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Abstract

A periodic line pattern, which is covered by a periodic lens structure of cylindrical lenses parallel to the lines of the line pattern, is imprinted on a substrate. The period of the lens structure corresponds with the period of the line pattern. The lenses preferably are aligned flush with the lines of the line pattern. The lines consist of paths of elementary printing dots or image dots (pixels). The number of paths of elementary printing dots in one period is at least 4 and not more than 16. The height of the cylindrical lenses at the apex is at least half the width of a period and not more than the width of a period of the line pattern. With advanced offset printing methods, which are employed for instance in safety printing (e.g. for banknotes), a printing resolution of about 4 .mu.m is achieved. Preferably, the elementary printing dots are chosen only a little larger than the achievable printing resolution. What is realistic are elementary printing dots of approximately square shape with a side length between 4 and 8 .mu.m. With minimum requirements as to the design possibilities for the line pattern, two lines per period are sufficient. Each line should consist of at least two paths of elementary printing dots. This corresponds to a period width of about 40 .mu.m. In the corresponding lens structure, the individual cylindrical lenses have a height at the apex of slightly more than half the period width. Such fine lens structures can be produced by imprinting a transparent mass with an intaglio printing method or by embossing the transparent mass with an intaglio gravure plate. The microrefraction image thus obtained is particularly useful for use in a certificate of authenticity.

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First Claim