EP2571699B1 - Method and device for producing colour images by way of a uv laser on pigmented substrates, and products produced as a result - Google Patents

Abstract

A method is described for producing a character, pattern, symbol and/or image (8) on a substrate (2) by way of pigment particles (1) which are arranged thereon and lose their colour effect under the action of a laser (23), wherein different pigment particles (1) with at least three different colour effects are arranged on and/or in the substrate (2). The invention is distinguished by the following method steps: (a) production of a colour chart (14), in which the individual colour effect of individual pigment particles (1) or individual clusters of pigment particles is contained as a function of their spatial coordinate on and/or in the substrate (2); (b) spatially resolved irradiation, which changes the colour effect of only individual pigment particles (1) or individual clusters of pigment particles, by way of a laser (23) at a single frequency on the basis of the colour chart (14) in order to produce a resulting colour effect. Furthermore, the present invention relates to substrates, in particular security documents, produced using a method of this type, and devices for carrying out methods of this type.

Description

TECHNICAL AREA

The present invention relates to methods of improving the production of counterfeit-protected color images on substrates, apparatus for performing such methods, and products made using such methods, such as, in particular, secure documents such as passport personalization pages, identity cards and other identity cards, etc.

STATE OF THE ART

Data carriers in the form of identity cards, personalization pages or inlays for passports or even credit cards and similar plastic cards must today have a high degree of protection against counterfeiting. There are a variety of different security features and special printing methods that can ensure such counterfeit security to a certain extent. A major challenge is to provide not only non-individualized security features, but in particular security features that are to some extent combined with the personalization respectively are part of it.

From the DE-A-2907004 For example, it is known that images in ID cards, but of course other visually recognizable information such as characters, patterns, etc., can be generated with a laser beam. In this document, the functional layer, from which the final image or any visible symbol or sign is generated during the process, consists of a thermosensitive layer. This functional layer extends over the map on a surface segment on which the image or other visually recognizable information is to be located later. The functional layer is usually in combination with other plastic layers from which the finished card is produced as a film laminate in the course of card making. The image is burned in this case, with the intensity of the laser beam is accompanied by a darkening of the irradiated spot. In this way, black and white images or grayscale images are routinely generated today. The already recognized advantage of this so-called laser engraving consists in the high security against counterfeiting and resistance to light and mechanical stress produced in this way Cards, especially if they are made of polycarbonate. This is for example through the EP-A-1574359 or the EP-A-1008459 busy. Security documents produced by laser engraving on polycarbonate laminates meet or exceed international travel document requirements (ICAO Doc. 9303 Part III Volume I).

It is a disadvantage of the method that the color envelopes thus achieved allow only the production of substantially monochrome images. Thus, in addition to the envelope from white to black, color changes from white to brown, from pink to black and yellow to reddish brown are known.

There is, for obvious reasons, great interest in producing high quality color images based on a laser-based process, as well as a need for such produced identification cards.

This fact is accounted for by a concept based on the irradiation of several colored components, eg. B. color body, pigments or dyes of different color is based. The coloring components of different colors must together result in a color space consisting of several, typically at least three, primary colors. For practical reasons, the primary colors cyan [C], magenta [M] and yellow [Y] are preferred. However, other colors are conceivable. The primary colors must also have an absorption spectrum that allows interaction with colored laser light. By nature, these are colors from the RGB system, which in practice is a partial incompatibility or non-ideal interaction between the colored components of the CMY system and the laser wavelength selected for the absorption maximum. In contrast to the above-mentioned method of charring components which are initially invisible, this method shows the coloration by means of bleaching, ie lightening, of a color which is visible before the irradiation. The substrate appears through the visible mixture of the colored components before irradiation in a very dark, ideally black tone. Such a method describes, for example, the WO-A-0115910 , Despite the advantages that this invention potentially offers, namely the further increased protection against forgery by a color representation of the document holder, the method described in this document and the products produced thereby have, in certain circumstances, drawbacks which limit its practical value for certain applications. On the one hand, the disadvantages are the complexity of the pigment formulation in the layer or layers to be decolorized on the card or the data carrier. They only allow limited to produce a pure white or pure black image. In addition, the absorption spectra of most of the colored components used are such that, to some extent, there is an undesirable interaction between a coloring component other than the desired laser wavelength. This effect can be problematic if pigments of different colors in the cross section of the three Wavelengths combined laser beam are. This above-mentioned non-ideality between the absorption spectrum and the exciting laser wavelength is manifested by a spectral crosstalk of the otherwise dye-specific laser bleaching. This results in a reduced image quality in the form of a color noise and a non-neutral reproduction of the hue. In addition, the adjustment and control of several coincident laser beams can be demanding in practice and, if carried out incorrectly, cause color and image errors.

One possible implementation of such an irradiation device is in the WO-A-0136208 described. By optimizing various parameters, the quality reduction can be limited. Nevertheless, due to its complexity, the method remains difficult to control with regard to the achievement of the required result. Finally, in practice, the method proves to be comparatively expensive due to the at least three laser devices required, and together with the associated beam-guiding device, can not be easily constructed as a compact unit.

The problem of the above-described methods and products for colored laser bleaching is that the production of color images in identity cards and similar articles does not always have the quality accepted by the market, the required control of the process, the reasonable costs and the desired apparatus Embodiments is possible.

The US 5,364,829 concerns the field of rewritable media. In a matrix layer of a material, which can be either placed in a transparent state with appropriate temperature control or in a cloudy and thus white appearing state, color particles are embedded. These color particles are particles that can produce only a single color and can not be changed accordingly by external action in their color effect. The color appearance is to some extent set via the matrix, namely, when the matrix is put in its transparent state, the data carrier appears colored, and when the matrix is set in its opaque state, the data carrier appears white. The change in the matrix properties to produce the color effect is triggered by a thermal head.

The WO 01/36208 refers to the use of latent pigments that can be activated to produce different colors.

In this case, a method for applying colored information is shown on an object which is provided with at least two different chromophoric particles, at least in a layer near the surface. The said particles change the color of this layer under the influence of laser radiation. The laser radiation with at least two different wavelengths (lambda 1, lambda 2, lambda 3) is used to change the color of the layer. The object is irradiated with laser radiation in accordance with the vector and / or screen method and by means of a beam deflection device, comprising two coordinates and a focusing device for focusing the laser radiation, on the applied layer of the article.

WO 89/05730 A1 discloses a method of forming a color image on a substrate, wherein the image-forming layer on the substrate is exposed to a beam having a predetermined wavelength. The image-forming layer comprises an array of different color imaging components that are color-forming compositions that are initially colorless or transparent. Each component is sensitive to the same predetermined wavelength range, so that when exposed to the beam, the composition in the region of the imaging layer is activated to activate the color corresponding to the color component to the exposed beam. The beam is thereby controlled to expose predetermined regions of the imaging layer to produce the colored image.

PRESENTATION OF THE INVENTION

The invention is therefore inter alia the object of finding an image-forming laser process for a particular example card-shaped data carrier that allows the production of colored images, symbols, texts, patterns et cetera in the required quality. Of Furthermore, the invention has for its object to perform the color images according to this method with apparatus or a system that meet or meet the required criteria of investment costs, operating costs, compactness and robustness of the process or sufficient. At the same time, the complexity of the process and the products produced with it ensure a high degree of protection against counterfeiting. The invention provides a solution to these and other problems in a manner which is surprising for a person skilled in the art and amounts to a new process, the products produced therewith and the devices or systems required for the implementation.

According to the invention the object is achieved in that instead of the spectral separation of the primary colors such. B. in the aforementioned WO-A-0115910 described using lasers of different frequencies, a spatially resolving method using a single irradiation frequency is used. In this case, the location of each pigment particle is determined in a first step and then bleached or activated site-specifically by a laser beam with a single wavelength, preferably with a high-energy wavelength in the blue or in the ultraviolet. It is surprising that the microscopic analysis of all color components or pigment grains on the image field of a card-shaped data carrier with respect to their color and position, the subsequent storage of this data and the corresponding control of a laser beam with a single irradiation frequency, the production of a high-quality color image (or of corresponding colored symbols, texts, patterns et cetera), for example, on a plastic laminate or other substrate with pigment particles embedded in or deposited thereon.

• a Erzeugung einer Farbkarte, in welcher die individuelle Farbwirkung von individuellen Pigmentpartikeln oder individuellen Clustern von Pigmentpartikeln (respektive die daraus erzeugbare respektive veränderbare Farbwirkung) als Funktion von deren Ortskoordinate auf respektive im Substrat enthalten ist;
• b räumlich aufgelöste, nur individuelle Pigmentpartikel oder individuelle Cluster von Pigmentpartikeln in ihrer Farbwirkung verändernde (einschließlich der Möglichkeiten der Vernichtung der Farbwirkung, der Erzeugung der Farbwirkung sowie der Verschiebung der Farbwirkung) Einstrahlung mit einem Laser bei einer einzigen Frequenz auf Basis der Farbkarte zur Erzeugung einer resultierenden Farbwirkung.

More generally, the present invention relates to a method of producing a sign, pattern, symbol and / or image in different colors on a substrate having on its substrate, under the action of a laser, the color effect losing (or more generally formulated, and subsequently so to understand - under the action of a laser, the color effect changing - wherein the change may be a destruction of the color effect, a generation of a color effect or a change in a color effect)) pigment particles, wherein different pigment particles with at least two or at least three different color effects on respectively Substrate are arranged. The method is characterized by the following method steps, wherein these method steps may be preceded or followed by further method steps:

• a generation of a color chart in which the individual color effect of individual pigment particles or individual clusters of pigment particles (respectively the color action that can be generated therefrom or variable) is contained as a function of their location coordinate on respectively in the substrate;
• b spatially resolved, only individual pigment particles or individual clusters of Pigment particles in their color effect changing (including the possibilities of destruction of the color effect, the generation of the color effect and the shift of the color effect) irradiation with a laser at a single frequency based on the color card to produce a resulting color effect.

With regard to the pigment particles which can be used in the context of such a process, reference is made to systems such as those described, for example, in US Pat WO-A-0115910 and WO-A-0136208 are described. Under a multicolor characters, patterns, symbols and / or image is to be understood as having not only black and white and intervening shades of gray, but also colors, for example, composed of C, Y, M, in the latter case then Each of these three primary colors should be provided with individual pigment particles.

• Eine örtliche (geometrische) Trennung der farbigen Komponenten auf dem Datenträger, der als Vorstufe für ein Sicherheitsdokument dient. Die geometrische Trennung der farbigen Komponenten genügt dabei bevorzugtermassen der Grundforderung, dass jedes Flächenelement nur mit einer farbigen Komponente belegt ist und zwischen zwei farbigen Komponenten ein minimaler Abstand besteht, d.h. Überlappung oder direktes aneinandergrenzen von Pigmentpartikeln oder Clustern von Pigmentpartikeln ist vorzugsweise weitestgehend vermieden.
• Eine Vorrichtung und ein Verfahren, das eine bestimmte farbige Komponente als mikroskopisch einheitliche Entität, beispielsweise ein einzelnes Pigment oder ein Cluster, auf dem Datenträger finden und durch seine Ortskoordinaten und seine Farbe (oder die auszulösende Farbe) charakterisieren kann. Die Vorrichtung ermöglicht durch ein systematisches Abfahren bzw. Scannen die Gesamtzahl aller farbigen Komponenten auf der Gesamtfläche des späteren Bildes zu kartieren. Alternativ ist es aber auch möglich, diese Information über eine flächige Einstrahlung und ein flächiges aber ortsaufgelöstes und farbaufgelöstes Detektionsverfahren zu ersetzen.
• Eine Laser-Vorrichtung, deren Strahlaustrittsoptik aufgrund der bekannten Ortskoordinaten eine farbige Komponente auf exakt anfahren und je nach geforderter Farbintensität diese farbige Komponente im gewünschten Grad bleichen (oder aktivieren) kann sowie das Verfahren, um mit dieser Laservorrichtung den Bleichvorgang durchzuführen.
• Eine programmierbare Steuerung für das örtliche Positionieren der Laseroptik und der Leistungssteuerung des Strahls, damit auf der gesamten mit Pigmentpartikeln (farbigen Komponenten) bedeckten Fläche jede einzelne Komponente gezielt so bestrahlt wird, dass ein Bild entsteht.

The invention thus consists of a combination of the following elements:

• A local (geometric) separation of the colored components on the volume, which serves as a precursor to a security document. The geometric separation of the colored components preferably satisfies the basic requirement that each surface element is only covered with a colored component and a minimum distance exists between two colored components, ie overlapping or direct contiguous of pigment particles or clusters of pigment particles is preferably largely avoided.
• An apparatus and method that can find a particular colored component as a microscopic entity, such as a single pigment or cluster, on the medium and characterize it by its location coordinates and its color (or color to be triggered). By means of systematic scanning, the device enables the total number of all colored components to be mapped on the total area of the later image. Alternatively, it is also possible to replace this information by a two-dimensional irradiation and a planar but spatially resolved and color-resolved detection method.
• A laser device, the beam exit optics due to the known location coordinates approach a colored component to exactly and depending on the required color intensity bleach (colored) this colored component in the desired degree and the method to perform the bleaching process with this laser device.
• A programmable controller for the local positioning of the laser optics and the power control of the beam, so that on the entire area covered with pigment particles (colored components) each individual component is specifically irradiated in such a way that an image is formed.

The elements of the invention meet requirements for working speed, Economy, ease of operation and reliability to meet an imaging using the invention under industrial requirements.

A first preferred embodiment of the proposed method is characterized in that steps a and b are performed in the same device and without any manipulation or displacement of the substrate between them. In fact, the determination of the color chart is a step in which precise positioning of the processed substrate over the success or failure of the subsequent processing by the laser is crucial. Accordingly, in particular in order to avoid a calibration between steps a and b, the entirety of the two steps a and b is preferably carried out in the same device, if appropriate using the same scanning device (for example linear motion unit).

A further preferred embodiment of the proposed method is characterized in that the device for color card production and the laser optics are fixed in a stationary manner and that the substrate is moved with a linear motion unit relative thereto. This variant is particularly recommended for light substrates or those substrates whose image field can not be swept with a conventional movable laser beam guide (Galvo mirror).

According to the invention, only one colored component should lie in the beam cone or focus circle of the laser for the bleaching process in a specific period of time, with all other colored components being in the shadow of the laser light in the same period of time. The distribution of the colored components within the area which serves as the basis for the image can be achieved by application by a printing process (for example gravure, high-pressure, flexo, et cetera). The imprint allows both a statistical distribution of the colored components as well as a distribution in lines, circles or complex figures such. B. Guilloche. A microscopic examination of the distribution of the colored components and a comparison thus makes possible as an added benefit the verification of the distribution pattern in the sense of an authenticity check. It is also possible to apply or print the colored components in the form of microfonts, numerical sequences and the like in order to accommodate hidden additional information in the image, for example a personalization of the owner of the document or the serial number of the document.

In other words, another preferred embodiment is characterized in that the pigment particles are arranged in a layer, preferably in a single layer, on and / or in the substrate, which itself may also be a composite of layers, and essentially randomly as a function the location coordinate are distributed. Basically, in this regard, the present invention differs significantly from other approaches of the prior art.

This is in contrast to solutions in which, for example, in a fixed, typically regular pattern, the dyes must be sorted sorted according to their color, so then in the knowledge of this regular arrangement, the dyes can be triggered (for example, juxtaposition of rectangles, each with different colors are "filled" in several rows and rows). In the procedure proposed here, it is precisely the distribution of the colors or the pigments that make them available that are not specified in the production process of the untreated substrate, and this can be produced in a very simple process. Only in the first processing step is the preparatory determination of the color distribution or the distribution of the color-triggering pigment particles determined and then processed accordingly in the second production step. It is then also typical for a fixed, systematic arrangement of pigments, for example by a precise printing process with a controlled, reproducible positioning of the halftone dots, that the necessary procedure be that the control allows laser irradiation exactly according to this predetermined pattern and the pattern of irradiation in the Stops register with the printed image.

This randomness of the distribution and the use of the random distribution for generating the symbols / images / characters et cetera can also be used as a further security level. For example, when the random arrangement of the image-forming pigment particles is stored in a database, the individualizing information (image) is combined with a fingerprint (random distribution of the image-forming pigment particles), which is a very high level of security that can not be substantially reproduced , allows. A corresponding data carrier can be compared with the associated information in the database during a check and the authenticity can be clearly determined.

A further preferred embodiment of the proposed method is characterized in that the different pigment particles are arranged in a layer, preferably in a single layer, on and / or in the substrate and are regularly arranged substantially in a microscopic pattern, the microscopic pattern of an arrangement straight or wavy lines, parent patterns or microfilm. Such a microscopic pattern may be, for example, a specific lettering (for example, a denomination or the like) and, because it is also virtually non-reproducible, can be used as an additional security feature that can only be verified with an enlarging agent.

A further preferred embodiment is to parallelize the method according to a and / or b, ie to process the substrate in sections at several locations on the image area at the same time.

The quality of a good printed or laser irradiated image becomes the Example evaluated on the sharpness impression (visually discernible diameter ratio in the 36-beam Siemens star of d = 0.1D to d = 0.001D, preferably d = 0.05D to d = 0.005D), the width of the color dynamics or the number of visually recognizable different shades or gray tones (5 bits to 16 bits, preferably 6 bits to 8 bits), the color neutrality (color proof) and the resolution (150 dpi to 1000 dpi, preferably 300 dpi to 500 dpi) allowed. At a print resolution of, for example, 500 dpi, all colored components must be combined on an area of the resulting pixel size of approximately 50 μm in diameter. For practical implementation, the size of a coloring component or a color body to a diameter of depending on the printing pattern of more than 16 microns to 25 microns out. Taking into account a minimum spatial separation of the individual color bodies, a size of 5 .mu.m to 12 .mu.m, preferably 8 .mu.m to 12 .mu.m is required. A particle size in these orders of magnitude can be represented by known methods.

A further preferred embodiment of the proposed method is accordingly characterized in that the individual pigment particles have an average diameter in the range of 5-15 μm, preferably in the range of 8-12 μm, and that they are arranged substantially all on or in the substrate, preferably individually separated laterally. The arrangement of the particles can be in one or more planes. This particularly preferably in such a way that the mean lateral distance between two pigment particles is greater than the mean diameter of the pigment particles, or greater than half the mean diameter of the pigment particles. Furthermore, the beam diameter of the laser beam (the beam diameter is taken at the 1 / e ² level, ie at about 13.5%) is preferably not more than twice the size of the average diameter of the pigment particles in step b. Preferably, the beam diameter of the laser beam in step b is in the range of 5-20 μm, preferably in the range of 8-15 μm, in particular preferably in the range of 8-12 μm.

According to the invention, a color body of this size should be approached by a laser beam guide so that the laser optics can assume a precise position in front of the color body or galvo mirrors can direct the laser beam precisely onto the color body. Furthermore, the beam diameter of the laser beam at the location of the color body should be adjusted so that no interaction with adjacent color bodies can occur. For this purpose, in the embodiment of the invention, the laser beam is focused in a suitable manner. The focus can not be less than a certain size diffraction-limited, but in practice without further example, on an area with a diameter in the size of the diameter of the color body, for example, adjustable. The standard scientific literature shows that a focus of <1 μm is possible. The monochromatic laser beam required for bleaching has a wavelength suitable for an efficient bleaching process, preferably in the UV range. A suitable wavelength generates, for example, the frequency tripled 1064 nm oscillation of a Nd: YVO4 laser. The US6002695 describes such a laser system. The power of such a laser should be in the range of 0.2 - 0.5 W, and a single pigment particle should be irradiated at such power for a period of 0.01 to 10 ns to ensure sufficient bleaching.

The positioning of a laser optics over a color body is possible with a precise linear motion unit, as offered, for example, by Heinrich Wolf, Eutin, Germany.

Before the lightening of the color bodies by a laser irradiation, it is necessary to map the totality of all color bodies on the area occupied by color bodies. This is carried out according to the invention, for example, in step a with an analytical scanning method. The position and color determination of the individual color bodies takes place, for example, via the detection of characteristic points from the absorption or scattering spectrum of the individual color body in the case of white light excitation. A suitable focus diameter is about one sixth of the diameter of a color body. The white light beam scans the area covered with color bodies with the aid of the above-described linear motion unit and can thus separately stimulate all color bodies on this area and detect them accordingly by collecting the scattered or transmitted light. The white light beam with the required focus is preferably mediated by a fiber optic, for example, from a single, but also from a bundle of oligomode fibers, eg. B. with a single fiber diameter of 10 to 15 microns, may exist. A colored body in the focus of the exciting white light beam is reflected by the character of the reflected or transmitted light, which makes both the position and the color of the color body detectable. Depending on the primary colors and pigments used, the spectral analysis of a color body usually requires at least three characteristic values which, by means of a logical comparison algorithm, yield a value for the base color of the color body. The characteristic values can be detected simultaneously, for example, by three photodiodes with suitably selected color filters. The position of all colored components is captured in this way and as it were stored as a map in a database. The color map is used in the following step of laser bleaching for the two-dimensional navigation of the laser optics or the bleaching laser beam.

Accordingly, a further preferred embodiment of the proposed method is characterized in that for carrying out the step a using the reflection light, the top of the substrate or in the case of the use of the transmission light, the underside of the substrate, preferably using a linear motion unit with an artificial or natural white light source and / or detection unit (for example, photodiodes), is scanned, wherein, preferably as a function of the spatial coordinate, white light is irradiated and the reflected or transmitted light is spectrally analyzed as a function of the location coordinate, preferably by exclusively at least two, preferably at least three discrete frequencies, which allow a distinction of the substrate disposed in the different pigment particles, preferably using a photodiode, the signal is detected, and the position and the associated color effect of individual pigment particles or clusters of pigment particles in a data matrix forming the color chart are recorded as a data tuple. A variant of the spectral analysis can also consist in that, instead of the white light, several irradiations with light of different colors are carried out for a limited time in quick succession. In other words, the color of a pigment particle also with a series of flashes of different frequency ranges, eg. B. in the colors red, green and blue. In practice, this method of scanning an original is used with some flatbed scanners. For the analysis of the light in this case, but not necessarily, the spectral evaluation can be limited to a photodiode.

A further preferred embodiment is characterized in that, to carry out step b, the surface of the substrate is scanned, preferably using a linear motion unit with a laser source arranged thereon, on the basis of the color card the laser source being directed to individual pigment particles or clusters of pigment particles individually in their color effect to destroy or activate.

For the steps a and b, the same linear motion unit can preferably be used, as has already been explained above.

In a data processing unit, starting from the color card for the character, pattern, symbol and / or image determined in step a, a processing protocol for the laser or the plurality of lasers can be generated in step b, this processing protocol receiving the information which individual pigment particles, as a function of the spatial coordinate, to produce a specific macroscopic color effect for the character, pattern, symbol and / or image in their color effect by the laser targeted to be influenced locally targeted, in particular destroyed by the laser in their color effect (bleaching) to be.

Thus, methods are proposed which detect at a microscopic level the smallest particles of different color, register their color and position on a field of view and store and then undergo a selective treatment.

The primary application of the method consisting of the sub-methods of analytical scanning or color body mapping and lightening of the color bodies with a laser beam is to produce an image on a substrate, for example a plastic card, preferably a portrait image in a security document such as an image on a ID card or on the personalization page of a passport. The sizes of the pictures and more Specifications for the plastic carrier are described in ICAO Document 9303, Part 3.

The digitally fabricated map of colored components according to this invention, such as color bodies, pigments, dyes, etc., may also be used in the context of using a security document for verification thereof. Commercially available devices such as scanners or digital microscopes are sufficient to test the distribution pattern. It is also possible to use for verification in addition to the usual printer loupes, digital microscopes and other devices electronic portable devices such as mobile phones and their optical recording devices. To facilitate this, specific, on the portable devices or mobile phones running programs (apps) can be provided, which automatically such recording via a mobile phone connection, a wlan connection or a remote connection, for example via the Internet, with the information stored in a database compares over the disk and accordingly issued in turn via the mobile phone allows a statement about the authenticity. The digital images generated locally with these devices, for example in the form of JPG files, provide information on the authenticity of the document by comparison with the color body map of the document stored in a central database. The corresponding application programs can be installed both on the portable devices and on central servers. This proof is naturally possible for an individual document.

Furthermore, the present invention relates to a data carrier having a character, pattern, symbol and / or image generated by a method as set forth above.

According to a first preferred embodiment of such a data carrier, this is characterized in that it has been produced on the basis of a substrate with random arrangement of the pigment particles, and that on the data carrier and / or in a database the random arrangement and its use for generating the character, pattern , Symbols and / or image is deposited to increase security.

Preferably, such a data carrier is an identification card, credit card, passport, user card or nameplate.

Furthermore, the present invention relates to a device for carrying out a method as described above, in particular characterized in that the device comprises means for fixing or at least stationary placement of a substrate, a first unit for determining the color card of the substrate, and a second Unit for spatially resolved, only individual pigment particles or individual clusters of pigment particles in their color effect changing irradiation with a laser at a single frequency based on the color chart (14) to produce a resulting color effect. The first and the second unit can use the same linear motion unit.

The device thus typically additionally has at least one Data processing unit and at least one, by this data processing unit two-dimensionally controllable linear motion unit, which carries the first and / or the second unit.

Among other things, the invention is based on the insight to map individual pigments in a color chart and then to individually control these individual and also with regard to their color change properties different pigments with a laser with a single frequency. Further embodiments are given in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1

in schematischer Darstellung mögliche Pigmentverteilungen auf Substrat en, wobei in a) eine statistische Verteilung dargestellt ist, in b) eine Verteilung in Linien, in c) eine Verteilung in Form von Mäandern, in d) eine kreisförmig sich wiederholende Verteilung, in e) eine Verteilung in Form von Mikroschrift;

Fig. 2

in a) in schematischer Darstellung eine Aufteilung einer Fläche in Flächenelement mit zugeordneten Pigmentpartikeln, in b) die Ansteuerung eines Pigmentpartikels durch einen Laser und in c) die beugungsbedingte Einschnürung des Laserstrahls in der fokalen Ebene;

Fig. 3

die unterschiedlichen Erscheinungen je nach Vergrößerungsgrad, wobei in a) die Erscheinung mit dem unbewehrten Auge und in b) die Erscheinung mit einem Vergrößerungsmittel dargestellt ist;

Fig. 4

die unterschiedlichen Schritte der Bilderzeugung, wobei in a) der Schritt der Bestimmung der Position und Art der Pigmentpartikel dargestellt ist, und in b) die lokale Beeinflussung der Pigmentpartikel durch den Laser dargestellt ist;

Fig. 5

einzelne Schritte des vorgeschlagenen Verfahrens in ihrer Reihenfolge; und

Fig. 6

beispielhafte Identifikationskarten

Fig. 7

Mikroskopische Aufnahme eines mit farbigen Streifen bedruckten Substrates vor der Behandlung mit einem Laserstrahl (a) und eine weitere jedoch nicht mikroskopische Aufnahme eines bestrahlten Substrates mit einem Laser einer einzigen Wellenlänge (b).

Preferred embodiments of the invention will be described below with reference to the drawings, which are given by way of illustration only and are not to be interpreted as limiting. In the drawings show:

Fig. 1

a schematic representation of possible pigment distributions on substrate en, where in a) a statistical distribution is shown, in b) a distribution in lines, in c) a distribution in the form of meanders, in d) a circularly repeating distribution, in e) a Distribution in the form of micro-typeface;

Fig. 2

in a) a schematic representation of a division of a surface area element with associated pigment particles, in b) the control of a pigment particle by a laser and in c) the diffraction-induced constriction of the laser beam in the focal plane;

Fig. 3

the different phenomena according to the degree of magnification, wherein in a) the phenomenon with the unreinforced eye and in b) the phenomenon with an enlarging means is shown;

Fig. 4

the different steps of imaging, wherein in a) the step of determining the position and type of the pigment particles is shown, and in b) the local influence of the pigment particles by the laser is shown;

Fig. 5

individual steps of the proposed method in their order; and

Fig. 6

exemplary identification cards

Fig. 7

Microscopic image of a substrate printed with colored stripes before treatment with a laser beam (a) and a further, but not microscopic, photograph of an irradiated substrate with a laser of a single wavelength (b).

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a picture surface 2 covered with pigments 1. The variant according to FIG. 1a shows a random, ie essentially statistical distribution of the pigments 3, while the other variants after Figure 1b to Figure 1d line-shaped 4, meandering 5 or circular 6 arrangements of the pigment particles show. Figure 1e finally demonstrates a superimposition of a static distribution with a microwriting 7. All these variants of the pigment distribution can be represented by printing processes and can be used as starting material for the implementation of the proposed method.

FIG. 2a is an abstract and schematic representation of a picture surface, which in this case consists of 25 to some extent theoretically imaginary surface elements 22, which each contain only one pigment grain. In this example, the pigment grains have the three primary colors cyan [C] 20, magenta [M] 21 and yellow [Y] 19 in a random distribution, but only one corresponding pigment particle in each surface element. FIG. 2b shows the profile of a laser beam 23 with a specific beam diameter 24. After passing through a focusing element 25, this laser beam is focused to a diameter that allows the complete irradiation of a pigment grain 1 and its focus diameter is sufficiently small to lighten only one pigment grain 1, this but essentially completely irradiated over the entire cross-section. Fig. 2c shows the constriction of the laser beam 23 after diffraction when passing the focusing element 25 in the focal plane to a smallest diameter 27th

The FIGS. 3a and 3b illustrate the difference between the macroscopic view and effect Fig. 3a of an image 8 made on the image area 2 according to a method of this invention and the microscopic observation Fig. 3b , which allows a view of the pigment structure with a magnification device 9. The microscopic observation of a specifically controlled pigment distribution allows precisely to verify this pigment distribution, since this distribution is combined with the actual individualizing information of the image, the fingerprint effect of the pigment distribution is combined in a synergy with the individualizing information, so that a significant increase in the Safety standards results. In practice, this pigment distribution can also be a special grid that can be assessed with a printer magnifier. A combination of a special grid with a random background distribution is also possible, so that the special grid can be verified without reference to a database, and the random background distribution can be verified by querying the corresponding identification information in a database. Thus, the microscopic structure can be checked both in a simple verification process (special grid) and in a safety-related verification process (query of the random distribution from the database).

The painting Fig. 4a and Fig. 4b demonstrate the two main process steps a and b of this invention, consisting of the local and spectral analysis of the pigments using reflected light with the aid of a white light source 11 and a photoreceiver 12, which with a two-way linear motion 10 micrometer accurate over the sample or the image field can be positioned ( FIG. 4a , Step a), and a UV laser system 17, which decouples a laser beam 23 so that according to the data from the apparatus according to FIG. 4a this laser beam can hit every single pigment exactly FIG. 4b , Step b). As an alternative to the movement of the white light source and of the photoreceiver as well as of the laser optics shown here, the substrate can also be moved by means of a two-way tracking unit. This alternative is in Fig. 4a / 4b not shown. Furthermore, mention should be made in the representation of the photoreceiver 12 that the structure of the photoreceptor has been simplified. It is not shown that the detector in the case of a white light excitation consists of several color-specific components, which may for example consist of several provided with different colored filters photodiodes, or that the detector, for example, a CCD sensor or a CMOS sensor with upstream multi-color filter (eg Beyer filter), wherein in the case of a Foveon CMOS sensor can be dispensed with a color filter. Furthermore, in the graphic embodiment of the exciting light source 11 in FIG Fig. 4a not shown that in the case of excitation in time with light in different colors, the excitation light is generated with several different-colored, narrow-band light sources, the exciting light source consists of several components. Furthermore, when focusing the laser beam in Fig. 4b note that the diameter of the laser beam 24 is collimated by the focusing element 25 much more to the smallest diameter 27 than in 4b illustrated, so the drawing is not to scale. Similarly, a widening of the laser beam after decoupling from the laser resonator is not shown separately, but part of the UV laser system 17th

The entire workflow of the method according to this invention is described in FIG. 5 shown. The essential steps are the local and color detection of each individual pigment grain 13, production of the color chart 14, the filing of the data thus obtained as a color chart in a database 15, the data respectively the driving protocol for the laser control 16 supplies, which in turn the process of selective laser bleaching with the UV laser system 17 controls. The color chart in the database also serves as a signature for subsequent authentication of the security document via its image data.

The drawings after Fig. 6a and 6b explain a possible application of this technology for the production of portrait on a card-shaped data carrier 26. The portrait produced according to this invention also contains additional data based on the. By the Pressure of the pigments achieved pigment distribution in the image field 2 are deposited. This data may be, for example, personalization data of the document owner (as in Fig. 6b shown), which serve the identification of the document owner or z. B. Possibilities of authentication of the document via a serial number or information about the statistical distribution of the particles in a particular area, etc.

The picture after Fig. 7a shows a microscope image of a printed with a high-resolution process substrate on which the colors yellow (19), cyan (20) and magenta (21) are printed in strip form. On the microscopic scale, the distribution of color shows conspicuous irregular distortions due to imperfections in the printing process. Fig. 7b shows the macroscopic representation of a 355nm 2W laser (free jet, unfocused) bleaching of a color pigment mixture of yellow, cyan and magenta pigments. The thickness of the strip is about 500μm. The pigments are bleached regardless of their color, a spectral selection at 355nm no longer in contrast to visible light range.

A: Improvement of conventional printing methods:

A print original is printed with the aid of a known printing process (offset printing, gravure printing, etc.) in such a way that there is a color print pattern, which is regular after superficial observation and defined by the production process, on the print original. The print pattern has all the color components required for color mixing. In a pattern of the colors shown in stripes (19), (20) and (21) as in Fig. 7a For example, at a resolution of 500 dpi, the color stripes are less than 10 μm in width and have an irregular microscopic shape attributable to the shortcomings of the printing process. The technical design of such a precise 3-color printing is flawed according to the current state of the art. In particular, it does not allow to work completely without overlapping of the color components and with seamless area filling in the entire image area. On the contrary, due to technical inadequacies of the printing process remain small displacements (Passer), which manifest themselves as overlapping or unprinted areas. Further, even when separating from the original by warping the slightly raised print areas in the automated production of the actually printed area will not be printed homogeneously. Fig. 7a shows the microscopic scale visible irregular shape of the stripe-printed areas made with a high-resolution printing process in an impressive way. For this reason, a method is advantageously used which digitally detects the objective, statistically distributed defectiveness of the print in which the arrangement is checked by means of a detector, which is subsequently stored and taken into account in the exposure following later. For this purpose, an xy linear motion is advantageously used with a mechanical repeatability of 2 microns (eg Fa. Heinrich Wolf, Eutin) to the printed Substrate with it to move a microscope field of view. In this way, the entire pressure range is recorded. The microscope has a digital camera on its tube. Advantageously, an imaging ratio of about 1: 3, because modern digital cameras can realize pixel sizes in the range of 3 microns and below (eg products of the company Point Gray). Deviations of 2 μm in the range of visible light are reliably resolved by this magnification without entering the diffraction limit. After the linear traversing unit has traversed the entire printing area with the aid of a corresponding computer control, an image of the actual, faulty printed image with the resolution of 2 μm is present in the memory. The detection of the resolution is about 25 times higher than the resolution of the print (500dpi corresponds to about 50μm / pixel). The dyes used for printing can be ablated or bleached by means of a laser. In a second step, the dye is selectively ablated or bleached with a suitably chosen focus size. With a wavelength of 355nm that can also be used for bleaching, a focus diameter below 2μm can be achieved so that the focus size can be adapted to the actual desired resolution. In this way, the combination of high-precision detection with the precise operation of the laser achieves a resolution and color fidelity that was previously unachievable with conventional printing methods, without the printing method itself having to be changed in any way. An optically induced bleaching process can be carried out in this way also within a laminate, as far as the pressure-bearing layer is covered by a transparent layer. This application option is particularly advantageous in the personalization of security document blanks such as personal documents or driver's licenses. A representation of pigments of a different color bleached with a 355nm UV laser can be found in FIG Fig. 7b ,

B: Significant increase in counterfeit security in conventional printing processes:

Here is worked mainly according to the embodiment A. The method is used to personalize security documents, for example, and opens up an additional opportunity for greatly increasing the security against counterfeiting. In this application example, therefore, the exact detection of the color regions is no longer used, as in the preceding, merely to improve the printing process with regard to its technical defects. It is additionally exploited that it is not necessary to know the arrangement of the strips or patterns prior to the personalization of the blank. The arrangement of the colors can also be done in a random pattern, changing from blank to blank, as this can be detected by the corresponding control unit. Thus, a blank can only be printed if, prior to exposure to the laser, the method according to a. is used, otherwise it would come to a false color representation. This would blanks for a forgery as long as unusable, as well as the counterfeiter does not use a microscopic analysis according to method a. A special possibility to make a falsifkat instantly recognizable even to the eye of the untrained observer is, for example, in the case of personal papers, the pseudo-random mixing of the color pattern, for example, in the area in which the forehead of the portrait usually comes to rest in its regularity in that the false color representation changes and, for example, the word "counterfeiting" becomes color-readable unless the exact micro-position of the color pattern is taken into account.

C: Improvement of special printing methods:

According to the script WO-A-0115910 For example, it is possible to selectively produce the color effect of pigment mixtures consisting of yellow, cyan and magenta pigments by irradiating them with the wavelengths of a laser complementary to the pigment color and thus bleaching them. Thus, the complete exposure requires a red, green and blue laser. Within the focus of the laser beam, which at the same time corresponds to the desired pixel size, ie about 50 μm for a resolution of 500 dpi, there are always several pigment grains of different coloration in this method, since these are significantly smaller. However, only the pigments which absorb the laser radiation of the respectively used wavelength are always bleached. Yellow pigments therefore absorb the blue wavelength and thereby bleach out. The remaining cyan and magenta pigments remaining in their color mix subtly to blue when viewed under reflective light. Thus, blue radiation produces a blue tint. The same applies to the red and green laser radiation when it encounters the same pigment mixture. In this embodiment, the grain sizes of the pigments are in the range of 10 microns. They therefore have the same order of magnitude as the strips in embodiments A and B. Accordingly, they can be accurately detected in their position to 2 μm in the same way as described there by means of a microscopic scanning method. Also, their diameter is suitable to individually address them with a UV laser beam with a focus of about 10 microns, because said mechanical Linearverfahreinheiten with 2μm location accuracy can be purchased (Heinrich Wolf, Eutin). Fig. 7b It can be seen that all 3 types of pigment are bleached with only one wavelength in the UV (typically 355nm). Thus, this embodiment opens the possibility to work with only one laser instead of 3 lasers, since now the individual color components of the pigments are no longer addressed via the wavelength of the light, but over the place. Thus, the transition to only one wavelength achieves a significant cost reduction of the technical system. At the same time, the combination with the embodiment B can lead to the fact that the position of all the pigment grains is not only known but also permanently stored. This subsequently allows an authenticity control to be extremely error-proof, since it is almost impossible to adjust the distribution of the pigment granules. The error safety is so high that it can be sufficient in everyday life should, for example, at border controls, only small sections of an image with, for example, a low-cost USB microscope to photograph and make a first authenticity check from a central server. Only in case of doubt the whole picture would be used.

LIST OF REFERENCE NUMBERS

1 pigment particles 15 Storage in a database 2 Substrate, image area 16 laser control 3 Area with statistical 17 laser bleaching Distribution of the pigment particles 17 UV laser system 4 Area with regular distribution of pigment particles, line shape 19 Surface element with pigment particles ground yellow (yellow) 5 Area with regular distribution of pigment particles, meanders 20 Surface element with pigment particles primary color cyan 6 Area with regular distribution of pigment particles, circular arrangements 21 Surface element with pigment particles Primary color magenta 7 Area with regular distribution of pigment particles, 22 surface element microscript 23 laser beam 8th Picture, symbol, lettering 24 Beam diameter of 23 9 Magnifying device, magnifying glass 25 focusing element for example lens, grid 10 x / y linear motion unit 26 card-shaped data carrier 11 White light source 12 Light sensor, photoreceiver 27 Diameter of the laser beam in the focal plane 13 Detection of the pigment particles as a color element as a function of the location coordinate 14 Storage of the data as a color chart

Claims (17)

1. A method for producing a multi-coloured character, pattern, symbol and/or image (8) on a substrate (2) having pigment particles (1) which are arranged thereon and lose or change their colour effect under the action of a laser (23), wherein different pigment particles (1) having at least two or at least three different colour effects are arranged on or in the substrate (2) and wherein the different pigment particles (1) are distributed substantially randomly as a function of the location coordinates., having the following method steps:

   a production of a colour map (14), in which the individual colour effect of individual pigment particles (1) or individual clusters of pigment particles is contained as a function of the location coordinates thereof on or in the substrate (2);

   b spatially resolved irradiation, which only changes the colour effect of individual pigment particles (1) or individual clusters of pigment particles in their colour effect, with a laser (23) at a single frequency on the basis of the colour map (14) to produce a resulting colour effect.
2. The method according to Claim 1, characterised in that steps a and b are carried out in the same device and without manipulation or displacement of the substrate (2) taking place in between.
3. The method according to one of the preceding claims, characterised in that the different pigment particles (1) are arranged in a layer, preferably in a single layer, on and/or in the substrate (2).
4. The method according to one of the preceding claims, characterised in that the different pigment particles (1) are arranged in a layer, preferably in a single layer, on and/or in the substrate (2) and are substantially arranged regularly in a microscopic pattern, wherein the microscopic pattern can be an arrangement of straight or waved lines, basic patterns or microprint.
5. The method according to one of the preceding claims, characterised in that the individual pigment particles (1) have an average diameter in the range 5-15 µm, preferably in the range 8-12 µm, and that they are arranged substantially on the substrate or in the substrate, preferably separated laterally, in particular preferably in such a manner that the normal projection of the average spacing into the printing layer plane between two pigment particles (1) is equal to or greater than the average diameter of the pigment particles, wherein preferably the beam diameter of the laser beam in step b is no more than twice the size of the average diameter of the pigment particles (1), wherein in particular preferably the beam diameter of the laser beam in step b is in the range 5-20 µm, preferably in the range 8-15 µm, in particular preferably in the range 8-12 µm.
6. The method according to one of the preceding claims, characterised in that, in order to carry out step a, the surface of the substrate is scanned, preferably using a linear displacement unit (10) having a white light source and/or detection unit arranged in the vicinity, wherein, preferably as a function of the location coordinates, white light or a sequence of light flashes of different colours is irradiated and the reflected or transmitted light is spectrally analysed as a function of the location coordinates, preferably in that the signal is determined only at at least two, preferably at least three discrete frequencies, which allow a distinction between the different pigment particles (1) arranged in the substrate, preferably using a photodiode, and in that the position and the colour effect of individual pigment particles or clusters of individual pigment particles (1) or clusters of pigment particles (1) are recorded as a data tuple in a data matrix forming the colour map (14).
7. The method according to one of the preceding claims, characterised in that, in order to carry out step b, the surface of the substrate is scanned, preferably using a linear displacement unit (10) with a laser source arranged in the vicinity, in that the laser source is directed at individual pigment particles (1) or clusters of pigment particles on the basis of the colour map (14), in order to destroy or activate the colour effect thereof individually.
8. The method according to one of the preceding claims 1-6, characterised in that, in order to carry out step b, the laser optics are fixed in position and the substrate is moved with the aid of a linear displacement unit (10) in such a manner that the laser source passes over the substrate on the basis of the colour map (14) and the laser beam meets individual pigment particles (1) or clusters of pigment particles in order to destroy their colour effect individually.
9. The method according to one of the preceding claims, characterised in that, proceeding from the colour map (14) determined in step a for the character, pattern, symbol and/or image (8), a processing protocol for the laser or the plurality of lasers is produced in a data processing unit in step b, wherein the said processing protocol receives the information on which individual pigment particles are to be locally influenced in their colour effect by the laser in a targeted manner, in particular destroyed in their colour effect by the laser, as a function of the location coordinates to produce a certain macroscopic colour effect for the character, pattern, symbol and/or image (8).
10. The method according to one of the preceding claims, characterised in that the laser used in step b is a UV laser.
11. The method according to one of the preceding claims, characterised in that in the case of a defective or absent assessment of the colour map (14) for the control of the laser system (17), a readable marker appears on a data carrier, which indicates a forgery or that the image is defective.
12. A data carrier having a character, pattern, symbol and/or image (8) produced by a method according to one of the preceding claims, characterised in that it has been produced on the basis of a substrate (2) with a random arrangement of the pigment particles (1), and that the random arrangement and its use for producing the character, pattern, symbol and/or image is stored on the data carrier and/or in a database to increase security.
13. The data carrier according to Claim 12, characterised in that it is a foil, a transfer foil or a laminate.
14. The data carrier according to one of Claims 12 or 13, which has a readable marker indicating a forgery or an image error following defective production according to one of Claims 1 to 10.
15. The data carrier according to one of Claims 12 to 14, characterised in that it is an identification card, credit card, passport, user credentials or a name badge.
16. A device for carrying out a method according to one of Claims 1 to 11, characterised in that the device has means for fastening a substrate, a first unit (10-12) for determining the colour map (14) of the substrate, and a second unit (17) for the spatially resolved irradiation, which only changes individual pigment particles (1) or individual clusters of pigment particles in their colour effect, with a laser (23) at a single frequency on the basis of the colour map (14) in order to produce a resulting colour effect, wherein preferably the first unit and the second unit are usable without manipulation or displacement of the substrate (2) taking place in between.
17. The device according to Claim 16, characterised in that the device has at least one data processing unit and at least one linear displacement unit (10) which can be controlled in a two-dimensional manner by the said data processing unit and bears the first and/or second unit.

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