OPTICAL EFFECT LAYERS SHOWING A VIEWING ANGLE DEPENDENT OPTICAL EFFECT; PROCESSES AND DEVICES FOR THEIR PRODUCTION; ITEMS CARRYING AN OPTICAL EFFECT LAYER; AND USES THEREOF

摘要

The invention relates to the field of the protection of security documents such as for example banknotes and identity documents against counterfeit and illegal reproduction. In particular the invention relates to optical effect layers (OEL) showing a viewing angle dependent optical effect devices and processes for producing said OEL and items carrying said OEL as well as uses of said optical effect layers as an anti counterfeit means on documents. The OEL comprises a plurality of non spherical magnetic or magnetizable particles which are dispersed in a coating composition comprising a binder material wherein in at least a loop shaped area of the OEL at least a part of the plurality of non spherical magnetic or magnetizable particles are oriented such that their longest axis is substantially parallel to the plane of the OEL and wherein in a cross section perpendicular to the OEL and extending from the centre of the central area the longest axis of the oriented particles present in the loop shaped area forming the impression of the loop shaped body follow a tangent of either a negatively curved or a positively curved part of a hypothetical ellipse or circle.