AN OPTICAL DISPLAY COMPOSITE

Abstract: An optical display composite is described for use as an identifying mark, comprising at least one lens array and at least one recorded image aligned to generate a recognisable three-dimensional image. The use of the optical display composite as an identifying mark and a method of manufacture thereof are also described.

Description: AN OPTICAL DISPLAY COMPOSITE The present invention relates to an optical display composite, uses thereof and a method of manufacture thereof. The invention has applications wherever a visible and recognisable image is required and thus can be used in many sectors where display of, for example, security or identifying information or an aesthetic effect is required. Such sectors include household decoration, security and anti-tamper marking of valuable objects, credit cards, smart cards and packaging, and marking and identification of vehicles and other non- fixed objects or constructions. In particular, the invention has applications in security marking of vehicle windows and other transparent panels and anti-tampering labels on packaging and elsewhere. It is known to security mark glass in cars and other vehicles by chemically or mechanically etching the registration number of the car onto the outside of the glass. This can be achieved in a matter of minutes using dedicated equipment or by simply buying a transfer kit from a shop. The purpose of this type of security mark is to help prevent the vehicle theft. Another known application of a security mark is to dissuade criminals from trying to break the glass to gain access to the car and its contents. This use is in conjunction with laminated glass. Conventional tempered glass is formed in a single layer. Laminated glass, on the other hand, comprises two pieces of glass laminated together with one or more anti-shattering sheets of polymer and/or other material between them. One function of the polymer and/or other material is to prevent the glass from shattering, however other functions may be provided. Typical thickness of the glass sheets is approximately 1.8 mm. Typical thickness of the polymer sheets is approximately 1.5 mm. The polymer material can be, for example, PVB (poly vinyl buterate). Optionally, a thin plastic film is inserted in the centre of the laminate structure to give solar control effects. Optionally, a thin plastic film is laminated onto the outside of the glass to reduce spall (fine glass debris) when the glass is broken. In order to form the laminate, the tempered and shaped glass and polymer sheets are heated under pressure to a temperature higher than the softening point of the polymer. Laminated glass is used in vehicle windscreens but previously has been too expensive for use in the other windows of the vehicle. Laminated glass is now becoming more popular and should deter criminal interest in the vehicle as it is more robust than tempered glass. However, it is not possible to tell the two types of glass apart by eye. The prior art security marks cannot be used effectively to distinguish between laminated and tempered glass because they do not demonstrate with certainty that the glass is laminated. There is thus a need to identify the glass as laminated rather than tempered. A mark is required which also cannot easily be copied or imitated, is distinctive and is visible in as many different lighting conditions as possible. Three dimensional images from holograms can be used in conjunction with windscreens (DE3532120) however, there are problems adding the hologram to the laminated glass. Volume (full colour) holograms are recorded in a special emulsion or dichromated gelatin (DCG) or other materials. These materials are very sensitive to heat and moisture. Other holograms, such as surface relief holograms, do not produce a realistic colour 3D image when replayed with white light but rather give a rainbow effect. There is also a need to provide a cost effective identifying mark for anti- tamper labels on packaging. Holograms including separation layers have often been used for this purpose (W09614992 A, GB2136352 A). Any attempt to tamper with packaging damages the hologram and is thus easy to detect. Such labels are often costly to produce and/or do not give a sufficiently coloured or three dimensional image effect so that it is obvious they have not been tampered with. It is an object of the present invention to overcome the disadvantages of the prior art, in particular to provide an effective deterrent or anti-tamper means. It is a further object of the present invention to provide a cost effective optical display composite that produces a colour three dimensional (3D) image. It is a further object of the present invention to provide a composite optical display composite that may integrated into other products. In its broadest aspect there is provided according to the present invention a optical display composite comprising at least one lens array and at least one recorded image aligned to generate a recognisable three dimensional image for use as an identifying mark. This use of a recorded image in conjunction with a lens array is known as an integral photograph. Surprisingly we have found that the techniques of integral photography can be used to provide an optical display composite with a number of advantages. Integral photography was invented by Gabriel Lippmann in 1908 [M.G.Lippman, "Epreuves reversibles. Photographies integrales", Comptes Rendues, 146, 446-451 (1908). M.G.Lippmann, "Epreuves reversible donnant la sensation du relief, Journal de Physique Theoriquee et appliquee, 7, 821- 825 (1908)]. Lippman proposed a form of photography that involves using a lens array to record an image. The lenses are usually small and often essentially hemispherical. They record an array of small pictures of an object (as seen from the range of viewpoints subtended by the array) onto a light sensitive medium. By this method, three-dimensional images can be recorded and reconstructed without the need for the observer to wear special glasses. The image is replayed by viewing the medium or a reproduction of the medium through a replay lens array with its refracting surfaces facing the viewer. Integral photography and holography are different in that the latter records phase information and requires coherent light sources and a stable environment whereas the former is possible with incoherent light sources. Precise alignment of the replay lens array to the recorded image is required to reconstruct the image correctly. Also, in the case where a different replay lens array is used from the recording lens array, there must be a match between (a) the ratio of the pitch of the recording lens array and the pitch of the replay lens array and (b) the ratio of the size of the recorded image to the size of the image when replayed. If these ratios are not equal, or if the replay lens array and recorded image are not properly aligned, then the image is not replayed correctly and a series of dark bands (called "Moire fringes") can be seen. These properties make it very difficult to copy the optical display composite. The integral photograph provides all the visual cues, such as parallax, retinal disparity, convergence and accommodation required for the eye to differentiate the mark from any 2D printed image that simulates a 3D effect. Furthermore, the image can be viewed in ordinary daylight; no special lighting is required. The image can be in full colour. This differentiates the mark from any surface relief hologram mark that produces a rainbow colour effect when replayed using white light. The recorded image can be recorded by various methods: in particular the methods described by Davies and McCormick [US 5,040,871, US 5,420,718, US 5,615,048, 25 and Street [WO8303686]. Reference herein to an optical display composite is to a composite that displays one or more detectable and recognisable images, whether for security, identity, aesthetic or other purposes. The image may be detectable under certain light only (such as infrared or ultraviolet) or may be visible under normal conditions or the image may be comprised of two or more sub- images overlayed or interlaced together in such a way that each sub-image is detectable at different wavelengths and/or at different viewing angles. Reference herein to a lens array is to a plurality of adjacent lenses provided in a regular arrangement, such as a parallel arrangement. The lenses suitably provide overlapping optical paths. They may be in a grid, row or other suitable pattern. The lens array has also been variously referred to in the art as a "lenticular array" or "microlens array". Reference herein to a recorded image is to an image recorded for example, printed on any suitable medium, such as photographic film. The image is generally a multiple image, for example comprising a number of smaller images of the object recorded by the recording lens array. Additionally or alternatively, the image is a multiple image made from a series of layers over printed or overlaid on top of each other. Such different layers may be adapted to produce different images at different angles and/or responsive to different like frequencies. Preferably, the image is recorded on an imaging medium is substantially translucent. The optical display composite may comprise layers or other construction parts that allow construction and alignment of the lens array and image. Preferably, the optical display composite comprises a plurality of layers. The separate layers may be defined by differing refractive index or other properties and/or material(s). The lens array and recorded image may be provided in the same or different layers of the optical display composite. In one preferred embodiment the lens array forms a layer or a part of a layer of the optical display composite and the recorded image is printed onto or formed as part of the lens array layer. In a further preferred embodiment the lens array and recorded image are provided in different layers of the optical display composite. The layers containing the lens array and recorded image may be separated by further layers, or adjacent. The optical display composite parts may be held together by any conventional bonding means or combination of means, for example by at least one adhesive layer, by lamination, heat bonding, by compression forces (when the composite is part of a larger item) or by any combination thereof. Each bonding means may produce a permanent or releasable bond. Preferably, the composite forms a composite laminate, in which at least some of the parts are laminated together. In one preferred embodiment the whole composite or parts of the composite are positioned, and preferably laminated, between two sheets of transparent material, such as glass or transparent polymer. Thus, the composite may comprise the transparent material or be added between the sheets of transparent material to form a larger object, such as a window. The recorded image is incorporated between the transparent material and therefore cannot be removed without destroying the material. This embodiment is particular suitable for use in laminated glass windows of vehicles and other transparent panels. In this case the composite may take the place of a portion of the anti-shattering and/or other material between the outer sheets in the laminate. Preferably, therefore, the thickness of the optical display composite is selected to be substantially identical to the thickness of the anti- shattering and/or other material. The image cannot be imitated by a label or graphic stuck onto the outside of the laminate without the imitation being immediately obvious by virtue of its thickness. In a further preferred embodiment, at least one bonding means between at least two of the layers is releasable, in the sense that it does not provide a rigid, permanent bond, but provides a bond between layers which may be broken by outright separation of layers, or by sliding or other relative movement of the layers, on application of a separating or sliding force or the like thereto. The at least one releasable bonding means may be between any layers. More preferably, it is in a position between the layers containing the lens array and recorded image. This allows separation of the lens array and the recorded image, and relative movement/therebetween. This further embodiment is particularly suitable for use in anti-tamper marking and other applications relying on the deterioration in the image that occurs when the recorded image and lens array are out of alignment. In the case of anti-tamper marking, the optical display composite as hereinbefore defined preferably comprises at least one attachment layer such as an adhesive layer adapted to attach it to two different surfaces (for example a lid and a container body). Separation or other relative movement of the surfaces (for example, by opening the lid) causes the releasable bond to break or move enough to destroy the 3D image. Preferably the composite is flexible to allow attachment, for example, to curved surfaces and around edges. The lens array part or layer may be formed by any suitable method. Various methods have been proposed. For example: D Daly, R F Stevens, M C Hutley and N Davies, "The manufacture of microlenses by melting photoresist", Meas.Sci.Technol., 1, 759-766 (1990); Z D Popovic, R A Sprague and N Connell, "Technique for monolithic fabrication of microlens arrays", Applied Optics, 24, 1-37 (1988); H W Lau, N Davies and M McCormick, "Microlens array fabricated in surface relief with high numerical aperture", SPIE Vproc. Miniature and Micro-optics: Fabrication and system applications, Vol 1544,, ppl78-188, (1991); M.T.Gale, Chapter 6 "Replication" in Micro-optics, Elements, systems and applications, Edited by Hans Peter-Herzig, Taylor and Francis, 1997; and T G Harvey, N Carter, M Cinderey, D E Laidler, T G Ryan and P Summersgill, "Replication of free space micro-optical elements on glass substrates by UV embossing", European Optical Society, topical Meetings Digests Series:Volume 9, Free-space micro-optical systems, Engleberg, Switzerland, 1-3 April 1996, ρ20-21, (1996) all describe such methods. In particular, the methods described in our co-pending applications W096/35971 and WO95/09726 are preferred and are incorporated herein by reference. The same method may be used to manufacture the entire composite where appropriate and is advantageous in providing improved optical characteristics and a high radius of curvature for a short focal length where necessary. The lens array may be of any suitable optically transmissive material known in the art such as polymer thermoplastic or cured resin or glass. Preferably, the lens array is formed from a light curable adhesive for example siloxanes, styrenes, imides, acrylates, methacrylates, photocationic epoxy resins, silica filled light curable resins and UV curable liquid crystal resins. The lens array may also be formed in thermoplastic polymers including; transparent polyolefins such as poly (4-methyl pentene-1) including copolymers, those with high Tg inducing cycloalipatic repeat units and including copolymers with fluorinated co-monomers, transparent condensation thermoplastic polymers including wholly or partially aliphatic or aromatic polymers with carbonate, ester, amide, imide, sulphur, sulphone, ether, ketone and mixtures thereof, transparent addition polymers including polymers and copolymers of styrene, acrylates and methacrylates, acrylonitrile, butadiene, maleic anhydride etc, thermosetting and polymers polymerised in the mould by addition or condensation polymerisation,, siloxanes, urethanes, and those described in W096/35971 or WO95/09726. Also possible are reaction formed resins particularly at ambient temperature including the use of actinic radiation and ionic initiation of, for example, siloxanes and epoxies such as those in W096/35971 or WO95/09726 The lens array may be rigid or flexible and is preferably flexible for any applications in labelling. The lens array is a replay lens array and must match the optical characteristics of the recorded image and have related characteristics, such as lens shape, to the recording array so that it produces an accurate reconstruction of the 3D image of the object when viewed. The direction of viewing is through the lens array onto the recorded image. The lens array may consist of lenses of any suitable shape or any variety of suitable shapes with any suitable height to width ratio. For example, the lenses may be pyramidical, conical, frusto-conical or hemispherical or in the shape of other portions of a sphere (known as spherical lenses) or form half a cylinder or another portion of a cylinder (known as cylindrical lenses) or cone. Alternatively, the lenses may be formed from material having a modulating refractive index allowing it to act as a lens having one of the aforementioned shapes. The lenses may comprise repeating sections of identical or differently shaped lenses. Preferably, each lens or the effect of the repeating refractive index modulation is substantially in the shape of a spherical or cylindrical portion cap and substantially identical in size. The lens array may further have any suitable lens pitch, which, in spherical or cylindrical lenses, is approximately equal to or slightly greater than the diameter. Preferably the pitch (and therefore diameter) of the lenses is of the order of 50 - lOOOμm, more preferably 125 - 500 μm. The focal length of the lenses in air may differ or be identical and is preferably identical and of the order of 100 - 2000μm, more preferably 250 -800μm. Preferably, the distance in the optical display composite between the recorded image and the back of the lens array in the direction of viewing is substantially equal to the back focal length of each lens to give optimum image replay. Preferably therefore, the thickness of the lens array layer and optionally other layers is selected so that the back focal plane of the lens array is co-incident with the plane of the recorded image. The refractive surfaces of the lens array may form the outer surface of the optical display composite or may be an internal layer surface. In the latter case, the adjacent layer or immersion overlayer around and between the lenses preferably has a refractive index lower than that of the lens array material and preferably as low as possible to avoid lengthening the focal length of the lens and increasing the resulting composite thickness. For example, the material adjacent the refractive surfaces of the lens array may be air, silicone or a fluorine containing polymer. Preferably it has a refractive index less than or equal to 1.5 at 633nm. Where the adjacent material is an immersion overlayer, which may not therefore form a complete layer but pockets of material and serves to produce a uniform surface for further layers, the lenses may abut a further full layer. Alternatively, sections of adhesive or other spacing material may be provided, preferably at the periphery of the composite, to space the lens array from a further layer. This is particularly advantageous in providing a full layer of air, rather than simply pockets of air around the lens surfaces. The adhesive layer may be deposited by various coating techniques known in the art, such as gravure coating, bead coating, bar coating or it may be laminated onto one of the layers in the composite by heat, pressure or light cure for example. In one preferred embodiment a plurality and preferably two lens arrays as hereinbefore defined are provided. They are preferably positioned to either side of a recorded image as hereinbefore defined with the refracting lens surfaces facing outwards. This allows a 3D image to be seen from either side of the optical display composite. Preferably the lens arrays either have the same characteristics and are aligned or have substantially differing characteristics. The recorded image may be recorded in any suitable way, for example by printing. Preferably, the recorded image is an integral photograph on photographic emulsion or a reproduction thereof. The recorded image may be printed onto one side of a layer of the optical display composite or transferred by any other suitable means in conventional photography. The lens array and recorded image as hereinbefore defined must be precisely aligned to replay the image. Preferably, they are also substantially parallel at least over a portion of their extent. This allows at least partial replay given an array of identical lenses. More preferably they are substantially parallel over substantially all their overlap in the direction of viewing. More preferably, at least the portions of the layers containing the lens array and recorded image are parallel. The optical display composite as hereinbefore defined may comprise further layers optionally providing extra features such as increased thickness, strength, adhesion, or any other desired property such as refractive index modulation between layers. In many applications, the further layers should be at least translucent and preferably transparent. In other applications at least one layer should act as a mirror or a partial mirror. Additionally or alternatively the optical display composite may comprise air gaps or different refractive index composites, for use as light guides or for other purposes. For example, the layer associated with the lens array could comprise a laminate of the following composition; Transparent polymer resin with lens array, transparent polymer film substrate, transparent adhesive layer and transparent polymer sheet substrate. The composite may in one preferred embodiment further comprise a structure of an optional adhesive layer for the lens array layer, optional plastic film layer, optional adhesive layer, optional plastic sheet layer and glass sheet. The recorded image may be either printed directly onto the back of the lens array layers or printed onto the surface of the optional plastic film layer. The optional plastic film layer may be coated with a transparent conducting material such as Indium Tin Oxide (ITO). Optionally there could be a thin coating layer on the back of the lens array sheet to improve wetting and adhesion of ink used to print the recorded image. Optionally, the back of the recorded image could be metallised so that the graphic can only be seen in reflection. Optionally one of the layers behind the recorded image could be metallised to give the same effect. Optionally, the metal layer could be semi-transparent allowing the image to be seen in both reflection and transmission. The composite may be viewed in ordinary daylight or other ambient lighting conditions and/or may be provided with additional lighting. In one preferred embodiment, the optical display composite comprises a light path formed from at least one light guide to direct illumination onto the recorded image. The at least one light guide is preferably conventionally formed by a combination of the angle of incidence of the light and refractive indices of adjacent layers and/or parts. By this design of the glass laminate, it is possible to light up the image using a lamp or an LED or a distant light source connected to an optical fibre. The light source is preferably located at or near the edge of the glass laminate Access to the light path is preferably provided from one edge of the optical display composite onto the recorded image, rather than from an outer layer of the optical display composite. Preferably, the light guide is formed from a preferably transparent first layer sandwiched between two trapping layers substantially of a lower refractive index buffer material, core material of an equal or higher refractive index to the first layer is provided at at least one portion in place of the buffer material. Preferably the at least one portion corresponds to the position of the recorded image. Light entering the layer only escapes through the core material. The core material may be any of suitable refractive index and may comprise, for example, adhesive, polymer or glass sheet. Preferably the core material is adhesive, which thus has a further use in bonding. The adhesive may be provided as a pattern of opaque or semi-transparent dots whose density increases with distance from the light source. This would serve to make illumination more uniform. The lower refractive index material may be any suitable material such as polymer, water or air. Preferably, the lower refractive index material is air. In a further aspect of the present invention there is provided a transparent panel, preferably a vehicle window or windscreen comprising an optical display composite as hereinbefore defined. Preferably, the transparent panel is provided with side lighting for illumination of the optical display composite. In a further aspect there is provided a use of the optical display composite as hereinbefore defined in tamper-proof labelling of packaging. In a further aspect of the present invention there is provided a use of the optical display composite as hereinbefore defined in providing a security marking on vehicle and other windows. In a further aspect of the present invention there is provided a method of manufacture of the optical display composite. The method comprises manufacture of the lens array, alignment of the lens array and recorded image, and lamination of the lens array, recorded image and further optional layers. Method steps correspond to the physical features defined hereinbefore. Preferably, the recorded image is printed directly onto the back surface of the lens array substrate. Alignment between the printed image and the lens array is achieved during the printing process for example by locating the lens array into a known position relative to the print head each time or by means of a vision system with a feedback loop or other similar techniques used for printing overlays. Lens array manufacture may comprise embossing or casting or injection moulding the lens array onto or into a layer and optionally simultaneously or subsequently laminating with further layers. Embossing preferably comprises the flexible embossing methods defined in W096/35971 or WO95/09726. A suitable method comprises (a) forming a line of contact between a receptive surface and at least one mould feature corresponding to a lens array formed in a flexible dispensing layer; (b) applying sufficient of a resin, capable of being cured to form the lens array layer, to substantially fill the at least one mould feature, along the line of contact; (c) progressively contacting the receptive surface with the flexible dispensing layer such that (1) the line of contact moves across the receptive surface; (2) sufficient of the resin is captured by the mould feature so as to substantially fill the mould feature; and (3) no more than a quantity of resin capable of forming the remainder of the lens array layer passes the line of contact; (d) curing the resin filling the at least one mould feature so as to form the lens array layer; and, optionally, thereafter (e) releasing the flexible dispensing layer from the lens array layer. The method may further comprise the lamination of the composite between two glass sheets in place of a section of anti-shattering material for a laminated glass window. The invention is now illustrated in non-limiting manner with reference to the following figures and examples, in which: Figure 1 shows a cross sectional view of an optical display composite according to the present invention; Figure 2 shows a cross sectional view of an optical display composite according to the present invention, comprised within a glass sheet; Figure 3 shows a cross sectional view of an optical display composite according to a further embodiment of the present invention; Figure 4 shows a cross sectional view of the optical display composite according to figure 3, comprised within a glass sheet; Figure 5 shows a cross sectional view of an optical display composite according to a further embodiment of the present invention; Figure 6 shows a cross sectional view of an optical display composite according to a further embodiment of the present invention including a light guide; and Figure 7 shows a plan view of an optical display composite according to a the embodiment of the present invention shown in figure 6. Figure 8 shows a cross sectional view of an optical display composite according to a further embodiment of the present invention. Figure 1 illustrates a plastic laminate with an embedded integral photograph designed to be incorporated into a laminated glass sheet. The recorded image can be (a) printed directly onto the back of the lens array sheet or (b) printed onto a separate thin transparent plastic film which is placed behind the lens array sheet. In either case the image needs to be precisely aligned with the microlens array so that the 3-d image replays correctly. The optical display composite comprises glass sheet (1), optional transparent adhesive layer (2), transparent plastic sheet layer (3) of controlled thickness with lens array surface on one side (4). The recorded image (5) is located behind transparent polymer (3) on the opposite side to the lens array (4). Figure 2 shows the position of the optical display composite within a laminated glass sheet. The optical display composite is laminated onto a PET layer at one side and held within a layer of PVB. Another layer of PVB is positioned at the opposite side of the PET layer and the whole is sandwiched between two layers of glass. Figure 3 shows a optical display composite having an extra laminated layer for increased thickness. Figure 4 shows the position of the optical display composite of figure 3 within a laminated sheet. Figure 5 shows an optical display composite comprising layers. The layers are (from the top) microlens array (4), PET film, adhesive (8), PVB, adhesive (8), recorded image (5), PET film, adhesive (8) and PVB. Figures 6 and 7 illustrate the optical display composite comprising a light guide. The optical display composite comprises: glass sheet (1), optional plastic film layer (7), optional transparent adhesive layer (2) and transparent plastic sheet layer (3) of controlled thickness with lens array (4) on one side. Recorded image (5) is located behind transparent layer (3) on the opposite side to array (4). Optional adhesive layer (6) and optional plastic film layer (7) are located behind the recorded image (5). Adhesive layer (81) is only deposited underneath the recorded image and around the border of the laminate. Spacer structures (12) are inserted on either side of plastic sheet layer (9) and adhesive layer (82) is only deposited around the border of the laminate. A glass sheet (10) is on the bottom. The recorded image and lens array (4) are aligned so that the recorded image replays accurately. The refractive index of the adhesive layers (81 and 82) is chosen to be higher than that of the plastic sheet layer (9). The key feature of this design is the thin air gap that is incorporated into the laminate structure. This allows the bottom plastic sheet layer (9) to be used as a lightguide to guide the light from one edge to the area of the recorded image. In order for the light to be totally internally reflected in layer (9) it must be directed into the edge of the sheet at an angle greater than the critical angle for the layer (9) to air interface. When the light in the layer (9) sheet reaches the area behind the recorded image, where the patch of adhesive is placed, it is able to escape and illuminate the image because the light is now going from a region of low refractive index to a region of high refractive index. Light is coupled into the bottom plastic sheet (9) for example by placing a tube lamp in close proximity to the edge of the layer or by using a lens to focus the light from a lamp into the edge of the layer. An LED or aπay of LEDs could be used in a similar way. Another advantage of this design is that the inclusion of the air gap does not significantly change the optical appearance or function of the recorded image in natural light. In a further refinement of this design, the adhesive patch under the recorded image could be printed as a pattern of dots whose density increases with distance from the light source. This would serve to make the illumination more uniform. Figure 8 illustrates a variant of this design where the air gap is replaced by a coating of lower refractive index than the plastic sheet (9). This has a similar effect to the air gap i.e. causes the light to be trapped in the layer (9). The lower refractive index coating could also act as an adhesive layer. The laminate would then comprise; glass sheet (1), optional plastic film layer (7), optional transparent adhesive layer (2), transparent plastic sheet layer (3) of controlled thickness with lens array surface (4)on one side . Recorded image (5) is then located behind layer (3) on opposite side to lens array (4), optional plastic film layer (7) and low refractive index coating (12), , plastic sheet layer (9), low refractive index coating (11), glass sheet (10). The recorded image and lens array surface (4) are aligned so that the recorded image replays accurately. Example 1. 1.8 mm thick glass sheet, 175 μm thick PET film with approximately 35 μm thick transparent acrylate resin coating into which has been embossed a lens array surface. The lens array surface has spherical microlenses on a 250 μm pitch with hexagonal packing. The front focal length of the microlens array in air is 585 μm. The refractive index of the acrylate resin material is 1.52 at 633 nm. The back surface of the microlens film has approximately 25 μm thick adhesive layer. The film is laminated to a PVB (polyvinyl buterate) sheet of thickness approximately 0.7 mm (exact thickness of the acrylate resin/PET/adhesive/PVB laminate chosen so that back focal plane of microlens array is located at back surface of PVB sheet i.e. approximately 0.9 mm). On the back of the PVB sheet is the 3-d image that has been laminated on. The 3-d image is printed onto the surface of a 100 μm thick PET film. There is then a second 25 μm thick adhesive layer, a second 0.7 mm thick PVB sheet and finally a second 1.8 mm thick glass sheet. Example 2. As example 1 but using an array of cylindrical microlenses. Example 3 As example 1 except lens array comprises single sheet of PMMA (replacing layers 7, 2 and 3) with spherical microlens array of pitch 250 μm and focal length in air of 585 μm. Refractive index of PMMA sheet is 1.49. Thickness of PMMA sheet is 0.87 mm. Example 3b As example 1 except 3-d image is printed directly onto back of PMMA sheet. Example 4. 1.8 mm thick glass sheet, 0.87 mm thick PVB sheet with microlens array on top surface made in transparent acrylate resin. 3-d image laminated onto back of PVB sheet. 25 μm thick adhesive layer and second PVB sheet of approx 0.7 mm thickness, 1.8 mm thick glass sheet to complete the laminate. Example 4b As example 4 except 3-d image is printed directly onto back of PVB sheet. Example 5. As example 1 but with 3-d image printed onto back of PVB sheet. Example 6. As example 2 but with 3-d image printed directly onto back of first PVB sheet. Example 7. As Examples 1, 2, 3 or 4 but with 3-d image defined in photographic emulsion layer on surface of PET film. REFERENCE NUMERALS 1. Glass sheet 2. Adhesive layer 3. Plastic sheet layer 4. Lens array 5. Recorded image 6. Optional adhesive layer 7. Optional plastic film layer 8. Adhesive layer 9. Bottom plastic sheet layer 10. Glass sheet layer 11. Low refractive index coating or air 12. Spacer structures 13. Light source References M.McCormick and N.Davies, Physics World, June 1992, p29-33. This paper describes a number of different technologies for three-dimensional displays. The binocular and monocular cues that our brain uses to perceive depth are also described. N.Davies, M McCormick and L Yang, "Three dimensional imaging systems: a new development", Applied Optics, 27, 4520 (1988). Background paper on integral photography. Dudnikov, "Autosereoscopy and Integral Photography", Soviet Journal of Optical Technology, 37 (7), 422-426 (1970). Background paper on integral photography. Yu Dudnikov and B K Rozhkov, Soviet Journal of Optical Metrology, 45, pt VI (1978). Background paper on integral photography. Takanori Okoshi, "Three dimensional Imaging Techniques", Academic Press, 1976. Background paper on integral photography. R.F.Stevens and N.Davies, The Journal of Photographic Science, Vol 39, pl99-207 (1991). Discusses applications of lens arrays to the formation of photographic images.

Claims: CLAIMS 1. An optical display composite comprising at least one lens array and at least one recorded image aligned to generate a recognisable three-dimensional image for use as an identifying mark. 2. An optical display composite in accordance with Claim 1 wherein the lens array comprises a plurality of adjacent lenses provided in a regular arrangement. 3. An optical display composite in accordance with Claim 1 or Claim 2 wherein the image is a multiple image comprising a number of smaller images. 4. An optical display composite in accordance with any preceding claim where the image is a multiple image made from a series of layers overprinted or overlaid on top of each other. 5. An optical display composite in accordance with any preceding claim wherein the image is recorded in or printed on an imaging medium which is translucent. 6. An optical display composite in accordance with any preceding claim wherein the composite comprises a plurality of layers. 7. An optical display composite as claimed in Claim 6 wherein individual layers are defined by differing refractive index. 8. An optical display composite as claimed in Claim 6 or Claim 7 wherein the lens array forms a layer or a part of a layer of the optical display composite and the recorded image is printed onto or formed as part of the lens array layer. 9. An optical display composite as claimed in Claim 6 or Claim 7 wherein the lens array and recorded image are provided in different layers of the optical display composite. 10. An optical display composite as claimed in any one of Claims 6 to further and comprising additional layers to provide additional materials features or properties. 11. An optical display composite as claimed in any one of Claims 6 to 10 wherein the layer is at least translucent and preferably transparent. 12. An optical display composite as claimed in any one of Claims 6 to 10 wherein at least one of the layers acts as a mirror or partial mirror. 13. An optical display composite as claimed in any one of Claims 6 to 12 wherein the composite forms a composite laminate in which at least some of the layers are laminated together. 14. An optical composite according to any preceding claim wherein the composite is positioned between two sheets of transparent material. 15. An optical composite as claimed in Claim 14 wherein the sheets of transparent material together comprise a laminated glass window. 16. An optical display composite as claimed in any one of Claims 1 to 13 wherein a releasable bond is provided between at least two of the layers. 17. An optical display composite as claimed in Claim 16 wherein the releasable bond is in position between the layers containing the lens array and the recorded image to allow separation of the lens array and the recorded image. 18. An optical display composite as claimed in Claim 16 or 17 for us an anti- tamper marking and further comprising at least one attachment layer adapted to attach it to two different surfaces, such that relative movement of the surfaces causes the releasable bond to break or move enough to destroy or change the 3D image. 19. An optical display composite as claimed in any preceding claim wherein the lens array is formed from a light curable adhesive. 20. An optical display composite as claimed in any one of Claims 1 to 18 wherein the lens array is formed from thermoplastic polymer. 21 An optical display composite as claimed in any one of Claims 1 to wherein the lens array is formed from reaction formed resin. 22. An optical display composite as claimed in any preceding claim wherein the lens array has a pitch of the order of 50 to 1000 μm. 23. An optical display composition as claimed in any preceding claim wherein the focal length of the lens is making up the lens array is of the order of 100 to 2000 μm. 24. An optical display composite as claimed in any preceding claim wherein the lens array comprises a material having modulating refractive index, allowing it to act as a lens. 25. An optical display composite as claimed in any preceding claims wherein two lens arrays are provided, positioned to either side of the recorded image with refracting lens surfaces facing outwardly therefrom. 26. An optical display composite as claimed in any preceding claim wherein the lens array and recorded image are substantially parallel over substantially all their overlap in the direction of viewing. 27. An optical display composite as claimed in any preceding claim further comprising a light formed from at least one light guide to direct illumination onto the recorded image. 28. An optical display composite as claimed in Claim 27 wherein the at least one light guide is formed by a combination of the angle of incidence of the light and refracted indices of adjacent layers. 29. An optical display composite as claimed in Claim 27 or Claim 28 further comprising a distant light source connected to an optical fibre to illuminate the image. 30. A transparent panel comprising an optical display composite in accordance with any preceding claim contained therewithin. 31. A transparent panel in accordance with Claim 31 provided with side lighting for illumination of the optical display composite. 32. The use of an optical display composite as claimed in any preceding claim in tamper proof labelling of packaging. 33. The use of an optical display composite as claimed in any preceding claim as a security marking on vehicle or other windows. 34. A method of manufacture of an optical display composite comprising manufacture of a lens array, alignment of the lens array with a recorded image, and lamination of the lens array and recorded image. 35. The method of Claim 34 wherein the lens array is manufactured by an embossing method comprising the steps of: (a) forming a line of contact between a receptive surface and at least one mould feature corresponding to a lens array formed in a flexible dispensing layer; (b) applying sufficient of a resin, capable of being cured to form the lens array layer, to substantially fill the at least one mould feature, along the line of contact; (c) progressively contacting the receptive surface with the flexible dispensing layer such that (1) the line of contact moves across the receptive surface; (2) sufficient of the resin is captured by the mould feature so as to substantially fill the mould feature; and (3) no more than a quantity of resin capable of forming the remainder of the lens array layer passes the line of contact; (d) curing the resin filling the at least one mould feature so as to form the lens array layer; and, optionally, thereafter (e) releasing the flexible dispensing layer from the lens array layer. (f) 6. The method of Claim 34 or 35 further comprising the lamination of the composite between two glass sheets in place of a section anti-shattering material for a laminated glass window.

Inventors: HARVEY THOMAS GRIERSON, RYAN TIMOTHY GEORGE, HARVEY, THOMAS, GRIERSON, RYAN, TIMOTHY, GEORGE
Applicants: EPIGEM LTD, HARVEY THOMAS GRIERSON, RYAN TIMOTHY GEORGE, EPIGEM LIMITED, HARVEY, THOMAS, GRIERSON, RYAN, TIMOTHY, GEORGE
Application year: 2000
Main classification: G09F3
IPC codes: B44F1, G02B3, G03H1, G09F3, G09F19