Security thread, a film and a method of manufacture of a security thread

Abstract

The present invention relates in one aspect to a method of manufacture of a security thread suitable for use in security articles including security paper such as that used for banknotes. In the method a magnetic metal is deposited on a film of polymeric substrate as the substrate passes through a solution containing the magnetic metal and a preparatory operation is carried out on a surface of the substrate prior to immersion of the substrate in the solution. The preparatory operation ensures that magnetic metal is deposited on the substrate in a pattern such that when the security thread is produced from the film by cutting the film the magnetic metal on the security thread has a specific pattern and provides both a visually discernible security feature and a magnetically detectable security feature. In a second aspect the present invention provides a security thread for security paper such as banknotes, the security thread comprising a polymeric substrate catalytic material covering at least a portion of one surface at the polymeric substrate and a layer of electrolessly deposited magnetic metal covering at least a portion of the catalytic material with a depth in the range 0.01-3.0 .mu.m. The layer of magnetic material has a specific pattern and provides the security thread with both a visually discernible security feature and a magnetically detectable security feature, the security thread having an average magnetic remanence in the range 0.001-0.05 emu cm.sup.-2.