Optical Structure Having a Relief Effect

Abstract

The invention relates to an optical structure (5) having a relief effect, comprising: - a support (7) adapted for aligning liquid crystals, - a deposit (9) in contact with the support of a substance in the form of at least one pattern (11), which partially covers the support, and - a liquid crystal layer (13) which at least partially covers the support and said pattern and is in contact with the support.

Claims

1-26. (canceled)

27. An optical structure with relief effect, comprising: a support suitable for aligning liquid crystals; a pattern comprising an ink or a varnish deposited on the support; and a layer of liquid crystals disposed on the support and at least partially covering the pattern.

28. The structure of claim 27, wherein the pattern is transparent and colorless in the visible range.

29. The structure of claim 27, wherein the pattern comprises the ink.

30. The structure of claim 27, wherein the pattern is a solid color.

31. The structure of claim 27, wherein a dry weight of the pattern is less than or equal to 1.5 g/m.sup.2.

32. The structure of claim 27, wherein a portion of the liquid crystals disposed in a transition zone that at least partially surrounds the pattern have a different light alignment quality than a remainder of the liquid crystals.

33. The structure of claim 27, wherein the support is transparent or translucent.

34. The structure of claim 27, wherein the support comprises an axially stretched plastic film.

35. The structure of claim 34, further comprising an adhesion primer layer disposed between the film and the layer of liquid crystals.

36. The structure of claim 27, wherein a portion of the liquid crystals directly contact the pattern.

37. The structure of claim 27, wherein: the pattern comprises nematic liquid crystals; the layer of liquid crystals comprises cholesteric liquid crystals that are configured to produce a goniochromatic effect; and a first portion of the cholesteric liquid crystals contact the pattern and a second portion of the cholesteric liquid crystals contact the support.

38. The structure of claim 37, wherein when the structure is observed in polarized light from a first observation direction: the first portion of the cholesteric liquid crystals have a first appearance; and the second portion of the cholesteric liquid crystals have a second appearance that is different from the first appearance.

39. The structure of claim 38, wherein when the structure is observed in polarized light from a second observation direction: the first portion of the cholesteric liquid crystals have a third appearance; and the second portion of the cholesteric liquid crystals have a fourth appearance that is different from the third appearance.

40. The structure of claim 39, wherein: the first appearance and the third appearance are identical; and the second appearance and the fourth appearance are identical.

41. A security element comprising the optical structure of claim 27, the security element optionally comprising at least one additional security structure.

42. A secure document comprising the optical structure of claim 27.

43. The document of claim 42, wherein the optical structure is visible on a front side and an opposing back side of the document.

44. The document of claim 42, wherein: the document comprises a fibrous substrate having a window; and the security element is disposed in the window.

45. A method for manufacturing an optical structure, the method comprising: depositing an ink comprising nematic liquid crystals on a support to form a pattern on the support; and depositing a layer of cholesteric liquid crystals on the pattern and the support, the cholesteric liquid crystals being configured to produce a goniochromatic effect.

46. The method of claim 45, wherein: the depositing of the ink comprises printing the ink on the support; and the depositing of the liquid crystal layer comprises inkjet printing, flexography, screen printing, photogravure, or typography.

47. A method for authenticating the security element of claim 44, the method comprising observing the optical structure through the window to determine whether the pattern appears as a relief image.

48. The method of claim 47, wherein the observing the optical structure comprises observing the optical structure from at least two different observation directions from a same side of the support, in order to determine whether the appearance of the pattern changes.

49. The method of claim 47, wherein the observing the optical structure comprises observing the optical structure from opposing sides of the support, in order to determine whether the pattern appears as reversed relief images.

50. The method of claim 47, wherein the observing the optical structure comprises observing polarized light radiated onto the optical structure, in order to determine whether first portion of the cholesteric liquid crystals that contact the pattern and a second portion of the cholesteric liquid crystals that contact the support have different appearances.

51. The method of claim 50, further comprising moving the optical structure, in order to determine whether there is a change in the appearances of the first portion of the cholesteric liquid crystals and the second portion of the cholesteric liquid crystals.

52. The method of claim 51, wherein the polarized light is emitted by a liquid crystal display screen.

Description

[0175] The invention will be able to be better understood on reading the following description of nonlimiting examples of implementation thereof, and on studying the attached drawing in which

[0176] [FIG. 1] FIG. 1 schematically represents a top view of an example of an optical structure according to the invention,

[0177] [FIG. 2] FIG. 2 represents a cross section on I-I of FIG. 1,

[0178] [FIG. 3] FIGS. 3a-d illustrate different relief visual effects observed for different lighting directions,

[0179] [FIG. 4] FIG. 4 is a cross section of a variant element,

[0180] [FIG. 5] FIG. 5 is a cross section of another variant embodiment,

[0181] [FIG. 6] FIG. 6 is a cross section of another variant embodiment,

[0182] [FIG. 7] FIG. 7 represents a front view of a secure document according to the invention,

[0183] [FIG. 8] FIG. 8 is a cross section of another example of a secure document,

[0184] [FIG. 9] FIG. 9 is a photograph of an example of PET coated with an ink deposit,

[0185] [FIG. 10] FIG. 10 is a photograph of an example of an optical structure produced from the coated film of FIG. 9,

[0186] [FIG. 11] FIG. 11 is a photomontage of halves of the photographs of FIGS. 10 and 11 according to a same scale,

[0187] [FIG. 12] FIG. 12 is a photograph acquired in optical microscopy in polarized light of a part of the optical structure of FIG. 11,

[0188] [FIG. 13] FIG. 13 is a photograph of another example of coated film performing an optical structure,

[0189] [FIG. 14] FIG. 14 is a photomontage of a photograph of the optical structure produced from the coated film of FIG. 13 and of a corresponding part of the photograph of FIG. 13,

[0190] [FIG. 15a] FIG. 15a is a photograph of the front of an example of an optical structure,

[0191] [FIG. 15b] FIG. 15b is a photograph of the back of the optical structure of FIG. 15a,

[0192] [FIG. 16a] FIG. 16a is a photograph of an example optical structure lit according to a lighting direction,

[0193] [FIG. 16b] FIG. 16b is a photograph of the optical structure of FIG. 16a lit according to another lighting direction,

[0194] [FIG. 16c] FIG. 16c is a photomontage comprising the left and right portions respectively of the photographs of FIGS. 16a and 16c and a central portion corresponding to the central portion of FIGS. 16a and 16c not coated by the layer of liquid crystals,

[0195] [FIG. 17a] FIG. 17a is a photograph of an example of optical structure observed in non-polarized light,

[0196] [FIG. 17b] FIG. 17b is a photograph of the optical structure of FIG. 17a observed in polarized light, and

[0197] [FIG. 17c] FIG. 17c is a photograph of the optical structure of FIG. 17a observed in polarized light after rotation by 90° about an axis normal to the support.

[0198] In the figures, the constituent elements of the structure are not necessarily represented to scale, in the interests of clarity.

[0199] FIGS. 1 and 2 illustrate an example of an optical structure 5 according to the invention, which comprises a support 7, a deposit 9 of a substance on the support to form a pattern 11, and a layer of liquid crystals 13.

[0200] The substance is for example an ink printed on the support by means of a thermal or piezoelectric ink-jet printer. It partially covers the face 15 of the support on which it is deposited. In the example of FIGS. 1 and 2, the pattern has a circular form, but any other form can be considered, for example a series of alphanumeric symbols, notably a currency, a landscape, a person or a monument.

[0201] The deposit 9 is in contact with the support 7 and the layer of liquid crystals.

[0202] When observed according to at least one observation direction D.sub.1, the optical structure has a relief visual effect, notably in a transition zone 17 delimited by the pattern 11 and extending around the pattern. In the transition zone 17, the layer of liquid crystals can be in contact with the support 7. The transition zone 17 extends between a first zone 19 in which the liquid crystals are superposed on, notably in contact with, the substance of the deposit 9 and a second zone 21 in which the liquid crystals are in contact with the support 7. The alignment quality of the liquid crystals in the transition zone 17 can thus be different from the alignment quality of the liquid crystals in the first 19 and second 21 zones.

[0203] When the optical structure is lit by means of the light radiation E.sub.1g which comprises a component, parallel to the support, oriented from the left edge 23 toward the opposite right edge 25 of the deposit 9, a part 27 of the transition zone in contact with the right edge, delimited by the broken lines in FIG. 3a, can appear light, and notably have a specular glossy appearance. A part of the transition zone 29 in contact with the left edge, delimited schematically by broken short lines in FIG. 3a, can appear dark, and notably matt.

[0204] When the optical structure is by means of the light radiation E.sub.2g, oriented like the radiation E.sub.1g from the left edge 23 toward the right edge 25 of the deposit 9, and having an incidence, with respect to the support, different from the light radiation E.sub.1g, the part 27 of the transition zone appears light as illustrated in FIG. 3b, the appearance being able to be different from that observed in FIG. 3a, and the appearance of the part 29 of the transition zone has changed with respect to that observed by means of the lighting E.sub.1g. Notably the part 29 appears lighter than when lit according to the direction E.sub.1g. In particular, it can have a specular glossy appearance.

[0205] Moreover, the first 19 and second 21 zones can have goniochromatic effects, which can be substantially identical, when lit by means of the light radiations E.sub.1g and E.sub.2g.

[0206] When the optical structure is lit by means of the light radiations E.sub.1d and E.sub.2d oriented in directions opposite to the radiations E.sub.1g and E.sub.2g, that is to say from the right edge 25 toward the left edge 23 of the deposit, the observed effects are reversed, as illustrated schematically in FIGS. 3c and 3d. The part 27 of the transition zone appears dark and the part 29 appears light when lit according to the direction E.sub.1d, and the part 27 appears lighter when lit according to the direction E.sub.2d.

[0207] The optical structure can comprise a dark background 31, as illustrated in FIG. 4. The dark background can take the form of an opaque layer 33, covering the face 35 of the support opposite the face 15 in contact with which the deposit and the layer of liquid crystals are disposed. The opaque layer is, for example, a print of a black ink or a metallization. It is superposed at least partly with the deposit and the layer of liquid crystals. Thus, when observed on the side of the support where the liquid crystals are disposed as indicated by the arrow D2, the visibility of the liquid crystals is improved and the relief effect is amplified.

[0208] As a variant, as illustrated in FIG. 5, the dark background 31 is disposed on the opposite side of the support which is translucent, or preferably transparent It is in contact with the layer of liquid crystals 13. The dark background 31 and the support 7 sandwich the layer of liquid crystals and the deposit Thus, the relief effect is amplified when the optical structure is observed on the side of the support opposite the side coated by the deposit, as indicated by the arrow D.sub.3.

[0209] The example illustrated in FIG. 6 differs from that illustrated in FIG. 4 in that the optical structure comprises another transparent film 37, for example made of PET, which is fixed, for example pasted, on the semi-opaque dark background. The optical structure also comprises a metalized layer 39 provided with at least one recess 41, produced for example by selective demetallization and opening through to the other film 37. Thus, the optical structure provides a relief visual effect when observed on the side of the support coated with the layer of liquid crystals and the deposit. It obtains another visual effect, when observed on the other side of the support, the metalized layer having a glossy appearance according to at least one direction, and the dark background being discernible through the recess or recesses.

[0210] FIG. 7 represents a secure document 45, in the form of a banknote, comprising a fibrous substrate 47, for example made of paper, and a security element 49 in the form of a security wire extending in window(s) between two edges 53, 55 of the substrate 47. The security wire comprises a part inserted into the mass of the substrate, represented by broken lines, and another part disposed in a window 57 appearing on the surface of the fibrous substrate 47. The security wire contains the optical structure, the deposit 9 being disposed in the window 57. The pattern 11 can be located elsewhere on the document, for example in an identical form 58.

[0211] FIG. 8 represents another example of a secure document 45, in the form of a banknote, comprising a fibrous substrate 47, for example made of paper, and a security element 49 in the form of a security film extending between two edges 53, 55 of the substrate 47 and at least partially covering an opening 60 passing right through the thickness of the substrate 47. The security film contains the optical structure, the deposit 9 being at least partially, for example totally, superposed on the opening 60. The pattern 11 can be located elsewhere on the document, for example in an identical form 58.

[0212] The optical structure can comprise a background, as illustrated in FIGS. 4 and 5. As a variant, as represented in FIG. 8, the optical structure can be as according to the example illustrated in FIG. 1 and the secure document can be disposed facing a standalone dark background 31 to amplify the relief visual effect.

EXAMPLES

Example 1

[0213] A film of Sarafil S56C reference polyester PET marketed by the company Polyplex was chosen. It has a surface texture suitable for the alignment of the liquid crystals. The Sarafil S56C film is a bi-stretched film coated with a co-polyester-based adhesion primer.

[0214] Several optical structures were produced by forming deposits of a yellow ink or of a cyan ink by ink-jet printing on a face of the film.

[0215] The yellow ink has the reference C8766[Y] and is printed by means of an HP6540 reference ink-jet printer. The cyan ink has the reference C8766[C] and is printed by means of an HP6540 reference ink-jet printer.

[0216] Prints are produced with different inking rates and, for each deposit, the dry weight of the ink deposit is measured by weighing. Table 1 summarizes the results of these measurements, and those of the measurements of the color of the film alone and of each deposit, in accordance with the ISO 5631-1 standard. It also mentions the saturation difference ΔC and the clarity difference ΔL between the support film and the deposit The values C* and L* correspond to the values of the measurements of saturation and of clarity of the deposits and of the uncoated film.

TABLE-US-00001 Inking rate Deposited dry weight (g/m.sup.2) L* C* h ΔL ΔC Film 0% 0 89.5 4.8 113.8 / / Yellow 20% 0.10 89.3 13.3 105.7 -0.2 8.5 60% 0.40 87.3 48.2 99.1 -2.2 43.4 100% 0.80 85.4 71.2 94.5 -4.1 66.4 Cyan 20% 0.05 84.6 10.6 195.5 -4.9 5.8 60% 0.25 75.0 30.0 211.2 -14.5 25.2 100% 0.80 63.2 50.4 218.0 -26.3 45.6

[0217] The various coated samples were then dried for 5 minutes at a temperature of 60° C.

[0218] Moreover, the samples of film coated with the different deposits are printed with an ink with liquid crystals with 576 nm yellow/green goniochromatic effect marketed by the company BASF under the reference Lumogen S ink 6525T.

[0219] The deposition of the liquid crystal ink is performed to a thickness of between 2 and 3 microns to the coating bar. The liquid crystals were then aligned during the drying of the ink under blown hot air then set by UV cross-linking.

[0220] The most accentuated relief visual effects were observed for the deposits having an inking rate of at least 60%.

[0221] FIGS. 9 to 16 are photographs illustrating the relief effects obtained for different optical structures comprising deposits of yellow ink with an inking rate of 60%.

[0222] FIG. 9 is a photograph of a zone of a Sarafil S56C film coated with a deposit of yellow ink forming a rosette pattern on the Sarafil S56C film and FIG. 10 is a photograph of the same zone coated by the layer of liquid crystals. The zone has a height of 10 mm and a width of 13 mm. As can be seen, the contours 59 of the pattern appear in relief. Transition zones are defined around each portion of the pattern. Parts 17.sub.1 of the transition zones 17 appear dark and matt while others 17.sub.2 appear light and glossy, visually suggesting a print of depth.

[0223] FIG. 12 is a photograph acquired by optical microscopy in non-polarized light of a part of the optical structure, in which a transition zone 17 with a width of approximately 300 .Math.m extends between a first zone 19 in which the ink is in contact with the support and a second zone 21 in which the liquid crystals are in contact with the support. The analysis by optical microscopy in non-polarized light informs on the alignment of the liquid crystals. Thus, the density of the domains informs on the alignment of the liquid crystal or crystals imaged. As can be seen in FIG. 12, domains 18a-c are observed, within which the alignment of the liquid crystals varies little. The size of the domains is different between the transition zone and the first and second zones. In other words, the number of domains per unit of surface area is different between the transition zone and the first and second zones. It appears notably that the domains are of greater dimensions in the zone 17, which indicates that the alignment quality of the crystals is better there than in the first and second zones.

[0224] The deposit photographed in FIG. 13 is discontinuous and defines a pattern in the form of an animal. A relief visual effect is observed, as observed in FIG. 14, which, by superimposing the photograph of the optical structure with that of the support coated with just the deposit, makes it possible to view precisely the position of the transition zones, notably with respect to the contour of the patterns.

[0225] FIG. 15a is a photograph of another example of an optical structure, seen from a front side of the support and FIG. 15b is a photograph of the optical structure seen from the opposite back side of the support. The transition zones that appear in relief on the back side appear depressed on the front side and vice versa.

[0226] A dynamic effect appears, illustrated by means of the photographs presented in FIGS. 16a-c.

[0227] An example of an optical structure lit according to a first direction is photographed in FIG. 16a. The component of the lighting direction in the plane of the support is oriented from the bottom to the top of the page of FIG. 16. Portions 17.sub.1 of the transition zones extending around the edges of the printed patterns oriented downward appear dark and portions 17.sub.2 around the edges of the same patterns oriented upward appear bright. Moreover, the first 19 and second 21 zones have different colors, notably slightly different.

[0228] When it is lit according to a second direction different from the first direction, the visual appearance of the optical structure changes. The portions of the transition zones which appear dark, respectively bright, in FIG. 16a, appear bright, respectively brighter, in FIG. 16b. Moreover, an effect of change of color is observed in the first and second zones. They have two color hues that vary gradually yellow green according to the angle of observation and/or of illumination.

Example 2

[0229] A film of Sarafil S56C reference polyester PET marketed by the company Polyplex was chosen. It has a surface texture suited to the alignment of the liquid crystals. The Sarafil S56C film is a bi-stretched film coated with a co-polyester-based adhesion primer.

[0230] An optical structure was produced by forming a deposit of a black ink by ink-jet printing on a face of the film.

[0231] The black ink has the reference Liojet AP-KB027-K and is printed by means of a Kyocera KJ4B-1200 reference piezoelectric print head.

[0232] The duly coated film was then dried for 5 minutes at a temperature of 60° C.

[0233] Moreover, the coated film was printed with an ink with liquid crystals with 576 nm yellow/green goniochromatic effect marketed by the company BASF under the reference Lumogen S ink 6525T.

[0234] The deposition of the liquid crystal ink was performed to a thickness of between 2 and 3 microns, to the coating bar. The liquid crystals were then aligned during the drying of the ink under blown hot air then set by UV cross-linking.

[0235] A black ink was deposited on the back of the coated film in order to serve as dark background to augment the visibility of the liquid crystals.

[0236] An intense relief effect was obtained by authentication of the face printed with the liquid crystals.

Example 3

[0237] A film of Sarafil S56C reference polyester PET marketed by the company Polyplex was chosen. It has a surface texture suited to the alignment of the liquid crystals. The Sarafil S56C film is a bi-stretched film coated with a co-polyester-based adhesion primer.

[0238] An optical structure was produced by forming a deposit of a black ink by flexographic printing on a face of the film.

[0239] The black ink has the reference Liojet AP-KB027-K. Its viscosity was modified by the addition of 0.35% of a cellulosic derivative marketed by the company Shin Etsu under the reference Tylose HS100000YP2. The application was performed by means of a Flexiproof 100 flexographic applicator from the company Rk Print.

[0240] The duly coated film was then dried for 5 minutes at a temperature of 60° C.

[0241] Moreover, the coated film was printed with an ink having liquid crystals with 576 nm yellow/green goniochromatic effect marketed by the company BASF under the reference Lumogen S ink 6525T.

[0242] The deposition of the liquid crystal ink was performed to a thickness of between 2 and 3 microns, to the coating bar. The liquid crystals were then aligned during the drying of the ink under blown hot air then set by UV cross-linking.

[0243] A black ink was deposited on the back of the coated film in order to serve as dark background to augment the visibility of the liquid crystals.

[0244] An intense relief effect was obtained by authentication of the face printed with the liquid crystals.

Example 4

[0245] A film of Sarafil S56C reference polyester PET marketed by the company Polyplex was chosen. It has a surface texture suited to the alignment of the liquid crystals. The Sarafil S56C film is a bi-stretched film coated with a co-polyester-based adhesion primer.

[0246] An optical structure was produced by forming a deposit of an ink comprising nematic liquid crystals by ink-jet printing on a face of the film.

[0247] The ink has the reference Lumogen Hide N700 and is printed by photogravure.

[0248] The duly coated film was then dried for 5 minutes at a temperature of 105° C. to align the liquid crystals. The alignment was then set by UV cross-linking.

[0249] Moreover, the coated film was printed with an ink with liquid crystals with 576 nm yellow/green goniochromatic effect marketed by the company BASF under the reference Lumogen S ink 6525T.

[0250] The deposition of the liquid crystal ink was performed to a thickness of between 2 and 3 microns, to the coating bar. The liquid crystals were then aligned during the drying of the ink under blown hot air, then set by UV cross-linking.

[0251] An intense relief effect was obtained by authentication of the face printed with the liquid crystals, as can be seen in FIG. 17a.

[0252] Moreover, the optical structure was placed between an LCD screen and an observer in order to detect another optical effect in polarized light. As a variant, an unpolarized light source and a polarizing filter can be used. The optical structure can be placed between the unpolarized light source and the polarizing filter and the observer can look at the optical structure through the polarizing filter.

[0253] As can be seen in FIG. 17b, according to a first configuration of observation of the optical structure, the zone 19 in which the pattern comprising the nematic crystals and the layer of cholesteric liquid crystals are superposed has a blue color and the zone 21 in which the cholesteric liquid crystals are in contact with the support has a pink color.

[0254] After rotation of the optical structure by 90° with respect to the support, a change appearance of each of the zones 19 and 21 is observed, in the form of a reversal of colors. The zone 19 has a pink color and the zone 21 has a blue color.

[0255] The invention is not limited to the examples described.

[0256] In particular, the invention is also suitable for producing coatings or decorative objects.

[0257] When the invention is applied to the production of security documents, the optical structure according to the invention can be present on security elements other than a security wire.

[0258] It is very particularly advantageous for the pattern of the optical structure to be located elsewhere on the document, in an identical form or to a different scale, or in any other recognizable form, the observer being able to recognize the link that exists between the pattern of the structure and that which appears elsewhere.