EP2454102B1 - Parallax effect security element - Google Patents

Description

The present invention relates to the field of security elements used for authentication and / or identification of articles, documents or various objects.

Background

In order to guard against counterfeiting or falsification and in order to increase the level of security, it is known to use security elements applied on the surface or introduced in bulk or in windows in a security article, in particular a security article. security document, or other object, for example a label, packaging, especially for drugs, food, cosmetics, electronic parts or spare parts.

The security article may in particular be chosen from among a means of payment, such as a bank note, a check or a restaurant ticket, an identity document such as an identity card, a visa, a passport or a driving license, a lottery ticket, a ticket or a ticket to events.

The revelation of animated images by a parallax effect has been known for a great many years.

Several patents based on this principle have been filed, for example US 5,098,302 , US 5,525,383 and US 6,286,873 .

Methods for creating motion illusions as described in the documents are known US 5,901,484 and US 6,286,873 using a support carrier Multiple coded images, corresponding for example to the decomposition of the movement of an object or an animal, and a transparent film carrying a network of parallel lines, placed on the support. A relative movement between the coded images and the network of parallel lines creates the illusion of movement.

US 6,286,873 teaches the possibility of observing coded images on each side of an optical system having a revelation frame and a combined image, located on either side of a substrate. US 6,286,873 does not disclose a security article.

We still know from publications US 3,241,429 , US 3,154,872 , US 4,645,301 , US 4,892,336 , WO 94/27254 , US 6,856,462 , US 2005/184504 , US 5,708,871 , WO 2005/052650 , WO 2005/058610 , US 2005/150964 and WO 2007/020048 various other optical systems.

It is known to make security elements with lenticular arrays associated with specific impressions, in order to produce movement effects. The SECURENCY company markets under the MOTION ^® brand.

US 2007/0279697 discloses a security element having an optical system for producing a moire effect.

DE 10 2006 061905 discloses a security element according to the preamble of claim 1 with a transparent substrate, a plurality of interleaved coded pictures and a revelation frame superimposed on the coded pictures, the coded pictures being observable from two opposite sides of the substrate. However, there is no mention in this document DE 10 2006 061905 integration in an article of such a security element and the observation of images of the article from two opposite sides of the substrate integrated in the article.

summary

There is a need to benefit from security elements having an optical system capable of producing optical effects that can contribute to the authentication or identification of an article or object, and the possible incorporation into an article or object such as that a paper can be done relatively easily.

• un substrat transparent ou translucide,
• du côté d'une première face du substrat une image combinée comportant une pluralité d'images codées imbriquées,
• du côté d'une deuxième face du substrat, opposée à la première, une trame de révélation superposée à l'image combinée, permettant d'observer les images codées lors d'un changement de la direction d'observation de l'élément de sécurité relativement au système optique,

les images codées étant observables du côté de la première face et du côté de la deuxième face du substrat.The subject of the invention is, according to a first aspect of the invention, a security article, in particular a security document, comprising a security element comprising an optical system, comprising:

• a transparent or translucent substrate,
• on the side of a first face of the substrate a combined image comprising a plurality of interleaved coded images,
• on the side of a second face of the substrate, opposite to the first, a revelation frame superimposed on the combined image, making it possible to observe the coded images during a change in the observation direction of the security element relative to the optical system,

the coded images being observable on the side of the first face and the side of the second face of the substrate.

The combined image may include at least two nested encoded images. Preferably, it comprises at least three nested coded images in order to accentuate the visual animation effect during successive observations of the images coded by changing the viewing direction of the security element relative to the optical system.

The revelation of the coded images can be done by parallax effect.

The invention offers new possibilities to authenticate and / or identify an article or object carrying the security element, for example a security document.

The user can, by varying the inclination of the optical system, show a succession of images, which can create an animation effect for example.

The revelation frame may allow the human eye to visualize a different coded image at a time, the observer's brain being able to reconstitute for example a movement or observe hidden information.

In the invention, the different images that the observer can see are other than images resulting from a phenomenon of spatial interference between two superimposed networks, in other words a moiré effect. Such an effect can result from an offset orientation of the superimposed arrays by a non-zero specific angle and can disappear when the arrays are exactly superimposed or are shifted by an angle different from the specific angle. The invention preferably seeks to avoid such an effect. The transition from observation of one coded image to another when the viewing angle varies can be done without a gradual transition.

The security element can provide anti-photocopying security. In particular, the fineness of the revelation screen and / or the combined image, especially less than 200 microns, can prevent reproduction by photocopying and also provide protection against the use of scanners.

The resolution of the combined image and / or the revelation frame can be directly related to the thickness of the substrate. It may be greater than or equal to 800 dpi, preferably greater than 2000 dpi and more preferably greater than 3000 dpi.

The revelation screen and / or the combined image can be as such of homogeneous appearance to the naked eye, given its fineness. In particular, the revealing frame may appear to the naked eye as having an appearance, especially a uniform color.

The fact of having a revelation frame of homogeneous appearance with the naked eye can make the security article according to the invention pleasant and interesting for the general public.

Authentication and / or identification of the article can be done either by observation of the front or back side of the security article.

Indeed, the revelation frame and the combined image being present respectively on either side of the substrate, the coded images can be observed in recto-side reflection, which coincides for example with the side of the revelation frame, but also on the back side. When the security element is integrated in a security document, for example in windows, it may be advantageous to render observable both the front and back sides of the security element.

Advantageously, the security element may appear in a window of a security article.

The window may be formed by a lack of material, for example the local absence of paper, above or below the security element, the window being at least partially transparent or translucent on the side of the security element opposite to the lack of material. Thus, it may be possible to observe a first side of the security element on the side of the lack of material and a second side of the security element, opposite the first, on the side of the transparent or translucent zone of the window .

The window may still not have a lack of material. The window may for example be at least partially transparent or translucent on both sides of the security element, the transparent or translucent areas being superimposed on one another so as to be able to observe the two opposite sides of the security element. security element.

The window can still be through. The window may have missing material superimposed on both sides of the security element. Both sides of the security element can thus be observed directly and not through transparent or translucent areas. The security element can be incorporated totally in the window or partially.

The article may still have a plurality of windows as described below. The windows may or may not all be of the same type. The article may include a security element whose opposite sides are visible at the windows, through transparent or translucent areas or directly by the presence of material shortages.

Examples of embodiment of windows in the security documents are for example described in GB 1 552 853 which discloses the creation of a particular window by transparency, laser cutting, abrasion or mechanical incision, EP 0 229 645 which describes the creation using masks of a window on one side or on both sides of a bijet paper, WO 2004/096482 which describes the creation of a window by laser cutting, CA 2,471,379 which describes the creation of a transparent window and association with a security element and WO 2008/006983 which describes the creation of a transparent window on a bijet paper.

The security article may in particular be a security document comprising paper fibers.

The invention can notably make it possible to secure security articles, in particular security documents, including paper fibers, such as banknotes or passports, with security elements having a relatively small thickness. The use of a relatively thin substrate, for example of thickness less than or equal to 50 microns, preferably 30 microns, requires the use of printing or marking systems of a very important definition, further increasing the degree of security.

The coded images can represent information hidden and revealed successively by changing the observation angle of the optical system. The security element can be configured to allow the observation of the succession of several images when the viewing direction changes, which is also called "animation effect". In the context of the invention, the term "animation" is to be understood in the broad sense. It can be several images of the same object, representing different angles of view, to provide a 3D effect or relief, rather than a motion effect. The combined image may correspond to the decomposition of the movement of a pattern, for example text, alphanumeric signs, ideograms, an object, a person and / or an animal. Coded images (also called more simply nested images) may represent successive steps in the movement of a pattern, for example an object, a person and / or an animal.

The revelation screen may have any contour of shape, for example circular, oval, star, polygonal, for example rectangular, square, hexagonal, pentagonal or diamond, among others.

The outline of the revelation frame may for example represent a text, an alphanumeric sign, an ideogram, an object, a person and / or an animal.

The combined image and / or the revelation screen may be carried on the substrate by a printing process, for example offset, intaglio, laser, gravure or screen printing. For example, the combined image and / or the revelation screen may be printed with colored or non-colored inks, visible to the naked eye, under ultraviolet (UV) and / or infrared (IR) light, opaque or luminescent, in particular fluorescent, thermochromic, photochromic, interferential, in particular iridescent, or optically variable depending on the angle of observation (gonochromatic), including liquid crystals, metallic or not, magnetic or otherwise, among others. When a magnetic ink is used, the drawn pattern may constitute a magnetic signature allowing additional authentication of the substrate by detecting said signature. The combined image and / or the revelation screen may also include metallizations and / or demetallizations, for example aluminum. Metallizations and / or demetallizations can be used to prevent counterfeiting by printing. Metallizations and / or demetallizations can still be used when the security element is incorporated in a security article, especially when the security element is of the security wire type.

The combined image and / or the revelation screen can still be printed with liquid crystals, so that the coded images are for example visible only through a polarizer.

The optical system can be carried by a patch and / or a foil. The patch and / or the foil may comprise metallizations and / or demetallizations, for example of aluminum, or all types of prints. The optical system can still be carried by a security thread incorporated in the surface, mass or window (s) in the security article. The width of the security thread is for example between 3 and 20 mm, being for example equal to about 4 mm.

The substrate of the optical system may comprise or consist of a thermoplastic material, for example a polyolefin, for example polyethylene (PE), polyvinyl chloride (PVC), polyester, polyethylene terephthalate (PET), polycarbonate (PC ), polyester carbonate (PEC), polyethylene terephthalate glycol (PETG), acrylonitrile butadiene styrene (ABS) or a light-collecting film, for example of the "waveguide" type, for example a luminescent film based on polycarbonate marketed by Bayer under the name LISA ^® .

The substrate may comprise cellulosic fibers and in particular paper. In particular, the substrate may be sufficiently translucent paper to allow revealing the coded images, including a tracing paper.

The substrate may also be rendered transparent by application of a generally oily composition which permanently renders it transparent, for example a composition made of oil and transparent mineral material, as described in US Pat. US 2,021,141 , or for example a composition in the form of a wax combined with a solvent, as described in the patent US 1,479,437 .

The substrate can also be made transparent by locally applying a wax by heat transfer, as described in the patent. US 5,118,526 .

It is also possible for the substrate to use a fibrous layer comprising a hot-melt material, for example polyethylene, as described in patent EP 0 203 499 , which under the local action of heat will see its transparency vary.

Advantageously, the revelation frame and / or the combined image may each be made with at least two superimposed colors, so that on the reverse side the coded images are observed of a first color and a front side of a second color.

The revelation frame and / or the combined image may be monochromatic or polychromatic. In particular, at least one coded image of the combined image may be monochromatic or polychromatic. The nested encoded images can still be made at least in part with thermochromic and / or photochromic inks. In this way, only a part of the coded images can for example be observable under predefined lighting and / or temperature conditions.

The combined image and / or the revelation frame can be made with different colors. In this way, it may be possible to obtain a colored animation effect when observing the coded images.

The use of color to achieve the security element may make it possible to further secure an article incorporating such a security element. Most printers use four color process with "black", "cyan", "magenta" and "yellow" colors. A photocopier with a maximum resolution of 1200 dpi can reproduce a black combined image for which the line width of a coded image is 21 μm or larger. However, to reproduce the colors, especially the different colors of the

black, cyan, magenta or yellow, this photocopier uses cyan, magenta and yellow frames. The maximum effective resolution of this copier in reproduction of a combined image is thus estimated at about 1200/3 3 = 400 dpi. Such a resolution corresponds to a combined image for which the width of a line of an encoded image is 63 μm or more. Increasing the resolution of the frame and the combined image and / or the use of color can thus increase the security level of the security element.

For example, all nested coded images of the combined image may have the same color and the revelation frame a different color. Alternatively, the nested encoded images of the combined image may have different colors and the revelation field may have a different color than the nested encoded or color-like images of at least one of the nested encoded images. The revelation frame and / or the combined image may or may not be opaque. In particular, the revelation screen and / or the combined image may be at least partially translucent or transparent, and for example colored or absorbent at a given wavelength, in the UV or IR.

The security element may also comprise two revelation frames associated respectively with two combined images, the orientation of the bands of one of the revelation frames being different from that of the other revelation frame. When the strips are non-rectilinear, their orientation is defined by the general direction in which they extend.

The security element may comprise two revealing frames juxtaposed or not, superimposed or not, with bands having different orientations or not. One of the revelation frames may be wholly or partially surrounded by the other revelation frame. The possible area of superposition of the revelation frames may reveal a grid pattern when the bands of the revelation frames have different orientations.

The thickness of the substrate is for example between 10 μm and 1 mm, in particular between 6 μm and 1 mm, preferably between 6 μm and 300 μm, preferably between 10 and 100 μm, being for example between 30 μm and 50 μm. .mu.m.

It can still be less than 50 microns, especially 25 microns. The period of the revelation frame and / or the combined image is preferably less than or equal to the thickness of the substrate.

A security element with a resolution of the combined image and / or the revelation frame greater than or equal to 800 dpi, as well as with a substrate thickness and a period relationship of the revelation frame and / or the combined image and thickness of the substrate as above can provide an animation visible to the naked eye, despite the fineness of the frame and the combined image, and enhance the safety of the device vis-à-vis photocopies and copies thereof.

The number of interleaved coded images is, for example, between 2 and 15, in particular between 2 and 5, preferably being greater than or equal to 3. The distance between two elements constituting the same coded image may be between 2 μm and 1 mm, in particular between 10 .mu.m and 1 mm, preferably being substantially equal to the period of the revealing frame. The width of a constituent element of a coded image is preferably less than or equal to 500 μm, better 100 μm. The width of an opacifying strip of the revealing frame is preferably less than or equal to the thickness of the substrate, especially at 1 mm.

The revelation screen may comprise opacifying strips with parallel edges, possibly non-rectilinear. The presence of opacifying tapes with non-rectilinear edges may make it more difficult for the counterfeiter to reproduce the optical system.

The revelation screen may be printed or made differently, in particular by metallization or demetallization, as indicated above.

The security element may also comprise a revelation frame comprising at least a first fluorescent zone capable of fluorescently emitting, in a predefined lighting condition, a visible light of a first color, and a combined image comprising at least a second fluorescent zone capable of emitting fluorescence, in the predefined lighting condition, a visible light of a second color, different from the first, at least one of the first and second fluorescent zones, in particular both, being at least partially opaque, at least in the predefined illumination condition, and the first and second fluorescent zones overlapping at least partially so that, in the condition predefined lighting, a light passing through the two fluorescent zones successively has a third color different from the first and second colors. In particular, the security element may use the principle described in the international application WO 2006/051231 . The predefined lighting condition can in particular correspond to ultraviolet lighting, especially near-visible wavelength or infrared lighting, depending on the fluorescent compounds used. At least one of the first and second fluorescent zones, in particular both, may be substantially colorless in white light.

The security element may include a plurality of optical systems associated with different observation directions. For example, the security element may comprise an alternation of optical systems associated with two respective perpendicular directions, in particular optical systems whose respective revelation frames have perpendicular orientations.

The security element can be totally or partially covered with invisible material in "normal" illumination, that is to say when illuminated by daylight or an artificial light source. This invisible material in normal illumination is for example a visible material under a specific illumination, especially a luminescent material, for example a fluorescent or phosphorescent material visible under UV or IR illumination.

Alternatively, the material may comprise nematic liquid crystals visible on a reflective background (the frame and / or the image and / or the background then being reflective) with a polarizing filter, in particular circular.

The total or partial coverage of the security element by such an invisible material in "normal" illumination can form additional security in the form of a pattern, for example a word, acronym, code, symbol, image, alphanumeric character or ideogram.

In a variant, said invisible material in "normal" illumination does not cover the security element but is disposed between the frame and the image, being then partially but sufficiently observable.

The use of an invisible material in "normal" illumination can thus confer additional security of the second level to the security element. A second level security element is defined below.

The security article may comprise a security element comprising a plurality of optical systems associated with different observation directions, a part of the optical systems being such that the associated coded images are only observable on a first side of the optical system. a security element and another part of the optical systems being such that the associated coded images are observable only on a second side of the security element, opposite to the first. In a variant, the coded images associated with the optical systems can be observed on both sides of the security element.

Observation of the coded images can be further facilitated and improved by the choice of a background on which is placed the security element or on which one comes to place the security element or the security article comprising it.

When the security element is incorporated in a window in an article, either in a through window or appearing alternately on the side of a first face of the article and on the side of a second face of the article, for example opposite at the first, the bottom may be arranged alternately on either side of the security element so that the nested images and / or the revelation frame are observable both from the first face of the article and from the second side of the article.

The security element may thus include the bottom, the latter being located so that the revealing frame is between the bottom and the substrate, or the combined image is between the substrate and the bottom.

The bottom may still be independent of the security element. For example, the user can place the security element or the security article nearby, better in contact with the background, the latter being colored or not.

The bottom may consist of any substrate, preferably being flattened, for example a sheet of paper or a cardboard.

The bottom may be arranged in such a way that the user can observe the side of the security element having the revealing frame or the side having the combined image.

Observation in the presence of the background may allow the appearance of a contrast effect between the background, the combined image and the revelation frame. The contrast effect can in particular be improved when using a combined image, a revelation frame and a background of different colors.

The bottom may comprise at least one luminescent element, for example fluorescent and / or phosphorescent. The effect can be observed under predefined lighting, for example UV or IR. The bottom may still include a layer of metal.

The contrast effect can also be achieved without the presence of the background, including the simple fact of using a light source when the security element is observed in transvision on the side of the combined image or on the side of the image. the revelation plot. Indeed, the light source can play the same role as a colored background and allow the appearance of a contrast effect by the combination of the different colors of the light source, the combined image and the image frame. revelation.

The combined image and the revelation frame may have the same color, and the background may be different in color, in particular being more contrasted.

The security article may also comprise a perforation in which the security element is placed at least partially, the latter corresponding, for example, to the juxtaposition of two sub-elements, in particular in the form of foils or patches, respectively comprising a frame of revelation and the corresponding combined image.

The sub-elements may at least partially cover the edges of the perforation, with or without thickness compensation.

The security article may also comprise a revelation frame or a combined image made in the form of prints and a sub-element, in particular in the form of a foil or patch, at least partially covering the impressions formed, the sub-element comprising the combined image or the corresponding revelation frame. The prints of the combined image may for example be made on the surface of the security article.

The or each sub-element may comprise a transparent or translucent substrate.

The or each sub-element, in particular the patch or the foil, may be incorporated into the security article by gluing or by incorporation into the fibrous substrate of the article during its manufacture.

The optical system may comprise at least two combined images and a single frame allowing, during a change of the observation angle, to successively observe the nested images of the two combined images. The two combined images can be arranged in such a way that a relative movement of an image combined with the other is perceived by a user upon a change in the viewing direction of the security element relative to the optical system.

The substrate may comprise at least two distinct layers and the optical system may comprise at least two combined images, one of them being arranged facing one another, in particular on one external face of one of the layers of the substrate and the other combined image being disposed between the two layers.

The two layers of the substrate may have the same thickness. These two layers can be transparent.

Each combined image may comprise a plurality of nested encoded images.

Each combined image may comprise the same number of coded images and / or each combined image may have the same resolution, in particular one of the resolution values mentioned above and / or the distance between two elements constituting the same coded image of the first combined image may be equal to the distance between two constituent elements of the same coded image of the second combined image.

The subject of the invention is also a method for authenticating a security article according to one of claims 1-13, comprising the step of observing the security article by varying the observation direction of the system. optical and to conclude on the authenticity of the article or object associated with the security article according to the images observed. The observation can for example be done front and back sides of the substrate.

The article or object, or even the security element, especially in the form of a wire, a patch or a security foil, may include one or more other security elements, as defined below.

In general, among the security elements, some are detectable to the naked eye, in daylight or artificial light, without the use of a particular device. These security elements comprise for example colored fibers or boards, fully or partially printed or metallized wires. These security elements are called first level.

Other types of security elements are detectable only with a relatively simple device, such as a lamp emitting in the ultraviolet (UV) or infrared (IR). These security elements comprise, for example, fibers, boards, strips, wires or particles. These security elements may be visible to the naked eye or not, being for example luminescent under a lighting of a Wood lamp emitting in a wavelength of 365 nm. These security elements are said to be second level.

Other types of security elements still require for their detection a more sophisticated detection device. These security elements are for example capable of generating a specific signal when they are subjected, simultaneously or not, to one or more external excitation sources. The automatic detection of the signal makes it possible to authenticate, if necessary, the article. These security elements comprise, for example, tracers in the form of active materials, particles or fibers capable of generating a specific signal when these tracers are subjected to optronic, electrical, magnetic or electromagnetic excitation. These security elements are said to be third level.

Security features within the security article may have first, second, and / or third level security features.

• la figure 1 représente en coupe, de façon schématique et partielle, un exemple de système optique réalisé conformément à un exemple de mise en oeuvre de l'invention,
• la figure 2 représente, en vue de face, à échelle agrandie, un exemple de trame de révélation,
• la figure 3 illustre la décomposition de l'image combinée en images codées,
• la figure 4 illustre la formation d'une image codée,
• la figure 5 représente une succession d'images codées telle qu'elle peut être observée quand l'angle d'observation varie,
• les figures 6A à 6H représentent d'autres exemples de trames de révélation,
• la figure 7 est une vue similaire à la figure 1, d'une variante de réalisation d'un système optique,
• la figure 8 illustre la possibilité de faire varier l'inclinaison en déformant le substrat,
• la figure 9 représente un élément de sécurité comportant plusieurs système optiques correspondant à des directions d'observation respectives différentes,
• les figures 10 et 11 représentent deux exemples de documents de sécurité selon l'invention,
• les figures 12A, 12B, 12C et 12D représentent des exemples de documents de sécurité selon l'invention,
• les figures 13A et 13B représentent un exemple de document de sécurité selon l'invention, respectivement après photocopie et avant photocopie,
• les figures 14 à 16 illustrent des variantes d'observation d'éléments de sécurité,
• la figure 17 illustre une variante de réalisation de la trame de révélation et de l'image combinée,
• les figures 18 et 19 illustrent des variantes de réalisation d'articles de
  sécurité selon l'invention, et
• la figure 20 illustre des autres articles de sécurité.

The invention will be better understood on reading the following description, non-limiting examples of implementation thereof, and on examining the appended drawing, in which:

• the figure 1 represents in section, schematically and partially, an example of an optical system produced according to an embodiment of the invention,
• the figure 2 represents, in front view, on an enlarged scale, an example of a revelation frame,
• the figure 3 illustrates the decomposition of the combined image into coded images,
• the figure 4 illustrates the formation of a coded image,
• the figure 5 represents a succession of coded images as can be observed when the observation angle varies,
• the Figures 6A to 6H represent other examples of revelation frames,
• the figure 7 is a view similar to the figure 1 , an alternative embodiment of an optical system,
• the figure 8 illustrates the possibility of varying the inclination by deforming the substrate,
• the figure 9 represents a security element comprising a plurality of optical systems corresponding to different respective viewing directions,
• the Figures 10 and 11 represent two examples of security documents according to the invention,
• the Figures 12A, 12B, 12C and 12D represent examples of security documents according to the invention,
• the Figures 13A and 13B represent an example of a security document according to the invention, respectively after photocopying and before photocopying,
• the Figures 14 to 16 illustrate alternative observation of security elements,
• the figure 17 illustrates an alternative embodiment of the revelation frame and the combined image,
• the Figures 18 and 19 illustrate alternative embodiments of articles of
  security according to the invention, and
• Figure 20 illustrates other security items.

We have shown figure 1 a security element 1 that can be incorporated in a security article according to the invention, which comprises a non-opaque substrate 2, for example perfectly transparent, having a first face 2a carrying a plurality of coded images I ₁ , I ₂ ,. .., I _n nested, the constituent element 3 of these images are eg in the form of continuous or broken lines, usually discontinuous. The set of coded images I ₁ , ..., = I _n forms a combined image I, as can be seen on the figure 3 .

The second face 2b of the substrate 2, opposite the first, carries a revelation screen 4 (also called decomposition filter) comprising opacifying strips 5 (or lines).

The revelation screen 4 is composed of a periodic pattern, in this case the opacifying strip 5, of constant p period, as can be seen on the figure 2 . The periodicity is observed parallel to the direction of the relative displacement X between the optical system and the observer to observe the different coded images.

The simplest embodiment of the revealing frame 4 is a succession of opacifying strips 5 of constant width at regular intervals, as illustrated in FIG. figure 2 . The period p corresponds to the sum of the width of an opacifying strip 5 and of a transparent interval between two consecutive opacifying strips 5. In the illustrated example, each of the opacifying strips 5 is oriented perpendicularly to the relative displacement axis X.

The revelation weft 4 may comprise other patterns than strips of constant width with straight and parallel edges, such as crenellations or corrugations, as illustrated respectively in FIGS. Figures 6A and 6B .

If N is the total number of coded images, a possible relation between the period p of the revelation field, the width w of the transparent zone between two opacifying bands of the frame 4 and the number N is: $$\mathrm{NOT}=\left(\mathrm{p}/\mathrm{w}\right)$$

The transparent intervals 8 of the revelation frame 4 may allow, if desired, to reveal a single image at a time. A coded image then corresponds to the portions of the combined image present in the transparent gaps of the frame for a given viewing angle. Each coded picture can be visible by shifting the observation of the width of a transparent interval 8.

All the constituent elements of the same coded image are arranged, in the example described, with the same period p as opacifying bands of the revelation frame 4, along the X axis.

We illustrated at the figure 3 an example of forming a combined image I by adding a plurality of coded images, for example four coded images I ₁ to I ₄ .

We illustrated at the figure 4 the production of an encoded image I _i from an original image J to which the image of the revelation frame 4 is subtracted.

We have shown figure 5 the appearance of the different images I ₁ to I ₄ , when the observation angle represented on the figure 1 , relative to the optical system, changes. The animation corresponding to the coded images can be revealed in reflection, revealing frame side and combined image side.

On the other hand, although only one revelation frame is used to create the combined image, several different revelation frames can be used to reveal the encoded images.

For example, all the revelation frames retaining the same period and the same pattern as the initial field, in the direction perpendicular to the translation, but with a different transparent gap width, can be used, as illustrated in FIGS. Figures 6C to 6E . This can make it possible to visualize several coded images at the same time, which can bring clarity to the animation, to the detriment of the definition.

Revelation frames having a period multiple of the period p of the initial frame also work, which amounts to artificially increasing the number N of coded images to the detriment of the definition of the images, as illustrated in FIGS. Figures 6F to 6G .

Of course, various actions over the period p and over the width of the transparent interval 8 can be simultaneously performed, as illustrated in FIG. Figure 6H .

In order to be able to view all the coded images up to an inclination angle of about 45 °, the period p is preferably less than or equal to approximately the thickness e of the substrate, as shown in FIG. figure 1 .

A safety wire generally has a maximum thickness of 50 microns, which corresponds to a frame of less than or equal to 50 microns period. In the case where four nested images are provided, the lines 3 composing the nested images will generally have a width of less than or equal to 12.5 μm. The system for shaping the combined image then has a minimum resolution of (2.54 x 10 ^-2 ) / (12.5 x 10 ^-6 ) i.e. 2032 dots per inch (dpi or dpi) ).

The weft can then be in the form of a succession of lines of 3 × 12.5 = 37.5 μm in width and separated by a distance of 12.5 μm.

For example, if a substrate of about 100 μm thick e is used, the period p of the frame is less than 100 microns and the constituent elements in the form of lines 3 composing the coded images are less than 33 microns, in the case of three images by animation.

A width of 12.5 μm corresponds to about 2000 dpi, which is a limit for conventional printers that generally have a maximum definition of 600 dpi, or 1200 dpi, which is a factor of security, including copy protection or anti-photocopy.

It may thus be advantageous to have a substrate whose thickness e is less than or equal to 30 μm, better 25 μm, for example between 20 and 30 μm, or even 20 and 25 μm, limits included or excluded.

A sufficiently fine revelation frame makes it possible to provide anti-photocopying security and the existence of several coded images having details to be viewed according to different observation directions also creates a protection against the use of scanners.

Furthermore, since the human eye does not perceive details less than approximately 200 μm, a sufficiently fine revelation screen appears with a homogeneous appearance, for example gray when black opacifying strips are used. Despite the fineness of the revelation frame, the animation can be preserved, with coded images of scale greater than one millimeter, which contrast with the homogeneous appearance of the frame.

As explained above, one might think that the resolution values mentioned above are too important to allow the observation of an optical effect, this impression being corroborated by the fact that the eye can not distinguish the lines of the frame and sees this one as a flat solid.

It can be considered that the resolving power of the human eye is one minute of arc, corresponding for an observation distance of 30 cm, acceptable in the case of a security document, to a value of 2 x tan (1/120) x 30 × 10 ^-2 = 87 × 10 ^-6 m, ie 87 μm.

Despite the fineness of the frame and the combined image, the nested images can be successively visible during a loading of the viewing angle.

Resolutions over 2000 dpi, or 3000 dpi, can help secure the device.

Also, regardless of the color or colors used for the revealing frame and / or the combined image, the print definition may be accurate enough that the color mixing appears as homogeneous.

For example, we have illustrated on Figures 13A and 13B , greatly enlarged, an example of security document 10 according to the invention comprising a plurality of security elements 1.

The figure 13A represents the observation of the security document 10 after photocopying, and the Figure 13B represents the observation of the document 10 before photocopying. As can be seen, the invention provides anti-photocopying security. high. In addition, the revelation screen may be fine enough to provide a homogeneous coloring effect during the observation, contrary to what is observed on the screen. Figure 13B which is greatly enlarged.

Since the optical system can operate in transmitted or reflected light, it can be used for windows or wires introduced into windows, for example in a banknote.

It is not necessary to locate the revelation frame with respect to the combined image in the direction of the relative displacement X. But depending on the pattern of the frame, a registration may be necessary in the direction perpendicular to this displacement. For example, for a linear revelation frame as illustrated in figure 2 no identification is necessary; on the other hand, for a corrugated frame, a more or less precise location, depending on the amplitude and the frequency of the corrugations, may be desirable. The invention thus offers a possibility of modular security depending on the protection requested and the difficulty of implementation.

The combined image I and / or the revelation screen 4 may be formed by printing, demetallization, laser marking, lithography or any other technique for fixing or displaying an image.

To improve security, it is possible to use liquid-crystal inks, for example to print the combined image I. The animation, to be revealed, may then require in addition to the decomposition frame, the use of a filter polarizer, which may be present on the document or the substrate, or not.

For the security elements formed of a wire introduced in window (s) in a security document, the combined image I can be obtained by micro-photolithography of the wire and the revelation screen 4 can be achieved by means of offset printing. UV performed in a second step, when printing the document.

The revelation frame 4 may be associated, where appropriate, with a printing design of the document.

The pattern of the revelation screen 4 may be printed elsewhere than in superposition with the combined image I, on the document, on the same scale or on a different scale.

The printing of the revealing frame 4 may overflow the security element 1 and extend over the security document 10, as illustrated in FIG. figure 10 .

It is possible to use several colors, for example a first color for the revelation screen 4 and one or more other colors for the combined image I, for example as many different colors as there are coded images.

It is still possible to superimpose two colors on the revelation screen 4 and the combined image I, as illustrated in FIG. figure 7 which allows to have the animation of a color in case of observation of the optical system of the side of the frame and another color in case of observation of the optical system on the side of the combined image.

This double coloration can be achieved by demetallization or photolithography, for example.

On the figure 7 , the revealing frame 4 comprises superimposed opacifying strips 5a and 5b respectively of a first color C ₁ and a second color C _2, the opacifying bands 5a of color C ₁ being external. The elements 3 of the combined image I are printed respectively with the two colors C ₁ and C ₂ superimposed, the color elements C ₂ being external. Thus, the order of color superposition can be the same on each side of the substrate 2.

One possibility for varying the observation direction of the optical system may be to deform the substrate, for example around a folding axis, as illustrated in FIG. figure 8 .

Several optical systems, for example having the shape of small squares or rectangles of a few millimeters of sides, may be present on the same security thread 20, as illustrated in FIGS. figures 9 and 11 .

Rotating a quarter-turn of an optical system 1 out of two may make it possible to obtain a wire producing animations from relative movements of the wire in the two main axes Y ₁ and Y ₂ relative to the observer.

When the security element is an integrated wire in window (s), as shown in Figures 12A and 12B the document 10 may comprise at least two windows 31 and 32 for respectively observing each of the faces of the wire, in reflection.

The document substrate may comprise, at the level of the windows 31 and 32, material gaps and transparent areas 35 and 36 enabling the coded images to be observed on both sides of the security document.

The coded images are observable through the revealing frame 4 of the sides of the window 31 and with the revealing frame as a background, on the side of the window 32.

The document 10 may also include a through window 31, as shown in FIG. figure 12D , the security element 1 being located at least partially in this through window. In this way, it is possible to observe the coded images on both the front and back sides of the security document 10.

The security element 1 in the form of a security thread can still be incorporated into a security document 10 which has an alternation of windows 31 and 32 on the front and back sides, as shown in FIG. figure 12C . It is thus possible to observe the coded images of both the front side and the back side of the security document 10 at the level of the windows 31 and 32, and in particular because of the presence of the material gaps and the transparent areas 35 and 36.

We have illustrated on Figures 14 and 16 observation variants of security elements 1 that can be incorporated into a security article according to the invention. For the sake of simplicity, the security article was not represented.

The observation of the security element 1 can be done through the use of a bottom 30 on which the article comprising the security element 1 would be placed. In particular, the face 2b of the security element 1 comprising the revealing frame 4 may be in contact with the bottom 30, as shown in FIG. figure 14 . As a variant, the face 2a of the security element 1 comprising the combined image I may be in contact with the bottom 30, as illustrated in FIG. figure 15 .

In these exemplary embodiments, the revelation screen 4 is black, the combined image I is red and the background 30 is green. In this way, the observation of the security element 1 generates a significant contrast effect resulting in particular from the choice of colors of the revelation frame, the combined image and the background.

In the example of the figure 14 , the user can thus observe a revealing frame 4 of black color and a spiral of red color in contrast with the black color of the revelation frame and the green color of the bottom.

In the example of the figure 15 , the user can thus observe a revealing frame appearing as a mixture of red and black, the red color of the coded images being able to be formed by pixels, and a spiral of red color in contrast with the green color of the background and the mix of black and red colors of the revelation frame.

The contrast effect obtained can also result from the simple observation in transvision of the security element 1 near a light source 31, for example solar light, as shown in FIG. figure 16 .

We have shown on the figure 17 an alternative embodiment of a revelation frame 4 and a combined image 1 that can be used in a security element 1 of a security article 10 according to the invention.

In particular, this exemplary embodiment illustrates the possibility of producing a revelation frame 4 and a combined image I so that the coded images can be observable in the two main directions of inclination of the security element 1, especially in the sense of width and length.

The revelation weft 4 can thus result from the superposition of two frames 4a and 4b having bands extending along perpendicular axes, as can be seen in FIG. figure 17 . In the same way, the combined image I can result from the superposition of combined images Ia and Ib which respectively correspond to the combined images associated with the frames 4a and 4b.

The animation effect obtained can thus be observed in at least two directions of inclination of the security element 1.

We have shown on the figure 18 an example of a security article 10 comprising a perforation 40 in which at least two sub-elements are placed, in particular in the form of foils or patches, 41 and 42 to form a security element 1 according to the invention.

Sub-element 41 comprises, for example, a revelation frame 4 and sub-element 42 comprises, for example, the corresponding combined image I.

The sub-elements 41 and 42 can be superimposed at least partially on the borders of the perforation 40 with or without a thickness compensation.

Sub-elements 41 and 42 may be at least partially transparent or translucent.

Observation of the coded images can be done by observation in reflection or in transvision, for example using a light source located behind the article during the observation.

In the variant illustrated in figure 19 the security article 10 includes a combined image I made in the form of prints. The impressions are for example made on the surface of the security article 10. In addition, a sub-element, in particular in the form of a foil or patch, 43 is placed on the prints constituting the combined image I, the sub-element 43 comprising the frame of corresponding revelation 4, for example made on the surface of the sub-element 43.

The security article 10 may be opaque or not. The security article 10 may be at least partially transparent or translucent to allow the observation of the coded images, in particular on the side of the combined image I.

In the examples of Figures 18 and 19 the revelation frames 4 and / or the combined images I could be made differently, for example being incorporated or located above or below the sub-elements 41, 42 and 43.

In the example of the figure 20 , a security element 1 differs from that of the figure 1 in that it comprises two non-opaque, for example perfectly transparent, substrate layers 2 and two combined images I and I '. The two substrate layers here have the same thickness, for example 25 microns.

The first combined image I is arranged facing the face 2b of the security element and represents for example a pattern such as a cloud.

The second combined image I 'is disposed between the two substrate layers 2 and represents in the example in question a pattern such as a horse.

The period p of the revelation frame is in the example considered equal to the thickness of a substrate layer, that is to say to 25 microns.

The nested images I _i and I ' _i forming respectively the first and the second combined image are in the example of the figure 20 arranged in the same way so that when changing the viewing angle from the face 2a of the security element, the pattern represented by the second combined image I 'will move twice as slowly as the pattern represented by the first combined image 1 since only half as many nested images I ' _i as nested images I _i will have been visualized by the eye. This example makes it possible to demonstrate the possibility with the invention of obtaining a movement effect between the patterns represented on the nested images. Such an effect, which can still be described as "effect of depth" is for example similar to that provided by the "differential scrolling" of the first video games.

The example of figure 20 may be obtained by assembling, in particular by gluing, the different layers of substrate 2. According to another method, the example of the figure 20 is obtained from a laser-markable monolayer substrate in which at least the combined image I is formed in the substrate by exposure to laser radiation. The combined image I 'and / or the revelation screen are in particular printed or labeled by laser irradiation.

The use of the laser makes it possible to mark said laser-markable substrate at the desired depth, and also to mark said substrate at at least two different depths (thicknesses), for example to form in a monolayer substrate at least two of the elements among the weft of revelation and the combined images.

The invention is not limited to the illustrated examples. The security element can be realized with other first, second or third level security, for example.

The expression "having one" should be understood as being synonymous with "having at least one".

Claims (14)

1. A security article (10), especially a security document, comprising a security element (1) comprising an optical system, comprising:

   - a transparent or translucent substrate (2),

   - on the side of a first face (2a, 2b) of the substrate (2) a combined image (1) comprising a plurality of interleaved coded images (I₁,.., I_N),

   - on the side of a second face (2a, 2b) of the substrate (2), opposite from the first face, an exposure screen (4) overlaid on the combined image (I), making it possible to observe the coded images (I₁, ... I_N) upon a change of the direction of observation of the security element (1) in relation to the optical system, wherein
   the coded images (I₁, ... I_N) are observable from the side of the first face and from the side of the second face of the substrate (2).
2. The security article as claimed in claim 1, the security element (1) featuring in a window (31, 32) of the security article (1).
3. The security article as claimed in claim 2, the window (31, 32) being formed by one or more voids of material above or below the security element (1), the window (31, 32) being at least partially transparent or translucent on the side of the security element (1) opposite from the void of material.
4. The security article as claimed in claim 2, the window being at least partially transparent or translucent on either side of the security element (1).
5. The security article as claimed in claim 2, the window (31) being a through window.
6. The security article as claimed in any one of the preceding claims, the exposure screen (4) and/or the combined image (I) being of homogeneous aspect to the naked eye.
7. The security article as claimed in any one of the preceding claims, the exposure screen (4) and/or the combined image (I) being formed with at least two overlaid colors, the coded images being observable from the side of the first face and from the side of the second face of the substrate (2) with different colors.
8. The security article as claimed in any one of the preceding claims, comprising an alternation of optical systems associated with two mutually perpendicular respective directions of observation, especially optical systems whose respective exposure screens have perpendicular orientations.
9. The security article as claimed in any one of the preceding claims, the security element taking the form of a security thread, foil or patch.
10. The security article as claimed in any one of the preceding claims, the exposure screen (4) comprising at least one first fluorescent zone capable of emitting by fluorescence, under a predefined lighting condition, visible light of a first color, and a combined image (I) comprising at least one second fluorescent zone capable of emitting by fluorescence, under the predefined lighting condition, visible light of a second color, different from the first, at least one of the first and second fluorescent zones, especially both, being at least partially opaque, at least under the predefined lighting condition, and the first and second fluorescent zones being overlaid at least partially in such a way that, under the predefined lighting condition, light passing successively through the two fluorescent zones exhibits a third color different from the first and second colors.
11. The security article as claimed in any one of the preceding claims, the security element (1) comprising two exposure screens (4a, 4b) respectively associated with two combined images (Ia, Ib), the orientation of the strips of one of the exposure screens being different from that of the other exposure screen.
12. The security article as claimed in any one of the preceding claims, comprising a perforation (40) in which is at least partially placed the security element (1) corresponding to the juxtaposition of two sub-elements (41, 42), especially in the form of foils or patches, comprising respectively the exposure screen (4) and the corresponding combined image (I).
13. The security article as claimed in any one of claims 1 to 23, the exposure screen (4) or the combined image (I) being produced in the form of prints on the surface of the article, a sub-element (43), especially in the form of a foil or patch, overlapping at least partially the prints formed, the sub-element (43) comprising the combined image (I) or the corresponding exposure screen (4).
14. A method for authenticating a security article such as defined in any one of claims 1 to 25, comprising the step consisting in observing the security article while varying the direction of observation and concluding as to the authenticity of the article or of an object associated with the security article at least as a function of the coded images observed.

Images