Printed matter – Having revealable concealed information – fraud preventer or... – Utilizing electromagnetic radiation
Patent
1993-06-10
1995-09-05
Fridie, Willmon
Printed matter
Having revealable concealed information, fraud preventer or...
Utilizing electromagnetic radiation
B42D 1500
Patent
active
054473357
DESCRIPTION:
BRIEF SUMMARY
The invention relates authenticatable items such as security documents, for example banknotes, and to security devices for fixing to such authenticatable items to provide authentication and protection against fraudulent reproduction of the item.
Optically variable devices such as holograms and diffraction patterns are used widely on financial transaction cards and the like for authentication purposes and protection against fraudulent reproduction. Banknotes bearing single holographic images have been issued by a few countries including Australia and Austria. The use of such devices on substrates such as banknotes which flex during handling has been relatively limited, however. This limitation is due to a number of reasons and includes the aesthetic requirement for flatness required for viewing a hologram of a complete object, which is generally difficult to achieve with a flexible substrate such as a banknote which is regularly crumpled in use.
A further limitation arises from the uneven, fibrous structure of paper substrates which causes minute local contouring effects to be imparted to hot stamped holograms.
WO90/07133 published on the 28th Jun. 1990 describes the crinkling problems which are encountered particularly with banknotes and a solution to this problem of providing a two dimensional optical catastrophe image diffraction pattern. In other words, a rather unusual and complex diffraction pattern is created to overcome the problem.
U.S. Pat. No. 4,568,141 also addresses the problems of providing security devices on documents and in particular the problems arising from the crumpling of such documents. In this case, the solution is to provide a set of adjacent diffraction gratings arranged along a track such that when the document is rotated a special colour pattern is generated by the successive plain diffraction grating blocks.
Another security device for use with banknotes and the like is described in GB-A-2093404 and once again use is made of diffraction gratings designed to separate incident polychromatic light into at least a pair of adjacent, separate and distinct reflective beams of contrasting colours. The diffracting grating structures are produced by embossing a metallised structure in which there is a diffractive grating of one type set in a background of a colour contrasting grating. The use of two (or more) such structures is mentioned.
GB-A-2108428 describes a security device which is designed to be machine-readable and to be concealed from the naked eye. The device, in one example, comprises a number of identical holograms which, when scanned, cause diffraction maxima to occur in a pretermined sequence. These maxima can be detected and compared with a reference by a suitable reading machine to determine whether the document to which the device is fixed is authentic.
In accordance with the present invention, we provide an authenticatable item carrying a number of symbols identifiable to the naked eye, there being at least two sets of at least three symbols, wherein all the symbols within a set are substantially identical, are positioned in a non-overlapping, regular geometric arrangement, and at at least one common viewing angle of inclination, exhibit substantially the same optical performance, the optical performance varying with inclination viewing angle.
The invention provides an authenticatable item and a security device which enable a relatively untrained user easily to verify the authenticity of the device or item while at the same time the device can be used in conjunction with flexible documents, such as banknotes, which are subject to crumpling so that immediate authentication recognition can occur given that the entire device may not be visible at any one time, or facets may be presented at uncommon angles.
Thus even if the surface on which the security device is fixed is crumpled, there will be at least one complete symbol still readily visible which will be sufficient for authentication purposes; and secondly by using easily identifiable symbols (i.e. attractive graphical
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patent: 5344192 (1994-09-01), Phillips
"Optical Interference Coatings for Inhibiting of Counterfeiting", J. A. Dobrowolski et al, Optica Acta, 1973, vol. 20, No. 12, pp. 925-937.
Fridie Willmon
Thomas De La Rue Limited
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