DE29700289U1 - Surface pattern - Google Patents

Description

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Surface pattern

The invention relates to a surface pattern of the type mentioned in the preamble of claim 1.

Such surface patterns have structureless, optically diffractive image elements in the surface shape, which as a whole form a pattern and serve as security elements to certify the authenticity of an object.

Surface patterns are known from the European patent application EP-537'439 Al, which, however, have an image structure made up of visually recognizable, geometric shapes with optically diffractive relief structures. The surface patterns described in the European patent application EP-375'833 Al are made up of structureless image elements. All surface patterns with diffraction gratings have the property in common that, depending on the viewing direction, the surface patterns reveal a different pattern that stands out from the surroundings due to its light intensity.

A method for producing a semi-transparent, optical security element is known from the British application GB-A 2136352. After embossing relief structures into the surface of a plastic film and metallizing the entire embossed surface, parts of the metal layer are coated with a protective varnish and the unprotected parts of the metal layer are removed with an etchant. The partial areas of the security element without a metal layer are transparent, while in the remaining parts the metal layer on the relief structures diffracts and reflects incident light.

Starting from an intermediate product, which is a plastic film with embossed and fully metallized relief structures, the Swiss application 20 299/95-6 describes the direct printing application of the etching agent to the metal layer in predetermined areas. The etching agent removes the reflective metal layer in these areas, which then become transparent and are no longer able to diffract light. The areas not treated with the etching agent retain the ability to diffract light at the relief structures or to reflect it on smooth surfaces. Finally, the plastic film is fully coated with a transparent protective varnish so that the parts of the reflective layer are embedded in the plastic laminate of the security element.

The European patent application EP - 201 323 A2 contains a compilation of all known materials that are suitable for the production of plastic laminates with diffractive-optical relief structures. The information includes in particular the refractive index.

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The security elements of the type mentioned can only be produced cost-effectively in large quantities; for unique items or small series the effort is prohibitive.

The invention is based on the object of creating a security element with a partially metallized surface pattern that is cost-effective to manufacture even for unique items.

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

Embodiments of the invention are illustrated and described in more detail with reference to the drawings.

Show it

Figure 1: an intermediate product,

Figure 2: an arrangement of transparent surfaces and image elements with relief structures,

Figure 3: a security element in cross section,

Figure 4: the generation of a pattern,

Figure 5: a security mark and

Figure 6: a surface pattern.

Figure 1 shows an enlarged section of a band-shaped carrier film 2 coated with a transparent lacquer layer 1. The free surface of the lacquer layer 1 is covered with a reflective layer 3. The lacquer layer 1 and the carrier film 2 can include an intermediate layer 5. The carrier film 2 gives the applied layers of a laminate 4 the mechanical strength necessary for carrying out the further production steps. Such coated carrier films 2 are commercially available as rolls in various widths with or without a reflective layer 3, which can serve as the starting material for the production of surface patterns.

The carrier film 2, for example a polyester tape with a thickness of 10 to 50 micrometers, is first coated on one side with the intermediate layer 5 made of a waxy substance with a thickness of 0.1 to 0.4 micrometers. The intermediate layer 5 is then coated with at least one lacquer layer 1 of a

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Thickness in the range of 1 to 5 micrometers. An acrylic-based varnish is advantageously used. As explained below, such an intermediate layer 5 enables easy detachment of the carrier film 2 from the varnish layer 1.

Many variants are known for the layer structure of the laminate 4. For example, if the carrier film 2 is to remain firmly connected to the lacquer layer 1 as a transparent protection, the waxy substance of the intermediate layer 5 is replaced by a transparent adhesion promoter, which can be a lacquer made of polyurethane, for example. If the lacquer layer 1 adheres well to the carrier film 2, the intermediate layer 5 can also be omitted. For ID and prepaid cards, the carrier film 2 can serve as a card substrate, the thickness of which is typically in the range of 0.1 mm to 1 mm. The carrier film 2 itself can be designed as a layer composite in order to achieve good dimensional stability of the card.

Microscopically fine, diffractive relief structures 6 with height differences of up to one micrometer are molded into the lacquer layer 1. The reflection layer 3 has a thickness in the range of 10 to 100 nm, which can be applied before or after the relief structures 6 are molded. For example, layers of aluminum, chromium, tellurium, copper, etc. deposited chemically or thermally by vapor deposition are suitable for the reflection layer 3. The term relief structure 6 refers to moldable diffraction gratings of all kinds, diffusely scattering matt structures and also high-gloss, reflective surfaces.

For example, in the drawing of Figure 1, three different relief structures 6 are formed in parallel strips 7, 8 and 9, as indicated by the graphic means of hatching. Each strip 7, 8 or 9 has the same dimensions and is advantageously arranged transversely or lengthwise to the strip running direction 10. The strips 7, 8 and 9 repeat cyclically (7, 8, 9; 7, 8, 9; 7, 8, 9; etc.) lengthwise or transversely to the strip running direction 10 and form strip cycles 11. The strips 7 and 8, 8 and 9 and 9 and 7 can touch each other in pairs with their long sides or are separated by a narrow gap. The intermediate product obtained in this way is wound on rolls and stored temporarily for a first manufacturing process until it is needed for the last processing steps to produce the diffractively active surface patterns.

For a second manufacturing process, after the relief structures 6 have been molded, a transparent top coat or one that absorbs in a predetermined spectral range, e.g. acrylic-based, a few micrometers thick is applied as a top coat 12 to the reflective layer 3 and the relief structures are leveled to protect them from mechanical damage. The intermediate product thus obtained for the second manufacturing process of the surface patterns is again wound onto rolls and stored temporarily.

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The resin of the cover layer 12 can be formulated as a hot-melt adhesive, which enables a section separated from the laminate 4 to be glued to the surface of an object to be protected or authenticated. The section thus serves as an optical security element.

Figure 2 shows a simple example with only two stripes 8 and 9, which form the stripe cycle 11 and are distinguished by two different relief structures 6 (Figure 1). The surface pattern of the security element shown as an example comprises two nested patterns, which are composed of small, structureless image elements 13 and 14, respectively, so-called pixels. The surfaces of the image elements 13 and 14 are drawn as rectangles and distinguished using the graphical means of hatching. The image elements 13 are all located on the parallel stripes 8 with one relief structure 6 and form a first pattern, the letter "B". The image elements 14 are arranged on the parallel stripes 9 with the other relief structure 6 and join together to form the second pattern, the letter "A". In reality, the surfaces of the image elements 13, 14 are not limited to rectangles and are not bordered by lines, as would be expected from the drawing. In the areas covered by the two patterns, the relief structures 6 are covered by the reflective layer 3. Using a magnifying glass, it can be observed that the areas of the image elements 13, 14 are only defined by the presence of the reflective layer 3 (Figure 1) and by the relief structure 6 and can be shaped as desired. Likewise, the relief structures 6 are microscopically fine, light-diffracting optical gratings and not hatchings produced by printing technology. Light incident on the relief structures 6 of the image elements 13, 14, which are designed as gratings, is reflectively diffracted according to the grating parameters (spatial frequency, relief depth, orientation in the grating plane {azimuth &thetas;} and profile shape). Due to the interference of the light diffracted at the associated grating, the entirety of the image elements 13 and 14 produces a brilliant color pattern that stands out clearly from the surroundings for the observer as soon as the diffracted light of one of the diffraction orders of the corresponding grating of the image elements 13 and 14 falls into the eye of the observer.

Outside the areas occupied by the image elements 13 and 14 of the two patterns, the reflection layer 3 on the relief structure 6 is missing, i.e. these areas form colored or transparent areas composed of entire pixel units 15, depending on the type of topcoat of the topcoat 12. When a transparent topcoat is used, such surface patterns are semi-transparent, since the totality of the transparent areas, which are distributed almost evenly over the surface pattern, usually cover more than half of the surface pattern. For an observer, structures arranged behind the security element can be recognized through the transparent areas. The structures are usually larger than the surface pattern and also cover areas within the patterns.

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The illuminated optical gratings of the surface pattern of the security element produce their patterns only in the direction predetermined by the grating parameters of the relief structure 6 of the image elements 13 and 14. Depending on the lighting and viewing conditions, the observer recognizes either the first pattern "A" or the second pattern "B" on the security element. Outside of these viewing directions, the security element appears essentially transparent, with the transparent surfaces being separated from the metallically shimmering partial surfaces of the image elements 13 and 14.

For reasons of graphic representation, the two patterns "A" and "B" in Figure 2 are greatly enlarged. In reality, the strip cycle 11, consisting of two or more different strips 7 (Figure 1) to 9, has a height h of less than 0.5 mm. In the example in Figure 2, the strip cycle 11 only has the two strips 8 and 9, whereby the width of the strips 8 and 9 is less than 0.3 mm. The dimension of the image elements 13, 14 in the longitudinal direction of the strips 8 and 9 is equal to the width B of the strips 8 and 9 or an integer multiple thereof. The height of the letter "A" in the example in Figure 2 would be around 4 mm. At normal viewing distance, such image elements 13 and 14 are no longer visually perceptible separately and merge into the first and second patterns visible in the viewing direction. For each pattern, image elements 14 or at least one of the strips 7 to 9 are required in each strip cycle 11. The number N of patterns visible from different viewing directions is therefore at most equal to the number M of strips 7 to 9. The number M is limited on the one hand by the molding and the effectiveness of the grid, whereby the strips 7 to 9 must have a minimum width of about 20 μm, and on the other hand the accuracy with which the narrow strips 7 to 9 can be located in the manufacturing processes described below is crucial.

In contrast to the known two-dimensional surface patterns with optical diffraction gratings, the simultaneously visible image elements 13 and 14 lie on one of the parallel strips 7 to 9, because to produce the visible patterns, only the reflectivity of the material in the reflective layer 3 is reduced in the transparent areas not required for the patterns.

The destruction of the high reflectivity of the material in the reflection layer 3 can be achieved by completely chemically or thermally removing the exposed reflection layer 3 in the pixel elements 15 intended for color or transparent areas. The color or transparent areas can also be created by using thermal energy through the lacquer layer to change the internal structure of the reflective material between the lacquer layer 1 and the cover layer 12 in the pixel elements 15.

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Figure 3 shows a security element in cross-section. The image elements required for the patterns or 14 (Figure 1) with the relief structure 6 of each strip 7 (Figure 1) to 9 (Figure 1) are covered with a protective lacquer 16. In the pixel units 15 not required for the patterns, the reflection layer 3 is chemically removed, while in the places protected with a protective lacquer 16, the reflection layer 3 is retained. In the pixel units 15, the cover layer 12 combines with the material of the lacquer layer 1. The optically active boundary layer between the lacquer layer 1 and the cover layer 12 disappears completely if the material of the lacquer layer 1 and the cover layer 12 have almost the same refractive index. This means that the diffraction effects on the relief structure 6 not covered with the reflection layer 3 remain practically invisible to the naked eye. In Figure 3, the boundary layer is therefore drawn with a dashed line. The stripe cycles 11 (Figure 1) can be produced with ten different stripes 7 (Figure 1) to 9 (Figure 1) of 0.05 mm width without exceeding the height h (Figure 2) of 0.5 mm. If the height h reaches a value of over 0.5 mm, the grid of the image elements 13, 14 becomes too coarse and visible to the observer. Such coarse grids could be used for artistic reasons.

If the relief structures 6 in the strips 7 to 9 of the laminate 4 differ only in the azimuth θ, then, depending on the orientation of the laminate 4 in its plane, only those of the strips 7 to 9 are visible whose relief structure 6 is oriented essentially transversely to the viewing direction. Two or more of the strips 7 to 9 of the strip cycle 11 can have relief structures 6 with the same azimuth θ and differ in other grid parameters. For example, the monochromatically illuminated image elements 13, 14 of these strips 7 to 9 are visible one after the other when tilted about an axis perpendicular to the viewing direction if the relief structure 6 of the image elements 13, 14 only have different spatial frequencies.

In Figure 4, a security mark 33 cut from the laminate 4 (Figure 1) is glued to a flat surface 34 of a substrate 35 to be secured. The security mark 33 is initially a section of the laminate 4, the reflective layer 3 of which has already been completely covered with the cover layer 12 in the intermediate product before the design of the image elements. The security mark 33 is connected to the surface 34 with the cover layer 12 and the carrier film 2 (Figure 1) is then removed. Because the parallel stripes 7 (Figure 1) of the successive stripe cycles 11 (Figure 1) have the same grid parameters in the relief structures 6 and are arranged at a distance of only about 0.45 mm, the eye cannot perceive the highly luminous stripes 7 separately. The completely flat laminate 4 of the security mark 33 can appear to the observer as a uniformly luminous color surface. If the direction of observation is changed by turning or tilting the laminate 4, other colors are visible or the surface of the laminate 4 is inconspicuous and has a metallic shimmer.

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Substrates 35 can be customized at a later date, i.e. the individual security mark 33 receives its own surface pattern.

The device required for this directs the light beam 37 of a dye laser, which is focused with an optical element 36, onto the pixel unit 15 so that the lacquer layer 1 is penetrated and the reflection layer 3 is heated locally at the focal point of the optical element 36 until the material of the reflection layer 3 in the pixel unit 15 melts or evaporates and, when cooled, forms microscopically small spheroids instead of the uniform, optically high-quality reflection layer 3. At these points, the security mark 33 becomes transparent due to the absence of the reflection layer 3, i.e. the transparent surfaces are created. At most a _faint gray haze remains visually visible from the reflection layer 3. At the same time, the material of the lacquer layer 1 bonds with the transparent material of the cover layer 12 in a process similar to welding.

The pixel units 15 of the transparent surfaces can be individually inscribed into the security mark 33 using the light beam 37 controlled by the personal computer. The light beam 37 first scans the relief structure 6 with low light output and determines the alignment of the strip cycles 11 (Figure 1) and the position of the individual strips 7 (Figure 1) to 9 (Figure 1) in the strip cycle 11. The light beam 37 then controls the pixel units 15 of the transparent surfaces and destroys the reflective layer 3 at high light output. What remains are the partial surfaces of the reflective layer 3 in the image elements 13, 14 predetermined by the surface pattern. Since the reference of the successive strips 7 to 9 and the strip cycles 11 is destroyed, individual image elements 13, 14 can only be removed with great effort in order to change the surface pattern.

Figure 5 shows an example of the security mark 33, which is glued to the substrate 35 as a section from the preliminary product for the second production process. The surface pattern to be created is based on the strip cycle 11 (Figure 1) with the three strips 7, 8 and 9 (Figure 1), whose relief structures 6 (Figure 1) differ only in the azimuth θ. Before the security mark 33 is individualized, the security mark 33 illuminated with polychromatic light in the direction 39 shows the eye 40 of the observer in the direction 41 of observation a uniform appearance in accordance with these conditions, e.g. with an intense color or like a metallically shimmering surface if no diffracted reflected light falls into the eye 40. When rotating around an axis Z perpendicular to the surface pattern, the intense color can alternate with the metallic shimmering, matte color, while when tilting around an axis perpendicular to the Z axis, the color changes before changing to the metallic shimmering, matte appearance.

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By individualizing, the pixel elements 15 of the surface pattern of the security mark 33 are created, whereby the reflectivity of the reflection layer 3 (Figure 4) is destroyed in the pixel elements 15. The reflectivity is retained in the image elements 13, 14. As a result of this process, the image elements 13 and 14 with the same relief structures 6 (Figure 4) are arranged on the parallel strips 7 and 8, respectively. Under the predetermined viewing condition, all image elements 13 of the first pattern with the relief structures 6 of the azimuth θ&igr; on all parallel strips 7 are visible to the eye 40 at the same time. When the security mark 33 is rotated about the axis Z, the second pattern of the image elements 14 with the relief structures 6 of the azimuth S ₂ appears on the parallel strips 8 after a rotation angle α that is equal to the difference between the two azimuths, i.e. α = �i - θ ₂ .

The surface pattern of Figure 6 comprises three simple patterns, each consisting of a differently oriented rectangular frame 42 or 43 or 44. In the example shown here, the center points of the nested rectangular frames 42 to 44 coincide. The rectangular frame 42 or 43 or 44 of each pattern is formed from the image elements 13 (Figure 5) or 14 (Figure 5) assigned to the patterns or third image elements not shown here. In the illustration in Figure 6, the rectangular frames 42 to 44 are drawn as simple lines, although they are composed of the image elements 13 or 14 and have a width of 1.5 mm, for example. After individualization, the security mark 33 is transparent, except in the areas occupied by the image elements 13, 14 of the rectangular frames 42 to 44. If, under the same lighting conditions, the substrate 35 is rotated in its plane 34 around the Z axis in the direction of the azimuth θ, one of the three rectangular frames 42 to 44 lights up brightly in one color for the observer. Rotating and tilting also change the color of the rectangular frame that is currently visible if white light falls on the security mark 33. This kinematic effect is the same as that described in the European patent EP-105'099 Bl.

According to Figure 4, structures 38 on the surface 34, such as printed images or letters, etc., can be seen through the transparent surfaces of the pixel elements 15, particularly well when the reflection structures 6 appear dark, since no diffracted light falls into the eye 40 (Figure 5) of the observer. If, on the other hand, the cover layer 12 or the surface 34 is color-absorbent, the patterns of the illuminated surface pattern are visible against this background.

If the M different relief structures 6 differ in more than just one of the lattice parameters, further surface patterns can be produced whose appearance is determined by the diffraction behavior of the image elements 13, 14.

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Advantageously, the intermediate product of the second manufacturing process, as shown in Figure 1, is cut lengthwise into strips in bands 45 and rolled up. The width of the bands 45 corresponds to the width of the security mark 33 (Figure 4).

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Claims (8)

Protection claims 1. Surface pattern with N visually recognizable patterns (42; 43; 44) composed of image elements (13; 14) separated by pixel elements (15) with microscopically fine relief structures (6), the optical effectiveness of which is determined by a reflection layer (3) on the relief structures (6) and which are embedded in a laminate (4) made of plastic, characterized in that that each of the image elements (13; 14) has a single relief structure (6) different from M, that the M different relief structures (6) differ in at least one of the lattice parameters and that the image elements (13 or 14), whose relief structure (6) have the same grid parameters, are arranged on parallel strips (7 or 8 or 9). 2. Surface pattern according to claim 1, characterized in that the number M of the different relief structures (6) is greater than or equal to the number N of the visually recognizable patterns (42; 43; 44) which are visible one after the other when rotating about an axis Z perpendicular to the plane of a security mark (33) or when tilting about an axis perpendicular to the axis Z. 3. Surface pattern according to claim 1 or 2, characterized in that a strip cycle (11) comprises a group of the M adjacent strips (7 to 9), each of which has one of the M different relief structures (6) and that the strip cycle (11) has a height h of less than 0.5 mm. 4. Surface pattern according to one of the preceding claims 1 to 3, characterized in that the laminate (4) comprises at least one transparent lacquer layer (1) and a transparent cover layer (12) between which the reflection layer (3) of the image elements (13 or 14) is embedded. 5. Surface pattern according to one of claims 1 to 3, characterized in that the laminate (4) comprises at least one transparent lacquer layer (1) and a visible light-absorbing cover layer (12), between which the reflection layer (3) of the image elements (13 or 14) is embedded. 6. Surface pattern according to one of claims 1 to 5, characterized in that the transparent area formed by the totality of the pixel areas (15) is larger than the total area of the image elements (13; 14). P2783DEg/rev. 28.04.97 7. Surface pattern according to one of claims 1 to 6, characterized in that for connecting a substrate to be secured (35) the laminate (4) has an adhesive as a top coat of the cover layer (12). 8. Surface pattern according to claim 7, characterized in that the section of the laminate (4) glued to the substrate (35) to be secured is customizable, wherein each of the predetermined pixel elements (15) is no longer reflective but transparent after the action of a focused light beam (37) through the lacquer layer (1), so that in the pixel element (15) the cover layer (12) or a structure (38) on the surface (34) of the substrate (35) is visible through the cover layer (12). P2783DEg/rev. 28.04.97