EP1397259B1 - Optically variable surface pattern - Google Patents

Abstract

An optically variable surface pattern ( 1 ) contains relief structures ( 9.1; 9.2; 9.3 ) for producing at least two representations ( 2; 3; 4 ). The relief structures ( 9.1; 9.2; 9.3 ) have a period length (L) of at least five micrometers and are sawtooth-shaped. The relief structures ( 9.1; 9.2; 9.3 ) associated with different representations ( 2; 3; 4 ) have different angles of inclination (alpha;beta;gamma). The angles of inclination are so selected that the representations ( 2; 3; 4 ) can be perceived separately by a viewer on the one hand and on the other hand when producing a copy by means of a color photocopier they are all transferred onto the copy.

Description

The invention relates to an optically variable surface pattern which in the preamble of Claim 1 mentioned type.

Such surface patterns contain structures, mostly microscopic in shape of fine relief structures that diffract incident light. These diffractive patterns are suitable, for example, as authenticity and security features for increasing security against counterfeiting. They are particularly suitable for the protection of Securities, banknotes, means of payment, identity cards, passports, etc.

The function as an authenticity feature consists in the recipient of the provided object, e.g. a banknote to convey the feeling that the object is real and not a fake. The function as The security feature is to prevent unauthorized copying or at least to make it extremely difficult.

Such surface patterns are known from many sources; be representative called EP 0 105 099 B1, EP 0 330 738 B1, EP 0 375 833 B1 here. she are characterized by the brilliance of the pattern and the movement effect in the pattern from, are embedded in a thin laminate of plastic and are in shape a mark on documents such as banknotes, securities, ID cards, Passports, visas, identity cards etc. applied, e.g. glued. For the production The materials that can be used for the security elements are in EP 0 201 323 B1 compiled.

A pixel-oriented optically variable surface pattern is from the European Patent EP 0 375 833 B1 known. Such a surface pattern contains one predetermined number N of different images. The area pattern is in pixels subdividing. Each pixel is divided into N sub-pixels, with each of the N sub-pixels a pixel of one of the N images is assigned to a pixel. Any sub-pixel contains a diffraction structure in the form of a microscopic relief that Information about a color value, a level of the brightness value and about contains a viewing direction. Provides a viewer of the surface pattern only one image is shown at a time, with the respective visible image being tilted or rotating the surface pattern or by changing the viewing angle of the Viewer can be changed.

Another optically variable surface pattern is from US Pat. No. 6,157,487 known. In this surface pattern, the microscopically fine Relief structures have a comparatively small number of lines per millimeter, so that incident light is almost achromatically diffracted.

It is also known that the differences in the spectral sensitivity of the human eye and the color copier based idea, documents with a equip colored background and background information in one different color, with information and background from one human eye have perceptible contrast, but that of the Color copier cannot be reproduced.

The invention has for its object an optically variable surface pattern propose that has improved copy protection.

According to the invention, the stated object is achieved by the features of Claim 1.

A diffraction-optically effective surface pattern comprises at least two Representations nested on the surface pattern are. The representations contain light diffractive, reflective structures that incident light under ordinary lighting conditions in bend different directions so that a viewer is only ever one of the Can see representations. By rotating and / or tilting the surface pattern or by changing the perspective, the viewer can do one or the other make another representation visible. The invention is now based on the idea of making the differences in the diffraction directions so small that on the one hand the representations from the viewer from a typical distance of 30 cm are perceptible separately and that on the other hand when copying using a color copier either all representations are copied so that on the Copy a picture that corresponds to the overlay of all representations, or that none of the representations are copied.

Diffraction structures are preferably symmetrical or asymmetrical sawtooth-shaped relief structures are used, which are compared to the wavelength of the visible light a relatively long period, but different Have inclination angles. The period length can be used for the relief structures of all Representations be the same; but it can also be of different sizes. The Period length L is typically 5 µm or more. The bigger the Period length, the more the relief structure acts like an inclined mirror which reflects the incident light and is hardly bent anymore. That the Relief structure increasingly diffracts the light achromatically and the diffraction angle is determined by the law of reflection and diffraction and is for perpendicular striking light at least twice the angle of inclination.

Diffraction structures can also be achromatic gratings with a Period length L of more than 5 µm and a sine-like relief profile, e.g. a sinusoidal relief profile can be used. The relief structures of the Different representations differ in the period length L and / or in the structure depth of the relief profile, so that the representations by the observer are perceptible separately.

The diffraction structures can also be in the form of a Volume hologram can be realized.

The surface pattern according to the invention can therefore be characterized by that the different representations when illuminated with perpendicular to the Surface pattern of light hitting a human viewer below different angles are perceptible separately, and that the difference the viewing angle of at least two of the representations is so small that one copy made by means of a copier the at least two representations reproduces one above the other.

The directions of diffraction are from the given direction of illumination Orientation of the surface pattern depending. So when copying using a Color copier all regardless of the orientation of the surface pattern Representations can be copied onto the copy, several per representation Representations of the same content may be present by linear, but lattice structures rotated against each other are formed. Another solution is there in using circular grids as a grid.

Exemplary embodiments of the invention are described below with reference to the drawing explained in more detail.

Fig. 1

die Struktur eines pixelorientierten Flächenmusters in der Aufsicht,

Fig. 2

grafische Darstellungen,

Fig. 3

das Flächenmuster im Querschnitt,

Fig. 4

einen Farbkopierer,

Fig. 5, 6

Lichtverhältnisse beim Kopiervorgang,

Fig. 7

ein Gitter mit kreisförmigen Furchen,

Fig. 8

eine Reliefstruktur mit einer symmetrischen Profilform und

Fig. 9

ein nicht pixelorientiertes Flächenmuster.

Show it:

Fig. 1

the structure of a pixel-oriented surface pattern in the supervision,

Fig. 2

graphic representations,

Fig. 3

the cross-sectional area pattern,

Fig. 4

a color copier,

5, 6

Lighting conditions during the copying process,

Fig. 7

a grid with circular furrows,

Fig. 8

a relief structure with a symmetrical profile shape and

Fig. 9

a non-pixel oriented surface pattern.

1 shows the structure for a first exemplary embodiment in top view of a pixel-oriented surface pattern 1, for example k = 3 image motifs contains that from a human viewer from different angles are perceptible separately. The motifs are shown below as graphic Representations 2, 3 and 4 (Fig. 2) designated. The surface pattern 1 is matrix-like divided into n * m pixels or fields 5. Each field 5 is in k = 3 partial areas 6, 7 and 8 divided. The entirety of the partial areas 6 includes the first graphic Representation 2, the entirety of the partial areas 7 includes the second graphic Representation 3 and the entirety of subareas 8 include the third graphic Representation 4. The dimensions of a field 5 are typically less than 0.3mm x 0.3mm, so that the individual fields 5 from the human eye at one Visible distance of 30 cm cannot be resolved.

darstellen. Die Schriftzüge sind hell auf dunklem Hintergrund (in der Zeichnung ist es umgekehrt). Die Darstellungen 2, 3 und 4 sind ebenfalls matrixartig in n*m Rasterfelder 2.1, 3.1 bzw. 4.1 unterteilt, die entweder hell oder dunkel sind. Aus zeichnerischen Gründen sind die Rasterfelder 2.1, 3.1, 4.1 im Vergleich zu den Schriftzügen viel zu gross und zudem jeweils nur einige der Rasterfelder 2.1, 3.1, 4.1 dargestellt. Jedem Rasterfeld 2.1 der ersten Darstellung 2 ist eine Teilfläche 6 (Fig. 1) zugeordnet. Auf gleiche Weise ist jedem Rasterfeld 3.1 der zweiten Darstellung 3 eine Teilfläche 7 (Fig. 1) und jedem Rasterfeld 4.1 der dritten Darstellung 4 eine Teilfläche 8 (Fig. 1) zugeordnet.2 shows the three representations 2, 3 and 4, which, for example, the lettering "100", "EUR" and

represent. The lettering is light on a dark background (the reverse is true in the drawing). The representations 2, 3 and 4 are also subdivided into n * m grid fields 2.1, 3.1 and 4.1, which are either light or dark. For reasons of drawing, the grid fields 2.1, 3.1, 4.1 are much too large compared to the lettering and, in addition, only some of the grid fields 2.1, 3.1, 4.1 are shown. A partial surface 6 (FIG. 1) is assigned to each grid field 2.1 of the first representation 2. In the same way, a partial area 7 (FIG. 1) is assigned to each grid area 3.1 of the second representation 3 and a partial area 8 (FIG. 1) is assigned to each grid area 4.1 of the third representation 4.

If one of the grid fields 2.1 of the first representation 2 is dark, it contains the assigned partial area 6 a mirror or a cross grating with at least 3000 Lines per millimeter, which reflects, absorbs or reflects the incident light high angle is scattered. If one of the grid fields 2.1 is bright, it contains the assigned partial surface 6, as shown in FIG. 3, a sawtooth Relief structure 9.1. The relief structure 9.1 has a compared to the wavelength visible light has a comparatively large period length L, which is typically Is 5 µm or more. The first representation 2 (FIG. 2) thus appears at Illumination with white light, and when the viewer has his point of view in accordance with the reflection conditions of the geometric optics, than Image of light and dark dots, which are usually the color of the Covering the relief structure 9.1 used reflection layer 11 and / or Have cover layer 12.

a) ein Betrachter, der das Flächenmuster aus einer typischen Distanz von 30 cm betrachtet, jeweils nur eine der drei Darstellungen 2, 3 oder 4 sieht,
und

b) beim Kopieren mittels eines Farbkopierers entweder wenigstens zwei oder überhaupt keine der Darstellungen 2, 3 und 4 mitkopiert werden.

The two other representations 3 (FIG. 2) and 4 (FIG. 2) are realized with a sawtooth-shaped relief structure 9.2 or 9.3 similar to the relief structure 9.1 of the first representation 2. The angles of inclination α, β and γ of the sawtooth of the three relief structures 9.1, 9.2 and 9.3 with respect to the plane of the surface pattern 1 are selected such that

a) an observer who looks at the surface pattern from a typical distance of 30 cm sees only one of the three representations 2, 3 or 4,
and

b) when copying by means of a color copier, either at least two or none of the representations 2, 3 and 4 are copied at the same time.

The furrows of the different relief structures 9.1, 9.2 and 9.3 run approximately parallel, i.e. the maximum difference in the angle that the furrows assume with respect to any axis in the plane of the surface pattern 1, the so-called azimuth angle, should be less than about 10 °, so below the lighting conditions prevailing when copying either all three or transfer none of representations 2, 3 and 4 to the copy become. In addition, the furrows preferably run parallel to a side edge of the object to be protected with the surface pattern so that the furrows are aligned as parallel as possible to the scanner of a color copier.

The surface pattern 1 is, as shown in cross-section in FIG. 3, advantageously as Layered composite formed. The layer composite is formed by a first one Paint layer 10, a reflection layer 11 and a second paint layer, the Cover layer 12. The lacquer layer 10 is advantageously an adhesive layer, so that the Layer composite can be glued directly onto a substrate. With the term substrate is for example a security, a banknote, an identity card, a Credit card, passport, or more generally an item to be protected meant. The cover layer 12 advantageously covers the relief structures completely on. It also preferably has an optical one in the visible range Refractive index of at least 1.5, so that the geometric profile height h a results in the largest possible optically effective profile height. The top layer also serves 12 as a scratch-resistant protective layer. For the sake of simplicity of description, the Influence of refraction at the boundary between air (refractive index = 1) and the Cover layer 12 with a refractive index of around 1.5 neglected.

3 shows side by side the bright pixels of the three representations 2, 3 and 4 of FIG. 2 assigned sawtooth-shaped relief structures 9.1, 9.2 and 9.3, which are present in the corresponding partial areas 6, 7 and 8 of the fields 5 are. When viewed from a distance of 30 cm and at a Pupil diameter of 5 mm, the human eye takes the representations 2, 3 and 4 separately true if the difference in the angle of inclination between each two adjacent representations is approximately 0.5 ° - 5 °. The angle of inclination are, for example, α = 12.5 °, β = 15 ° and γ = 17.5 °. The value for the largest angle of inclination, i.e. here for the angle of inclination γ, should be at most 25 ° amount so that on the one hand the relief structures 9 do not become too deep and thus on the other hand, all three representations 2, 3 and 4 when copying using a Copier can be transferred to the copy.

Fig. 4 shows schematically the geometric relationships when copying by means of a color copier 13. The color copier 13 has a glass plate 14 the document 15 to be copied, e.g. one banknote, one, and one in the x direction Mobile carriage 16 on which a light source 17, a deflecting mirror 18 and a detector 19 with photosensors 20 contains. When copying, this happens light 21 emitted by the light source 17 at a certain angle at an angle to document 15 and thus at an angle to that on document 15 existing surface pattern 1 with the differently inclined relief structures 9.1,9.2 and 9.3 (Fig. 3). Part of the incident light becomes approximately vertical thrown back to the glass plate 14, hits the deflecting mirror 18 and is thus the photosensors 20 of the color copier 13 are shown.

The angles of inclination α, β and γ are chosen such that the relief structures 9.1, 9.2 and 9.3 with correct orientation on the glass plate 14 of the color copier 13 reflect light emitted by the light source 17 onto the deflecting mirror 18. 5 shows this situation. Each of the representations 2, 3 and 4 is one associated sub-area 6, 7 or 8 on a very greatly enlarged scale shown, a bright point of the representation assigned to these partial areas is. The light beam reflected on the relief structure 9.1 has the reference symbol 22, the light beam reflected on the relief structure 9.2 has the reference symbol 23 and the light beam reflected on the relief structure 9.3 is with the Reference numeral 24 denotes. The 6.7 on these three partial areas shown or 8 reflected light beams 22, 23 and 24, as shown in FIG. 6, almost side by side on the deflecting mirror 18 and are there in the direction the photosensors 20 deflected. Although the light rays 22, 23 and 24 below different angles on the deflecting mirror 18, they are on the Photosensors 20 shown, since the angle differences are sufficiently small. at a conventional color copier namely angle differences of typically recorded at 30 °. The limits of the area covered by the color copier are shown with dashed lines 25. In the present example with the The maximum angle of inclination is α = 12.5 °, β = 15 ° and γ = 17.5 ° Angle difference between the light beams 22, 23 and 24 only 10 °.

At 15 °, the mean angle of inclination is also the typical angle of 30 ° adjusted under which the light emitted by the light source 17 of the Color copier 13 falls on the document to be copied. This means that then the light diffracted at the associated relief structure approximately vertically is bent down to the deflecting mirror 18.

So that the representations of a human viewer under ordinary Lighting conditions and separated at a viewing distance of 30 cm the surface of the surface pattern 1 receiving document have a relatively smooth surface, otherwise the Representations are smeared because of the roughness, so they don't are visible separately. For use with documents that are relatively rough The surface, as they have for example banknotes, are therefore larger Inclination angles of α = 10 °, β = 15 ° and γ = 20 ° or even α = 5 °, β = 15 ° and γ = 25 ° are provided. In this case, too, all hunched over Light rays 22, 23 and 24 on the photosensors 20 of the color copier 13. Die Difference between the largest and the smallest inclination angle be at most 20 ° so that all representations are copied when copying.

When copying, all or none of the three displays are displayed transfer the copy. The in the representations of the surface pattern 1 Stored information becomes illegible or disappears completely.

In the previous numerical examples, the differences were between successive angles of inclination, i.e. the difference β-α and the difference γ-β, the same size. The differences between successive However, angles of inclination can also be of different sizes.

The dependence of the effect on the orientation of the surface pattern to keep the color copier as small as possible or even eliminate them Relief structures 9.1, 9.2 and 9.3 with advantage non-linear grids with straight lines Furrows, but grids with serpentine corrugated furrows, i.e. grids with furrows with alternating curvature, or grids with circular or the Circle approximated, polygonal furrows. A relief structure with circular furrows is shown in FIG. 7. The distance between two circular lines correspond to the period length L.

Instead of the asymmetrical relief structures 9.1, 9.2, 9.3 can also Relief structures with a symmetrical profile shape can be used incident light essentially not in one direction, but in two Reflect directions. Such an example is shown in FIG. 8. Also drawn is the angle α, which is the inclination of the relief structures 9 referred to the horizontal.

The embodiment of the invention is not based on pixel-oriented surface patterns limited. 9 shows sections of an example of one not pixel-oriented surface pattern with two representations 2 and 3 that are not overlap. The area occupied by the surface pattern 1 is divided into three Subareas 6, 7 and 26. The subarea 26 serves as a common background for the two representations 2 and 3. The partial surface 6 contains sawtooth-shaped Relief structures which have a first angle of inclination and which are the light ones Create points of the first representation 2. The partial surface 7 contains sawtooth-shaped relief structures that have a second, from the first angle of inclination have different angles of inclination and the bright points of the generate second representation 3. The partial surface 26 is used to generate a dark or nondescript background. It is for example as a mirror or designed as a cross grid with at least 3000 lines per millimeter or transparent, so that at this point the substrate on which the surface pattern is glued on, is visible.

The two representations 2 and 3 are thus from a human viewer can be perceived separately for a given direction of illumination because it is below different angles are visible. However, the angles of inclination are the sawtooth-shaped relief structures chosen so small that when copying using a copier both representations 2 and 3 are mapped onto the copy. On the copy, the two representations 2 and 3 are therefore visible without the Viewer must change the angle of view or the direction of illumination.

If the two representations partially overlap, the invention can be either as pixel-oriented according to the first embodiment Area pattern, or as not according to the above embodiment Realize pixel-oriented surface pattern, whereby the overlapping Areas are assigned to either the first or the second display. The surface pattern can also be a combination of the two Realize embodiments, the overlapping areas as in pixel-oriented surface patterns are executed.

Claims (12)

1. Optically variable surface pattern (1) comprising part surfaces (6; 7; 8) with light-diffracting, reflective structures and reflective part surfaces (26) for the production of two or more illustrations (2; 3; 4) which, when illuminated with light incident vertically on the surface pattern (1), can be perceived separately by a human observer at a viewing distance of 30 cm at various viewing angles
   characterized in that
   the part surfaces (6; 7; 8) contain achromatically diffracting, sawtooth-like relief structures (9.1; 9.2; 9.3) with angles of inclination (α; β; γ) of the sawtooth with respect to the plane of the surface pattern (1), in that the different illustrations (2; 3; 4) have associated relief structures (9.1; 9.2; 9.3) with different angles of inclination (α; β; γ), and in that the value of the greatest angle of inclination α; β; γ) is at most 25°, so that the difference of the viewing angle of light beams (22; 22; 23) reflected at the relief structures (9.1; 9.2; 9.3) of at least two of the illustrations (2; 3; 4) is less than an angular difference of 30° registered by the copier, as a result of which a copy produced by means of a copier reproduces at least two illustrations (2; 3; 4) over one another.
2. Surface pattern (1) according to Claim 1, characterized in that the light-diffracting, reflective structures are microscopically fine relief structures (9.1; 9.2; 9.3) and have a period length (L) of at least five micrometres.
3. Surface pattern according to Claim 1 or 2, characterized in that the difference between the angles of inclination (α; β; γ) of two illustrations is at least 0.5°.
4. Surface pattern according to one of Claims 1 to 3, characterized in that the difference between the greatest and smallest angles of inclination (α; β; γ) is at most 20°.
5. Surface pattern according to one of Claims 1 to 4, characterized in that an average angle of inclination (α; β; γ) has the value 15°.
6. Surface pattern according to one of Claims 1 to 5, characterized in that the differences (β-α; γ-β) between successive angles of inclination (α; β; γ) are equal in size.
7. Surface pattern according to one of Claims 2 to 6, characterized in that the relief structures (9.1; 9.2; 9.3) have a symmetrical profile shape.
8. Surface pattern according to Claim 7, characterized in that the profile shape is similar to a sinusoid.
9. Surface pattern according to one of Claims 1 to 8, characterized in that the furrows of the relief structures (9.1; 9.2; 9.3) are wavy, circular or polygonal.
10. Surface pattern according to one of Claims 1 to 8, characterized in that the furrows of the relief structures (9.1; 9.2; 9.3) are straight and the furrows of the various relief structures (9.1; 9.2; 9.3) are approximately parallel.
11. Surface pattern (1) according to one of Claims 1 to 10, characterized in that the reflective part surfaces (26) have crossed gratings with at least 3000 lines per millimetre.
12. Surface pattern (1) according to Claim 1, characterized in that the light-diffracting, reflective structures are implemented in the form of a volume hologram.

Images