Research And Application Of Optically Variable Magnetic Thin Film For Anti-counterfeiting

Optically variable anti-counterfeiting technology is an advanced anti-counterfeiting technology that based on the principle of multi-beam interference of optical thin film.Its color shifts from one to another with the change of the viewing angle of observer.Due to the special and significant color-shift characteristic,optically variable device(OVD)cannot be copy by any high-resolution copier,scanner or any other equipment,and it's hard for anyone to counterfeit.Currently,OVD has been widely used in most countries as a kind of first-line anti-counterfeiting technology directly to the public in banknote security printing,important information and valuable document protecting,with its gradual opening to the market,OVD mostly used in the security of product packaging.Optically variable anti-counterfeiting technology has effectively curbed the spread of forgery and plays an important role in maintaining market economy stability and information security.On the bases of traditional optically variable anti-counterfeiting technology,the optically variable magnetic anti-counterfeiting appeared,which increased the existing anti-counterfeiting level.Compared with traditional OVD,optically variable magnetic device(OVMD)not only maintain the high chroma and strongly shift in color display,but also hold a new characteristic that its film flakes can be realigned by pre-set external magnetic field to offer a special "3D" effect pattern,the magnetic material can interact with the external magnetic field.Different applications need different alignment for making different pattern.This task is mainly study about OVMD in the following aspects:principle introducing,structure designing,thin film preparing,optical performance testing,and application implementing.The multi-beam interference of optical thin film and metal-dielectric Fabry-Perot structure has been presented.On the structure design,we use a super thin Cr film as adhesive layer between reflecting layer and magnetic layer to use only one material(Ni)both as reflecting layer and magnetic layer,after optimize design,electron beam evaporation technology was adopted for coating the above thin film stack.In the step of optical performance testing,we found the obvious deviations between design structure and experiment results,that the reflectance,color saturation decrease in varying degree,and the hue is a bit deviated,and then we summarized the factors that led to those deviations.In spite of this,the practicability of structure 1 in solving problem and the feasibility of structure 2 in theoretical practice.In the application implementing step,we did some presentational experiments about magnetic orientation and analyzed the magnetic field distribution of permanent magnets in different shapes,and used for the realignment of thin film pigment flakes,finally obtained stereoscopic patterns like cat's eye,rolling bar,torus,and petals.At last,a three dimensional controlled magnetic orientation set that integrated magnetic orientation,ultra-violet curving process,dynamic observation,data recording.This paper systematically studied the design,preparation and application of optically variable magnetic thin film for the first time,broke the monopoly of foreign patents,filled the void of domestic research.It has contributed to the autonomy of intellectual property rights for optically variable anti-counterfeiting technology,and has further increased the level of anti-counterfeiting of optically variable ink.