| 摘要 |
1510105 Security printing EMI Ltd 8 April 1975 [17 April 1974] 16699/74 Headings B6A and B6C A document is printed with a design wherein at least part of the design is printed with an ink containing circular magnetic particles, the magnetic particles in at least a selected area being aligned into a pattern of remanence variation. This may be achieved by a printing method in which a design of wet ink is formed on a carrier the particles are subjected to magnetic alignment process to produce the pattern, whilst the ink is still wet, and the resulting wet ink containing the pattern transferred to the document. The viscosity of the ink may be reduced, e.g. by heating, during formation of the magnetic pattern, and increased before transfer, e.g. by cooling. The pattern may be formed by sequential application of two perpendicular magnetic fields, the second of which may be varied to achieve selective orientation. A multitrack recording head may be used to achieve areas of different orientation. Only a selected part of the printing on a document is preferably aligned to protect against forgery, e.g. the down-stroke of a "T".
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