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US 4,244,998 AGranted
Patterned layers including magnetizable material
AssigneeE M I Limited
InventorAndrew L. Smith
Life of this patent
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AssigneeE M I Limited
InventorAndrew L. Smith
Estimating the term…
A layer including magnetizable material and a pigment of lower magnetic susceptibility in a settable coat are subjected to a selectively applied magnetic field gradient in the layer while the coat is unset to cause the magnetizable material to selectively break through the pigment. The coat is then set, while the materials remain in position, to produce a detectable pigmentation pattern of said break-through. The magnetic material may itself be a pigment and break-through the first one to produce an eye-visible pattern. The magnetizable material forms a magnetic susceptibility distribution pattern equivalent to the pigment break-through pattern. The layer having the pigment pattern may be used as a security feature in, e.g. a security document, both the patterns being alterable, once the coating has set, only by damage to the layer.
A security document including on a support a security feature layer formed by two overlaid coatings of differently pigmented materials of different magnetic susceptibility, the coating including the material of higher susceptibility breaking through the other coating to an outward surface thereof and at distinct fixed positions in the layer to form a pattern of the pigments one against the other, the material of higher susceptibility also forming a pattern of magnetizability variation in a layer region adjacent said outward surface of the pattern corresponding to said pattern of pigments, the fixed positions of the patterns providing the security feature.
Dependencies are inferred from the claim text.