Optically variable pigments

Table 5.2 Manufacturers ofpearlescent/lustre/optically variable pigments...

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... 

A CVD-process is known to produce iron-oxide-coated aluminum flakes which form high brilliance colored aluminum pigments with highly interesting interference effects [5.174]. Some of the very new optically variable pigments consist of multilayer flake pigments with a metallic core to obtain metaUic reflection and coverage ]5.175]. 

Figure 7.16 Scheme of design of optically variable pigments (OVP). 

Luster Pigments with Optically Variable Properties. Raimund Schmid, Norbert Mronga, Volker Radtke, Oliver Seeger, BASF Corporation, http //www.coatings.de/articles/ schmid/schmid.htm... 

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. ... 

Uses Pigment for water- and solv.-based paints/coatings, UV-curing paints, powd. coatings, cosmetics, plastics Features Optically variable effect color reflection with copper-red-green color, deep gloss, high brilliance stable to 330 C Properties Colorless, yish. wh. powd. (platelets) dens. 1.3 g/cm bulk dens. 400 g/l surf, area = 1.0 nf/g pH = 7 (10% aq. susp.) conduct. 32 S (10% aq. susp.)... 

Finally, in the field of functional pigments such as corrosion inhibiting or optically variable types, the development of high performance types has been necessary. 

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]. 

Optical Spectra. The main (a) band in a variety of visual pigments exhibits absorption maxima in the range between 430 and 580 nm. It is this variability, as well as the basic bathochromic shift relative to a free PRSB in solution, which have provided the basis for most of the spectroscopic theories relevant to the structure of the chromophore and its environment in the binding site. Attempts to rationalize the shift in terms of charge-transfer complex formation between the (unprotonated) Schiff base and a protein functional group (200,210,212,228) have never... 

This chapter has attempted to present the basics of colour measurement as applied to foods. It is important to realise that the wide variability in the nature of foods and food products, from both their structure and pigmentation, may limit any colour measurement technique applicable only to that particular food. This is because the numeracy of the data is unlikely to match the visual experience of equivalent reference atlas colours. In some cases this discrepancy may be large and has to be recognised as an intrinsic property of the food. These differences may arise from the difference of the visual experience of the product when viewed under normal lighting conditions as opposed to the limitations of its optical properties when presented to the particular colour-measuring instrument. This is... 

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