Optical variable light ink characteristics and applications

Optical film OVI type anti-counterfeit principle is that the color material uses multi-layer interference optical fragmentation film, ie multi-layer optical film flake powder which can generate optical interference, is produced as a dispersion material, and the ink matrix will multilayer optical film sheet (requiring positive and negative The design-like powder is fixed on the printed substrate in a directional manner. Visual incident angles of 900 and 300 can be visually changed colors (such as gold/green, magenta/green, green/blue, green/magenta, green/black, gold/gray, etc.). Anti-counterfeiting features change the color of the print when it is viewed.

The application of multilayer optical films to the field of anti-counterfeiting was first proposed by scientists from the Canadian National Institute of Research. Based on the interference effects of multilayer optical films, they produced anti-counterfeiting effects. Because this interference effect is unique to multi-layered films, the angular effect of the printed color cannot be copied with high-resolution scanners, color copiers, and other methods, and thus its anti-counterfeiting effect is very good. The color film anti-counterfeiting technology they successfully developed was applied to the 1988 version of the 50-dollar denomination banknote. Because of its excellent anti-counterfeiting effect, this anti-counterfeiting technology is now used on Canadian dollar bills of 100 Canadian dollars and 20 Canadian dollar denominations.

Color ink anti-counterfeiting technology has a good anti-counterfeiting effect. However, due to the need for some special film devices, it is difficult for users to apply the technology. Therefore, researchers from OCLI Corporation in the United States have proposed an improved solution that peels off the plated color film from the substrate and then crushes it to a small size of a certain size. These small pieces still retain the original color film. Some optical properties. By incorporating these small pieces into the transparent ink, a color-changing ink with a forgery preventing effect can be obtained. Since this kind of ink can be printed by conventional printing process, it does not increase any technical difficulty for the user, and therefore it is favored by the money printing industry in many countries. Nowadays, this color shifting ink product supplied by Swiss SICPA company has been applied in the currency of more than 40 countries, as well as passports and visas of some countries. After a long period of time of argumentation and preparation, the United States finally unveiled on March 25, 1996, a new version of $100 worth of banknotes printed with this color-changing ink. Visible security inks are used in the Maple Leaf pattern on visas in Canada and the "VISA" on visas in the United States. China’s 1999 edition of RMB 100 and 50 also adopted this technology. So far, as many as six new RMB counterfeit coins have been seized in the market, and no counterfeit money using optical color ink has been found. At present, domestic companies have successfully developed similar products, breaking the monopoly of U.S. and Swiss companies. The new edition of the Hong Kong and Macau Pass, which was launched on May 20 this year, has also adopted light-variable ink security. In terms of anti-counterfeiting, in addition to government uses, light-variable inks have gradually been used for the packaging and printing of cigarettes, alcohol, medicine, and chemical products.

Optically variable ink prints have a metallic luster, and the color patches generally exhibit a pair of colors. For example, purple turns green, dark green turns purple, green turns red, green turns dark blue, red turns gold, red turns green, gold turns silver, and yellow turns green. Some colors present up to three colors. Such as: green - purple - yellow. Due to the characteristics of the flake and larger particle size of the optically variable pigment powder, there are certain limitations in the application of the printing ink. At present, the main technically mature varieties are: screen printing inks, common gravure printing inks and engraving gravure inks.

The application of optical color shift ink anti-counterfeiting technology has the following advantages:

1. Photochromic inks are typical "first-line anti-counterfeiting" technologies.

2. Product design and production technologies are highly specialized and have high technological content. It is difficult for general companies or individuals to deal with them.

3. The use of engraving and gravure printing process on the license has a high reliability of anti-counterfeiting.

4. Dedicated colors can be provided to further enhance the security against fraud.

At present, there is a refractive ink also has a refractive color effect (such as mother titanium pearlescent ink: a layer of high refractive index transparent titanium dioxide wrapped in mica, titanium dioxide thickness produces different colors, 40 ~ 60nm is silver, 60 ~ 80nm is yellow, 80 to 100 nm is red, 100 to 120 nm is blue, and 120 to 160 nm is green.) Since the raw material processing is simple, although the color change effect is far less than that of OVI, it can also provide anti-counterfeit effect and the cost is relatively low.

In addition, the liquid crystal OVI type: its intrinsic pitch is comparable to that of visible light, and it has an optically variable effect of Bragg reflection. Apply on dark color background.