EP1434695B1 - Security element - Google Patents

Abstract

A security element ( 2 ) in the form of a laminate can be used for the authentication of a document ( 1 ). The laminate has at least a transparent protective layer, a transparent lacquer layer and an adhesive layer, the lacquer layer being arranged between the protective layer and the adhesive layer. An interface in the form of a reflection layer separates the adhesive layer and the lacquer layer. The interface is divided into regions of a pattern ( 25 ) with flat surface portions and with relief structures which are formed in the lacquer layer. The flat surface portions form background surfaces ( 3 ) providing flat mirror surfaces for light which is incident into the laminate, while the regions with the relief structures of a predetermined, optically effective structure depth form pattern elements ( 4 ). The relief structures of the pattern elements ( 4 ) absorb the incident light. In the reflected light of the reflecting background surfaces ( 3 ) the dark pattern elements ( 4 ) form a strong contrast and the pattern ( 25 ) is clearly visible. In directions other than that of the reflected light the contrast between the background surfaces ( 3 ) and the pattern elements ( 4 ) disappears so that a copier apparatus reproduces the background surfaces ( 3 ) and the pattern elements ( 4 ) as black surfaces.

Description

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

Such security elements are used to authenticate documents, such as Securities, checks, banknotes, credit cards, identity cards of all kinds, Entry tickets, tickets, etc., are used, with the security elements For example, as a thin layer composite is glued to the document.

Modern copying machines for color copies provide for printing technology produced Documents pose a significant potential hazard because of the visual differences between the original and the copy are so small that only one with the appropriate specialist equipped the original of the copy often other criteria such as intaglio printing, watermarks, Fluorescence, optically variable security elements with diffraction structures etc., must be used as the appearance of the printed image.

From EP 0 522 217 B1 it is known that on a document arranged, reflecting pieces of film good protection against unauthorized Copy of such documents cause. The difference between the original with the reflecting foil pieces and a copy is clearly recognizable, since the Copy machines reflect reflective surfaces in black. However, they are Reflective films readily available commercially. The black areas in such Copies are therefore easy to cover with reflective film to make the copy more genuine to look like.

DE 44 10 431 A1 describes further developments of the above described film pieces. The security element is one of one Laminate cut piece of foil with a flat, reflective Reflective layer. In area parts that have an individual identifier on the area form the film piece, the reflective layer is removed, so that one under the Reflection layer arranged black layer is visible. On the of the Copy machine produced copy disappears the black identifier in the Reproduction of the remaining mirror surface, since the surface parts in which the Reflection layer is removed, and the remaining mirror surface in the copy appear uniformly black. Another security element has instead the plane mirror surfaces a hologram structure with the identifier and behaves like the ones discussed in the next paragraph Diffraction structures. In the copy, the identifier is in the copied image of the Hologram therefore recognizable.

It is also e.g. From GB 2 129 739 B known, valuable documents with a optically variable security element having diffractive structures (e.g., holograms, mosaic-like surface patterns of diffractive surface elements, for example according to EP 0 105 099 A1, EP 0 330 738 A1, EP 0 375 833 A1, etc.). These security items have a pattern or image that is dependent changes from the viewing condition. For unauthorized persons these are Imitate security elements only with great effort. Unfortunately, in the Color copy of the document of one of the patterns or images of the security element which is visible in the original under the viewing condition, which is in the Copier is set for the picture. Of course, in the copy is no Change of pattern or picture when changing the View condition more to recognize, but inattention of the Recipient can easily be kept a copy for the real document.

Versions of the layer composite for the security elements and thereto usable materials are described in EP 0 401 466 A1 and US Pat. No. 4,856,857.

The invention is based on the object, a cost optically variable security element to create that of a photocopier not can be reproduced and not with holographic methods can be copied.

The object is achieved according to the invention by the in the plate of the Claim specified features 1 solved. Advantageous embodiments of Invention will be apparent from the dependent claims.

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

Figur 1

ein Dokument,

Figur 2

das um eine Achse gekippte Dokument,

Figur 3

ein Sicherheitselement im Querschnitt,

Figur 4

die Grenzfläche einer Reliefstruktur,

Figur 5

eine erste Beobachtungsbedingung,

Figur 6

eine zweite Beobachtungsbedingung,

Figur 7a, 7b

das Sicherheitselement mit Graustufen und

Figur 8

eine Reliefstruktur.

Show it:

FIG. 1

a document,

FIG. 2

the document tilted about an axis,

FIG. 3

a security element in cross section,

FIG. 4

the interface of a relief structure,

FIG. 5

a first observation condition,

FIG. 6

a second observation condition,

Figure 7a, 7b

the security element with grayscale and

FIG. 8

a relief structure.

In the figure 1 1 signify a document, 2 a security element, 3 a Background area, 4 a pattern element and 5 an imaginary, in the plane of Document 1 tilting axis. Document 1 is in directional artificial light illuminated laterally and obliquely from above and viewed vertically from above. On the document 1, the security element 2 is attached. The security element 2 has for identification a pattern 25 of the pattern elements 4, which from the background surfaces 3 are surrounded. To the drawing of Figure 1 to make clear, the pattern 25 consists of a single Pattern element 4 and forms a simple "V" character. In a practical Execution are more of the background surfaces 3 and the pattern elements. 4 arranged to the pattern 25. Among the mentioned lighting and Viewing conditions, the pattern 25 is not visible to an observer, because there is no contrast between the pattern element 4 and the background surface 3 is present and both surfaces, both the background surface 3 and the Pattern element 4, appear dark, for example, metallic matt. In the diffuse Daylight or diffuse room lighting, however, and below mentioned, certain lighting conditions, the pattern element 4 lifts dark of the light. Background area 3 and is therefore good for the observer visible, noticeable.

is, as the figure 2 shows the document 1 with the security element 2 to the tilting axis 5 is tilted such that the background surface 3 light in the eye of the observer reflects, the observer recognizes the pattern 25, since the Pattern element 4 remains dark and with high contrast of the Background area 3 lifts off. Under this observation condition is the Reflection condition for the observer fulfilled. A turn of the Security element 2 in its plane changes that for the observer Appearance of the pattern 25 in the reflection condition not, i. an azimuthal Orientation of security element 2 is not required.

FIG. 3 shows the security element 2 (FIG. 2) in cross section, wherein the Cutting plane, for example, the tilt axis 5 (Fig. 2) contains. The Security element 2 consists of a layer composite 6 of a variety of Layers 7, 8, 9 and 11. Examples of the structure of the composite layer 6 and the for the composite layer 6 suitable materials are EP 0 401 466 A1 and US 4,856,857.

In the simplest case, the layer composite 6 comprises at least one Protective layer 7, an adhesive layer 8, one between the protective layer 7 and the , Adhesive layer 8 arranged paint layer 9. The adhesive layer 8 connects the Security element 2 with the document 1. An interface between the Adhesive layer 8 and the varnish layer 9 reflected by the cover layer 7 and the Lacquer layer 9 incident light 10, when the refractive index at the Boundary layer during the transition from the lacquer layer 9 into the adhesive layer 8 changes abruptly. With the materials in Table 6 of US 4,856,857 falls the Difference in the refractive indices too small to obtain a strong reflection. The reflectivity is therefore due to a arranged at the interface Reflective layer 11, which forms a thin layer (<0.4 microns) of a Metal or one with a suitable inorganic dielectric layer coated metal, wherein the dielectric layer on the incident Light 10 facing side of the metal is arranged.

The materials for the reflection layer 11 are shown in Tables 1 to 5 of US 4,856,857; Tables 1 to 6 are expressly in this Description included. The tellurium not mentioned in Table 5 is suitable also for the reflection layer 11. With the incident light 10 is daylight or Visually visible polychromatic light with wavelengths between Meant 380 nm and 780 nm.

In one embodiment of the layer composite 6, that of the lacquer layer 9 opposite surface of the cover layer 7 of the composite layer 6 by means of a Separating layer 12 connected to a carrier tape 13 to the transfer of the To facilitate fragile layer composite 6 on the document 1. The carrier tape 13 made of paper or a plastic film, e.g. PC or PETP, can be after the Glue the layer composite 6 remove so that the pattern 25 (Fig. 2) by the protective layer 7 and the lacquer layer 9 is visible therethrough. This is on the already mentioned in the beginning GB 2 129 739 B referenced.

As can be seen from FIG. 3, paint coating 9 is in the region of Pattern elements 4 a relief structure 14 with a geometric profile depth p shaped. In the area of the background surfaces 3, the lacquer layer 9 is flat and smooth and is parallel to the other layers of the composite layer. 6 The material of the adhesive layer 8 fills the depressions of the relief structure 14. Die Interface with or without additional reflective layer 11 follows both the Relief structure 14 as well as mirror planes of the background surfaces 3.

The relief structure 14 is a cross lattice of two Basisgittem with periods d smaller than a cut-off wavelength λ at the short-wave end in the spectrum of visible light, i. λ = 380 nm to λ = 420 nm and has an optically active Structure depth h, that is the profile depth p multiplied by the refractive index of the Lacquer layer 9, preferably in the range of h = 50 nm to h = 500 nm. Such Relief structures 14 absorb almost everything incident on the pattern elements 4 visible light 10 and scatter a small fraction of the incident light 10 in the half space above the pattern element 4 back. The percentage of absorbed light 10 depends in a non-linear manner on the structure depth h and can by means of the choice of the structure depth h in the above range between 50% and about 99% are controlled, where, the flatter the relief structure 14 the more incident light 10 is backscattered and the less light 10 is absorbed. The given percentages apply to the relief structure 14 with a reflection layer 11 of, for example, aluminum. Abutting Regions of the pattern elements 4 with different texture depths h therefore show a gray scale.

The embodiment of the relief structure 14 shown in FIG. 4 is a cross lattice formed by two sinusoidal base lattices intersecting at right angles. The sine function of the first basic lattice extending along the coordinate x has a period d _x and an amplitude h _x , while the sine function of the second base lattice extending along the coordinate y has a period d _y and an amplitude h _y . Over the plane defined by the coordinates x and y, the interface h (x, y) formed by the cross lattice in the layer composite 6 (FIG. 3) follows the function, for example h (x, y) = [h x + h y ] • sin 2 (Πx / d x ) • sin 2 (Πy / d y ).

In other embodiments, h (x, y) = h _x • sin ² (πx / d _x ) + h _y • sin ² (π _y / d _y ), rectangular or pyramidal structures are used as the interface h (x, y).

In one embodiment, the two periods d _x , d _y and the texture depths h _x ; h _y same, different in other versions. The structure depth h = [h _x + h _y ] can be chosen larger than the period d, but the relief structure 14 is difficult to produce with today's production methods. The interface h (x, y) is similar to an egg carton and is shown in FIG.

The optical behavior of the security element 2 is included in FIG. 5 a first observation condition explained. The incident light 10 forms with a normal 15 to the level of the security element 2 an angle of about 40 °. In one example, the pattern elements 4 absorb with the described relief structure 14 in the visible range up to 95% of incident light 10, the rest is scattered. The reflecting background surface 3 however, only about 10% of the incident light 10 absorbs and reflects that rest. Since surface parts of the pattern elements 4 to the specular Background surfaces 3 adjoin, therefore results for the observer so strong contrast, that on a given background surface 3 of the Security elements 2 arranged in the predetermined pattern 25 Pattern elements 4 are easily recognizable as information. The pattern 25 stops Logo, text, picture or other graphic sign.

The drawing of Figure 5 corresponds to the lighting conditions in Copy machine. Depending on the model of the copier, the directional, on the Document 1 and the security element 2 incident light 10 of the copier with the normal 15 the angle of incidence α in the range of about 40 ° to 50 °. The Document 1 scatters the incident light 10 into the whole half space. Thereby scattered light is arranged in a direction of the normal 15 Light receiver 16 of the copier. In contrast, that will be done by the Background area 3 reflected light 17 according to the law of reflection with the the same angle α deflected in a line of sight 18 of the observer 19 and does not get into the light receiver 16. If the light 10 falls below the same Incidence angle α on the pattern element 4, the incident light 10, however practically absorbed; both the light receiver 16 and the observer 19 register no light from the pattern element 4. The pattern element 4 is therefore dark.

The background surfaces 3 form for the incident in the layer composite 6 Light 10 the plane mirror surfaces of the pattern 25, while the pattern elements 4 as absorber surfaces swallow the incident light 10 for the most part. Therefore, the observer 19 recognizes the background surfaces in the reflected light 17 3 as intensely bright partial surfaces and the pattern elements 4 as dark partial surfaces of the pattern 25. Scattered in directions other than that of the reflected light 17 the security element 2 only a small part of the incident light 10. The Intensities per unit area of the background surfaces 3 and the Pattern elements 4 scattered light are practically the same size, so that no Contrast between the background areas 3 and the pattern elements 4 is available. In the illumination with the directional incident light 10 is the from the background surfaces 3 and the pattern elements 4 formed pattern 25 in Contrary to a black and white image produced by printing technology only in that when specular reflection reflected light 17 recognizable.

In the copying machine, the background surface 3 and the pattern member 4 throw so small a portion of the incident light 10 into the light receiver 16 that the copying machine reproduces the background field 3 and the pattern element 4 indiscriminately as black areas. The advantage of this security element 2 is that the copying machine can not reproduce the information represented by the pattern element 4, while the observer 19, who in directed incident light 10 almost automatically tilts the security element 2 in such a way that he regards the background area 3 in reflection, the information of the pattern element 4 with great contrast in front of the background surface 3 sees. The security element 2 can thus easily be distinguished by an attentive observer from reflecting metal foils on good color copies of the document 1. A further advantage is the use of the relief structure 14 in the security element 2 with the periods d _x (FIG. 4), d _y (FIG. 4), which are shorter than the wavelengths of the coherent light sources usable for holographic copying methods; Therefore, a copy of the security element 2 can not be produced with the holographic methods.

FIG. 6 shows a second illumination condition for the two observers 19, 20 of the security element 2. A polychromatic radiation source 21, eg halogen lamp, incandescent lamp etc., is arranged above the second observer 20 and transmits the incident light 10 to the pattern element 4 at a large angle of incidence α of approximately 60 ° to 80 °. The first observer 19 recognizes the pattern 25 (Fig. 2) of the pattern elements 4 against the background 3 (Fig. 5) at the reflection angle α, as stated above. If the periods d _x (FIG. 4), d _y (FIG. 4) of the relief structure 14 are in the range of half and one entire cut-off wavelength λ; ie λ ≥ d ≥ λ / 2, where d = d _x or d _y , a portion of the incident light 10 is deflected at a large diffraction angle β in the minus first order as diffracted light 22. The second observer 20 is able to recognize the diffracted light 22. The diffracted light 22 includes the short wavelength part of the visually visible spectrum of the electromagnetic radiation. The diffracted light 22 is therefore in a cyan to violet color depending on the diffraction angle β and the periods d _x , d _y . The color of the diffracted light 22 observed at a predetermined diffraction angle β to the normal 15 also depends on the azimuth in intensity. Note: In the above consideration, the refractive influence of the protective layer 7 has been disregarded.

The first observer 19, on the other hand, looks in the direction of the reflected light Light 17 and recognizes the background surfaces 3 as shiny bright faces and the pattern elements 4 as dark faces of the pattern 25th

If the period d _x or d _{y is} smaller than λ / 2, the diffracted light 22 can no longer be seen by the second observer 20 in the direction of the coordinate x or y, since the relief structure 14 no longer diffracts any visible light 22. The first observer 19, who observes the security element 2 at the reflection angle α, sees the pattern elements 4 unchanged in a dark brown to black color under these conditions.

The color of the visible under the reflection angle α pattern elements. 3 depends on the nature of the reflection layer 11, since different Combinations of the materials in and on the reflective layer 11 the incident Light 10 not in the whole spectral range of the visible electromagnetic Reflect radiation evenly. Deep black pattern elements 3 have with Advantage a gradual transition of the refractive index of the paint layer 9 to Reflection layer 11; the transition is by means of at least one layer of a inorganic dielectric 23 between the resist layer 9 and a Metal layer 24 of the reflection layer 11 is generated. For the flat mirror surface the background surfaces 3 affects those of the dielectric 23 and the Metal layer 24 formed reflective layer 11 is not noticeable. In the Relief structure 14, however, causes this reflection layer 11 due to Interference an almost complete extinction of the incident light 10, especially evenly over the entire spectral range of the visible electromagnetic radiation takes place. An example has a 50 nm thick layer of the dielectric 23 of ZnS and 100 nm of aluminum as the metal layer 24. One Another advantage is the high refractive index for ZnS of n = 2.4 compared to the refractive index of the lacquer layer 9 of n = 1.5 increased Structure depth h at constant profile depth p of the relief structure 14.

In addition to the gray scale with pattern elements 4 with different Structural depths h are in one embodiment of the security element 2 the Grayscale by means of different dense grid with grid points of less than 0.4 mm dimension produced. It is irrelevant whether the Halftone dots as a background field 3 in a pattern element 4 or as Pattern element 4 are arranged in the background field 3.

FIGS. 7a and 7b show further examples for the production of Grayscale within a security element 2 from the dark pattern element 4 until the bright shiny background field 3 shown. In the figure 7a are in one fixed grid of a maximum of 0.5 mm spacing according to the gray level different sized grid points used. In a lightly brightened zone 26 touch the grid points, in a brightened zone 27 have the Halftone dots have an average dimension of about 0.25 mm while in one slightly darkened zone 28, the grid points have about 0.15 mm. In the FIG. 7b is a line grid with a maximum of 0.5 mm instead of the dot grid , Distance used. A corresponding line width causes the here Grayscale in zones 26 (Figures 7a) to 28 (Figure 7a).

In one of the zones 26 to 28, the grid points of the pattern areas 4 the same dimensions. A very fine gray gradation is by means of correspondingly stepped structure depths h in the relief structures 14 (FIG. 6) reached, which is sufficient for the reproduction of a black and white photo.

In FIG. 8, two patterns 25 of the security element 2 are simple Example shown. In the upper half of the security element 2 is the Pattern 25 from a ribbon 29 with a star 30. The ribbon 29 is from the dark pattern element 4 is formed. The environment of the band 29 and the star 30 form the bright background areas 3. Without limitation of the date Described are the background surfaces 3 and the pattern elements 4 interchangeable, as shown in the lower half of the security element 2 is.

The security element 2 in Fig. 1 will be even more difficult to duplicate if the pattern 25 is a background for a mosaic-like surface pattern 31 forms with diffraction structures whose spatial frequencies have values in the range 300 lines per mm to 2000 lines per mm. Such mosaic Surface patterns 31 are from the above-mentioned EP 0 105 099 A1, EP 0 330 738 A1, EP 0 375 833 A1. The content of these patents is hereby incorporated in the description included.

Claims (13)

1. Security element (2) having a pattern (25) comprising subareas and in the form of a layer composite (6) for authenticating a document (1), which composite comprises at least one transparent protective layer (7), a transparent varnish layer (9) and an adhesive layer (8), the varnish layer (9) being arranged between the protective layer (7) and the adhesive layer (8) and the refractive index changing abruptly at the interface between the adhesive layer (8) and the varnish layer (9), and the subareas of the pattern (25) being composed of background areas (3) and pattern elements (4),
   characterized in that, in the region of the background areas (3), the varnish layer (9) is smooth and flat and, in the region of the pattern elements (4), relief structures (14) having a predetermined optically active structure depth (h) are moulded into the varnish layer (9),
   in that the background areas (3) are flat reflective areas for light (10) falling into the layer composite (6), and
   in that the relief structures (14) are crossed gratings formed of basic gratings with periods (d_x; d_y) and the periods (d_x; d_y) are shorter than a predetermined limiting wavelength (λ) at the short-wave end in the spectrum of visible light (10), so that the pattern elements (4) absorb and scatter the incident light (10), the ratio of the absorbed and of the scattered light in each relief structure (14) being dependent in a predetermined manner on the optically active structure depth (h) prevailing in the relief structure (14).
2. Security element (2) according to Claim 1, characterized in that the crossed grating of the relief structures (14) is composed of two basic gratings arranged substantially perpendicular to each other and having the periods (d_x; d_y).
3. Security element (2) according to Claim 1 or 2, characterized in that the basic gratings are sinusoidal.
4. Security element (2) according to one of Claims 1 to 3, characterized in that at least one of the periods (d_x; d_y) is longer than half the limiting wavelength (λ) but shorter than the limiting wavelength (λ).
5. Security element (2) according to one of Claims 1 to 4, characterized in that the limiting wavelength (λ) is chosen in the range between 380 nm and 420 nm.
6. Security element (2) according to one of Claims 1 to 5, characterized in that the periods (d_x; d_y) of the two basic gratings have the same value.
7. Security element (2) according to one of Claims 1 to 6, characterized in that the values for the optically active structure depth (h) of the relief structures (14) are chosen in the range from h = 50 nm to h = 500 nm.
8. Security element (2) according to one of Claims 1 to 7, characterized in that the reflective layer (11) contains a metal from the group comprising aluminium, silver, gold, chromium, copper, nickel and tellurium.
9. Security element (2) according to Claim 8, characterized in that the reflective layer (11) on the side of the metal layer (24) facing the varnish layer (9) has at least one layer of an inorganic dielectric (23).
10. Security element (2) according to Claim 9, characterized in that the layer of inorganic dielectric (23) consists of ZnS and the metal layer (24) consists of aluminium.
11. Security element (2) according to one of Claims 1 to 10, characterized in that the pattern (25) has zones (26; 27; 28) with grey steps, and that the pattern elements (4) of the zones (26; 27; 28) having different grey steps differ in the optically active structure depth (h) of the relief structures (14).
12. Security element (2) according to one of Claims 1 to 10, characterized in that the pattern (25) has zones (26; 27; 28) with grey steps, in that the pattern elements (4) have identical values of the optically active structure depths (h), and in that the zones (26; 27; 28) differ in differently dense screening of halftone points with dimensions of less than 0.4 mm.
13. Security element (2) according to one of Claims 1 to 12, characterized in that the pattern (25) forms a background for a mosaic-like surface pattern (31) comprising diffraction structures with spatial frequencies in the range from 300 lines per mm to 2000 lines per mm.

Images