OPTICAL EFFECT DEVICE

Abstract

OPTICAL EFFECT DEVICE The invention relates to an optical effect device (300) comprising: a substrate (302) having a first surface (304) and a second surface (306); a plurality of structures (308) arranged on the first surface (304), each structure (308) having a first facet (310) and a second facet (314), the first facet (310) of each structure (308) being essentially parallel to the first surface (304) of the substrate (302), the second facet (314) of each structure (308) defining a slope with respect to the first surface (304), and the first facets (310) of the plurality of structures (308) forming a first set of facets. The first set of facets defines a first optical effect when the optical effect device (300) is viewed from a first range of viewing angles. Figure 1

Description

Title of the invention: OPTICAL EFFECT DEVICE Technical field

[0001] The invention relates generally to the field of optical effect devices, in particular optical security devices, for example those used on banknotes.

[0002] BACKGROUND OF THE INVENTION

[0003] It is well known that a large number of banknotes worldwide, as well as other security documents, carry optical devices, which serve as security features for authentication purposes. Some optical security features produce optical effects that may vary depending on the range of viewing angles or require a predetermined optical illumination source in order to reveal the optical effects. Incorporating such optical security features into security documents therefore acts as a deterrent against counterfeiting of the document.

[0004] Some optical security devices, for example, lenticular images, interlaced images, stereograms, integral images, magnifying moiré patterns, and the like, suffer from a number of similar problems. For example, limited pixel resolution, pixel addressability, and the registration of different colors relative to each other. The physical size of lenses used in a security device application is usually determined by a number of factors, including the drop height of the lens and the focal length of the lens (closely related to the thickness of the material on which the lens will be formed and the distance from the focusing surface, usually on the obverse of the lens).

[0005] Problems concerning high resolution images and color registration (especially multi-color images) have been addressed in the past by different methods.

[0006] One method involves using diffractive imaging elements, where colors are created by diffraction elements located in a single surface. With this method, different colors are produced by varying the spacing between parallel elements of the diffraction grating to preferentially diffract a wavelength of light at a given viewing angle.

[0007] Another method uses plasmonic structures on which conductive surfaces with sub-wavelength periodic structures are created, so that standing (resonant) waves of a particular frequency are created between the structures.

[0008] Another method involves using a laser to modify the structures of the interference layers in a vacuum-deposited multilayer structure.

[0009] Another method is to create a structural color by mixing chiral and nematic liquid crystals. While the use of these two materials has long been known to create color pairs at a given angle, the color created is achieved by controlling the ratio of the liquid crystal pair. The helical pitch of the materials is controlled by the ratio of the two materials, which creates the perceived color pair. OPSEC Security (www.opsecurity.com) has created a process that controls the pitch by controlling the amount of exposure to a given frequency of light. As the quantum of light increases, the color shifts from one end of the spectrum to the other. It is envisioned that this effect could be achieved by using a grayscale mask to control the amount of light exposure.

[0010] All these methods suffer from certain drawbacks.

[0011] With the diffractive imaging method, the color of the image varies depending on the range of viewing angles. The efficiency of diffraction varies depending on the size of the pixels and, importantly, when used with a lens, the device only works when the diffraction gratings are at 90 degrees to the direction of the lens, i.e., it only works with cylindrical lenses and not with round lenses, which limits this effect to a single plane.

[0012] Plasmonic devices require highly conductive metal surfaces to operate effectively. They generally have relatively low color intensity and tend to produce soft hues rather than bright colors. Their ability to be integrated into a high-speed manufacturing process is limited due to the high aspect ratio of the structures as well as, typically, the need to metallize the structure in a vacuum to achieve the required surface conductivity.

[0013] The current process using interference layers requires that the multi-layer refractive stack be produced using a magnetron deposition process. Each individual pixel must then be written separately using a laser. This limits the technology to batch processing with a very slow write rate (even though the laser can have relatively high write speeds, a large number of pixels would require tens of seconds of writing for each image, or even minutes).

[0014] The UV nematic-cholesteric pair by way of light exposure presents the additional complexity of having to control not only the degree of light exposure through a mask but also the aging of the light source as a function of time. Any variation will result in a variation in the color of the images. This requires that the device to be exposed be correctly aligned with the surface of a material on which it is deposited, which further complicates the manufacturing process.

[0015] At least preferred embodiments of the present invention provide an optical device and a method for forming the same, which address one or more limitations of the prior art, or at least provide an alternative choice for the general public. Summary of the invention

[0016] According to a first aspect, the present invention provides an optical effect device, comprising:

[0017] a substrate having a first surface and a second surface;

[0018] a plurality of structures arranged on the first surface, each structure having a first facet and a second facet, the first facet of each structure being substantially parallel to the first surface of the substrate, the second facet of each structure defining a slope relative to the first surface, and the first facets of the plurality of structures forming a first set of facets,

[0019] the first set of facets defining a first optical effect when the optical effect device is viewed from a first range of viewing angles.

[0020] In one embodiment, each structure has a third facet and a fourth facet, the third facet of each structure being substantially parallel to the first surface of the substrate, the fourth facet of each structure being directed in a second direction and defining a slope relative to the first surface of the substrate, the third facets of the plurality of structures forming a second set of facets that defines a second optical effect when the optical effect device is viewed at a second range of viewing angles.

[0021] In one embodiment, the optical effect device further comprises a surface structure disposed on one or more of the second facets and fourth facets of the plurality of structures.

[0022] In one embodiment, the optical effect device further comprises a surface structure disposed on one or more of the first facets and third facets of the plurality of structures.

[0023] According to a second aspect, the present invention provides an optical effect device comprising:

[0024] a substrate having a first surface and a second surface;

[0025] a first plurality of structures arranged on the first surface of the substrate, the first plurality of structures having a first in-plane orientation relative to the first surface of the substrate, each structure of the first plurality of structures having a facet that is directed in a first direction, the facets of the first plurality of structures forming a first facet set; and

[0026] a second plurality of structures arranged on the first surface of the substrate, the second plurality of structures having a second in-plane orientation relative to the first surface of the substrate, each structure of the second plurality of structures having a facet that is directed in a second direction, the facets of the second plurality of structures forming a second set of facets,

[0027] the first set of facets defining a first optical effect when the optical effect device is viewed from a first range of viewing angles and the second set of facets defining a second optical effect when the optical effect device is viewed from a second range of viewing angles.

[0028] In one embodiment, the optical effect device further comprises a third plurality of structures arranged on the first surface of the substrate, the third plurality of structures having a third in-plane orientation relative to the first surface of the substrate, each structure of the third plurality of structures having a facet that is directed in a third direction, the facets of the third plurality of structures forming a third set of facets that defines a third optical effect when the optical effect device is viewed from a third range of viewing angles.

[0029] In one embodiment, each facet of each of the first plurality of facets, second plurality of facets, and third plurality of facets defines a slope relative to the first surface of the substrate.

[0030] In one embodiment:

[0031] the structures of the first plurality of structures are arranged at locations on the first surface of the substrate corresponding to pixels of the first optical effect;

[0032] the structures of the second plurality of structures are arranged at locations on the first surface of the substrate corresponding to pixels of the second optical effect; and

[0033] the structures of the third plurality of structures are arranged at locations on the first surface of the substrate corresponding to pixels of the third optical effect.

[0034] In one embodiment, the difference between the in-plane orientation of the first plurality of structures and that of the second plurality of structures is 120 degrees and the difference between the in-plane orientation of the second plurality of structures and that of the third plurality of structures is 120 degrees.

[0035] In one embodiment, the optical effect device further comprises a surface structure disposed on one or more of the first plurality of facets, the second plurality of facets, and / or the third plurality of facets.

[0036] According to a third aspect, the present invention provides an optical effect device comprising:

[0037] a substrate having a first surface and a second surface;

[0038] a plurality of structures arranged on the first surface, each structure having a first facet, the first facets of the plurality of structures forming a first set of facets, and the first set of facets defining a first optical effect when the optical effect device is viewed at a first range of viewing angles;

[0039] each structure corresponding to a pixel of the first optical effect, each pixel of the first optical effect having a scalar value corresponding to a shadow of the pixel in the first optical effect, and each structure being modulated according to the scalar value of the relative pixel.

[0040] In one embodiment, the first facet of each structure defines a slope having an angle relative to the first surface of the substrate and, for each structure, the angle of the slope of the first facet is modulated according to the scalar value of the respective pixel.

[0041] In one embodiment, each structure has an in-plane orientation relative to the first surface of the substrate and the in-plane orientation of each structure is modulated based on the scalar value of the respective pixel.

[0042] In one embodiment, the optical effect device further comprises a surface structure disposed on one or more of the first facets of the plurality of structures.

[0043] In one embodiment, each surface structure is a diffraction grating.

[0044] According to a fourth aspect, the present invention provides an optical effect device comprising:

[0045] a substrate having a first surface and a second surface;

[0046] a first plurality of structures arranged on the first surface, each structure of the first plurality of structures having a first facet that is directed in a first direction and a second facet that is directed in a second direction, the first facets of the first plurality of structures forming a first set of facets, and the second facets of the first plurality of structures forming a second set of facets,

[0047] the first set of facets defining a first optical effect when the optical effect device is viewed at a first range of viewing angles and the second set of facets defining the first optical effect when the optical effect device is viewed at a second range of viewing angles.

[0048] In one embodiment:

[0049] each structure of the first plurality of structures has a third facet;

[0050] for each structure of the first plurality of structures, the third facet is directed in a third direction;

[0051] the third facets of the first plurality of structures form a third set of facets; and

[0052] the third set of facets defines the first optical effect when the optical effect device is viewed from a third range of viewing angles.

[0053] In one embodiment, the optical effect device further comprises a second plurality of structures, each structure of the second plurality of structures having a first facet that is directed in a fourth direction and a second facet that is directed in a fifth direction,

[0054] the first facets of the second plurality of structures forming a fourth set of facets that defines a second optical effect when the optical effect device is viewed at a fourth range of viewing angles; and

[0055] the second facets of the second plurality of structures forming a fifth set of facets which defines the second optical effect when the optical effect device is viewed at a fifth range of viewing angles.

[0056] In one embodiment:

[0057] each structure of the second plurality of structures has a third facet;

[0058] for each structure of the second plurality of structures, the third facet is directed in a sixth direction;

[0059] the third facets of the second plurality of structures form a sixth set of facets; and

[0060] the sixth set of facets defines the second optical effect when the optical effect device is viewed from a sixth range of viewing angles.

[0061] In one embodiment:

[0062] the structures of the first plurality of structures are arranged at locations on the first surface of the substrate corresponding to pixels of the first optical effect; and

[0063] the structures of the second plurality of structures are arranged at locations on the first surface of the substrate corresponding to pixels of the second optical effect.

[0064] In one embodiment, the first plurality of structures has a first in-plane orientation relative to the first surface of the substrate and the second plurality of structures has a second in-plane orientation relative to the first surface of the substrate.

[0065] In one embodiment, the in-plane orientation of the first plurality of structures is perpendicular to the in-plane orientation of the second plurality of structures.

[0066] In one embodiment, each optical effect is visible from viewing positions located on the same side as the first surface and the second surface of the substrate.

[0067] In one embodiment, each optical effect is visible in reflection and transmission.

[0068] In one embodiment, the substrate and each structure are made of a transparent material.

[0069] In one embodiment, the substrate is made of an opaque material.

[0070] In one embodiment, each structure is made of a resin radiation curable.

[0071] In one embodiment, each structure is embossed in the radiation-curable resin.

[0072] In one embodiment, the optical effect device further comprises a reflective layer disposed on the plurality of structures.

[0073] In one embodiment, the reflective layer is comprised of a metallic ink.

[0074] In one embodiment, the optical effect device further comprises a protective layer disposed over the plurality of structures.

[0075] In one embodiment, the protective layer is a high refractive index layer.

[0076] In one embodiment, the reflective layer forms a first face of the optical effect device.

[0077] In one embodiment, the protective layer forms a first face of the optical effect device.

[0078] In one embodiment, the first face is planar.

[0079] In one embodiment, each optical effect is a binary image or a raster binary image.

[0080] According to a fifth aspect, the present invention provides a security document comprising a security element in the form of an optical effect device according to any one of the above aspects.

[0081] In one embodiment, the security device is arranged in a half-window or full window of the security document.

[0082] In one embodiment, the security document is a banknote. Security Document or Token

[0083] As used herein, the terms "security documents" and "tokens" include all types of valuable documents and tokens and identification documents including, but not limited to, the following documents: currency items such as banknotes and coins, credit cards, checks, passports, identification cards, stock and share certificates, driver's licenses, property deeds, transportation documents such as airline or train tickets, admission cards and tickets, birth, death and marriage certificates, and transcripts.

[0084] The invention applies in particular, but not exclusively, to security documents or tokens such as banknotes or identification documents such as identity cards or passports formed from a substrate on which one or more printing layers are applied. The diffraction gratings and optically variable devices described herein may also have application in other products, such as packaging. Safety device or feature

[0085] As used herein, the terms "security device or feature" include any of a variety of security devices, elements, or features intended to protect the security document or token from counterfeiting, copying, alteration, or falsification.Security devices or features may be embodied in or on the substrate of the security document or in or on one or more layers applied to the base substrate, and may take a wide variety of forms, such as security threads embedded in layers of the security document; security inks such as fluorescent, luminescent and phosphorescent inks, metallic inks, iridescent inks, photochromic, thermochromic, hydrochromic or piezochromic inks; printed and embossed features, including relief structures; interference layers; liquid crystal devices; lenses and lenticular structures; optically variable devices (OVDs) such as diffractive devices including diffraction gratings, holograms, diffractive optical elements (DOEs). Substrate

[0086] As used herein, the term "substrate" refers to the base material from which the security document or token is formed. The base material may be paper or other fibrous material, such as cellulose; a plastic or polymeric material including, but not limited to, polypropylene (PP), polyethylene (PE), polycarbonate (PC), polyvinyl chloride (PVC), polyethylene terephthalate (PET); or a composite material of two or more materials such as a laminate of paper and at least one plastic material, or two or more polymeric materials. Transparent windows and half-windows

[0087] As used herein, the term "window" refers to a transparent or translucent area in the security document as compared to the substantially opaque region to which the print is applied. The window may be completely transparent so that it transmits light substantially unaltered, or it may be partially transparent or partially translucent allowing light transmission but not allowing objects to be seen clearly through the window area.

[0088] A window area may be formed in a polymeric security document that has at least one layer of transparent polymeric material and one or more opacifying layers applied to at least one side of a transparent polymeric substrate, by omitting at least one opacifying layer in the region forming the window area. If opacifying layers are applied to both sides of a transparent substrate, a fully transparent window may be formed by omitting the opacifying layers on both sides of the transparent substrate in the window area.

[0089] A partly transparent or translucent area, hereinafter referred to as a "half-window", may be formed in a polymeric security document which has opacifying layers on both sides by omitting the opacifying layers on only one side of the security document in the window area, such that the "half-window" is not totally transparent, but allows some light to pass through without allowing objects to be seen clearly through the half-window.

[0090] Alternatively, it is possible for the substrates to be formed from a substantially opaque material, such as paper or fibrous material, with a transparent plastic material insert inserted into a cutout or recess formed in the paper or fibrous substrate to form a transparent window or translucent half-window area. Opacifying layers

[0091] One or more opacifying layers may be applied to a transparent substrate to increase the opacity of the security document. An opacifying layer is such that LT < Lo, where Lo is the amount of light incident on the document and L; is the amount of light transmitted through the document. An opacifying layer may comprise any one or more of various opacifying coatings. For example, the opacifying coatings may comprise a pigment, such as titanium dioxide, dispersed in a binder or carrier of heat-activated, crosslinkable polymeric material. Alternatively, a substrate of transparent plastic material could be sandwiched between opacifying layers of paper or of another partially or essentially opaque material on which marks can subsequently be printed or otherwise applied. Refractive index n

[0092] The refractive index n of a medium is the ratio of the speed of light in a vacuum to the speed of light in the medium. The refractive index n of a lens determines the amount by which light rays reaching the surface of the lens will be refracted, according to Snell's law: n % Sin(a) = n*Sin (0)' °where a is the angle between an incident ray and the normal to the point of incidence on the surface of the lens, 0 is the angle between the refracted ray and the normal to the point of incidence, and ni is the refractive index of air (as an approximation, ni can be taken equal to 1). Radiation-curable ink

[0093] The term "radiation-curable ink" as used herein refers to any ink, lacquer, or other coating that can be applied to the substrate in a printing process, and that can be printed or embossed in a soft, or semi-soft, state to form a relief structure and cured by radiation to secure the relief structure. The curing process typically does not occur until the radiation-curable ink has been printed or embossed, but it is possible for the ink to be partially cured (semi-soft), in some processes, before printing or embossing, and also for the curing process to occur either after printing or embossing, or substantially concurrently with the printing or embossing step. The radiation-curable ink is preferably curable by ultraviolet (UV) radiation.Alternatively, the radiation-curable ink may be cured by other forms of radiation, such as electron beams or X-rays. References to UV-curable ink(s) in the remainder of the description are by way of example. All embodiments are substitutable for inks curable by other radiations, so long as they meet the criteria required by the embodiment (such as viscosity before curing). Similarly, a reference to UV lamps reflects that the description refers to UV-curable inks. If an electron-beam-curable ink is used, then clearly an electron-beam device will be used instead of the UV lamps.

[0094] The radiation-curable ink is preferably a transparent or translucent ink made of a clear resin material. Such a transparent or translucent ink is particularly suitable for printing light-transmitting security features such as subwavelength gratings, transmissive diffraction gratings, and lenticular structures.

[0095] The transparent or translucent ink preferably comprises a clear, acrylic-based, UV-curable lacquer or coating. Such UV-curable lacquers may be obtained from various manufacturers, including Kingfisher Ink Limited, ultraviolet type product UVF-203 or the like. Alternatively, the radiation-curable coatings may be based on other compounds, for example nitrocellulose.

[0096] The radiation-curable inks or lacquers used herein have been found to be particularly suitable for printing or embossing microstructures, including diffractive structures such as diffraction gratings and holograms, and microlens and lens arrays. However, they may also be printed or embossed with larger relief structures, such as non-diffractive optically variable devices.

[0097] The ink is preferably embossed and cured by ultraviolet (UV) radiation at essentially the same time.

[0098] Preferably, to be suitable for gravure printing, which is the preferred method for applying the radiation-curable ink, which is then embossed, the radiation-curable ink has a viscosity substantially between about 20 and about 175 centipoise, and more preferably between about 30 and about 150 centipoise. The viscosity can be determined by measuring the time required to empty the lacquer from a No. 2 Zahn Cup. A sample that empties in 20 seconds has a viscosity of 30 centipoise, and a sample that empties in 63 seconds has a viscosity of 150 centipoise.

[0099] With some polymeric substrates, it may be necessary to apply an intermediate layer to the substrate prior to application of the radiation-curable ink, to improve the adhesion of the structure formed by the ink to the substrate. The intermediate layer preferably comprises a primer layer, and more preferably the primer layer comprises a polyethyleneimine. The primer layer may also include a crosslinking agent, for example, a multifunctional isocyanate. Examples of other primers suitable for use in the invention include: hydroxyl-terminated polymers; copolymers based on a hydroxyl-terminated polyester; crosslinked or uncrosslinked hydroxylated acrylates; polyurethanes; and UV-curable anionic or cationic acrylates.Examples of suitable crosslinking agents include: isocyanates; polyaziridines; zirconium complexes; aluminum acetylacetone; melamines; and carbodiimides. Brief description of the drawings

[0100] Embodiments of the invention will now be described with reference to the accompanying drawings. It will be understood that the embodiments are given for the purpose of illustration only and that the invention is not limited to this illustration. In the drawings:

[0101] [Fig-1] is an isometric view of an optical effect device according to a first embodiment of the present invention;

[0102] [Fig.2] is a side view of the optical effect device of [Fig.l];

[0103] [Fig.3] is an example of an optical effect projected by the optical effect device of the [Fig.l];

[0104] [Fig.4] is another example of an optical effect projected by the optical effect device of [Fig.l];

[0105] [Fig.5] is a variation of the optical effect device of [Fig.l];

[0106] [Fig.6] is another variation of the optical effect device of [Fig.l];

[0107] [Fig.7] is another variation of the optical effect device of [Fig.l];

[0108] [Fig.8A] illustrates how the maximum thickness of the structures of the optical effect device of the Figure can be reduced;

[0109] [Fig.8B] illustrates how the maximum thickness of the structures of the optical effect device of the Figure can be reduced;

[0110] [Fig.9] is a top view of a physical embodiment of the optical effect device of [Fig.l];

[0111] [Fig. 10] is a top view of another physical embodiment of the optical effect device of [Fig.l];

[0112] [Fig. 11] is a top view of another physical embodiment of the optical effect device of [Fig.l];

[0113] [Fig. 12] is an isometric view of an optical effect device according to a second embodiment of the present invention;

[0114] [Fig. 13] is a top view of the optical effect device of [Fig. 12];

[0115] [Fig. 14] shows the general viewing angle ranges of the optical effects of the device optical effect of [Fig. 12];

[0116] [Fig. 15] is a top view of an optical effect device according to a third embodiment of the present invention;

[0117] [Fig. 16] is a sectional view of the optical effect device of [Fig. 15], taken along line 15-15 shown in [Fig. 15];

[0118] [Fig. 17] is a variant of the optical effect device of [Fig. 15];

[0119] [Fig.18] is another variant of the optical effect device of [Fig.15];

[0120] [Fig. 19] is a top view of an optical effect device according to a fourth embodiment of the present invention;

[0121] [Fig.20] is a sectional view of the optical effect device of [Fig. 19], taken along of line 19-19 shown in [Fig. 19];

[0122] [Fig.21] is a top view of an optical effect device according to a fifth embodiment of the present invention;

[0123] [Fig.22] is an enlarged view of the optical effect device of [Fig.21];

[0124] [Fig.23] is a top view of an optical effect device according to a sixth form of carrying out the present invention;

[0125] [Fig.24] is a sectional view of the optical effect device of [Fig.23], taken along of line 23-23 shown in [Fig.23];

[0126] [Fig.25] is a top view of an optical effect device according to a seventh embodiment of the present invention;

[0127] [Fig.26] is a partial side view of the optical effect device of [Fig.25];

[0128] [Fig.27] is a top view of one of the structures of the optical effect device of [Fig.25];

[0129] [Fig.28] is an isometric view of the structure of [Fig.27];

[0130] [Fig.29A] shows the black and white pixels of each of two optical effects produced by the arrangement of structures shown in [Fig.25];

[0131] [Fig.29B] shows the black and white pixels of each of two optical effects produced by the arrangement of structures shown in [Fig.25];

[0132] [Fig.30] illustrates how multiple structures such as that of [Fig.26] can be arranged in the optical effect device of [Fig.25] to produce a three-permutation optical effect;

[0133] [Fig.31] is a top view of an optical effect device according to an eighth embodiment of the present invention;

[0134] [Fig.32] shows the viewing angle ranges and projection angle ranges of the structures of the optical effect device of [Fig.31];

[0135] [Fig.33] shows the projection angles of the image channels of the effect device optics of [Fig.31];

[0136] [Fig.34] is a side view of the optical effect device of [Fig.l] having a clear protective layer or a reflective layer disposed on the structures, the clear protective layer or the reflective layer defining a planar face of the optical effect device of [Fig.l]; and

[0137] [Fig.35] is a security document having a security device, the device of safety being any of the optical effect devices described herein.

[0138] DESCRIPTION OF A PREFERRED EMBODIMENT

[0139] For the purposes of the following discussion, the figures should be considered illustrative and not to scale unless otherwise noted. The figures illustrate simplified representations of the described embodiments.

[0140] "Incident light" or "incident illumination" is light from a light source falling on one side of the substrate, and is generally considered to be unpolarized white light (e.g., light from an incandescent or fluorescent light source), unless otherwise stated.

[0141] A "visual effect" is a visually identifiable image, pattern, or other effect. A visual effect may be a covert visual effect, which is visible only under certain conditions, or an overt visual effect, which is visible under normal viewing conditions. A visual effect may also be a diffractive visual effect or a non-diffractive visual effect.

[0142] As used herein, the term "color" refers to a color as perceived and may correspond to a single wavelength range or a mixture of different wavelength ranges.

[0143] It should be noted that, throughout this description, the term "multicolor" is used to mean at least two colors and, preferably, a wide range of different colors. Furthermore, if a polarization image shows, for example, a pattern, a number or an icon, then the pattern, number or icon must itself comprise a plurality of different colors to be considered a multicolor image.

[0144] First examples of embodiments of the invention

[0145] [Fig.l] shows an optical effect device 100 in the form of a security device according to a first embodiment of the present invention. As shown in [Fig.2], the optical effect device 100 comprises a substrate 102 having a first surface 104 and a second surface 106.

[0146] Arranged on the first surface 104 of the substrate 102 are a plurality of structures 108 having a maximum thickness t. Each structure 108 has a first facet 110 directed in a first direction and a second facet 112 directed in a second direction, which is different from the first direction. The first facets 110 of the plurality of structures 108 together form a first set of facets that defines a first image channel having a first range of projection angles and the second facets 112 of the plurality of structures 108 form a second set of facets that defines a second image channel having a second range of projection angles. The first facet 110 of each structure 108 is adjacent to the second facet 112 of an adjacent structure 108 such that the first facets 110 are interlaced with the second facets 112.Each first facet 110 defines a slope forming an angle [3 relative to the first surface 104 of the structure 102 and each facet 112 defines a slope forming an angle co relative to the first surface 104 of the substrate 102. .

[0147] On each first facet 110 are arranged one or more diffraction gratings 114 and on each second facet 112 are arranged one or more diffraction gratings 116. As best seen in [Fig.l], the lines of the diffraction gratings 114, 116 extend parallel to the direction of the maximum slope of the respective facets 110, 112. In other words, the lines of the diffraction gratings 114 arranged on the first facets 110 extend in a direction parallel to the angle [3 and the lines of the diffraction gratings 116 arranged on the second facets 112 extend in a direction parallel to the angle co.It is however also contemplated that the lines of each diffraction grating 114, 116 may be oriented in other directions according to the desired viewing angle ranges of the respective first and second image channels, for example in a direction extending along the length of the respective first facet 110, 112 (e.g., in the Y direction in [Fig.l]) or at an angle to the direction of the maximum slope of the respective facet 110, 112. .

[0148] Referring to Figures 1, 2 and 3, when the first set of facets is viewed at a first range of viewing angles indicated generally by arrow 10, the diffraction gratings 114 disposed on the first facets 110 define a first optical effect, for example, a rectangular shape as illustrated in [Fig. 3]. Referring to Figures 1, 2 and 4, when the second set of facets is viewed at a second range of viewing angles indicated generally by arrow 12, the diffraction gratings 116 disposed on the second facets 112 define a second optical effect, for example, a cross as illustrated in [Fig. 4]. It will be understood that the first and second optical effects may be any desired image.

[0149] As best seen in [Fig. 2], the first viewing angle range 10 and the second viewing angle range 12 provide observation positions that are located on the same side as the first surface 104 of the substrate 102. The first optical effect and the second optical effect may also be visible from observation positions located on the same side as the second surface 106 of the substrate 102, if the substrate 102 and the structures 108 are made of a transparent material. In this case, the first and second optical effects may be visible from the same side as the second surface 106, from observation positions having a viewing angle range respectively generally indicated by the arrows 14 and 16.

[0150] The optical effect device 100 thus interlaces two images (namely the first and second optical effects) which can be projected towards an observer according to a corresponding one-dimensional set of viewing angle ranges, thereby sampling the first and second optical effects along a single axis. will therefore understand that the optical effect device 100 provides a dual visual optical effect.

[0151] It is also contemplated that only facets of one of the facet sets (i.e., the image channels) may have diffraction gratings. In this case, it will be understood that the optical effect device 100 provides an image disappearance effect.

[0152] The general structure of the embodiments of the optical effect device 100 is described below: • The structures 108 may be made of a transparent material, for example, a radiation-curable resin (described in more detail below); • The substrate 102 may also be transparent and in the form of a sheet (as for application to a security document) or a polymer substrate (for example, a polymer substrate for a banknote); • The structures 108 may be covered with a clear protective layer that may have a different refractive index than the material used to form the structures 108. The clear protective layer may be sufficiently thick to prevent mechanical copying (i.e., contact copying) of the structures 108 (described in more detail below); and • Alternatively, the structures 108 may be covered with a reflective layer. The reflective layer may be sufficiently thick to prevent mechanical copying (i.e., contact copying) of the structures 108. Alternatively, the reflective layer may be thin and covered with a clear protective layer that is sufficiently thick to prevent mechanical copying (i.e., contact copying) of the structures 108.

[0153] If the structures 108 are not covered with a reflective layer or are covered with a semi-transparent reflective layer, the first and second optical effects can be seen in transmission as well as in reflection. In this case, the first optical effect can be visible from observation positions located on the same side as the first surface 104 having viewing angle ranges respectively indicated generally by the arrows 10 and 12 (see [Fig. 2]). Similarly, the second optical effect can be visible from an observation position located on the same side as the second surface 106 having viewing angle ranges respectively indicated generally by the arrows 14 and 16 (see [Fig. 2]). This will also be the case if the structures 108 are covered with a thin reflective layer (e.g., of a thickness less than the maximum thickness of the structures 108, but thick enough to prevent almost 。 completely the transmission of light), however, in this case the first and second optical effects will only be visible in reflected light.

[0154] If the structures 108 are covered with a thick reflective layer so that mechanical copying of the structures 108 can be prevented / limited, the first and second optical effects will only be visible in reflection from observation positions located on the same side as the second surface 106 having viewing angle ranges respectively generally indicated by the arrows 14 and 16 (see [Fig.2]).

[0155] If the structures 108 are not covered with a reflective layer, when the optical effect device 100 is viewed in reflected or transmitted diffuse white light, the first and second optical effects are observed in black and white and, when the optical effect device 100 is rotated about the Y axis, or offset from the light source, the observed optical effects switch between the first and second optical effects. When the optical effect device 100 is viewed in reflected or transmitted white light that is at least partially collimated, or that comes from a point source, the first and second optical effects are observed in multiple colors and, when the optical effect device 100 is rotated about the Y axis, or offset from the light source, the observed optical effects switch between the first and second optical effects.

[0156] By properly selecting the grating frequency, depth, and line orientation of the diffraction gratings 114, 116, the first and second optical effects projected by the respective first and second image channels at a particular angle may be a true color image. For example, the grating frequency, depth, and line orientation of the diffraction gratings 114, 116 may be selected such that they project a two-dimensional array of RGB color image pixels such that the first and second sets of facets each define a desired color image to be viewed at a particular angle with substantially collimated white light. The images defined by the respective diffraction gratings 114, 116 of each set of facets could have multiple tones of one or more desired colors.

[0157] It is also contemplated that the substrate 102 may be made of an opaque material (e.g., a foil or banknote polymer) and that the structures 108 may be made of a transparent material (e.g., a radiation-curable resin). In this case, it will be understood that the optical effects will only be visible in reflection from viewing positions located on the same side as the first surface 104 of the substrate 102. The visibility of the effects optics can in this case be improved by covering the structures 108 with a thin reflective layer.

[0158] The diffraction gratings 114, 116 may be arranged on the respective first and second facets 110, 112, such that the first and / or second image channels define: • a binary image of a monochromatic “silhouette”; • a halftone raster binary image; or • a rasterized binary image.

[0159] According to one embodiment of the optical effect device 100, each structure 108 has a maximum thickness t of 6 microns and each facet 110, 112 may have a width of 25 microns. It is, however, contemplated that the structures 108 and the facets 110, 112 may have other dimensions. Each diffraction grating 114, 116 may have a period of 1.2 pm to 3.2 pm, however, other periods are also contemplated depending on the colors that are desired to be seen from the respective diffraction gratings 114, 116.

[0160] [Fig. 5] shows an optical effect device 110a that is similar to the optical effect device 100, except that each structure 108a of the optical effect device 100a has a third facet 122a directed in a third direction, which is different from the first and second directions. The third facets 122a of the plurality of structures 108a together form a third set of facets that defines a third image channel having a third range of projection angles. Similar to what has been described above in connection with the optical effect device 100, at least one diffraction grating may be disposed on one or more of the third facets 122a, such that the third set of facets defines a third optical effect when viewed from the same side as the first surface 104a, from an observation position having a range of viewing angles indicated generally by the arrow 18a.The third viewing angle range 18a is different from the first and second viewing angle ranges. Similar to the optical effect device 100, if the substrate 102a and the structures 108a are made of a transparent material, the third optical effect may be visible from the same side as the second surface 106, from an observation position having a viewing angle range generally indicated by the arrow 20a.

[0161] [Fig. 6] shows an optical device 100b that is similar to the optical effect device 100, except that each structure 108b of the optical effect device 100b has a third facet 122b directed in a third direction and a fourth facet 124b directed in a fourth direction. The third direction and the fourth direction are different from each other and from the first and second directions. The third facets 122b of the plurality of structures 108b form together a third set of facets that defines a third image channel having a third projection angle and the fourth facets 124b of the plurality of structures 108b together form a fourth set of facets that defines a fourth image channel having a fourth projection angle. Similar to what was described above in connection with the optical device 100, at least one diffraction grating may be disposed on one or more of the third facets 122b and the fourth facets 124b.

[0162] The third set of facets of the optical effect device 100b defines a third optical effect when viewed from the same side as the first surface 104b, from an observation position having a viewing angle range generally indicated by the arrow 18b. The fourth set of facets of the optical effect device 100b defines a fourth optical effect when viewed from the same side as the first surface 104b, from an observation position having a viewing angle range generally indicated by the arrow 22b. The third viewing angle range and the fourth viewing angle range are different from each other and from the first and second viewing angle ranges.Similar to optical effect device 100, if substrate 102b and structures 108b are made of a transparent material, the third and fourth optical effects may be visible from the same side as second surface 106b, from observation positions having viewing angle ranges generally indicated by arrow 20b and arrow 24b, respectively.

[0163] Other structural variants described in relation to Figures 1 to 4, in particular in relation to the properties of the substrate and the structural layers and the presence or otherwise of different protective and / or refractive / reflective layers, also apply to the embodiments of Figures 5 and 6, and in fact to all other embodiments described below.

[0164] [Fig.7] shows an optical effect device 100c which is similar to the optical effect device 100b, except that the configuration of the structures 108c of the optical effect device 100c is different from the configuration of the structures 108b of the optical effect device 100b. In particular, the configuration of the first facet 110c, second facet 112c, third facet 122c and fourth facet 124c of each structure 108c is different from the configuration of the first facet 110b, second facet 112b, third facet 122b and fourth facet 124b of each structure 108b. The operation, behavior of the optical effects, and viewing angle ranges of the optical effects of the optical effect device 100c are similar to those of the optical effect device 100b.

[0165] Figures 8A and 8B show the optical effect device 100 and an optical effect device 100d, respectively. Figures 8A and 8B illustrate how the thickness maximum t of each structure 108 can be reduced. With reference to [Fig.8B], each facet 110 of [Fig.8A] is subdivided into two smaller facets 110a, 110b and each facet 112 of [Fig.8A] is subdivided into two smaller facets 112a, 112b. The angle [3 of the slope defined by each facet 110a, 110b in [Fig.8B] is equal to the angle [3 of the slope defined by each facet 110 in [Fig.8A]. The angle co of the slope defined by each facet 112a, 112b in [Fig.8B] is equal to the angle co of the slope defined by each facet 112 in [Fig.8A]. Facets 110a, 110b define the first image channel and facets 112a, 112b define the second image channel. The operation, behavior of the optical effects, and viewing angle ranges of the optical effects of the optical effect device 100d are similar to those of the optical effect device 100.It will be understood that the maximum thickness of the structures 108 of the optical effect device 100 can be further reduced by subdividing the facets 110, 112 into two more smaller facets.

[0166] According to one embodiment of the optical effect device 100d, each structure 108 has a maximum thickness of 3 microns and each facet 110a-b, 112a-ba has a width of 12.5 microns.

[0167] Practical examples of the optical effect device 100

[0168] [Fig.9] shows a first practical example of the optical effect device 100e in which the first image channel (i.e., the first facets 110) and the second image channel (i.e., the second facets 112) each define a monochromatic "silhouette" binary image. The lines of the diffraction gratings 114, 116 extend in a direction parallel to the direction of the maximum slope of the respective facet 110, 112.

[0169] If the structures 108 are not coated with a reflective layer, when viewing the optical effect device 100e in transmission with the structures 108 oriented horizontally (i.e., extending along the X-axis), a double-visual optical effect is observed when the optical effect device 100e is moved up or down in the Y-direction, or from left to right in the X-direction, offset from a light source. When viewing the optical effect device 100e in reflection with the structures 108 oriented horizontally (i.e., extending along the X-axis), a double-visual optical effect is observed when the optical effect device 100e is tilted about the X-axis.In transmission and reflection, when observing the first and second optical effects of the 100e optical effect device, the first and second optical effects appear in gray scale when viewed in diffuse white light and appear in multiple colors when viewed in at least partially collimated white light or white light emanating from a point source.

[0170] [Fig. 10] shows a second practical example of the optical effect device 1 lOf wherein the first image channel (i.e., the first facets 110) and the second image channel (i.e., the second facets 112) each define a monochromatic "silhouette" binary image. The lines of the diffraction gratings 114, 116 extend in a direction perpendicular to the direction of maximum slope of the respective facets 110, 112 (i.e., in the X direction along the length of the respective facet 110, 112). The behavior of the first and second optical effects of the optical effect device lOOf is similar to the behavior of the first and second optical effects of the optical effect device 100e. However, the color contrast of the first and second optical effects of the optical effect device lOOf was lower compared to the color contrast of the first and second optical effects of the optical effect device 100e.

[0171] [Fig. 11] shows a third practical example of the optical effect device 100g in which the first image channel (i.e., the first facets 110) and the second image channel (i.e., the second facets 112) each define a halftone raster binary image. The behavior of the first and second optical effects of the optical effect device 100g is similar to the behavior of the first and second optical effects of the optical effect device 100e.

[0172] If the structures 108 are not coated with a reflective layer, when viewing the optical effect device 100g in transmission and reflection, the first and second optical effects of the optical effect device 100g contain multiple gray tones when viewed in diffuse white light and multiple color tones when viewed in at least partially collimated white light. The multiple gray and color tones visible in the first and second optical effects of the optical effect device 100g may be obtained using halftone image patterns.

[0173] Second exemplary embodiment of the invention

[0174] [Fig. 12] shows an optical effect device 200 in the form of a device of security according to a second embodiment of the present invention. The optical effect device 200 comprises a substrate 202 having a first surface 204 and a second surface 206.

[0175] A plurality of structures 208 are arranged on the first surface 204 of the substrate 202, each structure 208 having nine facets 210. Each facet 210 of each structure 208 is directed in a different direction and has a unique slope and / or orientation (i.e., a unique vector gradient) relative to the first surface 204 of the substrate 202.

[0176] [Fig. 13] is a top view of the optical effect device 200 in which each facet 210 of each structure 208 has been numbered from 1 to 9. The facets 210 having the same number are all directed in the same direction to form a set of facets that defines an image channel having a unique range of projection angles. For example, the facets 210 numbered "1" in the plurality of structures 208 are all directed in the same direction to form a first set of facets that defines a first image channel having a first range of projection angles. It will therefore be understood that the optical effect device 200 has nine sets of facets that each define an image channel having a unique range of projection angles.

[0177] A diffraction grating 212 is disposed on one or more facets 210 of each set of facets. The lines of each diffraction grating 212 extend in a direction parallel to the slope of the respective facet 210. In other words, the lines of each diffraction grating 212 extend in the direction of the maximum slope of the respective facet 210.However, it is also contemplated that the lines of each diffraction grating 212 may be oriented in other directions depending on the desired viewing angle ranges for the respective image channels, for example, in a direction extending perpendicular to or at an angle to the direction of maximum slope of the respective facet 210. Each diffraction grating 212 may have a period of 1.2 pm to 3.2 pm, however, other periods are also contemplated depending on the colors desired to be seen from the respective diffraction grating 212. It is also contemplated that all facets 210 of one or more of the facet sets may have no diffraction gratings 212.

[0178] With reference to Figures 12 and 14, each image channel has a unique viewing angle range. For example, the first image channel (i.e., the facets 210 labeled "1" in each of the structures 208) has a viewing angle range generally indicated by the line numbered "1" in [Fig. 14]. Accordingly, each of the lines numbered 1 through 9 in [Fig. 14] indicates a general viewing angle range for each respective image channel.

[0179] When each image channel is viewed from its respective range of viewing angles, the diffraction gratings 212 disposed on the one or more facets 210 of the respective set of facets define an optical effect. For example, when the first image channel (i.e., the facets 210 labeled "1" in each of the structures 208) is viewed from the first range of viewing angles (i.e., generally indicated by the numbered line "1" in [Fig. 14]), the diffraction gratings 212 disposed on the one or more facets 210 of the first set of facets define a first optical effect.

[0180] The optical effect device 200 thus interlaces nine two-dimensional images (e.g., in the X and Y dimensions) that can be projected toward an observer along a corresponding set of viewing angle ranges, thereby enabling the effects optics to be displayed when the device is rotated around more than one axis relative to a light source.

[0181] The general structure of the embodiments of the optical effect device 200 is described below: • The structures 208 may be made of a transparent material, for example, a radiation-curable resin (described in more detail below); • The substrate 202 may also be transparent and in the form of a sheet (as for application to a security document) or a polymer substrate (for example, a polymer substrate for a banknote); • The structures 208 may be covered with a clear protective layer that may have a different refractive index than the material used to form the structures 208. The clear protective layer may be sufficiently thick to prevent mechanical copying (i.e., contact copying) of the structures 208 (described in more detail below); and • Alternatively, the structures may be coated with a reflective layer. The reflective layer may be sufficiently thick to prevent mechanical copying (i.e., contact copying) of the structures 208. Alternatively, the reflective layer may be thin and coated with a clear protective layer that is sufficiently thick to prevent mechanical copying (i.e., contact copying) of the structures 208.

[0182] If the structures 208 are not covered with a reflective layer or are covered with a semi-transparent reflective layer, the optical effects can be seen in transmission as well as in reflection. In this case, the optical effects can be seen from respective observation positions located on the same side as the first surface 204 having viewing angle ranges indicated generally by the numbered lines 1 to 9 (see [Fig. 14]) and on the same side as the second surface 206 having viewing angle ranges indicated generally by the numbered lines 1' to 9' (see [Fig. 14]).This will also be the case if the structures 208 are covered with a thin reflective layer (e.g., of a thickness less than the maximum thickness of the structures 208, but thick enough to almost completely prevent the transmission of light), however, in this case, the optical effects will only be visible in reflected light.

[0183] If the structures 208 are covered with a thick reflective layer so that mechanical copying of the structures 208 can be prevented / limited, the optical effects will only be visible in reflection from observation positions located on the same side as the second surface 206 having viewing angle ranges generally indicated by lines 1' to 9' (see [Fig. 14]).

[0184] If the structures 208 are not covered with a reflective layer, when viewing the optical effect device 200 in reflected or transmitted diffuse white light, the optical effects are observed in black and white and, when the optical effect device 200 is rotated about the X and / or Y axes, or offset from the light source, the observed optical effects change over the relevant viewing angle range. When viewing the optical effect device 200 in reflected or transmitted white light that is at least partially collimated, or that comes from a point source, the optical effects are observed in multiple colors and, when the optical effect device 200 is rotated about the X and / or Y axes, or offset from the light source, the observed optical effects change over the relevant viewing angle range.

[0185] By properly selecting the grating frequency, depth, and line orientation of the diffraction gratings 212, the optical effects projected by each set of facets of the optical effect device 200 at a particular angle can be a true color image. For example, the grating frequency, depth, and line orientation of the diffraction gratings 212 can be selected such that they project a two-dimensional array of RGB color image pixels such that each set of facets defines a desired color image to be viewed at a particular angle with substantially collimated white light. The image defined by the diffraction gratings 212 of each set of facets of the optical effect device 200 could have multiple tones of one or more desired colors.

[0186] It is also contemplated that the substrate 202 may be made of an opaque material (e.g., a foil or banknote polymer) and that the structures 208 may be made of a transparent material (e.g., a radiation-curable resin). In this case, it will be understood that the optical effects will only be visible in reflection from viewing positions located on the same side as the first surface 204 of the substrate 202. The visibility of the optical effects may in this case be enhanced by covering the structures 208 with a thin reflective layer.

[0187] The diffraction gratings 212 may be arranged on one or more facets 210 of each set of facets such that the respective image channel defines: • a binary image of a monochromatic “silhouette”; • a halftone raster binary image; or • a rasterized binary image.

[0188] Although the structures 208 of the optical effect device 200 have been described and illustrated as having nine facets 210, it will be understood that the structures 208 of the optical effect device 200 may have more or less than nine facets 210.

[0189] It is also contemplated that the thickness of each structure 208 may be reduced using the approach described above relative to the optical effect device 100d.

[0190] Third exemplary embodiment of the invention

[0191] Figures 15 and 16 respectively show a top view and a sectional view of an optical effect device 300 in the form of a security device according to a third embodiment of the present invention. The optical effect device 300 comprises a substrate 302 having a first surface 304 and a second surface 306.

[0192] A plurality of structures 308 are arranged on the first surface 304 of the substrate 102. Each structure 308 has one or more first facets 310, one or more second facets 312, a third facet 314 and a fourth facet 316. For each structure 308, the one or more first facets 310 and the one or more second facets 312 are substantially parallel to the first surface 304 of the substrate 302 and are directed in a first direction. In other words, none of the first facets 310 and none of the second facets 312 define a slope relative to the first surface 304 of the substrate 302. All of the first facets 310 of all of the structures 308 together form a first set of facets that defines a first image channel and all of the second facets 312 of all of the structures 308 together form a second set of facets that defines a second image channel. [Fig.16] shows that the first facets 310 of each structure 308 are arranged at the bottom of the structure 308. Similarly, the second facets 312 of each structure 308 are also arranged at the bottom of the structure 308.

[0193] For each structure 308, the third facet 314 is directed in a second direction and the fourth facet 316 is directed in a third direction. As best seen in [Fig. 16], the first, second and third directions are all different from each other. For each structure 308, the third facet 314 defines a slope having an angle [3 relative to the first surface 304 of the substrate 302 and the fourth facet 316 defines a slope having an angle co relative to the first surface 304 of the substrate 302.

[0194] When the first set of facets is viewed at a first viewing angle range generally indicated by arrow 30 in [Fig. 16], the first set of facets defines a first optical effect and, when the second set of facets is viewed at a second viewing angle range generally indicated by arrow 32 in [Fig. 16], the second set of facets defines a second optical effect. With reference to [Fig. 16], the first viewing angle range 30 and the second viewing angle range 32 provides viewing positions that are located on the same side as the first surface 304 of the substrate 302.

[0195] The general structure of the embodiments of the optical effect device 300 is described below: • Structures 308 may be made of a transparent material, for example, a radiation-curable resin (described in more detail below); • The substrate 302 may also be transparent and in the form of a sheet (as for application to a security document) or a polymer substrate (for example, a polymer substrate for a banknote); • The structures 308 may be covered with a clear protective layer that may have a different refractive index than the material used to form the structures 308. The clear protective layer may be sufficiently thick to prevent mechanical copying (i.e., contact copying) of the structures 308 (described in more detail below); and • Alternatively, the structures 308 may be covered with a reflective layer. The reflective layer may be sufficiently thick to prevent mechanical copying (i.e., contact copying) of the structures 308. Alternatively, the reflective layer may be thin and covered with a clear protective layer that is sufficiently thick to prevent mechanical copying (i.e., contact copying) of the structures 308.

[0196] If the structures 308 are not covered with a reflective layer or are covered with a semi-transparent reflective layer, the first and second optical effects can be seen in transmission as well as in reflection. In this case, the first optical effect can be visible from observation positions located on the same side as the first surface 304 having viewing angle ranges respectively generally indicated by the arrows 30 and 32 (see [Fig. 16]). Similarly, the second optical effect can be visible from an observation position located on the same side as the second surface 306 having viewing angle ranges respectively generally indicated by the arrows 34 and 36 (see [Fig. 16]).This will also be the case if the structures 308 are covered with a thin reflective layer (e.g., of a thickness less than the maximum thickness of the structures 308, but thick enough to almost completely prevent the transmission of light), however, in this case, the first and second optical effects will only be visible in reflected light.

[0197] If the structures 308 are covered with a thick reflective layer so that mechanical copying of the structures 308 can be prevented / limited, the first and second optical effects will only be visible in reflection from observation positions located on the same side as the second surface 306 having viewing angle ranges respectively generally indicated by the arrows 34 and 36 (see [Fig. 16]).

[0198] Each first facet 310 and each second facet 312 may correspond to a foreground pixel (picture element), or a background pixel, of a binary image pattern. The first and second optical effects (i.e., images) may be obtained by applying a dithering algorithm. For example, amplitude modulation or frequency modulation dithering may be used to introduce a grayscale image, which may allow high-contrast optical effects with a simulated grayscale to be projected to the viewer.

[0199] The first and second optical effects of the optical effect device 300 may be projected toward an observer according to a corresponding one-dimensional set of viewing angle ranges, thereby sampling the optical effects along a single axis. It will therefore be understood that the optical effect device 300 provides a dual-visual optical effect.

[0200] When the optical effect device 300 is viewed in reflected or transmitted diffuse white light, the first and second optical effects are observed in black and white and, when the optical effect device 300 is rotated and / or tilted relative to the light source, the observed optical effects switch between the first and second optical effects.

[0201] It is also contemplated that the optical effect device 300 may project a plurality of optical effects toward an observer over a two-dimensional array of viewing angle ranges by implementing the structures 308 with a shape and configuration similar to those of the structures 208 illustrated in [Fig. 12]. For example, in this case, the structures 308 will be similar to the structures 208 but will have one or more facets 210 of each set of facets substantially parallel to the first surface 304 of the substrate 302.

[0202] Although [Fig. 16] shows that the first facets 310 are disposed at the bottom of each structure 308, as indicated by the solid line, it is also contemplated that the first facets 310 may be disposed at the top of each respective structure 308, as indicated by the broken lines. Similarly, the second facets 312 may also be disposed at the top of each respective structure 308. [Fig. 17] shows a top view of an optical effect device 300a that is similar to the optical effect device 300, except that the first facets 310 and the second facets 312 of each structure 308 of the optical effect device 300a are disposed at the top of each respective structure 308. The optical behavior of the first and second optical effects of the optical effect device 300a is similar, otherwise identical to the optical behavior of the first and second optical effects of the optical effect device 300.

[0203] It is also contemplated that the substrate 302 may be made of an opaque material (e.g., a foil or banknote polymer) and that the structures 308 may be made of a transparent material (e.g., a radiation-curable resin). In this case, it will be understood that the optical effects will only be visible in reflection from viewing positions located on the same side as the first surface 304 of the substrate 302. The visibility of the optical effects may in this case be enhanced by covering the structures 308 with a thin reflective layer.

[0204] Each image channel of the optical effect device 300, 300a can be designed so as to define: • a binary image of a monochromatic “silhouette”; • a halftone raster binary image; or • a rasterized binary image.

[0205] [Fig. 18] shows an embodiment of an optical effect device 300b which is similar to the optical effect device 300a, except that the diffraction gratings 318 are arranged on the third facets 314 and fourth facets 316 of the structures 308 of the optical effect device 300b. The lines of the diffraction grating 318 extend in a direction parallel to the slope of the respective facet 314, 316. In other words, the lines of each diffraction grating 318 extend in the direction of the maximum slope of the respective facet 314, 316. It is, however, also contemplated that the lines of each diffraction grating 318 may be oriented in other directions depending on the colors that are desired to be projected in the viewing angle ranges of the respective first and second image channels, for example, in a direction extending perpendicular or at an angle to the direction of the maximum slope of the respective facet 314, 316.Each diffraction grating 318 may have a period of 1.2 pm to 3.2 pm, however, other periods are also contemplated depending on the colors that are desired to be seen from the respective diffraction gratings 318.

[0206] With respect to the optical effect device 300b, it is also contemplated that the diffraction gratings 318 may be disposed on the first facets 310 and the second facets 312 instead of the third facets 314 and fourth facets 316. It is also contemplated that the diffraction gratings 318 may be disposed on all of the first facets 310, second facets 312, third facets 314, and fourth facets 316, or disposed on one or more of the first facets 310, second facets 312, third facets 314, and fourth facets 316. For example, diffraction gratings 318 oriented in a first direction may be formed across the first and second facets 310, 312, and diffraction gratings 318 oriented in a second and third direction may be formed across the third and fourth facets 314, 316. This arrangement would allow for some variance in the optical effect when oriented in directions not associated with the typical tilting optical effect.

[0207] The addition of diffraction gratings 318 introduces color into the first and second optical effects when viewed in at least partially collimated light, when the light is diffracted, and color effects are therefore visible, and also expands the range of viewing angles in which each of the image channels are visible due to the light scattering effect of the diffraction gratings 318. If the structures 308 are not coated with a reflective layer, when viewing the optical effect device 300b in reflected or transmitted white light that is at least partially collimated, or that comes from a point source, the first and second optical effects are observed in multiple colors and, when the optical effect device 300b is rotated about the X-axis, or offset from the light source, the observed optical effects switch between the first and second optical effects.

[0208] Although the first facets 310 and the second facets 312 have been described and illustrated as not defining a slope relative to the first surface 304 of the substrate 302, it is contemplated that the first facets 310 and the second facets 312 may define an angle relative to the first surface 304 of the substrate that is different from the angle [3 and the angle co. In this case, the first facets 310 and the second facets 312 would be directed in directions different from each other and different from the first and second directions of the third facets 314 and fourth facets 316, respectively.

[0209] It is also contemplated that the thickness of each structure 308 may be reduced using the approach described above with respect to the optical effect device 100d.

[0210] Fourth exemplary embodiment of the invention

[0211] [Fig. 19] shows an optical effect device 400 in the form of a security device according to a fourth embodiment of the present invention. The optical effect device 400 comprises a substrate 402 having a first surface 404 and a second surface 406 (see [Fig.20]).

[0212] Arranged on the first surface 404 of the substrate 402 are a first plurality of structures 408 that define a first image channel having a first range of projection angles, a second plurality of structures 410 that define a second image channel having a second range of projection angles, and a third plurality of structures 412 that define a third image channel having a third range of angles. projection. Each structure 408 has a facet 414 that is directed in a first direction, each structure 410 has a facet 416 that is directed in a second direction that is different from the first direction, and each structure 412 has a facet 418 that is directed in a third direction that is different from the first and second directions.

[0213] Each facet 414, 416, 418 defines a slope relative to the first surface 404 of the substrate 402. The facets 414 of the structures 408 define the same slope angle [3 relative to the first surface 404 of the substrate 402 and the structures 408 have the same maximum thickness t (see [Fig.20], for example). In a similar manner, the facets 416, 418 of the respective structures 410, 412 define the same slope angle relative to the first surface 404 of the substrate 402 and the structures 410, 412 have the same maximum thickness. It is contemplated that the maximum thickness of the structures 408, 410, 412 may or may not be uniform and / or that the slope angle defined by each of the facets 414, 416, 418 relative to the first surface 404 of the substrate 402 may or may not be uniform.

[0214] As best seen in [Fig. 19], the different structures 408, 410, 412, each have a unique orientation in the XY plane. It will therefore be understood that the different structures 408, 410, 412 each have a unique in-plane orientation relative to the plane of the first surface 404 of the substrate 402. The structures 408 have an in-plane orientation of 90 degrees relative to the plane of the first surface 404 of the substrate 402, such that the respective facets 414 are directed in a first direction. The structures 410 have an in-plane orientation of 210 degrees relative to the plane of the first surface 404 of the substrate 402, such that the respective facets 416 are directed in a second direction. The structures 412 have an in-plane orientation of 330 degrees relative to the plane of the first surface 404 of the substrate 402, such that the respective facets 418 are directed in a third direction.The various structures 408, 410, 412 thus have in-plane orientations relative to the plane of the first surface 404 of the substrate 402 that are separated from each other by 120 degrees. It is contemplated that the plurality of structures 408, 410, 412 may have in-plane orientations and / or may have an in-plane separation angle other than 120°.

[0215] The facets 414 of the first plurality of structures 408 define a first optical effect when viewed from a first range of viewing angles, the facets 416 of the second plurality of structures 410 define a second optical effect when viewed from a second range of viewing angles that is different from the first range of viewing angles, and the facets 418 of the third plurality of structures 412 define a third optical effect when viewed from a third range of viewing angles that is different from the first and second viewing angle ranges. The optical effects may be visible from positions on the same side as the first surface 404 and the second surface 406 of the substrate 402 if the substrate 402 and the structures 408, 410, 412 are made of a transparent material.

[0216] Each optical effect defined by the respective image channel is a rasterized binary image obtained by applying an amplitude modulation or frequency modulation rasterization algorithm to a grayscale input image. An example of a rasterization algorithm is a diffusion rasterization algorithm. Each binary "on" pixel of the first optical effect is implemented in the optical effect device 400 as one or more structures 408. Similarly, each binary "on" pixel of the second and third image channels are respectively implemented in the optical effect device 400 as one or more structures 410 and one or more structures 412. Therefore, the structures 408, 410, 412 are only arranged at locations on the first surface 404 of the substrate 402 that correspond to the binary "on" pixels of the first, second, and third optical effects.Each pixel defined by one or more respective structures 408, 410, 412 represents a foreground or background pixel. It will therefore be understood that portions of the first surface 404 of the substrate 402 will be absent from any structures 408, 410, 412 in which the respective image requires a binary "off". More specifically, in one embodiment, a black and white binary input image for the first optical effect is converted to the optical effect device 400 by providing structures 408 where a black pixel is found in the input binary image of the first optical effect and not providing a corresponding structure 408 where a white pixel is found in the input binary image of the first optical effect. It will be understood that the same will be true for the second and third optical effects.

[0217] The optical effect device 400 therefore interlaces three images which can be projected towards an observer according to three predefined viewing angle ranges. In addition, the choice of orientation in the plane makes it possible to obtain effects which are visible when a rectangular document is rotated around one or the other of the principal axes (the two axes X and Y in [Fig. 19]) relative to a light source, or when a rectangular document is rotated around the Z axis (rotation in the plane) relative to a light source. It will therefore be understood that the optical effect device 400 provides an optical effect with three visuals.

[0218] The general structure of the embodiments of the optical effect device 400 is described below: • Structures 408, 410, 412 may be made of a transparent material, for example, a radiation-curable resin (described in more detail below); • The substrate 402 may also be transparent and in the form of a sheet (as for application to a security document) or a polymer substrate (for example, a polymer substrate for a banknote); • The structures 408, 410, 412 may be covered with a clear protective layer that may have a different refractive index than the material used to form the structures 408, 410, 412. The clear protective layer may be sufficiently thick to prevent mechanical copying (i.e., contact copying) of the structures 408 (described in more detail below); and • Alternatively, the structures 408, 410, 412 may be covered with a reflective layer. The reflective layer may be sufficiently thick to prevent mechanical copying (i.e., contact copying) of the structures 408, 410, 412. Alternatively, the reflective layer may be thin and covered with a clear protective layer that is sufficiently thick to prevent mechanical copying (i.e., contact copying) of the structures 408, 410, 412.

[0219] If the structures 408, 410, 412 are not covered with a reflective layer or are covered with a semi-transparent reflective layer, the optical effects can be seen in transmission as well as in reflection. In this case, the optical effects can be visible from respective observation positions located on the same side as the first surface 404 and on the same side as the second surface 406, having respective viewing angle ranges. This will also be the case if the structures 408, 410, 412 are covered with a thin reflective layer (e.g., of a thickness less than the maximum thickness of the structures 408, 410, 412, but thick enough to almost completely prevent the transmission of light), however, in this case, the optical effects will only be visible in reflected light.

[0220] If the structures 408, 410, 412 are covered with a thick reflective layer so that mechanical copying of the structures 408, 410, 412 can be prevented / limited, the optical effects will only be visible in reflection from observation positions located on the same side as the second surface 406 having respective viewing angle ranges.

[0221] It is also contemplated that the substrate 402 may be made of an opaque material (e.g., a foil or banknote polymer) and that the structures 408, 410, 412 may be made of a transparent material (e.g., example, a radiation-curable resin). In this case, it will be understood that the optical effects will only be visible in reflection from observation positions located on the same side as the first surface 404 having respective viewing angle ranges. The visibility of the optical effects can in this case be improved by covering the structures 408, 410, 412 with a thin reflective layer.

[0222] Although the optical effects projected by the optical effect device 400 have been described as being binary images, it will be understood that the optical effects may be implemented by the respective image channels in the form of: • a binary image of a monochromatic “silhouette”; or • a halftone raster binary image.

[0223] Diffraction gratings may be arranged on one or more of the facets 414, 416, 418. The lines of each diffraction grating may extend in a direction parallel to the slope of the respective facet 414, 416, 418. In other words, the lines of each diffraction grating extend in the direction of the maximum slope of the respective facet 414, 416, 418. Alternatively, the lines of the diffraction gratings may be oriented in other directions depending on the colors that are desired to be projected in the respective viewing angle ranges of the first, second, and third image channels, in a direction extending perpendicular to or at an angle to the direction of the maximum slope of the respective facet 414, 416, 418. The diffraction gratings may have a period of 1.2 pm. at 3.2pm, however, other periods are also considered depending on the colors that are desired to be seen from the respective diffraction gratings.

[0224] The addition of diffraction gratings introduces color into the optical effects when viewed in at least partially collimated light and also expands the range of viewing angles in which each of the image channels is visible due to the light scattering effect of the diffraction gratings. In this embodiment, if the structures 408, 410, 412 are not coated with a reflective layer, when viewing the optical effect device 400 in reflected or transmitted white light that is at least partially collimated, or that originates from a point source, the optical effects are observed in multiple colors and, when the optical effect device 400 is rotated about the X and / or Y and / or Z axes, or offset relative to the light source, the observed optical effects switch between the optical effects.

[0225] It is also contemplated that the thickness of each structure 408 may be reduced using the approach described above with respect to the optical effect device 100d.

[0226] Fifth exemplary embodiment of the invention

[0227] Figures 21 and 22 show an optical effect device 500 in the form of a security device according to a fifth embodiment of the present invention. The optical effect device 500 is similar to the optical effect device 400, except that the structures 508, 510, 512 are arranged over the entire first surface 504 of the substrate 502 and that diffraction gratings 520, 522, 524 are arranged on one or more of the respective facets 514, 516, 518.

[0228] Features of the optical effect device 500 that are identical or equivalent to those of the optical effect device 400 are designated by reference numerals equivalent to those of the optical effect device 400 but incremented by 100. For features that are identical between the optical effect device 400 and the optical effect device 500, it will be understood that the above description regarding those features in connection with the optical effect device 400 also applies to the corresponding identical / equivalent features found in the optical effect device 500. Therefore, features identical between the optical effect device 400 and the optical effect device 500 will not be described again hereinafter in connection with the optical effect device 500, because those features of the optical effect device 500 have already been described above in connection with the optical effect device 400.

[0229] The first plurality of structures 508 defines a first image channel having a first range of projection angles, the second plurality of structures 510 defines a second image channel having a second range of projection angles, and the third plurality of structures 512 defines a third image channel having a third range of projection angles.The diffraction gratings 520 disposed on one or more of the facets 514 of the first plurality of structures 508 define a first optical effect when viewed at a first range of viewing angles, the diffraction gratings 522 disposed on one or more of the facets 516 of the first plurality of structures 510 define a second optical effect when viewed at a second range of viewing angles that is different from the first range of viewing angles, and the diffraction gratings 524 disposed on one or more of the facets 518 of the first plurality of structures 512 define a third optical effect when viewed at a third range of viewing angles that is different from the first and second ranges of viewing angles.The optical effects of the optical effect device 500 may be visible from viewing locations located on the same side as the first surface 504 and the second surface 506 on the substrate 502 if the substrate 502 and the structures 508, 510, 512 are made of a transparent material.

[0230] The diffraction gratings 520, 522, 524 are arranged on one or more respective facets 514, 516, 518 according to a screening pattern obtained by a screening algorithm. dithering to introduce a grayscale image. The lines of each diffraction grating 520, 522, 524 extend in a direction parallel to the slope of the respective facet 514, 516, 518. In other words, the lines of each diffraction grating 520, 522, 524 extend in the direction of the maximum slope of the respective facet 514, 516, 518. It is, however, also contemplated that the lines of each diffraction grating 520, 522, 524 may be oriented in other directions depending on the color that is desired to be projected at the viewing angle ranges of the respective first, second, and third image channels, for example, in a direction extending perpendicular to or at an angle to the direction of the maximum slope of the respective facet 514, 516, 518. Each diffraction grating 520, 522, 524 can have a period from 1.2qm to 3.2qm, however, other periods are also considered depending on the colors that one wishes to be able to see from the respective diffraction gratings 520, 522, 524. .

[0231] The optical effect device 500 therefore interlaces three images which can be projected towards an observer according to three predefined viewing angle ranges. In addition, the choice of orientation in the plane makes it possible to obtain effects which are visible when a rectangular document is rotated around one or the other of the principal axes (the two axes X and Y in [Fig. 21]) relative to a light source, or when a rectangular document is rotated around the Z axis (rotation in the plane) relative to a light source. It will therefore be understood that the optical effect device 500 provides an optical effect with three visuals.

[0232] The general structure of the embodiments of the optical effect device 500 is described below: • Structures 508, 510, 512 may be made of a transparent material, for example, a radiation-curable resin (described in more detail below); • The substrate 502 may also be transparent and in the form of a sheet (as for application to a security document) or a polymer substrate (for example, a polymer substrate for a banknote); • Structures 508, 510, 512 may be covered with a clear protective layer that may have a different refractive index than the material used to form structures 508, 510, 512. The clear protective layer may be sufficiently thick to prevent mechanical copying (i.e., contact copying) of structures 508 (described in more detail below); and • Alternatively, structures 508, 510, 512 may be coated with a reflective layer. The reflective layer may be sufficiently thick to prevent mechanical copying (i.e., contact copying). structures 508, 510, 512. Alternatively, the reflective layer may be thin and covered with a clear protective layer that is sufficiently thick to prevent mechanical copying (i.e., contact copying) of structures 508, 510, 512.

[0233] If the structures 508, 510, 512 are not covered with a reflective layer or are covered with a semi-transparent reflective layer, the optical effects can be seen in transmission as well as in reflection. In this case, the optical effects can be visible from respective observation positions located on the same side as the first surface 504 and on the same side as the second surface 506, having respective viewing angle ranges. This will also be the case if the structures 508, 510, 512 are covered with a thin reflective layer (e.g., of a thickness less than the maximum thickness of the structures 508, 510, 512, but thick enough to almost completely prevent the transmission of light), however, in this case, the optical effects will only be visible in reflected light.

[0234] If the structures 508, 510, 512 are covered with a thick reflective layer so that mechanical copying of the structures 508, 510, 512 can be prevented / limited, the optical effects will only be visible in reflection from observation positions located on the same side as the second surface 506 having respective viewing angle ranges.

[0235] It is also contemplated that the substrate 502 may be made of an opaque material (e.g., a foil or banknote polymer) and that the structures 508, 510, 512 may be made of a transparent material (e.g., a radiation-curable resin). In this case, it will be understood that the optical effects will only be visible in reflection from viewing positions located on the same side as the first surface 504 of the substrate 502. The visibility of the optical effects may in this case be enhanced by covering the structures 508, 510, 512 with a thin reflective layer.

[0236] If the structures 508, 510, 512 are not covered with a reflective layer, when the optical effect device 500 is viewed in transmitted or reflected diffuse white light, the optical effects are observed in black and white and, when the optical effect device 500 is rotated about the X and / or Y and / or Z axes, or offset from the light source, the observed optical effects switch between the first, second and third optical effects. When the optical effect device 500 is viewed in reflected or transmitted white light that is at least partially collimated, or that comes from a point source, the optical effects are observed in multiple colors and, when the optical effect device 500 is rotated about the X and / or Y and / or Z axis, or offset from the light source, The observed optical effects switch between the first, second and third optical effects.

[0237] By appropriately selecting the grating frequency, depth, and line orientation of the diffraction gratings 520, 522, 524, the optical effects projected by each of the respective image channels of the optical effect device 500 at a particular angle may be a true color image. For example, the grating frequency, depth, and line orientation of the diffraction gratings 520, 522, 524 may be selected such that they project a two-dimensional array of RGB color image pixels such that the respective image channels define a desired color image to be viewed at a particular angle with substantially collimated white light. The images defined by the respective diffraction gratings 520, 522, 524 of each image channel could have multiple tones of one or more desired colors.

[0238] The diffraction gratings 520, 522, 524 may be arranged on one or more of the respective facets 514, 516, 518 such that the respective image channels define: • a binary image of a monochromatic “silhouette”; • a halftone raster binary image; or • a rasterized binary image.

[0239] It is also contemplated that the thickness of each structure 508 may be reduced using the approach described above relative to the optical effect device 100d.

[0240] Sixth example of embodiment of the invention

[0241] [Fig. 23] shows an optical effect device 600 in the form of a security device according to a sixth embodiment of the present invention. The optical effect device 600 comprises a substrate 602 having a first surface 604 and a second surface 606 (see [Fig. 24]).

[0242] A plurality of structures 608 are arranged on the first surface 604 of the substrate 602. Each structure 608 has a plurality of facets 610 that each define a slope having an angle [3 relative to the first surface 604 of the substrate 602. Each structure 608 has an orientation in the XY plane. Therefore, each structure 608, with its respective facets 610, has an orientation in the plane of X degrees relative to the plane of the first surface 604 of the substrate 602.

[0243] The in-plane orientation and / or slope angle [3 of the facets 610 of each structure 608 is modulated according to an input set of scalar values. For example, for grayscale images having 256 gray levels per pixel, the scalar values ​​for the grayscale may have a value in the range of 0 to 255, where zero is taken for black and 255 for white.

[0244] In one embodiment of the optical effect device 600, the slope angle [3 of each facet 610 is the same, but the in-plane orientation of each structure 608 relative to the plane of the first surface 604 of the substrate 602 is modulated as a function of an input scalar value, by a grayscale scalar value of an input image. It will therefore be understood that each structure 608, with its respective facets 610, has an orientation of between 0 degrees and say 180 degrees relative to the plane of the first surface 604 of the substrate 602, as a function of the grayscale scalar value of the input image.For example, the facets 610 of a structure 608 at a particular location (X, Y) on the first surface 604 of the substrate 602 may have a constant slope angle [3 but have an in-plane orientation relative to the first surface 604 of the substrate 602 equal to an input grayscale value (e.g., 0 to 255) divided by 255 and multiplied by 180 degrees.

[0245] In another embodiment of the optical effect device 600, each structure 608 may have the same orientation in the X-degree plane relative to the plane of the first surface 604 of the substrate 602 but the slope angle [3 of the facets 610 of each structure 608 may be modulated based on an input scalar value, for example, a grayscale scalar value of an input image. For example, the facets 610 of the substrate 602 may have a slope angle [3 equal to an input grayscale value (for example, from 0 to 255) divided by 255 and multiplied by 45 degrees.

[0246] In another embodiment of the optical effect device 600, it is contemplated that the in-plane orientation relative to the plane of the first surface 604 of the substrate 602 and the slope angle [3 of the facets 610 of each structure 608 may be modulated as a function of an input scalar value, for example a grayscale scalar value of an input image.

[0247] The facets 610 of the optical effect device 600 define a contrast-switching optical effect when viewed over a range of viewing angle ranges. The contrast-switching optical effect provided by the optical effect device 600 may be a rasterized binary image obtained by applying an amplitude modulation or frequency modulation rasterization algorithm to introduce a grayscale image. An example of a rasterization algorithm is a diffusion rasterization algorithm.

[0248] Each pixel of the contrast-swappable optical effect is implemented in the optical effect device 600 as a structure 608. The structures 608 are arranged only at locations on the first surface 604 of the substrate 602 that correspond to pixels in the input grayscale image. Each pixel defined by the structure 608 may represent a foreground or background pixel. In some embodiments, it will therefore be understood that portions of the first surface 604 of substrate 602 will be absent of any structures 608. In other embodiments, each input image pixel (whether considered a foreground pixel, a background pixel, or neither) is represented by a corresponding structure 608.

[0249] According to one embodiment, each of the foreground and background pixels of an image will be defined by a respective structure 608 which is modulated in the manner described above. In this case, when the viewing angle of an observer observing the optical effect device 600 is changed, the brightness of the foreground and background pixels begins to reverse until the contrast between the foreground and background pixels is swapped (i.e., the contrast of the optical effect is reversed).

[0250] For a grayscale image having different gray levels (i.e., shades of gray), the image will generally have no identifiable foreground or background pixels. Therefore, all pixels in a grayscale image will be defined by a respective structure 608 that is modulated in the manner described above. When the viewing angle of an observer viewing the optical effect device 600 is changed, the brightness of each pixel begins to invert until the contrast of each pixel is swapped (i.e., the contrast of the optical effect is reversed).

[0251] According to another embodiment, only the foreground pixels or the background pixels of an image will be defined by a respective structure 608 which is modulated in the manner described above. In this case, instead of a contrast switching effect, an image disappearing effect will be provided. When the viewing angle of an observer looking at the optical effect device 600 is changed, the brightness of each pixel increases or decreases, which gives an image disappearing appearance.

[0252] The optical effect device 600 may be projected toward an observer along a two-dimensional set of viewing angle ranges, thereby allowing sampling of the contrast-switching optical effect along two axes.

[0253] The general structure of the embodiments of the optical effect device 600 is described below: • The structures 608 may be made of a transparent material, for example, a radiation-curable resin (described in more detail below); • The substrate 602 may also be transparent and in the form of a sheet (as for application to a security document) or a polymer substrate (for example, a polymer substrate for a banknote); • The 608 structures may be coated with a clear protective layer which may have a different refractive index than the material used to form the 608 structures. The clear protective layer may be sufficiently thick to prevent mechanical copying (i.e., contact copying) of the 608 structures (described in more detail below); and • Alternatively, the structures 608 may be covered with a reflective layer. The reflective layer may be sufficiently thick to prevent mechanical copying (i.e., contact copying) of the structures 608. Alternatively, the reflective layer may be thin and covered with a clear protective layer that is sufficiently thick to prevent mechanical copying (i.e., contact copying) of the structures 608.

[0254] If the structures 608 are not covered with a reflective layer or are covered with a semi-transparent reflective layer, the optical effects can be seen in transmission as well as in reflection. Therefore, in this case, the optical effects can be visible from respective observation positions located on the same side as the first surface 604 and on the same side as the second surface 606, having respective viewing angle ranges. This will also be the case if the structures 608 are covered with a thin reflective layer (e.g., of a thickness less than the maximum thickness of the structures 608, but thick enough to almost completely prevent the transmission of light), however, in this case, the optical effects will only be visible in reflected light.

[0255] If the structures 608 are covered with a thick reflective layer so that mechanical copying of the structures 608 can be prevented / limited, the optical effects will only be visible in reflection from observation positions located on the same side as the second surface 606 having respective viewing angle ranges.

[0256] It is also contemplated that the substrate 602 may be made of an opaque material (e.g., a foil or banknote polymer) and that the structures 608 may be made of a transparent material (e.g., a radiation-curable resin). In this case, it will be understood that the optical effects will only be visible in reflection from viewing positions located on the same side as the first surface 604 of the substrate 602. The visibility of the optical effects may in this case be enhanced by covering the structures 608 with a thin reflective layer.

[0257] Diffraction gratings may be arranged on one or more of the facets 610 of the optical effect device 600. The lines of each diffraction grating may extend in a direction parallel to the slope of the facet 610. In other words, the lines of each diffraction grating extend in the direction of the maximum slope of the respective facet 610. Alternatively, the lines of the diffraction gratings may be oriented in other directions according to the colors that are desired to be projected at the viewing angle ranges of the contrast-switching optical effect, for example, in a direction extending perpendicular to or at an angle to the direction of maximum slope of the respective facet 610. The diffraction gratings may have a period of 1.2 pm to 3.2 pm, however, other periods are also contemplated depending on the colors that are desired to be seen from the respective diffraction gratings.

[0258] The addition of diffraction gratings introduces color into the contrast-switching optical effect when viewed in at least partially collimated light and also expands the range of viewing angles in which the contrast-switching optical effect is visible due to the light-scattering effect of the diffraction gratings. In this embodiment, if the structures 608 are not coated with a reflective layer, when viewing the optical effect device 600 in reflected or transmitted white light that is at least partially collimated, or that originates from a point source, the contrast-switching optical effect is observed in multiple colors, and when the optical effect device 600 is rotated about the X and / or Y and / or Z axes, or offset relative to the light source, the color contrast of the contrast-switching optical effect varies.

[0259] It is also contemplated that the thickness of each structure 608 may be reduced using the approach described above with respect to the optical effect device 100d.

[0260] Seventh example of an embodiment of the invention

[0261] [Fig. 25] shows an optical effect device 700 in the form of a security device according to a seventh embodiment of the present invention. The optical effect device 700 comprises a substrate 702 having a first surface 704 and a second surface 706 (see [Fig. 26]).

[0262] A plurality of structures 708 are arranged on the first surface 704 of the substrate 702. Referring to Figures 26-28, each structure 708 is approximately in the form of a V-shaped groove and has a first facet 710 and a second facet 712. As best seen in [Fig. 26], the first facet 710 and the second facet 712 of each structure 708 are directed in different directions.

[0263] With reference to [Fig. 25], the plurality of structures 708 are grouped into a first group of structures 714 that defines a first image channel and a second group of structures 716 that defines a second image channel. As best seen in [Fig. 25], the first group of structures 714 extends in the X direction in [Fig. 25], and the second group of structures 716 extends in the Y direction in [Fig. 25],

[0264] The first group of structures 714 and the second group of structures 716 each have a unique in-plane orientation, in the XY plane. It will therefore be understood that the first group of structures 714 and the second group of structures 716 each have a unique in-plane orientation relative to the plane of the first surface 704 of the substrate 702.

[0265] Each structure 708 of the first group of structures 714 has an in-plane orientation of 90 degrees relative to the plane of the first surface 704, such that, for each structure 708 of the first group of structures 714, the first facet 710 is directed in a first direction indicated generally by the arrow 74 and the second facet 712 is directed in a second direction indicated generally by the arrow 76. The first facets 710 and the second facets 712 of the first group of structures 714 respectively define a first set of facets and the second set of facets.

[0266] Each structure 708 of the second group of structures 716 has an in-plane orientation of 0 degrees relative to the plane of the first surface 704, such that, for each structure 708 of the second group of structures 716, the first facet 710 is directed in a third direction indicated generally by the arrow 70 and the second facet 712 is directed in a fourth direction indicated generally by the arrow 72. The first facets 710 and the second facets 712 of the second group of structures 716 define a third set of facets and the fourth set of facets, respectively. It will be understood that the in-plane orientation of the first group of structures 714 is perpendicular to the in-plane orientation of the second group of structures 716.

[0267] With reference to [Fig. 25], the optical effect device 700 is subdivided into a plurality of cells 718. Each cell 718 corresponds to a pixel of a first optical effect as well as a second optical effect. Each cell 718 is subdivided into first areas 722a, 722b corresponding to a pixel of the first optical effect and second areas 720a, 720b corresponding to a pixel of the second optical effect. Three structures 708 of the first group of structures 714 are arranged in several of the first areas 722a, 722b of the cells 718 to define respective black (or white) pixels of the first optical effect. Similarly, three structures 708 of the second group of structures 716 are arranged in several of the second areas 720a, 720b of the cells 718 to define respective black (or white) pixels of the second optical effect. Although the [Fig.25] shows three structures 708 in several of the respective first zones 722a, 722b and second zones 720a, 720b, it will be understood that it is possible to arrange more or less than three structures 708 in several of the first zones 722a, 722b and second zones 720a, 720b.

[0268] The first set of facets defines the first optical effect when the optical effect device 700 is viewed at a first range of viewing angles indicated generally by arrow 82. The second set of facets defines the first optical effect when the optical effect device 700 is viewed at a second range of viewing angles indicated generally by arrow 84. The third set of facets defines the second optical effect when the optical effect device 700 is viewed at a third range of viewing angles indicated generally by arrow 78. The fourth set of facets defines the second optical effect when the optical effect device 700 is viewed at a fourth range of viewing angles indicated generally by arrow 80.It will therefore be understood that the first image channel defined by the first group of structures 714 has two projection angles and that the first optical effect is visible from two respective viewing angle ranges. It will also be understood that the second image channel defined by the second group of structures 716 has two projection angles and that the second optical effect is visible from two respective viewing angle ranges. The optical effects may be visible from viewing positions located on the same side as the first surface 704 and the second surface 706 of the substrate 702 if the substrate 702 and the structures 708 are made of a transparent material.

[0269] For the optical effect device 700 shown in [Fig. 25], when the optical effect device 700 is viewed from viewing directions generally indicated by arrows 78 and 80, the optical effect shown in [Fig. 29A] will be projected toward an observer. Similarly, when the optical effect device 700 is viewed from viewing directions generally indicated by arrows 82 and 84, the optical effect shown in [Fig. 29B] will be projected toward an observer.

[0270] Referring to Figures 25 and 29A-B, cell 718a has several structures 708 of the second group of structures 716 but no structures 708 of the first group of structures 714. Therefore, when optical effect device 700 is viewed from viewing angle ranges generally indicated by arrows 78 and 80, cell 718a projects a black pixel in the first optical effect (see [Fig. 29A]) and, when optical effect device 700 is viewed from viewing angle ranges generally indicated by arrows 82 and 84, cell 718a projects a white pixel in the second optical effect (see [Fig. 29B]). It will be understood that any cell 718 having structures 708 of the first structure group 714 projects a black pixel in the first optical effect when the optical effect device 700 is viewed from viewing angle ranges generally indicated by arrows 82 and 84.

[0271] Cell 718b does not have any structure 708 from either the first or second group of structures 714, 716. Therefore, cell 718b projects a white pixel in the first and also in the second optical effect.

[0272] The optical effect device 700 therefore interlaces two images (namely the first and second optical effects) which can be projected towards an observer by rotating the optical effect device 700 around an axis which is normal to the plane of the optical effect device 700. It will therefore be understood that the optical effect device 700 offers a dual-visual optical effect.

[0273] The general structure of the embodiments of the optical effect device 700 is described below: • Structures 708 may be made of a transparent material, for example, a radiation-curable resin (described in more detail below); • The substrate 702 may also be transparent and in the form of a sheet (as for application to a security document) or a polymer substrate (for example, a polymer substrate for a banknote); • The structures 708 may be covered with a clear protective layer that may have a different refractive index than the material used to form the structures 708. The clear protective layer may be sufficiently thick to prevent mechanical copying (i.e., contact copying) of the structures 708 (described in more detail below); and • Alternatively, the structures 708 may be covered with a reflective layer. The reflective layer may be sufficiently thick to prevent mechanical copying (i.e., contact copying) of the structures 708. Alternatively, the reflective layer may be thin and covered with a clear protective layer that is sufficiently thick to prevent mechanical copying (i.e., contact copying) of the structures 708.

[0274] If the structures 708 are not covered with a reflective layer or are covered with a semi-transparent reflective layer, the optical effects can be seen in transmission as well as in reflection. In this case, the optical effects can be seen from respective observation positions located on the same side as the first surface 704 and on the same side as the second surface 706, having respective viewing angle ranges. This will also be the case if the structures 708 are covered with a thin reflective layer (e.g., of a thickness less than the maximum thickness of the structures 708, but thick enough to almost completely prevent the transmission of light), however, in this case, the optical effects will only be visible in reflected light.

[0275] If the structures 708 are covered with a thick reflective layer so that mechanical copying of the structures 708 can be prevented / limited, the optical effects will only be visible in reflection from observation positions located on the same side as the second surface 706 of the substrate 702 having respective viewing angle ranges.

[0276] It is also contemplated that the substrate 702 may be made of an opaque material (e.g., a foil or banknote polymer) and that the structures 708 may be made of a transparent material (e.g., a radiation-curable resin). In this case, it will be understood that the optical effects will only be visible in reflection from viewing positions located on the same side as the first surface 704 of the substrate 702. The visibility of the optical effects may in this case be enhanced by covering the structures 708 with a thin reflective layer.

[0277] The optical effects projected by the optical effect device 700 can be implemented by the structures 708 in the form of: • a binary image of a monochromatic “silhouette”; • a halftone raster binary image; or • a rasterized binary image.

[0278] It will be understood that more than two images may be interlaced in the optical effect device 700 by arranging more groups of structures on the first surface 704 of the substrate 702. For example, with reference to [Fig. 30], the optical effect device 700 may have a third group of structures 724 that defines a third image channel. Similar to the first and second groups of structures 714, 716, the first facets 710 of the structures 708 of the third group of structures 724 define a third optical effect when the optical effect device 700 is viewed from a fifth range of viewing angles and the second facets 712 of the structures 708 of the third group of structures 724 define the third optical effect when the optical effect device is viewed from a sixth range of viewing angles.It will therefore be understood that the third image channel defined by the third group of structures 724 has two ranges of projection angles and that the third optical effect is visible from two respective ranges of viewing angles.

[0279] In the example shown in [Fig.30], the first group of structures 714 has an in-plane orientation of 0 degrees relative to the plane of the first surface 704, the second group of structures 716 has an in-plane orientation of 60 degrees relative to the plane of the first surface 704, and the third group of structures 724 has an in-plane orientation of 120 degrees relative to the plane of the first surface 704. It will therefore be understood that each group of structures 714, 716, 724 has an orientation in the plane of 60 degrees.

[0280] The in-plane separation angle between each structure group 714, 716, 724 is calculated by dividing 180 degrees by the number of structure groups. For example, if the optical effect device 700 interlaces 4 images, there will be four structure groups and the in-plane separation angle between adjacent structure groups will be 45 degrees.

[0281] Eighth exemplary embodiment of the invention

[0282] [Fig. 31] shows an optical effect device 800 in the form of a security device according to an eighth embodiment of the present invention. The optical effect device 800 is similar to the optical effect device 700, except for the shape and configuration of the structures 808 of the optical effect device 800.

[0283] Features of the optical effect device 800 that are identical or equivalent to those of the optical effect device 700 are designated by reference numerals equivalent to those of the optical effect device 700 but incremented by 100. For features that are identical between the optical effect device 700 and the optical effect device 800, it will be understood that the above description regarding those features in connection with the optical effect device 700 also applies to the corresponding identical / equivalent features found in the optical effect device 800. Therefore, features identical between the optical effect device 700 and the optical effect device 800 will not be described again hereinafter in connection with the optical effect device 800, because those features of the optical effect device 800 have already been described above in connection with the optical effect device 700.

[0284] A plurality of structures 808 are arranged on the first surface 804 of the substrate 802. Each structure 808 has approximately the geometry of a truncated triangular pyramid and has a first facet 810, a second facet 812 and a third facet 814. The first facet 810, the second facet 812 and the third facet 814 of each structure 808 are directed in different directions.

[0285] The plurality of structures 808 are grouped into a first group of structures 816 that defines a first image channel and a second group of structures 818 that defines a second image channel. As best seen in [Fig. 31], the first group of structures 816 points upward in the Y direction of [Fig. 31] and the second group of structures 818 points downward in the Y direction of [Fig. 31]. The angle between the in-plane orientation of the first group of structures 816 and that of the second group of structures 818 is 180 degrees, however, other angles are also contemplated.

[0286] Referring to [Fig. 32], for each structure 808 of the first group of structures 816, the first facet 810 is directed in a first direction generally indicated by the arrow 81a, the second facet 812 is directed in a second direction generally indicated by the arrow 82a, and the third facet 814 is directed in a third direction generally indicated by the arrow 83a. The first facets 810, the second facets 812 and the third facets 814 of the first group of structures 816 respectively define a first set of facets, a second set of facets and a third set of facets.

[0287] For each structure 808 of the second group of structures 818, the first facet 810 is directed in a fourth direction indicated generally by arrow 84a, the second facet 812 is directed in a fifth direction indicated generally by arrow 85a, and the third facet 814 is directed in a sixth direction indicated generally by arrow 86a. The first facets 810, second facets 812, and third facets 814 of the second group of structures 818 respectively define a fourth set of facets, a fifth set of facets, and a sixth set of facets. As best seen in [Fig. 33], the first and fourth sets of facets are directed in opposite directions, the second and fifth sets of facets are directed in opposite directions, and the third and sixth sets of facets are directed in opposite directions.

[0288] With reference to [Fig.31], the optical effect device 800 is divided into a plurality of cells 820. Each cell 820 corresponds to a pixel of the first optical effect as well as the second optical effect. Each cell 820 is subdivided into a first zone 822 which corresponds to a pixel of the first optical effect and a second zone 824 which corresponds to a pixel of the second optical effect.

[0289] The first set of facets defines the first optical effect when the optical effect device 800 is viewed at a first range of viewing angles indicated generally by the arrow 81b. The second set of facets defines the first optical effect when the optical effect device 800 is viewed at a second range of viewing angles indicated generally by the arrow 82b. The third set of facets defines the first optical effect when the optical effect device 800 is viewed at a third range of viewing angles indicated generally by the arrow 83b. The fourth set of facets defines the second optical effect when the optical effect device 800 is viewed at a fourth range of viewing angles indicated generally by the arrow 84b.The fifth set of facets defines the second optical effect when the optical effect device 800 is viewed at a fifth range of viewing angles generally indicated by arrow 85b. The sixth set of facets defines the second optical effect when the optical effect device 800 is viewed at a fifth viewing angle range generally indicated by arrow 86b. It will be understood that the first image channel defined by the first group of structures 816 has three projection angle ranges and that the first optical effect is visible from three respective viewing angle ranges. It will also be understood that the second image channel defined by the second group of structures 818 has three projection angle ranges and that the second optical effect is visible from three respective viewing angle ranges. The optical effects may be visible from viewing positions located on the same side as the first surface 804 and the second surface 806 of the substrate 802 if the substrate 802 and the structures 808 are made of a transparent material.

[0290] Referring to [Fig.31], the cell 820a has a structure 808 of the first group of structures 816 but no structures 808 of the second group of structures 818. Therefore, when the optical effect device 800 is viewed from any of the first to third viewing angle ranges 81b-83b, the cell 820a projects a black pixel in the first optical effect and, when the optical effect device 800 is not viewed from any of the first to third viewing angle ranges 81b-83b, the cell 820a projects a white pixel in the second optical effect. It will be understood that any cell 820 having a structure 808 of the second structure group 818 projects a black pixel in the second optical effect when the optical effect device 800 is viewed from any of the fourth to sixth viewing angle ranges 84b-86b.

[0291] The cell 820b has a structure 808 of the first as well as the second group of structures 816, 818. Therefore, when the optical effect device 800 is viewed from any one of the first to third angle ranges 81b, 83b, the cell 820b projects a black pixel in the first optical effect and, when the optical effect device 800 is viewed from any one of the fourth to sixth viewing angle ranges 84b-86b, the cell 820b projects a black pixel in the second optical effect.

[0292] Cell 820c does not have any structure 808 from any of the first and second groups of structures 816, 818. Therefore, cell 802c projects a white pixel in both the first and second optical effects.

[0293] The optical effect device 800 therefore interlaces two images (namely the first and second optical effects) which can be projected towards an observer by rotating the optical effect device 800 around an axis which is normal to the plane of the optical effect device 800 and / or by tilting the optical effect device 800. It will therefore be understood that the optical effect device 800 offers a dual-visual optical effect.

[0294] The dual-visual optical effect provided by the tilting of the optical effect device 800 is possible because, for each respective viewing angle range 81b-83b of the first optical effect, there is an opposite viewing angle range 84b-86b of the second optical effect. Referring to [Fig.32], the first viewing angle range 81b of the first optical effect is opposite to the fourth viewing angle range 84b of the second optical effect, the second viewing angle range 82b of the first optical effect is opposite to the fifth viewing angle range 85b of the second optical effect, and the third viewing angle range 83b of the first optical effect is opposite to the sixth viewing angle range 86b of the second optical effect. For example, the first optical effect is projected toward an observer viewing the optical effect device 800 from the first viewing angle range 81b and, when the observer tilts the optical effect device 800 about an axis parallel to the in-plane orientation of the first set of facets, the optical effect projected toward the observer switches from the first optical effect to the second optical effect.

[0295] The general structure of the embodiments of the optical effect device 800 is described below: • The structures 808 may be made of a transparent material, for example, a radiation-curable resin (described in more detail below); • The substrate 802 may also be transparent and in the form of a sheet (as for application to a security document) or a polymer substrate (for example, a polymer substrate for a banknote); • The 808 structures may be covered with a clear protective layer that may have a different refractive index than the material used to form the 808 structures. The clear protective layer may be sufficiently thick to prevent mechanical copying (i.e., contact copying) of the 808 structures (described in more detail below); and • Alternatively, the structures 808 may be covered with a reflective layer. The reflective layer may be sufficiently thick to prevent mechanical copying (i.e., contact copying) of the structures 808. Alternatively, the reflective layer may be thin and covered with a clear protective layer that is sufficiently thick to prevent mechanical copying (i.e., contact copying) of the structures 808.

[0296] If the structures 808 are not covered with a reflective layer or are covered with a semi-transparent reflective layer, the optical effects can be seen in transmission as well as in reflection. In this case, the optical effects can be visible from observation positions located on the same side as the first surface 804 and on the same side as the second surface 806, having respective viewing angle ranges. This will also be the case if the structures 808 are covered with a thin reflective layer (e.g., less than the maximum thickness of 608 structures, but thick enough to almost completely prevent light transmission), however, in this case, the optical effects will only be visible in reflected light.

[0297] If the structures 608 are covered with a thick reflective layer so that mechanical copying of the structures 808 can be prevented / limited, the optical effects will only be visible in reflection from observation positions located on the same side as the second surface 806 of the substrate 802 having respective viewing angle ranges.

[0298] The optical effects projected by the optical effect device 800 can be implemented by the structures 808 in the form of: • a binary image of a monochromatic “silhouette”; • a halftone raster binary image; or • a rasterized binary image.

[0299] It is also contemplated that the substrate 802 may be made of an opaque material (e.g., a foil or banknote polymer) and that the structures 808 may be made of a transparent material (e.g., a radiation-curable resin). In this case, it will be understood that the optical effects will only be visible in reflection from viewing positions located on the same side as the first surface 804 of the substrate 802. The visibility of the optical effects may in this case be enhanced by covering the structures 808 with a thin reflective layer.

[0300] It will be understood that more than two images may be interlaced in the optical effect device 800. Similar to the optical effect device 700 illustrated in [Fig. 30], the optical effect device 800 may interlace more than two images by having more than two structure groups, where each structure group defines an image channel that projects an optical effect. Each structure group will have an in-plane orientation relative to the first surface 804 of the substrate 802. Reflection and Transmission

[0301] When the optical effects of each optical effect device 100-800 are viewed in reflection, the viewing angle range of each image channel is defined by the specular reflection angle on the respective facet set, which depends on the position and orientation of the respective facet set relative to the light source.

[0302] When the optical effects of each optical effect device 100-800 are viewed in transmission, the viewing angle range of each image channel is defined by the angle of refraction on the respective facet set, which depends on the position and orientation of the facet set relative to the light source. Protective layer and reflective layer

[0303] According to one embodiment of each optical effect device 100-800, to improve the visibility of the optical effects, a reflective layer may be disposed on the plurality of structures. The reflective layer is preferably thin, such that the optical effects can be seen from viewing positions located on the same side as the first surface 104-804 and the second surface 106-806 of the substrate 102-802. The reflective layer may be formed of a metallic ink. However, other suitable materials known in the art may be used to form the reflective layer.

[0304] The reflective layer may be covered with a clear protective layer. Preferably, the clear protective layer is sufficiently thick so that the clear protective layer forms a first planar face of the optical effect device 100-800. As an example, [Fig. 34] shows the optical effect device 100 having a clear protective layer 126 disposed over the reflective layer (not shown) and the plurality of structures 108 that form a first planar face 128 of the optical effect device 100. It will be understood that each of the optical effect devices 100-800 may have a clear protective layer disposed over their respective structures in a manner similar to that shown in [Fig. 34].

[0305] The planar face of the optical effect device 100-800 defined by the clear protective layer is advantageous in that the clear protective layer can prevent mechanical copying of the plurality of structures, which could be used to produce counterfeits of the optical effect devices.

[0306] The planar face of the optical effect device 100-800 defined by the clear protective layer is also advantageous in that the clear protective layer prevents contaminants such as liquids and / or particles from contacting the plurality of structures, which could interfere with the plurality of structures and reduce the visibility of the optical effects. This is particularly advantageous for optical effect devices 100-800 having structures that have shallow depths, being only a few microns deep. Protective layer

[0307] According to another embodiment of the optical effect devices 100-800, a thick clear protective layer may be disposed over the plurality of structures 108-808 such that the clear protective layer forms a first planar face of the optical device (see for example [Fig. 34]). The clear protective layer may be comprised of a high refractive index layer, however, other suitable materials known in the art may be used to form the high refractive index layer.

[0308] The advantages described above in relation to the embodiment concerning the protective layer and the reflective layer also apply to the present embodiment. Reflective layer

[0309] According to another embodiment of the optical effect devices 100-800, a thick reflective layer may be disposed on the structures such that the reflective layer forms a first planar face of the optical effect device 100-800 (see for example [Fig. 34], in which, for this embodiment, the reference numeral 126 refers to the thick reflective layer). It will be understood that the optical effects in this embodiment will only be visible from viewing positions located on the same side as the second surface 106-806 of the substrate 102-802. The reflective layer may be formed of a metallic ink, however, other suitable materials known in the art may be used to form the reflective layer.

[0310] The planar face of the optical device defined by the reflective layer is advantageous because the reflective layer can prevent mechanical copying of the plurality of structures, which could be used to produce counterfeits of the optical effect device. Surface structures

[0311] Although the above optical effect devices 100-800 have been described as having diffraction gratings disposed on one or more of the facets, it is also contemplated that other surface structures / textures may be applied to the facets of each of the above optical effect devices 100-800. Examples of other surface structures / textures that may be disposed on the facets of each of the above optical effect devices 100-800 include surface roughness, surface micro-roughness, light scattering surfaces, micro-texture, micro-texture, or combinations thereof. Security Document

[0312] [Fig.32] shows an embodiment of a security document 950 having a security device 900.

[0313] The security document 950 has a substrate 902, which is the primary support for various security and design features of the security document 950. For simplicity of illustration, only one security feature 900 is shown, but it is well recognized that security documents typically have multiple security features. The substrate 902, which is typically made of a transparent polymeric material, includes a first surface 904 and an opposing second surface 906, both of which are substantially planar. One or several opacifying layers 952 may be provided in selected regions of the security document 950, particularly when the substrate 902 is substantially transparent, so that design patterns, solid colors, text, or the like may be formed directly on the opacifying layer 952 in a selected region of the substrate 902. The security feature 900 according to one embodiment of the invention is located in the window region 960 of the security document 950, but this is not essential. Since the security feature 900 is integrally formed as a single piece with the security document 950, the substrate 902 also acts as the substrate of the security feature 900.

[0314] According to one embodiment of the security document 950, the security device 900 may be any of the optical effect devices 100-800. It will therefore be understood that, if any of the optical effect devices 100-800 are formed integrally with the security document 950, the substrate 902 of the security document 950 will form the respective substrate 102-802 of the optical effect device 100-800. The substrate 902 of the security device 950 forming the substrate 102-802 of the optical effect device 100-800 may be a polymer substrate (which is the substrate of the relevant article or document) or a foil (typically understood to be an element that is applied, for example by hot stamping, to a relevant article or document).

[0315] According to another embodiment of the security document 950, the security device 900 may be any of the optical effect devices 100-800, which is formed, for example, as a transfer film for the application of the substrate 902 of the security document 950. The substrate 102-802 of the optical effect device 100-800 applied to the security document 950 may be a polymer substrate or a foil. Manufacturing

[0316] As an example, the optical effect device 100-800 can be manufactured in the following manner.

[0317] A focused laser beam is applied in a recursive scan to a photoresist surface. The power of the laser beam is varied to form the structures of the optical effect device 100-800 in the photoresist. The power of the laser beam is further varied slightly during the scan depending on the desired maximum thickness of the structures. After the scan, the photoresist is developed / washed to produce the structures. Then, if necessary, the focused laser beam is applied in a recursive scan to the photoresist to form the diffraction gratings on one or more of the structures. After the second scan, the photoresist is used to form a negative (or positive) of the photoresist on a plate, which is then fixed to an embossing roller. Although two passes of the laser beam have been described to form the structures and any diffraction gratings disposed on the structures, it is also contemplated that a single pass of the laser beam may be required to form the structures as well as any diffraction gratings disposed on the structures.

[0318] After the plate is attached to an embossing roll, a radiation-curable resin, preferably a UV-curable resin, is applied to the first surface 104-804 of the substrate 102-802 by a suitable printing process. While the radiation-curable resin is still soft, the plate attached to the embossing roll is applied in the radiation-curable ink to form the structures and any diffraction gratings on the structures. The radiation-curable resin may be cured during embossing of the structures and any diffraction gratings on the structures 108-808 or at a later time.

[0319] In another method, the laser methods described above may be used to form a negative of the optical effect device structures 100-800 in the photoresist. The photoresist is used to form a negative (or positive) of the photoresist on a plate attached to an embossing roller, which is used to emboss the structures and any diffraction gratings on the structures in a radiation-curable resin applied to the first surface 104-804 of the substrate 102-802. The radiation-curable resin may be cured during the embossing of the structures and any diffraction gratings on the structures 108-808 or at a later time.

[0320] In another method in which diffraction gratings are not required, a positive or negative of the structures of the optical effect devices 100-800 may be laser etched directly into the embossing roller using a pulsed laser etching system, for example a picosecond pulsed laser engraver.

[0321] For example, the optical effect devices 700-800 can be manufactured in the following manner.

[0322] A positive (or negative) of the structures 708, 808 of the optical effect device 700, 800 may be etched directly into an embossing roller. After the positive (or negative) of the structures 708, 808 has been etched into the embossing roller, a radiation-curable resin, preferably a UV-curable resin, is applied to the first surface 704, 804 of the substrate 702, 802 by a suitable printing process. While the radiation-curable resin is still soft, the embossing roller is pressed into the radiation-curable ink to form the negative (or positive) of the structures 708, 808 of the optical effect device 700, 800. The radiation-curable resin may be cured during the embossing of the structures 708, 808 or at a later time.

[0323] Etching a positive or negative of the structures 708, 808 of the optical effect device 700, 800 directly into the embossing roller provides a number of advantages over the manufacturing method described above in connection with the optical devices 100-600 using a photoresist. These advantages include: • Low cost - due to the fact that there is no need to form expensive plates and apply them to the embossing roller. • Shorter production times - because the production times associated with plate formation are very long, since individual master plates must first be made, followed by recombination of the master plates into a full-size plate, which is then applied to an embossing roll. In this embodiment, production times can be reduced, because standard gravure cylinder manufacturing processes can be used to form the positive or negative of the structure 708, 808 directly in the embossing roll. • More robust / mechanically durable embossing tooling. Since it is not necessary to apply the plates to the embossing roller, the embossing tooling in this process is more robust and durable. In addition, the embossing tooling can be cleaned more often without suffering damage compared to plates. • No witness markings. The step of recombining master plates to make a full-size plate typically introduces "witness markings" into the production of the full-size plate. These markings appear as lines forming a rectangular perimeter around the structure in the plate that is to be embossed. These markings can cause UV-curable resin to build up on the plate during production, requiring too frequent shutdowns of the production process to clean the plate. On the other hand, etching the positive or negative of the 708, 808 structures directly into the embossing roll makes the production process more efficient, since less downtime is required for tooling cleaning, and the roll manufacturing process does not require the production of witness markings.

[0324] Those skilled in the art will understand that numerous variations and / or modifications may be made to the invention as shown in the embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments should therefore be considered in all respects as illustrative and not restrictive.

[0325] Although the invention has been described in connection with a preferred embodiment, those skilled in the art will understand that the invention may be embodied in many other forms. Those skilled in the art will understand that many variations and / or modifications may be made to the technology as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments should therefore be considered in all respects as illustrative and not restrictive.

Claims

Claims

1. Optical effect device (400, 500) comprising: a substrate (402, 502) having a first surface (404, 504) and a second surface (406, 506); and a plurality of structures comprising: a first plurality of structures (408, 508) arranged on the first surface (404, 504) of the substrate (402, 502), the first plurality of structures (408, 508) having a first in-plane orientation relative to the first surface (404, 504) of the substrate (402, 502), each structure of the first plurality of structures (408, 508) having a facet (414, 514) that faces in a first direction, the facets (414, 514) of the first plurality of structures (408, 508) forming a first facet set; and a second plurality of structures (410, 510) arranged on the first surface (404, 504) of the substrate (402, 502), the second plurality of structures (410, 510) having a second in-plane orientation relative to the first surface (404, 504) of the substrate (402, 502), each structure of the second plurality of structures (410, 510) having a facet (416, 516) that is directed in a second direction, the facets (416,516) of the second plurality of structures (410, 510) forming a second set of facets, wherein the first set of facets defines a first image channel and when the optical effect device (400, 500) is viewed from a first viewing angle range, the first image channel defines a first optical effect, and the second set of facets defines a second image channel and when the optical effect device (400, 500) is viewed from a second viewing angle range the second image channel defines a second optical effect, wherein the optical effect device (400, 500) comprises a surface structure disposed on one or more of the facets of the first set of facets and / or on one or more of the facets of the second set of facets, and, wherein the surface structure comprises diffraction gratings (520, 522, 524).

2. The optical effect device (400, 500) of claim 1, wherein the plurality of structures comprises a third plurality of structures (412, 512) arranged on the first surface (404, 504) of the substrate (402, 502), the third plurality of structures (412, 512) having a third in-plane orientation relative to the first surface (404, 504) of the substrate (402, 502), each structure of the third plurality of structures (412, 512) having a facet (418, 518) that is directed in a third direction, the facets (418, 518) of the third plurality of structures (412, 512) forming a third set of facets that defines a third optical effect when the optical effect device (400, 500) is viewed at a third range of viewing angles and / or each facet of each of the first plurality of facets (414, 514), second plurality of facets (416, 516) and third pluralities of facets (418, 518) defines a slope relative to the first surface (404, 504) of the substrate (402, 502).

3. The optical effect device (400, 500) according to claim 2, wherein: the first plurality of structures (408, 508) are disposed at locations on the first surface (404, 504) of the substrate (400, 500) corresponding to pixels of the first optical effect; the second plurality of structures (410, 510) are disposed at locations on the first surface (404, 504) of the substrate (400, 500) corresponding to pixels of the second optical effect; and the third plurality of structures (412, 512) are disposed at locations on the first surface (404, 504) of the substrate (400, 500) corresponding to pixels of the third optical effect.

4. An optical effect device (400, 500) according to claim 2 or claim 3, further comprising a surface structure disposed on one or more of the facets of the third set of facets (418, 518).

5. An optical effect device (400, 500) according to claim 4, wherein each surface structure is a diffraction grating (520, 522, 524).

6. An optical effect device (400, 500) according to any one of claims 1 to 5, wherein each optical effect is visible in reflectance and transmission.

7. An optical effect device (400, 500) according to any one of claims 1 to 6, further comprising a reflective layer disposed on the plurality of structures.

8. An optical effect device (400, 500) according to any one of claims 1 to 7, further comprising a protective layer disposed over the plurality of structures.

9. A security document (950) comprising a security device (900) in the form of an optical effect device (400, 500) according to any one of claims 1 to 8.

10. The security document (950) of claim 9, wherein the security device (900) is disposed in a half window or a full window (960) of the security document (950).

Images