Optically variable ink

A novel application for the metal flake based materials is in security outlets because they are non-photocopyable. Pigments from Flex Products have been used by SIPCA to produce optically variable green-to-black inks for printing secure images on US dollar bills. ... 

Such types of effect pigments can be used for several applications and are on the market as so-called optically variable pigments (OVP). They have found broad application, especially in preventing counterfeiting of important documents such as banknotes, stock certificates, visas, passports, or car licenses. When incorporated into security inks and printed on bank notes and other documents of value, the pigments... 

The security of our currency also depends on substances in the ink, which is optically variable. This color-changing ink shifts from green to black depending on how the bill is tilted. The ink used for the numbers in the lower right corner on the front of 10, 20,... 

By casting films from suspensions of cellulose microcrystals, cellulose films with the optical properties of chiral nematic liquid crystals can be prepared. The films can be tailored to give different colors of reflected light by altering the salt content of the suspension for a given source of cellulose and set of hydrolysis conditions. Possible areas of application include optical variable films and ink pigments for security papers [81]. 

It is clear that this volume is truly different from the preceding accounts. Photochemists will appreciate Volume 2 as a nice complement to Volume 1, although it can be read independently. Organic photochromic systems are known for their applications in variable-transmission optical materials, ophthalmic lenses, authentification devices (photochromic inks), and novelty items, but they also have great potential in any domain where reversible physical properties are desired (optical memories, gradation masking, optoelectronic systems, nonlinear optical devices, etc.). This book is thus strongly recommended to anyone interested in materials science. 

Fibre types - changes in fibre type which cause a variation in wet-end chemistry also need to be monitored. Use of BCTMP in fine papers for increased bulk, for instance, can lead to increased demand for retention aid as well as for other effect chemicals, e.g. size, optical whitener. Variation in carry over of chemicals from de-inking plants can cause variable wet-end chemisfiy at the paper machine and where swings are significant this needs to be confiolled. Addition of fixative may be necessary to reduce negative impacts. 

---