METHOD OF PRODUCING A TRANSPARENT POLYCHROMATIC PRINTED IRIDESCENT IMAGE

Abstract

A method of producing a transparent polychromatic printed iridescent image (8) of any kind in which at least two colors change simultaneously when there is a change in the viewing angle of the image under illumination by at least one visible light source.

Claims

1. A method for marking, in which at least one transparent image that has at least one first pattern comprising at least one interferential pigment is printed, with at least one first pattern being formed by a first initial color at a first viewing angle under lighting by at least one visible light source, with the first initial color changing into a first final color at a second viewing angle under lighting by at least one visible light source, distinct from the first viewing angle, the method comprising: printing at least one printing composition that comprises a powder that comprises at least one interferential pigment is used, wherein said powder is dispersed with a proportion by mass in a liquid printing medium, and wherein each interferential pigment and said proportion by mass are selected in such a way that each image is transparent, with the proportion by mass of interferential pigment in the printing composition being selected so that the marking makes it possible to distinguish subjacent patterns by normal viewing, without a specific instrument, at least under lighting with visible light.

2. The method according to claim 1, wherein the proportion by mass of interferential pigment in the printing composition is between 10% and 25%.

3. The method according to claim 1, wherein at least one transparent image presents at least one second pattern that comprises at least one interferential pigment, with at least one second pattern being formed by a second initial color at a first viewing angle under lighting by at least one visible light source, and in which the second initial color changes into a second final color at a second viewing angle under lighting by at least one visible light source that is distinct from the first viewing angle.

4. The method according to claim 1, wherein at least two transparent images are printed; each transparent image is printed by using a printing composition that comprises a proportion by mass of interferential pigment in the printing composition of between 10% and 25%.

5. The method according to claim 1, wherein at least two transparent images are printed separately, one after the other, with the different transparent images formingaccording to a first angular display rangea transparent polychromatic image according to a first additive-synthesis color composition, andaccording to a second angular display rangea transparent polychromatic image according to a second color composition, distinct from the first color composition.

6. The method according to claim 3, wherein the first pattern and the second pattern are printed so that the first initial color and the second initial color are not superposed.

7. The method according to claim 6, wherein a first interferential printing pigment of the first pattern and a second interferential printing pigment of the second pattern are selected so as to make it possible to swap the first initial color into the second final color and the second initial color into the first final color, with the first initial color being essentially identical to the second final color and the second initial color being essentially identical to the first initial color.

8. A marking, with at least one transparent printed image that has at least one first pattern comprising: at least one interferential pigment of a first initial color at a first viewing angle, wherein the first initial color changes into a first final color at a second viewing angle that is distinct from the first viewing angle, with the marking making it possible to distinguish subjacent patterns by normal viewing, without a specific instrument, at least under lighting with visible light.

9. The marking according to claim 8, further comprising: at least one second transparent printed image that has at least one second pattern that comprises at least one interferential pigment and that forms a second initial color at a first viewing angle and in which the second initial color changes into a second final color at a second viewing angle that is distinct from the first viewing angle, with the marking making it possible to distinguish subjacent patterns by normal viewing, without a specific instrument, at least under lighting with visible light.

10. The marking according to claim 8, wherein at least one first transparent printed image and at least one second transparent printed image are superposed, with the marking making it possible to distinguish subjacent patterns by normal viewing, without a specific instrument, at least under lighting with visible light.

11. The marking according to claim 8, wherein at least one first transparent printed image and at least one second transparent printed image are juxtaposed, with the marking making it possible to distinguish subjacent patterns by normal viewing, without a specific instrument, at least under lighting with visible light.

12. The marking according to claim 11, wherein a first initial color changes into a first final color and a second initial color changes into a second final color, with the first initial color being essentially identical to the second final color and the second initial color is essentially identical to the first final color.

13. The marking according to claim 8, wherein an initial green color at a first viewing angle changes into a final red color at a second viewing angle that is distinct from the first viewing angle, with the marking making it possible to distinguish subjacent patterns by normal viewing, without a specific instrument, at least under lighting with visible light.

14. The marking according to claim 8, wherein an initial red color at a first viewing angle changes into a final green color at a second viewing angle that is distinct from the first viewing angle, with the marking making it possible to distinguish subjacent patterns by normal viewing, without a specific instrument, at least under lighting with visible light.

15. The marking according to claim 8, wherein an initial blue color at a first viewing angle changes into a final yellow color at a second viewing angle that is distinct from the first viewing angle, with the marking making it possible to distinguish subjacent patterns by normal viewing, without a specific instrument, at least under lighting with visible light.

16. The marking according to one of claims 8 to 15, wherein an initial yellow color at a first viewing angle changes into a final blue color at a second viewing angle that is distinct from the first viewing angle, with the marking making it possible to distinguish subjacent patterns by normal viewing, without a specific instrument, at least under lighting with visible light.

17. The marking according to one of claim 8, wherein according to a first angular display range, the different images of any type form a transparent polychromatic image according to a first composition of additive-synthesis colors, and according to a second angular display range, the different images of any type form a transparent polychromatic image according to a second color composition, distinct from the first color composition.

18. An official document comprising a marking according to claim 8, said official document being one of a passport, an identity card, a driver's license, a vehicle registration card, a fiduciary document, in particular a bank note, a check, a credit card, a trip ticket, an admission ticket, and a pass to various performances.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0089] Other objects, features and advantages of the invention will become apparent upon reading the following description, which refers to the accompanying figures showing preferred embodiments of the invention, which are given solely by way of non-limiting examples, and in which:

[0090] FIG. 1 is a diagrammatic representation showing an installation which allows a step of a method according to the invention to be carried out,

[0091] FIG. 2 is a diagram showing various steps of a method according to the invention,

[0092] FIG. 3 is a diagram showing an example of a document protected by a transparent image according to the invention, and

[0093] FIG. 4 is a diagram showing the example of the document of FIG. 3 as seen from a viewing angle of 25 relative to the plane of the transparent image.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0094] An installation for carrying out a method according to the invention shown in FIG. 1 comprises a polychromatic original image 1 colored according to the material-color principle (subtractive synthesis), visible in visible light, such as a photograph or an image printed by conventional four-color printing, which is to be reproduced with all the nuances of color and of form in order to obtain a transparent polychromatic printed iridescent image 8 of any kind in which each color changes simultaneously according to the same variation in the viewing angle under illumination by at least one visible light source. An original of the polychromatic original image 1 is illuminated by a visible light source 2 such as daylight or an incandescent lamp. The light illuminating the polychromatic original image 1 is a visible white light which is reflected by the original image 1 in the direction towards a CCD camera 3, which is connected to a microcomputer 4 allowing the images captured by the camera 3 to be stored. A bandpass filter 5 is interposed in the optical path of the reflected light. The filter 5 is chosen from at least three interference bandpass filters 5a, 5b 5c whose spectral bandwidth is less than 15 nmespecially of the order of 10 nmand whose filtering wavelength is chosen to be at least approximately equal to the wavelength of a peak of light reflected by an interference pigment under illumination in visible light, that pigment additionally being suitable for permitting the subsequent printing of an image, that is to say for being compatible with the printing means and techniques that are used, as described hereinbelow. The filtering wavelengths are chosen from the wavelengths of at least three primary colors which are able to form all the colors of the visible spectrum by additive synthesis. In particular, three wavelengths are sufficient, provided that each primary color cannot be balanced out by the other two. It is also possible to use more than three wavelengths.

[0095] The image obtained from the filter 5 is a filtered monochromatic high-contrast image. The camera 3 is, therefore, a monochrome camera. Three filtered monochromatic images 6a, 6b, 6c are produced from the same 20 polychromatic original image 1 with each of the three monochromatic filters 5a, 5b, 5c, respectively. The three filtered monochromatic images 6a, 6b, 6c are images which are digitized and stored in the computer 4. Each filtered monochromatic image 6a, 6b, 6c captured and digitized by the CCD camera 3 is recorded by the computer 4. In a variant which is not shown, the polychromatic original image can be a recorded digitized image, and digital filtering means are used to produce, by software calculation, each filtered monochromatic image 6a, 6b, 6c. It is also possible to use the digital filtering of a scanner having a transfer function suitable for the filtering wavelengths.

[0096] There are then produced, as shown in FIG. 2, from the three filtered monochromatic images 6a, 6b, 6c, three print rasters 7a, 7b, 7c plotted in the manner conventional in the field of screen printing, using, for example, a raster of from 60 to 133especially of the order of 80. The fineness of the raster is adapted according to the viscosity of the printing composition and its solids content in a manner known per se in the field of screen printing.

[0097] The print rasters 7a, 7b, 7c are each formed of a film bearing a high-contrast image whose raster dot density at each dot of the image corresponds to the light intensity of the polychromatic image 1 that is to be reproduced. In the case where a positive reproduction of the polychromatic original image 1 is to be produced, the raster dot density at each dot of the high-contrast image in the print raster that is negative corresponds to the luminous flux of the polychromatic original image 1 reflected by the interference pigment at that dot, according to each filtering wavelength. In that case, therefore, it is necessary to carry out an inversion of the filtered monochromatic images 6a, 6b, 6c, which are positives, in order to obtain negative screen printing rasters 7a, 7b, 7c. The inversion can be carried out either by image capturing software by the CCD camera 3 or with the aid of conventional image processing software starting from the digitized and recorded images, or by the processing software of the plotter permitting production of the print rasters.

[0098] In the opposite case, in which a negative reproduction of the polychromatic original image 1 is to be produced, inversion of the filtered monochromatic images 6a, 6b, 6c is not carried out, and the screen printing rasters 7a, 7b, 7c are positives.

[0099] The screen printing rasters 7a, 7b, 7c are produced on transparent films, allowing the subsequent production, for example by exposure of a photopolymer, of screen printing stencils, one for each filtered monochromatic image 6a, 6b, 6c.

[0100] Each screen printing stencil is produced, by way of non-limiting example, from a fabric whose mesh comprises from 120 to 165 threads/cm, the threads having a diameter of from 27 m to 34 m. A layer of photopolymeric material having a thickness of 18 m is used.

[0101] Each screen printing stencil accordingly represents, for each filtering wavelength, a luminous flux reflected by the polychromatic original image 1 in the filtering wavelength corresponding to the filter used, or the inverse of that luminous flux.

[0102] There are then printed, and one above the other separately, one after the other, (with or, preferably, without the interposition of a transparent intermediate layer), on a transparent print substrate 9, three printed monochromatic images, called images 8a, 8b, 8c, of the same format corresponding to the format of the polychromatic printed iridescent image 8 of any kind that is to be formed. The transparent print substrate 9 can be of any kind, provided that it is compatible with the printing technique used. For each printed monochromatic image 8a, 8b, 8c there is used the screen printing stencil produced from one of the filtered monochromatic images 6a, 6b, 6c and a transparent printing composition comprising an interference pigment whose wavelength of the reflected light peak, under illumination 2 in visible light, is equal to the filtering wavelength used to obtain said filtered monochromatic image 6a, 6b, 6c. By using in succession the three screen printing stencils corresponding to the three filtered monochromatic images 6a, 6b, 6c, the three printed monochromatic images 8a, 8b, 8c are printed in succession.

[0103] There are advantageously used as the interference pigment mineral pigmentsespecially chosen from the metallic oxideswhich are highly suitable for printing by screen printing and are resistant to the radiation of a nonvisible light source used for the employment of authentication devices (in particular, as described in WO 00245S7) and which are stable over time.

[0104] As the monochromatic filter 5 there can be used, for example, interference bandpass filters marketed by LOT ORIEL (Courtaboeuf, France) as mentioned in Table 1 below.

TABLE-US-00001 TABLE 1 Filter Filtering wavelength Color 440 FS 10-50 440 nm Blue 460 FS 10-50 460 nm Blue 480 FS 10-50 480 nm Blue 510 FS 10-50 510 nm Green 530 FS 10-50 530 nm Green 550 FS 10-50 550 nm Green 620 FS 10-50 620 nm Red 660 FS 10-50 660 nm Red

[0105] Each time a printed monochromatic image 8a, 8b, 8c is printed, the chosen interference pigment is incorporated into a liquid printing medium formed of a screen printing varnish chosen for its ability to be transparent when it is dry and illuminated by at least one visible light source. In that manner, the light of the visible light source will be able to reach and be reflected by the interference pigments contained in the printed screen printing varnish so as to be visible from the outside, without unbalancing the colors.

[0106] The printed monochromatic images 8a, 8b, 8c are transparent in visible light, so that the polychromatic printed iridescent image 8 of any kind is itself transparent to visible light and allows any underlying lettering 12 previously applied to the transparent print substrate 9 to be seen, owing to its transparency.

[0107] The three images 8a, 8b, 8c are printed on the transparent print substrate 9 preferably starting with printed image 8a, the interference pigment of which reflects, according to a first angle of visualization substantially perpendicular to the plane of each image 8a, 8b, 8c and to the plane of the print substrate 9, and under illumination in visible light, in the blue region (wavelength from 440 to 480 nm in the table above), then by printing image 8b, the interference pigment of which reflects, according to the same viewing angle, and under illumination in visible light, in the red region (wavelength from 620 to 660 nm in the table above), and finishing with printed image 8c, the interference pigment of which reflects, according to the same viewing angle, and under illumination in visible light, in the green region (wavelength from 500 to 550 nm in the table above).

[0108] Accordingly, the different printed monochromatic images 8a, 8b, 8c, according to the same viewing angle, are in the order 8a, blue, 8b, red and 8c, green, of the wavelengths of reflection, under illumination by at least one visible light source, of the blue, red and green interference pigments.

[0109] By reorientation of the polychromatic image 8 as described above according to a second angle of visualization forming, with the first angle of visualization, an angle having a value of from 10 to 45, the same polychromatic image 8S is obtained in which: [0110] printed image 8a appears, under illumination in visible light, in a yellow color according to this viewing angle, and [0111] printed image 8b appears, under illumination in visible light, in a green color according to this viewing angle, and [0112] printed image 8c appears, under illumination in visible light, in a red color according to this viewing angle.

[0113] The different printed monochromatic images 8a, 8b, 8c are printed in succession, either directly one on top of another, while observing a drying time between each layer, or by optionally interposing continuous transparent layers between them. Such a transparent layer is, for example, a layer of two-component polymerisable printing composition containing a hydroxylated polyol and an isothiocyanate or a poly-isothiocyanate in order to cause the in situ polymerisation of the mixture, yielding a thin transparent film of polyurethane, as described, for example, in EP 0 271 941 or U.S. Pat. No. 5,232,527.

[0114] All three printed monochromatic images 8a, 8b, 8c are printed using the same printing tools (the screen printing stencils used being produced from the same fabrics and with the same photopolymeric material). In particular, the printed monochromatic images 8a, 8b, 8c are printed with the same print thickness. That thickness is advantageously 25 from 3 m to 12 m according to the characteristics of the screen printing stencil used. Of course, the actual thickness of the printed monochromatic image 8a, 8b, 8c at each dot depends on the motif of the image, as is always the case in screen printing. Accordingly, for each positive printed monochromatic image 8a, 8b, 8c, the quantity of interference pigment at each dot is a function of the intensity reflected, under illumination in visible light, by the polychromatic original image 1 at that dot according to the corresponding filtering wavelength.

[0115] The screen printing varnish used, incorporating the interference pigment, is chosen so that it is not capable of emitting, by photoluminescence of the screen printing varnish, light under illumination in visible light and is not capable of unbalancing the colors of the transparent polychromatic printed iridescent image 8 of any kind.

[0116] The screen printing varnish used is advantageously a non-aqueous varnish based on volatile organic solvent(s) of the type which hardens by solvent evaporation. Such solvent(s) contained in such a screen printing varnish evaporate(s) during drying and permit(s) good adhesion of the pigments to the lower layer on which the printing composition is printed. In a variant, the screen printing varnish used can be a varnish whose polymerisation is induced by ultraviolet illumination.

[0117] There is then applied, by printing, a surface layer formed of an adhesive material suitable for permitting fixing of the transparent image 8 to a document that is to be identified and/or authenticated. After fixing of the transparent image 8 to the surface of the document 10, the outside surface layer of the transparent image 8 is formed of the transparent substrate 9. The monochromatic images 8a, 8b, 8c extend in succession from the outside surface accessible under illumination by at least one visible light source in the direction of the document 10 in the order blue, red and green.

[0118] There has been described above the production of a transparent polychromatic printed iridescent image 8 of any kind in which each color changes according to the same value of variation of a viewing angle under illumination in visible light, which image is formed by three printed monochromatic images 8a, 8b, 8c.

[0119] A transparent polychromatic printed iridescent image 8 of any kind is shown in FIG. 3 according to a first viewing angle substantially perpendicular to the plane of said transparent image 8. Such a transparent image 8 has an underlying document 10 which is to be identified and/or authenticated, on which there extend in visible manner, by way of non-limiting example, lettering 12especially written characters 12. In the front view shown in FIG. 3, the three superposed printed monochromatic images 8a, 8b, 8c do not appear. In this configuration, in which the angle of vision is substantially perpendicular to the plane of the document 10 and of the superposed printed monochromatic images 8a, 8b, 8c: [0120] a third printed monochromatic image 8c, comprising a third interference pigment, extends at the surface of and in contact with the document 10 and has a green color (indicated diagrammatically by horizontal dashes); [0121] a second printed monochromatic image 8b, comprising a second interference pigment, extends at the surface of and in contact with the third printed monochromatic image 8c and has a red color (indicated diagrammatically by oblique lines); and [0122] a first printed monochromatic image 8a, comprising a first interference pigment, extends over the free accessible face of the transparent polychromatic image 8 affixed to the document 10 and has a blue color (indicated diagrammatically by a grid of oblique dashes). The transparent print substrate 9 extends at the surface of the first printed monochromatic blue image 8a.

[0123] In this configuration, the first printed monochromatic image 8a comprising the first, blue interference pigment extends beneath the print substrate 9, close to the surface of the transparent polychromatic image 8, covering the second printed monochromatic image 8b comprising the second, red interference pigment, said second printed monochromatic image 8b covering the third printed monochromatic image 8c comprising the first, green interference pigment.

[0124] It is to be noted that, in the example of the transparent polychromatic image 8 shown in FIG. 3, the interference pigments of the three printed monochromatic images 8a, 8b, 8c are not superimposed and do not generate, by additive synthesis, new colors distinct from the colors of the three blue, red and green interference pigments. However, such a superimposition is, of course, possible and makes it possible to obtain all the colors of the visible spectrum by additive synthesis by superimposing larger or smaller portions of the three monochromatic images 8a, 8b, 8c.

[0125] The same transparent polychromatic printed iridescent image 8 of any kind is shown in FIG. 4 according to a first viewing angle oriented at 250 relative to the plane of said transparent image 8 shown in FIG. 3. Such a transparent image 8 has the same underlying document 10 as shown in FIG. 3, on which there extends, in visible manner, by way of non-limiting example, lettering 12especially written characters 12. In this configuration, in which the viewing angle is substantially at 250 relative to the plane of the document 10 and of the superposed printed monochromatic images 8a, 8b, 8c: [0126] the third printed monochromatic image 8c, comprising the third interference pigment, extends at the surface of and in contact with the document 10 and has a red color (indicated diagrammatically by oblique lines); [0127] the second printed monochromatic image 8b, comprising the second interference pigment, extends at the surface of and in contact with the third printed monochromatic image 8c and has a green color (indicated diagrammatically by horizontal dashes); and [0128] the first printed monochromatic image 8a, comprising a first interference pigment, extends beneath the transparent print substrate 9, close to the accessible free face of the transparent polychromatic image 8 affixed to the document 10, and has a yellow color (indicated diagrammatically by oblique dashes).

[0129] In this configuration, the first printed monochromatic image 8a comprising the first interference pigment of yellow color extends at the surface of the transparent polychromatic image 8, covering the second printed monochromatic image 8b comprising the second interference pigment of green color, said second printed monochromatic image 8b covering the third printed monochromatic image 8c comprising the first interference pigment of red color in this viewing angle, said third printed monochromatic image 8c being applied at the surface of the document 10 to be identified and/or authenticated.

[0130] In this configuration, the change in the viewing angle of said transparent image 8 leads to the colors red and green being interchanged and the color blue being shifted to yellow and the color yellow to blue.

Example 1

[0131] There is produced a transparent polychromatic printed iridescent image of any kind in which each color changes when there is a change in the viewing angle of said image under illumination by at least one visible light source. Such an image is formed in which a red color and a green color are interchanged when said image is reoriented at 25. Two filtered monochromatic images are printed in succession by screen printing on a transparent print substrate 9 formed of a film of the Fasprotek, Fasfilm or Transfilm type (FASVER, Baillargues, France). Each screen printing stencil is produced from a fabric whose mesh comprises 120 threads/cm, the threads having a diameter of 34 m. A first printing composition comprising 20 wt. % of a powder formed of particles of a red interference pigment (Xirallic, T60-21 SW, Solaris Red, Merck, Darmstadt, Germany), dispersed in a liquid printing medium (Solubilis, Tiflex, Poncin, 25 France), is prepared. A second printing composition comprising 20 wt. % of a powder formed of particles of a green interference pigment (Xirallic, T60-24 SW, Stellar green, Merck, Darmstadt, Germany), dispersed in a liquid printing medium (Solubilis, Tiflex, Poncin, France), is prepared in parallel. The first composition is deposited using and reproducing a first filtered monochromatic image, so as to form a first printed monochromatic transparent image. The second printing composition is then deposited on top of said first printed monochromatic transparent image, using and reproducing a second filtered monochromatic image, so as to form a second printed monochromatic transparent image superimposed on the first filtered monochromatic image and suitable for forming with the first filtered monochromatic image suitable for forming by additive synthesis all the colors of an original image. There is then printed a layer of an adhesive suitable for permitting the fixing of the transparent polychromatic printed iridescent image of any kind in which each color changes when there is a change in a viewing angle of said image under illumination by at least one visible light source to a document.

Example 2

[0132] Printing is carried out by screen printing as described in Example 1. A first printing composition comprising 20 wt. % of a powder formed of particles of a yellow interference pigment (Xirallic, T60-20 SW, Sunbeam gold, Merck, Darmstadt, Germany), dispersed in a liquid printing medium (Solubilis, Tiflex, Poncin, France), is prepared. A second printing composition comprising 20 wt. % of a powder formed of particles of a blue interference pigment (Xirallic, T60-23 SW, Galaxy blue, Merck, Darmstadt, Germany), dispersed in a liquid printing medium (Solubilis, Tiflex, Poncin, France), is produced in parallel.

Example 3

[0133] There is produced a transparent polychromatic printed iridescent image of any kind in which each color changes when there is a change in a viewing angle of said image under illumination by at least one visible light source. Such a polychromatic transparent image is formed in which a red color and a green color are interchanged while a blue color changes to a yellow color when said image is reoriented at 25. Starting from a polychromatic image obtained by subtractive synthesis, three filtered monochromatic images obtained by filtering the original image are recorded and stored in a computer memory. Such filtered monochromatic images are obtained by means of a narrow bandpass filterespecially of the order of 15 nmso as to obtain three filtered monochromatic images corresponding to the blue, red and green tones of the original image. The three filtered monochromatic images are printed in succession by screen printing on a transparent print substrate formed of a film of the Fasprotek, Fasfilm or Transfilm type (FASVER, Baillargues, France) Each screen printing stencil is produced from a fabric whose mesh comprises 120 threads/cm, the threads having a diameter of 34 m. A first printing composition comprising 20 wt. % of a powder formed of particles of a blue interference pigment (Xirallic, T60-23 SW, Galaxy blue, Merck, Darmstadt, Germany), dispersed in a liquid printing medium (Solubilis, Tiflex, Poncin, France), is prepared. A second printing composition comprising 20 wt. % of a powder formed of particles of a red interference pigment (Xirallic, T60-21 SW, Solaris Red, Merck, Darmstadt, Germany), dispersed in the same liquid printing medium (Solubilis, Tiflex, Poncin, France), is prepared. A third printing composition comprising 20 wt. % of a powder formed of particles of a green interference pigment (Xirallic, T60-24 SW, Stellar green, Merck, Darmstadt, Germany), dispersed in a liquid printing medium (Solubilis, Tiflex, Poncin, France), is also prepared. The first, blue printing composition is deposited using and reproducing the filtered monochromatic image (obtained with the filter in the blue region) so as to form a first printed monochromatic (blue) transparent image. Then the second, red printing composition is deposited on top of said first, blue printed monochromatic transparent image using and reproducing the filtered monochromatic image (obtained with the filter in the blue region) so as to form a second printed monochromatic (red) transparent image superimposed on the first filtered monochromatic (blue) transparent image. The third, green printing composition is then deposited on top of the second, red printed monochromatic transparent image using and reproducing the filtered monochromatic image (obtained with the filter in the green region) so as to form a third printed monochromatic (green) transparent image superimposed on the second filtered monochromatic (red) transparent image.

[0134] Such a superimposition of the three blue, red, green filtered monochromatic transparent images is suitable for forming, by additive synthesis, all the colors of an original image. There is then printed a layer of an adhesive suitable for permitting the fixing of the transparent polychromatic printed iridescent image of any kind in which each color changes when there is a change in a viewing angle of said image under illumination by at least one visible light source to a document.

[0135] The invention can be the subject of very many variants. In particular, it is possible to add other types of pigments in addition to the interference pigments.