Apparatus for orienting magnetic flakes
A printing apparatus includes a magnetic rotatable roller with a smooth even outer surface for aligning magnetic flakes in a carrier, such as an ink vehicle or a paint vehicle to create optically variable images in a high-speed, linear printing operation. Images can provide security features on high-value documents, such as bank notes. Magnetic flakes in the ink are aligned using magnetic portions of the roller, that can be formed by permanent magnets embedded in a non-magnetic roller body, or selectively magnetized portions of a flexible magnetic cover of the roller. In some embodiments, the roller is assembled for a plurality of interchangeable sections, which can include spinning magnets. Selected orientation of the magnetic pigment flakes can achieve a variety of illusive optical effects that are useful for decorative or security applications.
1. An apparatus for orienting magnetic flakes in a fluid carrier printed on a substrate in a printing process, the apparatus comprising:
a rotatable roller for positioning with an outer surface proximate to the substrate, said roller comprising a cylindrical body encased by a flexible magnetic sheet of a same magnetisable material having an even outer surface forming the outer surface of the rotatable roller, wherein the flexible magnetic sheet comprises one or more selectively magnetized portions surrounded by non-magnetised or differently magnetized portions thereof, said one or more selectively magnetized portions creating a magnetic field emanating from the outer surface of the roller so as to orient the magnetic flakes during the printing process in a selected pattern when the rotatable roller is positioned with an outer surface proximate to the substrate.
2. The apparatus of claim 1 , wherein the cylindrical body is non-magnetic.
3. The apparatus according to claim 2 , wherein the one or more selectively magnetized portions comprise at least one magnetized portion of the flexible magnetic sheet that is in the form of an image of an object, indicia, or a logo, and is surrounded by a non-magnetized portion of the flexible magnetic sheet of the same magnetisable material.
4. The apparatus according to claim 2 , wherein location and shape of the one or more selectively magnetized portions of the flexible magnetic sheet are selected so that the image provides a dynamic optical effect when viewed at a varying viewing angle or at a varying illumination angle.
5. The apparatus according to claim 4 , wherein the location and shape of the one or more selectively magnetized portions of the flexible magnetic sheet are selected so that the image comprises a rolling object or a flip-flop.
6. The apparatus according to claim 4 , wherein the location and shape of the one or more selectively magnetized portions of the flexible magnetic sheet are selected so that the dynamic optical effect comprises color shifting or color changing.
7. The apparatus according to claim 2 , wherein the one or more selectively magnetized portions of the flexible magnetic sheet are surrounded by non-magnetized portions of the magnetic sheet of the same magnetisable material, and wherein location and shape of the one or more selectively magnetized portions of the flexible magnetic sheet are selected so that the image provides an illusive optical effect.
8. The apparatus according to claim 7 , wherein the location and shape of the one or more selectively magnetized portions of the flexible magnetic sheet are selected so that the image provides an illusion of depth exceeding the substrate thickness.
9. The apparatus according to claim 2 , wherein the one or more selectively magnetized portions comprise at least one magnetized portion of the flexible magnetic sheet that is magnetized so as to create the magnetic field emanating from the outer surface of the roller that reproduces a magnetic field of a permanent magnet that is recessed into the cylindrical body of the roller in the absence of such permanent magnet in the roller.
10. The apparatus according to claim 1 , wherein the flexible magnetic sheet is removably attached to the cylindrical body with a pressure-sensitive adhesive.