Abstract:
A method and apparatus for viewing or authenticating a diffractive device and a diffractive security device (1) are provided in which a first diffractive relief structure (200) is responsive to a first wavelength of visible monochromatic light, a second diffractive relief structure (200) is at least partially interlaced with the first diffractive relief structure (100) and responsive to a second wavelength of visible monochromatic light, and a third diffractive relief structure (400) is at least partially interlaced with the first and second diffractive relief structures (100, 200) and responsive to a third wavelength of visible monochromatic light. Under illumination by the first, second and third wavelengths of monochromatic light, the first diffractive relief structure (200) produces a first partial image of a first colour in a reconstruction plane, the second diffractive relief structure (300) produces a second partial image of a second colour in the reconstruction plane and the third diffractive relief structure (400) produces a third partial image of a third colour in the reconstruction plane, and the first, second and third partial images at least partially overlap in the reconstruction plane to form a multicoloured image. The diffractive security device may be used in a security document and the device may be authenticated by comparing the multicoloured image to a reference image.
Abstract:
A method of forming a polarising liquid crystal device, including the step of: embossing at least one relief structure in a radiation curable liquid crystal material, whereby the embossing step also aligns the liquid crystal material with a predetermined polarisation pattern. The method also includes curing the embossed liquid crystal material, the curing and embossing steps being carried out substantially simultaneously. Also described is a polarising liquid crystal device including at least one relief structure in an embossed area or areas of a radiation curable liquid crystal device. The relief structure may include a diffractive structure. The liquid crystal material may be aligned with a predetermined polarisation pattern in the embossed area or areas, the predetermined polarisation pattern including two or more areas having different polarisations.
Abstract:
A polarising security element for polarising light of a predetermined wavelength is provided which includes a first dielectric material (30) having a refractive index nb, and at least one polarising region of mutually parallel segments (34) of a second material having a refractive index np which is different to nb, the second material being a dielectric or conducting material. The segments (34) of the second material are in contact with the first material (30) and the segments (34) have a width and/or an average spacing which is less than a predetermined range of wavelengths. A method of manufacturing such a security element is also provided in which a relief structure is embossed in the layer of the first dielectric material (30), the relief structure including a plurality of mutually parallel peaks and troughs (32,33), and the second layer of dielectric or conducting material is applied on the relief structure, preferably by printing, to form the at least one polarising region of mutually parallel segments (34).
Abstract:
A method of registration for an embossed security feature on a security document, including steps of providing a substrate, applying an embossable ink to an area (120) of the substrate at a first printing station (106), and embossing at least part of said area (120) of the embossable ink with embossing means to form the embossed security feature (123). The method further includes printing a registration region (121) of embossable ink on the substrate at the first printing station (106), embossing at least part of said registration region to form a detectable registration key (124), detecting the position of the registration key (124), comparing the position of the registration key with at least one registration mark (122; 128; 130), and adjusting the position of the printing means relative to the embossing means in response to said comparison.
Abstract:
An optical security device (10; 700) is provided which includes a transparent or translucent substrate (15; 705), at least one first array of repeating elements (20; 720) in or on a first side (16; 706) of the substrate (15; 705), at least one second array of repeating elements (30; 730) on a second side of the substrate. The second array of repeating elements (20; 720) is substantially in register with the first array of elements (30; 730), whereby a first image (130; 725) is visible when viewing the device from the first side, and a second image (200; 735) is visible when viewing the device from the second side. The brightness or colour levels of repeating image elements (30; 720, 730) on at least one side of the substrate may be modulated region-wise to produce a greyscale or coloured image. In one embodiment, the first array of repeating elements in or on a first side of the substrate is an array of focussing elements (20), and the second array of repeating elements in or on the second side of the substrate is an array of image elements (30) having substantially identical shape to each other, such that, when viewing the device from the first side, a magnified image including at least one magnified version of the image element shape is visible, and when viewing the device from the second side, the greyscale or coloured image is visible. In another embodiment, the repeating elements of both the first and second arrays are partially or fully opaque image elements (720, 730) which respectively form the first and second images (725;735).
Abstract:
High refractive index coatings comprising metal oxide particles are provided. Dispersions of metal oxide particles in solvent are also provided. These find use in the protection of surface relief structures. In some embodiments, the coatings or dispersions contain UV-curable resins. The coatings and dispersions find application in the field of security devices and documents and tokens incorporating security devices.