Embossing foils having magnetic storage media and holograms have been described in US 4,631,222 and US 4,684,795. Such foils have the disadvantage that any data stored by the magnetic storage media is not secure.

It is an object of the present invention to provide a more secure foil to be carried by, for example, a document of value.

According to a first aspect of the present invention there is provided a flexible magnetic foil or label as specified in the claims.

The invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:- Figure 1 shows a cross-sectional view of a flexible foil according to the invention, Figure 2 shows a cross section of a second flexible foil according to the invention, and Figure 3 shows a flexible adhesive label according to the present invention Figure 1 shows a cross-sectional view of a flexible foil for attachment to an object such as a document by stamping, blocking, or roll application, according to the present invention. It consists of or includes a carrier layer (1) typically made of polyester 15 microns thick, a release layer (2), a protective layer (3), in the present embodiment consisting of lacquer layers 10 and 11, a magnetic layer (4) consisting of magnetic material having a permanently structured magnetic characteristic which varies from place, and an adhesive layer (5). The flexible foil has an

optically diffractive structure formed in the protective layer by embossing.

The magnetic layer 4 in the present embodiment can be manufactured by the method described in US 4,023,204, for example, which is hereby incorporated herein by reference. In this method, a flexible substrate such as a polyester film is coated with a liquid slurry having anisotropic magnetic particles (such as for example acicular ferric oxide particles) which have a generally random orientation. The coated substrate is moved past a first permanent magnet, which makes an oblique angle with the direction of motion of the substrate. This causes the particles to become aligned. The coated substrate continues to move past a further magnet, which is an electromagnet, and thus can generate a controllably variable magnetic field. This magnet is arranged to make an oblique angle with the direction of the first magnet. By switching the strength of the magnetic field being generated by the further magnet, the particles become aligned in a different direction. The slurry is then solidified to fix the particles in place. With this arrangement it will be noted that the magnetic properties of the coating are constant across the width of the substrate, but change in the direction of motion of the substrate. The substrate is subsequently slit along its length (i. e. direction of arrow to provide thin lengths of magnetic tape.

The foil shown in Figure 1 is made in the following way. The release layer (2) is coated onto the carrier layer (1), then the first lacquer layer (10) is applied and allowed to dry. This layer is then embossed with an optically diffractive structure (9), which is then metallised to provide a reflective layer (12) to improve its visibility after attachment to an object. A second lacquer layer 11 is applied and allowed to dry, then the magnetic layer (4) is formed as described for example in US 4,023,204, and finally a hot melt adhesive layer (5) is applied to give the finished foil.

Although in the embodiment described above the protective layer is embossed after deposition onto the substrate, as an alternative, the substrate may be embossed prior to deposition of the protective layer. The reflective layer 12 in Figure 1 is optional, as are the release layer and layer 11.

A second embodiment of the present invention is shown in Figure 2. The foil shown in Figure 2 is made in the following way. The first lacquer layer (10) is applied to the substrate (1) and allowed to dry. Then the magnetic layer (4) is formed as described for example in US 4,023,204. This magnetic layer is embossed with an optically diffractive structure (9), and metallised as before. A second lacquer layer 11 is applied and allowed to dry, and finally the whole assembly, including the substrate, is attached to an object by lamination.

A third embodiment of the present invention is shown in Figure 3. The label shown in Figure 3 is made in the following way. A substrate, such as a polyester film (20) is embossed with an optically diffractive structure (21), and metallised (12) as before. A lacquer layer (11) is applied and allowed to dry. Then the magnetic layer (4) is formed as described for example in US 4,023,204. Finally, a pressure sensitive adhesive layer (23) is applied, and a release treated carrier layer 1 added on the opposite side of the label to that of the optically refractive structure. Note in this embodiment the polyester layer 1 is not a carrier layer, but an integral part of the label.

In both the second and third embodiments, an optional lacquer layer can be applied immediately before the embossing stage. This lacquer layer can be optimised to improve the brightness of the diffusive structure or hologram or the throughput of the embossing process.