EP1042125B2 - Method for producing a particular photoluminescent polychromatic printed image, resulting image and uses - Google Patents

Abstract

A process for producing any photoluminescent printed polychromatic image (8), and the image obtained thereby. At least one set of at least three monochromatic filtered images (6a, 6b, 6c) is prepared from any original polychromatic image (1) visible in visible light which is filtered with a spectral pass-band below or equal to 15 nm, according to at least three wavelengths of fundamental colors equal to the wavelengths of the luminescent pigments used, with the corresponding monochromatic filtered images (6a, 6b, 6c), in order to print separately, one above the other, three monochromatic printed images (8a, 8b, 8c). The invention concerns the image obtained, a protective device and a document carrying such an image.

Description

The invention relates to a method for producing a photoluminescent printed polychromatic image of any kind (that is to say that can incorporate all shades of colors and various shapes including possibly continuous color variations (degraded, melted, etc.). .) shadows, variations of intensity, effects of mottled ...) invisible under lighting in visible light, and visible under illumination by at least one non-visible light source, designated hereinafter throughout the text "image any photoluminescent printed polychromatic ".

By "visible light" is meant a light whose spectral composition is located in the visible spectrum, from 0.4 μ to 0.8 μ. "Non-visible light" denotes a light whose spectral composition is located outside the visible spectrum, especially in the ultraviolet and / or infrared spectrum.

Photoluminescent printed monochromatic imprints invisible under visible light and visible under non-visible light (ultraviolet or infrared) are often used for authentication of documents such as banknotes. Various printed monochromatic markings can be juxtaposed and / or superimposed, which creates color spots composed in finite number and discontinuously.

Nevertheless, these photoluminescent monochromatic markings do not make it possible to produce a true photoluminescent printed polychromatic image reproducing, with all the shades of colors and shapes, any polychromatic image visible in visible light such as a non-digitized non-screened photographic image.

Such a photoluminescent printed polychromatic image may have many interests and various applications, especially as an authentication element and / or for decoration purposes.

As authentication, any photoluminescent printed polychromatic image may provide at least three levels of authentication: image printing creates raised patterns and / or visible opalescence in visible light; under illumination in non-visible light, it is possible to verify the conformity of the image which is extremely difficult to counterfeit with perfection, given its complexity and the fact that it is applied to a background of a document with other visible patterns by transparency, except to have the original visible in visible light, the reproduction from the visible image in non-visible light does not provide the original image; a spectrophotometric analysis makes it possible to identify the photoluminescent components used, and therefore their authentic character.

As a decorative matter, it turns out that any such photoluminescent printed polychromatic image illuminated in non-visible light has a particular unusual appearance.

But the various attempts to make such a photoluminescent polychromatic image any print, which are more than sixty years old, have ended in failure.

In particular, traditional printed polychromatic images visible in visible light are generally made in four-color process (yellow, magenta, cyan, black) on a white background. The original image is filtered with three color filters (blue, green, red) having a spectral bandwidth of 100μ (one third of the visible spectrum). The appearance of the colors on the printed image is due to the reflection of the visible natural light (daylight or a lighting lamp) by the medium printed through the transparent colored inks which selectively absorb the incident light according to the principle called "matter color" in subtractive synthesis. For each colored ink, the support reflects two-thirds of the visible spectrum, according to a spectral composition complementary to the absorption spectrum of the ink in the visible. With this technique, it is not possible to produce a photoluminescent printed polychromatic image. In fact, if photoluminescent pigments corresponding to the fundamental colors of the color filters used for the four-color process are used, in inks which are printed from the three negatives obtained after filtering using traditional color filters it is not practical to reproduce the polychromatic image photoluminescent, reliably and with good quality.

US-2,302,645 , US-2,277,169 , US-2,434,019 thus describe various attempts to produce images using fluorescent pigments.

Nevertheless, the methods described in these documents do not allow the production of a photoluminescent polychromatic image by automatic and reliable reproduction of a polychromatic image. Indeed, the methods described in these documents consist in first producing a trichromatic positive manually. Subsequently, this trichromic positive is used to be reproduced by printing using inks some of which incorporate fluorescent pigments. Consequently, these documents show that the automatic obtaining of a tri-chromic positive photoluminescent had been abandoned, since these documents consider that this positive is necessarily achieved manually.

Also, the document RJ TUTOR "Fluorescent Multicolor Additive System" XP 002108747, PRODUCT LICENSING INDEX., No. 84, pages 81-85, INDUSTRIAL OPPORTUNITIES LTD. HAVANT., GB ISSN: 0374-4353, April Issue, 1971 , teaches to make by printing with the aid of an etching plate press, a multicolor fluorescent image under ultraviolet. The method implemented in this document consists in producing red, green and blue separation negatives from a continuous positive by exposure through a red, green and blue filter, respectively. With this method, since each of the negatives is not finely filtered, the largest proportion of the surface of the final image comprises an abnormal overload of the three predominantly white colors. Therefore, the fluorescent image obtained is extremely pale and is in practice, either invisible or a "ghost" image, despite the realization of a large number of successive final layers of green ink.

The invention therefore aims generally to allow the realization of any photoluminescent printed polychromatic image. Thus, the invention aims to enable the reproduction in printed and photoluminescent form of an image of polychromatic origin formed in subtractive synthesis (material color principle), any visible in visible light (printed image, painted, photograph,. ..) automatically and reliably.

The invention also aims to provide a simple and inexpensive method for quickly obtaining and reproducing such an image on an industrial scale automatically and reliably, especially in a similar way to traditional printing techniques, without requiring the manually performing a tri-chromatic positive by an artist, and providing an image of high quality and high contrast.

The invention also aims to propose applications of such a photoluminescent printed polychromatic image of any kind.

• on choisit ou on réalise une image d'origine polychromatique formée en synthèse soustractive (principe de la couleur matière) visible en lumière visible,
• on réalise et on enregistre au moins un jeu d'au moins trois images, dites images filtrées, par filtrage de l'image d'origine,
• on imprime séparément, l'une après l'autre et l'une au-dessus de l'autre, au moins un jeu d'au moins trois images, dites images imprimées, en utilisant et en reproduisant respectivement l'une des images filtrées avec une composition d'impression comprenant un pigment photoluminescent, les différents pigments photoluminescents des différentes images imprimées d'un même jeu émettant, sous éclairage par au moins une source de lumière non visible, des couleurs aptes à former par synthèse additive toutes les couleurs du spectre visible,

caractérisé en ce que :

• on réalise les images filtrées, dites images filtrées monochromatiques, par filtrage de l'image d'origine, selon une bande passante spectrale inférieure ou égale à 15nm centrée selon une longueur d'onde, dite longueur d'onde de filtrage, choisie parmi les longueurs d'onde d'au moins trois couleurs fondamentales, les différentes longueurs d'onde de filtrage des images filtrées monochromatiques étant deux à deux distinctes, et étant adaptées pour permettre de former par synthèse additive toutes les couleurs du spectre visible, chacune de ces longueurs d'onde de filtrage étant au moins approximativement égale à une longueur d'onde d'un pic d'émission d'un pigment photoluminescent sous éclairage par au moins une source de lumière non visible,
• on imprime chaque image imprimée, dite image imprimée monochromatique, en utilisant et en reproduisant l'une des images filtrées monochromatiques avec une composition d'impression comprenant un pigment photoluminescent ayant une longueur d'onde de pic d'émission, sous éclairage par au moins une source de lumière non visible, qui est au moins approximativement égale à la longueur d'onde de filtrage utilisée pour obtenir ladite image filtrée monochromatique.

To this end, the invention relates to a method for producing an invisible photoluminescent printed polychromatic image under visible light, and visible under illumination by at least one non-visible light source, in which:

• one chooses or realizes an image of polychromatic origin formed in subtractive synthesis (principle of the color matter) visible in visible light,
• at least one set of at least three images, called filtered images, is produced and recorded by filtering the original image,
• one after the other and one above the other is printed separately, at least one set of at least three images, called printed images, using and reproducing respectively one of the filtered images with a printing composition comprising a photoluminescent pigment, the different photoluminescent pigments of the different printed images of the same set emitting, under illumination by at least one non-visible light source, colors capable of forming by additive synthesis all the colors of the visible spectrum,

characterized in that

• the filtered images, called monochromatic filtered images, are produced by filtering the original image, according to a spectral bandwidth less than or equal to 15 nm centered at a wavelength, referred to as the filtering wavelength, chosen from among the wavelengths of at least three fundamental colors, the different filtering wavelengths of the monochromatic filtered images being two by two distinct, and being adapted to allow additive synthesis to form all the colors of the visible spectrum, each of these filtering wavelengths being at least approximately equal to a wavelength of a peak emission of a photoluminescent pigment under illumination by at least one non-visible light source,
• each printed image, called the monochromatic printed image, is printed using and reproducing one of the monochromatic filtered images with a printing composition comprising a photoluminescent pigment having a peak emission wavelength, under illumination by at least a non-visible light source, which is at least approximately equal to the filtering wavelength used to obtain said monochromatic filtered image.

By "at least approximately equal" is meant either a perfect equality between wavelengths, or the fact that the wavelengths are sufficiently close so that their difference does not produce a significant effect on the image obtained. In particular, the wavelength of the emission peak may be in the entire bandwidth less than or equal to 15 nm of the filtering wavelength. In other words, we accept a certain margin of error for the wavelengths, and this margin of error is of the order of the bandwidth of the filters used.

• pour réaliser chacune des images filtrées monochromatiques, on éclaire un original de l'image d'origine polychromatique quelconque visible en lumière visible, et on filtre l'image polychromatique réfléchie par cet original éclairé, selon une bande passante spectrale inférieure ou égale à 15nm centrée selon la longueur d'onde de filtrage de la couleur fondamentale correspondant à l'image filtrée monochromatique ; avantageusement, on filtre l'image polychromatique réfléchie avec des filtres passe-bande ayant une bande passante spectrale de l'ordre de 10nm, notamment avec des filtres interférentiels passe-bande ;
• on choisit, à titre de longueurs d'onde de filtrage et des pics d'émission des pigments photoluminescents (en sélectionnant des moyens de filtrage et des pigments photoluminescents appropriés), des différentes images imprimées monochromatiqucs d'un même jeu réalisant une reproduction d'une image d'origine, au moins une longueur d'onde dans le vert, au moins une longueur d'onde dans le rouge, et au moins une longueur d'onde dans le bleu ; avantageusement, on choisit des longueurs d'onde adaptées pour être séparées d'une même distance spectrale comprise entre 80nm et 100nm, notamment égale à 90nm ; notamment une longueur d'onde dans le vert comprise entre 520 et 570nm, une longueur d'onde dans le rouge comprise entre 610 et 680nm, et une longueur d'onde dans le bleu comprise entre 430 et 480nm ;
• on imprime les images imprimées monochromatiques de façon que, dans l'ordre de réception de la lumière d'éclairage, elles se présentent dans l'ordre bleu, rouge, vert des longueurs d'onde de filtrage et des pics d'émission des pigments photoluminescents ; on imprime les images imprimées monochromatiques les unes sur les autres sans couche intermédiaire ;
• pour un même jeu réalisant une reproduction d'une image polychromatique d'origine, on imprime uniquement trois images imprimées monochromatiques, une dans le vert, une dans le rouge et une dans le bleu ; on imprime chaque image imprimée monochromatique en une seule couche d'impression ;
• pour réaliser et enregistrer chaque image filtrée monochromatique, on capte l'image filtrée avec des moyens photosensibles à transfert de charges CCD et on enregistre une image numérisée correspondante ; on forme, à partir de chaque image filtrée monochromatique, une image tramée que l'on utilise ensuite pour imprimer l'image imprimée monochromatique ; avantageusement, l'image tramée présente une trame de 60 à 133, notamment de l'ordre de 80 (cette valeur correspondant au nombre de lignes de points par pouce (2,54 cm) ;
• on imprime les différentes images imprimées monochromatiques d'un même jeu au moins sensiblement selon la même épaisseur d'impression ; on imprime chaque image imprimée monochromatique de façon que la quantité de pigment photoluminescent en chaque point soit fonction de l'intensité lumineuse de l'image d'origine polychromatique en ce point selon la longueur d'onde de filtrage correspondante (cette fonction étant proportionnelle dans le cas d'un positif, et inversement proportionnelle dans le cas d'un négatif) ; et on utilise des pigments photoluminescents présentant un facteur de pureté (rapport de la quantité de lumière monochromatique selon la longueur d'onde dominante du pic d'émission sur la somme de cette quantité de lumière monochromatique et de la quantité de lumière blanche émise) égal à 1, quasi-monochromatique ayant un pic d'émission principal, ou monochromatique ayant un et un seul pic d'émission ;
• on laisse sécher et/ou durcir chaque image imprimée monochromatique après l'avoir imprimée et avant d'imprimer une autre image imprimée inonochromatique ;
• pour réaliser un même jeu d'images imprimées monochromatiques, on utilise des pigments photoluminescents sous éclairage par une seule et même source de lumière non visible ; en variante, pour réaliser un même jeu d'images imprimées monochromatiques, on utilise au moins un premier pigment photoluminescent sous éclairage par au moins une première source de lumière non visible, et au moins un deuxième pigment photoluminescent sous éclairage par au moins une deuxième source de lumière non visible de longueur(s) d'onde distincte(s) de celle(s) de la première source de lumière non visible ;
• on imprime un jeu d'images imprimées monochromatiques qui sont des images positives d'une image d'origine, adaptées pour reproduire en synthèse additive un positif de l'image d'origine ;
• on imprime un jeu d'images imprimées monochromatiques qui sont des images négatives d'une image d'origine, adaptées pour reproduire en synthèse additive un négatif de l'image d'origine ;
• on imprime un premier jeu d'images imprimées monochromatiques positives avec des pigments photoluminescents sous éclairage par une première source de lumière non visible -notamment ultraviolette ou infrarouge-, et on imprime un deuxième jeu d'images imprimées monochromatiques négatives avec des pigments photoluminescents sous éclairage par une deuxième source de lumière non visible de longueur d'onde distincte de celle de la première source de lumière non visible -notamment infrarouge ou ultraviolette- ;
• les longueurs d'onde des pics d'émission des pigments photoluminescents utilisés pour imprimer le premier jeu sont au moins approximativement égales aux longueurs d'onde des pics d'émission des pigments photoluminescents utilisés pour imprimer le deuxième jeu, de sorte que les mêmes images filtrées monochromatiques peuvent servir pour imprimer les deux jeux ;
• on imprime en outre au moins une image, dite image infrarouge, avec une composition d'impression comprenant au moins un pigment ayant au moins une longueur d'onde de pic d'émission située dans le domaine des infrarouges mais aucune émission dans le domaine de la lumière visible lorsque ce pigment est activé par éclairage sous une source de lumière visible ; l'image infrarouge est une image monochrome qui peut être de même nature (positive ou négative) que les images imprimées monochromatiques ou, de préférence, de nature opposée ; il est aussi possible de prévoir un premier jeu positif et un deuxième jeu négatif, comme indiqué ci-dessus, et une image infrarouge positive ou négative ;
• pour imprimer chaque image imprimée monochromatique, on utilise une composition d'impression qui incorpore un pigment photoluminescent, mais qui est, au moins après séchage, transparente ou translucide pour la lumière visible lorsqu'elle est placée sous éclairage par la source de lumière non visible ou par chacune des sources de lumière non visible ; en outre, avantageusement, pour imprimer chaque image imprimée monochromatique, on utilise une composition d'impression qui, au moins après séchage, est transparente ou translucide pour la lumière visible lorsqu'elle est placée sous éclairage en lumière visible ;
• on imprime les images imprimées monochromatiques par sérigraphie ; avantageusement, on utilise une composition d'impression formée d'un vernis sérigraphique à polymérisation sous rayons ultraviolets ; on réalise un écran d'impression sérigraphique, à partir de chaque image filtrée monochromatique, et on réalise les différents écrans d'impression sérigraphique à partir du même tissu ;
• on utilise des pigments photoluminescents sous éclairage par au moins une source de lumière non visible dont la composition spectrale est située dans le domaine des ultraviolets ou des infrarouges ;
• on utilise des pigments photoluminescents minéraux
• notamment de la famille des terres rares- ; en variante, on utilise des pigments photoluminescents organiques de meilleure transparence (opalescence moindre) mais qui sont moins durables que les pigments minéraux ;
• on imprime les images imprimées monochromatiques successivement sur la face externe libre d'une pellicule transparente dans le visible comprenant au moins une couche formée d'une impression continue d'une composition d'impression, par exemple un film tel que décrit dans EP-0 271 941 ou US-5 232 527 .

Advantageously, a method according to the invention is also characterized by at least one of the following characteristics:

• to make each of the monochromatic filtered images, an original of the image of any polychromatic origin visible in visible light is illuminated, and the polychromatic image reflected by this illuminated original is filtered with a spectral bandwidth less than or equal to 15 nm centered according to the filtering wavelength of the fundamental color corresponding to the monochromatic filtered image; advantageously, the reflected polychromatic image is filtered with bandpass filters having a spectral bandwidth of the order of 10 nm, in particular with interference bandpass filters;
• as filtering wavelengths and emission peaks, photoluminescent pigments (in selecting appropriate filtering means and photoluminescent pigments), different monochromatic printed images of the same set producing a reproduction of an original image, at least one wavelength in the green, at least one length of wave in the red, and at least one wavelength in the blue; advantageously, wavelengths adapted to be separated by the same spectral distance between 80 nm and 100 nm, in particular equal to 90 nm, are chosen; in particular a wavelength in the green of between 520 and 570 nm, a wavelength in the red of between 610 and 680 nm, and a wavelength in the blue of between 430 and 480 nm;
• the monochromatic printed images are printed so that, in the order of reception of the illumination light, they are in the order blue, red, green of the filtering wavelengths and the emission peaks of the pigments photoluminescent; the monochromatic printed images are printed on each other without an intermediate layer;
• for the same game making a reproduction of an original polychromatic image, only three monochromatic printed images are printed, one in green, one in red and one in blue; each printed monochromatic image is printed in a single printing layer;
• to make and record each monochromatic filtered image, the filtered image is captured with CCD charge transfer photosensitive means and a corresponding digitized image is recorded; a halftone image is formed from each monochromatic filtered image, which is then used to print the monochromatic printed image; advantageously, the raster image has a frame of 60 to 133, in particular of the order of 80 (this value corresponding to the number of lines of dots per inch (2.54 cm);
• the different monochromatic printed images of the same set are printed at least substantially according to the same printing thickness; each monochromatic printed image is printed so that the amount of photoluminescent pigment at each point is a function of the light intensity of the image of polychromatic origin at that point according to the corresponding filtering wavelength (this function being proportional in the case of a positive, and inversely proportional in the case of a negative); and using photoluminescent pigments having a purity factor (ratio of the amount of monochromatic light according to the dominant wavelength of the emission peak to the sum of this amount of monochromatic light and the amount of white light emitted) equal at 1, quasi-monochromatic having a main emission peak, or monochromatic having one and only one emission peak;
• each monochromatic printed image is allowed to dry and / or cure after printing and prior to printing another inonochromatic printed image;
• to make the same set of monochromatic printed images, photoluminescent pigments are used under illumination by a single non-visible light source; alternatively, to produce the same set of monochromatic printed images, at least one first photoluminescent pigment is used under illumination by at least one first non-visible light source, and at least one second photoluminescent pigment is illuminated by at least one second source non-visible light of distinct wavelength (s) from that (s) of the first non-visible light source;
• printing a set of monochromatic printed images which are positive images of an original image, adapted to reproduce in additive synthesis a positive of the original image;
• printing a set of monochromatic printed images which are negative images of an original image, adapted to reproduce in additive synthesis a negative of the original image;
• printing a first set of positive monochromatic printed images with photoluminescent pigments under illumination by a first non-visible light source - especially ultraviolet or infrared - and printing a second set of negative monochromatic printed images with photoluminescent pigments under illumination by a second non-visible light source of wavelength distinct from that of the first non-visible light source - in particular infrared or ultraviolet -;
• the wavelengths of the emission peaks of the photoluminescent pigments used to print the first set are at least approximately equal to the wavelengths of the emission peaks of the photoluminescent pigments used to print the second set, so that the same images monochromatic filtered can be used to print both games;
• at least one image, said infrared image, is further printed with a printing composition comprising at least one pigment having at least one emission peak wavelength located in the infrared range but no emission in the field of the visible light when this pigment is activated by illumination under a visible light source; the infrared image is a monochrome image which may be of the same nature (positive or negative) as the monochromatic printed images or, preferably, of opposite nature; it is also possible to provide a first positive game and a second negative game, as indicated above, and a positive or negative infrared image;
• for printing each monochromatic printed image, a printing composition is used which incorporates a photoluminescent pigment, but which is, at least after drying, transparent or translucent for the light visible when placed under illumination by the non-visible light source or by each of the non-visible light sources; in addition, advantageously, for printing each monochromatic printed image, a printing composition is used which, at least after drying, is transparent or translucent for visible light when it is placed under visible light;
• monochromatic printed images are printed by screen printing; advantageously, a printing composition formed by an ultraviolet-ray-treated serigraphic varnish is used; a screen printing screen is made from each monochromatic filtered image, and the different screen printing screens are made from the same fabric;
• photoluminescent pigments are used under illumination by at least one non-visible light source whose spectral composition is located in the ultraviolet or infrared range;
• we use mineral photoluminescent pigments
• especially of the rare earth family-; alternatively, organic photoluminescent pigments of better transparency (less opalescence) but which are less durable than mineral pigments are used;
• the monochromatic printed images are printed successively on the free external face of a transparent film in the visible including at least one layer formed of a continuous printing of a printing composition, for example a film as described in EP-0 271 941 or U.S. 5,232,527 .

The invention thus makes it possible for the first time to automatically obtain any photoluminescent printed polychromatic image which is a faithful reproduction, with all the color shades and shapes that can infinitely vary to infinity, of a original image of any polychromatic origin visible in visible light. This original can be printed or a stored analog image (photographic, cinematographic, video ...), or a digitized image stored on a computer mass memory or other.

It should be noted that this result is obtained by not implementing broadband filtering as in conventional printing, but instead of selective narrow-band filtering in visible light and additive trichromatic synthesis under lighting in non-visible light.

The method according to the invention makes it possible to obtain an invisible photoluminescent printed polychromatic image under light in visible light, and visible under illumination by at least one non-visible light source, comprising at least one set of at least three images, called printed images, printed one above the other, each printed image comprising a photoluminescent pigment emitting a color under illumination by a non-visible light source, the different colors of the printed images of the same set being adapted to be able to form by synthesis additive all the colors of the visible spectrum under illumination by at least one non-visible light source, characterized in that each printed image, called monochromatic printed image corresponds to the filtering of an image of polychromatic origin in subtractive synthesis visible in visible light, at a spectral bandwidth less than or equal to 15 nm centered a wavelength, referred to as the wavelength of filtering, chosen from wavelengths of at least three fundamental colors, the different filtering wavelengths being two by two distinct and adapted to make it possible to form by additive synthesis all colors of the visible spectrum, each of these filtering wavelengths being at least approximately equal to a wavelength of an emission peak of the photoluminescent pigment of the corresponding monochromatic printed image.

• elle comprend au moins une image imprimée monochromatique ayant au moins une longueur d'onde de pic d'émission dans le vert, au moins une image imprimée monochromatique ayant au moins une longueur d'onde de pic d'émission dans le rouge, et au moins une image imprimée monochromatique ayant au moins une longueur d'onde de pic d'émission dans le bleu ; pour un même jeu d'images imprimées monochromatiques réalisant une reproduction d'une image d'origine, elle comprend trois images imprimées monochromatiques, une dans le vert, une dans le rouge et une dans le bleu ;
• les longueurs d'onde des pics d'émission des images imprimées monochromatiques sont séparées d'une même distance spectrale comprise entre 80nm et 100nm, notamment de l'ordre de 90nm ; avantageusement, elle comprend une image imprimée monochromatique ayant une longueur d'onde de pic d'émission dans le vert comprise entre 520 et 570nm, une image monochromatique ayant une longueur d'onde de pic d'émission dans le rouge comprise entre 610 et 680nm, et une image imprimée monochromatique ayant une longueur d'onde de pic d'émission dans le bleu comprise entre 430 et 480nm ;
• les images imprimées monochromatiques d'un même jeu se succèdent dans l'ordre de réception de la lumière dans l'ordre bleu, rouge, vert des longueurs d'ondes des pics d'émission ; avantageusement, les images imprimées monochromatiques sont empilées les unes sur les autres sans couche intermédiaire ; les images imprimées monochromatiques présentent au moins sensiblement la même épaisseur d'impression:

• chaque image imprimée monochromatique est formée d'une composition d'impression qui est transparente ou translucide pour la lumière visible lorsqu'elle est placée sous éclairage par la source de lumière non visible ou par chacune des sources de lumière non visible, et qui incorpore un pigment photoluminescent ; chaque image imprimée monochromatique est formée d'une composition d'impression qui est transparente ou translucide pour la lumière visible lorsqu'elle est placée sous éclairage en lumière visible ;
• les pigments photoluminescents d'au moins un même jeu d'images imprimées monochromatiques émettent sous éclairage par au moins une source de lumière non visible dont la composition spectrale est située dans le domaine des ultraviolets ou des infrarouges ; les différentes images imprimées monochromatiques d'un même jeu comprennent des pigments photoluminescents émettant sous éclairage par au moins une source de lumière non visible monochromatique ; avantageusement, les différents pigments photoluminescents d'au moins un même jeu d'images imprimées monochromatiques sont adaptés pour présenter une longueur d'onde de pic d'émission sous éclairage par une et une seule et même source de lumière non visible ; en variante, pour au moins un même jeu d'images imprimées monochromatiques, au moins un premier pigment est photoluminescent sous éclairage par au moins une première source de lumière non visible, et au moins un deuxième pigment est photoluminescent sous éclairage par au moins une deuxième source de lumière non visible de longueur(s) d'onde distincte(s) de celle(s) de la première source de lumière non visible ;
• elle comprend plusieurs jeux d'images imprimées monochromatiques visibles sous éclairage par des sources de lumière différentes (par exemple un jeu formant une reproduction visible sous ultraviolet et un jeu formant une reproduction visible sous infrarouge) ;
• elle comprend un premier jeu d'images imprimées monochromatiques positives comprenant des pigments photoluminescents sous éclairage par une première source de lumière non visible -notamment ultraviolette ou infrarouge- et adaptées pour reproduire en synthèse additive, un positif d'une image d'origine polychromatique, et un deuxième jeu d'images imprimées monochromatiques négatives comprenant des pigments photoluminescents sous éclairage par une deuxième source de lumière non visible de longueurs d'onde distincte de celle de la première source de lumière non visible - notamment infrarouge ou ultraviolette- et adaptées pour reproduire en synthèse additive, un négatif d'une image d'origine polychromatique ; ces deux jeux peuvent être superposés et sont des reproductions d'une même image d'origine polychromatique, l'un en négatif et l'autre en positif ; en variante, ils sont des reproductions de deux images d'origine différentes ;
• elle comprend en outre au moins une image, dite image infrarouge, visible dans le domaine des infrarouges mais invisible dans le domaine de la lumière visible sous éclairage par une source de lumière visible ; cette image infrarouge peut être une reproduction inverse d'une reproduction d'une image d'origine polychromatique réalisée par un jeu d'images imprimées monochromatiques sur le même support, et peut être superposée sur ce jeu.

Advantageously, an image obtained by a method according to the invention is also characterized by at least one of the following characteristics:

• it comprises at least one monochromatic printed image having at least one green emission peak wavelength, at least one monochromatic printed image having at least one emission peak wavelength in the red, and at least one minus a monochromatic printed image having at least one emission peak wavelength in the blue; for the same set of monochromatic printed images producing a reproduction of an original image, it comprises three monochromatic printed images, one in green, one in red and one in blue;
• the wavelengths of the emission peaks of the monochromatic printed images are separated by the same spectral distance between 80 nm and 100 nm, in particular of the order of 90 nm; advantageously, it comprises a monochromatic printed image having a green emission peak wavelength between 520 and 570 nm, a monochromatic image having a peak emission wavelength in the red between 610 and 680 nm. , and a monochromatic printed image having a blue emission peak wavelength between 430 and 480 nm;
• the monochromatic printed images of the same game succeed one another in the order of reception of the light in the blue, red, green order of the wavelengths of the emission peaks; advantageously, the monochromatic printed images are stacked one on the other without intermediate layer; the monochromatic printed images have at least substantially the same printing thickness:

• each monochromatic printed image is formed of a printing composition that is transparent or translucent for visible light when illuminated by the non-visible light source or by each of the non-visible light sources, and incorporates a photoluminescent pigment; each monochromatic printed image is formed of a printing composition that is transparent or translucent for visible light when placed under visible light;
• the photoluminescent pigments of at least one set of monochromatic printed images emit under illumination by at least one non-visible light source whose spectral composition is located in the ultraviolet or infrared range; the different monochromatic printed images of the same set include photoluminescent pigments emitting under illumination by at least one monochromatic non-visible light source; advantageously, the various photoluminescent pigments of at least one set of monochromatic printed images are adapted to present a peak emission wavelength under illumination by one and only one non-visible light source; alternatively, for at least one set of monochromatic printed images, at least one first pigment is photoluminescent under illumination by at least one first non-visible light source, and at least one second pigment is photoluminescent under illumination by at least a second non-visible light source of distinct wavelength (s) from that (s) of the first non-visible light source;
• it comprises several sets of monochromatic printed images visible under illumination by different light sources (for example a game forming a visible reproduction under ultraviolet and a game forming a visible reproduction under infrared);
• it comprises a first set of positive monochromatic printed images comprising photoluminescent pigments under illumination by a first non-visible light source - in particular ultraviolet or infrared - and adapted to reproduce, in additive synthesis, a positive of an image of polychromatic origin, and a second set of negative monochromatic printed images comprising photoluminescent pigments under illumination by a second non-visible light source of wavelengths distinct from that of the first non-visible light source - in particular infrared or ultraviolet - and adapted to reproduce in additive synthesis, a negative of an image of polychromatic origin; these two games can be superimposed and are reproductions of the same image of polychromatic origin, one in negative and the other in positive; alternatively, they are reproductions of two images of different origin;
• it further comprises at least one image, called infrared image, visible in the infrared range but invisible in the visible light field under illumination by a visible light source; this infrared image can be an inverse reproduction of a reproduction of an image of polychromatic origin performed by a set of monochromatic printed images on the same support, and can be superimposed on this game.

• la figure 1 est un schéma illustrant une installation permettant la mise en oeuvre d'un procédé selon l'invention,
• la figure 2 est un schéma illustrant diverses étapes d'un procédé selon l'invention,
• la figure 3 est un schéma montrant un exemple de document protégé par un dispositif de protection selon l'invention, vu éclairé en lumière visible,
• la figure 4 est un schéma montrant le document de la figure 3 éclairé en lumière non visible.

Other objects, features and advantages of the invention will appear on reading the following description which refers to the appended figures in which:

• the figure 1 is a diagram illustrating an installation allowing the implementation of a method according to the invention,
• the figure 2 is a diagram illustrating various steps of a method according to the invention,
• the figure 3 is a diagram showing an example of a document protected by a protection device according to the invention, seen lit in visible light,
• the figure 4 is a diagram showing the document from the figure 3 illuminated in non-visible light.

On the figure 1 a colored polychromatic origin image 1 is represented according to the principle of color matter (subtractive synthesis), visible in visible light such as a photograph or a printed image in traditional quadrichromy, which one wants to reproduce with all the nuances of colors and forms, obtaining a printed polychromatic image any photoluminescent any invisible under lighting in visible light and visible under illumination by at least one non-visible light source. An original of this original image 1 is illuminated from a visible light source 2 such as an incandescent lamp or daylight. The light illuminating the original image 1 is a visible white light which is reflected by the original image 1 towards a CCD camera 3 connected to a microcomputer 4 for storing the images captured by the camera. 3. On the optical path of the reflected light, a bandpass filter is interposed. This filter 5 is chosen from at least three interference filters 5a, 5b, 5c which have a spectral bandwidth of less than 15 nm, in particular of the order of 10 nm, and whose filtering wavelength is chosen at less than approximately equal to the wavelength of an emission peak of a photoluminescent pigment under illumination by at least one non-visible light source, this pigment being otherwise adapted to allow the subsequent printing of the image polychromatic, that is to say to be compatible with the means and printing techniques used as described below. The filtering wavelengths are chosen from wavelengths of at least three fundamental colors that can form all the colors of the visible spectrum by additive synthesis. In particular, three wavelengths are sufficient provided that each fundamental color can not be balanced by the other two. It is also possible to use more than three wavelengths.

The monochromatic image from the filter 5 is a contrasted monochromatic filtered image. The camera 3 is a monochrome camera. Three monochromatic filtered images 6a, 6b, 6c are thus produced with, respectively, each of the three filters 5a, 5b, 5c, monochromators from the same original image 1. These three monochromatic filtered images 6a, 6b, 6c are digitized images recorded in the microcomputer 4. Each monochromatic filtered image 6a, 6b, 6c captured and digitized by the CCD camera 3 is recorded by the microcomputer 4.

In a variant not shown, the image of polychromatic origin may be a digitized image recorded and digital filtering means are used to perform, by software calculation, each monochromatic filtered image 6a, 6b, 6c. It is also possible to use digital filtering of a scanner having a transfer function adapted to the filtering wavelengths.

Then, from the three monochromatic filtered images 6a, 6b, 6c, three printing frames 7a, 7b, 7c, flashed in the traditional way of silk-screen printing are made, using a screen of 60 to 133-notably of the order of 80-. The fineness of the screen is adapted according to the viscosity of the printing composition and its dry extract in a manner known per se in the field of screen printing.

These printing frames 7a, 7b, 7c are each formed of a film carrying a contrasting image whose dot density at each point of the image corresponds to the luminous intensity of the polychromatic image that is wish to reproduce.

In the case where it is desired to carry out a positive reproduction of the original image 1, the dot density at each point of the contrasting image of the negative printing frame corresponds to the luminous flux of the image. the original polychromatic image 1 reflected at this point, respectively according to each filtering wavelength. It is therefore necessary in this case to perform an inversion of the monochromatic filtered images 6a, 6b, 6c, which are positive, to obtain negative frames of screen printing 7a, 7b, 7c. This inversion can be performed either by the image capture software by the CCD3 camera, or by using traditional image processing software from the scanned and recorded images, or by the image processing software. the printer to make the printing frames.

In the case, on the other hand, where it is desired to produce a negative reproduction of the original image 1, the inversion of the monochromatic filtered images 6a, 6b, 6c is not performed, and the screen printing frames 7a, 7b, 7c are positive

The printing frames 7a, 7b, 7c are produced on transparent films which then make it possible, by exposure of a photopolymer, to screen silk screen printing, one for each monochromatic filtered image 6a, 6b, 6c.

Each screen is made for example from a fabric whose mesh comprises 165 threads / cm, the son having a diameter of 27μ. A layer of photopolymer material 18 microns thick is used.

Each screen is thus representative, for each filtering wavelength, of a luminous flux reflected by the original polychromatic image 1 in the filter wavelength corresponding to the filter used, or of the inverse of this luminous flux.

Then one prints separately, one after the other, and one above the other (with or without interposition of a transparent intermediate layer) on a printing medium 9, three images, called images. monochromatic prints 8a, 8b, 8c, of the same size corresponding to the format of the photoluminescent printed polychromatic image 8 that is desired to be formed. The printing medium 9 can be of any kind as long as it is compatible with the printing technique used. Advantageously, this printing medium 9 is itself not photoluminescent, -party devoid of optical brightener- not to disturb the chromatic balance of the image 8 to form. For each monochromatic printed image 8a, 8b, 8c, the screen-printing screen made from one of the monochromatic filtered images 6a, 6b, 6c, and a transparent printing composition comprising a photoluminescent pigment whose length is emission peak wave, under illumination by at least one non-visible light source 14, is equal to the filtering wavelength used to obtain said monochromatic filtered image. By successively using the three screen-printing screens corresponding to the three monochromatic filtered images 6a, 6b, 6c, the three monochromatic printed images 8a, 8b, 8c are successively printed.

As photoluminescent pigments, it is advantageous to use mineral pigments - especially selected from the rare earths - which are well adapted to be printed by screen printing, and resist the radiation of the non-visible light source. which ensures the maintenance in time of the chromatic balance. We can also choose organic pigments whose durability is a little less good, but have a better transparency.

As a monochromator filter 5, it is possible to use, for example, the interference bandpass filters marketed by the company LOT ORIEL (Courtaboeuf, France) as mentioned in the table below, and in which are also indicated examples of references of corresponding photoluminescent pigments which can be used, marketed by the company RIEDEL DE HAN (Germany) (RDH in the table) or USR OPTONICS (New Jersey, USA) (USR in the table). Reference Provider Type Excitation wavelength Peak emission and filtering wavelength Filtered CD 144 RDH Mineral blue 365 nm 440 nm 440 FS 10-50 CD 105 RDH Mineral red 365 nm 620 nm 620 FS 10-50 CD 166 RDH Mineral green 365 nm 530 nm 530 FS 10-50 CD 163 RDH Mineral green 365 nm 530 nm 530 FS 10-50 P 22 USR Mineral red 365 nm 620 nm 620 FS 10-50 2205 USR Mineral blue 365 nm 480 nm 480 FS 10-50 CD 329 RDH Organic blue 365 nm 460 nm 460 FS 10-50 CD 308 RDH Organic green 365 nm 510 nm 510 FS 10-50 CD 335 RDH Red 365 nm 620 nm 620 FS 10-50 Red UC 6 RDH organic 980 nm 660 nm 660 FS 10-50 Green UC 6 RDH Mineral red 980 nm 550 nm 550 FS 10-50 Blue UC 6 RDH Mineral green 980 nm 480 nm 480 FS 10-50 Mineral blue

For each printing of a monochromatic printed image 8a, 8b, 8c, the chosen pigment is incorporated in a screen-printing varnish chosen to be transparent, or at least translucent, when it is dry and placed under illumination by the source (s). (s) of light 14 not visible, at least for wavelength light corresponding to the wavelength of the emission peak of this photoluminescent pigment, and for each of the emission peak wavelengths of the photoluminescent pigment (s) of the monochromatic printed image (s) previously printed on the printing medium. In this way, the light emitted by each of the photoluminescent pigments can pass through the printed screen printing varnish to be visible from the outside, and without color imbalance.

For example, with the pigments CD 144, CD 166 and CD 105, the concentrations of each pigment in the screen-printing varnish may be as follows: 27% for the blue pigment, 27% for the red pigment and 13.5% for the pigment green. These values can be decreased or increased (provided that the composition can be printed) provided that the relative proportions of the different colors for the chromatic balance are respected.

The three monochromatic printed images 8a, 8b, 8c blue, red, green are printed on the support 9, starting with the monochromatic printed image 8a whose photoluminescent pigment emits in green (wavelength of 530 nm in the example above), then printing the monochromatic printed image 8b whose photoluminescent pigment emits in the red (wavelength of 620 nm in the example above), and ending with the monochromatic printed image 8c whose photoluminescent pigment emits in the blue (wavelength of 440nm in the example above).

Thus, the various monochromatic printed images 8a, 8b, 8c are in the order 8c blue, 8b red, 8a green emission wavelengths of the photoluminescent pigments, in the order of reception of the non-visible light causing this show.

The silk-screen printing varnish used must also be transparent for light to length wave of the source 14 of non-visible light (or non-visible light sources when multiple sources are used), so as to allow photoluminescence of the various pigments.

The different monochromatic printed images 8a, 8b, 8c are printed successively, either directly on one another, respecting a drying time between each layer, or by interposing possibly continuous transparent layers between them. Such a transparent layer is for example a layer of polymerizable two-component printing composition containing a hydroxylated polyol and an isocyanate or a polyisocyanate so as to cause the polymerization in situ of the mixture leading to a thin transparent polyurethane film, as described for example by EP-0 271 941 or U.S. 5,232,527 .

The monochromatic printed images 8a, 8b, 8c are all printed with the same printing tools (the screen screens used being made from the same fabrics and with the same photopolymer material). In particular, the monochromatic printed images 8a, 8b, 8c are printed with the same printing thickness. This thickness is advantageously between 3μ and 12μ according to the characteristics of the screen screen used, in particular and is of the order of 5μ in the example above. Of course, the actual thickness of the monochromatic image 8a, 8b, 8c at each point depends on the image pattern, as is always the case in screen printing. Thus, for each monochromatic printed image 8a, 8b, 8c in positive, the amount of photoluminescent pigment at each point is a function of the light intensity of the image of polychromatic origin at this point according to the corresponding filtering wavelength. .

The screen printing varnish used incorporating the photoluminescent pigment is chosen to be itself non-photoluminescent so as to allow the formation of the image 8 by additive synthesis later by the three pigments of the three monochromatic images 8a, 8b, 8c. In addition. advantageously, the different monochromatic printed images 8a, 8b. 8c are transparent or translucent in visible light when placed under illumination in visible light, so that the image 8 formed is itself, in total, transparent or translucent for visible light when it is placed under illumination. visible light. In this way, it allows the display of any mentions 12 previously listed on the support 9, by transparency. The screen printing varnish used is advantageously a varnish curing under ultraviolet rays. Indeed, the photoluminescent inorganic pigments are generally sensitive to temperature.

In the example given above, the photoluminescent pigments all have the same absorption spectrum, and emit visible light at a single emission peak under illumination by a non-visible light source 14, for example ultraviolet length wave equal to 365nm. However, nothing prevents the combination of different pigments whose absorption spectra may be different, for example a photoluminescent pigment whose absorption spectrum is included in the long ultraviolet (the non-visible light source may emit at a length of wave of the order of 365 nm) and / or a photoluminescent pigment whose absorption spectrum is located in the short ultraviolet (the corresponding non-visible light source can emit at a transmission wavelength in the order of 250 nm) and / or a photoluminescent pigment whose absorption spectrum is located in the infrared (the corresponding non-visible light source can emit at a wavelength of the order of 950 nm). The advantage of using photoluminescent pigments having different absorption spectra is to require the use of several different sources of non-visible light to view the image later, which enhances the protection obtained against forgery.

It has been described above the realization of a photoluminescent polychromatic image 8 formed by a set of three monochromatic printed images 8a, 8b, 8c. It is possible to make several sets of similar images on the same printing medium 9, from several polychromatic origin images 1 and / or with photoluminescent pigments visible under illumination by different non-visible light sources (from distinct wavelengths) and / or natures (negative or positive) different. In particular, it is possible, for example, to produce a first set of photoluminescent images under ultraviolet with photoluminescent pigments under ultraviolet which form a positive of the original image 1, visible under ultraviolet light but invisible under visible light; and a second set of infrared photoluminescent images with infrared photoluminescent pigments which form a negative of the same original image 1, visible under infrared illumination but invisible under visible light. Thus, when viewing the support 9 under illumination by an ultraviolet source, a positive of the original image 1 appears, whereas when viewing the support 9 under illumination by an infrared source, a negative of the original image 1 appears.

Other similar variants are possible. For example, one can make on the same support 9 two successive positive, one visible under ultraviolet, the other under infrared. One can also make more than two reproductions, by printing more than two sets of images, superimposed or not superimposed. The number of sets of images that can be superimposed is limited by the transparency properties of the different printed layers, and by the number of different excitation light sources available.

The different sets of monochromatic printed images can be printed successively, the two photoluminescent reproductions thus formed being superimposed on one another. On the contrary, as a variant, the monochromatic printed images of different games can be nested. For example, we can print first of all the different monochromatic printed images with green pigments, then the different monochromatic printed images with red pigments, then the different monochromatic printed images with blue pigments.

Preferably, to produce on the same support 9 two photoluminescent polychromatic reproductions under illumination by two different sources, photoluminescent pigments are chosen whose wavelengths of the emission peaks are at least approximately equal, so as to use the same images. monochromatic filtered 6a, 6b, 6c to achieve these two photoluminescent reproductions. It suffices to perform the inversion of these monochromatic filtered images during the preparation of the printing screens to obtain positive polychromatic reproductions, and not to perform this inversion to obtain the polychromatic reproduction in negative.

It should be noted that since the emission intensities of the pigments under infrared excitation are lower than those of the ultraviolet-excited pigments, the concentration of the infrared-excited pigments must be greater in the printing varnish than that of the pigments with excitation under ultraviolet light.

In addition, at least one image, called an infrared image, can be printed with a printing composition comprising at least one pigment, called infrared pigment, having at least one emission peak wavelength located in the infrared range. , but no emission in visible light, when this pigment is activated by lighting under a visible light source. Such an infrared image is a monochrome image that will be visible in the infrared range but will remain invisible in the visible light domain. On the same support 9, one prints either a single infrared image or several infrared images juxtaposed or offset (that is to say, not superimposed).

For example, a photoluminescent polychromatic reproduction 8 is carried out under ultraviolet or infrared as indicated above which is a positive reproduction of the original image, then an infrared image which is a negative reproduction of the image of origin. Alternatively, the infrared image is a positive while the photoluminescent polychromatic reproductions is a negative. As the excitation sources of the pigments are different, nothing prevents even printing on the same printing medium 9 an infrared image in positive or negative on two superimposed photoluminescent polychromatic reproductions 8 made as indicated above.

To produce an infrared image, use is made of a printing composition comprising, for example, the reference varnish CD 170 marketed by the company Riedel de Han (Germany). In addition, the reflected image of the original image 1, picked up by the CCD3 camera without filtering, is used, and the steps of dithering, possible inversion, flashing, insolation, revelation and printing are carried out as described above. .

To read such an infrared image, the support 9 is illuminated with a visible light source. Preferably, a filtered light source is used in a spectral band of 40 nm to 100 nm centered on 585 nm. The infrared image formed, for example, is then read by means of an infrared camera, or a CCD camera via a high-pass filter having a cutoff threshold of 800 nm filtering the light directly from the visible light source. excitation.

The printing medium 9 can be a transparent protective film or a transparent film of such a film, so that the image 8 according to the invention is carried by or incorporated in a protective film. For example, the image 8 according to the invention can be formed inside a transparent protective film as described by EP-0 271 941 or U.S. 5,232,527 .

The Figures 3 and 4 represent an example of application of a transparent protective film 9 carrying a photoluminescent printed polychromatic image 8 of any kind according to the invention. This film 9 is applied to a part of a face 13 of a document 10 to serve as an authentication means. The face 13 of the document 10 is coated with an image 11 visible in visible light and common or variable mentions 12 visible by transparency through the film 9 when it is illuminated in visible light. As one can see figure 3 where the document 10 is only illuminated by a visible light source 15, the image 8 carried by the film 9 is not visible in visible light. Indeed, the image 8 is formed of a transparent composition in visible light, and the photoluminescent pigments do not emit light in visible light. The presence of the photoluminescent pigments in the image 8 results in practice, in general, to make it slightly whitish and translucent. In addition, especially when the monochromatic printed images 8a, 8b, 8c are printed in serigraphy and with inorganic pigments, the thickness variations of the patterns of these different images create opalescence on the surface (represented schematically by dotted lines figure 3 ) allowing to distinguish certain contours of the image 8, but without allowing the precise vision of the outlines, or especially the colors of the polychromatic image.

In the situation represented figure 4 the document 10 is illuminated by a source 14 of non-visible light corresponding to the absorption spectrum of the different photoluminescent pigments of a set of monochromatic printed images 8a, 8b, 8c of the image 8. Where appropriate, several sources non-visible light must be used to excite the photoluminescent pigments of the image 8. Thus, the polychromatic image 8 appears photoluminescent with all of its color shades, identical to the image of polychromatic origin 1. Photoluminescence also creates a certain decorative and surprising effect, the colors appearing with a luminosity and unusual chromatic purity according to the principle of light color. The photoluminescent polychromatic image 8 is superimposed on the indications 12 carried by the face 13 of the document, which are still visible by transparency through the film 9 and the image 8.

The document 10 thus protected may be a passport, an identity card, a driver's license, a vehicle registration card or other official documents of identification and / or authentication, a fiduciary document such as a ticket bank, a check, a card or other payment.

The film 9 can be applied to the face 13 of the document 10 in the traditional way, by means of an adhesive layer, for example by cold dry transfer or hot rolling. The film 9 may itself be an anti-forgery film that can incorporate other authentication marks or prevent its reproduction by optical reading. The transparent image 8 being applied to the document can not be infringed because of the other mentions of the document or mentions embedded in the film 9 which, by combining with the image 8, prevent its reproduction by non-illuminated light. visible and filtering. The photoluminescent printed polychromatic image 8 also protects the document 10 against any reproduction in optical reading in visible light, for example by photocopy or otherwise. Moreover, it is possible to combine, on the same document, several images according to the invention. For example, the references 12 of the document may themselves be formed at least in part of an image according to the invention printed on the face 13 of the document. In this case, it is advantageous to use for the second image pigments different from those of the first image.

The invention is also applicable for purely decorative or advertising purposes to produce images 8 particularly aesthetic and providing a surprising effect. Depending on whether the non-visible light source is switched on or off to excite the photoluminescent pigments, the image 8 can be shown or disappear intermittently.

EXAMPLE 1

With the method described above, a photoluminescent ultraviolet polychromatic image according to the invention was printed on a white paper free of optical brightener from a printed quadrichromic origin image formed of a complete continuous visible color spectrum. . The mineral pigments CD144, CD105 and CD166 are used. It is found that the image according to the invention perfectly reproduces the color spectrum under illumination in ultraviolet light.

EXAMPLE 2

A quadrichromic landscape image printed in A4 format is used which is reproduced by a process according to the invention as described above on the free face of a transparent adhesive polyurethane protective film marketed by the company FASVER (France) under the FASPROTEK ® name, corresponding format. This transparent film is then applied to an official document to be protected bearing a pre-printed text. We note that the film does not prevent the reading of the pre-printed text. The screen printed image forms visible opalescent reliefs at low incidence. It is not visible in visible white light. Under illumination by an ultraviolet lamp, the image appears with all its shades of colors.

EXAMPLE 3

• une reproduction polychromatique photoluminescente sous ultraviolets reproduisant en positif le spectre coloré visible continu complet, avec les pigments CD329, CD308 et CD335,
• une reproduction polychromatique photoluminescente sous infrarouges reproduisant en négatif le spectre coloré visible continu complet, avec les pigments rouge UC6, vert UC6, bleu UC6,
• une image infrarouge reproduisant en négatif le spectre coloré visible continu complet, avec le pigment CD170.

With the method described above, one printed on the same white paper without optical brightener successively:

• a photoluminescent polychromatic reproduction under ultraviolet reproducing in positive the complete continuous visible color spectrum, with the pigments CD329, CD308 and CD335,
• infrared photoluminescent polychromatic reproduction reproducing the complete continuous visible color spectrum in negative, with the red UC6, green UC6, blue UC6 pigments,
• an infrared image reproducing in negative the complete continuous visible color spectrum, with the pigment CD170.

Under illumination by an ultraviolet light source, the polychromatic image of the spectrum appears positive. Under illumination by an infrared light source, the polychromatic image of the spectrum appears in negative. Under visible light, no image in visible light appears. Under illumination in visible light filtered at 585 nm and detection in infrared by means of a high-pass filter at 800 nm by a CCD camera, an image is observed which is a monochromatic negative of the spectrum.

The invention can be the subject of multiple embodiments with respect to the embodiments described and shown. In particular, other printing techniques than screen printing can be used, provided that that the photoluminescent pigments used are compatible with these printing techniques. The printing can be performed on a support other than a transparent film 9, and the original polychromatic image 1 can not be a photographic or printed image, but an image previously digitized in a computer system that is printed. for example using a color laser printer to allow its filtering by the filters 5, or even that is filtered by numerical calculation.

Claims (21)

1. Process for producing any photoluminescent printed polychromatic image (8) invisible under illumination in visible light and visible under illumination by at least one source (14) of invisible light, wherein:

   - an original polychromatic image (1), visible in visible light, is chosen or produced by subtractive synthesis,

   - at least one set of at least three images, known as filtered images (6a, 6b, 6c), is produced and recorded by filtering the original image (1),

   - at least one set of at least three images, known as printed images (8a, 8b, 8c), is printed separately one after the other and one above the other, by using and reproducing respectively one of the filtered images (6a, 6b, 6c), with a printing composition containing a photoluminescent pigment, the different photoluminescent pigments of the different printed images of the same set emitting, under illumination by at least one source (14) of invisible light, colours capable of forming all the colours of the visible spectrum by additive synthesis,

   characterized in that:

   - filtered images, known as monochromatic filtered images (6a, 6b, 6c), are produced by filtering the original image (1) in a spectral pass-band lower than or equal to 15 nm centred on a wavelength, known as the filtering wavelength, chosen from the wavelengths of at least three fundamental colours, the different filtering wavelengths of the monochromatic filtered images being distinct in pairs and being adapted so as to enable all the colours of the visible spectrum to be formed by additive synthesis, each of these filtering wavelengths being at least approximately equal to a wavelength of an emission peak of a photoluminescent pigment under illumination by at least one source (14) of invisible light,

   - each printed image, known as the monochromatic printed image (8a, 8b, 8c), is printed by using and reproducing one of the monochromatic filtered images (6a, 6b, 6c) with a printing composition containing a photoluminescent pigment having an emission peak wavelength under illumination by at least one source (14) of invisible light, which is at least approximately equal to the filtering wavelength used for obtaining the said monochromatic filtered image (6a, 6b, 6c).
2. Process according to claim 1 characterized in that, in order to produce each of the monochromatic filtered images (6a, 6b, 6c), an original of any original polychromatic image (1) visible in visible light is illuminated, and the polychromatic image reflected by this illuminated original is filtered in a spectral pass-band below or equal to 15 nm centred on the filtering wavelength of the fundamental colour corresponding to the monochromatic filtered image (6a, 6b, 6c).
3. Process according to claim 2, characterized in that the reflected polychromatic image (1) is filtered with monochromatic filters (5a, 5b, 5c) having a spectral pass-band of the order of 10 nm, in particular interference pass-band filters (5a, 5b, 5c).
4. Process according to one of claims 1 to 3, characterized in that there is chosen, as filtering wavelengths and the emission peaks of the photoluminescent pigments, at least one wavelength in the green region, at least one wavelength in the red region and at least one wavelength in the blue region.
5. Process according to claim 4, characterized in that the wavelengths are chosen so that they are separated by a same spectral distance of between 80 nm and 100 nm, in particular equal to 90 nm.
6. Process according to either of claims 4 or 5, characterized in that a wavelength is chosen in the green region of between 520 and 570 nm, a wavelength is chosen in the red region of between 610 and 680 nm and a wavelength is chosen in the blue region of between 430 and 480 nm.
7. Process according to one of claims 4 to 6, characterized in that the monochromatic printed images (8a, 8b, 8c) are printed so that, in the order in which the illuminating light is received, they exhibit the filtering wavelengths and the emission peaks of the photoluminescent pigments in the order blue, red and green.
8. Process according to one of claims 1 to 7, characterized in that, in order to record the monochromatic filtered images (6a, 6b, 6c), the filtered image is captured by charge transfer photosensitive means CCD (3), a corresponding digitised image is recorded and there is formed, from each monochromatic filtered image, a digitised and half-tone image (7a, 7b, 7c) which has a half-tone of 60 to 133 and which is then used for printing the monochromatic printed image (8a, 8b, 8c).
9. Process according to one of claims 1 to 8, characterized in that the monochromatic printed images (8a, 8b, 8c) are printed at least substantially with the same print thickness, and so that the quantity of photoluminescent pigment at each point is a function of the luminous intensity of the original polychromatic image (1) at this point according to the corresponding filtering wavelength, and photoluminescent pigments are used having a purity factor equal to 1.
10. Process according to one of claims 1 to 9, characterized in that each monochromatic printed image (8a, 8b, 8c) is allowed to dry and/or harden after it has been printed and before another monochromatic printed image (8a, 8b, 8c) is printed.
11. Process according to one of claims 1 to 10, characterized in that in order to produce the same set of monochromatic printed images (8a, 8b, 8c) pigments are used which are photoluminescent under illumination by one and the same source (14) of invisible light.
12. Process according to one of claims 1 to 10, characterized in that in order to produce the same set of monochromatic printed images (8a, 8b, 8c) at least one first pigment is used which is photoluminescent under illumination by at least one first source of invisible light, and at least one second pigment which is photoluminescent under illumination by at least one second source of invisible light with a wavelength or with wavelengths distinct from that or those of the first source of invisible light.
13. Process according to one of claims 1 to 12, characterized in that a set is printed of monochromatic printed images (8a, 8b, 8c) which are positive images of an original image (1), adapted so as to reproduce a positive of the original image (1) by additive synthesis.
14. Process according to one of claims 1 to 13, characterized in that a set is printed of monochromatic printed images which are negative images of an original image (1), adapted so as reproduce a negative of the original image (1) by additive synthesis.
15. Process according to claims 13 and 14, characterized in that a first set of positive monochromatic printed images (8a, 8b, 8c) is printed with pigments which are photoluminescent under illumination by a first source of invisible light (in particular infrared or ultraviolet light) and wherein a second set of negative monochromatic printed images (8a, 8b, 8c) is printed with pigments which are photoluminescent under illumination by a second source of invisible light with a wavelength which is distinct from that of the first source of invisible light, in particular infrared or ultraviolet.
16. Process according to claim 15, characterized in that the wavelengths of the emission peaks of the photoluminescent pigments used to print the first set are at least approximately equal to the wavelengths of the emission peaks of the photoluminescent pigments used for printing the second set, so that the same monochromatic filtered images (6a, 6b, 6c) can serve to print the two sets.
17. Process according to one of claims 13 to 16, characterized in that there is additionally printed at least one image, known as an infrared image, with a printing composition containing at least one pigment having at least one emission peak wavelength situated in the infrared region but with no emission in the visible light region when this pigment is activated by illumination under a source of visible light.
18. Process according to one of claims 1 to 17, characterized in that in order to print each monochromatic printed image (8a, 8b, 8c), a printing composition is used which incorporates a photoluminescent pigment but which is, at least after drying, transparent or translucent for visible light when placed under illumination by the source (14) of invisible light or by each of the sources of invisible light.
19. Process according to one of claims 1 to 18, characterized in that in order to print each monochromatic printed image (8a, 8b, 8c), a printing composition is used which is, at least after drying, transparent or translucent for visible light when placed under illumination in visible light.
20. Process according to one of claims 1 to 19, characterized in that the monochromatic printed images (8a, 8b, 8c) are printed by screen printing, a screen printing screen is produced from each monochromatic filtered image (6a, 6b, 6c) and different screen printing screens are produced from the same fabric, and wherein a printing composition is used formed of a screen printing varnish polymerizable under ultraviolet radiation.
21. Process according to one of claims 1 to 20, characterized in that pigments are used which are photoluminescent under illumination by at least one source (14) of invisible light of which the spectral composition is situated in the ultraviolet or infrared regions.

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