EP1458578B1 - Diffractive safety element - Google Patents

Abstract

A security element ( 2 ) comprising a plastic laminate ( 1 ) has a surface pattern which is composed mosaic-like at least from surface elements, wherein in the surface elements a reflecting interface ( 8 ) between a shaping layer ( 5 ) and a protective layer ( 6 ) of the plastic laminate ( 1 ) forms optically effective structures ( 9 ). Light ( 11 ) which is incident on the plastic laminate ( 1 ) and which passes through a cover layer ( 4 ) of the plastic laminate ( 1 ) and through the shaping layer ( 5 ) is deflected in a predetermined manner by means of the optically effective structures ( 9 ). Shaped in the surface of at least one of the surface elements is a diffraction structure which is produced by a superimposition of a linear asymmetrical diffraction grating ( 24 ) with a matt structure. The linear asymmetrical diffraction grating ( 24 ) has a spatial frequency from the range of values of between 50 lines/mm and 2,000 lines/mm. The matt structure has a mean roughness value from the range of between 20 nm and 2,000 nm and at least in one direction a correlation length of between 200 nm and 50,000 nm.

Description

The invention relates to a diffractive security element according to the preamble of claim 1.

Such diffractive security elements are used to authenticate items, such as banknotes, ID cards of all kinds, and valuable documents, to determine the authenticity of the item without much effort. The diffractive security element is firmly connected to the object in the output of the article in the form of a cut from a thin layer composite brand.

Diffractive security elements of the type mentioned are from the EP 0 105 099 A1 and the EP 0 375 833 A1 known. These security elements comprise a pattern of tessellated surface elements having a diffraction grating. The diffraction gratings are azimuthally arranged in such a way that, during a rotation, the visible pattern produced by diffracted light changes optically.

In the EP 0 360 969 A1 diffractive security elements are described in which the surface elements have asymmetrical diffraction gratings. In each case in two surface elements with a common border, the asymmetrical diffraction gratings are arranged in pairs and in mirror symmetry. Special asymmetric diffraction gratings, which look like oblique mirrors, are in the WO 97/19821 described.

The diffraction properties of the diffraction grating can be depicted using a Fourier space representation. The Fourier space representation indicates in a circle the direction of the diffracted light rays by means of a point, the light being incident perpendicular to the diffraction grating in the center of the circle. The circle center corresponds to the diffraction angle β = 0 ° and the circumference to the diffraction angle β = 90 °, while a radius indicating a point located in a circle indicates the diffraction angle β of the light rays diffracted at the diffraction gratings. Polar angles of different points in the Fourier space representation reflect the azimuthal orientation of the diffraction gratings.

The diffractive security elements generally consist of one piece of a thin laminate of plastic. The boundary layer between two of the layers has microscopically fine reliefs of light-diffracting structures. To increase the reflectivity, the boundary layer between the two layers is covered with a reflective layer. The structure of the thin layer composite and the materials used for this purpose are, for example, in US 4,856,857 and the WO 99/47983 described. From the DE 33 08 831 A1 It is known to apply the thin layer composite with the aid of a carrier film on the object.

The disadvantage of these diffractive security elements is due to the narrow solid angle and the extremely high surface brightness, under which a surface element occupied by a diffraction grating is visible to an observer. The high surface brightness can also make the recognizability of the shape of the surface element more difficult.

It is also from the EP 0 712 012 A1 In the case of a sinusoidal, submicroscopically fine diffraction grating, it is known to locally vary the ratio of the structure depth to the valley width. In one embodiment, non-reproducible, anisotropic process steps cause such a change in the diffraction grating. In another embodiment, the diffraction grating is superimposed with a macro roughness for the modulation of the structure depth. White light incident on the diffraction grating is diffracted and reflected at the angle of reflection, with an interference color dependent on the spatial frequency of the diffraction grating occurring with color saturation, the proportion of reflected white light in the diffracted light being determined by the texture depth.

The invention has for its object to provide a cost-effective, diffractive security element that shows a highly visible, static surface pattern in a large angular range in the diffracted light.

The above object is achieved by the features specified in the characterizing part of claim 1 according to the invention. Advantageous embodiments of the invention will become apparent from the dependent claims.

Embodiments of the invention are illustrated in the drawings and will be described in more detail below.

Figur 1

ein Sicherheitselement im Querschnitt,

Figur 2

das Sicherheitselement in Draufsicht,

Figur 3

eine Fourierraumdarstellung eines linearen Beugungsgitters,

Figur 4

die Fourierraumdarstellung einer isotropen Mattstruktur,

Figur 5

die Fourierraumdarstellung einer anisotropen Mattstruktur,

Figur 6

Ablenkcharakteristiken optisch wirksamer Strukturen,

Figur 7

eine Beugungsstruktur in einem Schichtverbund,

Figur 8

die Fourierraumdarstellung der Beugungsstruktur,

Figur 9

das Sicherheitselement mit einem Musterelement in Draufsicht,

Figur 10

das Sicherheitselement nach der Figur 9 um 180° gedreht,

Figur 11

eine zweite Ausführungsform des Musterelements,

Figur 12

eine dritte Ausführungsform des Musterelements,

Figur 13

die dritte Ausführungsform des Musterelements um 180° gedreht,

Figur 14

die Fourierraumdarstellung einer anderen Beugungsstruktur,

Figur 15

ein Flächenmuster als vierte Ausführungsform und

Figur 16

eine fünfte Ausführung des Musterelements.

Show it:

FIG. 1

a security element in cross section,

FIG. 2

the security element in plan view,

FIG. 3

a Fourier space representation of a linear diffraction grating,

FIG. 4

the Fourier space representation of an isotropic matt structure,

FIG. 5

the Fourier space representation of an anisotropic matt structure,

FIG. 6

Deflection characteristics of optically active structures,

FIG. 7

a diffraction structure in a layer composite,

FIG. 8

the Fourier space representation of the diffraction structure,

FIG. 9

the security element with a pattern element in plan view,

FIG. 10

the security element after the FIG. 9 turned 180 °,

FIG. 11

a second embodiment of the pattern element,

FIG. 12

a third embodiment of the pattern element,

FIG. 13

the third embodiment of the pattern element rotated by 180 °,

FIG. 14

the Fourier space representation of another diffraction structure,

FIG. 15

a surface pattern as the fourth embodiment and

FIG. 16

a fifth execution of the pattern element.

In the FIG. 1 3 denotes a layer composite, 2 a security element, 3 a substrate, 4 a cover layer, 5 an impression layer, 6 a protective layer, 7 an adhesive layer, 8 a reflective boundary layer, 9 an optically active structure and 10 a transparent site in the reflective boundary layer 8. The composite layer 1 consists of several layers of different, successively applied to a carrier film not shown here plastic layers and includes in the order typically the top layer 4, the impression layer 5, the protective layer 6 and the adhesive layer 7. The carrier film is in one embodiment, the cover layer 4 itself, in another embodiment, the carrier film is used for applying the thin layer composite 1 on the substrate 3 and is then removed from the layer composite 1, as in the above-mentioned DE 33 08 831 A1 is described.

The boundary layer 8 forms the common contact surface between the impression layer 5 and the protective layer 6. The optically active structures 9 of an optically variable pattern are formed in the impression layer 5. Since the protective layer 6 fills the valleys of the optically active structures 9, the boundary layer 8 has the shape of the optically active structures 9. In order to obtain a high reflectivity of the optically active structures 9, a jump in the refractive index is required at the boundary layer 8. This jump in the refractive index generates, for example, a metal coating, preferably of aluminum, silver, gold, copper, chromium, tantalum, which as boundary layer 8 separates the impression layer 5 and the protective layer 6. Due to its electrical conductivity, the metal coating causes a high reflectivity for visible light at the boundary layer 8. The jump in the refractive index can instead of a metal coating also produce a coating of an inorganic, dielectric material with the advantage that the dielectric coating is additionally transparent. Suitable dielectric materials are, for example, in the writings mentioned above US 4,856,857 , Table 1 and WO 99/47983 listed.

The composite layer 1 can be produced as a plastic laminate in the form of a long film web with a multiplicity of juxtaposed copies of the optically variable pattern. For example, the security elements 2 are cut out of the film web and joined to a substrate 3 by means of the adhesive layer 7. The substrate 3, usually in the form of a document, a banknote, a bank card, a passport or other important or valuable object, is provided with the security element 2 in order to authenticate the authenticity of the object.

At least the cover layer 4 and the impression layer 5 are transparent to visible light 11 incident on the security element 2. At the boundary layer 8, the incident light 11 is reflected and deflected in a predetermined manner by the optically active structure 9. The optically active structures 9 are, for example, diffractive structures, light-scattering relief structures and planar mirror surfaces.

The FIG. 2 shows the applied to the substrate 3 security element 2 in plan view. Surface elements 12 form a mosaic-like surface pattern in the plane of the security element 2. Each surface element 12 is provided with one of the optically active structure 9 (FIG. Fig. 1 ). In one embodiment of the security element 2, transparent locations 10, at which the reflective metal coating is interrupted, are introduced into the boundary layer 8 (FIG. Fig. 1 ), so that lying under the security element 2, located on the substrate 3 Indicia 13 can be seen through the security element 2 therethrough. In another embodiment of the security element 2, the boundary layer 8 has a transparent dielectric coating so that the indicia 13 remain visible under the security element 2. Of course, in these transparent embodiments, the protective layer 6 ( Fig. 1 ) and the adhesive layer 7 ( Fig. 1 ) transparent. For particularly thin embodiments of the layer composite 1 ( Fig. 1 ), the protective layer 6 is omitted. The adhesive layer 7 is then applied directly to the optically active structures 9. Advantageously, the adhesive is a hot-melt adhesive, which develops its adhesion only at a temperature around 100 ° C. In the aforementioned US 4,856,857 different embodiments of the layer composite 1 are shown and the materials that can be used for this purpose are listed.

A diffraction grating 24 ( Fig. 1 ) is characterized by its parameters spatial frequency, azimuth, profile shape and profile height h ( Fig. 1 ), certainly. The linear asymmetric diffraction gratings 24 mentioned in the Examples described below have a spatial frequency in the range of 50 lines / mm to 2,000 lines / mm, with the range of 100 lines / mm to about 1,500 lines / mm being preferred. The geometric profile height h has a value from the range 50 nm to 5,000 nm, preferred values being between 100 nm and 2,000 nm. Since the shaping of the diffraction gratings 24 into the impression layer 5 (FIG. Fig. 1 ) for geometric profile heights h which are greater than the reciprocal of the spatial frequency, is technically difficult, large values for the geometric profile height h only make sense at low values for the spatial frequency.

In the FIG. 3 is the diffraction property of a linear diffraction grating 24 (FIG. Fig. 1 ) Based on the Fourierraumdarstellung described above with the first and second diffraction orders 14, 15, wherein a grating vector 26 of the diffraction grating 24 is parallel to the direction x. The diffraction grating 24 of the surface element 12 arranged in the center of the circle disassembles the light 11 which is incident perpendicular to the plane of the drawing (FIG. Fig. 1 ) in spectral colors. Rays of the diffracted light of the different orders of diffraction 14, 15 are in the same, determined by the incident light 11 and the grating vector 26, not representable here diffraction plane and are therefore strongly directed. Short-wave light with the wavelength λ = 380 nm (violet) has in each of the diffraction orders 14, 15 a shorter distance from the circle center than long-wavelength light with the wavelength λ = 700 nm (red). The number of propagating diffraction orders 14, 15 depends on the spatial frequency of the diffraction grating 24. In the range below a spatial frequency of about 300 lines / mm, the higher diffraction orders overlap, so that the diffracted light is achromatic there. After a rotation of the linear diffraction grating 24 in the azimuth by the angle θ of a few angular degrees, the surface element 12 occupied by the diffraction grating 24 becomes invisible to the observer viewing the diffraction grating 24 from the x coordinate direction, since the grating vector 26 and thus the diffraction plane with the rays of the diffracted light no longer point in the direction of the x - coordinate.

The matte structures have microscopic scale fine relief features that determine the scattering power and can only be described with statistical parameters, such as average roughness R _a and correlation length I _c , the values for the average roughness R _a in the range 20 nm to 2,000 nm with preferred values of 50 nm to 500 nm, while the correlation length l _c in at least one direction values in the range of 200 nm to 50,000 nm, preferably between 500 nm to 10,000 nm.

The FIG. 4 FIG. 4 shows the Fourier space representation for the surface element 12 (shown in FIG. 2) with an isotropic matt structure. FIG. Fig. 3 ) with vertically incident light 11 (FIG. Fig. 1 ). The microscopically fine relief structure elements of the isotropic matt structure have no azimuthal preferred direction, which is why the scattered Light with an intensity greater than a predetermined limit, for example, given by the visual recognizability, evenly distributed in a predetermined by the scattering power of the matte structure solid angle 16 in all azimuthal directions and the surface element 12 appears white to gray in daylight. In all other directions, the surface element 12 is dark. Strongly scattered matt structures distribute the scattered light into a larger solid angle 16 than a weakly scattering matt structure.

In the FIG. 5 The relief elements of the matt structure have a preferred direction of the microscopically fine relief structure elements parallel to the coordinate x. The scattered light therefore has an anisotropic distribution. In the presentation of the FIG. 5 is the predetermined by the scattering power of the matte structure solid angle 16 ellipse-shaped in the direction of the coordinate y apart.

In the FIG. 6 this fact is shown in cross-section. The security element 2 has the pattern of the surface elements 12 which are connected to the optically active structures 9 (FIG. Fig. 1 ) are occupied. A plane mirror surface casts the light 11 incident at an incident angle α to the surface normal 17 as a reflected beam 18 at the reflection angle α ', where α = α'. The direction of the incident light 11, the surface normal 17 and the reflected beam 18 together span a diffraction plane 19 which is in the FIG. 6 is arranged parallel to the plane of the drawing. The optically active structure 9 has the shape of the linear diffraction grating 24 (FIG. Fig. 1 ) whose grating vector 26 ( Fig. 3 ) is aligned parallel to the coordinate x. The incident light 11 is irradiated according to its wavelength λ at the diffraction angles β ₁ , β ₂ as diffracted beams 20, 21 in each of the diffraction orders 14 (FIG. Fig. 3 ), 15 ( Fig. 3 ) is deflected from the direction of the reflected beam 18. If the optically effective structure 9 is one of the matt structures, the end points of intensity vectors of the backscattered light form club-shaped surfaces. The club-shaped surfaces intersect the diffraction plane 19, for example in sectional curves 22, 23. If the relief structure elements of the matt structure have no preferred direction, the light beams are scattered almost concentrically around the direction of the reflected beam 18. The matt structure with the cutting curve 22 scatters the incident Light 11 stronger and into a larger solid angle 16 ( Fig. 4 Because of the greater scattering, the intensity of the light scattered in the direction of the reflected beam 18 is weaker, as indicated by the cutting curve 22 in comparison to the cutting curve 23. If the relief structure elements are oriented essentially to a preferred direction, here perpendicular to the diffraction plane 19, the locations of equal intensity are on flattened, club-shaped surfaces which have an elliptical cross section in a sectional plane perpendicular to the reflected beam 18, not shown here on the sectional plane of the centroid of the cross section coincides with the piercing point of the reflected beam 18 and the longitudinal axis of the elliptical cross section is aligned perpendicular to the diffraction plane 19. The distribution of the scattered light is therefore anisotropic. In contrast to diffraction structures, the matt structures are unable to split the incident light 11 into the spectral colors.

In the diffraction of the incident light 11 at the in the FIG. 1 asymmetric linear diffraction gratings 24 shown are the intensity l ^{- of} the diffracted beam 20 ( Fig. 6 ) in the negative diffraction order 14 ( Fig. 3 ), 15 ( Fig. 3 ) and the intensity I ^{+ of} the diffracted beam 21 (FIG. Fig. 6 ) in the positive diffraction order 14, 15 unequal. The intensity I ^{+ of} the diffracted beam 21 exceeds the intensity l ^{- of} the diffracted beam 20 at least by a factor p = 3, preferably p = 10 or greater, ie I ⁺ = p • l ^- . The factor p depends essentially on the formation of the sawtooth-shaped profile of the diffraction grating 24, the profile height h and the Spatialfrequenz. Below a spatial frequency of about 300 lines / mm, the asymmetric diffraction grating 24 acts like an inclined mirror, ie, the intensity l ^{+ of} the diffracted beam 21 in the positive diffraction orders almost reaches the intensity of the incident light 11, while the intensity l ^{- of} the diffracted beam 20 is practically vanishingly small in the negative diffraction orders. The factor p reaches values of 100 or more. A splitting of the incident light 11 into the spectral colors no longer occurs, which is why such diffraction gratings 24 are characterized by the term "achromatic". More about this can be found in the document mentioned above WO 97/19821 ,

The FIG. 7 shows a schematic representation of the embedded in the molding layer 5 and the protective layer 6, optically active structure 9 (FIG. Fig. 1 ), which generates a diffraction structure 25 generated by an additive superimposition from the linear asymmetric diffraction grating 24 (FIG. Fig. 1 ) and the matt structure is. The matt structure is drawn for illustrative reasons with a small average roughness value R _a compared to the profile height h and much too regular. The profile of the linear asymmetrical diffraction grating 24 has, as further parameters, blaze angles ε ₁ and ε ₂ , which have both profile surfaces of the asymmetrical diffraction grating 24 with the plane of the security element 2 (FIG. Fig. 6 ) lock in.

In the FIG. 8 is the Fourier space of the diffraction structure 25 (FIG. Fig. 7 ), wherein the matte structure is isotropic. The means of the diffraction grating 24 ( Fig. 1 ) strongly directed diffracted beams 20 ( Fig. 6 21, Fig. 6 ) are widened by the matt structure. This results in the advantage that the diffracted beams 20, 21 are radiated into the large solid angles 16 and that for the observer, the surface element 12 with the diffraction structure 25 in the entire solid angle 16, albeit with a reduced surface brightness, is easily recognizable. The stronger the matt structure scatters, the greater is the solid angle 16 under which the surface element 12 can be seen and the lower the surface brightness of the surface element 12 is for the observer. In addition, the intensity I ^{+ of} the rays 20 diffracted into the plus first diffraction order 14 is about Factor p greater than the intensity I ^- the rays diffracted into the minus first diffraction order 14 '. This is shown in the drawing of FIG FIG. 7 represented by differently dense dot patterns in the solid angles 16.

For spatial frequencies of the diffraction grating 24 above about 300 lines / mm, the incident light 11 (FIG. Fig. 5 ) split into spectral colors. In daylight, the matt structure causes a smearing of the pure spectral colors to pastel shades to virtually white scattered light regardless of the Spatialfrequenz the diffraction grating 24. The pastel shades with decreasing Spatialfrequenz the diffraction grating 24 to an ever higher proportion of white. If the spatial frequency falls below the value of about 300 lines / mm, none is found noticeable splitting of the incident light 11 instead, ie the surface element 12 is visible in the color of the incident light 11.

From the Fourier space representation, it can be seen that, in the case of the surface element 12, both during tilting about an axis lying in the plane spanned by the coordinates x and y, also during a rotation about the surface normal 17 (FIG. Fig. 6 ) the light deflected by the diffraction structure 25 remains visible to the observer over a wide angular range, for example from the range ± 20 ° to ± 60 °, in contrast to diffraction gratings according to the above-mentioned EP 0 105 099 A1 , which are visible only in a narrow angular range of a few degrees and therefore when tilting and rotating the security element 2 ( Fig. 2 ) flash. The surface element 12 with the diffraction structure 25 has the advantage that the surface element 12 forms a quasi-static pattern element in the surface pattern of the security element 2.

The FIG. 9 1 shows a simple example of the quasi-static pattern element formed of two surface elements 27, 28 in the security element 2. The first surface element 27 with the first diffraction structure 25 (FIG. Fig. 7 ) adjoins the second surface element 28 with the second diffraction structure 25. The first surface element 27 and the second surface element 28 are arranged in a surface pattern on the security element 2 with regions 29 occupied by other optically active structures. The first and the second diffraction structure 25 differ only by the direction of their grating vector 26 (FIG. Fig. 3 ) and have that in the FIG. 8 shown diffraction behavior. The grating vectors 26 are in the FIG. 9 in the surface elements 27, 28 substantially antiparallel, ie the azimuth of the second diffraction structure 25 (FIG. Fig. 7 ) is equal to the sum of the azimuth of the first diffraction structure 25 and an additional azimuth angle θ ( Fig. 3 ) from the value range 120 ° to 240 °, wherein the value for the azimuth angle θ = 180 ° is to be preferred. The grating vector 26 of the first diffraction structure 25 is aligned parallel to the coordinate x. The matt structure extends homogeneously over the entire surface of the two surface elements 27, 28. The observer looks in the direction of the coordinate x and sees the first surface element 27 with a low surface brightness, whereas the second one Surface element 28 with a high surface brightness, as in the drawing of the FIGS. 9 and 10 used dot matrix implies. Now, the security element 2 is rotated in its plane by 180 °, as in the FIG. 10 shown, the security element 2 is considered against the direction of the coordinate x. The surface brightnesses of the two surface elements 27, 28 are then reversed, that is, the contrast between the two surface elements 27, 28 is opposite to the representation in the FIG. 9 vice versa.

In the following embodiments, both the parameters of the asymmetric diffraction gratings 24 (FIG. Fig. 1 ) as well as the parameters of the different matt structures depending on the location within the surface element 12, or of a surface element 12, 27, 28 to the other, independently of each other or coupled together according to Table 1 changeable to easily observable, different, striking optical effects to achieve the quasi-static pattern elements. Table 1: Examples (overview) example Asymmetrical diffraction grating 24 ( Fig. 1 ) matt structure 1 homogeneously homogeneous and isotropic 2 varies locally (area coverage or profile shape) homogeneous and isotropic 3 homogeneously varies locally 4 varies locally (orientation of the lattice vector 26) varies locally 5 varies locally (tread depth) homogeneous and anisotropic

In a second embodiment, in the quasi-stationary pattern element of FIG. 11 a plurality of the first surface elements 27 are arranged on the second surface element 28 as a background surface, wherein the grating vectors 26 (FIG. Fig. 3 ) of each asymmetrical diffraction grating 24 ( Fig. 1 ) in the diffraction structure 25 (FIG. Fig. 7 ) of the first surface elements 27 on the one hand and the second surface element 28 on the other hand are aligned substantially anti-parallel. In one embodiment, the first surface elements 27 have, in a preferred direction 30, a surface coverage ratio of the diffraction structure 25 that decreases from surface element 27 to surface element 27, by inserting a plurality of partial surfaces 31 having dimensions in at least one dimension of less than 0.3 mm into the first Surface elements 27 can be achieved. In the partial areas 31, the diffraction structure 25 of the second Surface element 28 molded. The small sub-areas 31 are not visible to the naked eye, but effectively reduce the surface brightness of the first area elements 27. A similar effect is achieved in another embodiment by changing the asymmetry of the profile shape of the diffraction grating 24 from surface element 27 to surface element 27 in the preferred direction 30. The profile shape of the diffraction grating 24 changes from a first strongly asymmetrical shape via a symmetrical profile back to a mirror-symmetrical shape to the first asymmetric shape. The surface brightness of the first surface elements 27 therefore decreases in the preferred direction 30. In contrast, the matt structure extends homogeneously over the entire quasi-stationary pattern element. When rotating through 180 ° of the pattern element in the plane spanned by the coordinates x and y, the observer noticeably changes the contrasts between the first surface elements 27 and the second surface element 28.

In the third, in the FIG. 12 shown example of the quasi-stationary pattern element 27 at least a partial surface 31 is disposed within the first surface element. The first surface element 27 and the partial surfaces 31 differ only by the scattering property of the diffraction structure 25 (FIG. Fig. 7 ) used matt structure. For example, in the first surface element 27, the asymmetrical diffraction grating 24 (FIG. Fig. 7 ) superimposed on a strongly scattering matt structure, while in the sub-surface 31, the asymmetrical diffraction grating 24 is superimposed on a weakly scattering matt structure. As long as the observer when tilting or rotating the pattern element or the security element 2 ( Fig. 9 ) within the smaller of the two solid angles 16 ( Fig. 4 ) remains, the faces 31 are clearly visible against the background of the first surface element 27 because of their higher surface brightness. Outside the smaller solid angle 16 ( Fig. 4 ), but still within the larger solid angle 16 of the diffraction structure 25 in the first surface element 27, the contrast between the partial surfaces 31 and the first surface element 27 is reversed, so that the partial surfaces 31 are darkly recognized against the light background of the surface of the first surface element 27. The partial surfaces 31 may form a lettering or logo and have at least a font height of 1.5 mm for easy recognition; this requires correspondingly large surface elements 27, 28. At spatial frequencies below about 300 lines / mm, the contrast between the first surface element 27 and the partial surfaces 31 disappears outside the larger solid angle 16 of the diffraction structure 25 in the first surface element 27; For the observer, the first surface element 27 and the partial surfaces 31 are uniformly dark, eg also as in the US Pat FIG. 13 shown after the rotation of the security element 2 ( Fig. 1 ) in the range of the azimuth angle θ of about 180 °. Advantageously, as in the first example, the first surface element 27 adjoins the second surface element 28 in order to obtain an additional contrast change between the first and the second surface element 27, 28, which facilitates the observer finding the information contained in the surface portions 31.

In the FIG. 14 the relief elements of the matt structure in the diffraction structure 25 (FIG. Fig. 7 ) has a preferred direction oriented to the grating vector 26 with the azimuth θ. The microscopically fine relief structure elements of the matt structure are perpendicular to the lattice vector 26 of the asymmetrical diffraction grating 24 (FIG. Fig. 1 ). The scattered incident light 11 ( Fig. 6 ) therefore has an anisotropic distribution. In the Fourierraum representation of the FIG. 14 are the solid angles 32 and 33 of the two diffraction orders 14 (15) predetermined by the scattering power of the matt structure. Fig. 3 ) are pulled apart in the form of an ellipse along the grid vector 26. The major axis of the ellipse of the solid angles 32 and 33 transversely to the lattice vector 26 is very small so that the surface element 12 (FIG. Fig. 2 ) is visible in the scattered light in a large angular range when tilted about an axis transverse to the grating vector 26 and only in a narrow range in the azimuth. The intensity l ⁺ in the solid angle 32 of the positive diffraction order 12 ( Fig. 3 ) diffracted beams 21 ( Fig. 6 ) is larger by the factor p than the intensity I ^{- of} the rays 20 diffracted into the solid angle 33 of the negative diffraction order 12 ( Fig. 6 ).

An application of this diffraction structure 25 is in the FIG. 15 shown. A plurality of elliptical, self-contained narrow bands 34 form the surface pattern of the security element 2. The bands 34 are evenly distributed in azimuth arranged so that their centers of gravity 35 coincide. Each band 34 has an azimuth of the grating vector 26 predetermined by the major axis azimuth angle, for example, the bands 34 having the main axis azimuth angles 0 °, 45 °, 90 ° and 135 ° form a group and have the same azimuth of the grating vector 26 (FIG. Fig. 14 ) with θ = 0 °. The four bands 34 with the same azimuth of the grating vector 26 are simultaneously visible from the same direction. The surface of each of the bands 34 forms the pattern element described above and is divided into the two surface elements 27 (FIG. Fig. 9 ), 28 ( Fig. 9 ). The division into the two with the diffraction structures 25 (FIG. Fig. 7 ) occupied surface elements 27, 28 is carried out according to an outline 36 in a predetermined shape, such as a simple logo, a letter, a number, for example, for the in the FIG. 15 shown outline 36 is selected the shape of a cross. A part of the band 34 located outside the cross is designed, for example, as the first surface element 27 and the part of the band 34 located inside the cross as the second surface element 28. The direction of the grating vectors 26 of the diffraction structures 25 in the first surface elements 27 and the diffraction structures 25 in the second surface elements 28 are substantially antiparallel in each band 34. The relief elements of the matt structures are aligned in each band 34 transversely to the grating vector 26. When the security element 2 is rotated, those groups of the bands 34 that are blinking for the observer flash briefly, whose diffraction plane 17 (FIG. Fig. 6 ) coincides with the observation direction of the observer, ie with respect to the observation direction of the observer, the grating vectors 26 of the visible bands 34 have the azimuth θ = 0 ° or 180 °. The brightness of the band parts lying within the outline 36 is, for example, greater than that of the band parts outside the outline 36. When tilting, the contrast does not change, but the mixed color perceived by the observer, as long as the viewing direction of the observer within the solid angle 32 (FIG. Fig. 14 ) of the positive diffraction order remains. Once the line of sight of the observer with directions within the solid angle 33 (FIG. Fig. 14 ) of the negative diffraction order coincides, the contrast between the lying within the outline band parts 36 and lying outside the outline 36 band parts is reversed, ie the band parts within the outline 36 are less bright than the outboard Band parts. Outside the solid angles 32 and 33, the areas of the bands 34 are uniformly dark or unobservable.

In the FIG. 16 the fifth example is illustrated. A plurality of the surface elements 12 is disposed within the surface pattern of the security element 2 predetermined along the preferred direction 30, wherein adjacent surface elements 12 are spaced or aligned directly abutting. In each surface element 12, that for the diffraction structure 25 (FIG. Fig. 7 ) used diffraction gratings 24 ( Fig. 1 ), the blaze angle ε ₂ ( Fig. 7 ) of the wider profile flank of a surface element 12 to the adjacent surface element 12 between the extreme values ± ε _{2 Max} . changes in steps by one of the predetermined Blazewinkelstufen Δε ₂ . For example, in the drawing of FIG. 16 in the middle area element 12, the blaze angle ε ₁ ( Fig. 7 ) and ε _{2 of} the diffraction structure 25 equal zero, ie the diffraction structure 25 in the central surface element 12 is a plane mirror superimposed with the matte structure. The diffraction structures 25 of the two outer surface elements 12 have the blaze angle + ε _2Max . or -ε _{2 Max} . on. The matte structure is homogeneous in all surface elements 12 and anisotropic as shown by the FIG. 5 is beschieben. The elliptical solid angles 16 ( Fig. 5 ) of each of the surface elements 12 are in the Fourier space representation along the coordinate x ( Fig. 5 ) arranged in accordance with the blaze angle ε _{2 of} the diffraction structure 25 shifted next to each other. The grating vectors 26 ( Fig. 3 ) are aligned substantially parallel or antiparallel to the preferred direction 30. When the security element 2 is tilted about an axis 37 aligned transversely to the preferred direction 30, one of the surface elements 12 lights up brightly for the observer looking in the preferred direction 30, so that the observer lights a bright strip 38 on the security element 2 in the preferred direction 30 sees. When tilting about the preferred axis 30, the strip 38 remains visible in a large tilt angle dependent on the solid angle 16.

Instead of the isotropic matt structures used in the above examples, anisotropic matt structures can also be used. Conversely, anisotropic matt structures used in the above examples can be replaced by isotropic matt structures.

Claims (11)

1. Diffractive security element (2) made of a plastic laminate (1) with a mosaic-type surface pattern composed of surface elements (12; 27; 28), wherein a reflective boundary layer (8) between a moulded layer (5) and a protective layer (6) of the plastic laminate (1) forms optically active structures (9) in the surface elements (12; 27; 28) and light (11), which is incident on the plastic laminate (1) and passes through a cover layer (4) of the plastic laminate (1) and through the moulded layer (5), is deflected using the optically active structures (9) in a predetermined manner, characterized
   in that the optically active structure (9) of at least one of the surface elements (12; 27; 28) is a diffractive structure (25) produced from an additive superposition of a matt structure on a linear asymmetric diffraction grating (24),
   in that the linear asymmetric diffraction grating (24) has a spatial frequency from the value range of 50 lines/mm to 2000 lines/mm and
   in that the matt structure has an average roughness value from the range of 20 nm to 2000 nm and has at least in one direction a correlation length of 200 nm to 50,000 nm.
2. Security element (2) according to Claim 1, characterized in that a second surface element (28) adjoins a first surface element (27), in that the diffractive structure (25) is moulded into the surface of the second surface element (28) and in that the grating vector (26) of the linear asymmetric diffraction gratings (24) in the first surface element (27) is orientated substantially antiparallel with respect to the grating vector (26) of the linear asymmetric diffraction gratings (24) in the second surface element (28).
3. Security element (2) according to Claim 1 or 2, characterized in that partial surfaces (31) with a diffraction structure (25) are arranged in the surface element (12, 27), wherein the diffraction structure (25) of the partial surfaces (31) differs from the diffraction structure (25) of the surface element (12, 27) only in terms of the scattering capability of the matt structure.
4. Security element (2) according to Claim 3, characterized in that the partial surfaces (31) form an item of information in the form of a logo or text.
5. Security element (2) according to Claim 2, characterized in that a large number of the first surface elements (27) are arranged on the surface of the second surface element (28), in that the first surface elements (27) in a grid contain a large number of partial surfaces (31) with a maximum dimension in at least one dimension of less than 0.3 mm, in that the diffraction structure (25) of the second surface element (28) is moulded in the partial surfaces (31) and in that the degree of surface coverage of the diffraction structure (25) of the first surface element (27) varies from surface element (27) to surface element (27) along a preferential direction (30).
6. Security element (2) according to Claim 2, characterized in that a large number of the first surface elements (27) are arranged on the surface of the second surface element (28) and in that the asymmetry of the diffraction gratings (24) used for the diffraction structure (25) in the first surface elements (12) varies from surface element (27) to surface element (27) along a preferential direction (30).
7. Security element (2) according to Claim 1 or 2, characterized in that a large number of surface elements (12) are arranged next to one another on the surface of the surface pattern and in that a blaze angle (ε₂) of the asymmetric diffraction grating (24) used for the diffraction structure (25) in the surface element (12) is varied from one surface element (12) to another surface element (12) by one of the predetermined blaze angle stages (Δε) along a preferential direction (30).
8. Security element (2) according to one of Claims 1 to 7, characterized in that the matt structure is isotropic.
9. Security element (2) according to one of Claims 1 to 7, characterized in that the matt structure is anisotropic.
10. Security element (2) according to one of Claims 1 to 9, characterized in that the diffraction grating (24) is achromatic and has a spatial frequency of between 50 lines/mm and 300 lines/mm.
11. Security element (2) according to one of the preceding claims, characterized in that the boundary layer (8) is a coating made of a metal from the group of aluminium, silver, gold, chromium or tantalum.

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