Optically variable devices are used in a wide variety of applications, both decorative and utilitarian. Optically variable devices can be made in multitude of ways to achieve a variety of effects. Optically variable devices (OVDs) such as holograms are imprinted on credit cards and authentic software documentation; color-shifting images are printed on banknotes, and OVDs enhance the surface appearance of items such as motorcycle helmets and wheel covers.
Optically variable devices can be made as a film or a foil that is pressed, stamped, glued, or otherwise attached to an object, and can also be made using optically variable pigments. One type of optically variable pigment is commonly called a color-shifting pigment because the perceived color of images appropriately printed with such pigments changes as the angle of view and/or illumination is tilted. A common example is the number “20” printed with color-shifting pigment in the lower right-hand corner of a U.S. twenty-dollar banknote, which serves as an anti-counterfeiting device.
Some anti-counterfeiting devices are covert, while others are overt intended to be noticed. Unfortunately, some optically variable devices that are intended to be noticed are not widely known because the optically variable aspect of the device is not sufficiently dramatic or distinguishable from its background. For example, the amount of color-shift of an image printed with color-shifting pigment might not be noticed under uniform fluorescent ceiling lights, but may be more noticeable in direct sunlight or under single-point illumination. This can make it easier for a counterfeiter to pass counterfeit notes without the optically variable feature because the recipient might not be aware of the optically variable feature, or because the counterfeit note might look substantially similar to the authentic note under certain conditions.
Optically variable devices can also be made with magnetic pigments. These magnetic pigments may be aligned with a magnetic field after applying the pigment (typically in a carrier such as an ink vehicle or a paint vehicle) to a surface. However, painting with magnetic pigments has been used mostly for decorative purposes. For example, use of magnetic pigments has been described to produce painted cover wheels having a decorative feature that appears as a three-dimensional shape. A pattern was formed on the painted product by applying a magnetic field to the product while the paint medium still was in a liquid state. The paint medium had dispersed magnetic non-spherical particles that aligned along the magnetic field lines. The field had two regions. The first region contained lines of a magnetic force that were oriented parallel to the surface and arranged in a shape of a desired pattern. The second region contained lines that were non-parallel to the surface of the painted product and arranged around the pattern. To form the pattern, permanent magnets or electromagnets with the shape corresponding to the shape of desired pattern were located underneath the painted product to orient in the magnetic field non-spherical magnetic particles dispersed in the paint while the paint was still wet. When the paint dried, the pattern was visible on the surface of the painted product as the light rays incident on the paint layer were influenced differently by the oriented magnetic particles.
Similarly, a process for producing of a pattern of flaked magnetic particles in fluoropolymer matrix has been described. After coating a product with a composition in liquid form, a magnet with desirable shape was placed on the underside of the substrate. Magnetic flakes dispersed in a liquid organic medium orient themselves parallel to the magnetic field lines, tilting from the original planar orientation. This tilt varied from perpendicular to the surface of a substrate to the original orientation, which included flakes essentially parallel to the surface of the product. The planar oriented flakes reflected incident light back to the viewer, while the reoriented flakes did not, providing the appearance of a three dimensional pattern in the coating.
By way of background prior art, United States Patent Application 20050106367, incorporated herein by reference, published May 19, 2005 in the name of Raksha et al., assigned to JDS Uniphase Corporation, describes a method and apparatus for orienting magnetic flakes such as optically variable flakes.
Although some of the aforementioned methods for providing visually appealing and useful optical effects are now nearly ubiquitous, these devices require enhancements and additional features to make them more recognizable as an authentic article; for example it would be preferable to have the ability to provide yet additional security features.
For example it would be highly desirous to have a security device which provided a color shift with change in incident light or viewing angle including magnetically aligned flakes and optical features associated therewith; and, providing such a device which had a reasonable amount of tactility would be highly advantageous. It would also be preferably to have such a device wherein there was significant contrast and sharpness between regions of the device that Were functionally different. For example a magnetically aligned region of thin film color shifting flakes directly adjacent an embossed region could offer benefits not realizable in two adjacent different magnetically aligned regions.
It is an object of this invention to provide a method for forming an image of a plurality of contrasting, discernible regions, wherein at least one region has magnetic flakes thereon aligned by an applied magnetic field having a predetermined orientation, and another of the discernible regions adjacent to the first discernible region having flakes thereon or an absence of flakes caused by mechanically impressing or pushing away flakes from said second region.
It is an object of this invention to provide a tactile image wherein a tactile transition can be sensed by touching a transition between at least the first and second discernible regions.
It is an object of this invention to provide a banknote or security document which has tactile properties to assist the blind in verifying the authenticity of the note or document.
It is an object of this invention to provide an image having an optically variable region and having a tactile region about the optically variable region.