Optical: systems and elements – Diffraction – From grating
Reexamination Certificate
1997-01-27
2004-03-02
Chang, Audrey (Department: 2872)
Optical: systems and elements
Diffraction
From grating
C359S567000, C359S566000, C359S002000, C283S086000
Reexamination Certificate
active
06700705
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention concerns a structure arrangement comprising a plurality of portions having a relief structure which has an optical-diffraction effect, in particular for visually identifiable, optical security elements for value-bearing documents, for example banknotes, credit cards, passes or cheque documents, or other items to be safeguarded.
In the simplest case a structure arrangement of that kind is afforded by a rectilinear wave or corrugation structure which is disposed on the surface of a carrier element and at which incident ambient light is reflected with diffraction and/or refraction. In the form of the reflected light, a viewer can receive a visually perceptible item of information which corresponds to the relief structures of the portions, which structures have an optical-diffraction effect, the information being dependent inter alia on the viewing angle.
Diffraction of incident ambient light at the relief structures of the portions and thus the information which is emitted therefrom in the form of an optical diffraction image are determined by the number of wave or grating lines per unit of length of a portion, the so-called spatial frequency, and by the cross-sectional shape of the relief structure which is defined inter alia by the differences in respect of height in the relief structure, more specifically both by the differences in respect of height between the individual raised portions relative to each other, and also between raised portions and troughs of the relief structure. The relief structures of the portions can be of such a configuration and the portions can be so arranged that a given item of information can be emitted in a given viewing angle range and thus perceived by a viewer, while in another viewing angle range no information or another item of information can be perceived.
By virtue of the use of per se known security elements with a structure arrangement having an optical-diffraction effect, in regard to the articles to be safeguarded, as were referred to in the opening part of this specification, it is possible for items of authenticity information in respect of the safeguarded article to be rendered visible even to the unpractised lay person, and at the same time for forgery, for example in the form of duplication, having regard to known forgery procedures, in particular optical duplication procedures, to be rendered impossible or made sufficiently difficult.
The endeavour is so to design a structure arrangement that a visually perceptible item of information produced therefrom satisfies aesthetic aspects so that a viewer has for example a particularly brilliant or highly homogenous, uniform image impression which in particular can include a symbol or character which provides an item of information. However the endeavour can also be to arouse, on the part of the viewer, the impression of a particularly brilliant colour representation or the impression of highly homogenous uniform colouring (including within larger surface portions). It is frequently also desirable to produce with the utmost sharpness and precision a change in the information, as can be caused for example by varying the viewing angle, for example by pivoting the carrier element which carries the structure arrangement, about an axis which is in the plane of the carrier element, or by rotating it about a notional axis perpendicular to that plane. In the past, the attempt was made to achieve that by using structure arrangements with portions as the smallest carrier unit of a given item of optical information, so-called pixels, the dimensions of which were of the order of magnitude of 60×60 &mgr;m, which therefore can no longer be resolved with the naked eye. It was therefore possible, on a given macroscopically perceptible area, to provide a plurality of portions which give mutually different items of optical information and which can be “activated” simultaneously or singly in dependence on the above-mentioned viewing parameters. In order further to enhance the impression of homogenous uniform image perception, it has already been proposed that the size of the portions is to be further reduced. Due to the accordingly required larger number of correspondingly smaller portions however that procedure suffers from the disadvantage that the influence of the edges of the portions on the diffraction image produced increases, insofar as there are undesirable additional diffraction phenomena which are caused by the transition from one relief structure within a portion to a further relief structure in adjoining portions. Furthermore, that measure reduces the effective degree of utilisation of the surface area in the structure arrangement as the number and therewith the total area of the regions which do not contribute to affording information are drastically increased, for example the corner regions of a square portion with in particular arcuately curved relief lines whose length decreases towards the corners.
SUMMARY OF THE INVENTION
The object of the present invention is to improve a structure arrangement of the kind set forth in the opening part of this specification, in such a way that it is superior to conventional structure arrangements in regard to the brilliance and the homogeneity of the image impressions afforded and also in regard to the exactitude of changes, which can be achieved by means of the structure arrangement, between different image impressions, while the structure arrangement can be produced in a simple and economical manner.
In accordance with the invention, in a structure arrangement of the kind set forth in the opening part of this specification, that object is attained in that a predominant number of the portions is of a strip or band configuration and has a transverse extent which can no longer be resolved with the naked eye and is below 0.3 nm.
In this context the term strip or band configuration means that the longitudinal extent of the portions is a multiple of their transverse extent. Thus, with such a structure arrangement, the number and the total area of the regions which do not contribute to providing optical information, within the structure arrangement, can be reduced. The invention further provides that the undesired influence of the transitional regions between relief structures of mutually adjoining portions on the desired diffraction image which affords a given item of information is reduced by drastically reducing the edge length of the portions. The fact that the portions of strip or band configuration have a transverse extent which can no longer be resolved with the naked eye and is below 0.3 mm means that a viewer also has the impression of a uniform homogenous colour sensation. Preferably the transverse extent is selected to be very much smaller, but is more than 3 &mgr;m, preferably more than 5 &mgr;m. In addition it has been found particularly advantageous for the longitudinal extent of the portions to be more than 0.3 mm; preferably portions with a longitudinal extent of more than 0.4 mm and in particular more than 0.5 mm are selected for the formation of the structure arrangement according to the invention.
It is further proposed that the portions of strip or band configuration are to be of such a design that their longitudinal extent is at least ten times their transverse extent.
It will be appreciated that a structure arrangement according to the invention can be formed, at least in a region-wise manner, from portions of a single relief structure which has an optical-diffraction effect. Structure arrangements according to the invention which comprise a first group of portions with a first structure having an optical-diffraction effect and at least one further group of portions with a structure which has an optical-diffraction effect and which is different from the first structure are found to be particularly advantageous when for example there is a wish to “store”, in an in particular limited surface region of the structure arrangement, which can be perceived by a viewer, a plurality of items of optical
Herrmann Jürgen
Reinhart Werner
Chang Audrey
Hoffmann & Baron , LLP
Leonhard Kurz GmbH & Co.
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