (26) opposite to the side facing the micro-optical structure (03) is produced by an offset printing method.

5. 3. The security document (02) according to claim 1 or 2, characterized in that the printed image (27) arranged on the side of the substrate (26) opposite to the side facing the micro-optical structure (03) consists of an overprint or consists of a superposition of several partial printed images, each printed with a different printing ink.

6. 3. The confidential document (02) according to claim 1 or 2, characterized in that the micro-optical structure (03) is formed as a lens array or as a lenticular, the lens array or the lenticular each consisting of a plurality of plano-convex micro-lenses (11), which in the case of a lens array are formed rotationally symmetrically spherically or aspherically, and in the case of a lenticular, are formed axially symmetrically rod-shaped.

7. The security document (02) according to claim 1 or 2, characterized in that a plurality of image elements (28a-28j) of the printed image (27) arranged under the micro-optical structure (03) in the viewing direction are formed so as to belong to a plurality of different printed motifs.

8. 3. The security document (02) according to claim 1 or 2, characterized in that the printed image (27) is formed so as to contain information directly identifiable by a human being or is simply machine-readable.

9. 3. The security document (02) according to claim 1 or 2, characterized in that the fold line (07) is arranged spaced apart from the layer (39) covering a portion of the first printed image (27).

10. Security document (02) according to claim 1 or 2, characterized in that the substrate (26) is a fibrous printable material or a polymer film.

11. 3. The security document (02) according to claim 1 or 2, characterized in that the security document (02) is in the form of a banknote.

Images